A Novel Nonbinary LDPC-Coded Time Sharing Hybrid Probabilistic Shaping Scheme for 128QAM

A novel nonbinary (NB) LDPC-coded time sharing (TS) hybrid probabilistic shaping (HPS) scheme for 128QAM is proposed. For the NB LDPC-coded conventional probabilistic shaping (CPS) scheme, the demodulator uses bit-metric decoding (BMD). However, the demodulator for the NB LDPC-coded Nyquist system adopts symbol-metric decoding (SMD) to avoid symbols to bits mapping loss. In order to use the benefit of SMD demodulation for NB LDPC codes, we consider that the NB LDPC information symbols use constant composition distribution matcher (CCDM) to generate unequal probabilistic shaped quadrature amplitude modulation (QAM), while the NB LDPC parity symbols yield approximately uniform probability distribution. The theoretical average mutual information (AMI) analysis of the CPS system and the proposed TS HPS system are analyzed, which shows that the proposed NB LDPC-coded TS HPS scheme is better than the NB LDPC-coded CPS scheme for 128QAM. Simulation results verify the information-theoretical analysis. Moreover, the LDPC code rate of the proposed TS HPS scheme is more flexible than the CPS scheme. At a frame error rate at 10, the proposed GF(128) LDPC-coded TS HPS scheme for 128QAM can obtain 0.30 dB gain compared with GF(128) LDPC-coded regular 128QAM system with spectral efficiency at 3.5 bits/s/Hz. Therefore, the proposed NB-LDPC coded TS HPS scheme is more reliable and flexible for 128QAM, and thus suitable for the sixth generation (6G) communication system.