Underwater Acoustic Modems with Synchronous Chip-Scale Atomic Clocks for Scalable Tasks of AUV Underwater Positioning

Abstract

Accurate time synchronization of the nodes of digital underwater acoustic (UWA) networks is necessary for the effective use of information obtained from various kinds of underwater sensors over a vast water area. The sensors of autonomous underwater vehicles (AUV) are widely used to address new challenges. One of them is time synchronization of sensors on mobile carriers, as well as synchronization of the clocks on mobile nodes of UWA networks, for example, teams of AUVs that perform coordinated and/or cooperated operations. The paper presents theresults of the experiments on using UWA modems for AUV positioning, namely, UWA modems with chip-scale atomic clocks (CSAC) that allow accurate measurements of delays in propagation of UWA signals and, thus, accurate estimation of ranges to their georeferenced sources. In addition, the accuracy of CSAC operation in various situations as well as positioning accuracy of AUVs having UWA modems with integrated CSACs are analyzed based on the experimental results. Also given are practical recommendations on how to "discipline" (steer) CSACs and provide their phase synchronization with a source of timekeeping signals.

Cooperative path following of constrained autonomous vehicles with model predictive control and event‐triggered communications

“…As shown in the proof of Lemma 1, the reference speed for u [i] , given by (28), satisfies the constraint…”

“…max for all i ∈  . Replacing the vehicle speed u in (4) by (28) for vehicle i, the resulting path following error system for vehicle i is given byẋ…”

“…Notice that according to (28), |u| ≤ (v dmax + k c )max(g( )). Hence, Choosing k 1 such that (35) is satisfied and using condition (33), it follows that |v| ≤ v max .…”

“…where u is given by (28). Notice that system (A6) is nonautonomous since u(t) is in general a function of time (as v c depends on the the triggering functions that are time-dependent).…”

Dual-Hop TDA-MAC and Routing for Underwater Acoustic Sensor Networks

“…The drawback of such coordinated scheduling protocols is their need for clock synchronization across different nodes, which can be a challenging task in UASNs due to long propagation delays, noisy time-varying multipath channels, and the signaling overhead that is not negligible compared with terrestrial radio systems [9] [24]. The use of chip-scale atomic clocks is an alternative way of providing an accurate synchronized time reference to the network nodes for long periods of time, but they are not feasible in many scenarios, in particular due to their relatively high cost, higher power consumption and ageing [25] [26]. Many of the proposed collision-free scheduling MAC protocols do not require a precise global time reference; however, their throughput performance tends to visibly deteriorate with loose clock synchronization.…”