Luận văn tìm hiểu và nghiên cứu mạng không dây wimax

Mix dins MO DAU De dap ang nhu cau thuc to hien nay ve toe deo truyen da lieu cao, bang th8ng Ong han, h6 trq nhieu mire djch vu QoS, tinh di dOng nOi mang hay gifta cac mang sir dung co

BO GIAO DI C VA DAC, TAO

TWANG 13$1 HQC THONG LONG

-o0o -

KHOA LUAN TOT NGHIEP

TIM HIEU VA NGHIEN °UV M4NG

KHONG DAY VVIMAX

Ciao vien hirerng chin : Mani Thanh Giang Sinh vien thvc hien : Tan Thai Linh

Ma sinh vien : a13520 Chuyen nghanh : CONG NCH* THONG TIN

HA NQI - 2013

MUC LUC

1.7.1 rmh hinh trien khai WiMAX tren the glen 13 1.7.2 Tinh hinh trien khai WiMAX this nghiem tai Viet Nam 13

2.2.5 Cac uu vi nhtrqc diem cita ki thuit OFDM 19

2.3.4 He thong OFDMA 25

Phv Ivc A: Gil trj truirng Type trong thong blo quin trj lop MAC 59

MVC LUC HIM! VE

Hinh 1.2 Truyen sling trong tnrang hop NLOS [10] 10

Hinh 3.2 Chile nang ck lap trong m8 hinh phan lop chart IEEE 802.16 31

Filth 4.1 Module WiMAX trong kien true NS-2 [13] 46

Hinh 4.5 Ck tratmg event trong file barn vet —.tr 52

MUC LVC BANG

MVC LVC BIEU De)

Bleu 6 4.1 Thong Itrong SS khi MN di chuyen veri ttic dO 1 m/s 54 Bieu 6 4.2 Thong luong SS khi MN di chuyen vai t6c do 4.147 m/s 54 Bieu 6 4.3 Thong luong SS khi MN di chuyen v6i tin dO 8.3 m/s 55

Danh myc thy& ngti va cac tic viit tat

DA' MVC THUAT Nay VA cAc Te VIET TAT

AAS Advanced Antenna Systems - Cac he then anten thich nghi AES Advanced Encryption Standard - Chitin ma hem nang cao

AK Authentication Key - Khoa chimg thgc

ARQ Automatic Repeat reQuest - Tis dOng lap lai yeu au

ATM Asynchronous Transfer Mode

AWGN Additive White Gaussian Noise - Nhieu Gaussian trang cong

BE Best Effort

BER Bit Error Rate - Ti le lei bit

BPSK Binary Phase Shift Keying - dilu the pha nhj phan

BS Base Station - Tram gee

CDMA Code Division Multiple Access - Da truy cap phan chia theo ma CID Connection Identifier - Dinh danh ket not

CP Cyclic Prefix - Tien to Wong

CPE Customer Premise Equipment

CRC Cyclic Redundancy Check - Kiem tra 18i du yang

DFS Dynamic Frequency Selection — bra chgn tin se dOng

FDD Frequency Division Duplex - Ghtp kenh phan chia theo tan se FFT Fast Fourier Transform - Chuyen dei Fourier nhanh

Global System for Mobile communications - He thong thong tin

di dOng town cau InterChannel Interference - Nhieu xuyen kenh Inverse Discrete Fourier Transform - Bien dei Fourirer tin rac ngtrgc

Institute of Electrical and Electronics Engineers - HQC Vien ciia cac Ky Su Dien va Dien Tar

Inverse Fast Fourier Transform - Bien del Fourier ngugc nhanh Inter-Symbol Interference - Nhieu xuyen ky tir

Danh myc thueit ngt7 va cdc tit vdt tin

Key Encryption Key

Line Of Sight - Tim nhin thing Mobile Station Handover Request — yeu ciu chuyen giao tram

di dOng Media Access Control - Dieu khien truy nhop m8i twang Metropolitan Area Network — Mang do thj

Multiple Input Multiple Output - Nhieu dau vao, nhieu dau ra Multiple Input Single Output - Nhieu dau vio, mOt dau ra

Quadature Phase Shift Keying - dieu the pha trvc giao Receive Signal Strength Indicator — Cuong dO tin hieu nhin duqc

Radio Frequency - Tin so v8 tuyen

real-time Polling Service Service Data Unit - Dun vj dtk lieu djch vtr Service-Level Agreement - Theta thu$n mirc (Bch vv Signal-to-Noise Ratio — Ti le tin hieu ten nhien

