MC LC

MC LC1CC T VIT TT2LI M U3TNG QUAN V CNG NGH PHT THANH S41.GII THIU CHUNG42. PHT THANH S THEO TIU CHUN CC NC CHU U52.1. Nguyn tc52.2. Mng pht thanh s62.3. Nhng u nhc im ca tiu chun pht sng E147243. PHT THANH S THEO TIU CHUN IBOC HD RADIO v DRM253.1.Tiu chun IBOC-HD Radio:253.2.Nhng u nhc im ca cng ngh IBOC263.3. Tiu chun DRM27TI LIU THAM KHO37

CC T VIT TT DSBDigital Sound Broadcasting

DRMDigital Radio Mondiale

E147Eureka 147

DMBDigital Multimedia Broadcasting

HD RadioHigh Definition Radio

FMFrequency Modulation

AMAmplitude Modulation

POTSPlain Old Telephone Service

3GH thng cng ngh s th h th ba da trn h thng.

UMTSUniversal Mobile Telecommunications System

LCDMn hnh tinh th lng

WAPWireless Applications Protocol

PADProgramm Associated Data

X- PADeXtended-Programm Associated Data

DVB-TDigital Video Broadcasting Terrestial

DVB-HDigital Video Broadcasting Handhelds

DQPSKiu ch s

ETI NIEnsemble Transport Interface Network Independent

ETI NAEnsemble Transport Interface Network Adaption Layer

CRCCyclic redundancy checks

FECForward Error Correction

UEPUnequal error protection

LI M U

C th ni chng ta ang sng trong thi k pht trin rc r nht ca cng ngh thng tin ni chung v pht thanh ni ring, cho n nay mc d c nhiu loi hnh thng tin tuyn truyn pht trin nhng ngi ta vn phi tha nhn rng pht thanh l mt trong cc loi hnh thng tin tuyn truyn ph bin nht, cn thit nht v t hiu qu cao nht. Nhn li mt chng ng di tn ti v pht trin ca k thut, cng ngh pht thanh k t nhng ngy u s khai ch pht i c cc bn tin n gin vi mc ch thng tin l chnh, nn cht lng m thanh rt thp cho n nay chng ta d dng c thng thc nhng ba tic m nhc ngay ti nh mnh vi cht lng m thanh trung thc nh chng ta ang nghe trc tip dn nhc biu din trong nh ht thng qua thit b thu (my thu). c c thnh qu nh ngy nay, cng vi s pht trin ca cng ngh in t, cng ngh vt liu .th cng ngh k thut s ng mt vai tr v cng quan trng. Sau mt thi gian nghin cu ti liu v tm hiu v cng ngh pht thanh s, y l mt lnh vc cn mi i vi nc ta ( theo thng tin em c bit th n nm 2020, Vit Nam mi chuyn sang cng ngh pht thanh s) nn ti liu v lnh vc ny khng c nhiu, kh nng ngoi ng ca bn thn cn hn ch. Knh mong c gio ht sc gip , ch dy em, em xin trn trng cm n!

