* ENST-Bretagne, BP 832, 29285 Brest Cedex, France
** G.E.S.M.A. (Groupe d'Etudes Sous-Marines de l'Atlantique), BP 42, 29240 Brest Naval, France

The GESMA is developing a high data rate acoustic link whose robustness must allow communication between a mobile and a surface vessel. The selected multi-channel blind equalizer is designed to follow strong variations of underwater acoustic channel (UWA). This patented equalizer developed by ENST-Bretagne is the heart of a digital processing whose integration on a DSP (Digital Signal Processor) platform is currently carried out. Acquisition, timing, carrier and phase recovery, equalization, and decision are jointly optimized. Its validation must make it possible the GESMA to transmit real-time informations to data rate higher than 25 kbps in horizontal configuration.

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* ENST-Bretagne, BP 832, 29285 Brest Cedex, France
** G.E.S.M.A. (Groupe d'Etudes Sous-Marines de l'Atlantique), BP 42, 29240 Brest Naval, France

There is no doubt about the growing interest in underwater acoustic communications. Among all existing applications, the objective of the Groupe d Etudes Sous-Marines de l Atlantique (GESMA) is to develop a sufficiently robust high data rate acoustic link, named TRIDENT. For that purpose, different kinds of information (text, images...) could be periodically emitted through the acoustic channel. A real-time receiver, based on a spatio-temporal blind adaptive decision feedback equalizer, developed and patented by ENST Bretagne was designed to cope with all perturbations induced by such harsh channels. Some sea trials were realized on June 2002. The first results are clearly convincing since most of the 48 sequences of 5 minutes are successfully demodulated by the DSP in realtime. This acoustic system allows the transmission to data rate from 8 to 25 kbps in horizontal configuration.

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* ENST-Bretagne, BP 832, 29285 Brest Cedex, France
** G.E.S.M.A. (Groupe d'Etudes Sous-Marines de l'Atlantique), BP 42, 29240 Brest Naval, France

This paper deals with blind adaptive equalization for short burst communication syste m. Until now, blind adaptive equalizers have been mainly dedicated to continuous data stream ap plications because of their supposedly well-known slow convergence. The aim of the paper is two fold. It intends both to combat this latter idea and to stress the relevance of the blind appro ach, under two mild conditions of sufficient burst length and channel stationarity. In some cas es, conventional results of equalization are not adequate. This paper proposes two different te chniques for improving the performance of equalization processing. For that purpose, the blind decision feedback equalizer introduced in is combined with an iterative procedure and operates on both direct and time reverse sequences. Performances are illustrated with examples of 4-PSK short bursts and underwater acoustic signals. The results are very convincing since, at a low computational cost, the challenge of recovering all the data has now been taken up.

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* ENST-Bretagne, BP 832, 29285 Brest Cedex, France
** G.E.S.M.A. (Groupe d'Etudes Sous-Marines de l'Atlantique), BP 42, 29240 Brest Naval, France

There is no doubt about the growing interest in underwater acoustic communications. Among all existing applications, the objective of the Groupe d'Etudes Sous-Marines de l'Atlantique (GESMA) is to develop a sufficiently robust high data rate acoustic link, named TRIDENT. A real-time receiver, based on a spatio-temporal blind adaptive decision feedback equalizer, developed and patented by ENST Bretagne was designed to cope with all perturbations induced by such harsh channels. Some sea trials were realized on 2002. The first results are clearly convincing since most of the 48 sequences of 5 minutes are successfully demodulated by the DSP in real-time. This acoustic system allows the transmission to data rate from 8 to 25 kbps in horizontal configuration and stand for an important step in the design of future operational acoustic communications.

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