A new class of focussing matrices for coherent signal-subspace method

It is shown on the basis of theoretical and simulation results that the specific structure of the focussing matrix may have profound consequences in the statistical characteristics of the direction-of-arrival estimates. First, the focussing array signal-to-noise ratio (ASNR) loss and relative sufficiency measure are defined. Both can serve as performance measures for choosing a good focussing matrix. Next, factors that lead to the degradation of performance for the coherent-signal-subspace method based on the focussing matrices are identified. A new focussing matrix that is useful for general multigroup situations is introduced to provide a possible remedy. Various classes of focussing matrices are compared from the points of view of relative sufficiency of the reduced data and estimator/detector performance