1

LLuunn vvnn

TTNNHH TTOONN VV TTHHIITT KK

HH TTHHNNGG VV TTIINNHH VVSSAATT

2

11.. GGIIII TTHHIIUU CCHHNNGG

MMcc cchh cchhnnhh ccaa vviicc tthhiitt kk ll tthhiitt llpp tt ss CC//NN tthheeoo yyuu ccuu ..VV vvyy

ttrrnngg ttmm ccaa cchhnngg nnyy ll ttnnhh ttoonn cc llyy tthhnngg ttiinn,, kktt nnii nngg llnn,, nngg

xxuunngg.. TT kkiimm ttrraa xxeemm ttuuyynn tt cchhtt llnngg ssoo vvii yyuu ccuu hhaayy kkhhnngg,,qquuaa

tthhiitt llpp ttrrmm mmtt tt pphh hhpp..

Cu trc truyn dn tin tin i vi c 2 ng ln v xung.

II. CC THNG S CN CHO TNH TON

1. Cu hnh trm mt t cn chn ch yu l cc tham s:

Loi anten (ng knh, hiu sut, h s phm cht, nhit tp m).

Cng sut my pht.

Ngi Dng

Tp on, Vn phng, Dch v, ISPs (Nh

cung cp Dv Internet), Di pht thanh

Cp Quang

iPSTAR GATEWAY

Other iPSTAR Gateways

Internet, PSTN, Public & Private networks

Return Links (from Terminal to Gateway)

Forward Links (from Gateway to Terminal)

3

2. Vic tnh ton s da trn mt s gi thit cho trc nh:

Cht lng tn hiu yu cu.

Cc tham s suy hao.

H s d tr.

3. Cc tham s s dng trong tnh ton thit k c th phn chia theo thnh

phn h thng lin quan nh:

Trm mt t

+ V tr a l ca trm, tnh ton cc tham s nh suy hao do ma (y cng l

ngun gy nhiu lon ngu nhin nht), gc nhn v tinh, c ly thng tin, suy hao

ng truyn.

+ Mc cng sut pht x ng hng tng ng (EIRP_Equivalent Isotropic

Radiated Power): cng sut pht x, h s phm cht (G/T)e ca trm.

+ Nhit tp m h thng: lin quan ti nhy v h s phm cht.

+ nh hng ca tp m iu ch bn trong ti t s tn hiu trn tp m.

+ Cc c im ca thit b (suy hao fi, suy hao phn cc anten, c tnh b

lc ...) bit h s d tr kt ni T.

V tinh

+ V tr ca v tinh trn qu o.

+ Mc EIRP ca v tinh, h s phm cht (G/T)s ca v tinh.

+ Bng thng my pht p, dng phn cc, di tn lm vic.

+ Mt thng lng bo ho.

+ Mc li cng sut u vo (IBO), u ra (OBO).

5. Khi xem xt n nhiu cc nh vn hnh v tinh s dng nhiu phng php

khc nhau (nh Intersat s dng thng s C/N(dB) xem xt nhiu trong khi

Eutesat th ngc li s dng C/No(dBHz)). Cht lng v sn dng oc nh

ngha l cc khong % thi gian m trong cc mc ngng BER khng c vt

qu.

Trc khi i vo tnh ton bi ton c th ta cn xem xt vn nh :

4

Vic xc nh kch thc Aten v cng sut yu cu trn mt ng truyn

l ty thuc vo li ca b pht p. li ny thng c a ra trng

thi bo ha ca b pht p. iu ny cn ty thuc vo c tnh phi tuyn

TWT hay SSPA ca b pht p.

S chim dng ca mt mng VSAT c th c miu t bi 2 i lng :

+ S chim dng bng thng : l t s tng cc bng tn c phn phi

cho mi sng mang ca mng chia cho rng bng thng b pht p.

+ S chim dng cng sut : l t s EIRP cn dng cho mi sng mang

ca mng chia cho EIRP hu dng ca b pht p (EIRP trng thi

bo ha tr cho ton b mc li u ra.

22.. BBII TTOONN TTHHCC TT::

2.1. Gii thiu chung

Mc ch chnh ca vic thit k l thit lp t s C/No theo yu cu ti u vo

my thu. V vy trng tm ca chng ny l tnh ton cc thng s c la chn k

lng nhn dc t s C/No u vo my thu t yu cu, t kim tra xem

tuyn t cht lng so vi yu cu hay khng. Qua , da vo cc thng s tnh

c la chn cc cu hnh cn thit cho vic thit lp trm mt t trong thng tin

v tinh.

2.2 M hnh v cc thng s ca mt tuyn thng tin

2.2.1 M hnh tuyn

5

Hnh 2.2 : M hnh hot ng ca mng VSAT IPSTAR.

2.2.2 Tnh ton gc ngng v gc phng v

2.2.2.1 Gc ngng

tnh gc ngng anten trm mt t, ta c th da vo hnh v 2.3

Hnh 2.3 : Tnh ton gc ngng

Trong hnh 2.3 : O l tm tri t, A l v tr ca trm mt t, S l v tr ca v tinh,

0 l gc tm, e l gc ngng ca trm mt t.

Trm Uts pht

Trm Uts thu

Trm cng GW

V TINH

M

V tinh

e

r Tm qu t

Re 0

R

S

A

6

Ta c SMMAtg e

Trong , eRrOAOSOAOMMA 00 coscos.

00 sinsin. rOSSM

T suy ra: 0

0

0

0

sin

cos

sincos

rR

rRrtg

e

ee

2.2.2.2 Gc phng v

Gc phng v l gc dn ng cho anten quay tm v tinh trn qu o a tnh

theo hng t ng sang Ty.

