Research On Urban Scenario Oriented Routing Protocols In Vehicular Ad Hoc Networks

Vehicular Ad-hoc NETworks(VANETs) have brought a lot of convenience to people’s daily life. As an important part of the intelligent transportation system, it has attracted more and more research institutions and researchers. Gradually, VANETs have become a very important research area and lots of valuable researches have been put forward in recent years.Since the environment of VANETs is complex and the network topology highly dynamic changes, the link connection will suffer frequently interrupted. In particular, when the vehicle density is small, the probability of the network scission is higher. In addition, the prediction of the link failure is difficult. So, it is very difficult to establish a complete and reliable end-to-end transmission path between mobile terminals. Currently, the most widely used routing protocol in VANETs is the geographic routing which can better adapt to the highly dynamic environment. However, such protocols still suffer two problems. First, the node’s location information is not accurate and the link quality is unstable. Second, most of the geographic routings are almost planar routings, while the real VANETs urban scenarios are three-dimensional(3D). Applying these planar routings in the 3D urban scenarios will undermine the performance of these protocols. Therefore, the study of designing suitable routing protocols for VANETs is very important. In this paper, a geographic opportunistic directional routing protocol GOD and a link state aware hierarchical road routing protocol LSHR are proposed.GOD is an opportunistic routing, which could improve the reliability of data transmission by making full use of the broadcast characteristics and assist in data transmission through additional backup links. It makes the packets have more opportunities to be received. When GOD selects the candidate neighbor set, it takes a combination of the geographic location, the moving direction of each neighbor node and the link state information into account. GOD prioritizes the forwarders by timer-based scheduling method according to the average expected advance that a packet can make towards the destination through one transmission.LSHR is proposed for a simple 3D urban scenario which composed of two or more than two parallel but with different height roads. LSHR contains intersection judgment strategy and data transmission strategy on 3D sections. Firstly, when LSHR selects the next temporary objective intersection, besides considering a general distance factor, it focus on the effect of road connectivity which expressed by the unit of communication delay. Therefore, the selected path not only has shortest possible transmission distance, but also has stable network connectivity to ensure rapidly and effectively packet transmission. Secondly, during the transmission of a packet, the agreement combines the 3D characteristics of the actual scenarios and the 3D distribution of nodes, and prior selects the neighbor who has the largest transmission range of two hops as the forwarding node. LSHR reduces routing hop count and the transmission delay, while increasing packet delivery ratio and enhancing the overall performance of the routing.