TNG QUAN V CNG NGH PHT THANH S

1. GII THIU CHUNGS pht trin mnh m ca cng ngh pht thanh ni chung v pht thanh s ni ring trong thi gian va qua, lm cho pht thanh khng ch gn vi mt thit b n l hay ch cn truyn qua sng in t, qua h thng truyn dn, pht sng. Chng ta thy in thoi di ng i mi c km theo my thu FM, CAMERA, thit b tr gip c nhn PDA. Theo iu tra ca hng sn xut in thoi nht ca Phn Lan i vi model in thoi u tin c km theo chc nng thu FM, th chc nng nghe FM l chc nng c yu thch th hai v c n 80% ngi dng nghe FM t nht mt tun mt ln. trong thi gian ti, thnh gi x nghe pht thanh ngoi nh s s dng in thoi di ng nghe nhiu hn l nhng ngi s dng my thu thanh. Do vy chng ta c th thy rng kh c th c mt thit b di ng no c kh nng cung cp tt c cc dch v khc nhau m ch da trn mt cng ngh duy nht. i vi lin lc dng im vi im mng in thoi di ng l s la chn tt hn. Nhng i vi dng truyn t mt im ti nhiu im th pht thanh vn l gii php hu hiu nht. Cc nh cung cp dch v ca pht thanh c th da trn nhng u im ca pht thanh s l c th truyn cc d liu ln m khng cn thu thm ph ti d liu.n cng d dng tch hp vi cng ngh vin thng a ra cc dch v tng tc. Pht thanh s l mt trong nhng ng dng rng ri ca m ha m thanh theo nhn thc. Trong khi cc chun MPEG 1,2 LAYER3 c ng dng trong cc h thng pht thanh s theo tiu chun chu u EUREKA 147 v WORLD SPACY, th chun mi MPEG AAC s c s dng trong cc h thng IBOC ca M v AAC cng l mt trong cc ng c vin cho cc h thng pht thanh mi trong di tn di 30 MHz. Trong tng lai , m ha m thanh vn s l mt trong nhng phn mm trng yu ca cng ngh pht thanh s.Pht thanh s cung cp cc dch v a dng hn pht thanh truyn thng , ngoi cc chng trnh pht thanh l vn bn, d liu thm ch l tn hiu video. Cht lng chng trnh vi m thanh s p ng yu cu ca c cc thnh gi quen vi cht lng m thanh CD cng nh yu cu ca cc thnh gi tr . thu c chng trnh pht thanh s, my thu thanh khng ch cn mi loa cung cp thng tin m tr thnh mt kho thng tin a phng tin vi nhiu chc nng trong c mn hnh LCD hin th cc thng tin nh tn bi ht, ca s th hin, thng tin v giao thng, thi titMt h thng pht thanh thng thng vn l mt qu trnh cung cp thng tin mt chiu v khng c thng tin phn hi li. D vi rt nhiu sc mnh ca mnh, pht thanh s vn l phng tin truyn thng mt chiu. Hin nay pht thanh s ang th nghim kh nng kt hp vi mt s cng ngh vin thng khc nh 3G hay GPRS, to ra mt knh phn hi. Vic kt hp ny a ra nhiu kh nng phc v mi ngoi cc chng trnh pht thanh.Hin nay trn th gii tn ti nhng xu hng khc nhau trong cng ngh pht thanh s. nhng y ch nu ra mt s chun c th p dng cho Vit Nam.2. PHT THANH S THEO TIU CHUN CC NC CHU U Do cc nc chu u khi xng, h nghin cu hon thin thnh tiu chun v c mt s t chc quc t cng nhn l tiu chn quc t v c gi l tiu chun E147.2.1. Nguyn tc Vi pht thanh s, h thng truyn dn v pht sng pht thanh c nhiu thay i mang tnh cch mng. - Nh cung cp dch v, v d mt i pht thanh bt k no, s a ra dch v ca h km theo tt c cc d liu cn thit. Thng thng dch v l mt chng trnh m thanh c m ho, d liu km theo chng trnh, thng tin v dch v c dng m t dch v ny trong b ghp knh. Ngoi ra, h cng c th cung cp nhng dch v d liu khc c th lin quan ti chng trnh, nhng cng c th nm ngoi chng trnh. - Nh cung cp dch v ghp knh : y l mt thnh phn mi trong dy chuyn pht thanh s vi pht thanh truyn thng. Do mt my pht c th pht i nhiu chng trnh khc nhau, cc dch v ring bit vi cc thng tin dch v tng ng s c nh cung cp dch v ghp knh tng hp li to thnh tn hiu tng hp (ensemble ) a tn hiu n cc i pht. - Nh pht sng pht thanh s : iu hnh hot ng cc my pht pht thanh s. y nhn tn hiu tng hp, thc hin vic iu ch theo cch iu ch s COFDM v truyn i. Ngi nghe s thu li tn hiu s ny v chn la mt trong bt k dch v no ca tn hiu tng hp ny. 2.2. Mng pht thanh s Mng pht thanh s c chia thnh ba khi chnh : dch v chng trnh hay dch v chng trnh thnh phn ; dch v ghp knh hay dch v tng hp tn hiu; mng pht sng.

