DO an -Khojduy

7/31/2019 DO an -Khojduy

1/61

Ti u ha mng

B GIO DC V O TO CNG HA X HI CH NGHA VIT NAMTRNG I HC CNG NGHIP H NI

--------------------------------------------------c lp - T do - Hnh phc---------------------------------

NHIM V N TT NGHIP

H v tn sinh vin: ..... S hiu sinh vin:

Kho:.Khoa: Cng ngh in t Ngnh: .........

1. u n:....................................................................................................................................................................................................................................................................................................

2. Cc s liu v d liu ban u:

....................................................................................................................................................................................................................................................................................................

3. Ni dung cc phn thuyt minh v tnh ton:......................................................................................................................................................................................................................................................................................................................................................................................................................................................

4. Cc bn v, th ( ghi r cc loi v kch thc bn v ):......................................................................................................................................................................................................................................................................................................................................................................................................................................................

5. H tn ging vin hng dn: .6. Ngy giao nhim v n:.

7. Ngy hon thnh n:

Ngy thng nm

Ch nhim B mn Ging vin hng dn

Sinh vin hon thnh v np n tt nghip ngy thng nm

Cn b phn bin

Ngun Duy Khi in t 1 K31


2/61

Ti u ha mng

B GIO DC V O TO

TRNG I CNG NGHIP H NI

---------------------------------------------------

BN NHN XT N TT NGHIP

H v tn sinh vin: ............................................ S hiu sinh vin: .....................................

Ngnh: ............................................................Kho: ..............................................................

Ging vin hngdn:..............................................................................................................

Cn b phn bin: Ni dung thit k tt nghip:

.....................................................................................................................................................

.....................................................................................................................................................

.....................................................................................................................................................

.....................................................................................................................................................

.....................................................................................................................................................

...................................................................................................................................

1. Nhn xt ca cn b phn bin:

.....................................................................................................................................................

.....................................................................................................................................................

.....................................................................................................................................................

.....................................................................................................................................................

.....................................................................................................................................................

.....................................................................................................................................................

................................................................................................................................

Ngy thng nmCn b phn bin

( K, ghi r h v tn )



3/61

Ti u ha mng

LI M U

Thng tin lin lc l mt nhu cu ca bt k mt x hi pht trin no. p

ng nhu cu lin lc ngy cng cao ca x hi, thng tin di ng c nghin cu

pht trin t rt sm, bt u vi cc h thng thng tin di ng s dng cng ngh

analog, cho n nay cc mng di ng s dng cng ngh s c ng dng rng

ri v pht trin v cng mnh m.

Thng tin di ng ang trin khai Vit Nam bao gm 2 h.

+ S dng cng ngh GSM: MobiFone, VinaFone, Viettel, VietnamMobile,

Beeline (GTEL).

+ S dng cng ngh CDMA: EVN Telecom, v S-Fone.

Trong s lng thu bao s dng cng ngh GSM l p o.

ng trc s pht trin ca s lng thu bao trong thi gian ti v nhu cu

tng cao v cc dch v cao cp hn ca khch hng. Cc nh mng cn phi thchin m rng dung lng v nng cp cho mng li. Vic nghin cu v a ra cc

gii php k thut c kh nng p dng thc t v trin khai trong thi gian ngn l

v cng cn thit.

ti: Thit k xy dng trm BTS phc v cho mt vng v kim tra hot

ng trm BTS bng phng php o Driver Test

Trong qu trnh lm kha lun tt nghip, mc d em c gng nhiu nhng dotrnh c hn nn khng th trnh khi nhng sai st, em rt mong c s ph

bnh, gp ca thy c v bn b.

Trc khi trnh by ni dung ti ny, em xin chn thnh cm n ti cc thy

c trong b mn v tuyn cng nh cc thy c trong khoa Vt L thuc trng H

KHTN trang b cho em kin thc trong sut bn nm hc va qua.

c bit, em xin gi li cm n ti Thy V Thnh Thi tn tnh gip , trctip hng dn v to mi iu kin thun li cho em hon thnh kha lun.



4/61

Ti u ha mng

Em cng chn thnh cm n ti anh Nguyn Thnh Hng, Trng Phng k

thut - cng ty C phn Pht trin Dch v Vin thng ITC cung cp ti liu v

hng dn em hon thnh kha lun.

Cui cng, l li cm n su sc em mun gi n gia nh cng bn b ng

vin gip em trong sut thi gian qua em c iu kin hon thnh tt nht kha

lun tt nghip ny.

Sinh vin thc hin



5/61

Ti u ha mng

MC LC

Phn m u ...........................................................................................................................................................10

Phn 1......................................................................................................................................................................12TNG QUAN MNG DI NG........................................................................................................................12

Chng I ..................................................................................................................................................................12

MNG DI NG GSM .......................................................................................................................................12

Gii thiu chung ................................................................................................................................. ........ .......12

Cc c trng c bn ca h thng GSM ..........................................................................................................13

Cu trc mng GSM .............................................................................................................................. ........ ....14

...........................................................................................................................................................................14

1.1Chc nng cc khi trong h thng GSM ............................................................................................. ........14

CHNG II ...........................................................................................................................................................19

TNG QUAN V BTS .........................................................................................................................................19

Gii thiu chung v BTS ..................................................................................................................... ........ .......19

Cu trc chung ca h thng BTS ......................................................................................................................23

Nguyn l hot ng ca BTS .................................................................................................................... ........27

Phn 2......................................................................................................................................................................31

TI U HA MNG...........................................................................................................................................31

Chng 3 .................................................................................................................................................................32

DRIVE TEST TRONG MNG GSM ..................................................................................................................32

Mc ch ca vic thc hin Drive Test ...........................................................................................................32

Thit b o v th tc o drive test ....................................................................................................................32

4.3 Drive test trong chu trnh ti u ..................................................................................................................35

Chng 4 .................................................................................................................................................................38

4.1 Cc yu t nh hng n cht lng thoi ......................................................................................... .......394.2 Mt s k thut tng cht lng h thng: .................................................................................................43

Chng 5 Chuyn giao cuc gi v phn tch li handover ...........................................................................48

5.1 L thuyt ...........................................................................................................................................................48

5.1.1 Phn loi Handover ......................................................................................................................... ........48

5.1.2 Khi to th tc Handover ...................................................................................................................... .51

5.1.3 Quy trnh chuyn giao cuc gi ..................................................................................................... ........ ...52

5.2 o kim tra tri mt s trm li Handover .................................................................................................57



