tong quan ve mang truy nhap bang rong wimax 0017

TRNG . KHOA.

-----[\[\-----

Tng Quan V Mng Truy Nhp Bng Rng-WiMAX

H Cng Ngh - HQGHN T-VT

______________________________________________________________________ Lun vn:Tm hiu kh nng ng dng WiMAX ti Vit Nam

1

Chng 1

Tng Quan V Mng Truy Nhp Bng Rng-WiMAX

1.1 Mng Truy Nhp bng rng

nh ngha mng truy nhp:Theo cc khuyn ngh ca ITU-T(Lin minh vin thng quc t pht trin cc tiu chun quc t),mng truy nhp l mt chui cc thc th truyn dn gia SNI (Service Node Interface Giao din nt dch v) v UNI (User Network Interface Giao din ngi s dng - mng). Mng truy nhp chu trch nhim truyn ti cc dch v vin thng. Giao din iu khin v qun l mng l Q.

Hnh 1 :Kt ni mng truy nhp vi cc thc th mng khc

Thit b u cui ca khch hng c kt ni vi mng truy nhp qua UNI, cn mng truy nhp kt ni vi nt dch v (SN Service Node) thng qua SNI. V nguyn tc khng c gii hn no v loi v dung lng ca UNI hay SNI. Mng truy nhp v nt dch v u c kt ni vi h thng qun l mng TMN (telecom management network) qua giao din Q.

S thay i ca c cu dch v l yu t then cht nh hng n s pht trin ca mng truy nhp. Khch hng yu cu khng ch l cc dch v thoi/ fax truyn thng, m c cc dch v s tch hp, truyn hnh k thut s phn gii cao,..vv. Mng truy nhp truyn thng r rng cha sn sng p ng cc nhu cu dch v ny..

Trong nhng nm gn y mng truy nhp v tuyn bng rng tc cao khng ngng c nghin cu v pht trin ,cung cp cc dch v Multimedia nh:

Mng truy nhp

Thu bao

Cc thc th mng (PSTN ,ISDN..)

Q

SNI- Giao din nt dch v

UNI- Giao din ngi

s dng mng



2

truy cp Internet, VoIP, in thoi truyn hnh (Video Telephony), hi ngh truyn hnh (Video conferencing), truyn hnh qung b (Broadcast TV), xem phim theo yu cu (Video on Demand), tr chi trn mng (Game online) .vv

C th ni mng bng rng l xu hng pht trin tt yu.Sau y chng ta s cp ti mt s cng ngh truy cp bng rng in hnh l :xDSL, Modem cp ,iPSTAR v mt s k thut truy nhp v tuyn nh WiFi v WiMAX.

1.1.1 Mng xDSL [9]

Truy nhp xDSL ( x Digital Subscriber Line ):ng dy thu bao s (xDSL ) l phng thc truyn thng tin s tc cao qua ng in thoi truyn thng v s l nn tng cho vic phn b dch v bng rng ny n cc thu bao. S d iu ny thc hin c l nh ng dng cc k thut truyn s phc tp, l s b tr cc suy gim truyn dn trn ng dy in thoi v cc b x l s c nng lc rt ln.Cng ngh ny tn dng c s h tng ng dy thu bao cp ng c sn

Khi nng lc x l ca b x l tn hiu s tng ln, th tc ca xDSL cng tng ln. Cng ngh DSL bt u t 144 kbit/s, pht trin ti 1,5 n 2 Mbit/s HDSL, 7 Mbit/s vi ADSL, v by gi vi VDSL l 52 Mbit/s

ng dy thu bao s bt i xng ADSL (Asymmetric DSL)

- S dng mt i dy cp xon - Tc lung xung ln (1,5Mbps khong cch 6 km n 8Mbps vi

khong cch 3 km).Tc hng ln t 16kbps n 640kbps

ng dy thu bao s tc thch nghi RADSL (Rate Adaptive DSL)

- S dng mt i dy cp xon - Tc lung xung ln (1 Mbps n 12 Mbps vi).tc hng ln t 128

kbps n 1Mbps tc truyn i xng trong khong t 1 n 2 Mbps - Cc modem RADSL c kh nng nh gi cht lng ng y v t ng

iu chnh mc iu ch hoc s dng cc bc sng (ty thuc vo phng php m ha ng y)

ng dy thu bao s tc rt cao VDSL(very high bit rate DSL)

Tc lung xung ln (30Mbps n 50 Mbps vi c ly ngn thng nh hn 300m . Tc truyn i xng trong khong t 2 n 4 Mbps v khong cch xa hn.



3

Cc cng ngh xDSL i xng nh HDSL, SDSL, HDSL2

- High bit rate DSL (HDSL)l mt trong nhng cng ngh u tin c khai thc . Tc truyn i xng 1.54 Mbps trn 2 i dy cp xon hoc 2Mbps trn 3 i cp xon.,HDSLversion 2 ging HDSL nhng ch s dng 1 i cp xon.Khong cch truyn l 4 Km

- SDSL (Symmetric DSL) s dng 1 i cp xon, vi tc h tr ln ti 2Mbps cho frame-relay hay truyn hnh hi ngh.,khong cch truyn khong 3 Km.

Tn Tc d

liu C

ly(km) c im ng dng

HDSL

1.544 (kbps) 2.048 (kbps)

3.6 Khng s dng truyn dn c c d liu v tn hiu thoi

Mng cung cp T1/E1 , truy sut WAN, LAN

SDSL 1.5447(kbps) 2.048(kbps)

3.6 Ghp c tn hiu thoi v d liu trn cng mt i dy Tc ti d liu cng vi tn hiu thoi khng cao Thch hp cho cc doanh nghip va v ln

Ni ht, thay th trung k T1/E1c dng b lp,Kt ni cc PBX vi nhau, Kt ni mng LAN

ADSL 1.5-9 Mbps 16-640 (kbps)

5 D trin khai do s dng c s mng in thoi sn c.Chi ph hp l. S dng ng thi fax, voice m khng cn ngt mng. Hot ng Fulltime. Ph hp vi cc doanh nghip va v ln

Truy nhp internet,/intranet video theo yu cu,VPN,VoIP ,truy nhp LAN t xa

VDSL 13-52 Mbps 1.5-2.3 Mbps

1.4 S dng ng thi fax, voice tch hp Splitter Cha c h tr bi cc ISP ch dng cho mng LAN m rng

Truy nhp Mutimedia intern et.cc trng trnh broadcard TV

Bng 1 :Cc cng ngh xDSL



4

Nhng u im v hn ch ca cng ngh xDSL:

- Gim gi thnh v tc trn khai nhanh nhng khu vc m mng cp ng c sn

- C th trin khai trn din rng vi nhiu loi m hnh khc nhau - sn sng ca mng cp ng mt s ni nh vng nng thn ,vng su

vng xa , hoc hi o hu nh khng c ,v nu c th cht lng ca mng cp ng cha t yu cu nn m bo tc truy nhp cao DSL l rt kh.

- Vng ph nh, bn knh phc v t l nghch vi tc truy nhp nn mc u t s cao vng phn tn rng.

- Khng c tnh di ng.

1.1.2 Modem cp [5]

Modem cp l thit b c dng chuyn d liu trn cc ng truyn cho truyn hnh cp. Loi ng truyn ny, l cp ng trc, mang li bng thng ln hn nhiu so vi ng in thoi thng thng. Ni modem ny vi cp truyn v vi PC s mang li kh nng truy cp Internet tc cao.Trn l thuyt, tc ti xung ca cc thit b ny c th t 35M bit/s, nhng thc t thng ch t 1,5M bit/s, ty thuc vo nh cung cp dch v cp. Tc gi thng ip i t PC, cn c gi l tc ti ln vo khong 128K bit/s,

u nhc im ca Modem cp l: - Vic dng chung lm nh hng n tc . truy cp mng s t l nghch

vi s ngi truy cp trn cng mt nt mng - Mt vn khc cng c quan tm l tnh bo mt, - Kh trin khai trn nhng vng n c phn tn . - Khng c tnh di ng - Chi ph cao,v do phi lp t ng cp truyn hnh

l nhng nguyn nhn m dch v ny khng c pht trin ph bin. 1.1.3 Truy nhp dch v bng rng qua v tinh (iPSTAR) [12]:

H thng v tinh c nh:VSAT(Very Small Aperture terminal) c trin khai ch yu cc tnh min ni ca Vit Nam. Cc h thng ny c th cung cp tc t 9.6Kbps dn 8Mbps. Vit Nam hin ang s dng hai h thng VSAT DAMA/SCPC ch y phc v cho vng su vng xa v VSAT TDM/TDMA phc v cho nhu cu internet .[5]

Nhc im chnh ca cc h thng ny l gi thnh cao,tr hnh trnh ln v chu nh hng ca thi tit.



5

gim thiu nhng hn ch trn cng ty SSA-nh khai thc v tinh hng u chu pht trin h thng VSAT IP hay iPSTAR.i

iPSTAR c nh gi l h thng v tinh bng rng a dch v em li nhiu tin ch.H thng thng tin v tinh bng rng iPSTAR h tr truyn s liu theo hng xung tc 4Mbps v 2Mbps hng ln..Cung cp cc dch v vin thng trn nn giao thc IP. c im ca VSAT-IP l thit b gn nh, d lp t, gi thnh thp hn nhiu so vi VSAT DAMA. V tin ch, VSAT-IP ngoi cung cp dch v in thoi, cn c kh nng cung cp cc ng dng m ch c dch v bng rng nh: thoi VoIP, Internet tc cao, truyn hnh hi ngh, mng ring o (VPN), knh thu ring, trung k mobile, truyn hnh qung b, truyn hnh theo yu cu. Vi dung lng h thng 35 Gbit/s. Dch v truy nhp bng rng cho vng nng thn c th thc hin qua truy nhp v tinh bng rng 2 ng.

Hnh 2 h thng truy nhp v tinh iPTSAT

Nhng u im v nhc im: - Cc h thng thng tin v tinh c phm vi trin khai dch v ln, khng ph

thuc vo a bn, c th trin khai vng su vng xa ,nhng ni c a hnh phc tp m khng th trin khai c cc h thng nh xDSL .

- Hn ch ca truy nhp bng rng qua v tinh l s ph thuc ca nh cung cp dch v vo nh qun l h thng v tinh. Hin nay, VNPT mua dung lng 2,5 Gbit/s trin khai dch v VSAT bng rng Vit Nam. Vic mua dung lng s ph thuc vo chnh sch ca nh qun l h thng iPSTAR. Bi vy, gii php ny khng th trin khai c lp trong vng nng thn khi lng khch hng ln, n cn phi kt hp vi cc gii php truy nhp mt t khc.



6

- Ngoi ra, chi ph trin khai dch v cao, tui th ca h thng iPSTAR theo thit k l 12 nm v th gi thnh bng tn s khng gim d nhu cu s dng tng.

1.1.4 Mng truy nhp v tyn

Hin nay mng truy nhp v tuyn bng rng c xu hng pht trin nhanh hn so vi cc cng ngh truy nhp bng rng khc. L do l cng ngh ny c nhiu u im khi trin khai trn a hnh him tr m mng cp kh c th trin khai. So vi s dng v tinh th phng n ny c chi ph thp hn rt nhiu.

n nay c rt nhiu cng ngh v tuyn kt ni bng rng mi, Trong lun vn ny ch cp n mt s cng ngh v tuyn bng rng sau.

a/ HIPERLAN [14]

HIPERLAN- L h thng cc chun cho WLAN ca vin tiu chun vin thng chu u ETSI- European Telecommunications Standards Institute. Nm 1991, ETSI thnh lp nhm RES10 .Nhm RES10 xy dng tiu chun HIPERLAN l chun thng tin lin lc s khng dy tc cao bng tn 5,1-5,3GHz 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.

HYPERLAN 1

HYPERLAN 2

HYPERLAN 3

HYPERLAN 4

ng dng Wireless LAN

Truy nhp WATM

Truy nhp WATM c nh t xa

Kt ni PTP WATM

Bng tn 2.4 GHz 5 GHz 5 GHz 17 GHz

Tc t c

23.5 Mbps 54 Mbps 54 Mbps 155Mbps

Bng 2 Cc tiu chun ca ETSI HYPERLAN

Cc chun m ETSI thit lp nh HiPerLAN/2 l mt chun cnh tranh trc tip vi chun 802.11 ca IEEE. Sau IEEE a ra chun 802.11h c th tng tc c vi chun HiPerLAN/2 ca ETSI.

Trc , chun HiPerLAN/1 h tr tc ln n 24 Mbps s dng cng ngh DSSS trong phm vi 50m.HiPerLAN/1 s dng bng tn UNII thp v trung bnh ging nh HiPerLAN/2, 802.11a v 802.11h.

HiperLAN2 [5].



7

Trong cc chun ca HiperLAN, HiperLAN2 l chun c s dng rng ri nht bi nhng c tnh k thut ca n. Tc truyn d liu ca HiperLAN2 c th t ti 54 Mbps.C- th t c tc v HiperLAN2 s dng phng php gi l OFDM (Orthogonal Frequence Digital Multiplexing dn knh phn chia tn s). 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 loi 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.

u nhc im ca HIPERLAN

- HIPERLAN bo mt tt hn IEEE802.11 - HIPERLAN2 c h tr QoS ,v cc HIPERLAN cn h tr cc loi mng li

khc nh ATM,kt ni Ethernet trong khi 802.11 ch h tr kt ni Ethernet - HIPERLAN 2 cn c c tnh u vit nh c kh nng chn tn ng ,iu

khin cng sut. - Hn ch ca HIPERLAN l pham vi ph sng gii hn 50m - Gi thnh thit b cao.

b/ WiFi

WiFi l mt nhn hiu cho dng sn phm tun th theo cc chun cho WLAN ca Vin k thut in t IEEE(Institute of Electrical and Electronics Engineers) vi cc chun sau:

Chun IEEE

Tc max:

Mbit/s

Phm vi (m)

Di tn (GHz)

Phm vi(Trong

nh)

Phm vi(ngoi

tri)

K thut v tuyn

802.11 2 2,4 FHSS DSSS

802.11b 11



8

802.11 : y l chun u tin ca h thng mng khng dy. Chun ny cha tt c cng ngh truyn hin hnh bao gm Direct Sequence Spectrum (DSSS), Frequence Hopping Spread Spectrum (FHSS) v tia hng ngoi. 802.11 l mt trong hai chun miu t nhng thao tc ca sng truyn (FHSS) trong h thng mng khng dy. Nu ngi qun tr mng khng dy s dng h thng sng truyn ny, phi chn ng phn cng thch hp cho cc chun 802.11.

