Reconciliation of Weakly Correlated Information Sources Utilizing Generalized EXIT Chart.

The current bottleneck of continuous-variable quantum key distribution (CV-QKD) is the computational complexity and performance of key reconciliation algorithms. CV-QKD requires capacity approaching error correcting codes in the low signal-to-noise (SNR) regime (SNR u003cu003c 0 dB) with very low code rates. Multilevel coding (MLC) combined with multistage decoding (MSD) can solve this challenge. Multi-edge-type low-density parity-check (MET-LDPC) codes are ideal for low code rates in the low SNR regime due to degree one variable nodes. Here, we introduce the concept of generalized extrinsic information transfer (G-EXIT) charts for MET-LDPC codes and demonstrate how this tool can be used to analyze their convergence behavior. We calculate the capacity for each level in the MLC-MSD scheme and use G-EXIT charts to exemplary find the best codes for some given thresholds. In comparison to the traditional density evolution method, G-EXIT charts offer a simple and fast asymptotic analysis tool for MET-LDPC codes.