Antenna and Transponder Unit for Underwater PNT
Underwater wireless communications links have almost exclusively been implemented using acoustic systems. Optical links have proved impractical for many applications. Although underwater radio links were experimented in the pioneering days of radio, they did not meet the requirements of the time.
Given modern operational requirements and digital communications technology, the time is now ripe for using electromagnetic signals in the underwater environment.
Above 10kHz, electromagnetic propagation is more than a hundred times faster than acoustic. This has important advantages for command latency and networking protocols, where many signals have to be exchanged. Doppler shift is inversely proportional to propagation velocity, so is much smaller for electromagnetic signals.
Systems have already been proposed that function through use of a small unit that is most commonly hung from a dive boat or a larger unit buoy (the “GPS gateway”) with a pre-fixed transmitter at a fixed depth. The GPS gateway has a floating radio antenna in order to determine its exact location, and communicates with the wrist units via its underwater transducer portion. As a result of this communication, the wrist units know their range and bearing from the GPS gateway, as well as the exact position of the gateway. This allows the wrist units to calculate their own absolute position, independent of the position or motion of the GPS gateway. The gateway or the boat to which it may be attached is free to drift without affecting the position displayed. The position is displayed on the wrist-mounted screen, both as latitude and longitude values as well as a “dot”.
The main objective of the proposed activity is to design, manufacture and test a low cost / low profile antenna and transponder unit that performs well in a marine environment based on use of electromagnetic signals.
The tasks to be performed will include:
- definition of PNT requirements for on-surface and under-surface marine applications and definition/consolidation of antenna requirements;
- state-of-the-art review of antenna concepts and technologies;
- preliminary design of the antenna and associated front end;
- consolidation of evolutions of existing systems, as floating buoys ”GPS gateways”, based on innovative antenna design;
- manufacturing, underwater testing and development plan of the unit;
- assessment of benefits of Radio Frequency for underwater Communications/ PNT, integrating benefits of underwater sensor and on-surface sensors
hybridization platforms that can provide wide area availability to applications and services;
- trade off advantages and disadvantages of using RF signals, including GNSS repeater networks, in order to support PNT requirements of current and emerging underwater applications;
- analysis of requirements and constraints, for deployment of a RF-based system for wide area coverage for close to surface and under water applications;
The results of the activity will provide:
- solutions for low-cost, low-profile unit for underwater PNT;
- performance and cost/benefit assessments recommending innovative PNT applications to be enabled underwater.