Long Term Evolution 3G to 4G

L TRNH PHT TRIN DI HN CA THNG TIN DI NG T 3G LN 4G (LONG TERM EVOLUTION)I. TNG QUAN V 4G V QU TRNH PHT TRIN T 3G LN 4G:1. Th no l mng 4G?

Ngnh cng ngh vin thng chng kin nhng pht trin ngon ngc trong nhng nm gn y. Khi m cng ngh mng thng tin di ng th h th ba 3G cha c thi gian khng nh v th ca mnh trn ton cu, ngi ta bt u ni v cng ngh 4G (Fourth Generation). Th nhng, ni mt cch chnh xc th 4G l g? Liu c mt nh ngha thng nht cho th h mng thng tin di ng tng lai 4G? Ngc dng thi gian... Trong hn mt thp k qua, th gii chng kin s thnh cng to ln ca mng thng tin di ng th h th hai 2G. Mng 2G c th phn ra 2 loi: mng 2G da trn nn TDMA v mng 2G da trn nn CDMA. nh du im mc bt u ca mng 2G l s ra i ca mng D-AMPS (hay IS-136) dng TDMA ph bin M. Tip theo l mng CdmaOne (hay IS-95) dng CDMA ph bin chu M v mt phn ca chu , ri mng GSM dng TDMA, ra i u tin Chu u v hin c trin khai rng khp th gii. S thnh cng ca mng 2G l do dch v v tin ch m n mng li cho ngi dng, tiu biu l cht lng thoi v kh nng di ng.

Nhm 8

1

Long Term Evolution 3G to 4G

Hnh 1: S tm lc qu trnh pht trin ca mng thng tin di ng t bo Tip ni th h th 2, mng thng tin di ng th h th ba 3G v ang c trin khai nhiu ni trn th gii. Ci tin ni bt nht ca mng 3G so vi mng 2G l kh nng cung ng truyn thng gi tc cao nhm trin khai cc dch v truyn thng a phng tin. Mng 3G bao gm mng UMTS s dng k thut WCDMA, mng CDMA2000 s dng k thut CDMA v mng TD-SCDMA c pht trin bi Trung Quc. Gn y cng ngh WiMAX cng c thu nhn vo h hng 3G bn cnh cc cng ngh ni trn. Tuy nhin, cu chuyn thnh cng ca mng 2G rt kh lp li vi mng 3G. Mt trong nhng l do chnh l dch v m 3G mang li khng c mt bc nhy r rt so vi mng 2G. Mi gn y ngi ta mi quan tm ti vic tch hp MBMS (Multimedia broadcast and multicast service) v IMS (IP multimedia subsystem) cung ng cc dch v a phng tin. Khi nim 4G bt ngun t u? Nhiu t chc, c nhn s dng thut ng "4G" ch mt giao thc cng ngh vin thng th h mi c tnh nng hot ng tt hn nhiu so vi chun 3G hin ti. Trn thc t, khng ging nh 3G c nh ngha r rng trong H thng Thng tin Di ng Ton cu cho nm 2000 (IMT 2000 International Mobile Telecommunications 2000), cha c mt t chc hay c nhn no a ra mt nh ngha y , r rng 4G l g. IMTAdvanced l h thng mi nht chng ta c th tm thy c a ra mt khi nim l m v yu cucamtmng4G. Khc vi 1G, 2G v 3G, 4G khng phi l cng ngh ng dng thng qua giao din v tuyn. Tri li, 4G s khng c g lin quan n cc loi giao din v tuyn c s. h tr thng lng, chun mc tiu c phc tho bi Lin minh Vin thng quc t (ITU International Telecommunication Union), chc chn n s da trn iu bin gii php a truy nhp phn chia theo tn s trc giao OFDMA (Orthogonal Frequency Division Multiple Access) vi cng ngh MIMO (multiple input, multiple output) v cc ci tin antenna thng minh khc. 4G chnh l vin cnh ca mt mng bng thng di ng qua giao thc Internet khng ng nht h tr cc giao din v tuyn, cc mng hi t di ng c nh, cc nhn t hnh thnh

Nhm 8

2

Long Term Evolution 3G to 4G thit b v cung cp cho khch hng hiu qu bng thng c kt ni tt nht, gc tr thp v cht lng dch v cao Theo dng pht trin Nht, nh cung cp mng NTT DoCoMo nh ngha 4G bng khi nim a phng tin di ng (mobile multimedia) vi kh nng kt ni mi lc, mi ni, kh nng di ng ton cu v dch v c th cho tng khch hng. NTT DoCoMo xem 4G nh l mt m rng ca mng thng tin di ng t bo 3G. Quan im ny c xem nh l mt quan im tuyn tnh trong mng 4G s c cu trc t bo c ci tin cung ng tc ln trn 100Mb/s. Vi cch nhn nhn ny th 4G s chnh l mng 3G LTE , UMB hay WiMAX 802.16m. Nhn chung y cng l khuynh hng ch o c chp nhn Trung Quc v Hn Quc. Gn y trn nhiu blog cng ngh a thng tin: rng ITU s cng b trong 2008/2009, 4G chnh l LTE, UMB v IEEE 802.16m WiMAX. Bn cnh , mc d 4G l th h tip theo ca 3G, nhng tng lai khng hn ch gii hn nh l mt m rng ca mng t bo. V d chu u, 4G c xem nh l kh nng m bo cung cp dch v lin tc, khng b ngt khong vi kh nng kt ni vi nhiu loi hnh mng truy nhp v tuyn khc nhau v kh nng chn la mng v tuyn thch hp nht truyn ti dch v n ngi dng mt cch ti u nht. Quan im ny c xem nh l quan im lin i. Do , khi nim ABC-Always Best Connected (lun c kt ni tt nht) lun c xem l mt c tnh hng u ca mng thng tin di ng 4G. nh ngha ny c nhiu cng ty vin thng ln v nhiu nh nghin cu, nh t vn vin thng chp nhn nht hin nay. D theo quan im no, tt c u k vng l mng thng tin di ng th h th t 4G s ni ln vo khong 2010-2015 nh l mt mng v tuyn bng rng tc siu cao. Thin v hng lin i Mng 4G s khng phi l mt cng ngh tin tin vt bc, kh nng p ng tt c cc loi hnh dch v cho tt c cc i tng ngi dng. Nhng cng ngh nh m ni ln gn y nhWiMAX 802.16m, Wibro, UMB, 3G LTE, DVB-Hmc d chng p ng tc truyn ln, tuy nhin chng ch c xem l nhng cng ngh pre-4G (tin 4G). Mng 4G s l mt s hi t ca nhiu cng ngh mng hin c v ang pht trin nh 2G, 3G, WiMAX, Wi-Fi, IEEE 802.20, IEEE 802.22, pre-4G, RFID, UWB, satellite cung cp mt kt ni v tuyn ng ngha rng khp (ubiquitous), mi lc, mi ni, khng k mng thuc nh cung cp no, khng k ngi dng ang dng thit b di ng g. Ngi dng trong tng lai s thc s sng trong mt mi trng t do, c th kt ni mng bt c ni u vi tc cao, gi thnh thp, dch v cht lng cao v mang tnh c th cho tng c nhn.

Nhm 8

3

Long Term Evolution 3G to 4G

Hnh 2: M hnh mng hn tp 4G Khch hng l thng Hin ti khi chng ta mua mt kt ni di ng, kt ni y gn vi mt hp ng, vi cc rng buc ca nh cung cp mng. Ngi dng hu nh khng c bt c s la chn no khc ngoi dch v m nh cung cp cung ng. Mi ngi t nht cng c vi loi hp ng khc nhau s dng cc loi hnh dch v khc nhau: hp ng dng in thoi di ng, hp ng dng in thoi c nh, hp ng dng Internet, hp ng dng GPS, hp ng dng dch v TV di ng,.Mi lin lc, kt ni ca ngi dng iu chu s qun l cht ch ca nh cung cp dch v (nn cn gi l "network-centric). Thc t, ngi dng chnh l mc ch cui cng m mt sn phm hay mt cng ngh mun hng ti. Do vy, liu ch cn cung cp tc d liu cao l p ng nhu cu ca ngi dng cha hay 4G cn phi p ng cc yu cu khc na? Sau y chng ta th cng nhau xem xt nhng g ngi dng cn m cng ngh mng hin ti cha p ng c. y chnh l cha kha cho s thnh cng ca 4G! Tnh hung 1: Trc khi bn i ra khi nh n ni lm vic, bn cn bit nhng thng tin nh gi tu/but, tnh trng kt xe trn ng, cng nh d bo thi gian cn thit i n ch lm vic. Mt khi ngi dng chn mt phng tin i li, th thng tin v thi gian, thi im chuyn i phng tin tip theo,..s c cp nht lin tc vi thi gian thc. Trong lc ngi trn phng tin cng cng, bn mun c e-mail, nghe raio, xemTV, kt ni vi intranet ca cng ty chun b ti liu cho bui hp,. Tnh hung 2: Bn c th s rt thch nhn c nhng thng tin shopping, hng gim gi, thng tin vui chi gii tr hp dn khi bn ngi relax nh hay ang trong xe but. Tuy nhin s c nhiu bn li rt ght nhng thng tin kiu th ny. Do , dch v ny phi ty theo s thch, thi quen ca tng ngi dng. Cng tng t v d khi bn i du lch sang mt thnh ph hay nc no , bn s rt hi lng khi nhn c nhng thng tin hng dn nh bn , nhng a danh cn tham quan, cc mn ngon nn thng thc Mi khi n trc mt a im tham quan bn s nhn c thng tin c th v lch s, c im ni bn ang tham quan. c bit hn na nu cc thng tin cung cp n bn theo ng ting m ca bn.

Nhm 8

4

Long Term Evolution 3G to 4G Trn y ch l hai tnh hung tiu biu m ngi dng trong tng lai ch i. lm c iu , h thng mng 4G phi t ngi dng vo v tr trung tm (user-centric), v cc dch v trong tng lai s phi tnh n s thch, yu cu, a im, tnh hung, thuc tnh ca tng ngi dng nh ngh nghip, tui tc, quc tch.

Tm li :Mc d thut ng 4G vn cha c bt k mt t chc chun ha no nh ngha mt cch r rng, tuy nhin mng 4G c k vng p ng cc c im sau:

c tnh c k vng nht ca mng 4G l cung cp kh nng kt ni ABC, mi lc, mi ni. tha mn c iu , mng 4G s l mng hn tp (bao gm nhiu cng ngh mng khc nhau), kt ni, tch hp nhau trn nn ton IP. Thit b di ng ca 4G s l a cng ngh (multi-technology), a mt (multi-mode) c th kt ni vi nhiu loi mng truy nhp khc nhau. Mun vy, thit b di ng s s dng gii php SDR (Software Defined Radio) c th t cu hnh nhiu loi raio khc nhau thng qua mt phn cng raio duy nht. Mng 4G cung cp gii php chuyn giao lin tc, khng vt ngt (seamless) gia nhiu cng ngh mng khc nhau v gia nhiu thit b di ng khc nhau. Mng 4G cung cp kt ni bng rng vi tc tm 100Mb/s v c ch nhm m bo QoS cho cc dch v a phng tin thi gian thc. vt ln khi tnh trng bo ha ca th trng vin thng, cc nh cung cp mng s phi tm kim khch hng bng cc dch v ty bin theo yu cu ca khch hng. Mng 4G s ly ngi dng lm tm im.

2.

Yu cu k thut cho mt h thng 4G:

Cc h thng t bo m ra mt thi k tin b trong cng ngh v tuyn v nhng thay i trong nhu cu ca ngi s dng nh trong hnh 1. Bng 1 ch ra s tin ho ca cc h thng t bo t 1G n 4G. Cng vi s bng n ca lu lng Internet trong mng c nh, yu cu cho cc di dch v ang tr nn mnh m hn thm ch trong cc mng thng tin di ng. H thng t bo 4G s h tr tc d liu cao hn cc h thng t bo 3G (W-CDMA, cdma2000).

Nhm 8

5

Long Term Evolution 3G to 4G Cc h thng m h tr cc dch v d liu tc cc cao (v d 1Gbit/s) thng l khng c kh nng cung cp mt vng bao ph ton quc. Nhng ni m ngi s dng yu cu cc dch v d liu tc cc cao c th l cc khu vc im nng (hot spot) nh, gia nh, ch, cc nh ga, sn bay, khch sn Do vy khng th no xy dng c mt siu h thng v tuyn p ng c mi nhu cu. Mt vn quan trng l lm cch no c cho ngi s dng cc dch v a phng tin bng rng cho c nhng ngi s dng di ng v nhng ngi di c khp mi ni.

Hnh 3. S pht trin ca cc h thng t bo H thng v tuyn ton cu Mt gii php tt l a ra mt h thng v tuyn ton cu c th kt ni mt cch hiu qu nhiu mng v tuyn ring (v d cc h thng t bo 2G/3G/4G, WLAN, cc h thng qung b), c ti u ho ti cc mi trng truyn thng khc nhau, s dng cng ngh Internet bng rng. Khi nim ny cho php mi h thng v tuyn pht trin c lp vi cc h thng khc nh trong hnh 2. Cc h thng t bo cung cp vng bao ph rng, trong khi h thng WLAN s ch bao ph cc khu vc im nng nhng vi tc d liu cao hn nhiu cc h thng t bo.Cc h thng qung b c th c vng bao ph rng cung cp cho ngi dng di ng v di c vi cc chng trnh video v ca nhc cht lng cao mt chiu. S kt hp ngy cng gn ca cc h thng t bo, WLAN v qung b v cc h thng v tuyn khc s l ht sc quan trng cung cp cc dch v ton quc.

Nhm 8

6

Long Term Evolution 3G to 4G

Hnh 4. H thng v tuyn ton cu Cc yu cu v tc d liu Nhu cu v ti s lng ln thng tin ngy cng tng s tr nn cao hn v cao hn. Ghp d liu mm do nhiu di cc tc thng tin ln hn cc h thng v tuyn 3G hin nay l yu cu cho cc lin kt ng xung (trm gc ti my di ng). Yu cu t ra cho cc tc d liu c th l: - Cc im nng v mi trng ng dn c: 100M n 1Gbit/s - Mi trng phng tin vn ti: ~100Mbit/s Do gii hn ca nhiu bng tn hin nay, cc h thng yu cu phi c hiu sut ph rt cao. t c iu ny, cc h thng anten a u vo, a u ra (MIMO) s ng mt vai tr quan trng. Mng truy nhp v tuyn Lu lng gi s thng tr lu lng chuyn mch knh trong tng lai gn. Hnh 3 a ra mt khi nim v cu hnh mng t bo 4G. Phn v tuyn ca mng s gn vi mt mng WLAN, nhng vi s qun l tnh di ng vng rng nh trong cc h thng t bo 2G/3G. Cc h thng t bo yu cu nhiu chc nng kim sot cuc gi v c s d liu c phn phi. Tt c cc chc nng ny s c lin kt qua mng ton IP. Lu lng thoi s c truyn nh cc gi IP nhng lm cch no m bo cc yu cu QoS khc nhau v gim tr l vn k thut chnh m cc h thng 4G phi i mt.

