Adaptive Symbol Mapping for QC-LDPC Coded BICM HARQ Systems

This paper presents an analysis of the asymptotic performance of bit-interleaved coded modulation (BICM) with hybrid automatic repeat and request (HARQ) systems employing quasi-cyclic low-density parity-check (QC-LDPC) codes. To enhance the BICM-HARQ systems, we propose a modified reciprocal channel approximation density evolution (RCA-DE) algorithm, which approximates the
$M$
-ary input channel with HARQ combining to log2
$M$
parallel binary-input white Gaussian noise channels (BI-AWGNCs). A practical application of the proposed RCA-DE technique involves investigating bit-level mapping and modulation for a wide range of code lengths, rates, and modulation orders. Numerical results show that up to 4.8 dB gain is achieved by the mapping designed using the proposed RCA-DE, compared to the original fifth-generation (5G) New Radio (NR) system. Furthermore, our numerical results demonstrate a strong correlation between the simulation and analysis results, validating the effectiveness of the proposed RCA-DE approach for practical system implementation.