Research On Vehicular Routing Protocol In 3D Street Scenarios And DSRC-mmWave Communication Scenarios

As an important component of urban intelligent transportation system(ITS),ve-hicular ad hoc network(VANET)provides an efficient networking interconnection and communication services between vehicles and vehicles,vehicles and roadside units(RSU).The existing applications in vehicular ad hoc network include mainly the end-to-end data exchanging services between a vehicle and another,and the data forwarding services between a vehicle or roadside unit and multiple vehicles.Routing protocols play a key role in the data transmission and the performance of applications.Therefore,we will mainly study the routing protocols for these two applications.At present,most routing protocols aim at the simple plane city scenarios and single-band data forwarding tasks.They design the routing strategies by considering these factors:vehicular distribution,mobility,street connectivity,and the status of wireless links.However,urban scenes are complex and diverse(i.e.,the dimension of street topology changes from one-dimensional,two-dimensional to three-dimensional),and the scale of transmission data is ever-increasing(i.e.,the data varies from the simple lo-cation and control information to large-scale video streams).Existing routing protocols for vehicular ad hoc network are difficult to meet the service requirements of current vehicular ad hoc network applications,including low latency and high throughput.The end-to-end routing issues in complex multi-dimensional scenarios and the transmis-sion schedule issues in DSRC-mmWave(5.9GHz and 60GHz)communication scenar-ios need to be solved urgently.The latest researches about two topics are confronting some serious challenges induced by the non-uniform spatial distribution of vehicles and high inter-level transmission cost;high beamforming delay and low concurrency of millimeter-wave links.Therefore,in order to deal with the above challenges,a low-delay unicast routing protocol for three-dimensional urban scenarios is designed and a high-throughput broadcast routing protocol in DSRC-mmWave hybrid scenarios is proposed in this paper.(1)The core issues of the end-to-end unicast routing protocol in the three-dimensional scenes are how to select the next forwarding direction in intersections,and how to select the next-hop forwarding node(including intra-level neighbors and inter-level neigh-bors)within the current street.The traditional three-dimensional routing protocols ana-lyze street connectivity according to the number or density of vehicles when they select the next street.However,they ignore the significant impact of the uneven vehicle distri-bution on street connectivity.In this paper,we not only consider the number of vehicles within segments,but also pay attention to the position distribution.Then,a new as-sessment for connectivity and node weight is designed based on the spatial-distribution parameters.Considering that the inter-level transmission will introduce more overhead than the intra-level transmission,we design a merging rule for the connectivity qual-ity of levels in multi-level streets.Further,we propose a spatial-distribution-based connectivity-aware routing protocol.Experiment results show that the proposed pro-tocol can effectively improve the end-to-end delivery rate and reduce the transmission delay.(2)The core issues of broadcast strategies in DSRC-mmWave hybrid communica-tion scenarios are how to select the cluster-head gateway nodes,and how to schedule efficiently millimeter-wave links.In the traditional DSRC-mmWave hybrid commu-nication strategies,all original nodes exchange control messages and registration mes-sages with the central node only through low-frequency links.In addition,the schedule of high-frequency millimeter-wave links is decided by the central node.Due to the highly dynamic topology in vehicular ad hoc network,complex switching process of millimeter-wave links and common dense scenarios,the centralized schedule method is not suitable.Therefore,for the hybrid communication scenarios,we design a novel distributed broadcast transmission schedule strategy,which selects the cluster-head ac-cording to the speed,position and degree of each node,then uses the mobility of nodes transmitted by DSRC to accelerate the millimeter-wave beamforming and neighbor dis-covery processes.And the state information of surrounding millimeter-wave links is used to improve the concurrency of system.Experiments show that the strategy could improve the throughput of system effectively.