Nhm 8

7

Long Term Evolution 3G to 4G

Hnh 5. Cu hnh h thng t bo 4G

Hnh 6. Kin trc mng 4G

3. Cng ngh then cht :Hin nay c rt nhiu cng ngh v tuyn mi v tim nng ang c nghin cu a vo ng dng trong cc mng 4G tng lai nh: OFDM, cng ngh bng cc rng UWB (Ultra-Wide-Band), cng ngh v tuyn bc sng milimt v anten thng minh (MIMO), WIMAX Tuy nhin, y xin cp n hai cng ngh chnh ca mng 4G: OFDM : Mt trong nhng cng ngh chnh ca mng 4G l ghp knh phn chia tn s trc giao OFDM (Orthogonal Frequency-Division Multiplexing). OFDM l mt dng ca iu ch a sng mang, lm vic theo nguyn tc phn chia dng bit truyn ti di thng B thnh nhiu dng bit song song N vi khong cch B/N. (Hnh 5). mi dng bit N c tc Nhm 8 8

Long Term Evolution 3G to 4G bit nh hn dng bit ban u, nhng tng ca chng l mt dng bit c tc rt cao. Cc

Nhm 8

9

sng mang con trc giao N iu ch dng bit song song, sau c tng hp li trc khi truyn dn. Mt b pht OFDM chp nhn d liu t mng IP, bin i v m ho d liu trc khi iu ch. Mt b IFFT (bin i ngc Fourier nhanh) bin i tn hiu OFDM thnh tn hiu tng t IF v c gi ti b thu RF. Mch thu khi phc li d liu bng cch o chiu chu trnh ny. Vi cc sng mang con trc giao, b thu c th tch bit v x l mi sng mang con m khng c nhiu t cc sng mang con khc. Khng b pha inh v tr a ng nh cc cng ngh truyn dn khc, OFDM cung cp lin kt v cht lng thng tt hn.

Hnh 7. iu ch OFDM lm tng hiu qu s dng bng tn v lm gim nhiu knh lin k. Anten thng minh (MIMO): Trong h thng anten MIMO (a u vo, a u ra), dng s liu t mt thit b u cui c tch thnh n dng s liu ring bit c tc thp hn (N l s anten pht). Mi dng s liu ny s c iu ch vo cc symbol (tn hiu) ca cc knh truyn. Cc dng s liu lc ny c tc ch bng 1/N tc dng s liu ban u, c pht ng thi, v vy, v mt l thuyt, hiu sut ph tn c tng ln gp N ln. Cc tn hiu c pht ng thi qua knh v tuyn trn cng mt ph tn v c thu bi M anten ca h thng thu. Hnh 6 m t cu trc ca h thng thng tin v tuyn MIMO. H thng MIMO c hiu sut s dng ph tn cao bi h thng c th lm vic c trong mi trng phn tn. Tn hiu t cc anten pht hon ton khc bit nhau ti v tr ca cc anten thu. Khi truyn qua cc knh khng tng quan gia h thng pht v thu, tn hiu t mi anten pht ti v tr thu c s khc nhau v tham s khng gian. H thng my thu c th s dng s khc bit ny tch cc tn hiu c cng tn s c pht ng thi t cc anten khc nhau.

Hnh 8.H thng an ten MIMO c th lm tng ng k dung lng ca h thng v tuyn 4G

4. Hnh trnh n 4G:Mc d nhng ngi ng h WiMax khng nh rng 4G chnh l WiMax, nhng c v nh y l mt quan im sai lm. Cc phin bn ca WiMax trong tng lai c th s tr thnh cc "ng c vin" tim tng ca 4G, v iu bin OFDMA s l thnh phn ch cht ca 4G, nhng chc chn 4G khng phi l WiMax. WiMax hot ng nh mt cht xc tc ca 3G (hay 3GPP - cng ngh truyn thng th h th ba) v 3GPP2, ng dng iu bin OFDM, b sung cng ngh MIMO v cc cng ngh antenna thng minh khc, nhm thc y cc bc ci tin tip theo. C hai u nh hng r rng hnh trnh "ln" 4G. Nhng ngi ng h WiMax vn t ho v mt s u im ca cng ngh ny, bao gm chi ph, thi gian tung ra th trng v c mt mi trng sinh thi mnh. Vi vic c a vo ng dng vo nm 2007, c v nh Mobile WiMax s c li th v thi gian c mt trn th trng (time-to-market) hn cc cng ngh LTE (Long Term Evolution tin ha di hn) v UMB (Ultra Mobile Broadband bng thng siu di ng). Tuy nhin, th h u tin ca cc cng ngh WiMax di ng, khng c s ci tin ca cng ngh MIMO, s khng th c c thng lng cao hn ng k so vi cc cng ngh 3,5G nh HSDPA (High-Speed Downlink Packet Access - truy nhp ti gi tc cao) c ng dng. Cc u im v chi ph m cc nh cung cp dch v WiMax qung co vn cha c chng minh. Sprint khng nh rng Mobile WiMax s hot ng theo nguyn tc tnh tin theo tng bit ca cng ngh EVDO (Evolution-Data Optimized pht trin, ti u ha d liu), nhng s c nhiu li th t di bng thng rng hn ca Mobile WiMax. Mobile WiMax c hiu sut quang ph cao hn nhng chc chn s c phm vi ph sng nh hn, c th ch bng mt na hoc mt phn t bn knh ph sng ca cng ngh HSPA (High-Speed Packet Access cng ngh truy cp tc cao). Theo cc chuyn gia cng ngh, chi ph cho cng ngh WiMax hin ti c th t gp 5 n 10 ln chi ph ca HSDPA. Cc kt qu s b t mng thng mi ca SKT v KT ti Hn

Quc, d ch l ra mt vi quy m nh, c v nh khng ch ra nhng u im v chi ph v vn hnh ca WiMax nh nhiu ngi qung co. WiMax s dn dn s c ci thin, v cng ngh 3GPP v 3GPP2 cng ang pht trin h tr thng lng cao hn, gc tr thp hn v c hiu qu kinh t ln hn nh cn i cng ngh MIMO vi cc cng ngh antenna thng minh khc, di bng tn rng hn v cui cng l iu bin OFDM. Xt v mi trng sinh thi, 3GPP v 3GPP2 vn c h tr mnh hn t pha cc hng cng ngh, v chng vn ang c tch hp trong cc laptop v cc thit b c nhng khc. Cc cuc "di c" t WCDMA sang HSDPA v t EVDO sang EVDO Rev. A din ra kh sun s v mang li nhiu li nhun, trong khi cc nh cung cp dch v khng cn thit phi xy dng mt mng mi. nng cp t mt mng WCDMA ln mng HSPA, chi ph b sung s ch di 10% chi ph trin khai mng 3G. Hu ht cc nh cung cp dch v s tip tc u t vo cc mng 3G v 3,5 G a ra cc dch v thoi v truyn d liu c cht lng cao hn. H vn cha th thu hi c cc khon u t 3G ca mnh v cng vn cha tin rng nhu cu tiu dng i vi dch v truy cp di ng bng thng rng khng hn ch thc s tn ti trc mt. C 3GPP v 3GPP2 u ang c k hoch ci tin khng ngng i vi HSPA v EVDO nhm a ra di tn bng thng cao hn vi hiu qu kinh t ln hn. Nhiu nh cung cp dch v c th s chn nhng kiu "di c" th ny thay v xy dng mt mng mi song song. C 3GPP v 3GPP2 cui cng cng s chuyn sang cc cng ngh da trn OFDMA nh LTE v UMB. Mobile WiMax s cnh tranh vi hai cng ngh ny, v nu xt v cc tiu chun v li ch thng mi th qu tht WiMax c mt li th v thi gian ra mt trn th trng. Tuy nhin, hu ht cc nh cung cp dich v vn cha sn sng trin khai bng thng di ng, iu ny lm li th v thi gian gim bt ngha. K c khi h quyt nh xy dng mt mng bng thng di ng song song nhm p ng cc nhu cu v d liu ti cc tr trng ng dn c, c th h vn s chn LTE thay v Mobile WiMax. Theo t chc thng mi 3G Americas, mt s i l cng ngh cng b k hoch bin c h tng hin ti ca h tr thnh ti s dng c i vi LTE. Cc cu trc c s h tng mng tng lai c th s xut hin trn th trng vo nm sau hoc nm sau na. Chn mt con ng Hu ht cc nh cung cp dch v c di bng tn IMT-2000 chc chn s ng dng cng ngh HSPA v cui cng l LTE. Cc hng cung cp di ng trung thnh vi CDMA cng s theo con ng di c 3GPP2, d cha bit h s chn cng ngh OFDMA no trong tng lai. Cng vi cch ny, Qualcomm s tip tc tn ti vi danh mc cng ngh v u th chuyn mn v mng v cc thit b "a mode. Trong s cc "lnh mi" ang tm cch thm nhp th trng trong thi gian ngn, Mobile WiMax c l s gt hi c nhiu thnh cng nht. Khng nn nh gi thp tim nng ca cc

th trng ny. Cng ty t vn v nghin cu th trng Parks Associates d bo cho n nm 2012, s c hn 80 triu thu bao di ng trn ton cu s dng Mobile WiMax. Mt i l cng ngh c c mun tp trung vo WiMax hay khng cn ph thuc vo nhiu yu t, nh chin lc tng th ca nh i l, v th ca h trong ngnh cng ngh di ng, v cc trng im ca h theo tng vng. Vn mu cht l ch liu h mun ginh c 10% th phn ti mt th trng tng ng vi 80% th phn tim nng ca tng th trng khng dy ton cu, hay mun c c 30% th phn mt th trng tng ng vi di 20% th phn ca tng th trng ton cu. Mt vn quan trng khc l liu nhu cu t pha cc khch hng hin ti v cc khch hng tim nng ca cc i l c ln h xy dng mt mng WiMax mi bao ph. i vi nhng i l khng c mt v th mnh vi 3G, WiMax c th c coi nh cnh ca vo gip h ginh c th phn cao hn trn th trng khng dy ton cu. i vi nhng i l thng tr 3GPP, v d nh Ericsson, chin lc tt nht c th l tp trung ci tin tt hn na cc cng ngh HSDPA, ng thi u t mnh vo LTE, h tr a ch (a mode) v mng tch hp LTE/HSDPA.

4.1. Cc cng ngh 3G c pht trin tin ln 4G:a) i nt v WiMAX WiMAX l tn thng dng thng dng ch cng ngh truy nhp khng dy bng rng s dng giao din ca chun IEEE 802.16. Gn y WiMAX c ITU-R chnh thc cng nhn l mt chun 3G trong h IMT-2000. iu ny c ngha rt ln i vi tng lai ca WiMAX v n s thc y s trin khai rng khp ca WiMAX, c bit trn bng tn 2.52.69GHz, cung cp dch v Internet bng rng, bao hm c VoIP v nhiu dch v thng qua kt ni Internet. Trong h IEEE 802.16 ni bt nht l chun 802.16e-2005 vi kh nng p ng c cc ng dng c nh cng nh cc dch v di ng, nn cn c gi l WiMAX di ng. Chun ny v ang c th nghim nhiu nc. Hin ti, WiMAX di ng "Wave 2" dng 2 ng- ten pht v 2 ng-ten thu cho tc ti a tm 75Mbps. Bn cnh , nhm lm vic IEEE 802.16 ang pht trin phin bn 802.16j trong nghin cu trin khai cc trm relay (tip sc) bn cnh cc trm pht sng BS s dng knh truyn mt cch hiu qu, tng tc truyn dn v m rng vng ph sng. Nhm IEEE 802.16 cng ang nghin cu phin bn 802.16m vi mc ch y tc d liu ca WiMAX ln hn na trong khi vn tng thch vi WiMAX c nh v di ng v ang c trin khai. Phin bn ny theo d kin s c hon thin vo cui nm 2009, nh l mt bc tin vt tri hn3G LTE. Phin bn 802.16m s vn da trn k thut ng-ten MIMO trn nn cng ngh a truy nhp OFDMA vi s lng ngten pht v thu nhiu hn WiMAX di ng Wave 2 . 802.16m trang b 4 ng-ten pht v 4 ng-ten thu s c th y tc truyn ln ln hn 350Mbps. Theo d kin,WiMAX Release 2 vi s hon thin ca 802.16m s hon thnh vo cui nm 2009 v c th bt u trin khai dch v t 2010 (xem hnh 1).

Hnh 9 : S pht trin ca cng ngh WiMAX Ni ti WiMax , ngi ta c th ngh ti rt nhiu gii php thay th m cng ngh ny c th mang li. chnh l kh nng thay th ng xDSL gip tip cn nhanh hn cc i tng ngi dng bng rng m khng cn phi u t ln. c bitWiMAX rt hu ch cung cp dch v bng thng rng nhng vng xa xi m gii php ADSL hoc cp quang l rt tn km. Bn cnh cc dch v c nh, WiMAX cn cung ng cc dch v di ng ging nh nhng dch v ca mng 3G : thoi VoIP, internet di ng, TV di ng. Trong nm ti 2008, cc thit b di ng m hin nay c tch hp WiFi s c tch hp WiMAX. i vi cc thit b c s cn phi trang b thm th PCMCIA WiMAX, hoc usb WiMAX c th kt ni bng rng ca WiMAX. b) i nt v 3G LTE 3G LTE l mt cng ngh di ng mi ang c pht trin v chun ha bi 3GPP (The Third Generation Partnership Project). D n c bt u t cui nm 2004, nhm m bo tnh cnh tranh ca mng 3G trong vng 10 nm ti. Mc d 3GPP pht trin HSPA tng tc d liu (tc ti a c th l 14.4 Mbps), nhng 3G HSPA vn khng th cung cp tt nhng dch v nh video, TV di ng.... ng trc s ra i v cnh tranh ca WiMAX cng nh nhu cu cung cp dch v bng thng rng ngy cng cao, 3GPP buc phi pht trin 3G LTE c th ng vng. 3G LTE ha hn s cho tc d liu truyn trn knh xung (downlink) ln hn 100 Mbps v trn knh ln (uplink) ln hn 50 Mbps. Ging nhWiMAX, 3G LTE da trn nn gi IP do s khng cn chuyn mch knh nh trong cc th h 2G, 3G hin ti. Kin trc mng ca 3G LTE s n gin hn so vi mng 3G hin thi. Tuy nhin mng 3G LTE vn c th tch hp mt cch d dng vi mng 3G v 2G. iu ny ht sc quan trng cho nh cung cp mng trin khai 3G LTE m khng cn thay i ton b c s h tng mng c. 3G LTE s dng cng ngh a truy cp OFDMA cho knh xung v SC-FDMA cho knh ln v n vn da trn cng ngh ng-ten MIMO tc truyn d liu cao nh mong t mun.