6/61

Ti u ha mng

BNG K HIU VIT TT

AB Access Burst Cm truy nhp

AGCH Access Grant Channel Knh cho php truy nhp

AMPS Advanced Mobile Phone System H thng in thoi di ng tin tin

ARQ Automatic Repeat Request Yu cu lp li t ng

AUC Authentication Center Trung tm nhn thc

BCCH Broadcast Control Channel Knh iu khin qung b

BCH Broadcast Channel Knh qung b

BER Bit Error Rate T s bit li

BSC Base Station Controller B iu khin trm gc

BSIC Base Station Identity Code M nhn dng trm gc

BSS Base Station System H thng trm gc

BTS Base Transceiver Station Trm thu pht gc

C/A Carrier to adjacent ratio T s sng mang trn sng ln cn

C/I Carrier to interference ratio T s sng mang trn nhiu

CI Cell IdentityNhn dng xc nh v tr trong

vng nh v

C/R Carrier to reflection ratio T s sng mang trn sng phn x

CCCH Common Control Channel Knh iu khin chung

CCITT

International Telegraph &

Telephone Consultative

Committee

U ban t vn quc t v in thoi

v in bo

CEPT

European Conference of Postal

and Telecommunication

Lin minh chu u v bu chnh vin

thng



7/61

Ti u ha mng

DCCH Dedicated Control Channel Knh iu khin ring

DCS Data Communication Subsystem Phn h thng tin s liu

DCS Digital cellular System H thng t ong s

EIR Equipment Identity Register Thanh ghi nhn dng thit b

ETSIEuropean Telecommunication

Standards Institude

Vin tiu chun vin thng chu u

FACCH Fast Associated Control Channel Knh iu khin lin kt nhanh

FB Frequency Correction Burst Cm hiu chnh tn s

FCCH Frequency Correction Channel Knh hiu chnh tn s

FDMAFrequency Division Multiple

Accessa truy nhp phn chia theo tn s

GMSC Gateway MSC MSC cng

GPRS General Packet Radio Service Dch v v tuyn gi chung

GSM

Global System for

Mobile Communication Thng tin di ng ton cu

HLR Home Location Register Thanh ghi nh v thng tr

IMEIInternational Mobile Equipment

IdentityNhn dng thit b di ng quc t

IMSIInternational Mobile Subscriber

IdentityNhn dng thu bao di ng quc t

ISDNIntegrated Service Digital

NetworkMng s a dch v

ISI Intersymbol Interference Nhiu giao thoa gia cc k hiu

IWF Inter Working Function Chc nng tng tc

LA Location Area Vng nh v

LAC Location Area Code M vng nh v



8/61

Ti u ha mng

LAI Location Area Identity Nhn dng vng nh v

MCC Mobile Country Code M quc gia

ME Mobile Equipment Thit b di ng

MMS Multimedia Messaging Service Dch v nhn tin a phng tin

MNC Mobile Network Code M mng di ng

MOU Memoradum Uderstanding Bn ghi nh

MS Mobile Station Trm di ng

MSCMobile services Switching

Center

Trung tm chuyn mch cc dch v

di ng

MSISDN Mobile Station ISDN Number S ISDN trm di ng

MSRNMobile Station Roaming

NumberS lu ng trm di ng

NB Normal Burst Cm bnh thng

NMT Nordic Mobile Telephone in thoi di ng Bc u

OMCOperation and Maintenance

CenterTrung tm bo dng v vn hnh

OSS Operation and Support System H thng khai thc v h tr

PCH Paging Channel Knh tm gi

PCM Pulse Code Modulation iu ch xung m

PIN Personal Identification Number S nhn dng c nhn

PLMN Public Land Mobile Network Mng di ng mt t cng cng

PSPDNPacket Switch Public Data

Network

Mng s liu cng cng chuyn mch

gi

PSTNPublic Switched Telephone

Network

Mng in thoi chuyn mch cng

cng

RACH Random Access Channel Knh truy nhp ngu nhin



9/61

Ti u ha mng

RAND Random number S ngu nhin

SACCHSlow Associated Control

ChannelKnh iu khin lin kt chm

SB Synchronization Burst Cm ng b

SCH Synchronization Channel Knh ng b

SDCCHStand alone Dedicated Control

Channel

Knh iu khin ring ng mt

mnh

SIM Subscriber Identity Module Mun nhn dng thu bao

SMS Short Message Service Dch v nhn tin ngnSRES Signed Response Mt khu

SS Switching System H thng chuyn mch

TACSTotal Access Communication

SystemH thng thng tin truy nhp ton b

TCH Traffic Channel Knh lu lng

TDMA Time Division Multiple Access a truy nhp phn chia theo thi gian

TMN Telecommunication

Management NetworkMng qun l vin thng

TRAU Transcoder/Rate Adaptation UnitKhi chuyn i m v thch ng

tc

VLR Visitor Location Register Thanh ghi nh v tm tr

CGI Cell Global Indentity Nhn dng ton cu

HNH V

Hnh v 2.1: Cu trc mng GSM.......................................................................................................................19

Hnh v 2.2: Cu hnh kt ni BTS ti BSC.......................................................................................................20



10/61

Ti u ha mng

Hnh v 2.3: BTS MBI...........................................................................................................................................21

Hnh v 2.4: BTS MBO..........................................................................................................................................22

Hnh v 2.5: Cu trc chung ca h thng BTS.................................................................................................23

Hnh v 2.6: Kin trc khi SUMA......................................................................................................................24

Hnh v 2.7: Kin trc khi TRE.........................................................................................................................25

Hnh v 2.8: Kin trc khi ANC.........................................................................................................................26

Hnh v 2.9: Kin trc khi ANC.........................................................................................................................27

Hnh v 4.1: Chu trnh Drive Test........................................................................................................................37

Hnh 4-1 Intra-cell Handover..............................................................................................................................49

Hnh 4-2 Inter-cell Handover...............................................................................................................................50

Hnh 4-3 Intra-MSC Handover...........................................................................................................................50

Hnh 4-4 Inter-MSC Handover...........................................................................................................................51

Hnh 4-5 G 1: Trong lc kt ni, MS vn tip tc o c mc thu v cht lng truyn dn ca cellphc v v nhng cell xung quanh......................................................................................................................53

Hnh 4-6 Quyt nh chuyn giao_Handover Decision....................................................................................53

Hnh 4-7 G 1: BSC khai bo thng tin vi MSC............................................................................................54

Hnh 4-8 G 2: MSC1 yu cu MSC2 cp Handover Number.......................................................................55

Hnh 4-9 G 2: Cp m HON v knh v tuyn cho MSC1...........................................................................55

Hnh 4-10 G 3: MSC1 chuyn mch kt ni cho MS trn knh lu lng thit lp vi MSC2...............56

Hnh 4-11 Kt ni vi BTS c c gii phng ...............................................................................................57

Phn m u

Tm tt ni dung



11/61

Ti u ha mng



12/61

Ti u ha mng

Phn 1

TNG QUAN MNG DI NG

Chng I

MNG DI NG GSM

Gii thiu chung

Khi nim GSM c s dng ln u tin vo nm 1982, l ch vit tt ca

Groupe Speciale Mobile, l t chc thuc Hi ng Bu chnh v Vin thng Chu

u CEPT (Conference Europeenne des Postes et Telecommunications). T chc ny

c giao nhim v pht trin mt chun mi dng cho lin lc di ng trong di tn

900MHz, v kt qu ca n chnh l mng GSM ln u tin vo nm 1991. Trongnm ny, t GSM cng chuyn i ngha, tr thnh ch vit tt ca cm t H

thng thng tin di ng ton cu (Global System for Mobile Communications), v

ngi ta cng ra tiu chun cho mng GSM hot ng trong bng tn 1800MHz,

c gi l h thng DCS1800.

T n nay, nh c tnh chun ha rng ri trn ton th gii cng vi kh

nng chuyn vng quc t mnh m, GSM t c nhng thnh cng v cng to

ln trong s pht trin. Theo s liu bo co ca hip hi GSM GSMA (GSM



13/61

Ti u ha mng

Association), tnh cho n thng 4 nm 2008, c 3 t thu bao di ng s dng

cng ngh GSM vi tng s 218 nh khai thc trn phm vi ton th gii.

Xut pht im ban u, GSM ch yu cung cp dch v thoi v d liu tc

thp, GSM cng c cc u im nh: tnh bo mt cao, kh nng chng nhiu mnh

m, hiu sut s dng ph cao. T h thng GSM ban u ch cung cp dch v thoi

l ch yu, GSM c tch hp thm cc chc nng nh gi tin nhn (SMS), hin

th s in thoi gi n, chuyn cuc gi p ng yu cu truyn d liu vi

tc cao, GSM c pht trin thm vi Dch v gi d liu v tuyn tng

qut GPRS (General Packet Radio Service), a tc truyn d liu trn c s

mng v tuyn GSM c th ln n 171.2 kbit/s.

Ngy nay, trc nhu cu ngy cng cao v thng tin di ng, c bit l cc ng dng

yu cu tc d liu cao, mng 3G l mt xu hng tt yu, trong GSM khng phi

l ngoi l. Trong qu trnh nng cp v dch chuyn , tnh hiu qu l yu

t v cng quan trng, do i hi s thay i ti thiu trong cu trc mng li,

c s h tng k thut mng. Theo l trnh c cc t chc chun ha a ra v

c cc nh khai thc chp nhn rng ri, mng GSM s tr thnh mng thng tin di

ng bng rng th h 3G vi mi trng truy nhp WCDMA trong tng lai.

Cc c trng c bn ca h thng GSM

+ GSM nguyn thu hot ng bng tn 900 MHz vi knh ng xung: 890-

915 MHz v knh ng ln: 935 - 960 MHz.

+ DCS 1800 (Digital Cellular System) hot ng bng tn 1800 MHz vi knh

ng xung: 1710 - 1785 MHz v knh ng ln: 1805 - 1880MHz.

+ PCS 1900 (Personal Communication Services) hot ng bng tn 1900 MHz

vi knh ng xung: 1850 - 1910 MHz v knh ng ln: 1930 - 1990 MHz.

+ Khong cch song cng (Khong cch gia tn s ln v tn s xung) ca

GSM 900, DCS1800 v PCS 1900 ln lt l 45MHz, 95MHz v 80MHz.

+ Khong cch gia cc knh ln cn (ng ln hoc ng xung) l 200 kHz.



14/61

Ti u ha mng

+ Phng thc truy cp l TDMA cho php nhiu cuc gi khc nhau cng

chia s mt tn s.

Cu trc mng GSM

1.1 Chc nng cc khi trong h thng GSM

MS (Mobile station)

MS l thit b dng truy cp vo mng. Mt MS gm hai thnh phn chnh c

lp:

- Thit b u cui (ME - Mobile Equipment).

+ Thit b u cui bao gm in thoi di ng hoc mt thit b c th truy cp vo mng.

+ Mi in thoi di ng c phn bit bi mt s nhn dng in thoi di ng

IMEI (nternational Mobile Equipment Identity).

- SIM (Subcriber Identity Module)


BSC TRAU MSC

VLR

HLR

EIR AuC

Ccmngkhc:PSTN,PLMN,ISDN.

Abisinterface

Uminterface

Aterinterface

A interface

OMC

BSS

NSS

Hnh v 1.1: Cu trc mng GSM

14

MS BTS


15/61

Ti u ha mng

+ SIM l mt card thng minh dng nhn dng u cui. u cui khng th

hot ng nu khng c SIM. SIM lu tr cc thng tin lin quan n thu bao di

ng, cc dch v GSM v cc thng tin lin quan n PLMN.

