Research On Non-orthogonal Multiple Acess In High-speed Railway Communication System

With the development of 5G networks,the number of global devices has increased dramatically,the demand for network services has greatly increased,and spectrum resources are increasingly scarce.The power domain non-orthogonal multiple access(NOMA)adds the concept of power domain to the traditional access technologies,which can greatly increase the number of system equipment accesses and obtain better spectrum efficiency under the same spectrum resource,and it is considered as a potential 5G access technology solution.High-speed railway network construction is an important economic development strategy in China.In the future,with the rapid increase in the speed of high-speed rail and the number of high-speed rail users,we put forward higher requirements for the communication services of high-speed rail.However,the current railway network is difficult to meet the demand for high-speed rail communication services.Exploring the application of 5G technologies in high-speed rail scenarios has always been a research hotspot in the field of railway communications.The main work of this paper is to apply non-orthogonal multiple access technology(NOMA)to high-speed rail scenarios,and design corresponding resource management schemes based on maximizing system capacity and fairness indicators.The main achievements made in the paper include the following three points:By analyzing the traditional high-speed rail model,combining the two-hop model and the distributed antenna system,we can regard the high-speed rail as a collection of multiple users.At the same time,combining the two-hop model and distributed multi-antenna system,we propose a non-orthogonal multiple access transmission scheme suitable for high-speed rail scenarios.The whole process of high-speed rail through the cell is divided into multiple segments,and the corresponding precoding and detection vectors are designed at the sending end and the receiving end to achieve multi-user grouping and interference cancellation.For the first time,the power domain non-orthogonal multiple access technology(NOMA)is applied to high-speed rail communication scenarios.Based on the designed NOMA transmission scheme,we made a complete theoretical analysis of the signal processing process at the transceiver of the system.We combine cognitive radio(CR)and non-orthogonal multiple access(NOMA)technology,and propose a dynamic resource allocation scheme that maximizes system capacity while meeting the basic Qos requirements of weak users.Simulation results shows that the system capacity obtained by our dynamic power allocation scheme is superior to traditional resource allocation schemes.However,in low-power scenarios,the dynamic allocation scheme cannot achieve high system fairness.According to the correlation of channels between users,a new user grouping algorithm is proposed to make the grouping more efficient.In addition,the previously proposed high-speed rial NOMA transmission scheme hase been optimized to make its system model more flexible.At the same time,in view of the problem of poor fairness among users in the low power zone of the dynamic power allocation scheme,we have established a new fairness index(user satisfaction)and used the cooperative game to achieve the overall resource scheduling of the system.Simulation results show that in the low-power area,this resource allocation scheme can greatly improve the fairness between users while ensuring user satisfaction.