Improving the energy efficiency of underwater acoustic sensor networks (UW-ASNs) is a crucial issue due to the reduced and\nnonrechargeable energy resource of the underwater sensor nodes. In this work, we address the energy sink hole problem in UWASNs\nwhile considering the unique and harsh characteristics of the underwater channel. Our goal is to determine the optimal\ndeployment and routing settings that surmount the energy sink hole problem and hence maximize the network lifetime. We prove\nthat sensors can evenly consume their initial battery power provided that first they adjust their transmission power when they\ntransmit the route through traffic and second they are appropriately placed while deployed. Mainly, we propose a deployment\nscheme and the corresponding balanced routing strategy that lead to uniform energy consumption among all underwater sensors\nsubject to a predefined reliability level at the sink. Specifically, we look for the optimal deployment settings especially in terms of\nnodesâ?? separation distances that help achieving uniform energy consumption in the network while satisfying the application\nrequirement especially in terms of desired information reliability. Jointly, at the routing layer, we assume that each sensor is\nprovided with the possibility of dynamically adjusting its transmission power up to a given number of levels N. To this goal, we\nmainly deal with two main cases: fixed and variable nodes separation distance. For the fixed case, we suppose that any two\nsuccessive nodes in the network are equally spaced, and we strive for deriving the optimal distance as well as the optimal number\nof transmission power levels along with optimal load weight corresponding to every possible transmission power level for every\nsensor node. For the variable case, we deal with two subcases: first, we suppose that the distance separating successive nodes\nfollows an arithmetic progression, and second, we assume that the distance separating successive nodes is following a geometric\nsequence. Note that for both cases, namely, fixed and variable, we succeed to determine the optimal distances separating successive\nnodes and the optimal number N of transmission power levels along with the corresponding optimal load weight that overcome\nthe energy holes problem, and hence the network lifespan is maximized while respecting the desired reliability level.
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