Luận văn tốt nghiệp WiMAX - Lê Quang Đạo

7/29/2019 Lun vn tt nghip WiMAX - L Quang o

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B GIO DC V O TO

TRNG I HC BCH KHOA H NI

---------------------------------------

LUN VN THC S KHOA HC

CNG NGH WiMAX

NGHIN CU V XY DNG M HNH MU TRIN KHAI

CHO VNG A HNH C TH TI VIT NAM

NGNH: K THUT IN TVIN THNG

M S:23.04.3898

L QUANG O

Ngi hng dn khoa hc: TS. NGUYN XUN DNG

H Ni 2007


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LI CM N

thc hin tt lun vn tt nghip ny ti xin gi li cm n ti thy gio

TS. Nguyn Xun Dng tn tnh hng dn tn ti trong sut thi gian lm lun

vn va qua.

Ti cng xin gi li cm n ti tp th cng nh lnh o phng Tch hp v

pht trin h thng, lnh o cng ty in ton v truyn s liu (VDC) to iu

kin v mt cng tc giao cho ti nhim v trng nhm k thut th nghim Cng

ngh WiMAX ti Lo Cai ca cng ty m nh ti c th tip cn, nghin cu,

thit k, trin khai h thng WiMAX cng nh qu trnh nghin cu, nh gi cc

yu t k thut cng ngh, kinh t, x hi v gio dc t nhng d n th nghim

khi qut ha thnh nghin cu in hnh ng dng WiMAX trong vic mang

Internet tc cao v thoi VoIP ti cc khu vc c a hnh c th ca Vit Nam.

Bn cnh , ti cng xin gi li cm n ti nhng ngi bn ca ti t Tp

on Intel, c bit l TS. Bernd Nordhausen, chuyn gia cao cp v WiMAX ca

tp on Intel cng phi hp tt v gip ti rt nhiu trong qu trnh thc hin

nhng nghin cu thng qua vic trin khai d n th nghim WiMAX ti Lo Cai.

Cui cng ti xin gi li cm n ti cc thy c gio ca Khoa in t vin

thng, nhng ngi thn trong gia nh v bn b - nhng ngi hng dn, gip

ti sut thi gian hc tp ti trng cng nh trong vic hon thnh lun vn tt

nghip.


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Lun vn thc skhoa hc i

LI CAMOAN

Ti cam oan y l Lun vn nghin cu ca ti.

Cc s liu, kt qu nu trong lun vn l trung thc v cha tng c

cng b trong bt k Lun vn no khc. Cc s liu m phng c ch

thch, trch dn tham kho t bi bo, ti liu gc c th.

H ni, thng 10 nm 2007

Hc vin thc hin

L Quang o

L Quango, KTTVT 2005-2007,i hc Bch Khoa H Ni


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Lun vn thc skhoa hc ii

MC LC

LI CAM OAN ....................................................................................................... i

MC LC.................................................................................................................. ii

DANH SCH BNG BIU.......................................................................................v

DANH SCH HNH NH, HNH V V S................................................. vi

THUT NGV CHVIT TT....................................................................... vii

PHN MU.........................................................................................................1

CHNG I: GII THIU V CNG NGH WIMAX ...........................................3

1.1 Khi nim v mng khng dy bng rng ............................................................31.2 Cng ngh WiMAX ..............................................................................................5

1.2.1 WiMAX l g? ........................................................................................................5

1.2.2 Gii thiu cc chun IEEE 802.16..........................................................................8

1.2.3 WiMAX c cng nhn l chun ton cu.........................................................12

1.3 c im cbn ca WiMAX............................................................................14

1.3.1 c im Fixed WiMAX......................................................................................14

1.3.2 c im Mobile WiMAX ...................................................................................151.4 Tnh hnh th nghim, thng mi ha WiMAX trn th gii v ti Vit Nam 16

1.4.1 Th nghim v thng mi ha WiMAX trn th gii ........................................16

1.4.2 Th nghim WiMAX ti Vit Nam......................................................................18

1.5 Kt lun ...............................................................................................................19

CHNG II: C IM CNG NGH WIMAX...............................................20

2.1 WiMAX cnh - IEEE 802.16d-2004 ..............................................................21

2.1.1 Lp MAC..............................................................................................................212.1.2 Lp PHY...............................................................................................................30

2.2. WiMAX di ng - IEEE 802.16e - 2005 ...........................................................38

2.2.1 Lp PHY...............................................................................................................38

2.2.2 Lp MAC..............................................................................................................45

2.3 Kt lun ...............................................................................................................50

CHNG III: M HNH NG DNG V CC VN K THUT CN

QUAN TM KHI THIT K MNG WiMAX ................................................51

L Quango, CHTVT 2005-2007,i hc Bch Khoa H Ni


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Lun vn thc skhoa hc iii

3.1 M hnh trin khai WiMAX vi cc yu cu truy cp di ng ..........................51

3.2 M hnh trin khai WiMAX vi cc yu cu truy cp cnh...........................52

3.3 Cc vn k thut cn quan tm khi thit k v trin khai mng WiMAX. ....54

3.3.1 La chn bng tn.................................................................................................543.3.2 La chn phng thc song cng.........................................................................57

3.3.3 Tng lu lng, bn knh ph sng v s sector ca mi trm gc .....................61

3.3.4 Quy hoch v ti s dng tn s c tnh ton ti cc loi nhiu...........................63

3.3.5 Anten v cc cng ngh nng cao.........................................................................65

3.3.6 Qun l s di ng (i vi ng dng Mobile WiMAX)....................................73

3.3.7 Trung tm qun l.................................................................................................76

3.3.8 S kt ni mng WiMAX ................................................................................783.4 Kt lun ...............................................................................................................80

CHNG 4: NGHIN CU V XY DNG M HNH MU NG DNG

WiMAX CUNG CP DCH V INTERNET V THOI CHO KHU VC

A HNH C TH TI VIT NAM ............................................................81

4.1 Gii thiu d n th nghim WiMAX ti T Van ..............................................81

4.1.1 c im in hnh ca a im th nghim ......................................................82

4.1.2 Mc tiu ca vic nghin cu v xy dng m hnh mu trin khai ng dngthc tin t th nghim cng ngh WiMAX ti T Van ...............................................84

4.1.3 Chun WiMAX v thi gian th nghim .............................................................84

4.2 H thng WiMAX th nghim thc t ti x T Van.........................................85

4.2.1 c im cng ngh ca d n th nghim..........................................................85

4.2.2 Thit b WiMAX c th nghim ......................................................................85

4.2.3 Cc a im tham gia th nghim .......................................................................86

4.2.4 Cc ng dng c th nghim............................................................................884.2.5 Kin trc h thng.................................................................................................89

4.2.6 M hnh kt ni ti trm gc.................................................................................91

4.2.7 M hnh kt ni pha khch hng..........................................................................92

4.2.8 H thng VoIP trn nn WiMAX.........................................................................93

4.2.9 Ci t v cu hnh h thng WiMAX .................................................................97

4.3 Kt qu nghin cu, nh gi trn phng din k thut ca h thng WiMAX

th nghim.........................................................................................................1004.3.1 Kh nng bao ph ca mng...............................................................................100



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Lun vn thc skhoa hc iv

4.3.2 Kh nng qun l t xa ca h thng trin khai ti T Van................................100

4.3.3 n nh/tin cy ca h thng.........................................................................101

4.3.4 Tc truy nhp ti a/trung bnh t c ......................................................101

4.3.5 Cc ng dng chy tt trn nn WiMAX...........................................................102

4.3.6 tr ..................................................................................................................102

4.3.7 Jitter ca h thng v tinh...................................................................................102

4.3.8 Cht lng dch v VoIP trn nn h thng WiMAX:.......................................103

4.4 Kt qu nghin cu, nh gi v hiu qu kinh t x hi, gio dc v nng cao

dn tr .................................................................................................................104

4.4.1 Nhu cu s dng v li ch mang li t vic truy cp Internet tc cao ca

ngi dn nng thn l rt ln.....................................................................................104

4.4.2 Cch thc o to da trn phng thc truyn t kinh nghim thc t pht huy

hiu qu cao .................................................................................................................108

4.4.3 Chia s bng thng gia cc ngi dng khc nhau...........................................109

4.4.4 Bu in vn ha x v UBND x ng vai tr quan trng trong s thnh cng

ca vic mang bng thng rng ti ngi dn nng thn: ..........................................109

4.5 M hnh bn vng c khuyn ngh khi trin khai bng thng rng ti vng

nng thn Vit Nam ..........................................................................................110

4.5.1 M hnh k thut, cng ngh v cc i tng c th hng dch v bng

thng rng khng dy: .................................................................................................110

4.4.2 Cung cp ni dung thng tin c chun ha ti mi ngi dn.......................111

4.5.3 Chi ph u t h thng ban u v chi ph khai thc hng thng......................112

4.5.4 M hnh kinh doanh bn vng vi s h trca nh nc................................114

4.6 Kt lun .............................................................................................................115

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

TI LIU THAM KHO.......................................................................................117

TM TT LUN VN .........................................................................................119



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Lun vn thc skhoa hc v

DANH SCH BNG BIU

Bng 1.1: So snh cc chun IEEE 802.16..................................................... ......................................... 12Bng 2.1: Cc loi kho bo mt sdng trong IEEE 802.16-2004....................... ................................ 29Bng 2.2: Thng ssymbol OFDM theo chun 802.16-2004....................................................... ........... 32Bng 2.3: M sa lii vi cc phng thc iu ch..................................................... ..................... 34Bng 2.4: Kch ckhi bit xen k............................................................ .................................................. 35Bng 2.5: Thng sSOFDMA...................................................... ........................................................... . 41Bng 2.6: Cc phng thc iu chv M ha c htrtrong 802.16e.................... ...................... 42Bng 2.7: Tc dliu lp PHY Mobile WiMAX.................................................................................. 43Bng 2.8: Cc dch v WiMAX ding v QoS ........................................................ ............................... 47Bng 3.1: Phn btn scho cc cng ngh khng dy .................................................... ..................... 56Bng 3.2 Tc dliu cho cc cu hnh SIMO/MIMO.................................................. ..................... 71



