2005-06-1

PrintedPages- 5 EC - 607

(FollowingPaperID andRollNo.tobefilledinyourAnswerBook)I I I I I

Roll No.

B.Tech.

SIXTH SEMESTER EXAMINA nON, 2005-2006

COMMUNICATION ENGINEERING

'---nme : 3 Hours ..Total Marks: 100

Note: (i)

(ii)

(iii)

AttemptALL questions.

All questionscarryequalmarks.

In caseof numerical problemsassumedatawhearevernot provided.

(iv) Beprecisein your answer.

1. Attemptanyfour partsof thefollowing: (5x4=20)

(a) EvaluatetheFouriertransformof the followingsignalg(t)=t exp(- t) cas(2'ITfct)

wherefe is a constant.

(b) In DSB systemthecarrieris c(t)=A cas (2'ITfet)andthemessagesignalis givenby m(t)=sine(t).Findthefrequencydomainrepresentationandthebandwidthof themodulatedsignal.

EC - 607 1 [Turn Over

,,-,..--~------~--~~-------------------------------------

(c) A SSBAM signalis generatedbymodulatingan800 kHz carrier by the signal m(t) = cos(2000'TTt)+2 sin(2000'TTt). Theamplitudeof thecarrieris Ac=100.Determinethetime-domainexpressionof themodulatedsignal.

(d) Describebriefly the operationof the RingmodulatortogeneratetheDSB-SCsignal.

(e) An anglemodulatedsignalhastheform

s(t) =100cos((2X 107'TTt)+4 sin (2000'TTt))

Determinetheaveragetransmittedpower,and Vpeakfrequencydeviation.Is thisanFM oraPMsignal? Explain.

(f) DescribebrieflytheindirectmethodofgenerationofFM signals.

:2. Attemptanyfour partsofthefollowing: (5x4=20)

(a) StateandprovetheParseval'spropertyof theFouriertransform.

(b) Supposeanamplifierisdesignedofthreeidenticalstages,eachofwhichhasa gainof Gi=5 andanoisefigureFi =6; i =1,2,3.Determinetheoverallnoisefigure(in dB)of thecascadeof thethreestages.Derivetheexpressionused for yourcalculation. V

(c) A signal g(t) = cos (5'TTt) +0.5cos (10'TTt) isinstantaneouslysampledwithsampleperiodTs'FindthemaximumallowablevalueforTs'

(d) DescribebrieflythemethodofgenerationofPAMsignals.

~r_"n7 ?

(e) Describebriefly the Pulse Width Modulationtechnique.

(f) What do you meanby under-sampling?Describebriefly the aliasing effectin theunder-samplingprocess.

3. Attemptany twopartsof thefollowing: (lOx2=20)

(a) (i) Discuss briefly the functions of a (3)compander and an expander in a

~ nonunifromquantizer.

(ii) Show thatfor a sinusoidalmodulating (5)signal,theoutputsignal-to-quantizationnoiseratioofauniformquantizeris(1.8+6R) dB,whereR is thenumberof bitspersampleusedintheconstructionofbinarycodes.

(iii) What is theManchestercode? Explain (2)with a suitableexample.

(b) Describebrieflytheoperationof an AdaptiveDifferentialPulseCodeModulationsystem.

(c) A PCM system uses a uniform quantizerfollowedbya7-bitbinaryencoder.Thebitrateof thesystemis equalto50x 106bits/sec.

(i) What is the maximum message (3)bandwidthforwhichthesystemoperatessatisfactorily? -J

(ii) Determine the output signal to (7)quantizationnoiseratiowhenafull-loadsinusoidalmodulatingwaveoffrequency1 MHz is appliedtotheinput.

pr -1107 3

4. Attemptany twopartsof thefollowing: (10x2=20)(a) Sixindependentmessagesourcesofbandwidths

W, W, 2W, 2W, 3W and 3W Hz are to betransmittedonaTimeDivisionMultiplexedbasisusinga commoncommunicationchanneL(i) Setup a schemefor accomplishingthe (7)

multiplexing'requirement,with eachmessagesignalsampledaNyquistrate.

(ii) Determinetheminimumtransmission (3)bandwidthrequiredforthetransmission

.of themultiplexedsignalthroughthechannel.

(l?) (i) Draw thewaveformof the co~erent (3)QPSKsignalcorrespondingtotheinputdatasequence:011010001.

(ii) Derivean expressionfor theimpulse (7)response of a matched filtercorrespondingto any arbitraryinputsignalg(t) ; O$;t$;T.

(c) Discussbrieflytheoperationof thetransmitterandreceiverofanoncoherentPSKsystem.Alsoderiveanexpressionfor theprobabilityof errorof thereceiver.

5. Attemptany twopartsof thefollowing: (10x2=20)

(a) (i) A Source has an alphabet (3){aI'a2'a3'a4,as,a6}withcorrespondingprobabilities{0.1,0.2,0.3,0.05,0.15,0.2}. \Findtheentropyofthesource.Comparethis entropy with the entropy of auniformlydistributedsourcewith thesamealphabet.

(ii) Showthat:I(X; Y)=H(X)+H(Y)- H(X,Y) (7)

EC - 607 4 [Turn Over

(b) Considera sequenceof symbolsemittedby asourcewiththeirprobabilitiesasgivenbelow:Symbol xl x2 x3 x4 xS x6 x7 x8Probability0.18 0.18 0.14 0.13 0.11 0.10 0.10 0.06

Determinethecodewordsof thesymbolsusingShannon-Fanocodingtechnique.Alsodeterminetheaveragecode-wordlength. '

(c) DesignaHuffmancodeforasourcewithnoutputletters and corresponding probabilities

{l 1 1 l}2'22'....,2n-1'2!l . Showthattheaveragecoq.ewordlengthforsuchasourceisequaltottlesourceentropy.

-000-

EC - 607 5