FAST SEARCH METHOD FOR VECTOR QUANTIZER COMMUNICATION AND PATTERN RECOGNITION SYSTEMS

An encoder apparatus for communication and pattern recognition systems employing a nearest neighbor search method for signal and data compression, based on a vector encoding quantization technique which optimizes systems performance with substantially reduced computational complexity using a fast geometrically-oriented search procedure. The apparatus comprises pre-procesing apparatus for providing off-line reorganization of a codebook having a set of reference vector patterns constituting codevectors with which the input vector is to be compared in a search procedure, and on-line apparatus for encoding the random input vector through quantization in accordance with the search procedure in the codebook. The on-line encoding apparatus comprises: apparatus for providing a transform domain vector having a set of eigenvectors associated therewith; apparatus for determining a surface vector nearest to the transform domain vector on the axis having the largest variance; apparatus for determining a distance value providing the distortion between the transform domain vector and the surface vector, defined by the Euclidean distance; apparatus for determining a codebook contiguous sub-group range having contained therewithin codevectors and being bounded by a hypersphere having a k-dimensional radius defined as the square root of the distance value; and apparatus for performing a full search over the contiguous sub-group range within the hypersphere to select the one of the codevectors nearest to the transform domain vector for encoding it in accordance with the one selected codevector.