Enhancement Of Wireless Communications In Vehicular Environment Of Its Based On IEEE 802.11p/1609 Protocols

With the development of Intelligent Transportation System, Wireless Access in Vehicular Environment (WAVE) has been gaining more and more attentions during past years. Many protocols has been proposed for wireless communications in ITS. Among these, IEEE 802.11p/1609 protocol suite, which is the representative, is being developed aiming to provide timely traffic safety related communications for drive aiding as well as traditional Internet services with high quality of service (QoS) for passengers. In IEEE 802.11p/1609 protocols, control channel (CCH) is dedicated for safety critical message transmissions, so that traffic accident avoidance, sudden brake warning and other applications can be realized. Service channel (SCH) is used for non-safety services, such as Web browsing, Email, video on demand and so on, in order to provide better travel experience for passengers.In this thesis, the basic introduction of IEEE 802.11p/1609 protocol suite is given first. Furthermore, new features of MAC layer in IEEE 802.11p dedicated for ITS applications are carefully studied. After that, the performance deterioration and unfairness phenomenon in high density traffic scenario on CCH is carefully investigated through simulations. On the other hand, the bandwidth wastage problem is also considered. Based on the integration of 3G wireless communication network and IEEE 802.11p/1609-based vehicular wireless network, an adaptive periodic safety critical messages transmission interval and power adjusting scheme with neural network training and gradient descent back propagation algorithm is proposed in order to eliminate the unfairness and improve the performance of CCH. Meanwhile, the frame fit scheme is used by matching the estimated transmission time with the channel switching remaining time, in order to mitigate the bandwidth wastage on SCH. Extensive simulation results based on NCTUns software reveal that both of the proposed schemes can work well. The fairness can be guaranteed and bandwidth wastage can be eliminated with the help of the proposed schemes. Moreover, the performance of wireless communications on CCH and SCH can be improved a lot.