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PhD Thesis on Autonomous Swarm Navigation

18.06.2020

Siwei Zhang, Autonomous Swarm Navigation, Christian-Albrechts-Universität zu Kiel, 2020.

Journal Publication on Swarm Navigation

06.05.2020

S. Zhang, R. Poehlmann, T. Wiedemann, A. Dammann, H. Wymeersch, and P.A. Hoeher, "Self-aware swarm navigation in autonomous exploration missions," Proceedings of the IEEE, vol. 108, no. 7, pp. 1168-1195, Jul. 2020. DOI

Abstract

A multitude of autonomous robotic platforms collectively organized as a swarm attracts increasing attention for remote sensing and exploration tasks. A navigation system is essential for the swarm to collectively localize itself as well as external sources. In this article, we propose a self-aware swarm navigation system that is conscious of the causality between its position and the localization uncertainty. This knowledge allows the swarm to move in a way to not only account for external mission objectives but also enhance position information. Position information for classical navigation systems has already been studied with the Fisher information (FI) and Bayesian information (BI) theories. We show how to extend these theories to a self-aware swarm navigation system, particularly emphasizing the collective performance. In this respect, fundamental limits and geometric interpretations of localization with generic observation models are discussed. We further
propose a general concept of FI and BI based information seeking swarm control. The weighted position Cramér–Rao bound (CRB) and posterior CRB (PCRB) are employed flexibly as either a control cost function or constraints according to different mission criteria. As a result, the swarm actively adapts its position to enrich position information with different emerging collective behaviors. The proposed concept is illustrated by a case study of a swarm mission for gas exploration on Mars.

Journal Publication on Localization

14.04.2020

S. Zhang, E. Staudinger, T. Jost, W. Wang, C. Gentner, A. Dammann, H. Wymeersch, and P.A. Hoeher,
"Distributed direct localization suitable for dense networks," IEEE Transactions on Aerospace and Electronic Systems, vol. 56, no. 2, pp. 1209-1227, Apr. 2020. DOI

Abstract

Traditional network localization algorithms contain ranging and localization steps, which have systematic disadvantages. We propose an algorithm dubbed direct particle filter based distributed network localization (DiPNet). A node's location is directly estimated from the received signals, incorporating location uncertainty of neighboring nodes. The propagation effects on DiPNet become insignificant for dense networks, due to the massive-link collective physical layer processing. DiPNet achieves a near-optimal performance with low complexity, which is particularly attractive for realtime dense-network localization.

Journal Publication on Multi-Mode Antennas

14.04.2020

N.L. Johannsen, N. Peitzmeier, P.A. Hoeher, and D. Manteuffel, "On the Feasibility of Multi-Mode Antennas in UWB and IoT Applications below 10 GHz," in IEEE Communications Magazine, vol. 58, no. 3, pp. 69-75, March 2020, DOI

Abstract

While on one hand 5G and beyond 5G networks are challenged by ultra-high data rates in wideband applications like 100+ Gb/s wireless Internet access, on the other hand they are expected to support reliable low-latency Internet of Things applications with ultra-high connectivity. These conflicting challenges are addressed in a system proposal dealing with both extremes. In contrast to most recent publications, focus is on the frequency domain below 10 GHz. Toward this goal, multi-mode antenna technology is used, and different realizations, offering up to eight uncorrelated ports per radiator element, are studied. Possible baseband architectures tailored to multimode antennas are discussed, enabling different options regarding precoding and beamforming.

Journal Publication on Multi-Mode Antennas

26.03.2020

N.L. Johannsen and P.A. Hoeher, "Single-Element Beamforming using Multi-Mode Antenna Patterns," in IEEE Wireless Communications Letters, vol. 9, no. 7, pp. 1120-1123, Jul. 2020. DOI

Abstract

Multi-mode antennas have recently been studied for communication as well as localization purposes. In this work, the capabilities provided by a single planar multi-mode radiator as a steerable multi-port antenna are explored. As an original contribution, the radiation characteristics of individual groups of modes of the single radiator are combined to optimize beamforming performance. Three possible codebook realizations resulting from the optimization of gain, element factor, and, as a new criterion, gain by element factor are studied and compared. Numerical results show that the gain can be enhanced by about 3 dB at some angles.

PhD Thesis on Visible Light Communications

27.01.2020

G.J.M. Forkel, Binäre Superpositionsmodulation beschränkter Sequenzen und ihre Anwendung in der optischen Unterwasserkommunikation, Christian-Albrechts-Universität zu Kiel, 2020.

