chuong 2 cac phuong tien truyen

1Chng 2 Cc phng tin truyn

Th.S

ng

Ngc

KhoaKhoa in - in T

2Ni dung trnh by

Cc khi nim Cp xon Cp ng trc Cp quang Mi trng truyn v tuyn

3Khi nim knh truyn

Mi trng truyn: l phn kt ni gia hai lp vt l ca mt h thng thu/pht. C th chuyn ti tn hiu tng t hoc tn hiu s.

Khi cp n m hnh ton hc, knhtruyn c xem tng ng vi b lc.

4c tnh ca knh truyn

c tnh trong min tn s: trong min tn s, knh truyn c hai c tnh quan trng sau: Suy gim bin tn hiu: mc ty thuc vt

liu nhng ni chung t l vi chiu di ca knh truyn h s suy hao [dB/km].

Dch pha (phase shift) gia tn hiu ng ra so vi tn hiu ng vo h s pha [rad/m].

Mt knh truyn c c trng bi

( ) ( ) ( )jin

out efHfHVV ==

5c tnh ca knh truyn

c tnh trong min thi gian: knh truyn c c trng bi p ng xung (impulse response) h(t).

Trong

( ) ( ) ( ) ( ) ( )

== dthxthtxty *

( ) ( )fHth F

6c tnh ca knh truyn

Do nhng c tnh trn, ch c mt s tnhiu c tn s xc nh mi c th truynqua knh truyn. Khong tn s c gil bng thng ca knh truyn.

minmax ffBW =

7Phn

loi mi trng

truyn

Hu tuyn (guided media wire) Cp ng

Cp xon Cp ng trc

Cp quang V tuyn (unguided media wireless)

V tinh H thng sng radio, microware

8Phn b ph in t

9Ni dung trnh by


10

Cp xon (Twisted Pair)

Cp xon c hai dng chnh l: UTP (Unshielded Twisted Pair Cp xonkhng c v bc chng nhiu) v STP (Shielded Twisted Pair Cp xon c vbc chng nhiu) .

UTP l loi cp c dng ph bin nht trong vin thng hin nay

Cp xon bao gm hai si ng (mi si c bc cch in bng plastic vi mi mu khc nhau) xon cch in vi nhau.

11

Cc thng s s cp

Trong mt n v chiu di, cc thng s cang dy c xc nh nh sau:

Tr khng ni tip in tr tuyn tnh R [/m] in cm tuyn tnh L [H/m]

Dn np song song in dung tuyn tnh C [F/m] in dn tuyn tnh G [Siemens/m]

CG

R L

12

Cc thng s th cp

Tr khng c tnh:

H s truyn sng

: suy hao tuyn tnh [Np/m] (1Np/m=8.68dB/m) : di pha tuyn tnh: l vn tc lan truyn

''''

CjGLjRZc

++=

( )( )'''' CjGLjRj ++=+=

vv,=

13


Bng

thng

ca cp xon

100 Hz 600MHz

Twisted-Pair Cable

Lp cchin PVC

Dy

dnbng

ng

14


Trc y, ngi ta s dng cp dy dn song hnh truyn thng tin.

Cc loi nhiu in t sinh ra bi cc thit b nh motor c th to ra nhiu trn cc dy dn.

15


Tng nhiu16-12=4

16

12My pht My thu

Nhiu = 16 n v

Ngun nhiu

Nhiu = 12 n v

nh

hng

ca

nhiu

ln

dy

song hnh

16


Tuy nhin, nu hai dy xon cht vo nhau mt cch u n (t 6 n 40 ln xon trn 1m) th tc ng tch ly ca nhiu ln hai dy l bng nhau.

