Tìm hiểu và nghiên cứu mạng không dây Wimax.PDF

Chuang I: Gied thigu chung ve WiMAX CHUCING 1. GI61 THItU CHUNG VE WiMAX 1.1. GIOI THItU CHIANG WiMAX la mOt cong nghe cho phdp truy c#p bang Ong vo tuyen den du Si nhu mOt phuong thirc thay the cho cap va dyeing day thue bao so DSL. WiMAX cho phep ket n6i bang Ong vo tuyen c6 djnh, nomadic (nguOi sir dung co the di dOng nhung c6 djnh trong 18c kat rthi), portable (ngutri sir dung co the di chuyen vOi the do cham) vi cuOi ding la di dOng ma khong can a trong tam nhin thing LOS (Line-Of-Sight) tri,rc trap vii tram g6c BS (Base Station). WiMAX khac phuc duce cac nhuqc diem cita cac phuong phap truy nhip hien tai, cung cap mOt phuong tien truy nhip Internet khong day ding hqp co the thay the cho ADSL vi WiFi. He thtong WiMAX c6 kha nang cung cap duemg truyen co the dO len den 70Mbit/s vi yid ban kinh phit song cita mOt tram anten phat len den 50Km. MO hinh phu song dm mang WiMAX tuong tu nhu mang dien thoai to bao. Ben canh d6, WiMAX cling host dOng mem deo nhu WiFi khi truy cip mang. m6i khi may tinh mu& truy nhip mang no 0 ur Ong ket n6i den tram anten WiMAX gin nhat. Trong chuong nay, chitng to se tim hien khai niem co ban ve WiMAX, cac chuan WiMAX hien nay, cac bang tar t co the sir dung cho WiMAX, cac uu diem va lqi ich cua WiMAX mang lai, &mg thtd la tinh hinh trien khai WiMAX tren the gieri vi tai Viet Nam 1.2. ICHAI NEN WiMAX (Worldwide Interoperability of Microwave Access) la he thOng truy nhip vi ba co tinh tuong thich toin cAu dua ten co so tieu chuan IEEE 802.16 WirelessMAN (Wireless Metropolitan Area Network). Hq 802.16 nay dua ra nhUng lieu chuin, chi tieu ky thujt nhim tip trung giai quyet the van de trong mang vo tuyAn bang Ong diem — da diem ve giao dien vo tuyen bao Lip dieu khien truy cop mill trutmg (MAC) vi 16p v#t 1St (PHY). WiMAX la mOt chuan khong day dang phat trien rat nhanh, hira hgn tao ra khi nang ket not bang thong rung the dO cao cho ca mang c6 djnh Ian mang khong day di dOng. Hai phien ban cua WiMAX duqc dua ra: Fixed WiMAX (WiMAX co d(nh): Dva tren tieu chain IEEE 802.16-2004, duce thiet ke cho loai truy nh#p c6 djnh va luu dOng. Trong phien ban nay sir dung ky - 1 - Chuang 1: Gioi thieu chung v'J WiMAX thuat ghep kenh phan chia theo tan s6 trvc giao OFDM (Orthogonnal Frequency Division Multiple) host dOng trong ca m8i trutrng nhin thing — LOS (line-of-sight) va kh8ng shin thing — NLOS (Non-line-of-sight). San pham dva tren tieu churn nay hien tai da dopy cap chung chi va thuong mai hem. Mobile WiMAX (WiMAX di dOng): dva tren tieu chuan IEEE 802.16e, duqc thiet ke cho loai truy cap xach tay vi di dOng. ve co bin, tieu chuan 802.16e duqc pith trien tren co so seta doe tieu chuan IEEE 802.16-2004 de tOi uu cho cac kenh vo tuy6n di dOng, cung cap kha nang chuyin yang — handoff vi chuyen mang — roaming. Tieu chuan nay sir dung phucmg thirc da truy cap ghep kenh chia tan s6 tri,rc giao OFDMA (Orthogonnal Frequency Division Multiple Access) — 11 skr ph6i hqp dm k9 thuat ghep kenh vi ky that phan chia tan s6 co tinh chit tri,rc giao, rat phu hqp v6i moi toting truyen dan da &Ong nhim tang thong loqng cling nhu dung loqng mang, tang