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Now showing items 1 - 4 of 4

  • Estimation filtering for Deep Water Navigation

    Costanzi, Riccardo   Fenucci, Davide   Caiti, Andrea   Micheli, Michele   Vermeij, Arjan   Tesei, Alessandra   Munafo, Andrea  

    The navigation task for Unmanned Underwater Vehicles is made difficult in a deep water scenario because of the lack of bottom lock for Doppler Velocity Log (DVL). This is due to the operating altitude that, for this kind of applications, is typically greater than the sensor maximum range. The effect is that the velocity measurements are biased by sea currents resulting in a rapidly increasing estimation error drift. The solution proposed in this work is based on a distributed, cooperative strategy strongly relying on an acoustic underwater network. According to the distributed philosophy, an instance of a specifically designed navigation filter (named DWNF - Deep Water Navigation Filter) is executed by each vehicle. Each DWNF relies on different Extended Kalman Filters (EKFs) running in parallel on-board: one for own navigation state estimation (AUV-EKF), the other ones for the navigation state of the remaining assets (Asset-EKF). The AUV-EKF is designed to simultaneously estimate the vehicle position and the sea current for more reliable predictions. The DWNF builds in real-time a database of past measurements and estimations; in this way it can correctly deal with delayed information. An outlier detection and rejection policy based on the Mahalanobis distance associated to each measurement is implemented. The experimental validation of the proposed approach took place in a deep water scenario during the Dynamic Mongoose'17 exercise off the South coast of Iceland (June-July 2017); preliminary analysis of the results is presented. (C) 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
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  • A Robust, Opportunistic Clock Synchronization Algorithm for Ad Hoc Underwater Acoustic Networks

    Vermeij, Arjan   Munafo, Andrea  

    Proliferation of deployed sea-going autonomous platforms, such as autonomous underwater vehicles (AUVs), unmanned surface vehicles (USV), and sensor nodes anchored to the seabed, make the deployment of true underwater acoustic networks more and more feasible. An important feature of any network is the ability to synchronize the clocks of the participants, for the purpose of, e.g., time-slotted media access control (MAC) and navigation. Terrestrial clock synchronization protocols, such as the well-established network time protocol (NTP), are not readily applicable to underwater acoustic networks, because of long propagation times, low packet delivery success rates, communication ranges that vary over time in an unpredictable manner, and, in the presence of mobile nodes, the ad hoc nature of the composition of the network. This paper proposes a continuous estimation of internode clock offset and drift, based on the continuous exchange of modem packets, possibly containing transmission and reception timestamps. The proposed solution takes explicitly into account the limitations of the acoustic communication channel and network node mobility. This robust, opportunistic clock synchronization (ROCS) is robust against modem reset, and will work even if packet delivery success rates are not optimal or if no communication is possible for extended periods of time. Experimental results are given from the COLLaborative Asw Behaviours-Next Generation Autonomous Systems (COLLAB-NGAS14) campaign, held October 19-31, 2014, off the west coast of Italy. During the sea trial, the proposed clock synchronization algorithm was deployed and successfully tested within an underwater acoustic network composed of mobile and fixed nodes.
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  • [IEEE OCEANS 2015 - Genova - Genova, Italy (2015.5.18-2015.5.21)] OCEANS 2015 - Genova - Real-time clock synchronisation in underwater acoustic networks

    Vermeij, Arjan   Munafo, Andrea  

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  • [IEEE 2014 Underwater Communications and Networking (UComms) - Sestri Levante, Italy (2014.9.3-2014.9.5)] 2014 Underwater Communications and Networking (UComms) - Clock synchronisation in underwater acoustic networks

    Vermeij, Arjan   Munafo, Andrea  

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