On the capacity of noncoherent wideband MIMO-OFDM systems

We study the capacity behavior of full-band MIMO-OFDM systems in the absence of channel state information both at the transmitter and the receiver. Based on capacity lower and upper bounds, we quantify the transmission rate penalty due to channel uncertainty as a function of the number of transmit antennas, the number of resolvable taps in the channel, the power delay profile, and the bandwidth. Our analysis reveals that for a given bandwidth and transmit power there is an optimum, capacity-maximizing, number of transmit antennas. Numerical results show that using a large number of transmit antennas in systems employing bandwidths of several GHz (such as in ultrawideband systems) is detrimental from a capacity point of view. Finally, we evaluate the capacity performance of space-frequency unitary codebooks recently introduced in M. Borgmann and H. Bolcskei, (2005)