Bao Cao Do an Tot Nghiep

HC VIN CNG NGH BU CHNH VIN THNG C S TI THNH PH H CH MINH

KHOA VIN THNG II _____________

N TT NGHIP I HC

CHUYN NGNH: IN T - VIN THNG H I HC CHNH QUY

NIN KHA: 2008-2013

ti:

K THUT SC-FDMA TRIN KHAI TRONG LTE

M s ti: 12 408160003

Sinh vin thc hin: L THANH BNH MSSV: 408160003 Lp: 08VTA1 Gio vin hng dn: PHM THANH M

TP.HCM 12/2012

HC VIN CNG NGH BU CHNH VIN THNG C S TI THNH PH H CH MINH

KHOA VIN THNG II _____________

N

TT NGHIP I HC

CHUYN NGNH: IN T - VIN THNG H I HC CHNH QUY

NIN KHA: 2008-2013

ti:

K THUT SC-FDMA TRIN KHAI TRONG LTE

M s ti: 12 408160003

NI DUNG:

- CHNG I: TNG QUAN CNG NGH LTE - CHNG II: K THUT A TRUY NHP SC-FDMA - CHNG III: TRIN KHAI SC-FDMA TRONG 3GPP LTE - CHNG IV: M PHNG NH SC-FDMA

Sinh vin thc hin: L THANH BNH MSSV: 408160003 Lp: 08VTA1 Gio vin hng dn: PHM THANH M

TP.HCM 12/2012

Mc lc

SVTH: L Thanh Bnh LP: 08VTA1 ii

MC LC

MC LC ............................................................................................................................ i DANH MC HNH V ..................................................................................................... iii DANH MC BNG ........................................................................................................... iv LI M U ..................................................................................................................... v CHNG 1: TNG QUAN V CNG NGH LTE ....................................................... 1 1.1 LTE trn l trnh pht trin ln 4G ca 3GPP .................................................................. 1 1.2 c im yu cu thit k ca LTE ................................................................................. 3

1.2.1 Kh nng ca LTE ..................................................................................................... 3 1.2.2 Hiu nng h thng.................................................................................................... 3 1.2.3 Kin trc v qu trnh chuyn i .............................................................................. 4 1.2.4 Kha cnh lin quan ti trin khai .............................................................................. 5 1.2.5 Qun l ti nguyn v tuyn ...................................................................................... 5 1.2.6 Mc phc tp ....................................................................................................... 6 1.2.7 Chi ph, gi thnh v dch v ..................................................................................... 6

1.3. Cc tnh nng quan trng ca LTE ................................................................................. 6 1.3.1 S truyn dn ....................................................................................................... 6 1.3.2 Lp biu ph thuc knh v thch ng tc ............................................................. 7 1.3.3 iu phi nhiu gia cc ........................................................................................ 7 1.3.4 HARQ vi kt hp mm ........................................................................................... 8 1.3.5 H tr a anten .......................................................................................................... 8 1.3.6 H tr qung b v a phng ................................................................................... 8 1.3.7 Linh hot ph ............................................................................................................ 8

1.4 Kin trc mng LTE ........................................................................................................ 9 1.4.1 Kin trc truy nhp v tuyn E-UTRAN .................................................................. 9 1.4.2 H thng mng li EPC ........................................................................................... 10 1.4.3 Cc giao din lin kt .............................................................................................. 12 1.4.4 Giao thc giao din v tuyn ................................................................................... 13

1.5 Tng kt chng ........................................................................................................... 13 CHNG II: K THUT A TRUY NHP SC-FDMA .............................................. 14 2.1 S lc v cng ngh truyn dn ng xung OFDM ................................................ 14 2.2 H thng n sng mang vi b cn bng min tn s SC/FDE .................................... 15 2.3 Nguyn l truyn dn SC-FDMA .................................................................................. 16

2.3.1 S khi v nguyn l h thng SC-FDMA.......................................................... 16 2.3.2 Sp xp cc sng mang ............................................................................................ 20 2.3.3 Trnh by cc tn hiu SC-FDMA trong min thi gian ............................................ 21

2.3.3.1 Cc k hiu min thi gian ca IFDMA ............................................................. 21 2.3.3.2 Cc k hiu min thi gian ca LFDMA ............................................................ 23 2.3.3.3 Cc k hiu min thi gian ca DFDMA ............................................................ 24

Mc lc

SVTH: L Thanh Bnh LP: 08VTA1 iii

2.4 SC-FDMA v OFDMA ................................................................................................. 26 2.5 SC-FDMA v DS-CDMA/FDE ................................................................................ 28 2.6 SC-CFDMA .................................................................................................................. 29

2.6.1 Lp lch ph thuc knh .......................................................................................... 29 2.6.2 SC-CFDMA ............................................................................................................ 30

2.7 Tng kt chng ........................................................................................................... 32 CHNG III: TRIN KHAI SC-FDMA TRONG 3GPP LTE ...................................... 33 3.1 Lp giao thc v knh truyn ........................................................................................ 33 3.2 Cu trc khung thi gian v tn s ng ln ................................................................ 34

3.2.1 Khung v tuyn v khe thi gian ............................................................................. 34 3.2.2 Khi ti nguyn ....................................................................................................... 36

3.3. Cc tn hiu tham kho ................................................................................................. 38 3.3.1 Nhiu tn hiu tham kho ......................................................................................... 40 3.3.2 Cc tn hiu tham kho thm d knh .................................................................. 40

3.4 X l knh truyn ti ng ln .................................................................................... 41 3.5 Tng kt chng ........................................................................................................... 43 CHNG IV: M PHNG NH GI SC-FDMA ..................................................... 44 4.1 Gii thiu ...................................................................................................................... 44 4.2 Chng trnh m phng ................................................................................................ 45

4.2.1 Th hin min tn s v thi gian b lc Raise-cosin ............................................... 45 4.2.2 PAPR ca tn hiu SC-FDMA ................................................................................. 46

4.2.2.1 S thut ton tnh PAPR ............................................................................... 47 4.2.2.2 M phng PAPR vi cng h s Roll-off ........................................................... 49 4.2.2.3 M phng PAPR khng to dng xung .............................................................. 51 4.2.2.4 M phng PAPR vi cc h s Roll-off khc nhau ............................................ 53

4.2.3 SER ca tn hiu SC-FDMA .................................................................................... 54 4.2.3.1 S thut ton tnh SER .................................................................................. 55 4.2.3.2 M phng SER dng b can bng MMSE .......................................................... 56 4.2.3.2 M phng SER dng b can bng ZERO ........................................................... 57

4.3 Tng kt chng ........................................................................................................... 58 KT LUN ....................................................................................................................... 59 THUT NG & T VIT TT ...................................................................................... 60 TI LIU THAM KHO ................................................................................................ 63

Danh mc hnh v - Danh mc bng

SVTH: L Thanh Bnh LP: 08VTA1 iv

DANH MC HNH V Hnh 1.1 L trnh a ra cc pht hnh trong 3GPP ............................................................. 1 Hnh 1.2 Tin trnh pht trin 3G ln 4G ............................................................................. 2 Hnh 1.3 Chuyn i trng thi trong LTE .......................................................................... 3 Hnh 1.4 Yu cu i vi tr mt phng ngi s dng ....................................................... 3 Hnh 1.5 Bng tn hot ng ca LTE ................................................................................. 5 Hnh 1.6 Cc trng thi chuyn i ca UE trong LTE v UMTS ........................................ 6 Hnh 1.7 iu phi nhiu gia cc .................................................................................... 8 Hnh 1.8 Ghp song cng theo thi gian v tn s ............................................................... 9 Hnh 1.9 Kin trc mng LTE ........................................................................................... 10 Hnh 1.10 M hnh kin trc mng li EPC n gin .......................................................... 11 Hnh 2.1 Li ICI trong OFDMA ........................................................................................ 15 Hnh 2.2 Cu trc b thu v pht ca SC/FDE v OFDM .................................................. 15 Hnh 2.3 S khc nhau trong tin trnh tch sng gia SC/FDE v OFDM ........................ 15 Hnh 2.4 Sp xp k hiu iu ch ln sng mang con trong OFDM v SC/FDE ................ 16 Hnh 2.5 Cu trc b pht v thu ca SC-FDMA v OFDMA .......................................... 16 Hnh 2.6 Chn CP ............................................................................................................ 18 Hnh 2.7 Min thi gian v tn s b lc Raise-cosine....................................................... 18 Hnh 2.8 Phn b PAPR vi cc h s Rolloff ................................................................... 19 Hnh 2.9 Sp xp cc sng mang LFDMA v DFDMA ..................................................... 20 Hnh 2.10 Cp pht sng mang cho cc u cui theo ch phn b v ch ni vng ... 20 Hnh 2.11 Cc kiu sp xp sng mang trong SC-FDMA .................................................... 21 Hnh 2.12 Cc k hiu truyn dn SC-FDMA trong min thi gian ...................................... 25 Hnh 2.13 Bin cc k hiu SC-FDMA ........................................................................... 25 Hnh 2.14 PAPR ca cc tn hiu SC-FDMA ...................................................................... 26 Hnh 2.15 SC-FDMA v OFDMA vi s khc nhau trong b thu........................................ 26 Hnh 2.16 Khc nhau trong pht cc k hiu gia SC-FDMA v OFDMA ......................... 27 Hnh 2.17 So snh gia OFDMA v SC-FDMA vi vic pht cc k hiu QPSK ............... 27 Hnh 2.18 H thng DS-CDMA vi b cn bng min tn s .............................................. 28 Hnh 2.19 Tri ph vi vai trong chui d liu v trao i chui k hiu

tri ph vi (1, 1, 1, 1) vi kch c khi l 4 ................................................... 29 Hnh 2.20 Lp lch h thng SC-FDMA .............................................................................. 30 Hnh 2.21 Kiu sp xp sng mang lai SC-CFDMA ............................................................ 31 Hnh 2.22 H thng SC-CFDMA ........................................................................................ 31 Hnh 2.23 Sp xp sng mang trong SC-FDMA v SC-CFDMA ......................................... 31 Hnh 2.24 Thng lng theo tc di chuyn v kiu sp xp sng mang .......................... 32 Hnh 2.25 Thng lng ngi s dng theo cc kiu sp xp khc nhau ............................. 32 Hnh 3.1 Kin trc giao thc ca 3GPP LTE ..................................................................... 33 Hnh 3.2 Cu trc khung trong min thi gian ................................................................... 34 Hnh 3.3 Cu trc khung theo ghp song cng phn chia thi gian ..................................... 35 Hnh 3.4 Cu trc khung theo ghp song cng phn chia tn s .......................................... 35

Danh mc hnh v - Danh mc bng

SVTH: L Thanh Bnh LP: 08VTA1 v

Hnh 3.5 Khi ti nguyn gm 12 sng mang con v khong cch sng mang l 15Khz .... 36 Hnh 3.6 n nh ti nguyn ng ln LTE ..................................................................... 36 Hnh 3.7 Nhy tn ng ln LTE .................................................................................... 37 Hnh 3.8 Khi ti nguyn tng th ca ng ln LTE ...................................................... 37 Hnh 3.9 Cc tn hiu tham kho c chn vo khi th t tng khe ng ln ............... 38 Hnh 3.10 To tn hiu tham kho trong min tn s ............................................................ 38 Hnh 3.11 Phng php to tn hiu tham kho ng ln ................................................... 39 Hnh 3.12 Truyn dn cc tn hiu tham kho thm d knh ................................................ 41 Hnh 3.13 Cc bc x l knh truyn ti ng ln ........................................................... 42 Hnh 3.14 Chc nng HARQ ca lp vt l......................................................................... 42 Hnh 3.15 Khi x l DFT-OFDM ca cc k hiu .............................................................. 43 Hnh 4.1 Giao din chng trnh m phng ....................................................................... 44 Hnh 4.2 Giao din m phng hm lc Raise-cosin ........................................................... 45 Hnh 4.3 Min thi gian v tn s b lc Raise-cosin vi cc h s Roll-off khc nhau ..... 46 Hnh 4.4 Giao din m phng PAPR ................................................................................. 47 Hnh 4.5 Thut ton m phng PAPR ............................................................................... 48 Hnh 4.7 Kt qu m phng vi Roll-off = 0.3, iu ch QPSK ......................................... 49 Hnh 4.8 Kt qu m phng vi Roll-off = 0.3, iu ch 16QAM ...................................... 50 Hnh 4.9 Kt qu m phng vi Roll-off = 0.3, iu ch 64QAM ...................................... 50 Hnh 4.10 M phng PAPR khng to dng xung vi iu ch QPSK................................. 51 Hnh 4.11 M phng PAPR khng to dng xung vi iu ch 16QAM.............................. 52 Hnh 4.12 M phng PAPR khng to dng xung vi iu ch 64QAM.............................. 52 Hnh 4.13 Kt qu m phng vi Roll-off = 0.15, iu ch QPSK ....................................... 53 Hnh 4.14 Kt qu m phng vi Roll-off = 0.99, iu ch QPSK ....................................... 53 Hnh 4.15 Giao din m phng SER ................................................................................... 54 Hnh 4.16 Thut ton m phng SER .................................................................................. 55 Hnh 4.17 SER trong cc kiu sp xp sng mang ca SC-FDMA trong m

hnh knh cho ngi i b (3km/h) ..................................................................... 56 Hnh 4.18 SER trong cc kiu sp xp sng mang ca SC-FDMA trong m

hnh knh cho phng tin di chuyn (120km/h) ................................................ 56 Hnh 4.19 SER trong cc kiu sp xp sng mang ca SC-FDMA trong m

hnh knh cho ngi i b (3km/h) ..................................................................... 57 Hnh 4.20 SER trong cc kiu sp xp sng mang ca SC-FDMA trong m

hnh knh cho phng tin di chuyn (120km/h) ................................................ 57

