Prof. Dr.-Ing. Rüdiger Kays

associated member

TU Dortmund University

Author IDs

  • A reliable and unobtrusive approach to display area detection for imperceptible display camera communication
    Xu, J. and Klein, J. and Jochims, J. and Weissner, N. and Kays, R.
    Journal of Visual Communication and Image Representation 85 (2022)
    Object framework detection has been extensively studied in computer vision for applications such as document digitization and whiteboard scanning. Similarly, it is essential for display-camera communication systems, particularly when imperceptible data modulation is employed to enable simultaneous video playback and data transmission. Reliable and accurate localization of the encoded display area is critical for data demodulation and decoding. However, existing systems typically adapt established methods developed for other applications that do not meet the system requirements for high-rate data transmission. In this article, we propose a novel method for display area detection in the camera images by embedding a new localization marker into the display corners. While the localization marker is less obtrusive than conventional fiducial markers, our detection algorithm demonstrated excellent reliability regardless of the display content and background, according to simulation and experimental results. In addition, the detector achieved subpixel accuracy and real-time performance with modern smartphones. © 2022 Elsevier Inc.
    view abstract10.1016/j.jvcir.2022.103510
  • Channel Sounding Measurements for 5G Campus Networks in Industrial Environments
    Knitter, M. and Kays, R.
    2022 32nd International Telecommunication Networks and Applications Conference, ITNAC 2022 (2022)
    view abstract10.1109/ITNAC55475.2022.9998355
  • Spatial Reuse Insights for IEEE 802.11ax and IEEE 802.11be Wireless LANs and beyond
    Knitter, M. and Kays, R.
    IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2022-September (2022)
    view abstract10.1109/PIMRC54779.2022.9978080
  • Symbol Position Recovery for Optical Camera Communication with High-Density Matrix Codes
    Xu, J. and Brauers, C. and Klein, J. and Jochims, J. and Kays, R.
    IEEE Transactions on Circuits and Systems for Video Technology (2022)
    view abstract10.1109/TCSVT.2022.3231648
  • Combined spatial division multiplexing and spatial reuse across decentral wireless LANs
    Knitter, M. and Endemann, W. and Kays, R.
    2021 19th Mediterranean Communication and Computer Networking Conference, MedComNet 2021 (2021)
    The upcoming IEEE 802.11ax standard introduces spatial reuse and enhanced spatial division multiplexing as two measures to improve user throughput by parallel transmitting links and spatial streams. Related work shows that the proposed spatial reuse concept does not fully utilize the spatial reuse potential. The standard limits spatial division multiplexing to one network. This paper investigates a spatial division multiplexing concept across multiple, decentrally organized networks to cancel co-channel interference. The paper combines the concept with an improved version of spatial reuse and introduces a corresponding channel access protocol, CSMA/SDMSR. An IEEE 802.11ax based simulation of reference scenarios demonstrates a CSMA/SDMSR system performance improvement up to 108 % and decreased latency compared to standard CSMA/CA. © 2021 19th Mediterranean Communication and Computer Networking Conference, MedComNet 2021.
    view abstract10.1109/MEDCOMNET52149.2021.9501235
  • Influence of Roll-Off Pulse Shaping on a Parallel Sequence Spread Spectrum Signal
    Peter, E.L. and Endemann, W. and Kays, R.
    IEEE International Conference on Industrial Informatics (INDIN) 2021-July (2021)
    Parallel sequence spread spectrum (PSSS) is a novel physical layer (PHY) broadband technique, that offers a flexible resource allocation and benefits against fading on wireless channels at a relatively low complexity. This spread spectrum method may especially be used in industrial radio and for high data rates in the THz range. In this paper, we first present the characteristics of the root-raised cosine (RRC) pulse shaped PSSS signal. We examine the amplitude distribution and the peak-to-average power ratio (PAPR) for different roll-off factors. Surprisingly, for large roll-off values high amplitudes become more likely. We then analyze the performance of PSSS under the influence of a memoryless nonlinearity introduced by a solid-state power amplifier (SSPA) using baseband simulation. This power amplifier (PA) is modeled using the well-established Rapp model. We compare the system to a basic orthogonal frequency-division multiplexing (OFDM) implementation. © 2021 IEEE.
    view abstract10.1109/INDIN45523.2021.9557565
  • Investigations on Temporal Sampling and Patternless Frame Recovery for Asynchronous Display-Camera Communication
    Klein, J. and Xu, J. and Brauers, C. and Jochims, J. and Kays, R.
    IEEE Transactions on Circuits and Systems for Video Technology (2021)
    Alongside classic Visible Light Communication using LEDs and photodiodes, Optical Display-Camera Communication offers another promising way of transmitting data through visible light wirelessly: A display serves as a multi-parallel transmitter array and a camera as the corresponding receiver. Due to the high number of pixels, high data rates in the range of several Mbit/s can be achieved despite comparatively low temporal rates. A major challenge that all high rate system realizations have to overcome is the lack of synchronization between display and camera. Along with varying playback and recording behavior of the devices, this typically results in mixed recordings of display frames in the receiver, which complicates frame decoding. In this paper, we fundamentally investigate the temporal sampling process in display-camera communication. Using our improved modeling we determine the minimum temporal oversampling factor required for lossless frame acquisition, in order to maximize system efficiency in the temporal domain. We propose a solution for the synchronization problem for invisible system approaches with differential modulation, in which the original display frames are recovered from asynchronous recordings in the receiver. Experimental results show that this method works robustly even with high motion background videos and without the need for embedded synchronization markers. IEEE
    view abstract10.1109/TCSVT.2021.3106711
  • Parallel Sequence Spread Spectrum based Ultra-Reliable Low Latency Communication for Factory Automation
    Krishnegowda, K. and Peter, E.L. and Scheide, M. and Wimmer, L. and Kays, R. and Grass, E. and Kraemer, R.
    IEEE International Conference on Emerging Technologies and Factory Automation, ETFA 2021-September (2021)
    We propose a closed-loop industrial radio system with a star topology for factory automation using Parallel Sequence Spread Spectrum (PSSS) technology. This system implements all significant concepts for synchronization, duplex-communication, channel estimation/equalization based on an innovative transceiver concept. The industrial environment tends to have non-line of sight channels that lead to RMS delay spreads of less than 100 ns. Here, we propose a channel equalization scheme to compensate for these delay spreads. Another challenging aspect is the implementation of a code division duplexing (CDD) scheme. We propose a closed-loop system architecture that can achieve the targets set by Industry 4.0 bodies such as IWSAN. This paper gives an overview of the closed-loop systems concept. © 2021 IEEE.
    view abstract10.1109/ETFA45728.2021.9613492
  • CSMA/SR Decentral Spatial Reuse Channel Access Algorithm for Wireless LAN
    Knitter, M. and Endemann, W. and Kays, R.
    International Symposium on Advanced Networks and Telecommunication Systems, ANTS 2020-December (2020)
    The upcoming IEEE 802.11ax standard renews the discussion on spatial reuse by parallel transmitting links. The standard uses carrier sense threshold level and transmit power adjustments to potentially improve performance of the network. Related work shows that allocating dedicated transmit power and rate settings per link is key to fully utilize spatial re-use potential. This paper discusses how to best apply such spatial reuse concepts to a decentral channel access protocol. A state time model reflects fundamental performance drivers and limits of the approach. The proposed CSMA/SR algorithm shows up as a good compromise between needed protocol overhead and achieved throughput improvement. An IEEE 802.11ax based simulation demonstrates a CSMA/SR system performance improvement up to 46 % compared to standard CSMA/CA. © 2020 IEEE.
    view abstract10.1109/ANTS50601.2020.9342755
  • Improved Parallel Sequence Spread Spectrum Transmission for High Bandwidth Efficiency
    Peter, E.L. and Endemann, W. and Kays, R.
    IEEE Vehicular Technology Conference 2020-May (2020)
    Parallel Sequence Spread Spectrum (PSSS) is a spread spectrum physical layer (PHY) offering beneficial properties against the effects of fading as well as the possibility of a flexible resource allocation, while maintaining a low complexity. Additionally it is being investigated for high data rates in the THz range. In this paper, we give an overview on the current state of research on PSSS, its advantages, but also its challenges. We present simulations and measurements comparing the performance of PSSS with OFDM, showing its potential for future wireless communications. © 2020 IEEE.
    view abstract10.1109/VTC2020-Spring48590.2020.9128476
  • On Spatial Reuse Potential for Wireless LANs
    Knitter, M. and Endemann, W. and Kays, R.
