UNBIASED SEPARATION AND ENHANCEMENT OF SOURCES BY USING A ZERO TRACKING ALGORITHM WITH POST-PROCESSING ADAPTIVE NOISE-REDUCTION

This paper proposes and investigates a new structure for the unbiased separation, tracking, and enhancement of uncorrelated sources by a lin ear array. The structure consists of a matrix preprocessing beamformer followed by an adaptive linear combiner and a postprocessing beam-for mer. The weights of the adaptive linear combiner are updated by using the LMS algorithm and, together with the preprocessor, implement an ad aptive array whose response zeros are adjusted to minimize the output power with unity element weight vector norm constraint. By properly de signing the preprocessor, first-order movements in the response zeros can be individually and proportionally controlled by first order chang es in the weights in the linear combiner, and the preprocessor outputs will be due to individual sources and receiver noise in the steady st ate. By measuring the powers of the preprocessor outputs, it will be p ossible to determine if a particular preprocessor output is due to an actual source (if the associated zero is tracking a source) or merely receiver noise (if the associated zero is not tracking any source). Fu rther SNR enhancement is then carried out by making use of those prepr ocessor outputs due to receiver noise to remove the correlated receive r noise components in the other preprocessor outputs tracking actual s ources through the use of a matrix postprocessor. Apart from the imple mentation of the preprocessor and postprocessor which will be inevitab le in any source separation system and which have to be designed only occasionally and whenever the response zeros have been found to have c hanged significantly, the algorithm has an implementation complexity w hich is proportional to the array size. However, as the preprocessor o utputs are due primarily to individual sources in the steady state, th e algorithm has only one single asymptotic time constant controlled by the designed misadjustment level and has fast tracking performance. ( C) 1997 Academic Press.