DESIGN OF A FOUR BIT NUMERIC DATA TRANSCEIVER USING
OPTICAL FREE SPACE COMMUNICATION
Department:
Engineering – Telecomm
CHAPTER ONE
1.0 INTRODUCTION
1.1 Brief
Overview of Free-Space Communication
Telecommunication is
a process whereby information is encoded and transmitted over a distance
through a channel or a medium by a sender to one or more receiver
electronically (Advance English Dictionary). From the above definition the word
that is to be emphasis is “distance” gotten from the Greek prefix “tele”
meaning “distant”. Distance is a major point to consider when building a
telecommunication device or system, therefore scientist over the years have
worked and are still working on different means to enhance the efficiency of
the distance and data-rate of telecommunication systems. Examples of such works
are in the area of Radio and Microwave communications, Light Amplification by
Stimulated Emission of Radiation (LASER) or optical communication systems and
wired communication technology among others [5].
Optical
communication systems are in various form and have been used for thousands of
years. Among the early users of this system are the Ancient Greeks, they polish
their shields to sends signals during battle [6]. In modern era, semaphores and
wireless solar telegraphs called heliographs have been developed using coded
signal to communicate with the receiver.
In the past ten to
twenty years free-space optical communication (FSO) has attain a state of
interest as an alternative to radio frequency communication [1]. Free-space
optics also known as free-space photonics (FSP) is a branch of optical
communication system that deals with the transmission of modulated visible or
infrared (IR) beams through the atmosphere to obtain data or broadband
communication. Some of the sources of these beams used are LASER and non-lasing
sources like light-emitting
diodes or IR-emitting diodes (IREDs) [4]. This technology is useful in areas
with high electromagnetic interference (EMI) and therefore can be used for the
most demanding industrial and domestic applications [5].
The
growing need for high-speed and tap-proof communication systems to create links
to satellites, ground stations, deep-space probes, unmanned aerial vehicles
(UVAs), high altitude platforms (HAPs), aircrafts and other mobile or static
communication systems makes the improvement and works on free-space optics a
very high priority for telecommunication standards societies and space agencies
such as; International Telecommunications Union (ITU) and National Aeronautics
and Space Administration (NASA) among others. Links created by this technology
can be used in both military and professional fields [1]. For example, it will
take Radio frequency (RF) systems nine years to transmit a 30cm resolution map
of the entire Martian surface (at one bit per pixel), but with an FSO system
(such as LASERCOMM) this can be achieved in nine weeks.
FSO
links between much distanced buildings have long been developed and established
in developed countries such as the United State of America, but this technology
just seems to be lacking in African countries like Nigeria among others [6]. If
this technology is implemented in Nigeria it will greatly increase data-rate,
and “Last Mile Challenges” can be reduced or completely eliminated.
Furthermore,
free-space optic (FSO) systems are license-free access technologies with high
frequency and very short wavelength therefore allowing higher data
transmission, with less transmit power. It is a potential alternative or
complement solution to common physical layers like fiber optic links. But in
spite of the major merits of the FSO technology and diversity of its
applications, works is on-going on ways to reduce or eliminate some of the
major limitations of the technology such as fading resulting from
‘index-of-refraction turbulence (IRT) and link blockage by clouds, snow and
rain [4].
In
this project, a model will be designed to transmit and receive four bit
numerical integers over a reasonable distance in free space to illustrate the
working principle of the FSO systems.
1.2
Project Motivation
In
today’s data rich world, high speed connections has become almost as important
as the internet itself, broadband is faster and more accessible than ever
before. Almost 60 million people now pay premium to access data all over the
world with high speed connection, millions more want to join but cannot [3].
Service providers are always tasked to deliver high-speed internet access to
eagerly waiting customers but, lack of infrastructure, long distance
challenges, cost, competitive and regulatory issues are a constant problems especially
in Nigeria and Africa in general. But with development of (FSO) technology a
shortcut to broadband connectivity can be created to link with existing
networks such as wired and wireless local area networks (WLANs), fiber optics
and even satellite. These networks can then be extended using invisible beams
of light (LASER or IR-emitting diodes), resulting in a very fast broadband
wireless connections with merits such as no spectrum licenses, no
electromagnetic interference (EMI) and highly secured from vandalisation.
1.3
Aims and Objectives
The
aim of this project is to design and produce an optical-base system for
transmission of 4-bits single digit numeric data from one point to another
using free-space optical communication to illustrate the working principle of
an (FSO) system.
The
objectives of this project are:
1. To design an optical-base
transceiver system using free-space optics.
2. To design the model using infrared
(IR) beams.
3. To achieve a reasonable distance
of at least 10 meters.
4.
To illustrate the basic fundamental principle of the (FSO) systems.
1.4
Methodology
The
implementation of this project uses a digital serial transmission system where
single numeric integers are sent using 4-bits coding system over an optical
path sequentially. This system is efficient because it requires less signal
processing thereby less chance of error compared to parallel transmission and
thus a faster transfer rate. The model uses a transmitter which encodes the
integers into 4-bit codes then to a binary-to-frequency converter, next is to
an optical emitter over free-space and a receiver, which reproduces the numeric
integer from the received optical signal using a seven segment display.
1.5
Scope of Study
This
project seeks to cover the design and implementation of a 4-bit transceiver
using optical transmission channel. The maximum range of communication between
the optical transmitter and receiver is between 10 to 20 meters.
Intercommunication link between both the transmitter and receiver systems is
completely based on line of sight.
1.6
Project Outline
The Chapter one of this project
introduce the entire work. Chapter two reviews LASER in free-space optical and
modulation in data transmission, Chapter three deals with the design procedure,
Chapter four covers the construction, testing and result analysis. Chapter five
is the summery which consist of the conclusion, recommendation and references.