Frozen bits perturbation key transmission scheme based on subcarrier index modulation

This article proposes a secure transmission method that uses grouped multicarrier modulation, embedding encryption keys directly into the transmitted signal to allow simultaneous key and data transmission. A four-dimensional hyperchaotic system ensures security, while transmission quality is enhanced using a polar coding strategy that demonstrates superior error correction performance compared to conventional FEC schemes. By employing polar code modulation, preallocated frozen bits serve as physical-layer resources for secure key transmission, thereby improving spectral efficiency. Experimental validation over 20 km of standard single-mode fiber (SSMF) demonstrates a stable data rate of 8 Gb/s. Results show that the proposed scheme significantly enhances both transmission performance and security. The system's spectral efficiency has increased by 6.25% and maintaining a zero key error rate throughout the channel, and achieving a key space exceeding 10¹⁵⁰.