Multipath-diversity performance of direct-sequence CDMA using combined M-ary signalling

A combined binary PPM/orthogonal modulation is used in cellular CDMA reverse links in which the multipath-diversity performance for Rayleigh-fading channels is evaluated and compared. As for diversity techniques, equal gain combining (EGC), selection combining (SC), and its generalization, second or third order SC (SC2, SC3), are considered for noncoherent reception. Theoretical analyses show that noncoherent combining loss (NCL) severely degrades the symbol error-rate (SER) performance of EGC when the modulation level M is small, but NCL can be greatly reduced by increasing M greater than or equal to 16. We also And that SC2 and SC3 significantly improve the SER compared to SC, especially outperform EGC for small M.