A Time Sharing Hybrid Probabilistic Shaping Scheme for Nonbinary LDPC Codes

Zhanji Wu,Weimin Kang

doi:10.1109/access.2020.2985864

Abstract

A time sharing (TS) hybrid probabilistic shaping (HPS) scheme for nonbinary (NB) LDPC codes is proposed. For the conventional probabilistic shaping (CPS) scheme, the demodulator uses bit-metric decoding (BMD) for binary LDPC codes and NB LDPC codes. However, the demodulator for NB LDPC codes adopts symbol-metric decoding (SMD) on the AWGN channel to avoid the loss of symbol-to-bit mapping and obtain better performance than binary LDPC codes. In order to take advantage of SMD demodulation for NB LDPC codes, the NB-LDPC information symbols use constant composition distribution matcher (CCDM) to generate quadrature amplitude modulation (QAM) symbols with unequal probability distribution, while the NB-LDPC parity symbols are utilized to yield QAM symbols with approximately uniform distribution. The SMD demodulation of the proposed NB-LDPC-coded TS HPS scheme has lower demodulation complexity than the NB-LDPC-coded CPS scheme. The information-theoretical analysis of the CPS system and the TS HPS system turns out that the proposed NB-LDPC-coded TS HPS scheme is superior to the NB-LDPC-coded CPS scheme for 8QAM and 32QAM format. Simulation results verify the theoretical average mutual information (AMI) analysis and show that the proposed NB-LDPC-coded TS HPS scheme has up-to-0.24 dB and 1.10 dB performance gain compared with the NB-LDPC-coded CPS scheme for 8QAM and 32QAM format, respectively. Compared with the binary LDPC-coded regular Nyquist scheme for 8QAM and 32QAM format, the proposed NB-LDPC-coded TS HPS scheme has up-to-1.31 dB and 2.04 dB performance gain, respectively. Meanwhile, the LDPC code rate of the proposed TS HPS scheme is more flexible than the CPS scheme. Therefore, the proposed NB-LDPC-coded TS HPS scheme is more reliable, efficient, and flexible for 8QAM and 32QAM, and thus suitable for the sixth generation (6G) communication system.

Highlights

With the rapid development of data traffic, high spectral efficient and high reliable communications are required for the sixth generation (6G) communication system [1]
In order to take full advantage of NB LDPC codes, we propose a time sharing (TS) hybrid probabilistic shaping (HPS) scheme to obtain further coding gain
average mutual information (AMI) analysis of the conventional probabilistic shaping (CPS) system and the TS HPS system turns out that the proposed NB-LDPC-coded TS HPS scheme is superior to the NB-LDPC-coded CPS scheme for 8QAM format and 32QAM format

Summary

INTRODUCTION

With the rapid development of data traffic, high spectral efficient and high reliable communications are required for the sixth generation (6G) communication system [1]. In the conventional probabilistic shaping (CPS) LDPC-coded QAM/APSK scheme, all shaped modulation symbols are transmitted with the same desired unequal probability distribution, and the demodulator can use the bit-metric decoding (BMD) method for binary and NB LDPC codes [16], [17]. In [16], the authors proposed a symbol-metric decoding (SMD) scheme for NB LDPC codes in the CPS system, but the demodulator needs to separately calculate sign part probability and amplitude part probability. The coded NB LDPC symbols can be directly mapped to QAM symbols, so the demodulator can use SMD to generate symbol-level soft information for the NB LDPC decoder, which is different from [16], [17].

SYSTEM MODEL

DISTRIBUTION MATCHING FOR 8QAM AND 32QAM

TIME SHARING NONBINARY LDPC CODED HYBRID

CONCLUSION