Nghiên cứu kỹ thuật STBC OFDM trong thông tin di động

Ket-noi.com forum giao duc [Type the document title] LI CAM OAN Tụi xin cam oan ni dung ca ỏn ny khụng phi l bn chộp ca bt c ỏn hoc cụng trỡnh no ó cú t trc nng, thỏng 05/2011 Sinh viờn thc hin MC LC Trang Cỏc t vit tt SV thc hin: v Trang i [Type the document title] Li m u Chng Kờnh truyn vụ tuyn 1.1 Gii thiu chng viii . 01 . 01 1.2 Khỏi nim h thng thụng tin vụ tuyn 1.3 Cỏc c tớnh ca truyn vụ tuyn 01 03 1.3.1 Suy hao tớn hiu trờn ng truyn vụ tuyn 03 1.3.2 Hiu ng a ng 1.3.3 Hiu ng che chn v fading chm . 05 .. 06 . 08 1.3.4 Dch Doppler v fading nhanh 1.3.5 Tri tr (Delay spread) 04 1.3.6 Fading phng v fading la chn tn s . 09 1.4 Kt lun chng .. 09 Chng Tng quan v k thut OFDM 2.1 Gii thiu chng .. 10 10 2.2 OFDM vans so high than, pat trine . 10 2.3 Guyed lee c bn ca OFDM 12 2.4 Vn trc giao OFDM . 15 2.5 S h thng thu phỏt OFDM 2.5.1 Chuyn i S/P v P/S . 16 17 2.5.2 iu ch súng mang 2.5.3 Bin i IFFT v FFT 18 .. 22 2.5.4 Chốn khong bo v GP . 23 2.5.5 Chuyn i A/D c D/A 24 2.6 u v nhc im ca OFDM 25 SV thc hin: Trang ii [Type the document title] 2.6.1 Cỏc u im .. 25 2.6.2 Nhc im .. 26 2.7 ng dng k thut OFDM thụng tin di ng 27 2.8 Kt lun chng 27 Chng H thng MIMO v k thut STBC . 28 3.1 Gii thiu chng . 28 3.2 K thut phõn 28 3.2.1 Phõn thi gian 29 3.2.2 Phõn tn s .. 30 3.2.3 Phõn khụng gian . 31 3.3 Khỏi nim v mụ hỡnh h thng MIMO .. 31 3.4 Cỏc li h thng MIMO 33 3.4.1 li Beamforming .. 33 3.4.2 li ghộp kờnh khụng gian 34 3.4.3 li phõn khụng gian . 34 3.5 Cỏc mụ hỡnh v dung lng h thng thụng tin vụ tuyn 35 3.5.1 H thng SISO 35 3.5.2 H thng SIMO 35 3.5.3 H thng MISO . 36 3.5.4 H thng MIMO ... 37 3.6 K thut mó húa khụng gian-thi gian STC 38 3.6.1 Mó húa Alamouti STBC 39 3.6.2 STBC m rng vi nhiu anten thu . 44 3.7 Kt lun chng 45 SV thc hin: Trang iii [Type the document title] Chng K thut STBC-OFDM . 46 4.1 Gii thiu chng 46 4.2 Mụ hỡnh h thng STC-OFDM 46 4.3 H thng STBC-OFDM 51 4.4 Kt lun chng . 55 Chng Kt qu mụ phng 56 5.1 Gii thiu chng . 56 5.2 Mụ phng BER tớn hiu OFDM . . 56 5.2.1 BER ca tớn hiu OFDM cú chốn CP v khụng chốn CP . 56 5.2.2 BER ca tớn hiu iu ch OFDM v QAM . 57 5.3 Mụ phng h thng STBC . 59 5.3.1 Mụ phng Alamouti STBC . 59 5.3.2 Mụ phng STBC vi anten thu .. 61 5.4 Mụ phng h thng STBC-OFDM .. 62 Kt lun v hng phỏt trin ti . 64 Ti liu tham kho . 66 Ph lc . 68 SV thc hin: Trang iv [Type the document title] CC T VIT TT A ADSL Asynchronous Digital ng dõy thuờ bao s bt i xng Subscriber Line A/D Analog/Digital Chuyn i tng t-s AWGN Additive White Gaussian Noise Nhiu Gauss trng cng B BER Bit Error Rate Tc li bit BTS Base Transceiver Station Trm thu phỏt gc C CDMA Code Division Multiple Access a truy cp phõn chia theo mó CP CFO Cycle Prefix Carrier Frequency Offset Tin t lp Lch tn s súng mang CSI Channel State Information Thụng tin trng thỏi kờnh truyn D DAB Digital Audio Broadcasting Phỏt s qung bỏ DVB Digital Video Broadcasting Truyn hỡnh s qung bỏ DFT F Discrete Fourier Transform Phộp bin i Fourier ri rc FDM Frequency Division Multiplexing Ghộp kờnh chia theo tn s FEC Forward Error Control Kim soỏt li tin FFT Fast Fourier Transform Phộp bin i Fourier nhanh I ICI InterCarrier Interference Nhiu liờn súng mang ISI InterSymbol Interference Nhiu liờn ký t SV thc hin: Trang v [Type the document title] IDFT Inverse Discrete Fourier Phộp bin i ngc Fourier ri rc Transform IFFT Inverse Fast Fourier Transform Phộp bin i ngc Fourier nhanh L LAN Local Area Networks Mng mỏy tớnh cc b LTE Long Term Evolution S phỏt trin lõu di LOS Line Of Sight Tm nhỡn thng M MAN Metropolitan Area Networks Mng ụ th bng rng MIMO Multiple Input Multiple Output H thng a u vo-a u MS Mobile Station Trm di ng MRC Maximal Ratio Combining Kt hp t s ti a O OFDM OLOS Orthogonal Frequency Division Ghộp kờnh phõn