A Study of Opportunism for Multiple Antenna Systems
01 January 2005
Recently proposed opportunistic beam-forming exploits multi-user diversity to reduce the feedback by not requiring the pre-coding matrix used for closed loop schemes to be known at the transmitter. Opportunism could also be beneficially employed for other multiple antenna transmission techniques. For single antenna receivers, we study opportunistic beam-forming, co-phasing and antenna selection. For opportunistic beam-forming in particular, we give closed form expressions for the throughput that closely approximate the performance of the Proportionally Fair scheduler. Dependence of required number of users on the number of transmit antennas to achieve a fixed fraction of peak data rate is given. We show that opportunistic co-phasing is equivalent to opportunistic beam-forming when the number of transmit antennas is large. For multiple antenna receivers, we additionally examine an opportunistic MIMO scheme that is superior in performance than the previously considered opportunistic schemes.