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AI HOC A NANGTRNG AI HOC KY THUAT

KHOA CONG NGHE THONG TIN IEN T VIEN THONG------

OO AANN TTOOTT NNGGHHIIEEPP

E TAI: THIET KE TUYEN THONG TIN VE TINH

Giao vien hng danSinh vien thc hien : ANG ROLp : 20T-PY

Tuy Hoa , 10/2002


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Li Noi au

Trong nhng thap ky qua, cung vi s phat trien cua khoa hoc , cong nghenganh vien thong a co nhng phat trien vt bac, ap ng nhng nhu cau trao oi

thong tin gop phan khong nho trong cong cuoc xay dng va nh hng phat trien

cua xa hoi loai ngi.

Chung ta song trong ky nguyen cua s bung no thong tin, viec trao oi thong

tin dien ra khap moi ni tren the gii vi yeu cau nhanh chong va chnh xac. oi vi

thong tin quoc te, thong tin ve tinh a cung cap nhng ng thong tin dung lng

ln, khi tam lien lac xay ra trong dien rong th thong tin ve tinh the hien tnh u viet

cua no ve mat kinh te. Hien nay nc ta ang chuan b phong ve tinh cho rieng mnh

nham ap ng cac nhu cau thong tin ngay cang cao trong nc va quoc te. e hieuro he thong thong tin ve tinh bao gom cong nghe thong tin, cong nghe thiet b, s

lien lac qua he thong thong tin ve tinh va t o xay dng mot tuyen lien lac phu hp,

c s giup cua thay giao hng dan, em thc hien e tai :

Thiet ke tuyen thong tin ve tinh .c s hng dan tan tnh cua thay , em a co gang van dung cac kien

thc a hoc e hoan thanh o an, nhng v thi gian va kien thc con han che, chac

han trong o an nay khong tranh khoi nhng thieu sot. Em rat mong c s gop y,

ch bao, ong gop cua cac thay co va cac ban .Em xin chan thanh cam n cac thay co trong khoa Cong nghe thong tin

ien t vien thong a giup em trong suot thi gian hoc tap ma ac biet la s

hng dan ch bao cua thay giup em hoan thanh o an nay.

Tuy hoa, thang 11 nam 2002

Sinh vien

ang Ro


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MUC LUC------

LI NOI AUCHNG I : TONG QUAN VE THONG TIN VE TINH

1.1. S ra i cua cac he thong thong tin ve tinh 5

1.2. Qua trnh phat trien 5

1.3. ac iem cua thong tin ve tinh 6

1.4. Cac dang quy ao cua ve tinh 6

1.4.1. Quy ao elip 8

1.4.2. Quy ao tron 8

1. Quy ao cc 8

2. Quy ao nghieng 8

3. Quy ao xch ao 8

1.5. Cau truc mot he thong thong tin ve tinh 8

1.6. Cac phng phap a truy nhap en ve tinh 12

1.6.1. Phng phap a truy nhap phan chia theo tan so FDMA 121.6.2. Phng phap a truy nhap phan chia theo thi gian TDMA 13

1.6.3. Phng phap a truy nhap phan chia theo ma CDMA 14

1.7.Ket luan chng 16

CHNG II : SONG VO TUYEN IEN

2.1 . Tan so va cac ac tnh cua song vo tuyen ien trong thong tin ve tinh 172.1.1. Song vo tuyen va tan so 17

2.1.2. Cac tan so s dung cho thong tin ve tinh 17

2.2 . Phan cc song 17

2.2.1. nh ngha 17

2.2.2. Song phan cc elip 18

2.2.3. Song phan cc tron 18

2.2.4. Song phan cc thang 182.3. S truyen lan song vo tuyen ien 18


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2.3.1. Khai niem ve s truyen lan song vo tuyen trong thong tin ve tinh 18

2.3.2. Ton hao trong khong gian t do 19

2.3.3. Ca so vo tuyen 19

2.3.4. Tap am trong truyen lan song vo tuyen 20

2.3.5. S giam kha nang tach biet phan cc cheo do ma 20

2.3.6. EIRP : ac trng kha nang phat 20

2.3.7. G/T : ac trng o nhay may thu 21

2.3.8. S nhieu loan do cac song can nhieu 21

CHNG III : KY THUAT TRAM MAT AT

3.1 . Cong nghe va ac tnh cua anten 233.1.1. Yeu cau chat lng oi vi anten thong tin ve tinh 23

3.1.2. Phan loai anten 23

3.1.3. He thong anten bam ve tinh 24

3.1.4. Cac ac tnh ve ien 24

3.2 . Cong nghe may phat 27

3.2.1. May phat cong suat cao 27

3.2.2. Phan loai cac bo khuyech cong suat cao 273.2.3. Cau hnh 28

3.2.4. Meo do xuyen ieu che 29

3.3. Cong nghe may thu 30

3.3.1. Cau truc tram thu 30

3.3.2. Khuyech ai tap am thap 30

CHNG IV : TRAM VE TINH4.1. Cau hnh tram ve tinh vi mot bo phat ap n gian 32

4.2. Phan bo dai tan cua bo phat ap 32

4.3. Cac mang ve tinh nhieu chum 33

4.3.1.u iem cuave tinh nhieu chum 34

4.3.2. Lien ket gia cac vung bao phu 34

1. Lien ket nh bc nhay cua bo phat ap 34

2. Lien ket nh chuyen mach tren ve tinh (SS/TDMA) 35

3. Lien ket nh quet chum 36


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4.3.3. Cac tuyen noi lien ve tinh 36

1. Cac tuyen noi gia cac ve tinh a tnh vi ve tinh quy ao thap 362. Cac tuyen noi gia cac ve tinh a tnh 373. Cac tuyen noi gia cac ve tinh quy ao thap 37

4.4. Cac mang ve tinh tai tao 384.4.1. Bo phat ap tai tao 384.4.2. ac iem bo phat ap tai tao 38

CHNG V : THIET KE NG TRUYEN5.1. Gii thieu 425.2. Cac ch tieu chat lng 42

5.3. Cac ch tieu san sang 435.4. Quan he gia chat lng va C/N 435.5. C/N tong 465.6. Cong suat song mang 465.7. Cong suat tap am nhiet 48

5.7.1. Tap am ben ngoai 495.7.2. Tap am ben trong 495.7.3. Tap am he thong 51

5.8. Cong suat tap am nhieu 515.8.1. Can nhieu tap am khac 515.8.2. Nhieu cung tuyen 52

5.9. Phan phoi tap am 535.10. Tnh toan o san sang 53

5.11. Tnh toan ket noi a truy nhap 54

CHNG VI : TNH TOAN TUYEN THONG TIN6.1. Gii thieu chng 556.2. Tnh toan tuyen thong tin 55

6.2.1. Cac thong so can cho tnh toan 556.3. Tnh toan 56

6.3.1. C ly thong tin, goc ngang va goc phng v cua anten tram mat at 566.3.2. Tnh cac thong so c ban 57

6.4. Tnh d tr tuyen tram thu truyen hnh qua ve tinh (TVRO) 64Ket luan e tai 68Tai lieu tham khao


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CHNG ITONG QUAN VE THONG TIN VE TINH

1.1. S RA I CUA CAC HE THONG THONG TIN VE TINHThong tin vo tuyen qua ve tinh la thanh tu nghien cu trong lnh vc truyenthong va muc tieu cua no la gia tang ve mat c ly va dung lng vi chi ph thap .

Ket hp s dung hai ky thuat - ten la va viba a m ra ky nguyen thong tinve tinh. Dch vu c cung cap theo cach nay bo sung mot cach hu ch cho cac dchvu ma trc o oc nhat ch do cac mang di at cung cap, s dung vo tuyen va cap.

Ky nguyen vu tru c bat au vao nam 1957 vi viec phong ve tinh nhan

tao au tien (ve tinh Sputnik cua Lien xo cu ). Nhng nam tiep theo cac ve tinhkhac cung lan lt c phong nh SCORE phat quang ba (nam 1958 ), ve tinhphan xa ECHO (1960), cac ve tinh chuyen tiep bang rong TELSTAR va RELAY(1962) va ve tinh a tnh au tien la SYNCOM (1963).

Trong nam 1965, ve tinh a tnh thng mai au tien INTELSAT-1 anhdau s m au cho hang loat cac ve tinh INTELSAT. Cung nam o, Lien xo cucung phong ve tinh truyen thong au tien trong loat ve tinh truyen thongMOLNYA.

1.2. QUA TRNH PHAT TRIENCac he thong ve tinh au tien cung cap dung lng thap vi gia tng oi caonh ve tinh INTELSAT-1 nang 68kg khi phong, co dung lng 480 kenh thoai vi gia32.500USD mot kenh trong mot nam. Gia thanh nay cao la do chi ph phong, ket hpvi gia ve tinh co tnh en tuoi tho ve tinh ngan (1 nam ri ) va dung lng thap.

Viec giam gia la ket qua cua nhieu no lc, nhng no lc o a dan en viectao ra cac ten la phong co kha nang a cac ve tinh ngay cang nang hn len quyao (3750kg khi phong ve tinh INTELSAT-VI). Ngoai ra ky thuat viba ngay cangphat trien a tao ieu kien thc hien cac anten nhieu bup song co kha nang tao bienhnh ma bup song cua chung hoan toan thch ng vi hnh dang luc a, cho phep tais dung cung mot bang tan gia cac bup song va ket hp s dung cac bo khuyech aitruyen dan cong suat cao hn. Dung lng ve tinh tang len dan en giam gia thanhmoi kenh thoai (80.000 kenh tren INTELSAT-VI co gia thue moi kenh la 380USD).

Ngoai viec giam chi ph truyen thong, ac iem noi bac nhat la tnh adang cua cac dch vu ma cac he thong thong tin ve tinh cung cap va dien bao phurong cua ve tinh a c dung e thiet lap cac tuyen thong tin vo tuyen c ly xa,nh ve tinh INTELSAT-1 cho phep thiet lap cac tram hai ben b ai Tay Dng

ket noi c vi nhau. Khi kch thc va cong suat cua cac ve tinh cang tang lenth cang cho phep giam kch thc cua cac tram mat at va do vay giam gia thanh


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cua chung, dan en tang so lng cac tram mat at. Do o co the khai thac mottnh nang khac cua ve tinh, o la kha nang thu thap hoac phat quang ba cac tnhieu t hoac ti mot so a iem.Thay v phat cac tn hieu t iem nay ti iemkhac, bay gi co the phat t mot may duy nhat ti rat nhieu may thu phan bo trongmot vung rong ln, hoac ngc lai, co the phat t nhieu tram ti mot tram trungtam duy nhat. V vay, cac mang truyen so lieu a iem, cac mang quang ba qua vetinh va cac mang thu thap d lieu. Co the phat quang ba ti cac may phat chuyentiep hoac trc tiep ti khach hang ca nhan. Cac mang nay hoat ong vi cac trammat at nho co anten ng knh t 0,6 en 3,5m.

1.3. AC IEM CUA THONG TIN VE TINHThong tin ve tinh tuy ra i muon nhng c phat trien nhanh chong bi v

no co nhieu li the so vi cac he thong truyen thong khac, o la:

Vung phu song rong, ch can ba ve tinh la co the phu song toan cau. Thiet b phat song cua he thong thong tin ve tinh ch can cong suat nho. Viec lap at hoac di chuyen mot he thong thong tin ve tinh tren mat at

tng oi nhanh chong va khong phu thuoc vao cau hnh mang cung nh he thongtruyen dan .

He thong thong tin ve tinh co the phuc vu nhieu dch vu khac nhau nhvien thong thoai va phi thoai, tham do a chat, truyen hnh anh, quan sat muc tieu,nghien cu kh tng, phuc vu quoc phong an ninh, v.v

Thong tin ve tinh rat on nh. a co nhieu trng hp bao to, ong atmanh lam cho cac phng tien truyen thong khac mat tac dung ch con duy nhatthong tin ve tinh hoat ong.

Cac thiet b at tren ve tinh co the tan dung nang lng mat tri e cungcap ien hau nh ca ngay lan em.

Tuy vay thong tin ve tinh cung co mot so nhc iem, o la : Kinh ph ban au e phong mot ve tinh vao quy ao kha ln Bc xa cua song vo tuyen trong thong tin ve tinh b ton hao ln trong moi

trng truyen song.

