Mô hình mô phỏng hoạt động của hệ thống WiMAX VanLuong.Blogspot.Com

7/31/2019 M hnh m phng hot ng ca h thng WiMAX VanLuong.Blogspot.Com

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Li cam oan

LI CAM OANEm xin cam oan ni dung ca n ny khng phi l bn sao chp ca bt c

n hoc cng trnh c t trc.


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Mc lc

MC LC

Ni dung Trang

MC LC CC HNH VMC LC CC BNGCC T VIT TTM UChng 1: GII THIU CHUNG V WiMAX1.1. Gii thiu chng............................................................................................11.2. Khi nim.........................................................................................................11.3. Cc chun ca WiMAX...................................................................................51.3.1. Chun IEEE 802.16 2001.............................................................................51.3.2. Chun IEEE 802.16a........................................................................................51.3.3. Chun IEEE 802.16 2004.............................................................................6

1.3.4. Chun IEEE 802.16e........................................................................................61.4. Ph WiMAX....................................................................................................81.4.1. Bng tn ng k.............................................................................................81.4.2. Bng tn khng ng k 5GHz........................................................................91.5. Truyn sng.....................................................................................................91.6. u im v nhc im ca WiMAX...........................................................121.7. Tnh hnh trin khai WiMAX........................................................................14

1.7.1. Tnh hnh trin khai WiMAX trn th gii....................................................141.7.2. Tnh hnh trin khai WiMAX th nghim ti Vit Nam...............................141.8. Kt lun chng.............................................................................................15

Chng 2: CC K THUT C S DNG TRONG WiMAX2.1. Gii thiu chng..........................................................................................162.2. K thut OFDM.............................................................................................17


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Mc lc

2.2.1. Khi nim.......................................................................................................172.2.2. S khi OFDM.........................................................................................18

2.2.3. Chui bo v trong h thng OFDM.............................................................192.2.4. Nguyn tc gii iu ch OFDM...................................................................212.2.5. Cc u v nhc im ca k thut OFDM...................................................212.3. K thut OFDMA..........................................................................................232.3.1. Khi nim.......................................................................................................232.3.2. c im........................................................................................................232.3.3. OFDMA nhy tn..........................................................................................242.3.4. H thng OFDMA.........................................................................................262.4. iu ch thch nghi........................................................................................272.5. Cng ngh sa li..........................................................................................282.6. iu khin cng sut.....................................................................................282.7. Cc cng ngh anten tin tin........................................................................282.7.1. Phn tp thu v pht.......................................................................................29

2.7.2. Cc h thng anten thch nghi........................................................................302.8. Kt lun chng.............................................................................................31

Chng 3: KIN TRC MNG TRUY CP WIMAX3.1. Gii thiu chng..........................................................................................323.2. M hnh tham chiu.......................................................................................323.3. Lp iu khin truy nhp mi trng (MAC)...............................................34

3.3.1. Kt ni v a ch...........................................................................................353.3.2. Lp con hi t MAC......................................................................................363.3.3. Lp con phn chung MAC............................................................................373.3.4. C ch yu cu v cp pht bng thng.........................................................413.3.5. C ch lp lch dch v v cht lng dch v (QoS)....................................433.3.6. Lp con bo mt............................................................................................443.4. Lp vt l.......................................................................................................44


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Mc lc

3.5. Kt lun chng.............................................................................................46

Chng 4: KIN TRC BO MT CHUN IEEE 802.164.1. Gii thiu chng..........................................................................................474.2. Kin trc bo mt...........................................................................................474.2.1. Kt hp bo mt.............................................................................................494.2.2. Giao thc qun l kha PKM.........................................................................494.3. Quy trnh bo mt..........................................................................................504.3.1. Xc thc.........................................................................................................514.3.2. Trao i kha d liu.....................................................................................534.3.3. M ha d liu...............................................................................................544.4. Hn ch ca kin trc bo mt IEEE 802.16.................................................554.5. Kt lun chng.............................................................................................56

Chng 5: M PHNG HOT NG H THNG WiMAX

5.1. Gii thiu chng..........................................................................................575.2. Mi trng m phng....................................................................................575.3. M phng.......................................................................................................595.3.1. Gi thuyt.......................................................................................................595.3.2. Kch bn m phng........................................................................................605.4. Phn tch kt qu m phng...........................................................................615.4.1. Hot ng......................................................................................................61

5.4.2. Tnh lng bng thng c s dng trn BS...............................................635.5. Nhn xt.........................................................................................................65

KT LUN V HNG PHT TRIN TI..................................................66TI LIU THAM KHO.........................................................................................67


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Mc lc

PH LCPh lc A: Gi tr trng Type trong thng bo qun tr lp MAC

Ph lc B: Giao thc nh tuyn DSDVPh lc C: Ci t NS-2 trn nn Windows 9x/2000/XP s dng Cygwin


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Mc lc cc hnh v

MC LC CC HNH V

Trang Hnh 1.1. Minh ha hat ng WiMAX [10]............................................................11 Hnh 1.2. Truyn sng trong trng hp NLOS [10]...............................................11 Hnh 2.1. So snh gia FDM v OFDM...................................................................17 Hnh 2.2. S khi h thng OFDM......................................................................18 Hnh 2.3. Khi nim v chui bo v........................................................................19 Hnh 2.4. ISI v cyclic prefix....................................................................................20 Hnh 2.5. Tch chui bo v.....................................................................................21 Hnh 2.6. ODFM v OFDMA...................................................................................23 Hnh 2.7. V d ca biu tn s, thi gian vi OFDMA......................................24 Hnh 2.8. Biu tn s thi gian vi 3 ngi dng nhy tn a, b, c

u c 1 bc nhy vi 4 khe thi gian...................................................25 Hnh 2.9. 6 mu nhy tn trc giao vi 6 tn s nhy khc nhau............................25

Hnh 2.10. Tng quan h thng s dng OFDMA...................................................26 Hnh 2.11. Mu tn hiu dn ng trong OFDMA.................................................27 Hnh 2.12. Bn knh cell quan h vi iu ch thch nghi........................................27 Hnh 2.13. MISO.......................................................................................................29 Hnh 2.14. MIMO.....................................................................................................30 Hnh 2.15. Beam Shaping.........................................................................................30 Hnh 2.16. AAS ng xung...................................................................................31

Hnh 3.1. M hnh tham chiu. [5]...........................................................................32 Hnh 3.2. Chc nng cc lp trong m hnh phn lp chun IEEE 802.16.............33 Hnh 3.3. Lung d liu qua cc lp........................................................................33 Hnh 3.4. nh dng MAC PDU...............................................................................37 Hnh 3.5. nh dng ca tiu MAC PDU chung.................................................38 Hnh 3.6. nh dng tiu yu cu di thng........................................................40 Hnh 4.1. M hnh kin trc bo mt chun IEEE 802.16 [7].................................48


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Mc lc cc hnh v

Hnh 4.2. Quy trnh bo mt.....................................................................................50 Hnh 4.3. Qu trnh xc thc SS vi BS....................................................................51

Hnh 4.4. Qu trnh trao i kha d liu................................................................53 Hnh 4.5. nh dng payload trc v sau khi m ha............................................55 Hnh 5.1. Module WiMAX trong kin trc NS-2 [13].............................................58 Hnh 5.2. Kin trc mng m phng........................................................................60 Hnh 5.3. Cc SS gi yu cu ranging.....................................................................61 Hnh 5.4. BS gi p ng ranging...........................................................................62 Hnh 5.5. SS_2 gi yu cu bng thng...................................................................62 Hnh 5.6. SS_2 gi d liu (rtPS) cho BS.................................................................63 Hnh 5.7. th bng thng c s dng trn cc knh truyn............................63 Hnh 5.8. Thng tin trong file ~.tr c import vo excel.......................................64


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Mc lc cc cc bng

MC LC CC BNG

Trang Bng 1.1. Tm tt cc c trng c bn cc chun WiMAX [6]...............................8 Bng 3.1. Cc trng tiu MAC chung...............................................................39 Bng 3.2. Cc trng tiu MAC yu cu di thng.............................................40 Bng 3.3. c t vt l chun IEEE 802.16.............................................................45


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Cc t vit tt

CC T VIT TT

AAS Advanced Antenna Systems - Cc h thng anten thch nghiAES Advanced Encryption Standard - Chun m ha nng caoAK Authentication Key - Kha chng thcARQ Automatic Repeat reQuest - T ng lp li yu cuATM Asynchronous Transfer ModeAWGN Additive White Gaussian Noise - Nhiu Gaussian trng cngBE Best EffortBER Bit Error Rate - T l li bitBPSK Binary Phase Shift Keying - iu ch pha nh phnBS Base Station - Trm gcCDMA Code Division Multiple Access - a truy cp phn chia theo mCID Connection Identifier - nh danh kt niCP Cyclic Prefix - Tin t vngCPE Customer Premise EquipmentCRC Cyclic Redundancy Check - Kim tra li d vngDFS Dynamic Frequency Selection La chn tn s ngFDD Frequency Division Duplex - Ghp knh phn chia theo tn sFFT Fast Fourier Transform - Chuyn i Fourier nhanhGSM Global System for Mobile communications - H thng thng tin di

ng ton cuICI InterChannel Interference - Nhiu xuyn knhIDFT Inverse Discrete Fourier Transform - Bin i Fourirer ri rc ngcIEEE Institute of Electrical and Electronics Engineers - Hc Vin ca cc

K S in v in TIFFT Inverse Fast Fourier Transform - Bin i Fourier ngc nhanhISI Inter-Symbol Interference - Nhiu xuyn k tKEK Key Encryption KeyLOS Line Of Sight - Tm nhn thngMAC Media Access Control - iu khin truy nhp mi trngMAN Metropolitan Area Network Mng thMIMO Multiple Input Multiple Output - Nhiu u vo, nhiu u raMISO Multiple Input Single Output - Nhiu u vo, mt u raMS Mobile Station - Trm di ng NLOS NonLine-Of-Sight - Khng tm nhn thngnrtPS nonreal-time Polling ServiceOFDM Orthogonal Frequency Division Multiplexing - Ghp knh phn chia

theo tn s trc giaoOFDMA Orthogonal Frequency Division Multiple Access - a truy cp ghp


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Cc t vit tt

knh chia tn s trc giaoPDU Packet Data Unit - n v gi d liuPKM Privacy and Key Management - Qun l s ring t v khaQAM Quadrature Amplitude Modulation - iu ch bin trc giaoQoS Quality of Service - Cht lng dch vQPSK Quadature Phase Shift Keying - iu ch pha trc giaoRF Radio Frequency - Tn s v tuynrtPS real-time Polling ServiceSA Security Association Tp hp bo mtSDU Service Data Unit - n v d liu dch vSLA Service-Level Agreement - Tha thun mc dch vSNR Signal-to-Noise Ratio T l tn hiu trn nhiuSS Subscriber Station - Trm thu baoTDM Time Division Multiplexing Ghp knh phn chia theo thi gianTDMA Time Division Multiplexing Access a truy cp phn chia theo

thi gianTEK Traffic Encryption Key - Kha m ha lu lngUDP User Datagram ProtocolUGS Unsolicited Grant ServicesUMTS Universal Mobile Telephone SystemWiFi Wireless FidelityWiMAX Worldwide interoperability for Microwave Access

WLAN Wireless Local Area Network Mng cc b khng dy


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M u

M U

Xu hng pht trin ca cc mng th h sau c c trng bi kh nng ht, tc d liu cao, h tr nhiu mc cht lng dch v (QoS) i i vi kh ndi ng bn trong mng hoc gia cc mng s dng cc cng ngh khc nhau vgia cc nh cung cp dch v vi nhau. Mt kha cnh quan trng trong xu hng pht trin l vic chun ha, cho php xy dng kiu mng c lp vi thit b vkh nng tng tc gia cc kiu mng khc nhau mc cao. Mt cng ngh angc pht trin p ng c nhng c tnh k trn, c chun ha bi t chIEEE (Institute of Electrical and Electronics Engineers) l cng ngh IEEE802.16, thng c gi l cng ngh WiMAX.

WiMAX c thit k nhm mc ch b sung vo cc cng ngh truy cpkhng dy hin ti vi u im tc d liu cao, h tr QoS linh hot, phm vi phsng rng v chi ph trin khai thp trong phm vi vng th MAN (MetropolianAccess Network).

n ny tp trung vo vic nghin cu lp iu khin truy nhp mi trngMAC trong cng ngh WIMAX. n s trnh by nhng vn c bn nht vcng ngh WiMAX nh cc chun WiMAX, cc k thut c ng dng trongWiMAX, m hnh phn lp v bo mt trong WiMAX.

