Chuong5-Dieu Che So


2/94

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1 Cc k thu t i u ch t ng t

Trong k thut thng tin v tuyn in, khi mun truyn thng tin i xa ngi taphi chuyn tn s ca tn hiu tin tc lnmt tn s cao hn rt nhiu.Phng php thc hin chuyn ph ca tn hiu tin tc ln vng ctn s cao hn

l iu ch (iu ch bin , iu tn, iu pha), cc mch trn tn. pha my thuphi c mt qu trnhchuyn i ngc li, qu trnh l tch sng (gii iu ch).


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4/94

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1.1 i u bin AM(Amplitude Modulation)

iu bin l qu trnh lm cho bin ti tinbin i theo tintc.

n gin, gi thit tin tc u S v ti tin u t u l dao ng iu ho v tn s tin tc bin thin t Smin Smax, ta c:


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H s iu ch phi tho mn iu kin m 1 . Khi m > 1 thmch c hin tng qu iu ch lm chotn hiu b mo trm trng. (th hin nh

hnh bn )

th thi gian ca tin tc v tn hiu iu bin khi m 1


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Nh vy, ngoi thnh phnti tin, tn hiu iu bincn c hai bin tn:Bin tn trn c tn s t

( t + Smin ) n ( t+ Smax )Bin tn di t ( t- Smin )n ( t - Smax ).

Ph ca tin tc

Ph ca tn hiu iu bin


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iu ch n binSSB(Single SideBand)

Ph ca tn hiu iu bin gm ti tn v haibin tn, trong ch c bin tn mang tintc.V haidi bin tn mang tintc nh nhau nnch cn truyn i mt bin tn l thng tinv tin tc. Ti tn ch cn dng tch sng,do c th nn ton b hoc mt phn ti

tn trc khitruyn i.Qu trnh iu ch nhm to ra mt di bin tn gi l iu ch n bin.


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iu ch n binSSB(Single SideBand)

iu ch n bin tuy tn km nhng c ccu imsau:

+ rng di tn gim mt na .+ Cng sut bc x yu cu thp hn cng vi

mt c ly thng tin. V cth tp trung cngsut ca ti tn v mt bin tn cho bin tn

cn li.+ Tp m u thu gim do di tn ca tn hiu hp hn.


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iu ch n binSSB(Single SideBand)T s phn tch ph >> mun c tn hiu nbin cn lc bt mt di bin tn. Nhng thc tvic ch to b lc rt kh. V vy, ngi ta

dng mt b bin i trung gian c th hthp yu cu i vi b lc


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1.2 i u t n FM v i u pha PM(Frequency and Phase Modulation)

iu tn v iu pha l ghi tintc vo ti tinlm cho tn s hoc gc pha tc thi ca ti tinbin thin theodng tn hiu iu ch.

Khiiu ch tn s hoc iu ch pha th tn s hoc gc pha ca dao ng cao tn bin thin t l vi tn hiu iu ch v chngc xc nh ln lt theo biu thc:


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Trong: t l tn s trung tn ca tn hiu iu tn. 0 l gc pha banu ca tn hiu.

Biu thc ca dao ng iu tn:


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Biu thc ca dao ng iu pha khi = t =const :

Lng di phat c khiiu pha:

Tng ng ta c lng di tn:

iu tn v iu pha u lm cho gc phathay inn thng gichung liu ch gc


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1.3 Tch sng (gi i i u ch )

Tch sng l qu trnhly li tn hiu iu ch.Tc l tch ly s thay i bin , tn s haygc pha ly li tn hiu ban u. Tnhiu sautch sng phi ging dng tn hiu ban u.Thc t tn hiu iu ch u S sau khiiu ch vtruyn qua knh n b tch sng b modng thnh u S . Do mo phituyn trong b tch

sng, nn sau khi tch sng tali nhn c u S khc dng u S . Nh vy tn hiu sau tch sngthng khc dng tn hiu nguyn thu u S . Vvy yu cu c bn ca qu trnh tch sng lmo phituyn nh.


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1.3 Tch sng (gi i i u ch )

a) Tch sngiu binTch sng iu bin thc hin vic tchng bao ca tn hiu iu bin, l thnhphn bin thinchm (mang tintc).


