Luan Van Tot Nghiep_Cong Nghe LTE

8/3/2019 Luan Van Tot Nghiep_Cong Nghe LTE

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n tt nghip Cng ngh LTE cho mng di ng bngrng

MC LC

DANH MC HNH V ......................................................................................................3

DANH MC BNG BIU .................................................................................................6

LI M U ......................................................................................................................7

CHNG 1 GII THIU V CNG NGH V MC TIU THIT K LTE .............9

1.1 Gii thiu v cng ngh LTE ....................................................................................91.2 So snh cng ngh LTE vi cng ngh Wimax v nhng trin vng cho cng nghLTE ................................................................................................................................10

1.2.1 So snh cng ngh LTE vi cng ngh Wimax ...............................................101.2.2 Nhng trin vng cho cng ngh LTE .............................................................13

1.3 Mc tiu thit k LTE .............................................................................................151.3.1 Tim nng cng ngh .......................................................................................151.3.2Hiu sut h thng .............................................................................................161.3.3 Cc vn lin quan n vic trin khai .........................................................18

1.3.3.1 linh hot ph v vic trin khai ............................................................191.3.4 Kin trc v s dch chuyn (migration) .........................................................211.3.5 Qun l ti nguyn v tuyn ............................................................................211.3.6 phc tp ......................................................................................................221.3.7 Nhng vn chung ........................................................................................22

CHNG 2 TNG QUAN V TRUY NHP V TUYN TRONG LTE ....................23

2.1H thng truyn dn: ng xung OFDM v ng ln SC-FDMA .....................232.2Hoch nh ph thuc knh truyn v s thch ng tc (Channel-dependentscheduling and rate adaptation) .....................................................................................25

2.2.1 Hoch nh ng xung ..................................................................................262.2.2 Hoch nh ng ln .......................................................................................272.2.3 iu phi nhiu lin t bo (Inter-cell interference coordination) .............. .....28

2.3 ARQ hn hp vi vic kt hp mm (Hybrid ARQ with soft combining) ..............292.4 S h tr nhiu anten (Multiple antenna support) ...................................................292.5 H tr multicast v broadcast ..................................................................................302.6 Tnh linh hot ph ...................................................................................................31

2.6.1 Tnh linh hot trong sp xp song cng ............................................................32

2.6.2 Tnh linh hot trong bng tn hot ng ...........................................................322.6.3 Tnh linh hot v bng thng ............................................................................33

CHNG 3 KIN TRC GIAO DIN V TUYN LTE .............................................34

3.1 RLC: radio link control iu khin lin kt v tuyn ...........................................373.2 MAC: iu khin truy nhp mi trng (medium access control) ..........................38

3.2.2 Hoch nh ng xung..................................................................................413.2.3 Hoch nh ng ln.......................................................................................433.2.4 Hybrid ARQ ......................................................................................................46

3.3 PHY: physical layer - lp vt l ...............................................................................503.4 Cc trng thi LTE ...................................................................................................533.5 Lung d liu ...........................................................................................................54

GVHD: ThS. Trn Xun Trng SVTH: Nguyn Minh Tm1


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CHNG 4 LP VT L LTE ......................................................................................56

4.1 Kin trc min thi gian ton phn (Overall time-domain structure) .....................564.2 S truyn dn ng xung ................................................................................58

4.2.1 Ti nguyn vt l ng xung ........................................................................584.2.2 Cc tn hiu tham kho ng xung...............................................................63

4.2.2.1 Cc chui tn hiu tham kho v vic nhn dng t bo lp vt l(Reference signals sequences and physical layer cell identity) .............................644.2.2.2 Nhy tn tn hiu tham kho (Reference signal frequency hopping) .... ....654.2.2.3 Cc tn hiu tham kho cho truyn dn a anten (Reference signals formulti-antenna transmission) ...................................................................................66

4.2.3 X l knh truyn ti ng xung ..................................................................674.2.3.1 Chn CRC ..................................................................................................704.2.3.2 M ha knh ...............................................................................................704.2.3.3 Chc nng Hybrid-ARQ lp vt l ...........................................................71

4.2.3.4 Ngu nhin ha mc bit ........................................................................71

4.2.3.5 iu ch d liu ........................................................................................734.2.3.6 nh x anten ..............................................................................................734.2.3.7 nh x khi ti nguyn ..............................................................................734.2.4 Bo hiu iu khin L1/L2 ng xung .....................................................754.2.5 Truyn dn nhiu anten ng xung ...........................................................774.2.5.1 Hai anten m ha khi khng gian-tn s (SFBC) ....................................794.2.5.2 To dng tia (beam-forming) .....................................................................794.2.5.3 Ghp knh khng gian ...............................................................................80

4.2.6 Multicast/broadcast s dng MBSFN ...............................................................814.3 Scheme truyn dn ng ln .................................................................................82

4.3.1 Ti nguyn vt l ng ln .............................................................................82

4.3.2 Tn hiu tham kho ng ln ..........................................................................864.3.2.1 Nhiu tn hiu tham kho ..........................................................................894.3.2.2 Tn hiu tham kho cho vic d knh ........................................................90

4.3.3 X l knh truyn ti ng ln .......................................................................934.3.4 Bo hiu iu khin L1/L2 ng ln ..............................................................954.3.5 nh thi sm ng ln (Uplink timing advance) ..........................................98

CHNG 5 CC TH TC TRUY CP LTE ............................................................101

5.1 D tm t bo (cell search) .....................................................................................1015.1.1 Th tc d tm cell (cell search) .....................................................................1015.1.2 Cu trc thi gian/tn s ca cc tn hiu ng b ........................................103

5.1.3 D tm cell ban u v k cn .........................................................................1055.2 Truy cp ngu nhin ...............................................................................................106

5.2.1 Bc 1: Truyn dn Preamble truy cp ngu nhin ........................................1075.2.2 Bc 2: p ng truy cp ngu nhin ............................................................1115.2.3 Bc 3: Nhn dng u cui ...........................................................................1125.2.4 Bc 4: Gii quyt tranh chp ........................................................................113

5.3 Paging ....................................................................................................................114

KT LUN ......................................................................................................................116

CC THUT NG V T VIT TT .........................................................................117

TI LIU THAM KHO ...............................................................................................122



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DANH MC HNH V

1.1 Kin trc ca mng LTE

1.2 L trnh pht trin ca LTE v cc cng ngh khc

1.3 Phn b ph bng tn li ti 2 GHz ca nguyn bn IMT-2000

1.4 Mt v d v cch thc LTE thm nhp tng bc vo phn b ph ca mt h

thng GSM c trin khai

2.1 Hoch nh ph thuc knh truyn ng xung trong min thi gian v tn s

2.2 Mt v d v iu phi nhiu lin t bo, ni m cc phn ph b gii hn bi

cng sut truyn dn

2.3 FDD vs. TDD

3.1 Kin trc giao thc LTE (ng xung)

3.2 Phn on v hp on RLC

3.3 V d v s nh x cc knh logic ln cc knh truyn dn

3.4 Vic la chn nh dng truyn dn trong ng xung (bn tri) v ng ln

(bn phi)

3.5 Giao thc hybrid-ARQ ng b v khng ng b

3.6 Nhiu tin trnh hybrid-ARQ song song

3.7 M hnh x l lp vt l n gin cho DL-SCH

3.8 M hnh x l lp vt l n gin cho DL-SCH

3.9 Cc trng thi LTE

3.10 Mt v d v lung d liu LTE

4.1 Cu trc min thi gian LTE



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4.2 Cc v d v vic ch nh khung ph ng ln/ng xung trong trng

hp TDD v s so snh vi FDD

4.3 Ti nguyn vt l ng xung LTE

4.4 Cu trc min tn s ng xung LTE4.5 Cu trc khung ph v khe thi gian ng xung LTE

4.6 Khi ti nguyn ng xung dnh cho tin t chu trnh bnh thng

4.7 Cu trc tn hiu tham kho ng xung LTE dnh cho tin t chu trnh bnh

thng

4.8 Cu trc tn hiu tham kho trong trng hp truyn dn nhiu anten ng

xung

4.9 X l knh truyn ti ng xung

4.10 Chn CRC ng xung

4.11 Khi m ha Turbo LTE

4.12 Chc nng Hybrid-ARQ lp vt l

4.13 Ngu nhin ha ng xung

4.14 iu ch d liu

4.15 nh x khi ti nguyn ng xung

4.16 Chui x l cho bo hiu iu khin L1/L2 ng xung

4.17 Li thi gian/tn s LTE

4.18 Cc phn t knh iu khin v cc ng c knh iu khin

4.19 nh x anten LTE bao gm vic nh x lp sau qu trnh tin m ha

4.20 M ha hai anten khi khng gian-tn s trong kt cu khung nhiu anten

LTE

4.21 To dng tia (beam-forming) trong kt cu khung nhiu anten LTE4.22 Ghp knh khng gian trong kt cu khung nhiu anten LTE

4.23 Nhng k hiu tham kho ring t bo v chung t bo trong cc khung ph

MBSN

4.24 Kin trc c bn ca truyn dn DFTS-OFDM

4.25 Kin trc min tn s ng ln LTE

4.26 Cu trc khe thi gian v khung ph ng ln LTE

4.27 Cp pht ti nguyn ng ln LTE



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4.28 Nhy tn ng ln

4.29 Tn hiu tham kho ng ln c chn vo trong khi th t ca mi khe

thi gian ng ln

4.30 S hnh thnh tn hiu tham kho ng ln min tn s4.31 Phng php to ra tn hiu tham kho ng ln t chui Zadoff-Chu c

di tt nht

4.32Truyn dn cc tn hiu tham kho thm d knh ng ln

4.33 X l knh truyn ti ng ln LTE

4.34 Ghp knh d liu v bo hiu iu khin ng ln L1/L2

trong trng hp truyn dn ng thi UL-SCH v iu khin

L1/L2

4.35 Kin trc ti nguyn c s dng cho bo hiu iu khin

L1/L2 ng ln trong trng hp khng truyn dn ng thi UL-

SCH

4.36 xut nh thi ng ln

5.1 Tn hiu ng b s cp v th cp5.2 Vic pht tn hiu ng b trong min tn s

5.3 Tng quan ca th tc truy cp ngu nhin

5.4 Miu t nguyn l ca truyn dn preamble truy cp ngu nhin

5.5 nh thi Preamble eNodeB cho ngi s dng truy cp ngu nhin khc

nhau

5.6 S hnh thnh phn m u truy cp ngu nhin

5.7 Vic d tm phn m u truy cp ngu nhin trong min tn s

5.8 Vic thu nhn khng lin tc (DRX) cho tm gi (paging)



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DANH MC BNG BIU

1.1 Tin trnh pht trin cc chun ca 3GPP

1.2 LTE v WiMAX

1.3 Cc yu cu v hiu sut ph v lu lng ngi dng

1.4 Yu cu v thi gian gin on, LTE-GSM v LTE-WCDMA



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LI M U

Thng tin di ng ngy nay tr thnh mt ngnh cng nghip vin thng

pht trin rt nhanh v mang li nhiu li nhun cho cc nh khai thc. S pht

trin ca th trng vin thng di ng thc y mnh m vic nghin cu v

trin khai cc h thng thng tin di ng mi trong tng lai. H thng di ng th

h th hai, vi GSM v CDMA l nhng v d in hnh pht trin mnh m

nhiu quc gia. Tuy nhin, th trng vin thng cng m rng cng th hin r

nhng hn ch v dung lng v bng thng ca cc h thng thng tin di ng

th h th hai. S ra i ca h thng di ng th h th ba vi cc cng ngh tiu

biu nh WCDMA hay HSPA l mt tt yu c th p ng c nhu cu truy

cp d liu, m thanh, hnh nh vi tc cao, bng thng rng ca ngi s

dng.

Mc d cc h thng thng tin di ng th h 2.5G hay 3G vn ang pht

trin khng ngng nhng cc nh khai thc vin thng ln trn th gii bt u

tin hnh trin khai th nghim mt chun di ng th h mi c rt nhiu tim

nng v c th s tr thnh chun di ng 4G trong tng lai, l LTE (Long

Term Evolution). Cc cuc th nghim v trnh din ny chng t nng lc

tuyt vi ca cng ngh LTE v kh nng thng mi ha LTE n rt gn.

Trc y, mun truy cp d liu, bn phi cn c 1 ng dy c nh kt ni.

