G161 T H l f U
Gidi phdng dupc ngudn tdi nguyen phd tdn, mang lai lpi ich eho ca cac nhd cung cap dich vu vd khach hang; khai tode va su dung hifiu qua ha tdng traydn dan phat sdng tmydn hinh, ddy dupc coi Id nhung uu didm vd lpi ieh cua vide chuydn ddi sd hda traydn hinh. Trdn tod gidi, sd hda traydn hinh dugc bdt ddu tu ndm 2006, Luxembourg Id qufic gia ddu tidn ttdn hoan toanh qud trinh chuydn ddi tft traydn hinh tuong tu sang tiuydn hinh M toudt sd. Ddn nay, dd cd rdt nhidu qudc gia chdm dut vide phdt sdng truydn hinh tuong ta, dfi Id My, Phap, Hy Lap, Hto Qudc...
Cd rdt nhidu loai traydn hinh sd, vi du nhu: Traydn hinh sd vd tinh, traydn hiito sd mat ddt, traydn hinh sd cdp, traydn hinh OTT (Over-The-Top| vd traydn hinh Intemet (IPTV- hitemet Protocol Television).
Trong dd, toiydn huih sd mdt ddt Id mfit ttong cde gidi phap dupc nhidu nufic ttdn tod gidi lua chpn dd toay tod hfi todng traydn hinh tuong tu. Vdi viec todn khai hd todng traydn hlnh sd mdt ddt, cdc nhd khai tode ed tod tan dung dupe tdi da
ca sd ha tdng sSn cd eua cdng nghd tuong tu (efit phdt sdng, anten...}, do dd chl phi ddu tu khfing ldn vi tod gidm chl phi ngudi dftng.
Thu Thuy
Hdn nay trdn tiid gidi cd ba tieu chudn cho cdng nghfi ttuydn hinh sd quang bd mdt ddt bao gdm: ATSC cfta My, DVB-T cfta chau Au vd ISDB-T cua Nhdt Ban.
Do kha nang hd tra nhidu lo?! hinh djch vu bao gdm cdc djch vu SDTV vd HDTV, cdc dich vu traydn hinh dl ddng..., ndn chudn DVB-T cua chdu Au duoc nhidu nudc tadn khai traydn hinh sd quang bd mdt ddt dp dung vdi 2 phidn ban: DVB-T va DVB-T2.
Theo xu hudng chung, cac nufic bdt ddu todn khai sd hda traydn hinh mat ddt deu chpn ngay cdng nghfi DVB-T2. Didn hinh nhu An Dfi, Nga, Thdi Lan, Malaysia, Indonesia, cdc nude Dfing Au... Cdn cac nude da todn Mial DVB-T tiii bdt ddu ehuydn ddi sang phdt sdng trayen hinh DVB-T2 ttong dd cd Vipt Nam.
Vdy tai sao chuan DVB-T2 lal dupc lua chpn Id chuan cdng nghd khi todn khai sd hda traydn hinh mdt ddt? Bai bao phdn tich nhung bd sung, cdi tidn
DJ3m
TAP CHi CNTT&TT KY 1 (4.2013) 3 3
MPEG transport stream
ScrambJer
ModulaBcm
Outer codef Reed SOtonton
Guard (rtefvaJ Insertion
•
Outer Interteever
Inrwf coder ooncoluBonal
IFFT 4 iPIUinwrtlon
Inner interteever
QAM
1
constDllatlon mapping
Hinh 1: So do tmy&i tai ca b ^ cCe DVB-T
ndi bdt eua DVB-T2 so vdi DVB-T vd tdm lupc Id trlnh sd hda trayen hinh mat ddt tai Viet Nam.
DVB-T VA N H Q N G HAN CHE Chuan traydn hinh sd quang ba mat ddt DVB-T (Digitai Video Broadcasting -Terrestoal) cua Vien tidu chuan vidn todng Chdu Au - ETSI (European Telecommunication Standardisations Institute) dd duoc rtiiidu nude ttfin tod gifii sft dung dd thay tod cho hd tiidng trayen hinh tuong tu (analog).