DANH MC BNG Bng 1.1 So snh thng s tc v hiu sut s dng bng tn trn ng xung

v ng ln gia LTE vi HSDPA ...................................................................... 4 Bng 1.2 Bng m t gin on chuyn giao ......................................................................... 5 Bng 3.1 Knh vt l........................................................................................................... 33 Bng 3.2 Cc bng thng kh dng ng ln LTE ............................................................. 37

Li m u

SVTH: L Thanh Bnh LP: 08VTA1 vi

LI M U

S pht trin khng ngng ca cng ngh v tuyn cng vi nhu cu s dng ca con ngi ngy cng tng c v s lng, cht lng v cc dch v a phng tin mi nh: thoi, video, hnh nh v d liu thc y mnh m s pht trin, ci tin ca thng tin di ng. T cc th h di ng nn tng ban u 1G, 2G vi mc tiu ch yu l h tr dch v thoi v truyn s liu tc thp th nhanh chng pht trin ln cc th h thng tin di ng tc cao, ng dng rng nh 3G, LTE hay cc th h tip sau... K t khi ra i vo cui nm 1940, thng tin di ng pht trin qua nhiu th h v ang tin mt bc di trn con ng cng ngh ca n.

Thng tin di ng em li cho con ngi kh nng thng tin mi lc, mi ni. Nu nh h thng thng tin di ng 2G ra i vi mc tiu ch yu l h tr dch v thoi v truyn s liu tc thp da trn nn tng ca h thng tng t, c nh du l s thnh cng ca cng ngh GSM vi hn 70% th phn thng ti di ng trn ton cu hin nay th th h thng tin di ng th ba ra i li p ng cc nhu cu dch v s liu tc cao nh: in thoi thy hnh, video streamming, hi ngh truyn hnh, nhn tin a phng tin (MMS) Trong tng lai, nhu cu cc dch v s liu s ngy cng tng v c kh nng vt qu nhu cu thng tin thoi.

C th thy h thng thng tin di ng 3G kh ph bin v v vy, vic cc h thng thng tin di ng tin ln 4G l mt iu tt yu. LTE, mt chun ca t chc 3GPP, l mt trong cc con ng khc nhau tin ln 4G, vi mc tiu tng dung lng truyn dn, gim gi thnh dch v cng nh thit b u cui, ci thin cht lng cc dch v hin ti v tng lai.

im ng ch trong cng ngh LTE l p dng hai lc truy nhp OFDMA cho ng xung v SC-FDMA trin khai cho ng ln. SC-FDMA mang nhiu u th hn so vi OFDMA cho trin khai ng ln. Trong SC-FDMA cc k hiu c pht i ln lt thay v pht i song song nh OFDMA, v th cch sp xp ny lm gim ng k s thng ging ca ng bao tn hiu ca dng sng pht. Do cc tn hiu SC-FDMA c PAPR thp hn cc tn hiu OFDMA m vn o bo tc v phc tp tng ng nh h thng OFDMA, khi PAPR thp lm tng hiu sut b khuych i cng sut iu ny dn ti tng vng ph v chi ph my u cui gim thp. Hn na SC-FDMA c nhiu kiu sp xp sng mang khc nhau cho php linh hot hn trong cc ch , iu kin truyn dn khc nhau.

Xut pht t nhng vn trn, quyn n c xy dng vi la chn nghin cu ti K thut SC-FDMA trin khai trong 3GPP LTE, theo , ti tin hnh nghin cu cc ni dung chnh theo b cc gm bn chng: Chng 1: Tng quan v cng ngh LTE.

S lc l trnh tin ln 4G ca 3GPP, tng quan v cng ngh LTE vi cc mc tiu yu cu thit k, cc tnh nng quan trng ca LTE v kin trc h thng ca mng.

Li m u

SVTH: L Thanh Bnh LP: 08VTA1 vii

Chng 2: K thut a truy nhp SC-FDMA.

Trnh by nguyn l c bn ca k thut a truy nhp SC-FDMA, cng vi cc kiu sp xp sng mang khc nhau em li linh hot cao trong truyn dn, phn tch c tnh PAPR ca tn hiu SC-FDMA. So snh k thut SC-FDMA vi cc lc a truy nhp khc nh OFDMA v DS/CDMA. Kiu sp xp sng mang lai SC-CFDMA cho thng lng cao.

Chng 3: Trin khai SC-FDMA trong 3GPP LTE.

Trnh by cu trc tng th min thi gian khung truyn dn ng ln trong 3GPP LTE da trn lc truyn dn SC-FDMA, qu trnh x l knh truyn ti ng ln.

Chng 4: M phng nh gi SC-FDMA.

Da vo cc kt qu nghin cu, xy dng thut ton tnh ton, nh gi PAPR, SER ca lc truyn dn SC-FDMA vi cc kiu sp xp sng mang khc nhau vi lc truyn dn OFDMA.

c s quan tm, gip v ch bo tn tnh trong qu trnh nghin cu ca thy Th.s Phm Thanh m v nhng kin ng gp ca cc thy c gio trong b mn v tuyn cng vi s n lc ca bn thn, n c hon thnh vi ni dung c giao mc v phm vi nht nh. Tuy nhin do trnh v thi gian c hn, quyn n chc chn khng trnh khi nhng sai st. Rt mong c s ch dn ca cc thy c gio cng nh kin ng gp ca cc bn b.

Em xin chn thnh cm n Thy Phm Thanh m tn tnh hng dn em trong sut thi gian lm n em c c kt qu ngy hm nay.

Xin chn thnh cm n cc thy c trong b mn v tuyn cng nh cc thy c trong khoa vin thng v bn b c nhng kin ng gp v to iu kin cho em c hon thnh tt n tt nghip ca mnh.

Tp. H Ch Minh, ngy 20 thng 11 nm 2012

Sinh vin:

L Thanh Bnh

Chng 1: Tng quan v cng ngh LTE

SVTH: L Thanh Bnh LP: 08VTA1 1

CHNG 1 TNG QUAN V CNG NGH LTE

1.1. LTE trn l trnh pht trin ln 4G ca 3GPP

LTE vit tt ca Long Term Evolution l cng ngh c nhc n rt nhiu trn con ng pht trin ca ngnh vin thng ni chung hay thng tin di ng ni ring. c xem l cng ngh ca th h di ng th 4 tn ti trong giai on u 4G, LTE tip ni dng cng ngh GSM/GPRS/UMTS/HSPA, chun ha bi 3GPP, c pht trin nng cao tc truy cp d liu v tuyn khi m cc h thng thng tin di ng bng rng ang pht trin rng ri v 3G s dn khng p ng nhu cu s dng ng truyn tc cao.

m trch trong cc cng tc chun ha WCDMA/HSPA vi nhng thnh cng ng k, 3GPP v tip tc nghin cu pht trin h thng ln 4G, tin ti xy dng mt chun chung cho cng ngh 4G. C th tng kt hot ng tiu chun ha ca t chc 3GPP t nm 1999 n 2008 theo thi gian a ra cc pht hnh nh sau:

Hnh 1.1: L trnh a ra cc pht hnh trong 3GPP

Cui nm 1999 mc pht trin u tin cho WCDMA t c khi pht hnh R99 (R3) c cng b cha ng tt c cc c t WCDMA. Pht hnh R4 c a ra sau vo u nm 2001. Tip theo l pht hnh R5 c a ra vo nm 2002 v R6 vo nm 2004. Pht hnh R7 c a ra vo na cui nm 2006.

cc pht hnh u R99 cho n R4, mc d dung lng v tc truyn dn c ci thin ng k nhng khi cc dch v s liu c a vo trin khai trn cc mng thng mi th dung lng, tc vn l nhng i hi cn phi c gii quyt. Do , bc ci tin u tin i vi WCDMA ch c nh du bi s ra i ca knh truyn ti mi HS-DSCH R5 hon thnh vo u nm 2002 lm nn tng xy dng h thng truy nhp gi tc cao HSPA bao gm c ng ln (HSDPA: High Speed Down Link Packet Access) v ng xung (HSUPA: High Speed Up Link Packet Access). HSDPA c 3GPP chun ha trong R5 vi phin bn tiu chun u tin vo nm 2002 v c thng mi ha vo nm 2005 cn HSUPA c 3GPP



Cc nghin cu ca LTE c xy dng da trn vic pht trin hiu nng ca h

thng R6 RAN ci thin ng k tr, cung cp tc truyn d liu cao v nng cao hiu qu s dng ph tn s, l mt bc tin di so vi chun HSPA ca mng W-CDMA, cng ngh nguyn thy ca truyn d liu gi 3G. LTE l mt bc quan trng trn con ng xy dng h thng thng tin di ng th h 4.

Tm pht trin LTE c nh gi t n 3,9G, tin n rt gn trn con ng pht trin mng bng thng rng di ng tc cao tin tin th h th t, th h 4G.

LTE l mt trong s cc con ng tin ln 4G. LTE cho php chuyn i t t 3G UMTS sang giai on u 4G sau s l IMT Advance. Ngoi LTE ca 3GPP th 3GPP2 cng ang thc hin k hoch nghin cu LTE cho mnh, h thng do 3GPP2 a ra l UMB. Chng trnh khung ca k hoch ny bt u t nm 2000. Ngoi ra WiMAX cng c k hoch ln 4G.

Hnh 1.2: Tin trnh pht trin 3G ln 4G

chun ha trong R6 vo thng 12 nm 2004 cho n nm 2007 mng bt u c thng mi ha.

Vi tc ti a l 14,4 Mbps i vi ng xung HSDPA v t n 42Mbps trong pht hnh R7 HSPA+ (HSPA Evolution), cc phin bn trn mc d c ci tin kh nhiu song tc thc s cha cao c th p ng tt hn cho cc dch v hin ti v trong tng lai. Hn na cng vi s xut hin cng ngh WiMAX 802.16 c IEEE chun ha vi tc ln ti hng trm Mbps, 3GPP nghin cu v a ra cng ngh LTE hay gi l Super 3G. D n bt u t cui nm 2004 u nm 2005, nhm m bo tnh cnh tranh ca mng 3G trong vng 10 nm ti.