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b) Tch sng iu tn v iu pha Nguyntc tch sng iu tn v iu pha:

Bin i tn hiu iu tn hoc iu pha thnh tnhiu iu bin ri thc hin tch sng bin.Bin i tn hiu iu tn thnh tnhiu iu ch rng xung ri thc hin tch sng tnhiu iu ch rng xungnh mch tch phn.

Lm chotn s tn hiu cn tch sng bm theotn s ca mt b to dao ng nh h thng vnggi pha PLL,in p sai s chnh lin pcn tch sng.


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b) Tch sng iu tn v iu pha


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b) Tch sng iu tn v iu pha


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2 Cc k thu t i u ch s

Analog ADC Line coding DigitalModulation

SamplingQuantizationCoding

RZ,NRZ,AMI

ASK,FSK,PSK

Block diagram for digital transmission system


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Trongk thut iu ch tng t, chng ta bit cc tn hiu tng t c gi vo sngmang di dng thay i cc thng s nh:bin , tn s hay gc pha.Trongh thng truyn tn hiu s, ngun tin ltp cc tn hiu s nh phn v khin iu ch, tn hiu c th l cc tn hiu logichoc l cc symbol (khihp 1 nhm bit)Tp symbol biu din theo m Gray gm cM=2k symbolvi k l t hp cc bt to thnh

1 symbol.


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Cc symbol ny sau mi mang i iu ch s, ta c khiu ca tp symbol:

Nh vy, iu ch s lc ny cnhim v nhx 1 symbol thnh 1 dng sng si(t) (vi i=1,..,M) >>Truyn dn tn hiu s trn knh

lintc (knh tng t). iu ch s c ng dng tronghu ht cclnh vc ca vin thng: thng tin quang, ding, v tinh, viba, xDSL,truynhnh s

1,2,3..k ; 2; 1 k M ii M S


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iu ch s l qu trnh mt trong ba thngs bin , tn s v pha ca sng mang c thayi theo tnhiu (hay lung s) a vo iu ch thng tinca sng mang ph hp vi ng truyn.

Ti sao phi iu ch s?

CS lm gim bng thng nn c hiu qu s dng ph cao (gim bng thng, tng s lng knh thng tinc ghp vo lung bng gc s) Ph hp vi cc h thng i hi hiu qu ph ln nh iu ch nhiu mc.


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cos 2 cccamv t t f A

Nguyn l ca iu ch

Thay i thng s ca sng mang

Cc thnh phn mang thng tin: Ac(t) f c(t)

(t)

Ac(t) : amplitude modulation AM ASK

f c(t) : frequency modulation FM FSK (t) : phase modulation PM PSK

Ac(t) and (t) QAM (Digital)

DigitalAnalog


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Block diagram of a digital radio system


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2 Cc k thu t i u ch s Nu tn hiu bng gc tc ng vo bin ca sngmang th iu ch s gi l k thut iu ch ASK(Amplitude-Shift Keying): khodch bin .Nu tn hiu bng gc tc ng vo tn s ca sngmang th iu ch s gi l k thut iu ch FSK(Frequency-Shift keying): khodch tn s.Nu tn hiu bng gc tc ng vo gc phaca sngmang th iu ch s gi l k thut iu ch PSK

(Phase-Shift Keying): khodch pha.Nu tn hiu bng gc tc ng vo c bin v gcpha ca sng mang thiu ch s gi l k thut iu ch bin vung gc QAM (Quarature Amplitude

Modulation):iu ch bin cu phng.


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iu ch s nhiu mc (Mmc) .Khi tnhiu bng gc c bin i ni tip thnh song song (k bitni tip thnh M symbolsong song), ri c b tr thnh m Gray va i iu ch s gi l iu ch Mmc (M-ary).

k: ls bt/symbol. M: ls mc.M=2k k = log2MNh phn: M=2; k=1:biu din nh phn vi 2bt 0v 1


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Gin vc t IQ

Ta cng c th biu din tn hiu trn h trcta vung gc hay cn gi l biu din tnhiu trn gin vc t IQ.