Danh myc thuat ngu va ccic tit vilt tat

SS Subscriber Station - Tram thue bao

Time Division Multiplexing — Ghep With phan chia theo thin gian

Time Division Multiplexing Access — Da truy cap phan chia TDMA

theo thin gian TEK Traffic Encryption Key - Khda ma h6a luu lucrng

UDP User Datagram Protocol

UGS Unsolicited Grant Services

UMTS Universal Mobile Telephone System

WiFi Wireless Fidelity

WiMAX Worldwide interoperability for Microwave Access

WLAN Wireless Local Area Network — Mang cuc khong day

TDM

Mix dins

MO DAU

De dap ang nhu cau thuc to hien nay ve toe deo truyen da lieu cao, bang th8ng Ong han, h6 trq nhieu mire djch vu (QoS), tinh di dOng nOi mang hay gifta cac mang sir dung cong nghe khac nhau vit gifts cac nha cung cap djch v6i nhau VI vay xu huong phat trien mang the he sau di sau vio tinh chart h6a, cho phop xity dtmg kieu mang kh8ng phi; dmijc vao cac duet bi sir dung no vi tuang tac giOra cac kieu mpg khac nhau b mat dO cao MOt cling ngh'e da vi dang duqc phat trien nham dap (mg cac nhu au ke tren, duqc chuan hem beri t6 chic IEEE (Institute of Electrical and Electronics Engineers) - cling nghe IEEE 802.16 hay con duqc gqi la cong nghe WiMAX dinh cho ket not bang thong Ong khong day 6 khan cach 16n

Cac cong nghe truy cap kh8ng day hien tai con han the ve tee dO truyen du

lieu, h6 trq mac dich vu chua linh hog, pham vi phi song hp Do do cong nghe WiMAX duqc phat trien luting t6i nave dich khAc phuc, hob thin vi fling cao cac dac tinh manh me cita cong nghe mang khong day

Luan van nay se tap thing vao viec nghien cfru cac 16p Dieu khien truy nhop mei truang MAC trong cong nghe 802.16, qua do trinh bay nhOng van de co ban ve cong nghe WiMAX ding nhu cac chart WiMAX, cac Id thug img dung trong WiMAX, mo hinh phan 16p tong cong nghe WiMAX

Tiep theo, de lain re quy trinh lam viec cita he thong mang WiMAX, luan van se gieri thieu mo phong hog dOng dui he thong WiMAX cling nhu phan m'em

ho trq m8 phong cac hog dOng nay

Ulan van bao gem 4 clurcmg:

Chuang 1: Gi6i thieu chung ve WiMAX

Chuang 2: Cac kg dwelt duqc sir dung trong WiMAX

Chuang 3: Kien true mang truy cop WiMAX

Chuang 4: Chuang trinh m8 phi:mg WiMAX

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 thot 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 ere 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 tart ' 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-

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

C6 dinh vi di dOng, khong nhin thing (NLOS) Citu

Song

DO rOng 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

WirelessMAN-SCa, WirelessMAN-OFDM, WirelessMAN-OFDMA

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 tc 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 cilia 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 -

Chuang 1: Giol thieu chung v*J WiMAX

Si ved nha cung tip djch vg:

Tren cu so nen tang chung cho phep nha cung cap djch vu giam gia thank, tang kha nang canh tranh cling nhu khuyen khich sv ded mdi

ICha nang giain cac chi phi vit mac dau to cho phep nha khai thic tang pham vi phvc vv cia minh

Nha khai thac kh8ng con phv thuOc vAo mot nha cung cap thiet bj rieng do cac san pham rieng biet cua timg hang

He' thong vo tuyen cho phep giam cac rii ro cho nha khai thac

DOI vii nguriri sir dyng dich vy:

Ngtrai sir dung tai the khu vve Mem day chua dirge cung cap djch vv truy cop bang rOng nay co the duqc sir dung nha kha nang phi song rOng cua WiMAX

Nhieu nha cung cap dich vv tren thi truang tao dieu kien cho nguiri sir dung co them nhieu Iva chon cho djch vv truy nh#p bang rOng

Tao sv canh tranh co lqi cho nguai sir dung, giam cac chi phi djch vv

Cic nhusrc diem cfia cong nghe WiMAX:

Dai tin WiMAX sir dung khong tucmg thich tai nhieu qu6c gia, lam han the sv pile, hien cong nghe rOng rai