1.2. c im yu cu thit k ca LTE 1.2.1. Kh nng ca LTE

a. Tc s liu nh: Bng thng c cp pht linh hot t 1,25MHz ln n 20MHz (gp bn ln bng thng 3G-UMTS) do , LTE m bo tc s liu nh ng xung v ng ln tng ng t n 100Mbps v 50Mbps khi bng thng c cp pht cc i l 20MHz (5bps/Hz cho ng xung v 2,5bps/Hz ng ln). Tuy nhin tc nh c th ph thuc vo s anten pht v anten thu ti UE. Cc mc tiu v tc s liu nh ni trn c c t trong UE tham chun gm: (1) kh nng ng xung vi hai anten ti UE, (2) kh nng ng ln vi mt anten ti UE.

b. Tr mt phng iu khin v mt phng ngi s dng: Thi gian chuyn i cc trng thi trong LTE nh hn 100ms (nh t ch ri) vo trng thi tch cc (nh trong R6 Cell_DCH). N cng cn m bo thi gian chuyn i nh hn 50ms t trng thi ng (nh trong R6 Cell_PCH) sang trng thi tch cc (nh trong R6_DCH).

Hnh 1.3: Chuyn i trng thi trong LTE

Vi mt phng ngi s dng (mt phng U), m bo tr mt chiu khng vt qu 5ms trong iu kin mng khng ti (khng c cc u cui khc trong ). Tr mt phng U c nh ngha l tr mt chiu khi pht mt gi ti lp IP UE n lp IP trong node bin ca UTRAN hoc ngc li. Node bin ca UTRAN l giao din UTRAN vi mng li.

Hnh 1.4: Yu cu i vi tr mt phng ngi s dng

1.2.2. Hiu nng h thng

Hiu nng h thng ca LTE cp ti thng lng ca ngi s dng, hiu sut ph tn, h tr di ng, vng ph v MBMS tng cng hn.

Thng lng v hiu sut ph tn: Yu cu thng lng ca ngi s dng LTE c c t hai im: vng ph v 5% ca phn b ngi s dng (95% ngi s dng c hiu nng tt hn). Hiu sut ph tn c nh ngha nh l thng lng h thng trong c o bng bit/s/Hz. Mc tiu ca thng lng v hiu sut ph tn c c t nh sau:



Bng 1.1: So snh thng s tc v hiu sut s dng bng tn trn ng xung v ng ln gia LTE vi HSDPA.

Downlink Uplink

HSDPA (R6)

LTE ch LTE/ t

HSDPA (R6)

LTE ch LTE/ t

Tc nh (Mbps) 14,4 144 100/ t 5,7 57 50/ t

Hiu sut ph tn (bit/Hz/s)

0,75 1,84 3-4 ln HSDPA/ t 2,5

0,26 0,67 2-3 ln HSUPA/ t 2,6

Thng lng ngi s dng bin

0,006 0,0148 2-3 ln HSDPA/ t 2,5

0,006 0,015 2-3 ln HSDPA/ t 2,5

H tr di ng: LTE t c hiu nng cc i vi tc u cui di ng khong 0-15km/h, hiu nng ca h thng s gim khi tc u cui cao hn. i vi tc trn 120km/h, LTE m bo hiu nng cao duy tr kt ni trn ton mng t bo. H thng LTE c th qun l tc ln ti 350km/h thm ch l 500km/h ph thuc vo bng tn.

Vng ph: Cc yu cu v thng lng ngi s dng, hiu sut ph tn v di ng c m bo ti u cho cc bn knh ln n 5km (khong cch cc i t trm ti u cui di ng trong ). Vi cc bn knh ti 30km cho php gim nh thng lng v cho php gim kh ln hiu sut s dng ph tn tuy nhin vn phi p ng tnh di ng.

MBMS tng cng: MBMS l mng qung b dch v a phng tin c a vo trong R6. Ti nguyn v tuyn c thit lp trong tng nm trong vng qung b MBMS v tt c cc u cui khi ng k dch v u thu c cng mt tn hiu c pht ny. Mng khng cn theo di chuyn ng ca u cui v u cui khi ng k c th thu ni dung m khng cn thng bo cho mng. Nh vy, mt trong cc li ch ca dch v MBMS l tit kim ti nguyn mng v mt lung d liu c th cung cp cho nhiu ngi.

MBMS tng cng trong LTE m bo cc dch v tt hn cc dch v m R6 cung cp gm ch qung b v ch pht n phng. Vi trng hp pht qung b hiu sut s dng ph tn l 1bit/s/Hz tng ng vi 16 knh TV trong mi knh s dng 300Kbps trong bng thng 5MHz. Tt nhin LTE m bo cung cp cc dch v thoi v MBMS ng thi, c trn ln vi nhau.

1.2.3. Kin trc v qu trnh chuyn i

Kin trc LTE th hin cc c im sau: - Da trn nn gi, tuy nhin lu lng thi gian thc v hi thoi c h tr. - Gim thiu s tn ti mt im s c m khng lm tng gi thnh ng trc. - n gin ha so vi mng 3G v gim thiu s giao din c a ra. - Kh nng tng tc gia lp mng v tuyn (RNL) v lp mng truyn ti (TNL),

p ng ci thin hiu nng h thng khi c yu cu. - H tr QoS u cui - u cui. TNL m bo QoS do RNL yu cu. - Gim thiu thay i tr (Jilter) ng k, do da vo TCP/IP.



- Cc c ch QoS phi xt n cc kiu lu lng khc nhau m bo s dng bng thng hiu qu: Lu lng mt phng iu khin, lu lng mt phng ngi s dng, lu lng khai thc v bo dng

1.2.4. Kha cnh lin quan ti trin khai

LTE c th ng tn ti trn cng vng a l hoc cng i trm vi GERAN, UTRAN trn cc knh ln cn.

E-UTRA c kh nng hot ng c lp (khng cn sng mang khc). LTE h tr c ghp song cng, bn song cng phn chia theo tn s FDD v ghp

song cng phn chia theo thi gian TDD. Cc h thng FDD c trin khai trong cc n nh bng kp vi mt bng cho tryn dn ng xung v mt bng khc ca truyn dn ng ln. Cc h thng TDD c trin khai trong cc n nh bn tn n.

LTE cn c kh nng nh li kch c trong min tn s v hot ng trong cc bng tn khc nhau, linh hot trong cc di tn hot ng (1,25MHz; 1,6MHz; 2,5MHz; 5MHz; 10MHz; 15MHz v 20MHz).

Hnh 1.5: Bng tn hot ng ca LTE

Ngoi ra, LTE phi h tr tng tc vi cc h thng 3G hin c v vi cc h thng khng theo chun 3GPP. Tt c cc u cui LTE h tr khai thc UTRAN/GERAN phi c kh nng h tr o, chuyn giao n/t cc h thng UTRAN v GERAN, gia cc RAT vi nhau, m bo n nh. Bng 1.2: Bng m t gin on chuyn giao.

Phi thi gian thc (ms) Thi gian thc (ms) LTE sang WCDMA 500 300

LTE sang GSM 500 300

1.2.5. Qun l ti nguyn v tuyn LTE c kh nng h tr tng cng cho QoS u cui u cui m bo cc yu cu

v giao thc (bao hm c lp bo hiu cao hn) cho cc ti nguyn v tuyn RAN v cc c tnh RAN.

H tr chia s ti v qun l ti nguyn chnh sch trn cc cng ngh truy nhp v tuyn khc nhau.



H tr hiu qu cho truyn dn cc lp cao hn: LTE RAN c th cung cp cc c ch h tr truyn dn v khai thc hiu qu cc giao thc lp cao hn trn giao din v tuyn, chng hn nh nn tiu IP.

1.2.6. Mc phc tp

LTE c thit k gim thiu mc phc tp ca ton b h thng cng nh phc tp ca my di ng u cui.Theo , thit k LTE gim thiu s lng cc ty chn v m bo loi b cc tnh nng bt buc tha, gim thiu s lng cc trng hp kim tra cn thit chng hn gim s lng cc trng thi ca cc giao thc, th tc, cc thng s v tnh ht. i vi UE, gim thiu mc phc tp lin quan n kch thc, trng lng v dung lng acqui (ch ch v ch tch cc) nhng vn m bo cc dch v tin tin ca LTE. Hnh di th hin s n gin trong LTE so vi UMTS v cc trng thi UE.

a) b)

Hnh 1.6: Cc trng thi chuyn i ca UE trong LTE (a) v UMTS (b)

1.2.7. Chi ph, gi thnh v dch v

Kha cnh ny cp yu cu chung v gi thnh v dch v lin quan trong LTE vi mong mun gim thiu chi ph trong khi vn m bo hiu nng mong mun cho tt c cc dch v d kin.

1.3. Cc tnh nng quan trng ca LTE 1.3.1. S truyn dn

S d truyn dn ng xung ca LTE da trn cng ngh OFDM, m bo bn chc chng li chn lc tn s ca knh v tuyn cao hn. y l mt gii php l tng cho ng xung c bit khi c kt hp vi ghp knh khng gian.

Mt s li ch khc ca OFDM:

OFDM cung cp ti truy nhp min tn s, v th cho php m rng mc t do cho b lp biu ph thuc knh so vi HSPA.

OFDM d dng h tr n nh bng thng linh hot (t nht t quan im bng gc) bng cch thay i s lng cc sng mang con s dng cho truyn dn.

OFDM cho php thc hin n gin truyn dn qung b/a phng trong cng mt thng tin c pht i t nhiu trm gc.



i vi ng ln LTE, truyn dn n sng mang da trn OFDM tri ph c s dng DFTs-OFDM cho php gim PAPR so vi truyn dn a sng mang nh OFDM. iu ny thc s quan trng i vi u cui di ng c cng sut hn ch v PAPR cng nh th cng sut pht trung bnh cng cao i vi mt b khuch i cng sut cho trc. V th DFTs-OFDM cho php t c hiu sut s dng b khuch i cng sut cao hn v iu ny dn ti tng vng ph. Ngoi ra, vn x l mo tn hiu n sng mang do phainh chn lc tn s gy ra trn ng ln cng khng phi l quan trng v n c thc hin ti trm gc ni c kh nng x l tn hiu mnh hn.

1.3.2. Lp biu ph thuc knh v thch ng tc LTE s dng truyn dn knh chia s, trong ti nguyn tn s-thi gian c chia

s gia cc ngi s dng. Vic s dng ti nguyn knh chia s l hon ton ph hp vi cc yu cu ti nguyn thay i rt nhanh chng do truyn dn gi gy ra.

i vi tng thi im, b lp biu iu khin vic ngi s dng no c n nh ti nguyn chia s. N cng quyt nh tc s liu s c s dng cho tng lin kt v thch ng ng truyn cng c th c coi l mt b phn ca b lp biu. C ng xung v ng ln u chu s iu khin cht ch ca b lp biu. Lp biu ph thuc knh l a ra quyt nh da trn iu kin knh. Ngoi min thi gian, LTE cng c th truy nhp ti min tn s nh s dng OFDM cho ng xung v SC-FDMA cho ng ln. V th, vi tng min tn s b lp biu c th chn ngi s dng c iu kin knh tt nht.

Kh nng lp biu ph thuc knh trong min tn s c bit c ch ti tc s liu thp ni mt cch khc khi knh thay i chm theo thi gian. i vi cc dch v nhy cm tr, b lp biu ch cho min thi gian c th b buc lp biu cho mt ngi s dng cho d cht lng knh ca ngi ny khng tt lm. Trong trng hp ny, vic khai thc k c thay i cht lng knh trong min tn s s h tr ci thin tng hiu nng h thng. i vi LTE, cc quyt nh lp biu c thc hin mt ln trong 1ms v tnh ht trong min tn s l 180 Khz. iu ny cho php b lp biu bm theo iu kin knh thay i kh nhanh.

1.3.3. iu phi nhiu gia cc Gim nhiu hay iu khin nhiu gia cc em li li ch rt ln cho hiu nng LTE

(chng hn nh tc s liu) khi m nhiu gia cc hn ch n hiu sut s dng ph ca LTE, c bit l ti bin .

iu phi nhiu gia cc gip tng tc s liu ti bin c thc hin nh xt ti nhiu gia nhng ngi s dng. Vic a ra cc hn ch nht nh (min thi gian) cho cc b lp biu ng ln v ng xung gip iu khin nhiu gia cc . Bng cch hn ch cng sut ca mt s b phn ph trong mt , nhiu trong cc ln cn trong phn ph ny s gim. Phn ph ny c th c s dng cung cp tc s liu cao hn cho nhng ngi s dng trong cc ln cn. V thc cht h s ti s dng tn s trong cc phn t khc nhau ca s khc nhau.