dO linh host trong viec quin 19 tai nguyen, tan dung toi da ph6 tan, cai thin kha nang phi song von ac loai dja hinh da WiMAX da duqc phit trien va khic phuc duqc nh&ng nhirqc diem et' cac ding nghe truy cap bang rung truck day, cu the: Cau Vac mem deo: WiMAX h6 trq cac cau true he thOng bao gem diem — da diem, cling nghe lutri (mesh) vi pha song khap nu:A nod. Dieu khien truy nhap mai toting — MAC, phuong tien truyen din 1145 trq diem — da diem va djch vu rung khip bed lap ljch mot khe thtri gian cho mOi tram di dOng (MS). Neu co duy nhat WA MS trong mang, tram gOc (BS) se lien lac vori MS tren co sty diem — diem. Mot BS trong mot eau hinh diem — diem co the sir dung anten chum hyp ham de bao phu cac khoirtg cach xa han. Chat hung djch vu QoS: WiMAX co the duqc t6i uu dOng d6i yea Mn hqp lou lucmg se duqc mang. Co 4 loai djch vu doge h6 trq: djch vv cap phat to nguyen (UGS), djch vu h6i wing thin gian thvc (rtPS), djch vo h6i Wong khong theri gian thvc (nrtPS), no lye t6t 'that (BE). Trien khai nhanh, chi phi thap: So sinh yeti trien khai cac giai phip co day, WiMAX you cau it hoac kh8ng co bat cir sv xay dung thiet lop ben ngoii. Vi du, dao he) de tao ranh cac dutmg cap thi khong you au. Ngoii ra, dva ten cac chuin ma cua WiMAX, se khOng co sv dOc guy& v'e tieu chuan nay, dan den viec earth tranh cua nhieu nha sin xuat, lam cho chi phi du to mot he tho t ng giim ding ke. -2- Chuang 1: Geri thieu chung ve WiMAX Dich da mac: Cach thirc nai ma QoS duce phan phat not chung dva vao sv them thuan mire dich vti (SLA - Service-Level Agreement) giui nha cung cap dich vu va ngu&i sir dung cu6i cling. Chi tie[ hun, mOt nha cung cap djch vp c6 the cung cap the SLA khic nhau tai cac thud bao !chic nhau, then chi tad nhang ngtrai dung khac nhau sir dung cling MS. Cung cap troy nhap bang rang co djnh trong nheng khu vrc do thi va ngoai o, nth chat Itrqng cap diing thi kern hoac dua vao kh6 khan, khac phtic thiet bj s6 trong nheng viing mat do thap nai ma cac nhan M ding nghe vi kinh to thvc hien phat trien bang rung rat thach that. Tinh ttrcmg thich: WiMAX duqc xay dung de tra thanh mOt char' quok tot, tao ra str de ding d6i vii nguai dimg cu6i cling de truyen tai vi sir dung MS cia hp o cac vi tri khac nhau, hoac vii cac nha cung clip djch v4 khac nhau. Tinh ttrcmg thich bao ve str dau to ctia mOt nha van hanh ban dau vi no c6 the chpn Iva thiet bj to cac nhi dai ly thiet bj. Di dOng: IEEE 802.16e ba sung them cac dac diem chinh h8 trq khi flan di dOng. Nhftng cai tien lap vat ly OFDM (ghdp kenh phan chia tan sit') th e re giao) va OFDMA (da truy nhap phan chia tan s6 Dix giao) de ha trq cac thiet bi vi cac djch vu trong mOt moi truing di dOng. NhOng cai tien nay, bao g6m OFDMA ma ring dtrqc, MIMO (Multi In Multi Out - nhieu dau vao nhieu dim ra), vi h8 trq d6i vii che dO idle/sleep vi handoff, se cho phop khi thing di dOng day di 6 tic do ten 160 km/h. Mang WiMAX di dOng cho phdp ngtrai sir dung do the troy cap Internet khong day bang thong rung tai bat ca tau co phi sang WiMAX. Hoat dOng NLOS: Kha nang hpat dOng cia mang WiMAX ma khong del hei tam nhin thing giaa BS va MS. Kha thing nay cia no &dip cac sin pham