Tri ph trc tip chui hn lon ng dng trong OFDM s dng iu ch M-PSK TRNG I HC BCH KHOA H NIVIN IN T - VIN THNG---------------

BO CO THC TP TT NGHIPTri ph trc tip chui hn lon ng dng trong OFDM s dng iu ch M-PSK

GVHD: TS. Nguyn Xun Quyn

Sinh vin thc hinBi Vn NhnTVT 4 K5520101959

H Ni, 3/2015

LI NI UVn bng thng ca tn hiu l cc k quan trng trong thng tin truyn thng. Cc k thut truyn thng truyn thng nh: TDMA,FDMA,CDMA u chim mt bng tn rt ln. i vi mt tn hiu s, rng bng tn thit c cng gi tr vi tc bit ca ngun. rng bng tn chnh xc cn thit trong trng hp ny ph thuc vo kiu iu ch (BPSK, QPSK).Xut pht t thc t trn, phng php tri ph (vit tt l SS: Spread Spectrum) gip cho rng bng tn ca tn hiu c m rng rt nhiu, thng thng hng trm ln trc khi pht. Khi c mt ngi s dng trong bng tn SS th s khng c hiu qu. Tuy nhin, mi trng m nhiu ngi s dng, cc ngi dng ny c th dng chung mt bng tn SS lm cho h thng tr nn hiu qu v c hiu sut cao hn.OFDM (Orthogonal Frequency Division Multiplexing) l mt trng hp c bit ca phng php iu ch a sng mang trong c cc sng mang phtrc giao vi nhau, nh vy ph ca tn hiu ca cc sng mang ph cho php chng ln ln nhau m pha thu vn c th khi phc li tn hiu ban u.Vi nhng u im ca OFDM trong x l s tn hiu, nn rt nhiu cc h thng truyn tin ngoi thc t p dng phng php ny.Trong bo co ny, chng em s tm hiu tng quan v k thut OFDM, v k thut hn lon trong thng tin truyn thng. Em xin chn thnh cm n thy gio TS. Nguyn Xun Quyn tn tnh gip v ch bo chng em trong qu trnh thc tp.Vi thi gian v kin thc cn hn hp khng trnh khi tn ti nhiu thiu st. Chng em mong s nhn c s ch bo ca thy . Mong rng ti ny s c hon thin hn na. Ngi thc hin Bi Vn Nhn

TM TT BO COTrong bo co ny, chng em s trnh by tng quan v k thut hn lon trong thng tin truyn thng v m hnh h thng OFDM, to v thu tn hiu OFDM T , xy dng m hnh ng dng k thut tri ph hn lon trong OFDM s dng iu ch:Phn I: Tng quan v k thut hn lon trong thng tin v truyn thngPhn II: Tng quan v OFDM trong thng tin v truyn thngPhn III: Tri ph trc tip chui hn lon ng dng trong OFDM s dng iu ch M-PSK.Phn IV : Kt Lun.

MC LCTM TT BO CO3MC LC4DANH SCH HNH NH6DANH SCH BNG BIU61. L thuyt thng tin hn lon71.1. Hn lon71.1.1. Khi nim v phn loi71.1.2. Dng sng, dng ph v s tng quan81.1.3. Qu o di chuyn : vng ht101.1.4. Chaotic map101.2. Cc h thng thng tin s dng k thut hn lon141.2.1. Tri ph trc tip s dng chui hn lon (CDSSS)141.2.2. Sng mang hn lon (CC)161.2.3. Kha dch pha hn lon (CSK)171.2.4. Kha bt tt hn lon (COOK)191.2.5. iu ch mt n hn lon (CM)192. Tng quan v OFDM trong thng tin v truyn thng212.1. Lch s pht trin212.2. Nguyn l ca OFDM212.3. M t ton hc tn hiu OFDM242.4. Knh truyn v tuyn trong h thng262.4.1. Rayleigh Fading263. Tri ph trc tip chui hn lon ng dng trong OFDM s dng iu ch M-PSK283.1. H thng M-PSK-CDSSS-OFDM28Kt Lun31Ti liu tham kho32