Gc phng v c xc nh bi ng thng hng v phng Bc i qua trm mt

t vi ng ni n v tinh. Gc c xc nh theo chiu kim ng h nh hnh 2.3. Gc

phng v c tnh theo biu thc:

a = 1800 + kinh ty hoc

a = 1800 - kinh ng

a ph thuc vo kinh , va kinh ti im thu v kinh v tinh. Gc phng

v ca 2 v tinh c tnh theo cng thc:

V tinh 1: a1 = 1800- kinh ng

V tinh 2: a2 = 1800+ kinh ty

Gc phng v a c tnh theo cng thc:

Cc Bc

450W 300 E

Gc phng v ca v tinh 2 Gc phng v ca v tinh 1

V tinh 2 V tinh 1

Hnh 2.3 Gc phng v ca v tinh

7

)sin(

Ltgtg ea

(2.2)

Vi l v ca trm mt t ().

eL l hiu kinh ng ca v tinh vi trm mt t, eL = Ls - Le .

2.2.3 Tnh ton kt ni ng ln (UPLINK). 2.2.3.1 Cng sut pht ca trm mt t PTXe (e - phn bit ca trm mt t

"earth station", sl - l ca v tinh "satellite")

y l cng sut pht thc ca trm mt t tnh t Anten trm mt t v c tnh

bng tch li u ra OBO vi cng sut pht trm mt t bo ha PTXsat.

PTXe = OBO * PTXsat hay PTXe(dBW) = OBO(dB) * PTXsat (dBW) (2.3) OBO l li u ra ca Anten trm mt t cng l d tr cng sut cho trm khi

tri ma OBO = - Arain (suy hao do ma).

2.2.3.2. H s khuch i anten pht trm mt t GTXe

li anten l thng s rt quan trng trong trm mt t, anten t ng vo

khuch i tn hiu rt nh t picowatt n nanowatt. khuch i ln s lm tng t s

C/No, n lin quan n c tnh cho anten v bng tn cng tc:

2

log10

cDfG UTXe

hoc: dBcDfG UTXe )lg(20)lg(20)lg(10 (2.4) vi : D l ng knh ca anten pht.

Uf l tn s tn hiu pht ln.

l hiu sut ca anten, thng khong t 50% - 80% .

c l vn tc nh sng, c = 3.108 m/s.

2.2.3.3 Cng sut bc x ng hng tng ng ca trm mt t eEIRP .

Cng sut bc x hiu dng EIRP (Equivalent Isotropic Radiated Power) cn gi l

cng sut bc x ng hng tng ng, n biu th cng sut ca chm sng chnh pht

t trm mt t n v tinh. c tnh bng tch ca cng sut my pht a ti anten trm

mt t PTXe vi h s tng ch ca anten pht GTxe.

TXeTXee GPEIRP (W)

8

hoc: TXeTXee GPEIRP )lg(10 [dBW] (2.5)

EIRPe thng thng ca trm mt t c gi tr t 0dBW n 90dBW, cn ca v tinh

t 20dBW n 60dBW.

2.2.3.4. Tng suy hao tuyn ln LU.

Tng suy hao tuyn ln: AU LLL FS (dB) (2.6)

Trong : FSL - suy hao tuyn pht trong khng gian t do.

AL - suy hao do Anten (do ma v tng kh quyn).

Trong : Suy hao tuyn ln trong khng gian t do c tnh theo biu thc:

)lg(20)4lg(20 cRfL UFS (dB) (2.7)

Suy hao tuyn ln Anten c tnh theo biu thc:

rainAGA AAL . (dB) (2.8)

Vi: AAG: suy hao tng kh quyn.

Arain: suy hao do ma.

2.2.3.5. li Anten thu (/m2) G1 )/( 2mdBW .

li ca anten thu (trn 1m2) c tnh bng biu thc:

2

21 44

cfG URX

(2.9)

Vi : Uf : l tn s tn hiu pht ln.

c : l vn tc nh sng, c = 3.108 m/s.

2.2.3.6. Mt dng cng sut bc x hiu dng (trn 1m2) ca trm mt t

1(dBW/m2).

Mt dng cng sut bc x hiu dng trn 1m2 c tnh bng cng thc:

121 / GLdBWEIRPmdBW Ue (2.10) Vi : EIRPe : Cng sut bc x ng hng ca trm mt t

LU : Suy hao tuyn ln.

G1 : li ca anten thu (trn 1m2)

2.2.3.7. li u vo IBO.

a) li u vo IBO1 ca mt trm.

IBO1 c tnh bi cng thc:

9

sat

IBO1

1

Hay: 22121 /// mdBWmdBWmdBWIBO sat (2.11) Vi : 1 : Mt dng cng sut bc x mt t trn 1m2

sat : Mt dng cng sut bc x bo ha (v tinh) trn 1m2

b) li u vo tng IBOt.

IBO1 c tnh bi cng thc:

satsat

ttIBO

1

Hay: 222 /// mdBWmdBWmdBWIBO sattt (2.12) Vi : t : Tng mt dng cng sut bc x mt t trn 1m2

sat : Mt dng cng sut bc x bo ha (v tinh) trn 1m2

2.2.3.8. T s sng mang trn tp m tuyn ln (C/No)U Trong cc tuyn thng tin v tinh, cht lng ca tuyn c nh gi bng t s

cng sut sng mang trn cng sut tp m (C/No), hay cng sut sng mang trn nhit tp

m tng ng (C/To). Tp m ch yu ph thuc vo bn thn my thu, vo mi trng

bn ngoi nh mi trng truyn sng v can nhiu ph thuc cc h thng viba ln cn

1) T s sng mang trn tp m tuyn ln bo ha (C/No)Usat. T s sng mang trn tp m tuyn ln bo ha (C/No)Usat c tnh theo cng thc:

kTGGNC SLsatUsat 11/ 1

(Hz)

)/(log10)/()/()/()(/ 212 KdBJkKdBTGmdBGmdBWdBHzNC ooSLsatUsat (2.13)

Trong : sat : Mt dng cng sut bo ha (v tinh) trn 1m2

G1 : li Anten thu (/m2).

