Experimental validation of a chirp-based underwater acoustic communication method

Abstract

A wireless underwater acoustic communication algorithm based on the combination of chirp modulation and direct-sequence spread-spectrum signaling is presented. In this paper, the processing chain design is proposed, discussed, and demonstrated using real data. The communication algorithm is made of a transmission block encoding the bits with adequate linear chirps multiplied by pseudo noise (PN) sequences, and a rake receiver that allows one to positively exploit the energy present in the most significant propagation paths. The use of chirp signals takes advantage of the low Doppler sensitivity in the matched filter operation whereas the choice of PN sequences allows one to reduce narrowband interference arising from other users and self-interference due to multipath propagation. Moreover a tracking procedure that allows an adaptation to the instantaneous Doppler shift has been devised and tested. Some experiments have been carried out changing the distance and the speed between transmitter and receiver. Results show that the developed communication method is able to handle the multipath phenomenon and the Doppler effect, allowing one to achieve a bit error rate less than 10 (-3) for long ranges for bit rates of about 15 and 230 bit/s.