2022期末通信原理考題A及題解-2023修改整理

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電子科技高校2022至2022學(xué)年第1學(xué)期

>課程考試題(120分鐘)考試日期2022年1月10日

1.(20Points)BlankFilling:

1)ThethreebasicoperationsofthegenerationforPCMsignalare__sampling_,___quantizing__,__coding___.

2)Allcommunicationsystemsinvolvethreemainsubsystems:__Transmitter__,channeland_Receiver__.

3)Iftheanalogsignalis)10000

42sin()(tttsππ+?=,theminimumsamplingrateis_20kHz_.4)Ifthedatarateis100kbps,thefirstnullbandwidthfortheunipolarNRZsignal,thepolarNRZsignalandtheManchesterNRZsignalare__100kHz___,__100kHz_,___200kHz__separately.

5)FornoISI,andthe6dBbandwidthoftheraisedcosine-rollofffilter,f0,isdesignedtobe50kHz,thesymbolrateofcommunicationsystemis_100k_baud.

6)IftheAMsignalis)100002cos()]42cos(5.01[5)(ttts??+=ππ,itscomplexenvelopesignalis_)]42cos(5.01[5)(ttg?+=π_.

7)Twomaincompressionlawsfornon-uniformquantizingare:__u__-law,___A__-law.8)Assumethattheinputsignalsis

0()[cos][U(t)-U(t-T)]stttw=.Whentheinputnoiseiswhite,theimpulse

responseofthematchedfilterh(t)=___)]()())[(cos()(00000TttUttUtttt+ω___andtheoptimumsamplingtime=0t__T__.

9)Ifthebandwidthofmodulatingsignalis50kHz,thetransmissionbandwidthforAM、DSB-SC、SSB、signalsare_100kHz__,__100kHz__,__200kHz__separately.

10)IfthePSDofs(t)is[]

2

2222)4(12cos16)(fTf

TTAfbbbcg-=ππp

2.(10Points)Assume

()mtisaunipolarNRZsignaloccurringatarateof1000bits/s(Thepeakvalues

ofwhichis1V,andtheprobabilityofobtainingeitherabinary1or0is1/2).TheOOKsignalis

()()cosccstAmttω=,where1cAV=.

(a)EvaluatethePSDoftheOOKsignal.Assumeacarrierfrequencyof10KHz.（4分）

(b)PlotthePSDoftheOOK（2分）signalandindicatethevalueofthefirstnull-to-nullbandwidth.（1

分）

(c)EvaluatethespectralefficiencyfortheOOKsignal.（3分）

Solution:

(a)()()cosccstAmttω=,m(t)為單極性()()cgtAmt=

()sin()()bbbbfTtftFfTTfTππ??

=?=???

∏

2

2

:01,22

10,2

cnnk

nForkAaaaandI+=???===?

???依概率依概率

2

2

2

1

11(0)()0222c

nniiciA

RaaPA===?+?=∑

:0Fork≠,()[][][]2

4

c

nnknnkA

RkEaaEaEa++===

()2

2

,02

,04

ccAkRkAk?=??=??≠??(

)(

)()2

2

2

2

2

1

()1()4111()()

44

4

sinsinsincbgnb

bcbb

b

ATnb

PffTTb

ATTbbffTb

b

fTfTfTfTfTfTδδδππππππ∞

=-∞

??=

+-

????

??=

+=+???

?

??∑

???

????

????

?

?

3

311/1010bTRms==

=()(

)2

2

1

()[()()]

4

1()()16sin()sin()()()sggccbb

ccPfPffPffcbcbTTffffcbcbffTffTffTffTδδππππ=-+--?

???

=++-++??

????

-+??????-+?

???

