Research On Non-Orthogonal Multiple Access For 5G Relaying Systems

With the advent of the 5G era,artificial intelligence,big data,and the internet of things keep rising,users' requirements for spectral efficiency,reliability and power consumption are more and more stringent.The new non-orthogonal multiple access(NOMA)technology has attracted wide attention because of its ability to improve spectrum utilization effectively and serve more users in the same time-frequency resources.This article combines the NOMA technology with the relay cooperation technology,applies it to the downlink of the communication network,and combines multiple input multiple output(MIMO),relay selection and other technologies to design the network model.The impact of imperfect channel state information(CSI)and successive interference cancellation(SIC)errors on system performance is considered by analyzing the actual situation.The main research results can be summarized as follows:1? For the single-antenna NOMA relay cooperative system,the outage probability and ergodic sum rate of the system under Rayleigh fading channel are derived.The correctness of theoretical analysis is verified by experimental simulation.Compared with the traditional OMA relay cooperative system,the NOMA system has higher spectral efficiency.2? For the multi-user multi-antenna NOMA relay system model without direct links between the base station and the users,the system performance is analyzed under the Nakagamim fading channel.According to the proposed model,the accurate outage probability expression,the progressive outage probability expression,the ergodic rate of each user and the ergodic sum rate upper bound expression of the system are derived,the correctness of the theoretical analysis is verified by experimental simulation.The conclusions are as follows: The diversity gain that the user can obtain is related to the number of antennas,by increasing the number of antennas at the base station or the users,the outage probability of user can be significantly reduced;The performance of each user in the NOMA system is related to the relay position,the location can guarantee the fairness of each user of the system;The larger the m value in the Nakagami-m fading channel is,the smaller the channel fading is,the better the system performance is;Compared with the traditional OMA,under the premise of the total ergodic sum rate of the system,NOMA can serve more users in the same time.3? For the multi-antenna multi-relay NOMA system with direct links between base station and users,the system performance under Nakagami-m fading channel and the influence of imperfect CSI and SIC error on system performance are analyzed.According to the proposed model,the accurate outage probability expression,the progressive outage probability expression,the ergodic rate of the two users and the ergodic sum rate upper bound expression of the system are derived,the correctness of the theoretical analysis is verified by experimental simulation.The conclusions are as follows: Compared to the OMA relay system,the NOMA technology can serve more users in the same time band,and improve the spectrum efficiency and user fairness;Using the partial relay selection(PRS)strategy,when the number of relays increases from one to two,the outage probability of users is significantly reduced,when the number of relays is greater than or equal to three,the impact on the performance of users' outage probability is getting smaller and smaller;Due to the imperfect CSI considerations,as the average signal-to-noise ratio of the system increases,the outage probability will reach the error floor(EF);The existence of the SIC error indicates that at the users,except of demodulating the first user information,it will not be affected by the SIC error,the second and subsequent users will be affected,and the later the demodulation,the more serious user's performance impact;Ergodic rate of each user will tend to a fixed value as the average signal-to-noise ratio of the system increases,and the SIC error has a great influence on the ergodic sum rate of the system.In reality,the SIC error should be minimized and avoided.