Proposal of partially decodable Ziv-Lempel code

Abstract

With the digital representation of various data, such as speech, images, and messages, together with enhanced computer capabilities, it has become indispensable to apply data compression techniques to communication systems and recording systems. Among those, universal codes, including Ziv-Lempel codes, are widely used in computers, since the best compression can be realized asymptotically when the input string length is increased, even if the statistical properties of the input sequence are unknown. A problem arises, however, in connection with random data access or browsing, which are important functions in multimedia systems. In the Ziv-Lempel code, decoding must always be started from the top of the codeword sequence, even if only a part of the input coded sequence is to be decoded. This leads to an excessive load on computer resources. This paper proposes a code based on the Ziv-Lempel code in which partial decoding is possible. The proposed code is theoretically analyzed. The condition for the proposed code to be a universal code is presented. The encoding and decoding algorithms are implemented on a computer, and the result of the analysis is shown to be valid. It is shown that the proposed code has advantages over the Ziv-Lempel code from the viewpoint of applications, because the range of error propagation is restricted when an error is produced in decoding, and the decoding process can be accelerated by parallel processing. © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(12): 79–87, 1999