Subspace analysis of spatial time-frequency distribution matrices

Spatial time-frequency distributions (STFDs) have been recently introduced as the natural means to deal with source signals that are localizable in th e time-frequency domain. Previous work in the area has not provided the eig enanalysis of STFD matrices, which is key to understanding their role in so lving direction finding and blind source separation problems in multisensor array receivers. The aim of this paper is to examine the eigenstructure of the STFDs matrices. We develop the analysis and statistical properties of the subspace estimates based on STFDs for frequency modulated (FM) sources. It is shown that improved estimates are achieved by constructing the subsp aces from the time-frequency signatures of the signal arrivals rather than from the data covariance matrices, which are commonly used in conventional subspace estimation methods. This improvement is evident in a low signal-to -noise ratio (SNR) environment and in the cases of closely spaced sources. The paper considers the MUSIC technique to demonstrate the advantages of ST FDs and uses it as grounds for comparison between time-frequency and conven tional subspace estimates.