Research On Energy Optimization In Wireless Sensor Network Under Assistance Of Mobile Nodes

Wireless sensor networks(WSN)are always confronted with the challenges of limited sensor energy and insufficient network lifetime.Recent years,the concentration of sensor-based applications quickly transfer from specific domains to commercial ones,where sensors and resourceful mobile nodes(e.g.,smartphones and wireless mobile chargers)always coexist.These new scenarios provide superior opportunities to solve the above-mentioned energy and lifetime challenges.Based on the unified framework under the assistance of mobile nodes,aiming at the energy problem of WSN,this paper adopts a progressive research strategy and focuses on multiple optimization objectives including energy conservation of sensors,lifetime extension and profit maximization of wireless sensor networks.The main contents and contributions of this paper are summarized as follows:1.Surveying the convergence between wireless sensor network and other network systems.Focusing on wireless sensor networks(Internet of Things,IoT),its convergence status with the Internet,cloud computing,smartphone,social and industrial networks are comprehensively reviewed.With particular attention,the latest achievements,influential ongoing projects and technical challenges are described and analyzed.On its basis,we find more and more mobile resourceful nodes and sensors are coexisted in the future WSN applications.Therefore,further research efforts are required to study the energycentered optimization problems such as conserving sensor energy,optimizing network lifetime and profit.2.Designing energy conservation mechanism under the assistance of mobile relays(or resourceful mules).To solve the technical challenges including quick detection of random mobile relays(such as smartphones,whose power is more abundant than sensors),coordination between heterogenous devices and the tradeoff between energy efficiency and data delay,we design a practical energy conservation mechanism ECARM(Energy Conservation under Assistance of Resourceful Mules).After a mobile relay is automatically incorporated in the wireless sensor network,sensor behaviors are coordinated in a collaborative way,such that a part of sensors near the mobile relay could keep sleep and save energy.Through extensive experiments,we show that ECARM achieves 6.25 times longer lifespan for sensors close to a mobile relay.Applying in duty-cycled networks,ECARM further decreases sensor energy consumption by at least 20%.3.Proposing near optimal solution to maximize the network lifetime.We focus on applying RF-WPT(Radio Frequency based Wireless Power Transfer)charger in a wireless sensor network and avoiding charging interference meantime.Under the objective of maximizing network lifetime,we jointly consider data routing,the charger's path planning and charging scheduling,and designing a mechanism to avoid data loss caused by charging interference.Through a series of approximation and relaxation,we construct a near optimal solution of the NP-hard original problem,and theoretically prove the optimality of the proposed solution.Experiment results show that,the proposed near optimal solution achieves 99% optimality and 7.15-22.75 times longer network lifetime.4.Proposing near optimal solution to maximize the network profit.Aiming at the tradeoff between prolonged network lifetime and increased energy cost,this paper focuses on the objective of maximizing the network profit.After our step-by-step analysis,we find that the optimal profit is determined by the total charging time for each sensor,and irrelevant to the charger's specific traveling path.After relaxing the energy constraint of the optimization model,we transform the NP-hard original problem to a solvable linear programming problem.On its basis,we construct a near optimal solution.Experiment results show that,our solution achieves at least 90% optimality and 300% higher network profit compared with greedy-based solutions.