Research On Sidelink Radio Interface Synchronization Solution And Handover Technologies For LTE-V2X Systems

V2X communication is one of the main applications of 5G.The LTE-V2X technology can meet the needs of vehicles for transmission reliability and low-latency direct communication.However,with the base stations densely deployed,the user equipments rapidly grown and the vehicles moves fast,various technical challenges must be overcome.This thesis mainly based on Sidelink(SL)technology,mainly studies air interface synchronization scheme and handover technology,as the following aspects:For LTE-V2X system,acquiring the synchronization reference signal(SRS)is indispensable for vehicles to establish service connections in the network.However,due to the weak signals received by some vehicles with deteriorating radio propagation condition or even outside the basestation coverage area,they may not obtain the SRS and consequently fail to be synchronized with the network.In order to solve this problem,we propose a radio interface synchronization scheme based on the SL.The SRSs of downlink(DL)and SL are assigned different priorities,where the priorities of different synchronization sources can be distinguished in a time-shift based SRS transmit mechanism and meanwhile the interference among the SRSs of different sources can be effectively suppressed.Simulation results illustrate that even when the synchronization source is granted a low priority of level four,the synchronization error can still be kept at a satisfactory level,guaranteeing that the vehicles to attain synchronization from the basestation directly or indirectly.For LTE-V2X system,the cellular-link/SL are usually unstable in the handover process,and the situation is even deteriorating when the SL is employed to assist the normal handover process.To solve these problems,we propose a SL-assisted joint handover scheme for vehicles in the network.The vehicle's moving direction is speicifically taken into account in making the handover decision,and the SL is set up between the pair of vehicles with the best channel quality.With the SL,the reliability of the joint handover can be ensured and meanwhile the number of unnecessary handovers can be significantly reduced.In addition,in order to tackle the perplexing problem of SL being vulnerable in the fast changing radio environment,the joint handover signaling procedure is optimized with respect to two different realistic circumstances.Simulation results illustrate that the the proposed schem can effectively ameliorate the handover success rate and remarkably reduce the number of LTE handovers.