New MODE-based techniques for direction finding with an improved threshold performance

We propose two MODE-based direction finding techniques with a drastically improved SNR threshold as compared to the conventional MODE method. Our algorithms preserve all good properties of MODE, such as asymptotic efficiency, excellent performance in scenarios with highly correlated sources, as well as a reasonable computational cost, Similarly to conventional root-MODE, our techniques do not require any multidimensional search since they are based on a combination of polynomial rooting and a simple combinatorial search. The first algorithm referred to as MODEX (MODE with EXtra roots) makes use of a certain polynomial with a larger degree than that of the conventional MODE-polynomial, The second algorithm referred to as resampled MODEX is additionally based on a statistical resampling procedure to resolve subspace swap problems. In both our techniques, the source directions of arrival (DOAs) are estimated via checking a certain (enlarged) number of candidate DOAs using either the stochastic or the deterministic maximum likelihood (ML) function. To reduce the number of candidate DOAs and the whole computational cost in our procedures, a priori information about source localization sectors can be exploited straightforwardly. Computer simulations with uncorrelated and coherent sources show dramatic improvements of the threshold estimation performance that can be achieved by our techniques relative to conventional MODE. (C) 1999 Elsevier Science B.V. All rights reserved.