He Thong Thong Tin Quang Vo Tuyen 3248

7/31/2019 He Thong Thong Tin Quang Vo Tuyen 3248

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HTHNG THNG TIN QUANGV TUYN 1

I. HTHNG THNG TIN QUANG

1.1 THNG TIN QUANG

Khc vi thng tin hu tuyn v v tuyn - cc loi thng tin sdng 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 lic bini trli thnh thng tinban u. Hnh 1.1. Gii thiu mt h thng truyn dnsi quang digital

c sdng rng ri nhthin nay. Trongphn 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 tinskhai ca thng tin quang l kh nng nhn bit cacon ngi vchuynng, hnh dng v mu sc ca s vt thng quai mt. Tip , mt h thng thng tin iu ch n gin xut hinbng 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 sdng kh quyn nh l mt mi trng truyn dn v do chu nh hng ca cc iu kin v thitit. gii quyt hn ch


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

u nm 1980, A.G.Bell - ngi pht sinh ra h thng in thoi - nghra mt thit bquang thoi c kh nng bini dao ng ca myht thnh nh sng. Tuy nhin, s phttrin tip theo ca h thng ny b b b do s xuthin 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 As1965 My laser Co2 (BL)

1966 Khnngsdng 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 sdng abaston (Corning,20 dB/km)

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

1976 My laser GalnAsP dao ng lintc (MIT, KDD, TIT, NTT)

xutkhnngsn xut siquang 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 tosi 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 tosi 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) tntht 10 dB/km

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


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LD

Commercialization (NEC,Hitachi etc.)

tntht 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 chto 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 ks trn khp th gii btu tin hnh cc hotngnghin cu v pht trin v kt qu l cc cng nghmi v gim suy haotruyn dn, vtng 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 chto. Tui th ca n c clng 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 /dliun 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 ctin hnh trong lnh vccgi 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

phngtin nh sng. Photon hc c kh nng scng dng rng ritrong lnh vint v vin thng trong th k 21.

1.1.2. Cc c tnh ca thng tin quang

Trong thng tin si quang, cc uim sau ca si quang c sdngmt cch hiu qu: suy hao truyn dn thp vbng thng ln. Thmvo , chng c thsdng 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 nhimcm ng sng int. Trong thc tsi

quang lphngtin truyn dn thng tin hiu qu v kinh t nhtangc 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 hiuhn 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


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c thc truyn n nhng a im cch xa hng 100 km m khngcnn ccb ti to.

Th hai, siquang nh nh v khng c xuyn m. Do vy, chng c thc lpt d dng cc thnh ph, tu thu, my bay v cc to nhcao tng khng cn philp thm cc ng ng v cng cp.

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

Th t, do nguyn liu ch yusn xut si quang l ct v cht do -l nhng th r hnng nhiu - nn n kinh t hn cp ng trc nhiu.Gi thnh ca siquang s gim nhanh mt khi cng ngh mic ara. Ngoi ra, nh cptrn, do c trng l c tn tht thp gi

thnh 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 uim 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. Hnna, n khngb r r tn hiuv d ko di khi cn v c th ch to vi gi thnh thp. Trongbng1.2, chng ta tng hp cc u im trn. Nh nhng u im ny, siquang csdng cho cc mng liin thoi, sliu/ my tnh, vpht 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 uim Nhc im

tntht thp C ly ti to xa chiph thitb ngdy dn

Di thng ln Truyndn dung lngln

Gim kch thc ng

truyndn

D lpt v bodng

Gim chi phlptcng

Kh uni

Phi dn Ngnnga xuyn m

Thng tin an ton

Cn c cc ng dy

Cpngun chotippht

Ngun - ct Nguyn liu phong ph Cn c ccphng thc


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Chi phsn xut r chnh li mi (cp)

nh gi Dng truyndn tuytvi

C th gii quytbngcc tinb cngnghmi

1.2 CP SI QUANG

Si quang l nhng dy nh v do truyn cc nh sng nhn thycv cc tia hng ngoi. Nh c trnh by trong hnh 1.4, chng c ligia 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 hnchit sut cao mt cht.

Vbc pha ngoi o bo vsi quang khi bm v n mn, ng thichng xuyn m vi cc sii 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 quang

Li v o c lm bng thu tinh hay cht do (Silica), cht do, kimloi, fluor, siquang kt tinh). Ngoi ra chng c phn loi thnh ccloisi quang n mode v a mode tng ng vis lng mode canh sng truyn qua si quang. Ngoi ra chng cn c phn loi thnhsi qaung c chs bc v chs 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 sdng rng ri trn ton th gii. Cng ng nh vyi vih thng thng tin quang n mode. Da trn k thut c pht trin,ngy cng nhiu cp quang c sdng trong nhiu lnh vc. Trongphn ny, cc c tnh chung ca cp quang c gii thch v tip,


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chng ti s giithiu victhit k mt h thng s vtng 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 vphng php iu ch/ ghp knhphic xem xt trc tin. Cho n nay th khng gian c sdngmt cch rng ri cho thng tin v tuyn, cn cp i xng v cp ngtrc cho thng tin hu tuyn. Trongphn diy, chng ti ch bn ncc phng phptruyn dn hinang sn c da trn vic sdng cpquang. S iu ch sng mang quang ca h thng truyn dn quang hinnay c thchin visiu ch theo mt v cc nguyn nhn sau:

(1) Sng mang quang, nhnc t ccphnt 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 thic sdng.

(2) Hin nay, cc Laser bn dnc 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 bini tnscnthitiu ch pha - cn chac pht triny.

(3) Nu mt sng mang ntn c tns cao c pht i theo cpquang a mode - iu m c th x l mt cch d dng - th cc ctnh truyn dn thayi tng i phctp v cp quangb dao ngdo s giao thoa gy ra bi s bini 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 chmt c kh nng sc tip tc.

i vitrng hpu ch quang theo mt (IM) c rtnhiu phng

php bini tn hiu quang thng qua viciu ch v ghp knh cctn hiucn pht. Mt trong nhng v din hnh c trnh by tronghnh 1.19


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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 nhsliu, m thanh iu ch xungm PCM (64kb/s) v sliu video digital. Tuy nhin, trong truyn dncly ngn, ca cc tn hiu videobng rng ri cng c thsdng phng

php truyn dnanalog. Phng phpiu chmts DIM - phngphp truyn cc knh tn hiu videobng IM - vphng phpthchiniu ch tns (FM) v iu ch tns xung (PFM) sm tng c lytruyn dn c thc sdng cho mc tiu ny.

Ngoi TDM v FDM, phng php phn chia theo bc sng (WDM) -phng phpiu ch mt s sng mang quang c cc bc sng khcnhau thnh cc tn hiuin khc nhau v sau c th truyn chng quamt si cp quang - cng ang c sdng. Hn na, khi truyn nhiuknh thng qua cp quang, mt s lng ln cc dliu c thc gi

i nhgia tng s li cp sau khi ghp cc knh trn. Phng phpny c gi l ghp knh SDM. H thng truyn dn quang c thcthitlp bng cch sdng hn hp TDM/FDM, WDM v SDM. Chngta c th thy rng h thng truyn dn quang cng tng t nh phngphp truyn dn cp i v cp ng trc truyn thng, ch c khc l nbini cc tn hiuin thnh tn hiu quang v ngc li tiu thu.Hnh 1.20 trnh by cu hnh ca h thng truyn dn cp quang.


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Hnh 1.20. Cu hnh ca h thng truyn dn cp quang

Phng php truyn dn analog c th c tin hnh ch vi mt bkhuych i to iu kin pha thu nhn c mc ra theo yu cubng cch bini cc tn hiuin thnh cc tn hiu quang v ngc

li. Khi sdng phng phpiu ch PCM th mi chc nng giiiuch tng ng vi n cnc gn cho pha thu. Cho tiy, chng ta m t cc chc nng c bn ca h thng truyn dn quang. Ngoinhng phn trnh by trn h thng hotng thct cn c thmmt mch n nh u ra ca cc tn hiu quang cn pht, mt mch AGC duy tr tnh ng nht ca u ra tn hiuinpha thu v mt mch gim st mi pha.

2. Nhng thnh phn cbn ca h thng truyndn quang.

H thng truyn dn quang bao gm ccphnt pht x nh sng (ngun

sng), cc si quang (mi trng truyn dn) v cc phnt thu nhnnh sng truyn qua si quang.

Cc phnt sau y c chn sdng:

1. Phnt pht x nh snga. it Laser (LD)b. it pht quang (LED)c. Laser bn dn

2. Si quanga. Si quang a mode chs bcb. Si quang a mode chslpc. Si quang n mode

3. Phnt thu nh snga. it quang kiu thc (APD)b. it quang PIN (PIN - PD)


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1.4. PHNG PHP TRUYN DNNGBE

1.4.1. Csca tiu chun ho

Trc khi phng php truyn dnng b c c dng thc cao cpca cc c trng n nht, Metrobus v SONET c nhng ng gpto ln. Metrobus l h thng thng tin quang ng b ni ti m bell

Communications Research ca AT & T Hp chng quc Hoa Knghin cu v pht trin. Cn SONET l tiu chun ktni ca h thngthng tin quang m sau Bell communications reseach (Bellcore) xut v ri c u ban T1 chp nhn s dng v pht trin cho tiuchun Bc M. Metrobus chng li quan im ca thng tin quang cin, sdng s ghp tng u tin, chp nhns dng khi nimcontainer (cng ten), sdng Overhead (mo u) mt cch hiu quv thit lp khi nim h thng thng tin quang ng b ni ti, hthng ny coi tn hiu cp 150 Mbit/s lm cp tiu chun. Do vy, trn c

s cp 50 Mbit/s, SONET b sung quan nim v cu trc phn cp vphng phpng b nhcon tr h thng ho on mo u v sau mra chn trimi cho thng tin ton cu. Da trn nhng ci ,chnh phn cp ca ng b (SDH) hin nay ly tn hiu cp 150Mbit/s lm tiu chun, k c phn cps kiu Chu u, v c ph cpho mra kh nng thng tin ton cu.