Ngoi ra, n cng gii thiu mt m hnh m phng hot ng ca h thngWiMAX nhm mc ch lm r qu trnh lm vic ca h thng WiMAX.

n bao gm 5 chng nh sau:

Chng 1: Gii thiu chung v WiMAX.Chng 2: Cc k thut c s dng trong WiMAX.Chng 3: Kin trc mng truy cp WiMAXChng 4: Kin trc bo mt chun IEEE 802.16.Chng 5: M phng hot ng h thng WiMAX.


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Chng 1: Gii thiu chung v WiMAX

Chng 1GII THIU CHUNG V WiMAX

1.1. GII THIU CHNGWiMAX l mt cng ngh cho php truy cp bng rng v tuyn n u cui

nh mt phng thc thay th cho cp v ng dy thu bao s DSL. WiMAX cho php kt ni bng rng v tuyn c nh, nomadic (ngi s dng c th di nnhng c nh trong lc kt ni), portable (ngi s dng c th di chuyn vi tc chm) v cui cng l di ng m khng cn trong tm nhn thng LOS (Line-Of-Sight) trc tip vi trm gc BS (Base Station). WiMAX khc phc c cc nhim ca cc phng php truy nhp hin ti, cung cp mt phng tin truy nhInternet khng dy tng hp c th thay th cho ADSL v WiFi. H thng WiMAXc kh nng cung cp ng truyn c tc ln n 70Mbit/s v vi bn knh phsng ca mt trm anten pht ln n 50Km. M hnh ph sng ca mng WiMAXtng t nh mng in thoi t bo. Bn cnh , WiMAX cng hot ng m

do nh WiFi khi truy cp mng. Mi khi my tnh mun truy nhp mng n s tng kt ni n trm anten WiMAX gn nht.Trong chng ny, chng ta s tm hiu khi nim c bn v WiMAX, cc

chun WiMAX hin nay, cc bng tn c th s dng cho WiMAX, cc u im vli ch ca WiMAX mang li, ng thi l tnh hnh trin khai WiMAX trn th giiv ti Vit Nam

1.2. KHI NIM

WiMAX (Worldwide Interoperability of Microwave Access) l h thng truynhp vi ba c tnh tng thch ton cu da trn c s tiu chun IEEE 802.16WirelessMAN (Wireless Metropolitan Area Network). H 802.16 ny a ra nhngtiu chun, ch tiu k thut nhm tp trung gii quyt cc vn trong mng vtuyn bng rng im a im v giao din v tuyn bao gm: Lp iu khin tr

cp mi trng (MAC) v lp vt l (PHY).

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WiMAX l mt chun khng dy ang pht trin rt nhanh, ha hn to ra khnng kt ni bng thng rng tc cao cho c mng c nh ln mng khng dy d

ng. Hai phin bn ca WiMAX c a ra nh sau: Fixed WiMAX (WiMAX c nh):Da trn tiu chun IEEE 802.16-

2004, c thit k cho loi truy nhp c nh v lu ng. Trong phin bnny s dng k thut ghp knh phn chia theo tn s trc giao OFDM(Orthogonnal Frequency Division Multiple) hot ng trong c mi trng nhnthng LOS (line-of-sight) v khng nhn thng NLOS (Non-line-of-sight).Sn phm da trn tiu chun ny hin tai c cp chng ch v thngmi ha.

Mobile WiMAX (WiMAX di ng):da trn tiu chun IEEE 802.16e,c thit k cho loi truy cp xch tay v di ng. v c bn, tiu chun802.16e c pht trin trn c s sa i tiu chun IEEE 802.16-2004 tiu cho cc knh v tuyn di ng, cung cp kh nng chuyn vng handoff v chuyn mng roaming. Tiu chun ny s dng phng thc a truy cp

ghp knh chia tn s trc giao OFDMA (Orthogonnal Frequency DivisionMultiple Access) l s phi hp ca k thut ghp knh v k thut phn chiatn s c tnh cht trc giao, rt ph hp vi mi trng truyn dn a nnhm tng thng lng cng nh dung lng mng, tng linh hot trongvic qun l ti nguyn, tn dng ti a ph tn, ci thin kh nng ph snvi cc loi a hnh a dng.

WiMAX c pht trin v khc phc c nhng nhc im ca cc cng

ngh truy cp bng rng trc y, c th:o Cu trc mm do: WiMAX h tr cc cu trc h thng bao gm im

a im, cng ngh li (mesh) v ph sng khp mi ni. iu khin truynhp mi trng MAC, phng tin truyn dn h tr im a im v dcv rng khp bi lp lch mt khe thi gian cho mi trm di ng (MS). Nu cduy nht mt MS trong mng, trm gc (BS) s lin lc vi MS trn c s im

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v cc dch v trong mt mi trng di ng. Nhng ci tin ny, bao gmOFDMA m rng c, MIMO (Multi In Multi Out - nhiu u vo nhiu u

ra), v h tr i vi ch idle/sleep v handoff, s cho php kh nng di ngy tc ti 160 km/h. Mng WiMAX di ng cho php ngi s dngc th truy cp Internet khng dy bng thng rng ti bt c u c ph sngWiMAX.

o Hot ng NLOS: Kh nng hat ng ca mng WiMAX m khngi hi tm nhn thng gia BS v MS. Kh nng ny ca n gip cc sn phmWiMAX phn pht di thng rng trong mt mi trng NLOS.

o Ph sng rng hn: WiMAX h tr ng nhiu mc iu ch, bao gmBPSK, QPSK, 16QAM, 64QAM. Khi yu cu vi b khuch i cng sut caov hot ng vi iu ch mc thp (v d BPSK hoc QPSK). Cc h thnWiMAX c th ph sng mt vng a l rng khi ng truyn gia BS v MSkhng b cn tr. M rng phm vi b gii hn hin ti ca WLAN cng cng(hotspot) n phm vi rng (hotzone). nhng iu kin tt nht c th

c phm vi ph sng 50 km vi tc d liu b h thp (mt vi Mbit/s) phm vi ph sng in hnh l gn 5 km vi CPE (NLOS) trong nh v gn15km vi mt CPE c ni vi mt anten bn ngoi (LOS).

o Dung lng cao: C th t c dung lng 75 Mbit/s cho cc trm

gc vi mt knh 20 MHz trong cc iu kin truyn sng tt nht.o Tnh m rng: Chun 802.16 -2004 h tr cc di thng knh tn s v

tuyn (RF) mm do v s dng li cc knh tn s ny nh l mt cch tndung lng mng. Chun cng nh r h tr i vi TPC (iu khin cng su pht) v cc php o cht lng knh nh cc cng c thm vo h tr sdng ph hiu qu. Chun c thit k t t l ln ti hng trm thch hng nghn ngi s dng trong mt knh RF. H tr nhiu knh cho phpcc nh ch to thit b cung cp mt phng tin ch trng vo phm vi sdng ph v nhng quy nh cp pht c ni r bi cc nh vn hnh trong

cc th trng quc t thay i khc nhau.

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o Bo mt: Bng cch m ha cc lin kt v tuyn gia BS v MS, sdng chun m ha tin tin AES, m bo s ton vn ca d liu trao i qu

giao din v tuyn. Cung cp cho cc nh vn hnh vi s bo v mnh chngli nhng hnh vi nh cp dch v.

1.3. CC CHUN CA WiMAX

1.3.1. Chun IEEE 802.16 - 2001

Chun IEEE 802.16-2001 c hon thnh vo thng 10/2001 v c cng bvo 4/2002, nh ngha c t k thut giao din khng gian WirelessMAN cho ccmng vng th. c im chnh ca IEEE 802.16 2001:

Giao din khng gian cho h thng truy nhp khng dy bng rng cnh hat ng di tn 10 66 GHz, cn tha mn tm nhn thng.

Lp vt l PHY: WirelessMAN-SC.

Tc bit: 32 134 Mbps vi knh 28 MHz.

iu ch QPSK, 16 QAM v 64 QAM.Cc di thng knh 20 MHz, 25 MHz, 28 MHz.

Bn knh cell: 2 5 km.

Kt ni c nh hng, MAC TDM/TDMA, QoS, bo mt.

1.3.2. Chun IEEE 802.16a

V nhng kh khn trong trin khai chun IEEE 802.16, hng vo vic s dngtn s t 10 66 GHz, mt d n sa i c tn IEEE 802.16a c hon thnhvo thng 11/2002 v c cng b vo thng 4/2003. Chun ny c m rng htr giao din khng gian cho nhng tn s trong bng tn 211 GHz, bao gm cnhng ph cp php v khng cp php v khng cn tho mn iu kin tm nhthng. c im chnh ca IEEE 802.16a nh sau:

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B sung 802.16, cc hiu chnh MAC v cc c im PHY thm vocho di 2 11 GHz (NLOS).

Tc bit: ti 75Mbps vi knh 20 MHz.iu ch OFDMA vi 2048 sng mang, OFDM 256 sng mang,QPSK, 16 QAM, 64 QAM.Di thng knh c th thay i gia 1,25MHz v 20MHz.

Bn knh cell: 6 9 km.Lp vt l PHY: WirelessMAN-OFDM, OFDMA, SCa.

Cc chc nng MAC thm vo: h tr PHY OFDM v OFDMA, h tr cng ngh Mesh, ARQ.

1.3.3. Chun IEEE 802.16 - 2004

Thng 7/2004, chun IEEE 802.16 2004 hay IEEE 802.16d c chp thngqua, kt hp ca cc chun IEEE 802.16 2001, IEEE 802.16a, ng dng LOS ditn s 10 - 66 GHz v NLOS di 2 - 11 GHz. Kh nng v tuyn b sung nh lbeam forming v knh con OFDM.

1.3.4. Chun IEEE 802.16e

u nm 2005, chun khng dy bng thng rng 802.16e vi tn gi MobileWiMAX c ph chun, cho php trm gc kt ni ti nhng thit b ang dchuyn. Chun ny gip cho cc thit b t cc nh sn xut ny c th lm vic

tng thch tt vi cc thit b t cc nh sn xut khc. 802.16e hat ng cc bng tn nh hn 6 GHz, tc ln ti 15 Mbps vi knh 5 MHz, bn knh cell t 2 5 km.

WiMAX 802.16e c h tr handoff v roaming. S dng SOFDMA, mt cngngh iu ch a sng mang. Cc nh cung cp dch v m trin khai 802.16e cngc th s dng mng cung cp dch v c nh. 802.16e h tr cho SOFDMA ch php s sng mang thay i, ngoi cc m hnh OFDM v OFDMA. S phn chia

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sng mang trong m hnh OFDMA c thit k ti thiu nh hng ca nhi pha thit b ngi dng vi anten a hng. C th hn, 802.16e a ra h tr c

tin h tr MIMO v AAS, cng nh cc handoff cng v mm. N cng ci tin cckh nng tit kim cng sut cho cc thit b di ng v cc c im bo mt linhot hn.

802.16 802.16-2004 802.16-2005

Tnh trngHon thin vothng 12-2001

Hon thin vo thng 6-2004

Hon thin vo thng 12-2005

Di tn 10-66 GHz 2-11 GHz 2-11 GHz cho c nh;2-6 GHz cho di ng

ng dngC nh, tmnhn thng

(LOS)

C nh, khng nhn thng(NLOS)

C nh v di ng, khngnhn thng (NLOS)

Cu trclp MAC

im a im,mng li

im a im, mng li im a im, mng li

M hnhtruynsng

n sng mang n sng mang, 256OFDM, 2048 OFDM

n sng mang, 256 OFDMhoc S-OFDM vi 128, 512,1024, 2048 sng mang con.

iu chQPSK, 16QAM,

64QAMQPSK, 16QAM, 64QAM QPSK, 16QAM, 64QAM

Tng tns d liu

32-134.4 Mbps 1-75 Mbps 1-75 Mbps

Ghp knhKhi

TDM/TDMAKhi

TDM/TDMA/OFDMA Khi TDM/TDMA/OFDMA

Song cng TDD v FDD TDD v FDD TDD v FDD rng

knhtruyn(MHz)

20, 25, 281.75, 3.5, 7, 14, 1.25, 5, 10,

15, 8.751.75, 3.5, 7, 14, 1.25, 5, 10,

15, 8.75

Giao dinWirelessMAN- WirelessMAN-SCa, WirelessMAN-SCa,

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n 2 56 MHz.