Do cong nghe mai xuAt hien gAn day nen van con met s610 h6ng bao mat

Tuy duqc gqi la chuin cong nghe nhung th‘t su chua duce "chuan" do hien gin! dang sir dung gin 10 chuin cong nghe khac nhau Theo dien din WiMAX chi mai

co khoang 12 hang phat then churn WiMAX duqc chung nhan bao g6m: Alvarion, Selex Communication, Airspan, Proxim Wilreless, Redline, Sequnas, Siemens, SR Telecom, Telsim, Wavesat, Aperto, Axxcelera

C6ng nghe nay Icheri xuemg tir nude My, nhung thvc sv chua co thong tin chinh thirc nao de cap den viec My sir dung WiMAX nhu the nao, khic phut hat qua str

Alvarion) cling da mien khai o met sof) tinh mien nui phia Bat, cu the la a Lao Cai nhung cling chi gi6i han la cac diem truy cap Internet tai Buu dien tinh,huyen cho

chua c6 nhang ket luOn chinh thirc ve tinh hieu qua dang ke cua he th6ng

Nhu vay, co the thAy rang kha nang cling nhu lqi ich ctia cac he Meng WiMAX dva tren ho churn 802.16 la het sire to Ion mac dit no van tan tai met s6 han the NO

Chuang 1: Gioi thieu chung ve WiMAX

cho phep nha cung cap djch vv trien khai nhanh chong cac hg thOng mang cua minh, tang kha nang earth tranh eking theri cho phip ngutri tieu dimg co them nhieu Iva chon, fiat kiem hon trong cac chi phi Dieu nay chinh la dOng lye MIK day cac this san xuat t va cac nha 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 gioi, dA co cac mpg thu nghiem cong nghe WiMAX co djnh

va di dOng Theo danh gia cea Maravedis Inc thi thi trueng ten thong bang rOng

co djnh den nAm 2010 co doanh thu vugt 2 ty USD Hien nay, thc dO tang tramg hang nam la 30% Vic xuAt hien met ding nghe truy cop khong day bang rOng mai nhu WiMAX cho phep trien khai nhanh djch vv, se lim bung no thj tubing trong nheng nAm

Den nay, dA c6 met s6 nuerc da di vao trien khai va khai thac the nghiem cac djch

vv tren nen Mobile WiMAX nhu My, Uc, Brazil

MOt sv kien co the coi la met buck ngoOt quan tong cea WiMAX — to ngay 19/10/2007 — ca quan vien thOng qu6c to thuec lien hip (in& ITU di phe duyet cong nghe bang rOng kh8ng day nay vao be chuin IMT-2000 Quyet dinh nay dA dua WiMAX len ngang tam vol nhang k9 thufit k'et n6i v8 tuyen hang du hien nay trong be churn IMT-2000 gem co GSM, CDMA va UMTS Dieu nay dam boo cho cac nha khai thac vi quan 13% tren toan the giai yen tam du to vao Wing rOng di dOng thvc sv dung WiMAX

15-1.7.2 Tinh hinh trien khai WiMAX thin nghiem tai Viet Nam

VNPT trien khai the nghiem cong nghe WiMAX tai Lao Cai vao thang 10/2006

va dA nghiem thu thanh cong vao thang 4/2007

NAm 2006, tai Viet Nam, dA co 4 doanh nghiep duqc Be Buu chinh Vien thong cho phdp cung cAp thir nghiem djch vv WiMAX c6 djnh la Viettel, VTC, VNPT vi FPT Telecom Sau khi the nghiem xong, Be se Iva chon 3 nha cung cAp chinh the cho loci hinh bang rOng khong day nay

Ngay 1/10/2007, Chinh phu dA cep phep trier, khai djch vv thong tin di dOng 3G

ve dich vv truy nhOp bang Ong khong day WiMAX (theo cong van 5535/VPCP-CN

dm van phong Chinh pile) Deng that Phe the Wang dA deng y cep phep thir nghiem djch vv WiMAX di dOng cho 4 doanh nghiep EVN Telecom, Viettel, FPT

vi VTC the nghiem tai bAng tan 2.3 - 2.4 GHz; VNPT the nghiem tai bang tin 2.5 — 2.69 GHz

- 13 -

Chuang 1: Giol thieu chung ve WiMAX

1.8 KET LUAN CHIRING

Chuang 1 nay da khai plat duqc nhftng dac diem co ban caa WiMAX bao gam khai nid'm, cac phien ban, ph* vi cac bang tar' cluqc s* dung cho WiMAX Ngoli

ra, chtrang nay cling net' len duce cac tru diem va nhtrqc diem hg thong sir dung ding nghd WiMAX Chuang nay se la nen tang cho cac chtrcmg tier) theo nhim tim hieu sau ham vd hg th6ng WiMAX