1. Metrobus

Metrobus l mt h thng thng tin quang do J.D.Spalink, mt nhnghin cuti Bellcore ca AT & T, xutnm 1982. N c trinkhai theo quy m y vo unm 1984, c cng b vo thng chnnm 1985 v c th nghim thng mi ho vo u nm 1987.Chnh sch cbn ca Metrobus l pht trin h thng thng tin quangti u nht, c cn nhc n kha cnh tc cao, dung lng ln,vn lctrng ca mt h thng thng tin quang,phng hng tin trin camng thng tin, qu trnh pht trin ca cng ngh ct yu v xu hngi mi dch v. Tn gi ca Metrobus c ngun gc t mc tiu ngdng ca n nhm vo vng thnh ph ln (metropolitan). Trong qutrnh R&D cho ng dng ni ln mt s khi nim. in hnh l

khi nim v mng thng tin quang im - a im, khi nim v hthng ng bni ti, tm nhn ca DS-O, khi nim ghp knh tng utin, iu chnh ng thi nhng tnhiu nhiucp bng viciu khins hiu cng ten, thit lp tn hiu tiu chun ni ti 150Mbit/s v sdng mo u.

Do tt c cc h thng thng tin quang trc y u c xuttrong bi cnh ca cc h thng im - ni im, cho nn khi nim cathng tin quang c xem nh mt khi nim c tnh cht cch mng.


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Nhng khi nim khc ng vai tr khng th thiuc th hinkhi nim ny. Vi vic cn nhc n di thng v hn m thng tinquang cung cp, ta thy n bo m khong trng cho mo u, vbng vicsdng n cng nh bng vic hnh thnh knh truyn thngmo u, cho php ng dng lin kt ca ton b cc tuyn thng tinquang. Tuy nhin, do t l ca mo u vt qu 4,5% ca ton b,

cho nn khi nim ny kh c thc chp nhn trongbi cnh .Vic la chn 150 Mbit/s (c th l 146,432, Mbit/s) lm tn hiuni bca mng thc s l mt quan im tin phong. Sdnh vy l vnhng iu sau y c d kin : khi c xem xt theo kha cnh phnlp tn hiu digital, tc bt m tt c cc tn hiu c th bao gm l 150Mbit/s; theo kha cnh dch v, tn hiu thoi,sliu v video (k c tnhiu HDTV c nn) hintiu c thcsdng trong cp 150Mbit/sny; v kha cnh cng ngh bn dn c bn, cng ngh CMOS c thc sdng trongphm vi 150 Mbit/s chng kh khn g. Ngoi ra, v

kha cnh thu bao th cn c mt sli th: vi cp phn t 150 Mbit/s,cc nh sng c thc sdng nhs kt hp viit LED v PIN rtin, v cp si quang c thtoiu kin cho s kt hp hiu qu nynh vic s dng si quang a mode c ch s tng dn thay cho nmode.

Khi nim ghp knh tng u tin cng l mt khi nim mang tnh cchmng. N cho php ghp knh trctip tn hiu DS -1 thnh tn hiu tiuchun150 Mbit/s m khng cnchuyn qua tn hiu DS-2 hoc DS-3 iukhng th c trong h thng ghp knh khng ng b trcy. N tr

thnh nn tng thchin ktni tch/nhp v ni kt cho l nhngni kt thng thy trong mng thng tin quang.

c giithiu nh mt phng tin thchin ghp knh tng th nht,khi nim ny gip cho vic ghp knh tn hiu phn cp bng viciukhins hiu ca cc cng ten. Ngha l, bng vic xc nh cc ckch thc c nh, lm cho cc tn hiu DS -1. DS -1C, DS-2, DS-3v.v...lp y vo cc tng ng ca cc khi 1, cc khi 2, cc khi 4,cc khi 28 trong cng mt n v thi gian. Nh vy, ktni tch nhpv ktni cho rt tinli, bi v tt c cc tn hiuuc x l vi

n v ca s hiu .

Tn hiu tiu chun ni b bao gm 13Wx88 (1W=16 bt) nh trong hnh1.37. Tc bit l 146,432 Mbit/s (13x88x16x8 kbit/s). 88 n v ca tm (thuc v 88 ) xuthin trong 125m s/13, trong d 4 n vcsdng cho mo u v mi tn hiu DS-n chim s hiu tng ng ca .


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Hnh 1.37. Cu trc khung ca Metrobus

Vic gii thiu khi nim ng b ni ti cng l mt tin chomng thng tin ng b. C ngha l, do phm vi mc tiu chcgii hn cho khu vc thnh ph, da trn tiu chun ni b ca mng,bin php i ph trong trng hp vt qu gii hn cn ng b khng c chun b cht no. Trong trng hp ny tn hiunh this

sdng tns chunng b ho cbn BSRF v cng c thsdngtn hiunh thic n nhn t b dao ng ni v t tn hiu thuc.

nhn r ca tn hiu DS-O c to ra vi n v 125 m s. Khi vicchuyn t mi tn hiu phn cp sang cng tencng c thc hin vin v 125 m s, th cc tn hiu DS-O nhnc qua lymu 8 kbit/s cth xuthin mt cch trong sut ngay ti tn hiu phn cpmc cao.

Theo cch nh vy, vic phn tch knh DS-O 64 kbit/s khi tn hiu tiu

chunni b 150 Mbit/s c thc thc hin mt cch d dng.Hnh 1.38 biu din cu trc ca h thng Metrobus. Phn c trnh bynh bus ni b trong hnh v tng ng vi tn hiu tiu chunni b146,432 Mbit/s. Tn hiuc to ra t DS-1 n DS-3 qua PMB (bngghp knh c thlp trnh). Thng tin quang 146 Mbit/s c thphi hptrctip vi tn hiu ny, v i qua thit b truyn dn sng quang LTE-Lightwave Transmission Equipment). c thto nn thng tin quang 876Mbit/s hoc 1,7 Gbit/s bng vica 6 hoc 12 n v ca tn hiu nyvo WIM (ghp knh xen t m - Word Interleaved Multiplexing), ri sau

a qua LTE. Nhng qu trnh ny c m t trong hnh v. Ngoira, h thng PCCS (h thng ktni cho c thlp trnh) thchin chcnng ni kt cho qua cc cng ten do tiu chun ca tc bit DS-1to ra bng cch a vo tn hiu 146 Mbit/s.


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2. SONET

Hnh 1.38. Cu trc ca h thng Metrobus

Sonet l mt t vit tt ca Synchronous Optical Network (mng quangng b). N c R.J.Boehm v Y.J.Ching vin nghin cu truynthng Bell trnh ln u ban T1- t chc tiu chun truyn thng ca

Bc M - vo cui nm 1984 nh mt n tiu chun v u ni hthng thng tin quang. Vo thi gian , khung c xut c dng3x8x33B nh trong hnh 1.39, v tc bit l 50,688 Mbit/s (=3x8x33x8kbit/s). Tn hiu ny c gi l STS-1 (Synchronous Transport Signal -1 - Tn hiuchuyn giao ng b - 1) v DS - 3 hoc SYNTRAN DS-3,m n c chp nhn nh tnhiu phn cpcbn v c nnha vo qu trnh ghp knh xen byte qua STS-1.

Tng u tin ca SONET c ngh cho mc ch "gp ggiachng" v quan im nghi ngv tnh kh thi ca n chim u th.

Kt qu l vic tiu chun ho n hu nh khng c tin hnh trongkhong mt nm, sau khi khi nim SONET c gii thiu. Tuynhin, vic tiu chun ho bng nhin ca ra cng vi thng boca Metrobus vo thng chn nm 1985, v khi nim v h thng phncp v k thut ng b ho bng contr c cc thnh vin ca uban T1 xut thm. Nhng ngi xut SONET pht trin v hthng ho cu trc khung ca tng u tin v a ra cng thc (28+L)(24+M) (8+N). iu ny d tnh tn mo u ca mc DS-3 ln kchthc DS-1 ca L nv; mo u ca mc DS-1 ln kch thc DS-O

ca M n v v mo u ca mc DS-O ln Nbit. Tng gia ca khungSONET c cu trc 26Bx30 v 49,92 Mbit/s (30x26x8x8 kbit/s) ciu chnh vi L=2, M=2 N=0 da trn cng thc miu t trong hnh1.39. Vo khong thi gian vin nghin cu truyn thng Bell caAT&T nghrng tn hiu tiu chunni b ca Metrobus (c cu trc26x88W v 146,432 Mbit/s) cnc chp nhn l tn hiu tiu chun.Tn hiu ny c biu th bng cng thc ca Vin Nghin cu truynthng Bell s l: J+K (28+L) (24+M), (8+N), J=1, K=3; L=1, M=2; N=0;v L, M v N trong s c cng mt ngha nhc xc nh trc,


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K c ngha l s hiu ca tn hiu mc DS-3, cn J l kch thc ca DS-1 idin cho mo u gn vo ton b chng.

Hnh 1.39. Cu trc khung ca SONET

Mc d u ban T1 xem xt k nhng cuc tho lun lin quan n haid n ny, n vn khng th phn quytc tnh u vit theo kt qui chiu v kim nghim. im bn ci si ni nht l trong nh gigia 150Mbit/s v 50 Mbit/s th tc bit no u vit hn.

Tuy nhin, do s cnh tranh v phn chia thtrng vin thng v vai tr

gia cc cng ty, u nm 1986, u ban T1 i ti mt quytnh l tnhiu tiu chun STS -1 s l 49,92 Mbit/s. Trong khi ITU - T cng anghotng nhm tiuchun ho bng knh rng vo cng thi gian thu ban T1 quytnh nghly 149,976 Mbit/s lm d n ca Bc M,n gp ba ln 49,92 Mbit/s; c ngha l u ban T1, ngi quytnhchn cp 50 Mbit/s, tha nhn vmt k thut tnh thch hp ca 150Mbit/s. Sau , nhng hotng tiu chun ho SONRT c tin hnhmt cch sun s, ch yu nhu ban ngang cp T1X1, v i n mt


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tho thun v mt tiu chun thm ch kh chi tit. Mc d n tinhnh hot ng phi hp ngay tc khc mang tnh cht b mgoi, viITU-T v vn tiu chun kt ni NNI ca B-ISDN, song c rtnhiu mt hn ch trong vic iutit vi cc tn hiu digital kiu Chuu, bi v 13Bx60 v 49,92 Mbit/s (hoc 146,976 Mbit/s) ch ch yuph hp vi cc tn hiu digital ca Bc M.

Do vy,cu trc 9Bx270 v tc 155,520 Mbit/s, ci c tng ln balncu trc khung v tc bt ca SONET chnh l phn cpng bsm n c quy nh nh khuyn ngh G.707-G.709 ca ITU-T.