Journal Publication on Visible Light Communications

28.11.2019

A. Krohn, G.J.M. Forkel, P.A. Hoeher, and S. Pachnicke, "LCD-based optical filtering suitable for non-imaging channel decorrelation in VLC applications," IEEE/OSA Journal of Lightwave Technology, vol. 37, no. 23, pp. 5892-5898, Dec. 2019. DOI

Abstract

A novel approach for optical channel decorrelation in visible light communication (VLC) multiple-input multiple-output (MIMO) systems is presented. Frequently, illumination fixtures employing an array of white light emitting diodes (LEDs) are suggested for simultaneous illumination and data transmission. As white LEDs share the same optical spectrum and due to diffuse light propagation, a separation of the data streams at the receiver side is difficult, even if multiple photodetectors are applied, but necessary. As opposed to software-based solutions, our approach to the interference problem works in the hardware domain: a liquid crystal display (LCD) is placed in front of the photodetectors. This LCD suppresses the interference caused by modulated light sources and by ambient light. The LCD can be configured to form dynamic receiver apertures in the MIMO setup under investigation. In order to assess the main functionality of the proposed concept, a mixed hardware/software approach is performed. In an experimental testbed, we chose a black-and-white LCD with high contrast, i.e., with high transmittance ratio. We carried out measurements of the transmittance factors in “on” and “off” states, and created a numerical model of the selected LCD. Based on this model and on ray-tracing simulations of the environment, an analytical upper bound on the bit error rate is evaluated for a given VLC indoor scenario. Spatial modulation benefits with an improvement of up to 27 dB from the proposed kind of optical filtering.

Book Publication on Visible Light Communications

30.09.2019

P.A. Hoeher, Visible Light Communications: Solutions Manual. Munich: Hanser Fachbuch, 2019, ISBN: 978-3-446-46303-5.

Abstract

Visible Light Communication (VLC) is an emerging wireless data transmission technology. Light is used simultaneously for illumination as well as for communication and/or positioning purposes. If fully networked, dubbed Li-Fi, VLC systems complement Wi-Fi access points. VLC is an incident of optical wireless communications (OWC). OWC systems provide high data security, are license-free, and may substitute radio systems when these either fail or are not permitted. VLC technology enhances smart lighting infrastructure and Internet-of-Things (IoT) use cases. LED-based Car-to-X communication is an enabling platform towards autonomous driving.

This workbook complements the textbook “Visible Light Communications: Theoretical and Practical Foundations” and the exercises therein. The following areas are covered: OWC applications, fundamentals of illumination engineering, channel modeling, optical intensity modulation schemes, VLC standardization efforts, the software-defined radio concept, selection criteria of photonic devices, fundamental circuit designs, and visible light positioning.

The book is written for students in electrical and information engineering or adjacent areas, as well as for engineers, information scientists, and physicists in research and development.

 

Journal Publication on Magnetic Communications

13.08.2019

M. Hott, P.A. Hoeher, and S. Reinecke, "Magnetic communication using high-sensitive magnetic field detectors," Sensors, vol. 19, no. 15, article ID 3415, Aug. 2019. DOI

Abstract

In this article, an innovative approach for magnetic data communication is presented. For this purpose, the receiver coil of a conventional magneto-inductive communication system is replaced by a high-sensitivity wideband magnetic field sensor. The results show decisive advantages offered by sensitive magnetic field sensors, including a higher communication range for small receiver units. This approach supports numerous mobile applications where receiver size is limited, possibly in conjunction with multiple detectors. Numerical results are supported by a prototype implementation employing an anisotropic magneto-resistive sensor.

Journal Publication on Visible Light Communications

13.08.2019

G.J.M. Forkel, A. Krohn, and P.A. Hoeher, "Optical interference suppression based on LCD-filtering," Applied Sciences, vol. 9, no. 15, article ID 3134, Aug. 2019. DOI

Abstract

Using light emitting diodes (LED) for the purpose of simultaneous communication and illumination is known as visible light communication (VLC). Interference by ambient light sources is among the most critical challenges. Owing to the wideband VLC spectrum, the efficiency of wavelength-dependent optical filtering is limited, especially in the presence of sunlight. Multi-user VLC causes additional interference, since LEDs are characterized by a wide viewing angle. Although algorithm-based interference suppression is a feasible method, receiver saturation and especially noise enhancement are two challenges that can only by addressed effectively by filtering in the optical domain prior to the photodetector. In this publication, we propose the use of a liquid-crystal display (LCD) as receiver-side filter unit. The main advantage of this technology is the possibility to focus the field-of-view of the receiver on a specific light source and thereby suppress interference. Interference by ambient light, modulated interference and multi-aperture interference are introduced and signal-to-interference ratio improvements are derived using experimental results for a given LCD characteristic. By deriving the bit error rate for MIMO communications, the potential of the proposed interference reduction method is demonstrated.