Trong tng lai khng xa vi LTE, bn c th truy cp tt c cc dch v mi lc

mi ni trong khi vn di chuyn: xem phim cht lng cao HDTV, in thoi thy

hnh, chi game, nghe nhc trc tuyn, ti c s d liu v.v vi mt tc siu

tc. chnh l s khc bit gia mng di ng th h th 3 (3G) v mng di



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ng th h th t (4G). Tuy vn cn kh mi m nhng mng di ng bng rng

4G ang c k vng s to ra nhiu thay i khc bit so vi nhng mng di

ng hin nay.

Xut pht t nhng vn trn, em la chn ti tt nghip ca mnh

l: Cng ngh LTE cho mng di ng bng rng. ti s i vo tm hiu tng

quan v cng ngh LTE cng nh l nhng k thut v thnh phn c s dng

trong cng ngh ny c th hiu r thm v nhng tim nng hp dn m cng

ngh ny s mang li.

ti ca em bao gm 5 chng:

Chng 1 Gii thiu v cng ngh v mc tiu thit k LTE

Chng 2 Tng quan v truy cp v tuyn trong LTE

Chng 3 Kin trc giao din v tuyn LTE

Chng 4 Lp vt l LTE

Chng 5 Cc th tc truy cp LTE

Tuy nhin do LTE l cng ngh vn ang c nghin cu, pht trin v

hon thin cng nh l do nhng gii hn v kin thc ca ngi trnh by nn

n ny cha cp c ht cc vn ca cng ngh LTE v khng th trnh

khi nhng thiu st. Rt mong c s ng gp kin ca thy c v cc bn.

Sinh vin thc hin

Nguyn Minh Tm



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CHNG 1 GII THIU V CNG NGH V MC TIU THIT K LTE

1.1 Gii thiu v cng ngh LTE

LTE l th h th t tng lai ca chun UMTS do 3GPP pht trin. UMTS thh th ba da trn WCDMA c trin khai trn ton th gii. m bo tnhcnh tranh cho h thng ny trong tng lai, thng 11/2004 3GPP bt u d nnhm xc nh bc pht trin v lu di cho cng ngh di ng UMTS vi tngi Long Term Evolution (LTE). 3GPP t ra yu cu cao cho LTE, bao gm gimchi ph cho mi bit thng tin, cung cp dch v tt hn, s dng linh hot cc bngtn hin c v bng tn mi, n gin ha kin trc mng vi cc giao tip m vgim ng k nng lng tiu th thit b u cui. c t k thut cho LTE

ang c hon tt v d kin sn phm LTE s ra mt th trng trong 2 nm ti.Cc mc tiu ca cng ngh ny l:

- Tc nh tc thi vi bng thng 20 MHz:o Ti xung: 100 Mbps; Ti ln: 50 Mbps

- Dung lng d liu truyn ti trung bnh ca mt ngi dng trn 1MHz so vi mng HSDPA Rel. 6:

o Ti xung: gp 3 n 4 ln; Ti ln: gp 2 n 3 ln.

- Hot ng ti u vi tc di chuyn ca thu bao l 0 15 km/h. Vn

hot ng tt vi tc t 15 120 km/h. Vn duy tr c hot ng khithu bao di chuyn vi tc t 120 350 km/h (thm ch 500 km/h ty

bng tn)- Cc ch tiu trn phi m bo trong bn knh vng ph sng 5km, gim

cht t trong phm vi n 30km. T 30 100 km th khng hn ch.



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Hnh 1.1 - Kin trc ca mng LTE

- di bng thng linh hot: c th hot ng vi cc bng 1.25 MHz,1.6 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz v 20 MHz c chiu ln v xung.H tr c 2 trng hp di bng ln v bng xung bng nhau hoc khng.

t c mc tiu ny, s c rt nhiu k thut mi c p dng, trong ni bt l k thut v tuyn OFDMA (a truy cp phn chia theo tn s trc

giao), k thut anten MIMO (Multiple Input Multiple Output - a nhp a xut).Ngoi ra h thng ny s chy hon ton trn nn IP (all-IP network), v h tr c2 ch FDD v TDD.

1.2 So snh cng ngh LTE vi cng ngh Wimax v nhng trin vng chocng ngh LTE

1.2.1 So snh cng ngh LTE vi cng ngh Wimax

V cng ngh, LTE v WiMax c mt s khc bit nhng cng c nhiuim tng ng. C hai cng ngh u da trn nn tng IP. C hai u dng kthut MIMO ci thin cht lng truyn/nhn tn hiu, ng xung t trmthu pht n thit b u cui u c tng tc bng k thut OFDM h trtruyn ti d liu a phng tin v video. Theo l thuyt, chun WiMax hin ti(802.16e) cho tc ti xung ti a l 70Mbps, cn LTE d kin c th cho tc n 300Mbps. Tuy nhin, khi LTE c trin khai ra th trng c th WiMaxcng s c nng cp ln chun 802.16m (cn c gi l WiMax 2.0) c tc tng ng hoc cao hn.



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Hnh 1.2 L trnh pht trin ca LTE v cc cng ngh khc.

ng ln t thit b u cui n trm thu pht c s khc nhau gia 2cng ngh. WiMax dng OFDMA (Orthogonal Frequency Division MultipleAccess mt bin th ca OFDM), cn LTE dng k thut SC-FDMA (SingleCarrier - Frequency Division Multiple Access). V l thuyt, SC-FDMA cthit k lm vic hiu qu hn v cc thit b u cui tiu th nng lng thphn OFDMA.

LTE cn c u th hn WiMax v c thit k tng thch vi cphng thc TDD (Time Division Duplex) v FDD (Frequency Division Duplex).Ngc li, WiMax hin ch tng thch vi TDD (theo mt bo co c cng bu nm nay, WiMax Forum ang lm vic vi mt phin bn Mobile WiMax tchhp FDD). TDD truyn d liu ln v xung thng qua 1 knh tn s (dng

phng thc phn chia thi gian), cn FDD cho php truyn d liu ln v xungthng qua 2 knh tn s ring bit. iu ny c ngha LTE c nhiu ph tn sdng hn WiMax. Tuy nhin, s khc bit cng ngh khng c ngha quyt nhtrong cuc chin gia WiMax v TLE.

Bng 1.1: Tin trnh pht trin cc chun ca 3GPP

Phin

bnThi im hon tt Tnh nng chnh / Thng tin

Release

99Qu 1/2000

Gii thiu UMTS (Universal Mobile Telecommunications System) v WCDMA

(Wideband CDMA).

Release4

Qu 2/2001 B sung mt s tnh nng nh mng li da trn IP v c nhng ci tin choUMTS.



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Release

5Qu 1/2002

Gii thiu IMS (IP Multimedia Subsystems) v HSDPA (High-Speed Download

Packet Access).

Release

6Qu 4/2004

Kt hp vi Wireless LAN, thm HSUPA (High-Speed Upload Packet Access)

v cc tnh nng nng cao cho IMS nh Push to Talk over Cellular (PoC).

Release

7Qu 4/2007

Tp trung gim tr, ci thin cht lng dch v v cc ng dng thi gian

thc nh VoIP. Phin bn ny cng tp trung vo HSPA+ (High Speeed Packet

Evolution) v EDGE Evolution.

Release

8

D kin cui nm

2008 hoc u nm

2009

Gii thiu LTE v kin trc li UMTS nh l mng IP th h th t hon ton

da trn IP.

Hin ti WiMax c li th i trc LTE: mng WiMax c trin khaiv thit b WiMax cng c mt trn th trng, cn LTE th sm nht cng phin nm 2010 ngi dng mi c tri nghim. Tuy nhin LTE vn c li thquan trng so vi WiMax. LTE c hip hi cc nh khai thc GSM (GSMAssociation) chp nhn l cng ngh bng rng di ng tng lai ca h di nghin ang thng tr th trng di ng ton cu vi khong 2,5 t thu bao (theoInforma Telecoms & Media) v trong 3 nm ti c th chim th phn n 89%(theo Gartner) nhng con s trong m i vi WiMax. Hn na, LTE cho

php tn dng dng h tng GSM c sn (tuy vn cn u t thm thit b) trongkhi WiMax phi xy dng t u.

Bng 1.2:LTE v WIMAX

Tnh nng 3GPP LTE RAN1 802.16e/Mobile WiMax R1 802.16m/Mobile WiMax R2

Ghp knh TDD, FDD TDD TDD, FDD

Bng tn d kin 700MHz 2,6GHz 2,3GHz, 2,5GHz, 3,3-3,8GHz2,3GHz, 2,5GHz, 3,3-3,8GHz

Tc ti a

(Download/Upload)300Mbps /100Mbps 70Mbps /70Mbps 300Mbps /100Mbps

Di ng 350km/h 120km/h 350km/h

Phm vi ph sng 5/30/100km 1/5/30km 1/5/30km

S ngi dng VoIP ng

thi80 50 100

Thi im hon tt chunD kin cui nm 2008 hoc

u nm 2009

2005D kin trong nm 2009

Trin khai ra th trng 2009-2010/2012 2007-2008/2009 2010



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Thi th i thay, nhn thy li th ca LTE, mt s nh khai thc mng cn nhc li vic trin khai WiMax v c nh khai thc quyt nh t b conng WiMax chuyn sang LTE, ng k trong s c hai tn tui ln nhtti M l AT&T v Verizon Wireless. Theo mt kho st do RCR Wireless News

v Yankee Group thc hin gn y, c n 56% nh khai thc di ng chn LTE,ch c 30% i theo 802.16e. Kho st cho thy cc nh khai thc di ng BcM v Ty u nghing v LTE, trong khi cc nc mi pht trin (c bit l khu vc chu - Thi Bnh Dng) th ng h WiMax.

Nhiu hng sn xut thit b i nc i, mt mt tuyn b vn ng hWiMax, mt khc li dc tin u t cho LTE. Ngay nh Intel, u tu hu thunWiMax, cng i ging. C Siavash M. Alamouti, gim c k thut Wireless

Mobile Group v Sean Maloney, gim c tip th ca Intel, trong cc pht biugn y u cho rng WiMax c th ho hp vi LTE.

Trong cuc ua 4G, WiMax v LTE hin l hai cng ngh sng gi nht.Liu hai cng ngh ny c th cng tn ti c lp hay s st nhp thnh mtchun chung? Hiu nng ca WiMax v LTE tng ng nhau, do vy vic quytnh hin nay ph thuc vo yu t sn sng v kh nng thm nhp th trng.

1.2.2 Nhng trin vng cho cng ngh LTE

- Cc i gia vin thng hng n LTE:Nhn thy tim nng to ln ca cng ngh ny, ngnh cng nghip di

ng ang on kt xung quanh h thng LTE vi hu ht cc cng ty vin thnghng u th gii: Alcatel-Lucent, Ericsson, France Telecom/Orange, Nokia,

Nokia Siemens Networks, AT&T, T-Mobile, Vodafone, China Mobile, Huawei, LGElectronics, NTT DoCoMo, Samsung, Signalion, Telecom Italia, ZTE... K hochth nghim v trin khai cng ngh ny ang c cc cng ty trn cng hp tcthc y, d kin vo khong nm 2009-2010 s c thng mi ha n vi

ngi dng.

Mng NTT DoCoMo ca Nht s i tin phong khi t mc tiu khaitrng dch v vo nm 2009.

Cc mng Verizon Wireless, Vodafone, v China Mobile tuyn b hp tcth nghim LTE vo nm nay. Vic trin khai c s hng tng cho LTE s bt uvo na sau ca nm 2009 v k hoch cung cp dch v s bt u vo nm 2010.



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Vi vic dnh c s lng giy php s dng bng tn 700 MHz th 2sau Verizon, mng AT&T cng ln k hoch s dng bng tn ny cho LTE. Hngny tuyn b c bng thng 20 MHz dnh cho LTE ph sng 82% dn sca 100 thnh ph hng u ca M. Nh vy 2 mng chim th phn ln nht ca

M u chn LTE l gii php tin ln 4G.

Mng Telstra ca c gn y cng xc nhn pht trin theo hngLTE. Hng TeliaSonera, nh cung cp ln nht cho th trng Bc u v vngBaltic cng cam kt s s dng cng ngh LTE cho cc th trng ca mnh.

Ngy 11/6/2008, theo Financial Times, c phiu ca Nortel, nh sn xutvin thng ni ting ca Canada, tng 13% khi hng tuyn b tp trung cc n

lc nghin cu khng dy vo cng ngh LTE thay v cng ngh i th WiMAX.

- Tng lai khng cn xa

Vo ngy 19/12/2007, hng Nokia Siemens Networks cng b thnghim thnh cng cng ngh LTE vi tc ln n 173 Mb/s trong mi trng th vi nhiu thu bao cng lc. Trn bng tn 2,6 GHz vi 20MHz bng thng,tc ny vt xa tc yu cu l 100 Mbps.

