Drift and Confuse: A Symbol-Level Variable Compression Multicarrier Faster-Than-Nyquist System for Physical Layer Security

Physical layer security (PLS) has emerged as a critical research priorities, driven by the rapid proliferation of high-speed communication systems and their escalating service demands. This paper proposes a symbol-level time-varying compression for multicarrier faster-than-Nyquist (MFTN) signaling transmission systems to enhance confidentiality. Firstly, we have developed a time-varying compression factor MFTN architecture with drift, which confounds eavesdroppers due to severe interference, while legitimate receivers can mitigate the interference within the MFTN signal by leveraging their knowledge of the varying patterns. Secondly, we design a symbol-by-symbol maximum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$a$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$posteriori$</tex-math></inline-formula> probability (MAP) detection method based on an optimal state selection mechanism, combined with turbo iterative equalization decoding, which maintains the bit error rate (BER) performance without increasing demodulation complexity. Finally, we derive minimum Euclidean distance (MED) and the upper bound of secrecy rate of the proposed MFTN system. The simulation results indicate that the symbol intervals remain undetectable by eavesdroppers, which leads to the BER during demodulation hovers near 0.5. The implementation of a symbol-level variable compression factor has been demonstrated to significantly enhance the secrecy rate, consequently delivering superior security performance.