Journal Publication on Direction of Arrival Estimation by Multi-Mode Antennas

13.08.2019

S. Zhang, E. Staudinger, T. Jost, W. Wang, C. Gentner, A. Dammann, H. Wymeersch, and P.A. Hoeher, "Distributed direct localization suitable for dense networks," IEEE Transactions on Aerospace and Electronic Systems, accepted for publication.

Abstract

Traditional network localization algorithms contain ranging and localization steps, which have systematic disadvantages. We propose an algorithm dubbed direct particle filter based distributed network localization (DiPNet). A node's location is directly estimated from the received signals, incorporating location uncertainty of neighboring nodes. The propagation effects on DiPNet become insignificant for dense networks, due to the massive-link collective physical layer processing. DiPNet achieves a near-optimal performance with low complexity, which is particularly attractive for realtime dense-network localization

Book Publication on Visible Light Communications

18.06.2019

P.A. Hoeher, Visible Light Communications: Theoretical and Practical Foundations. Munich: Hanser Fachbuch, July 2019, ISBN: 978-3-446-46206-9.

Abstract

Visible Light Communication (VLC) is an emerging wireless data transmission technology. Light is used simultaneously for illumination as well as for communication and/or positioning purposes. If fully networked, dubbed Li-Fi, VLC systems complement Wi-Fi access points. VLC is an incident of optical wireless communications (OWC). OWC systems provide high data security, are license-free, and may substitute radio systems when these either fail or are not permitted. VLC technology enhances smart lighting infrastructure and Internet-of-Things (IoT) use cases. LED-based Car-to-X communication is an enabling platform towards autonomous driving.

The textbook covers OWC applications, fundamentals of illumination engineering, channel modeling, optical intensity modulation schemes, VLC standardization efforts, the software-defined radio concept, selection criteria of photonic devices, fundamental circuit designs, and visible light positioning.

The book is written for students in electrical and information engineering or adjacent areas, as well as for engineers, information scientists, and physicists in research and development.

 

Journal Publication on Simultaneous Wireless Information and Power Transfer

09.04.2019

P.A. Hoeher, "FSK-based simultaneous wireless information and power transfer in inductively coupled resonant circuits exploiting frequency splitting," IEEE Access, vol. 7, pp. 40183-40194, Mar. 2019.

Abstract

Inductively coupled resonant circuits are affected by the so-called frequency splitting phenomenon at short distances. In the area of power electronics, tracking of one of the peak frequencies is state-of-the-art. In the data transmission community, however, the frequency splitting effect is often ignored. Particularly, modulation schemes have not yet been adapted to the bifurcation phenomenon. We argue that binary frequency shift keying (2-ary FSK) is a low-cost modulation scheme which well matches the double-peak voltage transfer function H(s), particularly when the quality factor Q is large, whereas most other modulation schemes suffer from the small bandwidths of the peaks. Additionally we show that a rectified version of 2-ary FSK, coined rectified FSK (RFSK), is even more attractive from output power and implementation points of view. Analytical and numerical contributions include the efficiency factor, the impulse response, and the bit error performance. A low-cost noncoherent receiver is proposed.  Theoretical examinations are supported by an experimental prototype.

 

Journal Publication on Multi-Mode Antenna Modeling

21.02.2019

S.A. Almasri, R. Pöhlmann, N. Doose, P.A. Hoeher, and A. Dammann, "Modeling aspects of planar multi-mode antennas for direction-of-arrival estimation," IEEE Sensors Journal, vol. 19, no. 12, pp. 4585-4597, Jun. 2019.