17


My

pht My

thu

14

14

Tng

nhiu 14-14=0

Ngun nhiu

nh

hng

ca

nhiu

ln

dy

cp

xon

18

UTP -

Unshielded Twisted Pair

19

u ni cp UTP 8 dy

20

Phn

loi cp UTP

Tiu chun phn loi cp UTP theo hiphi cng nghip in t (EIA Electronic Industries Association) nh sau. Category 1 (Cat1): tc < 4MHz, c ng

dng trong mng PSTN. Category 2 (Cat2): thch hp cho truyn thoi

v data n tc 4Mbps Category 3 (Cat3): yu cu ti thiu 10 ln

xon trn 1m Tc truyn d liu ln ti 10Mbps L loi cp chun cho mng in thoi

21

Phn

loi cp UTP

Category 4 (Cat4): yu cu ti thiu 10 ln xon trn 1m, dng truyn d liu, tc t c 16Mbps cth ln n 20Mbps, ng dng cho mng Token Ring tc cao.

Category 5 (Cat5): dng truyn d liu, tc 100 Mbps c th t 1Gbps, ng dng trong mng Fast Ethernet.

Category 5e (Cat5e): dng truyn d liu, tc 1Gbps, gi thnh cao hn loi 5, ng dng trongmng Giga Ethernet

Category 6 (Cat6): dng truyn d liu, tc t1Gbps n 10Gbps, c ch ng thay th cho loi5e, ng dng trong mng Super Ethernet

Category 7 (Cat7): 10 Gbps

22

Cp xon UTP Category 6

CAT5e

23

Cp UTP nhiu cp

24

u ni cp nhiu cp

25

u nhc im ca UTP

u im ca cp xon UTP R Linh ng, d ghp ni D lp t

Nhc im ca cp UTP Kh nng chng nhiu km

26

STP -

(Shielded Twisted pair)

Cp c mt lp kim loi hoc mt li kim loi bao ngoi mi cp dy xon.

Lp kim loi c tc dng chng cc nhiu in t da trn c ch tp trung tt c tn hiu nhiu vo lp bo v.

Lp bo v ny cn c tc dng chng nhiu xuyn knh (crosstalk)

STP c cc phm cht tng t nh UTP v cng dng cng mt loi kt ni nh UTP, nhng lp bo v phi c ni mass.

27

STP -


Cp

STP

Shielded Twisted pair

V

Plastic Bc

kim

loi Cch

in Li

ng

28

STP -


ScTP: Screened Twisted-Pair

SSTP: Shielded Screened Twisted-Pair

29

u ni STP

30

Chun mu

Cp # Mu chnh

Mu ph

(sc)

ring

tip

1 Xanh

Trng

2 Cam

Trng

3 Lc Trng

4 Nu Trng

M mu cho loi cp 4 cp

31

Mu sc chunCp

#

Mu chnh

Mu ph

(sc)

ring

tip1 Blue White2

Orange

White3 Green White4 Brown White5

Slate

White

6 Blue

Red7

Orange

Red8 Green

Red9 Brown

Red10

Slate

Red

11

Blue

Black12

Orange

Black13

Green

Black14

Brown

Black15

Slate

Black

16

Blue

Yellow17

Orange

Yellow18

Green

Yellow19

Brown

Yellow20

Slate

Yellow

21

Blue

Violet22

Orange

Violet23

Green

Violet24

Brown

Violet25

Slate

Violet

White

Red

Black

Yellow

Violet

M mu cho cp 25 cp

32

ng dng ca cp xon

Mng LAN: 10/100Mbps Ethernet LAN, t ti 155Mbps vi ATM

Dy thu bao in thoi 56Kbps Vng thu bao s bt i xng (ADSL

Asymmetric Digital Subscriber Loop): 8Mbps t host n DSLAM Exchange (upload), 16Mbps t exchange (download)

33

Ni dung trnh by


34

Cp ng trc (Coaxial Cable)

Thay v s dng hai dy dn song song, cp ng trc s dng mt dy dn trung tm (li, lm bng hp kim m ng) v c bao bc bi mt lp kim loi bn ngoi (cch in vi lp li).

Lp kim loi pha ngoi va ng vai tr bo v chng nhiu, va l dy dn th hai hon thnh mch in thng tin.