(G/T)SL : H s phm cht my thu v tinh.

k : l hng s Boltzman, k =1,38.10-23 (J/oK).

2) T s sng mang trn tp m tuyn ln mt trm mt t (C/No)U1. T s sng mang trn tp m tuyn ln ca trm mt t (C/No)Usat c tnh theo

cng thc:

10

11/ IBONCNC satOU

(Hz)

1log10)(/ IBONCdBHzNC

satOU (2.14)

Trong : (C/No)Usat :T s sng mang trn tp m tuyn ln bo ha.

IBO1 : li u vo ca mt trm mt t.

2.2.4 Tnh ton kt ni ng xung (DOWNLINK). 2.2.4.1. H s khuch i anten thu trm mt t GRXe

H s khuch i anten thu trm mt t c biu thc tnh tng t nh i vi h s khuch i anten pht trm mt t:

2

log10

cDfG DRXe

dBcDfG DRXe )lg(20)lg(20)lg(10 (2.15) vi : D :ng knh ca anten pht.

Df :Tn s tn hiu pht xung.

: hiu sut ca anten, thng khong t 50% - 80% .

c l vn tc nh sng, c = 3.108 m/s.

2.2.4.2 Tng suy hao tuyn xung LD Tng suy hao tuyn ln: AFSD LLL (dB) (2.16)

Trong : LFS - suy hao tuyn xung trong khng gian t do.

LA - suy hao do Anten (do ma v tng kh quyn).

Trong *Suy hao tuyn xung trong khng gian t do c tnh theo biu thc: )lg(20)4lg(20 cdfL DFS (dB) (2.17)

*Suy hao tuyn ln Anten c tnh ging nh tuyn ln:

2.2.4.3. H s phm cht ca trm mt t (G/T)E.

H s phm cht ca trm mt t (G/T)E c tnh bng biu thc:

polREE LLTGTG max (dB/0K) (2.18) Trong : (G/T)Emax : H s phm cht cc i ca trm mt t.

LR : suy hao lch tm.

Lpol : Suy hao do phn cc.

: Tng suy hao do Feeder v do ma.

11

Hnh : hjg

y (G/T)Emax c tnh bng biu thc:

minmaxmax

1/D

ERE TGTG (oK-1)

minmaxmax log10/ DERE TGTG (2.20) Trong : GRmax: li Anten thu.

TDmin : Nhiu nhit ng xung(khng c thnh phn nhiu

do ma)

Hnh : a) TDmin Khng b nhiu do ma, b) TD B nhiu do ma

Vi TDmin c tnh bng biu thc:

RgroundskyD TTTT min

Trong : Tsky:nhiu nhit bu tri.

12

Tground:nhiu nhit mt t.

TR : nhiu nhit vo

2.2.4.4. T s sng mang trn tp m tuyn xung bo ha (C/No)Dsat.

T s sng mang trn tp m tuyn xung bo ha (C/No)Dsat c tnh theo cng

thc:

kTGLEIRPNC ESDSLsatDsat 11/ 0

(Hz)

)/(log10)/()()/()(/ 20 KdBJkKdBTGdBLmdBWEIRPdBHzNC ooESDSLsatDsat (2.21)

Trong : EIRPSLsat : Cng sut bc x bo ha (v tinh) trn 1m2

G1 : li Anten thu (/m2).

(G/T)SL : H s phm cht my thu v tinh.

k : l hng s Boltzman, k =1,38.10-23 (J/oK).

2.2.4.5. Cng sut bc x ng hng tng ng ca mt sng mang EIRP1.

Cng sut bc x ng hng tng ng mt sng mang EIRP1 c tnh bng

cng thc:

11 OBOEIRPEIRP SLsat (W)

hoc: )()( 11 dBIBOdBWEIRPEIRP SLsat [dBW] (2.22)

trong :

2.2.4.6. li u ra OBO.

a) Tng li u ra OBOt .

13

Figure A6.2 OBOt as a function of IBOt

Tng li u ra OBOt c tnh bng biu thc:

TXsat

TXt P

POBO

Hay:

dBIBOdBdBdBOBOdBIBOdBIBOdBOBO

tvi

t

tvi

tt

05)(0)(

5)5)((9.0)( (2.23)

Trong :

b) li u ra OBO1 . Tng li u ra OBOt c tnh bng biu thc:

nOBOdBOBO

nOBOOBO

t

t

log10)(1

1

Hay: )5)((9.0)( 11 dBIBOdBOBO (2.24)

Trong :

14

2.2.4.7. T s sng mang trn tp m nhiu tuyn xung trn mt sng mang

(C/No)D1.

Figure 5.18 Geometry of the downlink. P TX: carrier power at satellite

transmitter output; L FTX: feeder loss from satellite transmitter to antenna;

P T: carrier power fed to the satellite antenna GT: satellite antenna transmit

gain in direction of earth station; T: satellite antenna half beamwidth angle;

GRmax: earth station antenna receive gain at boresight; R: earth station

antenna depointing angle; L FRX: feeder loss from earth station antenna to

receiver input; CD: carrier power at receiver input; RX: receiver

T s sng mang trn tp m nhiu tuyn xung trn mt sng mang (C/No)D1 c

tnh bng biu thc:

Dsat

D NCOBONC

0110/ (2.25)

Trong :

2.2.4.8. T s sng mang trn tp m nhiu xuyn iu ch tuyn xung trn

sng mang (C/No)IM (IM intermodulation :xuyn iu ch).

