Coded Index Modulation for Non-DC-Biased OFDM in Multiple LED Visible Light Communication

TL;DR

This paper introduces a coded index modulation scheme for non-DC-biased OFDM in multi-LED visible light communication, improving reliability and spectral efficiency by coding index bits with LDPC.

Contribution

It proposes a novel CI-NDC OFDM scheme that uses coding on index bits to enhance performance in multi-LED VLC systems.

Findings

Coded index modulation improves reliability of index bits.

CI-NDC OFDM outperforms NDC OFDM at the same spectral efficiency.

LDPC coding enhances overall system performance.

Abstract

Use of multiple light emitting diodes (LED) is an attractive way to increase spectral efficiency in visible light communications (VLC). A non-DC-biased OFDM (NDC OFDM) scheme that uses two LEDs has been proposed in the literature recently. NDC OFDM has been shown to perform better than other OFDM schemes for VLC like DC-biased OFDM (DCO OFDM) and asymmetrically clipped OFDM (ACO OFDM) in multiple LEDs settings. In this paper, we propose an efficient multiple LED OFDM scheme for VLC which uses {\em coded index modulation}. The proposed scheme uses two transmitter blocks, each having a pair of LEDs. Within each block, NDC OFDM signaling is done. The selection of which block is activated in a signaling interval is decided by information bits (i.e., index bits). In order to improve the reliability of the index bits at the receiver (which is critical because of high channel correlation in multiple LEDs settings), we propose to use coding on the index bits alone. We call the proposed scheme as CI-NDC OFDM (coded index NDC OFDM) scheme. Simulation results show that, for the same spectral efficiency, CI-NDC OFDM that uses LDPC coding on the index bits performs better than NDC OFDM.