Thiết kế xây dựng trạm BTS phục vụ cho một vùng và kiểm tra hoạt động trạm...

7/30/2019 Thit k xy dng trm BTS phc v cho mt vng v kim tra hot ng trm BTS bng phng php o Driver

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Kha lun tt nghip GVHD: Ths. V Thnh Thi

MC LC

BNG K HIU VIT TT..............................................................................................2

.....................................................................................................................................4

LI M U....................................................................................................................................................4

CHNG I: MNG DI NG GSM.............................................................................................................5

1.1 Gii thiu chung...........................................................................................................................................5

1.2 Cc c trng c bn ca h thng GSM.....................................................................................................6

1.3 Cu trc mng GSM......................................................................................................................................71.4.1 MS (Mobile station).........................................................................................................................71.4.2 BSS (Base Station System - H thng trm gc).............................................................................81.4.3 NSS (Network Switching System - H thng chuyn mch)...........................................................91.4.4 Khi TRAU....................................................................................................................................11

CHNG II: TNG QUAN V BTS HNG ALCATEL - LUCENT.....................................................122.1 Gii thiu chung v BTS..............................................................................................................................12

2.1.1 Khi nim v BTS..........................................................................................................................122.1.2 V tr ca BTS trong h thng GSM .............................................................................................122.1.3 Phn loi BTS.................................................................................................................................132.2.1 Cu trc chung ca h thng BTS..................................................................................................152.2.2 Cu trc v chc nng ca cc khi chnh trong h thng BTS...................................................16

2.3 Nguyn l hot ng ca BTS.....................................................................................................................192.3.1 Kt ni cc khi chc nng trong h thng BTS...........................................................................192.3.2 BCB (Base Station Control Bus)....................................................................................................192.3.3 BSII (Base Station Internal Interface)............................................................................................192.3.4 Nguyn l hot ng ca BTS.......................................................................................................20

CHNG III: TNH TON MNG DI NG GSM................................................................................22

3.1 Lu lng trong mng GSM.......................................................................................................................22

3.2 Cp dch v - GoS (Grade of Service)..................................................................................................23

3.3 Nhiu ng knh C/I....................................................................................................................................24

3.4 Ti s dng li tn s..................................................................................................................................253.4.1 Khi Nim......................................................................................................................................253.4.2 Cc mu ti s dng tn s.............................................................................................................28

3.5 Cc cu hnh ca trm BTS.........................................................................................................................323.5.1 Cu hnh 4/4/4 (cu hnh Full).......................................................................................................32

3.5.2 Cu hnh 2/2/2...............................................................................................................................33

CHNG IV: DRIVE TEST TRONG MNG GSM..................................................................................34

4.1 Mc ch ca vic thc hin Drive Test......................................................................................................34

4.2 Thit b o v th tc o drive test..............................................................................................................344.2.1 i Drive test.................................................................................................................................344.2.2 Thit b Drive test v cc ngun h tr..........................................................................................344.2.3 Th tc o.......................................................................................................................................35

4.3 Drive test trong chu trnh ti u .................................................................................................................374.3.1 Drive test........................................................................................................................................384.3.2 Phn tch d liu.............................................................................................................................394.3.3 Yu cu thay i cu hnh Site.......................................................................................................514.3.4 Thc hin........................................................................................................................................52

Ng Ngc Cnh V tuyn in t K521


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CHNG V: BI TON THC T............................................................................................................52

5.1 Xy dng cc trm BTS phc v cho mt vng...........................................................................................535.1.1 Cc yu t cn quan tm trc khi i vo tnh ton.....................................................................535.1.2 Bi ton thc t..............................................................................................................................53

5.2 Bo co Drive test cht lng mng ti Bt Trng H Ni.....................................................................57

Thc hin Drive Test trm Bt Trng v phn tch ta c kt qu sau:.............................................................57

5.2.1Thng k cuc gi...........................................................................................................................575.2.2 Thng k KPIs DT ngy 15-10-2011.............................................................................................575.2.3Logfile call......................................................................................................................................585.2.4Logfile Scanning.............................................................................................................................605.2.5Phn tch:.........................................................................................................................................62

KT LUN......................................................................................................................................................63

TI LIU THAM KHO...............................................................................................................................64

BNG K HIU VIT TT

AB Access Burst Cm truy nhpAGCH Access Grant Channel Knh cho php truy nhp

AMPSAdvanced Mobile Phone

SystemH thng in thoi di ng tin tin

ARQ Automatic Repeat Request Yu cu lp li t ngAUC Authentication Center Trung tm nhn thc

BCCH Broadcast Control Channel Knh iu khin qung bBCH Broadcast Channel Knh qung bBER Bit Error Rate T s bit liBSC Base Station Controller B iu khin trm gcBSIC Base Station Identity Code M nhn dng trm gcBSS Base Station System H thng trm gcBTS Base Transceiver Station Trm thu pht gcC/A Carrier to adjacent ratio T s sng mang trn sng ln cnC/I Carrier to interference ratio T s sng mang trn nhiu

CI Cell Identity

Nhn dng xc nh v tr trong

vng nh vC/R Carrier to reflection ratio T s sng mang trn sng phn xCCCH 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

CEPTEuropean Conference of Postal

and Telecommunication

Lin minh chu u v bu chnh

vin thngDCCH Dedicated Control Channel Knh iu khin ring

DCS Data Communication Phn h thng tin s liu



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SubsystemDCS Digital cellular System H thng t ong sEIR Equipment Identity Register Thanh ghi nhn dng thit b

ETSIEuropean Telecommunication

Standards Institude

Vin tiu chun vin thng chu u

FACCH Fast Associated ControlChannel

Knh iu khin lin kt nhanh

FB Frequency Correction Burst Cm hiu chnh tn sFCCH Frequency Correction Channel Knh hiu chnh tn s

FDMAFrequency Division Multiple

Accessa truy nhp phn chia theo tn s

GMSC Gateway MSC MSC cngGPRS General Packet Radio Service Dch v v tuyn gi chung

GSMGlobal 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 tcLA Location Area Vng nh vLAC Location Area Code M vng nh vLAI Location Area Identity Nhn dng vng nh vMCC Mobile Country Code M quc giaME Mobile Equipment Thit b di ngMMS Multimedia Messaging Service Dch v nhn tin a phng tinMNC Mobile Network Code M mng di ngMOU Memoradum Uderstanding Bn ghi nh MS Mobile Station Trm di ng

MSC Mobile services SwitchingCenter

Trung tm chuyn mch cc dch vdi 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 thngNMT 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



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PCH Paging Channel Knh tm giPCM Pulse Code Modulation iu ch xung mPIN Personal Identification Number S nhn dng c nhnPLMN Public Land Mobile Network Mng di ng mt t cng cng

PSPDNPacket Switch Public Data

Network

Mng s liu cng cng chuyn

mch giPSTN

Public Switched Telephone

Network

Mng in thoi chuyn mch

cng cngRACH Random Access Channel Knh truy nhp ngu nhinRAND Random number S ngu nhin

SACCHSlow Associated Control

ChannelKnh iu khin lin kt chm

SB Synchronization Burst Cm ng bSCH Synchronization Channel Knh ng b

SDCCHStand alone Dedicated Control

Channel

Knh iu khin ring ng mt

mnhSIM Subscriber Identity Module Mun nhn dng thu baoSMS Short Message Service Dch v nhn tin ngnSRES Signed Response Mt khuSS Switching System H thng chuyn mch

TACSTotal Access Communication

SystemH thng thng tin truy nhp ton b

TCH Traffic Channel Knh lu lngTDMA Time Division Multiple Access a truy nhp phn chia theo thi gian

TMN TelecommunicationManagement Network

Mng qun l vin thng

TRAUTranscoder/Rate Adaptation

Unit

Khi chuyn i m v thch ng

tc VLR Visitor Location Register Thanh ghi nh v tm trCGI Cell Global Indentity Nhn dng ton cuLAC Lacation Area Code M nh v vng

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.



