6 2. Kt ni mng khng dy doanh nghip: Chun 802.16a c dng lm c s
lin thng cc mng LAN khng dy, hotspot WiFi 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. 3. Bng rng theo nhu cu. H thng
khng dy cho php trin khai hiu qu ngay c khi s dng ngn hn. 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. 4. M rng nhanh chng, tit kim. H thng 802.16a cho php ph sng
n nhng vng a hnh him tr. Khng ch trin khai dch v d liu tc cao, h
thng cn cho php trin khai dch v thoi. 5. Lin thng dich v. Vi cng
ngh IEEE 802.16e m rng t 802.16a, trong tng lai ngi dng s c h tr
dch v roaming. D kin n 2006, cng ngh WiMAX s c tch hp vo my tnh xch
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 1-2 M hnh trin khai WiMAX 7
Hng BellSouth s trin khai dch v wireless bng thng rng ti mt vi a im
Athens (Hy Lp) v Georgia (M) vo thng 8, sau s m rng timt s thnh ph
thuc bang Florida (M) ngay trong nm 2005. Tuy nhin nhng thit b nh b
x l, thit b nh tuyn v chip cho IEEE 802.16 vn cha kim nghim v cng
nh-n. Qu trnh kim tra bt u vo thng 7, v sn phm c hy vng s sm ti tay
cc nh cung cp dch v Internet khng dy v hng vin thng vo cui 2005.
Dch v Internet truy c-p nhanh (FastAccess Internet Service) ca
BellSouth c kh nng tng tc truy c-p ln ti 1,5 Mb/giy trong phm vi 3
n 5 dm (5 - 8 km). K hoch mi ny nhm h tr nhng vng xa xi ho lnh, ni
m dch v DSL v cp bng thng rng khng th tip c-n c. l bc tip theo sau
khi AT&T xc tin dch v WiMax ng dng cng ngh ca Navini Networks
ti Middletown, New Jersey thng 5-2005. Trong khi , hng Sprint cng s
sm a ra k hot pht trin thit b WiMax cui nm nay. Hip hi Vin thng M
ang xc tin chun ha ch s bng tn 3,65 - 3,70 GHz cho WiMax. Nhng cng
ngh ny ngy cng ln mnh, cn xy dng mt h thng kinh t nhm pht trin thit
b, ng dng, cng nh h tr vic theo ui th trng WiMax v sau. 1.5.2
WIRELESS USB Chun USB khng dy (WUSB) c pht trin da trn chun USB c
dy nhm a u im ca chun ny vo th gii khng dy tng lai. Chun WUSB c
thit k kt ning c s (s dng Aci mt knh c truyn song song. Vic chnh sa
li pha trc FEC (Forward Error Correction) cng c s dng trong 802.11a
(khng c trong 802.11) c th t c tc cao hn. Tt c cc bng tn dng cho
Wireless LAN l khng cn ng k, v th n d dng dn n s xung t v nhiu.
trnh s xung t ny, c 801.11a v802.11b u ca phin bn tiu chun chung ca
hai t chc tiu chun IEEE v ETSI (European Telecommunications
Standards Institute) trn nn IEEE 802.11a v HiperLAN/2. IEEE
802.11k: Cung cp kh nng o lng mng v sng v tuyn thch hp cho cc lp
cao hn. IEEE 802.11n: M rng thng lng (>100Mbps ti MAC SAP) trn
bng 2,4GHz v 5GHz. 2.2.2 HiperLAN S pht trin ca thng tin v tuyn bng
rng t ra nhng yu cu mi v mng LAN v tuyn. l nhu cu cn h tr v QoS, bo
m-t, quyn s dng, ETSI (European Telecommunications Standards
Institute _ Vin tiu chun vin thng chu u ) nghin cu xy dng b tiu
chun cho cc loi LAN hiu sut cao (High Performance LAN), tiu chun ny
xoay quanh m t cc giao tip mc thp v m ra kh nng pht trin mc cao hn.
17 Hnh 2-2 OSI v Hiperlan 2.2.2.1 Lch s pht trin ca HiperLAN Khong
vo gia nm 1991, ETSI thnh l-p nhm RES10. Nhm ny bt u cng vic
nghfaefafscacassdasdasddddsaddin cu vo u nm 1992. Nhm RES10 xy dng
tiu chun HIPERLAN c th l thng tin lin lc s khng dy tc cao bng tn
5,1-5,3 GHz v bng tn 17,2 - 17,3 GHz. C 4 loi HIPERLAN c a ra:
HIPERLAN/1, HIPERLAN/2, HIPERCESS v HIPERLINK.vo nm 1996. Cc tiu
chun ca ETSI HIPERLAN HIPERLAN 1 HIPERLAN 2 HIPERLAN 3 HIPERLAN 4
ng dng Wireless LAN Truy nh-p WATM Truy nh-p WATM c nh t xa Kt ni
point-to-point WATM Bng tn 2,4 GHz 5 GHz 5 GHz 17 GHz 18 Tc t c
23,5 Mbps 54 Mbps 54 Mbps 155 Mbps 2.2.2.2 HiperLAN2 Trong cc chun
ca HiperLAN, HiperLAN2 l chun c s dng rng ri nht bi nhng c tnh k
thu-t ca n. Nhng c tnh k thu-t ca HiperLAN2: Truyn d liu vi tc cao
Kt ni c nh hng H tr QoS Cp pht tn s t ng H tr bo m-t Mng v ng dng c
l-p Tit kim nng lng Tc truyn d liu ca HiperLAN2 c th t ti 54 Mbps.
