Research On Downlink Of Non-Orthogonal Multiple Access System

With the development of mobile Internet and multimedia service,people can obtain huge amounts of information anytime,anywhere.With the development of the times and the progress of society,people's spiritual and cultural needs continue to increase.And with the continuous development of software and hardware technologies,people have new expectations for mobile Internet,multimedia services,and even the Internet of Things and Internet of Vehicles.The development and upgrading of these services cannot be separated from the support of mobile communication,as people have new requirements for the development of mobile communication,such as faster data transmission rates,higher spectrum utilization,more access devices,and lower access delays,etc.Currently,the widely used mobile communication under the LTE / LTE-A standard is difficult to meet these requirements,and the proposal of a new generation of mobile communication is imminent.As we all know,the most critical technology in mobile communication in the past is the multiple access technology it uses.The multiple access technologies used in the first to fourth generation mobile communications are orthogonal multiple access schemes.They all use one or two of time domain,frequency domain and code domain to distinguish different users who share channel resources.Although orthogonal multiple access has the advantage of simple user detection,due to the orthogonal demands between users,the maximum number of access users and the maximum system throughput are greatly restricted.Therefore,in the new generation of mobile communication systems,researchers hope to propose a non-orthogonal multiple access technology.Against this background,Japanese mobile communication operator NTT DOCOMO has proposed a non-orthogonal multiple access(NOMA)solution.NOMA refers to the use of power multiplexing technology at the transmitting end to allow multiple user signals to be superimposed for transmission.The users in the cell are divided into several subcarrier user groups,and users in the same group allocate transmit power according to different channel gains.After the signal reaches the receiving end,the desired user signal is received through interference cancellation.This paper summarizes the current research status of NOMA at home and abroad,and clarifies the application prospects of NOMA and its significance for the future development of mobile communications.It will focus on analyzing the working principle of NOMA and establishing the NOMA downlink system model.The key technologies in the NOMA system include subcarrier grouping scheme and power allocation algorithm at the transmitting end,signal detection and interference cancellation at the receiving end.In addition,the similarities and differences between the principles of NOMA and other new non-orthogonal multiple access technologies not limited to the power domain are compared,some applications of combining NOMA with other communication technologies are introduced.After analyzing and evaluating the key technologies of the existing NOMA system,we propose a NOMA downlink subcarrier grouping scheme using a greedy algorithm that obtains the global optimum from a local optimum.Compared with traditional subcarrier grouping schemes such as random subcarrier grouping and full search subcarrier grouping,this algorithm can be used to obtain system throughput and achieve performance advantages in feasibility.Then,this paper proposes a user power allocation scheme based on particle swarm optimization algorithm.Compared with traditional power allocation schemes such as fixed power allocation and fractional order power allocation,the energy efficiency of NOMA system is improved.Finally,a design scheme of NOMA downlink receiver based on multi-user modulation constellation interference cancellation algorithm is proposed.Compared with the SIC receiver design scheme,the system performance is effectively improved,and the work delay and operation complexity are reduced.