Minimum Mean-Squared Error Pilot-Aided Transmission for MIMO Doubly Selective Channels

This paper considers cyclic-prefixed block-based pilot-aided transmission (PAT), with possibly superimposed pilot and data symbols, over multiple-input multiple-output (MIMO) doubly selective channels (DSCs) that obey a complex-exponential basis expansion model. First, a tight lower bound on the mean-squared error (MSE) of pilot-aided channel estimates is derived, along with necessary and sufficient conditions on pilot/data patterns that achieve this bound. From these conditions, novel minimum-MSE (MMSE) PAT schemes are proposed and upper/lower bounds on their achievable rates are derived. The pilot/data power allocation that maximizes the lower bound is also derived. A high-SNR asymptotic analysis of the achievable rates is then performed, which suggests that the channel spreading parameters should be taken into account when choosing among MMSE-PAT schemes. The number of antennas maximizing the high-SNR achievable rates is also derived.