3. Phn cp sng b

ITU-T thitlp cc knh H1, H2, H3, H4 nhi vi knh tc caoca khch hng trong qu trnh tiu chun ho ISDN vo u nm 1980.Trong s, knh H1, c tiu chun ho bng vic phn chia nhthnh knh H11 ca 1,536 Mbit/s da trn cs tn hiu DS-1 kiu Bc

M, v knh H12 ca 1,920 Mbit/s da trn c s tn hiu DS-1 kiuchu u. Miang ch c nhng nti cng mang tnh cht khi nimtng ng vi phn cps hin c lin quan n cc knh H2, H3, H4, n btu cpn tiu chun ca mt knh bng rng da trn ccknh . u tin n nghin cu cc tc bit 30-40, 45, 60-70 Mbit/s,sau n 149,976 Mbit/s ca ra, da trn tiu chun SONETca u ban T1.

Trong khi , ITU-T btu hotng tiu chun ho phn cpngbs cho NNI (giao din nt mng) vo thng by nm 1986, khc bitvi UNI (giao din khch hng - mng) ca ISDN. iu ny btumt giai on tiuchun ho ch thc hng ti phn cpsng b vITU-T cng u ban T1 duy tr mi quan h hp tc cht ch cho mcch , Hoa k chnh thc a ra cp 50 Mbit/s da trn tn hiuSTS-1 ang cs dng ca SONET ti hi ngh Brazin vo thngHai nm 1987 cn CEPT tm cch chng minh scn thit ca cp tc 150Mbit/s v n c th thch hp vi c hai h phn cps kiu Bc Mv kiu Chu u.

Kt qu l, n ca M c thay i thnh 149,976 Mbit/s ca cutrc 13Bx180, da trn tn hiu STS-3, ti Hi nghHamburg vo thng7 cng nm, cn CEPT xut tn hiu 155,520 Mbit/s ca 9Bx270i lp vi ca M. Ngi ta tranh ci sut mt thi gian di v haicu trc ny v im tranh ci si ni nht l s chung ho gia tn hiuDS-2 ca 8,448 Mbit/s v DS-3E ca 34,368 Mbit/s tho thun cui cngqua hi nghSeoul vo thng Hai nm 1988 l cu trc 9Bx270. Tiuchun NNI c tho thun l tiu chun trong cc khuyn ngh G-707 -G.709 ca ITU-T v phn cpsngb, tp trung trn tn hiu STM-1


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ca cu trc khung 9Bx270 v tc bt 155,520Mbit/s, c chnhthc ho.

Ngay c sau khi khuyn ngh ca ITU-T c n nh th cc hotng nghin cu v i mi v phn cpsng b vnc tip tc.Vo thiim khi tiu chun phn cpsng blnu tin c quynh, h thng ghp knh ng b c mt cu trc hon chnh nhhnh 1.40. Tuy nhin, khi nhngkhuyn ngh G.781 - 784 v G.957 - 958(u da trn c sphn cp sngb) c tiu chun ho honchnh trong qu trnh nghin cu hai nm sau , th h thng ghp knhng b c n gin honhcu trc trong hnh 1.41. C th thyc rng cc ng ghp knh phn cp kiu chu u tng ng mtcch ng k vi cc ng ghp knh phn cp kiu M, v rng bsung cc khi nim mi, chng hn nh AUG, TUG-3. Hiu theo ngngha ca n th phm vi m Metrobus ng gp cho vic tiu chun hoSONET v SONET ng gp cho vic tiu chun ho phn cpsng

b l cc k to ln.Rt nhiu ctrng ca phn cpng b c ngungc t tiu chun ca h thng Metrobus, chng hn nh quan im vmng thng tin quang, khi nim v h thng ng b (mt cch ni ti), r ca DS-O qua khung 125m s, khi nim v ghp knh tng thnht, phi hp tn hiu tc ghp knhbng viciu khins hiu cacng ten, thit lp tn hiu cp 150 Mbit/s tiu chun, v nng cao linh hot v tin cy ca h thng nhsdng mo u mt cch hiuqu. Cng nh vy, cu trc h thng phn cp, h thng ho cu trcmo u, ng b ho bng con tr, v kh nng cu trc mng thng tin

lin tc a, u xut pht t tiu chun kt ni ca SONET. Da trnnhng cs, tiu chun phn cpsng b l tiu chun cho phpcu trc nn mng thng tin ton cu qua vic iu chnh kt hphai kiuphn cps ca Bc M v ca Chu u.


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Hnh 1.40 Cu trc ghp knh ng b sgiai on u tin

Hnh 1.41. Cu trc ghp knh ng b

Mt khc, phn cpsng b vn c khiu v mc ch tiu chunho NNI ca B-ISDN, c nh hng rt lnn tiu chun UNI caB-ISDN. Trc ht,nh hng trc tip ca NNI ca B-ISDN l quy


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nh 155,520 Mbit/s cho tc bt tiu chun ca NNI ca B-ISDN vtrong s quy nh tc bt trng tin thp hn 149,760 Mbt/s. Ngoi ra,nh hng c tnh cht cbn khc na l n c cc t bo ATM cnh x trong ng bao ca trng tin VC-4 pht i csphn cpsng b ca UNI ca B-ISDN. Ni mt cch chnh xc, phn cps ngb ng mt vai tr ch cht trong vic hnh thnh khi nim B-ISDN

cng nhi ti mt phng php truyn dnng b mi.1.4.2. SHD v SONET

Nh trn gii thch v qu trnh tiu chun ho phng thc truyndnngb, SDH v SONET, c mt mi quan h ht scmt thit.chnh l: hotng tiu chun ho SONET to iu kin thun tin chotiu chun SDH v n cng mrng SONET SONET c sdngcho thng tin hon cu. Do vy cn phihiu rng gii thch SDH l bao hm c vic gii thch SONET. Tuy nhin vn c mt s khc bit

nh gia SDH v SONET. Nu nhng s khc bit tiubiu gia chngta c thm trn u ngn tay thim btucbn ca SDH l cp150Mbt/s, trong khi SONET l cp 50Mbt/s. C ngha l, trong khiSDH kt hp DS-4E vi tn hiumc thp thnh tn hiucp cao nht thSONET c DS-3 nh tn hiu cp cao nht. Do c mt khi nim v giaodin, cho nn, ng nhin,y chng phi l mt s khcbitng k.C ngha l nu ba ln ca tn hiu STS-1 (Tn hiuchuyn giaong bcp 1) l 51,840 Mbt/s tn hiu truyn dn c bn ca SONET - c

phi ghp to thnh STS-3C th n cng c th bng vi tn hiu STM-1-155,520 Mbt/s ca SDH, SDH v SONET c s khc bit no v

cc loi tc truyn dn. STM (155,520 Mbt/s, l mt khi c bn,STM - 4 (622,080 Mbt/s), gp bn ln ca STM-1 v STM-16(2.488,320 Mbt/s), gpbn ln ca STM-4, l nhng i tng quan tmchnh trong SDH. Trong khi , trng hp SONET, STS-1 (51,840Mbt/s) l tc c bn, STS-3 (155,520 Mbt/s) STS-9, STS-12(622,080 Mbt/s)STS-18, STS-24, STS-36, STS-36, STS-48 (2.488,320Mbt/s) l cc i tng quan tm (tham kho bng 1.9); khi , nichung, tn hiu STM-nbng vi tn hiu STS-3n trong tc truyn dn :

Bng 1.9 Tc truyn dn ca SDH v ca SONET

SDH SONET

N STM - N N STS - N

1 51.840 Mbps

1 155.520 Mbps 3 155.520 Mbps


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9 466.560 Mbps

4 622.080 Mbps 12 622.080 Mbps

18 933.120 Mbps

24 1,244.160 Mbps

36 1,866.240 Mbps

16 2,488.320 Mbps 48 2,488.320 Mbps

Vmt cu trc khung, SONET gim i ba ln so vi SDH. Nu SDH lSTM-1, n c cu trc 9x270B v STS-1 ca SONET c cu trc 9x90B,bng mt phn bakch thc ca SDH. Cng nh vy, mo uon caSTM-1 trong dng 9x9Bc b trhng u ca khung STM - 1, mouon ca STS-1 di dng 9x3B c b trhng u ca khung

STS-1. Sau , trong c hai trng hp, hng thtc dnh ring chocon tr (pointer). C th l, vic la chn hng th nht,tht v th byca mo uon trong STS-1 tng ng vi mo uon ca STS-1v vic sdng cc thnhphn ny l nh nhau trong c hai trng hp.

SDH v SONET c mt s khcbit trong khi tn hiucu thnh. Gcgc ca vn nh vy l v STM-1 l cp 155Mbt/s v STS - 1 l cp50Mbt/s. Do , trong trng hp STM - 1 cn phi ghp knh mt cchc h thng tt c cc tnhiu phn cp t DS-1 n DS-4E, trong khi ,trng hp STS-1 ch cn thit ghp knh chiu qunm loi tn hiu

phn cp l DS-1, DS-1E, DS-1C (3,152Mbt/s), DS-2 v DS-3. Do vy,trong trng hp STM-1, cc khi tn hiugia, chng hn nh C, VC,TU, TUG, AU, AUG v.v.... sc thitlp v th tc ghp knh ngb ton b h thng nh trong hnh 1.41 l cn thit. Ngc li, trongtrng hp STS-1 ch c mt khi tn hiu trung gian, gi l mt nhnho (VT-virtual tributary) l sc thitlp. VT nayftng ng vi VCca SDH. Cc VT tng ng vi VC-11, VC-12 VC-2 c gi tngng l VT 1,5, VT2 v VT6, cn VT3 c b sung cho DS-1C.

V n v tn hiu trung gian lin quan c khc nhau, cho nn SDH v

SONET cng khc nhau v cu trc ghp knh. Trong trng hp SDHcu trc thng k h thng nh trong hnh 1.41 l cn thit , trong nni kt C, VC, TU, TUG, AU, AUG ATM-n vi nhau, cn trong trnghp SONET, ch cnn mt th tc ghp knh n gin l uni DS-m, VT v STS-1. Sau , phng php nh x cc tn hiu phn cpthnh VT-1,5 VT 2 v VT 6 cng ging nh phng php nh x mi tnhiu phn cp thnh VC-11, VC-12 v VC-2, vphng php nh x DS-1C thnh VT3 ssdng php nh x tun theo cn chnh dng, khng


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v m. Phng php dng ghp knh cc VT ny thnh ng baotrng tin STS-1, tc l SPE (Synchronous Payload Envelope - ngbao trng tin ng b) cng ging nh phng php ghp knh VC linquan thnh VC-3 qua TUG-2. Trong trng hp th hai, vic nh x DS-3 thnh SPE cng ging nh phng php nh x DS-3 thanh VC-3,nhng php nh x SYNTRAN DS-3 th c cung cp ph thm.

