One- and Two-Way Travel Time Ranging in Underwater Acoustic Mobile Networks

In the last ten years several simulation studies on Autonomous Underwater Vehicle swarm fleet formation have been performed, and some preliminary sea demonstrations of proof-of-concept prototypes were carried out. However, their actual realization is hindered by the difficulties of keeping track of the vehicles’ positions due to the long latency required by traditional Two-way travel-time (TWTT) ranging measurements. One-way travel-time (OWTT) halves the latency, at the cost of a high precision oscillator such as an atomic clock or an oven controlled crystal oscillator, installed in the modem processing unit. In this paper we present two Medium Access Control (MAC) schemes for underwater acoustic mobile networks: a first MAC based on a time-division scheme with a high-precision oscillator to perform OWTT ranging, and a second MAC based on the token bus paradigm which, like regular TWTT ranging, does not require a high-precision oscillator. The main contributions of this work are the complete description of the ranging algorithms implementation, including MAC parameters and packet structure, and their realistic evaluation in both sparse and dense network scenarios with the DESERT Underwater Framework.