A new underwater acoustic communication system based on fractional Fourier transform

A new underwater acoustic (UWA) communication system is proposed based on fractional Fourier transform (FRFT) for complex condition of underwater environment. Because of using chirp-basis function in FRFT, this communication mode uses linear frequency modulation (LFM) as carrier signal of transmitted information, which has good anti-jamming capability. The code elements were divided into groups in time-domain and the transmitted information was decoded by using pulse position modulation (PPM) in fractional domain in this scheme. The method of inserting guard interval (GI) in transmitted signal and the Rake receiver was presented to suppress the UWA channel´s multi-path effect which could lead to intersymbol interference (ISI). The information rate is up to 800 bit/s and the feasibility and the robustness of this system were validated through the experimental results, which is helpful for UWA communication of Unmanned Underwater Vehicle (UUV) in complex working environment.