+ Card SIM cha mt s nhn dng thu bao di ng IMSI (International

Subcriber Identity) h thng nhn dng thu bao, mt mt m xc thc v cc

thng tin khc.

+ Card SIM c th chng vic s dng tri php bng mt khu hoc s nhn

dng c nhn (PIN).

BSS (Base Station System - H thng trm gc)

BSS thc hin cc chc nng lin quan n v tuyn trong h thng. N qun l

vic lin lc v tuyn vi cc khi di ng. N cng x l vic handover ca cc

cuc gi gia cc cell. BSS chu trch nhim qun l tt c cc ti nguyn mng v

tuyn v d liu v cu hnh cell. BSS trong CME 20 v CMS 40 u c kh nng x

l cc li thng thng m khng cn phi c s iu khin t OSS.

BSS gm mt BSC v mt s BTS.

BTS (Base Transceiver Station - Trm thu pht gc)

BTS bao gm tt c cc thit b v tuyn v cc thit b giao tip truyn dn v

tuyn phc v cho mt cell v tt c cc BTS u chu s qun l ca BSC.

Cc chc nng chnh ca BTS l:

- Cung cp kt ni vi MS

-X l tn hiu

-X l bo dng cc b.

-Kim tra v gim st.

Hu ht cc hot ng chnh BTS u c BSC iu khin.



16/61

Ti u ha mng

BSC (Base Station Controller- Trm iu khin gc)

BSC iu khin mt nhm BTS v qun l ti nguyn v tuyn. BSC chu trch

nhim iu khin vic handover, nhy tn, cc chc nng tng i v iu khin cc

mc cng sut, tn s v tuyn ca BTS c th l:

- Qun l mng v tuyn:

Qun l d liu m t cell, cu hnh cell, thng tin h thng v d liu nh v.

+ o c lu lng v cc knh ri.

+ Ghi li lu lng.

+ Chia s ti cell.

- Qun l cc trm v tuyn gc:

+ nh cu hnh cho BTS.

+ Thay i chc nng v ti chng trnh cho cc BTS.

+ Bo dng cc thit b BTS.

- Qun l mng truyn dn:

+ Chuyn i v thch ng tc trong BSC.

+ Vn hnh v bo dng bn trong BSC:

+ iu khin s kt ni gia cc MS: gm cc qu trnh tm gi, thit lp kt

ni bo hiu, ch nh knh lu lng, nh v, handover, iu khin cng sut ng

trong MS v BTS, nhy tn, dch v nhn tin qung b v tin vn.

NSS (Network Switching System - H thng chuyn mch)

H thng chuyn mch NSS chu trch nhim qun l s thng tin gia ngi s

dng mobile n nhng i tng s dng khc nh n cc thu bao di ng, n

mng ISDN, PSTN... N cn cha cc d liu cn thit lu tr thng tin v thu

bao.



17/61

Ti u ha mng

MSC (Mobile Service Switching Centre-Trung tm chuyn mch dch v di ng)

Nhim v chnh ca MSC l iu phi vic thit lp cuc gi n nhng ngi

s dng mng GSM. Mt mt MSC giao tip vi h thng con BSS, mt khc giao

tip vi mng ngoi. MSC thc hin cc chc nng sau:

- Thit lp v iu khin, phn phi cuc gi, cc bn tin ngn.

- X l cuc gi lin tc khi chuyn giao.

- Cp nht v tr, v d liu ca MS.

- Bo hiu gia cc thnh phn ca mng v gia cc mng khc nhau.

- Qun l xc nh c im d liu v x l MS.

- Kim tra IMEI v tnh cc

HLR (Home Location Register - Thanh ghi nh v thng tr)

HLR l mt c s d liu lu tr v qun l cc thng tin v thu bao. Trong

PLMN c nhiu HLR. i vi mi thu bao thuc vng ph sng ca MSC, HLR

cha d liu v thu bao nh: cc s ng k, danh sch dch v c ng k s

dng bi thu bao. HLR cng lu tr v cp nht cc thng tin ng v thu bao, baogm thng tin v v tr thu bao (a ch ca VLR), cc dch v c ng k ca

thu bao, cc s c tip tc gi, cc cuc gi b cm.

VLR (Visitor Location Register - Thanh ghi nh v tm tr)

VLR l mt c s d liu v tt c cc thu bao hin ang nh v vng dch v

ca MSC. N cha cc thng tin tm thi ca MS MSC c th cung cp cc dch

v cho cc MS ang c phc v. Khi MS di chuyn sang vng dch v mi caMSC th VLR kt ni vi MSC mi s yu cu ly v lu thng tin v MS t

HLR. Khi MS thc hin mt cuc gi th VLR cha sn cc thng tin cn thit

cho vic thit lp cuc gi.

VLR lun c tch hp vi MSC c th thc hin bo hiu bn trong. iu

ny lm loi b cc bo hiu khng cn thit gia hai nt mng, do lm gim lu

lng bo hiu trong mng.

AuC (Authentication Centre Trung tm nhn thc)



18/61

Ti u ha mng

Thanh ghi AuC c dng cho mc ch bo mt. N cung cp cc tham s cn

thit cho chc nng nhn thc v to mt m (ciphering). Cc tham s ny gip xc

minh s nhn dng thu bao.

EIR (Equipment Identity Register)

EIR c dng cho mc ch bo mt. N l mt thanh ghi lu tr cc thng tin

v cc thit b mobile. C th hn l n lu tr danh sch cc u cui hp l. Mt

u cui c nhn dng bng mt IMEI. EIR cho php cm cc cuc gi t cc u

cui b nh cp hay khng c php.

MSC cng (GMSC)

thit lp mt cuc gi n ngi s dng GSM, trc ht cuc gi phi c

nh tuyn n mt tng i cng c gi l GMSC m khng cn bit n hin

thi thu bao ang u. Cc tng i cng c nhim v ly thng tin v v tr ca

thu bao v nh tuyn cuc gi n tng i ang qun l thu bao thi im hin

thi (MSC tm tr).

1.1.1 Khi TRAU

Khi TRAU l khi chuyn i tc knh thoi TRAU (Transcoder/Rate

Adapter Unit), khi ny thc hin chc nng chuyn i tc v ghp 4 knh thoi

t trm BTS c tc 16Kb/s thnh mt knh PCM 64Kb/s trc khi giao tip vi

MSC. Mc d c xem l mt phn t ca mng truy nhp nhng TRAU thng

t chung v tr vi MSC gim chi ph kt ni truyn dn.



19/61

Ti u ha mng

CHNG II

TNG QUAN V BTS

Gii thiu chung v BTS

Khi nim v BTS

BTS l mt thit b dng pht tn hiu ra mi trng v tuyn n cc my di

ng v thu tn hiu t cc my di ng cng thng qua mi trng v tuyn. N

thng tin n cc MS thng qua giao din v tuyn Um v kt ni vi b iu khin

trm gc BSC (Base Station Controller) thng qua giao din Abis.

V tr ca BTS trong h thng GSM

CAUTRUCMANG GSM

Radio tow er

Radio tower

BSC

T

C

M

F

S

SGN

HLR

BTS

BTS

GGSN

PSTN

INTERNET

IPGPRSBACKBONE

BSS

OMC-R

MSC

S trn m t v tr ca BTS trong h thng mng GSM. Cc BTS c t

khp ni trong vng c k hoch ph sng v n c kt ni ti b iu khin trm

gc BSC (Base Station Controller). Ngoi ra v tr ca BTS cn ph thuc vo cu

hnh kt ni ti BSC, chng hn nh c cc cu hnh sau:

19

CU TRC MNG GSM

Hnh v 2.1: Cu trc mng GSM


20/61

Ti u ha mng

- Sectorised configuration

- Multipion configuration

- Chain configuration

- Star configuration

Phn loi BTS

Thit BTS b m cng ty ta s dng khu vc pha nam l loi thit b A9100

ca hng ALCATEL n gm c 2 loi chnh l:MBI

L loi BTS dng trong phng kn, trong loi BTS ny li chia thnh 2 dng,

l dng nh MBI3, n ch gm c 3 subrack vi trng lng ln nht l 150kg; loi

cn li l MBI5 n gm c 5 subrack vi trng lng ti a l 270kg. Kch thc v

hnh dng c c m t nh sau:

20

Hnh v 2.2: Cu hnh kt ni BTS ti BSC


21/61

Ti u ha mng

Mi Subrack c th lp t 8 SUMA, 4 TRE, 3 ANC.

21

Hnh v 2.3: BTS MBI


22/61

Ti u ha mng

MBO

L loi BTS c th t ngoi tri v cng ging nh BTS MBI n cng c 2

dng l MBO1 vi trng lng ln nht l 255kg v MBO2 l dng m rng ca

MBO1 vi trng lng ti a l 425kg. Kch thc v hnh dng c m ta m t

nh sau:

Cng tng t nh MBI, MBO cng c nhng tng qut v khu vc dng u

ni cp tn hiu v cp cnh bo. Ngoi ra n cn c thm cc khu vc dng lp

t acqui v nhng khu vc dng cho vic lp t cc thit b truyn dn.