Abstract

Multi-mode antennas are an alternative to classical antenna arrays, and hence a promising emerging sensor technology for a vast variety of applications in the areas of array signal processing and digital communications. An unsolved problem is to describe the radiation pattern of multi-mode antennas in closed analytic form based on calibration measurements or on electromagnetic field (EMF) simulation data. As a solution, we investigate two modeling methods: One is based on the array interpolation technique (AIT), the other one on wavefield modeling (WM). Both methods are able to accurately interpolate quantized EMF data of a given multi-mode antenna, in our case a planar four-port antenna developed for the 6-8.5 GHz range. Since the modeling methods inherently depend on parameter sets, we investigate the influence of the parameter choice on the accuracy of both models. Furthermore, we evaluate the impact of modeling errors for coherent maximum-likelihood direction-of-arrival (DoA) estimation given different model parameters. Numerical results are presented for a single polarization component. Simulations reveal that the estimation bias introduced by model errors is subject to the chosen model parameters. Finally, we provide optimized sets of AIT and WM parameters for the multi-mode antenna under investigation. With these parameter sets, EMF data samples can be reproduced in interpolated form with high angular resolution.

Journal Publication on Direction of Arrival Estimation by Multi-Mode Antennas

24.01.2019

R. Pöhlmann, S.A. Almasri, S. Zhang, T. Jost, A. Dammann, and P.A. Hoeher, "On the potential of multi-mode antennas for direction-of-arrival estimation," IEEE Transactions on Antennas and Propagation, vol. 67, no. 5, pp. 3374-3386, May 2019. DOI

Abstract

A multi-mode antenna (MMA) can be an interesting alternative to a conventional phased antenna array for directionof- arrival (DoA) estimation. By MMA we mean a single physical radiator with multiple ports, which excite different characteristic modes. In contrast to phased arrays, a closed-form mathematical model of the antenna response, like a steering vector, is not straightforward to define for MMAs. Instead one has to rely on calibration measurement or electromagnetic field (EMF) simulation data, which is discrete. To perform DoA estimation, an array interpolation technique (AIT) and wavefield modeling (WM) are suggested as methods with inherent interpolation capabilities, fully taking antenna nonidealities like mutual coupling into account. We present a non-coherent DoA estimator for low-cost receivers and show how coherent DoA estimation and joint DoA and polarization estimation can be performed with MMAs. Utilizing these methods, we assess the DoA estimation performance of an MMA prototype in simulations for both 2D and 3D cases. The results show that WM outperforms AIT for high SNR. The coherent estimation is superior to non-coherent, especially in 3D, because non-coherent suffers from estimation ambiguities. In conclusion, DoA estimation with a single MMA is feasible and accurate.

Journal Publication on OFDM in Molecular Communications

10.12.2018

M. Damrath, J. J. Koshy, and P. A. Hoeher, "Application of OFDM in diffusion-based molecular communication," in IEEE Trans. on Molecular, Biological and Multi-scale Commun., vol. 3, no. 4, pp. 254-258, Dec. 2018. DOI

Abstract

In this letter, the application of orthogonal frequency division multiplexing (OFDM) in the area of diffusion-based molecular communication is studied. The focus is on direct current biased optical OFDM, asymmetrically clipped optical OFDM, and pulse amplitude modulation discrete multi-tone transmission known from optical communications. Simulation results show that the OFDM parameters have to be chosen carefully and that the bit error rate performance is in-between that of standard on-off keying transmission with maximum-likelihood sequence estimation and fixed threshold detection. In addition, it is demonstrated that a proposed bit-loading algorithm can further improve the OFDM performance.

Journal Publication on Optical Underwater Communications

30.10.2018

J. Sticklus, M. Hieronymi, and P.A. Hoeher, "Effects and constraints of optical filtering on ambient light suppression in LED-based underwater communications," Sensors 2018, vol. 18(11), 3710, 2018. DOI

Abstract

Optical communication promises to be a high-rate supplement for acoustical communication in short-range underwater applications.  In the photic zone of oceanic and coastal waters underwater optical communication systems are exposed by remaining sunlight. This ambient light generates additional noise in photodetectors, thus degrading system performance. This effect can be diminished by the use of optical filters. This paper investigates light field characteristics of different water types and potential interactions with optical underwater communication. A colored glass and different thin film bandpass filters are examined as filter/detector combinations under varying light and water conditions, and their physical constraints are depicted. This is underlined by various spectral measurements as well als optical signal-to-noise calculations. The importance of matching the characteristics of the LED light source, the photodetector, and the filter on the ambient conditions utilizing wider angle of incidents is emphasized.

