Analog and digital communicaitons mod

Lecture 7

Overview of Analog and Digital Technologies

Overview of Analog Technology

AREAS OF APPLICATION

• Old telephone networks

• Most television broadcasting at present

• Radio broadcasting

ANALOG SIGNALS: THE BASICS

Cycle

Time

Signal

Amplitude

Frequency = Cycles/Second

A typical sine wave

AMPLITUDE AND CYCLE

• Amplitude

• Distance above reference line

• Cycle

• One complete wave

FREQUENCY

• Frequency

• Cycles per second

• Hertz is the unit used for expressing frequency

• Frequency spectrum

• Defines the bandwidth for different analog communication technologies

INFORMATION REPRESENTATION USING ANALOG SIGNALS

• Information can be represented using analog signals• Analog signals cannot be manipulated easily• Analog signals must be digitized for computer processing• They must also be presented in binary form for

computer processing

ANALOG TO DIGITAL CONVERSION

1 0 1 1 0 1 0 0

A to D Converters, Digital Signal Processors (DSP)

etc.

DATA TRANSMISSION USING ANALOG TECHNOLOGY

Digital0s and 1s

Analog0s and 1s

Digital-to-Analog Modulation and vice versa

Computer Modem

VOICE TRANSMISSION EXAMPLE

Voice

Carrier Wave

AM Radio Transmission

Analog-to-Analog Modulation

Frequency Spectrum

and Bandwidth

FREQUENCY SPECTRUM DEFINED

• Available range of frequencies for communication

• Starts from low frequency communication such as voice and progresses to high frequency communication such as satellite communication

• The spectrum spans the entire bandwidth of communicable frequencies

FREQUENCY SPECTRUM

Low Frequency High Frequency

Radio Frequency

CoaxialCable

MHz

SatelliteTransmission

MicrowaveMHz

Voice

KHz

FREQUENCY SPECTRUM

• Low-end

• Voice band

• Middle

• Radio wave

• High-end

• Satellite communication

BANDWIDTH DEFINITION

• Bandwidth, in general, represents a range of frequencies

300 MHz 700 MHz

Bandwidth is 400 MHz

USAGE OF THE TERM BANDWIDTH

• To specify the communication capacity

• A medium such as a coaxial cable is associated with a bandwidth

• To indicate the bandwidth of a technology• Voice grade circuits have a bandwidth of 4 KHz (0-

4000 Hz)

DIGITIZATION CONSIDERATION

• Sample at twice the rate of bandwidth for acceptable quality digitization of voice• Sampling rate for voice transmission is there 8000 Hz

• If each sample is represented by 8-bits, the bandwidth required for transmission is 64000 bps – Approximately 64K bps

COMMUNICATION CAPACITY

• Bandwidth is indicative of the communication capacity

• Communication speed is proportional to bandwidth

• Shannon's law

• Units used to represent bandwidth are Hz, bps etc.

COAXIAL CABLE EXAMPLE

• Bandwidth of 300 MHz

• Comparison with twisted pair

• Higher bandwidth

• Supports faster communication speeds

LIMITING FACTORS ON COMMUNICATION SPEED

Communication SpeedBandwidth Technology

IMPACT OF BANDWIDTH AND TECHNOLOGY ON COMMUNICATION SPEED

• Bandwidth limitation

• Use better technology such as data compression used in modems to increase speed of communication

• Bandwidth and technology limitation

• Move to higher bandwidth media such as fiber cables

SPEED DEPENDENCY ON BANDWIDTH AND TECHNOLOGY

Medium 1

Technology Medium 2

Higher Bandwidth

Medium 1 example can be shielded twisted pair and medium 2 example can be fiber.

IMPLICATION

• Whenever a new technology with higher communication speed is introduced, it is first introduced on a medium of higher bandwidth• Example: Optical fiber

• It is then moved to a widely used medium with further advancement of the technology• Example: Copper wire

An Overview of Digital Technology

AREAS OF APPLICATION

• Computers

• New telephone networks

• Phased introduction of digital television technology

DIGITAL TECHNOLOGY

• Basics

• Digital signals that could be assigned digital values

• Digital computer technology

• Digital signals

• Binary representation

• Encoded into ones and zeros

DIGITAL ADVANTAGE

• Processing using computer technology

• Programmable services

• Better quality due to being able to reconstruct exact digital patterns at the receiving end

• Faster communication speeds are possible

DIGITAL SIGNAL

1 0 1 1 0 1 0 0

Pulse

Time

Sig

nal

Str

eng

th

Pulse Duration

DIGITAL TERMS• Pulse

• Pulse duration

• Pulse amplitude

• Signal strength

CLOCK SPEED AND PULSE DURATION

PulseDuration

MHz

CLOCK SPEED AND EXECUTION SPEED

• Pulse duration is inversely proportional to the clock frequency

• Faster the clock speed, the smaller the pulse duration

• Smaller the pulse duration, the faster the execution in general

CLOCK SPEED AND COMMUNICATION SPEED

• Faster the clock speed, smaller the pulse duration

• Smaller the pulse duration, smaller the time taken to transmit one bit of information

• Therefore, faster the clock speed measured in MHz, faster the communication speed measured in Mbps in general

CLOCK SPEED AND COMPUTER OPERATION• Computer operations are timed by a clock, namely by the

clock speed measured in HZ• Faster the speed, the smaller the pulse duration• Computer operations are timed by the pulse duration• Therefore, faster the clock speed, faster the computer

operation• A 3 GHz computer is faster than a 2 GHz computer

Digital-to-Analog and

Analog-to-Digital Conversion

THE NEED FOR CONVERSION

• Analog-to-Digital Conversation

• Connection of a computer to an analog communication line

• Digital-to-Digital Interface

• Connection of a computer to a digital ISDN line

• Connection of different networks using a router

DIGITAL-TO-DIGITAL INTERFACE

Comp.Sys. 1

Comp.Sys. 2

DSLRouter

DSLRouter

DigitalIEEE 802.3

Digital IEEE 802.3

Digital Internet

DATA AND SIGNALS

• Usually use digital signals for digital data and analog signals for analog data

• Can use analog signal to carry digital data• Modem

• Sender Modulation

• Receiver Demodulation

• Can use digital signal to carry analog data • CODEC

• Sender Coding

• Receiver Decoding

ANALOG SIGNALS CARRYING ANALOG AND DIGITAL DATA

DIGITAL SIGNALS CARRYING ANALOG AND DIGITAL DATA