Low-Complexity Multiuser MIMO Downlink User Selection Based on Large-Scale Fading

We propose a low-complexity user selection scheme with zero-forcing precoding in multiuser MIMO downlink systems, where the base station (BS) is equipped with large-scale antenna arrays and the number of candidate-users is relatively small. The BS obtains the channel state information (CSI) of the user equipments (UEs) through the pilot-based minimum mean-square error channel estimation. Taking both the channel propagation and the UE location distribution into consideration, we first derive a deterministic approximation of the ergodic sum rate and investigate the optimal number of active UEs, K*, in the sense of sum rate maximization. Then, K* UEs are selected for simultaneous data transmission according to their large-scale channel fading. Small-scale channel fading is not taken into account in the selection procedure, thus reducing the computational complexity dramatically as well as improving the robustness of the proposed scheme in practice. Numerical simulations suggest that whether perfect CSI is available at the BS, our proposed scheme achieves high sum rate performance with very low complexity.