Research On User-oriented Wireless Resource Allocation In High-speed Railway Scenarios

As an economical,convenient,safe,reliable,green,intensive,fast and punctual mass transportation,high-speed railway(HSR)is not only the backbone of the national comprehensive transportation system,but also the strategic and critical national major livelihood project and basic industry,playing a vital role in supporting China’s economic and social development and national security.With the rapid development of mobile Internet and the emergence of various new services,the information needs of passengers in the process of HSR are becoming more and more intense,resulting in the contradiction between the growing communication needs of HSR users and limited spectrum resources is becoming more and more obvious,how to use limited wireless resources to meet the service needs of HSR users and improve the user experience,wireless resource management has become critical.With the development of 5G network,the Ministry of Industry and Information Technology,China Railway Group and other competent units have issued relevant documents in recent years,requiring scientific and pragmatic promotion of railway 5G technology application to help railway digital intelligence transformation.Power domain Non-orthogonal Multiple Access(NOMA)innovatively adds the concept of power domain,which can realize higher spectral efficiency,system capacity and large-scale user access,and fits the development needs of future intelligent HSR mobile communication system.Therefore,it is important to study the user-oriented wireless resource allocation in the HSR scenario by combining NOMA technology.In this thesis,we study the wireless resource allocation problem of NOMA system for HSR users in terms of power allocation,user clustering and sub-channel allocation through different system networks and optimization objectives.The main work and results contain the following two aspects:1.The energy-efficient wireless resource allocation scheme is studied for the Multi-Carrier Non-Orthogonal Multiple Access(MC-NOMA)system for HSR users.First,the energyefficiency optimization model of MC-NOMA system for HSR downlink is established by considering the maximum power limit of base station,sub-channel constraint and user quality of service(Qo S)constraint.Due to the complexity and non-convexity of the objective function,the problem is equivalently transformed using fractional programming theory,and the optimization problem is decoupled into two sub-problems of user grouping and power allocation.Then,to address the problem that the existing user-subchannel matching algorithm does not consider user Qo S and cannot guarantee the Qo S of HSR users well,a Qo S-based user-subchannel matching algorithm(USMA-Qo S)is proposed to complete user grouping,and after determining the results of user and subchannel assignment,the Lagrange dual method is used to complete the power allocation scheme.Finally,the optimal resource allocation scheme is obtained using a joint search algorithm for energy efficiency based on Dinkelbach algorithm.The simulation results show that the proposed resource allocation scheme not only improves the system energy efficiency,but also takes into account the Qo S of HSR users,and achieves a better balance between system energy efficiency and user Qo S,which can effectively improve the communication quality of HSR users and meet the research objectives of the scheme.2.For the Multiple-Input Multiple-Output Non-Orthogonal Multiple Access(MIMONOMA)system of HSR,the system capacity-based wireless resource allocation scheme is studied,and the MIMO-NOMA system capacity optimization model is established for the downlink of HSR.Firstly,in view of the existing user clustering algorithm’s high complexity,poor system performance,poor user fairness,and lack of universal applicability,an improved multi-user clustering algorithm(IMUCA-Fairness)based on fairness is proposed to reduce intra-cluster and inter-cluster interference of users by considering the influence of channel gain difference and channel correlation on system performance,and reasonably setting the cluster head users and threshold values of channel correlation,the remaining users that do not satisfy the channel correlation threshold are individually clustered using a greedy algorithm based on fairness.Then,on the basis of the determined user clustering scheme,the artificial fish swarm algorithm is introduced to complete the power allocation.Aiming at the problems of poor search accuracy,poor initialization and easy to fall into local optimum of traditional artificial fish swarm algorithm,a power allocation optimization scheme based on Improved Artificial Fish Swarm Algorithm(IAFSA)is proposed through chaotic initialization improvement and adaptive dynamic adjustment improvement of the view range and step size.Finally,the penalty function method is used to deal with the constraints and obtain the optimal resource allocation scheme of the system.The simulation results show that the proposed resource allocation scheme not only improves the total system capacity,but also takes into account the fairness among HSR users,and has significant advantages in terms of system capacity,user fairness and convergence compared with the comparison scheme,which can effectively improve the communication quality of HSR users and meet the research objectives of the scheme.