Prof. Dr.-Ing. Thomas Kaiser

Digitale Signalverarbeitung
University of Duisburg-Essen

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  • Analysis and Modelling of the Antenna Mode and Structural Mode Scattering of a Dielectric Resonator
    Alhaj Abbas, A. and Khaliel, M. and Abuelhaija, A. and El-Absi, M. and Alam, J. and Solbach, K. and Kaiser, T.
    15th European Conference on Antennas and Propagation, EuCAP 2021 (2021)
    This paper presents an analysis of the backscattering of a dielectric resonator (DR) due to the antenna mode and the structural mode. More specifically, we focus on the structural mode scattering since the discussion of the RCS of DRs in the past has concentrated on analyzing the 'Eigenmodes' only. Therefore, we present evidence for its existence and provide a qualitative and quantitative approximation. It is found that the structural scattering of a DR with high rel. permittivity can be approximated by the scattering of a metal body of the same dimensions as the DR. Furthermore, a mathematical model of the antenna mode scattering is provided using the multipole expansion and with the aid of filter theory. As a result of the superposition of both scattering modes, it is found that the structural mode scattering slightly alters the appearance of the 'Eigenmodes' in frequency position, scattering level, quality factor, and shape. © 2021 EurAAP.
    view abstract10.23919/EuCAP51087.2021.9411078
  • Scattering and Roughness Analysis of Indoor Materials at Frequencies from 750 GHz to 1.1 THz
    Sheikh, F. and Zantah, Y. and Mabrouk, I.B. and Alissa, M. and Barowski, J. and Rolfes, I. and Kaiser, T.
    IEEE Transactions on Antennas and Propagation (2021)
    The problem of wave propagation and scattering at terahertz (THz) frequencies has become increasingly important, in particular for accurate modeling of future indoor wireless communication channels. The reflective properties of indoor materials with different surface roughness and dielectric constants are important to explore diffuse scattering for accurate channel modeling. First and foremost, a THz Swissto12 system is adopted to obtain the first ever transmission measurements for a wide choice of indoor material groups such as wood, plastic and brick at frequencies from 750 GHz to 1.1 THz using up-conversion (frequency-domain) method. Both the reflection (S 11, S 22) and transmission coefficients (S 12, S 21) are measured using this novel and non-invasive electromagnetic technique. The inversion method based on Kramers-Kronig (K-K) relations is then applied to convert the calibrated scatter data into intrinsic material properties (i.e., refractive index, permittivity, absorption coefficient). Then, the surface topography of rough material samples is acquired using surface measurement instruments. Further, the optically smooth (σh/λ ≪ 1) materials are assorted as most to least rough based on Rayleigh roughness factor. Lastly, the ray tracer considering the Rayleigh-Rice (R-R) scattering model is employed to obtain the maximum achievable reflected paths of the above mentioned indoor material samples at 300 GHz followed by their experimental validation. IEEE
    view abstract10.1109/TAP.2021.3076577
  • A 1-bit High-Gain Flexible Metasurface Reflectarray for Terahertz Application
    Kazim, J.U.R. and Abohmra, A. and Al-Hasan, M. and Mabrouk, I.B. and Ur-Rehman, M. and Sheikh, F. and Kaiser, T. and Imran, M.A. and Abbasi, Q.H.
    2020 3rd International Workshop on Mobile Terahertz Systems, IWMTS 2020 (2020)
    In this paper, a 1-bit, high gain and wide-band reflectarray metasurface is proposed. The proposed reflectarray operates from 0.9 THz to 1.4 THz giving operational bandwidth of 0.5 THz. The realized gain achieved is 32 dB at 1.4 THz while the maximum simulated aperture efficiency is calculated to be 55%. The reflectarray is designed on polyimide substrate with permittivity of 3.48 and loss tangent of 0.03 at THz frequencies. The dimension of the metasurface is 3× 3mm2 and contains 3904 patch elements illuminated by a THz horn antenna. With high gain and flexible nature of the polyimide, the proposed metasurface is also suitable for wearable application. © 2020 IEEE.
    view abstract10.1109/IWMTS49292.2020.9166152
  • A Ray Tracing Approach to the Scattering of Electromagnetic Waves from Random Rough Surfaces at Terahertz Frequencies
    Sheikh, F. and Zhang, Y. and Zanteh, Y. and Mabrouk, I. and Hasan, M. and Kaiser, T.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2020-November (2020)
    In this paper, we analyze the in-room THz wireless links across 275 GHz to 325 GHz frequency spectrum in the presence of random rough surfaces interpreting the scattering phenomenon utilizing well-known reflection models. Focus is given to random rough surfaces which can be described statistically. Taking into account the intrinsic material properties (i.e., complex permittivity), we strive to demonstrate a comparison between Rayleigh-Rice (R-R) approach and the real 3D surface topography parameters. The R-R approach approximates the surface deviations or topography of any rough material with Gaussian height distribution. The ray-tracing simulations are conducted in a realistic but simple office environment for line-of-sight (LoS) and non-line-of-sight (NLoS) conditions to study the multipath propagation with its impact on total received power and channel delay profile. To the best of the authors' knowledge, no such work has hitherto been attempted. © 2020 IEEE.
    view abstract10.1109/IRMMW-THz46771.2020.9370474
  • A Study of Diffuse Scattering in Massive MIMO Channels at Terahertz Frequencies
    Sheikh, F. and Gao, Y. and Kaiser, T.
    IEEE Transactions on Antennas and Propagation 68 (2020)
    The use of massive multiple-input multiple-output (MIMO) systems is becoming progressively feasible, as well as progressively important, as the carrier frequency increases. Terahertz (THz) frequencies lead to smaller-sized RF components including antennas, so that even antenna arrays with a large number of antennas have a reasonable form factor while providing large beamforming gain and multi-user MIMO (MU-MIMO) capability. However, the THz propagation mechanisms differ in various ways from previously explored channels. In fact, reflections by a rough surface and diffuse scattering mechanisms are the most critical features contributing to spatial and temporal dispersion at THz frequencies. For this article, first, we develop a hybrid modeling approach of 3-D ray-tracing simulations in a realistic office room at 300 and 350 GHz to obtain estimates of the impact of surface roughness on the channel capacity which depends on generic channel characteristics. Then, the indoor multipath propagation and its impact on massive MIMO channels considering smooth and rough surfaces are investigated by employing the Beckmann-Kirchhoff (B-K) model. Finally, channel capacities of indoor THz massive MIMO channels with different surface roughnesses for both line-of-sight (LoS) and non-LoS (NLoS) scenarios are calculated. Though based on modeling results, the scattering properties of materials can favorably be exploited to maximize spatial multiplexing gains, especially in LoS scenarios. © 1963-2012 IEEE.
    view abstract10.1109/TAP.2019.2944536
  • Characterization of Dielectric Materials by Sparse Signal Processing with Iterative Dictionary Updates
    Thanthrige, U.S.K.P.M. and Barowski, J. and Rolfes, I. and Erni, D. and Kaiser, T. and Sezgin, A.
    IEEE Sensors Letters 4 (2020)
    Estimating parameters and properties of various materials without causing damage to the material under test (MUT) is important in many applications. Thus, in this letter, we address MUT's parameter estimation by wireless sensing. Here, the precision of the estimation depends on the accurate estimation of the properties of the reflected signal from the MUT (e.g., number of reflections, their amplitudes, and time delays). For a layered MUT, there are multiple reflections, and due to the limited bandwidth at the receiver, these reflections superimpose with each other. Since the number of reflections coming from the MUT is limited, we utilize sparse signal processing (SSP) to decompose the reflected signal. In SSP, a so called dictionary is required to obtain a sparse representation of the signal. Here, instead of a fixed dictionary, an iterative dictionary-update technique is proposed to improve the estimation of the reflected signal. To validate the proposed method, a vector network analyzer (VNA)-based measurement setup is used. It turns out that the estimated dielectric constants of the MUTs are in close agreement with those reported in literature. Further, the proposed approach outperforms the state-of-the-art model-based curve-fitting approach in thickness estimation. © 2017 IEEE.
    view abstract10.1109/LSENS.2020.3019924
  • Chipless RFID Infrastructure Based Self-Localization: Testbed Evaluation
    El-Absi, M. and Abbas, A.A.-H. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    IEEE Transactions on Vehicular Technology 69 (2020)
    This paper presents a realistic feasibility of radio frequency identification (RFID) based self-localization of objects in real environments using simple infrastructure composed of chipless tags. These tags are designed as arrays of dielectric resonators (DR) in order to overcome the range limitations of the traditional chipless tags, where the DR array structure of the tags boosts the radar cross section (RCS) and, consequentially, extends the range coverage. Furthermore, an efficient algorithm for tag detection is proposed considering the environmental and hardware impairments that alter the backscattered signal from the tag. In this system, the reader interrogates the reference nodes, i.e. chipless tags, by a frequency-sweep RF signal, and the backscattered signals from the tags are captured and analyzed at the reader for detection, ranging and location estimation. A testbed is implemented with fabricated chipless RFID tags in order to evaluate the validity and accuracy of the proposed self-localization system. Experimental measurements based simulations are conducted in several scenarios in order to evaluate the proposed system. Moreover, an object (the reader) is moved to several locations in an interrogation area of 2.5times 1.2 m, and, afterwards, its location is estimated. The averaged measured location error achieved based on the proposed system is approximately 5 cm with a variation of 0.9 cm as a minimum observed error and 7 cm as a maximum error. © 1967-2012 IEEE.
    view abstract10.1109/TVT.2020.2990480
  • Comparison Analysis of Small and Large Bandwidth Indoor SAR Multi-Object Imaging at Low Terahertz Spectrum
    Batra, A. and Wiemeler, M. and Goehringer, D. and Kaiser, T.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2020-November (2020)
    Indoor THz Synthetic Aperture Radar (SAR) is an emerging research domain. It expands the conventional SAR applications to sub-mm resolution imaging and localization due to high available bandwidth and compact antennas at this spectrum. In general, high resolution is always preferred but it comes with the cost of complexity of the radio front-end chain. Therefore, in this paper three SAR systems with different carrier frequency f_{c} and bandwidth B_{w} are studied. These systems are set-up with f_{c}= 230\ \text{GHz} and B_{w}= 20 \text{GHz}, f_{c}= 245\ \text{GHz} and B_{w}= 50\ \text{GHz} and lastly, f_{c}=275\ \text{GHz} and B_{w}= 110\ \text{GHz}. The paper presents the comparison between these systems w.r.t. the focused SAR image quality associated with the spatial resolution. © 2020 IEEE.
    view abstract10.1109/IRMMW-THz46771.2020.9370926
  • Experimental Demonstration of Double-Notch RCS Spectral Signature of Corner Reflector Tag for THz Self-Localization System
    Solbach, K. and Abbas, A.A. and El-Absi, M. and Abuelhaija, A. and Kaiser, T.
    2020 3rd International Workshop on Mobile Terahertz Systems, IWMTS 2020 (2020)
    Dihedral corner reflectors with arrays of dielectric resonators fixed on the metal plates are shown to exhibit notched spectral signatures of the monostatic Radar Cross Section. Two distinct notches can be created using two arrays with different diameter of resonators. Due to about 45 unique notch combinations, the double-notch corner reflector allows a 5-bit frequency position coding while still producing a sharp pulse shape in time domain. Example designs at V-through G-band are experimentally demonstrated. © 2020 IEEE.
    view abstract10.1109/IWMTS49292.2020.9166312
  • Experimental investigation of terahertz scattering: A study of non-Gaussianity and lateral roughness influence
    Alissa, M. and Friederich, B. and Sheikh, F. and Czylwik, A. and Kaiser, T.
    IEEE Access 8 (2020)
    The scattering phenomenon caused by rough surfaces has a dominant role in shaping the reflected field at terahertz (THz) frequencies, both in specular and non-specular directions. Most surfaces in nature are randomly rough, and the surface height obeys a certain statistical distribution. A Gaussian probability density function (PDF) for height distribution is often considered, and the correlation length is assumed to be longer than the wavelength. However, a clear understanding of how changing these assumptions affect the angular distribution of the scattered field is still lacking. In the first part of this work we investigate via microscopic measurements the statistical distribution of realistic indoor materials, and its deviation from the assumed normal distribution. After that, the influence of non-Gaussianity on the specular reflection in the low THz region is shown analytically. In the second part, a measurement campaign of diffuse scattering, caused by structured statistically-controlled surfaces, is reported. The correlation length assumption has been proven experimentally and via full-wave simulation to affect the diffuse scattering by rough samples, when the other statistical parameters are kept without changes. © 2020 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.
    view abstract10.1109/ACCESS.2020.3025361
  • Frequency Selective Surface Coded Retroreflectors for Chipless Indoor Localization Tag Landmarks
    Jimenez-Saez, A. and Schusler, M. and El-Absi, M. and Abbas, A.A. and Solbach, K. and Kaiser, T. and Jakoby, R.
    IEEE Antennas and Wireless Propagation Letters 19 (2020)
    This letter presents the integration of frequency selective surfaces (FSSs) with retroreflectors for the realization of chipless wireless indoor localization tag landmarks. As an example, the high radar cross section (RCS) of a trihedral corner reflector is signed with an FSS-based stopband filter, so that the backscattered power from several corner reflectors can be distinguished by a mobile reader according to the frequency response of the FSS. Measurement results with a 3 × 3 × 3 cm3 trihedral corner reflector and a stopband FSS in a Rogers RT/Duroid 5880 high-frequency laminate at 90 GHz shows an RCS above -25 dBsqm for 90° coverage in the TM plane. Due to the high RCS, measurements at distances up to 4 m with a standard 25 dBi gain horn antenna and a vector network analyzer as a reader are shown. These preliminary results show the potential of the concept for applications such as indoor localization with sub-mm accuracy, where high bandwidths, but only a low number of bits, are needed for the identification of the tag landmarks. © 2002-2011 IEEE.
    view abstract10.1109/LAWP.2020.2975143
  • Frequency-coded chipless RFID tags: Notch model, detection, angular orientation, and coverage measurements
    Alam, J. and Khaliel, M. and Fawky, A. and El-Awamry, A. and Kaiser, T.
    Sensors (Switzerland) 20 (2020)
    This paper focuses on the frequency coded chipless Radio Frequency Identification (RFID) wherein the tag’s information bits are physically encoded by the resonators’ notch position which has an effect on the frequency spectrum of the backscattered or retransmitted signal of the tag. In this regard, the notch analytical model is developed to consider the notch position and quality factor. Besides, the radar cross section (RCS) mathematical representation of the tag is introduced to consider the incident wave’s polarization and orientation angles. Hence, the influences of the incident wave’s orientation and polarization mismatches on the detection performance are quantified. After that, the tag measurement errors and limitations are comprehensively explained. Therefore, approaches to measureing RCS-and retransmission-based tags are introduced. Furthermore, the maximum reading range is theoretically calculated and practically verified considering the Federal Communications Commission (FCC) Ultra Wideband (UWB) regulations. In all simulations and experiments conducted, a mono-static configuration is considered, in which one antenna is utilized for transmission and reception. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/s20071843
  • Frequency-Coded mm-Wave Tags for Self-Localization System Using Dielectric Resonators
    Jiménez-Sáez, A. and Alhaj-Abbas, A. and Schüßler, M. and Abuelhaija, A. and El-Absi, M. and Sakaki, M. and Samfaß, L. and Benson, N. and Hoffmann, M. and Jakoby, R. and Kaiser, T. and Solbach, K.
    Journal of Infrared, Millimeter, and Terahertz Waves 41 (2020)
    The paper describes the development of passive, chipless tags for a novel indoor self-localization system operating at high mm-wave frequencies. One tag concept is based on the low-Q fundamental mode of dielectric resonators (DR) which exhibits peak scattering at its resonance frequency. As the radar cross-section (RCS) of DRs at mm-wave frequencies is far too low for the intended application, arrays of DRs and combinations with dielectric lens and corner reflectors are investigated to boost the RCS while keeping the scattering retro-directive over wide-angle incidence. Satisfactory results are demonstrated experimentally in W-band with metal corner reflectors combined with planar arrays of DRs; the tags produce a high RCS level over a moderately broad angular range and a wide frequency range where they exhibit a notch at the resonance frequency of the dielectric resonators. These designs suffer from low coding range of 3 to 6 bit, degradations of RCS in angular range, and a difficult separation of the tag response from strong clutter. Both the suppression of large clutter interference by using time gating of the tag response and a larger coding range are promised by a chipless tag concept based on multiple high-Q resonators in photonic crystal (PhC) technology. Experimental samples are characterized as transmission resonators and as retro-directive tags at the 230 GHz band. As a concept to boost the retro-directive RCS with a truly wide-angle response, the integration of PhC resonators with a Luneburg lens is discussed. © 2020, The Author(s).
    view abstract10.1007/s10762-020-00707-0
  • High Resolution VNA THz Imaging for Large Distances
    Damyanov, D. and Batra, A. and Friederich, B. and Kolpatzeck, K. and Liu, X. and Kaiser, T. and Schultze, T. and Balzer, J.C.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2020-November (2020)
    In this paper, we employ a terahertz vector network (VNA) analyzer system for high resolution imaging using a Kirchhoff migration algorithm. The imaging method makes use of a divergent terahertz beam and eliminates the requirement for any optomechanical elements. This enables high resolution imaging at distances larger than 1 m. Moreover, a method is presented which compensates for the low relative bandwidth of the VNA compared with typical terahertz time-domain spectroscopy systems. We validate the performance of the method with 2-dimensional 360° imaging of a sample at a distance of 1.35 m. © 2020 IEEE.
    view abstract10.1109/IRMMW-THz46771.2020.9370443
  • High-Resolution Long-Range THz Imaging for Tunable Continuous-Wave Systems
    Damyanov, D. and Batra, A. and Friederich, B. and Kaiser, T. and Schultze, T. and Balzer, J.C.
    IEEE Access 8 (2020)
    Imaging in the terahertz frequency range has attracted growing interests since the first image of a leaf more than 20 years ago, due to its countless applications in basic and applied research, medical imaging, and nondestructive testing. However, most terahertz imaging approaches rely on focusing optics which require knowledge about the imaging scene before the actual imaging takes place. Further, imaging is mostly restricted to short distances and high resolution is only achieved for systems with a high bandwidth. Here, we present a method that enables high-resolution imaging of small metallic and dielectric objects at distances up to 2 m based on a synthetic aperture. We derive a simple approximation for the resolution of partial circular synthetic apertures with limited bandwidth. The bandwidth limitation is encountered by replacing the measured signals with replica signals of high bandwidth and equal round-trip time so that the resolution is only limited by the carrier frequency and signal-to-noise ratio of the measurement system. © 2013 IEEE.
    view abstract10.1109/ACCESS.2020.3017821
  • Indoor large-scale mimo-based rssi localization with low-complexity rfid infrastructure
    El-Absi, M. and Zheng, F. and Abuelhaija, A. and Abbas, A.A.-H. and Solbach, K. and Kaiser, T.
    Sensors (Switzerland) 20 (2020)
    Indoor localization based on unsynchronized, low-complexity, passive radio frequency identification (RFID) using the received signal strength indicator (RSSI) has a wide potential for a variety of internet of things (IoTs) applications due to their energy-harvesting capabilities and low complexity. However, conventional RSSI-based algorithms present inaccurate ranging, especially in indoor environments, mainly because of the multipath randomness effect. In this work, we propose RSSI-based localization with low-complexity, passive RFID infrastructure utilizing the potential benefits of large-scale MIMO technology operated in the millimeter-wave band, which offers channel hardening, in order to alleviate the effect of small-scale fading. Particularly, by investigating an indoor environment equipped with extremely simple dielectric resonator (DR) tags, we propose an efficient localization algorithm that enables a smart object equipped with large-scale MIMO exploiting the RSSI measurements obtained from the reference DR tags in order to improve the localization accuracy. In this context, we also derive Cramer–Rao lower bound of the proposed technique. Numerical results evidence the effectiveness of the proposed algorithms considering various arbitrary network topologies, and results are compared with an existing algorithm, where the proposed algorithms not only produce higher localization accuracy but also achieve a greater robustness against inaccuracies in channel modeling. © 2020 by the authors.Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/s20143933
  • Indoor THz SAR trajectory deviations effects and compensation with passive sub-mm localization system
    Batra, A. and El-Absi, M. and Wiemeler, M. and Göhringer, D. and Kaiser, T.
    IEEE Access 8 (2020)
    In radar remote sensing, the Terahertz (THz) spectrum is presently being investigated worldwide with focus on short-range indoor and outdoor applications. The spectrum broadens the unmanned aerial vehicle (UAV) based synthetic aperture radar (SAR) applications to indoor room profiling with sub-mm resolution and material characterization as many materials have unique fingerprints at this spectrum. SAR technique requires precise localization information of the mobile radar sensor, which in conventional SAR is achieved using an existing localization infrastructure, such as a global positioning system (GPS) and inertial measurement unit (IMU). for the indoor THz SAR, the GPS does not provide coverage in indoor complex environments, and also the state-of-art compact IMU does not provide the required sub-mm accuracy. These limitations can be overcome by utilizing an indoor localization system. Therefore, this paper presents an indoor THz simultaneous localization and mapping (SLAM) system. The system comprises of passive tags based radio frequency identification (RFID) localization system and SAR that provides the UAV localization and mapping of the in-room objects. Another challenge for the UAV based indoor THz SAR that is addressed in this paper is motion compensation (MOCO). At the THz, MOCO requires special consideration due to very small trajectory deviation is in the range of carrier wavelength. Therefore, to study the effects of the sub-mm translational errors, a testbed has been set up, and measurement results are presented in this paper along with the 3D electromagnetic simulation results for a carrier frequency of 275 GHz and bandwidth of 50 GHz. Further, to compensate these errors, the sub-mm localization system is used and the results are presented to validate the proposed solution for indoor THz SAR MOCO. © 2020 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.
    view abstract10.1109/ACCESS.2020.3026884
  • Metallic reflectors with notched RCS spectral signature using dielectric resonators
    Abbas, A.A. and El-Absi, M. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    Electronics Letters 56 (2020)
    Dielectric resonators are placed in front of the metallic plane plate and corner reflectors. Excitation of the resonant mode produces strong scattering of an incident plane wave which shows up as narrow notch in the mono-static radar cross section (RCS) spectral signature at the resonance frequency. Experimental proof at V-band is given with a corner reflector of centimetre size with spherical dielectric resonators of 0.8 mm diameter showing a notch at 64 GHz. © The Institution of Engineering and Technology 2020.
    view abstract10.1049/el.2019.2942
  • OAM Mode Order Conversion and Clutter Rejection with OAM-Coded RFID Tags
    Hassan, M.H. and Sievert, B. and Svejda, J.T. and Abbas, A.A. and Jimenez-Saez, A. and Ahmad, A.M. and Schubler, M. and Rennings, A. and Solbach, K. and Kaiser, T. and Jakoby, R. and Sezgin, A. and Erni, D.
    IEEE Access 8 (2020)
    In this article a uniform helically arranged dielectric resonator array can generate Orbital Angular Momentum waves (OAM) causing a conversion of OAM mode orders $m$ from an incoming mode ${m}_{in}$ to an outgoing mode ${m}_{out}$. The operating frequency is set as 10 GHz to facilitate the measuring process. This new approach provides additional OAM values per digit in the RFID technology according to the excited OAM modes ${m}_{n}\\\in \\\{\ldots-2-1012\ldots \}$ instead of the conventional binary values ${b}_{n}~\in ~\{0 1\}$. Thus more information content is revealed. Through the OAM concept a ${m}_{1} {m}_{2}~2$-digits OAM coded tag is obtained upon the employment of two uniform helically arranged cylindrical dielectric resonator arrays operating at two different frequencies ${f}_{1} = 10\\\text {GHz}$ and ${f}_{2} = 11\\\text {GHz}$. Each array has 8 DRs but with different radius yielding a reduction of the mutual coupling between the varied circular arrays. The interaction between the phase delayed radiation of each DR element in the array generates different vortex waves with corresponding OAM mode orders. In order to achieve the correct phase delay the elevation of each DR is specified by the desirable OAM mode order the number of elements and the propagation wavelength. At first the generation of OAM mode orders-1 2 and-3 is carried out. Then mode conversion from 0 to-1 +1 to-2-1 to 0 +2 to-3 and-2 to +1 are depicted. After that two simulated examples of 2-digits OAM coded tags with the code $\{-11\}$ and $\{-20\}$ are presented. A conversion of mode 0 to mode 1 has been simulated and also measured where an additional metal sheet is used to evaluate the distortion in the OAM modes. As a result this study demonstrates that the uniform helically arranged DR arrays can convert the incoming OAM mode order into another one where the clutter from broadside direction is rejected due to the Butler matrix (BM) which interferes the clutter destructively. © 2013 IEEE.
    view abstract10.1109/ACCESS.2020.3043053
  • Passive Orbital Angular Momentum RFID Tag based on Dielectric Resonator Arrays
    Haj Hassan, M. and Alhaj Abbas, A. and Jimenez-Saez, A. and Mostafa Ahmad, A. and Sievert, B. and Schussler, M. and Rennings, A. and Solbach, K. and Kaiser, T. and Jakoby, R. and Sezgin, A. and Erni, D.
