Research On Security Performance Of Physical Layer Based On Cooperative MIMO System

With the rapid development of mobile communications, Multiple-Input Multiple-Output(MIMO) technology has been deeply well used in communication networks. Meanwhile, in order to further improve the performance of the MIMO systems and/or the multi-hop transmission systems,cooperative communication technologies including cooperation MIMO and multi-user cooperative relay have been developed, which may significantly improved our daily communication. However,due to the openness and complexity of wireless channels, keeping the confidentiality of the transmissions over the channels has been an increasing challenge. Physical layer security technologies are able to achieve secure information transmission by taking advantage of the characteristics of wireless channels such as broadcasting and fading. Therefore, it has become an effective method to combat eavesdropping.The indicators of security performance for MIMO wiretap channels are usually characterized by the secrecy capacity, which is calculated by maximizing the difference of the mutual information between the legitimate receiver and the eavesdropper. In this paper, we analyzed the security performance of MIMO wiretap channel for cooperative MIMO systems based on the secrecy capacity and the concept of geographical security zone. The main contents of this paper are listed as follows:(1) For the case MIMO wiretap channel with multi-antenna nodes, we take into account the impact of both large-scale fading and antenna coupling effect on system security capacity during simulation. Because of the limited size of the eavesdropper and the coupling effects between the antennas, there exists of an optimal value of the eavesdropping antenna. By simulation, we obtained the minimum secrecy capacity and safety zones.(2) In the MIMO wiretap channel with limited-size antenna arrays, we consider that the receiver can transmit the artificial noise in the communication mode of full duplex. The receiver sends the artificial noise to the eavesdropper when it receives the information from the sender.Simulation results show that the security capacity and the safety distance of the system can be greatly improved than that without sending artificial noise.(3) In the scenarios of cooperative MIMO, in order to solve the problems of the untrusted relay, we propose a physical layer transmission scheme that the receivers provide joint interference to against the untrusted relay. This scheme divides information transmission process into two phases.In the first phase, the sender sends messages to the relay and the friendly receivers that are closer to the sender, and at the same time, the friendly servers send noise signals to interfere the relay. In the second phase, the relay sends the signals mixed with noise to the destination receiver. Meanwhile,the friendly receivers send the noise cancellation signals to the destination receiver. And then the destination receiver restores the original information with the help of the friendly receivers. The secrecy capacity of the system is improved because of the relay constantly receives interference from the noise signal. The simulations show that, with suitable friendly receivers, the system still can get a larger security rate with the existence of an untrusted relay.