A 32 kHz Bandwidth, 8 Branch Diversity Underwater Acoustic OFDM Communication System

This paper describes a 32kHz bandwidth underwater acoustic Orthogonal Frequency Division Multiple Access (OFDM) communication system to transmit higher definition image or movie data packet from deep see AUV etc. to water surface ship. The transmission data rate is 150 kbps without error correction using 64QAM modulation and 641 sub-carriers. To increase the transmitting wave bandwidth to 32 kHz from 8kHz of the previous generation device, a new transmitting transducer was developed while 8 branches integrated receiver transducer was also developed. To realize a stable data communication with moving environment, two stage Doppler compensation is also applied. The system is verified by Ocean experiment at Uchiura Bay with 100m depth of transmitter in Shizuoka, Japan. By enabling the Doppler compensation signal processing, a stable data communication was confirmed. The approximately 4.7 dB of diversity gain using the 8 branches diversity was measured.