Capacity and Rate Performance of MIMO Systems with Channel State Information at the Transmitter

The capacity advantage of multiple input-multiple output (MIMO) channels lays in the decomposition of the channel into several spatial sub-channels. Knowledge of the channel at the transmitter can further increase the system capacity. This effect has been theoretically demonstrated. Here we illustrate the potential of channel state information (CSI) at the transmitter using actual channel measurements of a system with 4 transmitters and 4 receivers in an indoor environment, under line-of-sight and non line-of-sight conditions, considering both infinite and finite allowable modulation sizes. We show that CSI at the transmitter is more beneficial in the case of low signal to noise ratio and in cases where the channel richness is limited. In terms of achievable spectral efficiency, 60% of the theoretical capacity can be obtained without advanced coding techniques, as long as eigen mode transmission is used, and the performance is similar for all power and rate allocation schemes that we investigate