Hinh 1 la so dd chinh cua mfit bd phat sdng DVB-T. Ludng bit dft hdu dupc ttdn va dupe xu ly lan luot bdi mdt bd ma hfia ngodi Reed-Solomon (RS) va mfit bfi ma hda ndi su dung ma chap (convolution).
6 glai doan ma hoa ddu tidn cd toe loal bo dupc cdc ldi ndn (error floor) nhdm ndng eao ty Id tin hldu/tap dm (SNR- Signal to Noise). Giai doan ma hda toft hai giftp lam giam ty le loi bit (BER- Bit Error Rate) tai n d thu. Cdc bit todng tm da ma hda dupc dan xen ttd lai dd edp phat cae bit Ildn tidp cho cac sdng mang eon khae nhau. Sau dfi, eac bit thdng tin nay dupe sap xdp theo khdi (block), anh xa va didu chd su dung 1^ toudt ghdp kdnh phdn chia toeo tdn sd true giao (OFDM - Orthogonal Frequency Division Multiplexmg), ky toudt OFDM bao gdm mdt phep bidn ddi Fourier ngupc nhanh (ffFT) va bd sung mdt ttdn td tuan hodn (cyclic prefix) cho phep mdt khoang bao vd (Guard hiterval -GI) dd tianh giao toao gifta cde block ldn can. Vide
sft: dung cdc quy tiinh ma hda vd dan xen dua trdn OFDM cho phep vide traydn tai hidu qua toeo da hudng (multipato) ca vd todi gian vd tdn sd.
Mdc dft vide Wdn khai mang DVB-T dat duoc rdt nhidu uu didm, toy nhidn bdn eanh dd cOng hidn huu nhung han chd nhdt djnh. Thft nhdt, sd lupng vd ty Id bit cila cac kdnh traydn tdi Id gifil han so vdl cdc ky thudt traydn ddn vd tuydn mdi. Thft hai, khd ndng tuong tde nhidu hon vdl ngudi sft diing ehua eao. Thft ba, DVB-T duoc thidt kd cho cdc mdi tradng tou cd djnh, vi thd chdt lupng tiiu sdng di ddng rdt kdm, chdng han nhu trdn cdc phuong tidn giao todng.
Cudi cftng, vide ttdn khai DVB-T ttrong cdc mang don tdn {SFN-Single Frequency Network) da vd vdn gdy nhung dp Iftc ddng kd, vi ttong mang SFN cd su giao thoa giua cdc bfi ldp (traydn tai cftng mdt tofing tin ttdn cdng mfit bdng tdn). Didu nay ed tod gdy ra hidn
34| TAP CHI CNTT&TT KY 1 ( 4 . 2 0 1 3 )
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MMuMoo vdPV nnMiiiMion
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mwriiniw
R«etNncy im*fiMnr Hinh 2: Sodd tmyfin song c o b ^ ciia DVB-T2
tupng suy giam tin hidu ttdm tipng ngay ca ttong nhung vftng cfi didu kien phu sfing tdt.
CHUAN DVB-T2
Dua ttdn nhftng kdt qua nghien cftu gdn ddy vd mdt tdp hpp cde ydu cdu vd mdt touong mai, nhdm DVB da cfing bd chudn cfing nghd DVB-T2 efi tod cung edp dung lupng cao hon va tin hieu manh hon ttong mdl trudng mdt ddt, ehu ydu Id cho traydn tdi tmydn hinh dfi phdn giai cao (HDTV- High Definition
Soloimm) !hu(K- ni(»/ Idp con ciia md BCH • ldp mH IK H khong nhj pliAii. MS BCH (mii Bose. Ci "
i.-i llocqucnglicm) la m(u loai mS sua loi vong ng^it nliiOn quan Ir^mg. m iilta nang sira ducrc nliidu loi
\ il iluac irnii dutiif rat ning dai. Trong mii BCH co 2 Idp con lii imi [iCIl nhi piian va ma BCH khong nhi plum. Ma BCII nhi phan du{rc Ilocqiicnghem dira ra viio niim 1959. sau do du<,jc Bosc va Cbaudlwri lim r.
i>i(>t ciich doc l^p vao nam I960. Trong so nhO'ng m3 lii 'II khong nhj phan, quan trong nhat la mii R-S. Mil HC 11 killing nbi phan nghia la inH BCH Uong do gia Iri cua cue h^ so duf,yc lay lit Uudng Galois GF (2m).
