Soft Handover_hoan Chinh

8/6/2019 Soft Handover_hoan Chinh

1/83

HC VIN CNG NGH BU CHNH VIN THNG

C S THNH PH H CH MINH

KHOA VIN THNG 2

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N

TT NGHIP I HC

NGNH: IN T- VIN THNG

H: O TO CHNH QUY

NIN KHA : 2005-2010Tn ti:

CHUYN GIAO MM TRONG MNG WCDMA

M s ti: 09405160029

Sinh vin thc hin : L TRUNG HIU

MSSV : 405160029

Lp : 05VTA1

Gio vin hng dn : NGUYN HUY HNG

TP H CH MINH THNG 11/2009


2/83

NHN XT CA GIO VIN HNG DN

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*V*

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Tp. H Ch Minh, ngy..thngnm 2009

Gio vin hng dn

Nguyn Huy Hng


3/83

NHN XT CA GIO VIN PHN BIN

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*V*

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Tp. H Ch Minh, ngy..thngnm 2009Gio vin phn bin


4/83

LI CM N

Li u tin, em xin chn thnh cm n cc thy c trng Hc vin Cngngh Bu chnh Vin thng ging dy v truyn t cho em nhng kin thc trong

thi gian qua. c bit, em xin cm nthyNguyn Huy Hng nh hng v chdn cho em. Bng s nhit tnh cng vi nhng gp , gi m, nhng kin thc qubu t Thy, gip em c th hiu c mt cch su sc v r rng hn nhng iu

cn vng mc trong thi gian lm lun n ny.

K n, em xin cm n s gip v ch dn ca cc bn lp 05VT, tuy s

gip khng ln nhng cng gip em gii p mt s thc mc khi lm lun nny.

V cui cng, em xin gi li cm n su sc n gia nh, ba m cng nh ccanh ch em ca em, nhng ngi lun ng vin, cng c tinh thn cho em trong

sut thi gian lm lun n ny.

Mc d Em c nhiu c gng hon thin lun vn bng tt c s nhit tnh v

nng lc ca m nh, tuy nhin khng th trnh khi nhng thiu st, rt mong nhn

c nhng ng gp qu bu ca qu thy c v cc bn.

Tp H Ch Minh, thng 11 nm 2009

Sinh vin

L Trung Hiu


5/83

Bo co tt nghip Mc lc

SVTH: L Trung Hiu Lp 05VTA1 Trang 1

MC LCMC LC ............................................................................................................................. 1MC LC HNH V ............................................................................................................ 3MC LC BNG ................................................................................................................. 4LI M U ....................................................................................................................... 5CHNG I: TNG QUAN V MNG THNG TIN DI NG ......................................... 6

1.1 S pht trin ca mng di ng ................................................................................ 6

1.1.1 H thng di ng tng t th h u tin ......................................................... 61.1.2 H thng di ng th h th 2 v giai on 2 + ................................................. 61.1.3 H thng di ng th h th 3 v cao hn na................................................... 9

a) Cu trc mng thng tin di ng th h th 3 UMTS ...................................... 11b) H thng thng tin di ng th h tip theo: .................................................... 13

1.2 Tng quan v cng ngh CDMA............................................................................ 131.2.1 Nguyn l tri ph (CDMA)........................................................................ 131.2.2 Tri ph v gii tri ph .............................................................................. 141.2.3 a truy xut ................................................................................................ 151.2.4 Cc c im chnh ca cng ngh WCDMA .............................................. 16

1.3 Qun l ti nguyn v tuyn (RRM: Radio Resource Management) ....................... 171.3.1 RRM trong mng di ng ............................................................................... 171.3.2 Chc nng ca RRM....................................................................................... 18

a) iu khin cng sut (Power Control)............................................................. 18b) iu khin chuyn giao (Handover control) .................................................... 21c) iu khin thm nhp (Admission control) ..................................................... 21d) iu khin Ti (iu khin tc nghn) ............................................................ 23

CHNG II: CHUYN GIAO TRONG H THNG 3G WCDMA ................................... 252.1 Tng quan v chuyn giao trong mng di ng ...................................................... 25

2.1.1 Cc kiu chuyn giao trong h thng 3G WCDMA ........................................ 252.1.2 Cc mc tiu ca chuyn giao ......................................................................... 262.1.3 Cc th tc v php o chuyn giao ................................................................ 27

2.2 Chuyn giao mm (SHO) ....................................................................................... 282.2.1 Nguyn l ca chuyn giao mm .................................................................... 292.2.2 Thut ton chuyn giao mm .......................................................................... 312.2.3 c im ca chuyn giao mm...................................................................... 34

CHNG III : PHN TCH HIU SUT CP NG DN V CP H THNG ...... 373.1 Phn tch hiu sut cp ng dn ......................................................................... 37

3.1.1 Phn tch nhiu hng xung............................................................................... 37a) Nhiu intra-Cell v nhiu inter-Cell ................................................................ 38b) Nhng tc ng ca chuyn giao mm n nhiu hng xung ...................... 42


6/83

Bo co tt nghip Mc lc


3.1.2 S phn b cng sut hng xung ..................................................................... 43a) Phn b cng sut khng c SHO ................................................................... 43b) Phn b cng sut vi SHO ............................................................................ 44

3.1.3 Kt lun ............................................................................................................... 503.2 Phn tch hiu sut cp h thng ............................................................................ 50

3.2.1

li chuyn giao mm hng xung............................................................ 50

a) li chuyn giao mm ................................................................................. 51b) Nhng tc ng i vi li chuyn giao mm ............................................ 54

3.2.2 S chn la v ti chn la Cell ................................................................. 55a) Nguyn l cbn ca cc s chn la Cell (CS) khc nhau ........................ 56b) Nhng tc ng ca cc s chn la Cell khc nhau n li SHO ......... 58

3.2.3 Cc thut ton chuyn giao mm..................................................................... 58a) Cc thut ton SHO khc nhau........................................................................ 59b) Vng SHO ca cc thut ton chuyn giao mm khc nhau ............................ 62

3.2.4 iu khin cng sut hng xung ................................................................. 62a) Phn b cng sut di 3 iu kin iu khin cng sut ................................ 63b) li SHO di nhng tc ng ca iu khin cng sut............................. 65

CHNG IV: CHIN LC IU KHIN CNG SUT TI U TRONG CHUYNGIAO MM......................................................................................................................... 67

4.1 Nguyn l ca cch tip cn mi............................................................................ 674.2 nh gi tnh kh thi .............................................................................................. 68

CHNG V: CHNG TRNH DEMO ............................................................................ 72KT LUN ......................................................................................................................... 73BNG T VIT TT ......................................................................................................... 74PH LC ............................................................................................................................ 77TI LIU THAM KHO .................................................................................................... 79


7/83

Bo co tt nghip Mc lc hnh v


MC LC HNH V

Hnh I.1 S pht trin ca mng di ng ............................................................................ 7

Hnh I.2 L trnh pht trin t 2G n 3G......................................................................... 10Hnh I.3 Tri ph v gii tri ph ..................................................................................... 15Hnh I.4 Cc cng ngh a truy xut................................................................................. 15Hnh I.5 Nguyn l a truy xut tri ph .......................................................................... 16Hnh I.6 Cc v tr in hnh ca RRM trong mng WCDMA .......................................... 18Hnh I.7 Hiu ng gn xa (iu khin cng sut hng ln) ............................................. 19Hnh I.8 B nhiu inter-cell (iu khin cng sut hng xung) ..................................... 20Hnh I.9 Thut ton chung ca iu khin cng sut vng ngoi .......... ............................. 21Hnh I.10 ng cong ti................................................................................................... 22

Hnh II.1 Cc vin cnh ca cc kiu chuyn giao khc nhau ......................................... 26Hnh II.2 Cc th tc chuyn giao .................................................................................. 28Hnh II.3 S so snh gia chuyn giao cng v chuyn giao mm.................................. 30Hnh II.4 Nguyn l chuyn giao mm (trng hp 2 ng) ........................................ 31Hnh II.5 Thut ton chuyn giao mm ca IS-95A ........................................................ 32Hnh II.6 Thut ton chuyn giao mm WCDMA .......................................................... 33Hnh II.7 Gim nhiu hng ln bng cch s dng SHO .............................................. 35Hnh III.1 Nhiu hng ln ............................................................................................. 37Hnh III.2 Nhiu hng xung ........................................................................................ 38Hnh III.3 ,Nhiu inter-Cell hng xung tng i ..................................................... 40Hnh III.4 , T s nhiu inter-Cell v intra-Cell ............................................................. 41Hnh III.5 nhy ca nhiu hng xung tng i vi cc thng s v tuyn ............ 41Hnh III.6 Nhng tc ng ca chuyn giao mm n nhiu hng xung ...................... 42Hnh III.7 ngha ca 1 2 3 vi cc v tr MS khc nhau ............................................. 47Hnh III.8 Hm phn b tch lu ca 1 2 v 3 .............................................................. 48Hnh III.9 Cng sut tng trung bnh i vi v tr ca trm di ng................................ 49Hnh III.10 Cng sut knh lu lng hng xung.......................................................... 49Hnh III.11 Vng chuyn giao mm v vng ph sng hiu qu ca Cell .......................... 51Hnh III.12 S b tr Cell .................................................................................................. 52Hnh III.13 S chn la Cell......................................................................................... 56Hnh III.14 Lu chn la Cell hon ho ....................................................................... 57Hnh III.15 Lu chn la Cell bnh thng................................................................... 58Hnh III.16 Lu thut ton chuyn giao mm IS-95A ................................................... 60Hnh III.17

Lu thut ton chuyn giao mm UTRA .................................................... 61

Hnh III.18 So snh vng SHO ca cc thut ton khc nhau............................................. 62Hnh IV.1 iu khin cng sut hng xung trong Chuyn giao mm ........................... 67Hnh IV.2 Cng sut truyn tng tng i cho cc MS trong chuyn giao mm............. 71Hnh V.1 M hnh chuyn giao ...................................................................................... 72


8/83

Bo co tt nghip Mc lc bng


MC LC BNG

TABLE I.1 Cc thng s k thut ca h thng s th h th 2 ........................................... 8TABLE III.1 Bng lin kt ............................................................................................... 54TABLE IV.1 Cc thng s h thng..................................................................................... 71


9/83

Bo co tt nghip Li m u


LI M U

Nh ta bit, cc u cui di ng cho php thu bao truy xut cc dch vtrong khi ang di chuyn, iu ny c bit thc y s pht trin 1 cch nhanhchng ca ngnh cng nghip mng di ng, v thay i n t mt cng ngh mi

thnh mt ngnh cng nghip ln trong vng t hn hai thp k.Chuyn giao l mt chc nng thit yu i ph vi tnh di ng ca cc

thu bao di ng. So vi chuyn giao cng truyn thng c s dng trong mng di

ng GSM, th chuyn giao mm s dng trong IS-95 v c xut cho mng 3Gc hiu sut tt hn trn c hai cp ng dn v h thng.

Trong hu ht cc phn tch trc y v chuyn giao mm u tp trung vo

hng ln. Tuy nhin, trong cc mng di ng tng lai th hng xung li cc kquan trng i vi dung lng h thng bi tnh bt i xng ca cc dch v mi,

chng hn nh lu lng Internet. Hiu c vn , n n lun n ny s i su

nghin cu cc c tnh ca chuyn giao mm cng nh nhng tc ng ca n ndung lng hay hiu sut hng xung trong mng WCDMA. C th l:

Chng 1: s gii thiu tng quan v mng thng tin di ng

Chng 2 + chng 3: gii thiu v chuyn giao mm v nhng tc ng ca n cp

ng dn v h thng.

