Research On Physical Layer Security Transmission Technology In Multiple Antenna Wireless Communication

Due to the openness and broadcast nature of the propagation medium,guaranteeing the security for the wireless transmission is a serious challenge.Traditional communication security techniques apply cryptography to the data encryption at the upper layers,which is “computational security”.However,the physical layer security of the wireless communication has been ignored in the traditional method,which is the weakness of the current wireless communication security.Therefore,designing an unbreakable security technology to secure the wireless communication at the physical layer becomes the most urgent problem to be solved.Different from “computational security”,the physical layer security is the information theoretic security,which does not impose any constraint on the computational capability of the eavesdropper.The physical layer security transmission technology explores the differentiation between the legitimate channel and the wiretap channel to design the encoding scheme and process the transmit signal for securing the confidential information transmission.Taking the multiple-antenna physical layer security transmission technology as the study object,this thesis systemically studied its two common technologies: secure beamforming and artificial jamming.In secure beamforming,the direction of beam is designed to increase the reception quality of the legitimate receiver while reducing the confidential information leakage to the eavesdropper.In artificial jamming,the jamming signal is transmitted to degrade the reception quality of the eavesdropper.Multi-antenna systems consist of multiple-input multiple-output(MIMO)systems and cooperative systems which are commonly known as virtual MIMO.Based on the characteristics of different multi-antenna systems,this thesis designed tailored physical layer security transmission methods for them,and analyzed their secrecy performance.The main contributions can be summarized as follows:1.A joint optimization framework for the channel training overhead,feedback overhead,the confidential signal and the artificial jamming in the MIMO secure transmission was proposed.In the MIMO wiretap channel,the transmitter transmits the confidential signals and artificial jamming simultaneously for covering the confidential signal transmission,where the design of the transmit precoding matrix depends on the quality of the channel estimation at the legitimate receiver and the quality of the information feedback from the legitimate receiver.The more resource is spent on the channel training and feedback,the more accurate information would be estimated by the transmitter.However,the system resource used for the confidential signal transmission would be decreased,and the achievable effective ergodic secrecy rate would be decreased.Therefore,there should be an optimal tradeoff among the channel training,the feedback and the information transmission.For maximizing the achievable effective ergodic secrecy rate,this thesis proposed a joint iterative optimization algorithm to design the channel training overhead,feedback overhead,the confidential signal and the artificial jamming.2.A secure transmission technology based on the large-scale channel state information(CSI)in distributed antenna systems was proposed,and a joint optimization method of the confidential signal and artificial jamming transmitted by each antenna port(AP)was given.Coherent secure transmission technologies need strict phase synchronization among multiple APs and the instaneous CSI.For reducing the required capacity of the backhaul links between multiple APs and central processor,and the system implementation complexity,utilizing the large-scale CSI,a low-complexity secure transmission scheme was designed for distributed antenna systems.In the proposed secure transmission scheme,each AP transmits the confidential signals and jamming signals independently without coherent transmission,where the transmit power of the confidential signals and jamming signals at each AP is optimized according to the large-scale CSI of the legitimate receiver and the eavesdropper for maximizing the achievable ergodic secrecy rate.3.A hybrid opportunistic relaying and cooperative jamming secure transmission scheme for the cooperative system was proposed,and a joint optimization method of the relay selection and the jamming power was given.Due to the confidential information leakage during two cooperative phases,the security of the cooperative transmission is under serious threat.Considering the decode-and-forward(DF)cooperative network,this thesis proposed a hybrid opportunistic relaying and cooperative jamming secure transmission scheme for maximizing the achievable ergodic secrecy rate of the network.Specifically,an optimal relay is selected to forward the confidential information,while other relays transmit jamming signals collaboratively for covering the confidential information transmission during two cooperative phases.Opportunistic relaying can make the most of the spatial diversity to maximize the reception quality of the legitimate receiver,while the cooperative jamming can make the most of the spatial degrees-of-freedom to transmit jamming signals for jamming potential eavesdroppers.This thesis further investigated the effect of the outdated CSI on the secrecy performance of the proposed scheme.4.A robust joint optimization framework for the hybird cooperative relaying and cooperative jamming in the cooperative system was proposed.Considering amplify-and-forward(AF)cooperative networks,a robust joint cooperative secure beamforming and cooperative jamming optimization method was proposed.When the exact eavesdropper's CSI is unavailable,the design of cooperative secure beamforming and cooperative jamming based on the imperfect eavesdropper's CSI would result in the leakage of confidential signals and jamming signals,which would deteriorate the secrecy performance of cooperative systems.Assuming that only the imperfect eavesdropper's CSI is available,based on the robust optimization,this thesis proposed a joint cooperative secure beamforming and cooperative jamming optimization method to maximize the achievable worst-case secrecy rate.5.A cooperative jamming scheme based on the opportunistic jammer selection was proposed,and optimization methods of the selection threshold were given.Considering the single-input multiple-output(SIMO)wiretap channel including multiple single-antenna jammers and multi-antenna eavesdroppers,this thesis proposed an opportunistic jammer selection criterion for maximizing the average secrecy throughput and average ergodic secrecy rate of the wiretap channel.It is difficult for multiple geographically distributed jammers to transmit jamming signals coherently.But,if multiple jammers transmit jamming signals without coherent cooperation,the reception quality of the legitimate receiver and eavesdropper would both be deteriorated.For balancing the system complexity and the achievable secrecy performance,this thesis proposed an opportunistic jammer selection scheme.To be specific,for jamming eavesdroppers while protecting the legitimate receiver from jamming signals as far as possible,the jammers whose channel directions are nearly orthogonal to the legitimate channel direction,are selected to transmit jamming signals independently.Finally,two optimization algorithms are also proposed to design the jammer selection threshold for maximizing the achievable average secrecy throughput and average ergodic secrecy rate,respectively.