Optimal Ratio between Coherent and Orthogonal Signals in Sparse MIMO Radar

This paper addresses the problem of spatial waveform design for collocated multiple-input multiple-output (MIMO) radar systems with sparse antenna arrays. The use of sparse arrays allows to obtain narrower beams and therefore higher angular resolution and accuracy. However, if the spatial waveform is not designed properly, the resulting transmit-receive beam-pattern may suffer from significant sidelobes or ambiguity, which can strongly degrade the estimation performance. The Bayesian Cramer-Rao bound (BCRB), which is commonly used for waveform design, may produce inappropriate results as it considers only local errors and ignores the effect of sidelobes and ambiguity. To overcome this limitation, we propose using the arbitrary test-point transformation Weiss-Weinstein bound (AT-WWB) that was recently proposed, as an optimization criterion. This bound is a simpler and tighter version of the Weiss-Weinstein bound (WWB). This bound is derived for collocated MIMO radar and is minimized with respect to the ratio between coherent and orthogonal signals. The proposed method is demonstrated via simulations, and compared to optimization schemes using the BCRB and the WWB. It is shown that the spatial waveform optimized by AT- WWB exhibits superior performance in terms of direction-of-arrival estimation accuracy.