-14-

Chuang 2: Cac k-St thudt &roc ste dung trong WiMAX

CHUONG 2 CAC KY TI1U4T DU'QC DING TRONG WiMAX

2.1 GIell THItU CHVONG

Yeti kien triic ma, linh hoat, dung luqng lan va chi phi then khai thip dA lam cho WiMAX tres thanh mot giai phap hang diu cho cac dich vu v8 tuyen bang rOng

KM nang cung cap ket not bang 'tong veri nhieu kjch ban sir dung tir truy cap co djnh va di dOng tren ding mot ha ring mang va vi the se tao nen mot can lit mang linh hoat, mang lai cac dich vv truy Gip bang rang gia re va hira hen mot mo hinh kinh doanh hip din d6i veri cac nha cung cap djch vu

Veri cong nghe tuang to truerc day (FM, AM) va bieu 416 dieu the so h6a hieu suit thip (PSK, BPSK va QPSK) duqc sir dung rOng rai trong cac mang ngay nay, cong nghe bang Ong khong day yeu ciu sir dung cac bieu dE dieu the theo thU ig cao han veri hieu qua trai phE tot hem Tuy nhien, bleu dE dieu the theo thir ig cao han nay Mt a 1:1 tic dOng bed nhieu va hien tucmg da &rang clan Ca hai yeu to nay d'eu phE bien trong cac triEn khai mang kh8ng day c6 mAt khip nai va s6 itrong

nguiii dung lem

OFDM, OFDMA va S-OFDMA la nhftng cong nghe truy nhip mOi cai tien hb'

trq kenh can thiEt de dat duqc hieu qua trai phi tot han va th6ng lucmg kenh cao han Nhang cong nghe 'my nhip meri nay la nen tang cho WiMAX va la lua chqn cho cac he thEng bang rOng di ding tiep theo khac nhim cung cap nhieu loci hinh dich vv truyen th6ng da phuang tien tic dO cao

Trong chuang nay, chung to se khao sat tong quan cac kg thuo Wan tien duqc ap dung trong cong nghe WiMAX nhu la icy digit OFDM, OFDMA, he thEng anten tien tien

- 15 -

011-1 >Pa ape nava Frespoeuar

I-13MA epectesrmo

Chuang 2: Cac ky thuat &tor sei dung trong WiMAX

2.2 Ki? THQAT OFDM

2.2.1 Khei nifm

Ky thuat OFDM la kji thuat ghip kenh phial chia theo ten s6 true giao (Orthogonal Frequency Division Multiplexing) Trong OFDM, chuti du lieu toi Mu phat thueng c6 the do rat cao Deng aft lieu nay duqc chia thanh nhieu deng dOr lieu song song the do thip ham nhe bo chuyen dti not tiep-song song (S/P) Moi deng

du lieu song song sau do dtrqc di'eu the beri melt song mang, cac song mang nay duqc chen true giao veri nhau de dim bio co the tach rieng timg luring chi lieu tai dau thu Ke den cac song mang nay dirge tong hqp lei va dua len tan se Oat

Hinh 2.1 So scinh giito FDMA vn OFDM

Se lugng cac song mang con phy thuOc vio nhieu yeu to nhtr do Yong kenh va mUc do nhieu Con s6 nay trong 1mg yen kich thuem FFT Chu'An giao tiep ve tuyen 802.16-2004 xac djnh 256 song mang con tucmg img FFT 256 diem, hinh thanh chuan Fixed WiMAX, yen do rOng kenh co djnh Chuin giao tiep 802.16 - 2005 cho

hinh thanh chusan Mobile WiMAX (Scalable OFDMA), de duy tri tuong &Si khoing thei gian khong del cim cac ki hieu vi khoang clan each gift cac song mang veri dO reng kenh

CO the thiy re lqi ich caa OFDM khi xet qua kenh truyen Neu luring der lieu goc

duqc chuyen true tiep len song mang va phat len kenh truyen, thi bang thong rOng

dm tin hieu phat se bj tae Ong chen lee an se Bed vi, khi tin hieu truyen co bang thong reing (do Mc do bit cao), cac tan M khic nhau se co do suy hao khic nhau khi truyen qua kenh truyen vo tuyen Dieu nay dim den viec kh6i phqc tin hieu tai may

- 16 -

Chuang 2: Ccic kfr thigh &or sir citing trong WiMAX

thu se phut tap, dei hoi phai co be can bang Trong OFDM, (ding dr! lieu duqc tach

thanh N luting da Ru Mc de thip, co bang thong hcp Do 46, khi truyen, cac

da lieu nay chju Fading phing cling de

Tai may thu, ling dii lieu trate tien dirge dua v'e' bang geic bed be trOn Luting

du lieu nay sau d6 duqc txich ra thanh N ling dii lieu Mc de thap, theo sau la be lqc

