Tong Quan Ve Wimax

8/2/2019 Tong Quan Ve Wimax

1/22

Tng quan v cng ngh Wimax Trang 11. TNG QUAN CNG NGH WIMAX

1.1Lch s

Ngy nay s pht trin ca mng vin thng vi dch vngy cng a dng lm cho

cc cng ngh truy nhp tin tin ngy cng c pht minh v a vo phc v. Hin

nay chng ta bit n truy nhp Internet vi cc dch v quay s Modem thoi, ADSL

hay cc ng thu bao ring hoc s dng cc h thng v tuyn nh in thoi di ng

hay mng WiFi. Mi phng php truy nhp mng u c c im ring:

Vi Modem quay sin thoi th thc thp. ADSL c tc ln ti 8Mb/s nhng cn c ng dy kt ni. Cc ng thu bao ring th gi thnh t m li kh trin khai vi cc khu vc

c a hnh phc tp.

H thng thng tin di ng hin nay cung cp tc truyn 9,6Kb/s l rt thp sovi nhu cu ca ngi s dng.

GSM (2G),GPRS (2,5G) cho php truy nhp tc 172,2Kb/s hay EDGE 300n 400Kb/s cng cha p ng nhu cu ngy cng tng ca cc dch v

Internet.

H thng di ng 3G th tc truy nhp Internet cng khng vt qu 2Mb/s.

Mng WiFi (hay LAN khng dy) ch c th p dng cho cc my tnh trao ithng tin khong cch ngn.

Vi thc t cc cng ngh nh vy, WIMAX (Worldwide Interoprability for

Microwave Access) ra i nhm cung cp mt phng tin truy nhp Internet khng

dy tng hp c th thay th cho ADSL v WiFi. H thng WIMAX c th cung cp

ng truyn vi tc ln ti 70Mb/s v c bn knh ph sng ca mt trm l 50Km.

M hnh ph sng ca WIMAX tng t nh mng t bo. Hot ng ca WIMAX rtmm do v tng tnh ca WiFi khi truy nhp mng tc l khi mt my tnh c nhu

cu truy nhp mng th n s tng kt ni n trm anten WIMAX gn nht.iu quan

trng nht WIMAX xy dng da trn tiu chun IEEE.802.16.


2/22

Tng quan v cng ngh Wimax Trang 21.2 Chun IEEE 802.16

C th nhiu nh cung cp dch v v vn hnh cn xa l vi chun IEEE 802.16

(WiMAX) nhng y s l cng ngh khng dy mang tnh cch mng trong ngnh cng

nghip dch v khng dy bng rng. Chun 802.16, giao tip dnh cho h thng truy cp

khng dybng rng c nh cn c bit n vi tn chun giao tip khng dy IEEE

WirelessMAN. Chun c thit k mi hon ton vi mc tiu cung cp nhng trc kt

ni trc tip trong mng ni th (Metropolitan Area Network-MAN) t bng thng

tng ng cp, DSL, giao din T1/E1 ph bin hin nay.

PAN

LAN

MAN

WANIEEE 802.20

IEEE 802.16

Wireless MAN

IEEE 802.11

IEEE 802.15ETSI

HIPERPAN

ETSI

HIPERLAN

ETSI HIPERMAN

& HIPERACCESS

3GPP EDGE

(GSM)

Hnh 1Chun khng dy ton cu

Thng 1/2003, IEEE cho php chun 802.16a s dng bng tn t 2GHz n 11GHz;rng hn bng tn t 10GHz n 66GHz ca chun 802.16 pht hnh thng 4/2002 trc

. Nh c tnh khng dy m cc nh cung cp dch v v vn hnh c th trin khai

ng trc d dng, tit kim chi ph n nhng vng a hnh him tr, m rng nng

lc mng ti nhng tuyn cp ngtrc ang qu ti; c bit ng ph khng b "o

ln lp xung" nh hin nay. Thit b pht IEEE 802.16a c th lp ngay trn nc ta nh

ch khng cn u t t trn thp cao hoc nh ni nh nhng cng ngh khc.H

thng 802.16a chun c th t n bn knh 48km bng cch lin kt cc trm c bnknh lm vic 6-9 km.

Trong qu trnh pht trin 802.16, tnh lin thng lun c cao. u tin, din n

Worldwide Interoperability for Microwave Access (WiMAX) c thnh lp vo nm

2003 v qui t c nhiu cng ty hng u nh Intel, LG Electronics, Motorola, Fujitsu,


3/22

Tng quan v cng ngh Wimax Trang 3Siemens... thc y cc nh sn xut h thng truy xut khng dy bng rng a ra

thit b tng thch IEEE 802.16, WiMAX cng hp tc cht ch vi lin minh Wi-Fi

h tr tt chun IEEE 802.11. t c s lin thng, WiMAX buc phi to mt

s System Profile tng ng vi qui nh s dng tn s khc nhau ca tng khu vc a

l.V d, nh cung cp dch v ti chu u dng bng tn 3,5GHz vi bng thng

14MHz i hi thit b h tr knh bng thng 3,5MHz hoc 7 MHz, chc nng TDD

(Time Division Duplex) hoc FDD (Frequency Division Duplex).Tng t, nh cung cp

dch v Internet khng dy (WISP) ti M li dng bng tn 5,8GHz UNII nn thit b h

thng cn phi h tr bng thng 10MHz v k thut TDD.

