He Thong Thong Tin Quang Vo Tuyen_360

Click here to load reader

download He Thong Thong Tin Quang Vo Tuyen_360

of 78

  • date post

    07-Apr-2018
  • Category

    Documents

  • view

    215
  • download

    0

Embed Size (px)

Transcript of He Thong Thong Tin Quang Vo Tuyen_360

  • 8/3/2019 He Thong Thong Tin Quang Vo Tuyen_360

    1/78

    H THNG THNG TIN QUANG V TUYN 1

    I. H THNG THNG TIN QUANG

    1.1 THNG TIN QUANG

    Khc vi thng tin hu tuyn v v tuyn - cc loi thng tin s dng ccmi trng truyn dn tng ng l dy dn v khng gian - thng tinquang l mt h thng truyn tin thng qua si quang. iu c nghal thng tin c chuyn thnh nh sng v sau nh sng c truynqua si quang. Ti ni nhn, n li c bin i tr li thnh thng tin

    ban u. Hnh 1.1. Gii thiu mt h thng truyn dn si quang digital

    c s dng rng ri nht hin nay. Trong phn ny chng ta s xem xtcc giai on pht trin ca h thng ny v so snh cc c tnh ca nvi cc c tnh ca nhng h thng ang tn ti. Cui cng, chng ta sgii thch cc tnh cht ca nh sng.

    Hnh 1.1. H thng truyn dn si quang digital

    1.1.1. SPHT TRIN CA THNG TIN QUANG

    Cc phng tin s khai ca thng tin quang l kh nng nhn bit cacon ngi v chuyn ng, hnh dng v mu sc ca s vt thng quai mt. Tip , mt h thng thng tin iu ch n gin xut hin

    bng cch s dng cc n hi ng cc n hiu. Sau , nm 1791,VC.Chape pht minh ra mt my in bo quang.

    Thit b ny s dng kh quyn nh l mt mi trng truyn dn v do chu nh hng ca cc iu kin v thi tit. gii quyt hn ch

  • 8/3/2019 He Thong Thong Tin Quang Vo Tuyen_360

    2/78

    H THNG THNG TIN QUANG V TUYN 2

    ny, Marconi sng ch ra my in bo v tuyn c kh nng thchin thng tin gia nhng ngi gi v ngi nhn xa nhau.

    u nm 1980, A.G.Bell - ngi pht sinh ra h thng in thoi - nghra mt thit b quang thoi c kh nng bin i dao ng ca myht thnh nh sng. Tuy nhin, s pht trin tip theo ca h thng ny

    b b b do s xut hin h thng v tuyn.( Bng 1.1) Cc giai on pht trin ca thng tin cp si quang

    Nm Ngun quang Cp si quang

    1960 Trin khai my laser Ruby(HUGHES)

    1962 My laser Ga As

    1965 My laser Co2 (BL)

    1966 Kh nng s dng ng truyndn cp quang (ST, tn tht1000dB/km)

    1970 My laser GaAIAS to dao nglin tc (BL, Nga, NEC)

    Trin khai thnh cng si spquang s dng abaston (Corning,20 dB/km)

    1973 Phng php sn xut si quang c tn tht thp (MCVD, BL, 1dB/km)

    1976 My laser GalnAsP dao ng lin

    tc (MIT, KDD, TIT, NTT)

    xut kh nng sn xut si

    quang florua (France, Lucas).1977 My laser GaAIAs c tui thclng l 100 nm (BL, NTT)

    1979 My laser GalnAsP 1,55 um(KDD, BL, TIT) dao ng lin tc

    Ch to si quang c Abastoes c tn tht ti thiu (NTT, 0.18dB/km (1.55um))

    1980 Cu trc laser ging lng tcch to (Bell Lab).

    Ch to si quang Flo (NRL) tn tht 1000 dB/km

    1981 GalnAsP LD (1.6 um) Continuous

    Oscillation (TIT)

    1982 LD Array High Power

    (2.5 W ContinuousOsciltation)

    1983 Single Mode, Single FrequencyLD

    (KDD, Bel Lab.)

