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PH TN HIU DCH PH TN TN HIU_OFDM

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<p>1Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationTI LIU THAM KHO CHUYN NGHNH V TUYNKHOA VIN THNG 1Summarized by Nguyen Viet DamFaculty of Telecommunications IPosts and Telecommunications Institute of TechnologiesAddress: PTIT- Km10-Nguyen Trai Street, HaDong, HaNoiOffice : (0)84-(0)4-8549352, (0)84-(0)34- 515484Mob: 0912699394PH TN HIUDCH PH TN TN HIU_OFDM2Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationNI DUNGTN HIU V PH TN TN HIUKT LUN V THO LUNIU CH V DCH PH TN TNHIUK THUT OFDM3Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication 1.1. Tn hiu v ph tn hiu1.2. iu ch tn hiu v dch ph tn1.3. X l tn hiu trong min thi gian Time Processing1.4. X l tn hiu trong min tn s Frequency Processing14Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationTn hiu v phn loi:Tn hiu c cc gi tr thay i theo thi gian =&gt; Tn hiu tng t, tn hiu sMc c th m t hoc d on tnh cch ca hm =&gt; Tn hiu tt nh v tn hiu ngu nhin.Thi gian tn ti tn hiu (hm) =&gt; hm qu , hm v tn (tun hon)Tn hiu kiu nng lng, tn hiu kiu cng sut Tn hiu tt nh: Xc nh c gi tr ti mi thi im v c m hnh ha bicc biu thc ton r rng, VD x(t)=5cos(10t) Tn hiu ngu nhin: Tn ti mc bt nh trc khi n thc s xy ra, khngth biu din bng mt biu thc ton r rng, nhng khi xt trong khong thigian di dng sng ngu nhin c coi l mt qu trnh ngu nhin c th: (i)biu l mt qui tc no ; (ii) c m t dng xc sut v trung bnh thng k.Cch m t dng xc sut ca qu trnh ngu nhin thng rt hu hiu ctnh ha tn hiu, tp m, nhiu,.... trong h thng truyn thng.1.1. Tn hiu v ph tn hiu5Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication Khi nim: Mt tn hiu ngu nhin (qu trnh ngu nhin) X(t) l tphp cc bin ngu nhin c nh ch s theo t. Nu c nh t = ti, thX(ti) l mt bin ngu nhin. S th hin thng k ca cc bin ngunhin c th c trnh by bng hm mt xc sut (pdf: Probabilitydensity function) lin hp ca chng. S th hin ca mt qu trnhngu nhin c th c trnh by bng cc hm mt xc sut (pdf)lin hp ti cc thi im khc nhau. Tuy nhin, trong thc t ta khngcn bit pdf lin hp m ch cn bit thng k bc 1 (trung bnh) vthng k bc 2 (hm t tng quan l ).Tn hiu ngu nhin1.1. Tn hiu v ph tn hiu6Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationTrung bnh ca mt qu trnh ngu nhin X(t) l k vng(trung bnh tp hp) ca X(t):ACF ca qu trnh ngu nhin| |( ) of X(t) at time t( ) ( ) ( ) ( )X X tpdft E X t X t p x dx = = } ( ) ( ) 1 2 1 2( , ) [X(t)X(t+ )] ( , )XX t X tt t Ep x x dx dxt| t t + + == } }Tn hiu ngu nhin1.1. Tn hiu v ph tn hiu7Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationNu trung bnh X(t) v hm t tng quan |X(t,t+t) khngph thuc thi gian, th X(t) l c coi l qu trnh dngngha rng (WSS: Wide sense stationary) =&gt; c th b quabin ngu nhin t v s dng |X(t) cho hm ngu nhin.