Trong qu trnh xy dng khung chun, 802.16a k tha cc h thng c c th

c ng dng rng ri nh thit k ban u. OFDMA dng trong 3 lp PHY c thitk m c th iu chnh linh hot, thch ng vi tt c cc knh c rng bng thng

t 1,75MHz n 20MHz. Single Carrier Access (SCa) trong Wi-Fi c gi li trong

802.16a lm ng lin kt xng sng, trong khi OFDM vi FFT (Fast Fourier

Transform) 256 im li h tr nhng truy xut c nh bng thng ln n 10MHz. K

thut OFDMA c ci tin da trn OFDM h tr h di ng tc cao, cho php

knh ha d liu ti xung (Downlink-DL) v ti ln (Uplink-UL), n nh hng s t l

gia kch thc FFT vi rng knh...


4/22

Tng quan v cng ngh Wimax Trang 4

Hnh 2:Cu trc 802.16 cng nghip.

Lp MAC 802.16 c thit k h tr ng dng im-a im da trn CSMA/CA

(Collision Sense Multiple Access with Collision Avoidance).MAC AP 802.16 qun l ti

nguyn UL, DL v gm lun c chc nng nh thi truyn v nhn. Lp MAC cn c

mt s chc nng h tr ng dng din rng m tnh di ng khng n nh nh tch hp

dch v di ng: bnh chn tc thi (realtime Polling Service) v khng tc thi (non-

realtime Polling Service)...; ng gi/phn mnh tng hiu qu s dng bng tn;

Qun l kha ring t (PKM-privacy key management) bo mt t lp MAC; H trpht a lung; Chuyn mch tc cao; Qun l nng lng. PKM phin bn 2 cn c

kh nng kt hp vi giao thc xc thc m rng (EAP-Extensible Authentication

Protocol).

Tin chun Hu chun

Sau khi chun ha, nh sn xut thit b ch

cn tp trung y nhanh thit k v gimgi (biu din bng cc lp mu xanh).


5/22

Tng quan v cng ngh Wimax Trang 5Vi tc ti d liu ln n 75Mbps, mt knhp ng ca trm 802.16a hon ton

nng lc cng lc phc v 60 khch hng kt ni cp T1 v hng trm kt ni DSL gia

nh, vi bng thng knh l 20MHz. Trong thc t, t hiu qu kinh t, cc nh vn

hnh v cung cp dch v thng phi chp nhn cn i phc v thnh phn khch hng

doanh nghip doanh thu cao vi thnh phn thu bao gia nh s ng. V th, chun

802.16a h tr thit thc nh vn hnh mng, cho php cu hnh mc u tin cho tng

cp dch v.Nh th, doanh nghip c th t ch u tin dch v cp T1 cho doanh

nghip hoc dch v tc DSL cho ngi dng gia nh.c t 802.16a cn bao gm

tnh nng bo mt v QoS cn thit h tr nhng dch v thoi v video trc

tuyn.Dch v thoi 802.16 c th dng k thut thoi TDM (Time Division Multiplexed)

hoc VoIP (Voice over IP).

1.3 ng dng cng ngh WiMAX

Sau khi ra i, 802.16a nhanh chng c trin khai ti chu u, M v th hin mt

s li ch c th.

1.3.1 Mng ng trc:

802.16a l cng ngh khng dy l tng lm mng trc ni cc im hotspot thng

mi v LAN khng dy vi Internet. Cng ngh khng dy 802.16a cho php doanhnghip trin khai hotspot 802.11 linh hot khi gp a hnh him tr, i hi thi gian

ngn v nng cp linh hot theo nhu cu th trng.

Chun 802.16a cho php trin khai nhng mng trc tc cao, chi ph thp.Ti chu

u, ni cc nh vn hnh t chp nhn chia s cp trc vi i th cnh tranh, mng trc

WiMax c t pht trin v c s dng trong 80% thp sng. Ring ti M, do c

iu lut qui nh cc nh cung cp dch v th ba phi thu tuyn cp trc t nh cung

cp mng trc Internet nn tc ng dng WiMax chm hn chu u. Tuy vy, t l

ng dng WiMax lm mng trc cng chim n 20% v sp ti s pht trin rt

nhanh v FCC ang chun b b rng buc v tuyn cp trc vi cc nh cung cp dch v

th ba. i vi cc nc ang pht trin th gii php kt ni khng dy 802.16a cho


6/22

Tng quan v cng ngh Wimax Trang 6php nng cp nng lc dch v nhanh chng theo nhu cu thc t m khng phi lo ngi

v vn o ng, thay i kin trc h tng.

