Some properties of the capacity of MIMO systems with co-channel interference

The mutual information of a multiple-input multiple-output (MIMO) system with co-channel interference is considered. Perfect channel information is assumed to be available to the receiver, but the transmitter has no channel information. It is theoretically proved that the worst interference condition is when the total power is equally distributed among all available interfering antennas. Moreover, equal-power interferers give worse performance than unequal-power interferers, and a smaller number of interferers each with larger power degrades performance less than a larger number of interferers each with lower power. Finally, it is shown that, for asymptotically large interference, when the number of interfering antennas, N_I, is smaller than the number of receive antennas, N_R, the system is equivalent to a reduced MIMO system with N_R-N_I receive antennas. When N_I≥N_R, the mutual information approaches zero as interference becomes asymptotically large.