    Proceedings of 2020 3rd International Conference on Advances in Electronics, Computers and Communications, ICAECC 2020 (2020)
    Spatial reuse is an approach to better utilize the wireless medium by allowing a certain level of interference between parallel transmitting links. This paper presents a systematic approach to model networks of interfering links. Two proposed algorithms identify best sets for transmit power and rate allocation per link and allow to estimate the spatial reuse potential for a given scenario. Two introduced spatial reuse indicators help to benchmark the performance of any algorithm against the spatial reuse potential. An IEEE 802.11ax simulation using a fading channel model shows that a scheduler can use the identified best sets to increase overall system throughput. For a given example scenario the performance increase is 50 % compared to CSMA/CA time multiplexed channel access. The simulation also shows that IEEE 802.11ax OBSS_PD based spatial reuse does not utilize the full spatial reuse potential. © 2020 IEEE.
    view abstract10.1109/ICAECC50550.2020.9339483
  • Channel measurement campaigns for wireless industrial automation
    Düngen, M. and Hansen, T. and Croonenbroeck, R. and Kays, R. and Holfeld, B. and Wieruch, D. and Wilke Berenguer, P. and Jungnickel, V. and Block, D. and Meier, U. and Schulze, H.
    At-Automatisierungstechnik 67 (2019)
    The factories of the future will be highly digitalized in order to enable flexible and interconnected manufacturing processes. Especially wireless technologies will be beneficial for industrial automation. However, the high density of metallic objects is challenging for wireless systems due to multipath fading. In order to understand the signal propagation in industrial environments, this paper provides results from a number of channel measurement campaigns funded by the German research initiative "Reliable wireless communication in the industry". We give an overview of different measurement scenarios covering visible light communication and radio communication below 6 GHz. We analyze large and small scale parameters as well as delay statistics of the wireless channels. Finally, we discuss the importance of the results for the definition of industrial channel models. © 2019 Walter de Gruyter GmbH, Berlin/Boston.
    view abstract10.1515/auto-2018-0052
  • Modeling Differential Screen-Camera Data Transmission for Parallel Video Presentation
    Brauers, C. and Kays, R. and Klein, J. and Xu, J.
    2018 IEEE Globecom Workshops, GC Wkshps 2018 - Proceedings (2019)
    Optical data transmission from display to camera is a promising new communication concept, which could be a very good solution for wireless communication in different cases. It seems attractive for many conceivable scenarios to maintain the primary function of a screen - displaying a video playback - while transmitting data imperceptible for human viewers. In the DaViD (Data Transmission Using Video Devices) project, we are developing a high-rate data transmission scheme on said display-camera link. To find the optimum parameters for such a transmission, thorough knowledge of the optical channel is needed. In this paper, we introduce a model of our display-camera transmission system, focusing on the peculiarities of an optical free-space channel with display-to-camera projection. We analyze the impact of data overlay onto video content, the influence of non-optimal camera alignment and the need for display-camera synchronization. We employ this channel description in the model of our data transmission system, whose current demonstration setup achieves net data rates of over 10 Mbit/s. © 2018 IEEE.
    view abstract10.1109/GLOCOMW.2018.8644133
  • Orthogonalization of parallel sequence spread spectrum codes for high order modulation
    Endemann, W. and Kays, R. and Peter, E.L.
    Proceedings of the International Symposium on Wireless Communication Systems 2019-August (2019)
    Parallel Sequence Spread Spectrum (PSSS) is a potential physical layer (PHY) for a robust high rate wireless transmission. PSSS uses pseudo noise bipolar m-sequences with increasing cyclic temporal shift as spreading codes. These codes are used similar to the sinusoid carriers of an orthogonal frequency division multiplex (OFDM) system with a spectral efficiency of 1 bit/s/Hz for the simplest case of BPSK modulation. For optimal performance, these codes have to be in exact time synchronization. A disadvantage of unmodified PSSS is the limited orthogonality of its spreading codes, which leads to inter code interference resulting in a BER penalty. This penalty can be mitigated for BPSK and QPSK modulation by an iterative decoding algorithm. For higher modulation such as QAM, this iterative decoding will turn out as suboptimal. In this paper we present a method for the orthogonalization of the m-sequences, thus eliminating the inter code interference and enabling high order modulation for PSSS. © 2019 IEEE.
    view abstract10.1109/ISWCS.2019.8877368
  • ParSec: An innovative radio system for factory automation [ParSec: Ein innovatives Funksystem für die Fertigungsautomation]
    Underberg, L. and Kraemer, R. and Von Hoyningen-Huene, J. and Kays, R.
    At-Automatisierungstechnik 67 (2019)
    As part of "Industry 4.0" wireless communication networks are increasingly incorporated in industrial applications. However, up to now the requirements of factory automation applications, which are especially strict with respect to reliability and latency, are only partly covered by specific wireless technologies like WirelessHART or WSAN. In order to provide a wireless communication system for critical factory automation applications, the ParSec project investigates the promising parallel sequence spread spectrum (PSSS) approach. This article gives an overview of the ParSec system, its properties and scope. PSSS basics are explained and advantages regarding a flexible medium access and resource sharing are pointed out. The integration of the ParSec system into an existing Industrial Ethernet network is discussed. © 2019 Walter de Gruyter GmbH, Berlin/Boston.
    view abstract10.1515/auto-2018-0056
  • Performance of PSSS Systems in Multipath Channels
    Peter, E.L. and Endemann, W. and Kays, R.
    SCC 2019 - 12th International ITG Conference on Systems, Communications and Coding (2019)
    In many current wireless transmission systems, orthogonal frequency-division multiplexing (OFDM) is employed as the default physical layer (PHY). However, new communication systems with extremely high data rates as well as ultra-reliable low-latency communications (URLLC) in the context of factory automation set up new challenges. Therefore, new communication systems might need to rely on alternative PHY solutions. One promising approach is parallel sequence spread spectrum (PSSS). Since PSSS offers flexibility in terms of bandwidth, data rate and resource distribution, a low latency or high data rate can be achieved. Even under critical channel conditions, it seems to be very robust. In this paper, we give an overview of current research concerning PSSS. Furthermore, we analyze the performance of a PSSS system with respect to system design aspects as well as its bit error performance in multipath channels. © 2019 VDE VERLAG GMBH - Berlin - Offenbach.
    view abstract10.30420/454862029
  • Timing Evaluation of Cascaded Industrial Communication Networks
    Von Hoyningen-Huene, J. and Heeren, H. and Underberg, L. and Dietrich, S. and Kroos, P. and Wulf, A. and Wetter, O. and Kays, R.
    IEEE Transactions on Industrial Informatics 15 (2019)
    Wireless extensions of time-critical industrial communication systems could provide many benefits including increased flexibility and mobility. Moreover, they might enable completely new manufacturing solutions. On the other hand, seamless integration to the existing infrastructure and high performance with minimal increase of latency and jitter are key requirements. A wireless network with these features is developed in the project ParSec. Here, especially the MAC layer design and the gateway concepts between the existing Industrial Ethernet solutions and the wireless ParSec system are improved. In this paper, we show the ParSec system's proof of concept using typical industrial components. In the experimental evaluation, low round-trip times and low jitter were measured that satisfy the majority of industrial requirements. © 2005-2012 IEEE.
    view abstract10.1109/TII.2019.2903340
  • Transmitter design and synchronization concepts for DaViD display camera communication
    Xu, J. and Klein, J. and Brauers, C. and Kays, R.
    2019 28th Wireless and Optical Communications Conference, WOCC 2019 - Proceedings (2019)
    Visible Light Communication is a promising technology for data transmission, which has become more and more relevant in recent years. Other than the common approach of modulated LED lighting, display-camera communication has become an attractive novel take on the concept. As outlined in earlier papers, the DaViD (Data Transmission Using Video Displays) system provides a modulation concept allowing for a data overlay onto video content which is nearly invisible to the viewer, i.e. causing hardly any perceptible degradation in video quality. This is achieved by differentially modulating the chrominance information of the underlying video frames with low amplitudes. The resulting color differences within the recorded images can be interpreted by the receiver, allowing for reconstruction of the transmitted data. In this paper, we introduce further system details and improvements to the DaViD concept. In addition to traditional transmission systems, on the display-camera link, the receiver has to be not only temporally but also spatially synchronized to the transmitter. We address the spatial synchronization problem by utilizing localization patterns for detecting the modulation area and a separate optimization on columns and rows for data resampling. Using a slight temporal oversampling, clean data frames can be reconstructed on the receiver side. Based on our modulation and coding concept, we achieve a data rate up to 34.56 Mbit/s in our current demonstration setup with hardly any visible degradation in video quality. © 2019 IEEE.
    view abstract10.1109/WOCC.2019.8770659
  • Bit error performance of a PSSS transmission system in industrial environments
    Underberg, L. and Peter, E.L. and Croonenbroeck, R. and Kays, R.