Vphng din thut ng, khi mi quan htng ng gia SONET vSTM c tm lc, th VT 1,5 VT2, VT6 ln lt tng ng vi VC-11, VC-12, VC-2, STS-1SPE tng ng vi VC-3 v STS-3C vi STM-1. Khi cc thut ng lin quan n phn cp cni snh,phngtin vtl, on ti to,on ghp knh v lpng truynct ra trongSDH s c gi l lp quang, lp on, lp ng dy v lp ngtruyn trong SONET. Cc thut ng xc nh khc lin quan n nh x,ghp knh, mo u v ng b ho th hu nh ging nhau.

SONET cng nh SDH u da trn khi nim phn cp, sdng khung125 m s, dng mo u h thng, v c tc truyn dncbn gingnhau. Nhng n ciutit nhslin kt tt c cc tnhiu phn cps Bc M k c tn hiu DS-1E kiu Chu u, v n cha ng c thtc ghp knh tng th nht.

Ngoi ra, SONET s dng ng b ho lin quan ti phng php contr, ging nh ca SDH, cho nn c th ktni ton b ncM bngmng truyn dnngb.

1.4.3 Phn cp s cn ng b so ving b

Lp (mc) s hin c bao gm cc tn hiu DS-1-DS-4 ca h thngChu u/ Bc M, c b phn tiu chun ho vin thng ca ITUv Bell System quy nh. Trong s, cc tn hiu ca h thng BcM c u ban T1 ca BcM tha nhn trli nh tiu chun Bc M,ng thi, tiu chun cng c bit n nh l tiu chun do BellSystem thit lpli.

phnbit lps ny vi phn cpsng bc thc thi gny,n cgi l phn cpscnngb.

Phn cps cnng b, mt h phn cp s tiu chunang c sdng, c phn loi thnh h thng Chu u v h thng Bc M nh(a) v (b) trong Hnh 1.42 Phn cp s cn ng b ca Bc M chnh thnh t DS-1 (1,544 Mbt/s), DS-1C (3,152 Mbt/s), DS-2 (6,312Mbt/s) v DS-3 (44,736 Mbt/s), DS-4E (139,264 Mbt/s). Phn cpscn ng b Chu u bao gm DS-1E (2,048 Mbt/s), DS-2E (8,448


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trn. Trong s chng, SOH bao gm mt mo uonng trc vuon ghp knh.

Hnh 1.43.ng truyn dn (mt ng) v khi nim phn lpca tn hiu s

Mo u on ti to Mo u ng truyn

ca lp c mc cao

Mo u ng truyn ca

lp c mc thpCon trMo u on ti to

Hnh 1.44. Cu trc khung v cc khi nim phn lp ca STM-n

SOH c chn vo trong giai on cui cng khi tn hiu STM-n chnh thnh cn POH c chn vobt k khi no tn hiu cng tenoc to thnh.

SOH c chn vo v c tch ra trong on ti to hoc on ghpknh ch th hiu nng truyn dn cng nh hotng v bo dngtn hiu STM-n. Nhc minh ho trong hnh 1.44, cc SOH nm bntrn v bn di ca con trcsdng tng ng cho on ti to von ghp knh. C ngha l B1, SOH cho BIP-8 (Bit Interleaved Parity-8) c b tr trn phn pha trn ca PTR v n c kim tra v tnhton li trong mi b ti to.

Tuy nhin, ba byte ca B2-SOH cho BIP-24- c b tr phn pha

di ca PTR v chng chc kim tra cui ng dy. Nh cptrn, POH c phn chia thnh POH ca lp c mc cao cho VC-4 hoc VC-3 v POH ca lp c mc thp hn dng cho VC-11, VC-12v VC-3. Trong bt k trng hp no POH cng c s dngchotruyn thng u cui - ti - u cui gia nhng im, ni cc VC tngng c hnh thnh v gii to.


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gii thch cu trc ca mo u on v mo u ng hy xemkhung STM-1 trong hnh 1.45, (a), (b). Vic s dng mi loi mo utrong hnh ny nh sau: A1, A2 dng cho bt sp xp khung; B1, B2; B3dng kim tra ngangbng chn l, C1, C2 dng cho slng tn hiuv D1-D12 dng cho knh truyn s liu, cn E1 v E2 dng cho knhnghipv; F1, F2 dng cho knh khch hng; G1 l kim tra trng thi

ng truyn, H4 dng ch th a khung; J1 dng ghi du tchng truyn; K1, K2 dng cho chuyn mch bo vtng; Z1~ Z5 lcc mo u d phng cho cc mc ch khc.

1 2 3 4 5 6 7 8 9 J1

1 A1* A1* A1* A2* A2* A2* C1* X* X* B3

2 B1 E1 F1 X X C2

3 D1 D2 D3 G1

4 con tr F2

5 B2 B2 B2 K1 K2 H4

6 D4 D5 D6 Z3

7 D7 D8 D9 Z4

8 D10 D11 D12 Z5

9 Z1 Z1 Z1 Z2 Z2 Z2 E2 X X

Hnh 1.45. Cu trc mo u* Cc byte khng c pha trn(a) Mo u on (b) Mo u ng truyn

1.4.5. Cu trc ca khung STM-n

Khung STM-n c mt cu hnh nhc trnh by trong hnh 1.46, datrn cscc khi nim phn lpnh ngha trong phn trc. Do cutrc ny chim mt vng 9Bxnx270 (B=Byte) trong vng 125 m s, cho


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nn n c mt tc bt l n x 155,520 Mbt/s (=9 x n x 270 x 8 x 8kbit/s). Trong , 9B x n x 9 c phn b cho vng mo u SOH vcon tr AU (Khi qun l) vphn cn lica 9B x n x 261 c phnb cho ng bao trng tin ca STM-1.

Do vy, STM-1, mt tn hiu cbn ca phn cpsngb, s c kchthc l 9B x 270. Cng nh vy, 9B x 9 trong s l cng ca mouon v con tr AU, v cng chng y 9B x 261 l ngbao trngtin, v tc bt trthnh 155,520 Mbt/s.

Theo quan im cu trc khung STM-1, SOH cto thnh t hai khuvc 3 x 9B v 5 x 9B, con tr AUPTR bao gm khu vc 1 x 9B v cuhnh ca n nhc trnh by trong hnh 1.45. Mt VC-4 c nh xtrong vng cn li,hoc ba tn hiu VC-3 c thc nh x sang vng cng vi mo ucnh (FOH-Fixed Overhead). Cc tn hiu VC-4v VC-3 u bao gm hnh bao trng tin v vng POH c kch thc 9

x 1B c b trtrc mi hnh bao trng tin. ng thi, cu hnh bntrong ca POH nh trong (b) ca hnh 1.45. VC-4 hoc VC-3 m cgn con tr AUPTR th c gi l AU-4 hoc AU-3.

Hnh 1.46. Cu trc ca khung STM-n

Do vy, trong cu trc ca khung STM-1, AU-4 l t hp ca vngtrng tin STM-1 v vng con tr AU, v cu trc cui cng ca STM-1c thtc khi cc vng SOH tng ng c t ln lt vophnpha trn/ pha di ca AU-4.

1.4.6 Cu trc ghp knh ng b

Nh c m t, qu trnh ghp knh ng b x l tt c cc tn hiuphn cp s mt cch ngang bng v n s thit lp nn cc tn hiuSTM-n. Trong hnh 1.41, s tng th ca cu trc ghp knh ng btrn cc tn hiu phn cp c a ra.


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Cc con tr ca lp c mc cao ni trn cnh du vi H1, H2 v

H3. cc con tr ca lp c mc thp, chng hn nh TU-11 PTR, TU-2

PTR v TU-12 PTR cnh du bng V1, V2 v V3. Cc con tr ca

lp mc thp ny c cu trc nh sau: ba trong s cc byte u tin ca

mi onstc nhphn chia TU tng ng thnh mt on 125

m s. Trong s, vicng dng cc on m ba byte u tin ca chngl cc con tr V1, V2 v V3, cn byte tht l V4, th cn cha c xc

nh. ng thi, vng trng tin ca mi TU s b tr cc a ch trn

byte ng ngay ng sau V2 v sau , theo trnh t 0, 1, 2 ....

Cc con tr H1, H2, H3 v V1, V2, V3 c cng mt chc nng nh nhau,

trong khi chng c dnh du mt cch khc nhau. Hnh 1.48 ch r

phi xcnh cch sdng ba byte ny nh th no. Bn bt ca chiu

sliumi (NDF-New Data Flag) ch th trng thi ca sliu mi, cnbt SS c sdng phn nh loi ca TU hoc AU tng ng.a

ch bt u ca VC tng ng c ghi trn 10 bt sau . 10 bt ny

c phn chia thnh 5 bt I (Increment - gia tng) v 5 bt D (Decrement

- gim) nhc trnh by trong hnh. Trong s, bt I s b hu b mi

khi a ch ca im xut pht c giatng v bt D b hu b mi khi

a ch ca im xut pht gim i. Cui cng, byte H3 (hoc V3) c

sdng np cc s liu hpl khi thchin vic chn m.

Hnh 1.48. Cu hnh v chc nng ca con tr

Khi thc hin mt ghp chn dng, cc s liu hp lc phti bngcch np ti cho byte ng ngayng sau H3 (V3). Khi xy ra s khcnhau vtns gia khung TU v AU hoc gia cc VC (l cc trng tinca chng) th cc byte con tr c thc sdng gii quyt cc vn ny nh s dng php chn dng/ khng/m. Nu tn s ca VCtng ng btuln hn so vi khung TU/AU th trng tin cn pht sc giatng.ng thi,i cho ti khi tng s cc dliuc tch tdo s khcbit tnstrnnbng 1 byte (trong trng hp VC-4 l ba


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dy) th mng vng c thtit kim dc 58% chi phut so vii tc hng tm ca n. By gichng ta nghin cu mt trnghp khc, trong mng hng tm 1:1/DP sdng h thng 565Mbit/s v mng vng sdng h thng 2,40 Gbit/s. Gi thit rng githnh tng i ca mt thit b kt cui 565 - Mbit/s l 1 v chi phca thit b 2,40 Gbit/s gp ba ln gi thnh ny. Mng vng ang

nghin cuy cnnbn b ADM 2,4 cobit/s, iu ny dn nmt gi thnh tng i l 12 (1 x 3 x 4 = 12), trong khi mnghng tm 1:1/DP cn n 12 b OLTM 565 Mbit/s, iu ny dnn mt gi thnh tng i l 9,6 (1 x 0,8 x 12 = 9,6). Do vy, trongth dctrng ny, mng hng tm 1:1/DP dng nh t t hnmng vng. Tuy nhin, c th phi cn n cc b ti to cho ccchng bo v phn tp di hn trong cc mng hng tm cp quangrng hn v c th iu chnh nhng li th ca vic s dng ccOLTM tc thp. Khi s lng cc nt trong mng vng tng lnti tm hoc ln hn, mng 1:1/DP s btu t hp dn hn so vimch vng.