1.4. CAC DANG QUY AO CUA VE TINHQuy ao cua ve tinh la hanh trnh cua ve tinh trong khong gian ma trong

o ve tinh c can bang bi hai lc oi nhau. Hai lc o la lc hap dan cua traiat va lc ly tam c hnh thanh do o cong cua hanh trnh ve tinh. Quy ao cuave tinh co ba thong so quan trong : Khoang cach t quy ao ve tinh en mat at,hnh dang va goc nghieng so vi mat bnh o. Mot thong so chung cua no la matphang chuyen ong cua ve tinh phai i qua tam trai at. Quy ao cua ve tinh namtren mot mat phang co the la hnh tron hoac hnh elp. Neu quy ao la tron th tam

cua quy ao tron trung vi tam cua trai at (hnh 1-1).


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Hnh 1.1 Ve tinh quy ao tron

Neu quy ao la elp th co mot au elp nam xa trai at nhat goi la vieniem (apogee) va au gan trai at nhat goi la can iem (perigee) (hnh 1-2)

Trai at

Hnh 1.2- Quy ao Elip

Phng cua mat tri

Tram mat at

Can iem


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Quy ao thong dung hien nay cua ve tinh la nhng dang quy ao sau ay1.4.1. Cac quy ao hnh elp .Loai quy ao nay am bao phu song cac vung v o cao di mot goc

ngang ln. Goc ngang ln la ac biet can thiet trong nhng ng dung nh :- Giam thieu viec chan cac tia do s che khuat ve tinh cua cac cao oc va

cay coi- Viec bam ve tinh c de dang hn .- Giam bt c tap am ma anten tram mat at thu nhan do can nhieu t

cac he thong thong tin vo tuyen di mat at.1.4.2. Cac quy ao tron .1. Quy ao cc :Ve tinh co quy ao tron va co o cao khoang vai tram en nghn km vi

mat phang quy ao cha truc quay cua trai at, loai quy ao nay am bao rang ve

tinh co the i qua cac vung cua trai at . Ngi ta s dung loai quy ao nay chocac ve tinh quan sat (observation satellite) nh ve tinh SPOT va phu song toan caunh chum ve tinh IRIDUM (gom 77 ve tinh ).

2. Quy ao nghieng :Khi mat phang quy ao khong cha truc quay trai at va cung khong vuong

goc vi truc o. Mot so ve tinh c to chc thanh chum ve tinh co quy ao dangtron nay, o cao thap (c 1000 km) co kha nang phu song toan cau trc tiep enngi s dung nh ( GLOBAL STAR, LEOSAT,).

3. Quy ao xch ao :Quy ao nay nam trong mat phang xch ao cua trai at va cac ve tinh trenquy ao c goi la ve tinh a tnh (GEO-geostationary satellite). o cao quy aola 35.768km. Ve tinh trong trng hp nay xuat hien nh mot iem co nh trenbau tri vi vung phu song cua ve tinh la 43% dien tch cua be mat trai at. Ba vetinh a tnh trong trng hp nay co the phu song toan cau .

Viec la chon quy ao nao trong thc te con phu thuoc vao cac ng dungcu the, o can nhieu ma he thong co the chap nhan c .

e ve tinh co the gi nguyen v tr cua mnh trong quy ao a c xacnh, ngi ta s dung mot trong hai ky thuat on nh, o la on nh quay hoac onnh ba truc.

1.5. CAU TRUC MOT HE THONG THONG TIN VE TINHCau truc mot he thong thong tin ve tinh gom hai phan : phan khong gian

(space segment) va phan mat at (ground segment). Hnh 1-3 mo ta cau truc tongquat mot he thong thong tin ve tinh.


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Hnh 1.3- Cac thanh phan cua mot he thong thong tin ve tinh

1.5.1.Phan khong gianPhan khong gian bao gom ve tinh cung cac thiet b at trong ve tinh va he

thong cac trang thiet b at tren mat at e kiem tra, theo doi va ieu khien ve tinh(cac he thong bam, o ac va ieu khien). Ban than ve tinh bao gom phan tai(payload) va phan nen (platform). Phan tai bao gom cac anten thu/phat va tat cacac thiet b ien t phuc vu cho viec truyen dan cac song mang. Phan nen bao gomcac he thong phuc vu cho phan tai hoat ong, v du nh : Cau truc vo va khung,nguon cung cap ien, ieu khien nhiet o, ieu khien hng va quy ao, thiet bay, bam, o ac, v.v

Cac song vo tuyen c truyen t tram mat at len ve tinh c goi la

tuyen len (uplink). Ve tinh en lt mnh lai truyen cac song vo tuyen (sau khi abien oi tan so va khuyech ai ) ti cac tram thu ve tinh at tren mat at va cgoi la tuyen xuong (downlink).

Chat lng cua mot lien lac qua song vo tuyen o c xac nh bi thongso song mang tren tap am (C/N). Chat lng cua tong the tuyen lien lac t trammat at nay en tram mat at khac c quyet nh bi chat lng cua tuyen lenva tuyen xuong trong o bao gom ca ky thuat ieu che va ma hoa c s dung .

Trong moi ve tinh c at mot so bo phat ap (transponder) e thu tn hieu ttuyen len, bien oi tan so, khuyech ai cong suat va truyen tr lai tren tuyen xuong .

Tramieu khien

TT&C

Cac may phat Cac may thu

oan mat at

Cac tuyen xuongCac tuyen len

oan vu truco


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Hnh 1.4a- S o khoi chc nang cua mot bo phat ap n gian

Hnh 1-4a mo ta s o khoi chc nang mot bo phat ap n gian, aykhong co nhiem vu giai ieu che tn hieu thu c va cung khong x ly tn hieu.No ch ong vai tro nh bo chuyen oi xuong co he so khuyech ai cong suat ln.Bo khuyech ai cong suat trong bo phat ap thng dung hai loai : Khuyech aidung en song chay (TWTA- Traveling Wave Tube Amplifier) va khuyech aidung ban dan tranzitor (SSPA Solid State Power Amplifier). Cong suat bao hoa

tai au ra cua TWTA thng t 20W en 200W va cua SSPA thng t 20W en40W. Trong cac ve tinh loai mi c trang b cac bo phat ap a chum tia(multibeam satellite tranponders) va cac bo phat ap tai sinh (regrativetranponders). Do han che ve kch thc va trong lng cho nen cac anten thu/phatcua bo phat ap thng co kch thc nho va do o o tang ch cua anten trongtrng hp nay b gii han.

Ve tinh trong trng hp nay hnh thanh mot iem trung chuyen tn hieugia cac tram mat at va c xem nh mot iem nut cua mang vi hai chc nang

chnh sau ay :Khuyech ai cac song mang thu c t tuyen len e s dung cho viec

truyen dan lai tren tuyen xuong. Cong suat song mang tai au vao cua may thu vetinh co yeu cau t 100pW ti 1nW, con cong suat tai au ra cua bo khuyech aicong suat phat cho tuyen xuong co yeu cau t 10 en 100W. Nh vay o tang chcua anten cua bo phat ap ve tinh co yeu cau t 100 en 130dB. Song mang trongbang tan c bc xa en cac vung phu song tren be mat trai at vi cac mc

EIRP tng ng.

Bo chuyen oi xuong

LO

Bo daoong noi

BPF TWTBPF LNA

Bo locthongthap

Bo khuechai congsuat en

song chay

Tnhieu ttuyenlen

Bokhuechai tap

am thap

Bo locthongthap

Anten

thu

6GHz

Tuyenxuong

Anten phat4 GHz


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Thay oi tan so song mang (gia thu va phat) nham tranh hien tng motphan cong suat phat tac ong tr lai pha au thu. Kha nang loc cua cac bo loc auvao oi vi tan so tuyen xuong ket hp vi o tang ch thap cua anten, gia au raphat va au vao thu can am bao s cach biet khoang 150dB.

Tuy nhien khi xem xet mot ve tinh cu the th co the co mot so chc nangkhac. V du, oi vi ve tinh co nhieu bup song hoac bup song quet th bo phat apve tinh phai co kha nang tao tuyen song mang en cac vung phu song yeu cau.Trong trng hp oi vi ve tinh tai sinh th bo phat ap con co them chc nangieu che va giai ieu che .

Phan tai (payload) cua ve tinh truyen thong c ac trng bi cac thongso ky thuat trong tng bang tan cong tac nh sau :

Bang tan cong tac .So lng bo phat ap .o rong dai thong cua moi bo phat ap .Phan cc tn hieu cua ng len va ng xuong.Cong suat bc xa tng ng ang hng (EIRP) hoac mat o thong

lng cong suat tao ra tai bien cua vung phu song phuc vu .Mat o thong lng cong suat bao hoa tai anten thu cua ve tinh (SPD

Saturation Power Density).

He so pham chat G/T cua may thu ve tinh tai bien cua vung phu songhoac gia tr cc ai .

Vung phu song .Cong suat au ra cua bo cong suat phat.Cau hnh d phong cho may thu va bo khuyech ai cong suat cao .1.5.2 Phan mat atPhan mat at bao gom tat ca cac tram mat at va chung thng c noi

vi cac thiet b cua ngi s dung thong qua cac mang mat at hoac trong trnghp s dung cac tram VSAT(Very Small Aperture Terminal) th co the lien lac trctiep ti thiet b au cuoi cua ngi s dung. Cac tram mat at c phan loai tuyvao thuoc vao kch c tram va loai hnh thong tin c truyen cung nh x ly(thoai, hnh anh hoac d lieu ). Co the co cac tram mat at va thu va phat nhngcung co loai tram mat at ch lam nhiem vu thu (v du tram TVRO TelevisionReceiver Only). Cac tram mat at ln c trang b anten co ng knh 30-40m,trong khi o cac tram mat at loai nho ch dung anten ng knh 60cm hoac tham

ch co the nho hn (cac tram di ong, cac may cam tay). Hnh 1-4b mo ta mot trammat at n gian bao gom ca thu va phat.


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Hnh 1-4b Cau hnh cua mot tram mat at

oi vi mot tram mat at c ln, do o rong cua bup song chnh cua antenrat hep cho nen tram mat at can phai co cac thiet b bam ve tinh e am bao chatlng ng truyen (truc anten hng ung ve tinh). Vi cac tram mat at c nhodo o rong bup song anten kha ln cho nen trong trng hp nay khong can thietphai co cac thiet b bam ve tinh .

Trong thc te mot bo phat ap cua ve tinh co the phuc vu cung mot lucnhieu tram mat at khac nhau. o la nh vao phng phap a truy nhap. Ky thuat

ma cac tram mat at dung e truy nhap bo phat ap ve tinh o la (FDMA,TDMA,CDMA).

1.6. A TRUY NHAPTrong cac he thong thong tin ve tinh ky thuat a truy nhap la mot phng

phap e cho nhieu tram s dung chung mot bo phat ap. Hien nay co ba phngphap chnh c dung o la :

1.6.1. a truy nhap phan chia theo tan so (FDMA - Frequency DivisionMultiple Access). Phng phap nay c s dung rong rai nhat. Vi he thong nay

moi tram mat at phat mot song mang co tan so song mang khac vi tan so songmang cua cac tram khac ; moi mot song mang c phan cach vi cac song mang

Thiet b anten bam May thu tap am thap Thiet b a truy nhapieu che va giai ieuche

Thiet b bam

Bo khuechai tap am

thap

Bo oitan

xuong

He thongtiep song

Bo khuechai congsuat cao

Bo nangtan

May phat cong suat cao

Bo daoong

Bo daoong

Bokhuechai IF

Bo giaiieu che

Thiet b atruy nhap

Bokhuechai IF

Bo ieu che


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khac bang nhng bang tan bao ve thch hp, sao cho chung khong chong lan lennhau (hnh 1-5).

FDMA co the c s cho bat ky he thong ieu che nao, ieu che tng thoac ieu che so. Mot tram mat at thu chon la cac tn hieu no can thong tin bangmot bo loc bang thong .

Phng phap nay cho phep tat ca cac tram truyen dan lien tuc ; no co uiem khong can thiet ieu khien nh thi ong bo, va thiet b s dung kha ngian; hieu qua s dung cong suat ve tinh cua no cung khong thap. Tuy nhien

phng phap nay thieu linh hoat trong viec thay oi cach phan phoi kenh.1.6.2. a truy nhap phan chia theo thi gian ( TDMA Time Division

Multiple Access ). La mot he thong trong o cac tram mat at dung chung mot bophat ap tren c s phan chia theo thi gian. e lam c viec nay can s dungmot song mang ieu che so. He thong TDMA thng nh ra mot khung trong mienthi gian goi la khung TDMA; khung nay c phan chia ra va moi mot khoangchia c phan cho tng tram.

