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8/8/2019 Chng 3 - M ha v iu ch d liu- Phn 2
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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
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