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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 thc

hin 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 nhngdo trnh 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 ,

trc tip hng dn v to mi iu kin thun li cho em hon thnh kha lun.

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

Ng Ngc Cnh

CHNG I: MNG DI NG GSM

1.1 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



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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.

Trong nm 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

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 truynd 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.

1.2 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.



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+ 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.

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

chia s mt tn s.

1.3 Cu trc mng GSM

1.4 Chc nng cc khi trong h thng GSM

1.4.1 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.


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

7

MS BTS


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+ 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)

+ 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).1.4.2 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.1.4.2.1 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.

1.4.2.2 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:



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- 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.

1.4.3 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.

1.4.3.1 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

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



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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,

bao gm 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.

1.4.3.3 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

ca MSC th VLR kt ni vi MSC mi s yu cu ly v lu thng tin v MS tHLR. 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.

1.4.3.4 AuC (Authentication Centre Trung tm nhn thc)

Thanh ghi AuC c dng cho mc ch bo mt. N cung cp cc tham s cnthit cho chc nng nhn thc v to mt m (ciphering). Cc tham s ny gip xc

minh s nhn dng thu bao.

1.4.3.5 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.

1.4.3.6 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).



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1.4.4 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.



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CHNG II: TNG QUAN V BTS HNG ALCATEL - LUCENT

2.1 Gii thiu chung v BTS

2.1.1 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.

2.1.2 V tr ca BTS trong h thng GSM

CAUTRUCMANG GSM

BSC

T

C

M

F

S

SGN

HLR

BTS

BTS

GGSN

PSTN

INTERNET

IPGPRS

BACKBONE

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:

- Sectorised configuration

- Multipion configuration

- Chain configuration

- Star configuration


CU TRC MNG GSM

Hnh v 2.1: Cu trc mng GSM


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2.1.3 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:

2.1.3.1 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:


Hnh v 2.2: Cu hnh kt ni BTS ti BSC


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

2.1.3.2 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 tnh sau:


Hnh v 2.3: BTS MBI


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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.

2.2 Cu trc chung ca h thng BTS

2.2.1 Cu trc chung ca h thng BTS

CLOCK

T

R

A

NS

OMU

SUM

TRE ANAbis

BTS-TE

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

+ SUMA


Hnh v 2.4: BTS MBO

Hnh v 2.5: Cu trc chung ca h thng BTS


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+ TRE

+ ANC

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

2.2.2.1 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.

- 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).


Hnh v 2.6: Kin trc khi SUMA


17/64


- 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 )

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

2.2.2.2 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).


Hnh v 2.7: Kin trc khi TRE


18/64


+ Gii iu ch (DEM).

+ M ho v pht (ENCT).

+ u cui BCB.

- TREA:

+ 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 icng sut tn hiu cao tn bi TXRFCC.

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

2.2.2.3 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

RXd RX 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.


Hnh v 2.8: Kin trc khi ANC


19/64


+ 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.

2.3 Nguyn l hot ng ca BTS2.3.1 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

BTSTERM

Abis

KET NOI BEN TRONG

OMU

TRANS&CLOCK

TRE

ANx

ANy

FACB

AC/DC&BATTEIES

ISL

ISL

ISL

ISL

ISL

TRE FW/SWO&M/TELECOM

ANxFW

ISLpilot

EBCB

BSC

OML/IOM/IOM-CONF

TCH/RSL

2.3.2 BCB (Base Station Control Bus)

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

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.

2.3.3 BSII (Base Station Internal Interface)

BSII l giao din chnh bn trong BTS


Hnh v 2.9: Kin trc khi ANC


20/64


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 hay

Q_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).

2.3.4 Nguyn l hot ng ca BTS

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

TCH TCH TCH TCH

TCH TCH TCH TCHTS31

- 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.



21/64


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 TCHTS31(OML2+Qmux2)TS25(RSL2)TCH TCH TCH TCHTCH TCH TCH TCHTS28(RSL1)TCH TCH TCH TCHTCH TCH TCH TCHTS31(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.



22/64


+ 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.

CHNG III: TNH TON MNG DI NG GSM

3.1 Lu lng trong mng GSM

Trong h thng vin thng, lu lng l tin tc c truyn dn qua cc knh

thng tin.

Lu lng ca mt thu bao c tnh theo cng thc:

A =3600

* tC

Trong :

C: s cuc gi trung bnh trong mt gi ca mt thu bao.

t: thi gian trung bnh cho mt cuc gi.



23/64


A: lu lng thng tin trn mt thu bao (tnh bng Erlang).

3.2 Cp dch v - GoS (Grade of Service)

Lu lng mun truyn = Lu lng c truyn + Lu lng nghn.

Offered Traffic = Carried Traffic + Blocked Traffic

Cp phc v (GoS = Grade of Service):

mt knh ng trc c cht lng phc v cao th xc sut nghn phi

thp. Vy nn s ngi dng c th phi b gii hn, tc l lu lng mun truyn

phi gi trong dung lng knh. Nu chp nhn mt cp phc v thp hn, tc l

xc sut nghn ln hn, th tng ng tng c dung lng mun truyn (tng s

ngi dng). GoS cng mt ngha vi xc sut nghn:

Lu lng mun truyn: A (lu lng mun truyn)Lu lng b nghn: A*GoS (lu lng mt i)

Lu lng c truyn: A*(1 - GoS) (lu lng pht ra)

Theo thng k cho thy th cc thu bao c nhn s khng nhn ra c s tc

nghn h thng mc di 10%. Tuy nhin mng hot ng vi hiu sut cao

th mng cellular thng c GoS = 2 % ngha l ti a 2% lu lng b nghn, ti

thiu 98% lu lng c truyn.

M hnh ERLANG By l m hnh h thng thng tin hot ng theo kiu tiu hao. Thu bao

khng h gi li khi cuc gi khng thnh. ng thi gi thit rng: Xc sut cuc

gi phn b theo lut ngu nhin, s ngi dng rt ln so vi s knh dng chung,

khng c knh d tr dng ring, cuc gi b nghn khng c gi li ngay.


Hnh v 3.1: Xc sut nghn GoS


24/64


M hnh Erlang B l m hnh thch hp hn c cho mng GSM. T cc cng

thc ton hc, ngi ta lp ra bng Erlang B cho tin dng

V d: S knh dng chung l 10, GoS l 2%. Tra bng Erlang B ta c lu

lng mun truyn l A = 5,084 Erl. Vy lu lng c truyn l:

A*(1 - GoS) = 5,084*(1 0,02) = 4,9823 Erl.

