Asymptotic Analysis on Spatial Diversity versus Multiuser Diversity in Wireless Networks

Spatial diversity provided by multiple antennas implemented at the physical layer (PHY) can protect a wireless link from harmful fading, while opportunistic scheduling that exploits multiuser diversity at the media access control (MAC) layer can increase the system throughput with the aid of constructive fading in a multiuser wireless network. In this paper, by studying the average system capacity of opportunistic scheduling and scheduling gain (defined as the average system capacity difference between opportunistic scheduling and conventional round-robin scheduling), we investigate the cross-layer interaction between spatial diversity and multiuser diversity. Our analyses focus on the asymptotic scenarios, by allowing either the number of users or the number of antennas, or both, to go to infinity, for which some succinct closed-form expressions can be obtained and the connections among system parameters become clear.