LONG RANGE REAL-TIME UNDERWATER ACOUSTIC COMMUNICATION AT LOW BIT RATE WITH CHANNEL CODING PROTECTION

The TRIDENT1 project was launched a few years ago by GESMA(2). The First objectives were to develop a multiple rate underwater acoustic link for images, text and data transmission. This link was designed to provide a wireless communication to AUVs(3). Recently the platform was extended to low bit rate speech transmission using a MELP [1] coder working at 2400 bit/s. This allows us to use a lower carrier frequency able to reach a longer range. In order to increase the link reliability, channel coding was added to the system. Different kinds of error correcting schemes including Convolutional Code (CC) and Reed Solomon codes(RS) were checked during river and sea trials. The purpose of this paper is to present the whole platform including both the emitter and the receiver and an overview of the results during the trials. Among the numerous possible applications, one can note mine warfare, offshore activities with the development of digital acoustic links between divers, boats, submarines etc... or a digital underwater acoustic phone. Such an acoustic link is likely to increase underwater activity safety and also widely develop such activities.