Bounds on the Sum-Rate Capacity of the Gaussian MIMO X Channel
The authors consider the MIMO X Channel (XC), a system consisting of two transmit-receive pairs, where each transmitter communicates with both the receivers. Both the transmitters and receivers are equipped with multiple antennas. First, they derive an upper bound on the sum-rate capacity of the MIMO XC under individual power constraint at each transmitter. The sum-rate capacity of the two-user Multiple Access Channel (MAC) that results when receiver cooperation is assumed forms an upper bound on the sum-rate capacity of the MIMO XC. They tighten this bound by considering noise correlation between the receivers and deriving the worst noise covariance matrix.