lecture 1 professor: dr. miguel alonso jr.. outline intro to the history of data communications a...
TRANSCRIPT
Lecture 1
Professor: Dr. Miguel Alonso Jr.
Outline
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
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!
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
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
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
A Basic Communication System
Typical Digital Communication System
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
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
Transmitter (Power requirements)
Antennas Power Generation
(Efficiency, Solar Panels, Lack of Sun)
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
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
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
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
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
Example: Compute the Channel Capacity for: BW = 44kHz, M = 2 BW = 22.5kHz, M = 4 BW = 100MHz, M = 8
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)
LAB Volt Unit 1