Protograph LDPC-Coded BICM-ID With Irregular CSK Mapping in Visible Light Communication Systems

Abstract

This paper designs and analyzes the bit-interleaved coded modulation with iterative demapping and decoding (BICM-ID) framework under color-shift-keying (CSK) modulation to achieve spectrally efficient transmissions in visible light communication (VLC) systems. Specifically, we investigate the protograph low-density parity-check (LDPC) codes, bit-to-symbol mapping schemes, and constellation labeling rules in higher-order CSK-aided VLC systems. To fully explore the BICM-ID benefit, we propose an irregular CSK mapping, in which an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$M$</tex-math></inline-formula> -ary standardized constellation (called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">“Standard constellation”</i> ) and a new <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$M$</tex-math></inline-formula> -ary constellation (called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">“Target constellation”</i> ) are separately applied to modulate two different coded sub-blocks in a codeword to optimize the error performance of the CSK-aided VLC systems. Furthermore, using a modified protograph extrinsic information transfer (PEXIT) algorithm, we construct two types of protograph LDPC codes (i.e., unpunctured and punctured protograph LDPC codes) that outperform the conventional protograph LDPC codes. Both analytical and simulation results show that the proposed irregular-CSK-mapped BICM-ID employing the new protograph LDPC codes and Target constellation is capable of achieving outstanding performance, and is a promising transmission solution for high-speed VLC applications.