Pre-coded LDPC coding for physical layer security

This paper examines a simple and practical security preprocessing scheme for the Gaussian wiretap channel. A security gap based error rate is used as a measure of security over the wire-tap channel. In previous works, information puncturing and scrambling schemes based on low-density parity-check (LDPC) codes were employed to reduce the security gap. Unlike the previous works, our goal is to improve security performance by using the precode of the feed-forward (FF) structure. We demonstrate that the FF code has an advantage for the security gap compared to the perfect scrambling scheme. Furthermore, we propose the joint iterative decoding method between LDPC and FF codes to improve the reliability/security performances. The proposed joint iterative method is able to achieve outstanding performance by using the proposed scaling and correction factors based on signal-to-noise ratio (SNR) evolution. The improved performances by these factors are demonstrated through the extrinsic information transfer (EXIT) chart and simulation results. Finally, the simulation results suggest that the proposed coding scheme is more effective than the conventional scrambling scheme.