In this letter, we examine the statistical distribution of the signal-to-interference-plus-noise ratio (SINR) of the optimum combining (OC) technique in receive-antenna diversity systems. We decompose the SINR into two components by projection onto the interference subspace for systems with more antennas than interferers. For the case when the number of interferers is larger than the number of antennas, upper and lower bounds on performance are provided.

We examine the statistical properties of the output signal to interference plus noise ratio (SINR) of a spatial combiner where the spatial weights used are either the Maximal Ratio Combiner (MRC) weights or the Optimal Combining (Wiener Hopf) weights. The channels are modeled as slow flat Rayleigh fading channels and multiple interferers are assumed present. In particular, the modified F-distribution is introduced to provide an exact characterization of a MRC receiver and to bound the performance of the OC receiver. Simulation results are provided to support the analytical results and to provide insight.