Chirp-based LPD/LPI underwater acoustic communications with code-time-frequency multidimensional spreading.

Most underwater acoustic communication systems incorporate well-recognized, easily detectable narrowband signals modulated over low-frequency carriers at high transmission powers, which ultimately limits LPD/LPI performance of the communication scheme. While there have been promising works concentrating on LPD/LPI performance, they are for the most part based on direct-sequence spread spectrum (DSSS) techniques, which have been shown to be blindly detectable in previous work at relatively low SINR values. As a result, there is likely significant room to improve the LPD/LPI performance of underwater acoustic communication schemes. To this end, in this paper, we propose the preliminary design of a novel communication scheme based on transmitting chirp signals that are further spread over a multidimensional domain spanning code, time, and frequency. We evaluated the performance of the proposed scheme both with simulation and experimental studies.