chia theo tn s Multiplexing trc giao Obstructed Line Of sight Tm nhỡn thng b che chn S SCE Space-Time Encoding Mó húa khụng gian-thi gian SCD Space-Time Decoding Gii mó khụng gian-thi gian STBC Space Time Block Coding Mó húa khụng gian-thi gian STTC Space-Time Trellis Code Mó húa li khụng gian-thi gian W Mng LAN khụng dõy-Wireless LAN WLAN Wireless Local Area Networks WMAN Wireless Metropolitan Area Networks SV thc hin: Mng ụ th khụng dõy Trang vi [Type the document title] CHNG KấNH TRUYN Vễ TUYN 1.1 Gii thiu chng Trc i vo ni dung chớnh ca ỏn, ta i tỡm hiu v kờnh truyn tớn hiu vụ tuyn Khi m nhu cu s dng mụi trng vụ tuyn truyn tớn hiu ngy cng ln v thụng dng hn thỡ vic nghiờn cu tỡm hiu v kờnh truyn vụ tuyn v cỏc c tớnh ca nú tr nờn rt quan trng v cn thit Chng ny cung cp mt cỏch ngn gn cỏc c im chớnh ca kờnh truyn vụ tuyn, v nhng ny gõy vic truyn thụng tin s Nhng hiu ng truyn vụ tuyn nh suy hao ng truyn, fading la chn tn s, dch Doppler v tri tr a ng lm hn ch hiu qu ca vic truyn thụng tin vụ tuyn Hiu c truyn vụ tuyn l cn thit trc i sõu vo tỡm hiu k thut OFDM, h thng MIMO v ng dng mụi trng vụ tuyn Chng ny cung cp mt cỏch tng quỏt nhng hiu ng truyn quan trng v m rng nhng ny xem xột cỏc hiu ng trờn bng thụng rng 1.2 Khỏi nim v h thng thụng tin vụ tuyn Kờnh truyn tớn hiu l mụi trng truyn súng gia mỏy phỏt v mỏy thu Trong kờnh truyn vụ tuyn lý tng, tớn hiu nhn c bờn thu c truyn theo tm nhỡn thng (Line Of Sight) Tuy nhiờn thc t, kờnh truyn tớn hiu vụ tuyn chu tỏc ng ca rt nhiu yu t lm cho tớn hiu b thay i Vic nghiờn cu cỏc c tớnh ca kờnh truyn l rt quan trng vỡ cht lng ca h thng truyn vụ tuyn l ph thuc vo cỏc c im ny Cht lng ca cỏc h thng thụng tin ph thuc nhiu vo kờnh truyn, ni m tớn hiu c truyn t mỏy phỏt n mỏy thu Tớn hiu c phỏt i, qua kờnh truyn vụ SV thc hin: Trang vii [Type the document title] tuyn, b cn tr bi cỏc to nh, nỳi non, cõy ci , b phn x, tỏn x, nhiu x, cỏc hin tng ny c gi chung l fading V kt qu l mỏy thu, ta thu c rt nhiu phiờn bn khỏc ca tớn hiu phỏt iu ny nh hng n cht lng ca h thng thụng tin vụ tuyn Cú ba c ch chớnh nh hng n s lan truyn ca tớn hiu h thng di ng: Phn x xy khớ súng in t va chm vo mt mt bng phng vi kớch thc rt ln so vi bc súng tớn hiu RF Hỡnh 1.1 truyn a ng thụng tin vụ tuyn Nhiu x xy ng truyn súng gia phớa phỏt v thu b cn tr bi mt nhúm vt cn cú mt cao v kớch thc ln so vi bc súng Nhiu x l hin tng gii thớch cho nguyờn nhõn nng lng RF c truyn t phớa phỏt n phớa thu m khụng cn ng truyn thng Nú thng c gi l hiu ng chn (shadowing) vỡ trng SV thc hin: Trang viii [Type the document title] tỏn x cú th n c b thu c b chn bi vt cn khụng th truyn xuyờn qua Tỏn x xy súng in t va chm vo mt mt phng ln, g gh lm cho nng lng b tri (tỏn x ) hoc l phn x tt c cỏc hng Trong mụi trng thnh ph, cỏc vt th thng gõy tỏn x l ct ốn, ct bỏo hiu, tỏn lỏ 1.3 Cỏc c tớnh ca truyn vụ tuyn 1.3.1 Suy hao tớn hiu trờn ng truyn vụ tuyn Trong quỏ trỡnh truyn, tớn hiu vụ tuyn tr nờn b yu i t l vi khong ng i ca nú Khi tớn hiu truyn mụi trng vụ tuyn, nú s b suy hao i ng truyn di, cỏc vt cn nh nh ca, cõy ci v hiu ng a ng Khi tớn hiu c truyn thng, khụng b nh hng bi cỏc vt cn cng nh cỏc hin tng a ng thỡ tớn hiu b suy hao [3] ú gi l suy hao khụng gian t Din tớch hỡnh cu l t l vi bỡnh phng bỏn kớnh[3], v ú khụng gian t cng trng RF gim t l vi bỡnh phng khong cỏch Cụng sut thu c khụng gian t c tớnh nh sau : PR = PT G T G R ổ l ỗ ữ ố 4p d ứ (W) (1.1) Trong ú : PT l cụng sut phỏt (W) GT v GR ln lt l li anten phỏt v anten thu l bc súng ca súng mang RF (m) d l khong cỏch truyn tớn hiu t anten phỏt ti anten thu (m) SV thc hin: Trang ix [Type the document title] Hỡnh 1.2 Tớn hiu b nh hng bi fading, Shadowing v Pathloss Hỡnh 1.2 trờn mụ t cng tớn hiu thu c theo khong cỏch truyn mụi trng vụ truyn Ta thy rng cng tớn hiu thu c b suy gim dn khong