DANH SCH HNH NHHnh 11 Bin i theo thi gian ca bin trng thi trong h Lorenz hn lon8Hnh 12 Bin i theo thi gian ca bin x(t) vi hai iu kin khi ng sai khc nhau rt nh9

Hnh 13 Qu o ca h Lorenz cho cc gi tr r = 28, =10, b = 8/310Hnh 14 Logistic map 2 (a = 3.99, g0=0.5)12Hnh 15 Bermounli Map13Hnh 16 Tent map13Hnh 17 S tri ph trc tip chui hn lon (CDSSS)16Hnh 18 S khi h thng sng mang hn lon17Hnh 19 S kha dch pha hn lon (CSK)18Hnh 110 S khi iu ch mt n hn lon (CM)20Hnh 21 S khi h thng OFDM23Hnh 22 . Tn hiu a ng27Hnh 23 Fading khi thieeurt b di ng di chuyn tn s 900 Hz28

DANH SCH BNG BIU

Bng 1.Cc phng php iu ch tn hiu29

L thuyt thng tin hn lonHn lonKhi nim v phn loiKhi nim v hn lon c s dng rng ri trong k thut c a ra nh sau: Hn lon l trng thi vn ng khng c chu k trong mt qu trnh ca mt h thng xc nh. S vn ng ny ph thuc nhy cm vi iu kin khi ng ca h thng.Ba tnh cht quan trng ca hn lon c nu ra trong khi nim trn l:Vn ng khng c chu k: ng di chuyn ca h thng trong mt phng pha khng i vo bt k im c nh hay qu o c chu k no khi thi gian vn ng tin ti v cng.H thng xc nh: l h thng khng c cc thng s thng k xc sut. y l im khc nhau quan trng gia h thng hn lon v h thng nhiu vi qu trnh ngu nhin.Vn ng bt thng trong h thng hn lon c to ra do tnh phi tuyn bn trong n ch khng phi do nhiu.Ph thuc nhy cm vi cc iu kin khi ng: ng di chuyn xut pht t cc iu kin khi ng c sai khc nhau rt nh (gn nh l nh nhau) s phn tch rt nhanh theo lut s m to ra cc qu o di chuyn hon ton khc nhau.Cc h thng ng hn lon c phn loi theo theo hai dng sau: Dng lin tc ca thi gian, (1.1) trong l bin trng thi c th mt hoc nhiu chiu, v l thi im v gi tr khi ng ca h thng. Dng ri rc ca thi gian, (1.2) vi l gi tr khi ng, l bin trng thi mt hoc nhiu chiu ca h thng bc lp th n.Dng sng, dng ph v s tng quan minh ha cho cc tnh cht trn ca hn lon, chng ta xem xt h thng ng Lorenz lin tc ba chiu c biu din bi h phng trnh vi phn sau: (1.3)

Hnh 11 Bin i theo thi gian ca bin trng thi trong h Lorenz hn lontrong l cc bin trng thi v l cc tham s ca h thng. Vi b tham s , h Lorenz ri vo trng thi vn ng hn lon. R rng tnh h thng xc nh hon ton c tha mn vi h thng ny bi v n c biu din bng h phng trnh vi phn xc nh vi cc thng s c th (khng c thng s thng k). Vi mt iu kin khi ng xc nh, chng ta hon ton c th xc nh trng thi ca h thng mt thi im bt k.Cc Hnh 1.1, 1.2 ch ra kt qu m phng s dng Matlab ca h thng Lorenz vi b tham s nh trn. Trc thi gian chun ha trong cc kt qu m phng l s vng lp tnh ton c thc hin. Chng ta c th nhn thy tnh vn ng khng c chu k ca h thng thng qua s bin i bin khng d on c ca cc bin theo thi gian nh trong Hnh 1. Tnh cht ph thuc nhy cm vi cc iu kin khi ng c th hin trong Hnh 2. Trong bin i bin ca bin vi hai iu kin khi ng c gi tr sai khc rt nh c ch ra. Chng ta c th thy rng cc tn hiu ban u xut pht gn nh cng mt im, nhng sau chng tch bit nhanh chng v tr nn khc nhau hon ton.

