A Research On Clock Synchronization Of Ad Hoc Networks

Ad hoc network is a temporary network built rapidly and non-dependent on pre-established infrastructure. Due to the characteristics of distributed, multi-hop, self-organization, and decentralized, it has advantages as convenient and strong survivability, and has important applications in many fields. Clock synchronization is a critical fundamental support technology in Ad hoc network. It is the prerequisites to complete data fusion, cooperative sensing, multiple access, power management, and some other functions.Due to the characteristics of Ad hoc network, traditional clock synchronization solutions based on structured architecture are not entirely suitable for decentralized Ad Hoc network. While current clock synchronization solutions based on distributed architecture pay more attention to the distributed synchronization strategies of entire network, they can not effectively achieve precise clock synchronization between two neighbor nodes.In order to solve the above problems, a new kind of distributed clock synchronization solution which is suitable for multi-hop Ad hoc network is proposed. The proposed solution conducts deeply research on two key technical subjects. One is the difficulty of accurately in measuring the clock offset, and the other is how to get the reference clock on entire network.In response to the first subject, an offset estimation strategy based on Kalman filter algorithm is proposed, which is built upon the detailed analysis of 802.11 asymmetric delays. This strategy effectively guarantees the precision clock synchronization between two neighbor nodes and verified on the embedded platform.In response to the second subject, a distributed synchronization strategy for entire network clock based on mean field model is proposed. The mean field model for entire network clock synchronization based on the energy of Ising model is established by mapping clock offset to clique potential. No special node needs to be maintained, and a virtual reference clock for entire network is gotten by an averaged effect of neighbor nodes using mean field theory. Finally, a parallel energy minimization is adopted to get clock distributed synchronization for entire network clock.Combining with the implementation of offset estimation strategy and distributed synchronization strategy for entire network clock, a Mean Field based Synchronization Protocol(MFSP) is realized, which is the core content of the thesis. By exchanging timestamp in broadcast mode, MFSP effectively reduces the number of time messages. Based on Kalman filtering algorithm and mean field model, MFSP realizes a complete distributed clock synchronization solution from the accurate synchronization of two neighbor nodes to the fast synchronization of entire network clock.This thesis elaborates on the realization and performance of MFSP protocol, and makes design and implementation in QualNet platform. Through simulating different scenarios and comparing with GTSP and ATS, this thesis validates the features of fast convergence, stable convergence time, insensitive to scale changes, and suitable for large-scale Ad Hoc Network of MFSP protocol.