He Thong TT Ddong Chuong I

8/2/2019 He Thong TT Ddong Chuong I

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MC LC

M C L C 1

IV. C u trc a l c a h th ng thng tin di ng. ...............11

Tn bit 48BSS............................................................................................................................................................................70MSC..........................................................................................................................................................................70

CHNG I: TNG QUAN V THNG TIN DI NG

I. Qu trnh pht trin

1. Lch s ca thng tin di ng

a. Tnh t nhin ca thng tin v tuyn

Xt v hnh thc, thng tin v tuyn c quan h cht ch vi hot ng ca con

ngi. Cc k thut thng tin v tuyn hin i c pht minh v pht trin trongmi lnh vc lm cho vic trao i thng tin ngy cng tin li, tng cng y mnhhoc nng cao cch nhn thc v tm hiu ca con ngi. Do nhng k thut ny

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c pht minh sng to trong qu trnh nhn thc v ci to t nhin ca con ngi.Nn gi n l thng tin v tuyn hin i.

b. Ngun gc ca thng tin di ng hin i

Thng tin v tuyn hin i bt ngun t thc nghim bc x sng in t caHc th k XIX, lm cho con ngi nhn thc c vic c th iu khin pht xca sng in t v nng lng sng in t. Thng tin v tuyn in vt i TyDng ca Mc-c-ni chng minh kh nng mang theo thng tin ca sng in.C s l lun ca n l h phng trnh Mc-xoen do Mc-xoen sng lp sau ny:

H = -j D

D = B

. B = 0 . D =

Tuy vy, thc nghim thng tin di ng theo ngha hin i bt u t unhng nm 20 ca th k XX Detroit ca M. Mi n u thp nin 30 ca th kXX, cc h thng thng tin di ng trn ton th gii u s dng iu ch bin AM (Amplitude Modulation). Cui nhng nm 30, Cc cnh st Connecuicut (M) lp t h thng thng tin di ng iu ch tn s FM (Frequecy Modulation) utin. Thc tin chng minh trong mi trng truyn thng di ng, tn s FM hiu

qu hn nhiu so vi tn s AM. V vy, n nm 1940, tt c nhng h thng thngtin di ng ang s dng u c i thnh h thng FM.

2. S pht trin ca h thng thng tin t bo, v tuyn v c nhn

Cui nhng nm 40 ca th k XX, khi nim t bo xut hin trong kinngh ca h thng Bell. tng (phi k thut) mang tnh sng to ny a lnh vcthng tin di ng sang mt m hnh mi.

2

A

B

C

A

D

D

A

B

C

A

D D

B

A

B

C C

BD

A

B

C

C

A

DB

D

A

B

A

A

B

A

Kt cu camng 4 nhmt bo A,B,C,D

Khong cchD

ca t bo


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Hnh 1.1. Biu th kt cu 4 t bo A, B, C, D hp thnh mt nhm

V l thuyt, thc hin phn tch kt cu t bo ny c th hin bng hnhlc gic nhm biu th chnh xc cc khu vc ph sng trn m hnh. i vi hthng t bo, thng chia ton b knh thnh nhiu nhm khc nhau, mi t bo sdng mt nhm trong . Mt knh trong t bo ny khng th xut bin trong cc t

bo ln cn trnh gy nhiu cho cc knh c khong cch gn, nhng n c th lixut hin trong mt t bo khc c khong cch . Tc l 3 t bo to thnh mtnhm c bn, mi t bo s dng cc knh khc nhau. Mi nhm 3 t bo s dng ttc cc knh, cc nhm 3 t bo lin tc lp li hnh thnh vng ph sng ln.

c im quan trng th 2 ca m hnh t bo l: Nhiu khng c quan h vikhong cch tuyt i gia cc t bo m ch c quan h vi t l gia khong cchca cc t bo s dng cng nhm knh v bn knh R ca mi t bo, tc l nhiu cquan h vi D/R.

c trng th 3 ca m hnh t bo l: Chia ct li, t hp li t bo. H thngc th chia t bo ca khu vc ny thnh nhiu t bo nh hn tu theo tnh hnh thct nhm nng cao mc s dng tn ph, tng dng lng thng tin ca khu vc ny. qu trnh thng tin lin tc khng gin on, trong m hnh t bo, s ct chuyn

ca ngi s dng di chuyn gia cc t bo l rt quan trng. V khi ngi s dngdi chuyn nhanh qu trnh thng tin rt kh thc hin trong mt t bo tng i nh.

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AC

BSC

BSC

BSC

MS

C

OMC

CMT

HLR VLR

PSTN

BTS

BTS

BTS

MS

MSHnh 1.2. L kt cu m hnh chc nng

v lung tn hiu ca h thng thng tin di ngt bo


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x l vn trn, bn thn h thng t bo phi c kh nng trao i v iukhin cp h thng, h thng phi hiu c trm di ng bin gii t bo haygn bin gii t bo hay cha thng qua vic lin tc gim st cng tn hiu hoccc tham s mang tnh ch th khc. V iu khin trm di ng vo t bo mi viiu kin khng gin on thng tin. V vy h thng t bo phi c t nht 4 ctrng c bn sau:

- My pht x cng sut thp, phm vi ph sng nh.

- Lp li tn s hoc lp li knh.

- Chia ct v t hp t bo p ng dung lng thng tin trong mi trngnht nh.

- Ct chuyn tng khu vc v iu khin ca trung tm.a. H thng thng tin di ng th h th nht - H thng thng tin di ng t botng t.

Thng 12/1971 cng ty Bell a ra ngh v h thng thng tin di ng tbo HCMTS vi U ban thng tin Hoa K (FCC). FCC chp nhn ngh ny, vcung cp ti nguyn thng tin 40MHz trong di tn 850MHz. HCMTS lp t nm1978, nm 1983 bt u trin khai dch v thng mi. H thng ny pht trin k

thut thng tin t bo v di ng trn nhiu phng din, n thp k 80 ca th kXX, tr thnh tiu chun quc gia ca h thng tng t ca Trung Quc, AMPS lh thng chnh.

b. H thng thng tin di ng th h th 2 - H thng thng tin di ng t bo s

Xt v l lun, ch cn lin tc phn tch t bo v t hp ng cc knh, th sdng k thut t bo c th gii quyt vn ngun tn ph c hn mt cch hiuqu. Nhng thc t, cng vi vic tng s lng t bo v tuyn, khi din tch ph

sng ca mt t bo thu nh li th gii k thut v cc nh cung cp thit b thng tindi ng s gp phi hn ch thc t. V ngi ta vn khng th iu khin chnh xch thng t bo, gm cng sut pht x, ct chuyn nhanh. Bn cnh , i vi hthng FDMA tng t, cng vi vic thu nh t bo ngy cng kh loi b nhiu nt nhiu ngun. V trn thc t hn ch thit k l tng l thu nh t bo v hn.

Ngoi vn b tc v dung lng, h thng thng tin di ng th h th nht cnchu s chi phi ca tiu chun h thng.

Do mt s u im ca k thut s hn hn so vi k thut tng t v do thngtin di ng cn kh nng tnh ton mnh dn n lm cho u ban tiu chun quc t chn h thng s lm chun ca thit b thng tin v tuyn t bo th h th hai.

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S la chn ny m bo hai mc tiu: Mt l kh nng nng cp ca thng tin ding. Hai l kh nng tng hp ca cng ngh thng tin di ng v cng ngh thngtin khc.

Mt trong nhng u im thu ht nht ca k thut s l kh nng chng nhiuv c dung lng ln. Trong nhng phm vi nht nh kh nng chng nhiu tt cah thng s lm cho h thng t bo th h t hai c dung lng thng tin ln hn vcht lng dch v cao hn th h th nht.

Tm li h thng k thut s c nhng c im sau:

- Tnh linh hot ca h thng.

- K thut iu khin s hiu qu cao v tiu hao cng sut thp.

- Dung lng hu hiu ca h thng.

- Cng ngh m ho ti nguyn thng tin v knh.

- Kh nng chng nhiu.

- B tr di tn linh hot.

- Dch v mi.

- Kh nng v hiu sut truy nhp v ct chuyn.

c. H thng thng tin di ng t bo th h th ba - H thng bng rng vi tc truyn ti 2Mb/s

* Nhng mc tiu cha thc hin ca h thng thng tin di ng s th h th hai

Do h thng thng tin di ng s th h th hai vn cha thc hin mc tiu banu trn rt nhiu phng din. Cho nn kh nng truyn s liu vi tc vi nghn

bit/s khng th p ng nhu cu truyn ti tc cao ca mt s ngi s dng.Khng th thc hin mt cch hiu qu mt s k thut mi nh IP, nhng nhu cu

ny l ng lc th trng nhm pht trin h thng GPRS (General Packet Radio

Services) c tc truyn 9 150kb/s v nhng h thng khc bt u xut hin vtr thnh k thut trung gian qu sang h thng thng tin di ng th ba.

* Nhng mc tiu c bn cn thc hin ca h thng thng tin di ng th h th ba.

Bt u t nhng nm cui ca thp nin 90 h thng thng tin di ng th hth ba ra i bng k thut a truy nhp CDMA v TDMA ci tin. L thuyt vCDMA c xy dng t nhng nm 1950 v c p dng trong thng tin qun

s t nhng nm 1960. Cng vi s pht trin ca cng ngh bn dn v l thuytthng tin trong nhng nm 1980, CDMA c thng mi ho t phng php

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thu GPRS v Ommi-TRACKS, phng php ny cng c xut trong hthng t ong ca QUALCOM - M vo nm 1990.

Trong thng tin CDMA th nhiu ngi s dng chung thi gian v tn s, m

PN (tp m gi ngu nhin) vi s tng quan cho thp c n nh cho mi ngis dng. Ngi s dng truyn tn hiu nh tri ph tn hiu truyn c s dng mPN n nh. u thu to ra mt dy gi ngu nhin nh u pht v khi phcli tn hiu d nh nh vic tri ph ngc cc tn hiu ng b thu c.

So vi hai h thng thng tin di ng th nht v th hai th h thng thng tindi ng th h th ba l h thng a dch v v a phng tin c ph khp toncu. Mt trong nhng c im ca n l c th chuyn mng, hot ng mi lc,mi ni l u thc hin c. iu c ngha l mi thu bao di ng u c

gn mt m s v nhn dng thng tin c nhn, khi my bt c ni no, quc giano trn th gii u c th nh v c v tr chnh xc ca thu bao. Ngoi ra hthng thng tin di ng th h th ba l mt h thng a dch v, thu bao c th thchin cc dch v thng tin d liu cao v thng tin a phng tin bng rng nh:hp th thoi, truyn Fax, truyn d liu, chuyn vng quc t, Wap (giao thc ngdng khng dy)... truy cp vo mng Internet, c bo ch, tra cu thng tin, hnhnh... Do c im bng tn rng nn h thng thnh tin di ng th h th ba cn c

th cung cp cc dch v truyn hnh nh, m thanh , cung cp cc dch v in thoithy hnh...

S pht trin ca h thng thng tin di ng th ba ngoi vic phi gii quytnhng vn k trn, cn phi c kh nng p ng yu cu ngy mt tng ca conngi i vi kh nng truyn s liu. V vy hi vng h thng thng tin di ng thh th ba ti thiu phi thc hin c nhng yu cu c bn sau:

- Tiu chun thng nht ton cu

- C kh nng truyn ti a phng tin.- Tng dch v chuyn mch gi

3. Tng kt qu trnh tin ha ca h thng thng tin di ng

Ta xt tng kt cc nn tng cng ngh chnh ca h thng thng tin di ng tth h mt n th h ba v qu trnh tin ha ca cc nn tng ny n nn tng cath h ba. tin ti th h ba c th th h hai phi tri qua mt giai on trunggian, giai on ny c gi l th h 2.5.

Bng : Tng kt mt s nt chnh ca cc nn tng cng ngh thng tin di ngt th h mt n th h ba

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Th h thng tin ding

H thng Dch v chung Ch thch

Th h 1 (1G)

Th h 2 (2G)

Trung gian (2.5G)

Th h ba (3G)

AMPS, TACS,NMT

GSM, IS-136,IS-95

GPRS, EDGE,cdma2000-1x

cdma2000,WCDMA

Ting thoi

Ch yu cho dch vting v bn tin ngn

Trc ht l dch vting c a thm ccdch v gi

Cc dch v ting vs liu gi c thitk truyn ting vs liu a phng tin.L nn tng thc sca th h ba

FDMA, tng t

TDMA hoc CDMA, s,bng hp (8-13 kbps)

TDMA, CDMA, s dngtrng ln ph tn ca th hhai nu khng s dng ph

tn mi, tng cng truyns liu cho th h hai

CDMA, CDMA kt hp viTDMA, bng rng, s dngtrng ln ln h thng haihin c nu khng s dng

ph tn mi

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TACSGSM (900)

NMT(900)

GPRSWCDMA

GPRSIS-136(1900)

IS-95 (J-STD-008)

(1900)EDGE

IS-95 CDMA(800) CDMA20001x CDMA2000

MC

2 G

AMPS

SMR IDEN(800)

3G2.5 G1 G

GSM(1800)

GSM(1900)

IS-136 TDMA

(800)


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Hnh 1.4. M hnh tham kho ca h thng thng tin di ng

2. Cc phn t chc nng

a. Trm di ng, MS

MS (Mobile Station) c th l mt thit b t trong t hay thit b xch tayhoc thit b cm tay. Ngoi vic cha cc chc nng v tuyn chung v x l chogiao din v tuyn MS cn phi cung cp cc giao din vi ngi s dng ( nh:micro, loa, mn hin th, bn phm qun l cuc gi) hoc giao din vi mt sthit b khc (nh: Giao din vi my tnh c nhn, Fax...).

b. Trm thu pht gc, BTS

Mt BTS (Base station Transceiver Station) bao gm cc thit b pht thu,anten v x l tn hiu c th cho giao din v tuyn. C th coi BTS l ccMODEM v tuyn phc tp c mt s cc chc nng khc. Mt b phn quan trngca BTS l TRAU (Transcoder/ Adapter Rate Unit: Khi chuyn i m v tc ).TRAU l thit b m qu trnh m ho v gii m ho ting c th ring cho hthng di ng c tin hnh, y cng thc hin thch ng tc trong trnghp truyn s liu.

c. B iu khin trm gc, BSC

BSC (Base station Controller) c nhim v qun l tt c giao din v tuynthng qua cc lnh iu khin t xa ca BTS v MS. Cc lnh ny ch yu l cclnh n nh, gii phng knh v tuyn v qun l chuyn giao (Handover). Mt phaBSC c ni vi BTS cn pha kia ni vi MSC. Trong thc t BSC l mt tng inh c kh nng tnh ton ng k. Vai tr ch yu ca n l qun l cc knh giaodin v tuyn v chuyn giao.

c. Trung tm chuyn mch cc dch v di ng, MSC

Nhim v chnh ca MSC iu phi vic thit lp cuc gi n cc ngi sdng mng thng tin di ng. Mt mt MSC giao din vi BSC, mt khc n giaodin vi mng ngoi. MSC lm nhim v vi mng ngoi c gi l MSC cng(GMSC: Gate MSC). Vic giao din vi mng ngoi m bo thng tin cho cc

ngi s dng cc kh nng truyn ti ca cc mng ny cho vic truyn ti s liuca ngi s dng hoc bo hiu gia cc phn t mng.

