TTVT-Chuong 2-Phan Tich Tuyen

8/14/2019 TTVT-Chuong 2-Phan Tich Tuyen

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MN HCTHNG TIN V TINH

Chng 2:Phn tch tuyn (7t)


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Chng 2:

Phn tch tuyn2.1 Cc thng s c tnh ca anten

2.2 Cng sut pht mt hng cho

2.3

Cng sut thu c anten thu trong ng truyn khngcan nhiu

2.4 Cng sut tp m ti u vo my thu

2.5T s cng sut sng mang trn tp m ti u vo mythu

2.6nh hng ca mi trng truyn song n cht lngtruyn dn C/N

2.7 B nh hng ca mi trng truyn sng

2.8 T s cng sut sng mang trong tuyn n trm n trm


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Cc thng s c tnh ca anten:

li nh ngha: li t cc i theo hng pht x cc i

Hng trc ca Anten


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rng bp sng rng bp sng chnh ca anten:

Gc gia hai im m li ca anten gim 3dB Cn gi l rng bp sng na cng sut Gc c gi l gc 3 dB.


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rng bp sng Antenna radiation pattern (cu trc bp sng ca Anten)


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rng bp sng Vi anten parabol:

Trn hng lch vi hng trc mt gc : li ca anten (ch ph hp vi gc nh hn gc 3 dB):


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rng bp sng Ta c:

Nu =0.6, ta c:

li theo dB v rng bp sng 3 dB theo :


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Chng 2:



2.3








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Cng sut pht mt hng cho Mt hng c li l GTs bc x qua mi n v

gc khi (solid angle) mt cng sut l:

Cng sut bc x ng hng tng ng :

EIRP: Equivalent isotropically radiated power(Cng sut bc x ng hng tng ng)


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Cng sut pht mt hng cho Mt b mt:

C din tch hiu dng A, Cch anten pht R

C mt gc khi vi anten pht l A/(R^2) Thu c mt lng cng sut l:

i lng

c gi l mt lung cng sut(power flux density)

hay mt cng sut thu c, mt thng lng cng sut.


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Chng 2:



2.3








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Cng sut thu c anten thu

trong ng truyn khng can nhiu Mt anten thu:

C din tch hiu dng Areff (din tch tng ng) Cch anten pht R

Thu c mt lng cng sut l:

Din tch tng ng ca mt anten l mt hmtheo li ca anten thu:


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Cng sut thu c anten thu

trong ng truyn khng can nhiu V vy, cng sut thu c:

Trong , suy hao trong khng gian t do:


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Cng sut thu c anten thutrong ng truyn khng can nhiu

V d 1: tuyn ln Anten trm mt t c D = 4m Cng sut pht PT= 100 W, tc l 20 dB(W) fu = 14 GHz

VT cch TM 40.000 km, nm trn trc anten TM Bp sng thu 3dB ca v tinh l 2 Gi thit trm mt t t trung tm vng ph ca anten

v tinh ( li cc i) Hiu sut ca anten v tinh l 0.55 v mt t l 0.6 Tnh mt lung cng sut v cng sut thu c bi v

tinh


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V d 1: p s Mt lung cng sut: = -89.9 dB (W/m^2) PR= -96.1 dB (W) tc l 0.25 nW hay 0.25 pW


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V d 2: tuyn xung Cng sut pht PT= 10 W, tc l 10 dB(W) fD = 12 GHz

Bp sng 3dB ca v tinh l 2 TM c anten D = 4m, nm trn trc ca anten v tinh TM cch VT 40.000 km Hiu sut ca anten v tinh l 0.55 v mt t l 0.6

Tnh mt lung cng sut v cng sut thu c bitrm mt t


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V d 2: p s Mt lung cng sut: = -114.8 dB (W/m^2) PR= -106.1 dB (W) tc l 25 pW


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Trong thc t cn cn c thm suy hao do cc yut: Suy hao do kh quyn Suy hao do cc thit b ti u pht v u thu Suy hao do ng b khng hon ho ti cc anten Suy hao do lch phn cc


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Suy hao do cc thit b ti u pht v u thu: Suy hao ca cc fider (LFTX, LFRX) c c cng sut PTti anten, cng sut cn c ti u

ra my pht: PTX= PT.LFTX (W) EIRP = PT GT = PTX GT/ LFTX (W)

Tng t, cng sut ti u vo my thu: PRX= PT/LFTX (W)


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Suy hao do lch phn cc: Do anten thu khng hng ng vi phn cc ca sng thu

c Do sng mang phn cc b xoay mt phng phn cc di

tc ng ca ng truyn nh fading, Faraday

Trong : : gc gia mt sng thu c vi mt sng phn cc LPol: thng ly 3 dB trong trng hp phn cc trn


