Research On Relay Selection For Multi-source Nodes In Vanet

Vehicular ad hoc network(VANET)plays an important role in intelligent transportation.It can transmit road conditions,traffic and parking information,etc.to vehicles and control centers in real time by using communications between vehicle-vehicle?vehicle-pedestrian and vehicle-roadside facilities,which can reduce road congestion,traffic safety and save person's time.The application of cooperative communication in the VANET can mitigate the communications limitations caused by fast changing topology,channel time variation and channel capacity to some extent.By using cooperative communications and relay technology,a vehicle can be used as a relay of other vehicles,which can greatly improve the communications quality of VANET.The main works of this thesis are as follows:1.This thesis introduces the development background and research status of cooperative communication and VANET,and briefly describes the evolution of algorithms for relay selection.The transmission protocol in cooperative communication and the outage probability of the relay selection algorithm under each protocol are analyzed.Then physical layer requirements in VANET and basic principles of OFDM are discussed.2.This thesis studies relay selection algorithms for multi-source nodes and DF protocols.Under the premise that the number of source nodes is greater than that of relay nodes,both CSI-based and none-CSI-based algorithms are discussed.Moreover,an improved comparative relay selection algorithm is proposed.Finally,the thesis analyzes and simulates the system outage probabilities and bit error rates of above three algorithms.The simulation results show that the system performance of the proposed algorithm has some advantages.3.This thesis further studies relay selection algorithms for multi-source nodes and AF protocols.Under the premise that the number of source nodes is less than that of relay nodes,the optimal algorithm and the naive-RS algorithm are discussed.Then,an improved naive-RS algorithm is proposed.The performances such as outage probabilities and bit error rates of above three algorithms are simulated and analyzed.The simulation results show that the improved naive-RS algorithm is superior to the ORS algorithm in complexity and better than the naive-RS algorithm in performance.4.All of algorithms shown in this thesis are discussed for a VANET system.Considering the Jakes channel model and the 3GPP V2 V channel model,this thesis studies the outage probabilities of these relay selection algorithms in vehicular environments.Simulation results show that the proposed algorithms have certain practicability in the vehicle environment.