(b)

2nullBKHz=

(c)1/1//22

nullRKbsbsHzBKHzη=

==

3.(10Points)Ananalogsignalwiththebandwidthof3400HzistobetransmittedoveraPCMsystem.Thenumberofquantizingstepsis6

4.Assumethechannelbandwidthis15KHz.(a)Findtheminimumsamplingrate.（4分）

(b)DeterminetheminimumbitraterequiredinthePCMsignal.（3分）

(c)Assumetheoverallequivalentsystemtransferfunctionisoftheraisedcosine-rollofftype.Whenweuse4-levelsignalforsendingdata,isthereISI？（3分）

Solution

a.2234006800sfBHz==?=

b.

646

6680040.8/sMnRnfKbs

=→===?=

c.20.42302channelR

DKBdBKHz=

=<=()230

115110.471220.4

TTDBBrKHzrD=+=→=-=-=

So,wecanrealizingzeroISItransmission.

4.(10Points)Anmodulatedsignalisdescribedbythequestion]2sin102cos[100)(tftftsmcππ+=wherefc=10MHz,fm=1000Hz.

(a)EvaluatethepercentageofAM.

(b)Assumethats(t)isanFMsignal,findthefrequencymodulationindexandthetransmissionbandwidth.

(c)Assumethats(t)isaPMsignal,findthepeakphasedeviationandthephasemodulationindex.(d)Assumethats(t)isfedintoa50-Ωload,evaluatetheaveragepowerintheload.

解：(a)0

(b)Hzdt

tdFt

ftm10000})(max{212sin10)(==

?=θππθkHzfBfFmfTmf221000)110(2)1(2101000

10000

=?+=+===?=

ββ

(c)1010=?==?θβθPrad

(d)WAPc10050

21005022

2=?=?=

5.(10Points)Ifthebinarybasebandsignalispassedthrougharaisedcosine-rollofffilterwith50%rollofffactorandisthenmodulatedontoacarrier,thedatarateis32kbits/s.Evaluate(a)TheabsolutebandwidthofresultingQPSKsignal.

(b)TheapproximatebandwidthofaresultingFSKsignalwhenthemarkfrequencyis50kHzandthespacefrequencyis60kHz.Solution:

(a)

(1)(1)22baseband

DR

Brrl

=+=+where2=lforQPSK320002(1)(10.5)242

Tbaseband

RBBrkHzl==+=+=

(b)

1222()(1)TbasebandBFBffRr=?+=-++

(6000050000)32000(10.5)58kHz=-+?+=

6.（10分）Abinarydatastream{1011010010100001001011}istransmittedusingπ/4QPSKsignal,andthefirstbitontheleftisfirstpassedintothemultilevelsystem,thedatarateisR.Assumethephaseshiftπ/4for00,-π/4for01,+3π/4for10,-3π/4for11.Evaluate(a)calculatethecarrierphaseshift.（2.5分）

(b)whatistheminimumtransmissionbandwidth?（2.5分）

(c)Assumethebasebandsignalispassthrougharaisedcosine-rollofffilterwitha50%rollofffactorfirst,whatisthetransmissionbandwidth?（2.5分）(d)Whatisthespectrumefficiency?（2.5分）Solution:

(a)Thecarrierphaseshiftis

Fromthedescriptionofπ/4QPSK,usethetableshownatthefollowing:

Sothecarrierphaseis,assumetheinitialphaseis0

(b)Theminimumtransmissionbandwidthis:

Whenthewaveshapeissinc(x)typefunction,wecangettheminimumtransmissionbandwidth

02(1)2

4

TrDR

D

RBr===

+=

(c)Assumethebasebandsignalispassthrougharaisedcosine-rollofffilterwitha50%rollofffactorfirst,thetransmissionbandwidthis:

0.523(1)2

8

TrDR

D

RBr===

+=

(d)Thespectrumefficiencyis

For(b):44T

RR

RBη===

For(c):833

8

TRRRBη===

7.(10Points)Thecommunicationsystemisshowninthefollowingfigure,findthe(S/N)forthereceiveroutput.

(()cos210mtπ=?()

outmt10cos210t?n(t)

NoisePSD1mW/Hz

Solution:

()10coscoscstt