Research On Efficient Routing Protocol In IRS-assisted Mmwave Vehicular Networks

In the complex urban road environment,vehicles need to exchange a large amount of sensor data through low-latency and high-reliability transmissions to expand the perception range of vehicles.This is of great significance for the realization of advanced technologies such as automatic/assisted driving and danger warning.With its huge available bandwidth,mmWave technology is promising to enable large-scale vehicular sensor data transmissions.However,high-frequency mm Wave signals suffer from severe attenuation,have a limited transmission distance and are susceptible to obstacles.Recently,intelligent reflecting surface(IRS)technology has attracted a lot of attention from academia due to its ability to improve the wireless communication environment.By configuring the phase and amplitude coefficient of each reflective element of the IRS,the direction and strength of the signal reflected by the IRS can be controlled.The IRS can improve the propagation distance of mmWave signals,build virtual LOS links to solve NLOS problems,and enable multi-user transmissions.Therefore,this thesis proposes to deploy IRSs in mmWave vehicular networks and design efficient routing protocols to improve the transmission performance.In mmWave vehicular networks,the special propagation characteristics of mmWave signals,the instability of wireless links,and the variation of traffic flows all bring challenges to the design of routing protocols.In addition,after deploying IRSs in vehicular networks,reflected signals aggravate the signal interference between wireless links.As a new network resource,IRS also needs to be selected and allocated in routing protocols.These factors bring new challenges to the design of routing protocols for IRS-assisted vehicular networks.How to deal with these challenges and design an efficient routing protocol for IRS-assisted mmWave vehicular networks is an urgent problem to be solved.This thesis deeply studies the transmission characteristics of wireless links in IRS-assisted mmWave vehicular networks,and designs an efficient unicast routing protocol and an efficient broadcast routing protocol to achieve low-latency and high-reliability transmissions between vehicles.The main content of this thesis is as follows:(1)In view of the high delay overhead of multi-hop unicast in mmWave vehicular networks,this thesis proposes to deploy IRSs in mmWave vehicular networks to obtain reflection gains and increase the single-hop transmission distance,thereby reducing the number of forwarding hops and improving the unicast delay.The selection of links in unicast routing needs to trade off factors such as delay and reliability,and also needs to avoid the resource and signal conflicts with other transmissions.This thesis designs a unicast routing protocol based on forwarding efficiency and IRS allocation(FE-IA).The protocol trades off the link quality,forwarding distance and transmission time to evaluate candidate links.The forwarding efficiency is maximized based on IRS allocation and spatial reuse time division multiple access mechanisms are adopted to alleviate conflicts in link selection.Simulation results showed that the FE-IA based protocol proposed in this thesis can effectively reduce the multi-hop unicast delay and improve the multi-hop unicast delivery rate.(2)In view of the low broadcast efficiency in mmWave vehicular networks,this thesis proposes to deploy IRSs in mmWave vehicular networks to enable multi-user transmissions and improve the broadcast efficiency.Narrow beam directional transmissions provide conditions for improving the broadcast efficiency through multi-hop forwarding and concurrent transmissions,and the IRS can support multi-user transmissions to further improve the broadcast efficiency.This thesis designs a broadcast routing protocol based on multi-user transmissions and concurrent transmissions(MU-C).The protocol evaluates the priority of candidate links based on the link quality and the geographical location of the receiver.In each round of scheduling,a transmitter is first selected for each IRS to enable multi-user transmissions,and then the candidate link search is completed to find out all candidate links.Finally,a graph-based algorithm is used to schedule as many conflict-free links as possible for concurrent transmissions.Simulation results showed that the MU-C-based protocol proposed in this thesis can effectively improve the delay and coverage of the mmWave broadcast.