COMPARISON OF SPACE-TIME MMSE DETECTION SCHEMES IN A MULTI-SATELLITE ENVIRNOMENT

This paper deals with the introduction of two new schemes of space-time MMSE reception implemented for the forward link of a WCDMA multi-satellite UMTS environment. The receivers make joint use of space-time transmit diversity [3] and minimum mean squared error (MMSE) filtering. The idea has come from the realization that the diversity gain is limited by a medium-high level of multiple access interference ([14], [2]). The proposed schemes can be distinguished by the order in which the space-time processing and the MMSE interference suppression are performed. We named MMSE Pre STTD if the MMSE filtering is performed before the space-time combining and MMSE Post STTD if the interference suppression and the space-time combining are jointly processed. These new schemes are then compared with other space-time MMSE receivers already presented in the literature [17] [18]. A realistic multi-satellite environment [13], where more than one satellite covers the same ground cell, has been simulated. Bit error rates have been calculated by mean of Monte Carlo simulations assuming a time-varying satellite channel model [7]. The results show that if the MMSE filtering follows the space-time combining, the receiver performance improves. Anyway, both the proposed schemes highlight significantly better performance than the existing ST-MMSE receivers in high loaded cells and, especially, in the vehicular environment (i.e., when the mobile terminal is moving with an average speed equal to 50km/h). Anyway, all the schemes yield better performance than the standard STTD receiver or conventional RAKE receiver.