Joint Time Synchronization And Localization For Underwater Wireless Sensor Networks

Underwater wireless sensor networks(UWSNs)working as ocean data acquisition systems,have been widely applied in military and civilian area.The sensors in UWSNs could get their positions and clocks through underwater synchronization and localization technologies.Therefore,we attach great importance to underwater synchronization and localization technologies.However great challenges exist in underwater synchronization and localization.First of all,the underwater localization is always accomplished through the time-of-arrival(TOA)localization and the angle-of-arrival(AOA)techniques.In this paper,we adopt the TOA localization technique.This technique always depends on synchronized clock.However,the time synchronization problem is coupled with localization problem.Secondly,the underwater complex environment cause the anchor position uncertainties,measurement errors,and packet unsuccessful reception.These conditions will degrade the performance of localization and synchronization.Therefore,appropriate methods should be adopted to localize and synchronize sensors in UWSNs accurately,and we should design the parameters of the localization system to increase the probability of successful localization.These alway are the research hotspots in underwater localization area,and also are the research topics of this paper.In order to solve the coupled problems of clock synchronization and localization,we build up a joint time synchronization and localization model in this paper.In the localization process,we utilize a single mobile anchor to broadcast its position and clock to help with localization and synchronization.The localization problem is settled through the time-of-flight measurement.Considering the anchor position uncertainties,we utilize the expectation maximization(EM)algorithm to solve the synchronization and localization problems.Moreover,we use least squares(LS),weighted least squares(WLS),generalized total least squares(GTLS)to have a fair comparison.The simulation results show that the expectation maximization method has best performance compared with other algorithms.In addition,considering underwater long propagation delay,we define the opportunistic localization from the space and time domain.We also design the operation mode for the mobile anchor.After that,we design the packet avoidance scheme for target sensors.As for underwater energy consumption,the target sensors are designed to work in(q,p)duty-cycle to prolong the lifetime of target sensors.The value of parameters could be designed based on the simulations of probability for opportunistic localization.Finally,we design the experiment for underwater localization,and we choose appropriate algorithm for the localization experiment based on the experiment equipment.We also verify the algorithm through simulations.