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Hnh v 2.4: BTS MBO


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Ti u ha mng

Cu trc chung ca h thng BTS

Cu trc chung ca h thng BTS

CLOCK

T

R

A

NS

OMU

SUM

TRE AN

Abis

BTS-TE

H thng BTS gm c cc khi chc nng chnh sau:

+ SUMA

+ TRE

+ ANC

Cu trc v chc nng ca cc khi chnh trong h thng BTS

Khi SUMA

- XCLK (External clock): l giao din tn hiu ng h ng b bn ngoi. Tn

hiu ny c th c ly t mt tn hiu tham chiu bn ngoi nh: Abis link, GPS,

BTS khc, c th c to ra trong kiu xung ri bi mt b pht tn s bn trong.

- CLKI: l h thng ng h ch c phn phi ti TRE v AN.

- MMI: thng qua serial link kt ni ti BTS Terminal, thc hin qun l

li, tc ng trc tip n h thng bng mt s lnh n gin.

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Hnh v 2.5: Cu trc chung ca h thng BTS


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Ti u ha mng

- XBCB: External BTS control bus l bus iu khin cnh bo ngoi(Alarm).

- BCB: BTS control bus: Bus nay mang thng tin v trng thi, cu hnh, cnh

bo n cc Module trong BTS.

- BSII: mang thng tin TCH, RSL, OML, IOM-CONF.

- SUMA: l khi trung tm ca mt BTS, mt BTS ch c mt SUMA bt k s

sector v TRX l bao nhiu.

Transmission

& Clock

O&M

RI

BSII

SWITCH

2 Mbit/s2 Mbit/s2 Mbit/s

XBCB BCB

MMI

Abis 1

XCLOCK

External interface Internal interface

CLKI

BSII 0,1

KIEN TRUC SUMA

SUMA c cc chc nng chnh sau:

- Qun l link truyn dn Abis (ln n 2 giao din Abis).

- To xung ng h cho tt c cc modul BTS, cc ng h ny c th c

ng b t mt ng h tham chiu bn ngoi: Abis link, GPS, BTS khc, c th

c to ra trong kiu xung ri bi mt b pht tn s bn trong.

- Thc hin chc nng vn hnh v bo dng cho BTS

- Qun l ghp cc d liu TCH, RSL, OML, QMUX

- iu khin chc nng AC/DC khi chng c tch hp bn trong BTS

- iu khin ngun (dung lng, in p, nhit )

24

Hnh v 2.6: Kin trc khi SUMA


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Ti u ha mng

- Thit lp in p v dng cho vic np pin.

Khi TRE

KIEN TRUC C SCUA TRE

TRED

TREA

TREPPSI

RFI

CLKI

BSII

BCB PSWITCH

LEDS

DEBUG

RCD CUI I2CA

Module TRE bao gm ba khi chnh nh trn. Khi TRE-A (Analog) thu tn hiu t

Antenna chuyn thnh tn hiu sTRE-D (Digital) a ti SUMA, v ngc li.

- TRED:

H thng TRED chiu trch nhim v phn s ca TRE:

+ X l iu khin v bo hiu, n chu trch nhim qun l cc chc nng

O&M ca TRE.

+ Ghp knh, nhy tn, mt m v gii mt m.

+ M ho (DEC).

+ Gii iu ch (DEM).

+ M ho v pht (ENCT).

+ u cui BCB.

- TREA:

25

Hnh v 2.7: Kin trc khi TRE


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Ti u ha mng

+ iu ch

+ iu khin v bin i cao tn phn pht (TXRFCC).

+ ng b phn pht (TXSYN).

+ Bin i trung tn phn thu (RXIF).

+ ng b phn thu (RXSYN).

+ Gii iu ch trung tn (ISD).

+ TRE PA board bao gm b khuch i cng sut, n m nhim khuch i

cng sut tn hiu cao tn bi TXRFCC.

+ TREP: Cung cp ngun cho TRE (DC/DC)

Khi ANC

COMBINING MODE

Duplexer

Filter Filter

LNA

Spliter

Duplexer

Filter Filter

LNA

Spliter

Spliter SpliterSpliterSpliterWBC WBC

ANTA ANTB

TRE 1

TX RX RXd

TRE 2

TX RX RXd

TRE 3

RXd RX TX

TRE 4

RXdRX TXBridgeBridge

ANC kt ni 4 my thu - pht n 2 antenna.

Phn phi tn hiu nhn c t mi antenna n 4 my thu - pht (thu thng v

thu phn tp)

Modul ny bao gm 2 cu trc ging nhau, mi cu trc bao gm:

+Antenna: n c chc nng l pht sng ra mi trng v tuyn v thu sng t

my di ng pht n.

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Hnh v 2.8: Kin trc khi ANC


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Ti u ha mng

+ Filter: Lc b tn hiu khng cn thit.

+ Mt khi duplexer: dng kt hp hai hng pht v thu mt antenna.

+ Mt khi LNA: khi ny c chc nng khuch i tn hiu m antenna thu

c ln mc ln cho TRE c th x l c.

+ Hai khi Spliter: khi ny c chc nng tch tn hiu thu ca TRE.

+ WBC: (Wide band combiner) b ny c chc nng kt hp hai ng pht li

vi nhau i trn cng mt ng n b duplexer. Thc t ta ch dng b

ny khi ta dng hn 2 TRX trn cng mt sector, nu khng dng kt hp th ta

phi g cu ra v kt ni trc tip vi duplexer m khng thng qua b WBC.

Khi qua b WBC tn hiu s b suy hao l 3.3 dBm.

Nguyn l hot ng ca BTS

Kt ni cc khi chc nng trong h thng BTS

Giao tip bn trong BTS c thc hin thng qua cc bus BCB v BSII.

BSII 1

BSII 2

BTS TERM

Abis

KET NOI BEN TRONG

OMU

TRANS& CLOCK

TRE ANx ANy

FACB

AC/DC&BATTEIES

ISL ISL ISL

ISL ISL

TRE FW/SW O&M/TELECOM

ANx FW

ISL pilot

EBCB

BSC

OML/IOM/IOM -CONF

TCH/RSL

BCB (Base Station Control Bus)

BCB: Bus iu khin BTS c kt ni n tt c cc module trong BTS.

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Hnh v 2.9: Kin trc khi ANC


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Ti u ha mng

N c s dng trao i thng tin gia SUMA v cc module khc. Bus ny

ch s dng cho mc ch vn hnh v bo dng.

BSII (Base Station Internal Interface)

BSII l giao din chnh bn trong BTS

BSII c s dng mang cc loi thng tin sau:

- TCH (Traffic Channel): Mi TCH chim mt Nibble 16kbit/s(Full rate), hoc

8kbit/s(harf rate) trong lung PCM 30.

- RSL (Radio Signalling Link): Cho php ghp mt vi thng tin trn cng mt

kt ni vt l nh: Trn TS 64kbit/s c th mang thng tin v Telecom, O&M hayQ_mux (gia TRE v SUMA).

- OML (Operation Maintenance Link): Cho php ghp mt vi thng tin trn

cng mt kt ni vt l nh: Trn knh 64kbit/s c th mang thng tin v Telecom,

O&M hay Q_mux (gia BSC v SUMA).

Nguyn l hot ng ca BTS

Nguyn l hot ng ca BTS da trn qu trnh x l cc tn hiu m n nhn

c t my di ng (MS) v t BSC.

Tn hiu t BSC a ti BTS thng qua giao din Abis trn ng truyn PCM

gm c cc tn hiu sau:

- Tn hiu thoi TCH (traffic channel).

- Tn hiu bo hiu RSL (radio signalling link).

- Tn hiu vn hnh bo dng OML (operation maintenance link).

- Tn hiu truyn dn Q_mux.

Cc tn hiu ny c phn b trn khung PCM nh sau:

Khi khng s dng ghp

Cu hnh chain end

TS0

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Ti u ha mng

TCH TCH TCH TCHTCH TCH TCH TCH

TS31

- Trong cu trc khung PCM th khe thi gian TS0 c s dng cho mc ch

ng b.

TS31 c s dng truyn tn hiu OML, Qmux.

+ Cc khe thi gian cn li c s dng truyn d liu TCH, tn hiu RSL.

+ Cc khe thi gian trong khung PCM c chia thnh 4 nibble mi nibble

16Kbps c s dng cho mt knh lu lng TCH.

Trong khung PCM giao din Abis th mt RSL chim ton b mt khe thi

gian trong khung v s RSL ph thuc vo s TRX m mt BTS c. Tc l s lng

ca RSL s bng s TRX.