    IEEE International Workshop on Factory Communication Systems - Proceedings, WFCS 2018-June (2018)
    In various fields of industrial communication, wired networks based on Industrial Ethernet are installed nowadays. Since these wired networks entail high installation and maintenance efforts, wireless solutions gain importance for both existing and future industrial applications. However, their reliability in terms of low latency has to be enhanced, especially in industrial environments. In this context, parallel sequence spread spectrum (PSSS) is a promising approach. Similar to an orthogonal frequency division multiplex (OFDM)-based system, properties like bandwidth and data rate as well as the multiple access can be flexibly chosen in order to adapt the PSSS system to a specific use case. In order to evaluate the PSSS physical layer's (PHY) behavior in an industrial environment, the performance of a PSSS system emulator is compared to a PSSS prototype setup. Here, the PSSS prototype setup shows the current state of functionality of the PSSS system, whereas the system emulator indicates its potential performance. © 2018 IEEE.
    view abstract10.1109/WFCS.2018.8402341
  • Optimized resource allocation for cascaded communication networks in factory automation
    Dietrich, S. and May, G. and Underberg, L. and Kays, R. and Fohler, G.
    Proceedings of the IEEE International Conference on Industrial Technology 2018-February (2018)
    Cascaded communication systems consisting of multiple, hierarchically ordered wired and wireless subnetworks are of increasing interest for industrial applications to support reliability and flexibility simultaneously. Therefore, additionally arising latencies due to the cascading have to be minimized to meet the application's real-time requirements. Within this paper, we identify the resource allocation as promising approach to minimize such latencies. By reviewing basic allocation schemes of wired and wireless communication networks, we show their advantages and disadvantages with respect to the physical data transmission. Based on this comparison, we introduce methods to optimize the resource allocation of individual subnetworks. Moreover, we present an algorithm, which finds an optimized scheduling for the data transmissions in cascaded networks. © 2018 IEEE.
    view abstract10.1109/ICIT.2018.8352423
  • Parallel Sequence Spread Spectrum: Performance Analysis in Industrial Wireless Channels
    Croonenbroeck, R. and Underberg, L. and Endemann, W. and Kays, R.
    Proceedings of the International Symposium on Wireless Communication Systems 2018-August (2018)
    Reliable and low latency wireless networks gain importance in industrial communication. A promising approach in this context is parallel sequence spread spectrum (PSSS). Its parameter set is very flexible and can thus be adapted to specific application requirements including very low latency. Moreover, first evaluations revealed that PSSS might be robust against fading channels, which is desirable in industrial environments. In order to enhance the understanding of the PSSS concept, its behavior in real industrial channels is investigated in this paper. A PSSS baseband simulation is combined with industrial channel transfer functions, which were extracted from comprehensive channel measurements in factory floors and mechanical workshops. In this paper, we evaluate a PSSS system's performance for good, median and bad LOS and NLOS channels. By this we show that PSSS is suitable for industrial environments even in disadvantageous channels. © 2018 IEEE.
    view abstract10.1109/ISWCS.2018.8491193
  • Towards hybrid wired-wireless networks in industrial applications
    Underberg, L. and Kays, R. and Dietrich, S. and Fohler, G.
    Proceedings - 2018 IEEE Industrial Cyber-Physical Systems, ICPS 2018 (2018)
    Cyber-physical systems (CPS) will facilitate current and enable future industrial applications, if interoperability issues are overcome and full flexibility is accessible. However, the currently employed wired networks, especially in demanding factory automation applications, are rigid in their communication protocol and their physical structure. Moreover, they will not be completely replaced by a more flexible and retrofittable wireless network in the near future. In order to support the implementation of industrial CPS, hybrid wired-wireless networks have to be developed. Here, the cooperation of wired and wireless network has to be efficient to fulfill the challenging industrial requirements and maintain the wired network's performance. In this paper, we specify these requirements by reviewing industrial applications and identify the relevant properties of state of the art industrial networks. This review reveals a lack of wired-wireless networks in factory automation, since current wireless networks are not suitable to fulfil the applications' requirements. Therefore, basic wireless concepts are discussed and a recommendation for a suitable hybrid communication network design is given. © 2018 IEEE.
    view abstract10.1109/ICPHYS.2018.8390804
  • A PSSS Approach for Wireless Industrial Communication Applying Iterative Symbol Detection
    Underberg, L. and Croonenbroeck, R. and Wulf, A. and Endemann, W. and Kays, R.
    IEEE Transactions on Industrial Informatics (2017)
    Wireless industrial communication requires high reliability and low latencies. In order to fulfill both requirements simultaneously, wireless approaches are being developed. One of these technologies is parallel sequence spread spectrum (PSSS). In comparison to direct sequence spread spectrum (DSSS) approaches, which employ a set of appropriate pseudo noise (PN)-sequences, PSSS data symbols are spread based on a single cyclically shifted m-sequence. Each cyclic shift of the chosen m-sequence is used as an individual PN-sequence. This enables a code division multiple access (CDMA) scheme with simple processing and thus a fast hardware implementation. In order to investigate the impact of an inaccurate time synchronization, this paper presents a theoretical and simulative PSSS evaluation. Moreover, an iterative symbol detection is introduced, which neutralizes the impact of the non-orthogonal m-sequences and mitigates the degradation due to inaccurate synchronization. In addition, several reasonable resource allocation schemes are presented, which emphasize the PSSS system's flexibility. IEEE
    view abstract10.1109/TII.2017.2779471
  • Coverage Range Analysis and Performance Evaluation of Wireless Technologies in Industrial Channel Conditions
    Wulf, A. and Underberg, L. and Croonenbroeck, R. and Kays, R.
    Communications in Computer and Information Science 764 (2017)
    While current reliable and ultra low latency industrial communication is based on wired fieldbus systems, wireless communication is the key to enable future industrial applications. However, the reliability of state-of-the-art wireless technologies is not sufficient for many industrial application scenarios. Thus, novel wireless approaches are being investigated at the moment, from which three promising physical layer (PHY) technologies are depicted for detailed evaluation in this paper: Ultra Wide Band (UWB), Frequency Hopping Spread Spectrum (FHSS) and Parallel Sequence Spread Spectrum (PSSS). In order to assess each system’s performance, Key Performance Indicators, (KPI) are derived from industrial application constraints. In this paper, industrial applications are therefore categorized by vital requirements such as spatial extent, number of nodes, cycle time, PER and user data length. The depicted technologies are evaluated regarding the KPIs error rate and coverage range in AWGN and industrial fading channel conditions. © 2017, Springer International Publishing AG.
    view abstract10.1007/978-3-319-67876-4_21
  • Measurements for the development of an enhanced model for wireless channels in industrial environments
    Croonenbroeck, R. and Underberg, L. and Wulf, A. and Kays, R.
    International Conference on Wireless and Mobile Computing, Networking and Communications 2017-October (2017)
    Novel wireless systems are often first evaluated by simulation, before prototypes are tested and the concepts are standardized. In order to ensure relevant simulation results, the wireless channel has to be modelled properly and application oriented. Currently, only few considerable industrial channel models are available. The IEEE 802.15.4a model is the most commonly used. CM 7 applies for LOS modelling and CM 8 for NLOS environments. Both are only applicable for distances up to 8 m. In order to enhance the existing channel models, an extended wide band measurement campaign including seven scenarios at three different industrial locations was performed. From different LOS and NLOS measurement series in a warehouse, a manufacturing shop and a mechanical workshop, values for the path loss exponent, RMS delay spread, coherence bandwidth and fading statistics were obtained, valid for distances up to 40 m. Setup, scenarios and the results of these measurements are presented in this paper. The abundance of metallic reflectors and scatterers leads to a dense multipath environment, which causes Rayleigh distributed small scale fading for both LOS and NLOS scenarios. The path loss exponent is smaller than 2 for LOS scenarios and the PDPs show very small power decay constants due to the rich scattering environment. Moreover, the RMS delay spread was found to increase proportionally to the distance. Corresponding to this, the coherence bandwidth decreases inversely proportional to the distance. The measurement results are compared to the related work and especially with the IEEE 802.15.4a channel model. © 2017 IEEE.
    view abstract10.1109/WiMOB.2017.8115764
  • Modulation concepts for high-rate display-camera data transmission
    Kays, R. and Brauers, C. and Klein, J.