802.11b Hu ht mng WLAN ngy nay tng thch vi chun 802.11b ca IEEE, cc sn phm bt u c xut xng vo cui nm 1999 v khong 40 triu thit b 802.11b ang c s dng trn ton cu

802.11b c tc tn hiu ti a 11Mbps, vi thng lng trung bnh khong t 4 n 6 Mbps. Tc ny vn nhanh hn mt kt ni bng rng DSL hoc cp v cho m thanh lin tc (streaming audio), 802.11b li khng nhanh truyn nhng hnh nh c nt cao. Li th chnh ca 802.11b l ch ph phn cng thp.Do hot ng tn s 2.4GHz Ph ny b chia s bi cc thit b khng c cp php, chng hn nh cc thit b Bluetooth, in thoi khng dy v sng viba l ngun gc gy nhiu (v lm gim hiu sut hot ng) mng dng chun 802.11b. Cc mng dng chun 802.11b cng c th gy nhiu cho nhau, 14 knh ca chun 802.11b c chia thnh tng phn v ch c th dng 3 knh cng mt phm vi trnh chng cho. Cc knh thng c s dng trnh chng cho l 1, 6 v 11.

802.11b+ PBCC (Packet Binary Convolutional Code) do Texas Instruments (TI) pht trin c th cung cp tc 22 v 33 Mbps. TI sn xut chipset da trn chun 802.11b v h tr PBCC 22 Mbps. Nhng thit b tch hp chipset ny c gi l thit b 802.11b+. Nhng thit b ny hon ton tng thch vi 802.11b, khi hai thit b 802.11b+ giao tip vi nhau c th t ng dng tc 22 Mbps. im ni bt khc ca TI khi giao tip gia cc thit b 802.11b+ l hot ng ch 4x, c ngha l dng cc gi tin c kch thc ln hn - 4000 byte - gim ti v tng thng lng ln n ba ln.

802.11a : Vo cui nm 2001, cc sn phm da trn mt chun th hai, 802.11a, bt u c xut xng ,hot ng tn s 5GHz Thng lng l thuyt ti a ca n l 54 Mbit/s, vi tc ti a thc t t 21 n 22 Mbit/s. Mc d tc ti a ny vn cao hn ng k so vi thng lng ca chun 802.11b, phm vi pht huy hiu lc trong nh t 25 n 75 feet ca n li ngn hn phm vi ca cc sn phm theo chun 802.11b. Nhng chun 802.11a hot ng tt trong nhng khu vc ng c:

Vi mt s lng cc knh khng gi ln nhau tng ln trong di 5 GHz,Trong mi trng vn phng thng thng, tm hot ng ca 802.11a c th ln n ti a 46m tc thp nht, v khong 23m tc cao nht.



9

Khng ging dy tn s 2.4GHz, dy tn s 5GHz gn nh khng b nhiu. Vi u th v kch thc ca dy tn s, cc knh ca 802.11a khng b chng cho. Mt s nc nh ngha 4 knh, 8 knh hoc nhiu hn. Mt li ch khc m chun 802.11a mang li l bng thng cao hn ca n gip cho vic truyn nhiu lung hnh nh v truyn nhng tp tin ln tr nn l tng.

802.11g : l chun ni mng khng dy c IEEE ph duyt thng 6 nm 2003. c tc ca 802.11a v tm hot ng ca 802.11b v tng thch ngc vi 802.11b.

Tc ti a l thuyt ca cc sn phm theo chun 802.11a, 54 Mbit/s, vi mt thng lng thc t t 15 n 20 Mbit/s. Ging 802.11b, 802.11g c 14 knh v ch c th dng 3 knh cng mt phm vi trnh chng cho.Tc cao hn ca chun 802.11g cng gip cho vic truyn hnh nh v m thanh, li Web tr nn l tng. 802.11g thit k tng thch ngc vi 802.11b v chng chia s cng ph 2,4GHz. Vic ny lm cho cc sn phm ca 2 chun 802.11b v 802.11g c th hot ng tng thch vi nhau. 802.11g t tc ny bng cch dng OFDM (Orthogonal Frequency-Division Multiplexing), cng c ch vi 802.11a, v phi s dng thit b cng chn 802.11g. c th kt ni vi cc thit b 802.11b phi dng c ch iu bin CCK (Complimentary Code Keying). 802.11g cng tng thch vi cc thit b 802.11b+ hot ng tc 22 v 33Mbps s dng PBCC (Packet Binary Convolutional Code) ca Texas Instrumnets.

802.11g+ :Ging 802.11b+, 802.11g+ do Texas Instruments (TI) pht trin da trn 802.11g ca IEEE vi cc tnh nng khc c thm vo. Cc thit b 802.11g+ tng thch vi cc thit b 802.11b v 802.11g. Khi kt ni vi thit b 802.11b+, cc u im ca TI s c pht huy. Khi kt ni cc thit b 802.11g+ vi nhau, c th t tc tn hiu ln n 100Mbps.

802.11n :Task Group N ca IEEE 802.11 c thnh lp vo thng 7 nm 2003 chun ha cho Physical Layers (PHY) v Medium Access Control Layer (MAC) ca 802.11, cho php cc ch hot ng c th t c thng lng t nht l 100Mbps.

y l d n u tin ca 802.11 hng ti thng lng thay v tc tn hiu. Mt mc ch khc l t c thng lng cao tm hot ng rng, tng thch vi cc thit b 802.11a v 802.11g. Ban u d kin, cng vic chun ha s hon thnh vo cui nm 2005.Sau hon li v d kin s c cng nhn chnh thc vo cui nm 2006 nhng cho ti thi im ny vn cha c mt chun chnh thc.

802.11n s dng h thng a ng ten v cng ph ln, u l nhng vn hc ba i vi hi k s in t (IEEE). Sau nhiu tr ngi vi xut v mt



10

tiu chun mng khng dy tc cao, cui cng hip hi Wi-fi cng a ra c phin bn Draft 2.0 ca 802.11n, ng thi coi y l tiu chun sn cc nh sn xut c th xy dng cc thit b hot ng tt vi nhau.

Hin nay, IEEE vn ang nghin cu a ra chun 802.11n chnh thc v hy vng cng vic s kt thc vo thng ba nm 2009. Tuy nhin cha c g m bo cc thit b da trn Draft 2.0 s tng thch vi cc thit b ca b chun chnh thc ny.v c phin bn Draft 2.0 ln chun chnh thc u c thit k c tc truyn d liu trn 100Mb/giy, nhanh hn c mt s kt ni Ethernet qua dy dn..

u nhc im ca cng ngh theo chun IEEE 802.11

- Kh nng di ng - cho php kt ni bt k u trong vng ph sng.. - D lp t v trin khai,thi gian trin khai nhanh. - Tc cao,tnh linh ng v nng cp d. - Gi thit b r v nhiu trn th trng. - Nhc im ca mng khng dy c th k n nht l kh nng nhiu sng

do thi tit,cc thit b khng dy khc, hay cc vt chn - Vng ph sng ca IEEE 802.11cao hn HIPERLAN nhng cng ch hn

ch tm vi chc n vi trm mt. - Bo mt cn nhiu l hng.

c/ WiMAX.

Trong thc t cng ngh WiFi pht trin rt rng ri tuy nhin vi phm vi ph sng nh,khng p ng c nhu cu ngy cng cao ca ngi dng, WiMAX c thit k cho mng MAN nn khc phc hn c ch trn. Cng ngh ny s c ni chi tit trong mc 1.2

Tng kt

- xDSL ph hp cho vng c mng cp ng. Gii php ny em li li nhun ngay cho nh cung cp .

- iPSTAR s l gii php truy nhp bng rng hiu qu cho cc vng khng th trin khai cc gii php truy nhp mt t, c bit l vng su vng xa, tuy nhin gi c v chi ph vn cao hn so vi truy nhp v tuyn.

- HIPERLAN tt hn v u vit hn IEEE 802.11 nhng gi thnh thit b li cao v thit b t

- Wi-Fi.cho tc d truy nhp cao .Vic trin khai kh n gin, m gi thnh li thp hn nhiu so vi cng ngh trn . Tuy nhin vng ph sng ca WiFi b hn ch.



11

- WiMAX:gii php cng ngh ra i sau nn c tch hp rt nhiu cc u im v khc phc phn ln nhc im ca cc cng ngh trc,y l cng ngh hin i v c nh gi cao.

1.2 Tng quan v WiMAX [13]

Wi-Fi c bn knh ph sng ca mt im thu pht sng (hotspot) ch l 150 m nn cn nhiu hotspot cho mt khu vc nht nh v cng c nhiu ngi s dng Wi-Fi th tc cng gim.Mt khc,cht lng ca Wi-Fi khng c tt bng ADSL, khng m bo c ch u tin nh WiMAX.

WiMAX l t vit tt ca Worldwide Interoperability for Microwave Access c ngha l kh nng tng tc ton cu vi truy nhp vi ba.Vi WiMAX c nh c tc tng ng vi ADSL, trong khi khng cn dng dy dn n cc thu bao. Ngi s dng cc thit b u cui ch cn mua mt thit b Indoor WiMAX (kch thc bng mt modem ADSL) l c th dng c Internet tc cao. WiMAX di ng c t ln hn WiFi nhng phm vi ph sng ln hn rt nhiu so vi Wifi

Cng ngh WiMAX, l cng ngh khng dy bng thng rng ang pht trin rt nhanh vi kh nng trin khai trn phm vi rng v c coi l c tim nng to ln tr thnh gii php dm cui l tng nhm mang li kh nng kt ni Internet tc cao ti cc gia nh v cng s

1.2.1 Din n WiMAX

Din n WiMAX l mt t chc ca cc nh khai thc v cc cng ty thit b v cu kin truyn thng hng u.

Mc tiu ca Din n WiMAX l thc y v chng nhn kh nng tng thch ca cc thit b truy cp v tuyn bng rng tun th chun 802.16 ca IEEE v cc chun HiperMAN ca ETSI.

Din n hp tc cht ch vi cc nh cung cp v cc c quan qun l .m bo cc h thng c din n ph chun s p ng cc yu cu ca khch hng v ca cc chnh ph nhm loi b cc ro cn tin ti vic chp nhn rng ri cng ngh truy cp v tuyn bng rng BWA (Broadband Wireless Access), v ring mt chun th khng khuyn khch vic chp nhn rng ri mt cng ngh.

1.2.2 Cc c im ca WiMAX

WiMAX c tiu chun ho IEEE 802.16. H thng ny l h thng a truy cp khng dy s dng cng ngh OFDMA c cc c im sau :



12

- Khong cch gia trm thu v pht c th ti 50km - Tc truyn c th thay i, ti a 70Mbit/s. - Hot ng trong c hai mi trng truyn dn: ng truyn tm nhn thng

LOS (Line of Sight) v ng truyn b che khut NLOS (Non line of sight). - Di tn lm vic 2-11GHz v t 10-66GHz hin v ang c tiu chun

ho. - Trong WiMAX hng truyn tin c chia thnh hai ng ln v xung.

ng ln c tn s thp hn ng xung v u s dng cng ngh OFDM

- WiMAX s dng iu ch nhiu mc thch ng t BPSK, QPSK n 256-QAM kt hp cc phng php sa li d liu nh ngu nhin ho, vi m ho sa li Reed Solomon, m xon t l m t 1/2 n 7/8.

- rng bng tn ca WiMAX t 5MHz n trn 20MHz c chia thnh nhiu bng con . Vi cng ngh OFDMA, cho php nhiu thu bao c th truy cp ng thi mt hay nhiu knh mt cch linh hot m bo ti u hiu qu s dng bng tn.

- Cho php s dng c hai cng ngh TDD (time division duplexing) v FDD (frequency division duplexing) cho vic phn chia truyn dn ca hng ln (uplink) v hng xung (downlink).

- H thng WiMAX c phn chia thnh 4 lp con : Cc lp ny tng ng vi hai lp di ca m hnh OSI v c tiu chun ho c th giao tip vi nhiu ng dng lp trn .

1.2.3 Chun IEEE 802.16

WiMAX da trn tiu chun 802.16 ca IEEE v HiperMAN ca ETSI.

IEEE 802.16-2001: Chun ny c xy dng t thng 9/2000 v c IEEE thng qua vo thng 12/2001. 802.16-2001 xc nh giao din v tuyn gm lp MAC v PHY ca h thng truy nhp v tuyn c nh im a im vi nhng mc ch:

- Cho php trin khai nhanh chng v rng ri cc h thng truy nhp v tuyn bng rng vi chi ph hiu qu.

- m bo kh nng tng thch gia cc thit b truy nhp v tuyn bng rng ca cc hng khc nhau.

- Tng tc qu trnh thng mi ha ,ph cp truy nhp v tuyn bng rng ,a ra cc gii php thay th cho truy nhp bng rng hu tuyn.