-j2 f-1 j2 f-2 j2 f- -0: ( ) [ ( )]= ( )e: ( ) [ ( )]= ( )eP[ ]=E[X ( )]= (0)= ( )e ( )X X XX X XX Xf F dF f f dft f df f dft tt tt tt| t | t t| t| =u == u u ( u = u ( }}} }PSDACFTn hiu ngu nhin1.1. Tn hiu v ph tn hiu8Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication0t t =0 =0t t = 0 =0 0 0( ) ( , ) x t x t =( ) ( , ) x t x t =0( ) ( , ) x t x t =0 0( ) ( , ) x t x t =Ergodic SS WSS qu trnh ngu nhin c c c Qu trnh ngu nhinHm muS thc (phc)Bin ngu nhinAll Random Processes: Mi qu trnh ngu nhinWSS: Qu trnh ngu nhin dng ngha rngSS: Qu trnh ngu nhin dng chtErgodic: Qu trnh ErgodicTn hiu ngu nhin1.1. Tn hiu v ph tn hiu9Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication( )( )K TkX t A p t kT == Tn hiu nh phn ngu nhin bng gc( )2sin( ):( ) ( ) 1xSinc xxNoteSinc x dx Sinc x dxtt = = =} }X(t)tA-A0-T T 2T 3T 4T5T 6T 7T-2T0A1A2A1A2A 3A4A5A6A7A8TMt thc hin ca tn hiu nh phn ngu nhin bng gc X(t) ::1 0( )0Trong : l bin NN phn b ng nht c lp i.d.d, nhn gi tr A ng xc xut l bin NN phn b u trong khong [0 n T] X(t) tr thnh WSSnu nu khcKTAt Tp t s s =1.1. Tn hiu v ph tn hiu10Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication| |22( ) ( ) ( )1 ,0 ,( )xTE X t X tA TTA| t tttt= + ( s (= = AACF:nu khc2 2 ( ) . ( )X f A T Sinc fT u =PSD| | ( ) | | ( )221 ; 11 ;( ) ( )0; 10;( )( ) .Tam gic n vHm tam gic n v y 2TTnh cht t l c TTtt t t T tt t TT tt TFT t SinC fFT t T SinC Tf s s | |A = A = A = |&gt; \ . &gt;A = A = a FTa) Hm tng quan AFCb) Mt ph cng sut PSD-2fT( )X f u2A T0 1 2 3 -1-30-T +T( )X| t2AtHm t tng quan ACF v mt ph cng sut PSD ca tn hiu nh phn ngu nhin bng gc1.1. Tn hiu v ph tn hiu11Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationTn hiu bng thng (1/2)( ):( ) ( ).cos 2c f : tn s sng mang gc pha ngu nhin phn b u trong [0,2 ] khng ph thuc vo X(t) Y(t) thnh WSS Y X ct t f tu tt u= +{ }222 21: ( ) ( ) )21: ( ) ( ) ( )4: ( ) ( ) )2: ( ) ( ) ( )4cNu X(t) l tn hiu nh phn ngu nhin, th c os(2 f os(2 f [ T] [Y XY X c X cY TY c ccf f f f fAcA Tf Sinc f f Sinc f f| t | t t t| t t t t=u = u + u += Au = + +ACFPSDACFPSD{ }T]( )Y| t-TT2A /22-A /24/cf T =t( )Y f u( )2A T /4cfcf 1cfT+2cfT+3cfT+1cfT2cfT3cfT1cfT +2cfT +3cfT +1cfT 2cfT 3cfT fT tng quan ACF v PSD ca tn hiu nhi phn X(t) c iu ch 1.1. Tn hiu v ph tn hiu12Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communicationnh hng ca hn ch bng thng v nh l Nyquist a) Hm truyn t ca b lc thng thp l tngb) Xung kim u vo v p ng u ra c) Dy xung kim u vo v p ng u ra T02T03T0-T0-2T0-3T00h(t)2f02f0h(t) h(t-T)t00T tT 2T 3T -T -2T -3T 0t| | |\ .