Why Optical Transmission?

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Transcript Why Optical Transmission?

Telecommunications: Past,
Present and Future
Branimir Vojcic
ECE Dept, GWU
Outline
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•
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Why is telecommunications important?
History of telecommunications
What is the state-of-the art?
What can we expect in the future?
Telecommunications versus
Society/Economy
Ancient Communications
Systems
• Pigeons
• Messengers
• Optical signals using mirrors and light
sources
• Smoke signals
• …
History of Modern
Communications (1)
• 1837: The telegraph was invented by Samuel
Morse (telegraph = distance writing) which marks
the beginning of electrical communications;
Morse code consists of a dot, a dash, a letter space
and a word space
• 1864: James Clerk Maxwel formulated the
electromagnetic theory of light and predicted the
existence of radio waves
History of Modern
Communications (2)
• 1875: Emile Baudot invented telegraphic
code for teletypewritters; each code word
consists of 5 mark/space symbols (1/0 in
today’s terminology)
• 1875: Alexander Graham Bell invented the
telephone for real-time speech transmission
(the first step-by-step switch was invented
in 1897 by Strowger)
History of Modern
Communications (3)
• 1887: Heinrich Hertz demonstated the
existence of radio waves
• 1894: Oliver Lodge demonstrated radio
communication over short distance (150
yards)
• 1901: Guglielmo Marconi received in
Newfoundland a radio signal that originated
in England (1700 miles)
History of Modern
Communications (4)
• 1904: John Ambrose Fleming invented the
vacuum-tube diode
• 1906; Lee de Forest invented the vacuum-tube
triode
• 1918: Edwin Armstrong invented the
superheterodyne radio receiver
• 1928: First all-electronic television demonstrated
by Philo Farnsworth (and then in 1929 by
Vladimir Zworykin) and by 1939 BBC had
commercial TV broadcasting
History of Modern
Communications (5)
• 1937: Alec Reeves invented pulse-code
modulation (PCM) for digital encoding of speech
signals
• 1943: D.O. North invented the matched filter for
optimum detection of signals in additive white
noise
• 1946: The idea of Automatic Repeat-Request
(ARQ) was published by van Duuren
History of Modern
Communications (6)
• 1947: Kotel’nikov developed the geometric
representation of signals
• 1948: Claude Shannon published “A Mathematical
Theory of Communication”
• 1948: The transistor was invented in Bell Labs by
Walter Brattain, John Bardeen and William
Shockley
• 1950: Golay and Hamming proposed first nontrivial error correcting codes
History of Modern
Communications (7)
• 1957: Soviet Union launched Sputnik I for
transmission of telemetry signals (satellite
communications originally proposed by
Arthur Clark in 1945 and John Pierce in
1955)
• 1958: The first silicon IC was made by
Robert Noyce
• 1959: The Laser (Light Amplification by
Stimulated Emission of Radiation) was
invented
History of Modern
Communications (8)
• 1960: The first commercial telephone
system with digital switching
• 1965: Robert Lucky invented adaptive
equalization
• 1966: Kao and Hockham of Stanford
Telephone Laboratories (UK) proposed
fiber-optic communications
• 1967: Viterbi Algorithm for max. likelihood
decoding of convolutional codes
History of Modern
Communications (9)
• 1971: ARPANET was put into service
• 1982: Ungerboeck invented trellis coded
modulation
• 1993: Turbo codes introduced by
Berrou, Glavieux and Thitimajshima
• What’s next?
Communication Systems
An Overview
Communication Systems
INPUT
MESSAGE
Model of Communication
Systems
INPUT
TRANSDUCER
INPUT
SIGNAL
TRANSMITTED
SIGNAL
TRANSMITTER
CHANNEL
OUTPUT
MESSAGE
OUTPUT
TRANSDUCER
DISTORTION
NOISE
INTERFERENCE
RECEIVER
OUTPUT
SIGNAL
RECEIVED
SIGNAL
COMMUNICATION USING ELECTRICAL AND
OPTICAL SIGNALS IS:
 Fast
 Far reaching
 Economical
Carried Information
The input messages can be:
• SPEECH
•
MUSIC
•
PICTURES
•
• COMPUTER
DATA
1
0
1
1
0
VIDEO
1
t
INPUT MESSAGES ARE TRANSDUCED TO ELECTRICAL OR
OPTICAL SIGNALS IF NECESSARY
Physical Media
EXAMPLES OF COMMUNICATION CHANNELS ARE:
 WIRE
Communication
channels are
physical media
through which
signals propogate.
