A multimode adaptive beamformer for quadrature-amplitude-modulated signals

The authors present the results of recent work on an adaptive beamformer designed to enhance the reception of N-state quadrature amplitude modulated (N-QAM) signal in the presence of multipath distortion and cochannel interference. Adaptation of the beamformer is based on a series of performance criteria derived from known properties of the transmitted signal. Neither calibrated look-direction constraints nor prearranged training signals are required. Instead, the beamformer uses blind adaptation to initially suppress multipath distortion and cochannel interference and then switches into decision-directed adaptation to achieve optimal combining