Research On Physical-layer Security Mechanism In Wireless Communication

Due to the broadcast nature of wireless channels,wireless communications are vulnerable to malicious security attacks,such as eavesdropping and interception.Compared with cryptographic technologies implemented at upper layers,physical layer security has several advantages.For example,with the help of appropriate encoding and signal processing,physical properties of wireless channel can be utilized to guarantee the confidentiality of the information,and make sure that only the intended receiver could decode the confidential information.In addition,physical layer security does not require a large amount of communication resources or infrastructure to share secret keys between legitimate transceiver,and it does not require the consideration of how security protocols is implemented,or any additional security mechanisms implemented on other layers.Hence,physical layer security has attracted increasing attention,and has become an important research direction of wireless communication security.This dissertation designs secure wirless transmission schemes for several practical wirless communication scenario.Specifically,we investigate how to realize the physical layer security in typical three-node communication system,how to use the new fast forward full-duplex node as the cooperative node to realize the physical layer security,how to establish a secure channel between full-duplex transmitters and half-duplex receivers,and the physical security in D2 D cooprative multicast communication,respectively.The main contents and contributions are as follows:(1)For realizing physical-layer security in the typical single-antenna three-node wireless communication system,a receiver originated two-phase secure communication scheme is proposed.In phase 1,the receiver sends a pseudorandom signal(only known by itself)to the transmitter and in phase 2,the transmitter directly sends out the mixture of its confidential message and the received pseudorandom signal.The receiver could estimate the channel with the help of the pseudorandom signal before cancelling it from the received mixed signal,and finally detect the confidential information.By contrast,without the help of pilot signal in both phases,the eavesdropper can hardly obtain any confidential information because it cannot estimate the channel.Further,from the aspect of information theory we give the numerically computation method for the channel capacity of the eavesdropper.Simulation results show that,the proposed scheme can achieve much higher secrecy capacity than the traditional scheme,even without any channel information at the transmitter.(2)In order to improve the physical-layer security transmission performance of cooperative relay communication,this dissertation designs a cooperative relay scheme to secure wireless communications by adopting a fast-forward full-duplex(F3D)node.The relayed signal from F3 D relay could enhance the SINR of the receiver,whereas weaken that of the eavesdropper and thus build up a secure channel.Furthermore,for obtaing the optimal relay scheme,an optimization problem is formulated to maximize the security capacity.The formulated optimization problem is nonconvex and challenging to deal with.We then design an iterative algorithm based on generalized fractional programming to solve it.One key step in the iterative algorithm involves another nonconvex optimization and we decompose it into a two-level optimization.Simulation results validate that,compare with the benchmark,the proposed scheme could obtain the higher secrecy capacity with smaller transmit power.(3)For realizing the secure communication from a full-duplex transmitter to a half-duplex receiver,we design a two-phase transmission scheme: in Phase 1,the full-duplex transmitter and the half-duplex receiver transmit two independent artificial noises simultaneously,while in Phase 2,the transmitter superimposes the artificial noise received in Phase 1 with its confidential signal and sends out the mixed signal.Since the superimposed artificial noise by the transmitter in Phase 2 can be effectively cancelled by the receiver,while remains an interference to the eavesdropper,a secrecy rate could then be achieved.Importantly,we derive the approximate closed-form solutions of the average secrecy rate and secrecy outage probability of the proposed scheme under a Rayleigh block-fading channel.Numerical results show that the secrecy performances of our scheme are obviously superior to the benchmark.(4)In order to achieve the security of D2 D cooperative multicast communication(D2DCM).In this paper,with the aid of distributed beamforming technology,D2 D transmitter group can cooperatively broadcast confidential information,and attempt to improve the SINR(Signal to Interference plus Noise Ratio)of user who has the lowest SINR in D2 D receiver group and reduce the SINR of eavesdroppers,so as to realize the physical-layer security in D2 DCM.Moreover,the signal from the base station to the cellular user could be regarded as cooperative interference signal to prevent eavesdroppers from overhearing the confidential information.The corresponding mathematical optimization problem is formulated to obtain the optimal beamforming vectors.Further,the case that several eavesdroppers cooperate with each other is also studied and the corresponding optimal beamforming vectors are obtained.Finally,a low complexity algorithm is proposed to obtain the suboptimal beamforming vector.Simulation results show that the proposed algorithm can effectively improve the secrecy rate of the D2 D cooperative multicast communication and the achievable rate of cellular user.Last but not least,the suboptimal algorithm can also quickly yield a beamforming vector with better performance.