[0fH(f) =2ff0: tn s ct f f0-f01( ) tT( ) t ( ) ( ) x t t = ( )0 0( ) ( ) ( ) ( )2 2 y t t h t h tf Sinc f t= == f1( ). ( ) ( )( ) Y f X HffHf ==-f0 f0 f| | ( ( ) ) f t X o = FT( ) t ( ) tT10 0t12121,( )0, fff s[ = &gt; c gi l khong cch Nyquist 000T1T T2f= =1.1. Tn hiu v ph tn hiu13Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationNu rng bng tn ca ng truyn dn b hn ch =&gt;xung thu m rng y =&gt; ISI (InterSymbol Interference).Cc im khng xut hin ti thi im kT0 = k/(2f0) vi khckhng, T0c gi l khong cch Nyquist.Nu pht i mt dy xung kim oT(t) cch nhau mt khong Nyquist v tin hnhphn bit cc xung ny ti kT0, th c th trnh c ISI (hnh c).Nu T +a) c tnh dc cosinnh hng ca hn ch bng thng v nh l Nyquist1.1. Tn hiu v ph tn hiu15Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationBng thng ti thiu cn thiti vi truyn dn bng gc: Bng thng Nyquist, bng thng ti thiu cnhit phn bit cc xung m khng b ISI:BN = f0(1+o) = Rs(1+o)/2i vi ng truyn dn bng thng: Bng thng Nyquist:BN = f0(1+o) = Rs(1+o)trong Rs l tc truyn dn hay tc k hiu.Quan h gia tc k hiu v tc bitRs=Rb/ktrong k l s bit trn mt k hiu.nh hng ca hn ch bng thng v nh l Nyquist1.1. Tn hiu v ph tn hiu16Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communicationsin( x) x( x)sinc(x) sinc (x) sincT T: x 01 : x 0' t1 = 111 t = =! ( ) 1= 11+Hm sinc(x) &amp; sincT(x)1.1. Tn hiu v ph tn hiuT-3TsincT(t)t1-T2T-2T3T4T -4T17Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationPh ca xung rect &amp; sincT.sinc1/T(f)tT/2 -T/21rectT(t)fT1/T-1/T2/T-2/T3/T-3/T4/T-4/TFourier transformReal part shownImag part = 0f1/(2T) -1/(2T)TT.rect1/T(f) sincT(t)t1T -T2T-2T3T-3T4T-4TFourier transformReal pt shownImag pt = 01.1. Tn hiu v ph tn hiu18Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationPh ca xung RC 50% &amp; phRC(f)tT/2 -T/21rc(t)fT1/T-1/T2/T-2/T3/T-3/T4/T-4/TFourier transformReal part shownImag part = 0-3T/43T/4f1/(2T)-1/(2T)TRC(f) rc(t)t1T -T2T-2T3T-3T4T-4TFourier transformReal pt shownImag pt = 03/(4T)-3/(4T)1.1. Tn hiu v ph tn hiu19Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication1.1. Tn hiu v ph tn hiuFourier transform pair of Square waveformFourier transform pair of triangular waveformFourier transform pair of Gaussian waveform20Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication221Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationTi sao phi iu ch tn hiu? s dng c mi trng truyn dn vo mc ch truyn thng cn phi:c tnh ha, thng s ha mi trng truyn dn (xc nh, khm ph ti nguyn truyn dn), chng hn nh xc nh ca s truyn dn quang, ca s truyn dn v tuyn, di tn truyn dn ca cp ng...kh nng truyn dn ca mi trng v tham s c trng.c tnh ha ngun tn hiu cn truyn, chng hn: m thanh, hnh nh, d liu, tn hiu in,.. =&gt; rng bng tn (lng tin) ca cc ngun tin v tham s c trng ca ngun tin.Dng cc sng mang (hay tn hiu) c cc thng s c trng ph hp vi thng s c trng ca mi trng truyn truyn tn hiu tin tc bng cch iu ch sng mang, bin i tn hiu, s kt hp gia chng, chng hn: truyn tn hiu m thanh trn cp ng bng cch dng Micro bin i thanh p thnh tn hiu in m tn; iu ch quang truyn tn hiu trn mi trng cp si quang (ph hp ha gia thng s sng nh sng v ca