    IEEE International Conference on Communications (2017)
    Display-camera data links can be regarded as a massive MIMO visible light communication. They are a research topic since several years. Imperceptible data transmission while simultaneously presenting video sequences for human viewers on the display is an innovative approach allowing for many new applications. Several groups work on this concept. This paper describes a new approach with specific modulation schemes and proposes a system, which combines concepts from digital data transmission and real time video processing while carefully taking the characteristics of the human visual system into account. The modulation parameters are selected as a compromise between picture quality deterioration and decoding performance in terms of data rate and bit error probability. Characterizing a video representation by luminance Y and chrominance U and V as usual in electronic media distribution and video source coding, subjective tests show that data modulation of the chrominance signals is a promising option. An early experimental setup applying modulation of U and V video components already provided data rates of 4.5 Mbit/s at acceptable error rates without significant degradation of perceived video quality. © 2017 IEEE.
    view abstract10.1109/ICC.2017.7996371
  • ParSec: Wireless industrial communication first PSSS measurements in industrial environment
    Underberg, L. and Croonenbroeck, R. and Kays, R. and Kraemer, R.
    IEEE International Workshop on Factory Communication Systems - Proceedings, WFCS (2017)
    Wireless technologies gain importance in various fields of industrial communication as they facilitate control and data acquisition tasks. In this context, Parallel Sequence Spread Spectrum (PSSS) is a promising new approach. The parametrization of a PSSS system is very flexible and thus can be precisely adapted to the application's requirements. Independent of the PSSS parametrization, the transmission resources can be assigned efficiently since their management is very flexible. With full duplex and a resource stream in both up- A nd downlink, even a network with high node density and varying QoS requirements can be served in a single PSSS system. Especially cycle times smaller than 1 ms are possible. A PSSS system for ultra low latency and highly reliable industrial applications is parametrized in the German research project ParSec. In ParSec, the PSSS system is evaluated analytically as well as in practice. In order to allow early measurements, in ParSec a rapid prototype system was developed, with which first PSSS measurements were performed. This paper gives an overview of the fundamental PSSS concept, while it points out the overall system's potential in industrial communication. Moreover, the measurement results are discussed to evaluate the bit error distribution in a PSSS frame. Rolf Kraemer IHP Microelectronics Frankfurt (Oder), Germany. © 2017 IEEE.
    view abstract10.1109/WFCS.2017.7991941
  • Augmenting OFDM wireless local networks with motion detection capability
    Brauers, C. and Endemann, W. and Kays, R.
    IEEE International Conference on Consumer Electronics - Berlin, ICCE-Berlin 2016-October (2016)
    Ubiquitous wireless local networks which use channel transfer function estimation to compensate for echoes on the wireless channel are uniquely suited for motion detection as a secondary use. In this way, added value can be provided without additional hardware. This paper presents a procedure with uses channel state information of an IEEE 802.11 High Throughput wireless link to reliably detect the presence of moving items, such as people crossing a room. By leveraging CSI instead of RSSI, the frequency-selective fading characteristic of indoor wireless channels can be taken into account while eliminating the effect of power level fluctuations in consumer-grade wireless hardware. © 2016 IEEE.
    view abstract10.1109/ICCE-Berlin.2016.7684768
  • Coverage range analysis of wireless technologies for industrial automation: System overview and performance evaluation
    Wulf, A. and Underberg, L. and Kays, R.
    ICETE 2016 - Proceedings of the 13th International Joint Conference on e-Business and Telecommunications 6 (2016)
    Reliable wireless communication is crucial to current and future industrial applications, but is however not yet applicable in many scenarios. Thus novel approaches are being investigated at the moment, from which three physical (PHY) layer technologies are depicted for detailed evaluation in this paper. Preceding the performance analysis, industrial application requirements and constraints as spatial extent, number of nodes, cycle time, PER and user data length are summarized. Error rates and coverage ranges are calculated and presented for Ultra Wide Band (UWB), Frequency Hopping Spread Spectrum (FHSS) and Parallel Sequence Spread Spectrum (PSSS) assuming an AWGN channel. Copyright © 2016 by SCITEPRESS - Science and Technology Publications, Lda. All rights reserved.
    view abstract10.5220/0005971600740083
  • Industrial WSN based on IR-UWB and a low-latency MAC protocol
    Reinhold, R. and Underberg, L. and Wulf, A. and Kays, R.
    Frequenz 70 (2016)
    Wireless sensor networks for industrial communication require high reliability and low latency. As current wireless sensor networks do not entirely meet these requirements, novel system approaches need to be developed. Since ultra wideband communication systems seem to be a promising approach, this paper evaluates the performance of the IEEE 802.15.4 impulse-radio ultra-wideband physical layer and the IEEE 802.15.4 Low Latency Deterministic Network (LLDN) MAC for industrial applications. Novel approaches and system adaptions are proposed to meet the application requirements. In this regard, a synchronization approach based on circular average magnitude difference functions (CAMDF) and on a clean template (CT) is presented for the correlation receiver. An adapted MAC protocol titled aggregated low latency (ALL) MAC is proposed to significantly reduce the resulting latency. Based on the system proposals, a hardware prototype has been developed, which proves the feasibility of the system and visualizes the real-time performance of the MAC protocol. © 2016 by De Gruyter 2016.
    view abstract10.1515/freq-2015-0166
  • Modeling the long term fading behaviour in residential wireless sensor networks
    Schaefer, F.-M. and Kays, R.
    2016 13th IEEE Annual Consumer Communications and Networking Conference, CCNC 2016 (2016)
    Many statistical wireless channel models for different standards and environments have been defined. However, a single stationary statistical model does not reproduce the long term characteristics of the wireless transmission channel sufficiently. When a wireless link is modeled over longer periods of time, changes of the environment must be considered. These changes can be characterized by different phases, which are alternatively experienced by the channel. On top of that, when a whole network is considered, there are interdependencies between the phases experienced by different links. In this paper, a two level hidden Markov wireless residential channel model is described. The global state reflects the presence of residents in the house. It affects all links. The local state of a single link depends on actual movement in the vicinity of that link. Based on the observation of channel measurements a reasonable parameterization is identified. The model can be used to analyze systems for residential control applications with 24/7 operation. © 2016 IEEE.
    view abstract10.1109/CCNC.2016.7444730
  • Parallel Sequence Spread Spectrum: Analytical and simulative approach for determination of bit error probability
    Underberg, L. and Wulf, A. and Croonenbroeck, R. and Endemann, W. and Kays, R.
    IEEE International Conference on Emerging Technologies and Factory Automation, ETFA 2016-November (2016)
    Communication in industrial applications like factory automation (FA) demands very low latency combined with high reliability. Since state of the art wireless technologies are not entirely fulfilling FA requirements, novel approaches are being developed. © 2016 IEEE.
    view abstract10.1109/ETFA.2016.7733502
  • ParSec: A PSSS approach to industrial radio with very low and very flexible cycle timing
    Kraemer, R. and Methfessel, M. and Kays, R. and Underberg, L. and Wolf, A.C.
    European Signal Processing Conference 2016-November (2016)
    Industry 4.0 is a subject of current relevance which targets detailed information acquisition from industrial production processes. Wireless communication to ease this acquisition process is highly interesting but suffers today from problems of low reliability, high latency and small flexibility. ParSec addresses these subjects by investigating an innovative, CDMA based approach with very low latency of < 50 μs, flexible resource block scheduling and BER of ≤ 10-9. While the latency figure is completely based on the assumption that a minimum of 3 symbol durations are needed the BER comes from the requirement specification. Two forms of FEC are used to achieve this requested figure. The radio will be used in the frequency range from 5,725 to 5,875 GHz and work without listen before talk. A rapid prototype has been built to conduct channel measurements and prove the promised properties of the PSSS255 approach. The project is conducted in the framework of other "Industrial Radio" oriented projects supported by the German federal ministry of education and research (BMBF). © 2016 IEEE.
    view abstract10.1109/EUSIPCO.2016.7760443
  • Performance and interoperability evaluation of radiofrequency home automation protocols and Bluetooth Low Energy for smart grid and smart home applications
    Courreges, S. and Oudji, S. and Meghdadi, V. and Brauers, C. and Kays, R.
