Tong Quan Ve He Thong Di Dong GSM

1TONG QUAN VEH THNG DI ONG GSM

CHNG 1

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2GSM la viet tat cua Global System for Mobile

communications

GSM la he thong ien thoai di ong ma mang li hoan toan s dung ky thuat so, khac vi he thong mang ien thoai Analog co ien nh he thong AMPS (Advanced Mobile Phone Service: Dch vu ien thoai di ong cao cap).

He thong thong tin di ong toan cau


31. CA1. CAU TRUU TRUC HEC HE THOTHONG GSMNG GSM

MS: Mobile StationBTS: Base Transceiver StationBSC: Base Station ControllerBSS: Base Station SubsystemMSC: Mobile services Switching Center

VLR: Visitor Location RegisterHLR: Home Location Register

EIR: Equipment Identitfication RegisterAuC: Authentication CenterSMSC: Short Messaging Service CenterOMC: Operation & Maintenance CenterGMSC: Gateway MSC

BTS

BTS

BSC

BSS

MSC+VLR

GMSC

PSTN / ISDN

EIR HLR AuC

SMSC Billing OMC

BTS

BTS

BSC

BSS

MS

MS

MS

MS

NSS


4Cau truc cua mot he thong GSM co the c chia lam 3 he thong con:

He thong con tram goc (BSS Base Station Subsystem), gom BTS va BSC.

He thong con chuyen mach mang (NSS Network Switching Subsystem) gom: MSC/GMSC, HLR, VLR, EIR, AUC.

Ngoai ra trong mang con co cac thue bao, c goi la MS.

He thong con van hanh bao dng (OMS Operation and Maintenance Subsystem) cha OMC.


5SD

Mobile Station

BTSMSC/VLR

SIM MEBSC

Base StationSubsystem

GMSC

Network Subsystem

AUCEIR HLR

Other Networks

Note: Interfaces have been omitted for clarity purposes.

+

PSTN

PLMN

Internet

Cau truc cua mot he thong GSM

MS BSS

NSS


61.1 MS (Mobile Station)

La thiet b cam tay trong mang di ong GSM, thc hien chc nang thu va phat tn hieu vo tuyen vi mot BTS (trong vung phu song).

oi vi he thong GSM, mot MS gom 2 thanh phan la ME (Mobile Equipment) va SIM (Subscriber Identity Module).


7 La thiet b cng thc hien chc nang thu phat tn hieu, notng oi thong minh va c ieu khien bi 1 chng trnh ben trong may.

ME tr thanh MS ch khi nao SIM c chen vao trong ME.

Noi ME thong minh v no co kha nang t ieu chnh cong suat phat tiet kiem pin va han che hien tng near and far.

Moi ME co cha mot so IMEI (International Mobile Equipment Identity) dung e nhan dang thiet b. So IMEI la

duy nhat cho tat ca cac MS tren toan the gii.

a. ME (Mobile Equipment)

So IMEI co the c hien th hau het cac may ien thoai bang cach bam *#06#


8SIM la mot the chip, ben trong co bo nh e lu tr thong tin ca nhan cua thue bao va thong tin cua nha cung cap dch vu.

Trong qua trnh hoat ong, MS se s dung cac thong tin co san trong SIM. Thong tin lu tr trong SIM gom:

IMSI (International Mobile Subscriber Identity): sonhan dang thue bao di ong quoc te. So nay la duy nhat tren the gii nhng khi lam viec MS khong sdung so nay.

b. SIM (Subscriber Identity Module)


9 LAI (Location Area Identifier): So vung ang ky.

Khoa nhan thc thue bao Ki: c MS s dung trong qua trnh nhan thc thue bao.

u iem cua viec s dung SIM card ri ?

TMSI (Temporary Mobile Subscriber Identity): sonhan dang thue bao tam thi.

c MS s dung e lien lac tren ng vo tuyen, sonay ch ton tai toi a 3 gi khi MS ang am thoai, neu qua 3 gi th mang t ong thay oi so nay ma ngi s dung khong biet.


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a. BTS (Base Transceiver Station): Tram thu phat goc

BTS thc hien chc nang thu va phat tn hieu vi cac MS nam trong vung phu song cua no.

1.2 Cac thanh phan cua he thong con BSS

Vung phu song cua mot BTS goi la cell (te bao).


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a. BTS (Base Transceiver Station(tt)


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BTS giao tiep vi MS qua ng vo tuyen.

BTS lam viec thu ong, moi hoat ong cua no eu c ieu khien bi BSC.

Giao dien gia BTS va MS c goi la giao dien Um.

Giao tiep vo tuyen



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500 m khu vc thanh th

15 km khu vc nong thon, vung ven,

Ban knh phu song cua cac tram BTS la:


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b. BSC (Base Station Controller): Bo ieu khien tram goc

Chc nang chnh cua BSC la ieu khien hoat ong cua cac BTS nh:

ieu khien cong suat phat cho cac MS.

Cap phat kenh tan so cho cac BTS va MS.

ieu khien nhay tan so gia cac MS e giam nhieu.

ieu khien chuyen giao,

Moi BSC co the ieu khien nhieu BTS (40 en 65 BTS).


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ng noi gia BTS va BSC co toc o la 2Mbps va co thes dung:

Cap ong neu BTS gan BSC.

ng truyen viba neu BTS xa BSC, cac tuyen viba nay co c ly cc ai la 20km.

Cap quang neu BTS c at tnh con BSC thanh pho.


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1.3 Cac thanh phan cua he thong con NSS (Network Switching Subsystem):

a. MSC (Mobile services Switching Center) Thc hien chc nang chuyen mach cac cuoc goi gia

cac MS. MSC c xem nh tong ai cua mang di ong.

ay la ni duy nhat trong he thong thc hien chc nang nay.

MSC chu trach nhiem thiet lap cac ket noi:

Ngoai ra MSC con thc hien quan ly cac cell va cac location areas (LA) (LA la mot vung gom nhieu cell).

- en BSS- en MSC khac- en cac mang khac (nh mang PSTN)


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PSTNISDN

GMSC

HLR

AuC

EIR

OMC

MSC Khac

a. MSC (Mobile services Switching Center)


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Mot MSC quan ly c nhieu BSC trong mot vung.

Cac MSC cac vung se au noi vi nhau e cho phep thc hien cuoc goi lien vung. Ngoai ra MSC con c noi vi mang PSTN e thc hien cuoc goi en cac thue bao co nh.

MSC c at cac thanh pho ln.

MSC thc hien cac chc nang giong nh mot tong ai cua mang ien thoai co nh. Tuy nhien viec quan lythue bao th khac.

Vay cac thue bao di ong c quan ly au va nh thenao?


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b. HLR (Home Location Register)

Trong mang GSM, viec quan ly thue bao khong do cac tong ai thc hien v thue bao di ong khong c ket noi lau dai vi mot MSC. Thay vao o, v tr hien tai cua thue bao xac nh MSC chu trach nhiem quan ly no tai thi iem o.

Do o, mang GSM co mot thanh phan c goi la HLR echa d lieu cua thue bao cua mot vung nao o.

HLR la mot c s d lieu ni ma cac thue bao di ong c tao ra, b chan hoac b xoa bi nha khai thac.

HLR cha tat ca cac thong tin lau dai cua thue bao cung nh cac dch vu va cac gii han ma mot thue bao di ong c phep s dung, cu the gom: so IMSI, Ki, VLR hien tai cua thue bao va cac dch vu cua thue bao di ong.

HLR


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Thong tin nay khong cho biet v tr cu the cua thue bao di ong ma ch cho biet VLR ma thue bao ang hien dien.

Mot phan ln d lieu cua thue bao trong HLR c s dung e thiet lap va xoa ket noi.

e am bao d lieu nay co the c s dung ngay lap tc cho mot cuoc goi th no con c lu tr mot c s d lieu na, c goi la VLR va VLR c lien ket vi MSC.

Goi la thanh ghi nh v thng tru v thong tin cua thue bao c lu tr lau dai trong HLR va du thue bao o codi chuyen en au th thong tin trong HLR van khong b xoa.


