High-Speed Acoustic Data Link Transmitting Moving Pictures for

Autonomous Underwater Vehicles

A0153 Junichi Kojima KDDI R&D Laboratories

A0148 Tamaki Ura Underwater Technology Research Center, Institute of Industrial Science, University of Tokyo

A0154 Hiromoto Ando National Maritime Research Institute

A0130 Kenichi Asakawa Deep Sea Research Department, Japan Marine Science and Technology Center

This paper will describe a new high-speed acoustic data link for an

Autonomous Underwater Vehicle that can inspect underwater structures

at the depth of up to 3000 metes. The acoustic transmission will be

performed between the AUV and a repeater that will be suspended from a

mother ship using an optical fiber cable at distance of 500 meters

from the seabed. This configuration reduces the transmission distance

and enables high-speed transmission of compressed moving video signal.

KDD R&D laboratories have already developed acoustic data transmission

system of 32 kbits/s transmitting compressed still pictures. The

maximum transmission speed for the new link was increased to 128

kbits/s that was enough for transmitting moving video signal.

A wideband transducer is a key device to realize the high-speed

transmission. A new transducer was developed using a composite

oscillator that consists of a number of separated thin cylindrical

piezoelectric ceramic. With this configuration, wide frequency

bandwidth and wide directivity could be realized at the same time.

The frequency band and the directivity of the fabricated transducer is

80kHz to 120 kHz and 30 degrees respectively, that is enough for

transmitting 128 kbits/s signal. The size of the transducer is 60 mm

in diameter and 80 mm in length, that is small enough for being

mounted on a small-sized AUV.

The electronics of the underwater system consists of a DSP board for

the modulation and a power amplifier. The size and weight of the

electronics are very small (160mm (L), 90mm (W), 60mm (D) ) and light

enough to be put on a small AUV.

Tank tests were performed in order to optimize the parameters of the

adaptive equalizer, the carrier recovery circuit and the timing

recovery circuit. As a result, it was confirmed that this acoustic

data link could transmit 128kbits/s signals.