cỏch d tng lờn Khi tớn hiu b suy hao khụng gian t cng thờm vi hin tng a ng, shadowing thỡ tớn hiu s b nhiu nng c biu din nh hỡnh trờn (c ký hiu bi pathloss+fading+shadowing) [1] Suy hao khụng gian t ph thuc vo khong cỏch v tn s súng mang Suy hao ny c biu din bng ng thng xung dc (l ng pathloss) nh hỡnh trờn Cụng thc tớnh suy hao khụng gian t nh sau : ổ 4p d L = 20 log ỗ ữ ố l ứ (1.2) Vi d [m], [m] ln lt l khong cỏch truyn tớn hiu v bc súng ca súng vụ tuyn SV thc hin: Trang x [Type the document title] 10 10 Bit Error Rate 10 10 10 10 10 BER cho DieuChe 4-QAM voi MMRC va Alamouti tren kenh Rayleigh nTx=1,nRx=1 nTx=1,nRx=2,MRC nTx=1,nRx=4,MRC nTx=2,nRx=1,Alamouti nTx=2,nRx=2,Alamouti -1 -2 -3 -4 -5 -6 10 15 20 25 SNR (dB) Hỡnh 5.5 BER cho MRC v STBC trờn kờnh truyn Rayleing Kt qu mụ phng: BER gim dn t s SNR tng lờn, cỏc trng hp cú s dng nhiu anten hn thỡ cú BER thp hn Trng hp ch s dng 1Tx-1Rx cú BER ln nht tc cht lng tớn hiu l kộm nht, trng hp 2Tx-2Rx-Alamouti cú BER rt thp nhng trng hp s dng 1Tx-4Rx li cú BER thp nht, tc cho cht lng tớn hiu tt nht Trng hp 2Tx-2Rx s dng anten cú bc phõn l 2x2 = Cũn trng hp 1Tx-4Rx cng cú bc phõn l nhng li s dng anten SV thc hin: Trang lxxii [Type the document title] KT LUN V HNG PHT TRIN TI Vi ti Nghiờn cu k thut STBC-OFDM thụng tin di ng , ni dung ỏn ó trỡnh by cỏc v kờnh truyn vụ tuyn, k thut ghộp kờnh phõn chia theo tn s trc giao OFDM, k thut mó húa khụng gian thi gian STBC v h thng STBC-OFDM Cỏc v kờnh truyn vụ tuyn nh truyn a ng, fading la chn tn s, hiu ng dch Doppler, shadowing lm nh hng rt ln n cht lng tớn hiu truyn trờn mụi trng vụ tuyn K thut OFDM i ó khc phc c cỏc ú OFDM cú th loi b hon ton nhiu liờn ký t ISI bng cỏch chốn khong bo v GP Khc phc c fading la chn tn s bng vic chia bng thụng kờnh truyn thnh nhiu bng con, lỳc ny mi súng mang gn nh l phng K thut STBC cú kh nng hn ch fading a ng, trỏnh c hao phớ bng thụng, nõng cao dung lng kờnh truyn vụ tuyn vi nhiu u im vt tri so vi nhc im ca nú, vic ng dng v kt hp hai k thut OFDM v STBC vo thụng tin vụ tuyn l cn thit nhm khai thỏc ti a u im ca c hai k thut ny Hn ch ca ỏn: Do thi gian thc hin ti ny cú hn, kh nng dch v hiu ti liu ting anh cha tt nờn ni dung ca ỏn ny cha cp c sõu, rng mt s liờn quan n OFDM v STBC Mt s phn trỡnh by cha c rừ rng, hp lý cú th khin ngi c gõy khú hiu V phn STBC mi ch nờu c anten phỏt, cha nờu c h thng tng quỏt vi nhiu anten phỏt V k thut OFDM, cỏc ng b khung, c lng kờnh truyn cha nhc ti c SV thc hin: Trang lxxiii [Type the document title] Vi mc ớch tỡm hiu v k thut OFDM v STBC, h thng STBC-OFDM thụng tin di ng, ngi thc hin ỏn ny rt mong cú c s trao i, gúp ý ca cỏc thy cụ v cỏc bn Hng phỏt trin ti : Trc ht tin hnh khc phc nhng hn ch m ỏn ny cha thc hin c i sõu vo vic tỡm hiu cỏc c lng, ng b OFDM V phn MIMO, em s nghiờn cu hai k thut khỏc l STTC v V-BLAST so sỏnh u v nhc im ca cỏc k thut mó húa ny K thut OFDM cú nhiu u im ng dng vo cỏc h thng thụng tin vụ tuyn, ú vic tỡm hiu ng dng ca OFDM v MIMOOFDM vo WiMAX, LTE cng l mt nờn lm sau hon thnh ỏn ny Túm li, k thut OFDM vi nhng u im vt tri nh s dng bng thụng hiu qu, loi b c nhiu ISI bng khong bo v, chng li c fading la chn tn s ang chng t c vai trũ quan trng thụng tin vụ tuyn hin i Cựng vi k thut STBC cú kh nng gim nh hng ca fading, trỏnh c hao phớ bng thụng, nõng cao dung lng kờnh truyn Vic kt hp hai k thut ny li ta s hi t c u im ca c hai nõng cao dung lng v cht lng cho kờnh truyn vụ tuyn, õy hn s em li nhiu li ớch ln cho cỏc nh cung cp dch v vin thụng SV thc hin: Trang lxxiv [Type the document title] TI LIU THAM KHO [1] Nguyn Lờ Hựng, H Bỏch Khoa Nng, Wireless channel models [2] ng Lờ Khoa, H Khoa Hc T Nhiờn TP.HCM, Kờnh truyn vụ tuyn [3] Eric Phillip LAWREY BE, Adaptive Techniques for Multiuser OFDM, December 2001, James Cook University [4] ERICSSON, GSM System Survey, Student Book ZLT 123 3321 R7A, Ericsson 2007 [5] Nguyn Lờ Hựng, HBK Nng, OFDM Fundamentals [6] Trn Xuõn Nam, Hc vin KTQS, Tng quan v OFDM [7] Jian (Andrew) Zhang, Multicarrier Comunications Canberra,Australia,2007 [8] Rohde & Schwarz, Heinz Semmerow, 09/2006, WiMAX Overview [9] Kamran Arshad, Channel Estimation in OFDM Systems August, 2002 [10] Wireless Access Tech Lab, the basic Principles of OFDM [11] Eric Phillip LAWREY BE, Adaptive Techniques for Multiuser OFDM, December 2001 [12] Nguyn Lờ Hựng HBK Nng, Diversity techniques [13] Bikas Sinha, R Bera, M Mitra Capacity and V-BLAST techniques for MIMO wireless channel SV thc hin: Trang lxxv [Type the document title] [14] Siavash M Alamouti A Simple Transmit Diversity Technique for Wireless Communications IEEE Journal on select areas in Communications, VOL 16, NO 8, October 1998 [15] Krishna Pillai, Alamouti STBC 16th October 2008 http://dsplog.com [16] From Wikipedia, the free encyclopedia, Spacetime block code http://en.wikipedia.org/wiki/Space%E2%80%93time_block_code [17] Mohinder Jankiraman, Space-Time codes and MIMO systems [18] Tran Xuan Nam, The University of Electro-Communications Chofu-shi, Tokyo, Japan Simulation of STBC-OFDM systems under frequency selective fading channels [19] Branka Vucetic & Jinhong Yuan, "Space-Time Coding" SV thc hin: Trang lxxvi [Type the document title] PH LC ỹ So sỏnh BER ca tớn hiu OFDM cú chốn CP v khụng chốn CP %%% code so sanh he thong OFDM su dung CP va khong su dung CP clear all nFFT = 64; % fft size nDSC = 52; % number of data subcarriers nBitPerSym = 52; % number of bits per OFDM symbol (same as the number of subcarriers for BPSK) nSym = 10^4; % number of symbols EbN0dB = [0:35]; % bit to noise ratio nTap = 3; EsN0dB = EbN0dB + 10*log10(nDSC/nFFT) + 10*log10(64/80); % converting to symbol to noise ratio for ii = 1:length(EbN0dB) % Transmitter ipBit = rand(1,nBitPerSym*nSym) > 0.5; % random 1's and 0's ipMod = 2*ipBit-1; % BPSK modulation > -1, > +1 ipMod = reshape(ipMod,nBitPerSym,nSym).'; % grouping into multiple symbolsa % Assigning modulated symbols to subcarriers from [-26 to -1, +1 to +26] xF = [zeros(nSym,6) ipMod(:,[1:nBitPerSym/2]) zeros(nSym,1) ipMod(:,[nBitPerSym/2+1:nBitPerSym]) zeros(nSym,5)] ; % Taking FFT, the term (nFFT/sqrt(nDSC)) is for normalizing the power of transmit symbol to xt = (nFFT/sqrt(nDSC))*ifft(fftshift(xF.')).'; % Appending cylic prefix xtcp = [xt(:,[49:64]) xt]; % multipath channel ht = 1/sqrt(2)*1/sqrt(nTap)*(randn(nSym,nTap) + 1i*randn(nSym,nTap)); % computing and storing the frequency response of the channel, for use at recevier hF = fftshift(fft(ht,64,2)); % convolution of each symbol with the random channel for jj = 1:nSym xht(jj,:) = conv(ht(jj,:),xt(jj,:)); xhtcp(jj,:) = conv(ht(jj,:),xtcp(jj,:)); end xt = xht; xtcp = xhtcp; % Concatenating multiple symbols to form a long vector xt = reshape(xt.',1,nSym*(64+nTap-1)); xtcp = reshape(xtcp.',1,nSym*(80+nTap-1)); SV thc hin: Trang lxxvii [Type the document title] % Gaussian noise of unit variance, mean nt = 1/sqrt(2)*[randn(1,nSym*(64+nTap-1)) + 1i*randn(1,nSym*(64+nTap-1))]; ntcp = 1/sqrt(2)*[randn(1,nSym*(80+nTap-1)) + 1i*randn(1,nSym*(80+nTap-1))]; % Adding noise, the term sqrt(80/64) is to account for the wasted energy due to cyclic prefix yt = sqrt(64/64)*xt + 10^(-EsN0dB(ii)/20)*nt; ytcp = sqrt(80/64)*xtcp + 10^(-EsN0dB(ii)/20)*ntcp; % Receiver yt = reshape(yt.',64+nTap-1,nSym).'; % formatting the received vector into symbols yt=yt(:,[1:64]); ytcp = reshape(ytcp.',80+nTap-1,nSym).'; ytcp = ytcp(:,[17:80]); % removing cyclic prefix % converting to frequency domain yF = (sqrt(nDSC)/nFFT)*fftshift(fft(yt.')).'; yFcp = (sqrt(nDSC)/nFFT)*fftshift(fft(ytcp.')).'; % equalization by the known channel