Interference-Free Criterion for Interference-Unaware Receive Transform in MIMO Co-Channel Interference

In this letter, we derive the upper bound and the lower bound of the achievable rate for the interference-unaware receive transformation (IURT), which does not require interference knowledge or precoding, to obtain the criterion for making IURT become interference free in multiple-input-multiple-output (MIMO) systems under co-channel interference. We prove that if the receive-antenna number is larger than or equal to the interference-free threshold, which is equal to the summation of the transmit-antenna number and the interference's covariance-matrix rank, then the derived upper bound reaches the interference-free MIMO channel capacity. Furthermore, we prove that by increasing both the transmit-antenna number and the receive-antenna number the derived lower bound can come closer to the interference-free MIMO channel capacity. Simulation results show that if the receive-antenna number is larger than the interference-free threshold, then the achievable rate of IURT can achieve the interference-free MIMO channel capacity.