Đề BÁO CÁO THỰC TẬP MÔN THÔNG TIN DI ĐỘNG

8/2/2019 BO CO THC TP MN THNG TIN DI NG

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H THNG THNG TIN CDMAMC LC

CHNG I - TNG QUAN V H THNG THNG TIN DI NG

1 : Lch s pht trin HTTTD.

2 : Cc th h trong thng tin di ng.

2.1 : H thng thng tin di ng th h th nht.

2.2 : H thng thng tin di ng th h th hai.

2.3 : H thng thng tin di ng th h th ba.

3 : Cc phng php a truy nhp trong thng tin di ng.

3.1 : nh ngha v phng php a truy nhp.

3.2 : Phng php a truy nhp phn chia theo tn s FDMA.

3.3 : Phng php a truy nhp phn chia theo thi gian TDMA.

3.4 : Phng php a truy nhp phn chia theo m CDMA.

CHNG II : H THNG THNG TIN CDMA (Code Division MultiplexAccess)

1 : Khi qut h thng CDMA.

1.1 : Tng quan v CDMA.

1.2 : Cu hnh h thng CDMA.

2 : K thut tri ph trong CDMA.

2.1 : c im ca h thng tri ph.

2.2 : Tri ph trc tip DS/SS - Direct Sequence/Spread Spectrum.

2.3 : Qu trnh pht v thu tn hiu trong CDMA.


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3 : iu khin cng sut trong CDMA.

3.1 : iu khin cng sut trong CDMA.

3.2 : iu khin cng sut vng m.

3.3 : iu khin cng sut vng kn.

3.4 : iu khin cng sut vng ngoi.

3.5 : B m - gii m thoi v tc s liu bin i.

3.6 : My di ng chuyn vng mm.

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LI M U

Trong tnh hnh bng n s pht trin ca cng ngh thng tin hin khngch Vit Nam ni ring m trn ton th gii ni chung. Hin nay, Vit Namang s dng h thng mng GSM. Tuy nhin, trong tng lai mng di ng nys khng p ng c cc nhu cu v thng tin di ng. Bi v, nhu cu v thngtin di ng khng n thun ch l nghe gi thoi m cn l : chia s d liu, hnhnh, tin tc, nghe nhc, video...vi tc cao, cc yu cu v bo mt v chtlng cng c t ra. iu ny t ra mt yu cu mi cho mt phng thcmi i vi cc nh cung cp dc v. V cng ngh CDMA tr thnh mc tiuhng ti ca thng tin di ng trn ton th gii.

Cng ngh CDMA da trn nguyn l tri ph c hiu qu s dng dithng ln hn so vi cc cng ngh tng t hoc s khc do s lng thu baoa truy nhp ln hn nhiu. Nh dn rng ph tn hiu m c th chng li ccc tc ng gy nhiu v bo mt tn hiu. Cc mng thng tin di ng s dngcng ngh CDMA c th p ng c cc nhu cu v thng tin trong tng lai.

Vi ti " H thng thng tin CDMA " em hy vng s c th mang li mt chthiu bit v h thng ny.

Ni dung ca ti ny l xt v tng quan CDMA, v cng ngh tri phv k thuth iu khin cng sut trong CDMA ni chung.

ti bao gm 2 chng :


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Chng 1 : Tng quan h thng thng tin di ng.

Chng 2 : H thng thng tin CDMA.

CHNG I - TNG QUAN V H THNG THNG TIN DI NG.

1 : Lch s pht trin HTTTD

- in thoi di ng ra i vo nm 1920 u tin n thun ch l linlc gia n v cnh st ca m.

- n 1960 in thoi di ng mi ng dng c cc k thut tri ph viu ch s mc dng c tuy nhin vi dung lng thp.

- Nm 1980 cng ngh FDMA ( Frequency Division Mulntiple Access) atruy nhp phn chia theo tn s c a vo ng dng vi ch lm vic songcng u tin.Sau n cui 1980 khi s lng thu bao tng ln cng ngh ny khng th p ng c v ngi ta a ra gii php l s dng k thutthng tin s vi cng ngh a truy nhp phn chia theo thi gian ( TDMA - TimeDivision Mulntiple ) ra i u tin chu u c tn gi l GSM ( GroupSpecial Mobile ) " Nhm c trch "

- Nm 1985 h thng s c quyt nh thnh lp.- Nm 1986 H thng bng hp TDMA c la chn v 13 nc ng

k vo bin bn ghi nh thc hin cc quy nh , nh vy hnh thnh nn mtth trng di ng s tim nng rng ln v tt c cc nc k hip nh ha nngy 1/7/1991 s c mt h thng GSM vn hnh.

