Research On Key Technologies Of Non-Orthogonal Multiple Access System

In recent years,with the rapid development of mobile communications,new business models and applications continue to emerge,and next-generation mobile communication systems(5G)will face enormous challenges such as rapidly increasing data traffic,massive device connectivity and diversified services.The traditional multiple access technology has been unable to meet the 5G networking requirements,so the new multiple access scheme has become a research hotspot.Among them,the power domain non-orthogonal multiple access(NOMA)has received extensive attention from related industries for its excellent spectral efficiency and capacity performance,and is expected to be used in 5G systems.This thesis takes NOMA as the research object and studies some key technologies from the perspective of system throughput and energy efficiency.For the resource allocation problem of OFDM-based NOMA system,this thesis proposes a user packet and power allocation scheme to optimize system throughput performance.Considering the non-convexity of the optimization problem,this thesis decomposes it into the user grouping problem on the subcarrier and the power allocation problem.Firstly,a user grouping strategy based on greedy algorithm is proposed to reduce the computational complexity while ensuring the difference of channel gain between superimposed users.Then,based on the result of user grouping,the power allocation problem is studied,and the power allocation problem is further decomposed into two sub-problems: the power allocation of the superimposed user in the sub-carrier and the power allocation between sub-carriers.The optimization scheme based on mathematical derivation and water injection algorithm is proposed respectively.Simulation results show that the scheme can effectively improve the system capacity.Aiming at the joint optimization problem of energy efficiency(EE)and spectral efficiency(SE)of NOMA system,this thesis proposes a power allocation scheme to maximize EE under the premise of system SE.Under the condition of the maximum available transmit power of the base station and the minimum rate requirement of the user,the joint optimization problem of maximizing the NOMA system EE is formulated.In order to solve this non-convex optimization problem,the feasible range of the transmission power that can support the minimum rate requirement of each user is first established,and then the original problem is equivalently transformed into a two-layer optimization problem.The inner layer uses the QoS-based power allocation algorithm to solve the closed-form expression of the optimal power allocation factor between the multiplexed users;the outer layer proves the pseudo-concavity of the objective function and then uses a bisection algorithm to obtain the optimal solution of the problem.Simulation results show that the scheme can improve the system EE while ensuring SE is guaranteed.Compared with the traditional OMA,NOMA has superior EE performance.