Research On Consensus In Blockchain-Based Vehicular Networks

Blockchain-based vehicular networks enable a group of vehicles that do not trust each other to exchange information in a trusted way without an authoritative third party.However,when blockchain is employed in the vehicles,the dynamic topology incurred by the mobility of vehicles results in the information exchange behaviors changing from the deterministic communications to the opportunistic communications.In this way,the time of the imperfect communication during the consensus is nonnegligible.And meanwhile,the highly dynamic topology,the imperfect wireless links,and the limited communication range between vehicles may further slow down the blockchain consensus process,thus resulting in lower transaction per second(TPS).To tackle these problems,this thesis focuses on the the impact of mobility on block propagation during the consensus and the challenge of low TPS issue.The main research work is summarized as follows.The impact of mobility on block propagation during the consensus is analyzed from the macroscopic view.Based on the differences in the type of participants and communication modes,vehicular networks are divided into vehicular ad hoc dynamic networks composed of mobile vehicles,and edge collaborative hybrid dynamic vehicular networks composed of mobile vehicles and static roadside units(RSUs).First,based on the dynamic equation of information propagation,the closed-form expression of the single-block propagation time is derived in two dynamic vehicular networks.Then,this thesis characterizes the blockchain forking as the multiblock competitive propagation.On this basis,the expressions of multiblock competitive propagation are given in two scenarios.Simulation results demonstrate that higher mobility and more moving nodes can speed up the block propagation,and meanwhile distinct propagation capabilities of moving nodes contribute to the forking reduction in the blockchain consensus.Based on the above research,this thesis considers dynamic probabilistic forwarding in the design of block propagation decision,and proposes a high-TPS consensus algorithm based on the sharding technology.First,a geographical based sharding scheme is designed in the consideration of the local validity and verifiability of the information in vehicular networks.Then,this thesis proposes a reputation-assisted intra-shard consensus and a vehicle-assisted inter-shard consensus.The robustness of the intra-and inter-consensus is analyzed.Simulation results demonstrate the improved performance on TPS and trustworthiness of the proposed system.Higher mobility can improve the TPS of the proposed system,and meanwhile the trustworthiness of the four-shard blockchain system can be improved by at least 66%even under the conditions of attacked RSUs and malicious vehicles.