Lp kim loi ngoi c bc trong mt lp cch in plastic

35


Lp dn

ngoi LiV plastic

Cch

in

Cu to ca cp ng

trc

36


Bng

thng

ca cp ng

trc

100 KHz 3GHz

Cp

ng

trc

37

u ni cp ng trc

38

Chun cp ng trc

c phn loi bi radio gorvernment (RG) Da vo kch thc vt l cp ng trcc phn loi thnh RG-8, RG-9, RG-11: Thick Ethernet RG-58: Thin Ethernet RG-59: CATV

39


Tr khng c tnh:

Tr khng c tnh khng ph thuc vo kch thc tuyt i ca cp (li v v) m ch ph thuc vo t l gia chng

r

irc

cv

ddZ

=

= 0ln60 :,0 idd ng knh

dy

dn

ngoi

v

trong

:r H

s in mi ca cp

:v Vn tc

pha

40


suy hao ca cp c xc nh nh sau, tn s cao, hiu ng da phi c tnh n.

l in tr sut h t gi tr nh nht khi

suy hao bin t l nghch vi ng knh ca cp, t l vi cn bc hai ca tn s f v ph thuc vo vt liu ch to ca cp

[ ]mNphd

frR /1.0

0 =i

i

ddd

dh0

0

ln

11

+=

rc

iopt

Rdd

776.30 ==

41


Suy hao theo tn s

42

u nhc im

u im Bng thng rng 400-600MHz D dng kt ni t b nh hng bi nhiu Bn

Nhc Kch thc ln suy hao cao

43

ng

dng

ca cp ng

trc

H thng truyn hnh cp (CATV) ng trung k cho cc tng i in

thoi, truyn tn hiu baseband trong h thng vi ba s.

Dy dn tn hiu bandpass cao tn (VHF,UHF,...) dy feeder ra antenna.

Truyn tn hiu thoi khong cch di C th ti ng thi 10.000 cuc gi. Hin nay c thay th bng cp quang

44

Bi tp 1

Mt tn hiu c khong tn s t 100 n600MHz. Cn truyn tn hiu ny trn cpng trc vi khong cch 200m. Cngsut yu cu pha thu l 65dBu. Xcnh cng sut my pht v lch cngsut pht theo tn s (equalizer).

Suy hao ca cp c cho slide 41.

45

Bi tp 2

Mt my pht pht tn hiu mc cngsut 100dBu ( tn s 800MHz) v cEqualizer l 20dB (cng sut pht 80dBu tn s 100MHz). Mt my thu yu cucng sut tn hiu ng vo t 60-70dBu. Xc nh chiu di ti a gia my phtv my thu.

46

Bi tp 3

Vi cc thng s ging bi 2, hy xc nhli thng s Equalizer h thng c thtruyn tn hiu i xa nht.

47

Ni dung trnh by


48

Cp quang (Fiber Optics)

Cp quang c ch to t thy tinh, n chophp truyn tn hiu di dng sng nh sng.

Sng nh sng: Lan truyn vi vn tc bng c = 3.108 (m/s) trong

chn khng. Trong cc mi trng khc, tc ny nh hn c v

cng gim i vi cc mi trng c mt vt liu dy c

49


Cu to ca cp quang

Cp quang hot ng da vo nguyn lphn x nh sng

Core: liCladding: lp phCoating: lp ngoi

Strengthening Fibers: Cc si bo vCable jacket: v cp

50


Hai lp chnh ca cp quang l core v cladding. C hai u c lm t si thy tinh. Core c chit sut n1, cladding c chit sut n2

vi n1>n2 S khc bit gia n1 v n2 l rt nh Khu ( m) ca cp:

022

21 sin== nnNA

51


Mt ct ngang ca si quang

Lp m

V ngoi

Vt liu gia cng

125

m

900

m

52


Kch thc cp quang c c trng bi cp thng s ng knh li (core) v ng knh ca lp ph (cladding) tnh bng m (v d 50/125)

Loi a mode100/140

Loi a mode62.5/125

Loi a mode50/125

Loi n mode8/125

53

Cc kiu cp quang

Cc kiu ng gi cp quang

54

Cp quang 6 core

55


56

u ni cp quang

57

u ni cp quang

SC

MT-RJ

FC

58

u ni cp quang

ST

LC

59

u ni cp quang

60

Phn loi cp quang

Da theo ch truyn nh sng: cng ngh hin nay cho php truyn nh sng trong si quang theo hai ch single mode v multimode.