1.4.2. Bng tn khng ng k 5GHz

Phn ln cc quc gia ton th gii s dng ph 5 GHz cho cc phng tinlin lc khng ng k. Cc bng 5,15 GHz v 5,85 GHz c ch nh nh khngng k trong phn ln th gii.

Cc gii php khng ng k cung cp mt vi thun li chnh hn cc gii phpng k, bao gm chi ph ban u thp hn, rt ra nhanh hn, v mt bng chung c

th c s dng phn ln th gii. Cc li ch ny ang thu ht s quan tm v ckh nng cho s chp nhn bng rng nhanh chng.

Tuy nhin mt gii php khng ng k th kh nng nhiu cao hn, v nhiu scnh tranh i vi cc nh kinh doanh bt ng sn cho vic trin khai. Mt gii phkhng ng k s khng c xem nh mt s thay th cho gii php ng k. Migii php cung cp mt th trng khc nhau da vo s tha hip gia chi ph vQoS.

1.5. TRUYN SNG

Trong khi nhiu cng ngh hin ang tn ti cho khng dy bng rng ch c thcung cp ph sng LOS, cng ngh WiMAX c ti u cung cp ph sng NLOS. Cng ngh tin tin ca WiMAX cung cp tt nht cho c hai. C LOS v NLOS b nh hng bi cc c tnh ng truyn mi trng ca chng, tn th

ng dn, v ngn qu kt ni v tuyn.Trong lin lc LOS, mt tn hiu i qua mt ng trc tip v khng b tc

nghn t my pht n my thu. Mt lin lc LOS yu cu phn ln min Fresnel thnht th khng b ngn cn ca bt k vt cn no, nu tiu chun ny khng tha mth c s thu nh ng k cng tn hiu quan st. h Fresnel c yu cu ph thuc vo tn s hot ng v khong cch gia v tr my pht v my thu.

Trong lin lc NLOS, tn hiu n my thu qua phn x, tn x, nhiu x. Cc tn

hiu n my thu bao gm cc thnh phn t ng trc tip, cc ng c ph

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x nhiu ln, nng lng b tn x, v cc ng truyn b nhiu x. Cc tn hiu nc khong tr khc nhau, suy hao, phn cc, v n nh quan h vi ng truy

trc tip. L nguyn nhn gy ra nhiu ISI v mo tn hiu. iu khng phi lvn i vi LOS, nhng vi NLOS th li l vn chnh.

Hin tng a ng cng c th gy ra s phn cc tn hiu b thay i. V vys dng phn cc nh l bin php s dng li tn s, nh c thc hin thnthng trong cc trin khai LOS c th kh gii quyt trong cc ng dng NLOS.

Mt h thng v tuyn s dng cc tn hiu a ng ny nh th no hng tmt thun li l cha kha cung cp dch v trong cc iu kin NLOS. Mt s phm m ch n thun tng cng sut xuyn qua cc vt cn (i lc c gi lgn tm nhn thng) th khng phi l cng ngh NLOS bi v phng php nyvn cn da vo ng truyn trc tip mnh m khng s dng nng lng xuhin trong cc tn hiu gin tip.

C nhiu u im m nhng trin khai NLOS to ra ng mong mun. V d,cc yu cu lp k hoch cht ch v gii hn chiu cao anten m thng khng ch

php anten c b tr cho LOS. Vi nhng trin khai t bo k nhau phm vi rngni tn s c s dng li l ti hn, h thp anten l thun li gim nhiu kchung gia cc v tr cell lin k. iu ny thng c tc dng thc y cc trm ghot ng trong cc iu kin NLOS. Cc h thng LOS khng th gim chiu caanten bi v lm nh vy s c tc ng n ng quan st trc tip c yu cu tCPE n trm gc.

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Hnh 1.1. Minh ha hat ng WiMAX [10]

Cng ngh NLOS cng gim ph tn ci t bng cch t di cc mi che thi b CPE ng nh nguyn bn v gim bt kh khn nh v tr cc a im t CPEthch hp. Cng ngh cng gim bt nhu cu quan st v tr thit b pha trc v c

thin chnh xc ca cc cng c lp k hoch NLOS.Cng ngh NLOS v nhng tnh nng c nng cao trong WiMAX to kh

nng s dng thit b pha u khch hng (CPE) trong nh. iu ny c hai khkhn chnh; u tin l khc phc nhng tn hao xuyn qua ta nh v th hai, phsng cc khong cch hp l vi cng sut truyn v cc anten thp hn m thngc kt hp vi cc CPE trong nh.

Hnh 1.2. Truyn sng trong trng hp NLOS [10]

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1.6. U IM V NHC IM CA CNG NGH WiMAX

Mc tiu ca t chc IEEE khi pht trin tiu chun 802.16:- Xy dng mt phm vi chun d dng cho s pht trin v phi hp gia

cc nh sn xut, nh cung cp v c ngi s dng.- Thc y qu trnh chng nhn phi hp hot ng v tun th cho cc h

thng truy nhp v tuyn bng rng trn ton cu. Nh vy, vi mc tiu ra, cc tiu chun cho WiMAX c li ch ht sc to

ln i vi cc nh sn xut, cc nh cung cp dch v v c ngi s dng dch v i vi nh sn xut:- Trn c s tiu chun chung, nh sn xut c th nhanh chng pht trin cc

sn phm m t phi chi ph cho vic nghin cu, to thnh phn v dch vmi.

- Mt nh sn xut c th tp trung vo mt lnh vc (chng hn trm gc haCPE) m khng cn thc hin y gii php t u cui n u cui.

i vi nh cung cp dch v:- Trn c s nn tng chung cho php nh cung cp dch v gim gi thnh,

tng kh nng cnh tranh cng nh khuyn khch s i mi.- Kh nng gim cc chi ph v mc u t cho php nh khai thc tng phm

vi phc v ca mnh.- Nh khai thc khng cn ph thuc vo mt nh cung cp thit b ring do

cc sn phm ring bit ca tng hng.- H thng v tuyn cho php gim cc ri ro cho nh khai thc. i vi ngi s dng dch v:- Ngi s dng ti cc khu vc trc y cha c cung cp dch v truy

cp bng rng nay c th c s dng nh kh nng ph sng rng caWiMAX.

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- Nhiu nh cung cp dch v trn th trng to iu kin cho ngi s dnc thm nhiu la chn cho dch v truy nhp bng rng.

- To s cnh tranh c li cho ngi s dng, gim cc chi ph dch v.Cc nhc im ca cng ngh WiMAX:

- Di tn WiMAX s dng khng tng thch ti nhiu quc gia, lm hn chs ph bin cng ngh rng ri.

- Do cng ngh mi xut hin gn y nn vn cn mt s l hng bo mt.- Tuy c gi l chun cng ngh nhng tht s cha c chun do hin

gi ang s dng gn 10 chun cng ngh khc nhau. Theo din dnWiMAX ch mi c khong 12 hng pht trin chun WiMAX c chngnhn bao gm: Alvarion, Selex Communication, Airspan, Proxim Wilreless,Redline, Sequnas, Siemens, SR Telecom, Telsim, Wavesat, Aperto,Axxcelera.

- Cng ngh ny khi xng t nc M, nhng thc s cha c thng tinchnh thc no cp n vic M s dng WiMAX nh th no, khc ph

hu qu s c ra sao. Ngay c Vit Nam, VNPT (vi nh thu nc ngoil Motorola, Alvarion) cng trin khai mt s tnh min ni pha Bc,c th l Lo Cai nhng cng ch gii hn l cc im truy cp Internet tiBu in tnh,huyn ch cha c nhng kt lun chnh thc v tnh hiu qung k ca h thng.

Nh vy, c th thy rng kh nng cng nh li ch ca cc h thng WiMAXda trn h chun 802.16 l ht sc to ln mc d n vn tn ti mt s hn ch. N

cho php nh cung cp dch v trin khai nhanh chng cc h thng mng ca mnhtng kh nng cnh tranh ng thi cho php ngi tiu dng c thm nhiu lachn, tit kim hn trong cc chi ph. iu ny chnh l ng lc thc y cc nhsn xut v cc nh cung cp dch v pht trin h thng WiMAX.

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1.7. TNH HNH TRIN KHAI WiMAX

1.7.1. Tnh hnh trin khai WiMAX trn th gii Hin nay, trn th gii, c cc mng th nghim cng ngh WiMAX c nh

v di ng. Theo nh gi ca Maravedis Inc. th th trng vin thng bng rng cnh n nm 2010 c doanh thu vt 2 t USD. Hin nay, tc tng trng hngnm l 30%. Vic xut hin mt cng ngh truy cp khng dy bng rng mi nhWiMAX cho php trin khai nhanh dch v, s lm bng n th trng trong nhng

nm ti.n nay, c mt s nc i vo trin khai v khai thc th nghim cc dch

v trn nn Mobile WiMAX nh M, c, BrazilMt s kin c th coi l mt bc ngot quan trng ca WiMAX t ngy 15

19/10/2007 c quan vin thng quc t thuc lin hip quc ITU ph duyt cngngh bng rng khng dy ny vo b chun IMT-2000. Quyt inh ny aWiMAX ln ngang tm vi nhng k thut kt ni v tuyn hng u hin nay tron b chun IMT-2000 gm c GSM, CDMA v UMTS. iu ny m bo cho cc nhkhai thc v qun l trn ton th gii yn tm u t vo bng rng di ng thc sdng WiMAX.

1.7.2. Tnh hnh trin khai WiMAX th nghim ti Vit NamVNPT trin khai th nghim cng ngh WiMAX ti Lo Cai vo thng 10/2006

v nghim thu thnh cng vo thng 4/2007. Nm 2006, ti Vit Nam, c 4 doanh nghip c B Bu chnh Vin thng

cho php cung cp th nghim dch v WiMAX c nh l Viettel, VTC, VNPT vFPT Telecom. Sau khi th nghim xong, B s la chn 3 nh cung cp chnh thcho loi hnh bng rng khng dy ny.

Ngy 1/10/2007, Chnh ph cp php trin khai dch v thng tin di ng 3Gv dch v truy nhp bng rng khng dy WiMAX (theo cng vn 5535/VPCP-CN

ca vn phng Chnh ph). ng thi, Ph th tng ng cp php th nghim

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dch v WiMAX di ng cho 4 doanh nghip EVN Telecom, Viettel, FPT v VTCth nghim ti bng tn 2.3 - 2.4 GHz; VNPT th nghim ti bng tn 2.5 2.69

GHz.

1.8. KT LUN CHNGChng 1 ny khi qut c nhng c im c bn ca WiMAX bao gm

khi nim, cc phin bn, ph v cc bng tn c s dng cho WiMAX. Ngoi rachng ny cng nu ln c cc u im v nhc im h thng s dng cnngh WiMAX. Chng ny s l nn tng cho cc chng tip theo nhm tm hisu hn v h thng WiMAX.

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Chng 2: Cc k thut c s dng trong WiMAX

Chng 2CC K THUT C S DNG TRONG WiMAX

2.1. GII THIU CHNGVi kin trc m, linh hot, dung lng ln v chi ph trin khai thp lm cho

WiMAX tr thnh mt gii php hng u cho cc dch v v tuyn bng rng.Kh nng cung cp kt ni bng rng vi nhiu kch bn s dng t truy cp c

nh v di ng trn cng mt h tng mng v v th s to nn mt cu trc mnlinh hot, mang li cc dch v truy cp bng rng gi r v ha hn mt m hnhkinh doanh hp dn i vi cc nh cung cp dch v.

Vi cng ngh tng t trc y (FM, AM) v biu iu ch s ha hisut thp (PSK, BPSK v QPSK) c s dng rng ri trong cc mng ngy nay,cng ngh bng rng khng dy yu cu s dng cc biu iu ch theo th t cahn vi hiu qu tri ph tt hn. Tuy nhin, biu iu ch theo th t cao hny rt d b tc ng bi nhiu v hin tng a ng dn. C hai yu t ny

ph bin trong cc trin khai mng khng dy c mt khp ni v s lng ngdng ln.

OFDM, OFDMA v S-OFDMA l nhng cng ngh truy nhp mi ci tin htr knh cn thit t c hiu qu tri ph tt hn v thng lng knh cao h Nhng cng ngh truy nhp mi ny l nn tng cho WiMAX v l la chn cho cch thng bng rng di ng tip theo khc nhm cung cp nhiu loi hnh dch vtruyn thng a phng tin tc cao.