Tn hiu thng c biudin di dng mt vc t,bao gm 2 thnh phn:bin v gc pha. VQ

VI

Bin Pha

Q (Quadrature)

I(Inphase)

V


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iu ch tng t trn th IQ

Q

I

B

A

C

D

AM

PM


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th thi gian v trng thi

Sng mang

= 0 deg. = 180 deg.

Trng thi0 Trng thi 1

th chm sao(constellation)Q

I

t

Trng thi 1 Trng thi0


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3 iu ch kho dch bin ASK (Amplitude Shift Keying)

iu ch kho dch bin l qu trnh lmthay i bin ca sng mang tu theo tnhiu a vo iu ch ( l chui nh phn).

Khi tnhiu a vo iu ch l mt chui nh phn, tnhiu u ra ca b iu ch c bin thay i hai mc (A0 v A1) tng ng vihai gitr nh phn 0 v 1.Xydng cng thc:

Chuitn hiu bng gc: d(t)= {0, 1} (hoc m(t))Sng mang: S c (t)= Ac .cos( c t + )


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iu ch bin : (d(t) tc ng vo bin )

Biu din tn hiu: (=0 )

S nguyn l:

d(t)

S c (t)

S ASK (t)

ASK signalgeneration

0; 0

1;)()cos().()(

d(t)

d(t)t St At d t S C C C ASK

sin C t

cos C t


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Biu din dng sng ca tn hiu ASK:

Tb bit period ; R bit rate

1b

T R

1 0 1 0 1 0 1Data

UnipolarModulation

BipolarModulation

ASK signal (on-off signal)

d(t)

d(t)

s(t)

d(t) R f

f

k

f B b

bb ASK

1


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Amplitude-shift keying (ASK or OOK)1 0 1 1 0 0 1

T b

t

modulated carrier

t

unmodulated carriert


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Cc phng php to tn hiu ASK:

d(t)

v c (t)

v ASK (t)

Using multiplier

d(t)

v c (t)

v ASK (t)

Using ON and OFF switch


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C 2 phng php tch sng tn hiu iu bin: tch sngkt hp hoc khngkt hp.Tch sng trc tip (non-coherent)s dng itv mt b lc thng thp.Tch sng kt hp dng phng php ghp(nhn) tnhiu ASK thuc vi mt tn hiu sng mang thamchiu c tn s trngvi tn s pht, sau dng b lc loi b thnhphn cao tn.


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Cc phng php tch sng tn hiu ASK.

v ASK (t) d(t)

Tch sng trc tip s dngit

Tch sng kt hp

v ASK (t) d(t)

vc(t)


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Mt ph cng sut (PSD) ca tn hiuASK hai trng thi:


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3 iu ch kho dch bin ASK (Amplitude Shift Keying) iu ch kha dch bin nhiu mc: M-ASKNguyn tc ging ASK hai trng thi, tuy nhindy d(t) phi t hp chui s thnh dibit, tribit,

(to thnh cc symbol). Biu din (4-ASK):sin C t

cos C t

4 ASK


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4-ASK00 01 10 11 01 00 11

T S

t

unmodulated carriert

t

modulated carrier

data

Linecode

A1A2A3


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Kho dch tn s l qu trnh lmthay itn s ca sng mang theo tn hiua vo iu ch ( l chui nh phn).

Khi tn hiu a vo iu ch l mt chunh phn, tn s sng mang thay i haimc f0 (tn s thp) v f1 (tn s cao) tngng vi hai gi tr nh phn 0 v 1.Xydng cng thc:

Chuitn hiu bng gc: d(t)= {0, 1} (hoc m(t))Sng mang: S c (t)= Ac .cos( c t + )

4 iu ch kho dch tn FSK (Frequency Shift Keying)


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i h kh d h FSK


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Trng hp bng gc c m thnh:Binary 1 => 1V cn Binary 0 => -1V,

khi sng mang s b dch i:f or -f v vy tn s sng mang l:f S =f c +f or f m = f c - f .Khi dm (t) = +1V (logic 1) :

Khi dm (t) = -1V (logic 0) :

t f f At SccFSK

)(2cos)()(

t f f At S ccFSK )(2cos)()(



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S nguyn l:


f 1

f 2

d(t)

a) S dng tn sca 2 b dao ng

b) S dng b dao ng ciu khin bi in p

VCO(Voltage ControledOscilator)d(t)


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Biu din tn hiu trn trc tn s v bin .