Tuy nhin iu phi nhiu gia cc ch yu l mt chin lc lp biu xt ti tnh trng trong cc ln cn. iu ny c ngha l iu phi nhiu gia cc c th c p dng ch cho mt tp cc c chn ph thuc vo cc yu cu ca mt trin khai c th.



Hnh 1.7: iu phi nhiu gia cc 1.3.4. HARQ vi kt hp mm

Cng ging nh HSPA, HARQ nhanh vi kt hp mm c s dng u cui c th yu cu pht li nhanh cc khi truyn ti b mc li v cung cp mt cng c cho thch ng tc s liu n tng. Vi nhiu x l HARQ dng v i. gim thiu nh hng ln hiu nng ca ngi s dng u cui, cc pht li c yu cu nhanh sau mi ln pht gi. Tng phn d c s dng nh mt chin lc kt hp mm v my thu nh m cc bt mm c th thc hin kt hp mm gia cc ln pht.

1.3.5. H tr a anten LTE h tr a anten ti c trm gc v u cui. y l mt cng ngh then cht

t c cc mc tiu tng tc hiu nng ca LTE. Hin ti, chun h tr cu hnh a anten 2x2 trn ng xung v 1x2 trn ng ln.

1.3.6. H tr qung b v a phng LTE ci tin thm dch v MBMS cung cp qung b a phng hiu qu cao.

Ngoi vic pht cc tn hiu ging nhau ti nhiu (vi m ha v iu ch nh nhau), cn ng b thi gian gia cc , tn hiu ti u cui s th hin ht nh tn hiu c pht i t mt . Do OFDM c kh nng chng phainh a ng tt, pht a cng cn c gi l pht ca mng a phng qung b mng n sng mang MBSFN. Cch ny khng ch ci thin c cng tn hiu thu m cn hn ch c nhiu gia cc . Nh vy i vi OFDM thng lng qung b/a phng a ch c th b gii hn bi tp m gy ra v v th trong trng hp cc nh c th t c thng lng ny rt cao.

Vic s dng pht MBSFN cho qung b/a phng a i hi s ng b cht ch v ng chnh thi gian cho cc tn hiu c pht i t cc trm khc nhau.

1.3.7. Linh hot ph Linh hot trong sp xp song cng LTE c th trin khai c ph n v ph kp, ngha l phi h tr c TDD v FDD.

Trong FDD truyn dn ng ln v ng xung c thc hin trong cc bng khc nhau.



Trong TDD truyn dn ng ln v ng xung xy ra trn cng mt bng tn nhng lun phin theo thi gian.V th TDD c th hot ng trong ph n cn FDD i hi ph kp.

DLf DL ULf

ULf

Hnh 1.8: Ghp song cng theo thi gian v tn s Linh hot trong khai thc bng tn LTE c thit k trong ph hot ng c n nh mi cho thng tin di ng hay

t ph hin ang s dng cho cc cng ngh di ng khc nhau (chng hn nh h thng GSM) hay thm ch l khng phi cc cng ngh di ng. V th truy nhp v tuyn LTE phi hot ng trong ph tn rng t 460MHz ti t nht l 2,6GHz.

Linh hot bng thng LTE h tr mt di rng cc bng tn hot ng n nh. h tr hiu qu cc tc

s liu cao khi c ph kh dng cn c bng thng truyn dn rng trong di t 1MHz n 20MHz vi bc nhy 180kHz. 1.4. Kin trc mng LTE

Kin trc mng LTE bao gm hai min: min E-UTRAN v EPC. Trong LTE khng c node tng ng vi RNC ca WCDMA/HSPA. Do khng c h tr phn tp v m ng ln v ng xung cho lu lng ring ca ngi s dng v hn na vic thit k gim thiu s lng Node trong mng gip gim phc tp, d qun l. Kin trc LTE phn chia ring r logic gia mng truyn ti d liu v bo hiu. Cc chc nng E-UTRAN v EPC c hon ton tch bit t cc chc nng truyn ti. Lc a ch c s dng trong E-UTRAN v EPC khng b rng buc t lc a ch ca cc chc nng truyn ti.

1.4.1 Kin trc truy nhp v tuyn E-UTRAN

E-UTRAN bao gm cc eNodeB, l mt trm gc v tuyn kim sot tt c cc chc nng v tuyn lin quan trong phn c nh ca h thng. Cc trm gc nh eNodeB thng phn b trn ton khu vc ph sng ca mng. Mi eNodeB thng c tr gn cc anten v tuyn hin ti ca chng. eNodeB phc tp hn NodeB trong WCDMA/HSPA, n chu trch nhim cho cc quyt nh RRM ca mt , cc quyt nh chuyn giao, lp biu Cc eNodeB c kt ni ti mng li thng qua giao din S1. Ngoi ra giao din gia cc eNodeB l X2. Giao din X2 ch c s dng gia cc eNodeB c cc ln cn h tr di ng ch tch cc. Giao din ny cng c s dng cho cc chc nng qun l ti nguyn v tuyn RRM nhiu .

DL: ng xung UL: ng ln



Chc nng ca eNodeB bao gm: - iu khin cc kt ni di ng. - Cp pht cc ti nguyn v tuyn cho cc u cui di ng. - Nn tiu IP v m ha lung d liu ngi s dng. - nh tuyn d liu v chuyn tip ti SGSN. - Lp lch v truyn dn bn tin tm gi (c khi to t MME). - Lp lch v truyn dn bn tin qung b (c khi to t MME hay O&M). - o lng v cu hnh bo co o lng cho b lp lch v di ng.

Hnh 1.9: Kin trc mng LTE

1.4.2 H thng mng li EPC

Mng li s dng cho WCDMA/HSPA v LTE c xy dng trn s pht trin mng li GSM/GPRS. Mng li s dng cho WCDMA/HSPA rt gn vi mng li gc ca GSM/GPRS ngoi tr s khc nhau trong vic phn chia chc nng vi RAN. Tuy nhin mng li c s dng kt ni ti LTE RAN l s pht trin trit hn ca mng li GSM/GPRS. V th ni c tn l li gi pht trin EPC.

Mng li EPC xy dng phn mng SAE h tr cho phn v tuyn ca LTE. c im h thng mng li ca LTE ci tin v pht trin ch s dng duy nht mt phng thc l chuyn mch gi. Cch thc truyn d liu, xc nh v tr thu bao bng phng thc nh tuyn IP trong ton b h thng. Kin trc mng c rt gn hn so vi mng 3G gp phn lm gim gi thnh khi trin khai mng.



Hnh 1.10: M hnh kin trc mng li EPC n gin

Cng phc v S-GW c chc nng: - Truyn ti d liu ngi dng gia mng v tuyn v mng li thng qua giao thc

GTP. - nh tuyn v hng cc gi d liu ngi s dng. - Thc y th tc yu cu dch v. - Khi cc UE trng thi ri, SGW kt thc ng d liu downlink v kch hot tm

gi khi d liu downlink chuyn ti UE. - Qun l v lu tr ni dung ca UE. - Thc hin sao chp lu lng s dng trong trng hp ngn chn hp php.

Cng mng d liu gi P-GW cung cp kt ni cho UE ti cc mng d liu gi bn ngoi ti cc im vo ra ca lu lng cho UE. Mt UE c th ng thi kt ni vi nhiu hn mt P-GW truy nhp nhiu PDN.Chc nng ca P-GW gm c:

- Qun l mt qu a ch IP v cp pht cc a ch IP cho cc UE. - Thc hin chc nng chn lu lng v lc theo yu cu bi cc chnh sch

c thit lp cho UE v cc dch v ni n. - Lc gi cho mi user. - H tr tnh cc, thu thp cc thng tin chi ph lin quan. - Ngn chn hp php. - nh v a ch UE. - Chc nng DHCP, cung cp a ch cho UE.

Thc th qun l di ng MME (Mobility Management Entity): MME l node iu khin quan trng ca mng truy nhp LTE. MME qun l tnh lu ng, xc nhn UE v nhng tham s bo mt. Chc nng ca MME bao gm:

- Bo hiu NAS (Non Access Stratum) hon thnh ti MME, v n cng chu trch nhim v s pht sinh v s nh v ca s nhn dng tm thi cc UE.

- MME cung cp chc nng iu khin phng cho tnh lu ng gia LTE v mng truy nhp 2G/3G.

- Trng thi UE ri (Idle) theo di v kh nng lin lc (bao gm iu kin v thc hin cc chuyn tip tm gi).



- Theo di qun l danh sch vng. - Kim tra tnh xc thc ca UE n trm trn dch v ca nh cung cp PLMN v

gim st vic thi hnh s gii hn Roaming cho UE. - La chn GW (s la chn Serving GW v PDN GW). - La chn MME cho chuyn giao khi thay i MME. - La chn SGSN chuyn giao ti cc mng truy nhp 2G, 3G. - N chu trch nhim chng thc cc user (bng cch tng tc vi HSS Home

Subscriber Service). - MME l im cui cng trong mng thc hin vic dch mt m, bo v ton din

cho bo hiu NAS v vn hnh qun l kho bo mt. Chc nng chnh sch v tnh cc ti nguyn (PCRF): PCRF l phn t mng chu trch nhim v chnh sch v iu khin tnh cc. N to ra cc quyt nh v cch x l cc dch v v QoS v cung cp thng tin cho PCEF c t trong P-GW v nu c p dng cho c BBERF c t trong S-GW, cho vic thit lp cc phn t mang thch hp v vic lp chnh sch. PCRF l mt my ch v thng c t vi cc phn t CN khc ti cc trung tm iu hnh chuyn mch.

Ngoi ra, EPC cn c ni vi thnh phn HSS qua giao din S6. y l pht trin ca giao din Gr c s dng cho mng li WCDMA/HSPA ni ti HLR. V th, mt HLR/HSS kt hp cho EPC c th ging nh HLR i vi GSM v WCDMA/HSPA hin ti.

My ch thu bao thng tr (HSS) l kho d liu thu bao cho tt c d liu ngi dng thng xuyn. N cng ghi li v tr ca ngi s dng mc ca nt iu khin mng tm tr, chng hn nh MME. N l mt my ch c s d liu v c duy tr ti cc phng trung tm ca nh iu hnh.

HSS lu tr bn gc ca h s thu bao, cha cc thng tin v cc dch v c p dng i vi ngi s dng, bao gm thng tin v cc kt ni PDN c cho php, v liu c chuyn ti mt mng tm tr ring c hay khng. HSS cng lu nhng nhn dng ca cc P-GW c s dng. Kha thng trc c s dng tnh ton xc thc v c gi ti mng tm tr xc thc ngi dng v cc kha pht sinh tip sau m ha v bo v tnh ton vn l c lu tr ti cc trung tm xc thc (AUC), thng l mt phn ca HSS.

Trong tt c cc tn hiu lin quan ti cc chc nng ny th HSS phi tng tc vi MME. Cc HSS s cn phi c kh nng kt ni vi mi MME trong ton b mng li, ni m cc UE ca n c php di chuyn. i vi mi UE, cc h s HSS s ch ti mt MME phc v ti mt thi im v ngay sau l bo co v mt MME mi m n phc v cho UE, HSS s hy b v tr ca MME trc.

1.4.3. Cc giao din lin kt Giao din S1: L giao din phn cch gia E-UTRAN v EPC. N c chia thnh hai

phn: S1-U c th mang theo d liu truyn ti gia cc eNodeB v cc S-GW, S1-MME l mt giao din bo hiu ch gia cc eNode B v cc MME.

Giao din X2: L giao din gia cc eNodeB, gm hai phn: X2-C l giao din cc mt phng iu khin gia eNodeB trong cc chc nng chun b chuyn giao v duy tr tan b



s lin h gia cc eNodeB, trong khi U-X2 l giao din ngi dng gia eNode-B. Ngi ta cho rng lun lun tn ti mt giao din X2 gia eNode-B rng cn phi giao tip vi nhau, v d, h tr bn giao.

Giao dn S3: L giao din gia S-GW v cng SGSN ca mng 2G, 3G. N cho php ngi s dng v trao i thng tin ghi tn cho lin mng di ng 3GPP truy cp trng thi nhn ri v/hoc hot ng.