Moi mot tram phat song mang cua no trong mot khoang thi gian ngan a

c phan (khe thi gian) trong khung thi gian. Can e ra mot khoang thi giantrong (thi gian bao ve) gia hai khe thi gian canh nhau sao cho cac song mangphat t nhieu tram khong chong len nhau trong bo phat ap (hnh 1-6).

Thi gian

Tan so

12

N

Bo phat ap

FDMA

1

2

t

N

FDMA

B 2

N

t

t

Hnh 1.5- a truy nhap phan

chia theo tan so (FDMA)

1

2

N

TDMA

Bo phat ap

Ma

Thi gianTDMA

B

t

1

2N

1 2 N


15/73


Hnh 1.6- a truy nhap phan chia theo thi gian (TDMA)

Moi tram thu se tach ra nhng phan song mang cua chnh no da tren c sphan chia theo thi gian trong nhng tn hieu nhan c. He thong TDMA co thes dung tot nhat cong suat ve tinh va co the de dang thay oi c dung lngtruyen tai nen he thong nay co u iem la linh hoat trong viec chap nhan thay oitrong thiet lap tuyen.

1.6.3. a truy nhap phan chia theo ma ( CDMA Code Division MultipleAccess) hay a truy nhap trai pho (SSMA Spread Spectrum Multiple Access ) .

Vi a truy nhap phan chia theo ma (CDMA) cac tram cua mang phat lientuc va cung phat tren mot bang tan nh nhau cua kenh. Nhng cac song mang naytrc o a c ieu che bang mot mau bt ac biet quy nh cho moi tram mat

at trc khi phat tn hieu a ieu che. Do o loai a truy nhap nay ngay ca khico nhieu tn hieu ieu che c a vao bo phat ap, th tram mat at thu co thetach tn hieu thu t cac tn hieu khac bang cach s dung mot mau bt ac biet thchien qua trnh giai ieu che .

Cac tn hieu t tat ca cac tram eu co cung mot v tr trong bo phat ap cave thi gian lan tan so. pha thu thc hien qua trnh trai pho ngc s dung magiong nh ma trai pho s dung pha phat va lay ra tn hieu ban au. ieu nay chophep ch thu cac tn hieu mong muon ngay ca khi cac song mang trai pho vi cac

ma khac en cung thi gian (hnh 1-7).

Hnh 1.7-a truy nhap phan chia theo ma

u iem he thong CDMA la hoat ong n gian, do no khong oi hoi batky s ong bo truyen dan nao gia cac tram. ong bo duy nhat la ong bo cua maythu vi chuoi cua song mang thu c. Ky thuat nay at hieu qua trong viec chonglai s can nhieu t cac he thong khac va can nhieu do hien tng a ng truyen.Nhc iem chnh la hieu suat thap. Bang 1-1 tom tat u iem va nhc iem cuacac he thong a truy nhap khac nhau .

Bo phat ap

Ma

Thi gianCDMA

Tan so1

N

2

1

2N

Ma

1


16/73


Bang 1-1 Tnh nang cua cac he thong a truy nhap

He thong u iem Nhc iem Nhan xet

FDMA

-Thu tuc nhap ngian-Cau hnh cac phngtien tram mat at ngian

-Thieu linh hoattrong thay oi thietlap tuyen-Hieu qua thap khiso song mang tang

-De dang ngdung viecphan phoitheo yeu cau

TDMA

-Hieu qua s dungtuyen cao tham ch khitang so cac tram truynhap-Linh hoat cao trongviec thay oi thiet laptuyen

-Yeu cau ong bocum-Cong suat phatcan thiet cua trammat at cao

-Co the ngdung SS-TDMA neu cothe

CDMA

-Chu c nhieu vameo-Chu c s thay oicac thong so khacnhau cua ng truyen- Bao mat tieng noicao

-Hieu qua s dungbang tan kem- Yeu cau ngtruyen vi bangtan ln

-Phu hp vicac he thongco cac tramlu lng nho

Ngoai ra con the s dung mot trong cac ky thuat sau :1. Che o a truy nhap gan co nh (FAMA Fixed Assigned MultipleAccess).2. Che o a truy nhap gan theo nhu cau ( DAMA- Demand AssignedMultiple Access ).3. a truy nhap phan chia theo thi gian chuyen mach ve tinh (SS-TDMA).Vi gan co nh, cac kenh ve tinh c phan bo co nh cho tat ca cac tram

mat at khac nhau, bat chap co hay khong co cac cuoc goi phat i, con gan theo


17/73


18/73


CHNG IISONG VO TUYEN IEN

2.1. Tan so va cac ac tnh cua song vo tuyen ien trong thong tin ve tinh2.1.1. Song vo tuyen va tan soSong vo tuyen la mot bo phan cua song ien t va giong nh song anh

sang, tia hong ngoai, tia X, v.v S khac nhau gia chung ch tan so. Song votuyen c quy nh la nhng song ien t co tan so nho hn 3000GHz. Cac songco tan so t 3kHz en 270 GHz c phan nh cho nhieu muc ch khac nhau.Cac tan so s dung trong thong tin ve tinh hien nay nam trong khoang 1GHz en

30GHz2.1.2. Cac tan so s dung cho thong tin ve tinh co nha.Bang C (Bang 6/4GHz)

Tan so phat cho ng len t 5,925GHz en 6,425GHz va cho ngxuong t 3.7GHz en 4,2GHz. Bang tan nay suy hao rat t do ma va trc aya s dung cho cac he thong vi ba di mat at ; do o s phat trien cua thiet b a mot mc tien tien, no c s dung cho cac he thong ve tinh khu vc va noi a.

b.Bang Ku (cac bang 14/12 va 14/11 GHz)

Tan so phat cho ng len t 14GHz en 14,5GHz va cho ng xuong t12,25GHz en 12,75GHz hoac t 10,95GHz en 11,7GHz. Bang nay a c sdung rong rai tiep sau bang C cho vien thong cong cong. No c a dung hn chothong tin noi a va thong tin gia cac cong ty, do tan so cao nen cho phep cac trammat at s dung c cac anten co kch thc nho e lien lac.

c.Bang Ka (30/20 GHz)Bang Ka lan au tien c s dung cho mot kenh thong tin thng mai qua

ve tinh thong tin SAKURA cua Nhat Ban. u iem cua thong tin ve tinh s dungbang tan nay la cho phep s dung cac tram mat at nho va khong gay nhieu vicac he thong vi ba tren mat at. Tuy nhien bang tan nay b suy hao ln do ma.

2.2 . Phan cc song2.2.1. nh nghaSong bc xa bi anten bao gom cac thanh phan ien trng va t trng.

Hai thanh phan nay trc giao vi nhau va vuong goc vi phng truyen song,

chung bien oi theo tan so cua song. Phan cc cua song c xac nh bi hngien trng. Song ien t phang co cac dang phan cc nh : phan cc elp, phancc tron, phan cc thang (hnh 2)


19/73


2.2.2. Phan cc elpTrong qua trnh truyen song neu au cuoi vec t cng o ien trng cua

song vach nen mot hnh elp trong khong gian th song goi la phan cc elp .2.2.3. Phan cc tronTrong qua trnh truyen song neu vec t cng o ien trng cua no ve nen

mot vong tron th song goi la phan cc tron. Neu nhn theo chieu truyen song, vect ien trng quay theo chieu kim ong ho th ta co song phan cc tron quay phai,trong trng hp vec t ien trng quay ngc chieu kim ong ho ta goi la songphan cc tron quay trai .

2.2.4. Phan cc thangSong co vec t cng o ien trng luon hng song song theo mot ng

thang trong qua trnh truyen song goi la song phan cc thang hay phan cc tuyentnh. Tuy theo hng cua vec t ien trng ta co phan cc ngang hoac phan cc

ng.2.3. S truyen lan song vo tuyen ien

2.3.1. Khai niem ve s truyen lan song vo tuyen trong thong tin ve tinhCo nhng van e khac nhau lien quan ti s truyen lan song vo tuyen

trong thong tin ve tinh v viec phat va thu song thc hien gia mot tram mat at vamot ve tinh thong tin mot c ly kha xa (35.786km). Van e ln nhat la ton haotruyen lan khi truyen gia tram mat at va ve tinh. Co the noi rang cong nghethong tin ve tinh luon luon c cai tien e khac phuc c cac ton hao truyen lan.

Ngoai ton hao truyen lan ra, song vo tuyen s dung trong thong tin ve tinh con chu

Hng

truyen

lan

P

y

xE

Anten

E max

Emin

E

x

y

Hnh 2- Phan cc song


20/73


anh hng cua cac tac ong nh ton hao hap thu do tang ien ly, kh quyen va macung nh tap am gay ra t ben ngoai bi tang ien ly, kh quyen, ma va mat at .

2.3.2. Ton hao trong khong gian t do

Trong thong tin ve tinh, song vo tuyen i qua khoang khong vu tru (gan nhchan khong). Trong mot moi trng nh vay, co rat t cac chat co the suy hao songhoac lam lech hng truyen lan cua no. S suy hao song gay ra ch do s khuyechai t nhien cua no. Moi trng nh vay c goi la khong gian t do. Khi song votuyen truyen trong khong gian t do ty so cong suat phat tren cong suat thu taiiem cach ni phat mot khoang R se la :

= (4R/)2 ay la bc song cua vo tuyen ien

c goi la ton hao khong gian t doT bieu thc co the thay rang ton hao khong gian t do ty le bnh phng

vi khoang cach truyen lan song .Trong thong tin ve tinh, v hau het s truyen lan song i xay ra trong khong

gian la chan khong, do o ton hao truyen song co the coi nh bang ton hao khonggian t do. Tuy nhien khoang cach truyen song rat dai nen gay ra ton hao rat ln(khoang 200dB vi song co tan so khoang 6GHz ). V vay nen can s dung cacmay phat cong suat ln va may thu co o nhay cao cung nh anten thu va phat cohe so tang ch ln.

2.3.3. Ca so vo tuyenTrong mot so trng hp, cac song vo tuyen truyen en hay i t cac ve

tinh thong tin, ngoai ra con chu anh hng cua tang ien ly va kh quyen en tonhao truyen lan do c ly xa .

Song truyen i t ve tinh va tram mat at b anh hng bi tang ien ly khitan so thap va b anh hng do ma khi tan so cao. o th hnh 2-1 ch ra ac tnhtan so suy hao do tang ien ly va do ma.

100

50

10

5

10,1 0,5 1 5 10 50 100

Tan so (GHz)

Ton hao do ma(25mm/gi)

Hap thu dotang ien ly

Ca so vo tuyen

Hnh2.1- Ca so vo tuyen


21/73


T o th nay ta thay cac tan so nam khoang gia 1GHz va 10GHz th suyhao do tang ien ly va ma la khong ang ke, do vay bang tan nay c goi la

ca so vo tuyen. Neu ta s dung tan so nam trong khoang nay th ton hao truyenlan gan nh bang ton hao khong gian t do, v vay cho phep thiet lap cac kenhthong tin ve tinh on nh .

2.3.4. Tap am trong truyen lan song vo tuyenCac chat kh cua kh quyen va ma khong ch hap thu song ma con la cac

nguon bc xa tap am nhiet. Tap am do cac chat kh trong kh quyen anh hngkhong nhieu en s truyen lan song so vi suy hao ln hn do tap am gay ra doma. V vay khi thiet ke cac kenh thong tin, ngoai viec giam suy hao song phai tnhthem tap am do ma. Hnh 2-2 ch ra tap am do ma.

Cung co tap am mat at phat sinh trong khi truyen lan song. ay la tap amnhiet gay ra bi trai at, nhiet tap am gan nh nhiet o be mat trai at. Nhiet otap am mat at khoang 250 en 3000K va anh hng chu yeu en tram ve tinh .

2.3.5. S giam kha nang tach biet phan cc cheo do maTrng ien va t cua song co hng dao ong khac nhau; hai song co ien

trng vuong goc vi nhau oi khi ket hp lai thanh mot va tao ra mot song phancc cheo. Mot song nh vay co the dung mot anten e tach ra cac song rieng biet.Tuy nhien, khi song i qua ma, hnh dep cua cac hat ma oi khi lam nghiengphan cc cheo, do o sinh ra cac thanh phan vuong goc trong qua trnh anten tachra cac song rieng biet. Ty so thanh phan vuong goc hon hp tren thanh phan mongmuon c goi la s tach biet phan cc cheo.

