Forward/Backward Spatial Smoothing Techniques For Coherent Signal Identification

In the context of coherent signal classification, a spatial smoothing scheme first suggested by Evans et al., and subsequently studied by Shan et al., is further investigated. It is proved here that by making use of a set of forward and complex conjugated backward subarrays simultaneously, it is always possible to estimate any K directions of arrival using at most 3K/2 sensor elements. This is achieved by creating a smoothed array output covariance matrix that is structurally identical to a covariance matrix in some noncoherent situation. By incorporating the eigenstructure-based techniques on this smoothed covariance matrix, it then becomes possible to correctly identify all directions of arrival irrespective of their correlation.