Chng 4: s a ra chin lc iu khin cng sut ti u sut trong qu trnhchuyn giao mm.

Trong qu trnh thc hin lun n c th em s khng trnh khi nhng sai st.

Rt mong nhn c s ph bnh, gp ca qu thy c v cc bn. Em xin chnthnh cm n.


10/83

Bo co tt nghip Chng I: Tng quan v mng thng tin di ng


CHNG I: TNG QUAN V MNG THNG TIN DI NG1.1 S pht trin ca mng di ng1.1.1 H thng di ng tng t th h u tin

Nm 1980 bt u k nguyn mng in thoi di ng t bo, v t

truyn thng di ng tri qua nhng thay i ng k v pht trin ln v mt kinh

nghim.Hnh I.2 cho thy s tin trin ca mng di ng.H thng di ng th h u tin s dng phng thc truyn tng t i

vi cc dch v thoi. Nm 1979, h thng di ng u tin trn th gii c avo hot ng bi Nippon Telephone and Telegraph (NTT) Tokyo, Japan.H thng

s dng 600 knh hai chiu trn ph tn 30 MHz bng tn 800 MHz, vi khongcch knh l 25 kHz. 2 nm sau, k nguyn di ng t bo hng ti Chu u. 2ph bin nht ca h thng tng t l Nordic Mobile Telephones (NMT) v TotalAccess Communication Systems (TACS).Nm 1981, h thng NMT-450 c

thng mi ho bi NMT Scandinavia. H thng hot ng di tn 450 MHz v

900 MHz vi bng thng tng cng l 10 MHz. TACS, c ra mt ti Anh vo nm1982, hot ng ti tn s 900 MHz vi bng tn dnh cho mi ng l 25 MHz vbng thng mi knh l 25 kHz. TACS c m rng trin khai vo nm 1985. Ngoi

NMT v TACS, mt s h thng tng t khc cng c gii thiu vo nm 1980trn ton Chu u. V d, c, h thng di ng t bo C-450 , hot ng ti bngtn 450 MHz v 900 MHz (sau ny) , c trin khai vo thng Chn nm 1985. Tt ccc h thng ny cung cp kh nng chuyn vng v chuyn giao nhng mng di ng

t bo li khng cho php lin kt ni gia cc quc gia. y l mt trong nhng khkhn khng th trnh khi ca mng di ng th h u tin. Ti Hoa K, mng in

thoi di ng AMPS (Advanced Mobile Phone System) c a ra vo nm 1982.H thng c phn b mt bng thng 40 MHz trong di tn t 800 n 900 MHz.

Nm 1988, AMPS c b sung thm 10 MHz bng thng v gi l ph m rngExpanded Spectrum (ES).

1.1.2 H thng di ng th h th 2 v giai on 2 +H thng di ng th h th 2 c gii thiu vo cui nhng nm 1980.Cc

dch v d liu tc thp cng nh cc dch v thoi truyn thng c h tr. Cch thng ny s dng k thut truyn dn s ch khng phi truyn dn tng t. Do

vy, so vi h thng di ng th h th nht, hiu sut ph ca th h th 2 cao hn,

dch v d liu v kh nng chuyn vng tt hn. Chu u, h thng ton cu dnhcho truyn thng di ng c tn gi l GSM (Global System for MobileCommunications) c trin khai cung cp mt tiu chun mang tnh thng nht.

iu ny cho php cc dch v khng c ng ni ra khi Chu u bng phngthc chuyn vng quc t. H thng GSM sm nht hot ng bng tn 900 MHz

vi bng thng tng cng l 50 MHz. Sut trong qu trnh pht trin hn 20 nm, cngngh GSM lin tc c ci tin cung cp cc dch v tt hn trn th trng.


11/83



Nhng cng ngh mi tin tin hn c bit n nh l h thng th h 2,5 (2,5G)

u c pht trin da trn nn tng ca h thng GSM gc. Chon nay, nh l mt

h thng di ng ln nht trn ton th gii, GSM l cng ngh ca s la chn tihn 190 quc gia vi khong 787.000.000 thu bao.

Hnh I.1 S pht trin ca mng di ngTi Hoa K, c 3 dng pht trin ca h thng di ng t bo s. H thng

u tin, c gii thiu vo nm 1991, l IS-54 (North America TDMA DigitalCellular), trong c mt phin bn mi h tr cc dch v b sung (IS 136) cgii thiu vo nm 1996. Trong , IS-95 c trin khai vo nm 1993. S unhim truyn thng lin bang M Federal Communications Commision (FCC) cngbn u gi mt khi ph mi trong di tn 1900 MHz (PCS), cho php GSM 1900nhp vo th trng M. Nht Bn, h thng Personal Digital Celluar (PDC), banu c bit n nh l JDC (Japanese Digital Cellular) bc u c nh nghavo nm 1990. Dch v thng mi c bt u bi NTT vo nm 1993 bngtn 800 MHz v nm 1994 bng tn 1,5 GHz. Bng I.1 cho thy cc thng s kthut ca bn h thng di ng s th h th hai in hnh.


12/83



GSM IS-136 IS-95 PDC

a truy xut TDMA TDMA CDMA TDMA

iu ch GMSK

/4-DQPSK

Coherent /4-DQPSK

Coherent 8-PSK

QPSK/O-QPSK /4-DQPSK

rng knh 200 kHz 30 kHz 1.25 kHz 25 kHzTc bit 270.833 kbit/s 48.6 kbit/s(/4-DQPSK)

72.9 kbit/s(8-PSK)

1.2288 Mchip/s 42 kbit/s

di khung 4.615 ms 40 ms 20 ms 20 ms

S khe/khung 8/16 6 1 3/6

Bng tn

(ln/xung)

(MHz)

880 915/935 960

1720-1785/1805-1880

1930-1990/1850-1910

824-849/869-894

1930-1990/1850-1910

824-849/869-894

1930-1990/1850-1910

810 826/910 956

1429-1453/1477-1501

Tc d liu

cho php ti a

(kbit/s)

HSCSD: 57.6

GPRS: 115.2-182.4

IS-136+: 43.2 IS 95A: 14.4

IS 95B: 115.2

28.8

Chuyn giao Cng Cng Mm Cng

TABLE I.1 Cc thng s k thut ca hthng s th h th 2Ngy nay, h thng di ng t bo s th h th hai vn chim u th trong

ngy cng nghip di ng trn ton th gii. Tuy nhin, h ang tin trin theo hng

h thng th h th ba (3G) v nhng nhu cu v lu lng di ng v s xut hin cacc loi hnh dch v mi. Cc h thng mi, chng hn nh l HSCSD (High Speed

Circuit Switched Data), GPRS (General Packet Radio Service), v IS 95B, thngc gi chung l th h 2,5 (2,5G).

HSCSD, GPRS v EDGE tt c u da trn nn tng ca h thng GSM banu. HSCSD l s ci tin u tin ca giao tip v tuyn GSM: n b cc khe thigian GSM cho ra mt tc d liu ti a v mt l thuyt l 57,6 Kbit/s ( 4

bit/s). HSCSD cung cp c 2 loi hnh dch v i xng v bt i xng v nc trin khai tng i d dng. Tuy nhin, HSCSD khng d dng v mt gi ccnh tranh.

Sau HSCSD, GPRS l bc pht trin tip theo ca giao tip v tuyn GSM.Ngoi b cc khe thi gian, th 4 s m ho knh mi c xut. GPRS cungcp always on cc gi d liu chuyn mch gi vi bng thng ch c s dng khi

cn thit. V vy, GPRS cho php GSM truy xut Internet vi hiu sut ph cao bngcch s dng cc khe thi gian khc nhau gia cc User. V mt l thuyt, GPRS c


13/83



th h tr tc d liu ln ti 160 Kbit/s (hin ti GPRS cung cp 40 Kbit/s). Trinkhai GPRS khng d dng nh l HSCSD v mng li cn phi c nng cp tt.

EDGE s dng cu trc v tuyn GSM v khung TDMA nhng vi mt s

iu ch mi, 8QPSK, thay v GMSK, qua tng gp 3 ln so vi GSM thng quavic s dng cng mt bng thng. EDGE kt hp vi GPRS s cung cp tc d

lieu cho mi User ln n 384 Kbit/s.1.1.3 H thng di ng th h th 3 v cao hn na

H thng thng tin di ng chuyn t th h 2 sang th h 3 qua mt giai on

trung gian l th h 2,5 s dng cng ngh TDMA trong kt hp nhiu khe hocnhiu tn s hoc s dng cng ngh CDMA trong c th chng l n ph tn ca thh hai nu khng s dng ph tn mi, bao gm cc mng c a vo s dng

nh: GPRS, EDGE v CDMA2000-1x. th h th 3 ny cc h thng thng tin di

ng c xu th ho nhp thnh mt tiu chun duy nht v c kh nng phc v tc bit ln n 2 Mbit/s. phn bit vi cc h thng thng tin di ng bng hp hin

nay, cc h thng thng tin di ng th h 3 gi l cc h thng thng tindi ng bngrng.

Nhiu tiu chun cho h thng thng tin di ng th h 3 IMT-2000 c

xut, trong 2 h thng W-CDMA v CDMA2000 c ITU chp thun v avo hot ng trong nhng nm u ca nhng thp k 2000. Cc h thng ny us dng cng ngh CDMA, iu ny cho php thc hin tiu chun ton th gii chogiao din v tuyn ca h thng thng tin di ng th h 3.

- W-CDMA (Wideband Code Division Multiple Access) l s nng cp ca cc

h thng thng tin di ng th h 2 s dng cng ngh TDMA nh: GSM, IS -136.

- CDMA2000 l s nng cp ca h thng thng tin di ng th h 2 s dngcng ngh CDMA: IS-95.


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Hnh I.2 L trnh pht trin t 2G n 3GYu cu i vi h thng thng tin di ng th h 3:

Thng tin di ng th h th 3 xy dng trn c s IMT -2000 c a vo

phc v t nm 2001. Mc ch ca IMT-2000 l a ra nhiu kh nng mi nhngcng ng thi bo m s pht trin lin tc ca thng tin di ng th h 2.

Tc ca th h th ba c xc nh nh sau:

- 384 Kb/s i vi vng ph sng rng.

- 2 Mb/s i vi vng ph sng a phng.

Cc tiu ch chung xy dng h thng thng tin di ng th h ba (3G):

- S dng di tn quy nh quc t 2GHz nh sau:

+ ng ln : 1885-2025 MHz.

+ ng xung : 2110-2200 MHz.

- L h thng thng tin di ng ton cu cho cc loi hnh thng tin v

tuyn:

+ Tch hp cc mng thng tin hu tuyn v v tuyn.

+ Tng tc vi mi loi dch v vin thng.

- S dng cc mi trng khai thc khc nhau: trong cng s,ngoi

ng trn xe, v tinh.

- C th h tr cc dch v nh:


15/83



+Mi trng thng tin nh o (VHE: Virtual Home Environment)

trn c s mng thng minh, di ng c nhn v chuyn mng

ton cu.

+m bo chuyn mng quc t.

