Research On Improved Anti-eavesdropping Technology Of LT Codes

In the information age of rapid dEvelopment,wireless communication has dEveloped from the information exchange between people to the establishment of connections among all things,becoming the protagonist of the times.HowEver,its broadcast transmission mode makes it easy for information to be stolen by illegal eavesdroppers during transmission,which damages the basic rights and interests of legitimate communicators.LT codes have better anti-eavesdropping advantage over eavesdropping channel owing to its low cost,simple coding and strong adaptability,and encoding method is one of the main factors affecting the performance of LT codes.Therefore,in order to ensure the security of wireless transmission,this paper takes the LT codes as the research object from the perspective of channel coding of physical layer,studies its coding method and puts forward the improvement method of LT encoding with recombinant encoding matrix and the way of eliminating "similar number loop" to improve the anti-eavesdropping performance of LT codes over eavesdropping channel.LT codes adopts decoding method of MP,which starts decoding only when the degree 1 coding symbol is received.The distribution of degrees' size in the encoding matrix generated by traditional LT codes based on the RSD degree distribution function is random.If the degree 1 encoding symbol is sent to the receiver and eavesdropper earlier,there is the possibility that the eavesdropper can recover the source encoding symbol before the legitimate receiver,which makes the eavesdropper wiretap informations successfully.In view of the randomness of the degree's distribution in the encoding matrix of traditional LT codes,an improvement method for LT coding with recombination of the encoding matrix is proposed,which rearranges the columns of the encoding matrix of traditional LT codes from large to small in order to get a new encoding matrix.The purpose of this method is to move the degree 1 encoding symbol randomly backwards to delay its sending time and the starting time of decoding.The experimental results show that the LT codes obtained from the LT recombination matrix presented in this paper can effectively reduce the intercept probability of the eavesdropper compared with traditional LT codes,without increasing the decoding expenses,and reduce the probability of the eavesdropper successfully decoding the information.In the LT codes of recombination encoding matrix obtained from the recombination of the encoding matrix,the degree 1 encoding symbol has been moved backwards,but there may be a "similar number loop" structure before the degree 1 symbol,which indirectly generates the degree 1 encoding symbol,enabling the receiver and eavesdropper to start decoding earlier.To solve the problem,this paper proposes the method to improve LT codeing by eliminating "similar number loop",which eliminates "similar number loop" structure by gradually searching and deleting,excluding the situation that decoding begins before the degree 1 encoding symbol is sent.This method further improves the anti-eavesdropping performance of LT codes and enhances the security of wireless transmission.The experimental results show that,compared with the reconstruction matrix of LT codes and the traditional LT codes,the LT codes obtained by eliminating the "similar number loop" matrix increase the decoding expenses slightly,but it can further reduce the intercept probability of the eavesdropper and achiEve the purpose of safe transmission.Therefore,the method to improve the LT coding of recombinant coding matrix and the way of eliminating the "similar number loop" based on it can reduce the intercept probability of the eavesdropper and ensure the safe transmission of wireless communication.