Research On Roadside Units Assisted Opportunistic Routing Protocol For Vehicular Ad Hoc Network

Vehicular Ad-hoc Networks(VANET)is a core component that supports intelligent transportation systems for intelligent driving,traffic warning,and entertainment applications.VANET has characteristics of high-speed movement,fast-changing topology and uneven load distribution which bring many difficulties and challenges to the design of VANET routing protocols.Aiming at the problem that traditional opportunistic routing protocols are troubled by low delivery rate and high latency when the node density is either too low or too high,this thesis utilizes Roadside Units(RSU)to provide additional information sources and stable wired links for routing protocols,and designs three VANET opportunistic routing protocols.The main work of this thesis is as follows:(1)Aiming at the problem that the topological holes and local maximum problem are easy to occur when the density of vehicles is too low,a Markov Prediction Duplicate Transmission Routing Protocol(MPDTR)is proposed.When a RSU traps into local maximum problem,it utilizes Markov chain prediction to predict a set of RSUs that are probably visited by the target vehicle in next step.Duplicates of data packet are delivered to the predicted RSU set,and then keep on greedy forwarding until reaching the target vehicle.(2)Aiming at the problem that part of RSUs have extremely heavy load due to the high density of vehicles,an Infrastructure Assisted Load Balancing Routing Protocol(IALBR)is proposed.The protocol estimates the time required for the data packet to pass through RSUs network and makes load balancing decisions to determine entry RSU and exit RSU that are suitable for the data packet,so as to avoid the packet entering heavy load RSUs.(3)Combining the advantages of MPDTR and IALBR,a Multi-Mode Switching Routing Protocol(MMSR)is proposed.MMSR designs three RSU working modes: V2I2 V greedy forwarding mode,"prediction + duplicate transmission" mode and load balancing mode.MMSR designs switching criteria of three modes,aiming to solve the local maximum problem and load imbalance problem in VANET.(4)An urban scene simulation environment is built to evaluate the performance of GPSR,V2I2 V and three protocols proposed in this thesis.The results show that MPDTR is suitable for working in the VANET environment where the vehicles density is low and the localmaximum problem is frequently occur.IALBR can effectively balance the load among RSUs,and has a better performance than V2I2 V,GPSR and MDPTR.MMSR combines the advantages of both MPDTR and IALBR protocols to achieve the best delivery and latency performance among five routing protocols.