| Internet of vehicles(IoV)plays an important role in improving traffic safety and ameliorating the comfort of drivers and passengers,so it becomes a research hotspot in wireless communication network.Due to the uneven distribution of vehicles and the explosive growth of the business,it is easy to lead to problems such as load imbalance,low utilization of network resources,and even serious channel conflicts in high-load scenarios.These problems will become a bottleneck to constrain the development of IoV technology.Load balancing is considered to be one of the effective ways to solve these problems.In addition,the software-defined vehicular network(SDVN)integrated by software-defined networking(SDN)and IoV can obtain global network information in real time,so it is helpful to improve the transmission performance of IoV,such as MAC and routing,and has been widely concerned.In the SDVN,although the centralized control mode can improve the link utilization and ensure the reliability of communication,when there is traffic congestion or the skyrocketing traffic volume,there will still be local network congestion.Thus,load balancing technology is also the focus of SDVN research.According to the survey,there are few researches on SDVN load balancing technology.This paper combines load balancing technology with the advantages of SDVN network architecture to discuss the problems of improving the transmission performance of IoV.The main work and innovations are as follows:(1)In view of the difficulty in real-time access to global network information in many IoV clustering networks,as well as serious network congestion and channel interference in the case of the dense vehicles and large load,an Interference-free MAC protocol with load aware based on SDVN is proposed.Specifically,in the clustering algorithm of the proposed protocol,the factors such as link reliability,adjacency,load and direction are considered to select cluster heads,and load balancing between cluster heads is realized by considering the load of nodes and limiting the size of clusters.In the part of MAC mechanism,an interference-free MAC algorithm is designed,which is composed of inter-cluster multi-channel allocation technology and intra-cluster dynamic TDM A frame allocation technology,to avoid the co-channel interference and hidden terminal interference between inter-cluster and intra-cluster communication.(2)Aiming at the problems of local optimization,poor network connectivity and network congestion caused by distributed geographic location routing protocol in urban scenario,a hierarchical routing mechanism(HRLB)with load balancing is proposed under the network architecture of SDVN.The routing design of HRLB is divided into two hierarchies.The first hierarchy is the coarse-grained routing design,which looks globally for a series of grids with high vehicle density;The second hierarchy is fine-grained routing design,which selects the transmission path from the area connected by the selected grid,and then a series of relay nodes are selected from the selected path.When selecting the path and the relay node,the load factors of the path and each node are considered respectively,so as to avoid the problem of traditional routing protocol adopted "to congestion,then solve it".Simulation results show that HRLB routing algorithm is superior to other routing algorithms in terms of delivery ratio,throughput and average delay.(3)Taking into account the problem that the performance of current VANETs cross layer routing protocol will be significantly reduced under the condition of low vehicle density,a hybrid routing mechanism of V2V and V2BS is proposed.Based on the global path connectivity information,the SDVN central controller decides whether to use V2BS route or V2V cross layer route for the transmission of data packets between source and destination.In the V2V cross layer routing mechanism,the load balancing of the network is achieved by considering balancing the load of each node when selecting relay nodes.The experimental results show that compared with other protocols,the performance of network transmission packets under various vehicle densities is improved by the proposed hybrid routing mechanism.(4)According to the current LTE-V heterogeneous network restricting the transmission performance of beacon,two software-defined LTE-V heterogeneous networks with different transmission mechanisms are proposed,namely,LTE-V heterogeneous network associated with and decoupled from uplink and downlink,respectively.Especially for the latter heterogeneous network,the transmission rate of the uplink and downlink between the base stations and the vehicles is transformed into a global optimization problem.This optimization problem can make each vehicle node connected to the base station with lighter load,so as to ensure the load balance between each base station.The experimental results verify the superiority of the proposed mechanism in improving the transmission rate of beacon messages. |
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