Frequency-domain Differential Detection and Equalization of Differentially Encoded DS-CDMA Signals

Similar to the single-carrier transmission [1], the bit error rate (BER) performance of DS-CDMA in a frequency-selective fading channel can be significantly improved with coherent frequency-domain equalization (FDE) instead of using Rake combining [2][3]. However, coherent FDE requires accurate channel estimation and the imperfect channel estimation results in the performance degradation. For pilot-assisted channel estimation, the known pilot chip blocks need to be periodically transmitted. For better tracking against fast fading, pilot block transmission rate must be increased with transmission efficiency reduced. In this paper, a frequency-domain differential detection and equalization (FDDDE) scheme that requires no channel estimation is proposed. At a transmitter, the differentially encoded data symbol is spread and transmitted. At a receiver, differential detection, equalization and despreading are simultaneously performed in the frequency-domain. Computer simulation results show that its BER performance is not only very close to that of coherent FDE detection but also much more robust against the Doppler spread.