    2016 IEEE International Conference on Consumer Electronics, ICCE 2016 (2016)
    The paper presents an evaluation of the performances and the coexistence of standard home automation radiofrequency protocols such as KNX-RF Multi, Zigbee and EnOcean with Bluetooth Low Energy protocol available in smartphone and tablets in the domain of smart grid and smart home. This work allows describing an overall interoperable and efficient radiofrequency system in this domain based on the strengths of each available RF standard. © 2016 IEEE.
    view abstract10.1109/ICCE.2016.7430660
  • Adaptive differential refinement of block-matching based correspondence vector fields
    Bruggemann, M. and Kays, R. and Springer, P. and Erdler, O.
    IEEE International Conference on Consumer Electronics - Berlin, ICCE-Berlin 2015-February (2015)
    In this paper we propose a post-processing method for block-matching based correspondence vector fields. We combine image adaptive filtering for object accurate vector field refinement with differential floating point precise optical flow estimation. More precisely, image warping and large cross-adaptive filter kernels are integrated into the Horn and Schunck optical flow estimation approach to break the block structure of the input correspondence vector fields and compute flow field updates fulfilling the smoothness constraint inside object borders. To reduce the influence of occlusion areas we integrate in-loop occlusion detection and adjust the adaptive filter weights after every iteration. © 2014 IEEE.
    view abstract10.1109/ICCE-Berlin.2014.7034317
  • Adaptive predictive block matching with weighted histogram filter postprocessing
    Bruggemann, M. and Kays, R.
    5th IEEE International Conference on Consumer Electronics - Berlin, ICCE-Berlin 2015 (2015)
    In this paper we propose to increase the precision of block matching motion estimation by introducing adaptive weights known from bilateral filtering into the SAD cost function. Estimation is carried out pixel-wise, such that a dense vector field is estimated of same resolution as the input images. A combination of hierarchical and spatio-temporally predictive estimation framework is used for processing. With the proposed method highly precise motion vectors even for fine image structures can be computed. We further propose a histogram based adaptive filter method for vector field postprocessing to reduce the amount of remaining outliers while further increasing the vector field precision to boundaries of moving objects. © 2015 IEEE.
    view abstract10.1109/ICCE-Berlin.2015.7391210
  • Combined block-matching and adaptive differential motion estimation in a hierarchical multi-scale framework
    Brüggemann, M. and Kays, R. and Springer, P. and Erdler, O.
    Proceedings of SPIE - The International Society for Optical Engineering 9443 (2015)
    In this paper we present a combination of block-matching and differential motion field estimation. We initialize the motion field using a predictive hierarchical block-matching approach. This vector field is refined by a pixel-recursive differential motion estimation method. We integrate image warping and adaptive filter kernels into the Horn and Schunck differential optical flow estimation approach to break the block structure of the initial correspondence vector fields and compute motion field updates to fulfill the smoothness constraint inside motion boundaries. The influence of occlusion areas is reduced by integrating an in-the-loop occlusion detection and adjusting the adaptive filter weights in the iteration process. We integrate the combined estimation into a hierarchical multi-scale framework. The refined motion on the current scale is upscaled and used as prediction for block-matching motion estimation on the next scale. With the proposed system we are able to combine the advantages of block-matching and differential motion estimation and achieve a dense vector field with floating point precision even for large motion. © 2015 SPIE.
    view abstract10.1117/12.2179165
  • Frequency hopping for indoor fading channels with varying level of environmental mobility
    Schaefer, F.-M. and Kays, R.
    IEEE Wireless Communications Letters 4 (2015)
    The operation range and reliability of single-carrier wireless transmission systems are limited due to effects of the indoor multipath propagation environment. Multichannel systems can exploit frequency diversity and increase the reliability. Common frequency-hopping protocols change the channel continuously without consideration of the actual channel quality and require regular frame exchange for synchronization. However, in residential application scenarios, control data traffic occurs only very sporadic. In this letter, we describe an asynchronous wireless multichannel system, which utilizes good channels and avoids unnecessary overhead, but at the same time is able to change the frequency in case of a deep fade. The optimal protocol for the initial connection setup is extended for efficient long-term operation. The hopping sequences are modified based on successful transmissions in the past. The method is evaluated and simulated. © 2012 IEEE.
    view abstract10.1109/LWC.2014.2365455
  • Modulation concepts for visible light communication using video displays
    Kays, R.
    5th IEEE International Conference on Consumer Electronics - Berlin, ICCE-Berlin 2015 (2015)
    Visible light communication (VLC) is an attractive alternative to radio frequency communication for applications requiring a wireless short-range link. Different solutions have been developed, usually applying LEDs as transmitters and photodiode receivers. This paper refers to a new system, which uses video displays as massive parallel modulators and cameras as receiver. Data transmission is designed such that it can run on top of a video reproduction without annoying viewers. Different modulation schemes for such a transmission setup can be applied. Their parameters have to be chosen as a compromise between visibility of the data modulation and decoding performance in terms of data rate and bit error probability. In this paper, a system model is introduced that supports the design of the key components of the system. © 2015 IEEE.
    view abstract10.1109/ICCE-Berlin.2015.7391288
  • Radiofrequency interconnection between smart grid and smart meters using KNX-RF and 2.4 GHz standard protocols for efficient home automation applications
    Oudji, S. and Courrèges, S. and Paillard, J.N. and Magneron, P. and Meghdadi, V. and Brauers, C. and Kays, R.
    Journal of Communications 10 (2015)
    Smart grids have attracted considerable interest in the research community and among market actors. The main interest of smart grid is to continuously monitor the whole system energy and optimize it in order to increase the overall energy efficiency. To this purpose, a power energy manager like Linky (ERDF project - France) is needed to ensure the exchange of control and sensor information between the smart grid network and the smart grid end-device equipment within the house. This paper gives a full understanding of the Linky meter that operates under a two-way efficient radio home automation protocol: KNX-RF (868MHz) and ZigBee (2.4 GHz). In this context, the paper presents a study over the KNX-RF protocol with respect to the ZigBee protocol in terms of range, consumption, robustness and configuration. It also provides a study of a typical use-case scenario including Linky smart meter. © 2015 Journal of Communications.
    view abstract10.12720/jcm.10.10.812-820
  • Visible light communication using TV displays and video cameras
    Kays, R.
    2015 IEEE International Conference on Consumer Electronics, ICCE 2015 (2015)
    Visible light communication (VLC) is an attractive alternative to radio frequency communication for applications requiring a wireless short range link. A lot of research work has been done on this topic. Different concepts for VLC are specified in standard IEEE 802.15.7. An interesting feature is the application of existing infrastructures like LED lighting to carry data transmission on top. In this paper, we describe a new approach which applies a video display as transmitter and a digital camera as receiver. Due to a multi-parallel transmission based on individual modulation of all pixels of the screen, high data rates can be achieved. A special feature is the option to design the modulation such that data transfer runs on top of a video presentation without annoying the viewer. © 2015 IEEE.
    view abstract10.1109/ICCE.2015.7066522
  • Aggregated time-critical MAC protocol for factory automation
    Reinhold, R. and Underberg, L. and Kays, R.
    IEEE International Symposium on Industrial Electronics (2014)
    Communication in industrial applications like wireless factory automation demands high reliability and low latency. Due to the fact that state of the art wireless sensor networks do not entirely fulfill the high requirements, new approaches have to be developed. An ultra-wideband system in combination with a MAC protocol for time-critical applications seems to be a promising approach. This paper introduces an optimized MAC protocol to guarantee the stringent real-time requirements of factory automation. Based on a realistic network scenario and IEEE 802.15.4 impulse-radio ultra-wideband physical layer simulations, both reliability and latency are examined. Moreover, the impact of retransmissions is analyzed. The proposed MAC protocol minimizes the resulting latency meeting entirely the requirements of factory automation. © 2014 IEEE.
    view abstract10.1109/ISIE.2014.6864765
  • CAMDF based synchronization for IEEE 802.15.4 IR-UWB systems in rich scattering environments
    Reinhold, R. and Kays, R. and Kledewski, I.
