Research On Key Technologies Of Medium Access Control In Vehicular Ad Hoc Networks Based On IEEE802.11p

In recent years，the rapid growth of vehicles has brought a lot of problems to urban traffic,which makes the intelligent transportion system and Vehicular Ad hoc Network attract muchattention. Through vehicle to vehicle and vehicle to infrastructure communication, VANET can notonly improve traffic security and efficiency but also provide entertainment. This thesis focuses onIEEE802.11p MAC protocol in VANET and the main works are as follows.Firstly, the broadcast performance on IEEE802.11p control channel is simulated and theresults show that broadcast performance changes greatly in different Minimum contention window(CWmin) and vehicle density. Besides, fixed CWmindoesn’t match the dynamic vehicles density,which affects MAC broadcast scalability. Then the impact of unicast performance on IEEE802.11pservice channel under different vehicles density is simulated, which proves that vehicle density hasa great influence on the network performance and the BEB algorithm can not adapt to the fastchange of vehicle density.Secondly, a CWminadjustment algorithm based on neighbor nodes number estimation isproposed in order to solve the broadcast scalability of IEEE802.11p on control channel. First of all,in order to minimize the collision probability, the relationship between CWminand active nodenumber is deduced on the basis of IEEE802.11broadcast backoff Markov model. Then CWminisadjusted dynamically by estimating neighbor nodes number. Simulation results show that theproposed algorithm is superior to the original method in broadcast reception rate.Thirdly, CVSBA (Contending nodes number and Vehicle density based Self-adaptive BackoffAlgorithm) is proposed. In order to maximize the network throughput, the proposed algorithmselects the appropriate CWmindynamically by estimating the competing nodes number. Then nodescontinuing monitor surrounding vehicle density and adjust the CW according to the relationshipbetween the nodes surrounding vehicle density and vehicle density threshold. Finally, the proposedalgorithm and BEB algorithm are compared by simulation and results show that CVSBA can reducethe delay and improve network throughput, which improve the performance of the IEEE802.11p.