Key Technology Research On Opportunistic Routing In VANETs

The Vehicular Ad Hoc Networks (VANETs) is an important component of intelligent traffic system, which is composed of vehicular nodes or Roadside Units (RSUs) equipped with short distance communication devices. The highly mobility of nodes, frequently changing topology, intermittent communication among the vehicles and complicated applications’requirements are some of big challenges in VANETs. Usually, VANETs nodes also have processing and storage capabilities, which have enabled vehicular network the ability to form a new intelligent network. The vehicles’trajectories are predictable for that their movements are limited by traffic pattern and road layout. The message transfer is happened only when the nodes meet.A large number of researches have been devoted to the routing algorithm and related works in VANETs. The target of these researches are concentrated on improving the message delivery ratio, puling down the delivery delay and reducing the overhead of the whole VANETs.The requirements for message delivery are complicated since differen-t kinds of message exist in VANETs. The research of providing different kind of message delivery strategy is significant. The nodes in VANETs are mov-ing with high speed, which will shorten the communication time when nodes meet. It is important to improve the message delivery assisted by RSUs, which is based on studying the vehicles’movement law. The topology in VANETs is frequently changing; and the traffic flow varies noticeably between different ar-eas or times. The traffic flow can affect the message delivery, thus considering the traffic flow can improve the efficiency of the routing algorithms. It is neces-sary to analyse the influence on the delivery efficiency from the nodes’setting. However, the relationship between nodes’setting and the network performance still need in-depth studies.Base on the above problems, this thesis studied the opportunistic routing in VANETs, and the research result are shown as follow.1. A Moving target ORiented opportuNistic routing algorithm in vehicular networks (MORN) is proposed for message delivery from information source to a moving target vehicle. In order to adapt the constantly chang-ing topology of networks, the forwarding decisions are made locally by each intermediate vehicle based on the trajectory information of the tar-get vehicle. The simulation and real trace experiment show that MORN provides an efficient message delivery with a higher success ratio, short-er delivery delay, and lower transmission overhead compared with other reference approaches.2. A novel multi-hop message delivery method which is called Coverage Area based opportunistic message forwarding algorithm (CAP) is pro-posed. The main idea of CAP is to cover the potential area of moving target vehicle as much as possible with the reachable area of required delivery messages, so that the message can be delivered successfully. To achieve this, CAP calculates and compares the candidature carriers’ reachable area, and finds the best candidate with a maximum coincident area between the candidates’reachable area and the target vehicle’s po-tential area. Being different from existing approaches, it makes use of target vehicle’s potential area which is predicted according to the target vehicle’s movement model, the source and destination location, and the road layout. The simulation results show that CAP provides an efficient message delivery with a higher success ratio and a shorter message delay.3. The message delivery ratio and delay is affected deeply by traffic flow. An opportunistic routing based on geography and traffic for VANET (ORRIS) is proposed, which leverages the knowledge of the geography position, motion vector and the traffic flow. In order to estimate the traffic flow density, the history of encounter number for the vehicles in the opposite direction is considered in ORRIS. The forwarding are made locally based on the geography topology and the traffic flow.The simulation result show that, ORRIS has a better performance, especially when the traffic is busy or the flow rates have a great differences between roads.4. The messages in VANETs would burst in many cases, which would have a greater negative impact on the message delivery ratio of routing algo-rithms. In order to mitigate the degraded performance, an advanced OR-RIS algorithm (ORRIS+) is proposed, which improves the forwarding s-trategy of VANETs nodes. The ORRIS+makes the message a diversion to other paths by increasing the path number for message delivery; and adapts queue management scheme for each node. The simulation result-s have validated the effectiveness of ORRIS+in mitigating the degraded delivery performance when messages burst.