Hnh 12 Bin i theo thi gian ca bin x(t) vi hai iu kin khi ng sai khc nhau rt nh trong h Lorenz hn lonQu o di chuyn : vng ht

biu din mt cch r rng nht s vn ng h thng hn lon, chng ta v qu o di chuyn theo thi gian ca cc bin trong khng gian pha ca chng. Dng hnh hc c v ra c gi l vng ht (Attractor). Hnh 3 l qu o ca h Lorenz cho cc gi tr r =28, = 10,b = 8/3

Hnh 13 Qu o ca h Lorenz cho cc gi tr r = 28, =10, b = 8/3

Chaotic mapNhng nm gn y, l thuyt hn lon c nghin cu rng ri v c nhiu m hnh ton hc khc nhau c a ra v hn lon. Cc phin bn chaotic map n t nhiu hng khc nhau. N c th l m hnh iu khin n gin hoc phc tp, mt phng trnh ton hc nh vi phn hoc mt mch in n gin. Mt trong nhng l thuyt hn lon c t rt sm v bt u vo nm 1900, c nghin cu bi Henri Poincare v vn chuyn ng ca ba i tng trong mt lc hp dn ln nhau. Bng cch gii quyt ny, ng m ra mt cch phn tch mt h thng phc tp d dng hn bng cch s dng h thng n gin m vn gi c tnh nng ca h thng gc. y, mt h thng chuyn ng lin tc trong khng gian n-chiu c biu din bng mt h thng ri rc M trong khng gian n-1 chiu trn cc giao im ca mt qu o cng b mt. (1.1) Henry Poincare thy rng c th qu o khng tun hon, khng tng mi v cng khng tip cn mt im c nh. T , nhiu loi thuyt hn lon khc nhau cng bt ngun t phng trnh vi phn tuyn tnh v phi tuyn tnh, bao gm: phng trnh l tha Lyapunov, phng trnh Lorenz, Entropy Kolmororov.Sau y, chng ta s tp trung phn tch mt s a thc n gin biu din chui hn lon sinh ra t mt phng trnh ng hc phi tuyn. Mt m hnh ton hc theo thuyt hn lon thng lin quan n s lp i lp li ca mt cng thc ton hc n gin. Logistic Map 1 (1.2) Logistic map 1 l mt trong nhng logistic map n gin nht c dng trong iu ch tn hiu hn lon. Loi map ny c ng dng trong truyn thng s. s dng loi map ny nh mt chaotic map, iu kin u g0 phi thuc trong khong [-1, 1]. Logistic Map 2. (1.3) Logistic map 2 l mt h thng ng c th biu din c tnh hn lon. Phng trnh logistic ny c gi l m hnh Ver-Hulst. c Pierre Verhulst gii thiu vo gia th k 18, n thng c dng m hnh ha qu trnh tng trng dn s. Cc nh ton hc nghin cu chui ri rc ny v thy rng s biu din ca chui hn lon vi tham s a nm trong khong [3.57, 4], biu din mt h thng hn lon khng tun hon. Loi map ny cng c xut cho h thng truyn thng tri ph.

Hnh 14 Logistic map 2 (a = 3.99, g0=0.5)

Mt s loi chaotic map khc Ngoi 2 phng trnh biu din chui hn lon trn, chng ta c th biu din chui hn lon bng nhiu phng trnh khc nhau. V d nh: Bernoullimap, Tentmap Bernoulli map. (1.4) Bernoulli map cn c bit nh map cp i, thng c dng trong iu ch m ha v chui tri ph.

Hnh 15 Bermounli Map

Tent Map. (1.5)Tent map l chui hn lon cng ging nh vi cc chui hn lon khc, n cng c dng trong tri ph v m ha.

