datn-tim hieu cong nghe voip trong wimax

8/3/2019 DATN-Tim Hieu Cong Nghe VOIP Trong Wimax

1/104

PHN GII THIU


2/104

Tm hiu cng ngh Voip trong Wimax ii

LI CM N

Trong sut qu trnh hc tp ti trng, nhsgip v dy dca qu thy cNhm

thc hin ti tch ly c mt skin thc nn tng cho nghnghip sau ny.

Vi tm lng tn s trng o v tri n su sc, nhm sinh vin thc hin xin by tlng

bit n n c Phm Hng Lin, ngi tn tnh hng dn, gp , ng vin trong

sut qu trnh thc hin ti. Vi phng php lm vic khoa hc, kinh nghim thc

tin, c truyn t cho nhm nhng li khuyn qu bu n tt nghip ny hon

thnh tt p.

Nhm thc hin ti xin chn thnh bit n su sc n tt ccc thy c trong trng

ni chung v thy c trong bmnin TVin Thngni ring.

Cm n tt c bn b, nhng ngi lun ng vin, khuyn khch, gip n

ny hon thnh ng tin .

Tp. HCh Minh, thng 1 nm 2011

Sinh vin thc hin


3/104

Tm hiu cng ngh Voip trong Wimax iii

QUYT NH GIO TI

Hv tn sinh vin: Hunh Hong Triu MSSV: 06117087L Kim Bo MSSV: 06117003

Ngnh: CngNghin T Vin ThngTn ti: Tm Hiu Cng Ngh Voip Trong Mng Wimax

1) C sban u:.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

2) Ni dung cc phn thuyt minh v tnh ton:.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

3) Cc bn v:.............................................................................................................................

.............................................................................................................................

.............................................................................................................................

4) Gio vin hng dn: PGS.TS Phm Hng Lin

5)Ngy giao nhim v: 27/9/2010

6)Ngy hon thnh nhim v: 10/1/2011

Gio vin hng dn Ngy ........thng....nm20

Ch nhim bmn

BGIO DC V O TO

TRNG I HC S PHM K THUT TP.HCH MINH

CNG HA X HI CHNGHA VIT NAM

c lpT doHnh phc


4/104

Tm hiu cng ngh Voip trong Wimax iv

NHN XT C GIO VIN HNG DN

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

Tp. H Ch Minh, thng 1 nm 2011

Gio vin hng dn


5/104

Tm hiu cng ngh Voip trong Wimax v

NHN XT C GIO VIN PHN BIN

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

Tp. H Ch Minh, thng 1 nm 2011

Gio vin phn bin


6/104

Tm hiu cng ngh Voip trong Wimax vi

LI NI U

t vn

- Mc d dch v truyn s liu ngy cng ph bin nhng dch v truyn thoivn l ngun doanh thu chnh ca nh cung cp dch v mng. Hai loi mng cungcp dch v thoi ph bin nht l mng in thoi cnh PSTN v mng inthoi di ng. Vic trin khai hai cng ngh mng ny i hi c sh tng rt ttin. Do , ngi ta ra sc tm kim cc gii php khc c th cung cp dch vthoi cht lng tt vi chi ph thp hn. S dng c sh tng IP c sn l mtgii php c chi ph thp. Giao thc dng truyn tn hiu thoi trong mng IPc gi l giao thc VoIP.

- Chng ta gp phi nhiu kh khn khi nghin cu trin khai cc ng dng thigian thc trn mng Internet. Nhng dch v nh VoIP i hi s bo m chtlng dch v ti thiu. Trong khi , mng IP li c cu trc n lc ti a ngha lkhng c bt c mt s bo m no v cht lng dch vhay u tin. Xc sutmt gi v trty thuc vo hin trng ti trn mng. Mc d mt s bm hac khnng hn ch li mt mc no nhng cht lng cuc gi VoIP vncn nhy i vi s gim st cng nng trong mng. Duy tr nhng cuc gi VoIPcht lng tt li trnn thch thc hn khi mng IP c mrng sang lnh vckhng dy, thng qua mng LAN khng dy da trn chun 802.11 hay mng in

thoi tbo th h th ba (3G). Vic cung cp cc dch v trong mng khng dytrnn cp thit v nhu cu s dng dch v thi gian thc qua mng khng dy lrt cao.- Mc d hin ti cng ngh mng in thoi tbo 3G v mng LAN khng dy h trcc phin bn s cp ca cc dch v tin tc thi gian thc, nghe nhc trctuyn v xem phim theo yu cu, nhng li khng c khnng p ng nhu cu sdng rng ri v i hi bng thng cao cho nhng chng trnh ng dngmultimedia ny. Ngoi ra, hu ht cng ngh truy cp u khng c c tnh phnbit nhu cu ca tng ng dng c th. Cng vi s pht trin nhanh chng cacng ngh khng dy, nhim v cung cp kt ni on ng cui bng rng vncn l mt th thch. on ng cui l thut ng ch kt ni t mng ca nhcung cp dch v n ngi dng gia nh hoc doanh nghip. Trong s nhngcng ngh truy cp bng rng khng dy ang c pht trin, WiMAX c ll ith nng k nht.

Mc tiuti

Tm hiu khi nim Wimax, cc u im chnh ca Wimax.

Tm hiu nhng c tnh ca dch v Voip qua mng Wimax.

Tm hiu phn mm m phng Opnet.


7/104

Tm hiu cng ngh Voip trong Wimax vii

Kho st cht lng cuc gi Voip n gin qua mng Wimax s dng Opnet.

Thng qua qu trnh lm ti, nhm thc hin ti cng mong mun cng c

li nhng kin thc hc, rn luyn thi quen v tc phong nghin cu khoa hc

nhm trang bhnh trang chun bsau khi ra trng. Cui cng, nhm thc hin

ti mong mun bng kin thc nhb ca mnh c thgip y nhanh tc tip

cn cng ngh mi ca nn cng nghip nc ta trong tng lai.

i tng nghin cu

H thng Wimax v vic ng dng cng nghVoip vo trong Wimax nhm ci

thin cht lng dch v.

Phn mm ng dng m phng mng Opnet.

Phm vi nghin cu Tm hiu tng quan v h thng Wimax v Voip trong mt mng cc b n

gin nh trng hc, bnh vin

ng dng dch vVoip vo trong mng Wimax v nhng u im m Wimax

mang li Voip.


8/104

Tm hiu cng ngh Voip trong Wimax viii

MC LC

PHN A. GII THIU ......................................................................................................................... i

LI CM N ...................................................................................................................................... ii

QUYT NH GIAO TI ............................................................................................................ iii

NHN XT CA GIO VIN HNG DN .................................................................................. iv

NHN XT CA GIO VIN PHN BIN ...................................................................................... v

LI NI U .................................................................................................................................... vi

MC LC ......................................................................................................................................... viii

LIT K BNG ................................................................................................................................. xi

LIT K HNH...................................................................................................................................xiiPHN B. NI DUNG ........................................................................................................................ xiv

CHNG 1-TNG QUAN V MNG WIMAX .............................................................................. 15

1.1 GII THIU CHUNG V MNG D LIU KHNG DY .............................................. 15

1.1.1 Mng khng dy bng rng ......................................................................................... 15

1.1.2 Cc mng d liu khng dy ....................................................................................... 16

1.2 GII THIU V WIMAX ................................................................................................... 17

1.2.1 Gii thiu chung ......................................................................................................... 17

1.2.2 Qu trnh pht trin, xu th chung v phn loi wimax ................................................. 18

1.2.3 M hnh h thng ........................................................................................................ 19

1.3 C IM C BN CA WIMAX................................................................................... 20

1.3.1 u im...................................................................................................................... 21

1.3.2Nhc im................................................................................................................ 23

1.4 CU TRC CA WIMAX ................................................................................................. 23

1.4.1 Lp vt l (PHY) ........................................................................................................ 24

1.4.2 Lp iu khin truy nhp mi trng (MAC) .............................................................. 25

1.5 CC K THUT S DNG TRONG WIMAX ................................................................. 31

1.5.1 K thut OFDM.......................................................................................................... 31

1.5.2 K thut OFDMA ....................................................................................................... 34

1.5.3 Cc cng ngh anten tin tin ...................................................................................... 36

1.6 NG DNG CA WIMAX ................................................................................................ 37

1.6.1 Mng dng ring ......................................................................................................... 39

1.6.2 Cc mng phc v cng ng...................................................................................... 41

1.7 WIMAX VI CC CNG NGH TRUY CP V TUYN BNG RNG KHC ........... 42


9/104

Tm hiu cng ngh Voip trong Wimax ix

1.7.1 So snh WiMAX c nh v LMDS, MMDS............................................................... 43

1.7.2 So snh WiMAX di ng vi 3G................................................................................. 44

1.7.3 So snh WiMAX di ng vi WiBro ........................................................................... 46

1.7.4 So snh WiMAX vi WiFi .......................................................................................... 47

CHNG 2-TNG QUAN V CNG NGH VOIP ........................................................................ 50

2.1 GII THIU V CNG NGH VOIP ................................................................................. 50

2.1.1 Gii thiu chung ......................................................................................................... 50

2.1.2Nguyn l lm vic ..................................................................................................... 51

2.1.3 c tnh ca mng VoIP ............................................................................................. 53

2.2 CC GIAO THC S DNG TRONG VOIP..................................................................... 55

2.2.1 Cc giao thc truyn ti trong mng Voip ................................................................... 55

2.2.2 Cc giao thc bo hiu Voip ....................................................................................... 612.3 YU CU CHT LNG I VI VOIP ........................................................................ 70

2.4 NH GI CHT LNG CUC GI VOIP ................................................................... 71

2.4.1 im s kin trung bnh MOS .................................................................................. 73

2.4.2 R-Score....................................................................................................................... 74

2.4.3 nh gicht lng cuc gi t R-score ..................................................................... 77

2.4.4 nhy tr v mt gi ca VoIP ................................................................................. 78

2.5 KT NI MNG VOIP VI MNG PSTN ........................................................................ 80

2.5.1 Cuc gi bt u t mng VoIP (SIP) v kt thc ti PSTN ......................................... 80

2.5.2 Cuc gi bt u t PSTN v kt thc mng VoIP .................................................... 82

CHNG 3-NG DNG VOIP TRONG MNG WIMAX .............................................................. 83

3.1 M HNH VOIP TRONG MNG WIMAX ........................................................................ 83

3.2 XC SUT KHI PHC GI ............................................................................................ 84

3.1.1 Gim ti trng, vi kch thc m c nh ................................................................... 84

3.1.2 Tng kch thc m vi ti trng c nh .................................................................... 85

3.1.3 Tng c kch thc ti trng ln kch thc m ........................................................... 85

3.3 CHO PHP C CH ARQ .................................................................................................. 85

3.4 KCH THC MPDU TI U ........................................................................................... 86

3.5 CP PHT NG MINISLOT ........................................................................................... 88

CHNG 4-M PHNG V KT QU.......................................................................................... 89

4.1 GII THIU PHN MM M PHNG OPNET ................................................................ 89

4.2 KT QU M PHNG....................................................................................................... 89

PHN C. KT LUN........................................................................................................................ 99

HNG PHT TRIN TI ...................................................................................................... 101


10/104

Tm hiu cng ngh Voip trong Wimax x

CC THUT NG VIT TT ....................................................................................................... 102

TI LIU THAM KHO ................................................................................................................ 104


11/104

Tm hiu cng ngh Voip trong Wimax xi

LIT K BNG

Bng 1.1 c t vt l chun IEEE 802.16

Bng 1.2 Cc ng dng WiMax di ng v QoSBng 1.3 So snh gia chun 802.16-2004 v LMDS, MMDSBng 1.4 So snh WiMAX di ng v 3GBng 1.5 Cc c tnh chnh ca WiMAX di ng v WiBroBng 2.1 Cc chun m ha thoiBng 2.2 So snh cc c tnh ca TCP, UDP v SCTPBng 2.3 Phn chia cc lp ResponseBng 2.4 So snh gia H.323 v SIPBng 2.5 Cc gi tr ca MOSBng 2.6 V d tm thi cho h s thun li ABng 2.7 Thng s suy hao mt giBng 3.1 Phn loi feedback


12/104

Tm hiu cng ngh Voip trong Wimax xii

LIT K HNHHnh 1.1 Minh ha cc loi mng khng dy.Hnh 1.2 Cc cu hnh mng trong cc vng thnh thv nng thn.Hnh 1.3 M hnh phn lp trong h thng WIMAX so vi OSI.Hnh 1.4 Lp MAC vi cc im truy nhp dch vHnh 1.5 Cc nh dng MAC PDUHnh 1.6 So snh gia FDM v OFDM.Hnh 1.7 S khi h thng OFDM.Hnh 1.8 Khi nim v chui bo v.Hnh 1.9 ISI v cyclic prefix.Hnh 1.10 ODFM v OFDMA.