frequency response yF = yF./hF; yFcp = yFcp./hF; % extracting the required data subcarriers yMod = yF(:,[6+[1:nBitPerSym/2] 7+[nBitPerSym/2+1:nBitPerSym] ]); yModcp = yFcp(:,[6+[1:nBitPerSym/2] 7+[nBitPerSym/2+1:nBitPerSym] ]); % BPSK demodulation % +ve value > 1, -ve value > -1 ipModHat = 2*floor(real(yMod/2)) + 1; ipModHat(find(ipModHat>1)) = +1; ipModHat(find(ipModHat1)) = +1; ipModHatcp(find(ipModHatcp -1; -> %%%%% Alamouti STBC %%%%% sCode = zeros(2,N);%tao ma tran voi 2xN sCode(:,1:2:end) = (1/sqrt(2))*reshape(s,2,N/2); % [x1 x2 sCode(:,2:2:end) = (1/sqrt(2))*(kron(ones(1,N/2),[1;1]).*flipud(reshape(conj(s),2,N/2))); % [-x2* x1* ] .] h = 1/sqrt(2)*[randn(1,N) + j*randn(1,N)]; % Kenh truyen Rayleigh hMod = kron(reshape(h,2,N/2),ones(1,2)); % repeating the same channel for two symbols n = 1/sqrt(2)*[randn(1,N) + j*randn(1,N)]; % nhieu Gauss trang % Channel and noise Noise addition y = sum(hMod.*sCode,1) + 10^(-Eb_N0_dB(ii)/20)*n; %%%%% BO THU %%%%% yMod = kron(reshape(y,2,N/2),ones(1,2)); % [y1 y1 ; y2 y2 ] SV thc hin: Trang lxxix [Type the document title] yMod(2,:) = conj(yMod(2,:)); % [y1 y1 ; y2* y2* ] % forming the equalization matrix hEq = zeros(2,N); hEq(:,[1:2:end]) = reshape(h,2,N/2); % [h1 ; h2 ] hEq(:,[2:2:end]) = kron(ones(1,N/2),[1;1]).*flipud(reshape(h,2,N/2)); % [h1 h2 ; h2 -h1 ] hEq(1,:) = conj(hEq(1,:)); % [h1* h2* ; h2 -h1 ] hEqPower = sum(hEq.*conj(hEq),1); yHat = sum(hEq.*yMod,1)./hEqPower; %[h1*y1+h2y2*,h2*y1-h1y2*, ] yHat(2:2:end) = conj(yHat(2:2:end)); % receiver - hard decision decoding ipHat = real(yHat)>0; % counting the errors nErr(ii) = size(find([ip- ipHat]),2);%tinh so bits loi end simBer = nErr/N; % simulated ber EbN0Lin = 10.^(Eb_N0_dB/10); Ber_nRx1 = 0.5.*(1-1*(1+1./EbN0Lin).^(-0.5)); p = 1/2 - 1/2*(1+1./EbN0Lin).^(-1/2); BerMRC_nRx2 = p.^2.*(1+2*(1-p)); pAlamouti = 1/2 - 1/2*(1+2./EbN0Lin).^(-1/2); BerAlamouti_nTx2_nRx1 = pAlamouti.^2.*(1+2*(1-pAlamouti)); close all figure semilogy(Eb_N0_dB,Ber_nRx1,'bp-','LineWidth',2); hold on semilogy(Eb_N0_dB,BerMRC_nRx2,'kd-','LineWidth',2); semilogy(Eb_N0_dB,BerAlamouti_nTx2_nRx1,'mo-','LineWidth',2); axis([0 25 10^-5 0.5]) grid on xlabel('Eb/No, dB'); ylabel('Bit Error Rate'); title('BER cho DieuChe BPSK voi Alamouti STBC'); legend('nTx=1,nRx=1', 'nTx=1,nRx=2,MRC', 'nTx=2,nRx=1,Alamouti'); SV thc hin: Trang lxxx [Type the document title] ỹ BER vi 2Tx, 2Rx Alamouti STBC Clear N = 10^6; % number of bits or symbols Eb_N0_dB = [0:25]; % multiple Eb/N0 values nRx = 2; for ii = 1:length(Eb_N0_dB) % Transmitter ip = randint(1,N); % tao chuoi bit ngau nhien s = 2*ip-1; % BPSK modulation -> -1; -> % Alamouti STBC sCode = 1/sqrt(2)*kron(reshape(s,2,N/2),ones(1,2)) ; % channel h = 1/sqrt(2)*[randn(nRx,N) + j*randn(nRx,N)];%Rayleigh channel n = 1/sqrt(2)*[randn(nRx,N) + j*randn(nRx,N)];%nhieu Gauss trang y = zeros(nRx,N); yMod = zeros(nRx*2,N); hMod = zeros(nRx*2,N); for kk = 1:nRx hMod = kron(reshape(h(kk,:),2,N/2),ones(1,2)); % repeating the same channel for two symbols hMod = kron(reshape(h(kk,:),2,N/2),ones(1,2)); temp = hMod; hMod(1,[2:2:end]) = conj(temp(2,[2:2:end])); hMod(2,[2:2:end]) = -conj(temp(1,[2:2:end])); % Channel and noise Noise addition y(kk,:) = sum(hMod.*sCode,1) + 10^(-Eb_N0_dB(ii)/20)*n(kk,:); % Receiver yMod([2*kk-1:2*kk],:) = kron(reshape(y(kk,:),2,N/2),ones(1,2)); % forming the equalization matrix hEq([2*kk-1:2*kk],:) = hMod; hEq(2*kk-1,[1:2:end]) = conj(hEq(2*kk-1,[1:2:end])); hEq(2*kk, [2:2:end]) = conj(hEq(2*kk, [2:2:end])); end % equalization hEqPower = sum(hEq.*conj(hEq),1); yHat = sum(hEq.*yMod,1)./hEqPower;%[h1*y1+h2y2*,h2*y1-h1y2*, ] yHat(2:2:end) = conj(yHat(2:2:end)); % receiver - hard decision decoding SV thc hin: Trang lxxxi [Type the document title] ipHat = real(yHat)>0; % counting the errors nErr(ii) = size(find([ip- ipHat]),2); % tinh so bits loi end % mo phong tinh BER Ber = nErr/N; EbN0Lin = 10.