BLIND CMA BEAMFORMING FOR NARROW-BAND SIGNALS WITH MULTIPATH ARRIVALS

The constant modulus algorithm (CMA) is a popular and effective method for blind adaptive beamforming in various wireless communication syst ems. Traditionally, signals of arrival are considered to be independen t However, multipath propagation in wireless systems often results in several correlated signal arrivals. Because of multipath arrivals, CMA beamformers cannot be expected to place nulls in the direction of all interferers as assumed in some existing beamforming. In this paper, w e present a simple convergence analysis of CMA under multipath correla ted arrival signals. We propose two adaptation techniques based on CMA to capture different source signals. One approach is to use an orthog onal projection constraint on the beamformer parameters. The other app roach relies on the independence of source signals and exploits a Gram -Schmidt orthogonalization at the beamformer outputs. Both methods are tested through computer simulations. (C) 1998 John Wiley & Sons, Ltd.