- n nm 1993 h thng GSM mi c a vo Vit Nam hin nay angc cng ty VMS v GPC khai thc rt l hiu qu.

- Vo gia nhng nm 1980 M a vo s dng h thng tng tAMPS - Advanced Mobile Phone Service (dch v in thoi di ng tin tin )v cng ngh FDMA .

- Cui nhng nm 1980 cng ngh AMPS khng p ng c nhu cuca nc M v sau M quyt nh a vo cng ngh TDMA vi mng GSM


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v i tn l IS - 54 sau mt thi gian th nghim th cho thy IS - 54 c chtlng khng bng AMPS M lnh nht vi GSM.Ngay sau hng AT&T cho pht trin h thng s mi IS - 136 cn gi l D - AMPS s dng cngngh TDMA, khng ging nh IS -54, IS - 136 thc s thnh cng.

- n nm 1985 cng ngh CDMA c QUALCOM pht trin bng cngngh tri ph v s dng a truy nhp phn chia theo m (CDMA - Code DivisionMultiple Access ) hay cn gi l " Thng tin QUALCOM " v n nay cngngh CDMA thng tr Bc M c QUALCOM tung ra phin bn u tinl IS - 95

-Nm 1993 NTT ra tiu chun dnh ring cho h thng thng tin ding s ring ca Nht Bn JPD ( Japanese Personal Digital Cellular System -

h thng t ong s Nht Bn ).-Nm 1998 hai h thng thng tin di ng mt t v v tinh : Global v

Iridium cng c a vo thng mi.

- Vit Nam GPC v VMS hin ang khai thc hai mng thng tin di ngs l VinaPhone v Mobiphone theo tiu chun GSM. V vo cui nm 2001 thhai cng ty ln l SPT v SLD a IS - 2000 vo s dng. Cho n nay mngthng tin di ng pht trin rng khp vi nhng h thng mng thng tin lin

lc ln nh : Viettel , Vinaphone , Mobiphone , VNPT , EVN telecom... ngy mtpht trin v ln mnh.

- Ti Vit Nam h thng thng tin di ng cng ngy mt pht trin mnhvi s ra i ca hng lot cc cng ty vin thng nh : cng ty GPC ra i nm1996 v c i tn thnh Vinaphone vo nm 2006 , cng vi nm 1989 cngty SIGELCO tin thn ca cng ty vin thng Viettel by gi cng c ra i vn nm 2004 Viettel chnh thc ra i , ngay sau l cng ty Mobiphone cngc thnh lp nm 1994 , Evntelecom , VNPT... dn dn hnh thnh nn mtmng li thng tin di ng pht trin ti Vit Nam.

- n nm 2012 cc dch v vin thng lin tc c pht trin v ra i vis tham gia ca cc hng di ng mi, v cc cng ngh c a vo ng dng

pht trin mnh m l 2G, 3G vi cc dch v khng ch l cung cp cc cucgi thoi m cn cho php truyn ti d liu hnh nh, email, video, lt web trnmobile ngy mt pht trin hnh thnh nn mt mng li thng tin di ng ytim nng Vit Nam.


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********

2 : Cc th h trong thng tin di ng.

2.1/ H thng thng tin di ng th h th nht.

- H thng thng tin di ng th nht ch h tr cc d liu thoi tng t vs dng k thut iu ch tng t mang d liu thoi ca mi ngi.H thngth h ny s dng phng php a truy nhp phn chia theo tn s FDMA :

H1.1 : Ph ca h thng FDMA.

trn l ph ca h thng FDMA bng thng ca h thng c chia thnh ccph c rng Wch , gia cc knh k nhau c mt khong bo v chnh hin


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tng chng ph do s khng n nh ca tn s sng mang. Khi c ngi dnglin h vi trm BS (Base Station) , BS s n nh ngi dng vo mt knh chac s dng v khi cuc gi kt thc th knh s ucj s dng cho mt ngikhc.

- c im ca h thng ny :+ Mi MS (Mobile Station) c cp pht i knh lin lc thng

tuyn.

+ Nhiu giao thoa do tn s cc knh ln cn nhau l ng k.

+ BTS (Base Trainceiver Station) phi c b thu pht ring lm vicvi mi BS.

