GSM Va GSM Len 3G_Hoang Thi Hue_45

8/2/2019 GSM Va GSM Len 3G_Hoang Thi Hue_45

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MC LC

MC LC...................................................................................................................1

LI NI U.............................................................................................................4CHNG 1. MNG THNG TIN DI NG GSM.............................................5

I. Gii thiu chung v GSM.................................................................................5

1. Gii thiu v GSM.........................................................................................5

2. Lch s mng GSM........................................................................................5

3. Cc ch tiu k thut ca mng GSM............................................................5

4. Bng tn s dng trong mng GSM..............................................................6

5. Phng php truy nhp trong mng GSM.....................................................7

II. Cu trc ca h thng thng tin di ng GSM............................................81. Cu trc ca h thng....................................................................................8

2. Chc nng ca cc phn t trong h thng....................................................9

2.1. H thng con chuyn mch SS..............................................................9

2.2. H thng con trm gc BSS..................................................................10

2.3. H thng con khai thc OSS.................................................................11

2.4. Trm di ng MS..................................................................................12

III. Qu trnh x l cc tn hiu s v bin i vo sng v tuyn..................12

1. Chuyn i A/D.............................................................................................132. M ha ting..................................................................................................13

3. M ha knh..................................................................................................13

4. Ghp xen........................................................................................................14

5. Mt m ha....................................................................................................14

6. iu ch.........................................................................................................15

7. Cn bng Viterbi............................................................................................15

8. Chuyn i D/A.............................................................................................16

IV. Giao din v tuyn Um..................................................................................161. Knh vt l.....................................................................................................16

2. Knh logic......................................................................................................19

2.1. Knh lu lng TCH............................................................................19

2.2. Knh bo hiu iu khin......................................................................19

V. Cc trng hp thng tin................................................................................20

1. Cc trng thi ca my di ng MS...............................................................20

2. Th tc nhp mng........................................................................................20

3. Lu ng v cp nht v tr............................................................................204. Th tc ri mng...........................................................................................21

Hong Th Hu 45K2 T - VT Khoa Cng Ngh1


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5. Cc trng hp cuc gi................................................................................21

5.1. Trm di ng MS thc hin cuc gi....................................................21

5.2. Trm di ng MS nhn cuc gi...........................................................23

6. Cc trng hp chuyn giao (Handover)......................................................25

VI. Cc dch v trong GSM.................................................................................25VII. Bo mt trong GSM.....................................................................................26

1. nh s nhn dng thu bao v cc vng mng............................................26

2. Nhn thc thu bao........................................................................................27

CHNG 2. L TRNH PHT TRIN T GSM LN 3G................................28

I. Gii thiu............................................................................................................28

II. L trnh pht trin t GSM ln 3G...............................................................28

1. Cng ngh s liu chuyn mch knh tc cao HSCSD............................29

2. Dch v v tuyn gi chung GPRS................................................................312.1. Gii thiu GPRS...................................................................................31

2.2. Cc c im ca mng GPRS.............................................................31

2.3. Cu trc ca mng GPRS......................................................................33

2.4. Giao thc trong mng GPRS.................................................................36

2.5. Giao din v tuyn................................................................................37

a. Lp vt l ca GPRS..........................................................................37

b. RLC/MAC ca GPRS.........................................................................38

c. Lp iu khin ng truyn logic LLC............................................382.6. Cc chc nng ca GPRS.....................................................................39

2.7. Nhp mng GPRS.................................................................................47

2.8. Kh nng pht trin ca GPRS ln 3G..................................................48

3. Tc s liu tng cng pht trin GSM (EDGE).................................49

3.1. K thut iu ch trong EDGE.............................................................49

3.2. Giao tip v tuyn.................................................................................50

CHNG 3. CNG NGH W-CDMA...................................................................52

I. Gii thiu............................................................................................................52II. Cc c im ca W-CDMA..........................................................................52

III. Cc c tnh c bn ca W-CDMA.............................................................53

IV. Cu trc mng W-CDMA.............................................................................54

V. Cc dch v trong mng W-CDMA...............................................................58

VI. Giao din v tuyn..........................................................................................58

1. Cc knh logic...............................................................................................60

2. Cc knh truyn ti........................................................................................60

3. Cc knh vt l..............................................................................................613.1. Cc knh vt l ng ln.....................................................................61

3.2. Cc knh vt l ng xung...............................................................62



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VII. Cc gii php k thut trong W-CDMA....................................................63

1. Thit b thu pht v tuyn trong h thng TTD th h 3............................63

a. My pht...................................................................................................63

b. My thu....................................................................................................63

2. M ha v an xen.........................................................................................642.1. M vng................................................................................................64

2.2. M xon.................................................................................................65

2.3. M Turbo...............................................................................................66

2.4. an xen trong W-CDMA......................................................................66

3. iu ch BPSK v QPSK..............................................................................67

3.1. iu ch BPSK.....................................................................................67

3.2. iu ch QPSK.....................................................................................68

4. iu khin cng sut v chuyn giao............................................................694.1. iu khin cng sut.............................................................................69

a. iu khin cng sut vng h OLPC.................................................70

b. iu khin cng sut vng kn CLPC................................................70

4.2. Chuyn giao..........................................................................................71

a. Chuyn giao mm...............................................................................71

b. Chuyn giao mm hn........................................................................72

c. Chuyn giao cng...............................................................................72

VIII. K thut tri ph trong W-CDMA...........................................................721. Gii thiu.......................................................................................................72

2. Nguyn l tri ph DSSS...............................................................................74

3. M tri ph.....................................................................................................74

4. Cc h thng DSSS BPSK..........................................................................76

4.1. My pht DSSS BPSK.......................................................................76

4.2. My thu DSSS BPSK.........................................................................77

5. Cc h thng DSSS QPSK.........................................................................79

5.1. My pht DSSS QPSK.......................................................................795.2. My thu DSSS QPSK.........................................................................80

IX. Thit lp mt cuc gi trong W-CDMA UMTS.........................................81

KT LUN.................................................................................................................85

BNG TRA CU CC T VIT TT..................................................................86

TI LIU THAM KHO.........................................................................................92



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LI NI U

T xa ti nay, thng tin lin lc lun l mt lnh vc quan trng ca i sng x

hi. c bit l ngy nay khi m mng thng tin di ng ang ngy cng pht trinmnh m th nhu cu ca con ngi khng ch dng li . Cng ngh GSM c nhng

c tnh ni bt nh dung lng ln, tnh bo mt cao,Tuy nhin v l h thng bng

thng hp, s dng cng ngh chuyn mch knh nn GSM ch c th h tr truyn s

liu vi tc ti a l 9,6 kbit/s, khng p ng c nhu cu ngy cng cao ca

ngi s dng v cc dch v mi nh truyn s liu tc cao, in thoi c hnh, truy

cp Internet tc cao t my di ng v cc dch v truyn thng a phng tin khc.

V nhng l do trn, cc nh khai thc GSM ang tng bc nng cp mng GSM. Tuy

nhin vic loi b hn cng ngh ang dng tip cn ngay mng 3G l rt tn km v

mt kinh t. V vy h phi chn gii php nng cp mng GSM qua bc trung gian

2,5G tm thi p ng nhu cu ca ngi s dng cng nh chun b c s h tng

k thut sau mi tin ln 3G.

c th nm vng cc k thut s dng trong qu trnh nng cp GSM ln 3G

cng nh tm hiu v cng ngh W-CDMA, em chn ti Cng ngh GSM v

qu trnh pht trin GSM ln 3G .

Ni dung trnh by trong bn n:

Chng 1: Mng thng tin di ng GSM

Chng 2: L trnh pht trin t GSM ln 3G

Chng 3: Cng ngh W-CDMA

Em xin gi li cm n chn thnh n PGS.TS Nguyn Quc Trung tn

tnh hng dn em trong sut qu trnh lm n.

Em cng xin chn thnh cm n cc thy c gio trong khoa Cng Nghtrng i Hc Vinh ch bo cho em trong sut thi gian qua.

Vinh, ngy 03 thng 05 nm 2009

Sinh vin thc hin

Hong Th Hu



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CHNG I

MNG THNG TIN DI NG GSM

I. GII THIU CHUNG V GSM

1. Gii thiu v GSM

GSM (Global System for Mobile Communication) - h thng vin thng ton cu,

s dng tn s 900 MHz cng nh 1800 MHz Chu u v 1900 MHz Bc M.

GSM h tr truyn thoi vi tc 13 kbit/s v truyn s liu vi tc 9,6 kbit/s.

Mng GSM s dng phng php a truy nhp phn chia theo thi gian TDMA kt hp

a truy nhp phn chia theo tn s FDMA.2. Lch s mng GSM

Vo u thp nin 1980, ti Chu u ngi ta pht trin mt mng in thoi di

ng ch s dng trong mt vi khu vc. Sau vo nm 1982 n c chun ha bi

CEPT (European Conference of Postal and Telecommunications Administrations) v to

ra Groupe Spccial Mobile (GSM) vi mc ch s dng chung cho ton Chu u.

Mng in thoi di ng s dng cng ngh GSM c xy dng v a vo s

dng u tin bi Radiolinja Phn Lan.

Vo nm 1989 cng vic qun l tiu chun v pht trin mng GSM c

chuyn cho vin tiu chun vin thng Chu u (European Telecommunications

Standards Institute - ETSI) v cc tiu chun, c tnh phase 1 ca cng ngh GSM

c cng b vo nm 1990. Vo cui nm 1993 c hn 1 triu thu bao s dng

mng GSM ca 70 nh cung cp dch v trn 48 quc gia.

3. Cc ch tiu k thut ca mng GSM

H thng thng tin di ng GSM cho php chuyn vng t do ca cc thu baotrong chu u, c ngha l mt thu bao c th thm nhp sang mng ca nc khc khi

di chuyn qua bin gii. Trm di ng GSM MS (GSM Mobile Station) phi c kh

nng trao i thng tin ti bt c ni no trong vng ph sng quc t.

* V kh nng phc v:

- H thng c thit k sao cho MS c th dng c trong tt c cc nc c

mng.

- Cng vi phc v thoi, h thng phi cho php s linh hot ln nht cho cc

loi dch v khc lin quan ti mng s lin kt a dch v (ISDN).



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- To mt h thng c th phc v cho cc MS trn cc tu vin dng nh mt

mng m rng cho cc dch v di ng mt t.

* V cht lng phc v v an ton bo mt:

- Cht lng ca thoi trong GSM phi t nht c cht lng nh cc h thng ding tng t trc trong iu kin vn hnh thc t.

- H thng c kh nng mt m ho thng tin ngi dng m khng nh hng

g n h thng cng nh khng nh hng n cc thu bao khc khng dng n kh

nng ny.

* V s dng tn s:

- H thng cho php mc cao v hiu qu ca di tn m c th phc v

vng thnh th v nng thn cng nh cc dch v mi pht trin.- Di tn s hot ng l 890-915 v 935-960 Mhz.

- H thng GSM 900Mhz phi c th cng tn ti vi cc h thng dng 900Mhz

trc y.

* V mng:

- K hoch nhn dng da trn khuyn ngh ca CCITT.

- K hoch nh s da trn khuyn ngh ca CCITT.- H thng phi cho php cu trc v t l tnh cc khc nhau khi c dng

trong cc mng khc nhau.

- Trung tm chuyn mch v cc thanh ghi nh v phi dng h thng bo hiu

c tiu chun ho quc t.

- Chc nng bo v thng tin bo hiu v thng tin iu khin mng phi c

cung cp trong h thng

4. Bng tn s dng trong mng GSM

H thng GSM lm vic trong bng tn 890 960 MHz, chia lm 2 phn:

- Bng tn ln (Uplink band) t 890 915 MHz cho cc knh v tuyn t MS

n BTS

- Bng tn xung (Downlink band) t 935 960 MHz cho cc knh v tuyn t

BTS n MS

Mi bng rng 25MHz, chia lm 124 sng mang tng ng vi 124 knh vtuyn. Cc sng mang cnh nhau cch nhau 200KHz. Mi knh s dng 2 tn s ring



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bit cho ng ln v cho ng xung. Cc knh ny c gi l knh song cng.

Khong cch gia 2 tn s l khng i v bng 45MHz. Knh v tuyn ny c 8 khe

thi gian, mi khe thi gian l mt knh vt l trao i gia BTS v MS.

Ngoi bng tn c s cn c bng tn GSM m rng v bng tn DCS:

- Bng tn GSM m rng: 882 915MHz v 927 960 MHz

- Bng tn DCS: 1710 1785 MHz v 1805 1880 MHz

5. Phng php truy nhp trong mng GSM

Mng GSM s dng phng php TDMA (Time Division Multiple Access) kt

hp FDMA (Frequency Division Multiple Access).