    2020 3rd International Workshop on Mobile Terahertz Systems, IWMTS 2020 (2020)
    In this paper, a novel approach is proposed to increase the information content of RFID tags using uniform helically arranged spherical dielectric resonator arrays. The proposed tag design is scalable to operating frequency in the mm-wave/THz range and provides a larger information content due to new additional values per digits according to the excited OAM modes (mn=-2,-1,0,1,2,) instead of the binary values (bn=0 and 1). This new values can be called OAM values. By means of the orbital angular momentum (OAM) concept three uniform helically arranged spherical dielectric resonator arrays operating at three different frequencies f1=10GHz,\ f2=10.5 GHz, and f3=11GHz are established to provide a m1m2m3 3-digits OAM coded tag. Each array consists of 8 dielectric resonators (DRs) with three different radii in order to enhance the isolation between the different arrays. The OAM mode orders are generated by the interaction of phase delayed radiation from each DR element in the array. Each DR element is elevated in order to achieve the right phase shift, which is related to the mode order, the number of elements, and the propagation wavelength. Two examples of 3-digits OAM coded tags with the code -110 and -210 have been simulated and compared with a b1b2b3 3-digits conventional coded tag with the code 111 in order to compare the two approaches. © 2020 IEEE.
    view abstract10.1109/IWMTS49292.2020.9166434
  • Physical layer security of interference aligned mixed RF/unified-FSO relaying network
    Tubail, D., dtubail@gmail.com and El-Absi, M. and Salhab, A. and Ikki, S. and Zummo, S. and Kaiser, T.
    IET Communications 14 (2020)
    In this study, the authors secure the mixed radio frequency/free space optical (FSO) relay-aided interference aligned system using a proposed physical layer security algorithm. This algorithm reduces the quality of the received signal at the eavesdropper through two procedures. First, it minimises the data transmission power from the legitimate users and the relays. Second, it jams the eavesdropper by broadcasting artificial noise from the users and the relays. Therefore, a joint optimisation problem is formulated to degrade the received signal at the eavesdropper from the users and the relays and to maximise the jamming artificial noise power, which is solved using an iterative optimisation algorithm beside a semi-definitive programming algorithm. Furthermore, the pre-coding and decoding matrices of the users and the relay are designed to enable the legitimate users to cancel the artificial noise, while the eavesdropper is disabled from distinguishing the artificial noise from the real streams. Moreover, the security performance of the proposed algorithm is analysed, and the impact of the FSO link's state on the security performance is studied. The extensive simulation results show the efficiency of the proposed algorithm and illustrate the role of the FSO link's state on the security performance. © The Institution of Engineering and Technology 2020.
    view abstract10.1049/iet-com.2019.0892
  • Simulation Validation of High Resolution Indoor Terahertz Synthetic Aperture Radar Imaging
    Batra, A. and Wiemeler, M. and Goehringer, D. and Kaiser, T.
    14th European Conference on Antennas and Propagation, EuCAP 2020 (2020)
    Indoor Terahertz Synthetic Aperture Radar (SAR) is an emerging technology for material characterization, high resolution imaging and localization. In comparison to optical technology, it provides benefits in hazardous scenarios such as fire in a building as objects inside the building can be characterized and localized. The principles of SAR are well established but the main challenge lies with extending this technology to high frequencies and indoor environment. To investigate this technology, imaging geometry and system parameters have to be evaluated respectively. This paper explains the signal processing of SAR and presents the imaging geometry for an indoor scenario. Further, it evaluates the parameters for high resolution imaging and localization. Based on these parameters, system design has been simulated and results of 2D high resolution indoor SAR imaging at 300 GHz are presented. Additionally, the proof of theoretical resolution across the range and azimuth is shown with the simulation results. © 2020 EurAAP.
    view abstract10.23919/EuCAP48036.2020.9135521
  • Sub-mm Resolution Indoor THz Range and SAR Imaging of Concealed Object
    Batra, A. and Vu, V.T. and Zantah, Y. and Wiemeler, M. and Pettersson, M.I. and Goehringer, D. and Kaiser, T.
    2020 IEEE MTT-S International Conference on Microwaves for Intelligent Mobility, ICMIM 2020 (2020)
    In radar systems, the frequency range is being extended to high frequencies such as THz for sub-mm resolution. The spectrum offers high resolution but on the contrary, propagation distance and penetration depth are limited because of smaller wavelength. It suffers from higher atmospheric absorption in comparison to sub-GHz systems. In comparison to optical technology, the radar technique majorly benefits with respect to the penetration property such as cloud/smoke cover penetration and detection of concealed objects. However, the THz range and synthetic aperture radar (SAR) imaging of concealed objects are not very well established. Therefore, this paper examines this property at THz. A testbed has been set up with a bandwidth of 110 GHz at a carrier frequency of 275 GHz. The imaging is performed of a very small metal object. Firstly, the sub-mm resolution is validated with the experiment after that the range and SAR imaging are performed in which this object is covered with different types of materials. The backscattered data is processed with the image reconstruction algorithms and the results are presented in this paper with respect to sub-mm resolution and detection. © 2020 IEEE.
    view abstract10.1109/ICMIM48759.2020.9299034
  • Terahertz Wave Scattering by Rough Surfaces including Higher Moments: Ray-Tracing Developments
    Alissa, M. and Sheikh, F. and Zarifeh, N. and Kreul, T. and Kaiser, T.
    Proceedings of the 2020 IEEE International Conference on Computational Electromagnetics, ICCEM 2020 (2020)
    The most common analytical model used in raytracing to estimate the scattered field by a random rough surface is the Kirchhoff approximation, where a normal distribution of the surface heights is assumed. When approximating the non-Gaussian surface roughness with a Gaussian distribution, the high peaks and valleys cause an overestimation of the heights' standard deviation and yields to inaccurate valuation of the coherent component of specular reflection. In this work, for an accurate scattering modeling of a non-line-of-sight (NLOS) propagation scenario, a curve fitting method is applied to calculate the effective roughness from non-Gaussian surfaces and then implemented in a self-programmed three-dimensional ray-tracer. When considering the third moments of the heights distribution, a deviation of (0 - 3.5) dB is observed in the scattering power depending on the material roughness. © 2020 IEEE.
    view abstract10.1109/ICCEM47450.2020.9219485
  • Wide-Angle RCS Enhanced Tag Based on Dielectric Resonator - Lens Combination
    Alhaj Abbas, A. and El-Absi, M. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    Frequenz 74 (2020)
    In a novel mm-wave localization system, dielectric resonators (DR) have been proposed as passive chipless RFID tags to mark fixed reference nodes. To counter clutter and improve the limited read range due to the low RCS level of a DR at millimeter-wave frequencies we propose a combination of several DRs with a dielectric spherical lens which allows improvement of up to 30 dB. The paper presents the design principle and shows simulation results and experimental verification of a scaled tag operating in the 10-12 GHz range and covering a range of incidence angle of the reader signal of ± 50°. A frequency sweeping RF reader can identify the tag (information) by the peak of the RCS level at its DR resonant frequency. For a multiple-tag scenario we can realize up to 12 different tags which can be discriminated unambiguously by their resonant frequencies in a 1: 1.2 frequency bandwidth. © 2020 Walter de Gruyter GmbH, Berlin/Boston.
    view abstract10.1515/freq-2019-0068
  • A compact measurement setup for in-situ material characterization in the lower THz range
    Barowski, J. and Jebramcik, J. and Alawneh, I. and Sheikh, F. and Kaiser, T. and Rolfes, I.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    Frequency Modulated Continuous Wave radar systems offer a very large dynamic measurement range, while at the same time they can be fabricated very compact and cost efficient. Due to this, FMCW-sensors are a feasible alternative to costly measurement equipment like vector network analyzers. Applying calibration techniques and algorithms from the VNA domain, they can also be used to characterize materials with very high precision. At the same time, the short measurement time allows their use in mobile high precision measurement setups. This paper presents such a mobile setup that is easily calibrated an can be used for in-situ material parameter estimation and data collection for e.g. channel models. For this purpose, a SiGe-radar system in the lower THz range from 200 GHz to 250 GHz is used. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823700
  • A modified beckmann-kirchhoff scattering model for slightly rough surfaces at terahertz frequencies
    Sheikh, F. and Kaiser, T.
    2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, APSURSI 2019 - Proceedings (2019)
    The diffuse reflection of electromagnetic waves is merely dependent on the surface roughness, incident angles, complex refractive index of materials and wavelength at hand. At terahertz frequencies, diffuse reflection tends to be particularly strong due to the increased surface roughness and this causes an additional attenuation even in the specular direction of reflection. In this paper, we examine the terahertz (THz) channel from 300 GHz (0.3 THz) to 310 GHz (0.31 THz) in the presence of slightly rough surfaces (0 < g ≪ 1) by using the approximate solutions from Rayleigh-Rice (R-R) and Beckmann-Kirchhoff (B-K) scattering theories. However, the classical Beckmann-Kirchhoff theory contains a small-angle limitation (i.e., it fails at large angles of incidence and wide scattering angles). Thus, we also endeavor to demonstrate the modified Beckmann-Kirchhoff scattering theory, an approach by Verold and Harvey, using multipath channel transfer function (CTF) dynamics for line-of-sight (LoS) and non-line-of-sight (NLoS) conditions in a simple office environment. © 2019 IEEE.
    view abstract10.1109/APUSNCURSINRSM.2019.8889095
  • An Information-Theoretic Approach to the Chipless RFID Tag Identification
    Chen, Y. and Zheng, F. and Kaiser, T. and Vinck, A.J.H.
    IEEE Access 7 (2019)
    In this paper, we focus on the chipless radio-frequency identification (RFID), where the tag information bits are encoded by the peak/notch pattern appeared in the frequency spectrum of the radar cross section (RCS) of the tag. In particular, we restrict our attention to a simple yet prevalent 'binary' coding method, where a bit 0 or bit 1 is encoded by the absence or presence of the peak/notch, respectively. We provide an information-theoretic framework for the tag identification based on such a binary coding method. Our aim is to accommodate more bits in the limited bandwidth without degrading the identification performance. To this end, we first formulate the detection of each bit as a binary asymmetric channel (where a signal processing approach is integrated into each interrogation to enhance the underlying channel quality). Moreover, it is proposed to perform multiple interrogations with majority rule-based detection (in correspondence to the signal processing approach in each interrogation). Furthermore, we introduce some error-detecting codes to further improve the performance of tag identification. For instance, motivated by the asymmetric property of the channel model, we propose to apply the constant weight code and the Berger-Freiman code (as two representatives of non-systematic and systematic codes, respectively) to the problem to be addressed in this paper. In addition, an investigation is also conducted into the cyclic redundancy check (CRC) codes (as a representative of those codes that are not dedicated to the binary asymmetric channel but could be potentially competitive for error detection). The system's performance is analyzed through the key parameters, namely the successful transmission rate, the false identification rate (i.e., the probability of undetected errors), and the expected number of retransmissions/interrogations. The effectiveness of the proposed methods is demonstrated by the numerical results. © 2013 IEEE.
    view abstract10.1109/ACCESS.2019.2929243
  • Antenna Selection Performance of Distributed Antenna Systems in Full-Duplex Indoor Base Station
    Zarifeh, N. and Alissa, M. and Kreul, T. and Kaiser, T.
    GeMiC 2019 - 2019 German Microwave Conference (2019)
    The work in this paper is trying to answer the question: In a full-duplex indoor base station with antenna selection, what are the benefits of using distributed antennas instead of co-located antennas? In other words, how much the use of distributed antennas would contribute in mitigating the self-interference in the full-duplex system. A ray-tracing tool is used to characterize the indoor multi-path channel environment. Subsequently, a baseband analysis is done to evaluate the performance of the full-duplex system. The distributed antenna system slightly outperforms the co-located system in the studied scenario. © 2019 IMA - Institut fur Mikrowellen- und Antennentechnik e.V.
    view abstract10.23919/GEMIC.2019.8698126
  • Atmospheric attenuation analysis in indoor thz communication channels
    Sheikh, F. and Alissa, M. and Zahid, A. and Abbasi, Q.H. and Kaiser, T.
    2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, APSURSI 2019 - Proceedings (2019)
    In this paper, we study the terahertz (THz) transmission channels from 100 GHz (0.1 THz) to 1000 GHz (1 THz) by including the effects of frequency-dependent atmospheric attenuation and diffuse reflection (non-specular scattering) due to surface roughness for short-range indoor wireless communications. First and foremost, the ITU-R Rec. P. 676-8 model has been used for this study to compute the effects of water-vapor content in the atmosphere by demonstrating the multipath channel transfer function (CTF) dynamics for line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios in a simple realistic office environment. Then, the indoor multipath propagation and its impact considering rough surfaces has been investigated employing the classical Beckmann-Kirchhoff (B-K) model by using our self-developed ray tracing algorithm (RTA). Finally, the relative received power and contribution of the diffusely scattered power at 300 GHz has been illustrated at each scenario point with different surface roughness to predict the achievable signal-to-noise ratio. © 2019 IEEE.
    view abstract10.1109/APUSNCURSINRSM.2019.8888704
  • Channel measurements in lecture room environment at 300 GHz
    Zantah, Y. and Sheikh, F. and Abbas, A.A. and Alissa, M. and Kaiser, T.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    Channel measurements across 300 GHz to 310 GHz spectrum are performed to realize the ultra-broadband wireless communication channel behaviour for various channel configurations in lecture room environment. At terahertz (THz) frequencies, it is believed that high directional antenna based line-of-sight (LoS) communication possibly achieves terabitper-second (Tbps) links. Thereupon, the VNA-based channel measurements are performed using 26 dBi horn antennas at both the transmitter (TX) and receiver (RX) sides for retrieving the channel parameters (i.e., path loss exponent, shadowing factor) to derive the single-slope path loss model in LoS scenario for distances up to 5 m. Moreover, the results are also evaluated with waveguide antenna (open) for horn-open, and open-open configurations to estimate the propagation losses for different antenna directivities. So far, the results from such a long-distance channel measurement campaign are not recorded yet. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823666
  • Dielectric resonator-based passive chipless tag with angle-of-arrival sensing
    Alhaj Abbas, A. and El-Absi, M. and Abualhijaa, A. and Solbach, K. and Kaiser, T.
    IEEE Transactions on Microwave Theory and Techniques 67 (2019)
    Passive chipless tags based on dielectric resonators (DRs) have been proposed for a novel millimeter-wave indoor self-localization system to mark fixed reference nodes. The tags employed in the system provide a unique spectral signature (resonance peaks) with much-increased radar cross section (RCS) by placing several identical DRs at the focal line of a spherical dielectric lens. Resonators of optimized geometry allow a modification of this original DR-lens tag by combining the lens with different size DRs which exhibit resonant frequencies separated by large frequency gaps. For easier manufacturing and testing, a demonstrator tag was designed for a 'scaled' frequency range of 5-6 GHz with this configuration and is shown to produce spectral signatures of the monostatic RCS which are uniquely related to the angle of arrival (AoA) of the incident wave from a reader. Simulated signatures of a lens of 120-mm diameter with seven spherical DRs are presented and results are supported by experiment. Correlation processing of the signatures can give a resolution of few degrees in AoA while the bistatic RCS half-power beamwidth is on the order of 20°, and RCS levels of resonant peaks are produced between 0 and -6 dBm2. © 1963-2012 IEEE.
    view abstract10.1109/TMTT.2019.2901447
  • Electromagnetic identification from UHF to THz: State of the art, novel approaches and outlook
    Khaliel, M. and Kaiser, T.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    This paper presents a brief review of the passive EM identification technologies up to THz frequency range. Special attention is devoted to THz identification, where a Dielectric Resonator (DR) is considered to be the most effective frequency encoding element up to date. In this paradigm, the recent advances in DR based identification are comprehensively reviewed. Furthermore, the DR resonance modes are for the first time separated and thus the corresponding RCS of each mode is accurately evaluated. However, the literature counterpart, the superposition of all modes is considered to be the DR RCS. After that, the clutter suppression is discussed in the context of a specific indoor localization scenario. Accordingly, the backscattering signal and system models for separating and detecting these modes are presented. Hence, these developed models are paving the way for developing a unifying evaluation framework which aspires to evaluate performance of the various tag design approaches in different real scenarios. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823715
  • Experimental Investigation of Terahertz Wave Scattering by Statistically Controlled Rough Surfaces
    Alissa, M. and Friederich, B. and Kolpatzeck, K. and Czylwik, A. and Kaiser, T.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    In this work, the experimental investigation of electromagnetic wave scattering by statistically controlled rough surfaces in the lower THz band is demonstrated. Rough surfaces with height fluctuations following normal statistics are fabricated using two different 3D printing techniques. The results presented here confirm that the surface roughness has a noticeable effect on the level of the diffuse scattering energy. In the future, the applied method can be used to validate analytical models as well as to gain scattering patterns from more complicated rough surface structures which fall outside the limits of most analytical approximations. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880134
  • Full-Duplex Femto Base-Station with Antenna Selection: Experimental Validation
    Zarifeh, N. and Zantah, Y. and Gao, Y. and Kaiser, T.
    IEEE Access 7 (2019)
    Full-Duplex (FD) is an emerging technology that allows the communication device to use the same frequency to simultaneously transmit and receive. The cancellation of the high power Self-Interference (SI) is the main challenge in FD systems. Hybrid SI mitigation and cancellation schemes in propagation, analog, and digital domains, have to be used in order to mitigate the SI. Antenna selection (AS) can be employed to select the best antenna, or set of antennas, that guarantees jointly the maximization of the desired signal, and the minimization of SI. In this paper, we aim to experimentally enable FD transmission in an indoor femto base-station (BS) with antenna selection. Receive antenna selection is combined with cross-polarization and antennas conditional placement in order to achieve the required SI cancellation. Half-duplex (HD) Uplink (UL) user-equipments (UE) are used to measure the effect of downlink (DL) SI on the UL reception at the FD BS receiver. Different scenarios are experimented in the testbed such as, changing the number of antennas, the type of isolation (vertical/horizontal), and the type of antennas (Omnidirectional/directional). Three AS criteria are used, and the performance of the system is evaluated in terms of bit-error-rate, sum-rate, residual SI, and FD/HD sum-rate enhancement ratio. The measurement results show that the proposed hybrid solution is feasible to enable FD transmission in the considered scenario. © 2013 IEEE.
    view abstract10.1109/ACCESS.2019.2933427
  • High RCS Passive Tag based on Dielectric Resonator - 2D Lens Combination
    Abbas, A.A. and El-Absi, M. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    GeMiC 2019 - 2019 German Microwave Conference (2019)
    In this paper, a Lens-Dielectric Resonator combination is proposed to improve RCS of dielectric resonator tags to be used in a self-localization system where high RCS is essential to combat clutter signals. As a proof of concept, a cylindrical dielectric resonator is located in the focal area of a 200 mm diameter (3.5 λ at 5.2 GHz) 2D Luneburg Lens sandwiched between two tapered metal plates. Two approaches of realizing the continuous variation of the Luneburg lens dielectric permittivity are implemented, fabricated, and tested: by using stepped cylindrical layers of dielectric material (fabricated by machining process) and by using effective medium theory in which the lens is constructed from a group of cells made of various cuboids sizes connected to trapezoidal rods (fabricated by 3D printing technology using PP). A good compatibility between DR and lens is observed. The improvement in RCS is found to vary depending on DR resonance mode. For the HE11 mode, a 20 dB improvement is achieved. © 2019 IMA - Institut fur Mikrowellen- und Antennentechnik e.V.
    view abstract10.23919/GEMIC.2019.8698178
  • Indoor Material Properties Extraction from Scattering Parameters at Frequencies from 750 GHz to 1.1 THz
    Sheikh, F. and Mabrouk, I.B. and Alomainy, A. and Abbasi, Q.H. and Kaiser, T.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    This paper reports the first ever transmission measurements for a wide choice of different indoor materials such as wood, plastic, paper, brick, glassand leatherat frequencies from 750 GHz to 1.1 THz using up-conversion (frequency-domain) method employing Swissto12system. This commercially available system consists of three parts, namely, vector network analyzer (VNA), the material characterization kit (MCK), and two waveguide extenders which measure the S -parameters in the frequency range of interest to derive the complex dielectric properties of material samples using stepwise Nicolson-Ross-Weir (NRW) method. These frequency dependent material parameters such as permittivity, refractive index and absorption coefficient are mandatory to analyze and model the wave propagation thoroughly for the aforementioned unexplored frequencies along with the ability to classify and localize these different materials precisely. Until previously, only THz time-domain spectroscopy (THz TDS) system based on down-conversion (time-domain) method is employed to measure the spectroscopic responses for this cause. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880096
  • Monitoring health status and quality assessment of leaves using terahertz frequency
    Zahid, A. and Abbas, H.T. and Sheikh, F. and Kaiser, T. and Zoha, A. and Imran, M. and Abbasi, Q.H.
    2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, APSURSI 2019 - Proceedings (2019)
    This paper presents a new and non-invasive electromagnetic technique that utilizes the terahertz frequency waves to monitor the plant health. To do so, the water content of a plant leaf is obtained using the measured scattering response in the frequency range of 0.75 to 1.1 THz. Leaves of three commonly used herbs were observed for four consecutive days and the electromagnetic material parameters such as the permittivity were extracted using a material characterization algorithm. The decreasing moisture level and in turn the plant health can therefore be directly inferred from the leaf permittivity which approaches to that of free space with the passage of days. © 2019 IEEE.
    view abstract10.1109/APUSNCURSINRSM.2019.8889356
  • Preliminary analysis of candle flame impact on THz electromagnetic wave propagation
    Ghwaji, A. and Sheikh, F. and Schultze, T. and Willms, I. and Kaiser, T.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    This paper presents a preliminary analysis of candle flame impact on the ultra-broadband terahertz (THz) communication links across a spectrum of interest from 300 GHz to 310 GHz. This approach is based on complex transfer functions extracted from channel measurements using a vector network analyzer (VNA) to study the variations in total received power and phase. The channel measurements are performed in a lecture room under line-of-sight (LoS) environment. By evaluating the results, it turns out that the ray trajectories remain unchanged with candle flame but have slightly altered amplitudes of paths and phases. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823748
  • RCS enhancement of dielectric resonator tag using spherical lens
    Alhaj Abbas, A. and El-Absi, M. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    Frequenz 73 (2019)
    The RCS of flat cylindrical Dielectric Resonators DR) is investigated and found to be too low for an application of the resonators as tags in a novel indoor localization system at mm-wave frequencies. As a method to increase the RCS of a DR tag, we propose the combination with a constant-index spherical lens. The collimation and scattering properties of this lens type are found suitable for a combination with DRs. The optimum relative permittivity of the lens is found in the range of ?r=1.6 to 2.8 and the optimum distance between lens surface and DR is found slightly larger than the radius of the DR. RCS enhancement is found to vary with the modes of the DR but increases approximately with the fourth power of the lens radius. However, RCS signatures become corrupted by scattering due to mismatch effects of large lenses such that the lens diameter has to be limited to 4 to 5 wavelengths with the RCS enhancement limited to about 30 to 35?dB. Simulation and experimental verification are performed at a down-scaled frequency range from 4?GHz to 7?GHz using lenses of 60?mm and 120?mm diameter made of paraffin wax. © 2019 Walter de Gruyter GmbH, Berlin/Boston 2019.
    view abstract10.1515/freq-2018-0224
  • Reliability Analysis of Centralized Radio Access Networks in Non-Line-of-Sight and Line-of-Sight Scenarios
    Peethala, D. and Kaiser, T. and Han Vinck, A.J.
