Research On Time Synchronization In Wireless AD HOC Network

Mobile ad hoc networks is a centerless network with multi-hop and dynamic topology.These features bring great convenience to network deployment and communication expansion,but also bring great challenges to related technologies.The time synchronization technology of mobile ad hoc networks is a difficult problem,which affects network operation efficiency in terms of delay,synchronization accuracy and network collision rate.In this thesis,the relevant technologies are proposed respectively in terms of delay and and flooding time synchronization algorithm,so that time synchronization technology can adapt to mobile ad hoc networks.This thesis optimizes CSMA / CA(Carrier Sense Multiple Access with Collision Avoidance)backoff algorithm for time synchronization and adopts a dynamic weighted linear backoff algorithm.The algorithm considers the back-off times and back-off indexes in the back-off parameters synthetically,and dynamically adjusts these parameters according to the topology of the ad hoc networks and the network congestion.In order to take into account both the dynamic of the network and the back-off time of the competing channel of the nodes,the five backoff times are dynamically weighted,and the backoff exponential is adjusted by comparing the current and weighted backoff times.The simulation results show that the DMLB greatly reduces the access delay compared to the CSMA / CA and OrderGain algorithms.This thesis improves a bias estimation algorithm based on mean compensation.In order to reduce the synchronization error,the algorithm removes the outliers,then estimates the frequency offset and the phase offset based on the FTSP(Flooding Time Synchronization Protocol)using local weighted linear regression.The handling delay is estimated using maximum likelihood method,which ensures the accuracy of the samples.Finally,the algorithm estimates the frequency offset to reduce the frequency deviation in the cycle synchronization.The simulation results show this algorithm reduces the maximum synchronization error about 1.5 ?s in the network with 36 nodes compared with the Improve-FTSP.This thesis improves a clustered FTSP network model.Every node in FTSP participates in broadcasting synchronization packets,which makes the synchronization packets in the network collision frequently.This algorithm only allows nodes selected as cluster heads to broadcast packets,and other nodes only receive and not broadcast,which reduces the number of synchronization packets in the network.The simulation results show that the number of nodes participating in the broadcast synchronization packet in this algorithm is reduced by about 50% compared with the FTSP.