Applications Of LT Codes To The Wiretap Channel

Wireless communication has the characteristic of openness.All recipients within the receiving range of radio can receive the messages in messages transmission process,which may result in information disclosure.In recent years,in order to prevent such information leakage,scholars and researchers began to study the physical layer secure coding technology.This technology mainly utilizes the difference between the eavesdropping channel and the legal channel to prevent passive eavesdropping of information.Compared with traditional channel coding schemes,physical layer secure coding schemes can guarantee both the security and reliability of information simultaneously.In traditional coding schemes,LT codes are random,rateless and non-systematic.The random and non-systematic characteristics of LT codes can ensure that eavesdroppers cannot obtain information directly from the leaked codewords.The rateless feature ensures the reliability of information transmission in the legal channel.Therefore,the research on LT codes in the eavesdropping channel is of great significance.This thesis mainly studies the applications of LT codes to the eavesdropping channel.At the beginning of this thesis,the advantages of LT codes in the eavesdropping channel are introduced.Meanwhile,the traditional channel models and the eavesdropping channel models are detailed.Then performance indicators that are used to evaluate the eavesdropping channel are introduced.In the second part of this thesis,the performance of LT codes in the eavesdropping channel is researched deeply.Firstly,the encoding and decoding algorithm in gaussian channel and degree distribution of LT codes are introduced.Then the performance of LT codes in the AWGN eavesdropping channel is analyzed in security and reliability.Afterwards,based on the results of the study,this thesis improves the robust soliton distribution,and compares the degree distribution and security before and after the improvement.The results show that the improved degree distribution can reduce the security gap of the LT codes.In the last part,this thesis proposes a secure coding scheme based on feedback and unequal error protection.This scheme mainly utilizes the difference between legitimate channel and eavesdropping channel,and introduces feedback between legitimate information receivers and message senders.Based on reception of information,the legitimate receiver feeds back the possible error codewords to the sender of messages that will adjust the encoding process according to the received feedback information.The sender utilizes an unequal error protection mechanism to increase the coding weight of a possibly erroneous code word and sends the message again.Since the feedback information is generated based on the decoding situation of the legitimate recipient,it has no meaning to the illegal eavesdropper.The sender of information encodes the information according to the decoding condition of the legitimate receiver,which will reduce the decoding overhead of the legal channel,thereby the leakage of information will reduce.The experimental simulation shows that the scheme proposed can effectively reduce the decoding overhead and the security gap.