Research On User Resource Allocation In Cooperative Communication System Based On SWIPT And NOMA

The development of mobile internet(MI)has brought a surge of data demand and a larger number of intelligent terminal access,as well as higher requirements for user quality of service(QoS).However,the contradiction between the explosive growth of data transmission requirements and scarce spectrum resources runs through the development of communication technology.Traditional Orthogonal Multiple Access(OMA)technology from the perspective of information theory can no longer for the current communication system expansion.Therefore,more and more attention has been paid to non-orthogonal multiple access(NOMA)technology.NOMA allocates different transmission power to different users with different channel gains at the transmitter,which allows multiple users to send their messages in the same band simultaneously.In order to obtain independent information for each user,successive interference cancellation(SIC)is required when decoding at the receiver.In NOMA,low channel gain users will be allocated more power for transmitting and to be given priority decoded at demodulation.In other words,the high channel gain users will obtain the information of the low channel gain users in the decoding process.By using this decoding feature,NOMA and cooperative communication can be perfectly combined.Because of the advantage in the aspect of improve the system efficiency,simultaneous wireless information and power transfer(SWIPT)has become the research hotspot in recent years.In the SWIPT system,the terminal receives radio frequency(RF)signals while collecting the energy in the signal,one part if the signals are used for decoding,and the other part are used for storing energy.In the cooperative forwarding stage,the high channel gain user forwards the information of the low channel gain user as the partner.Through SWIPT,it is expected that the forwarding device only uses the energy of the RF signal to achieve "zero power" forwarding.This thesis focuses on NOMA and SWIPT to study the optimal allocation of user resources under different cooperative communication scenarios.The technical background,such as NOMA principles,cooperative NOMA and SWIPT principles are briefly described.Then we focus on the specific research content as follow:the optimal user resource allocation based on SWIPT and cognitive radio(CR)uplink NOMA cooperative communication system.Multi-user simultaneous access the system by using NOMA in the uplink transmission process,ensuring the interference to primary user(PU)is limited while maximizing the achievable rate of the secondary user network.In the research of downlink D2D cooperative communication scenario based on SWIPT and NOMA,the transmission power and time slot allocation are jointly optimized to maximize the achievable rate of D2D user pair while guaranteeing QoS of Cellular User(CU).The main innovations and contributions of this paper are as follows:1)Aiming at the improvement of system energy efficiency and frequency efficiency,the uplink NOMA multi-relay cooperative communication system based on cognitive radio was designed,and SWIPT technology was introduced to make the relay nodes do not consume their own energy in the process of transmitting signals.Under the premise of guaranteeing primary user QoS,the achievable rate of secondary user network is maximized by jointly optimizing the transmission power of secondary users,SWIPT power allocation factor and the selection of relay nodes.Aiming at the optimization goal,the genetic algorithm(GA)is used to solve the multi-variable non-convex problem,the numerical simulation is compared with the traversal optimal solution and the random relay selection results,and the influence of different parameters in the system on the final optimization goal is analyzed.By maximizing the achievable rate of secondary user network,the spectrum utilization of the system can be optimized.2)The optimal allocation of user resources in D2D cooperative communication system based on NOMA and SWIPT in downlink is studied.When there is no direct connection path between the base station and the cellular user,the D2D user participate in cooperative communication to complete the forwarding of the cellular user's signal.Under the requirement of ensuring the QoS of the cellular user,the achievable rate of D2D user pair is maximized.The D2D users use SWIPT for energy harvesting while receiving the signal sent by the base station to the cellular user.In cooperative communication process,D2D users do not need to consume their own energy when forwarding the signal and get the opportunity to send their own signals with NOMA.Aiming at the complex multi-variable non-convex problem,the original optimization problem was solved by splitting the problem and relaxing the constraints.A cyclic iterative algorithm is proposed to obtain the suboptimal solution of the original optimization problem with lower computational complexity.Through numerical simulation,the performance differences between the proposed algorithm and the ergodic optimal solution and the random slot assignment are compared,and the influence of different parameter changes in the system on the system optimization goals is analyzed.