+m bo cc dch v a phng tin ng thi cho thoi, s liu

chuyn mch theo knh v s liu chuyn mch theo gi.- D dng h tr cc dch v mi xut hin.

a) Cu trc mng thng tin di ng th h th 3 UMTSH thng W-CDMA c xy dng trn c s mng GPRS. V mt chc nng

c th chia cu trc mng W-CDMA ra lm hai phn : mng li (CN ) v mng truynhp v tuyn (UTRAN ), trong mng li s dng ton b cu trc phn cng camng GPRS cn mng truy nhp v tuyn l phn nng cp ca W-CDMA. Ngoi ra hon thin h thng, trong W-CDMA cn c thit b ngi s dng (UE) thc hin

giao din ngi s dng vi h thng. T quan im chun ha, c UE v UTRAN

u bao gm nhng giao thc mi c thit k da trn cng ngh v tuynWCDMA, tri li mng li c nh ngha hon ton da trn GSM. iu ny chophp h thng W-CDMA pht trin mang tnh ton cu trn c s cng ngh GSM.

Cu trc ca UMTS

UE (User Equipment)

Thit b ngi s dng thc hin chc nng giao tip ngi s dng vi h thng.UE gm hai phn :


16/83


17/83



- Giao din IU : Giao din ny ni UTRAN vi CN , n cung cp cho cc nh khaithc kh nng trang b UTRAN v CN t cc nh sn xut khc nhau.

- Giao din IUr : Cho php chuyn giao mm gia cc RNC t cc nh sn xut

khc nhau.

- Giao din IUb : Giao din cho php kt ni mt nt B vi mt RNC. IUb c

tiu chun ha nh l mt giao din m hon ton.b) H thng thng tin di ng th h tip theo:

H thng thng tin di ng th h 3 sang th h 4 qua giai on trung gian l

th h 3,5 c tn l mng truy nhp gi ng xung tc cao HSDPA. Th h 4 lcng ngh truyn thng khng dy th t, cho php truyn ti d liu vi tc ti a

trong iu kin l tng ln ti 1 cho n 1.5 Gb/giy. Cng ngh 4G c hiu lchun tng lai ca cc thit b khng dy. Cc nghin cu u tin ca NTT

DoCoMo cho bit, in thoi 4G c th nhn d liu vi tc 100 Mb/giy khi dichuyn v ti 1 Gb/giy khi ng yn, cho php ngi s dng c th ti v truyn ln

hnh nh ng cht lng cao. Chun 4G cho php truyn cc ng dngphng tintruyn thng ph bin nht, gp phn to nn cc nhng ng dng mnh m cho cc

mng khng dy ni b (WLAN ) v cc ng dng khc.

Th h 4 dng k thut truyn ti truy cp phn chia theo tn s trc giaoOFDM, l k thut nhiu tn hiu c gi i cng mt lc nhng trn nhng tn skhc nhau. Trong k thut OFDM, ch c mt thit b truyn tn hiu trn nhiu tn sc lp (t vi chc cho n vi ngn tn s). Thit b 4G s dng my thu v tuyn

xc nhn bi phn mm SDR (Software - Defined Radio) cho php s dngbngthng hiu qu hn bng cch dng a knh ng thi. Tng i chuyn mch mng

4G ch dng chuyn mch gi, do , gim tr thi gian truyn v nhn d liu.1.2 Tng quan v cng ngh CDMA1.2.1 Nguyn l tri ph (CDMA)

H thng truyn thng s c thit k ti a ho dung lng s dng.Tnguyn tc dung lng knh ca Shannon c biu din (1.1), hin nhin rng

dung lng knh c th c tng ln bng cch tng bng thng knh.

(1.1)

Trong Bl bng thng (Hz), Cl dung lng knh (bit/s), S l cng sut tnhiu v N l cng sut nhiu.Do , i vi mt t s S/N c th (Signal to Noiseratio:SNR), dung lng s c tng ln nu bng thng s dng truyn thng tinc tng ln.CDMA l mt cng ngh tri ph ca tn hiu bng hp thnh tn hiu

bng rng trc khi truyn.CDMA thng c gi l Spread-Spectrum MultipleAccess (SSMA).

)1(log. 2 NSBC


18/83



T s ca bng thng truyn v bng thng d liu c gi l li x l Gp

(cng c gi l h s tri ph):

Hoc (1.2)

Trong Bt l bng thng truyn, Bil bng thng ca tn hiu mang thng tin,B l bng thng RF v R l tc thng tin d liu. T s S/N lin quan n t s

Ec/N0, trong Eb l nng lng ca 1 bit, v N0 l mt ph cng sut nhiu, iuny dn n:

(1.3)

Do vy, i vi yu cu Eb/N0 c nh, li x l cao th t s S/N phi nh.Trong h thng CDMA u tin IS 95, bng thng truyn l 1,25 MHz. Trong hthng WCDMA, bng thng truyn l khong 5 MHz.

Trong CDMA, mi User c gn mt chui m duy nht (m tri ph) cs dng tri tn hiu bng hp thnh tn hiu bng rng trc khi c truyn i.

i vi my thu, do bit c chui m i vi mi User nn n c th gii m phc

hi li d liu ban u.

1.2.2 Tri ph v gii tri phTri ph v gii tri ph l nhng hot ng c bn nht ca h thng

DS-CDMA, ca ra hnh I.3. D liu ngi dng y c gi s l iu chBPSK vi tc chui bit l R. Nguyn l tri ph l nhn mi bit d liu ngi dng

vi mt chui m chu k n bit, c gi l chips. y, n=8, do h s tri ph l8.D liu sau khi tri ph c tc l 8 R v n c cng dng ngu nhin ging nh

l m tri ph.S gia tng tc d liu bng h s 8 tng ng vi s m rng phang s dng ca tn hiu d liu ngi dng. Tn hiu bng rng sau s c

truyn i thng qua mt knh v tuyn n u cui nhn.

i

t

pB

BG

R

BGp

p

bb

GI

E

BI

RE

N

S 1

00


19/83



Hnh I.3 Tri ph v gii tri phTrong gii tri ph, tn hiu cao tn nhn c t my thu s c nhn tr li

vi mt chui m ging ht nh trong qu trnh tri ph.Nh c hin th trn hnh,d liu ngi dng ban u c phc hi hon ton.

1.2.3 a truy xutMt mng truyn thng di ng l mt h thng a ngi dng, trong mt s

lng ln ngi s dng cng chia s chung mt ti nguyn vt l truyn v nhn

thng tin.Kh nng a truy xut l mt trong nhng thnh phn c bn. Vic tri phtn hiu c truyn cho mt tnh kh thi v a truy xut ca h thng CDMA. Hnh

I.4 a ra ba cng ngh a truy xut khc nhau l : CDMA, TDMA, FDMA

Hnh I.4 Cc cng ngh a truy xut

Trong FDMA (Fequency Devision Multiple Access), cc tn hiu ca cc Userkhc nhau c truyn trong mi knh khc nhau vi mt tn s iu ch khc nhau.

Trong TDMA (Time Division Multiple Access), tn hiu ca cc User khc nhau ctruyn trong cc khe thi gian khc nhau. Vi hai cng ngh trn, s User ti a c thchia s cc knh vt l ng thi l c nh. Tuy nhin, trong CDMA, tn hiu ca ccUser khc nhau c truyn trn cng mt bng tn ti cng mt thi gian. Mi tn

hiu ca User ny nh l nhiu i vi tn hiu ca User khc v do dung lng cah thng CDMA c mi lin quan cht ch n cp nhiu: khng c s lng ti a


20/83



c nh, do , dung lng gii hn mm c a vo s dng. Hnh I.5 a ra mtv d v cch 3 User c th truy xut ng thi trong mt h thng CDMA.

Ti u thu, User 2 thc hin gii tri ph tn hiu thng tin ca n tr li dng

tn hiu bng hp,nhng cc User khc khng lm c. iu ny l bi mi tngquan cho gia m ca User ch nh v m ca cc User khc l rt nh: mch d ch

t cng sut ca tn hiu ch nh v mt phn nh tn hiu t cc User khc votrong bng thng thng tin.

li x l, cng vi bn cht bng rng ca qu trnh x l a ra nhng

li ch ca h thng CDMA, nh l dung lng mm v hiu sut ph cao.

Tuy nhin, tt c nhng li ch ny i hi vic s dng chuyn giao mm v

iu khin cng sut cht ch trnh tn hiu ca mt User che khut tn hiu caUser khc.iu khin cng sut v chuyn giao mm s c gii thch chi tit hn

cc phn sau.

Hnh I.5 Nguyn l a truy xut tri ph1.2.4 Cc c im chnh ca cng ngh WCDMA

WCDMA (Wideband CDMA) l cng ngh thng tin di ng th h ba gip

tng tc truyn nhn d liu cho h thng GSM bng cch d ng k thut CDMAhot ng bng tn rng thay th cho TDMA. Trong cc cng ngh thng tin di ng

th h ba th WCDMA nhn c s ng h ln nht nh vo tnh linh hot ca lpvt l trong vic h tr cc kiu dch v khc nhau c bit l dch v tc bit thp

v trung bnh.

WCDMA c cc c im c bn sau :

- L h thng a truy cp phn chia theo m tri ph trc tip, c tc

bitln cao (ln n 2 Mbps).

- Tc chip 3,84 Mcps vi rng sng mang 5 MHz, do h trtc d liu cao em li nhiu li ch nh li a phn tp.


21/83



- H tr tc ngi s dng thay i lin tc. Mi ngi s dngcung cp mt khung, trong khung tc d liu gi c nh

nhng tc c th thay i t khung ny n khung khc.

- H tr hai m h nh v tuyn FDD v TDD. Trong m hnh FDDsng mang 5 MHz s dng cho ng ln v ng xung, cn trong

m hnh TDD sng mang 5 MHz chia x theo thi gian gia ngln v ng xung.

- WCDMA h tr hot ng khng ng b ca cc trm gc, do

d dng pht trin cc trm gc va v nh.

- WCDMA s dng tch sng c tham chiu n sng mang da trn

knh hoa tiu, do c th nng cao dung lng v vng ph.

- WCDMA c thit k d dng nng cp hn cc h thng CDMAnhtch sng a ngi s dng, s dng anten thng minh nng

cao dung lng v vng ph.

- WCDMA c thit k tng thch vi GSM m rng vng phsng v dung lng ca mng.

- Lp vt l mm do d thch hp c tt c thng tin trn mt sngmang.

- H s ti s dng tn s bng 1

- H tr phn tp pht v cc cu trc thu tin tin.

Nhc im chnh ca W_CDMA l h thng khng cho php trong bng TDDpht lin tc cng nh khng to iu kin cho cc k thut chng nhiu cc mi

trng lm vic khc nhau.H thng thng tin di ng th h ba WCDMA c th cung cp cc dch v vi

tc bit ln n 2 Mbps. Bao gm nhiu kiu truyn dn nh truyn dn i xng vkhng i xng, thng tin im n im v thng tin a im. Vi khnng , cc

h thng thng tin di ng th h ba c th cung cp d dng cc dch v mi nh:in thoi thy h nh, ti d liu nhanh, ngoi ra n cn cung cp cc dch v a

phng tin khc.

1.3 Qun l ti nguyn v tuyn (RRM: Radio Resource Management)1.3.1 RRM trong mng di ng

Radio Resource Management (RRM) trong mng 3G c trch nhim ci thinvic s dng cc ngun ti nguyn giao tip khng gian.Cc mc tiu ca RRM c thc tm tt nh sau:

m bo QoS i vi cc ng dng khc nhau.

Duy tr vng ph sng theo k hoch.

Ti u ho dung lng h thng.