13

Hnh 3 : cc chun ca IEEE 802.16

c im ca 802.16-2001: - Di tn t 10 66GHz knh vt l thng l 25/28 MHz - ng truyn LOS. - Phng php iu ch l QPSK,16/64QAM - Tm hot ng t 2-7 km

Ta nhn thy nhc im ca truyn LOS v hu ht trn thc t l kiu NLOS hoc ng truyn thng nhng c vt cn (OLOS),trc nhng hn ch th bn 802.16.2 c a ra.

IEEE 802.16.2-2001 cp vo thng 10/2007 tp trung vo gii quyt vn can nhiu.trong di hot ng c nh 10 66GHz nhng c bit quan tm ti di t 23.5-43.5GHz.

IEEE802.16 Con 1-2003:[5] chun ny cng b s ph hp v thc thi giao din khng gian MAN-SC v tuyn trong di 10-66GHz. Tiu chun ny cng b s ph hp v thc thi giao thc cc ch tiu k thut ph hp ca cc trm gc v cc trm thu bao da trn giao din khng gian MAN-SC (10-66GHz) c xc nh trong tiu chun 802.16.

IEEE 802.16 Con 2-2003: [5] Tiu chun ny gii thiu cu trc thit b o v mc ch o ,kim tra s ph hp cc ch tiu k thut ca cc trm gc v cc trm thu bao da trn giao din khng gian c xc nh trong chun 802.16.

IEEE 802.16a . c thng qua thng 1/2003.phin bn ny b sung cho thiu st ca 802.16-2001 vi vic b xung thm di tn s 2- 11 GHz. Gip cho vic



14

truyn sng trong mi trng c vt cn v b che khut dng hn.,b sung cc k thut cho lp vt l gip ti u knh truyn theo bng tn ca ng dng

IEEE 802.16b: Chun ny hot ng trn bng tng t 5 6 Ghz vi mc ch cung ng dnh v vi cht lng cao (QoS). C th chun u tin truyn thng tin ca nhng ng dng video, thoi, real-time thng qua nhng lp dch v khc nhau. Chun ny sau c kt hp vo chun 802.16a

IEEE 802.16c. c chp nhn vo thng 12/2002 y l bn sa i ca chun 802.16-2001 Chun ny nh ngha thm cc profile mi cho di bng tng t 10-66GHz vi mc ch ci tin thao tc ga cc phn(interoperability).

IEEE 802.16-2004 hay IEEE 802.16d c IEEE thng qua thng 6/2004. Chun ny s dng bng tng c bn quyn t 2 11 Ghz. y l bng tng thu ht c nhiu quan tm nht v tn hiu truyn c th vt c cc chng ngi trn ng truyn. 802.16a cn thch ng cho vic trin khai mng Mesh m trong mt thit b cui (terminal) c th lin lc vi BS thng qua mt thit b cui khc. Vi c tnh ny, vng ph sng ca 802.16a BS s c m rng.

IEEE 802.16-2004 Tp trung vo cc ng dng c nh v lu tr trong di tn s 2 -11 GHz. Hai k thut iu ch a sng mang c h tr trong 802.16-2004:

- OFDM vi 256 sng mang v - OFDMA vi 2048 sng mang.

Cc h s chng nhn u tin ca .Din n WiMAX u da trn OFDM, nh c nh ngha trong phin bn ny ca tiu chun . Cc thit b WiMAX hin ti c trn th trng l da trn chun ny.

IEEE 802.16e c thng qua thng 12/2005. Din n WiMAX s bt u qu trnh chng nhn thit b ban u trong cc bng tn 3.3 n 3.8 GHz v 5.7 n 5.8 GHz.Vi kh nng p ng c cc ng dng c nh cng nh cc dch v di ng, nn cn c gi l WiMAX di ng. Chun ny v ang c th nghim nhiu nc. Hin ti, WiMAX di ng "Wave 2" dng 2 ng-ten pht v 2 ng-ten thu cho tc ti a tm 75Mbps.

IEEE 802.16e: H tr cho vic khai thc s kt hp gia dch v c nh v di ng ti cc tn s di 6 GHz.

Tiu chun ny m ra s h tr SOFDMA (mt bin th ca OFDMA), n tnh n s lng cc sng mang c th bin i, ngoi cc phng thc OFDM v OFDMA c nh ngha trc y. Vic gn sng mang trong cc phng thc



15

OFDMA c thit k gim thiu tc ng ca can nhiu ti thit b ngi dng vi cc anten ton hng.

Tng cng h tr cho MIMO (Multiple Input Multiple Output) v cc h thng anten thch nghi (AAS), cng nh chuyn v (handoff) cng v mm. N cng ci thin c cc kh nng tit kim ngun cho cc thit b di ng v cc tnh nng an ton mnh hn. C hai sn phm da trn OFDM v trn OFDMA u c th tn dng cc dung lng mi m rng.

Trong phn sau, chng ta coi cc nh dng ca 802.16e WiMAX ch yu nh l vic chp nhn SOFDMA, cn cc nh dng 802.16-2004 nh l vic s dng OFDM vi 256 sng mang. Phin bn mi ca tiu chun 802.16 c tnh tng thch ngc, cho nn cc yu cu k thut mi ca phng thc OFDM l tng thch vi cc phin bn trc. Tuy nhin, cc hng thc OFDM v SOFDMA s khng tng thch nu chng da trn hai k thut iu ch khc nhau. Kt qu l, loi CPE ca OFDM ch n mode (single mode) s khng lm vic c trong mt mng SOFDMA v ngc li, mt CPE ca SOFDMA s khng lm vic trong mt mng OFDM.y cugnx l mt hn ch ca .

IEEE 802.16j: By gi IEEE ang bt tay vo chun ha 802.16j phc v cho vic Relay (WiMAX Mesh network).

Hnh 4: m hnh mng Mesh trong WiMAX



16

Li ch ca vic dng nhng relay BS c lit k trong hnh v. C th k n cc li ch sau:

- Thay v lin lc trc tip vi BS, ngi dng c th lin lc thng qua nhiu Relay BS vi ng truyn tt hn v tc cao hn, hiu qu truyn cao hn, v.v..

- Relay BS c th dng tng vng ph sng ca mng WiMAX (relay BS r hn lp t BS WiMAX)

- Ngi dng s khng cn tiu tn mt nng lng ln lin lc vi BS (tit kim nng lng tiu th thit b di ng).

802.16m: ang c nghin cu v chun ha. Chun ny hng ti tng tc truyn ca WiMAX ln 1Gbps bng cch dng MIMO trn nn cng ngh a truy nhp OFDMA vi s lng ngten pht v thu nhiu hn WiMAX di ng Wave 2 . 802.16m trang b 4 ng-ten pht v 4 ng-ten thu s c th y tc truyn ln ln hn 350Mbps,v vn tng thch vi WiMAX c nh v di ng v ang c trin khai Theo d kin, WiMAX Release 2 vi s hon thin ca 802.16m s hon thnh vo cui nm 2009 v c th bt u trin khai dch v t 2010

Bng 4 :So snh cc chun 802.16 [4]

802.16 802.16a 802.16d 802.16e Ph (GHz) 10 66 2 11 2 11 2 6

Cu hnh Trc x Khng trc xa Khng trc x Khng trc x

Tc bit 32 134 Mbps

Knh 28 MHz

75 Mbps

Knh 20 MHz



17

Ngoi ra cn c nhiu chun b sung khc ang c trin khai hoc ang trong giai on chun ha nh 802.16g, 802.16f, 802.16h...

im khc nhau gia cc phin bn 802.16 nh 802.16a,802.16-2004 v 802.16e

- Chun 802.16a ca IEEE tp trung vo truy cp bng rng c nh. - Chun m rng 802.16-2004 ca IEEE ci tin hn nh h tr cho CPE trong

nh. - Chun802.16e l mt m rng ca chun 802.16-2004. Mc ch ca chun

802.16e l b sung kh nng di ng d liu cho chun hin thi, m ban u thit k ch yu dnh cho c nh.

WiMAX 802.16-2004. Chun ny da trn phin bn 802.16-2004 ca IEEE 802.16 v ETSI - HiperMAN. N s dng Ghp knh Phn chia theo tn s trc giao (OFDM -Orthogonal Frequency Division Multiplexing), h tr truy nhp c nh v di tr trong cc mi trng Trc th (LOS - Line of Sight ) v Khng trc th (NLOS Non Line of Sight). Cc hng sn xut ang trin khai Thit b khch hng (CPE) trong nh v ngoi tri v th PCMCIA cho laptop. Cc nh dng (profile) ban u ca Din n WiMAX trong bng tn 3,5 GHz v 5,8 GHz. Cc sn phm c chng nhn u tin xut hin vo cui nm 2005.

WiMAX 802.16e. Ti u ho cho cc knh v tuyn di ng, phin bn ny da trn s hiu chnh 802.16e v h tr chuyn v (handoff) v chuyn vng (roaming). N s dng Truy nhp ghp knh phn chia theo tn s trc giao c th m rng thang (SOFDMA Scalable Orthogonal Frequency Division Multiplexing Access), mt k thut iu ch a sng mang c s dng to knh ph (sub-channelization). Cc nh cung cp dch v ang trin khai 802.16e cng c th s dng mng ny cung cp dch v c nh. Vic cp chng ch d kin s c bt u vo gia nm 2006, khi khai trng cc phng th nghim chng nhn WiMAX di ng, vi cc sn phm c cp chng ch u tin c mt nm 2007

im khc nhau gia IEEE 802.16 v cng ngh WiMAX

Mc tiu chnh ca Din n WiMAX l to ra mt chun tng thch t chun 802.16 ca IEEE v cc chun HiperMAN ca ETSI. iu ny s thc hin c nh vic hnh thnh cc m t h thng. Da trn nhng g m Din n WiMAX xem xt v cc iu khon ca nh cung cp dch v v cc k hoch thit b ca cc nh cung cp, Din n WiMAX quyt nh tp trung trc tin vo cc m t cho phng thc PHY OFDM 256 ca chun 802.16 nm 2004, c IEEE thng qua vo thng 6/2004. Lp vt l (PHY) s c kt hp vi mt b iu khin truy nhp phng tin (MAC) c lp m bo mt nn tng thng nht cho tt c nhng trin khai WiMAX.



18

Tun th theo chun 802.16 khng c ngha l thit b c Din n WiMAX chng nhn hoc c th tng thch vi cc thit b ca cc nh cung cp khc. Tuy nhin nu mt thit b tun th thit k c Din n WiMAX chng nhn th va tun th chun 802.16 v tng thch vi c thit b ca cc nh khai cp khc.

1.2.4 Cc nh dng ca din dn WiMAX [5]

Vic la chn cc nh dng c thc y bi nhu cu th trng, kh dng ca ph tn, nhng rng buc v chnh sch, cc dch v cn cung cp v u t ca cng ty.

V d nh, tnh kh dng ph tn cho cc dch v v tuyn bng rng mt s nc l ng lc thc y vic to ra cc nh dng ban u trong bng tn 3,5 GHz. Tnh kh dng ca cc ph min php v nhu cu v cc dch v c nh quyt nh vic to ra mt nh dng trong bng tn 5,8 GHz. Nhu cu v cc dch v di ng v tnh kh dng ph lm cho cc bng tn 2,3 GHz v 2,5 GHz chc chn tr thnh mc tiu cho cc nh dng ca 802.16e. Cc nh dng ca Din n WiMAX c xc nh bi cc tham s sau y:

- Di ph : bng tn c dng cho dch v WiMAX do cc t chc qun l cung cp .Hin ti c 2 loi bng tn dnh cho WiMAX l:

o Bng tn cp php :2.3 2.6 GHz v 3.3 3.6 GHz o Bng tn khng cp php 5.7 -5.8 GHz

- Song cng. Hai tu chn sn c: Song cng phn chia theo thi gian (TDD) cho cc nh khai thc c ph khng cp i hoc ph min php, v Song cng Chia theo Tn s (FDD). FDD i hi hai knh, mt cho lu lng tuyn ln v knh kia cho lu lng tuyn xung. Trong mt mng TDD, lu lng ch chim mt knh duy nht vi lu lng tuyn ln v tuyn xung c gn cc khe thi gian khc nhau.

- rng (Bng thng) knh. Bng thng ca knh ph thuc rt cao vo ph do cc nh chnh sch phn b. Nhng nh dng ban u c hn ch cho 3,5 MHz v 7 MHz trong phtn c cp php khi chng l cc knh c ph thng dng c phn b trong bng tn 3,5 GHz. Khi cc nh khai thc c kh nng s dng cc knh rng hn, th cc thnh vin ca Din n WiMAX s b sung cc nh dng chng nhn vi cc bng thng ca knh rng hn.

- Tiu chun IEEE. Cc nh dng ca 802.16-2004 s dng OFDM vi 256 sng mang. Cc nh dng ca 802.16e hu nh chc chn da trn SOFDMA. Ch tiu chun ny mi h tr tnh di ng.



19

Tt c cc nh dng chng nhn da trn 802.16-2004 u theo mt nh dng h thng chung. nh dng ny bao gm cc yu cu k thut ca WiMAX, duy tr bt k tham s no d l tn s, kch thc knh hay phng php to song cng. Mt nh dng h thng mi va c pht trin gn y cho cc nh dng chng nhn 802.16e. Nu c mi quan tm t cng ng cc nh sn xut, mt nh dng h thng th ba c th c gii thiu cho cc sn phm 802.16-2004 h tr kh nng xch tay v di ng gii hn. Cc nh dng ban u c Din n WiMAX xc nh h tr truy nhp c nh v lu tr trong cc bng tn 3,5 GHz v 5,8 GHz.

