Energy Efficient Resource Allocation In Downlink Non-Orthogonal Multiple Access Systems

With the development of the mobile Internet,more and more devices are connected to the mobile network,new services and applications are emerging,and the demand for mobile data traffic has exploded.Due to the limitation of the number of orthogonal resource blocks,some current multiple access technologies,such as code division multiple access(CDMA),time division multiple access(TDMA),and frequency division multiple access(FDMA)are facing huge challenges.In order to meet the higher speed experience requirements of users,the connection of massive equipment and the transmission of high traffic density,the new generation of network technology must improve the efficiency in many aspects such as spectrum,energy and cost.In order to provide a thousand times the network capacity,5G systems must support higher spectral efficiency.Non-Orthogonal Multiple Access(NOMA)technology,which is one of 5G candidate technologies,uses superimposed coding at the transmitting side to make multiple users can be supported on the same resource block(such as time,frequency,and coding).At the receiving side,successive interference cancellation(SIC)is used to distinguish multiplexed users and enable users of the system to access,thus the number of inputs and spectral efficiency have been greatly improved,which has attracted widespread attention.In recent years,with the increase of mobile network energy consumption,considering the sustainable development of future mobile communication networks,energy efficiency has become a key performance of mobile communication development after spectral efficiency.Therefore,as a research motivation,this paper starts from the two aspects of user grouping and power allocation,and studies the downlink resource allocation of multi-user NOMA system based on energy efficiency.Firstly,this article focuses on the downlink resource allocation of a multi-user NOMA system with the goal of maximizing energy efficiency.We divide the problem into two sub-problems: user grouping and power allocation.A user grouping method based on the greedy algorithm is adopted to reduce the computational complexity of the exhaustive method.Then,according to the determined grouping method,a closed-form expression of the power allocation coefficient of the multiplexed users on each sub-channel is obtained.In order to further improve the energy efficiency of the system,a non-equal power allocation scheme between sub-channels is studied.The sub-channel power allocation problem is planned as a non-linear non-convex ratio and problem,and a Dinkelbach-like algorithm is used to obtain a suboptimal solution.Simulation results show that the scheme used in this paper can achieve better system capacity and energy efficiency.Secondly,the advantages and disadvantages of the two existing user grouping schemes are analyzed through the channel gain matrix,and a greedy user grouping scheme based on worst-case user first principle is proposed.The complexity is less than the exhaustive user grouping scheme.Then,based on the grouping scheme,the problem of multiplexing user power allocation and sub-channel power allocation is equivalently converted to the optimization of the minimum value of the difference between the two functions,and the original power allocation is iteratively solved using the difference of convex(DC)planning algorithm suboptimal solution to the problem.The simulation proves that the user grouping scheme and power distribution scheme adopted in this paper can effectively improve the performance of cell edge users while ensuring the energy efficiency of the system.