High security lossless key-accompanying transmission method based on noise-masked 3D index mapping over four-core fiber

A lossless key-accompanying transmission method based on noise-masked three-dimensional (3D) index mapping over four-core fiber is proposed. This scheme utilizes a four-dimensional (4D) chaotic model to mask the bits of the original data and orthogonal frequency division multiplexing (OFDM) symbols. Its initial value key is transformed into binary bits, and the error-free transmission of the key is ensured by periodic key repetition. And the masking of the key is achieved by introducing noise bits. In the process of constellation mapping, the 16 constellation points are divided into inner constellations and outer constellations. The traceless loading of the key is achieved by controlling the mapping rule using noisy key bits. A 115-kilometer four-core fiber transmission experiment of the noise-masked 3D index mapping method was successfully verified. The experimental results show that the difference between different cores of the four-core fiber is no more than 0.35 dB. There is almost no signal-noise ratio (SNR) penalty before and after signal encryption. The difference in sensitivity at the receiver is only 0.05 dB, which proves that this scheme can achieve lossless key transmission. As this scheme adopts the method of key repetition, it can ensure the correct demodulation of the key and the precise index of the constellation B. Compared with the traditional 16 quadrature amplitude modulation (QAM) signal, a sensitivity gain of 0.75 dB can be achieved. As for the illegal receiver, due to the lack of correct keys and encryption methods, the accuracy rate of key extraction is 0%, and the bit error rate (BER) remains at around 0.5. Even if the key index position is displaced by one bit, the BER will soar above 0.48. And through five repetitions, 100% correct recovery of the key at the legitimate receiver can be guaranteed. This scheme has excellent transmission effect and security, and can effectively guarantee the performance of the next-generation communication system.