Tn s (MHz)

Song cng

Bng thng knh (MHz)

K hiu nh dng

Ghi ch

3400-3600 TDD 3.5 3.5T1 Hin ti

3400-3600 FDD 3.5 3.5 F1 Hin ti

3400-3600 TDD 7 3.5T2 Hin ti

3400-3600 FDD 7 3.5 F2 Hin ti

5725-5850 TDD 10 5.8T Hin ti

2300-2600 TDD 5.0/5.5 2.5 T1 Tng lai

2300-2600 FDD 5.0/5.5 2.5 F1 Tng lai

Bng 5 :cc nh dng chng nhn ca in n WiMAX

1.3 Cc m hnh ng dng [2]

WiMAX c xut 2 m hnh ng dng l c nh vdi ng.

1.3.1 M hnh ng dng c nh (Fixed WiMAX)

M hnh c nh s dng cc thit b theo tiu chun IEEE.802.16-2004. Tiu chun ny gi l khng dy c nh v thit b thng tin lm vic vi cc anten t c nh ti nh cc thu bao. Anten t trn nc nh hoc trn ct thp tng t nh cho thng tin v tinh

Tiu chun IEEE 802.16-2004 cng cho php t anten trong nh nhng tt nhin tn hiu thu khng tt bng anten ngoi tri. Bng tn cng tc (theo quy nh v phn b ca quc gia) trong bng 2,5GHz hoc 3,5GHz. rng bng tng l 3,5MHz. Trong mng c nh, WiMAX thc hin cch tip ni khng dy n cc modem cp, n cc i dy thu bao ca mch xDSL hoc mch Tx/Ex (truyn pht/chuyn mch) v mch OC-x (truyn ti qua sng quang).



20

Hnh 5 :M hnh ng dng WiMAX c nh

WiMAX c nh c th phc v cho cc loi ngi dng nh: cc x nghip, cc khu dn c nh l, mng cp truy nhp WLAN cng cng ni ti mng th, cc trm gc BS ca mng thng tin di ng v cc mch iu khin trm BS. V cch phn b theo a l, ngi dng c th phn tn ti cc a phng nh nng thn v cc vng su vng xa kh a mng cp hu tuyn n .

1.3.2 M hnh ng dng WiMAX di ng



21

Hnh 6 :M hnh ng dng WiMAX di ng

M hnh WiMAX di ng s dng cc thit b ph hp vi tiu chun IEEE 802.16e c thng qua trong nm 2005.Tiu chun 802.16e b sung cho tiu chun 802.16-2004 hng ti cc ngi dng c nhn di ng, lm vic trong bng tn thp hn 6GHz. Mng li ny phi hp cng WLAN, mng di ng cellular 3G c th to thnh mng di ng c vng ph sng rng. Hy vng cc nh cung cp vin thng hip ng cng tc thc hin c mng vin thng s truy nhp khng dy c phm vi ph sng rng tha mn c cc nhu cu a dng ca thu bao.

Vic la chn trin khai trn din rng vi WIMAX di ng hay c nh l cu hi ca nhiu nc.S so snh di y s lm r s khc bit gia 2 chn ny

1.4 So snh WiMAX 802.16-2004 v 802.16e [ 4]

Cc trin khai di ng v c nh c cc nhu cu rt khc nhau v cc mc tiu phn on th trng khc nhau v c bn, vi cc v tr v m hnh s dng, cc nhu cu v thng lng, cc dng thit b ngi dng v cc SLA khc nhau. C hai s b sung ca WiMAX c nh ngha p ng cc nhu cu khc nhau ca hai phn on th trng v cc yu cu khc nhau ca cc ng dng khc nhau.

Trong mt trin khai c nh vi cc chc nng c bn, 802.16-2004 v 902.16e ngh hiu nng tng ng. Thng lng cc ai mt sector cho c hai phin bn ca WiMAX l 15Mbps cho knh 5MHz, hoc 35Mbps cho knh 10MHz. Phm vi trm gc trong cc vng dn c ng c c th khong vi km ty thuc vo cc thuc tnh nh l loi CPE, bng tn, tnh di ng ..vv. Trong cc mng m dung lng b chi phi, s lng trm gc c lp t ty thuc vo nhu cu thng lng v phm vi.

Tuy nhin, hiu nng ca hai phin bn WiMAX c th thay i v c bn cho cc ng dng c th bi v 802.16-2004 l ti u cho truy nhp c nh v 802.16 l cho truy nhp di ng mc d WiMAX cng c th c s dng cho truy nhp c nh.

Cc mng c nh c th thu li nhun t nhiu thun li c a ra bi cc sn phm c chng nhn ca WiMAX Forum theo 802.16-2004.

iu ch t phc tp: OFDM l mt cng ngh iu ch n gin hn v ph hp hn trin khai m khng yu cu h tr tnh di ng.

Cc bng tn khng cp php: Cc dch v di ng yu cu ph cp php cung cp s bao ph trong cc vng rng ln. Tuy nhin cc trin khai c nh thng s dng thnh cng cc bng tn khng cp php trong cc vng m cc



22

mc nhiu l c th chp nhn c. V l do ny m hu ht cc Profile nhm vo cc bng tn khng cp php l ph hp khi da trn c s 802.16-2004.

Thng lng cao hn: Cc bng ph cao hn c la chn cho cc Profile 802.16-2004 dn n kt qu thng lng cap hn. iu ny l mt thun li d thy, c bit khi nhm vo cc ngi dng kinh doanh vi mc lu lng cao hn v vi cc CPE c cc anten t ngoi tri.

Thi im a vo th trng ph hp hn: Tnh sn sng v thng mi sm hn ca cc sn phm 802-16-2004 cho php cc nh khai thc p ng nhu cu dn nn cho cc kt ni bng rng trong cc vng di mc phc v, v bt u t ti s chia s th trng gia cc nh cnh tranh hng u.

Mt mt khc, mt s nh khai thc c th quyt nh i cc Profile 802.16e v nhiu l do:

H tr tnh di ng: Cc sn phm 802.16e l ti u cho tnh di ng v s c h tr chuyn giao ln n 120km/h.

H tr cho cc kiu cng sut sleep v saving tng thi gian sng ca cc thit b ngi dng di ng

Bao ph trong nh tt hn: Bao ph trong nh tt hn t ng thng qua knh con ha v cc li ch ca ty chn AAS c cc ng dng c nh v di ng, bi v cc ngi dng thng l trong nh hay khng trong tm nhn thng. Tuy nhin, trong khi cc anten ngoi tri c th b li v hn ch bao ph trong nh cc trin khai c nh th iu ny r rng khng phi l mt ty chn cho cc ngi dng di ng vi mt laptop hay mt PDA.

mm do tt hn trong vic qun l cc ti nguyn ph: knh con ha cng mang li kh nng s dng s thng minh ca mng cp pht ti nguyn cho cc thit b ngi dng khi c nhu cu. Thc t iu ny dn n kt qu tng hiu nng s dng ph, iu khin thng lng cao hn v bao ph trong nh tt hn v trong mt vi trng hp lm cho chi ph trin khai thp hn. Iu ny c bit hiu qu vi cc nh khai thc vi ph hn ch.

Phm vi rng ln ca cc dng nhn t cho cc thit b ngi dng: trong khi cc CPE trong nh v ngoi nh, v cc card PCMCIA my tnh xch tay c mong i thng tr th trng 802.16-2004 th cc card PCMCIA my tnh xch tay, cc card mini, cc modem trong nh, cc PDA v cc in thoi s sn sng gia cc thit b ngi dng 802.16e. S a dng ny cho php cc nh khai thc m rng cc dch v ca h n cc phn on th trng mi v tng thm s t do cho cc thu bao ca h. Mc d cc sn phm 802.16e c gii thiu mun hn



23

nhng c th hi vng rng gi c CPE ca chng s nhanh chng gim thp hn cc CPE theo 802.16-2004 khi cc sn phm 802.16e c nhm vo mt th trng rng ln hn. Vi chi ph CPE in hnh l thay i quan trong nht trong bt k k hoch kinh doanh ca nh khai thc, tnh sn c ca cc Chip CPE s l mt trong cc nhn t hng dn cho vic quyt nh phin bn no ca WiMAX c thng qua.

La chn gia 802.16-2004 v cc sn phm 802.16e ty thuc phn ln vo cc loi dch v c cung cp v cc kiu kinh doanh ca cc nh khai thc. Trong mt vi trng hp, la chn s l hin nhin. Mt nh khai thc di ng xy dng mt mng bao ph b sung cho mng 3G s tin thng n 802.16e. Mt nh cung cp dch v Internet khng dy cung cp truy nhp khng dy cho lin lc vng nng thn s chn cc sn phm WiMAX 802.16-2004 da trn OFDM t phc tp hn.

Thm vo cc nh khai thc cn tnh n nhiu nhn t khc m c th nh hng n la chn gia cc sn phm 802.16-2004 v 802.16e.

Mc tiu th trng: nu nh khai thc nhm vo cc ngi dng kinh doanh v cc ngi dng vng dn c trong mt mi trng hu nh l tm nhn thng, cc CPE vi mt anten ngoi tri s c thng lng tt hn v hiu nng LOS c th ph hp hn. iu ny c th lm cho nh khai thc hng ti mt trin khai 802.16-2004. Nu thay th nh khai thc nhm vo th trng di ng, cc CPE 802.16e chi ph thp c th c yu cu cho k hoch kinh doanh c th pht trin.

Ph: Trong khi WiMAX Forum s tip tc thm vo cc Profile mi ph hp vi nhu cu th trng, iu ch ph hp vi cc Profile 802.16-2004 hoc 802.16e trong mt s bng tn. Trong hu ht cc trng hp nh khai thc s c mt vi la chn qua cc bng ph sn c v la chn ca WiMAX c th ty thuc vo tnh sn c ca sn phm. N c th l cc Prpfile 802.16e s c thm vo cc bng tn in hnh dnh cho cc ng dng c nh v mang xch, bi v 802.16e c t c kh nng xy ra nhiu a ng.

iu tit: Mt s nh iu tit y quyn cc loi dch v c th m c th c ngh trong mt bng ph. Chng hn, mt s nh iu tit Chu u gii hn ph 3.5GHz cho cc dch v c nh v mang xch, iu ny c th ngn cn s thng qua ca 802.16e khi WiMAX h tr cc dch v di ng, thm ch cc giy php ph in hnh khng y quyn s dng mt cng ngh c th.

Tnh hp thi: Tnh c sn sm hn ca cc sn phm 802.16-2004 trong cc bng tn 3.5GHz s l mt nhn t quan trng cho cc nh cung cp dch v mun trin khai mt mng WiMAX nhanh chng.



24

1.5 Bng tn cho WiMAX[4]

Cc bng c WiMAX Forum tp trung xem xt v vn ng c quan qun l tn s cc nc phn b cho WiMAX l:

1. 3600-3800MHz 2. 3400-3600MHz (bng 3.5GHz) 3. 3300-3400MHz (bng 3.3GHz) 4. 2500-2690MHz (bng 2.5GHz) 5. 2300-2400MHz (bng 2.3GHz) 6. 5725-5850MHz (bng 5.8GHz) 7. 700-800MHz (di 1GHz).

Bng 3400-3600MHz (bng 3.5GHz)

Bng 3.5Ghz l bng tn c nhiu nc phn b cho h thng truy cp khng dy c nh (Fixed Wireless Access FWA) hoc cho h thng truy cp khng dy bng rng (WBA). WiMAX cng c xem l mt cng ngh WBA nn c th s dng bng tn ny cho WiMAX. V vy, WiMAX Forum thng nht la chn bng tn ny cho WiMAX.

Bng tn ny s dng cho chun 802.16-2004 cung cp cc ng dng c nh v nomadic, rng phn knh l 3.5MHz hoc 7MHz, ch song cng TDD hoc FDD.

Mt s nc quy nh bng tn ny ch dnh cho cc h thng cung cp cc dch v c nh, khng c ng dng nomadic, nn trin khai c WiMAX cn thit phi sa i li quy nh ny.

i vi Vit Nam, do bng tn ny c u tin dnh cho h thng v tinh Vinasat nn hin ti khng th trin khai cho WiMAX.

Bng 3600-3800MHz:

c mt s nc chu u xem xt cp cho WBA. Tuy nhin, do mt phn bng tn ny (t 3.7-3.8GHz) ang c nhiu h thng v tinh vin thng s dng (ng xung bng C), c bit l khu vc chu , nn t kh nng bng tn ny s c chp nhn cho WiMAX chu .



25

Bng 3300-3400MHz (bng 3.3 GHz):

Bng tn ny c phn b n , Trung Quc v Vit Nam ang xem xt phn b chnh thc. Do n v Trung Quc l hai th trng ln, nn d cha c nhiu nc cp bng tn ny cho WBA, nhng thit b WiMAX cng c sn xut.

Chun WiMAX p dng bng tn ny tng t nh vi bng 3.5GHz, l WiMAX c nh, ch song cng FDD hoc TDD, rng knh 3.5MHz hoc 7MHz.

Do n ch cho php s dng on bng tn 3316-3400MHz, nn cc thit b WiMAX hin ti cng ch lm vic trong on ny vi ti a 2x9 knh 3.5MHz. V vy, nu c 4 nh khai thc s dng bng tn ny th thng mi nh khai thc ch c cp s dng 2x2 knh 3.5MHz. Trong khi , theo kin ca cc chuyn gia Alvarion, mt trong nhng hng cung cp thit b WiMAX, th khai thc hiu qu, mi nh khai thc nn c cp t nht 2x3 knh 3.5MHz.

Bng 2500-2690MHz (bng 2.5 GHz)

Bng tn ny l bng tn c WiMAX Forum u tin la chn cho WiMAX di ng theo chun 802.16-2005. C hai l do cho s la chn ny.

- Th nht, so vi cc bng trn 3GHz iu kin truyn sng ca bng tn ny thch hp cho cc ng dng di ng.

