Research On Time Synchronization Algorithms In Ubiquitous Cooperative Environment

With the development of wireless communications and the growth of user demands, user-centric ubiquitous access environment with multiple networks and multiple terminals appears. In such environment, multiple terminals cooperate with each other to provide personalized services for users. Obviously, as the key technology of multi-terminal cooperation, time synchronization determines whether the corresponding services perform better or not. Therefore, this thesis researches on time synchronization algorithms in ubiquitous cooperative environment. The main works are as follows:I. Ubiquitous access environment and multi-terminal cooperation scenarios are given. Then, the basic contents of time synchronization algorithms are introduced. Furthermore, mainstream time synchronization algorithms are surveyed and compared in detail.II. A novel time synchronization algorithm based on delay estimation and noise suppression is proposed. Considering characteristics of multi-terminal cooperation scenario, an estimation formula of packet transmission delay is constructed based on two-way message exchange between terminals for achieving the accurate clock offset compensation. Furthermore, an adaptive adjustment method of execution interval and a weighted correction method of slope compensation parameter are proposed for achieving the accurate clock slope compensation. Simulation results validate the effectiveness of this algorithm.III. A novel time synchronization algorithm based on maximum likelihood estimation is proposed. Considering characteristics of multi-terminal cooperation scenario, a maximum likelihood estimation model for single network and a fusion model of synchronization parameters for multi-network are established respectively, so as to achieve the accurate time synchronization between target terminals in general case. Furthermore, two special cases(i.e. time sample subsets are orthogonal and mutual neighbor nodes are sparse) are analyzed, and then the corresponding solving methods are proposed, so as to achieve the accurate time synchronization between target terminals in special cases. Simulation results verify the effectiveness of this algorithm.Finally, the conclusions are summarized, and the future research directions are given.