- a truy nhp phn chia theo thi gian TDMA:

Khi c yu cu mt cuc gi th mt knh v tuyn c n nh. Cc thu bao

khc nhau dng chung mt knh nh ci xen thi gian. Mi thu bao c cp mt khe

thi gian trong cu trc khung tun hon 8 khe.

- a truy nhp phn chia theo tn s FDMA:

Phc v cc cuc gi theo cc knh tn s khc nhau. Ngi dng c cp pht

mt knh trong tp hp cc knh trong lnh vc tn s. Ph tn s c chia thnh 2N

di tn s k tip, cch nhau mt khong bo v. Mi di tn c gn cho mt knh

lin lc, N di dnh cho lin lc hng ln, N di cn li cho lin lc hng xung.

Cc knh tn s c s dng GSM nm trong di tn quy nh 900 MHz xc

nh theo cng thc:

FL = 890,2+0,2(n-1) MHz

FU = FL(n) + 45 MHz

1 n 124

Trong :

FL: Tn s na bng thp

FU: Tn s na bng cao

0,2 MHz: Khong cch gia cc knh ln cn

45 MHz: Khong cch thu pht

n: S knh tn v tuyn



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cho cc knh ln cn khng gy nhiu cho nhau mi BTS ph mt ca

mng phi s dng cc tn s cch xa nhau v cc s dng cc tn s ging nhau hoc

gn nhau cng phi xa nhau.

Truyn dn GSM c chia thnh cc cm (Burst) cha hng trm bit c

iu ch. Mi cm c pht i trong mt khe thi gian 577 s trong mt knh tn s

c rng 200KHz. Mi mt knh tn s cho php t chc cc khung thm nhp theo

thi gian, mi khung bao gm 8 khe thi gian t TS0 n TS7.

II. CU TRC CA H THNG THNG TIN DI NG GSM

1. Cu trc ca h thng

Mt h thng GSM c chia thnh cc h thng con sau y:

- H thng con chuyn mch (SS Switching Subsystem )- H thng con trm gc (BSS Base Station Subsystem)

- H thng con khai thc (OSS Opration Subsystem)

- Trm di ng (MS Mobile Station)

* H thng con chuyn mch SS bao gm cc khi chc nng sau:

- Trung tm chuyn mch cc nghip v di ng (MSC Mobile Services

Switching Center)- B ghi nh v thng tr (HLR Home Location Register)

- B ghi nh v tm tr ( VLR Visitor Location Registor)

- Trung tm nhn thc (AUC Authentication Center)

- B ghi nhn dng thit b (EIR Equipment Identification Register)

- Trung tm chuyn mch cc nghip v di ng cng (GMSC Gateway MSC)

* H thng con trm gc BSC gm cc khi chc nng sau:- B iu khin trm gc (BSC Base Station Controller)

- Trm thu pht gc (BTS Base Transceiver Station)

* H thng con khai thc OSS gm cc khi chc nng sau:

- Trung tm qun l mng (NMC Network Management Center)

- Trung tm qun l v bo dng ( OMC Operation & Maintenance Center)

* Trm di ng MS gm:

- Thit b di ng (ME Mobile Equipment)



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- Modul nhn dng thu bao (SIM Subscriber Identity Module)

2. Chc nng ca cc phn t trong h thng

2.1. H thng con chuyn mch SS

H thng con chuyn mch bao gm cc chc nng chuyn mch chnh ca GSM

cng 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 SS l qun l thng tin gia nhng ngi s dng mng GSM

vi nhau v vi mng khc.

- Trung tm chuyn mch cc nghip v di ng MSC

Tng i di ng MSC thc hin chc nng chuyn mch cho cc thu bao di ng

thng qua trng chuyn mch ca n. MSC qun l vic thit lp cuc gi, iu khin

cp nht v tr v th tc chuyn giao gia cc MSC. Vic cp nht v tr ca thu bao

cho php tng i di ng MSC nhn bit c v tr ca cc thu bao di ng trong qu

trnh tm gi trm di ng MS. MSC c tt c cc chc nng ca mt tng i c nh

nh tm ng, nh tuyn, bo hiu,iu khc bit gia tng i ca mng c nh(PSTN, ISDN, ) v MSC l MSC thc hin x l cho cc thu bao di ng, thc hin

chuyn vng gia cc cell.

Hong Th Hu 45K2 T - VT Khoa Cng Ngh

Hnh 1.1 M hnh h thng GSM

PSTN

PLMN

CSPDN

PSPDN

9

SS

VLR EIRHLR

MSCOSS

BSSBSC

BTS

MS

ISDN

AUC

Truyn bo hiu

Truyn lu lng


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Chc nng ca tng i MSC ngoi vic kt ni vi cc phn t ca mng di ng

n cn kt ni vi cc phn t ca mng khc nh PSTN, ISDN, PSPDN, CSPDN,

PLMN. MSC thc hin chc nng trn gi l MSC cng (GMSC). Vic giao tip vi

mng ngoi m bo thng tin cho nhng ngi s dng mng GSM i hi cng

thch ng ( Cc chc nng tng tc IWF Interworking Function). IWF l cng giaotip gia ngi dng mng GSM vi cc mng ngoi. N c th c thc hin trong

cng chc nng MSC hay c th thit b ring.

- B ghi nh v thng tr HLR

HLR cha y cc thng tin lin quan n vic ng k dch v v v tr ca cc

thu bao. Thng HLR l mt my tnh ng ring khng c kh nng chuyn mch

nhng c kh nng qun l hng trm ngn thu bao. Khi mng c thm mt thu bao

mi th cc thng tin v thu bao s c ng k trong HLR.- B ghi nh v tm tr VLR

L c s d liu th hai trong mng GSM, cha cc thng tin v v tr hin thi

ca thu bao di ng trong vng phc v ca MSC tng ng v ng thi lu gi s

liu v v tr ca cc thu bao ni trn cp nht cho MSC vi mc chnh xc hn

HLR.

- Trung tm nhn thc AUC

c ni n HLR, chc nng ca AUC l cung cp cho HLR cc tn s nhn

thc v cc kha mt m s dng cho bo mt.ng v tuyn cng c AUCcung cp m bo mt chng nghe trm, m ny c thay i ring bit cho tng

thu bao.

- B ghi nhn dng thit b EIR

EIR c chc nng kim tra tnh hp l ca thit b di ng ME thng qua s liu

nhn dng di ng quc t (IMEI International Mobile Equipment Identity) v cha

cc s liu v phn cng ca thit b.

2.2. H thng con trm gc BSS

L mt h thng cc thit b c th ring cho cc tnh cht t ong v tuyn ca

GSM. BSS thc hin u ni cc MS vi tng i v nh vy u ni nhng ngi s

dng cc trm di ng vi nhng ngi s dng vin thng khc. BSS bao gm 2 loi

thit b: BTS giao din vi MS v BSC giao din vi MSC.

- Trm thu pht gc BTS



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Bao gm cc thit b thu pht, anten v x l tn hiu c th cho giao din v

tuyn. Mt b phn quan trng ca BTS l TRAU (khi chuyn i m v thch ng tc

). TRAU l thit b m qu trnh m ha v gii m ting c th ring cho GSM

c tin hnh, y cng thc hin thch ng tc trong trng hp truyn s liu.

- B iu khin trm gc BSC

C nhim v qun l tt c giao din v tuyn thng qua cc lnh iu khin t

BTS v MS, ch yu l cc lnh n nh, gii phng knh v tuyn v qun l chuyn

giao. Mt BSC trung bnh c th qun l ti vi chc BTS ph thuc vo lu lng ca

cc BTS ny.

2.3. H thng con khai thc OSS

OSS thc hin 3 chc nng chnh sau:

- Khai thc v bo dng mng:

+ Khai thc: L hot ng cho php cc nh khai thc mng theo di hnh vi ca

mng nh: ti ca h thng, mc chn, s lng chuyn giao (Handover) gia hai ,

Nh vy nh khai thc c th gim st c ton b cht lng ca dch v m h

cung cp cho khch hng v kp thi x l cc s c. Khai thc cng bao gm vic thay

i cu hnh gim nhng vn xut hin thi im hin thi, chun b tng lu

lng trong tng lai, tng vng ph sng.

+ Bo dng: C nhim v pht hin, nh v, sa cha cc s c v hng hc. N

c mt s quan h vi khai thc. Bo dng cng bao gm c cc hot ng ti hin

trng nhm thay th thit b c s c.

- Qun l thu bao v tnh cc:

Bao gm cc hot ng qun l ng k thu bao. Nhim v u tin l nhp v

xa thu bao khi mng. ng k thu bao cng c th rt phc tp, bao gm nhiu dch

v v cc tnh nng b sung. Qun l thu bao mng GSM ch lin quan n HLR vmt s thit b OSS ring, chng hn mng ni HLR vi cc thit b giao tip ngi my

cc trung tm giao dch vi thu bao. Simcard cng ng vai tr nh mt b phn ca

h thng qun l thu bao.

- Qun l thit b di ng:

c b ng k nhn dng thit b EIR thc hin. EIR lu gi tt c cc d liu

lin quan n trm di ng. EIR c ni n MSC qua ng bo hiu kim tra s

c php ca thit b. Mt thit b khng c php s b cm.2.4. Trm di ng MS



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MS c th l thit b xch tay, thit b t trong t hay thit b cm tay. Ngoi

vic cha cc chc nng v tuyn chung v x l cho giao 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 s thit b khc nh my tnh c nhn, Fax

MS thc hin hai chc nng:

- Thit b vt l giao tip gia thu bao di ng vi mng qua ng v tuyn

- ng k thu bao: mi thu bao phi c mt th gi l Simcard truy nhp vo

mng

V cu trc MS gm hai phn chnh:

- Thit b di ng ME: l b phn x l cc cng vic chung nh thu, pht,

- Modul nhn dng thu bao SIM: l thnh phn nhn dng thu bao trong qutrnh MS hot ng trong mng, n l mt card in t thng minh c th lu tr thng

tin.

III. QU TRNH X L CC TN HIU S V BIN I VO SNG V TUYN

my pht, ting t Micro qua b lc thng di 0,3 3,4 KHz a vo b A/D.

Ti y tin hnh ly mu (8000 mu/s), s dng 13 bit m ha tng ng tc

8000 x 13 = 104 kbit/s.

Tn hiu 13 bit, 8000 mu/s c chia ra cc khong 160 mu/20ms (chia 8000

mu/s thnh 50 on) a vo m ha ting. Sau m ha ting dng s ra l

260bit/20ms. 260 bit ny c phn cp theo tm quan trng v c m ha knh. Sau

m ha knh tn hiu c ghp xen, mt m ha, lp khun cm v sau c iu

ch vo sng mang trong di tn GSM.


M hating

Giiiuch

D/A

3KHz160 mu

13 bit 260 bit/20ms 456 bit/20ms22,8 kbit/s

270 kbit/s khe TS

A/DPhnon

M haknh

Ghpxen

Mt mha

Lpkhuncm

iuch

Gii mting

Gii mViterbi

Giighpxen

Giimt m

CnbngViterbi

12

Hnh 1.2 X l tn hiu s v bin i vo sng v tuyn MS


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my thu tin hnh gii iu ch, cn bng Viterbi. Sau tn hiu c gii

mt m, gii m knh, gii m ting, qua b D/A v ti loa.

1. Chuyn i A/D

Bin i tn hiu thoi tng t t micro ca MS bn pht sang tn hiu PCM 13bit/mu, tn s ly mu 8 KHz a n b m ha.

2. M ha ting

c th cho ra ting ni 13 kbit/s, b m ha ny da trn nguyn l m ha

phn tch bng cch tng hp thng qua vic s dng phng php m ha d on

tuyn tnh kch thch xung u. B m ha ting a cc khi 260 bit/20 ms n b m

ha knh. Cc bit ny c chia thnh 182 bit loi I (cc bit c bo v), 78 bit loi II

(cc bit khng c bo v).

3. M ha knh

M ha knh truyn thm cc bit d vo vng d liu bn thu c th pht hin

v sa li bit sinh ra trong qu trnh truyn. Thut ton m ha ting a ra mt khi

260 bit/20ms tng ng 13 kbit/s. B m ha knh thm 3 bit parity vo mi 50 bit rt

quan trng (m ha khi) to thnh 53 bit. 53 bit ny cng thm 132 bit quan trng v 4

bit ui tip tc c m ha nhp thnh 378 bit. Sau 378 bit ny cng vi 78 bit cn

li thnh khung ting ni 456 bit/20ms tng ng 22,8 kbit/s. Khung ting ni 456 bit

ny tip tc c ghp xen.