WiMAX phan phat dai thong Ong trong mOt mei truemg NLOS. Phi song rung han: WiMAX ho trq dung nhieu mire dieu che, bao gom BPSK, QPSK, 16QAM, 64QAM. Khi yeu cau yeti bO khuech dai cling suit cao vi hoot dOng vii dieu che mire thap (vi du BPSK hoac QPSK). Cac he th6'ng WiMAX co the phi sang mOt yang dia ly Ong khi &rang truyen gigra BS va MS khong bi can tra. Ma Ong pham vi bj giai han hien tai cia WLAN cling cling (hotspot) den pham vi rung (hotzone). nhang dieu kien Mt nhat co the dat duqc pham vi phi song 50 km vii tic do da lieu bi ha thap (melt vii Mbit/s), pham vi phi song dien hinh la gan 5 km veri CPE (NLOS) trong nha va gin 15km vii mOt CPE duqc n6i vii mOt anten ben ngoai (LOS). -3- Chuang 1: Gieri thieu chung ve WiMAX Dung liking cao: Co the dot dirge dung lugng 75 Mbit/s cho cac tram g6c vgi met kenh 20 MHz trong cac dieu kiln truyen song tot nhit. Tinh ma rOng: Chitin 802.16 -2004 h6 try cac dai thong kenh tin s6 ve tuyen (RF) mem deo va sir dung 1a1 cac kenh tar t . ' so nay nhtr la mot cach de tang dung lugng ming. Chuan ding dinh re h6 try &Si yeti TPC (dieu khien cong suit phat) vi cac phop do chat lugng kenh nhu cac cong cu them vao de hO try sir dung ph6 hieu qua. Chuan da dugc thiet ke de dat tS le len ten hang tram tham chi hang nghin ngtkri sir dung trong mOt kenh RF. HO try nhieu kenh cho phdp cac nha the tao thiet bi cung cap met phuong tin de chit trcing vao pham vi sir dung ph6 vi nhUng quy dinh cap phat duck not re beri cac nha van hank trong cac thi twang quiic to thay dei khac nhau. 1.3. CAC CHUAN CIA WiMAX 13.1. Chitin IEEE 802.16 - 2001 Chuin IEEE 802.16-2001 duck hoar . ' thanh vao thing 10/2001 va dugc cong b6 vao 4/2002, dinh nghia dac to Icy thuot giao dien kh8ng gian WirelessMANTm cho cac mang yang do thi. Dk diem chinh dm IEEE 802.16 — 2001: Giao din khong gian cho hg thong truy Whip kung day bang rOng co dinh hgat dOng o dai tin 10 — 66 GHz, can thoa man tint nhin thing. Lop vat IS , PHY: WirelessMAN-SC. T6c dO bit: 32 —134 Mbps vol kenh 28 MHz. Dieu the QPSK, 16 QAM va 64 QAM. Cac dai thong kenh 20 MHz, 25 MHz, 28 MHz. Ban !anti cell: 2 — 5 km. Ket n6i co dinh huOng, MAC TDM/TDMA, QoS, bao mat. 13.2. ChuAn IEEE 802.16a Vi nhang kh6 khan trong then khai chart IEEE 802.16, Inking vao viec sir dtmg tin so tir 10 — 66 GHz, mOt dy an sira &Si co ten IEEE 802.16a da dugc hoin thanh vao thing 11/2002 va dugc cong b6 vao tang 4/2003. Chuan nay dugc ma king h6 . try giao din khong gian cho ithang tan s6 trong bang tan 2-11 GHz, bao g6m ca -4- Chuang 1: Gioi thieu chung ve WiMAX nhang ph6 cAp phep va khong cap phdp vi khong can thoa man dieu kien tam nhin thing. Dac diem chinh ctia IEEE 802.16a: B6 sung 802.16, cac hieu chinh MAC vi cac dac diem PHY them vao cho dal 2 — 11 GHz (NLOS). T6c de bit: UM 75Mbps yeti kenh 20 MHz. Dieu the OFDMA vai 2048 song mang, OFDM 256 song mang, QPSK, 16 QAM, 64 QAM. Dai thong kenh co the thay deoi Ora 1,25MHz vi 20MHz. Bin kinh cell: 6 — 9 km. Lop It 13% PHY: WirelessMAN-OFDM, OFDMA, SCa. Cac chirc nang MAC them vao: 116 trq PHY OFDM vi OFDMA, h6 trq ding nghe Mesh, ARQ. 1.3.3. Chan IEEE 802.16 - 2004 Thing 7/2004, chitin IEEE 802.16 — 2004 