RF-chain constrained multi-pair massive MIMO relaying using hybrid precoding and detection

Abstract

We consider a multi-pair massive multiple-input multiple-output (MIMO) two-way relay network, where multiple pairs of single-antenna users exchange data with the help of a multi-antenna relay station. We assume that the relay is equipped with a large antenna array, but driven by a far smaller number of RF chains, which can enormously reduce the hardware cost and complexity for practical applications. We propose a hybrid precoding scheme for both uplink and downlink of the network and analyze the sum rate performance under imperfect channel estimate. Numerical results verify that the proposed scheme incurs limited degradation compared to traditional full-dimensional digital precoding. Given the relationship between the number of relay antennas, N, and the RF chain number, L, satisfying N > 4L2/π, we further discover that the transmit power of each user and the relay can be respectively scaled down by a factor of 1 /√N and L/√N if the pilot power scales with the signal power, or by a factor of 1/N and L/N if the pilot power is kept fixed, while maintaining an asymptotically unchanged performance.