HC VIN CNG NGH BU CHNH VIN THNGKHOA VIN THNG 1----------

BO COTHC TP TT NGHIP

TRUYN HNH K THUT S MT T V QU TRNH CHUYN I SANG DVB-T2Gio vin hngdn: C THNH

Sinh vin thc hin: LU DON BC

LpKhaH: D10VT4: 2010 2015: i Hc Chnh Quy

H NI 7/2014

NHN XT CA N V THC TP

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H Ni, ngy thng nm 2014

LI CM NEm xin gi li cm n chn thnh v su sc n cc thy c Hc Vin Cng Ngh Bu Chnh Vin Thng d tn tnh dy d v to iu in cho em c nghin cu, hc tp v cung cp cho em cc thng tin, kin thc v cng qu bu v cn thit trong sut thi gian hc tp cng nh lm n em c th thc hin v hon thnh tt ti ny.c bit, em xin chn thnh cm n thy NCS. c Thnh Vin Khoa Hc K Thut Bu in tn tnh hng dn v gip em trong thi gian thc hin ti.Mc d em c gng hon thnh ti Thc Tp Tt Nghip ny trong phm vi v kh nng cho php nhng chc chn s khng trnh khi nhng thiu st v hn ch nht nh. V vy, em rt mong nhn c s ch bo v kin ng gp ca thy c v cc bn ti ca em c th hon thin hnEm xin chn thnh cm n !

MC LCNHN XT CA N V THC TP2LI CM N3MC LC4DANH MC HNH V, BNG BIU6THUT NG VIT TT7LI NI U8CHNG I: TNG QUAN V TRUYN HNH S101.1 Gii thiu v truyn hnh s101.2 c im ca truyn hnh s111.2.1 Yu cu v bng tn111.2.2 T l tn hiu/tp m (S/N)111.2.3 Mo phi tuyn121.2.4 Chng ph121.2.5 X l tn hiu121.2.6 Khong cch gia cc trm truyn hnh ng knh121.2.7 Hiu ng Ghosts (bng ma)131.3 u im chnh ca truyn hnh s131.4 Truyn dn tn hiu s131.4.1 Truyn qua cp ng trc:131.4.2 Truyn tn hiu truyn hnh s bng cp quang141.4.3 Truyn tn hiu truyn hnh s qua v tinh.141.4.4 Pht sng truyn hnh s trn mt t.141.5 Cc tiu chun truyn hnh s mt t hin nay trn th gii151.5.1 Chun ATSC151.5.2. Chun ISDB-T171.5.3. Chun DVB181.5 Kt lun chng I19CHNG II: TRUYN HNH S MT T THEO TIU CHUN CHU U TH H TH NHT (DVB-T)202.1. Gii thiu v h thng truyn hnh s mt t DVB-T202.2. S khi h thng truyn hnh s mt t DVB-T202.2.1. H thng pht DVB-T202.2.2 H thng thu DVB-T212.3 iu ch COFDM trong DVB-T222.3.1 Nguyn l232.3.2 S lng sng mang232.3.3 c tnh trc giao v vic s dng DFT/FFT252.3.4 T chc knh trong OFDM282.3.5. Phng thc mang d liu trong COFDM312.6 Kt lun chng II33CHNG III: TRUYN HNH S MT T THEO TIU CHUN CHU U TH H TH 2 (DVB-T2)343.1. Gii thiu343.2. Nhng yu cu c bn i vi chun DVB-T2353.3. Tiu chun DVB-T2353.3.1. M hnh cu trc DVB-T2353.3.2. Lp vt l DVB-T2373.4. Kt lun chng III38CHNG IV: QU TRNH CHUYN I T DVB-T SANG DVB-T2 CHU U V MT S KIN NGH KHI TRIN KHAI DVB-T2 TI VIT NAM.394.1. S ra i tt yu ca tiu chun truyn hnh s mt t th h th hai DVB-T2.394.1.1. Cc yu cu v thng mi i hi cho ra i mt th h th hai cho tiu chun truyn hnh k thut s DVB-T.394.1.2. Mi quan h vi tiu chun s mt t DVB-T hin ti.404.1.3. Mc ch ca cc yu cu thng mi404.2. Qu trnh chuyn i t DVB-T sang DVB-T2. Mt s vn cn xem xt khi trin khai DVB-T2404.2.1. Cc yu cu ca chun DVB-T2404.2.3 Kh nng chuyn i t DVB-T sang DVB-T2424.2.4 Cc chin lc trin khai DVB-T2434.2.5. Hin trng (th nghim, thng bo trin khai dch v)444.2.6 Cc kin ngh v cng ngh cho ton Chu u.454.3. Qu trnh trin khai truyn hnh s mt t Vit Nam464.4. Nhng kin ngh khi trin khai DVB-T2 Vit Nam484.5. Kt lun chng IV48TI LIU THAM KHO49

DANH MC HNH V, BNG BIU

THUT NG VIT TTASKAmplitude Shift KeyingKha dch bin

ATSCAdvanced Television System Committeey ban h thng truyn hnh mi (ca M)

BPSKBinary Phase Shift KeyingKha dch pha hai mc

COFDMCode Orthogonal Frequency Division MultiplexingGhp a tn trc giao c m

DBPSKDiferential Binary Phase Shift KeyingKha dch pha vi sai hai mc

DCTDiscerte Cosine TransformChuyn i cosin ri rc

DFTDiscrete Fourier TransformChuyn i Fourierri rc

DPCMDifferential Pulse Code Modulationiu ch xung m vi sai

DQPSKDifferential Quadratue Phase Shift KeyingKho dch pha vi sai bn mc

DTTBDigital Terrestrial Television BroadcastingTruyn dn truyn hnh s mt t

DVBDigital Video BroadcastingQung b truyn hnh s

EDTVEnhanced Definition TeleVisionTruyn hnh phn gii nng cao

FECForward Error CorrectionHiu chnh li trc

FFTFast Fourier TransformChuyn i Fourier nhanh

IDFTInverse DFTDFT ngc

IFFTInverse FFTFFT ngc

ISDB-TIntergeted Services Digital Broadcasting TerrestrialH thng truyn hnh s mt t s dng mng a dch v (Nht

LDTVLimited Definition TeleVisionTruyn hnh phn gii gii hn

MPEGMoving Pictures Experts GroupNhm chuyn gia nghin cu v tiu chun hnh nh ng

OFDMOrthogonal Frequency Division MultiplexingGhp a tn trc giao

PALPhase Alternating LineH truyn hnh mu PAL (pha thay i theo dng qut)

PSKPhase Shift KeyingKho dch pha

QAMQuadrature Amplitude Modulationiu ch bin vung gc

QPSKQuadratue Phase Shift KeyingKho dch pha vung gc

SDTVStandard Definition TeleVisionTruyn hnh phn gii tiu chun

SFNSingle Frequency NetworkMng n tn s

UHFUltra-High Frequency

VHFVery-High Frequency

VLCVariable Length CodingM c di thay i

VSBVestigial sidebandBin tn ct

LI NI UVi s pht trin ca kinh t v khoa hc k thut, cc nghnh cng ngh trong c cng ngh in t vin thng c s pht trin vt bc trong ba thp k va qua em li nhiu thnh tu pht minh ng dng trong sn xut, trong i sng x hi. Cng ngh truyn hnh l mt b phn quan trng trong lnh vc in t vin thng, n c nhng ng dng rng ri to lntrong pht trin vn ha i sng tinh thn x hi. Trong hn mt thp k qua chng ta chng kin s chuyn i mnh m ca cng ngh truyn hnh t phng thc tng t xang cng ngh s. Vit Nam qu trnh chuyn i ny thc s ngon mc vi s ph cp tng bc trong lnh vc truyn hnh qung b v truyn hnh tr tin. T u nhng nm 90 cho n nay nghnh truyn hnh ng dng cc thnh tu v cng ngh truyn hnh s trong truyn dn v tinh, pht trinmng truyn hnh cp v ph cp h thng truyn hnh s mt tCng vi s pht trin ca cng ngh truyn hnh, chun truyn hnh sDVB-T l chun pht sng truyn hnh s mt t c trin khai thnh cng, c nhiu nc chp nhn. Tuy nhin, t sau s ra i ca chun DVB-T th cc nghin cu v k thut truyn dn vn tip tc ctrin khai. Mt khc, nhu cu v ph tn cao cng khin cho vic gia tng hiu qu s dng ph tn ln mc ti a cng cp thit. T pht trin ln chun truyn hnh s mt t th h th 2 l DVB-T2.Vic nghin cu tm hiu cc c tnh cng ngh ca tiu chun truyn hnh s DVB-T trong qu trnh pht trin ln th h mi DVB-T2 l nhim v cn thit i vi cc c quan nghin cu ng dng truyn hnh cng nh cn b k thut nghin cu trong lnh vc ny . l l do em chn ti: Truyn hnh k thut s mt t DVB-T v qu trnh chuyn i sang DVB-T2B cc bi bo co gm 4 chng:CHNG I: TNG QUAN V TRUYN HNH SCHNG II: TRUYN HNH S MT T THEO TH H TH NHT DVB-TCHNG III: TRUYN HNH S MT T THEO TIU CHUN CHU U TH H TH HAI (DVB-T2)CHNG IV: QU TRNH CHUYN I T DVB-T SANG DVB-T2 CHU U V MT S KIN NGH TRIN KHAI VIT NAMSau mt thi gian tm hiu v nghin cu, c s hng dn khoa hc tn tnh ca Thy gio NCV.Nguyn c Thnh, bi bo co c hon thnh.Do thi gian c hn, trnh bn thn cn hn ch, thm vo lun vn ca em l vn tng i mi nn khng th trnh khi nhng sai st. Knh mong c s ng gp ca cc thy, cc c cng cc bn.