2.3.6. EIRP : ac trng kha nang phat

Nhiettap

am

Suy hao do ma (dB)

300

250

200

150

100

50

00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

( K)O

Hnh 2.2- Tang tap am do ma


22/73


Tch so gia he so tang ch cua anten va cong suat may phat cung cap choanten goi la cong suat bc xa tng ng ang hng (EIRP), ay la thong so cban bieu th kha nang cua mot tram phat.

PEIRP = PT GT2.3.7. G/T : ac trng o nhay may thu1. Nhiet tap am may thuMac du tap am trong thong tin ve tinh do nhieu nguon tao ra, nhng cong

suat cua no vo cung nho. Nhiet tap am c dung lam n v e bieu th cong suatnho nh the. Neu dung nhiet tap am (T) th cong suat tap am (P) co bieu thc :

P = kTB (W)Trong o :k Hang so Boltzmann (k = 1.38062 x 10-23 J/0K)B o rong bang thong (Hz)

T Nhiet o tuyet oiCac nguon tap am trong thong tin ve tinh co the c phan loai nh sau :-Tap am do anten thu c :+ Tap am t vu tru+ Tap am kh quyen+ Tap am do mot bup song phu+ Tap am do ma- Tap am do ton hao cua he thong tiep song (nhiet tap am tang khoang 70K

tren ton hao 0,1dB).

-Tap am may thuTrong so cac loai tap am do anten thu c th tap am t vu tru gay ra chvai o K, hau nh khong ang ke. Tap am kh quyen tang ac biet bang songmilimet la nguyen nhan chu yeu gay ra tap am vu tru trong thi tiet tot. Tap am doma tang theo cng o ma.

Tap am t mot bup song phu la do anten thu tiep nhan bang bup song phumot lng tap am t mat at va kh quyen. Gia tr tap am nay phu thuoc vao gocngang va tan so .

Tap am t he thong tiep song, sinh ra do ton hao he thong tiep song. V

ton hao nay khong nhng lam suy giam tn hieu au vao, ma con sinh ra tap am, doo may thu at cang gan anten cang tot e giam ton hao va tap am .

2. G/T (He so pham chat cua thiet b thu )Ty so cua he so tang ch tren tap am nhiet tong c ky hieu la G/T va ty

so nay bieu th cho chat lng o nhay cua tram thu. G/T c dung nh mot he sochat lng cho toan bo he thong thu bao gom ca anten. n v s dung la dBm/0K .

2.3.8. S nhieu loan do cac song can nhieuHau het cac bang tan an nh cho thong tin vo tuyen vu tru th cung c

an nh cho thong tin vo tuyen tren mat at do o co bon loai can nhieu gia cache thong co the xay ra :

- Mot ve tinh can nhieu vi mot tram ve tinh mat at .


23/73


- Mot tram ve tinh mat at can nhieu vi mot ve tinh.- Mot tram truyen thong mat at can nhieu vi mot ve tinh .- Mot tram truyen thong mat at can nhieu vi mot tram ve tinh mat at.Hnh 2-3 mo ta cac dang can nhieu.

Nham e giam bt s can nhieu co the xay ra. Cac to chc a ra cacKhuyen ngh sau :

Han che mat o thong lng nang lng tao ra tren mat at cua ve tinh. Han che EIRP phat t cac tram truyen thong tren mat at theo hng

ve quy ao ve tinh a tnh . Han che goc ngang nho nhat cua anten tram ve tinh tram mat at.

S2

S1

E3 E1 E2 E4

T R

R TR T R T

Ve tinh

Tram mat at hoat ong bang tan 4GHz

Tram mat at Tram mat at hoat ong Bang tang 6 GHz

(Vi Ba) (Vi Ba)(Ve tinh)

B

D

4 GHz 6 GHz

C

A

T: May phat

R: May thu:Tn hieu mong muon:Tn hieu nhieu

4 GHz 6 GHz

4 GHz 6 GHz

Hnh 2.3- Can nhieu t cac ve tinh khac va he thong vi ba tren mat at


24/73


CHNG III

KY THUAT TRAM MAT AT

3.1. Cong nghe va ac tnh cua anten

3.1.1. Yeu cau chat lng oi vi thong tin ve tinhe thu c nhng song yeu en t ve tinh va phat i cac song co congsuat u manh len ve tinh, anten can co mot so ac tnh sau :

1. He so tang ch cao va hieu suat caoMac du he so tang ch cua anten ty le thuan vi dien tch cua no, nhng

tuy thuoc vao tnh kinh te va tnh thuan tien khi khai thac ma ta chon loai antenva co he so tang ch cao ma dien tch cang nho cang tot.

2. Hng tnh cao va bup song phu nho

Anten dung trong thong tin ve tinh can phai co tnh nh hng cao, bupsong phu nho e chung khong can nhieu vao cac he thong thong tin khac.3. ac tnh phan cc totAnten can phai co tnh phan cc tot e s dung tan so mot cach hieu qua

bang cach ghep cac song phan cc ngang va ng thanh phan cc vuong goc hoacthanh cac song phan cc tron quay trai va quay phai trong phan cc tron.

4. Tap am thap .

3.1.2. Phan loai antenHnh 3-1 trnh bay hnh dang cac loai anten hay c s dung trong thong tin

ve tinh. Moi anten co mot bo phan xa chnh parabon va c thiet ke sao cho nguonbc xa at tai tieu iem cua parabon e song bc xa t mat parabon la song phang.

TenAnten parabon co

nguon bc xa s capat tai tieu iem chnh

Anten CassegrainAnten

parabon lechAnten

Gregorlan lech

Hnhdang

Mat phan xa chnh Mat phan xa chnh

Hnh 3.1- Cac loai anten tram mat at


25/73


1. Anten parabon co nguon bc xa s cap at tai tieu iem ay la loai anten co cau truc n gian nhat. No c dung chu yeu cac

tram ch thu va cac tram nho vi dung lng thap. V hieu qua he so tang ch thapbup song phu khong c tot va cap noi t loa tiep song en may phat b dai.

2. Anten Cassegrainay la loai co them mot bo phan xa phu vao bo phan xa chnh, he so tang

ch cua anten c nang cao va ac tnh bup song phu cung c cai thien chut t.Anten c s dung cho cac tram bnh thng, co quy mo trung bnh. Cap noi giamay phat va loa tiep song ngan hn.

3. Anten lech

Anten lech co bo phan tiep song, mot mat phan xa phu c at v trlech mot t so vi hng truc cua mat phan xa e cac bo phan tiep song va matphan xa nho khong chan ng i cua song. Do o bup song phu c cai thien rat

ln dan en he so tang ch ln hn. Ngoai anten lech mot mat phan xa con co hailoai anten khac thuoc loai nay : Mot la loai Gregorian lech co mat phan xa phudang elp, hai la loai Gregorian lech vi mat phan xa phu co dang hyperbol. Cacanten nay co hieu qua ac biet khi can thiet giam can nheu t cac kenh thong tinviba tren mat at hoac tren cac ve tinh khac cac v tr ke nhau tren quy ao.

3.1.3. He thong anten bam ve tinhNgay ca ve tinh quy ao a tnh; v tr cua chung cung luon thay oi

khoang 0,10 theo cac hng ong, tay, nam, bac. Do vay can ieu khien anten

tram mat at e bam theo ve tinh. Cac loai he thong anten bam ve tinh :- He thong xung n : He thong nay luon xac nh tam bup song anten co

hng ung vao ve tinh hay khong e ieu khien hng cua anten. He thong nays dung bon loa bc xa, moi loa bc xa co hng bup song hi khac vi hng bupsong chnh e lay ra tn hieu bao loi.

- He thong bam tng nac : He thong nay dch chuyen nhe v tr anten cackhoang thi gian nhat nh e ieu chnh sao cho mc tn hieu thu la cc ai.

- He thong ieu khien theo chng trnh : He thong nay ieu khien anten

da tren thong tin quy ao d oan trc lien quan en ve tinh.3.1.4. Cac ac tnh ve ien1. He so tang ch

He so tang ch cua mot anten la ty so gia mat o cong suat bc xa (hoacthu) cua anten mot hng a cho va tai mot iem tren hng ay tren mat ocong suat bc xa (hoac thu) cua anten vo hng cung tai hng va iem tren khihai anten co cong suat cap cho anten la nh nhau. He so tang ch cc ai hngbc xa cc ai co gia tr cho bi cong thc :

Gmax =

A2

4

(3-1) ay : la bc song = c/f


26/73


c : la van toc anh sang = 3.108 m/sf : la tan so song ien t

A : la dien tch be mat =4

2D

D : la ng knh anten gng parabol co mat phan xa tron : hieu suat toan bo cua anten la do mot so tham so tnh en quy

luat chieu xa, mat mat do s tran, be mat phan xa xau, v.v Thong thng co giatr bang 0,55 en 0,75 .

V vay :

Gmax =2

D = 2

c

Df (3-2)

Bieu th dang dB (decibel) :

Gmax

dB

=22

log10log10

=

c

DfD

(dB) (3-3)

2. o th bc xa

o th bc xa bieu th cac thay oi gia tr cua he so tang ch theo cac hngkhac nhau. Vi anten co mat phan xa tron th o th co dang oi xng va tron xoayc bieu th trong he toa o cc (hnh 3-2a) hay toa o e- cac (hnh 3-2b) . Bupsong chnh co hng cc ai va dang cac bup song phu .

Hnh 3.2 o th bc xa anten

1.o rong bup songo rong cua bup song chnh c bieu th bang goc hp bi hai hng ma

o he so tang ch giam i mot na so vi he so tang ch hng cc ai c mota nh (Hnh 3-2a). o rong bup song nay con c goi la o rong bup song nacong suat (1/2) hay o rong bup song 3dB (3dB) . o rong bup song 3dB lien quanti ty so /D bi mot he so co gia tr phu thuoc vao luat chieu xa. oi vi motanten parabol thong thng, o rong bup song 3dB c xac nh :

3dB =fD

c

D

7070=

(o) (3-4)

CacBup Phu

Bup Chnh

3dB

Giam 3dB

maxG = / 2

3dB

= 1

D

3dB

1

GMax, dB

-3dBien hnh30dB

o tang ch cua ang ten


27/73


Vi bieu thc tren ta thay o rong bup song 3dB giam ty le nghch vi tanso va ng knh anten.

iem hng so vi truc (hng cc ai) th he so tang ch c tnh bang:

G()dB = Gmax - 122

3

dB

(dB) (3-5)

Cong thc nay ch ung vi goc u nho dB30 .

T cong thc (3-2) va (3-4) ta co moi quan he gia he so tang ch cc aivi o rong bup song 3dB :

Gmax =2

3

270

=

dBc

Df

(3-6)

Moi quan he gia o rong bup song 3dB vi he so tang ch cc ai cbieu dien nh (hnh 3-3).

- ac tnh bup song phu :Neu giam bup song phu cang nhieu cang tot e tranh can nhieu vi he

thong khac. Theo Khuyen ngh cua CCIR cho cac anten co D/> 100, he so tangch cua bup song phu (Gs) phai nho hn cac he so tang ch sau tng ng vi gochp bi truc chnh :

10

< < 480

Gs = 32 - 25 log (dB)

> 480

Gs = 10dB

20

30

40

50

60

70

1 100,1

Hes

ota

ngch

Anten(dB)

o rong bc song 3dB cua Anten (o)

Hnh 3.3- He so anten hng bc xa cc ai la ham cua o rong goc 3dB


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Cac anten lech co cac ac tnh bup song phu rat tot, v khong co s can trcua mat phan xa phu va cac thanh , chung c s dung khi co yeu cau nghiemngat giam can nhieu trong thiet ke mach .

3.2 . CONG NGHE MAY PHAT

3.2.1. May phat cong suat caoe bu vao ton hao truyen song ln trong thong tin ve tinh, au ra may phatcan phai co cong suat cang ln cang tot, do vay tram mat at s dung bo khuyechai cong suat cao (HPA). Trong cac he thong vo tuyen tren mat at, khoang cachgia cac tram chuyen tiep ch vai chuc km nen cong suat may phat nho (khoang10W) con oi vi thong tin ve tinh do khoang cach chuyen tiep dai (36.000km) nenmay phat tram mat at phai co cong suat ln khoang vai tram W en hang KW.