^(Eb_N0_dB/10); Ber_nRx1 = 0.5.*(1-1*(1+1./EbN0Lin).^(-0.5)); p = 1/2 - 1/2*(1+1./EbN0Lin).^(-1/2); BerMRC_nRx2 = p.^2.*(1+2*(1-p)); pAlamouti = 1/2 - 1/2*(1+2./EbN0Lin).^(-1/2); BerAlamouti_nTx2_nRx1 = pAlamouti.^2.*(1+2*(1-pAlamouti)); close all figure semilogy(Eb_N0_dB,Ber_nRx1,'bp-','LineWidth',2); hold on semilogy(Eb_N0_dB,BerMRC_nRx2,'kd-','LineWidth',2); semilogy(Eb_N0_dB,BerAlamouti_nTx2_nRx1,'c+-','LineWidth',2); semilogy(Eb_N0_dB,Ber,'mo-','LineWidth',2); axis([0 25 10^-5 0.5]) grid on xlabel('Eb/No, dB'); ylabel('Bit Error Rate'); title('BER cho DieuChe BPSK voi 2Tx,2Rx Alamouti STBC'); legend('nTx=1,nRx=1', 'nTx=1,nRx=2,MRC', 'nTx=2,nRx=1,Alamouti', 'nTx=2,nRx=2, Alamouti'); ỹ STBC-OFDM %written by Hung Nguyen-Le, Jan 12 2011 %developed by Toni Lastest update: Jan 20, 2011 clear all; clc N_trial = 1000; % number of simulation trials M_QAM = 4; % MQAM modulation level used %======LTE downlink timing settings============== N_slot = 1;%Number of time slots (each with a length of 0.5ms) in a LTE frame SV thc hin: Trang lxxxii [Type the document title] N_sym_slot = 7;%number of OFDM symbols in a time slot in a LTE frame, i.e.,normal mode in "Downlink Control Channel Design for 3GPP LTE", WCNC 2008 sym_pos = [1:N_slot*N_sym_slot]; % position indices of all considered (data/pilot) OFDM symbols pilot_pos = [2]; % positions of pilot OFDM symbols in a burst of "N_slot*N_sym_slot=14" considered OFDM symbols SNR = [0:2:25]; data_pos = data_sym_index_gen(N_slot*N_sym_slot,pilot_pos); % generate positions of data OFDM symbols (given the pilot OFDM symbols' position) N_data_sym = length(data_pos); % number of data OFDM symbols in a considered burst N_pilot_sym = length(pilot_pos); % number of used pilot OFDM symbols N_sym = N_data_sym + N_pilot_sym; % total number of data and pilot OFDM symbols in a burst %============== OFDM settings -L = 3; % number of resolvable multipaths < N_cp N_fft =128; % FFT size used, N_cp = 10; % CP length in normal mode, refered to "Downlink Control Channel Design for 3GPP LTE", WCNC 2008 %fs = 1.92e6; % sampling freq corresponding to N_fft = 128 in "Downlink Control Channel Design for 3GPP LTE", WCNC 2008 %fc = 2e9; %carrier frequency in Hz (in LTE standard band IV) in "Downlink Control Channel Design for 3GPP LTE", WCNC 2008 Ns = N_fft + N_cp; % OFDM symbol length after CP insertion PDP = exp(-(0:L-1)/4)/sum( exp(-(0:L-1)/4) );% Power Delay Profile in according to COST 259, subcarr_len = log2(M_QAM); % number of bits per subcarrier/MQAM constellation point BER = zeros(5,length(SNR)); tic for SNR_index = 1:length(SNR) % AWGN power determination for trial = 1:N_trial disp(['Current SNR=', num2str(SNR(SNR_index)), '; Current trial=', num2str(trial)]); % Data-modulated signal generation [tx_data_sig,data_bit_seq,data_sym] = Tx_data_signal_generator_Alamouti_FD(subcarr_len,N_fft,N_data_sym,L); % Khong phan tap (SISO) N_tx = 1; % anten phat N_rx = 1; % anten thu SV thc hin: Trang lxxxiii [Type the document title] SigPow = N_tx*1; % power of noise-free received signal at user when the powers of both the transmitted signals and CIR have been normalized to No = SigPow/(10^(SNR(SNR_index)/10)); % AWGN power % Block-fading channel generation CIR = zeros(L,2,4); for rx_anten = 1:4 for tx_anten = 1:2 CIR(:,tx_anten,rx_anten) = sqrt(PDP.'/2).