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e. B ghi nh v thng tr, HLR

Cc thng tin lin quan n vic cung cp cc dch v vin thng c lu gi HLR. HLR (Home location Rigister) cng cha cc thng tin lin quan n v tr

hin thi ca thu bao.f. B ghi nh v tm tr, VLR

VLR (Visitor Location Risgiter) l c s d liu th hai trong mng TTD. Nc ni vi mt hay nhiu MSC v c nhim v lu gi tm thi s liu thu baoca cc thu bao hin ang nm trong vng phc v ca MSC tng ng v ngthi lu gi s liu v v tr cc thu bao ni trn mc chnh xc hn HLR. Ccchc nng VLR thng c lin kt vi cc chc nng MSC.

g. MSC cng, GMSCMng TTD c th cha nhiu MSC, VLR. thit lp mt cuc gi n

ngi s dng TTD, trc ht cuc gi phi c nh tuyn n mt tng i cngc gi l GMSC m khng cn bit n hin thi thu bao ang u. Cc tngi cng c nhim v ly thng tin v v tr ca thu bao v nh tuyn cuc gi ntng i ang qun l thu bao thi im hin thi. vy trc ht cc tng icng phi da trn s thoi danh b ca thu bao tm ng HLR cn thit v hiHLR ny. Tng i cng c mt giao tip vi cc mng bn ngoi, thng qua giaotip ny n lm nhim v cng kt ni cc mng bn ngoi vi mng TTD.

Ngoi ra tng i ny cng c giao din bo hiu s 7 c th tng tc vi ccphn t khc ca mng TTD.

h. Khai thc v bo dng mng,OS

H thng khai thc 0S (Operation System) thc hin khai thc v bo dng tptrung cho mng TTD.

Khai thc l cc hot ng cho php nh khai thc mng theo di hnh vi camng.

Bo dng c nhim v pht hin, nh v v sa cha cc s c v hng hc.N c mt s quan h vi khai thc.

i. Qun l thu bao v Trung tm nhn thc, AUX

Qun l thu bao gm cc hot ng qun l ng k thu bao. AUC(Authetication Center) qun l cc thng tin nhn thc v mt m lin quan n tng

c nhn thu bao da trn kho b mt ny. AUC c th c t trong HLR.

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IV. Cu trc a l ca h thng thng tin di ng.

Do tnh cht di ng ca thu bao di ng nn mng di ng phi c t chctheo mt cu trc a l nht nh mng c th theo di c v tr ca thu bao.

1. Phn chia theo vng mngTrong mt quc gia c th c nhiu vng mng vin thng, vic gi vo mt

vng mng no phi c thc hin thng qua tng i cng. Cc vng mng ding c i din bng tng i cng GMS. Tt c cc cuc gi n mt mng ding t mt mng khc u c nh tuyn n GMSC. Tng i ny lm vic nhmt tng i trung k vo cho mng GSM/PLMN. y l ni thc hin chc nnghi nh tuyn cuc gi kt cui trm di ng. GMSC cho php h thng nh

tuyn cc cuc gi vo t mng ngoi n ni nhn cui cng: Cc trm di ng bgi.

2. Phn chia theo vng phc v MSC/VLR

Mt mng thng tin di ng c phn chia thnh nhiu vng nh hn, mivng nh ny c phc v bi MSC/VLR (hnh 1.4). Ta gi y l vng phc vca MSC/VLR. nh tuyn mt cuc gi n mt thu bao di ng, ng truynqua mng s c ni n MSC ang phc v thu bao di ng cn gi. mi vng

phc v MSC/VLR thng tin v thu bao c ghi li tm thi VLR. Thng tin nybao gm hai loi sau:

* Thng tin v ng k v cc dch v ca thu bao.

*Thng tin v v tr ca thu bao (thu bao ang vng nh v no).

Hnh 1.5. Cc vng phc v MSC/VLR

3. Phn chia theo vng nh v

11

IV

IIIII

III

MS

C

MSC

VLRMS

C

MSC

VLR

MSC

MSC

VLRMSC

MSC

VLR


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Mi vng phc v MSC/VLR c chia thnh mt s vng nh v LA (Locatioarea) (Hnh 1.5). Vng nh v l mt phn ca vng phc v MSC/VLR m mt trm di ng c th chuyn ng t do v khng cn cp nht thng tin v v trcho MSC/VLR qun l v tr ny. C th ni vng nh v l v tr c th nht catrm di ng m mng cn thit nh tuyn cho mt cuc gi n n. vng nhv ny thng bo tm s c pht qung b tm thu bao di ng b gi. H thngc th nhn dng vng nh v bng cch s dng nhn dng vng nh v (LAI:Location Area Identity). Vng nh v c th bao gm mt s v thuc mt haynhiu BSC, nhng ch thuc mt MSC.

Hnh 1.6. Phn chia vng phc v MSC/VLR thnh cc vng nh v LA

4. Phn chia theo

Vng nh v c chia thnh mt s (hnh 1.6). l mt vng ph v tuync mng nhn dng bng nhn dng ton cu (CGI: Celi Global Identity). Trmdi ng nhn dng bng m nhn dng trm gc (BSIC: Base Station IdentityCode). Vng ph ca cc thng c m phng bng hnh lc gic tin chovic tnh ton thit k.

L A

L A

L A

L A

L AL AM S V L R

1 2 3 4 5

H n h 1 . 6 . P h n c h i a

V. Truyn sng trong thng tin di ng

1. nh hng ca truyn dn v tuyn

a. Suy hao ng truyn

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MSCMSC

LA2

LA3

LA6LA5LA4

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Kt hpB tch

sngPht hin

m

thng tin v tuyn im dn im do anten t cao, nn suy hao ng t lvi bnh phng khon cch R gia Anten tu v pht(R2). thng tin di ng Antendt gn mt t(khong 1,5m) nn suy hao t l vi ly tha n khong cch R giaAnten thu v pht (Rn), trong n>2. tnh ta suy hao ng ruyn ngi ta lpcc m hnh truyn sng khc nhau. Do c im truen sng khng n nh, nn ccm hnh ny du mang tnh thc nghim.

b. Pha inh

Cc MS thng hot ng mi trng c nhiu vt chn(i ni, ta nh...)gia n v BTS. iu ny dn n hin tng che ti lm gim cng in trngthu. Vy Fading l hin tng bin i cng tn hiu sng mang v tuyn siucao tn thu c do s thay i ca kh quyn, cc phn x ca t v nc trong

ng truyn sng. C hai loi Fading :

+ Fading phng ch yu tc ng n cc tuyn dung lng nh lm

suy gim n tn hiu sng mang i qua di tn s lm vic.

+ Fading la chn tn s c tc ng nhiu n cc tuyn dung lng cao.

Hai loi fading ny c th xut hin c lp vi nhau hoc xut hin ng thi.

2. Cc phng php phng nga suy hao

t c truyn dn tn hiu s tin cy cao m khng tng qu ln ccng sut pht v khong cch ti s dng ng knh cn p dng cc k thut ph

tr c th x l cc hiu ng phading nhiu tia nhanh. Nh chng ta bit, r rngthu phn tp l mt trong nhng k thut hiu qu nht chio mc ch ny. V vn nguyn l cng c th p dng phn ln cc k thut thu phn tp i vi v tuyn ding s. Nhng trong phn ny, ta ch cp n mt s loi quan trng ng k vih thng s.

Cc phng php kt hp phn tp ni chung c phn thnh hai loi:

Kt hp trc tch sng v sau tch sng:

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B tchsng

B tchsng

Kthp

Pht hinm

Hnh 1.8 :Kt hp sau tch sng.

Hnh1.7 :Kt hp phn tp trc tch sng.

Phng php kt hp phn tp trc tch sng i hi chc nng ng pha tnhiu . V th rt kh p dng phng php ny cho mi trng v tuyn di ng nim tn hiu thu thay i nhanh. Hn na phng php trn lc trc tch sng lmcho pha khng lin tc ti thi im chuyn mch nhnh. Phng php ny lm gimcht lng t s bit li. Mt khc phn tp sau tch sng yu cu cng c s b tchsng nh cc nhnh phn tp. Tuy nhin, tt c cc u ra b tch sng c cng phanh nhau. V th, qu trnh ng pha l khng cn thit i vi kt hp. Ngt qung

pha s khng xy ra khi la chn. iu c ngha l phng php phn tp sau tchsng l ph hp nht i vi h thng di ng mt t.

VI. Cc phng php a truy cp

1. Gii thiu chung

lm tng dung lng ca di v tuyn dng cho h thng thng tin t bo,ngi ta s dng cc k thut ghp knh. Hin nay c rt nhiu dng ghp knh

nhng c ba hnh thc thng dng nht l:- a truy nhp phn chia theo tn s (FDMA - Frequency Division Multiple

Access)

- a truy nhp phn chia theo thi gian (TDMA - Time Division MultipleAccess)

- a truy nhp phn chia theo m (CDMA - Code Division Multiple Access)

Lin quan n vic ghp knh l di thng m mi knh hoc mi mch chim

trong mt bng tn no . Di thng n gin ch l s chnh lch gia cc tn s

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cao nht v thp nht trong bng. Cng mt khi nim nh vy di thng ca knhc p dng theo quy m nh hn.

Trong mi h thng ghp knh trn u s dng thut ng a truy nhp, tc lcc knh v tuyn c nhiu thu bao dng chung ch khng phi l mi thu baoc gn mt tn s ring.

Sau y s i chi tit v ba k thut ghp knh.

2. Cc phng php a truy cp

a. a truy cp phn chia theo tn s (FDMA)

Cc h thng t bo hin ti ang s dng k thut ghp knh FDMA, chia tonb bng tn c phn phi cho mt nh khai thc mng t bo (25 MHz) thnh ccknh ri rc. V mi knh c di thng ( rng di) l 30 KHz, cho nn h thng ctt c 832 knh. Mi cuc m thoi cn s dng hai tn s, cho nn mi nh khaithc c 416 cp tn s kh dng, mi cp c th gn cho mt thu bao mng t bovo bt k lc no.

Hnh v trn minh ho k thut FDMA, c p dng cho h thng t boanalog Hoa K. Mi knh chim 30 kHz di thng v p ng cho mt cuc mthoi. Tn s ca mi knh tuy khc nhau nhng nhiu my v tuyn c th truy nhpc.

15

Thoianalog

30 KHzknh1

Thoianalo

g

30 KHz knh832

.

.

.

Hnh 1.9 : K thut FDMA


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b. a truy nhp phn chia theo thi gian

Vi TDMA mi knh v tuyn c chia thnh cc khe thi gian. Tng cuc

m thoi c bin i thnh tn hiu s m sau c gn cho mt trong nhngkhe thi gian ny. S lng khe trong mt knh c th thay i bi v n l mtnhim v ca thit k h thng. C t nht l hai khe thi gian cho mt knh, vthng th nhiu hn, iu c ngha l TDMA c kh nng phc v s lngkhch hng nhiu hn vi ln so vi k thut FDMA vi cng mt lng di thngnh vy.

TDMA l mt h thng phc tp hn FDMA, bi v ting ni phi c s ho

hoc m ho, sau c lu tr vo mt b nh m gn cho mt khe thi giantrng v cui cng mi pht i. Do vic truyn dn tn hiu l khng lin tc vtc truyn dn phi ln hn vi ln tc m ho. Ngoi ra, do c nhiu thng tinhn cha trong cng mt di thng nn tht b TDMA phi c s dng k thut

phc tp hn cn bng tn hiu thu nhm duy tr cht lng tn hiu.

Hnh v di y minh ho k thut TDMA, cc knh analog 30 kHz dng chomng t bo h tr c ba knh digital. Cc ng truyn m thanh analog ca micuc m thoi i qua b bin i A/D v sau chim mt khe thi gian trong knh

analog 30 kHz.

.

16

B biniA/D

B biniA/D

B biniA/D

B biniA/D

B biniA/D

B biniA/D

30 kHz knh

1

30 kHz knh832

.

.

.

.

.


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d. a truy nhp phn chia theo m

Trong k thut CDMA, tn hiu mang tin ( v d nh ting ni) c bin i

thnh tn hiu digital, sau c trn vi mt m ging nh m ngu nhin. Tnhiu tng cng, tc ting ni cng vi m gi ngu nhin, khi c pht trong mtdi tn rng nh mt k thut gi l tri ph.

Khng ging FDMA hay TDMA, truyn dn tri ph m CDMA s dng ihi cc knh c gii thng tng i rng (thng l 1,25 MHz). Tuy nhin theo tnhton l thuyt th CDMA c th cha c s thu bao gp 20 ln m FDMA c thc trong mt di thng tng cng nh nhau .

