Space–Time MMSE Advanced Detector for Multisatellite Systems Under Nonideal Conditions

The transmitter diversity is accepted as one of the main techniques for improving performance, capacity, or simply for facing fading or power impairments in wireless communication systems such as downlink universal mobile telecommunications system (UMTS), satellite UMTS, and short-range communications (IEEE802.11 family, UWB, etc.). Unfortunately, the space- time transmit diversity (STTD) needs the channel knowledge at the receiver, and thus, errors in the estimation process at the receiver can drastically reduce the diversity gain. This paper deals with the development of two new schemes of space-time MMSE receivers implemented for the forward link of a wideband code division multiple access (WCDMA) multisatellite system and their performance evaluation under nonideal conditions. The aim of this paper is to show that the schemes proposed are able to better mitigate multiple access interference, that they show robustness against an imperfect knowledge of the channel state, and that they do not need a synchronization of the symbols transmitted by the satellites in order to let STTD technique work properly. A comparison with other two space-time MMSE detectors which have already been dealt with in the literature is also included. The detectors are compared by means of the simulation of a realistic multisatellite WCDMA environment. Bit error rates are calculated by means of Monte Carlo simulations, assuming a time-varying satellite channel model. The results show that the receivers proposed in this paper outperform the detectors presented in the literature in the vehicular channel, i.e., when the receiver has a high mobility, although a 30deg of channel phase coefficient estimation error is present.