Performance Analysis Of Link Transmission And Channel Access In Vehicular Networks

Vehicular networks is a carrier for communication between vehicles or for vehicle to communicate with other things and plays an important role in intelligent transportation system(ITS).With the rapid development of modern ITS,vehicular networks have received increasing attention from the industry and academia.As of vehicular networks has its own characteristics,such as changes in the topology,regular driving directions,and limited delay,the performance of the vehicular networks is severely limited.Some traditional wireless network technologies are not very suitable for vehicular networks.In order to analyze characteristics of vehicular networks and improve the performance of vehicular networks,this dissertation focuses on the modeling of channel transmission characteristics of vehicular networks and studies some key technologies on vehicular networks applications.Furthermore,this dissertation focuses on the modeling and analysis of different applications in different network scenarios.The main work and contributions of this dissertation including the following six aspects:Firstly,high channel congestion phenomenon following a channel switching when vehicle access channel in vehicular is studied and a theoretical analysis model with channel switching is established for analyzing and calculating the packet collision probability and transmission delay caused by channel switching.In process of establishing the model,vehicle dynamic contention behavior reveals high channel congestion phenomenon as of burst packet arrival.On basis of model,two solutions including a centralized equal-spaced algorithm and a distributed random-spaced algorithm are proposed and packet transmission collision probability and transmission delay are also proposed respectively for two solutions.The accuracy and effectiveness of the packet transmission collision probability model and transmission model which depict high channel congestion phenomenon following a channel switching are verified through simulation results.Meanwhile our proposed solutions can effectively mitigate high channel congestion phenomenon caused by channel switching,reduce packet transmission collision probability and transmission delay and improve system throughput.Secondly,transmission capacity in vehicular D2 D relay networks with multi-user case is studied and a transmission capacity theoretical analysis model is established for analyzing and calculating the transmission capacity.In the process of analyzing and calculating,we assume multi-user including service vehicle(SV)and helper vehicle(HV)in D2 D relay network work in overlay mode.According to stochastic geometry theory,SVs and HVs all are modelled as Poisson Point Process(PPP)in vehicular networks,respectively.When SV communicates with SV,the HVs existence probability and the expectation dista nce with HV link are achieved to calculate the successful transmission probabilities.In the characteristics of enlarging transmission distance for HV,transmission capacity between SV and SV with assisted HV is further achieved and reveals the influence o f vehicles density and transmission power.Besides,the relationship between transmission capacities and variable direct link distance of SV to SV communication are also analyzed.Simulation results indicate that transmission capacity can be improved by a HV and influenced by some system parameters,including communication distance between SV and SV assisted by HV,vehicle density and so on.Thirdly,reliable link transmission in 5G enabled vehicular network is studied and a link quality of service(QoS)indicator(LQSI)model is established for analyzing and calculating the reliability of transmission link.In millimeter wave vehicular network,we consider link transmission successful probability and transmission delay to judge link QoS and different weight factor for transmission successful probability and transmission delay reflect different link QoS,respectively.In establishing the LQSI model,the relationship between LQSI and vehicles number and transmission of vehicle is analyzed and compared.Based o n the proposed LQSI model,an optimal selection algorithm based on vehicular cloud(VC)is proposed.Simulation results indicate that link QoS of vehicular network can be improved by increasing number of vehicles.Simultaneously,the influence of vehicles number,transmission distance and different weight factors for link QoS is evaluated in vehicular.For different service requirements,there is always an optimal link to satisfy user service requirements.Fourthly,the outage performance of two-hop vehicular networks,including direct communication and indirect communication is studied and an outage probability expression model is established for analyzing and calculating outage probability of relay transmission link.In establishing outage probability model,the probability density function for vehicle to vehicle(V2V)communication is obtained by calculating the over transmission signal-noise-ratio(SNR)of the relay-assisted link under Rayleigh fading channels.Then,the outage probability of V2 V communication link is further achieved and reflects the influence of transmission SNR for two-hop links and relay gain.The ratio of transmission and threshold judge the link is good or bad.In addition,an optimal relay selection algorithm for vehicle device function structure is designed.The accuracy and effectiveness of outage probability model is verified through simulation results.For different link SNR,simulation results indicate the relationship of outage probability and link SNR.Then,the backoff algorithm under different traffic load conditions in contention-based vehicular network is studied and a dynamic adaptive success-collision(DASC)backoff algorithm is proposed to improve the performance of vehicular networks.The collision probability reflects the performance of vehicular networks and restricted by vehicles traffic loads and the variation of contention window(CW).The threshold is defined to reflect different traffic loads.In addition,the proposed algorithm improve s throughput and transmission delay of vehicular networks by reducing CW value after consecutive successful transmission times and increasing CW value after consecutive collision times.Simulation results indicate that the proposed DASC backoff algorithm could improve the throughput and transmission delay of vehicular networks and give out the influence of CW and vehicles density in vehicular networks which can provide theoretical reference for reasonable deployment in practical environment.Finally,the fairness problem of the access channel under the coexistence of dual-radio vehicles and single-radio vehicles in vehicular networks is studied and a fairness model is established for analyzing and calculating the fairness of the access channel.In the process of establishing the model,the difference duration for dual-radio vehicles and single-radio vehicles cause the different throughput and further to causing unfairness problem.With the goal of throughput when the vehicle accesses the channel,we analyze the throughput of dual-radio vehicles and single-radio vehicles,respectively.The access channel is fairness if one dual-radio vehicle and one single-radio vehicle have same throughput.The accuracy and effectiveness of the fairness access channel model are verified in simulation r esults.Simulation results indicate that the relationship between the fairness of the access channel of a dual-radio vehicle and a single-radio vehicle and the number of dual-radio vehicles,the number of single-radio vehicles,the minimum contention windo w of a dual-radio vehicle,and the minimum contention window of a single-radio vehicle.In addition,there is always an appropriate CW to ensure fairness access channel.