Transcript Introduction

Communication Systems
(0331411)
First semester 2008/2009
Dr. Ali Jamoos
Email: [email protected]
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Historical Background
1844 – The Telegraph was invented by Samuel Morse
1864 – James Clerk Maxwell formulated the electromagnetic theory
1875 – The Telephone was invented by Alexander Graham Bell
1887 – Heinrich Hertz confirmed the existence of radio waves
1901 – Marconi received a radio signal, 1700 miles across the Atlantic
1904 – John Ambrose Fleming invented the vacuum-tube diode
1906 – John Ambrose Fleming invented the vacuum-tube triode
1918 – Edwin Armstrong invented the superheterodyne radio receiver
1928 – The Television system was demonstrated by Philo Farnsworth
1933 – Edwin Armstrong demonstrated the Frequency Modulation (FM)
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Historical Background
1946 – The first computer, ENIAC, was built at Pennsylvania university
1948 – The transistor was invented at Bell Laboratories
1958 – The first Integrated Circuit (IC) was produced by Robert Noyce
1962 – The Telstar satellite, built by Bell Laboratories, was lunched
1971 – The first computer network, called the ARPANET, was built
1985 – The ARPANET was renamed the Internet
1983 - Advanced Mobile Phone System (AMPS) was lunched in US
1991 - Global System for Mobile (GSM) was lunched in Europe
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A communication Model
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Source - generates data to be transmitted, examples are telephones and computers
Transmitter - converts data into transmittable signals
Transmission System - carries data from source to destination
Receiver - converts received signal into data
Destination - takes incoming data
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Communications Tasks
Transmission system utilization Addressing
Interfacing
Routing
Signal generation
Recovery
Synchronization
Message formatting
Exchange management
Security
Error detection and correction
Network management
Flow control
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Data Communication Model
1. user keys in message m comprising bits g buffered in source PC memory
2. input data is transferred to I/O device (transmitter) as sequence of bits g(t) using voltage
shifts
3. transmitter converts these into a signal s(t) suitable for transmission media being used
4. whilst transiting media signal may be impaired so received signal r(t) may differ from s(t)
5. receiver decodes signal recovering g’(t) as estimate of original g(t)
6. which is buffered in destination PC memory as bits g’ being the received message m’
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Elements of digital communication systems
Source of
Source
Channel
Information
encoder
encoder
Modulator
Noise and interference
(Unwanted signals)
User of
Source
Channel
information
decoder
decoder
Channel
Demodulator
1. The information source generate a message signal
2. The source encoder removes redundant information from the message signal and produce a
source code word
3. The channel encoder add some bits for the purpose of error detection and correction and
produce the channel code word
4. The modulator represent each symbol of the channel code word by a corresponding analog
symbols (resulting in signal waveform) suitable for the transmission through the channel
5. Noise and interfering signals corrupt the transmitted signal in the channel
6. Channel types: guided media (twisted pair, coaxial, fiber optic), unguided (wireless)
7. At the receiver, the received signal is processed in reverse order to that in the transmitter so
as to recover the message signal
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Cellular telephone system
 The cellular mobile telephone system consists of:
Mobile Stations (MS), Base Stations (BS) and Mobile Switching Center
(MSC), connected to the Public Switching Telephone Network (PSTN)
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Satellite Communication system
The information-bearing signal is transmitted from the earth terminal to the
satellite via the uplink, amplified by the transponder (electronic circuitry on
board the satellite), and then retransmitted from the satellite via the
downlink to the other earth terminal
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Computer Networks and the Internet
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OSI Network Model
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Electromagnetic Spectrum
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Electromagnetic wavelength, frequency and
photon energy
 The electromagnetic wave at a particular wavelength λ has
an associated frequency f and photon energy E :
c
 
f
E  hf 
hc

where
c  3 108 m / s
is the light speed
h  6.626 1034 J .s  4.13567 eV / GHz
Planck’s constant
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Operating frequency of various guided and unguided
transmission techniques
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Atmospheric Transparency for Electromagnetic
waves
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Electromagnetic Spectrum
Band
Frequency
range
Propagation
characteristics
Typical use
ELF (extremely low frequency)
30 to 300 Hz
Ground Wave (GW) propagation
Power line frequencies
VF (voice frequency)
300 to 3000 Hz
GW propagation
Used by the telephone
system for analog
subscriber lines
VLF (very low frequency)
3 to 30 kHz
GW propagation
Long-range navigation;
submarine communication
LF (low frequency)
30 to 300 kHz
GW propagation
Long-range navigation;
marine communication
MF (medium frequency)
300 to 3000 kHz
Sky-Wave (SW) ionospheric
propagation
AM broadcasting
HF (high frequency)
3 to 30 MHz
SW ionospheric propagation
international broadcasting,
military communication;
longdistance aircraft and ship
communication
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Electromagnetic Spectrum
Band
Frequency
range
Propagation
characteristics
Typical use
VHF (very high frequency)
30 to 300 MHz
SW ionospheric and tropospheric
propagation;
Line-Of-Sight (LOS) Propagation
VHF television; FM broadcast
AM aircraft communication;
Aircraft navigational aids
UHF (ultra high frequency)
300 to 3000 MHz
LOS Propagation
UHF television;
cellular telephone; radar;
microwave links; personal
communications systems
SHF (super high frequency)
3 to 30 GHz
LOS Propagation
Satellite communication;
radar; terrestrial microwave
links; wireless local loop
EHF (extremely high frequency)
30 to 300 GHz
LOS Propagation
Experimental; wireless local
loop
Infrared
300 GHz to 400 THz
LOS Propagation
Infrared LANs; consumer
electronic applications
Visible light
400 THz to 900 THz
LOS Propagation
Optical communication
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