Tn ti hai dng m knh khc nhau: m khi tuyn tnh v m xon.

- Cc m khi tuyn tnh: loi m ny lung thng tin c chia thnh cc

khi c di bng nhau. Cc bit d c b sung vo cc khi theo mt thut ton

nht nh ph thuc vo loi m c s dng. Cc m khi tuyn tnh c xc nh

bng ba thng s: di khi n, di thng tin k (bit) v khong cch cc tiu d. Cc

m khi tuyn tnh trong cc bn tin xut hin phn u ca khi c gi l m h

thng. T s r = k/n c gi l t l m.

Khong cch cc tiu c nh gi bng s bit khc nhau gia hai t m ging

nhau nht. Khong cch cc tiu ny c gi l khong cch Hamming nh nht gia

hai t m.


B mha knh

T m n bitk bit bn tin

Hnh 1.3 V d b m ha knh

13


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- M xon: m xon mt khi n bit m to ra khng ch ph thuc vo k bit

bn tin ca khi ny m cn ph thuc vo cc bn tin ca cc khi trc . M xon

c xc nh bi cc thng s sau:

+ T l m: r = k/n, trong n s bit u ra khi ng vi k bit u vo.

+ di hu hn (ph thuc vo s phn t nh ca thanh ghi dch).

Mt b m xon bao gm mt thanh ghi dch to thnh t cc Flip-Flop, cc u

vo hoc u ra ca cc thanh ghi dch c cng vi nhau theo mt quy lut nht nh

to nn cc chui xon, sau cc chui xon c ghp chung vi nhau to ra

khi m.

4. Ghp xen

Cc li bit thng xut hin thnh chm li nhng m ha knh ch pht hin vsa li cc bitv cc chm li ngn. Phng php ghp xen c s dng loi b

vn ny bng cch chia khi bn tin cn gi thnh cc cm ngn ri hon v cc cm

ny vi cc cm ca cc khi bn tin khc. Nh vy khi xy ra cm li di mi bn tin

ch mt i mt cm nh, phn cn li ca bn tin vn cho php cc dng m ha knh

khi phc li c bn tin ng sau khi sp xp li cc cm ca bn tin theo th t

nh pha pht.

5. Mt m ha

Mt m ha bo v thng tin v ngi dng v bo hiu tng i gia cc

BTS v cc MS i vi cc c nhn mun xm nhp tri php.

Mt m ha tn hiu t c bng thao tc hoc loi tr (XOR) gia mt chui

ngu nhin vi 114 bit ca cm bnh thng, ngha l vi tt c cc bit thng tin tr cc

c ly cp. gii mt m ngi ta thc hin thao tc hoc loi tr (XOR) gia tn hiuthu vi chui ngu nhin.


1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4

1 x 3 4 1 x 3 4 1 x31

4 1 x 341

Cc khi bn tinghp xen

Cc khi bn tinc ghp xen

Hnh 1.4 Nguyn l ghp xen

14


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6. iu ch

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

(Gaussian Minimum Shift Keying). Phng php ny tha mn c cc yu cu t ra:

- Ph cng sut u ra hp: m bo yu cu cng sut ngoi bng tn pht xvo cc knh ln cn nh hn 60 80 dB trong cc knh yu cu. iu ny l cn thit

trnh nhiu cc knh ln cn gy ra trong qu trnh truyn lan.

- Xc sut li qu trnh truyn lan nh

- Ngun sng ti s dng cng knh trong vng a l phi cao

- Ch s khuch i tuyn tnh nh

- c s sc bn v mm do hn khi thay i pha, tn hiu bng gc c lc

vi b lc thng di vung Gaussian. GMSK cung cp mt bng thng hp hn MSKbnh thng nhng sc chng nhiu tt hn.

GMSK l phng php iu ch bng hp da trn k thut iu ch dch pha,

thc hin bng cch ni dy chuyn mt b lc Gauss v mt b iu ch MSK. MSK

chnh l phng php iu ch FSK lin tc trong trng hp h s iu ch bng 0,5.

FSK l phng php iu tn, n bin i thng tin thnh cc tn hiu tn s trong sng

mang ri truyn i. C th s dng b VCO ( Voltage Controlled Oscillator) thc

hin FSK

Hnh 1.5 Cu to nguyn l FSK7. Cn bng Viterbi

B cn bng Viterbi s to m hnh ton hc ca knh truyn dn. S liu c

truyn trong cc cm t trong cc khe thi gian 577s. gia mi cm c mt mu

bit S c (chui hun luyn) c bit trc. Bng cch so snh cc chui tun t

bit trong mt tng quan bn thu vi mu bit nhn c (S), b cn bng s to nn

mt m hnh knh.


VCO

Tn hiu m mc

FSK m gi tr

15


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B cn bng Viterbi GSM cho php x l cc tn hiu phn x tr ti 15s. B

cn bng cng a ra thng tin mm n b gii m knh to iu kin cho b ny

hiu chnh li c tt hn.

8. Chuyn i D/A

Dn tn hiu PCM c nn vi 8 bit/mu, tn s ly mu 8000 mu/s thnh tn

hiu PCM u 13 bit/mu.

IV. GIAO DIN V TUYN Um

Giao din v tuyn l giao din phc tp v c th nht ca mt h thng thng

tin di ng t ong. Giao din v tuyn GSM 900 bao gm hai bng tn song cng

25MHz cho c ng ln v ng xung. Trong h thng GSM, cng ngh a truy

nhp phn chia theo thi gian TDMA c ng dng cho mi sng mang c rng

bng tn 200KHz. Trong bng tn 25 MHz chia lm 124 knh sng mang bt u t

890,2 MHz , tch bit song cng 45MHz gia tn s ln v xung.

Mi sng mang c ghp vo 8 khe thi gian (mi khe c di 577s) theo

cng ngh TDMA gi l mt khung TDMA, mt khung c lu l 4,616 ms. Mi khethi gian l mt knh vt l.

1. Knh vt l

Trong GSM mi khe thi gian c coi l mt knh vt l. H thng GSM c

124 knh, mi knh c 8 khe thi gian nn s c 124 x 8 = 992 knh vt l.

V mt thi gian, cc knh vt l mt knh tn s c t chc theo cu trc

khung, a khung, siu a khung v siu siu khung.


B tngquan

M hnhknh

Khc ?

Chn saocho khcnhau tnht

S liu S S liu

Thng tinmm

Cm thuViterbi

? ?S

Hnh 1.6 B cn bng Viterbi

16


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Mt siu siu khung c lu l 3 gi 28 pht 53 giy 760 ms. Cc khung

TDMA c nh s trong siu khung t 0 n 2715647. Mt siu siu khung c


10 2 3 4 2044 2045 2046 2047

47 48 49 500 1 2 3

0 1 2 3 22 23 24 25 0 1 2 3 47 48 49 50

0 1 24 25

0 1 2 3 4 5 6 7

1 siu siu khung = 2048 siu khung = 2715648 khung TDMA

1 siu khung = 1326 khung TDMA (6,12 giy)

TB3

57 bitc mt m ha

F1

chui hngdn26 bit

F1

57 bitc mt m ha

TB3

GP8,25

TB

3 42 bit c nh

TB

3

GP

8,25

TB3

39 bitc mt m ha

chui ng b64 bit

39 bitc mt m ha

TB3

GP8,25

TB3

Cc bit hn hp58 bit

chui hng dn26 bit

Cc bit hn hp58 bit

TB3

GP8,25

TB3 chui ng b

41 bit

Cc bit c mt m36 bit

TB3

GP68,25

1 khung TDMA = 8 khe thi gian ( ~ 4,615 ms)

1 khe thi gian = 156,25 bit (~ 0,577 ms)

Cm bnh thng NB (C F ch tng ng vi TCH)

Cm hiu chnh tn s (FB)

Cm ng b (SB)

Cm thm nhp (AB)

Cm gi (DB)

Hnh 1.7 T chc khung v cm

K hiu:TB: bit uiF: c ly cpGP: on bo v

17


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chia thnh 2048 siu khung, mi siu a khung c lu l 5,12 giy. Mi siu khung

c chia thnh cc a khung. C 2 loi a khung:

- a khung 26 khung (51 siu khung trn mt siu siu khung): c lu 120 ms

v cha 26 khung.

- a khung 51 khung (26 siu khung trn mt siu siu khung): c lu 235,4

ms v cha 51 khung.

Cu trc cc cm

Khe thi gian 577 s tng ng vi lu ca 156,25 bit l ni dung vt l ca

mt cm. Tn ti bn dng cm khc nhau trong h thng:

- Cm bnh thng NB (Normal Burst): c s dng mang cc thng tin v

cc knh lu lng v cc knh kim tra. i vi knh lu lng TCH, cm ny cha114 bit c mt m, ba bit ui (0, 0, 0) u v cui, 2 bit c ly cp (ch cho TCH),

26 bit hng dn v khong thi gian bo v c lu bng 8,25 bit. NB c dng cho

TCH v cc knh iu khin tr RACH, SCH v FCCH.

- Cm hiu chnh tn s FB (Frequency Correction Burst): c s dng

ng b tn s cho trm di ng. Cm cha 142 bit c nh bng 0 to ra dch tn s

+67,7 KHz trn tn s danh nh, ba bit ui (0, 0, 0) u v cui v khong bo v 8,25

bit. FB c s dng cho FCCH.

- Cm ng b SB (Synchronization Burst): c s dng ng b thi gian

cho trm di ng. Cm cha 78 bit c mt m ha mang thng tin v FN (Frame

Number - s khung) ca TDMA v BSIC (Base Transceiver Station Identity Code

M nhn dng trm thu pht gc), ba bit ui u v cui, chui hng dn di 64 bit

v khong bo v 8,25 bit. SB c s dng cho SCH.

- Cm thm nhp AB (Access Burst): c s dng thm nhp ngu nhin v

thm nhp chuyn giao. Cm cha 36 bit thng tin, 41 bit ng b, 8 bit ui u, 3 bit

ui cui v khong bo v 68,25 bit. AB c s dng cho RACH v TCH.

- Cm gi DB (Dummy Burst): c pht i t BTS trong mt s trng hp.

Cm khng mang thng tin. Cm c cu trc ging nh cm NB nhng cc bit mt m

c thay th bng cc bit hn hp.

2. Knh logic

Cc knh logic c t vo cc knh vt l truyn i, cc knh ny mang

thng tin iu khin v bo hiu gia BTS v MS. C 2 loi: Knh lu lng TCH vknh bo hiu iu khin CCH.



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2.1. Knh lu lng TCH

- Knh ton tc Bm: Mang thng tin ting hoc s liu tc khong 22,8

Kbps

- Knh bn tc Lm: Mang thng tin tc vo khong 11,4 Kbps2.2. Knh bo hiu iu khin

- Cc knh iu khin qung b:

+ Knh iu khin qung b BCCH (Broadcast Control Channel): pht qung b

cc thng tin chung v . y l knh ng xung t mt im n a im.

+ Cc knh hiu chnh tn s FCCH (Frequency Correction Channel): mang

thng tin hiu chnh tn s cho cc trm MS.

+ Knh ng b SCH (Synchoronization Channel): mang thng tin ng b

khung cho trm di ng MS v nhn dng BTS.

- Knh iu khin chung CCCH(Common Control Channel): bao gm:

+ Knh tm gi PCH (Paging Channel): c s dng cho ng xung tm

trm di ng MS.

+ Knh truy cp ngu nhin RACH (Random Access Channel): c MS s

dng yu cu dnh mt knh SDCCH.+ Knh cho php truy cp AGCH (Access Grant Channel): ch c s dng

ng xung ch nh mt knh SDCCH cho MS.

- Knh iu khin dnh ring DCCH(Dedicated Control Channel): bao gm:

+ Knh iu khin dnh ring ng mt mnh SDCCH (Stand alone Dedicated

Control Channel): ch c s dng dnh ring cho bo hiu vi mt MS. SDCCH

c s dng cho cc th tc cp nht v trong qu trnh thit lp cuc gi trc khi

n nh knh TCH, s dng cho c ng ln ln ng xung.

+ Knh iu khin lin kt chm SACCH (Slow Associated Control Channel):

lin kt vi mt TCH hay mt SDCCH. y l mt knh s liu lin tc mang cc

thng tin lin tc, s dng cho c ng ln ln ng xung.