22/83



Trong mng 3G, tin phn b (pre-allocating) ti nguyn v qu kch thc(over-dimensioning) mng l khng kh thi bi v khng d on trc c s cn

thit v cc yu cu khc nhau ca cc dch v khc nhau. V vy, qun l ti nguynv tuyn bao gm 2 phn: cu hnh ti nguyn v tuyn v ti cu hnh. Cu hnh ti

nguyn v tuyn c trch nhim phn b ti nguyn mt cch hp l khi c cc yucu mi vo h thng mng n nh v khng ri vo tnh trng qu ti. Nhng, s

tc nghn c th xy ra trong mng 3G bi v tnh di ng ca ngi dng, ti cu hnhti nguyn v tuyn chu trch nhim phn b li ti nguyn trong mng khi ti tngln hoc tt nghn bt u xut hin. N c trch nhim iu chnh li h thng qu ti

mt cch nhanh chng v iu khin tr li ti mc tiu.

1.3.2 Chc nng ca RRMQun l ti nguyn v tuyn c th c chia thnh cc chc nng l iu khincng sut, chuyn giao, iu khin thm nhp v iu khin ti. Hnh I.6 th hin ccv tr in hnh ca RRM trong mng WCDMA.

Hnh I.6 Cc v tr in hnh ca RRM trong mng WCDMAa) iu khin cng sut (Power Control)

iu khin cng sut l mt yu t cn thit trong tt c cc h thng di ngbi cc vn v pin v cc l do an ton, nhng trong h thng CDMA, iu khincng sut l iu cn thit bi bn cht nhiu c gii hn trong h thng CDMA.

Trong GSM, iu khin cng sut chm (tn s xp x 2 Hz) c trinkhai.Trong IS-95 iu khin cng sut nhanh vi tn s 800 Hz c h tr ngln, nhng ng xung, mt vng iu khin cng sut tng i chm (xp x 50Hz) iu khin cng sut truyn i.Trong WCDMA, iu khin cng sut nhanh vitn s 1,5 kHz c h tr trong c 2 ng ln v ng xung. iu khin cng

sut nhanh v cht ch l mt trong nhng kha cnh quan trng ca h thngWCDMA.


23/83



Cc l do s dng iu khin cng sut l khc nhau i vi ng ln v

ng xung. Cc mc tiu ca iu khin cng sut c th c tm tt nh sau:

Khc phc hiu ng gn xa ng ln

Ti u ho dung lng h thng bng cch iu khin nhiu

Ti a ho tui th pin ca u cui di ng

Hnh I.7 cho thy vn gn xa hng ln. Cc tn hiu t cc MS (mobilestation) khc nhau c truyn i ng thi trn cng mt bng tn trong h thngWCDMA. Nu khng c iu khin cng sut, tn hiu n t mt MS gn BS nhts c th chn cc tn hiu t cc MS khc ang xa hoc rt xa BS (Base station).

Trong trng hp xu nht mt MS cng sut qu cao c th chn ton b cc MStrong mt cell. Gii php a ra l s dng iu khin cng sut m bo rng cctn hiu n t cc u cui khc nhau c cng mt cng sut v SIR (Signal-to-interference Ratio) khi chng n trm gc BS.

Hnh I.7Hiu ng gn xa (iu khin cng sut hng ln)

hng xung, khng c vn gn xa trong vin cnh mt MS nh hng

n nhiu MS khc.iu khin cng sut c trch nhim b nhiu inter-cell m cctrm di ng phi chu, c bit l ranh gii gia cc cell gn nhau nh trong hnh I.8.

Hn na, iu khin cng sut hng xung c nhim v gim thiu nhiu tng gi gi tr QoS cho php.


24/83



Hnh I.8 B nhiu inter-cell (iu khin cng sut hng xung)Trong hnh I.8, mobile 2 phi chu nhiu inter-cell nhiu hn mobile 1. Do ,

p ng cng mt mc tiu cht lng, phn cng sut thm vo cn thit phic phn b cho cc knh hng xung gia BS v mobile 2.

C 3 kiu iu khin cng sut trong h thng WCDMA l: iu khin cngsut vng h, iu khin cng sut vng ng v iu khin cng sut vng ngoi.

iu khin cng sut vng h

iu khin cng sut vng h c s dng ch FDD UMTS dnh chothit lp cng sut ban u cho di ng.Trm di ng c tnhsuy hao ng truyn

gia trm gc v trm di ng bng cch s dng mt mch iu khin li t ng(AGC:Automatic Gain Control) o cng tn hiu nhn c.Theo c tnh suyhao ng truyn , trm di ng c th quyt nh cng sut truyn hng ln. iukhin cng sut vng h c hiu qu trong h thng TDD bi v hng ln v hng

xung l i ng, nhng n khng phi rt hiu qu cho h thng FDD bi cc knhhng ln v hng xung hot ng cc di tn khc nhau v fading Rayleigh

ng ln v ng xung l c lp nhau. V vy, iu khin cng sut vng hc

chnh xc khng cao.V l l do ti sao n ch c s dng nh l thit lp

cng sut ban u trong h thng FDD.

iu khin cng sut vng kn

iu khin cng sut vng kn, cng cn c gi l iu khin cng sutnhanh trong h thng WCDMA, c nhim v iu khin cng sut truyn ca MS

(hng ln) hoc ca trm gc (hng xung) chng li fading ca knh v tuynv p ng SIR mc tiu thit lp bi vng ngoi. Ly v d, hng ln, trm gc so

snh SIR nhn c t MS vi SIR mc tiu. Nu SIR nhn c ln hn mc tiu,BS s truyn mt lnh TPC 0 n MS thng qua knh iu khin c ch nh

hng xung. Cn nu SIR nhn c nh hn mc tiu, BS s truyn mt lnh TPC1 n MS.Bi v tn s ca iu khin cng sut vng kn l rt ln nn n c th b

fading nhanh cng nh fading chm.Mt v d khc hng xung, MS s cn c vo


25/83



SIR nhn c t BS v s iu khin cng sut t trm gc, n s iu khin cngsut pht ca n mt cch thch hp.

iu khin cng sut vng ngoi

iu khin cng sut vng ngoi l cn thit duy tr cht lng ca truynthng ti mc yu cu bng cch thit lp gi tr mc tiu cho iu khin cng sut

vng kn. N nhm mc ch cung cp cht lng yu cu l khng xu v khngtt. Tn s ca iu khin cng sut vng ngoi in hnh l t 10-100 kHz. Hnh I.9th hin cc thut ton chung ca iu khin cng sut vng ngoi.

Hnh I.9 Thut ton chung ca iu khin cng sut vng ngoiiu khin cng sut vng ngoi so snh cht lng thuc vi cht lng

yu cu.Thng thng cht lng c nh ngha nh l mt BER (Bit Error Rate)

hoc FER (Fame Error Rate) mc tiu nht nh. Mi quan h gia SIR mc tiu vcht lng mc tiu ph thuc vo tc di ng v cu hnh a ng. Nu chtlng nhn c l tt, iu c ngha l SIR mc tiu hin ti cao m bo

QoS yu cu. gim thiu khong tha, SIR mc tiu s c gim. Tuy nhin, nucht lng thu c xu hn cht lng yu cu, SIR mc tiu cn phi c tng ln

m bo yu cu v QoS.

b) iu khin chuyn giao (Handover control)Chuyn giao l mt phn cn thit ca cc h thng truyn thng di ng t

bo. Tnh di ng l nguyn nhn dn n nhng bin ng v cht lng ng dn

v mc nhiu trong h thng di ng t bo, i khi i hi mt User c th phithay i trm gc dch v ca n. V s thay i ny c gi l Chuyn Giao(Handover). Phn sau s trnh by chi tit hn v vn ny.

c) iu khin thm nhp (Admission control)Nu ti giao tip khng gian c php tng qu mc th vng ph sng ca

Cell s gim xung di gi tr mong mun ( cn c gi l t bo th) v QoS cacc kt ni ang tn ti s khng th m bo. L do ca hin tng t bo th l v

Cht lng nhnc tt hn cht

lng yu cung Sai

Tng SIR mc tiu Gim SIR mc tiu


26/83


c tnh gii hn nhiu ca h thng CDMA. Do , trc khi nhn mt kt ni mi,iu khin thm nhp cn phi kim tra rng vic nhn kt ni mi s khng hi sinh

i vng ph sng mc tiu hoc QoS ca cc kt ni tn ti. iu khin thm nhps chp nhn hoc t chi mt yu cu thit lp mt ng bao truy xut v tuyn

trong mng truy xut v tuyn. Chc nng ca iu khin thm nhp c t RNC,ni m c th thuc thng tin ti ca nhiu Cell.

Gii thut iu khin thm nhp c tnh s tng ln ca ti thit lp ngbao trong mng truy xut v tuyn. c tnh ti c a vo trong c 2 hng ln v

hng xung. ng bao yu cu ch c th c chp nhn nu iu khin thmnhp trong c 2 hng chp nhn n, ngc li n s b t chi bi nhiu th m vo

mng l qu mc.

Ni chung, cc chin lc iu khin thm nhp c th c chia thnh 2 loi l: chin lc iu khin thm nhp da trn cng sut bng rng v chin lc

iu khin thm nhp da trn s lng a vo.

Hnh I.10 a ra iu khin thm nhp da trn cng sut bng rng.

Hnh I.10ng cong tiNgi s dng mi s khng c chp nhn nu kt qu mi ca mc nhiu

tng cao hn gi tr ngng:

(1.4):

:

_

_

thresholdoldtotal

thresholdoldtotal

IIIadmid

IIIreject


27/83



Gi tr ngng ging nh l mc tng ln nht ca nhiu hng ln v c thc thit lp bi quy s hoch mng v tuyn.

Trong chin lc iu khin thm nhp da trn s lng a vo, mt User

yu cu mi s khng c chp nhn vo mng truy xut v tuyn nu kt qu mica ti tng cao hn gi tr ngng:

(1.5)

Cn lu rng chin lc iu khin thm nhp c p dng ring r chohng ln v hng xung, cc chin lc iu khin thm nhp khc nhau c thc s dng trong mi hng.

d) iu khin Ti (iu khin tc nghn)Mt nhim v quan trng ca chc nng qun l ti nguyn v tuyn l chc

chn rng h thng khng b qu ti v vn n nh. Nu h thng ng mc tiu, v

iu khin thm nhp lm vic tt th tnh trng qu ti s him khi xy ra. Tuy nhin,trong mng di ng, t nh trng qu ti mt vi ni l khng th trnh khi bi ti

nguyn v tuyn khng th c phn b trc trong mng. Khi gp phi tnh trngqu ti th iu khin ti (cng c gi l iu khin tc nghn) s tr li h thng

mt cch nhanh chng v iu khin tr li t nh trng ti mc tiu, c nh nghabi s quy hoch mng v tuyn. Cc cng vic iu khin ti gim bt hoc cn

bng ti c lit k bn di:

T chi cc lnh cp ngun hng xung nhn c t MS.

Gim t s Ec/N0 mong mun hng ln c s dng bi iu khin cng sutnhanh hng ln.

Thay i kch c vng chuyn giao mm cha nhiu User hn.

Chuyn giao n mt sng mang WCDMA khc.(inter-frequency handover)

Chuyn giao n mng chng lp khc(mng UMTS hoc mng GSM khc)

Gim tc bit ca ngi s dng thi gian thc, v d m ho thoi AMR.

Gim lu lng d liu gi vo (dch v khng thi gian thc).

Rt cuc gi trong cch iu khin.

Hai cng vic u tin trong danh sch l 2 thao tc nhanh c thc hin trongBS. 2 thao tc c th t trong 1 khe thi gian,vi tn s 1,5 kHz v cung cp utin cho cc dch v khc nhau. Gii php th 3, thay i kch c vng chuyn giaomm c bit hu dng trong mng gii hn hng xung v s c tho lun r hn cc chng sau.