Logic 0

Logic 1

f c f s f m

- f f

Binary inputsignal

f

Amplitude


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Bn tin Tn hiu n cc Tn hiu

lng cc

FSK(khng lin tc)

1b

T R

FSK(Lin tc)

(1) : f1(0) : f2

1 0 1 0 1 0 1 d(t)

d(t)

S FSK (t)

S FSK (t)

FSK lin tc v FSK khng lin tc

Dng sng ca Binary FSK (BFSK)


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mc 51

FSK

1 0 1

X

=

0 1 0

X

=

+ASK 1 ASK 2

Unipolar

m m 3 m 5

Amplitud, V

w(rad/s)

Amplitud, V

w(rad/s)

Amplitud, V

w(rad/s)

1c

The generation

of an FSKwaveform at theTransmitter canbe achieved bygenerating twoASK waveformand adding themtogether with asummingamplifier.

MARKSPACE

i h kh d h FSK


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K thut iu ch thc t.


i h kh d h FSK


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Ph v rng bng tn ca tn hiu BFSK

FSK is generated by adding two ASK signals (mark and space).Therefore the bandwidth of the periodic FSK signal is then:


ASK FSK B f B 22 bFSK f f B 22Where fb is bit rate in Hertz

i h kh d h FSK


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iu ch nhiu mc: MFSK Dng nhiu hn2 tn s. Bng thng c dng hiu qu hn. Kh nng li nhiu hn so vi tn hiu dchtn BFSK. Mi phn t tn hiu biu din nhiu hn1 bit

d liu. t li hn v c s dng nhiu hn so viM-ASK


4-FSK


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4-FSK00 01 10 11 01 00 11

T S

modulated carrier

t f 1 f 2 f 3 f 4 f 2 f 1 f 4

t

i h kh d h h PSK


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iu ch kha dch pha l qu trnh lm thayi gc pha ban u ca sng mang theo tnhiu a vo iu ch.

Trong k thut iu ch PSK th tn s vbin sng mang khng i, trong khi phasng mang c thay i theo dng chui avo iu ch.Khichui tn hiu vo l chui nh phn th tnhiu u ra c mt pha thay i, mt pha l00 v mt pha l 1800 tng ng vi hai btnh phn 0v 1v gi l BPSK.

5 iu ch kho dch pha PSK (Phase Shift Keying)


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i h kh d h h PSK


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S nguyn l pht tn hiu BPSK:


d(t)

vPSK (t )

f c

-1

iukhinmcS liu nh ph n

d(t) Acos 0t

Acos 0t

S(t)

B dao ng

i h kh d h h PSK


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S nguyn l pht tn hiu BPSK:


X

BinaryData sequence in

polar form

Accos(2 f ct )

BinaryPSKsignal

t

vPSK (t )LPF

d(t)

f c

Using multiplier

5 i h kh d h h PSK


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Coherent binary PSK ReceiverX

Accos(2 f ct )

Binary PSKwave

b

0

dT

t Decisiondevice

Threshold = 0

Choose 1 if > 0

Choose 0 if < 0


Non-coherent Differential Binary PSK Receive

DelayT b

XDBPSKwave Decision

deviceChoose 1 if > 0Choose 0 if < 0

b

0

dT

t

Threshold = 0

5 i h kh d h h PSK


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Tn hiu iu ch BPSK


Tn hiu lngcc

1bT R

1 0 1 0 1 0 1 Bn tinTn hiu n

cc

u raPSK

d(t)

d(t)

s(t)

Hnh - iu ch s PSK vi tn hiu nhi phn


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c

PSK

1 0 1 1 0

X

=

Bipolar

m

m 3

m 5

Amplitud, V

w(rad/s)

Amplitud, V

w(rad/s)

mc 5

mc 5

c

Amplitud, V

w(rad/s)

The phase of the carrier isset to 0o or 180o depending on the digitalsignal.

t t E t v ccPSK cos

PSK signal can berepresented by :

(t) = 0 => 1 (t) = 180o => 0 , so ;

