Research On Key Technologies Of Power Allocation In 6g-oriented NOMA System

With the commercialization of the fifth-generation mobile communication technology,the number of mobile users continues to grow,and the demand for information transmission and energy supply in various application scenarios is increasingly diversified,all of which bring huge challenges to the design of mobile communication networks.In the fifth-generation mobile communication and the future-oriented sixth-generation mobile communication,the Non-Orthgonal Multiple Access(NOMA)technology has been widely used by people because of its ability to meet user experience requirements and improve spectral efficiency.The cooperative NOMA technology under the integration of NOMA and cooperative communication technology serves non-line-of-sight users through the relay of line-of-sight users,which greatly expands the upper limit of NOMA technology and effectively improves the user experience.However,in traditional cooperative NOMA systems,the power allocation is skewed towards weak users,ignoring the burden of strong users who undertake the relay task.In addition,the different Quality of Service(QoS)requirements of different users are rarely considered in traditional NOMA systems.The efficient allocation of resources in the NOMA system has become the focus of research in the academic community.From the above problems,this thesis focuses on the resource allocation problem in the NOMA system,and proposes corresponding power allocation methods for two different communication scenarios.The details are as follows:In the traditional cooperative NOMA system,the strong user usually undertakes the task of relay,but the system allocates less power to them,resulting in a heavy burden on the strong user.This thesis proposes a new power allocation strategy based on relay communication and simultaneous wireless information and power transfer(SWIPT).Energy harvesting equipment is used to collect energy.The optimal power splitting factor of SWIPT and the closed expression of the system outage probability are derived through maximizing the sum rate.Considering the nature of the optimization problem,a monotonic optimization algorithm is proposed to solve the power splitting factor of SWIPT under the condition of the fixed power allocation.Simulation results show that without losing the performance of weak users,the outage probability of strong users is improved compared with the conventional power allocation strategy,and the overall sum-rate increases by nearly 20%compared with conventional power allocation strategy in cooperative NOMA system.The Intelligent Reflecting Surface(IRS)can also be regarded as a "relay" with special functions in the communication network which can cooperate with the NOMA system to construct a coordinated information transmission scheme.Considering the different requirements of different user equipments for communication in the future IoT scenario,this thesis proposes an IRS-assisted NOMA system communication model,and designs a power allocation method based on iterative optimization for the QoS requirements of two types of users(information users and energy users).This method minimizes the total transmit power of the system by jointly designing the phase shift matrix of the IRS,the beamforming of the base station and the successive interference cancellation sequence of NOMA,so as to reduce the energy consumption burden of the base station in the communication system.The simulation results show that,compared with the scenario without IRS,the NOMA system based on IRS can effectively reduce the energy consumption of the base station.In the scenario with IRS,the energy consumption of the proposed power allocation method is significantly lower than the way of randomly selecting the phase at the IRS and the way of directly adopting zero-forcing beamforming at the base station.