Minh 2.2 Sc cle; khdi he thcing OFDM

Dau tien, dong da lieu vao yeti Mc de cao duqc chia thanh nhieu dong dii lieu

song song toc de thap hcm nhe be chuyen doi not 4p-song song (S/P) Mai dong

du lieu song song sau do duqc ma h6a (Coding) sir dung twat toan FEC (Forward

Error Correcting) va duqc sip xep (Mapping) theo met trinh to hon hqp NhOng ky

to hem hqp dirge dua den dau vao cua khoi IDFT (6 day de thuc hien phdp bien d6i

IDFT ngued to &mg thuat toan IFFT) Sau de khoing bio v'e duqc chen vao de gilun

nhieu xuyen 147 to (ISI), nhieu xuyen kenh (ICI) do truyen tren cac kenh vo tuyen di

Ong da clueing Deng dii lieu song song lai dirge chuyen thanh not tiep nher be

chuyen dbi song song-n6i flap (P/S) Cuoi cling, Ix) A/D phia phat djnh clang tin

hieu thin gian lien tuc va chuyen did ten mien tan so cao de truyen di xa

- 17 -

Chuang 2: Cdc 1c9 thu<it dupt sir dung trong WiMAX

Trong qua trinh truyen, tren cac kenh se co cac ngurin nhieu tac (long den nhu

nhieu Gausian tring cong (Additive White Gaussian Noise-AWGN)

phia thu, tin hieu thu dirge chuyen xu6ng tan s6 thap va tin hieu rtri rac nhan

dirge sau bo D/A thu Khoang bao vg dirge loai be va cac mau dirge chuyen cl6i to

mien died gian sang mien din so bang phep bien d6i DFT dung thuat toan FFT (khoi

FFT) Sau do, thy vao sir c16 dieu the dirge sir dung, sr dich chuyen ve bien do va

pha cua cac song mang nhanh se dirge sip xtp ngugc tres lai vi dirge gill ma Cuoi

cimg, chimg to than lai dirge clang dir lieu nil tiEp ban du

2.2.3 Chugi bao vg trong ht' thOng OFDM

lfu diem dm phuong phap dieu chE OFDM khong chi the hien 6 hieu qua sir

dung bang thong ma con co kha nang lam giam hay loai trir nhieu xuyen ki hieu ISI

TINY sir dung chutii bao ve (Guard Interval- GI) MOt matt tin hieu co t10 dai la Ts,

churai bao ve tucmg img la mOt chuSi tin hieu co dO daft Too phia sau duct sao chep

len phin phia fru& cila mail tin hieu nay nhu hinh ve sau (do de, GI con doge poi la

Cyclic Prefix-CP) Su sao chop nay co tac dung ch6'ng lai nhieu xuyen ki hieu ISI

do hieu img phan tap da dtrang

Pluin tin hieu c6 ich

Ifinh 2.3 Khdi niem va chuiii bit° ve

Nguyen tic nay giai thich nhu sau: Gia sir may phat di mOt khoang tin hieu co

chieu dai la Ts, sau khi Chen them chuai bao ve co chiEu dai To thi tin hieu nay co

chieu dai la T=Ts+TG Do hieu img da dutrng multipath, tin hieu nay se taxi may thu

theo nhiEu dtrimg khac nhau Trong hinh ve mo to cluti day, hinh 2.4, tin hieu theo

&rang thir that khong co tre, cac throng thir hai va thir ba dEu bi tre mOt khoang

than gian so yeti dirtmg thin nhat.Tin hieu thu dirge 6 may thu se la tong hgp ciia tit

ca cac tuyen, cho thiy ki hieu &mg trink se chting lin vao ki hieu ngay sau d6, day

chinh la hien tugng 151 Do trong OFDM co sir dyng chubz i bao ye co do dai To se

a ding loai be hien tugng nay Trong trutmg hgp T6 ?T tux nhu hinh ve mo to thi

phan bi chOng lin ISI nim trong khoang cua chuoi bao ve, can thanh phan tin hieu

co ich van an toan 6 phia may thu se gat be chutii Wm ye trutrc khi gin tin hieu den