1.4.4. Giao thc giao din v tuyn D liu c truyn trn ng xung di dng cc gi IP trn mt trong nhng ti

tin SAE. Trc khi truyn i qua giao din v tuyn, nhng gi IP n (incoming IP packets) s i qua nhiu phn t di y:

iu khin ti nguyn v tuyn (RRC - Radio Resource Control): Cc lp RRC thc hin chc nng kim sot bao gm duy tr mt phng, nhn tin v pht hnh x l kt ni di ng, bo mt, v qun l QoS.

Giao thc hi t s liu gi (PDCP - Packet Data Convergence Protocol): thc hin vic nn tiu IP (IP header) lm gim s lng bit cn thit cho vic truyn dn thng qua giao din v tuyn.

iu khin lin kt v tuyn (RLC - Radio Link Control): m nhim vic phn on, ghp ni, iu khin vic truyn li, v phn pht ln cc lp cao hn theo th t. Khng ging nh WCDMA, giao thc RLC c nh v trong eNodeB v ch c mt loi node n trong kin trc mng truy nhp v tuyn LTE. RLC cung cp cc dch v cho PDCP di dng cc ti tin v tuyn. Ch c mt phn t RLC trn mt ti tin v tuyn c cu hnh cho mt thit b u cui di ng.

iu khin truy cp mi trng (MAC - Medium Access Control): iu khin vic truyn li hybrid-ARQ v hoch nh ng ln, ng xung. Chc nng hoch nh c nh v trong eNodeB, v n ch c mt phn t MAC cho mt t bo, cho c ng ln v ng xung. Phn giao thc hybrid ARQ c mt trong c u cui pht v thu ca giao thc MAC. Khi MAC cung cp cc dch v cho RLC di dng cc knh logic.

Lp vt l (PHY - Physical layer): iu khin vic m ha / gii m, iu ch / gii iu ch, nh x a anten (multi antenna mapping), v cc chc nng lp vt l tiu biu khc. Lp vt l cung cp dch v cho lp MAC di dng cc knh truyn ti.

1.5. Tng kt chng Chng I gii thiu s lc v l trnh pht trin ca h thng thng tin di ng, cc

mc nh du tin trnh pht trin 3G ln 4G ca 3GPP. Chng a ln ci nhn tng quan v LTE, cng ngh c xem l cng ngh tin 4G. Nhn chung mc tiu ca cng ngh LTE u nhm ci thin cc thng s hiu nng v gim gi thnh so vi cc cng ngh trc . S dng cc k thut mi cho truy nhp v tuyn cho php tng hiu nng truyn dn v tuyn ca LTE c bit l dung lng h thng mt cch ng k.

Chng ny cng xt n kin trc h thng, m hnh mng cng nh cc tnh nng quan trng, c th ca LTE.

Chng 2: K thut a truy nhp SC-FDMA


CHNG II K THUT A TRUY NHP SC-FDMA

2.1. S lc v cng ngh truyn dn ng xung OFDM Ghp knh phn chia tn s trc giao OFDM l cng ngh truyn dn a sng mang

tit kim bng tn s dng trong cc h thng thng tin v tuyn bng rng. Nguyn l ca OFDM l phn chia ton b bng thng cn truyn vo nhiu sng mang con v truyn ng thi trn cc sng mang ny. Theo , lung s tc cao c chia thnh nhiu lung tc thp hn. Vic chia tng bng thng thnh nhiu bng con vi cc sng mang con dn n gim rng bng con trong min tn s ng ngha vi tng di k hiu. S sng mang con cng ln th di k hiu cng ln. iu ny c ngha l di k hiu ln hn so vi thi gian tri rng tr ca knh phainh phn tn theo thi gian, hay rng bng tn tn hiu nh hn rng bng tn nht qun ca knh. V th c th gim nh hng ca tr a ng v chuyn i knh phainh chn lc thnh knh phainh phng. Nh vy OFDM l mt gii php cho tnh chn lc ca cc knh phainh trong min tn s, cho php gim thiu mo tuyn tnh do tnh phn tn ca knh truyn dn v tuyn gy ra.

OFDMA l phng php a truy nhp da trn OFDM, trong mi ngi s dng c cp pht mt s sng mang con trong tng s sng mang con kh dng ca h thng.

Mt s c trng quan trng ca h thng OFDM: - S dng nhiu sng mang bng hp, chng hn vi h thng MC-WCMDA bng

thng 20MHz s dng 4 sng mang vi mi sng mang c bng tn l 5MHz, th i vi h thng OFDM c cng bng tn nh vy th c th ln ti 2048 sng mang con vi bng thng sng mang con l 15MHz.

- Cc sng mang con trc giao nhau, mt ph cng sut cc sng mang con ny c th chng ln ln nhau m khng gy nhiu cho nhau. V th khng cn on bng bo v so vi FDMA.

Kh nng gim thiu tr a ng tuy nhin vic pht thng tin trn nhiu sng mang con trc giao cng mang li mt s hn ch cho OFDM:

- PAPR ln do OFDM s dng nhiu sng mang truyn thng tin, gi tr cc i ca k t trn mt sng mang c th vt xa mc trung bnh trn ton b sng mang. V vy khng lm mo tn hiu pht b khuch i cng sut phi t ch d tr ln nn hiu sut s dng khng cao. iu ny dn ti chi ph my cm tay.

- Nhy cm cao vi dch tn s, do cc sng mang trong min tn s trc giao nhau nn ch mt nh hng nh nh dch Doppler cng c th gy nn cc sng mang chng ln ln nhau gy nhiu ICI.

- V cc sng mang c iu ch, m ha v pht i mt cch c lp nn cc sng mang con ny b suy gim rt nhiu do nh hng ca phainh. V vy cn c cc lc iu ch v m ha thch ng trnh hin tng ph rng, nu khng s khng th khi phc c d liu trn sng mang .



Hnh 2.1: Li ICI trong OFDM 2.2. H thng n sng mang vi b cn bng min tn s SC/FDE

Cc nhc im ca OFDM lm cho n khng thc s thch hp cho vic truyn dn theo ng xung, v vy mt phng php a truy nhp mi s dng DFTS-OFDM vi tn gi SC-FDMA c 3GPP nghin cu v p dng trn ng ln cho LTE. SC-FDMA ci tin ca h thng n sng mang vi b cn bng min tn s FDE. S SC/FDE nh sau:

Hnh 2.2: Cu trc b thu v pht ca SC/FDE v OFDM

Nhn chung cu trc h thng OFDM v SC/FDE tng t nhau, ch khc v v tr ca b IDFT. i vi OFDM thc hin tch sng trn mt sng mang trong min tn s, trong khi SC/FDE thc hin tch sng sng mang trong min thi gian sau khi qua b IDFT. Do s khc nhau ny OFDM nhy cm hn i vi ph rng v n yu cu vic iu khin tc /cng sut hoc m ha knh khc phc hin tng ph rng ny.

Hnh 2.3: S khc nhau trong tin trnh tch sng gia SC/FDE v OFDM



Hnh 2.4: Sp xp k hiu iu ch ln sng mang con trong OFDM v SC/FDE

C th ni u im ca h thng SC/FDE so vi OFDM l: - Park thp hn do iu ch n sng mang ti pha pht, - Nhy cm vi dch tn s sng mang thp hn. - n nh vi ph rng. - B cn bng phc tp ch trm c s ch khng phi u cui di ng l li ch

ln cho ng ln.

2.3. Nguyn l truyn dn SC-FDMA 2.3.1. S khi v nguyn l h thng SC-FDMA

Hnh 2.5 th hin s khi h thng SC-FDMA v OFDMA :

Hnh 2.5: Cu trc b pht v thu ca SC-FDMA v OFDMA xp: K hiu s liu th p (p = 0,1,2,,P-1) trong khi s liu u vo SC-FDMA. Xn: Mu n (n = 0,1,2,,P-1) trong min tn s ca tn hiu u ra ca DFT. Xi: Sng mang con th i (i = 0,1,2,,N-1) c iu ch trong min tn s ti u vo

b IFFT.



xi: Sng mang con th i (i = 0,1,2,,N-1) ca tn hiu OFDM trong min thi gian ti u ra b IFFT.

xi,k(m): Mu th m (m = 0,1,2,,N-1) ca tn hiu OFDM ti u ra ca b bin i t song song vo ni tip (PS) ti thi im k, vi k l mt s nguyn c g tr t ti .

My pht DFTS-OFDM chuyn cc tn hiu nh phn u vo thnh mt chui cc sng mang iu ch. X l tn hiu c thc hin theo tng khi k hiu iu ch. Mi khi bao gm P k hiu trong mi k hiu c di l Tsmod. Do mt khi c khong thi gian l P.Tsmod. Ti u vo b iu ch bng gc bin i u vo nh phn thnh mt chui nhiu mc cc s phc v nhm chng thnh cc khi k hiu {x }p (p = 0, 1,, P-1) c khun

dng ca mt trong cc s iu ch BPSK, QPSK, 16QAM v 64QAM. Bin i Fourier ri rc (DFT) thc hin trn kch thc P to ra th hin min tn s {X }n ca cc k hiu u vo, trong n = 0, 1,, P-1 v P



Hnh 2.6: Chn CP

Sau x l DFT kch thc P cho cc k hiu iu ch, tn hiu c nh k tri rng trong min tn s. Sau qu trnh to dng ph c thc hin bng cch nhn cc mu tn s vi hm to dng ph. Hm to dng ph thng thng l hm Raise-cosin. Min tn s v min thi gian ca hm c th c cho nh sau:

Min tn s:

1 0 | |2

1 1 1( ) 1 os (| | ) | |2 2 2 2

10 | |2

T fT

T TP f c f fT T T

fT

(2.1)

Hnh 2.7: Min thi gian v tn s b lc Raise-cosin



Min thi gian:

2 2 2

sin( / ) os( / )( ) ./ 1 4 /t T c t TP t

t T t T

(2.2)

T l chu k k hiu cn l h s dc (Roll-off).

Theo hnh 2.7, thay i t 0 n 1, n iu khin s bc x ngoi bng. Nu = 0, khng to ra bc x ngoi bng, nu tng bc x ngoi bng tng, trong min thi gian xung c thy vng cao hn khi tin gn ti 0 v iu ny tng cng sut nh cho pht tn hiu sau dng ph.

Hnh 2.8: Phn b PAPR vi cc h s Roll-off

Hnh 2.8 cho thy to dng ph cho php gim hn na s bin i cng sut ca tn hiu pht nh vy t c hiu sut ca b khuych i cng sut cao hn. Tuy nhin nhc im ca to dng ph l gim hiu sut s dng ph tn do ph tr ln rng hn trong khi bng thng khng i. V d nh trn hnh v trn minh ha cho trng hp h s = 0.15 c ngha bng thng l tng thm 15% so vi khng to dng ph. V th to dng ph ch p dng cho cc trng hp b hn ch cng sut khi cng sut pht ch khng phi l do ph ti nguyn him. Khi ny vic thay i cng sut pht nh to dng ph cho php ci thin c ly ng truyn.

R rng, s khc nhau gia OFDM v SC-FDMA ch ch SC-FDMA s dng thm b DFT ti pha pht trc khi sp xp cc k hiu ln cc sng mang v b IDFT ti pha thu trc khi tch sng cc sng mang. V th, SC-FDMA cn c gi l DFT spread OFDM (OFDM c tri ph bng DFT) hay iu ch OFDM c m ha trc.

Ti my thu, SC-FDMA thc hin cc qu trnh ngc vi my pht nh nu trn. Trc ht x l FFT kch thc N c thc hin, tip theo l loi b cc mu tn s khng lin quan ti tn hiu cn thu, sau cc tn hiu qua b cn bng min tn s b tr tnh



chn lc tn s ca knh, my thu SC-FDMA s dng b cn bng min tn s tuyn tnh t phc tp hn. Cui cng l x l DFT ngc kch thc P sau thc hin gii iu ch.

2.3.2. Sp xp cc sng mang Trong SC-FDMA cc k hiu truyn dn c sp xp ln cc sng mang con theo hai

cch l phn b (DFDMA: Distributed FDMA) v ni vng (LFDMA: Localized SC-FDMA). Vi LFDMA mi u cui s dng mt tp sng mang con lin k pht i k hiu

ca mnh, v th bng thng truyn dn LFDMA bng mt phn bng thng h thng. Vi DFDMA, cc sng mang dnh cho mt u cui c phn b trn ton b bng

tn tn hiu. Mt phng n ca DFDMA c gi l FDMA an xen (IFDMA: Interleaved SC-FDMA), trong cc sng mang con c chim cch u nhau trng hp N = Q.P.

