6630300 damh1-mc-cdma

  • View
    1.427

  • Download
    0

Embed Size (px)

Transcript

  • 1. LI NI U Trong x hi hin i ngy nay, nhu cu trao i thng tin l mt nhu cu thityu. Cc h thng thng tin di ng ra i to cho con ngi kh nng thng tin milc, mi ni. Nhu cu ny ngy cng ln nn s lng khch hng s dng thng tindi ng ngy cng tng, cc mng thng tin di ng v th c m rng ngy cngnhanh. Chnh v vy, cn phi c cc bin php tng dung lng cho cc h thngthng tin di ng hin c. H thng CDMA ra i v chng t c kh nng htr nhiu user hn so vi cc h thng trc . Hn na, so vi hai phng phpa truy nhp truyn thng l phn chia theo tn s FDMA v phn chia theo thi gianTDMA th phng php truy nhp phn chia theo m CDMA c nhng c im nitri: chng nhiu a ng, c tnh bo mt cao, h tr truyn d liu vi tc khc nhau Tuy nhin, trong tng lai, nhu cu v cc dch v s liu s ngy cngtng, mng thng tin di ng khng ch p ng nhu cu va i va ni chuyn mcn phi cung cp cho ngi s dng cc dch v a dng khc nh truyn d liu,hnh nh v video Chnh v vy, vn dung lng v tc cn phi c quantm. Trong nhng nm gn y, k thut ghp knh theo tn s trc giao OFDM(Orthogonal Frequency Division Multiplexing), mt k thut iu ch a sng mang,c s dng rng ri trong cc ng dng v tuyn cng nh hu tuyn. u imca OFDM l kh nng truyn d liu tc cao qua knh truyn chn lc tn s,tit kim bng thng, h thng t phc tp do vic iu ch v gii iu ch a sngmang bng gii thut IFFT v FFT. p ng nhu cu ngy cng cao ca ngi s dng, tng v k thutMC-CDMA ra i, da trn s kt hp ca CDMA v OFDM. MC-CDMA k thatt c nhng u im ca CDMA v OFDM: tc truyn cao, tnh bn vng vifading chn lc tn s, s dng bng thng hiu qu, tnh bo mt cao v gim phc tp ca h thng. Chnh v vy, MC-CDMA l mt ng c vin sng gi cho hthng thng tin di ng trong tng lai. Nhim v ca ti: Tm hiu mng thng tin di ng s dng k thut MC-CDMA (Multicarrier Code Division Multiple Access).

