Application of Expurgated PPM to Indoor Visible Light Communications - Part II: Access Networks

TL;DR

This paper introduces two novel multiple access techniques based on expurgated PPM for indoor VLC networks, enabling multi-user support, dimming control, and higher bit-rates with LED lighting constraints.

Contribution

It presents two new multiple access schemes using EPPM tailored for LED-based VLC networks, supporting dimming and multi-user communication.

Findings

Supports multi-user access with dimming control

Enables higher bit-rates for bandwidth-limited LEDs

Provides control over optical power ratios

Abstract

Providing network access for multiple users in a visible light communication (VLC) system that utilizes white light emitting diodes (LED) as sources requires new networking techniques adapted to the lighting features. In this paper we introduce two multiple access techniques using expurgated PPM (EPPM) that can be implemented using LEDs and support lighting features such as dimming. Multilevel symbols are used to provide M-ary signaling for multiple users using multilevel EPPM (MEPPM). Using these multiple-access schemes we are able to control the optical peak to average power ratio (PAPR) in the system, and hereby control the dimming level. In the first technique, the M-ary data of each user is first encoded using an optical orthogonal code (OOC) assigned to the user, and the result is fed into a EPPM encoder to generate a multilevel signal. The second multiple access method uses sub-sets of the EPPM constellation to apply MEPPM to the data of each user. While the first approach has a larger Hamming distance between the symbols of each user, the latter can provide higher bit-rates for users in VLC systems using bandwidth-limited LEDs.