*( randn(L,1) + 1j*randn(L,1) ); end end % Received signal generation [rx_sig,FD_rx_sig] = Rx_Sig_Generator(N_tx,N_rx,L,N_fft,data_pos,No,CIR,tx_data_sig); % Demodulation [reco_bits, reco_sym] = Alamouti_FD( CIR, FD_rx_sig, data_pos, subcarr_len, N_fft, N_data_sym, N_rx, L,N_tx ); BER(1,SNR_index) = BER(1,SNR_index) + sum(abs(data_bit_seq - reco_bits)); %%% nTx=1, nRx=2, MRRC %%%%%%%% N_tx = 1; % anten phat N_rx = 2; % anten thu SigPow = N_tx*1; % power of noise-free received signal at user when the powers of both the transmitted signals and CIR have been normalized to No = SigPow/(10^(SNR(SNR_index)/10)); % cong suat nhieu (AWGN power) % Received signal generation [rx_sig,FD_rx_sig] = Rx_Sig_Generator(N_tx,N_rx,L,N_fft,data_pos,No,CIR,tx_data_sig); % Demodulation [reco_bits, reco_sym] = Alamouti_FD( CIR, FD_rx_sig, data_pos, subcarr_len, N_fft, N_data_sym, N_rx, L,N_tx ); BER(2,SNR_index) = BER(2,SNR_index) + sum(abs(data_bit_seq - reco_bits)); %%% nTx=1, nRx=4, MRRC N_tx = 1; % anten phat SV thc hin: Trang lxxxiv [Type the document title] N_rx = 4; % anten thu SigPow = N_tx*1; No = SigPow/(10^(SNR(SNR_index)/10)); %cong suat nhieu (AWGN power) % Received signal generation [rx_sig,FD_rx_sig] = Rx_Sig_Generator(N_tx,N_rx,L,N_fft,data_pos,No,CIR,tx_data_sig); % Demodulation [reco_bits, reco_sym] = Alamouti_FD( CIR, FD_rx_sig, data_pos, subcarr_len, N_fft, N_data_sym, N_rx, L,N_tx ); BER(3,SNR_index) = BER(3,SNR_index) + sum(abs(data_bit_seq - reco_bits)); %%% nTx=2, nRx=1, Alamouti %%%%% N_tx = 2; % anten phat N_rx = 1; % anten thu SigPow = N_tx*1 No = SigPow/(10^(SNR(SNR_index)/10)); %cong suat nhieu (AWGN power) % Received signal generation [rx_sig,FD_rx_sig] = Rx_Sig_Generator(N_tx,N_rx,L,N_fft,data_pos,No,CIR,tx_data_sig); % Demodulation [reco_bits, reco_sym] = Alamouti_FD( CIR, FD_rx_sig, data_pos, subcarr_len, N_fft, N_data_sym, N_rx, L,N_tx ); BER(4,SNR_index) = BER(4,SNR_index) + sum(abs(data_bit_seq - reco_bits)); %%% nTx=2, nRx=2, Alamouti %%%%% N_tx = 2; % anten phat N_rx = 2; % anten thu SigPow = N_tx*1; No = SigPow/(10^(SNR(SNR_index)/10)); %cong suat nhieu (AWGN power) % Received signal generation [rx_sig,FD_rx_sig] = Rx_Sig_Generator(N_tx,N_rx,L,N_fft,data_pos,No,CIR,tx_data_sig); % Demodulation SV thc hin: Trang lxxxv [Type the document title] [reco_bits, reco_sym] = Alamouti_FD( CIR, FD_rx_sig, data_pos, subcarr_len, N_fft, N_data_sym, N_rx, L,N_tx ); BER(5,SNR_index) = BER(5,SNR_index) + sum(abs(data_bit_seq - reco_bits)); end % for trial = 1:N_trial end % for SNR_index = 1:length(SNR) BER = BER/(N_trial*subcarr_len*N_fft*2*N_data_sym); clc toc figure semilogy(SNR,BER(1,:),'mo-','LineWidth',2); % nTx=1, nRx=1 hold on; semilogy(SNR,BER(2,:),'k+-','LineWidth',2); % nTx=1, nRx=2, MRRC semilogy(SNR,BER(3,:),'cs-','LineWidth',2); % nTx=1, nRx=4, MRRC semilogy(SNR,BER(4,:),'r+:','LineWidth',2); % nTx=2, nRx=1, Alamouti semilogy(SNR,BER(5,:),'bp-','LineWidth',2); % nTx=2, nRx=2, Alamouti xlabel('SNR (dB)'); ylabel('Bit Error Rate'); %axis([0 30 10^-9 0.5]) grid on; title('BER cho DieuChe 4-QAM voi MMRC va Alamouti tren kenh Rayleigh'); legend( 'nTx=1,nRx=1', 'nTx=1,nRx=2,MRRC', 'nTx=1,nRx=4,MRRC', 'nTx=2,nRx=1,Alamouti', 'nTx=2,nRx=2,Alamouti'); SV thc hin: Trang lxxxvi [...]... k thut OFDM trong thụng tin di ng Phỏt qung bỏ s : - Phỏt thanh s DAB - Truyn hỡnh s DVB Thụng tin hu tuyn : - ADSL - HDSL Thụng tin vụ tuyn : - WLAN : 802.11a/g/n (Wifi) - WMAN : 802.16 (WiMax) - Di di ng 4G LTE 2.8 Kt lun chng Qua chng ny, ta ó tỡm hiu c th no l k thut OFDM, bit c lch s hỡnh thnh v phỏt trin ca nú Nguyờn lý c bn v s khi, cỏc khi chc nng trong h thng OFDM Nhc im chớnh ca OFDM l nú... dn OFDM ang chng t nhng u im ca mỡnh trong cỏc h thng vin thụng trờn thc t c bit l trong cỏc h thụng vụ tuyn ũi hi tc cao nh thụng tin di ng v c trong truyn hỡnh s 2.6.2 Nhc im S dng k thut OFDM cú rt nhiu u im vt tri, nhng bờn cnh ú nú cng tn ti mt s nhc im nh sau : - Mt trong nhng nhc im chớnh ca OFDM l nú cú t s cụng sut nh trờn cụng sut trung bỡnh PAPR (Peak to Average Power Ratio) ln Tớn hiu OFDM. .. OFDM cho thụng tin di ng ỹ L Cimini , phõn tớch v mụ phng kờnh mobile k thut s s