Asymptotic Gains of Generalized Selection Combining Over Correlated Fading Channels

In this paper, we derive general asymptotic moment generating function (MGF) expressions of the GSC output signal- to-noise ratio (SNR) for generalized correlated fading channels assuming large average signal-to-noise ratio (ASNR). Based on the MGF result, the asymptotic diversity and combining gains for correlated-diversity GSC are derived. Our analytical results reveal that over correlated channels when the channel covariance matrix is full rank the diversity gain of GSC is to equivalent to that of maximum ratio combining (MRC) with independent fading branches. The combining gains for different modulation formats and fading types in correlated channels are also derived. As is known and analytically verified in this paper, for channels without line-of-sight (LoS) components, correlation generally degrades the GSC combining gain. However, we show that for Rician channels the LoS phase vector affects the performance, and near-optimal LoS phase vector brings a larger combining gain than even the independent fading channels.