Capacity limits of MIMO channels with co-channel interference

We consider both analytically and via Monte Carlo simulation the variation of the information theoretic capacity of multiple-input, multiple output (MIMO) communication systems. We present a way of explicitly examining the effect of interference on the MIMO sub-channel gains. Using this, we derive asymptotic lower bounds on capacity with many interferers and in high interference-to-noise ratio and present simulation results for them. We also study the behaviour of the capacity as a function of the number of interferers, the interference-to-noise ratio (INR) and the transmit and receive array sizes. It is found that, in interference, the benefit of providing multiple transmit antennas is very small indeed from a capacity perspective, whilst the number of receive antennas is critical both to the capacity and the number of users the system can mitigate interference from. Unusually, it is seen that, with a modification of the MIMO channel matrix to incorporate interference, higher correlation in the channel yields higher capacity rather than the more familiar desire for decorrelated channels.