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c. VLR (Visistor Location Register)

Cung la mot c s d lieu e cha thong tin cua thue bao di ong. Thong tin nay cho biet v tr hien tai, trang thai cua MS, va VLR se cung cap d lieu cua thue bao ex ly cuoc goi bat c khi nao c yeu cau.

Thong tin trong VLR co tnh chat tam thi, no thay oi kha thng xuyen va khong phai c cap nhat bang tay nh trong HLR ma c cap nhat thong qua thu tuc cap nhat v tr.

VLR


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Thu tuc cap nhat v tr xay ra trong vai giay khi co 1 trong 3 ieu kien sau:

MS chuyen t tat " m may

MS di chuyen

Theo nh ky

Cap nhat v tr la mot thu tuc e thong bao cho mang ve v tr hien tai cua thue bao di ong.

v Thu tuc cap nhat v tr


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Thong qua thu tuc cap nhat v tr, d lieu cua thue bao c chuyen t HLR sang VRL hien tai.

D lieu nay c lu tr trong VLR chng nao ma thue bao o con di chuyen quanh quan trong vung do VLR nay quan ly.


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V du: Vao nhng nam 1993 1994, cac thue bao di ong c anh so theo khu vc Mien Bac, Mien Trung va Mien Nam, cu the nh mang MobiFone

Th trong HLR thuoc mien Bac ch cha d lieu cua cac MS co au so la 0904 nhng trong VLR cua mien nay th ngoai cac thue bao co au so 0904 con co cac thue bao co cac au so 0908 va 0905 di chuyen t mien Nam va mien Trung ra.

- 0901,2,3, xxxxxx: la cac thue bao di ong ang ky mien Bac- 0907,8,9 xxxxxx: la cac thue bao di ong ang ky mien Nam- 0905,6 xxxxxx: la cac thue bao di ong ang ky mien Trung


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Neu mot thue bao di chuyen sang vung phuc vu cua mot VLR khac th thu tuc cap nhat v tr se c lap lai: VRL mi yeu cau d lieu cua thue bao nay t HLR quan lythue bao o.

ong thi, d lieu cua thue bao nay trong VLR cu se b xoa. Ngoai ra, thong tin trong VLR cung se b xoa khi thue bao tat may.


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Ngoai ra, VLR con tham gia kiem tra mot thue bao co uquyen e truy xuat vao mang hay khong, ngha la thc hien nhan thc thue bao.

d. AuC (Authentication Center): Trung tam nhan thc thue bao

Chc nang: ket hp vi HLR cung cap cho VLR cac thong so e nhan thc mot MS co quyen truy nhap vao mang hay khong.

e. EIR (Equipment Identity Register): Thanh ghi nhan dang thiet b.

Chc nng: Dung e lu tr so IMEI (International Mobile Equipment Identity) cua tat ca cac thue bao trong vung phuc vu cua no.


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Moi ME c san xuat ra eu co mot so IMEI duy nhat tren the gii, so nay va c lu trong ROM cua ME, va c lu trong EIR.

Trong EIR, so IMEI cua tat ca thiet b di ong c sdung c phan vao 3 danh sach (list):

WHITE LIST cha cac ME khong b gii han

GREY LIST cha cac thiet b ang c giam sat, theo doi

BLACK LIST cha cac thiet b khong hp le (vd: thiet b o a b an cap,)


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e kiem tra mot ME co hp le hay khong th au tien MSC se yeu cau so IMEI t MS sau o MSC se gi soIMEI nay en EIR. EIR se kiem tra xem thiet b o thuoc danh sach nao

va gi ket qua ve lai cho MSC.


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V du: Neu ME o thuoc BLACK LIST th no khong thethc hien/nhan cuoc goi.

Thanh ghi EIR khong quan trong nhng neu quan lythanh ghi nay tot th se khong co hien tng mat may di ong!


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1.4 He thong con OMS (Operation & Maintenance Subsystem)

Mot OMS gom 1 hoac nhieu OMC. Mot OMC ho tr cac chc nang sau:

Quan ly cau hnh mang

Quan ly qua trnh lam viec cua mang

Quan ly bao mat

OMC c ket noi vi NSS (SSS) va BSC thong qua mot mang d lieu goi X.25.


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OMC bao gom cac may tnh ma t ay nha khai thac co the nhap cac lenh e ieu hanh, bao dng hethong. Cac may tnh nay c ket noi vi nhau qua mot mang LAN.

ay cung la ni duy nhat ma ngi khai thac giao tiep c vi mang di ong.

TCP/IP (LAN)

OMS

OMS

Printer

Console

Console

MSC


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Ngoai ra, trong mang GSM con co:v He thong billing:

v SMSC (Short Message Service Center)

Thc hien chc nang cung cap dch vu SMS cho cac MS.

Lu tr tam thi cac ban tin SMS.

Thc hien chc nang tnh cc cho cac cuoc goi. Billing bao gm:

H thong tra trc - Prepaid H thong tra sau - Postpaid

Co 2 loai ban tin la : 80 ky t (mang Sfone thi kyau) va 160 ky t.


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2. GIAO DIEN VO TUYEN Um

Sau khi hoan tat phan nay, chung ta co the:

Liet ke c cac bang tan ma cac he thong di ong GSM ang s dung.

Giai thch c cau truc vat ly cua cac kenh giao dien vo tuyen.

Phan biet c cac loai kenh logic giao dien vo tuyen.

Giai thch c cau truc cua kenh lu lng.

Giai thch c chc nang va cau truc cua cac kenh ieu khien.

2.1 Muc tieu:


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2.2 Cac bang tan so trong GSM

He thong GSM co hai bang tan lam viec la bang tan 900 MHz c goi la GSM 900 va bang tan 1800 MHz c goi la DCS 1800.

Trong o, moi bang tan nay lai c chia lam 2 bang tan con:

Bang tan hng len (UPLINK UL): la bang tan c MS s dung e truyen tn hieu en BTS.

Bang tan hng xuong (DOWNLINK DL): la bang tan c BTS s dung e truyen tn hieu en MS.


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GSM 900 lam viec trong dai tan so t 890MHz en 960MHz, trong o:

Bang tan hng len nam trong dai tan so t 890MHz en 915MHz.

Bang tan hng xuong nam trong dai tan so t935MHz en 960MHz.

Dai tan so t 915MHz en 935MHz la khoang bao ve.


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DCS 1800 lam viec trong dai tan so t 1710 MHz en 1880 MHz, trong o:

Bang tan hng len nam trong dai tan so t 1710 MHz en 1785 MHz.

Bang tan hng xuong nam trong dai tan so t 1805 MHz en 1880 MHz.

Dai tan so t 1785 MHz en 1805 MHz la khoang bao ve.


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Chu y: Song mang au tien (200kHz) khong c s dung.

Khoang cach gia song mang hng len va hng xuong trong cung mot kenh la 45 MHz.

o rong bang tan cua moi song mang la 200 kHz.

Moi hng cua bang tan GSM 900 c chia thanh 124 song mang (Carrier C).

Toan bo bang tan GSM 900 c chia lam 124 kenh tan so vo tuyen (RFC Radio Frequency Channel), moi RFC gom 2 song mang: 1 cho hng len va 1 cho hng xuong.


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Chu y: Cung nh bang tan GSM 900, song mang au tien (200kHz) khong c s dung.

Khoang cach gia song mang hng len va hng xuong trong cung mot kenh la 95 MHz.

o rong bang tan cua moi song mang cung la 200 kHz.

Tng t, moi hng cua bang tan DCS 1800 c chia thanh 374 song mang.

Toan bo bang tan DCS 1800 c chia lam 374 kenh tan so (RFC), moi kenh gom 2 song mang: 1 cho hng len va 1 cho hng xuong.


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v Viec truy cap vao mang thong qua cac kenh tan so vo tuyen trong mot dai tan c goi la a truy cap phan chia theo tan so (FDMA).


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v Bang sau liet ke cac s khac nhau gia bang tan GSM 900 va DCS 1800.

75 MHz25 MHzo rong bang tan moi hng

95 MHz45 MHzKhoang cach gia hai tan sotrong 1 kenh tan so

374124So lng kenh tan so

Hoat ong bang tan 1800 MHz

Hoat ong bang tan 900 MHz

Tan so hoat ongDCS 1800GSM 900ac iem so sanh


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Tuy thuoc vao lu lng, mot cell co the s dung mot hoac nhieu kenh tan so (RFC).