Hnh 10: K hoch chun ha 3G LTE Nhng th nghim gn y cho thy rng i th ca cng ngh di ng WiMAX 3G LTE t c nhng kt qu kh quan nh d kin. Cho d c ra i mun hn rt nhiu so vi WiMAX, nhng vi nhng kt qu bc u mang tnh ha hn cng ngh LTE mi ny vn c tnh cnh tranh cao trong tng lai. Gn y trong dp trin lm di ng chu (Mobile Asia Congress), hip hi GSM (GSM Association GSMA), hip hi ca nhiu nh cung cp mng trn th gii, cho bit s chn cng ngh LTE nh l mt chun di ng tng lai, cng ngh tip ni ca HSPA. Thng bo ny y LTE tin mt bc trn cuc cnh tranh gia LTE vi WiMAX v c cng ngh UMB (Ultra Mobile Broadband) ca Qualcom. GSMA ng h cc cng ty v cc t chc ang pht trin cng ngh LTE. Tuy nhin vic chun ha cng ngh LTE theo d kin th cha th kt thc trc 2010 (xem hnh 2).

4.2. So snh cng ngh k thut dng trong WiMAX v 3G LTE

Bng 2 : So snh c im ni bt ca WiMAX v 3G LTE

Hin ti WiMAX di ng Rel 1 (802.16e) c sc cnh tranh v mt cng ngh so vi 3G LTE. Tuy nhin, nu nhn k trn bng so snh th ta thy cng ngh 3G LTE vn vt hn 802.16e v c tnh nng di ng v tc truyn d liu. Song, i vi nhng nh pht trin WiMAX th h khng chp nhn so snh 3G LTE vi 802.16e m phi l 802.16m (ct th 3 trn bng 1). Nhn vo y ta thy WiMAX di ng Rel 2 ha hn nhng tnh nng vt tri so vi 3G LTE. Ngy nay tt c u ng vi nhau rng t c tc d liu cao ch c th nh vo cng ngh ngten MIMO v k thut a truy cp OFDMA. 3G LTE ra i mun hn WiMAX v n cng khng th no khng dng MIMO v OFDMA. Do vy, nu xt trnh bnh din k thut truyn thng khng dy (wireless communication) th 3G LTE khng c bt c mt k ngh c bn no vt tri so vi WiMAX di ng. Nu nhn li bng so snh trn s thy im khc nhau ni bt l 3G LTE s dng k thut a truy nhp SC-FDMA cho ng ln thay v OFDMA nh trong WiMAX. Song, theo nhiu chuyn gia th s khc bit ny li l mt im yu ca 3G LTE. Thc t SC-FDMA cho php ci tin PAR (Peak-to-Average power Ratio) tm 2dB my pht. Tuy nhin n li gy mt tm 2-3dB v hiu sut (performance) truyn thng trn knh truyn nhiu fading u my thu. Nhiu nghin cu gn y cho thy SC-FDMA thc t cho mt hiu sut trn knh ln thp hn so viOFDMA. Nhn chung v mt k thut, hai cng ngh WiMAX v 3G LTE dng nh ngang ti ngang sc vi nhau. Song, cng ngh mnh nht, vt tri nht i khi khng phi l cng ngh ginh chin thng m mt cng ngh thnh cng l mt cng ngh ph hp nht, ha hp nht. By gi chng ta s xem xt cc kha cnh khc lin quan n s cnh tranh caWiMAX v 3G LTE trn ng tin ti mng di ng th h th 4. Cnh tranh gia WiMAX v 3G LTE WiMAX l mt khao kht gia nhp vo th trng thng tin di ng ca cng ng cng ngh thng tin . WiMAX l thut ng c bt u nhc n t nhng nm 2000, vi mc ch ban u ch hng n th trng Internet bng rng cc vng ho lnh. Tip theo, WiMAX hng n cung cp gii php Internet bng rng di ng. K t , n c xem nh l mt i th cnh tranh ca mng thng tin di ng 3G v by gi l 3G LTE. Nu t WiMAX vo v tr cnh tranh vi mng thng tin di ng, bit rng mng thng tin di ng ngy nay c khong hn 2,6 t thu bao trn th gii, r rngWiMAX gp nhiu kh khn tm kim th phn ca mnh. Li im ca WiMAX so vi 3G LTE l WiMAX sn sng c trin khai dch v rng khp : thit b mng WiMAX hon thin, thit b u cui WiMAX s c mt trong nm ti trong khi 3G LTE phi i thm vi nm na. WiMAX va cung cp gii php c nh va cung cp gii php di ng bng rng vi chi ph trin khai thp hn so vi trin khai mt mng3G/3G LTE hon ton mi. Do vy, WiMAX thc s gy c ch ca cc nc ang pht trin m mng 3G cha c, mng Internet tc cao bng cp xDSL cha rng khp.

So vi WiMAX, 3G LTE c mt cng ngh i trc l 2G, 3G vi s lng thu bao c sn. y l mt li th ln trin khai 3G LTE. c bit cc thit b di ng 3G LTE s tng thch vi cc mng thng tin di ng th h trc, do vy ngi dng s c th chuyn giao d dng gia mng 3G LTE vi cc mng 2G GSM/GPRS/EDGE v 3G UMTS tn ti. iu ny cho php nhng nh cung cp mng 3G LTE c th trin khai mng dn dn cng ging ht khi h nng cp mng 2G ln 3G. Trong khi WiMAX phi trin khai mng t con s khng. Do WiMAX khng tng thch vi cc chun di ng khng dy trc nn vic thit b u cui WiMAX c c tch hp vi chip 2G/3G hay khng vn cn l mt cu hi m. N hon ton khng phi l mt cu hi v k thut m l mt vn mang tnh chin lc. N ty thuc vo tc nhn no s trin khai mngWiMAX trong tng lai : nh cung cp mng thng tin di ng 2G/3G hin ti hay mt nh cung cp mng WiMAX hon ton mi. Nu l mt nh cung cp mng 2G/3G th chc chn h s trin khai 3G LTE nu nh WiMAX khng mang li li ch no t bit vt tri so vi 3G LTE. Nu nh cung cp ch c mng 2G/2.5G, h cng c th chn la WiMAX nh mt s nhy cc ln gn 4G thay v i ln 3G/3.5G ri 3G LTE. Nh phn tch trn, vic trin khai 3G LTE t mng 3G, 3.5G c sn l mt con ng d dng. Lm nh vy cc nh cung cp mng c th trin khai 3G LTE dn dn khng cn thit phi m bo mt vng ph rng kn. Bn cnh nh cung cp mng vn tn dng c mng li 3G c, tn dng h thng qun l thu bao v tnh cc c sn. T ny n khi 3G LTE hon thin v c vo s dng, 3.5G c kh nng p ng nhu cu dch v bng rng trc khi WiMAX thc s chim c mt th phn quan trng. V thc t c th nhn thy l cc nh cung cp mng 3G/3.5G h khng h vi vng trong vic tin n 3G LTE. V kha cnh kinh t h s khng trin khai 3G LTE trc khi thu li c vn v li t vic nng cp ln 3G. Tm li: Du rng mi ngi c nhng nhn nh khc nhau, nhng ci nhn khc nhau v tnh cnh tranh ca hai cng ngh ny. C mt iu thng nht l hai cng ngh ny thu ht c mt s quan tm ln, to c mt bc nhy trong cng ngh thng tin di ng khng dy. im yu caWiMAX l n khng c tnh k tha t cc h thng mng c sn nh 3G LTE i khi li tr thnh mt im mnh v n cho php nhiu tc nhn mi thm nhp vo th trng thng tin di ng. S thm nhp ny s lm tng tnh cnh tranh, tng cht lng dch v v gim gi cc vin thng cho ngi dng.

II. 3G LTETrong khun kh tiu lun ny chng ta ch xt n s pht trin ln 4G ca h thng 3G LTE bao gm cc chc nng phn lp cng nh cc cng ngh mi cn c.

1. Kin trc mng :1.1. Mc ch v yu cu ca 3G LTE:3G LTE ra i vi mc ch : - Nng cao hn na di ng 3G bng rng. - Cung cp s chuyn i d dng ln truy nhp v tuyn 4G. - M rng hn na bng thng. - Cc truy nhp v tuyn mi. - Cho c ph n v i. - Tc d liu rt cao: + Tc ti a hn 100Mbps (hng ln) v hn 50Mbps (hng xung). + Tng s lng ngi dng. - Tim n rt thp: + t hn 10ms (mt bng user RAN NTT). + t hn 50ms (mt bng iu khin khng p dng cho hot ng chuyn i). - Hiu sut s dng ph cao. - Ph linh hot: + Kh nng trin khai s phn phi kch thc khc nhau trong mt di ph rng. + Bao gm c ph n v i. - Hiu qu kinh t khi chuyn i t h thng 3G hin ti. 3G LTE 3GPP cc mc thi gian:

SAE (System Architecture Evolution) song song vi LTE.

1.2. Kin trc tng quan:

}

}

EPC : Evolved Packet Core MME: Mobility Management Entity

Hnh 11: Kin trc 3G MME v SAE GW l 2 node ring bit vi giao din m gia chng.

Hnh12: Kin trc mng 3G LTE

Nhng c im chnh yu ca truy nhp v tuyn 3G LTE:

-

Ph linh hot: Bng thng linh hot Linh hot kp

-

Gii php Antenna ci tin a dng Dng chm Truyn dn nhiu lp (MIMO)

-

Truy nhp v tuyn mi Downlink : OFDM Uplink : SC-FDMA Ph linh hot : Cho php hot ng trong mt di rng ph khc nhau Ph 3G tng lai v hin ti (2Ghz, 2.6 Ghz). S di chuyn ca ph 2G (v d 900 MHz) Re-farming ca ph khc, v d bng UHF + Kch thc khng xc nh ca s phn b ph tng lai. + Hiu qu hot ng trong cc phn phi ph c kch thc khc nhau. Ln n 20 MHz cho php cc tc d liu rt cao. Di 5MHz cho php s di chuyn ph phng. S cn thit cho bng thng truyn dn linh hot.

-

Bng thng linh hot: - Lp vt l LTE h tr bt k bng thng no t 1.25 MHz ti xa hn 20MHz vi tng khong ~ 200KHz (Resource block).

- S phc tp/nhu cu gii hn tp cc bng thng c h tr thc t: V d 1,25 MHz, 1,8 MHz, 5 MHz, 10 MHz, 20 MHz.. - Nhng gn y ang tin ti m rng thm bng thng. V d lm ph hp cc phn b ph mi. - Tt c cc u cui LTE phi h tr bng thng cc i (ln n 20 MHz). Sp xp kp:

FDD: Truyn dn uplink v downlink trong cc bng tn ring bit. - Yu cu ph kp. - Dng trong tt c cc h thng t bo thng mi TDD: Truyn dn uplink v downlink khng chng lp trong cng mt bng tn. - C th trin khai trong ph n. - Cn thit phi sp xp cht ch ng b/kt hp gia cc cell. - Gim s mc bao ph da vo truyn dn khng ni tip. (chu k trc tc d liu ti a cao. - C kh nng hiu qu cho cc ti trng hiu dng nh v cc thit b u cui ngi dng gii hn cng sut.

Thm vo trc giao trong min tn s - Frequency Division Multiple Access (FDMA) - Ton b bng thng c th chia s bi nhiu ngi dng. c - H tr hiu qu cho cc ti trng nh v cc thit b u cui ngi dng gii hn cng sut. - Bng thng truyn dn gi tr tc thi. Ti sao phi truyn dn n sng mang: - OFDM c hiu qu tt trong truyn dn bng rng da vo s mnh m c hu ca phn chia knh thi gian v tuyn. - Nhng n cng c nhng mt hn ch nh: T s cng sut nh trn cng sut trung bnh cao -> hiu sut khuch i cng sut. nhy li tn s. Hiu qu trong phn chia thi gian cng c th t c vi truyn dn n sng mang cng vi lng t ho min tn s bn thu. Downlink : - hiu qu khuch i tn s t hn ti hn ti pha trm c s. - trnh s phc tp qu mc ca my thu u cui ngi dng. Uplink: - S phc tp khuch i cng sut cao ti hn trong gii hn gi tr u cui v cng sut tiu th v bao ph ng ln. - phc tp u thu t hn ti pha trm c s.

Hnh 14: Mi lin h gia n sng mang v OFDM Nh vy khuch i cng sut thc t, truyn dn n sng mang c u im c bit trong trng hp khong cch gia cc v tr ln hn.

3. Lp MAC ( Medium Access Control):Lp 2 iu khin truy nhp phng tin thc hin chc nng lp iu khin lin kt v tuyn bao gm iu khin truy nhp phng tin, iu khin trm c s v cc thu bao truy nhp vo giao din ti nguyn khng gian. Ti nguyn c sp xp theo yu cu cht lng dch v (QoS), s dng phn on/ ghp ni cc gi. Truyn li thng qua cc yu cu pht li t ng (ARQ) v cn c yu cu pht li t ng lai ghp (HARQ) kt hp vi lp 1. Lp lin kt 3G LTE c chia thnh 3 lp ph: iu khin truy nhp phng tin (MAC), iu khin lin kt v tuyn (RLC), v giao thc hi t d liu gi (PDCP). Mt trong nhng nt mi ch yu l c lin h vi phn m u ca bin kch thc RLC cc n v giao thc d liu (PDUs)nh trnh c t mo u khng cn thit. Hn na, 3G LTE ging nh cc loi mng khng dy khc phi chu tc li cao mc knh v tuyn (vt l), th c th a ra ngha s gim st hiu sut ca giao thc TCP. lm gim s thay i ca BER, k thut tin trnh hiu chnh li (FEC) hoc yu cu pht li t ng (ARQ) c th c s dng. 3G LTE xem c c hai l m u ca Hybrid ARQ (HARQ) ti lp MAC cng nh ARQ ti lp RLC. Trong trng hp ARQ, h thng nhn kim tra CRC. Trong trng hp CRC ng, mt ACK c gi li u pht v gi nhn c a ti lp cao hn ca chng giao thc x l. Trong trng hp CRC kim tra c li, gi b b qua hoc khai bo ph nh ACK (NACK) gi ti u pht. ARQ c xem nh s b sung trong 3G LTE l loi go- back N, ch r mi gi

nhn thnh cng N vi mt bo co trng thi.

Trong HARQ, trng hp CRC khng ng, gi khng c b ti pha thu. N c lu tr li cho trng hp khi m gi truyn li vn b li v kt hp c gng khi phc li. K thut ny c bit s kt hp truy tm. Cui cng th cng gii quyt c li hoc s lng ln cc gi truyn li c a n. Mi gi truyn li bao gm cc thng tin d tha thm vo (tng s d tha). mt HARQ dng v ch c xem nh s b sung MAC, n cung cp cho u pht mt ACK/NACK nh phn feedback cho mi gi c truyn. Kt hp cch dng ARQ v HARQ ti cc lp khc nhau ci thin tc li knh bi cc -2 -3 -6 trnh t khc: BER gn bng 10 cho khng truyn li, v 10 sau HARQ ti lp MAC, v 10 sau ARQ ti lp RLC. Trong khi s thc hin lp lin kt 3G LTE a lp ARQ, n khng ch c nhim v khi phc li: s ng tin cy TCP l thu c thng qua s tn dng cc lch bit r m u thu TCP xc nh d liu nhn thnh cng t u thu. TCP header d tr cc vng c bit kch hot n mang i thng tin xc nhn. Kt qu l, u thu TCP c th a ra mt xc nhn TCP (TCP- ACK) nh gi c lp hay trong trng hp chuyn i d liu trc tip nh phn, gi gn trong on TCP hng ra. Hnh 15 minh ho s phn pht mt gi d liu TCP n l trong mng 3G LTE. eNB sau khi nhn gi d liu TCP t li gi chuyn n ln lin kt v tuyn n UE(Unit Equipment) thch hp. ng truyn hng xung ny bao gm mt t mo u lin hp vi PHY, MAC, RLC header. Trong trng hp nhn thnh cng, UE pht HARQ ACK hi p li eNB chuyn gi d liu TCP nhn ln lp cao hn ca chng giao thc. theo trnh t lp TCP pht TCP ACK. TCP ACK ny i din cho ti trng thng thng cho mt lp lin kt UE: trc n c th c truyn trn lin kt khng dy, ti nguyn hng ln c th c yu cu v cp pht nhim v tng ng c th c nhn ti lp MAC. Ngoi ra, truyn dn TCP ACK yu cu mt xc nhn s tn ti HARQ tp trung ti eNB.

