Construction of Rate-Compatible Raptor-Like Quasi-Cyclic LDPC Code With Edge Classification for IDMA Based Random Access

Recently, rate-compatible raptor-like quasi-cyclic low-density parity-check (RL-QC-LDPC) codes, which are a typical class of multi-edge type LDPC codes with excellent performance and high flexibility, have been adopted in the technical specification of 5G new radio (5G-NR). In this paper, the rate-compatible RL-QC-LDPC coded interleave division multiple access (IDMA), or called the enhanced IDMA, is developed as non-orthogonal multiple access (NOMA)-based random access solution, and various spectral efficiencies can be flexibly supported thanks to the rate compatible capability. First, 5G-NR LDPC codes are directly incorporated into enhanced IDMA-based random access, which can support a wide range of user loads with relatively low system throughput. Second, to improve the supported user load and system throughput, an edge-classification-based extension (ECE) algorithm is proposed to construct rate-compatible RL-QC-LDPC codes toward enhanced IDMA while taking into consideration the novel structural features of 5G-NR LDPC codes. Based on the two proposed edge-classification methods, the ECE can efficiently reduce the search space of base matrices for each extension round and effectively maintain enough diversity in the selected seed base matrices to facilitate further extension. Multi-edge type density evolution-aided extrinsic information transfer chart is employed to predict the asymptotic performance during the base matrix extension and optimization. As an example, a rate-compatible RL-QC-LDPC code family with fine code-rate granularity is constructed via the proposed ECE. Compared with 5G-NR LDPC coded IDMA, the outage performance of enhanced IDMA with the new code family can be significantly improved at high user load and system throughput for NOMA-based random access.