Spectrum efficiency analysis of adaptive transmission with Selection Diversity in Rayleigh Fading Channels with branch correlation impairments

In this paper, we derive the Capacity per unit bandwidth (Spectrum Efficiency) of Correlated Rayleigh Fading Channels under Selection Combining Diversity at Low average SNR levels. This paper provides closed-form expressions for Spectrum efficiency among M diversity branches under different adaptation policies, like (i) Optimal Power and Rate Adaptation (OPRA) policy, (ii) Optimal Rate Adaptation (ORA) policy (iii) Channel Inversion with Fixed Rate (CIFR) policy, (iv) Truncated channel Inversion with Fixed Rate (TIFR) policy for Selection Combining. If M branch signals are correlated at low average SNRs, the spectrum efficiency achieved is lower compared to that achieved when the signals are uncorrelated. This is the focal point of this paper. Analytical results show accurately that OPRA policy provides the highest capacity over other adaptation policies. The spectrum efficiency for all four policies and outage probability for the correlated case at low average SNRs are derived, plotted and analyzed in detail in this work.