hay IEEE 802.16d duqc chap thong qua, kat hqp cua cic chitin IEEE 802.16 — 2001, IEEE 802.16a, img citing LOS 6 dai tan s6 10 - 66 GHz vit NLOS o dal 2 - 11 GHz. Kha Tian vo tuyen b6 sung nhir la "beam forming" vi kenh con OFDM. 1.3.4. Chuin IEEE 802.16e DAu nam 2005, chuan khong day bang thong rung 802.16e van ten gni Mobile WiMAX da duqc phe chuan, cho phep tram gtic kAt n6i toi nhOng thiet bi dang di chuyen. Chuan nay giup cho cac thitt bi tir cac nha sin xuat nay co the lam viec, ttrong thich tot veci cic thiet bi tir cic nhil sin xuat khac. 802.16e hnat dOng 0 cac bang tan nho ham 6 GHz, t6c dO len tai 15 Mbps veri kenh 5 MHz, ban kinh cell tir 2 — 5 km. WiMAX 802.16e co hit trq handoff vi roaming. sa dung SOFDMA, mOt cling nghe dieu the da sang mang. Cic nhl cung cap dich vu ma then khai 802.16e cling co the sir dung mang del cung cAp dich vu c6 dinh. 802.16e h6 trq cho SOFDMA cho phep s8 song mang thay d6i, ngoli cic m8 hinh OFDM vi OFDMA. Sr phan chia song mang trong mo hinh OFDMA (kw thiet ke de tai thieu anh hueng cua -5- Chuang 1: Giol thieu chung ve WiMAX nhiOu phia thiet bj nguen clUng veri anten da huerng. Cu the ham, 802.16e dua ra hO trq cai ties ho trq MIMO va AAS, cling nhtr cac handoff cling vi mem. NO cling cai lien cac kha nang tiet kiem cling suet cho cac thiet bi di dOng va cac die diem bao mat linh host hon. 802.16 802.16-2004 802.16-2005 Tinh trang Hoin thie'n vao thing 12-2001 Holm thie'n vao thang 6-2004 Hoan thin vao thing 12- 2005 Dii tin 10-66 GHz 2-11 GHz 2-11 GHz cho c6 djnh; 2-6 GHz cho di dOng (J'ng dyng Co dinh, tam nhin thing (LOS) Co djnh, lchting nhin thing (NLOS) C6 dinh vi di dOng, khong nhin thing (NLOS) Citu true lop MAC Diem — da diem, mang luai Diem — da diem, mang lueri Diem — da diem, mang lucid Mo hinh A truyen song Don song mang Don song mang, 256 OFDM, 2048 OFDM Don sang mang, 256 OFDM hoac S-OFDM veri 128, 512, 1024, 2048 song mang con. Dieu chi QPSK, 16QAM, 64QAM QPSK, 16QAM, 64QAM QPSK, 16QAM, 64QAM Ting tin so de lieu 32-134 Mbps 1-75 Mbps 1-75 Mbps Ghip Werth Khii Kh6i Kh6i TDM/TDMA TDM/TDMA/OFDMA TDM/TDMA/OFDMA Song cengs TDD va FDD TDD va FDD TDD va FDD DO rOn g 20, 25, 28 1.75, 3.5, 7, 14, 1.25, 1.75, 3.5, 7, 14, 1.25, 5, -6- Chuang 1: Glen thiOu chung 14 . WiMAX kenh truyan (MHz) 5, 10, 15, 8.75 10, 15, 8.75 Giao then kheng gian WirelessMAN- SC WirelessMAN-SCa, WirelessMAN-OFDM, WirelessMAN-OFDMA WirelessMAN-SCa, WirelessMAN-OFDM, WirelessMAN-OFDMA Xir 1f WiMAX Khong 256-OFDM nhu 11 WiMAX co dish S-OFDMA nhu la WiMAX di dOng Bang 1.1. Tom kit cac clOc trung ca ban czia churn WiMAX[6] 1.4. PH6 WiMAX 1.4.1. Bang tan ding ky Cac giii phap dang ky cung cap cac uu diem chit ltrqng dich vu duqc cai thien cao ham cac giii phap kh6ng dang ky, chap &tan NLOS Mt han a cac tan M thip, no co mot ngan qiiy cong sulk clueing xu6ng rang han va co the ho trq cac anten trong nhit tot han. Giai phap dang ky cho phep kient soit qua cach sir dung ph6 va nhieu. Bang tin Mug ky 2,5 GHz DA duqc cAp phat trong phan lan cac ntrac tren the giai, bao g6m bitc My, My Latin, (long va tay Au va nhiau vimg cila chin A - thai birth &rang. M6i quitoc gia throng cap phat dai