Hnh 15: Phn pht gi TCP trong mng 3G LTE

Tm li, truyn dn gi d liu TCP n c xc nhn 3 ln: mt ln ti ng vn chuyn, 2 ln ti lp lin kt. Ngoi ra, trong khi HARQ ACK l mt bit feedback n, TCP ACK cng vi t mo u giao thc thm vo ti lp lin kt v lp vt l dng ht mt lng tng i ln ti nguyn bng thng hng ln lm gim ton b hiu sut ca h thng. Cc phn tip theo xut mt gii php m a ra c s ti u ca cc thc th ARQ/HARQ t ti cc lp khc nhau cu chng giao thc vi mc tiu lm gim yu cu cho ti nguyn bng thng hng ln bng cch cho php bo hiu v to gia cc thc th ti cc cp khc nhau ca chng nghi thc.

III. CC CNG NGH MI:1. Mt s cng ngh a truy nhp mi:Hin nay c rt nhiu cng ngh v tuyn mi v tim nng ang c nghin cu a vo ng dng trong cc mng 4G tng lai nh: OFDM, cng ngh bng cc rng UWB (Ultra- Wide-Band), cng ngh v tuyn bc sng milimt v anten thng minh (MIMO), WIMAX Tuy nhin, y xin cp n mt s cng ngh chnh ca mng 4G.

1.1 K thut ghp knh phn chia tn s trc giao (OFDM):1.1.1 Gii Thiu: OFDM: Mt trong nhng cng ngh chnh ca mng 4G l ghp knh phn chia tn s trc giao OFDM (Orthogonal Frequency-Division Multiplexing). OFDM l mt dng ca iu ch a sng mang, lm vic theo nguyn tc phn chia dng bit truyn ti di thng B thnh nhiu dng bit song song N vi khong cch B/N. Mi dng bit N c tc bit nh hn dng bit ban u, nhng tng ca chng l mt dng bit c tc rt cao. Cc sng mang con trc giao N iu ch dng bit song song, sau c tng hp li trc khi truyn dn. Mt b pht OFDM chp nhn d liu t mng IP, bin i v m ho d liu trc khi iu ch. Mt b IFFT (bin i ngc Fourier nhanh) bin i tn hiu OFDM thnh tn hiu tng t IF v c gi ti b thu RF. Mch thu khi phc li d liu bng cch o chiu chu trnh ny. Vi cc sng mang con trc giao, b thu c th tch bit v x l mi sng mang con m khng c nhiu t cc sng mang con khc. Khng b pha inh v tr a ng nh cc cng ngh truyn dn khc, OFDM cung cp lin kt v cht lng thng tt hn.

iu ch OFDM lm tng hiu qu s dng bng tn v lm gim nhiu knh lin k. OFDM khc vi k thut truyn dn ghp knh phn chia theo tn s FDM l khng phi dng b lc thng di tch ring ph ca mi sng mang m dng k thut bin i fourier IFFT/FFT tch ring cc sng mang con. Tn s gia cc cc sng mang con trong OFDM c chn sao cho chng trc giao vi nhau, ph ca cc sng mang con chng lp ln nhau nhng c th x l tch ra c. Nh vy m hiu qu s dng ph ca OFDM cao hn k thut a sng mang thng thng. T lung tn hiu bng rng truyn ni tip tc cao c chia thnh M ng song song c tc truyn dn gim M ln, sau tng lung d liu thnh phn s nh x vo cc sng mang thnh phn, hnh thnh tn hiu iu ch OFDM, rng trong mi k hiu tng, khong cch gia cc sng mang nh, tit kim ph tn knh truyn, rng ca k t tng, gim c nh hng nhiu xuyn k t ISI (ISI: Inter Symbol nterference), nhiu xuyn knh ICI (ICI: Inter Channel Interference), gim nh hng tr a ng, chuyn nh hng ca knh Fading chn lc tn s thnh knh Fading phng.OFDM c pht minh vo nhng nm 1970s v ng dng trong cc h thng truyn hnh s v truyn thanh s bng rng.

1.1.2 M Hnh H Thng OFDM: Hnh 3.1 m t chi tit h thng OFDM. Tng knh d liu bng rng tc cao truyn ni tip c a vo b chuyn i ni tip song song S/P chuyn thnh cc lung d liu song song tc thp. Sau , cc lung d liu song song ny c iu ch vi cc sng mang thnh phn, k thut iu ch c th s dng cc phng php iu ch thng thng ty theo yu cu ca tng lai dch v nh iu pha s nhiu mc M-PSK, iu ch bin s cu phng nhiu mc M-QAM. Gi s h thng s dng N sng mang, cc sng mang ny c ly mu vi tc ly mu fS=N/TS ,vi TS l chu k k hiu OFDM. Cui cng, cc mu tn hiu iu ch trn mi sng mang thnh phn c ghp li vi nhau hnh thnh mt mu tn hiu iu ch OFDM.

Hnh 1.1 : S h thng OFDMMt k hiu OFDM s gm N mu v mu th m ca mt k hiu OFDM c vit theo cng thc nh sau: (1.1)

trong Xn , n = 0,,N 1, biu din cho cc tn hiu PSK/QAM, c gi tr phc, truyn trn sng mang th n . Phng trnh (1.1) tng ng vi bin i IFFT trn chui d liu Xn . Sau cc mu xm c a qua b chuyn i song song ni tip P/S ghp N mu tn hiu v cc cc mu tn hiu bo v GI, tn hiu bo v giao thoa u v cui chu k tn hiu TFFT. B

bin i tn hiu s sang tn hiu tng t D/A cho php chuyn tn hiu trong min tn s sang min thi gian, cng thc tn hiu pht trong min thi gian c vit nh sau: (1.2) Phng trnh (1.2) c th vit li nh sau: (1.3) trong tn s ca cc sng mang thnh phn l fn = n , n=0,1,N-1. Ts Sau , tn hiu x(t) c a qua b iu ch nng tn tr thnh tn hiu pht v truyn qua knh truyn ti my thu.Tn hiu pht v bng thng ca cc knh thnh phn c trnh by nh sau: (1.4)

trong x(n) l dng tn hiu iu ch; fn =nf , n =0,1, 2,...,(N-1): l tn s ca cc sng mang iu ch thnh phn th n; n l pha tn hiu iu ch; f l khong cch tn s gia 2 sng mang lin tip nhau, f =1/TFFT, TFFT l chu k k hiu OFDM, TFFT=NTb,Tb l rng bt d liu. Xt h thng a ngi dng (K ngi dng), tng chui tn hiu s i vo c chia thnh M ng song song, k hiu d(m) iu ch dch pha s M-PSK hoc iu ch s M- QAM vi tng sng mang thnh phn, gi thit rng xc sut khi phc tn hiu ca bit 1 v bit 1 l nh nhau, knh truyn c nhiu cng trng phn b Gauss AWGN,chn tn s pht th n l fn; fn = n / NTb , khi dng tn hiu ca ngi dng th k c vit li nh sau:

Hay l:

(1.5)

Sau khi IFFT, chu k tn hiu OFDM bng gc c chn thm khong bo v TGI,chn on bo v giao thoa u khung v cui khung k hiu TFT to thnh dng ph tn hiu nh hnh (1.2 ).

Hnh 1.2:Dng khung tn hiu trong mt chu k OFDM Xt trong mt chu k tn hiu OFDM l T=TFFT+TGI+TFT th tn hiu OFDM pht phc bng tn gc u ra ca b chuyn i s sang tng t cng thc (1.4) c vit li y theo thi gian nh sau: (1.6)

trong : T l di k hiu OFDM; TFFT l thi gian FFT; TGI l thi gian bo v; TFT l thi gian bo v giao thoa u v cui khung; f =1/TFFT l khong cch tn s gia hai sng mang; N l di FFT hay cn gi l s im FFT; k l ch s v k hiu c truyn; xi,k l vc-t tn hiu iu ch ca sng mang con th i trong k hiu OFDM th k;i{-N/2, -N/2+1, -1, 0, +1, ., -N/2}; w(t) l hm tn hiu xung dng hnh ch nht c biu din nh cng thc sau:

(1.7)

Tn hiu u ra ca b iu ch nng tn v khuch i cng sut cao c xc nh nh sau: (1.8)

trong cc k hiu trong cng thc (1.6) c nh ngha nh trong (1.4) v w(t) c xc nh theo (1.7). Tn hiu thu OFDM k hiu r(t) = S(t) + n(t) xt trong iu kin knh truyn c nhiu trng AWGN c p ng knh truyn min thi gian l h (t) n th p ng trong min tn s s c dng:

(1.9)

B qua tc ng ca nhiu th dng ri rc ca tn hiu thu r(n) l tch chp gia tn hiu pht v hm c tnh knh truyn, cng thc tn hiu thu c biu din nh sau:

(1.10)

trong : (*) l biu din tch chp; x(p) l tn hiu iu ch, H(p) l p ng knh truyn.Nh vy, tn hiu ti ng ra ca khi FFT s l: (1.11) B gii iu ch c dng tch d liu trong cc chm sao tn hiu iu ch thu ca tng knh thnh phn khi phc li cc lung d liu thnh phn, tng lung d liu thnh c a qua b bin i song song ni tip ghp M ng d liu song song thnh 1 ng d liu tn hiu ni tip c dng gn ging vi chui d liu nh ban u. Tuy nhin, khi thc hin chuyn i fuorier IFFT N im ca { Xn } , chng ta s nhn c chui gi tr phc trong min thi gian. V vy, to ra chui gi tr thc, cn to ra = 2N k t, { Xn } trong cng thc (1.1) c vit nh sau: (1.12) thc hin bin i IFFT im ca chui {Xn} to ra chui gi tr thc:

(1.13) 1.1.3 Tnh Trc Giao (Orthogonality): a) Trc giao trong min thi gian: Bng tn h thng a sng FDM c chia thnh N di tn con (sub-band) sp xp lin tip nhau, mi di tn con c t cch nhau mt khong tn s ngn nga can nhiu gia cc tn hiu trong di tn k cn. Trong h thng OFDM, di thng ca h thng c th s dng mt cch hiu qu hn nu ph ca cc di tn con c ghp chng ln nhau, bng cch s dng cc sng mang trc giao v phng php gii iu ch kt hp, d liu ban u c th c khi phc nguyn vn. Hnh 1.3 minh ha hiu qu s dng bng thng gia hai h thng FDM v OFDM.

Hnh 1.3: M hnh khi nim tn hiu OFDM: (a) K thut a sng mang thng thng (FDM) (b) K thut iu ch a sng mang trc giao (OFDM) Cc tn hiu c gi l trc giao nu chng c lp tuyn tnh vi nhau. Trc giao l mt c tnh gip cho cc tn hiu c truyn mt cch hon ho qua knh truyn v c tch ra my thu m khng gy nhiu xuyn knh. Vic truyn mt tnh trc giao s to ra s chng lp gia cc tn hiu mang tin v lm suy gim cht lng tn hiu. Trong min tn s, hu ht cc h thng FDM u c tnh trc giao v mi tn hiu c t cch nhau trn trc tn s ngn chn xuyn knh. K thut OFDM c gi l mt dng c bit ca k thut FDM. Cc sng mang con trong mt k hiu OFDM c t gn nhau m vn gi c tnh trc giao gia chng. OFDM t c tnh trc giao trong min tn s bng cch chia cc tn hiu mang thng tin ring bit vo mi sng mang thnh phn khc nhau. Tn hiu OFDM bao gm cc hm sin c bn, mi hm tng ng vi mt sng mang. Tn s bng tn gc ca mi sng mang c chn bng s nguyn ln ca ga tr nghch o thi gian ca mt k hiu. Do , tt c cc sng mang u c s nguyn ln chu k trong mi k hiu. Kt qu biu din trong min tn s l cc sng mang trc giao vi nhau.

Hnh 1.4 m t cu trc ca mt tn hiu OFDM vi 4 sng mang thnh phn.Tp hp cc hm s trc giao vi nhau nu chng tha iu kin trong phng trnh (1.6). Nu 2 hm bt k trong tp hp cc hm trc giao khi nhn vi nhau v ly tch phn trong khong thi gian

mt chu k, kt qu s bng khng. Khi xem xt b thu kt hp tng ng cho tng hm trc giao trong cc hm trc giao khi b thu c. Kt qu cc hm trc giao trong tp hp sau khi ly tch phn u bng khng v do khng gy nh hng.(1.14)

Hnh 1.4: Cu trc trong min thi gian mt tn hiu OFDM

(1a), 2(a), (3a), (4a) m t 4 sng mang thnh phn ring l (tng ng vi 1, 2, 3, 4 chu k trong mt k hiu). Pha ca tt c cc sng mang thnh phn u bng khng. Ch rng mi sng mang thnh phn c s nguyn ln chu k trn mi k hiu. (1b), (2b), (3b), (4b) m t bin i FFT ca hnh (a) tng ng. (5a), (5b) m t tng ca 4 sng mang thnh phn. Phng trnh (1.7) m t 1 tp cc hm trc giao chun, y chnh l cc sng mang cho mt tn hiu OFDM thc trc khi iu ch. (1.15) trong f0 l khong cch gia cc sng mang, N l s sng mang, T l chu k 1 k hiu OFDM. Thnh phn tn s cao nht l Nf0 cho nn di tn truyn dn cng l Nf0. Nu cc sng mang thnh phn trc giao nhau th chng phi tha phng trnh (1.16). Ta c:

(1.16)

Khi n m , (n+m) v (n-m) l cc s nguyn khc khng nn cc hm cos 2 (n m) f0 v cos 2 (n + m) f0 nhn c cc gi tr ln lt bng nhau trong on [t0, t0 + T] . Do kt qu tch phn s bng khng. Khi n=m, tch phn trn bng T/2. V vy, nu cc sng mang c t cch nhau mt khong f0=1/T trn trc tn s,chng s trc giao vi nhau. Nhng sng mang trc giao vi nhau v khi ta nhn bt k 2 sng mang v ly tch phn trong thi gian mt k hiu, kt qu u bng khng. Nhn hai sng sin vi nhau cng ging nh l trn cc sng ny li vi nhau. iu ny dn n thnh phn tn s tng v hiu lun lun l s nguyn ln tn s f0. Bi v h thng tuyn tnh theo thi gian nn ta c th ly tch phn tng thnh phn ri cng li. Hai thnh phn sau khi trn c s nguyn ln chu k trong mt chu k k hiu nn tch phn ca cc thnh phn ny bng khng, do tng ca hai tch phn bng khng. Kt qu l ta chng minh c cc sng mang thnh phn trc giao. b) Trc giao trong min tn s: Mt cch khc xem xt tnh cht trc giao ca tn hiu OFDM l xem ph ca n. Ph ca tn hiu OFDM chnh l tch chp ca cc xung Delta Dirac ti cc tn s sng mang. Ph ca xung hnh ch nht bng 1 trong khong thi gian k hiu v bng 0 ti v tr khc. Ph bin ca xung hnh ch nht l hm sinc( fT). Hnh dng ca hm sinc c mt bp chnh hp v nhiu bp ph c bin suy hao gim dn so vi cc tn s cch xa trung tm. Mi sng mang thnh phn c mt nh bin cao nht ti tn s trung tm v bng khng ti tt c cc tn s l bi s ca ga tr tn s (f=1/T). Hnh 1.5 m t ph ca mt tn hiu OFDM.