Hnh 1.11 V d ca biu tn s, thi gian vi OFDMA.Hnh 1.12 MISO.Hnh 1.13 MIMO.Hnh 1.14 Beam Shaping.Hnh 1.15 Minh ha mt sng dng dm cui ca WiMAXHnh 1.16 Cc chun v mng truy nhp v tuyn bng rngHnh 1.17 Phm vi ca WiMAX di ng v WiBro trong chun 802.16eHnh 2.1 Kin trc VoIP n gin haHnh 2.2 Giao thc bo hiu H.323

Hnh 2.3 Q.931 trong thit lp cuc giHnh 2.4 Thit lp cuc gi SIP vi Proxy ServerHnh 2.5 Tng tr t ming n tai trong cuc gi VoipHnh 2.6 Vic to gi d liu da vo tn hiu tch ccHnh 2.7 Kt ni tham chiu ca E-modelHnh 2.8 R v cc tnh ton suy haoHnh 2.9 Hm MOS theo RHinh 2.10 R-score theo trHnh 2.11 R-score theo mt giHnh 2.12 Qu trnh thit lp cuc gi SIP-PSTNHnh 2.13 Qu trnh thit lp cuc gi PSTNSIPHnh 3.1 M hnh trin khai mng Wimax-VoipHnh 3.2 Ghp nhiu MSDU thnh MPDU (aggregation)Hnh 3.3 Mt MSDU c phn mnh n cho nhiu MPDUHnh 4.1 M hnh h thng Wimax c bnHnh 4.2 Thit lp thng s cho BSHnh 4.3 Thit lp thng s cho WS

Hnh 4.4 Thit lp thng siu ch wimaxHnh 4.5 Cu hnh Wimax


13/104

Tm hiu cng ngh Voip trong Wimax xiii

Hnh 4.6 Thit lp modul applicationHnh 4.7 Thit lp modul ProfileHnh 4.8 So snh Jitter ca cc WSHnh 4.9 So snh mt gi gia 2 WS xa BSHnh 4.10 So snh mt gi gia 2 WS gn BSHnh 4.11 So snh delay gia 2 WS cc khong cch khc nhauHnh 4.12 Jitter ca cc WSkhi thay i thng s ca WSHnh 4.13 Mt gi gia 2 WS xa BS khi thay i thng s ca WSHnh 4.14 Mt gi gia 2 WS gn BS khi thay i thng s ca WSHnh 4.15 Delay ca cc WS khi thay i thng s ca WSHnh 4.16 Jitter ca cc WS khi thay i thng s ca BSHnh 4.17 Mt gi gia 2 WS xa BS khi thay i thng s ca BSHnh 4.18 Mt gi gia 2 WS gn BS khi thay i thng s ca BS

Hnh 4.19 Delay gia cc WS khi thay i thng s ca BSHnh 4.20 Jitter ca cc WS khi thay i thng s ca WS v BSHnh 4.21 Mt gi gia 2 WS xa BS khi thay i thng s ca WS v BSHnh 4.22 Mt gi gia 2 WS gn BS khi thay i thng s ca WS v BSHnh 4.23 Delay gia cc WS khi thay i thng s ca WS v BS


14/104

PHN B NI DUNG


15/104

Tm hiu cng ngh Voip trong mng Wimax 15

Chng 1-Tng quan v mng Wimax

CHNG 1-TNG QUN V MNG WIMX

1.1GII THIU CHUNG V MNG D LIU KHNG DY1.1.1 Mng khng dy bng rng

- Ngy nay, nhu cu ca khch hng ngy cng cao gia tng. Ngi tiu dngkhng n thun ch mun truyn email, vn bn text, fax, m h mong mun sdng cc dch va phng tin nh: hi ngh truyn hnh, nghe nhc, xem phimtrc tuyn, xem tivi trc tuyn, cc chng trnh trc tuyn trn mng....Khi tc 33,6Kbps, thm ch 56Kbps trn i cp ng bng phng thc dial-up khngth trin khai cc dch v loi ny.- Hin ti, khi m tc ca mng li ca cc nh cung cp dch v Internet (ISP)

c tng ng k, khnng xl ti u cui pha khch hng cng ngy mtmnh th vic mng truy nhp vn hn chnh vy sgy ra hin tng nghn cchai (bottleneck). Vn c t ra l cn phi ci thin nt mng truy nhp np ng c nhu cu ca cnh cung cp dch v ln khch hng.

Cng nghbng rng:chnh l cc cng nghsinh ra gii quyt vn vmng truy nhp. l thut ng ch bt k loi truy cp internet tc cao no.Cng nghbng rng cho php cc c nhn hoc t chc c th truy cp internet c24 gitrong mt ngy, to mi trng cho vic s dng hoc cung cp cc dch vcht lng cao.

c im ni bt ca mng khng dy bng rng:- c im u tin l cho php thay i, di chuyn, thu hp v m rng mtmng mt cch rt n gin, tit kim, c ththnh lp mt mng c tnh cht tmthi vi khnng c ng mm do cao, c th thit lp mng nhng khu vc rtkh ni dy, tit kim chi ph i dy tn km.- c im thhail nhanh, n cho php truy cp vi mt tc gp 10-20 ln sovi phng php quay sthng thng, thm ch hn na. Khi ta dng modem quay s, tc chc tht t30 n 50Kbps cn vi mt kt ni bng rng, tcln ti t256Kbps n 10Mbps, ph thuc vo dch vm ta chn.- c im thbal lun kt ni. Bt k khi no my tnh c bt ln th n utrng thi kt ni vi internet. iu ny c ngha l khng phi lng ph thi giancho vic quay svi modem kt ni mi ln mun vo interntet. Skhng cchuyn b cnh bo mng bn hoc him khi b rt ra khi mng. Khng bt bucphi ngng dch vin thoi trong khi dng dch v internet. Tc l thu bao honton khng phi tr tin cho ng dy thu bao thhai. Hn th na cng c thchia s gia nhiu my vi nhau thng qua mt kt ni internet.- Trong 3 c im trn, c im ng ni nht ca cng nghbng rng chnh l

tc . Chnh v t c tc cao nh vy nn c th trin khai c rt nhiucc dch v khc m vi cc kt ni quay s thng thng khng th lm c.


16/104



iu ny ng ngha vi vic thc y spht trin ca internet, spht trin cacc dch vx hi khc. C th k qua y mt s dch vng ch nh: dchvcho php truyn cc tp tin vi dung lng ln, c th l tp vn bn, tp mthanh, tp hnh nh, tp phim; cc dch v nhn tin nhanh (instant message); dch- v hi t tc cao (video conferencing).

1.1.2 Cc mng d liu khng dy- Mt slng ln cng ngh truyn dn khng dy ang tn ti, nhng h thngkhc vn cn ang c thit k. Nhng cng nghny c thc phn phi trnnhng h mng khc nhau. Trong hnh 1.1, chng ta thy cc loi mng khng dycng vi cc cng ngh ni ting nht cho mi loi mng.

Hnh 1.1 Minh ha cc loi mng khng dy

- PAN l mt mng d liu khng dy c s dng giao tip gia nhng thitb gn ngi dng. Phm vi ca PAN l khong vi mt, ni chung l di 10m,mc d mt scng nghWPAN c th truyn xa hn. Mt s v dcng nghWPAN l Bluetooth, UWB v Zigbee.- LAN l mng d liu c s dng cho giao tip gia cc thit bnh my tnh,in thoi, my in v PDA. Mng ny phsng mt khu vc tng i nh, nhmt ngi nh, mt vn phng hay mt khun vin nh. Phm vi ca LAN khong100m. Hin ti cc mng LAN c s dng nhiu nht l Ethernet (LAN cnh)v WiFi (Wireless LAN, hay WLAN).- MAN l mng d liu c th phsng ln n vi km, in hnh l mt trnghc ln hay mt thnh ph. V dnh mt trng i hc c mt mng MAN clin kt t nhiu mng LAN, mi mng LAN phsng khong 1/2 km2. T mngMAN ny, trng i hc c thlin kt vi nhiu mng MAN khc hnh thnh nnmt mng WAN. Nhng v d vcng nghMAN l FDDI, DQDB v Ethernet-based MAN. WiMAX cnh c thc xem nh l mt mng MAN khng dy(WMAN).

- WAN mng d liu phsng mt vng a l rng ln, cmt quc gia. MngWAN d

a

trn nhng k

t n

i LAN, cho php ngi dng thnh ph

ny c th

giao tip vi ngi dng thnh ph khc. Thng thng, mt mng WAN baogm nhiu node chuyn mch. Nhng kt ni ny s dng knh thu ring, phng


17/104



php chuyn mch mch v chuyn mch gi. Hin ti mng WAN c s dngnhiu nht l mng Internet. Nhng v dkhc l mng WiMAX di ng v 3G,chng c gi l mng WAN khng dy. Mng WAN thng c tc truyn dliu nhhn nhiu so vi LAN (v dnh Internet v Ethernet).

1.2GII THIU V WIMX1.2.1 Gii thiu chung

- Nh chng ta thy trn, h thng cc cng nghv tuyn l mt h thngrt rng v pht trin tlu vi nhng cng ngh hin nay ang c s dngkh rng ri nh wifi, vtinh, vi ba tuy nhin ngi ta vn ang tip tc nghincu v pht trin cc cng nghv tuyn do nhng cng nghc cha png nhu cu ngy cng cao ca th trng. WiMAX l mt cng ngh mi vinhng tnh nng vt tri v ang c lp t th nghim cng nh i vo hotng chnh thc trn quy m ton cu.- WiMAX (Khnng tng tc ton cu vi truy nhp vi ba) l mt cng ngh rai da trn chun 802.16 ca IEEE cho php truy cp v tuyn u cui nh mt

phng thc thay thcho cp, DSL v WLAN.- Cng nghWiMAX, hay cn gi l chun 802.16 l cng nghkhng dy bngthng rng ang pht trin rt nhanh vi khnng trin khai trn phm vi rng vc coi l c tim nng to ln trthnh gii php dm cui l tng nhmmang li khnng kt ni Internet tc cao ti cc gia nh v cng s.

- Cng nghWiMAX c khnng phsng rng hn, bao ph c mt khu vcthnh th hay mt khu vc nng thn nht nh. Cng nghny c th cung cp vitc truyn d liu n 75 Mbps ti mi trm pht sng vi tm phsng t 2 kmn 10 km. Vi bng thng nh vy, cng nghny c khnng h trcnglc (thng qua mt trm pht sng n l) kh nng kt ni ca hn 60 doanhnghip vi tc kt ni ca ng T1/E1 v hng trm gia nh vi tc kt niDSL.

- Sbng n mng WLAN Mv Chu u cho thy nhu cu v mng khngdy c bit l truy cp Internet khng dy l rt ln. Trong khi nhu cu i vi cc

dch vbng thng rng trn ton th gii ngy cng gia tng, WiMAX chnh lgii php tim nng gip chohng triu ngi c th truy cp Internet bng thngrng m khng cn dy ni khong cch xa.- WiMAX l cng ngh mi, do IEEE pht trin nhm gii quyt cc vn trongmng v tuyn bng rng im im, im a im. WiMAX c nhiu ngdng, nh kt ni xa cho nh ring v c skinh doanh v kt ni ng trc giacc im truy cp nng ca mng WiFi.- C thni rng WiMAX hot ng tng tnh mng LAN khng dy WiFinhng vi tc cao hn, khong cch xa hn v s lng ngi s dng nhiuhn. Cng ngh ny c th gip ph sng nhng khu vc khng c dch vInternet bng rng cc vng ngoi v nng thn.


18/104



1.2.2 Qu trnh pht trin, xu th chung v phn loi wimax- Tri qua snm khng nhiu, WiMAX pht trin v i mi kh nhanh,hinnay WiMAX ang c th nghim v i vo hot ng.- Xu hng bng thng rng di ng :

ng Michael Lai, Gim c iu hnh Packet One, cng ty vin thngang trin khai th nghim WiMAX ti Malaysia, cho rng WiMAX nmtrong xu hng pht trin mi. Theo , xu hng ln u tin trong ngnhvin thng l xu hng di ng, xu hng ln thhai l bng thng rng. Bng thng rng hin nay vn ch yu dng cnh v chia s, tc lnhiu ngui dng chung mt bng thng (ADSL, cp...). Tuy nhin, xu hngln thba ang bt u din ra l bng thng rng di ng, hay cn c coil bng thng rng c nhn, ngha l mi ngi c mt bng thng ring tithit bc nhn ca ring mnh. WiMAX ra i nhm p ng xu hng ny.

