Analysis of hybrid selection/maximal-ratio combining in Rayleigh fading

The performance of a hybrid selection/maximal ratio combining (H-S/MRC) diversity system in a multipath-fading environment is analyzed. With H-S/MRC, L out of N diversity branches are selected and combined using maximal-ratio combining (MRC). This technique provides improved performance over L branch MRC when additional diversity is available, without requiring additional electronics and/or power. In particular, we consider independent Rayleigh fading on each diversity branch with equal signal-to-noise ratio averaged over the fading. We analyze this system using a "virtual branch" technique which results in a simple derivation and formula for the mean and the variance of the combiner output SNR for any L and N