+ H thng ny c dung lng v tc thp.

2.2/ H thng thng tin di ng th h th hai.

- H thng thng tin di ng th hai l h thng s s dng hai phng phpa truy nhp chnh :

+ a truy nhp phn chia theo thi gian TDMA.

+ a truy nhp phn chia theo m CDMA.

- H thng ny c dung lng v tc ln p ng c s lng thu baoln cc dch v pht trin hn.

2.3/ H thng thng tin di ng th h th ba.

- H thng thng tin di ng th h ba s dng cc mng nh : GPRS

(General Packet Radio Service - Dch v v tuyn gi chung), EDGE (EnhancedDatarates for Global Evolution - Nng cao tc truyn dn d liu) ,CDMA2000 - 1x.

- c im ca h thng :

+ Tc ln c th ln ti 2Mb/s L h thng bng thng rng.

+ H thng ny s dng cc cng ngh : CDMA , W-CDMA s dngcng ngh TDMA nh GSM (Group Special Mobile - Nhm di ng c th) IS -136.

+ Th h ba c xy dng trn c s IMT - 2000.+ Tc 384Kb/s i vi vng ph sng rng v 2Mb/s i vi vng

ph sng a phng.

+ S dng di tn quy nh quc t 2Ghz :

Tn s ng ln : 1885 - 2025 Mhz.

Tn s ng xung : 2110 - 2200 Mhz.


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

+ Tng tc vi mi loi dch v vin thng.

+ H tr cc dch v mng : VHE - Vtrual Home Environment mitrng thng tin o , m bo chuyn mng quc t , cc dch v a phng tin

nh : thoi , s liu , hnh nh , video...+ D dng h tr cc dch v mi xut hin.

- Ngy nay vi s pht trin vt bc ca cng ngh thng tin ngi ta cng nghin cu v dn dn a vo th nghim cng ngh 4G, tin ti trong tnglai cng ngh ny cn pht trin cao hn na p ng nhu cu ca s lng thu

bao ngi dng ngy cng tng vi cc dch v v nhu cu ca ngi s dng hinnay.

*********3 : Cc phng php a truy nhp trong thng tin di ng.

3.1/ nh ngha v phng php a truy nhp.

- a truy nhp l k thut cho php nhiu knh vt l thu pht c th cngs dng mt knh vy l chung.

- VD :

MS - Mobile Station truy nhp BTS - Base Trainceiver Station , cctrm thu pht mt t truy nhp trm v tinh.

- Cc k thut a truy nhp c phn chia nh sau :+ Phng php truy nhp phn chia theo tn s FDMA

(Freqquency Division Multiple Access).

+ Phng php a truy nhp phn chia theo thi gian TDMA (TimeDivision Multiple Access).

+ Phng php a truy nhp phn chia theo m CDMA (CodeDivision Multiple Access).

3.2/ Phng php a truy nhp phn chia theo tn s FDMA.

- K thut a truy nhp phn chia theo tn s ra i u tin , vi k thutny mi mt user c cung cp mt knh hay mt khong tn s ring. TrongFDMA ton b bng tn c chia thnh nhng khong tn s khc nhau v nhngkhong tn s ny c n nh cho tng user v khng user no c chia s knhca mnh cho user khc ngay c khi n khng c s dng.

- u im :


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+ Bng thng ca mi knh l tng i hp nn hn ch c fadingchn lc c tn s.

+ Cc tnh ton cho h thng FDMA kh n gin.

+ Vic ng b l tng i dn gin.

- Khuyt im :

+ Mi user ch c cung cp mt khong tn s c nh do vy mtc khng i , h thng ny khng ph hp vi truyn dn s.

+ Cn phi c khong bng tn bo v gim thiu nhiu xuynknh v c th s dng b chn lc ly khong tn s mong mun.

+ Cn b lc bng hp tt.

3.3/ Phng php a truy nhp phn chia theo thi gian TDMA.

- Ph quy nh cho di tn lin lc c chia thnh cc di tn lin lc , midi tn lin lc c dng chung cho N knh lin lc mi knh lin lc l mt khethi gian trong chu k mt khung , cc thu bao khc dng chung knh nh ci xenthi gian mi thu bao c cp pht cho t khe thi gian trong cu trc khung.


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H1.2 : Ph h thng 3 khe thi gian vi 5 ngi dng.

- c im :

+ Tn hiu ca thu bao c truyn dn s.

+ Lin lc song cng.

+ Gim my thu pht trm gc BTS.

