Research On Secrecy Coding Schemes Using Polar Code Over Wiretap Channels

With development of communication technology, the security requirement of a communication system is increasing. Traditional Cryptosystem ensures security based on computational security but it is not absolutely secure. Therefore, physical layer security technique emerges, which proposes the implementation of secure communication on physical layer based on information theory. Polar code is proposed to achieve reliable and secure communication over degraded wiretap channels which are considered as binary symmetric channels. It is also proved the secrecy capacity is achievable asymptotically by polar code. Polar code has low encoding and decoding complexity and becomes a research hotspot in secrecy coding. In this paper, we mainly carry out research depend on the secrecy coding schemes using polar code.For non-degraded wiretap channels, we introduce a feedback structure which can equally degrade wiretap channels. Then we propose a feedback-based secrecy coding scheme using polar code over non-degraded wiretap channels. This scheme has low complexity of encoding and decoding, proved to achieve reliable and secure communication theoretically, and also tries to achieve the maximum secrecy rate as possible. Simulation results show the proposed scheme can achieve reliable and secure communication.For Gaussian degraded wiretap channels, using Gaussian Approximation method to construct polar code over AWGN channel, then we propose a secrecy coding scheme using polar code which is applicable to Gaussian degraded wiretap channels. To make full use of the bit-channels polarized by polar code at a large code length, we propose a modified method to choose bit-channels for secrecy messages. Simulation results show that Gaussian approximation method can construct polar code efficiently. The proposed secrecy coding scheme can increase security while ensure a limited bit error rate over main channel compared to the scheme without secrecy coding. While after apply the method to choose bit-channels for secrecy messages to proposed secrecy coding scheme, we gets more secure communications and keeps reliability.