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8/3/2019 Do an Tot Nghiep ( Pham Linh)
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MC LC
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LI M U
Thng tin di ng c coi nh l mt thnh tu tin tin trong lnh vc thng tin
vin thng ca con ngi vi c im cc thit b u cui c th truy cp dch v
ngay khi ang di ng trong phm vi vng ph sng. Thnh cng ca con ngitrong lnh vc thng tin di ng khng ch dng li trong vic m rng vng ph
sng phc v thu bao khp ni trn ton th gii, m cc nh cung dch v, cc
t chc nghin cu pht trin cng ngh di ng ang n lc hng ti mt h
thng thng tin di ng hon ho, cc dch v a dng, cht lng dch v cao. 3G-
H thng thng tin di ng th h 3 l ci ch m th gii ang hng ti.
Ho chung vi xu th pht trin ca th gii. Cc nh cung cp dch v thng tin
di ng Vit nam v ang n lc ht mnh cung cp ti khch hng nhng
dch v vi cht lng tt nht v vi yu cu ngy cng cao ca khch hng th
vic tin ln h thng thng tin di ng th h 3 l iu tt yu. a phn cc cng ty
cung cp dch v thng tin di ng Vit nam p dng cng ngh GSM v cung
cp dch v di ng cho phn ln thu bao di ng Vit nam. V vy, pht trin
ln 3G th l trnh bt buc s l t GSM tin ln WCDMA (a truy nhp phn chia
theo m bng rng) theo hp chun IMT_2000. V em chn ti: IU
KHIN CNG SUT V CHUYN GIAO TRONG H THNG THNG
TIN DI NG WCDMA lm ti nghin cu tt nghip. Ni dung ca tigm:
Chng I: Tng quan v h thng WCDMA
Chng II: iu khin cng sut v chuyn giao trong h thng thng tin
di ng CDMA
Chng III: iu khin cng sut v chuyn giao trong h thng WCDMA
Em xin chn thnh thnh cm n s hng dn nhit tnh ca thy Bi nh
Thnh cng nh s dy bo tn tnh ca cc thy, c trong t mn in t vin
thng khoa in- in t hng hi, trng i hc Hng hi Vit Nam. gip em trong sut bn nm hc tp v trong ba thng lm n va qua.
Mt ln na em xin chn thnh cm n !
Hi Phng , thng 2 nm 2011
Sinh vin: Phm Vn Linh
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CHNG I
TNG QUAN V H THNG WCDMA
1.1 KHI QUT CHUNG V WCDMA- WCDMA (Wide Code Division Multy Access): a truy nhp phn chia theo m
bng rng l cng ngh truy nhp v tuyn chnh ca h thng thng tin di ng
th h th 3- h thng UMTS (Universal Mobile Telecommunications System)
Nn tng cng ngh chnh ca WCDMA l cng ngh a truy nhp phn chia
theo m (CDMA). Trong lch s thng tin di ng tn ti cc phng thc a
truy nhp khc nhau l: FDMA a truy nhp phn chia theo tn s; TDMA a truy
nhp phn chia theo thi gian v CDMA. S khc nhau ca 3 phong thc truy
nhp c ch ra trong hnh 1-1
Hnh 1-1 : Cc phng thc a truy nhp
- Trong h thng a truy nhp theo tn s (FDMA), rng bng tn c cp
pht cho h thng l B Mhz c chia thnh n bng tn con, mi bng tn con c
n nh cho mt knh ring c rng bng tn l B/n Mhz. Cc tn hiu cho mi
ngi s dng khc nhau c truyn trong cc knh khc nhau vi cc tn s iu
ch khc nhau. Mi ngi s dng khi truy nhp mng s c n nh mt knh
tn s. V v mi ngi c cp pht mt knh tn ring trong di bng tn ca h
thng nn cn phi c khong bo v gia tng knh phng nga s khng hon
thin ca cc b lc v cc b dao ng trnh nhiu giao thoa knh ln cn. V
vy, m bo FDMA tt tn s phi c phn chia v quy hoch thng nht
trong ton h thng.
- H thng a truy nhp phn chia theo thi gian (TDMA), cc tn hiu ca ngi
s dng khc nhau c truyn i trong cc khe thi gian khc nhau. My pht ca
mi ngi s dng khng pht lin tc m ch pht vo ng khe thi gian c
n nh cho ngi s dng. S truyn dn ny c gi l cm. S pht i mt cm
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c a vo mt cu trc thi gian c gi l khung, tt c cc my u cui v
tuyn phi pht theo cu trc ny. TDMA vn ng b rt quan trng. ng
b cho php xc nh ng v tr ca cm cn ly ra my thu hay cn pht i
my pht tng ng. Ngoi ra, ng b cn phi xt n c v tr ca cc my di
ng so vi trm gc. So vi FDMA, TDMA cho php tit kim tn s v thit b
thu nh pht nh gn hn. Tuy nhin, nu ch s dng mt cp tn s sng mang
th khng m bo dung lng ca mng. V th TDMA thng c s dng
kt hp vi FDMA tng cao dung lng ca mng. Do , vn quy hoch
mang l mt vn rt quan trng trong cc mng TDMA c bit l c ch ti s
dng tn s.
- CDMA l phng thc a truy nhp m mi knh c cung cp mt tn
s v mt m duy nht. y l phng thc a truy nhp mi, phng thc ny datrn nguyn l tri ph. Trong cc h thng thng tin, thng thng rng bng
tn l vn quan tm chnh v cc h thng ny c thit k s dng cng t
rng bng tn cng tt. Trong cc h thng thng tin tri ph (SS: Spread
Spectrum) rng bng tn ca tn hiu c m rng trc khi pht i. Khi ch c
mt ngi s dng trong bng tn ca h thng SS th khng c hiu qu. Tuy
nhin, mi trng nhiu ngi s dng, cc ngi s dng ny c th dng chung
mt bng tn SS khi vic s dng bng tn c hiu sut cao hn. Mt h thng
thng tin c coi l h thng SS nu: Tn hiu pht chim rng bng tn ln
hn rng bng tn ti thiu cn thit pht tin; Tri ph c thc hin bng
mt m c lp vi s liu. Vi cc cng ngh khc nhau s ngi s dng ln nht
c th chia s ng thi cc knh vt l l c nh. Tuy nhin trong h thng
CDMA, cc tn hiu cho ngi s dng khc nhau c truyn i trong cng mt
bng tn ti cng mt thi im. Trong CDMA ti nguyn v tuyn c phn b
da trn cc m gi ngu nhin. Do vy, nhng ngi s dng ng thi c th
chim dng cng mt bng tn trong cng mt khong thi gian. Mi ngi sdng c gn cho mt hoc nhiu m ring bit. V nhng m c s dng
phn bit cell, knh truyn dn v ngi s dng. Mi tn hiu ngi s dng ng
vai tr nh l nhiu i vi tn hiu ca ngi s dng khc, do dung lng ca
h thng CDMA gn nh l mc nhiu, v khng c con s ln nht c nh, nn
dung lng ca h thng CDMA c gi l dung lng mm. CDMA l cng
ngh thc hin tri tn hiu gc thnh tn hiu bng rng trc khi truyn i. Ngoi
ra th do s dng cng mt bng tn cho tt c mi ngi s dng nn h s ti s
dng tn s ca h thng CDMA l bng mt.
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- WCDMA s dng k thut tri ph chui trc tip DS- CDMA vi tc Chip
l 3.84Mps lm vic bng tn 5Mhz v p dng phng php ghp song cng
phn chia theo tn s FDD. Gii php FDD l s dng hai bng tn 5 MHz vi
hai sng mang phn cch nhau 190 MHz: ng ln c bng tn nm trong
di ph t 1920 MHz n 1980 MHz, ng xung c bng tn nm trong di
ph t 2110 MHz n 2170 Mhz. Mc d 5 MHz l rng bng danh nh,
ta cng c th chn rng bng t 4,4 MHz n 5 MHz vi nc tng l 200
KHz. Vic chn rng bng ng n cho php ta trnh c nhiu giao
thoa nht l khi khi 5 MHz tip theo thuc nh khai thc khc. Bng tn rng
hn v tc tri ph cao lm tng li x l v mt gii php thu a
ng tt hn
- H thng WCDMA s dng ch khng ng b gia cc BS v vykhng cn duy tr mt qu trnh ng b chnh xc gia tt c cc BS. N
c s dng nhm mc ch m bo d dng vic trin khai ph kn sng
bi cc BS cho cc mi trng truyn sng trong nh v ngoi tri, cng nh
d dng trong vic lp thm cc BS tng lu lng phc v tai cc BS b
qu ti
- WCDMA h tr trn vn c dch v chuyn mch knh v chuyn mch gi tc
cao v m bo s hot ng ng thi cc dch v hn hp vi ch gi hotng mc hiu qu cao nht. Hn na, WCDMA c th h tr cc lp tc s
liu khc nhau, da trn th tc iu chnh tc . Chun WCDMA hin thi s
dng phng php iu ch QPSK, mt phng php iu ch tt hn 8-PSK, cung
cp tc s liu nh l 2Mbps vi cht lng truyn tt trong vng ph rng. V
h tr cc tc s liu khc nhau cho nhiu loi dch v ln cn c phng thc
hiu qu kt hp cc dch v vi cc tc khc nhau. V vy, trong WCDMA
i vi ng xung m tri ph OVSF c ng dng cc m trong b m ny
c to ra trc giao vi nhau cho d h s tri ph SF l khc nhau. iu ny chophp cung cp cc dch v vi tc bt khc nhau qua cc knh trc giao vi nhau.
ng ln s dng cc m ngu nhin phn bit gia cc ngi s dng khc
nhau. Cc m ngu nhin ny c mng n nh. MS s nhn c thng bo m
ngu nhin no c cp cho mnh trong bn tin cho php truy nhp trn knh tm
gi ng xung.
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Bng 1-1 ch ra mt s dch v ca h thng thng tin di ng th h 3
Bng 1-1 Cc loi loi dch v chnh ca WCDMA
Kiu knh Dch v h tr
CS 12.2Kb/s Voice
CS 64Kb/s Video Phone
PS 64Kb/s Email, Web
PS 384Kb/s Email, Web ,Video Streaming, Mobil TV
1.2 CU TRC H THNG WCDMA
1.2.1 Cu trc mng WCDMA
Cu trc mng vin thng di ng ton cu (UMTS) vi c s nn tng l h
thng a truy nhp phn chia theo m bng rng (WCDMA) c khi qut bi
hnh 1-2
UuIu
UE UTRAN CN
Hnh 1-2 Cu trc tng quan h thng UMTS
Theo chc nng th cc phn t mng c nhm thnh cc nhm:
+ Mng truy nhp v tuyn RAN (Mng truy nhp v tuyn mt t UMTS l
UTRAN). Mng ny thit lp tt c cc chc nng lin quan n v tuyn. M ha,
iu ch, ghp knh . . .
+ Mng li (CN): Thc hin chc nng chuyn mch v nh tuyn cuc gi v
kt ni d liu n cc mng ngoi.+ Thit b ngi s dng (UE) giao tip vi ngi s dng v giao din v tuyn.
V d: mn hnh, bn phm, micro, loa . . .
Theo cc c t ch ra trong quan im chun ha, c UE v UTRAN u bao gm
cc giao thc hon ton mi, vic thit k chng da trn nhu cu ca cng ngh v
tuyn WCDMA mi. Ngc li, vic nh ngha mng li (CN) c k tha t
GSM. iu ny em li cho h thng c cng ngh truy nhp v tuyn mi mt nn
tng mang tnh ton cu l cng ngh mng li c sn, nh vy s thc y s
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qung b ca n, mang li u th cnh tranh chng hn nh kh nng roaming ton
cu.