- 18 -

pain 02

path 12

Received

,

Chuang 2: Ccic kfr thudt chew sir dung trong WiMAX

be giai dieu the OFDM Do do, diEu kien can thief de cho hg thong OFDM khong

bi anh hut:mg beri ISI la: T G r max V ori Twocia tre truyEn dim gi da cua kenh

2.2.4 Nguyen tic gill dieu the OFDM

Cac biz& thgc hien 6 day deu ngtrqc Igi so vol phia may phat Tin hieu thu se

&lac Lich thuoi bao vg, giai dieu the de khoi phgc bang tan goc, giai diEu the ey the song mang con, chuyen d6i matt tin hieu phac thinh clang bit (tin hieu s6) va chuyen d6i song song sang nal nap

2.2.5 Cic wu va nhurut diem ciia ki thuilt OFDM

Qua viec phan tich va ca ban kg thuat OFDM nhu tren, chimg to co thE rut ra met s6 uu diem, nhugc diem chinh cua OFDM nhu sau:

Uu dam:

- 19 -

Chuang 2: Ccic kfr thuat dttqc sie citing trong WiMAX

Sir dung ph6 hieu qua nher ph6 tan s6 co clang gin nhu cira s6 cha nhat nett s6

song mang con da kin

Loai bei !Neu xuyen 14 to (ISI) va nhieu giaa cac khung (IFI) nher sir d0ng tiEn t6 yang CP (Cyclic Prefix)

Kha nang chring nhieu giaa cac kenh con rat tat nher viec sir dung cac song mang con true giao

Kyr thuat OFDM cho phop thong tin Mc el0 cao duqc truyen song song veri Mc dO thap hem tren cac kenh bang hyp Cac kenh con nay dugc coi la cac kenh fading kh6ng lira chip tan so nen co the dung cac b0 can bang don gian trong su6t qui trinh nhan th6ng tin Noi nhu vay, he thEng OFDM cluing duerc anti huemg cira fading lua chin tan so

K9 thuat OFDM la met phuang phap hieu qua de giai quy6t da duong, khang nhieu bang hyp Mt vi nhieu nay chi anh hu?mg met 4 le nhe cac song mang con Thuc hien don gian trong mien tan s6 bang cach dung giai thuat FFT Dang thin may thu don gian do khong can b0 kilter ICI va ISI nEu khoing du troy dti dai

- 20 -

Chuang 2: Cdc Icy thudt duvc ste dung trong WiMAX

Nhuyrc diim:

OFDM la tap hqp cita tin hieu tren nhiEu song mang, dai dOng cea tin hieu Ion nen cot s6 ding suit dinh/trung binh tucmg doi len se lam han che hi'E'u suit cea b0 khuech dai am tan

Mit mat hieu suit pht do then khoing do MI

Nhitu pha do so khong phti hqp gita cac be dao dOng 0 may phat va may thu,

co thE lam Anh hueng den chit lucmg he tilting

Phil co so dang b0 chinh xac vE tan s6 va thin gian, dac bier la tit' so

Nhu vay, ky thuat OFDM IA giiti phap rat pith hop cho truyen clan vo tuytn ttc

dO cao not chung va cho tong nghe Winn not rieng Theo phan tich ve ky thuat OFDM nhu tren , dung Wong cda 4 thting se duqc darth gia thong qua so luting cac sang mang con dime diEu che St lucmg the song mang con pho thuk vAo nhiEu yeu to nhu dO rang kenh, mire do nhieu, icieu diau cha r Con s6 nay (song mang con) ttrcmg (mg voi kich thuk FFT Cu the nhu chuin 802.16-2004 xic Binh re 256 song mang con, ttrcrng Cmg veri kich thuerc FFT 256 dO rtjng kenh dpc lap, chuan 802.16e-2005 cung cap kich ca FFT tir 512 den 2048 tuong img vei dO rOng kenh tir 5 MHz den 20 MHz dE duy tri khoing each trong clti khong dti cea ky hieu va khoing dan each gift cac sang mang con d'Oc 1#p veri dO rOng kenh Nhu vay, veri tong nghe OFDM, nha sir kat hqp cua cac song mang con ow giao truyEn song song veri cac icy hieu co khoang thtri gian dai dim bio rang luu luorng bang thong rOng kh8ng bi han cher' do mei truing khong theo tam nhin thing NLOS va nhitu do hien Wong da dutmg dn

