Passive Visible Light Communication

Passive Visible Light Communication: Utilizing the Unstable Region Of Liquid Crystals

Wervers, Michel (TU Delft Electrical Engineering, Mathematics and Computer Science; TU Delft Embedded and Networked Systems)

Langendoen, K.G. (mentor)
Ghiasi, S.K. (mentor)
Al-Ars, Z. (graduation committee)

Delft University of Technology

Electrical Engineering | Embedded Systems

2021-07-14

As more and more devices have become wireless, the traditional Radio Frequency (RF) spectrum has become densely populated. To relieve this pressure,
communication using light, visible light communication (VLC), has been proposed by many researchers. However, not all light sources can be modulated
to transmit information. Therefore, the use of materials that can change their
state between translucent and opaque has often been investigated in order to
modulate light. ChromaLux is a recent system that uses such a material. It uses
Liquid Crystal shutters to transmit information. However, instead of a single
crystal, a stack of crystals is used, which exposes an extra transient region.
This transient region shows several peaks that allow faster communication, but
makes the system unstable. This thesis addresses several issues that ChromaLux
experiences, in order to improve the performance.
The system is changed from open-loop to closed-loop, creating a stable system
that reaches higher speeds. However, in order to achieve this, part of the crystals
is blocked, causing a lower Signal-to-Noise Ratio (SNR). For shorter distances up
to 1 m, we are able to increase the data rate by 140 %, while at longer distances
of up to 3 m we achieve an increase of up to 92 %. A second improvement which
increases the SNR of the system, is the smart use of differential amplification.
This allows communication at even greater distances of at least 5 meters.

Passive visible light communication
Liquid crystals
Wireless Communication

http://resolver.tudelft.nl/uuid:cad0975a-43b0-4c1e-9d03-837df026020f

Student theses

master thesis

© 2021 Michel Wervers