15

Hnh : a) Nhiu xuyn iu ch tuyn xung do bp sng khc(v tinh).

b) Nhiu xuyn iu ch tuyn xung do trm GetWay khc.

T s sng mang trn tp m nhiu xuyn iu ch tuyn xung trn sng mang

(C/No)IM c tnh bng biu thc:

dBIBOdBOBOnNC tvitIM 5)5)((65.1log1079/ 0 (2.26) Trong :

GW UT

Satellite

GetWay UT

Satellite

a)

b)

16

2.2.4.9. T s sng mang trn tp m nhiu giao thoa tuyn xung trn sng

mang (C/Noi)D (i interference :giao thoa).

Hnh : a) Nhiu giao thoa tuyn xung do bp sng v tinh khc.

b) Nhiu giao thoa tuyn xung do trm GetWay khc.

a)

b)

17

T s sng mang trn tp m nhiu giao thoa tuyn xung trn sng mang (C/Noi)D

c tnh bng biu thc:

)65.1log(25,minlog10log10/ maxmax,max,0 RXiiSLiSLwDi GBNBBEIRPEIRPNC (2.27)

Trong :

2.2.4.10. T s sng mang trn tp m nhiu ton tuyn trn sng mang (C/No)t.

T s sng mang trn tp m nhiu ton tuyn trn sng mang (C/No)t c tnh bng

biu thc:

1110101010 ////// DiUiIMDUt NCNCNCNCNCNC (Hz-1) Hay:

10

/10

/10

/10

/

0 10101010log10/000 iIMDU NCNCNCNC

tNC (dBHz)

(2.28)

Trong :

========================

T s sng mang trn tp m tuyn xung (C/No)D Trong cc tuyn thng tin v tinh, cht lng ca tuyn c nh gi bng t s

cng sut sng mang trn cng sut tp m (C/No), hay cng sut sng mang trn nhit tp

m tng ng (C/To). Tp m ch yu ph thuc vo bn thn my thu, vo mi trng

bn ngoi nh mi trng truyn sng v can nhiu ph thuc cc h thng viba ln cn

a) T s sng mang trn tp m tuyn ln bo ha (C/No)Dsat.

18

2.4.1 Cng sut bc x hiu dng ca v tinh Cng sut bc x hiu dng EIRPs ca v tinh cn gi l cng sut pht x ng

hng tng ng, n biu th cng sut ca chm sng chnh pht t v tinh n trm mt t. EIRPs ca v tinh thng thng c cho trc .

2.4.4 Cng sut sng mang thu c trm mt t Cng sut sng mang nhn c ti u vo my thu trm mt t c xc nh theo

biu thc : ReDsRe GLEIRPC (dB) (2.12) vi : GRe l h s khuch i ca anten thu trm mt t 2.4.5 Cng sut tp m h thng Cng sut tp m h thng c tnh bng biu thc: BlogTlogklog)BkTlg(N SYSYSSSYS 10101010 6,228log10 k TSYS l nhit tp m h thng c xem l tng ca bn thnh phn c biu din

theo biu thc:

RF

FASSYS TL

TTTT [0K]

2.4.6 T s cng sut sng mang trn cng sut tp m tuyn xung T s cng sut sng mang trn cng sut tp m tuyn xung l: SYSReDsSYSReD NGLEIRPNC)N/C( (2.13)

4.2.2 Nhng yu t cn xem xt khi phn tch tuyn

T s C/N ti my thu l mt yu t quan trng trong vic thit k mt tuyn

thng tin m bo c cht lng yu cu, nhng C/N ti my thu c xc nh

bng cc c tnh ca thit b ring bit trong trm mt t, v tinh v cc nh

hng ca mi trng n vic thit lp tuyn.

Trm mt t :

Vic chn la v tr trm mt t rt phc tp phi xt n cc iu kin sau:

+ V tr a l ca trm mt t gip ta c th c lng c suy hao do ma

gc nhn v tinh, EIRP ca v tinh theo hng trm mt t v suy hao ng

truyn.

+ Trnh kh nng b nhiu lon cc trm viba cng di tn s.

19

+ V tr xa cc vng c cng trng ln.

+ Cc c tnh thit b (v d nh d tr, phn tp phn cc... ) quyt

nh mt phn d tr tuyn.

+ Quy m trm c th m rng trong tng lai, d qun l, bo v.

V tinh :

+ V tr v tinh lin quan n vng che ph v gc nhn ca trm mt t.

+ li anten pht, thu quyt nh n EIRP v vng che ph.

+ Cng sut pht lin quan ti EIRP.

+ li ca b pht p v c tnh tp m.

+ Tp m xuyn iu ch.

Knh truyn :

+ Tn s hot ng lin quan n suy hao tuyn v d tr tuyn.

+ Cc c tnh lan truyn lin quan n d tr tuyn v la chn phng

php iu ch.

+ Tp m gia cc h thng.

C ly thng tin, gc ngng v gc phng v ca anten trm mt t :

Hnh 4.2 Cc tham s ca ng truyn trm mt t - v tinh C ly thng tin :

Gc tm ( 0 ) ctnh theo cng thc:

eo L coscoscos 1.1

Vi: ( ) l v ca trm mt t ().

(Le) l hiu kinh ng ca v tinh vi trm mt t, Le = Ls - Le

20

Khong cch t trm mt t n v tinh tnh theo cng thc:

)cos2( 022 ee rRRrR (Km) 1.2

Trong : (0) l gc tm ().

R l khong cch t trm mt t n v tinh (Km).

Re l bn knh tri t, Re = 6378 (Km).

r l bn knh qu o v tinh a tnh, r = 42.146(Km).

