ns STBC for purely time-selective channels by transforming the

time-selective channels into frequency-selective channels, and by

adjusting existing space–time code designs over frequency-selective

MIMO channels to collect joint space–Doppler gains over purely

time-selective MIMO channels. Further, [14] uses the ideas of [12] to

develop a space–time code that can achieve full space-delay-Doppler

diversity for any number of transmit–receive antennas. However, to

quantify the maximum Doppler diversity order [2], the above papers

rely on a parsimonious critically sampled complex-exponential basis

expansion model (CCE-BEM) for the underlying purely time-selective

or doubly-selective channels [16]. However, the CCE-BEM may have

a large modeling error under certain channel conditions