Hnh 1.5: p ng tn s ca cc sng mang thnh phn (a) M t ph ca mi sng mang thnh phn v mu tn s ri rc c nhn thy ca b thu OFDM. (b) M t p ng tng cng ca c 5 sng mang thnh phn (ng t m). Tnh trc giao l kt qu xc nh bin nh ca mi sng mang thnh phn tng ng v cc gi tr khng ca tt c cc sng mang thnh phn khc. Tn hiu ny c tch bng cch s dng DFT, ph ca chng khng lin tc nh hnh v 1.5(a), m l nhng mu ri rc. Ph ca tn hiu c ly mu ti cc gi tr o trong hnh v. Nu DFT c ng b theo thi gian, cc mu tn s chng lp gia cc sng mang thnh phn khng nh hng ti b thu. Gi tr

nh o c tng ng vi gi tr null ca tt c cc sng mang thnh phn khc, t suy ra tnh trc giao gia cc sng mang thnh phn. 1.1.4 Nhiu Xuyn K T ISI V Xuyn Knh ICI: Trong mi trng v tuyn a ng, mt k hiu c truyn n my thu qua nhiu ng khc nhau. i vi knh tn x thi gian, chu k ca k hiu nhn c s b tri rng ra, lm cho k hiu nhn c hin ti chng lp vi k hiu nhn c trc v dn n ISI (inter symbol interference). Trong OFDM, tham s ISI dng ch n nhiu ca mt k hiu OFDM hin ti vi cc k hiu trc . Nh trnh by, trong h thng OFDM, ph ca cc sng mang thnh phn chng lp nhau nhng vn gi c tnh trc giao vi nhau. Ngha l ti im m ph ca mi sng mang thnh phn t cc i, tt c ph ca ca cc sng mang thnh phn khc l zero. My thu ly mu cc k hiu d liu trn cc sng mang thnh phn ring l ti im cc i ny v gii iu ch chng m khng b nhiu t cc sng mang thnh phn khc. Khi mt tnh trc giao th xut hiu nhiu. Nhiu gy ra bi cc k hiu d liu trn cc sng mang thnh phn k nhau c gi l ICI (intercarrier interference). Tnh trc giao ca mt sng mang thnh phn vi cc sng mang thnh phn khc b mt nu sng mang thnh phn ny c gi tr ph khng bng zero ti cc tn s ca cc sng mang thnh phn khc. Trong min thi gian, sng sin tng ng khng cn l mt s nguyn ln so vi chu k k hiu trong mt khang thi gian FFT. ICI xy ra khi knh a ng bin i trong khong thi gian ca mt k hiu. Khi iu ny xy ra, dch Doppler trn mi thnh phn a ng gy ra mt lch tn s trn cc sng mang thnh phn, dn n mt tnh trc giao gia chng. ICI cng c th xy ra khi mt k hiu OFDM b ISI. Tnh hung ny c th c quan st trong min thi gian m , s nguyn ln chu k ca mi sng mang thnh phn trong mt mt chu k FFT ca k hiu hin ti khng cn c duy tr do s dch chuyn pha ca k hiu trc . Cui cng, bt k mt lch no gia cc tn s ca cc sng mang thnh phn trong c my pht ln my thu cng u gy ra ICI cho mt k hiu OFDM. 1.1.5 Chn Khong Thi Gian Bo V: OFDM c kh nng t khc phc ISI v chu k k hiu ca n di hn so vi cc k hiu d liu trong lung d liu ni tip. i vi mt my pht OFDM c N sng mang thnh phn, nu chu k ca mt k hiu d liu l T , chu k ca mt k hiu OFDM ti ng ra my pht l: T sym =TN (1.17) V th, nu tri tr (delay spread) ca mt knh a ng ln hn T nhng nh hn T sym , cc k hiu d liu trong lung d liu ni tip s b nh hng ca fading la chn tn s trong khi k hiu d liu trn mi sng mang thnh phn s b nh hng ch bi fading phng. Hn na, tng kh nng khc phc ISI, mt khang thi gian bo v (guard time) c chn vo u mi k hiu OFDM trc khi truyn v loi b n ti my thu trc khi a qua b FFT. Nu khang thi gian bo v c chn ln hn tri tr, ISI c th c loi b hon ton. Hnh 1.6 minh ha khi nim chn khang thi gian bo v loi b ISI cho mt k hiu OFDM. Trong hnh 1.6a, mt k hiu OFDM nhn c t ng th nht b gy nhiu bi k hiu OFDM trc nhn c t ng th hai v th 3. Trong hnh 1.6b ch ra rng k hiu OFDM nhn c t ng th nht khng cn b nhiu bi k hiu OFDM trc . Tuy nhin, k hiu nhn c vn cn b nhiu bi chnh phn sao chp ca n v ta gi loi nhiu ny l loi t gy nhiu (self-interference). gi c tnh trc giao gia cc sng mang thnh phn, khong thi gian bo v c chn vo bng cch m rng theo chu k mt k hiu OFDM. Nu tri tr nh hn khong thi gian bo v, tri tr ch gy ra mt dch pha sai s nh cho mi sng mang thnh phn nhng

khng ph v tnh trc giao gia cc sng mang thnh phn.Vic chn khong thi gian bo v c th thc hin trong hai cch: 1. Trch mt phn cui ca mt k hiu OFDM v gn n vo u k hiu OFDM. 2. Trch mt phn cui ca mt k hiu OFDM v gn n vo u k hiu OFDM, v cng lc trch mt phn u ca k hiu OFDM v gn n vo cui k hiu OFDM.

Hnh 1.6: Cc k hiu OFDM nhn c sau khi i qua mt knh a ng: (a) khng c khong thi gian bo v , (b) c khong thi gian bo v

Vi cng chiu di khong thi gian bo v, phng php 1 cho ta mt chu ng tri tr cc i v ton b khong thi gian bo v u c dng loi b ISI.Phng php 2 ch dng mt phn khong thi gian bo v (phn t u ca mt k hiu OFDM) gim ISI. Phng php 2 thch hp hn khi ca s c dng trn mt k hiu OFDM gim ph ngoi bng v cc vng roll-off ti hai u cui ca k hiu khng lm suy gim cc k hiu

d liu trn cc sng mang thnh phn.

1.1.6 Cc Tham S Chnh Ca H Thng OFDM: T hai tham s chnh bit trc ca mt knh truyn c tc truyn d liu l R v tri tr l , cc thng s ca mt h thng OFDM c th xc nh nh sau: c -Khong thi gian bo v TGI nn chn t nht gp hai ln tri tr : 2 TGI TFFT (1.18) - gim thiu t s SNR b mt do chn thm khong thi gian bo v, khong thi gian k hiu nn c chn ln hn khong thi gian bo v rt nhiu. Tuy nhin, cc k hiu vi khong thi gian di qu th d b dch Doppler, nhiu pha v lch tn s (frequency offset). Do , khong thi gian k hiu OFDM Tsym nn c chn t nht l gp 5 ln khong thi gian bo v: 5 T GI T sym (1.19) -Khong cch tn s gia hai sng mang thnh phn k nhau l: f =1/ Tsym (1.20) -S bit tn hiu trn mt k hiu OFDM Binfo l: B info = RTsym (1.21) -S sng mang thnh phn N l: N = Binfo / Rsub (1.22) trong Binfo v s bit trn 1 k hiu, Rsub s bt trn mt sng mang thnh phn, Rsub thay i theo mc iu ch, Rsub = log2M . -Bng thng tn hiu OFDM c xc nh nh sau: BW = Nf (1.23) Nhn xt: -Tng khong thi gian k hiu lm gim khong cch tn s gia cc sng mang thnh phn. V th, vi mt bng thng cho trc, vic tng s sng mang thnh phn c th c thc hin. Mc khc, cho trc s lng sng mang thnh phn, vic tng khong thi gian k hiu s lm gim bng thng tn hiu. -Tng s sng mang thnh phn lm tng s mu trn mt k hiu OFDM. Tuy nhin, iu ny khng c ngha l khong thi gian k hiu tng ln. Nu khong thi gian k hiu vn gi nguyn, khong thi gian gia hai mu s gim, ngha l lm tng bng thng tn hiu OFDM. Mc khc, nu bng thng tn hiu OFDM l c nh, khi tng s sng mang thnh phn s lm gim khong cch tn s gia hai sng mang thnh phn, dn n tng khong thi gian k hiu. Khong thi gian gia hai mu vn gi nguyn trong trng hp ny.

1.2.K THUT KT HP OFDM V CDMA:1.2.1 Gii Thiu: K thut tri ph CDMA c kh nng khc phc c fading la chn tn s, ng dng trong thng tin thng mi, s dng trong cc h thng thng tin di ng t bo CDMA IS-95, h thng thng tin di ng th h th 3(3G) CDMA2000,WCDMA. Mc khc, k thut iu ch trc giao a sng mang OFDM cng c kh nng khc phc c fading la chn tn s. V vy khi kt hp hai h thng OFDM v CDMA xy dng h thng thng tin di ng OFDMCDMA, s khc phc c nh hng ca loi fading.

Nm 1993, h thng thng tin di ng iu ch a sng mang MC-CDMA hay cn gi l OFDM-CDMA c xut da theo s kt hp gia h thng OFDM v CDMA). Nm 2002, h thng MC-CDMA c chn l mt trong s cc cng ngh chnh xy dng cc lp giao thc vt l cho cc h thng thng tin di ng 4G. H thng thng tin di ng th h th t (4G) c yu cu rt cao v tc truyn dn d liu, Cng ngh OFDM s p ng c yu cu ny. Trong phn ny trnh by v cc c tnh ca h thng OFDM-CDMA. 1.2.2 M Hnh H Thng Thu Pht Tn Hiu OFDM-CDMA: a) S khi h thng thu pht tn hiu OFDM-CDMA: K thut iu ch a sng mang trc giao ghp theo tn s OFDM khc phc c nh hng fading la chn tn s nhng li c mt s nhc im nh kh ng b gia cc sng mang con, nhy vi dch tn s v khuch i phi tuyn. CDMA cng c kh nng khc phc c fading la chn tn s, bo mt cao, gim mt cng sut nhiu.Vic kt hp gia OFDM v CDMA lm tng thm cc u im chnh ca h thng thng tin di ng OFDM-CDMA nh sau: -C kh nng h thp tc truyn k hiu trong mi sng mang con, iu ny rt thun li cho vic thu mt tn hiu cn ng b ng ln.C th kt hp mt cch hiu qu nng lng ca tn hiu thu b tn x trong min tn s.c bit i vi cc trng hp truyn dn tc cao, knh fading a ng, c th c ti 20 ng tn hiu n mt my thu DS-CDMA, b kt hp Rake 20-finger khng th c thc hin trong my thu DS-CDMA, ngc li mt my thu OFDM-CDMA s c hiu qu cao hn trong trng hp ny mc d phi mt phn nng lng ca tn hiu thu trong khong bo v (Guard Interval).

Hnh 2.1. H thng thng tin di ng OFDM-CDMA

b) Phn tch qu trnh x l tn hiu trong my pht tn hiu tri ph a song mang OFDM-CDMA: My pht OFDM-CDMA thc hin tri ph tn hiu trong min tn s. Mt phn ca k hiu tng ng vi mt chp ca m tri ph s c truyn trn tng sng mang khc nhau. i vi vic truyn dn a sng mang, cc nh hng ca fading la chn tn s s c chuyn thnh fading phng trn mi sng mang con. V th, khi truyn tc k hiu ln v b nh hng ca fading la chn tn s, tn hiu cn c chuyn i t ni tip sang song song trc khi tri ph trong min tn s. Cu trc c bn ca mt my pht OFDM-CDMA tng t vi my pht OFDM. im khc nhau chnh l OFDM-CDMA truyn cng mt k hiu qua cc sng mang con khc nhau, trong khi OFDM truyn cc k hiu khc nhau qua cc sng mang con khc nhau. Hnh 2.1 m t m hnh h thng thu pht thng tin di ng OFDM-CDMA cho ngi dng th j s dng iu ch OFDM. Chui thng tin ng vo u tin c chuyn thnh P chui d liu song song (a j,0(i), a j,1(i), ..., aP1(i )) v mi ng ra ca b chuyn i ni tip/song song MC c nhn vi m tri ph nh dng knh dj(m) vi chiu di LS= K . Sau P chui d liu song song c chuyn li thnh mt chui d liu ni tip, chui ni tip ny li c nhn vi MC m tri ph ngu nhin cj(m) c chiu di (LL) ln hn nhiu so vi K . D liu tri ph c MC MC nh x vo K sng mang con thng qua K im IFFT, cui cng khong bo v G c chn gia cc k hiu OFDM khc phc ISI trn knh fading a ng. Dng tn hiu pht bng gc phc tng ng c vit li nh sau: (2.1) (2.2) (2.3) trong dj(m) v cj(m) c chun ha nh sau:

(2.4)

Hn na, t (2.2) n (2.3), Ts l chu k k hiu, f l khong cch gia hai sng mang con lin tip v ps(t) l dng xung tam gic c nh ngha nh sau: (2.5) Bng thng ca tn hiu pht c vit li nh sau: (2.6)

trong l h s m rng bng thng kt hp vi vic chn khong bo v. c) Phn tch qu trnh x l tn hiu trong my thu tn hiu tri ph a song mang MCCDMA: Hnh 2.1 ch ra my thu OFDM-CDMA, dng sng tn hiu thu cho ngi dng th j c vit li nh sau: (2.7)

(2.8)

trong zm, p, j(t) l ng bao phc thu c ti sng mang th (Pm + p) ca ngi dng th j. MC Tn hiu thu c u tin c a qua b bin i FFT PK im. Sau khi gii tri ph vi cc m di v m ngn, cc thnh phn sng mang con th m c nhn viG j (m) kt hp nng lng ca tn hiu thu b tn x trong min tn s. Bin quyt nh cho ngi dng th j ti t=iTs c vit li nh sau: (2.9)

