Physical Layer Security In MIMO System

With the rapid development of wireless technology, the wireless network has been widely exploited. However, the broadcast of the wireless channel and the various network structure make the communication system is susceptible to be attacked by the eavesdropper. Furthermore, the increasing computation-al capability of the terminal and the key distribution problem of the wireless network also lead to insecure of the traditional encryption system. Therefore, the physical layer security based information system is one of the hot topic in recent research field. The basic idea of physical layer security is to exploit the randomness of wireless channel to improve the security of the wireless system. Based on requirement that the total information transfer to the eavesdropper to tend to zero, we utilize the secrecy channel coding and precoding techniques to guarantee the correct decode of the information with certain secrecy rate.Under this situation, the thesis firstly describes the concept of physical layer security and focuses on the researches on precoding scheme at the trans-mitter in this fields. The main contributions of this thesis are as follow.Firstly, the precoding scheme in the broadcasting wiretap channel is in-vestigated to improve the secrecy outage probability performance. In order to exploiting the both time and space resources, the data symbol is extended to multiple time slots to be jointly transmitted with the exiting beamforming and artificial noise generation strategy. The secrecy outage probability can be reduced by obtaining extra time diversity. Furthermore, we also analyze the asymptotic secrecy outage probability quantitatively and derive the achievable diversitv order.Secondly, the beamforming scheme at the relay is investigated in the one-way relay wiretap channel. This thesis consider a more practical scenario in which the relay networks is wiretapped by multiple eavesdroppers and only imperfect channel state information on the main and eavesdropping channels is available at the relay. In order to improve the spectral efficiency, the ro- bust beamforming and artificial noise generation is simultaneously exploited to maximize the worst-case secrecy rate.Thirdly, the secrecy beamforming in two-way relay channels is investi-gated. This thesis consider that the relay broadcasts the superimposed signal of the two source messages based on physical layer network coding. A joint beamforming and power allocation scheme is proposed to maximize the lower bound of the secrecy sum rate. In order to reduce the complexity, we further propose an suboptimal scheme with closed-form solution.Finally, the coordinated secrecy beamforming in K-user interference chan-nel with multiple eavesdropper is investigated to maximize the secrecy sum rate. Under individual power constraint of each transmitter, an centralized iter-ative optimization algorithm is proposed to utilize the widespread interference signal in IF to degrade the eavesdropping channel while decrease the inter-interference between the legitimate receivers. As a result, the secrecy perfor-mance can be improved with the proposed algorithm.