Underwater RF Communications Using Conduction

Abstract

This project explores the limits and capacity of broadband wireless communications for underwater operations using radio frequency (RF) conduction. Ranges of operation can be shorter than 1 m, suitable for contact-less data collection by remotely operated vehicles (ROVs), and even as short as 1-10 cm, suitable for contact-less riser health monitoring for deep sea drilling sensors. Electric field in the water is generated by a pair of electrodes with opposite current and detected by two receiving electrodes. We have been experimenting at frequencies up to 6.5 MHz, using orthogonal frequency division multiplexing (OFDM). A rational polynomial model has provided the best match for the recorded channel magnitude characteristic, while a simple exponential model has been helpful in detecting near-field magnitude behavior. The large magnitude variation (20-25 dB) with frequency and time invariance of the channel motivate the design of an OFDM system with unequal bit loading. That is the direction of our current research. By improving our understanding of the electric field propagation in various specific scenarios through simulations and experiments, we will continue to build a more complete picture of the underwater RF conduction channel.