CHNG I: TNG QUAN V TRUYN HNH S1.1 Gii thiu v truyn hnh sTruyn hnh s (Digital Television) l mt phng php truyn hnh hon ton mi, l tn gi mt h thng truyn hnh m tt c cc thit b k thut t Studio cho n my thu u lm vic theo nguyn l truyn hnh s. Trong , mt hnh nh quang hocjdo camera thu c qua h thng ng knh, thay v c bin i thnh tn hiu in bin thin tng t nh hnh nh quang hc ni trn (c v chi v mu sc) s c bin i thnh mt dy tn hiu nh phn (dy cc s 0 v 1) nh qua trnh bin i tng t sTrn th gii, cc nh iu hnh cp, v tinh, trn mt t u ang chuyn ng n mi trng s. Chu u, truyn hnh s c s dng Anh (pht sng truyn hnh s, Chu u, truyn hnh s c s dng Anh (pht sng truyn hnh s 1999, c, Php, Ireland, Ty Ban Nha, Thy in). Hu ht cc nh phn tch cng nghip u d bo vic chuyn dch ln truyn hnh s l mt s tin ha (evolution), n lm thay i cch sng ca hng trm triu gia nh trn th gii, cc cng ty cho rng s hi t gia my tnh c nhn, my thu hnh (TV set) v Internet bt u v iu s dn n s chuyn ha cc i v my tnh, i vi ngi tiu dng, k nguyn mi v s s nng cao vic xem truyn hnh ngang vi cht lng chiu phim, m thanh ngang vi cht lng CD cng vi hng trm knh truyn hnh mi v nhiu dch v mi, truyn hnh s cho thu bao xem c nhiu chng trnh truyn hnh vi cht lng cao nht.i vi cc nh pht sng truyn hnh, vic chuyn dch ln mi trng s s lm gim vic s dng bng tn/knh, lm tng kh nng cung cp cc ng dng dng Internet cho thu bao v m ra mt lnh vc mi, cc c hi mi v thng mi. Nhiu dch v mi trn c s truyn hnh s s c hnh thnh: Truy cp Internet ti cc tc Chi Game trn mng vi nhiu ngi Video theo yu cu VOD (video-on-demand) Cung cp cc dng video v audio Dch v thanh ton tin t nh (home banking) Cc dch v thng mi in t Cp nht phn mm my tnh Truyn thanh, truyn hnh a phng tin (Multimedia) c bo in tTrn nm mi nm qua, truyn hnh s dng tn hiu tng t nh l mt phng tin truyn dn pht sng. Vic chm dt truyn hnh tng t v pht trin truyn hnh s i hi phi u t mi my thu hnh s, my pht hnh s, cc thit b sn xut v hu k s cho chng trnh truyn hnh. iu dn n phi s dng mt mt bng chung, m ra cc c hi cho th trng dn dng.Truyn hnh s c tc truyn d liu cao, cho php cung cp ni dung a phng tin phong ph v ngi xem truyn hnh c th lt qua Internet bng my thu hnh. Nh c k thut nn, c th pht sng nhiu chng trnh truyn hnh trn mt knh sng (truyn hnh tng t pht sng 1 chng trnh/ 1 knh sng).1.2 c im ca truyn hnh s1.2.1 Yu cu v bng tnYu cu v bng tn l mt s khc nhau r nht gia tn hiu s v tn hiu tng t, tn hiu s vn gn lin vi yu cu bng tn rng ln. i vi tn hiu s tng hp yu cu tn s ly mu bng bn ln tn s sng mang mu nh i vi h thng NTSC l 14,4 MHz nu thc hin m ha vi nhng m 8 bit, tc bt s l 115,2 Mbit/s rng bng tn khong 58 MHz. Trong khi , tn hiu tng t cn mt bng tn 4,3 MHz. Nu c thm cc bit sa li yu cu bng tn s phi tng ln na. tuy nhin trong thc t nng tn ny khng phi ch dng cho tn hiu hnh nh ngc li vi dng s kh nng cho php gim rng tn s l rt ln. Vi cc k thut nn bng tn t l t c c th ln ti 100:1 hay hn na. Cc tnh cht c bit ca tn hiu hnh nh nh s lp li, kh nng d bo cng lm tng thm kh nng gim bng tn tn hiu.1.2.2 T l tn hiu/tp m (S/N)Mt trong nhng u im ln nht ca tn hiu s l kh nng chng nhiu trong qu trnh x l ti cc khu truyn dn v ghi. Nhiu tp m trong h tng t c tnh cht cng, t l S/N ca ton b h thng l do tng cng cc ngun nhiu thnh phn gy ra. V vy lun nh hn t l S/N ca khu c t l thp nht. Nhiu trong tn hiu s dc khc phc nh cc mch sa li. Bng cc mch ny c th khi phc li cc dng bit nh ban u. Khi c qu nhiu bt li, s nh hng ca nhiu c lm gim bng cch che li.T l S/N ca h thng s gim rt t hay khng thay i cho n khi t l li BER qu ln, lm cho cch mch sa li v che li mt tc dng. Khi dng bit khng cn c ngha tin tc. Trong khi i vi cc h thng tng t khi c ngun nhiu ln tn hiu vn c th s dng c.Tnh cht ny ca h thng s c bit c ch cho vic sn xut chng trnh truyn hnh vi cc chc nng bin tp phc tp cn nhiu ln dc ghi. Ghi bng bng tn hiu s c s dng rng ri trong cc nm gn y. Vic truyn tn hiu nhiu chng cng c thc hin rt thun li vi tn hiu s m khng lm suy gim cht lng tn hiu hnh.Tuy nhin trong truyn hnh qung b, tn hiu s gp phi vn kh khn khi thc hin kim tra cht lng cc im trn knh truyn.1.2.3 Mo phi tuynTn hiu s khng b nh hng bi mo phi tuyn trong qu trnh ghi truyn cng nh i vi t l S/N, tch cht ny rt quan trongtrong vic ghi c chng trnh nhiu ln c bit vi cc h thng truyn hnh nhy cm vi cc mo phi tuyn khuych i vi sai nh h NTSC1.2.4 Chng phMt tn hiu s c ly theo mu c chiu thng ng v chiu ngang nn c kh nng xy ra chng ph theo c hai hng. Theo chiu thng ng, chng ph trong h thng s v tng t nh nhau. ln mo chng ph thep chiu ngang ph thuc v cc thnh phn tn s vt qu tn s ly mu gii hn Nyquyist. ngn nga hin tng chng ph theo chiu ngang, c th thc hin bng cch s dng tn s ly mu ln hn hai ln thnh phn tn s cao nht trong h thng tng t.1.2.5 X l tn hiuTn hiu s c th c chuyn i v x l tt cc chc nng m h thng tng t khng lm c hoc gp nhiu kh khn. Sau khi bin i A/D, tn hiu cn li mt chiu cc s bit 0, 1 c th thao tc cc cng vic phc tp m khng lm gim cht lng hnh nh. Kh nng ny c tng ln nh vic lu tr cc bit trong b nh v c th c ra vi tc nhanh. Cc cng vic tn hiu s c th thc hin c d dng l: Sa li gc thi gian , chuyn i tiu chun, gim rng bng tn.1.2.6 Khong cch gia cc trm truyn hnh ng knhTn hiu s cho php cc trm truyn hnh ng knh thc hin mt khong cch gn nhau hn nhiu so vi h thng tng t m khng b nhiu. Mt phn v tn hiu s t chu nh hng ca nhiu ng knh, mt phn l do kh nng thay th xung xa v xung ng b bng cc t m ni m h thng truyn dn tng t gy ra nhiu ln nht. Vic gim khong cch gia cc trm ng knh kt hp vi vic gim bng tn tn hiu, to c hi cho nhiu trm pht hnh c th pht cc chng trnh vi phn gii cao.1.2.7 Hiu ng Ghosts (bng ma)Hiu ng ny xy ra trong h thng tng t do tn hiu truyn dn n my thu theo nhiu ng. Vic trnh nhiu ng knh ca h thng s cng lm gim i hin tng ny trong truyn hnh qung b1.3 u im chnh ca truyn hnh sTruyn hnh s c nhiu u im so vi truyn hnh tng t nh: hnh nh sch, r nt, m thanh ngang vi m thanh ca CD, tnh chng nhiu cao, in sao nhiu ln vn m bo hnh nh cht lng tt, thun li cho khu hu k, lm k xo p hn Tuy nhin, truyn hnh s kt hp vi k thut nn s s cho nhiu im ni bt hn na nh tit kim b nh, tit kim knh truyn. Mt knh truyn hnh c th truyn trn sau chng trnh m mi chng trnh km theo hai n bn ng ting. Vi cc u im ca mnh, h thng truyn hnh s c thc hin hu ht cc quc gia trn th gii. y l mt qu trnh tt yu, Truyn hnh Vit Nam cng ang giai on chuyn tip. Vic nghin cu truyn hnh s v la chn cc tiu chun cho truyn hnh Vit Nam ang c tin hnh.Hin nay qu trnh s ha tn hiu truyn hnh Vit Nam l s thay th dn cc cng on, trang thit b t tng t sang s. l qu trnh s ha tng phn. Ri y truyn hnh s s thay th hon ton truyn hnh tng t, to iu kin cho ngnh cng nghip ny pht trin mnh m hn, kt hp vi cc mng truyn thng khc, to thnh mt th gii thng tin s, phc v cho con ngi mt cch hu hiu

1.4 Truyn dn tn hiu s1.4.1 Truyn qua cp ng trc: truyn tn hiu video s c th s dng cp ng trc cao tn. t c cht lng truyn hnh cao, cp c chiu di 2500km cn m bo mc li trn on trung chuyn 10-11 10-10. rng knh dng cho tn hiu video bng khong 3/5 tc bit ca tn hiu. rng knh ph thuc vo phng php m ho v phng php ghp knh theo thi gian cho cc tn hiu cn truyn v rng hn nhiu so vi rng knh truyn tn hiu truyn hnh tng t.1.4.2 Truyn tn hiu truyn hnh s bng cp quangCp quang nhiu u im trong vic truyn dn tn hiu so vi cp ng trc nh:+ Bng tn rng cho php truyn cc tn hiu s c tc cao.+ suy hao thp trn mt n v chiu di + Suy gim gia cc si quang n cao (80dB)Mun truyn tn hiu video bng cp quang phi s dng m truyn thch hp. pht hin c li truyn ngi ta s dng thm cc bt kim tra chn. 1.4.3 Truyn tn hiu truyn hnh s qua v tinh.Knh v tinh khc vi knh cp v knh pht sng trn mt t l c bng tn rng v s hn ch cng sut pht. Khuch i cng sut ca cc Transponder lm vic gn nh bo ho trong cc iu kin phi tuyn. Do s dng iu ch QPSK l ti u. Cc h thng truyn qua v tinh thng cng tc di tn s c Ghz.V d:Bng Ku: ng ln: 14 15GHz.ng xung: 11,7 12,5 GHz1.4.4 Pht sng truyn hnh s trn mt t.H thng pht sng truyn hnh s mt t s dng phng php iu ch COFDM (ghp knh theo tn s m trc giao). COFDM l h thng c kh nng chng nhiu cao v c th khc phc hiu ng bng ma, cho php bo v pht sng s trc nh hng ca can nhiu v cc knh ln cn.H thng COFDM hot ng theo nguyn tc iu ch dng d liu bng nhiu sng mang trc giao vi nhau. Do mi sng mang iu ch vi mt dng s liu.Cc tn hiu s liu c iu ch M-QAM, c th dng 16-QAM hoc 64-QAM. Ph cc sng mang iu ch c dng sinx/x trc giao. C ngha cc sng mang k nhau c gi tr cc i ti cc im 0 ca sng mang trc v sau iu ch v gii iu ch cc sng mang thc hin nh b bin i Fourier nhanh FFT di dng FFT 2K v FFT 8K. Vi loi vi mch trn c th thit k cho hot ng ca 6785 sng mang. Cc hng RACE c thit b pht sng truyn hnh cho 896 sng mang, hng NTL cho 2000 sng mang.1.5 Cc tiu chun truyn hnh s mt t hin nay trn th giiHin nay trn th gii c 3 tiu chun v truyn hnh s:- DVB-T: Chu u, Australia, New Zealand,- ATSC: Hn Quc, i Loan, Canada v M... - ISDB-T: Nht bn, BrasilC th tham kho s la chn cc tiu chun truyn hnh s trn th gii. cng l yu t gip ta nh hng vic nghin cu, vic la chn tiu chun ph hp cho ring mnh.1.5.1 Chun ATSCH thng ATSC c cu trc dng lp, tng thch vim hnh OSI 7 lp ca cc mng d liu. Mi lp ATSC c th tng thch vi cc ng dng khc cng lp. ATSC s dng dng thc gi MPEG-2 cho c Video, Audio v d liu ph. Cc n v d liu c di c nh ph hp vi sa li, ghp dng chng trnh, chuyn mch, ng b, nng cao tnh linh hot v tng thch vi dng thc ATM.Tc bit truyn ti 20Mbps cp cho mt knh n HDTV hoc mt knh truyn hnh chun a chng trnh.Chun ATSC cung cp cho c hai mc: truyn hnh phn gii cao (HDTV) v truyn hnh tiu chun (SDTV). c tnh truyn ti v nn d liu ca ATSC l theo MPEG-2.ATSC c mt s c im sau:Tham sc tnh

VideoNhiu dng thc nh (nhiu phn gii khc nhau). Nn nh theo MPEG-2, t MP@ML ti MP@HL.