Trong chng ny, chng ta s kho st tng quan cc k thut tin tin c pdng trong cng ngh WiMAX nh l k thut OFDM, OFDMA, h thng anten tintin

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2.2. K THUT OFDM

2.2.1. Khi nimK thut OFDM l k thut ghp knh phn chia theo tn s trc giao

(Orthogonal Frequency Division Multiplexing). Trong OFDM, chui d liu ti u pht thng c tc rt cao. Dng d liu ny c chia thnh nhiu dng d lisong song tc thp hn nh b chuyn i ni tip-song song (S/P). Mi dng dliu song song sau c iu ch bi mt sng mang, cc sng mang ny cchn trc giao vi nhau m bo c th tch ring tng lung d liu ti u thK n cc sng mang ny c tng hp li v a ln tn s pht.

Hnh 2.1. So snh gia FDM v OFDM S lng cc sng mang con ph thuc vo nhiu yu t nh rng knh v

mc nhiu. Con s ny tng ng vi kch thc FFT. Chun giao tip v tuy802.16-2004 xc nh 256 sng mang con tng ng FFT 256 im, hnh thnhchun Fixed WiMAX, vi rng knh c nh. Chun giao tip 802.16-2005 cho php kch c FFT t 512 n 2048 ph hp vi rng knh 5MHz n 20MHz,hnh thnh chun Mobile WiMAX (Scalable OFDMA), duy tr tng i khongthi gian khng i ca cc k hiu v khong dn cch gia cc sng mang vi rng knh.

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C th thy r li ch ca OFDM khi xt qua knh truyn. Nu lung d liu gc chuyn trc tip ln sng mang v pht ln knh truyn, th bng thng rng

ca tn hiu pht s b tc ng chn lc tn s. Bi v, khi tn hiu truyn c bnthng rng (do tc bit cao), cc tn s khc nhau s c suy hao khc nhau khitruyn qua knh truyn v tuyn. iu ny dn n vic khi phc tn hiu ti mthu s phc tp, i hi phi c b cn bng. Trong OFDM, lung d liu c tcthnh N lung d liu tc thp, c bng thng hp. Do , khi truyn, cc lungd liu ny chu Fading phng cng .

Ti my thu, lung d liu trc tin c a v bng gc bi b trn. Lund liu ny sau c tch ra thnh N lung d liu tc thp, theo sau l b lthng thp v b quyt nh.

2.2.2. S khi OFDM

Hnh 2.2. S khi h thng OFDM u tin, dng d liu vo vi tc cao c chia thnh nhiu dng d liu

song song tc thp hn nh b chuyn i ni tip-song song (S/P). Mi dng dliu song song sau c m ha (Coding) s dng thut ton FEC (Forward Error

Correcting) v c sp xp (Mapping) theo mt trnh t hn hp. Nhng k t h

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D

liu

Dliu

S/P Mha&spxp

ChnPilot IFFT

Chndi bo v

P/S

Knhtruyn

P/S

spxpli &gii

m

clngknh FFT

Loi b di bo v S/P

AWGN w(n)


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hp c a n u vo ca khi IDFT ( y thc hin php bin i IDFngi ta dng thut ton IFFT). Sau khong bo v c chn vo gim nhi

xuyn k t (ISI), nhiu xuyn knh (ICI) do truyn trn cc knh v tuyn di nga ng. Dng d liu song song li c chuyn thnh ni tip nh b chuyn song song-ni tip (P/S). Cui cng, b A/D pha pht nh dng tn hiu thi gianlin tc v chuyn i ln min tn s cao truyn i xa.

Trong qu trnh truyn, trn cc knh s c cc ngun nhiu tc ng n nhnhiu Gausian trng cng (Additive White Gaussian Noise-AWGN). pha thu, tn hiu thu c chuyn xung tn s thp v tn hiu ri rc nh

c sau b D/A thu. Khong bo v c loi b v cc mu c chuyn i min thi gian sang min tn s bng php bin i DFT dng thut ton FFT (khFFT). Sau , ty vo s iu ch c s dng, s dch chuyn v bin v pha ca cc sng mang nhnh s c sp xp ngc tr li v c gii m. Cucng, chng ta nhn li c dng d liu ni tip ban u.

2.2.3. Chui bo v trong h thng OFDM u im ca phng php iu ch OFDM khng ch th hin hiu qu s

dng bng thng m cn c kh nng lm gim hay loi tr nhiu xuyn k hiu ISnh s dng chui bo v (Guard Interval- GI). Mt mu tn hiu c di l TS,chui bo v tng ng l mt chui tn hiu c di TG pha sau c sao chpln phn pha trc ca mu tn hiu ny nh hnh v sau (do , GI cn c gi lCyclic Prefix-CP). S sao chp ny c tc dng chng li nhiu xuyn k hiu ISI do

hiu ng phn tp a ng.

Hnh 2.3. Khi nim v chui bo v. Nguyn tc ny gii thch nh sau: Gi s my pht i mt khong tn hiu c

chiu di l TS, sau khi chn thm chui bo v c chiu di TG th tn hiu ny c

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Phn tn hiu c chPhn tn hiu c chGI


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chiu di l T=TS+TG. Do hiu ng a ng multipath, tn hiu ny s ti my thutheo nhiu ng khc nhau. Trong hnh v m t di y, hnh a, tn hiu theo

ng th nht khng c tr, cc ng th hai v th ba u b tr mt khong thgian so vi ng th nht.Tn hiu thu c my thu s l tng hp ca tt c ctuyn, cho thy k hiu ng trc s chng ln vo k hiu ngay sau , y chnh lhin tng ISI. Do trong OFDM c s dng chui bo v c di TG s d dngloi b hin tng ny. Trong trng hp TG MAX nh hnh v m t th phn bchng ln ISI nm trong khong ca chui bo v, cn thnh phn tn hiu c ch van ton. pha my thu s gt b chui bo v trc khi gi tn hiu n b gii ch OFDM. Do , iu kin cn thit cho h thng OFDM khng b nh hn

bi ISI l: max GT vi MAXl tr truyn dn ti a ca knh.

Khng c GI

C GI Hnh 2.4. ISI v cyclic prefix

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2.2.4. Nguyn tc gii iu ch OFDM Cc bc thc hin y u ngc li so vi pha my pht. Tn hiu thu s

c tch chui bo v, gii iu ch khi phc bng tn gc, gii iu ch sng mang con, chuyn i mu tn hiu phc thnh dng bit (tn hiu s) v chuyni song song sang ni tip

Hnh 2.5. Tch chui bo v

2.2.5. Cc u v nhc im ca k thut OFDM

Qua vic phn tch v c bn k thut OFDM nh trn, chng ta c th rt ramt s u im, nhc im chnh ca OFDM nh sau:

u im: S dng ph hiu qu nh ph tn s c dng gn nh ca s ch nh

nu s sng mang con ln. Loi b nhiu xuyn k t (ISI) v nhiu gia cc khung (IFI) nh s

dng tin t vng CP (Cyclic Prefix). Kh nng chng nhiu gia cc knh con rt tt nh vic s dng cc

sng mang con trc giao. K thut OFDM cho php thng tin tc cao c truyn song song vi

tc thp hn trn cc knh bng hp. Cc knh con ny c coi l ccknh fading khng la chn tn s nn c th dng cc b cn bng ngin trong sut qu trnh nhn thng tin. Ni nh vy, h thng OFDM

chng c nh hng ca fading la chn tn s.

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t(k-1)T

(k-1)TS

kT

kTS


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K thut OFDM l mt phng php hiu qu gii quyt a ngkhng nhiu bng hp tt v nhiu ny ch nh hng mt t l nh cc

sng mang con. Thc hin n gin trong min tn s bng cch dng gii thut FFT.

ng thi my thu n gin do khng cn b kh ICI v ISI nu khongd tr di.

Nhc im: OFDM l tp hp ca tn hiu trn nhiu sng mang, di ng ca tn

hiu ln nn c t s cng sut nh/trung bnh tng i ln s lm hnch hiu sut ca b khuch i m tn.

Mt mt hiu sut ph do chn khong d tr. Nhiu pha do s khng phi hp gia cc b dao ng my pht v

my thu, c th lm nh hng n cht lng h thng. Phi c s ng b chnh xc v tn s v thi gian, c bit l tn s.

Nh vy, k thut OFDM l gii php rt ph hp cho truyn dn v tuyn t cao ni chung v cho cng ngh Wimax ni ring. Theo phn tch v k thutOFDM nh trn , dung lng ca h thng s c nh gi thng qua s lng csng mang con c iu ch. S lng cc sng mang con ph thuc vo nhiu yt nh rng knh, mc nhiu, kiu iu ch, Con s ny (sng mang contng ng vi kch thc FFT. C th nh chun 802.16-2004 xc nh r 256 sngmang con, tng ng vi kch thc FFT 256 rng knh c lp, chun 802.16e

2005 cung cp kch c FFT t 512 n 2048 tng ng vi rng knh t 5 MHzn 20 MHz duy tr khong cch tng i khng i ca k hiu v khong dcch gia cc sng mang con c lp vi rng knh. Nh vy, vi cng nghOFDM, nh s kt hp ca cc sng mang con trc giao truyn song song vi cc khiu c khong thi gian di m bo rng lu lng bng thng rng khng b hch do mi trng khng theo tm nhn thng NLOS v nhiu do hin tng ang dn.

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2.3. K THUT OFDMA

2.3.1. Khi nimOFDMA (Orthogonal Frequency Division Multiple Access- a truy nhp phn

tn trc giao) l mt cng ngh a sng mang pht trin da trn nn k thut OFDMTrong OFDMA, mt s cc sng mang con, khng nht thit phi nm k nhau, gp li thnh mt knh con (sub-channel) v cc user khi truy cp vo ti nguyn sc cp cho mt hay nhiu knh con truyn nhn ty theo nhu cu lu lung cth.

2.3.2. c imOFDMA c mt s u im nh l tng kh nng linh hot, thng lng v tnh

n nh c ci thin. Vic n nh cc knh con cho cc thu bao c th, victruyn nhn t mt s thu bao c th xy ra ng thi m khng cn s can thino, do s gim thiu nhng tc ng nh nhiu a truy xut (Multi access

Interfearence - MAI)

Hnh 2.6. ODFM v OFDMA

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Hnh 2.7 m t mt v d v bng tn s - thi gian ca OFDMA, trong c 7ngi dng t a n g v mi ngi s dng mt phn xc nh ca cc sng man

ph c sn, khc vi nhng ngi cn li.a d a d a da d a d a da c e a c e a c ea c e a c e a c e

b e g b e g b e g b e g b e g b e g b f g b f g b f g b f g b f g b f g

Hnh 2.7. V d ca biu tn s, thi gian vi OFDMA

Th d c th ny thc t l s hn hp ca OFDMA v TDMA bi v mingi s dng ch pht mt trong 4 khe thi gian, cha 1 hoc vi symbol OFDM7 ngi s dng t a n g u c t c nh (fix set) cho cc sng mang theo bn khe thi gian.

2.3.3. OFDMA nhy tnTrong v d trc ca OFDMA, mi ngi s dng u c mt s sp t c

nh (fix set) cho sng mang. C th d dng cho php nhy cc sng mang ph theokhe thi gian nh c m t trong hnh

Vic cho php nhy vi cc mu nhy khc nhau cho mi user lm bin i thc

s h thng OFDM trong h thng CDMA nhy tn. iu ny c li l tnh phn ttheo tn s tng ln bi v mi user dng ton b bng thng c sn cng nh l cli v xuyn nhiu trung bnh, iu rt ph bin i vi cc bin th ca CDMABng cch s dng m sa li hng i (Forward Error Correcting- FEC) trn cc bc nhy, h thng c th sa cho cc sng mang ph khi b fading su hay ccsng mang b xuyn nhiu bi cc user khc. Do c tnh xuyn nhiu v fading thayi vi mi bc nhy, h thng ph thuc vo nng lng tn hiu nhn c trun

bnh hn l ph thuc vo user v nng lng nhiu trong trng hp xu nht.

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f

t


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a bc

c ba

b c b a

ca

Hnh 2.8. Biu tn s thi gian vi 3 ngi dng nhy tn a, b, c u c 1bc nhy vi 4 khe thi gian

u im c bn ca h thng OFDMA nhy tn hn hn cc h thng DSCDMA v MC-CDMA l tng i d dng loi b c xuyn nhiu trong mt t bo bng cch s dng cc mu nhy trc giao trong mt t bo.

