Conjugate gradient method for adaptive direction-of-arrival estimation of coherent signals

A method for the direction-of-arrival (DOA) estimation of coherent signals is proposed, based on the adaptive version of Pisarenko´s harmonic retrieval method. It is known that for the DOA estimation of coherent signals, the computed covariance matrix of the sensor array must be spatially smoothed to preserve its full rank. Adaptive algorithms using the conjugate gradient (CG) methods can take advantage of this pre-processing by incorporating the available smoothed matrix into the algorithm. The proposed algorithm uses the CG algorithm presented previously (see IEEE ICASSP, p.2279-82, 1996) in combination with spatial and temporal smoothing techniques. Our simulations show that the proposed algorithm has a fast convergence rate even when the input signals are coherent. Due to the use of an updated covariance matrix at each time instant, no internal iterations are used as in regular CG methods, resulting in a more efficient algorithm than previously proposed CG methods