V cc thnh phn ca mng WCDMA c ch ra trong hnh 1-3.
UE UTRAN CN
UuIu
USIM
ME
Cu
Nt B
Nt B
Nt B
Nt B
RNC
RNC
MSC/VLR
SGSN
HLR
GMSC
GGSN
PLMN, PSTN,ISDN
Internet
Mng ngoi
IurIub
Hnh 1-3 Cc thnh phn ca mng WCDMA
Thit b ngi s dng(UE) bao gm 2 phn:
Thit b di ng(ME) l u cui v tuyn s dng giao tip v tuyn qua
giao din Uu.
Modul nhn dng thu bao UMTS (USIM- User Identity Module) l mt th
thng minh m nhn vic xc nhn thu bao, thc hin thut ton nhn thc, v
lu gi kho m mt, kho nhn thc v mt s cc thng tin v thu bao cnthit ti u cui.
UTRAN: nhim v chnh ca UTRAN l to v duy tr cc knh mng truy nhp
v tuyn thc hin thng tin gia thit b di ng UE vi mng li CN.
UTRAN bao gm 2 phn t:
Nt B: chuyn i d liu truyn gia giao din Iub v Uu. N cng tham gia
vo qun l ti nguyn v tuyn.
B iu khin mng v tuyn(RNC-Radio Network Controller) s hu v iu
khin ngun ti nguyn v tuyn trong vng ca n (gm cc Nt B ni vi n).. Cc phn t chnh ca mng li
HLR (B ng k thng tr) l mt c s d liu trong h thng thng tr ca
ngi s dng, lu tr cc bn gc cc thng tin hin trng dch v ngi s
dng, hin trng v dch v bao gm: thng tin v dch v c php s dng,
cc vng roaming b cm, thng tin cc dch v b sung nh: trng thi cc cuc
gi i, s cc cuc gi i N c to ra khi ngi s dng mi ng k thu
bao vi h thng, v c lu khi thu bao cn thi hn. Vi mc ch nh
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tuyn cc giao dch ti UE (cc cuc gi v cc dch v nhn tin ngn), HLR
cn lu tr cc thng tin v tr ca UE trong phm vi phc v ca MSC/VLR
hoc SGSN.
MSC/VLR (Trung tm chuyn mch di ng/B ng k tm tr) l mt b
chuyn mch (MSC) v c s d liu (VLR) phc v cho UE v tr tm thi
ca n cho cc dch v chuyn mch knh. Chc nng MSC c s dng
chuyn mch cc giao dch s dng chuyn mch knh, chc nng VLR l lu
tr bn sao v hin trng dch v ngi s dng l khch v thng tin chnh xc
v v tr ca thu bao khch trong ton h thng. Phn ca h thng c truy
nhp thng qua MSC/VLR thng l chuyn mch knh.
GMSC(MSC cng): l mt b chuyn mch ti v tr m mng di ng mt t
UMTS kt ni vi mng ngoi. Tt cc kt ni chuyn mch knh n v i uphi qua GMSC.
SGSN (Node h tr GPRS phc v) c chc nng tng t nh MSC/VLR
nhng thng c s dng cho cc dch v chuyn mch gi.
GGSN(Node cng h tr GPRS) c chc nng gn ging GMSC nhng phc v
cc dch v chuyn mch gi.
Mng ngoic th chia thnh 2 nhm:
Cc mng chuyn mch knh: Cc mng ny cung cp cc kt ni chuyn mchknh, ging nh dch v in thoi ang tn ti V d nh PSTN.
Cc mng chuyn mch gi: Cc mng ny cung cp cc kt ni cho cc dch v
d liu gi, chng hn nh mng Internet.
Cc tiu chun ca h thng vin thng di ng ton cu (UMTS) c cu trc
sao cho khng nh ngha chi tit chc nng bn trong ca cc phn t mng m ch
nh ngha giao din gia cc phn t mng logic
Cc giao din m chnh c nh ngha: Giao din Cu: y l giao din gia th thng minh USIM v ME. Giao din
ny tun theo tiu chun cho cc th thng minh.
Giao din Uu: y l giao din v tuyn WCDMA. Uu l giao din nh UE
truy cp c vi phn c nh ca h thng, v v th c th l phn giao din
m quan trng nht trong UMTS.
Giao din Iu: Giao din ny kt ni UTRAN ti mng li. Tng t nh cc
giao din tng thch trong GSM, l giao din A (i vi chuyn mch knh), v
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Gb (i vi chuyn mch gi), giao din Iu em li cho cc b iu khin UMTS
kh nng xy dng c UTRAN v CN t cc nh sn xut khc nhau.
Giao din Iur: Giao din m Iur h tr chuyn giao mm gia cc RNC t cc
nh sn xut khc nhau, v v th b sung cho giao din m Iu.
Giao din Iub: Iub kt ni mt Nt B v mt RNC. UMTS l mt h thng in
thoi di ng mang tnh thng mi u tin m giao din gia b iu khin v
trm gc c chun ho nh l mt giao din m hon thin. Ging nh cc giao
din m khc, Iub thc y hn na tnh cnh tranh gia cc nh sn xut trong
lnh vc ny.
1.2.2 Cu trc mng truy nhp v tuyn UTRAN
H thng thng tin di ng th h 3- WCDMA c xy dng trn c s mngca h thng GSM vi vic s dng cng ngh mng li ca GSM. Chnh v vy m
im khc bit ln nht v mt cng ngh gia WCDMA vi GSM l mng truy
nhp v tuyn UTRAN vi vic p dng k thut a truy nhp theo m hon ton
mi.
Kin trc UTRAN c m t nh hnh 1-4
UE
UTRANCN
UuIu CS
USIM
ME
Cu
Nut B
Nut B
Nut B
Nut B
RNC
RNC
MSC/
VLR
SGSN
IurIub
Iu PSRNS
RNS
Hnh 1-4: Kin trc UTRAN.
UTRAN bao gm mt hay nhiu phn h mng v tuyn (RNS). Mt RNS l
mt mng con trong UTRAN v bao gm mt b iu khin mng v tuyn (RNC)
v mt hay nhiu Nt B. Cc RNC c th c kt ni vi nhau thng qua mt giao
din Iur. Cc RNC v Nt B c kt ni vi nhau qua giao din Iub.
Cc yu cu chnh thit k kin trc, giao thc v chc nng UTRAN:
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Tnh h tr ca UTRAN v cc chc nng lin quan: Yu cu tc ng ti thit k
ca UTRAN l cc yu cu h tr chuyn giao mm (mt thit b u cui kt ni
ti mng thng qua 2 hay nhiu cell ang hot ng) v cc thut ton qun l
ngun ti nguyn v tuyn c bit ca WCDMA.
Lm tng s tng ng trong vic iu khin d liu chuyn mch gi v chuyn
mch knh, vi mt ngn xp giao thc giao din v tuyn duy nht v vi vic s
dng cng mt giao din cho cc kt ni t UTRAN n min chuyn mch gi
v chuyn mch knh ca mng li.
Lm tng tnh tng ng vi GSM.
S dng phng thc vn chuyn ATM nh l c cu chuyn vn chnh trong
UTRAN
a. B iu khin mng v tuyn (RNC)B iu khin mng v tuyn (RNC) l phn t mng chu trch nhim iu
khin ngun ti nguyn v tuyn ca UTRAN. N giao tip vi mng li (thng l
vi mt MSC v mt SGSN) v cng l phn t cui cng ca giao thc iu khin
ngun ti nguyn v tuyn, xc nh cc thng ip v th tc gia my di ng v
UTRAN, v mt logic, n tng ng vi BSC trong GSM.
RNC phc v (SRNC): RNC cho mi my di ng l mt RNC m xc nh
bin gii c lin kt Iu cho s vn chuyn d liu ngi s dng v bo hiu .
SRNC cng xc nh bin gii ca Bo hiu iu khin ngun ti nguyn v
tuyn, n l giao thc bo hiu gia UE v UTRAN. N thc hin x l cc d
liu chuyn qua giao din v tuyn. Hot ng qun l ngun ti nguyn v tuyn
c bn, nh l nh x cc thng s mang thng tin truy nhp v tuyn thnh cc
thng s knh chuyn vn giao din v tuyn, quyt nh chuyn giao, v iu
khin cng sut vng bn ngoi. Cc hot ng ny c thc thi trong SNRC.
SRNC cng c th l CRNC ca mt s Nt B s dng bi my di ng cho kt
ni vi UTRAN. Mt UE kt ni vi UTRAN th ch c duy nht mt SRNC. B RNC tri (Drif RNC) : DRNC l mt RNC bt k khc vi SRNC iu
khin cc c MS s dng. Khi cn DRNC c th thc hin kt hp v phn
tp v m. DRNC khng thc hin x l s liu trong lp kt ni s liu m ch
nh tuyn s liu gia cc giao din IUb v IUr. Mt UE c th khng c hoc c
mt hay nhiu DRNC.
Ch rng mt RNC mc vt l bao gm ton b cc chc nng CRNC,
SRNC v DRNC.
b. Nt B (Trm gc)
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Chc nng chnh ca Nt B l thc hin x l giao din v tuyn (ghp xen
v m ho knh, thch ng tc , tri ph .v.v.). N cng thc hin mt s hot
ng qun l ti nguyn v tuyn nh l iu khin cng sut vng bn trong. V
mt logic n tng thch vi trm gc trong h thng GSM. Lc u nt B c s
dng l mt thut ng tm thi trong qu trnh chun ho nhng sau n khng b
thay i.
1.3 CC KNH V TUYN
1.3.1 Knh vt l
Trong h thng CDMA th cc knh vt l tng ng vi tn s v m nh knh.
h thng WCDMA th rng bng tn l 5 MHz vi hai sng mang phncch nhau 190 MHz: ng ln c bng tn nm trong di ph t 1920 MHz
n 1980 MHz, ng xung c bng tn nm trong di ph t 2110 MHz
n 2170 Mhz. Mc d 5 MHz l rng bng danh nh, ta cng c th chn
rng bng t 4,4 MHz n 5 MHz vi nc tng l 200 KHz. Khung v
tuyn l mt khi x l bao gm 15 khe thi gian c chiu di 38400 chip,
mt khe thi gian c chiu di 10ms gm 2560 chip. V th s bit trn mt
khe c th khc nhau v trong mt vi trng hp c th bin i theo thi
gian. Cu trc khung v tuyn c biu din trn hnh 1- 5
Hnh !-5: Cu trc khung v tuyn
Ngoi ra th mi knh cn c n nh bi mt m nh knh. M nh
knh l cc m trc giao c h s tri ph bin i (OVSF) m bo s trc
giao gia cc knh vt l. Cc m OVSF c nh ngha theo cy m trn
hnh 1- 6. Mi mc trn cy m xc nh mt m nh knh vi chiu di
Khe 0
Khe 14Khe 1 Khe i
Data
Tslot
=2560 chip, 10.2k bit (k=0,1..,6)
Tf
= 10ms
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bng h s tri ph SF. Tt c cc m trong cy khng th dng ng thi
trong cng mt cell. Mt m ch c s dng trong mt cell khi trong cell
khng s dng mt m no khc nm trn ng t mt m c th ti gc
cy hay trong cy con di m y. iu y c ngha rng s m nh knh
kh dng l khng c nh m ph thuc vo tc v h s tri ph ca mi
knh vt l. Cc m nh knh c k hiu l Cch,SF,ktrong ch l knh, SFl h s tri ph v 0 k SF-1 l s m. H s tri ph l t s gia tc
chip vi tc k hiu a ln tri ph v n cng bng chu k hay di
ca chui tri ph. Mi cy m c xc nh bi mt m ngu nhin ha
nhn dng BS hoc UE.
