A new hybrid generalized selection combining scheme and its performance over fading channels

Emerging very high-data-rate wireless communications requires that traditional diversity systems be adapted so that some performance is sacrificed for complexity reduction. With this goal in mind, we investigate the recently-developed absolute threshold generalized selection combining (AT-GSC). We show that AT-GSC has poor bit-error rate (BER) performance when the average branch signal-to-noise ratio (SNR) is comparably lower than the preset threshold. This paper therefore develops a new diversity combining scheme, referred to as switching GSC (S- GSC). This scheme combines all branches whose SNR´s exceed a preset threshold and if all the branches drop below the threshold, the output is the single branch with the maximum SNR. We prove that for any two-dimensional amplitude/phase linear modulation schemes, the symbol error rate (SER) of S-GSC lies between those of maximal ratio combining (MRC) and selection combing (SC). Importantly, the complexity of S-GSC is only slightly above that of AT-GSC. We derive the moment generating function (mgf) of the S-GSC output SNR over independent fading channels. For identically and independently distributed (i.i.d.) Rayleigh fading channels, we also derive the output probability density function (pdf) and cumulative distribution function (cdf) and analyze the error rate and the outage probability performance of S-GSC. Higher order moments of the S-GSC output SNR are also derived. These theoretical results are sufficient to completely characterize the performance of S-GSC and enable one to compare S-GSC with conventional diversity schemes.