Mt v d ca vic nhy tn nh vy c m t trong hnh 2.9 cho N sngmang ph, n lun lun c th to ra N mu nhy trc giao.

a f e d c b b a f e d cc b a f e dd c b a f ee d c b a f f e d c b a

Hnh 2.9. 6 mu nhy tn trc giao vi 6 tn s nhy khc nhau

2.3.4. H thng OFDMA

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t

f

t

f


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Hnh 2.10. Tng quan h thng s dng OFDM Ngun tn hiu c iu ch bng tn c s thng qua cc phng php i

ch nh QPSK, M-QAM.Tn hiu dn ng (bn tin dn ng, knh hoa tiu pilot symbol) c chn vo ngun tn hiu, sau c iu ch thnh tn hiuOFDM thng qua bin i IFFT v chn chui bo v GI. Lung tn hiu s cchuyn thnh tn hiu tng t trc khi truyn trn knh v tuyn qua anten phtTn hiu ny s b nh hng bi fading v nhiu trng AWGN (Addictive WhiteGaussian Noise ).

Tn hiu dn ng l mu tn hiu c bit trc pha pht v pha thu, pht km vi tn hiu c ch nhm khi phc knh truyn v ng b h thng.

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iuch bng tn

gc

Chn Pilotsymbol

IFFT ChnGI

ADC

DACChnGI

IFFT

Tch Pilot

symbol

Cn bngknh

Khi phcknh truyn

Gii iuch bngtn gc

Knhtruyn


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2.7.1. Phn tp thu v pht

Cc lc phn tp c s dng li dng cc tn hiu a ng v phx xy ra trong cc mi trng NLOS. Bng cch s dng nhiu ng ten (truynv/hoc nhn), fading, nhiu v tn hao ng truyn c th c lm gim. Phn ttruyn s dng m thi gian khng gian STC. i vi phn tp nhn, cc cng nghnh kt hp t l ti a (MRC) mang li u im ca hai ng thu ring bit. VMISO (nhiu u vo mt u ra).

Hnh 2.13. MISO

M rng ti MIMO, s dng MIMO cng s nng cao thng lng v tng ccng tn hiu. MIMO s dng nhiu ng ten thu v/hoc pht cho ghp knh theokhng gian. Mi ng ten c th truyn d liu khc nhau m sau c th c gi

m my thu. i vi OFDMA, bi v mi sng mang con l cc knh bng hptng t, fading la chn tn s xut hin nh l fading phng ti mi sng mangHiu ng ny c th sau c m hnh ha nh l mt s khuch i khng phc hp v c th n gin ha s thc hin ca mt my thu MIMO cho OFDMA

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Hnh 2.14. MIMO

2.7.2. Cc h thng anten thch nghi

Cc h thng anten thch nghi (Adaptive Antenna systems AAS) l mt phnty chn. Cc trm gc c trang b AAS c th to ra cc chm m c th c litp trung nng lng truyn t c phm vi ln hn. Khi nhn, chng c th t

trung hng c th ca my thu. iu ny gip cho loi b nhiu khng mongmung t cc v tr khc.

Hnh 2.15. Beam Shaping

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Hnh 2.16. AAS ng xung

2.8. KT LUN CHNGChng 2 trnh by cc c im k thut ca WiMAX, ni bt l cc k

thut OFDM, OFDMA, cng vi cc k thut iu ch thch nghi, sa li v cc h

thng anten thng minh. chng tip theo, chng ta s xem xt n kin trc mntruy cp WiMAX.

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Chng 3: Kin trc mng truy cp WiMAX

Chng 3KIN TRC MNG TRUY CP WIMAX

3.1. GII THIU CHNGTrong chng 2, chng ta tm hiu v cc k thut c s dng trong

WiMAX, trong chng ny, chng ta s tip tc tm hiu v cu trc ca mngWiMAX bao gm m hnh tham chiu, cc phn lp MAC (Media Access Control -iu khin truy nhp mi trng) v PHY (Physical Layer - Lp vt l).

3.2. M HNH THAM CHIUHnh 3.1 minh ha m hnh tham chiu v phm vi ca chun. Trong m hnh

tham chiu ny, lp PHY tng ng vi lp 1 (lp vt l) v lp MAC tng ngvi lp 2 (lp lin kt d liu) trong m hnh OSI.

Hnh 3.1. M hnh tham chiu [5]

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Hnh 3. 2 Chc nng cc lp trong m hnh phn lp chun IEEE 802.16 Ti trm thu, phn cng WiMAX tip nhn d liu t cc lp cao. Hnh 3.3 m

t hng di chuyn ca lung d liu qua cc lp. Mi lp s thc hin encapsulati(ng gi) d liu nhn c t cc lp trn. Ti lp thp nht, d liu c truydi dng bit qua mi trng truyn n ni nhn. Ti trm thu, d liu s decapsulation (m gi) ly cc thng tin cn thit v cc thng tin ny c gi

ln cc lp cao hn.

Hnh 3.3. Lung d liu qua cc lpGia lp con phn chung MAC v lp con bo mt khng nh ngha im truy

nhp dch v. Cc packet t lp con phn chung MAC khng c encapsulation tilp con bo mt. Phn tiu lp con phn chung MAC s biu th thng tin m h payload. Qu trnh m ha payload c thc hin ti lp con bo mt.

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3.3. LP IU KHIN TRUY NHP MI TRNG (MAC)

Lp MAC chun IEEE 802.16 cung cp giao din hot ng c lp vi lp vl do giao din lp vt l l giao din v tuyn. Phn ch yu ca lp MAC tp trunvo vic qun l ti nguyn trn airlink (lin kt v tuyn). Gii quyt c bi tonyu cu tc d liu cao trn c hai knh downlink v uplink. Cc c ch iukhin truy cp v thut ton cp pht bng thng hiu qu c kh nng p ng chohng trm u cui trn mi knh.

Lp MAC chun IEEE 802.16 c xy dng da trn kin trc tp trung, h

tr m hnh Point-to-Point, Point-to-Multipoint (PMP) v Mesh. Trm BS ng vaitr trung tm vi mt sectorized anten c kh nng iu khin ng thi nhiu sectoc lp.

Cc giao thc lp MAC chun 802.16 l hng kt ni. Vo thi im truy nhpmng, mi SS s to mt hoc nhiu kt ni truyn ti d liu trn c hai h(downlink v uplink). n v lp lch lp MAC s s dng ti nguyn airlink cungcp cc mc QoS phn bit. Lp MAC cng thc hin chc nng tng thch lin k

(link adaption) v truyn li t ng ARQ (Automatic Repeat Request) nhm duy trthng lng d liu i a vi t l li bit BER (Bit Error Rates) chp nhn cLp MAC chun IEEE 802.16 cng iu khin qu trnh truy nhp v ri khi mngca SS, thc hin to v truyn cc n v d liu giao thc PDU (Protocol DataUnit). Ngoi ra, lp MAC chun IEEE 802.16 cn cung cp lp con hi t c t dchv h tr lp mng t bo ATM (Asynchronous Transfer Mode) v lp mng gi(Packet).

Lp MAC chun IEEE 802.16 bao gm 3 lp con Lp con hi t c t dch v (Service-specific Convergency Sublayer CS). Lp con phn chung MAC (MAC Common Part Sublayer CPS). Lp con bo mt.

3.3.1. Kt ni v a ch

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Kt niTt c cc dch v, bao gm c cc dch v khng kt ni (connectionless) u

c nh x thnh cc kt ni tng ng. Mi mt kt ni i km vi cc tham sQoS tng ng vi 4 lp dch v. iu ny cung cp mt c ch cho php cc SSyu cu bng thng, QoS v cc tham s lu lng t BS. Cung cp c ch chuynti v nh tuyn cc gi d liu n lp con hi t tng ng. Cc kt ni l hng, mi mt kt ni c tham chiu bi mt gi tr 16 bit nh danh kt ni CI(Connection Identifier). Bng thng c cp pht lin tc hay c cp pht theoyu cu trn cc kt ni.

C hai loi kt ni c bn: kt ni qun tr (Management Connection) v kt nchuyn ti (Transport Connection). Kt ni qun tr c s dng truyn cc thng bo qun tr. Kt ni chuyn ti c s dng truyn d liu.

Kt ni qun tr chia lm ba kiu: c bn (Basic Connection), s cp (PrimaryConnection) v th cp (Secondary Connection).

Basic Connection: c s dng truyn cc thng bo ngn, yu cu tr.

Primary Connection: c s dng truyn cc thng bo qun tr dihn, khng yu cu tr nh cc thng bo thc hin qu trnh xc thcv thit lp kt ni.

Secondary Connection: c s dng truyn cc thng bo qun trchun nh SNMP (Simple Network Management Protocol), DHCP(Dynamic Host Configuration Protocol)

Transport connnection l cc kt ni n hng c s dng chuyn ti d

liu, cc tham s QoS v cc tham s lu lng ph hp vi dch v tng ng Ngoi ra cn c mt s cc lin kt c dnh ring cho cc mc ch khc nh ktni qung b (Broadcast connection), kt ni chuyn ti cc bo hiu xung t, thmd

a ch

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Mi mt trm SS c mt a ch MAC 48 bit duy nht, c s dng nh danhSS hoc c s dng trong qu trnh xc thc.

Mi mt trm BS cng c 1 a ch 48 bit nh danh trm nhng khng phi la ch MAC.

CID c xem nh l a ch s cp sau khi c khi to v c s dngtrong qu trnh hot ng ca h thng.

3.3.2. Lp con hi t MAC

Lp con hi t c t dch v tip nhn cc gi d liu t cc lp cao thng qu

cc im truy nhp dch v lp con hi t CS SAP (CS Service Access Point), nh xthnh cc n v d liu dch v lp MAC SDU (Service Data Unit). MAC SDU lcc n v d liu c trao i gia hai lp giao thc k cn nhau. Cc MAC SDUny c chuyn n lp con phn chung MAC thng qua cc im truy nhp dchv lp con phn chung (CPS SAP). Ti lp con phn chung MAC, cc SDU c phn loi v kt hp vi mt gi tr nh danh lung dch v SFID (Service FlowIdentifier) v mt CID. Ngoi ra, lp con hi t cn thc hin cc chc nng phc tpkhc nh PHS (Payload Header Suppression) v Reconstruction nhm lm tng hiuqu s dng ti nguyn.

Lp con hi t chun IEEE 802.16 nh ngha hai c t cho vic nh x ccdch v:

Lp con hi t ATM dnh cho cc dch v ATM. Lp con hi t packet: c nh ngha cho vic nh x cc dch v gi nh

IPv4 hoc IPv6, Ethernet v VLAN (Virtual Local Area Network).Ba c t Packet CS: IP Specific: S dng chuyn ti cc frame IP. H tr IPv4, Ipv6 v mobile

IP. IEEE Std 802.3/Ethernet: S dng chuyn ti cc frame 802.3 Ethernet

qua mng 802.16. IEEE Std 802.1Q-1998 VLAN: S dng chuyn ti cc frame 802.1Q

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VLAN tagged qua mng 802.16.

3.3.3. Lp con phn chung MAC Lp con phn chung MAC (CPS) h tr kin trc Point-to-Multipoint. Mt trm

gc BS (Base Station) c th gi thng tin n cc trm thu bao SS (SubcribleStation) v nhn thng tin t cc SS. BS nh ngha hai n v uplink-MAP (UL-MAP) v downlink-MAP (DL-MAP) cha thng tin m t knh c phn chiathnh cc khe thi gian. Qu trnh ranging, truyn d liu v cp pht bng thngc thc hin ti cc khe thi gian ring bit.

BS v SS lin lc vi nhau qua cc lin kt c c trng bi gi tr CID cgn trong qu trnh thit lp lin kt. Mt SS c th s dng nhiu kt ni. Cc kni c th l unicast (mt BS v mt SS s dng kt ni) hoc dng multicast (mBS v mt s SS s dng chung mt kt ni).

Lp con CPS cng chu trch nhim cp pht bng thng. Bng thng c cp pht cho mt trm SS mi cng nh cp b sung cho mt trm SS nu c yu cu

Mt s cc kt ni ca SS c cc mc QoS khc nhau, do bng thng cp pht chotng kt ni ph thuc vo mc QoS tng ng ca kt ni. Trong qu trnh cp ph bng thng, trm SS s nhn 2 thng bo: UL-MAP v DL-MAP. Thng bo UL-MAP cha tham chiu n cc khe (slot) cho php SS gi d liu n BS v thng bo DL-MAP cha tham chiu n cc khe cho php SS nhn d liu t BS.

