Secure Resource Allocation For Downlink NOMA Systems

The rapid development of information technology has caused dramatic growth of data size,the number of wireless equipments and users.The future demands for the quality and transmission rate of mobile services will also become higher.Therefore,Non-Orthogonal Multiple Access(NOMA)has received a lot of attention.Different from the traditional Orthogonal Multiple Access(OMA)technology,NOMA allows multiple users to transmit information on the same time-frequency resource block,which greatly improves spectrum utilization and access capacity.At the same time,the heterogeneous network architecture of the 5G system allows nodes to access and leave the network anytime and anywhere,and thus there is a great risk of information leakage.In this regard,the physical layer security technology is different from the traditional security technologies,and can use the characteristics of the wireless channels to improve the security performance.Therefore,when spectrum resources are becoming increasingly scarce and security performance is becoming increasingly severe,how to schedule various resources in the NOMA systems to achieve high security performance is a question worthy of discussion.This thesis studies the secure resource allocation for downlink NOMA systems in the following two aspects:(1)Secure resource allocation for downlink single-carrier NOMA systems based on dynamic cooperative interferring.Since the channel conditions from the user to the base station and from the user to the eavesdropper are different,sometimes the decoding data rate at the legitimate user is very small or lower than that at the eavesdropper.Such situations are detrimental to the overall system security performance.Therefore,this thesis takes the user mode selection strategy into account for resource scheduling,and proposes a heuristic algorithm to optimize the mode selection and power coefficient of all users in the system.Under the minimum data rate constraint at the users and the maximum transmit power constraint at the base station are proposed,the proposed algorithm maximizes the system sum secrecy rate.The simulation results show that compared with the scheme without cooperative interferring,the proposed algorithm can achieve higher sum secrecy rate.(2)Secure resource allocation for downlink multi-carrier NOMA systems based on bilateral matching.For a downlink multi-carrier NOMA system,the problem of joint user sub-carrier matching and power allocation to maximize the sum secrecy rate of the system is studied.For solving the non-convex problem,a two-step bilateral matching algorithm is proposed to achieve stable matching between all users and subcarriers in the system,then under the minimum data rate constraint at the users and the transmit power constraint,the closed-form expression for the optimal power allocation is derived,and finally the subcarrier power allocation is obtained by the bisection method.The simulation results show that the proposed algorithm can significantly improve the security performance of the system while ensuring that the Quality of Service(QoS)of all users is satisfied.It is also shown that the proposed algorithm outperforms the traditional schemes.