Mil R-S duac liccd va Solomon gidi ihicu liin dau
Televlson). Hinh 2 Id sa dd traydn sdng co bdn cua DVB-T2.
Didm mfii ndi bat cua DVB-T2 ndy la d phuong toftc sua l5i. Chuan cdng nghd ndy su dimg ma hda kdnh gidng nhu da dupc thidt ke chp chudn edng nghfi traydn hinh sd quang ba vfi tinh tod hd toft 2 (DVB-S2: Digital Video Broadcastmg - Satellite - Second Generation). Cac toudt toan md hda dua ttdn su kdt hpp md kidm tta chdn Id mdt dd todp (LDPC- Low-Density Parity-Check code) vd md BCH (Bose-Chaudhim-Hocquenghem), cung cdp chat lupng tin hieu tdt, do dd nhdn duoe tin hidu rdt manh tai phia tou. Cdc ky toudt sfta ldi toifie (FEC - Forward Error Correction) dua ttdn LDPC ttong DVB-T2 Id mdt cai ttdn dang kd so vdi co chd sua loi chap (convolutional error correctmg scheme) dupe su dung ttong DVB-T.
DVB-T2 su dung ky touat didu chd OFDM 0dng nhu DVB-T. Kich toudc FTT tiong DVB-T2 dupc md rdng tdi 16K vd 32K nham tdng chidu ddi cua khoang bao vd (GI) ma khdng lam giam hipu qua phd tdn cfta hd todng. Chuan cdng nghd DVB-T2 rdt linh boat nhd cfi khd nang cung cdp mdt bd tham sd didu chd ldn bdng each kdt hop mdt sd sdng mang vd chidu ddi GI khac nhau (Bang 1). Ngodi ra, kich cd chdm sao ldn nhdt cd tod tdng ldn den 256 symbol (256 QAM).
Mdt eai tidn dang chu y khde cfta ehudn DVB-T2 Id viec bd sung todm 8 mau pilot phdn tan (Scattered Pilot) khdc nhau. Vide lua dipn eac mdu pilot nay
TAP CHf CNTT&TT K* I ( 4 . 2 0 1 3 ) 3 5
Bang l:C*;m(xlel«ttrgtroiigchujnDVB-T»aDVB-T2 ^
FEC Mode Khoang bao ve (GIj
Kich thuoc FFT Pilot phan tan Pilot lien tuc
DVB-T Ma chap + RS 1/2, 2/3, 3/4, 5/6, 7/8 QPSK, 16QAM, 64QAM
1/4, 1/8, 1/16, 1/32 2K, 8K 8% ctia tdng 2,6% cija tdng
DVB-T2 LDPC + BCH 1/2, 3/5, 2/3, 3/4, 4/5, 5/6 QPSK, 16QAM, 64QAM, 256QAM 1/4, 19/256, 1/8, 19/128, 1/16, 1/32, 1/128
IK, 2K, 4K, 8K, 16K, 32K 1%, 2%, 4% va 8% aia tong
0,35% Ciia tdng
phu thuOc vio cac tham sd truyen dSn hi6n c6 (Idch thuoc FFT va dd dai GI|. Chuin DVB-T2 cd khi nang Cctu hinh tat cd cac tham sd ndn phuong thiic didu che cd thd thich ling vdi cic dac tinh truydn dSn thiic td, dem lal hieu sudt su dung phd tan cao lihdt.
Sit dung 3 ldp dan xen la mdt cai tidn ntta dia chudn DVB-T2, bao gdm: dan xen bit (bit Interleaveil, dan xen thdi gian (time Interleaver) vd dan xen tan sd (frequency interleaver). Cdi tidn ndy se gitip tranh duoc vide sinh ra cac ldi tnim, cac ldi ngdu nhidn trong mdi khung LDPC FEC.
