| Vehicles have gradually become people’s daily travel transportation tools with the development of times. However, vehicles not only bring people convenience but also take a lot of troubles. When emergent events take place, the reaction time of human brain is limited, and they do not have enough time to deal with the emergency, which consequently brings traffic accidents. Therefore, how to transmit emergency message quickly and extend the reaction time of drivers is the research focus of Vehicular Ad-hoc Network (VANET).This thesis proposes an urban VANET multi-hop broadcast protocol (UVMBP) based on the urban environment with straight roads and intersections. UVMBP maintains three broadcast strategies by differentiating the positions of the sender without topology and density information. Firstly, the sender broadcasts an emergency message directly at the first hop transmission. The receivers within the farthest segment are selected by iterative method after receiving the emergency message. A unique node is then selected as the forwarding node by competing to broadcast the RTS (Request To Send) frame in the farthest segment. Secondly, when the emergency message are transmitted on straight road directionally, a forwarding node is selected by RTS/CTS (Clear To Send) handshake. The sender broadcasts a RTS frame, and the receivers in the farthest segment are selected by iterative method after receiving the RTS frame. Then the selected receivers compete to answer CTS frame in the farthest segment. Then, the sender broadcast emergency message after receiving CTS frame. Thirdly, when the sender is located at the intersection, multi-directional transmission of the emergency message is the same as that at the first hopUVMBP has better performance in terms of average one hop delay, distance between sender and forwarding node, message dissemination speed, and frame delivery rate by comparing some popular algorithms in VANET, which demonstrates that UVMBP is more suitable for urban VANET. |
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