Performance Comparison Among Conventional Selection Combining, Optimum Selection Combining and Maximal Ratio Combining

Reference introduced optimum selection combining (OSC) for binary phase shift keyed signals which selects the diversity branch having the maximum a posteriori probability. It performs much closer to maximal ratio combining (MRC) than the conventional selection combining (CSC) which selects the diversity branch having the maximal instantaneous signal power. It is known that these combining techniques have the same diversity order (DO), i.e., the same performance slope (log error probability versus signal-to-noise ratio (SNR) in dB)-the performance variation is the SNR difference (gap) between any two techniques to achieve the same bit error rate (BER). This paper derives closed-form expressions for the SNR gaps among these three combining schemes. The paper also analyzes the asymptotic BER for these three combining schemes as a function of DO for a fixed SNR.