- Th hai l kh nng bng tn ny s c nhiu nc cho php s dng WBA bao gm c WiMAX. WiMAX bng tn ny c rng knh l 5MHz, ch song cng TDD, FDD.

Bng tn ny trc y c s dng ph bin cho cc h thng truyn hnh MMDS trn th gii, nhng do MMDS khng pht trin nn Hi ngh Thng tin V tuyn th gii nm 2000 (WRC-2000) xc nh c th s dng bng tn ny cho h thng di ng th h 3 (3G hay IMT-2000 theo cch t tn ca ITU). Do cha c cu tr li r nn hin c mt s nc nh M, Brazil, Mexico, Singapore, Canada, Lin hip Anh (UK), Australia cho php s dng mt phn bng tn tn ny cho WBA. Trung Quc v n cng ang xem xt.

V d, Singapore chia bng 2.5GHz thnh 15 khi 6 MHz cho WBA u thu, theo nh khai thc c cung cp cc dch v c nh, nomadic v di ng, khng yu cu phi s dng mt cng ngh c th no. Cc nh khai thc trng thu c trch nhim t phi hp vi nhau v vi cc nh khai thc ca cc nc lng ging trnh can nhiu. Ti M, y ban Truyn thng Lin bang (FCC) chia bng



26

2.5GHz thnh 8 khi, mi nh khai thc c th c cp 22.5MHz, gm mt khi ph c rng 16.5MHz kt hp vi khi 6MHz.

Do ITU xc nh bng tn ny cho IMT-2000, nn WiMAX Forum ang c k hoch tham gia vo cc nhm nghin cu ca ITU thc y vic a chun 802.16 thnh mt nhnh ca h tiu chun IMT-2000

Vi Vit Nam, Quy hoch ph v tuyn in quc gia c Th tng Chnh ph ph duyt cui nm 2005 quy nh bng tn 2500-2690 MHz s c s dng cho cc h thng thng tin di ng th h mi, khng trin khai thm cc thit b khc trong bng tn ny. V vy, c th hiu cng ngh WiMAX di ng cng l mt i tng ca quy nh ny, nhng bng tn ny s c s dng cho loi hnh cng ngh c th no vn cn m.

Bng 2300-2400MHz (bng 2.3 GHz):

Bng 2.3GHz cng c c tnh truyn sng tng t nh bng 2.5GHz nn l bng tn c WiMAX Forum xem xt cho WiMAX di ng.

Hin c mt s nc phn b bng tn ny cho WBA nh Hn Quc (trin khai WiBro), c, M, Canada, Singapore. Singapore cho u thu 10 khi 5MHz trong di 2300-2350MHz s dng cho WBA vi cc iu kin tng t nh vi bng 2.5GHz. c chia bng tn ny thnh cc khi 7MHz, khng qui nh c th v cng ngh hay rng knh, u tin cho ng dng c nh. M chia thnh 5 khi 10MHz, khng qui nh c th v rng knh, cho php trin khai c TDD v FDD.

i vi Vit Nam, y cng l mt bng tn c kh nng s c s dng trin khai WBA/WiMAX.

Bng 5725-5850MHz (bng 5.8 GHz):

WiMAX Forum quan tm bng tn ny v c nhiu nc cho php s dng khng cn cp php v vi cng sut ti cao hn so vi cc on bng tn khc trong di 5GHz (5125-5250MHz, 5250-5350MHz), vn thng c s dng cho cc ng dng trong nh.Nn bng tn ny thch hp trin khai WiMAX c nh, rng phn knh l 10MHz, phng thc song cng c s dng l TDD, khng c FDD.

Bng di 1GHz:

Vi cc tn s cng thp, sng v tuyn truyn lan cng xa, s trm gc cn s dng cng t, tc mc u t cho h thng thp i. V vy, WiMAX Forum cng



27

ang xem xt kh nng s dng cc bng tn di 1GHz, c bit l bng 700-800MHz.

Hin nay, mt s nc ang thc hin vic chuyn i t truyn hnh tng t sang truyn hnh s, nn s gii phng c mt phn ph tn s dng cho WBA/WiMAX. V d, M cp on bng tn 699-741MHz trc y dng cho knh 52-59 UHF truyn hnh v xem xt cp tip bng 747-801MHz (knh 60-69 UHF truyn hnh).

Vi Vit Nam, do c im c rt nhiu i truyn hnh a phng nn cc knh trong gii 470-806MHz dnh cho truyn hnh c s dng dy c cho cc h thng truyn hnh tng t. Hin cha c l trnh c th no chuyn i cc h thng truyn hnh tng t ny sang truyn hnh s, nn cha thy c kh nng c bng tn cp cho WBA/WiMAX y

Tng kt

Ton chng mt a ra ci nhn tng quan nht v mt s cng ngh mng truy nhp bng rng, nhng c th ca cc loi cng ngh truy nhp ny nhm to c s khch quan nh gi v la chn cng ngh ph hp trong chng 3.

Chng ny cng trnh by r s khc bit ga hai m hnh ng dng WiMAX c nh v WiMAX di ng. Da vo nhng dc im khc nhau ca cc nh dng ny gip cc nh cung cp dch v trong tng hon cnh c th s la chn m hnh ph hp trong trin khai thc t .

Vi nhng tm hiu s lc ta cng thy cng ngh WiMAX t ra c rt nhiu c tnh u vit trong vic trin khai dch v bng thng rng cho c thit b c nh, xch tay v di ng, thm ch n cc vng m vi cc cng ngh trc y l kh khn hoc khng th.

Trong chng tip theo ta s tm hiu su hn v kin trc mng v cc k thut c s dng trong cng ngh WiMAX.



28

Chng 2

Mng WiMAX

2.1 M hnh cu trc h thng WiMAX [12]

WiMAX gm 2 mt phng tham chiu l:

- Mt phng qun l: l mt phng cha cc thc th qun tr mng nh qun l v tnh cc.

- Mt phng truyn tin :Mt phng ny tng ng vi hai lp di ca m hnh OSI m bo cho vic truyn tin ga 2 trm trong 1 cuc kt ni v c tiu chun ho c th giao tip vi nhiu ng dng lp trn

Hnh 7: M hnh cu trc ca WiMAX



29

2.2 Mt phng truyn tin:

Mt phng ny gm 2 lp v c phn chia thnh 4 lp nh hn:

- MAC o Lp con tip ng CS (Convergence

Sublayer) o Lp con phn chung CPS (Common

Part Sublayer) o Lp con bo mt PS (Privaci Sublayer)

- PHY (physical)

2.2.1 Lp con tip ng (hay lp con hi t dch v chuyn bit MAC_CS) [2]

MAC CS nm trn MAC CPS v s dng thng qua MAC SAP, cc dch v c cung cp bi MAC CPS. Lp ny thc hin cc chc nng sau:

- Nhn cc n v d liu giao thc (PDU) t lp cao hn - Thc hin phn loi cc PDU lp cao hn. - X l (nu cn) cc PDU lp cao hn trn c s phn loi. - Pht cc CS PDU n cc MAC SAP thch hp. - Nhn CS PDU t thc th cng cp.

Hin nay, c hai chi tit k thut CS c cung cp l:ATM CS v Packet CS.

Lp con hi t ATM, hay ATM CS l mt giao din logic kt hp cc dch v ATM khc nhau vi MAC CPS SAP. ATM CS nhn cc t bo ATM t lp ATM, thc hin phn loi v nu c cung cp PHS (nn tiu ti trng), sau pht cc CS PDU n MAC SAP ph hp.

Lp con hi t gi hay Packet CS dnh cho cc dch v d liu dng gi v d nh Ethernet, PPP, IP v VLAN. Cc CS khc c th c h tr trong tng lai.

Trong qu trnh gi thng tin.D liu t lp cao hn chuyn xung,lp CS c trch nhim pht cc MAC SDU n MAC SAP. MAC c trch nhim pht cc MAC SDU n cc MAC SAP ngang cp ph hp vi QoS, vic phn on, ghp ni, v cc chc nng truyn ti khc, kt hp vi cc c im lung dch v ca mt kt ni c th.



30

Vi qu trnh nhn tin.CS c trch nhim nhn MAC SDU t cc MAC SAP.sau khi s l nh phn loi,gii nn tiu v gi n thc th lp cao hn.

2.2.2 Lp con phn chung (MAC CPS- common part sublayer)

Phn li ca lp MAC IEEE 802.16 l MAC CPS, c nhim v l :

- nh ngha tt c cc qun l kt ni, - Phn phi bng thng, yu cu v cp pht, th tc truy nhp h thng, - Lp lch ng ln, iu khin kt ni v ARQ. - Truyn thng gia CS v CPS c cc im truy nhp dch v MAC (MAC

SAP) duy tr. Thit lp, thay i, xa kt ni v truyn ti d liu trn cc knh l bn chc nng c bn trong qu trnh truyn thng ti lp ny.

a/ nh dng v phn loi MAC PDU

Phn loi MAC PDU

MAC PDU d liu

- Tiu l tiu MAC chung vi HT=0. - Ti trng l cc MAC SDU, hay cc phn on l d liu t lp pha trn

(cc CSPDU). c pht trn cc kt ni truyn ti.

Cc MAC PDU qun l

- Tiu l tiu MAC chung vi HT=0 - Ti trng l cc bn tin qun l MAC. c pht trn cc kt ni qun l.

Cc MAC PDU yu cu bng thng (BW)

- Tiu l tiu yu cu bng thng vi HT=1 - khng c ti trng.

Tiu MAC chung



31

Cc trng trong tiu MAC chung c ngha nh sau:

- CI (1 bit) CRC Indicator: Nu CI c gi tr l 1 c ngha CRC c tnh n trong PDU bng cch gn vo ti trng PDU sau khi mt m ha, nu c gi tr 0 ngha l khng c CRC.

- CID (16 bit) Connection Identifier - EC (1 bit) Encryption Control: EC c gi tr bng 0 ngha l ti trng khng

c mt m ha.EC c gi tr 1 ngha l ti trng c mt m ha. - EKS (2 bit) Encryption Key Sequence Ch mc ca kha mt m ha lu

lng (TEK) v vector khi to c s dng mt m ha ti trng. Trng ny ch c ngha nu trng EC c thit lp l 1.

- HCS (8 bit) Header Check Sequence: Mt trng 8 bit c s dng pht hin li trong tiu . My pht s tnh ton gi tr HCS cho cc byte u tin ca tiu t bo v chn kt qu vo trng HCS (byte cui cng ca tiu ). N s l s d ca php chia (modulo 2) bi a thc c trng g (D=D8+D2+D+1) ca a thc D8 nhn vi ni dung ca tiu tr trng HCS.

- HT (1bit) Header Type: HT c thit lp l 0. - LEN (11bit) Length- Trng di theo byte ca MAC PDU bao gm tiu

MAC v CRC (nu c). - Type (6 bit) - Trng ny cho bit cc tiu con v cc loi ti trng c

bit trong ti trng ca bn tin.

Tiu yu cu bng thng

PDU yu cu bng thng s ch c tiu yu cu bng thng v khng cha ti trng.Yu cu bng thng s c cc c tnh sau:

- di ca tiu s lun l 6 byte. - Trng EC s c thit lp l 0, ch th khng mt m ha. - CID s cho bit kt ni cho SS yu cu bng thng ng ln. - Trng BR (Bandwidth Request) s cho bit s cc byte c yu cu.



32

- Cc loi yu cu bng thng c cho php l 000 cho tng dn v 001 cho ton b.

Mt SS nhn mt tiu yu cu bng thng trn ng xung s hy b PDU.Mi tiu c m ha, bt u vi cc trng HT v EC. M ha cc trng ny l byte u tin ca tiu MAC s khng bao gi c gi tr 0xFF. iu ny ngn chn li pht hin cc byte m.

Cc trng tiu yu cu bng thng:

- BR (19 bit)- S lng cc byte ca bng thng ng ln c yu cu bi SS. Yu cu bng thng l cho CID. Yu cu s khng bao gm bt k mo u PHY no.

- CID (16 bit) nhn dng kt ni - HT c gi tr l 1 - Type ( 3 bit) - Ch th loi tiu yu cu bng thng.

Cc kt ni qun l MAC

C 4 loi kt ni qun l.:

Kt ni c bn: Cc bn tin qun l MAC khn cp v thi gian v ngn.Cc bn tin qun l MAC nh yu cu hy, thit lp ARQ...

Kt ni qun l s cp :Cc bn tin qun l dung sai tr ln hn v di hn.Cc bn tin qun l MAC nh qun l kha bo mt, yu cu thay i dch v...

Kt ni qung b : Cc bn tin qun l MAC nh miu t knh, DL-MAP, UL-MAP...

Kt ni qun l Initial Ranging :Cc bn tin qun l yu cu Ranging.

nh dng bn tin qun l MAC



33

Bn tin qun l MAC c th c gi trn cc kt ni c bn, cc kt ni s cp, kt ni qung b v cc kt ni Initial Ranging.

Lc m ha TLV (type/ length/ value) c s dng trong bn tin qun l MAC v d nh trong bn tin UCD (miu t knh ng ln) cho trng thi burst ng ln.

( type=1, length=1, value=1)-> iu ch QPSK. ( type=1, length=1, value=2)-> iu ch 16-QAM. ( type=1, length=1, value=3)-> iu ch 64-QAM.

b\Truyn cc MAC PDU

Cc MAC PDU c truyn trong cc burst. Cc burst PHY c th cha nhiu khi FEC. Cc MAC PDU c th ko di qua cc ng bin khi. Qu trnh truyn gm cc bc sau:

- Ghp ni - Phn on - ng gi - Tnh CRC - m

Quy c Cc trng ca bn tin MAC s c pht theo th t nh xut hin trong cc

bng trn.Cc trng ca bn tin MAC v cc trng ca TLV, c ch ra l cc s nh phn (bao gm CRC v HSC) s c pht nh mt chui cc digit nh phn ca chng, bt u t MSB.

