analog and digital communicaitons()

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© N. Ganesan, Ph.D. , All rights reserved.

Chapter

Overview of Analog and DigitalTechnologies



Chapter Objectives Explain the basic concepts of analog anddigital technology

Show the importance of frequency spectrumto communication along with an explanationof the concept of bandwidth

Give an overview of the interface technologybetween analog and digital technology

Describe the process of digitizing data,audio, image and video

Discuss quality retention in digitaltransmission




Module

Overview of Analog Technology



A

reas of A

pplication Old telephone networks

Most television broadcasting at present Radio broadcasting



Analog Si gnals: The Basics

Cycle

Time

Signal

Amplitude

Frequency =

Cycles/Second

A typicalsine wave



Am plitude and Cycle

Amplitude

² Distance above reference line Cycle

² One complete wave



F requency

Frequency

²C

ycles per second² Hertz is the unit used for expressingfrequency

Frequency spectrum

² Defines the bandwidth for different analogcommunication technologies



I nfor mation Representation

Using Analog Si gnals Information can be represented using

analog signals

Analog signals cannot be manipulatedeasily

Analog signals must be digitized for

computer processing² They must also be presented in binary

form for computer processing



A

nalog to Di gital C onversion

1 0 1 1 0 1 0 0

A to D Converters, DigitalSignal Processors (DSP) etc.



Data Transmission Using Analog

Technology

Digital

0s and 1s

Analog

0s and 1s

Digital-to-Analog Modulation

and vice versa

Computer Modem



V oice Transmission Exam ple

Voice

Carrier Wave

AM Radio Transmission

Analog-to-AnalogModulation



End of Module




Module

Frequency Spectrum

and Bandwidth



F

requency Spectr um

De f ined Available range of frequencies for

communication

Starts from low frequency communicationsuch as voice and progresses to highfrequency communication such as satellitecommunication

The spectrum spans the entire bandwidth ofcommunicable frequencies



F requency Spectr um

Low Frequency High Frequency

RadioFrequency

CoaxialCable

MHz

SatelliteTransmission

Microwave MHz

Voice

KHz



F requency Spectr um

Low-end² Voice band

Middle² Microwave

High-end² Satellite communication



Si gnal Pr o pa gation Low frequency

² Omni-directional

High frequency (In general)² Unidirectional



Bandwidth De f inition

Bandwidth, in general, represents arange of frequencies

300 MHz 700 MHz

Bandwidth is 400 MHz



Usa ge of the Ter m

Bandwidth To specify the communication capacity

² A medium such as a coaxial cable isassociated with a bandwidth

To indicate the bandwidth of atechnology

² Voice grade circuits have a bandwidth of 4KHz (0-4000 Hz)



Di gitization C onsideration Sample at twice the rate of bandwidth

for acceptable quality digitization of

voice² Sampling rate for voice transmission is

there 8000 Hz

If each sample is represented by 8-bits,the bandwidth required fortransmission is 64000 bps ²Approximately 64K bps



C omm

unication Capacity Bandwidth is indicative of the

communication capacity

Communication speed is proportionalto bandwidth

² Shannon's law

Units used to represent bandwidth areHz, bps etc.



C oaxial Cable Exam ple

Bandwidth of 300 MHz

C

omparison with twisted pair² Higher bandwidth

² Supports faster communication speeds



Limiting F actors on

C ommunication Speed

Communication SpeedBandwidth Technology



I m pact of bandwidth and Technology

on C ommunication Speed Bandwidth limitation

² Use better technology such as datacompression used in modems to increasespeed of communication

Bandwidth and technology limitation

² Move to higher bandwidth media such asfiber cables



I m

plication Whenever a new technology with

higher communication speed is

introduced, it is first introduced on amedium of higher bandwidth² Example: Optical fiber

It is then moved to a widely usedmedium with further advancement ofthe technology² Example: Copper wire



End of Module




Module

An Overview of DigitalTechnology



A

reas of A

pplication Computers

New telephone networks Phased introduction of digital television

technology



Di gital Technology

Basics² Digital signals that could be assigned

digital values

Digital computer technology² Digital signals

² Binary representation

Encoded into ones and zeros



Di gital A

dvanta ge Processing using computer technology

Programmable services Better quality due to being able toreconstruct exact digital patterns at thereceiving end

