lecture 1 professor: dr. miguel alonso jr.. outline intro to the history of data communications a...
TRANSCRIPT
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Lecture 1
Professor: Dr. Miguel Alonso Jr.
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Outline
Intro to the History of Data Communications A Basic Communication System Elements of Microwave and Satellite
Communication Data Communications Terminology Shannon’s Law
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Intro to the History of Data Communications
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
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 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… http://www.k12.hi.us/~telecom/datahistory.html http://telecom.tbi.net/ Great Resource for info on telecom
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A Basic Communication System
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
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Elements of Microwave and Satellite Communication
Satellite Communication system uses satellites to relay radio transmissions between two points on earth
Active (Provides boost) Passive (Reflective)
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Components of a satellite communication system
Transmitter (Power requirements)
Antennas Power Generation
(Efficiency, Solar Panels, Lack of Sun)
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Data Communications Terminology
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
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Nyquist and Shannon’s Law
Channel capacity: Maximum rate at which data can be communicated 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
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Nyquist Bandwidth
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
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Shannon’s Law
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 SNRdb 10 log10 (Signal Power / Noise Power)
C = B log2 ( 1 + SNR)
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LAB Volt Unit 1