Gc ngng anten :

Theo hnh v (4.2), gc ngng E c tnh:

0

0

0

0

0 sin

cos

sincos

sin

r

R

rRr

rROB

BCABTg

e

eee

1.3

Gc phng v :

Gc phng v A c tnh theo cng thc : )sin(

eALtgtg

1.4 Cng sut sng mang :

Cng sut thu l mt yu t quan trng nht trong vic xc nh cht lng ca

tuyn thng tin v tinh.

PR = PT - LF - GT - LP - GR - LR 1.5

Trong :

PT - LF - GT biu th cng sut thc t pht ti my thu. Ngha l n tng

ng vi cng sut pht cn thit khi s dng anten khng c tng ch v h thng

fi khng c suy hao. Cng sut ny c gi l EIRP (cng sut pht x ng

hng tng ng), thng c dng biu th kh nng ca mt phng tin

truyn dn i vi thng tin v tinh.

EIRP = 10lg(P.G) dBw 1.6

PT: cng sut pht.

LF: suy hao h thng fi truyn dn.

GT: h s tng ch ca anten pht.

21

Suy hao truyn sng l tn chung i vi suy hao trong khng gian t do, suy

hao xy ra do hp th bi tng in ly, khng kh v ma. N c biu th:

LP = LA + LDL + LT + LFS

LP: Suy hao truyn sng.

LT: Suy hao do c tnh thit b.

LA : Suy hao do ma.

LFS: Suy hao trong khng gian t do

LFS = (4R/)2

4.7

LDL : Suy hao hp th trong tng i lu.

Suy hao trong khng gian t do chim phn ln suy hao ng truyn. Khi s

dng tn s ln hn 10GHz th suy hao do ma c th l nhn t quyt nh cht

lng tuyn.

Cng sut tp m nhit :

Tp m nhit c to ra trong my pht v n kt hp vi tp m bn ngoi i

vo anten thu v tp m bn trong to ra t bn trong my thu, anten v h thng fi.

Mc d s lng tp m to ra t my pht l ng k nhng n gim dc theo ng

truyn v th c th b qua. Ta ch cn xt n tp m bn trong v tp m bn ngoi.

Tp m bn ngoi:

Tp m bn ngoi bao gm tp m khng gian, tp m t b mt tri t, tp

m kh quyn v tp m ma. Tp m b mt tri t khng nh hung n trm mt

t bi v ta s dng anten c hng nhng n nh hng n v tinh thng tin v

anten ca n hng v pha tri t. Nhit tp m ca tp m b mt tri t thu

bng v tinh thng tin gn ging nh ca b mt tri t. Nhit tp m ca anten v

tinh thng ly TR = 2900K.

Tp m bn trong.

Tp m bn trong xy ra trong cc anten, cc h thng fi v cc my thu,

tng tp m l ton b cng sut tp m bn trong.

TIN = RF

FA TL

LTT

)1(0 4.8

22

TIN: tp m tng bn trong. T0(LF- 1): tp m h thng fi.

T0: nhit mi trng. TA: nhit tp m anten.

TR: nhit tp m my thu. LF: suy hao h thng fi (s thc).

Nguyn nhn chnh gy ra tp m anten l tp m nhit xy ra ti anten v c

nhit khong (30100)0K.

Nhit tp m i vi mt my thu bng tng nhit tp m gy ra trong mi

phn. Nhit tp m ca my thu c da trn cng thc :

)1(2121

3

1

21 ....

....

K

KR GGG

TGG

TGTTT 4.9

k : l s tng khuch i ca my thu.

G1,G2,G3,...GK l h s khuch i ln lt ca cc tng.

T1,T2,T3,...TK ln lt l nhit tp m ca cc tng.

V tn hiu tr nn ln hn khi i qua mi tng khuch i, nn tc ng tp

m ca mi tng li nh i. Nh vy khi cn gim tp m trong my thu xung nh

hn nh l trong h thng thng tin v tinh, th s dng tng khuch i u tin c h

s khuch i cao th tp m xy ra ti tng 2 v cc tng tip theo c th b qua. Tp

m u vo tng u tin l (70300)0K.

Xc nh d phng cng sut trm mt t :

Khi phn tch thit k cc tuyn phi xc nh d phng c th cho php

xc nh cc ch tiu k thut i vi trm mt t. Phi chp nhn mt d

phng no . Mi trng truyn dn Vit Nam th ta thy suy hao do ma l yu t

quan trng nht trong cc yu t nh hng. Cho nn vic tnh ton suy hao do ma

cn phi thn trng, ng vai tr quan trng i n d tr t gi tr no. Ngoi

ra, nhng yu t nh: s hp th kh quyn, nhiu mt tri, giao thoa bn trong h

thng v gia cc h thng, s lo ha thit b, tnh khng hiu qu ca thit b cng

cn phi xem xt. V vy ta phi tnh n cc yu t m bo d phng cng

sut ca trm v m bo c cht lng tuyn.

23

Cng sut sng mang thu l mt yu t quan trng trong vic xc nh cht lng ca mt tuyn thng tin v tinh, cng sut sng mang ph thuc vo thit b nh cng sut my pht, h s tng ch ca anten thu v tinh ... Cng sut sng mang nhn c ti u vo my thu v tinh c xc nh theo cng thc :

RSUeRS GLEIRPC (dB) (2.5) vi : GRS - h s khuch i ca anten thu v tinh. 2.3.6 Cng sut tp m tuyn ln BkTN UU hay tnh theo dB: )Blg()Tlg()klg(N UU 101010 (dB) (2.7) Trong k l hng s Boltzman, k =1,38.10-23 (W/Hz0K) B l bng thng ca my thu. TU l nhit tp m tuyn ln: ASRSU TTT Nhit tp m ca my thu v tinh c tnh theo biu thc:

010 110 T)(TF

RS Trong , F [dB] l h s tp m ca my thu v tinh v T0 l nhit

chun, KT 00 290 2.3.7 T s sng mang trn tp m tuyn ln Trong cc tuyn thng tin v tinh, cht lng ca tuyn c nh gi bng t s

cng sut sng mang trn cng sut tp m (C/N), hay cng sut sng mang trn nhit tp m tng ng (C/T). Tp m ch yu ph thuc vo bn thn my thu, vo mi trng bn ngoi nh mi trng truyn sng v can nhiu ph thuc cc h thng viba ln cn.