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Lun vn thc skhoa hc vi

DANH SCH HNH NH, HNH V V S

Hnh 1.1 L trnh cng ngh WiMAX................................. ........................................................... ............. 5Hnh 1.2: M hnh mng WiMAX................................................................... ......................................... 14Hnh 1.3: Tng quan v tnh hnh trin khai WiMAX trn thgii. ....................................................... 16Hnh 1.4: Tn sc sdng trong cc h thng WiMAX trin khai trn thgii........................16Hnh 2.1 Vtr tngi ca cc lp MAC v PHY ........................................................... ..................... 20Hnh 2.2 Qu trnh phn loi MAC SDU ........................................................ ......................................... 22Hnh 2.3 Cu trc ca MAC PDU .......................................................... .................................................. 24Hnh 2.4 Cu trc symbol trong min tn s................................................... ......................................... 31Hnh 2.5 Cu trc symbol trong min thi gian ........................................................ ............................... 31Hnh 2.6 Qu trnh truyn-nhn ................................................... ........................................................... . 33Hnh 2.7 Qu trnh xen k................................................... ........................................................... ........... 34Hnh 2.8 Cu trc khung TDD......................................................................... ......................................... 37Hnh 2.9 Cu trc khung con ng xung TDD............................................................... ..................... 37Hnh 2.10 Cu trc khung con ng ln TDD........................................................ ............................... 38Hnh 2.11 Cu trc sng mang con OFDMA (min tn s) ......................................................... ........... 39Hnh 2.12 OFDM v OFDMA.................................................................................... ............................... 40Hnh 2.13 Hiu ng knh con ho (sub channelization) .................................................... ..................... 40Hnh 2.14:iu chthch nghi v m ha da trn khong cch vi BS ..............................................42Hnh 2.15: Cchyu cu lp li khi li xy ra ...................................................... ............................... 44Hnh 2.16: HtrQoS trong Mobile WiMAX.......................................................... ............................... 46Hnh 3.1: ng dnga dng ca Mobile WiMAX.............................................................. ..................... 53Hnh 3.2: Hai ch song cng TDD v FDD.............................................................................. ........... 57Hnh 3.3: Cu trc khung WiMAX OFDM..................................................... ......................................... 59Hnh 3.4: Minh ha khung OFDMA vi cu trc a vng...................................................................... 60Hnh 3.5: M hnh ti sdng tn s..................................................... .................................................. 63Hnh 3.6: Phn on tn strong mt cell ...................................................... ......................................... 64Hnh 3.7: Phn on ti sdng tn strong mt site gm 3 cell ..................................................... ..... 65Hnh 3.8: Vng ph sng ca Sector Antenna......... ........................................................... ..................... 66Hnh 3.9: Vng ph sng ca Omni Antenna........................................................... ............................... 66Hnh 3.10: CPE vi Anten tch hp bn trong........................................................... ............................... 67Hnh 3.11: CPE vi Anten ngoi......................................... ........................................................... ........... 67Hnh 3.12: Cng ngh to chm tia n................... ........................................................... ..................... 68Hnh 3.13: M ha khng gian thi gian ..................................................... ......................................... 69Hnh 3.14: H thng Anten MIMO........................... ........................................................... ..................... 70Hnh 3.15: H thng Anten MIMO 4x4........................................................... ......................................... 72Hnh 3.16: Chuyn mch thch ng cho Anten thng minh....... ........................................................... . 72Hnh 3.17: Chuyn giao cng HHO ....................................................... .................................................. 74Hnh 3.18: Chuyn trm gc nhanh (FBSS) ................................................... ......................................... 75Hnh 3.19: Chuyn giao phn tp MDHO.......................... ........................................................... ........... 76Hnh 3.20: Trung tm qun l mng WiMAX........................................................... ............................... 77Hnh 3.21: S kt ni ca mng WiMAX ................................................... ......................................... 78Hnh 4.1: Ton cnh thung lng T Van ........................................................ ......................................... 83Hnh 4.2: Thit bBS outdoor MicroMAX SOC..................................... .................................................. 86Hnh 4.3: Thit bBS Indoor SDA 4S Type II....... ........................................................... ..................... 86Hnh 4.4: Thit bu cui khch hng outdoor ProST......................................................................... . 86Hnh 4.5: Hnh nh v thit btrm gc BSc lp trn nc nh im BVHX ................................87Hnh 4.6: S phn ba l ca cc im thnghim............................................................. ........... 87Hnh 4.7: Hnh nh thc tthit bOut door pha khch hng ................................................... ........... 88Hnh 4.8: Kin trc mng v tuyn ti x T Van........................ ........................................................... . 89Hnh 4.9: M hnh trm gc BTS............................................................ .................................................. 91Hnh 4.10: Su ni thit bWiMAX ti trm gc ...................................................... ..................... 92Hnh 4.11: M hnh mt SS, nhiu ngi dng. ....................................................... ............................... 93Hnh 4.12: S thc hin cuc gi VoIP c n gin ha .................................................... ..... 95Hnh 4.13: S thc hin cuc gi VoIP ra thu bao PSTN................................................................ 95Hnh 4.14: Kt ni my tnh vi thit btrm gc cu hnh h thng.......................... ....................... 98Hnh 4.16: Giao din ca phn mm qun trmng Netspan ...................................................... ........... 99Hnh 4.17: Hnh nh ngi dn T Van truy cp Internet...................................... ............................. 105



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Lun vn thc skhoa hc vii

THUT NG V CH VIT TT

ACK ACKnowledge Bo nhn d liu

AK Authorization Key Kha cp php

AMC Adaptive Modulation and Coding iu ch v m ha thch ng

AP Access Point im truy cp

BPSK Binary Phase-Shift Keying Kha dch pha nh phn

BS Base Station Trm gc

BTS Base Transceiver Station Trm thu pht gc (trong mng di

ng t ong)

CC Convolutional Code M xon (M chp)

CID Conection IDentifier Nhn dng kt ni

CINR Carrier to Interference + Noise Ratio T s nhiu tpCP Cyclic Prefix Di bo v

CPE Customer Premises Equipment Thit b ti nh khch hng

CPS Common Part Sublayer Lp con phn chung

CQICH Channel Quality Indicator CHannel Knh ch bo cht lng knh truyn

CS Convergence Sublayer Lp con hi t

CTC Convolutional Turbo Code M xon Turbo

DAMA Demand Assinged Multiple Access a truy nhp cp pht theo nhu cu

DCD Downlink Channel Descriptor Ch bo knh ng xungDHCP Dynamic Host Configuration

Protocol

Giao thc thit lp a chng

DSL Digital Subscriber Line ng dy thu bao s

ETSI European Telecommunications

Standards Institute

Hip hi tiu chun vin thng Chu

u.

FBSS Fast Base Station Switching Chuyn trm gc nhanh

FCH Frame Control Header Tip u iu khin khung

FDD Frequency Division Duplexing Song cng chia theo tn sFDM Frequency Division Multiplexing Ghp knh phn chia theo tn s

FEC Forward Error Correction M sa li bn thu

FFT Fast Fourier Transform Bin i Fourier nhanh

FIR Finite Impulse Response p ng xung hu hn

HARQ Hybrid Automatic Repeat reQuest Yu cu lp tng kiu kt hp

HHO Hard Hand Off Chuyn giao cng

IDU InDoor Unit Thit b trong nh

IEEE Institute of Electrical and

Electronics Engineers

Hip hi ksin t v in



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Lun vn thc skhoa hc viii

IFFT Inverse Fast Fourier Transform Bin i Fourier nhanh ngc

IP Internet Protocol Giao thc lin mng

ISI Inter Symbol Interference Nhiu lin k hiu

ISM Industrial, Scientific, and Medical Di tn dnh cho cng nghip, khoa

hc v y t.ITP Internet Time Protocol Giao thc nh thi lin mng

LAN Local Area Network Mng ni b

LDPC Low Density Parity Check Kim tra chn l mt thp

LMDS Local Multipoint Distribution

System

H thng phn phi a im ni b

LOS Line Of Sight Trong tm nhn thng

MAC Medium Access Control Lp iu khin truy nhp ng

truynMAN Metropolitan Area Network Mng th

MDHO Macro Diversity Hand Over Chuyn giao phn tp vm

MIMO Multiple Input Multiple Output H thng a u vo a u ra

MS Mobile Station Trm di ng

NACK Not ACKnowledge Bo khng nhn hoc nhn sai d

liu bn pht

NLOS Non Line Of Sight Khng trong tm nhn thng

NMS Network Management Software Phn mm qun l mng

OFDM Orthogonal Frequency Division

Mutiplexing

Ghp knh phn chia theo tn s

trc giao

OFDMA Orthogonal Frequency Division

Multiple Access

a truy nhp phn chia theo tn s

trc giao

OSI Open Systems Interconnection M hnh lin kt cc h thng m

P2P Point to Point M hnh mng im - im

PAN Personal Area Network Mng c nhn

PDA Personal Digital Assistant My trgip s c nhn

PDU Protocol Data Unit n v d liu giao thcPHY PHYsical layer Lp vt l

PKM Privacy Key Management Giao thc Qun l kha bo mt

PMP Point to Multi Point M hnh mng im a im

PSK Phase - Shift Keying Kha dch pha

PSTN Public Switched Telephone Network Mng thoi cng cng

QAM Quadrature Amplitude Modulation iu ch bin cu phng

QoS Quality of Service Cht lng dch v

QPSK Quadrature Phase- Shift Keying Kha dch pha cu phng



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Lun vn thc skhoa hc ix

RLC Radio Link Control iu khin kt ni v tuyn

RS Reed- Solomon M Reed- Solomon

RSA Ronald Rivest, Adi Shamir, Leonard

Adleman

M ha theo kiu kha cng khai

SC Single Carrier iu chn sng mangSDU Service Data Unit n v d liu dch v

SNMP Simple Network Management

Protocol

Giao thc qun l mng n gin

SOFDMA Scalable Orthogonal Frequency

Division Mutiple Access

a truy nhp phn chia theo tn s

trc giao.

SS Subcriber Station Trm thu bao

SVC Switched Virtual Connection Kt ni chuyn mch o

TC Transmission Convergence sublayer Lp con hi t truynTDD Time Division Duplexing Song cng theo thi gian

TDM Time Division Mutiplexing Ghp knh theo thi gian

TDMA Time Division Mutiple Access a truy nhp phn chia thi gian

TFTP Trivial File Transfer Protocol Giao thc truyn tp tin

UCD Uplink Channel Descriptor Phn m t knh ng ln

UGS Unsolicited Grand Service Dch v cp pht t nguyn

UNII Unlicensed National Information

Infrastructure

C s h tng thng tin quc gia

min cp php

VoIP Voice over Internet Protocol Thoi qua giao thc lin mng

WAN Wide Area Network Mng din rng

WiFi Wireless Fidelity

WiMAX Worldwide Interoperability for

Microwave Access



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Lun vn thc skhoa hc 1

PHN MU

Gii thiu ti nghin cu

Hin nay cng ngh WiMAX l mt trong nhng cng ngh bng rng khng

dy c nghin cu, th nghim v trin khai rng ri trn ton th gii cng nh

Vit Nam.

Vi tc truy cp ln ti 70Mbps trong bn knh ph sng 40km ca chun

WiMAX cnh, cng nh kh nng duy tr kt ni vi tc di chuyn ln ti

120km/h ca WiMAX di ng, cng ngh WiMAX ni chung ha hn s mang li

cuc cch mng thc s trong vic thay i cch thc truy cp Internet ca con

ngi trong vi nm ti.

Vic th nghim k thut v nghin cu cc yu t kinh t, x hi nh hng

bi WiMAX ang c cc doanh nghip kinh doanh hng u trong lnh vc vin

thng nc ta nh: VNPT, Viettel, VTC, FPT, EVN tin hnh i vi WiMAX c

nh t thng 03 nm 2006 v WiMAX di ng t 01 thng 10 nm 2007 chng

t vai tr quan trng ca WiMAX trong chin lc pht trin ca cc doanh nghip

cng nh li ch mang li cho ngi tiu dng khng chthnh th m cn ti tt

c cc khu vc c coi l kh khn nht trn c nc.

Vic nghin cu m hnh trin khai WiMAX cho hai khu vc thnh th v

nng thn trn tt c cc kha cnh k thut cng ngh, kinh t x hi cng nh gio

dc l mt vn cp thit hin nay. Vic trin khai WiMAX ti khu vc thnh th

l mt iu c th d dng nhn nhn c li ch mang li cho c doanh nghip

cng nh ngi tiu dng.

Vy bi ton cn li l trin khai WiMAX cho khu vc nng thn, nhng khu

vc kh khn nht va hnh him trliu c kh thi trn tt c cc phng din

k thut cng ngh, kinh t, x hi hay khng? Lun vn ny si su phn tch v

tr li cho cu hi .



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Phm vi nghin cu v ni dung lun vn

Lun vn ny nghin cu mt cch tng quan nht v cng ngh WiMAX (C

di ng v cnh), m hnh ng dng v cc vn k thut cbn cn quan tm

khi tin hnh thit k, trin khai mng WiMAX vo thc t. Chng 4 ca lun vn

tp trung nghin cu v xy dng mt m hnh mu trin khai WiMAX v

nhng vng kh khn nht va l ca Vit Nam.

B cc v ni dung chnh ca lun vn:

- Chng I: Gii thiu tng quan v cng ngh WiMAX, cc c im

chnh ca WiMAX cnh, WiMAX di ng. Tnh hnh th nghim, trin

khai thng mi WiMAX Vit Nam cng nh trn ton th gii.- Chng II: i su nghin cu cc c t v lp vt l v lp MAC

ca cc chun WiMAX cnh (IEEE 802.16 2004) v WiMAX di ng

(IEEE 802.16e 2005).

- Chng III: M hnh trin khai ng dng WiMAX vi yu cu truy

cp di ng cng nh cnh v cc vn k thut cbn nht cn quan

tm khi thit k v trin khai mt mng WiMAX vo thc t.