1cos t E t v ccPSK

0cos t E t v

ccPSK

5 iu ch kho dch pha PSK


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BPSK spectrum

S f ( )SS

f 0 00 f -f

00f - -f - 1

T b

1T b

00f + -f + 1

T b

1T b


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5 iu ch kho dch pha PSK


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Differential Binary PSK Transmitter


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Differential Binary PSK Transmitter

XBinarydata

Accos(2 f ct )

DBPSKwave

One-bitdelay

Levelshift

Binary data 1 1 0 0 1 1 0 1 1

Delayed Encoded data 1 1 1 0 1 1 1 0 0 0

Encoded data 1 1 1 0 1 1 1 0 0 0

Transmitted phase 0 0 0 0 0 0

Transmitted level 1 1 1 -1 1 1 1 -1 -1 -1

Detected bit 1 1 0 0 1 1 0 1 1

Encoded dataXNOR

Delayed Encodeddata

(Binary data) XNOR (Delayed Encoded data) =Encoded data

iu ch kho dch pha nhiu mc


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iu ch kho dch pha nhiu mcM-ary PSK (MPSK)

2

21

21

2211

2

sin 2

cos

sin2

)( cos2

)(

,,1 )()()(

iis

sisi

cc

iii

E E

M

i E a

M

i E a

t T

t t T

t

M it at at s

s

i

t T

E t s

c

s

i 2

cos2

)(


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iu ch kho dch pha nhiu mcQPSK: Quadrature PSK

QPSK spectrum

S f ( )SS

f 0 00 f -f

00f - -f - 1

T b

1T b

00f + -f + 1

T b

1T b



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QPSK Transmitter

Series toparallel

converter -90

X

Oscillator

X

QPSKsignal

Acsin(2 f ct )

Binarybipolardata

sequence

Accos(2 f

ct )

-

+



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Coherent QPSK Receiver

X

Accos(2 f ct )QPSKwave

b

0

dT

t Decisiondevice

Threshold = 0

Xb

0

dT

t Decisiondevice

Threshold = 0

Parallel toseries

converter-90

Binary Datasequence



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iu ch kho dch pha nhiu mc8-PSK.

100 )3152cos(

101 )2702cos(

111 )2252cos(

110 )1802cos(

010 )1352cos(011 )902cos(

001 )452cos(

000 )02cos(

)(

t f A

t f A

t f A

t f A

t f At f At f At f A

t s

c

c

c

c

c

c

c

c

Phng trnh biu din Symbol(Gray)



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Chm sao ca 8-PSK


3s

7s

110

)(1 t

4s

2s

s E 000

)(2 t

6s

8s

1s

5s

001 011

010

101

111 100

8PSK (M=8)



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So snh cc k thut iu ch kho


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So snh cc k thut iu ch khodch pha nhiu mc.


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SUMMARY OF DIGITAL MODULATION

)cos(1

)cos(0

2

1

t A

t A

cc

cc

)cos(1

00

t A cc

)cos(1

)cos(0

t A

t A

cc

cc

1 0 1 1 0

ASK

BFSK

BPSK

=

=

=

...5cos5

13cos

3

1

cos1

2

1)(

t t

t t d

mm

m

=


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SUMMARY OF DIGITAL MODULATION

)cos(1

)cos(0

2

1

t A

t A

cc

cc

)cos(1

00

t A cc

)cos(1

)cos(0

t A

t A

cc

cc

=

=

=

...5cos513cos

31

cos1

2

1)(

t t

t t d

mm

m

=

6 iu ch bin vung gc


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6 iu ch bin vung gcQAM: Quadrature Amplitude Modulation

Trong h thng ASK Mtrng thi (M-ASK)bin ca xung phtc bin i thnh Mmc gin on, cc trng thi bin c biu din thnh nhng im m ha dc theomt ng thng.Trong h thng PSK M trng thi (M-PSK)pha ca xung pht c bin i thnh M

gc pha khc nhau vc biu din thnhMimcch u trn 1ng trn.