3.3 Nhiu ng knh C/I

Nhiu ng knh xy ra khi c hai my pht pht trn cng mt tn s hoc trn

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 :

Pc = cng sut tn hiu thu mong mun

Pi = cng sut nhiu thu c.

Hnh 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


Hnh v 3.2: T s nhiu ng knh C/I


25/64


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.

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 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.3.4 Ti s dng li tn s

3.4.1 Khi Nim

i vi mng v tuyn ca GSM, do s lng knh pht trong di tn cho php

l hu hn, nn ti u vic s dng cc knh tn s, tng dung lng phc v,

ton b vng phc v c chia thnh cc phn khu nh hn, gi l cluster. Ti mi

cluster, tt c cc tn s (f1 .fn )c cp u c s dng. Trong trng hp

ny, rng vng ph sng v dung lng phc v u c nng cao, tuy nhin sxy ra trng hp nhiu ng knh gia tn s fi ca cluster ny vi tn s fi ca

cluster khc.

Nh vy, cn thit phi c mt k thut phn b, sp xp s dng cc tn s

sng mang ring l trong cc nhm hp l trnh gy nhiu v m bo cc thng

s k thut theo yu cu, chnh l k thut ti s dng tn s trong GSM.

Ty theo s lng tn s c cp, mc yu cu v dung lng, rng

vng ph m c nhiu k thut ti s dng tn s khc nhau, ta gi l mu ti s

dng tn s FRP (Frequency Reuse Pattern).

Kch c nhm N:

Kch c nhm N l s lng cell c trong mt nhm tn s, nhm tn s ny

c ti s dng trong mt khu vc ph sng, sao cho khong cch gia hai tn s

ging nhau thuc hai nhm khc nhau lD, trm pht sng BTS c xem nh t

ti trng tm ca hnh lc gic, bn knh ca cell lR.



26/64


Ta c cng thc tnh khong cch s dng li tn s:

D = R* N*3

(trong : R l bn knh cell)

- Tnh ton C/I

ng thi ta c cng thc tnh t s C/I nh sau:


RD

c

Df1

f2

f5

f3 f4

f7 f6

N= 7 ; i = 1 ,j = 2

Hnh v 3.3: Cc cell hnh lc gic, mi nhm gm 7 cell.

i=1j=2

26

Hnh v 3.4: Khong cch ti s dng tn s


27/64


P l v tr ca MS thuc cell A, chu nh hng nhiu knh chung t cell B l ln nht.

Ti v tr P (v tr my di ng MS) c:

C..Rx = I ..(D-R)x I

C=

x

x

R

RD )( =

x

R

D

1 = ( N.3 -1)x

Trong : x l h s truyn sng, ph bin nm trong khong t 3 n 4 i vi

hu ht cc mi trng.

)(dBI

C= 10*lg( N.3 -1)x


S cell (N)

Kch thc mng

T s C/I (dB)

x3,0 3,5 4,0

3 9,0 10,5 12,0

4 11,7 13,7 15,6

7 16,6 19,4 22,2

9 18,7 21,8 24,9

12 21,0 24,5 28,0

21 25,2 29,4 33,6

27

Hnh v 3.5: S tnh C/I


28/64


Bng quan h N & C/I

xc nh v tr ca cc cell ng knh ta s dng cng thc:

N = i2 + i.j + j2. (i; j nguyn)

3.4.2 Cc mu ti s dng tn s

K hiu tng qut ca mu s dng li tn s: Mu M /NTrong : M = tng s sites trong mng mu

N = tng s cells trong mng mu

Ba kiu mu s dng li tn s thng dng l: 3/9, 4/12 v 7/21.

3.4.2.1 Mu ti s dng tn s 3/9

Mu ti s dng li tn s 3/9 c ngha cc tn s s dng c chia thnh 9

nhm tn s n nh trong 3 v tr trm gc (Site). Mu ny c khong cch gia cc

trm ng knh l D = 5,2R.Cc tn s mu 3/9 (gi thit c 41 tn s t cc knh 84 n 124 - l s tn

s s dng trong mng GSM900 ca VMS):


n nh tn sA1 B1 C1 A2 B2 C2 A3 B3 C3

BCCH 84 85 86 87 88 89 90 91 92TCH1 93 94 95 96 97 98 99 100 101TCH2 102 103 104 105 106 107 108 109 110

TCH3 111 112 113 114 115 116 117 118 119

TCH4 120 121 122 123 124

28


29/64


Ta thy mi cell c th phn b cc i n 5 sng mang.

Nh vy, vi khi nim v knh nh ni phn trc th phi dnh mt khe

thi gian cho BCH, mt khe thi gian cho SDCCH/8. Vy s khe thi gian dnh

cho knh lu lng ca mi cell cn (5 x 8 2) = 38 TCH.Tra bng Erlang-B (Ph lc), ti GoS 2% th mt cell c th cung cp dung

lng 29,166 Erlang.

Gi thit trung bnh mi thu bao trong mt gi thc hin 1 cuc gi ko di

120s tc l trung bnh mi thu bao chim 0,033 Erlang, th mi cell c th phc v

c 29,166/0,033 = 833 (thu bao).

Theo l thuyt, cu trc mng 9 cells c t s C/I > 9 dB m bo GSM lm

vic bnh thng.


Hnh v 3.6: Mu ti s dng li tn s 3/9


30/64


T s C/A cng l mt t s quan trng v ngi ta cng da vo t s ny

m bo rng vic n nh tn s sao cho cc sng mang lin nhau khng nn c

s dng cc cell cnh nhau v mt a l.

Tuy nhin, trong h thng 3/9 cc cell cnh nhau v mt a l nh A1 & C3,

C1 & A2, C2 & A3 li s dng cc sng mang lin nhau. iu ny chng t rng t

s C/A i vi cc my di ng hot ng bin gii gia hai cell A1 v C3 l

0dB, y l mc nhiu cao mc d t s ny l ln hn t s chun ca GSM l (- 9

dB). Vic s

dng cc bin php nh nhy tn, iu khin cng sut ng, truyn dn gin on

l nhm mc ch gim ti thiu cc hiu ng ny.

3.4.2.2 Mu ti s dng tn s 4/12Mu s dng li tn s 4/12 c ngha l cc tn s s dng c chia thnh 12

nhm tn s n nh trong 4 v tr trm gc. Khong cch gia cc trm ng knh

khi l D = 6R.

Cc tn s mu 4/12:

n nh tn sA1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3

BCCH 84 85 86 87 88 89 90 91 92 93 94 95

TCH1 96 97 98 99 100 101 102 103 104 105 106 107TCH2 108 109 110 111 112 113 114 115 116 117 118 119TCH3 120 121 122 123 124

Ta thy mi cell c th phn b cc i l 4 sng mang.

Nh vy, vi khi nim v knh nh ni phn trc, mt khe thi gian

dnh cho knh BCH, mt khe thi gian dnh cho knh SDCCH/8. Vy s khe thi

gian dnh cho knh lu lng ca mi cell cn (4 x 8 2) = 30 TCH. Tra bng

Erlang-B ( Ph lc), ti GoS = 2 % th mi cell c th cung cp dung lng 21,932

Erlang. Gi s mi thu bao chim 0,033 Erlang th mi cell c th phc v c

21,932/0,033 = 664 thu bao.