- Chng IV: Nghin cu v xy dng m hnh mu trin khai ngdng WiMAX cung cp dch v Internet v thoi VoIP cho nhng ngi

dn nng thn, nhng vng c th kh khn va l in hnh ca Vit

Nam. Nghin cu cp mt cch ton din trn cc mt: k thut cng

ngh, kinh t x hi cng nh gio dc khi trin khai.



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CHNG I: GII THIU V CNG NGH WIMAX

Chng 1 cung cp mt ci nhn bao qut nht chng ta c th nm c

khi nim mng khng dy bng rng, cng ngh WiMAX l g, c im chung,

mc ch v vai tr ca n so vi nhng cng ngh ang tn ti. Bn cnh

chng ny cn cp ti tnh hnh ng dng WiMAX trn th gii v th nghim

WiMAX ti Vit Nam tnh n thi im thng 10 nm 2007.

1.1 Khi nim v mng khng dy bng rng

Mng khng dy

kt ni nhng thit b nh my tnh v my in, nhng mng my tnh

truyn thng i hi dy cp. Nhng dy cp th hin kt ni v mt vt l gia

nhng thit b nh hub, switch hoc nhng thit b khc to thnh mng. Mng

d liu khng dy kt ni nhng thit b m khng cn cp. Chng da trn nhng

tn s v tuyn truyn d liu gia cc thit b vi nhau. V pha ngi dng,

mng d liu khng dy lm vic ging nh h thng c dy. Ngi dng c th

chia s file v nhng ng dng, trao i e-mail, truy nhp my in, chia s truy nhp

Internet v thc thi cc tc v khc nh mng c dy.

Thno l bng rng?

Bng rng l khi nim th hin kh nng h trc hng t nh cung cp

ti khch hng (downstream) v t khch hng ti nh cung cp (upstream) vi tc

ti thiu l 200 kbps.

Ngy nay, nhu cu ca khch hng ngy cng cao gia tng. Ngi tiu dngkhng n thun ch mun truyn email, vn bn text, fax, m h mong mun s

dng cc dch va phng tin nh: hi ngh truyn hnh, nghe nhc, xem phim

trc tuyn, xem tivi trc tuyn, cc chng trnh trc tuyn trn mng....Khi tc

33,6Kbps, thm ch 56Kbps trn i cp ng bng phng thc dial-up khng

th trin khai cc dch v loi ny.

Hin ti, khi m tc ca mng lica cc nh cung cp dch v Internet

(ISP) c tng ng k, kh nng x l ti u cui pha khch hng cng ngy



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mt mnh th vic mng truy nhp vn hn ch nh vy s gy ra hin tng nghn

c chai (bottleneck). Vn c t ra l cn phi ci thin nt mng truy nhp

n p ng c nhu cu ca c nh cung cp dch v ln khch hng.

Cng ngh bng rngchnh l cc cng ngh sinh ra gii quyt vn vmng truy nhp. l thut ng ch bt k loi truy cp internet tc cao no.

Cng ngh bng rng cho php cc c nhn hoc t chc c th truy cp internet c

24 gitrong mt ngy, to mi trng cho vic s dng hoc cung cp cc dch v

cht lng cao.

c im ni bt ca mng khng dy bng rng

- c im u tin l cho php thay i, di chuyn, thu hp v mrngmtmng mt cch rt n gin, tit kim, c th thnh lp mt mng c tnhcht tm thi vi kh nng cng mm do cao, c th thit lp mng nhng khu vc rt kh ni dy, tit kim chi ph i dy tn km.

- c im th hai l nhanh, n cho php truy cp vi mt tc gp 10-20ln so vi phng php quay s thng thng, thm ch hn na. Khi tadng modem quay s, tc ch c tht t 30 n 50Kbps cn vi mtkt ni bng rng, tc ln ti t 256Kbps n 10Mbps, ph thuc vo

dch v m ta chn.- c im th ba l lun kt ni. Bt k khi no my tnh c bt ln th n

u trng thi kt ni vi internet. iu ny c ngha l khng phi lngph thi gian cho vic quay s v i modem kt ni mi ln mun vointerntet. S khng c chuyn b cnh bo mng bn hoc him khi b rt rakhi mng. Khng bt buc phi ngng dch vin thoi trong khi dngdch v internet. Tc l thu bao hon ton khng phi tr tin cho ngdy thu bao th hai. Hn th na cng c th chia s gia nhiu my vi

nhau thng qua mt kt ni internet.Trong 3 c im trn, c im ng ni nht ca cng ngh bng rng chnh

l tc . Chnh v t c tc cao nh vy nn c th trin khai c rt nhiu

cc dch v khc m vi cc kt ni quay s thng thng khng th lm c.

iu ny ng ngha vi vic thc y s pht trin ca internet, s pht trin ca

cc dch v x hi khc. C th k qua y mt s dch vng ch nh: dch

v cho php truyn cc tp tin vi dung lng ln, c th l tp vn bn, tp m

thanh, tp hnh nh, tp phim; cc dch v nhn tin nhanh (instant message); dch

v hi t tc cao (video conferencing).



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1.2 Cng ngh WiMAX

1.2.1 WiMAX l g?

WiMAX l tn vit tt ca Worldwide Interoperability for Microwave Access.

WiMAX l mt cng ngh khng dy bng rng, h trnhiu dng truy nhp

khc nhau: cnh hoc khng cnh. t ra nhng yu cu cho cc loi truy

nhp khc nhau ny, 2 phin bn ca WiMAX c IEEE nh ngha: phin bn

u tin da trn chun 802.16-2004, thch hp cho dng truy nhp cnh (Fixed

WiMAX); phin bn th 2 da trn chun 802.16e (c hp chun nm 2005), h

trcho dng di ng (mobile WiMAX).

L trnh ca cng ngh WiMAX c thc hnh dung qua hnh v 1.1:

Hnh 1.1 L trnh cng ngh WiMAX

Fixed WiMAXl cng ngh mng thch hp cho nhng thit b truy cp mngcnh ti ch, hoc c th di chuyn t ni ny qua ni khc nhng trong qu

trnh di chuyn th khng truy cp c mng (nu di chuyn chm th vn c th

truy cp). Cng ngh ny c nh ngha qua chun IEEE 802.16-2004 (bn chnh

thc)

Mobile WiMAX l mt gii php khng dy bng rng cho php hi t c

mng bng rng cnh v di ng s dng mt cng ngh truy cp bng rng

chung v mt kin trc mng mm do. Cng ngh mng h trcho cc ng dng



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di ng, cho php cc thit b c th di chuyn vi mt tc cao trong khi ang

truy nhp mng. Mobile WiMAX da trn chun 802.16e (c hp chun vo nm

2005). Chun 802.16e c nh ngha da trn chun 802.16d-2004 v c thm

nhiu c tnh mi u vit hn h trcho tnh nng di ng, cng ngh anten mi

nht cng c cp nht vo chun 802.16e.

WiMAX so vi mt scng ngh khc

Mng th MAN theo nh ngha l mng bao ph trn phm vi mt th.

V mt ng dng, trn mng MAN ngi ta c th trin khai cung cp thng tin cho

rt nhiu cc loi dch v cng cng khc nhau nh y t, vn ha, x hi V mt

kthut, mng MAN l tp hp ca rt nhiu cng ngh khc nhau, mi cng nghtng ng vi mt phn khc nhau trong mng. Cng ging nh cc mng LAN,

WAN, mng MAN chia lm hai loi: mng MAN c dy v mng MAN khng dy.

WiMAX l cng ngh cho mng MAN khng dy: c kh nhiu cng

ngh bng rng khng dy ra i, nhng cho ti nay, cha c mt cng ngh khng

dy bng rng no hng ti mc tiu cung cp tng hp cc gii php truy nhp

cho mng MAN mt cch ti u nh WiMAX. Cc cng nghi trc ch cung cpcc gii php n l, hng ti mt mc phn c th trong mng MAN v d nh

LMDS hay WiFi,

LMDS (Local multipoint distribution system): l cng ngh s dng di tn

trn 20GHz truyn sng. LMDS l mt chun hot ng di s hu thun ca

cc t chc quc t ATM Forum, ETSI, ITU,

di tn s ln, LMDS ch cho php truyn sng trong tm nhn thng (LOS)

trong phm vi vi cy s (5-7km). LMDS cho php trin khai cc dch v tc cao

nh thoi, video, Internet,

H thng LMDS c tc rt cao, hiu sut iu ch ca n c tht ti

5bit/Hz/s. LMDS ch thch hp vi cc mng trc, cc t chc doanh nghip c nhu

cu v tc ln. LMDS khng thch hp vi cc khch hng ring l, cc h gia

nh.



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WiFi: thc ra l cng ngh hng ti cc mng LAN khng dy nhng n vn

c th dng trin khai cho cc mng rng hn nh MAN.

Nhng chnh v n khng c thit k cho MAN nn vic trin khai n cho

mng MAN gp rt nhiu vn nh:

- Th nht, di tn lm vic ca 802.11 l di tn min ph, nhiu rt ln. Do

n hon ton khng thch hp vi vic trin khai cc dch v cng cng

cln.

- Th hai, 802.11 c thit k cho cc mng t thu bao, knh truyn ca n

cnh kch thc khong 20 MHz, rt km linh hot.

-

Th ba, 802.11 cha cung cp cch QoS, mt vn v cng quan trngi vi cc h thng mng a dch v.

- Th t, mc d nu ta truyn trong mi trng tt, t nhiu, LOS, s dng

cc Anten nh hng vi cng sut ln th WiFi c tht ti khong

cch vi km nhng phm vi bao ph nh th ny cng rt hp.

Nh vy, ch c s ra i ca WiMAX mi gii quyt c tt c cc loi dch

v cbn trn ca mng MAN. N c th s dng cc trm gc thit lp tuyn

trc, phn phi dch v ti khch hng ring l hoc thit lp nn cc vng truy

nhp dch v cho cc doanh nghip hoc a im cng cng.

Hin nay, WiMAX c xem l mt gii php ton din ca cng ngh khng

dy bng rng trong th, ngoi v nhng vng nng thn xa xi ho lnh

WiMAX cho php truyn khng dy cc loi d liu, hnh nh, m thanh nhanh hn

c DSL hay cable, v tt nhin l nhanh hn nhiu ln cc cng ngh khng dy

hin hnh nh 802.11a hay 802.11b m khng yu cu iu kin truyn thng.

Phm vi bao ph ca WiMAX c th ln ti vi chc km vi tc ln nht l

70Mbps. Bng thng ca WiMAX cung cp ng thi hng trm thu bao T1hoc hng trm thu bao DSL.

Hin nay, vic trin khai cc mng cable, DSL c th rt tn thi gian v tn

km, v kt qu l mt s lng ln khch hng c nhu cu m khng c cung

cp dch v. WiMAX khc phc hn ch ny, n c kh nng cung cp dch v

nhanh chng v d dng, ngay cnhng ni nh nng thn, rng ni, nhng

ni v cng kh khn v bt li i vi vic trin khai cc h thng c dy.

Trong tng lai, WiMAX sc tch hp vo cc thit b khng cnh nhmy xch tay, PDA,



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1.2.2 Gii thiu cc chun IEEE 802.16

Chun IEEE 802.16 - 2001

Nhng c t ban u ca chun IEEE 802.16 nh ngha lp MAC v PHYc kh nng cung cp truy nhp bng rng khng dy cnh (Fixed Fixed Wireless

Access) theo m hnh im - im v im - a im. Chun IEEE 802.16 c

thit k mra mt tp cc giao din khng gian (air interfaces) da trn mt giao

thc MAC thng thng nhng vi cc c t lp vt l ph thuc vo vic s dng

v nhng iu chnh ph c lin quan. Chun ny c m rng h trgiao din

khng gian cho nhng tn s trong bng tn 10 66 GHz. Vi phng php iu

chn sng mang 802.16 h trc hai phng php song cng phn chia theo thi

gian TDD (Time Division Duplexing) hay phn chia theo tn s FDD (Frequency

Division Duplexing).