S d c th t c tc v HiperLAN2 s dng phng php gi l OFDM (Orthogonal
Frequence Digital Multiplexing - b iu ch trc giao). OFDM c hiu qu
trong c cc mi trng m sng radio b phn x t nhiu im. HiperLAN Access
Point c kh nng h tr vic cp pht tn s t ng trong vng ph sng ca n. iu
ny c thc hin da vo chc nng DFS (Dynamic Frequence Selection) Kin
trc HiperLAN2 thch hp vi nhiu li mng khc nhau. Tt c cc ng dng chy c
trn mt mng thng thng th c th chy c trn h thng mng HiperLAN2. 2.2.3
Cc chun khc 2.2.3.1 HomeRF HomeRF l chun hot ng ti phm vi bng tn
2.4 GHz, cung cp bng thng 1.6 MHz vi thng lng s dng l 659 Kb/s.
Khong cch phc v ti a 19 ca HomeRF l 45m.HomeRF cng s dng c ch tri
ph FHSS ti tng v-t l. HomeRF cng t chc cc thit b u cui thnh mng
adhoc (cc my trao i trc tip vi nhau) hoc lin h qua mt im kt ni
trung gian nh Bluetooth. im khc bit gia Bluetooth v HomeRF hng ti
mt mc tiu duy nht l th trng phc v cc mng gia nh. T chc tiu chun
giao thc truy c-p v tuyn SWAP ca HomeRF thnh l-p ra nhm nng cao hiu
qu kh nng cc ng dng a phng tin ca HomeRF. SWAP kt hp cc c tnh u vit
ca 802.11 l giao thc trnh xung t CSMA/CA vi c tnh QoS ca giao thc
DECT (Digital Enhanced Cordless Telecommunications) cung cp mt k
thu-t mng hon chnh cho cc h gia nh. Phin bn SWAP 1.0 (Shared
Wireless Access Protocol) cung cp kh nng h tr 4 my trong mt mng ad
hoc, v cung cp c ch bo m-t l m ha 40 bit ti lp MAC. Phin bn SWAP
2.0 m rng bng thng ln ti 10Mbps, cung cp kh nng roaming trong truy
c-p cng cng. N cng h tr 8 my trong mt mng ad hoc. c tnh QoS cng c
nng cp bi vic thm vo 8 lung u tin h tr cho cc ng dng a phng tin nh
video. SWAP 2.0 cng c c ch bo m-t nh SWAP 1.0 nhng c m ha 128 bit.
2.2.3.2 OpenAir OpenAir l sn phm c quyn ca Proxim. Proxim l mt
trong nhng cng ty sn xut thit b v tuyn ln nht th gii. Proxim ang c
gng OpenAir cnh tranh vi 802.11 thng qua WLIF (Wireless LAN
Interoperability Forum). Proxim nm gi ht cc thng tin chi tit v
OpenAir, tt c cc sn phm OpenAir u da trn cc module ca chnh Proxim.
OpenAir l mt giao thc trc 802.11, s dng k thu-t nhy tn (2FSK v 4
FSK), c tc 1,6Mbps. OpenAir MAC da trn CSMA/CA v RTS/CTS nh 802.11.
Tuy nhin OpenAir khng thc hin vic m ha ti lp MAC, nhng li c 20 ID
mng da trn m-t khu. OpenAir cng khng cung cp chc nng tit kim cng
sut. 2.2.3.3 BlueTooth 2.2.3.3.1 Bluetooth l g? Bluetooth l tn ca
mt chun s dng kt ni bng sng radio tn s ngn nhm mc ch thay th vic kt
ni cc thit b in t bng cp. im c trng ca cng ngh ny l s thit thc, n
gin, nng lng nh v chi ph thp. Cng ngh ny cng cho php kt ni khng dy
vi mng LAN, mng in thoi di ng, v internet. 2.2.3.3.2 Lch s pht trin
ca Bluetooth Nm 1994, ln u tin Ericsson xng vic nghin cu pht trin
mt giao din v tuyn cng sut nh, r tin, s dng sng radio nhm kt ni
khng dy gia my di ng cm tay v cc b ph-n thng tin, in t khc. Nm
1997, Ericsson tip xc v tho lu-n vi mt s nh sn xut thit b in t cm
tay v vic nghin cu, pht trin v thc y cc sn phm khng dy c ly ngn. Nm
1998, nm cng ty ni ting th gii l Ericsson, IBM, Intel, Nokia v
Toshiba cng nhau thnh l-p nhm c bit quan tm n Bluetooth (gi l SIG
Special Interest Group) Thng 7/1999, cc chuyn gia ca SIG cho ra i
cc ch tiu v tnh nng k thu-t u tin ca Bluetooth - k thu-t Bluetooth
1.0. Nm 2000, SIG b xung thm 4 thnh vin mi l 3Com, Lucent
Technologies, Microsoft v Motorola. Sn phm Bluetooth u tin c tung
ra th trng.T cc th h sn phm Bluetooth lin tc ra i. Cng ngh khng dy
Bluetooth tr thnh mt trong nhng cng ngh pht trin nhanh nht ca thi
i.
