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An Underwater Acoustic OFDM Communication System with Robust Doppler Compensation


Taisaku Suzuki†, Tomohisa Wada††, Hiromasa Yamada†††, and Shigeo Nakagawa†††


Vol. 17  No. 9  pp. 172-179


This paper proposes an underwater acoustic QPSK/16QAM/64QAM OFDM communication system with robust Doppler compensation. This system has OFDM receiver which possesses additional time domain signal processing such as signal shrink-expansion processing and Doppler shift compensation capabilities in order to mitigate Doppler shift effect caused by transmitter and/or receiver movement. The outputs of the four OFDM receivers are further combined by frequency domain diversity combiner with Maximum-Ratio Combining (MRC) algorithm to improve Signal to Noise Ratio. Our system utilized 20-28[kHz] ultrasonic OFDM channel and subcarrier spacing of 100[Hz]. Total number of sub-carriers is 81. QPSK/16QAM/64QAM modulations are used. The proposed system is verified by computer simulations and ocean measurement at Shizuoka prefecture in Japan. By performing experiment in the ocean at depth of 1000m, BER of approximately less than 1E-2 has been successfully obtained using 64QAM, and surface ship received a taken image from 1000m deep camera system.


Underwater, Acoustic Communication, OFDM, MRC, Doppler Compensation