Design and Testing of Underwater Acoustic Communications for an AUV

This paper presents an autonomous underwater vehicle (AUV) underwater acoustic communication system. There are two communication modes integrated to meet the different requirements, that is, (1) spread spectrum underwater acoustic communication, with a variable transmission rate from 70 to 400 bps, to transmit instructions, (2) orthogonal frequency division multiplexing (OFDM) communication, with a variable transmission rate from 600 bps to 2.4 kbps, to transmit data information. The communication mode can be distinguished according to the sweep frequency direction of the Linear Frequency Modulation (LFM) chirp signal in the receiver. A four-element hydrophone array is lowered from the mother ship to a certain depth, and passive time reversal technology is adopted, the array element spacing is 4 times the wavelength of a signal (6–10 kHz bandwidth) at the center frequency. The symbol timing offset and Doppler shift caused by moving between the AUV and the mother ship were simultaneously estimated and corrected. The AUV communication lake test and sea trial were performed in August and September 2013, and the results of the experiments are reported in this paper.