MMSE-based receivers for asynchronous DS-CDMA communication systems in the presence of double-spread multipath channels

This paper examines the performance of linear and nonlinear minimum mean-square error (MMSE) receivers when coupled with a second-order phase tracking subsystem in time-varying frequency-selective fading channels. Two detection techniques based on MMSE equalization with and without decision-feedback (DF) are presented and compared. Results indicate that the proposed receiver algorithms are immune to the near-far problem and shown to offer an increase in capacity relative to the conventional matched-filter (MF) receiver. Furthermore, by adding extra taps in the forward section both structures can perform implicit time diversity by combining the received powers of all paths to improve the receiver performance. Finally it is demonstrated that the phase tracking subsystem is able to track the phase of fast varying fading channels when the stand-alone MMSE structures cannot work.