ky thuat OFDM va ung dung

8/7/2019 ky thuat OFDM va ung dung

1/24

KK THUTHUT OFDMT OFDM V V NGNG DDNGNG

SV:SV: PHAN VN HPHAN VN HPP

BBI QUANGI QUANG DDNGNG


2/24

II.. TTNG QUAN VNG QUAN V OFDMOFDM

KK thuthut OFDM bt OFDM bt ngut ngun tn t k k thuthut FDMt FDM ((ghghpp

knh theo tknh theo tn sn s).).Trong FDMTrong FDM cccc ssng mang con ng mang con cctt ccch nhau mch nhau mtt khokhong tng tn sn s.. Do Do gigiaa cccc ssngng

mangmang cc mmtt khokhong tng tn sn s khng skhng s d dngng mang tinmang tin

ttc.c.


3/24

K thuK thut ghp knh phn chia tt ghp knh phn chia tn sn s trtrc giaoc giao

(OFDM_Orthogonal Frequency Division Multiplexing)(OFDM_Orthogonal Frequency Division Multiplexing) ll kk thuthut it iuuchch a sng manga sng mang.. KK thuthut ny phn chiat ny phn chia ddi ti tn cho php thnhn cho php thnhrrt nhit nhiuu ddi ti tn con vn con vi cc sng mang khc nhaui cc sng mang khc nhau,, mmi sngi sngmang ny mang ny c ic iu chu ch truytruyn mn mt dng dt dng d liliu tu tc c ththp.p.TTp hp hpp cca cc dng da cc dng d liliu tu tc c ththp ny chnh l dng dp ny chnh l dng dliliu tu tc c cao ccao cn truyn truynn tti.i.

Cc sng mang trongCc sng mang trong kk thuthut it iu chu ch a sng mang la sng mang l hh ccccsng mang trsng mang trc giaoc giao.. iiu ny cho php ghp chu ny cho php ghp chng phng ph gigiaa

cc sng mangcc sng mang mm khng gy nhikhng gy nhiuu.. Do sDo s d dngng ddi thngi thngmmt cch c hit cch c hiuu ququ..


4/24


5/24

IIII.. TRTRC GIAO TRONG OFDMC GIAO TRONG OFDM

Tn hiTn hiu u cc ggi l tri l trc giao nhau nc giao nhau nu chng u chng c lc lp vp viinhaunhau.. TrTrc giao l mc giao l mt t c tnh cho php nhic tnh cho php nhiu tn hiu tn hiu mangu mangtin tin c truyc truyn i trn knh truyn i trn knh truyn thng thn thng thng m khng cng m khng cnhinhiu giu gia chnga chng.. MMt tnh trt tnh trc giao gic giao gia cc tn hia cc tn hiuu ss gygyra s ri lon gia cc tn hiu, lm gim cht lng thng tin.ra s ri lon gia cc tn hiu, lm gim cht lng thng tin.

OFDM t c s trc giao bng cch iu ch tn hiu voOFDM t c s trc giao bng cch iu ch tn hiu vomt tp cc sng mang trc giao. Tn s gc ca tng sngmt tp cc sng mang trc giao. Tn s gc ca tng sngmang con s bng mt s nguyn ln nghch o thi gian tnmang con s bng mt s nguyn ln nghch o thi gian tnti ca symbol. Nh vy trong thi gian tn ti symbol, miti ca symbol. Nh vy trong thi gian tn ti symbol, misng mang s c mt s nguyn ln chu k khc nhau, mc dsng mang s c mt s nguyn ln chu k khc nhau, mc d

ph tn ca chng chng ln ln nhau nhng chng khng gyph tn ca chng chng ln ln nhau nhng chng khng gynhiu cho nhaunhiu cho nhau


