Communication System Basics

Basics of Analog Communication System are presented here.

1. Introduction to
Communication System
Mr. A. B. Shinde
Assistant Professor,
Electronics and Computer Science Engineering,
P. V. P. Institute of Technology, Sangli

2. A. B. Shinde
Contents…
•Blockschematicofcommunication
system,
•Simplexandduplexsystems
•Modesofcommunication:
–Broadcastand
–pointtopoint
•Necessityofmodulation,
•Classificationofmodulation,
•Samplingtheoremand
•Pulseanalogmodulation,
•Multiplexing:TDMandFDM
2

3. A. B. Shinde
Communication ?
Transfer of information from one place to another.
What is Information ?
What is Data ?
Is there any difference between dataand Information ?
3

4. Communication System

5. A. B. Shinde
Intro to Communication System
•Communicationsystemhasfiveblocks.
•Informationsource,Transmitter,Channel,Receiveranddestination.
•ThecommunicationinelectricalformtakesplacemainlyinTransmitter,
Channel,Receiverblocks.
5
Black diagram of a communication system

6. A. B. Shinde
Intro to Communication System
InformationSource:
•Informationisaverygenericwordsignifyingasanythingintended
forcommunication(thought,news,feeling,visualscene&soon).
•Theinformationsourceconvertsthisinformationintoaphysical
quantity(e.g.thoughtstospeechsignal)
•Weneedtoconvertthemessagesignaltotheelectricalform,
whichisachievedusingasuitabletransducer.
•Transducerisadevicewhichconvertsenergyinoneformtothe
other.
6

7. A. B. Shinde
Intro to Communication System
Transmitter:
•Theobjectiveofthetransmitteristocollecttheincomingmessage
signalandmodifyitinasuitableform(ifneeded),suchthat,itcan
betransmittedviathechosenchanneltothereceivingpoint.
•Functionalityofthetransmitterismainlydecidedbythetypeor
natureofthechannelchosenforcommunication.
•Transmitterblockinvolvesseveraloperationslikeamplification,
generationofhigh-frequencycarriersignalandmodulationetc.
7

8. A. B. Shinde
Intro to Communication System
Channel:
•Channelisthephysicalmediumwhichconnectsthetransmitter
andreceiver.
•Thephysicalmediumincludescopperwire,coaxialcable,fiber
opticcable,waveguideandfreespaceoratmosphereetc.
8

9. A. B. Shinde
Intro to Communication System
Receiver:
•Thereceiverreceivestheincomingmodifiedversionofthemessage
signalfromthechannelandprocessesittorecreatetheoriginal
(nonelectrical)formofthemessagesignal.
•Receiverincludesprocessingstepslikereception,amplification,
mixing,demodulationandrecreationofmessagesignal.
9

10. A. B. Shinde
Intro to Communication System
Destination:
•Thedestinationisthefinalblockinthecommunicationsystem
whichreceivesthemessagesignalandprocessesittocomprehend
theinformationpresentinit.
•Usually,humanswillbethedestinations.
10

11. Types of Communication

12. A. B. Shinde
Types of Communication
There are 3 types of Communication Systems.
Simplex
Duplex
Half –Dulex
12

13. A. B. Shinde
Types of Communication
Simplex:
Themostbasictypeofserviceisknownassimplex.
Thisserviceprovidesone-waycommunication.
Itisaunidirectionalcommunication
ExamplesofthistypeofserviceareTVdistribution.
13

14. A. B. Shinde
Types of Communication
Duplex:
Mostnetworkstransferdataintwodirectionsandareknownas
duplexcommunicationslinks.
Itistwo-waydirectionalcommunicationsimultaneously.
SometimestheyarecalledasFullDuplex
14

15. A. B. Shinde
Types of Communication
Half-duplex:
Ahalf-duplexnetwork,isonewithafullduplexphysicallayer,but
thatonallowsthenetworktobeusedononedirectionatanyone
time.
Itistwo-waydirectionalcommunicationbutoneatatime.
15

16. A. B. Shinde
Types of Communication
Comparison:
16
Parameters Simplex HalfDuplex FullDuplex
The direction of
communication
Simplexmodeisauni-
directional
communication.
HalfDuplexmodeisa
two-waydirectional
communicationbut
oneatatime.
FullDuplexmodeisa
two-waydirectional
communication
simultaneously.
Sender and Receiver
Insimplexmode,
Sendercansendthe
databutthatsender
can’treceivethedata.
InHalfDuplexmode,
Sendercansendthe
dataandalsocan
receivethedatabut
oneatatime.
InFullDuplexmode,
Sendercansendthe
dataandalsocan
receivethedata
simultaneously
Channel usage
Usageofonechannel
forthetransmissionof
data.
Usageofonechannel
forthetransmissionof
data.
Usageoftwochannels
forthetransmissionof
data.

