Synchronization-Assisted Chaotic Permutation Information Encryption Security Enhancement Based on OFDM-FSO Probabilistic Shaping

In this article, we propose a method to encrypt the permutation information (PI) and insert the synchronization head based on digital chaos and constellation shaping for orthogonal frequency division multiplexing-free space optical (OFDM-FSO) communication. Probabilistic shaping technology can improve laser emission efficiency, but it will generate the PI, which, transmitted separately, will occupy channel bandwidth. Therefore, we use a digital chaotic algorithm to encrypt the PI and insert it into the synchronization head. This processing reduces the occupation of the PI on communication bandwidth and improves the security of the transmission system. The PI can be converted into a binary bit stream and encrypted by the pseudo-random binary sequence (PRBS) generated by a 1-dimensional chaotic map amplifier (1-DCMA). In the case of regional probabilistic shaping, it can improve by 3.8–10% transmission distance. The results show that the proposed method has about 0.8–1 dB improvement in the received optical power higher than the original model. The synchronization head assisted the chaotic PI can not only enhance security but also improve the performance of transmission bit error rate (BER).