Faster communication speeds arepossible



Di gital Si gnal

1 0 1 1 0 1 0 0

Pulse

TimePulse Duration



Di gital Ter m

s Pulse

Pulse duration Pulse amplitude

Signal strength



C lock Speed and Pulse Duration

PulseDuration

MHz



C lock Speed and

Execution Speed Pulse duration is inversely proportional

to the clock frequency

Faster the clock speed, the smaller thepulse duration

Smaller the pulse duration, the fasterthe execution in general



C lock Speed and C ommunication Speed

Faster the clock speed, smaller the pulseduration

Smaller the pulse duration, smaller thetime taken to transmit one bit ofinformation

Therefore, faster the clock speedmeasured in MHz, faster thecommunication speed measured in

Mbps in general



C lock Speed and C om puter Operation

Computer operations are timed by a clock,namely by the clock speed measured in HZ

Faster the speed, the smaller the pulseduration Computer operations are timed by the pulse

duration Therefore, faster the clock speed, faster the

computer operation² A 3 GHz computer is faster than a 2 GHz

computer



End of Module




Module

Digital-to-Analog and

Analog-to-DigitalC

onversion



The Need for C onversion

Analog-to-Digital Conversation² Connection of a computer to an analog

communication line

Digital-to-Digital Interface² Connection of a computer to a digital ISDN

line² Connection of different networks using a

router



Di gital-to- Analog I nter f ace

Comp.Sys. 1

Comp.Sys. 2Modem Modem

DigitalSerialRS-232C

DigitalSerialRS-232C

AnalogITU V.90

POTS



Di gital-to-Di gital I nter f ace

Comp.Sys. 1

Comp.Sys. 2DSLRouter DSLRouter

DigitalIEEE 802.3

DigitalIEEE 802.3

DigitalInternet



Di gital to Di gital I nter f ace

Network 2 Network 1Router



Di gital to Di gital I nter f ace

In general, in digital to digital interface,protocol conversion takes place² Example: Connecting an Ethernet network

to a campus backbone network using arouter



End of Module




Module

Overview of Digitization ofInformation



Di gitization of I nfor mation

Information need to be digitized forcomputer processing and thetransmission of information



C om ponents of I nfor mation

Alphanumeric data

Image

Audio

Video



Di gital I nfor mation Pr ocessing

DataAudio

Image

Video

DigitizedandEncoded

DigitalTransmission



The Advanta ges of Di gitization

Information can be processed by thecomputer

Easy transmission of information overthe Internet and other computernetworks

Minimize loss of quality duringtransmission



End of Module



The Basis

Alphanumeric data is digitized usingwell established coding systems



C odes Used in the Di gitization

O f Data Coding Standards

² ASCII

² EBCDIC

² Unicode

ASCII Code example

² A=1000001



The U nicode

Replaced the ASCII coding system inmicrocomputers

All variations of the Latin language

² English

² European languages

Chinese and Japanese

18 Major languages

² Eg: Tamil



U nicode Possibilities

It is a 16-bit code as opposed to theASCII code that is basically an 8-bit

code

It is therefore possible to have 65,536variations in UNICODE



C ommunication With ASC II And EBCD

I C

Latin languages can be transmitted incoded form

Other languages

² Bit-mapped image transmission

² Requires considerably more bandwidth

² An exception is the use of true-type fontsto display the characters of a language notsupported by ASCII



C ommunication With U nicode

Binary encoded transmission² Latin languages

² 18 major languages

² Chinese, Japanese etc.

Transmission itself requires less

bandwidth Universal usability of software in all the

supported languages



U nicode Advanta ge in WWW

Transm

issions

Client

TamilWebSite

Internet ExplorerBrowser retrievingTamil pages on a client

supporting Unicode.

Tamil pages are transmitted in their binary encoded form.

Site created using allthe tools such as theMS-IIS.



Transmission of Tamil Pa ges asI m

a ges on WWW

ClientTamilWebSite

Internet ExplorerBrowser retrieving Tamilpages similar to images.

Binary image

transmission ofTamil pages.

