Hybrid Processing Design for Multipair Massive MIMO Relaying With Channel Spatial Correlation

Abstract

Abstract-Massive multiple-input multiple-output (MIMO) avails of simple transceiver design which can tackle many drawbacks of relay systems in terms of complicated signal processing, latency, and noise amplification. However, the cost and circuit complexity of having one radio frequency (RF) chain dedicated to each antenna element are prohibitive in practice. In this paper, we address this critical issue in amplify-andforward (AF) relay systems using a hybrid analog and digital (A/D) transceiver structure. More specifically, leveraging the channel long-term properties, we design the analog beamformer which aims to minimize the channel estimation error and remain invariant over a long timescale. Then, the beamforming is completed by simple digital signal processing, i.e., maximum ratio combining/maximum ratio transmission (MRC/MRT) or zero-forcing (ZF) in the baseband domain. We present analytical bounds on the achievable spectral efficiency taking into account the spatial correlation and imperfect channel state information at the relay station. Our analytical results reveal that the hybrid A/D structure with ZF digital processor exploits spatial correlation and offers a higher spectral efficiency compared to the hybrid A/D structure with MRC/MRT scheme. Our numerical results showcase that the hybrid A/D beamforming design captures nearly 95% of the spectral efficiency of a fully digital AF relaying topology even by removing half of the RF chains. It is also shown that the hybrid A/D structure is robust to coarse quantization, and even with 2-bit resolution, the system can achieve more than 93% of the spectral efficiency offered by the same hybrid A/D topology with infinite resolution phase shifters.

Optimal Hybrid Beamforming Design for Millimeter-Wave Massive Multi-User MIMO Relay Systems

“…The differences between the two structures are that the sub-connected structures use less phase shifters than the full-connected structures with the same number of antennas and RF chains, but in performance, the sub-connected structures are slightly lower than the full-connected ones. The hybrid beamforming of relay system with full-connected structure have been designed in [20] and [21], but they are not based on mmWave large-scale antenna arrays. For the AF mmWave massive MIMO relay system with the full-connected structure, the joint optimal hybrid beamforming designs of downlink single-destination and multi-destination using matching pursuit (MP) algorithms have been studied in [22] and [23], respectively, and a separate design scheme of analog and digital beamforming of downlink multi-destination has been studied in [24].…”

Cell Partitioning Antenna System Performance in Multi-User Scenarios for mmWave Communications

“…A general downside of high-gain antenna systems can be the decreased beamwidth. In [5], it is shown that the reduced beamwidth restricts the angular spread of the received signals, which affects the channel covariance matrix's eigenvalues, resulting in a MIMO performance degradation. Therefore, in [6] it was studied how the decrease of the beamwidth influences the performance of fixed-beam antenna systems, which uses high-gain antenna elements to partition a sector in smaller areas.…”

Impact of Channel Aging on Cell-Free Massive MIMO Over Spatially Correlated Channels

“…Moreover, spatial channel correlation is an important property of multiuser MIMO [14]. The propagation channels and antenna arrays create spatial channel correlation, which has a non-negligible impact on the performance of CF massive MIMO [15].…”