الفهرس 
CHAPTER 1 : INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The Optical Wireless Communications (OWC) has seen rapid development
during recent years. This gro
wing popularity is due to several characteristics of
the
considerable importance
of the
consumer electronics products, such as large
bandwidth that is also not having spectrum regulations imposed, low cost, and
license free operation.
The
visible light com
munication (VLC) systems have their
own unique advantages, with several new technologies, products and patents
.
They have
been developed during the end of last century
.
Especially in indoor environments, VLC could enable wireless home
networking systems w
hich offload data traffic from existing RF systems. VLC
systems employ intensity modulation (IM) and direct detection (DD) of the optical
carrier. White LEDs (Light Emitting Diodes) in VLC is an emerging technology
that
required current research
so it can
eventually be used for common
communications systems. LEDs have a numbe
r of advantages, one of which
its
long life
time
. However, like many emerging technologies, VLC has many
technical issues that need to be addressed.
This thesis proposes
a VLC system f
or indoor application.
T
he
objective
of this
work
reduce
s
the
peak
-
to
-
average power ratio (PAPR) and achieves
acceptable bit
error rate (BER) performance for indoor use.
The proposed tech
niques
were
evaluated through computer simulations.
Orthogonal
Frequ
ency Division Multiplexing
(OFDM) is used with visible light
communication (VLC) systems to reduce the effects of
the
inter
-
symbol
interference (ISI) and to achieve communication with high speed of data
transmission
using
huge bandwidth. However, OFDM base
d VLC systems suffer
from high peak
-
to
-
average power ratios (PAPRs)The work
can be divided into three main parts. The first part gives a detailed
overview of
the
OWC, VLC and OFDM system. This is followed by an overview
of the PAPR problem in
the
multic
arrier systems.
The second part proposes
hybrid PAPR reduction technique based on signal
transformation combined with clipping. The Hadamard transform is used in the
proposed technique to reduce the PAPR without affecting the bit error rate (BER)
of the VL
C systems. The optimum clipping threshold at which the PAPR is
reduced simultaneously with the improvement the BER of the VLC systems is also
determined. The performance of the proposed system is
evaluated
in terms of
the
Complementary Cumulative Distribut
ion Function
(CCDF) and the BER.
The Third part proposes an
OFDM structure based on using
the
discrete cosine
transform (DCT) precoding before
using the
Inverse Fast
Fourier
Transform
(IFFT) stage with clipping to further
reduce
the PAPR and
the
BER. The
Partial
Transmit Sequence (PTS) strategy was modified to reduce the PAPR of
the
OFDM signal in
the
VLC system. PTS was appropriate for transmission in
the
VLC system and
which is
combined with the continuous phase modulation (CPM)
based OFDM (CPM
-
OFDM) sys
tem to reduce
the
PAPR of the optical OFDM
signal.