+ Trong khung PCM cn c tn hiu OML tn hiu ny s dng trong qu trnh

khai thc v bo dng. S lng ng OML s ph thuc vo s BTS. Mi

OML s phc v ch cho mt BTS

+ Vic n nh cc TS c thc hin t di ln (T TS31TS1)

Cu hnh chain: Tng t nh cu hnh chain end tc l thng tin OML v Qmux

cng c ghp trn cng mt TS v vic n nh thng tin cng c thc hin t

TS31TS1. V d c 2 trm BTS cu hnh 1/1 th vic n nh thng tin trn khung

PCM nh sau:

TSo

TCH TCH TCH TCH

TS31(OML2+Qmux2)

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Ti u ha mng

TS25(RSL2)

TCH TCH TCH TCH

TCH TCH TCH TCH

TS28(RSL1)

TCH TCH TCH TCH

TCH TCH TCH TCH

TS31(OML1+Qmux1)

Khi s dng kiu ghp ny th vic n nh cc thng tin vo cc TS ty thuc

vo tng cu hnh tuy nhin n theo xu hng l lm th no hn ch vic ghp

nhiu RSL vo mt TS. N ch s dng ghp 4RSL + 1OML khi lu lng trn

lung PCM c s dng ti a.

- Cc tn hiu ny u tin c a n khi SUMA v kt cui ti phn truyn

dn ca khi ny, sau n a n cc khi chc nng khc s l nh sau:

+ Tn hiu Qmux c kt cui ti phn truyn dn, thc hin qu trnh iu

khin truyn dn.Thng tin Qmux c ghp chung vi thng tin OML trn

cng mt TS

+ Cc tn hiu v vn hnh bo dng th kt cui ti khi OMU, khi nhn

thng tin O&M, x l v a ra cc lnh lin quan n qu trnh vn hnh bo dng.

+ Cc tn hiu v lu lng v bo hiu s c a n khi TRE y s

thc hin qu trnh x l thoi v sau a n ANC ri ti antenna ri pht

ra mi trng v tuyn.

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Ti u ha mng

Phn 2

TI U HA MNG

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Ti u ha mng

Chng 3

DRIVE TEST TRONG MNG GSM

Mc ch ca vic thc hin Drive Test

Thc hin Drive Test nhm nh gi cht lng v tuyn ca cc im/trm/khu

vc/vng nhm pht hin v x l cc tn ti trn mng di ng v nh hng cho

vic lp k hoch nhm tng cng ph sng ti cc im/trm/khu vc/vng o.

Thit b o v th tc o drive test

i Drive test

i Drive test phi cn t nht 2 ngi, mt li xe v mt k s Drive test. Ngi

li xe phi cn hiu c ng ph v cu trc ca khu vc cn o, v nh vy li

xe c th cung cp thng tin v tuyn ng c th v cung cp nhng thng tin c

th thay i.

3.4 Thit b Drive test v cc ngun h tr

3.4.1 Thit b Drive test

Thit b Drive test gm c:

- Mt phn mm o (TEMS) v mt my tnh xch tay

- Mt in thoi di ng test (T610 Ericsson)

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Ti u ha mng

- Mt GPS

- Ngun in cung cp (c ni vi Acqui ca xe chuyn i in thnh

220V cho my tnh v GPS)

- Cp d liu kt ni gia Laptop v my TEMS

- H thng antenna (anten gn t ng hng c cp ni vi in thoi)

Tems 8.0 v cp d liu GPS Holux

My tnh xch tay B i ngun DC - AC

3.4.2 Cc ngun h tr

- t phi c ngun lm vic n nh v acqui hot ng tt

- Mt bn ng ph cho php nh hng ng i

- V tr ca Site v cu hnh chi tit, c th trn cc bn ring r hoc trn bn

c th ch ra Azimuth, titls, cao v cc thng s cn thch hp khc

- S ng i, bao gm c bn ng ph v hng ch dn

- Mt simcard test

- Mt file m t mng vi nh dng tng ng vi phn mm cn o (CDD)

- Even Log m k s c th ghi ch cc s kin v thi gian a im m c th

nh hng n c chnh xc ca php o (v d nh i trong ng ngm cu

cao), nhng thng tin ny c th s dng cho vic phn tch li sau ny

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Ti u ha mng

Th tc o

Cc th tc chun b

ng i phi c xc nh cn thn trc khi thc hin, ng i l nh nhautrong sut qu trnh ti u. Cc im sau phi c cn nhc khi ln k hoc o:

- Khong thi gian ti a cho mi cluster l 4h. s cuc gi >=200 c th

cung cp mt s liu ng tin cy

- ng i phi bao gm tt c cc Cells ca mt cluster

- Nu c th ng i phi c ln k hoch c th i c handover c 2 chiu

- t nht tt c cc tuyn ng chnh phi c o

- ng i vo cc vng m khng c trn bn s th khng cn thit o

Trc khi Drive test c tin hnh tt c cc thng tin bao gm cao, gc v

hng anten phi c kim tra li. Nhng vn v ci t phi c gii quyt

trc khi thc hin php o.

Cc site cha hot ng cn phi c lu v nu cn thit c th hon li php

o v thay i tuyn ng

3.5.2 Ci t thit b

Cc li ngt ngun trong php o c th sinh ra li d liu khi tin hnh php o.

Vi mc ch ngn nga cc hin tng trn phi m bo rng my tnh xch

tay, in thoi test v GPS phi c np in. Kim tra tt c cc kt ni vi ngun

an ton cha v b chuyn i khng b qu ti.

H thng Anten c s dng v v tr anten c th thay i:

+ o mc tn hiu trn ng hoc kim tra mc tn hiu cho trc,

Anten phi c t trn nc ca xe khng gn hn 45cm t bt c cnh no.

Nu chiu cao ca xe ln hn 1.8m, th c th t Anten trn np y my t

v khng gn hn cnh no 45cm v cch knh chn gi l 1m.

+ o c tnh trong xe Antenna c th t mt v tr c nh ngang u li xe

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Ti u ha mng

Mt qui tc rt quan trng cn phi nh l gi cho cc thit b o c n

nh sut qu trnh o. iu ny m bo cho mt kt qu chnh xc.

Kim tra tt c cc kt ni m bo rng phn mm o c kt ni vi

cc thit b.

Kim tra xem phn mm o c th thu c cc bn tin lp ba v cc php o

khc t MS hay khng.

Ci t ch cuc gi theo th tc sau khi o bench marking l thi gian thit

lp cuc gi l 90s, ch 25s v lp li

Lu logfile vo v tr qui nh trn my tnh vi nh dng MMDDYY_Name.

3.5.3 Qu trnh kim tra

Bi v khi khi ng xe s c mt xu hng lm rt in th acqui do sinh ra

li hiu in th trn hu ht cc Inverter. Do vy cn phi gi xe chy lin tc trong

sut qu trnh cn o.

Tin hnh thc hin o ti mt tc xe c nh nu c th nhng khng qu

60km/h. Khong thi gian di dng li cn c ghi ch bi v c th sinh ra trn

mt vng mt kt qu sai lch c th rt tt cng c th rt xu.

Trong sut qu trnh o, k s nn quan st bn ngoi xem xt li (sai fio,

mc tn hiu thp, ci t Antena hoc vt chn) v ni no cn thit th ghi ch li

kim tra li.

m bo rng logfile c bt u v kt thc khi MS trng thi ri; iu ny

ngn nga s thng k sai.

4.3 Drive test trong chu trnh ti u

C 2 ngun c th cho mt k s s dng gim st mng li, bng di

y s th hin li u im cng nh nhc im ca 2 ngun ny.

c im Chi ph hiu qu Phm vi vt l

Field Test

measurement

Th hin mt ci

nhn ca khch hng

Tiu tn nhiu thi

gian

Trong mt vng gii

hn tt cho xc nh

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Ti u ha mng

mc tiu v cht

lng mng ph hp

cho phn tch i th

cc vn - xc nh

c l hng vng

ph sng

NMS/OMC Cho php la chn d

liu tp trung. Thng

tin lin tc, c ch cho

gim st.

Mt cch hiu qu

qun l cht

lng mng

V tr gii hn c th

xc nh cc vn

trong tng cell.

Trong qu trnh trc khi a vo khai thc, s lng cc thu bao nh nn vic

thu c cc thng k t NMS l khng ng k. Tuy nhin, cc thng bo khc ca

NMS nh Equipment Alarm l rt hu ch pht hin cc vn c th v cngcung cp cu tr li cho c tnh mng c tm thy trong Drive Test.

Ngoi ra cn c ngun d liu c ly t cc thng bo Measurement Report

c ly t MS v cc o c ng ln c ly t BTS khi knh c kch hot.

Acalter RMS v Ericson MRR l 2 h thng c th cung cp su hn v cc vn

nh la chn d liu nh Timing Advance Distribution, S phn b ca tn hiu

trn ng xung v ng ln, s phn b RxQual v s gim bt hoc iu khincng sut, cc d liu ny c th c biu din ring r hoc kt hp vi nhau

pht hin ra vn . V d nh RxQual v RxLev c th ch ra c vn vng

nhiu do mc tn hiu thp hoc do k hoch n nh tn s km.

