Cache-Aware Query Optimization In Multi-Application Sharing Wireless Sensor Networks

Wireless sensor networks(WSNs),which have been used extensively in widespread domain applications,are getting more and more attentionand research interest.Since sensor nodes nowadays are typically powered by batteryresources,which are difficult to be recharged.Energy efficiency is one of the most importantresearch challenges.Current WSNs are usually purpose-built for supportinga single-running application,which may lead to aninefficient use of sensor nodes and low cost-benefit result.Hosting multiple applications in a sharedinfrastructure of wireless sensor networks is a trendnowadays.Note that sensory data may notvary significantly in certain applications,and these applications may work well when a bias of sensory databeing used and being sensed in a real-time fashion iswithin a certain threshold.Sensory datagathered at a certain historical time slot may be reused for answeringforthcoming queries,rather than fetching from the networkreal-timely,which is an effective way to reduce the energy consumption.To address this challenge,we propose a cooperativecaching-based mechanism that aims to optimize the multi-application query processing in shared WSNs.The major contributions thisthesis brings are summarized as follows:Firstly,we propose a shared WSN for supporting multiple concurrent applications.Specifically,an application is assumed to have one,or several,task(s).A task retrieves sensory data in a certain network sub-region with a certain set of attributes for a certain timeduration.Query requests for concurrent applications arerepresented as binary strings,which are reduced to asingle one for data sharing.Secondly,a two-tier cooperativecaching-based mechanism is developed,where sensory data,whichmay be interested by forthcoming queries,are cachedat(i)the sink node,and(ii)the head nodesof grid cells,forfacilitating the reuse of sensory data when answeringconcurrent and forthcoming queries.Thirdly,an energy-efficient query optimization mechanism is proposed forsupporting multiple concurrent applications leveragingour two-tier cooperative caching mechanism.After multiple applications are reduced into a single one,sensory data required are firstly checked in sink node,and then in head nodesof grid cells.Sensory data are retrieved by an index tree,and will be cached in cache nodes.Sensory data replacement will be conducted if necessary.The prototype has been implemented in a Java program andexperiments are conducted for evaluating the performanceand efficiency of our technique.From theoretical analysis and evaluation result,we can see that our technique is feasible and energy efficient.In conclusion,the proposed cache-aware query optimization in multi-application sharing WSNs supporting multiple applications processingwill further promote query optimization with low energy consumption.