Impact of Channel Estimation Errors on the Performance of DFE Equalizers with Space Time Block Codes in Wideband Fading Channels

Multiple-input multiple output (MIMO) techniques can be applied to radio systems to enhance performance in fading channels, to exploit spatial and temporal diversity, and to increase the potential transmission rate. Here we investigate the combination of decision feedback equalizers (DFE's) with Alamouti space-time block codes (STBQ) in time-varying wideband channels. Most prior work considers the use of STBC in flat-fading channels. However, for many mobile applications, time and frequency selectivity in the wireless channel must be included in the analysis. As a result of delay spread and terminal mobility, the transmitted data stream can suffer from severe time varying inter symbol interference (ISI) which requires a form of channel equalization. For a quasi-static environment Alamouti's linear combining scheme provides a reliable and low complexity MIMO solution when perfect channel state information (CSI) is available. In this paper we address the mitigation of wideband channels effects on Alamouti STBC codes. The study considers the minimum mean square error (MMSE) performance as a function of channel estimation error for maximum likelihood (ML) and DFE equalizers.