Study On Efficient Data Dissemination Protocol In Millimeter Wave Vehicular Networks

As a key technology to realize intelligent transportation systems,vehicular ad hoc network(VANET)has attracted wide attention from all over the world.It contributes to increasing driving safety,enhancing traffic efficiency,improving travel experience,and promoting energy conservation and emission reduction.Data is the core of various vehicular applications.This thesis is dedicated to using millimeter wave(mmWave)frequency to replace lower frequency to achieve efficient distribution of massive data,such as vehicle sensor data and rich-media data,in VANETs.Mmwave has many special physical characteristics,such as directionality,high pathloss,low diffraction and low penetration.Wireless links have the characteristics of instability and vulnerability.Meanwhile,vehicles move quickly in VANETs.So the development of data distribution protocol based on mm Wave will face the challenges of low broadcast efficiency,frequent transmission errors,and easy blocking of links.In order to improve the broadcast efficiency,increase the fault-tolerance of transmission,and ensure the reliability of wireless links,this thesis mainly completes the following work:1.In response to the current situation where traditional point-to-point(P2P)transmission mode is difficult to maximize broadcasting efficiency in existing research,a distributed concurrent broadcasting strategy is proposed based on the broadcasting concept of point-to-multi-point(P2MP).The strategy mainly solves three key problems involved in broadcasting process:(1)Single hop broadcasting:an adaptive beamforming mechanism is utilized to determine the optimal direction and width of the beam for both the transmitter and receiver in single hop broadcasting area,thereby optimizing the efficiency of single hop broadcasting.(2)Multi-hop forwarding:a receiver-oriented candidate relay selection mechanism is employed to select the optimal forwarder for multi-hop broadcasting area,thereby optimizing the efficiency of multi-hop broadcasting.(3)Conflict management:a link concurrency mechanism based on mmWave/Dedicated Short Range Communications(DSRC)architecture is designed to coordinate transmissions between multiple regions,avoid transmission conflicts,and optimize global broadcasting efficiency.The experimental results show that the proposed concurrent broadcasting strategy can effectively address the adverse effects of mmWave physical characteristics such as directionality and limited transmission distance on broadcasting,and broadcast data to more vehicles more quickly.2.In response to the existing research on optimizing data push process by region based on the communication range of the roadside unit(RSU),but unable to maximize push efficiency,this thesis adopts the idea of overall optimization of the push efficiency of the entire network and proposes a distributed concurrent transmission strategy.This strategy mainly addresses two key issues involved in optimizing push process:(1)Optimizing the transmission efficiency of a single transmitter’s vehicle-to-vehicle(V2V)or vehicle-to-infrastructure(V2I)links:a graph-based encoding mechanism is utilized to solve the transmission errors caused by the instability and vulnerability of wireless links,as well as the contradiction between redundancy and capacity in multi-beam transmission.(2)Optimizing the concurrency efficiency of multi-transmitters’V2V or V2I links:a time-varying road segmentation mechanism is used to solve the problem of high global concurrency complexity;a concurrent transmission mechanism based on mmWave/DSRC communication architecture is employed to achieve the optimal matching between vehicles and the construction of concurrent links.The experimental results show that the proposed concurrent transmission strategy can effectively address the adverse effects of the vulnerability of mmWave links and high mobility of vehicles on data push,and push data to more vehicles with lower redundancy and higher efficiency.3.In response to the current situation where pure relay technology or pure intelligent reflecting surface(IRS)technology cannot efficiently schedule non-line-ofsight(NLOS)links in existing research,this thesis proposes a centralized concurrent scheduling strategy based on the idea of cooperation between relay and IRS.This strategy mainly solves two key problems involved in link scheduling process:(1)Building an efficient line-of-sight(LOS)path for each NLOS link:a relay/reflection link construction mechanism is utilized to evaluate the relative performance of relay and IRS schemes for each NLOS link,in order to select the optimal scheduling scheme.(2)Efficient concurrent scheduling of LOS links:a conflict graph based concurrent set construction mechanism is adopted to select a concurrent link set from the LOS links to be scheduled;By using a slot allocation mechanism based on the idea of overlapping concurrent sets,the problem of slot holes in existing slot allocation mechanism based on non-overlapping concurrent sets is solved,and transmission slots are allocated to concurrent sets to optimize the utilization of slot resources.The experimental results show that the proposed concurrent scheduling strategy can effectively address the adverse effects of the low diffraction and low penetration characteristics of mmWave on link scheduling,and achieve link scheduling with higher success rates under various network loads.