Cc nh dng MAC PDU

MAC-BS v MAC-MS trao i cc bn tin, v cc bn tin ny c xem nhcc PDU, mt PDU c chiu di ti a l 2048 byte.

Hnh 3.4. nh dng MAC PDU

Trn hnh ta c th thy bn tin bao gm ba phn: tiu MAC chiu di c nhl 6 byte, payload chiu di thay i v phn kim tra li d vng CRC (Cyclic

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Redundancy Check). Ngoi tr cc PDU yu cu di thng (khng c payload), ccMAC PDU c th cha hoc cc bn tin qun l MAC hoc d liu lp con hi t

MAC SDU. Payload l ty chn, CRC cng ty chn v ch c s dng nu MSyu cu trong cc tham s QoS.

C hai loi tiu MAC: tiu MAC chung (GMH) v tiu MAC yu cudi thng (BR). GMH c s dng truyn d liu hoc cc bn tin qun l MATiu BR c s dng bi MS yu cu nhiu di thng hn trn UL. Tiu MAC v cc bn tin qun l MAC khng c m ha.

nh dng tiu MAC chung.

Hnh 3.5. nh dng ca tiu MAC PDU chung

Trn hnh 3.5, minh ha nh dng ca mt tiu MAC chung. ngha cctrng c gii thch trong bng trong bng 3.1.

TnChiu

di (bit)M t

CI 1Ch th CRC. Nu CI=1 th CRC c gn vo payload PDU sau khi m ha(nu c). Nu CI= 0 th khng cha CRC.

CID 16 nh danh kt ni

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Hnh 3.6. nh dng tiu yu cu di thng

TnChiu

di (bit)M t

HT 1 Loi tiu . c thit lp l 0.

CI 1

Ch th CRC1 = CRC c gn vo payload PDU sau khi m ha, nuc.0 = Khng cha CRC.

EC 1iu khin m ha0 = Payload khng c m ha

1 = Payload c m ha

Type 3Trng ny ch ra cc loi tiu con v payload c bitc mt trong payload bn tin.

BR 19 Bng thng yu cuCID 16 nh danh kt ni

HCS 8

Tun t kim tra tiu Mt trng 8 bit c s dng pht hin cc li trong

tiu . Bn pht s tnh ton gi tr HCS cho 5 byte utin ca tiu , chn kt qu vo trng HCS (byte cuicng ca tiu MAC).

Bng 3.2. Cc trng tiu MAC yu cu di thng

3.3.4. C ch yu cu v cp pht bng thng

Yu cu

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C ch yu cu bng thng c trm SS s dng thng bo cho trm BS ccp pht bng thng. Thng bo yu cu bng thng c th l tiu yu cu bng

thng hoc thng bo PiggyBack.Cc yu cu bng thng chia lm bn kiu:

o Implicit request: Trong thc t, kiu yu cu ny l nhng tha thun ti

thi im thit lp kt ni.o Bandwidth Request message: C hai kiu thng bo incremental hoc

aggregate. Khi trm BS nhn c mt thng bo yu cu bng thng kiuincremental, s cp pht b sung mt lng bng thng theo yu cu chokt ni. Ngc li, khi trm BS nhn c mt thng bo yu cu bngthng kiu aggregate, s cp pht mt lng bng thng thay th cholng bng thng hin ti. Trng Type trong tiu yu cu bng thngch th kiu thng bo yu cu bng thng l incremetal hay aggregate.

o PiggyBacked request (cho cc dch v khc UGS): c cha trong tiu

con Grant Management, khng c trng Type, do mc nh kiu

incremental.o Poll-Me bit (ch cho dch v UGS): c trm BS s dng thm d

bng thng cho cc dch v khc UGS. Cp pht

Lp MAC chun IEEE 802.16 cung cp hai kiu cp pht bng thng cho trmSS, c phn bit hnh thc cp pht bng thng cho mi kt ni hay cp pht bng thng cho mi trm SS. C hai kiu cp pht u yu cu bng thng trn cckt ni, cho php cc trm BS iu chnh cc yu cu QoS cho ph hp khi tin hnhcp pht bng thng.

Hai kiu cp pht bng thng c nh ngha:o Cp pht trn mi kt ni GPC (Grant per Connnection): Bng thng

c BS cp pht ring cho mi kt ni, v SS s dng bng thng ccp pht ch cho kt ni . Thch hp trong trng hp s lng cc kt

ni hn ch trn mi trm SS.

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o Cp pht trn mi trm thu bao GPSS (Grant per SubScrible): Bng

thng c BS cp pht ton b tng ng vi yu cu ca SS. SS chu

trch nhim phn phi lng bng thng c cp pht cho cc kt ni,duy tr mc QoS trn cc kt ni v tha thun cc mc dch v. Thchhp trong trng hp c nhiu kt ni trn mi trm SS.

Trong thc t, mt s yu t nh hng n qu trnh cp pht bng thng nhTrm BS khng nhn c thng bo yu cu bng thng hay trm SS khng nhnc bng thng c cp do li lp vt l, hoc trm BS khng cung cp ln bng thng theo yu cu

Do , trong c hai kiu cp pht, lp MAC chun IEEE 802.16 s dng c cht sa li (self-correcting) thay cho c ch gi acknowledge. C ch self-correcting ttn bng thng v tr nh hn c ch acknowledge.

i vi c ch t sa li, cc yu t gy nh hng n qu trnh cp pht bnthng s c gii quyt cng mt lc. Sau mt khong thi gian timeout thch hptrm SS s gi Banwidth Request n trm BS. Thng thng loi thng bo yu c

l incremental ngha l trm SS yu cu b sung bng thng cho mt kt ni. Tuynhin i lc thng bo yu cu bng thng l aggregate ngha l trm SS yu cu bng thng cho ton b cc kt ni m n qun l. Polling

C ch polling c thc hin ti BS, l qu trnh thm d cp pht bngthng cho SS gi Banwidth Request. C th cp pht cho tng SS ring bit hay chomt nhm cc SS. C hai kiu polling:

o Unicast: thm d mt SS ring bit. Nu nh mt trm SS khng cn cp

pht bng thng, n gi li request c di 0 byte.o Multicast v Broadcast: thm d mt nhm hay ton b cc trm do khng

bng thng thm d tng trm SS ring l.

3.3.5. C ch lp lch dch v v cht lng dch v (QoS)

Mc ch chnh ca vic lp lch dch v nhm cung cp mt mc QoS hp l

cho lung lu lng nhng vn s dng hiu qu ti nguyn.

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Chun IEEE 802.16 nh ngha bn lp dch v:o UGS (Unsolicited Grant Service): c thit k h tr dch v

Constant Bit Rate (CBR) l loi dch v c s dng bi cc kt ni yucu bng thng c nh v kh dng lin tc trong thi gian kt ni. Dchv CBR thng c dng cho cc ng dng thi gian thc yu cunghim ngt v tr v suy hao. V d cc kt ni T1/E1, ng dngVoIP.

o rtPS (Real-time Polling Service): c thit k h tr cc lung d liuthi gian thc trn cc kt ni yu cu nghim ngt v tr nhng likhng yu cu bng thng c nh, kch thc gi bin i. V d: lung

audio/videoo nrtPS (Non-Real-time Polling Service): c thit k h tr cc lung

d liu khng i hi thi gian thc v tr, vi kch thc gi bin iv tc d liu ti thiu m bo. V d: giao thc truyn ti file FTPcc dch v ATM GFR (ATM Guaranted Frame Rate)

o BE (Best Effort): c thit k h tr cc lung d liu thng thngkhng i hi thi gian thc cng nh tr. V d: dch v duyt Web.

Mi mt kt ni trn knh uplink c nh x thnh mt lung dch v kt hpvi mt lp dch v c th, c nh danh bi gi tr SFID 32 bit (Service FlowIdentifier).

Mi mt n v lp lch dch v l mt tp cc quy tc c p t trn b llch (scheduler) ca trm BS. Mi mt kt ni tng ng vi mt dch v d liring, i km vi cc tham s QoS tng ng v c thng lng ti thi imthit lp kt ni.

Khi cc packet c phn loi ti lp con hi t, mi mt packet s c khp vi mt lp QoS thch hp vi yu cu ca ng dng. Kin trc chun IEEE802.16 h tr ng thi nhiu lung d liu vi cc mc QoS phn bit bao gmthoi, VoIP, video lung, TFTP, HTTP v email.3.3.6. Lp con bo mt

Ton b bo mt ca 802.16 da vo lp con bo mt. Lp con bo mt l lcon gia MAC CPS v lp vt l. Mc tiu ca n l cung cp iu khin truy

nhp v s cn mt ca lin kt d liu, chi trch nhim m ha v gii m d li

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m a n v i ra khi lp vt l PHY v cng c s dng cho cp php v traoi kha bo mt, Ngn chn nh cp dch v. Bo mt ca 802.16 gm cc thn

phn sau: cc tp hp bo mt (SA), chng nhn X.509, giao thc cp php qun lkha ring t (authorization PKM), qun l kha v ring t (PKM) v m ha dliu.

3.4. LP VT LLp vt l cung cp kt ni v tuyn gia BS v SS. Chun IEEE 802.16 nh

ngha cc k thut khc nhau truyn thng tin qua mi trng v tuyn.Chun IEEE 802.16 h tr 2 bng tn: bng tn 10-66 GHz v 2-11 GHz.

Bng tn 10-66 GHz h tr cho cc mi trng truyn dn yu cu tm nhnthng LOS, khng c vt cn gia trm pht v trm thu. c t giao tipkhng gian (air interface) ti bng tn 10-66 Ghz c gi l WirelessMAN-SC, s dng phng thc truy cp TDMA (Time Division MultiplexingAccess) cho hng truyn uplink v phng thc truy cp TDM (Time

Division Multiplexing) cho hng truyn downlink. Bng tn 2-11 GHz (cp php v khng cp php) h tr mi trng truyn

dn khng c tm nhn thng NLOS, tn hiu c th truyn qua cc vt cntheo nhiu cch khc nhau.

C 5 c t lp vt l chun IEEE 802.16 c m t trong bng bn di:

Bng 3.3. c t vt l chun IEEE 802.16

Lp vt l chun IEEE 802.16 s dng phng php iu ch OFDM, bng tn

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c chia thnh nhiu sng mang con trc giao vi nhau nhm t c thng lngd liu v khong cch truyn ti a, chng nhiu hiu qu.

Ngoi ra, lp vt l cn cung cp mt s phng thc iu ch nhiu mc nhBPSK, QPSK, 16-QAM, 64-QAMcho php truyn nhiu n v thng tin trn mtn v thi gian.

Lp vt l h tr c 2 phng thc truyn song cng : song cng phn chia theothi gian TDD (Time Division Duplex) v song cng phn chia theo tn s FDD(Frequency Division Duplex). Ch TDD s dng cc khe thi gian, mi mt SSc BS cp cho cc khe thi gian s dng truyn v nhn d liu, cho php dliu truyn khng ng thi trn c hai hng uplink v downlink nhng c th sdng chung tn s. Ch song cng FDD phn chia thnh hai knh uplink vdownlink hot ng trn hai tn s ring bit, cho php truyn d liu ng thi trc hai hng.

Cc qu trnh Ranging v DFS (Dynamic Frequency Selection) c thc thi tilp vt l.

Ranging l qu trnh thc hin iu chnh cng sut pht ca trm BS ntrm SS ph hp vi v tr ca trm SS.

DFS l qu trnh t ng qut di tn dnh ring cho SS tm mt tn shot ng ph hp.

3.5. KT LUN CHNGChng ny trnh by kin trc mng truy cp WiMAX bao gm lp PHY v

ch yu l lp MAC. Vi s tp trung vo lp MAC, chng ny s gip chng tatm hiu v bo mt trong h thng WiMAX, din ra ch yu lp MAC c trn by chng tip theo.

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Chng 4: Kin trc bo mt chun IEEE 802.16

Chng 4KIN TRC BO MT CHUN IEEE 802.16

4.1. GII THIU CHNGTrong mi trng Internet, h thng WiMAX phi i mt vi nguy c b e

da tn cng bi nhiu phng thc khc nhau. H thng WiMAX c th b tn cn lp vt l hay lp MAC. Cc phng thc tn cng ti lp vt l c th l Jamminhay Scrambling.