Hnh1: Mng pht thanh s

2.2.1.Nh cung cp dch v Nh cung cp dch v c th l nh cung cp dch v m thanh hay l nh cung cp dch v d liu hoc l cung cp c dch v m thanh v d liu. Nh cung cp dch v m thanh Chng trnh m thanh c ly ra t u ra ca phng thu hay tng khng ch c th di bt k chun no dng analog hay dng s v sau c m ho ti b m pht thanh s Musicam to ra phn tiu ISO v chn d liu gn vi chng trnh vo cc khung ca dng d liu MPEG. Ngoi chng trnh m thanh, nh cung cp dch v cn c th to ra d liu gn vi chng trnh tng thm tnh hp dn cho cc chng trnh pht thanh. Dng d liu gn vi chng trnh PAD c hai li im chnh sau : dung lng ca PAD hon ton do nh cung cp dch v kim sot, cn i vi nh cung cp dch v ghp knh PAD l mt phn ca dng d liu m thanh v khng th tch ri ra c. PAD ch nh mt ng ng dn d liu, nhng d liu ny c th c gii m my thu phi c cc giao thc chun trong vic x l cc file. PAD c th l nhng dng sau: - Nhn ng - Kim sot di ng - Video km theo m thanh ( i hi phi c X-PAD) Tc PAD c nh thng khng cao 0,667 kbit/s vi tn s ly mu 48kHz (24ms frame). V vy ngi ta s dng PAD m rng X-PAD cho nhng ng dng c nhiu d liu hn. Tt nhin lc ta phi ch rng, khi tng dng d liu vi X-PAD, c th phi gim phn d liu ginh cho m thanh v iu c th s lm gim cht lng m thanh. PAD c thm vo khung Musicam trong b m ho Musicam, thng b ny c lp t ti pha ngi sn xut chng trnh pha phng thu hay tng khng ch. Nh cung cp dch v d liu Nh cung cp dch v d liu c th to ra d liu c lin quan ti dch v m thanh hoc hon ton khng dnh dng ti dch v m thanh. Tng s dung lng d liu cho php hin nay c th t 10% n 20% (10% cho cc d liu c lin quan ti chng trnh v 10% khng lin quan).Mt s d liu thng dng hin nay pht theo chng trnh pht thanh l : - Thng tin kinh t - c phiu - Kt qu th thao - Bo gi Thng tin v dch v chng trnh SI ( Service Information ) Nh cung cp dch v c th thm cc thng tin b sung v dch v ca mnh- c dch v d liu v m thanh, qua thng tin v dch v chng trnh. Thng tin ny sau s c truyn v s dng lm tn hiu hng dn cho nh cung cp dch v ghp knh. Nhng thng tin v dch v chng trnh SI c th l : - Thng tin xc nh dch v.- Loi chng trnh.- Tn s lin quan ti cc dch v FM, MF v pht thanh s.- Thng tin thng bo( lin quan ti cc knh thng bo trong b ghp knh) 2.2.2. Nh cung cp dch v ghp knh Nh cung cp dch v ghp knh qun l dung lng ca t nht mt b ghp knh pht s. Mt b ghp knh c th c ti 64 knh ph, trong mi knh dng cho mt dch v hay mt thnh phn dch v. Nhng chc nng chnh ca nh cung cp dch v ghp knh l : - Nhn t nh cung cp dch v thng tin ca knh ph v cc d liu iu khin km theo, t nhng d liu to ra d liu theo chun thch ng to nn giao din truyn dn tng hp ETI- Ensemble Transport Interface. - To knh thng tin nhanh - FIC (Fast Information Channel ). FIC l knh thng tin i trc cho php my thu nhn bit thng tin thit lp ca b ghp knh.- Nhn t nh cung cp dch v cc d liu km theo dch v v to li thng tin ny a vo FIC. - Thm cc d liu km theo tn hiu tng hp vo FIC , chng hn nh tn b ghp knh.- Qun l cc cu hnh v dng d liu cho tng dch v - Qun l cc tnh ton vi cc nh cung cp dch v 2.2.3. Nh cung cp dch v pht sng Nh cung cp dch v pht sng chu trch nhim to ra tn hiu COFDM v truyn tn hiu ny hoc l t mt my pht hay mt mng my pht mt tn s. Nh cung cp dch v pht sng ch b sung thm thng tin xc thc my pht-TII ( Transmitter Identification Information ) vo tn hiu tng hp. y l mt lot cc sng mang uc truyn trong symbol 0- gn cho mi my pht mt thng tin xc thc c trng dng cho cc vng . Thng tin iu khin s l dng thng tin hai chiu gia 3 nh cung cp dch v. Trong , dng thng tin quan trng nht l thng tin gia nh cung cp dch v pht thanh v nh cung cp dch v ghp knh Thng tin (SI) v cu hnh b ghp knh. Hot ng ca h thng cng phc tp th vic iu khin, qun l b ghp knh cng phc tp hn. Chng hn nh c th cn s dng c ch thit lp cu hnh ng cho b ghp knh. Trong trng hp ny cn dng tn hiu iu khin hai chiu gia nh cung cp dch v v nh cung cp dch v ghp knh.2.2.4. Nh cung cp dch v chng trnh Vai tr ca nh cung cp dch v l to ra mt b hay nhiu thnh phn chng trnh cng vi cc thng tin km theo truyn ti nh cung cp dch v ghp knh. Cc thnh phn dch v chng trnh c th l : - Dch v m thanh : cc d liu m thanh v cc d liu km theo - y l nhng thnh phn chnh ca dch v m thanh - Dch v d liu v d nh qung co di dng m thanh v hnh nh c kt ni vi dch v m thanh.

