Application Of Polar Codes To The Broadcast Channel With Confidential Messages

With the rapid development of mobile communication technologies,diverse services provided by wireless communication networks arise and the dependence of people's daily activities on wireless communication networks grows stronger than ever.However,the wireless channel is a broadcast channel and accessible to all users.Theoretically,the information transmitted in wireless channels is within easy reach to every user,which poses a deadly threat to the information security.Facing this challenge,it's becoming increasingly clear that studying secrecy transmission schemes is of vital significance.But the computing power increases at such a rapid pace that traditional secrecy schemes won't be safe anymore for the foreseeable future.Under the circumstances,the unbreakable secrecy scheme in physical layer based on information theory arouses researchers' enthusiasm.Secrecy channel coding plays an important role in the research on physical layer security.As the first coding scheme strictly proved to achieve channel capacity,polar code is a perfect match to the channel coding scheme.In this paper,polar code is used as the coding scheme in a classic model named wiretap channel.Firstly,this paper gives a brief introduction of physical layer security and polar code.Based on the characteristics of polar code and wiretap channel,which is a particular model of broadcast channels,three secure coding schemes are proposed and implemented in BSC wiretap channel and AWGN wiretap channel respectively to study the secrecy performance of each scheme.In the first scheme,part of the information bits is spared to transmit confusing bits to exhaust the decoding capacity of the eavesdropper.In the second scheme,channel feedback is introduced to encrypt the frozen bits to interfere the decoding procedure of the eavesdropper.In the last scheme,feedback is used to encrypt the information bits so that the eavesdropper can't acquire the original message.In the latter part of this paper,the performance of three schemes implemented in BSC wiretap channel and AWGN wiretap channel is analyzed respectively and simulations of the decoding error rate performance of the legit receiver and the eavesdropper in each scenario are conducted.The numerical results show that secure transmission can be guaranteed in each scenario.Furthermore,this paper compares three schemes according to the secure transmission rate each scheme can achieve.It shows that the secure transmission rates the second and the third scheme can achieve are higher than the first scheme,because in the second and the third scheme,all information bits are used to carry secrecy message rather than confusing bits.Considering some extreme scenarios,the third scheme is more unbreakable than the others.Thus,the third scheme is superior to the other schemes and this conclusion is tenable in both BSC wiretap channel and AWGN wiretap channel.