  A multiple transmit antenna, single receive antenna (per receiver) downlink
channel with limited channel feedback is considered. Given a constraint on the
total system-wide channel feedback, the following question is considered: is it
preferable to get low-rate feedback from a large number of receivers or to
receive high-rate/high-quality feedback from a smaller number of (randomly
selected) receivers? Acquiring feedback from many users allows multi-user
diversity to be exploited, while high-rate feedback allows for very precise
selection of beamforming directions. It is shown that systems in which a
limited number of users feedback high-rate channel information significantly
outperform low-rate/many user systems. While capacity increases only double
logarithmically with the number of users, the marginal benefit of channel
feedback is very significant up to the point where the CSI is essentially
perfect.