1.3.2 Kt ni mng khng dy doanh nghip:

Chun 802.16a c dng lm c s lin thng cc mng LAN khng dy, hotspotWiFi 802.11 hin c. Doanh nghip c th t do m rng qui m vn phng m mi

trng mng cc b vn c lin lc nu c mng trung gian khng dy chun 802.16a.

Nhn rng hn, doanh nghip c th trin khai mng LAN khng dy thng nht cho tt

c vn phng trong phm vi mt quc gia.

1.3.3 Bng rng theo nhu cu:

H thng khng dy cho php trin khai hiu qu ngay c khi s dng ngn hn. Vi s

h tr ca cng ngh 802.16a, h thng hotspot 802.11 vn nng lc phc v dch v

kt ni tc cao ti nhng hi ch, trin lm c n hng ngn khch. Nh cung cp

dch v c th nng cp hoc gim bt nng lc phc v ca h thng theo nhu cu thc

t, gip nng cao hiu qu kinh doanh, tng tnh cnh tranh ca doanh nghip.

1.3.4 M rng nhanh vng ph sng

H thng 802.16a cho php ph sng n nhng vng him tr, thiu cp trc y. Do

tuyn cp DSL ch c th p ng trong bn knh 4,8km tnh t trm iu phi trung tm

nn cn nhiu vng a hnh him tr m nh cung cp khng th vi ti. Thng k gn

y cho thy c hn 2.500 nh cung cp dch v khng dy (Wireless ISP) a phng

hot ng hiu qu trn 6.000 th trng ti M. Khng ch trin khai dch v d liu tc

cao, h thng cn cho php trin khai dch v thoi cho nhng ngi dng vng su

vng xa.

1.3.5 Roaming dich vVi cng ngh IEEE 802.16e m rng t 802.16a, trong tng lai ngi dng s c h

tr dch v roaming tng t in thoi di ng, t ng chuyn kt ni n nh cung

cp dch v Internet khng dy a phng ngay khi ra ngoi vng ph sng ca mng

gia nh, cng ty. -D kin n 2006, cng ngh WiMAX s c tch hp vo my tnh


7/22

Tng quan v cng ngh Wimax Trang 7xch tay, PDA nh Wi-Fi hin nay v tng bc hnh thnh nn nhng vng dch v

khng dy bng rng mang tn "MetroZones".

Hnh 3 M hnh trin khai mng WIMAX

1.4 Gii thiu chung v cng ngh Wimax

Cng ngh truy nhp v tuyn bng rng Wimax l tn vit tt ca cm t Worldwide

Interoperability of Microwave Access. M t WiMAX trong b tiu chun IEEE 802.16

Wireless Metropolitan Area Network (MAN) cho rng cc h thng tng thch vi

Wimax s c s tng tc gia v tuyn c nh vi Internet cable v DSL thng.

Mt h thng Wimax tiu biu gm c 2 phn:

Mt trm gc Wimax: Trm gc gm cc khi in t t trong nh v mt antenWimax. Tiu biu, mt trm gc c bn knh ph sng ln n 10 km (Theo l

thuyt, mt trm gc c bn knh ph sng ln n 50 km, tuy nhin do iu kin


8/22

Tng quan v cng ngh Wimax Trang 8thc t nn ch gii hn bn knh khong 10 km). Bt k node v tuyn nm

trong vng ph sngiu c th truy cp n Internet.

Mt my thu WiMax: my thu v anten c th l mt hp n hay l mt cardPCMCA gn vo trong my tnh hoc laptop. Truy cp n trm gc Wimax ging

nh truy cp n im truy cp ca mng Wifi, nhng c vng ph sng th rng

hn.

Nhiu trm gc c th kt ni ln nhau bng cch s dng cc lin kt Viba backhaul tc

cao.iu ny cho php cc thu bao Wimax chuyn vng t trm gc ny n khu vc

trm gc khc, cng tng t nh chuyn vng trong mng in thoi t bo.

Cc c im k thut quan trng trong cng ngh Wimax (Wireless MAN IEEE 802.16)

Bn knh ph sng: 50 km tnh t trm gc Tc ti a: 70 Mbps Non-Line-of-sight (NLoS) gia ngi s dng v trm gc. Cc bng tn s: 2-11 GHz v 10-66 GHz (bng ng k v cha ng k) nh ngha c hai lp MAC v PHY v cho php nhiu chi tit k thut lp PHY.

Mng MAN v tuyn Wimax da trn b tiu chun IEEE 802.16 cung cp truy cp

Internet v tuyn bng rng ti nh ring v doanh nghip vi cc ph thp. Tc

truyn chia s ln n 75Mbps t mt trm n, c th cung cp truy cp bng rng m

khng cn c mt ng truyn vt l t ngi dng u cui ti nh cung cp dch v.