Gim c k thut ca hng, ng Stephan Scholz pht biu: Khi th gii

tin gn n con s 5 t thu bao vo nm 2015, theo tin on ca chng ti, ccnh cung cp dch v di ng s phi s dng tt c cc bng tn vi mt cu trcmng n gin nht v hiu qu chi ph cao nht phc v lu lng lin lc caohn 100 ln. Cuc th nghim thc t ny l mt chng minh ban u quan trngcho khi nim v LTE.

Cuc gi thoi u tin gia 2 in thoi LTE c trnh din vo Hingh Th gii di ng (Mobile World Congress) c t chc vo thng 2/2008 ti

Barcelona, Ty Ban Nha. Vo thng 3 va qua, mng NTT DoCoMo thnghim LTE t n tc 250Mbps.

Ti cc trin lm vin thng quc t gn y, cc nh sn xut Huawei,Motorola, Ericsson cng biu din LTE vi cc ng dng nh xem tivi chtlng cao HDTV, chi game online

Cc cuc th nghim v trnh din ny chng t kh nng tuyt vi

ca cng ngh LTE v kh nng thng mi ha LTE n rt gn.



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Trc y, mun truy cp d liu, bn phi cn 1 ng dy c nh kt ni. Trong tng lai khng xa vi LTE, bn c th truy cp tt c cc dch vmi lc mi ni trong khi vn di chuyn: xem phim cht lng cao, in thoithy hnh, chi game trc tuyn, ti c s d liu v.v V hy nh: vi tc

siu tc.

1.3 Mc tiu thit k LTE

Nhng hot ng ca 3GPP trong vic ci tin mng 3G vo ma xun nm2005 xc nh i tng, nhng yu cu v mc tiu cho LTE. Nhng mc tiuv yu cu ny c dn chng bng ti liu trong vn bn 3GPP TR 25.913.

Nhng yu cu cho LTE c chia thnh 07 phn khc nhau nh sau:

Tim nng, dung lng.

Hiu sut h thng

Cc vn lin quan n vic trin khai

Kin trc v s dch chuyn (migration)

Qun l ti nguyn v tuyn

phc tp

Nhng vn chung

1.3.1 Tim nng cng ngh

Yu cu c t ra l vic t tc d liu nh cho ng xung l100 Mbit/s v ng ln l 50 Mbit/s, khi hot ng trong phn b ph 20 MHz.Khi m phn b ph hp hn th tc d liu nh cng s t l theo. Do , iukin t ra l c th biu din c 5 bit/s/Hz cho ng xung v 2.5 bit/s/Hzcho ng ln. Nh s c tho lun di y, LTE h tr c ch FDD v

TDD. R rng, i vi trng hp TDD, truyn dn ng ln v ng xung,theo nh ngha khng th xut hin ng thi. Do m yu cu tc d liunh cng khng th trng nhau ng thi. Mt khc, i vi trng hp FDD,c tnh ca LTE cho php qu trnh pht v thu ng thi t c tc d liunh theo phn l thuyt trn.

Yu cu v tr c chia thnh: yu cu tr mt phng iu khin(the control-plane latency requirements) v yu cu tr mt phng ngi dng

(the user-plane latency requirements). Yu cu tr control-plane xc nh trca vic chuyn t cc trng thi thit b u cui khng tch cc khc nhau sang



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trng thi tch cc khi thit b u cui di ng c th gi v nhn d liu. Chai cch xc nh: cch xc nh th nht c th hin qua thi gian chuyn tipt trng thi tm tr (camped state) chng hn nh trng thi Release 6 idle mode,khi th th tc chim 100 ms; cch xc nh th hai c th hin qua thi gian

chuyn tip t trng thi ng chng hn nh trng thi Release 6 Cell_PCH, khi th th tc chim 50 ms. Trong c hai th tc ny, th tr ch ng v vic bohiu non-RAN u c loi tr. (Ch Release 6 idle l 1 trng thi m khithit b u cui khng c nhn bit i vi mng truy nhp v tuyn, ngha l,mng truy nhp v tuyn khng c bt c thuc tnh no ca thit b u cui vthit b u cui cng khng c ch nh mt ti nguyn v tuyn no. Thit bu cui c th trong ch ng v ch lng nghe h thng mng ti nhngkhong thi gian c th. Trng thi Release 6 Cell_PCH l trng thi khi m thit

b u cui khng c nhn bit i vi mng truy nhp v tuyn. Tuy mng truynhp v tuyn bit thit b u cui ang trong t bo no nhng thit b ucui li khng c cp pht bt c ti nguyn v tuyn no. Thit b u cui lcny c th ang trong ch ng).

Yu cu tr mt phng ngi dng c th hin quan thi gian truyn mt gi IP nh t thit b u cui ti nt bin RAN hoc ngc li co t lp IP. Thi gian truyn theo mt hng s khng vt qu 5 ms trong mngkhng ti (unloaded network), ngha l khng c mt thit b u cui no khc

xut hin trong t bo.Xt v mt yu cu i vi tr mt phng iu khin, LTE c th h

tr t nht 200 thit b u cui di ng trng thi tch cc khi hot ng khong tn 5 MHz. Trong mi phn b rng hn 5 MHz, th t nht c 400 thit bu cui c h tr. S lng thit b u cui khng tch cc trong t bo khngni r l bao nhiu nhng c th l cao hn mt cch ng k.

1.3.2 Hiu sut h thng

Cc mc tiu thit k cng nng h thng LTE s xc nh lu lngngi dng, hiu sut ph, linh ng, vng ph sng, v MBMS nng cao.

Nhn chung, cc yu cu c tnh LTE c lin quan n h thng chun sdng phin bn 6 HSPA. i vi trm gc, gi nh c mt anten pht v hai antenthu, trong khi th thit b u cui c ti a l mt anten pht v hai anten thu.Tuy nhin, mt iu quan trng cn lu l nhng c tnh nng cao nh l mt

phn ca vic ci tin HSPA th khng c bao gm trong tham chiu chun. V

th, mc d thit b u cui trong h thng chun c gi nh l c hai anten



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thu th mt b thu RAKE n gin vn c p dng. Tng t, ghp knh khnggian cng khng c p dng trong h thng chun.

Yu cu lu lng ngi dng c nh r theo hai im: ti s phn b

ngi dng trung bnh v ti s phn b ngi dng phn v th 5 (khi m 95%ngi dng c c cht lng tt hn). Mc tiu hiu sut ph cng c ch r,v trong thuc tnh ny th hiu sut ph c nh ngha l lu lng h thngtheo t bo tnh theo bit/s/MHz/cell. Nhng mc tiu thit k ny c tng hptrong bng 1.3.

Bng 1.3 - Cc yu cu v hiu sut ph v lu lng ngi dng

Phng php o hiu sut

Mc tiu ng xung so

vi c bn

Mc tiu ng ln so vi

c bnLu lng ngi dngtrung bnh (trn 1 MHz)

3 ln 4 ln 2 ln 3 ln

Lu lng ngi dng tibin t bo (trn 1 MHz,phn v th 5)

2 ln 3 ln 2 ln 3 ln

Hiu sut ph(bit/s/Hz/cell)

3 ln 4 ln 2 ln 3 ln

Yu cu v linh ng ch yu tp trung vo tc di chuyn ca ccthit b u cui di ng. Ti tc thp, 0-15 km/h th hiu sut t c l tia, v cho php gim i mt t i vi tc cao hn. Ti vn tc ln n 120km/h, LTE vn cung cp hiu sut cao v i vi vn tc trn 120 km/h th hthng phi duy tr c kt ni trn ton mng t bo. Tc ti a c th qun li vi mt h thng LTE c th c thit lp n 350 km/h (hoc thm ch n500 km/h ty thuc vo bng tn). Mt yu t quan trong c bit l dch v thoic cung cp bi LTE s ngang bng vi cht lng m WCDMA/HSPA h tr.

Yu cu v vng ph sng ch yu tp trung vo phm vi t bo (bnknh), ngha l khong cch ti a t vng t bo (cell site) n thit b u cui ding trong cell. i vi phm vi t bo ln n 5 km th nhng yu cu v lulng ngi dng, hiu sut ph v linh ng vn c m bo trong gii hnkhng b nh hng bi nhiu. i vi nhng t bo c phm vi ln n 30 km thc mt s gim nh cho php v lu lng ngi dng v hiu sut ph th ligim mt cch ng k hn nhng vn c th chp nhn c. Tuy nhin, yu cuv di ng vn c p ng. Khi m phm vi t bo ln n 100 km th khng

thy c c tnh k thut v yu cu hiu sut no c ni r trong trng hpny.



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Nhng yu cu MBMS nng cao xc nh c hai ch : broadcast (qungb) v unicast. Nhn chung, LTE s cung cp nhng dch v tt hn so vi nhngg c th trong phin bn 6. Yu cu i vi trng hp broadcast l hiu sut ph

1 bit/s/Hz, tng ng vi khong 16 knh TV di ng bng cch s dng khong300 kbit/s trong mi phn b ph tn 5 MHz. Hn na, n c th cung cp dch vMBMS vi ch mt dch v trn mt sng mang, cng nh l kt hp vi cc dchv non-MBMS khc. V nh vy th ng nhin c tnh k thut ca LTE ckh nng cung cp ng thi c dch v thoi v dch v MBMS.

1.3.3 Cc vn lin quan n vic trin khai

Cc yu cu lin quan n vic trin khai bao gm cc kch bn trinkhai, linh hot ph, tri ph, s cng tn ti v lm vic vi nhau gia LTE vicc cng ngh truy cp v tuyn khc ca 3GPP nh GSM v WCDMA/HSPA.

Nhng yu cu v kch bn trin khai bao gm: trng hp m h thngLTE c trin khai nh l mt h thng c lp v trng hp m LTE ctrin khai ng thi vi WCDMA/HSPA hoc GSM. Do m yu cu ny skhng lm gii hn cc tiu chun thit k. Nhng yu cu v linh hot ph vtrin khai s c phc tho chi tit hn trong phn 1.3.3.1.

Vn cng tn ti v c th hot ng phi hp vi cc h thng 3GPPkhc v nhng yu cu tng ng thit lp ra nhng iu kin v tnh linh nggia LTE v GSM, v gia LTE v WCDMA/HSPA cho thit b u cui di ngh tr nhng cng ngh ny. Bng 1.4 lit k nhng yu cu v s gin on, l, thi gian gin on di nht trong lin kt v tuyn khi phi di chuyn gia cccng ngh truy cp v tuyn khc nhau, bao gm c dch v thi gian thc v phithi gian thc. C mt iu ng ch l nhng yu cu ny khng c cht ch

cho lm i vi vn gin on trong chuyn giao v hy vng khi m trin khaithc t th s t c nhng gi tr tt hn ng k.

Yu cu v vic cng tn ti v c th lm vic vi nhau cng xc nhvic chuyn i lu lng multicast t phng php broadcast trong LTE thnh

phng php unicast trong c GSM hoc WCDMA, mc d khng c s lngcho trc.

Bng 1.4 - Yu cu v thi gian gin on, LTE-GSM v LTE-WCDMA



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1.3.3.1 linh hot ph v vic trin khai

Nn tng cho nhng yu cu v linh hot ph l nhng iu kin LTE c th c trin khai trn nhng bng tn IMT-2000 hin hnh, ngha l khnng cng tn ti vi cc h thng c trin khai trn nhng bng tn ny, baogm WCDMA/HSPA v GSM. Mt phn lin quan n nhng yu cu LTE v

mt linh hot ph l kh nng trin khai vic truy nhp v tuyn da trn LTEcho d phn b ph l theo cp hay n l, nh vy LTE c th h tr c Songcng phn chia theo tn s (FDD) v song cng phn chia theo thi gian (TDD).

S song cng hay vic qui hoch song cng l mt thuc tnh cacng ngh truy cp v tuyn. Tuy vy, mt phn b ph cho trc th cng clin kt vi mt qui hoch song cng c th. H thng FDD c trin khai theomt cp phn b ph, vi mt di tn cho truyn dn ng xung v mt di tn

khc dnh cho ng ln. Cn h thng TDD th c trin khai trong cc phnb ph n l.

Ly mt v d l ph ca IMT-2000 ti tn s 2 GHz, gi l bng tnli IMT-2000. Nh trnh by trong hnh 1.3, n bao gm cp bng tn 1920-1980MHz v 2110-2170 MHz dnh cho truy cp v tuyn da trn FDD, v hai bngtn l 1910-1920 MHz v 2010-2025 MHz dnh cho truy cp v tuyn da trnTDD. Ch l c th v nhng qui nh ca a phng v vng m vic s dng

ph ca IMT-2000 c th khc so vi nhng g c trnh by y.

