| As an emerging field that is developing rapidly,wireless sensor networks have attracted the attention of scholars from all walks of life in recent years.Time synchronization,as one of the key technologies of wireless sensor networks,is also highly valued.The inaccurate clock has a great impact on network security.Based on this,this paper introduces the important application of clock synchronization in wireless sensor networks,and summarizes that the deterministic factors of clock asynchrony are affected by deviation and drift rate.Five synchronization methods are compared:reference broadcast synchronization(RBS),delay measurement clock synchronization(DMTS),sensor network timing synchronization protocol(TPSN),micro-synchronization(Tiny-sync),lightweight tree(LTS).Uncertainty factors are summarized,and the new development direction and trend of clock synchronization methods are analyzed.In wireless sensor networks,some classical time synchronization methods have been studied and improved.This paper proposes that the joint location of AOA and TDOA can effectively improve the position accuracy.The combination of them has been studied more in two-dimensional(2-D)environment than in more practical three-dimensional(3-D)environment.In this paper,an AOA-TDOA joint localization algorithm in three-dimensional environment is proposed.The global optimal solution is obtained by minimizing the auxiliary function to solve the constrained optimization problem.The localization accuracy of the TDOA-AOA joint localization algorithm when the measurement noise is wrong,the estimation error caused by the measurement error and the reduction of the sensor position error are solved.Experiments show that the proposed algorithm can meet the requirements of Kramer bound error in the presence of sensor position error,and its positioning error is lower than other algorithms.Moving target tracking,namely the motion path and parameter obtaining of moving target has important research value in the application of wireless sensor networks(WSNs).Based on the TOA measurement method between mobile target node and beacon node,a method to capture the parameters of moving targets is proposed in WSNs.Using the built estimation model of motion parameter for mobile target,the unconstrained linear least squared(ULLS)and constrained linear least squares(CLLS)methods are deduced to estimate the initial position and moving speed of the linear moving target.By relaxing the estimation model into convex semidefinite programming(SDP)problem,the SDP algorithm is designed to capture the motion parameters.The simulation results show that in the three designed algorithms,the estimation error of the ULLS algorithm is the largest.The SDP algorithm ranks secondly,and the estimation error of the CLLS algorithm is the smallest. |
