THESIS
2019
xiv, 77 pages : illustrations ; 30 cm
Abstract
The ever increasing demand for higher data rate and increased bandwidth has pushed
radio frequency spectrum towards congestion. To fulfill this demand, a natural extension
is towards the exploration of optical spectrum for communication. Fueled by mass adaptation
of light emitting diodes (LEDs) for illumination purposes, mainly due to its energy
efficient properties and high frequency switching characteristics, a new type of communication
has emerged known as visible light communication (VLC). Recently, VLC has
gained much attention not only for its utilization in indoor positioning and localization applications,
but also it is paving the way towards outdoor applications related to intelligent
transportation systems (ITS).
Despite VLC's popularity as a complementary communicati...[
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The ever increasing demand for higher data rate and increased bandwidth has pushed
radio frequency spectrum towards congestion. To fulfill this demand, a natural extension
is towards the exploration of optical spectrum for communication. Fueled by mass adaptation
of light emitting diodes (LEDs) for illumination purposes, mainly due to its energy
efficient properties and high frequency switching characteristics, a new type of communication
has emerged known as visible light communication (VLC). Recently, VLC has
gained much attention not only for its utilization in indoor positioning and localization applications,
but also it is paving the way towards outdoor applications related to intelligent
transportation systems (ITS).
Despite VLC's popularity as a complementary communication technology, it faces
many challenges including the low data rate, limited communication distance and robustness
to interference, specifically in multi-user environment representing real-world
scenarios. Much work has been done to increase the data rate, however very few works
found in literature deal with increasing the robustness and communication distance of a
VLC link, both of which are critical parameters due to the visible nature of the link. In
this work, we propose to address these challenges in four phases.
In the first phase, we propose a polarization based transceiver methodology to mitigate
channel interference thereby increasing the robustness of the optical link. Experimental
results demonstrate a 32.6% more robust VLC link compared to the conventional
transceiver under severe optical interference.
In the next phase, we extend the work to support for multi transmitter environment.
With additional capabilities of spatially separating interference sources, image sensor
based VLC receivers have been studied. The main challenges include evaluation of shutter
speed imposing restrictions on minimum SNR requirement of the transmitter and
variable frame rate phenomenon resulting in inconsistent sampling intervals. To cater
for these issues, an adaptive threshold under-sampled communication technique has been
proposed that enables the receiver to sample at slower shutter speeds thereby increasing
the communication distance for low-SNR transmitters. We extend this work to propose a
hybrid phase-frequency modulation technique to establish a record 160 m long communication
link, making it the longest communication distance achieved till date using visible
light.
In the third phase, we propose channel modeling of a camera communication system
using perspective projection. Perspective projection provides better approximation of
channel parameters compared to conventional pin-hole model. The work is extended to
estimate the channel length of a MIMO camera communication system, which is a critical
parameter specifically for distance-critical applications.
In the last phase, we use the channel model to predict the behavior of the system
in a real-world scenario where multiple transmitters and receivers would be operating
simultaneously specifically in ITS applications. Either the transmitter, or the receiver, or
both could be moving in a random fashion independently of each other. Vehicle vibration
analysis was analyzed to quantify the extent of vibrations a transmitter, or a receiver,
undergoes in a real-world environment. Based upon the channel model simulations, we
propose a passive detection and tracking methodology to detect and track a moving
transmitter, while maintaining a robust communication link between the transmitter and
the receiver. The proposed methodology caters for the worst case vehicle vibrations,
validated through experimental results.
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