+ Gim nhiu giao thoa.3.3/ a truy nhp phn chia theo m CDMA.

- CDMA s dng k thut tri ph cho nn nhiu ngi c th cng chimdng mt knh v tuyn ng thi tin hnh cc cuc gi m khng s gy nhiuln nhau , nhng ngi s dng ni trn c phn bit vi nhau nh dng mt mc trng khng trng vi bt k ai. Knh v tuyn CDMA c dng li mi


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(cell) trong ton mng v nhng knh ny c phn bit nhau nh m tri ph gingu nhin (Pseudo Noise - PN).

- c im :

+ Di tn tn hiu hng Mhz.

+ S dng k thut tri ph phc tp.

+ K thut tri ph cho php tn hiu v tuyn s dng c cng trng hiu qu hn FDMA v TDMA.

+ Thit b truyn dn n gin , s dng phng thc chuyn giaomm , iu khin dung lng rt linh hot.

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CHNG II - H THNG THNG TIN CDMA.

1 : Khi qut h thng CDMA.

1.1/ Tng quan CDMA.

- H thng thng tin di ng CDMA l h thng m ton b vng phc vca n c chia thnh nhiu vng phc v nh gi l cc , mi c mt trmgc ph trch v uc iu khin bng tng i sao cho thu bao c th vn duy trcuc gi c mt cch lin tc khi di chuyn gia cc .

- Trong h thng thng tin di ng t ong th tn s ca cc knh l khngc nh mt knh no c m knh m thoi c xc nh nh knh bo hiu vmy di ng dc ng b v tn s mt cch t ng. V vy cc k nhau phi

s dng tn s khc nhau nhng cc cch xa nhau mt khon cch nht nh cth s dng cng mt tn s.

- c im :

+ H thng ny s dng cng ngh tri ph tn hiu vi cng ngh triph trc tip DS/SS (Direct Sequence - Spread Sprectrum) v k thut tri phnhy tn FH (Frequency Hopping) cng vi l k thut iu khin cng sut sdng mch tch hp mt cao LSI - Large Scale Intergration lm tng dunglng ng k cho h thng.

+ S dng cc b m thoi tc bin i c lm gim nhiu khiknh thoi khng c tn hiu v vy lm gim CCI - Co-Chanel Interference nhiung knh.

- Ngoi ra s ra i ca DS/CDMA v mch tch hp mt cao rt lnVLSI - Verry Large Scale Interference , x l tn hu s DSB - Digital SignalBrocessing nm 1980 n nm 1990 DSP du phy ng ra i vi h thng l64bit so vi nm 1980 l 16 bit th dung lng b nh tng gp 50 ln.


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- Hiu qu s dng tn s ca h thng in thoi di ng tng ln v ccknh RS Gia cc BS c th c nh v mt cch c hiu qu nh vic ti sdng tn s v do dung lng s dng thu bao cng c tng ln.

1.2/ Cu hnh h thng CDMA.

H1.3 : Cu hnh h thng CDMA.

BSC - Base Station Controller (B iu khin trm gc).MSC/VLR- Mobile Service Switching Center/Visitor Location Register (Trungtm chuyn mch dch v di ng/B ghi nhn dng thit b).

IWF - Inter Working Function (Chc nng tng tc mng).

PDSN - Packet Data Serving Node (nt dch v d liu gi)


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*********

2 : K thut tri ph trong CDMA

2.1 : c im ca h thng tri ph.

- hu ht cc h thng thng tin th bng tn l iu c quan tm chnh, cc h thng ny phi thit k sao cho s dng cng t bng tn cng tt. Tuynhin, cc h thng thng tin tri ph th bng tn c m rng hng trm lntrc khi pht. KHi mt ngi s dng trn bng tn SS - Spread Spectrum (Tri

ph) th khng thy c hiu qu, nhng trong mi trng nhiu ngi s dngth mi ngi c th dng chung bng tn tri ph (SS) v h thng bng tn vnc hiu sut m vn duy tr c cc u im ca tri ph.

- c im ca h thng thng tin tri ph :

+ Tn hiu c pht chim rng bng tn ln hn rng bngtn cn thit.

+ TRi ph c thc hin bng m c lp vi s liu.

- Phn loi tri ph :

+ K thut tri ph trc tip DS/SS - Direct Sequence/SpreadSpectrum.

+ K thut tri ph nhy tn FH/SS - Frequency Hopping/SpreadSpectrum.