V so lng kenh tan so la co han nen mot RFC phai c s dung lai rat nhieu lan.

Tuy nhien, e tranh hien tng nhieu ong kenh th cac cell gan nhau phai s dung cac RFC khac nhau.

Do o, cac BTS s dung cung mot RFC phai am bao cach nhau mot khoang cach an toan (safe distance).

Khoang cach an toan nay c goi la REUSE DISTANCE (KHOANG CACH S DUNG LAI TAN SO).


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2.3 Cac kenh vat ly Giong nh he thong PCM32 (1 luong PCM32 gom 32

kenh), 1 RFC bao gom 8 kenh. V the, nhieu thue bao di ong co the truy cap mot RFC.

Phng phap truy cap nay c goi la a truy cap phan chia theo thi gian (Time Division Multiple AccessTDMA).


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2.3 Cac kenh vat ly (tt) Kenh vat ly la tan so dung e truyen tai thong tin.

V du kenh tan so 890Mhz la kenh vat ly.

Kenh Logic la do kenh vat ly tach ra, trong GSM mot kenh vat ly c chia ra lam 8 kenh logic.


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Mot kenh vat ly c xac nh bi mot cap song mang cu the (ngha la bi mot RFC) va mot khe thi gian trong khung TDMA.

So lng kenh vat ly toi a cua mot he thong GSM la bao nhieu?


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Mot kenh vat ly co the hoat ong nh:Mot kenh lu lng (traffic channel) e truyen thoai va

d lieu cho ngi dung.

2.4 Cac kenh logic Kenh Logic la do kenh vat ly tach ra


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Hoac nh mot kenh ieu khien e truyen thong tin ieu khien va bao hieu.

v Kenh lu lng va kenh ieu khien c goi chung lakenh logic (logic channel).


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Cac kenh lu lng (Traffic Channel TCH) khac nhau tuy theo:

Loai thong tin ma chung van chuyen: thoai c sohoa hoac d lieu cua ngi dung.

Toc o truyen cua kenh: full rate hoac half rate.

Toc o cua d lieu oi vi truyen d lieu (ngha la toc o d lieu cua ngi dung thc s c truyen), nh:

2.4.1 Cac kenh lu lng

o D lieu toan toc cho 9.6 kb/s, 4.8 kb/s, 2.4 kb/s.

o D lieu ban toc cho 4.8 kb/s, 2.4 kb/s.


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Hnh sau cho ta thay cac loai kenh lu lng


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v Kenh thoai toan toc va ban toc (Full/Half rate speech) Thong tin thoai c truyen qua giao dien vo tuyen

c nen thanh toc o 13 kb/s (full rate) hoac 6.5 kb/s (half rate) bang cac thuat toan ma hoa thoai ac biet.

Ma hoa thoai ban toc co c trien khai hay khong phuthuoc vao s tng thch cua thiet b chuyen oi ma trong BSC va trong MS.

Toc o kenh la 22.8 kb/s oi vi full rate va 11.4 kb/s oi vi half rate co c la do viec chen them cac bit sa loi e truyen i cung vi thong tin thoai giao dien vo tuyen.


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Bang sau cho ta thay toc o kenh thoai full rate va half rate trc va sau khi ma hoa (them cac bit sa loi).


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Khi truyen thoai va d lieu half rate, so lng kenh lu lng tang len gap oi v mot khe thi gian vat lycung luc phuc vu en hai ket noi.

ieu nay at c la do 2 ket noi nay thay phien nhau s dung cung mot khe thi gian.

Tuy nhien, ban se khong cam nhan c s suy giam chat lng ket noi.


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2.4.2 Cac kenh ieu khien

Ngi ta nh ngha ba nhom kenh ieu khien sau:

Cac kenh quang ba (BCHBroadcast Channel)

BCH la cac kenh ieu khien hng xuong, c s dung e mang thong tin ac thu cua cell dung trong viec ong bo, sa loi,

Cac kenh ieu khien chung (CCCHCommon Control Channels)

CCCH la cac kenh ieu khien c s dung bi tat caMS va BTS chang han nh e yeu cau va cung cap cac kenh ieu khien danh rieng.


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Cac kenh ieu khien danh rieng (DCCHDedicated Control Channels)

DCCH c an nh cho mot MS e no thc hien mot phien giao dch cu the khi ma cac kenh lu lng cha c cung cap.

Moi nhom kenh ieu khien bao gom nhieu kenh ieu khien e cung cap cac chc nang ieu khien can thiet cho mang GSM, nh c the hien tren hnh sau.


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Kenh ieu khien quang ba (BCCHBroadcast Control Channel) L knh ng xung cung cp thng tin chung v

mng, cell m MS ang v cc cell ln cn.

Kenh hiu chnh tn s (FCCHFrequency Correction Channel)

La kenh ng xuong cung cap thong tin e MS ong bo tan so noi cua no (bo dao ong noi) en tan so mamang cap cho MS o s dung.

Khi thc hien nhay tan th noi dung cua kenh nay thay oi lien tuc.

Sau ay se mieu ta chc nang cua tng kenh:a. Cac kenh quang ba


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Kenh ng b (SCHSynchronization Channel)

La kenh ng xuong mang thong tin ve ong bokhung va nhan dang tram BTS.

S d phai co kenh ong bo la v mot MS co the cach BTS ang phuc vu no en 30 km mang thng phai ieu chnh thi gian phat cua mot MS sao cho tn hieu thu c tai BTS c ong bo vi ong ho cua BTS.

BTS cung xuat lenh phat sm en MS qua kenh SCH nay.


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vV du ng dung cua kenh BCH

Thong qua kenh quang ba, BTS truyen d lieu mot cach lien tuc chang han nh truyen thong tin nhan dang cell en MS.

Bang cach nay, MS co the xac nh c hien tai noang ng cell nao.


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b. Cac kenh ieu khien chung

Kenh tm goi (PCHPaging Channel)

La kenh hng xuong, dung e thong bao cho MS biet la co cuoc goi en no.

Ngoai ra, PCH con c s dung e truyen cac ban tin SMS en MS.

Kenh truy xuat ngau nhien (RACHRandom Access Channel)

La mot kenh hng len, c MS s dung e phuc ap lai mot ban tin tm goi t kenh PCH.

Ngoai ra, RACH con c MS s dung e bao cho mang biet la no muon thc hien mot cuoc goi.


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Khi can thc hien cuoc goi, MS phat ban tin nay roi ch BTS tra li.

Neu sau mot khoang thi gian khong nhan c tn hieu tra li t BTS th MS t ong phat lai ban tin nay nen kenh nay co ten la kenh truy xuat ngau nhien.

Kenh cho phep truy cap (AGCHAccess Grant Channel)

La mot kenh hng xuong, c BTS s dung e ap lai 1 RACH.

Muc ch cua kenh AGCH la e cap phat cac tai nguyen cho MS (SDCCH va TCH).


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c. Cac kenh ieu khien danh rieng

Co 3 loai kenh ieu khien danh rieng trong GSM.

Cung giong nh cac kenh lu lng, cac kenh ieu khien danh rieng la 2 chieu va co format cung nhchc nang giong nhau ca hng len va hng xuong.


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Kenh ieu khien danh rieng mot mnh (SDCCHStand-alone Dedicated Control Channel)

SDCCH mang d lieu bao hieu sau khi ket noi gia MS va BTS c thiet lap nhng trc khi BTS cap phat mot TCH cho MS.

SDCCH am bao MS va BTS van duy tr ket noi trong khi BSS va MSC xac minh MS co quyen truy cap vao mang hay khong.

Do o, SDCCH co the c xem la mot kenh tam thi, trung gian.

SDCCH c s dung e gi thong tin nhan thc vacac ban tin canh bao.


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Kenh ieu khien ket hp cham (SACCHSlow Associated Control Channel)

SACCH luon luon c ket hp vi mot kenh lu lng TCH hoac mot kenh SDCCH.

hng xuong, SACCH c s dung e gi nhng thay oi ve thong tin ieu khien en MS nh cac hng dan ve mc cong suat phat, cac ch dan ve thi gian phat sm.