Giao dch v ti khch hng u cui ging nh giao knh truyn 300Kbps cho nh ring

v 2Mbps cho doanh nghip.


9/22


Giao dch v ti khch hng u cui ging nh giao knh truyn 300Kbps cho nh ring

v 2Mbps cho doanh nghip. (Chun m t phn cui)

Cng ngh ny c bit hu ch cho cc vng nng thn v cc ni khc m cha c

truy cp bng rng. C s h tng hin hu do cc nh cung cp ko cp s hu ch cung

cp dch v ti nhng vng cn gii hn, ph hp cho truyn cp; m rng c kh

nng cung cp dch v bng rng th chi ph cao, v th s ngn cn pht trin n nhngvng c mt dn c thp.

Cng ngh DSL gii hn ngi dng u cui phi trong vng 3 dm t tng i PTC

hoc trm phn phi ca nh khai thc, v th nhiu ngi c bit nhng vng nng

thn th cng ngh DSL khng p ng c. Ngc li vng ph sng rng v mi

trng truyn khng dy gip cho Wimax vt qua nhng gii hn ny.Mc d vng

ph sng ti u l 4-6 dm vi tc cao, tuy nhin khi gim tc s tng khang cch

ln xp x 30 dm.Chi ph tng i thp trin khai dch v Wimax c lin quan n

cp hoc DSL, s khuyn khch cc nh cung cp dch v m rng vng ph sng ti

nhng khch hng nh ring v doanh nghip mi. Trong khi cng ngh ny khng cung

cp dch v bng rng chung, lc ny nn m rng vng dch vhin vt qu gii hn

ca h v s c th ph ht cc vng dn c.


10/22

Tng quan v cng ngh Wimax Trang 10Wimax ha hn cung cp d phng nhanh cc dch v bng rng. Thng thng PTCL

yu cu nhiu thng mi cung cp ng E1 mi v cc kt ni mc d liu thng mi

cho cc khch hng doanh nghip di iu kin tt nht, chi ph lp t cn kh cao.Nh

khai thc DSL b gii hn cung cp cc kt ni tc cao ch trong nhng vng h c

thit b nh trm v tng i. Da vo kch thc doanh nghip v ti nguyn d phng

pht trin t bin trong cc nm va qua v s pht trin trong tng lai nh

hng theo t chc thng mi th gii WTO. S cn tr ca thi gian lp t lu v chi

ph d phng cao s kim hm s pht trin ca n. Mng backbone trong nc ta cng

vi tuyn trung k chnh to cho n hin r u im vt tri ca cng ngh ny trin

khai bng rng ti cc vng su vng xa v xa cc tuyn trung k.

K hach pht trin thng bo trong din n pht trin ca Intel, Intel s cho ra mtchip Wimax u tin nm 2004. Kt ni bng rng c nh ti nh ring v doanh nghip

c a ra trong b chun 802.16a ( c chun ha vo thng 01 nm 2003), tip

theo l truy cp di ng ti my tnh xch tay theo b chun 802.16e (ang hp chun).

Chun 802.16a cho php cng ngh ny hat ng vng tn s t 2-11 GHz v khng

b gii hn LOS. Tuy nhin, cc cng ty khc cng c s pht trin ng k nh Navini,

Proxim, Alvarion,

Nhiu c hi n cho cc cng ty ny pht trin nhng ng dng da trn nhng u

im cacng ngh mi ny. Gii php kinh doanh b sung nh gim st khu vc, phng

vin tin tc, chm sc sc khe ti nh, cn b cng ty cng ch, cc dch v yu cu

kt ni vi cc my tnh doanh nghip ca h hoc vi h thng Internet. VPN v cc

dch v tng t khc cng c th tn dng c cc u im ca cng ngh ny, d cn

trang b li mt s cng c.

Mang bng rng ti cc vng cha pht trin, cha c dch v, h tng c s mng dy

dn bng rng cho nh ring, doanh nghip cha tn ti hoc khng ng tin cy. m

rng dch v Internet ti vng su, vng xa, nh cung cp dch v phi cung cp c s h

tng vin thng mt t mi, bt buc phi chu gi c dch v rt cao.y l nguyn

nhn chnh lm cho t trng dch v din thng nc ta thp. t c li rng hp


11/22

Tng quan v cng ngh Wimax Trang 11l v khang thi gian c th chp nhn c, chi ph h tng c s phi c gi mc

thp v c qun l cht ch.Yu t chi ph gi vai tr rt quan trng nhng vng dn

c tha tht, cha trin khai cng ngh vin thngtruyn thng.

Cng ngh v tuyn tm xa ha hn mang li dch v c ch cho nhiu vng m cng

ngh dy dn truyn thng thc t cha c.Theo mt s chuyn gia nh Sean Maloney

(ph ch tch hi ng qun tr Intel v tng gim c ca nhm vin thng Intel), mt s

hng truyn thng ang xem xt cung cp dch v Wimax din rng nhng quc gia

pht trin v ang pht trin.

