Uplink SDMA with limited feedback: Throughput scaling

Abstract

Combined space division multiple access (SDMA) and scheduling exploit both spatial multiplexing and multiuserdiversity, increasing throughput significantly. Both SDMA andscheduling require feedback of multiuser channel sate information(CSI). This paper focuses on uplink SDMA with limited feedback,which refers to efficient techniques for CSI quantization andfeedback. To quantify the throughput of uplink SDMA and derivedesign guidelines, the throughput scaling with system parameters isanalyzed. The specific parameters considered include the numbers ofusers, antennas, and feedback bits. Furthermore, different SNRregimes and beamforming methods are considered. The derivedthroughput scaling laws are observed to change for different SNRregimes. For instance, the throughput scales logarithmically withthe number of users in the high SNR regime but doublelogarithmically in the low SNR regime. The analysis of throughputscaling suggests guidelines for scheduling in uplink SDMA. Forexample, to maximize throughput scaling, scheduling should use thecriterion of minimum quantization errors for the high SNR regime and maximum channel power for the low SNR regime.