Hnh 1.11. a truy nhp phn chia theo m (CDMA)

Hnh v trn minh ho k thut CDMA. Di thng tng t 30 kHz ln 1,25MHz, nhng trong di thng ny by gi cn xp x 20 cuc m thoi. Mi ngthoi analog trc ht c bin i thnh digital nh b bin i A/D ng nh viTDMA. Tuy nhin sau thm mt bc na l chn mt m c bit qua mt b tom. Sau tn hiu c pht i, tri rng thm 1,25 MHz di thng ch khngchim mt khe thi gian ring trong di ny.

chi tit hn v CDMA, ta so snh n vi FDMA v TDMA nh sau:

3. So snh cc cng ngh FDMA, TDMA vi CDMA ng dng trong thng tin ding t bo

Trong FDMA mi mt khe tn s c dnh ring cho mt ngi s dng v

ngi ny s dng khe tn s ny sut qu trnh cuc gi . Trong s TDMA mingi dng c cp cho mt khe thi gian trong qu trnh gi. S lng ngi dngc quyt nh bi s lng cc khe thi gian hay tn s khc nhau c sn. Trong s

17

B biniA/D

Tom

B biniA/D

Tom

(1)

(20)

B bini

A/D

Tom

B biniA/D

Tom

(1)

(20)

1,25 MHzknh 1

1,25 MHzknh 20

Hnh 1.10 : K thut TDMA


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CDMA tt c cc ngi dng pht ng thi v trn mt tn s. Tn hiu cpht i chim ton b di thng ca h thng v cc dy m c s dng phnbit ngi s dng ny vi ngi s dng kia.

CDMA hn hn so vi cc k thut a truy nhp khc. N c th tnh cphng sai trong hm truyn ca knh gy ra bi b chn lc tn s. Cc my thuCDMA c thit k tn dng u im t c tnh nhiu ng lin quan nfading chn lc tn s v lm gim ti thiu nh hng ca chng n dung lngca h thng.

u im ch yu v dung lng ca CDMA c c trong mi trng v tuyna t bo. Trong thng tin di ng trc y mt trm gc cng sut ln c sdng ph sng mt vng rng ln. H thng ny b hn ch kht khe v mt bng

tn v khng th p ng cc dch v di ng. Trong h thng in thoi di ng tbo, my pht ca trm gc n l c thay th bi rt nhiu cc trm gc c cngsut nh, mi my pht ph sng cho mt vng c dng t ong, gi l mt t bo.Trong cc h thng FDMA hay TDMA mi t bo c chia cho mt phn t cady tn s c sn. Dy tn c dng trong mt t bo c th c s dng li trongt bo khc cch xa sao cho tn hiu trong hai t bo ny khng gy nhiu nnhau. S L t bo s dng ht ton b ph tn c sn c gi l cluster (cm).

Cc cluster c b tr nh hnh v sau:

Hnh 1.4. Cu trc c bn ca h thng t bo

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G C

DF

A

E

G

B

C

DF

A

E

G

B

C

DF

A

E

B

C

D

A

E

GB

C

DF

A

G

B

F

A

E

G

B

C

DF

A

E

C

F


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Trong h thng FM/FDMA hay TDMA/FDMA s lng cc knh trong mt t

bo t l nghch vi h s ti s dng tn s L, lin quan n s lng cc knh trndy tn xc nh, v mi t bo trong mt cluster ch c dnh cho 1/L phn ph tnsn c trong bng tn. Trong hnh v L=7.

Trong khi , CDMA c th ti s dng ton b bng tn vi tt c cc t bo.H s ti s dng trong h thng t bo CDMA do bng 1. iu ny khin chodung lng ca h thng c ci thin. rng dung lng c xc nh nh lmt s lng ti a nhng ngi s dng tch cc trong tt c cc t bo ch khng

phi l ch s lng ca nhng ngi dng trong dy tn hay trong mt t bo n v.Vic ci thin v mt dung lng tng th nh nh ngha ca h thng CDMA sovi h thng TDMA hay FDMA theo yu cu t 4 n 6 v so vi h thngFM/FDMA l h s khong 20.

Nhng tn hiu c bn ca ngi s dng khc ng thi trn cng bng tn sgy ra nhiu ng knh. Nhiu ng knh l mt tham s gii hn ca h thng vtuyn di ng. Phng php ti s dng tn s trong TDMA/FDMA v FM/FDMAgy ra nhiu ng knh v c cng mt di tn c s dng li mt t bo khc.

Vic s dng cc cluster 7 t bo trong nhiu h thng v tuyn di ng l khng trnh hin tng nhiu ng knh. C th tng L ln hn 7 gim nhiu ngknh nhng s lm gim s lng cc knh trong mt t bo, do vy s lm gimdung lng ca h thng. Tng t nu gi nguyn h s ti s dng l 7 v chia t

bo thnh nhng vng nh hn. Mi t bo c chia thnh ba hoc su vng nh ss dng ba hoc su anten nh hng tng ng ti trm gc phc v cho c thu ln

pht. Mi vng nh ny s dng mt di tn ring, khc vi di tn ca cc vng kia.Th d, nu mt t bo c chia thnh ba vng nh th nhiu thu c trn antennh hng ch sp x mt phn ba ca nhiu thu c trn anten v hng t titrm gc. S dng t bo chia nh thnh ba vng th s lng ngi dng trong mtt bo c th tng thm gp ba ln trong cng mt cluster.

Mt vn quan trng khc trong vic tng dung lng ca h thng l tnh tchcc ca thoi. Trong mt cuc thoi gia hai ngi, mi ngi ch ni khong 35%n 40% thi gian v nghe ht thi gian cn li. Trong h thng CDMA tt c nhngngi s dng cng chia s mt knh v tuyn. Khi nhng ngi s dng trn knh

ang lin lc khng ni th nhng ngi s dng ang m thoi khc s ch chu nhhng rt nh ca nhiu. Do vy vic gim st tnh tch cc ca ting ni lm gim

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nhiu a truy nhp n 65%. iu ny dn n vic tng dung lng ca h thng lnh s 2,5.

Trong a truy nhp FDMA hoc TDMA vic ngi s dng c phn chia tn

s hoc thi gian trong thi gian din ra cuc gi v h thng cp li hai ti nguynny cho hai ngi khc trong khong thi gian rt ngn khi knh n nh yn lng lkhng thc t v iu ny yu cu phi chuyn mch rt nhanh gia nhng ngi sdng khc nhau. Trong FDMA v TDMA vic t chc tn s l yu cu kh khn vn kim sot nhiu ng knh. Trong h thng CDMA ch c mt knh chung nnkhng cn thc hin t chc tn s.

Trong FDMA v TDMA, khi my di ng ra khi vng ph sng ca t botrong qu trnh m thoi th tn hiu thu c s b yu i v trm gc s yu cu

chuyn giao (handover). H thng s chuyn mch sang mt knh mi khi cuc gitip tc. Trong CDMA cc t bo khc nhau, khc nhau ch s dng cc dy mkhc nhau nhng ging nhau l u s dng cng ph tn. Do khng cn phithc hin handover t tn s ny qua tn s khc. Chuyn giao nh vy c gi lchuyn giao mm (soft handover).

Trong h thng CDMA khng c mt gii hn r rng v s lng ngi dngnh trong FDMA v TDMA. Tuy vy cht lng hot ng ca h thng i vi tt

c nhng ngi s dng gim t nhiu khi s lng ngi s dng cng lin lc tngln. Khi s ngi s dng tng ln n mc no th s khin cho nhiu c thlm cho ting ni tr nn kh hiu v gy mt n nh h thng. Tuy nhin trongCDMA ta quan tm n iu kin phong to mm, c th gii to c tri viiu kin phong to cng nh trong TDMA v FDMA khi m tt c cc knh u

b chim.

Vn s dng li tn s CDMA cng c bit so vi FDMA,TDMA. Cc hthng thng tin di ng bng hp (FDMA, TDMA) khng th s dng li tn s

ngay cell lin k v nhiu, v vy phi c quy hoch tn s khi thit k h thng, v dp ng s tng dung lng th phi thay i quy hoch tn s. Trong CDMA, dodng chung mt di tn nn c th thm vo mt vi cuc gi m cht lng chungc th gim cht t. Bng s tr gi bng vic tng s bit li, nhng mng di ngCDMA vn c th tng thm cuc gi khi nhu cu cp bch m khng dn n tcnghn nh mng di ng FDMA hay TDMA. Khi s thu trong bao cell tng ln qumc cho php, mng di ng CDMA s chuyn giao mm v iu khin cng sutgim, lm cho cell nh i, chuyn cc thu bao vng bin sang cc thu bao link. Kh nng cn bng ti ny c gi l dung lng mm (Soft Capacity). Ni mt

cch khc, mng di ng CDMA khng cn k hoch s dng li tn s, vic quyhoch v dung lng v vng ph sng ca mng thay th quy hoch tn s.

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H thng CDMA cng c mt vi nhc im. Hai nhc im ni bt l: hiung t nhiu v hiu ng xa gn. Hiu ng t nhiu do cc dy m khng trc giaogy ra. Trong h thng v tuyn di ng cc my di ng truyn tin c lp vi nhau,tn hiu ca chng khng n trm gc mt cch cng lc. Do tr thi gian ca chng

lphn b ngu nhin nn s tng quan cho gia cc tn hiu thu c t nhngngi s dng l khc khng. nhn c nhiu c mc thp tt c tn hiu phi ctng quan cho nh v mi tr thi gian tng i. Tng quan cho gia cc k tc c bng vic thit k mt tp cc dy trc giao. Tuy nhin khng c mt tp dym no c bit l hon ton trc giao khi c dng trong h thng khng ng

b. Cc thnh phn khng trc giao ca tn hiu ca nhng ngi s dng khc sxut hin nh l nhiu trong tn hiu iu ch mong mun. Nu s dng my thu c

b lc thch ng trong h thng nh vy th s lng ca ngi s dng b hn ch

bi nhiu gy ra bi nhng ngi s dng khc. iu ny khc vi trong cc hthng TDMA v FDMA, trong cc h thng ny tnh cht trc giao ca tn hiu thuc b duy tr bng vic chn lc v ng b chnh xc.

Hn ch chnh ca CDMA l hiu ng xa gn. Hin tng ny xut hin khi mttn hiu yu t mt my di ng xa thu c ti trm gc b chn p bi tn hiumnh t ngun nhiu . Tn hiu nhiu vi cng sut ln hn n ln cng sut tnhiu mong mun s tc dng gn nh l n tn hiu nhiu c cng sut bng cng sutca tn hiu. khc phc hiu ng xa gn trong hu ht cc ng dng CDMA ngi

ta s dng cc s iu khin cng sut. Trong h thng t bo iu khin cngsut c thc hin bi cc trm gc, cc trm ny nh k ra lnh cc my di ngiu chnh cng sut my pht sao cho tt c cc tn hiu thu c ti trm gc vimc cng sut l nh nhau.

CHNG 2 : MT S H THNG THNG TIN DI NG

I. H thng thng tin di ng GSM

1. M uGSM (Global System for Mobile communication) l h thng thng tin di ng s

ton cu di tn 900Mhz, 1800Mhz, v 1900Mhz c tiu chun vin thng chu u(ETSI) quy nh. GSM l mt t hp cc gii php bao gm h thng chuyn mchknh, h thng chuyn mch gi, nt iu khin v tuyn v cc trm pht gc cng vic s d liu mng, cc dch v c bn v cc nt qun l mng. D dng vn hnh bodng (O&M) c tch hp trng mng thng minh (IN/GSM). GSM cng lm vicvi cc k thut IP v k thut gi l mt nn tng chnh hng ti h thng vin thngdi ng ph bin (UMTS) trong di ng th h th 3 v hn na. Lu ng (Roaming)quc t cho php thu bao chuyn ng ton b vng ph sng ca GSM l hon ton

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t ng. H thng s t ng cp nht thng tin v v tr thu bao. GSM cung cp mt stnh nng nh thoi, thng tin s liu tc cao, Fax v dch v nhn tin ngn.

2. Cu trc v thnh phn ca mng GSM

a. Cu trc tng thMng thng tin di ng thc cht l mng di ng mt t cng cng PLMN (Public

Land Mobile Network). Mt cch tng qut th mng PLMN hp tc vi mng c nh thit lp cuc gi, qua cc giao din PLMN tip xc vi bn ngoi, bao gm cc mngngoi, nh khai thc v ngi s dng.

Nh vy mt h thng GSM c chia thnh nhiu h thng con nh sau:

- Phn h chuyn mch NSS (Network Switching Subsystem).

- Phn h trm gc BSS (Base Station Subsystem).

- Phn h bo dng v khai thc OSS (Operation Subsystem).

- Trm gc MS (Mobile Station).b. Cc thnh phn ca mng

22

Hnh 2.1 : Cu trc tng th GSM

OSS

NSS

AUC

HLR

MSC

EIRVLR

ISDN

PSPDN

CSPDN

PSTN

PLMN

BSS

BSC

BTS

MS

..............:Truyn bo hiu

: Truyn lu lng

Hnh 2.2 : Cc thnh phn mng GSM


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Cc k hiu :

AUC Trung tm nhn thc OSS Trung tm khai thc v bo dng

VLR B ghi nh v tm tr PSPDN Mng chuyn mch cng cng theo gi

BTS Trm thu pht gc PSTNMng in thoi cng cng c chuynmch

NSS H thng con chuyn mch CSPDNMng s liu cng cng chuyn mch theo

mch

ISDN Mng lin kt a dch v PLMN Mng di ng cng cng mt t

HLR B ghi nh v thng tr MSCTrung tm chuyn mch cc dch

v di ng

EIR B ghi nhn dng thit b MS Trm di ng

BSC B iu khin trm gc BSS H thng con trm gc

Phn h chuyn mch NSS

Phn h chuyn mch bao gm cc chc nng chuyn mch chnh ca GSMcng nh cc c s d liu cn thit cho s liu thu bao v qun l di ng ca thu

bao. Chc nng chnh ca NSS l qun l thng tin gia nhng ngi s dng mng

GSM vi nhau v vi mng khc, phn h NSS bao gm cc thit b MSC, VLR,HLR, EIR, AUC nh c ni di y:

- Tng i MSC

MSC (Mobile Switching Center) L giao din gia GSM v PSTN, n c trchnhim kt ni v gim st cuc gi n MS v t MS i. C nhiu chc nng cthc hin trong MSC, v d lp m xc nhn.