- Qu trnh pht trin ca WiMAX tri qua mt scc chun nh l: 802.16a : Chun ny s dng bng tn c bn quyn t 2 - 11 GHz. y l

bng tn thu ht c nhiu quan tm nht v tn hiu truyn c th vtc cc chng ngi trn ng truyn. 802.16a cn thch ng cho vic trinkhai mng Mesh m trong mt thit b cui (terminal) c th lin lc viBS thng qua mt thit b cui khc. Vi c tnh ny, vng ph sng ca802.16a BS sc ni rng.

802.16b: Chun ny hot ng trn bng tn t 5 6 Ghz vi mc chcung ng dnh v vi cht lng cao (QoS). C th chun u tin truyn thngtin ca nhng ng dng video, thoi, real-time thng qua nhng lp dch vkhc nhau. Chun ny sau c kt hp vo chun 802.16a. 802.16c : Chun ny nh ngha thm cc profile mi cho di bng tn t10-66GHz vi mc ch ci tin interoperability. 802.16d : C mt s ci tin nh so vi chun 802.16a. Chun ny cchun ha 2004. Cc thit b pre-WiMAX c trn thtrng l da trn chunny.

802.16e : ang trong giai on hon thin v chun ha. c im ni bt

ca chun ny l khnng cung cp cc dch vdi ng (vn tc di chuynln nht m vn c thdng tt dch vny l 100km/h). IEEE 802.16e hayIEEE 802.16e-2005 l mt chun m rng (amendment) ca chun 802.16-2004, thng c gi l WiMAX di ng (Mobile WiMAX) v n c kh nng p ng dch vcho ngi dng di ng thng qua cc giao thc chuyngiao. 802.16e dng k thut a truy nhp SOFDMA, s dng k thut MIMOv AAS ci thin vng phv nng sut, m Turbo v LDPC tng tnhan ton v ci thin hiu nng ca NLOS.

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


19/104



- C hai m hnh ng dng WiMAX l: M hnh ng dng cnh v m hnhng dng di ng.

M hnh cnh: s dng cc thit btheo tiu chun IEEE 802.16-2004.Tiu chun ny gi l khng dy cnh v thit b thng tin lm vic vicc ng ten t cnh ti nh cc thu bao. ng dng LOS di tn s 10-66 GHz v NLOS di 2- 11 GHz.

M hnh ng dng di ng: S dng cc thit bph hp vi tiu chunIEEE 802.16e. Tiu chun 802.16e b sung cho tiu chun 802.16-2004hng ti nhng ngi dng di ng, lm vic trong bng tn thp hn 6GHz.Tiu chun IEEE 802.16e mi c thng qua trong nm 2005.

1.2.3 M hnh h thngThnh phn h thng:

- H thng WIMAX gm 2 phn: Trm gc WIMAX: trm gc bao gm thit bin t trong nh v thpWIMAX. Thng thng, mt trm gc c th phsng trong bn knh 10 km(theo l thuyt, mt trm gc c th ph sng trong bn knh 50 km). Minode v tuyn bn trong vng phsng c th truy cp internet.

My thu WIMAX:my thu v anten c thl hp ring l hoc card PC trong my tnh hay my tnh xch tay. Truy cp ti trm gc WIMAX tngng vi truy cp ti im truy cp v tuyn trong mng WiFi, nhng vngphsng ln hn. Mt vi trm gc c kt ni vi mt trm gc khc vivic s dng cc lin kt sng vi ba backhaul tc cao.

Hnh 1.2Cc cu hnh mng trong cc vng thnh thv nng thn

- Mt vi trm gc c th c ni vi mt trm gc khc s dng cc lin ktbackhaul tc cao. iu ny cho php thu bao WIMAX chuyn vng t mt

trm gc ny ti vng trm gc khc, ging nh chuyn vng c cho php bicc cng ty in thoi t ong.


20/104



- Mt vi la chn backhauling v cu hnh c h tr cho cc trm gcWIMAX: backhauling c dy (thng qua Ethernet), kt ni vi ba im ti im,cng nh backhaul WIMAX. i vi la chn sau cng, trm gc c kh nng

backhaul chnh n. iu ny c tht c bng cch d tr phn rng bngtn thng c dng cho lu lng ngi s dng u cui v s dng n cho ccmc ch backhauling.

Thnh phn cng ngh:

- Nhn chung v mt cng nghth WiMAX s dng nhng cng nghsau y lquan trng nht:

Chun IEEE802.16 Lp MAC ca chun IEEE802.16

K thut OFDM FEC

Phng php truyn khung dng v ch ARQ, truyn li c la chnARQ.

- Trn y l nhng thnh phn cng ngh m WIMAX ni chung s dng.WIMAX c xy dng trn chun ca ITU y l tiu chun ca cng nghkhngdy chun cho WIMAX, ngoi ra xung quanh chun ngi ta cn s dng thmnhiu cc k thut khc na nh ni trn.- i vi WIMAX di ng th do c th ca tnh di ng nn ngi ta cn ph ich trng nhiu n nhng vn lin quan tng khnng pht sng v thu sng

ca thit bdi ng.

1.3C IM C BN C WIMX- Chng ta c thhnh dung c ch hot ng ca mng WiMAX nh mng inthoi di ng. Ngha l c mt tng i pht sng v mt mng li cc trm phtWiMAX phsng n tng ngi dng cui. Phm vi phsng ln nht catrm WiMAX t 50km.- V cng ngh WiMAX h tr cho c dng truy nhp cnh (Fix) v di ng(mobile) nn h thng WiMAX cng c nhng c im khc nhau i vi 2 dng

truy nhp khc nhau ny.c im Fixed WiMAX:

- Khong cch gia trm thu v pht c th ti 50km.- Tc truyn c ththay i, ti a l 70Mb/s.- Hot ng trong c2 mi trng truyn dn: ng truyn tm nhn thng LOSv ng truyn che khut NLOS.- Di tn lm vic 2-11GHz v 10-66GHz.- Hng truyn tin c chia thnh 2 ng ln v xung. Phn chia ng ln v

xung c thdng c2 cng ngh: TDD v FDD.


21/104



- Fixed WiMAX s dng phng php iu ch OFDM, nh ngha kch thcca FFT l 256 vi 192 sng mang d liu, 8 sng mang dn ng v 55 sngmang bo v.- Cc phng php iu ch sc s dng l: QPSK, 16QAM, 64QAM; dngphi hp cc phng php m ha sa li l m khi (Reed Salomon) v m xon(m chp) CC.- rng bng tn ca WiMAX t5MHz n trn 20MHz c chia thnh nhiu

bng con 1,75MHz. Mi bng con ny c chia nh hn na nh cng nghOFDM, cho php nhiu thu bao c th truy cp ng thi mt hay nhiu knh mtcch linh hot m bo ti u hiu qu s dng bng tn.- V cu trc phn lp, h thng WiMAX c chia thnh 4 lp: Lp con hi t(convergence layer) lm nhim v giao din gia lp a truy nhp v cc lp trn,lp a truy nhp (MAC layer), lp bo mt (Security) v lp vt l (Physical). Cc

lp ny tng ng vi hai lp di cng ca m hnh OSI v c tiu chunha c th giao tip vi nhiu ng dng lp trn.c im Mobile WiMAX:

- Khong cch gia trm thu v pht trong khong 1.75 km.- Tc truyn: 1030Mb/s- Khng yu cu truyn trong tm nhn thng.- Di tn lm vic ca Mobile WiMAX tp trung trong khong tn sdi 6GHz (2,3 GHz; 2,5 GHz; 3,3 GHz; 3,5 GHz).

- rngbng tn ca h thng t 1,2520MHz- ng ln v xung c th c phn chia theo cng ngh TDD hoc FDD,nhng TDD c khuyn ngh s dng nhiu hn v nhng tnh nng u vit can.- im khc bit r nt so vi Fixed WiMAX l Mobile WiMAX s dng cngnghiu ch h tra truy nhp Scalable OFDMA (S- OFDMA), cho php thayi kch thc FFT tc l thay i ssng mang con. Ssng mang con c thl128, 512, 1024 hay ln nht l 2048. Ssng mang con ny c chia thnh ccknh con vi slng knh con ln nht l 32.

- Mobile WiMAX s dng phng php iu chv m ha thch ng, h trcckiu iu ch QPSK, 16QAM, 64QAM. Phng php m ha sa li dng m xonCC v m CTC.

1.3.1 u im- c xy dng trn tiu chun IEEE.802.16, WIMAX l h thng a truy nhpkhng dy bng rng dng cng ngh OFDM vi c hai kiu ng truyn LOS vNLOS.

- 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 WIMAX h trim ti aim v cc dch vkhp ni bng cch sp xp mt khe thi gian cho mi trm


22/104



thu bao (SS). Nu chc mt SS trong mng, th trm gc WIMAX sthng tinvi SS trn c sim ti im. Mt BS trong cu hnh im ti im c th sdng mt anten bp hp hn phcc 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 dinkhng dy bng rng. Bo mt cng cung cp cho cc nh khai thc s bo vmnh m chng n trm dch v. WIMAX cng c xy dng h trVLAN, mcung cp s bo v d liu c truyn bi cc ngi s dng khc nhau trn cngmt BS.- Trin khai nhanh: so vi s trin khai ca cc gii php dy, WIMAX yu cu thoc khng yu cu xy dng k hoch mrng. V d, o h h trrnh cacc 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 tnkhng c cp php, khng cn thit xem xt su hn cc ng dng cho ChnhPh. Khi anten v thit bc lp t v c cp ngun, WIMAX s sn sngphc v. Trong hu ht cc trng hp, trin khai WIMAX c thhon thnh trongkhong my gi, so vi my thng cho cc gii php khc.- Dung lng cao: S dng iu ch bc cao (64-QAM) v rng bng tn (hinti l 7 MHz), cc h thng WIMAX c th cung cp rng bng tn ng k chocc 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 sutln v hot ng vi iu ch mc thp (v d, BPSK hoc QPSK), cc h thngWIMAX c th bao ph mt vng a l rng khi ng gia BS v SS thng sut.- Mang li li nhun: WIMAX da trn chun quc t m. Chun c thng quaa s, s dng chi ph thp, cc chipset c sn xut hng lot, siu khin gih xung; v cnh tranh gi c lm cho cc nh cung cp dch v, ngi s dngu cui tit kim c chi ph.- Dch va 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 vc tha ra cc SLA khc nhau cho nhng ngi ng k khc nhau, hoc thmch cho nhng ngi s dng khc nhau trong cng mt SS.- Khnng cng vn hnh: WIMAX da vo cc chun cung cp trung lp, quct, lm cho ngi s dng u cui ddng truyn ti v s dng SS ca h ti ccvtr khc nhau, hoc vi cc nh cung cp dch vkhc nhau. Khnng cng vnhnh bo v vn u t ban u ca nh khai thc v n c th chn thit b tcci l thit bkhc 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


23/104



cn SS c ng k trong c sd liu h thng, v sau m phn cc c tnhtruyn dnph hp.- Tnh di ng: Chun 802.16e IEEE c thm mt s c im ch yu trongvic h trtnh di ng. Cc ci tin c to ra cho lp vt l OFDMA v OFDM cung cp cc thit bv dch vtrong mi trng di ng. Cc mi trng nybao gm: OFDMA c th chia t l c, MIMO, v h tr ch idle/sleep,chuyn giao, cho php tnh di ng hon ton ti tc 160 km/h. Chun h trbiForum WIMAX c hng hiu nng NLOS tt hn ca OFDM v hot ngchu c a ng, lm cho n ph hp hn vi mi trng di ng.- Qu trnh hot ng tm nhn khng thng:NLOS thng m chng dn vtuyn c min Fresnel th nht b chn hon ton. WIMAX da vo cng nghOFDM c dung lng vn c ca cc mi trng NLOS. Dung lng ny gip ccsn phm WIMAX phn pht rng bng tn rng trong mi trng NLOS, m

cc sn phm v tuyn khc khng lm c.- Ngoi ra WiMAX cn cho php s dng cng nghTDD v FDD cho vic phnchia truyn dn hng ln v hng xung.

