Abstract
To increase underwater acoustic signal detectability and conserve energy, nodes leverage directional transmissions. In addition, nodes operate in a three-dimensional (3D) environment that is categorized as inhomogeneous where a propagating signal changes its direction based on the observed sound speed profile (SSP). Coupling 3D directional transmission with frequent node drifts and the varying underwater SSP complicates the process of selecting suitable transmission angles to maintain underwater communication links. Fundamentally, utilizing directional transmission while nodes are drifting causes breaks in established communication links and thus nodes need to find new angles to reestablish these links. Moreover, selecting arbitrary transmission angles may lead to overlapping beams or result in leaving an underwater region uncovered. To tackle the abovementioned challenges, this paper proposes an autonomous beam selection approach that optimizes underwater communication by selecting non-overlapping beams while mitigating the possibility of missing a region, i.e., maximize coverage. Such optimization is achieved by utilizing a structured angle selection mechanism that accounts for the capability of the used transducer. Moreover, we introduce an algorithm suited for resource constrained nodes to classify rays into different types. Then we divide the underwater medium into regions where each region is identified by the limits of the coverage area of each ray type. Finally, we utilize the limits of these regions to aid nodes in selecting the best ray to reestablish communication with drifted nodes. We validate our contribution through simulation where actual SSPs are leveraged to validate the beam classification process.
Highlights
Recent advances in acoustic underwater networks (AUN) have enabled the development of applications such as environmental state monitoring, search and rescue, seabed profiling, and coastal surveillance [1]
Since sound is characterized as a sequence of pressure waves that propagates in underwater environment, ray tracing attempts to find the path taken by each ray where a ray has an infinitesimal beam width
To fully test the proposed algorithm’s capability, we generated within M-SSP1 and M-SSP2 more than 1600 rays and used the proposed ray classification technique to determine the ray type
Summary
Recent advances in acoustic underwater networks (AUN) have enabled the development of applications such as environmental state monitoring, search and rescue, seabed profiling, and coastal surveillance [1]. When the spreading reaches a point where the signal power drops below the inhomogeneity is mainly manifested by means observing theinsound speed zones profilecannot (SSP) detect of the receiver sensitivity, a shadow zone is created Such of sound (SS)shadow along the propagation of acoustic signals transmissions byvariation neighboring nodes,speeds avoiding zones for nodespath becomes inevitable to causes refraction and often yields a continuous change in the gazing angle of a propagating signal. Selecting disjoint beams may result in missing the ray types connecting the pairs and placing the neighbor in the shadow zone Given these challenges and the fact that nodes in AUNs are usually sparsely located [3], a method is required to govern the selection of9,transmitted beams to ensure minimal overlaps while avoiding shadow zones, as.
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