Showing papers by "Allen Gersho published in 1982"

On the structure of vector quantizers

Abstract: Vector quantization is intrinsically superior to predictive coding, transform coding, and other suboptimal and {\em ad hoc} procedures since it achieves optimal rate distortion performance subject only to a constraint on memory or block length of the observable signal segment being encoded. The key limitation of existing techniques is the very large randomly generated code books which must be stored, and the computational complexity of the associated encoding procedures. The quantization operation is decomposed into its rudimentary structural components. This leads to a simple and elegant approach to derive analytical properties of optimal quantizers. Some useful properties of quantizers and algorithmic approaches are given, which are relevant to the complexity of both storage and processing in the encoding operation. Highly disordered quantizers, which have been designed using a clustering algorithm, are considered. Finally, lattice quantizers are examined which circumvent the need for a code book by using a highly structured code based on lattices. The code vectors are algorithmically generated in a simple manner rather than stored in a code book, and fast algorithms perform the encoding algorithm with negligible complexity.

Image coding using vector quantization

Abstract: An image is partitioned into cells of pxp pixels. Each cell is regarded as a vector of dimension p2and is encoded by searching through a codebook for a nearest matching representative vector. A binary word identifying the selected representative vector is assigned as the codeword to describe the original cell. The decoder uses this codeword to address a codebook. Each entry of the codebook contains a full precision digital representation of one of the N representative vectors. The codebook design is based on a clustering technique for vector quantizer design preceded by a classification of training cells into edge or shade cells. Results for coding rates from 0.5 to 1.5 bits/pixel are discussed. Vector quantization appears to be a powerful and promising technique for image coding.

Interference cancellation method and apparatus

Abstract: Weighted sums of samples of an interference-corrupted data signal are generated to form phase-compensated, symbol-spaced samples. The interference-corrupted signal is at the same time subjected to conventional adaptive equalization and is otherwise processed so as to form tentative decisions as to the transmitted data. Cancellation signals representing the interference components of the phase-compensated samples are generated by forming respective weighted sums of the tentative decisions and each cancellation signal is combined with a respective phase-compensated sample to provide cancelled samples from which final data decisions are made. The weighting coefficients used to form the phase-compensated samples and the cancellation signals are adaptively updated in response to error signals derived from the difference between each cancelled sample and the corresponding final decision.

Multidimensional channel coding

Abstract: An n-dimensional channel code is used in a data transmission system. The alphabet of codewords (data symbols) comprises a subset of points of a selected coset of a selected lattice. The alphabet includes at least one point of the coset whose norm (signal energy) is greater than at least one other point of the coset which is excluded from the alphabet.