Web pages scanned andstored as images.



Using Downloaded F onts to H ost

and Transm

it Tam

il Pa ges

ClientTamilWebSite

Internet Explorerretrieving Tamilpages.

Site createdwith toolssuch as MS-IIS.

Download and install

theT

amil fonts.

Binary encoded form.

Bandwidth

requirements are low.

F i L W b P



F orei gn Langua ge Web Pa geOptions

Store the page as an image

Use a font for the language, if available

Use Unicode to develop the web page



UN I CODE Usa ge

Currently all the computers supportUNICODE

Also, the operating systems and theapplications also support UNICODE

Both hardware and software support is

necessary for the successfulimplementation of UNICODE



End of Module




Module

Digitization Of Audio



Di gitization O f Audio: Overview

Take samples of audio at pre-determined time intervals known as thesampling rate

Represent the sampled audio withdigital signals

² Pulse AmplitudeModulation (PAM)

Encode signals into binary code

² Pulse Code Modulation (PCM) thatincorporates PAM as well

² Required for computer processing



Di gitization of Audio: Pulse Am

plitude Modulation (P A M)

Audio

9 8 7 6 7 9

Digital Signals mustfurther be encodedinto binary signalsfor computerprocessing and

transmission.

Sampling Interval

Di iti ti d E di f A di



Di gitization and Encoding of Audio:Pulse C ode Modulation (PC M)

PCM is a two step process

First the audio is sampled andrepresented by digital signals

The digital signals are then encoded inbinary form



Binary Encoding of Si gnals in

Pulse C ode Modulation (PC M)

9 8 7 6 5 6

1001 1000 0111 0110 0101 0110

The integer numbers have effectively beencoded into zeros and ones. The ones and zerosnow contain the audio information encoded ina form that could be processed by a computer.

PCM



Salient Points on the

Di gitization O f Audio

Sampling rate and the number of bitsused for representing the samples will

determine the quality of the audio Quality is retained in transmission

because only codes are transmitted

Audio can be recreated to the originalquality by extracting the pattern fromthe digital code



Sam pling F actors

Sampling interval determined bysampling frequency

² Measured in Hz

Sampling depth² Measured in bits

Sampling channels² Mono or stereo, for example



Sam pling Exam ple

CD quality audio² 44 KHz

² 16 Bits

² Stereo



End of Module




Module

Audio Quality, Bandwidth andStreaming



F actors A ff ecting Quality

Number of bitsused for binaryencoding.Example: 4 bits

allow1

6amplitudevariations to berepresented.

9 8 7 6 7 9

Sampling Interval



E ff ect of Sam pling F requency

Higher sampling frequency² Smaller sampling intervals

² Frequent sampling

² Better quality because the audio pattern iscaptured better

² Higher bandwidth required fortransmission

² Higher disk space required for storage

Computation of Bandwidth



C om putation of BandwidthRequirement for Transmission

Problem:² Compute the audio streaming rate for a

voice grade circuit given that the number

of bits used in the sampling is 8 Background information

² A voice grade circuit has a bandwidth of

approximately 4000 Hz General rule

² For acceptable quality, the audio must besampled at twice the frequency of the voice

rade bandwidth

R f S li t T i th



Reason for Sam pling at T wice theF requency

Two peaks in each cycle² Half of a cycle is above the datum line

² The other half of the cycle is below thedatum line

Therefore, sample the audio at twice the

frequency rate



CD Sam pling?

Sampling in this case is done for higherquality

² 44 KHz

² 16-bits

² Stereo



Pr oblem Representation

79 68 57 46 57 79

1/8000 Seconds (8000 HZ twice the frequency of the voicegrade circuit)or 2X4000 samples per second

8 bits are used enabling 256 amplitudes to

represent the humanvoice which is consideredto be adequate.