Thong tin nay c gi cham nhng eu an.

hng len, SACCH mang thong tin ve chat lng cua kenh TCH cung nh ket qua cng o trng cua cac cell lan can ma MS o lng c e mang s dung trong viec ieu khien chuyen giao.


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Kenh ieu khien ket hp nhanh (FACCHFast Associated Control Channel)

FACCH mang cac ban tin khan va tren thc te th nocha cung loai thong tin nh SDCCH.

Mot FACCH c cap phat bat c khi nao mot kenh SDCCH khong c danh rieng cho mot MS nao o vakhi co mot ban tin khan (nh mot yeu cau chuyen giao).

FACCH lam viec che o lay cap. ieu nay c thc hien bang cach set 2 bit ac biet, c goi la cac bit lay cap trong kenh TCH len 1.

Neu cac bit lay cap c thiet lap th khe thi gian c coi nh cha d lieu FACCH ch khong phai la TCH.

N2


N2 Sa SACCH li thnh SDCCHNhan, 10/5/2007


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vV du ve cac kenh DCCH, CCCH

Mot MS quay so thue bao can goi

Cac loai kenh nao se c cap cho MS nay va loai thong tin nao se c truyen?


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Trc khi MS co the gi so thue bao b goi en BTS thMS yeu cau mot kenh ieu khien danh rieng t BSC thong qua mot kenh ieu khien chung, o chnh la kenh RACH.


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BSC cap phat mot DCCH cho MS cung lai thong qua mot CCCH, o chnh la kenh AGCH.


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Thong qua DCCH, tat ca tn hieu bao hieu dung e thiet lap ket noi c trao oi (v du nh nhan thc thue bao, gi so thue bao b goi, cap phat kenh lu lng).


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2.5 Cac cum (bursts):

Cau truc bit cua mot kenh phu thuoc vao viec no c s dung nh kenh lu lng hay kenh ieu khien.

Mot kenh lu lng co cau truc bit nh sau:

Mot chuoi bit c nh ngha nh tren goi la mot cum. Cum tren c goi la cum thng (Normal Burst).


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Trong o:

TB = Tail Bits: Phan nay gom 3 bit va c dung e xac nh cac c cua khe thi gian.

Coded Bits: Cac phan nay cha thong tin cua ngi dung a c ma hoa (thoai hoac d lieu) trong 2 57 bits.

Training Sequence: Phan nay cha mot mau bit dai 26 bit, c s dung e cho phep bo can bang thch ng trong may thu cua MS hoac BTS phan tch cac ac tnh cua kenh vo tuyen trc khi giai ma d lieu cua ngi dung.

GP = Guard Period: 8,25 bit nay c s dung nham tranh cac s lech pha (xay ra do s di chuyen cua MS).


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Mot khe thi gian c s dung nh kenh ieu khien co thecha:

Hoac mot cum ieu chnh tan so (Frequency Correction Burst FB) cho kenh ieu chnh tan so.

Hoac la mot cum ong bo (Synchronisation Burst SB) e s dung cho kenh ong bo.


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Hnh sau mieu ta tat ca cac cum trong GSM.


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Trong o cum truy xuat (Access Burst) c s dung bi tat ca cac MS khi co nhu cau truy cap dch vu cua hethong.

Ngoai ra trong GSM con co mot loai cum na c goi la cum gia (Dummy Burst), c s dung e lam ay thong tin cho cac khe thi gian khong c s dung hng xuong.

Cum gia nay co cau truc hoan toan giong vi cum thng.


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2.6 Cau truc thi gian cua cac kenh vat ly

Neu mot khe thi gian c s dung e truyen thong tin ieu khien th no cha cac loai kenh ieu khien khac nhau hay noi cach khac no cha cac loai cum khac nhau.

Cu the, cac kenh BCH va CCCH ch c truyen TS0 trong cac khung TDMA nao o trong mot a khung gom 51 khung lap i lap lai nhng RFC danh cho muc ch quang ba.

a khung nay c goi la a khung ieu khien.

Nh vay, t TS1 en TS7 cua cac khung nay van mang lu lng TCH bnh thng.


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oi vi cac RFC quang ba, khung th 51 khong cha bat ky d lieu cua cac kenh BCH/CCCH hng xuong nao va c coi nh mot khung roi.

Tuy nhien, kenh CCCH hng len co the nhan thong tin cua thue bao trong suot TS0 cua moi khung (tham ch ngay ca khung roi).


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Tng t nh cac kenh ieu khien, cac kenh lu lng cung c ket hp lai e tao thanh mot a khung vac goi la a khung thoai.

Moi a khung thoai gom 26 khung TDMA.

Khung 13 cha d lieu cua kenh SACCH.

Khung 26 cha cac bit roi khi cac kenh lu lng toan toc c s dung, va cha d lieu cua kenh SACCH khi cac kenh lu lng ban toc c s dung.

Trong 26 khung, khung th 13 va 26 khong c dung cho lu lng ma cho cac muc ch ieu khien, cu the:


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Vi mot kenh lu lng ban toc, cau truc thi gian cua khe thi gian th x nh sau:


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2.7 Cau truc khung cua GSM

Co 8 khe thi gian trong mot khung TDMA, va chu kykhung la 4.615 ms.

Mot khung cha 8 156.25 = 1250 bit.

Cac khung (frame) thng c nhom thanh cac cau truc ln hn c goi la a khung (multiframe), cac a khung c nhom thanh cac super frame va cac super frame lai c nhom thanh cac hyper frame.


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Mot multiframe gom 26 TDMA frame.

T hnh ve ta thay, oi vi kenh lu lng th:

Mot super frame gom 51 multi frame (tc gom 1326 TDMA frame).

Mot hyper frame gom 2048 super frame (tc gom 2715648 TDMA frame).

Mot multiframe gom 51 TDMA frame.

Con oi vi kenh bao hieu (ieu khien) th:

Mot super frame gom 26 multi frame (tc gom 1326 TDMA frame).

Mot hyper frame gom 2048 super frame (tc gom 2715648 TDMA frame).


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2.8 T2.8 T CHCHC MC MNG VNG V MMT T A L CA L CA GSMA GSM Trong mt quc gia c th

c nhiu mng GSM cng tn ti v chng c thbao ph ln nhau v mt a l.


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Mt h thng GSM quc gia u tin c chia thnh cc vng phc vca MSC.

2.8 T2.8 T CHCHC MC MNG VNG V MMT T A L CA L CA GSM (TT)A GSM (TT)


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Cc thu bao di ng m tin hnh th tc cp nht v tr trong vng phc v ca MSC no th s c ng k trong VLR lin kt vi MSC .


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MSC c kt ni vi cc BSS trong vng phc v ca n. BSS chu trch nhim qun l cc cell. Cell l vng phc v nh nht ca mng GSM.

Mt BTS chu trch nhim cung cp cc ng truyn v tuyn cho mt cell.


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Kch thc ca cc cell khc nhau tu thuc vo a hnh v mt thu bao; c th l cell vng ng dn c lun lun c bn knh nh hn so vi cc cell cc vng nng thn.

gc qun l, nhiu cell c kt hp li hnhthnh mt Location Area (LA).

Mi LA c mt s nhn dng ring c gi l LAI (Location Area Identity), s ny l duy nht trn th gii.


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S LAI bao gm cc trng sau:

MCC (Mobile Country Code) dng nhn dng quc gia, gm 3 ch s.

MNC (Mobile Network Code) dng nhn dng cc mng GSM khc nhau trong 1 quc gia, gm 2 ch s.

LAC (Location Area Code) dng ch r mt LA no trong mt mng GSM bng cch s dng 2 byte.


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2.9 C2.9 CC SC S NHNHN DN DNG THU BAO DI NG THU BAO DI NG TRONG GSMNG TRONG GSM

2.9.1. S MSISDN

Bng cch quay mt t hp cc con s no , bn c th gi mt thu bao di ng.

T hp cc con s ny c gi l s MSISDN (Mobile Station ISDN).

Nh vy, MSISDN l mt s c th quay c (dialable), c thu bao ch gi s dng tip cn vi thu bao b gi.