MSC c giao din vi BSS pha MS v c giao din vi cc mng ngoi. Mt

MSC cng lm nhim v phi ghp thch ng vi mng ngoi bo m thng tin gia

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thu bao di ng v thu bao c nh. MSC thng l mt tng i ln thch ng vivng th mt triu dn c.

kt ni MSC vi cc mng khc cn phi thch ng cc c im truyn dn

PLMN vi cc mng . Cc thch ng ny gi l cc chc nng tng tc IWF(Internet Working Funtions). m trch IWF l thit b thch ng th tc v truyndn. IWF cho php PLMN kt ni vi cc mng PSTN, ISDN, PSPDN, CSPDN.IWF c th c thc hin kt hp trong MSC hay c th c thc hin thit bring.

- B ng k nh v thng tr HLR

Trong GSM mi mt hot ng c lu gi s liu cng nhng thng tin v tt

c thu bao. Ph thuc vo PLMN chi tit ny. Nhng d liu lu gi ny c thc thc hin trn mt hoc nhiu HLR. Nhng thng tin c lu gi trong cc dliu l s ch nh ca thu bao v phc v yu cu.

Bt k MS u, HLR u lu d mi thng tin lin quan n vic cung cp ccdch v vin thng k c v tr hin thi ca MS. HLR thng l mt my tnh ngring c kh nng qun l hng trm ngn thu bao, nhng khng c kh nngchuyn mch. Mt chc nng na ca HLR l nhn dng thng tin do AUC cung cp(s liu bo mt v tnh hp php ca thu bao).

- B ng k nh v tm tr VLR

VLR c thc hin trong cng mt h chuyn mch MSC, y tc l bngMSC/VLR. VLR cha ng nhng thng tin tm thi v thu bao di ng c mttrong vng phc v MSC/VLR xc nh. VLR l mt c s d liu c ni vi mthay nhiu MSC. Cc s liu nh v thu bao MS lu gi trong VLR chnh xc hn sliu tng ng trong HLR.Chc nng ca VLR thng c lin kt vi chc nngMSC. MSC/VLR thc hin chuyn mch cc cuc gi v trm nn im iu khin

cp nht v tr v chuyn giao MSC ch yu chu trch nhim cho thit lp cucgi (bao gm c th tc nhn thc), iu khin cuc gi v tnh cc.

Cc chc nng VLR vi cc mng chu trch nhim lu gi v cp nht s liuthu bao (xem b ghi nh v tm tr). MSC/VLR coi tt c cc thu bao tm trMSC cng (GMSC) ni PLMN vi cc mng khc. y l im m cc cuc gi ncc thu bao di ng i vo mng PLMN. GMSC c phng tin hi, ngha l GMSCc cc chc nng nhn thng tin t HLR v v tr hin thi ca thu bao. N cng

c cc chc nng nh tuyn li cuc gi n trm di ng theo thng tin nhn ct vic hi ni trn.

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- Tng i GMSC

Tng i GMSC l mt MSC cng (Gate MSC). Nu mt ngi no mngc nh PSTN mun thc hin mt cuc gi n mt thu bao GSM. Tng i

PSTN s ni cuc gi ny n mt MSC c trang b mt chc nng c gi l chcnng cng. Tng i ny c gi l tng i cng GMSC. GMSC s phi tm ra vtr ca MS cn tm bng cch hi HLR ni MS ng k. HLR tr li vng MSC hinthi. Lc ny MSC nh tuyn li cuc gi n MSC cn thit v VLR y s bitchi tit v v tr MS.

mt mng GSM tt c cc cuc gi kt ni di ng u c nh tuyn nGMSC. GMSC c chc nng hi nh tuyn cuc gi.

OSTC: Mch u cui tng i ST: u cui bo hiu knh chung s 7

Hnh 2.3. cu trc ca MSC/VLR

- Trung tm nhn thc AUC

Vi l do an ton v cht lng, ngn ng, d liu v bo hiu s c m ho

v c nhp di dng k hiu u vo, cha kho b mt c ct gi trong AUCv c s dng trong MS. Ban u AUC s c thc hin bng mt hoc nhiuthng tin ring l, c ni n HLR. AUC ch yu cha mt s cc my tnh cnhn. AUC c coi nh mt thit b u vo/ra (I/O), lc u n c ni bng lnhchun.

Chc nng AUC l cung cp cho HLR cc thng s nhn thc v kho mt m s dng cho bo mt.

- B ghi nhn thc thit b EIR

25

Chuynmch nhm

APT 21008/R85

H thng iu khin

APZ212

ETC

ST

ST

BSC

HLRETC

PSTNTrung k


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Trong GSM c s khc bit gia b nhn dng m ho v thit b di ng. Tathy AUC s c nhp v di dng k hiu khi nhp vo. Cc thit b di ng ckim tra trong EIR. ngn chn s nh cp v nhng dng khng c ph chunm MS s dng. EIR c ni vi MSC qua mt ng bo hiu. N cho php MSCkim tra s hp l ca thit b. Bng cch ny c th cm MS c dng khng c

ph chun. EIR c chc nng kim tra tnh hp l ca ME thng qua s liu nhndng di ng quc t (IMEI-International Mobile Equipment Identity) v cha cc sliu v phn cng ca thit b. ME thuc mt trong ba danh sch sau:

- Nu ME thuc danh sch trng (White List) th n c quyn truy nhp v sdng cc dch v ng k.

- Nu ME thuc danh sch xm (Gray List) tc l c nghi vn v cn kim tra.

- Nu ME thuc danh sch en (Black List) tc l b cm

khng cho truy nhp vo mng.

Cn nh rng vic nhn thc ng k thu bao bng cc thng s t AUC

- Mng bo hiu knh chung s 7 (CCS7).

Nh khai thc GSM c th c mng bo hiu CCS7 ring hay chung ph thucvo quy nh ca tng nc. Nu nh khai thc c mng bo hiu ny ring th cc

im chuyn bo hiu SPT (Signalling Transfer Point) c th l mt b phn ca NSSv c th c thc hin cc im nt ring hay kt hp trong cng mt MSC tuthuc vo iu kin kinh t. Nh khai thc GSM c th dng mng ring nhtuyn cc cuc gi ra n im gn nht trc khi s dng mng c nh. Lc nycc tng i qu giang TE (Transit Exchange) c th s l mt b phn ca mngGSM v c th thc hin nh mt nt ng ring hay kt hp vi MSC.

Phn h trm gc BSS

BSS giao din trc tip vi cc trm di ng MS thng qua giao din v tuynnn n bao gm cc thit b pht v thu ng v tuyn cng vi cc thit b qun lcc chc nng ny. Mt khc BSS thc hin giao din vi cc tng i NSS. Tm liBSS thc hin u ni cc MS vi tng i, tc l kt ni thu bao di ng MS vinhng ngi s dng vin thng khc. Do vy, BSS phi phi ghp vi NSS bngcc thit b BSC. Ngoi ra do BSS cng cn phi c iu khin nn n c uni vi SS. BSS bao gm hai thit b: BTS giao tip vi MS v BSC giao tip viMSC.

- i v tuyn gc BTS

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BTS gm tt c cc thit b giao tip truyn dn v v tuyn cn thit trm vtuyn (h thng anten, b khuch i tn v cc thit b s cn thit) d trm ph mthay nhiu . Nhim v chc nng ch yu ca n l truyn dn v tuyn. V mt vtl BTS phi c t v tr gn anten t c s bao ph v tuyn cn thit.BTS nh l mt modem v tuyn phc tp. Khi chuyn i m v tc TRA lquan trng nht ca BTS. TRA thc hin m ho v gii m thoi rt c th chothng tin di ng s Cellular. TRAU cng thc hin thch ng tc truyn s liu.TRAU c th t cch xa BTS chng hn gia BSC v MSC.

Mi BTS lm vic tp hp cc knh v tuyn khc vi knh v tuyn lncn chng nhiu giao thoa ng knh.

* Cc chc nng tim nng chung(biu th cc tim nng chung ca TRX c

s dng cho lu thng vi cc MS thuc v mt ) bao gm:

Qung b thng tin ca h thng: BSC xc nh cc thng bo v thng tin cah thng c lu gi v nh k qung b ti h thng con thu pht TRX knhiu khin qung b BCCH. Nu my thu-pht TRX c dnh cho BCCH xy ras c, s c c bo co n BSC, BSC gi thng tin BCCH n mt TRX mic chn chu trch nhim knh BCCH.

Tm gi: Cc nhn dng trm di ng c xc nh t BSC c gi i knh

BCCH.

Yu cu knh t MS: TRX pht hin cc yu cu t cc MS v bo co chng viBSC. BSC n nh mt knh DCCH cho bo hiu gia MSC v MS. DCCH sau MS c n nh mt TCH cho thng tin ting v s liu.

* Cc chc nng tim nng ring (biu th tt c cc chc nng c s dngcho thng tin vi cc MS thuc v phn TRX phc v mt ) bao gm:

a knh vo hot ng: BSC ra lnh cho TRX a knh vo hot ng mttim nng knh ring s dng bng mt knh logic lin kt ca mnh. Khi mtknh c n nh BSC thng bo TRX v cc thng s nh kiu knh, m knh v.v.

Hu hot ng knh: TRX hu hot ng knh.

Khi u mt m: Khi u mt m c TRX thc hin trn c s kho mtm. Kho mt m c tnh ton th tc nhn thc t thng s, RAND v khoring ca thu bao.

Pht hin chuyn giao: Khi mt knh c thit lp cho chuyn giao, TRXnghe knh thm nhp ngu nhin.

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* Cc chc nng knh mt t(l nhm cc chc nng thc hin, chuyn i vthch ng s liu) bao gm:

Chuyn i m ting: Chuyn i m ting c thc hin gia 64Kb/s v

13Kb/s. Chc nng ny c t xa trong TRA BSC.iu khin trong bng ca TRAU xa: Thng tin iu khin c b xung n

s liu v ting dn n tng tc knh v 16Kb/s.

Bn knh thng tin c ghp chung vo mt knh 16Kb/s gia BSC v TRS.

* M ho v ghp knh (l chc nng lp khun dng thng tin cc knh vtl) bao gm:

Ghp knh ng v tuyn: Cc knh logic c ghp chung cc knh vt l.

M ho v ghp xen knh: Lung bit c lp khun dng cho tng khe thigian knh vt l.

Mt m/ gii mt m: Ting ni c mt m v gii mt m bng kho mt m.

Mt m v gii mt m c thc hin cc bt mang thng tin quan trng.Kho mt m c to ra AC v np vo TRS.S ngu nhin (RAND) c gin MS.

* iu khin h thng con v tuyn (m bo iu khin cc tim nng vtuyn).

o cht lng: Cc php o cht lng v cng tn hiu c thc hin tt c cc knh ring hot ng trn ng ln (MS n BTS). Cc php o ny cthc hin trong thi gian hot ng ca knh. Cc kt qu o t MS v cht lngng xung (BTS n MS), cng tn hiu v cc mc tn hiu ca BTS xungquanh c gi i v x l BTS.

ng b thi gian: Mt tn hiu c pht i t TRX n MS nh trc thigian truyn dn n TRX b tr thi gian tr gy ra do truyn sng. TRX lin tcgim st v cp nht ng b thi gian. Cng vi s liu o cho ng ln, ng bthi gian hin thi cng c bo co cho BSC.

iu khin cng sut ca TRX v MS: Cng sut ca TRX v MS c iukhin t BSC gim ti thiu mc cng sut pht gim nhiu ng knh.

Pht: Pht v tuyn bao gm nhy tn. Nhy tn c thc hin bng chuyn

mch bng tn c s vi cc my pht khc nhau cho tng tn s.Thu tn hiu v tuyn bao gm c cn bng v phn tp.

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S c ng truyn v tuyn: S c c pht hin v bo co cho BSC.

* iu khin TRX chc nng ny gm cc lnh:

LAPD: Kt ni ng bo hiu gia BSC v TRX.

Bo co li: Pht hin v bo co li thng bo t BSC.

S c ni thng: TRX pht hin ng ni thng no b gin on ng vtuyn hay khng.

* ng b (l khi con ng b TRX)

Chun tn s: Thng tin nh thi c ly ra t cc ng PCM t BSC.

S khung: C th t v c s khung t b m s khung.

* Khi ng h thng v np phn mm bao gm:

Khi ng h thng: Khi u mt trm hay mt phn trm bao gm c npphn mm cho cc b x l c khi ng.

Khi ng li: a mt b phn ca tht b v mt trng thi nht nh.

* Lp cu hnh (l lp ra cc thng s khc nhau v t hp cc knh khc nhau TRX cho lu lng hoc khai thc) bao gm:

Pht v tuyn: Thit lp tn s v cng sut ra cho cc my pht.Thu v tuyn: Thit lp tn s cho cc my thu k c my thu nhy tn v my

thu khng nhy tn.

iu khin v tuyn: nh ngha vic sp xp thng tin h thng cc khe thigian.

Kt hp knh logic: Sp xp cc knh logic cc knh vt l.

n nh nhn dng . Thit lp m mu trm c s v m mu trm PLMN.

* iu khin bo dng ti ch:

Chc nng ny c s dng khng cn ni vi BSC. BTS thit b ny ch ccc ch th trng thi v cnh bo cung cp tng quan. Tt c cc ch th trnh bychi tit v iu khin cng nhn c thc hin u cui bo dng ti ch (LMT).

* Qun l ng bo hiu

TRX qun l ng bo hu gia BSC v MS.

* Gim st v kim tra chc nng c thc hin theo hai cch sau:

Cc kim tra lp t trong c thc hin khi khai thc bnh thng.

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Cc kim tra c thc hin cc lnh c bit hay cc iu khin c bit.

- i iu khin trm gc BSC

BSC l khi chc nng iu khin v gim st cc BTS v cc lin lc v tuyn

trong h thng. BSC iu khin cng sut, BSC qun l giao din v tuyn thng quacc lnh iu khin ca BTS v MS. l cc lnh n nh, gii phng knh v tuynv qun l chuyn giao. BSC c ni vi BTS mt pha v MSC pha SS. BSCl mt tng i nh c kh nng tnh ton nht nh. Vai tr ch yu ca BSC l qunl cc knh v tuyn v qun l chuyn giao. Mt BSC c th qun l c hngchc BTS to thnh mt trm gc. Mt tp hp cc trm gc gi l phn h trm gc.Giao din Abis c qui nh gia BSC vi MSC. Sau giao din Abis cng cqui nh gia BSC v BTS.