    Proceedings - IEEE International Conference on Ultra-Wideband (2014)
    Wireless communication based on impulse-radio ultra-wideband technology can be basically characterized by a high bandwidth, a low power spectral density and its coexistence capability. Nevertheless, the synchronization of impulse-radio ultra-wideband systems in multipath environments is still a demanding task. In this paper, the synchronization performance of the IEEE 802.15.4 impulse-radio ultra-wideband physical layer is analyzed. Based on channel measurement campaigns, which have been performed in industrial environments, the performance in terms of packet error rate and coverage range is evaluated. A novel synchronization approach based on circular average magnitude difference functions (CAMDF) is presented. The main idea of this approach is to preselect the correlation window by CAMDF calculations. This reduces the fault detection ratio and thus increases system reliability. Apart from the CAMDF based synchronization procedure, the analysis involves the impact of both a fine and coarse synchronization procedure. © 2014 IEEE.
    view abstract10.1109/ICUWB.2014.6958981
  • Energy saving in an integrated home network infrastructure
    Schaefer, F.-M. and Wulf, A. and Rosnick, G. and Kays, R.
    ISCCSP 2014 - 2014 6th International Symposium on Communications, Control and Signal Processing, Proceedings (2014)
    Future home networking applications rely on a converged, robust and easy-to-use network infrastructure. When different technologies complement each other, high efficiency and high coverage range can be achieved. To support application fields like home automation, energy efficient technologies with low data rates must be integrated into the home network. These low data rate networks can be used to configure the high data rate network. In this contribution, the concept of a heterogeneous integrated home network infrastructure is described. Methods to save energy by switching on and off interfaces are presented. Their performance is analyzed by simulation and test bed implementation. By utilizing a wireless low data rate technology for network organization, the energy consumption of a typical home network can be reduced significantly. © 2014 IEEE.
    view abstract10.1109/ISCCSP.2014.6877849
  • Time-critical MAC protocol based on IEEE 802.15.4 IR-UWB optimized for industrial wireless sensor networks
    Reinhold, R. and Underberg, L. and Kays, R.
    IEEE International Workshop on Factory Communication Systems - Proceedings, WFCS (2014)
    Communication in industrial applications like wireless factory automation demands high reliability and low latency. Since state of the art wireless sensor networks do not entirely meet the high requirements, new approaches have to be developed. An ultra-wideband system in combination with a suitable MAC protocol seems to be a promising approach. The proposed ultra-wideband system already provides reduced interference and coexistence issues. Nevertheless, the MAC protocol has to be optimized to guarantee the stringent real time requirements of factory automation. This paper introduces an optimized MAC protocol to be used in combination with the IEEE 802.15.4 impulse-radio ultra-wideband physical layer. Based on a realistic network scenario and physical layer simulations, both reliability and latency are examined. © 2014 IEEE.
    view abstract10.1109/WFCS.2014.6837592
  • Delayed Decision feedback equalization with adaptive noise filtering for IEEE 802.11p
    Budde, R. and Kays, R.
    IEEE Vehicular Networking Conference, VNC (2013)
    In this paper a receiver making use of a complexity-optimized Decision feedback equalization (DFE) structure and adaptive noise filtering is presented. Vehicular transmission systems such as IEEE 802.11p are facing serious challenges originating from the vehicular channel. Due to the channels high Doppler frequencies and long path delays, channel estimation and equalization is a pivotal aspect of the receiver structure. Consequently, a wide variety of tracking concepts have been proposed to tackle the challenge of these time- and frequency-selective channels, ranging from the introduction of additional pilots to complex message passing algorithms. DFE inarguably allows best tracking of the channel's impulse response but is often rejected due to its alleged computational complexity. With the proposed Delayed DFE receiver concept, complex buffering structures are avoided while already existent transmitter structures can be reused. Due to the high precision of the obtained channel state information, further optimization can be applied to adaptively suppress channel noise. © 2013 IEEE.
    view abstract10.1109/VNC.2013.6737585
  • Energy consumption of 6LoWPAN and Zigbee in home automation networks
    Schaefer, F.-M. and Groß, T. and Kays, R.
    IFIP Wireless Days (2013)
    Current home networks are often split up in high data rate networks for multimedia and internet applications and low data rate networks for home automation. This separation leads to inefficient and cumbersome network configurations. It also hinders the widespread use of home automation networks. The IPv6 adaptation for resource constrained devices can help to realize a common addressing scheme for the complete home network. Often the overhead of IPv6 is considered as a drawback for its utilization in home automation networks with low data rates. In this paper, the overhead and the energy consumption of 6LoWPAN in an exemplary home network is calculated and compared with Zigbee. Assuming efficient configurations of both protocol stacks only small differences can be observed. Additionally, the energy consumption of both 6LoWPAN and Zigbee reference implementations on the same hardware is evaluated. Both protocols have comparable energy consumption. For an energy efficient home automation network an intelligent network configuration with only a small number of routers is most important. © 2013 IEEE.
    view abstract10.1109/WD.2013.6686463
  • Gaze adaptive convergence in stereo 3D applications
    Eickelberg, S. and Kays, R.
    Proceedings 2013 IEEE 3rd International Conference on Consumer Electronics - Berlin, ICCE-Berlin 2013 (2013)
    The accommodation vergence conflict is one of the the main sources for visual fatigue caused by stereo 3d. Special care has to be taken during content production in order to maintain a high quality of experience. However, the common approaches of doing so are not always viable and might come with certain disadvantages as well. In this paper, we therefore propose and analyze a method, which solves the accommodation vergence conflict. The basic idea is to constantly shift the point currently gazed upon into the display plane. This is done via convergence shifts of the stereoscopic imagery, which are known to be unperceivable if done slowly. The proposed method is based on gaze tracking, signal processing and disparity maps. © 2013 IEEE.
    view abstract10.1109/ICCE-Berlin.2013.6697981
  • Improvement of IEEE 802.15.4a IR-UWB for time-critical industrial wireless sensor networks
    Reinhold, R. and Kays, R.
    IFIP Wireless Days (2013)
    Wireless sensor networks for industrial factory automation require high reliability and low latency. Since state of the art wireless sensor networks do not entirely meet these requirements, novel system approaches need to be developed. In this regard, ultra wideband communication systems seem to be a promising approach due to their high bandwidth and robustness against frequency selectivity. This paper analyzes the feasibility of the IEEE 802.15.4a impulse-radio ultra-wideband physical layer in the application domain of factory automation. The IEEE 802.15.4e media access control layer which is specified to meet the requirements of industrial applications is included in the analysis. Based on a realistic network and application scenario, the resulting system latency is examined. Parameter adaptions and system enhancements for latency reduction considering both physical and media access control layers are given. As a result, the performance investigation serves as a guide for selecting a suitable wireless system for the establishment of a wireless sensor network. A lower bound of resulting latency is presented. © 2013 IEEE.
    view abstract10.1109/WD.2013.6686434
  • Soft-decision based position estimation for wireless localization in indoor scenarios
    Dammes, T. and Kays, R.
    2013 10th Workshop on Positioning, Navigation and Communication, WPNC 2013 - Proceedings (2013)
    Wireless localization in non-line of sight scenarios suffers from ambiguous range measurements. To solve the resulting problems, a novel probabilistic localization approach is investigated in this work. Following up the soft-ranging algorithm from a former work, we define an algorithm for soft-decision based position estimation. In this paper, we focus on the calculation and evaluation of direct-path probability density functions. The functions serve as a ranging metric instead of the common single-value range estimates. Supporting multiple range hypotheses with corresponding probabilities used as weights, we expect a major improvement of the localization accuracy in critical non-line of sight conditions. The proposed algorithm is evaluated using the IEEE 802.15.4a channel model. © 2013 IEEE.
    view abstract10.1109/WPNC.2013.6533295
  • Study of receiver concepts for vehicular channels in IEEE 802.11p systems
    Budde, R. and Nowak, S. and Kays, R.
    IEEE Vehicular Technology Conference (2013)
    Vehicular channels are among the most challenging wireless channels due to their high Doppler frequencies and multiple path delays. To meet these challenges, the IEEE standard 802.11p was developed. To improve performance, a vast variety of extended receiver concepts has been proposed and evaluated under different test conditions. In this paper, we study the two most promising standard-compliant receiver extensions with respect to their performance in demanding vehicular channels. First, there is maximum ratio combining (MRC), which exploits antenna diversity by using multiple antennas. The second approach is often referred to as decision feedback equalization (DFE), which allows tracking the channel's impulse response throughout the packet without requiring additional pilot data. Consequently, we also present the combination of both approaches to identify complementing effects. © 2013 IEEE.
    view abstract10.1109/VTCSpring.2013.6692770
  • Enhanced frequency hopping for reliable interconnection of low power smart home devices
    Langhammer, N. and Kays, R.
