Research On Downlink Power Allocation In Non-Orthogonal Multiple Access Systems

In recent years,non-orthogonal multiple access has received wide attention as the key technology of 5G.Compared with the existing orthogonal multiple access,NOMA can carry users without limitation of the number of resources,which can meet the large-scale connection requirements in 5G application scenarios and improve the spectrum efficiency of the system.NOMA distinguishes different users through power domain,so power allocation directly affects the performance of the system.This paper aims to design effective power allocation to optimize system throughput.Firstly,this paper introduces the basic principle of non-orthogonal multiple access system,then describes the model of non-orthogonal multiple access system from three aspects: power allocation algorithm,user grouping algorithm and interference cancellation algorithm,and analyses the advantages and disadvantages of each algorithm.It lays a theoretical foundation for future research.Due to the high complexity of existing algorithm,this paper proposes an improved power allocation algorithm.Power allocation is split into two sub problems,namely power allocation inter-subbands and intra-subbands,which are solved by joint design of iterative water-filling algorithm and proportional fair scheduling algorithm.In addition,considering the existence of residual interference in the process of signal detection and separation,the error propagation model is simulated and analyzed in this paper.The simulation results show that the performance of the improved algorithm is slightly lower than that of the iterative water-filling algorithm,but it greatly reduces the computational complexity and has practical significance.Finally,for the downlink power allocation problem of non-orthogonal multiple access system based on energy efficiency,particle swarm optimization is used to optimize it.Particle swarm optimization(PSO)has the characteristics of fast convergence and strong searching ability.After several iterations,it solves the power allocation problem with energy efficiency as the optimization objective while guaranteeing the lowest data transmission rate of all users in the cell.The simulation results show that this scheme can effectively improve the energy efficiency of the system.