Resource Allocation For Downlink Non-orthogonal Multiple Access Systems

In order to meet the needs of human society and respond to some special application scenarios,intelligent office,life and learning have become the general trend.This new intelligent approach will bring tremendous pressure on the existing wireless communication networks,because it will occupy the resource of the existing networks,blocking the networks or making networks down.In order to solve this problem,the future wireless communication system need to be able to accommodate a large number of devices and handle a variety of services,5th Generation Mobile Communication Systems(5G)has become research focus of scholars in the field of communication and is gradually moving towards commercial.At the same time,due to the Orthogonal Frequency Division Multiple Access(OFDMA)technology that the number of concurrent users are subject to the orthogonal resource blocks in the 4th Generation Mobile Communication Systems(4G)systems cannot meet the demand of future large-scale communication systems,Non-Orthogonal Multiple Access(NOMA)technology is favored by scholars due to its large number of connections and ultra-high system capacity and has become one of the key technologies of 5G systems.For better applying NOMA technology to 5G,resource allocation method is studied to obtain optimal system performance in perfect and imperfect channel NOMA downlink systems.For multi-carrier NOMA system with perfect channel,the resource allocation scheme is mainly researched to maximize the sum rate.Due to the optimization problem is non-convex,it is very difficult to directly solve,so this paper divides it into two sub-problems: subchannel allocation and power allocation.Firstly,this paper adopts a sub-optimized sub-channel allocation algorithm,which can allocate appropriate sub-channels for users with low computational complexity;Secondly,for the power allocation among sub-channels,this paper adopts Fractional Transmit Power Allocation(FTPA)algorithm with low complexity and easy implementation.For the power allocation within sub-channels,the optimal solution of each user is obtained by analyzing Karush-Kuhn-Tucker(KKT)optimization conditions.Finally,the simulation results depict that the performance of the proposed scheme is better than that of the Orthogonal Multiple Access(OMA)system and other existing resource allocation schemes.For the single-carrier NOMA system with imperfect channel,the resource allocation scheme is mainly discussed to maximize the weighted sum rate.First,this paper proves that the convexity of the objective function of optimization problem,and obtains the relationship between the convexity of the objective function and the weighted coefficient;Second,the optimization equation in the case of two users is gave and the power allocation range of the weak user is determined,and the relationship between the weighted coefficient ratio and the optimal solution is got by discussing the situation where the stagnation point of the objective function is less than the minimum value of the allocation power,between the minimum and maximum values,and greater than the maximum value.Third,this paper solves the optimization function in the case of multiple users.The method is a generalization in the case of two users.Based on the analysis results,a low-complexity power allocation algorithm is proposed.Finally,the simulation results show the effectiveness of the proposed algorithm and compare the weighted sum rate between perfect channel and imperfect channel.