    IEEE Access 7 (2019)
    The fifth generation (5G) wireless network technology is set to be standardized by 2020, where the main goals are to improve capacity, reliability, and energy efficiency while reducing latency and massively increasing connection density. 5G systems target to support a vast number of services with heterogeneous requirements. In recent years, a centralized processing radio architecture called centralized radio access network (C-RAN) or Cloud-RAN has got a lot of attention because of its potential to meet the 5G goals. In this paper, we present a lower layers centric C-RAN analysis methodology, which is designed on the key design principles of 5G systems: flexibility and reliability. In this paper, reliability at lower layers is defined as the probability of achieving a minimum required signal-to-interference-plus-noise-ratio at a user equipment location. The main contributions of our work are the reliability analysis of C-RAN systems in non-line-of-sight and line-of-sight conditions. Furthermore, a real-time C-RAN testbed with measurement results are presented to validate the reliability analysis. © 2013 IEEE.
    view abstract10.1109/ACCESS.2019.2896410
  • SAR signal processing architecture and effects of motion errors for MmWave and THz frequencies
    Batra, A. and Wiemeler, M. and Kreul, T. and Goehringer, D. and Kaiser, T.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    Most commonly used frequencies in Synthetic Aperture Radar (SAR) imaging are from hundreds of MHz to tens of GHz. Nowadays, the unexplored mmWave and THz regimes are being investigated for SAR imaging to have higher resolution. Two research challenges for this technology - motion compensation and real-time processing - are addressed in this paper. SAR image reconstruction algorithms lack data dependencies. Therefore, it can be processed in a parallel computing environment to accelerate the image reconstruction. This paper presents the theoretical model of a distributed signal processing testbed. The performance enhancement with the inclusion of high performance computing for image processing is also explained. Another challenge for this technology comes from a motion compensation point of view. The SAR signal processing assumption is that the radar-carrying platform follows an ideal path. However, in reality, the platform deviates from this path. Especially at THz, very small deviations in the range of sub-mm produce motion errors because of wavelengths in the range of deviations. It degrades the image quality and provides wrong estimations of range and azimuth scatters. The paper summarizes motion error types, their characterization, and constraint on the amplitude of deviation. Also, the paper presents effects of these errors at 100 GHz with simulation results. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823730
  • The Effect of Rough Surface Statistics on Diffuse Scattering at Terahertz Frequencies
    Alissa, M. and Kreul, T. and Kaiser, T.
    2019 European Conference on Networks and Communications, EuCNC 2019 (2019)
    In Terahertz region, the diffuse scattering phenomenon by rough surfaces has a remarkable effect of non-line of sight (NLOS) channel propagation. Several parameters contribute to form a specific distribution of the scattered rays, and the angular distribution of the scattered field varies depending on the surface roughness parameters. Yet, a clear understanding of how these parameters adjust the scattered field distribution is still missing. In this work, we investigate the scattering properties of indoor materials at Terahertz band. This is done via full-wave simulation of the diffused scattering by rough samples varies in their roughness characteristics. Then, the role of each statistical parameter is investigated separately. It was proven that both the surface correlation function and the correlation length have an influence on the far field scattered energy. While the height standard deviation has a direct effect on the specular part, the correlation length seems to affect the power distribution out of the specular direction. The longer the correlation length, the more energy is accumulated closer to the specular direction. The resulting angular distribution can be then applied for obtaining more accurate NLOS channel predictions. © 2019 IEEE.
    view abstract10.1109/EuCNC.2019.8802032
  • THz passive RFID tag based on dielectric resonator linear array
    Abbas, A.A. and El-Absi, M. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    In this paper, we propose a solution to mitigate the strong clutter signal for a use in a THz indoor self localization system using a chipless tag based on linear dielectric resonator arrays to enhance the Radar Cross Section (RCS) and therefore increase its detectability. Simulation results are presented for a five elements array separated by 0.8λ at 105 GHz where a 18 dB RCS enhancement is achieved. For a multiple tag scenario, seven frequency coded tags that take the binary values from 001 to 111 can be realized by coding bit 1 and 0 by the presence and the absence of three different resonance frequencies in the RCS spectrum, equivalently the presence and the absence of the dielectric resonator array with different dimensions. The tags can be discriminated with a free ambiguity over a wide range of incidence angle of the reader signal of −/+ 35◦. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823734
  • Towards interference alignment for distributed large-scale MIMO hardware architecture and implementation
    Galih, S. and El-Absi, M. and Kaiser, T.
    Universal Journal of Electrical and Electronic Engineering 6 (2019)
    Massive MIMO or Large Scale MIMO is a promising solution for achieving superior data rates in 5G communication systems. However it has limitation in term of scalability and coverage for users that has highly spatial separation. Distributed massive MIMO is expected to enhance these drawbacks. One main problem arises in this scheme is the MIMO interference channel conditon that can be coped by interference alignment algorithm. The main consideration for interference alignment algorithm in distributed Massive MIMO is to achieve low complexity precoding to eliminate interference channel condition and to design efficient hardware architecture for its implementation. Previous research regarding IA for Distributed Massive MIMO indicates that the complexity issues is still not widely discussed. This paper proposed the low complexity IA scheme for large scale MIMO system based on limited interferer and the implementation of low cost interference alignment and wireless synchronization for distributed MIMO using software defined radio hardware. From the simulation result it is shown that limited interferer IA algorithm achieve acceptable BER performance, i.e. in order of 10 -3 . The hardware implementation of the IA precoding matrix computation is also discussed and base on the experiment it is show that the proposed algorithm and architecture achieved higher hardware performance compared to the linear IA. © 2019 by authors.
    view abstract10.13189/ujeee.2019.061306
  • Wave scattering from non-Gaussian rough surfaces at terahertz frequencies
    Alissa, M. and Sheikh, F. and Abbas, A.A.-H. and Kaiser, T.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    Concerning the facile solution to the problem of electromagnetic waves' scattering by a random rough surface, the surface distribution is generally assumed to be Gaussian. In this work, the scattering by non-Gaussian rough surfaces is investigated analytically and by simulation at terahertz (THz) frequencies. We found that for a slightly rough surface, a change in the distribution plays no major role in the scattering behavior at frequency of interest. However, for a very rough surface, with standard height deviations in the order of wavelength, the scattering pattern was distinctly affected thus changing the distribution when all other scattering factors are constant. The simulation results agree well with the analytical model, and prove that a normally distributed surface model may exhibit as an overly general surface to all random rough surfaces at THz frequencies. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823778
  • A Comparison Study of Non-specular Diffuse Scattering Models at Terahertz Frequencies
    Sheikh, F. and Lessy, D. and Alissa, M. and Kaiser, T.
    2018 1st International Workshop on Mobile Terahertz Systems, IWMTS 2018 (2018)
    At terahertz (THz) frequencies, dimensions of optically thin building materials (e.g., sand-lime brick, gypsum plaster) are comparable to or even larger than the wavelength. Such materials, normally neglected and assumed smooth evidently become rough now. A smooth material will reflect the incident ray specularly in a single direction, whilst a rough material will scatter it into various directions. Perhaps, for very rough materials the specular reflection loses its privileged position, and the non-specular diffusely scattered rays dominate the reflection behaviour. Likewise, a widely known fact that the surface roughness alters the scattered field far more than its electrical properties, emphasizes that these unique features lead to new multipath scattering models to characterize the THz channel. Effective Roughness (ER) and Beckmann-Kirchhoff (B-K) models address the problem of diffuse scattering by means of approximate models. This paper compares the aforementioned models considering the impact of diffuse scattering on total received power by employing ray-tracing tool in an indoor office environment. For this study, particular attention is diverted to the non-line-of-sight (NLoS) scenario due to its imminence in terms of coverage and performance. © 2018 IEEE.
    view abstract10.1109/IWMTS.2018.8454692
  • A Massive MIMO Signal Processing Architecture for GHz to THz Frequencies
    Batra, A. and Wiemeler, M. and Kreul, T. and Goehringer, D. and Kaiser, T.
    2018 1st International Workshop on Mobile Terahertz Systems, IWMTS 2018 (2018)
    State-of-the-art wireless technology is reaching its technical limits and future technologies such as millimeter wave (mmWave), massive MIMO and full duplex transmission included in upcoming 5G standards will be key in fulfilling demands for higher data rate and spectrum efficiency. Massive MIMO systems operating in the mmWave spectrum have many advantages in terms of e.g. beamforming and channel capacity, not only for communication systems but also for radar systems. Therefore, an experimental real time massive MIMO testbed utilizing sub-6GHz and the mmWave spectrum is to be constructed at Institute of Digital Signal Processing (DSV), University of Duisburg-Essen, Germany to investigate this technology in a practical manner for indoor radar system applications. The proposed testbed will initially be implemented for sub-6GHz frequencies with more than hundred antennas and later extended to the mmWave region. Obviously, the testbed design is very complex and a detailed design study is required before implementation. This paper summarizes findings of the design study. Firstly, a theoretical model of a signal processing architecture for a massive MIMO testbed is presented. This is followed by requirements and comparison of parameters processing power, bandwidth, data throughput etc. for sub-6GHz and mmWave spectrum. Also, mapping of algorithms on heterogeneous computational resources, such as FPGA, GPU and CPU is discussed. Based on the study, parameters for the proposed testbed are selected. © 2018 IEEE.
    view abstract10.1109/IWMTS.2018.8454699
  • A Novel Ray-Tracing Algorithm for Non-Specular Diffuse Scattered Rays at Terahertz Frequencies
    Sheikh, F. and Lessy, D. and Kaiser, T.
    2018 1st International Workshop on Mobile Terahertz Systems, IWMTS 2018 (2018)
    This paper presents a novel self-programmed three-dimensional (3D) ray-tracing algorithm (RTA) based on Beckmann-Kirchhoff (B-K) model for modeling diffuse scattering mechanism in non-specular directions at terahertz (THz) frequencies. The terahertz or submillimeter-wave frequencies pose unique challenges for channel modeling due to sparse and extreme frequency selective behaviour of the propagation mechanism. In particular, the most critical feature proved to provide important contributions in determining spatial and temporal dispersion in the submillimeter-wave band is the diffuse scattering mechanism, wherein an incident ray may split into a specular and several non-specular (diffused scattered) rays after bouncing off from rough materials. This makes the diffuse scattering or scattering from rough surfaces a necessary design consideration constituting a high proportion of all the propagation rays and hence, must be accounted for propagation modeling to accurately predict channel characteristics. Next, we integrate our MATLAB-based proposed algorithm to a commercial ray-tracing tool to derive a spatiotemporal model of scattered multipath propagation channels considering rough materials in a realistic office environment for both line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios. So far none of the commercially available ray-tracing tools have implemented this scattering model yet. © 2018 IEEE.
    view abstract10.1109/IWMTS.2018.8454694
  • Artificial Noise-Based Physical-Layer Security in Interference Alignment Multipair Two-Way Relaying Networks
    Tubail, D. and El-Absi, M. and Ikki, S.S. and Mesbah, W. and Kaiser, T.
    IEEE Access 6 (2018)
    This paper introduces two novel physical-layer security algorithms for interference alignment (IA)-based multipair communication systems with a single half-duplex relay and a single eavesdropper. According to these proposed physical-layer security algorithms, users mix their information signals with jamming signals, and broadcast them at the multiple access phase, while the relay forwards the mixed signals at the broadcast phase. Moreover, the relay and users' precoding and decoding matrices are designed in a way which enables the legitimate receivers to eliminate the jamming signals while the hidden eavesdropper is unable to eliminate these jamming streams. In this context, the proposed algorithms are designed to transmit the information streams with minimum power, preserving the user received signal to noise ratio above a pre-determined threshold and utilizing the remaining power for the jamming signals. Therefore, the user and relay power budgets allocation is formulated as a joint optimization problem that can be solved using an iterative optimization algorithm and semi-definite programming. In such fashion, four transmission models are proposed to manage the artificial noise transmission among the different users to achieve a tradeoff between the users sum-rate and secrecy rate. Extensive simulation results are provided to show the efficiency of the proposed algorithms and the transmission models in achieving the transmission security for IA-based multiuser relaying networks. © 2013 IEEE.
    view abstract10.1109/ACCESS.2018.2817264
  • Chipless tags infrastructure based localization in indoor environments
    El-Absi, M. and Abuelhaija, A. and Abbas, A.A.-H. and Zheng, F. and Solbach, K. and Kaiser, T.
    GeMiC 2018 - 2018 German Microwave Conference 2018-January (2018)
    In this work, we study dielectric resonator (DR) tag based localization using time difference of arrival (TDOA) method in indoor environments. DRs, which act as chipless tags, are used as reference nodes in order to localize an object equipped with a reader. The ringing behavior of the DR tags is utilized as the fingerprint of the tags, which is used to estimate TDOA using the cross-correlation algorithm. Simulations and measurements are performed to examine the performance of the proposed DR tags and the localization algorithm. © 2018 IMA.
    view abstract10.23919/GEMIC.2018.8335081
  • Distance and Tag Aware Localization in Indoor Terahertz Systems
    El-Absi, M. and Abbas, A.A.-H. and Abuelhaija, A. and Solbach, K. and Kaiser, T.
    2018 1st International Workshop on Mobile Terahertz Systems, IWMTS 2018 (2018)
    The accuracy of radio frequency identification (RFID) based time-of-flight ranging is considerably affected by the wireless channel within an indoor radio environment, where the bandwidth is considered the major limited factor for localization accuracy. Terahertz (THz) band offers bandwidth orders of magnitude greater than the lower-frequency communications; however, this band has different prorogation mechanisms influencing a wireless transmission compared to the lower frequency bands. The bandwidth of transmission at THz band is highly distance-dependent. Furthermore, since the wireless channel of RFID systems is a two-way pinhole channel, the design of the tag plays a key-role in capturing the usable bandwidth in THz bands. This paper studies RFID based localization at THz band in indoor environments. We analyze the impact of distance and tag design on the RFID link budget. We also characterize the tag and distance dependent spectral windows that are feasible for RFID based localization. The localization requirements for RFID based localization are also presented in order to achieve high accuracy localization. © 2018 IEEE.
    view abstract10.1109/IWMTS.2018.8454696
  • High-Accuracy Indoor Localization Based on Chipless RFID Systems at THz Band
    El-Absi, M. and Alhaj Abbas, A. and Abuelhaija, A. and Zheng, F. and Solbach, K. and Kaiser, T.
    IEEE Access 6 (2018)
    Highly accurate indoor localization based on significantly low complex infrastructure has recently gained great interest for a variety of innovative location-based applications. In this regards, the chipless radio frequency identification (RFID) system is presented to be the low-cost solution, while time-based ranging using the ultrawide-band spectrum is promising to offer precise ranging capability. However, the current wide-band systems suffer from the spectrum and power limitations, which restrict the function of chipless RFID-based localization systems. Therefore, we propose terahertz (THz)-based chipless RFID localization system that enables a smart object localizing itself using the infrastructure composed from reference chipless tags. In more details, THz band offers huge bandwidth providing superior-resolution localization and large coding capacity. Moreover, we utilize the combination between dielectric resonator (DR) and lens to be designed as a frequency-coded chipless tag, where this combination increases the radar cross section of the chipless tags and, hence, extends their coverage zone. This cost-efficient design of the tag enables the dense deployment of low-cost infrastructure acting as reference anchors. Furthermore, we investigate the link budget of the proposed system in order to characterize the tag and distance-dependent spectral windows that are feasible for RFID-based localization. Afterward, the time-domain backscattered signal from a DR-Lens tag is analyzed in order to perform ranging and to calculate the relative distances between the DR-Lens tags and the reader leading to determining the reader position. Measurements are performed to prove the concept of the DR-Lens tag, while the numerical simulation is conducted to evaluate the proposed localization system. Simulation results show that the proposed system can reach superior accuracy of millimeter-levels. © 2013 IEEE.
    view abstract10.1109/ACCESS.2018.2871960
  • Long reading range for the frequency coded Chipless RFID system based on reflectarray antennas
    Khaliel, M. and El-Awamry, A. and Fawky, A. and Kaiser, T.
    International Journal of Microwave and Wireless Technologies 10 (2018)
    This work proposes the utilization of a high gain and pencil beam reflectarray (RA) antenna at the reader of the frequency coded (FC) chipless radio-frequency identification (RFID) system to minimize the environmental reflections and increase the reading range. Moreover, the reader antenna should operate over ultra wideband (UWB) range of frequencies to accommodate multiple bits. However, the conventional antenna arrays cannot operate over UWB range of frequencies with high gain and pencil beam characteristics. Therefore, a novel UWB RA antenna dedicated to the chipless RFID reader is developed. The developed RA antenna operates over UWB range of frequencies from 4 to 6 GHz to fulfill the requirements of the FC chipless RFID system. Therefore, the antenna is successfully integrated with the FC chipless RFID tags, and a reading range of 1 m is achieved. Copyright © Cambridge University Press and the European Microwave Association 2018.
    view abstract10.1017/S1759078718000442
  • Massive MIMO Antenna Selection: Switching Architectures, Capacity Bounds, and Optimal Antenna Selection Algorithms
    Gao, Y. and Vinck, H. and Kaiser, T.
    IEEE Transactions on Signal Processing 66 (2018)
    Antenna selection is a multiple-input multiple-output (MIMO) technology, which uses radio frequency (RF) switches to select a good subset of antennas. Antenna selection can alleviate the requirement on the number of RF transceivers, thus being attractive for massive MIMO systems. In massive MIMO antenna selection systems, RF switching architectures need to be carefully considered. In this paper, we examine two switching architectures, i.e., full-array and sub-array. By assuming independent and identically distributed Rayleigh flat fading channels, we use asymptotic theory on order statistics to derive the asymptotic upper capacity bounds of massive MIMO channels with antenna selection for the both switching architectures in the large-scale limit. We also use the derived bounds to further derive the upper bounds of the ergodic achievable spectral efficiency considering the channel state information (CSI) acquisition. It is also showed that the ergodic capacity of sub-array antenna selection system scales no faster than double logarithmic rate. In addition, optimal antenna selection algorithms based on branch-and-bound are proposed for both switching architectures. Our results show that the derived asymptotic bounds are effective and also apply to the finite-dimensional MIMO. The CSI acquisition is one of the main limits for the massive MIMO antenna selection systems in the time-variant channels. The proposed optimal antenna selection algorithms are much faster than the exhaustive-search-based antenna selection, e.g., 1000 × speedup observed in the large-scale system. Interestingly, the full-array and sub-array systems have very close performance, which is validated by their exact capacities and their close upper bounds on capacity. © 1991-2012 IEEE.
    view abstract10.1109/TSP.2017.2786220
  • Probability of coverage based analysis of distributed antenna system and its implementation on LTE based real-time-testbed
    Peethala, D. and Zarifeh, N. and Kaiser, T.
    International Congress on Ultra Modern Telecommunications and Control Systems and Workshops 2017-November (2018)
    Distributed Antenna Systems (DASs) provide solutions to the future wireless challenges targeted for 5G systems using distributed remote radio heads (RRHs). In the case of a multi-user DAS, the sum rate can be increased by pairing the UEs with specific RRHs, thereby facilitating independent transmissions from different RRHs. In this work, probability of coverage metric is derived and used for the analysis of different DAS scenarios using selection transmission (ST) based pairing. This work also describes PHY level modelling of processing blocks, implementation details, hardware and procedures for DAS based on 3GPP LTE. The implementation details of realtime LTE based DAS testbed besides the relevant LTE procedures for the deployment of DAS are presented. Verification of the LTE based DAS testbed is achieved using the vector signal analyzer (VSA) software running on Keysight's mixed signal analyzer (MXA) and commercial LTE UEs. The results of our analysis based on probability of coverage metric in different DAS scenarios, i.e., with varied number of remote radio heads (RRHs) and targeted SINR at different UE positions are presented. © 2017 IEEE.
    view abstract10.1109/ICUMT.2017.8255196
  • Secure interference alignment based multiuser relay system using artificial noise
    Tubail, D. and El-Absi, M. and Ikki, S. and Mesbah, W. and Kaiser, T.
    2017 IEEE Global Communications Conference, GLOBECOM 2017 - Proceedings 2018-January (2018)
    This paper proposes a novel physical layer security algorithm in interference alignment (IA) based multiuser communication system with a single amplify-And-forward (AF) relay in the coexistence of an eavesdropper that tries to hide its existence. Thus, the relay and the users cannot estimate the eavesdroppers channel state information (CSI). In the proposed algorithm, the users broadcasts artificial noise in the null of the relay at the multiple access (MAC) phase, and the relay jams the eavesdropper by broadcasting the artificial noise in the null of users at the broadcast (BC) phase. Therefore, the proposed algorithm is formulated as a joint optimization problem consisting of two semidefinite programming (SDP) problems aiming at maximizing the power of the artificial noise and preserving the quality-of-services (QoS) of the users. An iterative optimization algorithm is proposed to solve the joint problem. Extensive simulation results are provided to show the effectiveness of the proposed algorithm for IA based relaying networks. © 2017 IEEE.
    view abstract10.1109/GLOCOM.2017.8254184
  • Self-interference mitigation in full-duplex base-station using dual polarized reflect-array
    Zarifeh, N. and Alissa, M. and Khaliel, M. and Kaiser, T.
    GeMiC 2018 - 2018 German Microwave Conference 2018-January (2018)
    This paper proposes the use of reflect-array to mitigate self-interference in the propagation domain aiming to achieve a full-duplex mobile system. An ultra-wideband reflect-array is designed to enable full-duplex in an indoor/outdoor LTE base-station with half-duplex users. The antenna design is customized to meet the full-duplex requirements by generating two cross-polarized beams using two separate feeders to achieve high isolation between the downlink and uplink signals. The paper also analyzes the components of self-interference in the direct and back-scattered paths, and the amount of isolation that can be achieved in a wideband system. Both reflect-array and full-duplex technologies are strong candidates to be used in 5G. © 2018 IMA.
    view abstract10.23919/GEMIC.2018.8335059
  • A distributed interference alignment algorithm using min-maxing strategy
    El-Absi, M. and El-Hadidy, M. and Kaiser, T.
    Transactions on Emerging Telecommunications Technologies 28 (2017)
    Interference alignment is a joint-transmission strategy that significantly increases the sum rate of interference channels at high signal-to-noise ratios (SNRs). The recent iterative interference alignment approaches are incapable of guaranteeing the best sum-rate performance with the increase of the SNR amongst different K-user interference channels, especially at high SNR regime. In this paper, a new interference alignment algorithm is developed to improve the sum-rate performance of K-user multi-input multi-output (MIMO) and multi-carrier interference channels by minimising the interference leakage and maximising the desired power concurrently, which is called by min-maxing strategy. For a K-user MIMO interference channel, we design transmit precoding matrices and receive decoding matrices through an efficient iterative algorithm based on min-maxing strategy in a distributed way, in which each receiver maximises the desired signal power, whereas it preserves the minimum leakage interference as a constraint. This optimisation problem is reformulated and relaxed into a standard semidefinite programming form. The convergence of the proposed algorithm is proved as well. Furthermore, a simplified min-maxing algorithm is proposed for rank-deficient interference channels to achieve the targeted performance with less complexity. The numerical simulations show that the proposed algorithm proffers significant sum-rate improvement in K-user MIMO interference channels compared with the existing algorithms at high SNR regime. Moreover, the simplified algorithm matches the optimal performance in the systems of rank-deficient channels. Finally, the developed min-maxing algorithm has been extended to K-user multi-carrier interference channels, which outperform the previous approaches in terms of sum rate in several scenarios. Copyright © 2014 John Wiley & Sons, Ltd. Copyright © 2014 John Wiley & Sons, Ltd.
    view abstract10.1002/ett.2897
  • A novel adaptive spectrum scanning technique for reducing the identification time of the UWB chipless RFID system
    El-Awamry, A. and Fawky, A. and Khaliel, M. and Kaiser, T.
