Effect of transmit correlation on the sum-rate capacity of two-user broadcast channels

This letter investigates the effect of the transmit correlation on the sum-rate capacity of a two-user broadcast channel (BC) with the use of equal-power allocation in high signal-to-noise ratio (SNR) environments. It is shown using an upper-bound analysis that the sum-rate capacity of a correlated two-user BC at high SNR highly depends on the phase difference between the transmit correlation coefficients of two users as well as the magnitude of the transmit correlation coefficients, and it is maximized (or minimized) when the principal eigenvectors of the transmit correlation matrix of two users are orthogonal (or parallel) to each other. The analytic results are verified by computer simulation.