Cc mt n bit (v d nh trong ARQ) c xem nh cc trng s. Cc s MSB nh du c nh v lm du.

Trng di trong dng xc nh ca ITU-T X.690 cng c xem nh mt trng s. Cc trng c ch th nh cc SDU hay phn on SDU (v d ti trng MAC PDU) c pht theo th t cc byteb nh nhn c t lp trn.



34

Cc trng ch th nh cc chui cng c pht theo th t cc symbol trong chui.Trong trng hp 3 v 4, cc bit trong mt byte c pht theo nguyn tc MSB trc.

Bc 1:Ghp ni MAC PDU

C nhiu MAC PDU c ghp ni trong cng mt burst PHY. Cc MAC PDU c th c ghp trong mt lung truyn dn n ng ln hoc ng xung. Do mi MAC PDU c nhn dng bi mt CID, thc th MAC nhn c th to ra MAC SDU (sau khi lp rp MAC SDU t mt hay nhiu MAC PDU nhn) n trng hp chnh xc ca MAC SAP. Cc bn tin qun l MAC, d liu ngi dng, v cc MAC PDU yu cu bng tn c th c ghp vo cng mt lung truyn dn.

Hnh 8 :Ghp ni MAC_PDU

Bc 2:Phn on MAC PDU

Mi MAC SDU c th c phn on thnh nhiu phn on, mi phn on c ng gi thnh mt MAC PDU. Qu trnh ny c m bo cho php s dng bng tn c sn hiu qu lin quan n cc yu cu QoS ca mi lung dch v ca mt kt ni. Kh nng phn on v lp rp l bt buc.



35

tin cy ca lu lng phn on trn mt kt ni c nh ngha khi kt ni c to ra bi MAC SAP. Vic phn on c th c khi to bi BS cho cc kt ni ng xung v bi SS cho cc kt ni ng ln.

Cc kt ni khng ARQ: vi cc kt ni khng ARQ, cc phn on c pht ch mt ln v theo tun t. S tun t c gn cho mi phn on cho php u thu ti to li ti trng ban u v pht hin mt bt k gi no ngay lp tc. Mt kt ni c th ch c mt trng thi phn on mt thi gian bt k cho trc

Cc kt ni ARQ: vi cc kt ni ARQ, phn on c nh dng cho mi lung truyn dn bng cch ghp mt tp hp cc khi ARQ vi cc s tun t lin nhau.Gi tr BSN trong tiu con phn on l BSN cho khi ARQ u tin xut hin trong phn on. FSH l tiu con phn on c di 8 bit.

Hnh 9: Phn on MAC_PDU Bc 3 :ng gi cc MAC PDU

ng gi c thc hin trn mi kt ni, MAC c th gi nhiu MAC SDU vo mt MAC PDU n. ng gi to ra vic s dng ch s thuc tnh kt ni l kt ni mang cc gi c di thay i hay di c nh. Pha pht hon ton ch ng trong vic ng gi hay khng mt nhm cc MAC SDU trong mt MAC PDU n. Kh nng khng ng gi l bt buc.

Cu trc ca cc PDU thay i vi cc kt ni ARQ v khng ARQ vi cc c php phn on v ng gi c th.



36

Vi cc kt ni khng s dng ARQ: ng gi cc khi c di c nh, iu khon Request/ Transmission c thit lp cho php ng gi v cm phn oan,v kch c SDU s c bao gm trong bn tin DSA-REQ khi thit lp kt ni. Trng di tiu MAC biu th s cc MAC SDU c gi trong mt MAC PDU n. Nu kch c MAC SDU l n byte, pha thu c th m gi bi bit rng trng di trong tiu MAC s l (nk+j) vi k l s MAC SDU c ng gi trong MAC PDU v j l kch c tiu MAC. Mt MAC PDU cha mt chui cc MAC SDU c gi. Khng c thm tiu do ng gi trong trng hp MAC SDU di c nh v mt MAC SDU n th n gin l mt chui c gi c di l 1.

Khi ng gi cc kt ni MAC SDU di thay i, MAC gn mt tiu con gi (PSH) cho mi MAC SDU. Mt MAC PDU bao gm mt chui cc MAC SDU di thay i c ng gi. Nu c hn mt MAC SDU c ng gi, trng Type trong tiu MAC ch th s c mt ca cc PSH. Khi mt PSH c mt, thng tin phn on cho cc MAC SDU c th hay cc phn on MAC SDU c cha trong PSH tng ng. Nu khng c PSH, thng tin phn on cho cc phn on MAC SDU c th c cha trong tiu con phn on (FSH) tng ng.

Vi cc kt ni cho php ARQ: S dng PSH cho mi kt ni tng t nh trn, ngoi tr cc kt ni ARQ s thit lp bit Extended Type trong tiu MAC chung. Nu ng gi c thc hin cho mt kt ni, MAC c th gi nhiu MAC SDU vo trong mt MAC PDU n. Gi cc MAC SDU c di thay i cho cc kt ni cho php ARQ tng t cc kt ni khng ARQ khi phn on c cho php. BSSN ca PSH s c dng bi giao thc ARQ nhn dng v pht li cc phn on mt. Khi trng Type ch th rng PSH c dng, thng tin phn on cho mi MAC SDU c th hay phn on MAC SDU c cha trong PSH kt hp. Khi PSH khng c dng, thng tin phn on cho mi ti trng ca MAC PDU (MAC SDU hay phn on MAC SDU) c cha trong FSH.

Mt MAC SDU c th c chia thnh nhiu phn on v sau c gi trong cng mt MAC PDU cho ln truyn u tin. Cc MAC PDU c th c cc phn on t cng mt SDU hay cc SDU khc nhau, bao gm s trn ln gia ln truyn u tin v ln truyn li. Cc trng BSN (11 bit) v FC (2 bit) nhn dng mi SDU phn on hay SDU khng c phn on.

Khi ng gi cc MAC SDU kch c c nh th khng cn thit cc tiu con gi. Cc MAC SDU loi ny v d nh cc t bo ATM trn cng mt kt ni.



37

Cc MAC SDU kch c thay i v d nh cc gi IP trn cng mt kt ni. Khi ng gi chng cn phi c tiu con gi PSH c di 16 bt.

Bc 4:Tnh CRC

Mt lung dch v c th yu cu CRC thm vo mi MAC PDU mang d liu cho lung dch v . Trong trng hp ny vi HT=0, mt CRC s c gn vo ti trng MAC PDU. CRC s kim sot tiu MAC chung v ti trng MAC PDU. CRC s uc tnh ton sau khi mt m ha chng hn CRC bo v tiu chung v mt m ha ti trng.

Mt m ha cc MAC PDU

Khi pht mt MAC PDU trn mt kt ni c nh x n mt SA, pha gi s thc hin mt m ha v nhn thc d liu ca ti trng MAC PDU khi c ch th bi SA. Khi nhn mt MAC PDU trn mt kt ni c nh x n mt SA, u thu s thc hin gii mt m v nhn thc d liu ca ti trng MAC khi c ch th bi SA.



38

Tiu MAC chung s khng c mt m ha. Tiu cha tt c thng tin mt m ha (trng EC, trng s tun t kha mt m EKS v CID) cn gii mt m mt ti trng trm thu.

Hai bit ca tiu MAC cha mt s tun t kha. Kha kt hp vi mt SA c thi gian sng hn ch v BS theo nh k lm mi kha ca SA. BS qun l 2 bit s tun t kha c lp vi mi SA v phn phi s tun t kha ny cho mi ln to ra kha mi. Tiu MAC bao gm s tun t nhn dng vic to c th mt kha SA c s dng mt m ha ti trng c gn. L mt con s 2 bit, s tun t t 0 n 3.

So snh s tun t kha ca MAC PDU nhn vi ci m n tin tng l s tun t kha hin hnh, BS hay SS c th d dng nhn ra mt ng b kha. Mt SS s duy tr hai kha mi nht cho mi SA. Gi hai kha ny l cn thit duy tr cho dch v khng ngt qung trong khi chuyn tip kha ca SA.

Mt m ha ti trng c ch th bi trng bit EC. Gi tr 1 cho bit ti trng c mt m ha v trng EKS cha d liu c ngha. Gi tr 0 cho bit ti trng khng c mt m ha. Bt k MAC PDU no cha m ha c nhn trn mt kt ni nh x n mt SA yu cu mt m ha th d liu s b loi b.

Bc 5 :m

Khng gian c n nh trong mt burst d liu m cha c s dng s c khi to cho mt trng thi c nhn bit. iu ny c th c hon thnh bng cch thit lp mi byte cha dng thnh mt gi tr byte m (0xFF). Nu kch c vng cha s dng t nht l kch c ca tiu MAC, vng ny cng c th c khi to bng cch nh dng khng gian cha s dng mt MAC PDU. Khi lm vic , trng CID tiu MAC s c thit lp gi tr ca CID m, cc trng Type, CI, EC, HT s c thit lp l 0, trng di s c thit lp s byte cha s dng (bao gm c kch c tiu MAC to ra cho MAC PDU m) trong burst d liu v HCS s c tnh ton theo cch thng thng.

c\ Mt s k thut trong lp MAC_SAP

K thut ARQ:

K thut ARQ dng truyn li cc khung b li khng sa c bi FEC. Khi c b sung, ARQ c th c cho php trn mi kt ni. Mi kt ni ARQ s c nh r v thng lng trong khi to kt ni. Mt kt ni khng th c s pha trn gia lu lng ARQ v khng ARQ.



39

Vi cc kt ni ARQ, cho php phn on l ty chn. Khi phn on c cho php, u pht c th phn chia mi SDU thnh nhiu phn on truyn dn ring bit da trn gi tr ca tham s ARQ_BLOCK_SIZE. Khi vic phn on khng c php, kt ni s c qun l ging nh khi c php. Trong trng hp ny, lin quan n kch c khi tha thun, mi phn on c nh dng truyn dn s cha tt c cc khi d liu kt hp vi SDU gc.

K thut ny cho php tng tin cyh ca dch v nhng ng thi gim dung lng ng truyn v tng thi gian tr

K thut yu cu v cp pht bng tn

thc hin qu trnh yu cu v cp pht bng tn s c cc qu trnh nh polling yu cu v cp pht:

Phn Polling:

Polling l qu trnh c s dng bi BS cp pht cc c hi yu cu bng tn cho cc SS. Khi BS mun thng bo cho mt SS mt c hi yu cu bng tn ang n, n s s dng mt phn t thng tin IE bn tin UL-MAP lm vic . UL- MAP IE s chp nhn bng tn cho SS hay cc SS xem xt cc yu cu bng tn ca chng trong chu k yu cu theo l thuyt. Cp pht c hi yu cu bng tn s c thc hin trn c s n im, a im, hay qung b.

Polling n im :Trong trng hp ny, mt SS c kim sot vng mt cch ring bit bi BS. SS s tr li vi cc byte trn nu bng tn c cp l khng cn thit.

Polling a im v qung b: BS s s dng n kim sot vng a im hay qung b n cc SS nu bng tn ang sn c khng kim sot nhiu SS mt cch ring bit. Cc CID bt k c d tr cho cc nhm a im v cho cc bn tin qung b. Kim sot vng a im hay qung b cng c thc hin qua bn tin UL-MAP trong cng mt kiu vi polling n im. S khc bit c bn y l bn tin polling c nh hng n mt CID a im hay qung b thay v CID c th hoc SS.

Poll-me bit: Poll-me bit c s dng bi cc SS s dng dch v UGS thng bo cho BS rng chng cn c kim sot vng. Poll-me bit l mt phn ca tiu con qun l cp pht. Khi poll-me bit c pht hin, BS s s dng mt polling n im n SS yu cu n. gim thiu nguy c BS lm mt Poll-me bit, SS c th thit lp bit trong tt c tiu con qun l cp pht MAC UGS khong thi gian lp lch ng ln.



40

Phn Yu cu:

l k thut m cc SS s dng thng bo cho BS rng n cn c cp pht bng tn ng ln. Mt yu cu c th n nh mt tiu yu cu bng tn ng mt mnh hoc c th n nh mt PiggyBack Request.

Bi v profile burst ng ln c th thay i linh ng, nn tt c cc yu cu bng tn s c to thnh s hng ca s cc byte cn mang tiu v ti trng MAC, nhng khng tnh lp vt l. Bn tin yu cu bng tn c th c pht trong bt k thi im no ng ln ngoi tr trong khong thi gian Initial Ranging.

Bandwidth Request Header: SS c th yu cu cp pht bng tn vo bt k thi im no bng cch gi mt MAC PDU yu cu bng tn vi mt tiu yu cu bng tn v khng c ti trng. Tiu yu cu bng tn c s dng yu cu thm bng tn.

Piggyback Request : Phng php thng dng yu cu bng tn s dng mt tiu con qun l cp pht mang mt yu cu cho bng tn thm vo cho cng mt kt ni trong MAC PDU. Mang mt bn tin BW Request trn mt gi d liu.

Yu cu bng tn c th l tng dn hoc ton b. Khi BS nhn mt yu cu bng tn tng dn, n s ghi nh s lng bng tn c yu cu hin thi ca kt ni. Trng Type trong tiu yu cu bng tn cho bit yu cu l tng dn hay ton b. Do PiggyBack Request khng c trng Type, nn n s lun l tng dn.

Phn Cp pht

Cp pht trn mi kt ni (GPC): SS ch nhn cc cp pht cho cc kt ni c th (bao gm c cc kt ni qun l) v kt qu phi yu cu bng tn cho mi kt ni c th khi c nhu cu. Hn na, SS phi yu cu thm bng tn p ng cc yu cu ca RLC khng c mong i. V th, cc h thng GPC l n gin nhng khng hiu qu. Vic cp pht c quyt nh da trn bng tn yu cu v cc yu cu QoS v ti nguyn sn c.