    Si quang fluor c tn tht thp(NRT, NTT) tn tht 10 dB/km

    1986 Single Mode, Single Frequency Si quang fluor c tn tht thp,

  • 8/3/2019 He Thong Thong Tin Quang Vo Tuyen_360

    3/78

    H THNG THNG TIN QUANG V TUYN 3

    LD

    Commercialization (NEC,Hitachi etc.)

    tn tht 1dB/km (khong2.5 um)

    1989 GaAI/AIGa Laser Develoment

    S nghin cu hin i v thng tin quang c bt u bng s phtminh thnh cng ca Laser nm 1960 v bng khuyn ngh ca Kao vHockham nm 1966 v vic ch to si quang c tn tht thp. 4 nmsau, Kapron c th ch to cc si quang trong sut c suy haotruyn dn khong 20 dB/km. c c v bi thnh cng ny, cc nhkhoa hc v k s trn khp th gii bt u tin hnh cc hot ngnghin cu v pht trin v kt qu l cc cng ngh mi v gim suy haotruyn dn, v tng gii thng v cc Laser bn dn ... c pht trinthnh cng trong nhng nm 70. Nhc ch ra trong ,

    tn tht ca si quang c gim n 0,18 dB/km. Hn na, trongnhng nm 70 Laser bn dn c kh nng thc hin dao ng lin tc nhit khai thc c ch to. Tui th ca n c c lng hn100 nm. Da trn cc cng ngh si quang v Laser bn dn giy c th gi mt khi lng ln cc tn hiu m thanh / d liu n cc aim cch xa hng 100 km bng mt si quang c dy nh mt sitc, khng cn n cc b ti to. Hin nay, cc hot ng nghin cunghim chnh ang c tin hnh trong lnh vc c gi l photon hc- l mt lnh vc ti quan trng i vi tt c cc h thng thng tinquang, c kh nng pht hin, x l, trao i v truyn dn thng tin bng

    phng tin nh sng. Photon hc c kh nng sc ng dng rng ritrong lnh vin t v vin thng trong th k 21.

    1.1.2. Cc c tnh ca thng tin quang

    Trong thng tin si quang, cc u im sau ca si quang c s dngmt cch hiu qu: suy hao truyn dn thp v bng thng ln. Thmvo , chng c th s dng thit lp cc ng truyn dn nh vmng (nh), khng c xuyn m vi cc ng si quang bn cnh vkhng chu nh hng ca nhim cm ng sng in t. Trong thc t si

    quang l phng tin truyn dn thng tin hiu qu v kinh t nht angc hin nay

    Trc ht, v c bng thng ln nn n c th truyn mt khi lngthng tin ln nh cc tn hiu m thanh, d liu, v cc tn hiu hn hpthng qua mt h thng c c ly n 100 GHz-km. Tng ng, bng cchs dng si quang, mt khi lng ln cc tn hiu m thanh v hnh nh

  • 8/3/2019 He Thong Thong Tin Quang Vo Tuyen_360

    4/78

    H THNG THNG TIN QUANG V TUYN 4

    c thc truyn n nhng a im cch xa hng 100 km m khngcn n cc b ti to.

    Th hai, si quang nh nh v khng c xuyn m. Do vy, chng c thc lp t d dng cc thnh ph, tu thu, my bay v cc to nhcao tng khng cn phi lp thm cc ng ng v cng cp.

    Th ba, v si quang c ch to t cc cht in mi ph dn nn chngkhng chu nh hng bi can nhiu ca sng in t v ca xung int. V vy, chng c th s dng truyn dn m khng c ting n.iu c ngha l n c th lp t cng vi cp in lc v c th sdng trong mi trng phn ng ht nhn.

    Th t, do nguyn liu ch yu sn xut si quang l ct v cht do -l nhng th r hn ng nhiu - nn n kinh t hn cp ng trc nhiu.Gi thnh ca si quang s gim nhanh mt khi cng ngh mi c ara. Ngoi ra, nh cp trn, do c trng l c tn tht thp githnh lp t ban u cng nh gi thnh bo dng v sa cha thp biv chng cn t cc b ti to hn.

    Ngoi nhng u im nu trn, si quang c an ton, bo mt cao,tui th di v c kh nng khng mi trng ln. N cng d bodng, sa cha v c tin cy cao. Hn na, n khng b r r tn hiuv d ko di khi cn v c th ch to vi gi thnh thp. Trong bng1.2, chng ta tng h p cc u im trn. Nh nhng u im ny, siquang c s dng cho cc mng li in thoi, s liu/ my tnh, v

    pht thanh truyn hnh (dch v bng rng) v s c s dng choISDN, in lc, cc ng dng y t v qun s, cng nh cc thit bo.

