BER analysis of a novel hybrid modulation scheme for noncoherent DS-CDMA systems

A novel DS-CDMA transmission scheme combining the two well-known techniques of M-ary orthogonal and differential PSK-modulation is presented. This “hybrid” scheme is applicable to the noncoherent uplink of the IS-95 system where up to now only M-ary orthogonal modulation is used. The additional, PSK-modulated data show a slightly increased bit error rate (BER) compared to the data from M-ary modulation. However, the overall degradation caused hereby is far outweighed by the gain achieved by a higher spreading factor. Analytical results confirmed by simulations yield an improvement of approximately 1.0 dB in terms of E¯_b/N₀ on a Rayleigh fading channel when no channel coding is used. This considerable gain is achieved upon only slight modification of the conventional modulation/demodulation procedure at a low additional complexity. It is demonstrated that the IS-95 system is not properly designed since the full exploitation of noncoherent demodulation techniques results in a gain of nearly 2.0 dB