Cc thao tc iu khin ti khc c trng chm hn.Chuyn giao inter-

frequency v chuyn giao inter-system c th khc phc t nh trng qu ti bng cch

thresholdoldtotal

thresholdoldtotal

Ladmid

Lreject

_

_

:

:


28/83



cn bng ti.Thao tc cui cng l rt User thi gian thc (thoi hoc User d liuchuyn mch knh) gim ti. Cng vic ny ch c a vo nu ti ca ton b

mng vn rt cao ngay c khi a vo cc thao tc iu khin ti khc gim quti. Giao tip khng gian WCDMA v s gia tng d kin ca lu lng khng thi

gian thc trong mng th h th 3 a ra mt s la chn ln v cc thao tc c th x l tnh trng qu ti, v v vy vic gim ti bng cch thc hin rt User thi gian

thc l rt him khi.


29/83

Bo co tt nghip Chng II: Chuyn giao trong h thng 3G WCDMA


CHNG II: CHUYN GIAO TRONG H THNG 3G WCDMA

2.1 Tng quan v chuyn giao trong mng di ngTrong mng di ng cc thu bao c th truy nhp dch v khi ang di chuyn

hay ni cch khc mng di ng cung cp tnh t do cho thu bao trong mt phm di

ng nht nh. Tuy nhin, tnh t do ny mang n s khng chc chn trong hthng di ng. Tnh di ng ca cc thu bao l nguyn nhn dn n nhng bin ngtrong c cht lng ng dn v mc nhiu, i khi i hi rng mt thu bao c

th phi thay i trm gc dch v ca n. V thao tc ny c gi l chuyn giao(Handover:HO).

Chuyn giao l mt thnh phn thit yu i ph vi tnh di ng ca thu bao. N m bo tnh lin tc ca cc dch v khng dy khi thu bao di ng dichuyn qua cc ranh gii t bo.

Trong h thng di ng t bo th h th nht nh AMPS, chuyn giao l tng

i n gin. Trong h thng di ng th h th 2 nh GSM v PACS th chuyn giaoc a ln mt mc cao hn nhiu h nh thc bao gm cc gii thut c sdng. Phc tp hn, cc th tc quyt nh chuyn giao v x l tn hiu c tchhp trong nhng h thng ny v s tr hon quyt nh chuyn giao cng c gimthiu ng k. T lc cng ngh CDMA c gii thiu, mt tng khc c

xut ci tin qu tr nh chuyn giao, l chuyn giao mm v y l cng victrng tm trong lun n ny.

2.1.1 Cc kiu chuyn giao trong h thng 3G WCDMAC 4 kiu chuyn giao khc nhau trong mng di ng WCDMA. l:

Chuyn giao trong cng mt h thng ( Intra-system HO )

Chuyn giao trong cng h thng c th c chia thnh chuyn giao cng tn

s v chuyn giao khc tn s. Chuyn giao cng tn s xut hin gia cc cell thuccng sng mang WCDMA. Chuyn giao khc tn s xut hin gia cc cell hot ng

trn cc tn s sng mang khc nhau.

Chuyn giao ngoi h thng ( Inter-system HO )

Chuyn giao ngoi h thng xut hin gia cc Cell thuc 2 cng ngh truyxut v tuyn (RAT) khc nhau hoc cc ch truy xut khc nhau. Trng hp

c mong i thng gp nht trong kiu th nht l gia h thng WCDMA vGSM/EDGE. Chuyn giao gia cc h thng CDMA khc nhau cng thuc kiuchuyn giao ny. Ly mt v d v chuyn giao gia cc ch truy xut khc nhau l gia UTRA FDD v UTRA TDD.

Chuyn giao cng ( Hard Handover:HHO )


30/83



Chuyn giao cng l mt th loi ca cc th tc chuyn giao, trong tt ccc kt ni c ca mt trm di ng c gii phng trc khi mt kt ni mi c

thit lp.i vi cc knh yu cu thi gian thc th n c ngha l ngt mt kt ningn ca knh, cn i vi cc knh khng yu cu thi gian thc th HHO c ngha l

khng tn hao. Chuyn giao cng c th t trong kiu chuyn giao cng tn s hockhc tn s.

Chuyn giao mm ( SHO ) v chuyn giao mm hn ( Softer HO )

Chuyn giao mm l chuyn giao gia hai BS khc nhau, cn chuyn giao mm

hn l chuyn giao gia t nht 2 sector ca cng mt BS. Trong sut qu trnh chuyngiao mm, MS giao tip mt cch tc th vi hai (chuyn giao haing) hoc nhiu

cell ca cc BS khc nhau thuc cng RNC (Intra-RNC) hoc cc RNC khc nhau(Inter-RNC). Trn ng xung my di ng nhn hai tn hiu vi t s kt hp ln

nht; ng ln, knh m ho di ngc pht hin bi c hai BS (chuyn giao haing), v c gi n RNC cho vic la chn kt hp. Hai vng iu khin cng

sut tch cc tham gia vo qu trnh chuyn giao mm, mi vng cho mt BS. Trongtrng hp chuyn giao mm hn, MS c iu khin t nht bi hai sector ca cng

BS, do RNC khng c tham gia v ch c mt vng iu khin cng sut tchcc. Chuyn giao mm v mm hn ch s dng mt sng mang, do chng l cc

qu trnh chuyn giao trong cng mt tn s.

Hnh II.1 cho thy mt vi vin cnh ca cc loi chuyn khc nhau.

Hnh II.1Cc vin cnh ca cc kiu chuyn giao khc nhau2.1.2 Cc mc tiu ca chuyn giao

Chuyn giao c th c bt u trong 3 cch khc nhau l: bt u t thu

bao di ng, bt u t mng v h tr thu bao.


31/83



Bt u t thu bao: thu bao thc hin cc php o v cht lng, lachn trm gc tt nht, v chuyn mch, vi siu phi ca mng. Kiu

chuyn giao ny thng c kch hot bi cc lin kt km cht lngc o t thu bao.

Bt u t mng: Trm gc thc hin cc php o v bo co v RNC

quyt nh c nn chuyn giao hay khng. Ngoi iu khin ng dn v tuyn, chuyn giao bt u t mng cn c thc hin bi nhng l do

khc hn, v d nh iu khin s phn phi lu lng gia cc Cell.Chng hn nh chuyn giao v l do lu lng c iu khin bi trmgc (TRHO). Nu ti ca Cell ngun vt qu mc cho php, v ti camt Cell ln cn thp hn mt mc cho php khc, th khi Cell ngun s

thu hp vng ph sng ca n, chuyn giao mt s lu lng n Cell lncn. V vy, t l chn tng th c th gim, dn n vic s dng tinguyn Cell tt hn.

H tr thu bao: y mng v thu bao u thc hin cc php o. Thubao bo co cc kt qu o lng t nhng trm gc gn v mng s

thc hin quyt nh c nn chuyn giao hay khng.

Cc mc tiu ca chuyn giao c th c tm tt nh sau:

m bo tnh lin tc ca cc dch v khng dy khi cc thu bao ding di chuyn qua cc ranh gii ca Cell.

Gi QoS c yu cu

Gim ti a mc nhiu ca ton h thng

Chuyn vng gia cc mng khc nhau Phn phi ti t cc khu vc im nng.(Cn bng ti)

Cc yu t c th c s dng khi xng qu trnh chuyn giao c l:

cht lng ng dn (hng ln hoc hng xung), s thay i dch v, thay i tc, v cc l do lu lng hoc s can thip ca O&M (Operation and Maintenance).

2.1.3 Cc th tc v php o chuyn giaoTh tc chuyn giao c th c chia thnh ba giai on: o lng, quyt nh

v thc hin, c minh ho trong hnh II.2.

Trong giai on o lng chuyn giao, cc thng tin cn thit thc hinquyt nh chuyn giao c o. hng xung, trm di ng thc hin cc php o

o t s Ec/I0 ca knh hoa tiu chung (CPICH: Common Pilot Channel) ca Celldch v ca n v cc Cell ln cn. i vi mt s loi chuyn giao no , cc php

o khc l ht sc cn thit. Ly v d trong mng bt ng b nh UTRA FDD(WCDMA), thng tin nh thi tng i gia cc Cell cn c o iu chnhnh thi truyn trong chuyn giao mm cho php 1 s kt hp cht ch my thu


32/83



Rake. Tuy nhin, vic truyn dn t cc trm gc khc nhau s rt kh kt hp v

c bit l hot ng iu khin cng sut trong chuyn giao mm s b tr hon thm.

Hnh II.2Cc th tc chuyn giaoTrong giai on quyt nh chuyn giao, cc kt qu o lng c so snh vi

ngng c xc nh trc v sau n quyt nh c bt u thc hin chuyngiao hay khng. Cc gii thut chuyn giao khc nhau s c cc iu kin kch hot

khc nhau.

Trong giai on thc hin, qu trnh chuyn giao c hon thnh v cc thngs lin quan cng c thay i tu theo cc kiu chuyn giao khc nhau. V d, trong

giai on thc hin ca chuyn giao mm, khi trm di ng vo hoc ri b trng thichuyn giao mm th mt trm gc mi s c a vo hoc gii phng, cc ci ttch cc c cp nht v cng sut ca mi knh tham gia vo qu trnh chuyn giaomm c iu chnh.

2.2 Chuyn giao mm (SHO)Chuyn giao mm c gii thiu bi cng ngh CDMA. So vi tiu chunchuyn giao cng th chuyn giao mm c mt s u im li th hn. Tuy nhin, n

cng c nhng nhc im nh s phc tp v s tiu th ngun ti nguyn b sung.Vic quy hoch tng ph Chuyn giao mm (soft handover overhead) l mt trong

nhng thnh phnc bn ca vic quy hoch v ti u ho mng v tuyn. Trong phnny s trnh by cc nguyn l c bn ca chuyn giao mm.

o lng thng tin cn thit quyt nhchuyn giao.(vd: E

c/I

0ca knh CPICH ca

Cell dch v v cc Cell ln cn,thng tinnh thi tng i gia cc Cell.

Tho tiu chunchuyn giao

Hon thnh qu trnh chuyn giao.Cp nht cc thng s lin quan.

Giai on o lng

Giai on quyt nh

Giai on thc hin

Yes

No


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2.2.1 Nguyn l ca chuyn giao mmChuyn giao mm khc vi qu tr nh chuyn giao cng truyn thng. Vi

chuyn giao cng, mt quyt nh xc nh c thc hin chuyn giao hay khng

chuyn giao v trm di ng ch truyn thng vi mt trm gc ti thi gian . Cnvi chuyn giao mm, mt quyt nh c iu kin c thc hin quyt nh c

chuyn giao hay l khng. Tu thuc vo nhng thay i ca cng tn hiu knhhoa tiu t 2 hoc nhiu trm gc tham gia vo qu trnh, mt quyt nh tt nht cui

cng s c thc hin truyn thng vi mt v ch mt trm gc m thi. V iuny thng xy ra sau khi chc chn rng tn hiu n t trm gc c chn mnhhn tn hiu n t cc trm gc khc. Trong chu k chuyn tip ca qu trnh chuyngiao mm, trm di ng truyn thng ng thi vi tt c trm gc ang kt ni vi

n. S khc nhau gia chuyn giao cng v chuyn giao mm ging nh s khc nhaugia cc cuc thi bi tip sc v chy tip sc. Chuyn giao cng xy ra ti mt imthi gian, trong khi chuyn giao mm ko di trong mt chu k thi gian.