+ Knh iu khin lin kt nhanh FACCH (Fast Associated Control Channel):

lin kt vi mt TCH. FACCH lm vic ch ly cp bng cch thay i lu

lng ting hay s liu bng bo hiu.

V. CC TRNG HP THNG TIN



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1. Cc trng thi ca my di ng MS

- MS tt my:

Mng khng th tip cn n MS v n khng tr li thng bo tm gi cng nh

khng thng bo cp nht v tr. Trng hp ny mng cho rng MS ri mng.- MS bt my, trng thi ri:

Trong khi chuyn ng, MS lin tc kim tra xem n c th c ni vi mt

knh qung b hay khng. MS cng lin tc thng bo cho h thng nhng thng tin v

cp nht vi tr sau nhng khong thi gian nht nh.

- MS bt my, trng thi bn:

C mt knh TCH ni gia mng v MS, khi chuyn ng MS c th chuyn

n mt knh thng tin mi. Qu trnh ny gi l chuyn giao (Handover). quytnh chuyn giao, h thng phi din gii thng tin nhn c t MS v BTS. Qu trnh

ny c gi l nh v.

2. Th tc nhp mng

Khi MS bt my n s qut c 124 tn s tm tn s c cng ln nht. Tn

s m n tm kim cha thng tin qung b v c thng tin tm gi. MS s t ng kha

n tn s thch hp nh vic hiu chnh tn s. Sau MS gi thng bo cp nht n

MSC. Lc ny MSC cha c thng tin g v MS ny. MS gi yu cu cp nht v tr tiHLR km theo thng tin v v tr. HLR s thc hin cc th tc nhn thc. Nu xt thy

MS l hp l, HLR s ghi thng tin v v tr vo trng d liu ca MS v gi thng bo

xc nhn cp nht v tr ti MSC. T y MS xem l c nhp mng v c nh du

mt c nhp mng vo s thu bao di ng quc t.

3. Lu ng v cp nht v tr

Khi MS trong mt BTS n s lun c ni n mt tn s v tuyn nht nh.

Khi n chuyn ng ra xa dn so vi BTS th cng tn hiu thu s gim dn. mtv tr gn bin gii gia hai , cng thu gim n mc m MS quyt nh chuyn

sang tn s mi ca ln cn c cng ln hn tn s c. Sau khi kha n tn s

mi ny, MS li tip tc nghe cc thng bo tm gi v cc thng tin cp nht v tr t h

thng. Quyt nh v vic thay i ca MS khng cn thng bo cho mng tr khi tn

s c v tn s mi khng thuc cng mt vng nh v.

C hai trng hp cp nht v tr:

- Khi MS chuyn ng t vng nh v ny sang vng nh v khc thuc cngmt MSC:



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Vng nh v ca MS c ghi b ghi nh v tm tr VLR. V MS khng

chuyn ng n vng phc v mi nn qu trnh cp nht v tr ch l MS gi thng

bo cp nht v tr v s nhn dng vng nh v mi cho MSC. MSC tip nhn thng

bo cp nht v tr, ghi gi tr mi vo c s d liu ca VLR v gi thng bo xc nhn

cp nht v tr cho MS.

- MS lu ng gia hai vng phc v (MSC/VLR):

Khi MS chuyn sang vng phc v mi n s gi thng bo cp nht v tr cho

MSC mi cng vi s nhn dng ca n. MSC mi ny s gi cc thng tin ti HLR

yu cu nhn thc. Sau khi HLR gi thng bo xc nhn MS l hp l ng k trong

mng cho MSC hin thi v xa vng phc v c thay bng gi tr ca vng phc v

mi, VLR cng ghi cc s liu v MS vo c s d liu ca n nh l mt thu bao tm

thi v gi thng bo xc nhn cp nht v tr cho MS.4. Th tc ri mng

Khi MS tt my hay ra khi vng ph sng n s gi thng bo cui cng cha

yu cu cho th tc v cc s nhn dng ca n. Khi thu c thng bo ny, VLR ca

MSC ang qun l MS ny s nh du mt c ri mng vo a ch s nhn dng thu

bao di ng quc t. Khi c mt cuc gi ti thu bao ny nh c c ri mng nn

thng bo tm gi s khng c pht ra lm gim ti trn cc knh trung k v knh

qung b.5. Cc trng hp cuc gi

5.1. Trm di ng MS thc hin cuc gi

-MS yu cu n nh knh:

Sau khi thc hin vic quay s, MS yu cu c n nh knh trn knh truy

cp ngu nhin RACH. Nhn c yu cu ny trm thu pht gc BTS s gii m bn

tin. Phn mm ca trm gc BSS n nh knh SDCCH vi bn tin n nh knh tc

thi gi trn knh cho php truy nhp AGCH.

- MS tr li:

MS tr li bn tin n nh knh tc thi v chuyn ti n nh knh SDCCH.

Trn knh SDCCH, MS s truyn i cc bn tin SAMB (Set Asynchronous Balance

Mode Kiu cn bng khng ng b t hp). Bn trong bn tin SABM bao gm cc

ch th yu cu cc dch v khc nh bn tin yu cu thc hin cuc gi hay cp nht v

tr.Cc bn tin ny s c x l ti trm gc BSS v c chuyn ti trung tm chuyn

mch MSC thng qua giao din A.

- Yu cu nhn thc:



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Sau khi nhn c cc yu cu v dch v, MSC s gi i mt yu cu nhn thc

i vi MS. Cc yu cu nhn thc s c gi ti BSS thng qua ng bo hiu.

Trm thu pht gc BTS s lm nhim v truyn cc yu cu ny ti MS trn knh

SDCCH.

- MS tr li nhn thc:

Trm di ng MS tr li yu cu nhn thc bng mt p ng nhn thc. p

ng nhn thc ca MS s c BTS chuyn ti BSC trn ng bo hiu v tuyn.

- Yu cu m ha:

Sau qu trnh nhn thc c hon thnh, MSC s gi n BSC mt lnh yu

cu m ha qu trnh trao i thng tin gia MS v MSC. Qu trnh ny c thit lp

hay khng l ph thuc vo BSC v MSC thit lp ch m ha l ON hay OFF.

- Hon thnh qu trnh m ha:

MS tr li hon thnh qu trnh m ha bng cch gi bn tin thc hin xong qu

trnh m ha.

- MS thit lp cuc gi:

MS gi bn tin thit lp cuc gi trn knh SDCCH. N gi ti tng i MSC

dch v yu cu thit lp cuc gi

- Yu cu n nh knh lu lng:

Sau khi MSC nhn c bn tin yu cu thit lp cuc gi, MSC s gi li hthng BSS bn tin n nh knh lu lng, Bn tin ny ch th loi knh lu lng sc yu cu l knh bn tc hay ton tc hoc truyn s liu. BTS s ch nh v nnh cho MS mt knh lu lng TCH bng cch gi mt lnh n nh trn knhSDCCH.

- MS hon thnh vic n nh knh lu lng TCH:

p ng lnh n nh knh, MS chim ly knh TCH ng thi gi bn tinhon thnh vic n nh knh trn knh iu khin lin kt nhanh FACCH.

- Bn tin chung:

Tng i MSC gi bn tin chung ti my di ng MS. Bn tin ny thng bo cho

MS hon thnh vic gi v c tn hiu hi m chung c nghe thy t MS. Bn tin

ny l trong sut i vi BSS.

- Bn tin kt ni:

Khi bn b gi nhc my tr li th mt bn tin kt ni c gi n trm di ng

MS. Tn hiu ny l trong sut i vi trm gc BSS. Bn tin kt ni c truyn thng



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qua knh FACCH. tr li tn hiu kt ni, MS m mt ng ting v truyn i

thng qua knh FSCCH. Bn tin kt ni ti tng i MSC v cuc gi c thc

hin.

5.2. Trm di ng MS nhn cuc gi

- Nhn tin tm gi:

Khi thu bao c tm gi th tng i di ng MSC s gi ti mt bn tin

yu cu nhn tin (Paging Request) n h thng iu khin trm gc BSC. BSC s x

l bn tin ny v truyn chng trn knh PCH.

- Thu bao tr li:

Sau khi thu c bn tin Paging Request, MS tr li bng cch gi bn tin yu

cu knh trn knh RACH.- n nh knh SDCCH:

Nhn c bn tin n nh knh, BSS s x l bn tin v ngay lp tc n nh

mt knh SDCCH. Vic n nh ny s c m ha v truyn trn knh cho php truy

nhp AGCH. Trm di ng MS c n nh mt knh SDCCH v truyn mt bn tin

kiu cn bng khng ng b t hp SABM tr li nhn tin. Sau khi c x l ti

BSS, bn tin tr li tm gi s c gi ti MSC.

- Yu cu nhn thc:

Sau khi nhn c bn tin tr li tm gi, tng i di ng MSC s gi i mt

yu cu nhn thc i vi trm di ng MS. Yu cu nhn thc c gi ti trm gc

BSS thng qua ng bo hiu. Trm thu pht gc BTS s lm nhim v truyn cc yu

cu ny ti trm di ng MS trn knh SDCCH.

-MS tr li nhn thc:

MS tr li yu cu nhn thc bng mt p ng nhn thc. p ng ny s c

BTS chuyn ti BSC trn ng bo hiu v tuyn.

- Yu cu m ha:

Qu trnh nhn thc c hon thnh, MSC s gi n BSC mt lnh yu cu m

ha qu trnh trao i thng tin gia MS v MSC.

- Hon thnh qu trnh m ha:

MS tr li hon thnh qu trnh m ha bng cch gi bn tin hon thnh ch

m ha

- Bn tin thit lp:



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MSC gi bn tin thit lp ti MS yu cu cc dch v. BSS gi bn tin thit lp

trn knh SDCCH.

- MS xc nhn cuc gi:

Khi nhn c thng tin v vic thit lp cuc gi, trm di ng MS gi i mtbn tin xc nhn cuc gi. Bn tin ny thng bo rng MS nhn c bn tin thit lp

cuc gi v cho bit MS c th nhn cuc gi.

- n nh knh:

Khi nhn c bn tin xc nhn, tng i di ng MSC gi mt bn tin n nh

knh. H thng trm gc BSS nhn c bn tin ny n nh knh lu lng TCH v

gi bn tin n nh knh ti trm di ng MS trn knh SDCCH.

- Hon thnh n nh knh:Trm di ng chim ly knh TCH v gi bn tin hon thnh vic n nh knh

trn knh FACCH. H thng trm gc nhn bn tin ny v gi n n tng i di ng

MSC.

- Bn tin chung:

MS gi bn tin chung ti tng i di ng MSC trn knh FACCH. Bn tin

ny thng bo tng i MSC tm gi c trm di ng MS v MS ang chung.

Tng i MSC gi hi m chung ny cho my ch gi.

- MS thc hin kt ni:

Khi trm MS tr li, MS gi bn tin kt ni trn knh FACCH v thit lp mt

ng thoi n ngi s dng. Bn tin kt ni c truyn qua BSS ti tng i di

ng MSC i n tng i ca my ch gi.

- Thit lp thnh cng:

Kt ni cuc gi c thit lp v cuc thoi c tin hnh.6. Cc trng hp chuyn giao ( Handover)

Mng quyt nh chuyn giao nh cc thng s o cng trng v cht

lng truyn dn t MS v BTS. Khi Handover xy ra th c nhiu thng tin iu khin

cn c truyn nn knh SDCCH khng p ng c v h thng phi s dng knh

FACCH trao i thng tin iu khin.

-Handover gia cc BTS ca cng mt BSC:

Trong trng hp ny, BSC phi thit lp mt ng ni ti BTS mi, n nh

mt knh TCH ca BTS ny chun b Handover, gi lnh cho MS chuyn tn s sang



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knh v tuyn mi v ch ra khe thi gian ca knh TCH mi ny. Handover ch xy ra

trong vng BSC nn c th x l ti BSC m MSC khng cn bit. Nu thay i vng

nh v, MS mi cn c thng bo cp nht v tr cho MSC.

- Handover gia cc BSC cng mt MSC/VLR:

Trong trng hp ny mng phi can thip nhiu hn. BSC mi nhn c yu

cu chuyn giao t MSC. Sau mt ng ni mi t MSC n BSC n BTS c

thit lp v mt knh TCH dnh cho Handover. Sau MS c lnh chuyn tn s

mi cho TCH mi.

