Nested array processing for distributed sources

We consider the problem of using linear nested arrays to estimate the directions of arrival (DOAs) of distributed sources and to detect the source number, where we have more sources than actual physical sensors. Angular spread, caused by the multipath nature of the distributed sources, makes the commonly used point-source assumption challenging. We establish the signal model for distributed sources, using a nested array. Due to the characteristics of distributed sources, the regular spatial smoothing technique, which is used to exploit the increased degrees of freedom provided by the co-array, no longer works. We thus propose a novel spatial smoothing approach to circumvent this problem. Based on the analytical results, we construct the corresponding DOA estimation and source number detection methods. The effectiveness of the proposed methods is verified through numerical examples.