Error Probability of Multicarrier CDMA with Orthogonality Restoring Combining Over Nakagami-m Fading

Orthogonality restoring combining (ORC) is appealing for the downlink of multicarrier code-division multiple- access (MC-CDMA) since it can eliminate multiple access interference (MAI) which would otherwise fundamentally limit the CDMA system performance. The ORC output instantaneous signal-to-noise ratio (SNR), however, takes the form of a harmonic mean of SNRs on different subcarriers, making its error performance difficult to analyze. In this paper, we tackle the problem in the framework of characteristic functions (CF) ending up with useful results for various modulation schemes including M-ary phase-shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM). The general solution for arbitrary real m can be evaluated numerically, and reduces to closed form for m being an odd multiple of half. Extensive simulations are conducted to verify the theoretical analysis. It is found that in general MQAM outperforms MPSK, and the error performance of MC-CDMA with ORC is insensitive to the number of subcarriers and to the correlation among subcarriers.