New Hybrid Decision Feedback Equalization for DS-CDMA Systems

This paper proposes a novel hybrid decision-feedback equalizer (HDFE) for direct sequence code-division multiple-access (DS-CDMA) systems to improve their performance in highly time-dispersive fading environments. In the proposed scheme, despreading and re-spreading are integrated in the feedback process to improve the accuracy of feedback signals. Instead of performing chip detection to obtain the instantaneous feedback signals as in the conventional HDFE, the authors buffer the spread signals for a symbol, carry out the despreading, and then apply symbol detection to derive the feedback signals. In the feedback process, re-spreading is applied since equalization must be implemented at ´chip-level´. Through the use of symbol detection and re-spreading, more accurate feedback signals are achieved. Additionally, the proposed method effectively mitigates the effect of error propagation that may dramatically degrade the performance of conventional decision-feedback equalization schemes. Simulation results demonstrate the superior error performances of the proposed scheme over the conventional HDFE and RAKE schemes in highly dispersive channels such as those described in the recommendation ITU-M.1225 for mobile communications.