Research On Energy-Efficient Transmission Scheme For IRS-Assisted NOMA Systems

As the number of communication devices accessing the network continues to increase,data traffic presents an explosive growth,resulting in huge energy consumption.As a consequence,the greenhouse gas emissions and electromagnetic pollution will affect the ecological environment significantly.For these reasons,energy efficiency(EE)is rapidly becoming a key performance metric for wireless networks,and there is an urgent need to design higher EE transmission schemes.In recent years,intelligent reflecting surface(IRS)has attracted the attention from the academic and the industrial communitiesas as a promising green and economical innovation technology.By integrating a large number of low-cost passive reflective components on the plane and intelligently reconfiguring the wireless propagation environment,the performance of wireless communication networks can be significantly improved.In addition,non-orthogonal multiple access(NOMA)is considered a key multiple access technology for future wireless systems due to its advantage of improving spectral efficiency and supporting large-scale wireless connections.It can provide services to multiple users on the same resource block.Due to the potential advantages of IRS and NOMA technologies,combining IRS and NOMA is a very attractive solution for the next generation mobile communication system.Therefore,this thesis aims at reducing the power consumption in the future communication industry,and conducts research on high energy efficiency transmission schemes for IRS assisted NOMA systems.The specific research work is as follows:In order to maximize the energy efficiency performance for an uplink multiuser IRS-NOMA system,a joint optimization problem of power control and phase shift matrix is formulated under the constraints of the minimum data rate,the maximum user transmit power,and the IRS phase shift matrix.A block coordinate descend(BCD)method is proposed to decouple the optimization variables and optimize each variable separately.The dinkelbach algorithm is invoked to effectively solve the optimization problem of transmission power,and then the semidefinite relaxation(SDR)technique is used to design the phase shifts of the IRS.Based on these operations,an iterative algorithm with fast convergence is proposed to further improve the energy efficiency of the system.Simulation results show that the proposed transmission method can achieve better EE performance compared to the IRS assisted orthogonal multiple access(OMA)and the traditional pure NOMA schemes.For a downlink IRS-NOMA multiuser system,the energy efficiency maximization problem under the constraints of each user’s minimum rate and the maximum transmission power of base station(BS)is decomposed into two subproblems,i.e.,the BS power allocation and the IRS phase offset optimization.Besides,a power allocation strategy based on the optimal EE is developed to design the power coefficient of each user,and a sequential refinement algorithm(SRA)is proposed to sequentially optimize the phase shifts of the IRS.Due to the fact that both of the above two subproblems can obtain the optimal solutions,an alternating optimization algorithm with low complexity and rapid convergence is proposed to find a high-quality solution.The experimental results show that the proposed IRS-NOMA transmission scheme can significantly improve the energy efficiency performance compared with the IRS-OMA method and the benchmarking scheme without the aid of IRS.