2.3 Kt THU*T OFDMA

2.3.1 IChai nit'm

OFDMA (Orthogonal Frequency Division Multiple Access- Da truy nhap phin tin troc giao) la met ding nghe da song mang phit then doa tren nen ki thuat OFDM Trong OFDMA, met so cac song mang con, khong nhAt thiEt phai nim ke nhau, dugc gap Iai thanh mot kenh con (sub-channel) va cac user khi truy cap vao tai nguyen se duqc cap cho met hay nhieu kenh con dt truyEn !Man thy theo nhu

cau luu Wong cu the

-21-

OFDMA eel met s6 uu diem nhu la Ling kha fling linh hoot, thong Wong va tinh

on djnh dune cai Mien Viec an djnh cac kenh con cho cac thue bao cu the, viec truyen nhan tir met s6 thue bao co the xay ra deng then ma kh6ng can sv can thiep nao, do d6 se giiun thieu nhang tac d(mg nhu nhieu da truy xuat (Multi access Interfearence - MAI)

Di p a l ut pert

SOFDIAA

DI Dort UL part-

Userl User?

User3 User4

111 users

Hinh 2.5 ODFM va OFDMA

Hinh 2.6 mO to met vi du ve bang tin s6 - thai gian cua OFDMA, trong d6 co 7 ngueri dimg tir a den g va in& ngueri sir dung met phin xac djnh cua cac song mang phy co sin, khac veri nhang ngu&i can lai

- 22 -

Chuang 2: Ccic kJ; thrall dupe sze dung trong WiMAX

Hinh 2.6 Vi du czia b'iu do tan so, then■

gian vai OFDMA

Thi du cv the nay thvc to la scr hill hqp cria OFDMA va TDMA beri vi mui ngueri sir dung chi phat a mOt trong 4 khe thai gian, chira 1 hoc vai symbol OFDM 7 ngu&i sir dung tin a den g deu duqc d4t c6 djnh (fix set) cho the sang mang theo bein khe than gian

2.3.3 OFDMA nhily tan

Trong vi du truck cda OFDMA, moi ngtrai sir dung deu c6 mOt sv sap (tat c6 dinh (fix set) cho song mang Co the de ding cho phdp nhay cac song mang phu theo khe tired gian nhu d uqc mo to trong birth

Vic cho phep nhay vai cac mau nhay khac nhau cho mui user lam bien dti thvc

sv 110 thOng OFDM trong h0 thtng CDMA nhay tan Dieu nay co lqi la tinh phan tap theo tan s6 tang len beri vi meii user dung toan b0 bang thong co sin cling nhu lit

có lqi ve xuyen nhieu trung binh, dieu rat pht bien dti vai cac bi '6n the cda CDMA Bing each sir dung ma sira loi htreng di (Forward Error Correcting- FEC) tren cac bulk nhay, hg thong co thE sera cho cac song mang phu khi 131 fading sau hay cac sang mang b1 xuyen nhiZu beri cac user khk Do dac tinh xuyen nhieu va fading thay dOi yen mai btrerc nhiy, hg thtng phu thu(ic vao nang hrong tin hiOu nhan duqc

trung binh hon la php thugc vito user vi nAng lugng nhieu trong truing hqp Vitt

Slat

•

- 23 -

Chuang 2: Cac ky thudt duce sti dung trong WiMAX

tru diem ca ban dm hg th6ng OFDMA nhay tan ham hin cac hg th6ng CDMA va MC-CDMA la tuang d6i a ding loci b6 ductc xuyen nhiZu trong mot to bao bang each stir dvng cac mau nhay true giao trong mot to bao

DS-MOt vi dv cua viOc nhay tan nhu vOy doge mO to trong hinh 2.9 cho N sang mang phv, n6 luon luon co the do ra N mau nhay true giao

GI IFFT

Chuang 2: Ccic ky thu it &tor sit dung trong WiMAX

2.3.4 Hg thimg OFDMA

Dieu the bang ten g'c

Chen pilot symbol

Giii dieu the bang 4-

Can bang 4-

tan geic kenh

Tach pilot symbol

Khoi phmc kenh truyen

Hinh 2.8 Tang quan he Meng sir dung OFDMA

Ngu6n tin hie'u ducc dieu the er bang ten ca sti thong qua ck phucmg phap dieu

the nhu QPSK, MQAM Tin hieu din clueing (ban tin din duang, kenh hoa tieu pilot symbol) duce cher' vao ngu6n tin hieu, sau ci6 duk dieu the thanh tin hien OFDMA thong qua bin d6i IFFT va chen chuOi bao vg GI Luling tin hieu s6 duce chuyen thanh tin hieu tucmg tu try& khi truyen tren kenh vo tuyen qua anten phat Tin hieu My se bi anh hung beri fading va nhieu tang AWGN (Addictive White Gaussian Noise )