Journal Publication on 5G Positioning

23.10.2018

S. Zhang, T. Jost, R. Pöhlmann, A. Dammann, D. Shutin, and P.A. Hoeher, "Spherical wave positioning based on curvature of arrival by an antenna array," IEEE Wireless Communication Letters, vol. 8, no. 2, pp. 504-507, Apr. 2019.

Abstract

Array processing is a key technology for emerging mobile networks, especially in short to moderate range and line-of-sight scenarios. In these scenarios, the incoming wavefront can be modeled by a spherical wave. The wavefront curvature, i.e., curvature of arrival (CoA), contains position information of the transmitter and is observable by an antenna array potentially asynchronous and non-coherent to the transmitter. We derive a simplified expression of the spherical wave positioning (SWP) Cramer-Rao bound for arbitrary centro-symmetric array, which provides a geometrical inference about the achievable performance. Additionally, a low complexity CoA positioning algorithm is proposed. In contrast to conventional methods, the proposed algorithm requires neither multiple anchors nor coordination between devices. It also outperforms the Fresnel approximation based SWP algorithms by overcoming the model mismatch. Therefore, the proposed CoA positioning algorithm is promising for precise positioning in future mobile networks.

Journal Publication on Molecular MIMO Communications

19.10.2018

M. Damrath, H. B. Yilmaz, C.-B. Chae, and P. A. Hoeher, "Array gain analysis in molecular MIMO communications," IEEE Access,  vol. 6, pp. 61091-61102, Oct. 2018. DOI

Abstract

In this work, spatial transmission techniques in the area of multiple-input multiple-output (MIMO) diffusion-based molecular communications (DBMC) are investigated. For transmitter-side spatial coding, Alamouti-type coding and repetition MIMO coding are analyzed. At the receiver-side, selection diversity and equal-gain combining are studied as combining strategies. Throughout the numerical analysis, a symmetrical 2x2 MIMO-DBMC system is assumed. Furthermore, a trained artificial neural network is utilized to acquire the channel impulse responses. The numerical analysis demonstrates that there is no spatial diversity gain in the DBMC system under investigation,
but that it is possible to achieve an array gain instead. In addition, it is shown that for MIMO-DBMC systems repetition MIMO coding is superior to Alamouti-type coding.

Journal Publication on Optical Underwater Communications

19.10.2018

J. Sticklus, P. A. Hoeher, and R. Röttgers, "Optical underwater communication: The potential of using converted green LEDs in coastal waters," IEEE Journal of Oceanic Engineering, vol. 44, no. 2, pp. 535-547, Apr. 2019. DOI

Abstract

Compared to the open ocean where blue light-emitting diodes (LEDs) perform well for data communications, in coastal and harbor environments optical transmission becomes worse and the color of lowest attenuation shifts to green. Another problem concerns the “green–yellow gap” of LEDs, as the quantum efficiency of current commercially available green LEDs is poor. Since energy consumption is an important factor, particularly for battery-powered systems, using blue LEDs is a tradeoff. Recently, phosphor-converted green LEDs, which are pumped by highly efficient blue LEDs, have been introduced to the market, and this type of LED promises better performance. This paper compares the use of blue, green, and converted green LEDs for applications in optical underwater communication systems in coastal waters. Theoretical aspects of the overall LED-water-detector channel are presented. A method for determining individual system coefficients is developed, and the impact on the communication system performance is explained. Practical approaches are introduced, complemented by measurements in the Baltic Sea.

Journal Publication on Low-Complexity Symbol Detection

19.10.2018

M. Damrath, P. A. Hoeher, and G. J. M. Forkel, "Piecewise linear detection for direct superposition modulation," Digital Communications and Networks, vol. 4, no. 2, pp. 98-105, April 2018. DOI

Abstract

Considering high-order digital modulation schemes, the bottleneck in consumer products is the detector rather than the modulator. The complexity of the optimal a posteriori probability (APP) detector increases exponentially with respect to the number of modulated bits per data symbol. Thus, it is necessary to develop low-complexity detection algorithms with an APP-like performance, especially when performing iterative detection, for example in conjunction with bit interleaved coded modulation. We show that a special case of superposition modulation, dubbed Direct Superposition Modulation (DSM), is particularly suitable for complexity reduction at the receiver side. As opposed to square QAM, DSM achieves capacity without active signal shaping. The main contribution is a low-cost detection algorithm for DSM, which enables iterative detection by taking a priori information into account. This algorithm exploits the approximate piecewise linear behavior of the soft outputs of an APP detector over the entire range of detector input values. A theoretical analysis and simulation results demonstrate that at least max-log APP performance can be reached, while the complexity is significantly reduced compared to classical APP detection.

