Research On Synchronization Technology Of Device-to-Device Network

The goal of new generation of cellular communications is to achieve broader coverage,greater spectrum efficiency,higher system throughput and green energy savings.The key technology of Device-to-Device(D2D)is establishing a direct communication link between user equipment to implement direct communication between devices.Synchronization is the basis of successfully communication between user equipment.This thesis focuses on self-organized synchronization technology of D2D network.Firstly,we study the synchronization strategy defined in protocol,analyze its existing problems and design new synchronization strategy to improve its adaptability,stability and convergence speed.Based on timing synchronization error,we propose better synchronization algorithms with minimum timing error to improve probability of successfully communicating.And one simulation model is established,which is used to verify effectiveness of the proposed algorithm.Main contributions and innovations of this thesis are as follows:1.We research D2D synchronization mechanism in Protocol.By studying the sidelink synchronization technology in 3GPP Release-12 version protocol,we analyze the development of existing synchronization technology,investigate the classical synchronization algorithms in self-organized network and analyze their characteristics.D2D synchronization strategy is based on multi-hop relays.One disadvantage of this kind of synchronization strategy is existence of cumulative asymmetric errors.This thesis improves synchronization algorithm based on this drawback.2.We analyze synchronization scenario and improve synchronization strategy.First of all,for the synchronization strategy defined in protocol,we analyze its adaptability in different scenarios.Furthermore,problems of the synchronization strategy are proposed.The selection criterion of synchronization source is too simple.There is no clear priority between synchronization groups and user equipment in one synchronization group.Synchronization strategy is not adaptive to complicated scenario,and synchronization process is not stable enough.From the perspective of strategy design,we consider the corresponding solution.By analyzing complicated scenario,it elaborates that the strategy design is supplemented to adapt to more complex and changeable synchronization scenarios.Build system-level simulation platform to verify the improved strategy achieves better stability and faster convergence speed.3.A synchronization algorithm based on minimum timing error is proposed.Firstly,we analyze the system time-frequency synchronization process,analyze the cumulative asymmetric error and model it,and analyze the upper limit of the system tolerance on timing error.The root mean square error is used to evaluate timing error of the whole network,and the synchronization algorithm is improved.More UE's RMS error is within the system tolerance,which ensures successful implementation of D2D communication between terminals.On the dynamic system-level simulation platform,it is verified that the improved synchronization algorithm has 5%performance improvement on system timing synchronization error.We analyze influence of user density and size of threshold on synchronization system performance.We also propose system performance evaluation index such as probability of successfully communicating,probability of failing to communicate and hops of synchronization network.On simulation model,the improved synchronization strategy makes the network get a higher probability of successfully communicating.