- Handover gia hai vng phc v MSC/VLR:

y l trng hp phc tp nht vi nhiu tn hiu c trao i trc khi

Handover. MSC c phi gi thng bo yu cu Handover ti MSC mi. MSC ny m

nhn vic phi ghp n BTS mi. Sau khi thit lp xong ng ni gia hai MSC,

MSC c s gi lnh Handover ti MS.

VI. CC DCH V TRONG GSM

- Dch v thoi:

L dch v quan trng nht ca GSM. N cho php cc cuc gi hai hng din

ra gia ngi s dng GSM vi thu bao bt k mt mng in thoi ni chung no.

Tc truyn thoi trong GSM l 13 kbit/s- Dch v s liu:

S liu cng nh thoi trong GSM s dng cng ngh chuyn mch knh. GSM

c thit k a ra rt nhiu dch v s liu. Cc dch v s liu c phn bit vi

nhau bi ngi s dng phng tin (ngi s dng cc mng in thoi PSTN,

ISDN), bi bn cht cc lung thng tin u cui (d liu th, fax, videotex, teletex,

), bi phng tin truyn dn (gi hay mch, ng b hay khng ng b,) v bi

bn cht thit b u cui. Tc truyn s liu trn mng GSM l 9,6 kbit/s.- Dch v bn tin ngn SMS:

L mt loi dch v s liu. Dch v nhn tin ngn SMS cho php cc thu bao

GSM gi cho nhau cc bn tin ch di khng qu 160 k t. C th s dng mt trung

tm dch v mt thu bao c bn tin n . Sau bn tin s c pht n thu

bao. Nu thu bao ngoi vng ph sng ca h thng hay tt ngun th bn tin s c

lu gi v gi i khi thu bao li sn sng. C th thu hay gi cc thng bo ngn

trng thi ri hay trong qu trnh cuc gi.



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Ngoi ra cn c cc dch v ph khc nh: chn hng cuc gi, gi cuc gi,

tnh cc cho thu bao...

VII. BO MT TRONG GSM

Ging nh cc mng thng tin khc, mng thng tin di ng GSM phi thc hinchng vic truy nhp tri php. Cc bin php chng vic truy nhp tri php:

- nh s nhn dng thu bao, cc vng phc v, vng nh v

- Nhn thc thu bao bng cc cha kha mt m

- Mt m tin tc

1. nh s nhn dng thu bao v cc vng mng

- S nhn dng thu bao di ng quc t IMSI:

IMSI = MCC (m nc) + MNC (m mng) + MSIN (s nhn dng thu bao)

Ngoi ra cn c tin t 00 ( gi quc t )

- S lu ng ca trm di ng (cp vo VLR):

MSRN = MCC + NDC (s MSC) + SN (s thu bao tm thi)

Mi mt vng phc v khc nhau th cc thu bao s c MSRN khc nhau.

- S nhn dng thu bao di ng tm thi mi vng nh v IMSI nh hn hocbng 4 byte. N ch c ngha tng vng nh v LA (Location Area).

- S nhn dng trm di ng theo phn cng IMEI: S nhn dng phn cng cami thu bao s c nhn thc nh EIR.

- S nhn dng vng nh v:

LAI = MCC + MNC + LAC

N gip cho vic nh tuyn cc cuc gi n tng BSC.

- S nhn dng :

CGI = LAI + CI CI (Cell Identity): S nhn dng t bo 16 bit

Dng nh tuyn cuc gi n tng BTS. M nhn dng vng nh v s cpht lin tc trn knh iu khin qung b BCCH cc MS bit s vng nh v camnh.

- M nhn dng trm gc BSIC: dng MS bit c BTS ca mnh v cc

BTS ln cn. Trm BTS pht BSIC trn knh ng b SCH. Khi MS mun truy nhp th

n s pht BSIC trn knh truy nhp ngu nhin RACH.

2. Nhn thc thu bao

- Cc trng hp nhn thc:



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+ Khi MS mi truy nhp vo mng

+ Khi MS bt u mt cuc gi hoc tr li mt cuc gi

+ Khi MS chuyn vng nh v

Mc ch l xc nh xem MS c phi l thu bao ca mnh hay khng. Nhnthc l cch kim tra quyn truy nhp ca cc thu bao

- B ba cha kha mt m:

+ S ngu nhin R: ly ngu nhin mi khi cn nhn thc

+ Mt khu S: dng hi p

+ Kha mt m kc: kha mt m tin tc

AUC to ra cc b ba cha kha v c lu gi trong MSC d tr cho cc thubao ang nm trong vng .

- Trnh t nhn thc:

BTS pht s ngu nhin R cho MS. MS pht mt khu S vo mng, mng s

kim tra xem gi tr S c ng hay khng.

CHNG II


BTSMS

R

S

27


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L TRNH PHT TRIN T GSM LN 3G

I. GII THIU

H thng thng tin di ng GSM cung cp cc dch v thoi v s liu trn c s

chuyn mch knh bng thng hp. Do tc truyn thp, 13 kbit/s vi truyn thoiv 9,6 kbit/s vi truyn s liu. Tc ny khng p ng c nhu cu ngy cng cao

ca ngi s dng v cc dch v mi nh truyn s liu tc cao, in thoi c hnh,

truy cp Internet tc cao t my di ng v cc dch v truyn thng a phng tin

khc. V nhng l do trn, cc nh khai thc GSM ang tng bc nng cp mng GSM

ln mt h thng thng tin di ng th h th 3. Con ng tin ti 3G duy nht ca

GSM l CDMA bng thng rng. Trn th trng chu u, W-CDMA c gi

l h thng vin thng di ng ton cu UMTS (Universal Mobile Telecommunication

System). Trong cu trc dch v 3G cn c bng thng rt ln v nh th cn nhiu phtn hn. Tuy nhin vic loi b hn cng ngh ang dng tip cn ngay mng 3G l

rt tn km v mt kinh t. V vy h phi chn gii php nng cp mng GSM qua

bc trung gian 2,5G tm thi p ng nhu cu ca ngi s dng cng nh chun

b c s h tng k thut sau mi tin ln 3G. Ni chung 2,5G bao gm mt hoc tt

c cc cng ngh sau:

- S liu chuyn mch knh tc cao (HSCSD)

- Dch v v tuyn gi chung (GPRS)

- Tc s liu tng cng pht trin GMS (EDGE)

II. L TRNH PHT TRIN T GSM LN 3G

L trnh nng cp GSM ln W-CDMA nh sau:

HSCSD (High Speed Circuit Switched Data): S liu chuyn mch knh tc

cao.

GPRS (General Packet Radio Service): Dch v v tuyn gi chung.

EDGE (Enhanced Data Rates for GSM Evolution): Tc s liu tng cng

pht trin GSM.

W-CDMA (Wideband Code Division Multiple Access): a truy cp phn mbng rng.


GSM HSCSD GPRS EDGE

W-CDMA

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1.Cng ngh s liu chuyn mch knh tc cao HSCSD

GSM ch h tr cc dch v s liu vi tc cc i m mt khe thi gian c

th cung cp l 9,6 kbit/s. h tr tc s liu cao hn cho GSM, MS phi s dngnhiu khe thi gian. Cng ngh HSCSD s dng nguyn tc ny.

Cng ngh HSCSD cho php nng cao kh nng truyn s liu trn mng GSM

bng cch cp pht nhiu khe thi gian hn cho ngi s dng. HSCSD phi hp 4

knh thoi GSM 14,4 kbit/s thnh mt knh 57,6 kbit/s. i vi dch v s liu th tc

ti a l 64 kbit/s t c vi 4 khe thi gian. D liu truyn trong dch v HSCSD

c hnh thnh di dng cc lung song song a vo cc khe thi gian khc nhau

v chng s c kt hp li ti u cui. Tt c cc khe thi gian s dng trong mt

kt ni HSCSD phi thuc v cng mt sng mang. Vic cp pht cc khe thi gian ph

thuc vo th tc cp pht khe thi gian.Cng ngh HSCSD c trin khai da trn c s h tng sn c ca mng

GSM, ch cn nng cp phn mm hin c m khng cn lp t thm cc phn t mng

mi. N cho php cp pht ti nguyn khng i xng giao din v tuyn. Tuy nhin

do vn s dng chuyn mch knh nn hiu sut s dng ti nguyn v tuyn ca

HSCSD khng cao.

Cu trc h thng HSCSD:

Hnh 2.1 Cu trc h thng HSCSD

TE (Terminal Equipment): Thit b u cui

MT (Mobile Terminal): My di ng u cui

TAF (Terminal Adaptation Function): Chc nng thch ng u cui

IWF (Interworking Function): Chc nng kt ni mng

- Chc nng thch ng u cui TAF:


TE MT BTS MSC IWF

PDNPLMNISDN

PSPDN

TRAU

TAFBSC

Knh 64 kbit/sKnh nx 16 kbit/snx cc knh ton tcnx khe thi

gian/khung TDMA

Giao din v tuyn

Abis A

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ng vai tr tip nhn s liu ca thit b u cui TE a ti v chia chng vo

cc khe thi gian c chn trc. Mi khe thi gian mang s liu vi cc tc

c chun ha 1,2 kbit/s; 2,4 kbit/s; 4,8 kbit/s; 9,6 kbit/s; 14,4 kbit/s.

- MT v giao din v tuyn:

S liu t TAF a ti u cui di ng MT, ti y mi khe thi gian c m

ha knh. u ra sau m ha l lung s liu tc 22,8 kbit/s cho mi khe thi gian v

n c chuyn ti giao din v tuyn.

- Trm thu pht gc BTS:

BTS tip nhn lung s liu t giao din v tuyn, n thc hin gii m cho mi

khe thi gian thu c lung s liu c tc ph hp vi khung TRAU (16

kbit/s). Sau lung s liu c chuyn ti khi TRAU t ti b iu khin trm gc

BSC. Cc khung TRAU 16 kbit/s c gi ti BSC thng qua giao din Abis.

- Giao din Abis:

Cc khung TRAU 16 kbit/s c gi ti BSC thng qua giao din Abis.

- B chuyn i m v thch ng tc TRAU:

TRAU tip nhn cc khung s liu 16 kbit/s t giao din Abis v n nh dng li

thng tin ca mi lung s liu thnh dng A - TRAU truyn i trn giao din A.

- Giao din A:

Cho php cha c 4 khung A-TRAU tc 16 kbit/s t mt ngi s dng

a n. Cc khung ny c ghp li vi nhau pht i trn mt ng 64 kbit/s.

- Trung tm chuyn mch di ng MSC v cc khi IWF:

MSC tip nhn cc khung A-TRAU ca ng kt ni 64 kbit/s v nh tuyn

chng thng qua IWF. Sau khi tip nhn, khi IWF ly ra cc thng tin s liu trong A-

TRAU v kt hp chng thnh nhng lung s liu ghp trc khi chuyn ti ccmodem ca mnh. Modem tip nhn s liu v nh tuyn chng qua mng PSTN ti

cc modem ch v cc thit bi u cui s liu DTE (Data Terminal Equipment) ni

khc.

2. Dch v v tuyn gi chung GPRS

2.1 Gii thiu GPRS

GPRS (General Packet Radio Service) l cng ngh chuyn mch gi c cc

nh khai thc GSM la chn nh l mt bc chun b c s h tng k thut tin ln3G. N s gip cc nh khai thc c th trin khai nhiu ng dng i vi mng in



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thoi di ng. GPRS h tr dch v s liu tc cao cho GSM vi tc ti a ng

truyn c th t 171,2 kbit/s. Nh c th truy cp Internet t MS c tnh nng WAP

(Wireless Application Protocol) gi tin nhn hnh nh v m thanh. V c th truy

cp mng Internet gi email, nhn fax, truy cp cc c s d liu. GPRS cho php

cung cp dch v nhn tin a phng tin (MMS Multimedia Message Service) v dchv truyn nh ng VTS (Video Streaming). c bit vi tnh nng lun lun kt ni,

mng GPRS cho php ngi s dng va c th kt ni mng Internet va c th m

thoi ng thi. Mt MS trong mng GPRS c th truy nhp n nhiu khe thi gian.

Vi GPRS, ngi s dng c th dng chung mt ti nguyn v tuyn. V th hiu sut

s dng ti nguyn v tuyn rt cao, cc ph truy cp mng cng ch tnh theo lu

lng d liu c truyn ti.

Giao din v tuyn ca GPRS c xy dng trn cng nn tng nh giao dinv tuyn ca GSM, cng sng mang v tuyn rng 200KHz v 8 khe thi gian. Nh

vy c dch v chuyn mch knh v chuyn mch gi u c th s dng cng sng

mang. Tuy nhin mng ng trc ca GPRS c thit k sao cho n khng ph thuc

vo giao din v tuyn. Mng GPRS l mt mng s liu gi c xy dng trn c s

cu trc mng GSM, v vy vic a chuyn mch gi vo i hi phi b sung thm

thit b cho mng.