17. A. B. Shinde
Types of Communication
17
Parameters Simplex HalfDuplex FullDuplex
Performance
Thesimplexmode
provides less
performancethanhalf
duplexandfullduplex.
TheHalfDuplexmode
provides less
performancethanfull
duplex.
FullDuplexprovides
betterperformance
thansimplexandhalf
duplexmode
Bandwidth Utilization
Simplexutilizesthe
maximumofasingle
bandwidth.
The Half-Duplex
involves lesser
utilizationofsingle
bandwidthatthetime
oftransmission.
The Full-Duplex
doublestheutilization
of transmission
bandwidth
Suitable for
when thereis
requirementoffull
bandwidth for
deliveringdata.
when thereis
requirementofsending
datainbothdirections,
butnotatthesame
time.
when thereis
requirementofsending
andreceivingdata
simultaneouslyinboth
directions
Examples Keyboardandmonitor.Walkie-Talkies. Telephone

18. Modes of Communication

19. A. B. Shinde
Modes of Communication
Modes of Communication
Broadcast Communication
Point to Point Communication
19

20. A. B. Shinde
Modes of Communication
BroadcastCommunication:
Inabroadcastsystemthereisonetransmitterandmorethanone
receivers.Atransmitterprocessestheincomingsignalandmakesit
suitablefortransmissionthroughachannel.
Areceiverreceivesthesignalandextractsthemessageorcontents
fromthesignalatsignaloutput.
Consideringthebroadcastcommunicationsystem,theradioand
televisionareexamplesofbroadcastingsystems.
20

21. A. B. Shinde
Modes of Communication
BroadcastCommunication:
Consideringthebroadcastcommunicationsystem,theradioand
televisionareexamplesofbroadcastingsystems.
Fordifferentbroadcastingsystemswehavedifferentfrequencybands.
ForstandardAMbroadcastthefrequencybandis540−1600kHz.
ForFMbroadcastthefrequencyrangeisfrom88−108MHz.
Fortelevisionbroadcastingsystemswehavedifferentrangesoffrequencies
dependingonthetypeover50MHzto900MHz.
Televisionbroadcastandsatellitecommunicationsystemsusespacewavemode
ofpropagation
21

22. A. B. Shinde
Modes of Communication
Point-to-pointCommunication:
Point-to-pointisaformofcommunicationprovidingadirectroutefrom
onefixedpointtoanother.
Here,thereexistsadedicatedlinkbetweentwonodes.Thereisone
transmitterandonereceiver
Inthistypeofsystem,thesmallestdistancehasmostimportanceto
reachthereceiverterminal.
Here,thecommunicationgivessecurityandprivacytothetransmitted
signalbecausethechannelofcommunicationisnotshared.
22

23. A. B. Shinde
Modes of Communication
Point-to-pointCommunication:
Anexampleisatelephonecall,inwhichonetelephoneisconnectedto
another.
ThePointtoPointProtocol(PPP)isusedtocreatedirectcommunication
betweentwonodesinthenetwork.Itauthenticatestheconnections,
compressesthemandtransmitsthemafterencryption,thusgiving
privacy.
PPPisdesignedprimarilytolinktwonetworksandconnectionsareable
tohavebidirectionalfunctionssimultaneously
23

24. Modulation

25. A. B. Shinde
Modulation
Thetermmodulatemeanstoregulate.
Theprocessofregulatingismodulation
Forregulationweneedonephysicalquantitywhichistoberegulated
andanotherphysicalquantitywhichdictatesregulation.
•Thesignaltoberegulatedistermedascarrier.
•Thesignalwhichdictatesregulationistermedasmodulatingsignal.
25

26. A. B. Shinde
Modulation
NeedforModulation:
•LengthofAntenna:
•Fortheeffectivetransmissionofasignal,theheighthoftheantenna
shouldbeλ/4inlength.
•Thelow-frequencymessagesignalhasaveryhighvalueofλwhichwill
requireaveryhighantenna(practicallynotpossible).
•Forexample:
•Ifwehavetotransmitasignalof20kHzthenλ=C/fandheightofthe
antennah≈λwhereCisthewavevelocity,hereC=3×10
8
m/s.
•h≈λ=(3×10
8
)/(20×10
3
)=15km.
26

