A 40 Mb/s VLC System Reusing an Existing Large LED Panel in an Indoor Office Environment.

Xicong Li,Zabih Ghassemlooy,Stanislav Zvánovec,Paul Anthony Haigh

doi:10.3390/s21051697

Abstract

With advances in solid-state lighting, visible light communication (VLC) has emerged as a promising technology to enhance existing light-emitting diode (LED)-based lighting infrastructure by adding data communication capabilities to the illumination functionality. The last decade has witnessed the evolution of the VLC concept through global standardisation and product launches. Deploying VLC systems typically requires replacing existing light sources with new luminaires that are equipped with data communication functionality. To save the investment, it is clearly desirable to make the most of the existing illumination systems. This paper investigates the feasibility of adding data communication functionality to the existing lighting infrastructure. We do this by designing an experimental system in an indoor environment based on an off-the-shelf LED panel typically used in office environments, with the dimensions of 60 × 60 cm. With minor modifications, the VLC function is implemented, and all of the modules of the LED panel are fully reused. A data rate of 40 Mb/s is supported at a distance of up to 2 m while using the multi-band carrierless amplitude and phase (CAP) modulation. Two main limiting factors for achieving higher data rates are observed. The first factor is the limited bandwidth of the LED string inside the panel. The second is the flicker due to the residual ripple of the bias current that is generated by the panel’s driver. Flicker is introduced by the low-cost driver, which provides bias currents that fluctuate in the low frequency range (less than several kilohertz). This significantly reduces the transmitter’s modulation depth. Concurrently, the driver can also introduce an effect that is similar to baseline wander at the receiver if the flicker is not completely filtered out. We also proposed a solution based on digital signal processing (DSP) to mitigate the flicker issue at the receiver side and its effectiveness has been confirmed.

Highlights

Flicker is a common problem in light-emitting diode (LED) lighting, which is mainly caused by the lowfrequency ripple of the current generated by the power driver in most cases [42]
Unlike the precise voltage sources that were used in our measurements, the commercial LED driver converts AC mains to a “noisy” DC current to drive the LED
There are two major disadvantages: (i) the reduced modulation depth for visible light communication (VLC) signals—since the VLC signal is superimposed onto the bias current, the headroom left for VLC signals is reduced if the bias current has a high ripple amplitude; (ii) the low-frequency flicker can interfere with the signal falling in the frequency range

Summary

Introduction

The outdoor lighting infrastructure covers a variety of LED-based luminaries that range from street lights, traffic lights, to car lights, which have inspired the use of VLC in infrastructure-to-vehicular (I2V) and vehicular-to-vehicular (V2V) communications [10,11]. When compared with the outdoor environment, the indoor scenarios often find large LED luminaries installed in the ceiling or relatively small LED desk lamps placed directly above the table to provide a guaranteed light level for illuminance. This benefits the indoor VLC applications greatly since those

Methods

Results

Conclusion