Performance of multicarrier CDMA with DPSK modulation and differential detection in fading multipath channels

Multicarrier (MC) direct sequence (DS) code division multiple access (CDMA) with differential phase-shift keying (DPSK) modulation and differential detection is proposed. Transmitted data bits are differentially encoded after being serial to parallel converted to a number of parallel streams. On each branch encoded bit is direct sequence spread spectrum (SS) modulated and transmitted using different carriers. The system is analyzed with differential detector in static Rayleigh fading multipath channel in fast Rayleigh-fading multipath channel and for variable overlapping between carrier spectra in static fading channel. Closed-form expressions are derived for the probability of error and evaluated for many cases. The performance is compared to that of a system using phase-shift keying (PSK) with conventional matched filter (CMF) coherent receiver. It is shown that for static fading channel, the probability of error performance of the differential detector is close to that of CMF receiver. For fast fading, it is shown that the performance degrades slightly with increasing the fading rate. Finally, successive carriers of the system are allowed to overlap with various overlapping percentages. It is shown that the condition of a single path can be achieved by increasing both the number of carriers and the separation between successive carriers. It is also shown that for each number of carriers, there exists an optimum overlapping percentage at which the system performance is optimized. It is concluded that the performance of the DPSK with differential detection system proposed in this paper is close to that of PSK with CMF receiver, but the former is simpler to implement.