Audiom thanh Surround ca h thng Dolby AC-3

D liu phCho cc dch v m rng (v d hng dn chng trnh, thng tin h thng, d liu truyn ti ti computer).

Truyn tiDng ng gi truyn ti a chng trnh. Th tc truyn ti MPEG-2.

Truyn dn RFiu ch 8-VSB cho truyn dn truyn hnh s mt t

Bng 1.1: c im c bn ca ATSCPhng php iu ch VSB ca tiu chun ATSC. Phng php iu ch VSB bao gm hai loi chnh: Mt loi dnh cho pht sng mt t (8-VSB) v mt loi dnh cho truyn d liu qua cp tc cao (16-VSB). C hai u s dng m Reed - Solomon, tn hiu pilot v ng b tng on d liu. Tc biu trng (Symbol Rate) cho c hai u bng 10,76Mb/s. N c gii hn t s tn hiu trn nhiu (SNR) l 14,9dB v tc d liu bng 19,3 Mb/s.D liu c truyn theo tng khung d liu. Khung d liu bt u bng on d liu ng b mnh u tin v ni tip bi 312 on d liu khc. Sau n on d liu ng b mnh th 2 v 312 on d liu ca mnh sau.Mi on d liu bao gm 4 biu trng dnh cho ng b on d liu v 828 biu tng d liu.Mt gi truyn ti MPEG-2 cha 188 bytee d liu v 20 byte tng sy cho 208 buyte. Vi t l m ha 2/3, u ra ca m sa sai ta c:208 x 3/2 = 312 bytes. 312 bytes x 8 bit = 2.496 bit. Tm li mt on d liu cha 2.496 bit. Cc biu trng s c iu ch theo phng thcnn sng mang v hu ht di bin di iu bin ct. Tn hiu pilot c s dng phc hi sng mang ti u thu, c cng thm ti v tr 350 KHz pha trn gii hn di di tn.

Hnh 1.1: Khung d liu VBS1.5.2. Chun ISDB-TH thng chuyn dng cho pht thanh truyn hnh s mt t c hip hi ARIB a ra v c hi ng cng ngh vin thng ca B thng tin bu in (MPT) thng qua nh mt bn d tho tiu chun cui cng Nht Bn. Bn thng s k thut di m t chi tit h thng truyn hnh s mt t s dng mng a dch v (ISDB-T). H thng ny c th truyn dn cc chng trnh truyn hnh, m thanh hoc d liu tng hp. ISDB-T s dng tiu chun m ho MPEG-2 trong qu trnh nn v ghp knh. H thng s dng phng php ghp a tn trcgiao OFDM cho php truyn a chng trnh phc tp vi cc iu kin thu khcnhau, truyn dn phn cp, thu di ng v.v... cc sng mang thnh phn c iu ch QPSK, DQPSK, 16QAM hoc 64QAM. Chun ISDB-T c th s dng cho cc knh truyn c rng 6, 7 hay 8Mhz.KiuKiu 1Kiu 2Kiu 3

S on d liu Ns13

rng bng tn (Mhz)7.4337.4317.426

Khong cch sng mang (Khz)5.2912.6451.322

S sng mang140528095617

Kiu iu ch sng mangQPSK, 16QAM, 64QAM, DQPSK

S biu tng trong mt khung204

Khong thi gian tch cc trong mt biu tng (S)189378765

Khong bo v (S)47.2594.5189

1/823.62547.2594.5

1/1611.812523.62547.25

1/325.9062511.812523.625

M ha trongM ha cun (1/2, 2/3, 3/4, 5/6, 7/8)

M ha ngoiM Reed Solomon (204, 188)

Bng 1.2: Cc thng s truyn dn ISDB-T cho knh truyn 8 Mhz1.5.3. Chun DVBDVB (Digital Video Broadcasting) l mt t chc gm trn 200 thnh vin ca hn 30 nc nhm pht trin k thut pht s trong ton Chu u v cho cc khu vc khc. T chc DVB phn ra nhiu phn ban, trong c cc phn ban chnh:DVB-S - Pht trin k thut truyn s qua v tinh: H thng DVB -S s dng phng php iu ch QPSK (Quadratue Phase - Shift Keying), mi sng mang cho mt b pht p. Tc bit truyn ti ti a khong 38,1Mbps. B rng bng thng mi b pht p t 36 n 54 Mhz. DVB-C - Pht trin pht s qua cp: S dng cc knh cp c rng bng thng t 7 n 8 MHz v phng php iu ch 64QAM (64 Quadratue Amplitude Modulation). DVB-C c mc SNR (t s Signal/Noise) cao v iu bin k sinh (Intermodulation) thp. Tc bit lp truyn ti MPEG-2 ti a l 38,1 Mbps. DVB-T - Pht trin mng pht hnh s mt t: Vi vic pht minh ra iu ch ghp a tn trc giao (COFDM) s dng cho pht thanh s (DAB) v pht hnh s mt t (DVB), rt nhiu nc s dng phng thc ny. Tc bit ti a 27,14 Mbps (ng vi di thng cao tn 8Mhz).1.5 Kt lun chng ITrong nhiu nm tr li y, truyn hnh s tr thnh i tng nghin cu ca nhiu nh khoa hc v nhiu t chc trn th gii. Cng vi s tin b vt bc ca cng ngh ch to cc vi mch t hp cao, cng ngh cao, tc cao, p ng yu cu lm vic vi thi gian thc, cng ngh truyn hnh c nhng tin b vt bc. Truyn hnh s mt t c nhng u im vt tri so vi truyn hnh tng t nh s dng mt my pht c kh nng truyn ti c t 6 n 8 chng trnh ng thi; vi cng mt vng ph sng th cng sut pht yu cu ca my pht s s nh hn t 5 n 10 ln so vi my pht tng t, iu ny gip cho vic tit kim ng t v chi ph vn hnh. Mt iu c quan tm na l cht lng chng trnh trung thc, t b nh hngbi nhiu ng truyn , trnh c hin tng bng hnh thng gp truyn hnh tng t. ng dng pht hnh s Vit Nam l nhm cc mc ch: - Tin kp cc nc tin tin v cc nc xung quanh trn lnh vc thng tin i chng ni chung v truyn hnh ni ring.- Pht ng thi nhiu chng trnh truyn hnh: Truyn hnh Vit Nam ly nhu cu xem nhiu chng trnh vi cht lng ng u l mc tiu s mt tin ti pht s. Khc phc c tnh trng can nhiu. - Vng tn s VHF (174-230Mhz) hin nay ginh cho pht PAL analog thc s chim ht. Nhiu tnh v khu vc pht chng trnh quc gia phi pht PAL analog trn knh UHF. Nhng cng sut my pht PAL analog trn knh UHF phi ln hn trn knh VHF hng 20 ln, khi ph sng cng mt vng. Hn na s chn knh, nhiu knh PAL analog ang xy ra mt s vng. ng thi nhu cu pht nhiu chng trnh ang t ra kh gay gt. Nn vn pht s l mc tiu cp thit gii quyt nhng yu cu trn. - Sm la chn vng tn s cho cc mng pht hnh s trn c s cn i nhu cu pht trin ca nhiu ngnh. V d xt v tng th li ch ca ton x hi, pht hnh s mt t c th chuyn hn sang bng UHF sau ny dnh bng tn VHF cho cc dch v khc. - Tit kim nng lng in cho ton b my pht hnh, kch thch th trng tiu dng ca ngi dn (mua TV s, SETTOP box)... CHNG II: TRUYN HNH S MT T THEO TIU CHUN CHU U TH H TH NHT (DVB-T)2.1. Gii thiu v h thng truyn hnh s mt t DVB-TDVB-T l tiu chun truyn hnh s mt t chnh thc c t chc ETSI cng nhn (European Telecommunications Standards Institute) vo thng 2 nm 1997.DVB-T s dng k thut COFDM (Coded Orthogonal Frequency Division Multiplexing). COFDM l k thut c nhiu c im u vit, c kh nng chng li phn x nhiu ng, ph hp vi cc vng dn c c a hnh phc tp, cho php thit lp mng n tn (SFN Single Frequency Network) v c kh nng thu di ng, ph hp vi cc chng trnh c nt cao HDTV.DVB-T l thnh vin ca mt h cc tiu chun DVB, trong bao gm tiu chun truyn hnh s qua vtinh, mt t, cp. 2.2. S khi h thng truyn hnh s mt t DVB-T2.2.1. H thng pht DVB-T

Hnh 2.1: S khi h thng pht DVB-TCc thnh phn tham gia vo qu trnh m ha knh bao gm:- B phn tn nng lng: Trong qu trnh ny, dng truyn ti (payload stream) s b xo trn. Qu trnh ny l cn thit bi v dng truyn ti c th cha cc nhm 0, 1 m iu ny thng gy bt li cho vic khi phc clock trong my thu v cng sut ca my thu s khng phn phi theo thi gian.- B m ha ngoi: S dng m Reed-solomon. M ny c u im c bit trong cc knh c xc sut li kp cao v trong cc ng dng s dng phng php sa li lin tip.- B m ha trong: Thc hin vic m ha tch chp ti mc bit v cung cp cc t l m t 1/2 n 7/8.- B hon v trong: B hon v trong c chc nng xo trn d liu trong tn hiu a sng mang trong min tn s.- B hon v ngoi: B hon v ngoi c chc nng hon v byte cho cc gi c chng li. iu ny to ra mt cu trc d liu hon v.2.2.2 H thng thu DVB-TTn hiu analog c thu t anten c dch tn xung, u ra b dch tn xung l tn hiu trung tn thp c tn s trung tm 4,57 Mhz. Tip theo d liu s c ng b tn s, ng b thi gian v loi b khong bo v. Sau qua khi gii iu ch OFDM, cc tn hiu c a song song n b nh gi knh v cn bng knh (Gi l ng b knh thch hp). K , d liu i qua khi gii chn v gii m Reed-Solomon). Sau khi qua khi gii m MPEG-2 v gii ghp knh, cc dng d liu u ra sau cng l tn hiu video, audio v cc d liu s.

