Self-differential joint frequency and phase modulation for long-range underwater acoustic communications

Narrow available bandwidth, strong multi-path disturbance and serious fading in the long-range channel are main obstacles to the high-rate reliable underwater acoustic communications. In traditional underwater acoustic communication systems, frequency-shift-keying (FSK) and phase-shift-keying (PSK) are typical modulation schemes that are efficient in power and in bandwidth, respectively. But they can’t solve effectively the conflicting demands between the high data rate and reliability. A novel self-differential joint frequency and phase modulation (SD-JFPM) approach is presented in this paper, which is well suited in shallow water channels. In SD-JFPM, phase information is transmitted by the difference between initial phases of the former and latter halves of a certain symbol. The theoretical analysis is given, and also the experiments in lake are conducted. The results demonstrate that the SD-JFPM modulation is effective for the multi-path influence in the fading channel, and can overperform single-carrier modulation by increased data rate and communication reliability.