Hnh 2:Xem xt chi tit hn v cc nh cung cp dch v

Hnh 3 :B n knh dch vTi nh cung cp dch v, b ghp dch v - SCM ( Service Component Muxtiplexer l mt thit b quan trng ca h thng thit b chnh Chc nng chnh ca thit b ny l trn tn hiu u ra b m ho m thanh vi cc tn hiu khc theo giao din truyn dn dch v- STI ( Service Transport Interface ). Giao thc STI c thit k giao tip qua mng vin thng v truyn thng tin hai chiu gia nh cung cp dch v chng trnh v dch v ghp knh. B ghp dch v hot ng di s iu khin ca my tnh qun l dch v - n dng thit lp lch pht sng v xc nh tc m thanh m ho. Kt ni vi h thng iu khin ca nh cung cp dch v qua giao din STI, b iu khin s iu khin thit lp cu hnh cho b ghp knh.

Hnh 4: Cu hnh thng dng ca b ghp knh dch vThng thng b SCM c hai b m ho m thanh. S dng cc thit b ny to tn hiu m thanh theo nh dng t tn hiu analog hay digital, cng c th nhn tn hiu c m ho qua cc ng truyn dn, hay d liu km theo chng trnh qua u vo RS232. Hai b m ho c ni vi nhau qua giao din WG1 v WG2- y l hai chun giao din c la chn cho E147 kt ni tc cao gia cc b m ho MUSICAM v b to sng COFDM. Nh c giao din ny, ngi ta c th ni ln lt ti 16 b m ho c tc ln n 384 kbit/s cho mi b m ho. Bn cnh , cng c b gii m kim tra ngun m thanh c truyn trn bus WG1/ WG2. C th tu chn u ra b ghp dch v theo cc chun truyn dn nh ISDN; G703; X21. Tn hiu sa li cng c b sung vo giao din STI bo v d liu cho b ghp knh dch v v b ghp knh tng hp. 2.2.5. Nh cung cp dch v ghp knh B ghp knh tng hp. Trn thc t ch c mt dng ETI NI hay ETI NA c truyn i trn mng truyn dn. u vo STI ly tn hiu t nh cung cp dch v c a n b ghp knh qua mng truyn dn ca h thng vin thng. Thng tin trong STI c chia ra thnh cc thnh phn dch v v cc thng tin tng ng vi dch v - SI. Ton b thng tin v dch v - SI l tp hp li t tt c cc dch v v m ho a vo knh FIC. Tt c cc thnh phn dch v c ghp li. i vi cc dch v d liu, c th c ghp trc ti b ghp d liu ng gi to ra mt knh d liu ph cha nhiu gi dch v d liu. Bn cnh l cc tn hiu iu khin v ch dn, k c tn hiu xc thc b ghp knh trong knh thng tin nhanh FIC; thng tin v cu hnh b ghp knh MCI ( Multiplexer Configuration Information ) v thng tin thit lp cu hnh b ghp a ti nh cung cp dch v chng trnh. Dung lng d liu ca b ghp knh Dung lng d liu ti a ca b ghp knh pht thanh s, p dng m ho vi 1536 DQPSK sng, mang, l 2,4Mbit/s. Mt phn trong c dng cho knh ng b v phn cn li c chia thnh hai knh knh thng tin nhanh- FIC ( Fast Information Channel) v knh dch v chnh-MSC (Main Service Channel), c th c chia nh sau : FIC : 96kbit/s v MSC : 2,304Mbit/s.