Th trng kinh doanh nh hin nay c phc v mc ln bi v tuyn im-im

hoc mng cp DSL phm vi nh cho kt ni bng rng. Hn na gii hn v tr tho

lun ri, cc cng ngh ny in hnh l cung cp bng thng upstream b gii hn, mgii hn ng k cho nhng khch hng doanh nghip, ty vo nhu cu c th ca h.

Cc doanh nghip ny c k hach t my ch Web,h tr hoc lp k hach h tr

ngi dng xa c nhu cu, m c th ni tm thy gii hn ny c ngha rt c

bit.Hn na, t khi cc nh cung cp mng dy dn xy dng ni ch yu phc v

th trng truyn hnh cp, th khi h khng cn xy dng nhiu khu vc thng

mi na.

Mng Wimax cung cp tng tc vi knh phn phi ny t khi h khng ph thuc vo

h tng c s on cui hin c v h cung cp bng thng upstream ln hn rt nhiu so

vi cp v DSL. Cc mng ny cng c tin cycao t khi cc nh cung cp lp thm

cell ti nhng vng dch v vi mc chi ph thc thp hn so vi m rng mng cp hoc

DSL.

Trong khi cc quc gia pht trin c sn mng ln cp v/hoc DSL phc v khu

vc doanh nghip v dn c ng.V vy, cc phng thc phc v mi phi c thi giancnh tranh trn th trng ny, khi m khch hng y c dch v phc v tt. V vy,

Wimax em li nhiu li ch vng su, vng xa v nhng vng cha c dch v bng

rng, li ch mang li cho nh cung cp y l kh thp v cn tr s pht trin chung.


12/22

Tng quan v cng ngh Wimax Trang 12iu kin nc ta th kh tri ngc, chng ta khng c cu trc bng rng thnh ph

v nhng vng su, vng xa, Wimax s khng c dch v i lp.

Mt kha cnh ca chun 802.16a ang tn ti s hp dncc nh cung cp dch v v

cng nh khch hng u cui l cung cp mc a dch v. Trm gc n cung cp

ng truyn vi tc chia s d liu ln n 75 Mbps v ti khch hng doanh nghip

bo m c tc 2 Mbps (tng ng lung E1), cng nh ti khch hng nh ring

dch v 128 kbps khng bo m best-effort.

Theo nhu cu ca tng vng nn a ra chun a dng v dch v rng cho nh cung

cp.Cung cp dch v mm do v cu trc ti tng loi khch hng, mt nh cung cp

Wimax c th hp dn bi tnh a dng v nhu cu cho tng im phn phi.

vng su, vng xa khong cch gia cc khch hng l ln, 802.16 h tr iu ch

thch nghi adaptive modulation cho php t ng tng vng ph sng ng thi s

gim thng lng nhng ni cn thit. iu ch (nh QAM 64) cung cp thng lng

cao vi vng ph sng ph ti a.

Lc iu ch do trm gc gn ng tu vo khong cch n my khch, cng nh

thi tit, nhiu tn hiu v cc nhn t nht thi khc,Tng lai s mm do ny cho

php cc nh cung cp dch v p ng cc khu vc phn phi ring l, v cho php dchv Wimax mang li li ch cho cc vng a l v dn c rng.

Chun 802.16 cng h tr QoS khc nhau chi phi tha hip gia t l li thc v li

tim tng.Kh nng ny cho php cng ngh a ra h tr tt hn ti cc loi ng

truyn d liu khc nhau.Hu ht cc loi ng truyn d liu chu ng mc li

tim tng ln nhng t l li thc phi c iu khin cht.Mi trng thi gian thc

nh truyn thoi v hnh nh, nicch khc, l yu cu li tim tng thp nhng c mt

vi mc li ng truyn c th chp nhn c. V vy, QoS khc nhau cho php

mt chun truyn d liu bt tay c vi tt c cc dch v khc nhau c hiu qu.


13/22

Tng quan v cng ngh Wimax Trang 13Nguyn tc hat ng

Tht khngd dng c ci nhn nhanh chng cch hot ng ca cng ngh Wimax.

Wimax cung cp hai dng dch v v tuyn:

- l NLOS, loi dch v Wifi, c mt anten nh gn trn my tnh kt ni vi thpanten.Trong ch ny, Wimax s dng bng tn s thp 2-11 GHz (ging Wifi). ng

truyn bc sng ngn hn th khng d dng t do cn tr vt l, chng c th tt hn

lm nhiu x, ch cong xung quanh khu vc chng ngi vt.

- i vi dch v LOS, cc im anten a c nh t trn nh nh hay im cc hng

thng n thp anten Wimax.Kt ni LOS th mnh v n nh hn, v th n c th gi

nhiu d liu vi mc li thp. ng truyn LOS s dng tn s cao hn ln n 66

GHz. Ti mc tn s cao th nhiu thp v s dng bng thng rng hn.