URSUeURSU NGLEIRPNCN/C (dB) (2.8) (C/N)U l t s sng mang trn tp m ti u vo b gii iu ch my thu v tinh.

24

4.3 V d tnh ton ng truyn tuyn thng tin v tinh Vinasat i vi

trm mt t t ti Nng

TNH TON THNG S CA TUYN THNG TIN V TINH TINH

VI TRM MT T TI TP H CH MINH V V TINH THAICOM Trong phn ny ta tnh cc thng s ca tuyn thng tin v tinh c th, xt mt

trm mt t t ti TP Nng c v 13004, kinh 100 0 ng, thng tin vi v tinh a tnh THAICOM c kinh 1200 ng l qu o v tinh ta xin ng k vi ITU c kh nng chp nhn nht. Ta gi s ang lm vic vi bng Ku vi tuyn xung 12 (GHz) v tuyn ln 14(GHz).

S liu ban u

Bng tn hot ng

Vic tnh ton thit k c thc hin trn bng Ku vi ng ln l 14GHz v ng

xung l 12GHz. Vi mt trm GetWay(trm cng-Hub) v 3 nhm (G = 3) UserTerminal.

Mi nhm gm 20 trm UT (L = 20).

Trm mt t:

Trm mt t t ti Nng c cc c im sau:

V l 160 Bc.

Kinh 1020 ng.

Trm mt t c anten ng knh

DUT 1,20m v hiu sut 60% ( = 60%).

DGW 5,5m v hiu sut 75% ( = 75%)

(ng knh-cng sut GW ln hn UT).

Cng sut my pht trm mt t

PTX(UT)sat = 1W.

PTX(GW)sat = 5W.

cao anten trm mt t so vi nc bin 10m.

V tinh:

V tr ca v tinh l 1200 ng.

EIRP SLsat ca v tinh l 43 dBW

Bng thng knh truyn B = 36MHz.

H s tp m ca my thu v tinh F = 3dB.

H s phm cht ca my thu v tinh (G/T)s = 1dB/0K.

25

Vi mt s gi thit sau:

Suy hao lch hng phn cc (Depointing Loss):

i vi UT LT = 1,2 dB(pht) v LR = 0,9 dB(thu).

i vi GW LT = LR = 0,5 dB.

Suy hao do fi:

LFTX = 0,2dB(pht) v LFR = 0,5dB (thu)

H s suy hao do ma ( cao vng ma 3,028Km) chn Arain = 6dB.

H s suy hao do tng i lu 0,02dB/Km.

Nhit mi trng xung quanh trm mt t Txq = 3000K.

4.3.2 Tnh ton c ly thng tin, gc ngng, gc phng v

Tnh ton c ly thng tin

T cng thc 4.1

00000 94,0)3,108120cos().16cos()cos(.coscos es LL

0 =19,730.

c ly thng tin 022 cos..2 rRrRR ee

Thay s vo ta c :

94,0.42146.6378.2421466378 22 R =1311606,7(km).

Tnh gc ngng e :

34,2337,0788,0

73,19sin42146637894,0

sin

cos0

0

0

r

R

Tge

e

T suy ra e = 66.80

Gc phng v e Gc phng v A tnh theo cng thc 4.4 :

)sin(

eeLtgtg

= 75,016sin7,11

0

0

tg l mt s m v bng -36,870.

Suy ra e =1800-36,870 =143,130.

4.3.3 Tnh ton tuyn ln

26

4.3.3.1 Tnh ton EIRPe ca trm mt t

Tnh ton li GTe ca anten trm mt t

li ca anten c xc nh bng cng thc sau:

GTe = 10lg2

c

Dfu , hoc

GTe = 10lg() + 20lg( Dfu) - 20lg(c) dB 4.10

Ta c : l hiu sut hiu dng ca anten ( 0,65)

ng knh anten pht D = 1,20 m v tn s pht bng Ku l: fu = 14GHz.

Thay s vo biu thc trn ta tnh c:

dBGTe 4310.3lg20lg2010.14lg2020,1lg2065,0lg1089

Vy li ca anten trm mt t l 43dB.

Cng sut pht ca trm mt t

Do ng i ca thng tin v tinh l rt ln nn trm mt t ta phi pht vi cng

sut ln anten thu trn v tinh c th nhn c tnh hiu. Theo gi thit cng sut ca

trm mt t l PTe = 2W. Cng sut ny tnh theo dB s l :

PTe(dB) = 10lg(2 )= 0,3 dBw

Cng sut bc x ng hng tng ng ca trm mt t

Cng sut bc x ng hng tng ng ca trm mt t c xc nh bng

cng thc sau :

EIRPe= PTe..GTe (W). 4.11

Trong PTe l cng sut pht ca HPA tr i suy hao ca fid t my pht n

anten. Cng thc trn c tnh theo n v dB :

EIRPe(dB) = PTe(dB) + GTe(dB) - Lf = 0,3 + 43 - 1 = 42,3(dB)

Vi Lf l suy hao do fi v gi thit l 1dB.

Mt thng lng sng mang trn v tinh.