1.3.2 Nhc im- Vi bt c h thng truyn thng v tuyn no th nh hng ca mi trngtruyn sng l khng thtrnh 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 cc

dch v. Cc sng v tuyn in ln cn c thgy 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 strn phm vi ton th gii nn kh khn trong lp rp, thay thcckhu vc khc nhau.

- Cng nghny khi xng tnc M, nhng thc scha c thng tin chnhthc no cp n vic M s dng WiMAX nh thno, khc phc hu qu sc ra sao. Ngay c Vit Nam, VNPT ( vi nh thu nc ngoi l Motorola,Alvarion) cng trin khai mt s tnh min ni pha Bc, c thl Lo Cainhng cng ch gii hn l cc im truy cp Internet ti Bu in tnh, huyn chcha c nhng kt lun chnh thc vtnh hiu qung k ca h thng.

1.4CU TRC C WIMX- V cu trc phn lp, h thng WiMAX c phn chia thnh 4 lp:

Lp con tip ng (Convergence) lm givai tr giao din gia lp a truynhp v cc lp bn trn.

Lp a truy nhp ( MAC ). Lp truyn dn (Transmission).


24/104



Lp vt l (Physical ).- Cc lp ny tng ng vi 2 lp di cng cng ca m hnh OSI,c tiuchun ha giao tip vi nhiu ng dng lp trn.

Hnh 1.3 M hnh phn lp trong h thng WIMAX so vi OSI

1.4.1 Lp vt l (PHY)- Lp vt l cung cp kt ni v tuyn gia BS v SS. Chun IEEE 802.16 nhngha cc k thut khc nhau truyn thng tin qua mi trng v tuyn. ChunIEEE 802.16 h tr2 bng tn: bng tn 10-66 GHz v 2-11 GHz.

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

thc truy cp TDM cho hng truyn downlink. Bng tn 2-11 GHz (cp php v khng cp php) h tr mi trngtruyn dn khng c tm nhn thng NLOS, tn hiu c th truyn qua cc vtcn theo nhiu cch khc nhau.

- C 5 c t lp vt l chun IEEE 802.16 c m tnh sau:Bng 1.1c t vt l chun IEEE 802.16

- Lp vt l chun IEEE 802.16 s dng phng php iu chOFDM, bng tnc chia thnh nhiu sng mang con trc giao vi nhau nhm t c thnglng d liu v khong cch truyn ti a, chng nhiu hiu qu.


25/104



- Ngoi ra, lp vt l cn cung cp mt sphng thc iu ch nhiu mc nhBPSK, QPSK, 16-QAM, 64-QAMcho php truyn nhiu n v thng tin trnmt n v thi gian.- Cc qu trnh Ranging v DFS c thc thi ti lp vt l.

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

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

1.4.2 Lp iu khin truynhp mi trng (MC)- Lp MAC chun IEEE 802.16 cung cp giao din hot ng c lp vi lp vtl do giao din lp vt l l giao din v tuyn. Phn ch yu ca lp MAC tptrung vo vic qun l ti nguyn trn airlink. Gii quyt c bi ton yu cu tc

d liu cao trn chai knh downlink v uplink. Cc c chiu khin truy cpv thut ton cp pht bng thng hiu quc khnng p ng cho hng trm ucui trn mi knh.Ti nguyn c cp pht cho mt ngi dng bi trnh lp lchMAC c ththay i t mt khe thi gian n n ton bkhung, do cung cpthng lng nng ng n ngi dng ring ti bt c thi gian no. Hn th, dothng tin cp pht ti nguyn c vn chuyn trong thng ip MAC u mikhung, trnh lp lch c ththay i hiu qu s cp pht ti nguyn theo kiu tngkhung mt (frame by frame) thch ng vi trng thi tnhin ca lu lng.- Lp MAC ca chun IEEE 802.16 c thit k cho nhng ng dng truy cp

khng dy bng rng im-a im. Nhim vc bn ca lp MAC WiMAX lcung cp mt giao din gia nhng lp cao hn v lp vt l.- Lp MAC nhn packet t lp bn trn, nhng packet ny c gi l MSDU, va chng vo trong MPDU pht trong khng kh. i vi pha thu, lp MAClm ngc li.- Thit k lp MAC ca chun IEEE 802.16-2004 v chun IEEE 802.16e-2005bao gm mt phn lp convergence c th giao tip vi nhiu giao thc lp caohn, chng hn nh ATM TDM Voice, Ethernet, IP, v cc giao thc khc trongtng lai.


26/104



Hnh 1.4 Lp MAC vi cc im truy nhp dch v- Cc giao thc lp MAC chun 802.16 l hng kt ni. Vo thi im truy nhpmng, mi SS s to mt hoc nhiu kt ni truyn ti d liu trn chai hng(downlink v uplink). n v lp lch lp MAC s s dng ti nguyn airlink cung cp cc mc QoS phn bit. Lp MAC cng thc hin chc nng tng thchlin kt (link adaption) v truyn li tng ARQ nhm duy tr thng lng d liui a vi t l li bit BER chp nhn c. Lp MAC chun IEEE 802.16 cngiu khin qu trnh truy nhp v ri khi mng ca SS, thc hin to v truyn ccn v d liu giao thc PDU. Ngoi ra, lp MAC chun IEEE 802.16 cn cung

cp lp con hi t c t dch v h tr lp mng tbo ATM v lp mng gi(Packet).- Lp MAC kt hp nhiu tnh nng thch hp cho nhiu ng dng cc tc dichuyn khc nhau, chng hn nh cc tnh nng sau:

PKM cho bo mt lp MAC. PKM phin bn 2 kt hp h trgiao thcchng thc mrng EAP.

H trqung b broadcast and multicast. Handover tc cao.

Ba cp qun l ngun: hot ng bnh thng, sleep v idle. Header suppression, packing v fragmentation s dng hiu qu phtn. Nm lp dch v: unsolicited grant service (UGS), real-time polling service(rtPS), non-real-time polling service (nrtPS), best effort (BE) v Extendedreal-time variable rate (ERT-VR) service.


27/104



Bng 1.2 Cc ng dng WiMax di ng v QoS

- Nhng tnh nng ny kt hp vi nhng li im ca OFDMA khin cho 802.16thch hp cho nhng ng dng d liu multimedia tc cao.- H tr QoS l mt phn c bn ca thit k lp MAC ca WiMAX. WiMAXmn mt s tng c bn cho thit k QoS ca n t chun DOCSIS.- Kim sot QoS cht chc thc hin bng cch dng kin trc MAC hngkt ni, tt c kt ni chiu ln v chiu xung u c iu khin bi BS.- Lp MAC chun IEEE 802.16 bao gm 3 lp con.

1.4.2.1 Lp con hi t dch vc trng (CS):- Lp con hi tc t dch v tip nhn cc gi d liu tcc lp cao thng quacc im truy nhp dch v lp con hi tCS SAP, nh xthnh cc n v d liudch v lp MAC SDU.

Tip nhn cc n v d liu giao thc (PDU) ca lp cao hn.

Thc hin phn loi cc PDU Xl (nu cn thit) cc PDU da vo vic phn loi

Chuyn giao cc PDU CS thnh MAC SAP Nhn cc CS PDU t thc thngang hng


28/104



- Hin ti CS cung cp 2 c tnh kh dng: CS ATM (kiu truyn dn khng ngb), thch ng lu lng ATM v CS gi, thch ng lu lng IP v Internet.

1.4.2.2 Lp con phn chung (CPS):- Lp con phn chung MAC (CPS) h trkin trc Point-to-Multipoint. Mt trm

gc BS c th gi thng tin n cc trm thu bao SS v nhn thng tin tcc SS.- Lp con CPS cng chu trch nhim cp pht bng thng. Bng thng c cp

pht cho mt trm SS mi cng nh cp b sung cho mt trm SS nu c yu cu.

a)Xl cc kt ni:- Lp MAC l hng kt ni. iu ny c ngha l trc khi gi thng tin ngis dng, n cn thit lp mt kt ni gia SS v BS hoc mt SS v mt SS khc,ph thuc vo cu hnh s dng. H trmulticast. Mi kt ni c mt nh danh ktni (CID) 16 bit.

- C 2 loi kt ni: cc kt ni qun l v kt ni vn chuyn d liu. Kt ni qun l c 3 loi: c bn, s cp v th cp. Kt ni c bn l ktni c to ra cho mi SS khi n ng nhp vo mng. Kt ni ny cdng cho cc bn tin qun l khn v ngn. Kt ni s cp cng c to racho mi SS vo lc n gia nhp mng, nhng n c s dng cho cc bn tinqun l dung sai tr. Kt ni th cp c s dng cho cc bn tin qun lvic ng gi IP (nh l DHCP, SNMP, TFP).

Kt ni vn chuyn c thl dphng hoc c thc thit lp tu theoyu cu. Kt ni ny c dng cho lung lu lng ngi s dng.

- Kt ni d liu thng c s dng truyn thng tin ngi s dng trn mtng khng trc tip, trong khi ba loi cn li c s dng truyn thngtin iu khin.

b)MAC PDU:- Cc MAC PDU c chia lm ba phn: mt tiu chung (6 byte); mt ti trngdi thay i v mt m kim tra d vng (4 byte).

Hnh 1.5 Cc nh dng MAC PDU- di PDU ln nht l 2 Kbyte. Ti trng c thc s dng truyn thngtin iu khin qua cc tiu con. Ti trng c th rng hoc y cc tiu con,cc MAC PDU hoc cc on. m phn bng thng, n c pht trin mtMAC PDU dnh ring.PDU ny c mt tiu c bit, cha cc thng sbngthng.

- C 5 loi tiu con: phn on, gi, qun l trcp, li v cp pht hi tipnhanh. Tiu con phn on c s dng iu khin phn on MAC SDUthnh hai hoc nhiu MAC PDU, trong khi tiu con gi c s dng tp


29/104



hp mt hoc nhiu MAC SDU thnh mt MAC PDU. Tiu con qun l trcpcho php yu cu bng thng m khng cn gi mt PDU dnh ring. Yu cuc xc nhn cng vi mt MAC PDU chung. Cc MAC PDU c sp xp trongcc khung lp vt l.

c)Phn knh:- Khng chTDD m cFDD cng c h tr. Trong FDD chai pha pht ngthi vi cc tn skhc nhau, cn trong TDD ch mt tn sc s dng v nc chia s da vo thi gian. Khung TDD c hai phn: khung con ng xungv khung con ng ln. Mi khung con c phn chia thnh cc khe vt l (PL)i vi cc giao din v tuyn n sng mang v thnh cc cm i vi cc giaodin v tuyn OFDM. Cc MAC PDU c chn trong cc PL hoc cc cm theocc giao din v tuyn c trin khai. Vi FDD, m hnh song cng v bn songcng c cho php.

d)Sp xp:- Sp xp c trin khai cp pht bng thng cho cc kt ni. i vi giaodin khng gian n sng mang, BS gi trong khung con ng xung mt sp xpng ln (UL-MAP) v mt sp xp ng xung (DL-MAP). UL-MAP chacc PL m mt SS c th s dng pht trn ng ln. DL-MAP cha cc khethi gian m mt SS phi nghe trong ng xung. Khung con ng xung btu vi cc sp xp ny, c gi qua giao din khng gian ti tt ccc SS. V

vy, UL-MAP v DL-MAP xc nh bng thng c cp pht cho cc kt ni (quascc PL kh dng), cc PL mi trm phi pht v nhn v hs cm c sdng. Vi giao din v tuyn OFDM, sp xp c thc hin s dng cc k hiuthay v cc PL. Vi giao din khng gian OFDMA, cc k hiu OFDM v cc knhcon c s dng.

e)Lp lch, yu cu v cp pht bng thng:- Lp lch c trin khai xc nh quyn u tin truyn dn cc MAC SDUqua cc kt ni MAC ang tn ti. Vi mi kt ni n c kt hp vi mt loi

lp lch c xc nh trc. Mi loi c mt tp cc thng sxc nh cc yu cucht lng dch v(QoS). C bn loi c nh ngha: dch v cp pht t nguyn(UGS), dch v thm d thi gian thc (rtPS), dch v thm d phi thi gian thc(nrtPS) v n lc tt nht (BE: best effort). UGS c nh ngha cho lu lng tcbt khng i thi gian thc. rtPS c nh ngha cho lu lng tc bt thayi thi gian thc nh lu lng video. nrtPS lin quan ti lu lng tc bt thayi phi thi gian thc dung sai tr. i vi lu lng d liu tc bit thay i, nc nh ngha bi lp n lc tt nht (BE). i vi cc kt ni UGS, BS cp phtmt cch nh k mt lng bng thng cnh, m c m phn khi thit lp

kt ni. Cc loi khc phi yu cu nh k bng thng, c cp pht t ngtrong sut thi gian truyn dn.


