Novel detection technique for DS-CDMA with frequency domain oversampling

In synchronous DS-CDMA systems, multi-access interference (MAI) due to severe frequency-selective fading degrades the system performance. Based on the frequency domain oversampling (FDO) and minimum mean-square error (MMSE) principle, a novel linear per-user MMSE detector is proposed to approximately restore the orthogonality among the spreading sequences and suppress the MAI. Based on a discussion on the optimal MMSE detector, a low complexity diagonal MMSE detector is proposed with only a slight degradation in performance. It is shown by numerical results that the proposed detector obviously outperforms the conventional linear MMSE detector in severe MAI environment.