Space-time-frequency multiuser detection over fast-fading multipath channels for synchronous DS-CDMA systems

RAKE receivers suffer degradation in performance under fast fading due to errors in channel state estimation. The wide-sense stationary uncorrelated scatterer channel model lends itself to time-frequency canonical representation, and provides additional diversity in the frequency axis. Using the joint spatial-multipath-Doppler diversity model based on this canonical representation with multiple antennas, we first develop linear space-time-frequency multiuser detectors based on decorrelating and MMSE interference suppression techniques and further present nonlinear space-time-frequency decision-driven multiuser detectors based on interference cancellation ideas to operate over the fast-fading multipath synchronous CDMA channels. Simulation results based on realistic fast-fading assumptions demonstrate that the nonlinear detectors present improved bit-error-rate performance over the linear detectors and all proposed detectors exhibit significant resistance to the near-far effect.