Downlink MIMO Diversity with Maximal-Ratio Combining in Heterogeneous Cellular Networks

We present a stochastic model for analyzing the performance of multiple-input multiple-output (MIMO) diversity in a downlink heterogeneous cellular network. Multi-antenna receivers are assumed to perform maximal-ratio combining (MRC). We consider interference-blind (IB) MRC and interference-aware (IA) MRC, where the latter takes the interference power at each antenna into account. Using tools from stochastic geometry, we derive the coverage probability for both types of MRC as a function of various tier-specific system parameters, including the number of base station transmit antennas in each tier. The model is then used to compare the performance of IB-MRC and IA-MRC. One important insight is that IA-MRC becomes less favorable than IB-MRC in a transmit-diversity system due to a larger interference correlation across receive antennas.