Quadratically constrained adaptive beamforming in coherent interference environments

In linearly constrained minimum variance (LCMV) adaptive beamforming, signal cancellation often results if coherent interferers are present. The authors propose adding a constraint to prevent such signal cancellation. The additional constraint limits the beamformer output mean squared error to be less than a specified level for a set of likely interference scenarios and is thus a quadratic constraint. For a properly chosen constraint, it is shown that the original LCMV adaptive beamformer´s signal cancellation can be reduced to an arbitrarily small level without interference cancellation degradation. This approach does not require a uniform array structure and is applicable to both broadband and narrowband signals. Its effectiveness is illustrated through simulation results.<>