Research On Media Access Control Technology And Routing Method In Vehicle Network

Along with rapid development of the technology of wireless communication and modem auto industry, the research of VANET (Vehicular Ad-hoc Network) gets wide attention of the whole world. VANET plays an important role on the construction of the intelligent transport system and the improvement of traffic safety. However, the high mobility and the uneven distribution of the traffic stream bring great challenge of the multiple access scheme using for vehicular communications. Additionally, the scale of the VANETs is greater than traditional mobile ad-hoc networks. So, in order to improve the communication capacity of the whole network, we should make full use of the different kinds of wireless resource. By introducing the technology of the cognitive radio, the on-board unit should take full advantage of the licensed spectrum to data transmission on the condition of not interfering the using of the primary user. To an extent, the communication capacity can be improved by using this method.Based on the current findings, this paper begin the research of the technology of wireless multiple access control in vehicular communications firstly. We proposes a location-based random medium access scheme. Consider a vehicular network with a wireless a wireless bandwidth of several orthogonal channels shared by multiple vehicles used to achieve the V2V and V2R communications. Efficient distributed channel access mechanism should be used to improve the bandwidth utilization. We observe that each vehicle has a unique location, which could be exploited as a key information to identify its access channel. Motivated by this observation, we design a location-to-channel (L2C) randomized mapping approach. In the approach, each vehicle will access to the channels with optimal location-dependent probabilities. The simulation results are presented to demonstrate the performance of this MAC scheme by comparing it to the general random MAC scheme. It is shown that the average collision probability of channel access is clearly reduced and the average throughput of the channel is significantly enhanced.To improve the capacity of the whole network, this paper also start the research of routing algorithm in wireless environment of cognitive radio. We observe that Primary Users (PUs) in CRNs exhibit unevenly geographic distribution due to their social behaviors. In the area with densely-distributed PUs, the low spectrum availability will severely decrease the Secondary Users (SUs) communication reliability. We are motivated to exploit Primary User (PU) social features to set up a multi-hop routing path providing reliable end-to-end communications. We first propose the concept of PU community. Maximum likelihood estimation method is then employed to predict the number of potential PUs. The estimated results effectively reflect the spectrum utilization, and hence, provide important information for PU community formulation. After that, considering the existence of PU communities, we propose a hybrid routing scheme to alleviate the impact of PU communities on packet-forwarding reliability. Simulation results demonstrate that the proposed scheme significantly improves the reliability of end-to-end communications.