Spectral efficiency of CDMA systems with transmit and receive antenna arrays

Multiple antennas and space-time processing are known to provide large link-level capacity gains. In this paper we investigate the system-level impact of using antenna arrays with up to four elements at both transmitter and receiver in a downlink CDMA system. We consider the following uses for multiple transmit antennas: transmit diversity, BLAST transmission (using the same spreading code to radiate independent data from different antennas), and directive beam steering. Link spectral efficiencies can be calculated as a function of the required signal-to-interference ratio (SIR) assuming capacity-approaching channel coding. System-level simulations provide the probability distribution of received SIR in a multi-cell CDMA system, with and without directive beam steering. The link- and system-level results are then combined to yield the number of equal-rate users that can be supported at some outage level. We show that 10 fold increases in user capacity can be achieved when up to four antenna elements are used on each side of the link (assuming a per-user rate of 1.25 Mbps and a 5-MHz bandwidth)