27. A. B. Shinde
Modulation
NeedforModulation:
•NarrowBandingofSignal
•Anaudiosignalusuallyhasafrequencyrange(20Hzto20kHz),ifitis
directlytransmittedthentheratioofhighesttothelowestfrequency
becomes(20kHz/20Hz)=1000.
•Butifthisaudiosignalismodulatedoveracarriersignalof
frequency1000kHzthentheratioofhighesttothelowestfrequency
becomes:(1000kHz+20kHz)/(1000kHz+20Hz)≅1.2
•Hence, we need modulation to convert a wideband signal into a narrow
band signal.
•
27

28. A. B. Shinde
Modulation
NeedforModulation:
•FrequencyMultiplexing
•Allsoundisconcentratedwithintherangefrom20Hzto20kHz,sothat
allsignalsfromthedifferentsourceswouldbeinseparablymixedup.
•Itispracticallynotpossibletodistinguishbetweenthedifferentaudio
signalswhentransmittedsimultaneously.
•Hence,eachofthesesignalsistranslatedtoalow-frequencyrange
beforetransmissionwhichmakesitquiteeasiertorecoverthemand
distinguisheachofthemfromoneanotheratthereceiver’send.
28

29. A. B. Shinde
Modulation
NeedforModulation:
•EffectivePowerRadiatedByAntenna
•Powerradiatedbyanantenna∝(l/λ)
2
wherelisthelengthoftheantennaand
λisthewavelengthofthesignalwhichistobetransferred.
•Thisrelationclearlyshowsthatwhensignalshavingalowfrequencyand
highwavelengthistransmitteddirectlythepowerradiatedbythe
antennaisverylowandthesignalwillvanishaftertravelingsome
distance.
•Hence,totransmitsuchsignalsoverlongdistances,wesuperimpose
theselow-frequencysignalsoverthehighfrequencycarriersignalsothat
thepowerradiatedbytheantennaofthesamelengthwillbeverylarge.
29

30. A. B. Shinde
Modulation
Classification of Modulation:
Analog Modulation
Amplitude Modulation
Angular Modulation
Frequency Modulation
Phase Modulation
Digital Modulation
30

31. A. B. Shinde
Modulation
31

32. A. B. Shinde
Modulation
•AmplitudeModulation(AM):
•InAM,theamplitudeofthecarrierwaveisvariedinproportiontothe
messagesignal,andtheotherfactorslikefrequencyandphaseremain
constant.
32

33. A. B. Shinde
Modulation
Frequencymodulation(FM):
Frequencymodulation(FM)variesthefrequencyofthecarrierin
proportiontothemessageordatasignalwhilemaintainingother
parametersconstant.
TheadvantageofFMoverAMisthegreatersuppressionofnoise.
33

34. A. B. Shinde
Modulation
PhaseModulation(PM):
Inphasemodulation,thecarrierphaseisvariedinaccordancewiththe
datasignal.
Inthistypeofmodulation,whenthephaseischangeditalsoaffectsthe
frequency,sothismodulationalsocomesunderfrequencymodulation.
34

35. Sampling Theorem

36. A. B. Shinde
Sampling Theorem
Analogsignalsarecontinuousintimeanddifferenceinvoltagelevelsfor
differentperiodsofthesignal.
Theamplitudekeepschangingalongwiththeperiodofthesignal.
Ananalogsignalcanbeconvertedtodigitalformusingthesampling
technique.
Theoutputofthistechniquerepresentsthediscreteversionofitsanalog
signal.
36

37. A. B. Shinde
Sampling Theorem
•Definition
•Thesamplingtheoremisdefinedastheconversionofananalogsignal
intoadiscreteformbytakingthesamplingfrequencyastwicetheinput
analogsignalfrequency.
Fm = Input signal frequency
Fs = Sampling signal frequency.
•Theoutputsamplesignalisrepresentedbythesamples.
•Thesesamplesaremaintainedwithagap,thesegapsaretermedas
sampleperiodorsamplinginterval(Ts).
•Andthereciprocalofthesamplingperiodisknownas“sampling
frequency”or“samplingrate”.
Sampling frequencyFs=1/Ts
37