Hnh 16 Tent mapHenon map. (1.6) Henon map l mt trong nhng map nghch 2 chiu n gin nht. Map ny c gii thiu bi Michel Henon nh mt m hnh n gin ha ca phn Poincare trong m hnh Lorenz. N c s dng trong cc h thng bo mt thng tin. Map ny c th biu din di dng khc nh sau: (1.7) (1.8)

Cc h thng thng tin s dng k thut hn lonTrong ny, chng ta s tp trung nghin cu s dng l thuyt hn lon trong k thut thng tin, c bit l trong truyn thng s tri ph. Tn hiu hn lon c th c s dng truyn c tn hiu tng t v s. Khi iu ch mt tn hiu tng t, iu ch tham s hn lon v mt n hn lon l hai phng php in hnh nht. Mt khc, iu ch kha dch hn lon (CSK), kha dch hn lon vi sai (DCSK), kha bt tt hn lon (COOK), v CDMA hn lon c s dng trong iu ch tn hiu s. Hiu sut ca cc h thng ny c th thay i ty thuc vo mi trng truyn dn v cn ph thuc vo phng php gii iu ch.Tri ph trc tip s dng chui hn lon (CDSSS)Trong h thng thng tin tri ph trc tip (DSSS), m gi ngu nhin (PN ) vi tnh nng t ng tng quan v tng quan cho, v d nh chui Gold v chui Kasami c dng lm m tri ph. Trong h thng thng tin tri ph hn lon, s thay m gi ngu nhin(PN) bng chui hn lon. Mt h thng hn lon c trnh by di y, mi biu tng chui hn lon b(k) c th c to ra t cc tn hiu hn lon x(t) bng cch chuyn i sau: (1.9) y, g(x) = 1 nu x = 0 v g(x) =0 nu x1). Sng mang hn lon c th to ra khng gii hn v khng xc nh.

Hnh 18 S khi h thng sng mang hn lonS khi ca h thng CC c trnh by hnh1.6. H thng CC c cu trc tng t nh CSS v DSSS. Tuy nhin, trong iu ch CC thc hin bi sng mang hn lon tng t ch khng phi chui nh phn nh trong CSS. Kha dch pha hn lon (CSK)Trong iu ch kha dch pha hn lon nh phn, tn hiu hn lon mang nng lng bit khc nhau c dng truyn thng tin nh phn. Mt tn hiu thng tin c m ha bng cch truyn mt tn hiu hn lon x1(t) hoc x0(t) ti mt thi im. V d, nu bt nh phn thng tin l 1 xy ra ti thi im t, tn hiu hn lon x1(t) c gi i, v nu bit l 0, tn hiu hn lon x0(t)c gi i. Hai tn hiu hn lon c th n t hai h thng hn lon khc nhau hoc cng h thng vi tham s khc nhau. Tn hiu truyn l: (1.11) Ngi ta cn a ra k thut iu CSK i cc, t l x0(t) =-x1(t). Tn hiu truyn i c th biu din nh sau: (1.12)