3.2.2. Phan loai cac bo khuyech ai cong suat cao

Cac en song chay (TWT), Klystron (KLY), transistor hieu ng trng(FET) c dung trong bo khuyech ai cong suat cao. Tuy theo cong suat ra cuamay phat va bang tan cong tac ma s dung loai khuyech ai nao cho thch hp.

Bang 3-1 : So sanh cac bo khuyech ai cong suat cao.

HPA

Tham soLoai KLY Loai TWT Loai FET

Cong suat ra Ln Ln NhoKch thc Ln Trung bnh NhoTrong lng Ln Trung bnh NhoBang tan Vai chuc MHz Vai tram MHz Vai tram MHzLam lanh -Lam lanh bang

khong kh khi congsuat ti vai kW- Lam lanh bang

nc khi cong suatra khoang 10kW

-Lam lanh bangkhong kh khi congsuat ti vai kW- Lam lanh bang

nc khi cong suatra khoang 10KW

- Lam lanh bangkhong kh t nhien

ien ap cungcap

Trung bnh Cao Thap

en song chay (TWT) co bang tan khuyech ai rong, co the phu c tatca cac bang tan phan nh cho truyen dan, ieu o co li cho viec s dung nhieusong mang hn.


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Con oi vi en Klystron (KLY) co o rong bang tan khuyech ai tngoi hep, nhng tan so khuyech ai co the ieu chnh en bat ky gia tr nao trongkhoang tan so phan nh cho truyen dan .

Transistor hieu ng trng (FET) c s dung tram dung lng thap,cong suat ra nho. e at c cong suat cao hn ngi ta au song song cactransistor lai vi nhau .

3.2.3. Cau hnhCau hnh cua mot tram mat at c mo ta hnh 1-4b, ta thay may phat

cong suat cao gom co mot bo khuyech ai trung tan, bo chuyen oi tan so len vamot bo khuyech ai cong suat cao. Bo khuyech ai trung tan khuyech ai tn hieut bo ieu che a ti, tan so trung tan sau o c bien oi len tan so cc ngannh bo oi tan. Sau o tn hieu c bo khuyech ai tan so cao khuyech ai lenen mc yeu cau e phat en ve tinh .

Cau hnh cua may phat cong suat cao c quyet nh bi loai song mangva so lng song mang, nhng nhn chung co hai dang thng c thc hien sau :

1.Mot may phat khuyech ai ong thi nhieu song mang (hnh 3-4)

U/C : Bo nang tan

MOD : Bo ieu cheHnh 3-4 Cau hnh cua bo khuyech ai cong suat cao

s dung mot HPA

Vi cau hnh nay can thoa man cac yeu cau sau :- o rong bang u rong e khuyech ai mot song mang vi bat ky tan so nao.- Cong suat ra co o d tr u sao cho meo do ieu che phat sinh t skhuyech ai ong thi cua nhieu tn hieu di mc quy nh.Cau hnh nay thuan li trong khai thac .

HPAcombiner

U/C

U/C

MOD

MOD

MOD

U/C


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2. Moi song mang c khuyech ai rieng bang mot bo khuyech ai cong

suat cao (hnh 3-5 )

Hnh 3.5 Cau hnh cua bo khuyech ai cong suat cao s dung nhieu bo khuyech ai

Vi cau hnh nay moi bo khuyech ai khong yeu cau phai co bang tan ronge ieu chnh tan so khuyech ai oi vi moi song mang cho trc. Cau hnh nayphu hp vi tram co song mang t .

3.2.4. Meo do xuyen ieu cheBo khuyech ai cong suat cao la bo khuyech ai tuyen tnh nhng no se tr

thanh phi tuyen khi khuyech ai vung bao hoa. Luc o ien ap au ra khong ty levi ien ap au vao. Bi vay khi nhieu song mang c khuyech ai ong thi th

se phat sinh cac tap am. Hnh 3-6 minh hoa van e tren, khi khuyech ai ong thiba tn hieu vao co tan so f1,f2, f3 th au ra ngoai ba tn hieu c ban tren con cocac tn hieu khac co tan so : (2f1-f2 ), (f1+ f2 - f3 ), (f1 f2 + f3 ),( 2f2 f1 ), ( f2 +f3 f1).

f1+f2-f3 2f2-f1Pho tan so au vao ac tuyen vao va ra Pho tan so au ra

Hnh 3-6 Meo do xuyen ieu che

Do o oi vi mot bo khuyech ai cong suat cao, khi khuyech ai nhieusong mang ong thi th iem lam viec cua bo khuyech ai phai c chon sao chomc au ra thap hn mc bao hoa khoang 6 en 10dB, nham muc ch e triet tieucac tn hieu tap, iem lam viec o c goi la iem lui (back-off).

f1 f2 f3 f1 f2 f32f1-f2 f1-f2+f3 f2+f3-f1

HPA

HPA BoPhoi Hp

U/C

U/C

U/C MOD

MOD

MOD

HPA

HPA


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Ngoai ra con co mot phng phap khac e triet tieu nhieu xuyen ieu che,c goi la tuyen tnh hoa. Phng phap nay la ngi ta chen vao tang trc motmach ien co ac tuyen bu vi ac tuyen phi tuyen cua bo khuyech ai e caithien tuyen tnh toan bo . Hnh 3-7 minh hoa phng phap tren .

ac tuyen meo trc ac tuyen phi tuyen ac tuyen cua HPA

cua bo tuyen tnh hoa cua HPA sau khi buHnh 3-7 Tuyen tnh hoa

3.3. Cong nghe may thu3.3.1. Cau truc tram thu

Cau truc cua tram thu c mo ta nh hnh 1-4b thiet b gom co : Anten ,khoi thu tap am thap , khoi giai ieu che va thiet b a truy nhap .

Trong khoi thu tap am thap gom co : Bo khuyech ai tap am thap, bo oi

tan xuong, bo dao ong, bo khuyech ai trung tan.3.3.1. Khuyech ai tap am thapSong bc xa t ve tinh en anten vi cong suat cc ky nho, sau khi c

anten khuyech ai nhng mc o van cha u e thc hien giai ieu che do o canphai khuyech ai chung len mot mc u ln va ty so S/N phai at ngng chophep, do o oi hoi tang khuyech ai nay phai co he so tap am nhiet nho, v ay latang khuyech ai au tien. Hien nay co hai loai khuyech ai tap am thap thngdung la khuyech ai dung GaAs-FET, khuyech ai dung HEMT .

1- Khuyech ai dung GaAs-FETKhuyech ai dung GaAs-FET la bo khuyech ai nhieu thap co he so tapam khoang 1,2 en 2dB . Transistor hieu ng trng dung loai ban dan hp chatgia gali va asenic . Bo khuyech ai nay c s dung rong rai tan so cao vi cacac tnh bang tan rong, co he so khuyech ai va o tin cay cao.

2. Khuyech ai dung HEMT (High Electron Mobility Transistor)Transistor co o linh ong ien t cao (HEMT) s dung tiep giap pha tron

gia GaAs va AlGaAs (hnh 3-8) , gia dai dan cua AlGaAs co mot sai khac nanglng, dai nay c kch thch loai n, con GaAs khong c khch thch. V vayhnh thanh mot lp giau ien t trong AlGaAs gan be mat tiep giap vi GaAs. Khiat mot ien trng vao lp giau ien t nay, cac ien t se chuyen ong vi o


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linh hoat rat cao v chung khong chu s tan xa bat ky cua cac nguyen t cho cuavat lieu sinh ra chung. HEMT co cac ac tnh tap am thap tot hn so vi GaAs-FET.

Hnh 3.8- Cau tao cua HEMT

Cac ac tnh noi bac cua HEMT nh bang tan rong, kch thc nho, giathanh thap, de bao quan va thuan li cho san xuat hang loat, bi vay no c s

dung rong rai. Bo khuyech ai nay lam viec on nh nhiet o phong nhng co khichung c lam lanh nham e cai thien hn na cac ac tnh tap am thap cuachung.

Bang 3-2 So sanh cac bo khuyech ai tap am thap (LNA)

LNAMuc

GaAs-FET HEMT

ieu kien lam viec Nhiet o phong Lam lanh Lam lanh

Bangtan

Bang4GHz Xap x 550

K Xap x 450

K Xap x 520

K

Bang12GHz

1800K hoacthap hn

Xap x 1200K Xap x 1200K

Bang20GHz

3000K 2000K hoacthap hn

Xap x 1600K

Tnh nang Tap am thapBang tan rong

Kch thc nho

Tap am thapKch thc vo

cung nho

b)

As (AlGa) loai n Khong pha GaAs

ien tLo trong (Si)

a)

Nen GaAs ban dan

GaAs

NguonCong Mang bao ve

Cc mang

Lp ien to linh ong cao

(AlGa)As

Dai dan

Dai hoa tr


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CHNG IVTRAM VE TINH

4.1. Cau hnh tram ve tinh vi mot bo phat ap n gian

Anten phat Anten thu

Hnh 4-1 Cau truc bo phat ap thong thng

Tn hieu t tram phat mat at truyen lan en anten thu cua ve tinh canten khuyech ai len roi qua mach loc thong dai e loai bo cac tn hieu ngoai daitan cong tac cua bo phat ap, tiep en tn hieu c khuyech ai u ln e thc

hien oi tan, yeu cau cua tang khuyech ai nay la he so tap am thap(LNA). Tan sotn hieu nay tron vi tan so dao ong noi tao ra cac tan so khac, cac tan so o ca qua mach loc thong dai e lay ra tan so can thiet (tan so phat xuong). Tn hieusau khi qua bo loc c a vao mach khuyech ai cong suat cao (HPA) khuyechai tn hieu en mc thiet ke roi a en anten bc xa xuong tram mat at. Linhkien khuyech ai tang nay cung thng dung en song chay (TWT) hoac transistorhieu ng trng FET .

4.2. Phan bo dai tan cua bo phat apBang tan phan bo cho bo phat ap ve tinh co the t vai tram MHz len en

vai GHZ. Bang tan nay thng c chia thanh cac bang tan con (theo phan nhcua ITU). Hau het cac bo phat ap thng c thiet ke vi dai thong 36MHz,54MHz, hoac 72MHz, trong o dai thong 36MHz la chuan c dung pho bien chodch vu truyen hnh bang C (6/4 GHz). Hien nay mot so loai loai bo phat ap co xly tn hieu a c a vao s dung va nh vay co the cai thien c chat lng loi(oi vi truyen tn hieu so ). Trong quy ao a tnh, moi ve tinh c at mot vtr toa o xac nh va lam viec vi mot bang tan xac nh. V du, trong bang tan C(6/4GHz) ve tinh c s dung mot phan nh pho rong la 500MHz. Nh vay ve

tinh co the at 24 bo phat ap lien ke nhau va moi bo phat ap s dung dai thong36MHz trong dai thong phan nh 500MHz. Co the thc hien c ieu o bangcach bo tr 12 bo phat ap lam viec vi tn hieu song bc xa phan cc ng va 12

BPF

LO

LNA MIX BPF TWT


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bo phat ap lam viec vi phan cc ngang. Hnh 4-2 mo ta s bo tr 12 kenh phancc doc va 12 kenh phan cc ngang trong dai thong phan nh la 500MHz .

Hnh 4.2- Phan bo dai tan cua bo phat ap ve tinh 6/4GHz

Cac ve tinh loai nay chu yeu chuyen tiep cho tn hieu hnh. e cac ve tinha tnh khong gay nhieu lan nhau thng phai at toa o cach nhau 20 cho ve tinhbang C, cach nhau 30 cho bang Ku.

4.3. Cac mang ve tinh nhieu chumCac mang ve tinh mot chum tia co the cung cap mot vung bao phu toan bokhu vc trai at ma co the nhn thay ve tinh va do vay co the thiet lap c cactuyen lien lac c ly xa. Nhng trong trng hp nay o tang ch cua anten b giihan bi goc m cua chum tia .

oi vi ve tinh cung cap vung bao phu ch gom mot phan cua trai at (motvung hoac mot quoc gia ) nh mot chum tia hep ( mot chum tia vung hoac motviec). Th o tang ch anten c cao hn nh s giam goc m cua cua chum tia

anten (hnh 4-3).