Nhim v quan trng nht ca BSC l m bo kh nng s dng tim nng vtuyn cao nht. iu by c thc hin khi BSC iu khin mt phn chnh camng v tuyn. Ch c th san bng c s mt cn i ca ti lng khi s thu

bao ln.

V tr ti u ca BSC ng truyn dn gia MSC v trm v tuyn gc thayi tu theo cch thc hin. Gii php hp dn nht trong nhiu trng hp F tMSC v BSC cng mt ch. iu ny ph hp vi s phn tn MSC gim ti thiu

gi truyn dn PSTN. Trong nhiu trng hp kch thc kinh t nht ca mtMSC bng kch thc ca mt BSC ph hp.

Vic t cng mt ch cng gim cc thm nhp truyn dn v gim gi thnhtruyn dn.

Mt khc mt s v tr thch hp cho BSC nhng li khng thch hp cho MSCdo thiu thu bao. Khi c th t mt BSC xa v khi s lng thu bao nmc c th, c th nng cp i bng cch c c chc nng MSC.

Phng n ny c th gim gi thnh hn na khi c th thc hin BSC v MSCtrn cng mt phn cng.

Tm li BSC c n nh cc trch nhim chc nng chnh sau:

- iu khin cuc ni ca trm di ng.

- Qun l mng v tuyn.

- Qun l trm v tuyn gc.

- Chuyn i m v thch ng tc .- Tp trung lu lng.

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-Qun l truyn dn n BTS

Trm di ng MS

Cc kiu trm di ng v cng sut ca chng

- My lp trn t.

- L mt thit b lp trn t v thit b ny anten lp pha ngoi t.

- Cc my xch tay.

L mt thit b c th xch tay v thit b ny v mt vt l anten khng gnvi phn thit b cha kt cui di ng. Cc my ny c th thc hin tt c cc mccng sut cn thit trong h thng.

- Cc my cm tay.

L mt thit b cm tay v y anten c th cm vi phn thit b cha kt cuidi ng. Cc my cm tay c thit k ngi s dng cm tay c d dng, ccmy cm tay c th c lp trn t v thng gm mt my cm tay tiu chuncm vo mt giao tip t. Giao tip ny cho php np c quy v ni ghp vianten lp bn ngoi.

GSM, MS c phn thnh nm loi theo cng sut nh danh nh nh sau:

Loi 1 20w Lp trn xe v xch tay

Loi 2 8w Lp trn xe v xch tay

Loi 3 5w Cm tay

Loi 4 2w Cm tay

Loi 5 0,8w Cm tay

Cc my di ng phi c kh nng gim c cng sut ra ca my pht minc 2dB theo lnh t trm gc.

Modul nhn dng thu bao SIM (Subscriber Identity Module)SIM chnh l mt b phn ca qun l thu bao

SIM cha chc nng bo mt v nhn thc thu bao

SIM l mt modul tho rt cm v mi khi s dng.

C hai phng n c a ra:

* SIM card IC

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L mt modul c mt giao tip vi bn ngoi theo tiu chun ISO v cc cardIC. SIM c th l mt b phn ca card a dch v, trong vin thng di ng GSMl mt trong cc ng dng.

* SIM dng cm.L mt modul ring hon ton c tiu chun ho trong h thng GSM. N d

inh lp t bn c nh ME (l my di ng khng c SIM).

SM s m bo cc chc nng sau nu n nm trong khai thc ca mngGSM:

. Lu gi thng tin bo mt lin quan n thu bao v thc hin cc c ch nhnthc v to kha mt m.

. Khai thc s nhn dng c nhn PIN ca ngi s dng (nu cn c PIN) vqun l.

.Qun l thng tin lin quan n thu bao di ng ch c th thc hin khaithc mng GSM khi SIM co mt s IMSI ng.

SIM phi c kh nng x l mt s nhn dng c nhn PIN, thm ch c khikhng bao gi s dng n. PIN bao gm 4 n 8 ch s. Mt PIN ban u c np

bi b hot ng dch v thi im ng k. Sau ngi s dng c th thay i

PIN cng nh di ca PIN. Ngi s dng c th quyt nh c s dng chcnng PN hay khng bng mt chc nng SIM-ME c gi l chc nng cm PIN.Vic cm hay gi nguyn cho n khi ngi s dng cho php kim tra li PIN.

Nhn vin c php ca nh khai thc c th chn chc nng cm PIN khing k thu bao, ngha l thu bao khi b chn chc nng cm PIN phi s dngPIN. Nu a PIN sai, ngi s dng nhn c mt ch th. Sau khi a vo ba lnsai lin tip SIM b chn, thm ch c khi rt SIM ra hay tt MS. Vic chn SIM t

n vo trng thi cm cc khai thc mng GSM. c s iu khin ca kho giito chn c nhn c th gii to chn.

Kho gii m chn c nhn l s c 8 ch s. Nu a vo ch s sai ngi sdng nhn c ch th. Sau 10 ln lin tip a vo sai, SIM b chn ngay c khi rt SIM ra hay tt MS.

SIM phi c mt b nh khng mt thng tin cho mt s khi thng tin nh:

. S seri

. Trng thi SIM

. IMSI

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. Kho mt m

. S trnh t kho mt m

. Loi iu khin thm nhp thu bao

. PIN

Hot ng ca MS

Anten ca MS c ni vi b thu pht qua mt b ghp i cho php thu phtcng lc bi mt anten. Tn hiu nhn c b thu ca MS s c chuyn i t

bng VHF (cao tn) 850 MHz thnh bng IF (trung tn) qua b tng hp tn s. Tnhiu IF c a qua b lc thng qua di SAW vi bng 1,25 MHz v chuyn ithnh tn hiu s qua b ADC (bin i tng t thnh s), tip tc tn hiu c gi

n bn b lin quan. Mt b tm kim cung cp ng truyn dn cho ba b thus liu. S liu t ba b thu s liu c t hp tc ln nht xc nh t l tnhiu trn nhiu. u ra ca b t hp vi cc tc khc nhau ln nht c chuynn b gii m ly ra mt tc c chn vo t cc trnh t tn hiu c thp trc v u ra c gii m nh b gii m chun ho hng i, s dngthut ton Vitebi. Bt gii m c x l bi b m ho ting.

Ngc li ting ni t MS truyn ti BTS phi qua b m ho ting ni s v

c m ho theo sng mang. Sau n c chuyn thnh RF v a qua b tnghp tn s sp xp tn hiu theo tn s ra ring. Cc tn hiu ny c khuych iti mc u ra cui cng v chuyn ti anten qua b ghp ng.

Tm li MS c ba chc nng:

- Thit b u cui: thc hin cc dch v ca ngi s dng (thoi, fax,s liu.)

- Kt cui di ng: thc hin truyn dn giao din v tuyn v mng.

- Thch ng u cui: B thch ng u cui trong MS c vai tr ca ni thngthit b u cui vi kt cui di ng. Khi lp t cc thit b u cui trong mitrng di ng MS c b thch ng u cui tun theo tiu chun SDN. Cn thit bu cui th c giao din vi modem.

Cc tnh nng ca my di ng

Tnh nng ca my di ng c hiu nh mt b phn ca thit b hay chcnng lin quan trc tip n s vn hnh ca MS. Cc tnh nng ny c phnthnh: bt buc v tu chn. Cc tnh nng ny c nh sn sut m bo s khngmu thun vi giao tip v tuyn, cng nh khng gy nhiu n mng hoc MS

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khc hay bn thn MS ca mnh. Do vy c s phi hp iu khin tp hp ti thiucc tnh nng.

* Cc tnh nng c bn ca MS:

. Hin th s b gi (bt buc)

. Hin th cc tn hiu trong qu trnh cuc gi (bt buc)

. Ch th quc gia/ mng PLMN (bt buc)

. Chn quc gia/ mng PLMN (bt buc)

. Qun l nhn dng ng k thu bao

. Hin th PN khng nng lc (bt buc)

. Nhn dng thit b my thng tin di ng quc t IMSI (btbuc)

. Ch th v xc nhn bn tin ngn

. Ch th thng bo ngn b trn

. Giao tip DTE/DCE

. Giao tip u cui SDN `S`

. Giao tip tng t

. Chc nng thm nhp quc t

. Chuyn mch bt/ tt

. Ch th nghip v (bt buc)

* Cc tnh nng ph:

. Ch th tnh cc

. iu khin cc dch v ph

* Cc tnh nng b sung:

. Quay s rt gn

. Gi s thoi c nh

. Lp li s thoi

. khai thc khng nhc my

. Cm cuc gi ra. ch th cht lng thu

. T kim tra (bt buc)

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. My o n v tnh cc cuc gi

. My di ng nhiu ngi s dng

Phn h khai thc v bo dng OSS

i vi s qun l h thng GSM, OSS ng h s hot ng theo cc hnh thchot ng sau:

- S qun l thu bao di ng

- S qun l mng cellular

- iu khin chung

H thng OSS c ni n tt c cc thit b h thng chuyn mch v ni

n BSC. OSS thc hin ba chc nng chnh l: Khai thc v bo dng mng, qunl thu bao v tnh cc, qun l thit b di ng.

- Chc nng khai thc v bo dng mng

Khai thc: L thot ng cho php nh khai thc mng theo di hnh vi camng nh ti ca h thng, mc chn, s lng chuyn giao gia hai cell.v.v..

Nh vy nh khai thc c th gim st c ton b cht lng dch v m h cungcp cho khch hng v kp thi nng cp. Khai thc cn bao gm vic thay i cu

hnh gim nhng vn xut hin thi im hin thi, chun b tng lulng trong tng lai v m rng vng ph sng.

Bo dng: C nhim v pht hin, nh v v sa cha cc s c v hng hc,n c mt s quan h vi khai thc. Bo dng bao gm cc hot ng ti hintrng nhm thay th cc thit b c s c, cng nh vic s dng cc phn mm iukhin t xa.

- Chc nng qun l di ng

Bao gm cc hot ng qun l ng k thu bao. Nhim v u tin l nhp vxo thu bao khi mng. ng k thu bao cng c th rt phc tp, bao gm nhiudch v v cc tnh nng b xung. Khi HLR, SM-Card ng vai tr nh mt b

phn qun l thu bao.

- Chc nng qun l thit b di ng

Qun l thit b di ng c thc hin bi b ng k nhn dng thit b EIR(Equipment Indentity Rergister). R lu gi tt c cc d liu lin quan n trm di

ng MS. EIR c ni n MSC qua ng bo hiu kim tra tnh hp l cathit b, GSM, EIR c coi nh thuc h thng NSS.

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c. Cu trc a l ca mng

Mi mng in thoi cn mt cu trc a l nht nh nh tuyn cc cucgi vo n tng i cn thit v cui cng n thu bao b gi. Trong mt mng di

ng, cu trc a l ny rt quan trng do tnh lu thng ca cc thu bao trongmng. Vi GSM cu trc a l c phn thnh cc vng nh di y:

- Vng mng

Cc ng truyn gia mng GSM/PLMN v mng PSTN/ISDN hay cc mngPLMN khc. Tt c cc cuc gi vo GSM/PLMN s c nh tuyn qua GMSC.GMSC lm vic nh mt i trung k vo cho GSM/PLMN. Mt vng mngGSM/PLMN c chia thnh mt hay nhiu vng phc v MSC/VLR.

- Vng phc v MSCVng MSC/VLR l b phn ca mng c mt MSC qun l nh tuyn

mt cuc gi n mt thu bao di ng, ng truyn qua mng s c ni nMSC vng phc v MSC/VLR ni thu bao ang . Vng phc v l mt b phnca mng c nh ngha nh l mt vng m c th t n mt trm di ngnh vic trm ny c ghi li mt b ghi nh v VLR khch. Mi vng phc vMSC/VLR c chia thnh mt s vng nh v.

- Vng nh v LA (Lication Area)Vng nh v l mt phn ca vng phc v MSC/VLR, m trm di ng

c th chuyn ng t do m khng cn cp nht thng tin v v tr cho tng i MSCiu khin vng nh v ny.

Vng nh v ny l vng m mt thng bo tm gi s c pht qung b tm thu bao di ng b gi. Vng nh v c th c mt s cell v ph thuc vomt hay vi BSC nhng n ch ph thuc MSC/VLR.

- (Cell)

l n v nh nht ca mng, l mt vng bao ph v tuyn c mng nhndng bng nhn dng ton cu (CG Cell Global dentity)

Cc vng a l v quan h gia chng trong mng GSM c th hin di y:

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MS

CVLR

MSC

MSC

MS

C

VLR

VLR

VLRGMSC

I II

IV III


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Hnh 2.4 Cc vng phc v

Hnh 2.5 Phn vng mt vng phc v MSC/VLR thnh

cc vng nh v v cc

Hnh 2.6 Quan h gia cc vng GSM3. Giao din v tuyn

37

MSC VLR

Vng phc v GSM (tt c cc n-c thnh vinVng phc v PLMN (mt hay nhiu vng

mt n-c)Vng phc v MSC (vng -c iukhin bi mt MSC)Vng nh v LA (vng

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a. Khi nim knh

Trong GSM, giao din radio s dng tng hp c hai phng thc phn knhtheo tn s v thi gian: FDMA (Frequency Division Multiple Access) c TDMA

(Time Division Multiple Access). Trong FDMA, GSM s dng cc bng tn ti 900Mhz (gi l GSM 900) v 1800 Mhz (gi l GSM 1800). n gin ha ch cpn GSM 900. Mi knh c c trng bi mt tn s (sng mang) gi l knh tns RFCH (Radio chanel) cho mi hng thu pht, cc tn s ny cch nhau 200MHz. Trong GSM 900, MS s dng 124 RFCH trong dy tn 25Mhz (t 890 n 915MHz) v BTS s dng 124 RFCH trong dy tn t 935 n 960 Mhz pht (ttnhin MS pht th BTS thu v ngc li). Ti mi tn s TDMA li chia thnh 8 khethi gian (time slot) tc l s knh c tng ln 8 ln. Trong tng lai, s khe s

c tng ln l 16. Mt cp RFCH (thu v pht) ti mt khe thi gian c gi lmt knh vt l. Mt knh c s dng truyn mt nhm nht nh tham sthng tin c gi l knh logic (logical chanel). Mi knh vt l c gn cho mthoc mt s knh logic. Cc knh c chia thnh 2 loi:

- Knh dng ti thng tin ca thu bao, nh thoi, s liu c gi l knhtraffic TCH (traffic chanel). C 2 loi tc truyn trn TCH l tc y (fullrate) THC/F l loi tc ang c s dng hin nay v tc bng mt na (half

rate) TCH/H s c s dng trong tng lai.- Knh iu khin CCH (control chanel) c s dng truyn thng tin bo

hiu cc thng tin qun l giao din Um.