Hnh 5: B ghp knh tng hpTrong knh MSC, d liu gm c knh ph d liu pht thanh s ( m thanh hoc d liu) v mt s sa li. Trong knh FIC c d liu FIC vi tc 32kbit/s vi phn bo v khng thay i l 64kbit/s. truyn dn tn hiu t b ghp knh n cc i pht, thng ngi ta c gi tc d liu di 2,048Mbit/s, l dung lng knh d liu trong dch v vin thng. C th t c iu nh sa li trc FEC ( Forward Error Correction) cho knh ph ti b iu ch COFDM thay v thc hin ti b ghp knh . Tc d liu ca knh ph (d liu m thanh hay d liu khc) tng ln bao nhiu khi c m ho OFDM ph thuc vo mc bo v (cp) c chn khi thc hin FEC. Thng tin v mc bo v s c truyn ti b iu ch COFDM theo knh thng tin v cu hnh ca b trn knh. Thng tin c to ra b ghp knh. Ti b iu ch COFDM, sau khi c x l sa li trc tt c cc knh ph c ghp li to knh MSC. Knh MSC bao gm cc khung CIF ( Common Interleaved Frame). CIF l mt khi chnh ca tn hiu COFDM. 1 CIF c truyn i theo chu k 24ms v cha 55296 bit. n v c a ch nh nht trong CIF l CU c dung lng 64 bit. Nh vy mt CIF s c 864 CU. Mt CU ch c th cha thng tin t mt knh ph. Cch tnh s CU cn thit cho mt dch v m thanh:

Mc bo vTc m ha

10,34

20,43

30,43

40,43

50,75

Mt knh ph mang mt thnh phn dch v chng trnh m thanh, ph thuc vo mc bo v, s c mt s lng CU nm trong dy s sau : 16,21,24,29,32,35,40,42,48,52,58,64,70,80,84,96,104,116,128,140,160,168,192,208,232,280,416. Tc dng bt ca CU c tnh t tc gi l 24ms vi 64 bit/ 1 CU v s l 2.667 kbit/s. Nh vy s CU cn thit cho mt knh m thanh ph l tc dng bit( kbit/s) sau khi p dng mc bo v FEC chia cho 2,667 (kbit/s). bo v tt nht vi tc dng bit l 1/3; mc 5 s cho mc bo v t nht vi tc dng bit l . Chng hn nh i vi dch v m thanh 256kbit/s vi mc bo v 3 ( tc m FEC l 0,5), s CU cn thit s c tnh : (256 kbit/s * 1/0.5) / 2.667 = 191,1. Trong dy s CU - s gn nht l 192CU.Cch tnh s CU cn thit cho mt dch v d liu. Cc knh ph dng cho dch v d liu phi c mt tc truyn bit l s nguyn ln 8kbit/s Ta s c cch tnh s CU nh sau:Dch v d liu vi tc bit l s nguyn n ln ca 8kbit/s. ( n = tc d liu / 8(kbit/s))

Mc bo v1-A2-A3-A4-A

Tc m ho3/83/4

Kch thc knh ph (s CU)12n8n6n4n

Dch v d liu vi tc bit l s nguyn n ln ca 32kbit/s ( n = tc d liu / 32(kbit/s)) Mc bo v 1-B 2-B3-B4-B