Chu trnh ti u

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Ti u ha mng

4.3.1 Drive test

4.3.1.1 K hoch kho st kim tra

Nhm RNP t chc cc i v cc thit b tin hnh kho st o c, bi v

hnh ng ny tiu tn rt nhiu thi gian, do c th phi thm nhn lc. Trong

trng hp ny nhm RNP s hng dn i kho st c th tp trung nhiu hn vo

phn tch cc kt qu php o

37

Hnh v 4.1: Chu trnh Drive Test


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Ti u ha mng

4.3.1.2 nh dng tuyn ng kim tra

Nhm s xc nh tuyn ng cho nhm kho st, nhng tuyn ng ny nn

nht qun v nn xem trc ch vi thng hoc nhng vng c kh nng thay i

V d s thay i gm c: tch hp site mi, cc nh cao tng mi xy dng,

nhng con ng mi.

Trong trng hp c thm ngi tin hnh php o, RNP nn a ra mt form

yu cu php o vi bn km theo.

4.3.1.3 La chn php o

i Drive test nn iu khin php o tun theo hng dn k hoch v nhng

tuyn ng c xc nh bi RNP.

Cc i nn ghi ch li nhng vn v thit b v cc s kin khng bnh

thng khc (sai phi ) v thng bo n cc i tng ng. Nu cc vn c

sa cha ngay ti im , i o nn tin hnh tip tc Drive Test, nu khng th

php o phi c hon li vo ngy khc.

4.3.2 Phn tch d liuS phn tch ca nhm Drive test s cho php nhm RNP c th quyt nh c

tnh mng, pht hin ra cc vn v khuyn co thay i ci thin mng.

kt ni tt c cc ngun ca d liu l rt cn thit c mt s kim tra hon

chnh ca cc giai on mng lui sau ny. Phn ny m t mt s li thng thng

c tm thy trong mng li v cch gii quyt.

Chng 4

MT S YU T NH HNG N

CHT LNG TN HIU

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Ti u ha mng

4.1 Cc yu t nh hng n cht lng thoi

Mt c im ca cell l cc knh ang s dng c th c s dng cc

cell khc. Nhng gia cc cell ny phi c mt khong cch nht nh. iu ny c

ngha l cell s b nhiu ng knh do vic cc cell khc s dng cng tn s. Cui

cng vng ph sng ca trm gc s b gii hn bi l do ny hn l do tp m thng

thng. V vy, ta c th ni rng mt h thng t ong hon thin l gii hn c

nhiu m c qui chun, loi tr c nhiu h thng. Mt vn trong thit k

h t ong l iu khin cc loi nhiu ny mc chp nhn c. iu ny c

thc hin mt phn bi vic vic iu khin khong cch s dng li tn s. Khong

cch ny cng ln th nhiu cng b.

cht lng thoi lun c m bo th mc thu ca sng mang mong

mun C (Carrier) phi ln hn tng mc nhiu ng knh I (Interference) v mc

nhiu knh ln cn A (Adjacent).

4.1.1 Nhiu ng knh

Hnh 2.1: Nhiu ng knh.

Nhiu ng knh xy ra khi c hai my pht pht trn cng mt tn s hoctrn cng mt knh. My thu iu chnh knh ny s thu c c hai tn hiu vi

cng ph thuc vo v tr ca my thu so vi hai my pht.

T s sng mang trn nhiu c nh ngha l cng tn hiu mong mun

trn cng tn hiu nhiu.

C/I = 10log(Pc/Pi) .

Trong :

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Ti u ha mng

Pc = cng sut tn hiu thu mong mun

Pi = cng sut nhiu thu c.

Hnh 2.2: T s nhiu ng knh C/I.

Hnh 2.1 trn ch ra trng hp m my di ng (cellphone) t trong xe

ang thu mt sng mang mong mun t mt trm gc phc v (Serving BS) v ng

thi cng ang chu mt nhiu ng knh do nhiu pht sinh ca mt trm gc khc(Interference BS).

Gi s rng c hai trm u pht vi mt cng sut nh nhau cc ng

truyn sng cng tng ng (hu nh cng khng khc nhau trong thc t) v

im gia, my di ng c C/I bng 0 dB, c ngha l c hai tn hiu c cng

bng nhau. Nu my di ng i gn v pha trm gc ang phc v n th C/I > 0 dB.

Nu my di ng chuyn ng v pha trm gy ra nhiu th C/I < 0 dB.

Theo khuyn ngh ca GSM gi tr C/I b nht m my di ng vn c th lm

vic tt l 9 dB. Trong thc t, ngi ta nhn thy rng gi tr ny cn thit phi ln

n 12 dB ngoi tr nu s dng nhy tn th mi c th lm vic mc C/I l 9dB.

mc C/I thp hn th t l li bit BER (Bit Error Rate) s cao khng chp nhn

c v m ho knh cng khng th sa li mt cch chnh xc c.

T s C/I c dng cho cc my di ng ph thuc rt ln vo vic quy

hoch tn s v mu ti s dng tn s. Ni chung vic s dng li tn s lm dung

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Ti u ha mng

lng tng ng k tuy nhin ng thi cng lm cho t s C/I gim i. Do vic

quy hoch tn s cn quan tm n nhiu ng knh C/I.

4.1.2 Nhiu knh ln cn

Nhiu knh ln cn xy ra khi sng v tuyn c iu chnh v thu ring

knh C song li chu nhiu t knh ln cn C-1 hoc C+1. Mc d thc t sng v

tuyn khng c chnh thu knh ln cn , nhng n vn ngh mt s p

ng nh l cho php knh ln cn gy nhiu ti knh m my thu ang iu chnh. T

s sng mang trn knh ln cn c nh ngha l cng ca sng mang mong

mun trn cng ca sng mang knh ln cn.

C/A = 10.log(Pc/Pa)

Trong :

Pc = cng sut thu tn hiu mong mun

Pa = cng sut thu tn hiu ca knh ln cn

Gi tr C/A thp lm cho mc BER cao. Mc d m ho knh GSM bao gm

vic pht hin li v sa li, nhng vic thnh cng th cng c gii hn ivi nhiu. Theo khuyn ngh ca GSM, cho vic quy hoch tn s c tt th gi

tr C/A nh nht nn ln hn - 9 dB.

Khong cch gia ngun to ra tn hiu mong mun vi ngun ca knh ln

cn ln s tt hn cho C/A. iu ny c ngha l cc cell ln cn khng nn c n

nh cc sng mang ca cc knh cnh nhau nu C/A c c ngh trong

mt gii hn nht nh.

C hai t s C/I v C/A u c th c tng ln bng vic s dng quy hoch

cu trc tn s.

4.1.3 Phn tn thi gian

Phn tn thi gian xy ra l do c nhiu ng truyn sng t my pht n

my thu. Hin tng phn tn thi gian gy ra mt s vn cho mng thng tin di

ng s. Vic s dng truyn dn s cng gy ra mt s vn khc nh: phn tnthi gian do cc tn hiu phn x (Reflection) gy ra.

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Hnh 2.3: S phn tn thi gian.

S phn tn thi gian s gy ra hin tng giao thoa gia cc k t. Githit chng ta pht i mt chui bit 1 v 0. Nu tn hiu phn x i chm hn tn hiu

i thng ng 1 bit th my thu pht hin bit 1 t sng phn x ng thi cng pht

hin bit 0 t sng i thng.

Ca s thi gian c nh ngha l khong thi gian 15 ms sau khi my thu

nhn c tn hiu trc tip t my pht. Gi s cc tia phn x n my thu bn

ngoi ca s thi gian, tc l sau 15 ms, s gy phin phc cho h thng ging nh l

nhiu.Ta bit gi tr ti thiu ca C/I trong h thng GSM l 9 dB.

Chng ta c th coi gi tr ny l gi tr cc i ca phn tn thi gian. Ngha

l tt c cc tn hiu phn x m n tr hn 15 ms, bn ngoi ca s thi gian, phi

c gi tr tng nh hn 9 dB. T s ny chnh l C/R.

Phn tn thi gian ch c th xy ra khi hiu qung ng gia tn hiu trc

tip v tn hiu phn x t nhng chng ngi vt k trn ln hn ca s cn bng

(4,5 km).

Ni chung, s nguy him ca phn tn thi gian s tng cng vi khong cch

gia BTS v MS. Khi mt MS gn BTS c th nhn c tn hiu phn x mnh vi

hiu qung ng ln nhng vn khng nh hng g do tn hiu trc tip mnh

m bo t s C/R trn ngng ti hn. Khi MS chuyn ng ra xa BTS th nguy c t

s C/R thp s tng ln do tn hiu trc tip yu i.

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Tuy nhin, mt iu cn ch l tia phn x cng l mt phn ca sng

mang cho nn vic quy hoch mt h thng cn phi ch ra c cc trng hp c

th c th xy ra hin tng giao thoa k t.

4.1.4 Nhiu gia cc h thng

Trong mt vi trng hp cng c th b nhiu t cc ngun nhiu ngoi, nh t

cc h thng GSM khc c tn s ln cn nhau, hoc t cc ng vi ba c hoc cc

h thng ca qun i c cng tn s hoc gn bng tn GSM. Loi nhiu ny thng

kh x l, v phi c quan tm trong qu trnh thit k tn s c bin php trnh

nhiu trn h thng tng trm v tng vng c th.