+ K thut tri ph dch thi gian TH/SS - Time Hopping/SpreadSpectrum.

2.2/ Tri ph trc tip DS - Direct Sequence.

- H thng ny s dng phng php tri ph bng cch nhn tn hiu ngunvi tn hiu gi ngu nhin. h thng ny nhiu ngi s dng cng chung mth thng bng tn v c pht i cc tn hiu ca h mt cch ng thi, my thus s dng tn hiu gi ngu nhin chnh xc ly ra d liu cn thit bng cchtri ph.


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- H thng DS l s iu ch cc dy m c iu ch thnh cc dngsng iu ch trc tip. H thng ny l h thng c bit n nhiu nht trongthng tin tri ph, chng c dng rt n gin v chng khng yu cu tnh n nhnhnh hoc tc n nh tn s cao.

* c tnh tn hiu ca DS.

- DS iu ch sng mang c dy m bng iu ch AM, FM hay iuch pha hoc bin n tng t nh iu ch BPSK 1800. Dng iu ch tn hiuca DS l dng iu ch hai pha n gin .

H1.5 : Dng sng iu ch ca DS hai pha.

- c im ca DS :

+ Rt kh pht hin c cc sng mang b trit nu khng ccc k thut phc tp. Cc b thu thng thng rt kh tch c sng mang vmc sng mang nm bn di ca mc tp m khi iu ch m.

+ Yu cu cng sut cho vic truyn thng tin ch cn s dngi vi vic truyn thng tin m ha.

+ Hiu qu s dng cng sut pht trong trng hp s dnghng s duy tr rng bng thng l ln nht v cc thnh phn tn hiu c mcgii hn nht nh.

* Dng sng v cu hnh ca h thng DS.


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H1.6 : Dng sng v cu hnh DS.

- Hnh trn biu th dng sng v cu hnh DS cho thy n tng t nhmch thng tin trong AM v FM. Sng mang khng c iu ch trc tip tthng tin ca bng gc m phi a qua th tc iu ch nh b m v b tch ly

bi dy m tc thi.

- Tn hiu thu c khuychs i v nhn vi m ng b lin quan ti upht v u thu. Nu cc m ti u pht v u thu c ng b th sng mangtch pha l lowns hn 1800 v sng mang c khi phc. Cc sng mang bng tnhp ny c khi phc i qua b lc bng thng c thit k sao cho ch cc

sng mang iu ch bng gc c i qua.- Cc sng mang gi cng c i qua cng mt th tc nhn tn s nh

hot ng ca pha thu m ti y tn hiu DS thu c s chuyn thnh bng tnsng mang ban u. Tn hiu thu m khng c ng b vi tn s lin quan cau thu th c cng vi bng tn lin quan v c tr ra.

- B lc bng thng c th gii hn hu ht cc cng sut tn hiu gi v tnhiu bng tn khng ng b s tr ra bng tn lin qua ca b thu.

2.3/ Qu trnh pht v thu tn hiu.

* My pht DS/SS - BPSK ( Binary Phase Shift Keying ).


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H1.7 : S my pht DS/SS - BPSK.

- Ta c th biu din bn tin nhn c cc gi tr sau :

bk : Bt s liu th k.

T : rng xung (tc s liu l 1/T (bit/s)).

- Tn hiu b(t) c tri ph bng m gi tp m PN - Pseudo Noise c(t)bng cch nhn hai tn hiu ny vi nhau. Tn hiu nhn c : b(t).c(t) sau sc iu ch sng mang s dng BPSK to ra c tn hiu DS/SS - BPSK

c xc nh cng thc sau :s(t) = A.b(t).c(t).cos(2pi.fc.t + phi).

A : Bin .

fc : Tn s sng mang.

phi : Pha ca sng mang.


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* My thu DS/SS - BPSK.

H1.8 : S my thu DS/SS - BPSK.

- Mc ch ca my thu l ly ra bn tin b(t) ( S liu tn hiu thu c baogm c tn hiu pht vi tp m ). Do c tr nn tn hiu thu c c dng :

n(t) : tp m ca knh v u vo my thu.

- Gi s mi trng khng c tp m th trc ht tn hiu c a vo triph a t bng tn rng v bng tn hp sau n c gi iu ch nhntn hiu bng gc. gii tri ph ta ly tn hiu thu c nhn vi tn hiu ng

b PN( t - ttr) c to my thu ta c :

- Tn hiu thu c l tn hiu bng hp vi rng bng tn l 2/T giiiu ch ta gi thuyt bit pha ca tn hiu v tn s fc cng nh im khi u ca


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tungf bit. Mt b gii m iu ch bao gm mt b tng quan i sau l mt thitb nh gi ngng. tch ra s liu th i b tng quan phi tnh ton :

ti : l thi im ca bit th i.

