EXIT-Chart Aided Design of Irregular Multiple-Rate Quantum Turbo Block Codes

We propose a novel quantum turbo short-block code, which subsumes multiple-rate quantum short-block codes (MR-QSBCs) as the outer codes and a quantum unity-rate code (QURC) as the inner code. The proposed design is denoted as MR-QSBC-QURC. More specifically, the proposed design exhibits multiple quantum coding rates despite relying only on a single quantum encoder. Moreover, the flexibility offered by the single-encoder MR-QSBCs enables us to leverage extrinsic information transfer (EXIT) chart based heuristic optimization for determining the optimal weighting in the fractional encoding of MR-QSBCs. Our simulation results show that the MR-QSBC-QURC scheme conceived performs relatively close to the ultimate limit of the quantum hashing bound. Specifically, when considering the target quantum coding rates of rQ = {0.3, 0.4, 0.5, 0.6, 0.7}, the MR-QSBC-QURC operates at a distance of D = {0.042, 0.029, 0.030, 0.024, 0.017} from the quantum hashing bound, respectively, at a quantum bit error ratio (QBER) of 10(-3).