Truy cp kiu Wifi b gii hn trong bn knh t 4 -6 dm (vng bao ph khong 25 dm

vung hoc 65 km vung ging nh vng ca in thoi t bo). Do anten LOS mnh

hn, trm pht Wimax gi d liu ti my tnh h tr Wimax hoc b nh tuyn thit lp

trong vng bn knh 30 dm so vi trm pht (vng bao ph khang 3.600 dm vung

hoc 9.300 km vung). Vng ph sng rng l u im ni bt ca cng ngh Wimax.

Bng cch xem xt gim bt gii hn ca vng ph sng v bng thng di ng, s chpnhn ph bin ca mng MAN v tuyn s pht trin th trng mi cho phn mm

mobilized (di ng). Khi khch hng doanh nghip chp nhn dch v Wimax, nhu cu s

pht trin gii php thng mi di ng rng, t bit trn c s chun 802.16e, trm gc

s cung cp dch v trc tip ti thit b di ng u cui ngi dng.

Doanh nghip c th s cung cp kt ni trc tip ti field personnel ngang qua khu vc

rng tri rng hn cc cng ngh hin nay. Bng thng cao v phm vi cc dch v trn

Wimax lin quan ti cc cng ngh v tuyn khc cng to ra nhu cu cho cc gii php

phn mm mobilized (di ng) m cc cng ngh ph bin hin nay khng s dng

chng.


14/22


15/22

Tng quan v cng ngh Wimax Trang 15 D n 802.16d c thay th bi 802.16-RE-VD c IEEE-SA standards Board

chp nhn vo ngy 11/09/2003 v cng b nh chun IEEE 802.16 -2004 thay th

cc b tiu chun 802.16-2001, 802.16c-2002 v 802.16a-2003.

D n 802.16e v lp MAC v lp vt l cho di ng v c nh bng tn cpphp, c IEEE-SA Standards Board chp nhn vo 07/12/2005 v ch c

cng b vo 01/2006.

D n 802.16f v qun l thng tin c IEEE-SA Standards Board chp nhnvo 22/09/2005 v cng b vo ngy 01/12/2005.

D n 802.16g v qun l th tc v dch v, d n 802.16h ang pht trin.Phin bn tiu chun u tin ca Wimax l 802.16 tp trung x l trong vng bng tn

10-66 GHz; phin bn mi hn l 802.16a hat ng trn ph tn 2-11 GHz. Kt hp c

hai 802.16 v 802.16a nh ngha mt lc iu ch sng mang n gin cho ng

lin kt LOS bng tn pha trn 10 GHz. Hn na, nh ngha thm hai giao thc iu

khin truy cp mi trng OFDM cho ng lin kt NLOS pha dui 11 GHz v TDD/

FDD. B tiu chun khng nh ngha c th QoS v thut ton lp chng trnh, nhng

li cho php thc thi mm do gia cc nh cung cp.

1.6.u nhc im ca Wimax

1.6.1 u im

c xy dng trn tiu chun IEEE.802.16, WIMAX l h thng a truy nhp khng

dy bng rng dng cng ngh OFDM vi c hai kiu ng truyn LOS v NLOS.

Chun WIMAX pht trin vi nhiu mc tiu, chng c tng kt di.

Kin trc mm do: WIMAX h trmt vi kin trc h thng, bao gm im ti im,

im ti a im, v bao ph khp ni. MAC (iu khin truy nhp phng tin)

WIMAX h trim ti a im v cc dch vkhp ni bng cch sp xp mt khe

thi gian cho mi trm thu bao (SS).Nu ch c mt SS trong mng, th trm gc


16/22

Tng quan v cng ngh Wimax Trang 16WIMAX s thng tin vi SS trn c sim ti im.Mt BS trong cu hnh im ti

im c th s dng mt anten bp hp hn ph cc vng ln hn.

Bo mt cao: WIMAX h trASE (chun mt m ha tin tin) v DES (trong l

chun mt m ha s liu). Bng cch mt m ha cc lin kt gia BS v SS, WIMAX

cung cp cc thu bao ring (chng nghe trm) v bo mt trn giao din khng dy bng

rng. Bo mt cng cung cp cho cc nh khai thc s bo v mnh m chng n trm

dch v. WIMAX cng c xy dng h trVLAN, m cung cp s bo v d liu

c truyn bi cc ngi s dng khc nhau trn cng mt BS.

Trin khai nhanh: so vi s trin khai ca cc gii php dy, WIMAX yu cu t hoc

khng yu cu xy dng k hoch mrng. V d, o h h trrnh ca cc cp

khng c yu cu. Cc nh khai thc c giy php s dng mt trong scc bng

tn c cp pht, hoc c k hoch s dng mt trong cc bng tn khng c cp

php, khng cn thit xem xt su hn cc ng dng cho Chnh Ph. Khi anten v thit b

c lp t v c cp ngun, WIMAX s sn sng phc v. Trong hu ht cc trng

hp, trin khai WIMAX c th hon thnh trong khong my gi, so vi my thng cho

cc gii php khc.