Trong khi chun IEEE 802.11 dng phng php truy nhp nhy cm sng

mang c c ch trnh xung t (Carrier Sense Multiple Access with Collision

Avoidance - CSMA/CA) cho php khi no mt node trn mng c php

truyn d liu, th lp MAC ca IEEE 802.16-2001 s dng mt m hnh hon tonkhc iu khin s truyn dn trn mng. Trong thi gian truyn dn, phng

php iu chc n nh bi BS v chia s vi tt c cc node trong mng trong

thng tin broadcast cho cng ln v ng xung. Bng vic lp lch cho vic

truyn dn, vn cc node o c loi tr. Thu bao ch cn nghe tn hiu t

BS v sau l t cc node trong phm vi ph sng ca BS . Ngoi ra, thut ton

lp lch c th thay i khi xy ra qu ti hoc khi s thu bao tng ln qu nhiu.

Trm thu bao (Subscriber Stations - SS) c th thng lng v rng di

tn c cp pht trong mt burstto - burst c bn, cung cp mt lch truy nhp

mm do. Cc phng php iu chc nh ngha bao gm: PSK, 16-QAM v

64-QAM. Chng c th thay i t khung (frame) ny ti khung khc, hay t SS

ny ti SS khc tu thuc vo tnh trng ca kt ni. Kh nng thay i phng

php iu ch v phng php sa li khng ln ngc FEC (forward error

correction) theo cc iu kin truyn dn hin thi cho php mng thch ng nhanhchng vi iu kin thi tit, nh fading do ma. Cc tham s truyn dn ban u



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c tho thun thng qua mt qu trnh tng tc gi l Initial Ranging. Trong qu

trnh ny th nng lng, phng php iu ch v timing feedbackc cung cp

bi BS c kim sot v qun l theo iu kin hin thi ca kt ni.

Phng php song cng ca knh ng ln v ng xung c s dng

hon ton theo mt trong hai phng php TDD (time division duplexing) hoc

FDD (frequency division duplexing).

Quan trng hn na, chun IEEE 802.16-2001 kt hp cht ch cc c tnh c

kh nng cung cp cht lng dch v khc nhau xung lp vt l. Kh nng h tr

cht lng dch vc xy dng da theo khi nim v lu lng dch v (service

flows), n c xc nh mt cch va bi mt ID lu lng dch v. Nhng lulng dch v ny c m t bi cc tham s QoS ca chng nh thi gian tr ti

a v lng jitter cho php. Lu lng dch v l n hng v n c thc to

ra bi BS hoc SS.

ng vai tr ct li trong vic bo mt ca chun IEEE 802.16 l lp con

ring bit (privacy sublayer). Mc ch chnh ca lp con ring bit l cung cp s

bo mt trn cc kt ni khng dy ca mng. N c thc hin thng qua vic

mt m ho d liu gi gia BS v SS. ngn cn vic trm dch v, SS c th

c nhn thc qua chng ch s X.509. Chng ch ny bao gm kho cng khai

ca SS v a ch MAC.

Chun IEEE 802.16a

Nm 2003, IEEE a ra chun khng dy 802.16a cung cp kh nng truy

cp bng rng khng dy u cui v im kt ni bng bng tn 2-11 GHz vikhong cch kt ni ti a c tht ti 50 km trong trng hp kt ni im im

v 7-10 km trong trng hp kt ni tim a im. Tc truy nhp c tht

ti 70 Mbps. Trong khi, vi di tn 10-66Ghz chun 802.16 phi yu cu tm nhn

thng th vi di tn 2-11Ghz chun 802.16a cho php kt ni m khng cn tho

mn iu kin tm nhn thng, trnh c tc ng ca cc vt cn trn ng

truyn nh cy ci, nh ca. Chun ny s gip ngnh vin thng c cc gii php



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nh cung cp bng thng theo yu cu, vi thi gian thi cng ngn hay bng thng

rng cho h gia nh m cng ngh thu bao s hay mng cp khng tip cn c.

IEEE 802.16a bao gm cc t lp PHY v ci tin lp MAC cho kh nng

truyn dn a ng v gim ti a nhiu. Cc c tnh c thm vo cho php s

dng k thut qun l nng lng cao cp hn, v dy anten thch ng. Phng

php dn knh phn chia theo tn s trc giao OFDM (Orthogonal Frequency

Division Multiplexing_OFDM) cung cp thm mt s la chn cho phng php

iu chn sng mang. cung cp mt k thut gim thiu can nhiu trong cc

mng khng dy hin nay, IEEE 802.16a cng nh ngha thm phng php iu

cha truy nhp phn chia theo tn s trc giao (Orthogonal Frequency Division

Multiple Access OFDMA Modulation) trong phm vi di tn 2 11 GHz .

Vn bo mt cng c ci tin, vi rt nhiu c trng lp con ring bit

c a thm vo. Cc c tnh ring bit c s dng nhn thc tc nhn gi

(sender) ca mt thng ip MAC no .

IEEE 802.16a cng a thm cc tu chn h trcho mng Mesh, nhng

ni m lu lng c thc nh tuyn t SS ti SS. y l s thay i t ch

PMP, khi m lu lng chc php truyn gia BS v SS. S b sung nhng c

t lp MAC thch hp cho php vic lp lch truyn dn gia cc SS ca mng

Mesh m khng cn phi c s kim sot ca BS.

Chun IEEE 802.16c - 2002

Chun IEEE 802.16c c a ra vo thng 9/2002. Chun c nng cp ln

t chun 802.16 2001. Bn cp nht sa mt s li v s mu thun trong bntiu chun ban u v thm vo mt s profiles h thng chi tit cho di tn 10 66

GHz.

Chun IEEE 802.16d - 2004

Chun IEEE 802.16-2004 c chnh thc ph chun ngy 24/07/2004 v

c cng b rng ri vo thng 9/2004. IEEE 802.16 2004 thng c gi vi

tn 802.16-REVd. Chun ny c hnh thnh da trn s tch hp cc chun



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802.16-2001, 802.16a, 802.16c. Chun mi ny c pht trin thnh mt tp

cc c t h thng c tn l IEEE 802.16-REVd, nhng ton din phn loi

nh l mt s k tha hon chnh chun IEEE 802.16 ban u.

Chun 802.16d h trc 2 di tn s, cho php kt ni thc hin cc mi

trng khc nhau:

- Bng tn 10 66 Ghz: vi bng tn ny thng c dung trong mi trng

tm nhn thng (LOS). rng knh c khuyn ngh cho di tn ny l 25

n 28 MHz. N cung cp kh nng h tr tt trong nhng ng dng m

hnh im a im.

- Bng tn 2 11 GHz: vi bng tn ny thng c dng trong mi trngkhng trong tm nhn thng (NLOS). N cung cp kh nng h trtt trong

nhng ng dng m hnh Mesh.

Chun IEEE 802.16e 2005

Chun 802.16e - 2005 c t chc IEEE a ra vo thng 11 - 2005. y

l phin bn pht trin da trn vic nng cp chun 802.16 - 2004 nhm h tr

thm cho cc dch v di ng. Chun ny s dng k thut a truy nhp SOFDMA

(Scalable Orthogonal Frequency Division Multiplexing Access), k thut iu ch

a sng mang s dng knh ph. Bng tn c khuyn co dnh cho chun l


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Bng 1.1 so snh cc chun trong WiMAX

Bng 1.1: So snh cc chun IEEE 802.16

802.16 802.16-2004 802.16eDi tn s 10-66GHz


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bo cho cc nh khai thc v nh qun l trn ton th gii c th yn tm u t

vo bng thng rng di ng thc s dng cng ngh WiMAX. iu ny c bit

quan trng ti chu i vi bng tn 2.5 GHz. y cng l mt bc ngot quan

trng gip xo b cc hoi nghi lu nay v kh nng ng dng rng ri WiMAX ci thin vic pht trin bng thng rng cc nc ang pht trin ti chu ".

Trong bn thng co bo ch ca Hip hi Truyn thng V tuyn in Quc

t (WCA), Gim c Hip hi Steve Sharkey ca Motorola, trng nhm nghin

cu t vn cho WCA v cc t chc ng h khc trong lnh vc ny khng nh:

ITU c mt bc tin quan trng, m bo cng chng sc hng li t

cc cng ngh khng dy hin i nht hin nay, khi quyt nh a WiMAX voh cng ngh IMT-2000. ng thi ny em WiMAX ln ngang tm vi cc cng

ngh GSM v CDMA v m bo cho cc nh khai thc c th yn tm trin khai

cng ngh theo nhu cu ca ngi s dng ch khng phi b hn ch bi cc qui

nh qun l.

WiMAX v 3G

Vi vic c a vo h chun quc t IMT-2000, WiMAX ng nganghng vi 3G trong kha cnh chun ha quc t trin khai vo thc t.

Theo quan im ca ngi vit, WiMAX v 3G s song song tn ti, vi

nhng li th ring ca mnh:

- 3G s l xu hng chnh cho cc nh cung cp dch vin thoi di ng

ang s dng h thng GSM mun cung cp ti khch hng ca mnh kh

nng truy cp Internet nh l mt dch v gia tng, trn nhng thit b cm

tay nh gn.

- WiMAX s l xu hng chnh cho cc nh cung cp dch v Internet, mun

khng dy ha cc dch v truyn dn ca mnh thay cho h thng cp c chi

ph u t, duy tu bo dng ln. Bn cnh WiMAX cng c th cung

cp dch v thoi VoIP. Vt qua 3G v kh nng iu ch, WiMAX c th

cung cp dch v d liu ln gp 5-10 ln so vi 3G lm li th cnh tranh

vi 3G trong thin hng cung cp dch v d liu vi ngi dng s dng

Laptop v PDA cng nh truy cp Internet khng dy cnh.



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1.3c im c bn ca WiMAXChng ta c th hnh dung c ch hot ng ca mng WiMAX nh mng

in thoi di ng. Ngha l c mt tng i pht sng v mt mng li cc trm

pht WiMAX ph sng n tng ngi dng cui. Phm vi ph sng ln nhtca trm WiMAX t 50km.

Hnh 1.2: M hnh mng WiMAX

V cng ngh WiMAX h trcho c dng truy nhp cnh (Fix) v di ng

(mobile) nn h thng WiMAX cng c nhng c im khc nhau i vi 2 dngtruy nhp khc nhau ny.

1.3.1 c im Fixed WiMAX

- Khong cch gia trm thu v pht c th ti 50km.

- Tc truyn c th thay i, ti a l 70Mb/s.

- Hot ng trong c 2 mi trng truyn dn: ng truyn tm nhn thng

LOS v ng truyn che khut NLOS.

- Di tn lm vic 2-11GHz v 10-66GHz.

- Hng truyn tin oc chia thnh 2 ng ln v xung. Phn chia ng

ln v xung c th dng c 2 cng ngh: TDD v FDD.

- Fixed WiMAX s dng phng php iu ch OFDM, nh ngha kch

thc ca FFT l 256 vi 192 sng mang d liu, 8 sng mang dn ng v

55 sng mang bo v.



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- Cc phng php iu ch sc s dng l: QPSK, 16QAM, 64QAM;

dng phi hp cc phng php m ha sa li l m khi (Reed Salomon)

v m xon (m chp) CC.

-

rng bng tn ca WiMAX t 5MHz n trn 20MHz c chia thnhnhiu bng con 1,75MHz. Mi bng con ny oc chia nh hn na nh

cng ngh OFDM, cho php nhiu thu bao c th truy cp ng thi mt

hay nhiu knh mt cch linh hat m bo ti u hiu qu s dng bng

tn.

- V cu trc phn lp, h thng WiMAX oc chia thnh 4 lp: Lp con hi

t (convergence layer) lm nhim v giao din gia lp a truy nhp v cc

lp trn, lp a truy nhp (MAC layer), lp bo mt (Security) v lp vt l

(Physical). Cc lp ny tng ong vi hai lp di cng ca m hnh OSI

v oc tiu chun ha c th giao tip vi nhiu ng dng lp trn.

