Research On Physical Layer Secure Scheme Based On Mulitipath Spatial Precoding

The massive use of wireless devices on the Internet has caused the explosive growth of wireless data traffic.As a result,communication systems are under significant bandwidth pressure.It has also led to a worsening problem of wireless signal security.Therefore,two key problems restricting communication security and reliability in wireless communication arise: 1)With the increase of communication rate,when the signal bandwidth is greater than the channel bandwidth,the signal will experience multipath fading.2)Due to the spatial radiation characteristics of wireless signals,eavesdroppers can easily receive wireless signals,which makes the communication system subject to eavesdropping,thus endangering the security and privacy of users.The traditional information encryption technology generally adopts the public key cryptography theory,but the efficiency of the public key algorithm is very low,and the management,distribution and maintenance of the key is also very challenging for legitimate users,so the research on the encryption technology without the key has become an important research direction in the field of communication.In the field of communication technology,Physical Layer Security(PLS)has been regarded as a promising technology to realize the confidentiality at the physical layer by utilizing the randomness of wireless channels.Its core purpose is to use different types of signal processing technology to ensure the safe transmission of signals.With the development of antenna technology,the current main research on physical layer security is focused on the link signal space matrix of Multiple Input Multiple Output(MIMO)system.Through the signal space noise,interference alignment and other technologies,In order to achieve the correct demodulation of legitimate users and suppress the demodulation performance of eavesdropping users.However,the actual communication link is affected by multipath fading under the demand of large bandwidth,which makes each user show unique multipath characteristics.In view of this,this paper conducts an in-depth study on the physical layer security precoding technology for multipath channels under the eavesdropping environment,and innovatively analyzes the unique multipath Channel State Information brought by the environment of the legitimate user(Bob)and the eavesdropping user(Eve)and the broadband signal.Based on CSI features,a precoding scheme is designed to improve the physical layer security of legitimate users,which lays a solid foundation for extending the research from MIMO link space matrix to MIMO multipath tensor space.The main research content is divided into two parts according to passive eavesdropping and active eavesdropping,namely the precoding technology of unknown eavesdropping user CSI and the precoding technology of known eavesdropping user CSI.The main research results are as follows:(1)In the multi-path channel scenario of passive eavesdropping,in the case that the transmitter(Alice)does not know the eavesdropping user CSI,a precoding scheme is proposed to ensure the physical layer security of the legitimate user CSI by using the legitimate user CSI,so as to improve the security performance of the system by improving the quality of the signals received by the legitimate user.First of all,since Eve only carries out passive eavesdropping without transmitting any radio signals,the transmitter(Alice)cannot determine any information of the eavesdropping terminal.Therefore,without considering Eve,a pre-coding scheme that can reach the upper bound of Bob’s channel capacity is given only according to Bob’s known CSI.The channel specificity between Alice-Bob and Alice-Eve links is used to obtain stable security capacity.Secondly,in the Rayleigh fading environment,an accurate closed expression of Bob’s mean bit error rate is derived from Bob’s interrupt probability.The simulation results show that the proposed scheme can ensure that the channel capacity of Bob is always better than that of Eve without changing the complexity of the receiver.At the same time,the proposed scheme can effectively improve Bob’s bit error rate performance under the condition that Eve’s bit error rate performance is greatly inhibited.Even if Eve’s position condition is better than Bob’s,the safe capacity can always exist.(2)In the multipath channel scenario of active eavesdropping,a physical layer security transmission scheme against eavesdropping is proposed in view of the known CSI of Bob and Eve at the transmitter,and information confidentiality is realized at the physical layer by maximizing the security capacity.Firstly,an optimization scheme based on the Generalized Rayleigh Quotient(GRQ)theory is established by using the CSI of legitimate users and eavestapping users.Secondly,a matrix bundle is constructed according to the CSI of Bob and Eve,and the eigenvector corresponding to the maximum eigenvalue of the matrix bundle is further calculated to preencode the signal.The proposed precoding scheme can improve the channel capacity of Bob and reduce the channel capacity of Eve,so that the communication system can generate capacity difference at the receiving end to obtain safe capacity.Finally,the channel capacity and interrupt probability of the communication system are simulated and analyzed under Rayleigh fading environment.It is proved that the proposed scheme can guarantee a positive security capacity and ensure that the interruption probability of legitimate users is always lower than that of eavesdropping users on the basis of secure communication.