N4


N4 THAM KHAO FILE Introduction to GSM (file Internet explorer)Nhan, 10/11/2007


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2.9 C2.9 CC SC S NHNHN DN DNG THU BAO DI NG THU BAO DI NG TRONG GSM (TT)NG TRONG GSM (TT)

MSISDN bao gm: Country Code (CC): M quc gia dng nhn dng

quc gia v n chnh l m quc gia trong mng PSTN quc t. S lng cc ch s ca CC l khng c nh.

NDC (National Destination Code): Dng nhn dng mng di ng mt t v cng c chiu di bin i.

SN (Subscriber Number): S ny dng nhn dng mt thu bao di ng.

Hin ti, chiu di ti a ca MSISDN l 12 ch s.


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2.9.2 S IMSI

IMSI (International Mobile Subscriber Identity): L snhn dng thu bao di ng quc t, l mt s non-dialable duy nht c cp pht cho mi thu bao di ng trong h thng GSM nhn dng thu bao trong mng.

S IMSI c s dng trong lc trao i bo hiu trong ni b h thng di ng nhn dng mt thu bao.


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S IMSI c cu trc nh sau:

MCC (Mobile Country Code): L m nhn dng quc gia, s dng 3 ch s.

MNC (Mobile Network Code): M mng di ng dng nhn dng mng di ng mt t s dng 2 ch s.

MSIN (Mobile Subscriber Identification Number): Cchiu di c nh l 10 ch s, 2 ch s u dng nhn dng HLR qun l thu bao, 8 ch s cn li dng nhn dng tng thu bao di ng.


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IMSI c lu tr lu di, c nh trong SIM card. Tuy nhin, thu bao di ng khng bit s IMSI ny.

Trong HLR, IMSI c s dng nh a ch ca b nhd liu ca thu bao.


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2.9.3. S TMSI

Cc bo hiu giao din v tuyn phi c kh nng nhn dng mt thu bao.

Khi cc bn tin bo hiu khng c m ho hon tonth s IMSI khng ph hp truyn trn cc giao din v tuyn v cc nguyn nhn v vn bo mt.

Ni cch khc, s bo mt ca thu bao khng c bo m trong mt s trng hp no .


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y l nguyn nhn gii thch ti sao giao din v tuyn th s IMSI c thay th bi mt s nhn dng khc, s ny c cp pht tm thi v c lu trtrong VLR v trong SIM card.

S nhn dng ny c gi l TMSI (Temporary Mobile Subscriber Identity). S ny c cu trc bin i.

TMSI l mt s gi ngu nhin c to ra t s IMSI.

TMSI c s dng trnh vic phi truyn IMSI qua giao din v tuyn. iu ny gip gi s IMSI c bo mt hn.


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theo di mt thu bao di ng thng qua IMSI/TMSI, ngi nghe trm phi thm nhp vo qu trnh lin lc ca mng GSM khi s TMSI c tho thun ngay t lc ban u.

Ngoi ra, v s TMSI c tho thun li theo nh k nn ngi nghe trm phi thm nhp vo mng mi khi s TMSI c tho thun li.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSMNH TRONG GSM2.10.1 Th tc nhn thc Th tc nhn thc c thc hin trong rt nhiu hot

ng khc nhau ca thu bao di ng nh trong qu trnh cp nht v tr, trc khi nhn cuc gi, trc khi thc hin cuc gi, kim tra xem mt thu bao di ng c quyn truy cp vo mng hay khng.

Vic to ra mt thu bao trong mng di ng GSM bt u bng vic sn xut ra mt SIM card.

Ngoi IMSI, LAI, TMSI v Ki, trong SIM cn lu tr cc thut ton A3 v A8.

D liu ny (IMSI, Ki, A3 v A8) cng c lu tr trong AC v c s dng tnh ton cc thng s nhn thc thu bao (b ba triples).

B ba nhn thc bao gm: RAND, SRES v Kc.Su tm bi: www.daihoc.com.vn

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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt)


107

2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Vic tnh ton b ba trong AC c thc hin nh sau:


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AC lun to ra nhiu b ba cho mi thu bao di ng v gi n n VLR thng qua HLR khi c yu cu.

Trong qu trnh nhn thc, VLR gi s ngu nhin (RAND) n MS. SIM s dng thng tin ny tnh ra SRES v gi s ny (SRES) tr li VLR so snh.

Nu VLR so snh thy 2 SRES ny ging nhau th coi nh qu trnh nhn thc thnh cng.

Trong ln nhn thc sau , VLR s s dng b ba ktip. Nu VLR s dng ht cc b ba th n s yu cu mt tp b ba mi t HLR.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Hnh sau minh ho th tc nhn thc trong GSM.


110

2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Cng nh hnh trn, hnh sau cng minh ho th tc

nhn thc trong GSM.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt)2.10.2 Th tc cp nht v tr

Nu LAI c lu trong SIM khc vi LAI nhn c knh qung b ca cell th lc ny MS s khi ng thtc cp nht v tr.

Ni cch khc, cp nht v tr c khi xng bi MS khi n di chuyn sang LA khc.

Gi s mt thu bao di ng ng k HLR Munich sdng SIM card ca anh ta ln u tin MSC thuc vng Berlin.

Lc ny, MS nhn thy LAI m n nhn c knh qung b khc vi LAI c lu trong SIM card nn n s yu cu mt th tc cp nht v tr s dng IMSI.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) VLR Berlin nhp IMSI vo c s d liu ca n v yu

cu cc b ba t AC Munich thng qua HLR Munich thc hin th tc nhn thc.

AC Munich cung cp cc b ba theo yu cu v gi chng n VLR Berlin thng qua HLR Munich.

Trong VLR Berlin, cc b ba ny c s dng cho thtc nhn thc.

By gi VLR Berlin yu cu d liu ca thu bao di ng t HLR Munich. Cng vi yu cu ny, VLR Berlin sgi s VLR ca n v mt LMSI n HLR Munich.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) VLR number: L a ch bo hiu quc t ca VLR.

VLR number c format ging vi mt MSISDN.

LMSI (Local Mobile Subscriber Identity) l a ch dliu ca thu bao trong VLR cho php truy cp dliu ny mt cch nhanh chng.

S VLR v LMSI c bit quan trng trong th tc tm gi.

HLR Munich lu tr s VLR Berlin v LMSI v cung cp d liu ca thu bao nh c yu cu cho VLR Berlin.

VLR Berlin lu tr d liu ca thu bao v cp pht mt TMSI cho thu bao di ng.

TMSI c m ha v gi n MS, ti y n c lu tr trong SIM card cng vi LAI mi.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Hnh sau minh ha th tc cp nht v tr.


116

2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Nh vy, sau khi cp nht v tr th:

VLR cha tt c d liu ca thu bao cn thit xl mt cuc v LAI hin ti ca thu bao di ng .

HLR cha a ch ca VLR hin ti v c s dng khi c cuc gi n thu bao di ng ..

D liu c lu tr trong SIM card sau khi th tc cp nht v tr c thc hin l:

A3A8

TMSIKiLAIIMSI

D liu tm thiD liu c nh


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt)2.10.3 Th tc nhn cuc gi (Mobile Terminating CallMTC)

Xt mt thu bao di ng ng k Munich nhng hin ti di chuyn sang Berlin.

Gi s mt thu bao PSTN quay s MSISDN ca thu bao di ng ny.

Sau khi phn tch s, mng PSTN s thit lp mt knh lu lng gia tng i ch gi v MSC ca mng di ng. MSC ny c gi l Gateway MSC (GMSC).


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) GMSC cn thm thng tin nh tuyn thit lp knh

lu lng n ng MSC m thu bao di ng hin ti ang c mt .

Thng tin nh tuyn ny c gi l Mobile Station Roaming Number (MSRN).

Qu trnh cung cp s MSRN bao gm cc bc sau:


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Bc 1: GMSC xc nh HLR Munich bng cch s

dng HLR-ID trong s MSISDN nhn c, sau yu cu s MSRN t HLR Munich.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Bc 2: HLR Munich xc nh VLR hin ti ca thu

bao ny (VLR Berlin) v yu cu mt MSRN t VLR ny s dng s IMSI.

