The performance of underwater sensor networks (UWSNs) is greatly limited by the low bandwidth and high propagation delay of acoustic communications. Deploying multiple surface-level radio-capable gateways can enhance UWSN performance metrics, reducing end-to-end delays and distributing traffic loads for energy reduction. In this paper, we study the problem of gateway placement for maximizing the cost-benefit of this UWSN architecture. We develop a mixed integer programming (MIP) gateway deployment optimization framework. We analyze the tradeoff between the number of surface gateways and the expected delay and energy consumption of the surface gateway architecture in the optimal case. We used an MIP solver to solve the developed optimization problem and integrated the optimal results to serve as an input for our simulations to evaluate the benefits of surface gateway optimization framework. We investigated the effect of acoustic channel capacity and the underwater sensor node deployment pattern on our solution. Our results show the significant advantages of surface gateway optimization and provide useful guidelines for real network deployment.
Geo-routing protocols can provide the scalability, robustness, lower overhead and energy efficiency requirements for underwater sensor networks (UWSNs). However, these protocols require localisation service, which is another challenging problem. In this paper, we introduce a novel energy efficient schema that does not need location information. In this schema, nodes assign themselves to concentric layers around sink nodes and routing paths are determined on the fly based on nodes' layers and residual energy information. Nodes can adaptively adjust their transmission power level to cater for network mobility and residual energy constraints. Extensive simulation results show that our routing protocol achieves high delivery ratio and low energy consumption while reducing end to end delay when compared with other routing strategies. In particular, our schema can guarantee a relatively higher delivery ratio in presence of mobility.
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