2.2 Cc c im ca mng GPRS

- S dng cng ngh chuyn mch gi:

Vi vic s dng cng ngh chuyn mch gi, mt thit b c th lun lun c

kt ni v sn sng gi mt thng tin m khng cn chim dng mt knh ring trong

sut thi gian truyn s liu v knh c th c chia s cho nhiu ngi dng khc

nhau. iu ny mng chuyn mch knh khng th lm c. Ngoi ra, trong GPRS

nu mt li c pht hin trong mt khung d liu thu c trong BSS th khung s

c yu cu pht li cho n khi chnh xc trc khi gi qua mng li GPRS.

- Cho php kt hp nhiu khe thi gian truyn d liu:

GPRS s dng cng mt sng mang vi bng thng 200 KHz v 8 khe thi gian

nh GSM. Tuy nhin trong GPRS c th kt hp cc khe trong s 8 khe thi gian

truyn d liu nn s gi d liu truyn i trong mi khung truyn tng ln. Kt hp

vic cp pht ti nguyn ng nn hiu qu s dng bng tn tng ln ng k.

- Kt ni tc thi v tnh cc thun li:

GPRS d dng kt ni tc thi v ngi dng c th thit lp lun kt ni mkhng chim dng ti nguyn, do thng tin c th gi hoc nhn tc thi ngay khi c



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nhu cu. Tc thi l mt u im ca GPRS khi so snh vi s liu chuyn mch knh

GSM v n p ng c cc ng dng c tnh cp bch.

Trong chuyn mch knh th vic tnh cc l ton b thi gian chim dng knh

mc d c nhng khong thi gian khng c d liu c gi i. Vi GPRS ch tnh

cc theo dung lng c gi i. iu ny thun li cho vic kt ni trc tuyn vi

mng trong thi gian di.

-H tr cc dch v bng rng:

Cng nh Internet, GPRS s dng cng ngh chuyn mch gi v cc giao thc

trong h TCP/IP nn tt c cc ng dng nh email, truy cp Web tin nhanh v truyn

file u c th thc hin qua mng GPRS. Tc truyn s liu nhanh hn cho php

GPRS cha ng cc ng dng bng rng vn khng thch hp vi cc kt ni quay s

chm hn nh GSM.

- Tnh bo mt cao hn:

GPRS cho php thm vo cc giao thc s dng cho nhn thc trc khi thu

bao c php truy cp vo Internet hoc cc mng s liu khc. GPRS ph tr vic m

ha d liu ngi dng qua giao din Wireless t u cui di ng n SGSN ( nt h

tr dch v).

- Hiu qu trong vic s dng ph:

Trong GPRS ti nguyn v tuyn ch c s dng khi ngi s dng thc ti

ang gi hoc nhn d liu. Mt ti nguyn v tuyn hin c c th c chia s ng

thi gia vi ngi s dng khc nhau. Nh hiu sut s dng ti nguyn v tuyn ny

m mt s ln ngi s dng GPRS c th chia s cng mt bng thng v c phc

v t cng mt cell.

2.3. Cu trc ca mng GPRS



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Hnh 2.2 Cu trc mng GPRS

Cc phn t trong mng GPRS

- Nt h tr dch v GPRS(SGSN - Serving GPRS Support Node): thc hin cc

chc nng chnh sau:+ Qun l vic di chuyn ca cc u cui GPRS bao gm vic qun l nhp

mng, ri mng ca thu bao; mt m, bo mt ca ngi s dng; qun l v tr hin

thi ca thu bao

+ nh tuyn v truyn cc gi d liu gia cc my u cui GPRS. Cc lung

c nh tuyn t SGSN n BSC thng qua BTS n MS.

+ Qun l trung k logic ti u cui di ng bao gm vic qun l cc knh lu

lng gi, lu lng nhn tin ngn SMS v tn hiu gia cc my u cui vi mng.+ X l cc th tc d liu gi PDP (Packet Data Protocol) bao gm cc thng

s quan trng nh tn im truy nhp, cht lng dch v khi kt ni vi mt mng d

liu khc bn ngoi h thng.

+ Qun l cc ngun knh ti nguyn BSS.

+ Cung cp cc file tnh cc dnh cho d liu gi.

+ Qun l truy nhp, kim tra truy nhp cc mng d liu ngoi bng mt m v

s xc nhn.


SMS-GMSCSMS-IWMSC SMS-C

MSC/VLR HLR

BSC GGSN

SGSN EIR

PCU SGSN

Mng PLMN khc

GGSN

PDNBTS

MT

TE

E CGd

D

Cs Gr GcAUm

R

Gb Gn Gi

Gn Gp Gf

Bo hiu

Bo hiu v lu lng

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- Nt h tr cng GPRS(GGSN - Gateway GPRS Support Node):

L im giao din vi cc mng s liu gi bn ngoi. Mt SGSN c th giao

din vi mt hay nhiu GGSN.y l giao din trn c s IP c s dng mangbo hiu v s liu ngi s dng. Giao din ny truyn xuyn s liu gia SGSN v

GGSN qua mng ng trc IP. GGSN chuyn i cc gi d liu GPRS n t SGSN

thnh khun dng giao thc d liu gi (PDP).

Chc nng chnh ca GGSN:

+ H tr giao thc nh tuyn cho d liu my u cui.

+ Giao tip vi cc mng d liu gi IP bn ngoi.

+ Cung cp chc nng bo mt mng.

+ Qun l phin GPRS theo mc IP, thit lp thng tin n mng bn ngoi.

+ Cung cp d liu tnh cc (CDRs - Charging Data Records).

- H thng trm gc BSS

BSS cung cp tt c cc chc nng iu khin v truyn dn thng tin v tuyn

ca mng, bao gm:

+ Khi iu khin d liu gi PCU: c nhim v kt hp cc chc nng iu

khin v tuyn GPRS (iu khin truy nhp giao din v tuyn) vi phn h thng trmgc BSS ca mng GSM. PCU nh tuyn cc bn tin bo hiu v truyn ti d liu ca

ngi s dng. PCU s lp rp v sp xp li d liu chuyn ti SGSN. Ti PCU cc

khi d liu RLC s c sp xp trong khung LLC (iu khin lin kt logic), sau

c chuyn ti SGSN. PCU t ti BSC v phc v BSC .

+ B iu khin trm gc BSC: trong mng GPRS, BSC ng vai tr trung tm

phn phi, nh tuyn d liu v thng tin bo hiu GPRS. BSC c th thit lp, gim

st v hy b kt ni ca cc cuc gi chuyn mch knh cng nh chuyn mch gi.

+ Trm gc BTS: cung cp kh nng n nh knh vt l ti cc khe thi gian

cho cuc gi chuyn mch knh trong mng GSM v d liu chuyn mch gi trong

mng GPRS. BTS kt hp vi BSC thc hin cc chc nng v v tuyn.

- Phn chuyn mch:

+ MSC/VLR: c s dng cho vic ng k v lin lc vi thu bao nhng

khng ng vai tr g trong vic nh tuyn d liu GPRS. Trong h thng GSM,

MSC/VLR khng c dng cho th tc nhn thc thu bao nh trong h thng GSMm thay vo l HLR. Do SGSN s nhn b ba thng s dnh cho vic nhn thc

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+ HLR/AUC: HLR lu gi tt c cc thng tin v thu bao GSM cng nh

GPRS. Thng tin v thu bao GPRS c trao i gia HLR vi SGSN. HLR thc hin

qun l di ng cho cc thu bao GPRS bng cch lu tr cc thng tin nh tuyn ca

cc thu bao GPRS t vng cp nht v tr trong SGSN v bo cho SGSN c bit s thay

i v tr ca thu bao. HLR c s dng trc tip cho vic nhn thc thu bao thaycho MSC/VLR.

AUC cung cp b ba thng s nhn thc v thc hin m ha ng truyn.

+ EIR: thc hin cc chc nng nh trong h thng GSM. EIR lu gi tt c cc

d liu lin quan n thit b u cui MS, n c ni n MSC qua ng bo hiu

kim tra s hp php ca thit b.

- Thit b cung cp dch v nhn tin ngn SMS-GMSC(tng i di ng c

cng cho dch v SMS) v SMS-IWMSC(tng i di ng lin mng cho dch v SMS):

c kt ni vi SGSN qua giao din Gd nhm cung cp kh nng truyn ti cc

bn tin ngn.

- Thit b u cui GPRS(MS):

C th chia lm 3 loi:

+ Loi 1: H tr s dng ng thi cc dch v thoi v s liu. Ngi s dng

loi 1 c th va ni chuyn va truyn s liu GPRS cng mt lc (s dng c hai dchv chuyn mch knh v chuyn mch gi ng thi).

+ Loi 2: H tr ng thi vic nhp mng GPRS v nhp mng GSM nhng

khng cho php s dng ng thi c hai dch v. Ngi s dng loi 2 c th c

ng k mng GSM v mng GPRS ng thi nhng khng th va ni chuyn va

truyn s liu.

+ Loi 3: C th nhp mng GPRS hoc GSM nhng khng th nhp ng thi

c hai mng. Ti mt thi im nht nh, thit b loi 3 hoc l thit b GSM hoc lthit b GPRS. Nu nhp mt loi dch v th c th coi rng thit b ri b dch

v kia.

- Mng ng trc GPRS (Backbone):



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Mng Backbone kt hp mt s giao din chun d liu chun dng kt nigia cc nt SGSN, GGSN v cc mng d liu bn ngoi. C hai loi mng Backbone:

- Mng intra-backbone: Kt ni cc phn t trong cng mt PLMN nh cc nt

SGSN, GGSN.

- Mng inter-backbone: Dng kt ni gia cc mng intra-backbone ca hai

PLMN khc nhau thng qua cng BG (Border Gateway).

Mng Backbone gii quyt vn tng tc gia cc mng GPRS. L do chnh

m h thng h tr vn tng tc gia cc mng GPRS l cho php roaming giacc thu bao GPRS. Cc thu bao roaming s c mt a ch PDP c cp pht bimng PLMN ch, mt router chuyn tip gia mng PLMN ch v mng PLMN mthu bao di chuyn n. nh tuyn ny c dng cho c thu bao hon ton hay btu truyn d liu. Thng tin c truyn thng qua cc cng bin BG.

2.4. Giao thc trong mng GPRS

Cc giao thc ca GPRS cung cp cc chc nng iu khin v truyn ti d liu

trn mt phng bo hiu v mt phng truyn dn.* Cc giao thc trong mt phng truyn dn:

- Giao thc to ng hm GTP (GPRS Tunnelling Protocol): phc v cho vic

truyn ti d liu gia cc nt GSN trong mng ng trc GPRS.

- Giao thc iu khin truyn dn/giao thc d liu gi ngi s dng

TCP/UDP: TCP chuyn cc khi d liu gi PDU ca giao thc GTP trong mng ng

trc GPRS cho cc giao thc cn thit lin kt d liu tin cy. TCP cung cp kh

nng iu khin lung v bo v chng li s tht thot hay ngt qung cc PDU caGTP.


Mng ni ht

Mng intrabackbone

Mng interbackbone

Mng intrabackbone

Mng s

liu

Operator 1Operator 2

MS caOperator1

MS caOperator1

GPRSRegister

GPRSRegister

Hnh 2.3 Mng ng trc ca GPRS


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- Giao thc IP (Internet Protocol): c s dng trong mng ng trc GPRS,

phc v cho vic bo hiu v nh tuyn d liu.

- iu khin kt ni logic LLC (Logical Link Control): cung cp lin kt d liu

tin cy gia my u cui v SGSN ang phc v my u cui . LLC phc v

truyn ti cc PDU gia my u cui v SGSN, pht hin v khi phc cc PDU ca

LLC b tht lc hoc ngt qung.

- Chuyn tip (Relay): Trong BSC chc nng ny s chuyn tip cc PDU ca

LLC gia giao din Um v Gb. Ti SGSN n s chuyn tip cc PDU ca PDP gia cc

giao din Gb v Gn.

- iu khin kt ni v tuyn/iu khin truy nhp mi trng RLC/MAC: RLC

cung cp mt lin kt tin cy trn giao din v tuyn. MAC iu khin cc th tc bo

hiu truy nhp trn knh v tuyn v sp xp cc khung LLC vo cc knh vt l.