Cp pht trn mi trm thu bao (GPSS): SS nhn mt cp pht bng tn c s dng p ng cc nhu cu ca tt c cc kt ni ca n. T SS phi qun l bao nhiu bng tn c cp pht cho mi kt ni. Nu mt kt ni yu cu nhiu hn bng tn c th phc v, SS c th ly cp bng tn t mt kt ni khc lp y lng bng tn cn thiu. BS cng m nhn hng i u tin trn c s cc loi lu lng. SS sau c th gi mt yu cu n BS yu cu tng thm bng tn nhm p ng cc nhu cu mi ca n.



41

Cc cp pht bng tn c cung cp trn c s giao thc t hiu chnh tri ngc vi giao thc bit trn. Trong giao thc ny, nu SS khng nhn mt cp pht bng tn tr li yu cu bng tn ca n, SS s tha nhn rng yu cu b mt hay tr li khng c tha mn, v n gin s gi mt yu cu khc n BS m khng i mt s xc nhn ca yu cu ban u. Giao thc ny b qua tiu kt hp vi cc bn tin xc nhn.

K thut dch v lp lch ng ln

Cht lng dch v ni n kh nng cung cp u tin cho cc dch v khc nhau ca mng. Cc tham s chnh ca QoS trong mng bao gm rng bng tn chuyn dng, gc tr, jitter v t l mt. C nhiu dch v vi QoS khc nhau, iu ny c ngha l cc dch v khc nhau c cp pht cc ti nguyn khc nhau v cht lng dch v m bo. Phn loi dch v ng ln da trn cc yu cu khc nhau v bng tn, gc tr v jitter.

Dch v cp pht khng yu cu (UGS) :Ti nguyn v tuyn ng ln c cp pht mt khong thi gian nh k. B lp lch BS a ra bng tn ng ln kch c c nh chp nhn c s thi gian thc theo chu k.Dch v UGS c thit k cho cc lung lu lng thi gian thc m pht cc gi d liu kch c c nh trn nn tng nh k nh T1/E1 v VoIP. Dch v kim sot vng thi gian thc (rtPS)

Dch v ny cung cp cc c hi yu cu truyn dn ng ln cc khong thi gian c nh. Theo cch ny, ti nguyn trc ht phi c yu cu v sau c cp pht bi im truy nhp. Thng tin v cc ngun ti nguyn c cp pht trong ng ln l qung b thng qua ng xung n tt c cc u cui ngi dng. Dch v rtPS c dnh cho cc lung lu lng thi gian thc m pht cc gi d liu kch c thay i trn nn tng nh k nh l video MPEG. B lp lch BS a ra cc c hi yu cu bng tn ng ln theo nh k, thi gian thc. SS s dng c hi yu cu UL-BW a ra ch nh vic chp nhn UL-BW c mong mun. SS khng th s dng yu cu BW trn c s tranh chp.

Dch v kim sot vng phi thi gian thc (nrtPS):Dch v ny cung cp k thut lp lch ng ln ging nh rtPS m khng thm d gc tr thp. Ph hp nht vi cc lung lu lng phi thi gian thc yu cu d liu kch c thay i chp nhn trn nn tng cch u nhau nh l FTP rng di tn cao. Cho cc dch v nrt-VBR nh truyn tp, cn nhiu rng di tn. B lp lch BS s cung cp cc c hi yu cu UL-BW theo thi gian (khong 1s hay t hn). SS c th s dng cc c hi yu cu BW trn c s tranh chp gi yu cu BW.

Dch v Best Effort (BE):Vi dch v ny, cc khong thi gian yu cu tranh chp, cc c hi yu cu n im hay cc loi burst chp nhn d liu c th



42

c cp pht. Trong cch ny, cc yu cu ti nguyn c th tranh chp ch trong khi kt ni ang xy ra. Cc gi d liu c pht qua cc ti nguyn c dnh ring theo cc yu cu ti nguyn bi b lp lch ng ln trong im truy nhp. Cho lu lng best-effort v d nh HTTP, SMTP. SS s dng cc c hi yu cu BW trn c s tranh chp.

2.2.3 Lp MAC_PS [2]

Hai chc nng chnh: - Bo mt qua cc khng gian truyn dn. - Bo v khi cc nh cp dch v.

Lp con bo mt thc hin m ha d liu trc khi truyn i v gii m d liu nhn c t lp vt l. N cng thc hin nhn thc v trao i kha bo mt.

Chun IEEE 802.16 ban u s dng phng php DES 56 bit cho m ha lu lng d liu v phng php m ha 3-DES cho qu trnh trao i kha. Trong mng IEEE 802.16, trm gc cha 48 bit ID nhn dng trm gc (ch rng y khng phi l mt a ch MAC), cn SS c 48 bit a ch MAC 802.3.

C 2 giao thc chnh hot ng trong lp con bo mt: giao thc m ha d liu thng qua mng bng rng khng dy, v giao thc qun l kha bo v bo mt (PKM- Privacy and Key Management Protocol) m bo an ton cho qu trnh phn phi kha t BS ti SS. N cng cho php BS t iu kin truy nhp cho cc dch v mng. Giao thc PKM s dng thut ton kha cng khai RSA, chng thc s X.509 v thut ton m ha mnh thc hin trao i kha gia SS v BS. Giao thc bo mt ny da trn giao thc PKM ca DOCSIS BPI+ c ci tin cung cp mt lc m ha mnh hn nh chun m ha ci tin AES.

MAC trong IEEE 802.16 l phn lp hng kt ni, c thit k cho cc ng dng truy nhp khng dy bng rng theo cu hnh im a im (PMP), hay dng mesh. C hai loi kt ni MAC c xc nh bi 16 bit nhn dng kt ni CID l: Cc kt ni qun l v Cc kt ni vn chuyn d liu. Cc kt ni qun l li gm 3 loi:

- c s, - s cp - th cp

Trong c s s dng cho truyn ti, iu khin lin kt v tuyn...,cn s cp lin quan n thit lp nhn thc v kt ni, v kt ni qun l th cp l cc bn tin qun l da trn chun truyn ti nh DHCP, TFTP, SNMP. Kt ni qun l s cp v kt ni c s c to ra khi mt MS/SS ra nhp vo mt BS phc v ca



43

mng. Kt ni vn chuyn d liu c th c thit lp da trn nhu cu. Chng c s dng cho cc lung lu lng ngi s dng, cc dch v n hng (Unicast) v a hng (Multicast). Cc knh b sung cng c MAC d tr gi ra ngoi cc thng tin lp lch ng xung v ng ln.

Cc thnh phn c bn ca mng l trm gc BS v trm thu bao SS (Subscriber Station), trm gc BS ging nh cc im truy nhp (AP) trong mng WiFi. BS c ni vi phn hu tuyn, n pht qung b cc thng tin ti SS. Khc vi phng php CSMA/CA trong 802.11, 802.16 s dng cc nh x ng xung v ng ln khc phc xung t trong mi trng truy nhp. SS s dng phng thc truy nhp TDMA chia s ng ln trong khi BS s dng phng thc TDM. Tt c cc chc nng ny c thc hin thng qua bn tin DL_MAP v UL_MAP.

2.2.4 c im lp MAC ca WiMAX

a/ QoS

im ni bt trong kin trc MAC trong IEEE 802.16 l QoS.Ging nh mi h thng h tr QoS khc, vic phn loi dch v cng l im ct li trong vic m bo QoS. Xem cc loi hnh dch v QoS trong bng di y:

QoS ph thuc vo 3 yu t sau:

- Giao thc MAC hot ng hng kt ni (connection oriented). Mi mt gi tin u c a vo mt kt ni c th, kt ni ny l kt ni o, c xc nh bi tham s CID. Vic to nn cc kt ni o ny khin cc gi tin c gi i mt cch hiu qu v nhanh chng.

- C ch cp pht bng thng Request/Grant: C ch ny lm tng hiu qu s dng bng thng ca h thng, c bit l cc h thng m c nhiu thu bao. Trong c ch ny, MS yu cu thng lng bng thng cp pht t BS thng qua mt s cc phng thc khc nhau. BS s cp pht bng thng bng cch cp pht cc timeslot ti cc MS c yu cu.

- C ch lp lch (scheduling) trong WiMAX khng c qui nh c th trong chun. C nhiu hnh thc lp lch khc nhau, mc ch l lm th no s dng ti nguyn UL va DL mt cch c hiu qu nht trong khi lun m bo c QoS yu cu.



44

Bng 6: Dch v QoS

Yu cu QoS ng dng c tnh k thut Dch v cho php t nguyn (Unsolicited Grant Service-UGS)

VoIP

- Tc duy tr ti a - Dung sai tr ti a - Dung sai jitter

Dch v thi gian thc(Real time Polling service-rtPS)

Lung audio hoc video

- Tc knh dnh ring ti thiu

- Tc duy tr ti a - Dung sai tr ti a - u tin lu lng

Dch v thi gian m rng (Extnded Real time Polling service-ErtPS)

Thoi vi d tm hot ng

- Tc knh dnh ring ti thiu

- Tc duy tr ti a - Dung sai tr ti a - Dung sai jitter - u tin lu lng

Dch v khng theo thi gian thc (Non Real time Polling service-nrtPS)

Giao thc truyn file (FTP)

- Tc dnh ring ti thiu - Tc Tc duy tr ti a - u tin lu lng

Dch v tt nht(Best Effort Service -BE)

Truyn d liu, duyt Web

- Tc duy tr ti a - u tin lu lng

b/ iu khin cng sut

WiMAX di ng h tr hai ch vn hnh l: Sleep Mode v Idle Mode tit kim nng lng tiu th.

Sleep Mode l trng thi m MS trong giai on trc khi c bt c trao i thng tin g vi trm gc qua giao din v tuyn. Sleep Mode cho php MS ti thiu nng lng tiu th v ti thiu ti nguyn v tuyn ca trm gc. Sleep Mode cng cung cp kh nng linh hot cho MS d cc trm gc khc thu thp thng tin h tr chuyn giao trong Sleep Mode.

Idle Mode cung cp mt c ch cho MS sn sng mt cch nh k nhn cc bn tin qung b DL m khng cn ng k vi mt trm gc xc nh no khi



45

MS di chuyn trong mt mi trng c ng truyn v tuyn c ph sng bi nhiu trm gc.

c/ Qun l di ng

C ba phng php chuyn giao c chun IEEE 802.16 h tr l :

- Chuyn giao cng (Hard Handoff HHO), - Chuyn trm gc nhanh (Fast Base Station Switching FBSS) - Chuyn giao phn tp v m (Macro Diversity Handover MDHO)

Trong , chuyn giao HHO l bt buc cn FBSS v MDHO l hai ch ty chn.

Cng ging ging nh chuyn giao nhanh (FBSS hay MDHO) trong h thng CDMA, chuyn giao nhanh trong WiMAX cng ch c th thc hin gia cc BS nm trong ci gi l Diversity Set (tp hp cc BS hot ng trong cng tn s, c SINR ln MS c th kt ni c v c bit l chng phi ng b (synchronisation)). Trong Diversity Set ny th ch c 1 ci BS c gi l anchor (ci BS ch lc, hay cn gi l im kt ni, khp ). S khc nhau gia MDHO v FBSS l ch: i vi FBSS, MS ch communicate thng tin data thng qua BS anchor thi, cn MDHO th MS communicate thng tin data traffic qua tt c cc BS nm trong Diversity Set.

d/ Bo mt

WiMAX h tr tt nht cc c tnh bo mt lp nh p dng cc cng ngh tt nht ang sn c hin nay. N h tr nhn thc gia thit b/ngi dng, giao thc qun l kha linh ng, m ha lu lng, bo v bn tin iu khin v ti u ha giao thc bo mt cho cc chuyn giao nhanh.

Giao thc qun l kha: Giao thc qun l kha v bo mt phin bn 2 (Privacy and Key Management Protocol Version 2 PKMv2) l mt trong nhng khi nim bo mt c bn ca WiMAX di ng. Giao thc ny qun l bo mt MAC s dng bn tin PKM REQ/RSP. Nhn thc PKM EAP, iu khin m ha lu lng, trao i kha chuyn giao v cc bn tin bo mt Mutilcast/Broadcast u da trn giao thc ny.

Nhn thc thit b/ngi dng: WiMAX di ng h tr nhn thc thit b v ngi dng s dng giao thc IETF EAP bng cch cung cp h tr credentials c da trn SIM, hoc da trn USIM hoc chng nhn s hoc da trn tn ngi s dng/mt khu.



46

M ha lu lng: AES-CCM l mt m ho c s dng bo v tt c s liu ngi s dng qua giao din WiMAX MAC di ng.

Bo v cc bn tin iu khin: D liu iu khin c bo v bi AES da trn CMAC, hoc s HMAC da trn MD5.

H tr chuyn giao nhanh: Mt s bt tay 3 bc c h tr bi WiMAX di ng ti u c ch nhn thc li cho h tr chuyn vng nhanh. C ch ny cng hu ch trong vic chng li vic tn cng gia chng ca hacker.

e/ Dch v Muticast v Broadcast MBS

Dch v MBS trong WiMAX di ng kt hp cc c tnh tt nht ca DVB H, MediaFLO v 3GPP E UTRA, tha mn nhng yu cu sau:

- Tc d liu cao v kh nng ph sng s dng mng mt tn s (SFN Single Frequency Network)

- Cp pht ti nguyn v tuyn linh ng. - MS tiu th nng lng thp. - H tr d liu ngang hng bao gm cc lung audio v video. - Thi gian chuyn mch knh nh.