V b(t - ttr) l +1 hoc -1 trong thi gian mt bit

v qua tnh ton b tng quan tnh ra c kt qu l AT/2 hoc - AT/2 v qua bnh gi ngng ta c u ra l c s hai, ngoi thnh phn AT/2 u ra cn ctp m nn c th gy ra li.

- Tn hiu PN l tn hiu bit trc my thu ch nh nn n c th khiphc bn tin cn cc my thu khc th nhn thy tn hiu ngu nhin. my thuc th khi phc bn tin th my thu phi ng b vi tn hiu thu c, qu trnhxc nh c i l qu trnh ng b thng c thc hin qua hai bc l bt v

bm, qu trnh khi phc ti- c gi l qu trnh khi phc ng h (STR -Symbol Timing Recovery), qu trnh nhn c ( cng nh fc ) gi l a trnh khi

phc sng mang.

* Cc h thng DS/SS - QPSK.

- Ngoi iu ch BPSK ngi ta cn s dng cc h thng iu ch khcnh QPSK - Quadrature Phase Shift Keying ( iu ch cu phng ) hay MSK -Minimum Shift Keying.

- My pht DS/SS - QPSK.


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H1.8 : S my thu v dng sng ca h thng DS/SS - QPSK.

- My thu DS/SS - QPSk :


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H1.9 : S my thu DS/SS - QPSK.

- Cc thnh phn ng pha v vung gc c tri ph c lp vi nhau bic1(t) v c2(t). Gi thuyt c thi gian tr v b qua tp m tn hiu s c dng :

Tng cc tn hiu trn c ly khong thi gian mt bt kt qu ca bntin Zi = AT v tt c cc gi tr 2fc trung bnh bng 0 v th u ra b so snh bng1 ( mc logic ).

- Hai tn hiu PN c th l tn hiu c lp hay c th ly cng t mt tn

hiu PN. Cc tn hiu c xt trn s dng pht tn hiu c tc 1/T bit/s.PG rng bng tn chim bi tn hiu DS/SS - QPSK ph thuc vo tc chipc1(t) v c2(t). Ta cng c th s dng h thng DS/SS - QPSK pht tn hiu ctc i/T bit/s bng cch mi tn hiu iu ch mt nhnh.

+ u im ca h thng ny :


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-> H thng DS/SS - QPSK ch s dng bng tn bng mt na so vibng tn ca h thng DS/SS - BPSK khi coa cng PG v SNR.

-> H thng DS/SS - QPSk c t l li bit thp hn DS/SS - BPSK khic PG bng nhau v s dng bng tn nh nhau.

-> H thng DS/SS - QPSK cn c th pht i s liu gp hai ln sovi h thng DS/SS - BPSK khi s dng bng tn nh nhau v c PG, SNR bngnhau.

+ KHuyt im ca h thng ny :

-> H thng DS/SS - QPSK phc tp hn h thng DS/SS - BPSK .

-> Cht lng ca h thng s b gim v d xy ra xuyn m nu h thng my thu khng thc s trc giao.

- li x l PG : li x l c nh ngha l PG bng rngbng tn ca tn hiu tri ph (SS) chia cho hai ln rng ca bng tn tn hiu. li x l cho thy bn tin pht c tri ph bao nhiu ln, y l mt thng scht lng quan trng ca h thng tri ph, v PG c ngha l kh nng chngnhiu tt hn.

3 : iu khin cng sut trong CDMA.

3.1/ iu khin cng sut trong CDMA.

- CDMA cung cp chc nng iu khin cng sut hai chiu t BS n mydi ng v ngc li.

- Mc ch : ca vic iu khin cng sut : iu khin cng sut pht cadi dng sao cho tn hiu pht ca tt c cc my di ng trong vng phc v c thc thu vi nhy trung bnh ti b thu ca BS.

- B thu CDMA ca BS chuyn cc tn hiu CDMA thu c t my ding tng ng thnh tn hiu s bng hp v trong trng hp ny tn hiu ca

cc my di ng khc ch nh tn hiu tp m ca bng rng. Th tc thu hp bngc gi l li x l nhm nng cao t s tn hiu trn giao thoa tnh theo db tmc m cho n mt mc ln cho php hot ng c vi li bt chpnhn c.