(2.10)

trong yp, i(m ) v nm, p (iTs) tng ng l thnh phn bng gc phc ca tn hiu thu v nhiu Gaussian phc ti sng mang con (Pm + p) ti thi im t = iTs . Trong thng tin di ng OFDM-CDMA thng s dng k thut kt hp (combining) ng xung v k thut d tn hiu a ngi dng (multiuser detection) ng ln.Trn ng truyn sng hng xung cc mu tn hiu gn nh cn bng nhau tc l: (z m, p,1 = z m, p,2 == z m, p,J= z m, p ) , k thut kt hp trc giao ORC (Orthogonality Restoring Combining) cho php chn c li tn hiu nh cng thc sau: (2.11) v th my thu c th loi b c nhiu a truy nhp MAI (Multiple Access Interference) nn cc bin d liu thu s c vit li nh cng thc sau: (2.12)

Trong (2.12), cc sng mang con mc thp c nhn vi cc tn hiu c li cao v cc thnh phn nhiu c khuch i ti cc sng mang con c mc yu hn do ci thin c ga tr BER. K thut cn bng li EGC (Equaler Gain Combining) s chn li tn hiu nh cng thc sau: (2.13) K thut chn t s cc i MRC (Maximum Ratio Combining) l chn t s li nh cng thc sau: (2.14) Cui cng, cn p dng bi ton chn ga tr cc tiu li bnh phng trung bnh MSE (Mean Square Error) c cho bi: (2.15) Theo nguyn l trc giao, li phi trc giao vi tt c cc thnh phn bng gc ca cc sng mang con thu c l: (2.16) T p s (2.15), li ca k thut MMSEC (Minumum Mean Square Error Combining) c chn nh sau: (2.17) Ch rng, ng xung, i vi z m, p nh, li s nh trnh khuch i nhiu qu mc. Ngc li, i vi z m, p ln, li s t l vi nghch o ca ng bao sng mang con z* m, p /z m, p 2 khi phc tnh trc giao gia cc ngi dng. Bin quyt nh k hiu pht cho h thng DS-CDMA v h thng OFDM-CDMA (2.9). Hai phng trnh ny cho ta thy thm mt u im na ca h thng OFDM-CDMA. l, i vi vic quyt nh k hiu, h thng DS-CDMA i hi cn phi s dng mt php tnh tch chp rt phc tp, trong khi h thng OFDM-CDMA ch yu cu mt php nhn thng thng, y chnh l mt b cn bng cp mt (one-tap)cho mi sng mang con. iu ny cng chng t, bin i Fourier tch chp ca hai hm trong min thi gian s cho ra php nhn hai hm trong min tn s. Cc k thut d tn hiu a ngi dng ng ln chn tn hiu c n gin m khng lm mt tnh tng qut, chng ta s b i cc ch s di i v p trong (2.15).K thut d tn hiu a ngi dng tuyn tnh (Linear multiuser detection) s dng mt php tng tuyn tnh cc sng thu c, c nh ngha nh sau: (2.18) trong wj l vector trng s (KMC

1) cho user th j c xc nh nh sau: (2.19)

v y l vector sng thu c (K 1)MC . i vi mt ng ln OFDM-CDMA cn ng b, y l vector h s Fourier (K 1) c nh ngha nh sau: (2.20)

MC

vit li phng trnh (2.20) di dng vector, ta nh ngha vector m tri ph b MC MC mo dng(K 1) cho user th j, vector symbol pht (J 1) v vector nhiu (K 1) nh cng thc sau: (2.21)

(2.22) (2.23) hn na, ta nh ngha ma trn m tri ph b mo dng (K 1) nh sau: D =[ d1,, dJ] (2.24) S dng (2.22) ,(2.23),(2.24), cng thc (2.20) c th vit li nh sau: c y = Da + n (2.25) Tn hiu thu c th gii tri ph vi cc m tri ph b mo dng: c H H H D y = D Da + D n (2.26) H Tuy nhin, D D trong (2.26) khng th l ma trn n v (J J ) v tnh trc giao gia cc m tri ph b mt khi i qua knh fading la chn tn s. K thut gii tng quan (Decorelating Multiuser Detection) loi b tng quan cho gia cc m tri ph bng cch nhn (2.26) vi H -1 (D D) : H 1 H H 1 H (D D) D y = a + (D D) D n (2.27) V th vc-t trng s ca k thut gii tng quan cho user th j l: (2.28) trong [A] j , j l phn t ( j, j) ca ma trn A. Mc khc, k thut MMSE cc tiu ha li bnh phng trung b h:(2.28) hMC

Li bnh phng trung bnh c th vit li nh sau: c

trong E [a j y ] = d j

(2.29) v Y =1/2 E [yy ] l ma trn tng quan ca vector sng thu c.H

d) M hnh knh truyn OFDM-CDMA a ngi dng:

Hnh 2.2. S m hnh h thng knh truyn OFDM-DS-CDMA a ngi dng Ngun d liu K ngi dng c hnh thnh t b chia lung d liu vo t 1 ng sang K ng k hiu l 1:K. Trong m hnh knh OFDM-DS-CDMA th b iu ch tn hiu tri ph trc tip ngu nhin DS-CDMA cng s dng lai iu ch MQAM hoc iu ch MPSK, sng mang s dng l 256; 512 FFT. e) M hnh h thng OFDM-DS-CDMA a ngi dng c s dng b ghp knh tun t (MUX) cc lung tn hiu tri ph thnh phn: M hnh h thng knh truyn tn hiu OFDM-DS-CDMA a ngi dng c s dng b ghp knh tun t cc lung tn hiu tri ph thnh phn nh hnh 2.3, trong phn pht c s dng b ghp knh tun t MUX, phn thu s dng b phn chia knh tun t (DEMUX). Ngun d liu K ngi dng c hnh thnh t b chia. Tn hiu sau khi tri ph c iu ch vi sng mang theo phng thc iu ch MQAM hoc iu ch MPSK, sng mang s dng l 256, 512 FFT.

Hnh 2.3. S m hnh knh truyn OFDM-DS-CDMA a ngi dng c s dng b ghp knh tun t. Tm Li: M hnh knh truyn OFDM-DS-CDMA c s dng b ghp knh tun t cc lung tn hiu tri ph thnh phn ca cc knh ngi dng, cho php tn hiu tri ph ca K ngi dng c tri rng trn ton bng thng knh truyn, nng cao h s tri ph ln N ln (N l s ng ra ca b S/P). B ghp knh tun t c N ng vo, tng ng vi h thng c N bng thng con thnh phn. n gin th chn s knh ngi dng K=N. Khi s dng b ghp knh tun t th N lung d liu thnh phn ca N knh ngi dng sau b S/P s c ghp li theo tun t thnh mt lung d liu chung tri ph trn tng bng thng con thnh phn. Nh vy N lung d liu ca mi knh c ln lt tri ph trn ton bng thng knh truyn, li tri ph tng ln, tng cht lng truyn dn tn hiu. knh OFDM-DS-CDMA l m hnh rt ph hp tip tc nghin cu la chn ng dng cho cc h thng thng tin di ng CDMA bng rng th h sau.

1.2.3 H thng MC-CDMA:

Hnh 2.4 :H thng MC-CDMA Hnh 2.4.a, minh ha trn truyn tn hiu ca ngi s dng th j . Chui thng tin a vo tun t ni tip c chuyn sang chui tun t song song v mi ng ra ni tip/song MC song c nhn vi m tri ph ngn dj(m) vi chiu di l K . P chui d liu song song a ra c chuyn i ngc li thnh chui tun t ni tip v kt MC chui d liu c qu nhn mt ln na vi m tri ph di cj(m) vi chiuMC ln hn K . Chui d liu c di MC tri ph c nh x vi PK sng mang con vi PK im IDFT, v chn thm cc xung tn hiu bo v TG vo gia d liu OFDM trnh nhiu ISI, lm xut hin nhiu nhiu hng.

Khi s dng b ghp chng ph ca (PxK ) knh ngi dng, thu c kt qu nng lng tri ph ca tn hiu K ngi dng. Khng c thay i s xut hinMC trong ph ca tn ph hiu ngi dng nhng ph ca d liu c nh x tng cng n K sng mang con. 1.3 K THUT MIMO-OFDM: 1.3.1 Gii thiu: Trong h thng anten MIMO (a u vo, a u ra), dng s liu t mt thit b u cui c tch thnh n dng s liu ring bit c tc thp hn (N l s anten pht). Mi dng s liu ny s c iu ch vo cc symbol (tn hiu) ca cc knh truyn. Cc dng s liu lc ny c tc ch bng 1/N tc dng s liu ban u, c pht ng thi, v vy, v mt l thuyt, hiu sut ph tn c tng ln gp N ln. Cc tn hiu c pht ng thi qua knh v tuyn trn cng mt ph tn v c thu bi M anten ca h thng thu. M t cu trc ca h thng thng tin v tuyn MIMO. H thng MIMO c hiu sut s dng ph tn cao bi h thng c th lm vic c trong mi trng phn tn. Tn hiu t cc anten pht hon ton khc bit nhau ti v tr ca cc anten thu. Khi truyn qua cc knh khng tng quan gia h thng pht v thu, tn hiu t mi anten pht ti v tr thu c s khc nhau v tham s khng gian. H thng my thu c th s dng s khc bit ny tch cc tn hiu c cng tn s c pht ng thi t cc anten khc nhau.

MC

Hnh 3.1:H thng anten MIMO c th lm tng ng k dung lng ca h thng v tuyn 4G Ngoi cc nh hng do suy hao, can nhiu, tn hiu khi truyn qua knh v tuyn di ng s b phn x, khc x, nhiu x, tn x, v gy ra hin tng fading a ng. iu dn n tn hiu nhn c ti b thu s yu hn nhiu so vi tn hiu ti b pht, lm gim ng k cht lng truyn thng. Cc fading kh ph bin trong thng tin v tuyn l fading Rayleigh v fading Ricean .Nhng nghin cu gn y cho thy, s kt hp phng php iu ch OFDM vo h thng MIMO cho php ci thin ng k nhng nh hng fading t mi trng truyn, cho php nng cao cht lng v dung lng truyn thng. MIMO l h thng s dng cc dy anten c hai u knh truyn vi nhiu anten cho pha thu v nhiu anten cho pha pht . 1.3.2.Nhng khi nim c bn cng ngh anten thng minh:

Nguyn tc c bn ca cc anten thng minh c s dng iu khin v gim nhiu h thng. Thng thng, nguyn tc ny c thc hin bng cch s dng cc bp hp ti cc v tr trm gc, trn c hai hng ln v xung. Mt h thng anten thng minh kt hp nhiu phn t anten c kh nng x l tn hiu ti u ha m hnh bc x ca n v/hoc m hnh thu p ng mi trng tn hiu. Cc m hnh pht v thu c t ng cp nht khi thu bao dch chuyn qua (cell) hoc khi cc iu kin tn hiu thay i.

Mc tiu ca h thng anten thng minh l cung cp cho ngi dng tn hiu ca ng ln v ng xung vi cht lng cao nht. Cc anten thng minh dng mt mng cc phn t anten, c ni vi mt mng kt hp hoc tng t hoc s. Quy m ca mng v s lng cc phn t quyt nh tng ch ti a v rng bp ti thiu ca mng anten.Mt s cn bng phi t c gia quy m ca mng anten v tng ch ca anten, v vi ch tiu bp bn ca anten mc nh hn.Cc anten thng minh to thnh cc bp bng cch iu chnh cc bin v cc pha ca cc tn hiu c thu t mi mt phn t anten cho, khi c cng vo vi nhau, chng s to thnh bp nh mong mun. Qu trnh ny c gi l s to bp. Cc b to bp c th to thnh loi bp: cc bp c qut, a bp, cc bp c to dng, v cc bp vi nhng s khng iu chnh hng. Trong cc h thng anten thng minh, cc h thng bp sng v cc h thng thch ng l hai loi h thng quan trng nht. Anten chuyn bp (beam): bao gm mt s cc loi beam c nh c nh dng tng nhy mt hng xc nh. H thng ny do cng tn hiu chn mt beam thch hp nht ti thi im nhn tn hiu phc v v n s chuyn t beam ny sang beam khc khi my mobile di chuyn v tr trong sector. Thay v nh dng cc bp sng bng cch thay i cu trc vt l cc chn t nh kiu anten nh hng, anten chuyn beam kt hp u ra ca nhiu anten mt cch c bit nhm t c s sector ho chm beam mt cch tinh vi v linh hot hn nhiu. Anten thch nghi: l loi anten thng minh nht cho n nay. Bng cch s dng nhiu thut ton x l tn hiu mi, n c kh nng vt tri hn hn trong vic nh v, theo di v x l cc loi tn hiu nhm gim thiu xuyn ln cng nh tng ti a cng tn hiu nhn.Mc d c anten chuyn beam v anten thch nghi u c gng tng tng ch, tuy nhin ch c anten thch nghi l c th cho mt tng ch ti u cng vi vic nh v, theo di v gim thiu xuyn ln. 1.3.3 Cu trc cc h thng anten thng minh: Nguyn l lm vic ca cc anten thng minh l t ng iu chnh nhm hng beam cc i v pha ngi dng mong mun ng thi c gng loi b cc xuyn ln v nhiu t bn bp sng chnh. ng ln c anten chuyn beam v anten thch nghi u o c cng cc tn hiu nhn c t ma trn anten v thc hin iu chnh phc tp v bin cng nh cc pha tn hiu. iu ny cho php chng thay i c tuyn lm vic ti u ho tn hiu nhn c.S khc nhau c bn ca anten chuyn beam v anten thch nghi th hin vic truyn tn hiu ng xung. Anten chuyn beam da vo cng tn hiu la chn beam thch hp nhm ci thin lin lc vi ngi dng cui. Ngc li, anten thch nghi c gng tm hiu su hn mi trng cao tn (RF) v thc hin vic iu chnh lin tc c tuyn pht x ca anten truyn tn hiu mt cch hiu qu hn. a) Anten chuyn beam: V mt c tuyn bc x, anten chuyn beam chnh l s m rng ca phng php sector ha nhm chia nh cc . Anten chuyn beam chia cc macrosector thnh cc microsector nhm ci thin phm vi ph sng v dung lng. Mi microsector c cha mt beam c nh vi nhy c tp trung ti a ti vng trung tm ca beam v ti thiu cc vng khc. Tu theo s beam m rng mi beam c th l 20, 30 hoc thm ch nh hn. Thit k ny i hi cc chn t phi c tng ch cao v chm beam hp.Ti mi thi im lm vic, anten chuyn beam chn trong s cc beam c nh mt beam c cng tn hiu ln nht cho ngi dng mong mun.Vic la chn ny c iu khin bi cc tn hiu cao tn (RF) hoc bi cc thit b phn cng v phn mm x l s. Khi mt ngi dng i vo mt macrosector, anten chuyn