Hnh 1.3 Phn b ph bng tn li ti 2 GHz ca nguyn bn IMT-2000



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Cp phn b cho FDD trong hnh 1.3 l 2 x 60 MHz, nhng ph khdng cho mt nh khai thc mng n l c th ch l 2 x 20 MHz hoc thm chl 2 x 10 MHz. Trong nhng bng tn khc ph kh dng c th cn t hn na.

Ngoi ra, s dch chuyn ca ph ang c s dng cho nhng cng ngh truy

cp v tuyn khc cn phi din ra mt cch t t chc chn rng lng phcn li phi h tr cho nhng ngi dng hin ti. V vy, lng ph banu c dch chuyn ti LTE c th tng i nh, nhng sau c th tng lnt t, c th hin trong hnh 1.4. S khc nhau ca nhng din tin ph c thxy ra s dn n mt yu cu v linh hot ph cho LTE di dng bng thngtruyn dn c h tr.

Hnh 1.4 Mt v d v cch thc LTE thm nhp tng bc vo phn b phca mt h thng GSM c trin khai

Yu cu v linh hot ph i hi LTE phi c kh nng m rngtrong min tn s v c th hot ng trong nhiu bng tn khc nhau. Yu cu v linh hot trong ti liu tham kho c lit k thnh danh sch cc phn b phca LTE (1.25, 1.6, 2.5, 5, 10, 15 v 20 MHz). Ngoi ra, LTE cn c kh nnghot ng theo cp ph cng nh l n l. LTE cng c th trin khai trong nhiu

bng tn khc nhau. Nhng bng tn c h tr c ch r da vo c lpphin bn (release independence), ngha l phin bn u tin ca LTE khngphi h tr tt c cc bng tn ngay t u.



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Hn na, ti liu tham kho cng xc nh v vn cng tn ti vlp t chung vi GSM v WCDMA trn nhng tn s ln cn, cng nh l scng tn ti gia nhng nh khai thc v h thng mng ln cn trn nhng qucgia khc nhau nhng s dng ph chng nhau (overlapping spectrum). y cng

c mt iu kin l khng c h thng no khc c yu cu hp l khi mt thitb u cui truy cp vo LTE, ngha l LTE cn phi c tt c tn hiu iu khiucn thit c yu cu cho vic kch hot truy nhp.

1.3.4 Kin trc v s dch chuyn (migration)

Mt vi nguyn tc ch o cho vic thit k kin trc LTE RAN c ara bi 3GPP c lit k trong [86]:

- Mt kin trc n LTE RAN c chp nhn.- Kin trc LTE RAN phi da trn gi (packet), tuy vy lu lng lp

thoi v thi gian thc vn c h tr.- Kin trc LTE RAN c th ti thiu ha s hin din ca nhng h hng

cc b (single points of failure) m khng cn tng chi ph cho ng truyn(backhaul).

- Kin trc LTE RAN c th n gin ha v ti thiu ha s lng giaotip c gii thiu.

- Tng tc lp mng v tuyn (Radio network layer: RNL) v lp mngtruyn ti (Transport network layer: TNL) c th c loi tr nu ch cn quantm n vn ci thin hiu sut h thng.

- Kin trc LTE RAN c th h tr QoS end-to-end. TNL c th cung cpQoS thch hp khi c yu cu bi RNL.

- Cc c cu QoS c th tnh ton n cc dng lu lng ang tn ti khcnhau mang li hiu sut s dng bng thng cao: lu lng mt phng iukhin (Control-Plane), lu lng mt phng ngi dng (User-Plane), lu lng

O&M, v.v- LTE RAN c th c thit k theo li lm gim bin i tr (delayvariation - jitter) i vi lu lng cn jitter thp, v d TCP/IP.

1.3.5 Qun l ti nguyn v tuyn

Nhng yu cu v qun l ti nguyn v tuyn c chia ra nh sau: h trnng cao cho QoS end to end, h tr hiu qu cho truyn dn lp cao hn, v h

tr cho vic chia s ti cng nh l qun l chnh sch thng qua cc cng nghtruy cp v tuyn khc nhau.



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Vic h tr nng cao cho QoS end to end yu cu ci thin s gia thch nggia dch v, ng dng v cc iu kin v giao thc (bao gm bo hiu lp caohn) vi ti nguyn RAN v cc c tnh v tuyn.

Vic h tr hiu qu cho truyn dn lp cao hn i hi LTE RAN phi ckh nng cung cp c cu h tr truyn dn hiu sut cao v hot ng ca ccgiao thc lp cao hn qua giao tip v tuyn, chng hn nh qu trnh nn tiu IP (IP header).

Vic h tr chia s ti v qun l chnh sch thng qua cc cng ngh truycp v tuyn khc nhau i hi phi xem xt n vic la chn li cc c cu

nh hng cc thit b u cui di ng theo cc dng cng ngh truy cp vtuyn thch hp c ni r cng nh l h tr QoS end to end trong qu trnhchuyn giao gia cc cng ngh truy cp v tuyn.

1.3.6 phc tp

Yu cu v phc tp trong LTE xc nh phc tp ca ton h thngcng nh l phc tp ca thit b u cui di ng. V c bn th nhng yu

cu ny cp n s lng nhng ty chn c th ti thiu ha vi nhng ctnh d tha khng bt buc. iu ny cng a n vic ti gin nhng trnghp kim th cn thit.

1.3.7 Nhng vn chung

Phn ny cp n nhng yu cu chung trong LTE v nhng kha cnhlin quan n chi ph v dch v. R rng, mong mun t ra l gim thiu cc chi

ph trong khi vn duy tr hiu sut yu cu cho tt c cc dch v. Cc vn vng truyn, hot ng v bo dng cng lin quan n yu t chi ph. Nh vykhng ch giao tip v tuyn, m vic truyn ti n cc trm gc v h thngqun l cng phi c xc nh r. Mt yu cu quan trng v giao tip nhiunh cung cp (multi-vendor interfaces) cng thuc vo loi yu cu ny. Ngoi rath cc vn nh: phc tp thp, thit b u cui di ng tiu th t nnglng cng c i hi.



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CHNG 2 TNG QUAN V TRUY NHP V TUYN TRONG LTE

Trong chng trc, chng ta tho lun v nhng mc tiu ca LTE vt nhng tho lun ny th r rng l LTE c pht trin vi nhng mc tiu

hot ng mnh m ng ghi nh. V n chng ny th chng ta s c cungcp mt ci nhn tng quan v mt s c im v thnh phn quan trng ca LTE.Chng 3 5 s i vo chi tit hn na v vn truy cp v tuyn LTE mt cchtng qut cng nh l nhng c tnh ch yu c th ca n.

2.1 H thng truyn dn: ng xung OFDM v ng ln SC-FDMA

H thng truyn dn ng xung ca LTE da trn cng ngh OFDM. Nh

bit th OFDM l mt h thng truyn dn ng xung hp dn vi nhiu ldo khc nhau. V thi gian k t OFDM tng i di trong vic kt hp vi mttin t chu trnh, nn OFDM cung cp mnh chng li s la chn tn sknh (channel frequency selectivity). Mc d trn l thuyt th vic sai lch tnhiu do knh truyn chn lc tn s c th c kim sot bng k thut cn bngti pha thu, s phc tp ca k thut cn bng bt u tr nn km hp dn trongvic trin khai i vi nhng thit b u cui di ng ti bng thng trn 5 MHz.V vy m OFDM vi kh nng vn c trong vic chng li fading la chn tn s

s tr thnh s la chn hp dn cho ng xung, c bit khi c kt hp vighp knh khng gian (spatial multiplexing).

Mt s li ch khc ca k thut OFDM bao gm:

OFDM cung cp kh nng truy nhp vo min tn s, bng cch thit

lp mt t do b sung (degree of fredom) cho khi hoch nh phthuc knh truyn (channel dependent scheduler) so vi HSPA.

OFDM d dng h tr cho vic phn b bng thng mt cch linh hot,

bng cch bin i bng tn c s thnh cc sng mang ph truyn



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i. Tuy nhin ch rng l vic h tr nhiu phn b ph i hi cnphi c b lc RF linh hot (flexible RF filtering) khi th s truyn dn chnh xc l khng thch hp. Tuy nhin, vic duy tr cutrc x l bng tn c s ging nhau (the same baseband processing

structure), khng ph thuc bng thng s ni lng vic trin khai ucui.

H tr d dng cho vic truyn dn broadcast/mulitcast, khi m nhng

thng tin ging nhau c truyn i t nhiu trm gc.

i vi ng ln LTE, truyn dn n sng mang da trn k thut DFT-spread OFDM. Vic s dng iu ch n sng mang cho ng ln em li t snh trn trung bnh (peak to average ratio) ca tn hiu c truyn thp hn khi

m so snh vi k thut truyn dn a sng mang v d nh OFDM. T s nhtrn trung bnh ca tn hiu c truyn cng nh th cng sut pht trung bnh ivi mt b khuch i cng sut nht nh cng cao. V vy m truyn dn nsng mang cho php s dng hiu qu hn b khuch i cng sut, ng thi lmtng vng ph sng. iu ny c bit quan trng i vi nhng thit b u cui

b gii hn v nng lng. Ti cng mt thi im, vic cn bng cn thit kim sot li ca tn hiu n sng mang do fading la chn tn s l vn nhtrong ng ln v t gii hn trong ngun to tn hiu ti trm gc hn so vi thit

b u cui di ng.

Tng phn vi ng ln khng trc giao ca WCDMA/HSPA (cng datrn truyn dn n sng mang), th ng ln LTE li da trn k thut phn tchtrc giao gia nhng ngi dng trong min thi gian v tn s (Trn l thuyt,vic phn chia ngi dng trc giao c th thc hin c trong min thi gianch bng cch n nh ton b bng thng truyn dn ng ln cho mt ngidng ti 1 thi im, iu ny c th thc hin c vi ng ln nng cao). Kthut phn tch ngi dng trc giao trong nhiu tnh hung mang li li ch trongvic trnh c nhiu trong t bo (intra cell interference). Tuy nhin, vic phn

b mt lng ti nguyn bng thng tc thi rt ln cho ngi dng li khngphi l mt chin lc hiu qu trong nhng tnh hung m chnh tc d liu bgii hn bi cng sut truyn dn hn l bng thng. Trong nhng tnh hung nhvy, mt thit b u cui s ch c phn b mt phn ca tng bng thngtruyn dn v nhng thit b u cui khc c th truyn song song trn phn phcn li. V vy m ng ln LTE s bao gm mt thnh phn a truy nhp mintn s (frequency domain multiple access component), h thng truyn dn ng



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ln LTE nhiu khi cng c xem nh l h thng Single Carrier FDMA (SC-FDMA).

2.2 Hoch nh ph thuc knh truyn v s thch ng tc (Channel-dependent scheduling and rate adaptation)

Trung tm ca h thng truyn dn LTE l vic s dng k thut truyn dnchia s knh truyn (shared channel transmission), khi ti nguyn min tn s -thi gian c chia s t ng gia nhng ngi dng. K thut ny tng t vi

phng php c dng trong HSDPA, mc d cng thy r s khc nhau trongvic chia s ti nguyn gia thi gian v tn s trong trng hp ca LTE v giathi gian v m phn knh (channelization codes) trong trng hp ca HSDPA.

Vic s dng truyn dn chia s knh truyn rt ph hp vi nhng yu cu t raca d liu gi do ti nguyn cn phi thay i nhanh chng cng nh l cho phpnhiu cng ngh quan trng khc c dng bi LTE.

Khi hoch nh (scheduler) s iu khin vic phn pht ti nguyn chia scho ngi dng ti mi thi im. N cng quyt nh tc d liu c sdng cho mi ng truyn, l gi l thch ng tc v n l c th xem lmt phn ca b scheduler. Scheduler l thnh phn chnh v mang tnh quyt

nh ln i vi hiu sut ca ton b ng xung, c bit trong nhng mng cti trng cao. C truyn dn ng ln v ng xung u phi c hoch nhcht ch. tng ch thc cht trong kh nng h thng c th t c nu ctnh knh truyn c lu n trong vic quyt nh phn b, v c gi lhoch nh ph thuc knh truyn. K thut ny hin ang c khai thc trongHSPA, khi scheduler ng xung s truyn ti ngi dng vi tc d liuti a nu iu kin knh truyn gp thun li v trong mt chng mc no thk thut ny cng c p dng cho ng ln nng cao (enhanced uplink). Tuynhin, ngoi min thi gian th LTE cng truy cp ti min tn s, do vic s dng

OFDM cho ng xung v DFTS-OFDM cho ng ln. V vy i vi mimin tn s, b scheduler c th la chn cho ngi dng knh truyn c c tnhtt nht. Mt khc, vic hoch nh trong LTE c th quan tm n s bin iknh truyn khng ch trong min thi gian, nh HSPA, m cn trong c min tns. iu ny c minh ha trong hnh 2.1.