Bc 3: VLR Berlin gi MSRN n GMSC thng qua HLR Munich.


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MSRN l mt t hp s c cu trc ging nh MSISDN.

VLR Berlin s nh s MSRN cung cp cho thu bao di ng ny.

GMSC thit lp mt kt ni lu lng v gi tr li s MSRN nhn.

MSC Berlin yu cu VLR ca n cung cp TMSI v LAI cho thu bao ny thng qua MSRN.

p ng yu cu ny, VLR Berlin cung cp TMSI v LAI c lu tr trong ln cp nht v tr sau cng cho MSC Berlin.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) V MSC Berlin ch bit LA ca ln cp nht cui cng

nn n s iu khin tt c cc BSC phc v LA ny pht mt bn tin tm kim tt c cc cell trong LA.

Th tc ny c gi l Paging.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) MS trong cell hin ti tr li bng mt paging respone.

paging respone ny s c chuyn n MSC thng qua BSC.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Sau khi tin hnh nhn thc li v VLR cp pht mt

TMSI mi th qu trnh thit lp cuc gi n MS c hon tt.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt)2.10.4 Th tc xut pht cuc gi (Mobile Originating Call

MOC)

iu g s xy ra nu mt thu bao di ng mun gi cho mt thu bao (di ng/c nh) khc ?


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Nu mt thu bao di ng quay mt s in thoi th c

ngha l thu bao ang yu cu mt knh lu lng cho n.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) VLR thc hin th tc nhn thc, cp pht mt TMSI

mi v kim tra xem thu bao c c quyn s dng dch v m thu bao yu cu hay khng (qu trnh ny c gi l subsciption check).


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Nu qu trnh subsciption check thnh cng, MSC s

thit lp knh lu lng n BSC v thu bao, ngha l thu bao c cp pht mt knh lu lng thc hin cuc gi.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt)2.10.5 Th tc chuyn giao (Handover/Handoff) Khi nim: Chuyn giao l qu trnh chuyn i BTS

phc v ca MS khi MS ny ang trong ch m thoi.

Cc iu kin xy ra chuyn giao: iu kin 1:

Khi MS ang m thoi nhng di chuyn t vng phsng ca BTS ny sang vng ph sng ca BTS khc th cng trng ca BTS phc v gim dn, cng trng ca BTS ln cn tng ln nhiu.Nu MS tip tc di chuyn theo hng ny th n mt thi im no cng trng ca BTS phc v khng hot ng. Do , mun tip tc m thoi th phi chuyn giao sang BTS ln cn.


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iu kin 2:

Khi MS khng di chuyn nhng n ang trong vng ph sng l giao ca 2 BTS.

Khi , v mt l do no lm cho ch s bit li trn BTS ang phc v tng ln th h thng cng thc hin chuyn giao sang BTS mi ci thin cht lng.

Chuyn giao ny c gi l chuyn giao cht lng.


136


iu kin 3:

Khi MS khng di chuyn nhng n ang trong vng ph sng l giao ca 2 BTS.

Khi , nu lu lng trn BTS ang phc v bo ho hoc sp bo ho th h thng cng thc hin chuyn giao mt s MS sang BTS mi BTS ny cth phc v c cho cc MS mi khc.

Chuyn giao ny c gi l chuyn giao lu lng.


137


Chuyn giao c phn thnh cc loi sau: Chuyn giao do BSC iu khin. Loi chuyn giao ny c chia thnh 2 loi:

Chuyn giao trong cng mt cell (Intra-Cell Handover). Chuyn giao gia cc cell thuc cng mt BSC (Inter-

Cell Handover). Chuyn giao do MSC iu khin. Loi chuyn giao ny

cng c chia thnh 2 loi: Chuyn giao gia cc cell thuc 2 BSC khc nhau v 2

BSC ny thuc cng mt MSC (Intra-MSC Handover). Chuyn giao gia cc cell thuc 2 BSC khc nhau v 2

BSC ny thuc hai MSC khc nhau (Inter-MSC Handover).


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139


Nguyn tc chuyn giao

V c bn, mt th tc chuyn giao c thc hin qua 4 giai on.

Giai on 1: BSC quyt nh xem mt s chuyn giao cn phi c tin hnh hay khng ?

Giai on 2: Mt kt ni mi c thit lp song song vi kt ni ang c.

Giai on 3: MSC chuyn mch cuc gi sang kt ni mi.

Giai on 4: Kt ni ban u c xa.

By gi chng ta s xt cc giai on ny chi tit hn, sdng mt Inter-MSC Handover nh mt v d.


140


Giai on 1:

Gi s mt thu bao di ng thc hin mt cuc gi cell A v ang di chuyn sang cell B.

Trong khi thc hin cuc gi, MS lin tc o lng cht lng ca kt ni hin ti v cng trng thu c t cc cell xung quanh.

Cc kt qu o lng c truyn n BSC v BSC syu cu MS chuyn giao sang cell no c cht lng truyn dn cao hn.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) Trong v d ny, BSC pht hin cn phi thc hin mt s

chuyn giao m c iu khin bi MSC v thng bo cho MSC1.


145


Giai on 2:

MSC1 yu cu mt s chuyn giao (Handover Number HON) t MSC2 v thng bo MSC2 v cell B.

MSC2 yu cu VLR cung cp mt HON v BSC cung cp cc knh v tuyn.


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2.10 C2.10 CC THC TH TTC CHC CHNH TRONG GSM (tt)NH TRONG GSM (tt) D liu ca knh v tuyn v HON c gi tr li cho

MSC1.


148


Giai on 3:

Vi HON, by gi MSC1 c th thit lp mt kt ni lu lng vi MSC2. Kt ni ny c m rng cho n BTS.

Sau , MSC1 thng bo cho MS v knh v tuyn mn phi chuyn giao sang.


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150


Giai on 4: Kt ni vi BTS c c gii phng.


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2.10.6 Th tc MS nhn bn tin nhn ngn (SMS MT)


152

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM U TRONG GSM Hnh sau minh hoa tat ca cac hoat ong cua GSM t

au phat en au thu.


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2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt)1) So hoa:

Trong GSM, tieng noi c micro bien oi thanh tn hieu ien dang tng t (analog). Tn hieu nay c bien oi sang tn hieu so (digital) dung ky thuat ieu che xung ma PCM vi tan so lay mau la 8 kHz va ma hoa moi mau bang 13 bit.

Nh vay trong GSM, luong tn hieu so sau khi bien oi co toc o la 8 13 = 104 (kb/s).


154

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt)2) Ma nguon:

Ma nguon tc la nen tn hieu, ngha la lam cho toc o bit giam xuong. oi vi tn hieu tieng noi, viec nen tn hieu phai am bao c thi gian thc va chat lng co the chap nhan. Nguyen tac cua ky thuat nen nay la thay v truyen i cac bit mang noi dung cua tieng noi th ta ch truyen i cac thong so cua bo loc trong thanh quan e tao ra tieng noi o.Ngha la trc tien ngi ta phai nghien cu cach phat am, phat ra tieng noi cua con ngi. Khi day thanh quan mnh rung theo kieu rung khac nhau th phat ra tieng noi khac nhau ngi ta khong truyen i tieng noi ma truyen i thong so, thong so nay lien quan en cach tao ra tieng noi.


155

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) Tn hieu so ngo ra cua bo A/D co toc o 104 kbps

c chia thanh tng oan co chieu dai 20 ms, moi oan cha 2080 bit (tng ng 160 mau).

Thay v truyen i 160 mau, th ngi ta truyen i thong so cua bo loc tao ra 160 mau o, thong so cua boloc nay ch co o dai la 260 bit nen toc o truyen thc s la 13 kbps.

Ngi ta con co the nen xuong toc o thap hn na la6.5 kb/s nhng chat lng kem hn nen ngi ta t sdung.


156

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt)

3) Ma hoa kenh (cho kenh thoai toan toc):

Ma hoa kenh la them vao mot so bit d tha egiup cho au thu phat hien va sa c cac loi bit, muc ch cuoi cung la giam ty so bit loi BER (Bit Error Rate) e nang cao chat lng.