s truyn dn ca si quang); s kt hp gia iu ch sng mang RF (dch ph tn ca tn hiu thng tin ln vng tn RF) v anten bc x sng in t tng (chuyn tn hiu RF thnh in t trng) truyn dn tn hiu trn mi trng v tuyn...1.2. iu ch v dch ph tn tn hiu22Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication Gim kch thc anten: in thoi di ng, anten c kch thc tiu biu bng Nu truyn tn hiu bng c s (3000Hz), kch thc anten l Phi iu ch trn sng mang tn s cao RF (v d 900MHz)km 254 4 = =fc 25km8cm Dch ph tn: t ph tn ca tn hiu vo mt ditn c ch nh trc, t ph tn tn hiu thngtin vo ca s truyn dn nhm: s dng ht tinguyn ph tn (ghp knh phn chia tn sFDM, WDM), phn b ph tn, quy hoch vqun l ti nguyn ph tn... Phc v cc k thuts dng hiu qu ti nguyn....1.2. iu ch v dch ph tn tn hiu23Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication Phn loi tn hiu viu ch: Da vo tinguyn ph tn v mcch truyn thng:Tn hiu bng tn c s,iu ch/gii iu chbng tn c s, truyn dntn hiu bng tn c s.Tn hiu thng di (thngbng), iu ch/gii iuch tn hiu thng bngChuyn i tn hiu bng gc-tn hiu thng bng trong min thi gian (vng trong)v min tn s (vng ngoi)Tn hiu bng tn gc phcTn hiu thng bng gi tr thc1.2. iu ch v dch ph tn tn hiu24Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationBaseband signalBandpass signalLocal oscillatorMinh ha tn hiu bng tn gc v tn hiu thng bng1.2. iu ch v dch ph tn tn hiu25Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communicationnh gi hiu nng: Tiu ch c bn nh gi v sosnh cc phng php iu ch/gii iu ch khc nhaul: hiu nng dung lng v hiu nng cht lng (khnng i ph nhc im ca mi trng truyn dn:phainh, suy hao, nhiu... v hn ch bng thng caknh).Hiu nng cht lng: BER hay kh nng i ph nhc im vcht lng (kh nng khc phc nh hng ca phainh, suyhao...) ca mi trng truyn.Hiu nng dung lng: Hiu qu chim dng ph tn hn ch cami trng truyn.1.2. iu ch v dch ph tn tn hiu26Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationMc tiu thit k1. Ti a tc s liu.Mt s mc tiu i lp nh: mc tiu (1&amp;2) i lp vi mc tiu (3&amp;4), vvy cn la chn mt gii php dung ha (ti u) sao cho tha mn nhiu mc tiu.2. Gim thiu xc sut li k hiu.3. Gim thiu cng sut sut pht.4. Gim thiu rng knh.5. Ti a kh nng chng nhiu.6. Gim thiu mc phc tp ca mch v ti a tn dngti nguyn (trang thit b &amp; ph tn, khng gian, m, thigian).Cc rng buc rng bng tn cc tiu theo l thuyt NyquistL thuyt dung lng knh ShannonPhn b ph tn.Hn ch v k thutCc yu cu khc nh qu o v tinhDung ha iu ch v m ha c xem l thay i quan im khai thc hiu nng xc sut li &amp; hiu qu s dng bng thng1.2. iu ch v dch ph tn tn hiu27Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationTo tn hiu si(t) v khi phc cc h s sij. M hnh pht/thu tn hiu:B tng quanB tng quanB tng quan1( ) t |( )N t |1 isiNs( )} -T0dt( )} -T0dt2( ) t |2 is( )} -T0dt1( ) t |2( ) t |( )N t |1 is2 isiNs) t ( si10( ) . ( )1, 2,..., ; Ni ij jjt Ts t s ti M|=s s==0( ). ( )Tij i js s