Hnh 2.9 cho thy hai cch sp xp ni trn, trong c ba u cui, mi u cui pht i cc k hiu trn bn sng mang con trong mt h thng c 12 sng mang con. Trn hnh 2.10, vi cch sp xp IFDMA u cui mt s dng cc sng mang con s 0, 3, 6 cn trong cch sp xp LFDMA u cui mt s dng cc sng mang con s 0, 1, 2.

Hnh 2.9: Sp xp cc sng mang (a) LFDMA v (b) DFDMA

Hnh 2.10: Cp pht sng mang cho cc cc u cui theo ch phn b v ch ni vng



Xt v kh nng thch ng i vi li truyn, SC-FDMA phn b c kh nng khng pha inh chn lc tn s tt hn SC-FDMA ni vng v thng tin cn truyn c tri rng trn ton b bng tn tn hiu. Do vy n s cung cp kh nng phn tp tn s. Tri li LFDMA cho php t c phn tp ngi s dng khi xy ra phainh chn lc tn s nu n n nh cho tng ngi s dng phn bng tn trong ngi s dng ny c c trng truyn dn tt nht ( li knh cao).

Mt v d sau trong min tn s cho N=12 (tng s sng mang con), Q=3 (h s tri ph bng), P = 4 (kch thc khi d liu)

{x }p

{X }n

,IF{X }i DMA

, F{X }i L DMA

, F{X }i D DMA

21

0

. , 4pP j n

Pn p

px x e p

Hnh 2.11: Cc kiu sp xp sng mang trong SC-FDMA

i vi IFDMA, cc k hiu thi gian ch l lp li ca cc k hiu u vo gc vi quay pha h thng c p dng cho tng k hiu trong min thi gian, v th PAPR ca k hiu SC-FDMA ging nh trng hp tn hiu n sng mang thng thng. Trong trng hp LFDMA, tn hiu thi gian l cc bn sao chnh xc ca cc k hiu thi gian u vo trong P v tr mu. N-P l tng c trng s ca tt c cc k hiu trong khi vo.

2.3.3. Trnh by cc tn hiu SC-FDMA trong min thi gian 2.3.3.1. Cc k hiu min thi gian ca IFDMA

Ta c th biu din tn hiu IFDMA trong min thi gian nh sau:

1 2

0

( ) .iN j mN

ii

x m X e

(2.3)

Trong : . (0 1)

0 khcn

i

X i Q n n PX

(2.4)



Vi m = P.q+p v N = Q.P; 0 q Q-1 v 0 p P-1 (2.5)

Theo nh trong v d trn ta c th cho v d l N=12, Q=3, P=4 l kch thc FFT vi tng s 12 sng mang con, v c ba ngi s dng mi ngi s dng c cp pht bn sng mang con cho bn k hiu iu ch u vo. T (2.4) ta c:

Xi=0 = Xn=0 ; Xi=3 = Xn=1 ; Xi=6 = Xn=2 ; Xi=9 = Xn=3; S dng (2.5) ta c th bin i phng trnh (2.3) nh sau:

1 12 2

0 0( ) . .

i nN Pj m j mN P

i ni n

x m X e X e

(2.6)

.1 12 ( . ) 2 2

0 0

. .n n pP Pj P q p j nq jP P

n nn n

X e X e

(2.7) Vi q = 0 ta c:

1 2

0( ) .

nP j pP

n pn

x m X e x

(2.8) T phng trnh (2.8) ta c th thy rng tn hiu sau bin i IFFT theo thi gian l

khng khc g tn hiu u vo (xp). Trong hnh 2.12 s minh ha vic truyn dn cc k hiu IFDMA theo thi gian, ta c th thy rng cc k hiu c truyn i ln lt theo thi gian, iu ny hon ton khc vi OFDM cc k hiu c pht i song song theo thi gian.

Nu trong trng hp cp pht sng mang khng phi l sng mang con th 0 cho u cui m l sng mang con th r (0< r Q-1) no th ta c.

(1/ ) . (0 1)

0 khcQ r

i

X i Q n r n PX

(2.9)

Vy theo trn ta cng gi s c 12 sng mang con cp pht cho bn u cui vi h s tri ph bng thng l Q=3.

Xi=0 = X-r ; Xi=3 = X1-r ; Xi=6 = X2-r ; Xi=9 = X3-r; Nh vy ta c th thy nu r=0 (cp pht ti sng mang con th 0) th s c dng nh

trn, ta c: .1 12 2 ( )

0 0

( ) . .Q n r nm rmN Pj m j

N P Ni n

i nx m X e X e

(2.10)

1 2 22

0. . .

mr mrnmP j jjN NP

n nn

X e e x e

(2.11) Nh vy khi cp pht sng mang ti sng mang con th r thay v s 0 th thc cht

chnh l s quay pha i2 mrj

Ne

. S quay pha c th c p dng cho cc kiu cn li.



2.3.3.2. Cc k hiu min thi gian ca LFDMA

Cc k hiu LFDMA trong min thi gian c biu din nh sau:

1 2

0( ) .

iN j mN

ii

x m X e

(2.12)

(0 1)0 khc

ni

X i n n PX

(2.13)

Vi m = Q.p+q v N = Q.P; 0 q Q-1 v 0 p P-1 (2.14) Theo nh trong v d trn ta c th cho v d l N=12 l kch thc FFT vi tng s

12 sng mang con, v c ba ngi s dng mi ngi s dng dc cp pht bn sng mang con cho bn k hiu iu ch u vo. T (2.13) ta c:

Xi=0 = Xn=0 ; Xi=1 = Xn=1 ; Xi=2 = Xn=2 ; Xi=3 = Xn=3; m = Q.p (q=0) S dng (2.13) ta c th bin i phng trnh (2.12) cho q=0 nh sau:

1 12 2

0 0

( ) . .i nN Pj m j mN N

i ni n

x m X e X e

(2.15)

1 12 ( . ) 2.

0 0. .

n nP Pj Q p j pQ P Pn n

n nX e X e

= xp (2.16) T phng trnh trn ta thy rng khi q=0 th tn hiu u ra ging tn hiu u vo. Vi q 0 ta nhn c biu din tn hiu u ra IFFT trong min thi gian nh sau:

.1 1 2 .2 .

0 0

( ) . .Q p qiN P j nj m Q PN

i ni n

x m X e X e

(2.17) Cng theo hnh 2.5 ta c:

1 2 .

0.

pP j nP

n pp

X x e

(2.18) S dng (2.18) thay vo (2.17) ta c

.1 1 2 .2 . .

0 0

( ) . .Q p qpP P j nj n Q PP

pn p

x m x e e

(2.19)

1 1 1 12 . 2 .. .

0 0 0 0. .

q qP P P Pj n j nQ P Q P

p pn p p n

x e x e



21 12

2 20 0. .

1. (1 ).1 1

qj qQP Pj pQp q qj jp pQ P Q P

xex ee e

1

,0

.P

p m pp

c x

(2.20) T (2.20) ta c th thy rng cc tn hiu LFDMA trong min thi gian l copy cc k

hiu u vo vi h s t l 1/Q trong cc v tr mu bi P v gia cc gi tr l tng ca tt c cc k hiu u vo min thi gian trong khi u vo vi trng s phc cp,m khc nhau.

2.3.3.2. Cc k hiu min thi gian ca DFDMA

Cc k hiu DFDMA trong min thi gian c biu din nh sau:

1 2

0( ) .

iN j mN

ii

x m X e

(2.21)

. (0 1)0 khc

ni

X i H n n PX

(2.22)

Vi m = Q.p+q; N = Q.P; 0 q Q-1; 0 p P-1 v 0 H < Q (2.23) Vi gi thit N=12 l kch thc FFT vi tng s 12 sng mang con, v c ba ngi

s dng mi ngi s dng dc cp pht bn sng mang con cho bn k hiu iu ch u vo. S d t (2.22) ta c h s tri ph bng thng H < Q l do vi kiu IFDMA do cc sng mang c cp pht tri u trn ton b bng tn, cch u nhau cn kiu DFDMA c tri trong bng tn nhng c th khng u nhau. T (2.23) v gi s H = 2 ta c:

Xi=0 = Xn=0 ; Xi=2 = Xn=1 ; Xi=4 = Xn=2 ; Xi=6 = Xn=3; m = Q.p (q=0) S dng (2.23) ta c th bin i phng trnh (2.21) nh sau:

.1 1 2 ( . )2 .

0 0( ) . .

H niN P j Q p qj m Q PNi n

i nx m X e X e

(2.24)

mod( . ).1 12 . 2 .

0 0. .

PH pH pP Pj n j nP P

n nn n

X e X e

mod mod mod( ) ( ( ) )P P PHp H mx x (2.25)

Vi q 0 ta nhn c biu din tn hiu u ra IFFT trong min thi gian nh sau:

.1 1 2 ( . )2 . .

0 0( ) . .

H npP P j Q p qj n Q PPp

n px m x e e

(2.26)



.2. 2 ( 1)1 1 12 ( 1) ..

.2 ( 1)0 0 0 .

1 .. .

1

H qjp H q j H p QP P Pj H nP Q P

p p p H qj Hn p p P Q P

e ex e x

e

.21

.2 ( 1)0 .

1.

1

H qjQP

p p H qj Hp P Q P

ex

e

. 1 12

,.2 ( 1)0 0.

(1 ) . .

1

H q P Pj pQp p m pp H qj Hp pP Q P

xe x c x

e

(2.27)

Ti y ta c th thy rng cc tn hiu LFDMA v DFDMA c cng cu trc pht i. Hnh 2.12 minh ha vic truyn i cc k hiu DFDMA, cc k hiu ny cng c

pht i ln lt trong min thi gian. Chng ta c th thy rng cc k hiu min thi gian ca DFDMA c cng cu trc nh cc k hiu LFDMA.

3

*, ,

0. ,p m p p m

pm c x c

l trng s phc. Hnh 2.12: Cc k hiu truyn dn SC-FDMA trong min thi gian

Hnh 2.13: Bin cc k hiu SC-FDMA



Da trn hnh sp xp cc sng mang ca cc ch khc nhau cho N=12, P=4, Q=3. V hnh v th hin bin ca tn hiu cho mi lc sp xp cc sng mang cho N=64, NTx=16, Q=4 v QPSK chng ta c th thy rng DFDMA v LFDMA c s dao ng nhiu hn v nh cao hn so vi kiu IFDMA. Do PAPR ca cc tn hiu DFDMA l cao nht sau ti LFDMA v cui cng thp nht l IFDMA.

Hnh 2.14: PAPR ca cc tn hiu SC-FDMA v OFDMA

2.4. SC-FDMA v OFDMA

Lc khi ca b pht OFDMA v SC-FDMA cho thy chng c nhiu im chung. im khc bit duy nht gia chng l s hin din ca khi DFT trong lc khi SC-FDMA. V l do ny m SC-FDMA i khi cn c gi l DFTS-OFDMA. Cc im ging nhau khc gia hai khi bao gm: x l v iu ch d liu da trn khi, phn chia bng thng truyn dn thnh cc bng con hp hn, x l cn bng min tn s. V s dng CP chn vo mi k hiu trnh nhiu ISI.

Hnh 2.15: SC-FDMA v OFDMA vi s khc nhau trong b thu



Hnh 2.16: Khc nhau trong pht cc k hiu pht gia SC-FDMA v OFDMA Theo iu kin pht hin d liu ti b thu, OFDMA thc hin chng trn mi sng

mang trong khi SC-FDMA thc hin chng sau khi hot ng ca IDFT, bi v s khc nhau ny, OFDMA l nhy cm hn i vi hin tng ph rng trong ph knh v n yu cu iu khin cng sut/ tc hoc m ha knh chng li hin tng ph rng . Hn na, trong OFDMA cc k hiu c sp xp ln sng mang c truyn dn song song vi chu k thi gian c ko di ra trong khi cc k hiu iu ch SC-FDMA c nn thnh cc chp nh hn vi truyn dn ni tip cc khi d liu, iu ny tht s ging nh h thng a truy nhp phn chia theo m chui trc tip (DS-CDMA). Ngoi ra, SC-FDMA c nhiu kiu sp xp sng mang khc nhau cho php linh hot hn trong cc ch , iu kin truyn dn khc nhau.