    Proceedings of the 2017 IEEE 14th International Conference on Networking, Sensing and Control, ICNSC 2017 (2017)
    The main objective of this contribution is to introduce a novel technique for reducing the time taken from the reader to identify the Frequency Coded (FC) chipless RFID tags existed in the reader's interrogation region, system latency. The frequency scanning methodology, number of averaging for clutter removal and hop duration are the three main parameters that significantly affect the overall system latency. Consequently, the Adaptive Frequency Hopping (AFH) methodology is proposed and proofed to be efficient for the chipless RFID systems from the latency and accuracy perspectives. Likewise, the performance of the designed AFH technique is compared with the classical Fixed Frequency Hopping (FFH) methodology with a fine frequency step to validate the accuracy of the proposed technique. A real-world testbed is designed including a Software Defined Radio (SDR) platform by which the proposed adaptive algorithm and classical FFH methodology are implemented. All the measurements are performed in an indoor realized scenario, including the environmental effects. The experiments show that the proposed AFH algorithm significantly reduce the system latency by 58%. © 2017 IEEE.
    view abstract10.1109/ICNSC.2017.8000118
  • A novel beamforming algorithm for massive MIMO chipless RFID systems
    Abouzeid, M.S. and Zheng, F. and Gutiérrez, J. and Kaiser, T. and Kraemer, R.
    Wireless Telecommunications Symposium (2017)
    This paper discusses the idea of merging massive Multiple Input Multiple Output (mMIMO) technology into backscatter radio communication systems. Specifically, we consider a passive - battery-less - Radio Frequency IDentification (RFID) system. The paper provides a mathematical framework for channel modelling of mMIMO-RFID system including the effect of large scale fading on the communication process. Furthermore, a novel beamforming scheme will be proposed which enhances the overall mMIMO-RFID system detection capability in terms of bit error rate over different interrogator ranges. The proposed idea would shift the complexity and cost to the reader side while simplifying the tag. The overall mMIMO-RFID system performance is investigated considering the case of multiple tags; each of them is equipped with a single antenna, in the interrogation zone of mMIMO based reader. © 2017 IEEE.
    view abstract10.1109/WTS.2017.7943545
  • A novel FDD massive MIMO system based on downlink spatial channel estimation without CSIT
    Esswie, A.A. and El-Absi, M. and Dobre, O.A. and Ikki, S. and Kaiser, T.
    IEEE International Conference on Communications (2017)
    Channel state information (CSI) acquisition is a crucial issue in downlink FDD-based massive multi-input multioutput (MIMO) networks, where the channel reciprocity is not applicable. Thus, users are expected to feedback the bestmatch quantized channels to serving transmitters. Hence, an extensively large size of the feedback overhead is needed, which is linearly scaled at each user with the number of transmit antennas at the base-station (BS). In turn, the uplink (UL) channel capacity may be consumed and the overall performance becomes fundamentally limited by the downlink (DL) channel quantization precision. An alternative CSI acquisition scheme is critically needed. In this paper, we propose a novel FDD massive MIMO system based on a spatial DL channel estimation scheme; it relies on the statistical spatial correlation of the UL and DL channel clusters, given an arbitrary frequency band gap between the UL and DL channels. A transformation matrix is constructed to precode the observed UL channel on the estimated dominant DL angles of departure. The proposed scheme significantly outperforms the recent state-of-the-art techniques, without the cost of user feedback overhead bits and prior knowledge of the channel statistics. © 2017 IEEE.
    view abstract10.1109/ICC.2017.7997169
  • A novel multi-tag identification technique for frequency coded chipless RFID systems based on look-up-table approach
    El-Awamry, A. and Khaliel, M. and Fawky, A. and Kaiser, T.
    2017 11th European Conference on Antennas and Propagation, EUCAP 2017 (2017)
    The main objective of this contribution is to introduce a novel multi-tag anti-collision protocol based on Look-Up-Table (LUT) scheme. The proposed protocol includes an enhancement for the spectrum utilization and coding capacity. This is accomplished by transferring the tag-ID to be stored in a table in the main memory of the reader (look-up-table). Moreover, the unique signature of each tag represents the address of the tag's ID. The proposed protocol is modeled and simulated for identifying 10-chipless tags in order to set the regulations of the tag and reader design. Moreover, a novel real-world testbed for the multi-tag UWB chipless RFID system based on a software defined radio is introduced. In this testbed, all the signaling schemes related to the transmitted signal, detection techniques, empty room calibration for the clutter removal process and identification protocol are applied. © 2017 Euraap.
    view abstract10.23919/EuCAP.2017.7928652
  • Adaptive spectrum scanning techniques for reducing the identification time of the frequency coded chipless RFID system
    El-Awamry, A. and Khaliel, M. and Fawky, A. and Kaiser, T.
    Transactions on Emerging Telecommunications Technologies (2017)
    The main objective of this contribution is to introduce novel techniques for reducing the time taken from the reader to identify the frequency coded chipless radio frequency identification tags existed in the reader's interrogation region, system latency. The frequency scanning methodology, number of averaging for clutter removal, and hop duration are the 3 main parameters that significantly affect the overall system latency. Consequently, the adaptive frequency hopping (AFH) and adaptive sliding window (ASW) methodologies are proposed and proofed to be efficient for the chipless radio frequency identification systems from the latency and accuracy perspectives. Likewise, the performance of the designed AFH and ASW techniques are compared with the classical fixed frequency hopping methodology with a fine frequency step to validate the accuracy of the proposed methods. Moreover, 4 different coded frequency coded chipless tags are manufactured and used in the measurements. A real-world testbed is designed including a software-defined radio platform by which the proposed adaptive algorithms and traditional fixed frequency hopping methodology are implemented. All the measurements are performed in an indoor realized scenario, including the environmental effects. The experiments show that the proposed AFH combined with ASW algorithms significantly reduce the system latency by 58%. © 2017 John Wiley & Sons, Ltd.
    view abstract10.1002/ett.3173
  • Cyclic prefix-based noise estimation with DVB-T input for spectrum sensing in cognitive radio
    Farahiyah, D. and Nguyen, T.T. and Kaiser, T.
    Proceedings - 2016 3rd International Conference on Information Technology, Computer, and Electrical Engineering, ICITACEE 2016 (2017)
    The existing blind noise estimation called cyclic prefix based noise estimation without knowledge of a priori signal is simulated along with input of DVB-T and the multipath channel ITU-T pedestrian model A. The simulation is done by means to know NMSE and noise uncertainty over time observation with varied SNR. The NMSE shows a very good result and close to the result of the previous research. The corresponding noise uncertainty is simulated in order to observe the performance of detection of spectrum sensing. It has the result that such limitation of detection called SNR wall will not occur. Based on the research, the estimator is expected to be applied along with spectrum sensing in cognitive radio network. © 2016 IEEE.
    view abstract10.1109/ICITACEE.2016.7892485
  • Efïicient and low-complexity space time code for massive MIMO RFID systems
    Abouzeid, M.S. and Lopacinski, L. and Grass, E. and Kaiser, T. and Kraemer, R.
    Iberian Conference on Information Systems and Technologies, CISTI (2017)
    In this paper, a Space-Time Block Code (STBC) based on the Golden number, Golden code is proposed for a massive MIMO-RFID systems. Based on channel modelling for massive MIMO-RFID system, the proposed space-time code is applied to the tag side. Simulation results show that the proposed code for massive MIMO-RFID systems outperforms Alamouti code while simplifying the receiver's complexity. The Bit Error Rate (BER) performance of the proposed technique demonstrates that high diversity gain for the tag is achieved leading to a highly reliable and more robust RFID range. Furthermore, the link capacity between the tagged item and the reader can be increased. The proposed RFID technique provides superior performance against the state-of-the-art RFID techniques. © 2017 AISTI.
    view abstract10.23919/CISTI.2017.7976046
  • Frequency coded chipless RFID tag localization using multiple antennas
    Fawky, A. and Khaliel, M. and El-Awamry, A. and Kaiser, T.
    2017 11th European Conference on Antennas and Propagation, EUCAP 2017 (2017)
    In this paper a frequency coded chipless RFID localization algorithm is proposed. Unlike other techniques, one reader with multiple antennas is used to interrogate, identify and localize the tag. The Received Signal Strength (RSS) technique is used to detect the range of the tag, while Matrix Pencil Method (MPM) is used to calculate the Angle of Arrival (AoA). To validate both techniques a ray tracing tool was used to calculate the system link budget using tag RCS patterns exported from CST-MWS. The ray-tracing tool also calculated the interrogation zone considering all environmental factors. Moreover, a real-time testbed was created using fabricated chipless tags. The testbed was implemented using both measurement tools and Software Defined Radio (SDR). Both simulation and measurements show a great potential for the chipless tag to be used in localization and tracking application. © 2017 Euraap.
    view abstract10.23919/EuCAP.2017.7928650
  • Long reading range chipless RFID system based on reflectarray antennas
    Khaliel, M. and El-Awamry, A. and Fawky, A. and Kaiser, T.
    2017 11th European Conference on Antennas and Propagation, EUCAP 2017 (2017)
    This work proposes the utilization of the Reflect Array (RA) antenna in the reader of the Frequency Coded (FC) chipless RFID systems aiming at increasing the reading range, minimizing the environmental reflections and acquiring a lot of novel capabilities that can not be provided by the conventional antenna systems. The FC chipless RFID system requires an UWB range of frequencies to accommodate multiple bits. However, this UWB operation can not be provided by the conventional antenna arrays. Even though, the RA antenna is also suffering from bandwidth limitation, an UWB RA antenna dedicated to the chipless RFID readers is accomplished. The presented RA antenna operates over UWB range of frequencies from 4 to 6 GHz fulfilling the requirements of the FC chipless RFID systems. Furthermore, the RA antenna beam is 4 times narrower than the feeder beam and thus 6 dB higher in gain with -10 dB SLL. Therefore, this developed UWB RA antenna is successfully integrated with the FC chipless RFID tags and a reading range of 1 m is attained. To the best of the author knowledge, this is the highest reading range achieved in the FC chipless RFID systems, considering real-world indoor environment and Universal Software Defined Radio Platform (USRP). © 2017 Euraap.
    view abstract10.23919/EuCAP.2017.7928651
  • Noise power estimation with DVB-T input for spectrum sensing in cognitive radio network
    Farahiyah, D. and Nguyen, T.T. and Kaiser, T.
    Proceedings - ICWT 2016: 2nd International Conference on Wireless and Telematics 2016 (2017)
    Noise estimation is an essential issue on the wireless communication system. Cognitive radio network uses the spectrum sensing to detect opportunistically the unoccupied spectrum holes and the licensed user. Several methods of spectrum sensing need the knowledge of noise power in advance. In this paper, we proposed noise power estimation that suitable for the condition of cognitive radio. The estimator does not need any a priori information about the signal. The simulation is done with the input of Digital Video Broadcasting - Terrestrial (DVBT) signal which passes through AWGN channel in two condition, ideal and real condition. The performances are given in normalized mean-square-error (NMSE) and noise uncertainty. It is shown a low value of NMSE. The estimator with DVB-T input also works well at low SNR and avoid SNR wall phenomenon. © 2016 IEEE.
    view abstract10.1109/ICWT.2016.7870859
  • Novel notch detection techniques for Frequency Coded chipless RFID
    Fawky, A. and El-Awamry, A. and Khaliel, M. and Kaiser, T.
    Proceedings of the 2017 IEEE 14th International Conference on Networking, Sensing and Control, ICNSC 2017 (2017)
    Notch identification is a major challenge in Frequency Coded (FC) chipless RFID. The main objective of this contribution is to introduce three signal processing techniques for notch identification and detection. The three algorithms are Matched Filter(MF), Window Based- Singular Value Decomposition (WB-SVD) and Dynamic Time Warping (DTW). The algorithms should be able to detect both notch bandwidth and shift in a real environment, where the notch is likely to be highly distorted. In this work both a simulation model and a testbed is performed to analyze and verify each algorithm using fabricated tags. © 2017 IEEE.
    view abstract10.1109/ICNSC.2017.8000116
  • Photonic-Assisted mm-Wave and THz Wireless Transmission towards 100 Gbit/s Data Rate
    Hermelo, M.F. and Chuenchom, R. and Rymanov, V. and Kaiser, T. and Sheikh, F. and Czylwik, A. and Stöhr, A.
    Frequenz 71 (2017)
    This paper presents photonic-assisted 60 GHz mm-wave and 325 GHz system approaches that enable the transmission of spectral-efficient and high data rate signals over fiber and over air. First, we focus on generic channel characteristics within the mm-wave 60 GHz band and at the terahertz (THz) band around 325 GHz. Next, for generating the high data rate baseband signals, we present a technical solution for constructing an extreme bandwidth arbitrary waveform generator (AWG). We then report the development of a novel coherent photonic mixer (CPX) module for direct optic-to-RF conversion of extreme wideband optical signals, with a >5 dB higher conversion gain compared to conventional photodiodes. Finally, we experimentally demonstrate record spectral efficient wireless transmission for both bands. The achieved spectral efficiencies reach 10 bit/s/Hz for the 60 GHz band and 6 bit/s/Hz for the 325 GHz band. The maximum data rate transmitted at THz frequencies in the 325 GHz band is 59 Gbit/s using a 64-QAM-OFDM modulation format and a 10 GHz wide data signal. © 2017 Walter de Gruyter GmbH, Berlin/Boston.
    view abstract10.1515/freq-2017-0147
  • Printable, high coding capacity chipless RFID tags for low-cost item tagging
    Khaliel, M. and Fawky, A. and El-Awamry, A. and Mahmoud, A.-E. and Kaiser, T.
    Proceedings of the 2017 IEEE 14th International Conference on Networking, Sensing and Control, ICNSC 2017 (2017)
    This work presents two completely printable chipless RFID tags for low-cost item labeling. The first developed tag is based on circular ring resonators where each resonator codifies a tag coding notch position. Therefore, the tag structure is scalable, printable and compact size. Moreover, a novel encoding methodology is employed to preserve the notch width and position while coding. The second developed tag is a depolarizing tag, where the polarization isolation between the reader interrogation signal and the tag response is utilized to minimize the environmental clutter reflections. Furthermore, the tag is scalable, printable and compact size within the credit card format. The proposed tags and their associated physical encoding schemes are validated using EM simulations and real-world testbed measurements. © 2017 IEEE.
    view abstract10.1109/ICNSC.2017.8000117
  • Rotman Lens Based Hybrid Analog-Digital Beamforming in Massive MIMO Systems: Array Architectures, Beam Selection Algorithms and Experiments
    Gao, Y. and Khaliel, M. and zheng, F. and Kaiser, T.
    IEEE Transactions on Vehicular Technology (2017)
    Hybrid analog-digital beamforming is a well-known cost-efficient signal processing method for massive MIMO systems. In this paper, we propose a hybrid beamforming massive MIMO system based on Rotman lens analog beamforming with beam selection and digital beamforming. Rotman lens is a lowcost true-time-delay analog beamforming network supporting wide bandwidth signals, which is thus more attractive than the analog beamforming networks based on conventional high-cost phase shifters. To study our system based on Rotman lens, we first examine two potential array architectures, i.e., fullarray and sub-array architectures, concerning the RF design feasibility, insertion loss and system scalability. Since the beam selection is required in our system, we propose two beam selection algorithms, i.e., greedy search based method and branch and bound based method, aiming to optimize the hybrid beamforming system in terms of error-rate performance for both the fullarray and sub-array architectures. To validate our system in practice, the proposed system is also investigated and verified experimentally. In particular, we design and fabricate a sample of Rotman lens operating in the 5-GHz band, whose measured results agrees well with the computer simulation results. The measurement results are incorporated into the Monte-Carlo simulation with the proposed beam selection algorithms to study the error-rate performance. Our simulation results show that the hybrid beamforming system using the low-cost Rotman lens has performance comparable to that of the system using the highcost phase shifters, and exhibits wideband capability and superior performance over the small-scale MIMO system under the same number of RF transceivers. IEEE
    view abstract10.1109/TVT.2017.2714693
  • Spatial Channel Estimation-Based FDD-MIMO Interference Alignment Systems
    Esswie, A.A. and El-Absi, M. and Dobre, O.A. and Ikki, S. and Kaiser, T.
    IEEE Wireless Communications Letters 6 (2017)
    The practical feasibility of interference alignment (IA) is a major challenge in real-world implementation. The majority of the research contributions assume ideal channel reciprocity, which may be valid in time division duplex systems. In frequency division duplex (FDD) systems, large codebooks are utilized for channel quantization, and consume the feedback channel capacity. In this letter, a spatial channel estimation method is proposed for FDD-MIMO IA systems. The method utilizes the path correlation between the forward and reverse channels, where channels are on different frequency bands. A transformation matrix is employed to estimate the angles of departure of the forward channel. The proposed method shows a significant improvement of the sum rate without the need of feedback overhead bits. © 2017 IEEE.
    view abstract10.1109/LWC.2017.2668408
  • Wideband hybrid analog-digital beamforming massive MIMO systems based on Rotman lens
    Gao, Y. and Khaliel, M. and Kaiser, T.
    2016 IEEE International Conference on Communication Systems, ICCS 2016 (2017)
    Hybrid analog-digital beamforming is a well-known cost-efficient signal processing method for massive MIMO systems. In this paper, we propose a hybrid beamforming massive MIMO system based on Rotman lens analog beamforming with beam selection and digital beamforming. Rotman lens is a true-time delay analog beamforming network supporting wide bandwidth signals, which is thus more attractive than the analog beamforming networks based on traditional narrow-band phase shifters. Hence, the performance of the proposed system is investigated and verified experimentally. In particular, we design and fabricate a sample of Rotman lens operating in 5 GHz band, whose measured performance agrees well with the computer simulation. To optimize our hybrid beamforming system in terms of error-rate performance, a low-complexity greedy beam selection algorithm is proposed. Our measurement and simulation results on the error-rate performance show that the hybrid beamforming system based on Rotman lens has a wide bandwidth and exhibits superior performance over the small-scale MIMO system under the same number of RF transceivers. © 2016 IEEE.
    view abstract10.1109/ICCS.2016.7833647
  • A Robust Opportunistic Relaying Strategy for Co-Operative Wireless Communications
    Jiang, W. and Kaiser, T. and Vinck, A.J.H.
    IEEE Transactions on Wireless Communications 15 (2016)
    Using outdated channel state information (CSI) in an opportunistic relaying system (ORS) leads to wrong selection of the best relay, which substantially deteriorates its performance. In this paper, therefore, we propose a robust cooperative scheme coined opportunistic space-time coding (OSTC) to deal with the outdated CSI. A predefined number (i.e., N) of relays, instead of a single relay in ORS, are opportunistically selected from K cooperating relays. At the selected relays, N-dimensional orthogonal space-time coding is employed to encode the regenerated signals in a distributed manner. Then, N branches coded signals are simultaneously transmitted from the relays to the destination, followed by a simple maximum-likelihood decoding at the receiver. To evaluate its performance, the closed-form expressions of outage probability and ergodic capacity are derived, together with an asymptotic analysis that clarifies the achievable diversity. Analytical and numerical results reveal that a full diversity of K is reaped by the proposed scheme when the knowledge of CSI is perfect. In the presence of outdated CSI, where the diversity of ORS degrades to one, the diversity of N can be kept. Moreover, OSTC's capacity is remarkably higher than that of the existing schemes based on orthogonal transmission. From the perspective of multiplexing-diversity tradeoff, the proposed scheme is the best cooperative solution until now. © 2015 IEEE.
    view abstract10.1109/TWC.2015.2506574
  • Adaptive Aloha anti-collision algorithms for RFID systems
    Zheng, F. and Kaiser, T.
    Eurasip Journal on Embedded Systems 2016 (2016)
    In this paper, we propose two adaptive frame size Aloha algorithms, namely adaptive frame size Aloha 1 (AFSA1) and adaptive frame size Aloha 2 (AFSA2), for solving radio frequency identification (RFID) multiple-tag anti-collision problem. In AFSA1 and AFSA2, the frame size in the next frame is adaptively changed according to the real-time collision rate measured in the current frame. It is shown that AFSA1 and AFSA2 can significantly improve the transmission efficiency of RFID systems compared to the static Aloha, and AFSA2 produces transmission efficiency similar to that of the electronic product code (EPC) Q-selection algorithm (Variant II), while the mean identification delay of AFSA2 is much smaller than that of EPC Q-selection algorithm (Variant II). It is also shown that the transmission efficiency of AFSA2 and EPC Variant II is very close to its upper bound which is obtained by assuming that the reader knows the number of unidentified tags. It is worth noting that when the threshold of the collision rate is chosen to be 0.5 or 0.6, AFSA2 can maintain the transmission efficiency well above 0.65 for the case of a typical EPC code length of 96 bits and for the investigated range of tag population, i.e., from 2 to 1000, while keeping the mean identification delay below ten transmit contentions. Very light computational burden at the reader is needed: the reader needs only to measure the collision rate in the current frame and then to double or halve the frame size accordingly. No additional computational burden is required at the tag side. © 2016, Zheng and Kaiser.
    view abstract10.1186/s13639-016-0029-7
  • Antenna Selection for Reliable MIMO-OFDM Interference Alignment Systems: Measurement-Based Evaluation
    El-Absi, M. and Galih, S. and Hoffmann, M. and El-Hadidy, M. and Kaiser, T.
    IEEE Transactions on Vehicular Technology 65 (2016)
    Interference alignment (IA) is a promising transmission technology enabling, essentially, the maximum achievable degrees of freedom (DOF) in K-user multiple-input-multiple-output (MIMO) interference channels. The ideal DOF of IA systems have been obtained using independent MIMO channels, which is, usually rarely observed in reality, particularly in indoor environments. Therefore, the data sum rate and symbol error-rate of IA are dramatically degraded in real-world scenarios since the correlation between MIMO channels decreases the signal-To-noise ratio (SNR) of the received signal after alignment. For this reason, an acceptable sum rate of IA in real MIMO-orthogonal frequency-division multiplexing (MIMO-OFDM) interference channels was obtained in the literature by modifying the distance between network nodes and the separation between the antennas within each node to minimize the spatial correlation. In this paper, we propose to apply transmit antenna selection to MIMO-OFDM IA systems either through bulk or per-subcarrier selection, aiming at improving the sum-rate and/or error-rate performance under real-world channel circumstances, while keeping the minimum spatial antenna separation of 0.5 wavelengths within each node. Two selection criteria are considered: maximum sum rate (Max-SR) and minimum error rate (Min-ER). To avoid subcarrier imbalance across the antennas of each user, which is caused by per-subcarrier selection, a constrained per-subcarrier antenna selection is operated. Furthermore, a suboptimal antenna selection algorithm is proposed to reduce the computational complexity of the optimal algorithm. An experimental validation of MIMO-OFDM IA with antenna selection in an indoor wireless network scenario is presented. The experimental results are compared with deterministic channels that are synthesized using hybrid electromagnetic (EM) ray-Tracing models. Our performance evaluation shows that the practical feasibility of MIMO-OFDM IA systems is significantly increased by antenna selection in real-world scenarios. © 1967-2012 IEEE.
    view abstract10.1109/TVT.2015.2441133
  • Antenna selection in massive MIMO systems: Full-array selection or subarray selection?
    Gao, Y. and Kaiser, T.
    Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop 2016-September (2016)
    This paper presents a concept of subarray antenna selection in massive MIMO systems, i.e., the whole antenna array is segmented into subarrays and only one antenna is selected in each subarray. The subarray antenna selection can reduce the hardware complexity of the RF switching network, but at the cost of performance degradation due to the introduced selection constraint. We evaluate such performance degradation not only with the ideal independent and identically distributed (i.i.d.) but also with the realistic measured channels. To serve our evaluation, an antenna selection algorithm based on branch and bound method is presented, which aims to select an optimal channel submatrix with the largest minimum singular value. A qualitative analysis is also given to compare the performance between the full-array and subarray selection. Simulation results show that the massive MIMO subarray antenna selection has close performance to the full-array antenna selection, no matter with the i.i.d. channels or the realistic channels. The results in this paper imply that the with the concept of subarray antenna selection, antenna selection is still a practical and promising technology in the realistic massive MIMO systems. © 2016 IEEE.
    view abstract10.1109/SAM.2016.7569725
  • Experiments on multi-channel spectrum sensing with filter bank realization for cognitive LTE-A systems
    Nguyen, T.T. and Hoffmann, M. and Kreul, T. and Kaiser, T.
