Research On Relaying Networks Based On Non-Orthogonal Multiple Access

With the development of the mobile communication technology,applications such as smart device,high end manufacture equipment,and HD video have become more and more popular.At the meantime,they bring challenges and demands for next generation of communication system.These new applications require higher quality services,such as faster data transfer rates and lower data transmission delays.All these require the breakthroughs on the Fifth Generation Mobile Communication System(5G).In general,the requirements can be summarized as follows.1)1000x capacity boost,2)100 billion+ device access guarantee,3)higher than 10 GB/s data rate,4)less than 1ms latency.The application of relay technology in mobile communication networks has greatly facilitate the 5G research and development process.Relay cuts the long distance between the two communication terminals,saving the energy consumption caused by the transmission and ensuring the reliability of the communication.In addition,the relays can not only avoid extreme large load for single base station,thus can reduce the cost of the base station,but also improve the utilization of spectrum.One promising way to address the massive amount of service access issue is called Non-Orthogonal Multiple Access(NOMA),which received extensive attention due to its ability to support sharing the same radio source among the users.The First Generation Mobile Communications System(1G),the second generation mobile communication system(2G),the Third Generation Mobile Communications System(3G),and the Fourth Generation Mobile Communications System(4G)use orthogonal multiple access Orthogonal Multiple Access(OMA),the same time domain resource,frequency domain resource,or code domain resource can only be used by one user.Regardless of whether the information contained by the served user is useful,other users are not allowed to share the already occupied radio resources,which results in lower resource utilization.NOMA technology overcomes this problem,and its basic idea is the power multiple access method.The specific implementation of NOMA technology is: at transmitter,the base station allocates different power ratios based on its different channel state information(CSI),and uses it as a coefficient to superimpose multi-user information.Based on NOMA technology,base station allocates smaller transmission power to users with strong CSI and larger transmission power to users with weak CSI,so that multiple users can improve spectral efficiency to a certain extent on the basis of realizing user fairness.the receiver adopts corresponding interference cancellation technology to detect and distinguish the su-perimposed user information.This article utilizes successive interference cancellation(SIC)technology to distinguish users.Considering 5G requirements and research status,this paper focus on NOMA technology,and the corresponding research on selection of the relay protocol,the estimation of the channel state,the measurement of the number of users,etc.,the main contributions are stated as follows:1.The traditional one-way relay wireless communication network and the two-way relay wireless communication network have certain applications in actual network scenarios.This paper studies both one-way and two-way networks and applies two relay protocols: Amplify-and-Forward(AF)and Decode-and-Forward(DF)which will help better understand the advantages and disadvantages of different relay protocols.About the time-varying CSI in the actual network scenario,this paper assumes the Perfect Channel State Information(PCSI)and Imperfect Channel State Information(ICSI),and verifies the impact of CSI.One of the factors is the effect of channel estimation error on network performance.In addition,this paper analyzes the network performance by using the system outage probability,uses different optimization algorithms to improve the performance of the system and verifies the conclusions by simulations.2.This paper applies NOMA technology to wireless relay communication network,and studies the performance of two different network scenarios under PCSI.The first scenario is that in a downlink relay wireless communication network,the base station can not communicate directly with users due to channel fading and multiple obstacles.The relay node acts as a bridge to establish the information interaction between the base station and the user side.The second scenario is that in a downlink relay wireless communication network,the distance between the base station and the edge users of the cell is limited to a feasible value based on the limitation of cell area,and the base station can communicate with the user directly without relay nodes.However,due to the advantages of high spectral efficiency and energy saving of relay technology,this paper considers both direct communication links and relay communication links with relay nodes,namely cooperative relay wireless communication networks.Finally,the system performance is analyzed by outage probability,ergodic and rate two indexes respectively.The simulation results verify the correctness of the theoretical analysis,and show the superiority of NOMA technology in realizing user fairness and improving network capacity.3.NOMA technology is applied to wireless relay communication network to study the performance of different networks in the case of ICSI.This article mainly discusses the following two scenarios.In the first scenario,users have the same service priority.Assuming that the cell coverage is infinite and continues to increase,this paper uses hybrid algorithm to divide users into different user groups.Orthogonal multiple access OMA technology is used among user groups,and NOMA technology is used within user groups.In the second scenario,users no longer have service fairness,but divide different service priorities according to specific emergencies.While allowing all users to serve together,NOMA ensures the quality of service of users with high priority,and then optimizes the quality of service of other users.The simulation results show that,compared with OMA technology,NOMA technology can help the system to achieve better performance in the network in which users rank according to channel state information and quality of service.Through the research of this paper,the knowledge of wireless relay communication network has been deepened.And through the application of NOMA in different networks,the superiority of NOMA is verified.