Da trn h thng ny ta c v d minh ha so snh gia SC-FDMA v OFDMA gi s vi kiu iu ch QPSK, ta c th biu din cc k hiu c pht nh sau.

Hnh 2.17: So snh gia OFDMA v SC-FDMA vi vic pht cc k hiu QPSK



Tm li SC-FDMA c cc u im so vi OFDM:

PAPR thp hn do truyn dn n sng mang. Do truyn dn n sng mang nn n trnh c hin tng ph rng. nhy cm dch tn s thp hn. phc tp ti b pht thp hn c th hn chnh l cc u cui di ng s c

li hn v tnh n gin vi mch trong thng tin di ng do chi ph thit b u cui tng i thp.

2.5. SC-FDMA v DS-CDMA/FDE

a truy nhp phn chia theo m chui trc tip (DS-CDMA: Direct Sequence CDMA) vi FDE l mt k thut thay th cho my thu Rake thng thng c s dng trong h thng DS-CDMA vi b cn bng min tn s. Mt my thu Rake bao gm cc b hiu chnh, mi b hiu chnh mt thnh phn tn hiu a ng. S tn hiu a ng tng th chn lc tn s trong knh cng tng v phc tp ca my thu Rake cng tng ln v cn nhiu cc b hiu chnh hn. Vic s dng FDE thay v my thu Rake c th lm gim bt vn phc tp trong h thng DS-CDMA. Lc khi ca h thng DS-CDMA vi FDE c th c cho nh hnh v di y.

Hnh 2.18: H thng DS-CDMA vi b cn bng min tn s

My pht DS-CDMA/FDE tng t nh h thng DS-CDMA thng thng tuy nhin c mt khi khc l khi chn CP. FDE trong b thu s loi b mo knh t cc k hiu chp c thu khi phc cc k hiu chp khng b nhiu ISI. Vi h s tri ph nh, hiu nng lin kt ca my thu Rake gim ng k cho nhiu a lin ng v FDE s c hiu nng tt hn. Vi h s tri ph ln, c hai s cho cng hiu nng. SC-FDMA tng t nh DS-CDMA/FDE:

C hai u tri ph khi d liu bng hp vo bng rng hn. u t c li x l hoc li tri ph khi tri ph. Chng u duy tr PAPR thp do truyn dn n sng mang.

Mt c bit na gia DS-CDMA trc giao v IFDMA l c trao i vai tr chui tri ph v d liu, iu ch DS-CDMA tr thnh iu ch IFDMA. Mt v d c minh ha trong hnh di. Chng ta c th thy rng kt qu tri ph vi vic hon i vai tr l theo dng cc k hiu iu ch IFDMA. Mt u im ca SC-FDMA so vi DS-CDMA/ FDE l c kh nng lp lch ph thuc knh li dng chn lc tn s ca knh.



0x 1x 2x 3x

0x 0x 0x 0x 1x 1x 1x 1x 2x 2x 2x 2x 3x 3x 3x 3x



Hnh 2.19: Tri ph vi vai trong chui d liu v trao i chui k hiu tri ph vi (1, 1, 1, 1) vi kch c khi l 4

2.6. SC-CFDMA 2.6.1. Lp lch ph thuc knh

Nh ni chng trc, lp lch l mt trong cc yu t quan trng, quyt nh dung lng v cht lng trong LTE. Trong LTE b lp lch lp lch c trong min thi gian v tn s. Nu lp lch trong min thi gian, tt c cc ti nguyn c dnh cho ti mt ngi s dng trong mi khong thi gian lp lch. Trong min tn s v thi gian, mi khong thi gian lp lch nhiu ngi s dng c cp pht ti nguyn. T quan im cp pht ti nguyn, vic cp pht ti nguyn ti cc ngi s dng c th da trn cc iu kin knh hoc khng da trn cc iu kin knh. C hai phng php cp pht ti nguyn:

Phng quay vng (Round Robin - RR) cp pht ti nguyn ti ngi s dng m ngi s dng ch lu nht pht sau khi ng nhp vo mng m khng cn quan tm ti iu kin knh ca ngi s dng .

Phng php CDS da trn cc iu kin knh, CDS cp pht ti nguyn ti cc ngi s dng c cht lng knh tt nht.

C th thy rng nu iu kin knh khng thay i hoc thay i t, phng php RR l thch hp. i vi iu kin knh thay i CDS l thch hp hn c. Tuy nhin thc t, CDS c s dng nhiu hn do cc u cui di chuyn trong mi trng di ng.

Trong hnh v di th hin h thng c K ngi s dng vi chc nng truyn knh c lp ln nhau. cung cp cho u cui vi thng tin knh, u cui s pht cc tn hiu trn cc sng mang trong khong thi gian ton b bng tn. Da trn cc thng tin ny, b



lp lch ti trm gc tm mt tp ngi s dng c tng s dung lng cc i. Sau n s quyt nh chm sao iu ch da trn SNR ca cc khi sng mang c cp pht ti ngi s dng. B lp lch sau s cp pht mt tp N sng mang ti mi u cui v truyn cp pht khi sng mang ny v chm sao iu ch ti mi ngi s dng.

Hnh 2.20: Lp lch h thng SC-FDMA

2.6.2. SC-CFDMA

Chng ta c th thy rng c ch lp lch RR c u im l n gin, d trin khai v khng tnh ton nn khng yu cu tiu trong vic truyn ti, n khng quan tm ti iu kin knh, n gin n ch dnh ti nguyn cho ngi s dng no ng nhp vo mng thnh cng v c thi gian ch lu nht truyn d liu. Nh vy c ch RR c th t thng lng cao c bit trong trng hp u cui di chuyn vi tc thp (iu kin knh thay i chm) v s gim dn khi u cui di chuyn vi tc cao. T hnh 2.12 c th thy vi kiu sp xp sng mang IFDMA s cho thng lng cao hn khi u cui di chuyn tc cao so vi LFDMA do IFDMA c kh nng khng phainh tt hn LFDMA.

Ngc li khi ngi s dng di chuyn vi tc thp vi c ch CDS th kiu sp xp sng mang LFDMA s cho thng lng cao hn kiu sp xp sng mang IFDMA do LFDMA cho php t c phn tp ngi s dng khi xy ra phainh chn lc tn s nu n n nh cho tng ngi s dng phn bng tn trong ngi s dng ny c c trng truyn dn tt nht ( li knh cao).

Do , khi nhiu ngi s dng di chuyn vi tc thp v tc cao ti cng thi im, chng ta c th kt hp hai phng php sp xp sng mang trn t c thng lng cao hn.

SC-FDMA khng th thc hin c vi c hai kiu sp sp trn khi cc sng mang khng b chng ln nhau duy tr tnh trc giao gia cc ngi s dng. K thut s dng tri ph chui trc tip trc giao iu ch SC-CFDMA, vi phng php ny c hai kiu sp xp sng mang s ng tn ti vi cc sng mang c chng ln nhau.



Hnh 2.21: Kiu sp xp sng mang lai SC-CFDMA

Ngoi u im trn phng php sp xp lai cn c u im l tn dng c bng thng. Kiu lc a truy nhp trn c gi l a truy nhp phn chia tn s m n sng mang SC-CFDMA nh hnh sau th hin lc khi truy nhp ca h thng SC-CFDMA. Hnh 2.23 th hin s so snh SC-FDMA v SC-CFDMA vi cc sng mang l nh nhau ca cc ngi s dng.

Hnh 2.22: H thng SC-CFDMA

Hnh 2.23: Sp xp sng mang trongSC-FDMA v SC-CFDMA



Da vo hnh c th thy phng php SC-CFDMA c u im rt ln l tit kim c bng tn h thng. Bn tri l vi kiu sp xp sng mang DFDMA trong cn ti bn sng mang cp pht cho bn u cui. Trong khi bn phi l kiu SC-CFDMA ch cn hai sng mang c tri chui trc tip cp pht cho bn u cui.

Hnh 2.24: Thng lng theo tc di chuyn v kiu sp xp sng mang

Hnh 2.25: Thng lng ngi s dng theo cc kiu sp xp khc nhau

Hnh trn ta thy rng thng lng ngi s dng trong trng hp u cui di ng vi tc thp v cao c ci thin hn vi c ch sp xp sng mang lai SC-CFDMA.

2.7. Tng kt chng

SC-FDMA l mt k thut a truy nhp mi m hin ti ang c trin khai trn ng ln LTE. Trong chng II i su vo tm hiu nguyn l h thng SC-FDMA, phn tch vi cc kiu sp xp sng mang khc nhau l IFDMA, DFDMA v LFDMA. Nghin cu cc c tnh PAPR ca tn hiu SC-FDMA vi to dng ph, so snh gia cc s truyn dn khc nhau nh OFDM v DS/CDMA...

Chng 3: Trin khai SC-FDMA trong 3GPP LTE


CHNG III TRIN KHAI SC-FDMA TRONG 3GPP LTE

3.1. Lp giao thc v knh truyn Trong kin trc giao thc ca giao din v tuyn LTE, c ba loi knh chuyn thng

tin gia cc tng giao thc, my pht v my thu l knh vt l (physical channel), knh vn chuyn (transport channel), v knh logic (logical channel). SC-FDMA v OFDM l cc nh dng tn hiu ca knh vt l. K thut LTE xc nh chn knh vt l: su knh dnh cho ng xung v ba knh dnh cho ng ln.

Hnh 3.1: Kin trc giao thc ca 3GPP LTE Bng 3.1 Knh vt l

Tn knh vt l T vit tt Downlink Uplink Knh vt l qung b PBCH x Knh vt l ch th nh dng cc iu khin PCFICH x Knh vt l iu khin ng xung PDCCH x Knh vt l ch th c ch ARQ PHICH x Knh vt l ch s ng xung PDSCH x Knh vt l a phng PMCH x Knh vt l iu khin ng ln PUCCH x Knh vt l chia s ng ln PUSCH x Knh vt l truy nhp ngu nhin PRACH x

PUSCH (Physical Uplink Shared Channel) mang HARQ Ack/ Nack, thng tin ngi dng v kim sot thng tin nhn c trn knh truyn ti chia s ng ln (UL-SCH). PUCCH (Physical Uplink Control Channel) mang thng tin iu khin nhn c trn UL-SCH, yu cu lp k hoch, bo co thng tin cht lng knh (CQI). PRACH (Physical Random Access Channel) truyn ti mt tin t vng (CP) v thng tin nhn c t cc knh



truyn ti truy cp ngu nhin. Mc ch ca n l truyn ti mt yu cu i vi cc ngun ti nguyn truyn dn trn mt trong cc loi khc ca knh vt l. Trong SC-FDMA hn ch ngi dng khng th truyn ti cng mt lc trn PUCCH v PUSCH. 3.2. Cu trc khung thi gian v tn s ng ln

SC-FDMA cng c th coi nh l truyn dn OFDM thng thng kt hp vi tin m ha da trn DFT. V th cc thng s c bn trong s truyn dn ng ln LTE c chn ng b tt nht vi cc thng s ng xung tng ng.

LTE quy nh c th truyn tn hiu trong by bng thng knh t 1.25 ti 20MHz. Mi bng thng knh c chia thnh cc khong f = 15kHz lm khong cch gia cc sng mang con. L do s dng khong cch cc sng mang con l f = 15kHz n gin ha thc hin u cui a ch WCDMA/HSPA/LTE. Tt c cc tn hiu LTE u c nh thi t mt ng h hot ng ti 30.72Mhz = 15kHz 2048. y l thi gian cn thit cho bin i Fourier ri rc 2048 im quy nh cho bng thng 20Mhz. V vy, khong thi gian c bn trong mt knh vt l LTE s l:

= 1/(30.72 10) 32.255 ns per clock period (3.1) 3.2.1. Khung v tuyn v khe thi gian

Truyn dn ng ln v ng xung u c t chc vo khung v tuyn vi: Tf = 307200 Ts =10 ms/khung (3.2) bao gm 10 khung con c di nh nhau Tsub = 1ms

CPT 66.7FFTT s

66.7FFTT sCP eT TCP = 160.TS 5,2 s (khi DFT th nht) 144.TS 4,7 s (cc khi DFT cn li) TCP-e = 512.TS 16,7 s

Hnh 3.2: Cu trc khung trong min thi gian



Trong mi khung con chia thnh hai khe thi gian c di l Tslot = 0.5ms. Mi khe thi gian mang by k hiu OFDM v CP i vi trng hp thng thng v 6 k hiu OFDM cho trng hp CP m rng. Cc tn hiu tham chiu ng ln lun c t ln k hiu s 3. Cc tn hiu tham chiu ng xung c s dng vi mc ch c lng knh trong b thu eNodeB gii iu ch knh d liu v knh iu khin, v mc ch th hai chnh l cung cp thng tin cht lng knh cho b lp lch ti trm gc v cc tn hiu tham chiu ny c gi l channel souding, cc tn hiu tham chiu ng ln c xut pht t kiu s tun t Zadoff-Chu CAZAC.

