Capacity of MIMO Systems in Rayleigh Fading with Sub-Optimal Adaptive Transmission Schemes

Closed form expressions for the capacity of multiple antenna systems in the presence of Rayleigh flat fading is derived for two sub-optimal adaptive transmission schemes, namely channel inversion (CI) and truncated channel inversion (TCI), assuming channel state information (CSI) is available at both the transmitter and the receiver. Moreover, an upper bound for the capacity of a multiple-input multiple-output (MIMO) system with only receiver-side channel state information (RxCSI) is also presented. Our results suggest that the difference in capacity between the optimal and these sub-optimal schemes reduces as the number of diversity branches increases. Further, in some cases, the capacity with sub-optimal adaptive schemes can be greater than that of a Rx-CSI only system.