Research On MAC Protocols For Logistics Vehicle-Group Networks

With the popularization of vehicles and the continuous development of wireless ad hoc network, VANETs have gradually become a new research area. With the technology, the interconnection among vehicles and among vehicles and the fixed roadside facilities can be realized, through which people can do vehicles cooperation and traffic information sharing. VANETs have the characteristics of fast network creation, flexibility and free from the constraint of wired networks, which makes the development of VANETs has a broad prospect in the area of intelligent traffic, network communication and military application. In the logistics area, road logistics application requirements become more and more widely for China’s gradual improvement of infrastructure and transport facilities. Communications of logistics vehicle-group who is the carrier of highway logistics, become more intelligent, and the vehicle wireless communication network construction is totally the key part of it. Moreover, with the different communication and mobility characteristics of logistics vehicle-group from others, the MAC protocol of logistics vehicle-group networks attracts more and more attention and become a hotspot for researchers.Closely integrated with the actual task and requirements of logistics vehicle-group, this paper proposes a new network architecture of the logistics vehicle-group network according to the network characteristics. A group controller, called VGC is installed on the first vehicle of a group to control the entire internal and external communications. Based on the architecture, this paper further proposes two adaptive MAC protocols to support the communications of logistics vehicle-group network: IVGC-MAC and the VG / R-MAC.IVGC-MAC protocol mainly supports the communication among vehicle-groups, which includes two parts separately for internal communication of groups and communication between different groups. Communication between the vehicles in a group is completed through forwarding by its VGC. The protocol can reduce communication conflict and improve network performance based on a hybrid MAC way with the consideration of network scale, vehicle-group scale and vehicle-group predictable mobility. For solving the bottleneck problem existing in the communication, this paper also considers the existence of interferences among vehicle-groups, and further develops an algorithm called IVGC-O to control the communication among VGCs. With it, the IVGC-MAC protocol can attain the optimal performance in this case.VG/R-MAC protocol mainly satisfies the communication between vehicle-groups and an AP. The protocol uses a super-frame structure, and divides into two phase, contention phase of the data request and scheduling phase of the data response. With the dynamical contention period mechanism which controls the length of contention pahse and piggybacking mechanism which reduces contention probability, the protocol can greatly improve extensive access contention in and out of the vehicle-group and effectively increase the network throughput. Besides this, a mathematical model of communication access for VG/R-MAC protocol is developed. The theoretical analysis can make some conclusions for practical application.This paper lastly investigates the performance of the two proposed MAC protocols based on extensive simulations based on NS2. Through the comparison to related MAC protocols in different scenarios, the proposed MAC protocols can be verified to have better performance and be more adaptive to the communication of logistics vehicle-groups.