6/24

Tnh trc giao ca cc sng mang con th hin ch: ti miTnh trc giao ca cc sng mang con th hin ch: ti minh ca mt sng mang con bt k trong nhm th cc sngnh ca mt sng mang con bt k trong nhm th cc sngmang con khc bng 0. pha thu, khi dng DFT tch sngmang con khc bng 0. pha thu, khi dng DFT tch sngtn hiu OFDM th ph ca n khng cn l lin tc m l cctn hiu OFDM th ph ca n khng cn l lin tc m l ccmu ri rc. Cc mu c biu din bi cc khuyn trnmu ri rc. Cc mu c biu din bi cc khuyn trn(o) trn hnh v. Nu DFT c ng b thi gian th tn s(o) trn hnh v. Nu DFT c ng b thi gian th tn smu ca DFT s tng ng vi nh ca cc sng mang con.mu ca DFT s tng ng vi nh ca cc sng mang con.V c nh vy th s chng ph ca cc sng mang con khngV c nh vy th s chng ph ca cc sng mang con khngnh hng n my thu.nh hng n my thu.


7/24

IIIIII.. NGUYNNGUYN LL THUTHU PHPHT OFDMT OFDM


8/24

IVIV.. NHINHIU TRONG OFDMU TRONG OFDM

NHINHIU ISIU ISI TTn hiu c biu din cng tri di trong min thi gian th cn hiu c biu din cng tri di trong min thi gian th cph cng hp trong miph cng hp trong min tn tn sn s v ngc li, tn hiu c phv ngc li, tn hiu c ph

trong min tn s cng rng th biu din trong min thi giantrong min tn s cng rng th biu din trong min thi giancng hpcng hp

Tn hiu cn truyn qua knh c biu din trong min thi gian l hp ( v chTn hiu cn truyn qua knh c biu din trong min thi gian l hp ( v chtrong thtrong thi gian t ri gian t rt ngnt ngn)) v th n c ph tn s rv th n c ph tn s rt rngt rng.. Trong khi Trong khi knhknhtruyn tin th c bng thng c hn nn khi pht tn hiu qua knh ph tn catruyn tin th c bng thng c hn nn khi pht tn hiu qua knh ph tn ca

tn hiu b bng tn cho php ca knh ct ngntn hiu b bng tn cho php ca knh ct ngn.. Do Do tn hiu thu c c phtn hiu thu c c phtn hp. Khi chuyn qua min thi gian th n li l ko di nntn hp. Khi chuyn qua min thi gian th n li l ko di nn 22 tn hiu gntn hiu gnnhau c phn ko di chng ln ln nhau gy ra nhinhau c phn ko di chng ln ln nhau gy ra nhiu ISIu ISI


9/24

Nh ta bit, di thng ca mt tn hiu OFDM s bng diNh ta bit, di thng ca mt tn hiu OFDM s bng dithng cho trc trn chia cho N sng mang con. Do vy tcthng cho trc trn chia cho N sng mang con. Do vy tc bit ca mi tn hiu OFDM s nh hn N ln tc bit trn bit ca mi tn hiu OFDM s nh hn N ln tc bit trnmt sng mang trong h thng n sng mang. Tc symbolmt sng mang trong h thng n sng mang. Tc symboltrn sng mang con thp to cho OFDM c kh nng chu ISItrn sng mang con thp to cho OFDM c kh nng chu ISIrt ttrt tt

Tuy nhin, cn c th ci thin hn na kh nng chu ISI caTuy nhin, cn c th ci thin hn na kh nng chu ISI cah thng OFDM bng cch chn thm cc di bo v vo trch thng OFDM bng cch chn thm cc di bo v vo trcmi symbol. Di bo v ca mi symbol l mt phn bn saomi symbol. Di bo v ca mi symbol l mt phn bn saoca chnh symbol , thng th ngi ta hay dng phn cuica chnh symbol , thng th ngi ta hay dng phn cuica symbol lm di bo v.ca symbol lm di bo v.

Chn thm di bo v lm thi gian truyn ca symbol tngChn thm di bo v lm thi gian truyn ca symbol tngln, do lm tng kh nng chu ISI. Mi sng mang conln, do lm tng kh nng chu ISI. Mi sng mang conmang mt phn tin tc ca 1 symbol, dng mt phn symbolmang mt phn tin tc ca 1 symbol, dng mt phn symbollm di bo v cn to cho vic truyn dn c lin tc,lm di bo v cn to cho vic truyn dn c lin tc,khng c s ngt qung gia cc symbol.khng c s ngt qung gia cc symbol.


