Lookahead in growing tree-structured vector quantizers

A technique is presented for directly designing an unbalanced variable rate tree-structured vector quantizer. The algorithm is an extension of an algorithm for decision tree design which grows the tree one node at a time rather than one layer at a time. The node that is split is the one that yields the greatest slope of decrease in distortion to increase in rate. This is performing a lookahead step of depth one. The authors then modify the growing technique to allow for lookahead of depths two and three. It is found that two- and three-step lookahead provide only slight improvement in the signal to noise ratio of the overall tree (on the order of 0.6 dB)