    International Conference on Advanced Technologies for Communications 2016-January (2016)
    Wideband spectrum sensing is an attractive topic in cognitive radio (CR). Filter-banks are a good approach for wideband sensing with different detection algorithms. A wideband sensing scheme with filter-bank realization was proposed as in [1] for long-term evolution advanced (LTE-A) signals. The scheme is able to detect and classify LTE-A signals in multi-channels in parallel. In this work, we validate the reliability of the scheme in realistic scenarios of mobile communications. Real wideband LTE signals are processed by the scheme with an integrated test-bed for LTE base-stations in emergency situations. The experimental results agree with previous works to approve the reliability of the spectrum sensing scheme. Besides, they lead a successful integration approach of the scheme into LTE base-stations. © 2015 IEEE.
    view abstract10.1109/ATC.2015.7388396
  • Massive MIMO exploitation to reduce HARQ delay in wireless communication system
    Zarifeh, N. and Kabbani, A. and El-Absi, M. and Kreul, T. and Kaiser, T.
    2016 IEEE Middle East Conference on Antennas and Propagation, MECAP 2016 (2016)
    As recommended by 5th generation Public-Private Partnership (5G-PPP) and Next Generation Mobile Networks (NGMN), one of the most important 5G requirements is to minimize the delay within the network for delay-sensitive services. Main objective of this work is to exploit massive MIMO technology to reduce Hybrid Automatic Repeat Query (HARQ) retransmission delay. Massive MIMO indoor environment is created by a 3D ray-tracing tool to simulate the received power, phase, delay, and angle of arrival of each ray in the channel. Two sizes of rectangular antenna array are used to evaluate the performance of beamforming in enhancing the bit error rate. This reflects directly on the mean and maximum numbers of packet retransmission. The angle between user-equipments is considered to evaluate the effect of inter-user interference on HARQ. This work opens the door to develop smarter resource allocation algorithms in 5G for delay-sensitive services based on the location and the angle of arrival of the users. © 2016 IEEE.
    view abstract10.1109/MECAP.2016.7790122
  • Performance analysis of a MIMO-RFID system in Nakagami-m fading channels
    Maichalernnukul, K. and Zheng, F. and Kaiser, T.
    Annales des Telecommunications/Annals of Telecommunications 71 (2016)
    We analyze the bit error rate (BER) performance of a multiple-input multiple-output (MIMO) radio-frequency-identification (RFID) system employing orthogonal space-time block codes when the forward and backward channels exhibit independent but not necessarily identically distributed Nakagami-m fading. A closed-form upper bound on the BER performance is derived, and the corresponding diversity order is quantified. Numerical results provide some insight into the impact of several different parameters on the system performance. © 2015, Institut Mines-Télécom and Springer-Verlag France.
    view abstract10.1007/s12243-015-0481-8
  • Real-world testbed for multi-tag UWB chipless RFID system based on a novel collision avoidance MAC protocol
    El-Hadidy, M. and El-Awamry, A. and Fawky, A. and Khaliel, M. and Kaiser, T.
    Transactions on Emerging Telecommunications Technologies 27 (2016)
    Chipless radio frequency identification (RFID) tags are dummy, memoryless, with limited number of bits, very low backscattered power, and short reading range. Therefore, the existing RFID standards and protocols designed for the chipped RFID systems are not applicable for the chipless systems. Main objective of this contribution is to introduce a novel real-world testbed for multi-tag ultra-wideband (UWB) chipless RFID system. In this testbed, a new Notch Position Modulation scheme is implemented as the first medium access control algorithm for handling the multi-tag identification scenario of the frequency signature based chipless RFID tags. This intelligent Notch Position Modulation algorithm reduces the sensing and identification time and accordingly the overall system latency. The proposed protocol enables fetching the frequency signatures of the chipless RFID tags through the whole UWB range effectively. Moreover, an advanced signaling scheme is designed for the RFID reader in order to make the best use of the Federal Communications Commission UWB regulations for increasing the maximum transmitted power and the corresponding reading range. The signaling scheme, real-time channel estimation, and clutter removal technique are implemented on the software defined radio platform in a heavily dense multipath indoor environment. Based on the medium access control protocol, the mitigation of the undesired environmental reflections as well as the interference between the chipless RFID tags is well demonstrated in the developed testbed. Copyright © 2016 John Wiley & Sons, Ltd.
    view abstract10.1002/ett.3124
  • Terahertz band: Channel modelling for short-range wireless communications in the spectral windows
    Sheikh, F. and Zarifeh, N. and Kaiser, T.
    IET Microwaves, Antennas and Propagation 10 (2016)
    The channel in the terahertz (THz) band is extremely frequency selective. This study demonstrates a ray-tracing method for modelling short-range propagation channels at THz band. The propagation response of sounding bandwidth and centre frequency on power delay profile (PDP) is investigated in five spectral windows with relatively low attenuations and higher available bandwidths which could possibly offer terabit-per-second links also. In this approach, a very detailed non-cubic three-dimensional model of an ultra-broadband indoor realistic office environment has been drawn up. Furthermore, the frequency-dependent standard electrical parameters for the common building materials were taken from the literature. The transmitter (Tx) and the receiver (Rx) are 10 m apart in line-of-sight scenario with exactly same height of 1.5 m above the floor. The simulations were performed using 25 dBi horn antennas at the transmitter and receiver sides, respectively, to combat high path loss. These frequency-dependent horn antennas were designed for the respective five spectral windows. Meanwhile, the corresponding channel impulse response of multipath components with spatial and temporal information such as angle of arrival, angle of departure and time of arrival has been captured to derive PDP models. Up to four reflections (i.e. fourth order) have been considered in the modelling process. © The Institution of Engineering and Technology.
    view abstract10.1049/iet-map.2016.0022
  • A differential space-time coded RFID system
    Maichalernnukul, K. and Zheng, F. and Kaiser, T.
    International Congress on Ultra Modern Telecommunications and Control Systems and Workshops 2015-January (2015)
    We propose a differential space-time coded (STC) radio-frequency-identification (RFID) system where the tag has two antennas and the reader has a single or multiple antennas. In this system, the M-ary phase-shift keying constellation is used, and encoding at the tag and decoding at the reader are simple. Simulation results show that the proposed STC RFID system can achieve a performance improvement over the corresponding non-STC RFID system. © 2014 IEEE.
    view abstract10.1109/ICUMT.2014.7002124
  • A multi-channel spectrum sensing scheme with filter bank realization for LTE signals
    Nguyen, T.T. and Cao, H. and Kreul, T. and Kaiser, T.
    Proceedings of the WoWMoM 2015: A World of Wireless Mobile and Multimedia Networks (2015)
    In cognitive ratio (CR), spectrum sensing is a crucial technique aiming at exploiting spectrum white spaces. This sensing task is more difficult for multiple channels in wide bands. In this paper, we investigate spectrum sensing tasks for long-term evolution (LTE) networks in large frequency-bands. We propose an effective spectrum sensing scheme to detect LTE signals and classify the cell-identities transmitted in multi-channels in parallel. To prove the concept and validate the performance of the proposed scheme, a secondary LTE transmission in TV bands is modeled in our simulations. At the perspective of realistic scenarios, the identified information could be utilized for some functions such as the co-ordination among secondary networks or initial-cell-search procedures between secondary user-equipments and their serving base-stations in the secondary LTE transmission. The simulation results show that the detection and classification performance of the proposed scheme is close tightly to that in the case of a single channel. The scheme works well in multi-path fading environment with carrier frequency offset (CFO) and is tolerant to noise uncertainty. © 2015 IEEE.
    view abstract10.1109/WoWMoM.2015.7158195
  • A novel co/cross-polarizing chipless RFID tags for high coding capacity and robust detection
    Khaliel, M. and El-Awamry, A. and Fawky, A. and El-Hadidy, M. and Kaiser, T.
    2015 Ieee International Symposium on Antennas and Propagation \& Usnc/ursi National Radio Science Meeting 2015-October (2015)
    The aim of this work is to introduce a novel tag design enhancing the coding efficiency for the Frequency Coded (FC) chipless RFID system. The proposed approach relies on exploiting the backscattered co/cross-polarized signals from a tag excited with a linear-polarized wave. Consequently, the tag signature is encoded into Notch/Peak (N/P) format in two orthogonal planes. Furthermore, the introduced tag design exhibits narrow resonance bandwidth ensuring best utilization of the operating frequency range and sufficient coding capacity with compact tag size. Hence, 80-bit coding capacity is reached employing physical amplitude On Off-N/P (OO-N/P) modulation and N/P-Position (N/P-P) modulation principles. The presence or absence of a resonator resembles the OO-N/P modulation while the shift in the frequency position imitates the (N/P-P) modulation. In addition, the depolarization property increases the probability of tag detection in a real-world heavily dense multi-path environment. An asymmetry crossed dipole structure is employed to facilitate coding in both divergent polarities separately. The manufactured tags are verified in indoor real-world environment to proof the robustness of the introduced tag design and encoding algorithm. In the full paper, various parameters such as reading range, tag miniaturization and angular stability will be investigated. © 2015 IEEE.
    view abstract10.1109/APS.2015.7304465
  • An enhanced spectrum sensing algorithm with maximum ratio combination of spectral correlation
    Nguyen, T.T. and Kreul, T. and Kaiser, T.
    2015 23rd European Signal Processing Conference, EUSIPCO 2015 (2015)
    In cognitive radio networks, the task of spectrum sensing is required to be reliable at low signal-to-noise ratios (SNRs). Spectral correlation is an effective approach to satisfy the requirement. The algorithms based on statistic spectral correlation profiles are a good method as shown in some previous works. In this paper, we propose an algorithm with maximum ratio combination for the profiles to enhance the method. We construct a formula of statistic test and describe an implementation for our algorithm in practice. Extensive simulations are carried out to verify the performance of algorithms. As a result, the proposed algorithm outperforms the existing algorithms with a neglectful cost of additional complexity. © 2015 EURASIP.
    view abstract10.1109/EUSIPCO.2015.7362579
  • Design an adaptive electronically beamsteering reflectarray antenna for RFID systems
    Hasan, K. and Khaliel, M. and El-Hadidy, M. and Kaiser, T.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 2015-October (2015)
    The main objective of this paper is to design an electronically scanning reflectarray antenna for the RFID system to precisely identify and locate the tags. The RA consists of a novel cell design utilizing a varactor diode to provide the phase shifts required to steer the beam in a certain direction. The cell used in the design is Split Slotted Dipole (SSD) that provide minimum re-radiation loss and sufficient phase range and phase slope. The achievable phase range is 300° over the frequency range from 4.8 GHz to 5.9 GHz. Finally, we achieved a steerable directive beam with a beamwidth of 16° from -65° to +65° with low Side Lobe Level (SLL) and a considerable high gain from 14 dB to 17 dB over the operating frequency range. © 2015 IEEE.
    view abstract10.1109/APS.2015.7305467
  • Energy-efficient resource allocation based on interference alignment in MIMO-OFDM cognitive radio networks
    El-Absi, M. and Ali, A. and El-Hadidy, M. and Kaiser, T.
    Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST 156 (2015)
    In this paper,we propose an energy-efficient interference alignment (IA) based resource management algorithm for multi-input multioutput (MIMO) orthogonal frequency division multiplexing (OFDM) cognitive radio (CR) systems. The proposed algorithm provides the secondary users (SUs) with the opportunity for underlay sharing of the primary system spectrum. The proposed algorithm ensures the quality-ofservice (QoS) of the primary system by guaranteeing the minimum transmission rate. The problem is formulated as a mixed-integer non-convex optimization problem, in which the objective is tomaximize the energy efficiency, and the constraints are the per-user power budget andQoS demand of the primary system.To tackle mixed-integer and non-convexity nature of the problem, we propose a sub-optimal energy-efficient algorithm through two successive steps. The first step schedules the subcarriers among the SUs based on IA while the second step iteratively allocates the power based on Dinkelbach’s scheme. Simulations reveal that the proposed algorithm achieves significant improvement in the energy efficiency compared to the traditional spectrum-efficient algorithm. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2015.
    view abstract10.1007/978-3-319-24540-9_44
  • Experiments on spectrum sensing algorithms of pilot-added OFDM signals with a cognitive LTE-A system
    Nguyen, T.T. and Kabbani, A. and Peethala, S. and Kreul, T. and Kaiser, T.
    2015 IEEE 20th International Workshop on Computer Aided Modelling and Design of Communication Links and Networks, CAMAD 2015 (2015)
    The reliability of spectrum sensing is a challenging issue in cognitive radio (CR) systems. In this paper, we validate the reliability of two spectrum sensing algorithms for pilot-added OFDM signals: time-domain symbol cross-correlation (TDSC) and periodical peaks of autocorrelation (PPA) with a real system in real environments. To validate, these two algorithms carry out detection function for real signals captured by a test-bed of cognitive Long Term Evolution Advanced (LTE-A) systems. Moreover, we use a transmission between a vector generator and a spectrum analyzer to cross-check with results by the test-bed. The experimental results agree with each other and with simulated results in previous works. Two algorithms work well in real-environments and are insensitive to noise-uncertainty. The results show that PPA algorithms outperform TDSC algorithms by 1 dB - 2.5 dB with the observation durations in experiments. Additionally, PPA algorithms are suitable for short observations. For example, PPA algorithms can work with a 5 ms duration of 8K mode Digital Video Broadcasting Terrestrial (DVB-T) signals, but TDSC algorithms cannot. The results also show the performance of TDSC and PPA algorithms by a test-bed of cognitive LTE-A systems. They give clues to apply suitable algorithms for different operations such as in-band and out-band sensing modes in cognitive cellular systems. © 2015 IEEE.
    view abstract10.1109/CAMAD.2015.7390529
  • Implementation aspects of a DSP-based LTE cognitive radio testbed
    Kabbani, A. and Ali, A.R. and Cao, H. and Güven, A.B. and Gao, Y. and Peethala, S. and Kaiser, T.
    Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST 156 (2015)
    One of the key issues of designing radio communication systems is to enhance the efficiency and flexibility of the available radio spectrum. In this context, reconfigurable implementation of the different system layers such as Media Access Control (MAC), Physical (PHY), and RF layers with optimal cross-layer design is driving nowadays research on designing reliable and robust mobile communication systems. This paper presents the software and hardware implementation aspects of a DSP-Based cognitive LTE testbed and addresses the design, the implementation and the realistic verification of the key components of the system. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2015.
    view abstract10.1007/978-3-319-24540-9_62
  • Interference Alignment with Frequency-Clustering for Efficient Resource Allocation in Cognitive Radio Networks
    El-Absi, M. and Shaat, M. and Bader, F. and Kaiser, T.
    IEEE Transactions on Wireless Communications 14 (2015)
    In this paper, we investigate the resource management problem in orthogonal frequency division multiplexing (OFDM) based multiple-input multiple-output (MIMO) cognitive radio (CR) systems. We propose performing resource allocation based on interference alignment (IA) in order to improve the spectral efficiency of CR systems without affecting the quality of service of the primary system. IA plays a role in the proposed algorithm to enable the secondary users (SUs) to cooperate and share the available spectrum, which leads to a considerable increase in the spectral efficiency of CR systems. However, IA based spectrum sharing is restricted to a certain number of SUs per subcarrier in order to satisfy the IA feasibility conditions. Accordingly, the resource allocation problem is formulated as a mixed-integer optimization problem, which is considered an NP-hard problem. To reduce the computational complexity of the problem, a two-phases efficient sub-optimal algorithm is proposed. In the first phase, frequency-clustering is performed in order to satisfy the IA feasibility conditions, where each subcarrier is assigned to a feasible number of SUs. Whenever possible, frequency-clustering stage considers the fairness among the SUs. In the second stage, the available power is allocated among the subcarriers and SUs without violating the constraints that limit the maximum interference induced to the primary system. Simulation results show that IA with frequency-clustering achieves a significant sum rate increase compared to CR systems with orthogonal multiple access transmission techniques. © 2015 IEEE.
    view abstract10.1109/TWC.2015.2464371
  • Low cost implementation for synchronization in Distributed Multi antenna using USRP/GNU-radio
    Galih, S. and Hoffmann, M. and Kaiser, T.
    2014 1st International Conference on Information Technology, Computer, and Electrical Engineering: Green Technology and Its Applications for a Better Future, ICITACEE 2014 - Proceedings (2015)
    Carrier Frequency Offset Synchronization is play a very important rule in the Distributed Multi antenna system, since the system has different individual clock instead of common clock as in the centralized multi Antenna system. One of the established synchronization methode for different transmitter devices is Costas Loop. Some implementation of the synchronization for distributed multi antenna is discussed in some research works. In this paper we propose the low cost implementation of synchronization in distributed multi antenna and more simplified measurement method of synchronization in distributed multi antenna. The measurement result showed that the syncronization can compensate 0.5 kHz frequency offset experienced by the transmitters in the Distributed Multi antenna system. © 2014 IEEE.
    view abstract10.1109/ICITACEE.2014.7065791
  • Novel adaptive sliding window algorithm reducing latency for multi-tag chipless RFID systems
    El-Awamry, A. and Khaliel, M. and Fawky, A. and El-Hadidy, M. and Kaiser, T.
    2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2015 - Proceedings (2015)
    The main contribution of this work is to introduce a novel technique for reducing the latency of multi-tag Frequency Coded (FC) chipless RFID systems, which is defined as the time required for the reader to identify the tagged objects within the same interrogation zone. The frequency scanning methodology, windowing and notch detection are the three main processing blocks that significantly affect the overall system latency. © 2015 IEEE.
    view abstract10.1109/USNC-URSI.2015.7303490
  • Novel notch modulation algorithm for enhancing the chipless RFID tags coding capacity
    El-Awamry, A. and Khaliel, M. and Fawky, A. and El-Hadidy, M. and Kaiser, T.
    2015 IEEE International Conference on RFID, RFID 2015 (2015)
    The main objective of this contribution is to introduce a novel technique for increasing the coding capacity of the Frequency Coded (FC) chipless RFID system. The proposed scheme encodes 4 bits per single resonator exploiting the notch bandwidth and its corresponding frequency position. Hence, 72-bits could be achieved from 2 to 5 GHz preserving the operating frequency bandwidth. Furthermore, a Smart Singular Value Decomposition (SSVD) technique is utilized to estimate the notch bandwidth and ensure low probability of error. Consequently, high encoding efficiency and accurate detection could be achieved with simplified reader design. Likewise, a novel 4 × 5 cm2 tag is designed to fit the requirements of the devised coding technique. Different tag configurations are manufactured and validated with measurements using Software Defined Radio (SDR) platform. The introduced coding methodology is conclusively validated using Electromagnetic (EM) simulations and real world testbed measurements. © 2015 IEEE.
    view abstract10.1109/RFID.2015.7113069
  • Novel Pseudo-Noise coded chipless RFID system for clutter removal and tag detection
    Fawky, A. and Khaliel, M. and El-Awamry, A. and El-Hadidy, M. and Kaiser, T.
    2015 IEEE International Conference on RFID, RFID 2015 (2015)
    In this contribution a novel Frequency Coded (FC) chipless RFID system is introduced to significantly enhance the tag detection. The proposed system exploits the properties of Pseudo Noise (PN) random sequence, as a transmitted signal, to accurately estimate the Channel Impulse Response (CIR). Consequently, the undesired environmental clutter is filtered by a Selective-RAKE receiver. Hence, the tag is accurately identified in a heavily dense multipath environment using neither reference tags for calibration nor the non-practical no-tag deduction process. A real world simulation, based on ray-tracing tool is performed for to verify the system performance. Furthermore, the system testbed is realized on Software Defined Radio (SDR) platforms, where the tag detection is achieved with minimum latency and optimal precision. © 2015 IEEE.
    view abstract10.1109/RFID.2015.7113079
  • Terahertz band: Analysis of sounding bandwidth and center frequency on power delay profile model
    Sheikh, F. and El-Absi, M. and Gao, Y. and Kaiser, T.
    2015 Loughborough Antennas and Propagation Conference, LAPC 2015 (2015)
    This paper investigates the impact of different sounding bandwidths and center frequencies on power delay profile (PDP) at Terahertz (THz) band based on ray-tracing simulations. The effect of transmit power is also investigated for the center frequencies 300 GHz and 1500 GHz. This approach is based on complex frequency responses extracted for the Transmitter (Tx) and Receiver (Rx) pair, 10 m apart in Line of Sight (LoS) scenario. An accurate 3D model of the office environment has been modeled considering real-world parameters. By evaluating the optimal bandwidth and center frequency, one can construct the precise ultra-broadband terahertz channel models. Such characterization would allow the system designer to deal with trade-offs between performance and complexity when the optimal operating bandwidth and the corresponding center frequency are formerly known. It is also of great significance nowadays to explore Terahertz band for parametrization and standardization of future wireless systems. © 2015 IEEE.
    view abstract10.1109/LAPC.2015.7366040
  • Terahertz band: Indoor ray-tracing channel model considering atmospheric attenuation
    Sheikh, F. and El-Hadidy, M. and Kaiser, T.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 2015-October (2015)
    In this paper, we present first results of ray-tracing simulations of a realistic office environment across a wide spectrum from 100 GHz (0.1 THz) to 1000 GHz (1.0 THz). This ray-tracing model is used to study the channel characteristics and analyze the variation in received power and the channel delay profile. Furthermore, the frequency dependent atmospheric attenuation has been considered in this contribution as an important parameter affecting each path in the ray-tracing model based on the ray-path length. We succeeded to incorporate the atmospheric attenuation models of International Telecommunication Union (ITU) with the ray-tracer results. A very detailed 3D model of the office environment has been drawn up while the parameters of the common building materials were taken from literature. Simulation results based on frequency sweeping will be presented. In the full version of this paper, time domain results would be illustrated with the corresponding channel parameters such as Delay Spread (DS) and Power Delay Profile (PDP). © 2015 IEEE.
    view abstract10.1109/APS.2015.7305280
  • Wireless synchronization and interference alignment with limited interferer for distributed large scale multi user MIMO
    Galih, S. and El-Absi, M. and Hoffmann, M. and Kaiser, T.
    2015 7th Computer Science and Electronic Engineering Conference, CEEC 2015 - Conference Proceedings (2015)
    Large Scale (Massive) MIMO enhances the advantages of the conventional MIMO in terms of data rate, energy efficiency and reliability. To increase the scalability of conventional massive MIMO, the distributed large scale MIMO is recommended. Synchronization for distributed large scale MIMO is needed due to the lack of common clock source to synchronize the transmitters. Limited Inter-User Connected Interference Alignment for K-User is proposed for Large Scale MU-MIMO precoding scheme. Moreover, we discuss phase rotation factor estimation and compensation to synchronize the distributed large scale MIMO. The Interference Alignment algorithm with antenna selection also employed to show the effect of the synchronization in distributed large scale MIMO performance. © 2015 IEEE.
    view abstract10.1109/CEEC.2015.7332733
  • Achieving high reliability in Aerial-Terrestrial networks: Opportunistic space-time coding
    Jiang, W. and Cao, H. and Wiemeler, M. and Kaiser, T.
    EuCNC 2014 - European Conference on Networks and Communications (2014)
    To rapidly deploy a communication network in the aftermath of disaster or emergency event, an Aerial-Terrestrial architecture integrating aerial base stations mounted on the balloons has been investigated in EU FP7 ABSOLUTE project. Since the signal coverage provided by aerial base stations is patchy and unstable, the opportunistic relaying is applied to increase the link reliability and the system robustness. However, the performance of relay selection drastically degrades due to the outdated Channel State Information (CSI) from the feedback delay over the Aerial-to-Terrestrial radio channels. In this paper, therefore, we present a novel method named opportunistic space-time coding (OSTC) to combat the outdated CSI. The link reliability in terms of outage probability is evaluated using both Rayleigh channels and the realistic models of Aerial-to-Terrestrial and Device-to-Device channels. The numerical results reveal that OSTC obviously outperforms the opportunistic relaying in the presence of outdated CSI. Moreover, the improvement of reliability comes without any sacrifice in the spectral efficiency. © 2014 IEEE.
    view abstract10.1109/EuCNC.2014.6882624
  • Active self-interference cancellation mechanism for full-duplex wireless transceivers
    Askar, R. and Kaiser, T. and Schubert, B. and Haustein, T. and Keusgen, W.
    Proceedings of the 2014 9th International Conference on Cognitive Radio Oriented Wireless Networks and Communications, CROWNCOM 2014 (2014)
    This paper investigates active cancellation techniques for a Full-Duplex transceiver. An auxiliary transmit chain is employed to create the cancellation signal, which is then injected at the receiver RF front-end by using a microstrip cou-pler. Two methods are proposed to calculate the self-interference cancellation signal. While the first method assumes the transmit chain to be strictly linear, the second one additionally incorporates nonlinear effects, occurring especially in the RF power amplifier. The linear method reports experimentally around 48 dB of self-interference suppression under linear system behavior. Experimental results show also 50 dB of suppression by using the nonlinear method and under nonlinear system behavior, whereas the linear one reports 47 dB of suppression under the same conditions. © 2014 ICST.
    view abstract10.4108/icst.crowncom.2014.255732
  • An MGF-based performance analysis of opportunistic relay selection with outdated CSI
    Jiang, W. and Cao, H. and Kaiser, T.
