Secure transmission over the wiretap channel using polar codes and artificial noise

In this study, the authors propose a secure transmission scheme using polar codes and artificial noise (AN) for the wiretap system without assuming the channel quality advantage of main channel over wiretap channel. They first derive lower and upper bounds on the symmetric capacity of the polarised bit-channels , which depend on the signal-to-noise ratio of each use of physical channel. According to the bounds, they prove existence of the bit-channels that are beneficial to the signal reception of the main channels but hostile to the wiretap channel, and a method based on injecting the AN at the transmitter is introduced to achieve those bit-channels. Through theoretical analysis, the security of the proposed AN method is proven. Thereafter, they elaborate two AN power allocation schemes denoted by AN-PA-I and AN-PA-II for each use of physical channel. The former proves the existence of the minimum AN power to achieve the secrecy rate that is equal to the capacity of the main channel, referred to as the maximum secrecy rate, and the latter introduces how to obtain it with an optimisation method. Numerical results show that both the two schemes can achieve the maximum secrecy rate.