Kh nng ca k thut hoch nh ph thuc knh truyn trong min tn sc bit hu ch khi m tc ca thit b u cui l thp, ni cch khc ngha l

knh truyn thay i chm theo thi gian. K thut hoch nh ph thuc knhtruyn da trn s thay i cht lng knh gia nhng ngi dng t c



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tng ch trong hiu sut h thng. i vi nhng dch v nhy cm vi tr,scheduler min thi gian c th c hoch nh cng bc cho mt ngi dngring bit, cho d cht lng knh truyn khng t c gi tr nh. Trongnhng tnh hung nh vy, vic khai thc s thay i cht lng knh truyn trong

min tn s s gip ci thin hiu sut ca ton h thng. i vi LTE, vic quytnh phn b (scheduling decisions) c th c a ra vi nh k sau mi 1msv chi tit trong min tn s l 180 KHz. iu ny cho php nhng s thay iknh truyn tng i nhanh c th c theo di bi b scheduler.

2.2.1 Hoch nh ng xung

Trong ng xung, mi thit b u cui s bo co mt nh gi v cht

lng knh truyn tc thi cho trm gc. Nhng nh gi ny c c bng ccho lng mt tn hiu tham kho, c truyn t trm gc v n cng c sdng cho mc ch gii iu ch. Da trn nhng nh gi v cht lng knhtruyn, scheduler ng xung c th n nh lng ti nguyn cp pht cho ccngi dng v cht lng knh truyn vn c m bo. Trn l thuyt, mt thit

b u cui c phn b c th c ch nh mt t hp bt k ca cc khi tinguyn rng 180 KHz trong mi khong thi gian phn b 1ms. (1ms schedulinginterval).



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Hnh 2.1 Hoch nh ph thuc knh trong min thi gian v tn s.

2.2.2 Hoch nh ng ln

ng ln LTE da trn s phn cch trc giao gia cc ngi dng vnhim v ca scheduler ng ln l phn pht ti nguyn c v thi gian v tns (kt hp TDMA/FDMA) cho cc ngi dng khc nhau. Quyt nh phn b

c a ra sau mi 1 ms, c nhim v iu khin nhng thit b u cui noc php truyn i thuc phm vi 1 cell trong sut mt khong thi gian chotrc, v quyt nh ti nguyn tn s no c dng cho qu trnh truyn dncng nh l tc d liu no ang c s dng. Ch rng ch mt min tn sk nhau c th c cp cho nhng thit b u cui trong ng ln nh l mth qu ca vic s dng truyn dn n sng mang cho ng ln LTE.

Trng thi knh truyn cng cn c quan tm trong qu trnh hoch nh

ng ln, tng t nh hoch nh ng xung. Tuy nhin, nh s c tholun chi tit hn trong chng 3, vic thu thp thng tin v trng thi knh truyn



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ng ln khng phi l mt tc v n gin. Do , mt s phng php khc thu phn tp ng ln tr nn quan trng nh mt phn b sung cho nhng tnhhung khi m ti k thut hoch nh ph thuc knh truyn khng c sdng.

Hnh 2.2 Mt v d v iu phi nhiu lin t bo, ni m cc phn ph bgii hn bi cng sut truyn dn

2.2.3 iu phi nhiu lin t bo (Inter-cell interference coordination)

LTE cung cp s trc giao gia nhng ngi dng trong mt t bo trong cng ln v ng xung. V vy, hiu nng ca LTE v mt hiu sut ph v tc d liu kh dng ni mt cch tng i th c nhiu gii hn bi nhiu tnhng t bo khc (inter-cell interference) hn so vi WCDMA/HSPA. Do , cc

phng php lm gim v iu khin nhiu lin t bo c kh nng mang linhng li ch tht s cho hiu sut ca h thng LTE, c bit v mt cc dch v(tc d liu, v.v) c th c cung cp cho ngi dng ti bin t bo (celledge).

iu phi nhiu lin t bo l mt chin lc hoch nh m trong tc d liu ti bin t bo c tng ln bng cch gim st nhiu lin t bo. V c

bn, vic iu phi nhiu lin t bo s a n nhng gii hn chnh xc i vischeduler ng ln v ng xung trong t bo kim sot nhiu lin t bo.Bng vic hn ch cng sut pht ca cc thnh phn ph (parts of the spectrum)trong t bo, m nhiu xut hin trong nhng t bo ln cn thuc thnh phn phny s c gim bt. Thnh phn ph ny c th c s dng cung cp tc d liu cao hn cho nhng ngi dng thuc t bo ln cn. Thc ra th h sti s dng tn s l khc nhau i vi nhng phn khc nhau ca t bo.

Ch rng vic iu phi nhiu lin t bo l mt chin lc hoch nhquan trng m trong cn quan tm n v tr ca nhng t bo ln cn. Do ,



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vic iu phi nhiu lin t bo l mt vn trin khai vi phm vi ln v kh cth nhn thy c trong cc chi tit k thut. iu ny cng c ngha l vic iu

phi nhiu ch c th c p dng vi mt nhm cc t bo c la chn,da trn nhng yu cu trin khai ring bit c t ra.

2.3 ARQ hn hp vi vic kt hp mm (Hybrid ARQ with soft combining)

K thut ARQ hn hp nhanh vi vic kt hp mm (Fast hybird ARQ withsoft combining) c s dng cho LTE v nhng l do tng t nh trong HSPA,c th l kh nng cho php thit b u cui nhanh chng yu cu truyn linhng khi truyn ti thu c b li v cung cp cng c cho vic thch ng tc n (implicit rate adaptation). Giao thc c bn cng tng t vi ci c s

dng cho HSPA, l phng php s dng nhiu stop and wait ARQ hn hpsong song (multiple parallel stop and wait hybrid ARQ). Vic truyn li c thc yu cu nhanh chng sau mi gi truyn, do c th gim thiu cnhng nh hng n hot ng ca ngi dng cui do nhng gi tin thu c bli gy ra. S d tha gia tng (incremental redundancy) c s dng nh lchnh sch kt hp mm (the soft combining strategy) v u thu s nh m(buffer) nhng bit mm c th thc hin vic kt hp mm gia nhng lntruyn.

2.4 S h tr nhiu anten (Multiple antenna support)

LTE ngay t u h tr k thut nhiu anten ti c trm gc v thit b ucui nh l mt phn khng th thiu trong c im k thut. Xt trn nhiu mtth vic s dng nhiu anten l mt k thut quan trng t c nhng mctiu mnh m cho hiu nng ca LTE. Nh bit th vic s dng nhiu antenc p dng cho nhiu trng hp vi nhiu mc ch khc nhau:

Nhiu anten thu c th c s dng cho vic thu phn tp (receivediversity). i vi truyn dn ng ln, k thut ny c s dngcho cc h thng t bo t nhiu nm trc. Tuy nhin, khi m cu hnhhai anten thu tr thnh c s cho tt c cc thit b u cui LTE th hiusut ng ln cng c ci thin ng k. Phng php n gin nhtca vic s dng nhiu anten l k thut phn tp thu c in khfading, nhng li ch thm c l vic gii hn c nhiu nu ccanten c s dng khng ch cung cp s phn tp chng fading,

m cn dng trit nhiu.



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Nhiu anten pht ti trm gc c th c s dng cho phn tp pht v

cc dng to chm tia khc (beam forming). Mc tiu chnh ca vic tochm tia l ci thin t s SNR hoc SIR thu c, ng thi ci thinnng sut h thng v tm ph sng.

Ghp knh khng gian, i khi cng c xem nh l MIMO, vic s

dng nhiu anten cho c my pht v my thu c h tr bi LTE.Vic ghp knh khng gian dn n vic cho php tng tc trongnhng tnh hung m iu kin knh truyn c bng thng b gii hn

bng cch to ra nhiu knh song song.

Ni chung, cc k thut a anten u mang li li ch trong nhng hon cnhkhc nhau. V d, ti t s SNR v SIR tng i thp, chng hn nh khi ti

trng cao hoc ti bin t bo, vic ghp knh khng gian s em li mt s li chnht nh. ng l, trong nhng trng hp ny, phi dng nhiu anten ti u

pht nng SNR/SIR bng phng php to chm tia (beam forming). Mt khc,trong trng hp khi m SNR v SIR tng i cao, v d nh trong nhng t bonh, vic nng cao cht lng tn hiu mang li nhng li ch ph khi m tc d liu thu c b gii hn ch yu bi bng thng hn l do gii hn vSIR/SNR. Trong nhng trng hp nh vy, ng l ra phi dng k thut ghpknh khng gian khai thc trit nhng trng thi knh truyn tin cy. H

thng a anten c s dng di s iu khin ca trm gc t c th lachn c s ph hp cho mi ng truyn.

2.5 H tr multicast v broadcast

Pht qung b nhiu t bo (multi-cell broadcast) ngha l vic truyn i nhngthng tin ging nhau t nhiu t bo. Bng vic khai thc k thut ny ti thit bu cui, vic s dng hiu qu nng lng tn hiu t nhiu vng t bo ti b

pht hin (the detection) cng ci thin ng k vng ph sng. K thut ny c khai thc i vi trng hp broadcast/multicast nhiu t bo trongWCDMA, khi mt thit b u cui c th nhn tn hiu t nhiu t bo v kchhot vic kt hp mm (soft combine) nhng tn hiu ny ti b thu.

LTE s tin thm mt bc nng cao hiu qu broadcast nhiu t bo. Bngvic truyn i khng ch nhng tn hiu ng nht t nhiu site t bo (vi s iuch v m ha ng nht) m cn ng b thi gian truyn dn gia nhng t bo,tn hiu ti thit b u cui di ng s c ti hin chnh xc nh tn hiu c truyn i t mt site t bo n l v gii quyt c hin tng truyn a



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ng. Do kh nng chng li hin tng truyn a ng mnh m ca OFDM,vic truyn dn nhiu t bo nh vy (multi cell transmission), cng c xemnh l truyn dn Mng n tn s Multicast-Broadcast (MBSFN: Multicast-Broadcast Single Frequency Network), khi s khng ch ci thin cng tn

hiu thu c m cn loi tr c nhiu lin t bo. V vy, vi OFDM, lulng broadcast/multicast ch b gii hn bi tp m v trong trng hp vinhng t bo nh, c th t n nhng gi tr rt cao.

Cn phi ch rng vic s dng truyn dn MBSFN cho broadcast/multicastnhiu t bo i hi s cht ch trong vn v lin kt thi gian v ng b(synchronization and time alignment) ca nhng tn hiu c pht t nhng sitet bo khc nhau.

2.6 Tnh linh hot ph

Nh c tho lun trong chng 1, mc linh hot ph cao l mt trongnhng c tnh ch yu ca cng ngh truy nhp v tuyn LTE. Mc tiu ca tnhlinh hot ph l vic cho php trin khai truy nhp v tuyn LTE trong nhiu phtn vi nhng c tnh khc nhau, bao gm nhng s khc nhau v sp xp songcng (duplex arrangements), bng tn hot ng, v kch thc ca ph tn kh

dng.

Hnh 2.3 -FDD vs. TDD. FDD: Frequency Division Duplex; TDD: Time DivisonDuplex; DL:Downlink; UL: Uplink



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2.6.1 Tnh linh hot trong sp xp song cng

Mt phn quan trng trong nhng yu cu ca LTE v mt tnh linh hot phl kh nng trin khai truy nhp v tuyn da trn LTE trong c ph tn theo cp

hoc khng theo cp, nh vy LTE c th h tr sp xp song cng phn chia theoc thi gian v tn s. FDD c minh ha trong hnh 2.3a, theo truyn dnng ln v ng xung xut hin trong nhng bng tn khc v hon ton tch

bit. TDD theo nh minh ha trong hnh 2.3b, th truyn dn ng ln v ngxung xut hin trong nhng khe thi gian khng trng nhau. Do vy, TDD c thhot ng vi ph khng theo cp (unpaired spectrum), trong khi FDD li yu cu

ph theo cp (paired spectrum).

