Sparse Coding Quantization for Downlink MU-MIMO with Limited CSI Feedback

A novel quantization method, sparse coding quantization (SCQ), is proposed for downlink multiuser multiple-input multiple-output (MU-MIMO) systems. Compared to conventional vector quantization (VQ), SCQ utilizes a linear combination of several codewords rather than a single one to represent the channel matrix. Both analytical and simulation results reveal that the proposed technique can achieve the same sum rate performance as VQ at a reasonable cost in feedback overhead. Thus, SCQ is more practical because it significantly reduces the time and space complexity for generating, searching and storing the codebook. % The net capacity, which indicates the tradeoff between sum rate and overhead, is also studied.