HIERARCHICAL VECTOR QUANTIZERS WITH TABLE-LOOKUP ENCODERS.

A technique is presented for the design of vector quantizer (VQ) encoders implemented by table lookups rather than by a minimum distortion search. In a table lookup encoder, input vectors to the encoder are used directly as addresses in code tables to choose the channel symbol codewords. In order to preserve manageable table sizes for large dimension VQs, the authors use hierarchical structures to quantize the signal successively in stages. The encoder of a hierarchical VQ (HVQ) consists of several stages, each stage being a VQ implemented by a lookup table. Since both the encoder and the decoder are implemented by table lookups, there are no arithmetic computations required in the final VQ implementation. Preliminary simulation results are presented which demonstrate that the degradation using HVQ over full search VQ is less than 1 dB for speech waveform coding.