Lu rng tho lun y ch ch n gi thnh ca tht b ghpknh, bi v n l yutni tri nht ca ton b gi thnh h thngchuynti bng cp quang i vi cc mng "intra LATA".

Trong nhiu trng hp, mng vng c cc uim v kinh t so vii tc hng tm ca n, tuy nhin, n c th gp kh khn hnhoc t hn nng cp h thng khi dung lng mch vng cn kit. Mch vng cng c th cn n mt h thng iu khin

mng phc tp hn so vii tc nh tm ca n, bi v rng tt ccc nt s tng tc vi nhau khi cc tnh hung sc xy ra hoc cyu cu ti cu hnh. Tuy nhin, vn cn kit ca dung lng mchvng c thcgim bt hoc c gii quyt nhquy hochmngcn thnhoc trin khai ADM tc cao hn nhiu(chng hn, tnhkhdng ca cc ADM 9,6 Gbit/s). V li (xem mc 4.5), h thngiu khin dng cho mng vng c thcn gin ho khi thit bSONET c trin khai. Bng 1.17 tng kt ho mt s so snhtng i gia cc cu trc mng vng v nh tm vimng bo v

phn tp (Hub/DP).Bng 1.17. So snh gia nh tuyn bo v phn tp v cu trc SHR

Cc thuc tnh Hub/DP SHR/ADM

Khnng nng cp D dng Kh khn - t

Tngs cp quang Nhiuhn t hn

Tngs ucui Nhiuhn t hn

Tc ucui Thphn Cao hn


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Khnng sinh tn ca cp si quang 100% * 100%Khnng sinh tn ca trung tm ** Ngho Tthn

* Ph thuc vo cp bo v 1:1 hay 1: N

** Gi thit ton b to nh trung tm b hhng.

2. SHR ca SONET

SHR l mt mng ng vng cung cp di thng hoc v thit bmng d tha, sao cho cc dch v b gin on c th c khi

phc mt cch tng. Gii php chung bo m mt kh nng thn gn l cung cp mt vng truyn thng th hai song song vivng lm vic th nht. Trong trng hp ny, mt s c trn vngc thc b qua nhchuyn cc cuc truyn thng sang vng thhai; ni chung n c coi nh mt chc nngchuynmchngdy (hoc chuynmch bo v).Hn na, nu vng th hai pht theo

hng ngc li so vi vng th nht th mt s ngt trong c haivng gia hai nt klin nhau c thc cu vn nhcc nt trnmt trong hai pha b ngt bng vicu vng cc cuc lin lc ngctrlisang vng th hai. N c gi mt cch thng dng l chcnng u vng ngc. Hnh 1.69 miu t cc thd vchuynmchng dy v mch vng ngc phc hi.

Ch rng mt s kt hp cc chc nng vng ngc v chuynmch ng dy (trn mt trong hai pha b ngt) c th c sdng phc hi dch v b gin on. Do vy, mt thuc tnh quan

trng ca SHR l: nu vng b "gy"ti bt k mt im no , thhng truyn dni vi cc tn hiu c thcoli nhm trnhvicmtdch v.

Cc SHR ca SONET c thc phn chia thnh hai loi ph binl n hng v song hng theo hng ca lung lu lng dicc iu kin bnh thng. Cu trc ca SHR thuc v mt trong hailoi ph bin ny c th khc nhau v cchiu khin bo v cnsdng phc hi cc dch v b gin on.

SHR nhng

Trong SHR n hng (USHR) lu lng lm vic c chuynquanh mng vng ch theo mt hng (chng hn ngc chiu kimng h). Hy tham kho hnh 1.70(a). Lulng tbt k mt ntno cnh tuyn theo cc ng truyn thng lm vict Nt1 ti Nt 3 (tc l ng 1-2-3). Lu lng quay v tip tc i theovng t Nt 3 quay v Nt 1 theo cng mt chiu nht Nt 1 nNt 3, sdng phn cn li ca vng lm vic (tc l ng 3-4-1).


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Cc vng chuyn mch ng truyn STS v VT tng ng c sdng ch yu trong cc mng lin tng i v cc mng u vng.

Hnh 1.71 miu t cc yu cu k thut ca cu trc vng SONETda trn csnh truyn yu cu v cchiu khin bo v.

Hnh 1.71.

1.7 STIN TRIN SANG BISDN

B-ISDN c pht triniutit cc th loi khc nhau ca cc tnhiu bng rng, da trn nhng khi nim v tiu chun ISDN v tiuchun thng tin quang ngb, trong khi h thng thng tin ATM c pht trin ci t B-ISDN. Mc tiu ch yu ca BISDN l linkt tt c cc tn hiu lin tc theo thi gian thc v cc tn hius liutheo nhm c s phnb di tnrng (cn thit cung cp cc dch vbng hp, pht hin t xa, chng hn nh gim st t xa, u cui sliu,

in thoi v fax, v cc dch v bng rng, chng hn nh in thoithy hnh, hi ngh truyn hnh, truyn tn hiu truyn hnh nt cao,truyns liu tc cao v.v). B-ISDN i hi mt phng php hiu qu c th x l chung tt c cc dch v ni trn. H thng truyn thngATM (phng thc chuyn giao khng ng b) c xut nh lmt gii php.

Cc khi nim v BISDN c pht trinp ng mt cch hiuqu cc nhu cu ang cng ngy cng gia tng v cc th loi dch vbng rng khc nhau. iutit tt c cc loi tn hiu bng rng ny,

cc dch v thng tin, chng hn nh cc th loi in thoi video, cnc lin kt vi cc loidch v phn b, chng hn nh CATV. Ngoira, phi c mt chc nng cung cpc cc dch v ch knh, c ccdch v ch gi.

Mt khc, li tng c mt i hi v kh nng mng c kh nng cungcpdch v gim st t xa hotng ti mt tc truyn dn thp (bit/s)cng nh dch v thoi/th tn hot ng tc truyn dn trungbnh/cao (vi chc kbit/s cho thoi v vi trm Mbit/s cho video). Mt


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gii php cho vic ny l xut tiu chun ho cc loi tn hiu khcnhau ca cc dch vng c cc hnh thc bngoi nh nhau v sau, tch trchng li ghp knh. Cc t bo ATM c sdng tiu chun ho cc hnh thc b ngoi ca cc tn hiu dch v v hthng ATDM (ghp knh khng ng b phn chia theo thi gian) c sdng ghp mt nhm cc t bo ATM; mt h thng truyn

thng da trn cscc t bo ATM v ghp knh ATDM cgi l hthng thng tin ATM.

H thng truyn thng ATM lin kt h thng thng tin digital chknh ang hotng vi h thng thng tin ch gi. H thng thngtin ATM ging nh h thng thng tin gi, trong n s dng cc tbo ATM nh mt phng tin truyn dncbn, trong khi n khcvichuyn mch gi ch n ng thi c th x l c cc tn hiuthi gian thc v tng ng. Ngoi ra, cc h thng chuyn mch gini chung csdng mt cch cc b trong cc mng LAN, cn

i vi h thng ATM th do n c thit k s dng trn ccmng cng cng nh cln, cho nn n khc phc c nhng kh khntrong vic gn a ch, iu khin kt ni v lu trnh, chuyn mch vtruyn dn. Mt khc, so vi h thng thng tin ch knh (phn bknh cho mi dch vri sau thng qua cc knh ny m chuyn cctn hiu thng tin i nh mt dy bt lin tc), ATM phn chia cc tnhiu mang thng tin ri sau np chng vo cc t bo ATM chuynchng i qua cc knh o. Do vy, mt s vnmi lin quan n victhit lpni kt, qu trnh bo hiu,n truyn dn v chuyn mch

pht sinh.B-ISDSN hay h thng thng tin ATM c trin khai vo cui nm1980, t n nay n vnc nghin cu v nng cp. Do vy trongmc sau y s xem xt li cc vn lin quan nchng, da trn cciu khon thuc v BISDN ca ITU-T.

H thng thng tin ATM c pht trin ci t B-ISDN cho nni khi n c xem l "mng ATM".

1.7.1 Cc khi nim cbn ca B-ISDN

Khi x hi pht trin, khi cng ngy cng c nhiu cng ty mc ln, thnhu cu v cc dch v a phng tin v cc dch v bng rng khcnhau cng ang gia tng mt cch ng k. By gicng ngy cng cnhiu ngi sdng cc u cui sliu, cc my tnh c nhn, cc myFax v cc h thng hi ngh video, v s lng cc cng ty nhn thamgia vo cc dch v CATV cng tng ln.


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Ngoi ra, nhu cu v cc dch v nhin thoi thy hnh (video), truynhnh phn gii cao, truyn s liu tc cao, dch v gim st bngvideo, truy tm bng video, video text bng rng cng ang tip tc giatng. Nhng dch v k trn bao gm cc dch v giao lu cng nh ccdch v phn phi m mt s trong cc dch v c th cn n ccmng ring ca mnh (do mt s trong cc dch v l cc dch v ch

knh, mt s l cc dch v ch gi). Song lm c iu cnphi u tmnh v s lm cho thng tin trnn km hiu qu. Do ,hinang c mt nhu cu lin kt cc dch v ni trn thnh mt mngtruyn thng chung cho tt c cc dch v lin kt.

BISDN - mt mng thng tin s, c kh nng cung cp cc loi hnh dchv bng hp, chng hn nhin thoi, cc u cui sliu, gim st txa, facximin, teletext, cng nh cc dch v bng rng, chng hn nhin thoi thy hnh, hi ngh truyn hnh, truyn dn hnh nh c phn gii cao, truyns liu tc cao, gim stbng video v CATV...

Do vy, B-ISDN c th c xem nh mt mng thng tin m n c pht trin tmng ISDN bng hp hinang c sdng.

1.7.2 Cc c trngtn hiu ca dch v B-ISDN

B-ISDN c nhng mc ch cbn l kt hptt c cc dch v hin huvo mt mng truyn thng trong tng lai. Do vy, v cbn n cungcp cc dch v bng hp, chng hn nh in thoi, u cui s liu,fasimile, son tho vn bn t xa, c s o t xa, videotex, bu chnhint, teletex. Ngoi ra, n c kh nng cung cp cc dch v bng rng,chng hn nhin thoi thy hnh, hi ngh truyn hnh v truyns liutc cao, facsimile mu, CATV, phn phi HDTV, m thanh nhycmcao, th truyn hnh, gim st bng video, truyn chng trnh chiuphim phn gii cao v videotex bng rng.