Trong mu 4/12 s lng cc cell D sp xp theo cc cch khc nhau nhm

phc v cho cc cell A,B,C. Hiu qu ca vic iu chnh ny l m bo hai cell

cnh nhau khng s dng hai sng mang lin nhau (khc vi mu 3/9). Vi mu

ny, khong cch ti s dng tn s l ln hn.



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V l thuyt, cm 12 cells c t s C/I > 12 dB. y l t s thch hp cho php

h thng GSM hot ng tt. Tuy nhin, mu 4/12 c dung lng thp hn so vi

mu 3/9 v:

a) S lng sng mang trn mi cell t hn (mi cell c 1/12 tng s sng mang

thay v 1/9).

b) H s s dng li tn s thp hn (ng ngha vi khong cch s dng li l

ln hn).

3.4.2.3 Mu ti s dng tn s 7/21

Mu 7/21 c ngha l cc tn s s dng c chia thnh 21 nhm n nh trong

7 trm gc. Khong cch gia cc trm ng knh l D = 7,9R.

Cc tn s mu 7/21: Hnh v 3.8

Ta thy mi cell ch c phn b ti a 2 sng mang.Nh vy vi khi nim v knh nh ni phn trc. Phi c mt khe thi

gian dnh cho BCH v c t nht mt khe thi gian dnh cho SDCCH, s khe thi

gian dnh cho knh lu lng ca mi cell cn (2 x 8 2) = 14 TCH. Tra bng

Erlang-B (Ph lc), ti GoS = 2% th mi cell c th cung cp mt dung lng

8,2003 Erlang.

Gi s mi thu bao chim 0,033 Erlang, nh vy mt cell c th phc v c

8,2003/0,033 = 248 thu bao.


Hnh v 3.7: Mu ti s dng li tn s 4/12Hnh v 3.7: Mu ti s dng li tn s 4/12


32/64


Nhn xt:

Khi s nhm tn s N gim (21, 12, 9), ngha l s knh tn s c th dng cho

mi trm ( /N) tng th khong cch gia cc trm ng knh D s gim 7,9R; 6R;

5,2R. iu ny ngha l s thu bao c phc v s tng ln l: 248, 664 v 883,

nhng ng thi nhiu trong h thng cng tng ln.

Nh vy, vic la chn mu s dng li tn s phi da trn cc c im a l

vng ph sng, mt thu bao ca vng ph v tng s knh ca mng.

- Mu 3/9: s knh trong mt cell l ln, tuy nhin kh nng nhiu cao. Mhnh ny thng c p dng cho nhng vng c mt my di ng cao.

- Mu 4/12: s dng cho nhng vng c mt lu lng trung bnh.

- Mu 7/21: s dng cho nhng khu vc mt thp.

3.5 Cc cu hnh ca trm BTS

3.5.1 Cu hnh 4/4/4 (cu hnh Full)


Hnh v 3.8: Mu ti s dng li tn s 7/21


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Mt trm BTS c cu hnh l 4/4/4. Nh vy th mi cell c 4 TRx v s c s

knh vt l l: 4x8 =32 knh trong s knh phc v cho thoi l 32-2=30 knh

(v 1 knh dng truyn tn BCCH, v 1 hay nhiu knh dng cho knh SDCCH,

y l dng 1 knh cho SDCCH). Nh vy l mt cell th c th phc v ti a 30

cuc gi ng thi cng 1 lc v c trm s phc v l 3x30=90 cuc gi ng thi

cng mt lc.

3.5.2 Cu hnh 2/2/2

Tng t th mt trm BTS c cu hnh 2/2/2 th mi cell c 2 TRX v s c 2 x

8=16 knh trong s knh phc v cho thoi l: 16 - 2=14 knh

Nh vy th mt cell c th phc v ti a 14 cuc gi ng thi cng 1 lc v c

trm s phc v 14 x 3=42 cuc gi ng thi.



34/64


CHNG IV: DRIVE TEST TRONG MNG GSM

4.1 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.

4.2 Thit b o v th tc o drive test

4.2.1 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.

4.2.2 Thit b Drive test v cc ngun h tr

4.2.2.1 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)

- 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

34


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My tnh xch tay B i ngun DC - AC4.2.2.2 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

4.2.3 Th tc o

4.2.3.1 Cc th tc chun b

ng i phi c xc nh cn thn trc khi thc hin, ng i l nh

nhau trong 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

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4.2.3.2 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 xeMt 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 thitlp cuc gi l 90s, ch 25s v lp li

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

4.2.3.3 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.

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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 lField Test

measurement

Th hin mt ci

nhn ca khch hng

mc tiu v cht

lng mng ph hp

cho phn tch i

th

Tiu tn nhiu thi

gian

Trong mt vng gii

hn tt cho xc nh

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

cng cung 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 khin

cng 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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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

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

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Hnh v 4.1: Chu trnh Drive Test


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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 liu

S 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.

4.3.2.1 Khng th xc nh c hoc thiu NeighborVn ny c lit k u tin bi v cc triu chng c th ging vi cc vn

ny nh c nu phn sau. Mt v d ca vic chun on nhm ca vic

thiu Neighbour l khi Drive test ch ra rng mc tn hiu ri xung di mc

ch tiu. V iu ny c ch ra l c vn v vng ph. Do tt hn l phn

tch d liu Drive test cho vic thit lp handover trc khi tin hnh cc th tc khc.

Trc khi xem qua cc v d v chn on thiu handover, phi ch rng iu

khin cng sut c kch hot trn kt ni hin ti hay khng. iu khin cng

sut s c nh hng n mc tn hiu o c c th khng c thc hin vi

BTS ti mc cng sut ti a do n c th so snh vi mc tn hiu neighbor

c thng bo chng lun c pht i bi BTS ti mt mc c nh.

iu ny c th c thc hin bi vic kim tra cc thng s ca Cell trong

OMC, Drive test hoc dng bng di y. N s gip cho vic quyt nh kh

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nng no ca mc tn hiu ca kt ni hin ti c gim i bi nh hng ca

vic iu khin cng sut.

Kt ni hin ti ch s dng BCCH Khng dng iu khin cng sutiu khin cng sut khng c kch hot Khng dng iu khin cng sut

BCCH serving cell trong danh sch BA-Active v c thng bo c RxLev lin

quan vi RxLev ca kt ni (1-2dB)

Khng dng iu khin cng sut

Rxlev di mc tn hiu ng xung

mong mun hoc ngoi khong iu khin

cng sut

Nhiu kh nng khng s dng iu

khin cng sut

Rxlev gn vi mc tn hiu mong mun

ng xung hoc bn trong ca s iu

khin cng sut ng xung

Nhiu kh nng iu khin cng sut

c s dng

BCCH ca cel ang phc v trong danh

sch BA list c thng bo c mc tn

hiu ln hn so vi Rxlev ca kt ni

Nhiu kh nng s dng iu khin

cng sut

C th thy trn bng trn, c nhng trng hp m khng th ni tuyt i

rng c s dng iu khin cng sut hay khng, nguyn nhn ch yu l do thc t

rng BTS khng thng bo ti MS v iu khin cng sut c s dng. Do

trong trng hp cn nghi ng, Drive Test c th c thc hin li kim tra vn .