6 iu ch bin vung gc


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Trong vic la chn ti u tp tn hiu u mong mun tng hiu qu s dng ph (bit/second/Hz),gim rng bng tn trongiu kin gii hn cng sut tn hiu.Trong M-PSK v M-ASK, tng M lngp i th cng sut sng mang tng trung bnhl 6,5dB. Trong khi, bng cch kt hp haiphng php ny th tng M thch cn tng cng sut sng mang ln 2,5dB. Vvic gim rng bng tn ca 3 phng phptrn lnh nhau v bng log2M.

6 iu ch bin vung gc


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Kt hp M-PSK v M- ASK c gi l khapha bin kt hp (CAPK:Coherent Amplitude Phase Keying )

Dng tng qut ca tn hiu CAPK M trngthi:

Vi: i =1 Mk: ch s khe thi gian ca Symbol

Ak, Bk = 1, 3, ,

t Bt A

t C t s

k k

iii

00

0

sincos

)cos()(

)1( M

6 iu ch bin vung gc


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Biu thc tng qut ch r dng sng kt hp gm hai sng mang ring bit ghp cu phng v misng mang c mt b bin gin on iu ch (A

kv B

k).

S CAPK nythng c gi l iu ch bin cu phng (iu ch bin vung gc) QAM: Quadrature Amplitude

Modulation. V M-QAMc gi l iu ch bin vung gc M-mc (M-ary Quadrature Amplitude Modulation)

6 iu ch bin vung gc


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th chm sao tnhiu 8-CAPK (khng mtheo Gray) v biu din dng sng ca tnhiu .


6 iu ch bin vung gc


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thchm saoca mts mciu chM-QAM.Thit b

QAM thct ch c:M=4, 16,64, 256.

I

Q

M-ary Quadrature Amplitude Mod


86/94

2006-02-13 Lecture 7 86

ic

i

it

T

E t s cos

2)(

3

1(2 andsymbolsPAMareandwhere

sin2

)( cos2

)(

,,1 )()()(

21

21

2211

M E aa

t T

t t T

t

M it at at s

sii

cc

iii

,1()1,3()1,1(

,1()3,3()3,1(

,1()1,3()1,1(

, 21

M M M M M

M M M M M

M M M M M

aaii

M ary Quadrature Amplitude Mod.(M-QAM)


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2006-02-13 Lecture 7 87

)(1 t

)(2 t

2s

1s 3

s4

s0000 0001 0011 0010

6s

5s 7s

8s

10s

9s 11

s 12s

14s

13s 15

s 16s

1 3- 1- 3

0100 0101 0111 0110

1100 1101 1111 1110

1000 1001 1011 1010

1

3

-1

-3

16-QAM

6 iu ch bin vung gc


88/94

88


Q0000 00110001

01010100 0111

1100

0010

1101

0110

10011000 1010

1110

1011

1111

I

-3 -1

1

3

3

-1

-3

1

S1

S2

t t t s 001 sin.3cos.1)(

t t t s 002 sin.1cos.3)(

Dng chmsao ca 16-QAM

6 iu ch bin vung gc


89/94

89

6 g gQAM: Quadrature Amplitude Modulation

S iu ch tn hiu M-QAM. M L k k 2 / 12 / 22

S/P

2/L

2/L

900

NRZ

k/2

bit

k/2 bit

NRZ

Ts - k bit

a(t)

b(t)

Ak

Bk

sin 0t

cos 0tM-QAM

LPF

LPF

6 iu ch bin vung gc


90/94

90


S gii iu ch tn hiu M-QAM.

P/S

2/L

2/L

900

Ts - k bit

Ak

Bk

M-QAM signal

t B

t At s

k

k i

0

0

sin

cos2)(

t 0cos2

t 0sin2

t B Bt A A k k k k 00 2sin0sin2cos0cos

6 iu ch bin vung gc


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91


Kt hp gia ASK v PSK M rng logic ca QPSK Gi ng thi2 tn hiu khc nhau cng tn

s mang. Dng 2bn sao ca sng mang, mt ci cdch i900 Mi sng mang l ASK c iu ch 2 tn hiu c lp trn cng mi trng Gii iu ch v kt hp li hai sng mang scho d liu nh phn ban u


92/94

92


93/94

93

Shannon

limit


94/94

Chuong5-Dieu Che So

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