Spatial Multiplexing in Cellular MIMO-CDMA Systems with Linear Receivers: Outage Probability and Capacity

Even though spatial multiplexing provides a significant spectral efficiency advantage in a single point-to-point noise- limited link, recent studies have shown that this advantage can be lost in cellular MIMO systems unless extra diversity is provided. Spread spectrum is a likely candidate for the extra diversity because spread spectrum can simultaneously provide frequency diversity and robustness to interference. This paper investigates the effectiveness of spatial multiplexing in the forward link of cellular MIMO-CDMA systems with linear receivers. Through the development of new closed-form results on outage probability and capacity for MIMO-CDMA, we show that even MIMO-CDMA loses the spatial multiplexing gain in a cellular context. These results indicate that a practical cellular MIMO system, which will be interference-limited and have a low-complexity receiver, requires new study on techniques to efficiently reduce the impact of the other-cell interference. The developed analytical framework can be used for evaluating other techniques.