khac nhau, vi vay ph6 duqc cAp phitt qua cac vimg co the tir 2,495 GHz din 2,690 GHz. Tong ph6 kha dung la 195 MHz, bao g6m cac dai ph6ng ve va cac kenh MDS, gtla 2.495 GHz va 2.690 GHz. H6 trq FDD, TDD. Phi; tren moi dang ky la 22.5 MHz, met block 16.5 MHz va met block 6 MHz, tong s6 8 dang ky. Bang tin dang ky 3,5 GHz. chau Au, vien chitin vien thong chau au da phan ph6i dai 3,5 GHz, bit dau duac sir dung cho WPLL, cho cac giii phip WiMAX dang ky. Ring ph6 kha dung, thay del theo qu6c gia nhung nal chung khoang 200MHz giaa 3,4 GHz va 3,8 GHz. HO trq ca FDD va TDD, met vai quac gia chi sir dung FDD trong khi cac quo t c gia -7- Chuang 1: GUN thieu chung ve WiMAX khac cho phdp sir dung FDD hoac TDD. Pho tren moi clang ky thay dei tir 2x5MHz dEn 2x56 MHz. 1.4.2. BAng tan khOng clang k5T 5GHz Phan 16n the quoc gia town the gieri da six dung phi) . 5 GHz cho cac phircmg tin lien lac kh8ng dang ky. Cac bang 5,15 GHz vi 5,85 GHz CIA duqc chi dinh nhu khong dang Icy trong phap lent the gieri. Cac gill phap kh8ng ding Icy cung cap melt vii thuitn lqi chinh ham cac giii phap Bang ky, bao gem chi phi ban dAu thAp ham, rut ra nhanh han, vi mOt bang chung co the duqc sir dung 6 phan torn the gi6i. Cac lqi ich nay dang thu hat sq quan tam vi co khA nang cho su chap nhan bang rOng nhanh chung. Tuy nhien met giai phip khong Clang ky thi khA nang nhieu cao han, vi nhiEu su canh tranh dal v6i cac nha kink doanh bat dOng sin cho viec trien khai. Mot giii phap khong clang Icy se khong duqc xem nhu mot su thay the cho giii phap clang Icy. Moi giii phap cung cap mOt thi twang khac nhau dua vao su them hie]) gifra chi phi va QoS. 1.5. TRUYEN SoNG Hien tai nhieu cong nghe !thong day bang th8ng rong chi co the cung cAp phu song clang LOS, cong nghe WiMAX duqc thi uu cung cAp ca Icha nang phi' song LOS va NLOS. Mac dit vay, ca 2 clang phii song deu bi anh htrerng it nhieu bed cac dac tinh cda moi trutmg truyen, cac Mn that Iron throng din vi tai nguyen het n6i v8 tuyen. MOt tin hieu trong lien lac LOS la mOt tin hieu ma duqc phat ten 1 duting truyEn true tiep, khong co vat can tir may phat den mot may thu hay tir may pith den may thu IA thin shin thing. lien lac LOS you au phi') 16n mien Fresnel khong bi ngan can bai SS vat nao, neu you cau nay khong duce th6a man thi co su giam thieu Bang ke cueing dO tin hieu gift tram thu vi tram phat. DO her Fresnel dtrqc yeu eau bed tin s6 hog dOng cila lien lac vi kiting each gifra may phat vi may thu. Trong lien lac NLOS, tin hieu den may thu bi phin xa, tin xa vi nhieu xa do dtrtmg truyen bi cac vat can gay ra. Cac tin hiEu den may thu bao gem cac tin hiEu tir dyeing true tiep (tin bleu chink), cac tin hiEu bi phin xa nhiEu Ian, nang 1uqng bi -8- INTERIMT BACKBONE MINAS 802.24 TRANSMITTER LIRE OF SIGWI WICKHAM SIMM T=ESTA V trOMI LIMAS YEA RSTWOINI Chuang 1: Glut thieu chung ve WiMAX tan xa va cac duemg truyen bi nhieu xa. Cac tin hieu nay co khoang tre khac nhau, suy hao, phan cuc, DO chinh la nguyen lain gay ra nhieu ISI va meo tin hieu, day kheing phai la yin de Ion del vol lien lac LOS, nhung veri LOS lai la van de chinh. Ngoai ra, hien tugng da duOng co the gay ra hieu tugng phan