Design of self-localization strategies for networks of underwater drifters

Our understanding of many ocean processes hinges on collection of spatially-rich data. To this end, future underwater sensing systems are envisioned to consist of a large number of devices that collaborate to collect data, as opposed to stand alone systems. Knowing the position of devices while submerged is crucial to deduce spatial information about the processes being sensed. For this purpose position-estimation algorithms can be used, which largely rely on inter-node distance estimates obtained from time-of-flight (TOF) measurements. Further, since node positions continuously change under the impact of ocean currents, distance estimation has to be repeated periodically. We consider two approaches to obtain distance estimates: a traditional link-based approach and another using broadcast. The latter scheme takes advantage of the fact that multiple nodes require to estimate distances with their neighbors at around the same time. We present a framework to evaluate the relative performance of broadcast and link-based ranging for the specifics of any mobile system. We further show that with the advent of cheap and accurate clocks, broadcast ranging is favored. By using such clocks, broadcast ranging can potentially reduce the energy consumed for distance-estimation to 9% of that in a link-based scheme.