Hnh 2.2: S khi my thu truyn hnh s mt tChc nng cc khi c bn sau:- Khi ng b: Nhim v u tin ca khi ng b l phc hi thi gian symbol, c ngha l tm ra im u ca mi symbol v ly ra tin tc, trnh c hin tng giao thoa gia cc symbol. N cn c nhim v c bn l iu chnh tn s ca b dao ng ti ch trong tuner sao cho tn s trung tm ca trung tn thp u vo bng gi tr danh nh ca n.- Khi nh gi v sa li do knh truyn: Khi ny c nhim v so snh mi t bo pilots tn x thu c vi gi tr truyn i bit t c t c p ng tuyn tnh tc thi ca knh i vi sng mang tng ng khong thi gian . Cc t bo d liu cn sa nm gia cc pilot tn x,c v tn s v v thi gian. Thc t vic chn thch hp tng ng vi pilor tn x o c dng sa mi t bo d liu. Nh vy, vic nh gi hm truyn t knh c s dungjddeer b li nh hng ca knh truyn.- Khi cn bng knh v nh gi knh: iu ch COFDM s dng chu k symbol di v loi b mt s tc d liu c th xut hin trong khong thi gian bo v hn ch can nhiu gia c symbol. Cc symbol can nhim l nhng symbol ging ht nhau, mang cng mt gi tr nhng b tr. Do cn phi s dng k thut cn bng v nh gi knh. Phng php COFDM vi khong symbol di hn so vi thi gian tr v khong bo v thch hp, chng ta c th nh gi giao thoa gia cc symbol (ISI) v gii quyt can nhiu gia cc symbol.- Khi gii m knh: Tn hiu sau khi qua khi nh gi v cn bng knh c a ti khi gii m knh. Tai y chng c gii nh x (De-mapping), tc l qu trnh ly cc d liu ra. Sau d liu c a ti b b gii chn theo tn s ( Frequency De-interleaving) c sp xp theo ng tn s. Bng cch ny, cc b li xy ra khi cc sng mang cch nhau b hng do phn x b phn tn ra, cho php b gii m viterbi lm vic tt hn. Sau tn hiu i qua b gii m viterbi v b gii chn theo thi gian loi b li mt song mang COFDM n mang theo. Cui cng dng tn hiu c a qua b gii m Reed-solomon loi b nt cac bit li v u ra c dong truyn TS nh dng c truyn i. Dng ny c a ti khi tch knh MPEG v qua khi gii m video v audio MPEG. Sau tn hiu c a qua thit b cui tng ng.2.3 iu ch COFDM trong DVB-T p ng cc yu cu cng nh tnh nng ca truyn hnh s mt t, nhm nghin cu ca DVB-T a ra mt phng thc iu ch mi COFDM. Tnh u vit cng nh l do ti sao dng phng thc ny s c trnh by trong phn sau, y l nguyn l ct li ca mt h thng DVB-T.2.3.1 Nguyn l- COFDM l mt phng thc ghp knh a sng mang trc giao trong vn s dng cc hnh thc iu ch s c s ti mi sng mang. Tuy nhin ta c th gi l phng thc iu ch COFDM. Phng thc ny rt ph hp cho nhng yu cu ca pht hnh mt t.- COFDM ph hp vi iu kin truyn sng nhiu ng, thm ch c khi c tr ln gia cc tn hiu thu c. Chnh iu ny dn n khi nim mng n tn (SFN), ni c nhiu my pht cng gi tn hiu ging nhau trn cng mt tn s, m thc ra y chnh l hiu ng "nhiu ng nhn to". COFDM cng gii quyt c vn nhiu ng knh di hp. y l hin tng thng thy trong cc dch v tng t do cc sng mang gy ra.- tng u tin ca COFDM xut pht t khi xem xt s suy yu xy ra trong pht sng cc knh mt t. p ng ca knh khng tng ng vi tng di tn nh do c nhiu tn hiu nhn c (tn hiu chnh + tn hiu echo), ngha l s khng cn nng lng thu hoc s thu c nhiu hn mt tn hiu. gii quyt vn ny th c ch u tin l phi phn tch lung d liu truyn ti trn mt s lng ln cc di tn s nh cch bit nhau, ngha l iu ch d liu ln mt s lng ln sng mang da trn k thut FDM. V c th xy dng li c nhng d liu mt bn thu th cn m ha d liu trc khi pht. Do cmt s c im ch cht sau y gip cho COFDM rt ph hp cho cc knh mt t, l: Cc sng mang trc giao orthogonality (COFDM) Chn thm cc khong bo v - guard interval S dng m sa li (COFDM), xen bit symbol v thng tin trng thi knh Phn ny chng ta s cng gii thch cc c im ny cng nh ngha ca chng.2.3.2 S lng sng mang- Gi thit rng chng ta iu ch cc thng tin s cho mt sng mang. Trong mi symbol, chng ta truyn sng mang vi bin v pha xc nh. Bin v pha ny la chn theo chm sao iu ch. Mi symbol vn chuyn mt lng bt thng tin nht nh, lng bit ny bng vi loga (c s 2) ca s trng thi khc nhau trong chm sao.- By gi hy tng tng l c hai ng tn hiu nhn c vi mt tr tng i gia chng. Gi s ta xem xt symbol th n c pht i, th my thu s c gng gii iu ch d liu bng cch kim tra tt c thng tin nhn c lin quan n symbol th n k c thng tin thu trc tip ln thng tin thu c do tr.- Khi khong tr ln hn mt chu k symbol (xem hnh 2.2- tri), th tn hiu thu c t ng th hai s ch thun tu l nhiu, v n mang thng tin thuc v cc symbol trc . Cn nhiu gia cc symbol (ISI) ng rng ch c mt cht t tn hiu tr nh hng vo chu k symbol mong mun (mc chnh xc tu thuc vo chm sao s dng v mc suy hao c th chp nhn).- Khi khong tr nh hn mt chu k symbol (hnh 2.2) th ch mt phn tn hiu thu c t ng th hai c xem nh l nhiu v n mang thng tin ca symbol trc . Phn cn li s mang thng tin ca chnh symbol mong mun, tuy nhin s ng gp ca n cng c th c ch hoc c th mang tnh tiu cc i vi thng tin t ng thu chnh thc.

Hnh 2.3: Hin tng tr gy xuyn nhiu gia cc symbol- iu ny cho chng ta thy rng, nu chng ta mun gii quyt vi tt c cc mc tn hiu tr khc nhau th tc symbol phi c gim xung sao cho tng khong tr (gia tn hiu thu c u tin vi tn hiu thu c cui cng) cng ch l mt phn khim tn ca chu k symbol. Khi thng tin m mt sng mang n vn chuyn s b gii hn khi c hiu ng nhiu ng. Vy th nu mt sng mang khng th vn chuyn c tc thng tin theo yu cu th tt nhin s dn n tng chia dng d liu tc cao thnh rt nhiu dng song song vi tc thp hn, mi dng c vn chuyn bi mt sng mang, ngha l s c rt nhiu sng mang. y chnh l mt dng ca FDM - bc u tin tin ti COFDM.- Mc d vy th vn c th tn ti ISI vi cc symbol trc . kh hon ton th phi ko di khong truyn ca mt symbol sao cho n ln hn khong tng hp tn hiu m my thu thu c. Vy th vic chn thm khong bo v c th l tng tt (chng ta s tr li vn ny sau).2.3.3 c tnh trc giao v vic s dng DFT/FFTa. Trc giaoVic s dng mt s lng ln cc sng mang c v nh khng c trin vng lm trong thc t: chc chn, chng ta s cn rt nhiu b iu ch, gin iu ch km theo? V cng c v nh s cn mt di thng ln hn chc cc sng mang ny. Nhng tht may c hai iu lo lng ny u c xua tan nu chng ta thc hin mt vic n gin sau y: cc sng mang c t u n cch nhau mt khong fU= 1/TU, vi TU l khong symbol hu ch (u: useful) vi iu kin l cc sng mang ny phi c t trc giao nhau. V mt ton hc, vic trc giao s nh sau: sng mang th k c biu din:

Vi U = 2/TU, v iu kin trc giao m sng mang phi tha mn l:

, k L = TU, k =l V ngha vt l: khi gii iu ch tn hiu cao tn ny, b gii iu ch khng nhn thy cc tn hiu cao tn kia, kt qu l khng b cc tn hiu cao tn khc gy nhiu. V phng din ph: im ph c nng lng cao nht ri vo im bng khng ca sng mang kia. Hn na chng ta s khng b lng ph v mt ph. Cc sng mang c t rt gn nhau v th tng cng di ph cng ch nh iu ch sng mang n - nu chng c iu ch vi tt c d liu v s dng b lc ct nh l tng.b. Cng c tnh trc giao bng khong bo vThc t, cc sng mang c iu ch c th phn tch thnh cc s phc. Nu khong t hp thu c tri di theo 2 symbol th khng ch c nhiu ca cng sng mang (ISI) m cn c nhiu xuyn sng mang (ICI). trnh iu ny chng ta chn thm khong bo v gip m bo cc thng tin tng hp l n t cng mt symbol v xut hin c nh.

Hnh 2.4: Chn thm khong bo vMi khong symbol c ko di thm v th n s vt qu khong t hp ca my thu TU. V tt c cc sng mang u tun hon trong TU nn ton b tn hiu c iu ch cng vy. V th on thm vo ti phn u ca symbol to nn khong bo v s ging vi on c cng di ti cui symbol. Min l tr khng vt qu on bo v, tt c thnh phn tn hiu trong khong t hp s n t cng mt symbol v tiu chun trc giao c tho mn. ICI v ISI ch xy ra khi tr vt qu khong bo v. di khong bo v c la chn sao cho ph hp vi mc hin tng nhiu ng. DAB s dng khong bo v xp x TU/ 4; DVB-T c nhiu la chn hn nhng ti a cng ch l TU/ 4.Cn nhiu th na c th gy ra s suy gim tnh trc giao v do s gy ra ICI. Chng c th l cc li xy ra trong cc b to dao ng ni hoc trong vic ly mu tn s ca my thu hay cc tn hiu tp pha (phase-noise) trong cc b to dao ng ni. Tuy nhin trong thc t, nhng nh hng ny c th c gi mc gii hn c th chp nhn c.c. S dng FFTChng ta trnh c hng ngn b lc, nh tnh trc giao, vy th vic thc hin gii iu ch cc sng mang, cc b ghp knh v cc b t hp th sao?Thc t, chng ta lm vic vi tn hiu thu c di dng ly mu (theo nh l Nyquyst). Qu trnh t hp tr thnh qu trnh tng kt, v ton b qu trnh gii iu ch da trn dng bin i Furier ri rc (DFT). Rt may l vic thc hin bin i Furier nhanh c ri (cc mch t hp sn c), v vy chng ta c th xy dng thit b COFDM phng th nghim rt d dng. Cc phin bn chung ca FFT u hot ng trn c s cc mu thi gian 2M (tng ng vi cc mu c ly trong khong t hp) v vn chuyn cng s lng cc h s tn (frequency coefficient). Cc h s ny tng ng vi d liu c gii iu ch t nhiu sng mang. Thc t v chng ta ly mu trn c s gii hn Nyquyst, nn khng phi tt c cc h s c ly u tng ng vi cc sng mang tch cc m chng ta sdng.d. La chn iu ch c sTi mi symbol, mi sng mang s c iu ch bi mt s phc ly t tp chm sao. Nu cng c nhiu trng thi trong chm sao th mi sng mang cng vn chuyn c nhiu bit trong mt symbol, tuy nhin khi cc im trong chm sao cng cng gn nhau hn, trong khi cng sut pht th c nh nn s gim kh nng chng li. Do vy cn c s cn i gia tc v mc li.Ti my thu, gi tr gii iu ch tng ng (h s tn ly t FFT my thu) c nhn vi mt s phc tu (p ng knh ti tn s sng mang). Chm sao s c quay lun phin v thay i v kch c. Vy th lm th no chng ta xc nh c im trong chm sao m chng ta gi i?Cch n gin l gii iu ch vi sai (differentialdemodulation), kiu nh DQPSK trong DAB. Thng tin c mang i chnh l s thay i v pha ca symbol ny so vi symbol tip theo. Min l knh thay i chm th s khng c vn g vi p ng knh ca n. S dng qu trnh gii iu ch vi sai (khc vi gii iu ch kt hp - coherent demodulation) s gy ra suy gim v ch tiu ca nhiu tp m nhit (thermal noise) - tuy nhin DAB khng cn l h thng chng li mnh. Khi i hi tc ln hn (nh trong DVB-T), s rt c li nu s dng gii iu ch kt hp . phng php ny, p ng knh s c xc nh v chm sao nhn c c cn bngchnh xc ri mi xc nh xem im no trn chm sao c pht i (ngha l xc nh c bit no truyn i). lm c iu ny DVB-T th mt s pilot phn tn phi c pht km theo (gi l scattered pilots). Sau php ni suy sc thc hin, s dng blc mt chiu hoc hai chiu cn bng tt c chm sao mang d liu.2.3.4 T chc knh trong OFDMa. Phn chia knhCOFDM thc hin vic phn chia knh truyn dn c trong min thi gian v min tn s, t chc knh RF thnh tp cc "di tn ph" hp v tp cc "on thi gian" lin tip nhau. Xem trn hnh 2.5 sau y:

Hnh 2.5: Phn chia knh

Hnh 2.6: V d v p ng knh thay i theo thi gian vi hai ng trb. Chn cc sng mang phTrong mi on thi gian, gi l mi symbol OFDM, mi di tn ph c trang b mt sng mang ph. trnh nhiu gia cc sng mang, chng c b tr vung gc vi nhau, ngha l khong cch gia cc sng mang c t bng vi nghch o ca mt chu k symbol.

Hnh 2.7: Chn cc sng mang phc. Chn khong bo vDo cc "echo" c to ra bi cc bn sao ca tn hiu gc khi b tr, nn ti phn cui ca mi symbol OFDM s c nhiu lin symbol vi phn u ca symbol tip theo. trnh iu ny, mt khong bo v c chn vo mi symbol nh ta thy hnh 2.8 sau:

Hnh 2.8: Chn khong bo vTrong khong bo v ny, m thc ra tng ng vi mt nhiu giao thoa gia cc symbol, cc my thu s b qua tn hiu thu c.

Hnh 2.9: Dng tn hiu minh ha khi c khong bo vd. ng b knh gii iu ch tn hiu mt cch chnh xc, cc my thu phi ly mu chnh xc tn hiu trong sut khong hu ch ca symbol OFDM (b qua khong bo v). Do , mt ca s thi gian s c n nh chnh xc ti khong thi gian mi chu k symbol din ra. H thng DVB-T s dng cc sng mang "pilot", tri u n trong knh truyn dn, ng vai tr lm cc im nh du ngb, nh trn hnh 2.10:

Hnh 2.10: Cc sng mang ng bCc tnh nng khc nhau ny (phn chia knh, m ho d liu, chn khong bo v v cc sng mang ng b) to ra cc c tnh c s ca phng thc iu ch COFDM. Tht khng may, tt c tnh nng ny li lm gim tc hu ch ca ti thng tin. Tuy nhin, ta cng c th cn bng gia kh nng chng li vi dung lng knh. V gip cc nh pht hnh c th thoi mi s dng cc h thng truyn dn ca mnh trong tng iu kin c th, DVB-T a ra nhiu tham s c th la chn nh: kch c FFT (2K, 8K), t l m ha (1/2, 2/3, 3/4...), v khong bo v (1/4 TS, 1/8 TS, 1/16 TS...).2.3.5. Phng thc mang d liu trong COFDMCOFDM cho php tri d liu truyn i trn c min thi gian v min tn s, sau khi s dng m ha vng bo v d liu.Do c hin tng fading tn s gia cc di tn cn k, nn COFDM c s dng xen tn s, ngha l cc bit d liu lin tip nhau s c tri ra trn cc sng mang cch bit nhau.

Hnh 2.11: Thc hin mapping d liu ln cc symbolTrong DVB-T vic mapping d liu ln cc symbol OFDM thc ra l diu ch tng sng mang ring r, v c th theo mt trong ba chm sao ta phc 4-QAM, 16-QAM, 64-QAM, nh sau:Hnh 2.12: Chm sao c s ca DVB-TTu theo dng iu ch c la chn, ti mt chu k symbol cho mi sng mang s c 2 bit (4 QAM), 4 bit (16 QAM) hay 6 bit (64 QAM) c truyn i. Mi dng iu ch c mt kh nng chng li khc nhau. Thng th 4 QAM c khong dung sai chu nhiu ln gp 4 n 5 ln so vi 64 QAM.2.6 Kt lun chng IIT nhng phn tch trn ta c th thy c nhng u, nhc im khi s dng k thut iu ch DVB-T:- u im: p ng c nhu cu truyn thng tc cao (nht l vi cng ngh truyn hnh khi ghp nhiu knh chng trnh) vi kh nng khng nhiu tt trn knh pha inh chn lc tn s. Tnh phn tp tn s cao do thng tin c tri ra trn nhiu sng mang con khc nhau, to nn kh nng chng c cc nh hng ca knh pha inh chn lc tn s. Hiu qu s dng ph cao do OFDM s dng nhiu sng mang con sng mang ny trc giao ngha l cc sng mang con c mt phn chng ln nhau trong min tn s m vn m bo chng ISI ti u thu. Rt n gin v hiu qu trong trin khai h thng.- Nhc im: T s cng sut cc i trn cng sut trung bnh cao do tn hiu OFDM l tng ca nhiu thnh phn tn hiu nn bin ca n c nh cao dn n t s PAPR l cao. Qu trnh ng b gp nhiu kh khn hn so vi h thng thng thng v h thng kh nhy vi nhiu tp m, li dch tn s sng mang, li nh thi tn s ly mu... Vi nhng u im trn cng vi tnh tin ch khi xt n yu t trao i chng trnh, vi s lng ln cc quc gia ly chun DVB lm tiu chun. i truyn hnh Vit Nam quyt nh la chn DVB lm chun, ngy 26/3/2001 i Truyn Hnh Vit Nam quyt nh chn h DVB-T cho pht s mt t v sau khong 5 nm th nghim cho kt lun v tnh ng n ca phng n la chn. Hin nay s ha tn hiu truyn hnh Vit Nam l s thay th dn cc cng on, trang thit b t tng t sang s. l qu trnh s ha tng phn. Ri y truyn hnh s s thay th hon ton truyn hnh tng t to iu kin cho nghnh cg nghip truyn hnh pht trin mnh m hn kt hp vi cc mng truyn thng khc to thnh mt th gii thng tin s phc v cho con ngi mt cch hu hiu.CHNG III: TRUYN HNH S MT T THEO TIU CHUN CHU U TH H TH 2 (DVB-T2)3.1. Gii thiuTruyn hnh k thut s ra i v nhanh chng khng nh c v th ca n trn th trng. Chnh v nhng u im ni trica truyn hnh s m hu ht cc nc pht trin trn th gii u a ra l trnh pht trin truyn hnh s v ngng pht sng truyn hnh tng t: Anh (2012), M (17/02/2009), Nht (24/07/2011) c (2008), Php (30/11/2011) v rt nhiu quc gia khc s ngng hon ton vic pht sng mt t tng t. Hin nay, mt s nc khc nhau c la chn cho mnh nhng tiu chun truyn hnh s mt t khc nhau nhng DVBT vn l tiu chun c nhiu nc la chn nht. Vit Nam cng c quyt nh chnh thc la chn DVB-T l tiu chun pht sng s mt t ca mnh. Vi xu th hi t trong lnh vc Media, ng thi vi s pht trin mnh m ca truyn hnh phn gii cao HDTV, tiu chun truyn hnh s mt t DVB-T nhanh chng cn b sung thm cc tnh nng khc h tr c v mt k thut ln mt thng mi. Rt nhiu yu cu mi v dch v c a ra v chng l tin xy dng mt th h th hai cho DVB-T. Chun DVB-T l chun pht sng truyn hnh s mt t c trin khai thnh cng, c nhiu nc chp nhn. Ngay t khi cng b ln u nm 1995, chun ny c s ng h ca trn 50% cc quc gia trn th gii. Tuy nhin, t sau s ra i ca chun DVB-T th cc nghin cu v k thut truyn dn vn tip tc c trin khai v cc ty chn v iu ch, v khng li ng truyn vn tip tc c pht trin. Mt khc, nhu cu v ph tn cng gia tng v vi p lc v ph tn dng cho cc dch v phi qung b (cng cng chia x vng bng tn ca cc dch v qung b) cng khin cho vic gia tng hiu qu ca ph tng ln mc ti a cng cp thit. T , nhm DVB Project pht trin chun truyn hnh s mt t th h th 2 l DVB-T2. Tiu chun ny c xut bn ln u tin vo 6/2008 v c ETSI (European Telecommunication Standardisations Institute) chun ha t thng 9/2009. Vic trin khai v pht trin sn phm cho chun mi ny cng bt u. Kh nng gia tng dung lng trong mt multiplex truyn hnh s mt t l mt trong nhng u im chnh ca chun DVB-T2. So snh vi chun truyn hnh s hin nay l DVB-T th chun th h th hai DVB-T2 cung cp s gia tng dung lng ti thiu 30% trong cng iu kin thu sng v dng cc anten thu hin c. Tuy nhin, mt s th nghim s b cho rng dung lng trong thc t c th gia tng n gn 50%. iu ny cng thun li cho vic trin khai cc dch v qung b mi i hi nhiu dung lng hn.3.2. Nhng yu cu c bn i vi chun DVB-T2- DVB-T2 phi tun th tiu ch u tin c tnh nguyn tc l tnh tng quan gia cc chun trong h DVB. iu c ngha l s chuyn i gia cc tiu chun DVB phi thun tin cao nht n mc c th, v d gia DVB-S2 (tiu chun truyn hnh s qua v tinh th h th 2 vn ly) v DVB-T2.- DVB-T2 phi k tha nhng gii php tn ti trong cc tiu chun DVB khc. DVB-T2 phi chp nhn 2 gii php k thut c tnh then cht ca DVB-S2, c th:+ Cu trc phn cp trong DVB-S2, ng gi d liu trong khung BB (Base Band Frame). + S dng m sa sai LDPC (Low Density Parity Check). - Mc tiu ch yu ca DVB-T2 l dnh cho cc u thu c nh v di chuyn c, do vy, DVB-T2 phi cho php s dng c cc anten thu hin ang tn ti mi gia nh v s dng li cc c s anten pht hin c. - Trong cng mt iu kin truyn sng, DVB-T2 phi t c dung lng cao hn th h u (DVB-T) t nht 30%. - DVB-T2 phi t c hiu qu cao hn DVB-T trong mng n tn SFN (Single Frequency 3.3. Tiu chun DVB-T23.3.1. M hnh cu trc DVB-T2H thng DVB-T2 c chia thnh 3 khi chnh pha pht (SS1, SS2, SS3) v 2 khi chnh pha thu (SS4, SS5) nh trnh by trong hnh 3.1