17/22


QoS WIMAX: WIMAX c thc ti u ha hn hp lu lng c mang

Loi dch v M t

Dch v cp

t nguyn

(UGS)

UGS c thit k h trcc lung d liu thi gian thc bao gm cc

gi s liu kch thc cnh c pht ra ti cc khong tun hon, nh

T1/E1 v thoi trn nn IP

Dch v kim

sot vng

thi gian

thc (rtPS)

rtNS c thit k h trcc lung d liu thi gian thc bao gm cc

gi s liu kch thc thay i m c pht ra ti cc khong tun hon,

nh MPEG video

Dch v kim

sot vng phi

thi gian

thc (nrtPS)

nrtPS c thit k h trcc lung s liu dung sai tr bao gm cc

gi s liu kch thc thay i m yu cu tc s liu ti thiu, nh

FTP.

Best Effort

(BS)

Dch vBS c thit k h trcc lung s liu m khng yu cu

mc dch v ti thiu v c th xl trn c sgi tr khng gian.

Dung lng cao: S dng iu ch bc cao (64-QAM) v rng bng tn (hin ti l 7

MHz), cc h thng WIMAX c th cung cp rng bng tn ng kcho cc ngi s

dng u cui.

bao ph rng hn: WIMAX h trcc iu cha mc, bao gm BPSK, QPSK,

16-QAM, v 64-QAM.Khi c trang b vi mt b khuych i cng sut ln v hot

ng vi iu ch mc thp (v d, BPSK hoc QPSK), cc h thng WIMAX c th bao

ph mt vng a l rng khi ng gia BS v SS thng sut.


18/22

Tng quan v cng ngh Wimax Trang 18 Mang li li nhun: WIMAX da trn chun quc t m. Chun c thng qua a s,

s dng chi ph thp, cc chipset c sn xut hng lot, siu khin gi h xung; v

cnh tranh gi c lm cho cc nh cung cp dch v, ngi s dng u cui tit kim

c chi ph.

Dch v a mc: L loi m QoS t c da vo hp ng mc dch v (SLA) gia

nh cung cp dch vv ngi s dng. Hn na, mt nh cung cp dch v c tha ra

cc SLA khc nhau cho nhng ngi ng k khc nhau, hoc thm ch cho nhng ngi

s dng khc nhau trong cng mt SS.

Khnng cng vn hnh: WIMAX da vo cc chun cung cp trung lp, quc t,

lm cho ngi s dng u cui d dng truyn ti v s dng SS ca h ti cc v tr

khc nhau, hoc vi cc nh cung cp dch v khc nhau. Khnng cng vn hnh bo

v vn u t ban u ca nh khai thc v n c th chn thit b tcc i l thit b

khc nhau, v n s tip tc lm gim gi thit b.

Khnng mang theo c: Vi cc h thng t ong hin nay, khi SS WIMAX c

cp cng sut, n t nhn dng, xc nh cc c tnh ca lin kt vi BS, ch cn SS

c ng k trong c sd liu h thng, v sau m phn cc c tnh truyn dn

ph hp.

Tnh di ng: Chun 802.16e IEEE c thm mt sc im ch yu trong vic h

trtnh di ng. Cc ci tin c to ra cho lp vt l OFDMA v OFDM cung cp

cc thit b v dch vtrong mi trng di ng. Cc mi trng ny bao gm: OFDMA

c th chia t lc, MIMO, v h trch idle/sleep, chuyn giao, cho php tnh ding hon ton ti tc 160 km/h. Chun h trbi Forum WIMAX c hng hiu

nng NLOS (tm nhn khng thng) tt hn ca OFDM v hot ng chu c a

ng, lm cho n ph hp hn vi mi trng di ng.


19/22

Tng quan v cng ngh Wimax Trang 19 Qu trnh hot ng tm nhn khng thng:NLOS thng m chng dn v

tuyn c min Fresnel th nht b chn hon ton. WIMAX da vo cng ngh OFDM c

dung lng vn c ca cc mi trng NLOS.Dung lng ny gip cc sn phm

WIMAX phn pht rng bng tn rng trong mi trng NLOS, m cc sn phm v

tuyn khc khng lm c.

WIMAX cho php c hai cng ngh TDD (Time Division Duplexing) v FDD

(Frequency Division Duplexing) cho phn chia truyn dn ca hng ln v hng

xung.

1.6.2.Nhc im

Vi bt c h thng truyn thng v tuyn no th nh hng ca mi trng truyn sng

l khng th trnh khi. H thng WIMAX cng c nhng hn ch vng truyn:

nh hng ca thi tit xu c bit l ma to c thlm gin on ccdch v.

Cc sng v tuyn in ln cn c th gy nhiu vi kt ni WIMAX v lnguyn nhn gy suy gim d liu trn ng truyn hoc lm mt kt ni.