Jamming l phng thc tn cng s dng mt ngun pht tn hiu ccng sut ln gy nhiu trm BS.

Scrambling l phng thc tn cng nhm mc ch chim dng bngthng ca SS yu cu t cc BS. [8]

Trong m hnh phn lp, lp con bo mt nm trn lp vt l, do lp vt lkhng c bo v. Tuy nhin trong khun kh chng ny ch trnh by c ch bomt c thc hin ti lp con bo mt chun IEEE 802.16.

Thc thi bo mt cho h thng WiMAX nhm bo v tnh ring t cho cc SS chng li cc nguy c e da tn cng v ngn chn cc truy cp tri php t bnngoi. C ch bo mt c thc thi trn c s m ha cc kt ni gia BS v SSgm mt s th tc c bn nh xc thc, iu khin truy cp, m ha thng boqun l kha

4.2. KIN TRC BO MTLp MAC c th b tn cng trong qu trnh xc thc hoc trong qu trnh truyn

d liu trn cc kt ni. Trong qu trnh xc thc, BS v SS s dng cc thng boqun tr trao i thng tin. Do , cc thng bo ny c th b nghe trm hoc bthay i ni dung nu nh khng c m ha. Trong qu trnh truyn d liu, lunglu lng cng c th b nghe trm hoc b mt.

M hnh kin trc bo mt chun IEEE 802.16 c m t bn di.

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Hnh 4.1. M hnh kin trc bo mt chun IEEE 802.16 [7] Mt SS trc khi truyn d liu phi thc hin xc thc vi BS c c

quyn truy nhp h thng. Lung d liu trc khi c truyn t BS n SS cc xc thc. Sau khi c cp quyn, d liu trong phn payload ca MAC PDUs c m ha trc khi truyn. Ti my thu cng thc hin xc thc d liu, trai cc thng tin cn thit gii m d liu. Tt c cc qu trnh ny c thc hiti lp con bo mt.

Lp con bo mt c hai giao thc thnh phn: Giao thc ng gi cc gi d liu c m ha truyn qua mng.

Giao thc ny c nh ngha gm hai thnh phn. Thnh phn th nhtl mt tp cc b m ha (cryptographic suite) c h tr. B m ha lmt tp hp cc phng thc m ha d liu, xc thc d liu v trao ikha m ha lu lng (TEK). Thnh phn th hai l cc quy tc c pdng cho cc thut ton m ha PDU payload.

Giao thc qun l kha PKM (Privacy and Key Management): cung cp

c ch bo v qu trnh phn phi kha t BS n SS. Thng qua giao

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thc ny, BS v SS c th ng b kha d liu vi nhau, ngoi ra, BS cth s dng thit lp quyn truy cp h thng i vi cc SS.

4.2.1. Tp hp bo mt Tp hp bo mt - Security Association (SA) l khi nim gm mt tp hp cc

thng tin bo mt cho cc kt ni gm cc kha v cc thut ton m ha. SA cchia s gia mt BS v cc SS nhm bo v qu trnh lin lc gia BS v SS. Mmt SA cha mt danh sch cc b m ha (cc thut ton m ha c la chn),cc kha m ha lu lng TEK (Traffic Encryption Key) v cc vector khi to(initialization vector) v c tham chiu bi mt gi tr nh danh SAID (SAIdentifier) 16 bit.

C ba loi SA: primary SA, static SA v dynamic SA. Mi SS c mt primary SA, c thit lp ti thi im khi to kt ni. Static SA c BS to trong qu trnh khi to SS, BS c th cung cp

nhiu dch v, mi dch v tng ng vi mt static SA. Dynamic SA c to ra khi mt lung lu lng mi xut hin v b

hy b khi lung lu lng b hy.Static SA v Dynamic SA c th chia s cho nhiu SS.Kt ni qun tr basic v primary khng c nh x sang cc SA tng ng,

nhng cc thng bo truyn trn hai kt ni ny c th c bo v. Mi mt kt nqun tr secondary c nh x thnh mt Primary SA. Tt c cc kt ni Transporlun c nh x thnh cc SA c sn, ring kt ni multicast Transport c nh xthnh static SA hay dynamic SA bt k.

4.2.2. Giao thc qun l kha PKM Chun IEEE 802.16 s dng giao thc PKM thit lp lin kt bo mt gi

BS v SS. SS s dng giao thc PKM yu cu BS chng thc v mt kha thc trao i. Ngoi ra, giao thc PKM cn h tr SS thc hin yu cu chng thc l

(reauthorization) v cp nht kha. PKM s dng chng thc X.509, thut ton m

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ha public key RSA, v cc thut ton m ha mnh thc hin trao i kha giaBS v SS.

Giao thc PKM s dng m hnh client-server. Trm SS ng vai tr l ccclient gi yu cu chng thc n BS, ng vai tr l server c trch nhim p ngyu cu m cc client gi n. M hnh ny bo m mi mt SS ch c duy nht mkha thc c chng thc. Cc thng bo qun tr lp MAC (PKM-REQ vPKM-RES) c s dng trong giao thc PKM.

4.3. QUY TRNH BO MTQuy trnh bo mt trong h thng WiMAX gm ba bc [7]

Hnh 4.2. Quy trnh bo mt Xc thc (Authentication)

Trm SS thc hin xc thc vi BS bng cch gi thng bo yu cu xc thc(chng thc X.509). BS thc hin xc thc SS v thng lng kh nng bo mvi SS (cc thut ton m ha m SS h tr), sau khi thng lng, mt SA c tv c tham chiu bi gi tr SAID. Tip , SS gi thng bo AuthorizationRequest yu cu cp quyn truy cp. BS s kim tra v gi li thng boAuthorization Reply cha kha AK (Authentication Key) cho SS c s dng trongqu trnh trao i kha. Qu trnh xc thc hon tt khi c BS v SS u gi khaAK.

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Trao i kha d liu (Data Key Exchange)Trm SS gi thng bo TEK Key Request yu cu BS cp cho mt kha m ha

lu lng TEK (Traffic Encryption Key), c s dng trong qu trnh m ha dliu. BS sau khi kim tra li cc thng tin c SS gi n, nu cc thng tin hp lBS s to ngu nhin mt kha TEK v gi li cho SS thng bo TEK Key Respondcha kha TEK. Qu trnh trao i kha d liu hon tt khi c BS v SS u gikha TEK. M ha d liu

Sau khi qu trnh trao i kha d liu thc hin xong, SS tin hnh m had liu trc khi truyn. Qu trnh m ha ch c thc hin cho phn payload cMAC PDU. Cc thng bo qun tr khng c m ha.

4.3.1. Xc thcQu trnh xc thc c trnh by trn hnh

Hnh 4.3. Qu trnh xc thc SS vi BS u tin, SS gi thng bo Authentication Information cha chng thc X.509

(RFC 3280) ca nh sn xut SS [8]. Chng thc ny gm mt public key v mt a

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ch MAC ca SS. Tip , SS gi thng bo Authorization Request cho BS, thng bo ny yu cu BS cp cho mt kha AK v cc gi tr SAID nh danh cc Static

SA tng ng vi cc dch v m SS ng k. Thng bo Authorization Request bao gm:

o Mt chng thc X.509 ca nh sn xut SS.o Mt b m ha (Cryptographic Suite) m SS h tr. Mi mt n v trong

b m ha bao gm mt cp thut ton m ha v xc thc gi d liu mSS h tr.

o Mt gi tr SAID tng ng vi Primary SA.

Sau khi nhn c thng bo Authorization Request, BS tin hnh xc thc SSda vo cc thng tin trong thng bo Authorization Request. Sau khi nh danhc SS l hp php v xc nh c cc thut ton m ha v cc giao thc cSS h tr, BS s s dng public key ca SS to kha AK (128 bit). Sau BS gthng bo Authorization Reply cho SS, thng bo Authorization Reply bao gm:

o Mt kha AK.o Mt s tun t kha (0-15) phn bit cc kha AK vi nhau.o Mt gi tr thi gian sng (life-time) ca kha AK. Gi tr ny trong

khong 1-70 ngy, mc nh l 7 ngy.o Mt gi tr SAID tng ng vi Primary SA v mt hoc nhiu gi tr

SAID nh danh cc Static SA tng ng vi cc dch v SS ng k.Sau mt thi gian nht nh, SS thc hin qu trnh yu cu cp quyn li

(Reauthorization) cp nht kha AK. Qu trnh Reauthorization tng t nh qutrnh Authorization ngoi tr vic SS khng gi thng bo AuthenticationInformation.

Mi kha AK c mt thi gian sng nht nh. V c BS v SS u h tr ngthi hai kha AK tn ti cng mt lc nn thi gian sng ny c th chng ln nhaugia cc AK nhm trnh tnh trng cc dch v b tm ngng t ngt do gi tr life-time ca kha ht hn.

V BS xc thc SS bng chng thc X.509, do c th trnh c nguy c b

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tn cng t cc SS gi danh.

4.3.2. Trao i kha d liuQu trnh trao i kha d liu c m t bn di [7]

Hnh 4.4. Qu trnh trao i kha d liuQu trnh trao i kha c thc hin tng ng vi tng dch v m SS

ng k trong qu trnh thit lp kt ni. Mi dch v tng ng vi mt Static SA vc nh danh bi mt gi tr SAID tng ng.

Sau khi nhn c thng bo Authorization Reply, SS s dng gi tr khaAK to hai kha gm: kha m ha kha (KEK Key Encryption Key) 128 bit

c s dng m ha kha TEK trong sut qu trnh truyn v kha xc thcthng bo (HMAC - Hash functionbased Message Authentication Code) 160 bit. Tip SS gi thng bo TEK Request yu cu BS cp cho mt kha m ha lulng TEK, kha ny c dng m ha d liu. Thng bo TEK Request gm:

o S tun t kha AK c cp trong qu trnh xc thc.o Mt gi tr SAID tng ng vi mt Static SA ca mt dch v c th m

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SS ng k.o Mt gi tr HMAC-SHA1.

Sau khi nhn thng bo TEK Key Request t SS, BS s dng thng tin trongthng bo TEK Key Request kim tra gi tr kha AK, nu ph hp s tin hnhto ngu nhin mt kha TEK (128 bit). Kha TEK c to bi cc phng thcTriple-DES (s dng 128 bit KEK), hoc phng thc RSA (s dng public key caSS), hoc phng thc AES (s dng 128 bit KEK). Cc phng thc m ha nyc ch th bi gi tr ca mt n v trong b m ha. Sau , BS gi thng boTEK Key Reply cho SS, thng bo TEK Key Request gm:

o S tun t kha AK c cp trong qu trnh xc thc.o Mt gi tr SAID tng ng vi mt Static SA ca mt dch v c th m

SS ng k.o Mt kha TEK m ha.o Mt gi tr thi gian sng (life-time) ca kha TEK.o Gi tr CBC-IV (CBC Inittialization Vector) m ha d liu.o Mt gi tr HMAC-SHA1 xc thc cc thng bo.

Qu trnh trao i kha d liu hon tt khi c BS v SS u gi kha TEK.

4.3.3. M ha d liuSau khi thc hin xong qu trnh trao i kha, phn d liu payload s c m

ha trc khi truyn s dng kha TEK. Ring cc thng bo qun tr th khng c

m ha.

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Hnh 4.5. nh dng payload trc v sau khi m haKhi d liu payload sau khi m ha c b sung hai trng: trng PN

(Packet Number) c di 4 byte biu th s tun t gi sau khi m ha, c tngln mt n v mi khi mt MAC PDU c truyn. Trng Ciphertext ICV(Ciphertext Integrity Check Value) m t gi tr kim tra tnh ton vn phn payload c m ha.

Chun IEEE 802.16 h tr hai thut ton m ha d liu:o Thut ton DES (Data Encryption Standard).o Thut ton AES (Advanced Encryption Standard).