    IWCMC 2012 - 8th International Wireless Communications and Mobile Computing Conference (2012)
    The interconnection of smart home devices plays a key role in future smart grid energy systems. It is reasonable to apply wireless technologies for smart home networks, as they can be easily retrofitted in existing homes. Due to multipath propagation in indoor environments, wireless technologies have to cope with frequency selective fading. Thus, this paper presents an enhanced frequency hopping mechanism for reliable interconnection of low power smart home devices. The evaluations are based on the Bluetooth Low Energy standard. Different options are compared by evaluating the indoor coverage range, the energy consumption, and the latency. © 2012 IEEE.
    view abstract10.1109/IWCMC.2012.6314221
  • Interleaver design for spectrally-efficient bit-interleaved LDPC-coded modulation
    Nowak, S. and Kays, R.
    International Symposium on Turbo Codes and Iterative Information Processing, ISTC (2012)
    A design methodology for interleavers in bit-interleaved coded modulation systems deploying (binary irregular) low-density parity-check (LDPC) codes and higher-order modulation is presented. The interleaver is introduced to balance unequal error protection characteristics inherent in coding and modulation. For this purpose, mapping distributions are used to describe the interleaver configuration. Furthermore, an optimization procedure is applied to derive good mapping distributions for practical block lengths in the order of 10 2-103 bits. Exemplary numerical results are presented for higher-order modulation and LDPC codes as defined in the IEEE standard 802.11n. © 2012 IEEE.
    view abstract10.1109/ISTC.2012.6325235
  • On matching short LDPC codes with spectrally-efficient modulation
    Nowak, S. and Kays, R.
    IEEE International Symposium on Information Theory - Proceedings (2012)
    The combination of low-density parity-check (LDPC) codes and higher-order modulation does usually neither require an interleaver in between nor elaborated signal mapping design rules. However, as the constellation size increases, a matching interleaver can be employed to compensate performance losses, especially in case of structured codes. This interleaver can be generally described by mapping distributions. In this paper, we discuss optimized mapping distributions for short LDPC codes, i.e. in the order of 10 2-10 3 bits. We point out that mapping distributions optimized by means of density evolution may not be suited for short codes. An alternative framework is introduced that utilizes an extended version of extrinsic information transfer functions. Their visualization feature helps to identify good mapping distributions for short codes. © 2012 IEEE.
    view abstract10.1109/ISIT.2012.6284238
  • Performance evaluation of wireless home automation networks in indoor scenarios
    Langhammer, N. and Kays, R.
    IEEE Transactions on Smart Grid 3 (2012)
    Transmission of control information in home local networks is gaining increasing importance. Especially in the context of smart grids several applications already exist and evolve that demand the transmission of control information in home networks. Important examples are the so called smart homes and intelligent buildings, where household appliances and sensor devices are interconnected. They are remotely controlled by an automated energy management system (EMS) according to the demands of the overlying smart grid. This paper presents a methodology for the evaluation of wireless smart homes and home automation networks (HANs) in indoor scenarios. The methodology is applied to investigate the performance of actual wireless technologies that can be used to interconnect devices in a smart home environment. The technologies are compared with each other by investigating the performance in realistic European indoor scenarios. Additionally, they are evaluated with respect to their reliable indoor coverage range. The main intention of this paper is to provide a decision guideline, which wireless standard is most suitable for a certain smart home scenario. © 2010-2012 IEEE.
    view abstract10.1109/TSG.2012.2208770
  • Probabilistic soft-range estimator for wireless localization in indoor scenarios
    Dammes, T. and Kays, R.
    2012 Ubiquitous Positioning, Indoor Navigation, and Location Based Service, UPINLBS 2012 (2012)
    Currently, ultra-wideband develops towards a suitable technology for wireless indoor localization with sub-meter accuracy. Still, the indoor channel complicates the correct interpretation of the measurement especially in non-line-of-sight scenarios. This paper deals with the range estimation in challenging indoor channels as a first step of robust indoor localization. Contrary to the classical hard-decision range estimators, we propose a soft-range estimator which outputs a direct-path probability density function with multiple possible distances and corresponding likelihoods. The proposed method is evaluated based on wideband channel measurements and compared with common state-of-the-art threshold methods. © 2012 IEEE.
    view abstract10.1109/UPINLBS.2012.6409752
  • Technical and economic analysis of future smart grid applications in the E-DeMa project
    Belitz, H.-J. and Winter, S. and Müller, C. H. and Langhammer, N. and Kays, R. and Wietfeld, C. and Rehtanz, C.
    IEEE PES Innovative Smart Grid Technologies Conference Europe (2012)
    The increasing power feed-in from renewable energy sources entails an impact on the operation of transmission and distribution grids as well as the energy market and its players. It offers new opportunities for existing market players to expand their business and supports the market launch for new market players with new products. In this paper, different electricity products which are tested within the field testing deployment of the German research project 'Development and Demonstration of Locally Networked Energy Systems to the E-Energy Marketplace of the Future' (E-DeMa) will be described. To provide these demand-oriented tariffs, an appropriate well dimensioned information and communication infrastructure and its components are required and therefore described in detail. Three scenarios and four topologies are defined for the analysis of the technical and economic potential for market players regarding these products. At the end, the results for the market players customer, retailer and aggregator are presented. © 2012 IEEE.
    view abstract10.1109/ISGTEurope.2012.6465663
  • Temporally recursive robust detail reconstruction from stereo 3D sequences
    Brüggemann, M. and Kays, R. and Springer, P. and Nishi, T. and Erdler, O.
    IEEE International Conference on Consumer Electronics - Berlin, ICCE-Berlin (2012)
    Current HD and 3D TV sets still have to cope with various input content resolutions that have to be displayed in native Full HD or higher resolution. Typical up-scaling methods only make use of spatial information in order to compute a high resolution output. Most of these methods show a low ability to reconstruct high frequency details. In this paper a method for reconstructing details from multiple input frames of a Stereo 3D sequence and generating a high detail output is presented. Utilizing temporally recursive processing, a memory efficient method is realized, which can be used for detail level enhancement post-processing in current 3D TV sets. Due to internal reliability estimation for motion and disparity vectors, the proposed method shows a high robustness against artifacts from erroneous motion and disparity compensation. © 2012 IEEE.
    view abstract10.1109/ICCE-Berlin.2012.6336505
  • Channel models for the design of OFDM-based wireless indoor transmission
    Reinhold, R. and Kays, R.
    Proceedings of the International Symposium on Wireless Communication Systems (2011)
    Comprehensive and well-founded knowledge of the wireless indoor channel is fundamental in order to enable realistic modeling of the dynamic channel characteristics. Many modeling approaches are available in the literature. However, the usage of a single representative channel model is desirable to ensure scientific reproducibility and a common basis for system design. In this paper, the often cited channel model of the IEEE 802.11n task group (TGn) is analyzed in comparison to a large number of channel measurements in home environments. A non-negligible deviation between both approaches can be noticed. In order to overcome this divergence, parameter modifications for the IEEE 802.11n model are proposed to match the measurement results. © 2011 IEEE.
    view abstract10.1109/ISWCS.2011.6125436
  • Dynamic frequency selection for next generation hierarchical wireless home area networks
    Budde, R. and Langhammer, N. and Schilling, C. and Kays, R.
    IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, BMSB 2011 - Conference Programme (2011)
    This article presents a dynamic frequency selection algorithm for next generation wireless home area networks based on the IEEE 802.11 family of standards. In contrast to existing WLANs, the presented architecture enables a wireless network to operate on multiple channels. This is achieved by using a hierarchical networking concept by combining a WLAN and a ZigBee network. In this approach, the ZigBee network is used as a control network to transmit messages in order to set the WLAN transmission parameters. Finally, the results of a practical implementation and evaluation are presented. © 2011 IEEE.
    view abstract10.1109/BMSB.2011.5954927
  • Efficient adaptation of modulation and coding schemes in high quality home networks
    Koetz, H. and Kays, R.
    Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 6557 (2011)
    The increasing number of wireless devices exchanging high quality digital multimedia content within the home necessitates high rate, reliable transmission technologies, like IEEE 802.11n. Though providing very high throughput, IEEE 802.11n is not perfectly adapted to the requirements of a wireless multimedia transmission. However, the IEEE 802.11n amendment allows for efficient adaptation of modulation and coding schemes (MCS) to optimize achievable throughput and to fulfill quality of service requirements without any effort for the user. This paper describes an MCS adaptation scheme using information from both PHY and MAC layer with the objective to choose the optimal MCS in an autonomous, fast and robust way which can be applied to both a single link and an entire network. In contrast to existing adaptation schemes, it accounts for volatile channel conditions as well as increased collision probability in dense wireless home networks. © 2011 Springer-Verlag.
    view abstract10.1007/978-3-642-19167-1_8
  • Evaluation of wireless smart metering technologies in realistic indoor channels
    Langhammer, N. and Kays, R.
    Proceedings of the International Symposium on Wireless Communication Systems (2011)
    The European energy system is currently evolving into a smart grid, and the transmission of metering values between smart meters is gaining increasing importance. Since wireless technologies have a high flexibility and can be easily integrated into existing installations, it is feasible to use them for transmission of metering values. This paper presents an evaluation of wireless smart metering standards operating in the 868 MHz frequency band according to European regulation. The standards are compared by evaluating the indoor coverage range and the energy consumption. © 2011 IEEE.
    view abstract10.1109/ISWCS.2011.6125389
  • High efficiency broadband transmission with LDPC codes over GF(2s)
    Nowak, S. and Smietanka, G. and Kays, R.
    IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, BMSB 2011 - Conference Programme (2011)
    In this paper, we discuss the suitability and the improvement potential of LDPC codes over a finite extension field GF(2 s) for future high efficiency broadband transmission systems through comparison with state-of-the-art coding schemes, i.e. LDPC codes according to IEEE 802.11n and DVB-X2. We first point out the differences between non-binary LDPC codes and their binary counterparts and discuss their advantages for high efficiency broadband transmission systems. For this, two mapping strategies can be introduced which allow for directly combining higher-order modulation and non-binary LDPC codes. We present simulation results in terms of bit error rates and packet error rates for various higher-order (square) quadrature amplitude modulations and LDPC codes over different finite extension fields for the AWGN channel and the Rayleigh fading channel. The evaluation reveals that the application of non-binary LDPC codes allows for the design of efficient transmission schemes with high spectral efficiencies. However, this is achieved at the expense of increased complexity. © 2011 IEEE.
    view abstract10.1109/BMSB.2011.5954946
  • PHY modifications of IEEE 802.11 systems for transmission at very low SNR
    Langhammer, N. and Reinhold, R. and Kays, R.
    2011 8th International Workshop on Multi-Carrier Systems and Solutions, MC-SS 2011 (2011)
    Consumer electronic devices based on IEEE 802.11 are widely-used in home networks. Recent evolution of IEEE 802.11 mainly focused on increased data rates. Besides, the transmission of control information in smart home networks is gaining increasing importance with the emergence of the "Internet of Things". This scenario demands robust and reliable transmission at low signal to noise ratio (SNR) while allowing for lower data rates. Therefore, this paper presents physical layer (PHY) modifications of IEEE 802.11 systems to increase the SNR robustness and communication range by reusing common system components. The performance of the presented modifications is evaluated in terms of resulting bit-error-rate (BER). © 2011 IEEE.
    view abstract10.1109/MC-SS.2011.5910716
  • Reliable broadcast transmission in vehicular networks based on fountain codes
    Budde, R. and Nowak, S. and Kays, R.
    IEEE Vehicular Technology Conference (2011)
    Car-to-car and car-to-infrastructure communications are currently under intense research as they enable a wide variety of applications. Besides security-driven applications which require only small amounts of individual data there are also applications which require medium to high amounts of uniform data delivered to an unknown number of nodes. For this kind of broadcast and multicast applications, the use of fountain codes is highly suitable. In this paper, we investigate the applicability of fountain codes in an infrastructure-based automotive communication system and introduce an expedient method to design a system deploying IEEE 802.11p and fountain codes. By means of simulation results obtained for three representative vehicular scenarios we compare the performance of our method to an alternative method also applied in this field, i.e. the data carousel. For specific configurations the system based on fountain codes outperforms the conservative approach by a factor of four in terms of the overall throughput and thus provides the potential to significantly increase the overall efficiency. ©2011 IEEE © 2011 IEEE.
    view abstract10.1109/VETECS.2011.5956793
  • Towards a convergent digital home network infrastructure
    Nowak, S. and Schaefer, F.-M. and Brzozowski, M. and Kraemer, R. and Kays, R.
    IEEE Transactions on Consumer Electronics 57 (2011)
    Many communication standards are available to set up consumer home networks. An intelligent combination of wired and wireless communication technologies allows exploiting many technology specific advantages while compensating disadvantages. Such a convergent digital home network infrastructure increases robustness, coverage range and availability of applications and services. In this paper, we discuss the general concept of such home networks. We present the Inter-MAC convergence sublayer as a very first approach to this concept. With the help of a typical scenario we demonstrate its feasibility. The recently initiated standardization activity IEEE P1905.1 is introduced. A global standard for convergent digital home networks can be the basis for a user-friendly network of consumer electronic devices in the home. © 2006 IEEE.
    view abstract10.1109/TCE.2011.6131143
  • Detecting QoS degradation in wireless networks to assist reliable media streaming
    Dammes, T. and Schilling, C. and Kays, R.
    Proceedings of the International Symposium on Consumer Electronics, ISCE (2010)
    This paper describes an approach to detect Quality of Service degradation due to packet congestion within wireless networks. The proposed approach can assist management systems to detect a degradation based on easy determinable packet metrics. Metrics like interface queue length, round trip times and retry ratio are evaluated regarding thresholds and detection performance. With a combination of metrics, a robust detection can be achieved for TCP and UDP streams using a IEEE 802.11 a/b/g ad-hoc network. As soon as a detection event occurs, a channel transition is engaged as an exemplary countermeasure. This successfully solves transmission problems due to congestion. © 2010 IEEE.
    view abstract10.1109/ISCE.2010.5523707
  • Efficiency of frame aggregation in wireless multimedia networks based on IEEE 802.11n
    Hoffmann, O. and Kays, R.
    Proceedings of the International Symposium on Consumer Electronics, ISCE (2010)
    This paper evaluates the major MAC enhancement of IEEE 802.11n to realize high throughput, i.e. frame aggregation. In contrast to existing studies of this enhancement, we analyze the efficiency instead of the mere performance. The results show significant efficiency improvement by frame aggregation. Furthermore, the efficiency analysis leads to important conclusions for system configuration and adaptation and reveals effects which are beyond the scope of existing work. It is shown that the most feasible configuration is to apply maximum aggregation and to adapt the modulation and coding scheme (MCS) instead of the frame size. Furthermore, the efficiency analysis points out that in case the network is not saturated the 20 MHz mode is more efficient than the 40 MHz option. ©2010 IEEE.
    view abstract10.1109/ISCE.2010.5523729
  • Prioritized medium access in ad-hoc networks with a systemclick model of the IEEE 802.11n MAC
    Hoffmann, O. and Schaefer, F.-M. and Kays, R. and Sauer, C. and Loeb, H.-P.
    IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC (2010)
    For ad-hoc home networks without central coordinator, IEEE 802.11 systems merely support service differentiation. In many usage scenarios of a typical home network with applications requiring a strict quality of service (QoS), this MAC functionality is not sufficient. In order to counteract this problem, we developed in previous works a modified MAC scheme based on the IEEE 802.11 enhanced distributed channel access (EDCA) function. This paper describes enhancements of the modified MAC scheme enforcing prioritized medium access for strict QoS applications. For the first time, the established concept is realized in a distributed way with in-band signaling. Our enhanced MAC is embedded into a comprehensive IEEE 802.11n reference application to demonstrate its effectiveness in combination with the latest amendments like frame aggregation. The reference application is modeled in SystemClick, a framework for describing and evaluating packet processing applications on resource constraint network nodes. This enables functional validation and provides a path to future, cost-efficient implementations on programmable devices. On this basis, the paper presents simulation results substantiating the significant improvement of QoS parameters like delay and throughput. Besides enforcing strict priorities, collisions can be reduced to zero and the average waiting time can be decreased by up to 33 % for typical usage scenarios. ©2010 IEEE.
    view abstract10.1109/PIMRC.2010.5671829
  • automation

  • local networks

  • smart homes

  • ultra-wideband

  • wireless sensor networks

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