Trong trng hp Rxlev ca cell ang phc v cng ch c thng bo mt

trong cc neighbor, khi nh s dng gi tr Rxlev ny nh hng ca iu khin

cng sut c loi b. Nu khng phi l trng hp ny v iu khin cng sut

c th c s dng cho kt ni khi Drive test c th ra cc thao tc thng thng.

Nu Neighbor b thiu s dng tn s BCCH nh l mt phn ca BA list ca

cell ang phc v khi vic pht hin thiu neigbor l kh d dng. Mt v d ca

iu ny c ch hnh v di y.

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T hnh v ta c th thy rng kt ni trn BCCH, do t bng cho trc c

th thy rng iu khin cng sut khng c s dng. Chng ta c th thy r hn

rng MS thng bo mt mc tn hiu mnh hn mc tn hiu ang c phc v

nhng khng c s chuyn giao no xy ra vo cell c cng mnh hn.

V d ny ch ra rng Cell l mt ng c cho vic missing neighbor, nhng

cc bc kim tra di y cn thit phi c tin hnh chc chn:

- Kim tra nu kt hp BCCH/ BSIC c thng bo ph hp cha. Nu

BSIC khng c gii m, s dng planning tool tm ra mt cell thch hp, nukhng c cell no c tm thy phi kim tra xem c mng no khc ang s

dng tn s ny.

- Nu quan h neighbor c xc nh cho cell ng c:

+ Trong trng hp ny BSIC khng gii m c hoc khng lin tc th phi

kim tra xem c kh nng nhiu trn knh khng. Nu c mt BSIC khng

ng tin cy c decode, mt handover s khng c xy ra.

+ Kim tra xem nu cell c iu khin bn trong BSC, LAC v hoc MSC.

Nu bt k mt trong cc yu t trn l khc, th kim tra xem cc c s d liu

lin quan m bo rng cc thng tin nh dng cell v handover l xc nh ng.

+ Kim tra xem c nghn khng trn cell ng c. Nu n nghn, khng mt

hand-over no xy ra.

41

Hnh v 4.2: V d thiu vng Neighbor


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+ Kim tra thng s disable hand-over cho cell ng c. Nu Handover n b

kho, MS s khng chuyn giao c ti cell kim tra ci t lp HCS v cc

thng s thut ton handover ca cc nh cung cp tm ra nguyn nhn c th.

+ Kim tra s truyn dn gia cc cell ng c. Mt s nh cung cp thit k

thit b ca h tip tc truyn dn knh BCCH thm ch ngay c BTS khng

c ni vi phn cn li ca mng li. Tuy nhin nu nhn sau khi drive test

c th thy cell ng c c s dng, li truyn dn c v nh khng ng.

Mt yu cu thay i c th c pht ra ch cho missing neighbor trong trng

hp sau khi kim tra cc tnh hung trn m khng tm c nguyn nhn. Cc vn

c pht hin trong qu trnh kim tra c th c sa li nh cc change request.

Nu missing neigbour s dng tn s khng c xc nh trong BA list khi vic pht hin thiu neighbor l kh hn nhng vn c th xc nh c.

Trong v d ny chng ta c th thy rng mt handover n mt cell c pht

hin l mnh hn so vi cell ang phc v, tip n lp tc handover sang cell

mi c mc tn hiu ln hn c cell c v cell mi. Handover ln th 2 c thc

hin sang cell mnh nht.

Trong trng hp ny nn ch ra rng cell phc v ban u v cell phc v ln

cui nn c quan h neighbor vi nhau. Nu quan h neigbor l c xc nh

n cell ng c, cc bc kim tra sau y nn c thc hin:

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Hnh v 4.3: V d trong phn tch Neighbor


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- Km tra danh sch tn s o c t hoc l bn tin h thng s 5 hoc t

OMC. Nu tn s neighbor khng xut hin trong danh sch khi hand-over s

khng xy ra c.

- Kim tra nu cell ang c iu khin trong cng BSC, LAC hoc MSC.

Nu tt c cc trng hp trn l khc nhau tip kim tra c s d liu lin quan

m bo rng thng tin handover v nh dng cell c xc nh ng.

Nu khng c quan h c xc nh th mt yu cu thay i c th c a ra

thm missing neighbor.

Trong mt s trng hp c th xo i hoc to ra mt quan h neighbor trong

trng hp c li ca cu hnh d liu OMC/BSC.

4.3.2.2 Vn v vng phy l mt vn tng i n gin pht hin v phn tch. Tuy nhin gii

php cho vn ny khng phi l n gin.

Nguyn nhn cho tnh trng mc tn hiu thp c nh gi l bi v mt nh

hng, ngoi ra l tn hiu thp s ko theo C/I b gim. C/I gim gy nn chst

lng thoi gim, trc tin BER c tng ln ch ra mt im m cht lng

thoi b gim v tip khi FER tng khi cc mu tn hiu b mt tt c v dn n

rt cuc gi.Nu nhiu c nh gi trc mc tn hiu, ngi ti u c th b cun ht bi

xc nh vn nh l cht lng thp v iu chnh tn s, iu lm lng ph

thi gian bi nguyn nhn thc s ca nhiu l nhiu nhit hoc nhiu nn chng

khng th b loi b bi vic thay i tn s.

Gii php gii quyt vn vng ph thp l:

- Tng cng sut pht ra ca BTS hoc gim suy hao BTS.

- Chnh li hng tilt hoc tng cao anten

- S dng mt Repeater m rng vng ph.

- Xy dng thm trm mi.

Tu vo thit b ca nh cung cp, c th tng cng sut n ti a thng qua

yu cu phn mm hoc thay TRX vi cng sut cao hn.

Mt kh nng na l gim suy hao combiner hoc feeder nh s dng air

combining hoc feeder c suy hao thp. Air combining l mt khi nim m thay

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v s dng filter hoc Hibrid combiner kt ni 2 TRX vi mt Anten, mt anten

ring r c s dng cho 1 TRX v do gim c 3dB n 3.5 dB suy hao.

iu quan trng phi nh rng vng ph uplink v downlink l phi cn bng,

do vic tng cng sut ng xung cn thit phi kt hp vi tng vng ph

ng ln nh thm vo TMA.

Nu vn vng ph tn ti trong mt vng m gn vi site hin ti v nguyn

nhn bi vt chn, khi c th gii quyt vn ny nh tng cao anten

vt qua vt chn.

Nu vn vng ph tn ti trong khu vc gn vi mt cell hin ti nhng v

tr nm gia 2 sector khi ta c th chnh li hng anten thu c s ci thin.

Quay li hng l k thut hiu qu tc th, n s a mt s tn hiu cho vngby gi trong beam chnh v ly i mt s tn hiu m trc y l beam chnh.

Tuy nhin nu trong hng ca beam c c mc tn hiu mnh hoc c mt site

khc c th cover c vng ny, th xoay hng l thun tin v tng c tng s

vng t c tiu chun.

Uptilt ca anten c th cung cp mt s tng ch. Tuy nhin c mt bt li ca

vic lm ny l s lm tng s trn ca cell c th gy ra nhiu n cc cell khc.

Trong hu ht cc trng hp nng thm mt gc -3 dB trn ng ngang s khngcung cp thm c s ci thin v tng ch.

