Research On MAC Protocol For Vehicular Ad Hoc Networks

Vehicular Ad Hoc Network (VANET) is a kind of dynamic Ad hoc networks and is used in the transport field. As one of the fundamental parts of Intelligent Transport System (ITS), VANET is constructed by Inter-Vehicle Communication (IVC) and Roadside to Vehicle Communication (RVC). It should be able to deliver time-critical emergent message for assistant driving or accident avoidance. Meanwhile, VANET can support data-oriented application such as in-car entertainment or Internet access, and is supposed to make traffic much safer, more convenient and more efficient. In this thesis, we mainly study the MAC procotols used for VANET, our works include in the following parts:1. Based on the Binary Exponential BackOff (BEB) algorithm, we propose a new back-off algorithm to adapt the Contending Window (CW) by statistical counts. That is to say, we imposely increase the CW of the relativly high priority node, to reduce its capability of contending the wireless channel; and decrease the CW of the low contending ability node, to enhance the competence to access wireless channel. It is clearly shown by the simulation in NS-2 that the proposed back-off mechanism is able to remove the impact of hidden terminal to some extent, and raise the fairness in terms of node contending wireless channel.2. Based on the characteristic of vehicle nodes'moving direction, we propose a direction-based slot scheduling mechanism for vehicle nodes to contending wireless channel. This mechanism is based on the Time Division Multiple Access (TDMA), utilising the opposite-orientation moving feature of vehicle nodes to contend the slots. The experiment results show that the proposed channel access strategy is able to largely reduce the collision probability. It can increase the using rate of wireless channel resource and improve the communication real-time performance of the VANET.