    IEEE Vehicular Technology Conference 2015-January (2014)
    Up to now, a closed-form expression of the ergodic capacity for amplify-and-forward opportunistic relaying in the presence of outdated channel state information(CSI) is still not available in the literature. That is mainly due to the mathematical intractability in the conventional performance analysis through manipulations of probability density function (PDF). In this paper, therefore, we take advantage of a novel mathematical approach based on moment generating function (MGF) to evaluate the performance. MGF of the end-to-end signal-to-noise ratio for opportunistic relaying over independent and identically distributed Rayleigh channels with outdated CSI is given. Then, the closed-form expressions of ergodic capacity and outage probability are derived directly from MGF without any involvement of PDF. Finally, Monte-Carlo simulations are set up to corroborate the validity of the theoretical analysis. © 2014 IEEE.
    view abstract10.1109/VTCSpring.2014.7022828
  • Analysis of generalized selection combining in cooperative networks with outdated CSI
    Jiang, W. and Cao, H. and Kaiser, T.
    IEEE Wireless Communications and Networking Conference, WCNC (2014)
    Until now, the performance analysis of Generalized Selection Combining (GSC) applied to cooperative diversity networks in the presence of outdated channel state information (CSI) is still not available in the literature. In this paper, therefore, we derive closed-form expressions of the ergodic capacity and outage probability for amplify-and-forward GSC over independent and identically distributed Rayleigh channels. Monte-Carlo simulations are set up to corroborate the correctness of our theoretical analysis. The analytical and numerical results reveal that GSC is an effective way to combat the effect of outdated CSI. When using the perfect CSI, a full diversity on the number of all cooperating relays K is available. With the outdated CSI, where the performance of the conventional opportunistic relaying drastically degrades and its diversity order is limited to 1 (i.e., no diversity), a diversity order on the number of selected relays N can still be achieved. However, the performance gain on the diversity comes at the price of sacrifice in the spectral efficiency. © 2014 IEEE.
    view abstract10.1109/WCNC.2014.6952118
  • BER analysis of space-time coded RFID system in Nakagami-m fading channels
    Maichalernnukul, K. and Zheng, F. and Kaiser, T.
    Electronics Letters 50 (2014)
    The exact bit error rate (BER) analysis of a space-time coded radio frequency identification (RFID) system is presented, where the tag has multiple antennas and the reader has a single antenna. In the analysis, the forward and backward channels exhibiting independent but not necessarily identically distributed Nakagami-m fading are considered, and the diversity order that the system can achieve is found to be Nmin (mh, mg), where N is the number of antennas at the tag and mh and mg are the fading parameters corresponding to the forward and backward channels, respectively. The analytical results are verified through comparison with the simulation results. © 2014 The Institution of Engineering and Technology.
    view abstract10.1049/el.2013.0621
  • Bidirectional branch and bound based antenna selection in massive MIMO systems
    Gao, Y. and Jiang, W. and Kaiser, T.
    IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2015-December (2014)
    Antenna selection is a low cost solution to massive MIMO systems. There are two well-known design criteria of antenna selection in MIMO systems, i.e., maximizing MIMO capacity and maximizing post-processed Signal to Noise Ratio (SNR). This paper focuses on the latter one that can be achieved by selecting the largest Minimum Singular Value (MSV) of channel submatrices. A novel antenna selection is proposed by using the bidirectional Branch And Bound (BAB) searching algorithm to find the globally optimal channel submatrix with largest MSV. Simulation results demonstrate that, with both independent and identically distributed (i.i.d.) and sparse channels, the proposed method not only can achieve the same Bit Error Rate (BER) as the exhaustive search, but also has much lower complexity than the exhaustive search. Although the bidirectional BAB based antenna selection still has a high complexity, it can serve as a benchmark purpose for the future low complexity antenna selection design, especially when the exhaustive search is infeasible in massive MIMO systems, which is the main motivation of this paper. © 2015 IEEE.
    view abstract10.1109/PIMRC.2015.7343363
  • I/Q imbalance calibration for higher self-interference cancellation levels in Full-Duplex wireless transceivers
    Askar, R. and Zarifeh, N. and Schubert, B. and Keusgen, W. and Kaiser, T.
    Proceedings of the 2014 1st International Conference on 5G for Ubiquitous Connectivity, 5GU 2014 (2014)
    This paper investigates a Full-Duplex transceiver using an active cancellation technique where an additional transmit chain is employed to create the self-interference cancellation signal. Both transmitters and also the receiver are impaired by frequency-dependent I/Q imbalance with different parameters. It is shown how an I/Q parameter deviation in these chains deteriorates the achievable self-interference suppression level. Three different types of pre-equalization units, with variable complexity degree and different implementation approach, are then introduced and investigated. These units correct the I/Q imbalance and retain the self-interference level to its value as in a perfectly I/Q matched full-duplex transceiver. They can even be used to fully calibrate the I/Q imbalance. Simulative results show that self-interference suppression levels of more than 71 dB can be achieved. © 2014 ICST.
    view abstract10.4108/icst.5gu.2014.258148
  • Interference alignment with frequency-clustering for efficient resource allocation in cognitive radio networks
    El-Absi, M. and Shaat, M. and Bader, F. and Kaiser, T.
    2014 IEEE Global Communications Conference (2014)
    In this paper, the problem of resource allocation in overloaded orthogonal frequency division multiplexing (OFDM) based multiple-input multiple-output (MIMO) cognitive radio (CR) system is considered. The objective is to allocate the different subcarrier and distribute the available user power in order to maximize the CR system throughput. The interference induced to the primary system should not be harmful and hence, should not exceed the prescribed limit. Interference alignment (IA) technique is employed in order to achieve an efficient use of the available radio resources. Without affecting the quality of service of the primary system, IA enables the secondary users to share the available spectrum which increases the CR system degrees-of-freedom. Due to IA feasibility condition, the spectrum sharing with perfect IA is restricted to a certain number of user per subcarrier. Accordingly, the resource management problem is formulated as a mixed-integer optimization problem which is considered as an NP-hard problem. To reduce the computational complexity of the problem, a two-phase efficient sub-optimal algorithm is proposed. Frequency-clustering is performed in the first phase to the overcome IA feasibility conditions while the power is distributed among subcarriers in the second phase. Simulations show that IA technique achieves a significant sum-rate increase of CR systems compared with the traditional CR systems that use orthogonal multiple access transmission techniques. © 2014 IEEE.
    view abstract10.1109/GLOCOM.2014.7036936
  • Joint diagonalization in ACMA and its application to multiple-tag RFID systems
    Duraisamy, P. and Zheng, F. and Kaiser, T.
    IEEE TechSym 2014 - 2014 IEEE Students' Technology Symposium (2014)
    This paper discusses the separation of signals in multiple-tag radio frequency identification (RFID) systems. First, a model for the RFID system in both single and multiple tag environments is presented. Then, an analytical constant modulus algorithm (ACMA) for the blind source separation problem is reviewed. An alternative approach to the traditional ACMA using joint diagonalization is considered. Finally, both the ACMAs are applied to the multiple-tag RFID environment and performance of the system is studied. Simulations are carried out for 4-QAM and 16-QAM modulations at tag and analyses of the simulation results reveal that the ACMA with joint diagonalization takes lesser CPU time to execute compared to the traditional ACMA, but with higher average modulus error (AME). The variation of system performance with the number of measurements, SNR (signal to noise ratio), number of tags and number of antennas at the reader is also studied. Based on these, some design guidelines are presented. Interestingly both the ACMA algorithms work for the 16-QAM case and yield trends similar to those of 8-PSK and 4-QAM. © 2014 IEEE.
    view abstract10.1109/TechSym.2014.6808088
  • MISO beamforming for RFID systems via Second-Order Cone Programming
    Nagy, B. and Fawky, A. and Khaliel, M. and El-Hadidy, M. and Kaiser, T.
    8th European Conference on Antennas and Propagation, EuCAP 2014 (2014)
    This paper presents a beamforming design for Multiple-Input Single-Output (MISO) Radio Frequency Identification (RFID) systems. The design insures good Quality of Service (QoS) as well as optimal total power transmitted by the reader. Furthermore, a solution using Second-Order Cone Programming (SOCP) for the RFID beamforming problem is proposed. This SOCP algorithm yields optimal beamforming weights for the antenna array of the RFID reader transmitter. the RFID-reader transmitter. Such weight optimization can be considered as guidelines for RFID engineers to implement a high QoS RFID system that can compete with the well established traditional barcode technology. Simulation results are provided to show the effectiveness of the proposed algorithm. © 2014 European Association on Antennas and Propagation.
    view abstract10.1109/EuCAP.2014.6902410
  • On the design of MIMO antennas for cognitive radio systems
    Bouezzeddine, M. and Schroeder, W.L. and Kaiser, T.
    2014 1st International Workshop on Cognitive Cellular Systems, CCS 2014 (2014)
    Cognitive radio constitutes a very promising solution to improve spectrum usage of communication systems. However, being equipped with MIMO antennas, the design of CR devices poses tremendous challenges. In this paper, antennas requirements as well as the limitations imposed on the system performance are reviewed. Well decoupled and reconfigurable antennas guarantee the flexibility needed during spectrum scanning and data transmission. Nevertheless to achieve the desired performance, many challenges have to be overcome. The different aspects are illustrated by an example of a 4-port MIMO antenna in the frequency range [470, 790] MHz, or the so-called TV white spaces. © 2014 IEEE.
    view abstract10.1109/CCS.2014.6933787
  • Opportunistic relaying over Aerial-to-Terrestrial and Device-to-Device radio channels
    Jiang, W. and Cao, H. and Goratti, L. and Wiemeler, M. and Kaiser, T.
    2014 IEEE International Conference on Communications Workshops, ICC 2014 (2014)
    To enable the rapid deployment of a public safety communication network, a novel system architecture integrating an aerial base station mounted on a low-altitude platform has drawn many attentions. However, the signal coverage provided by such a rapidly-deployed network is patchy and unstable, which conflict with the high requirement on link reliability in the case of disaster relief and emergency events. Opportunistic relaying is a simple but effective method to reap the spatial diversity in cooperative systems. It can be used to increase the link resilience and improve the system robustness in such a rapidly-deployed and highly-dynamic network. Until now, the theoretical analyses and performance evaluations regarding the opportunistic relaying are merely based on the idealized small-scale fading, i.e., Rayleigh or Rician, without taking into account the path loss and shadowing. To close that gap, therefore, we study the existing channel models and choose the most appropriate ones reflecting the realistic characteristics of Aerial-to-Terrestrial and Device-to-Device channels. In this paper, the impacts of power allocation strategies, carrier frequencies, number of relays, altitudes of low-altitude platform and distances among terminals on spectral efficiencies of opportunistic relaying over Aerial-to-Terrestrial and Device-to-Device radio channels are investigated. © 2014 IEEE.
    view abstract10.1109/ICCW.2014.6881197
  • Opportunistic space-time coding to exploit cooperative diversity in fast-fading channels
    Jiang, W. and Cao, H. and Kaiser, T.
    2014 IEEE International Conference on Communications, ICC 2014 (2014)
    In this paper, we propose a novel scheme coined opportunistic space-time coding (OSTC) to deal with the outdated channel state information (CSI) problem for opportunistic relay selection (ORS) systems. A pair of relays, instead of a single relay, is opportunistically selected in terms of the instantaneous CSIs. Alamouti scheme, a unique space-time code achieving both full-rate and full-diversity, is applied to encode the regenerated signals at this pair of relays. To evaluate the performance, a closed-form expression of outage probability is derived for OSTC. The analytical and simulated results reveal that a full diversity on the number of cooperating relays is achieved by OSTC when using perfect CSI. In the fast-fading channels, where the outdated CSI drastically degrades the performance of ORS and reduces its diversity order to 1 (i.e., no diversity), a cooperative diversity with an order of 2 can still be achieved by the proposed scheme. Most importantly, this performance gain comes without any sacrifice in the spectral efficiency, which is the drawback of Generalized Selection Combining schemes. © 2014 IEEE.
    view abstract10.1109/ICC.2014.6884082
  • Optimal resource allocation based on interference alignment for OFDM and FBMC MIMO cognitive radio systems
    El-Absi, M. and Kaiser, T.
    EuCNC 2014 - European Conference on Networks and Communications (2014)
    In this paper, we present a radio resource allocation algorithm based on interference alignment (IA) for orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC) based MIMO cognitive radio (CR) systems. The algorithm provides the opportunity for all secondary users to share the available subcarriers simultaneously using IA technique. Besides, it allocates the power budget of each secondary user over the subcarriers in order to maximize the sum-rate of the system without inducing excessive interference to primary users. Simulations show that CR systems based on IA achieves a significant sum-rate increase compared to CR systems based on frequency division multiple access (FDMA). Moreover, IA based CR using FBMC physical layer achieves considerable throughput improvement compared to OFDM physical layer. © 2014 IEEE.
    view abstract10.1109/EuCNC.2014.6882676
  • Parallel In-band signal detection with self-interference suppression for cognitive LTE
    Cao, H. and Jiang, W. and Kaiser, T.
    2014 IEEE Wireless Communications and Networking Conference Workshops, WCNCW 2014 (2014)
    Recently, there has been an increasing interest in enhancing the mainstream cellular technology Long Term Evolution Advanced (LTE-A) with cognitive radio as one of the key enablers towards the fifth generation (5G) wireless communications. For dynamically accessing wider range of spectrum bands in a friendly manner, the cognitive LTE system should be able to discover the possible coexisting heterogeneous wireless systems in different bands. To this end, we propose a novel parallel in-band sensing scheme with effective self-interference suppression (SIS) in time and frequency domains, which doesn't require any modification to the existing standard specification or unrealistic a priori knowledge or extra hardware components. Preliminary simulation results show that over 10dB gain in signal-to-noise ratio (SNR) is achieved in detecting DVB-T signal submerged into very strong LTE self-interference. © 2014 IEEE.
    view abstract10.1109/WCNCW.2014.6934862
  • Power loading and spectral efficiency comparison of MIMO OFDM/FBMC for interference alignment based cognitive radio systems
    El-Absi, M. and Shaat, M. and Bader, F. and Kaiser, T.
    2014 11th International Symposium on Wireless Communications Systems, ISWCS 2014 - Proceedings (2014)
    Interference alignment (IA) has been proposed to optimally manage the interference aiming at providing the maximum degrees of freedom for multiuser interference channels. Therefore, IA has been used in cognitive radio (CR) systems to perform resource management in order to improve the throughput of the OFDM/FBMC based MIMO CR systems. In this work, a sub-optimal IA based power loading method is proposed for OFDM/FBMC based MIMO CR systems to approach the optimal approach with fewer complexity. In the proposed algorithm, all secondary users are enabled to share the available spectrum on the base of IA technique without affecting the quality-of-service of the primary system. Furthermore, spectral efficiency comparison between MIMO-OFDM and MIMO-FBMC is presented. Simulation results show that IA based power loading achieves a significant sum-rate increase of CR systems compared to traditional orthogonal multiple access techniques. Additionally, IA based power loading achieves better sum-rate improvement with FBMC than OFDM physical layer. © 2014 IEEE.
    view abstract10.1109/ISWCS.2014.6933401
  • Power optimal allocation in decode-and-forward opportunistic relaying
    Jiang, W. and Cao, H. and Kaiser, T.
    IEEE Wireless Communications and Networking Conference, WCNC (2014)
    To combat the bottleneck effect in the relay channels, this paper proposes a simple power-control algorithm for decode-and-forward cooperative networks with opportunistic relay selection. Taking advantage of the existing channel state information, which is a by-product during the process of relay selection, an optimal power allocation factor can be easily figured out. This factor is quantized into a few control bits and then fed back to the source via the existing feedback channel, i.e., the flag packet. Using the channel capacity and outage probability as metrics, the theoretical analysis and Monte-Carlo simulation corroborate that such distributed power allocation between the source and the best relay can effectively boost the system performance. Most importantly, this performance gain comes at almost no price due to just reusing the existing CSI and flag packet. © 2014 IEEE.
    view abstract10.1109/WCNC.2014.6952245
  • UWB chipless RFID system performance based on real world 3D-deterministic channel model and ZF equalization
    Fawky, A. and Mohammed, M. and El-Hadidy, M. and Kaiser, T.
    8th European Conference on Antennas and Propagation, EuCAP 2014 (2014)
    In this paper a 3D-deterministic channel model for UWB chipless RFID system is presented. The tag in this work will be modeled as a 3D object, with frequency dependent Radar Cross Section (RCS), embedded in the channel which has several incident and reflected multipath at various directions both from the reader-tag and the reader-reader environment effect. In this model all channel effects as multipath components, fading, frequency dependence, reflections, diffractions and polarization dependence will be considered. Moreover, a novel chipless RFID reader system model with Zero Forcing (ZF) based equalizer is proposed. The equalizer based system will increase the chipless tag identification distance by mitigating the aforementioned channel effect. The concept is tested using a deterministic channel from a ray-tracing model with a 8-bit frequency coded concept of a compact printable orientation independent chipless RFID tag. Furthermore, a 3D-Electromagnetic (EM) simulation tool is used to compute the Frequency Coding Response (FCR) and the RCS of the CFC-RFID tag. Simulation results show constructive guidelines for designing multi-tag UWB RFID communications and enhancing the channel estimation process of the chipless RFID tag systems. © 2014 European Association on Antennas and Propagation.
    view abstract10.1109/EuCAP.2014.6902135
  • UWB reflectarray antenna for chipless RFID applications
    Khaliel, M. and Fawky, A. and El-Hadidy, M. and Kaiser, T.
    National Radio Science Conference, NRSC, Proceedings (2014)
    The main limitation of any chipless Radio Frequency Identification (RFID) system is the very short reading range. In this paper, we propose an Ultra Wideband (UWB) Reflectarray Antenna (RA) system with 2.2 GHz bandwidth centered at 6 GHz for the reader of chipless RFID applications. The proposed reader antenna system enhances reader sensitivity, reduces multipath effects, helps in tag localization and a lot of novel capabilities that cannot be provided by the conventional antenna systems. The cell used in the design is the double circular ring where the antenna panel consists of 100 elements (10×10). Simulations show that the proposed antenna system reaches fractional bandwidth (FBW) 37% covering all the feeder bandwidth. This achieved ultra wide bandwidth (UWB) satisfies the requirements of the frequency signature based chipless RFID systems. © 2014 IEEE.
    view abstract10.1109/NRSC.2014.6835055
  • A robust radio access technology classification scheme with practical considerations
    Cao, H. and Jiang, W. and Wiemeler, M. and Kaiser, T. and Peissig, J.
    IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC (2013)
    This paper presents a robust radio access technology (RAT) classification framework for acquiring comprehensive knowledge on multiple types of coexisting wireless systems. It is built upon the combination of a group of RAT-specific feature metrics using maximum likelihood estimation (MIE) based decision rules. The classification scheme is enhanced by our proposed dimension cancellation (DIC) method for mitigating the noise uncertainty in practical receivers. Based on this framework, a signal classifier for TV white space (TVWS) is designed and implemented which is capable of detecting and classifying DVB-T, 3GPP LTE, IEEE 802.22, ECMA-392 and wireless microphone signals. The classifier is validated by both simulation and real-world experiment using a spectrum sensing testbed. The simulation and experiment performances agree with each other well, which confirms the effectiveness and robustness of the proposed classification scheme. The proposed classification framework will be further applied to our on-going projects kogLTE and ABSOLUTE in which the LTE network is enhanced with cognitive radio for operating in complex radio environment. © 2013 IEEE.
    view abstract10.1109/PIMRCW.2013.6707832
  • Cognitive radio-A current snapshot and some thoughts on commercialization for future cellular systems
    Kaiser, T. and Cao, H. and Jiang, W. and Zheng, F.
    Journal of Signal Processing Systems 73 (2013)
    Cognitive Radio (CR) has received tremendous interest during the past decade from almost all research disciplines in wireless communications. Meanwhile, companies across the world in the value chain are showing more and more interest in CR. This is due to the expected significant scarcity of spectrum caused by data-consuming modern smartphones or similar mobile devices. However, partly conflicting interests and severe technical challenges remain for a successful commercialization of CR ideas, in particular for Long-Term Evolution (LTE) cellular systems. The aims of this survey are as follows: 1) we try to limit the various physical parameters (e.g. the carrier frequency range, the cell size) being relevant for cognitive cellular systems either in qualitative or in quantitative terms, 2) a conceptual approach for a performance bound being of practical relevance will be pointed out, 3) different players in the value chain of cellular systems and potential conflict of interests will be discussed, 4) the technical state-of-the-art CR and the remaining major challenges will be highlighted, 5) a current snapshot about the quickly evolving area of regulation and standardization will be provided. Finally, some products, services and prototypes for CR will be presented. © 2013 Springer Science+Business Media New York.
    view abstract10.1007/s11265-013-0837-0
  • Key issues towards beyond LTE-Advanced systems with cognitive radio
    Jiang, W. and Cao, H. and Nguyen, T.T. and Guven, A.B. and Wang, Y. and Gao, Y. and Kabbani, A. and Wiemeler, M. and Kreul, T. and Zheng, F. and Kaiser, T.
    IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC (2013)
    In this paper, we give an introductory presentation on the state of the art of the key technologies in the field of cognitive radio, including spectrum awareness, cognitive engine, location awareness, digital front-end and baseband spectral shaping. The technical feasibility of opportunistically operating the future evolution of long-term evolution (LTE) over cognitive white spaces is discussed. A platform implementing these new concepts is briefly introduced. © 2013 IEEE.
    view abstract10.1109/SPAWC.2013.6612102
  • Min-maxing interference alignment algorithm as a semidefinite programming problem
    El-Absi, M. and El-Hadidy, M. and Kaiser, T.
    IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC (2013)
    The main objective of this contribution is to develop a new interference alignment (IA) algorithm, which improves the sum-rate performance of multiuser MIMO communication systems. The recent iterative IA approaches cannot guarantee robust sum-rate performance in different K-user MIMO interference channels, especially at high SNR regime. In our proposed distributed optimization algorithm, each receiver maximizes the desired signal power while preserving the minimum interference leakage as a constraint. A convex relaxation has been applied to this optimization problem after reformulating it into semidefinite programming form. This algorithm provides orthogonal precoders and decoders, which is fairly simple in practical implementation. Simulation results of the proposed algorithm proffer significant sum-rate improvement in various interference channels compared to existing algorithms. © 2013 IEEE.
    view abstract10.1109/SPAWC.2013.6612058
  • Multi-channel robust spectrum sensing with low-complexity filter bank realization
    Cao, H. and Jiang, W. and Kaiser, T.
    IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC (2013)
    In this paper, we propose a robust spectrum sensing scheme which can reliably detect signals in multiple channels within short observation time at the cost of low computational complexity. The scheme consists of two parts. The first part is the signal detection algorithm essentially based on the crosscorrelation of the feature sequence generated utilizing the signal's periodical pilot structure, which is further enhanced in terms of reducing sensitivity to clock mismatch and mitigating the noise uncertainty problem. The second part is the filter bank realized using the polyphase network (PPN) structure, which enables the simultaneous sensing of multiple wideband channels with low complexity which is favourable for the reduction of implementation cost and power consumption, especially for mobile terminals. In addition to the simulations for performance evaluation under practical conditions, the proposed spectrum sensing scheme is validated using the 8-channel wideband signal captured in UHF TV band. The visualized crosscorrelation values from both measurement and simulation are perfectly matched, which successfully confirms the effectiveness and feasibility of the proposed spectrum sensing scheme in real-world implementation. © 2013 IEEE.
    view abstract10.1109/PIMRC.2013.6666257
  • Reference selection for hybrid TOA/RSS linear least squares localization
    Wang, Y. and Zheng, F. and Wiemeler, M. and Xiong, W. and Kaiser, T.