Bandwidth C om putation for V oice

Number of samples² 8000 per second

Number of bits per sample² 8

Bandwidth requirement

² 8X8000 bps = 64,000 bps

² Approximately 64K bps

64K bps is the speed of a single ISDN

B channel desi ned to carr voice



Bandwidth of V oice Circuits

Generally speaking, the bandwidthrequirement for uncompressed voice

circuit is 64 Kbps An example is the ISDN ² B channel

that was originally intended to carry

voice² Its bandwidth is 64 K bps

Examples in Audio Quality and



Exam ples in Audio Quality and Bandwidth Requirement

CD quality² 44,100 Hz, 16 bit, Stereo

² 1376K bps Radio quality

² 22,050 Hz, 8 bit, mono

²1

76K bps Telephone quality² 11,025 Hz, 8bit, mono

² 88K bps

R di Q lit d B d idth



Recor ding Quality and Bandwidth

Requirem

ent Dem

onstration



Recor ding Used in this Exam ple

Settings for recording² 11K Hz, 8 bit and mono

Audio bandwidth requirement is 88Kbps

Streaming is required to send the audio

alone over the Internet Approximate bandwidth required for

both video and audio is 133K bps



D li f I t ti O th



Delivery of I nstr uction Over the

WWW

Client

WebSite

Receive audio/video usingInternet Explorer and MediaPlayer.

Audio/Video streaming.

Store streamed audio/video using Windows Media.

28-56K bps

Streaming Classroom Lectures on



Streaming C lassr oom Lectures on CD

Bandwidth requirement as computedearlier is

Internet Ramp Bandwidth



I nter net Ram p Bandwidth

C om

putation

WWW

A T1 line operating at approximately 1.354M bpscan support approximately 10 connections in theory.

In practice, 7 connections which is 70 percent of 10connections can be supported with due considerationgiven tobandwidth bottlenecks.



Types of Multimedia Transmission

Unicasting

Multicasting

Broadcasting

Sampling Considerations In



Sam pling C onsiderations I n

C omm

unications

Sender Receiver

Digital audio transmission

Adjust quality (sampling interval and bitrepresentation) to suit bandwidth availability.



Audio F iles

Audio can be stored in different formats² Uncompressed or raw file format (wav)

² Compressed format

² Streaming formatStreamed audio is also compressed

It is also designed for real-time delivery ofaudio



Audio F ile F or mat

wav file format² Basic file format in audio storage or raw file

rm file format

² Real audio·s streamed file format² Streamed file

wma file format² Microsoft·s audio streamed file format² Streamed file

mp3 file format² Compressed file

aac file format²



End of Module




Module

Quality Retention in Digital

Transmission



Quality Retention

Quality is retained in digitaltransmission because only the codes are

transmitted Quality is subject to some deterioration

in analog transmission because the

wave pattern is transmitted



Analog Audio Transmission

Audio Priorto Transmission

Audio withInterference

Transmission

Audio After Filtering

Passage of Analog Audio Over



Passa ge of Analog Audio Over Analog Lines

AnalogAudio

Analog

Signals

AnalogSignals

AnalogAudio

Telephone

Telephone

Recreation of Audio from Analog



Recreation of Audio f r om Analog

Si gnals A difficult task

Complex algorithms are used to filter

noise etc. for better audio transmission

Signal Passage in Digital Audio



Si gnal Passa ge in Di gital Audio

Transm

issionEncode

TransmitRecreate

Decode

Audio

Audio

A Sample Digital Audio



A Sam ple Di gital Audio

Transm

ission Path

AnalogAudio

DigitalAudio

DSL

Modem

DSLM

odem

DigitalAudioAnalogAudio

SoundCard

SoundCard

DigitalNetwork



Sound Generation

Sound is recreated at destination² Using FM synthesis

² Using wave table generation Noise is not an issue in digital

communication although it is an issuein digital transmission² The reason, once again, is due to the fact

that only codes are transmitted in digitaltransmission



Better Sound Generation

Wave table generation provides bettersound reproduction that FM synthesis

Digital Advantage in Audio



Di gital Advanta ge in Audio Transmission

Only codes are transmitted

Original encoding is recreated

Original audio is reproduced

Again, sampling rate and number ofbits used in each sample will determine

the quality of audio transmitted

Digitized Signal Transmission



Di gitized Si gnal Transmission Over Analog Lines

Encode

TransmitRecreate

Decode

Audio

Audio

Sampled Signals

Sample Digital Audio Transmission



Sam ple Di gital Audio Transmission Path Over Analog Lines

AnalogAudio

DigitalAudio

Modem

Modem

DigitalAudioAnalogAudio

SoundCard

SoundCard

AnalogPSN



Audio Transmission I n WWW

Client

WebSite

Receive audio usingInternet Explorerand Windows Media Player.