Vic h tr c ph theo cp v khng theo cp l mt phn trong c im kthut ca 3GPP t phin bn 99 (Release 99) thng qua vic s dng truy nhp vtuyn WCDMA/HSPA da trn FDD i vi phn b theo cp v truy nhp vtuyn TD-CDMA/TDSCDMA i vi phn b khng theo cp. Tuy nhin, iuny t c bng cch s dng nhiu cng ngh truy cp v tuyn tng ikhc nhau v v th m nhng thit b u cui c kh nng hot ng vi c FDDv TDD vn cn cha c ph bin. Mt khc, LTE c th h tr c FDD vTDD vi ch mt cng ngh truy cp v tuyn, dn n vic ti thiu lch giaFDD v TDD cho nhng truy nhp v tuyn da trn LTE. Nh l mt h qu caiu ny, phn tng quan v truy nhp v tuyn h tr c FDD v TDD ca LTE sc bn n chi tit hn trong nhng chng tip theo, trong trng hp c skhc nhau gia FDD v TDD th s khc nhau ny s c trnh by r rng.

2.6.2 Tnh linh hot trong bng tn hot ng

LTE c trin khai da trn c s theo nhu cu, c th to ra ph tn khdng bng cch n nh ph tn mi cho thng tin di ng, chng hn bng tn 2.6

GHz, hoc bng cch dch chuyn cho LTE ph tn hin ang c s dng chocng ngh thng tin di ng khc, v d nh nhng h thng GSM th h th hai,hoc thm ch l nhng cng ngh v tuyn khng phi ca di ng (non mobileradio technologies) v d nh nhng ph tn broadcast hin nay. H qu l n yucu truy nhp v tuyn LTE phi c kh nng hot ng trong mt di bng tnrng, t nht l t bng tn thp nh 450 MHz cho n bng tn 2.6 GHz.

Kh nng vn hnh mt cng ngh truy cp v tuyn trong nhiu bng tnkhc nhau, t bn thn n khng c g l mi. V d, nhng thit b u cui 3

bng tn l rt ph bin, c kh nng hot ng trn c bng tn 900, 1800, v



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1900 MHz. T mt trin vng v chc nng truy cp v tuyn, iu ny khng choc tc ng rt hn ch v c im k thut ca LTE khng gi nh bt c mt

bng tn c th no. Nhng ci c th khc v c im k thut, gia nhng bngtn khc nhau ch yu l vic yu cu nhiu RF c th hn nh cng sut pht ti

a cho php, nhng yu cu/gii hn v pht x ngoi bng (out of band emission)v.v Mt nguyn nhn cho vic ny l do nhng rng buc bn ngoi, c pt bi nhng khung quy nh (regulatory bodies), c th khc nhau gia nhng

bng tn khc nhau.

2.6.3 Tnh linh hot v bng thng

C lin quan n kh nng trin khai truy nhp v tuyn LTE trn nhiu bng

tn khc nhau l vic c th vn hnh LTE vi nhng bng thng truyn dn khcnhau trn c ng xung v ng ln. L do chnh ca vic ny l s lng phtn kh dng cho LTE c th khc nhau ng k gia nhng bng tn khc nhauv cng da trn tnh trng thc t ca nh khai thc. Hn na, vic c th vnhnh trn nhiu phn b ph tn khc nhau cng mang li kh nng cho vic dchchuyn dn dn ph tn t nhng cng ngh truy nhp v tuyn khc cho LTE.

LTE c th hot ng trong mt di phn b ph tn rng, do tnh linh hot

trong bng thng truyn dn l mt phn trong c tnh k thut ca LTE. htr hiu qu cho tc d liu rt cao khi ph tn kh dng th mt bng thngtruyn dn rng l cn thit. Tuy nhin, mt lng ph tn ln v y c thkhng phi lc no cng t c, hoc do bng tn hot ng hoc do s dchchuyn dn dn t mt cng ngh truy nhp v tuyn khc, khi LTE c th hotng vi mt bng thng truyn dn hp hn. Hin nhin, trong nhng trng hpnh vy, tc d liu ti a c th t c s v l m b gim xung.

c im k thut lp vt l LTE khng cp n vn bng thng vkhng a ra bt c gi nh c th no v bng thng truyn dn h tr ngoi mtgi tr ti thiu. Nh s c bit trong phn tip theo, c im k thut v truynhp v tuyn c bn bao gm lp vt l v cc tiu chun giao thc, cho php btc bng thng truyn dn no nm trong khong t 1 MHz ln ti hn 20 MHztheo tng bc 180 KHz. ng thi, ti giai on ban u, nhng yu cu v tns v tuyn ch c ch nh cho mt nhm nh bng thng truyn dn gii hn,tng ng vi nhng d on lin quan n cc kch thc phn b ph v ccdin tin dch chuyn (migration scenarios). Nh vy, trong thc t truy nhp v

tuyn LTE h tr mt nhm gii hn cc bng thng truyn dn, tuy nhin nhng



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bng thng truyn dn b sung c th d dng c h tr bng cch cp nht lic im k thut ca RF.

CHNG 3 KIN TRC GIAO DIN V TUYN LTE

Tng t vi WCDMA/HSPA cng nh l hu ht nhng h thng truynthng hin i khc, quy trnh k thut dnh cho LTE c cu trc thnh nhiulp vt l khc nhau. Mc d c mt s lp trong nhng lp ny th tng t vi

nhng lp c s dng cho WCDMA/HSPA nhng vn c mt s khc bit,chng hn nh s khc nhau v kin trc tng th gia WCDMA/HSPA v LTE.Chng ny gm c nhng m t cho cc lp giao thc bn trn lp vt l, stng tc gia chng, v s giao tip vi lp vt l.

Tng quan v kin trc giao thc LTE cho ng xung c minh ha tronghnh hnh 3.1 . C mt vn s tr nn r rng hn trong phn tho lun tip theo l khng phi tt c nhng phn t c minh ha trong hnh 3.1 u c pdng trong mi trng hp. V d nh trong trng hp broadcast thng tin hthng th MAC scheduling v hybrid ARQ u khng c s dng. Hn na,



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kin trc giao thc LTE lin quan n ng ln th tng t vi kin trc ngxung trong hnh 3.1, mc d cng c mt s s khc bit v s la chn nhdng truyn ti (transport format selection) v truyn dn a anten (multi-antennatransmission) v vn ny cng s c tho lun.

D liu c truyn trn ng xung di dng cc gi IP trn mt trongnhng ti tin SAE (SAE bearers). Trc khi truyn i qua giao din v tuyn,nhng gi IP n (incoming IP packets) s i qua nhiu phn t, c tng ktdi y v c m t chi tit hn trong nhng phn sau:

Giao thc hi t s liu gi (Packet Data Convergence Protocol

-PDCP): 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.C ch nn tiu da trn ROHC, mt thut ton nn tiu tiuchun c s dng trong WCDMA cng nh l trong cc tiu chunthng tin di ng khc. PDCP cng m nhim vic m ha v bo vtnh ton vn ca d liu c truyn i. Ti pha thu, giao thc PDCPs thc hin cng vic gii nn v gii m thng tin. Ch c mt phn tPDCP trn mt ti tin v tuyn c cu hnh cho mt thit b u cuidi ng.

iu khin lin kt v tuyn (Radio Link Control - RLC): m nhimvic phn on / ghp ni, iu khin vic truyn li, v phn pht lncc lp cao hn theo th t. Khng ging nh WCDMA, giao thc RLCc nh v trong eNodeB v ch c mt loi node n trong kin trcmng truy nhp v tuyn LTE (LTE radio access network architecture).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 chomt thit b u cui di ng.



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Hnh 3.1 Kin trc giao thc LTE (ng xung)

iu khin truy cp mi trng (Medium Access Control - MAC): iu

khin vic truyn li hybrid-ARQ v hoch nh ng ln, ngxung. Chc nng hoch nh c nh v trong eNodeB, v n ch cmt 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 cagiao thc MAC. Khi MAC cung cp cc dch v cho RLC di dngcc knh logic.

Lp vt l (Physical layer PHY): iu khin vic m ha / gii m,

iu ch / gii iu ch, nh x a anten (multi antenna mapping), vcc chc nng lp vt l tiu biu khc. Lp vt l cung cp dch v cholp MAC di dng cc knh chuyn ti (transport channels).

Nhng phn sau s cung cp nhng m t chi tit hn v cc giao thc RLC vMAC ca LTE cng nh l tng quan v lp vt l khi c nhn t lp MAC,



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trong khi nhng chi tit y ca lp vt l LTE s c cp n trongchng 4. Nhng thng tin khc c th c tm thy trong c tnh k thut caLTE v nhng tham kho trong .

3.1 RLC: radio link control iu khin lin kt v tuyn

RLC LTE, tng t nh WCDMA/HSPA, m nhim vic phn on (nn tiu) cc gi IP, cn c xem nh l RLC SDUs, t PDCP thnh nhng n v nhhn, RLC PDUs (Nhn chung, cc phn t d liu n/t mt lp giao thc caohn th c xem nh l mt n v d liu dch v SDU Service Data Unit v

phn t tng ng n/t mt lp giao thc thp hn c biu th nh n v dliu giao thc PDU Protocol Data Unit). N cng iu khin vic truyn li ccPDUs b nhn nhm, cng nh l xa b nhng PDUs b nhn i (duplicate

removal) v ghp ni cc PDUs nhn c. Cui cng, RLC s m bo vic phnpht theo trnh t cc RLC SDUs ln cc lp bn trn.

C ch truyn li RLC c trch nhim cung cp d liu phn pht khng b licho cc lp cao hn. lm c iu ny, s c mt giao thc truyn li hotng gia cc phn t RLC ti u thu v u pht. Bng vic gim st cc s tht i n (incoming sequence numbers), RLC thu c th pht hin ra nhng PDUs

b thiu. Cc bo co trng thi s c phn hi tr v RLC pht, yu cu truyn

li cc PDUs b thiu. Khi phn hi mt trng thi bo co c cu hnh, mt boco c trng ch cha thng tin v nhiu PDUs v t khi c truyn i. Da trn

bo co trng thi thu c, phn t RLC ti u pht c th a ra nhng hnhng thch hp v truyn li nhng PDUs b thiu nu c yu cu.

Khi RLC c cu hnh yu cu truyn li cc PDUs b thiu nh c mt trn, n c gi l ang hot ng trong ch bo nhn (AcknowledgedMode AM). iu ny cng ging nh c ch tng ng c dng trong

WCDMA/HSPA. Thng thng AM c s dng cho cc dch v da trn TCPnh khi truyn tp tin m yu t phn pht d liu khng b li c t ln hngu.

Hnh 3.2 Phn on v hp on RLC



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Tng t nh WCDMA/HSPA, RLC cng c th c cu hnh theo ch khng bo nhn (Unacknowledged Mode UM) v ch trong sut (TransparentMode TM). Trong ch UM, s cung cp vic phn pht ng th t ln cc

lp cao hn, nhng s khng truyn li cc PDUs b thiu. Thng thng UMc s dng cho nhng dch v nh VoIP khi m vic phn pht khng li khngquan trng bng thi gian phn pht ngn. TM, mc d c h tr, nhng chc s dng cho nhng mc ch ring bit nh truy cp ngu nhin.

Mc d RLC c kh nng kim sot li truyn dn do nhiu, s bin i knhtruyn khng th d on (unpredictable channel variations), v.v, nhng tronghu ht trng hp nhng li ny c kim sot bi giao thc hybrid-ARQ da

trn MAC. Vic s dng c ch truyn li trong RLC c th v vy m tr nnkhng cn thit. Tuy nhin, nh s c tho lun trong phn 3.2.4 di y,khng phi trng hp no cng vy v vic s dng c hai c ch truyn li datrn MAC v RLC trn thc t cng c mt tch cc khi m c s khc nhau trongvic truyn tn hiu phn hi.

Ngoi vic iu khin vic truyn li v phn pht theo trnh t, RLC cngchu trch nhim vic phn on v ghp ni theo nh minh ha trong hnh 3.2.Da trn quyt nh ca scheduler (scheduler decision), mt lng d liu no

c la chn truyn i t b m RLC SDU v cc SDUs s c phnon/ghp ni to thnh RLC PDU. Do , i vi LTE th kch thc RLCPDU thay i mt cch ng (varies dynamically), trong khi WCDMA/HSPAtrc phin bn 7 li s dng kch thc PDU bn tnh (semi-static PDU size).Khi m tc d liu cao, kch thc PDU ln dn n phn mo u nh hntng ng, cn khi m tc d liu thp, i hi kch thc PDU phi nh nukhng th ti trng s tr nn qu ln. V vy, khi tc d liu nm trong khongt mt vi kbit/s ti trn mt trm Mbit/s, kch thc PDU ng (dynamic PDU

sizes) s c iu chnh bi LTE. T RLC, scheduler v c ch thch ng tc u c nh v ti eNodeB, v kch thc PDU ng s d dng c h tr choLTE.

