Hybrid Processing for Multi-pair Massive MIMO Two-Way Relay Network

Massive multiple-input multiple-output (MIMO) technology in combination with cooperative communications is an emerging paradigm which adds advantages of high spectral efficiency and diversity gains to extended coverage and increased network capacity of relay systems. However, the implementation cost and hardware complexity is limiting factor imposed by large number of required radio frequency (RF) chains. The hybrid processing with a far reduced number of RF chains is a solution being performed in analog and low-dimensional digital domains. In this paper, we consider a multi-pair two-way relay system where the relay node equipped with large-scale antennas assists to exchange information between single-antenna users. We propose low complexity three stages hybrid beamforming techniques based on linear baseband processing zero-forcing reception/transmission (ZFR/ZFT) and maximum ratio combining/transmission (MRC/MRT) schemes by applying phase controls in reception and transmission stages and performing low-dimensional digital beamforming in the middle stage. Our simulation results show performance of proposed hybrid processing techniques and corresponding full digital processing methods are close together.