Trong vng nng thn v nhng ni m dung lng yu cu l thp, c th s

dng repeater gii quyt vn vng ph. C nhiu loi repeater c cung cp

trn th trng do vy c th la chn trong tng trng hp c th.

Khi phn tch vng ph thp n rt quan trng kim tra nu mc tn hiu

thp l do iu khin cng sut hay khng, nu trng hp ny cht lng c th

chp nhn c, khng c vn g thay i.

Hnh v di y v bn di y l mt v d v vng ph thp, kh nng

v thiu neighbor c loi b.

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mc tn hiu tip theo trn biu , c th thy rng mc tn hiu gim ing k t khi cuc gi c bt u n na chng cuc gi ti n bt u tng.

Nh cp trc khi mc tn hiu gim th C/I v quaility cng gim theo, iu

ny c th c nhn thy th; C/I tnh ton gim, RxQual tng, SQI gim v

FER tng.

Trong bn hnh v 4.5 im gia c la chn. Mc tn hiu gim khi

MS dch chuyn ra xa trm BTS cho n im gia, ti thi im MS thay i

hng v quay ngc tr li BTS. Trong danh sch serving v Neighbor cell c th

thy rng mc tn hiu ca Cell phc v v Neighbor l di -100 dBm v mc

ngng thit k.

45

Hnh v 4.4: V d v vng ph thp

Hnh v 4.5: Biu phn tch trn MapInfo


46/64


Trong v d ny khong cch o c n vng phc v thp l kh xa t

hng Anten v nm trong khong null gia 2 sector 1 v 2, nhng n khng hiu

qu nu ch thay i hng ca Anten.

Phn tch su hn ta thy rng mc tn hiu di mc phc v ngoi tri do

vic s dng TRX c cng sut ln hn v gim suy hao ca Feeder l khng

gip c nhiu. Khng c cell no pha ng Nam do cell ang phc v nm

pha ra ca mng, nhng xem xt thy rng vng ph thp vn nm bn trong

th x do gii php tt nht l xy dng thm trm mi.

bn tip theo trang bn ch ra mt v d khc v vn vng ph thp,

tuy nhin trong v d ny vng phc v ny c bao quanh bi cc Site v khng

nm trong ngoi ra ca mng. Phn tch vng ny thy rng khng c vt cn ngk gn cell ang phc v v khong cch ca vng c vn l nm trong bn knh

c phc v. Nghin cu k hn trong vng ph thp ta thy rng khu vc ny l

khu ng c (ng rt hp v cc to nh l lin k nhau) c rt t c hi c

mt tn hiu ng thng hoc phn x v khc x t cc cell ln cn thm nhp

c n MS.

Gii php tt nht l xy mt SITE mi trong hoc gn vi khu vc trn bi

v khu vc ny l ng c v do lu lng ca khu vc ny s rt ln (Repeaterkhng th tng c lu lng) v ch c nhng tn hiu trn nh mi c kh

nng thm nhp n MS (Gim suy hao phi hoc tng cng sut pht s

khng ci thin c s thm nhp vo khu vc ny).

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4.3.2.3 Nhiu nhiu v vn v cht lng ti

S suy gim cht lng mng gy ra bi nhiu ln v cht lng ti c th

bao gm:

- Cht lng thoi ti cng tng

- Tc chuyn i trong GPRS gim vi s ln truyn li tng ln

- Rt cuc gi tng

- Chuyn giao khng thnh cng v rt chuyn giao tng ln

- S ln thit lp cuc gi khng thnh cng tng

Ngun nhiu chnh l nhng cell bn trong cng mt mng v do thng

thng c th iu khin c v c th loi b hon ton bi ngi vn hnh.

Cc mng khc c cng k thut theo bi k thut khc nhau v cng bng tn

l nhng ngun nhiu thm vo vi mt mc thp hn.

Mt im cn ghi nh l thnh thong ngun nhiu t nhng ngun ny

khng th xc nh c nh drive test bi v chng hoc trong band uplink ca

GSM hoc l mt k thut khc. Trong nhng trng hp nh vy, nhng my o

phn tch ph c th tr gip pht hin ra ngun nhiu.

Nhiu nn v nhiu nhit l nhng ngun nhiu cui cng v chng thng

thng ch nh hng n tn hiu c cng rt thp (


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trong mt vng vi mt site tng i cao, nhiu sn (t nhiu nhit cng vi s

trn ra t cc cell khc) c th c tng ng k v gy ra vn nhiu rt kh gii quyt.

Bi v hu ht nhiu l t bn trong cng mt mng. N l mt kiu nhiu c

nhm ti trong sut qu trnh ti u.

Mt s phng php c th ci thin tnh trng nhiu:

- Thay i tn s trn cell phc v hoc/ v ngun nhiu.

- Downtilt ngun nhiu trong trng hp b trn ra qu nhiu.

- Tng cng sut ca cell phc v v hoc gim cng sut pht ca ngun nhiu.

- Tin hnh iu khin cng sut, nhy tn hoc pht gin on

Pht hin nhiu t logfile Drive Test l mt iu g d nhng Log Drive Test

thng thng khng xc nh c r rng ngun nhiu. Mt s v d t php oDrive Test c ch ra di y:

trong hnh trn, c th thy rng trong phn trc khi handover th nht c

nhiu neighbor c thng bo xung quanh mc tn hiu, iu ny ch ra rng

thiu mt cell vt tri. Nhiu handover din ra trong mt khong ngn vi mt sr rng l do nhiu (bi v tiu chun power budget - HO d tr l khong 3dB -

khng t ti). Trong trng hp ny kh c th gii quyt vn nh ch thay i

mt tn s. Gii php cho kiu tnh hung ny s c tho lun k hn.

Nhiu n

48

Hnh v 4.7: V d khc v vng ph thp


49/64


Trong nhng trng hp m nhiu gia 2 cell c th l phng php u

tin - thay i mt tn s hoc trn cell phc v hoc trn ngun nhiu - c th sa

c vn nhiu ny.

S pht hin c hoc khng ngun nhiu t mt ngun n hoc nhiu c th

bin i rt phc tp. Bc u tin l xem xt k hoch tn s cho cho mt vng

v tm ra ngun nhiu c nhiu kh nng nht. Thnh thong c mt cell ni tri c

th gii quyt vn ny

a nhiu

Khi vng vi ngun nhiu ln nhn c nhiu mc tn hiu t cc cell khc

nhau ti nhng mc tng t lm cho ti t hn theo hm m vi mi nhiu ngoi.

Trong nhng trng hp ny s thay i tn s trong mt khu vc c th cn thit gim nhiu trong mt gii hn c th chp nhn c. Trong cc trng hp

nghim trng l c rt nhiu tn hiu v mc nhiu sn s tng, trong trng hp

ny vic thay i tn s khng thu c nhiu hiu qu.

Trong mng vi s qui hoch tn s cht ch hoc s dng trong mt nhm c

nh, hoc trong vng mt cell thp xung quanh vng c mt cell ln, iu

ny lm tng ln nhiu nhit c th tr nn vn nghim trng. Tin hnh nhy tn

c th c ch nh vic trung bnh nhiu ny nhng khng th loi tr c n.Khi i mt vi s tng nhiu sn ny, phng php cn li l c ph hp tt

hn ci thin cht lng trong khu vc nhiu. i tng chnh ca n l gim

nhiu m khng phi gim cng sut pht do C/I c ci thin t n cht

lng thoi tt.

