Lehrstuhl für Informations- und Codierungstheorie

New 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," accepted for publication in IEEE Access, 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.

New publication on Optical Underwater Communication

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, published online since May 2018. 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.

New 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.

New 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.

New 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.

New 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.

New 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.

New 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.

New 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.

New 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.