Mi ch i hi nhng loi cp quang c c tnh vt l ph hp: Loi a mode (multimode):

chit sut nhy nc chit sut bin thin lin tc.

Loi n mode (single mode)

61

Multimode

Gi l a mode bi v c nhiu tia sng t ngun pht quang i trong li cp theo nhiu ng khc nhau.

Cp quang a mode chit sut nhy nc

Ngun ch

62

Si quang a mode

i vi loi cp quang a mode chit sut nhy nc (step-index), mt ca li khng i t tm ra ngoi ra ca li.

Tia sng i trong li cp theo mt ng thng cho ti khi chm vo tip gip gia core v cladding.

tip gip, s thay i chit sut t ngt t n1sang n2 lm cho tia sng b i hng.

Cc tia sng dc theo trc li cp s i theo ng thng m khng b khc x hay phn x.

63

Si quang a mode

Mt s tia sng n mt phn cch vi gc ti nh hn gc gii hn phn x ton phn s tip tc khc x vo trong lp cladding v i khi cp.

Cc tia cn li n mt phn cch vi gc ti ln hn gc gii hn s phn x lin tip nhiu ln trong cp cho n khi n ch.

64

Si quang a mode

Cc tia sng n mt phn cch vi gc ti cng nh s phn x cng nhiu ln trong li cp.

Do tia sng vi gc ti cng nh s i qung ng cng di khi truyn t ngun n ch.

Tt c cc tia sng s c kt hp li vi nhau ti u thu.

Cc tr hon truyn khc nhau nh trn s lm mo dng tn hiu thu

65

Multimode graded-index

L loi cp quang c chit sut bin ilin tc.

Loi cp ny c mt vt cht ca li thay i lin tc t trong ra ngoi.

Mt cao nht ti trc ca li (chit sut ln nht) v gim dn khi i ra xa trc.

66


Multimode graded-index fiber

Tn hiu c a vo cp ti v tr trc ca li. T v tr ny, ch c tia sng i dc theo trc ca

li l i theo ng thng n cui cp. Cc tia sng khc i qua mt mi trng c mt vt cht lin tc thay i.

67


S bin thin chit sut lm tia sng khc x theo mt ng cong. S khc x lm thay i khong cch m mi tia i c, kt qu l cc tia s gp nhau ti cng mt thi gian xc nh.

S tnh ton v lp t cn thn b thu v im hi t cc tia cho php khi phc tn hiu vi chnh xc cao hn.

68

Single mode (n mode)

Ch n mode s dng loi cp quang c chit sut thay i nhy nc v hi t cc tia sng trong mt khong gc vo rt hp, gn nh nm trng vi trc cp.

Single mode fiber

69

Cp quang n mode

Cp quang n mode c ch to vi ng knh li nh hn nhiu ln v chit sut hi nh hn so vi cp quang a mode.

S gim chit sut lm cho gc ti gii hn gn nh bng 90 lm cho cc tia gn nh trng vi trc cp, tr hon truyn ca cc tia gn nh nhau do c th b qua hiu ng do tr.

Cc tia sng n ch gn nh cng lc v ta c th khi phc tn hiu ban u khng b mo dng

70

Bc sng ct ca

cp

quang

Bc sng ct (cut-off wavelength): l bc sng gii hn ch n mode. Vi cc bc sng ln hn gi tr ny, tia sng trong cp quang ch c mt ch truyn (n mode).

n1 v n2 ln lt l chit sut ca core v cladding a l ng knh li V= 2.405 vi cp quang chit sut nhy nc.

22

21

2 nnVa

c =

71

Bi tp 4

Hai bc sng c s dng trong thng tin quang l 1310nm v 1550nm. Chit sut ca li v v ln lt l 1.45 v 1.449. Tnh ng knh li cp hot ng ch n mode.