Hnh 1-6: Cu trc cy m ca m nh knh
Phng php xc nh m nh knh c xy dng trn c s ma trn
Hadamard nh sau:
Cch,4,0 = (1,1,1,1)
Cch,4,1
= (1,1,-1,-1)
Cch,4,2
= (1,-1,1,-1)
Cch,4,3
= (1,-1,-1,1)
Cch,2,0
= (1,1)
Cch,2,1
= (1,-1)
Cch,1,0
= (1)
SF= 1 SF= 2 SF= 4
Cch,2
n
,0C
ch,2
n
,0
Cch,2
n
,0- C
ch,2
n
,0
n n
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Gi tr ngoi cng bn tri trong tng t m nh knh l chui chip c
truyn u tin. Khi kt ni s dng h s tri ph kh bin vic s dng ng n
cy m cng cho php gii tri ph theo h s tri ph nh nht. Do vy, ch cn s
dng m nh knh chn t nhnh c ch th bi m c h s tri ph nh nht.
m bo tnh trc giao gia cc m trong mt cy m cn tha mn quy nh
sau cho vic chn m nh knh cng mt cy m (cng 1 BS hoc cung 1 UE):
ch c th s dng mt m khi v ch khi khng c m no khc c s dng
cng nm trn ng dn t m ny n gc cy hoc cy con pha di m
ny. Cc m trc giao ng xung trong mt trm gc c qun l bi b iu
khin mng v tuyn RNC trong mng.
1.3.2 Knh logic
Cc knh logic l mt nhm cc bit mang mt thng tin c th no : c th l
thng tin v lu lng hay thng tin bo hiu , iu khin. Cc knh ny c phn
chia theo ng xung (t BS n MS) v cc knh ng ln ( t MS n BS).
Cc knh logic WCDMA gm: knh hoa tiu PiCH (ng xung), knh tm gi
PCH (ng xung), knh ng b SCH (ng xung), knh qung b BCH
(ng xung), knh truy nhp ngu nhin RACH (ng ln), cc knh lu lng
TCH c s dng mang thng tin ca ngi s dng (thoi hoc s liu) cng
vi bo hiu gia BS v MS, y l cc knh hai chiu
Cch,1,0
= 1
Cch,2,0
Cch,2,0
Cch,1,0
Cch,1,0
Cch,1,0
- Cch,1,0
1 1
1 -1
ch,2 ,1 - ch,2 ,1..
Cch,2
n
,2
n -1 Cch,2
n
,2
n -1
Cch,2
n
,2
n -1 - Cch,2
n
,2
n -1
Cch,2
n
,2
n -1
Cch,2
n
,0
Cch,2
n
,1
Cch,2
n
,1
.
Cch,2
n
,2
n -1
Cch,2
n
,2
n -1
Cch,2
n
,0
Cch,2
n
,1
Cch,2
n
,1 .
Cch,2
n
,2
n -1
Cch,2
n
,2
n -1
Cch,2
(n+1)
,0
Cch,2
(n+1)
,1
Cch,2
(n+1)
,2
Cch,2
(n+1)
,3 .
.C
ch,2
(n+1)
,2
(n+1) -2
Cch,2
(n+1)
,2
(n+1) -1
= =
=
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a. Knh hoa tiu (PiCH)
Knh hoa tiu PiCH lun c trm gc pht mi knh WCDMA ng
xung. Knh hoa tiu c s dng cung cp tham s chun cho tt c cc tram
di ng, n cung cp tham chun pha cho gii iu ch nht qun. PiCH khng
mang thng tin v l mt tn hiu tri ph khng c iu ch c s dng
ng b cc trm di ng nm trong vng ph ca trm gc, v th cu trc ca
knh ny l mt chui ton khng c tri ph bi hm Walsh 0. Tn hiu hoa tiu
c duy tr mc cao hn knh lu lng vi cng sut tn hiu khng i. Tn
hiu hoa tiu c s dng so snh cng tn hiu gia cc BS khc nhau khi
thc hin chuyn giao v l c s MS iu khin cng sut pht khi truy nhp
mng.
c. Knh ng b (SCH)
Knh ng b c s dng m bo ng b khung, thi gian v cu hnh
h thng cho trm di ng. knh ny ch c mt bn tin c pht i l bn tin
knh ng b. Cc thng s ca bn tin ng b l:
- Nhn dng h thng (SID: System Identification): s nhn dng cho h
thng
- Nhn dng mng (NID: Network Identificatin): s nhn dng mng
- Trng thi m di: m di ti mt thi im xc nh thi gian h thng
- Thi gian h thng
- Tc s liu knh tm gi s knh tm gi, th t khe ca knh tm gi
Bn thn cc bn tin knh ng b c th chim nhiu khung
b. Knh tm gi (PCH)
Knh tm gi mang thng tin t trm gc ti trm di ng. Tn ti bn kiubn tin chnh: b sung, tm gi, lnh v n nh knh. Ni dung ca cc bn tin ny
nh sau:
- Cu hnh ca h thng c truyn cc bn tin b sung: bn
tin thng s h thng, bn tin thng s truy nhp, bn tin danh sch
trm ln cn v bn tin danh sch knh CDMA
- Cc bn tin tm gi cha cc tm gi n mt hay nhiu trm di
ng. Cc tm gi ny thng c pht i khi trm gc nhn c
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mt cuc gi cho mt trm di ng v chng thng c pht t
nhiu trm gc khc nhau.
- Cc bn tin n nh knh cho php trm gc n nh mt knh lu
lng cho mt trm di ng, hay thay i n nh knh tm gi cho
trm di ng ny.
Knh tm gi c mt ch c bit c gi l ch c nh khe. ch
ny cc bn tin cho mt trm di ng ch c pht i cc khong thi gian
nh trc. Kh nng ny cho php trm di ng c th gim cng sut cc khe
thi gian khng dnh cho n, nh vy c th tit kim ng k nng lng ngun
c quy ca my cm tay. Mi MS s c mng n nh mt khe ca knh tm gi.
MS s ly thng tin khe tm gi trn cc bn tin ca knh ng b.
d. Knh qung b (BCH)
L knh ng xung c pht trn ton b cell. BCH c dng pht cc
thng tin mang tnh cht qung b thng tin c truyn di dng kiu truyn n
e. Knh truy nhp ngu nhin (RACH)
Knh truy nhp ch c ng ln. N c trm di ng s dng khi uthng tin vi trm gc v tr li cc bn tin ca knh tm gi. Mi knh truy nhp
u i cp vi mt knh tm gi. Cc knh truy nhp c phn bit vi nhau bi
mt m PN di
f. Knh lu lng (TCH)
Knh lu lng c c ng xung v ln. Knh lu lng truyn:
- Thng tin ca ngi s dng: thoi, s liu
- Thng tin bo hiu
- Thng tin mo u
- Thng tin iu khin
C bn loi bn tin c pht trn TCH: cc bn tin iu khin cuc gi, cc
bn tin iu khin chuyn giao, cc bn tin iu khin cng sut ng xung, cc
bn tin bo mt v nhn thc, cc bn tin cung cp cc thng tin c bit t/ti trm
di ng
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1.4 QUY HOCH PH TN CA WCDMA
Cc bng tn s dng cho WCDMA FDD trn ton cu c cho trn hnh 1-7
WCDMA s dng phn b tn s quy nh cho IMT-2000 (International Mobile
Telecommunications-2000) nh sau. chu u v hu ht cc nc chu bng
tn IMT-2000 l 2 60 MHz (1920-1980 MHz cng vi 2110-2170 MHz) c th s
dng cho WCDMA/ FDD. Bng tn s dng cho TDD chu u thay i, bng tn
c cp theo giy php c th l 25 MHz cho s dng TDD 1900-1920 (TDD1)
v 2020-2025 MHz (TDD2). Bng tn cho cc ng dng TDD khng cn xin php
(SPA= Self Provided Application: ng dng t cp) c th l 2010-2020 MHz. Cc
h thng FDD s dng cc bng tn khc nhau cho ng ln v ng xung vi
phn cch l khong cch song cng, cn cc h thng TDD s dng cng tn s
cho c ng ln v ng xung.UMTS quy nh khai thc song cng phn chia theo tn s l ch tiu
chun cho thng tin thoi v s liu. Hot ng ng thi v lin tc ca cc mch
in pht v thu l cc thay i ng k nht so vi hat ng ca GSM.
Hnh 1-7. Phn b tn s cho WCDMA/FDD.
a) Cc bng c th dng cho WCDMA FDD ton cu; b) Bng tn IMT-2000.
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Bng tn cho hat ng FDD cho cc bng I, II v III c cho trn hnh 1-7.
Bng I (B1) l n nh bng chnh Chu u. Quy nh dnh hai cp pht 60MHz
vi khong cch song cng chun 190MHz, tuy nhin quy nh cng cho php song
cng kh bin, trong khong cch pht thu nm trong khong 130 n 250MHz.
H thng song cng kh bin t ra cc yu cu b sung i vi thit k my pht
thu v cc b t hp tn s my pht v my thu phi hot ng c lp vi nhau.
Bng II (B2) ti s dng bng hin c ca h thng thng tin di ng c nhn v d
nh s dng M m bo ng tn ti UMTS v GSM. Khong cch song
cng ch bng 80MHz i vi bng II v th t ra cc yu cu kh khn hn i
vi phn cng ca my thu pht.
Ti Vit Nam bng tn 3G c cp pht tn s theo tm khe tn s nh cho trong
bng 1-2, trong hai hoc nhiu nh khai thc c th cng tham gia xin cp phtchung mt khe.
Bng 1-2. Cp pht tn s 3G ti Vit Nam
Khe tn s FDD TDD
BSTx* BSRx** BSTx/BSRx
A 2110-2125 MHz 1920-1935 MHz 1915-1920 MHz
B 2125-2140 MHz 1935-1950 MHz 1910-1915 MHz
C 2140-2155 MHz 1950-1965 MHz 1905-1910 MHzD 2155-2170 MHz 1965-1980 MHz 1900-1905 MHz
* BSTx: my pht trm gc
** BSRx: my thu trm gc
L do cp pht cc knh 5MHz khc nhau ti cc nc khc nhau l ch cc
nh khai thc phi quy hoch m v phi trnh vic s dng cc m gy ra nhiu
knh ln cn trong cng mt nc hoc cc nh khai thc khc trong nc lin k.
V th cn phi nghin cu quan h gia cc t hp m tri ph v hot ng cacc knh ln cn. Hin nay ti Vit Nam bng tn I dnh cho WCDMA c
chia l bn khe v c cp pht cho bn nh khai thc: Viettel, VMS, GPC,
EVN+HT
Chng II
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IU KHIN CNG SUT V CHUYN GIAO TRONG H
THNG THNG TIN DI NG A TRUY NHP PHN
CHIA THEO M
Trong h thng thng tin di ng m bo tnh di ng ca thu bao th cc
trm pht phi c t khp ni. Mi trm s ph sng mt vng nht nh v
chu trch nhim vi cc thu bao nm trong vng ph sng ca mnh v h thng
phi m bo tnh lin tc ca tn hiu lin lc khi thu bao di chuyn gia cc trm
pht. Mt khc, do trong h thng CDMA cc thu bao cng s dng chung mt
bng tn ln xy ra hin tng tn hiu mnh ln t tn hiu yu (hiu ng gn xa),
nhiu ng knh. V vy, m bo cht lng QoS yu cu ca dch v h thngphi p dng cc k thut iu khin cng sut v chuyn giao nhm hn ch nhiu
ng knh, gii quyt vn gn xa v lm tng dung lng h thng, tha mn
yu cu roanming.
