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加密系统中Alice端通过光纤传送相干态量子信号给Bob端,得到的一系列相关的高斯连续变量,然后从中提取出二进制密钥,这一过程称作高斯连续变量量子密钥分发。其中的数据协调步骤,即对相关连续变量的错误校正,是本文的研究问题。本文在分层错误校正协议(SEC)和多电平编码/多级解码(MLC/MSD)协议的基础上,用基于LDPC码的Slepian-Wolf编译码器实现协调。根据连续变量的多级Tanner信息传输流图,本文推导了多级迭代的内信息和外信息置信传播(LLR-BP)更新公式,并用实验比较了MSD三种译码模式的收敛性质及性能。仿真结果表明该算法可在信道信噪比2.5dB以上实现10000个连续变量序列的可靠协调,协调效率可达92.3%。
In the encryption system, Alice sends a series of related Gaussian continuous variables to the Bob side through the optical fiber, and then extracts the binary key from it. This process is called Gaussian continuous variable quantum key distribution. The data reconciliation step, that is, the error correction of the related continuous variables, is the research question in this paper. Based on the hierarchical error correction protocol (SEC) and multi-level coding / multistage decoding (MLC / MSD) protocols, this paper uses the Slepian-Wolf codec based on LDPC codes to achieve the coordination. According to the multi-level Tanner information flow diagram of continuous variables, this paper deduces the update formula of LLR-BP with multi-level iteration, and compares the convergence properties and performance of three kinds of MSD decoding modes by experiments. The simulation results show that the algorithm can achieve the reliable coordination of 10,000 continuous variable sequences with channel SNR above 2.5dB, and the coordination efficiency can reach 92.3%.