Low Complexity Iterative Receiver With Lossless Information Transfer for Non-Binary LDPC Coded PDMA System

Hanqing Ding,Jin Xu,Qingqing Liu,Weihua Liu,Zihang Ding,Zhe Zhang,Xueyan Chen

doi:10.1109/access.2020.3016697

Abstract

In this work, we first proposed a non-binary low-density parity-check (NB-LDPC) coded pattern division multiple access (PDMA) scheme with the order of the Galois field equal to the size of modulation alphabet which can avoid the symbol-to-bit or bit-to-symbol probability conversion between the detector and decoder as in binary coded system. Specifically, we considered a 4-ary LDPC over Galois field (GF(4)-LDPC) coded PDMA system with quadrature phase shift keying (QPSK) modulation. At the receiver side, Gaussian approximation based message passing (GAMP) detection algorithm instead of standard message passing (SMP) is employed to achieve a tradeoff between the computational complexity and the detection performance. When iterative detection and decoding (IDD) algorithm is used, the symbol-wise extrinsic information of the detector and GF(4)-LDPC decoder can be exchanged without information loss. At last, we proposed a symbol-wise EXIT (S-EXIT) based iterative optimization algorithm to improve the system performance. Both the S-EXIT chart based analysis and numerical simulation results show the validity of the proposed scheme above.

Highlights

In current, non-orthogonal multiple access (NOMA) becomes a hot research topic in fifth-generation or beyond wireless communication system
A key issue obstacle non-binary Low-density parity check (LDPC) from widely use is its underlying high decoding complexity if the Galois field (GF) order is high [8]. This drawback does not play a leading role in pattern division multiple access (PDMA) system with quadrature phase shift keying (QPSK) since we only consider LDPC code over low-order GF, i.e. GF(4)-LDPC code, which is of reasonable computational complexity
GF(4)-LDPC decoder is of reasonable computation complexity and low memory consumption when compared with high order LDPC code such as q ≥ 16, and can be coupled with the Gaussian approximation based message passing algorithm (GAMP)-based multiple user detection (MUD) seamlessly without information loss for QPSK system

Summary

INTRODUCTION

Non-orthogonal multiple access (NOMA) becomes a hot research topic in fifth-generation or beyond wireless communication system. H. Ding et al.: Low Complexity Iterative Receiver With Lossless Information Transfer for Non-Binary LDPC Coded PDMA System advantage over traditional linear detection algorithm such as zero-forcing and minimum mean square error or theirs variants, in which case SMP algorithm is impractical. A key issue obstacle non-binary LDPC from widely use is its underlying high decoding complexity if the GF order is high [8] This drawback does not play a leading role in PDMA system with quadrature phase shift keying (QPSK) since we only consider LDPC code over low-order GF, i.e. GF(4)-LDPC code, which is of reasonable computational complexity. GF(4)-LDPC decoder is of reasonable computation complexity and low memory consumption when compared with high order LDPC code such as q ≥ 16, and can be coupled with the GAMP-based MUD seamlessly without information loss for QPSK system.

SYSTEM MODEL

PROPOSED JOINT FACTOR GRAPH BASED OPTIMIZATION

COMPLEXITY COMPARISON

CONCLUSION