38. A. B. Shinde
Sampling Theorem
38

39. A. B. Shinde
Sampling Theorem
•NyquistCriteria:
•Ifthesamplingfrequency(Fs)equalstwicetheinputsignalfrequency
(Fm),thensuchaconditioniscalledtheNyquistCriteriaforsampling.
•Whensamplingfrequencyequalstwicetheinputsignalfrequencyis
knownas“Nyquistrate”.
Fs=2Fm
•Ifthesamplingfrequency(Fs)islessthantwicetheinputsignal
frequency,suchcriteriacalledanAliasingeffect.
Fs<2Fm
39

40. A. B. Shinde
Sampling Theorem
40

41. A. B. Shinde
Sampling Theorem
AliasingEffect:
If,aninformationbearingsignalisnotstrictlyband-limited,somealiasing
isproducedbythesamplingprocess.
Aliasingreferstothephenomenonofahighfrequencycomponentinthe
spectrumofthesignalseeminglytakingontheidentityofalower
frequencyinthespectrumofitssampledversion.
41

42. A. B. Shinde
Sampling Theorem
CorrectiveMeasuresforAliasing:
Priortosampling,alow-passanti-aliasingfilterisusedtoattenuatethose
highfrequencycomponentsofthesignalthatarenotessentialtothe
informationbeingconveyedbythesignal.
ThefilteredsignalissampledatarateslightlyhigherthantheNyquist
rate.
42

43. Pulse Analog Modulation

44. A. B. Shinde
Pulse Analog Modulation
Inanalogmodulationsystems,someparameterofasinusoidalcarrieris
variedaccordingtotheinstantaneousvalueofthemodulatingsignal.
InPulsemodulationmethods,thecarrierisnolongeracontinuoussignal
butconsistsofapulsetrain.
Someparameterofwhichisvariedaccordingtotheinstantaneousvalue
ofthemodulatingsignal.
44

45. A. B. Shinde
Pulse Analog Modulation
TypesofPulseModulation
45

46. A. B. Shinde
Pulse Amplitude Modulation
Theamplitudeofthepulsesofthecarrierpulsetrainisvariedin
accordancewiththemodulatingsignal,thatisamplitudeofthepulses
dependsonthevalueofm(t)duringthetimeofpulse.
46

47. A. B. Shinde
Pulse Amplitude Modulation
InfactthepulsesinaPAMsignalmayofFlat-toptypeornaturaltypeor
idealtype.
TheFlat-topPAMismostpopularandiswidelyused.Thereasonfor
usingFlat-topPAMisthatduringthetransmission,thenoiseinterferes
withthetopofthetransmittedpulsesandthisnoisecanbeeasily
removedifthePAMpulseasFlat-top.
InnaturalsamplesPAMsignal,thepulsehasvaryingtopinaccordance
withthesignalvariation.Suchtypeofpulseisreceivedatthereceiver,it
isalwayscontaminatedbynoise.Thenitbecomesquitedifficultto
determinetheshapeofthetopofthepulseandthusamplitude
detectionofthepulseisnotexact
47

48. A. B. Shinde
Pulse Amplitude Modulation
TransmissionBandwidthofPAM:
InPAMsignalthepulsedurationτisassumedtobeverysmallcompared
totimeperiodTsbetweenthetwosamples
τ < Ts
Ifthemaximumfrequencyinthemodulatingsignalx(t)isfmthen
samplingfrequencyfsisgivenby
fs>=2fmor Ts <= 1/2fm
Therefore,transmissionbandwidth>=fmax
Butfmax=1/2τ
B.W>=1/2τ
B.W>=1/2τ>>fm
48

49. A. B. Shinde
Pulse Amplitude Modulation
DrawbacksofPAMsignal:
ThebandwidthrequiredforthetransmissionofaPAMsignalisverylarge
incomparisonwithmodulatingsignalfrequency.
SincetheamplitudeofthePAMpulsesvariesinaccordancewiththe
modulatingsignalthereforetheinterferenceofnoiseismaximumina
PAMsignal.Thisnoisecannotberemovedeasily.
SincetheamplitudeofthePAMpulsesvaries,therefore,thisalsovaries
thepeakpowerrequiredbythetransmitterwithmodulatingsignal.
49

50. A. B. Shinde
Pulse Width Modulation
InPWM,Widthofthepulsesofthecarrierpulsetrainisvariedin
accordancewiththemodulatingsignalbuttheamplitudeofthesignal
remainsconstant.
50