Hnh 3.1: M hnh cu trc DVB-T2a. SS1: M ha v ghp knhKhi SS1 c chc nng m ho tn hiu video/audio cng cc tn hiu ph tr km theo nh PSI/SI hoc tn hiu bo hiu lp 2 (L2 Signalling) vi cng c iu khin chung nhm m bo tc bit khng i i vi tt c cc dng bit. Khi ny c chc nng hon ton ging nhau i vi tt c cc tiu chun ca DVB. u ra ca khi l dng truyn ti MPEG-2TS (MPEG-2Transport Stream).b. SS2: Basic T2 Gatewayu vo ca SS1 c nh ngha trong [1], u ra l dng T2 - MI. Mi gi T2-MI bao gm Baseband Frame, IQ Vector hoc thng tin bo hiu (LI hoc SFN). Dng T2-MI cha mi thng tin lin quan n T2-FRAME. Mi dng T2-MI c th c cung cp cho mt hoc mt vi b iu ch trong h thng DVB-T2. Dng thc giao din ca T2-MI c nh ngha trong[2].c. SS3: B iu ch DVB-T2 (DVB-T2 Modulator)B iu ch DVB-T2 s dng Baseband Frame v T2- Frame mang trong dng T2-MI u vo to ra DVB-T2 Frame.d. SS4: Gii iu ch DVB-T2 (DVB-T2 Demodulator)B gii iu ch SS4 nhn tn hiu cao tn (RF Signal) t mt hoc nhiu my pht (SFN Network) v cho mt dng truyn ti (MPEG-TS) duy nht ti u ra.e. SS5: Gii m dng truyn ti (Stream Decoder)B gii m SS5 nhn dng truyn ti (MPEG-TS) ti u vo v cho tn hiu video/audio ti u ra.3.3.2. Lp vt l DVB-T2

Hnh 3.2: Lp vt lM hnh lp vt l ca DVB-T2 c trnh by trong hnh 3.2. u vo h thng c th bao gm mt hoc nhiu dng truyn ti MPEG-TS hoc dng GS (Generic Stream). u vo ca lp vt l l tn hiu cao tn RF. Tn hiu u ra cng c th c chia thnh hai ng cung cp cho anten th 2, thng l 1 my pht khc. Vic x l dng d liu vo v FEC phi c la chn sao cho c kh nng tng thch vi c ch s dng trong DVB-S2. iu c ngha, DVB-T2 phi c cng cu trc baseband-frame, baseband-header, gi 0 (Null packet) LDPC/BCH FEC v ng b dng d liu nh DVB-S2.Cc thng s COFDM ca DVB-T cng c m rng so vi DVB-T, trong bao gm:- FFT: 1K, 2K, 4K, 8K, 16K, 32K - Khong bo v: 1/128, 1/32, 1/16, 19/256, 1/8, 19/128, # - Pilot phn tn: 8 bin th khc nhau ph hp vi cc khong bo v khc nhau- Pilot lin tc: tng t nh DVB-T, tuy nhin tiu hn - Tro: bao gm tro bit, tro t bo, tro thi gian v tro tn sVic c mt khong la chn rng hn cc thng s COFDM cng vi m sa sai mnh hn, cho php DVB-T2 t c dung lng cao hn DVB-T gn 50% i vi mng MFN v thm ch cn ln hn i vi mng SFN.DVB-T2 cn c mt s tnh cht mi gp phn ci thin cht lng h thng. - Cu trc khung (Frame Structure), trong c cha symbol nhn din c bit c s dng qut knh (channel scanning) v nhn bit tn hiu nhanh hn. - Chm sao xoay, nhm to nn tnh a dng trong iu ch tn hiu, h tr vic thu tn hiu c t l m sa sai ln. - Cc gii php k thut c bit nhm gim t s gia mc nh v mc trung bnh ca tn hiu pht. - Tu chn i vi kh nng m rng khung d liu trong tng lai.3.4. Kt lun chng IIITiu chun truyn hnh s mt t th h th 2 (DVB-T2) c cng b thng 2-2009 (sau DVB-S2 v DVB-C2 cho truyn hnh s trn v tinh v truyn hnh cp). DVB-T2 s dng nhiu gii php k thut mi nh: ng vt l, bng tn ph, cc mode sng mang m rng, MISO da trn Alamouti, symbol khi u (P1, P2), mu hnh tn hiu Pilot, chm sao xoay, mc ch l lm tng tin cy ca knh truyn v tng dung lng bit. Trn thc t, DVB-T2 c kh nng truyn ti dung lng bit ln hn DVB-T gn 50% i vi mng a tn (MFN) v thm ch cao hn i vi mng n tn (SFN). DVB-T2 l h thng truyn hnh s mt t l tng cho truyn hnh c phn gii cao HDTV (High Defination Televition). S sn sng ca chun DVB-T2 mang n cc c hi mi cho mi trng truyn hnh mt t. Cc nh qung b v nh cung cp dch v khc c th quan tm h tr cc dch v mi trn DTT m trc kh trin khai do hn ch v dung lng bng thng trong cc bng tn VHF v UHF.Vic pht trin chun truyn hnh s mt t th hth hai p ng c yu cu thc t. l s gia tng dung lng bng thng gip cung cp cho ngi xem cc dch v truyn hnh mi. Trong nhiu quc gia, chun DVB-T2 h tr c hi cho cc nh qung b trin khai mt chui cc dch v HDTV trn mi trng DTT. Chun DVB-T2 cng c kh nng h tr cc dch v c th trong tng lai. Cc dch v th h k tip nh 3D TV c th hng li t vic gia tng dung lng sn c ca DVB-T2.Theo sau s kt thc chuyn i tng t, ngi ta hy vng rng cc quc gia s bt u trin khai cc dch v dng chun DVB-T2. Trong mt s quc gia, chun mi ny s dng h tr cc dch v HDTV (c min ph v tr tin) v cng dng ci tin hay thay th cc dch v truyn hnh c phn gii chun hin nay. Tuy nhin, vic thay th chun DVB-T bi DVB-T2 cng cn c mt khong thi gian qu trong qu trnh chuyn i. Ngi ta cng cho rng chun DVB-T v DVB-T2 s cng tn ti trong nhiu nm, mi chun h tr ngi xem cc loi dch v khc nhau.Nhn chung, DVB-T2 s em n nhiu c hi trin khai cc dch v mi. Vi vic gia tng dung lng ln mc gii hn vt l c th, chun DVB-T2 s rt thch hp vi nhiu dch v trong tng lai. Mt khc, cc thit b cn cho chun ny hin vn cha trng thnh nn kh nng ng dng rng ca DVB-T2 s ch c quan tm nhiu trong vi nm ti.

CHNG IV:QU TRNH CHUYN I T DVB-T SANG DVB-T2 CHU U V MT S KIN NGH KHI TRIN KHAI DVB-T2 TI VIT NAM.4.1. S ra i tt yu ca tiu chun truyn hnh s mt t th h th hai DVB-T2.4.1.1. Cc yu cu v thng mi i hi cho ra i mt th h th hai cho tiu chun truyn hnh k thut s DVB-T.DVB-T khng nh v th ng u cho truyn hnh qung b k thut s. T khi ra i, DVB-T lun lun pht trin v hon thin hn trong c cng ngh m ha ln tnh kinh t ca dy chuyn truyn dn. n nay c mt s phng php mi trong vic m ha v bo v sai s cho dng truyn ti, gi tr thng mi ca truyn hnh s ngy cng tng trng, chi ph v tnh kh thi cho c cc cng ngh phc tp mc chp nhn c i vi mt u thu cho php cn i phc tp ca u thu vi hiu qu ca bng thng. Chng ta c th thy trc rng, s hi t gia truyn hnh truyn thng vi cc dch v truyn thng khc nh thng tin di ng v cc dch v bng thng rng khc. Tt c cc xu th ny u c tch hp vi nhau trong truyn hnh phn gii cao HDTV v do vy i hi s ra i ca mt tiu chun truyn hnh th h hai cho DVB-T. Vn t ra l liu cc ng dng TV trong tng lai c yu cu kh nng xem cng mt tn hiu trn nhng thit b thu c phn gii khc nhau (chng hn thu di ng v thu c nh) hoc l s dng cng mt h thng phn phi ca cng mt dch v trn cc nh dng khc nhau thch hp vi cc u thu v ngi s dng. Tiu chun DVB-T mi cn phi h tr cho c hai vin cnh ny. Vic ngng pht sng truyn hnh tng t s cho ra i cc ng dng v cc dch v mi. Thi k chuyn i ny s to ra mt c hi gii thiu cc cng ngh mi v yu cu DVB-T2 trong mt khong thi gian ngn phi a ra c nhng quyt nh s dng tn s tun th hip nh Geneva 2006 sau khi ngng pht sng truyn hnh tng t. Mt iu quan trng na cn tha mn l sn sng cho vic ngng honton pht sng tng t, tiu chun DVB-T2 phi to ra nhng li ch r rt trn nn tng sn c ca DVB-T.