2.1 IU KHIN CNG SUT
2.1.1 C s ca iu khin cng sut
cc h thng thng tin di ng t ong CDMA, cc my di ng u pht chung
mt tn s cng thi gian nn chng gy nhiu ng knh i vi nhau. Chtlng truyn dn ca ng truyn v tuyn i vi tng ngi s dng trong mi
trng a ngi s dng ph thuc vo t s Eb/N0, trong Ebl nng lng bitcn N0 l mt tp m trng Gaus cng bao gm t tp m v tp m quy i t
my pht ca cc ngi s dng khc. m bo t s Eb/N0 khng i v ln
hn ngng yu cu cn iu khin cng sut ca cc my pht ca cc ngi s
dng theo khong cch ca n vi trm gc. Nu nh cc h thng FDMA v
TDMA vic iu chnh cng sut ny khng bt buc th h thng CDMA iuchnh cng sut l bt buc v iu chnh ny phi nhanh nu khng dung lng
ca h thng s gim. Chng hn nu cng sut thu c ca mt ngi s dng
no trm gc ln hn mi ln cng sut pht ca cc ngi s dng khc, th
nhiu giao thoa ng knh do ngi s dng ny gy ra cng ln gp mi ln
nhiu ca cc ngi s dng khc. Nh vy dung lng ca h thng s gim i
mt lng bng chn. Cng sut thu c trm gc ph thuc vo khong cch
ca cc my di ng so vi trm gc v c th thay i n 80 dB. Hin tng cng
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sut thu thay i theo khong cch gia MS v BS c gi l hin tng gn- xa
hin tng ny nh hng ln ti h thng, c th c minh ha nh sau:
Hnh 2-1 : M t hin tng gn- xa
Gi s c hai trm di ng MS1v MS2cch u trm gc BS mt khong l d v
pht i cng mt cng sut l Pt1= Pt2pht cng thi gian v tn s nn MS1v
MS2s gy nhiu ln nhau. Do c hai trm di ng c cng cng sut pht v cchu trm gc nn t s tn hiu trn can nhiu s bng 1:
C/I=Pr1/Pr2= 1
Trong : Pr1, Pr2 l cc tn hiu m BS thu c t MS1v MS2. By gi nu
MS1 ng yn cn MS2 tin gn li trm gc sao cho khong cch t MS2 ti trm
gc l d/2. Gi s suy hao ng truyn t l vi m 4 khong cch th cng sutthu trm gc i vi MS1 s suy hao vi t l d
4 cn i vi MS2s suy hao theo
t l (d/2)4= d4*1/16. Do cng sut thu c trm gc ca MS2 s ln hn cng
sut thu c ca MS1 l 16 ln v t s tn hiu trn can nhiu trong trng hp
ny s l:
C/I=Pr1/Pr2= 1/16
iu c ngha l t s tn hiu trn can nhiu gim 16 ln so vi trng hp
hai trm di ng cng khong cch. gii quyt vn ny ngi ta cn iukhin cng sut pht ca cc trm di ng sao cho cc trm di ng gn trm gc
s pht cng sut nh hn so vi cc trm di ng xa trm gc. Trong trng hp
ny cng sut pht ca trm MS2 s phi gim 16 ln C/I=1.
Dung lng ca mt h thng di ng CDMA t gi tri cc i nu cng sut
pht ca cc my di ng c iu khin sao cho trm gc cng sut thu c l
nh nhau i vi tt c cc ngi s dng. Ngoi vic gim hin tng gn xa,
iu khin cng sut cn c s dng gim hin tng che ti v duy tr cng
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sut pht trn mt ngi s dng, cn thit m bo t s li bit mc cho trc,
mc ti thiu. Nh vy, iu khin cng sut cn cho mt ci li khc l ko di
tui th ca c quy ca MS.
- Ngoi ra th vic iu khin cng sut cn lm tng kh nng gii tri ph tn
hiu thu, lm cho vic thu, tch tch tn hiu c d dng hn: Nu c hai trm di
ng MS1 v MS2 cng thu, pht trn mt knh CDMA c ph tn hiu tng ng
l D1(f) v D2(f). Ph D1(f) v D2(f) c th nm gn hoc xa nhau trn di tn.
Trc khi truyn i cc ph ny s c tri rng ra nh m tri ph c 1(t) v c2(t)
tng ng. Lc ny ph ca tn hiu c dng gn ging ph ca tp m.
Gi s tn hiu ca trm di ng MS1 l tn hiu cn thu, th tn hiu ca MS2 coi
nh l nhiu. Ti pha thu tn hiu cn thu s c a vo gii tri ph vi m gii
tri ph c1(t) l bn sao ng b ca m tri ph ti pha pht. Nh vy ph tn hiu
D1(f) s c nn li ging nh ph ban u. Cc nhiu di hp sinh ra trong qu
trnh truyn tin s c tri ph ra vi m c1(t) v nh vy ta s thu c tn hiu
cn thu ca MS1. Nhng nu ti pha thu tn hiu tri ph tn hiu ca MS2 thu c
vn cn cao hn (do cng sut pht ln) ph tn hiu ca MS1 sau khi nn (ni
cch khc ph tn hiu D1(f) b chm trong nn nhiu) th my thu cng s khng
thu c tn hiu ca MS1 lm mt thng tin. Nh vy thu c tn hiu ca MS1th phi iu chnh cng sut pht ca nn tp m thu c ti my thu ca BTS
l ng u nhau
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Hnh 2-2: M t s tc ng ca cng sut n vic gii tri ph
Nh vy cng sut ca cc my di ng c iu chnh sao cho sau khi gii tri
ph th ph ca tn hiu cn thu s ln hn nn nhiu my thu c th tch v gii
iu ch.
2.1.2 Phn loi iu khin cng sut
iu khin cng sut nhanh v nghim ngt l nt quan trng nht cc h
thng thng tin di ng CDMA, nht l ng ln. Thiu iu khin cng sut,
mt MS pht cng sut ln hn s chn mt b phn ln dn n hin tng gn-
xa CDMA lm gim dung lng h thng. iu khin cng sut ca mt h
thng th ngi ta cn vo cc tham s sau:
- Trn c s o cng tn hiu
- Trn c s t s tn hiu trn tp m SIR
- Trn c s t l li bt BER
Da vo cc tham s trn chng ta c cc phng php iu khin cng sut sau:
a/ iu khin cng sut cho ng xung v ng ln
iu khin cng sut cho ng ln (t MS n BS) h thng DS-CDMA l
mt yu cu rt quan trng v hiu ng gn-xa. Trong trng hp ny, c mt di
ng iu khin cng sut chng 80 dB. Trn ng xung, khng c hiu ng
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gn-xa do m hnh mt-ti nhiu. iu khincng sut c nhim v b nhiu bn
trong cell gy ra bi cc trm di ng, c bit l nhiu gn bin gii ca ca cc
cell ny (c ch ra trong hnh 2-3). Hn th na, iu khin cng sut trn ng
xung c nhim v lm gim thiu nhiu bng cch gi QoS ti mc gi tr mc
tiu.
Hnh 2-3 B nhiu bn trong cell (iu khin cng sut ng xung)
b/ iu khin cng sut phn tn v tp trung
Mt b iu khin tp trung c tt c cc thng tin v cc kt ni c thit lp
v li knh, v iu khin tt c cc mc cng sut trong mng hay mt phn
ca mng. iu khin cng sut tp trung theo yu cu tn hiu iu khin phm vi
rng trong mng v khng th ng dng trong thc t. Chng c th s dng a
ra gii hn v hiu sut ca thut ton phn tn.
B iu khin phn tn ch iu khin cng sut ca mt trm pht n v thut
ton ch ph thuc vo ni b, nh SIR hay li knh ca ngi s dng c bit.
Nhng thut ton ny thc hin tt trong trng hp l tng, nhng trong cc h
thng thc t c mt s hiu ng khng thch hp nh :
- Tn hiu o v iu khin lm mt thi gian dn n thi gian tr trong h
thng- Cng sut pht hp l ca my pht b hn ch bi gii hn vt l v s
lng t ha. Nhng hn ch bn ngoi khc nh cng sut pht cc i trn mt
knh c bit tc ng n cng sut ra.
- Cht lng l mt s o c ch quan v cn phi tn dng s o c khch
quan hp l.
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c/ iu khin cng sut vng kn, iu khin cng sut vng h
Tn ti ba phng php iu khin cng sut sau y:
iu khin cng sut vng h (ch c UE thc hin qu trnh iu
khin) iu khin cng sut nhanh vng kn (c UE v BS cng tham gia qu
trnh iu khin cng sut) gm iu khin cng sut vng trong v
iu khin cng sut vng ngoi.
H thng WCDMA cung cp chc nng iu khin cng sut hai chiu, chiu
v (t BS n my di ng), chiu ln (t my di ng n BS) kt hp vi qu
trnh iu khin cng sut vng h v vng kn. Nhm nng cao dung lng h
thng, m bo cc dch v cht lng cao
2.2 CHUYN GIAO
Do tnh cht di ng ca thu bao di ng nn mng di ng phi t chc theo
mt cu trc a l nht nh tin cho vic kt ni mng v thng tin lin lc ca
UE cng nh cho vic theo di v qun l thu bao di ng ca nh mng. Mt
phng php t chc hp l m ngy nay hu nh tt c cc mng in thoi di
ng u p dng l phng php t chc mng c cu trc nh mng t ong.
Trong thng tin di ng CDMA ni ring, thng tin di ng ni chung th cc thu
bao di ng MS lun di chuyn t vng ny sang vng khc, ni cch khc l MS
lun di chuyn qua lai gia cc t bo ca mng. Vic di chuyn ny c th dn
ti vic ng k v tr mi vo VLR, s canh nghe trn knh tm gi, ng truyn
thng tin trn cc knh lu lng cng phi thay i ph hp vi s thay i ca
tng trm gc BS khc nhau. Qu trnh thay i cho ph hp gi l qu trnh
chuyn giao. Chuyn giao l phng tin cn thit thu bao c th di ng trong
mng. Khi thu bao di chuyn t vng ph sng ca cell ny sang vng ph sng
ca mt cell khc th kt ni vi cell mi phi c thit lp v kt ni vi cell cphi b hy b.
2.2.1 Mc ch ca chuyn giao ( Handoff)
C nhiu l do cn phi thc hin vic chuyn giao. L do c bn ca chuyn
giao l kt ni v tuyn khng tha mn mt b tiu chun nht nh v do hoc
UE hoc UTRAN s thc hin cc cng vic ci thin kt ni . Cc iu kin
chuyn giao thng gp l: iu kin cht lng tn hiu, tnh cht di chuyn ca
thu bao, s phn b lu lng, bng tn
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iu kin cht lng tn hiu l iu kin khi cht lng hay cng tn hiu
v tuyn b suy gim di mt ngng nht nh c nh ngha bi RNC, s suy
gim tn hiu s c nhn bit bng cch o mc tn hiu. Vic o tn hiu c
thc hin c UE v RNC. Chuyn giao ph thuc vo cht lng tn hiu c
thc hin cho c hng ln v hng xung cu ng truyn dn v tuyn.