10/24


11/24

Tng chu k k t lc ny lTng chu k k t lc ny lTtotal = Tg + TTtotal = Tg + T

Tg l khong thi gian bo vTg l khong thi gian bo v

T l chu k thc ca k t.T l chu k thc ca k t.

Khi khong bo v di hn p ng xung ca knh hayKhi khong bo v di hn p ng xung ca knh haytr a ng th nhiu xuyn k t ISI c loi b.tr a ng th nhiu xuyn k t ISI c loi b.

Mc ch dng khong bo v trc chu k k t lMc ch dng khong bo v trc chu k k t lduy tr ng b pha thu, tn hiu thay cho mt khongduy tr ng b pha thu, tn hiu thay cho mt khongdi im lng lun c truyn i.di im lng lun c truyn i.


12/24

NHI

NHI

UICIU

ICI

ICI l hin tng ph bin trong cc h thng a sng mang. Trong h thng OFDM,ICI l hin tng ph bin trong cc h thng a sng mang. Trong h thng OFDM,ICI cn c gi l nhiu giao thoa gia cc sng mang con, l hin tng nng lngICI cn c gi l nhiu giao thoa gia cc sng mang con, l hin tng nng lngph ca cc sng mang con chng ln qu mc ln nhau lm ph v tnh trc giao caph ca cc sng mang con chng ln qu mc ln nhau lm ph v tnh trc giao cacc sng mang con.cc sng mang con.

Nguyn nhn v nh hng ca ICINguyn nhn v nh hng ca ICIICI xy ra do tnh chn lc tn s ca knh pha inh (knh pha inh chn lc tn s),ICI xy ra do tnh chn lc tn s ca knh pha inh (knh pha inh chn lc tn s),nguyn nhn chnh l hin tng dch Doppler do tnh di ng ca my thu. Hu qu lnguyn nhn chnh l hin tng dch Doppler do tnh di ng ca my thu. Hu qu ls khng phn bit c ranh gii gia cc k hiu truyn trn cc sng mang con, dns khng phn bit c ranh gii gia cc k hiu truyn trn cc sng mang con, dnn pha thu s quyt nh sai k hiu mt tnh trc giao.n pha thu s quyt nh sai k hiu mt tnh trc giao.

Gii php khc phcGii php khc phcC th hn ch ICI bng cch chn khong thi gian bo v mt cch tun hon, vC th hn ch ICI bng cch chn khong thi gian bo v mt cch tun hon, vdng b cn bng knh c h tr bi hoa tiu (PSAM). Cc hoa tiu gip cho vicdng b cn bng knh c h tr bi hoa tiu (PSAM). Cc hoa tiu gip cho vicc tnh, cn bng c thc hin b .c tnh, cn bng c thc hin b .


13/24

VI. U IM V NHC IM CA OFDMVI. U IM V NHC IM CA OFDM

u imu im S dng c hiu qu bng thng v cc knh con c th chngS dng c hiu qu bng thng v cc knh con c th chng

gi ln nhau m gy nhiu rt t do cc sng mang con trcgi ln nhau m gy nhiu rt t do cc sng mang con trcgiao vi nhau.giao vi nhau.

OFDM cho php truyn dn tc cao trong mi trng diOFDM cho php truyn dn tc cao trong mi trng ding v chu k tn hiu tng nn dung sai tri tr ca h thngng v chu k tn hiu tng nn dung sai tri tr ca h thngtng v hiu qu s dng ph tn cao ca cng ngh OFDMtng v hiu qu s dng ph tn cao ca cng ngh OFDM

Chu k k t tng ln v vy nhy cm ca h thng vi triChu k k t tng ln v vy nhy cm ca h thng vi trirng tr gim xung.rng tr gim xung.


14/24

Nhc imNhc im

Tn hiu OFDM b nh hng bi mo phi tuyn caTn hiu OFDM b nh hng bi mo phi tuyn cab khuch i cng sut pha pht v n l t hp cab khuch i cng sut pha pht v n l t hp ca

iu ch bin iu ch bin -- tn s,tn s,

OFDM nhy cm vi dch tn s sng mangOFDM nhy cm vi dch tn s sng mang

bn thu kh quyt nh thi im bt u FFT bn thu kh quyt nh thi im bt u FFT


15/24

VIIVII.. NGNG DDNGNG CCA OFDMA OFDM

1.1. pht thanh s dabpht thanh s dab..