Gii: cp hot ng n mode th bc sng ct phi nh hn 1310nm. Do ng knh li phi tha

iu kin

mnn

Va c 2.91.2 2

221

=

72

So snh

cc

loi

cp

quang

Loi n mode: ng knh li rt nh Ghp rt kh, gi thnh cao, kh sn xut

Loi a mode chit sut nhy nc: ng knh li ln Tn x theo thi gian ln Ghp d, gi thnh r nht, d sn xut.

Loi a mode chit sut bin i lin tc: Hn ch c tn x do c b v tc . Cht lng v gi thnh trung bnh

73

S khc x

Hin tng khc x xy ra khi tia sng i qua nhng mi trng c chit sut khc nhau

Mi

trng

c

chit sut cao (nc, king, )

Mi

trng

c

chit sut thp (khng kh, )

74

nh lut khc x Snell

Khi tia sng i ti mt phn cch gia hai mi trng c chit sut khc nhau th tia sng s b i hng. Gia gc ti v gc khc x c quan h theo cng thc

2211 sinsin nn =

75

Gc ti gii hn

Khi nh sng truyn t mi trng 1 chit sut cao sang mi trng 2 chit sut thp hn

Gc ti gii hn ( )1

221 arcsin90sinsin n

nnn critcrit ==

Chiu sut n1

>n2

Chiu sut n2

76

Hin tng

phn x

ton

phn

Khi tia sng ti mt phn cch vi gc ti bng gc ti gii hn th tia khc x i dc theo mt phn cch.

Khi tia sng ti mt phn cch vi gc ti ln hn gc ti gii hn th tia sng khng cn khc x vo mi trng 2 na m phn x tr v mi trng 1. l hin tng phn x ton phn.

Gc phn x lun bng vi gc ti

77

Hin tng

phn x

ton

phn

Gc

ti Gc

phn x

78

Truyn

nh

sng

trong

si

quang

Si cp quang hot ng da trn nguyn lphn x ton phn.

Li thu tinh (core) c ph bi lp cladding c chit sut nh hn. Vi gc vo thch hp, tia sng i trong li v phn x nhiu ln ti ch tip xc vi cladding m khng khc x vo cladding.

Thng tin c m ho thnh nh sng theo dng chp tt (sng: bit 1, tt: bit 0)

79

Truyn

nh

sng

vo

si

quang

80

Truyn

nh

sng

vo

si

quang

Ti im vo ca tia sng, theo lut Snell ta c

Ti tip gip gia core v cladding, hin tng phn x ton phn xy ra th

( )21cosarcsin2

1

21

1

21

=nn

nn

crit

( )1sinsinsinsin '11'110 nnn inin ==

81

Truyn

nh

sng

vo

si

quang

Kt hp (1) v (2) ta c

Suy ra

l gc vo ti a cho php ca tin sng vo si quang

( )NAnnin arcsinarcsin 2221max ==

22

21

2

1

21 arcsin1sin nnn

nn inin

maxin

82

Khu

ca

cp

quang

-

NA

NA - Numerical Aperture Cc tia sng vo cp quang ch c nm trong mt

vng khng gian hnh nn gi l vng chp nhn (acceptance cone). Vng ny rng hay hp l tu vo gi tr NA, do NA gi l khu s hay m ca cp

83

Tn hao trong cp quang

Do cp quang khng h b nh hng bi nhiu, do vn tn hao l vn quan trng nht cn xem xt.

Tn hao cp dn n gim cng sut tn hiu, gim bng thng (tc truyn) v dung lng.

Ni chung, si a mode tn hao nhiu hn si n mode.

84

Tn hao trong cp quang

C bn nguyn nhn gy ra tn hao chnh i vi cp quang: Tn hao do vt liu hp th (Material Absorption

Loss) Tn hao do tn x (do vt liu khng ng nht)

(Scattering Loss) Tn hao do un cong cp (Bending Loss) Tn hao do ghp ni (Coupling ang Splicing Loss)

Trong tn hao do ghp ni l quan trn nht.

