Research On Time Domain Artificial Noise Of Physical Layer Security

With the development of 5G(the fifth generation mobile communication technology),high-speed and reliable transmissions are possible.Meanwhile,security issues need to be ensured.The original technologies to ensure safety are combined with 5 G.At the same time,the gap of existing technologies entails new technologies.For example,physical layer security is one of the security technologies ensuring secrecy transmission.It has attracted a wide range of attention.In physical layer security,the AN(Artificial Noise)is an important technique.The current research focuses on the artificial noise technology in space domain,which requires antennas and other space resources.It doesn't apply to some new scenes of 5G such as Internet of things.It is of great significance to explore the AN method outside space domain to extend the secrecy issues in physical layer security.At the same time,TR(Time Reversal)is one of the ideal techniques of 5G,which has the characteristic of spatial-temporal concentration.It is an ideal platform for time domain artificial noise.Therefore,based on the idea of TR,a new time domain artificial noise is proposed in this thesis.The combination of time domain artificial noise and TR is specified while the secrecy performance is analyzed.To the scenario with continuous signals transmitted in multipath channels,the secrecy performance of TR systems with artificial noise applied is studied.Using the concentration in time and space domain of TR systems,leveraging AN and signal processing to realize the design of time domain AN,we derive closed-form secrecy rate for the proposed scheme.Based on the closed-form secrecy rate,the secrecy performance is optimized by power allocation.Then we derive the expression of the optimal factor of power allocation.The secrecy performance of the proposed method can be considerably improved by more than 10%.To the scenario with concrete signals transmitted in multipath channels,as time reversal technique has MIMO(Multiple-Input Multiple-Output)effects,we study the control of multipath with the aid of precoding and derive the corresponding closed-form expression of secrecy rate.It is proved that the control of multipath could improve the secrecy performance of TR systems.The secrecy rate of the proposed method is improved by over 10%.For the SISO(Single-Input Single-Output)wiretap channel,we study the combination of the AN and the controlled multipath transmission.A scheme of adding artificial noise to mask the information signal on the remaining paths of multipath signal transmission is proposed.Closed-form expression for the corresponding secrecy rate is derived.It is proved that the scheme has a better secrecy performance and the transmission of artificial noise over selected multipath channels can enhance the secrecy performance over time reversal system by 20%.The method can be utilized to guide legitimate nodes on determining the optimal scheme to maximize the secrecy rate of the system.In sum,this thesis studies three points about secrecy communication of TR communications with the aid of AN.The method of inserting AN,the method of controlling the transmission of multipath in TR systems and the method of concrete AN in TR based on the control of multipath are studied.Parts of proposed methods are verified by simulations.