Hnh 19 S kha dch pha hn lon (CSK) Gii iu ch c th thng nht hoc khng thng nht. Gii iu ch thng nht c th c xem nh mt b tng quan, ni my thu c sn cc bn sao ca chui hn lon ti my pht. Ph thuc vo tn hiu c truyn, mt trong cc bn sao ny s c ng b vi tn hiu nhn c v bn cn li s c ng b trong trng hp cn li. Hai tn hiu hn lon c nhn vi nhau sau cho qua b tch phn tnh tng quan, cui cng c so snh vi gi tr ngng chn d liu u ra. Nu u vo ca b lc ngng l dng th u ra l 1 v ngc li th l -1. My thu khng thng nht i hi cc tn hiu hn lon c truyn nn c nng lng bit khc nhau.V d, cc mc khc nhau cho bit 1 gi v bit 0. Nu l t bit +1 gi trong khong[(1-l)Tb ,lTb ], tn hiu hn lon x1(t)vi nng lng bit trung bnh Ec c truyn i, cn nu l -1 hoc 0 c gi i, th tn hiu hn lon x2(t) vi nng lng bit trung bnh Ec c truyn i. Hoc ta c th dng mt b to chui hn lon to ra hai tn hiu hn lon vi nng lng bit khc nhau s dng h s tng ch khc nhau b khuch i. Do , bng cch so snh nng lng bit vi mt ngng, chng ta c th d dng khi phc bit thng tin gc c truyn. Hn na, phng php khng thng nht c th khai thc c tnh c th phn bit c ca my pht hn lon cho qu trnh gii iu ch. c bit, nu hai tn hiu hn lon n t dung mt h thng vi tham s phn nhnh khc nhau, gii iu ch c th thc hin bng cch c lng tham s phn nhnh ca tn hiu hn lon c xy dng li. Kha bt tt hn lon (COOK)Kha bt tt hn lon hot ng tng t nh kha dch hn lon ,nhng thay bng gi i hai tn hiu hn lon khc nhau, iu ch kha bt tt hn lon nh mt cng tc bt tt m trng thi ca n ph thuc vo bit thng tin 1 hay 0 tng ng. V d, khi bit thng tin l1. Tn hiu hn lon xo (t) gi i,trng hp cn li th khng c tn hiu gi i. K thut ny cng cp mt khong cch ln hn v nng lng E0 gia hai thnh phn ca mt tn hiu thng tin. Phng php ny c ph hp cho cc ng dng v tuyn trong nh.

iu ch mt n hn lon (CM)

iu ch mt n hn lon (CM) c xut ban u dng truyn cc tn hiu tng t. Cc thng tin tng t c che y bng mt tn hiu bng rng hn lon. Da trn kh nng ng b ha hn lon, tn hiu hn lon mt n c s dng ti bn thu ng b ha hn lon. Bng cch ly tn hiu hn lan ti to t tn hiu tn hiu nhn c, thng tin tn hiu c th sau c xc nh. Mi hot ng iu ch v gii iu ch c th hin hnh di y

Hnh 110 S khi iu ch mt n hn lon (CM)

Tng quan v OFDM trong thng tin v truyn thngLch s pht trinTrong nhng nm gn y,Phng thc ghp knh phn chia theo tn s trc giao FDM (Orthogonal Frequency Division Multiplexing) khng ngng c nghin cu v m rng phm vi ng dng bi nhng u im ca n trong tit kim bng tn v kh nng chng li Fading chn lc theo tn s cng nh xuyn nhiu bng hp.K thut OFDM do R.W Chang pht minh nm 1966 M. Tri qua 40 nm hnh thnh v pht trin nhiu cng trnh khoa hc v k thut ny c thc hin khp ni trn th gii. c bit l cc cng trnh ca Weistein v Ebert, ngI chng minh rng php iu ch OFDM c th thc hin bng php bin I IDFT v php gii iu ch bng php bin I DFT. Pht minh ny cng vI s pht trin ca k thut s lm cho k thutNguyn l ca OFDMK thut iu ch OFDM l mt trng hp c bit ca phung php iu ch a sng mang trong cc sng mang ph trc giao vi nhau, nh vy ph tn hiu cc sng mang ph cho php chng ln ln nhau m pha thu vn c th khi phc li tn hiu ban u. S chng ln ph tn hiu lm cho h thng OFDM c hiu sut s dng ph ln hn nhiu so vi cc k thut iu ch thng thng. Nh , OFDM chia dng d liu tc cao thanh cc dng d liu tc thp hn v pht ng thi trn mt s sng mang, ta thy rng trong mt s iu kin c th, c th tng dung lng ng k cho h thng OFDM bng cch lm thch nghi tc d liu trn mi sng mang ty theo t s tn hiu trn tp m SNR ca sng mang .Trong OFDM, d liu trn mi sng mang chng ln d liu trn cc sng mang ln cn. S chng chp ny l nguyn nhn lm tng hiu qu s dng ph ca OFDM. V bn cht, OFDM l mt trng hp c bit ca phng php a sng mang theo nguyn l chia dng d liu tc cao thnh dng d liu tc thp hn v pht ng thi trn mt s sng mang c phn b mt cch trc giao.Nh thc hin bin i chui d liu t ni tip sang song song nn thi gian symbol tng ln. Do , s phn tn theo thi gian gy bi tri rng tr do truyn dn a ng gim xung OFDM khc vi FDM nhiu im. Trong pht thanh thng thng mi i pht thanh truyn trn mt tn s khc nhau,s dng hiu qu FDM duy tr s ngn cch gia nhng i.Tuy nhin khng c s kt hp ng b gia mi trm vi cc trm khc.Vi cch truyn OFDM, nhng tn hiu thng tin t nhiu trm c kt hp trong mt dng d liu ghp knh n. Sau gia liu ny c truyn khi d dng khi OFDM c to ra t gi dy c nhiu sng mang. Tt c cc sng mang th cp trong tn hiu OFDM c ng b thi gian v tn s vi nhau, cho php kim sot can nhiu gia cc sng mang. Cc sng mang ny chng ln nhau trong min tn s, nhng khng can nhiu gia cc sng mang (ICI) do bn cht trc giao ca iu ch. Vi FDM nhng tn hiu truyn cn c khong bo v ln gia nhng knh ngn nga can nhiu. iu ny lm gim hiu qu ph. Tuy nhin vi OFDM s ng gi trc giao nhng sng mang lm gim ng k khong bo v ci thin hiu qu ph.

