Enhanced Multi-mode Transmission by User Scheduling in MISO Broadcast Channels with Finite-Rate Feedback

This paper investigates the user selection strategy in multiuser downlinks using zero-forcing beamforming (ZFBF) and finite-rate feedback (FRF). In order to mitigate the interference-limited effect in ZFBF-FRF systems, we propose an efficient user scheduling scheme combined with adaptive transmission mode selection strategy. In this scheme, each user first evaluates its preferred transmission mode and the corresponding achievable rate according to a derived tight lower bound of the rate. Given such information on the users through feedback, the BS then determines the global transmission mode of the system and selects users for simultaneous transmission. Asymptotic analysis shows that limited feedback beamforming to a single user is the best choice at both low and high SNR regimes. Simulation results demonstrate individual effects of different system parameters on the sum rate performance by the proposed scheme.