Hnh II.3 a ra qu tr nh cbn ca chuyn giao cng v chuyn giao mm(trng hp 2 ng). Gi s c mt u cui di ng bn trong chic xe hi di

chuyn t Cell 1 n Cell 2, BS1 l trm gc ban u ca trm di ng. Trong khi dichuyn, trm di ng o ng thi cng tn hiu knh hoa tiu nhn c t cc

trm gc ln cn. Vi chuyn giao cng a ra hnh II.3(a), vic kch hot c mt n gin nh sau:

If (pilot_Ec/I0)2 (pilot_Ec/I0)1 > D v BS1 l BS dch v

Handover to BS2

Else

Do not handover

end

Trong (pilot_Ec/I0)1 v (pilot_ Ec/I0)2 ln lt l t s Ec/I0 knh hoa tiunhn c t BS1 v BS2; D l s d tr tr.


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Hnh II.3S so snh gia chuyn giao cng v chuyn giao mmL do gii thiu s d tr tr D trong gii thut chuyn giao cng l trnh

tc ng ca hin tng ping-pong , l hin tng m khi trm di ng di chuyn

trong v ngoi bin gii ca Cell, th qu trnh chuyn giao cng thng xut hin.Ngoi tnh di ng ca thu bao, hin tng fading ca knh v tuyn cng lm cho

tc ng ping-pong cng tr nn nghim trng hn. Bng vic gii thiu s d trtr D, tc ng ca ping-pong s gim nh hn bi khi trm di ng s khng

chuyn giao ngay n trm gc tt hn. S d tr cng ln th tc ng ca hin tngping-pong cng gim. Tuy nhin, nu s d tr ln th iu cng ng ngha vi

tr hon tng. Hn na, trm di ng cng gy thm nhiu i vi cc Cell ln cndo cc kt ni cht lng km sut trong thi gian tr hon. Do , i vi chuyn

giao cng th s d tr tr D l kh quan trng. Khi qu trnh chuyn giao cng xuthin, kt ni lu lng ban u vi BS1 s b rt trc khi thit lp mt kt ni mi

vi BS2 v cng v l do m ta ni chuyn giao cng l mt qu trnh Break beforemake c ngha l ngt trc khi ni.

Trong trng hp chuyn giao mm, c a ra h nh II.3(b), trc khi

(pilot_ Ec/I0)2 vt qu (pilot_Ec/I0)1,ch cn iu kin kch hot chuyn giao mmc tho mn th trm di ng s vo trng thi chuyn giao mm v mt kt ni mi

c thit lp. Trc khi BS1 b rt (iu kin rt chuyn giao c tho mn) thtrm di ng s truyn thng ng thi vi c BS1 v BS2. V vy, khng ging nhchuyn giao cng, chuyn giao mm l mt qu tr nh ni trc ngt sau hay ngita cn gi l make before break. Cho n nay, mt s thut ton c xut


35/83



h tr chuyn giao mm v cc tiu chun khc nhau c s dng trong cc thutton khc nhau.

Qu trnh chuyn giao mm l khng ging nhau trong cc hng truyn khc

nhau. Hnh II.4 minh ho cho iu . hng ln, trm di ng truyn tn hiu nkhng gian thng qua ngten ng hng ca n. Hai trm gc ang kt ni vi n c

th nhn c tn hiu mt cch ng thi bi h s ti s dng tn s ca mt trongnhng h thng CDMA. Sau , nhng tn hiu ny s c truyn thng ti RNC

thc hin kt hp la chn. Khung no tt hn s c chn v khung kia s b b i.Do , hng ln, khng c knh b sung cn thit h tr cho qu tr nh chuyngiao mm.

Hnh II.4Nguyn l chuyn giao mm (trng hp 2 ng)

hng xung, c 2 BS s cng truyn cc tn hiu ging nhau n trm di

ng, v khi trm di ng nhn thy chng th n c th kt hp mt cch d dng cctn hiu ny. Thng thng, chin lc kt hp t l ti a s c s dng cungcp mt li ch b sung c gi l phn tp a dng. Tuy nhin, h tr cho qu

trnh chuyn giao hng xung th cn t nht mt knh hng xung b sung (SHO2 ng). Knh hng xung b sung ny tc ng n cc User khc ging nhnhiu b sung trong giao tip khng gian. V vy, h tr cho qu trnh chuyn giao

mm hng xung th yu cu phi c thm ti nguyn. V kt qu l, hngxung, hiu sut ca qu tr nh chuyn giao mm ph thuc vo s cn bng gia li phn tp a dng (macrodiversity) v s tiu th ngun ti nguyn b sung.

2.2.2 Thut ton chuyn giao mmThut ton c mt tm nh hng ln n hiu sut ca qu trnh chuyn giao

mm. Hnh II.5 a ra thut ton chuyn giao mm ca IS-95A (cng cn c gi lthut tonCDMAone c bn)


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Hnh II.5Thut ton chuyn giao mm ca IS-95ATrong hnh:

The Active set (Tp tch cc): l danh sch cc Cell m hin ang kt nivi trm di ng.

The Candidate set (Tp ng c): l danh sch cc Cell m hin khng

c s dng trong kt ni chuyn giao mm, nhng cc gi tr Ec/I0knh pilot ca chngl mnh c b sung vo tp tch cc.

The neighbouring set ( Tp ln cn): l danh sch cc Cell m tram ding o lng lin tc, nhng cc gi tr Ec/I0 knh pilot ca chng

khng mnh b sung vo tp tch cc.

Trong IS-95A, ngng chuyn giao l mt gi tr Ec/I0 c nh nhn c tknh hoa tiu. N rt d thc hin, nhng li gp nhiu kh khn khi phi i mt vi

nhng thay i ti ng. Da trn thut ton IS-95A, nhiu bin i ca thut toncdmaOne vi tnh nng ng hn ngng c nh c xut cho h thng IS-95B v cdma2000.

Trong WCDMA s dng cc thut ton phc tp hn, c minh ho nh trnhnh II.6


37/83



Hnh II.6Thut ton chuyn giao mm WCDMAThut ton chuyn giao mm WCDMA c th c m t nh sau:

Lc u. Ch c 1 v 2 nm trong tp tch cc

Ti s kin A. (Ec/I0)P-CPICH3 > (Ec/I0)P-CPICH1 - (R1a-H1a/2)trong (Ec/I0)P-CPICH1 l t s tn hiu trn nhiu knh hoa tiu ca

1 mnh nht, (Ec/I0)P-CPICH3 l t s tn hiu trn nhiu knh hoa

tiu ca 3 nm ngoi tp tch cc v R1a l hng s di bo co (doRNC thit lp, H1a/2 l thng s tr v (R1a-H1a/2) l ca s kt npcho s kin 1a. Nu bt ng thc ny tn ti trong khong thi gian T

th 3 c kt np vo tp tch cc

Ti s kin C. (Ec/I0)P-CPICH4 > (Ec/I0)P-CPICH2 +H1c/2, trong (Ec/I0)PCPICH4 l t s tn hiu trn nhiu ca 4 nm ngoi tp tch

cc v (Ec/I0)PCPICH2 l t s tn hiu trn nhiu ca 2 ti nht trongtp tch cc, H1C l thng s tr. Nu quan h ny tn ti trong thi gian

T v tp tch cc y th 2 b loi ra khi tp tch cc v 4 s th

ch ca n trong tp tch cc

Ti s kin B. (Ec/I0)P-CPICH1 < (Ec/I0)P-CPICH3- (R1b+H1b/2)trong (Ec/I0)P-CPICH1 l t s tn hiu trn nhiu knh hoa tiu ca

1 yu nht trong tp tch cc, (Ec/I0)P-CPICH3 l t s tn hiu trnnhiu ca 3 mnh nht trong tp tch cc, R1b hng s di bo co (do

RNC thit lp), H1b/2 l thng s tr v (R1b+H1b/2) l ca s loi cho


38/83



s kin 1B. Nu quan h ny tn ti trong khong thi gian T th 3 bloi ra khi tp tch cc

Trong thut ton WCDMA, ngi ta s dng ngng tng i ch khng s

dng ngng tuyt i. So vi IS-95A, li ch ln nht ca gii thut ny l s biudin tham s mt cch d dng, v nh c cc gi tr ngng tng i nn khng yu

cu bt k mt s thay i tham s no i vi cc khu vc c nhiu cao v thp.Hu ht cng vic trong lun n ny u da trn thut ton chuyn giao mm

WCMDA.

2.2.3 c im ca chuyn giao mmSo vi chuyn giao cng truyn thng th chuyn giao mm cho thy nhng u

im r rng hn, v d nh l loi b hin tng ping pong v lm cho ngtruyn dn lin tc hn, khng b gy khc. Khng c hin tng ping pong cngh a l s lng ti trn mng bo hiu thp hn v vi chuyn giao mm cng s

khng b mt d liu do s ph v truyn dn tm thi (xy ra trong chuyn giao

cng).Ngoi l do x l tnh di ng ca thu bao, cn c mt l do khc na thc

hin chuyn giao mm trong CDMA; l s dng n nh mt c ch gim nhiu(c thc hin cng vi iu khin cng sut). Hnh II.7 a ra 2 vin cnh. vincnh th nht (hnh a), iu khin cng sut c s dng. vin cnh th 2 (hnh b),

iu khin cng sut v chuyn giao mm u c h tr. Gi s rng trm di ngang di chuyn t BS1 n BS2. Ti v tr ang xt, tn hiu nhn c t BS2 mnhhn t BS1 iu ny c ngha l BS2 tt hn BS1.


39/83



Hnh II.7Gim nhiu hng ln bng cch s dng SHO h nh (a), vng iu khin cng sut lm tng cng sut truyn ca trm di

ng m bo QoS hng ln khi trm di ng di chuyn ra xa trm gc dch v

ca n (BS1). hnh (b), trm di ng ang trong trng thi chuyn giao mm v c 2trm gc truyn thng mt cch ng thi vi trm di ng, cc tn hiu thu c sau

c trm gc truyn thng ti RNC thc hin kt hp. hng ln, vic kthp la chn c s dng trong chuyn giao mm, khung no mnh nht s c

chn v khung yu hn s b xo b i. Bi v BS2 tt hn BS1 nn t c cngmt QoS mong mun th yu cu cng sut truyn ca trm di ng h nh (b) phi

nh hn so vi hnh (a). V vy, nhiu gp vo h thng bi trm di ng hng lns thp hn bi qu trnh chuyn giao mm lun lun gi cho trm di ng lin kt vi

BS tt nht. hng xung th c v phc tp hn, mc d t l kt hp ti a ramt li v phn tp a dngnhng cng cn thit phi h tr thm knh hng

xung b sung vo qu trnh chuyn giao mm.

C th tm tt cc c im chnh ca chuyn giao mm nh sau:

u im

Gim hin tng ping-pong, t dn ti gim tng ph v s lng

ti trn mng bo hiu


40/83



Truyn dn lin tc, khng xy ra gin on sut trong qu trnh chuyngiao mm.

Khng c s d tr tr, dn ti tr hon thp hn.

Gim nhiu hng ln, dn n: cht lng truyn thng tt hn cho mts lng ngi dng nht nhng thi tng s lng ngi dng vi

cng mt Qos yu cu. Cc rng buc v thi gian trn mng t hn, iu ny c ngh a l thi

gian xp hng c c mt knh mi t BS mong mun s di hn,

gip cho xc sut chn v rt cuc gi gim i.

