Research On Relay Network Transmission Strategy And Power Allocation Algorithm Based On NOMA

With the rapid development of mobile Internet,the society's requirements for mobile communication services are also rising,prompting people to carry out research on the fifth-generation mobile communication technology(5G).Non-orthogonal Multiple Access(NOMA)technology is considered as one of the most potential 5G alternatives due to its high spectrum utilization and fast rate.At present,the application of NOMA technology in the relay cooperative scenario is the research hotspot.Since NOMA technology in the power domain can distinguish the strong and weak users through different power,it is very important to allocate power and time resources for users with different channel conditions in the relay system.In this thesis,the NOMA cooperative communication system with relays is taken as the research object.The theoretical analysis of the ergodic rate and outage performance of the system and the power allocation algorithm of the system are studied.The problem of rate maximization in different relay communication scenarios and relay system with buffer system are discussed,and corresponding algorithms are proposed.The main research contents of this thesis are as follows:(1)In the relay scenario,when the number of users in the center of the cell is less than the number of users in the edge of the cell,the time and power allocation algorithm of the NOMA relay network is studied.Firstly,the two-hop DF relay scheme in downlink cooperative NOMA is presented,and the expressions of system user outage probability and ergodic rate are derived.On this basis,the optimization model of system rate maximization under the guarantee system equity index is proposed,and the joint time and power factor allocation algorithm is proposed to solve the model.The simulation results show that the system optimized by the power time optimization algorithm has a significant improvement in system speed compared with the traditional equal-slot allocation and transmission system under the premise of system fairness.(2)In the NOMA cooperative scenario of multi-user random distribution,the system outage probability and diversity order of system relay working in half-duplex and full-duplex modes are derived,and the closed-form expression of system outage probability is obtained,which provides a theoretical basis for grouping according to the number of users in the case of multi-user.In this thesis,we also consider the influence of system outage probability and rate when relay self-interference is not completely eliminated,and obtain the closed-form expression of outage probability when relay works in different modes.The simulation results show that the theoretical value of the outage probability expression is consistent with the simulation value,which proves the correctness of the derivation.(3)In the NOMA system with buffer at the relay,an optimal power rate allocation algorithm is proposed.The system focuses on the power and rate allocation of users in scenarios where the relay has multiple buffers and the buffer has a capacity limit.Firstly,the expressions of the optimal power and rate expression of the base station and the relay are derived,and then proposed the optimal power rate allocation algorithm of the system when the buffer capacity is limited.Since there are two transmission modes of NOMA and OMA during the system transmission,the theoretical probability of the system using NOMA transmission is analyzed and a closed-form solution is obtained.Simulation results show that the proposed optimal power rate allocation algorithm has a significant increase in system speed compared to traditional equal power allocation transmission systems.