Antenna ratio for sum-rate maximization in MU-MIMO with full-duplex large array BS

Abstract

This paper analyzes the ratio of the transmit antennas and receive antennas in multi-user multiple-input multipleoutput with a full-duplex and large array base station (BS) and half-duplex users (MU-MIMO FLB-HU) systems. We consider the BS exploits zero-forcing beamformer and zero-forcing receiver. We derive the deterministic approximation of the downlink and uplink sum-rates considering inter-user interference and self-interference, respectively. Based on the analyzed results, we formulate an optimization problem in terms of the number of transmit and receive antennas to maximize the sum of downlink and uplink sum-rates subject to the number of total antennas at the BS. From the optimization problem, the optimal antenna ratio between the number of transmit and receive antennas can be obtained. We analyze that the optimal antenna ratio converges to the ratio between the number of downlink users (K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> ) and uplink users (K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</inf> ) as the number of total antennas goes to infinity. Simulation results show that the optimal antenna ratio enhances the sum-rate performance compared to the same number of transmit antennas and receive antennas in the MU-MIMO FLBHU system. In particular, in the MU-MIMO FLB-HU system with K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> = 10 and K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</inf> = 5, the optimal antenna ratio can achieve about 5∼10bps/Hz performance gain compared to the same number of transmit antennas and receive antennas.