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- Vic ng m mch iu khin cng sut t my di ng ti BS l chcnng hot ng c bn ca my di ng my di ng iu chnh cng sut phttheo s bin i thu c t BS. My di ng o cng sut thu c t BS v iukhin cng sut pht t l nghch vi mc cng sut o c. Mch m ng

iu khin cng sut lm cho cc tn hiu pht ca tt c cc my di ng c thuvi cng mt mc ti BS. BS cung cp chc nng mch m ng iu khin cngsut qua vic cung cp cho cc my di ng mt hng s nh c , hng s nyc truyn i n cc my di ng nh l mt phn ca bn tin thng bo.

- BS thc hin chc nng kch hot mch i vi mch ng iu khincng sut t my di ng ti BS. Khi mch ng dn ti vic BS nh c cng sutmch m xc nh ca my di ng mt cch tc thi my di ng hiwux ccng sut pht ti u.

- BS so snh tn hiu thu c t my di ng lin quan n gi tr ngngbin i v iu khin cng sut tng hay gim sau mi khong thi gian l 1,25ms cho n khi t c kt qu. Vic nh c gi tr mch ng b cho gi trxc nh ca mch m m mch m ny b tng ch chp nhn c v suyhao ng truyn dn ca cc ng i v n gia BS v my di ng.

- BS cung cp vic iu khin cng sut t BS ti my di ng nh vic quynh cng sut ny tng ng vi cng sut o c ti my di ng. Mc ch

ca vic iu khin ny l lm gim cng sut pht ca my di ng khi ri hoc v tr tng i gn BS lm cho fading a ng thp v lm gim hiu ng bngrm hay lm gim giao thoa vi cc BS khc. Do , cng sut c cung cpthm i vi cc vng thu tn hiu b gin on hoc i vi cc my di ng xac t l li cao.

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

Khc phc hiu nggn-xa trn ng ln. Ti u dung lng h thng bng vic iu khin nhiu. Lm tng ti a tui th pin ca u cui di ng.

Mc tiu ca vic s dng iu khin cng sut l khc nhau trn ng ln v

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


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Khc phc hiu nggn-xa trn ng ln. Ti u dung lng h thng bng vic iu khin nhiu. Lm tng ti a tui th pin ca u cui di ng.

C 3 kiu iu khin cng sut trong cc h thng WCDMA: iu khincng sut vng m, iu khin cng sut vng kn v iu khin cng sut vng

bn ngoi.

3.2/ iu khin cng sut vng m (Open-loop power control)

- iu khin cng sut vng m c s dng trong h thng UMTS FDD

cho vic thit lp nng lng ban u cho MS. MS s tnh suy hao ng truyn

gia cc trm gc v MS bng cch o cng tn hiu nhn c bng cch s

dng mch iu khin tng ch t ng (AGC). Tu theo s tnh ton suy hao

ng truyn ny, MS c th quyt nh cng sut pht ng ln ca n. iu

khin cng sut vng m c nh hng ln trong h thng TDD bi v ng ln

v ng xung l tng h, nhng khng nh hng nhiu trong cc h thng

FDD bi v cc knh ng ln v ng xung hot ng trn cc bng tn khc

nhau v hin tng Fading Rayleigh trn ng ln v ng xung c lp nhau.

Vy iu khin cng sut vng m ch c th b mt cch tng trng suy hao do

khong cch. l l do ti sao iu khin cng sut vng m ch c s dng

nh l vic thit lp nng lng ban u trong h thng FDD.

3.3/ iu khin cng sut vng kn (Fast power Control)

- iu khin cng sut vng khp kn, c gi l iu khin cng sut

nhanh trong cc h thng WCDMA, c nhim v iu khin cng sut pht ca

MS (ng ln) hay l cng sut ca trm gc (ng xung) chng li Fading

ca cc knh v tuyn v t c ch tiu t s tn hiu trn nhiu SIR c

thit lp bi iu khin cng sut vng ngoi. Chng hn nh trn ng ln, trm


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gc so snh SIR nhn c t MS vi SIR mc tiu trong mi khe thi gian

(0,666ms). Nu SIR nhn c ln hn mc tiu, Node-B s truyn mt lnh TPC

0 n MS thng qua knh iu khin ring ng xung. Nu SIR nhn c

thp hn mc tiu, Node-B s truyn mt lnh TPC 1 n MS. Bi v tn s caiu khin cng sut vng kn rt nhanh nn c th b c Fading nhanh v c

Fading chm.

