| Reliability and security are two basic requirements of information transmission.Information security is the most important security issue and conventionally carried out by enciphered system in the upper layer,and the reliability of information is carried out by channel coding in the physical layer.Physical layer security is a technology that uses signal processing and channel coding to implement secure transmission of information in the physical layer,and the channel coding is one of the most important parts.The thesis researches the channel coding scheme that can ensure security and reliability of information simultaneously in the physical layer.The main contents are as follows:1.The joint system with secret key for error correction and encryption based on rateless error-correcting codes is researched,and a scheme that can realize the encryption and error correction of information is proposed.The sender generates random coding matrix of rateless codes and deleting pattern by setting up different pseudo-random number generators separately,enabling random generation and deletion of encoded symbols.The receiver generates the coding matrix asynchronously to decode by setting up corresponding pseudo-random number generators.The seed of pseudo-random number generator is the secret key to encrypt and decrypt.The eavesdropper can be regarded as impossible to decode without the seed due to the huge size of coding matrix and deleting pattern.Since the degree distribution of the encoded symbols after random deletion is not changed,the error correction performance of rateless codes is not affected.Theoretical analysis and simulations of system performance are provided,and the simulation results indicate that the bit-error-rate of the unexpected recipient is kept near 0.5,and the word-error-rate remains 1,while the error performance of the legitimate receiver is the same as conventional rateless coding systems,thus error correction and encryption are realized simultaneously.2.The security-enhanced physical layer communication system without secret key to reduce the security gap of secure channel coding is researched,and a scrambling scheme is proposed for reducing the security gap of channel coding.Two scramblers are added behind and ahead of the channel encoder at the sender,and the corresponding descramblers are added at the receiver.Descrambling can propagate errors artificially,thus the word-error-rate and bit-error-rate in low signal-noise ratio region is increased in the error-rate curve,and the decrease speed of the curve is increased in high signal-noise ratio region.Therefore,the security gap of word-error-rate and bit-error-rate are decreased simultaneously.The error rate of this scheme is analyzed,and simulations are performed on BCH channel codes.Theory analysis and simulation results indicate that the two-scrambling scheme can effectively reduce the security gap of channel coding. |