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Tng hp cc ngun suy hao, biu thc

Tr thnh:


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Chng 2:Phn tch tuyn

2.1 Cc thng s c tnh ca anten


2.3

Cng sut thu c anten thu trong ng truyn khng

can nhiu







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Cng sut tp m ti u vo mythu

Ngun gc ca tp m: Cc ngun bc x t nhin nm trong vng thu ca anten Cc thnh phn in t trong thit b

Tn hiu t cc my thu khc cng l mt dng tpm c gi l nhiu


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Cng sut tp m ti u vomy thu

M hnh tp m: tp m trng (white noise) Mt ph cng sut tp m N0(W/Hz) l hng s

Cng sut tp m tng ng N (W) o c trongbng thng B (Hz):


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Mt ngun tp m sinh ra mt cng sut tp m N cmt nhit tp m l:

Trong : k: hng s Boltzmann, = 1.379 x 10^-23 = -228.6 dB (W/HzK) T i din cho nhit ca mt in tr, m in tr ny sinh

ra mt cng sut tp m cng l N.


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Nhit tp m:


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Nhit tp m tng ng ca mt h thng(Te):


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H s tp m (noise figure) ca mt h thng: l t s gia tng cng sut tp m ti u ra ca h thng Vi thnh phn cng sut tp m do mt ngun sinh ra ti

u vo ca h thng vi nhit tp m l T0=290 K. K hiu: F


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Tp m ca anten: Do cc vt th bc x nm trong gin bc x ca anten c c trng bi nhit tp m ca anten:


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Tp m ca mt b suy hao: B suy hao l mt h thng ch c in tr


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Nhit tp m ca thit b gm nhiu phn t nitip:


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p dng vo nhit tp m u thu:


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V d 1: Nhit tp m ca anten: 50 K Nhit vt l ca kt ni (fider): 290 K Nhit tp m ca my thu: 50 K Tnh nhit tp m ca h thng trong hai trng hp:

Khng suy hao kt ni Suy hao kt ni l 1 dB

p dng:

Khng suy hao: T2 = 50 + 50 = 100 K

C suy hao: T2=50/10^0.1+290(1-1/10^0.1)+50 = 149.3 K


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Bi tp 1: Nhit tp m ca anten: 60 K Nhit vt l ca kt ni (fider): 290 K Nhit tp m ca my thu: 70 K Tnh nhit tp m ca h thng trong hai trng hp:

Khng suy hao kt ni Suy hao kt ni l 1.5 dB


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Bi tp 2: Nhit tp m ca anten: 70 K Nhit vt l ca kt ni (fider): 290 K Nhit tp m ca my thu: 60 K Tnh nhit tp m ca h thng trong hai trng hp:

Khng suy hao kt ni Suy hao kt ni l 2 dB


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Chng 2:Phn tch tuyn



2.3Cng sut thu c anten thu trong ng truyn khng

can nhiu



2.6 nh hng ca mi trng truyn song n cht lngtruyn dn C/N




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T s cng sut sng mang trn tpm ti u vo my thu

Cc nh ngha: C/N: t s cng sut tn hiu trn cng sut tp m C/N0: t s cng sut tn hiu trn mt cng sut tp m

Tnh bng Hz C/T: t s cng sut tn hiu trn nhit tp m

Tnh bng W/K

S dng rng ri nht: C/N0


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T s cng sut sng mang trntp m ti u vo my thu

Nhit tp m ca anten: Hng ln:

L mt hm theo qu o vi tn s t 1 51 GHz (Fig 2.14) C th ly gn ng: 290 K

Hng xung: Tri quang: TA= TSKY+ TGROUND

Tri ma: TA= TSKY/ARAIN+ Tm(1 - 1/ARAIN) + TGROUND ARAIN: suy hao do ma Tm: nhit vt l bn ngoi, trong khong 260 280 K


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V d: TLNA= 150 K, GLNA= 50 dB

TMX= 850 K, GMX= -10 dB (LMX= 10 dB)

TIF= 400 K, GIF= 30 dB

Vy, TR= 150 + 850/(10^5) + 400/(10^5).(10^-1)= 150 K.


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Bi tp: TLNA= 200 K, GLNA= 60 dB

TMX= 800 K, GMX= -20 dB (LMX= 10 dB)

TIF= 500 K, GIF= 30 dB

Vy, TR= ?.