* Cc knh vt l

Cc knh vt l l mt khe thi gian mt tn s v tuyn dnh truyn tithng tin ng v tuyn GSM. Nh phn trn ni GSM s dng bng tn

sau:

890 915 Mhz ng ln (MS pht)

935 960 Mhz ng xung (BTS pht)

Khong cch gia cc sng mang l 200 KHz.

Trong tng lai khi m rng n h thng DCS 1800 bng tn c s dng sl:

1710 1785 Mhz ng ln1805 1880 Mhz ng xung

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m bo cc quy nh v tn s bn ngoi bng phi c mt khong bo vgia cc bin ca bng (200 KHz). V th GSM 900 ta c 124 knh tn s v tuyn

bt u t 8972 Mhz v DCS 1800 ta c 374 knh tn s v tuyn bt u t 1710,2MHz.

Mi mt knh tn s v tuyn c t chc thnh cc khung TDMA c 8 khe

thi gian. Mt khe thi gian bt u c lu 15/26 s. 8 khe thi gian ca 1 khungTDMA c lu gn bng 4,62 ms. BTS cc khung TDMA tt c cc knh tn

39

Hnh 2.7 : Phn b knh vt l trong h thng di ng GSM

Hnh 2.8 : Phn b knh truyn v tuyn trong khung TDMA


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s trn ng xung ng ng b. ng b cng c p dng nh vy vi ngln. Tuy nhin, khi u ca khung TDMA ng ln tr mt khong thi gian cnh 3 khe. L do tr cho php MS s dng cng mt khe thi gian c ng lnln ng xung m khng phi thu pht ng thi. S tr ni trn c m t hnhv.

ng xungKTS

Khung

TDMA

Khung

TDMA

Khung

TDMA

ng xungKTS

Khung

TDMA

Khung

TDMA

Khung

TDMA

ng ln KTSKhung

TDMA

Khung

TDMA

Khung

TDMA

ng ln KTSKhung

TDMA

Khung

TDMA

Khung

TDMA

Hnh 2.9 : Cc khung TDMA

* Cc knh logic

Cc knh logic c c trng bi thng tin truyn gia BTS v MS. Cc knhlogic ny c t vo cc knh vt l ni trn.

C th chia cc knh logic thnh 2 loi tng qut: cc knh lu lng v ccknh bo hiu iu khin.

b. T chc cc knh logic

* Knh lu thng (TCH - Trafic channel)

Knh lu thng mang ting c m ho hoc s liu ca ngi s dng. Knhlu thng gm 2 loi c nh ngha nh sau :

- Bm hay TCH ton tc (TCH/F), knh ny mang thng tin ting hoc s liu tc khong 22,8 kbit/s.

- Lm hay TCH bo tc (TCH/H) knh ny mang thng tin tc vo khong11,4 kbit/s.

Cc knh bo hiu iu khin chia lm 3 loi: cc knh iu khin qung b,

cc knh iu khin chung v dnh ring.* Cc knh iu khin

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3TS


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Hnh 2.10 : V d v BCH

Hnh 2.11 : V d v knh iu khin chung CCCH

Cc knh iu khin qung b :

- Cc knh hiu chnh tn s (FCCH- Frequency Correction Channel):mang thng tin hiu chnh tn s cho cc trm MS. FCCH ch c s dng ng

xung- Knh ng b (SCH-Synchronization Channel) : mang thng tin ng b

khung cho trm di ng MS v nhn dng BTS. SCH ch s dng cho ng xung.

- Knh iu khin qung b (BCCH): pht qung b cc thng tin chung v .Cc bn tin ny gi l thng tin h thng. BCCH ch s dng cho ng xung.

Cc knh iu khin chung (CCCH- Common Control Channel):

- Knh tm gi (PCH-Paging Channel): knh ny c s dng cho ngxung tm trm di ng.

- Knh thm nhp ngu nhin (RACH-Random Access Channel): knh nyc MS s dng yu cu dnh cho mt knh SDCCH.

- Knh cho php thm nhp (AGCH-Access Granted Channel): knh ny chc s dng ng xung ch nh mt knh SDCCH cho MS.

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Cc knh iu khin dnh ring (DCCH-Dedicated Control Channel):

- Knh iu khin dnh ring ng mt mnh (SDCCH): knh ny ch cs dng dnh ring cho bo hiu vi mt MS. SDCCH c s dng cho cc thtc cp nht v trong qu trnh thit lp cuc gi trc khi n nh knh TCH.SDCCH s dng cho c ng xung ln ng ln.

- Knh iu khin lin kt chm (SACCH): knh ny lin kt vi mt TCHhay mt SDCCH. y l mt knh s liu lin tc mang cc thng tin lin tc

nh: cc bn bo co o lng, nh trc thi gian v iu khin cng sut.SACCH s dng cho c ng lean ln ng xung.

- Knh iu khin lin kt nhanh (FACCH): knh ny lin kt vi mt TCH.FACCH lm vic ch ly cp bng cch thay i lu lng ting hay s liu

bng bo hiu.

Knh qung b t bo (CBCH- Cell Broadcast Channel)

Knh CBCH ch c s dng ng xung pht qung b cc bn tin ngn (SMSCB) cho cc t bo CBCH s dng cng knh vt l nh knhSDCCH.

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Hnh 2.12 : V d v knh DCCH


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c. Cu trc cm

Ngi ta gi khun mu tin tc mt khe thi gian 577s vi lu ca156,25 bit l ni dung vt l ca mt cm (burst). C 4 cm khc nhau :

Cm bnh thng NB (Normal Burst). NB mang cc knh logic lu lng vkim tra. Knh logic lu lng TCH (Traffic Channel) c 144 bit tin v 2 bit c lyln trong mt NB, 26 bit hng dn v khong thi gian bo v c lu bng 8,25

bit. NB c s dng cho TCH v cc knh iu khin tr RACH, SCH v FCCH.

Cm hiu chnh tn s FB (Frequency Correction Burst). FB dng hiuchnh tn s cho MS theo chun h thng. FB c 142 bit 0 to ra dch tn 67,7KHz trn tn s danh nh , ba bit ui (0,0,0) v khong bo v 8,25 bit. FB c sdng cho knh logic FCCH (Frequency Correction Channel - Knh hiu chnh tns).

Cm ng b SB (Synchronization Burst). SB ng b cho MS c 78 bit tintc v FN (s khung) ca TDMA v BSIC, ba bit ui u v cui, chui hng dnko di 64 bit v khong bo v 8,25 bit. SB c dng cho knh logic SCH(Synchronization Channel - Knh ng b).

Cm truy cp AB (Access Burst). AB phc v vic MS truy cp h thng(ngu nhin hoc chuyn giao) - AB c 36 bit tin, 41 bit ng b (cc bit hng dn,

8 bit ui u, 3 bit ui cui v khong bo v di 68,25 bit (tng ng 252 s dnhcho s tr ngu nhin 0 35 km). AB dng cho knh logic TCH v RACH (RandomAccess Channel).

Cm b nhn DB (Dumny Burst) c pht i t BTS trong mt s trnghp. DB khng mang thng tin v c cu trc ging NB nhng cc bit mt m cthay bng cc bit hn hp.

4. Truyn dn thng tin t u cui ny n u cui kia ca mng GSM

Xt qu trnh truyn dn cc thng tin thoi cng nh phi thoi gia ngi sdng GSM vi ngi s dng GSM khc hay vi ngi s dng mng in thoi c

nh cng cng PSTN, mng s lin kt a dch v ISDN, mng s liu cng cngchuyn mch gi PSPDN v mng s liu cng cng chuyn mch theo mchCSPDN.

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Mt phng m thanh

Mt phng tng t

Mt phng s 13 kbit/s

Mt phng s 64 kbit/s

BT

S

B chuyni mting

a. Truyn dn ting (thoi)

Truyn dn ting gia mt thu bao GSM v mt thu bao PSTN. C th ctrnh by theo cu trc nhiu mt phng truyn dn vi mi mt phng th hin mt

dng tn hiu nh hnh 1.7.

T hnh ta thy tn hiu pht ra t ming ca thu bao di ng dng m thanhc bin i vo tn hiu s 13 kbit/s sau cc qu trnh bin i s khc nhau niu ch sng mang c pht vo khng trung c thu li anten BTS, c x l khi phc li tn hiu s ban u, c b i m ting bin i vo tn hiu 64kbit/s cho ph hp vi tng i s c chuyn mch n thu bao PSTN c bini vo tn hiu tng t v cui cng c bin i ngc tr li thnh m thanh

n tai nghe thu bao PSTN.C th chia ng truyn dn ting bn trong GSM thnh cc on sau:

- Trm di ng

- T trm di ng n trm gc

- T trm gc BTS n b chuyn i m ring (TRAU)

- T TRAU n MSC (hay IWF)

b. M ha ting trm di ng

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Hnh 2.13: Trnh by ting


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M ha ting trm di ng c th thc hin tc 13 kbit/s. S m hating GSM tc 13kbit/s. M ha ny cho php nhn c cht lng nh mngc nh nhng i hi rng ph tn v tuyn hp hn.

Tn hiu ting MS c a qua b lc thng thp, qua b bin i A/D c m ha PCM (iu xung m) ng u vi tn s ly mu 8Khz v 13 bit mha cho 1 mu sau tn hiu ny c a ln b bin i tng t s (A/D). ura ca b A/D ta c cc khi 20 ms m ha 200 bit lm cho tc lung ra 13kbit/s.

c. Truyn dn t MS n BTS

Tn hiu sau khi m ha c a n b m ha knh to ra cc khi 456bit/20ms vi tc d khong 22,8 kbit/s sau c ghp xen, mt m ha v tothnh cc cm c th t vo khe thi gian dnh cho knh v sau cng c iuch ri pht vo khng trung di sng 900MHz. u thu thc hin qu trnh

ngc li nhn tn hiu ting m ha nh u pht trc khi a vo b gii iuch.

d. Truyn ting trn on t BTS TRAU.

on ny nu TRAU t xa s c thm bo hiu b sung vo ting truyncc thng tin iu khin TRAU t b iu khin chuyn i m t xa RTH (Remotetrancoder handler) t BTS n TRAU BSC. S c 60 bit b sung vo 260 bitting trong 20 ms nng tng s bit trong 20 ms ln 320 bit v tc ca lung s cho

mi knh s t 16 kbit/s. Trong s 60 bit b sung s c 4 bit trng phn giacc khung 20ms. Nh vy trong mt khung 20ms ch c 316 bit mang thng tin.

e. Truyn dn trn on TRAU t xa ( BSC) n MSC/IWF

on ny s dng cc ng truyn dn 64 kbit/s lut A theo tiu chunG.711.

5. Truyn dn s liu

i vi truyn dn s liu bn trong GSM c th coi mng ny nh l mt DTE

phn b, cn mng bn ngoi nh l DCE. Cc giao din DTE/DCE c thc hin cc TAF, TRAU v IWF. xy dng cc giao din ny GSM ci tin khuyn ngh

45

1 LPF A/D B m ha

BTS

Hnh 2.14 : M ha ting


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V110 dnh cho giao din DTE/DCE trong trng hp DCE l mng ISDN. V vy hiu c truyn dn s liu trong mng GSM trc ht ta xt tiu chun V110.

Tiu chun V110

Tiu chun ny gii quyt cc vn sau:- Truyn ti cc thng tin b sung.

- Truyn ti cc s liu d b cc ng truyn ng b.

- Truyn ti cc s liu ng b cc ng truyn ng b s dng ng hc lp vi nhau.

S khi thc hin thch ng tc RA ca lung s liu cn truyn viISDN, cho hnh v.

- Chuyn i s liu d b vo ng b.

Chc nng ny c thc hin RAO. Lung s liu d b l mt chui cc kt thng c kh u bng 1 bit start v kt thc bng 1 bit stop. lung nykhng cn thit cc bit bin phi trng vi sn trc ca xung ng h. RAO c thloi b bit stop m bo ng h (hnh 1.11).

46

RA

1

R

A

2

RA0

Ly mu

Tc d b ban uChng hn: 300 hay 9600bit/s

ng b

mm

B

Tc trung gian(8hay 16 kbit/s)

Hnh 2.15: Thch ng tc ISDN

Lung d b

Lung ng bB mt tn hiudng

Hnh 2.16: Chc nng RAO


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- iu khin ng h t xa

Tc truyn dn trong mng s chng hn ISDN c iu khin bi ng hca mng. Trng hp mt u cui c u qua mng PSTN th tc gia haiu cui c th khc nhau. Trong trng hp ny khi thch ng tc phi gi ithng tin hiu chnh tc cho u kia cc thng tin ny c th c gi i cc

bit E4, E5, E6, trong lung s ra ca RA1.

- Cc tn hiu b sung

y l cc tn hiu iu khin modem. V101 cc tn hiu b sung ch gii hnhai tn hiu hng u cui (DTE) n modem (DCE) v 3 tn hiu theo hngngc li. Ty theo tc bit ca lung s liu c s 8 bit, tn hiu ny c truyni trong cc khong thi gian 5 hay 10 ms. Bng 1.12 di y a ra cc tn hiu

khc nhau ni trn v tc ly mu chng.thiBng 1.12: Truyn ti cc tn hiu iu khin modem V110.

u cui n modem Modem n u cui Tc ly mu trung bnh

Trng thi mch 108(Data terminal ready)

Trng thi mch 107 (Data setready)

1,25 ms hay 2,5 ms

Trng thi mch 105(Request to send)

Trng thi mch 109 (Datacarrier detect)

2,5 ms hay 5 ms

Trng thi mch 108 (Clear tosend)

2,5 ms hay 5 ms

ngha ca cc tn hiu iu khin bng sau:

- Data terminal ready: Thng bo cho modem rng b iu khin u cui snsng thng tin.