* Cc giao thc trong mt phng bo hiu:

- iu khin vic truy nhp mng GPRS nh nhp mng v ri mng

- iu khin thit lp cc kt ni trong mng nh qu trnh khi hot mt a ch

PDP

- iu khin vic nh tuyn trong mng

- iu khin vic n nh, cp pht ti nguyn.

2.5 Giao din v tuyn

a. Lp vt l ca GPRS

c chia lm 2 lp con:

- Lp RF vt l (Physical RF Layer): thc hin chc nng truyn dn c bn, thu

nhn nh iu ch v gii iu ch. Sau truyn ln lp ng truyn vt l.

- Lp ng truyn vt l (PLL Physical Link Layer): thc hin chc nngng khung n v d liu, m ha, hiu chnh li truyn dn trung k vt l v ghp

xen. Ngoi ra cn cung cp chc nng cho vic la chn li cell, iu khin cng sut.

b. RLC/MAC ca GPRS

Tn y ca lp 2 l iu khin truy nhp mi trng MAC v lp iu khin

lin kt v tuyn RLC. MAC l lp con thp cn RLC l lp con cao hn.

*Cc chc nng ca MAC:

- MAC cho php nhiu MS chia s mt ti nguyn truyn dn chung. MAC cho

php mt MS s dng song song mt vi knh vt l, ngha l s dng mt vi khe thi



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gian trong khung TDMA. i vi lu lng d liu kt cui di ng, thc th MAC

cung cp cc th tc xp hng v lp lch ca nhng ln c gng truy nhp. i vi lu

lng d liu c khi u bng di ng, MAC cung cp cch x l gia cc my di

ng c gng truy nhp mi trng c chia s cng lc.

- MAC cung cp cch ghp knh hiu qu d liu v bo hiu trn c hai hng

ng ln v ng xung.

- i vi truy cp knh c khi u bi di ng, MAC gii quyt tranh chp

gia nhng ln c gng truy cp knh bao gm d tm v khi phc xung t.

- i vi knh kt cui di ng, MAC lp biu nhng ln c gng truy cp,

nhng ln ny c th sp xp cc ln truy cp gi.

- MAC x l u tin.

*Cc chc nng ca RLC:

- Giao din Um cho php truyn cc LLC PDU gia lp LLC v lp con MAC.

- Phn on cc LLC PDU thnh cc khi d liu RLC ti bn truyn v rp li

ti bn nhn.

- Cc th tc hiu chnh li tr li cho php truyn li c chn lc cc khi d

liu RLC c phn phi khng thnh cng.

- S thch ng lin kt, l truyn cc t m ty theo cc iu kin ca knh.

c. Lp iu khin ng truyn logic LLC

LLC cung cp mt trung k kt ni logic ng tin cy hn gia SGSN v MS

cng nh bc cu cho hai giao tip Gb v Um. Ngoi ra LLC cng c thit k

khng ph thuc vo cc giao thc v tuyn c bn nhm c th a ra cc gii php v

tuyn GPRS thay i v sau. Cu trc khung LLC bao gm:

- Trng a ch: gm mt byte nhn dng im truy nhp (SAPI), mt bit phnbit giao thc PD v mt bit C/R (Command/Respone).

- Trng iu khin in hnh: gm t 1 n 3 byte dng xc nh kiu

khung.

2.6. Cc chc nng ca GPRS

* Cc chc nng iu khin truy nhp mng

Truy nhp mng l mt phng thc m mt ngi s dng kt ni vi mng

c th s dng cc dch v v cc phng tin ca mng . Giao thc truy nhp l mt

tp xc nh cc th tc cho php khai thc cc dch v v phng tin mng. Ngi



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truy cp GPRS c th t bn di ng hoc bn c nh ca mng GPRS. Giao din pha

mng c nh c th h tr nhiu giao thc truy nhp ti cc mng d liu ngoi (X.25,

IP). Phn qun l ca mi PLMN c th yu cu cc th tc iu khin truy nhp ring

cho php ngi truy nhp mng hay gii hn thu bao s dng cc dch v. Ngoi vic

truyn dn d liu theo chun im - im (PTP Point to Point), im a im(PTM Point to Multi Point), GPRS h tr thm loi truy nhp ngm nh (anonymous)

ti mng. Dch v ny cho php MS trao i cc gi d liu vi host xc nh trc

c nh a ch bi cc giao thc lin mng c xc nh. Tuy nhin ch c mt

s a ch ch PDP nht nh s dng trong dch v ny. IMSI hoc IMEI s khng

c s dng trong khi truy nhp mng do bo mt ngm nh cao. Do cc chc

nng nhn thc v m ha khng c xt trong kiu truy nhp ngm nh.

- Chc nng ng k:ng k l phng thc m ngi s dng dng IP Mobile (nhn dng di ng)

lin kt vi cc giao thc v a ch ca gi d liu trong mng PLMN cng nh lin

kt vi cc im truy nhp ra mng PDP ngoi. Kt ni ny c th l lin kt tnh (c

lu tr trong HLR) hoc ng (c n nh theo yu cu cn thit).

- Chc nng nhn thc v cp php:

Chc nng ny thc hin vic nhn dng v nhn thc ngi yu cu dch v,

hp thc ha loi yu cu dch v m bo rng thu bao c php s dng ccdch v mng. Chc nng nhn thc c thc hin kt hp vi chc nng qun l di

ng.

- Chc nng iu khin tip nhn:

Mc ch ca iu khin tip nhn l xc nh cc ti nguyn mng no cn cung

cp theo ng yu cu cht lng dch v QoS. Nu cc ti nguyn ny c php th

n phi tin hnh t trc. iu khin tip nhn c thc hin kt hp vi cc chc

nng qun l ti nguyn v tuyn ca mng m bo nhng yu cu s dng tinguyn v tuyn trong mi cell.

- Chc nng gim st bn tin:

Chc nng ny c thc hin bi chc nng lc gi tin trong cc rounter v cc

firewall cho php truyn hay loi b cc bn tin khng hp l, trnh s xm nhp tri

php t bn ngoi.

- Chc nng tng thch u cui:

Chc nng ny thc hin thch ng cc gi d liu nhn hoc truyn ti thit b

u cui vi phng thc truyn qua mng GPRS.



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- Chc nng thu thp d liu tnh cc:

Chc nng ny thu thp cc d liu cn thit tnh cc thu bao hoc tnh

cc lu lng. Cc ph c tnh bng s lng byte s dng. Thng tin tnh cc

do cc SGSN v GGSN thu thp. SGSN lu thng tnh cc ca mi thu bao lin quan

ti vic s dng mng v tuyn trong khi GGSN lu cc thng tin tnh cc lin quan

ti vic dng mng d liu bn ngoi ca mi thu bao. Trn c s nh khai thc

mng GPRS s s dng cc thng tin ny to ra ha n tnh cc cho tng thu bao.

Thng tin tnh cc ti thiu m SGSN thu thp bao gm:

+ Mc s dng giao din v tuyn: thng tin tnh cc v s lng d liu

c truyn theo hng MS pht i v MS thu v, c phn loi theo cht lng dch

v QoS v cc giao thc ngi s dng.

+ Mc s dng a ch giao thc gi d liu: thng tin tnh cc ghi li thi

gian MS s dng cc giao thc gi d liu PDP ca MS.

+ Mc s dng ti nguyn chung ca GPRS: thng tin tnh cc s m t mc

s dng ca thu bao i vi cc ti nguyn khc nhau c lin quan ti GPRS cng

nh cc hot ng trong mng GPRS ca MS.

+ V tr ca MS: cc thng tin v HPLMN, VPLMN v c th thm cc thng tin

v tr vi chnh xc cao hn.

Thng tin tnh cc ti thiu m GGSN thu thp bao gm:

+ a ch ch v a ch ngun ca thng tin trao i: mc chnh xc ca

thng tin ny c xc nh bi nh khai thc GPRS.

+ Mc s dng mng d liu ngoi: cc thng tin v khi lng d liu c

gi i v nhn t cc mng d liu ngoi.

+ Mc s dng cc a ch giao thc d liu gi: thng tin tnh cc lu li

thi gian MS s dng cc a ch giao thc d liu gi PDP ca MS.

+ V tr ca MS: cc thng tin v HPLMN, VPLMN v c th thm cc thng tin

v tr vi chnh xc cao hn.

* Chc nng nh tuyn v truyn dn gi

- Chc nng chuyn tip:

L mt phng thc m mt nt mng chuyn cc n v d liu gi PDU nhn

c t mt nt ri chuyn ti mt knh u ra thch hp cho nt tip theo trong tuyn.- Chc nng nh tuyn:



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Chc nng nh tuyn s dng a ch ch trong bn tin xc nh nt nhn

bn tin v s dng cc dch v lp di a cc bn tin ny ti GSN. Chc nng

nh tuyn s la chn ng truyn cho hop tip theo trong tuyn.

Cc chc nng nh tuyn v truyn dn gi:

+ nh tuyn v truyn dn gi gia thit b di ng v mng ngoi.

+ nh tuyn v truyn dn gi gia thit bi di ng v mng PLMN GPRS

khc.

+ nh tuyn v truyn dn gi gia cc thit b di ng khc nhau.

- Chc nng phin dch v sp xp a ch:

Phin dch a ch l s chuyn i mt a ch loi ny thnh mt a ch loi

khc. Chc nng phin dch v sp xp a ch chuyn i a ch giao thc mng ngoithnh a ch mng ni b nhm phc v cho vic nh tuyn cc gi tin trong mng

PLMN hoc gia cc mng PLMN.

- Chc nng ng gi:

GPRS truyn trong sut PDP PDU gia mng ngoi v MS. Cc PDP c ng

gi v tch gi nhm phc v nh tuyn trong mng. ng gi cho php gn thm

thng tin iu khin v a ch vo mt PDU. Tch gi l qu trnh tch a ch v thng

tin iu khin t gi ly ra n v d liu ban u. Chc nng ng gi c thchin gia cc SGN trong backbone v gia cc SGSN v MS.

- Chc nng Tunnelling:

Tunnelling l mt phng thc truyn dn cc PDU c ng gi trong hoc

gia cc mng PLMN t mt im ng gi ti mt im tch gi. Tunnel (ng hm)

l mt giao tuyn hai chiu kt ni im - im nhng ch c im cui ca tunnel l

c xc nh.

- Chc nng nn:

Chc nng ny cho php s dng ti u dung lng ca phn v tuyn bng cch

truyn i cc SDU cng nh cng tt m vn m bo ni dung trong n.

- Chc nng m ha:

Cho php bo mt d liu v d liu ca ngi s dng qua cc knh v tuyn v

bo v mng PLMN t nhng ngi xm phm.

- Chc nng qun l tn min:



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L chc nng Internet chun m bo thng nht tng ng gia tn gi, chc

nng v a ch ca cc GSN trong mng.

* Cc chc nng qun l di ng

Chc nng ny thc hin tng t nh trong h thng GSM. Cc chc nng qunl di ng c s dng theo di v tr hin ti ca MS trong mng PLMN hoc

trong mng PLMN khc.

Mi vng nh tuyn c phc v bi mt SGSN. Vic theo di v tr ca MS

ph thuc vo trng thi qun l di ng nh sau:

+ Khi MS trong trng thi Stanby (ch): v tr ca MS c bit cp mt vng

nh tuyn.

+ Khi MS trong trng thi Ready (sn sng): v tr ca MS c bit cp mtcell.

- Cc trng thi ca MS:

GPRS c 3 trng thi qun l di ng khc nhau:

+ Trng thi ri: trng thi ny c s dng khi thu bao MS khng hot ng

(khng khai bo kt ni mng GPRS). Trong trng thi ri, thu bao khng c gn

chc nng qun l di ng. Cc ni dung ca MS v SGSN khng cha cc thng tin

nh tuyn v thng tin v tr thu bao. Vic nhn tin v truyn d liu khng c thchin nhng MS c th nhn d liu trong dch v im a im. thit lp cc chc

nng qun l di ng trong MS v SGSN, MS phi thc hin th tc khai bo kt ni

mng GPRS.

+ Trng thi ch: Trong trng thi ny, thu bao khai bo kt ni mng v

c qun l di ng. Lc ny mng bit MS ang nm mt vng nh tuyn no. MS

c th nhn cc trang nhn tin bo hiu, d liu v c th c cc trang nhn ca dch v

chuyn mch knh. Trng thi ny cha th truyn v nhn d liu. MS thc hin lachn vng nh tuyn GPRS v chn cc b. MS s dng cc th tc di ng khai

bo cho SGSN khi vo vng nh tuyn mi nhng khng cn thng bo khi thay i

cell trong cng mt vng nh tuyn. Do thng tin v v tr ca MS trong qun l di

ng ca SGSN ch cha s nhn dng vng nh tuyn. Nu ht thi gian ch, MS

chuyn v trng thi ri v vic qun l di ng ht hiu lc. Nu MS cn gi d liu

th n chuyn sang trng thi sn sng.

