Transmission Capacity Of Spectrum Sharing With Cellular Uplink Spectrum In Cognitive Vanet

As the basis information platform for Intelligent Transport System (ITS),Vehicular Ad-Hoc Networks (VANET) has attracted increasing number of concerns. Different from the traditional wireless networks, in vehicular communication system, the high-speed mobility of vehicles makes the transmission environment change rapidly. Meanwhile, the contradiction between explosive growth of communication requirement and limited local resources have become increasingly prominent. Then CR-VANET (cognitive radio VANET) is proposed to solve transmission problems caused by such contradiction.Meanwhile, transimission capacity has been generally recognized as a solution to the capacity and quality of service measurement in the study of CR-VANET.However, existing researches in the transmission capacity of CR-VANET are still using the traditional models and protocols in wireless ad hoc network, and lack of considering actual distribution characteristics, therefore, this paper will study the transmission capacity of CR-VANET from this point.Firstly, we propose a CR-VANET model based on celluar uplink spectrum for large urban road environment, in which the bus Wi-Fi cellular network(primary network) and vecular ad hoc network (secondary network) share the uplink spectrum of celluar network, and vehicles in VANET have opportunity to access the primary network for transmission. Secondly, based on the model, we propose two ways to access the primary network: (1) In order to limit the interference of cognitive process on the primary network, we propose a cognitive-contention protocol based on power threshold, a method to find the spatial spectrum hole by detecting the power of beacon signals, and implement spectrum sensing in the region of spectrum hole with low latency and complexity; (2) In oder to consider the priority of different service, we propose a cognitive-contention protocol based on priority, a method considering both data type and requirement of transmission distance, which will promote the transmission opportunity of services with high priority. Finnaly, we derive the transmission opportunity and transmission capacity in such model and protocols, and validate the relation between transmission opportunity and various factors.Simulation results show that, with the model and protocols we proposed, the transmission opportunity is effected by many factors, such as the density of vehicles, the density of active primary transmitter, the threshold of beacom power,the threshold of contention, the number of subchannels and so on. After the prioritization, the transmission opportunity of secondary transmitters with higher priority have marked improvement, certainly, the transmission opportunity of secondary transmitters with lower priority have decreased. Meanwhile, with similar conditions, the transmission capacity of VANET improves significantly compared with no cognitive mechanism. This paper will provide some reference for the research on the transmission capacity of CR-VANET.