Nhng dch v BISDN ny bao gm tt c cc dch v c nhng c tnhkhc nhau. C ngha l, cc dch v tng tcchng hn nhin thoihoc in thoi thy hnh v cc dch v thng bo chng hn nh buchnh int hoc bu chnhbng hnh nh v cc dch v truy tm tracu bn v v vn bnuc bao gm trong . Cc dch v ny lcc dch v thng tin m tn hiu ca dch vc chuyn giao theo chai chiu, song bn cnh , chng cn c cc dch v phn phi mtchiu, chng hn nhdch v CATV.

Nhng ctrng ni bt nht ca cc tn hiudch v B-ISDN l phm viphnb di thng ca n rt rng. Trong khi tn hiu cu hnh cbn caISDN bng hpc phn b quanhtn hiu thoith vic phn b tc tn hiu ca B-ISDN bao gm cc lp digital khc, cc tn hiu video


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o (trong s cc t bo ATM) hin din trong mt lung thng tinATDM.

l chc nng do VPI (phnt nhn dng ng o) v VCI (phntnhn dng knh o) ch r trong (b) v (c) ca hnh 1.73.

(a) Cu trc ca t bo

(b) Cu trc u trong UNI

(c) Cu trc u trong NNI

Hnh 1.73 Cu trc ca t bo ATM

ng thi,ng o c ngha l mt b cc knh o cng sdng chungcc ng no v mo u t bo cng c phn loi thnh loitrng tin (PT) v ch th thm quynmt t bo v cung cp kh nngiu khin sa sai ca mo u. N cn cung cp thm chc nng iukhin lung chung cho mo ut bo trong giao din UNI.

1.7.8. Cu trc chc nng ca BISDN

M hnh cu trc chc nng chung ca ISDN bng rng vcbn gingnh ISDN bng hp. C ngha l vmt cu hnh tiu chun, nhm chcnng v im gc, c hai cu trc l nh nhau. N ch ra rng B-ISDNc hnh thnh trn cskhi nim ca ISDN. M hnh cu trc cbnca B-ISDN nhc trnh by trong hnh 1.74. Cu trc ca ISDN bngrng bao gm kh nng mc cao v kh nng mc thp.


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Kh nng mc cao l chc nng lin quan n thit bu cui (TE) vkh nng mc thp bao gm kh nng ISDN bng hpda trn kh nngbng rng, 64 bit/s, v kh nng bo hiu lin tng i.

Hnh 1.74. M hnh cu trc c bn ca B-ISDN

Cu hnh tiu chun ca B-ISDN c trnh by trong hnh 1.75

Hnh 1.75. Cu hnh tiu chun ca B-ISDN

im gc l Sb v Tb, nhm chc nng bao gm B-TE1, B-TE2 v B-TA, B-NT1, B-NT2. Trong hnh 1.75, cc thit b u cui (B-TE) ccha B-TE1, B-TE2 v B-TA. Cng nh vy, B-NT2 v B-NT1 tngng nm trong mng B-IDN dnh ring v B-ISDN cng cng. ch thim gc v nhm chc nng ca mnh, B c ngha l B-ISDN.

1.7.9. M hnh chun ca giao thc

M hnh chun giao thc (PRM) ca B-ISDN c hnh thnh t mtbng qun l, mt bng iu khin, v mt bng khch hng nh ctrnh by trong hnh 1.76. Chc nng ca mt bng qun l c phnchia thnh : qun l mt bng v qun l lp.


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rng ti 9kHz - 400 Ghz v xem xt li v b sung cho Quy ch thngtin v tuyn in (RR). gim bt can nhiu ca thng tin v tuyn,ITU tip tc nghin cu nhng vn sau y b sung vo ssp xpchnh xc khong cchgia cc sng mang trong Quy ch thng tin vtuyn:

- Dng cch che chn thch hp trong khi la chn trm.

- Cithinhng tnh ca anten

- Nhn dng bng sng phn cc cho.

- Tng cng ghp knh.

- Chp nhnsdng phng php iu ch chng li can nhiu.

2.2 CC C TNH CA SNG V TUYNTnssdng cho sng in t nh vai tr sng mng trong thng tinv tuyncgi ring l "tns v tuyn" (RF).Tns ny chim mtdirt rng t VLF (tns cc thp) ti sng milimt. Khng th l giiy sng v tuyn theo l thuyt, bi v n khng ch bnh hngbitng i lu v tng in ly m cn bi cc thin th, k c mt tri.

Do vy, vic nh gi cc trng thi ca cc hnh tinh, ca tng i luv in ly v vic d bo ng truyn sng v tuyn cng nh kh nnglin lc da trn nhiu dliu trong qu kh l ht sc quan trng. Phnsau y ca chng trnh ny s gip bnc hiuc c ch truynsng v tuyn theo tn s thng tin v tuyn cng nhng vn khc,lin quan n sng v tuyn.

2.2.1 Phn loi tn s v tuyn

Trong thng tin v tuyn, cch truyn sng v tuyn v vic sdngthit b truyn thng ph thuc vo tn s v tuyn s dng. Bng 2.1trnh by bng tn s v tuyn c phn loi theo tiu chun quc thin hnh v theo cch v phng thc sdng sng v tuyn.

Bng 2.1. Phn loi, c ch v s dng sng v tuyn

Tns Phn loibng tn

Cchtruynsng vtuyn

C ly thng tin v lnh vcsdng

3KHz~30 KHz VLF Sng t-in ly

Thng tin o hng qun skhpth gii


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tng. Ncgi l chng dn sng mtt - in ly m nhn,c th thng tin ti ton th gii. Bng tns cc thpc sdng chyu cho thng tin hng hi v thng tin o hng.

2. Struyn lan cabng tn scao

Thng tin c ly xa bng bng tns cao c thc hin nhs phn x

ca sng tri trn tng in ly. Trong phng thc thng tin ny, mtthu sng tri ph thuc vo tns v tuyn v trng thi ca tng in ly,trng thi ny thay i theo thi gian, theo ngy, theo ma v theo iukin thitit. Cho nn vic d bo trng thi ca tng in ly l v cngquan trng i vi thng tin lin lc sdng sng tri.

(1) Tng in ly

Tng in ly hnh thnh ti cao 100Km - 400Km l do kt qu cavic ion ho trng thi ca tng i lu bng cc tia cc tm v tia X do

mt tribc x.Tng in ly c phn chia thnh mt vi lp c gi trmtin t cc i. Mi tng c phn chia thnh cc lp D, E, Ftheo cao ca n. Lp F lic phn chia thnh lp F1, F2. Hnh 2.3trnh by mt tnh theo cao ca cc lp ion in hnh.

Hnh 2.3. Mt in t /ion ca tng in ly - theo cao

(2) Truyn sng trong lp Ion

Trong khi tng in ly c th xem nh mt tm dnin phng trong victruyn lan cc tn s thp th lp ion ho ging nh mt tm in mikhng l m hs khc x ca n bini lin tc, v s bini ca mt ion theobc sng l khng ng k trongbng tn s cao(bc sngngn hn).Hs khc x hiudng c xc nh nh sau:

Trong cng thc ny, N biu th cho s lng ion trong trng thi ccin tt do hoc plasma, trn m3. Hnh 2.4 trnh by ng i ca sng


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Tr mt vi trng hpcbit,gii hn trn m sng khng gian truynlan c l 30 MHz . Sng khng gian csdng cho cc tn hiulnhn VHF. S thay i hs khc x theo cao ca kh quyn gy nhhng n sng khng gian. Kh quyn tiu chun l mt kh quyn ltng c mt tl bini hs khc x theo cao mt cch un,bi v n c mt hs thay i cnh ca p sut kh quyn theo cao,

nhit v m. ITU-R quy nh ch s khc x ca kh quyn tiuchun theo cao h Km nh sau:

V c s bini hs khc x mt cch lin tc, cho nn ng i thct ca sng khng gian l khc ving trc tip (thng). b liskhc nhau ny, c ly thng tin cci thc tc tnh ton theo ngtrc tip da trn quy nh bn knh hiu qu ca tri t KR (K=4/3trong khquyn tiu chun) (tham kho Hnh 2.5).

a) iu kin thct

b) iu kin tng ng ca bn knh tri tc tnh bng KR(4=4/3)

Hnh 2.5. Khc x ca sng v tuyn trong kh quyn tiu chun

4) Sng tn xi lu.

Vic lan truyn cu sng v tuyn nhhiung tn xi lu ca khuvc kh quyn rng ln trong tng i luc dng cho bng tn trnVHF. Phng php ny cho php thng tin lin lc c ly xa cc bngtn VHF, UHF, v SHF v ph thuc rt nhiu vo thng tin trc thitrcy. Phng php ny c nhiuuim ca thng tinbng rng v

ghp knh cng nh thng tin ng thi cho mt khu vc rng. Mt khcn cng i hi cng sut pht ln v my thu c nhy cao.

2.5. H THNG THNG TIN DI NG

Gn y, thng tin di ng tr thnh mt ng dng trong lnh vcthng tin v tuyn. S pht trin ca thng tin di ng c btu bng


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pht minh th nghim v sng int ca Hertz v in bo v tuyn caMarconi v vo thi ku ca pht minh thng tin v tuyn, n csdng trong dch v vnti an ton ng biniu khin cc tu. ivi thng tin v tuynmt t, sau chin tranh th gii th nht, h thngin thoi v tuyn di ng clpt v khai thc trong ngnh cnhst ca M. Trong dch v thng tin di ng hng khng - mt h thng

c khai thc cc di thng HF v VHF c thit lp kim sotbay. Hin nay, h thng in thoi xe ctng v h thng in thoi ding tu b c thitlpsdng trong thc t. Ngi tasdngchung b ti, in thoi khng y, di bng nghip d cc nhn(CB_my bm... v cc dch v thng tin v tuyn di ng khc nhauchng hn nhdch v v tinh hng hi,in thoi trn tu ho my bayang c cung cp. Tn s s dng ln n VHF v UHF v trongtng lai khng xa tns cn vi ba (quasi microwave) (1-2 GHz) cng sc sdng. Trong mc ny, chng ta s xem xt cc dch v thng tindi ng khc nhau, s pht trin ca chng trong tng lai, c bit,thng tin di ng mttsc cpn mt cch t m hn.

2.5.1 Cc loi v cc c tnh ca thng tin di ng mt t.

1/ Thng tin di ng mt t.