Chuyn giao do nguyn nhn lu lng xy ra khi dung lng lu lng ca
cell t ti mt gii hn ti a cho php hoc vt qu ngng gii hn . Khi
cc thu bao ngoi ra ca cell (c mt ti cao) s c chuyn giao sang cell
bn cnh (c mt ti thp). Bng cch thc hin chuyn giao nh vy, ti h
thng s c phn b u v nh cu v dung lng v vng ph sng c iu
chnh mt cch c hiu qu p ng nhu cu lu lng trong mng.
S lng chuyn giao ph thuc vo tc di chuyn ca thu bao. Khi UE dichuyn theo mt hng nht nh khng thay i, tc di chuyn ca UE cng
cao th cng c nhiu chuyn giao thc hin trong RAN. trnh nhng chuyn
giao khng cn thit, thu bao chuyn ng vi tc cao c th c thc hin
chuyn giao t cc cell vi m (micro-cell) n cc cell v m (macro-cell). Trong
trng hp ngc li thu bao di chuyn vi tc chm, thu bao ny c th c
chuyn giao t cell v m sang cell vi m nhm ci thin cht lng tn hiu.
Quyt nh thc hin chuyn giao thng thng c thc hin bi RNC ang
phc v thu bao , loi tr trng hp chuyn giao v l do lu lng. Chuyngiao do nguyn nhn lu lng c thc hin bi trung tm chuyn mch di ng
(MSC)
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o lng:- o cc tham s
- Bo co cc tham so c
Quyt nh:-Cc tham s thutton-Cc c tnh chuyngiao
Thc hin;- Tn hiu chuyn giao- Phn b ti nguynv tuyn
2.2.2 Trnh t chuyn giao
Trnh t chuyn giao gm c ba pha nh hnh v, bao gm : pha o lng, pha
quyt nh v pha thc hin.
Hnh 2-4:Tin trnh thc hin chuyn giao
a/ o lngo lng l mt nhim v quan trng trong qu trnh chuyn giao v hai l do c
bn sau :
- Mc tn hiu trn ng truyn dn v tuyn thay i rt ln ty thuc
vo pha inh v tn hao ng truyn. Nhng thay i ny ph thuc vo
mi trng trong cell v tc di chuyn ca thu bao.
- S lng cc bo co o lng qu nhiu s lm nh hng n ti h
thng
thc hin chuyn giao, trong sut qu trnh kt ni, UE lin tc o cng
tn hiu ca cc cell ln cn v thng bo kt qu ti mng, ti b iu khin truy
nhp v tuyn RNC. D liu o lng ca UE c th chia thnh cc nhm sau :
- D liu o cng tn s l d liu o cng tn hiu cng tn s ca cc
knh vt l ng xung.
- D liu o cc tn s khc nhau l d liu o cng tn hiu c tn s
khc nhau ca cc knh vt l ng xung.
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- D liu o gia cc h thng bao gm d liu o cng ca cc knh
vt l ng xung ca cc h thng truy nhp khc, v d nh h thng
GSM.
- D liu o mt lu lng gm d liu o mt ng ln.
- D liu o cht lng l d liu o cc tham s cht lng, chng hn nh
FER ca ng xung.
- D liu o ni b gm cc s liu o cng sut truyn dn UE v mc tn
hiu thu ti UE
Tn hiu o c kch bi cc iu kin sau :
- Thay i ca cell tt nht (cell c mc tn hiu cao nht).
- Nhng thay i mc tn hiu ca knh hoa tiu
- Nhng thay i v t s tn hiu trn tp m SRN- Thng bo c tnh cht chu k.
- Thi im kch.
b/ Quyt nh chuyn giao
Pha quyt nh chuyn giao bao gm nh gi tng th v QoS ca kt ni so
snh n vi cc thuc tnh QoS yu cu v c lng t cc cell ln cn. Ty theo
kt qu so snh m ta c th quyt nh thc hin hay khng thc hin chuyn giao.
SRNC kim tra cc gi tr ca cc bo co o c kch hot mt b cc iu kinchuyn giao. Nu cc iu kin ny c kch hot, RNC phc v s cho php thc
hin chuyn giao.
Cn c vo quyt nh chuyn giao, c th phn chia chuyn giao ra thnh hai
loi nh sau :
- Chuyn giao quyt nh bi mng NEHO (Network Evaluated Handover).
- Chuyn giao quyt nh bi thu bao di ng MEHO (Mobile Evaluated
Handover)
Trong trng hp chuyn giao thc hin bi mng (NEHO), SRNC thc hin
quyt nh chuyn giao. Trong trng hp MEHO, UE thc hin quyt nh chuyn
giao. Trong trng hp kt hp c hai loi chuyn giao NEHO v MEHO, quyt
nh chuyn giao c thc hin bi s phi hp gia SRNC vi UE.
Ngay c trong trng hp chuyn giao MEHO, quyt nh cui cng v vic
thc hin chuyn giao l do SRNC. RNC c trch nhim qun l ti nguyn v
tuyn ca ton b h thng v cc thng tin cn thit khc phc v cho vic thc
hin chuyn giao.
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Quyt nh chuyn giao da trn cc thng tin o c ca UE v BS cng nh
cc iu kin thc hin thut ton chuyn giao. Cc thut ton chuyn giao
khng c tiu chun ha, chng c lp vi qu trnh xy dng h thng. Do
cc thut ton chuyn giao tin tin c s dng t do da trn cc tham s sn c
kt hp vi kh nng o c cc phn t ca mng, s phn b lu lng, quy
hoch mng, cu trc h tng mng v chin lc lu lng ca ton b h thng
c s dng bi cc nh cung cp dch v.
c/ Thc hin chuyn giao
Qu trnh chuyn giao c th xy ra trng thi ri hay trng thi knh lu
lng.
- Chuyn giao trng thi riChuyn giao ri hay thay i knh tm gi xy ra khi MS chuyn t vng ph
ca BS ny sang vng ph ca BS khc trng thi ri. MS xc nh rng xy ra
chuyn giao khi n pht hin ra hoa tiu mi ln hn hoa tiu hin thi.
Cc knh hoa tiu c nhn dng bi dch thi ca chui PN ngn. Cc knh
ny c nhm vo cc tp m t trng thi ca chng lin quan n cc th tc tm
kim hoa tiu. trng thi ri, ba tp hoa tiu c duy tr: tch cc, k cn, v cn
li. i vi mi tp hoa tiu, ca s tm kim c nh ngha. Ca s ny cho
php MS tm kim ng truyn trc tip cng nh cc thnh phn ca cc ngkhc ca tn hiu hoa tiu. Nu MS xc nh rng hoa tiu tp k cn hoc tp cn
li ln hn hoa tiu ca tp tch cc, chuyn giao ri c thc hin
- Chuyn giao trng thi knh lu lng
Chuyn giao trng thi knh lu lng l qu trnh chuyn giao xy ra khi MS
c n nh knh lu lng
C cc trng hp chuyn giao l: chuyn giao bn trong v chuyn giao gia cc .
Chuyn giao gia cc gm :
- Chuyn giao gia cc thuc hai BTS khc nhau nhng cng mt BSC
- Chuyn giao gia cc thuc hai BTS khc nhau ca hai BSC cng MSC
- Chuyn giao gia cc thuc hai BTS thuc hai MSC khc nhau.
Cn c vo cc trng hp chuyn giao khc nhau trong h thng CDMA tn ti
cc dng chuyn giao sau :
1) Chuyn giao cng ( chuyn giao cng lin tn v lin h thng)
2) Chuyn giao mm
3) Chuyn giao mm hn
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Chuyn giao cng
- Chuyn giao cng da trn nguyn tc: Ct trc khi ni. Trong chuyn giao
ny kt ni vi knh c b ct trc khi kt ni vi knh mi c thc hin. V vy
m trong qu trnh chuyn giao cng tn hiu lin lc s b gian on tuy nhin
khong gin on ny cc MS khng th nhn bit c. Trong CDMA th chuyn
giao cng ch yu dng chuyn giao gia cc sng mang CDMA khc nhau hay
chuyn giao vi cc h thng di ng khc
Chuyn giao mm v mm hn
- Chuyn giao mm v mm hn da trn nguyn tc kt ni: Ni trc khi ct.
Chuyn giao mm l chuyn giao trong trm di ng bt u thng tin vi mt
trm gc mi m vn cha ct thng tin vi trm gc c. Chuyn giao mm ch c
th c thc hin khi c trm gc c ln trm gc mi u lm vic cng tn s - Chuyn giao mm hn l chuyn giao mm c thc hin gia cc on cacng mt .
Cng nh iu khin cng sut chuyn giao mm v mm hn cn phi c cc
h thng thng tin di ng CDMA v l do sau: trnh hin tng gn- xa xy ra
khi MS tin su vo vng ph sng ca ln cn m khng c BTS ca ny
iu khin cng sut dn n n s gy nhiu rt ln cho cc MS khc ny.
Chuyn giao cng thng xuyn v nhanh c th trnh c iu ny, nhng
chuyn giao ny ch c th thc hin c vi mt thi gian tr nht nh, trongkhong thi gian ny c th xy ra hin tng gn- xa. V th cng vi iu khin
cng sut, cc chuyn giao mm v mm hn l cc cng c k thut quan trng
gim nhiu CDMA
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CHNG III
IU KHIN CNG SUT V CHUYN GIAO
TRONG H THNG WCDMA
3.1 IU KHIN CNG SUT
3.1.1. Cc dng iu khin cng sut
iu khin cng sut nhanh v nghim ngt l nt quan trng nht cc h
thng thng tin di ng WCDMA, nht l ng ln. Do cng ngh WCDMA
s dng k thut tri ph nn tt c cc thu bao c th thu, pht chung trn cng
tn s gy ra hin tng nhiu ng knh. Do , thiu iu khin cng sut, mt
MS pht cng sut ln hn s chn mt b phn ln dn n hin tng gn- xa
CDMA lm gim dung lng h thng. Nh vy dung lng h thng tc cc i cn iu khin cng sut pht ca tt c cc MS trong mt sao cho
mc cng sut m chng to ra BS s bng nhau. Trong h thng WCDMA tn
ti cc phng php iu chnh cng sut sau:
- iu khin cng sut vng h (ch c trm MS tham gia qu trnh iu khin)
- iu khin cng sut vng kn (c trm gc v trm di ng u tham gia
qu trnh iu khin) gm iu khin cng sut vng trong v iu khin
cng sut vng ngoi.
Ngoi ra gim nhiu do cc BTS gn nhau gy ra trong WCDMA cng thc
hin iu khin cng sut ng xung BTS da trn bo co kt qu FER
(Frame Error Ratio) o c t MS. Trn ng xung, khng c hiu ng gn-xa
do m hnh mt-ti nhiu. iu khincng sut c nhim v b nhiu bn trong
cell gy ra bi cc trm di ng, c bit l nhiu gn bin gii ca ca cc cell ny
(c ch ra trong hnh 3-1). Hn th na, iu khin cng sut trn ng xung
c nhim v lm gim thiu nhiu bng cch gi QoS ti mc gi tr mc tiu.
Hnh 3-1: B nhiu bn trong cell (iu khin cng sut ng xung)
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Trong hnh 3-1, MS2 phi chu nhiu nhiu bn trong cell hn MS1. V th
p ng mc tiu cht lng ging nhau, cn nhiu nng lng cp pht cho cho
cc knh ng xung gia BS v MS2.
3.1.2 Nguyn l iu khin cng sut vng hiu khin cng sut vng h ch yu iu khin cng sut ng ln, thchin nh gi gn ng cng sut ng xung ca tn hiu knh hoa tiu da trn
tn hao truyn sng ca tn hiu ny. Trong h thng WCDMA phng php iu
khin cng sut ny thng c s dng thit lp cng sut gn ng khi truy
nhp mng. Hnh 3-2 cho ta thy qu trnh iu khin cng sut khi MS truy nhp
mng trn knh RACH.