Mat khac, DVB-T2 duoc bd sung 2 ky thujt mdl dd
Id chdm sao quay {rotated constellation} vd Q-delay (RQD) nhdm chdng lai su suy giam tin hieu cdc mdl trudng phat sdng mat dat Ky thudt ndy trdnh duoc tdn hao trdn kdnh Gauss vd tao dugc dd lpi 0.7dB trdn kdnh cd phading. Do loi ndy cdn ldn hon trdn kdnh OdB phdn xa (SFNl vd kdnh xod (nhidu ddt bidn, phading cd chpn loc). Didu ndy cung ddng nghia vdl vide cd thd sil dung ty Id ma, tdc dd bit cao hon.
DVB-T2 ciing cung cdp kjr thudt dd didu chinh miic dd tin hieu manh ydu khdc nhau cho tiing Iogi dich vu trong mdt kdnh dd ddp ting da dang cdc didu B t o thu sdng (trong nhd, ngodi trdl....|. Ngodi ra, ma hda Alamoutl duoc dua vao DVB-T2 dd cai thien viing phii sdng trong cac SFN quy md nhd.
Cudi cimg, DVB-T2 cUng khdc phuc tdc ddng cua ty le cdng sudt dinh/cdng sudt trung binh (PAPR- Peak to Average Power Ratio) trong cdc thidt bl phdt sdng. PAPR trong cdc hd thdng OFDM cao gdy ra mdo tin hidu va ldm gidm hieu sudt tai (ac bd khudeh dai. Chudn DVB-T2 da dua ra hai ky thudt dd han chd PAPR ma khdng ldm bidn dang ddn vide phdt tin hidu, dd Id: sdng mang ddnh n t o g (camer reservation) vd mo rdng chdm sao tich cue (Active Constellation Extension -ACE).
361 TAP CHI CNTT&TT K * 1 (4.2013)
i r 5
Hinh 3; Lo trinh chuyen ddi ttrnay den natti 2020
V I | T NAM TRIEN KHAI TRUYEN H I N H so H 6 A MAT OAT V 6 I CHUAN DVB-T2
Tai Vidt Nam, ngdy 16/02/2009 Thti tudng Chinh phi da phS duydt Quydt dmh sd 22/2009/QB-TTg vd vide Quy hoach truydn ddn, phdt sdng phdt thanh, tniydn hinh ddn ndm 2020. Trong dd, timg budc tridn khai Id trlnh sd hda mang truydn ddn, phdt sdng truydn hlnh sd mdt ddt phd hop vdi didu kidn thuc td vd thidt bi thu truydn hlnh sd ctia nguoi dan trdn tiing dia bdn cu thd.
Cu the Id tinh ddn 31/12/2015, 5 thdnh phd hue thudc Trung uong bao gdm Hd Ndi (cQ), TP HCM, Hal Phdng, Di Ndng vd Cdn Tho, sd kdt thiic phit sdng cde kenh chuong trinh analog (tuong tu) dd hodn toin chuydn sang truydn hinh sd mat dat Giai doan hai eda 10 trinh sd hda sg kdt thiic trudc ngiy 31/12/2016 bao gdm Hi Mdi (md rdng), Vinh Phiic, Bde Ninh, Hdi Duong, Hung Ydn, Qudng Nmh, Thdi Nguydn, Thii Blnh, Hi Nam, Nam Dinh, Nmh Binh, Bic Giang, Phii Thp, Khdnh Hda, Binh Thudn, Nmh Thuin, Binh Duong, Ddng Nai, Bd Ria-Vting Tiu, long An, Tidn Giang, Bdn Tre, VInh Long, Ddng
Thdp, An Giang, Hiu Giang. Giai doan 3 vd 4 hodn thdnh vdo 31/12/2020 vd dp diing vdi ede tinh cdn lal trdn ei nudc.
Hidn nay, Vidt Nam ed 3 n h i cung cdp dich vu truydn hinh sd mat dit tidn phong Id Tdng edng ty truydn thdng da phuong tidn (VTC) dp dung chuan DVB-T, Cdng ty Cd phdn nghe nhin toin eiu (AVG) vi Dil tiuydn hinh Vidt Nam (VTV) i p diing chuan DVB-T2.
