Improvement of underwater acoustic communication using Reed Solomon Block Turbo Codes

TRIDENT project was launched a few years ago by GESMA (Groupe d´Etudes Sous-Marines de l´Atlantique) in collaboration with TELECOM Bretagne. First objectives were to develop a multiple rate underwater acoustic link for images, speech signal, text and data transmission. This link was designed to provide a wireless communication to AUVs. Recently the platform was extended to low bit rate speech transmission using a MELP coder working at 2400 bps. Such a bit rate allows the use a lower carrier frequency able to reach longer ranges for speech transmissions. More recently two channel coding options were added to the TRIDENT platform. Convolutionnal codes (CC) and Reed Solomon (RS) block codes were only checked. These simple codes were not able to improve significantly the BER at the channel decoding output. That is why, last year GESMA decided to check the turbo codes options and more precisely the Reed Solomon Block Turbo Codes (RS BTC) to enhance the channel decoding efficiency at the receiver side. This paper presents the different possibilities offered by the platform: images and speech transmissions and the different channel coding options. The data transmitted are interleaved and frame recovery is performed in reception. After system validation in Brest River (November 2009), sea trials have been recently conducted in Brest bay (March 22 to 26, 2010).