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.
Highlights
In a wireless communication system, using the spatial degrees of freedom, a base station with multiantennas can communicate with multiple users in the same time and frequency slot
The linear scaling factor is smaller than the number of antennas Nt, indicating the loss in the spatial multiplexing gain
Uplink space division multiple access (SDMA) with limited feedback is compared with uplink channelaware random access proposed in [28], which requires no channel state information (CSI) feedback
Summary
In a wireless communication system, using the spatial degrees of freedom, a base station with multiantennas can communicate with multiple users in the same time and frequency slot. This theory is useful for characterizing the number of users whose channel shapes lie in a same Voronoi cell. A bins-and-balls model for multiuser feedback of quantized channel shapes is introduced In this model as illustrated, U balls are thrown into N + 1 bins: N small bins and one big one, whose total volume is equal to one
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