3.2 MAC: iu khin truy nhp mi trng (medium access control)

Lp iu khin truy nhp mi trng MAC qun l vic ghp knh lun l(logical channel multiplexing), vic truyn li hybrid-ARQ, v hoch ch ngln, ng xung. Trong khi cng ngh HSPA s dng phn tp v m ng ln

(uplink macro diversity) v v th n xc nh c nhng t bo phc v v khng



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phc v (serving and non-serving cells), th LTE ch xc nh mt t bo phc vv khng c phn tp v m ng ln. T bo phc v (serving cell) l t bo mthit b u cui di ng c kt ni ti v t bo m chu trch nhim cho vichoch nh v iu khin hybrid-ARQ.

3.2.1 Knh logic v knh truyn ti (logical channels and transportchannels)

MAC cung cp cc dch v cho RLC di dng cc knh logic. Mt knhlogic c nh ngha bi dng thng tin m n mang theo v thng c phnloi thnh cc knh iu khin, c dng cho vic truyn dn cc thng tin vcu hnh v iu khin cn thit cho hot ng ca h thng LTE, v cc knh lulng (traffic channels), c s dng cho d liu ngi dng. Tp hp cc loi

knh logic c ch nh cho LTE bao gm:

Knh iu khin qung b (Broadcast Control Channel - BCCH): c

s dng cho vic truyn dn thng tin iu khin h thng t mng titt c cc thit b u cui di ng trong mt t bo. Trc khi truy nhpvo h thng, mt thit b u cui di ng cn phi c nhng thngtin c truyn trn knh BCCH tm ra cch thc h thng c cuhnh, v d nh bng thng ca h thng.

Knh iu khin tm gi (Paging Control Channel PCCH): c sdng cho vic tm gi ca cc thit b u cui di ng m mng khng

bit c v tr ca n v mc t bo (cell level) v v vy tin nhn tmgi cn c truyn trong nhiu t bo.

Knh iu khin dnh ring (Dedicated Control Channel DCCH):

c dng cho vic truyn dn thng tin iu khin ti hoc t thit bu cui di ng. Knh ny c s dng cho vic cu hnh ring ltng thit b u cui di ng v d nh nhng tin nhn chuyn giao

khc nhau. Knh iu khin multicast (Multicast Control Channel - MCCH): c

dng cho vic truyn dn thng tin iu khin c yu cu cho victip nhn ca MTCH, xem phn di y.

Knh lu lng dnh ring (Dedicated Traffic Channel - DTCH): c

dng cho vic truyn d liu ngi dng n hoc t mt thit b ucui di ng. y l 1 loi knh logic c dng truyn d liungi dng ng ln v ng xung phi-MBMS (non-MBMS).

Knh lu lng multicast (Multicast Traffic Channel MTCH): c

dng cho truyn dn ng xung nhng dch v MBMS.



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Tng t vi kin trc knh logic c dng cho WCDMA/HSPA. Tuynhin, khi so snh vi WCDMA/HSPA, th kin trc knh logic LTE c phn ngin hn, vi vic gim bt s lng cc loi knh logic.

T lp vt l, lp MAC s dng cc dch v di dng cc knh truynti (Transport Channels). Mt knh truyn ti c nh ngha bi nhng c tnhm thng tin c truyn i qua giao din v tuyn. Theo nhng ghi ch t HSPA,nhng phn c k tha cho LTE, d liu trn 1 knh truyn ti c t chcthnh cc khi truyn ti. Trong mi khong thi gian truyn ti (TransmissionTime Interval TTI), mt khi truyn ti vi kch thc no c truyn iqua giao din v tuyn khi khng c s hin din ca ghp knh khng gian.

Trong trng hp ghp knh khng gian (MIMO), c th ln ti 2 khi truyn titrn mi TTI.

Lin kt vi mi khi truyn ti l mt nh dng truyn ti (TransportFormat - TF), xc nh cch thc m khi truyn ti c truyn i thng qua giaodin v tuyn. nh dng truyn ti bao gm thng tin v kch thc khi truynti, s iu ch (the modulation scheme), nh x anten (the antenna mapping).Cng vi vic phn b ti nguyn, lu lng m cui cng c th nhn c tnh dng truyn ti. Bng vic thay i cc nh dng truyn ti, lp MAC c th

v vy m nhn ra c cc tc d liu khc nhau. Vic iu khin tc vvy m cn c xem nh vic la chn nh dng truyn ti.

Tp hp cc loi knh truyn ti c ch nh cho LTE bao gm:

Knh qung b Broadcast Channel (BCH): c mt nh dng truyn

ti c nh, c cung cp bi cc c tnh k thut. N c dng chovic truyn dn nhng thng tin trn knh logic BCCH.

Knh Paging Paging channel (PCH): c dng cho vic paging

thng tin trn knh logic PCCH. Knh PCH h tr vic thu nhn khnglin tc (discontinous reception DRX) nhm cho php thit b ucui di ng tit kim nng lng pin bng cch ng (sleeping) v chthc (wake up) khi nhn PCH ti nhng thi im xc nh trc. Cch paging c m t c phn chi tit hn trong chng 5.

Knh chia s ng xung Downlink Shared Channel (DL-SCH): l

knh truyn ti c dng cho truyn dn d liu ng xung trongLTE. N h tr nhng c tnh ca LTE nh c ch thch ng tc

ng (dynamic rate adaption) v hoch nh ph thuc knh truyn(channel-dependent scheduling) trong min thi gian v tn s, hybrid



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ARQ, v ghp knh khng gian (spatial multiplexing). N cng h trDRX nhm lm gim nng lng tiu th thit b u cui di ngtrong khi vn cung cp tri nghim lun m (always-on experience),tng t nh c ch CPC trong HSPA. DL-SCH TTI l 1 ms.

Knh multicast Multicast Channel (MCH): c dng h trMBMS v c c trng bi nh dng truyn ti bn tnh v hochnh bn tnh (semi-static transport format and semi-static scheduling).Trong trng hp truyn dn nhiu t bo (multi-cell transmission) sdng MBSFN, cu hnh nh dng truyn ti v hoch nh c iu

phi gia nhng t bo lin quan trong truyn dn MBSFN. Knh chia s ng ln Uplink shared channel (UL-SCH): l ng

ln tng ng vi DL-SCH.

Hnh 3.3 V d v s nh x cc knh logic vi cc knh truyn dn

Mt trong nhng chc nng ca MAC l vic ghp cc knh logic khcnhau v nh x cc knh logic vi cc knh truyn ti tng ng. Khng ging viMAC-hs trong HSDPA, MAC trong LTE h tr ghp knh cc RLC PDUs tnhiu truyn ti v tuyn khc nhau (radio bearers) vo cng khi truyn ti. V cmt vi mi quan h gia loi thng tin v cch thc m n c truyn i chonn vn tn ti nhng gii hn no trong vic nh x cc knh logic vi ccknh truyn ti. Mt v d v nh x cc knh logic vi cc knh truyn ti ca ra trong hnh 3.3. Nhng nh x khc cng c hnh dung.

3.2.2 Hoch nh ng xung.

Mt trong nhng nguyn l c bn ca truy nhp v tuyn LTE l victruyn dn chia s knh truyn trn DL-SCH v UL-SCH, ngha l ti nguyn thigian v tn s c chia s ng gia nhng ngi dng trong c ng ln v

ng xung. Scheduler l mt phn ca lp MAC v n iu khin vic phn bti nguyn ng ln v ng xung. Hoch nh ng ln v ng xung



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c tch ri trong LTE v nhng quyt nh phn b ng ln, ng xung cth c a ra c lp ln nhau (trong nhng gii hn c thit lp bi s phnchia UL/DL i vi hot ng TDD). Hoch nh ng ln s c bn ntrong mc 3.2.3, trong khi phn cn li ca mc ny s tp trung vo hoch nh

ng xung.

Nguyn tc c bn cho scheduler ng xung l quyt nh ng(dynamically determine), trong mi khong thi gian 1 ms, nhng thit b u cuino c php thu truyn dn DL-SCH v trn nhng ti nguyn g. Nhiu thit bu cui c th c hoch nh song song, trong mi trng hp ch c 1 DL-SCH trn mi thit b u cui c hoch nh, v n s c nh x ng(dynamically mapped) ti mt tp hp ti nguyn tn s duy nht. n v thi

gian-tn s c bn trong scheduler cn c gi l khi ti nguyn (resourceblock). Cc khi ti nguyn c m t chi tit hn trong chng 4 cng vi vicnh x d liu ti ti nguyn vt l, nhng v nguyn tc c bn th mt khi tinguyn l 1 n v rng 180 kHz trong min tn s. Trong mi khong thi gianhoch nh 1ms, scheduler s phn b cc khi ti nguyn cho mt thit b ucui tip nhn vic truyn dn DL-SCH, mt s phn b c s dng bi tintrnh lp vt l s c m t trong chng 4. Scheduler cng m trch vic lachn kch thc khi truyn ti (transport-block). Nh l mt h qu ca vicscheduler iu khin tc d liu, m s phn on RLC v ghp knh MACcng s b nh hng bi quyt nh phn b (scheduling decision). u ra tscheduler ng xung c th c nhn thy trong hnh 3.1.

Mc d chin lc hoch nh (scheduling strategy) l mt c trng bsung v khng c ch nh bi 3GPP, mc tiu chung ca hu ht nhngscheduler l li dng s thay i knh truyn gia nhng thit b u cui di ngv u tin hoch nh truyn dn cho thit b u cui di ng trn nhng tinguyn c iu kin knh truyn thun li. V mt ny, hot ng ca scheduler

LTE v c bn th tng t vi scheduler ng xung trong HSDPA. Tuy nhin,v s dng s truyn dn ng xung OFDM, LTE c th khai thc s bini knh truyn trong c min thi gian v tn s, trong khi HSDPA ch c thkhai thc s bin i trong min thi gian. iu ny c cp n trongchng 2 v c minh ha qua hnh 2.1. i vi nhng bng thng ln hn ch tr bi LTE, khi m lng fading la chn tn s (frequency-selective fading)s thng xuyn xy ra, kh nng khai thc s bin i knh ca min tn s cascheduler s tr nn cng quan trng khi so vi vic ch khai thc s bin i trn

min thi gian. c bit ti nhng tc thp, khi m s bin i trong min thi



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gian l tng i chm so vi yu cu v tr c t ra bi nhiu dch v, lcny kh nng khai thc c s bin i min tn s s tr nn c li.

Thng tin v trng thi knh truyn ng xung, cn thit cho vic

hoch nh ph thuc knh truyn, c phn hi t thit b u cui di ng tieNodeB thng qua nhng bo co cht lng knh truyn (channel-qualityreports). Bo co cht lng knh truyn, cn c bit nh B ch th cht lngknh truyn (Channel-Quality Indicator), bao gm nhng thng tin khng ch vcht lng knh truyn hin thi trong min tn s, m cn nhng thng tin cnthit cho vic a ra nhng quyt nh x l anten thch hp trong trng hp

phn knh khng gian. C s cho nhng bo co CQI l vic o lng nhng tnhiu tham chiu ng xung (the downlink reference signals). Tuy nhin, nhng

ngun ph v hin trng knh truyn, v d nh s trao i knh truyn trong hotng TDD, cng c khai thc bng cch ci t mt scheduler ring bit nhmt s b sung cho nhng bo co CQI.

Ngoi cht lng knh truyn, mt scheduler hiu nng cao cng phi cnnhc n tnh trng b m (buffer status) v mc u tin trong quyt nh

phn b (decision scheduling). C nhng khc nhau v loi dch v cng nh lloi thu bao (subscription type) c th gy nh hng n u tin khi hochnh. V d, mt ngi dng voice-over-IP vi mt ng k thu bao t tin philun c duy tr cht lng dch v cho d ti trng h thng ang mc cao,trong khi mt ngi dng ng k thu bao chi ph thp (a low-cost subscription)ang ti v mt file c th phi c tha mn vi nhng ti nguyn m khngc yu cu h tr cho nhng ngi dng khc.

S iu phi nhiu, s thc hin vic iu khin nhiu lin t bo trn cs chm (slow basis) c cp n trong chng 2, cng l mt phn cascheduler. Khi chin lc hoch nh khng c y nhim bi nhng c tnh k

thut, s iu phi nhiu (nu c s dng) l c th ca nh khai thc v cth nm trong phm vi t nhng trin khai ti s dng bc cao n gin (simplehigher-order reuse deployments) ti nhng s tin tin hn.

