Pulse-Based Modulation for VLC Systems

Using Programmable Systems-on-Chip

Master thesis (2017)

Authors

B. Johannsson Electrical Engineering, Mathematics and Computer Science

Contributors

K.G. Langendoen (mentor)
Faculty
Electrical Engineering, Mathematics and Computer Science, Electrical Engineering, Mathematics and Computer Science
Copyright: © 2017 Bjarki Johannsson
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Published Date

18-10-2017

Language

English

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Faculty

Electrical Engineering, Mathematics and Computer Science

Abstract

The use of Light Emitting Diodes (LED) as a main source of illumination
can help in significantly reducing global energy conspumtions. The LED is
well suited for modulating visible light, enabling a wireless communication
channel. A popular topic in Visible Light Communication (VLC) research
is to push data throughput past the LED bandwidth limitation of around
4-5 MHz. Less attention has been given to systems using cheaper and slower
components.
This thesis focuses on effectively utilizing the available bandwidth in low
cost dimmable VLC systems, to allow for increased data throughput, where
the system bandwidth is limited by the receiver. Non-
ickering constant
perceived light intensity must furthermore be maintained under variable
dimming conditions, to ensure positive user experience.
A novel modulation scheme for VLC systems with dimming support is pro-
posed. Adaptive Rectified Pulse-Width Modulation (ARPWM) modulates
the light source with fine-grained pulses within a defined symbol period. The
symbols are demodulated as light intensity levels. This allows for sending
multiple bits per symbol in a manner similar to Pulse Amplitude Modula-
tion (PAM). Upper and lower boundaries are applied to the duty cycle of
the pulses according to the desired dimming level, reducing the number of
light compensation symbols needed to maintain a constant perceived light
intensity for the user.
ARPWM is compared to existing modulation schemes, and a throughput
increase by a factor of 4.3 was observed compared to state-of-the-art Vari-
able On-Off Keying (VOOK). With the testbed used for the experiments
we have demonstrated the use of ARPWM in an indoor office environment,
with a maximum communication distance of 4.2 meters in a low-noise en-
vironment.
ARPWM is shown to offer valuable increase in data troughput at a low
complexity level. The relatively high SNR requirements of ARPWM make
it best suitable for short-range indoor VLC.