| Περίληψη: | In this thesis, we study problems related to the efficient energy management of sensor networks and propose protocols that exploit the Wireless Power Transfer (WPT) technology using magnetic resonant coupling. A common, realistic assumption of all problems that we investigate is that the amount of available energy supplies is finite; hence, it is crucial to manage it in the most efficient way in order to prolong the network lifetime, and achieve other required network properties as well. The problems on which we focus in this thesis can be classified in two main categories. In the first one, special network entities (called chargers) are required to store large amount of energy supplies and appropriately transfer it to the network devices. In the second category, we study different network models where no special devices are used for the energy management; in contrast, the ordinary network devices are capable to charge each other in a peer-to-peer manner.
In particular, we first study wireless rechargeable sensor networks using multiple mobile chargers. In such a setting, the most crucial questions that we aim to answer are the following two. How can the mobile chargers coordinate in order to partition the network area amongst them in fair way, based on the energy supplies they have? Further, what trajectory should each of them follow in order to traverse its assigned subregion and charge the sensor nodes therein? To answer these questions, we propose both centralized and distributed coordination solutions that exploit different levels of knowledge. Moreover, we propose a hierarchical collaborative charging scheme where the chargers are partitioned in two types, the mobile chargers, which are responsible for replenishing the energy of the sensor nodes, and the special chargers, which are responsible for recharging the mobile chargers. In this setting, we investigate how the special chargers must coordinate with each other, which trajectories they should follow, and how much energy must be transferred to each mobile charger. We also focus on the problem of selecting the appropriate power of a single static charger over time in mobile ad hoc networks in order to adapt to the mobility and energy consumption characteristics of the mobile nodes, as these are revealed in an online manner. Finally, we study the problem of designing interaction protocols for networks that consist of computationally weak devices, which are able to exchange energy in a peer-to-peer manner, thus eliminating the need for special entities, like the chargers. The objective is to let the devices distributively construct specific network structures (such as star and tree networks) and achieve appropriate energy distributions. For each of these problems we propose and analyze the properties (both theoretically and experimentally) of various protocols, which utilize different levels of knowledge about the network.
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