Analysis Of Physical Layer Security Performance Based On Cooperative Relay’s Behavior

Cooperation and information security are two hot issues in the area of wireless communication. In cooperative communications, multiple users share the antenna resources by forwarding each other’s information and then form a spatially distributed virtual MIMO system. For the research on information security, the impact of the eavesdropper on system security and the channel security constraints based on the wiretap channel model are investigated, where the signal-to-noise ratio(SNR) of the main channel is required to be greater than that of the eavesdropper’s channel.The combination of cooperation and security is: on the one hand, cooperation can enhance the efficiency and reliability of the transmission, whether it is conducive to security performance is what we should think; on the other hand, informations which are not related to the transmitter itself, needs to be forwarded, and this may result in the information disclosure. From the viewpoint of the information theory, this paper discussed the interrelationship between these two conceptions.According to the characteristics of the relay’s behavior, cooperative security model was divided into two categories: external eavesdropper model based on a trusted cooperative relay and internal eavesdropper model based on an untrusted cooperative relay. In the external eavesdropper model, security performance of AF and DF cooperation was investigated. In the internal eavesdropper model, security performance of AF cooperation with an untrusted relay under a quasi-static fading channel is considered. Relationship between outage probability and outage secrecy capacity is discussed and the influence of SNR and the nodes location on the outage probability is investigated. Simulation results show that the untrusted relay’s cooperation decreases the outage probability from 1/2 to 1/3 and achieves a higher outage secrecy capacity. Finally, optimum power allocations for these two models based on the security capacity maximization are formulated. Simulation results demonstrate the improvements of cooperation to the security and the efficiency of the optimum power allocations.