Ngoi ra v y l cng ngh hon ton mi do vic chun ha chathc s trn phm vi ton th gii nn kh khn trong lp rp, thay th

cc khu vc khc nhau.

1.7.Cc chun wifi trc y


20/22

Tng quan v cng ngh Wimax Trang 20Nm 1997, IEEE (Institute of Electrical and Electronics Engineers) gii thiu mt

chun u tin cho WLAN. Chun ny c gi l 802.11 sau khi tn ca nhm c

thit lp nhm gim st s pht trin ca n. Tuy nhin, 802.11ch h tr cho bng tn

mng cc i ln n 2Mbps qu chm i vi hu ht cc ng dng. Vi l do , cc

sn phm khng dy thit k theo chun 802.11 ban u dn khng c sn xut.

1.7.1.802.11b

IEEE m rng trn chun 802.11 gc vo thng By nm 1999, chnh l chun

802.11b. Chun ny h tr bng thng ln n 11Mbps, tng quan vi Ethernet truyn

thng.

802.11b s dng tn s v tuyn (2.4 GHz) ging nh chun ban u 802.11. Cc hng

thch s dng cc tn s ny chi ph trong sn xut ca h c gim. Ccthit b

802.11b c th b xuyn nhiu t cc thit b in thoi khng dy (ko di), l vi sng

hoc cc thit b khc s dng cng di tn 2.4 GHz. Mc d vy, bng cch ci t cc

thit b 802.11b cch xa cc thit b nh vy c th gim c hin tng xuyn nhiu

ny.

u im ca 802.11b gi thnh thp nht; phm vi tn hiu tt v khng d bcn tr.

Nhc im ca 802.11b tc ti a thp nht; cc ng dng gia nh c thxuyn nhiu.

1.7.2.802.11a

Trong khi 802.11b vn ang c pht trin, IEEE to mt m rng th cp cho chun802.11 c tn gi 802.11a.V 802.11b c s dng rng ri qu nhanh so vi 802.11a,

nn mt s ngi cho rng 802.11a c to sau 802.11b.Tuy nhin trong thc t,

802.11a v 802.11b c to mt cch ng thi. Do gi thnh cao hn nn 802.11a ch

c s dng trong cc mng doanh nghip cn 802.11b thch hp hn vi th trng


21/22

Tng quan v cng ngh Wimax Trang 21mng gia nh.

802.11a h tr bng thng ln n 54 Mbps v s dng tn s v tuyn 5GHz. Tn s ca

802.11a cao hn so vi 802.11b chnh v vy lm cho phm vi ca h thng ny hp

hn so vi cc mng 802.11b.Vi tn s ny, cc tn hiu 802.11a cng kh xuyn qua

cc vch tng v cc vt cn khc hn.

Do 802.11a v 802.11b s dng cc tn s khc nhau, nn hai cng ngh ny khng th

tng thch vi nhau. Chnh v vy mt s hng cung cp cc thit b mng hybrid cho

802.11a/b nhng cc sn phm ny ch n thun l b sung thm hai chun ny.

u im ca 802.11a tc cao; tn s 5Ghz trnh c s xuyn nhiu t ccthit b khc.

Nhc im ca 802.11a gi thnh t; phm vi hp v d b che khut.

1.7.3.802.11g

Vo nm 2002 v 2003, cc sn phm WLAN h tr mt chun mi hn l

802.11g, c nh gi cao trn th trng. 802.11g thc hin s kt hp tt nht gia

802.11a v 802.11b. N h tr bng thng ln n 54Mbps v s dng tn s 2.4 Ghz

c phm vi rng. 802.11g c kh nng tng thch vi cc chun 802.11b, iu

c ngha l cc im truy cp 802.11g s lm vic vi cc adapter mng khng dy

802.11b v ngc li.

u im ca 802.11g tc cao; phm vi tn hiu tt v t b che khut.Nhc im ca 802.11g gi thnh t hn 802.11b; cc thit b c th b

xuyn nhiu t nhiu thit b khc s dng cng bng tn.

1.7.4.802.11n

Chun mi nht trong danh mc Wi-Fi chnh l 802.11n. y l chun c thit k

ci thin cho 802.11g trong tng s bng thng c h tr bng cch tn dng nhiu tn

hiu khng dy v cc anten (cng ngh MIMO).


22/22

Tng quan v cng ngh Wimax Trang 22Khi chun ny c a ra, cc kt ni 802.11n s h tr tc d liu ln n 100

Mbps. 802.11n cng cung cp phm vi bao ph tt hn so vi cc chun Wi-Fi trc n

nh cng tn hiu mnh ca n. Thit b 802.11n s tng thch vi cc thit b

802.11g.

u im ca 802.11n tc nhanh v phm vi tn hiu tt nht; kh nng chung tt hn t vic xuyn nhiu t cc ngun bn ngoi.

Nhc im ca 802.11n chun vn cha c ban b, gi thnh t hn802.11g; s dng nhiu tn hiu c th gy nhiu vi cc mng 802.11b/g gn.

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