Research On Secure Wireless Communication For Full Duplex OFDM System

In recent years,the rapid development of wireless communication has brought convenience to people,but there are also some problems.Due to the broadcast characteristics of wireless channels,user privacy is easily eavesdropped by malicious nodes.Traditional high-level encryption algorithms based on cryptography are built on the basis of computational complexity to achieve security.With the development of encryption cracking technology and quantum computer,traditional encryption may be easily cracked,and the security of wireless communication are facing serious threats.Therefore,more and more attention has been paid to the study of physical layer security.In this thesis,a secure communication scheme based on self-relay is proposed.The so-called self-relay is that the sender acts as a relay to prevent eavesdroppers eavesdropping confidential information through phase noise.The main contents and contributions of this paper are as follows.(1)In this thesis,we propose a full-duplex OFDM system model based on self-relay without knowing the eavesdropper's CSI.The model includes a legitimate sender(node A),a legitimate receiver(node B)and one or more eavesdroppers.Node A acts as a relay when sending confidential information to prevent eavesdroppers from eavesdropping on confidential information.The random phase noise from node B is added to the confidential information to disturb the eavesdropper,node B can correctly decode the confidential information,while the eavesdropper cannot correctly decode the confidential information.(2)This thesis derives the secrecy capacity and secrecy outage probability of SISO-OFDM system.The secrecy capacity of this scheme is independent of CSI of eavesdropper channel,which is a great advantage compared with other schemes.The derived expression of the secrecy capacity shows that the scheme can guarantee the positive secrecy capacity of the system,so the scheme can achieve perfect secure communication.In order to solve the maximum secrecy capacity in power-constrained systems,this problem is modeled as a mathematical optimization problem,and the Lagrange multiplier is introduced to obtain the optimal solution through the method of finding the extremum.(3)In order to solve the above optimization problem,a bisection-greedy algorithm is proposed for power allocation and bit loading.The results show that the secrecy capacity of the bisection-greedy algorithm is better than that of the equal power allocation scheme,and the complexity of using the bisection-greedy algorithm is very low.In addition,the cost of secure communication compared with non-secret communication is also analyzed.The scheme is extended to MIMO-OFDM system and power allocation algorithm is applicable to MIMO-OFDM system.Finally,the error rate is analyzed for SISO-OFDM system.