Nhc im

Phc tp hn trong vic thc hin qu trnh chuyn giao cng

Cn phi b sung thm ngun ti nguyn mng hng xung ( ti

nguyn v m v cng sut )


41/83

Bo co tt nghip Chng III: Phn tch hiu sut cp ng dn v cp h thng


CHNG III : PHN TCH HIU SUT CP NG DN VCP H THNG

3.1 Phn tch hiu sut cp ng dn3.1.1 Phn tch nhiu hng xungTng quan

Nh cp trong chng 1, cc h thng CDMA l cc h thng gii hnnhiu v do vic nh gi nhiu l mt trong nhng th tc c bn phn tch h

thng CDMA. Nhiu tng c tri nghim bi trm di ng c th c chia thnh 2phn l : nhiu trong cng mt Cell(intra-Cell) v nhiu gia cc Cell khcnhau(inter-Cell).

hng ln, xt mt trm di ng no th nhiu intra-Cell n t tt cnhng trm di ng khc c phc v bi cng mt trm gc; i vi nhiu inter-Cell th bao gm tt c nhng tn hiu thu c t tt c cc trm di ng trong cc

Cell ln cn khc ngoi tr Cell dch v ca trm di ng. Do , hng ln, nhiuc lin quan n vic phn phi ti trong mng ch khng lin quan n v tr cachnh trm di ng .

Hnh III.1 Nhiu hng ln hng xung, c a ra trn h nh III.2, nhiu intra-Cell ca mt trm di

ng no n t chnh trm gc dch v ca n: loi nhiu ny l do mt mt phntnh trc giao gia cc User do hiu ng a ng. WCDMA s dng cc m trc giao

khc nhau hng xung i vi cc User ring bit v khng c bt k mt s lantruyn a ng no cng nh khng c nhiu intra-Cell khi tnh trc giao vn cn.

Thng thng, tnh trc giao nm gia 0,4 n 0,9 (trng hp l tng l bng 1).Nhiu intra-Cell trong thc t bao gm mt phn cng sut ca cc knh iu khin

chung v cc knh lu lng hng xung i vi cc User khc trong cng mt Cell.Nhiu inter-Cell l cng sut nhn c ca trm di ng t tt c cc trm gc lncn khc ngoi tr trm gc dch v ca n. Bi v trong ch FDD WCDMA, cc


42/83



trm gc l khng ng b, nn tnh trc giao khng c tc dng trong nhiu inter-Cell, v vy c s xut hin ca nhiu inter-Cell.

Hnh III.2 Nhiu hng xungBi v cc ngun nhiu c c nh bi nhng trm gc hng xung, nn

i vi mt trm di ng no th lun xut hin nhiu hng xung n v tr can.

a) Nhiu intra-Cell v nhiu inter-Celli vi mt MS ti khong cch rt trm gc dch v ca n, s suy gim lan

truyn l t l vi:

Trong , l mt ng dn vi gi tr in hnh l 4; (dB) c phn bGaussian, biu din s suy gim do hiu ng mn chn, vi trung b nh 0 v mt

lch chun c lp vi khong cch; n khong t 5 n 12 vi mt gi tr in hnh8-10dB i vi macroCell.

Xt trm di ng c t ti v tr(r1,1) trong hnh III.2, gi s rng BS1 ltrm gc dch v ca n. Khi nhiu intra-Cell hng xungIintra-Cell nhn c t

BS1 c th c biu din l:

(3.1)

Trong PT1 l cng sut truyn tng ca BS1 ; a l h s trc giao hng

xung (bng 1 i vi trc giao l tng v bng 0 i vi khng trc giao). Bi v cnhiu intra-Cell v tn hiu mong mun u c truyn t mt ngun, nn chng chucng mt s suy gim.V vy, khng cn thit phi s dng iu khin cng sut trongmt h thng Cell ring l.

Nhiu inter-Cell Iinter-Cell c th c biu din nh sau:

1010.),(

rrL

1011int

1

10)1(

raPI Tcellra


43/83



(3.2)

Trong PTi l cng sut truyn tng ca BSi ; ri l khong cch t trm di ngn BSi ; M l ch s ca cc trm gc gy nhiu inter-Cell. V l thuyt, nhiu inter-

Cell n t tt c cc trm gc xung quanh ngoi tr trm gc dch v. y, ch ccc trm gc thuc lp th nht v lp th hai c s dng bi v cng sut nhnc t nhng trm gc bn ngoi lp th 2 l khng ng k.

T (3.1), c th thy c rng nhiu intra-Cell da vo khong cch t trm ding n trm gc dch v ca n ,r1, nhng n khng ph thuc vo 1 . Tuy nhin,

nhiu inter-Cell li khng nhng ph thuc vo r1 m cn ph thuc vo 1 bi khongcch t trm di ng n cc trm gc khc, ri , l mt hm s ca r1 v 1.

(3.3)

R rng rng i vi mt trm di ng no , nhiu hng xung c mi quanh cht ch vi v tr ca trm di ng. iu ny l bi cc ngun nhiu c c nh

bi nhng trm gc hng xung. Gi s rng ti trong h thng c phn b mtcch thng nht v cng sut truyn tng ca mi trm gc l ging nhau, k hiu lPT, (3.2) c th c vit li thnh:

(3.4)

Trong , h s cung cp cho ta mt php o v nhiu inter-Cell vi cng sut

truyn tng BS. c mi quan h vi v tr ca trm di ng. y, bn knh Cellc tiu chun ho n 1. Hnh III.3 cho thy ngha ca i vi cc trm di ngti cc v tr khc nhau trong cng mt Cell lc gic. Trc x-y biu din v tr ca trmdi ng v trc z biu din gi tr ca . Bi v bn knh Cell R c tiu chun ho

n 1 nn khng phi l gi tr thc t ca t s nhiu inter-Cell vi PT nhng mcnhiu inter-Cell tng i c tri nghim bi cc trm di ng ti cc v tr khcnhau.

M

i

iTiceller

i

rPI2

10int 10

19,....11,96/)8(cos3..2)3(

18,....10,86/)8(cos32..2)32(

723/)2(cos3..2)3(

1122

1

1122

1

1122

1

iiRrRr

iiRrRr

iiRrRr

ri

M

i T

cellerTiTceller

P

IPrPI

2

int10int .10

1


44/83



Hnh III.3 ,Nhiu inter-Cell hng xung tng iR rng l nhiu inter-Cell c mi quan h cht ch vi v tr trm di ng,

khng ch c khong cch r m cn ph thuc c vo gc . Cc trm di ng gnbin gii Cell ( c gc v cnh ) s nhn c nhiu inter-Cell ln nht. Biu din khu

vc gn c(r = R, = 30) nh l gc ca Cell v khu vc gn c (r =

23 R,

= 0) nh l cnh ca Cell. Trong hnh a, = 0dB, ch c thnh phn tn hao ngdn. Trong hnh b, = 8dB th bao gm c cc tc ng ca s che khut v nghaca cng c tnh ton. V cng c th thy c rng s che khut n s lm tnggi tr nhiu trung bnh.

B qua nhiu nhit, t s ca nhiu inter-Cell v nhiu intra-Cell, k hiu l

c th c biu din l:

(3.5)

Hnh III.4 cho thy ngha ca t s nhiu inter-Cell v intra-Cell i vi cctrm di ng ti cc v tr khc nhau trong mt Cell lc gic. Khi khng c s che

khut trn vng ph sng, th gi tr ca nhiu inter-Cell s gp khong 5,5 ln so vinhiu intra-Cell i vi cc User gn gc ca Cell lc gic. S che khut l m cho gitr trung bnh ca tng n 32. Nh cp Chng 1 ( phn 1.3.2), nhiu inter-

Cell l nguyn nhn chnh s dng iu khin cng sut hng xungv n cbit quan trng i vi cc User gn gc Cell lc gic ca cc h thng a Cell.

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Hnh III.4 , T s nhiu inter-Cell v intra-CellHnh III.5 biu din nhy ca cc h s v vi cc thng s v tuyn

khc nhau: trc x biu din khong cch t trm di ng n trm gc dch v ca n, l mtng dn; l lch chun ca s che khut v a l h s trc giaohng xung.

Hnh III.5 nhy ca nhiu hng xung tng i vi cc thng s v tuyn Trong hnh III.5, ta thy khi khong cch t MS n trm gc dch v tng s

dn n c v cng tng theo, iu ny l d hiu bi c v u ph thuc var1,.Ti 1 v tr nht nh, xt 2 ng cong c cng = 4 v = 8, do c lp vi a

nn tng ng vi 2 gi tr a khc nhau (a = 0.6 v a = 0.9) th 2 ng cong vntrng nhau cn vi th ng cong no c a ln hn s c cao hn. Ly 1 dn

chng khc, xt 2 ng cong xanh dng v xanh lam trong c 2 hnh, ng congno c cao hn th s c v ln hn (do s gia tng ca l ln hn ca ). Qua, ta c th thy c rng c v u rt nhy vi s thay i ca cc thng slin quan (, , a, r1).


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V trong ch FDD WCDMA, cc trm gc l khng ng b vi nhau nntnh trc giao khng ci thin c nhiu inter-Cell, v vy h s trc giao a ch tc

ng n . Khi tnh trc giao gia cc knh hng xung trong cng mt trm gcc duy tr tt th nhiu intra-Cell c th c gim bt. Mt vi im cn lu na

l mt ng dn cng ln s tng ng vi nhiu inter-Cell cng thp v sche khut s lm tng nhiu inter-Cell v t s nhiu tng i.

b) Nhng tc ng ca chuyn giao mm n nhiu hng xung m bo QoS, trm gc cn phn b gi tr cng sutn mi trm di ng

mt cch hp l b cho s can nhiu. Nu trm di ng khng trong trng thichuyn giao mm, nh trm di ng 1 a ra trong h nh III.6(a) th ch duy nht c

mt knh hng xung c thit lp gia trm di ng v trm gc dch v ca n lBS1.Theo yu cu dch v v nhiu hng xung tng nhn c bi mobile 1 (k

hiu l I0) th cng sut P c phn b trn knh hng xung gia trm di ng vtrm gc. Knh ny hot ng nh l nhiu inter-Cell v nhiu intra-Cell n mobile 2

v mobile 3tng ng.Nu mobile 1ang trong trng thi chuyn giao mm th n s truyn thngng thi vi c 2 trm gc BS1 vBS2. Khi 2 knh dnh ring hng xung c

thit lp h tr cho qu tr nh chuyn giao mm, c a ra trn h nh III.6(b).Trong hnh, P1 v P2 ln lt l cng sut c phn b cho cc knh t trm gcBS1vBS2tng ng. P1tc ng nh l nhiu intra-Cell i vi mobile 2 v nhiu inter-Cell i vi mobile 3, cn P2 th tc ng nh l nhiu inter-Cell i vi mobile 2 v

nhiu intra-Cell i vi mobile 3.

Hnh III.6Nhng tc ng ca chuyn giao mm n nhiu hng xungSo snh 2 trng hp th ta thy nhng tc ng ca chuyn giao mm n

nhiuhng xung l kh phc tp. Khi khng c chuyn giao mm, th mobile 1 gp


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mt phn cng sut P n nhiu hng xung tng. Khi c chuyn giao mm, th sgp phn ny s bao gm c P1 v P2. S gia tng nhiu do mobile 1 s nh hng n

cc trm gc tch cc khc trong h thng: tt c cc trm gc ny cn iu chnh cngsut knh cachng p ng c nhng thay i v nhiu. iu ny b li s lm

thay i mc nhiu tng m mobile 1 nhn c, kt qu l s thay i ca P hoc P1v P2 (trng hp SHO). S tun hon ny s lp i lp li cho n khi h thng t

n mt s cn bng mi. Trong cc h thng CDMA, iu khin cng sut c trchnhim i vi vic iu chnh ny. Bi cc c tnh gii hn nhiu nn trong cc hthng CDMA, s chu ng nhiu thp lun lun l nguyn l chnh ca s phn b

ti nguyn v tuyn. Do , qu trnh chuyn giao mm c dn n mc nhiu thphn chuyn giao cng thng thng hay khng, cn ph thuc cht ch vo gi tr caP, P1 v P2 . Nhng gi tr cng sut ny lin quan n cc s kin nht nh, nh l vtr ca trm di ng, s suy gim knh v tuyn v chin lc phn chia cng sut

c s dng trong qu trnh chuyn giao mm.