- Data set ready: Ch th rng modem sn sng thit lp ng ni thng tin vtruyn s liu vi b iu khin ca u cui.

- Request to send: Thng bo cho modem rng b iu khin sn sng gi sliu.

- Data carrier detect: Ch th rng modem pht hin ra sng mang s liu.

- Clear to send: Modem sn sng pht.

Cc thng tin ny V110 c ghp vo lung s c s chc nng thch ngtc , RA1, cc bt thng tin b sung lung ra RA1 c cho bng 1.13.

Bng : Cc bit thng tin b sung V110

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Tn bit Thng tin c truyn Ch thch

S1, S3, S6,S8 (hay SA)

Trng thi mch 108 (Data terminalready) hay 107 (Datta set ready) ph

thuc vo phng truyn.S4, S9 Trng thi mch 105 (Requset to send

hay 109 (Data carrier detect) phthuc hng truyn

x Trng thi 106 (Clear to send) Gi 2 ln trong mtkhung

E1, E2, E3 Tc bit thc Biu thc tc bitgia hai u cui

E4, E5, E6 ng h mng c lp (c s dngtrong cc trng hp ng b iukhin ng h t xa khi cc modemkhng c ng b mng truyn

ti

Cc m ny lmnhanh hay chm

ng h bng cchb qua hay chn bit

T hnh 2.16 ta thy RA0 thc hin bin i lung s liu khng ng b volung ng b, u ra ca b ny ta c cc lung ng b RA1 thc hin thchng tc ln th nht. y n ghp cc bit b sung vi lung c s to thnh

cc lung s c tc 8 kbit/s (cho lung c s c tc 4800 kbit/s) v 16 kbit/s(cho lung c s c tc 9600 bit/s). i vi cc lung s c tc nh hn 4800kbit/s cc bit c pht lp li t c tc danh nh 4800 kbit/s. Cc khung RA1 c lu 5 ms cho 9600 kbit/s v 10 ms cho 4800 kbit/s. cc khung ny cc

bit thng tin c s, cc bit b sung v cc bit ng b c ghp chung t c

tc 16 v 8 kbit/s. T bng 1.12 ta thy c 15 bit thng tin b sung v 17 bit ngb c ghp vo mi khung RA2 thc hin bin i cc tc 16 v 8 kbit/s vo 64kbit/s cho ph hp vi mng ISDN. Vic bin i ny c thc hin bng cch ghp6 hoc 7 bit 1 vo mi byte.

6. Mt m ha

Mt trong cc u im ln ca h thng truyn dn s l d dng bo v tn hiuny khi s can thip ca ngi th ba khng c php bng cch mt m ha tn

hiu s. GSM phng php mt m ha khng ph thuc vo dng s liu cpht, nhng ch p dng cho cc cm bnh thng.

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Mt m ha tn hiu t c bng thao tc hoc loi tr (XOR) gia mtchui ngu nhin vi 114 bit ca cm bnh thng, ngha l vi tt c cc bit thngtin tr cc c ly cp bng 1.19. gii mt m ngi ta thc hin thao tc hoc loitr (XOR) gia tn hiu thu vi chui ngu nhin.

Bng : Nguyn l mt m v gii m tn hiu s

Tn hiu s

Chui mt m

Tn hiu m ha

010010111001

001011001110

011001110111

Chui ngu nhin c to ra t s khung v kha mt m Kc theo thut tonA5 (hnh 1.20). Kha Kc ging nhau gia thu v pht, s khung thay i t cm nyn cm khc, vy mi cm ca mt cuc thng tin trong mt hng s s dngchui mt m khc nhau. Thut ton A5 nh nhau cho mng GSM ton cu v phim bo kh nng chuyn mng MS 22 bit s khung kt hp vi 64 bit Kc theo thutton A5 to ra chui ngu nhin 144 bit.

7. iu ch

GSM s dng phng php iu ch kha chuyn pha cc tiu Gauss GMSK

(Gaussian Minimum Shift Keying). y l phng php iu ch bng hp da trnk thut iu ch dch pha.

8. B cn bng Viterbi

ng truyn dn v tuyn do nh hng phn x t nhiu vt khc nhau dnn giao thoa gia cc k hiu ISI gy ra li bit.

gii quyt vn ny ngi ta p dng nguyn l ca my thu ti u: y l

mt my thu thng minh c kh nng xy dng c m hnh knh truyn sng mi thi im. GSM my thu ny c thc hin b cn bng Viterbi (hnh1.26). b cn bng c th xy dng c m hnh knh cc thi im khc nhauchui bit hng dn (S=26) c pht i gia cm, chui ny s phn nh tngi ng tnh trng truyn sng cho my thu. Do chui ny c my thu bit trcnn da trn s sai lch chui ny my thu c th xy dng c m hnh knh thi im ang xt. Sau my thu s cho cc t hp bit khc nhau c th qua mhnh knh v chn t hp nhanh nht ngi ta s dng thut ton Viterbi

49Hnh 2.17: B cn bng Viterbi


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Nguyn l ca thut ton ny l trong khi tnh ton ta loi b cc t hp vo cxc sut thp nh vy gim c s lng tnh ton cn thit. B cn bng Viterbi GSM cho php x l cc tn hiu phn x tr ti 15s. B cn bng cng a rathng tin mm di b gii m knh to iu kin cho b ny hiu chnh li ctt hn.

9. Cc s nhn dng v cc trng hp thng tin

a. Cc s nhn dng

- S lin kt a dch v ca trm di ng(MSISDN : Mobile Station IntegratedService Digital Network)

Theo khuyn ngh ca CCITT ( nay l ITU-T) , s in thoi di ng hay s

danh b in thoi ca my di ng bao gm :

Trong :

CC(Country Code) : m nc

NDC(National Destination Code) : m ni nhn quc gia

SN(Subscriber Number) : S thu bao

50

CC NDC SN

S di ng quc gia

S ISDN di ng quc t MSISDN = CC + NDC +SN


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M ni nhn trong nc c n nh cho tng mng di ng. mt s c thcn nhiu NDC cho mi mng di ng. S MSISDN quc t c chiu di thay i.Chiu di cc i ca n l 15 ch s khng k cc tin t.

MSISDN l s nhn dng duy nht cho mt thu bao in thoi di ng trongk hoch nh s ca tng nh khai thc theo khuyn ngh ITU-T E.164

- Nhn dng thu bao di ng quc t (IMSI International Mobile SubscriberIdentity) :

nhn dng chnh xc ng truyn v tuyn cng nh trn ton mng ding, mi thu bao c n nh mt s nhn dng c th. S nhn dng ny cgi l s nhn dng thu bao di ng quc t v c s dng cho ton b bo hiu

trong mng di ng. IMSI gm ba phn khc nhau:

MSI : Nhn dng trm di ng

MCC(Mobile Country Code) : m nc di ng

MNC(Mobile Network Code):m mng di ng

MSIN(Mobile Station Identification Number): S nhn dng trm di ng

MCC c m ha theo khuyn gh ITU-T E.212. Vic m ha thuc trchnhim ca c quan qun l, tuy nhin s s dng m BCD(Binary Coded Decimal)

IMSI l thng tin nhn dng duy nht mt thu bao di ng thucmng di ng

Ton b thng tin v thu bao lin quan n mng u lin kt vi IMSI

- S lu ng ca trm di ng (MSRN : Mobile Station Roaming Number)

HLR bit thu bao di ng thuc vng phc v MSC/VLR no . cung cp stm thi cho vic nh tuyn HLR yu cu MSC/VLR ang phc v thu bao di ng

b gi n nh mt s lu ng ca trm di ng cho thu bao ny v gi cho n. Khi

51

MCC MNC MSIN

MSI quc gia

IMSIIMSI = MCC + MNC + MSIN

Max 15 ch s

3 ch s 2 ch s


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thu c MSRN, HLR gi n n MSC cng n nh tuyn cuc gi nMSC/VLR ang phc v thu bao b gi.

Chc nng nh tuyn cuc hi ( s MSRN) l b phn ca phn ng dng di

ng MAP. Ton b s liu c trao i giua GMSC-HLR-MSC/VLR cho mcch hi c pht i mng bo hiu s 7

Theo khuyn ngh, s lu ng ca trm di ng bao gm ba phn:

MSRN = CC + NDC+SN

CC(Country Code) : m nc

NDC(National Destination Code) : m ni nhn quc gia

SN(Subscriber Number) : S thu bao

- Nhn dng thu bao di ng tm thi TMSI : Temporary Mobile SubscriberIdentity)

TMSI c s dng gia b mt cho thu bao. V TMSI ch c ngha niht ( ngha l trong vng ca MSC/VLR), nn cu trc ca n c chn la bi nhqun l.

Nhn dng thit b trm di ng quc t IMEI : International Mobile Equipment

Identity)IMEI c s dng nhn dng thit b, IMEI nhn dng duy nht trm di

ng nh l mt b phn hay l t hp thit b. N gm:

TAC : Type Aproval Code ( m cng nhn kiu, do c quan qun l trung ngxc nh)

52

TAC FAC SNR

IMEI 15 ch sIMEI = TAC + FAC + SNR+sp

6 ch s 2 ch s 6 ch s

sp

1 ch s1


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FAC : Final Assembly Code ( M lp rp cui cng) , nhn dng nh sn xut

SNR : Seri Number ( s seri), mt s seri gm 6 ch s nhn dng duy nht thitb a tng TAC v FAC.

Sp : d phng cho tng lai.- Nhn dng vng nh v LAI : Location Area Identity

LAI c s dng cp nht v tr ca trm di ng

MCC(Mobile Country Code) : m nc di ng

MNC(Mobile Network Code):m mng di ng

LAC ( Local Area Code) : nhn dng mt vng nh v bn trong mng di ng. di cc i ca LAC l 16 bt, cho php xc nh 65 536 vng nh v khc nhau

trong mt mng di ng.- Nhn dng ton cu CGI : Cell Global Identity

CGI c s dng nhn dng trong mt vng nh v. iu ny cthuuwcj hin bng cch b xung nhn dng n nhn dng vng nh v.

CI(Cell Identity) : Nhn dng , nhn dng mt ca mt vng nh v, cc i16 bt

53

MCC MNC LAC

LAI LAI =MCC+MNC+LAC

3 ch s 1-2 ch s Max 16 bt

MCC MNC LAC

IMEI 15 ch s

CGI = MCC + MNC+LAC+CI

3 ch s 1-2 ch s Max 16 bt

CI

Max 16 bt

Nhn dng vng nh vN


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b. Cc trng hp thng tin

* Cp nht v tr

i vi thu bao di ng vic thay i vi tr xy ra lin tc. Do vic cp

nht v tr rt quan trng. Trong mng di ng, mt s cell to thnh vng nh vLA (Location Area). V mi vng LA c xc nh i thng s LAI (LocationArea Identifier).

hnh 3.10 ta thy cp nht v tr xy ra khi trm MS di chuyn t mt vngnh v c xc nh bi mt s nhn dng vng (LAI) ny sang mt vng nh vc s nhn dng khc. Tn ti hai dng cp nht v tr:

MS chuyn t cell 3 thuc LA2 sang cell 4 thc LA1. C hai v tr u

thuccngmt tng i MSC. Trong trng hp ny cp nht v tr khng cnthng bo n HLR v HLR ch qun l v tr ca MS n tng i MSC ph trchMS.

MS chuyn t cell 3 sang 5 c LA3. hai ny trc thuc hai tng i MSCkhc nhau. V th cp nht v tr phi c thng bo cho HLR n ghi li v trmi ca tng i qun l MSC.

545

Hnh 2.18 : Cc trng hp cp nht v tr


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Thng tin thc hin cp nht v tr da trn LAI trn c thng bothng xuyn BCCH ca mi . Ta thy cc trao i bo hiu cn thit khi thc

hin cp nht vi tr :1. MS nhn c thng bo v LAI mi knh BCCH.

2. Thit lp kt ni RR:

2a. Ms yu cu knh bo hiu

2b. MS nhn c mt knh iu khin dnh ring (SDCCH).

3. knh ny MS s yu cu dch v cp nht v tr

4. Nhn thc:4a. Nu VLR khng c thng s nhn thc. MSC ly thng s ny t HLR

4b. Thng s nhn thc c gi n MS, sau MS tr li nhn thc cho MSC.

5. Cp nht v tr c thc hin VLR v c HLR nu MSC l MSC mi:5a. VLR cp nht LAI mi

5b. HLR cp nht LAI nu MS cha c MSC bit. 6, 7a, 7b: Gii phngknh bo hiu.

55

Hnh 2.19 : Cp nht v tr kiu bnh thng


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* Th tc nhp mng & ng k ln u

Khi MS mi bt ngun n phi thc hin ng k ln u nhp mng. Qu

trnh ny c thc hin nh hnh sau : Trc ht trm MS qut tm c tn s ng (FCCH)

Sau tm n knh ng b SCH nhn c s khung TDMA chong b.

Cui cng n thc hin cp nht v tr thng bo cho VLR ph trch vHLR v v tr ca mnh. Cc c s d liu ny s ghi LAI hin thi ca MS. Gingnh cp nht v tr bnh thng thng tin v LAI c MS nhn t knh BCCH.

Bt u t gi MSC/HLR cng nhn l MS tch cc v nh du c thmnhp v tr tch cc vo trng d liu ca mnh. C ny gn vi IMSI.

* Tm gi

Khi c mt cuc gi ti trm MS, MSC/VLR s gi bn tin tm gi n MS.Bn tin ny s c thng bo trn tt c cc thuc vng nh v (LA) ang c MS.MS ang di ng trong LA ny s nghe thy bn tin ny CCCH v tr li ngay lptc.

56

Hnh 2.20 : ng k ln u

Hnh 2.21 : Tm gi mt MS LA2


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* Cuc gi khi xng t MS

- Khi trm MS trng thi tch cc v ng k MSC/VLR ph trch , MSc th thc hin cuc gi. Qu trnh thc hin cuc gi c cho hnh nh sau:

- Bng knh thm nhp ngu nhin MS gi yu cu knh bo hiu n BTS (1)

- MS thng bo rng n mun thit lp cuc gi (2). S nhn dng trm di ngc phn tch v MS c nh du bn VLR.