Ta c: = 24 R

EIRPe

, hoc tnh theo n v dB:

= EIRPe - 20lgR - 10lg(4) (dBW/m2) 4.12

= 42,3 - 20lg (35768.103) - 10lg(4) = - 119,76 (dBW/m2)

4.3.3.2 Tnh ton suy hao tuyn ln

4.3.3.2.1 Suy hao trong khng gian t do

27

Suy hao trong khng gian t do c xc nh bng cng thc: 4.13

Thay cc gi tr R, fu vo :

dB

cfRc

fRRL UTD

43,20610.3lg2010.14lg2010.35768lg204lg20

lg20lg20lg204lg20..4lg204lg20)(

893

4.3.3.2.2 Tnh ton suy hao do thi tit

Suy hao do thi tit ti Nng ch yu l suy hao do ma, cn suy hao do sng

m vi dy 0.1(g/m3) c th b qua. tnh suy hao do ma cn c s liu thng k ca

kh tng thu vn v mt ma, dng ma, cao ca m ma....theo bn v cng

ma ca mt nm trung bnh cho khu vc chu (ca ITU) th khu vc Nng c

cng ma 100 (mm/gi), h s suy hao do ma u = 3,96 (dB/km). Ta phi tnh ton

cao cn ma hm (km). V Nng nm v 160 Bc nn theo khuyn ngh CCIR564,

cao ca cn ma l: 3,028(km).

4.3.3.2.3 Tnh ton on ng thc t sng i qua cn ma:

48,38,66sin

01,0028,3sin 0

e

Sm hhLs

(km)

Trong :

LS l on ng thc t sng i trong cn ma.

hS chiu cao ca trm mt t so vi mc nc bin, ly hS = 0.01km.

e gc ngng anten trm mt t (tnh c trn).

Xc nh h s suy hao do ma tuyn ln u :

Suy hao do ma l hm ca tn s v cng ma ( u =3,96 dB/km).

Suy hao do ma tuyn ln l:

(LM)U = u LS = 3,96 . 3,48 = 13,78 (dB).

4.3.3.2.4 Suy hao do tng i lu

Tng i lu bao gm cht kh chnh hp th gy ra suy hao nh hi nc, oxy, ozon,

co2. Suy hao ny ph thuc nhiu vo tn s v gc ngng ca anten v ch ng k khi tn

s cng tc t 10GHz tr ln. Anten c gc ngng cng ln th suy hao do tng i lu cng

nh. Do tuyn thit k l tuyn c bng tng l Ku nn suy hao ny ta khng th b qua v

c tnh nh sau: Do suy hao trong cht kh c h s suy hao l k =0,02 (dB/km). Lc

cao ca tng i lu l 11km nn on ng ca sng i trong tng i lu s l :

28

Ldl = 67,128,66sin01,011

0 (km)

Vy suy hao l (Ldl)u = 12.67. 0,02 = 0,253 (dB).

4.3.3.2.5 Tng suy hao tuyn ln

LU = (LTD)U + (LM)U+ LPC + LBS + (LDL)U

= 206,43 + 13,78 + 0,1 + 0,9 + 0,253 =221,463 dB.

Trong : Lpc =0,1 l suy hao do lch phn cc (gi thit).

Lbs =0,9 l suy hao do lch bp sng(gi thit).

4.3.3.3 Tnh ton nhit tp m tuyn ln

11..11..11.. Nhit tp m ca tuyn ln ch yu do nhit tp m ca my thu v tinh v anten thu v tinh to ra .

Nhit tp m ca my thu v tinh c tnh bng cng thc:

010 )110( TTF

R

4.14

Trong :

F: h s tp m ca my thu v tinh, vi gi thit l F = 3dB.

T0 = 3000K

T suy ra TR = 298300).110( 103

(0K).

Nhit tp m ca anten thu v tinh: gi s ta chn nhit tp m ca anten thu v tinh

l TRS = 2900K

Nhit tp m tng cng ca tuyn ln l : Tu = TR + TRS = 298 + 290 = 5880K.

4.3.3.4 Tnh t s cng sut sng mang trn cng sut tp m ca tuyn ln

4.3.3.4.1 Cng sut sng mang thu c trn v tinh

Cng sut sng mang thu c trn v tinh c xc nh bng cng thc

FU

RSe

FIDOU

RSTTRS LL

GEIRPLL

GGPC..

...

4.15

hay cn c tnh theo n v dBw

dBw)(FURSeRS LLGEIRPC

29

Trong : EIRPe c tnh phn trn v bng 42,3dB.

Lu l suy hao tng cng ca tuyn ln c gi tr 221,463dB.

LF suy hao do fid ca v tinh (gi thit =1).

GGS li ca anten thu v tinh v c tnh bng cng thc sau:

USRS TTGG lg10)/(

(G/T)S l h s phm cht ca my thu v nh phn gi thit, ta c

(G/T)S = 1dB/0K

Tu l nhit tp m nhiu ca tuyn ln Tu = 5880K.

T ta tnh c : GRS = 1+10lg588 = 28,7 (dB/0K).

Thay vo, ta c : CRS = 42,3+28,7- 221,463- 1= -151,46 (dBw).

4.3.3.4.2 Tnh cng sut tp m tuyn ln

Cng sut tp m tuyn ln (NU) c xc nh bng cng thc :

NU = k.TU.B

4.16

Trong :

k: l hng s Boltzmann, k=1,38*10-23 w/0K.

TU: nhit tp m tuyn ln. TU = 5880K.

B : bng tn knh truyn. B = 54MHz.

