Sea trial results of a chaotic direct-sequence spread spectrum underwater communication system

Recent theoretical results show that use of chaotic dynamics can significantly increase privacy of digital communication signals. The purpose of this paper is to report sea trial results of a chaotic spread spectrum system. Due to its ability to simultaneously sharing the same frequency band for various users (through Code Division Multiple Access) and its robustness against channel imperfections, it is the Direct-Sequence scheme that we use in our system. This is done by using a chaotic dynamic for the spreading code generator. Two receiver structures are discussed; one is similar to the matched filter structure usually encountered in standard DS-SS systems; the other, more original, is based on a state-space formulation to recover various parameters of the incoming chaotic signal. Through these first sea trials, we aim to prove the feasibility of a chaos-based transmission for a single user that operates without any covertness constraint. Other tests will be conducted soon to evaluate the performances for a Signal-to-Noise Ratio below 0 dB.