Multichannel Adaptive Filtering for Signal Enhancement

An adaptive technique for enhancing a signal against additive noise is described. It makes use of two or more input channels containing correlated signal components but uncorrelated noise components. The various input signals need not be of the same waveshape, since the adaptive enhancer filters the inputs before summing them. The output is a best least squares estimate of the underlying signal in a chosen input channel. Adaptivity allows optimal performance even though the signal and noise characteristics differ from channel to channel and are unknown a priori. Formulas for signal distortion and output noise power are developed. The more input channels available containing correlated signal components, the better will be the system performance. Excellent performance is obtained when the sum of the filter input signal-to-noise ratios (SNR’s), was supported by the National Science Foundation under Grant ECS-7808526, Manuscript received March 25, 1980; revised December 10, 1980. This work by the Office of Naval Research under Contract N00014-76-C-0929, and by the Naval Air Systems Command under Contract N00019-80-C-0483. with ESL Inc., Sunnyvale, CA 94086. E. R. Ferrara, Jr., was with Stanford University, Stanford, CA. He is now B. Widrow is with Stanford University, Stanford, CA 94305. defined as functions of frequency, is large compared to unity at all frequencies of interest. In this case the output noise is small, the output signal distortion is small, and the output SNR is approximately equal to the sum of the filter input SNR’s. As such, the multichannel adaptive signal enhancer is a generalization of the classic time-delay-and-sum beamforming antenna.