The Study of Zero-Forcing Beamforming Gain for Multiuser MIMO with Limited Feedback

This paper discusses the finite-rate feedback-based ZF for multiuser MIMO in case of small number of candidate users to be selected and small number of quantization bits to be fed back. In this case, the multiplexing gain from ZF is limited. Under the assumption of small number of candidate users, then the paper further analyzes throughput of ZF with different number of co-scheduled users. From the analysis, the throughput of ZF is limited by the loss of target signal power and the residual interference from the co-scheduled users. The loss of target signal power comes from the steered precoder by ZF operation. From the simulation for theoretical throughput and throughput from Monte Carlo methods, we have some conclusions, for finite-rate feedback-base ZF multiuser MIMO with the small number of quantization bits, the ZF beamforming gain that is significant for perfect CSIT based ZF disappears, and the throughput for small value of co-scheduled users may be larger than the throughput for large value of co-scheduled users.