For DS/CDMA systems in the frequency-selective fading channels, an improved adaptive MMSE receiver is proposed in this thesis.
It is observed that multi-path interference of the desired user causes some bias in channel estimate of the receivers developed so far when the channel is frequency-selective. It is also observed that the BER performances of the receivers are degraded due to the above channel-bias problem in frequency-selective fading channels.
Based on these observations, we modified the channel estimation method of adaptive MMSE receiver to diminish the multi-path interference of the desired user. Specifically, with the aid of decision of the adaptive MMSE receiver, the multi-path interference of the desired user is regenerated and substracted from the received signal and then less noisy and unbiased ML estimates of the channel coefficients are obtained. Consequently, this accurate channel estimate leads to the BER performance gain in frequency-selective fading channels.
The above adaptive MMSE receiver is verified that it performs better than conventional adaptive MMSE receivers about 2~5dB in Wideband CDMA-featured environments by computer simulations.
