Research Of Time Reversal Based Physical Layer Security Techniques In Wireless Multipath Channels

With the gradual prosperity of 5G technology,there are more and more researches on new broadband wireless communication technologies.However,broadband wireless communication users are mostly in the multipath channel environment.Delays,fading,and information leakage caused by wireless multipath will be an important challenge that many scholars and research institutions have to face.In this context,physical layer security and time reversal have developed rapidly.The physical layer security technology mainly uses the inherent characteristics of the communication channel to enhance the security of signal transmission,and the time reversal technology combines its electromagnetic characteristics and physical channel characteristics to improve the security performance of the wireless communication system.Using the temporal and spatial focusing characteristics of time reversal technology can not only alleviate the communication quality problem caused by multipath effect to some extent,but also guarantee the security of information transmission process.Therefore,combining the time reversal technology with the physical layer security technology is an important research aspect of wireless communication in the future.Based on this,the main research contents of this thesis are as follows:Firstly,aiming at the problem of wiretap channel in the research of physical layer security,a physical layer security transmission mechanism combining time reversal technology and artificial noise of origin is proposed.First,the time reversal technology is used in the classical wiretap channel model,and its spatial and temporal focusing is used to improve the security during signal transmission.Second,since the information is focused on the vicinity of the receiving point,the eavesdropping user can easily eavesdrop legitimate information around the receiving point.The use of artificial noise makes it difficult for eavesdropping user to eavesdrop useful signals on and around legitimate user,thereby enhancing the reliability of signal reception by legitimate user.Through simulation experiments,and compared with the existing physical layer security transmission mechanism,the security performance of the system has been effectively improved.Secondly,for the case of active eavesdropping in frequency selective multipath channels,a new physical layer security transmission scheme based on time-reversal for joint simultaneous wireless information and power transfer is proposed.First,the sender uses the spatial and temporal focusing characteristics of the time-reversal technique to reduce the effect of frequency selective fading on the communication signal.Second,legitimate users use power dividers to collect information and energy sent by the sender.At last,two indicators of symbol error rate and energy collection are used to evaluate the system performance.The method based on the moment generation function is used to obtain the analytical solution of the symbol error rate energy region.Simulation results show that using the time-reversal technique can reduce the symbol error rate of the system.At the same time,eavesdropping on the interference signals sent by users can enhance the energy collection efficiency.