Microdiversity reception of spread-spectrum signals on Nakagami fading channels

An analytical framework to evaluate the performance of different predetection diversity techniques in various mobile radio environments is developed. The average bit-error rate analysis applies to phase coded spread-spectrum systems, over Nakagami multipath fading channels. A simple and practical selection combining rule is considered. Our numerical results reveal that this new low-complexity receiver structure exhibits comparable performance to that of an optimum linear diversity combiner when the channel does not experience severe fading and for small diversity orders, conditioned on the situation that all the diversity branches have identical mean signal strengths. In this study, we also investigate the effect of variations in the mean signal and noise power levels on each of the independent diversity branches. This is an important consideration because in practice equal mean signal strengths rarely occur, which results in loss of diversity gain. We found that the signal-plus-noise-and-interference selection model outperforms the traditional signal-to-interference-plus-noise ratio selection scheme if the discrepancy between the mean signal strengths are small, owing to the statistical nature of the multiple-access interference.