beam s chn microsector c tn hiu ln nht phc v ngi dng . Trong sut cuc gi th h thng s kim tra cng tn hiu v thc hin vic chuyn sang beam khc khi cn thit. b) Anten thch nghi: Nu anten chuyn beam da vo cng tn hiu ti mi thi im chn mt beam thch hp th anten thch nghi li dng cc d liu mi trng v tuyn (RF) ti u ho kt ni vi ngi dng. c tuyn pht x ca anten thch nghi c iu chnh lin tc theo s thay i ca mi trng v tuyn nhm m bo cho hot ng ca h thng l ti u. Anten thch nghi s dng k thut x l s phn bit tn hiu mong mun, tn hiu do hiu ng a ng v ngun xuyn nhiu, ng thi tnh ton xc nh hng xut pht ca cc thnh phn ny. N lin tc iu chnh c tuyn lm vic da vo s thay i v tr cng nh cng ca c tn hiu ln xuyn nhiu. S thay i lin tc nh th m bo cho bp sng lc no cng hng v pha tt nht, iu ny lm cho anten thch nghi vt tri hn hn anten chuyn beam v mt cht lng hot ng (s thay i beam trong anten chuyn beam l khng lin tc). c) So snh anten chuyn beam v anten thch nghi: S tch hp anten chuyn beam c thit k v s dng rng ri trong thng tin di ng t ong nh l mt thit b cng ngh thng minh c thm vo ci thin kh nng hot ng ca h thng. Trong khi anten thch nghi d c nhiu u im vt tri so vi anten chuyn beam nhng i hi c trin khai nh l mt h thng tch hp mi hon ton. Vng ph sng: tu theo mi trng v tuyn v cc phn cng/ phn mm s dng m cng ngh chuyn beam c th tng phm vi hot ng ca trm gc ln t 20 n 200% so vi cng ngh sector ha thng thng. Vic tng vng ph sng cng c ngha l gim chi ph cho nh cung cp dch v v do gim gi dch v cho khch hng. Ngoi ra cng ngh chuyn beam cng cho php ci thin dung lng ca h thng nh vic n khng gi tn hiu i tt c cc hng. Anten thch nghi c th ph sng mt vng rng hn v nng cao dung lng hn nhiu so vi anten chuyn beam, tuy nhin n i hi cng ngh rt phc tp v do vy chi ph u t cao hn nhiu. Ngn chn xuyn ln: anten chuyn beam c th ngn chn cc xuyn nhiu ca cc tn hiu pht ra t cc hng ngoi chm beam hot ng. Tuy nhin do c tuyn beam l c nh nn chm beam khng th tp trung chnh xc n hng xut pht ca tn hiu, iu ny lm cho t s C/I thp hn so vi anten thch nghi. Anten chuyn beam cng thng ch c dng nhn tn hiu (hng ln ) do n khng th xc nh chnh xc v tr ca my mobile, v nu dng truyn tn hiu (hng xung) th n c th lm t lin lc nu chn nhm beam. Ngoi ra, cng do c im cc beam l c nh m nhy ca anten chuyn beam c th b thay i khi MS thay i v tr. Anten chuyn beam s lm vic tt nht trong mi trng c xuyn nhiu thp, nhng trong trng hp ngun xuyn nhiu li nm trung tm ca chm beam c chn trong khi tn hiu mong mun li nm pha ra ca beam th cht lng tn hiu s rt xu. So vi anten chuyn beam th anten thch nghi nh s iu chnh lin tc chm beam nn cho php loi b xuyn nhiu v cung cp tn hiu tt hn nhiu. a truy nhp phn chia theo khng gian (SDMA) mt trong nhng ng dng phc tp nht ca anten thng minh l SDMA, y l phng thc s dng k thut x l tinh xo nh v v theo di mobile, iu chnh chm bc x truyn tn hiu v pha ngi dng mong mun v trnh xa ngun xuyn nhiu. Cng ngh ny a li cc u im vt tri v kh nng loi b xuyn nhiu v kh nng ti s dng tn s. V bn cht cng ngh ny cho php iu chnh u tin vic cung cp cc tn s cho nhng ni c mt ngi dng cao nht. N lin tc to ra cc sector khc nhau mt cch rt linh ng cho mi ngi dng v phn b cc knh tn cho mi sector theo yu cu ti thi im . iu ny cho php nng cao kh nng ti s dng knh tn s, thm ch c th ti s dng knh tn trong cng mt cell. Vic x l khng gian i hi phi

tch hp vic o c v phn chia mi trng v tuyn mc cao, do vy anten thch nghi thch hp hn anten chuyn beam nhiu trong vic thc hin cng vic ny. Tm li: Cng ngh anten thng minh c th ci thin mt cch ng k v hot ng cng nh tnh kinh t ca cc h thng thng tin di ng nhng ni c mt ngi s dng cao. N cho php cc nh cung cp dch v kh nng nng cao cht lng tn hiu, dung lng mng cng nh vng ph sng. Tu theo hon cnh c th m cc nh cung cp dch v thng c cc yu cu khc nhau trong vic phi hp cc li im ny ti cc thi im khc nhau.Do anten thng minh chnh l gii php kinh t v linh hot nht cho php h nh cu hnh cng nh nng cp h thng khi cn. Nhu cu tng dung lng v ci thin cht lng dch v h thng l mt vn cp thit cho hu ht cc nh cung cp dch v thng tin di ng ton cu. Anten thng minh l mt trong nhng gii php kh thi nht cho vn ny.

2.

Cc giao thc mi trong mng ton IP:

Mobile IP (MIP) (IP di ng) l mt giao thc ca IETF gip ngi dng vi thit b di ng ca mnh c th di chuyn t mng ny sang mng kia vi nhng a ch IP subnet khc nhau m vn duy tr c communication ang din ra. Mobile IP tr thnh giao thc khng th thiu trong th gii di ng, trong cng ngh tng lai (th h th 4G). Mobile IP c rt nhiu m rng v pht trin khc nhau nh: MIPv4, MIPv6, Hierarchical MIP, Fast MIP, Multiple CoA MIP, Proxy MIP, Mobile Network Mobility (NEMO), Hawaii,...

2.1. Nguyn l hot ng ca IP di ngNh bit l trong mng, mi mt thit b, mt nt mng s c gn lin vi mt a ch IP nht nh. Trong mt qu trnh lin lc, a ch IP chnh l im gn vt l vi Internet. Do khi mt CN (correspondent node) gi mt gi tin n mt nt di ng MN (Mobile Node), gi c nh tuyn n mng thng tr ca MN (home network), khng ph thuc. Nh bit l trong mng, mi mt thit b, mt nt mng s c gn lin vi mt a ch IP nht nh. C vo v tr ca MN v cc my CN khng c thng bo g v s di ng ny. cho gi tin y vn n c MN, chnh l vai tr ca MIP. 2.1.1 Cc khi nim cn bit: - Khi MN ang trong mng thng tr, n c phn phi mt a ch IP thng tr. Khi qu trnh lin lc din ra bnh thng: nt di ng MN nhn cc gi thng tin v tr li chng nh mt my ch thng thng. - Nu MN i khi mng thng tr, th MN cn c mt i din thay mt n. i din ny l i din thng tr HA (Home Agent). D hiu l vai tr ca HA l nhn thng tin gi n MN v tip tc gi n n ng a ch mi ca MN. - lm c nh vy th MN , khi i khi ni thng tr, phi c mt a ch tm tr, gi l CoA, v thng bo a ch ny cho HA bit a im hin hu ca MN. C nhiu cch c a ch ny, nhng tin nht l MN c a ch ny t mt i din. i din ny c gi l i din tm tr FA (Foreign Agent). n y th cc bn c lm quen vi cc khi nim HA, FA, CoA. y l 3 khi nim xuyn sut trong qu trnh tm hiu v xy dng gii php IP di ng.

2.1.2

Nguyn tc hot ng:

- Khi mt MN ra khi mng thng tr. Lm th no MN bit l n i ra khi mng thng tr cng nh tm i din mi nu mng khch? HA v FA thng xuyn gi qung b mt gi tin "coucou, ti ang y". Gi tin ny c gi broadcast v gi theo chu k. Nh m MN pht hin l n ang mng khc, v n s tin hnh qu trnh tm kim i din tm tr ca n. Ngoi ra MN cng c th gi yu cu ln Agent bo agent gi broadcast thng tin. C qu trnh ny c bit n vi tn l AgentDiscovery. - Mt khi nhn c thng tin v FA (a ch...), n c th bt u lin lc vi FA. MN gi yu cu ng k thng qua FA n HA c lu ng trong mt thi gian. Yu cu ny n MN (thng qua FA) cho php hoc t chi vic ng k ny. - Nu HA cho php s ng k ny, n s lm vic nh ngi c y nhim ca MN. Khi mng ni gc ca MN nhn c cc gi tn hiu c a ch n MN. HA nhn nhng gi ny (dng ARP y nhim) ng gi chng li v tip tc gi ti a ch ca FA m MN ng k. FA s m cc gi tin ny v gi ti MN v n bit MN ang mt cch chnh xc. HA dng phng php "ng gi" gi chuyn thng tin cho MN bng cch dng thm phn mo u IP (IP header) ca gi v chuyn theo ng hm (tunelling) n MN. - Qu trnh tip din cho n khi ht thi hn ng k (hoc MN chuyn n v tr mi). Khi xy ra hin tng ht hn, MN phi ng k li vi HA ca n thng qua FA (nu MN c th n hot ng nh FA ca n). Khi MN chuyn n mng khc, n gi mt yu cu ng k mi qua FA mi. Trong trng hp ny HA s thay i a ch nh chuyn CoA ca MN v n s gi tip cc gi ng gi ti a ch nh chuyn CoA. - Khi MN tr v mng thng tr, n khng cn di ng na, n gi mt yu cu ng k li n HA, ni r rng n ang " nh" khng thc hin ng hm v dn b cc a ch nh gi trc y. Ti im ny, MN khng phi ng k li na cho ti khi n chuyn khi mng. - Nghe c v kh n gin, tuy nhin n tn by gi ngi ta vn ang tip tc nghin cu ci tin n, bi v n l mt gii php gn nh l duy nht c hiu qu m bo s di ng trong th h mng tng lai, mng 4G. a) Nguyn l hot ng ca IP di ng phin bn 4 (MIPv4) IP phin bn 4 tha nhn a ch IP ca im nt gn lin "vt l" vi mng Internet mt cch duy nht. Do khi mt m y ch CH (Coresspondent Host) gi mt gi tin n mt nt di ng MN (Mobile Node), gi c nh tuyn n mng thng tr ca MN, khng ph thuc vo v tr ca MN v cc m y CH khng c thng bo g v s di ng. Khi MN ang trong mng thng tr ca n (HoA - Home Address), th nt di ng MN nhn cc gi ny v tr li chng nh mt my ch thng thng (y l mt yu cu quan trng ca IP di ng). Nhng nu MN i khi mng thng tr, th MN cn c mt i din thay mt n. i din ny l i din thng tr HA (Home Agent) c th thng tin vi MN sut c thi gian theo trc tuyn khng ph thuc vo v tr hin hu ca MN. Do ta c th coi HA l v tr vt l ca MN. Cng nh vy, khi MN i khi ni thng tr, n phi c mt a ch tm tr v thng bo a ch ny cho HA bit a im hin hu ca MN. C nhiu cch c a ch ny, nhng tin nht l MN c a ch ny t mt i din. i din ny c gi l i din tm tr FA (Foreign Agent). Do , khi mt MN ra khi mng thng tr n ni ti mng ngoi. MN pht hin l n ang mng khc, n gi yu cu ng k thng qua FA n HA c lu ng trong mt thi gian. Yu cu ny n MN (thng qua FA) cho php hoc t chi vic ng k ny. Trng

hp ny thc hin khi MN dng FA ng k. Nu MN bo v a ch theo cch khc th n khng cn bc ng k qua FA. Nu HA cho php s ng k ny, n s lm vic nh ngi c y nhim ca MN. Khi mng ni gc ca MN nhn c cc gi tn hiu c a ch n MN. HA nhn nhng gi ny (dng ARP y nhim) ng gi chng li v tip tc gi ti a ch ca FA m MN ng k. FA s m cc gi tin ny v gi ti MN v n bit MN ang mt cch chnh xc. HA dng phng php "ng gi" gi chuyn thng tin cho MN bng cch dng thm phn mo u IP (IP header) ca gi v chuyn theo ng hm (tunelling) n MN. Khi MN ang trn mng ngoi vng, MN dng i din HA chuyn gi ng gi n chnh n thng qua FA mi. Trng hp ny xy ra cho n khi ht thi hn ng k (hoc MN chuyn n v tr mi). Khi xy ra hin tng ht hn, MN phi ng k li vi HA ca n thng qua FA (nu MN c th n hot ng nh FA ca n). Khi MN chuyn n mng khc, n gi mt yu cu ng k mi qua FA mi. Trong trng hp ny HA s thay i a ch nh chuyn CoA (care-of address) ca MN v n s gi tip cc gi ng gi ti a ch nh chuyn CoA. Mt s giao thc IP di ng cho php MN c nhiu a ch nh chuyn th HA s chuyn cng mt thng tin n nhiu a ch nh chuyn. Trng hp ny thng xy ra khi MN vng gip ranh cc cell trong mi trng v tuyn v MN chuyn ng thng xuyn. Khi MN tr v mng thng tr, n khng cn di ng na, n gi mt yu cu ng k li n HA, ni r rng n ang " nh" khng thc hin ng hm v dn b cc a ch nh gi trc y. Ti im ny, MN khng phi ng k li na cho ti khi n chuyn khi mng.

Hnh 4.1

b) MIPv6 mt phin bn nng cp v hon thin so vi MIPv4 Mun hiu c c im ca MIPv6 (IP di ng phin bn 6) ta cn bit mc ch thit k ca MIPv6 hng ti: l thng bo kp thi nhng s khc bit gia cc nt mt cch chn thc v khng lm gim st s an ton. MIPv6 nhm gii quyt ng thi hai vn . Th nht, n cho php chuyn giao lin tc mc d my ch (MN) chuyn ng v thay i a ch IP. Th hai, n cho php gi tin tm n mt nt thng qua a ch IP tnh ti, a ch thng tr gc (HA). Ni mt cch khc, MIPv6 ch trng ti bn cht nhn dng ca cc a ch IP. Ta c th nhc li tng ca MIP (c MIPv4 v MIPv6) l cho php HA lm vic vi nt di ng MN ta nh ang tnh ti. Bt c lc no MN i khi mng thng tr gc th HA nhn gi tin gi n nt ny v chuyn tip gi ny ti a ch "nh chuyn" CoA. Lp vn chuyn s d ng a ch thng tr gc (HA) nh nhn dng "tnh" ca nt di ng MN. Hnh 4.2 phc ha c ch hot ng ca tng c bn ny.

Hnh 4.2 Theo s ny th gi tin chuyn theo ng tunnel thng qua i din HA, nn ng truyn di hn v dn ti cht lng gim. khc phc nhc im ny MIPv6 a ra vic ti u ha nh tuyn RO (Route Optimization) khi dng truyn ti u, nt di ng gi cc a ch "nh chuyn" CoA ca n (ang ) n nt gi bng cc tin bo cp nht lin quan ti vic nh tuyn BU (Binding Update). Khi MIPv6 dng ti u ha nh tuyn RO, nt gi thc hin 2 nhim v: th nht, n l ngun ca gi tin gi. Th hai, n hot ng nh b router u tin cho cc gi thng bo nh tuyn. Cc gi ny ri khi nt gi l ngun c nh tuyn n cc a ch nh chuyn CoA. Mi gi bao gm mt mo u nh tuyn (routing header), cha a ch thng tr gc HoA ca cc nt di ng. Theo l lun, gi tin c nh tuyn n CoA v tip theo qua knh o, gi tin c chuyn t CoA n HoA. Mi nguy him nht trong MIPv6 l a ch b "mt cp", tc l k gian (hacker) ng gi (mt cch bt hp php) l mt nt no ti mt a ch cho ri "n cp" cc lng tin gi n a ch .

