| With the gradual formation of 5G mobile communication and the continuous development of self-driving applications,the Public Land Mobile Network(PLMN)based on Roadside Base Station(RBS)and On Board Units(OBUs),with limited bandwidth resources and rapidly changing topology,is now constraining our real-time interaction of high bit-rate data and safety traffic beacons in the multi-user scenarios.Currently,the urban Internet of Vehicles(IoV)with Dedicated Short Range Communication(DSRC)technology and hand-over function of cellular network,is mainly adapting Planar Cellular Vehicle to Everything(C-V2X)system,which is oriented to public application and based on 4G-LTE or 5G-New Radio Systems(5G-NRS).However,in the Intelligent Transportation Systems(ITS)with complicated scenarios,on one hand,as the bandwidth resource is limited and the cellular cells cannot be split randomly,the communication capacity of C-V2X system is difficult to continuously improve to meet the high bit rate and intensive various data interaction;on the other hand,when the density of OBUs and the randomness of driving speed increases,high-frequency transmission of important safety beacons will easily lead to large interaction delay and low Packet Delivery Rate(PDR).Considering that the traditional planar C-V2X system has many particular characteristics,including limited spectrum bandwidth,the serious congestion of multi-user in the same channel slot,and the linear direction of typical road signal coverage,to improve the data interaction performance of IoV in urban expressway scenario,this paper proposes a novel C-V2X communication system which adopts the ribbon cellular topology and controls the multiple link resources dynamically and cooperatively.Based on the basic theory of such communication system,the four related research contents of this paper which goes deeper by deeper are:V2V/V2 B cooperative bandwidth resource allocation strategy and novel transmission protocol with improved slot structure;novel Adaptive Modulation and Coding(AMC)based on predictable short-term traffic flow channel estimation model;research of improved Adaptive Link Parameter(ALP)algorithm,and power control with link adjustment of beacon broadcast;the improved CO-HCCA access protocol which calculates the relevant time of moving vehicles and predicts the parameters of Adaptive Traffic Beacons(ATB).Moreover,in the research of these strategies,protocols,and methods,the corresponding simulation and the analysis of performance test data are described in detail.The main innovations in this thesis are summarized as follow:1)C-V2X wireless communication system with ribbon topology is the main research object.This paper theoretically proposes and describes a novel V2V/V2 B cooperative bandwidth resource allocation strategy.And then,with roadside ribbon enhancement factor,an IoV network protocol with improved time slot allocation is elaborated and analyzed,so as to improve the transmission quality of high bit rate data(mainly focus on traffic safety beacons).Different from the planar C-V2X model,this thesis first introduces the early cellular networking,which adopts ribbon directional coverage of base station signal.NS3 network platform in Linux is adopted,and a novel IoV communication model with multi base station is developed;then,integrates V2V(Vehicle to Vehicle)in DSRC protocol,analyzes and evaluates the system average bandwidth utilization efficiency(SABUE),the capacity requirement of communication channel(CRCC),the data dissemination latency,PDR and other important performance indicators.Next,in view of the dynamic values such as terminal location,velocity,and handover time follows Poisson stochastic process,which are predictable,in urbun wireless fading channel environments such as Rayleigh,extended-3,and Nak-m,the modeling calculation is carried out in combination with the ribbon enhancement factor,and then the feasibility of novel IoV transmission protocol with improved bandwidth allocation method and slot structure is demonstrated and evaluated.2)In the current 5G-IoV,under the network topology of OBUs in RBS covarage,the dynamic driving characteristics of each node is considered,and used to estimate the real-time wireless channel quality.Our research introduces the short-term traffic flow prediction algorithm of transportation to predict the fading of V2 X system,and then adjusts the digital modulation and signal transmission rate,which can reduce the latency and improve the network throughput.Aiming at the most important messages in IoV service,which are preventive active safety beacons,based on SUMO road traffic open source simulator and corresponding OMNET++public network simulation platform,a Channel Estimation Model Based on Predictable Traffic Flow(CEM-BPTF)is established.For the AMC modulation with optimized channel prediction,the formula derivation and mathematical analysis of link quality evaluation are made;then,the physical layer model of Hiper LAN/2 is configured by MATLAB,and the interaction evaluation of beacons with various settings are carried out.The results verify that this study can dynamically select the appropriate modulation and coding scheme(MCS)and signal transmission rate for traffic safety beacons with different transmission quality requirements.It also helps to improve the anti-fading of signal interaction in the ribbon C-V2X system.3)The most effective way to support the data interaction of self-driving is to continuously broadcast critical safety beacons among the related OBUs.By analyzing these beacons,the warning information will timely reach the relevant vehicles,and the corresponding operation will be carried out.This research also adopts the Veins framework of SUMO traffic simulator to develop the C-V2X beacon broadcast model with ribbon cellular topology,and the improved prediction algorithm of ALP in the network link layer is proposed and evaluated,then the real-time performance of broadcasting the safety beacons is further simulated and tested.The adaptive change of link parameters and the cooperative control of signal power determine the effective dissemination distance and appropriate broadcasting frequency of the occupied sub-channel,which can reduce the network congestion of high-density OBUs data interaction.Corresponding to the theoretical expectation of our thesis,the simulation results of the ribbon topology broadcasting model established on OMNe T++,show that the improved ALP prediction algorithm can adapt to the dynamic C-V2X channel;whether the link is congested or idle,the crucial dissemination indicators such as timeliness,PDR and SABUE are all improved;by adjusting the broadcasting term and Radio-Frequency power,the novel ALP algorithm can effectively control the security beacons congestion in the high bit-rate broadcasting scenario.Focusing on evaluating the interaction priority and anti-congestion level of safety beacons is the key difference between ATB and ALP.On one hand,in view of the Doppler shift characteristics with dynamic topology changes in the urban traffic scenario,a novel R-ATB(Relative-time based ATB)algorithm is proposed and studied,which takes the relevant time as an important congestion control level to dynamically measure the channel quality.It also can enhance the calculation performance of traditional scheme,and then improve the timeliness of link prediction and channel deployment.On the other hand,based on the prediction of R-ATB algorithm and the fundamental theory of No.7 signaling system in telecommunication ribbon C-V2X,considering the common HCCA(Hybrid Coordination Function Controlled Channel Access)protocol in the link layer,in different periods of time slots in IoV,to prevent CADI(Channel Access Demand Information)congestion,a CO-HCCA(CADI Ordered HCCA)link control protocol is proposed by adopting the strategy of fixed number and dynamic segmentation.In addition,using the OMNe T++ network platform,the index effect and theory feasibility of these two related researches are verified through the modeling calculation and comparative analysis in the ribbon C-V2X system. |
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