3.1.2S phn b cng sut hng xungS phn b cng sut l mt th tc rt quan trng i vi cc h thng CDMA.

Cng sut truyn tng ca trm gc c chia thnh 2 phn: mt phn l dnh cho ccknh iu khin chung hng xung, nh l knh hoa tiu chung (CPICH) v knh

ng b (SCH) v phn cng sut cn li c phn b cho cc User nh l cc knhhng xung dnh ring. Thng thng, phn cng sut dnh cho cc knh iu khin

chung chim khong 20 n 30% cng sut truyn tng ca trm gc. ti thiu hocan nhiu v s tiu th ti nguyn v tuyn, th h thng c gng phn b cng mt

lng cng sut thp nht c th n mi knh dnh ring i vi cc User ring r,

nhng iu ny l c lp vi yu cu QoS. Di s iu khin cng sut hngxung mt cch hon ho, th t s nng lng bit trn mt ph cng sut nhiuEb/I0 nhn c ca cc trm di ng s c gi gi tr mong mun. Khi trm di

ng ch c kt ni vi mt trm gc,th ch c mt knh dnh ring hng xung ltch cc i vi trm di ng ny, nhng khi trm di ng ang trng thi chuyn

giao mm, th c t nht 2 trm gc c tham gia vo s phn b cng sut. V c 2tnh hung ny s c phn tch ring r phn sau.

a) Phn b cng sut khng c SHOVn s dng v tr ti (r1,1) ca trm di ng c a ra h nh III.2. Khi

khng c chuyn giao mm, trm di ng ch truyn thng vi duy nht mt trm gcti mt thi im. Gi s rng BS1l trm gc dch v ca n, t s Eb/I0 nhn cca trm di ng c th c biu din l:

(3.6)

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Trong , Wl tc chip;R l tc bit dch v; l h s hot ng; ykhng quan tm n nhiu nhit. V vy, gi gi tr QoS mong mun, th cng sut

truyn yu cu ca knh hng xung Psc th c suy ra t (3.6) l:

(3.7)

Trong (Eb/I0)t l gi tr mong mun ca Eb/I0 . Gi tr ca Eb/I0c quyt

nh bi RNC. Theo BER, RNC c th thay i gi tr mong mun duy tr QoS.

Gi nh rng ti c phn phi ng u trn ton h thng, tt c cc trm

gc truyn cng mt gi tr cng sut. Ps c th c vit li l:

(3.8)

H s 1 biu din cng tng i ca cng sut yu cu i vi trm dingti v tr (r1,1) m khng c chuyn giao mm.

b) Phn b cng sut vi SHOKhi mt trm di ng ang trong trng thi chuyn giao mm, tt c cc trm

gc nm trong tp tch cc cn phn b cng sut mt cch thch hp i vi cc knh

hng xung c lin kt vi trm di ng . y, chuyn giao mm 2 ng v3 ng c tham chiu mt cch ring r.

SHO 2 ngVi SHO 2 ng, gi s rngBS1 v BS2l 2 trm gc dch v ca trm di ng,

tn hiu mong mun t 2 trm gc ny c tng hp vi nhau. Cc m hnh tng hpkhc nhau c th c s dng, nhng nh vi hu ht cc phn trc trong lunn ny th t s tng hp ti a c s dng y. T s Eb/I0 nhn c ca trm i

ng c th c biu din l:

(3.9)

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Trong r1 v r2biu din khong cch t trm di ng n BS1 v BS2 tngng; Ps1 v Ps2l cng sut truyn tBS1 v BS2 tng ng. Sut trong qu trnh chuyn

giao mm, 2 vng iu khin cng sut c tch cc. ngn chn s tri dt cngsut th c mt s chin lc c xut v chin lc iu khin cng sut cn

bng, c thng qua bi 3GPP c s dng. Cng nh bn trong iu khin cngsut vng kn, th mt vng iu chnh c thc hin cn bng cng sut hng

xung gia cc Cell trong tp tch cc trong phn tp a dng. Chin lc iu khincng sut ny trnh c s tri dt cng sut, dn n cng sut truyn ti tng l n vcc vn tr nn n nh.Trong trng hp l tng, Ps1 = Ps2 . S dng cng mt

gi nh, cng sut truyn i vi mi knh hng xung c th c biu din l:

(3.10)

Do , cng sut tng cn thit h tr cho trm di ng ny l:

TT

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(3.11)

H s 2 biu din cng tng i cng sut yu cu (cng sut tng) catrm di ng di qu trnh chuyn giao mm 2 ng.

SHO 3 ng

Tng t nh cc phn tch i vi SHO 2 ng, mt trm di ng di SHO 3ng s c t sEb/I0 nhn c l:

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2

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T a ra:

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(3.12)

Cng sut tng cn thit h tr cho trm di ng ny l:

TT

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(3.13)

H s 3 biu din cng tng i cng sut yu cu (cng sut tng) catrm di ng khi chuyn giao mm 3 ng.

Cng sut c phn b n mt User no ng vai tr nh l nhiu i vi

cc User khc. Do , cc gi tr 1 2 3 c s dng ch ra mc nhiu m cctrm di ng phi chu trong cc t nh hung khc nhau l bao nhiu. Hnh III.7 cho

thy ngha ca cc gi tr 1 2 3 i vi cc trm di ng ti cc v tr khc nhau.

Trong hnh r1/R l khong cch c tiu chun ho t trm di ng n BS1. Cctrng hp (a), (b), (c), (d) tng ng vi cc gi tr v 1 khc nhau. Cc thng skhc s dng cc gi tr in h nh nh W=3840kchip/s, R=12.2kbit/s, =0.5, =4,

a=0.6, (Eb/I0)t=5dB.


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Hnh III.7 ngha ca 123 vi cc v tr MS khc nhauCc kt qu trong cc trng hp(c hay khng c s che khut) c th c

gii thch nh sau. Khi khng tnh n s che khut, c a ra hnh (a) v (c), th

mi quan h gia 1 2 v 3 l 1 < 2 < 3 . iu ny c ngha l c thm mt phncng sut cn thit h tr cho qu trnh chuyn giao mm gi cng mt t s Eb/I0mong mun:cng nhiu trm gc trong tp tch cc th cng sut yu cu cng ln. Khic tnh n s che khut, th s suy gim knh v tuyn s thay i mt cch t ng.

p ng cng mt gi trEb/I0 mong mun th tt nht l phi thay i cng sutphn b cn thit. Trong hnh (b) v (d), ngha ca cc gi tr 1 2 v 3 c a ra

vi gi tr bng 8dB. R rng l i vi cc trm di ng gn bin gii Cell, vichuyn giao mm, th cng sut trung bnh cn thit p ng cng mt gi trEb/I0mong mun s thp hn. i vi cc User gn gc ca Cell, th thm ch cng suttng ca SHO 3 ng cn thp hn c SHO 2 ng. hnh (b) khi r/R > 0,8 th 3


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2 . Tuy nhin, i vi cc trm di ng nm trn ng c = 0, th SHO 2 nglun lun c hiu sut tthn SHO 3 ng.

Hnh III.8 biu din Hm phn b tch lu (Cumulative Distribution

Function:CDF) ca 1 2 v 3 i vi cc User gn gc ca Cell ti (r1=R,=30). 3c lch chun v gi tr trung bnh l nh nht. lch chun ca cng sut truyn

tng nh s tng ng vi d tr fade nh. Do , tng t nh nhng tc ng hng ln, chuyn giao mm cng c nhng ch li hng xung l gim d

tr fade cn thit p ng mt QoS nht nh ti cnh ca Cell. SHO 3 ng thmch c hiu sut hn c SHO 2 ng trong vic gim d tr fade.

Hnh III.8Hm phn b tch lu ca 12 v3Hnh III.9 biu din mi quan h gia gi tr trung bnh ca 1 2 v 3 trong

mt mt phng Cell 2 chiu. Nhng mu sc khc nhau s tng ng vi nhng tnh

hung khc nhau c a ra nh trong phn ch thch. R rng l chuyn giao mmc th lm gim cng sut yu cu i vi cc knh hng xung ca cc trm di ngti bin gii Cell. iu ny c ngha l vi chuyn giao mm th nhiu hng xung

trung bnh t MS ny nh hng n cc MS khc s c gim bt.

Cn lu rng tt c cc kt qu cho n nay u l da trn trng hp ltng: QoS c m bo, iu khin cng sut hon ho v khng c nhng gii hncng sut. Tuy nhin, trong mt mng thc t th li c nh sn nhng gii hn v

cng sut. Mc ch l trnh s m rng can nhiu c gy ra bi vic iu khincng sut nhanh chng li mt knh v tuyn xu. Trong hu ht cc trng hp, iu

khin cng sut nhanh v chnh xc c th mang li nhng li ch cho h thng bngcch b s tn hao truyn dn trong knh v tuyn. Tuy nhin, i vi mt knh v

tuyn xu th trm gc c th phn b cng sut cao, iu ny dn ti s m rng cannhiu n cc knh hot ng khc.


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Hnh III.9 Cng sut tng trung bnh i vi v tr ca trm di ng

Cc gi tr in h nh ca nhng gii hn cng sut i vi mt mi trngmacroCell l 43dBm(20W) v 30dBm(1W) tng ng vi cng sut truyn tngln nht ca trm gc v cng sut knh lu lng hng xung ln nht. Gi s rng

tt c cc trm gc ang truyn mt gi tr cng sut l ln nht, PT = 43dBm, hnhIII.10 biu din cng sut knh lu lng hng xung trung bnh i vi cc trm ding ti nhng v tr khc nhau( = 30). Trc x biu din khong cch tng i tMS n bn knh Cell. Gi s rng khi r/R > 0,82 th MS ri vo trng thi chuyn

giao mm.

Hnh III.10 Cng sut knh lu lng hngxungR rng rng khi khng thc hin chuyn giao mm, gi t s Eb/I0 mong

mun th cng sut knh lu lng hng xung trung bnh cn thit cho MS ti bin

gii ca Cell l ln hn gii hn cng sut ti a khi tt c cc trm gc truyn cng


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sut mc ti a. User c th b t chi hoc phc v vi mt QoS di gi tr mongmun. Chuyn giao mm c th gii quyt vn bng cch phn chia cng sut gia

2 trm gc. i vi mt MS ti bin gii Cell, t s Eb/I0 c th c m bo png gi tr mong mun m khng cn phn b cng sut cao n mi knh hng

xung. Tt nhin, nu h thng khng c np ti y , th cng sut ca cc User gn gc ca Cell c th khng vt qu mc ti a ngay c khi chuyn giao mm

khng c h tr. im quan trng y l chuyn giao mm s lm gim xc sutxu i ca QoS. Mt u im khc khi thc hin chuyn giao mm l s suy gimcng sut do tn hao ca s che khut (hiu ng mn chn) l khng nhiu nh trong

trng hp vi mt trm gc ring l bi v 2 tn hiu c tng hp xut pht t 2knh v tuyn khc nhau.

3.1.3Kt lunDa trn cc phn tch v nhiu hng xung v nhng tc ng ca chuyn

giao mm trn mt lin kt ring l, c th rt ra mt s kt lun nh sau:

hng xung, nhiu inter-Cel

Soft Handover_hoan Chinh

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