Audio stream over analog/digital line.

Real-time audiobroadcast supportusing Windows Mediastreaming server module.



Analog to Di gital C onverter

A to D and D to A converter The chip that is responsible for this

conversion is known as the DSP (DigitalSignal Processor) chip

It is used in sound cards, modems etc.wherever there is a need for A to D and D toA conversion

The mass use of this chip in various deviceshas led to a drastic drop in the price of thechip and the devices



Di gital Si gnal Pr ocessor (DSP )

DSP

DigitalAnalog



End of Module




Module

Digitization Of Image



I ma ge Di gitization

Image can be of the form black andwhite, gray scales, color

Factors that influence the digitization ofimage are as follows

² Resolution measured in pixels

² Color depth expressed in number of colorvariations

Di gitization O f I ma ge:O i



OverviewPixel

Horizontal Resolution



Di gitization of the Letter L

Number of bits

determine theamount ofinformation thatcouldbe stored.

Digitization Of Image: The



Di gitization O f I ma ge: ThePr ocess

Divide the image into a grid of pixelsthat may be considered as the sampling

points of the image Digitize information on each pixel

Store and transmit

R l ti



Resolution

Horizontal resolution² Number of horizontal pixels

Vertical resolution² Number of vertical pixels

Image resolution

² Horizontal by vertical resolution² Ex: 640 by 480

Digitization of Black and White



Di gitization of Black and WhiteI ma ge

White² A pixel lit represents a 1

Black² A pixel not lit represents a 0

Storage required per pixel² 1 bit

Storage required for 640 by 480resolution image² 640 times 480 bits = 307,200 bits = 38.4K

Bytes

Di gitization of I ma ge Using



g f g gGray Scales

A pixel may take a value between 0 and15 for 16 gray scales

A gray scale of 3 can be coded as 0011 and the others similarly using this 4digit code

The bandwidth requirement for thetransmission of a 640X480 image in thiscase is as follows:

² 640X480X4 =1

53.5K Bytes

Di iti ti f C l I



Di gitization of C olor I ma ge

Image coding² Each pixel may take a value between 0 and 255 if

256 colors are to be represented

Storage requirement² Digitizing of images requires substantial number

of bytes and hence large storage space forprocessing

Bandwidth requirement² Higher bandwidths are required to transmit color

images

Bandwidth C om putation for



I ma ge with 256 C olors

Resolution is 640X480

8 bits are required to represent 256

colors bandwidth requirement for the

transmission of one image is as follows:

² 640X480X8 = 307.2K Bytes

The E ff ect of C olor Depth and



ff f pResolution

Compare VGA, SVGA and XGA² XGA provides the highest resolution

Practical implication² More colors less resolution if bandwidth orstorage is the limiting concern

² Example 256 colors at lower resolution

16 colors at higher resolution Rule

² Higher the resolution the lower the number ofcolors available in general given the resourceconstraints such as bandwidth constraints

F actors A ff ecting Bandwidth



Requirement in I ma ge Transmission

The higher the resolution, the higher thebandwidth requirement for transmission

The higher the color re

presentation, alsoknown as color depth, higher the bandwidth

requirement

For true color, 24 (32) bits are required torepresent each pixel

The file sizes in raw image capture can thusbecome very large



End of Module




Module

Compression of Digitized Images

Compression of Digitized Images



C om pression of Di gitized I ma ges

Compression is required to reduce thesize of the image file

Large blocks of unchanged data in animage (background) offers anopportunity to compress the image

Image files are almost alwayscompressed



A F ew C om pression F or mats

GIF

JPEG

MIC (Microsoft Image Composer)

PCD (KODAK) - Used by Corel

Uncompressed file exist in the form ofbit mapped file with the extension of.BMP

Image File Format Extensions



I ma ge F ile F or mat Extensions

File formats often represent the compressionprocedure being used such as jpgrepresenting the jpeg compression technique

Examples:² Bmp ² uncompressed file format² Gif² jpg² pcd² tiff² pcx

Loss-less C om pression and



Others

Some compression formats offer loss-free compression of the image

Others sacrifice minimal loss for thesake of reduced storage and bandwidthrequirements

Fortunately, the loss is not easilydetected by the naked eye

I ma ge Transmission



C onsiderations

Sender Receiver

Adjust image to suit available bandwidth.