4.4. HN CH CA KIN TRC BO MT IEEE 802.16

Kin trc bo mt chun IEEE 802.16 s dng c ch xc thc da trn chngthc X.509 v cc c ch m ha kha hiu qu, nhng cng c mt s hn ch sau: Khng h tr c ch xc thc BS: C ch xc thc ch thc hin theo mt chi

t SS n BS. Khng c c ch cc SS c th xc thc BS m n kt ni tiiu ny c th dn n nguy c xut hin mt BS gi danh mt BS hp phgy nn s nhm ln cho cc SS khi thc hin kt ni n BS. Cc phng thtn cng theo kiu gi danh ny li ph thuc vo kiu mng. V d, i vi mn

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WiFi 802.11, s dng phng thc a truy nhp cm nhn sng mang, mt k tcng (acttacker) c c ID ca AP (Access Point) v to mt thng bo vi ID

hp php, acttacker s ch cho n khi mi trng mng nhn ri v khi truyn thng bo, iu ny c th gy ra s nhm ln. Tuy nhin i vi mngWiMAX, phng thc trn li kh thc hin do h thng s dng phng thc truy cp phn chia theo thi gian, BS gi danh cng c th to cc thng bo vinh danh ca BS thc. BS gi danh phi ch cho n khe thi gian c cp phcho BS v truyn cng thi im vi BS thc, tuy nhin n phi iu chnh cng ca tn hiu truyn phi ln hn cng ca tn hiu truyn ca BS thCc trm SS s nhn v gii m tn hiu c gi t mt BS gi danh thay cho Bthc.Do , c th b sung vo mt chng thc BS c s dng mt SS xc nhchnh xc BS m n s kt ni ti.

Khng h tr c ch m ha cc thng bo qun tr: Cc thng bo qun tr khngc m ha, nhng c xc thc. C ch xc thc thng bo qun tr c s

dng l HMAC (Hashed Message Authentication Code) c nhiu nhc im, do nguy c b mt thng tin t cc thng bo b tn cng s nh hng n hong lin lc gia cc trm vi nhau.

Khng h tr mt c ch hiu qu chng li hnh thc tn cng t chi dch vDoS (Denial of Service): Cc attacker c th s dng SS thc hin gi yu cuxc thc n BS vi s lng nhiu v lin tc, lm cho BS mt kh nng x l.

4.5. KT LUN CHNGChng 4 ny trnh by c bn v kin trc bo mt v cc quy trnh thc

hin bo mt gia BS v SS. Ngoi ra, chng ny cn nu ln c cc im cnhn ch ca kin trc bo mt IEEE 802.16 da trn chng thc X.509.

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Chng 5: M phng hot ng h thng WiMAX

Chng 5M PHNG HOT NG H THNG WiMAX

5.1. GII THIU CHNGVic m phng hot ng ca h thng WiMAX nhm mc ch kim chng l

nhng l thuyt nghin cu nh qu trnh truy nhp h thng, c ch yu cu vcp pht bng thng, c ch lp lch dch v v qu trnh trao i mt s cc thng bo bo hiu nh UL-MAP, DL-MAP, UCD v DCD, cc thng bo ranging(RNGREQ v RNGRES)...

5.2. MI TRNG M PHNGMi trng thc hin m phng l NS-2 (Network Simulator) phin bn 2.29.

NS-2 l mt cng c m ngun m cho php m phng mng chuyn mch gi, htr m phng cc giao thc nh TCP, UDP, cc giao thc nh tuyn, giao thc lpMAC trn mi trng mng v tuyn v hu tuyn nh wireless LANs, Mobile Ad

hoc Networks (MANETs), mng v tinh NS-2 l mt n v m phng hng i tng. Cu trc ngn ng bao gm ha

thnh phn: ngn ng hng i tng C++ v OTCL c phn bit theo 2 mciu khin v mc x l gi. C++ c s dng x l mc gi trong khi OTCLc s dng nh ngha cc thng s cu hnh m phng nh topology mngkiu n v lp lch, thi im khi u v kt thc lung d liu, kiu lung vnh danh nt ngun v ch

Tuy nhin, phin bn NS-2 mi nht 2.29 ch h tr m phng lp LL (Link Layer), lp MAC v lp vt l ca chun IEEE 802.11, khng h tr m phng ccthnh phn ca chun IEEE 802.16. Do , trong n ny s dng moduleWiMAX for NS-2(gi tt l module WiMAX) thc thi chun IEEE 802.16 trong NS-2 (phin bn 2.29).

Module WiMAX for NS-2 c thit k v pht trin bi cc thnh vin ca Networks and Distributed Systems Laboratory (NDSL) v Computer Science and

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Information Engineering thuc i hc Chang Gung, i Loan. Tt c cc phin bnca module WiMAX c dowload hon ton min ph ti a ch

http://ndsl.csie.cgu.edu.tw.V tr ca module WiMAX trong kin trc NS-2 c trnh by bn di.

Hnh 5.1. Module WiMAX trong kin trc NS-2 [13] Module WiMAX c tch hp vo kin trc sn c ca mt nt wireless trong

NS-2.Trong kin trc trn, mt nt wireless bao gm cc thnh phn: Traffic

Generating Agent (address classifier, port classifier, agent protocol, agent routing),lp LL (Link Layer), lp MAC, hng i v knh vt l. Cc classifier chu trchnhim phn phi cc gi tng ng vi cc agent. Agent protocol biu din cho lpapplication v agent routing biu din cho lp IP. Khi mt packet i t agent protocol

n agent routing, agent routing s t a ch ca ch vo gi v chuyn tip n

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lp LL. Lp LL s dng giao thc phn gii a ch ARP (Address ResolutionProtocol) xc nh a ch MAC ca ch. Lp LL t a ch MAC ca ch vo

gi v chuyn n lp MAC. Lp MAC s thc hin cc chc nng tng ng v xnh thi im gi gi trn knh. Sau , chuyn gi n lp vt l. Lp vt l chutrch nhim gi gi trn knh wireless n ni nhn.

Module WiMAX thc hin m phng lp con phn chung MAC chun IEEE802.16 trong NS-2. C th, cc thnh phn c thc thi trong module:

C ch cp pht bng thng GPC (Grant per Connection). UCD, DCD, DL-MAP, UL-MAP, RNG-REQ, RNG-RSP, BW-REQ. To v truyn MAC PDU (ti BS v SS), phn mnh v ng gi. C ch lp lch (trn knh uplink, downlink) bn kiu dch v (UGS,

rtPS, nrtPS, BE).Module thc thi lp MAC IEEE 802.16 c vai tr tng t nh module IEEE

802.11 v c t trong cng th mc ~/mactrong NS-2.

5.3. M PHNG5.3.1. Gi thuyt Cc gi thuyt c s dng trong m phng:

Ch thc thi lp con phn chung MAC chun IEEE 802.16, khng thcthi c ch bo mt c thc hin bi lp con MAC bo mt.

Khng cp n khong thi gian mt trm SS ng b vi BS.

Tt c cc trm BS v SS u s dng kiu anten omni-directional cthit lp sn trong lp vt l ca NS-2 truyn thng.

Khng thc thi lp vt l chun IEEE 802.16. Nhng s dng li ccthnh phn sn c ca lp vt l chun IEEE 802.11 c h tr trong NS-2 nh cc kiu knh truyn, kiu anten, m hnh truyn sng vtuyn

Kiu hng i l Droptail (FIFO First In First Out).

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Gi s trong qu trnh truyn gia BS v SS hoc ngc li khng xy rahin tng mt gi, do khng thc thi c ch ARQ (Automatic Repeat

Request).

5.3.2. Kch bn m phng M hnh mng c s dng m phng da trn kin trc Point-to-

Multipoint (chun IEEE 802.16) bao gm: mt trm gc BS (node_0) v 2 trm thu bao SS (node_1, v node_2), c t c nh ti cc ta cho trc.

Hnh 5.2. Kin trc mng m phng Trong kch bn m phng trn: SS_1 gi cc thng bo ranging, thng bo

BWREQ v bt u truyn d liu n BS (knh uplink). Sau , SS_2 gi d liun BS. Cc qu trnh truyn kt thc ti thi im 10s.

Cc thng s s dng: Bng thng kt ni: 10 Mbps/ sector. tr trn kt ni: 10 ms. Phm vi m phng: 1000 x 1000. Giao thc nh tuyn: DSDV (Destination Sequence Distance Vector). Kch thc ti a ca hng i l 50 (s gi ti a cha trong hng i).

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Lp dch v c thit lp trn kt ni gia BS v SS_1 l UGS (biudin cho cc ng dng VOIP) v lp dch v thit lp trn kt ni gia

BS v SS_2 l rtPS (biu din cho ng dng video, MPEG4). Drop packet rate: < 5%. Thi gian thc hin m phng: 10s.

5.4. PHN TCH KT QU M PHNG5.4.1. Hot ng

Vo thi im bt u m phng, cc SS tin hnh qut cc knh trongdi tn c nh ngha tm mt knh downlink thch hp v ng b. Sau , cc SS nhn cc thng bo m t knh vt l DCD (downlink)v UCD (uplink) ly cc thng s cn thit.

Tip , cc SS gi yu cu ranging (thng bo RNGREQ) n BS.

Hnh 5.3. Cc SS gi yu cu ranging Tip , BS gi li cc p ng ranging (thng bo RNGRSP) v cc

thng bo ULMAP, DLMAP cha cc thng tin lp MAC nh thi im

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truy cp v cc thng tin khc trn c hai knh uplink v downlink.

Hnh 5.4. BS gi p ng ranging Sau khi nhn c thng bo RNGRSP t BS. Ti thi im 1, SS_1

gi yu cu cp pht bng thng (thng bo BWREQ) cho BS, sau khinhn c bng thng cp pht, SS_1 bt u truyn d liu n BS.

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Hnh 5.5. SS_2 gi yu cu bng thng

Hnh 5.6. SS_2 gi d liu (rtPS) cho BS

5.4.2. Tnh lng bng thng c s dng trn BS

Hnh 5.7. th bng thng c s dng trn cc knh truyn

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Cc thng tin m phng c ghi li trong file ~.tr bao gm kiu s kin

(send, receive, drop, forward), thi im xy ra s kin, nt thc hin s kin, thngtin gi v kch thc gi, kiu trace c s dng

Hnh 5.8. Thng tin trong file ~.tr c import vo excel Sau khi import thng tin file ~.tr vo excel, chng ta tin hnh thng k cc s

liu ti node 0 (BS).Tng s gi (packet) trong qu trnh m phng m node 0 (BS) x l: 9259.Trong

Tng s gi nhn (r): 2712. Tng s gi gi (s): 6305. Tng s gi drop (d): 240.

Tng dung lng trong qu trnh m phng m node 0 (BS) x l: 794347 byte.

Trong : Dung lng nhn (r): 274148 byte.

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Dung lng gi (s): 375404 byte. Dung lng drop (d): 144795 byte.

Bng thng trung bnh node 0 (BS) s dng trong thi gian m phng:794347*8/10/(1024)2= 0.606 Mbps

5.5. NHN XT Bng thng trung bnh node 0 (BS) s dng trong sut qu trnh m

phng nm trong gii hn ra (10Mbps).

T l gi drop (d) chp nhn c (di 5%). H thng hot ng tt.

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Kt lun v hng pht trin ti

KT LUN V HNG PHT TRIN TI

Kt lun n gii quyt c cc vn c bn c t ra phn u bao gm

Tng quan v cng ngh WiMAX, cc c im v hot ng ca WiMAX, nhngc s quan trng ca WiMAX, cc chun WiMAX, cc k thut c ng dngtrong WiMAX, kin trc bo mt c xy dng trong WiMAX. Ch yu tp trung cc kha cnh sau: Hot ng ca WiMAX ch yu tp trung lp MAC (qu trnhtruy nhp mng, c ch yu cu v cp pht bng thng, c ch lp lch dch vKin trc bo mt c xy dng v quy trnh thc hin bo mt trong WiMAX; M phng hot ng h thng WiMAX.

Hng pht trin ti Nhng vn c trnh by trong n ny vn cn hn ch phm vi, ch t

trung vo chun IEEE 802.16 dnh cho cc ng dng truy cp bng thng rng c

nh (IEEE 802.16-2004). Do , trong thi gian ti hng pht trin ca ti stp trung vo nghin cu chun IEEE 802.16 dnh cho cc ng dng di ng WiMAX di ng (IEEE 802.16e).

WiMAX di ng l gii php khng dy bng rng cho php ph sng mngkhng dy v c nh nh cng ngh truy nhp v tuyn bng rng trn din rng vkin trc mng linh hot (Point-to-Point, Point-to-MultiPoint, Mesh). Mt s cim chnh WiMAX di ng h tr: Tc d liu cao; Tnh mm do; Kh nn bo mt mnh; Kh nng di ng; bao ph rn

Mô hình mô phỏng hoạt động của hệ thống WiMAX VanLuong.Blogspot.Com

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