Investigation of a full duplex acoustic link for a tetherless micro-ROV

Over the last decade, vast improvements have been made in overcoming Inter Symbol Interference (ISI) in a dynamic underwater channel, with recent work focussing on multi-carrier systems due to their inherent multipath tolerance. However, the practical implementation of a bi-directional link for a micro remotely operated vehicle (ROV) presents additional complications. Erratic acceleration poses a challenge to previously reported Doppler compensation techniques, thus improvements in estimation and tracking are required. The use of a single-carrier scheme is demonstrated and critically evaluated in the presence of severe Doppler and interference caused by the vehicle. Through the tuning of an adaptive closed loop Doppler compensation structure, single-carrier modulation schemes demonstrate reliable high data rate communications. Minimum latency is essential for precise control and simultaneous video transmission, which can be achieved through the use of an asymmetric full duplex link. In this paper, filtering techniques are demonstrated to enable isolation of frequency multiplexed data streams and to prevent saturation of receiver circuitry. Results are presented demonstrating both single-carrier and multi-carrier high data rate transmissions (>;30kbps) simultaneously with low data rate (<;100bps) control signals at distances of over 300m.