cuc. Khic phoc tinh trang nay, viec sir dung lai tin s6 nhu la mot Bien phap manh me cil ia LOS nhung lai kho giii guy& trong ang clang NLOS. MOt hg thing vo tuyen sir dung cac tin hieu da duemg hieu qua tao thuan Igi de cung cap dich vu trong dieu kiln NLOS. MOt san phin chi don thuin tang cong suit de xuyen qua cac vat can (doi khi ggi la "can tam nhin thing") thi kh8ng dugc coi la cong nghe NLOS bed vi phucmg phap nay can dui vao duong truyEn true ti'ep du manh chic khong sir dung cac !tang lugng sinh ra trong cac tin hieu gian dep. NLOS tao ra cac uu diem Clang ke, vi du nhu cac yeu au lap lich ke hoach chat the va gieri han chieu cao anten ma thutmg thi quy Binh chieu cao anten ciia LOS kh6ng cho phep. Vic ha thap chiEu cao ciia anten la met thuan Igi dE giam nhieu kenn chung gifra cac vi tri cell lien ke nai ma cac to bio tram g6c dugc then khai ke nhau tren pham vi Ong kitten tar ' s6 dugc sir dung co gieri hen. Hinh 1.1. Minh hpa hpat 445ng WiMAX [1O] - 9 - Chuang 1: Giai thieu chung ve WiMAX Cong nghe NLOS cling giam phi ten cai dot bang each dat clued cac mai the thiet bi CPE dung nhu nguyen ban va giam bat kh6 khan dinh vi tri cac dia diem dot CPE thich hqp. C6ng nghe cling giam bat nhu eau quan sat vi tri thiet bi phia throe va cal thien dO chinh xac cua cac cong cv lap ke hooch NLOS. C6ng nghe NLOS va Meng tinh nang duce fling cao trong WiMAX too !chit nang sir dung thiet bi phia dAu Ichach hang (CPE) trong nha. Dieu nay co hai kh6 khan chinh; dau tien la khic phvc nhOng ten hao xuyen qua tea nhA va thir hai, phi) song cac khoang each hqp IST vii cong suit truyen va cac anten th'Ap hen ma &rang duqc ket hap vii the CPE trong nha. Trartattry Antense Hinh 1.2. Truyin song trong Thremg hqp NLOS 1101 1.6. UV DIEM VA NHUQC DIEM CUA CONG NGHE WiMAX Mvc tieu cua t6 chirc IEEE khi phat trien tieu chuAn 802.16: Xay clung mot pham vi chuAn di a clang cho sv phat trien va phei hap gift cac nha san xuAt, nha cung cap va ca ngtrai sir dung. Thilc dAy qua Wirth chimg nhan ph6i hap hoot dOng va tuan chit cho cac he thring truy nhap vo tuyen bang rOng tren toan cAu. Nhu vay, voi mvc tieu de ra, cac tieu chuAn cho WiMAX co Iqi ich het sue to lan doi voi cae nhA san xuat, cac nhi cung cap dich vv va ca ngtrai sir dung dich vv. fled voi nhi sin ausit: Tren ca s6 tieu chuAn chung, nhi sin xuAt co the nhanh cheng phat trien cac san phini ma it phai chi phi cho viec nghien ciru, too thanh phAn va (Lich 91 mai. MOt nha sin xuAt co the top trung vao mot linh we (ching han tram g6c hay CPE) ma kh6ng can thvc hien day du giii phip tir du cued den dAu - 10 - . anten WiMAX gin nhat. Trong chuong nay, chitng to se tim hien khai niem co ban ve WiMAX, cac chuan WiMAX hien nay, cac bang tar t co the sir dung cho WiMAX, cac uu diem va lqi ich cua WiMAX. WirelessMAN-OFDMA Xir 1f WiMAX Khong 256-OFDM nhu 11 WiMAX co dish S-OFDMA nhu la WiMAX di dOng Bang 1.1. Tom kit cac clOc trung ca ban czia churn WiMAX[ 6] 1.4. PH6 WiMAX 1.4.1. Bang tan. cung cap djch vv phat trien hg thong WiMAX. - 12 - Chutmg 1: Gioi thieu chung IFJ WiMAX 1.7. TiNH HiNH TRIEN KHAI WiMAX 1.7.1. Tinh hinh trien khai WiMAX tren the gild Hien nay, tren the