Optimum feedback quantization in an opportunistic beamforming scheme

Abstract

In recent years, digital beamforming has evolved into an excellent technology to improve wireless communications over fading channels. Especially in slow fading environments with a sufficient number of users in the system, opportunistic beamforming through multiuser diversity [1] has offered some advantages over true beamforming methods that rely on full channel feedback and/or robust channel estimation methods. Opportunistic beamforming achieves good throughput with only signal-to-noise ratio (SNR) feedback from the users. The quality of the SNR feedback such as the degree of SNR quantization is essential for opportunistic beamforming because the base station selects the best receiving user based on the SNR measurements sent by the users. In this paper, we develop an optimum SNR quantization method performed by the users and analyze its impact on the system throughput. While keeping the fairness among the users, we show that the opportunistic beamforming gain can still be realized with the help of the proposed quantization method. Theoretical analysis and computer simulation results show the feasibility and effectiveness of the method which provides insights for engineers to implement opportunistic beamforming in practice.