Optimal Windowing and Decision Feedback Equalization for Space–Frequency Alamouti-Coded OFDM in Doubly Selective Channels

Space-frequency block coding with orthogonal frequency-division multiplexing (SFBC-OFDM) suffers from the effect of intercarrier interference (ICI) in doubly selective channels. In this paper, a scheme is proposed in which windowing is applied to the received signal to reduce the effect of ICI to a limited number of neighboring subcarriers. The subcarriers holding the SFBC components of each codeword are separated by a number of subcarriers larger than the ICI range, and hence, they do not interfere with each other. To preserve the structure of the SFBC, the separation between the codeword components is also selected within the coherence bandwidth of the channel. As a result, the diversity gain of the SFBC is preserved. By proper selection of the pilot locations, each OFDM symbol can be divided into subsymbols that can be decoded independently. We show that the proposed windowing technique allows the use of decision feedback equalization to estimate the data transmitted in each subsymbol with low complexity. Simulation results are presented showing the ability of the proposed scheme to significantly improve the performance of SFBC-OFDM and preserve its diversity gain.