-Tin hieu den dtaing la mkt tin hieu ducm bitt truck er phis phat va phis thu, ducic phat kem veri tin hieu co ich nham Ichoi phvc kenh truyen vi dong bet he tilting

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Chuang 2: Ccic kji thudt &my sit dung trong WiMAX

Dia caries

1111111J1111tt11111111J1111111111111111i11111111111J11ii1111

Tdii Fromm/ tat

Hinh 2.9 Maru tin hieu din throng trong OFDMA

Phia may thu se thvc hien nguqc lai so vai may phat De khoi phvc tin hieu phat thi ham truyen phai duqc kh8i phvc nher vao mau tin clan duerng di kern Tin hieu nho'n duqc sau khi giii dieu the OFDMA duqc chia lam hai luting tin hieu Luting thu nhat la tin hieu c6 ich duqc dua dEn be can bang kenh Luling thir hai la mau tin dan dtr?mg duqc dua vao be khOi phvc kenh truyen, sau 46 lai duqc dua den be can bing kenh de khoi phvc lai tin hieu ban du

2.4 Dieu the thich nghi

Dieu the thich nghi cho phep he thong WiMAX dieu chinh so do dieu the tin hieu phv thuOc vao dieu kien SNR cua lien ket vo tuyen }Chi lien kat vo tuyen chat luting cao, so de dieu the cao nhat &Km sir ding, dua ra he thong dung lucing lon hon

BPSK

= 6dB, lbit/liz QPSK

( C SNR = 9dB, 2bit/Hz

16QAM SNR = 16 dB, 4 bit/Hz 64QAM

SNR = 22dB, 6 bit/Hz

HIM 2.10 Ban kink cell quan he yin diiu chi thich nghi

Trong qua trinh suy gian tin hieu, he thong WiMAX ca the djch den mot so de dieu the thip hem de" duy tri chit luting ket not va on dinh lien kat D0c diem nay cho phep he thong khic phvc fading Iva chop tired gian

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Chuang 2: Cdc ky thudt duot s►i dung trong WiMAX

2.5 Cling nghe sea loi

Cac Gong nghe sira 161 da dirge sir dung trong WiMAX de dat cac yeu cA'u v'e ti s6 tin hieu tren tap am he thong Cac thujt toan FEC, ma h6a xonn va then duqc dung

de phat ffien va sira cac 161 cal thien thong luqng Cac tong nghe sira 161 manh giap khoi phut cac khung bj 161 ma co the bi mat do fading Iva chqn tan s6 va cac lei cum Tv (tang you eau lap lai (ARQ) chive dung de sira 161 ma khong the duce sira Mai FEC, giri lai thong tin bj 16i Dieu nay co y nghTa cai thien chit ltrqng ti le 161 bit (BER) dti veri met mire ngtafmg nhu nhau

2.6 Dieu khien cling suit

Cac thuat toan dieu khien cling suit dirge dung de cai thien chit lucmg toan b'e he thong, no dirge thvc hien bai tram g6c girl th8ng tin dieu khien cling suit den m61 CPE de dieu chinh mire cling suet truyen sao cho mire da nhan a tram g6c thi a mot mire da xac dinh truerc Trong mei truing fading thay d6i &gig, mire chi tieu dA dinh truerc nay co nghia la CPE chi truyen du cling suet th6a man yeu cau nay Dieu khien cling suit giarn sv tieu thu cling suet tAng the cue CPE va nhieu vii nhang tram g6c cling vi tri Veri LOS, cling suit trig& cim CPE gin tucmg ang veri echoing each dm n6 den tram gee, veri NLOS, tuy thuec nhieu vao de ha vi vat can

2.7 Cic cling nghe anten tien tien

Cong nghe anten co the dung de cal then truyen din theo hai each — sir dung coring nghe phan tap va sir dung cac he thong anten va cac cling nghe chuyen mach tien tien Cac cling nghe nay co the cal thien tinh co clan va ti s6 tin hieu ten tap am nhung khong bao dam phat dart se khong bj inh huang cue nhieu

2.7.1 Nub tap thu va phit

Ck luqc de phan tap duqc sir dung de lqi dung cac tin hieu da cluang va phan xa xay ra trong cac mei truong NLOS Bing each sir dung nhieu kg ten (truyen va/hoac !Man), fading, nhieu va tein hao &rang truyen co the dirge lam giam Phan tap truyen sir dung ma than gian kh8ng gian STC DM veri phan tap nhan, cac citing nghe nhu ket hqp tS le tai da (MRC) mang lai uu diem cue hai duang thu rieng biet

Ve MISO (nhieu dAu vao met &Au ra)

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