3.2.3 Hoch nh ng ln.

Chc nng c bn ca scheduler ng ln th tng t vi ng xung,c th l vic quyt nh ng (dynamically determine) cho mi khong thi gian

1 ms, lc nhng thit b u cui di ng truyn d liu trn knh UL-SCH ca



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n thuc ti nguyn ng ln (uplink resources). Hoch nh ng ln cngc dng cho HSPA, nhng v c s khc nhau gia nhng s a truy nhpc s dng (the different multiple-access schemes), cho nn v kha cnh nyth HSPA v LTE c mt vi s khc bit ng k.

Trong HSPA, ti nguyn chia s ng ln chnh l giao thoa cho phpti trm gc. Scheduler ng ln HSPA ch thit lp mt gii hn pha trn cho slng giao thoa ng ln m thit b u cui di ng c php to ra. Da trns gii hn ny, thit b u cui di ng s t ng la chn mt nh dngtruyn dn thch hp. Chin thut ny r rng to ra s nhy cm cho ng lnkhng trc giao m trong trng hp ny l HSPA. Mt thit b u cui di ngkhng s dng tt c ti nguyn m n c cp s truyn ti mc nng lng

thp hn, bng cch y c th lm gim c nhiu ni t bo (intra-cellinterference). Do , ti nguyn chia s khng c s dng bi mt thit b ucui di ng c th c khai thc bi mt thit b u cui di ng khc thngqua vic ghp knh theo thng k (statistical multiplexing). V c ch la chnnh dng truyn ti c kt hp trong thit b u cui di ng i vi ngln HSPA, cho nn cn phi c bo hiu ngoi bng khai bo cho eNodeB bitv s la chn c to ra.

i vi LTE, ng ln th trc giao v ti nguyn chia s c iukhin bi scheduler eNodeB l nhng n v ti nguyn thi gian tn s. Mt tinguyn c ch nh m khng c s dng trit bi mt thit b u cuidi ng no th phn ti nguyn cn li cng khng th cung cp cho mt thit

b u cui di ng khc s dng. V th, do ng ln trc giao, m li gimi ng k trong vic cho thit b u cui di ng la chn nh dng truynti khi c so snh vi HSPA. Cho nn, ngoi vic cp pht ti nguyn thi gian-tn s cho thit b u cui di ng, scheduler eNodeB cn chu trch nhim viciu khin nh dng truyn dn (kch thc ti trng, s iu ch) m thit b

u cui di ng s s dng. Khi scheduler bit c nh dng truyn ti m thitb u cui di ng s dng lc n pht i th khng cn phi bo hiu ngoi bngt thit b u cui di ng ti eNodeB. Li nhun c c t phi cnh vng phsng (coverage perspective) khi tnh n chi ph trn mi bit pht i ca thng tiniu khin ngoi bng c th cao hn ng k so vi chi ph truyn d liu khi tnhiu iu khin cn c thu vi mt tin cy cao hn.



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Hnh 3.4 Vic la chn nh dng truyn dn trong ng xung (bn tri)v ng ln (bn phi)

Mc d s tht l scheduler eNodeB s quyt nh nh dng truyn ticho u cui di ng, nhng c mt iu quan trng cn lu l quyt nh hochnh ng ln c a ra cho mi u cui di ng ch khng phi cho mi ti

tin v tuyn (radio bearer). Nh vy, mc d scheduler eNodeB iu khin titrng ca mt u cui di ng c hoch nh, th u cui vn chu trchnhim la chn t nhng ti tin v tuyn no m d liu c mang theo. Chonn, u cui di ng s t ng iu khin vic ghp knh logic (logical-channelmultiplexing). iu ny c minh ha trong phn bn phi ca hnh 3.4, ni mscheduler eNodeB iu khin nh dng truyn ti cn u cui di ng iu khinvic ghp knh logic. so snh, trong tnh hung ng xung tng ng, khim eNodeB iu khin c nh dng truyn dn v ghp knh logic, c miu t

bn tri hnh v.

Ghp knh ti tin v tuyn (radio-bearer) trong u cui di ng cthc hin theo nhng quy tc, thng qua cc thng s m c th c cu hnh bi

bo hiu RRC t eNodeB. Mi ti tin v tuyn c ch nh s u tin v tc bit u tin (prioritized bit rate). Sau u cui di ng s thc hin ghp knhsng mang v tuyn, nh vy cc sng mang v tuyn c x l theo th t utin ty tc bit u tin ca chng. Nhng ti nguyn cn li, nu c, sau khi

hon thnh tc bit u tin s c a n nhng sng mang v tuyn theo tht u tin.



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tr gip cho scheduler ng ln trong mi quyt nh ca n, ucui di ng c th pht i thng tin hoch nh (scheduling information) tieNode bng cch s dng mt tin nhn MAC. R rng, thng tin ny ch c th

c truyn i nu u cui di ng va c cp mt chn nhn hoch nh hpl (a valid scheduling grant). i vi nhng trng hp khc, mt ch th khi mu cui di ng cn ti nguyn ng ln s c cung cp nh mt phn cakin trc bo hiu iu khin ng ln L1/L2 (the uplink L1/L2 control-signalingstructure), xem thm trong chng 4.

Hoch nh ph thuc knh truyn thng c s dng cho ngxung. Trn l thuyt, k thut ny cng c th c s dng cho ng ln. Tuy

nhin, vic nh gi cht lng knh truyn ng ln th khng n gin nhtrng hp i vi ng xung. Tnh trng knh truyn ng xung c thc o lng bi tt c u cui di ng trong t bo ch n gin bng vic theodi tn hiu tham kho c truyn bi eNodeB v tt c cc u cui di ng cth chia s cng tn hiu tham kho cho mc ch nh gi cht lng knh truyn.Tuy nhin vic nh gi cht lng knh truyn ng ln li yu cu mt tn hiutham kho thm d (a sounding reference signal) c truyn i t mi u cuidi ng cho nhng eNodeB no mun nh gi cht lng knh truyn. Mt tnhiu tham kho thm d nh vy c h tr bi LTE s c m t thm trongchng 4, nhng iu ny li i km vi vn tng chi ph. V vy, nhng

phng php c cung cp cho phn tn ng ln s tr nn quan trng nh lmt phn b sung hoc thay th cho k thut hoch nh ph thuc knh truynng ln.

3.2.4 Hybrid ARQ

Hybird ARQ vi kt hp mm trong LTE p ng mt mc ch tng tvi c ch hybird-ARQ trong HSPA l cung cp sc chu ng chng licc li truyn dn. N cng l mt cng c nng cao nng sut. Khi m nhngc ch truyn li hybird-ARQ l nhanh, nhiu dch v cho php mt hoc nhiu struyn li, bng cch thit lp mt c ch iu khin tc n (vng lp kn) (animplicit (closed loop) rate-control mechanism). Tng t vi phng php trongHSPA, giao thc hybrid-ARQ l mt phn ca lp MAC, trong khi hot ng kthp mm c iu khin bi lp vt l.



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R rng, hybrid ARQ khng c p dng cho tt c cc dng lu lng.V d, truyn dn broadcast, khi m nhng thng tin ging nhau c dnh chonhiu ngi dng, thng thng khng ph thuc vo hybrid ARQ. V vy, hybridARQ ch c h tr cho DL-SCH v UL-SCH.

Giao thc hybrid ARQ trong LTE ging vi giao thc tng ng c sdng cho HSPA, l vic s dng nhiu tin trnh stop-and-wait song song.Trong lc tip nhn nhng khi truyn ti, u thu s tm cch gii m khi truynti v khai bo cho u pht v kt qu ca hot ng gii m thng qua mt bitn ACK/NAK ch th vic gii m c thnh cng hay khng hoc truyn likhi truyn ti nu c yu cu. Nhng chi tit khc v truyn dn ACK/NAKtrong ng xung v ng ln s c tm thy trong chng 4. ti thiu

ha chi ph, mt bit n ACK/NAK c s dng. R rng, u thu phi bit bitACK/NAK thu c c lin kt vi tin trnh hybid-ARQ no. Hn na, iuny c gii quyt bng cch s dng cng mt phng php nh trong HSPAkhi thi im ca ACK/NAK c s dng kt hp ACK/NAK vi mt tintrnh hybrid-ARQ no . iu ny c minh ha trong hnh 3.6. Ch rng, ivi trng hp hot ng TDD, mi quan h v thi gian gia vic tip nhn dliu trong mt tin trnh hybrid-ARQ no v vic truyn dn ACK/NAK thkhng b nh hng bi s phn b ng ln/ng xung.

Tng t vi HSPA, mt giao thc khng ng b l c s cho hot nghybrid-ARQ ng xung. V vy, s truyn li ng xung c th xy ra timi thi im sau khi vic truyn dn c khi to v mt con s tin trnhhybrid-ARQ tng minh (an explicit hybrid-ARQ process number) c s dng ch th tin trnh no ang c nh a ch (addressed). S truyn li ngln, mt khc, li da trn mt giao thc ng b v s truyn li xy ra ti mtthi gian xc nh trc sau khi khi to qu trnh truyn dn v s tin trnh(process number) c th nhn c hon ton. Hai trng hp c minh ha

trong hnh 3.5. Trong giao thc hybrid-ARQ khng ng b, s truyn li trn lthuyt c hoch nh tng t vi vic khi to qu trnh truyn dn. Mt khctrong giao thc ng b, thi im truyn li c c nh mt ln khi khi uqu trnh truyn dn c hoch nh, phi c tnh n cho hot ng hochnh. Tuy nhin, ch rng scheduler s phn bit t phn t hybrid-ARQ trongeNodeB u cui di ng no s thc hin truyn li hay khng.



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Hnh 3.5 Giao thc hybrid-ARQ ng b v khng ng b.

Hnh 3.6 Nhiu tin trnh hybrid-ARQ song song.

Vic s dng nhiu tin trnh hybird-ARQ song song, c minh hatrong hnh 3.6, cho mi ngi dng c th dn n s khng lin tc v d liuc phn phi t c ch hybrid-ARQ. V d, khi truyn ti th 5 trong hnhc gii m thnh cng trc khi truyn ti th 3, khi m vic truyn li cyu cu. V vy, i hi phi c mt vi dng c ch sp xp li (some form ofreordering mechanism). Sau khi gii m thnh cng, khi truyn ti c phnknh thnh cc knh logic thch hp v thc hin vic sp xp li trn mi knhlogic bng cch s dng cc s th t (sequence numbers). Ngc li, HSPA dngmt con s th t MAC ring bit cho vic sp xp li. Nguyn nhn ca vic nyl do s ph tr cho WCDMA v nhng l do v vn tng thch ngc, kintrc RLC hoc MAC vn c gi nguyn khi gii thiu HSPA. Mt khc, i vi

LTE, cc lp giao thc c thit k ng thi, dn n c t gii hn hn trong



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thit k. Tuy nhin, nguyn l ng sau s sp xp li th tng t i vi cc hthng, ch c s th t c s dng l khc nhau.

C ch hybrid-ARQ s sa nhng li truyn dn do nhiu hoc do nhng

bin i knh truyn khng d on c (noise or unpredictable channelvariations). Nh c tho lun trn, RLC cng c kh nng yu cu truynli, m khi mi nghe ln u th c v l khng cn thit. Tuy nhin, mc d struyn li RLC him khi cn thit khi m c ch hybrid-ARQ da trn MAC ckh nng sa hu ht cc li truyn dn, nhng hybrid-ARQ i khi c th tht bitrong vic phn phi cc khi d liu m khng b li ti RLC, gy ra mt khongtrng (gap) trong th t ca cc khi d liu khng li (error-free data blocks)c phn phi ti RLC. iu ny thng xy ra do tn hiu phn hi b sai, v d,

mt NAK c th hin sai thnh mt ACK bi u pht, l nguyn nhn ca vicmt mt d liu. Xc sut xy ra iu ny c th trong khong 1%, mt xc sutli rt cao i vi nhng dch v da trn TCP yu cu vic phn phi cc giTCP gn nh l khng c li. Mt cch c th hn, ngha l i vi nhng tc d liu c duy tr trn 100 Mbit/s th xc sut mt gi d liu chp nhnc phi thp hn 10-5. V c bn, TCP xem tt c cc li v gi d liu l do stt nghn. Cc li v gi d liu v vy s kch hot c ch trnh tc nghn, vimt s tng ln tng ng v tc d liu, v duy tr cht lng tt ti nhng tc d liu cao, RLC-AM s p ng mt mc tiu quan trng cho vic m bo

phn phi d liu khng b li ti TCP.

V vy, t nhng tho lun trn, l do c hai c ch truyn li nh trn c th c hiu r trong phn tn hiu phn hi. Tuy c ch hybrid-ARQthc hin vic truyn li rt nhanh, n cng cn thit phi gi mt bit bo

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