    IEEE Vehicular Technology Conference (2013)
    Linear least squares (LLS) estimation is a suboptimum but low-complexity localization method based on measurements of location-related parameters. It has been proved that selection of the reference anchor influences the LLS localization accuracy. In addition, hybridization of different types of measurements can fix the deficiencies of one type of measurements. In this paper, we proposed a new reference selection criterion for the hybrid TOA/RSS LLS localization technique (called H-LLSRS), which considers both measured ranges and the information about their coarse variances. Moreover, we consider a general scenario that variances of range measurements are different, and derive a weighted LLS (WLLS) estimator for hybrid TOA/RSS localization according to the information about the accurate ranging variances and the correlations among the observations. Simulation results show that if the RSS-based ranging variances are considerably larger than the TOA-based ranging variances, the H-LLS-RS localization technique yields better accuracy than the conventional LLS localization techniques. Furthermore, reference selection has no effect on the accuracy of WLLS localization technique. Copyright © 2013 by the Institute of Electrical and Electronic Engineers, Inc.
    view abstract10.1109/VTCFall.2013.6692388
  • Robust spectrum sensing of DVB-T2 signal using the first preamble symbol
    Nguyen, T.T. and Cao, H. and Guven, A.B. and Gao, Y. and Kabbani, A. and Kreul, T. and Kaiser, T.
    International Conference on Advanced Technologies for Communications (2013)
    In the research on spectrum sensing, many works focus on TV bands, in which primary user signals follow digital video broadcasting-terrestrial (DVB-T) standard. However, DVB-T2 is the next generation of this standard. Some characteristics of the primary signal are changed including the pilot pattern and the cyclic prefix (CP). This issue results that the existing sensing algorithms based on the characteristics of DVB-T are not suitable for DVB-T2 signal, or become complex. In this paper, we propose a new sensing algorithm for DVB-T2 signal based on the first preamble symbol of DVB-T2 frame. We derive analytical forms for the detection. The detector works well at the SNR of -10dB with the false alarm of 0.01, with very short sensing time (0.224ms) and with all configurations of DVB-T2. Moreover, we propose a sensing scheme based on this algorithm for practical cognitive radio systems. © 2013 IEEE.
    view abstract10.1109/ATC.2013.6698118
  • Spectrum awareness scheme of the rapidly deployable eNodeB for unexpected and temporary events
    Cao, H. and Jiang, W. and Javornik, T. and Wiemeler, M. and Nguyen, T.T. and Kaiser, T.
    2013 IEEE 18th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks, CAMAD 2013 (2013)
    In the EU FP7 leT project ABSOL UTE, a novel network architecture based on the LTE-A aerial and terrestrial rapidly deployable eNodeB (RD-eNodeB) systems has been proposed for emergency communications in unexpected and temporary events. T hese systems would experience complex spectrum environment with multiple unknown coexisting cellular networks, which needs to be quickly adapted with cognitive radio techniques for rapid deployment. To this end, this paper proposes a spectrum awareness scheme considering initial spectrum sensing on RDeNodeB, sensing using UE's measurement capability and the radio environment map (REM) during the roll-out and in-service phases of the system's operation. For the initial spectrum sensing, a novel scheme for detecting, classifying and measuring downlink signals from coexisting base stations with different radio access technologies (RATs) is presented, which is invulnerable to the noise uncertainty problem. Encouraging numerical results of effectively detecting and classifying coexisting UMTS signal and LTE signals with different physical layer identities have beenobtained via simulation. © 2013 IEEE.
    view abstract10.1109/CAMAD.2013.6708116
  • Two-step hybrid self-localization using unsynchronized low-complexity anchors
    Wang, Y. and Wiemeler, M. and Zheng, F. and Xiong, W. and Kaiser, T.
    2013 International Conference on Localization and GNSS, ICL-GNSS 2013 (2013)
    Self-localization using unsynchronized low-complexity anchors has a number of attractive features. Traditional self-localization techniques are not suitable to this scenario or have their applicability limitations. In this paper, a two-step hybrid self-localization technique using unsynchronized low-complexity anchors is proposed, which can achieve two-dimensional (2-D) instantaneous localization for both mobile and fixed agents and eliminate the need for heading information of the agents. In the first step, an initial location estimate is obtained utilizing range information based on received-signal-strength (RSS) measurements. In the second step, differential angle-of-arrival (AOA) measurements are converted to range measurements with the aid of the first step location estimate. Finally, a two-step hybrid localization algorithm is obtained using all the measurements in the first step and the second step. Simulation results show that the two-step hybrid self-localization technique has relatively high accuracy even in the scenarios with large RSS-based ranging variances and medium AOA measurement variances. © 2013 IEEE.
    view abstract10.1109/ICL-GNSS.2013.6577271
  • A comparison of robustness between interference alignment and direct transmission
    Zheng, F. and Kaiser, T.
    Conference Proceedings of the International Symposium on Signals, Systems and Electronics (2012)
    Interference alignment (IA) is a novel technique to manage interference for multiuser wireless communications. The basic idea of IA in managing interference is based on the subspace separation. Since this property can be easily damaged, one might image that IA is sensitive to errors appeared in channel state information (CSI), which is needed at the transmitter side of each user. In this work, we will show some comparison results between IA and direct transmission (DT). In the DT scheme, the maximum likelihood (ML) receiver is used at each user. The simulation results show that IA systems are indeed very sensitive to CSI errors compared with the DT-ML system, while the complexity of the IA systems in implementation is comparable with the DT-ML systems if the constellation of transmitted symbols is of moderate cardinality. © 2012 IEEE.
    view abstract10.1109/ISSSE.2012.6374302
  • A space-time coding approach for RFID MIMO systems
    Zheng, F. and Kaiser, T.
    Eurasip Journal on Embedded Systems 2012 (2012)
    This paper discusses the space-time coding (STC) problem for RFID MIMO systems. First, a mathematical model for this kind of system is developed from the viewpoint of signal processing, which makes it easy to design the STC schemes. Then two STC schemes, namely Scheme I and Scheme II, are proposed. Simulation results illustrate that the proposed approaches can greatly improve the symbol-error rate (SER) or bit-error rate (BER) performance of RFID systems, compared to the non space-time encoded RFID system. The SER/BER performance for Scheme I and Scheme II is thoroughly compared. It is found that Scheme II with the innate real-symbol constellation yields better SER/BER performance than Scheme I. Some design guidelines for RFID-MIMO systems are pointed out. © 2012 Zheng and Kaiser.
    view abstract10.1186/1687-3963-2012-9
  • Antenna selection for interference alignment based on subspace canonical correlation
    El-Absi, M. and El-Hadidy, M. and Kaiser, T.
    2012 International Symposium on Communications and Information Technologies, ISCIT 2012 (2012)
    The main objective of this contribution is to develop a novel antenna selection algorithm for Interference Alignment (IA) in multi-user communication systems. Successive IA requires high degree of independency among the channels, which could hardly exist in real-world environments. Therefore, the Bit Error Rate (BER) performance of the IA system suffers from a dramatic degradation, especially in indoor environments. Applying the developed antenna selection algorithm can effectively increase the channels diversity and improve the BER performance. This selection algorithm based on selecting the maximum Canonical Correlation (CC) between the desired signal subspace and the interference-free subspace in order to maximize the average received Signal-to-Noise Ratio (SNR) of the system. The influence of the CC on sum-rate would be presented mathematically. Simulation results show a significant improvement of the BER system performance based on the CC antenna selection algorithm compared with the maximum sum-rate selection algorithm. © 2012 IEEE.
    view abstract10.1109/ISCIT.2012.6380934
  • Artificial diversity for UWB MB-OFDM Interference Alignment based on real-world channel models and antenna selection techniques
    El-Hadidy, M. and El-Absi, M. and Kaiser, T.
    Proceedings - IEEE International Conference on Ultra-Wideband (2012)
    Main objective of this contribution is to apply Interference Alignment (IA) algorithms in real-world indoor environments for UWB MIMO MB-OFDM communication systems. In indoor environments, the required orthogonality between multiusers channels, which is necessary for proper IA, could be hardly reached. The spatial diversity among the users/nodes is mostly insufficient to obtain a robust performance for IA algorithms. In this work, a practical artificial channel diversity technique is applied through antenna selection to choose the best scenario providing the maximum orthogonality and consequentially the best overall system performance. Our analysis considers deterministic UWB MIMO channel model based on EM Ray-tracing in a real-world multi-user indoor environment. Simulation results present a significant enhancement in the overall system performance. Furthermore, the impact of the directional properties and the orientations of the antennas on the system are investigated. © 2012 IEEE.
    view abstract10.1109/ICUWB.2012.6340464
  • DSSS differential GMSK with space-time modulation for robust mobile data links
    Cao, H. and Maier, F. and Wilzeck, A. and Kaiser, T.
    IEEE Wireless Communications and Networking Conference, WCNC (2012)
    A new modulation scheme combing GMSK with direct-sequence spread spectrum (DSSS) and differential modulation is proposed in this paper, which is named DS-DGMSK. The demodulation can achieve BER performance comparable to DBPSK while the bandwidth efficiency and power efficiency are higher thanks to GMSK. By combining with spread spectrum and differential demodulation, the scheme is robust at low SINR and high moving speed without accurate carrier frequency recovery. It can be further enhanced by differential space-time modulation (DSTM) giving transmit diversity which further improves robustness. The proposed modulation is suitable for low-bitrate mobile data link which requires high robustness, low complexity and nonlinear power amplifier which is low-cost and less power-consuming. © 2012 IEEE.
    view abstract10.1109/WCNC.2012.6213949
  • Metrics and methods for evaluation of over-the-air performance of MIMO user equipment
    Feng, Y. and Schroeder, W.L. and Von Gagern, C. and Tankielun, A. and Kaiser, T.
    International Journal of Antennas and Propagation 2012 (2012)
    Commercial User Equipment (UE) testing and certification has become more complex for state-of-the-art mobile communication standards such as 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) due to the extensive use of Multiple Input-Multiple Output (MIMO) transmission techniques. The variety of different MIMO operating modes and the almost unlimited choice of possible multipath channel conditions under which UE performance may be evaluated are not accounted for by established Single Input-Single Output (SISO) Over-The-Air (OTA) performance metrics like Total Isotropic Sensitivity (TIS) and Total Radiated Power (TRP). As pointed out in this contribution, meaningful metrics and cost-effective, low-complexity measurement methods can, nevertheless, be derived by focusing on characterization of the physical attributes of UE and by adopting statistical metrics. Starting from a brief review of the most important MIMO operating modes in the 3GPP LTE standard, the relation between UE properties and UE performance, which is observed in these operating modes, is discussed. Two complementary metrics and corresponding measurement procedures for evaluation of MIMO OTA performance are presented in order to address the diversity of possible propagation scenarios. Measurement results from preliminary implementations of the two proposed measurement procedures, including comparison between different LTE devices, are presented. Copyright © 2012 Yifei Feng et al.
    view abstract10.1155/2012/598620
  • MIMO multi-user relay system
    Anggraini, A. and Le, T.C. and Peissig, J. and Kaiser, T.
    Conference Proceedings of the International Symposium on Signals, Systems and Electronics (2012)
    This paper presents the BER performance analysis of a MIMO multi-user relay network. A single relay is employed to assist the transmission between the base station and the mobile station at the cell edge of two neighbouring cells. The relay applies the linear precoding technique, namely, block diagonalization and interference alignment to suppress the interference, and afterwards to forward the signal to the intended user. © 2012 IEEE.
    view abstract10.1109/ISSSE.2012.6374326
  • On the fidelity of ultra-wideband antennas
    Sczyslo, S. and Rolfes, I. and Kaiser, T.
    Proceedings of the 2012 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications, APWC'12 (2012)
    Within this contribution two ultrawideband antennas, an almost omnidirectional bi-conical antenna of type SBA 9113 from Schwarzbeck and a directional Vivaldi antenna, are analyzed according to their time-domain characteristics. In this context the fidelity factor and the peak value play an important role. Hence both, the parameter's definition is recaped and the particular practical meaning is explained. Moreover, a new parameter, the two antenna fidelity is introduced which indicates an antenna's performance in context of a typical point to point link involving two antennas. To increase the accuracy the analysis is based upon a resimulation of both antennas. © 2012 IEEE.
    view abstract10.1109/APWC.2012.6324990
  • On the performance of the time reversal SM-MIMO-UWB system on correlated channels
    Nguyen, H. and Nguyen, V.D. and Nguyen, T.K. and Maichalernnukul, K. and Zheng, F. and Kaiser, T.
    International Journal of Antennas and Propagation 2012 (2012)
    The impact of spatial correlation on the multi-input multi-output ultrawide band (MIMO-UWB) system using the time reversal (TR) technique is investigated. Thanks to TR, several data streams can be transmitted by using only one antenna in a system named virtual MIMO-TRUWB. Since the virtual MIMO-TR-UWB system is not affected by the transmit correlation, under the condition of the high spatial correlation, it outperforms the true MIMO-UWB system with multiple transmit antennas. The channel measurements are performed in short-range indoor environment, both line-of-sight and non-line-of-sight to verify the adopted correlated channel model. Copyright 2012 Hieu Nguyen et al.
    view abstract10.1155/2012/929018
  • On the transmit signal design at the reader for RFID MIMO systems
    Zheng, F. and Kaiser, T.
    Proceedings - 2012 4th International EURASIP Workshop on RFID Technology, RFID 2012 (2012)
    This paper discusses the reader's transmit signal design problem for RFID MIMO systems. First a mathematical model for this kind of system is developed from the viewpoint of signal processing. Then two spatial matching transmission schemes, namely matched to a fixed antenna at the tag or matched to a selected antenna at the tag, for the reader's signals are proposed. Simulation results illustrate that the proposed approaches can greatly improve the BER performance of RFID MIMO systems, compared to the uniform transmission policy. © 2012 IEEE.
    view abstract10.1109/RFID.2012.11
  • Performances analysis of Vehicle-to-X Communication Systems
    Nguyen, H. and Nguyen, V.D. and Nguyen, T.H. and Ha, D.T. and Kaiser, T.
    2012 IEEE International Symposium on Signal Processing and Information Technology, ISSPIT 2012 (2012)
    This paper investigates the influence of the inter-carrier interference on a vehicle to infrastructure (V2X) communication system, which has been defined in the IEEE 802.11p standard. The frequency shift due to high speed of cars destroys the orthogonality between subcarriers in OFDM signals and rises the inter-carrier interference (ICI). The main contributions of this paper are proposed analytic formulas and simulation results of the signal to interference power ratio (SIR) by considering the statistical effects of ICI and evaluation of symbol error rate (SER) for several types of fading and Doppler spread in time domain approach. The results show that for the Rayleigh fading model, SIR decreases when the maximum Doppler spread increases. On the other hand, in the Rician channel, SIR depends not only on maximum Doppler spread but also on the angle of arrival (AoA) and Rician factor of the LOS component. Moreover, the simulation result in terms of SER is obtained for different channel models. It shows an excellent agreement between the theoretical calculation of SIR and the simulation results of SER. © 2012 IEEE.
    view abstract10.1109/ISSPIT.2012.6621309
  • Straightforward MIMO OTA characterization and statistical metrics for LTE devices
    Feng, Y. and Schroeder, W.L. and Kaiser, T.
    Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012 (2012)
    A straightforward Over-The-Air (OTA) characterization method is proposed and conducted to characterize the MIMO performance of LTE devices. A basic level measurement in form of a sensitivity measurement in Downlink (DL) Transmit Diversity (TD) mode is used to evaluate diversity performance of User Equipment (UE) with multiple antennas in noise-limited scenarios. An "advanced level" measurement in form of throughput measurements in Spatial Multiplexing (SM) modes is used to characterize peak performance of UE in MIMO-favourable scenarios. Experimental results are presented for an E-UTRA band 7 USB dongle with three different arrangements of external antennas. © 2012 IEEE.
    view abstract10.1109/EuCAP.2012.6205994
  • TDOA assisted RSSD localization in UWB
    Gerok, W. and Peissig, J. and Kaiser, T.
    WPNC'12 - Proceedings of the 2012 9th Workshop on Positioning, Navigation and Communication (2012)
    This paper considers ultra-wideband (UWB) based localization of mobile users in indoor environment. Because of severe multipath indoor localization still presents a challenging issue and UWB is often considered as technology enabling precise localization. Typically for UWB Time of Flight (TOF) based approaches like Time of Arrival (TOA) or Time Difference of Arrival (TDOA) are applied. Recently also localization based on Received Signal Strength (RSS) is gaining more interest, where position of the transmitting device is calculated based on the RSS on several Base Stations (BS) with known positions. To perform the positioning the transmit power must be known. This paper considers Received Signal Strength Difference (RSSD) based positioning, which does not require the knowledge of the transmit power. The positioning is further assisted with TDOA measurement. It is shown that including only one single TDOA information improves the localization performance significantly. © 2012 IEEE.
    view abstract10.1109/WPNC.2012.6268764
  • Virtual MIMO in WiMAX relay system
    Anggraini, A. and Peissig, J. and Kaiser, T.
    Conference Proceedings of the International Symposium on Signals, Systems and Electronics (2012)
    This paper presents the BER performance analyses of a virtual MIMO half-duplex relay system on a WiMAX OFDMA network with Alamouti coding. For such a condition where multi-antenna relay is not an option, employing multiple single-antenna relays in the system would be an alternative to still benefit the diversity gain. The impact of increasing the number of relay nodes to the system performance is also investigated. Furthermore, the performance comparison of Amplify-and-Forward (AF) and Decode-and-Forward (DF) relaying strategies applied on the system is also presented. © 2012 IEEE.
    view abstract10.1109/ISSSE.2012.6374349
  • A study of the key technology of IEEE802.11p-2010
    Hu, L. and Kaiser, T. and Kupferschmidt, C. and Nguyen, H. and Jing, H.
    Proceedings of SPIE - The International Society for Optical Engineering 8285 (2011)
    This article presents an overview of the vehicle wireless communication protocol IEEE802.11p-2010, which was issued in July 2010. The concepts, features, architecture and applications of protocol IEEE802.11p, as well as the required key technologies to implement IEEE802.11p are analyzed in detail, including the OFDM technology, 10MHz bandwidth, requirements of improved receiver, improved transmission standard, improved ACR and WBSS and so on. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
    view abstract10.1117/12.913563
  • A synchronization method for implementing an OFDM system based on the TMS320C6416 DSP
    Nguyen, V.D. and Dinh, Q.K. and Nguyen, M.H. and Pham, V.T. and Kuperschmidt, C. and Kaiser, T. and Bang Giang, T.V. and Nguyen, T.H.
    Proceedings of the 5th International Conference on Ubiquitous Information Management and Communication, ICUIMC 2011 (2011)
    This paper proposes a synchronization method for implementation of an OFDM system based on the TMS320C6416 DSP. The method is to meet the constraints of signal processing in real time conditions, and ensure the Quality of Services regarding the received signal quality. It is proven that the complexity of the proposed method is significantly reduced in comparison with the conventional one, and thus, the time constraint for synchronization is fulfilled. Moreover, the starting point of each OFDM frame stored in the receiver DSP buffers can be precisely detected. The data rate obtained by applying the Ping-Pong Buffer technique is significantly enhanced. Measurement results are compared with the theoretical results to validate our proposed mechanisms. Files and audio transfer are tested to demonstrate the performance of the implemented system. Copyright 2011 ACM.
    view abstract10.1145/1968613.1968666
  • Analysis of the influence of OFDM sidelobe interference on Femto rich systems
    Zhao, Z. and Thein, C. and Zheng, F. and Kaiser, T.
    2011 International Symposium on Modeling and Optimization of Mobile, Ad Hoc, and Wireless Networks, WiOpt 2011 (2011)
    This paper considers the existence of sidelobe emission in OFDM based rich-Femtocell systems. By modeling the interference from the arbitrary-distributed Femtocells as shot-noise process, the paper analyzes the effect of sidelobe interference on the system performance metrics such as transmission capacity (TC) and area spectral efficiency (ASE). The numerical results calculated for three different OFDM schemes show that, under the circumstance of very high Femto deployment intensity, the rigorous constraints on first-tier, namely the Macrocell outage probability and the reduction of first-tier ASE, prohibit the Femtocells from excessive subband access. Thus the out-of-band emissions contribute significantly to the system performance loss. Further analysis has shown that poor channel condition can even worsen the situation, making the existence of sidelobe interference not ignorable. Among the three schemes, OQAM-OFDM is proved to achieve the best performance. Although OQAM-OFDM has higher requirements of implementation, it is reasonable to be considered as one of the candidate transmission schemes for future Femtocell applications. © 2011 IEEE.
    view abstract10.1109/WIOPT.2011.5930061
  • Design and implementation of advanced algorithms for MIMO-UWB wireless communications
    Dimitrov, E. and Kupferschmidt, C. and Kaiser, T. and Korpi, J. and Nordman, R. and Anttonen, A. and Giorgetti, A. and Chiani, M.
    Proceedings - IEEE International Conference on Ultra-Wideband (2011)
    This paper describes the design and implementation of low-complexity multiple-input multiple-output (MIMO) signal processing techniques suitable for ultra-wideband (UWB) wireless communications. It provides the general system concept, description of the measurement set-up and modular FPGA platform for test and verification of the proposed multiple antenna schemes under real air-interface environment. We validate the performance of selected spatial multiplexing and diversity approaches applied to Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) and demonstrate the enhancements in capacity and link reliability of existing WiMedia devices through algorithm- and implementation-level investigations. © 2011 IEEE.
    view abstract10.1109/ICUWB.2011.6058847
  • Femtocell spectrum access underlaid in fractional frequency reused macrocell
    Zhao, Z. and Zheng, F. and Wilzeck, A. and Kaiser, T.
    IEEE International Conference on Communications (2011)
    This paper focuses on the Femtocell spectrum access problems when a certain amount of Femto Base Stations (FBS) are underlying in a two-tier cellular network, where the Macro Base Stations (MBS) are adopting Fractional Frequency Reuse (FFR) strategy. Under the first-tier outage constraints, the FBS transmission capacity in an analytic form has been presented. It is found via the relevant bound analysis that the optimal Femtocell spectrum access rate depends only on the basic configuration parameters of the Macrocell FFR, regardless the aspects of Femto transmit power and required QoS criteria. Consequently, the optimal Femtocell spectrum access algorithm is proposed in this paper, which achieves substantial gains over conventional algorithms. In the mean time, the maximal transmission capacity is not only related to the optimal access rate, but also to the system specific parameters such as Femto UE transmit power, target SIR and outage rate. Tuning these parameters enables the system to accommodate more number of FBSs simultaneously. Finally, the second-tier outage probability constraints are also derived, providing the optimal strategies for FBSs to maximize the second-tier throughput. © 2011 IEEE.
    view abstract10.1109/iccw.2011.5963546
  • Measurement and ray-tracing of wideband indoor channel in UHF TV white space
    Cao, H. and Zhao, Z. and Ni, W. and El-Hadidy, M. and Kaiser, T.
    ACM International Conference Proceeding Series (2011)
    The UHF TV band is now being opened by regulators to new wireless services and markets on light-licensing or licenseexempt basis, which is very attractive to low-power indoor applications. In this paper, we present our study on wireless indoor channel in UHF band using a novel measurement scheme. Comparing with reported channel measurement using vector network analyzer (VNA), there is no need of RF cable connection between transmitter and receiver sides in this scheme, hence the location range of measurement is extended significantly. We measured received signal power, channel impulse response and power delay profile in the scenario of our institute's floor, which characterizes a typical indoor office environment. The measured received signal power agree well with the predicted results generated by a ray-tracing software Wireless InSite. A further case study for reducing indoor-to-outdoor interference leakages of a femto cell is performed using this software. The work in this paper paves the way for further investigation on indoor applications in UHF TV band, such as cognitive wideband digital link and cognitive PMSE system in TV white space. © 2011 ACM.
    view abstract10.1145/2093256.2093279
  • Mobile Position Estimation Using Received Signal Strength and Time of Arrival in Mixed LOS/NLOS Environments
    Sieskul, B.T. and Zheng, F. and Kaiser, T.
    Handbook of Position Location: Theory, Practice, and Advances (2011)
    view abstract10.1002/9781118104750.ch18
  • Performance investigation of MMSE-based interference alignment for multiuser MIMO UWB
    Le, C. and Dimitrov, E. and Moghaddamnia, S. and Kaiser, T.