C nhiu cch n cp khc na. Xin nu thm mt cch n cp l n cp a ch gc. Nu tin cp nht BU khng c hp php ha trn mi a ch th k cp c th sn xut ra cc BU la bp ti nhiu a im trn Internet. Mi nt gi tin u b la. MIPv6 thc hin bo mt v ti u ha nh tuyn ngn nga hoc gim nh s v mt cp. an ton ca MIPv6 khng ch da vo giao thc mt m truyn thng m da vo h tng cu trc nh tuyn nt di ng MN c tip cn thng qua a ch thng tr gc HoA v c a ch chuyn gip CoA. m bo an ton v ti u ha nh tuyn, c ch hot ng ca MIPv6 da theo cch nh tuyn c phn hi RR (Return Routability). Lung vn chuyn ca gi tin nh trn hnh 4.3. N gm c 2 la chn: la chn a ch thng tr gc HoA v chn a ch nh chuyn CoA.

Hnh 4.3 Vic la chn nh tuyn RR thc hin bng 2 cp tin bo v . Cc gi th khi to a ch thng tr HoTI v th khi to a ch nh chuyn CoTI ch cn dng kch thch cc gi th. Gi cp nht a ch BU tr li cho c hai php th. Qu trnh th a ch HoA nh sau: Vic la chn a ch gm c th a ch HoT v cp nht BU. HoT c chuyn qua tunnel t i din HA n nt di ng MN. Ni dung ca HoT l mt hm s ln xn gm a ch gc ca HoTI c km theo kha bo mt Kcn (ch c nt gi bit mt k ha Kcn). Gi HoT c gi theo 2 ng ca Internet. ng th nht, t im gi n i din HA. Trn bc ny, gi khng c bo v, bt k hacker no cng bit ni dung. Tip theo HA gi tip gi n nt di ng MN. Trn ng, gi c truyn trong tunnel c bo v khng ngi ngoi no c c ni dung ca gi. Qu trnh th a ch nh chuyn CoA cng tng t. Ch c khc l by gi gi c gi trc tip t a ch CoA ca nt di ng MN. Ni dung ca CoT l mt hm s c km theo h s bo mt Kcn. Gi CoT chuyn trc tip t nt gi n nt di ng MN. Trn ng gi khng c bo v d b cc tin tc gn im gi, trn ng truyn hoc gn im MN. Khi nt di ng MN nhn c c hai tin HoT v CoT, n to ra kha rng buc Kbm. Kha Kbm c dng bo v tin cp nht BU, cho n khi MN di ng v cn c mt CoA

mi. Khi nhn c tin BU u tin, nt gi i qua mt qu trnh phc tp. l m bo cho nt MN va nhn c HoT v CoT l do HoA v CoA yu cu. Gi thit c mt tin tc c th n cp tin HoT, ti thi im no v tip theo. Nu HoT ko di m i th tin tc c th tip tc n cp. hn ch nguy hi ny ta truyn HoT trong thi gian ngn. Sau chu k vi pht, cp tin bo HoTI/HoT li thay i. Tm li, ta thy MIPv6 c nhiu c im ci tin so vi MIPv4 v cu hnh, an ton qun l, tnh di ng. MIPv6 c coi nh mt chin lc di hn cho cc nh qun l mng v cc nh cung cp dch v di ng. Nhng li ch ca IPv6 Ngy cng c nhiu thit b t bo v nhng dch v mi, "lin tc kt ni, lin tc xut hin", v in thoi thi gian thc l nhng l do 3GPP v 3GPP2 la chn phin bn IPv6 cho mng v tuyn, trong c mng truy nhp v tuyn (RAN), mng li (CN) do IPv6 c nhng u im c th gii quyt c s hn ch khi trin khai IPv4: - IPv6 c s a ch khng hn ch c th gii quyt c nhng vn v thiu a ch. - Kh nng c ci thin v nh tuyn hiu qu hn khi IPv6 c s dng do cc mo u t hn, vic chnh sa tham s mo u (Header file) v nn mo u hiu qu hn nu so vi IPv4. - IPv6 c s h tr bo mt (IPsec) - IPv6 c h tr tnh di ng (MIPv6) - IPv6 c cng mc qun l cht lng (QoS) nh IPv4. c) Gii thiu tm tt v IPv6 trong mng v tuyn 3GPP/3GPP2 Vic a IPv6 vo 3G s nh hng ng k ti thit b u cui v h tng c s. Rt nhiu vic lin quan n tiu chun ho lnh vc ny u c thc hin trn mng 3GPP v 3GPP2. Hnh 4.4 m t IPv6 c ng dng trong UMTS nh th no. Mc truyn ti v mc ngi s dng hon ton c lp, mng UTRAN v mng li cng l hai mng c lp, v vy vic s dng IPv6 c ngha bao gm ngi s dng IPv6, mng UTRAN IPv6 v mng li IPv6. Cc gi IP n/i t thit b u cui xuyn qua mng UMTS, chng khng c nh hng trc tip ti mc IP.

Hnh 2.4 Hnh 4.5 m t cu hnh mng WCDMA2000 lin kt vi mng IPv6 qua PDSN h tr IPv6. Kt ni PPP gia MS v PDSN s vn chuyn gi tin IPv6. Mng truy nhp v tuyn (RAN), bao gm giao din R-P, s c lp vi phin bn cc gi IP c truyn ti trong cc phin PPP.

Hnh 2.5 d) Nhng k thut lin kt IPv6 v IPv4 Nu mng IPv6 c trin khai, khng th trnh khi thi gian chuyn i ko di cc nt IPv6 v IPv4 cng tn ti v truyn tin. Mt s cc c ch chuyn i v cng mm do v mnh gia IPv4 v IPv6 l cn thit trong thi gian chuyn i ny. Thc t, lc lng c trch k thut Internet (IETF) pht trin hng lot nhng k thut lin kt IPv6 v IPv4. Nhng k thut ny c th tm tt thnh 3 loi sau: k thut ng hm, k thut chuyn dch, v k thut hai ngn xp. - Cc ng hm c th c s dng nh tuyn cc gi gia cc my ch IPv6 qua mng IPv4 bng cch chn thm phn mo u ca IPv4 vo gi IPv6. - K thut chuyn dch nhng b ghi dch c dng lin kt gia IPv6 v Ipv4. Cc b ghi dch - giao thc a ch mng (NAT-PT) v thut ton ghi dch khng trng thi IP/ICMP.

- K thut hai ngn xp c ngha l IPv4 v IPv6 cng song song tn ti trn cng mt my ch. C ba k thut ny c khuyn ngh mng cho 3GPP v 3GPP2. Hnh 4.6 a ra cu hnh lin kt mng t bo khng dy h tr c hai dch v IPv6 v IPv4. Hnh 4.7 l v d ca trng hp s dng k thut ng hm, khi my di ng IPv6 kt ni vi mt thit b ca IPv6 qua mng IPv4.

Hnh 4.6

Hnh 4.7

La chn phin bn IP Vic la chn phin bn IP c tho lun dng trong hai nhm 3GPP v 3GPP2 trong mt thi gian di. C 6 kh nng la chn cn cn nhc nh sau: 1. Ch dng IPv4 (H tr v s dng). 2. Ch dng IPv6 (H tr v s dng). 3. S dng IPv4, kt hp vi chn la IPv6. 4. S dng IPv6, kt hp vi chn la IPv4. 5. K thut chun hai ngn xp ti tt c cc nt. 6. Khng c mt thng bo v phin bn c s dng. S la chn 1, 2 v 6 ch c th dn n cc vn tng tc gia cc nh sn xut s dng nhng giao thc IPv4 hin nay v IPv6 ang pht trin, s la chn 5 khng hp dn do phc tp trong gii quyt thit b k thut hai ngn xp, v s pht trin b sung khi c yu cu. Nhng l do cho nhng ngi c s chn la th 4 l: - Khng gp phi vn ht a ch. - u t cho mt mng cc b nh tuyn IPv4 - Cc giao thc da trn mng cng cng hin nay do cc b nh tuyn IPv4 cu thnh. - Khng mun ch i s xut hin IPv6. - Khng quan tm n cc vn tng tc gia IPv6 v IPv4: mt gii php hiu qu c a ra i ph vi vn ny l k thut ng hm. Tuy nhin vic ny s dn n vic thay th gn nh ton b cc b nh tuyn bin kh tn km ca IPv6. - Khng mun gp phi nhng vn nng cp phn mm do nhng im m trong cc tiu chun.

Long Term Evolution 3G to 4G Nhng i vi nhng ngi c s chon la 5 th: - Vic chuyn IPv6 d dng hn. D dng tch hp vi IP di ng, cc h thng a phng tin c b sung chc nng vi IPv6. - Tit kim c chi ph nu nh pht trin t phin bn IPv4 thnh IPv6.

Kt lun IPv6 tht s cn thit cho mng 3G. Vic gii thiu IPv6 tt nhin s gy nh hng n cc thit b u cui v h tng c s ca 3G. l l do ti sao 3GPP v 3GPP2 ang hp tc cht ch vi IETF gii quyt nhng vn c lin quan ti IPv6 3G. Nh s chuyn giao cng ngh, vic lin kt gia 2 phin bn IPv4 v IPv6 c tnh kh thi, cho php chn la kh nng "S bt buc dng IPv6 v tu chn IPv4".

Long Term Evolution 3G to 4G

CC CH VIT TTA/D AMPS AWGN BER BPSK BS CBPSK CCITT CDF CDMA D/A DAB DFE DS-CDMA EGC ETSI FDMA F-FH FH-CDMA GMSK GSM ICI IDFT IFFT IMT ISI ITU LAN LPF MMSE MRC MS MT-CDMA NMT Analog/Digital Advance Mobile Phone Service Additive White Gaussian Noise Bit Error Rate Binary Phase Shift Keying Base Station Coherent BPSK International Telegraph and Telephone Consultative Committee Cumulative distribution function Code Division Multiple Access Digital/Analog Digital Audio Broadcasting Decision-feedback Equalizer Direct Sequence CDMA Equal Gain Combining European Telecommunications Standard Institute Frequency Division Multiple Access Fast-FH Frequency Hopping CDMA Gaussian Minimum Shift Keying Global System for Mobile Communication Inter-carrier Interference Inverse Discrete Fourier Transform Inverse Fast Fourier Transform International Mobile Telecommunications Intersymbol Interference International Telecommunication Union Local Area Network Lowpass Filter Minimum Mean Square Error Maximum Ratio Combining Mobile Station Multitone CDMA Nordic Mobile Telephone

Long Term Evolution 3G to 4G

OFDM ORC PAPR PLL PSD QAM QPSK RAKE RF RSSI RX S-FH SNR SSMA TCM TDMA TH-CDMA TX UHF WAP WCDMARAN CN 3GPP UMTS MS GGSN HA RNC BSS IETF

Othogonal Frequency Division Multiplexing Orthogonality-Restoring Combining Peak to Average Power Ratio Phase Locked Loop Power Septrum Density Quarature Amplitude Modulation Quadrature Phase Shift Keying Multiple tap multipath equalization for CDMA Radio Frequency Radio Signal Strength Indicator Receive Slow-FH Signal to Noise Ratio Spread-spectrum Multiple Access Trellis-Coded Modulation Time Division Multiple Access Time Hopping CDMA Transmit Ultra-high Frequency Wireless Application Protocol Wide-band Code Division Multiple AccessRadio Access Network - Mng truy nhp v tuyn Core Network - Mng li Third Generation Partnership Project: D n th h 3 Universal Mobile Telecommunication Systems Mobile Station Gateway GPRS support node Home Address Radio Network Cotroller CDMA Code Division Multiple Access Broadband Switching System Internet Engineering Task Force

Long Term Evolution 3G to 4G

MC LCI. TNG QUAN V 4G V QU TRNH PHT TRIN T 3G LN 4G: .........................11. Th no l mng 4G? ........................................................................................................................................... .1 2. Yu cu k thut cho mt h thng 4G:........................................................................................................... 5 .

3. Cng ngh then cht :............................................................................................................................................. .8 4. Hnh trnh n 4G: ............................................................................................................................................ .10 4.1. Cc cng ngh 3G c pht trin tin ln 4G: ....................................................................................12 a) i nt v WiMAX .................................................................................................................................... .12 b) i nt v 3G LTE .................................................................................................................................... .13 4.2. So snh cng ngh k thut dng trong WiMAX v 3G LTE ...................................................................14

II. 3G LTE ...................................................................................................................................171. Kin trc mng : .............................................................................................................................................. .17 1.1. Mc ch v yu cu ca 3G LTE: ...............................................................................................................17 1.2. Kin trc tng quan: .....................................................................................................................................18

2. Lp vt l: .............................................................................................................................................................. .20 3. Lp MAC ( Medium Access Control): ...............................................................................................................24 .

III. CC CNG NGH MI: ...................................................................................................271. Mt s cng ngh a truy nhp mi: ..................................................................................................................27 . 1.1 K thut ghp knh phn chia tn s trc giao (OFDM): ..........................................................................27 1.1.1 Gii Thiu:.............................................................................................................................................. .27 1.1.2 M Hnh H Thng OFDM:.................................................................................................................28 . 1.1.3 Tnh Trc Giao (Orthogonality): .........................................................................................................32 . a) Trc giao trong min thi gian:............................................................................................................32 . b) Trc giao trong min tn s: ................................................................................................................34 . 1.1.4 Nhiu Xuyn K T ISI V Xuyn Knh ICI: .................................................................................... 36 . 1.1.5 Chn Khong Thi Gian Bo V:.........................................................................................................36 . 1.1.6 Cc Tham S Chnh Ca H Thng OFDM: ....................................................................................... 38 . 1.2.K THUT KT HP OFDM V CDMA:.................................................................................................38 1.2.1 Gii Thiu:.............................................................................................................................................. .38 1.2.2 M Hnh H Thng Thu Pht Tn Hiu OFDM-CDMA: .................................................................... 39 a) S khi h thng thu pht tn hiu OFDM-CDMA: .......................................................................39 b) Phn tch qu trnh x l tn hiu trong my pht tn hiu tri ph a song mang OFDM-CDMA: .......................................................................................................................................................................40 c) Phn tch qu trnh x l tn hiu trong my thu tn hiu tri ph a song mang MC-CDMA: .....41 d) M hnh knh truyn OFDM-CDMA a ngi dng: ....................................................................44 e) M hnh h thng OFDM-DS-CDMA a ngi dng c s dng b ghp knh tun t (MUX) cc lung tn hiu tri ph thnh phn:...........................................................................................................44 . 1.2.3 H thng MC-CDMA: ......................................................................................