Thng tin di ng mtt thng c phn nhm thnh h thng cngcng v dng ring... H thng cng cng c ngha l h thng thng tinc th truy nhptimng in thoichuyn mch cng cng (PPTN) - cin thoi xe c, in thoi khng dp,chung b ti... Trong h thng

dng ring c 2 loi h thng. H thng th nht l h thng dch v cngcng chng hn nh cnh st, cuho, cp cu,in lc v giao thng.H thng th hai l dng cho cc c nhn hay cc cng ty. y, ngoidch v kinh doanh sdng sng v tuyn dnh ring, cn c h thngMCA h thng kinh t trung nhpa knh, s dng cc knh v tuyntrong thng tin v tuynni b cng ty v c nhn chng hn nh mybm v v tuyn nghip d.Ngoi nhng dch v k trn cn c cc dchv thng tin di ng mt t khc mi xuthin nh chung b ti cmn hin hnh, u cui xa... Cc c tnh ca thng tin di ng ctrnh by trongbng 2.2.


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Hnh 2.32 Cu hnh ca h thng vin thng xe c v tu b

1/ Trm chuyn mch vin thng.

Trm chuyn mch lin kt mng thng tin di ng vi PSTN v hthng chuyn mch trm chuyn mch l dng t ng v iu khintheo chng trnh lu tr. Cc chc nng chnh ca n l uni cc thubao di ng vi nhau v vi cc thu bao ca PSTN. V vy MTX cnphi c cc chc nng khc vi h thng chuyn mch PSTN, chng hnnh chuyn vng tm kim v tr v ng k.

Chuyn vng ngha l trong qu trnh cui gi, nu my di ng di

chuynkhi vng phc v ca mt khu vc c th th h thng schuyncuc gi ny sang mt knh tn s mi mt khu vc t bo mi mkhng lm gin on cuc gi. iu ny c thc hin bng mt hthng tnh ton phctp, mt h thng nhy cm v iu khin chnh xc.Phng php chung y l bng vic gim st cht lng tn hiu (mc)ca tng knh thuct cc trm gc khc, khi cht lng tn hiu btu gim di mc quy nh th khu vc t bo hin ti s chuyn tnhiu bo ng cho trmchuyn mch sau trm chuyn mch s yu


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(Hnh 2.3.3) miu t FDMA, TDMA v CDMA sdng thi gian v tns nh th no v thit b thu pht ca chng c cuto nh th no. FDMA, khi yu cu mt cuc gi th mt knh a v tuyn c chnh. Trong TDMA th knh v tuync chia li theo nhng khe thigian tun hon v khi yu cu mt cuc gi th n s ch nh khe no camt knh v tuyn no scsdng.

Hnh 2.33. So snh v tn s, thi gian v cu hnh thu pht caFDMA, TDMA v CDMA

Trong cc kiu truy nhp ny th khng c va chm bi v mi mt knhv tuyn v mt khe b him bi mt trm v tuyn.

Mt khc i vi CDMA th knh v tuyn bng rng c nhiu ngis dng chung, nhng mi ngi s dng th tin hnh thng tin nhndng m bng cch sdng m khuych tn trong trc giao.

Miu t skhi my thu pht trm gc. Trong FDMA

v CDMA th s my thu pht di ng ging nhtrm gc nhctrnh by hnh 2.33(b). Trong TDMA th trm di ng cn phi c chcnng pht v thu tn hiu theo khe thi gian c gn bi v n khng ccha chc nng a phn chia. Trong FDMA v TDMA. to ra tnsknhbng hp c gc th phi sdng b tng hp nh c trnh bytrong phn (a), (b) ca hnh 2.34.


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Hnh 2.34 Cu hnh ca h thng thu pht (trm gc)

Mt khc trong CDMA th sng c iu ch th nht ca s liupht c iu ch trc giao th hai bng m khuych tn. T l dithng gia sng iu chln th hai v sng iu chln th nhtgi lhiu qu khuych tn. Nu khuych tn ngc bng m khuych tn nyth chng ta li nhnc sng iu chln th nht.

Ngc li vi trng hp FDMA v TDMA trong tn hiu ltrc giaotrong tng mintns v tngmin thi gian, trnh s va chm, cctn hiu gc ca khch hng trong CDMA im c trng ca n l tnhiuc trc giao ho min m.

2/ Truy nhp ngu nhin.

Trong trng hp truyn thng gi m yu cu thng tin l ngu nhin vkh nng to nhm cao, mc d mt knh v tuync dng chung chonhiu ngis dng nhng xc sut va chm thp. Bng cch s dngtruyn thng gc theo thng k ny, vic truy nhp thc hin ghpknh cgi l a trung nhp thng k.


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Truy nhp ngu nhin n gin nht l ALOHA. T mi khi gc thngtin cn pht c to ra my di ng gi gc thng tin ny titrmgc.Khi c xut hin li trong gc thng tin ny ti trm gc. Khi c xuthin li trong gc thng tin thu c do va chm th trm gc yu cupht tr li cho my di ng. Chng ICMA pht hinc khi no ngthng n trm gc khng b chim (ch c my di ng no pht, v khi

no ng thng n trm gc ang c s dng (mt my di ngang pht) v trnh c va chm trong knh v tuynt trm gc xung(t trm gc n my di ng).

3/ FDMA

Phng phpn gin nht v truy nhp knh l a truy nhp phn chiatn s. FDMA l th hin knhbng hp m n gin l bt ku cuino cng c mt ng in thoi theo mi knh m n c th truy nhpti bt ktns no. i khi h thng ny cn c gi l mi knh trn

mt sng mang. Phn chia tn s y l mi my di ng c th sdng mt ng c to ra bng cch ny (xem hnh 2.35). a truynhp phn chia tns c ngha l nhiu khch hng c thsdng ditn c gn cho h m khng b trng nh vic chia ph tn ra thnhnhiuon.

Ghp knh phn chia tns l: tn hiu cnc pht ti mt s khchhng t mt my pht sc pht i bng cch phn chia cc bng tnv my thu s chn thng tin thuc bng tn ca n. FDMA l pht tnhiu ti mt s my thu. Do vy, nusdng FDMA trong h thng t

bo th FDMA phi l knh nghch (backward channal) FDM l knhthun (Forward channel). N c gi l FDM/FDMA.

Hnh 2.35 (trunked). 1 mch trn mt mch RF

Nhng u im ca a truy nhp phn chia tn s l mt trong nhng vn kh khn trong vic thchin h thng t bo s l s khuych tntr do thi gian n btr ca sng a ng trong knh t bo, n gy ra


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nhiu k hiu (ISI - Intersymbol Interference) v i khi lm gim chtiu ca h thng t bo. V vy,i ph vi ISI, cn phisdng bcn bng song i khi rt kh thchin. Tuy nhin nu chu k k hiuca d lius cng ln - tc l rng bng tn ca knh cng nh thISI cng khng bnh hng ca khuych tn tr thng xuyn. Tngng, chng ta bit l FDMA khng cnn b cn bng trong knh t

bobi v chu k ca d lius ln hna truy nhp phn chia thi gian.V trong FDMA, khng cnnng b mng ban u v vic hi phcnh thi bit hay ng bkhung rt d dng vphncng n gin trongvic thc hin modem. Nhng yuim ca a truy nhp phn chia tns l: Cn c b lc, b song cng (duplexer) - l b phn chia tn hiugi i v gi n ca u cui thng qua ngten khi thchinu cui tbo. Thng thng, do chnh lch v cng sutin giau vo v ura qua ngten l ln hn 100dBnn rt kh phn chia tn hiu. V vy, bsong cng m hin nay ang dng kh thc hin chc nng ny v mlng ln. V vy, chng ta phia tn tht xen 3dB vo khi b songcng cho tn hiui qua.Nhiu cng knh l mt vnna c th phtsinh do vic phn chia nh ph tns v do cn c bng tn bo vgia cc knh ti thiu ho nhiu ny.

4/TDMA

Thng tin di ng s Chu u (GSM), Chu M (ADC) v Nht(JDC) thng chp nhn s dng TDMA. S theo khi nim caTDMA c trnh by trong (Hnh 2.36). Trong thng tin di ngTDMA, trm gc pht tn hiu TDM n my di ng trong t bo. My

di ng nhn mt khe thi gian ca mnh trong s cc tn hiu TDM vgi tn hiukhi v trmgc mt cch tunt.

Cc s my di ng lin lc vi cc trm gc mt cch ng thi theomt knh v tuyn. Diy, chng ta miu t cc c tnh k thut cathng tin di ng TDMA.


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Hnh 2.36 S khi nim ca thng tin di ng TDMA

(1) nh thi pht v thu

Hnh 2.37 Ch r vicnh thi pht v thu ti trm gc v chnhthiti my di ng trong trng hp ba knh TDMA, chu k pht, thu,trng c lp i lp li trong my di ng. Do vic nh pht v thukhng trng nhau nn khng cnn b lc chn la thu pht trong mydi ng. Khong thi gian trng c s dng o mc thu ca cctrm gc ln cn.

Hnh 2.37nh thi pht thu trm gc

2/ Cu hnh ca khung

Cu hnh ca khung c trnh by trong (Hnh 2.38). Nhm ca tuynln (t my di ng n trmgc) bao gm phn mo u, t m ng bd liu iu khin, d liu ca ngi s dng v thi gian bo v. Vkhung ca tuynxung (ttrm gc n my di ng) l tn hiu lin tcnn khng cn thit phi cphn mo u v thi gian bo v. Phn moul h thng m ca ng b sng mang v ng b ng h. Khi phthin tr th vic ti to sng mang l khng cn thit v m ng b sngmang l m 1 bi v sng thu phi l sng chun pht hin bng cchto ra thi gian tr m 1).


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C = 1.44 W (S/N) (2/41)

V vy, khi W>S/N th C c th ln v hn,nu nhiu ngis dng phtv thu da nhau theo mt m khc nhau th c th truy nhpla chn 1-1giatns pht v thu.

