Robust Underwater Acoustic Communication Using the Overlapped Chirp Spread Carrier Technique in Doubly Spread Environments

The performance of underwater acoustic communication is significantly affected by multipath propagation and Doppler spread. In this paper, we propose a new communication technique called overlapped chirp spread carrier (OCSC) by modifying the existing sweep spread carrier (SSC) technique, which is robust in a multipath propagation environment. Our proposed OCSC technique uses a repeated carrier wave by combining up-chirp and down-chirp signals and estimates and corrects the Doppler shift frequency of the received signal by utilizing the characteristics of the correlation function of each up-chirp and down-chirp. To demonstrate the performance of the proposed OCSC technique, we provide the results of a simulation using an underwater channel simulator and sea trial conducted in the East Sea. As a result of the sea trial, when demodulating using only the estimated Doppler shift frequency, the uncoded bit error rate reached 0.135. However, when our proposed correction method was applied to the estimated Doppler frequency, the uncoded bit error rate decreased to 0.001.