4.1.5 Fading

- Fading l s bin i cng tn hiu sng mang cao tn ti anten thu do

c s thay i khng ng u v ch s khc x ca kh quyn, cc phn x ca t

v nc trn ng truyn sng v tuyn i qua.

- Nguyn nhn: Multipath cung l mt nguyn nhn gy ra fading ngoi ra

cn nhiu nguyn nhn khc nh kh hu thi tit, s phn x ca cc sng ti tng

in ly.....

- Phn loi fading

Fading phng.

Fading chn lc tn s.

- gim phn no tc hi do Fading gy ra, ngi ta thng tng cng sut

pht ln to ra mt lng d tr Fading, s dng mt s bin php nh: phntp anten, nhy tn ...

4.2 Mt s k thut tng cht lng h thng:

4.2.1 iu khin cng sut thu pht ca MS v BTS:

- iu khin cng sut nhm cc tiu ha nhiu ng knh v bo tn cng

sut trm di ng v trm thu pht gc hot ng vi mc cng sut thp nht m

vn duy tr cht lng tn hiu chp nhn c.

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- Cho php iu khin cng sut hng xung, BTS ch pht cng sut max

ti khe thi gian mang BCCH, cc TCH c iu chnh ti u theo yu cu cng

sut.

- Trm di ng o cng tn hiu hoc cht lng tn hiu v chuyn

thng tin n b iu khin trm gc BSC, cui cng quyt nh c thay i mc

cng sut hay khng v khi no.

- MS c iu khin cng sut nhm tit kim pin v gim nhiu hng ln.

- iu khin cng sut phi cn thn v c kh nng dao ng. iu ny xut

hin khi mt di ng trong cc cell ng knh nhn c tn hiu tng mc cng sut

trong cell ang xt ( trit nhiu ng knh) lm tng thm nhiu ng knh cellang xt.

4.2.2 Truyn pht gin on (DTX):

Thc cht ca phng php DTX (Discontinuous Transmission ) l BTS hay

MS ch pht khi nhn c tn hiu u vo (tn hiu thoi) v khi kt thc tn hiu

n s ngng pht.

Mc ch ca phng php ny l tit kim nng lng v gim nhiu trn

knh ln cn mt cch ti a.

Khi s dng phng php truyn dn gin on ta cn thm cc thit b ph

tr khc nh VAD (Voice Active Detector) pht hin tn hiu vo v to ra ting

n gi khi mt pha no ngng cung cp tn hiu.

4.2.3 Nhy tn:

Khi nim nhy tn

Mt tp hp cc tn s c s dng trong mi t bo v MS c th thay i

cc tn s ngay trong mi khung TDMA c gi l nhy tn. Tc nhy tn

trong h thng GSM l 217 ln/s.

c im chung ca k thut nhy tn

- Ch c cc knh SDCCH/8, TCH, v knh d liu gi c php nhy tn.

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- Khe thi gian s 0 mang knh BCCH ca sng mang BCCH (sng mang f0)

khng c php nhy tn cho d n thuc v nhm knh c nhy tn, v cho

php cc thu bao cc cell ln cn thc hin o lng trong ch ri.

u im ca k thut nhy tn

Lm gim nh hng ca fading a ng, ca nhiu nn cht lng thoi

c ci thin, lm cho qu trnh s dng li tn s cht ch v hiu qu hn.

4.2.4 Chia cell

Kch thc Cell v phng thc ph sng

Cell ln: Bn knh ph sng khong: n km n*10 km (GSM: 35

km)

V tr thit k cc Cell ln:

- Sng v tuyn t b che khut (vng nng thn, ven bin )

- Mt thu bao thp.

- Yu cu cng sut pht ln.

Cell nh: Bn knh ph sng khong: n*100 m. (GSM: 1 km)

V tr thit k cc Cell nh:

- Sng v tuyn b che khut (vng th ln).

- Mt thu bao cao.

- Yu cu cng sut pht nh.

C tt c bn kch thc cell trong mng GSM l macro, micro, pico v

umbrella. Vng ph sng ca mi cell ph thuc nhiu vo mi trng.

Macro cell c lp trn ct cao hoc trn cc to nh cao tng.

Micro cell li c lp cc khu thnh th, khu dn c.

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Pico cell th tm ph sng ch khong vi chc mt tr li n thng c lp

tip sng trong nh.

Umbrella lp b sung vo cc vng b che khut hay cc vng trng gia cc

cell.

Chia Cell (Cells Splitting)

Mt cell vi kch thc cng nh th dung lng thng tin cng tng. Tuy

nhin, kch thc nh i c ngha l cn phi c nhiu trm gc hn v nh th chi

ph cho h thng lp t trm cng cao hn.

Khi h thng bt u c s dng s thu bao cn thp, ti u th kch

thc cell phi ln. Nhng khi dung lng h thng tng th kch thc cell cng

phi gim i p ng vi dung lng mi. Phng php ny gi l chia cell.

Hnh 2.4: Phn chia Cell.

Ty theo nhu cu v lu lng v mt thu bao gia cc vng m c s

chia cell khc nhau cho ph hp vi cu trc mng ca vng .

4.2.5 cao v gc nghing ca anten (down tilt):

nhng khu vc th trn nh hay nng thn, lu lng ca h thng thp nn

vic ti s dng tn s l khng cn thit. Do vy, ta nn s dng cc v tr cao hay

t anten cao ti a ho vng ph sng.

Tuy nhin nhng khu vc th ln, lu lng h thng cao, kch thc cell

hp th c l thch hp nht l gim cao anten c th lm gim can nhiu knh

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chung. Tuy nhin, nu t qu thp, cc vt cn (nh cao tng...) s c nh hng ln

ti cht lng h thng. Do vy, hin nay cao anten cc th thng l

30 50m. gii quyt phm vi vng ph sng hp, mt k thut c a ra l

lm nghing hng bp sng chnh ca anten (down tilt).

Vic nghing gc anten c th dng gii quyt vn ph sng. Tuy nhin

vic p dng nghing gc anten cn c s phn tch k cng nhng yu t lin quan

c th xy ra trong vng ph sng.

4.2.6 Ti s dng tn s

Ton b di tn pht cho mng GSM 900Mhz l t 890Mhz-915Mhz tc l c

25Mhz, c chia thnh 125 knh thoi c th s dng cng lc, mi knh c

rng l 200Khz. Mi knh thoi li c chia nh thnh 8 khe thi gian, trong c

1 khe dnh cho tn hiu bo hiu-iu khin v 7 khe cn li dnh cho MS. Nh vy

tng s MS c th lin lc trong cng mt thi im l 7*125 = 875.

Tuy nhin i vi mt mng di ng th con s 875 thu bao lin lc ng thi

l qu t i. V th m "Ti s dng tn s ra i", y l phng php nhm tng s

lng thu bao c th lin lc cng mt thi im ln n con s hng triu.

Ti s dng tn s : Cc nhm tn s ging nhau c th c s dng cc

cell khc nhau min sao khong cch gia cc cell ln trnh nhiu do cc tn s

trng nhau gy ra.

Hnh 2.5: Ti s dng tn s.

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C ba kiu mu s dng li tn s ph bin l: 7/21, 4/12 v 3/9 s dng cho cc

trm gc c anten pht 3 hng, mi hng dnh cho mt v gc phng v phn

cch nhau 1200. Mi s dng cc anten pht 600 v hai anten thu phn tp 600 cho

mt gc phng v. Mi c xp x ho l hnh lc gic, c bn knh R (bng cnhhnh lc gic v bng 1/3 khong cch gia cc trm).

4.2.7 Chuyn giao cuc gi (Handover)

Mt tr ngi trong vic pht trin mng thng tin di ng t bo l vn pht

sinh khi mt thu bao di ng di chuyn t cell ny sang cell khc. Cc khu vc k

nhau trong h thng t bo s dng cc knh v tuyn c tn s khc nhau, khi thu

bao di ng di chuyn t cell ny sang cell khc th cuc gi hoc b rt hoc t ngchuyn t knh v tuyn ny sang mt knh khc thuc cell khc.

Thay v cuc gi b rt, qu trnh Handover (ting M: Handoff) gip cho

cuc gi c lin tc. Qu trnh Handover xy ra khi h thng thng tin di ng t

ng chuyn cuc gi t knh v tuyn ny sang knh v tuyn khc khi thu bao di

ng di chuyn t cell ny sang cell khc lin k vi n. Trong qu trnh m thoi,

hai thu bao cng chim mt knh thoi. Khi mt thu bao di ng chuyn ng ra

khi vng ph sng ca cell cho trc, tn hiu u thu ca cell ny s gim. Khi ,

cell ang s dng s yu cu mt Handover (chuyn giao) n h thng. H thng s

chuyn mch cuc gi n mt cell c tn s vi cng tn hiu thu mnh hn m

khng lm gin on cuc gi hay gi cnh bo n ngi s dng. Cuc gi s

c tip tc m ngi s dng khng nhn thy qu trnh Handover din ra.

Chng 5 Chuyn giao cuc gi v phn tch li handover

5.1 L thuyt

5.1.1 Phn loi Handover

H thng phn loi cc qu trnh chuyn giao cuc gi thnh nhng loi sau:

Intra-cell Hand Over.

