Tim Hälsig

Array Size Reduction for High-Rank LOS MIMO ULAs

In this letter we propose an extended LOS MIMO channel model, which considers an additional phase shifting term in the transmission path, and which provides the potential to improve channel conditioning significantly. We show that this phase shifting can, for example, be achieved by adding a dielectric material between the transmitting and receiving antennas, where the phase shift is dependent on the distance the waves travel in the medium. Using that distance as a design parameter we demonstrate that the optimal spacing between antenna elements of uniform linear arrays, achieving full spatial multiplexing, can be reduced compared with the well-known spacing criterion from previous investigations.

Next generation mm-Wave wireless backhaul based on LOS MIMO links

With the evolution of the mobile networks towards more dense and flexible configurations, novel wireless backhaul solutions that can match the high capacity and flexibility demands are required in addition to the fixed fiber optics solutions. In this work we analyze the core backhaul requirements and the related system design challenges for utilizing the mm-wave frequency band due to the large available bandwidth. We determine the key performance metrics in terms of achievable throughput and energy efficiency of several transmission schemes seeking for a viable solution for the small cell backhaul scenario. Finally, an insight to the structure of the baseband domain required for processing multiple transmitted streams at the full system bandwidth is presented for a proposed LOS SM-MIMO system concept.

Information Rates for Faster-Than-Nyquist Signaling with 1-Bit Quantization and Oversampling at the Receiver

Oversampling combined with low quantization resolutions has been shown to be a viable option when aiming for energy efficiency in multigigabit/s communications systems. This work considers the case of 1-bit quantization combined with oversampling and shows how the performance of such a system can be improved by using matched pulse shaping filters and faster than Nyquist signaling. The channel is considered with additive Gaussian noise and the performance of the system is evaluated in terms of achievable information rate under symbol-by-symbol detection.

Measurement Results for Millimeter Wave Pure LOS MIMO Channels

In this paper we present measurement results for pure line-of-sight MIMO links operating in the millimeter wave range. We show that the estimated condition numbers and capacities of the measured channels are in good agreement with the theory for various transmission distances and antenna setups. Furthermore, the results show that orthogonal channel vectors can be observed if the spacing criterion is fulfilled, thus facilitating spatial multiplexing and achieving high spectral efficiencies even over fairly long distances. Spacings generating ill-conditioned channel matrices show on the other hand significantly reduced performance.

Analog equalization and low resolution quantization in strong line-of-sight MIMO communication

In this work we show that the analog equalizing networks are suitable for low resolution quantization with limited mutual information loss in strong line-of-sight MIMO communication. More specifically, a simplified analog equalizing network design in comparison with state-of-the-art works is proposed in this work. Additionally, the new network design works equally good for larger displacement ranges. Furthermore, by using analog equalizing networks in line-of-sight MIMO systems, it is shown that the drawbacks of low resolution quantization can be minimized. This increases the energy efficiency of the analog-to-digital converters via minimizing the required magnitude resolution. Generally, low resolution quantization causes low entropy on the receive vectors which will effectively reduce the mutual information of the desired transmission. The analog equalizing network reshapes the distribution and reduces the dynamics of the received signals in the complex constellation plane before quantization. Therefore, the entropy loss after low resolution quantization is reduced and the system performs essentially as good as a system with higher resolutions. Finally, an algorithm is proposed to remove ambiguities which arise after analog-to-digital conversion with a given low resolution.

Spectral Efficient Communications Employing 1-Bit Quantization and Oversampling at the Receiver

To relax power consumption requirements in multi- gigabit/s communications systems low resolution quantization can be used. Information-theoretic results have shown that systems employing 1-bit quantization and oversampling are a viable option for this. This work investigates such a structure under the influence of additive Gaussian noise and two matched pulse shaping filters. It is described how a BCJR algorithm, based on a finite-state channel assumption, can be used to reconstruct symbols of higher order modulation schemes that allow the transmission of more than one bit per symbol. Furthermore, it is shown how symbol sources that are fitted to the 1-bit constraint can significantly improve the error rate performance of the system.

Hardware-in-the-loop demonstration of a 60GHz line-of-sight 2×2 MIMO link

The dawn of 5G requires significantly higher data rates, not only for the Radio Access Technology (RAT), but also for the transport network. Line-of-Sight MIMO links based on mmWave radios promise reaching ultra-high throughput with reasonably small antennas. mmWave links with optimally arranged antennas are one viable concept for spatial multiplexing, capable of potentially achieving Gb/s data rates. In the context of mmWave MIMO system design, providing hardware implementation solutions is essential for bridging the gap from theoretical concepts to real-time operational prototypes. In this paper, we focus on the investigation of the BER performance of an orthogonal spatial-multiplexing LoS MIMO link and its robustness to x- and z-axis antenna displacements. Hardware-in-the-loop measurements are performed with a custom demonstrator built for 60GHz LoS MIMO system verification achieving system data rates of 2.5Gb/s at uncoded BER of 1e−4. The results largely confirm the theoretical assumptions and the feasibility of LoS MIMO for short to medium range wireless backhaul applications.

High Throughput Line-of-Sight MIMO Systems for Next Generation Backhaul Applications

Abstract The evolution to ultra-dense next generation networks requires a massive increase in throughput and deployment flexibility. Therefore, novel wireless backhaul solutions that can support these demands are needed. In this work we present an approach for a millimeter wave line-of-sight MIMO backhaul design, targeting transmission rates in the order of 100 Gbit/s. We provide theoretical foundations for the concept showcasing its potential, which are confirmed through channel measurements. Furthermore, we provide insights into the system design with respect to antenna array setup, baseband processing, synchronization, and channel equalization. Implementation in a 60 GHz demonstrator setup proves the feasibility of the system concept for high throughput backhauling in next generation networks.