Journal Publication on Precoding in High-Speed Massive MIMO Systems

22.12.2017

N. Doose and P. A. Hoeher, "Joint precoding and power control for EIRP-limited MIMO systems," IEEE Transactions on Wireless Communications, vol. 17, no. 3, pp. 1727-1737, Mar. 2018. DOI

Abstract

This contribution elaborates on transmitter-side precoding for MIMO downlinks with full channel state information at the transmitter (CSI-T) and no channel state information at the receiver (CSI-R) under equivalent isotropic radiated power (EIRP) constraints. The optimization problem is formulated in standard form. Similarities and differences to current beamforming solutions are drawn. An illustrative example identifies weaknesses of sum-power optimized precoding schemes, when they are scaled to comply with an EIRP limit. In order to improve the achievable rate, semi-random approaches are investigated. Numerical results are presented in the context of massive MIMO and the utilization of multi-mode antennas.

Journal Publication on Visible Light Communications

15.12.2017

G. J. M. Forkel and P. A. Hoeher, "Constrained intensity superposition: A hardware-friendly modulation method," IEEE/OSA Journal of Lightwave Technology, vol. 36, no. 3, pp. 658–665, Feb. 2018. DOI

Abstract

One challenge in intensity modulation and direct detection communication systems is the power consumption at the transmitter-side driving circuit. For binary-switched LED-based transmission, boosting the data rate leads to an increased number of switching operations. Consequently, a larger fraction of the available power budget is dissipated in the driver. Hence the performance of communication and possibly illumination is affected by the reduced optical transmit power. The key idea is to lower the driver power consumption by decreasing the number of switching operations necessary for transmitting a fixed amount of data. This is possible by superimposing multiple binary sequences, where the individual sequences are matched to the hardware characteristics of the transmitter. We introduce a method to derive a graph-based representation for superimposing individually constrained binary sequences, and analyze the achievable constrained capacity.

Journal Publication on In-Car Communication Systems

15.12.2017

A. Mourad, S. Muhammad, M. O. Al Kalaa, H. Refai, and P. A. Hoeher, "On the performance of WLAN and Bluetooth for in-car infotainment systems," Vehicular Communications, vol. 10, Oct. 2017. DOI

Abstract

The connected car is ushering in a new era of automotive design. Driven by increasing customer demand for connectivity and advances in electronics, connected cars are now equipped with advanced infotainment systems with a variety of applications. Seamless integration of consumer electronic (CE) devices into car infotainment systems is crucial for mimicking home and office user experience. Because wireless communication is more user-friendly than wired communication, it has become the preferred method for connecting CE devices to car infotainment systems. WLAN and Bluetooth are the most promising technologies for this purpose. Both systems operate in the spectrum-scarce 2.4 GHz unlicensed industrial, scientific and medical (ISM) radio band. The coexistence between WLAN and Bluetooth has garnered a significant amount of attention from both academic and industry researchers. However, the unique features of vehicle mobility and the high density of devices in a limited roadway area necessitate further investigation in the automotive domain.

This paper focuses on the coexistence between WLAN and Bluetooth systems among vehicle infotainment applications, and on WLAN co-channel interference. Performance is evaluated using experimental measurements in real-world scenarios. The mobility effect is studied in detail. Results show that an onboard WLAN network is strongly affected by the surrounding networks. Coexistence duration decreases exponentially with relative speed between automobile networks. WLAN effect on Bluetooth is extremely high when WLAN's non-overlapped channels 1, 6, and 11 are simultaneously occupied. WLAN interference leads to a significant number of clippings in Bluetooth audio signals, especially in high WLAN traffic load situations. An exponential decease in the number of clipping events as a function of speed is observed.

Journal Publication on High-Speed Massive MIMO Systems

15.12.2017

P. A. Hoeher, D. Manteuffel, N. Doose, and N. Peitzmeier, "Ultra-wideband massive MIMO communications using multi-mode antennas," Frequenz, vol. 71, no. 9–10, pp. 439–448, Sep. 2017. DOI

Abstract

An ultra-wideband system design is presented which supports wireless internet access and similar short-range applications with data rates of the order of 100 Gbps. Unlike concurrent work exploring the 60 GHz regime and beyond for this purpose, our focus is on the 6.0–8.5 GHz frequency band. Hence, a bandwidth efficiency of about 50 bps/Hz is necessary. This sophisticated goal is targeted by employing two key enabling techniques: massive MIMO communications in conjunction with multi-mode antennas. This concept is suitable both for small-scale terminals like smartphones, as well as for powerful access points. Compared to millimeter wave and THz band communications, the 6.0–8.5 GHz frequency band offers more robustness in NLOS scenarios and is more mature with respect to system components.