t t dt | =}ng b sng mang0( ). ( )1, nu i j, Unit Energy0, nu i j OrthogonalityTi jt t dt | | = = =}1.2. iu ch v dch ph tn tn hiu28Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communicationp ng ca cc b tng quan ln tp mWGN( ) X t1( ) t |2( ) t |( )N t |1 is2 isiNs) t ( sing b sng mang( ) ( ) ( )iy t s t X t = +0( ) ( ), 1, 2,.., Tj jij jY Y t t dts X j N| == + =}B tng quanB tng quanB tng quan1( ) t |( )N t |( )} -T0dt( )} -T0dt2( ) t |( )} -T0dtNY2Y1YAWGN| |0 00 0( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ), 1, 2,...,jij jY ji lng tt nh s Bin ngu nhin Xm E Y T Tj j i jT T ij ji j jij jY Y t t dt s t X t t dtE s Xs t t dt X t t dts X j N| || |= = + ( ( = = + = + `= + = )} }} } 220N jijYso==is1( ) t |2( ) t |3( ) t |i1si2si3sxy+x1+x2+x3(Biu din tn hiu v tp m trong khng gian tn hiu)1.2. iu ch v dch ph tn tn hiu29Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationFDMFrequencyFrequency channelBmBcPower FDMATimeSerialTo Parallel(S/P)XXXcos(2tf1t)cos(2tfN-1t)EBPFBPFBPFs(t)cos(2tf0t)1.2. iu ch v dch ph tn tn hiu30Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationtT/2 -T/21rectT(t)Modulate FtT/2 -T/21rectT(t)Modulate F+2/TtT/2-T/21rectT(t)Modulate F+1/TT.sinc1/T(..)fTF+2/TFT.sinc1/T(f-F)fTF+1/TFT.sinc1/T(..)fF+2/TF+1/T F+3/TAssume purely real spectrumKt hp cc bng con OFDM &amp; Ph ca tn hiu OFDM1.2. iu ch v dch ph tn tn hiuf1/T3/TCombinerealspectraAssume purely real spectraFourier transformSUM31Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication 1.1. Tn hiu v ph tn hiu1.2. iu ch tn hiu v dch ph tn1.3. X l tn hiu trong min thi gian Time Processing1.4. X l tn hiu trong min tn s Frequency Processing232Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless CommunicationOFDM as: Multicarrier Modulation &amp; Multiplexing/Multi-Access1. OFDM as a Multicarrier Modulation: + Multi-Carrier Transmission+ OFDM Modulation + OFDM Demodulation2. OFDM IMPLEMENTATION USING IFFT/FFT PROCESSING3. CYCLIC-PREFIX INSERTION4. FREQUENCY-DOMAIN MODEL OF OFDM TRANSMISSION5. CHANNEL ESTIMATION AND REFERENCE SYMBOLS6. FREQUENCY DIVERSITY WITH OFDM: IMPORTANCE OF CHANNEL CODING7. SELECTION OF BASIC OFDM PARAMETERS:+ OFDM Subcarrier Spacing+ Number of Subcarriers+ Cyclic-Prefix Length8. VARIATIONS IN INSTANTANEOUS TRANSMISSION POWER9. OFDM AS A USER-MULTIPLEXING AND MULTIPLE-ACCESS SCHEME10. MULTI-CELL BROADCAST/MULTICAST TRANSMISSION AND OFDM333Nguyn Vit mOFDM:Concept_Basic_Solution In Wirless Communication1. OFDM as a Multicarrier Modulation:Single-Carrier vs. Multi-Carrier TransmissionSingle-carrier baseband communication system model.The structure of multichannel transmission systemThe frequency response of multichannel transmission systemStructure and frequency characteristic of multichannel transmission system.34Nguyn Vit mOFDM:Concept_Basic_Soluti...</p>