Estimation of the number of narrowband signals in the presence of multipath propagation

In this paper, we address with the problem of detection the number of narrowband signals impinging on a uniform linear array (ULA) in the presence of multipath propagation. Firstly, by forming a differencing matrix from the array covariance matrix to eliminate the effects of uncorrelated incident signals and additive noises, a combined matrix is constructed from this differencing matrix to decorrelate the coherence of signals. Since the number of coherent signals is revealed as the rank of this resultant matrix, a singular value based ratio criterion is proposed to estimate the number of coherent signals. Then, another singular value based ratio criterion is also presented to determine the number of uncorrelated signals from the array covariance matrix. The notable advantage of the proposed method is that it can detect more signals compared to some existing methods, and the number of signals resolved by our method can exceed the number of array sensors.