Mt knh OFDM c th truyn mt vi ch-ngMt knh OFDM c th truyn mt vi ch-ng trnhtrnhpht thanh, mi ch-ngpht thanh, mi ch-ng trnhtrnh c th c cht l-ng thayc th c cht l-ng thay

i mono hay stereo. Mi knh audio -c m ha -ci mono hay stereo. Mi knh audio -c m ha -cm ha m thanh vi tc t 32 Kbps n 382 Kbps.m ha m thanh vi tc t 32 Kbps n 382 Kbps.Dng bt ny -c m ha vng xon vi tc m 1/2Dng bt ny -c m ha vng xon vi tc m 1/2v -c ci xen (interleaving). Cc dng bt -c ghpv -c ci xen (interleaving). Cc dng bt -c ghpknh theo thi gian v -a ti b iu ch OFDM. Tcknh theo thi gian v -a ti b iu ch OFDM. Tc

bit tng cng l 3.2 Mbps. Bi bit tng cng l 3.2 Mbps. Bi vv tc ca cctc ca ccknh audio -c truyn trong mt knh OFDM cngknh audio -c truyn trong mt knh OFDM cngthay i theo. Mt h thng inthay i theo. Mt h thng in hnhhnh truyn 6 knhtruyn 6 knhaudio vi tc 192 Kbps.audio vi tc 192 Kbps.


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17/24

22.. truyntruyn HNHHNH s dvb.s dvb.

TruynTruyn hnhhnh s qung b DVB (Digitals qung b DVB (Digital

Video Broadcasting) l mt khi nim rngVideo Broadcasting) l mt khi nim rngbao gm truynbao gm truyn hnhhnh, cc ng dng a, cc ng dng aph-ng tin di ng (Mutilmedia Mobileph-ng tin di ng (Mutilmedia MobileAplication) v cc dch v cung cp dAplication) v cc dch v cung cp d

liu khng dy.liu khng dy.


18/24


19/24

OFDM -c s dng trong truynOFDM -c s dng trong truyn hnhhnh s DVBs DVB vv:: Loi b nhiu: s tn ti ng thi ca truynLoi b nhiu: s tn ti ng thi ca truyn hnhhnh s vs v

truyntruyn hnhhnh t-ng t yu cu h thng tuyt i khngt-ng t yu cu h thng tuyt i khnggy nhiu vi truyngy nhiu vi truyn hnhhnh t-ng t v cc nhiut-ng t v cc nhiubngbng

hp khc, bihp khc, bi vv truyntruyn hnhhnh t-ng t rt nhy cm vit-ng t rt nhy cm vinhiu.nhiu. Hiu ng a -ng: sng truyn theo nhiu -ng tiHiu ng a -ng: sng truyn theo nhiu -ng ti

my thu vi tr truyn dn khc nhau l nguyn nhnmy thu vi tr truyn dn khc nhau l nguyn nhnchnh lm suy gim cht l-ng cc knh truynchnh lm suy gim cht l-ng cc knh truyn hnhhnh mtmtt. Kin trc mng n tn SFN ca DVB to ra nhiut. Kin trc mng n tn SFN ca DVB to ra nhiu

tn hiu cng ti my thu t cc trm pht khc nhau v dotn hiu cng ti my thu t cc trm pht khc nhau v dophn x thng th-ng. S tn ti ca nhiu tn hiu viphn x thng th-ng. S tn ti ca nhiu tn hiu vi tr khc nhau ti my thu yu cu mt k thut iu tr khc nhau ti my thu yu cu mt k thut iuch mnh chng li hiu ng ny. OFDM cho phpch mnh chng li hiu ng ny. OFDM cho phploi b hon ton hiu ng a -ng min l di caloi b hon ton hiu ng a -ng min l di cakhong bo v GI -c thit k mt cch hp l.khong bo v GI -c thit k mt cch hp l.