2. AMH in t - Vin thng 1Mc lc TM HIU H THNG THNG TIN DI NG DNG K THUT MC CDMALi ni uChng 1: GII THIU CHUNG 11.1 Khi qut v H thng di ng t bo 11.2 S pht trin ca H thng thng tin di ng 3Th h th nht (1G) 3Th h th hai (2G)4Th h th 3 (3G)4Con ng i ln 3G ca Vit Nam 41.3 Knh truyn v tuyn v cc hin tng nh hngn cht lng knh truyn 5 1.3.1 Cc hin tng nh hng n cht lng knh truyn 5 a. Hiu ng a ng (Multipath)5 b. Hiu ng Dopler6 c. Hiu ng bng rm (Shadowing)6 1.3.2 Cc dng knh truyn6 a. Knh truyn chn lc tn s v Knh truyn Fading phng6 b. Knh truyn chn lc thi gian v Knh truyn khng chn lc thi gian 81.4 Cc k thut a truy nhp 91.4.1 Gii thiu chung91.4.2 FDMA : a truy nhp phn chia theo tn s101.4.3 TDMA : a truy nhp phn chia theo thi gian 111.4.4 CDMA : a truy nhp phn chia theo m12Chng 2: K THUT A TRUY NHP PHN CHIA THEO M (CDMA) 132.1 Gii thiu 132.2 K thut tri ph132.2.1 Gii thiu chung2.2.2 Chui nh phn gi ngu nhin (PRBS) 152.2.3 K thut tri ph bng cch phn tn ph trc tip (DS SS) 162.2.4 K thut tri ph bng phng php nhy tn s (FH SS) 192.2.5 K thut tri ph bng phng php nhy thi gian (TH SS)222.2.6 Cc chui tri ph 232.3 Nguyn l CDMA 242.4 My thu RAKE 25 Tm hiu H thng TTD dng k thut MC-CDMA 3. AMH in t - Vin thng 1Mc lc2.5 iu khin cng sut 262.5.1 Hiu ng Gn Xa262.5.2 iu khin cng sut 272.6 Chuyn giao (Handoff)272.6.1 Chuyn giao mm282.6.2 Chuyn giao cng 282.7 H hng DS CDMA292.8 W CDMA (Wideband Code Division Multiple Access)29Chng 3: MC CDMA (Multi Carrier Code Division Multiplexing Access)313.1 OFDM (Orthogonal Frequency Division Multiplexing)313.1.1 Gii thiu 313.1.2 Nguyn tc c bn ca OFDM 323.1.3 Tnh trc giao 333.1.4 H thng OFDM363.1.5 Chng nhiu lin k hiu (ISI) bng cch s dng khong bo v 383.1.6 u, khuyt im ca OFDM 403.1.7 Kt lun 403.2 MC CDMA413.2.1 Gii thiu 413.2.2 Nguyn l chung ca k thut MC CDMA 423.2.3 My pht v my thu MC CDMA theo m hnh 1 433.3 u, khuyt im ca h thng TTD dng k thut MC CDMA45 3.3.1 u im 45 3.3.2 Khuyt im 453.4 S khc nhau gia MC CDMA v OFDMA 46Kt lun v hng pht trin ti47Cc ch vit tt 48Ti liu tham kho 50 Tm hiu H thng TTD dng k thut MC-CDMA 4. AMH in t - Vin thng 1 Chng 1: Gii thiu chungCHNG 1:GII THIU CHUNG1.1 KHI QUT V H THNG DI NG T BOThay v dng cc my pht sng v tuyn cng sut cc ln cung cp ccdch v thng tin di ng cho mt lng ln users trong mt vng rng ln th thngtin t bo chia cc vng a l thnh cc (cell), mi s dng my pht sng cngsut nh hn v cc b iu khin c gi l trm gc (BS Base Station). Cc ny kt hp li to thnh mng t bo nh hnh 1.1.Cc trm gc (BS) c iukhin bi Trung tm chuynmch di ng (MSC MobileSwitching Center), cc MSC nyli c iu khin bi Mngin thoi chuyn mch cngcng (PSTN Public SwitchedTelephone Network).Hnh 1.1. H thng di ng t bo Tm hiu H thng TTD dng k thut MC-CDMATrang 1 5. AMH in t - Vin thng 1Chng 1: Gii thiu chungTrong h thng thng tin di ng t bo, tn s m cc my di ng s dngl khng c nh mt knh no m thay i ty theo v tr ca user. Mi cgn cho mt nhm tn s. V vy, cc k cn nhau s dng cc nhm tn s khcnhau trnh nhiu ng knh. Cn cc cch xa mt khong cch nht nh thc th s dng li nhm tn s (Frequency Reuse). Nh vy m dung lng cah thng c th c tng ln m khng cn tng thm di tn.iu ny c minh ho trong hnh 1.2.Ta nhn thy c mt nhm 7 cells tn sc s dng li. Nhm 7 cells ny cgi l 1 cluster.V d : cell th nht (c nh s 1)ca cluster ny s s dng cng tn svi cell 1 ca cluster khc.Hnh 1.2. S dng li tn s vi cluster gm 7 cells.Khi user di chuyn t cell ny qua cell khc trong khi ang thc hin cuc gith MSC s thc hin nh tuyn li cuc gi khng lm gin on cuc gi. Qutrnh ny gi l chuyn vng (Handoff). Nhng u im ca H thng thng tin di ng t bo: + Do s dng hiu qu di tn s m dung lng ca h thng tng rt nhiu. + Cht lng ca h thng c ci thin do kh nng chng nhiu ng knh (CCI Co-Channel Interference). + Tng cht lng truy cp v chuyn vng gia cc cell. Tm hiu H thng TTD dng k thut MC-CDMA Trang 2 6. AMH in t - Vin thng 1 Chng 1: Gii thiu chung1.2 S PHT TRIN CA H THNG THNG TIN DI NGThng tin di ng pht trin qua cc th h khc nhau. 3th Generation (3G) (2000s)DigitalVoice, Internet, Media W-CDMA , CDMA2000,2nd Generation (2G)IMT-2000(1990s) Digital Voice & Data1stGeneration (1G)GSM, IS-95, PDC(1980s)Analog VoiceAMPS, NMT Th h th nht 1G :+ Cc h thng thng tin di ng 1G c xy dng t nhng nm 80V d: NMT (Nordic Mobile Telephone) ca cng ty Ericsion, Thy in. AMPS (American Mobile Phone System) ca cng ty AT&T, M+ Da trn cng ngh analog, dng k thut a truy cp phn chia theo tn s(FDMA Frequency Division Multiple Access).