we present a new space–time block code for timeand frequency-selective (doubly-selective) channels. It can be interpreted

as the extension of the Alamouti code to doubly-selective channels, and relies on a joint time–frequency reversal of the transmitted sequences. Under

certain channel conditions, the proposed space–time block code belongs

to the class that achieves full spatial, delay, and Doppler diversity using a

maximum-likelihood (ML) receiver, as well as a linear zero-forcing (LZF)

or linear minimum mean-squared error (LMMSE) receiver. For realistic

doubly-selective channels, a real-valued linear data model is presented, for

which different receiver structures can be developed.