MMSE-beamforming for multi-user multiple-input multiple-output systems with distributed antennas

In this paper, we study the optimum transceiver design of multi-user multiple-input multiple-output (MU-MIMO) systems with distributed antennas. The basestation in the system is equipped with multiple distributed antenna units (DAUs) spreading out at different locations in a service area, and they are connected to a central unit (CU) through high-throughput low-latency links such as optical fibers. In the downlink, signals for multiple users are first modulated and precoded at the CU, and are then forwarded to the DAUs, which broadcast the signals to all the users in the system. Each user extracts its own information with a linear filter. The beamforming precoder at the CU and the linear filters at the UEs are jointly designed to minimize the sum mean squared error (MSE) of all the users. The optimum designs are performed under two different power constraints: a constraint on the total power of all DAUs, and constraints on the power consumption of each DAU. Simulation results demonstrate that the performance of the proposed system improve with the number of DAUs and the number of UEs under both power constraints.