C1 C3 C5 C7 C9

Dai thong 36 MHz

Dai thong 500 MHz

37003720

3760

38003840

3900

3880

3920 3960

40004040 4080

4100

41204160

f(MHz)4200

a) Phan cc ngang

C2 C4 C6 C83700

3740 3780

38003860

3900

3940 3980 4020 40604100

4140 41804200

3820

b) Phan cc ng

f(MHz)

Hnh 4.3- Vung baophu toan cau vavung bao phu cuamot so chum hep

3dB=17,5O

3

dB=1

,75O


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4.3.1.u iem cua ve tinh nhieu chum

- Khi thay oi t mot ve tinh co vung bao phu toan cau sang mot ve tinhnhieu chum th cho phep tiet kiem c kch thc tram mat at dan ti giam giathanh tram mat at .

- Cho phep tai s dung tan so.

Tai s dung tan so la viec s dung nhieu lan cung mot dai tan theo motcach thc sao cho lam gia tang tong dung lng cua mang ma khong lam gia tangdai tan c phan phoi. Trong ve tinh mot chum viec tai s dung tan so nh vaophan cc trc giao, con trong ve tinh nhieu chum tnh tach biet cua hng tnhanten co the c khai thac e tai s dung cung mot dai tan trong cac chum khacnhau.

Trong trng hp tai s dung tan so nh phan cc trc giao, dai thong B chc s dung hai lan. Trong trng hp tai s dung nh tach goc, dai tan B co thec tai s dung cho bao nhieu luong cung c neu mc can nhieu cho phep.

Ve mat ly thuyet mot ve tinh co M chum, dai tan B, ket hp hai kieu tais dung tan so noi tren th he so tai s dung tan so la 2M.

4.3.2. Lien ket gia cac vung bao phu

Mot he thong ve tinh a chum phai at mot v tr e lien ket tat ca cac

tram mat at cua mang do vay phai cung cap viec au noi qua lai gia cac vung phusong. Khi s dung bo phat ap thong thng co ba ky thuat lien ket cac vung phusong:

- Lien ket bang bc nhay bo phat ap .

- Lien ket bang chuyen mach tren ve tinh.

- Lien ket bang quet chum.

1. Lien ket nh bc nhay cua bo phat ap

Bang tan phan phoi cho he thong c chia thanh so bang tan con bang viso chum. Mot nhom cac bo loc tren ve tinh se phan cach cac song mang theo bangtan con ma chung chiem. au ra moi bo loc c ket noi ti anten cua chum chqua mot bo phat ap. Nhat thiet phai s dung mot so lng bo loc va bo phat ap tnhat cung bang bnh phng cua so lng cac chum. Hnh 4-4 minh hoa khai niemnay cho mot th du vi hai chum . Vi kieu lien ket nay, cac tram mat at phai cokha nang phat va thu tren nhieu tan so va nhieu phan cc nham nhay t bo phat

ap nay sang bo phat ap khac .


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Hnh 4.4- Lien ket chum nh bc nhay cua bo phat ap2. Lien ket nh chuyen mach tren ve tinh (SS/TDMA)Nguyen ly chuyen mach tren ve tinh c minh hoa trong hnh 4-5 .

Hnh 4.5- Nguyen ly cua chuyen mach tren ve tinh (SS-TDMA)

Phan tai bao gom mot ma tran chuyen mach co the c lap trnh co soau vao va au ra bang vi so cac chum. Ma tran nay ket noi moi chum thu vimoi chum phat nh mot may thu va mot may phat. So lng cac bo chuyen tiep dovay bang so chum. Khoi ieu khien phan bo ket hp vi ma tran nay e thiet lap

VE TINH

Chum Tia 1 Chum Tia 2

1 ti 1

1 ti 2

B11

B12

Tan so

Thi gian

2 ti 1

2 ti 2

B21

B22

Tan so

Thi gian

1 ti 1

B11

B21

Tan so

Thi gian

2 ti 1

2 ti 2

B12

B22

Tan so

Thi gian

TUYEN XUONG

BPF

BPF

BPF

BPF

B11

t11

B12

t12

B21

t21

B22

t22

1 ti 2

Khoi ieu khienphan bo

Ma tranchuyenmach

May thu May phat

May phatMay thu

Ve tinh

Tuyen xuongti vung 1

Tuyen xuongti vung 2

Tuyen lent vung 1

Tuyen lent vung 2


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chuoi cac trang thai ket noi gia moi au vao va cac au ra trong thi gian motkhung theo cach thc la cac song mang ti ve tinh trong moi chum se c nhtuyen ti cac chum ch. Do viec lien ket gia hai chum la tuan hoan, cho nen cactram phai lu tr lu lng t cac thue bao va phat no i di dang cac khoi bit khiviec lien ket gia cac chum c thc hien. Do vay tren thc te, ky thuat nay chco the c s dung vi truyen dan so va truy nhap kieu TDMA.

3. Lien ket nh quet chumMoi khu vc phu song c chieu roi nh ky bi mot chum anten ma viec

nh hng no c ieu khien bi mot mang tao chum la mot phan cua he thonganten phu at tren ve tinh. Cac tram cua vung phat hoac thu cac khoi cua chungkhi vung c mot chum chieu roi. Khi khong co bo nh tren ve tinh, t nhat co haichum c can en tai mot thi iem xac nh. Mot e thiet lap tuyen len va mote thiet lap tuyen xuong. Thi gian chieu roi ty le thuan vi lng tai can van

chuyen gia hai vung. Hnh 4-6 minh hoa cho khai niem nay.

Hnh 4.6- Lien ket nh quet chum

4.3.3. Cac tuyen noi lien ve tinhCac tuyen noi lien ve tinh (ISL Intersatellite Links) co the c xem nh cacchum ac biet cua cac ve tinh a chum. Cac chum trong trng hp nay khong phaihng ti trai at ma hng ti cac ve tinh khac. Co ba loai tuyen noi lien ve tinh :

- Cac tuyen noi gia cac ve tinh quy ao a tnh va quy ao thap .- Cac tuyen noi gia cac ve tinh a tnh .- Cac tuyen noi gia cac ve tinh quy ao thap .1. Cac tuyen noi gia cac ve tinh a tnh vi ve tinh quy ao thapKieu tuyen noi nay co nhiem vu thiet lap mot tram chuyen tiep co nh qua

mot ve tinh a tnh gia mot hoac nhieu tram va mot nhom cac ve tinh chuyenong tren mot quy ao thap. V nhng ly do kinh te, chnh tr, ngi ta khong lap

Bo phat ap

BFN BFN

Chum quet

Vung cua chum eu an


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at mot mang cac tram mat at qua ln e tai moi thi iem t nhat co mot trammat at nhn thay ve tinh i qua. Do vay mot ve tinh a tnh c s dung e cnhn thay thng xuyen va ong thi t cac tram mat at va t cac ve tinh quy aothap. Chung c s dung e chuyen tiep thong tin.

2. Cac tuyen noi gia cac ve tinh a tnhMot tuyen noi lien ve tinh ket hp vi mot cau hnh tram mat at phu hp lamgia tang dung lng cua mot he thong ma khong phai au t ln cho phan mat at.

Mot tuyen noi lien ve tinh a tnh cho phep cac tram mat at cua hai mangc lien ket va do vay m rong vung phu song cua he thong .

Cac tuyen noi c ly xa qua mot ve tinh duy nhat dan ti goc ngang cuatram mat at nho de b can nhieu. Neu tuyen noi nay i qua hai ve tinh a tnh noivi nhau bang mot tuyen noi lien ve tinh th goc ngang se tang len.

Hnh 4-7 trnh bay thiet ke cua mot mang toan cau da tren 9 ve tinh atnh STAR ; 9 ve tinh nay thiet lap nen mot c s e truyen thong toan cau va mottap hp cac ve tinh cuc bo c ket noi vi chung qua cac tuyen noi lien ve tinhkhu vc.

Hnh 4.7- Mot mang ve tinh toan cau

3. Cac tuyen noi gia cac ve tinh quy ao thap

Vi nhng li the cua cac ve tinh quy ao thap va s tac nghen cac quyao ve tinh a tnh cang ngay cang gia tang a dan ti s phat trien tiep theo cuacac ve tinh quy ao thap. Cac nhc iem cua mot ve tinh quy ao thap (nh odai thi gian truyen thong b han che va vung phu song tng oi hep) co the cgiam i trong mot mang cha mot so lng ln cac ve tinh c lien ket vi nhau

bang cac tuyen noi lien ve tinh va c trang b c che chuyen mach gia cac

15 WO

60 WO

Chau Au

Nam My

95 WO

Bac va

Trung My

135 WOBac My

175 WOCac ao Thai Bnh Dng

145 EOUc va Indonexia

105 EOong A

Tay A65 EO

Chau Phi

25 EO

120mS

276m

S

242mS

180mS

96mS

Cac vetinh cuc bo

120m

S

0O

E

W


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chum. Nh mang IRIDIUM dung cho dch vu thong tin ca nhan thuoc mang te baotoan cau. He thong nay ket hp mot chum 77 ve tinh.


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4.4. Cac mang ve tinh tai tao4.4.1. Bo phat ap tai tao

Hnh 4-8 mo ta cau truc mot bo phat ap tai tao

Hnh: 4.8- Cau truc cua bo phat ap tai tao

T hnh 4-1 mo ta cau truc cua mot bo phat ap thong thng ta thay skhac nhau gia hai bo phat ap la : Vi ve tinh tai tao cac tn hieu bang tan goc, adung e ieu che song mang tuyen len, co mat tai au ra bo giai ma ieu che vacac tn hieu nay c s dung e ieu che song mang cho tuyen xuong. Do vay, sthay oi tan so t tuyen len sang tuyen xuong at c la do ieu che mot songmang mi. Con oi vi bo phat ap thong thng tan so song mang tuyen xuong

at c nh s tron tan vi bo dao ong noi tren ve tinh.4.4.2. ac iem bo phat ap tai taoVi ac iem co san cac so nh phan tren bo phat ap nen tao ieu kien x

ly cac so o trc khi phat lai. V vay ve tinh tai tao co cac ac tnh sau :- Cho phep chuyen mach gia cac anten thu va phat khong con la chuyen

mach tan so vo tuyen ma la chuyen mach tai bang tan goc. Do o ma tran chuyenmach tan so vo tuyen c thay the bang bo nh, tiep sau la ghep kenh cac so nhphan c lu tr trc khi truyen dan tren cac tuyen xuong khac nhau. ieu nay

cho phep cac tram mat at phat i toan bo thong tin cua chung theo cung mot khoibit va do vay ch phat i mot khoi bit duy nhat cho moi khung. So lng khoi btcho moi khung giam xuong va hieu qua cua khung tang len .

- Cho phep chuyen oi toc o gia tuyen len va tuyen xuong nh giai ieuche tren ve tinh, cac so nh phan cua lu lng gia cac mang, c thu theo cacsong mang co cac toc o khac nhau co the c chuyen mach tai bang tan goc vac ket hp lai trc khi phat ti cac tuyen xuong khac nhau phu hp vi ni encua chung va khong phu thuoc vao dung lng cua song mang hnh 4-9 minh hoacho van e nay.

Bo phat ap tai tao

TUYEN LEN TUYEN XUONG

LNA


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-Thay the cac ve tinh a chum bang cac ve tinh n chum, chum nay quetlan lt cac khu vc khac nhau cua vung phuc vu. Tap hp cac khu vc c chumtia quet en hnh thanh vung phu song cua he thong. Khi chum nay nam tai mot

khu vc quet nao o, th thong tin danh san cho cac tram trong khu o se c tachra khoi bo nh tren ve tinh va c phat i trong dang ghep kenh. ong thi cactram trong khu vc o phat cac thong tin danh cho tat ca cac tram khac cua mangti ve tinh. Cac thong tin nay c lu tr trong bo nh tren ve tinh e phat i sauo tai thi iem khi chum i qua vung ch (hnh 4-10).

Ve tinh thong thng

Bo phat aptoc o cao

Bo phat aptoc o thap

Tram toco thap Tram toco cao

Ve sinh tai tao

Tram toco cao

Tram toco thap

Tram toco cao

Tram toco thap

Dong toc o cao Dong toc o caoT tram

toc o caoMa tran chuyen

mach viba

Ti tramtoc o cao

Giai ieu che

Bo phan phoiMa tranchuyenmachbang

tan goc

Bo ket hp

Tai ieu che

Giai ieu che

Giai ieu che

Tai ieu che

Tai ieu che

T cac tramtoc o thap

Cac dongtoc o thap

Cac dongtoc o thap T cac tramtoc o thap

Hnh 4.9: Lien ket hai mang vi cac song mang co dung lng khac nhau.

a) Trng hp ve tinh trong suot b) Trng hp ve tinh tai tao


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- Nham tao thuan tien cho viec lap at cac tram mat at gia thanh thap, sdung ve tinh tai tao vi ng len dung phng phap a truy nhap FDMA conng xuong dung ky thuat TDM. Vi giai phap nay cho phep bo phat ap lamviec che o bao hoa dan en EIRP cc ai va he so pham chat G/T cua tram matat co the giam i c. Giai phap nay c mo ta hnh 4-11 .