85

Tnh ton ng truyn

Cng sut thu

d tr cng sut: l t s gia cng sut pht vi nhy my thu (cng sut thu ti thiu m b thu c th pht hin c):

Tng suy hao trn ng truyn phi nh hn d tr cng sut ca h thng

( ) ( ) ( )dBmPdBmPdBtPowerBudgePPtPowerBudge

rt

r

t

min

min

==

( ) ( ) ( ) ( ) ( ) ( )dBLNdBkmLkmdBdBmPdBmP couplingfibertr 0../ =

( ) ( ) ( ) ( ) ( )dBtPowerBudgedBLNdBkmLkmdB couplingfiber ++ 0../

86

Tnh ton ng truyn

Ch gii:

cng sut phtcng sut thu

suy hao trn mt n v chiu di cpsuy hao trn mt ln ghp cp

tng s ln ni cptng cc suy hao khc

tP

rP

fibercouplingN

0L

87

Bi tp 5

Xt mt h thng thng tin quang c cng sut pht bng 2mW v nhy ca b thu l 0.5W. d tr cng sut ca h thng? Gi s suy hao theo chiu di ca cp l

0.3dB/km, suy hao mi hn 0.05dB v c d=10km phi ni cp mt ln. Tnh khong cch truyn ti a ca h thng

=mWPdBm

1log10 10

88

L = 118.16Km

Bi tp 5

Gii: d tr cng sut ca h thng

S ln ni cp:

Chiu di ti a:

( ) ( ) ( )( ) ( ) dB

dBmPdBmPdBtPowerBudge rt3610.5lg102lg10 4

min

===

dLN

dL

89

Cc ngun pht quang

thc hin qu trnh thng tin quang, cn c cc ngun pht quang chuyn i tn hiu in thnh tn hiu nh sng a vo si quang, ng thi pha thu phi c cc thit b cha cc t bo nhy quang chuyn i nh sng thnh dng in x l khi phc thng tin.

90

Cc ngun pht quang

Cc ngun pht quang c s dng bao gm cc diode pht quang (LED Light Emitting Diode) v diode laser (Injection Laser Diode).

Cc LED l loi ngun r hn, do vy hi t ca tia sng khng cao, nhiu tia i vo cp cc gc khng thch hp s pht tn vo khng gian. Do cc LED ch thch hp cho khong cch ngn.

91

Cc ngun pht quang

Cc tia laser c th hi t trong mt vng hp, cho php iu khin chnh xc gc vo ca chm tia sng. Do , khng b tiu tn ra ngoi cp v gi c tnh cht ca tn hiu trn khong cch di.

Diode laser pht tia laser bc sng nh trc vi cng sut ph thuc vo dng in vo.

Cn c iu khin nhit n nh cng sut v nhit , trnh qu nhit cho thit b.

92

Injection Laser diode (ILD)

93

Thit b thu quang

Gi chung l photodetector, c nhim v chuyn i tn hiu quang thnh dng in.

Bao gm cc photodiode, photoresistor, phototransistor, ...

94

u, nhc im

u im Bng thng rng, tn hao thp, tc truyn cao Khng b nh hng bi cc ngun nhiu bn ngoi. Kch thc nh gn, trng lng nh. an ton thng tin cao

Nhc im Kch thc nh nn kh hn, ni. Ch truyn n hng Sn xut kh, gi thnh cao

95

ng dng ca cp quang

S dng cho cc mng ng trc, i hi cht lng cao, tc cao, tin cy cao, v d cc ng lin lc lin tnh, quc t,...

Mng my tnh tc cao: mng LAN 10Gbps Ethernet, mng FDDI,...

Cc cng ngh quang: WDM, DWDM Cc mng quang: SONET, SDH, ...

96

Suy

hao

ca cc mi trng

truyn

97

Ni dung trnh by


98

Thng tin v tuyn

Thng tin v tuyn c s dng trong nhng trng hp truyn trn khong cch xa hoc nhng i tng thng xuyn di ng.

99

c

im ca

knh

truyn v tuyn

Vn tc truyn sng in t gn bng vn tc nh sng c = 3.108 m/s.