4.1.2. Mi quan h vi tiu chun s mt t DVB-T hin ti.Nhn t chnh to nn thnh cng ca DVB-T hin ti l s tin dng cho ngi s dng khi h chuyn i t ch tip nhn cc tn hiu tng t sang tip nhn tn hiu DVB-T. Phn ng ngi s dng c th lp t d dng u thu DVB-T m khng cn phi nng cp anten thu hay cp. Do vy, mt nguyn tc mu cht m DVB-T2 cn phi tha mn l khi chuyn i t DVB-T sang DVBT2 l ngi s dng khng cn mt thay i g m c th s dng h tng c sn t truyn hnh tng t v DVB-T. iu ny c khng nh sau khi c nhng phn hi t cc nh truyn thng ln Chu u. Nhng i hi v s tng thch c th lm nh hng n vic thc hin cc tnh nng mi, hin i. Tuy nhin, vi nhng bc tin vt bc ca cng ngh, cc tnh nng mi ny s c thc hin trong cc bc tip theo ca DVB-T.4.1.3. Mc ch ca cc yu cu thng miMc tiu ban u ca sng kin l a ra cc dch v mi cho truyn hnh mt t phn gii cao HDTV tun th hip c GA06 sau khi ngng pht sng tng t. Tuy nhin, do h thng DVB-T khng gii hn ch thu c nh m cn cho c thu xch tay v thm ch cho c thu di ng nn tiu chun DVB-T2 s cho cc nh truyn thng hay nhng ngi vn hnh mng truyn dn t quyt nh la chn m rng h thng cho ph hp vi cc iu kin thu c nh, xch tay hay thu di ng. T s c nhng thit k h thng tng ng. iu ny i hi mt tin b r rt v mt h thng trn c s h thng DVB-T hin c p ng nhng i hi v tng dung lng truyn. Chng ta c th nhn thy r rng v nhng tin b ca cc ng dng m ngun da trn c s MPEG-4 AVC v k thut ghp knh cng ang dn c nhng ci tin, tuy vy khng hy vng s c nhng bc nhy vt trong mt tng lai gn.Do vy, nhng i hi thng mi tp trung vo cc lp vt l v cc lp truyn ti ca h thng vi mc tiu l DVB-T2 s cung cp mt s gia tng ng k v dung lng truyn dn so vi tiu chun DVB-T hin thi.4.2. Qu trnh chuyn i t DVB-T sang DVB-T2. Mt s vn cn xem xt khi trin khai DVB-T24.2.1. Cc yu cu ca chun DVB-T2T kh nng gia tng dung lng theo c tnh k thut ca DVB-T2, mi trng truyn dn DTT c th gia tng thm cc dchv h tr v tng tnh cnh tranh so vi cc mi trng truyn dn khc. Nh , ti nhiu quc gia mi trng DTT s cung cp dung lng trin cc dch v mi. Vi cc quc gia thng bo k hoch dng chun DVB-T2, dch v HDTV s l dch v c nhm n trin khai u tin. C th thy, c hi cung cp c nhiu cc chng trnh truyn trnh HD trn mi trng mt t (vi s lng cc dch v HD l ng k) ch c th t c tt nht khi dng DVB-T2. Tuy nhin, vi mt s quc gia (nh Php, ) ph tn vn cn trin khai cc dch v HD ch cn dng chun DVB-T kt hp vi k thut nn MPEG-4 AVC. C th thy, cc dch v mi trong mi trng mt t d chim th trng nht v kh nng trin khai nhanh v phc v c s lng ngi xem. Ty theo m hnh kinh doanh, vic h tr cc dch v min ph hoc tr tin trn DTT c th c xem xt cung cp.a. Vi cc dch v min phVic trin khai cc dch v min ph l phng n gip gia tng nhanh s thu ht khn gi cho mi trng mt t. iu ny cng c ngha khi ngi xem sn sng tr tin mua thit b truy cp cc dchv mi, c bit trong cc quc gia ni vic h tr cc dch v s min ph ccung cp nhiu hn ng k so vi cc dch v trn mi trng tng t. Ngi ta k vng vi vic cung cp cc dch v min ph cho ngi xem th sc thu ht ca mi trng DTT s cng cnh tranh hn. cc quc gia c sn nhiu dch v min ph, vic s dng qung co h tr thng tin cho th trng khi cung cp thm nhiu dch v c th khng kh thi. Gii php kh thi hn l chuyn i cc dch v hin c t phn gii chun sang phn gii cao. Khi cc dch v HD gia tng, vic xem cc chng trnh c phn gii chun trn mn hnh HD ca ngi xem s dn dn b chi b. Tuy nhin, vic h tr min ph phi sc hp dn khuyn ngh ngi xem u t thit b mi.b. Vi cc dch v tr tinChun DVB-T2 cng c th dng cung cp cc dch v tr tin trn mi trng mt t (pay-DTT). t c hiu qu vi truyn hnh tr tin, mi trng mt t cn c dung lng cung cp ccdch v mi vi nhiu knh chuyn bit hoc nhiu knh truyn hnh c phn gii cao. Cc dch v pay-DTT c chng minh thnh cng ring trong cc th trng nh khi ngi xem c th truy cp n cc dch v chng trnh ny bng nhiu mi trng truyn dn khc nhau. Vic trin khai cc dch v pay-DTT cng gp phn gia tng sc thu ht cho mi trng truynDTT v tng s cnh tranh xt trong ton cnh truyn hnh tr tin. V d H Lan, vi s tn nhim cao trn mi trng truyn dn mt t, pay-DTT chng minh s thnh cng trong vic gia tng s thu ht ca mi trng truyn mt t thng qua ph thu bao vi gi cnh tranh. Vi cc dch v trin khai pht sng theo chun DVB-T2, cc nh iu hnh pay-DTT c th gia tng ng k dung lng truyn dn ca h h tr cc dch v mi, v linh hot trong vic trin khai thm ccdch v. Ni chung, vic gim chi ph ng truyn s to ra thm cc c hi kinh doanh cho cc dch v pay DTT. Trong mt s quc gia, gii php kh thi nht l h tr cc dch v mi dng chun DVB-T2 c kt hp pay-DTT.4.2.3 Kh nng chuyn i t DVB-T sang DVB-T2Chun DVB-T2 c pht trin xut pht t cng ngh qung b cn trin khai cc dch v mi trn DTT nhng b gii hn v mt bng thng tn s. Vi nhiu quc gia, DVB-T2 l c hi duy nht h tr cc dch v c tc bit ln nh HDTV trn mi trng DTT. Tuy nhin vi mt s quc gia, c tnh k thut DVB-T2 ch c xem nh chun thay th tim nng cho chun DVB-T ang dng. iu ny c ngha trong tng lai cc dch v hin ang c cung cp bi DVB-T c th c thay th bi cng dch v nhng dng DVB-T2. Tuy nhin, vic chuyn i cng i hi cc yu cu tng t qu trnh chuyn t truyn hnh tng t sang s.Vi mt s quc gia pht trin Chu u, mi trng truyn hnh mt t thng dng cho cc my thu hnh ph (dng trong phng ng hoc nh ngh mt), nn cng kh thuyt phc ngi xem chuyn i my thu hnh ca h dng chun mi. Mt khc, nhiu ngi xem cng ch mi chuyn i sang cc dch v s gn y v hi lng vi cc dch v trn DTT dng cho my thu hnh ph. Do , qu trnh chuyn i cng cn c thi gian di pht sng ng thi hai chun DTT v iu ny cng s gp phn tng chi ph i vi nh qung b.Khi pht sng theo chun DVB-T2, cc dch v mi c hng n b sung cho mi trng truyn theo chun DVB-T hin dng. Trong giai on u, ngi ta k vng cc thu bao s mua my thu DVB-T2 nng cp my thu hnh chnh ca h. Vi nhiu nh cung cp dch v, vic trin khai cc dch v dng chun DVB-T2 s m bo tnh cnh tranh ca mi trng DTT v nhm n mc tiu cc thu bao s chuyn dn sang s dng cc dch v trn DVB-T2 cho my thu hnh chnh ca h trong thi gian tip theo.4.2.4 Cc chin lc trin khai DVB-T2Hin trng chuyn i s c nhiu khc nhau trong cc quc gia Chu u. Mt s quc gia hon thnh qu trnh chuyn i trong khi mt s quc gia khc vn cha trin khai cc dch v DTT. C hai vin cnh kh thi cho vic trin khai DVB-T2. Tuy nhin, vic trin khai s kh hn nhng quc gia thc hin chuyn i xong mi trng truyn dn DTT.a. Vi cc th trng chuyn i s hon tonCc th trng hon ton chm dt pht sng tng t c ngha tch cc trong vic trin khai DVB-T2. Cc tn s sn c chovic trin khai cc dch v mi v ngi xem tin tng vo cc dch v DTT n nhn cc dch v mi trin khai trn mi trng DTT.Trong nhng quc gia ny, cn mt thi gian di pht sng ng thi c DVB-T v DVB-T2. Cc dch v dng DVB-T2 s c ngi xem chuyn sang dn thay th mi trng DVB-T hin c.b. Vi cc th trng cha trin khai dch v truyn hnh s mt t (DTT)Cc th trng cha trin khai bt k dch v DTT c th chn trin khai trc tip DTT dng DVB-T2 b qua vic s dng DVB-T. iu ny s loi b thi gian chuyn dch cn c ca qu trnh chuyn t DVB-T sang DVB-T2. Mt k hoch pht ng thi gia DVB-T2 v tng t cng cn c xem xt trong qu trnh chuyn i.Tuy nhin, vn phc tp li xy ra Chu u. Cc nh qun tr quc gia hin cng ang chu sc p t y ban Chu u hon thnh chuyn i s vo nm 2012 v cng rt kh h chn dng DVB-T2. Mc du, my thu DVB-T2 s c vo gia nm 2010, nhng chi ph mua vn cn cao nn cng kh ph cp nhanh c. Cn mt thi gian gi my thu gim xung mi c th thc y nhanh nhu cu ca ngi xem, nhng khi thi hn cui ca y ban v chuyn i s c th tri qua.Vic dch chuyn t dch v tng t sang s dng DVB-T2 b qua DVB-T c th hp l hn vi cc quc gia ngoi Chu u c thi gian chuyn i s di hn.c. Vi cc th trng ang tin hnh chuyn i s Chu u, hu ht cc quc gia hin ang trong qu trnh hon thnh chuyn i s. Cc dch v DTT c trin khai dng chun DVB-T v cc dch v tng t cng cha kt thc hon ton. Ni chung, c dch v DVB-T v tng t ang hot ng ng thi. S rt kh trin khai DVB-T2 cc quc gia ny khi cc tn s c sn th c dng cho hoc cc dch v DTT hoc dch v tng t. Hn na, cng nghqung b ang tp trung vo vic chun b thit b cho ngi xem khi dng pht tng t. iu dn n ngi ta mun trnh cho ngi xem phi bi ri khi cung cp thm cc thng tin v chun mi.4.2.5. Hin trng (th nghim, thng bo trin khai dch v)Hin nay, Anh v Phn Lan thng bo trin khai cc dch v HDTV trn ng truyn mt t dng chun DVB-T2. Ngoi ra, mt s th nghim pht sng DVB-T2 ang c k hoch trin khai hoc trin khai th nghim xong mt s nc khc nh : c, , Ty Ban Nha, Thy in... Anh, nhm iu hnh truyn thng OFCOM quyt nh dng mt trong 6 ghp knh DTT (Multiplex B) bng tn UHF cho vic cung cp cc dch v HD dng chun DVB-T2 kt hp vi k thut nn MPEG-4 AVC.H cung cp 4 dch v chng trnh HD ca cc nh qung b (BBC, ITV, Channel 4/S4C, v Five). Vic trin khai bc u trn Multiplex B s to tin cho vic gia tng dung lng trong cc ghp knh DTT khc sau khi vic chm dt hon ton pht sng tng t. Cc dich v SD trong Multiplex B s c chuyn sang cc ghp knh khc nn s khng c chng trnh SD no b mt i. iu ny cng c ngha vic trin khai cc dch v HD dng DVB-T2 s tngng vi l trnh chm dt pht tng t. Thc t, c vng ni cc dch v truyn hnh tng t kt thc th cc dch v HD c trin khai. My pht Witer Hill (pht cc dch v cho ngi xem Manchester v Liverpooll) s trin khai cc dch v u tin vo 2/12/2009. Trong cc vng m vic kt thc pht sng