1MIMO Communications in Ad Hoc Networks

We study in this paper the network spectral efficiency in terms of bits/s/Hz of a MIMO (multiple-input multiple output) ad hoc network with K simultaneous communicating transmitter-receiver pairs. Assume that each transmitter is equipped with t antennas and each receiver with r antennas and each receiver implements single user detection. We show that in the absence of channel state information (CSI) at the transmitters, the asymptotic network spectral efficiency is limited by r nats/s/Hz as K!1 and is independent of t and the transmit power. With CSI corresponding to the desired receiver available at the transmitter, we demonstrate that the asymptotic spectral efficiency is at least t+r+2 p tr nats/s/Hz. Asymptotically optimum signaling is also derived under the same CSI assumption, i.e., each transmitter knows the channel corresponding to its desired receiver only. Further capacity improvement is possible with stronger CSI assumption; we demonstrate this using a heuristic interference suppression transmit beamforming approach. The traditional non-interference transmission approach is also analyzed. In particular, we show tha