Research on Channel Allocation Mechanisms for Vehicular Ad-hoc Network

In recent years, vehicular ad-hoc network (VANET) has become a hotspot of the research on engineering and academia at home and abroad. VANET is greatly different from the traditional mobile ad-hoc network, such as high speed mobile nodes, rapid changes of the network topology, uneven distribution of nodes and channel interference. These characteristics increase the difficulty of channel resource allocation and instability of the vehicle communication quality in VANET. So it is necessary to design a proper channel allocation mechanism for VANET, which has important theoretical and practical significance to ensure communication between vehicles and the practical applications in VANET.In the real traffic environment, the vehicle node has a rapid moving speed, and a large number of nodes conflicts will occur when multiple vehicles need to access the network at the same time or the combination of sub-networks in different direction happens. In order to provide way that fast, without conflicts to access networks and reduce the access delay, a channel allocation mechanism based on the direction and location information is proposed. Firstly, the channel is divided into several time slots according to the TDMA mechanism; Secondly, depending on the difference among nodes, the time slots and the mobile nodes are divided into two sets as left and right. The protocol says that the node of the left or right direction can only compete for time slots in the corresponding direction; Finally, nodes on the basis of their location information, will occupy the time slots with the nearest distance from the neighbor nodes to each direction. The protocol proved that the allocated slot mechanism can reduce conflicts between the nodes and drop the access delay greatly.Due to the uneven distribution of nodes in VANET, traditional MAC protocol with fixed frame length cannot adapt to the changes the number of nodes. In high node density area, some nodes may not have enough time slots to access the network, and then become "blind nodes". In low node density area, time slots keep idle to decrease the utilization rate of the channel. To solve the problem, an adaptive TDMA slot allocation mechanism for VANET is proposed. Frame lengths can be doubled or halved the variety of nodes density. Theoretical analysis and experimental results show that the proposed time slot allocation strategy can improve the success rate of node competition, having a good scalability, and providing a better adaptability of the variety of nodes density.