1.3.2 c im Mobile WiMAX

- Khong cch gia trm thu v pht trong khong 1.7 5 km.

- Tc truyn: 10 30Mb/s

-

Khng yu cu truyn trong tm nhn thng- Di tn lm vic ca Mobile WiMAX tp trung trong khong tn s di

6GHz ( 2,3 GHz; 2,5 GHz; 3,3 GHz; 3,5 GHz)

- rng bng tn ca h thng t 1,25 20MHz

- ng ln v xung c thc phn chia theo cng ngh TDD hoc FDD,

nhng TDD c khuyn ngh s dng nhiu hn v nhng tnh nng u vit

ca n.

- im khc bit r nt so vi Fixed WiMAX l Mobile WiMAX s dng

cng nghiu ch h tra truy nhp Scalable OFDMA (S- OFDMA), cho

php thay i kch thc FFT tc l thay i s sng mang con. S sng

mang con c th l 128, 512, 1024 hay ln nht l 2048. S sng mang con

ny oc chia thnh cc knh con vi s lng knh con ln nht l 32.

- Mobile WiMAX s dng phng php iu ch v m ha thch ng, h tr

cc kiu iu ch QPSK, 16 QAM, 64 QAM. Phng php m ha sa li

dng m xon CC (Convolutional Code) v m CTC (Convolutional TurboCode



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1.4 Tnh hnh th nghim, thng mi ha WiMAX trnth gii v ti Vit Nam

1.4.1 Thnghim v thng mi ha WiMAX trn th gii

Tnh n thi im thng 9 nm 2007, trn th gii c hn 300 th nghim

WiMAX v hn 95 h thng WiMAX thng mi.

Hnh v 1.3 di y th hin cc h thng WiMAX c pht trin trn

th gii (ngun: Tp on Intel):

Hnh 1.3: Tng quan vtnh hnh trin khai WiMAX trn thgii.

Trong hnh v trn, tn sc th nghim c th hin bng mu sc nh

trong hnh 1.4 sau:

Hnh 1.4: Tn sc sdng trong cc h thng WiMAX trin khai trn thgii



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Trong ba di tn sc s dng th nghim v xy dng h thng thng

mi tnh n thng 09 nm 2007, chng ta c th thy:

- Tn s 3.3-3.8 Ghz c s dng nhiu nht. Tn s ny c s dng nhiu

Chu u, Chu , Chu Phi v Nam M.- Tn s 2.3 2.7 Ghz c s dng nhiu M, Nht v mt s nc

ng Nam .

- Tn s 5.0-6.0 Ghz, l tn s khng cn cp php, tng t nh di tn s

2.4Ghz ca WiFi, c s dng mt s ni, nhiu nht l Nga.

Thng 09 nm 2007 cc hng Acer, Lenovo, Asus, Matsushita cng b k

hoch bn my tnh xch tay gn chip WiMAX Centrino ca Intel h trchun kt

ni Internet khng dy din rng WiMAX mang tn Montevina vo nm 2008. Cc

my tnh xch tay ny sc tch hp chip tch hp c WiFi v WiMAX, to iu

kin cho ngi dng u cui c th d dng la chn kt ni vi mt trong hai

cng ngh trn.

M, Hn Quc v Nht l nhng nc i tin phong trong vic ng dng

WiMAX vo thng mi ha. Cc nc ny cam kt bng cng ngh WiMAX, h

s mang bng thng rng khng dy ti mi min ca t quc, t thnh ph cho ti

nhng khu vc xa xi ho lnh, cc hi o xa xi.

Hin ti mi nc u quyt nh u t nhiu t la cho nhiu d n

thng mi ha Mobile WiMAX, tiu biu nh:

- M: Hng in thoi Sprint u t 5 t USD trin khai WiMax ti 30

thnh ph v d kin 100 triu dn sng k thu bao dch v.

- Nht Bn: Ngy 18 thng 9 nm 2007, Tp on KDDI, Tp on Intel,

Cng ty ng st ng Nht Bn, Tp on Kyocera, cng ty DaiwaSecurities Group Inc, v Ngn hng Tokyo-Mitsubishi UFJ tuyn b cng

u t vo mt lin doanh c tn l Wireless Broadband Planning

K.K.(WBPK). WBPK d kin trthnh mt cng ty hng u th gii trong

lnh vc pht trin v trin khai cc dch v mi da trn cng ngh WiMAX

di ng, ng thi dnh s cung cp cc dch v ny trn ton cu thng

qua cc tha thun chuyn vng quc t.

- Hn Quc: SK telecom v Korean telecom l hai hng i u ng dngWiMAX vo thng mi ha. T nm 2006, Hn quc s dng WiBro



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mt bin th ca WiMAX cung cp dch v truy nhp bng thng rng

khng dy.

1.4.2 Thnghim WiMAX ti Vit Nam

Thnghim WiMAX cnh:

Thng 03 nm 2006, B bu chnh vin thng Vit Nam cp php cho 4 Tng

cng ty, tp on th nghim Fixed WiMAX di tn s 3.3-3.4Ghz gm:

- Tp on bu chnh vin thng Vit Nam VNPT

- Tng cng ty truyn thng a phng tin VTC

- Tng cng ty vin thng qun i Viettel

- Tp on FPT

Sau , cng ty vin thng in lc EVN cng c cp php th nghim

Fixed WiMAX.

Vi giy php th nghim c B BCVT cp ngy 17 thng 03 nm 2007,

Tp on VNPT giao cho Cng ty in ton v truyn s liu VDC tin hnh

nghin cu th nghim v nh gi Fixed WiMAX thng qua D n th nghimWiMAX c phi hp thc hin vi Tp on Intel, Qu h trpht trin quc t

M (USAID) trin khai ti Thnh Ph Lo Cai. D n ny c hai pha thc hin

khc nhau:

- Pha th nghim th nht: Trin khai ti Thnh ph Lo Cai vi mt trm gcc ni vi POP VNN ti bu in Lo Cai kt ni vi Internet. Haimi trm thu bao c trin khai trong ni thnh v ngoi thnh ca

Thnh ph. H thng thit b WiMAX th nghim c cung cp bi hngAlvarion, Israel.

- Pha th nghim th hai: Trin khai ti x T Van, l mt x vng su, vngxa ng s i li rt kh khn, l mt trong nhng x c h tng vin thngyu km nht ca tnh Lo Cai, khi ch ch 02 ng in thoi PSTN vy

ban nhn dn x v im bu in vn ha x. Sng di ng ti y l camt BTS cch 10km, vt qua a hnh him trvi nhiu dy ni caonn sng rt yu v chp chn. Pha th nghim th hai ny l mt in hnh

nghin cu v cc mt cng ngh, li ch x hi cng nh bi ton kinh tkhi s dng WiMAX a bng thng rng v nhng vng xa xi ho



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lnh, nhng ni m cc cng ngh truyn thng c kh c th phc vc. H thng thit b WiMAX th nghim c cung cp bi hngAirspan, M.

Cc n v cn li cng c nhng th nghim v nh gi ca ring mnh.Tuy nhin thng tin v cc th nghim ca cc n v trn chc cc phng tin

thng tin i chng a tin mt cch chung chung, khng c th nn ti khng tng

kt vo phn vit ca Lun vn ny.

Thnghim Mobile WiMAX:

Ngy 01 thng 10 nm 2007, chnh ph cp php th nghim Mobile

WiMAX ti Vit nam trong vng 01 nm cho 5 nh cung cp dch v, trong :- Tp on Bu chnh vin thng Vit Nam VNPT s th nghim ti di tn s

2.5Ghz.

- Bn doanh nghip s th nghim di tn 2.3Ghz l: Tng cng ty vin

thng qun i Vietel, Tng cng ty truyn thng a phng tin, Tp on

FPT, Cng ty vin thng in lc EVN.

Tp on bu vin thng Vit Nam VNPT d kin s trin khai th nghim

Mobile WiMAX H Ni, Thnh ph H Chnh Minh v Nng vi thit b th

nghim c cung cp bi hng Motorola, M.

1.5 Kt lun

Vi s lng ln hn 400 d n th nghim v trin khai thng mi trn ton

th gii tnh n thng 09 nm 2007, cam kt ca cc nh sn xut v quan trng

nht l vic ITU a WiMAX vo h chun cng ngh IMT-2000, chng ta c th

nhn thy rng nm 2008 s l nm bng n ca WiMAX trn th gii, c bit l cc quc gia M, Hn Quc, Php v Nht, nhng nc nc i u trong nhng

ng dng WiMAX phc v mc ch thng mi ha.

Ti Vit Nam, nm 2008 ha hn s l nm m cng ngh WiMAX s hon

thnh giai on th nghim v tng bc c thng mi ha. Theo nhn nh ca

ngi vit lun vn ny th cui nm 2008 n nm 2009 WiMAX sc ng

dng rng ri Vit Nam.



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CHNG II:CIM CNG NGH WIMAX

Chng 2 ca lun vn cp n nhng vn : bng tn WiMAX s dng,

cc m t k thut ca chun WiMAX (fixed v mobile)

Cng ging nh cc b chun khc h 802 ca IEEE, 802.16 ch tp trung vo

vic m t v chun ha hai lp lin kt d liu (Datalink Layer) v lp vt l

(Physical Layer) trong m hnh OSI. Hnh 2.1 th hin v tr tng i ca cc lp

MAC v PHY trong WiMAX.

Hnh 2.1 V tr tngi ca cc lp MAC v PHY

Slc v cc lp trong chun 802.16 ni chung:

Lp MACm t trong 802.16 bao gm ba lp con (Sublayer): lp con hi t

(CS), lp con MAC (CPS) v lp con bo mt.

Lp CS cung cp bt c vic chuyn i hoc nh x t cc mng m rng

khc nh ATM, Ethernet, thng qua mt im truy nhp dch v SAP. Chnh xc

hn, lp ny lm nhim v chuyn i cc gi tin t cc nh dng ca mng khc

thnh cc gi tin nh dng theo 802.16 v chuyn xung cho lp CPS. Cng ti

y s din ra s phn lp dch v ca cc mng ngoi nh x vo mt dch v

thch hp trong 802.16

Lp CPS cung cp cc chc nng chnh ca lp MAC, l cc chc nngnh truy nhp, phn b bng thng, thit lp, qun l kt ni. N s nhn d liu t



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cc CS khc nhau phn lp vo mt kt ni MAC ring. Cht lng dch v

cng sc p dng trong vic truyn v sp xp d liu.

Lp con bo mt cung cp cc cch chng thc, trao i kha v m ha.

Lp vt lbao gm rt nhiu cc nh ngha khc nhau, mi ci thch hp cho

mt dy tn s v ng dng ring.

Sau y s trnh by nhng c im chnh v lp MAC v PHY trong hai

chun WiMAX cnh (IEEE 802.16d-2004) v WiMAX di ng IEEE 802.16e-

2005).

2.1 WiMAX cnh - IEEE 802.16d-2004

2.1.1 Lp MAC

2.1.1.1 Lp con hi t CS

Khi nim CID: Mt kt ni c hiu l mt nh x t MAC-BS ti MAC-

SS vi mc ch vn chuyn lu lng ca mt loi dch v. Mi kt ni c xc

nh bi mt CID l vit tt ca chConnection Identifier, c di 16bit.

Lp con hi t CS thi hnh mt s cc chc nng nh nhn cc PDU t lp

cao hn, phn lp dch v cc PDU , ty theo cc dch v m x l cc PDU,

phn phi cc PDU ny xung lp con MAC thng qua mt im SAP thch hp.

Tuy nhin, nhim v chnh ca lp ny l phn loi cc n v dch v d liu

SDU, nh x n vo mt kt ni MAC ph hp, tc l vo mt CID, m bo cho

vic x l QoS. m bo thc hin c iu ny, lp CS c th s dng cc

thut ton tinh vi nh x hoc cng c th thm, thay i tiu mi gi tin calp trn x l. Hin ti ch c hai nh ngha c c cung cp trong 802.16:

ATM CS v Packet CS. ATM CS c nh ngha cho cc dch v ATM cn

Packet CS c nh ngha cho cc dch v gi nh Ipv4, Ipv6, Ethernet, VLAN,

ATM CS nhn cc t bo ATM, x l, phn lp dch v v phn phi n xung

lp di.

