MIMO enabled multipath clutter rank estimation

Multiple-input multiple-output (MIMO) radar is an emerging technology that has the capability of providing range dependent transmit-domain degrees of freedom via receiver processing. When providing these additional degrees of freedom for target tracking, MIMO radar exhibits a lower signal-to-noise ratio (SNR) when compared to that of traditional single-input multiple-output (SIMO) phased array radar. Previous work has indicated the efficacy of combining MIMO operation with space-time adaptive processing (STAP) techniques in the presence of multipath clutter to improve the signal-to-clutter-plus-noise ratio (SCNR). The tradeoff between target SNR and SCNR in multipath propagation environments is a crucial consideration in MIMO radar. In this paper, a transmit-receive directionality spectrum (TRDS) is used to examine the clutter characteristics at a range-Doppler bin of interest, most notably in multipath situations where MIMO operation is advantageous. In situations where ground clutter is spread in Doppler frequency and azimuth by motion in the propagation environment, the clutter rank can be significantly higher than a Brennan´s rule estimate. However, the transmit observability within the MIMO data vector allows for a low rank representation of the clutter when compared to the total available degrees of freedom. A TRDS-based method based on the resolution limits of uniformly spaced linear transmit and receive arrays is presented which furnishes an estimate of the transmit-receive clutter rank in scenarios where Brennans rule provides a significantly underestimated measure. The proposed TRDS-based clutter rank estimation method is applied to both numerical simulations and experimental data.