Transcript Lecture 1
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