Packet CS phn lp cc loi MAC SDU vo kt ni thch hp, g, thm cc

tiu , phn phi d liu n lp con MAC, nhn d liu t lp con MAC ri x l.



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Cc MAC SDU sc phn loi bng cch nh x n vo mt kt ni ring,

iu cng c ngha l MAC SDU sc nh x vo mt lung dch v ring,

c cc c im QoS ring. Hnh 2.2 th hin qu trnh phn loi MAC SDU.

Hnh 2.2 Qu trnh phn loi MAC SDU

2.1.1.2 Lp con MAC CPS

S trao i gia cc BS v SS trong mt vng thng c my dng kin trc

l P2P, PMP v Mesh.

- Kin trc P2P xy ra khi ch c mt BS v mt SS, cc kt ni xy ra giatng cp BS, SS.

- Kin trc PMP l s c mt kt ni gia mt BS vi nhiu SS khc nhau. So

vi P2P th PMP c kh nng phc v cao hn, hiu sut tt nhng phm vi

bao ph thng hp hn nhiu. Kin trc PMP trong trin khai thng c

t chc thnh cc vng (sector) v n h trtt trong truyn thng multicast.

- Kin trc Mesh l kin trc m bao gicng c mt ng lin kt gia hai

im bt k.

Mc d 802.16- 2004 h trc ba kiu kin trc trn nhng PMP l kin trc

c quan tm nht. Kin trc ny c mt BS lm trung tm s cung cp kt ni

cho nhiu SS. Trn ng xung (downlink), d liu a ti SS c hp knh

theo kiu TDM. Cc SS chia sng ln theo dng TDMA.

MAC 802.16 theo kiu hng kt ni (connection-oriented). Tt c nhng

dch v bao gm nhng dch v khng kt ni (connectionless) c hu, c nh xti mt kt ni. iu cung cp mt cch cho yu cu di thng, vic kt hp



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QoS v cc tham s v lu lng, vn chuyn v nh tuyn d liu n lp con

quy t thch hp v tt c cc hot ng khc c lin quan n iu khon hp ng

ca dch v. Cc kt ni c tham chiu n cc CID 16-bit (16-bit connection

identifier) v c th yu cu lin tip di thng c cp pht hay di thng theo

yu cu.

nh a chv kt ni

Mi SS s c mt a ch cng gi l a ch MAC 48bit, ging nhc nh

ngha trong 802 ni chung. a ch ny l duy nht cho thit b trn ton th gii.

N c s dng trong qu trnh khi to kt ni. N cng c thc dng

chng thc gia BS v SS vi nhau.

Lc vo mng, SS c gn ba kt ni qun l (management connection) cho

mi hng (Uplink hoc Down link). Ba kt ni ny phn nh ba yu cu QoS khc

nhau c s dng cho ba mc qun l khc nhau gia BS v SS. Kt ni u tin

l kt ni cs(basic connection) c dng truyn cc thng ip ngn, time-

critical MAC v RLC (radio link control). Kt ni qun l s cp (primary

management connection) c s dng truyn cc thng ip di hn, chu tr

nhiu hn nh nhng g c s dng chng thc v ci t kt ni. Kt ni

qun l th cp c s dng truyn cc thng ip qun l da trn csccchun nh DHCP (Dynamic Host Configuration Protocol), TFTP (Trivial File

Transfer Protocol) v SNMP (Simple Network Management Protocol). Ngoi

nhng kt ni qun l ny, cc SS c cp pht cc kt ni vn chuyn (transport

connection) cho cc dch v k hp ng. Nhng kt ni vn chuyn theo mt

hng duy nht n gin ho cc tham s QoS ng ln v ng xung khc

nhau v cc tham s lu lng. Ngoi ra MAC cn d tr cc kt ni b sung cho

nhng mc ch khc nh s truy nhp lc khi u trn cscnh tranh, s truynqung b (broadcast) cho ng xung hoc s kim tra tun t (polling).

nh dng MAC PDU

MAC PDU l n v d liu c dng trao i thng tin gia cc lp

MAC ca BS v SS. MAC PDU c hai dng, dng thng thng v dng yu cu

bng thng. MAC PDU thng thng bt u bi mt tiu c chiu di cnh.

Tip theo l ti (payload), ti c di thay i, chnh v vy m MAC PDU cng



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c chiu di thay i. V cui cng l m CRC. MAC PDU yu cu bng thng th

ch c phn tiu m thi.

Hnh 2.3 di y m t dng ca MAC PDU

Hnh 2.3 Cu trc ca MAC PDU

Mi MAC PDU bao gm phn tiu c chiu di cnh. Tip theo l ti, ti

thng thng bao gm cc tiu con (subheader) v MAC SDU. Ti cng c th

c di bng 0 trong trng hp l MAC PDU dng yu cu bng thng.

CRC (Cyclical Redundancy Checking) l m vng kim sot li cho c phn header

v payload trong MAC PDU tng ng vi n. CRC chc gn vo MAC PDU

khi l MAC PDU thng thng (cha thng tin qun l hoc d liu). Nh vy,

MAC PDU yu cu bng thng khng c bo v bng CRC.

Qu trnh xy dng MAC PDU

Trc khi c truyn i, lp MAC s phi xy dng MAC PDU mt cchhp l v hiu qu nht. Qu trnh ny bao gm cc bc sau:

- Qu trnh mc ni: Nhiu MAC PDU c thc kt hp vi nhau vo mt

phin truyn ( PDU d liu, PDU yu cu bng thng,). Qu trnh ny c

th thc hin cng ln v ng xung.

- Qu trnh phn mnh: Qu trnh ny chia mt MAC SDU c kch thc ln

thnh nhiu MAC PDU c kch thc hp l hn. Qu trnh ny c s

dng i vi cc dch v m gi tin c kch thc ln, nh voice, video,..c dng khai thc mt cch hiu qu bng thng lin quan n cht

lng dch v. N c thc thc hin cng ln v ng xung.

- Qu trnh ng gi (packing): Qu trnh kt hp nhiu MAC SDU thnh mt

MAC PDU. Cc kt ni phi cho php mang cc gi tin c kch thc thay

i khai thc c hiu qu tnh nng ny.



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C hai qu trnh phn mnh v ng gi c thc bt u bi mt BS cho

mt kt ni ng xung hoc mt SS cho mt kt ni ng ln. Hai qu trnh ny

c cho php ng thi c th s dng di thng mt cch hiu qu.

Yu cu di thng v cp pht

Khi vo mng, mi SS oc gn n 3 CIDs cho cc mc ch gi v nhn

nhng thng ip iu khin. 3 cp kt ni CID ny c s dng phn bit cc

mc QoS ca cc kt ni khc nhau. Yu cu tng hoc gim bng thng rt cn

thit cho tt c cc dch v ngoi tr kt ni UGS (dch v cp pht t nguyn) c

tc bit khng i. Ngoi ra cc kt ni khc c nhu cu tng hoc gim bng

thng ph thuc vo lu lng truyn.

Khi mt SS cn yu cu bng thng trn mt kt ni vi dch v lp lch BE

(Best Effort), n gi mt thng ip n BS bao gm nhu cu tc th v kt ni

DAMA (DAMA l mt dch v cung cp ti nguyn khi SS pht sinh nhu cu). QoS

cho kt ni c to lp ti lc thit lp kt ni v c tm kim bi BS.

HtrPHY v cu trc khung

MAC IEEE 802.16-2004 h trc TDD ln FDD. S la chn gia hai cng

ngh song cng ny c nhng nh hng nht nh n thng s lp PHY cng nhtc ng n cc c t h trca MAC.

h thng FDD, ng ln v ng xung c t nhng tn s ring

bit, d liu ng xung c thc pht "continuous" (lin tc) hoc theo tng

"burst" (khng lin tc). Cc ng xung continuous c tnh n cc k thut

nng cao hiu sut nh interleaving (chn). Cc ng xung burst (hoc FDD

hoc TDD) cho php s dng nhiu k thut nng cao kh nng v dung lng hn

nh burst-profiling thch ng mc thu bao v cc h thng ngten ci tin.

MAC xy dng khung con (subframe) ca ng xung bt u vi mt on

iu khin khung c cha cc thng ip DL-MAP v UL-MAP. Chng ch ra

nhng chuyn tip PHY trn ng xung cng nh nhng nh v di thng v cc

burst-profile ng ln.

DL-MAP lun c thng dng cho khung hin thi v lun c di ti thiu

l hai block FEC. S chuyn tip PHY u tin c biu th trong block FEC utin, cho php thi gian x l thch ng. Trong c hai h thng TDD v FDD, UL-



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MAP cung cp cc nh v bt u khng mun hn khung ng xung tip theo.

Tuy vy, UL-MAP c thnh v s khi u khung hin thi, min l nhng thi

gian x l v nhng tr ton phn (round-trip delay) phi c gim st.

iu khin Kt ni Radio (RLC- Radio Link Control)

Cng nghc ci tin ca PHY 802.16-2004 i hi RLC nng cao, c

bit kh nng PHY chuyn tip t mt burst-profile ti mt burst-profile khc.

RLC phi iu khin kh nng ny cng nh cc chc nng RLC truyn thng.

Uplink Scheduling Services (cc dch v lp lch ng ln) - Mi kt ni theo

hng ng ln c nh xn mt scheduling-service. Mi scheduling-service

lin quan n mt tp cc quy tc da trn trnh lp lch BS (BS-scheduler) chu

trch nhim cp pht dung lng cho ng ln v giao thc cp pht theo yu cu

gia SS v BS. c t chi tit cc quy tc v scheduling-service c dng cho mt

kt ni ng ln c th c tha thun ti thi gian ci t kt ni.

Dch v cp pht t nguyn UGS (unsolicited grant service) c bin i

mang li cc dch v to ra nhng n v cnh d liu theo chu k. Khi c s

dng vi UGS, u mc con qun l cp pht gm poll-me bit cng nh slip

indicator flag(cbo li) cho php SS bo co rng hng i truyn b n do ccyu t nh mt s cp pht hay lch gigia h thng v mng bn ngoi. Nhvo

s pht hin slip indicator flag, BS c th cp pht dung lng b sung no cho

SS, cho php n hi phc trng thi hng i trung bnh. Nhng kt ni c cu

hnh vi UGS th khng c php s dng nhng chi truy nhp ngu nhin cho

cc yu cu.

Qu trnh khi to v i vo mng

H thng h trnhng th tc cho qu trnh ng k vo mng ca mt SS

mi. Th tc ny bao gm nhng pha nh sau:

- Sthu nhn knh (Channel Acquisition):

Giao thc MAC bao gm mt th tc khi to c thit k loi tr nhu

cu cu hnh th cng. Vo lc ci t, mt SS bt u qut danh sch tn s ca n

tm ra mt knh hot ng. N c thc chng trnh ho ng k vi mt

BS xc nh, tham chiu n mt broadcast ID BS (c kh nng chng trnh ho).



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Sau khi quyt nh trn knh no, SS c gng th ng b ho s truyn

ng xung do pht hin ra cc on u khung theo chu k (periodic frame

preambles). Mt khi lp vt l c ng b ho, SS s tm kim nhng thng bo

UCD v DCD qung b nh k cho php SS nhn bit siu ch v cc k hoch

FEC s dng trn sng mang.

- Chng thc v ng k SS:

Mi SS c cha mt giy chng nhn s X.509 c ci t t nh my v

giy chng nhn ca nh sn xut. Cc giy chng nhn ny thit lp mt lin kt

gia a ch MAC 48-bit ca SS v kho RSA dng chung, c gi cho BS t SS

trong nhng thng bo yu cu cp php v thng tin chng thc. Mng c kh

nng xc minh s ging nhau ca SS bi vic kim tra cc giy chng nhn v sau kim tra mc cho php ca SS. Nu SS c cp php tham gia mng, BS s

p li yu cu ca n vi mt Authorization Reply (tr li cp php) c cha mt

kho AK (Authorization Key) c m ho vi kha dng chung ca SS v c

dng bo v nhng giao dch sau ny.

