A chaotic Direct-Sequence Spread-Spectrum system for underwater communication

The recent advances in acoustic modem technology have enabled the development of Underwater Acoustic Networks (UAN). Application interests include oceanographic information gathering, environmental monitoring or coastal defense. Due to its ability of simultaneously sharing the same frequency band for various users and the poor propagation conditions usually encountered in shallow water environment, the Code Division Multiple Access (CDMA) is a promising scheme for UAN. Recent results show that a standard CDMA direct-sequence spread spectrum approach is not sufficient to ensure Low Probabilities of Detection (LPD) and/or Interception (LPI), that is an unauthorized observer may notice that a communication signal is present. For many applications, this drawback is not acceptable. In this paper, the application of chaos to transmission of information is under investigation to achieve an LPI/LPD objective in an UAN context. Performance results of two receivers are shown for a single user through a realistic simulation scenario. An experiment at sea will be conducted by GESMA soon to confirm these first results.