| The event-driven wireless sensor network,abbreviated as EDWSN,is an important type of WSN,which can comprehensively,timely,and accurately monitor simple or complex events of interest to users with omnidirectional or directional sensors installed in sensor nodes,and it has important application value and research significance in multiple scenarios.EDWSNs should provide the abilities of comprehensive sensing,timely data transmission,and accurate estimation of events.However,the existing technologies still face a series of challenges,especially in the sensing coverage based on directed sensors,the congestion control related to the funnel effect of data traffic,and the lightweight and accurate estimation of the event statistical parameters.This thesis focuses on the key technical issues of EDWSNs and proposes a series of technical methods for sensing coverage,congestion control,and composite-event estimation.The main research contents and innovations are as follows:(1)Aiming at the sensing coverage optimization problem of EDWSN consisting of sensors installed with multiple directional sensors,where the coverage ratio is the optimization object and the sensor azimuths are the optimization parameter.The original coverage optimization problem is thus transformed into an equivalent problem with virtual boundary constraints,which effectively reduces the redundancy in the solution space.Furthermore,we propose a virtual boundarybased hybrid particle swarm coverage optimization algorithm,in which we generate constraints according to the geometric relationship between sensor azimuths and build a virtual boundary for the particle search to improve the computational efficiency of sensing coverage optimization and reduce the time to search the solution space.The simulation results show that in various scenarios for different coverage types,the proposed algorithm is superior to the classical algorithm and the existing improved algorithm in terms of convergence speed.(2)Aiming at the transmission congestion problem caused by the funnel effect near the sink node in the EDWSN.We discuss the observable and unobservable modes for the queue service of the sink node.According to the service capacity constraints of the sink node,the arrival rate thresholds of the two modes are theoretically obtained.We propose a game-based congestion control algorithm that takes the sink service queue into account for the non-uniform service value and variable arrival rate data.It switches between the observable and unobservable modes according to the aforementioned threshold so that the system can obtain maximum benefits and handle the congestion problems near the sink node.The simulation results verify the correctness of the proposed algorithm.Compared with the existing solutions,the proposed algorithm has improved the service-value throughput and significantly reduced the average service-value delay.Thus,it effectively alleviates the flow funnel effect and improves the timeliness of data transmission for EDWSNs.(3)Aiming at the composite event detection problem based on the characterization of the statistical distribution of inter-event intervals,we propose a lightweight statistical parameter estimation algorithm based on the adaptive binning strategy and differential evolution.With the adaptive binning strategy,we count the original data value in the given bins.Only these count results are used in the subsequent processing,which effectively reduces the space complexity of data storage.With the differential evolution algorithm to maximum likelihood estimation based on bin counting result,we can estimate the model parameters effectively because the time complexity is independent of the original data set size but only related to the number of bins and the number of bins is usually much smaller than the size of original data.The verification experiments show that the proposed algorithm can correctly and efficiently estimate the parameters of the inter-event interval statistical model,and is better than the Expectation Maximization(EM)algorithm in time complexity.To sum up,in view of the application requirements of EDWSN,this thesis proposes a series of technical methods including sensing coverage,congestion control,and composite event estimation in order to improve the comprehensiveness of event sensing,the timeliness of event transmission,and the lightness of accurate estimation of composite events for EDWSNs. |