Trong lc cp php thnh cng, SS sng k vi mng. iu s thit lp

kt ni qun l th cp ca SS v xc nh nhng kh nng c lin quan n ci t

kt ni v qu trnh hot ng MAC. Phin bn IP c s dng vi kt ni qun lth cp cng c xc nh trong thi gian ng k.

- To kt ni IP (ty chn):

Sau khi ng k, SS ginh c mt a ch IP qua DHCP v thit lp thi

gian trong ngy qua ng ITP (Internet Time Protocol). Server DHCP cng cung

cp a ch ca server TFTP (Trivial File Transfer Protocol), t SS c th yu

cu mt file cu hnh. File ny cung cp mt giao din chun a ra thng tin cu

hnh c trng ca nh cung cp.

- Ci t kt ni:

Nhn tng th, vic ci t cc lung dch v trong IEEE 802.16-2004 c

khi to bi BS trong thi gian khi to SS. Tuy vy, cc lung dch v c th cng

c thit lp ng bi BS hoc SS. in hnh SS ch khi to cc lung dch v

nu c mt kt ni c bo hiu ng nh mt SVC (switched virtual connection)

t mt mng ATM. S thit lp cc lung dch vc thc hin thng qua mt



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giao thc three-way handshaking" (bt tay ba bc) m ti yu cu thit lp

lung dch vc p li v sp li c xc nhn.

Cht lng dch v trong 802.16-2004

Mng bng rng l ni cung cp rt nhiu loi dch v vi cc yu cu khc

nhau. V th m QoS chnh l mt vn cbn i vi cc mng bng rng. So

vi cc mng bng rng khng dy khc, u im ln ca 802.16 l n h trrt tt

vn QoS. Mt lot cc tnh nng m bo cch QoS cho cc loi dch v khc

nhau gm c m thanh, hnh nh. 802.16 cho php cc nh cung cp dch v qun l

c lu lng i vi tng thu bo, da vo cc tha thun cam kt.

Cht lng dch v trong 802.16 ph thuc vo ba yu t sau:

- Giao thc MAC trong 802.16 hot ng hng kt ni (connection-

oriented).Mi mt gi tin trong 802.16 u c a vo mt kt ni c th,

kt ni ny l kt ni o, c xc nh bi tham s CID. Vic to nn cc

kt ni o ny khin cc gi tin c gi i mt cch hiu qu v nhanh

chng. N ging nh cc mch o trong ATM.

- C ch cp pht bng thng Request/Grant: C ch cp pht bng thng

Request/Grant lm tng hiu qu s dng bng thng ca h thng, c bit

l cc h thng m c nhiu thu bao. Trong cch ny, SS yu cu lng

bng thng cp pht t BS thng qua mt s cc phng thc khc nhau. BS

s cp pht bng thng bng cch cp pht cc timeslot ti cc SS c yu

cu.

- Phn loi dch v: Ging nh mi h thng h tr tt QoS khc, vic phn

loi dch v cng l im ct li trong vic m bo QoS ca h thng

802.16. Cch hot ng ch yu cung cp QoS trong 802.16 l a cc

gi tin khc nhau vo cc dch v khc nhau, cc dch v ny c xc nhbi chnh bi CID. 802.16 phn loi cc lung d liu vi yu cu QoS

khc nhau vo cc kt ni khc nhau. Mi kt ni s thuc mt loi dch v

v mi dch v li c cc tham s QoS khc nhau.

2.1.1.3 Lp con bo mt

Khc vi cc chun khng dy bng rng khc, 802.16- 2004 thit k hn mt

lp con bo mt, lp ny lm cung cp cc cchiu khin truy nhp tin cy, m



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bo an ton cho d liu trn ng truyn. 802.16 chng li vic truy cp tri php

cc dch v bng vic m ha cc lung dch v. N c cc giao thc qun l kha

ti BS thc hin chng thc v cp pht cc kha ti SS cn thit. Trong qu

trnh thng lng v bo mt gia SS v BS, nu mt SS khng cung cp cc c

ch bo mt ca 802.16-2004 th cc bc chng thc v cp pht kha sc b

qua. BS nu chp nhn iu th s vn cho php SS c truyn d liu, ngc

li BS s khng cho php. Ch c hai loi kt ni c bo v trong 802.16-2004 l

cc kt ni vn chuyn v kt ni th cp. Cc kt ni qun l, iu khin khc

khng cn phi bo v.

Trong bo mt 802.16-2004 c hai loi giao thc chnh.

-Giao thc lm nhim v x l ng gi, m ha: Giao thc ny lm ccnhim v nhnh ngha h thng m ha, kt hp gia m ha d liu v

chng thc, x l cc MAC PDU.

- Giao thc qun l kho bo mt PKM(Privacy Key Management): cung cp

cch phn phi kha t BS ti SS. Thng qua giao thc ny, BS v SS c

thng b kha vi nhau. BS s dng giao thc ny thi hnh cc iu

kin truy nhp vo mng. Giao thc s dng nhiu kho khc nhau khi thit

lp mt s m ho bo mt. Chng c tng hp li trong bng 2.1:Bng 2.1: Cc loi kho bo mt sdng trong IEEE 802.16-2004

Khoc to

bic sdng cho

Thi giantn ti

Thut ton

Cp khocng khai /bo mt

Nh sn xut- nhn thc SS

- trao chuyn AKlu di RSA

AK BS

- to ra cc KEK- tnh ton cc HMAC digest

- kim tra cc HMAC digestnhn c

1 n 70 ngy3 DES,SHA 1

KEK BS, SS

- m ho TEK cho victruyn dn (BS)

- gii m TEK s dng(SS)

ging AK 3 DES

TEK BS m ho lu lng s lng30 pht ti

7ngy DES



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2.1.2 Lp PHY

Lp vt l trong chun 802.16-2004 c bn c t:

- c t SC (Single Carrier): S dng mt sng mang duy nht mang thng

tin. c t ny c chun ha t 802.16 ban u.

- c t SCa: c t ny cng s dng mt sng mang duy nht mang

thng tin nhng n c thm mt s ci tin. c t ny c chun ha t

802.16a.

- c t OFDM: c t OFDM da trn nn cng ngh OFDM cho php

truyn thng tin trn nhiu sng mang khc nhau. c t ny c chun ha

t 802.16a.

- c t OFDMA: c t OFDMA cng da trn nn cng ngh OFDM

nhng n h tra truy nhp phn chia theo sng mang.

Phn di y s m t vc t OFDM cho WiMAX.

Thut ngy WirelessMAN- OFDM PHY da trn phng thc iu ch

OFDM v c thit k cho s truyn khng trong tm nhn thng (NLOS) trong

bng tn


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2.1.2.1 M t Symbol OFDM

Symbol OFDM trong min tn s

Mt OFDM Symbol c to thnh t cc sng mang con, s sng mang con

trong mt symbol quyt nh kch thc FFT s dng. OFDM Symbol gm tt c

cc thng tin m cc sng mang con vn chuyn sau mt bin i FFT. Trong mt

symbol c ba loi sng mang con: sng mang con d liu dng truyn d liu,

sng mang con dn ngcho mc ch d bo s thay i vsng mang con rng

s khng truyn bt c g, c dng lm khong bo v. Cu trc symbol trong

min tn s c dng nh hnh 2.4:

Hnh 2.4 Cu trc symbol trong min tn s

Symbol OFDM trong min thi gianCu trc theo min thi gian ca symbol c dng nh hnh 2.5:

Hnh 2.5 Cu trc symbol trong min thi gian

Symbol c di Ts, trong Tb l khong thi gian thc ca symbol cn

Tg=Ts-Tb l gi tr thm vo chng hin tng a ng. Phn ny cn c

gi l CP (Cyclic Prefix), n c th c cc gi tr khc nhau ty vo h thng. CP

thng l sao chp mt phn cui ca symbol. Khi khi to, mt SS s tm kim tt

c cc gi tr c th ca CP cho ti khi tm ra c gi tr CP c s dng bi

BS. SS cng s s dng gi tr ny cho ng ln. Mi khi mt gi tr CP c

chn bi BS, n khng nn thay i v thay i CP ng ngha vi vic cc SS phi

thc hin ng b li, tm kim li CP.



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nh ngha cc thng scsc t symbol OFDM

- BW: rng bng tn ca knh

- Nused: s sng mang con c s dng

-n: h s ly mu.

- G: t s khong thi gian Tg so vi khong thi gian hu ch ca symbol (Tb)

Cc thng sc suy ra:

- NFFT: kch thc bin i FFT (chnh l s sng mang con), > Nused

NFFT = Nused + s sng mang con bo v (2 bin tn trn, di)

+sng mang con trung tm

- Tn s ly mu:FS= floor (n . BW/8000) x 8000

- Khong cch gia cc sng mang con: f= FS / NFFT

- Thi gian hu ch ca symbol: Tb = 1 / f

- Khong thi gian CP (Cycle Prefix): Tg= G . Tb

- Thi gian tn ti symbol OFDM: TS= Tg + Tb

- Chu k ly mu = Tb / NFFT

Bng 2.2: Thng ssymbol OFDM theo chun 802.16-2004

Thng s Gi tr

NFFT 256

Nused 200

S sng mang dnng

8

S sng mang dliu 192

S sng mang bo v 55 (28 Thp, 27 cao)

G 1/4, 1/8, 1/16, 1/32

rng knh l bi ca 1,75MHz: n = 8/7





n

Cc trng hp khc: n = 8/7



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2.1.2.2 S khi qu trnh truyn nhn

Hnh 2.6 Qu trnh truyn-nhn

Thng tin t lp trn cng nh thng tin ca lp vt l sc nhi vo cc

symbol. truyn c d liu, cc qu trnh gm c m ha knh, iu ch

OFDM thnh cc symbol v iu ch cao tn. Qu trnh ngc li bn nhn.

M ha knh truyn

Gm ba qu trnh nh l qu trnh ngu nhin ha, qu trnh m ha sa li

FEC v qu trnh xen k:

- Qu trnh ngu nhin ha (Randomization):

Qu trnh c gi l ngu nhin nhng thc cht ch l s gi ngu nhin.

Tc l mt cm cc bit u vo sc bin i sao cho xc sut xut hin cc bit

0 v 1 l tng ng nhau, chng li hin tng qu nhiu bit 0 v bit 1 cng xut

hin. Nhng qu trnh ny c chu k lp li nn trong mt khong thi gian nht

nh th coi n l ngu nhin. iu ny c hai tc dng. Th nht, v quan trng

nht l n m bo c sng b vi bn thu, ng h bn thu s d dng c

khi phc hn, qua s gii iu cng d hn. Th hai, i vi cc thit b m

khng c c b gii iu ch ngu nhin th cc tn hiu ny ging nh cc tn

hiu nhiu, tp (xc sut bit 1 v 0 l ngang nhau), n s khng thu nhn c.

- Qu trnh m ha sa li FEC:

y l qu trnh m ha sa li trong trng hp cc bit b hng, b sai trn

ng truyn. Trong nhng iu kin truyn khng tt, d liu b hng, bn thu c

th da vo qu trnh gii m hi phc li nguyn vn thng tin. WiMAX kt



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hp c hai loi m sa li l m khi v m chp. D liu c m ha bng m

khi (dng m Reed-Salomon), sau s c m ha bng m chp

(Convolutional Code). Bng 2.3 di y m t c thi vi m sa li vi cc

la chn khc nhau.

Bng 2.3: M sa lii vi cc phng thc iu ch

- M ha RS(N, K, T) ngha l K bytes u vo, N bytes u ra v T bytes d

liu c sa li.

- M ha CC vi tc K/N ngha l ta c K bytes u vo v N bytes u ra

V d khi dng iu ch QPSK vi 24byte u vo cha c m ha. Khi qua

b m ha Reed-Solomon RS (32,24,4) ta s c 32byte u ra. Tip tc cho qua b

m ha CC 2/3 ta s c 48byte u ra. Nh vy s byte u vo l 24 v s byte u

ra tng cng l 48. Kt qu ta c h s m ha chung (Overall coding rate) l 1/2.