Inter-cell Hand Over.

Intra-MSC Hand Over.

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Inter-MSC Hand Over.

Intra-cell Hand Over (Chuyn giao trong ni b t bo): Th tc

chuyn giao thc hin gia hai knh vt l ca cell ang phc v.

Intra-cell Hand Over khng c s dng khi thu bao di chuyn sang cell

khc, ngoi tr trng hp nu mc nhiu trn knh ring l cao th mt s chuyn

giao sang mt knh vt l khc phi c thc hin.

Hnh 4-1 Intra-cell Handover

Inter-cell Hand Over (Chuyn giao lin t bo): MS c chuyn mch

sang mt knh v tuyn mi ca mt cell khc nhng c iu khin ca cng mt

b iu khin trm gc BSC.

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Hnh 4-2 Inter-cell Handover

Intra-MSC Hand Over (Chuyn giao trong ni b MSC): Chuyn mch

knh v tuyn gia hai BSC ca cng mt tng i di ng MSC.

Hnh 4-3 Intra-MSC Handover

Inter-MSC Hand Over (Chuyn giao lin MSC): Chuyn mch knh v

tuyn gia hai tng i di ng MSC.

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Hnh 4-4 Inter-MSC Handover

Trong trng hp ny, MSC ban u gi ton quyn iu khin cuc gi v

sp t truy nhp mng cho n khi kt thc cuc gi. Cuc gi c nh tuyn vt

l li t MSC ban u trc tip n MSC ch.

5.1.2 Khi to th tc Handover

Th tc Handover s c khi to vo bt k lc no mi khi xut hin nhu

cu chuyn i ng v tuyn gia BSS v MS sang mt knh mi, c th l cng

BSS hay mt BSS khc. BSS s nhn thy yu cu thit lp th tc Handover duy

tr s lin tc ca cuc gi trong khi MS di chuyn.

Nu cell ch u tin nm trong cng BSC th th tc Handover s c thc

hin bi BSC. Nu khng, BSC s gi n MSC mt danh sch u tin cc cell ch.

Trong danh sch ny, MSC ch cn nhc n ba cell u tin.

Gii thut MSC (vi v d l c ba cell c cn nhc) l bc th nht s th

vi cell u tin, nu khng c th s chuyn sang th vi cell th hai ri th ba,

m khng c vic tnh n nhng kha cnh lu lng. Nu nh trong khi th tc

handover ny ang din ra m c thm mt yu cu Handover khc nhn c t

BSC, danh sch s c cp nht tnh ton n cc cell mi. Vi mi ln th,

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MSC yu cu mt ti nguyn tn s thch hp ti phn h trm gc BSS ch m theo

mc nh l khng cho php vic xp hng i, hoc l cho php hng i nu cho

php nu nh c ch th tng ng trong yu cu handover nhn c t BSS ngun.

Nu nh MS khng hon thnh vic t c mt knh mi t cell ch th n

s gi mt bn tin thng bo chuyn giao tht bi thng qua cell trc ti mng

li v MSC s hi phc li kt ni trc ca MS hoc nu MSC nhn thy MS

mt kt ni th cuc gi s c gii phng.

5.1.3 Quy trnh chuyn giao cuc gi

V c bn, th tc Handover bao gm 4 giai on:

Giai on 1: BSC quyt nh thc hin th tc handover

m bo kt ni ca cuc gi.

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

ni gc.

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

Giai on 4: Kt ni gc c gii phng.

Giai on 1:

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Hnh 4-5 G 1: Trong lc kt ni, MS vn tip tc o c mc thu v cht lng

truyn dn ca cell phc v v nhng cell xung quanh.

Nhng kt qu o c c gi ti BSC v l cn c yu cu mt th tc

Handover sang mt cell khc c mt cht lng truyn dn tt hn.

Hnh 4-6 Quyt nh chuyn giao_Handover Decision

Handover Margin: Thc cht ca Handover Margin l s chnh lch gia

mc thu ca cell ang phc v v cc cell ln cn. Khi mc thu ca mt cell ln cn

no vt qu mc thu ca cell ang phc v mt khong ln hn gi tr Handover

Margin nh sn th mt Handover Alarm s c gi v h thng nhm a n

quyt nh chuyn giao. Thng thng th th tc Handover s c thc hin ngay

sau .

Nu vic t gi tr Handover Margin qu thp s dn ti vic Handover qu

nhiu, nhng ngc li khi gi tr ny t qu ln c th lm cho cht lng cuc gi

b gim xung.

V vy, ty vo tnh cht ph sng ca tng vng cng nh mc nhiu ca

tng cell phc v, Handover Margin cn c iu chnh thch hp t c cht

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lng tt nht. V d nh vng b nhiu nhiu c th t gi tr Handover Margin

thp MS c th nhanh chng chuyn giao sang cell khc c cht lng tt hn.

Gi tr khuyn ngh l 4 dB, trn mng VMS_Mobifone hin ang s dng

Handover Margin l 5 dB.

BSC s thng bo cho MSC v s cn thit thc hin th tc Handover, v

khai bo thng tin vi MSC1.

Hnh 4-7 G 1: BSC khai bo thng tin vi MSC

Giai on 2:

MSC1 yu cu mt Handover Number (HON) t MSC2 v thng bo vi

MSC2 thng tin v cell B.

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Hnh 4-8 G 2: MSC1 yu cu MSC2 cp Handover Number

M HON (Handover Number) ch quan trng trong trng hp Inter-MSC

Handover. N c dng MSC1 thit lp kt ni knh lu lng vi MSC2. Cu

trc ca m HON cng ging nh m MSRN v cng c cung cp bi VLR mi.

MSC2 yu cu VLR cung cp mt m HON, ng thi yu cu BSC cung cp

knh v tuyn. Sau , knh v tuyn v m HON c gi li cho MSC1.

Hnh 4-9 G 2: Cp m HON v knh v tuyn cho MSC1

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Giai on 3:

Hnh 4-10 G 3: MSC1 chuyn mch kt ni cho MS trn knh lu lng thit lp

vi MSC2

Vi m HON, MSC1 c th thit lp knh lu lng kt ni vi MSC2.

MSC1 thng bo cho MS v knh v tuyn m n phi chuyn mch ti.

Giai on 4:

Gii phng kt ni vi BTS c.

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Hnh 4-11 Kt ni vi BTS c c gii phng

5.2 o kim tra tri mt s trm li HandoverCng vi cc cng c khc, my TEMS c s dng thng xuyn trong

vic o v kim tra cht lng h thng.

Di y gii thiu vic s dng my TEMS ca Ericsson o kim tra t trm

Hng Thi.

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KT LUN

ti ca n trnh by nhng nt c bn nht v mng thng tin di ng

GSM, nghin cu chc nng, nhim v, cu hnh phc v nhm p ng lu lng

ca trm BTS s dng dng sn thit b ca hng Alcatel-lucent cng vi vic thc

hin Drive Test trong cng tc ti u ha h thng cho mng VMS Mobifone. ti

l mt cng vic kh khn v i hi ngi thc hin phi nm vng h thng thit

b, ngoi ra cng cn phi c nhng kinh nghim thc t v tnh ton v s tr gip

ca nhiu phng tin hin i c th gim st v kim tra ri t mi a ra

cc cng vic thc hin.

Qua thi gian thc hin em thy ti Thit k xy dng trm BTS phc

v cho mt vng v kim tra hot ng trm BTS bng phng php o

Driver Test l mt mng ti rng v lun cn thit cho cc mng vin thng

hin ti ni chung v mng thng tin di ng ni ring. Kh nng ng dng ca ti

l gip ch cho nhng ngi lm cng tc trong ngnh, l c s l thuyt phn tch

v tin hnh, t hon ton c th tm ra gii php ti u khoa hc nht.

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Tuy nhin do thi gian thc hin c hn v trnh , kinh nghim cn hn ch

nn trong qu trnh lm n em khng th trnh khi thiu st. Em rt mong c

c nhng kin nh gi, gp ca cc thy, c v cc bn. Hy vong trong tng

lai gn s tip tc c c hi tip tc nghin cu trn h thng thc t.

Em xin chn thnh cm n.

H Ni, thng 6 nm 2012

Sinh vin thc hin

Nguyn Duy Khi

TI LIU THAM KHO

[1] PTS.Nguyn Phm Anh Dng, Thng tin di ng GSM,Nh xut bn bu in,

H Ni 1999.

[2] V c Th, Tnh ton mng thng tin di ng s CELLULAR,Nh xut bn

gio dc, H Ni 1999.

[3] J. Dahlin,Ericssons Multiple Reuse Pattern For DCS 1800, in Mobile

Communications International, Nov., 1996.

[4] Asha K. Mehrotra, GSM System Engineering, Artech House, Inc Boston London

1996.

[5] Phng K thut, Quy trnh o Drive Test trong mng v tuyn, Cng ty ITC, H

Ni 2009

[6] Phng k thut, S tay BTS thit b Alcatel, Cng ty ITC, H Ni, 2009

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