+ Cung cp nhng dch v ch yu l thoi.+ Cc h thng di ng 1G c pht trin trong phm vi Quc gia, do khngc kh nng tng thch ln nhau.Do yu cu thng tin di ng ngy cng cao, hn th na l nhu cu phi cmt h thng thng tin di ng ton cu. V vy, h thng thng tin di ng th hth 2 (2G) ra i. Tm hiu H thng TTD dng k thut MC-CDMA Trang 3 7. AMH in t - Vin thng 1 Chng 1: Gii thiu chungTh h th hai 2G :+ c pht trin ngay trong thp nin 90.+ Da trn cng ngh s, dng k thut a truy cp phn chia theo thi gian(TDMA Time Division Multiple Access) v a truy cp phn chia theo m (CDMA Code Division Multiple Access).+ Theo quan im ngi s dng, h thng 2G hp dn hn h thng 1G bi vngoi dch v thoi truyn thng, h thng 2G cn cung cp thm mt s dch vtruyn d liu, tuy tc cn thp.+ Cha thc hin c h thng thng tin di ng ton cu, do trn th trngtn ti mt s h thng di ng 2G nh GSM (Global System for MobileCommunication), IS-95 (Interim Standard 95), PDC (Personal Digital Celular) Trong , GSM c s dng rng ri nht.n nhng nm 2000, h thng thng tin di ng th h th 3 (3G) ra i vi mctiu hnh thnh mt h thng thng tin di ng duy nht trn ton th gii.+ Da trn cng ngh s vi s khng nh u th vt tri ca CDMA .+ C kh nng cung cp nhng dch v c tc khc nhau nh thoi, Internettc cao, truyn hnh nh cht lng cao, nhn tin a phng tin (MMS) + Cc chun cho 3G: IMT-2000, CDMA2000, W-CDMA H thng di ng 3G cha c p dng rng ri, nhng cc nghin cu v hthng 4G, m cng ngh ch yu l cc k thut a sng mang, c tinhnh v MC-CDMA l mt ng c vin sng gi. V vy, vic tm hiu v H thngthng tin di ng dng k thut MC-CDMA l cn thit v mang ngha thc t.Con ng i ln 3G ca Vit Nam:Hin nay, cc nh cung cp dch v di ng chnh Vit Nam l Mobifone,Vinaphone, S-Fone v Viettel. Con ng i ln 3G t cc cng ngh khc nhau u c: cc nh khai thc GSM s i ln W-CDMA, cn cc nh cung cp s dngcng ngh CDMA s tin ln CDMA2000. By gi ch cn vic xc nh thi imtrin khai cho ph hp.Nm 2004, Ericsson cng Mobifone th nghim thnh cng dch v di ng3G. Vo cui nm nay, nh cung cp ny d nh s a ra dch v 2,5G hay cngi l EDGE. Trong khi , Vinaphone v Viettel vn ang s dng cng ngh thucth h th 2 (2G). Tm hiu H thng TTD dng k thut MC-CDMA Trang 4 8. AMH in t - Vin thng 1Chng 1: Gii thiu chungTnh n nay, S-Fone l nh cung cp u tin v duy nht s dng cng nghCDMA. Chun m S-Fone ang s dng l CDMA2000 1X, chun ny ch cchchun 3G CDMA 2000 1X Evdo mt khong khng xa. V vy, S-Fone s c khnng tin nhanh hn trn con ng hng ti 3G.Mc d hin nay a s thu bao di ng nc ta cha c nhiu nhu cu g khchn ngoi nhu cu m thoi di ng, nhng theo tuyn b ca cc nh u t thu nm sau (2006), mng 3G ca Vit Nam s c trin khai. (theo www.vtv.vn/vi-vn/VTV1/cuocsongso/2005/12/73939.vtv)1.3 KNH TRUYN V TUYN Cht lng ca cc h thng thng tin ph thuc nhiu vo knh truyn, nim tn hiu c truyn t my pht n my thu. Khng ging nh knh truynhu tuyn l n nh v c th d on c, knh truyn v tuyn l hon tonngu nhin v khng h d dng trong vic phn tch. Tn hiu c pht i, quaknh truyn v tuyn, b cn tr bi cc to nh, ni non, cy ci , b phn x(reflection), tn x (scattering), nhiu x (diffraction), cc hin tng ny c gichung l Fading. V kt qu l my thu, ta thu c rt nhiu phin bn khc nhauca tn hiu pht. iu ny nh hng n cht lng ca h thng thng tin vtuyn.1.3.1 Cc hin tng nh hng n cht lng knh truyn: a. Hiu ng a ng (Multipath) Nhiu a ng l kt qu ca s phn x, tn x, nhiu x ca tn hiu trn knh truyn v tuyn. Cc tn hiu c truyn theo cc ng khc nhau ny u l bn sao ca tn hiu pht i nhng b suy hao v bin v b tr so vi tn hiu c truyn thng (Line of Sight). Tn hiu thu c ti my thu l tng ca cc thnh phn ny, l mt tn hiu phc tp vi bin v pha thay i rt nhiu so vi tn hiu ban u. Hnh 1.3. Hiu ng a ng Tm hiu H thng TTD dng k thut MC-CDMA Trang 5 9. AMH in t - Vin thng 1 Chng 1: Gii thiu chung b. Hiu ng Doppler:Gy ra bi s chuyn ng tng i ca my thu v my pht v s dichuyn ca cc i tng trong knh truyn v tuyn. Khi s chuyn ng tng iny cng nhanh th tn s Doppler cng ln, v do tc thay i ca knhtruyn cng nhanh. Hiu ng ny c gi l fading nhanh (fast fading). c. Hiu