Downtilt Anten

Mc ch ca downtilt l ph hp vng ph ca mt cell vi vng phc v

ca cell . Nu vng ph ca Cell l rng hn so vi vng phc v v khi cell

s gy ra nhiu cc cell ln cn.

iu chnh ng tilt ca anten, ngi lp k hoch phi xc nh bin ca

cell v tip gc ca anten do cnh ca cell s bn trong phn trn ca na

bp sng chnh. Tilt chnh xc ph thuc vo rng chiu ngang ca cell v tilt

in ca anten v gii hn cui cng ca cell l g.

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Nh hng dn u tin, t mt im - 3dB trn nh ca antena trn phng

ngang khng c khuyn ngh bi v iu ny s dn n mt phn rng ln ca

nng lng b mt i vo trong khng gian hoc ti hn do b mc trong vt dn

nhit trong khng gian ch quay li tri t ti mt khong cch xa v gy ra nhiu

cc cell khc. Hnh di y c th ngh mt gc khng tun theo cc khuyn

co ban u v nu nh vy s ng v khng ng ca vic lm ny cn c

c lng v mt s tho hip c t n.

Nu mt cell cung cp ti mt vng c mt cell thp, bp sng chnh tp

trung ca anten c th hng v bin ca Cell. Nu cell c cung cp mt vng

ph trong mt vng m c mt cell cao, khi im -3dB nh ca bp sng

chnh c th c ch vo bin ca ca cell. nhng vng c a hnh khng bng phng, qu trnh quyt nh gc tilt cn

c cn nhc khc nhau tng i trong chiu cao tng i gia MS anten v

BTS. V d, nu anten c ch vo mt qu i, im -3dB ch nm bn trn qu

i mt cht. iu ny lm gim kh nng trn ra xa (ng thi gim lun nhiu

uplink ca cell) v tp trung vo cng sut truyn v nhn bn trong vng mc tiu.

Vi mc ch thu c mt nh dng r rng v bin ca cell nhiu Drive

test cn phi c tin hnh v phn tch. Tm kim vng ph ni m cc cell cnhn ti mc cng sut bng nhau, nu cc cell c h tilt ti vng bin v cng

sut cui cng nhn c ti vng bin l khng thay i nhiu nhng s trn s

c gim i ng k. Tuy nhin nu nhng mc tn hiu ti bin ca cell vn cao

(+3dB trn mc c th xem xt cho phc v tt trong nh) khi chnh gc

anten cho n khi mc tn hiu ti vng bin l c th chp nhn c.

Bin ca cell nn c khong cch n 2 cell l gn bng nhau to nn s cn

bng gia chng. Thnh thong mt vt chn m mt trong cc cell khng th vt

qua xc nh bin cell.

Khi bin ca Cell l mt khong bit, nhng php tnh n gin v lng

gic tnh ton gc tilt chnh xc. Nu d liu phn b Timing Advance l c th

t OMC/NMS khi nhng iu ny c th gip xc nh bin cell. S dng d

liu ny, mt k s c th chnh gc anten vi im nh -3dB ca bp sng chnh

cover c phn ln lu lng ngi dng.

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Di y l biu phn b Timing Advance ca cell m vng phc v b trn.

Trong v d ny, n tt hn l h gc anten m nh -3dB ri xung khong 6Km

(TA=12) t Site ny. iu ny nn dch chuyn lu lng khng mong mun xung

quanh 9 hoc 15km ra xa m lm suy gim c tnh ca cell.

iu chnh cng sut i vi cell phc v hoc nhiu

Trong mt vng c vng ph tt nhng nhiu km n c th gim mc tn hiu

ca ngun nhiu. iu ny lm tng t l C/I ca cell phc v v c th dn n s

ci thin c tnh ca cell.

Tng cng sut trn cell phc v c dung lng tt (mt site thp hoc mt

vng ph b gii hn bi vt chn) v b nhiu bi cc cell ln cn khc v thng

thng dn n C/I tt hn v c tnh mng c ci thin.

c tnh ca mng

Tin hnh thit lp iu khin cng sut mt cch n ho (c mc ngng cht

lng tt trong gi tr Rxqual tt v Rxlev cao) c th vn cung cp s ci thin bi

v nhng li ch chnh thu c c thu c vi s gim 2 - 3dB cng sut.DTX v nhy tn c th gim c nhiu m bt k gc no kt ni vi MS nhn

c do cht lng mng s tt hn.

4.3.3 Yu cu thay i cu hnh Site

Tt c cc vn c pht hin trong phn trc a v mt kt qu trong mt

s yu cu thay i cu hnh c th l phn mm hoc phn cng.

Bt k trng hp no c th cn thit chng minh s thay i bng cch

hon thnh mt yu cu thay i c ghi thnh vn bn. iu ny ngn nga mt

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Hnh v 4.8:Biu phn b TA ca cell c vng phc v b trn


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ngi no sau ny ri b tt c cc neighbor cn thit hoc cu hnh anten vi

khi nim rng cu hnh l khng hp l.

Yu cu thay i (changes Request) c th c a ra bng ti liu l do ca

s thay i, xc nh cc nh hng c th n mng nh cc b m c tnh c

th c nh gi xem s thay i c em li s ci thin cho mng hay khng.

4.3.4 Thc hin

Chu trnh ti u nn bt u li khi m yu cu thay i c tin hnh bi

thay i khc trong:

- n nh tn s trn cell phc v hoc cell b nhiu

- Cu hnh anten

- Xc nh neighbor- Cc thng s iu khin c tnh mng

Bi v khng phi tt c cc thay i s tr v mt kt qu tt, do cn thit

phi nh gi li mng sau khi thay i.

Qu trnh ti u c lp li cho n khi c tnh ch c th t c hoc cho

n khi tt c cc gii php c th c th. Nhng vn khng c gii

quyt nn lm thnh mt ti liu v c xem li sau vi thng trong trng hp c

mt gii php mi c tm ra (v d sau khi mt site c tch hp hoc mtc tnh mi c th).

CHNG V: BI TON THC T

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5.1 Xy dng cc trm BTS phc v cho mt vng

5.1.1 Cc yu t cn quan tm trc khi i vo tnh ton

a vo lp t mt h thng bao gi cng phi c nhng k hoch, nhng

d n v k thut, nhng d tr v kinh t. Trong thit k mng thng tin di ng s

cc vn cng c xem xt k lng. Vi kh nng s dng, kh nng v

ng vn m vng ph sng c th rng khp hoc ch p ng c mt s trng

hp no , tuy nhin trng hp m rng l ln. iu i hi phi quy hoch

mng. Cc bc thc hin nh sau:

- S phn b a l ca vng ph sng.

- Cht lng phc v cho thu bao.

- Mc phc v.

- S ph a l.

Thm vo cn mt s yu cu cn thit nh:

- Kh nng pht trin h thng.

- D on yu cu v lu lng chng hn bao nhiu thu bao c th c, s

phn chia v lu lng. Khi xt n vn cn phi dng cc s liu m

t nh:

- Phn b dn c.

- Cc trung tm bun bn hay ti chnh quan trng.

- Mc thu nhp ca ngi dn.

- Thng k s lng in thoi c nh.

- Tng ng vi cc mc cc thu bao, cc cuc gi.

