Recent concepts, developments and practical experience

A transmission technique for multiuser underwater acoustic communications

From the early days of AUV surveys there have been sound theoretical (e.g. area coverage rate) and practical (reliability through redundancy) grounds to use multiple small vehicles rather than one large vehicle, Bellingham and Willcox (1996). If a fleet of small vehicles is deployed in a common area a problem with acoustic interference may result if using conventional transmission methods. Bernard et al. (2020) describe a new group of transmission techniques that they call MultiUser Chirp Spread Spectrum (MU-CSS) that are straightforward to decode and provide resilience against interference from other users on the same channel. Importantly for use with moving AUVs, the method is also tolerant of Doppler shift. Initial experiments were carried out in Ty-Colo lake, St. Renan, France in 2019.

Bernard et al. (2020) is just one of several relevant papers from a special issue of the journal Sensors on Underwater Sensor Networks that contains several AUV-relevant papers, including:

• An AUV-Aided Cross-Layer Mobile Data Gathering Protocol for Underwater Sensor Networks, Alfouzan et al.

• A Survey on Underwater Wireless Sensor Networks: Requirements, Taxonomy, Recent Advances, and Open Research Challenges, Fattah et al.

Concept of mobile radio towers to act as communications gateways

Yonekura et al. (2021) have described the concept of autonomously moveable radio towers to act as communications gateways between AUVs in the Arctic and shore bases.

Delay-Doppler shift spread function of a test transmission of the MultiUser Chirp Spread Spectrum acoustic transmission method described by Bernard et al. (2020).