Colocated MIMO radar: Cramer-Rao bound and optimal time division multiplexing for DOA estimation of moving targets

Multiple-Input-Multiple-Output (MIMO) radars with colocated transmit and receive antennas offer the advantage of a larger (virtual) aperture compared to a conventional Single-Input-Multiple-Output (SIMO) radar. Hence a higher accuracy of the estimated direction of arrival (DOA) of a target can be achieved. In general, the accuracy of DOA estimators decreases in a MIMO radar if the target moves relative to the radar, because the motion causes an unknown phase change of the baseband signal due to the Doppler effect. We compute the Cramer-Rao bound (CRB) of DOA estimation of a non-stationary target for a MIMO radar with colocated antennas for a general time division multiplexing (TDM) scheme. This allows a quantitative comparison of different MIMO and SIMO radars. Moreover, we derive an optimal TDM scheme such that the CRB is as small as in the stationary case. The results are confirmed by simulations.