Tc m ho 4/94/72/34/5

Kch thc knh ph (s CU) 27n21n18n15n

Dung lng CU trong b ghp knh Trong mt CIF c 864 CU, v vy vic b tr d liu v mc bo v phi c thc hin sao cho s CU cn thit cho ton b cc knh ph khng vt qu 864 v ngc li cng khng qu thp hn 864 khng lng ph dung lng knh pht thanh. Mng truyn dn tn hiu ghp knh : y l h thng truyn dn ni b ghp knh vi mt hay nhiu b iu ch COFDM. Do tnh cht ca cc ng truyn dn khc nhau s khng ging nhau nn nu ch dng mt chun giao din chung l khng thch hp. Khi bt u thc hin E147, ngi ta a ra giao din mng ghp knh ETI ni gia nh cung cp dch v chng trnh v nh cung cp dch v ghp knh. V trong ETI ngi ta a ra hai lp giao thc truyn dn. l ETI NI giao din mng ghp knh khng ph thuc vo mng ( Ensemble Transport Interface Network Independent ) v ETI NA- giao din mng ghp knh tng thch vi tng mng ( Ensemble Transport Interface Network Adaption Layer)ETI NI giao din mng ghp knh khng ph thuc vo mng ( Ensemble Transport Interface Network Independent ) Nu b ghp knh tng hp v b iu ch COFDM cng mt a im - th ETI NI l mt phng php thch hp ni chng vi nhau. ETI NI c dng do giao din G703 s dng tc bit 2,048 Mbit/s.

D liu v tn hiu ng b c truyn trn cng kt ni ni tip dng m ho HDB-3. Lp ETI NI khng th dng cho mng truyn dn vin thng thng thng v khng p ng tiu chun ca G704. ETI NI s dng phng php sa li CRC ( cyclic redundancy checks) ch khng phi FEC ( Forward Error Correction). di khung tng i di ( 24ms) nn s khng tht s m bo cho cc ng truyn c ly xa. ETI NA- giao din mng ghp knh tng thch vi tng mng Nu khng th ni thng b ghp knh v b to sng COFDM, ngi ta khng th dng ETI NI m s s dng giao thc khc. Trong E147, ngi ta s dng giao din truyn dn th hai gi tn l ETI NA- giao din mng ghp knh tng thch vi tng mng. Vic dng cch tng thch vi tng mng cho php ETI c truyn trc tip qua mng vin thng. Tuy nhin cng c mt s vn sau cn quan tm : - Tc d liu m mi trng truyn thng h tr .- Tnh cht ca li ng truyn trong mng vin thng .- Tr do mng vin thng : lm cho NI v NA tng thch vi nhau, ngi ta a ra nh dng a khung. Mi khung pht thanh s 24ms c chia ra thnh 3 khi ln vi 2048 byte cho mi khi. Mi khi chnh li c chia thnh 8 khi nh. Mi khi ny c chia thnh 8 khung G704, mi khung c 32 thi gian 8bit. ETI NA c 1920 kbit/s cho d liu dch v v 56 kbit/s cho qun l khung, sa li v nh du thi gian ca cc khung pht thanh s. Du thi gian l mt trong nhng phn quan trng qun l tr trong mng vin thng sao cho c th thit lp c mng mt tn s. V mt in, ETI NA p ng G703 v v mt cu trc khung, p ng G704. Ngoi ra kim tra cht lng ng truyn v cht lng mch ngi ta c th dng TS16. C ETI NI v NA u c giao din ni tip truyn d liu kim tra qua RS232 , d liu ny c truyn t b ghp knh n i pht sng s dng dung lng d phng kim tra. 2.2.6. Pht sng H thng pht thanh s s dng k thut COFDM trong iu ch. y s kt hp gia k thut iu ch a sng mang OFDM vi k tht m ho xon. Theo cch , h thng c th tn dng c c nhng li im min tn s v min thi gian. Tn hiu sau khi c x l sa li trc s c tri v chn c min tn s v thi gian. Nh vy m li truyn dn s tri ra cho ton b d liu.Sau khi gii m v chn thi gian v tn s, tn hiu s c phc hi li sau khi sa li. Chn phng php sa li trc cho pht thanh s s cho php ta chn cc mc bo v khc nhau tu theo yu cu ca dch v. i vi cc chng trnh m thanh, n cho php p dng k thut bo v khng ng mc( UEP unequal error protection) ph hp vi mc quan trng cho tng phn trong dng d liu m thanh. Chng hn nh trong mt khung MUSICAM th on cha nhng thng tin iu khin nh tiu , bit ca band ph v.v ..s c bo v vi mc cao hn nhng mu m thanh. -iu ch OFDM v khung truyn dn OFDM l h thng a sng mang vi d liu c truyn ti mc symbol thp v s dng nhiu sng mang di hp. i vi pht thanh s c 4 mode truyn. Mi mode c thit k cho cc bng tn khc nhau, hay nh i vi Mode IV l kh nng thit lp mng mt tn s trn bng L. Ta cng xem xt Mode I, vi tn s dng cho pht thanh s l bng III VHF. Ta c thng s ca h thng truyn dn theo Mode I

