Research On Trajectory Planning And V2X Communication Technology For Connected And Automated Vehicle Platoons

Enabled by trajectory planning and Vehicle-to-Everything(V2X)communication,the Connected and Automated Vehicles(CAV)running in the same direction can move forward like a string with the same speed and autonomously form a platoon.By exploiting the trajectory planning technology,vehicles can move forward steadily with a close but safe inter-vehicle space,which brings many benefits,including enlarging the road capacity,lessening traffic congestion,saving fuel consumption,and reducing gas emissions.Meanwhile,as the fundamental technique for platoon management and information sharing between vehicles in a platoon,V2 X communication faces tremendous challenges of higher transmission requirements.Then,the CAV platoon,which has become one of the most important enhanced V2 X applications for autonomous driving,currently attracts high attention from both academic field and industrial field.Therefore,focusing on the CAV platoon,this dissertation studies the intersection trajectory planning problem,the V2 X communication problem between adjacent vehicles in a platoon,and the V2 X communication problem between the platoon leader(PL)and the platoon members(PM).The main contents of the dissertation are summarized as follows.· The Composite Platoon Trajectory Planning Strategy(CPTPS)is proposed.In the signal-controlled intersection,lacking the coordination of vehicles restricts the intersection throughput.Therefore,a vehicular trajectory optimization problem is formulated to maximize the intersection throughput.Since the intersection throughput maximization problem can be transformed into minimizing the intersection arrival time of vehicles in a green phase,the CPTPS is developed to make CAVs automatically queue up in a platoon and quickly pass the intersection with an optimized speed,reducing the stoppings at intersections and gas emissions.Three portions are designed in CPTPS to solve this problem,which are the Green Light Optimal Speed Advisory(GLOSA)-based trajectory planning method for platoon leaders,the Reinforcement Learning(RL)-based trajectory planning method for platoon followers,and the flexible platoon management protocol to ensure smooth operations in a platoon.The simulation results suggest that,CPTPS can effectively increase the intersection throughput while reduce the stoppings at intersections and gas emissions.Furthermore,the proposed data exchange message set of the basic GLOSA application has been accepted in the standard called Cooperative Intelligent Transportation System Vehicular Communication Application Layer Specification and Data Exchange Standard(T/ITS 0058-2017).This standard is developed by China Intelligent Transportation System Industry Alliance(C-ITS)and has been implemented in China at present.· The overhead-free vehicular-position-based beam alignment scheme and the corresponding beamwidth optimization method are proposed.Since the beam-sweeping-based beam alignment scheme is inefficient in millimeter-wavebased V2 X communication,the overhead-free vehicular-position-based beam alignment scheme is proposed in this dissertation to satisfy the transmission rates on the order of Gbps for the cooperative sensing between adjacent vehicles in CAV platoons.In the proposed beam alignment scheme,the beam is directly steered to the estimated vehicular position without any searching steps in beam training,eliminating the alignment overhead.In the meanwhile,given the localization errors,to avoid beam misalignment caused by inaccurate positioning,a beamwidth optimization problem is formulated to maximize the expected throughput.To solve the proposed beamwidth optimization problem,a Monte Carlo based Beamwidth Optimization(MCBO)method is developed to divide this optimization into two phases and derive the optimal beamwidths with some convex optimization approaches and statistical tools.Simulation results show that,in the simulation scenario close to reality,compared to the two existing beamwidth optimization methods,the proposed MCBO method can effectively improve the throughput performance of the V2 V links between adjacent vehicles.· The Unmanned Aerial Vehicle(UAV)relay placement optimization method is proposed.In a long platoon,because of the limited reliable communication range of the PL,the PMs far from the PL are not able to receive the information from the PL.Therefore,the UAV is exploited as a relay to forward information between the PL and PMs in this dissertation.For the sake of the communication reliability of the UAV-aided dual-hop links between the PL and PMs,a UAV placement optimization problem is formulated to maximize the average successful transmission probability of the UAV-aided links in the platoon.To solve this UAV placement optimization problem,the convexities of the successful transmission probability for the single-hop links between the UAV and vehicles and the UAVaided dual-hop links between the PL and PMs are analyzed.According to the theoretical analysis,the successful transmission probabilities in both cases are proved to be concave functions with regard to the UAV position coordinates.Hence,the UAV placement optimization problem is proved to be a standard convex problem and can be solved by existing convex optimization techniques.Simulation results validate that the proposed UAV placement scheme can effectively help build reliable intra-platoon communication between the PL and PMs.