30/104



- Bng thng c th c yu cu bi cc yu cu ring l (BW yu cu MACPDU) hoc mt yu cu xc nhn (tiu con MAC PDU). Cc yu cu c thtngln hoc kt hp li. Cc yu cu kt hp thay thcc kt ni trc c yu cu

bng thng, trong khi cc yu cu tng ci thin bng thng hin ti bi slngyu cu. Cc SS phi yu cu bng thng theo chu k i vi cc kt ni BE, rtPS,nrtPS, vvy gim s dng bng thng. Chu k cp nht ph thuc loi lp lch vcht lng lin kt. Thm vo cc yu cu ring l, BS c th cp pht mt khongthi gian yu cu, trong mt hoc nhiu SS c th gi cc bn tin yu cu bngthng. Qu trnh ny c gi l thm d. Thm d c thc thc hin theo haicch: thm d n hng v thm d da vo tranh chp. Trong thm d nhng, BS cp pht bng thng lng nghe cc yu cu ca ch mt SS, cn trongthm d da vo tranh chp, BS cp pht bng thng lng nghe yu cu ca mtnhm a hng cc SS hoc tt ccc SS.

- Bng thng c thc trcp trn kt ni (GPC) hoc trn SS (GPSS). Trongchai trng hp, cc yu cu bng thng c thng tin trn kt ni, m cithin cp pht bng thng BS. Tuy nhin, trong GPC bng thng c cp pht chocc kt ni c bit, cn trong GPSS n c cp pht cho SS.

f)Gii quyt tranh chp:- Mc d BS iu khin cp pht bng thng trong ng ln, nhng c th xuthin xung t trong khong thit lp v khong thi gian yu cu bng thng. Thutton backoff m nhphn rt gn c trin khai gii quyt cc tnh hung xung

t.g)ARQ:

- ARQ l qu trnh pht li cc MAC PDU b mt hoc sai lc. Theo IEEE802.16TM-2004, k thut ARQ da vo s chui phn on ca cc tiu con

phn on hoc gi.- H trARQ l tu chn v c thc la chn cho mi kt ni. La chn cthc hin trong khong thit lp kt ni. ARQ khng c thc s dng cng vigiao din khng gian sng mang n. Khi ARQ c cho php, cc MAC PDU c

thc phn on trong cc khi ARQ. Xc nhn ARQ c gi hoc trong bntin MAC ring l qua mt kt ni qun l c bn hoc c mang trn mt MACPDU qua mt kt ni d liu tn ti.

h)M tthch ng cm:- thch ng cc thay i trong iu kin lin kt v tuyn, IEEE 802.16TM-2004 trin khai mt k thut tin bm ho, iu ch, sp xp v cng suttruyn dn ng. M tthch ng cm c s dng thay i cc c tnh truyndn da vo trng thi lin kt. Mc tiu l cn bng gia sc mnh v hiu qu.

K thut l khc nhau gia ng xung v ng ln. Bn tin c s dng thng tin trao i gia cc thit b. BS khng chiu khin SS m t cm ng


31/104



ln s dng UL-MAP m cn tnh ton m t cm ng xung theo cht lngca tn hiu thu c t mi SS. Tuy nhin cc SS c thyu cu thay i trong mt cm ng xung nu iu kin mi trng qu xu.

1.4.2.3 Lp con bo mt:- Ton b bo mt ca 802.16 da vo lp con bo mt. Lp con bo mt l lpcon gia MAC CPS v lp vt l. Mc tiu ca n l cung cp iu khin truynhp v s cn mt ca lin kt d liu, chu trch nhim m ha v gii m d lium a n v i ra khi lp vt l PHY v cng c s dng cho cp php vtrao i kha bo mt, ngn chn nh cp dch v.

1.5CC K THUT S DNG TRONG WIMX- Vi kin trc m, linh hot, dung lng ln v chi ph trin khai thp lm choWiMAX trthnh mt gii php hng u cho cc dch vv tuyn bng rng.

- OFDM, OFDMA v S-OFDMA l nhng cng ngh truy nhp mi ci tin htrknh cn thit t c hiu qu tri ph tt hn v thng lng knh caohn. Nhng cng ngh truy nhp mi ny l nn tng cho WiMAX v l la chncho cc h thng bng rng di ng tip theo khc nhm cung cp nhiu loi hnhdch v truyn thng a phng tin tc cao.- Chng ta s kho st tng quan cc k thut tin tin c p dng trong cngnghWiMAX nh l k thut OFDM, OFDMA, h thng anten tin tin

1.5.1 K thut OFDM- K thut OFDM l k thut ghp knh phn chia theo tn s trc giao. TrongOFDM, chui d liu ti u pht thng c tc rt cao. Dng d liu ny cchia thnh nhiu dng d liu song song tc thp hn nh b chuyn i nitip-song song (S/P). Mi dng d liu song song sau c iu ch bi mtsng mang, cc sng mang ny c chn trc giao vi nhau m bo c thtch ring tng lung d liu ti u thu. Kn cc sng mang ny c tng hpli v a ln tn spht.

Hnh 1.6So snh gia FDM v OFDM


32/104



- S lng cc sng mang con ph thuc vo nhiu yu tnh rng knh vmc nhiu. Con sny tng ng vi kch thc FFT. Chun giao tip v tuyn802.16-2004 xc nh 256 sng mang con tng ng FFT 256 im, hnh thnhchun Fixed WiMAX, vi rng knh cnh. Chun giao tip 802.16-2005 cho

php kch cFFT t512 n 2048 ph hp vi rng knh 5MHz n 20MHz,hnh thnh chun Mobile WiMAX (Scalable OFDMA), duy tr tng i khongthi gian khng i ca cc k hiu v khong dn cch gia cc sng mang vi rng knh.

Hnh 1.7S khi h thng OFDM

- u tin, dng d liu vo vi tc cao c chia thnh nhiu dng d liu

song song tc thp hn nhb chuyn i ni tip-song song (S/P). Mi dngd liu song song sau c m ha (Coding) s dng thut ton FEC v csp xp (Mapping) theo mt trnh t hn hp. Nhng k t hn hp c a nu vo ca khi IDFT (y thc hin php bin i IDFT ngi ta dng thutton IFFT). Sau khong bo vc chn vo gim nhiu xuyn k t (ISI),nhiu xuyn knh (ICI) do truyn trn cc knh v tuyn di ng a ng. Dngd liu song song li c chuyn thnh ni tip nhb chuyn i song song-nitip (P/S). Cui cng, b A/D pha pht nh dng tn hiu thi gian lin tc vchuyn i ln min tn scao truyn i xa.- Trong qu trnh truyn, trn cc knh sc cc ngun nhiu tc ng n nhnhiu Gausian trng cng AWGN.- pha thu, tn hiu thu c chuyn xung tn s thp v tn hiu ri rc nhnc sau b D/A thu. Khong bo vc loi bv cc mu c chuyn i tmin thi gian sang min tn s bng php bin i DFT dng thut ton FFT (khiFFT). Sau , ty vo s iu chc s dng, s dch chuyn vbin vpha ca cc sng mang nhnh sc sp xp ngc trli v c gii m. Cuicng, chng ta nhn li c dng d liu ni tip ban u.

Chui bo v trong h thng OFDM:

D liu

D liu

S/P

Mha&spxp

ChnPilot

IFFT

Chndibo v

P/S

Knhtruyn

P/S

Spxpli &giim

clngknh FFT

Loi bdi bov S/P

AWGN w(n)


33/104



- u im ca phng php iu ch OFDM khng ch th hin hiu qu sdng bng thng m cn c khnng lm gim hay loi tr nhiu xuyn k hiu ISInhs dng chui bo v GI. Mt mu tn hiu c di l TS, chui bo vtngng l mt chui tn hiu c di TG pha sau c sao chp ln phn phatrc ca mu tn hiu ny nh hnh v sau (do , GI cn c gi l CyclicPrefix-CP). Ssao chp ny c tc dng chng li nhiu xuyn k hiu ISI do hiung phn tp a ng.

Hnh 1.8Khi nim vchui bo v

- Nguyn tc ny gii thch nh sau: Gi smy pht i mt khong tn hiu cchiu di l TS, sau khi chn thm chui bo vc chiu di TG th tn hiu ny cchiu di l T=TS+TG. Do hiu ng a ng multipath, tn hiu ny s ti mythu theo nhiu ng khc nhau. Trong hnh v m tdi y, hnh a, tn hiutheo ng th nht khng c tr, cc ng th hai v th ba u b tr mtkhong thi gian so vi ng th nht.Tn hiu thu c my thu sl tng hpca tt ccc tuyn, cho thy k hiu ng trc s chng ln vo k hiu ngay sau, y chnh l hin tng ISI. Do trong OFDM c s dng chui bo vc diTG s ddng loi b hin tng ny. Trong trng hp TG MAX nh hnh v

m tth phn b chng ln ISI nm trong khong ca chui bo v, cn thnh phntn hiu c ch vn an ton. pha my thu s gt b chui bo vtrc khi gi tnhiu n b gii iu ch OFDM. Do , iu kin cn thit cho h thng

OFDM khng bnh hng bi ISI l: maxGT vi maxl tr truyn dn ti aca knh.

Hnh 1.9ISI v cyclic prefix

Phn tn hiu c chPhn tn hiu c chGI


34/104



Cc u v nhc im ca k thut OFDM:

- Qua vic phn tch vc bn k thut OFDM nh trn, chng ta c thrt ra mtsu im, nhc im chnh ca OFDM nh sau:u im:

S dng ph hiu qu nhph tn sc dng gn nh ca s ch nht nussng mang con ln. Loi b nhiu xuyn k t(ISI) v nhiu gia cc khung (IFI) nhs dngtin tvng CP. Khnng chng nhiu gia cc knh con rt tt nhvic s dng cc sngmang con trc giao.

K thut OFDM cho php thng tin tc cao c truyn song song vitc thp hn trn cc knh bng hp. Cc knh con ny c coi l cc

knh fading khng la chn tn snn c thdng cc bcn bng n gintrong sut qu trnh nhn thng tin. Ni nh vy, h thng OFDM chng cnh hng ca fading la chn tn s.

K thut OFDM l mt phng php hiu qu gii quyt a ng,khng nhiu bng hp tt v nhiu ny chnh hng mt t l nhcc sngmang con.

Thc hin n gin trong min tn s bng cch dng gii thut FFT.ng thi my thu n gin do khng cn b khICI v ISI nu khong dtrdi.

Nhc im:

OFDM l tp hp ca tn hiu trn nhiu sng mang, di ng ca tn hiuln nn c t scng sut nh/trung bnh tng i ln slm hn ch hiusut ca b khuch i m tn. Mt mt hiu sut phdo chn khong d tr.

Nhiu pha do skhng phi hp gia cc bdao ng my phtv mythu, c thlm nh hng n cht lng h thng.

Phi c sng bchnh xc v tn sv thi gian, c bit l tn s.

- Nh vy, k thut OFDM l gii php rt ph hp cho truyn dn v tuyn tccao ni chung v cho cng nghWimax ni ring.Vi cng ngh OFDM, nhskt hp ca cc sng mang con trc giao truyn song song vi cc k hiu ckhong thi gian di m bo rng lu lng bng thng rng khng b hn ch domi trng khng theo tm nhn thng NLOS v nhiu do hin tng a ngdn.

1.5.2 K thut OFDM- OFDMA l mt cng ngha sng mang pht trin da trn nn k thut OFDM.

Trong OFDMA, mt scc sng mang con, khng nht thit phi nm k nhau,c gp li thnh mt knh con (sub-channel) v cc user khi truy cp vo ti


35/104



nguyn sc cp cho mt hay nhiu knh con truyn nhn ty theo nhu culu lng c th.- OFDMA c mt su im nh l tng khnng linh hot, thng lng v tnhn nh c ci thin. Vic n nh cc knh con cho cc thu bao c th, victruyn nhn t mt sthu bao c th xy ra ng thi m khng cn s can thipno, do s gim thiu nhng tc ng nh nhiu a truy xut (Multi accessInterfearence - MAI).