    Bng 1.2 Cc u nhc im ca si quang

    c tnh u im Nhc im

    tn tht thp C ly ti to xa chiph thit bngdy dn

    Di thng ln Truyn dn dung lng

    ln

    Gim kch thc ng

    truyn dn

    D lp t v bo dng

    Gim chi ph lp tcng

    Kh u ni

    Phi dn Ngn nga xuyn m

    Thng tin an ton

    Cn c cc ng dy

    Cp ngun cho tippht

    Ngun - ct Nguyn liu phong ph Cn c cc phng thc

  • 8/3/2019 He Thong Thong Tin Quang Vo Tuyen_360

    5/78

    H THNG THNG TIN QUANG V TUYN 5

    Chi ph sn xut r chnh li mi (cp)

    nh gi Dng truyn dn tuytvi

    C th gii quyt bngcc tin b cng nghmi

    1.2 CP SI QUANG

    Si quang l nhng dy nh v do truyn cc nh sng nhn thy cv cc tia hng ngoi. Nh c trnh by trong hnh 1.4, chng c li gia v c phn bao bc xung quanh li. nh sng c th phn xmt cch hon ton trong li th chit sut ca li ln hn chit sut cao mt cht.

    V bc pha ngoi o bo v si quang khi bm v n mn, ng thichng xuyn m vi cc si i bn cnh v lm cho si quang d x l.

    bc ngoi ta dng cc nguyn liu mm v tn tht nng lngquang ln.

    Hnh 1.4. Cu trc cp si quangLi v o c lm bng thu tinh hay cht do (Silica), cht do, kimloi, fluor, si quang kt tinh). Ngoi ra chng c phn loi thnh ccloi si quang n mode v a mode tng ng vi s lng mode canh sng truyn qua si quang. Ngoi ra chng cn c phn loi thnhsi qaung c ch s bc v ch s lp tu theo hnh dng v chit sutca cc phn ca li si quang. Cc vn ny sc trnh by t mmc 1.2.2

    1.3. H THNG CP QUANG

    Nh kt qu ca cc hot ng nghn cu v pht trin cng caotrong nhng nm 1970, hin nay cng ngh thng tin quang a modeang c s dng rng ri trn ton th gii. Cng ng nh vy i vih thng thng tin quang n mode. Da trn k thut c pht trin,ngy cng nhiu cp quang c s dng trong nhiu lnh vc. Trong

    phn ny, cc c tnh chung ca cp quang c gii thch v tip ,

  • 8/3/2019 He Thong Thong Tin Quang Vo Tuyen_360

    6/78

    H THNG THNG TIN QUANG V TUYN 6

    chng ti s gii thiu vict hit k mt h thng s v tng t cng nhcng ngh ghp knh phn chia bc sng.

    1.3.1. Tng quan v h thng thng tin quang

    1. Cu hnh ca h thng thng tin quang.

    thit lp mt h thng truyn dn hp l, vic la chn mi trngtruyn dn, phng php truyn dn v phng php iu ch/ ghp knhphi c xem xt trc tin. Cho n nay th khng gian c s dngmt cch rng ri cho thng tin v tuyn, cn cp i xng v cp ngtrc cho thng tin hu tuyn. Trong phn di y, chng ti ch bn ncc phng php truyn dn hin ang sn c da trn vic s dng cpquang. Siu ch sng mang quang ca h thng truyn dn quang hinnay c thc hin vi siu ch theo mt v cc nguyn nhn sau:

    (1) Sng mang quang, nhn c t cc phn t pht quang hin c,

    khng dn nh pht thng tin sau khi c s thay i v pha v khuych i v phn ln khng phi l cc sng mang n tn.c bit cc it pht quang u khng phi l nht qun v v vyc th coi nh sng i loi nh ting n thay v sng mang. Do ,ch c nng lng l cng nh sng tc thi c s dng.

    (2) Hin nay, cc Laser bn dn c ch to c tnh nht quntuyt vi v do c kh nng cung cp sng mang quang n nh.Tuy nhin, cng ngh to phch - Mt cng ngh bin i tn s cnthit iu ch pha - cn cha c pht trin y .

    (3) Nu mt sng mang n tn c tn s cao c pht i theo cpquang a mode - iu m c th x l mt cch d dng - th cc ctnh truyn dn thay i tng i phc tp v cp quang b dao ngdo s giao thoa gy ra bi s bin i mode hoc do phn x trongkhi truyn dn v kt qu l rt kh sn xut mt h thng truyn dnn nh. V vy, trong nhiu ng dng, vic s dng phng phpiu ch mt c kh nng sc tip tc.

    i vi trng hp u ch quang theo mt (IM) c rt nhiu phng

    php bin i tn hiu quang thng qua vic iu ch v ghp knh cctn hiu cn pht. Mt trong nhng v din hnh c trnh by tronghnh 1.19

  • 8/3/2019 He Thong Thong Tin Quang Vo Tuyen_360

    7/78

    H THNG THNG TIN QUANG V TUYN 7

    Hnh 1.19. Qu trnh ghp knh in

    Phng php phn chia theo thi gian (TDM) c s dng mt cchrng ri khi ghp knh cc tn hiu nh s liu, m thanh iu ch xungm PCM (64kb/s) v s liu video d