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V d 1: tuyn ln,tri quang

fu = 14 GHz

Trm mt t (ES): PTX = 100 W

LFTX= 0.5 dB

D = 4 m = 0.6 T = 0.1

R= 40 000km

LA= 0.3 dB

V tinh (SL): rng bp sng 3dB: 2 = 0.55

H s tp m F= 3dB LRTX= 1 dB

TF= 290 K

TA= 290 K

ES nm bin vng ph

sng 3 dB ca SL LR= 3 dB


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Kt qu: EIRP (ES) = 71.7 dB (W)

Lu = Lfs + LA = 207.7 dB

G/T = 6.6 dB K^(-1)

(C/N0)u = (EIRP).(1/Lu).(G/T)(1/k)

= 71.7 - 207.7 + 6.6 + 228.6 = 99.2 dB Hz


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V d 2: tuyn ln nh VD1,tri ma

fu = 14 GHz

Trm mt t (ES): PTX = 100 W

LFTX= 0.5 dB

D = 4 m

= 0.6

T = 0.1 R= 40 000km

Arain = 10 dB

LA= 0.3 dB + 10 dB = 10.3 dB

V tinh (SL): rng bp sng 3dB: 2 = 0.55

H s tp m F= 3dB LRTX= 1 dB

TF= 290 K

TA= 290 K

ES nm bin vng ph

sng 3 dB ca SL


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V d 3: tuynxung, tri quang

fu = 12 GHz

V tinh (SL): PTX = 10 W

LFTX= 1 dB

RBS 3dB = 2

= 0.55

R= 40 000km

LA= 0.3 dB

Trm mt t (ES): H s tp m F= 2.2 dB LRTX= 0.5 dB

TF= 290 K D = 4 m

= 0.6

R = 0.1 TGROUND= 45 K

TSKY = 20 K

ES nm bin vng phsng 3 dB ca SL LT= 3 dB


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Kt qu: EIRP (SL) = 44.2 dB (W)

LD = Lfs + LA = 206.4 dB

G/T (ES) = 26.2 dB K^(-1)

(C/N0)u = (EIRP).(1/Lu).(G/T)(1/k)

= 44.2 - 206.4 + 26.2 + 228.6 = 92.6 dB (Hz)


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V d 4: tuynxung, tri ma

fu = 12 GHz

V tinh (SL): PTX = 10 W

LFTX= 1 dB

RBS 3dB = 2

= 0.55

R= 40 000km

LA= 0.3 dB

Trm mt t (ES): H s tp m F= 2.2 dB LRTX= 0.5 dB

TF= 290 K D = 4 m

= 0.6

R = 0.1 TGROUND= 45 K

TSKY = 20 K Arain = 7dB

Tm = 275 K

ES nm bin vng phsng 3 dB ca SL LT= 3 dB


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Kt qu: EIRP (SL) = 44.2 dB (W)

LD = Lfs + LA =213.4 dB

TA = 265 K

G/T (ES) = 24.1dB K^(-1) (C/N0)u = (EIRP).(1/Lu).(G/T)(1/k)

= 44.2 - 213.4 + 24.1 + 228.6 = 83.5 dB (Hz)


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nh hng ca mi trng truynsng n cht lng truyn dn C/N

C 2 tng gy nh hng: Tng i lu: 0-15 Km Tng in ly: 70-1000 Km

Vng gy ng hng ln: tng i lu: ~ gn mt t tng in ly: ~ 400 km

Cc nh hng cp: Suy hao LA Nhit tp m ca anten

Mt s nh hng khc


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nh hng ca mi trng truynsng n cht lng truyn dn C/N

Cc nh hng khc: nh hng ca ma:

Suy hao

Phn cc cho Suy hao do cc loi kh trong kh quyn Suy hao do bo ct

S khc x Hiu ng faraday

S phn cc cho do tinh th nc Hin tng a ng trn mt t

Xem chi tit ti liu G.Maral, M.Bousquet, SatelliteCommunications Systems,


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Chng 2:Phn tch tuyn




can nhiu







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B nh hng ca mi trng truynsng

Phn cc cho Gia vo s iu chnh c tnh phn cc ca cc trm mt

t: Uplink: iu chnh phn cc ca anten pht ph hp vi phn

cc ca anten thu v tinh Downlink: iu chnh phn cc ca anten thu ph hp vi phn

cc ca tn hiu thu c

B suy hao: d tr fading

Phn tp khng gian Thch nghi

Xem ti liu


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Chng 2:Phn tch tuyn




can nhiu







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T s cng sut song mang trongtuyn n trm n trm


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TTVT-Chuong 2-Phan Tich Tuyen