Hnh 3-2 Qu trnh iu khin cng sut vng m khi MS truy nhp mng trn
knh RACH
truy nhp mng MS thc hin th truy nhp bng cch pht i nhiu chui
thm d truy nhp. Lc u chui thm d truy nhp c pht i mt cng sut
tng i thp trn c s nh gi cng sut m MS thu c (cng sut pht nyc xc nh theo nguyn tc l: khi thu c mt hoa tiu mnh t trm gc c
ngha l suy hao ng xung thp, nu coi suy hao ng ln cng nh vy th
trm di ng ch cn pht mt cng sut thp v ngc li). Nu khng nhn c
tr li t BTS trn knh PCH, MS pht thm d truy nhp tip theo vi mc cng
sut cao hn v qu trnh ny c lp nhiu ln cho n khi n nhn c tr li t
BTS.
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Mi bc cng sut Pi c gi l mt hiu chnh cng sut vng h. Khi ny cng
sut pht khi u ca trm di ng c xc nh nh sau:
Pt= -Pr-72+ NOM_PWR+INT_PWR
V cng sut pht ca trm di ng sau khi nhn c tr li ca BTS
Pt= -Pr-72+ NOM_PWR+INT_PWR+Tng cng sut ca cc ln hiu
chnh thm d truy nhp (Pi).
Trong :
Pt: Cng sut pht trung bnh (dB)
Pr: Cng sut thu trung bnh (dB)
NOM_PWR: iu chnh danh nh
INT_PWR: iu chnh ban u
c tnh c-ng hoa tiu
P_tx =1/C- ng hoa tiu
Hnh 3-3 : Nguyn tc iu khin cng sut vng h
Qu trnh iu khin theo vng m ny din ra lin tc sau khi trm gc xc
nhn yu cu truy nhp ca my di ng
Tuy nhin nhc im ln nht ca phng php ny l: do iu kin truyn
sng ca ng xung khc ng ln nht l do pha inh nhanh nn s nh gi sthiu chnh xc.
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3.1.3 Nguyn l iu khin cng sut vng kn
Phng php iu khin cng sut vng kn c m t nh hnh v
Cc lnhiukhincngsut ncc MS
MS 1
MS 2
Duytrcc mc
cngsut P1vP2bngnhau
Hnh 3-4 C ch iu khin cng sut vng kn
phng php ny BTS thng xuyn nh gi t s tn hiu trn can nhiu
(SIR) thu c v so snh n vi t s SIR ch im t
SIRsetpoint= (Eb/N0)req req = request
Nu SIR thu cao hn SIRsetpoint th BTS ra lnh cho MS h thp cng sut, tri li
n ra lnh cho MS tng cng sut. Chu k o lnh phn ng ny c thc hin
1500 ln trong mt giy. Tc ny s cao hn mi s thay i tn hao ng
truyn v thm ch c th nhanh hn pha inh nhanh khi MS di chuyn vi tc
thp. Bit iu khin cng sut (PCb) c ghp vo knh TCH ng xung. Cc
bit iu khin cng sut c ghp vo knh lu lng theo hng sau b m ha,
v th cc PCb khng c m ha chng li. iu ny c thc hin gim trc hu khi gii m ha. V iu khin cng sut theo vng kn c s dng
chng lai hin tng pha inh nhanh. Cc PCb khng c m ha my thu di
ng nhanh chng c th thu li PCb v iu chnh cng sut pht cho ph hp.
Mi bit iu khin cng sut ny to ra thay i 1,2,3 dB gn hn n gi tr ch.
Cn lu rng c th vic iu chnh cng sut ny khng thnh cng v N0 lun
lun thay i
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Hnh 3-5 Nguyn l iu khin cng sut vng kn
K thut iu khin cng sut vng kn nh vy c gi l vng trong cngc s dng cho ng xung mc d y khng c hin tng xa- gn. Tuy
nhin l do bt buc iu khin cng sut y nh sau: Khi MS tin gn ti bin
gii , n bt u chu nh hng ngy cng tng ca nhiu t cc khc. iu
khin cng sut trong trng hp ny to mt lng d tr cng sut cho cc
MS trong trng hp cc trng hp ni trn
-iu khin cng sut vng ngoi
iu khin cng sut vng ngoi thc hin iu chnh gi tr SIRsetpoint BTS cho
ph hp vi yu cu ca tng ng truyn v tuyn t c cht lng cc
ng truyn v tuyn nh nhau. Cht lng ca cc ng truyn v tuyn thng
c nh gi bng t s li bit BER hay t s li khung FER. L do cn t li
SIRsetpoint nh sau: SIR yu cu chng hn l FER=1% ph thuc vo tc ca
MS v c im truyn a ng. Nu ta t SIRsetpoint ch cho trng hp xu
nht (tc ca MS l cao nht) th s lng ph dung lng cho cc kt ni tc
Gii triph
My thuRAKE
o SIR
So snh vquyt nh SIR ch
o chtlng
So snh vquyt nh
To bit iukhin cng
sut
Chtlng
ch
Vngtrong
Vngngoi
Tnhiuthu
Ghp bit iu khin csvo lung pht
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thp. Nh vy, tt nht l SIRsetpoint th ni xung quanh gi tr ti thiu p ng
c yu cu cht lng.
Hnh 3-6 iu khin cng sut vng ngoiHnh 3-6 cho thy s thay i ca SIRsetpoint theo thi gian. thc hin iu
khin cng sut vng ngoi, mi khung s liu ca ngi s dng c gn ch th
cht lng khung l CRC. Vic kim tra ch th cht lng ny s thng bo cho
RNC v vic gim cht lng v RNC s lnh cho BTS tng SIRsetpoint. L do t
iu khin vng ngoi RNC v chc nng ny thc hin sau khi thc hin kt hp
cc tn hiu chuyn giao mm.
Tn s ca iu khin cng sut vng bn ngoi thng l 10-100Hz.
3.1.4 Qu trnh thc iu khin cng sut ng ln
Cng sut pht ca my di ng l mt hm ca qu trnh iu khin cng suttheo vng h v vng khp kn. Cc hnh 3-7 v hnh 3-8 ch ra qu trnh thc hin
lc iu chnh cng sut ng ln. i vi qu trnh iu khin cng sut
vng khp kn, trm gc c ton b vng iu khin ngoi v mt phn ca vng
iu khin trong; my di ng c cc phn khc ca vng iu khin trong. i vi
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qu trnh iu khin cng sut theo vng m, ton b phn iu khin theo vng m
nm trong my di ng.
Quyt nh:
Nu gi trEb/N0- c tnh >ng- ng thPCb=1(UE gim 1dB) Nu gi trEb/N0- c tnh
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c tnh cngsut thutrung bnh
Quyt inh: Nu PCb=0 tng cng
sut pht 1dB Nu PC b=1 gim cng
sut pht 1dB
G ii iuch
My thu
M y pht Kh nh l- u l- ng - ng lnS liu
P C b
S liu thuVng khp kn
antenthu
antenpht
K = 72 dB
NOM_ PW R (dB)
Tng tt c c c gi tri hiuchnh th m d truy nhp
INIT_P WR (dB)
P r
Hnh 3-8 Qu trnh iu khin cng sut ng ln c thc hin trm di ng
V pha my di ng (xem hnh 3-8), my di ng thu tn hiu t ng truynxung. N khi phc li cc bit PCb a ra quyt nh tng hoc gim cng sut
pht i 1,2,3 dB. Vic quyt nh l s hiu chnh theo vng khp kn
3.1.5 Qu trnh thc iu khin cng sut ng xung
Trong trng hp l tng th vic iu khin cng sut ng xung l
khng cn thit. L do l trm gc ang pht tt c cc knh nht qun trong cngmt bng tn RF, theo m hnh mt ti nhiu. Tuy nhin, trong thc t mt my di
ng c th gn mt ngun nhiu nghim trng v phi chu mt nn nhiu ln,
hoc my di ng c th phi chu mt suy hao ng truyn ln trn tn hiu tng
hp thu c ngoi tp m nhit. Ngoi ra, th iu khin cng sut ng xung
cn b v gim nhiu giao thoa gia cc cell ln cn. Nh vy, vic iu chnh
cng sut hng xung l vn cn thit. Tuy nhin, ni chung l yu cu iu khin
cng sut i vi hng xung l khng nghim ngt nh yu cu i vi iu
khin ng ln
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thc hin qu trnh iu khin ny th trm di ng c quy nh lun phi
bo co phn hi cht lng ca ng truyn xung ti trm gc. My di ng
lin tc gim st FER ca ng truyn xung v n bo co gi tr FER ny v
trm gc trn mt bn tin c gi l: bn tin bo co php o cng sut (PMRM).
Trm di ng thng gi bn tin ny theo mt trong hai cch sau: mt cch l my
di ng bo co thng k bn tin PMRM (Power Measurement Report Message)
v cch th hai l my di ng ch bo co PRMR khi gi tr FER ca ng truyn
xung vt qu ngng nht nh. Trm gc thi bn tin PMRM, nhn bit cht
lng ca ng truyn xung, sau c th iu chnh cng sut pht ca n ti
my di ng. Thut ton chnh xc ca qu trnh iu khin cng sut ny ph thuc
vo cc nh sn xut cu trc h tng ring bit. Qu trnh ny hu nh lun l c
quyn ca mi nh sn xut
3.1.6 iu khin cng sut trng thi chuyn giao mm
trng thi chuyn giao mm (trng m kt ni mi c thit lp trc khi ct
kt ni c), cng sut pht ca UE c iu chnh da trn vic la chn lnh iu
khin cng sut TPC ph hp nht t nhng lnh iu khin cng sut m n nhn
c t cc BS c kt ni n UE . Trong trng hp UE nhn cc lnh iu
khin cng sut c ni dung khc nhau. Cc lnh ny khc nhau c th do li trongkhi truyn dn cng c th do mng. Do vy, UE phi x l tnh hung c mu
thun gia cc lnh iu khin cng sut. gii quyt mu thun UE thc hin
lnh iu khin cng sut theo nguyn tc: nu cc lnh cng sut ging nhau l
cng tng th UE tng cng sut pht ca mnh, cn cc trng hp khc th UE s
gim cng sut pht. Qu trnh iu khin cng sut trong trng hp ny c m
t nh hnh v
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=>UE gim cng sut
TPC: "gim cng sut"
=>UE gim cng sut
TPC: "gimcng sut" TPC: "t ng cng sut" TPC: "gimcng sut"
=>UE t ng cng sut
TP C: "tng cngsut" TPC: "t ng cng sut"
Hnh 3-9: iu khin cng sut trng thi chuyn giao mm
3.2 CHUYN GIAO
Nh chng II chng ta bit bt k h thng thng tin di ng t bo no
cng phi p dng k thut chuyn giao p ng cc yu cu v cht lng dch
v, kh nng di ng ca cc thu bao, iu chnh ti ca h thng trnh tc
nghn mng. Trong h thng WCDMA do vic dng chung cng mt bng tn v
p dng k thut tri ph nn c kh nng h tr y chuyn giao mm. c bit
WCDMA kt hp chuyn giao mm vi vic iu khin cng sut nhanh v nghim
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ngt cng lm tng thm hiu qu trong vic chng nhiu v gii quyt vn gn-
xa. Tuy nhin do WCDMA l bc tin ha ca h thng GSM tin ln 3G ln
trong WCDMA cng p dng c k thut chuyn giao cng. Ngoi ra, th tuy rng
h s ti s dng tn s trong WCDMA c th bng mt nhng trong WCDMA vn
p dng quy hoch ti s dng tn s cho cc vng inh v LA khc nhau v vy
vic p dng chuyn giao cng l vn cn thit trong WCDMA.
