Research On Sum-capacity Optimization Of Wireless Powered OFDM-NOMA Systems

In recent years,wireless communication technology has been developing rapidly.The number of mobile terminals is proliferating fast,and then the age of Internet of Everything(IoE)is coming soon.Wireless communication is becoming an inseparable part of life,and users' demand for the quality of communication networks is also increasing.The need for two basic resources in IoE,namely,spectrum and energy,is more and more urgent.That is,the traditional supply mode of energy needs to be changed,and the utilization efficiency of spectrum needs to be improved.Note that wireless powered communication technology can effectively solve the problem that traditional batteries cannot provide power continuously.And non-orthogonal multiple access(NOMA)technology can effectively cope with the challenge brought by large-scale users accessing to spectrum resources.Therefore,wireless powered communication technology and NOMA technology are two key technologies of future wireless communication.In addition,the orthogonal frequency division multiplexing(OFDM)technology,which has the characteristics of fine-grained allocation for spectrum,can facilitate wireless powered communication networks(WPCN)to use spectrum flexibility.In this paper,OFDM technology and NOMA technology are combined,and then joint designed with WPCN to solve the issues of spectrum and energy.Then the resource allocation problem in wireless powered OFDM-NOMA systems is analyzed to achieve the efficient use of system spectrum.Firstly,under the condition that the subcarrier allocation scheme is known,we study the sum-capacity optimization problem of wireless powered OFDM-NOMA systems by optimizing the time and energy allocation.By substituting variables,the original problem is converted into an equivalent concave problem.Then an optimal algorithm based on the golden section search method,iterative water-filling algorithm and projected subgradient method is proposed.Simulation results show that the proposed joint time-energy allocation optimal algorithm can achieve higher average system sum-capacity while greatly reducing computational complexity when the subcarrier allocation is known.Furthermore,by joint optimizing the subcarriers,time and energy allocation,this paper studies the sum-capacity optimization problem of wireless powered OFDM-NOMA systems while taking users' fairness into account.Considering the coupling between multi-dimensional variables,the problem is decomposed into subcarrier allocation sub-problem and joint uplink-downlink time-energy allocation sub-problem.Based on the proposed joint time-energy allocation algorithm,the subcarrier assignment sub-problem with fairness consideration is studied to balance the system sum-capacity and users' fairness.By using the alternating iteration framework,the subcarrier,time and energy allocation scheme with fairness consideration is designed for the wireless powered OFDM-NOMA systems.The simulation results not only show the convergence of the proposed framework,but also verify its superiority and effectiveness.Compared with the normal matching algorithm that do not consider users' fairness,the proposed subcarrier allocation algorithm can balance the users' fairness and system capacity well.In addition,compared with traditional wireless powered OFDM systems,our wireless powered OFDM-NOMA systems can achieve higher system sum-capacity and users' fairness.