lecture 1 professor: dr. miguel alonso jr.. outline intro to the history of data communications a...

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