| Intelligent Transportation System (ITS) has a high demand for the performance of the Vehicular Ad-Hoc Network (VANET), while IEEE802.11p protocol is one of the most important cornerstones for VANET, it gradually become the focus of the communication research field. VanetMobiSim had been chosen as the vehicular mobility simulator, it was responsible for building a real-world traffic behavior model, then NS-2had been selected as the network simulator, it was in charge of simulating IEEE802.11p under static scenario and dynamic scenario respectively. When simulation was done, three main performance measurement, including throughput, end to end delay, and frame error rate, had been analysed respectively. The simulation results showed that the speed of vehicles would not impact the transmission performance, but the distances between vehicles and the length of broadcasting messages would significantly affect the transmission performance, while IEEE802.11p could meet the requirement of VANET in case of a lower traffic load. As might be expected, when the vehicle density is increased gradually, the traffic load will also been increased, then more and more collisions caused by medium competitions between vehicles will occur, so the performance of end to end delay and frame error rate will be decreased significantly. A kind of enhanced solution has been proposed in this article, in order to resolve above described problems, it consists of three aspects, including the priority refining, the priority absolutization, and the acknowledgement-retransmission mechanism for critical broadcasting messages. Via comparing and analyzing the performance of enhanced and original protocol, it shows that the proposed solution is able to improve the performance of IEEE802.11p under traffic conditions of high vehicle desity, the only price to pay is just increasing the delay of messages with low priority. |
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