20/24

33.. mmng lan khng dy (wireless lan).ng lan khng dy (wireless lan).cc tnh ca Wireless LAN l tc cao,tnh ca Wireless LAN l tc cao,

tnh di ng thp, tri tr truyn dn thptnh di ng thp, tri tr truyn dn thpv th-ng -c s dng mi tr-ng trong nh.v th-ng -c s dng mi tr-ng trong nh.Do Wireless LAN chn ph-ng thc iuDo Wireless LAN chn ph-ng thc iuch OFDM:ch OFDM:

OFDM gii quyt -c khOFDM gii quyt -c kh khnkhn ca Wirelessca WirelessLAN l b phn xLAN l b phn x a -ng ln do cc vt th a -ng ln do cc vt th

trong nh gy nn. Mc d tri tr do phntrong nh gy nn. Mc d tri tr do phnxx a -ng l nh nh-ng do truyn dn tc a -ng l nh nh-ng do truyn dn tc cao, chu k symbol nh nn nh h-ng ca trcao, chu k symbol nh nn nh h-ng ca tra -ng ti h thng Wireless LAN l rt ln.a -ng ti h thng Wireless LAN l rt ln.

T-ng i hiu qu trong vic s dngT-ng i hiu qu trong vic s dngbngbng

thng.thng.


21/24

Thch hp vi tc truyn thay i.Thch hp vi tc truyn thay i.

Chng nhiuChng nhiubngbng hp tt. Nhiuhp tt. Nhiubngbng hp gyhp gyra do nhiu ng-i s dng v do cc thit bra do nhiu ng-i s dng v do cc thit b

khc gy ra.khc gy ra. Hiu qu tnh ton cao: s dng bin iHiu qu tnh ton cao: s dng bin i

Fourier nhanh FFT cho php gim phc tpFourier nhanh FFT cho php gim phc tpxung.xung.

ng b tt: my thu OFDM t chu nh h-ngng b tt: my thu OFDM t chu nh h-ngca jitter thi gian hn so vi dng k thut trica jitter thi gian hn so vi dng k thut triph.ph.


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23/24

33. -ng dy thu bao s bt i xng.. -ng dy thu bao s bt i xng.

ngng truyn thu bao s bt i xngtruyn thu bao s bt i xngADSL l cng ngh -c ng dng v pht trinADSL l cng ngh -c ng dng v pht trin

nhiunhiu vv n t-ng thch vi cc h thng hin tn t-ng thch vi cc h thng hin tiiv ph hp vi nhu cu ca ng-i dng. ADSLv ph hp vi nhu cu ca ng-i dng. ADSLtruyn ti c thng tin s v t-ng t trn mttruyn ti c thng tin s v t-ng t trn mti dy ng. Knh truyn dn ADSL c thi dy ng. Knh truyn dn ADSL c th

chia thnh nhiu knh s liu tc cao vchia thnh nhiu knh s liu tc cao vcng lc phc v cho c tn hiu thocng lc phc v cho c tn hiu thoi.i.


24/24

D liu sau khi -c ng khung -c -aD liu sau khi -c ng khung -c -avo m ha pht hin v sa li pha thu.vo m ha pht hin v sa li pha thu.

ADSL cng s dng chui m ha gm m khi,ADSL cng s dng chui m ha gm m khi,m vng xon v ci xen. Tip tn hiu sm vng xon v ci xen. Tip tn hiu s

-c kt hp vi pilot ri qua b bin i d liu-c kt hp vi pilot ri qua b bin i d liuni tip thnh nhng dng s song song c tcni tip thnh nhng dng s song song c tc thp hn. Cc dng s song song ny s -c thp hn. Cc dng s song song ny s -ciu ch QAM v thc hin thut ton IFFTiu ch QAM v thc hin thut ton IFFT iu ch DMT. Sau tn hiu -c iu ch DMT. Sau tn hiu -c

iu ch s -c bin i thnh ni tip viu ch s -c bin i thnh ni tip vchn thm khong bo v CP chng ISI,chn thm khong bo v CP chng ISI,ng b khung. Cui cng tn hiu s -c quang b khung. Cui cng tn hiu s -c quab DAC bin i thnh tn hiu t-ng t b DAC bin i thnh tn hiu t-ng t truyn i.truyn i.

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ky thuat OFDM va ung dung