Modified Huffman based Text Compression Scheme for VLF Communication System

Ships and submarines, being the important and critical assets of Naval Forces, it becomes essential to convey tactical information to them during operation under hostile environment. Principally, Very Low Frequency (VLF) band is used across the world for communication with Naval vessels. The VLF communication system is used to broadcast text messages to ships and submerged submarines using land based high power transmitters. With accelerating developments in communication and changing global scenario, it is very challenging to increase data rate under low bandwidth constraint. To enhance the capacity of VLF system, lossless data compression with reference to text messages is required. There is enough work done on text compression as English dictionary text is said to have entropy of the order of 2.5 bits per character. Compression to this performance is achievable by use of higher order statistical coding schemes. However, the performance of these schemes is highly dependent on the input message size, making them practically not suitable for low data rate which requires small packet based communication to reduce latency. Additionally, a single bit error in the receive sequence produces unlimited character errors in adaptive data compression decoding schemes. Huffman scheme on the other hand has no such limitations. In this paper, modified Huffman based text compression scheme for low data rate and small packet based communication has been presented.