Research On Channel Allocation Algorithm Of Vehicular Network Based On RoF-DAS Architecture

In recent years, the research on the intelligent transportation system(ITS) is becoming more and more wide. ITS is a comprehensive transportation system which can ensure traffic safety, improve traffic efficiency, improve environment and save energy. Vehicular Ad-Hoc Network(VANET) is considered as an essential technology for ITS, which can provide vehicle to vehicle as well as vehicle to roadside unit with three categories of applications: safety applications, entertainment services and transportation management. Due to the fast-moving vehicles and the complexity of the vehicular environment, the communication performance of vehicles in VANET is poor. Especially with the number of vehicles increasing, the competition and interference between vehicles are becoming more and more serious. In order to satisfy the vehicle’s demand for high quality communication, an efficient frequency resource allocation is strongly required.To solve those problems, a lot of researches on the problem of channel allocation in the vehicular network have been done. According to the characteristic of spatial coverage, the channel allocation algorithms in VANET can be divided into distributed channel allocation algorithms and centralized channel assignment algorithms. The access point in the distributed channel allocation algorithm can not dynamicly adjust the channel allocation according to the load of the cell, which reduces the channel utilization. However, the central nodes in the centralized channel assignment algorithm, which have the function of information collection and central processing, can calculate the condition of channel usage and adjust the channel allocation dynamicly. In the vehicular network, vehicles move fast and the density of vehicles changes frequently. The distributed channel allocation algorithm can not meet the communication quality of vehicles. The centralized channel assignment algorithm is more suitable for VANET.This thesis adopts a new vehicular network which integrates Radio over Fiber technology with Distributed Antenna System which makes it possible for future ubiquitous and flexible communication and high bandwidth. Firstly, based on the RoF-DAS vehicular network, clustering algorithm according to the difference between vehicle’s speed and its neighbors’ average speed, the difference between vehicle’s position and its neighbors’ average position, and the connection degree with the remote antenna unit is proposed. Secondly, a CBCDM MAC protocol is proposed for wireless access in vehicular network which combines CSMA/CA and TDMA. The protocol in RoF-DAS network is divided into two kinds: the inter-cluster communication protocol and the intra-cluster communication protocol. The cluster heads communicate with RAU or other cluster head using CSMA/CA. The cluster member use the intra-cluster channel to transmit safety and unsafe messages based on TDMA and CSMA/CA respectively. Thirdly, channel allocation algorithms including the inter-cluster channel allocation algorithm and the intra-cluster slots allocation algorithm are designed for the RoF-DAS vehicular network. For the inter-cluster communication we propose a inter-cluster channel allocation algorithm based on game theory, which is to minimize the signal-to- interference ratio, to reduce the packet loss rate and to increase the throughput. For the intra-cluster communication, the intra-cluster channel is divided into fixed time slots by the cluster which assign the slots to the vehicles on the basis of vehicles’ reservation. Lastly, we compare the performance of the proposed channel allocation algorithm in RoF-DAS vehicular network with the traditional distributed channel allocation algorithm in VANET using OPNET modeler. Numerical simulation results show that the proposed channel allocation scheme outperforms the traditional one in terms of average frame service delay, normalized throughput of total network and the packet loss rate.