A Low Bit-Rate Speech Underwater Acoustic Phone using Channel Coding for Quality Improvement

GESMA´s (Groupe d´Etudes Sous-Marines de l´Atlantique) objective is to develop a sufficiently robust acoustic link allowing the transmission of different data (text, images, etc.). Implementation of the acoustic link has led the ENST Bretagne to develop a real-time platform called TRIDENT (TRansmission d´Images et de Données EN Temps réel). To reduce the various perturbations caused by the underwater acoustic channel (UWA), a blind spatio-temporal equalizer is used. The acoustic link performance was evaluated and has shown its robustness for transmission over a strongly disturbed channel. GESMA also wants to increase the link reliability and provide a strongly protected low bit rate speech (MELP, 2400 bit/s) transmission. In order to do so, channel coding will be added to the system. Different kinds of error correcting schemes will be tested including convolutional codes (CC) and Reed Solomon (RS) block codes.