2.2.5 Lp vt l (PHY, physical layer)

Ban u c t PHY c nh ngha cho 1066 GHz l :Truyn lan LOS (line-of-sight -tm nhn khng b vt cn),Kin trc im- a im,v S dng iu bin sng n mang. khc phc hn ch truyn LOS trong di 10-66 GHz,Lp vt l 211 GHz c thit k do nhu cu theo hng hot ng NLOS (non-line-of-sight) v mi c t u a ra tnh hot ng cng nhau.

V c bn, BS truyn mt tn hiu TDM vi nhng trm thu bao ring l c nh v nhng khe thi gian theo chu k. S truy cp theo hng ng ln cho bi TDMA. Tip theo nhng tho lun m rng v duplexing, mt thit k burst c chn cho php c TDD (timedivision duplexing), ti ng ln v ng xung dng chung mt knh nhng khng truyn cng lc v FDD (frequency-division duplexing), ti ng ln v ng xung hot ng trong nhng knh ring bit. Thit k burst ny cho php c TDD ln FDD c x l theo cch tng t. Nhng la chn mt trong hai TDD v FDD h tr nhng burst thch ng, trong nhng ty chn iu bin v m ha c th c gn ng trn c s tng burst mt.

a\ nh dng khung



47

c t PHY c nh ngha cho 1066 GHz s dng iu bin sng mng n dng burst vi burst-profiling thch ng, nhng tham s truyn, bao gm cc k hoch iu bin v m ha, c th c iu chnh ring cho mi trm thu bao (subscriber station, SS) trn c s tng khung (frame) mt.

H thng s dng mt khung 0.5, 1 hoc 2 ms. Khung ny c chia ra thnh nhng khe vt l cho mc ch cp pht v nhn bit di thng thuc cc chuyn tip PHY.

Mt khe vt l c nh ngha cho 4 k hiu QAM (quadrature amplitude modulation). Trong phng n TDD ca PHY, khung con ca ng ln k tip theo khung con ca ng xung trong cng mt tn s sng mang. Trong phng n FDD, cc khung con ca ng ln v ng xung cui cng cng trng khp nhng chng c mang trn nhng tn s ring bit.

Khung con ca ng xung bt u vi mt on iu khin khung c cha DL-MAP cho khung ng xung hin hnh cng nh UL-MAP cho thi gian nh r trong tng lai. Khung con ng xung c cha mt TDM-portion (on TDM) ngay tip theo on iu khin khung. D liu ng xung c truyn ti mi SS khi s dng mt burst-profile tha thun.

Mo u khi u khung l dy 32 k hiu c to ra bng lp mt dy 16 k hiu .Khung iu khin chc nng c s dng chuyn thong tin iu kim cho knh ti tt c cc SS,v d liu ny khng c bo mt.

Trong cc h thng, sau on TDM l mt on TDMA c cha mt on m du (preamble) ph ti im xut pht ca mi burst-profile mi. c tnh ny cho php h tr tt hn cc SS bn song cng.

Trong mt h thng FDD c hoch nh hiu qu vi nhiu SS bn song cng, mt s c th truyn sm hn trong khung hn l chng nhn. V bn cht bn song cng, cc SS ny mt s ng b ha vi ng xung. TDMA-preamble cho php chng ly li s ng b ha .

Type PHY Synchronization

DCD Count

BS_ID low BS_ID high Element count

Khun dng thng ip DL_MAP

- Type(8 bit) :kiu thng ip qun tr.c gi tr mc nh l 2. - PHY Synchronization (32 bit):trng ng b vt l - DCD Count (8 bit) :b m DCD - Base station _ID low (32bit) :m nhn dng BS thp



48

- Base station _ID high (16bit) :m nhn dng BS cao - Element count (16 bit) s lng phn t DL_MAP

DL-MAP ca on iu khin khung cung cp ti cc SS cc c tuyn cu ng xung. lun c th ng dng cho khung hin thi v lun c di ti thiu l hai block FEC. S chuyn tip PHY u tin c biu th trong block FEC u tin, cho php thi gian x l thch ng. Trong c hai h thng TDD v FDD, UL-MAP cung cp cc nh v bt u khng mun hn khung ng xung tip theo. Tuy vy, UL-MAP c th nh v s khi u khung hin thi min l nhng thi gian x l v nhng tr ton phn (round-trip delay) phi c gim st.

Type DL Ch_ID CCC PTR

Khun dng thng ip DCD

- Type: (8 bit) kiu thng ip qun tr c gi tr =1 - DL Ch_ID : Downlink Channel ID (8 bit) ch th knh ng xung - CCC (8 bit) :b m thay i cu hnh - PTR (16 bt):trng con tr nh dng cu trc c trng vt l cho knh

ng xung.

DCD l thng ip m t knh ng xung .mt b nhn dng BS 48 bit c th lp trnh trong DL_MAP. B nhn dng ny v DCD dng nhn dng knh ,c s dng trong trng hp khi SS nm trn ng bao vng ph sng.

Type UL Ch_ID UCD count

Element count

Allocation start time

Khun dng thng ip DL_MAP

- Type: (8 bit) kiu thng ip qun tr c gi tr =3 - UL Ch_ID : Uplink Channel ID (8 bit) ch th knh ng ln - UCD count: (8 bit) b m UDC - Element count: (16 bit) s lng phn t UL_MAP - Allocation start time(32 bit) :thi im bt u phn phi

Khun dng thng ip UCD Type UL Ch_ID CCC RngBS RngBE ReqBS ReqBE PHY_Ptr List_Ptr

- Type: (8 bit) kiu thng ip qun tr c gi tr =0



49

- UL Ch_ID : Uplink Channel ID (8 bit) ch th knh ng ln - CCC (8 bit) :b m thay i cu hnh - RngBS (8bit) im bt u sp xp - RngBE (8bit) im kt thc sp xp - ReqBS (8bit) im bt u gi yu cu - ReqBE (8bit) im kt thcgi yu cu - PHY_Ptr (16 bt):trng con tr nh dng cu trc c trng vt l cho knh

ng xung. - List_Ptr (16 bt):trng m t kiu con tr nh dng cc loi burst.

UDC c s dng cung cp cho cc SS thng tin v yu cu c ch cum ng ln.Thng tin UL_MAP nhn c bng vic s dng b nhn dng kt ni CID. Thng ip ny cung cp mt m s dng xung nhp ng ln UIUC c SS s dng truyn ln. Thng ip UL_MAP v UCD c m t nh hnh trn.

Khung con ng ln

Khng ging nh ng xung, UL-MAP cp gii thng cho cc SS c th. Cc SS truyn trong vng cp pht c n nh c s dng burst-profile ch r bi UIUC (Uplink Interval Usage Code) trong mc vo (entry) UL-MAP cp di thng cho chng. Khung con ng ln c th cng cha nhng nh v trn c s cnh tranh cho truy nhp h thng lc ban u v broadcast hay multicast cc yu cu di thng. Nhng c hi truy cp cho truy nhp h thng lc ban u c xc nh ln cho php thm thi gian bo v cc SS m chng khng c gii quyt thi gian truyn cn thit b li tr ton phn (round-trip delay) cho BS.

C 3 loi cm c th hin din trong bt k khung con ng ln no :

- Cm tranh chp :da trn duy tr ban u hoc cc c hi truy nhp ban u - Cm tranh chp da trn c hi mc dnh bng khong thi gian yu cu

p ng truyn a hng hoc vng qung b - Khng tranh chp da trn nh v khong thi gian c sp xp ti SS c

bit trong UL_MAP m bo bng thng t BS

Cc cm trn u c th c trong bt k khung no.Khng ging nh UL_MAP cp bng thng cho cc SS c th. Khung con ng ln c th cha cc nh v trn c s tranh chp cho truy nhp h thng lc ban u.

b\Lp con hi t truyn TC (transmission convergence). Gia PHY v MAC l mt lp con hi t truyn TC (transmission

convergence). Lp ny thc hin s bin i cc PDU (protocol data units) MAC di c th thay i vo trong cc block FEC di c nh (cng thm c th l mt



50

block c rt ngn vo on cui) ca mi burst. Lp TC c mt PDU c kch thc khp vi block FEC hin thi b y. N bt u vi mt con tr ch ra v tr u mc PDU MAC tip theo bt u bn trong block FEC.

Khun dng PDU_TC

Khun dng PDU TC cho php ng b ha li PDU MAC tip sau trong trng hp block FEC trc c nhng li khng th phc hi c. Khng c lp TC, mt SS hay BS nhn s mt ton b phn cn li ca mt burst khi mt li khng th sa cha xut hin.

2.2.6 Cc k thut truyn thng s trn lp PHY

a/ OFDM (Orthogonal Frequency Division Multiplexing) hay ghp knh phn chia theo tn s trc giao l mt k thut iu ch a sng mang.

K thut ny c th t c tc d liu rt cao, chng nhiu giao thoa k t - ISI (Inter symbol Interference) v gii quyt c vn tn hiu a ng.

Cng ngh OFDM chia lung d liu thnh nhiu ng truyn bng hp trong vng tn s s dng cc sng mang con trc giao vi mt sng mang con khc. Nhng sng mang con ny sau ghp thnh cc knh tn s truyn v tuyn.

OFDM khai thc s phn tp tn s ca knh a ng bng cch m ho v chn thng tin trn cc sng mang con trc khi truyn i. iu ch OFDM c th thc hin c vi bin i ngc Fourier nhanh - IFFT, php bin i ny cho php mt s lng ln cc sng mang con (ln ti 2048) vi phc tp thp. Trong mt h thng OFDM, ti nguyn sn c trong min thi gian chnh l cc symbol OFDM v trong min tn s chnh l cc sng mang con. Ti nguyn v thi gian v tn s c th c t chc thnh cc knh con (sub-channel) cp pht cho ngi dng.

b/OFDMA (Orthogonal Frequency Division Multiple Access)- a truy nhp phn chia theo tn s trc giao l cng ngh a truy cp phn chia theo sng mang , v c pht trin da trn cng ngh OFDM.

OFDMA cho php nhiu ngi dng cng truy cp vo mt knh truyn bng cch phn chia mt nhm cc sng mang con (subcarrier) cho mt ngi dng ti mt thi im. cc thi im khc nhau, nhm sng mang con cho 1 ngi dng

P(con tr 1byte)

Khi PDU u tin khi u trong TC ngay trc

Khi PDU u tin khi u trong TC hin ti

Khi PDU th 2 khi u trong TC hin ti



51

cng khc nhau. OFDMA c dng trong cng ngh mng 802.16e (WiMAX di ng),

OFDMA h tr cc nhim v ca cc sng mang con i vi cc thu bao nht nh. Mi mt nhm sng mang con c biu th nh mt knh con (subchannel) v mi thu bao c ch nh mt hoc nhiu knh con truyn pht da trn mi yu cu c th lu lng ca mi thu bao

OFDMA c mt s u im nh kh nng linh hot tng, thng lng v tnh n nh c ci tin. Bng vic n nh cc knh con cho cc thu bao c th, vic truyn pht t mt s thu bao c th xy ra ng thi m khng cn s can thip no, do s gim thiu tc ng nh nh hng a truy nhp.

c/ Cc h thng anten thch ghi AAS (Adaptive Antena System)

Cc h thng anten thch ghi AAS (Adaptive Antena System) l mt phn ca la chn tiu chun IEEE 802.16. AAS c kh nng iu chnh bp sng ch tp trung vo mt hng nht nh hoc cng c th tp trung vo nhiu hng. iu ny c ngha l trong khi pht tn hiu c gii hn theo mt hng nht nh ca pha thu, ging nh mt im sng. Cn khi thu, h thng AAS cng c kh nng gim nhiu ng knh t cc v tr khc. AAS c coi l s pht trin ca tng lai, c kh nng ci thin t l ti s dng ph tn v kh nng ca mt mng WiMAX

d/MIMO- Multiple-Input and Multiple-Output

La chn phn tp pht WiMAX s dng m ha thi gian khng gian, lm gim qu d tr yu cu v trnh nhiu. i vi phn tp pht, rt nhiu cc phng php kt hp ci thin kh nng ca h thng.

M khng gian thi gian (Space Time Code STC): H tr phn tp truyn nh m Alamouti cung cp kh nng phn tp khng gian v gim d tr suy hao tn hiu.

Ghp knh khng gian (SM): H tr ghp knh khng gian tn dng tc nh cao hn v gim thng lng. Nh ghp knh khng gian, nhiu lung s c truyn trn h thng nhiu anten. Nu pha thu cng c h thng nhiu anten, n c th phn tch cc lung khc nhau t c thng lng cao hn so vi cc h thng n anten.

e/iu ch thch nghi v m ha(AMC- Adaptive Modulation and Coding)



52

iu ch thch nghi cho php h thng WiMAX iu chnh c phng php iu ch tn hiu da trn iu kin SNR ca tuyn. Khi tuyn truyn dn c cht lng tt, kiu iu ch cao nht c s dng, lm tng dung lng ca h thng. Khi tuyn mc cht lng thp hn, h thng WiMAX c th chuyn sang mt kiu iu ch thp hn m bo cht lng kt ni v n nh ca tuyn.

Ngoi ra iu ch BPSK cng c dng gi cc thng bo tn hiu (signalling), broadcast...trong h thng WiMAX v n cho 1 vng ph ln nht.

f/ K thut sa li trc (FEC-forward error correction)

Cc k thut sa li trc c p dng trong h thng WiMAX gim t s tn hiu trn tp m yu cu. M ha sa li trc (FEC) Reed Solomon, m ha xon cc thut ton chn k t c s dng pht hin v sa li nhm ci thin thng lng ca h thng.

g/ S dng li tn s

c

tong quan ve mang truy nhap bang rong wimax 0017

Documents