- Qu trnh xen k (interleaving):

y cng l mt qu trnh nhm h tr vic khi phc thng tin bn thu.

Phng trng hp li bit xy ra mt cm lin tc nhau. Cc cm bit sc truynxen k vi nhau nh hnh 2.7 di dy:

Hnh 2.7 Qu trnh xen k



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Ta thy, gi s nu truyn nh trng hp 1, th s c trng hp m cm bit

a1a2a3a4 gp qu nhiu li n mc khng th sa c. Thc t khi truyn dn

ni chung, c khng dy v c dy, so vi cc li khc th xc sut xy ra li cm l

ln. V vy thay v truyn c cm a1a2a3a4 ta thc hin vic xen k vi cc cm

khc ri mi truyn. Gi d m c cm a1b1c1d1 b li, th khi khi phc xen k,

trong cm a1a2a3a4 cng ch c bit a1 l b li, s khi phc li d dng bng m

sa li.

Tt c cc bit d liu m ha sc qut xen k theo khi bit, kch c

khi bit ny ph thuc vo s bit m ha v s knh con trong 1 symbol OFDM.

Bng 2.4 di y m t kch ckhi bit xen k trong WiMAX.

Bng 2.4: Kch ckhi bit xen k

16

knh con

(Mc nh)

8

knh con

4

knh con

2

knh con

1

knh con

BPSK 192 96 48 24 12

QPSK 384 192 96 48 24

16QAM 768 384 192 96 48

64QAM 1152 576 288 144 72

iu chOFDM

Qu trnh ny c mt sim cn ch :

- Thm cc thng tin dn ng

Thng tin dn ng l cc thng tin c chn thm vo bn nhn c th

don c knh truyn. N c vn chuyn bi cc sng mang dn ng. Qu

trnh ny c thc hin trc khi nh x vo cc k hiu BPSK.

- iu ch s

Cc bit sc nh x vo cc k hiu BPSK, QPSK, 16QAM hoc 64QAM

ty trng hp. Do yu cu phi m bo tin cy, khe nht nht i vi cc

thng tin dn ng m cc thng tin ny bt buc iu ch vo cc k hiu BPSK.



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- IFFT

Qu trnh iu cha sng mang trc giao bng cch bin i Furie ri rcngc. Cc k hiu BPSK, QPSK, QAM c iu ch vo cc sng mang khcnhau.

WMAN-OFDM nh ngha kch thc ca FFT l 256. Vi 192 sng mang dliu, 8 sng mang dn ng v 55 sng mang bo v (sng mang trung tm khngc dng).

iu chcao tn

Cc sng mang trong qu trnh iu ch OFDM to thnh mt OFDM Symbolcbn, n vn cha th pht truyn i c. a ln Anten pht, cn phi cthm mt qu trnh iu ch cao tn na.

Qu trnh nhnc thc hin theo th t ngc li, qua cc khu gii iuch, gii m.

2.1.2.3 Lp con hi t truyn

Gia PHY v MAC c mt lp con hi t truyn TC (transmission

convergence). Lp ny thc hin s bin i cc MAC PDU di c th thay i

vo trong cc block FEC di cnh (cng thm c th l mt blockc rt

ngn vo on cui) ca mi burst. Lp TC c mt PDU c kch thc khp vi

block FEC hin thi by. N bt u vi mt con tr ch ra v tr u mc PDU

MAC tip theo bt u bn trong block FEC.

Khun dng TC PDU cho php ng b ha li MAC PDU tip sau trong

trng hp block FEC trc c nhng li khng th phc hi c. Khng c

lp TC, mt SS hay BS nhn s mt ton b phn cn li ca mt "burst" khi mt

li khng th sa cha xut hin.

2.1.2.4 Phng thc song cng

Cu trc im - a im trong Fixed WiMAX h trmt cu trc khung vi

hai ch truyn song cng TDD v FDD.

Ch TDD

Mt khung TDD bao gm mt khung con ng ln v mt khung con ng

xung nh hnh v 2.8:



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Hnh 2.8 Cu trc khung TDD

TTG v RTG l nhng khong trng phn cch d liu ng ln v ng

xung.

di cho php ca khung: 2,5; 4; 5; 8; 10; 12,5 v 20ms.

- Khung con ng xung (DL Subframe)

Khung con ng xung l mt n v giao thc d liu lp vt l (PHY

PDU) ng xung. N bao gm mo u (preamble), mt header iu khin

khung (FCH), v mt hoc nhiu burst d liu ng xung. Mi burst d liu

ng xung bao gm mt hoc nhiu MAC PDUs v c di bng mt s

nguyn ln di ca symbol OFDM. Cu trc mt khung con ng xung c

m t trong hnh 2.9 di y:

Hnh 2.9 Cu trc khung con ng xung TDD

- Khung con ng ln (Uplink Subframe)

Khung con ng ln bao gm mt hoc nhiu PHY PDU ca cc SS khc

nhau. Mi PHY PDU c mt mo u v mt burst d liu. Cng nhng

xung, mi burst d liu bao gm mt hoc nhiu MAC PDU, c di bng mt

s nguyn ln di ca symbol OFDM. Cu trc mt khung con ng ln c

m t trong hnh 2.10 di y:



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Hnh 2.10 Cu trc khung con ng ln TDD.

Ch FDD

ch FDD, khung con ng ln v ng xung c t nhng tn s

khc nhau. Cu trc khung cng ging nh cu trc khung con ng ln v ng

xung ch TDD.

2.2. WiMAX di ng - IEEE 802.16e - 2005

Chun 802.16e l phin bn 802.16-2004 b sung nhng c t cn thit htrcho kh nng di ng ca thit b thu. V vy, di y s ch trnh by nhng

chc nng khc bit c b sung trong lp MAC v lp PHY to nn phin bn

chun 802.16e.

2.2.1 Lp PHY

2.2.1.1 Csv OFDMA

OFDM l mt cng ngh ghp knh phn chia theo tn s trc giao, n chia

nh bng tn thnh nhng sng mang con tn s khc bit. Trong mt h thng

OFDM, chui d liu u vo c chia thnh nhng chui con song song c tc

thp v mi chui con ny c iu ch v pht i trn mt sng mang con trc

giao ring.

OFDM khai thc sa dng tn s ca knh truyn a ng bng cch m

ha v xen k thng tin c mang bi sng mang con trc khi truyn. iu ch



50/130


OFDM c thc nhn dng bng php bin i Fourier (nhanh) ngc IFFT, cho

php mt s lng ln sng mang con (ln ti 2048) vi phc tp khng ng

k. Trong h thng OFDM, ti nguyn sn c trong min thi gian th hin qua

symbol OFDM v trong min tn s th hin sng mang con. Ti nguyn thi

gian v tn s c thc t chc thnh nhng knh con (sub-channel) cp cho

nhng ngi dng ring. Cng ngh a truy nhp OFDMA l mt c ch ghp

knh/ a truy nhp cung cp s ghp nhng lung d liu t nhiu ngi s dng

vo nhng knh con trn ng xung v s a truy nhp vo mi knh con

ng ln.

Cu trc symbol OFDMA v Knh con ha

Cu trc symbol OFDMA bao gm 3 loi sng mang con: sng mang con dliu (data sub-carrier) cho vic truyn d liu; sng mang con dn ng (pilot sub-

carrier) cho nhng mc ch c lng knh v ng b; sng mang con rng (null

sub-carrier) khng mang d liu m c s dng lm di bo v v sng mang

mt chiu DC.

Hnh 2.11 Cu trc sng mang con OFDMA (min tn s)

Nhng sng mang con d liu v dn ng c nhm thnh NG Group.

Mi Group c NE sng mang con, to thnh NE knh con, mi knh con c mt

sng mang mi group. Trong h thng OFDMA dng 2048 sng mang con,

ng xung c NG = 48 sng mang con v NE = 32 knh con; ng ln NG = 53

sng mang con, NE = 32 knh con. M ha, iu ch v bin c thit lp ring

cho mi knh con ti u ha vic s dng ti nguyn mng.

Qu trnh knh con ha (sub-channelization) nh ngha nhng knh con c

cp pht cho nhng thu bao khc nhau ph thuc vo iu kin knh truyn v nhu

cu d liu ca h. iu ny em li cho h thng kh nng mm do trong qun l



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bng thng v cng sut pht, dn n s dng ti nguyn hiu qu hn. Hiu ng

knh con ha c trnh by trn hnh 2.12 v 2.13.

Hnh 2.12 OFDM v OFDMA

Hnh 2.13 Hiu ng knh con ho (sub channelization)

2.2.1.2 SOFDMA (Scalable OFDMA)

H thng Wireless MAN OFDMA chun IEEE802.16e da trn cng ngh

SOFDMA. SOFDMA chnh l cng ngh OFDMA nhng kch thc FFT c ththay i (tng hoc gim). Thay i sim FFT chnh l thay i s sng mang



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con s dng trong mt symbol, khi rng bng tn thay i th khong cch gia

cc sng mang con c gi khng i 10,94 kHz. i vi rng bng tn ln,

s sng mang con c tng ln; v ngc li rng bng tn hp th cn gim s

sng mang con. iu ny lm tng hiu sut s dng ph trong nhng h thng

rng knh tn s ln, v lm gim chi ph trong nhng h thng knh hp.

Thng s ca SOFDMA c lit k trong bng 2.5.

Bng 2.5: Thng sSOFDMA

Thng s Gi tr

rng bng tn h thng (MHz) 1,25 5 10 20

Tn s ly mu (FS) (MHz) 1,4 5,6 11,2 22,4

Kch thc FFT (NFFT) 128 512 1024 2048

S knh con 2 8 16 32

Khong cch sng mang con (f) 10,94 kHz

Thi gian c ch ca symbol (Tb = 1/f) 91,4 s

Thi gian bo v (Tg = Tb/8) 11,4 s

Thi gian tn ti symbol OFDMA (TS =Tg + Tb)

102,9 s

S symbol OFDMA trong 1 khung 5ms 48

2.2.1.3 Cc c tnh lp PHY cao cp trong Mobile WiMAX

Wimax di ng a ra cc k thut: iu ch thch nghi v m ho AMC

(Adaptive modulation and coding), Yu cu lp li tng kiu kt hp HARQ

(Hybrid Automatic Repeat Request) v Phn hi knh nhanh CQICH (Fast Channel

Feedback), nng cao kh nng ph sng, dung lng cho Wimax trong cc ng

dng di ng.

iu chthch nghi v m ha AMC

Trong bt k mng a t bo-cellular no, thu bao di ng s th nghim qua

cc iu kin ca ng truyn pht thay i theo thi gian v cc v tr tng ng.

Vi cng ngh OFDMA, Biu m ho v iu ch nht nh c th thch ngtrn mi thu bao ty theo cc iu kin ca ng dn ti a ho thng lng



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knh truyn, trong khi vn duy tr cht lng ng truyn ti mi thu bao. Vi h

thng OFDMA, cc sng mang con c iu ch vi QPSK hoc iu ch QAM

hiu qu hn v th t cao hn vi biu iu ch tinh vi hn, t c thng

lng cao hn nhng cng d b tc ng ca nhiu v cc tp m hn. Bng

phng php iu ch thch ng v biu m ho li, vic p ng t l ny ny

m bo s bit ca mi sng mang con c ti u tng ng vi CINR cn thit

m bo kt ni v tuyn n nh. Cc H thng OFDMA cng c th lm tng

thng lng ti cc thu bao c nhn bng cch lm tng s lng knh con cp

ti bt k thi im no.

Hnh 2.14:iu chthch nghi v m ha da trn khong cch vi BS

Trong WiMAX di ng ng xung, bt buc phi c cc h triu ch

QPSK, 16QAM v 64QAM. Cn ng ln, 64QAM l tu chn. C m ho

xon v m ho Turbo vng vi tc m tha

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