Research On Physical Layer Security For OFDM Systems

As wireless communication systems play an increasingly important role in modernsociety,users' demands for the performance of wireless communication system transmissions are increasing,and security issues are crucial in wireless networks.As an emerging security technology,physical layer security technology can effectively prevent eavesdropping and has been widely concerned.Due to the wide application of wireless communication technology,the demand for spectrum utilization is also increasing.OFDM technology has been widely used in broadband wireless communications due to its high spectrum utilization.Millimeter wave(mm Wave)communications can provide high data rates by leveraging the large unexploited bandwidths,making it a key technology that can solve spectrum congestion problems in future wireless communications.This article studies the physical layer security based on OFDM systems,and the main research work includes the following three parts:(1)This paper provides a physical layer security technology for MIMO-OFDM wireless communication systems.Firstly,a filter design technique is proposed which can destroy the orthogonality of the eavesdropper's received signal.The legitimate user can use the receiver filter to recover the original signals,while the message received by the eavesdropper is destroyed,therefore,the security of the system transmission is enhanced.Second,this article added artificial noise(AN)technology to further interfere with eavesdropper's reception.AN is generated in the null space of the legitimate channel by making use of residual power,which can interfere with the eavesdropper's reception without affecting the legitimate user.Simulation results show that the use of filters and AN can increase the BER performance of eavesdroppers and enhance the physical layer security of OFDM systems.(2)This paper studies the hybrid precoding design of mm Wave OFDM systems and proposes an iterative hybrid precoding technique based on MIMO-OFDM mm Wave systems.First,in the case of unknown channel information,the equivalent channel is effectively estimated using a compressive sensing technique,and then the analog precoding/combining matrix is designed to ensure the channel gain for each data stream.After all the analog beamformer pairs are determined,we design the baseband digital precoding/combining matrix to further mitigate the interference.Simulation results show that our proposed solution can achieve significant performance improvements.(3)This paper studies the physical layer security of large-scale mm Wave OFDM systems and proposes an iterative hybrid precoding design algorithm.In the scenarios where there are multiple eavesdroppers,the hybrid precoding is designed by maximizing the secrecy rate.First,we maximize the average SNR of legitimate recipients in the null space ofeavesdroppers' channels to prevent eavesdropping.Then,an iterative hybrid precoding design is proposed to maximize the lower bound of the secrecy rate.Simulation results show that the iterative hybrid precoding design can achieve a higher secrecy rate.