Hnh 21 S khi h thng OFDM u tin, d liu vo tc cao c cha thnh dng d liu song song tc thp nh b chuyn i ni tip thnh song song (S/P). Mi dng d lieu song song dau c m ha s dng thut ton sa li tin (FEC) v c sp xp theo mt trnh t hn hp. Nhng symbol hn hp c a n u vo ca khi IDFT. Khi ny s tnh ton cc mu thi gian tng ng vi cc knh nhnh trong min tn s. Sau , khong bo v c chn vo gim nhiu xuyn k t ISI do truyn trn cc knh di ng v tuyn a ng. Sau cng b lc pha pht nh dng tn hiu thi gian lin tc s chuyn i ln tn s cao trn ln cc knh truyn. Trong qu trnh truyn, trn cc knh s c c ngun nhiu gy nh hng nh nhiu trng cng AWGN, Rayleigh Fading ph thu, tn hiu c chuyn xung tn s thp v tn hiu ri rc t c ti b lc thu. Khong bo v c loi b v cc mu c chuyn t min thi gian sang min tn s bng php bin i DFT dng thut ton FFT. Sau ,ty vo s iu ch c s dng, s dch chuyn v bin v pha ca cc sng mang nhnh s c cn bng bng b cn bng knh. Cc symbol hn hp thu c s c sp xp ngc tr li v c gii m. Cui cng chng ta s thu nhn dng d liu ni tip ban u.M t ton hc tn hiu OFDM Tn hiu OFDM pht phc bng tn gc c xc nh nh sau:

(2.1)Trong sk(t-kT) l tn hiu OFDM pht phc bng gc th k c xc nh nh sau:

(2.2)Trong :T l di k hiu OFDMTFFT l thi gian FFT, phn hiu dng ca k hiu OFDMTG l thi gian bo v, thi gian ca tin t chu trnhTwin l thi gian m ca tin t v hu t to dng phf=1/TFFT l phn cch tn s gia hai sng mangN l di FFT, s im FFTk l ch s v k hiu c truyni l ch s v sng mang con, i{-N/2, -N/2+1, -1, 0, +1, ., -N/2} xi,k l vect im chm tn hiu, l k hiu phc (s liu, hoa tiu, rng) c iu ch ln sng mang con i ca k hiu OFDM th k.w(t) xung to dng c biu din nh sau:

(2.3)

