Signal Enhancement in AM-FM Interference
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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A new approach to interference suppression is developed to enhance the audibility of signals corrupted by amplitude-modulated AM and frequency- modulated FM tonal interference. The suppression algorithm uses a short-time, least-squares estimation of the parameters of an AM-FM model of the time-varying tonal interference. The method, developed in a sine-wave analysissynthesis framework, can be integrated with time and frequency modifications for further signal enhancement. Suppression is applied to single and multitone synthetic and actual AM-FM interference, the latter including man-made signals e.g., siren interference and those that occur naturally e.g., biologic interference. The relative advantages and disadvantages of the sine-wave framework in contrast to a short-time Fourier transform overlap-add framework are described. The enhancement techniques are robust in a large range of environments and can be designed to preserve a random noise background. Finally, it is shown that interference suppression on multichannels prior to beamforming enhances beamformer performance.