Parallel Lempel-Ziv-Welch (PLZW) Technique for Data Compression

Data Compression is one of the most fundamental problems in computer science and information technology. Many sequential algorithms are suggested for the problem. The most well known sequential algorithm is Lempel-ZivWelch (LZW) compression technique. The limitation of sequential algorithm is that ith block can be coded only after the (i-1)th block has completed. This limitation can be overcome by parallelizing the LZW coding technique. Attempt has also been made to parallelize the LZ technique [10]. But here is a new idea for parallelizing the LZW compression technique. It uses a common memory to store the encoded string parallely in a two dimensional array and stores -1 at the end in each row which works as the marker. Similarly each row is decoded parallely by different processors. It is suitably implemented in SMP cluster using MPI library function. The sequential algorithm takes θ(n) where n is the size of text. But the parallel algorithm takes θ (n/p) where p is the number of processor. KeywordsSymmetric multi processor (SMP), message passing interface (MPI), Lempel-Ziv-Welch (LZW)