Research And Simulation On The Physical Layer Security In The Two-way Relay Satellite Communication System

With the rapid development of the global economy,every country increases the requirements of the communication,and the relay satellite communication is becoming more and more popular in the world,because there are some advantages.Firstly it can realize the long-distance communication without paying more money,Secondly it can work in radio broadcasting mode that can achieve multiple access connection,thirdly it can meet the large capacity communication,support various traffic advantages,so it has become one of the global important means of communication.But due to the characters of wireless channel,the open and broadcast nature,it is vulnerable for eavesdropping node to wiretap information,the main method recently used is encryption technology,but with the development of computing power and the high data arriving,the encryption attracts more and more fast.In the meanwhile the development of the channel coding technology provides a new direction,and the physical layer security has gradually become the focus of research.There are two improved LDPC algorithms proposed in this thesis.By uniting the artificial scrambling,using the CSI and LDPC code technology.The first one is called kind encryption LDPC algorithm,the second one is called directly improved LDPC algorithm.The encryption LDPC algorithm includes three stages:channel estimation,artificial scrambling,and LDPC encryption.When getting the CSI of the legitimate channel,both the satellite and the ground station can share the information fairly,but the eavesdropper cannot get the CSI.Drawing the artificial scrambling the constraint extraction and by using the required matrix,generating a parity check matrix of the LDPC for multiplication,and use the PEG algorithm to decrease the number of the little loop.However,some of the damage is happened in the sparse of LDPC,and it may increase some new redundancy.The directly changing LDPC algorithm is proposed to generate the parity matrix and the information is added to the check matrix by the semi random CSI algorithm.It can increase the redundancy and meet the flaw of the sparsity.Through the simulation software Matlab,this thesis compares the overall performance and the performance of the two algorithms.The results show that the design of the algorithm achieves the requirements of the secure transmission,and reduces the bit error rate and improves the security capacity.