3.4/ iu khin cng sut vng ngoi

- iu khin cng sut vng ngoi cn thit gi cht lng truyn thng

vi cc mc yu cu bng cch thit lp mc tiu cho iu khin cng sut vng

kn nhanh thc hin. Mc ch ca n l cung cp cht lng yu cu. Tn s ca

iu khin cng sut vng bn ngoi thng l 10-100Hz.

- iu khin cng sut vng ngoi so snh cht lng nhn c vi chtlng yu cu. Thng thng, cht lng c nh ngha l t li bit mc tiu xcnh (BER) hay t s li khung (FER). Mi quan h gia SIR mc tiu v mc tiucht lng tu thuc vo tc di ng v hin tng a ng. Nu cht lngnhn tt hn, c ngha l mc tiu SIR cao m bo QoS yu cu.

3.5/ B m - gii m thoi v t bin i s liu.

- B m - gii m thoi trong CDMA c thit k vi tc bin i 8Kb/sv thng tin thoi c s dng thut ton m - gii m thoi tc s liu bini nggia BS v my di ng.

- B m - gii m thoi pha pht ly mu tn hiu thoi to ra cc gitn hiu thoi c m ha dng truyn ti b m - gii m thoi pha thu, b

m - gii mthoi pha thu s gii m cc gi tn hiu thoi thu c thnh ccmu tn hiu thoi.

- Hai b m - gii m thoi thng tin vi nhau 4 nc tc truyn 9600b/s,4800b/s, 2400b/s, 1200b/s, cc tc ny c chn theo iu kin hot ng vtheo bn tin hoc s liu, thut ton dng cho CDMA l QCELP.


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- B m - gii m thoi s dng ngng tng thichs chn tc s liu,ngng c iu khin theo cng ca tp m nn v tc s liu s chchuyn i thnh tc cao khi c tn hiu thoi vo. Do , tp m nn b trit i to ra s truyn dn thoi cht lng cao trong mi trng ca tp m.

3.6/ My di ng chuyn vng mm.

Chuyn giao trong cng tn s

Chuyn giao mmChuyn giao mm ch c trong cng ngh CDMA. So vi chuyn giao cng

thng thng, chuyn giao mm c mt s u im. Tuy nhin, n cng c mt s

cc hn ch v s phc tp v vic tiu th ti nguyn tng ln. Trong phn ny strnh by nguyn l ca chuyn giao mm.

Nguyn l chuyn giao mmChuyn giao mm khc vi qu trnh chuyn giao cng truyn thng. i vi

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

v my di ng ch giao tip vi mt BS ti mt thi im. i vi chuyn giao

mm, mt quyt nh c iu kin c to ra l c thc hin chuyn giao haykhng li tu thuc vo s thay i cng tn hiu knh hoa tiu t hai hay

nhiu trm gc c lin quan, mt quyt nh cng cui cng s c to ra giao

tip vi duy nht 1 BS. iu ny thng din ra sau khi tn hiu n t mt BS

chc chn s mnh hn cc tn hiu n t BS khc. Trong thi k chuyn tip ca

chuyn giao mm, MS giao tip ng thi vi cc BS trong tp hp tch cc (Tp

hp tch cc l danh sch cc cell hin ang c kt ni vi MS).


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Hnh 1.4 S so snh gia chuyn giao cng v chuyn giao mm

li lin kt chuyn giao mmMc ch u tin ca chuyn giao mm l em li mt s chuyn giao

khng b ngt qung v lm cho h thng hot ng tt. iu ch c th t

c nh 3 li ch ca c cu chuyn giao mm nh sau:

li phn tp v m: li ch phn tp nh Fading chm v s st tngt ca cng tn hiu do cc nguyn nhn chng hn nh s di chuyn ca

MS vng quanh mt gc.

li phn tp vi m: li phn tp nh Fading nhanh. Vic chia s ti ng xung: Mt MS khi chuyn giao mm thu cng

sut t nhiu Node-B, iu cho thy cng sut pht ln nht n MS trong khi

chuyn giao mm X-way c nhn vi h s X, ngha l vng ph c m rng.

Ba li ch ny ca chuyn giao mm c th ci thin vng ph v dung lngmng WCDMA.


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Đề BÁO CÁO THỰC TẬP MÔN THÔNG TIN DI ĐỘNG

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