Abstract
Combined space division multiple access (SDMA) and scheduling
exploit both spatial multiplexing and multiuser
diversity, increasing throughput significantly. Both SDMA and
scheduling 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 and
feedback. To quantify the throughput of uplink SDMA and derive
design guidelines, the throughput scaling with system parameters is
analyzed. The specific parameters considered include the numbers of
users, antennas, and feedback bits. Furthermore, different SNR
regimes and beamforming methods are considered. The derived
throughput scaling laws are observed to change for different SNR
regimes. For instance, the throughput scales logarithmically with
the number of users in the high SNR regime but double
logarithmically in the low SNR regime. The analysis of throughput
scaling suggests guidelines for scheduling in uplink SDMA. For
example, to maximize throughput scaling, scheduling should use the
criterion of minimum quantization errors for the high SNR regime and
maximum channel power for the low SNR regime.