An Efficient Text Compression Technique Based on Using Bitwise Lempel-Ziv Algorithm

This paper presents an efficient data compression technique based on using Lempel-Ziv coding algorithms such as the LZ-78 algorithm. The conventional LZ-78 algorithm was applied directly to a non-binary information source (i.e., original source) with a large number of alphabets (such as 256 characters in English text). However, this modified technique applies the LZ-78 algorithm to an nth-order extension equivalent binary source which includes 2n symbols. The equivalent binary source is generated by applying an efficient source encoding scheme on the original one. In this encoding scheme, each alphabet in the original source is given a weighted fixed-length code (e.g. eight bits/character). The weighted codes are chosen in such a way that the entropy of the generated binary source is made as close as possible to that of the original one. The reduction in number of symbols in the extended binary source leads to a better compression algorithm performance which can be measured based on the algorithm implementation complexity, memory usage, compression-decompression speed, and compression ratio. Analysis and simulation results obtained based on using the modified compression technique show that the bitwise LZ-78 encoder of the fourth-order extended binary source, which includes 16 symbols, achieves compression efficiency close to that of the conventional LZ-78 encoder, which includes 256 symbols.