A Study Of Physical Layer Security Transmission Technology Of Backscatter Communication Systems

The Internet of Things(Io T)is one of the industries with the most development potential and value after the Internet in the world today.It is also regarded as the third revolution in the information technology era.Its core idea of "Internet of Everything" breaks through the limitations of fixed equipments in traditional communication architecture.In order to meet the low-power,low-cost and low-complexity application scenarios of the Io T,and to ensure the security of the Internet of Things applications,this thesis first conducts a detailed study of the artificial noise(AN)-based technologies,and then explores the beamforming(BF)technologies in the considered systems.First of all,considering the Gaussian noise at the eavesdropper,for a single-antenna backscatter communication system using AN,this thesis studies the critical conditions for system's secrecy rate greater than 0,and solves the power allocation optimization problem of the maximum secrecy rate at a given power.The simulation results show that the distance of the eavesdropper and the antenna gain are important factors that affect the critical conditions of the system's secrecy rate.The AN method is not suitable for the scenario of low signal-tonoise ratio and high antenna gain at the eavesdropper.Compared with ignoring the Gaussian noise at the eavesdropper,the optimal power allocation result derived in this thesis can effectively save the power of the system with large Gaussian noise.Secondly,in the case of ignoring the Gaussian noise at the eavesdropper,for a singleantenna backscatter communication system using AN,this thesis derives a theoretical expression for the secrecy outage probability(SOP),and proposes an algorithm based on the golden section search to solve the optimization problem of the minimum SOP.The simulation results verify the correctness of the expression and algorithm presented in this thesis.Then,the optimal AN scheme of the multi-antenna backscatter communication system is analyzed.Under the fixed total transmission power of the system,the optimization problem is transformed into a dual scalar parameter optimization problem.A method based on genetic algorithm is then applied to obtain the optimal solution.At the same time,the critical conditions of the system's secrecy rate are also analyzed.The simulation results show that compared with the single-antenna system,the AN scheme of the multi-antenna system can not only increase the range of the reader to read the tag for low signal-to-noise ratio scenario,but also enhance the secrecy rate of the system.Finally,in a multi-antenna backscatter communication system,when the channel state information of the reader is known and the channel state information of the eavesdropper is unknown,this thesis proposes a transmission scheme that transmits both continuous carrier signal and AN in the reader-tag main channel space.The simulation results show that the scheme proposed in this thesis is better than the traditional zero-space scheme when the system reader can completely offset the AN.