Research On Adaptive Cooperative Mode And Relay Selection Algorithm In VANETs

Vehicle Ad hoc Networks(VANETs)is the main supporting platform of future intelligent transportation system.Compared with traditional wireless ad hoc networks.VANETs have specific characteristics,such as high speed,rapidly network topology change,deep fading and so on.All these characteristics will lead to unstable communication links and low information reliability.Introducing cooperative communication technology into VANETs can really achieve diversity gain and improve system' reliability.Though,it also causes the problems as delay and poor bandwidth utilization.Then,in order to guarantee the reliability,connectivity and rapidity of information transmission in VANETs,the adaptive cooperative communication mode and relay selection algorithms are studied in this dissertation.The major works are outlined as follows,(1)Three relay choice algorithms are proposed in VANETs based on cooperative communications technology.Namely random path algorithm(RP,Random path),optimal path based on channel gain algorithm(OPCG,Optimal path based on channel gain)and optimal path based on minimum packet loss rate algorithm(Optimal path based on minimum packet loss rate).Then,the symbol error rate performance of three algorithms at different speeds is given and compared.Finally,based on the results of performance analysis,three applicable scenarios of the algorithms are presented.(2)Considering delay,bandwidth utilization and fading simultaneously,this dissertation studies the adaptive cooperation mode in VANETs.The adaptive cooperation mode has two levels of meaning,one is the adaptability of relay cooperation strategy,that is,the choice of "cooperative opportunity".The second is the adaptation of relay forwarding strategy.Firstly,an adaptive decode and forward algorithm is proposed based on the characteristics of vehicle's move and that of different relay forwarding methods.And then,the closed-form expression of the symbol error rate performance is derived.Theoretical analysis and simulation results both show that the proposed ADF algorithm outperforms DF and IAF no matter what the vehicle is relative immobile or not.(3)To deal with high-speed movement of vehicles,the ADF algorithm is further optimized by combining above OPCG.Then an ADF-oprelay algorithm is proposed.The simulation results show that the ADF-oprelay algorithm has good performance at high speed and can effectively solve the relay collision problem.