Nh vay sau khi ma hoa kenh th so bit can truyen se tang len. ieu nay co ngha la phai tra gia trong viec s dung bang thong ng truyen la phai truyen i nhieu bit hn so can thiet cho thong tin nhng lai c o an toan chong loi cao hn.


157

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) Co the chia ma kiem tra loi thanh hai loai la ma khoi

va ma xoan (ma chap). Ma khoi: la ma khong nh, ngha la cac bit kiem tra

c tnh toan ch da tren khoi thong tin hien thi. V du ve ma khoi la ma CRC. Quy tac: at M(x) la thong tin can truyen (k bit) G(x) la a thc sinh (dai n + 1 bit, vi n la bac cua a

thc sinh). R(x) la phan d (dai n bit)


158

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) au phat thc hien:

)()()(

)()(

xGxRxQ

xGxxM n

+=

au thu thc hien:

)()().(

xGxRxxM n +

Sau o truyen i M(x).xn + R(x)

Neu so d bang 0 th khong co loi.

)()()(

)()()(

)()().( xQ

xGxR

xGxRxQ

xGxRxxM n

=++=+

Neu so d khac 0 th a co loi xay ra tren ng truyen.


159

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) V du:

Gia s d lieu can truyen la: 11100110

a thc sinh la: 11001

Tc: M(x) = x7 + x6 + x5 + x2 + x

G(x) = x4 + x3 + 1

M(x).xn = M(x).x4 = x11 + x10 + x9 + x6 + x5


160


= R(x) = 0110


161

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) Vay d lieu can truyen la 111001100110

Gia s d lieu thu la 101001100110 = x11 + x9 + x6 + x5 + x2 + x

x11 + x9 + x6 + x5 + x2 + x x4 + x3 + 1x7 + x6 + x3 + x2x11 + x10 + x7

x10 + x9 + x7 + x6 + x5+ x2 + xx10 + x9 + x6

x7 + x5+ x2 + xx7 + x6 + x3

x6 + x5+ x3 + x2 + xx6 + x5 + x2

x3 + x so d khac 0 co loi


162

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) Ma xoan: Ma xoan tot hn ma khoi v no co kha nang t

phat hien loi va sa loi.

ma xoan, bo ma hoa tao ra cac bit ma khong ch phuthuoc vao cac bit cua khoi ban tin hien thi c dch vao bo ma hoa ma no con phu thuoc vao cac bit cua cac khoi trc o.

Mot bo ma xoan bao gom cac thanh ghi dch tao thanh tcac Flip-Flop.

Ma xoan c xac nh bi cac thong so sau:

- Ty le ma: r = k/n, vi n la so bit au ra khi ng vi k bit au vao bo ma hoa.

- o dai hay so phan t nh cua thanh ghi dch.


163


Trong GSM th cac bit ngo ra cua bo so hoa vama hoa nguon c xap at thanh cac nhom can c vao s quan trong cua chung trong viec ong gop vao chat lng thoai.

Trong so 260 bit, 50 bit quan trong nhat c goi la cac bit loai Ia, c them vao 3 bit CRC e phat hien loi tao thanh 53 bit. Cac bit them vao nay c xac nh da tren a thc tao ma x3 + x + 1, cho phep phat hien 1 loi bit tren 1 khoi 50 bit.


164

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) 132 bit ke tiep cung vi 53 bit au tien (50 bit loai Ia

va 3 bit CRC) c xap at lai va noi vao them 4 bit uoi bang 0, do o tao ra mot khoi d lieu co 189 bit.

Sau o khoi d lieu nay c ma hoa s dung ma xoan vi ty le ma la 1/2, v the tao ra mot chuoi 378 bit.

Cuoi cung, 78 bit t quan trong nhat khong c ma hoa va c noi vao chuoi hien co e hnh thanh mot khoi 456 bit trong 20 ms.

Lc o ma hoa kenh nay lam tang toc o d lieu cua tn hieu thoai trong GSM len en 22.8 kbps. Lc oma hoa kenh nay c minh hoa trong hnh sau.


165



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2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) 4) Ghep xen: Trong thong tin di ong, do cac fading sau lau nen cac

loi bit thng xay ra tng cum dai. Tuy nhien ma hoakenh ch hieu qua nhat khi phat hien va sa sai cac loi ngau nhien n le va cac cum loi khong qua dai.

e oi pho vi van e nay, ngi ta chia khoi ban tin can gi thanh cac cum ngan roi hoan v cac cum nay vi cac cum cua khoi ban tin khac, nh vay khi xay ra loi dai th moi ban tin ch mat i mot cum nho, phan con lai cua ban tin van cho phep cac dang ma hoa kenh khoi phuc lai c ung.

Qua trnh tren c goi la ghep xen. Nh vay muc ch cua ghep xen la phan bo loi neu co v loi phan bo de dang khac phuc hn loi lien tuc.


167

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) Ghep xen cho thoai (tieng) trong GSM: Gom cac bc sau: Bc 1: Toan bo 456 bit c phan ra thanh tam khoi con 57 bit. Nhom A: 1, 9, 17, , 449 Nhom B: 2, 10, 18, , 450 Nhom C: 3, 11, 19, , 451 Nhom D: 4, 12, 20, , 452 Nhom E: 5, 13, 21, , 453 Nhom F: 6, 14, 22, , 454 Nhom G: 7, 15, 23, , 455 Nhom H: 8, 16, 24, , 456


168

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) Bc 2: Cac nhom noi tren lai c ghep xen mc th 2.

mc nay, 4 nhom au cua mot t ma (la A, B, C, D) c at vao v tr au tien cua 4 cum, 4 nhom con lai c at vao v trsau cua 4 cum tiep theo.

Phan con lai cua cac cum nay dung e ghep tn hieu cua cac tma lan can.


169

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) Vay moi cum truyen thong tin cho 2 t ma.

1 t ma can 8 cum e truyen.

2 t ma can 12 cum e truyen

3 t ma can 16 cum e truyen

Nhc iem: Neu khong ghep xen th ch can thu 4 cum la a biet c t ma, con neu dung ghep xen thphai thu 8 cum mi biet c t ma gay ra tre nhng van co the chap nhan c.

Neu mat 1 cum th he thong co the gan la bit 0 hoac bit 1 tuy y, qua bo giai ma se sa loi.


170

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) Ghep xen cho d lieu trong GSM: oi vi tn hieu d

lieu th ngi ta ghep xen nhieu hn na, 1 t ma c truyen i trong 22 cum v no can o chnh xac cao.

Khac vi ghep xen cho thoai la so bit cua mot t ma c cha trong cac cum khong eu nhau.


171

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt)A1

B1 A2

C1 B2 A3

D1 C2 B3 A4

D2 C3 B4 A5

D18 C19

D19

.

.

.

Cum 1

Cum 2

Cum 3

Cum 4

Cum 6

Cum 21

Cum 22


172

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) 5) To chc cum: la them d lieu nh phan vao cac khoi

a c ghep xen e giup ong bo tn hieu c thu.

6) Mat ma hoa:

Tren ng truyen vo tuyen, mac du thong tin a c ghep xen, ch truyen i thong so cua bo loc chkhong truyen tieng noi, nhng van cha am bao thong tin cua ngi dung c bao mat hoan toan

Do o, tn hieu sau khi a to chc cum, trc khi a vao ieu che th ngi ta a qua mot cong XOR eXOR tn hieu can truyen vi 1 chuoi gia ngau nhien.


173

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) e tao chuoi gia ngau nhien ngi ta s dung cac Flip-

Flop va c goi la cac phan t nh. Trong GSM, ngi ta s dung so phan t nh la 15

chu ky cua chuoi gia ngau nhien la 215 1. Trc khi lu lng c truyen th MS va BTS phai

thoa thuan vi nhau chuoi gia ngau nhien nay va bao cho MSC biet.

Lu y la mat ma hoa ch ap dung cho cac cum thng va ch lay 114 bit thong tin e XOR vi chuoi PN.

7) ieu che: Lc o ieu che c s dung bi GSM la GMSK, GMSK la mot kieu ieu che ac biet cua ieu che FM so.