51. A. B. Shinde
Pulse Width Modulation
AdvantagesofPWM:
Noiseisless,sinceinPWM,amplitudeisheldconstant.
Signalandnoiseseparationisveryeasy
PWMcommunicationdoesnotrequiredsynchronizationbetween
transmitterandreceiver.
DisadvantagesofPWM:
InPWM,pulsesarevaryinginwidthandthereforetheirpowercontents
arevariablethisrequiresthatthetransmittermustbeabletohandlethe
powercontentofthepulsehavingmaximumpulsewidth.
LargebandwidthisrequiredforthePWMascomparedtoPAM
51

52. A. B. Shinde
Pulse Position Modulation
PulsePositionModulation(PPM)isananalogmodulatingschemein
whichtheamplitudeandwidthofthepulsesarekeptconstant,whilethe
positionofeachpulsevariesaccordingtotheinstantaneoussampled
valueofthemessagesignal.
52

53. A. B. Shinde
Pulse Position Modulation
AdvantagesofPPM:
LikePWM,inPPM,amplitudeisheldconstantthuslessnoise
interference.
Signalandnoiseseparationisveryeasy
Becauseofconstantpulsewidthsandamplitudes,transmissionpower
foreachpulseissame
DisadvantagesofPWM:
Synchronizationbetweentransmitterandreceiverisrequired.
LargebandwidthisrequiredforthePPMascomparedtoPAM
53

54. A. B. Shinde
Comparison
PAM PWM PPM
Amplitudeisvaried Widthisvaried Positionisvaried
Bandwidthdependson
thewidthofthepulse
Bandwidthdependson
therisetimeofthepulse
Bandwidthdependson
therisetimeofthepulse
Instantaneoustransmitter
powervarieswiththe
amplitudeofthepulses
Instantaneoustransmitter
powervarieswiththe
amplitudeandwidthof
thepulses
Instantaneoustransmitter
powerremainsconstant
withthewidthofthe
pulses
Systemcomplexityishigh
SystemcomplexityislowSystemcomplexityislow
Noiseinterferenceishigh
NoiseinterferenceislowNoiseinterferenceislow
Itissimilartoamplitude
modulation
Itissimilartofrequency
modulation
Itissimilartophase
modulation
54

55. Multiplexing

56. A. B. Shinde
Pulse Position Modulation
Multiplexingisatechniqueofcombiningmorethanonesignalovera
sharedmediumchannel.
Types:
TDM
FDM
CDM
56

57. A. B. Shinde
Time Division Multiplexing
Thishappenswhenthedatatransmissionrateofmediaisgreaterthan
thatofthesource,andeachsignalisallottedadefiniteamountoftime.
Theseslotsaresosmallthatalltransmissionsappeartobeparallel.
Intime-divisionmultiplexing,allthesignalsoperatewiththesame
frequencyatdifferenttimes.
57

58. A. B. Shinde
Time Division Multiplexing
TDMATransmission
58

59. A. B. Shinde
Time Division Multiplexing
Types:
•SynchronousTDM:
•Thetimeslotsarepre-assignedandfixed.Thisslotisevengivenifthe
sourceisnotreadywithdataatthistime.Inthiscase,theslotis
transmittedempty.
•Asynchronous(orstatistical)TDM:
•Theslotsareallocateddynamicallydependingonthespeedofthesource
ortheirreadystate.Itdynamicallyallocatesthetimeslotsaccordingto
differentinputchannels’needs,thussavingthechannelcapacity.
59

60. A. B. Shinde
Frequency Division Multiplexing
Here,numberofsignalsaretransmittedatthesametime,andeach
sourcetransfersitssignalsintheallottedfrequencyrange.
Thereisasuitablefrequencygapbetweenthetwoadjacentsignalsto
avoidover-lapping.
60

61. A. B. Shinde
Frequency Division Multiplexing
Sincethesignalsaretransmittedintheallottedfrequenciessothis
decreasestheprobabilityofcollision.
Thefrequencyspectrumisdividedintoseverallogicalchannels,inwhich
everyuserfeelsthattheypossessaparticularbandwidth.
Anumberofsignalsaresentsimultaneouslyatthesametimeallocating
separatefrequencybandsorchannelstoeachsignal.
61

62. A. B. Shinde
TDM Vs FDM
62

63. This presentation is published only for educational purpose
[email protected]