Space-time MMSE receivers for non-ideal multi-satellite channels

The paper deals with the development of two new schemes of space-time MMSE receivers implemented for the forward link of a WCDMA multi-satellite system and their performance evaluation under non-ideal conditions. They are compared with two existing space-time MMSE detectors. The so called space-time transmit diversity (STTD) technique is coupled with MMSE interference suppression. The idea comes from the realization that the diversity gain is limited by a medium-high level of MAI. The classical Alamouti STTD technique needs symbol synchronicity at the receiver. First, we drop this need, extending the STTD technique to the asynchronous signals case. The schemes are named ST-MMSE pre STTD (MMSE filtering performed before the space-time combining) and ST-MMSE post STTD (interference suppression and space-time combining processed jointly). The paper investigates what happens when the channel coefficients are not perfectly estimated. A realistic multi-satellite WCDMA environment has been simulated to compare the detectors. Bit error rates have been calculated assuming a time-varying satellite channel model. The results show that the proposed post-combining scheme gives the best results, when estimation errors are not present, but it is more sensitive to estimation errors than other receivers in the pedestrian channel. Both of the proposed receivers outperform the other schemes in the vehicular channel, i.e., when the receiver has high mobility, although a channel phase coefficients estimation error of 30° is present.