Trong mt sng mang con, cc khung con ca mt khung v tuyn c th c s dng hoc cho ng ln hoc cho ng xung. Trong trng hp FDD (khai thc trong ph kp), tt c cc khung con ca mt sng mang con c th c s dng cho truyn dn ng xung hoc ng ln. Tri li, vi TDD trong ph n, khung con th nht v th su ca mi khung lun c n nh cho truyn dn ng xung v cn li c n nh linh hot cho c truyn dn ng ln v ng xung. Khung con th hai v th by mang tn hiu ng b ha v lun cha khong thi gian an ton (GP) cng vi hoc l UpPTS (uplink pilot time slots) hoc l DwPTS (downlink pilot time slots) ty thuc vo khe dnh cho ng ln hay ng xung.

Hnh 3.3: Cu trc khung theo ghp song cng phn chia thi gian

Hnh 3.4: Cu trc khung theo ghp song cng phn chia tn s

n nh cc khung con trong trng hp TDD l linh hot hn cho cc khi ti nguyn khc nhau (hay thay i t l) cho ng xung v cho ng ln. Cu trc min thi gian c minh ha trn i khi cn c gi l cu trc khung LTE kiu mt hay tng qut.



Cu trc khung ny c p dng cho c FDD v TDD. Bn cnh i vi LTE hot ng vi TDD cn c cu trc khung kiu 2. Cu trc ny c thit k cho ng tn ti vi cc h thng c xy dng trn chun 3GPP TD-SCDMA.

3.2.2. Khi ti nguyn

Trong min tn s, tng 12 sng mang SC-FDMA trong mt khe 0.5ms c nhm li thnh khi ti nguyn tng ng vi bng thng khi ti nguyn chun 180kHz. Khong cch cc sng mang con trong ng ln l f = 15KHz.

RBNRBNHnh 3.5: Khi ti nguyn gm 12 sng mang con

vi khong cch sng mang l 15KHz Khc vi ng xung, khi ti nguyn ng ln c n nh cho u cui di ng

phi lun lun lin tip trong min thi gian (hnh 3.6) v c thc hin trong hai khi ti nguyn lin tip. Ti nguyn ng ln s c n nh tng ng vi cng mt tp sng mang trong hai khe. Mt cch khc, nhy tn gia cc khe cng c n nh trong ng ln LTE. Nhy tn gia cc khe c ngha l cc ti nguyn vt l c s dng cho ng ln trong hai khe ca mt khung con khng chim cng mt tp sng mang con. Lu rng v bng thng truyn dn v tuyn ca u cui di ng bao trm ton b ph ng ln, nn nhy tn thun ty l hot ng bng gc, n gin ch l thay i sp xp DFT ti IFFT ca qu trnh x l DFTS-OFDM.

Hnh 3.6: n nh ti nguyn ng ln LTE



Hnh 3.7: Nhy tn ng ln LTE C hai li ch thu c t vic nhy tn ng ln l:

Nhy tn ng ln cung cp phn tp tn s b xung vi gi thit rng nhy tn cng i lng ln hn bng thng nht qun ca knh.

Nhy tn cung cp phn tp nhiu (trung bnh ha nhiu) vi gi thit l mu nhy tn khc nhau trong cc khc nhau.

ULSymN

1ULSymN

UL RBNRB SCN

RB SCN

RBSCN

ULSymN

Hnh 3.8: Khi ti nguyn tng th ca ng ln LTE

Bng 3.2 Cc bng thng kh dng ng ln LTE Bng thng (MHz) 1.25 2.5 5 10 15 20 S cc sng mang con 75 150 300 600 900 1200 S cc RU kh dng 3 6 12 24 36 48 S cc sng mang con trn RU 25 25 25 25 25 25



Khong thi gian truyn dn ng ln tng t nh truyn dn ng xung l 1ms. D liu ngi s dng c mang trn knh PUSCH. V PUCCH mang cc thng tin iu khin ng ln. PUCCH c pht trn mt vng tn s c d tr trn ng ln. Ch rng, UE ch s dng knh PUCCH khi n khng nhn c d liu c pht trn knh PUSCH. Nu UE c d liu c pht trn PUSCH, n s ghp knh cc thng tin iu khin vi cc thng tin d liu trn PUSCH.

3.3. Cc tn hiu tham kho Cc tn hiu tham kho c ghp knh theo thi gian vi s liu ng ln, c

pht trong khi th t ca tng khe v vi bng thng tc thi bng vi bng thng truyn dn s liu.

Cch thc hin cc tn hiu tham kho ny l to ra mt tn hiu tham kho min tn s XRS(k) c di MRS tng ng vi bng thng c n nh (s lng cc sng mang con DFTS-OFDM hay kch thc DFT tc thi) v a n vo u vo ca IFFT. Vic chn CP c thc hin nh vi cc khi ng ln khc. y, ta c th m t tn hiu tham kho nh l mt tn hiu DFTS-OFDM nhn c bng cch thc hin IDFT kch thc MRS cho chui min tn s XRS(k), chui nhn c sau c a ti x l DFTS-OFDM .

Hnh 3.9: Cc tn hiu tham kho c chn vo khi th t tng khe ng ln

( )RSX k

RSM

CPT 2048. ST

Hnh 3.10: To tn hiu tham kho trong min tn s

Cc tn hiu tham kho ng ln cn c cc thuc tnh sau: Bin khng i hoc hu nh khng i ging nh c tnh ca s truyn

dn ng ln LTE (sng mang n PAPR thp). Cc thuc tnh t tng quan min thi gian tt cho php c tnh knh

ng ln chnh xc.



Cc chui c thuc tnh ny i khi gi l CAZAC. Mt trong cc chui c thuc tnh CAZAC l chui Zadoff-Chu. Trong min tn s chui Zadoff-Chu c di MZC c th c biu din:

( 1)( ) ( ) ZC

k kj uMu

ZCX k e

(3.3)

Trong u l ch s ca chui Zadoff-chu trong tp chui Zadoff-chu c di MZC. S lng cc chui Zadoff-chu kh dng (s lng gi tr c th c ca u) bng s

lng cc s nguyn t tng i ca di chui MZC. Ngha l cc i ha s lng cc chui Zadoff-chu v nh vy c th cc i ha s lng cc tn hiu tham kho c th c, cn s dng cc chui Zadoff-Chu di nguyn t. Tuy nhin di min tn s MRC ca cc tn hiu tham kho ng ln phi bng bng thng c n nh, ngha l bi s ca 12 (kch thc khi ti nguyn) v r rng y khng phi l s nguyn t. V th cc chui Zadoff-Chu khng th s dng trc tip cho ng ln LTE. Nn cc tn hiu tham kho c rt ra t cc chui s Zadoff-Chu.

Hai phng php rt ra cc tn hiu tham kho ng ln c di MZC t cc chui Zadoff-Chu c di nguyn t c nh ngha cho lp vt l ca LTE.

Phng php 1(ct ngn): Cc chui Zadoff-Chu c di MZC trong MZC l s nguyn t c di nh nht ln hn hoc bng MRS c ct ngn c di MRS.

Phng php 2 (m rng vng): Cc chui Zadoff-Chu c di MZC trong MZC l s nguyn t c di ln nht nh hn hoc bng MRS c m rng nh k c di MRS.

Hai phng php ny ct ngn hay m rng vi ch mt k hiu v y khng phi l trng hp lun lun xy ra. Chng hn nu cn di tham kho MRS = 96, tng ng vi tm khi ti nguyn, phng php mt c th s dng chui Zadoff-Chu c di MZC = 97 (l mt s nguyn t) nh l im khi u. Tuy nhin s nguyn t ln nht m nh hn 96 l 89, v th cn s dng phng php hai cho chui Zadoff-Chu. di MZC = 89 nh l im khi u v s dng m rng vng by k hiu c di tn hiu tham kho l 96.

Hnh 3.11: Phng php to tn hiu tham kho ng ln



R rng c hai phng php ny phn no gim cp thuc tnh CAZAC ca cc tn hiu tham kho ng ln, phng php no tt hn (xt v thuc tnh CAZAC) ph thuc vo di tn hiu tham kho hay kch thc khi ti nguyn c n nh.

3.3.1. Nhiu tn hiu tham kho

Thng thng trong cc ln cn cng xy ra truyn dn ng thi ng ln trong cng mt ti nguyn ca cc u cui. Trong trng hp ny cn trnh hai u cui di ng trong cc cnh nhau s dng cng mt tn hiu tham kho ng ln trnh gy nhiu cao gia cc tn hiu tham kho. V th trong cc ln cn, cc tn hiu tham kho cn c xy dng trn cc chui Zadoff-Chu khc nhau (t cng mt tp cc chui Zadoff-Chu khc nhau). Ngha l cc gi tr khc nhau i vi ch s u trong phng trnh m t s CAZAC.

Ngoi cch to lp cc tn hiu tham kho ng ln ni phn trc, mt cch khc na l s dng thuc tnh t tng quan bng khng ca cc chui Zadoff-Chu. Thuc tnh ny c ngha l dch vng mt chui Zadoff-Chu s trc giao vi chnh n. V th nhiu tn hiu tham kho c th c to ra t chnh s dch vng ca cng mt tn hiu tham kho gc. Phng php ny c th c s dng khi hai ng b nhau. y thng l trng hp khi cc trc thuc cng mt eNodeB. Phng php ny cng c th c s dng nu hai u cui di ng pht trong cng mt ti nguyn trong cng mt chng hn nh trong a truy nhp SC-FDMA ng ln.

3.3.2. Cc tn hiu tham kho thm d knh

Lp biu ph thuc knh l mt tnh nng quan trng ca LTE. Vi ng ln, lp biu ph thuc knh c th tng cc tc s liu kh dng v gim nhiu n cc khc. thc hin lp biu ph thuc knh trong min thi gian v tn s cn thc hin cc c tnh cht lng knh min thi gian-tn s. Tuy nhin iu ny khng th thc hin bng cc tn hiu tham kho s dng cho gii iu ch nht qun ng ln do ch c pht trn bng thng c n nh ng cho tng u cui di ng. V th mng h tr lp biu ph thuc knh ng ln trong min tn s cn c thm cc tn hiu tham kho bng rng pht trn ng ln LTE. Cc tn hiu ny c gi l cc tn hiu thm d knh phn bit vi cc tn hiu tham kho cho gii iu ch nht qun c minh ha trn hnh sau.

Cc nguyn l c s ca cc tn hiu thm d knh cng ging nh cc nguyn l ca cc tn hiu tham kho gii iu ch. Cc tn hiu thm d knh c xy dng trn c s cc chui Zadoff-Chu v c pht trong mt khi DFTS-OFDM hon thin.

Cc tn hiu thm d knh thng c bng thng rng hn, c th ln hn nhiu so vi ti nguyn n nh cho mt u cui. Cc tn hiu thm d knh cng c th c pht t cc u cui di ng khng c n nh bt k mt ti nguyn no trn truyn dn UL-SCH.

Cc tn hiu thm d knh thng khng pht thng xuyn nh cc tn hiu tham kho gii iu ch. Nu tn hiu thm d knh c s dng trong mt , mng ch cn n nh tng minh cc khi trong cu trc khung con ng ln truyn dn cc tn hiu thm d knh (hnh 3.12). Cc khi ny khng c s dng truyn dn s liu.

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