174

2.11 X2.11 X LYLY TTN HIEN HIEU TRONG GSM (tt)U TRONG GSM (tt) au thu, sau khi tn hieu c giai ieu che thanh

thong tin nh phan th thong tin nh phan nay c giai mat ma, giai ghep xen, giai ma kenh, giai ma nguon va c bien oi D/A e khoi phuc lai tieng noi.


175

2.12 C2.12 Cu tru trc cc ca BSS va BSS v SSS (Switching Subsystem)SSS (Switching Subsystem)

Sau khi hon tt phn ny bn s c mt ci nhn tng quan v cu trc phn cng ca BSS v SSS (NSS), cth bn c th miu t:

Cu trc ca mt BTS

Cu trc ca mt BSC

Cc chc nng ca b TRAU

Cu trc ca SSS


176

2.12 C2.12 Cu tru trc cc ca BSS va BSS v SSS (Switching Subsystem) (tt)SSS (Switching Subsystem) (tt)


177


a) Cu trc ca BTS

V c bn mt BTS gm:

Mt n v iu khin

Mt mch giao din

Mt hoc nhiu h thng TDMA

Mt trm anten


178



179


Mi TDMA system chu trch nhim truyn dn cho 8 knh vt l trong khung TDMA ca mt RFC.

iu ny c ngha l s TDMA system bng vi s RFC c s dng bi BTS.

Thng qua cc kt ni ni m thng tin iu khin vthng tin v mng c truyn t cc TDMA system n antenna combiner v ngc li.


180



181

n v iu khin ca BTS iu khin v gim st cc n v chc nng khc ca BTS thng qua cc ng bo hiu ni.

Ngoi ra, n cn iu khin vic nhy tn.



182

2.12 C2.12 Cu tru trc cc ca BSS va BSS v SSS (Switching Subsystem) (tt)SSS (Switching Subsystem) (tt) Nhy tn c ngha l mi knh v tuyn logic (ngoi tr

knh BCCH) s thay i tn s ca n c mi khung TDMA theo mt thut ton xc nh.

Tuy nhin khe thi gian vn c gi c nh.

Mc ch ca nhy tn l phn b ngun nhiu m tc ng ln mt RFC cho tt c cc knh ang c m bo rng chng c mc cht lng truyn dn ging nhau.

Tt nhin MS cng phi thc hin vic nhy tn ny.

Do , BTS truyn thut ton nhy tn ny qua mt knh qung b xung MS. V vy, bn thn knh qung b khng c bao gm trong th tc nhy tn.


183



184

2.12 C2.12 Cu tru trc cc ca BSS va BSS v SSS (Switching Subsystem) (tt)SSS (Switching Subsystem) (tt) Mch giao tip (interface circuit) l thit b kt cui cho

lin kt 2 Mbit/s n BSC.

N x l tt c cc chc nng giao din vt l nh ng b, phn b knh n cc TDMA system.


185


b) Kin trc ca n v thch ng tc v chuyn m Transcoding and Rate Adaption Unit TRAU):

Vic chuyn i tc bit thoi t 64 kb/s thnh 13 kb/s cho thoi ton tc hoc 6.5 kb/s cho thoi bn tc c gi l chuyn i m v c x l bi b TRAU.


186


B TRAU gn thm mt header vo cc tn hiu 13 kb/s v 6.5 kb/s t c 16 kb/s, sau gi n phn hghp knh (submultiplexer).

ng ra ca b ghp knh ny, mt tn hiu mi 64 kb/s (t 4 kt ni thoi c chuyn m) sn sng cho vic truyn dn qua h thng PCM30.


187



188


hng ngc li, cc tn hiu 13 kbit/s hoc 6.5 kbit/s n c chuyn i thnh tn hiu 64 kbit/s.


189


D liu c truyn t MSC n BSS lun lun l tn hiu s v c ghp trong mt knh 64 kbit/s.

B TRAU lc d liu ra khi tn hiu 64 kb/s v thm header vo. Bng cch ny, ta thu c mt tn hiu 16 kb/s.


190



191


Trong b TRAU, cc knh 64 kb/s (nh cc knh bo hiu s 7) c chuyn mch trong sut.


192

2.12 C2.12 Cu tru trc cc ca BSS va BSS v SSS (Switching Subsystem) (tt)SSS (Switching Subsystem) (tt)c) Kin trc ca BSC:

BSC chu trch nhim iu khin BTS, qun l ti nguyn v tn s v tuyn.

BSC c cc mch giao din ph hp cho cc link 2 Mb/s n b TRAU v n BTS khc.

Cc knh iu khin v lu lng t v n BTS c chuyn mch thng qua thit b chuyn mch (switching device).

Cc chc nng qun l thc s ca BSC c thc hin trong mt n v iu khin trung tm. V vy, vic iu khin cc n v chc nng ca BSC c thc hin bi mt n v iu khin ca n.


193



194


Thng tin bo hiu CCS7 c chuyn mch thng qua b TRAU mt cch trong sut v c chuyn n mt n v iu khin cho cc chc nng thu pht.


195


Ti y, bn tin c chuyn i sang format m BSC cth hiu c.


196


d) Kin trc ca SSS

Vic trin khai cc phn t ca SSS thay i tu thuc vo nh sn xut. y bn s c lm quen vi gii php c ngh bi Siemens.

Cc phn t ca SSS gm MSC, VLR, HLR, AC vEIR v c bn c trin khai nh cc chc nng vphn mm v c da vo cng mt kin trc phn cng.

Vic mt phn t vt l ca mng thc hin chc nng g ph thuc ch yu vo vic phn mm c load vo n.


197



198



199



200


Kin trc phn cng ca mt phn t ca SSS lun lun bao gm:

Mt mng chuyn mch (switching network) chuyn mch cc knh lu lng v iu khin.

Cc mch giao din (interface circuit) cho cc h thng PCM30 n cc phn t mng khc.

Mt b x l iu khin (control processor) trung tm v

Mt n v iu khin cho cc knh bo hiu CCS7.


201


Nu mt phn t mng hot ng nh mt MSC th phi cn thm mt n v c bit na bn cnh cu hnh c bn ny. n v ny cung cp cc chc nng lin mng khi cn thit cho tt c cc dch v.

N cha MODEM v cc chc nng cn thit cho vic chuyn i cc tc d liu v cho vic x l giao thc.


202

2.13 C2.13 Cc kc kt nt ni vi vt l trong GSMt l trong GSM Tt c cc kt ni vt l trong SSS, BSS v n mng PSTN l

cc lung PCM30. Thng qua cc kt ni vt l m h thng c th truyn thoi

hoc thng tin bo hiu. Cc kt ni vt l th hin cc thuc tnh ca mt lin kt

truyn dn nh: Truyn dn c thc hin qua ng hu tuyn hay v

tuyn.

Truyn dn l tng t hay s

Truyn dn s dng k thut chuyn mch knh hay chuyn mch gi, tc bit bng bao nhiu,


203

2.13 C2.13 Cc kc kt nt ni vi vt l trong GSM (tt)t l trong GSM (tt)

a) Cc kt ni knh lu lng

Hnh sau miu t mt kt ni thoi trong mng PLMN.


204

2.13 C2.13 Cc kc kt nt ni vi vt l trong GSM (tt)t l trong GSM (tt) Knh lu lng gia mng PSTN v mng PLMN nh

sau:

Trong c 2 trng hp, cc lin kt PCM30 c s dng truyn dn.


205

2.13 C2.13 Cc kc kt nt ni vi vt l trong GSM (tt)t l trong GSM (tt)b) Cc kt ni bo hiu: Trong trng hp bo hiu, cc lin kt cng l cc knh

PCM30. Qu trnh bo hiu s dng h thng bo hiu knh

chung s 7 (CCS7): Gia cc phn t mng ca SSS. Gia MSC v BSC Gia MSC v tng i Gateway trong mng PSTN Bn cnh cc kt ni bo hiu CCS7 cn c cc kt ni

bo hiu gia BSC v BTS. V gia MSC v MS. Cc knh ny c chuyn mch

mt cch trong sut trong BSC v BTS.


206

2.13 C2.13 Cc kc kt nt ni vi vt l trong GSM (tt)t l trong GSM (tt)


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