3.2.1 Cc kiu chuyn giao trong WCDMA
- Chuyn giao cng c th c chia thnh: chuyn giao cng cng tn s v
chuyn giao cng khc tn s. Trong qu trnh chuyn giao cng, kt ni c c
gii phng trc khi thc hin kt ni mi. Do vy, tn hiu b ngt trong khong
thi gian thc hin chuyn giao. Tuy nhin, thu bao khng c kh nng nhn bitc khong ngng . Trong trng hp chuyn giao cng khc tn s, tn s
sng mang ca knh truy nhp v tuyn mi khc vi tn s sng mang hin ti.
Hnh 3- 10 th hin chuyn giao cng cng tn s.
Tn s f1 Tn s f1
BSBS
UE
Iur
RNC RNC
Hnh 3-10: chuyn giao cng cng tn s
Trn hnh 3- 10,do k hoch quy hoch mng, RNC bn cnh khng c kt
ni vi giao din Iur v vy chuyn giao mm gia cc RNC khng thc hin c.
Trong tnh hung nh vy, chuyn giao cng cng tn s l loi chuyn giao duy
nht h tr kt ni v tuyn khi thu bao di ng t BS ny sang BS mi. Trn thc
t, iu ny lm xut hin s kin chuyn giao RNC, trong MSC cng lin quan
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n qu trnh chuyn giao. Thng thng, h s ti s dng tn s i vi WCDMA
bng mt, iu c ngha l cc BS s dng chung mt tn s v tt c cc UE
dng chung tn s trong ton b mng. iu khng c ngha l vic s dng li
tn s khng c thc hin h thng WCDMA. Do , nu cc sng mang khc
nhau c phn b cho cc cell, chuyn giao khc tn s c s dng m bo
ng chuyn giao t cell ny sang cell khc.
Chuyn giao lin tn s cng c s dng trong mng t bo v c cu trc
(HCS) gia cc lp cell ring r, chng hn gia cc cell vi m v cc cell v m,
cc cell ny s dng tn s sng mang khc nhau trong cng mt vng ph sng.
Chuyn giao khc tn s c thc hin khng ch duy tr kt ni (nu khng
thc hin chuyn giao kt ni c th b ngt) m cn m bo yu cu QoS.
Chuyn giao cng lin tn thng thng l NEHO. Chuyn giao lin tn s c thxy ra gia hai mng truy nhp v tuyn khc nhau, v d gia GSM v WCDMA.
Khi , loi chuyn giao ny gi l chuyn giao lin h thng xem hnh 3- 11.
Chuyn giao lin h thng cng l chuyn giao lin tn nhng cc tn s khc nhau
thuc cc h thng khc nhau
Tns f2Tn s f1
BS BS
UE
Hnh 3-11 : Chuyn giao cng khc tn s
Chc nng chuyn giao lin h thng trong WCDMA c thc hin bi mtch lm vic c bit: ch nn. Khi UE ch nn, c th gim h s tri
ph ca knh. Do vy, kt ni giao din v tuyn ch s dng mt phn nh ca
khung WCDMA. Cc khe thi gian cn li c th s dng cho cc mc ch khc,
v d nh o mc tn hiu can nhiu t cc cell GSM bn cch. Ch nn c th
t c bng cch gim tc s liu lp cao hoc gim tc k hiu khi ghp
knh lp vt l. Khi UE s dng giao din Uu ch ny, ni dung ca khung
WCDMA c nn mt bit to ra mt ca s m qua UE c th nhn v gii
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m thng tin t knh qung b (BCH) ca h thng GSM. Ngoi ra, c RAN ca
UMTS v phn h trm gc BSS ca GSM phi c kh nng gi cc thng tin ch
th khc trn cc knh BCH UE c kh nng thc hin vic gii m chnh xc.
Chuyn giao lin h thng gia WCDMA v GSM c thc hin nhng khu
vc m c hai h thng ny cng tn ti. Chuyn giao lin h thng c yu cu
b xung vng ph gia hai h thng nhm m bo phc v lin tc. Chuyn giao
lin h thng c th c s dng iu chnh ti gia cc h thng GSM v
WCDMA, khi vng ph gia hai h thng chng ln ln nhau. Ngoi ra, chuyn
giao ny c th thc hin theo yu cu ca ngi s dng. Chuyn giao lin h
thng l loi chuyn giao NEHO. Tuy nhin, UE phi c kh nng h tr hon ton
loi chuyn giao ny. RNC pht hin chuyn giao lin h thng da trn cu hnh
mng v tuyn (cc nh ngha v cell ln cn) v cc tham s iu khin khc.- Khc vi chuyn giao cng, chuyn giao mm c thc hin theo nguyn l :
thit lp kt ni mi trc khi gii phng kt ni c. Trong h thng WCDMA, hu
ht chuyn giao l chuyn giao mm cng tn s
Tn s f1Tn s f1
BS BS
UE
Hnh 3-12: Chuyn giao mm cng tn s
Chuyn giao mm c thc hin gia cc cell thuc cc BS khc nhau nhng
khng nht thit phi cng mt RNC. Trong trng hp RNC c lin quan n
chuyn giao mm, RNC phi thc hin vic iu khin chuyn giao qua giao din
Iur. Trong trng hp chuyn giao mm, cc cell ngun v cell ch c cng tn s.
Trong trng hp cuc gi chuyn mch knh, cc my di ng thc t thc hin
chuyn giao mm hu nh lin tc nu vng ph sng c cu trc cell nh.
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Chuyn giao mm hn l loi chuyn giao trong tn hiu mi c thm vo
hoc xa khi tp tch cc, hoc thay th bi tn hiu mnh hn trong cc secter
khc nhau ca cng BS (xem hnh)
Secter 2f1
Secter 3f1
Secter 1f1Tn hiu a
-ng quasecter 1
Tn hiu a
-ng quasecter 3
Hnh 3-13: Chuyn giao mm hn cng tn s
Trong trng hp chuyn mm hn, BS pht trong mt secter nhng thu tnhiu secter khc. Trong trng hp ny, UE c cc kt ni v tuyn tch cc
ng ln ti mng qua nhiu secter ca cng mt BS. Nguyn nhn dn n
chuyn giao trong cc on l : do cc BTS thng s dng anten c tnh hng
ln ph ht mt 3600 ngi ta thng dng 3 on 1200 hay 6 on 600
3.2.2 Thut ton chuyn giao trong WCDMA
Nguyn tc chung thc hin thut ton chuyn giao c th hin trn hnh 3-14iu kin u l cc iu kin thc hin quyt nh ca thut ton da trn mc tnhiu hoa tiu do UE thng bo. Cc thut ng v cc tham s sau c s dng
trong thut ton chuyn giao :
- Ngng gii hn trn : l mc tn hiu ca kt ni t gi tr cc i cho
php tha mn mt cht lng dch v QoS yu cu.
- Ngng gii hn di : l mc tn hiu ca kt ni t gi tr cc tiu cho
php tha mn mt cht lng dch v QoS yu cu. Do mc tn hiu
ca kt ni khng c nm di mc .
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- Gii hn chuyn giao : l tham s c nh ngha trc, c thit lp ti
im m cng tn hiu ca cell bn cnh (cell B) vt qu cng
tn hiu ca cell hin ti (cell A) mt lng nht nh.
- Tp tch cc : l mt danh sch cc nhnh tn hiu hoa tiu (cc cell) m
UE thc hin kt ni ng thi ti mang truy nhp v tuyn (RAN).
- Tp ng c: tp ny cha cc hoa tiu khng c trong tp tch cc. Tuy
nhin MS vn thu c cc hoa tiu ny vi cng tn hiu ln
ch ra rng cc knh lu lng ng xung c th c gii iu ch
thnh cng.
- Tp ln cn : tp ny cha cc hoa tiu ln cn hin thi khng c trong
tp tch cc v tp ng c nhng c kh nng lm ng c cho chuyn
giao. Cc hoa tiu ln cn ca mt hoa tiu l tt c cc hoa tiu ca cc ,on nm gn hoa tiu ny. Danh sch hoa tiu ln cn c pht n
MS bn tin thng s h thng trn knh tm gi.
- Tp cn li : tp ny cha tt c cc hoa tiu c trong h thng tr cc hoa
tiu tp tch cc, ng c v ln cn.
Gi i hn chuyngiaoTn hiu tng
C-
ngtnhiu Ng- ng trn
Ng- ng d- i
Thi gian
(1) (2) (3)
Cell A Cell B
Tn hiu A Tn hiu B
Hnh 3-14: Nguyn tc chung ca cc thut ton chuyn giao
Gi s thu bao UE trong cell A ang chuyn ng v pha cell B, tn hiu hoa
tiu ca cell A (ti UE ang thc hin kt ni) b suy gim n ngng gii hn
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di nh hnh trn. Khi t ti mc ngng gii hn di, xut hin kch thch
chuyn giao theo cc bc sau y :
(1) Cng tn hiu A bng vi mc ngng gii hn di. Mt khc, ty
theo gi tr o ca UE, RNC pht hin c tn hiu ca cell bn cnh (tn hiu
B), tn hiu ny c cng ci thin cht lng kt ni. Do , RNC
s nhp tn hiu B vo tp tch cc. Khi UE c hai kt ni ng thi ti
UTRAN. UE s thu tn hiu tng hp ca hai kt ni ny.
(2) Ti v tr ny, cht lng tn hiu B tt hn tn hiu A. Do , RNC coi v
tr l im khi u khi tnh ton gii hn chuyn giao.
(3) Cng tn hiu B bng hoc tt hn ngng gii hn di. Do mc
tn hiu ny tha mn yu cu cht lng dch v QoS ca kt ni.
Bn cnh , tng tn hiu ti UE vt qu ngng gii hn trn v c khnng gy ra nhiu cho h thng. Do vy, RNC s xa tn hiu A khi tp
tch cc.
Kch c ca tp tch cc c th thay i c, thng thng tp tch cc c kch
thc trong khong t 1 n 3 tn hiu.
Do hng chuyn ng ca UE thay i ngu nhin, UE c th quay tr li cell
A ngay sau khi thc hin chuyn giao ln th nht. iu ny s lm xy ra hiu ng
gi l ping-pong. Hiu ng ny lm nh hng khng c li i vi lu lng h
thng cng nh hot ng ca ton b h thng. Vic s dng gii hn chuyn giaoc th trnh c mt s chuyn giao khng cn thit.
Nh trn chng ta bit l thc hin chuyn giao th MS lun lun phi thc
hin gim st cht lng dch v QoS v tm kim, o cng ca cc hoa tiu,
sp xp vo cc tp tng ng. Trong h thng CDMA s dng mt k thut tm
kim hoa tiu gi l ca s tm. Trm di ng thc hin tm kim knh hoa tiu
trong mt khong thi gian cho trc bng s chip ca mt chui hoa tiu PN.
