Basis Precoding Based on Probabilistic Constellation Shaping in QAM/QNSC

Quantum noise stream cipher (QNSC) is a physical-layer encryption approach for optical communications, and its security barrier is the "basis" that is used as the secret-key for symbol encryption. Regarding the fact that the basis is actually transmitted through the fiber, we propose a basis precoding scheme based on probabilistic constellation shaping, to better conceal the basis into the noise for security enhancement. Experimental results show our scheme can improve the security of the QAM/QNSC system in terms of Eve’s symbol error ratio.