Asymptotic Performance of Threshold-Based Generalized Selection Combining

In this paper, we study the asymptotic performance of absolute-threshold- and normalized-threshold-based generalized selection combining (AT-GSC and NT-GSC) schemes over generalized fading channels for high average signal-to-noise ratios (ASNRs). By evaluating the asymptotic moment-generating function of the threshold-based GSC output SNRs, we derive the diversity and combining gains for AT- and NT-GSCs with a large class of modulation formats and versatile fading conditions, including different types of fading channels and nonidentical SNR statistics across diversity branches. Our analytical results reveal that the diversity gains of AT- and NT-GSC are equivalent to that of maximal-ratio combining, and the differences in the combining gains for different threshold values and modulation and diversity formats are derived by using the concept of modulation factors.