CMA-based Techniques for Adaptive Interference Rejection

This paper surveys several recent developments in the area of applying the Constant Modulus Algorithm (CMA) to the problem of rejecting interference from a signal deemed to be of interest. This algorithm was originally developed for removing the dispersive effects of multipath propagation from constant envelope communications signals, but has proven useful in a variety of other applications, such as suppressing additive narrowband interference, combining diversity receiving channels to reject crosspolarized signal components, and steering nulls in a sensor array. The paper first reviews the algorithm itself and its original application. From this departure point, several applications, including those listed above, are examined and performance results cited where possible. Some of these applications have encouraged the development of modified algorithms - several of these are described, including one employing real-valued data and another which allows "fast" convergence rather than the slower convergence characteristic of the gradient-search-based algorithms.