Resource Allocation in Downlink Large-Scale MIMO Systems

Abstract

This paper investigates the downlink of a single-cell base station (BS) equipped with a large-scale antenna array system while considering a non-negligible transmit circuit power consumption. This consumption involves that activating all RF chains does not always necessarily achieve the maximum sum-rate when the total BS transmit power is limited. This paper formulates a sum-rate maximization problem when a low complexity linear precoder, such as conjugate beamforming or zero forcing beamforming, is used. The problem is first relaxed by assuming arbitrary antenna selection. In this case, we derive analytically the optimal number of activated RF chains that maximizes the sum-rate under either optimal power allocation or equal received power constraint for all users. Also, user scheduling algorithms are proposed when users require a minimum received signal-to-interference-plus-noise ratio. Two iterative user scheduling algorithms are designed. The first one is efficient in terms of fairness and the second one achieves the optimal performance. Next, the antenna selection is investigated and we propose iterative antenna selection algorithms that are efficient in terms of instantaneous sum-rate. Simulation results corroborate our analytical results and demonstrate the efficiency of the proposed algorithms compared with arbitrary and optimal brute force search antenna selection.