Phn tch (3.4) ta thy biu thc ny ging nh biu thc ca dy Fourier sau:

(2.4)trong cc h s Fourier phc th hin cc vect ca chm tn hiu phc cn nf0 th hin cc sng mang con i/TFFT. Trong h thng s, dng sng ny c th c to ra bng bin i Fourier ngc nhanh (IFFT). Chm s liu xi,k l u vo IFFT v k hiu OFDM min thi gian l u ra. Tn hiu u ra ca b iu ch v tuyn c xc nh nh sau:

(2.5)trong sRF,k(t-kT) l tn hiu OFDM v tuyn th k c biu din nh sau:

(2.6)Trong fc l tn s sng mang RF.

Knh truyn v tuyn trong h thngS suy gim tn hiu l s suy hao mc cng sut tn hiu trong qu trnh truyn t im ny n im khc. iu ny c th l do truyn ti, do cc ta nh cao tng v hiu ng a ng. Cc hnh di m t mt s nguyn nhn lm suy gim tn hiu. Bt k mt vt cn no trn ng truyn c th lm suy gim tn hiu.Rayleigh FadingTrong ng truyn v tuyn, tn hiu RF t my pht c th b phn x t cc vt cn nh i, nh ca, xe csinh ra nhiu ng tn hiu n my thu (hiu ng a ng) dn n lch pha gia cc tn hiu n my thu lm cho bin tn hiu thu b suy gim. Hnh di y ch ra mt s trng hp m tn hiu a ng c th xy ra.

Hnh 22 . Tn hiu a ngMi quan h v pha gia cc tn hiu phn x c th l nguyn nhn gy ra nhiu c cu trc hay khng cu trc. iu ny c tnh trn cc khong cch rt ngn, v vy y gi l fading nhanh. Mc thay i tn hiu c th thay i trong khong 10-30dB trn mt khong cch ngn. Hnh v di m t cc mc suy gim khc nhau c th xy ra do fading.Hnh 23 Fading khi thieeurt b di ng di chuyn tn s 900 HzTri ph trc tip chui hn lon ng dng trong OFDM s dng iu ch M-PSKH thng M-PSK-CDSSS-OFDMC rt nhiu m hnh khc nhau kt hp LCG vo trong h thng OFDM.Trong bo co ny, tp trung m t m hnh tng qut, phn tch kt qu m phng ca h thng MPSK-CDSSS-OFDM.Trong h thng m ti thc hin gm c 4 khi chnh, c th l cc khi nh sau:-Khi iu ch v gii iu ch tn hiu.-Khi thc hin tri ph v gii tri ph hn lon.-Khi thc hin cc bin i tn hiu h thng OFDM. -Knh truyn m phng gm 2 knh l: nhiu Guassian v Rayleigh Fading.Hnh 2.3 di y m t s tng qut ca h thng c thc hin trong trong bo co ny.Trong h thng OFDM, tn hiu u vo l dng bit nh phn. Do , iu ch trong OFDM l cc qu trnh iu ch s v c th la chn trn yu cu hoc hiu sut s dng bng thng knh. Dng iu ch c th qui nh bi bit ng u vo M v s phc dn = an +bn ng ra. Bng 1.Cc phng php iu ch tn hiuMDng iu chan ,bn

2BPSK

4QPSK

1616-QAM

6464-QAM

Figure 2.4. S khi h thng M-PSK-CDSSS-OFDMKt LunTrong bo co ny trnh by nhng khi nim v nguyn l c bn ca hn lon v OFDM, ng thi p dng n vo trong m hnh h thng tri ph trc tip chui hn lon s dng iu ch M-PSK.Qua y em xin cm n s hng dn nhit tnh ca thy gio TS. Nguyn Xun Quyn trong qu trnh tm hiu ti ny.

Ti liu tham kho1 . L Vn Cng ng dng k thut tri ph trong OFDM s dng iu ch M-PSK.2. Nguyn Xun Quyn Phng php iu ch v tri ph chui trc tip s dng thi gian xung hn lon cho thng tin s

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