Bc sng: Hai dng thng tin v tuyn ch yu l vi

ba mt t v thng tin v tinh. Vi ba mt t dng trong thng tin di ng,

truyn hnh cp MMDS. Thng tin v tinh dng cho cc dch v di ng truyn hnh trn khong cch xa

fc=

100

c

im ca mng

v

tuyn di ng

Hiu ng a ng

Trm gc

(BS)Trm di ng

(MS)

Truyn a ng

path-2

ng-2path-3

ng-3

path-1

ng-1

Thi gian

C

n

g

s

u

t

Tr ng dn

C

n

g

s

u

t

Xut hin cc nh

v

cc

im trng

ca cng sut thu

101

c

im ca mng

v

tuyn di ng

Hiu ng xa gn Khi tt c cc trm di ng pht tn hiu vi cng

cng sut (MS), mc cng sut thu trm gc (BS)s khc nhau i vi tng user.

Ph thuc vo khong cch gia BS v cc MS.

1k

102

c

im ca mng

v

tuyn di ng

Giao thoa a truy cp Gi s c K user s dng cng mt bng tn. User th 1 l user mong mun nhn tn hiu, cc

user khc l cc ngun giao thoa

4

13

5

2

6

103

c

im ca mng

v

tuyn di ng

Do truyn trn khong cch xa, vn suy hao l yu t chnh nh hng n cht lng tn hiu.

Ngoi yu t suy hao do khong cch, tn hiu cn b nh hng bi cc yu t t nhin nh nh hng ca bu kh quyn, ma, ...

104

Suy hao t nhin (FSL)

Khi truyn trong mi trng v tuyn, cng sut tn hiu gim t l vi bnh phng khong cch truyn. S suy hao ny gi l suy hao t nhin (suy hao trong khng gian t do Free Space Loss):

24

= dFSL

( )

= ddBFSL 4lg20

105

Bi tp 6

H thng thng tin c Khong cch 36.000km

Xc nh suy hao FSL tn s 400MHZ tn s 1GHz

Satellite

106

nh hng ca anten

Anten ng hng: cng sut bc x c phn b u theo mi hng.

Mt cng sut ti im cch antenna 1 khong d: ( ) 24 d

PdP t=

( ) 24 dAPAdPP erterr ==

d

Pt

Cng sut thu c ti anten thu

din tch hiu dng ca anten hiu sut ca anten

per AA =

107

Bi tp 7

Cho mt anten ng hng c cng sutpht 1W. Xc nh cng sut ti anten thubit din tch hiu dng ca anten thu l0,1m2.

2km

108

nh hng ca anten

Vi anten khng ng hng: cng sut c tp trung trong mt vi hng no .

nh hng ca anten ( li ca anten)Cng sut bc x cc i

Cng sut bc x trung bnhG =

109

nh hng ca anten

Nh vy, li antenna cho bit mc tp trung cng sut ca anten so vi mt anten ng hng tng ng.

li anten khng c ngha l mc khuch i cng sut.

n v ca Gt thng l dBi (i isotropic ng hng).

110

Cng sut bc x ng hng tng ng (EIRP)

Gi s t ng h o cng bc x trn hng cc i ca anten pht v cng sut o c l P.

Thay anten trn bng anten ng hng. ng h gi nguyn gi tr c, phi tng cng sut pht ln G ln.

Cng sut bc x ng hng c nh ngha(EIRP Equivalent Isotropic Radiated Power):

( ) ( ) ( ) ( )dBGdBWPGPdBWEIRPGPEIRP

tttt

tt

+===

lg10

111

Cng

thc tnh

li ca

anten

Gi Ae l din tch hiu dng ca antenna,Ap l din tch hnh hc ca antenna, l hiu sut antenna, l bc sng pht th:

22

44

pe AAG ==

112

Cc cng sut tnh cng sut thu

T cc phn tch trn, rt ra cc cng thc sau:

Mt cch tng qut, ta c phng trnh truyn v tuyn nh sau:

L0: cc suy hao khc

24.

dAGP

FSLGEIRPP erttrr ==

( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( )dBGdBLdBFSLdBGdBWP

dBGdBLdBFSLdBWEIRPdBWP

rtt

rr

++=+=0

0

113

Tnh ton ng truyn v tuyn da trn t s Eb

/No

yu cu

Thng thng cht lng tn hiu thu c nh gi qua t s Eb/No

t cht lng thu th Eb/No phi ln hn gi tr ngng:

( )kTRP

NTP

NE rbrb ==

00

( ) ( ) ( ) ( ) ( ) ( ) ( )( )rq

br

b

NEHzdBWkTdBbpsRdBiGdBLdBFSLdBWEIRPdB

NE

+=

00

0

/

( ) ( ) ( )kTRdBWPdBNE

rb lg10lg100

=

R: tc bit (bps)k: hng s Boltzman (J/K)T: nhit tuyt i (K)

Tb

: chu k bit (s)

114

Bi tp 8

Cho h thng thng tin v tinh c cc thng s nh sau: Cng sut pht trm mt t: 500W li antenna pht:18dBi Tn s pht: 375MHz Khong cch: 36000km Cc suy hao khc: 2dB Tc d liu: 100kbps T s G/T ca my thu: -12,9dB/K T s Eb/No yu cu: 10dB

Hi h thng c hot ng c khng? Nu c th d tr ca h thng l bao nhiu dB?

115

Cu hi?

Chng 2 Cc phng tin truynNi dung trnh byKhi nim knh truync tnh ca knh truync tnh ca knh truync tnh ca knh truynPhn loi mi trng truynPhn b ph in tNi dung trnh byCap xon (Twisted Pair)Cc thng s s cp Cc thng s th cpCap xon (Twisted Pair)Cap xon (Twisted Pair)Cap xon (Twisted Pair)Cap xon (Twisted Pair)Cap xon (Twisted Pair)UTP - Unshielded Twisted Pairu ni cp UTP 8 dyPhn loi cp UTPPhn loi cp UTPCap xon UTP Category 6Cp UTP nhiu cpu ni cp nhiu cpu nhc im ca UTPSTP - (Shielded Twisted pair)STP - (Shielded Twisted pair)STP - (Shielded Twisted pair)u ni STPChun muMau sc chunng dng ca cp xonNi dung trnh byCap ng truc (Coaxial Cable)Cap ng truc (Coaxial Cable)Cap ng truc (Coaxial Cable)u ni cp ng trcChun cp ng trcCap ng truc (Coaxial Cable)Cap ng truc (Coaxial Cable)Cap ng truc (Coaxial Cable)u nhc imng dng ca cp ng trcBi tp 1Bi tp 2Bi tp 3Ni dung trnh byCap quang (Fiber Optics)Cap quang (Fiber Optics)Cap quang (Fiber Optics)Cap quang (Fiber Optics)Cap quang (Fiber Optics)Cc kiu cp quangCp quang 6 coreCap quang (Fiber Optics)u ni cp quangu ni cp quangu ni cp quangu ni cp quangPhn loi cp quangMultimodeSi quang a modeSi quang a modeSi quang a modeMultimode graded-indexMultimode graded-indexMultimode graded-indexSingle mode (n mode)Cp quang n modeBc sng ct ca cp quangBi tp 4So snh cc loi cp quangS khc xnh lut khc x SnellGc ti gii hnHin tng phn x ton phnHin tng phn x ton phnTruyn nh sng trong si quangTruyn nh sng vo si quangTruyn nh sng vo si quangTruyn nh sng vo si quangKhu ca cp quang - NATn hao trong cp quangTn hao trong cp quangTnh ton ng truynTnh ton ng truynBi tp 5Bi tp 5Cc ngun pht quangCc ngun pht quangCc ngun pht quangInjection Laser diode (ILD)Thit b thu quangu, nhc imng dng ca cp quangSuy hao ca cc mi trng truynNi dung trnh byThng tin v tuync im ca knh truyn v tuync im ca mng v tuyn di ngc im ca mng v tuyn di ngc im ca mng v tuyn di ngc im ca mng v tuyn di ngSuy hao t nhin (FSL)Bi tp 6 nh hng ca antenBi tp 7 nh hng ca anten nh hng ca antenCng sut bc xa ng hng tng ng (EIRP)Cng thc tnh li ca antenCac cng sut tinh cng sut thuTinh toan ng truyn v tuyn da trn ty s Eb/No yu cuBi tp 8Cu hi?

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