tng t c ko di n thi hn cui (nm 2012), cc dch v HD s c ph sng gii hn trong mt s cng ng dn c dng cc tn s cp pht tm. Ngi ta cng k vng n 6/2010 s c n 50% dn s c th truy cp n cc dch v HD. Phn Lan, nh iu hnh mng in thoi di ng DNA Oy c cp php hot ng 2 ghp knh DVB-T2 dng cc tn s trong bng VHF. Trong khi cu hnh mng vn cn cha c th, hai ty chn ang c xem xt. DNA Oy c th thit k mng DVB-T2 dng chui cc my phtnh t ti h thng cc tr ca h hoc thit k mng qung b truyn thng vih thng truyn dn dng cc ct tr cao, cng sut ln pht cho cc anten t trn mi nh. D kin, hai ghp knh DVB-T2 s dng dnh dng nn MPEG-4 AVC v cung cp 8-10 dch v chng trnh HD cho ngi xem. Vic trin khai cc dch v k vng vo nm 2010 v s ph sng 60% dn s vo cui nm 2011.4.2.6 Cc kin ngh v cng ngh cho ton Chu u.c tnh k thut DVB-T2 cho php mt s ln cc ty chn v cc thuc tnh kt hp. Kh nng linh hot ca cc c tnh k thut gip ti u cc thng s trong qu trnh th nghim. Tuy nhin, tnh linh hot ca c tnh k thut trong chun DVB-T2 cng dn n phn ha th trng v to ra cc phin bn k thut theo tng quc gia. qu trnh sn xut thit b t hiu qu cao chotr trng Chu u, cc nh sn xut cam kt khi ng Digital Europe (EICTA trc y) vi mc tiu kt hp chun DVB-T2 vo phin bn HD ca E-Book. Mc ch l nh ngha cc yu cu phi p ng ca my thu DVB-T2 dng cho th trng Chu u. Nhng cam kt ny c k vng tr thnh tp con ca b c tnh k thut DVB-T2 m cc qun tr quc gia c th a ra mc quc gia (ph bin ch yu ti Chu u). E-Book ca Digital Europe cho DVB-T2 cd kin s xut bn vo gia nm 2010. Digital Europe c tham chiu thc t t cng vic ang thc hin Anh (ang chun b trin khai pht cc dch v dng DVB-T2). Vo 3/2009, DTG xut bn phin bn cp nht D-Book qui nh cc ctnh k thut m cc my thu DTT sn xut gn y nht s tng thch vi cc c im DVB-T2 c cc nh qung b chn s dng. Cc thnh vin DTG nh ngha cc h s hiu qu cho my thu DVB-T2 da trn cc kt qu m phng v cng b t cc th nghim ban u c thc hin Anh trong nm 2009. Cc my thu DVB-T2 s cn tri qua kim tra v c ch tng thch c cp php ng k nhn hiu Freeview HD. Hn na, cc i tc tham gia vo cng ngh qung b theo chun mi cng cn cng lm vic vi nhau tha thun c tnh k thut ti thiu cho my thu ph hp vi k hoch pht trin dch v v trin khai truyn dn. Cc yu cu v c tnh k thut cng thit lp tng t khu vc Bc u. Vo 6/2009, NorDig xut bn cc yu cu ti thiu cho my thu c th truycp c cc tn hiu theo qui nh ca NorDig da trn c tnh k thut ca chun DVB-T2. c tnh k thut DVB-T2 nh ngha thm mt profile ring kt hp time-slicing nhng khng dng TFS (time-frequency-slicing). Cc c im ny cho php kh nng thc thi trong tng lai (dng cho my thu vi 2 tuner/front-end) c thxem thm trong ph lc E (ETSI EN302755). Profile my thu NorDig DVBT2 cho php thc thi TFS sau nm 2012 gy ra s tranh ci vi nhiu nh sn xut cam kt thc hin theo c tnh kthut dng chung cho ton Chu u. Theo mt s nh sn xut, vic thc thi TFS c th gy phn ha th trng, to ra s phc tp hn trong my thu, tr hon vic pht trin DVB-T2 v k thut TFS cha c kim tra y v khng c nh ngha trong mt profile ring ca c tnh k thut DVB-T2.Ngi ta k vng cc nh sn xut in t dn dng s cung cp my thu DVB-T2 sm vo nm 2010 p ng nhu cu v my thu DVB-T2 Anh. Gii bng WorldCup FIFA 2010 c truyn dn cht lng HD cng l ng lc thu ht ln vi khn gi. V pha nh sn xut, cciDTV h tr chun DVB-T2 s l mc tin hng n. Sau , th trng set-top box DVB-T2 s c sc cun ht hn vi vic cung cp dch v HD cho ngi xem.4.3. Qu trnh trin khai truyn hnh s mt t Vit NamNgy 19 thng 12 nm 2000 cng ty VTC pht sng tn hiu truyn hnh s u tin Vit Nam ti 65 Lc Trung H Ni vi mt my pht c ci tin t my pht hnh analog trn cao anten 60 mt, v pht 4 knh truyn hnh vi cht lng m bo tiu chun. S kin ny nh du mt mc quan trng trong vic trin khai cc bc tip theo, l c s thc tin cho c quan qun l nh nc hoch nh nh hng cho ngnh truyn hnh Vit Nam. u nm 2001, VTC nng cng sut trm pht sng th nghim ti H Ni ln chnh thc, tng s lng knh truyn hnh ln 16 knh vi hai my pht sng, v th nghim trm pht lp li bng k thut repeater / gap filler ti Ph Lin Hi Phng. Nh vy, nm 2001, Vit Nam chnh thc c tn trn bn cc nc trin khai DVB-T, ch chm hn nc pht trin u tin cng ngh ny (nc Anh) c ba nm. Nm 2003, VTC th nghim thnh cng pht sng hai knh s lin k trn mt my pht sng, m ra mt gii php v cng hu ch: Tit kim my pht sng, tit kim tn s, iu m t trc n thi im cha c tin l. Gii php k thut pht sng truyn hnh s mt t ca VTC (chuyn i my pht hnh analog thnh my pht hnh digital theo tiu chun DVB-T) to cn c ngy 26-3-2001 Tng Gim c i Truyn hnh Vit Nam k quyt nh chn DVB-T l tiu chun truyn hnh s mt t chotruyn hnh Vit Nam. Nm 2003 i TH Bnh Dng v VTC phi hp trin khai h thng pht sng truyn hnh s ti i TH Bnh Dng, m ra mt thi k mi: s ha pht sng n i truyn hnh cp tnh. Ngy 5-4-2005 Ph Th tng Chnh ph Phm Gia Khim k vn bn cho php VTC m rng mng truyn hnh s mt t ra din rng, v giao cho VTC nghin cu th nghim dch v a phng tin trn truyn hnh s mt t. Ngay sau , VTC trin khai m rng mng truyn hnh s mt t ra nhiu tnh thnh. n nay mng s mt t ph sng trn 40 tnh thnh trong c nc, ang c m rng ra cc huyn, x, vng su vng xa. Hin nay VTC trin khai mng truyn hnh s rng khp c nc v ssang trn giai sson m rng v cc huyn, khu vc vng ni vng su xa, bin gii hi o nhm nhanh chng a truyn hnh s mt t n mi ngi dn c nc.Cng vi VTC v i TH Bnh Dng, i TH TP.HCM cng trin khai mt my pht s pht sng trong khu vc TP.HCM. Cng thi im ny, i truyn hnh K thut s VTC ra i t ti H Ni mang quy m quc gia, c Hip hi Pht thanh Truyn hnh chu Thi Bnh Dng (ABU) kt np lm thnh vin vo nm 2006. i truyn hnh K thut s VTC ang pht sng 100 knh truyn hnh, tr thnh mt trong nhng n v cung cp s knh truyn hnh ln nht Vit Nam, trong c 28 knh truyn hnh s mt t qung b min ph,72 knh cn li l truyn hnh tr tin cng ngh cao HD v ang pht th nghim truyn hnh 3D, cng ngh truyn hnh hin i nhtth gii. T li ch vic trin khai thnh cng mng pht sng truyn hnh din rng ca VTC, cng nh tc ng ca n ti ngi xem truyn hnh, m ngy 16-2-2009, Th tng Chnh ph k quyt nh ph duyt quy hoch truyn dn pht sng pht thanh truyn hnh n nm 2020, trong nu r: Tng bc trin khai l trnh s ha mng truyn dn - pht sng truyn hnh s mt t ph hp vi iu kin thc t v thit b thu truyn hnh s ca ngi dn trn tng a bn c th. V c bn s ngng pht sng truyn hnh mt t cng ngh tng t (analog) chuyn sang pht sng truyn hnh mt t cng ngh s (digital) khi 95% s h gia nh c my thu hnh c kh nng thu c cc knh chng trnh truyn hnh qung b bng nhng phng thc truyn dn v pht sng s khc nhau. Ngy 19-7-2010 Th tng Chnh ph k tip quyt nh ph duyt truyn hnh s mt t l 1 trong 46 cng ngh c u tin u t v pht trin. Cc sn phm lin quan n truyn hnh s mt t l 1 trong 76 danh mc thuc danh mc cc sn phm cng ngh cao c khuyn khch pht trin. nc ta hin c cc nh cung cp dch v truyn hnh s mt t DVB-T ca i truyn hnh TP. HCM (HTV), i truyn hnh Bnh Dng (BTV), i truyn hnh K thut s VTC, cng ty c phn nghe nhn ton cu (AVG) hin ang trin khai h thng truyn hnh s mt t DVB-T ph sng ton quc hin i nht Vit Nam s dng mng n tn (SFN) s chnh thc pht sng cui nm 2011 sau mt nm pht th nghim.4.4. Nhng kin ngh khi trin khai DVB-T2 Vit Nam- Nn s dng mng n tn (SFN) theo 3 vng: Bc, Trung, Nam dng cng ngh truyn dn DVB-T2 kt hp vi k thut nn MPEG-4 AVC khi trin khai mng truyn hnh mi, s dng chung c s h tng ca cc i truyn hnh cp tnh, cp huyn gim chi ph u t. Trin khai thm nhiu dch mi thu ht khch hng nh: HDTV, 3DTV.- Cng b tiu chun thng nht cho cc sn phm ti vi s v u thu truyn hnh s mt t nhp khu v sn xut mi h tr thu c truyn hnh s theo tiu chun DVB-T v DVB-T2. - ng thi phi pht song song c 3 mng truyn hnh trong thi gian chuyn i: truyn hnh tng t, truyn hnh s DVB-T, truyn hnh s DVB-T2. - Nh nc tr gi sn phm u thu truyn hnh smt t (Set-top-box), chuyn dn cc knh truyn hnh qung b xang pht s mt t. 4.5. Kt lun chng IVVic chuyn i t DVB-T xang DVB-T2 trn thc t ty thuc vo tng quc gia trong nhng iu kin hon cnh c th: + Vi nhng th trng chuyn i s hon ton pht DVB-T2 cng DVB-T mt thi gian, v trin khai cc dch v mi, ng dng mi trn nn DVB-T2. Qu trnh chuyn i tin hnh dn dn ging nh qu trnh chuyn i t truyn hnh tng t sang DVB-T. + Vi nhng th trng vn ang pht truyn hnh tng t cha pht truyn hnh s mt t th trin khai thng DVB-T2, pht song song c truyn hnh tng t v DVB-T2 mt thi gian. + Vi nhng th trng ang trong qu trnh chuyn i t truyn hnh tng t sang DVB-T qu trnh trin khai DVB-T2 kh khn hn do thiu tn s cp pht cho DVB-T2 do mng truyn hnh tng t v mng DVB-T vn ang s dng, nn trin khai mng n tn (SFN) dng cng ngh DVB-T2kt hp vi k thut nn MPEG 4AVC tit kim tn s, nng cao hiu qu s dng ph tn. Tuy nhin, vi mt s quc gia ph tn vn cn trin khai cc dch v HD ch cn dng chun DVB-T kt hp vi k thut nn MPEG-4 AVC.TI LIU THAM KHO1. Bi ging K Thut Pht Thanh Truyn Hnh, HV Cng Ngh Bu Chnh Vin Thng, 20132. Truyn Thng S, Hc Vin Cng Ngh Bu Chnh Vin Thng, Nh xut bn Bu in, 20133. Truyn hnh K thut s, Hong Long Dng Thanh Phng. Nh xut bn Khoa Hc v K Thut nm 20044. Quyt nh 2451/Q-TTg ngy 27 thng 12 nm 2011 ca Th tng Chnh ph ph duyt n s ha truyn dn, pht sng truyn hnh mt t n nm 2020

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