Abstract
Research work carried out in the Underwater Systems Laboratory of the Department of Electronic Engineering over the past seven years has shown that it is possible to design and build reliable ultrasonic based data links for use underwater.

The rapid expansion of underwater exploration and inspection that has occurred over the past decade has resulted in a thriving market for underwater data systems. These are used for monitoring remote sensing stations as well as communications with underwater-deployed personnel.

Current systems available on the market operate at from 2400 to 9600 baud transmission rate. This is barely adequate for most data communications applications, and it is clear, from market research and other similar activities, that higher speed data links are desirable now, and will be necessary in the near future.

This work has shown that transmission rates as high as 15,000 baud are possible with existing technology. At these data rates our work has shown that it is possible to send near-real time video signals along the link, something that is not currently available, and which would be welcomed by the underwater engineering industry. With further research and development work even higher rates should be achievable.

Future development of the data link would allow it to operate at a baud rate of up to 24k, making it possible to send even higher rates of compressed data. Current work will mean that speed and data accuracy are enhanced where multi-path channels are expected by optional adaptive channel equalisation. Operating at ranges of up to 1km, it may be used in both open water situations, such as the sea, and enclosed water situations, such as pipes, ducts and tanks.

Currently the link can operate in simplex mode without enhanced error correction up to a distance of 1km. Full duplex operation with a high degree of error correction is being developed.

Features
The use of a relatively open architecture based upon readily available components, as well as the use of advanced techniques in adaptive channel equalisation using pseudo-spread spectrum techniques is at the leading egde of the technology and is making this technology available at low cost to local industry.

Contact Information
Mr H Y Wong
Director, Technology Transfer Office
City University of Hong Kong
83 Tat Chee Avenue
Kowloon, Hong Kong
Tel : (852) 2788 8428
Fax : (852) 2788 9119
Email : hy.wong@cityu.edu.hk