Hnh 1.10 ODFM v OFDMA

a d a d a d

a d a d a d

a c e a c e a c e

a c e a c e a c e

b e g b e g b e g

b e g b e g b e g

b f g b f g b f g

b f g b f g b f g

Hnh 1.11V d ca biu tn s, thi gian vi OFDMA

f


36/104



- Hnh 1.11 m t mt v d v bng tn s - thi gian ca OFDMA, trong c 7ngi dng ta n g v mi ngi s dng mt phn xc nh ca cc sng mangphc sn, khc vi nhng ngi cn li.- Th d c thny thc tl s hn hp ca OFDMA v TDMA bi v mi ngis dng chpht mt trong 4 khe thi gian, cha 1 hoc vi symbol OFDM, 7ngi s dng ta n g u c t cnh (fix set) cho cc sng mang theo bnkhe thi gian.

1.5.3 Cc cng ngh anten tin tin- Cng ngh anten c th dng ci thin truyn dn theo hai cch s dngcng ngh phn tp v s dng cc h thng anten cng cc cng ngh chuynmch tin tin. Cc cng nghny c th ci thin tnh co dn v t stn hiu trntp m nhng khng bo m pht dn skhng bnh hng ca nhiu.

- Cc lc phn tp c s dng li dng cc tn hiu a ng v phn xxy ra trong cc mi trng NLOS. Bng cch s dng nhiu ng ten (truynv/hoc nhn), fading, nhiu v tn hao ng truyn c thc lm gim. Phntp truyn s dng m thi gian khng gian STC. i vi phn tp nhn, cc cngnghnh kt hp t l ti a (MRC) mang li u im ca hai ng thu ring bit.V MISO (nhiu u vo mt u ra).

Hnh 1.12 MISO

- Mrng ti MIMO, s dng MIMO cng snng cao thng lng v tng ccng tn hiu. MIMO s dng nhiu ng ten thu v/hoc pht cho ghp knh theokhng gian. Mi ng ten c th truyn d liu khc nhau m sau c thc giim my thu. i vi OFDMA, bi v mi sng mang con l cc knh bng hptng t, fading la chn tn s xut hin nh l fading phng ti mi sng mang.Hiu ng ny c thsau c m hnh ha nh l mt s khuch i khng iphc hp v c th n gin ha s thc hin ca mt my thu MIMO cho

OFDMA.


37/104



Hnh 1.13 MIMO

- Cc h thng anten thch nghi (AAS) l mt phn ty chn. Cc trm gc c

trang b AAS c th to ra cc chm m c th c li, tp trung nng lngtruyn t c phm vi ln hn. Khi nhn, chng c th tp trung hng cth ca my thu. iu ny gip cho loi b nhiu khng mong mun tcc vtrkhc.

Hnh 1.14 Beam Shaping

1.6NG DNG C WIMX- Ni ti WiMAX, ngi ta c thngh ti rt nhiu gii php thay thm cngnghny c th mang li. chnh l khnng thay thng xDSL gip tip cnnhanh hn cc i tng ngi dng bng rng m khng cn phi u t ln. cbit, WiMAX rt hu ch cung cp dch vbng thng rng nhng vng xaxi m gii php ADSL hoc cp quang l rt tn km. nhng nc ang phttrin nh Vit Nam, ni m Internet bng thng rng cha ph bin, WiMAX lmt gii php kinh t. Ngoi ra WiMAX cn gip vic trin khai WiFi thm nhanhchng do cc hotspot WiFi skhng cn ng leased-line m s ni trc tip vi

WiMAX BS. Kh nng roaming gia cc dch v Wi-Fi v WiMax s mang linhiu li ch cho ngi s dng.


38/104



Hnh 1.15Minh ha mt sng dng dm cui ca WiMAX

- c thdng dch vInternet bng thng rng ca WiMAX (fixed WiMAX),nh cung cp dch v ch cn lp t mt ng ten BS gia khu dn c. Mi ngidng sc cung cp mt ng ten thu (CPE), lp trn mi nh/ca s. CPE c thc ni trc tip vi my vi tnh hoc thng qua mt Access Point WiFi. Victrin khai kh n gin, m gi thnh li thp hn nhiu so vi cng ngh hinhnh.- Bn cnh dch v cnh, WiMAX cn cung ng cc dch vdi ng. Trongtng lai, cc thit b mobile m hin nay c tch hp WiFi s c tch hp

WiMAX. Khi , ngi dng c th kt ni mng mi lc mi ni thng quaWiMAX, v c bit l vn c thdng cc dch v ging nh nhng dch v camng tbo 3G. Hn na, tc truyn ca WiMAX cao hn hn 3G m gi hahn s r. i vi cc nh cung cp mng, gi thnh ca mt WiMAX BS rhnrt nhiu so vi gi ca mt BS UMTS. Do , c th nh cung ng mng 3G sdng WiMAX thay th 3G nhng khu vc tha dn c.- Trong tng lai gn WiMAX sc s dng nhiu nht bi cc nh cung cpdch v vin thng v cc hng ln. Tip n s l cc ng dng vi kt ni trctip vi ngi s dng. WiMAX sgip a ra nhng gii php cho cc ng dng

bng thng rng a cp.- iu quan tm ch yu ca cc nh nh cung cp dch vang trin khai mngWIMAX hin nay l:

Gim chi ph vn hnh.

Tng li nhun.

Gim chi ph u t. Tng th phn.

a cc dch v mi vo nhm lm tng doanh thu trn mi ngi s

dng (ARPU).


39/104



- Thut ngWiMax c thc hiu tng tnh Wi-Fi, mc d trong khi phmvi ca Wi-Fi c tnh bng mt th phm vi ca WiMax c tnh bng kilmt.Vi phm vi rng ln ca WiMax, cc nh cung cp dch v s c th phsngton bcc khu vc th vi ch mt vi thp. WiMax khng phi l gii phpduy nht dnh cho mng bng rng khng dy - Hiperman ca chu u (Mng khuvc thv tuyn hiu nng cao) ang c pht trin nhng khng c xemnh mt ng vin nng k.- ng dng cng nghWiMAX c thphn vo hai dng chnh: Khch hng truycp theo hnh thc c nhn, xy dng h thng truyn dn ring v khch hng ngdng WiMax cung cp mng truy cp cng cng.

1.6.1 Mng dng ring- Sdng lm mng ng trc cho cc mng in thoi di ng tbo (cellular

backhaul):Trong mi trng ngy cng cnh tranh cc dch vkhng dy cu trc theo kiu

tbo, mt nh kinh doanh truy cp thng tin lin tc vi mong mun thng tinnhanh, nhng gim thiu chi ph bng vic la chn cc gi cc ph hp. WiMAXs cung cp ng truyn imim vi khong cch ln n 50 km, tc dliu h trln n tc ca cc trung k E1, T1, thit bWiMAX xy dng nnh tng mnh ti trm gc t mrng ra cc cell xa.- Mng ngn hng:

Cc ngn hng trung tm c th kt ni n cc chi nhnh ca mnh thng qua

mng WiMAX c nhn chuyn ti thoi, data v video. Thng thng cc ngnhng thng nm phn btrong cc khu vc rng, nhng li cn bng thng lnv an ninh cao, do vy WiMAX chnh l mt gii php rt tt cho lin lc d liugia cc b phn ca mt ngn hng.- Mng gio dc:

Cc t chc dng mng WiMAX kt ni cc trng v cc vn phng trongcng mt khu vc qun, huyn. Chng hn vi yu cu bng thng cao (ln hn15Mbps), khnng thng tin im - im hoc im - a im vi mt vng phsng tri rng cung cp cc dch v nh: in thoi, data (s liu v sinh vin),email, internet, o to t xa gia vn phng ban ph trch trng vi cc trngtrong qun hay gia cc trng vi nhau. Trong mi trng gio dc , mtcamera trng B c th truyn tn hiu t lp hc (trong thi gian thc) ntrng A.

WiMAX c vng phsng rng, chi ph hp l nn sc bit hiu qui vicc trng nng thn ni c h tng c struyn dn km, ni m cc gii phpko cp lun i hi mc chi ph cao.- m bo an ton cho cc truy nhp cng cng (Public Safety):

WiMAX c thng dng bo vccc quan chnh phnh: cng an, chachy, cu h. C thdng mng WiMAX h tr trong cc tnh hung cn tr


40/104



gip khn cp, cung cp chc nng thoi hai chiu gia trung tm v cc i ngcu v.v.. Cht lng dch vny cng cho php thay i lu thoi theo nhng yucu khc nhau. Gii php WiMAX c phsng rng, iu gip cho cc i cuh ti ni xy ra tai nn, cc s kin, s vic hay cc thm ha thin nhin c thci t mt mng tm thi trong mt vi pht gi tn hiu vtrung tm. Hcngc th ch ng c lu lng khi gi tn hiu v trung tm thng qua mngWiMAX.

i vi mc tiu di ng cng vy, chng hn nh mt ngi cnh st c thtruy cp d liu trn mt chic xe ang chy, mt ngi lnh cha chy c th truycp thng tin vng i ngn nht n ni xy ra ha hon. Mt camera trn xecu thng c tha hnh nh vtnh trng ca bnh nhn chng cp cutrc khi xe a bnh nhn vn bnh vin. Tt ctrng hp trn u c thngdng WiMAX bng thng rng, trong khi cc h thng bng thng hp khc khng

thp ng c.- Thng tin lin lc xa b:

WiMax c thng dng trong cc cng ty du kh trong thng tin lin lc giat lin v gin khoan.

Trong cc hot ng thao tc thit b, i din vi cc vn phc tp, cc cngvic i hi mc gim st cao v cn truy xut d liu nng. Cc tn hiu nyc th gi v trm t lin cc b phn chuyn mn kp thi phn tch xl.Cng vic khai thc du kh cn m bo yu tan ton, trc cnh bo, gim stbng camera, bn cnh truyn ti c cc thng tin c bn nh: thoi, internet,

email , hi ngh truyn hnh.WiMAX trin khai lp t nhanh chng, cn thit iu chuyn n ni mi cng

ddng, c thkhng cn ngi trc thit b, thit b t hot ng bng cch trangbthm pin nng lng.- Kt ni nhiu khu vc:WiMAX c thdng kt ni nhiu ta nh trong phm vi mt khu vc a l no thay v phi dng cc ng cp hu tuyn.- Cc cng trnh xy dng (mang tnh tm thi):

Cc cng ty xy dng c thdng mng WiMAX thit lp ng lin lc nvn phng trung tm ti cng trng ni ang xy dng ti ni ch huy ti ch:nhng ngi qun c, cc ks, kin trc s c th lin lc vi vn phng camnh qua WiMAX.

Trong trng hp ny ng dng WiMAX da trn u im trin khai nhanh,iu ny quan trng i vi cc cng trnh ang thi cng v n cho php cung cpnhanh thng tin vcng trng bao gm c thoi ln d liu, cung cp c dch vtheo di qua hnh nh ti nhng im nng trong iu kin gim st kh khn.Cng c thci t mt im hotspot ti cng trng cho php mt c nhn c th

thng tin lin lc, trao i d liu, thng tin vcc tin trnh cng vic ang din ra.


41/104



Ging nh trong cc trng hp ng dng khc nu i hi v cht lng dchvth WiMAX c xem xt u tin. V thit b WiMAX nh gn, tho lp t ddng, iu chuyn n cc ni khc nhau theo yu yu cu cng vic xy dng tinli.- Cc khu vc cng cng:

WiMAX c thc lp t nhng khu vc vui chi gii tr, cc hot ngngoi tri, cc hot ng giao dch, trn xe but v cc dch v vn ti khc.

y WiMAX c th h tr lu thoi bng thng rng hai chiu gi t mttrung tm iu khin, hnh nh gim st bao qut ton cng vin, kim sot d liutruy cp, gim st tnh trng ti ch, video theo yu cu. Giao tip in thoi phcv va cnh va di ng, tnh bo mt cao, suy hao thp, vng phsng rng,vic di chuyn lp t ddng ng bin vi cc thay i xy ra l mt su tinla chn thit b WiMAX trong nhng khu vc nh th.