Giai ieu che Giai ieu cheBo nh(RAM)

ieu khien

BFN

Chum quet

Vung chumc tru

Hnh 4.10: Mang ve tinh quet n chum kieu tai

Thi gian

Tan soChe o lien tuc

1 2 M

Thi gian

Tan so

12

M

Che o lien tuc

Tuyen len FDMA

DEM: Giai ieu cheMOD: ieu che

Tuyen xuong TDM

Hnh 4.11: Mang lien quan en mot bo phat ap tai tao

TAC

HK

EN

H

Ma

tranchuyenmac

h

bangtan

goc

GhepkenhTMD

DEM

DEM

DEM

DEM

1

2

M

f

2

1

M

LNA

L0

f

f

f

MOD

TWT

TDM

f1

f2

fM

FDMA


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CHNG VTHIET KE TUYEN THONG TIN VE TINH

5.1. Gii thieu

Tuyen thong tin ve tinh la ng noi lien mat at khong gian - mat atgom co nhieu thanh phan khac nhau nh bo phat ap ve tinh, ng truyen dan,may thu phat tram mat at. Tai moi phan, chat lng cua tuyen b giam mot mco nao o do tap am sinh ra trong phan o. CCIR (Uy ban t van ve thong tin votuyen quoc te) a ra mot tieu chuan lien quan en cong suat tap am cho phep oivi viec truyen dan cac tn hieu thoai va truyen hnh trong dch vu ve tinh co nh.Thiet ke tuyen co the c xem nh la viec phan phoi cong suat tap am trong tngphan cua tuyen thong tin e phu hp vi cac yeu cau ve tap am a neu trong cac

khuyen ngh cua CCIR. Mot iem quan trong na la khi thiet ke ng truyen saocho at hieu qua cao nhat ngha la chat lng tuyen cao nhng gia thanh phu hp .5.2. Cac ch tieu chat lngCCIR thiet lap cac ch tieu chat lng e thoa man cho nhieu loai hnh dch

vu va thc hien cac qua trnh ieu che. CCIR a ra ba ngng chat lng khongc phep vt qua trong mot phan tram thi gian cho trc. oi vi thong tinthoai cac ngng chat lng c tom tat trong bang 5-1 .

Bang 5-1 Cac ch tieu chat lng oi vi thoai

Thoai tng tThoai so(PCM)

Cac ieu kien o Cong suat tap amtai mc chuan

BER

20% cua thang bat ky (gia tr trung bnh 1 phut)20% cua thang bat ky (gia tr trung bnh 10 phut)0,3% cua thang bat ky (gia tr trung bnh 1 phut)0,01% cua nam bat ky (gia tr tong tren 5ms)

0,01% cua thang bat ky (gia tr trung bnh 1s)

10.000 pWOp----50.000 pWOp1.000.000 pWOp( khong trong so)------

---10-610-4

----

10-3

oi vi truyen hnh ve tinh, ch tieu chat lng la ty so tn hieu tren tap am(S/N) (trong so ) phai bang hoac ln hn 53dB trong 99% thi gian va 45dB trong99,9% thi gian.

Khi co thong ke suy hao do cac ieu kien kh quyen, th co the tnh c tyso tn hieu tren nhiet tap am nhan c tai au vao may thu tram mat at cho cac


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phan tram thi gian khac nhau, t o kiem tra he thong co thoa man tieu chuanchat lng a e ra khong. Tuy nhien khi tnh toan ta phai e ra mot d tr nhatnh do co s sai khac gia ly thuyet va chat lng thiet b thc te va e e phongs giam tn hieu hoac tang tap am (nhieu do cac mang khac, nhieu a ng truyenhoac nhieu do cac kenh lan can ) .

5.3. Cac ch tieu san sangMot tuyen thong tin ve tinh co nh c xem la khong san sang neu nh

mot trong cac ieu kien sau ton tai thiet b thu au cuoi cua tuyen .- 0,2% cua nam trong trng hp hong hoc (thi gian ngng tre dch vu

phai nho hn 18 gi / nam).- 0,2% cua thang bat ky neu dch vu b ngng tre do truyen song .- Trong truyen dan tng t kenh thoai, cong suat tap am khong trong so

tai mc 0 tng oi, vi thi gian tch hp la 5ms, vt qua 10-6pWOp .- Trong truyen dan so, BER vt qua 10-3 .5.4. Quan he gia chat lng va C/NChat lng cua mot kenh thong tin vo tuyen c anh gia bang ty so song

mang tren tap am (C/N) va lng meo tn hieu thu. Trong tuyen thong tin ve tinh,anh hng kh quyen gay ra meo tn hieu thu la nho, v the chat lng ngtruyen co the ch can xac nh bang C/N cua ng truyen .

Quan he gia C/N va BER (trong he thong PSK so) hoac S/N (trong hethong FM tng t ) tn hieu thu tuy thuoc vao ieu che va giai ieu che trong he

thong. V the co the tnh C/N can thiet t ng cong C/N S/N hoac C/N BERoi vi chat lng tuyen yeu cau (BER hoac S/N), nh tren hnh 5-1.

Khi kha nang khong san sang do ma la chu yeu, th ta phai xac nh moiquan he gia gia tr lng ma theo gi va xac suat xay ra ma (da vao thi gianthong ke lng ma hang nam cua vung o). V du nh chau Au cng o ma30mm/h co xac suat 0,01% nam tng ng vi 53phut/nam. Con khu vc aTrung Hai th xac suat 0,01%nam la 50mm/h. Cac vung xch ao xac suat 0,01%

C/N can thiet

a) ieu che PSK

BER

BERcanthiet

I

IC/N can thiet

b) ieu che FM

S/N

S/Ncanthiet

I

I

Hnh 5.1: Quan he bnh thng gia C/N can thiet va chat lng tuyen truyen


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nam la 120mm/h. Hnh 5-2 bieu dien cac ng ang mc cng o ma vt qua0,01% thi gian trong nam.


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e xac nh suy hao do ma ngoai cac yeu to cng ma, xac suat ma conmot so yeu to khac nh tan so song, chieu dai oan ng thc te song i trongma (phu thuoc vao o cao cn ma, v o iem thu, goc ngang anten). c xacnh theo cong thc :

R = RL STrong o :R : o suy giam tren mot n v chieu dai (dB/km), phu thuoc vao tan so

cong tac va cng o ma, co the c xac nh bang o bieu. Hnh 5-3 la o bieudo CCIR cung cap e tnh he so nay.


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LS : Chieu dai oan ng thc te song i trong ma, phu thuoc vao gocngang va o cao cn ma.

LS =E

hh SR

sin

hR : o cao cn ma (hR = 4km vi 0 < v o


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He so tang ch cua anten ve tinh thng khoang 15dB oi vi mot antenphu song toan cau tan so 6GHz hoac t 30 en 40 dB cho tan so 14GHz .

He thong tiep song c thiet ke sao cho ton hao cang nho cang tot. Trongthc te ton hao he thong tiep song tram mat at thng t 1 en 2 dB va ve tinh

khoang 1dB hoac nho hn .(PT LT + GT) trong phng trnh (5.2) bieu th cong suat thc te phat ti

may thu. Ngha la, no tng ng vi cong suat phat can thiet khi s dung antenkhong co tang ch va he thong tiep song khong co ton hao. Cong suat o c goila EIRP (cong suat bc xa ang hng tng ng ) va c bieu th bang phngtrnh :

EIRP = PT - LT + GT (dB) (5.4)

EIRP thng c s dung e bieu th kha nang cua mot phng tien

truyen dan cua oi vi thong tin ve tinh .Ton hao truyen song la ten chung oi vi ton hao khong gian t do xac nh

bang c ly truyen song va ton hao xay ra do hap thu bi tang ien ly, khong kh vama. No c bieu dien bang phng trnh (5.5)

LP = + LI + LA + LR (5.5)

Trong o :

LP : Ton hao truyen song

LI : Ton hao hap thu trong tang ien lyLA : Ton hao hap thu trong khong kh

LR : Suy hao do ma

: Ton hao khong gian t do

=

24

R

R : C ly truyen song

: Bc song vo tuyen

Trong thong tin ve tinh ton hao khong gian t do chiem phan ln ton haong truyen, ton hao do hap thu bi tang ien ly va khong kh la khong ang keva co the bo qua trong thiet ke. Tuy nhien, neu s dung tan so ln hn 10GHz thsuy hao do ma la yeu to quan trong nhat quyet nh en chat lng tuyen.

Hnh 5.4 bieu dien s thay oi cong suat song mang tuyen xuong cua thongtin ve tinh. Qua o ta thay ton hao ng truyen la ang ke .


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-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

50 ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

0 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

-50 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

-100 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

-150 -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

dBm ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

5.7. Cong suat tap am nhietTap am nhiet c tao ra trong may phat va no ket hp vi tap am ben

ngoai i vao anten thu va tap am ben trong tao ra t trong may thu, anten, he thongtiep song. Mac du so lng tap am c tao ra may phat la ang ke, nhng nogiam doc theo ng truyen lan, v the khong can xet en loai tap am nay. Ta chcan xet en tap am ben trong va tap am ben ngoai nh hnh 5.5 .

Hnh 5.5- Phan loai nguon tap am (ng xuong)

Tap amben trong

Pha phat

Tap ammay phat

Tap am ben ngoai

May thu

Anten ve tinh

Tang chanten phat

au ra mayphat ve tinh

Ton hao truyen song

Ton hao botruyen song

Cong suat au vaotram thu mat at

Tang ch anten thu

Cong suat auvao tram mat at

Hnh 5.4: S thay oi cong suat song mang (ng xuong)

Mc

cong

suat


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5.7.1. Tap am ben ngoaiTap am ben ngoai bao gom tap am khong gian, tap am be mat trai at, tap

am kh quyen va tap am ma. Tap am hieu dung tai mat at chu yeu la tap amma la nguyen nhan chnh cua suy hao tn hieu. Khi bau tri trong, tap am gay ra lado kh quyen va khong gian. Tap am nay co nhiet o o c nho hn 100K, v vayta co the bo qua khi thiet ke tuyen s bo .

Tap am t be mat trai at khong anh hng en tram mat at bi v ta sdung anten co hng, nhng no anh hng en ve tinh thong tin v anten cua nohng ve trai at. Nhiet o tap am cua tap am be mat trai at thu bang ve tinhthong tin gan giong nh cua be mat trai at .

5.7.2. Tap am ben trongTap am ben trong xay ra trong cac anten, cac he thong tiep song va cac may

thu, tong tap am o la toan bo cong suat tap am ben trong. Tuy nhien tap am xay ra

tai cac iem khac nhau co anh hng khac nhau, v the cong suat tap am tch hpkhong the anh gia mot cach n gian bang viec xac nh tr so tap am. V C/N la trso au vao may thu, nen ta phai bien oi tap am xay ra tai anten va trong he thongtiep song thanh mot tr so tai iem au vao may thu nh cho thay tren hnh 5-6 .

Va c bieu dien vi phng trnh sau :

TIN = RFF

A TL

TL

T+

+

110 (5.6)

Trong o :TIN : Tong tap am ben trongTA : Nhiet tap am antenTR : Nhiet tap am may thu

T0

FL

11 : Tap am he thong tiep song

T0 : Nhiet o moi trng

May thu

To

TA

FiLFRX

TR

TIN

Anten

Hnh 5.6: So tap am he thong thu


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LF : Suy hao he thong tiep songPhng trnh (5.6) tnh cac tap am xay ra trong moi phan quy vao au vao.

Noi chung, tap am c sinh ra moi ni trong thiet b, nhng ch dung cac tr so quyve au vao cua cac tap am tao ra tai moi au vao trong thiet b.

Tap am he thong tiep song c bieu dien bang T0

FL

1

1 . o la congsuat tap am quy ve au vao tren mot ien tr, o cong suat tn hieu khi chay qua

no giam xuong LF tai nhiet o moi trng. V vay, T0

FL

11 tang khi LF he thong

tiep song tang, co ngha la cong suat tap am ben trong gay ra bi he thong tiepsong tang. Do o can phai thiet ke he thong tiep song ngan nhat, e giam bt tapam .

