A variable step-size CM array algorithm for fast fading channels

A new constant modulus (CM) array algorithm with a time-varying step size is presented. It is designed for use in a cascade multistage system where each beamformer stage recovers one cochannel source. We assume that each source has a small angular spread and that the antenna elements are closely spaced. For this scenario, the new algorithm ensures that a stage tracks the same source during fast fading conditions, thus yielding reliable source estimation in a nonstationary environment. We present the cost function associated with the algorithm and compare it with that of the original CM array. Computer simulations for Rayleigh fading channels are presented to illustrate the improved tracking behavior of the multistage CM array.