1.6.2 Cc mng phc v cng ngi vi mng cng cng, ti nguyn c xem l ca chung, nhiu ngi scngtruy xut v chia s. Xy dng mt mng cng cng ni chung yu cu mt chi phhiu qu, m cung cp c vng phsng ln v ngi s dng c thnhiu vtr khc nhau c th c nh hoc thay i. Nhng p ng chnh ca cc mngcng cng l thoi v d liu, truyn hnh nh trc tuyn. ng thi an ninh mngcng l mt yu cu quan trng, mc phc tp cao v c nhiu ngi i tngs dng, mt sng dng WiMAX mi trng trong mng cng cng nh sau:

- Mng truy nhp WSP:WiMAX c th mrng phm vi cung cp dch vi vi cc cc nh cung cp

dch vkhng dy (WSP).Cc nh cung cp dch vkhng dy dng mng WiMAX cung cp kt ni

cho ckhch hng l ngi dng ring l (thoi, d liu v truyn hnh) hay cng ty(thoi v internet tc cao).

WiMAX to ra mt h tng mng cung cp d liu thoi v video vi cht lngcao n ngi tiu dng trn c sdng chung mt ho n tnh tin duy nht vc tnh da trn lu lng d liu truyn ti.- Trin khai vng nng thn xa xi ho lnh:

Trin khai cng nghWiMAX c th thc hin cc vng nng thn, hoc ccni tp trung dn c hay cc khu vc ngoi thnh ph. Vic kt ni n nhngvng nng thn xa xi l mt trong nhng mc tiu trng im pht trin x hi camt quc gia trong vic phc v nhng nhu cu thit yu nh thoi v Internet.Nhng ni c sh tng gn nh khng c v vn ko cp l khng kh thi,do vy gii php WiMAX c cp n nh mt phng thc cho vng phsng rng, tit kim chi ph.


42/104



1.7WIMX VI CC CNG NGH TRUY CP V TUYN BNGRNG KHC

- Mt lot cc chun v mng truy nhp v tuyn bng rng c nhiu t chcnghin cu, xy dng v pht trin. Theo phm vi ng dng, cc chun ny c

phn chia thnh cc mng nh sau:

Hnh 1.16Cc chun vmng truy nhp v tuyn bng rng

- Mng cc nhn (PAN): Chun WPAN c ng dng trong phm vi gia nh,hoc trong khng gian xung quanh ca 1 c nhn, tc truyn dn trong nh ctht 480 MB/giy trong phm vi 10m. Trong m hnh mng WPAN, c s xuthin ca cc cng ngh Bluetooth, 802.15 (hin nay 802.15 ny ang c phttrin thnh 802.15.3 c bit n vi tn cng ngh Ultrawideband - siu bngthng).- Mng ni b (LAN): mng WirelessLAN s dng k thut 802.11x bao gm ccchun 802.11a, 802.11b, 802.11g, 802.11n, IPERLAN1/2.. WLAN l mt phn cagii php vn phng di ng, cho php ngi s dng kt ni mng LAN tcckhu vc cng cng nh vn phng, khch sn hay cc sn bay. Cng nghny cho

php ngi s dng c th s dng, truy xut thng tin, truy cp Internet vi tc ln hn rt nhiu so vi phng thc truy nhp gin tip truyn thng.- Mng th (MAN): Mng WMAN s dng chun 802.16, nh ngha c t kthut giao din khng gian WirelessMAN cho cc mng vng th. Vic a rachun ny m ra mt cng ngh mi truy nhp v tuyn bng rng WIMAX cho

php mng v tuyn mrng phm vi hot ng ti gn 50 km v c th truyn dliu, ging ni v hnh nh video vi tc nhanh hn so vi ng truyn cphoc ADSL. y sl cng chon ho cho cc ISP mun mrng hot ng vonhng vng dn c ri rc, ni m chi ph trin khai ADSL v ng cp qu cao

hoc gp kh khn trong qu trnh thi cng.


43/104



- Mng din rng (WAN): Trong tng lai, cc kt ni Wireless WAN s s dngchun 802.20 thc hin cc kt ni din rng, hin nay cc chun ny ang cchun ha.

1.7.1 So snh WiMX c nh v LMDS, MMDS- Phin bn WiMAX 802.16-2004 nhm cung cp cc truy nhp cnh hoc lung. Cc cng nghv tuyn cnh c khnng cnh tranh vi WiMAX cnhhin ang c xem xt bao gm: H thng phn ba im ni vng LMDSvH thng phn ba im a knh (MMDS).

H thng phn ba im ni vng (LMDS):

- Cng ngh LMDS cung cp gii php mng im-a-im v lm vic trong ccdi tn svi ba trn 10 GHz. Hai bng tn schnh c cp pht l 26/28 GHz v40 GHz. Vic s dng cc bng tn ny c th mang ti dung lng rt ln (Tc

ln ti 3 Gbps ti tn s 40 GHz).- Phm vi phsng ca h thng b gii hn trong phm vi 5 km do suy hao macao ti tn sny. Ngoi ra h thng cn yu cu tm nhn thng (LOS).- H thng LMDS hin nay da trn cc gii php ring. T2001, cc tiu chunIEEE 802.16 v ETSI BRAN HYPERACCESS cng hng dn cc mng LMDSnhm n khnng bt tay ca ca cc thit btrn ton cu nhm gim chiph.- Tt ccc h thng LMDS hin nay u da trn cc giao thc dng ring PHY& MAC. Tc truyn s liu t c trn mt knh RF (bng thng xp x 30MHz) l 45 Mbps. Tuy nhin khi cc k thut PHY & MAC c chun ha bi c

ETSI BRAN v IEEE th gi thnh thit bLMDS gim xung rt nhiu.- LMDS l hon ton ph hp vi cc yu cu ca dch vv tuyn bng rng.Cc th nghim thc t cho thy mng c trin khai trn c sLMDS khng bhn ch chng dng cc h thng truyn hnh tngtc hay qung b, m ta cnc th thc hin trin khai TCP/IP trn c sLMDS. iu ny c thc hinbng cch xy dng cc b tng cng giao thc TCP trn nn MPEG. Cc mphng v th nghim ch ra rng vic thc hin IP trn LMDS c th trin khaingay trn cc h thng v tuyn tiu chun. Tuy nhin, nh khai thc cng khng

nn nh gi thp s cn thit siu chnh trong vn thu v tuyn, trong mng,v cc tham s TCP/IP sao cho vic s dng phl hiu qu nht vi gi trQoS cth chp nhn c.

H thng phn ba im a knh (MMDS):

- MMDS c kin trc tng tnh kin trc LMDS. MMDS s dng tn s t 2,1GHz v 2.5-2.7 GHz. Tn hiu c pht i t trm pht sng thng c t trncc ngn i, hay to nh cao tng, ti cc anten c bit m cc anten ny nh ltrm chuyn tip pht ti cc khch hng trong phm vi nhn thng (LOS).- Ging nh cp ng, mt knh 6MHz vi iu ch c th truyn vi tc khong 30 Mbit/s v do h trt500 n 1500 thu bao. MMDS cung cp dchv vi trong vng bn knh 60km. y l u im nu so vi cng ngh LMDS,


44/104



bi v bn knh phc v ti a ca LMDS chl 5 km. MMDS l gii php l tngcho cc vng nng thn ni m k thut vin thng cha pht trin.- Nhng h thng ny cpht trin ln u tin ti US, Hng Kng, Canada, vc. Chu Phi, MMDS c s dng ti cc nc GaBon v Senegal. Chu u,cc h thng th nghim v ang hot ng ti cc nc Ireland, Iceland, v Php.Hu ht cc mng MMDS ang hot ng s dng bng tn 2,5-2,7 GHz, truyndn khong 30 knh s dng nh dng NTSC ( rng 6 MHz) v khong 20 knhs dng nh dng PAL hoc SECAM ( rng 8 MHz).- So snh cc c tnh chnh ca hai cng nghLMDS v MMDS vi WiMAX cnh 802.16-2004 qua cc thng schnh c thnh sau:

Bng 1.3 So snh gia chun 802.16-2004 v LMDS, MMDS

Chun 802.16-2004 LMDS MMDS

Phng thc iu

ch

OFDM/ TDMA

OFDMAn/a n/a

Ph tn s2-11GHz

10 - 66 GHz26/28, 40 GHz

2,1 GHz

2,5 - 2,7 GHz.

iu kin truyn LOS v NLOS LOS LOS

Tc ti ati 134 Mbps

(28 MHz)ti 3 Gbps 10 Mbps

Bng thng knh 1,25 - 28 MHz1,25MHz

5MHz5 MHz

Hiu sut 5bps/Hz 3,2 bps/Hz


45/104



- Tng tnh vy, CDMA 2000 c pht trin tng khnng truyn dn sliu ti phin bn 1x EVDO-Rev 0 v 1x EVDO-Rev A. Mt nng cao na l phinbn EVDO Rev B a vo khnng a sng mang.- Do 1xEVDO v HSDPA/HSPA c pht trin t tiu chun CDMA 3G cung cp dch v s liu thng qua mng ban u c thit k cho dch v thoi ding do n tha hng c nhng u im v c nhng hn ch ca h thng 3G.WiMAX ban u c pht trin cho truy nhp v tuyn bng rng cnh v nc ti u cho truyn s liu. WiMAX di ng c pht trin trn c s caWiMAX cnh v c iu chnh ph hp cho yu cu di ng. Vic so snhgia cc thuc tnh ca WiMAX di ng vi 3G trn c sh thng 1x EVDO vHSDPA/HDPA s cho ta thy r cng nghno sp ng c cc i hi camng ch v s liu bng rng di ng. Cc thuc tnh c thc a ra trongbng sau:

Bng 1.4 So snh WiMAX di ng v 3G

Thuc tnh 1x EVDO Rev AHSDPA/HSUPA

(HSPA)WiMX di ng

Tiu chun c sCDMA2000/IS-

95WCDMA IEEE802.16e

P.P song cng FDD FDD TDD

Hng sung (DL) TDM CDM-TDM

OFDMAa truy nhp h.ln

(UL)CDMA CDMA

rng bng 1,25 MHz 5,0 MHz5; 7; 8,75; 10

MHz

Kch ckhungDL 1,67 ms 2 ms

5 ms TDD

UL 6,67 ms 2/ 10 ms

iu ch DLQPSK/ 8PSK/

16QAMQPSK/ 16QAM

QPSK/ 16QAM/

64 QAM


46/104



iu ch ULBPSK, QPSK/

8PSKBPSK/ QPSK/ 16 QAM

M ha Turbo CC, Turbo CC, Turbo

Tc nh DL 3,1 Mbps 14 Mbps

46 Mbps,

DL/UL=3

32 Mbps,

DL/UL=1

Tc nh UL 1,8 Mbps 5,8 Mbps

7 Mbps,

DL/UL=1

4 Mbps,

DL/UL=3

H-ARQng b4 knh

nhanh IR

ng b6 knh

nhanh CC

ng ba knh

CC

Lp lchLp lch nhanh

DL

Lp lch nhanh

UL

Lp lch nhanh

DL v UL

Chuyn vng

(Handoff)

Chuyn vng

mn o

Ch. vng cng

khi u t mng

Ch. vng cng

khi u t mng

1.7.3 So snh WiMX di ng vi WiBro- Mng WiBro c Hn Quc trin khai th nghim v a vo khai thc tgia nm 2006. WiBro l tn vit tt ca cc t Korean Wireless Broadbandservice. y l mt mng truy nhp bng rng da trn tiu chun IEEE 802.16e,tuy nhin tnh nng p dng ca tiu chun ny khc vi cc tnh nng m din nWiMAX a ra cho WiMAX di ng nn mng ny khng thc sl WiMAX ding, v n nay WiBro phin bn 1 khng th hot ng c vi mng WiMAXdi ng. S khc bit gia WiMAX di ng v WiBro c minh ha nh hnh

sau:


47/104



Hnh 1.17 Phm vi ca WiMAX di ng v WiBro trong chun 802.16e

- Cc c tnh ca hai phin bn WiMAX v WiBro c so snh c thnh bng

sau:

Bng 1.5 Cc c tnh chnh ca WiMAX di ng v WiBro

c tnh WiMax di ng WiBro

Bng tn 2,3; 2,5 v 3,5 GHz 2,3 GHz

Bng thng 3,75; 5; 8,75; 10 MHz 8,75 MHz

di khung 5 ms, 48 k t 5 ms, 48 k t

Tc v tr


48/104



ni mng khng dy. y l cng ngh mng v tuyn c thng mi ha tintin th gii hin nay.- Mt mng Internet khng dy Wifi thng gm 3 b phn c bn: im truy cp(Access Point AP); card giao tip mng (Network Interface Card NIC); v b

phn thu pht, kt ni thng tin ti cc nt mng gi l Wireless CPE. Trong ,Access Point ng vai tr trung tm ca ton mng, l im pht v thu sng, traoi thng tin vi tt c cc my trm trong mng, cho php duy tr kt ni hocngn chn cc my trm tham gia vo mng. Mt Access Point c th cho php tihng ngn my tnh trong vng ph (khong 150m ) sng truy cp mng cng lc.- Wifi c bit thch hp cho nhu cu s dng di ng v cc im truy cp ngngi dng. N cho php ngi s dng truy cp mng ging nh khi s dng cngngh mng my tnh truyn thng ti bt c thi im no trong vng ph sng.Thm vo , Wifi c linh hot v kh nng pht trin mng ln do khng b

nh hng bi vic thay i li v tr, thit k li mng my tnh. Cng v l mngkhng dy nn Wifi khc phc c nhng hn ch v ng cp vt l, gim cnhiu chi ph trin khai thi cng dy mng v khng phi tc ng nhiu ti c sh tng.- Hn chca Wifi:

Gi c l tr ngi u tin i vi dch v ny. Chi ph ban u cho vic thit lpmt mng Wifi thng tn km hn nhiu so vi mng LAN thng thng. Vit

Nam, chi ph cho mt mng khng dy, gm tin thu ng mng, 3 Access Pointv khong hn 40 card modem khng dy cng cc thit b ng b khc tn

khong gn 100.000 USD. Thc ra, chi ph ny khng cao hn l bao so vi victhit lp mt mng LAN vi s ngi dng tng ng, m theo mt doanh nghipang s dng Wifi th tr ngi nm phn thit b ng b i km. Mt my tnhthng thng kt ni vo mng ch cn mt on dy nh, cn truy cp vomng khng dy phi cn ti mt card mng khng dy c gi t 60 200 USD/cihoc l my tnh tch hp sn cng ngh ny. Cng ngh khng dy c bit tngcng sc mnh cho cc thit b tnh ton di ng nh my tnh xch tay, PDA hayPocket PC.

- Kt ni WiFi nhanh nht c th truyn ln ti 54 megabit trn giy trong cc iukin ti u. WIMAX c th truyn ln ti 70 megabit trn giy. Thm ch khi m70 megabit b tch ra gia vi chc cng ty v hng trm gia nh ngi dng, tnht n s cung cp tc tng ng vi tc truyn ca modem cp cho mingi dng.- Cc c im k thut WIMAX cng cung cp cc iu kin thun li tt hnnhiu so vi WiFi, cung cp rng bng tn cao hn v an ninh d liu cao bngcch s dng cc k hoch m ha tng cng. WIMAX cng c th cung cp dchv theo c hai a im LOS v NLOS, nhng c ly s thay i cho ph hp.

WIMAX cho php thm nhp vo dch v bng rng VoIP, video, v truy cp


49/104



internet ng thi. Cc anten WIMAX c thchia s mt thp cell m khng cndn xp chc nng ca cc mng tong thch hp.


50/104

Tm hiu cng ngh Voip trong Wimax 50

Chng 2-Tng quan vcng ngh Voip

CHNG 2-TNG QUN V CNG NGH VOIP

2.1GII THIU V CNG NGH VOIP2.1.1 Gii thiu chung

- Internet Voice, cng c bit nh thoi qua giao thc Internet, l mt cngnghm cho php to cuc gi dng kt ni bng thng rng thay v dng ngdy in thoi tng t. Nhiu dch v dng Voice over IP c th ch cho phpchng ta gi ngi khc dng cng loi dch v, tuy nhin cng c nhng dch vcho php gi nhng ngi khc dng sin thoi nh s ni b, ng di, ding, quc t. Trong khi cng c nhng dch v chlm vic qua my tnh, hay loiin thoi qua IP (IP phone) c bit. Cng c vi dch vcho php dng in thoitruyn thng qua mt biu hp (adaptor).

Hnh 2.1 Kin trc VoIP n gin ha

- VoIP cho php thc hin cuc gi dng my tnh qua mng d liu nh Internet.VoIP chuyn i tn hiu thoi ttng tanalog thnh tn hiu strc khi truynqua Internet, sau chuyn i ngc li u nhn. Khi to mt cuc gi VoIPdng in thoi vi mt biu hp, chng ta snghe m mi gi, quay s s xyra sau tin trnh ny. VoIP c thcng scho php to mt cuc gi trc tip tmy tnh dng loi in thoi tng ng hay dng microphone.- VoIP cho php to cuc gi ng di qua mng d liu IP c sn thay v phic truyn qua mng PSTN. Ngy nay nhiu cng ty thc hin gii php VoIPca h gim chi ph cho nhng cuc gi ng di gia nhiu chi nhnh xanhau.

- Trc y, khi da vo giao tip thoi trn mng PSTN, trong sut cuc gi giahai a im, ng kt ni c dnh ring cho bn thc hin cuc gi. Khng c

thng tin khc c th truyn qua ng truyn ny, cho d vn cn tha lng bngthng sn dng. Sau vi s xut hin ca mng giao tip d liu, nhiu cng ty


51/104



u t cho mng giao tip d liu chia s thng tin vi nhau, trong khi thoi v fax vn tip tc s dng mng PSTN.- Nhng ngy nay iu ny khng cn l vn na, vi s pht trin nhanhchng v c s dng rng ri ca IP, chng ta tin rt xa trong khnng gimchi ph trong vic h trtruyn thoi v d liu. Gii php tch hp thoi vo mngd liu, v cng hot ng bn cnh vi h thng PBX hin ti hay nhng thit bin thoi khc, n gin cho vic mrng khnng thoi cho nhng vtr xa.Lu lng thoi thc cht sc mang tdo bn trn mng d liu thng qua csh tng v thit b phn cng c sn.- Mc d nhng khi nim v VoIP l n gin, nhng thc hin v ng dngVoIP l phc tp. gi thoi, thng tin phi c tch bit thnh nhng gi(packet) ging nh d liu. Gi l nhng phn thng tin c chia nh ddngcho vic gi gi, cng c thdng k thut nn gi tit kim bng thng, thng

qua nhng tin trnh codec (compressor/de-compressor).- C rt nhiu loi giao thc dng thc hin dch v VoIP, nhng giao thc bohiu (signaling) VoIP ph bin l SIP v H323. C SIP v H323 u cho phpngi dng thc hin cng cng vic: thit lp giao tip cho nhng ng dng a

phng tin (multimedia) nh audio, video, nhng giao tip d liu khc. NhngH323 ch yu c thit k cho nhng dch va phng tin, trong khi SIP th

ph hp cho nhng dch v VoIP.- RTP nh ngha nh dng chun ca gi tin cho vic phn phi audio v videoqua Internet.

- Cc thng s c bn ca Voip bao gm: Kch thc ti trng thoi (Voice payload size): l kch thc (byte) ca 1gi c to ra t b CODEC.

Kch thc gi (Packet size):l kch thc (byte) ca 1 gi bao gmRTP/UDP/IP overhead. S gi tingiy (PPS): S gi tin to ra trong 1 giy. PPS=CODEC BitRate/Voice Payload Size. Thi giangi (Packet duration): l thi gian gia cc bit start ca 2 gi

lin tip. Packet Duration=1/PPS.

2.1.2 Nguyn l lm vic- Trong dch vin thoi IP c thc s tham gia ca 3 loi i tng cung cpdch vnh sau:

Nh cung cp dch v IPS Nh cung cp dch vin thoi Internet ITSP

Nh cung cp dch v trong mng chuyn mch knh- c th s dng c dch v in thoi IP, ngi s

dng cn thng qua mng Internet v cc chng trnh ngdng cho in thoi IP. Trong khi cc nh cung cp dch


52/104



v Internet cung cp s truy cp Internet cho khch hng

ca h th cc nh cung cp dch v in thoi ITSP cung

cp dch v in thoi IP cho khch hng bng cch s

dng cc chng trnh ng dng dng cho in thoi IP.C th ni rng dch v truy cp Internet cung cp bi

cc ISP cha cung cp dch v in thoi IP. Ngis dng cn phi truy nhp vo nh cung cp dch v in

thoi IP khi s dng in thoi IP. H khng th gi

hoc nhn cc cuc m thoi thng qua dch v in

thoi IP nu ch c truy nhp vo mng Internet. phc

v cho vic truyn thng gia nhng ngi s dng trncc my tnh u cui ca mng Internet, cc cng ty

phn mm cung cp cc chng trnh ng dng dng cho

in thoi IP thc hin vai tr ca ITSP. i vi ngis dng trn mng chuyn mch knh, h s truy nhp vo

ISP hoc ITSP thng qua cc im truy nhp trong mng

chuyn mch knh.

- VoIP da trn s kt hp ca mng chuyn mch knh v

chuyn mch gi l mng IP. Mi loi mng c nhng c

im khc bit nhau. Trong mng chuyn mch knh mt

knh truyn dn dnh ring c thit lp gia hai thitb u cui thng qua mt hay nhiu nt chuyn mch

trung gian. Dng thng tin truyn trn knh ny l dng

bit truyn lin tc theo thi gian. Bng thng ca knh

dnh ring c m bo v c nh trong qu trnh linlc (64Kbps i vi mng in thoi PSTN), v tr

thng tin l rt nh ch c thi gian truyn thng tin

trn knh. Khc vi mng chuyn mch knh, mng chuyn

mch gis dng h thng lu tr ri truynti cc nt

mng. Thng tin c chia thnh cc gi, mi gi uc

thm cc thng tin iu khin cn thit cho qu trnhtruyn nhl a ch ni gi, a ch ni nhn... Cc

gi thng tin n nt mng c x l v lu tr trong

mt thi gian nht nh ri mi c truyn n nt tiptheo sao cho vic s dng knh c hiu qu cao nht.

Trong mng chuyn mch gikhng c knh dnh ring no

c thit lp, bng thng ca knh logic gia hai thit

b u cui thng khng c nh, v tr thng tinln hn mng chuyn mch knh rt nhiu.

- K thut s ha cho php truyn thng c tn hiu tng t gia cc imcch xa nhau mt cch kh trung thc. Tuy nhin nhc im c bn ca s ha


53/104



l n s lm tng rng bng tn cn thit. Trong mng in thoi thng thngtn hiu c m ha theo lut A hoc lut vi tc 64kps. Vi cch m hany cho php khi phc mt cch tng i trung thc cc m thanh vi tc cng thp cng tt. T xut hin mt s k thut m ha v nn tn hiu ting ninh G.723.1, G729A- V c bn cc b m ha ting ni c 3 loi: m ha dng sng (waveform), mha ngun (source) v m ha lai (hybrid) l s kt hp c 2 loi m ha trn.

Bng 2.1 Cc chun m ha thoi

CodecPeak rate

(kb/s)

Packet size

(bytes)

Bandwidth (gmoverheads)

Compression

gain

G.711 (PCM) 6440(5ms) 142.4kb/s 0.45

160(20ms) 83.6kb/s 0.77

G.726/G.727

(ADPCM)32

20(5ms) 110.4kb/s 0.58

80(20ms) 51.6kb/s 124

G.728 (LD-CELP) 1610(5ms) 94.4kb/s 0.68

40(20ms) 35.6kb/s 18

G.729 (CS-ACELP) 65(5ms) 86.4kb/s 0.74

20(20ms) 27.6kb/s 2.32

G.723.1 6.34(5ms) 83.5kb/s 0.77

16(20ms) 25.6kb/s 2.5

- Khi ni vo ng nghe hay microphone, ging ni s to ra tn hiu in t, lnhng tn hiu analog. Tn hiu analog c chuyn sang tn hiu s dng thutton c bit chuyn i. Nhng thit b khc nhau c cch chuyn i khcnhau nh VoIP phone hay softphone, nu dngin thoi analog thng thng th

cn mt TA. Sau ging ni c sha sc ng vo gi tin v gi trnmng IP.- Trong sut tin trnh mt giao thc nh SIP hay H323 s c dng iukhin cuc gi nh l thit lp, quay s, ngt kt ni v RTP th c dng chotnh nng m bo tin cy v duy tr cht lng dch vtrong qu trnh truyn.

2.1.3 c tnh ca mng VoIPu im:

- Gim chi ph: y l u im ni bt ca VoIP so vi in thoi ng dithng thng. Chi ph cuc gi ng di ch bng chi ph cho truy nhp Internet.Mt gi cc chung s thc hin c vi mng Internet v do tit kim ng k

8/3/2019 DATN-Tim

datn-tim hieu cong nghe voip trong wimax

Documents