Dual-Branch MRC Receivers in the Cellular Downlink under Spatial Interference Correlation

Although maximal-ratio combining (MRC) has become a widespread diversity-combining technique, its performance under interference is still not very well understood. Since the interference received at each antenna originates from the same set of interferers, but partially de-correlates over the fading channel, it exhibits a complicated correlation structure across antennas. Using tools from stochastic geometry, this work develops a realistic analysis capturing the interference correlation effects for dual-branch MRC receivers in a downlink cellular system. Modeling the base station locations by a Poisson point process, the probability of a typical dual-branch MRC receiver being covered by its serving base station is derived. For the interference-limited case, this result can be further simplified to an easy-to-use single-integral expression. Using this result, it is shown that ignoring interference correlation overestimates the true performance by 3%-10%, while assuming identical interference levels across antennas underestimates it by <2%. In both cases, however, the true diversity order of dual-branch MRC is preserved. Finally, the performance of MRC and selection combining under spatial interference correlation is compared.