di khung 96ms

di symbol1297us

di khong bo v 246us

di c ch ca symbol 1ms

Tng di symbol 1246us

S sng mang pht ra 1537 us

Khong cch xa nht ca Tx cho SFN75km

Bng thng ti a ti375MHz

Knh dch v chnh c chia thnh 4 *864 CU vi mi CU l 64bit. Khung truyn dn c 4 khung 24ms v d liu FIC km theo. Pha u ca khung l symbol s khng dng ng b v cng mang theo thng tin v my pht. Sau l symbol thi gian, tn s v pha s dng tinh chnh b to sng ca my thu v dng lm symbol chun v pha cho DQPSK. Ba symbol tip theo cha FIC, phn cn li ca khung truyn dn dng cho knh dch v chnh. M knh v bo v khng ng mc knh ph dnh cho d liu m thanh Pht thanh s theo tiu chun E 147 p dng sa li theo m xon - sa li trc FEC ( Forward Error Correction). Trong , i vi dch v d liu, FEC c p dng ging nhau cho ton b khung d liu v ta khng r ni dung trong khung d liu . Ngc li i vi dch v m thanh, ni dung ca khung r v v vy nhng thng tin quan trng hn s c p dng mc bo v cao hn. Phng php ny c gi l bo v khng ng mc. V d bo v khng ng mc cho mt khung MUSICAM c th c minh ho trong bng di y : C bn kiu bo v khng ng mc: kiu mt l cao nht, kiu hai v kiu bn thp hn v kiu ba c mc bo v thp nht.Kiu bo v Kiu 1 p dng cho cc d liu sau : - Tiu ISO : thng tin tiu - CRC : pht hin li trong thng tin iu khin - BAI : thng tin b tr bit - SCFSI : thng tin la chn h s thang m ho Kiu 2 p dng cho cc d liu sau - ScF : h s thang - SAMPLE : mu m thanh trong bng ph ( thay i Kiu 3 p dng cho cc d liu sau: - STUFF : bit stuff - X-PAD : thng tin m rng km theo chng trnh ( thay i) - X-PAD : thng tin m rng km theo chng trnh.Kiu 4 p dng cho cc d liu sau: - ScF CRC : pht hin li trong nhm cc h s .- F-PAD : thng tin km theo chng trnh.Knh thng tin nhanh c m ho vi mu bo v khng i l 1/3. Phi m bo chnh xc cho knh FIC c th gii m ng cc knh ph. Thm vo , knh FIC cng khng c tri d liu theo thi gian. V vy m p dng mc bo v cao nht cho knh FIC . Nh vy, b ghp knh tng hp t hiu qu cao nht, phi c s kt hp hi ho gia tc d liu, s lng chng trnh v mc bo v. y l trch nhim ca nh cung cp dch v chng trnh v nh cung cp dch v ghp knh. Tri d liu theo thi gian v tn s Trong min tn s, hin tng phn x nhiu ng c th lm suy gim mt s sng mang OFDM v ni chung cc sng mang cnh nhau c th b suy gim vi cng mc . Vic tri d liu theo thi gian v tn s s lm cho cc bit cnh nhau v thi gian trong dng d liu ca mt knh ph, sau khi c iu ch vo 1536 sng mang s khng cnh nhau v thi gian v tn s . M xon trong b iu ch COFDM v qu trnh gii m my thu to ra mt cng c mnh gip xc nh li v sa li khi cc li truyn dn xut hin, khng phi l dng vt. Do c tri d liu theo tn s v thi gian nn d liu b dng li vt s khng tp trung trong mt knh dch v v v vy vic sa li c th thc hin c tt gip cho d liu c khi phc li tng i hon chnh. Qu trnh tri d liu theo thi gian i vi h thng pht thanh s thc hin trn 16 khung 24ms v dn n tr tng cho qu trnh x l l 384ms. y l tr tng i ln so vi pht thanh analog truyn thng. Dng bit c chia thnh cc block 16bit v sau b lm tr theo mt s nguyn ln 24ms ( s ny c ly mt cch bt k trong dy s t 0 n 15). Ti b gii m, nhng bit c m ho s li b lm tr tip to li dng m thanh. -Tr trong mng pht thanh s Tng tr trong mng pht thanh, t khi nhn tn hiu n khi ra loa ca my thu s phu thuc vo k thut truyn dn nhng t nht s l 0,7s. Qu trnh m ho COFDM.

