A fast VQ encoding algorithm

Hadamard transform (HT) based equal-average equal-variance nearest neighbor codeword search algorithm (HTEENNS)

is presented.Before the search process

all codewords in the codebook are Hadamard-transformed and sorted in the ascending order of their first elements.During the search process

we firstly perform the HT on the input vector and calculate its variance

and initialize the current closest codeword of the input vector to be the codeword whose Hardamard-transformed first element is nearest to the input vector's

and secondly two efficient elimination criteria are used to find the nearest codeword to the input vector using the up-down search mechanism near the initial best-match codeword.Experimental results demonstrate that the performance of the proposed algorithm is much better than that of the ENNS

EENNS

and Hadamard transform based PDS algorithms.