A new preprocessing method is proposed for joint direction-of-arrival and frequency estimation in the presence of coherent signals by effectively extending the forward/backward spatial smoothing technique in the 1-D case to the spatio-temporal array data matrix in the 2-D case.This paper analyzes in detail how to construct the forward/backward smoothed spatio-temporal array data matrix and the conditions under which the identifiability of signal parameters is guaranteed.Unlike the existing methods using only the forward spatial smoothing technique

the performance of the proposed method is greatly improved due to utilizing both the forward and backward spatial smoothing technique.It requires few sensors

exhibits high accuracy and resolution and performs well under low signal-to-noise ratio (SNR).