Research On Secrecy Coding Schemes Using Polar Codes Over Degraded Wiretap Channel

With the development of wireless communication technology,communication security has always been an extremely important component.In recent years,the physical methods of secure coding to ensure the communication security has been a growing interest to researchers.Among those,Wyner's degraded wiretap channel model is one of the most important security models.Meanwhile,Polar code,as the earliest and the only deterministic coding scheme which is proved to be able to reach the Shannon limit theoretically,has the characteristics of simple encoding structure and low decoding complexity,which makes it advantageous to be used as a code word for secure coding.Therefore,the application of Polar codes in degraded wiretap channels for secure coding has become an important research direction in the past few years.This thesis mainly studies the problem of secure coding using Polar codes in degraded wiretap channels.On the one hand,in the case of limited degradation of wiretap channel,few secure bit channels can be created solely by the natural channel conditions,resulting in low information transmission rate.To solve this problem,based on the original Polar secure coding algorithm of the degraded wiretap channel,this thesis proposes a new secrecy coding scheme which uses artificial noise as interference in bit channels.Through the combination of original Polar secure coding and the artificial noise,the rate of information transmission and channel utilization increases.The simulation results show that the scheme can improve the information transmission rate while ensuring the security of information transmission.On the other hand,this thesis also addresses the problem of the Polar secure coding algorithm combined with key in wiretap channel.Firstly,in order to deal with the risks of fixed key in the original key-combined encoding scheme,a secure encoding algorithm combined with updating key is proposed.The numerical simulation results show that the scheme is more reliable than the original one.Secondly,this thesis proposes an improved key expansion algorithm based on the Genetic Algorithm due to the limitation of the original algorithm.The numerical simulation of the scheme proves that the improved scheme permits an increment of the rate and the reliability of information transmission.