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Truyn s liuData Communication

L c Nhng

Khoa Ton Tin - Trng i hc Hi Phng

E-mail: Nhuongld@yahoo.com

Cell Phone: 0987.394.900

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3.2 D liu s Tn hiu tng t (Digital Data - Analog Signal)2/54

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3.2 D liu s Tn hiu tng t (Digital Data - Analog Signal)3/54

Types of digital-to-analog conversion

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ng dng:

Truyn d liu Digital s dng tn hiu Analog

VD mng in thoi cng cng:

Di tn ca mng in thoi: di tn s ting ni t 300Hz n 3400Hz

Tn hiu s c a vo mng qua modem, c chc nng chuyn t

tn hiu s thnh tn hiu tng t v ngc li

Cc k thut c bn:

Amplitude shift keying (ASK): kho dch bin

Frequency shift keying (FSK): kho dch tn s

Phase shift keying (PSK): kho dch pha

3.2 D liu s Tn hiu tng t (Digital Data - Analog Signal)

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ASK: Kho dch bin :

Biu din d liu:

Cc gi tr nh phn nhng bin khc nhau ca sng mang

Bit 1: s c mt ca sng mang

Bit 0: s vng mt ca sng mang

nh gi:

Khi thay i t ngt h s khuch i hoc nhiu nh hng.

S dng cho truyn d liu trn cp quang

3.2.1 Amplitude shift keying (ASK)

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ASK: Kho dch bin :

3.2.1 Amplitude shift keying

cA cos 2 f t binary 1S t

0 binary 0

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ASK: Kho dch bin :

3.2.1 Amplitude shift keying (ASK)

Figure: Implementation of binary ASK

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FSK: Kho dch tn s:

Cc gi tr nh phn nhng tn s khc nhau gn tn s sng mang:

1 c biu din bng tn hiu c tn s f1

0 c biu din bng tn hiu c tn s f2

c im t b nh hng bi nhiu hn ASK

C th s dng sng radio cao tn (3-30MHz)

(V d mng LAN s dng cp ng trc)

3.2.2 Frequency shift keying (FSK)

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FSK: Kho dch tn s:

3.2.2 Frequency shift keying (FSK)

1

2

A cos 2 f t binary 1S t

A cos 2 f t binary 0

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FSK: Kho dch tn s:

3.2.2 Frequency shift keying (FSK)

Figure:Bandwidth of FSK

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FSK trn ng in thoi (300-3400Hz):

truyn full-duplex (ng thi theo 2 hng), phi chia i di tn

Theo 1 hng, tn s sng mang l 1170Hz, lch v hai pha l 100Hz

Theo hng kia, tn s sng mang l 2125Hz, lch v hai pha l 100Hz

C th t tc truyn 1200b/s trn ng truyn in thoi

3.2.2 Frequency shift keying (FSK)

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3.2.3 Phase shift keying (PSK)12/54

PSK: Kho dch pha:

Pha ca sng mang c dch i biu din cc gi tr nh phn.

V d:

Bit 0 vic gi mt on tn hiu cng phavi on tn hiu trc .

Bit 1 vic gi mt on tn hiu ngcphavi on tn hiu trc

Pha c o tng i so vi khong bit trc

c 1

c 2

A cos 2 f t binary 1S t

A cos 2 f t binary 0

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3.2.3 Phase shift keying (PSK)13/54

c

c

A cos 2 f t binary 1S t

A cos 2 f t binary 0

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3.2.3 Phase shift keying (PSK)14/54

Figure: Implementation of BPSK

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3.2.4 Quadrature Amplitude modulation (QAM)15/54

QPSK: kho dch pha cu phng:

S dng di tn hiu qu hn: mi phn t tn hiu c biu din nhiu hn 1bit. Cc mc dch pha l bi ca 900 (p/2) ( PSK l 180o )

Mi phn t tn hiu biu bi 2 bit

0

c

0

c

0

c

0

c

A cos 2 f t 45 bit 11

A cos 2 f t 135 bit 10S t

A cos 2 f t 225 bit 00

A cos 2 f t 315 bit 01

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3.2.4 Quadrature Amplitude modulation (QAM)16/54

QPSK: kho dch pha cu phng:

Figure: Three constellation diagrams

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3.2.4 Quadrature Amplitude modulation (QAM)17/54

QPSK: kho dch pha cu phng:

Figure: Constellation diagrams for some QAMs

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3.2.4 Quadrature Amplitude modulation (QAM)18/54

M rng:

S dng nhiu gc pha (th d: 8, 16 pha biu din cho 3, 4 bit)

Vi mi pha, tn hiu c th nhn nhiu mc bin

Modem 9600bps s dng 12 gc pha, trong 4 pha s dng 2 gi tr bin

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3.2.4 Quadrature Amplitude modulation (QAM)19/54

Figure: QPSK and its implementation