- Qu trnh nhn thc c thc hin (3)- Qu trnh m ha c thc hin (4)

- MSC nhn c bn tin thit lp t MS c cha thng tin v loi dch v mMS yu cu, s thoi b gi B (5). MSC kim tra l MS khng c cc dch v cm gira (dch v ny c th kch hot hoc bi thu bao hoc bi nh khai thc). Nukhng b cm gi ra qu trnh thit lp cuc gi c tin hnh. Gia MSC v BSCng truyn c thit lp v knh lu lng c chim. MSC gi yu cu n

BSC n nh mt knh lu lng cho ng v tuyn.- BSC kim tra nu c knh lu lng ri n n nh knh ny cho cuc gi v

yu cu BTS kch hot knh ny. BTS gi tr li cng nhn khi vic kch hot knhlu lng hon thnh (6). BSC thng bo cho MSC v s hon thnh ny. Hthng con iu khin lu lng s phn tch cc ch s ca s thoi B v thit lp ktni n thu bao b gi. Cuc gi c ni thng qua chuyn mch nhm.

- Bo chung s c gi n trm MS (7) cho thy rng pha b gi ang chung. Tng chung c to ra tng i pha thu bao B v c gi qua chuynmch nhm n MS. Nh vy tng chung c gi qua ng v tuyn ch khngto ra MS.

- Khi thu bao B tr li mng gi bn tin kt ni n MS thng bo rng cucthoi c chp nhn (8). MS tr li bng cng nhn kt ni, nh vy thit lp cucgi hon tt.

- Qu trnh thit lp cuc gi khi xng t trm di ng c trnh by trnl cho cuc gi MOC khng c OACSU (Without off Air Call set up:thit lp sm).

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Thit lp sm c ngha l mng cp pht knh lu lng cho MS trc khi n khiu thit lp cuc gi mng c nh. Cng c th c tu chn vi OACSU giaion sau ca GSM. (xem hnh 1.39). Lc ny mng s quyt nh khi no th cp

pht knh lu lng. Cp pht c thc hin thi im bt k sau khi khi uthit lp cuc gi mng c nh. Cc im nht l mng c th cp knh lu lngsau khi thu bao B tr li cuc gi.

- Bn tin bo chung s c gi n MS khi chung pha b gi. S khcnhau y so vi trng hp thit lp sm (Without OACSU) l tng bo hiuchung c to ra ngay MS v knh lu lng vn cha c cp pht. Khi thu

bao B tr li, mng khi xng th tc n nh cp pht knh lu lng.

* Cuc gi kt cui MS (MTC: Mobile Terminatil Call)

- MTC phc tp hn MOC v pha gi khng bit hin thi MS ang u.

- Pha ch gi quay s thu bao di ng b gi: s mng dch v, s lin kt cathu bao di ng (MS ISDN) (1). Nu cuc gi khi u t mng c nh PSTN th

tng i sau khi phn tch s thoi s bit rng y l cuc gi cho mt thu baoGSM.

- Cuc gi c nh tuyn n tng i GMSC gn nht (2), y l mt tngi c kh nng hi v nh li tuyn. Bng phn tch MSISDN tng i GMSC tmra HLR ni MS ng k.

- GMSC hi HLR (3) thng tin c th nh tuyn n MSC/VLR ang qun

l MS. Bng MSISDN tm ra IMSI v bn ghi ca thu bao. IMSI l s ca thu bao

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Hnh 2.2.2 : Thit lp cuc gi khi xng t MS khng c OACSU


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ch s dng trong mng bo hiu, a ch ca VLR ni MS ang ng k tm thic lu gi cng vi IMSI trong VLR.

- HLR giao tip vi VLR nhn c s lu ng thu bao (MSRN: Mobile

Subscriber Roaming Number) (4), y l mt s thoi thng thng thuc tng iMSC.

- VLR gi MSRN n HLR, sau HLR chuyn s ny n GMSC (S).

- Bng MSRN GMSC c th nh tuyn li cuc gi n MSC tng ng (6),GMSC gi bn tin nhn c t PSTN n MSC.

- gim ti thiu gi thnh, c th s dng PSTN nh tuyn li cuc gi, cc nc c mng PSTN t hoc hot ng khng tt th tt nht l xy dng mt

mng kt ni ring gia cc MSC v GMSC.- MSC bit c v tr ca MS v n gi bn tin tm gi n tt c cc BSC ang

qun l vng nh v ny (7). mng GSM tn ti hai kh nng hoc thng tin v cc trc thuc mt vng nh v c lu gi MSC, hoc thng tin ny c lu gi BSC. mng CME 20 chng hn thng tin ny c lu gi BSC.

- MSC gi LAI (nhn dng vng nh v) xung cc BSC v BSC phn pht bntin tm gi n cc BTS (8).

- tm gi MS, IMSI c s dng (9). C th s dng s nhn dng tm thiTMSI m bo b mt.

- Ngay sau khi nhn c bn tin tm gi MS gi yu cu knh bo hiu. MSCc th thc hin nhn thc v khi u mt m ha nh xt phn trn. MSC cth gi n MS thng tin v cc dch v c yu cu: ting, s liu, fax

- By gi BSC s lnh cho BTS kch hot knh TCH v gii phng knh bohiu, bo chung c gi i t MS cho thy rng tng chung c to ra MS.

Tng chung cho thu bao ch gi c to ra MSC.

- Khi thu bao di ng nhc my MS gi i bn tin kt ni. Mng hon thnhng ni thng v gi bn tin cng nhn kt ni n MS.

- y cng tn ti hai phng thc: c OACSU (cp pht TCH mun) vkhng c OACSU (cp pht TCH sm). S khc bit gia hai phng thc ny cch ra hnh 1.41. n nh TCH sm mng khi u n nh TCH khi nhn c

bn tin khng nh cuc gi (bo chung). n nh TCH mun bo chung khi

u ngay khi thu bao nhn c cuc gi, cn mng n nh TCH mi thi imsau khi bo chung c khi u.

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* Chuyn giao

Chuyn giao l qu trnh xy ra khi lu lng ca MS c chuyn t mt knhTCH ny sang mt knh TCH khc trong qu trnh gi. C 2 loi chuyn giao:

+ Chuyn giao bn trong (Intracell hand over).

+ Chuyn giao gia cc (Intercell hand over).

Chuyn giao gia cc c phn loi thnh (xem hnh 1.44).

Chuyn giao gia cc thuc cng mt BSC: chuyn giao ny do BSC iuhnh.

Chuyn giao gia cc thuc hai BTS khc nhau: chuyn giao ny lin quann cc tng i MSC qun l hai BTS.

Chuyn giao gia hai thuc hai tng i MSC khc nhau: chuyn giao ny linquan n c hai tng i ph trch cc ni trn.

Trong trng hp chuyn giao nhiu ln gia hai thuc hai MSC khc nhau,tng i MSC u tin ph trch MS c gi l tng i qu giang v cuc gi lunlun c chuyn mch qua tng i ny. Ln chuyn giao gia hai thuc hai tng

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Hnh 2.23 : Thit lp cuc gi khi xng t in thoi c nh n di ng


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i khc nhau th nht c gi l chuyn giao gia cc thuc 2 tng i ln u,cn cc ln sau c gi l chuyn giao gia cc thuc hai tng i tip theo.

Chuyn giao gia hai thuc cng mt BSC

Qu trnh chuyn giao ny c cho hnh sau:

Trong qu trnh gi MS lun lun o cng trng, cht lng knh TCH

ca mnh v cng ca cc ln cn. MS nh gi tr trung bnh ca kt qu o.Hai ln trong mt giy n gi bo co kt qu o (1) n BTS cng vi kt qu oca cc ln cn tt nht. BTS b sung thm kt qu o c chnh knh TCH vgi bo co v BSC (2). BSC chc nng nh v c tch cc quyt nh xemc cn chuyn giao cuc gi n khc do cht lng xu hoc nhiu ln ang

phc v hay khng.

Trng hp cn chuyn giao BSC s lnh chn BTS mi c cho tch cc

mt knh TCH (3) v lnh cho BTS ny gi bn tin n MS thng bo v tn s vkhe thi gian cn chuyn n (4).

MS iu chnh n tn s mi v gi bn tin thm nhp chuyn giao (HO) khethi gian tng ng (5). MS khng s dng bt k s nh thi trc no c, v vycm HO l cm rt ngn ch cha 8 bit thng tin. MS khng nhn c bt c thngtin no v nh thi trc cho n khi BTS pht hin ra cm HO.

MS cng nhn thng tin v cng sut cn s dng (6) knh FACCH ly cp tknh ting (c ly cp trong tng trng hp ny lp 1).

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Hnh 2.24 : Qu trnh chuyn giao


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BSC s nhn c thng tin t BTS l chuyn giao thnh cng sau khi MS gibn tin hon thnh chuyn giao (7). ng ting trong chuyn mch nhm thay iv BTS c c ra lnh tho g TCH c cng vi knh lin kt SACCH (8).

chuyn giao bn trong BSC ny chnh BSC x l mi vic khng c s canthip ca MSC. MSC ch c thng bo v vic thc hin chuyn giao.

Chuyn giao gia 2 thuc hai BSC khc nhau

Bo hiu thc hin chuyn giao gia hai thuc hai BSC khc nhau c cho hnh 1.46 nh sau:

BSC c da trn cc bo co v kt qu o quyt nh chuyn giao n mitrc thuc mt BSC khc. BSC c (ang phc v) gi bn tin "yu cu chuyn giao"cng vi nhn dng mi (1) n MSC.

MSC bit BTS iu khin ny, n gi yu cu chuyn giao n BTS ny (2).

BSC lnh cho BTS mi kch hot mt knh TCH nu cn knh ri (3).

Khi BTS kch hot knh TCH, n gi thng tin v khe thi gian v tn s nMSC (4).

MSC chuyn thng tin ny n BSC c (5).

MS c ra lnh chuyn n TCH mi (6).

MS gi i cm thm nhp chuyn giao (HO) TCH mi (7).

Ngay sau khi pht hin cm HO, BTS gi thng tin vt l cha nh trc thigian v cng sut ra n MS (8).

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Hnh 2.25 : Qu trnh chuyn giao gia hai thuc 02 BSC


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BSC mi nhn c thng tin rng BTS nhn c cm HO (9), n thngbo iu ny qua MSC (10) n BSC c (11).

MSC chuyn thng tin ni trn n BSC c (11).

BTS c gii phng TCH v SACCH c (12).MS nhn thng tin v mi SACCH lin kt vi TCH mi. Nu ny thuc

LAI mi MS phi cp nht v tr bnh thng sau khi cuc gi c gii phng.

Chuyn giao gia cc thuc tng i khc nhau.

Qu trnh chuyn giao gia hai thuc hai tng i MSC khc nhau c cho hnh 1.47 nh sau:

BSC ang phc v gi "yu cu chuyn giao" n MSC ging nh trng hptrn (1).

MSC yu cu MSC chuyn giao (MSC ch) (2) gip . MSC ch cp phtmt s chuyn giao (s in thoi thng thng) nh tuyn li cuc gi.

Yu cu chuyn giao c gi n BSC mi (3).

Nu c knh TCH ri, BSC yu cu BTS kch hot mt TCH (4).

MSC nhn c thng tin v knh TCH mi (5) v chuyn thng tin ny tr li

MSC c cng vi s chuyn giao (6).

ng truyn c thit lp n MSC mi (7).

Lnh chuyn giao c gi n MS cng vi thng tin v tn s v khe thigian s c s dng mi (8).

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Hnh 2.26 : Qu trnh chuyn giao


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Trong sch xanh ca CCITT (1988) cn a ra giao thc chung cho cc kh nnggiao dch (TCAP) v phn ng dng cho khai thc, bo dng. Chng cng ng vilp 7 trong m hnh OSI.

- Phn chuyn giao bn tin (MTP : Message Transfer Part)

MTP l mt h thng vn chuyn chung chuyn giao tin cy cc thng tinbo hiu gia cc im bo hiu. Phn chuyn giao bn tin truyn ti cc thng tinbo hiu gia cc phn ca ngi s dng khc nhau v ni dung ca cc tin bo ny

l hon ton c lp vi nhau.- Phn iu khin u ni bo hiu ( SCCP : Signalling Connection Control

Part)

SCCP cung cp cc chc nng b sung cho MTP v n c CCITT a vosch nm 1984. Khi chc nng SCCP nm trn MTP v s t hp ca SCCP vMTP c gi l phn dch v ca mng ( NSP - Network Service Part ). SCCP cm t trong cc khuyn ngh Q.711- Q.716 ca CCITT.

Mc ch ca SCCP:

Lp 7

Lp 6

Lp 5

Lp 4

Lp 3Lp 2

Lp 1

Mng bo

hiu

Knh bohiu

Knh s liubo hiu

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OSI

ISUP TUP

OMAP

TCAP

SCCP

MTP

Hnh 2.27 Mi quan h gia bo hiu s 7 v m hnh chun OSI

SS7


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Trong mt s trng hp , mong mun rng cc bn tin c chuyn giao tim ny ti im khc trong mng m khng lin quan ti mch in ( Thoi hocs liu ). MTP c thit k t u cho bo hiu lin quan ti mch in v v vyn khng p ng c yu cu ny. Mt s dch c khng lin quan n mch inl:

Dch v di ng : chuyn vng gia cc MSC.

Cc dch v c s d liu.

SCCP lm cho n c kh nng chuyn giao cho c bo hiu lin quan vkhng lin quan ti mch v thng tin ca ngi s dng gia cc tng i v cctrung tm c bit trong cc mng vin thng qua mng bo hiu s 7. Mt mc ch

khc ca SCCP l thc hin cho cc dch v ca mng khng u ni v nhhng u ni.

Phn ng dng kh nng giao dch ( TCAP : Application Part )

Trong tng lai, mng vin thng s c rt nhiu dch v mi. Nhiu trong scc dch v ny s i

He Thong TT Ddong Chuong I

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