dng OFDM ỹ 1987 Alard & Lasalle: COFDM cho phỏt thanh truyn hỡnh k thut s SV thc hin: Trang xviii [Type the document title] ỹ Thỏng 9 nm 1988, TH-CSF LER, ln u tiờn th nghim Ti vi k thut s trong OFDM, ti khu vc Pari ỹ 1994: Phng phỏp v thit b cho a truy nhp gia cỏc thit b thu phỏt trong thụng tin vụ tuyn s dng tri ph OFDM. .. (2.2) th biu din cỏc súng mang con trc giao ca tớn hiu OFDM trong min thi gian v min tn s nh hỡnh 2.4 di Hỡnh 2.4 Cỏc súng mang con trc giao trong min thi gian v min tn s Vic x lý (iu ch v gii iu ch) tớn hiu OFDM c thc hin trong min tn s, bng cỏch s dng cỏc thut toỏn x lý tớn hiu s DSP Nguyờn tc ca tớnh trc SV thc hin: Trang xxiii [Type the document title] giao thng c s dng trong phm vi DSP Trong toỏn... bin i nhanh IFFT cho b iu ch OFDM, s dng FFT cho b gii iu ch OFDM Ngy nay k thut OFDM cũn kt hp vi cỏc phng phỏp mó kờnh s dng trong thụng tin vụ tuyn Cỏc h thng ny cũn c gi vi khỏi nim l COFDM (Coded OFDM) Trong cỏc h thng ny tớn hiu trc khi c iu ch OFDM s c mó kờnh vi cỏc loi mó khỏc nhau vi mc ớch chng li cỏc li ng truyn Do cht lng kờnh ( fading v t l tớn hiu trờn tp õm) ca mi súng mang ph l khỏc nhau,... tim nng K thut OFDM nm trong mt lp cỏc k thut iu ch a súng mang trong thụng tin vụ tuyn í tng chớnh trong k thut OFDM l vic chia lng d liu trc khi phỏt i thnh N lung d liu song song cú tc thp hn v phỏt mi lung d liu SV thc hin: Trang xix [Type the document title] ú trờn mt súng mang con khỏc nhau Cỏc súng mang ny l trc giao vi nhau trong min tn s Nh ú gim c nhiu ISI v fading la chn tn s OFDM cũn cú tờn... Trong toỏn hc, s hng trc giao cú c t vic nghiờn cu cỏc vector 2.5 Cỏc khi chc nng trong h thng thu phỏt OFDM Mụ hỡnh cỏc khi chc nng trong h thng thu phỏt tớn hiu OFDM c biu din c th nh trong hỡnh 2.5 sau : s (t ) dn Xn sn x nT xn n(t ) d n X n ~ Xn ~ xn ~ xnT rn r (t ) Hỡnh 2.5 S khi h thng OFDM 2.5.1 Chuyn i S/P v P/S Trong mt h thng truyn d liu ni tip, cỏc ký t c truyn th t ni tip, vi ph tn s ca... di ký t Mi súng mang con, trong phn d liu ca ký t, cú mt s nguyờn ln chu k Do ú bng cỏch copy on cui ca mt symbol v gn vo nú vo u symbol, kt qu l ta c thi gian symbol di hn Hỡnh 2.12 di õy biu din vic chốn khong bo v GP bng cỏch copy mt on ca symbol vo u mi ký t ú SV thc hin: Trang xxxi [Type the document title] Hỡnh 2.12 Chốn khong bo v GP vo mt tớn hiu OFDM Tng chiu di ca symbol l TS=TG + TFFT trong. .. k Nu coherence time nh hn mt chu k tớn hiu di gc ta gi kờnh truyn ú l fading nhanh (fast fading), ngc li nu coherence time ln hn mt chu k tớn hiu thỡ ta gi kờnh truyn ú l kờnh truyn fading chm (slow fading) Hiu ng che chn(Shadowing) xy ra khi cú nhng vt chng ngi t nhiờn nh cỏc i nỳi hay building gia trm thu phỏt gc BTS v trm di ng MS[4] Hỡnh 1.4 Shadowing trong truyn vụ tuyn Cỏc vt tr ngi to ra hiu... c chun mng di ng t bo 3.75G (3GPP & 3GPP2 Long Term Evolution) t tờn l Truy cp gúi OFDM tc cao (HSOPA High Speed OFDM Packet Access ) ỹ 2005 : c cho tiờu chun mng 4G (CJK) ỹ Others : Optical OFDM, DSL (bin th ca k thut OFDM) 2.3 Nguyờn lý c bn ca OFDM Mt trong nhng yờu cu chớnh trong h thng bng rng l kh nng hot ng trong cỏc iu kin tm nhỡn thng b che chn OLOS v iu kin khụng cú tm nhỡn thng NLOS õy ... truyn D DAB Digital Audio Broadcasting Phỏt s qung bỏ DVB Digital Video Broadcasting Truyn hỡnh s qung bỏ DFT F Discrete Fourier Transform Phộp bin i Fourier ri rc FDM Frequency Division Multiplexing... thut s OFDM, ti khu vc Pari ỹ 1994: Phng phỏp v thit b cho a truy nhp gia cỏc thit b thu phỏt thụng tin vụ tuyn s dng tri ph OFDM ỹ 1995: Chun ETSI Digital Audio Broadcasting : tiờu chun c bn OFDM. .. thut OFDM thụng tin di ng Phỏt qung bỏ s : - Phỏt s DAB - Truyn hỡnh s DVB Thụng tin hu tuyn : - ADSL - HDSL Thụng tin vụ tuyn : - WLAN : 802.11a/g/n (Wifi) - WMAN : 802.16 (WiMax) - Di di ng