+ Trng thi sn sng: MS thc hin cc th tc qun l di ng v mng bit

thu bao ang cell no. SGSN gi d liu ti MS m khng cn tm gi MS v MS

gi d liu ti SGSN bt c lc no. Qun l di ng vn c duy tr trong trng thi



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sn sng d MS c hay khng c cung cp ti nguyn v tuyn thm ch khi khng c

d liu c truyn. Trng thi sn sng c gim st bi mt b nh thi. Mt phin

qun l di ng s chuyn t trng thi sn sng sang trng thi ch khi b nh thi sn

sng kt thc.

- Chc nng gn/tch GPRS:

L chc nng qun l di ng nhm thit lp hay kt thc kt ni ti mng

GPRS. SGSN ng vai tr tip nhn yu cu gn/tch v x l chng. Vic khai bo kt

ni mng (gn GPRS), thu bao di ng chuyn sang trng thi sn sng v ni dung

qun l di ng c thit lp, MS c nhn thc, kha m c to ra, ng kt ni

c m ha c thit lp v MS c cp pht mt TLLI (nhn dng knh logic tm

thi). SGSN nhn thng tin v thu bao t HLR, sau khi thc hin mt gn GPRS,

SGSN s lun bm theo v tr ca MS. Lc ny MS c th nhn v gi SMS nhngkhng thu pht c s liu. chuyn giao s liu, trc tin MS phi thc hin kch

hot ni dung giao thc s liu gi. Khi thu bao mun kt thc mt kt ni ti mng

GPRS th n thc hin tch GPRS. Vic thc hin tch GPRS cho php MS chuyn

sang trng thi ri v ngt ton b ni dung qun l di ng.

C hai kiu MS kt thc kt ni ti mng:

+ Mng (SGSN) gi yu cu tch ti MS hoc MS gi yu cu tch hon ton ti

SGSN.+ Mng ngt kt ni m khng thng bo cho MS khi t ti nh thi di ng

hoc khi c li v tuyn khng th khi phc gy ra mt kt ni knh logic.

MS c th thc hin tch GPRS t mng theo ch mc nh khi thi gian ch

ht hiu lc nhng thng thng vic tch GPRS l t MS.

- Chc nng bo mt:

C 3 chc nng bo mt sau:

+ Chng li vic s dng khng hp php dch v GPRS

+ Bo mt nhn dng ngi s dng

+ Bo mt d liu ngi s dng (m ha)

- Chc nng qun l v tr:

Cc chc nng qun l v tr:

+ Cung cp c ch chn v PLMN



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+ Cung cp c ch mng nhn bit vng nh tuyn (RA) ca MS trong trng

thi ch v sn sng.

Cc th tc qun l s kim sot s thay i hay vng nh tuyn, ng thi

nh k cp nht thng tin v vng nh tuyn ca MS. Nu mt MS trong thi gian di

khng thay i v tr th mng phi nhn c thng bo MS vn nm trong kh nng

nhn bit ca mng. Do vic cp nht vng nh tuyn phi c thc hin theo chu

k nht nh. Khi MS vo mi v c th vo vng nh tuyn mi th MS phi thc

hin mt trong ba th tc sau:

1/ Cp nht

2/ Cp nht vng nh tuyn

3/ Cp nht kt hp v vng nh tuyn

C hai kiu cp nht vng nh tuyn:

+ Cp nht trong mt SGSN

+ Cp nht gia cc SGSN

SGSN c th qun l vi vng nh tuyn. Nu vng nh tuyn mi thuc v s

qun l ca mt SGSN khc th kiu cp nht trong mt SGSN c s dng, nu vng

nh tuyn mi vn thuc s qun l ca SGSN c th kiu cp nht gia cc SGSN

c s dng. Thng thng SGSN c s chuyn cc gi tin ca ngi s dng tiSGSN mi cho ti khi n nhn c thng bo xa v tr t HLR th thi.

- Chc nng qun l thu bao:

Chc nng ny thc hin mt c ch thng bo cho cc nt ca GPRS khi d liu

thu bao GPRS ca mt ngi s dng thay i. Bt c khi no d liu thu bao GPRS

thay i trong HLR v s thay i tc ng n d liu c lu trong SGSN th SGSN

s thng bo s thay i bng mt trong hai cch sau:

+ Thc hin th tc chn d liu thu bao: b sung hoc sa i d liu thu bao

trong SGSN

+ Thc hin th tc xa d liu thu bao: xa d liu thu bao trong SGSN.

* Cc chc nng qun l knh logic

Cc chc nng qun l knh lgic lin quan ti vic duy tr mt knh thng tin

gia mt MS v PLMN qua giao din v tuyn. Cc chc nng ny thc hin iu phi

cc thng tin trng thi lin kt gia MS v PLMN cng nh gim st qu trnh chuyngiao d liu qua knh logic.



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- Chc nng thit lp knh logic:

Thit lp knh logic c thc hin khi MS khai bo s dng dch v GPRS

- Chc nng gim st knh logic:

Thc hin vic gim st tnh trng knh logic v iu khin khi thay i trngthi knh.

- Chc nng gii phng knh logic:

Thc hin ngt kt ni logic, gii phng cc ti nguyn lin quan ti kt ni

logic.

* Cc chc nng qun l ti nguyn v tuyn

Cc chc nng qun l ti nguyn v tuyn lin quan n vic n nh v duy tr

cc tuyn thng tin v tuyn.

- Chc nng qun l Um:

Chc nng ny qun l mt s knh vt l c s dng trong mi v xc nh

s lng cc ti nguyn v tuyn cung cp s dng cc dch v GPRS. S lng cc

ti nguyn v tuyn dnh cho GPRS c th thay i t ny ti khc ph thuc nhu

cu ngi s dng hoc c ch nh bi nh vn hnh mng PLMN.

- Chc nng la chn :Chc nng ny cho php MS la chn ti u thit lp mt ng truyn ti

mng PLMN. Vic ny lin quan n vic kim t v xc nh cht lng tn hiu t cc

ln cn cng nh vic pht hin v trnh tc nghn trong cc .

- Chc nng Um Tranx:

Chc nng ny cung cp kh nng chuyn giao gi d liu thng qua giao din

v tuyn gia MS v BSS. N bao gm cc th tc:

+ iu khin truy nhp qua cc knh v tuyn

+ Ghp cc gi tin trn qua cc knh v tuyn chung

+ Phn b gi trong MS

+ Pht hin v sa li

+ Cc th tc iu khin lu lng to i

- Chc nng qun l ng kt ni: chc nng ny qun l cc ng truyn

thng gia BSS v cc nt SGSN. Vic thit lp v gii phng cc tuyn ny c th lng hoc tnh.



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* Chc nng qun l mng

Chc nng ny cung cp cc c ch h tr chc nng khai thc v bo dng

lin quan ti GPRS nh: qun l li, cu hnh, ch tiu, bo mt,c thc hin t xa

hoc ti ch.

2.7. Nhp mng GPRS



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Khi bt ngun MS hoc khi tch cc trnh duyt, c th tch cc chc nng GPRS trong

MS. Mi khi khi u chc nng GPRS trong MS, MS phi nhp mng GPRS mng

ny bit rng MS kh dng i vi lu lng gi. Lc ny MS trng thi sn

sng. Khi trng thi sn sng, MS c th gi hoc nhn gi. Ngoi ra MS cng c th

vo trng thi ch sau khi trng thi sn sng tm ngng.

Hnh 2.4 m t trng hp MS loi 3 thc hin nhp mng GPRS:


MS BSS SGSN HLR/AUC SGSNYu cu knh gi

n nh ng ln gi

Cc khi RLC(yu cu nhp mng)

Cng nhn ng ln gi

Cng nhn iu khin gi

Cc khi RLC(yu cu nhn thc v mt m)

Yu cu knh gin nh ng ln gi

Cc khi RLC(Tr li nhn thc v mt m)

Cng nhn ng ln gi

Cng nhn iu khin gi

Cc khi RLC(Nhp mng c tip nhn)

Cng nhn ng xung

n nh ng xung gi

Cng nhn ng xung

Yu cu knh gi

n nh ng ln gi

Cc khi RLC(Nhp mng hon thnh)Cng nhn ng ln giCng nhn iu khin gi

Yu cu nhp mng

Yu cu nhn

thc v mt m

Tr li nhn

thc v mt m

Nhp mngc tip nhn

Nhp mng honthnh

Gi thng tin nhnthc

Gi thng tin nhnthc

Cp nht v tr GPRS

Chn s liuthu bao

Chn s liu thu bao

RRCp nht v trGPRS

Hy v tr

Hy b v tr RR

Mi C

Hnh 2.4 Nhp mng GPRS

47


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u tin MS yu cu knh gi (Packet Channel Request): MS a ra mc ch

ca yu cu l tr li tm gi, th tc qun l di ng (MM). Mng tr li bng n nh

ng ln gi (cp pht mt khe thi gian hoc cc khe thi gian) cho MS truyn

bn tin m MS nh gi.

MS tip tc gi yu cu nhp mng mt hay nhiu khi v tuyn n mng

trn cc ti nguyn c cp pht. MS c th gi s khi v tuyn bng s khi m

mng cp pht cho n.

Khi nhn c yu cu nhp mng ti BSS, BSS s dng PACCH cng nhn

l nhn c yu cu ny. Trng hp MS gi ton b thng tin cn gi, MS gi

bn tin cng nhn iu khin gi n mng v gii phng cc ti nguyn c cp pht.

Trong lc BSS chuyn yu cu nhp mng n mt SGSN. SGSN ny c th yu cu

cc th tc an ninh, trong n nhn cc b ba t HLR.BSS gi bn tin n nh ng xung gi n MS. Bn tin ny c th gi trn

knh PCCCH hoc PACCH. Bn tin n nh ng xung gi hng dn MS s dng

ti nguyn quy nh ng xung. Sau BSS gi i yu cu nhn thc v mt m

m n nhn c t SGSN. Khi nhn c yu cu ny, MS cng nhn bn tin ng

xung v yu cu cc ti nguyn ng ln n c th tr li. V th n gi mt yu

cu knh gi khc rt ging vi yu cu knh gi m n gi lc u. Mt ln na mng

lai n nh cc ti nguyn cho MS. MS s dng cc ti nguyn ny gi tr li vnhn thc v mt m n mng. Tr li ny c BSS chuyn n SGSN. BSS cng gi

cng nhn n MS. MS khng nh l nhn c cng nhn ging nh lm vi

yu cu nhp mng ban u.

Sau khi MS c SGSN nhn thc, SGSN gi cp nht v tr GPRS n HLR.

Qu trnh ny ging nh cp nht v tr GSM bao gm ti xung t HLR n SGSN

cc thng tin v thu bao, ghi li v tr ca MS vo HLR. Khi HLR nhn c cp nht

v tr GPRS, SGSN gi bn tin cp nht mng c tip nhn ti MS. i vi cc bn

tin khc, trc ht BSS n nh ti nguyn c th tr li bng mt bn tin nhpmng hon thnh n MS. BSS cng nhn vic nhn c s liu cha trong

nhp mng hon thnh v chuyn bn tin ny n SGSN. MS khng nh nhn

c cng nhn.

2.8. Kh nng pht trin ca GPRS ln 3G

C hai cch xy dng mt h thng thng tin di ng th h th 3 nng cp t

GPRS l:



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n tt nghip

- Nng cp tc truyn ca GPRS bng cch pht trin GPRS ln EDGE v

tip theo l thng tin di ng th h 3 UMTS (Universal Mobile Telecommunication

System - H thng vin thng di ng ton cu).

- Pht trin trc tip t GPRS ln UMTS.

Tuy nhin ti mt s quc gia th vic trin khai mng UMTS gp mt s kh

khn v ph tn v cc quc gia th ph tn c em bn u gi cng nh vn

cp giy php cho 3G. Do cc nh khai thc mng phi tr mt khon tin ln cho

vic xin cp php hot ng di tn UMTS. Trong khi EDGE l mt chun

c cng nhn ca 3G s dng bng tn GSM hin c v h tr tc truyn ti d

liu ln ti 384 kbit/s m khng cn thm bt k mt giy php no. V vy EDGE c

Documents

GSM Va GSM Len 3G_Hoang Thi Hue_45