Research On Reliable Transmission Technology Of Safety Messages In Vehicle Communication

Recently, with the rapid development of vehicle communication technologies, as a Vehicular Ad-hoc Network(VANET) basic application, vehicle safety application has attracted more and more attention. Safety application calls for high broadcast reception rate and low average end-to-end delay. However, owing to the lack of dynamic adaptability, traditional EDCA(Enhanced Distribution Channel Access) mechanism based on IEEE802.11 p cannot meet the demands of safety applications any more. Therefore, it is meaningful to deeply study the reliable transmission for vehicle safety messages based on EDCA. The main work of this thesis is:Firstly, defect of traditional EDCA mechanism in message transmission is analyzed. Static EDCA parameters couldn’t adapt to the rapid changes of network nodes, which leads to the sharp decline in network performance. What’s more, the larger vehicle network density significantly results in higher collision probability. In accordance with different network thresholds based on different network density, Simulations show that the adaptive EDCA mechanism to ensure reliable transmission of high-priority safety messages.Secondly, the existing EDCA mechanism has redundant priority divisions and can’t guarantee the reliable transmission of safety messages. To address this issue, EDCA mechanism is improved in this thesis. The service priorities of EDCA mechanism are classified and an AC(Access Category) separation mechanism is studied. While high-priority services have been activated and counter have changed to 0, low-priority services is still in listening status. That can reduce the collision probability of the services with different priorities. Simulations show that the AC separation mechanism can effectively reduce collision probability and improve the reliability of message transmission.