MCM-DSSS with DPSK modulation and equal gain combining in Doppler-spread Rician fading

A method for computing the bit error probability (BEP) of multi-carrier modulated (MCM) direct-sequence spread-spectrum (DSSS) using differentially coherent phase-shift keying (DPSK) with equal gain combining in Doppler spread Rician fading is given. It is based on Gauss-Chebyshev quadrature integration of the moment generating function of the decision statistic at the combiner output. The results show that as the specular-to-diffuse power ratio, K, increases the crossover points of the BEP curves for various orders of diversity (number of MCM carriers) occur at increasing values of average energy-per-bit-to-noise spectral density ratio (SNR). Thus, for low to moderate SNR's, increased diversity may not give improvement while, for sufficiently high SNR's it does.