Channel Coding for Underwater Acoustic Communication System

GESMA (Groupe d'Etudes Sous-Marines de l'Atlantique) objective is to develop a sufficiently robust acoustic link allowing the transmission of different information (text, images...). A real-time platform named TRIDENT (TRansmission d'Images et de Donnes EN Temps reel) was designed at ENST Bretagne. A blind spatio-temporal equalizer is used to reduce the various perturbations brought by the underwater acoustic channel (UWA). The acoustic link performances was evaluated and shown its robustness for transmission in a strongly disturbed channel. GESMA also wants to increase the link reliability and provides strongly protected low bit rate speech (MELP, 2400 bps) transmission. In order to do so, a channel coding will be added to the system. Different kinds of error correcting scheme will be tested including Convolutional Codes (CC) and Reed Solomon (RS) block code. A Differential Phase-Shift Keying (DPSK) is used to solve phase ambiguities in case of CC coding and Viterbi decoding utilization.