Research On Composite Event Monitoring In Battery-Free Wireless Sensor Networks

As an important task of the wireless sensor networks(WSNs),the composite event monitoring finds wide applications in environmental,body-area,and vehicle-area scenarios.With the growing complexity of events,the single modal data obtained by homogeneous sensor networks are not accurate enough for complicated events.Therefore,the composite event monitoring,which takes advantage of heterogeneous sensor networks with multiple types of sensors,is proposed.However,existing strategies to monitor composite events are primarily designed for traditional WSNs.Such networks rely on batteries.Although their power supply is stable,if some of the key nodes runs out of energy,the network is dead.Considering the severe environment,the battery-replacing is almost impossible.Thus,saving energy to prolong the network lifetime is the key aim of the researches on composite event monitoring in traditional WSNs.Recent years,the Battery-free Wireless Sensor Networks(BF-WSNs)are proposed to overcome the drawbacks of the traditional WSNs.Instead of being powered by batteries,the BF-WSNs harvest ambient energy so that their have unlimited lifetime for event monitoring.But on the other hand,the ambient energy is so unstable and the quality of service(Qo S)of BF-WSNs is generally not satisfactory.The primary objective of optimization in BF-WSNs is to promote the quality of event monitoring under the unstable ambient energy.In this paper,we study the optimization on deployment and scheduling for composite event monitoring in battery-free sensor networks.Firstly,the paper provides model for battery-free sensor networks with heterogeneous sensors,and gives the formal definition for the deployment(BF-DCEM)and scheduling(BF-SCEM)for composite event monitoring.To the best of our knowledge,this work is the first to discuss the BF-DCEM and BF-SCEM problem.Secondly,the paper presents the computational analysis on the above two problems,which are proven to be at least NP-Hard.Thirdly,the paper proposes solutions to the problems.Finally,simulations are conducted to evaluate the performance of the given solutions.