Research On The Opportunistic Unicast Routing Protocol In Vehicular Ad Hoc Networks

With the development of vehicular ad hoc networks (VANETs), a large number of applications for the actual demand are used to serve the communication between vehicles. Routing protocols provides the possibility to network interconnection and lays a technical foundation for data exchange. Meanwhile, unicast in the urban environment as the most basic routing protocol and having the most extensive application demand, has become the focus of this paper.Due to the high mobility of vehicles, the uneven distribution of vehicles, traditional routing protocol in mobile ad hoc networks cannot meet the basic needs of routing. In the face of the dynamic organization of network topology in VANETs, the opportunistic routing strategies making use of the wireless channel characteristics have attracted more and more researchers’attention. At the same time, the end-to-end routing path in the urban environment is divided to some natural sub-path sequences by several streets, thus, based on the street as the basic routing unit is the core element to optimize protocol performance in VANETs. In the routing protocol design based on the street, we need to face how to select relaying nodes to forward packets effectively when the packets travel in intra-street and how to determine the sequence of streets as the entire routing path at intersection In this paper, according to different optimization objectives, we design two opportunistic unicast routing protocols in VANETs for urban environments.Based on the high mobility of vehicle and the complexity of the communication environment in urban environments, a link model is built with the Wiener process to predict the probability of link availability, which considers the stable and unstable vehicle states according to the behavior of vehicles. We propose a novel concept called the Link Correlation which represents the influence of different link combinations in network topology to transmit a packet with lower network resource consumption and higher goodput. Based on this concept, we design an opportunistic routing metric called the expected transmission cost of multi-hop path (ETCoP) implemented with our link model as the guidance of relaying node selection in the intra-streets. This metric can provide assistance for the next street selection at the intersection. Finally, we propose a street-centric opportunistic routing protocol based on ETCoP for VANETs (SRPE). Simulation results show that our proposed SRPE outperforms the conventional protocols in terms of packet delivery ratio, average end-to-end delay, and network yield.The characteristics of topology in VANETs make its flow traffic from one intersection to the other intersection, and the width of the street is far less than the length of the street, so it forms a pseudo-chain link topology in the intra-streets. In the urban environment, the vehicle and the flow distribution will show a certain degree of hot spot effect, leading to the data packets in certain streets or vehicle nodes encounter significant congestion, resulting in a decline of routing performance. In this paper we estimate the maximum and remaining bandwidth of street, which becomes a reasonable guide for packet forwarding at the intersection. And it takes into account the impact of the geographical process, the average length of buffer and average contention window size for packet forwarding in an intra-street. This paper carry out a cross-layer design for opportunistic routing protocol, so packets can be forwarded in the intra-streets efficiently. Finally, this paper puts forward an opportunistic routing protocol for VANETs based on the bandwidth of street.