Research On Physical Layer Security Technology For Bidirectional Untrusted Relay SCMA System

This paper focuses on the security of the non-trusted relay link in the relay cooperative communication network.The aim of our research is to optimize the system security performance.As for the relay cooperative communication model,it deals with a communication network where each node has different security levels.In the network,the security level of the relay node is low.Therefore,the confidential information being relayed is untrusted.We can assume that confidential messages are used to identify the source node for authentication.In order not to be attacked by eavesdroppers,the confidential message should never be leaked to relay nodes.Therefore,the relay is not only regarded as a sender to assist in message transmission,but also as an eavesdropper to eavesdrop some information about the transmitted message.To solve these problems,this paper proposes a physical layer secure communication model for relay cooperative SCMA networks and designs a low complexity carrier allocation optimization scheme.In addition,cooperative interference nodes are added to the system model and we study the power allocation scheme between user nodes and cooperative interference nodes,so as to further enhance the security performance of the system.Firstly,according to the characteristics of multi-user signal transmission in SCMA communication system,we design a reasonable physical layer security communication model and analyze the security performance of the system.Assuming that the cooperative relay works in the amplification and forwarding mode.Through theory analysis and simulation,we study the influence of amplification and forwarding coefficient on the system security performance and a reasonable relay amplification and forwarding scheme is also designed.Secondly,we design a low-complexity carrier allocation optimization scheme to optimize SCMA user resource mapping matrix in order to maximize system sum secrecy rate.We propose resource allocation scheme based on two-sided many to many matching to achieve near exhaustive search performance with relatively lower complexity.The research also analyzes the convergence,stability and complexity of the proposed algorithm.Finally,in order to further improve the security performance of the system without affecting the normal communication of the system users,power allocation scheme is studied in our research.First,we study the power allocation in receiveing and sending user pairs without cooperative interference.Then,cooperative interference nodes are added to the system model,we analyze the effects of cooperative interference in the case that the interference signal is perfectly known or unknown by the system user nodes.We prove that only the cooperative interference signal is known by the user terminal node,the cooperative interference signal will improve the overall system security performance.As for the system model where the cooperative interference signal is known by system users,the power allocation scheme between the system user and the cooperative interference is studied.Moreover,the proposed scheme should avoid excessive power overhead.The scheme can solve the optimal power allocation between user nodes and cooperative interference nodes with the given design index of extra system power overhead.