5.1.2 Bi ton thc t

Tnh ton s b xy dng cu hnh cho trm BTS s dng thit b Alcatel ti

lng Bt Trng - H Ni.

5.1.2.1 Cc thng s kho st

- Phn b a l: vng ng bng, khng c i ni, nm c lp

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Hnh 5.1: Phn b a l lng Bt Trng

Khu dn c

Cu, ng


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Tng din tch khong 1.64 Km2

- Dn s l khong 3600 ngi

- c tnh trong x c khong 1500 my di ng. Do ta cn xy dng nn

trm BTS phc v cho 1500 thu bao di ng.

- S cuc gi trung bnh ca mt thu bao trong vng mt gi l 1.

- Cht lng phc v cho thu bao GOS l: 2%

5.1.2.2 Tnh ton lu lng

Lu lng ca mt thu bao c xc nh theo cng thc sau:

A = (nxT)/3600

n: S cuc gi trong mt gi ca thu bao.

T: Thi gian trung bnh ca cuc gi.

A: Lu lng mang 1 thu bao - n v tnh l Erlang. Theo gi tr thng k

in hnh n v T nhn gi tr sau:

n=1: Trung bnh 1 ngi 1 cuc trong mt gi.

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T=120s: Thi gian trung bnh ca cuc gi l 120s.

Vy A = (1x120)/3600 = 0,033 Erlang = 33m Erlang.

Nh vy phc v cho 1450 thu bao cn lu lng l 47,85 Erlang, t con s

ny tnh ton s knh yu cu trong mng t ong.Nu mt thu bao cn lu lng l 33m Erlang, n s chim 3,3% thi gian 1

knh TCH. Vy vi 30 thu bao c lu lng l 33m Erlang s chim 100% thi

gian 1 knh TCH nhng iu dn n tc nghn cao khng th chp nhn c.

gim tc nghn ny phi gim ti xung bng cch tng s knh thch hp

phi cn c vo tng lu lng v tng ng vi tc nghn c th chp nhn c.

Nghn chp nhn c gi l cht lng phc v (Grade of Service) thng l 2-5%.Nh vy 1 vng phc v cho khong 1450 thu bao s c lu lng l 47,85

Erlang vi GOS=2% tng s TCH cn thit tnh theo bng GOS l 60 knh. Vng

phc v c chia thnh 3 Cell.T kt qu trn ta c th lp mt d nh v t mt

s trm gc BTS:

Cell Lu lng % Erlang S knh

A

B

C

40

40

20

19,14

19,14

9,57

22

22

14

Tng s 3 Cell 100% 49,5 58

Nh vy, Ti Bt Trng ta cn lp t mt trm BTS vi 3 hng khc nhau

theo phn b 3 vng dn c. S dng BTS - Alcatel MBI5, vi gc phng v l

80/190/320 v tilt l 0/0/0. V hai cell A v cell B cn lp 22 knh lu lng. Nh

vy ta cn c 3 TRX.

V 3 TRX s c 3x8 = 24 knh vt l. Trong , ta cn 1 knh cho iu khin

qung b BCCH ( Broadcast Control Chanel) v mt knh dng cho SDCCH .

Vy s knh lu lng s l 24 - 2 = 22 knh TCH.

Tng t cell C cn 14 knh lu lng,v vy ta cn c 2 TRX

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Nh vy th trm BTS cn lp t c cu hnh l: 3/3/2

Trong GSM, knh logic TCH dng cho kt ni thoi gia my u cui v trm

BTS. Knh TCH c chia thnh 2 loi: knh ton tc (full rate) vi tc 16kb/s

(13kb/s cho thoi) v knh bn tc (half rate) vi tc 8kb/s (6.5kb/s cho thoi).

Khi s dng hon ton knh bn tc, dung lng mng truy cp c tng gp 2

ln, tuy nhin, t c yu cu v cht lng cuc gi khi s dng knh bn

tc, mc thu ca my u cui phi t mc cao. Khi s dng knh bn tc HR,

cn p dng k thut p ng a tc thch nghi AMR (Adaptive Multi Rate), vi

vic p dng AMR, cht lng thoi c nng ln ng k khi s dng knh Half Rate.

Nh tnh ton cu hnh trn, trm BTS lp t ti Bt Trng c cu hnh l

3/3/2 khi ta s dng knh TCH ton tc (Full Rate). Nhng v trn thc t, rt t thi

im m tt c cc thu bao trong vng cng thc hin cuc gi. Chnh v th m

nhng thi im m t ngi truy cp vo mng th cc knh lu lng s ri nhiu

gy lng ph. V th tit kim m vn mang li c cht lng phc v tt th ta

s s dng cu hnh 2/2/2 s dng knh ton tc vo gi thng (s ngi truy cp

mng va phi) v khai bo ti BSC t ng chuyn sang dng knh bn tc (Half

rate) khi lu lng truy cp mng tng vt qu mc ngng cho php.

Nh vy khi lp t trm BTS Bt Trng ta ch cn xy dng cu hnh thp

hn l 2/2/2 m vn mang li cht lng phc v tt.

Cu hnh trm BTS MBO cu hnh 2/2/2 s dng thit b Alcatel bao gm s

lng cc card nh sau:

- 01 card SUMA;

- 03 card ANC;

- 03 TRE Twin (tng ng vi 06 TRE single)

c b tr nh hnh 5.2

Trn y l nhng tnh ton ch cp n vic xy dng cu hnh cho trm

BTS nhm phc v tt c lu lng kho st cho trc. Cn nhiu tnh ton

khc cha c cp n, s tip tc nghin cu v hon thin thm trong cng

vic thi gian ti.

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5.2 Bo co Drive test cht lng mng ti Bt Trng H Ni

Thc hin Drive Test trm Bt Trng v phn tch ta c kt qu sau:

5.2.1 Thng k cuc gi

5.2.2 Thng k KPIs DT ngy 15-10-2011

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Hnh 5.2: Cu hnh BTS MBO 2/2/2

ANC

TRETWIN

SUMA


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5.2.3 Logfile call

RxLev

RxQual

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C/I

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Events

5.2.4 Logfile Scanning

Strongest Scanned RxLev

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Strongest Scanned BSIC

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5.2.5 Phn tch:

Nhn xt:

- Cht lng trm tt.Cc gi tr KPI nhn chung tt.T l CSSR hi thp do

xy ra 04 block call.

- Xy ra 04 block call cc trm :

GLM_BAT_TRANG_2_B (BCCH: 90);

GLM_BAT_TRANG_C (BCCH: 100);

LBN_CU_KHOI_B (BCCH: 95);

Do li khng hiu bn tin v khng gii m c bn tin knh SACCH;

- Khu vc khoanh trn b HO nhiu ch yu do chng ln vng ph gia

GLM_BAT_TRANG_2_A v GLM_BAT_TRANG_2_B;

Khuyn ngh

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- ng b ng h ng b ca cc trm b block call k trn.

- Tng ngng HO (Rxlev) gia cell A v B ca trm

GLM_BAT_TRANG_2.

- Cp tilt sector GLM_BAT_TRANG_2_A t 0 xung 1 .

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 phcv 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.

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 5 nm 2011

Sinh vin thc hin

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Ng Ngc Cnh

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,Ericsson s 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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