Hnh 2.40 Nguyn l ca h thng CDMA

y, hiu mt cch n gin qu trnh m hoph khuch tngiapht v thu ca h thng CDMA, nguyn l ca n c trnh by tronghnh 2.40. C th l pha pht, th i tng m ho v chn d liu

m thanh c s ho (9,6 Kbps) c ghp knh thnh tn hiuiuch nhm gitp m 1,2288Mbps (9,6kbps x 128) vitns sng mangFo. N c bc x qua ngten rng cch c ghim trong b lc bngthng c ng bng l 1,25MHz. Mt khc, pha thu th tn hiu thu tngten i qua b lc bng thng c di thng l 1,25MHz v ciu ch vi sng mang ging nhphn pht bng b m ho gi tpm 1,2288 Mbps, cng vi b tng quan v sau s liu m thanhnguyn thu v gitp m c lc bng b lc s. V sliu m thanhc thc ti to bng cch gii chn v gii m.

ng thisliu m thanh ca cc knh khc cng nhtp m v nhiuv s liu m thanh gc c thc phn chia v nhnc nh tronghnh 2.40. iu c ngha l s liu m thanh ging nh (a) cbcx cng vi (c) vi v mi tn hiu bng c khuch tnt b ghpknh ging nh (b) c bc xtnten ra khng trung vi cng chkhuych tn trong rng bng 1,25 MHz. nten thu c th thu ctp m nn (g), nhiu bn ngoi (h), nhiu ca t bo khc (i), tp m tngisdng khc (j) m n c pht ch khc, cng nh sng thu


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mong i. Nhm sng v tuyn ny c lc trong b lc c rngbng l fo+(1,25/x) MHz v c cng vo vi b tng quan cfo=91,2288/x) Mbps ca c to ra pha thu.

Khi i qua b lc, (g), (h), (i), (j) s tr thnh bng khuch tn trongphm vi 1,25MHz. Tn hiu khuch tn mong mun (b) b co li trongphm vi di 10KHz, nhng n chia s vi tn hiu mong mun (d) vtn hiu khuch tn khng cn thits phnb cng ca chung (nnglng in) vn gi nguyn nh l cng tp m rng bng10KHz ging nh (d), v vy (C/I) ca tn hiu mong i (c) trnn ttnh l hiu qu khuch tn (128 ln).

hiuc th tukhuch tn ny mt cch d dng, cng thcnginc trnh by nh sau. u tin nusliu m thanh 9,6kbps ciu ch ln th nhtphn pht l a(t), h thng PN l C(t), sng cpht l y(t) th khi chng ta c th nhnc cng thc lin quan nh

sau:Y(t) = a(t) x c(t) (2.42)

Nu tn hiu khng gim v khng c can nhiu hay tp m th y(t) thhin tn hiu thu nh n vn c. Trong trng hp khuch tn ngc don c nhn vi cng mt trong ca phn pht nn u ra khuch tnngc z(t) l:

Z(t) = Y(t) x c(t) = a(t) x {c(t)}2 (2.43)

Trong , mc d c(t) l s ngu nhin th gi tr ca n ch gii hntrong 1 vi bnh phng ca c(t) bao gicng = 1. Cho nn J(t) gingnhc trnh by diy:

z(t) = a(t) (2.44)

Tng t nh vy ta c th bitrng sng hon ton ging nh vy c thc to ra ti cng mt thiimpha thu. y nu h thng PN l 1s ngu nhin bn trong th l mt trng hp tt. Nhng nu l nhvy th khng thto ra c mt cch ng thi mt h thng hon ton

ging nh vy. V vy phi sdng s ginh.2.5.4. Cu hnh tbo

1/ Khi nim v h thng tbo.

Do ngun tns gii hn ca thng tin v tuyniu quan trng l cnphitndng tns mt cch tt nht. V vy khi chng ta thitlp mth thng vin thng di ng, vn ct li lphisdng li cng 1 tnsa im cch xa nisdng cng tns ny.


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Hnh 2.41 Cu hnh vng

Trong s cc dng truyn thng ca thng tin di ng th c nhng dngm cc my di ng lin lc vi nhau khng cn trm gc ging nhthitb thu pht v c nhng dng m cc my di ng lin lc vi nhau thngqua trm gc nhin thoi trn tc xi v trn xe c. i vi loi th I thbn thn ngi s dng kim tra xem c nhiu khng, sau mi linlc. C th sdng litns nhng hiu qu th thp. Mt khc i vidng thng tin thng qua trm gc c thsdng k hochtns lplimt cch rthiu qu bng cch phn b tn s trm gc. Tuy nhintrong trng hp h thng vin thng di ng c trm gc th n c 2loi: loi th I l trm baoph khu vc phc v ging nh l lin lc vtuyntc xi, loi th II l a trmgc bao ph khu vc phc v nh l hthng in thoi xe c. Vng l mt min m sng v tuyn c thnc trm gc v loi th nht l loi vng n, loi th II l loi avng.

Vng ncgi l vng ln bi v 1 trmgc bao ph mt khu vc

phc v ln. C thng tin v tuyn tc xi, h thng nhn tin v MCA(TRS). Dng ny c cu hnh n gin c ni vi my di ng, ccthit bpht/thu trmgc, tng i hay h thng chuyn mch. Nhng duy tr c vng phc vln th cng sut pht ca my di ng catrm gc cn philn. V vy, nuc ly khng ln th khng thsdng ng ten mt tn s. V nu so snh vi dng a vng th n vngkhng sdng litns theo a l v vy hssdng tns thp hni vi a vng. Sdgi l vng nh bi v vng ca trm gc nh hnso vi vng ca trm gc ca n vng trong vng phc vtng ngvi vng ny. Vng nh c cc c tnh sau nu so snh vi vng ln.

1/ Hiu qusdng tns tt hn bi v mt tns c thsdng nhiu vng khc nhau c c ly tng i xa nhau n trnh nhiutrong khu vc phc v. Trng cng nh th t l s dng li tnscng ln.

2/ Chtlng tt hn bi v vng phc v bao gm nhiu vng nhlin tc. Tng i dp ng c yu cu v c ly khu vc phcv, cu hnh v.v...


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3/ Cng sut pht c th thp hn. Cn phi gim st trng thi viu khin trung nhp bng cch trao i thng tin gia nhiu trmgc m bo hiu qu v tnh lin tc ca mt gc. Cu hnh cah thng th phctp. Mc d cu hnh ca vng nh phctp nhngn c th baoph 1 khu vc phc v rng ln v thchinc mth thng ln c hiu qutns cao.

V vy n c sdng trong h thng in thoi, xe c v h thng inthoi di ng. Trong cu hnh ca vng nh th khu vc phc v gingnhiu vng v mi vng trng nh mt t bo v nu trm gc l li thn cgi l h thng t ong (collular). Mi vng cgi l mt tbo. Trong h thng t ong cn phi xc nh slng v ln ca tbo bng xem xt a hnh, s lan truyn sng v tuyn lu lng v.v...c bit chng ta cn phi nghin cu nnb tr trm gc nh th no loitr nhng lhng ca khu vc phc v v cn nng cao hiu qusdng tns nh th no. Vic nghin cu ny c gi l phn bt bo.

2/ Phn btbo.

1/ Phn bt bo theo kiu tuyn tnh a theo kiua hnh khi phn bt bo c b tr theo kiu tuyn tnh do khu vc phc vnm trnb,dc theo b bin hay dc theo ng trc gia cc thnh ph ln cchnhau vi chc kilomt th t bo c b tr theo hng dc v sdng litns sau mi vng. Chng hn, 3 t bo sdng li cuc gi trn tu cng, cuc gi trn tu ho v cuc gi trn my bay. miuts lpli ca 3 t bo trn s phn bt bo kiu tuyn tnh.

Khi khu vc phc v c kiua hnh (mt phng) ging nh cc cucgi ca cc xe c th rtnhiu t bo c phn b mt cch phc tptheo m hnh t bo lpli trn khu vc phc v khng c ch h.

Phn bt bo theo a hnh nh sau:

Mc d hnh dng t bo thc t phctp do s lan truyn v tuyn chunh hng ca cc yutt nhin v a l, t bo sc m hnh hov cc v tr t bo c phn bun trn vng phc v.


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Hnh 2.42 V d kiu tuyn tnh lp li ba t bo

2/Hdng tbo

Nungten a hng pht sng v tuyn trn khu vcmt bng th vng

baoph c dng hnh trn. Khu vc t bo c xc nh bng ccimc cng v trmc thu trung bnh gia cc v trt bo trong khu vc lantruyn sng v tuyn v c dng hnh a gic. C 3 phng php baoph kn khu vc bng cc t bo hnh dng a gic c kch thc nhnhau (hnh 2.43).

Hnh 2.43 Hnh dng t bo

Bng 2.3 Khong cch tm gia cc t bo

Kiut bo n v Khong cch tm gia cc t bo k nhauTam gic u (a) R

Hnh vung (b) R

Lc gic u (c) R

Hnh v

(a) Trng hp t bo hnh tam gic u

(b) Trng hp t bo hnh vung

(c) Trng hp t bo hnh lc gic


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ng ni tm ca khu vcgc ln nhau s c hnh tam gic u, hnhvung hay hnh lc gic u. Khng c bt k hnh dng t bo a gic

phn bu no khc ngoi cc hnh trn. Chng cgi l kiu t botam gic u kiu t bo hnh vung v kiut bo lc gic u. Mi kiut bo c nhng c tnh ring ca mnh.

a. C ly t bo: Khi baoph khu vc vi mi dng t bo th khong cchtm s nh trong . Khong cch tm ca dng lc gic ul ln nht.

Bng 2.4 Khu vc tbo n v l khu vc gc ln nhau

Kiu t bo n v Khu vct bo nv Khu vcchng ln

Tam gic u

3

R2 1.3R2

4

( 2 - 3

)R2 1.2R2

2

Hnh vung 2R2 ( 2 - 4 )R2 0.73R2

Lc gic u

3

R2 0.26R2

2

( 2 - 3 )R2 0.35R2

R: rng ca t bo chng ln

Hnh v

Bng 2.5 rng ca t bo chng ln

Kiut bo n v rng ca t bo chng lnTam gic u R

Hnh vung (2 - ) R 0.59R

Lc gic u (2 - ) R 0.27R

R : Bn knh

Hnh v

b. Khu vc t bo v khu vc chng ln: Khi cc t bo phn chia khuvc thnh cc t bo n v c cng kch thc v khu vc chng lnskhc nhau tu theotng kiutbo nh . Khu vct bo nv l mt khu vcc baoph bi tam gic u ti thiu ho slng tbo bao ph mt khu vc. rng ca t bo chng lnc trnhby trong .


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c. S lng tns cn thit ti thiu: Do khng thsdng cng mt tns v nhiu vi cc t bo bn cnh, cho nn s lng tns cn thit tithiuc trnh by trong .

Bng 2.6 S lng tn s cn thit ti thiu.

Dng t bo n v Slng tnscn thit ti thiu

Tam gic u 6Hnh vung 4Lc gic u 3

Mi dng c nhng c tnh ring ca n. Dng tam gic u l khngthch hptrtrng hpcbit v dng t bo lc gic u l hiu qunht.

He Thong Thong Tin Quang Vo Tuyen 3248

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