Transcript Lecture 1

Lecture 1
Professor: Dr. Miguel Alonso Jr.
Outline
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Intro to the History of Data Communications
A Basic Communication System
Elements of Microwave and Satellite
Communication
Data Communications Terminology
Shannon’s Law
Intro to the History of Data
Communications
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Source: http://www.k12.hi.us/~telecom/datahistory.html
26 million phone lines
7.5 million cellular phone users
5 thousand AM radio broadcast stations
5 thousand FM radio stations
1 thousand television broadcast stations
9 thousand cable television systems
530 million radios
193 million television sets
24 ocean cables
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scores of satellite facilities!
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One of the earliest forms of
digital communications was
smoke signals
Words were encoded into
data represented by puffs of
smoke
The first electrical
communication system was
the telegraph, 1844
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The first telephone was then
patented in 1876
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Long distance call today are transmitted
digitally!
The first analog radio was
demonstrated in 1895
Television subsequently dominated
communication in the 1950s
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Since the Invention of the transistor, digital
communication has exploded and will continue to
develop!
 Cell Phones
 The Internet
 HD Television and Satellite Television (DirecTV, etc.)
 mp3’s
Exercise: Read this article on the history of
communications and comment on three facts that you
did not know…
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http://www.k12.hi.us/~telecom/datahistory.html
http://telecom.tbi.net/ Great Resource for info on telecom
A Basic Communication
System
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Typical Digital Communication System
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Tasks of a communication system
 Exchange data between two parties
 Source-> Transmitter -> Transmission System _>
Receiver -> Destination
Efficient Transmission System Utilization
Interfacing
Signal Generation
Synchronization
Error Detection and Correction
Addressing, Routing, Recovery, Message Format,
Security and Finally network management
Elements of Microwave and
Satellite Communication
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Satellite Communication system uses
satellites to relay radio transmissions
between two points on earth
Active (Provides boost)
Passive (Reflective)
Components of a satellite
communication system
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Transmitter (Power
requirements)
Antennas
Power Generation
(Efficiency, Solar Panels,
Lack of Sun)
Data Communications
Terminology
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Information: the communication or reception
of knowledge or intelligence
Analog Signal: Continuous and vary in
amplitude, frequency, or phase
Digital signal: Discrete and discontinuous and
only have two voltage levels
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Bit: a binary digit, 0 or 1, used to store
information
Baud: number of distinct symbols changes
made to the transmission medium per second
Bit rate and Baud are not equal!
Example: Transmission of 3000 bps in a 3bit
symbol transmission system is said to
operate at 1000 Baud
Nyquist and Shannon’s Law
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Channel capacity: Maximum rate at which
data can be communicated
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Data rate (bps)
Bandwidth (constrained by transmitter and
medium)
Noise
Error Rate
Goal of a good communication system is to
achieve the highest data rate possible given
the limitations of BW, Noise, and Error Rate
Nyquist Bandwidth
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First, consider a noise free channel
In this environment, the limitation on data rate
is simply the bandwidth of the signal
If the rate of signal transmission is 2B, then a
signal with frequencies no greater than B is
sufficient to carry the signal
Similarly, given a bandwidth B, the highest
signal rate that can be carried is 2B
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Example: transmitting binary signals over a
voice channel
BW = 3100Hz
C=2B = 6200 bps
If more levels are used however,
C=2B log2 M
Where M is the number of distinct levels
M = 8, C = 18600
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Example: Compute the Channel Capacity for:
BW = 44kHz, M = 2
BW = 22.5kHz, M = 4
BW = 100MHz, M = 8
Shannon’s Law
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The presence of noise complicates matters
Claude Shannon developed a formula that
allows for the computation of the maximum
theoretical channel capacity given the
bandwidth of the channel and the signal to
noise ratio
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SNRdb 10 log10 (Signal Power / Noise Power)
C = B log2 ( 1 + SNR)
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LAB Volt Unit 1