Tnh theo n v dB th c vit li nh sau:

NU = 10lgk + 10lgTU + 10lgB (dBw)

NU = 10lg1,38*10-23 + 10lg588 + 10lg(54*106)= -123,58(dBW)

4.3.3.4.3 Tnh t s cng sut sng mang trn cng sut tp m tuyn ln:

T s (C/N)U Tnh theo n v dB ta c (C/N)U = CRS - NU = -151,46 - (-123,58) =

23,36(dB)

4.3.4 Tnh ton tuyn xung 4.3.4.1 Tnh ton li GRe ca anten trm mt t

30

li ca anten ca trm mt t trong trng hp thu tnh hiu t v tinh c xc

nh bng cng thc:

cfDdBGRE lg20lg20lg20lg20lg10)(

Ta c = 0,65.

ng knh anten D=20m v tn s pht bng Ku c fd = 12GHz

Thay s vo biu thc trn ta tnh c

)(13,6610.3lg20lg2010.12lg2020lg2065,0lg10 89 dBGRE

Vy li ca anten trm mt t trong trng hp thu l (GRE)d =66,13dB

4.3.4.2 Tnh ton suy hao tuyn xung

Cng ging nh suy hao tuyn ln, suy hao tuyn xung bao gm:

Suy hao trong khng gian t do.

Suy hao do ma.

Suy hao do tng i lu.

Suy hao do t anten cha ng.

Suy hao do khng thu ng phn cc.

Do tn s pht xung khc vi tn s pht ln (fd=12GHz) nn suy hao do tuyn

xung khc vi suy hao tuyn ln. Vy c suy hao tuyn xung ta tnh li cc suy hao

trn.

Suy hao trong khng gian t do

T cng thc 4.13

Thay cc gi tr R v fd = 12GHz

dBcfRL dDTD

3,20510.3lg2010.12lg2010.7,36658lg204lg20

lg20lg20lg204lg20)(893

Cc suy hao khc ca tuyn xung cng tng t nh tuyn ln.

4.3.4.3 Tng suy hao tuyn xung

LD = DTDL )( + (LM)D + LBS + LPC+ (LDL)D

= 205,3 + 14,25 + 0.1 + 0,9 + 0,262 = 220,81dB

4.3.5 Tnh cng sut sng mang nhn c ti u thu ca trm mt t

Cng sut sng mang thu c trm mt t c xc nh bng cng thc sau :

FREDSRE LGLEIRPC (dBw) 4.17

31

Trong :

+ EIRPs = 41,46dBW.

+ Ld l suy hao tng cng ca tuyn xung c gi tr 220,81 dB.

+ Lf suy hao do fid ca trm mt t v theo gi thit c gi tr l 1dB

+ GGE l li ca anten thu trm mt t, GGE = 66,13dB

Thay tt c cc gi tr vo biu thc trn ta c :

CRE = 41,46 - 220,81 + 66,13 - 1= -105,68 dBw.

4.3.6 Tnh ton nhit tp m hng xung

4.3.6.1 Nhit tp m khng gian

Nhit tp m khng gian ch yu l nhit tp m v tr v nhit tp m mt tri.

Trong , nhit tp m v tr c ln khong 2,760K v nhit tp m mt tri c ln

khong 500K. Do , nhit tp m trong khng gian c ln l :

TS =2,76 + 50 =52,760K

4.3.6.2 Nhit tp m do ma

Nhit tp m do ma c xc nh bng cng thc :

KL

TTM

mM0)11( 4.18

Trong : + TM : Nhit tp m do ma.

+ LM: suy hao do ma, suy hao ny c xc nh phn

(4.3.4.2) c gi tr bng 14,25dB.

Nu khng tnh theo n v dB, ta c : LM = 10logLM (dB)

6,2610 1025,14

ML

+ Tm : nhit ca cn ma , nhit ny c xc nh :

Tm=1,12Txq-50 (0K) vi nhit Txq=3000K

Suy ra Tm=1,12x300 - 50 =2860K

Nh vy TM = 286(1- 6,26

1 ) = 2750K

4.3.6.3 Nhit tp m do h thng fi

Nhit tp m do h thng fi c xc nh bng cng thc :

TF =T0(LF-1)

Trong : T0 l nhit mi trng To= 3000K.

32

LF =1dB nn suy ra LF = 26,110101

TF = 300.(1,26 - 1) = 780K.

4.3.6.4 Nhit tp m do my thu :

Nhit tp m ca my thu c da trn cng thc 4.9.

Nhit tp m my thu ch yu ph thuc vo nhit tp m ca tng u tin. Nu h

s khuch i ti u vo ln th tp m ti cc tng sau c th b qua.

Gi tr ca nhit tp m tng th nht ph thuc vo loi my thu v c gi tr t

700K3000K. Ta chn my thu c nhit tp m u vo l 1000K.

Vy TR =1000K.

4.3.6.5 Nhit tp m h thng

Nhit tp m h thng c xc nh bng cng thc sau :

RF

FAssys TL

TTTT 4.19

Trong

+ Tsys : Nhit tp m h thng.

+ Ts : Nhit tp m bn ngoi.

+ TA: Nhit tp m nhn c u thu anten.

+ TF : Nhit tp m do h thng fi to ra.

+ TR : Nhit tp m ca my thu.

+ LF : H s suy hao do h thng fi to ra.

Trong ta c TS + TA = TS +TM = 52,76 + 275 =327,760K

+ Suy hao do fi c tnh trn : LF =1,26

+ Nhit tp m my thu l TF = 1000K

Tsys = K042210026,1

7876,327

H s phm cht trm mt t:

ETG

= GRE - 10lgTSYS =66,13 - 10lg422 = 39,88dB/0K

4.3.6.6 Cng sut tp m h thng

Nsys = 10lgk +10lgTsys+10lgB

=10lg1,38x10-23 + 10lg422+10lg36x106 = -126,78(dBw).

33

4.3.6.7 T s cng sut sng mang trn cng sut tp m

T s cng sut sng mang trn cng sut tp m l :

(C/N)D = CRE - Nsys

Trong CRE = -105,68

NSYS = -126,78

(C/N)D = -105,68 - (- 126,78) = 21,1dB