Adjustable features are as follows.- Resolution- Color depth

Adjusting the size also reduces the bandwidthrequirement because of a corresponding reductionin the number of pixels required to representthe image.

A Peek At Data Compression



A Peek At Data C om pression

0 0 0 0 0 0 0 0 0 0 0 - - - - - -0 1 1 1 1 1 11 «... 0

THE ABOVE CAN BE COMPRESSEDINTO = #9000$0#

² 9000 bits are compressed into 8 characters

that require approximately 64 bits fortransmission

² 9000 ZEROS ARE CODED INTO #900$0#

#600$1#

INTERPRET WITHIN THE # SIGN

600

NUMBER COUNT1

CHARACTER BEINGTRANSMITTED

C i l



C om pression Result

In the previous example, 9000 bits arecompressed into 8 characters

If 10 bits are used on the average fortransmitting each character, the 9000bits of information is now compressed

into 80 bits for transmission

Modem I m plication in I ma geT i i



Transmission

Modems also compress the data stream toachieve higher transmission speeds

Because of the fact that the images are alreadycompressed, the full speed benefit may not berealized when images are transmitted over amodem connection

An already compressed image file does not,for instance, offer itself well to furthercompression in the modem



End of Module




Module

Digitization Of Video

Di iti ti f Vid



Di gitization of V ideo

Digitization of video is an extension ofthe process of digitizing an image

It amounts to the transmission ofcertain number of still images known asframes per second

Obviously, digitized video requires

higher bandwidth for transmission andmore space for storage

Frame Rate



F rame Rate

30 frames of images per second, in general,defines continuos motion

In communications, 25 frames per second isconsidered to be continuous motion

15 frames per second is currently used invideo conferencing over digital lines foracceptable reception of video

It is also possible to engage in videoconferencing at a frame rate of 5 frames persecond

C om putation of Bandwidth for R T i i f Vid



Raw Transmission of V ideo

Image resolution is 640X480

Number of colors is 256 (8 bit)

Acceptable reception requires 15 framesper second

Therefore, the bandwidth for the raw

transmission is as follows:² 640X480X8X15 = 36.86M bps = 4.6M Bps

C om pression Standar ds Used in



the Di gitization of V ideo

MPEG 1, MPEG 2, MPEG 3 and MPEG 4

WindowsMedia Video

Real Media Indio

QuickTime

ActiveMovie AVI

St i F t f Vid



Streaming F or mats for V ideo

Various streaming formats aresupported by different vendors

² RealV

ideo Microsoft·s streaming format

² wma (WindowsMedia Audio)

² wmv (WindowsMedia Video)

² Active Streaming Format (ASF)

Apple·s QuickTime format

Etc.

Overview of V ideo Transmission



in V ideo C onf erencing

Minimum speed² 3 to 5 frames per second

Acceptable speed² 15 frames per second

Transmission techniques

² Data is compressed² Only changes to the frame are transmitted

Bandwidth Optimization in



V ideo C onf erencing

Minimize Windows for maximumefficiency

² Transmit less number of pixels inminimized form

Decrease the resolution² Has the same effect as above

Decrease the number of colorsdisplayed

C ommunication Links for V ideo



C onf erencing

Possible on analog lines using 56,000bps transmission speed but not

desirable Digital lines are preferred and the

guidelines are as follows:

² Possible at1

28k bps using ISDN lines² Acceptable at 384k bps

² 1M bps and above offer good quality videotransmission

ISDN Li S it bilit



I SDN Line Suitability

ISDN B channels can be assigned on adynamic basis depending on the

bandwidth requirement at any point intime during video conferencing

Vid C f i P d t



V ideo C onf erencing Pr oducts

Intel ProShare

CU-See Me

Picturetel

C-phone

etc.



End of Module

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