Nguyen nhan chnh gay ra tap am anten la tap am nhiet xay ra tai anten vano co nhiet o khoang 30 1000K . Trong mot tram VSAT, o co nhiet tap ammay thu cao nen co the bo qua tap am anten, nhng oi vi mot tram mat at lnngi ta s dung cac thiet b thu chat lng cao, v the anh hng do tap am antenla ln trong toan bo he thong .

Nhiet tap am oi vi mot may thu bang tong nhiet tap am xuat hien trongmoi phan. oi vi cac bo khuyech ai noi tiep cho trong hnh 5-7

c bieu dien nhiet tap am may thu theo phng trnh :

132121

3

1

21

......

++++=K

KR

GGGGT

GGT

GTTT (5.7)

V tn hieu tr nen ln hn khi i qua moi tang khuyech ai, nen tac ongcua tap am tai moi tang lai nho i. T phng trnh (5.7) ta thay neu he so khuyechai tang au u ln, th tap am xay ra tang th hai va cac tang khuyech ai tieptheo co the bo qua. V vay, khi can phai giam tap am trong may thu xuong nho hnnh la trong he thong thong tin ve tinh, th phai s dung tang khuyech ai au tienco he so khuyech ai cao va khuyech ai tap am thap. Do o, cac may thu thong

tin ve tinh s dung bo khuyech ai tap am thap (LNA), vi nhiet tap am au vaocua tang au tien la thap.

G1

Bo khuech ai 1

Nhiet tap am T1

G2

Bo khuech ai 2

Nhiet tap am T2

G3

Bo khuech ai 3

Nhiet tap am T3

GK

Bo khuech ai K

Nhiet tap am TK

Hnh 5.7: Bo khuech ai noi tiep


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5.7.3. Tap am he thongTap am ngoai va tap am ben trong eu ton tai trong mot he thong, v the

tap am tong oi vi he thong o bang tong cong suat tap am ben ngoai va bentrong cua no. ieu nay cho thay phng trnh :

( )R

F

FASSYS T

L

LTTTT +

++=

10 (5.8)

Trong o :TSYS : Nhiet tap am he thongTS : Nhiet tap am ben ngoaiTA : Nhiet tap am antenTR : Nhiet tap am may thuT0 : Nhiet o moi trng

LF : Ton hao he thong tiep songVi phng trnh tren ta s dung e tnh tap am ng xuong con oi vi

ng len cac nguyen nhan chnh gay ra tap am la tap am may thu va tap am ngoai(tap am be mat trai at ), v the ta co the bo qua tap am he thong tiep song va tap amanten. Nh vay ta co the bieu dien nhiet tap am oi vi ng len bang phng trnh:

TSYS = TS + TR (5.9)Nh vay ta co the s dung nhiet tap am(TSYS) e tnh cong suat tap am

(NSYS) cho toan bo he thong nh bieu th phng trnh :NSYS = 10log(k.TSYS.B) (dBW) (5.10)Trong o :

k : Hang so Boltzmann = 1,38 x 10-23 (W/Hz/0K)= -228,6 (dBW/HzK)

B : o rong bang tanS dung NSYS nay va PR t phng trnh (5.2) ta co the bieu th ty so C/N :

C/N = PR NSYS = PT LT + GT LP + GR LR - NSYS (5.11)

Vi phng trnh tren ta thay (GR LR - NSYS) bieu th ac tnh may thu.Tuy nhien thong so G/T dung TSYS thay cho NSYS e bieu th chat lng may thu,vi phng trnh sau :

G/T = GR 10logTSYS LR (5.12)5.8. Cong suat tap am nhieu

5.8.1. Can nhieu tap am khacNh a mo ta phan 2.3.8 . Co bon cach trong o cac tuyen thong tin ve

tinh co the can nhieu vi nhau. Trong so nay, nhieu ln xay ra gia tuyen viba matat va tram ve tinh mat at, nhieu t tuyen viba mat at en he thong ve tinh lakhong ang ke. Trong thiet ke tuyen ta can chu y v tr at tram sao cho nhieu xayra t nhat va s dung anten co ac tnh bup song phu tot. Nhieu t cac tn hieu co


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the xem nh la tng ng vi tap am neu nh mc cong suat tn hieu la u thap.T o viec tnh toan C/N co the ap dung oi vi tap am nhieu (I) .

Xac nh C/I giong nh xac nh C/N :C/I = PR - I (5.13)

Ta cung co the tnh c I nh tnh tap am neu nh ta biet cac ac tnh bupsong phu anten va cac thong so nh la khoang cach ng truyen oi vi tram gaynhieu. Ngoai ra, nhieu co the c xac nh bang phep o thc te theo nhieu cach .Khi o, cac ty so C/I va C/N c phoi hp e tm ra (C/N+I) bang phng trnh :

[C/N+I] = -10 log 10 [ 10(-1/10)C/N + 10(-1/10)C/I ] (5.14)

5.8.2. Nhieu cung tuyenNhieu co the t cac tuyen thong tin khac, nhng nhieu cung co the sinh ra

ngay trong tuyen va c goi la nhieu cung tuyen. Cac nguyen nhan gay ra nhieucung tuyen nh :

- Tap am nhieu kh phan cc- Tap am nhieu kenh lan canNh ch ra tren hnh 5-8

Nhieu kh phan cc xuat hien trong cac he thong thong tin phan cc kep.Loai nay b chi phoi bi ac tnh anten, con oi vi nhieu kenh lan can th do ac

tnh bo loc may thu .

Nhieu Nhieu

Tan so

Song phan cc ng

Song phan ccngang

Nhieu Nhieu

Tan so

Hnh 5.8: Nhieu khi phan cc va nhieu kenh lan can


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5.9. Phan phoi tap amTrong mot tuyen thong tin ve tinh cac loai tap am va phan bo cua chung

c bieu th nh tren hnh 5-9 .

Hnh 5-9 Phan bo tap am

Da vao phan bo tap am ta co the cai tien chat lng bang viec thay oithiet b sao cho phu hp gia chat lng va kinh te

5.10. Tnh toan o san sangKhi s dung cac tan so ln hn 10GHz trong cac tuyen thong tin ve tinh, chat

lng tuyen c quyet nh bang kha nang khong san sang do ma. Do o ta phaixet en lng tang ve tap am bau tri va nhieu kh phan cc do ma va suy haocong suat thu. e xac nh ty so thi gian khong san sang, ta can phai tm ra lngma cho phep t cac ac tnh ma tram mat at. T o thiet ke he thong co cac ch

tieu ky thuat oi vi thiet b oi hoi co chat lng tuyen cao hn bnh thng.

C/N + I tchhp khi

at cchatlng

tuyen theoyeu cau

C/N + loi vi

ong len

C/N + loi viongxuong

Tap

amnhietC/N

Tapam

nhieuC/l

Tapam

nhiet

C/N

Taoam

nhieuC/l

Tap amTap am

Tap am ngoai Tap am bemat mat

at

Nhieu khac he

Nhieu cung hethon

Nhieu kh

Nhieu kenhlan can

Tap am

Tap am

n oai

Nhieukhac

Nhieucung

Tap am may

Tap am anten

Tap am hethong tiep song

Tap am bau

Tap am ma

Nhieu ngviba tren mat

Nhieu kh

Nhieu kenh lan


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Tuy theo loai hnh thong tin ma chap nhan mot mc o khong san sang naoo. Nham e giam tnh khong san sang ta lap at mot tram mat at cach nhau vaichuc km va au noi chung bang tuyen thong tin tren mat at. Ky thuat nay goi laphan tap iem c bieu dien tren hnh 5-10 . Yeu to khong san sang ngoai ma

con co nhieu mat tri va s co thiet b. oi vi nhieu mat tri o khong san sangmot vai phut tren ngay trong 2 hoac 3 ngay vao luc thu phan va xuan phan. oi vithiet b, s co cho phep t 0,01 0,1% thi gian hoat ong vi tram khong co dphong, t 0,001 0,1% thi gian hoat ong oi vi tram co d phong .

Hnh 5.10- Lap at cac tram mat at phan tap a iem

5.11. Tnh toan ket noi a truy nhapMot ac tnh cua tuyen a truy nhap la song vo tuyen phat t mot so tram

mat at i vao mot bo phat ap tai cung mot thi iem. V vay khi thiet ke tuyenng len t tram mat at en ve tinh, ta phai xet en hai iem sau :

- Tai iem au vao ve tinh thong tin, cac mc cong suat thu t moi trammat at phai giong nhau.

- Khi s dung he thong a truy nhap theo tan so (FDMA), phai s dungmc lui au vao e tranh nhieu xuyen ieu che trong cac bo khuyech ai truyendan cua cac bo phat ap .

Thong tin ve tinh

ngxuongPhan tap a iem

(khong gian)

ng

len

Tuyen thong tin mat at

Tram matat phat

Tram matat thu

Tram matat thuMa


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CHNG VITNH TOAN TUYEN THONG TIN

6.1. Gii thieu chng

Trong thiet ke tuyen thong tin ve tinh a tnh, quan trong nhat la viec tnhtoan, la chon cau hnh va kch c cac tram sao cho gia thanh thiet b, chi ph thuekenh ve tinh la nho nhat. Ngoai ra, nh mot ac iem ln cua thong tin ve tinh,moi trng truyen song co anh hng ln en chat lng tn hieu va ban than nolai thng thay oi. V vay khi la chon cac tham so cua tram can tnh en he so dphong e duy tr mc tn hieu luon luon trong gii han cho phep vi mot dai thayoi rong cac ieu kien kh hau, ac biet khi co ma ln .

Sap ti nc ta se phong ve tinh noi a rieng cua mnh th cac dch vu vienthong qua ve tinh se phat trien nhanh chong va pho cap rong rai nh truyen hnh,ien thoai, truyen so lieu e lap at ung mot anten tram mat at va tnh toan sbo mot tuyen thong tin ve tinh, di ay trnh bay mot phng phap tnh toan ngian va de thc hien .

6.2. Tnh toan tuyen thong tin ve tinh6.2.1. Cac thong so can cho tnh toanCau hnh tram mat at can chon chu yeu la cac tham so : Loai anten (ng knh, hieu suat, nhiet o tap am). Cong suat may phat .

Viec tnh toan da tren mot so gia thiet cho trc nh : Chat lng tn hieu yeu cau . Cac tham so suy hao . He so d tr.Cac tham so s dung trong tnh toan thiet ke co the phan chia theo thanh

phan he thong lien quan nh :1- Tram mat at- V tr a ly cua tram, tnh toan cac tham so nh suy hao do ma, goc

ngang anten, c ly thong tin, suy hao ng truyen .- Mc cong suat phat xa ang hng tng ng (EIRP), cong suat phat

xa, he so pham chat (G/T).- Nhiet tap am he thong.- Anh hng tap am ti ty so tn hieu tren tap am .- Cac ac iem thiet b (suy hao fi, suy hao phan cc anten, ac tnh bo

loc ) e biet he so d tr ket noi .2 - Ve tinh

- V tr cua ve tinh tren quy ao.- Mc EIRP cua ve tinh, he so pham chat cua ve tinh.- Bang thong bo phat ap, phan cc song, dai tan lam viec .


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- Mat o thong lng cong suat tai ve tinh.- Mc lui cong suat au vao (IBO), au ra (OBO).6.3. Tnh toan6.3.1. C ly thong tin, goc ngang va goc phng v cua anten tram mat at1 C ly thong tin

d = ( ) ( ) cos222 hRRRhR +++ (6.1)

trong o :[ ] coscosarccos=

d : Khoang cach t tram mat at en ve tinh.R : Ban knh trai at (R = 6.341km).h : o cao ve tinh so vi be mat trai at tai xch ao (h = 35.587km). : V o cua tram mat at. : Hieu so gia kinh o tram mat at (

E) va kinh o ve tinh (

S) :

= (E -S) : goc tao bi gia hai ng thang tam trai at tram mat at va tam

trai at ve tinh (hnh 6-1)

Hnh 6.1

2- Goc ngang antenE : la goc c tao bi gia ng thang noi t ve tinh en tram mat at va

mat phang tai tram mat at, c goi la goc ngang (hnh 6-2) va c tnh theobieu thc :

E =( )

+