    Proceedings - IEEE International Conference on Ultra-Wideband (2011)
    To achieve the full multiplexing gains or the degrees of freedom of the K-multiuser MIMO interference channel, the interference alignment technique has been proposed and investigated. The main idea of interference alignment is to design the pre-coder at each transmitter, so that each receiver can align all interference from undesired transmitters in interference subspaces by exploiting knowledge of the channel state information (CSI) of all transmission links. Currently, a closed-form solution for the pre-coding filters exists only for the case of up to three users and provides poor sum-rate performance compared to iterative algorithms. Furthermore, all available algorithms for interference alignment were investigated only for the case, where each transmitter sends only one data stream. In this paper, the MMSE-based interference alignment is exploited to improve the BER and sum-rate performance of the system especially in the low SNR regime. This paper focuses on a multiuser MIMO UWB system based on MB-OFDM with arbitrary number of independent data streams per user. The simulation results confirm that the MMSE-based interference alignment provides sum-rate and BER superior to Orthogonal Frequency-Division Multiple Access (OFDMA) at marginal performance degradation. © 2011 IEEE.
    view abstract10.1109/ICUWB.2011.6058820
  • Performance of ultrawideband cooperative relay systems in the presence of narrowband interference
    Maichalernnukul, K. and Kaiser, T. and Zheng, F.
    Proceedings - IEEE International Conference on Ultra-Wideband (2011)
    In this paper, the performance of ultrawideband (UWB) cooperative relay systems in the presence of narrowband (NB) interference is evaluated for the first time. Specifically, we consider UWB cooperative amplify-and-forward and UWB cooperative detect-and-forward systems where a single-tone NB interferer exists, and present their bit-error-rate analysis. Simulation results based on such analysis demonstrate how the NB interference impacts on the system performance. © 2011 IEEE.
    view abstract10.1109/ICUWB.2011.6058874
  • Spatial fading correlation for local scattering: A condition of angular distribution
    Tau Sieskul, B. and Kupferschmidt, C. and Kaiser, T.
    IEEE Transactions on Vehicular Technology 60 (2011)
    Local scattering in the vicinity of the receiver or the transmitter leads to the formation of a large number of multipath components along different spatial angles. A condition of angular distribution, which is valid for only a uniform linear array, is proposed in this paper to justify whether the spatial fading correlation (SFC) remains simple as a Bessel function. If an angular distribution satisfies the condition, a class of angular distributions is revealed and results in simplifying the analysis of the SFC. To demonstrate its practical use, we apply the condition to several angular distributions that are considered in previous works. It is found that cosine and von Mises distributions follow the condition, whereas uniform, Gaussian, and Laplacian distributions do not satisfy the condition, and then, one needs to calculate the sinusoidal coefficients in the SFC computation. © 2011 IEEE.
    view abstract10.1109/TVT.2010.2103370
  • A correlated Gaussian spatial distribution
    Sieskul, B.T. and Kupferschmidt, C. and Kaiser, T.
    MECAP'10, 1st Middle East Conference on Antennas and Propagation (2010)
    We consider an angular distribution for modeling the local scattering in the vicinity of the receiver or the transmitter. The Gaussian spatial distribution is extended to capture the correlation between the x-coordinate and the y-coordinate, which gives rise to a generalization to the uncorrelated Gaussian spatial distribution. The probability density function of the correlated Gaussian spatial distribution for the azimuth angle is derived as a closed form. Numerical examples are conducted to illustrate the effects of the correlation coefficient on the distribution. © 2010-IEEE APS.
    view abstract10.1109/MECAP.2010.5724194
  • A novel positioning algorithm based on ultra-wideband technology
    Gerok, W. and Kaiser, T.
    Record - IEEE PLANS, Position Location and Navigation Symposium (2010)
    In this paper, we present a concept of combining the Time Difference of Arrival (TDOA) data with additional information from the receiving antenna properties. This additional information can be acquired for example, if closely spaced directional receiving antennas connected to the cross-correlation receiver are utilized. An Angle of Arrival (AOA) estimation is done using two very closely spaced receiving antennas. This estimated AOA and the additional information can be used for range estimation. Thus a novel two dimensional positioning algorithm is introduced. ©2010 IEEE.
    view abstract10.1109/PLANS.2010.5507257
  • A sorted parallel detector for coded mimo systems
    Awada, A. and Joham, M. and Utschick, W. and Goldyrjew, S. and Mulder, W. and Kaiser, T.
    IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC (2010)
    Computing the log likelihood ratios (LLR's) of the transmitted bits in a multiple-input multiple-output (MIMO) system is an NP hard problem. Many suboptimal soft MIMO detectors have been proposed to reduce the detection complexity. The state-of-the art tries to combine the search for the maximum a posteriori (MAP) estimate and the counter-hypotheses in a single tree pass. However, not all possible counter-hypotheses are tested and have to be selected to reduce complexity. In this paper, the sorted parallel detector (SPD) is developed that is based on the parallel smart candidate adding (PSCA). SPD has a better bit error rate (BER) performance than the PSCA and exhibits a lower average number of visited tree nodes. Moreover, SPD has a fixed complexity and is suitable for hardware implementation.
    view abstract10.1109/SPAWC.2010.5671041
  • An expending ring search algorithm for mobile adhoc networks
    Duy, N.P. and Van, D.N. and Van, T.P. and Ngoc, T.N. and Xuan, B.D. and Trung, D.N. and Kuperschmidt, C. and Kaiser, T.
    Proceedings - 2010 International Conference on Advanced Technologies for Communications, ATC 2010 (2010)
    Routing protocols are challenges in designing Mobile Ad-hoc networks with low energy consuming. This paper extends the expanding ring search (ERS) algorithm proposed in [3] to optimize the energy consuming caused by broadcasting redundance messages. Simulation results show that the required message packages for routing by using our algorithm is significantly reduced in comparison with that required by using the ERS method. ©2010 IEEE.
    view abstract10.1109/ATC.2010.5672725
  • Compensation techniques for Doppler effect in UWB-based rotor-telemetry system
    Ayadi-Miessen, A. and Kupferschmidt, C. and Kuchenbecker, H.-P. and Kaiser, T.
    MECAP'10, 1st Middle East Conference on Antennas and Propagation (2010)
    This paper covers a new scenario based on UWB-technique for transmission of data, which is the rotor-telemetry. The rotor-telemetry is a special type of a radio-telemetry, where measuring data of physical parameters like pressure or temperature are captured by sensors predominantly on rotating objects such as shafts or gear parts, transmitted over special on the rotor mounted along-moved antennas and received by static antennas. A new problem appears with this scenario: since the rotor moves fast, the impact of Doppler rises significantly. In this paper we will first analyze the Doppler effect mathematically, then we will give a short overview about techniques, how to estimate the frequency dependent Doppler shift of the UWB-signal and finally we will focus in detail on techniques to compensate the Doppler effect caused by very fast rotation speed. © 2010-IEEE APS.
    view abstract10.1109/MECAP.2010.5724193
  • Design and performance of dual-hop MIMO UWB transmissions
    Maichalernnukul, K. and Zheng, F. and Kaiser, T.
    IEEE Transactions on Vehicular Technology 59 (2010)
    To coexist with existing legacy wireless systems, the transmit power spectral density of ultrawideband (UWB) impulse radio systems is limited. The coverage range of UWB systems is then confined to within a few meters. Dual-hop relaying or multiple-inputmultiple-output (MIMO) technology is one possible way of achieving greater UWB system coverage. This paper presents the design of dual-hop UWB MIMO relay systems (in which a source, relay, and destination have multiple antennas) according to the availability of channel state information (CSI) and their performance analysis over a UWB multipath fading channel. In particular, the decouple-and-forward and decode-and-forward relay systems are proposed when partial CSI is only available at the receiver side. On the other hand, with partial CSI being available at the transmitter side, we propose the amplify-and-forward and detect-and-forward relay systems. The exact formulas for the outage probabilities of those systems are derived. Furthermore, we evaluate, in closed form, the amount of fading and bit error rate expressions under sufficiently high signal-to-noise ratio and verify them through comparison with the simulation results. The effect of spatial correlation on the performance of our proposed systems is also studied. Numerical examples of the results provide valuable insights into the design of UWB MIMO relay systems. © 2006 IEEE.
    view abstract10.1109/TVT.2010.2048347
  • Estimation algorithms of multiple channels and carrier frequency offsets in application to multiuser OFDM systems
    Häring, L. and Bieder, S. and Czylwik, A. and Kaiser, T.
    IEEE Transactions on Wireless Communications 9 (2010)
    This paper introduces new joint estimation methods of multiple carrier frequency offsets (CFOs) and channel impulse responses (CIR) in application to multiuser orthogonal frequency division multiplexing (OFDM) systems. The estimators are derived from the optimal maximum-likelihood (ML) principle. Complexity reductions are achieved by exploiting the correlation properties of the training sequence (TS). The grid search algorithm is converted into a polynomial root finding procedure which leads to low-complexity closed-form estimators for moderate CFOs. Furthermore, iterative estimators for larger CFOs are proposed. Numerical results confirm that the performance degradation due to the approximations compared to the Cramer-Rao bound (CRB) is small and may be negligible in practice. © 2006 IEEE.
    view abstract10.1109/TWC.2010.03.070963
  • Frequency dependence of the UWB indoor channel and the effects of the antenna directivity on path loss and multipath propagation
    El Din, S.A. and El-Hadidy, M. and Kupferschmidt, C. and Kaiser, T.
    MECAP'10, 1st Middle East Conference on Antennas and Propagation (2010)
    Aim of this contribution is to investigate the main channel parameters considering their frequency dependence and the effects of antenna directivity. The analysis relies on a hybrid Electromagnetic (EM) Ray-tracing Ultra Wideband (UWB) simulation technique, where the transfer functions of the antennas are determined using EM simulation tool and embedded in the ray-tracing tool in order to derive a deterministic description of the UWB wireless channel. The UWB channel is simulated from 1-11 GHz for an indoor environment using typical UWB omni-directional antennas and directional ones. A mathematical framework for the characterization of the main channel parameters, such as the environment dependent path loss exponent, the delay spread and the effects of the antennas characteristics and orientations will be discussed. Furthermore, the impact of different bandwidth and central frequencies on path loss exponent and multipath propagation would be also investigated. © 2010-IEEE APS.
    view abstract10.1109/MECAP.2010.5724170
  • Indoor localization with closely spaced vivaldi antennas in ultra-wideband
    Gerok, W. and Kaiser, T.
    5th International Conference on Digital Telecommunications, ICDT 2010 (2010)
    In this paper a positioning algorithm, based on the utilization of the receiving antenna properties is presented. The algorithm can be applied in Time of Flight (TOF) based localization systems with closely spaced receiving antennas additionally to the time estimation. In this work we present the practical measurements. But better result may be achieved using optimal receiving antennas and antenna spacing. The aim of the paper is to verify the concept in Ultra-Wideband by practical measurements. © 2010 IEEE.
    view abstract10.1109/ICDT.2010.14
  • Influence of the real UWB antennas on the AOA estimation based on the TDOA localization technique
    Gerok, W. and El-Hadidy, M. and El Din, S.A. and Kaiser, T.
    MECAP'10, 1st Middle East Conference on Antennas and Propagation (2010)
    Main contribution of this paper is to present the influence of the real ultra-wideband directional antennas on the Angle of Arrival estimation. Furthermore, is to mitigate this undesired impact of the ultra-wideband antennas to improve the overall system performance and enhance the Angle of Arrival estimation accuracy. In the first step we analyze the estimation error due to the antenna induced delay if Vivaldi antennas are used as receiving antennas within two different scenarios. In the second step we present the corrected AoA estimation after mitigation of the error resulting from the antenna induced delay. The Angle of Arrival estimations with error mitigation and without error mitigation are compared. Real measurements are used in the experiments. © 2010-IEEE APS.
    view abstract10.1109/MECAP.2010.5724210
  • Investigation of doppler effect in UWB-based rotor-telemetry system
    Ayadi-Miessen, A. and Kupferschmidt, C. and Le, T.C. and Kuchenbecker, H.-P. and Kaiser, T.
    Proceedings - 2010 International Conference on Advanced Technologies for Communications, ATC 2010 (2010)
    This paper covers a new scenario based on UWB-technique for transmission of data, which is the rotor-telemetry. The rotor-telemetry is a special type of a radio-telemetry, where measuring data of physical parameters like pressure or temperature are captured by sensors predominantly on rotating objects such as shafts or gear parts, transmitted over special on the rotor mounted along-moved antennas and received by static antennas. Most of the typical applications based on the UWB-technique are used on environments, where the channel is time invariant or very slow variant. A new problem appears with this scenario: since the rotor moves fast, the impact of Doppler rises significantly. The consideration of the effect of Doppler in UWB-signals is different than in narrowband signals. In narrowband systems, the Doppler shift is almost equal for all frequencies, so that the compensation is simple by translating the spectrum proportional to the carrier frequency. This assumption is no more fulfilled in UWB-systems, since the low frequencies of the band suffer from less Doppler shift than the upper ones. Not only the radio channel is of importance for the analysis of the Doppler effect but also the geometry of the antenna system has an important impact on understanding the Doppler effect. ©2010 IEEE.
    view abstract10.1109/ATC.2010.5672746
  • Method of doppler estimation for IR-UWB-system based on the rake-receiver
    Ayadi-Miessen, A. and Zhao, Z. and Kupferschmidt, C. and Kuchenbecker, H.-P. and Kaiser, T.
    2010 IEEE International Conference on Ultra-Wideband, ICUWB2010 - Proceedings 1 (2010)
    In [1] a new scenario based on UWB-technique for transmission of data was presented, which is the rotor-telemetry. The rotor-telemetry is a special type of a radio-telemetry, where measuring data of physical parameters like pressure or temperature are captured by sensors predominantly on rotating objects such as shafts or gear parts, transmitted over special on the rotor mounted along-moved antennas and received by static antennas. The antenna on the rotor is rotating with high velocity. A new problem appears with this scenario: since such systems become faster and faster, the impact of Doppler rises significantly. The consideration of the effect of Doppler in UWB-signals is different than in narrowband signals. In narrowband systems, the Doppler shift is almost equal for all frequencies, so that the compensation is simple by translating the spectrum proportional to the carrier frequency. This assumption is no more fulfilled in UWB-systems, since the low frequencies of the band suffer less from Doppler shift than the upper ones. © 2010 IEEE.
    view abstract10.1109/ICUWB.2010.5614730
  • Performance evaluation of blind source separation algorithms base on source signal statistics in convolutive mixtures
    Le, C.T. and Moghaddamnia, S. and Kupferschmidt, C. and Kaiser, T.
    ICCE 2010 - 3rd International Conference on Communications and Electronics (2010)
    In this paper, we have investigated the performance of algorithms, based on second and higher-order statistics, which are developed for blind source separation (BSS) of acoustic signals. Acoustic signals are recorded simultaneously in a reverberant environment and can be described as sums of differently convolved signals. We have performed the performance of the blind algorithms in term of signal to interference ratio (SIR) and the choice of optimal separation filter length and the convergence of both algorithms are studied as well. The results can be used to work out the applicability as well as the parameters setup of such kind of blind algorithms. ©2010 IEEE.
    view abstract10.1109/ICCE.2010.5670669
  • Performance of UWB MIMO relay systems in real UWB channels
    Maichalernnukul, K. and Nguyen, T.K. and Zheng, F. and Kaiser, T.
    Conference Record - Asilomar Conference on Signals, Systems and Computers (2010)
    In this paper, the performance of various ultra-wideband (UWB) multiple-input multiple-output (MIMO) relay systems is evaluated for the first time based on UWB channel measurements. In particular, the measurement results for UWB relay channels in line-of-sight as well as non-line-of-sight indoor environments are presented. The average bit error rates of dual-hop MIMO relay systems and cooperative MIMO relay systems are examined and compared in the measured channels. © 2010 IEEE.
    view abstract10.1109/ACSSC.2010.5757614
  • Practical issues in spectrum sensing for multi-carrier system employing pilot tones
    Cao, H. and Daoud, S. and Wilzeck, A. and Kaiser, T.
    2010 3rd International Symposium on Applied Sciences in Biomedical and Communication Technologies, ISABEL 2010 (2010)
    Multi-carrier techniques such as OFDM are widely adopted in the physical layer of nowadays radio communication and broadcasting systems. Therefore in cognitive radio, a robust spectrum sensing techniques for such signals is highly desired. Comparing with traditional Cyclic Prefix (CP) based method, newly reported Time-Domain Symbol Cross-correlation based spectrum sensing (TDSC) method [1][2] shows both advantages in sensing accuracy and robustness against shortness of and channel time spread pollution to CP. This sensing method is able to sense all multi-carrier signals with repeated pilot patterns. In this paper, further validations of TDSC-NP (Neyman-Pearson) and TDSC-MRC (Maximal Ratio Combining) methods are presented with practical issues taken into account, e.g. noise uncertainty, oscillator imperfection and computational complexity. The feasibility of applying TDSC for sensing Filter Bank Multi-Carrier (FBMC) signal is validated via simulation. Both simulated signal and captured DVB-T signal with real-world multi-path channel fading are analyzed and the sensing performance of captured signal agrees with that of simulated signal very well. ©2010 IEEE.
    view abstract10.1109/ISABEL.2010.5702768
  • Preequalizer design for spatial multiplexing SIMO-UWB TR systems
    Nguyen, H. and Zhao, Z. and Zheng, F. and Kaiser, T.
    IEEE Transactions on Vehicular Technology 59 (2010)
    A spatial multiplexing single-input-multiple-output (SM-SIMO) ultrawideband (UWB) communication system using the time-reversal (TR) technique is proposed in this paper. The system with only one transmit antenna, using a spatial multiplexing scheme, can transmit several independent data streams to achieve a very high data rate. To cope with the long delay spread of the UWB channel, the TR technique is adopted. TR can mitigate not only the intersymbol interference (ISI) but the multistream interference (MSI) caused by multiplexing several data streams simultaneously as well. Preequalization using the channel state information (CSI), which is already available at the transmitter in TR systems, is proposed to further eliminate the ISI and MSI. Simulation results show that the preequalization based on shortened equivalent channels can considerably improve the bit error rate (BER) performance of the system. © 2006 IEEE.
    view abstract10.1109/TVT.2010.2064345
  • Spatial correlation in SM-MIMO-UWB systems using a pre-equalizer and pre-Rake filter
    Nguyen, T.K. and Nguyen, H. and Zheng, F. and Kaiser, T.
    2010 IEEE International Conference on Ultra-Wideband, ICUWB2010 - Proceedings 2 (2010)
    In this paper, we investigate the impact of the spatial correlation on the performance of the spatial multiplexing (SM) Multiple-Input Multiple-Output (MIMO) Ultra-WideBand (UWB) system in which both the pre-equalizer and pre-Rake-filter are deployed at the transmitter. The combination of the pre-equalizer and the pre-filter is to mitigate the Multiple-Stream Interference caused by transmitting several independent data streams simultaneously and the Inter-Symbol Interference while the receivers are kept simple. In order to reduce the complexity of the transmitter, the selective-pre-Rake and the partial-pre-Rake filter are considered. Simulation results show that good performance can be achieved with a limited number of Rake fingers. © 2010 IEEE.
    view abstract10.1109/ICUWB.2010.5616816
  • Spatial correlation in the broadcast MU-MIMO UWB system using a pre-equalizer and time reversal pre-filter
    Nguyen, T.K. and Nguyen, H. and Zheng, F. and Kaiser, T.
    4th International Conference on Signal Processing and Communication Systems, ICSPCS'2010 - Proceedings (2010)
    In this paper, we investigate the impact of the transmit spatial correlation on the performance of the spatial multiplexing Multiple-Input Multiple-Output (MIMO) Multi-User (MU) Ultra-WideBand (UWB) system in which a pre-equalizer and a Time Reversal (TR) pre-filter are deployed at the transmitter. The combination of the pre-equalizer and the pre-filter is to mitigate the Multiple-Stream Interference (MSI) and Multiple-User Interference (MUI) caused by transmitting several independent data streams to different users simultaneously and the Inter-Symbol Interference (ISI) while the receivers are kept simple. In order to reduce the complexity of the transmitter, the selective-TR pre-filter is used. ©2010 IEEE.
    view abstract10.1109/ICSPCS.2010.5709711
  • Spatial fading correlation for semicircular scattering: Angular spread and spatial frequency approximations
    Sieskul, B.T. and Kupferschmidt, C. and Kaiser, T.
    ICCE 2010 - 3rd International Conference on Communications and Electronics (2010)
    Spatial frequency approximation (SFA) of spatial fading correlation (SFC) is addressed for the case that the exact infinite summation of Bessel functions is inconvenient or infeasible. The angular spread is derived for semicircular scattering, especially characterized by uniform, Gaussian, Laplacian, and von Mises distributions. The semicircular scattering on the range (-1/2π, 1/2π] happens, e.g., when the antenna is placed on the wall. In the usual SFA of the SFC, a characteristic function is involved with the infinite integration range due to a small angular spread and a near broadside nominal angle. In this paper, we propose a new SFA of the SFC with a finite integration range. Considering the Laplacian angular distribution, numerical examples illustrate that for a moderate angular spread, the new SFA yields higher accuracy in computing the SFC than the conventional SFA. For the von Mises distribution, the new SFA is able to approximate the SFC, while the ordinary SFA provides discrete solutions, which are unreliable to the SFC approximation. ©2010 IEEE.
    view abstract10.1109/ICCE.2010.5670713
  • Throughput coverage simulations based on signal level measurements at 825 MHz and 3535 MHz
    Thein, C. and Anggraini, A. and Kaiser, T. and Chee, K.L.
    4th International Conference on Signal Processing and Communication Systems, ICSPCS'2010 - Proceedings (2010)
    This contribution compares the predicted downlink throughput coverage of a WiMAX-like system - located in a rural environment - for different operating frequencies and transmit power levels. The throughput, which is simulated using the parameters of the IEEE 802.16e-2005 standard, is based on extensive received signal power level measurements carried out with a mobile radio scanner at the frequencies 825 MHz and 3.5 GHz. The resulting path losses are combined with a virtual transmitter-receiver system to compare the throughput coverage at different frequencies and transmit power levels for each location. The outcome of the throughput prediction clearly shows that in built-up areas the use of lower frequencies is beneficial in terms of both needed transmit power and achievable coverage to provide high data rates over the air. © 2010 IEEE.
    view abstract10.1109/ICSPCS.2010.5709678
  • Ultra Wideband Systems with MIMO
    Kaiser, T. and Zheng, F.
    Ultra Wideband Systems with MIMO (2010)
    Up-to-date coverage of the cutting-edge research on UWB Systems with Multiple Antennas In this book, the authors investigate the benefits of combining UWB and MIMO technologies; highlighting five aspects of this promising research field: channel capacity, space-time coding, beamforming and localization, time-reversal transmission, and UWB-MIMO relay. The book presents a systematic and in-depth discussion for each of the hot topics, providing an insight into the cutting-edge research currently undertaken. It is expected that the ideas and approaches illustrated in this book will inspire sparks for the emerging technologies in short-range high data-rate wireless communications and other related applications. Key Features: • Provides a thorough coverage combining the UWB and MIMO, outlining the opportunities and benefits created by the combination of these technologies • Highlights five aspects of this promising research field: channel capacity, space-time coding, beamforming and localization, time-reversal transmission, and UWB-MIMO relay • Covers UWB-MIMO channel measurement and models This book will serve as an invaluable reference for academic and professional researchers in wireless communications, and graduate students. Engineers and technical professionals will also find the book insightful. © 2010 John Wiley & Sons, Ltd.
    view abstract10.1002/9780470740019
  • UWB MIMO cooperative relay systems: BER analysis and relay regions
    Maichalemnukul, K. and Zheng, F. and Kaiser, T.
    2010 44th Annual Conference on Information Sciences and Systems, CISS 2010 (2010)
    In this paper, bit error rate (BER) analysis is presented for ultra-wideband (UWB) multiple-input multiple-output (MIMO) cooperative relay systems, where partial channel state information (CSI) is only available at the receiver side. In the analysis, decouple-and-forward (DCF) and decode-and-forward (DF) relaying schemes are considered. For these schemes, the relay regions, in which cooperative relaying outperforms direct transmission, and the effects of power optimization are studied through numerical results. ©2010 IEEE.
    view abstract10.1109/CISS.2010.5464739
  • antennas

  • mobile telecommunication systems

  • RFID

  • signal processing

  • ultra-wideband

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