Asymptotic Ergodic Capacity Region and Rate Optimization of a Multiple Access OFDM MIMO Channel with Separately-Correlated Rician Fading

The ergodic capacity region of a multiple access separately-correlated Rician fading multiple input and multiple output (MIMO) wideband channel is investigated by using an asymptotic approach. Our channel model is sufficiently general to allow for considering different spatial correlation matrices for each user and delay at the transmitter and the receiver. We provide two algorithms which can be used to maximize the (weighted) rate sums in order to obtain the ergodic capacity region. Both algorithms are based on an asymptotic approximation of the single-user wideband mutual information. Moreover, it is shown that sum rate maximization is based on water- filling, similarly to the well known case where the transmitter has perfect channel state information. It is assumed that the number of transmit and receive antennas grows asymptotically approaching finite ratios while the number of users and the signal-to-noise ratios are kept finite. Numerical simulations show that this asymptotic approach is very accurate even when the number of antennas is as low as a few units.