Energy-efficient coordination schemes for underwater acoustic sensor networks

Su, Ruoyu (2015) Energy-efficient coordination schemes for underwater acoustic sensor networks. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Underwater acoustic sensor networks (UWSNs) have attracted much research interest in recent years due to the wide range of their potential applications, such as environmental monitoring, natural resources development, and geological oceanography. While much research effort has been devoted to the improvement of acoustic signal reception and processing, the increase of throughput, and the reduction of packet delay, not really studies focus on reducing and balancing energy consumption among sensor nodes in long-term marine monitoring applications. In this dissertation, through a comprehensive understanding of underwater acoustic channels, we propose a series of solutions to achieve energy-efficient data transmission in UWSNs by considering both battery energies of sensor nodes and network connectivity. We first review different approaches to modelling the underwater acoustic channels to obtain a comprehensive understanding of the underwater acoustic communication environment. We propose an asynchronous wake-up scheme based on combinatorial designs to minimize the working duty cycle of sensor nodes for UWSNs in long-term marine monitoring applications. Network connectivity can be maintained using such a design, even with a reduced duty cycle. We conduct simulation experiments to evaluate performance of the proposed scheme. It is shown through our results that the proposed asynchronous wake-up scheme can effectively reduce the energy consumption for idle listening and can outperform other cyclic difference set (CDS)-based wake-up schemes. It is worth noting that all these are achieved without sacrificing the network connectivity among sensor nodes. We investigate the deployment strategy of UWSNs with a square grid topology to balance the network robustness and the energy consumption of sensor nodes. We propose a relay node selection scheme for such network applications. We evaluate its performance in different network sizes and using different initial battery energy to balance the network lifetime. Simulation results show that the proposed relay node selection scheme can effectively balance and prolong the network lifetime. Compared to routing algorithms solely based on the minimum hops, the performance of the proposed scheme is closer to the optimal theoretical value obtained by solving the linear programming problem. The network lifetime is further increased if sensor nodes are allowed to have different initial energy values based on their traffic load conditions. Finally, we propose an effective coordination scheme for data collection when an autonomous underwater vehicle (AUV) is used as a mobile data sink in UWSNs. We demonstrate the effectiveness of the proposed scheme when time synchronization is not available between the AUV and the sensor nodes. Based on the features available in existing acoustic modems, we introduce transmitting power control to further reduce energy consumption. Simulation results show that the proposed scheme with power control leads to lower energy consumption than without power control during underwater communication. The proposed schemes have been demonstrated to work well for underwater networks with a square grid topology. It can be also extended for other network topologies and more sophisticated modems.

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