Tuy nhidn, do nhiing uu didm vi nhOng cai tidn cua DVB-T2 so vol DVB-T nhu kha ning ghdp nhidu kdnh chuong trinh trdn mdt kdnh tdn sd don so vdi DVB-T; Hipu qua sii dung tii nguydn tdn sd cao hon;
Ddp ling dupe ede dich vu truydn hlnh chdt luong cao HDTV, 3DTV; Kha ning tiidn khai mang SFN hidu qua rdng hon.... vi ddc bidt li DVB-T2 Id chudn hipn dai va phd hpp vdi mtic Udu ddi han cua Vidt Nam, ndn mdi ddy t?l cudc thao luin. Ban ChJ dao De dn sd hda truydn hlnh Vidt Nam da thdng nhit xde dinh vide dp dung ngay ndu chuan tiuydn hinh sd DVB-T2 se dem lai nhidu hidu qud vd kmh td, xa hdi, phd hop vdi xu thd phdt ttidn cdng nghd, ddp
TAP CHi CNTT&TT K* 1 ( 4 . 2 0 1 3 ) I 3 7
ling ydu eiu edng nghidp hoa, hidn dai hoa den ndm 2020. Tren eo s6 db. Ban etu dao B6 an sd hba tmyen hinh Vi$t Nam d^ nghi Thil tu6ng Chinh phu giao Ban chl dao D^ an so hoa chinh thiic yeu ciu cae doanh nghifep cung cap djch vu tniyfin din, phat s6ng tnjyen hinh sd cin ap dung ngay ti6u c h u ^ phat s6ng DVB-T2, ehuin n6n tin hi6u am thanh hinh anh MPEG-4Ai.264.
Vdi nhQng uu diim n6i b$t cda mdt (^uSn mdi bi$n dai cho tmySn binh quing bi m$t dit DVB-T2 se li cdng nghS mang din su thinh cdng cho 10 trinh chuySn dSi sang s6 hda pbit thanh tniyin binh cua Vidt Nam d vi m$t thdi 0an va dbit
T a i l i e u t h a m Icliao [1]. www. micgov.vn
[21. (2uygt dinh s6 22/2009/QB-TTg cua Ttvj tudng chinh phu ngdy 16 thAig
02 n^ 2009 Phe dsyStOL^hc^htn^ din, phdt sdng f^at „ thaih, tnjy^i hinh d^ nam 2020.
[3]. (3uydt dinh 2226/QD-BCDBASHTH ngdy 22 thdng 11 n^ 2012 aia Tmdng Ban chl dao BS an so hda tn^ hilt Vi$t Nam Ban hdnh quy chd iam vi$c ciia Ban chl dao BS dn sd hda tnjySn hlnh Vi$t Nam.
[4], (3uydt dinh sd 714A3D-TTg ngay 14 thdng 6 ndm 2012 '•"
cda TW ttngChinhfMv6 vl$c thdnh lap Ban (^l dao BS dn sd hda buyfy) hlnh Viet N&n.
[51. Und&stmding DVB-T2, DigiTAG - The Digital Terrestrial Teievision Action Group.
[6]. MiKEL MENDICUTE, IKER SOBRON, LORENA MARTINEZ AND PELLO OCHANDIANO, DVB-T2: New Signal DVB-T2: New Si^ Processing AlgoriHwns for a Challenging Digital Video Broadcasting Stmidard.
[7]. ETSi EN 302 755: 'Digital Video Broadcasting (DVB); Frame staicture channel coding and modulation fa-a seaxidg&ieration digital t&restnal television broadcasting syst&n 0VB-T2)".
[8]. ETSI TS 102 773: "Digital Video Broadcasting (DVB);
Modulator tnt&fac^ CT2-MI} for a second generation digital tenestrial television broadcasting system (DVB-T2)'.
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3 8 | 11^ lf)P CHI CNTT&TT KY 1 (4.2013)