MS s dng ba ca s tm kim sau :
1. SRCH_A : l ca s tm m MS s dng bm tp tch cc v tp ng c
2. SRCH_N : l ca s tm m MS s dng gim st cc hoa tiu ln cn
3. SRCH_R : l ca s tm m MS s dng gim st cc hoa tiu tp cn li
Khi qu trnh quyt nh chuyn giao c thc hin theo lu hnh 3-15
Trong
T_ADD: Ngng pht hin hoa tiu
T_COMP : Ngng so snh
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Tmhoa tiutip theo (Px)Tpln cn hay cn li
P(x) v-t ng-ngT_Add
Sai
ng
1.Chuyn hoa tiu vo tpngc2.Gi bn tino c-ng tnhiu
hoa tiu ntrmgc
Sai ng
1. Gi bn tin o hoa tiu ntrmgc2. Thu bn tin h-ng dnchuyngiao ttrmgc3. Chuyn hoa tiuvo tp tch cc (trmding vo chuyn giao mm4. Gi bn tin hon thnhchuyngiao ntrmgc
P(x) v-t T_Comp
so vi 1hoa tiutch cc
VnP(x) tp ngc
Hnh 3-15Lu thut ton quyt nh chuyn giao
3.2.3 Lu thc hin chuyn giao
Sau khi quyt nh chuyn giao thi MS s tin hnh chuyn giao theo hng dn
ca BS. Qu trnh chuyn giao c biu din nh cc hnh di
Hnh 3-16 biu din qu trnh bt u chuyn giao mm
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1
23
4
5
6
7
8
Quyt nhchuyn giao
o c-ng hoa tiu
L-u l- ng rng
o c- ng hoa tiu
MSBS
Phc vMSC BS
ch
9
10
11
12
13
14
15
Yu cu chuyngiao gia c c BSYu cu chuyngiao gia c c BS
Join Request
J oin Acknowledge
InterBase Handoff Ack
InterBase Handoff Ack
Chthchuyn giao
Hon thnh chuyn giao
Thng b o chuyn giao
Handoff Information Ack
Lnh yu cu o hoa tiu
Hnh 3-16 : Chuyn giao mm bt u
1. MS xc nh rng mt trm BS khc c cng tn hiu hoa tiu tr thnh ch ca chuyn giao.2. MS pht bn tin Pilot Strength Measurement (o cng hoa tiu) n
BTS ang phc v n.3. BS ang phc v pht bn tin Interbase Station Handoff ( yu cu chuyn
giao) n MSC ch.4. MSC pht bn tin Interbase station Handoff ti BS ch.5. BS ch thit lp thng tin vi MS bng cch pht bn tin Null Traffic n
MS.6. BS ch pht bn tin Join Request ( yu cu kt ni lin lc ) n MSC.
7. MSC xem xt cc kt ni vi hai BS thc hin chuyn giao m khng lmgin on kt ni, sau pht bn tin Join Request Acknowledge (xc nhnkt ni) n BS ch.
8. BS ch pht bn tin Interbase Handoff Acknowledge n MSC.9. MSC pht bn tin Interbase handoff Acknowledge n BS ang phc v.10. BS ang phc v pht bn tin ra Handoff Direction n MS.11. Ms pht bn tin Handoff Complete n BS ang phc v.12.BS phc v mi pht bn tin Handoff Information ( thng bo chuyn giao)
n MSC.13. MSC khng nh bn tin ny bng bn tin Handoff Information Ack.
14. BS ch pht lnh Pilot Measurement n MS.
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15. Ms pht bn tin Pilot Strength Measurement n BS ch.Trong qu trnh chuyn giao th MS thng tin ng thi vi c hai BS v qu trnh
chuyn giao s kt thc khi tn hiu ca BS c khng cn mnh. Khi ny MS s
loi b trm gc c thc hin lin lc trn trm gc mi
Yu cu t bXc nhn t b
Lnh yu cu o hoa tiu
1
2
3
4
56
7
8
Quyt nhchuyn giao
o c- ng hoa tiu
Interface Primary Transfer
o c- ng hoa tiu
MSBS
Phc vMSC BS
ch
9
10
11
12
Interface Primary Transfer Acknowledge
Handoff Information
HO Information Ack
Chthchuyn giao
Hon thnh chuyn giao
Hnh 3-17 : Kt thc qu trnh chuyn giao MS ri b BS phc v
1. MS xc nh rng trm BS ang phc v n khng cng tn hiu tip tc trng thi chuyn giao mm.
2. MS pht bn tin Pilot Strength Measurement n BS. Bn tin ny yucu BS ri b chuyn giao.
3. BS ang phc v pht bn tin Handoff Direction n MS. Bn tin nych th rng BS ang phc v s ri khi chuyn giao.
4. MS pht bn tin Handoff Complete n BS ang phc v.5. BS ang phc v pht bn tin Interface Primary Transfer ( chuyn s cp
giao din) n BS ch cng vi thng tinbn ghi cuc gi tng ng.6. BS ch khng nh bn tin ny bng bn tin Interfacce Primary
Transfer ck ( xc nhn chuyn s cp giao din).7. BS ch pht bn tin Handoff Information n MSC.
8. MSC pht bn tin Handoff Information Ack n BS ch.
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9. BS ch pht lnh Pilot Measurement Request ( yu cu o hoa tiu)n MS.
10.Ms pht bn tin Pilot Strength Measurement n BS ch.11.BS ang phc v bn tin Remove Request ( yu cu ri b) n MSC
yu cu ri b kt ni.12.MSC khng nh bn tin ny bng bn tin Remove Ack n trm BS
gc.By gi MS lm vic vi BS ch ( BS phc v mi). Nu cn cc chuyn giao
mm b sung th qu trnh chuyn giao c lp li
3.2.4 u nhc im ca chuyn giao mm
Chuyn giao mm l loi chuyn giao c th ca h thng thng tin di ng
WCDMA da trn nguyn tc ni trc khi ct. So vi chuyn giao cng th HO c
mt s u nhc im sau :
a/ u im
- iu ha ti trn mng : trong trng hp ti ca 1 cell v l do no y
tng t ngt th h thng s chuyn giao sang cc cell ln cn c lu
lng thp hn
- Lm cho thng tin ca ngi s dng lin tc hn khng b ngt qung
nh trong chuyn giao cng
- Cung cp cht lng thng tin tt hn, khng b rt cuc gi
- Vic phn b ti ca cc cell lm dung lng h thng tng- Mt u im na ca chuyn giao mm l khi kt hp vi iu khin cng
sut. V thng v tr chuyn giao l ni m cng tn hiu yu ln nu
chuyn giao mm kt hp vi iu khin cng sut s lm gim nhiu ln
cc MS khc
Tuy nhin bn cnh nhng u im k trn th chuyn giao mm cng c mt
s nhc im
b/ Nhc im
- Chuyn giao mm lm gim dung lng ng xung ca h thng dotrong qu trnh thc hin chuyn giao MS thng tin ng thi vi c hai
trm gc tc l n c cp hai knh lu lng lm gim ti nguyn
mng. C MS v BS lun phi gim st cht lng h thng
- K thut chuyn giao mm phc tp hn chuyn giao cng
Tuy cn c nhng nhc im k trn nhng chuyn giao mm vn l k thut
chuyn giao p ng c cc yu cu kht khe ca h thng thng tin di ng
th h 3 vi nhiu dch v cht lng cao
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KT LUN
iu khin cng sut l qu trnh iu khin cng sut ca my pht trong qutrnh hot ng. iu khin cng sut c quan h mt thit vi chuyn giao mm.
Nu kt hp tt hai k thut ny th s gim ng k nhiu cng nh lm tng cht
lng h thng. Li ch chnh ca vic iu khin cng sut l gii quyt vn
gn- xa, hn ch pha inh cng nh s che ti i vi tn hiu ng ln, gim
nhiu giao thoa ng xung
Trong qu trnh thc hin ti em c bn hiu r v c ch cng nh cc thut
ton iu khin cng sut v chuyn giao c p dng trong h thng WCDMA.
Tuy nhin do trnh cng nh thi gian c hn ln ti ca em kh trnh khi
nhng thiu st. Mt ln na em xin chn thnh cm n thy Bi nh Thnh cng
cc thy, c gio trong t mn, dy bo, hng dn em trong nhng nm qua.
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TI LIU THAM KHO
[1] TS. Nguyn Phm Anh Dng, CDMA one v CDMA2000., Nh xut bn bu
in 7/2003
[2] TS. ng nh Lm, TS. Chu Ngc Anh, Ths. Hong Anh, Ths. Nguyn Phi
Hng, H thng thng tin di ng 3G v xu hng pht trin., Nh xut bn khoa
hc v k thut 2004
[3] K s Nguyn Vn Thun, H thng thng tin di ng WCDMA., Hc vin
cng ngh bu chnh vin thng 12/2004
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CC T VIT TT
3G Third Generation Th h 3
A.AMR Adaptive Multi-Rate codec B m ho v gii m a tc thch nghi
B.
BER
BLER
BPSK
BTS
Bit Error Rate
Block Error Rate
Binary Phase Shift Keying
Base Tranceiver Station
Tc li bit.
Tc li Block
Kho dch pha nh phn.
Trm gc
C.CDMA
CN
CRC
Code Division Multiple Access
Core Network
Cylic Redundancy Check
Truy nhp phn chia theo m
Mng li
M vng kim tra d thaD.
DL
DSSS
Downlink
Direct Sequence Spread Spectrum
ng xung
H thng tri ph chui trc tipE.
EDGE Enhanced Data Rates for Evolution
Equivalent Isotropic Radiated Power
Cc tc d liu tng cng
cho s tin hoF.
FDD
FDMA
FER
Frequency Division Duplex
Frequency Division Multiple Access
Frame Error Rate
Phng thc song cng phn chia
theo tn s
a truy nhp phn chia theo tn
s
T s li khungG.
GGSN
GPRS
GSM
Gateway GPRS Support Node
General Packet Radio Service
Global System for Mobile
Telecommunication
Nt h tr cng GPRS
Dch v v tuyn gi chung.
H thng vin thng di ng ton
cuH.
HLR
HO
Home Location Registor
Handoff
B ng k thng tr
Chuyn giaoI.
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IMT-2000
Iub
Iur
International Mobile
Telecommunication 2000
Thng tin di ng ton cu 2000
Giao din gia RNC v nt B
Giao din gia 2 RNC.
M.ME
MSC
MS
Mobile Equipment
Mobile Service Switching Centre
Mobile Station
Thit b di ng
Trung tm chuyn mch dch v di
ng.
Trm di ngO
OVSF Orthogonal Variabel Spreading
Factor
H s tri ph bin trc giao
P.PN Pseudo Noise Gi tp mQ.
QPSK Quardrature Phase Phase Shift
Keying
Kho dch pha cu phng.
R.RAN
RNC
RNSRRC
RRM
Radio Access Network
Radio Network Controller
Radio Network subsystemRadio Resoure Control protocol
Radio Resouse Management
Mng truy nhp v tuyn.
B iu khin mng v tuyn.
Phn h mng v tuynGiao thc iu khin ti nguyn v
tuyn
Thut ton qun l ti nguyn v
tuyn.S.
SGSN
SHO
SIRSNR
Serving GPRS Support Node.
Soft Handover
Signal to Interference RatioSignal to Noise Ratio
Nt h tr GPRS phc v
Chuyn giao mm.
T s tn hiu trn nhiuT s tn hiu trn tp m
T.
TDD
TDMA
TPC
Time Division Duplex
Time Division Multiple Access
Transmission Power Control
Phng thc song cng phn chia
theo thi gian
a truy nhp phn chia theo thi
gian
iu khin cng sut pht
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U.
UE
UL
UMTS
USIM
UTRAN
User Equipment
Uplink
Universal Mobile
Telecommunication System
UMTS Subscriber Identify Module
UMTS Terrestrial Radio Access
Network
Thit b ngi s dng
ng xung
H thng vin thng di ng ton
cu.
Modul nhn dng thu bao UMTS
Mng truy nhp v tuyn mt t
UMTSV.
VLR Visitor Location Registor B ng k tm trW.
WCDMA Wideband Code Division Multiple
Access
a truy nhp phn chia theo m
bng rng