 COAXIAL CABLE
 WAVEGUIDE
 OPTICAL FIBER
 RADIO LINK
Communication Channel
Communication channel introduces:
DISTORTION
1.2
1.2
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1
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0.6
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0.2
0.2
0
-0.2
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-0.2
0
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0
100
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NOISE
1.2
1.2
1
1
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-0.2
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-0.2
INTERFERENCE
1.2
1.2
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-0.2
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-0.2
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Modulation
• Modulation is the process that modifies the input signal into a form appropriate
for transmission over a communication channel (transmitted signal)
• Typically, the modulation involves varying some parameters of a carrier wave in
accordance with the input signal:
1
 CARRIER
0
-1
0
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150
1
0.5
 INPUT SIGNAL
0
-0.5
-1
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-1
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 AMPLITUDE
MODULATED WAVE
0. 8
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0. 2
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-0. 6
-0. 8
-1
1. 182
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1. 19
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x
4
10
 FREQUENCY
MODULATED WAVE
Modulation Type
 Receiver recovers the input signal from the received
signal.
 Modulation can be:
 ANALOG (Parameter changes of the transmitted signal directly
follow changes of the input signal)
 DIGIGAL (Parameter changes of the transmitted signal represent
discrete-time finite-precision measurements of the input signal)
-1
0
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ANALOG
1
0.5
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MODULATION
-0.5
-1
0
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1
100
+Δ
DIGITAL
MODULATION
 Primary communication system design considerations:
-Δ
Transmitted power, Channel bandwidth and Fidelity of output message
 Digital communication systems are more efficient and
reliable
Optical Networks
Why Optical Transmission?
•
•
•
•
•
•
•
Immune to electrical interference
No radiation
Low attenuation, long transmission distance
Less bulky than cables
Tremendous capacity
High data rates
Less maintenance cost
coaxial transmission generally has a
bandwidth limit of 500 MHz. Current fiber
optic systems have not even begun to
utilize the enormous potential bandwidth
that is possible.
Attenuation vs. Frequency
Attenuation vs. Wavelength
Attenuation and Dispersion
Multiplexing
TDM vs. WDM
TDM
WDM
Relationship Between WDM &
TDM
Optical Devices
Optical Networks Market
($Millions)
Wireless Networks
Wireless is Growing Rapidly
Source:
The Economist
Sept. 18-24, 1999
Traffic Increasingly Consists of Data
Source: http://www.qualcomm.com
Mobile/Cellular Communications
Mobile
Station
Base
Station
Cellular
Concept
F2
F7
F3
F1
F6
F2
F7
F4
F5
F3
F1
F6
F4
F5
• Every cell corresponds to the service area of one
Base Station
• Each frequency can be reused in a sufficiently
distant cell
Network Architecture
MS
PDN
BSC
BTS
MSC
BSC
HLR,
VLR
AUC
OMC
BTS
Base Station
Subsystem
Network Switching
Subsystem
ISDN
PSTN
Public
Networks
Ad-Hoc Mobile Internet
LEOS
Mobile/Portable
ISP
Satellite Communications
Un-tethered, Global, Broadband,
Mobile and Ubiquitous.
Wireless Mobility
Satellite
Regional Area
Wide Area
Local Area
Emerging Connectivity Solutions:
Cellular, Satellite, Microwave, and Packet Radio
SOURCE: CISCO
Satellite Features
• New Wideband Frequency Allocations
• Global Access
• Rapid Deployment
• User Mobility
• Multicasting, Broadcasting
• Bypass and/or Serve Terrestrial Disaster
• High Startup Costs, Lower Incremental Cost
Existing Systems
• Global and Regional Trunking
• Direct TV Broadcast
• VSAT Networks
• Mobile Satellite Systems (MSS)
• Paging
• Aeronautical/ Maritime
• Global Positioning (GPS and GLONASS)
Iridium 66 Polar Orbits with
spot beams
Local Area Networks
Local Area Networks (1)
• A local Area Network provides the interconnection
of a heterogeneous population of mainframes, work
stations,personal computers, servers, intelligent
terminals and peripherals.
• Topologically, LAN’s connect the devices or
stations in the form of a bus, a tree, a ring or a star
configuration.
• Wireline (Token Ring, Ethernet)
• Wireless (802.11, Bluetooth, UWB,…)
Wireless Local Area Networks
Source: Proxim
Local Area Networks
802.11 LAN
STA1
802.x LAN
BSS1
Portal
Access
Point
Distribution System
Access
Point
ESS
BSS2
STA2
802.11 LAN
STA3
Bluetooth
LAN Applications
• Client-Server communications
• Shared database access
• Word processing, Electronic mail
• Sharing of mass storage devices, printers and other
peripherals, software and computational resources
• Data exchange between computers and mass storage
devices
• CAD/CAM, Inventory control, Process control, Device
control
A Lesson From the Past
“Well Informed people know
it is impossible to transmit the
voice over wires and that, were
it possible to do so, the thing
would be of no practical value”
Excerpt from an 1865
BOSTON POST editorial