Journal Publication on Cognitive Networks

15.12.2017

A. Yaqot and P.A. Hoeher, "Efficient resource allocation in cognitive networks," IEEE Trans. Vehicular Technology, vol. 66, no. 7, pp. 6349–6361, July 2017. DOI

Abstract

Cognitive radio (CR) in conjunction with multiple-input multiple-output (MIMO) orthogonal frequency-division multiple access is a candidate technology for future mobile radio networks. The short communication range of underlay CR systems is commonly a major limiting factor. In this paper, we propose a computationally and spectrally efficient resource allocation scheme for multiuser MIMO orthogonal-frequency-division-multiplexing-based underlay CR networks to provide good spectral efficiency gain and, therefore, increased communication range. Since the formulated optimization problem defines a mixed-integer programming (combinatorial task) that is hard to solve, we propose a two-phase scheme to produce efficient solutions for both the downlink and the uplink. Particularly, the first procedure elaborates on an adaptive precoding that is characterized by spectral efficiency due to the degrees of freedom it can provide. The second procedure develops a fast subcarrier mapping algorithm, which can be worked out through optimal power distribution among the CR users. The proposed scheme is optimal for the downlink but, however, near-optimal for the uplink. Simulation results demonstrate the bandwidth and computational efficiencies of the proposed scheme compared with the state of the art.

Journal Publication on Channel Modeling for Molecular Communications

15.12.2017

M. Damrath, S. Korte, and P. A. Hoeher, "Equivalent discrete-time channel modeling for molecular communication with emphasize on an absorbing receiver," IEEE Trans. Nanobioscience, vol. 16, no. 1, pp. 60–68, Jan. 2017. DOI

Abstract

This paper introduces the equivalent discrete-time channel model (EDTCM) to the area of diffusion-based molecular communication (DBMC). Emphasis is on an absorbing receiver, which is based on the so-called first passage time concept. In the wireless communications community the EDTCM is well known. Therefore, it is anticipated that the EDTCM improves the accessibility of DBMC and supports the adaptation of classical wireless communication algorithms to the area of DBMC. Furthermore, the EDTCM has the capability to provide a remarkable reduction of computational complexity compared to random walk based DBMC simulators. Besides the exact EDTCM, three approximations thereof based on binomial, Gaussian, and Poisson approximation are proposed and analyzed in order to further reduce computational complexity. In addition, the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm is adapted to all four channel models. Numerical results show the performance of the exact EDTCM, illustrate the performance of the adapted BCJR algorithm, and demonstrate the accuracy of the approximations.

Journal Publication on Low-Complexity Symbol Detection

15.12.2017

M. Damrath, P. A. Hoeher, and G. J. M. Forkel, "Symbol detection based on Voronoi surfaces with emphasis on superposition modulation," Digital Communications and Networks, vol. 3, no. 3, pp. 141149, Aug. 2017, first published online Jan. 2017. DOI

Abstract

A challenging task when applying high-order digital modulation schemes is the complexity of the detector. Particularly, the complexity of the optimal a posteriori probability (APP) detector increases exponentially with respect to the number of bits per data symbol. This statement is also true for the Max-Log-APP detector, which is a common simplification of the APP detector. Thus it is important to design new detection algorithms which combine a sufficient performance with low complexity. In this contribution, a detection algorithm for two-dimensional digital modulation schemes which cannot be split-up into real and imaginary parts (like phase shift keying and phase-shifted superposition modulation (PSM)) is proposed with emphasis on PSM with equal power allocation. This algorithm exploits the relationship between Max-Log-APP detection and a Voronoi diagram to determine planar surfaces of the soft outputs over the entire range of detector input values. As opposed to state-of-the-art detectors based on Voronoi surfaces, a priori information is taken into account, enabling iterative processing. Since the algorithm achieves Max-Log-APP performance, even in the presence of a priori information, this implies a great potential for complexity reduction compared to the classical APP detection.