Hnh 6: M t tng th qu trnh m ho COFDM. Tn hiu tng hp c nhn qua mng vin thng theo dng NA. B chuyn i giao thc mng s c phn nh du thi gian do nh cung cp dch v ghp knh chn vo dng d liu NA. B chuyn i mng ny cng s lm tr tn hiu cho n khi du thi gian nhn c bng vi thi gian UTC do my thu GPS ch. V vy, tt c cc khung NA ra khi b chuyn i mng s c chnh khung nh nhau v c cng cch m khung c ngha l mng mt tn s s c ng b v thi gian. Sau , ETI s c chia thnh cc dng MUSICAM, dng d liu v dng FIC. Mi dng MUSICAM u c x l nh nhau - tri ph, m ho theo mc bo v cn thit v tri d liu theo thi gian. Tt c cc dng MUSICAM v d liu sau c ghp li ti b ghp knh knh dch v chnh Main Service Channel multiplexer. Dng FIC c tri ph v m ho (khng tri d liu theo thi gian). FIC cha d liu c lin quan n s lng CU cho mi dch v v cc mc bo v c p dng. u ra ca b ghp knh dch v chnh v knh FIC cng vi hai symbol ng b s c tng hp b ghp knh dch v chnh MSC - Main Service Multiplexer. Dng d liu a ra s c iu ch vo 1536 sng mang OFDM s dng php bin i Furier ngc IFFTQu trnh ton hc chuyn i tn hiu t min thi gian sang min tn s c gi l chuyn i Furie ( Fast Fourier Transform ). Qu trnh ngc li c gi l chuyn i Furie ngc IFFT ( Inverse Fast Fourier Transform ).

Hnh 7: Min thi gian v tn sMi thnh phn trong ph tn tn hiu u ra ng vi mt sng mang OFDM. Bin v pha ca cc sng mang ny ph thuc vo d liu c truyn i. Do y dng iu ch kiu DQPSK nn bin ca tt c cc sng mang s ging nhau, ch c pha thay i v c xc nh bi mi symbol truyn i. to ra 1536 sng mang OFDM iu ch, ngi ta dng FFT 2048 im a bin ca cc sng mang khng mong mun v 0. Pha ca cc sng mang c xc nh ti u vo ca IFFT v sau cc mu thi gian c ng b theo khong symbol 1,25ms. To ra mt symbol, 2048 mu thi gian c ng b vi IFFT trong 1ms sau khi lp li cc mu ca 0,25ms u tin to khong bo v. Ton b qu trnh ny xy ra hai ln song song vi hai thnh phn cng pha ( I Inphase) v vung gc ( Quadrative Q). Cc mu thi gian sau c a sang b chuyn i s sang analog v lc li. Sau tn hiu ny c a ra b trn v trn li a ra pht sng.

Hnh 8: OFDM transmitter2.3. Nhng u nhc im ca tiu chun pht sng E147Nhng u im ca E147:+ Nng cao cht lng m thanh.+ Nng cao hiu qu s dng ph tn s v tuyn in, to kh nng m rng nhng dch v mi.+ To thun li cho ngi nghe.+ C kh nng cung cp dch v truyn d liu.+ Tiu chun E147 s dng bng III VHF v bng L pht thanh s trn mt t, s dng cng ngh COFDM iu ch DQPSK v cc k thut sa li. kh nng thit lp mng mt tn s v cht lng thu lu ng cao l mt trong nhng u vit ca tiu chun ny. Cht lng m thanh t gn nh a CD, c kh nng pht km theo gi d liu PAD v cc dch v truyn d liu. Nu pht cht lng nh FM mono c th pht ti 16 chng trnh trong 1 knh. Bnh thng ngi ta pht 6 knh chng trnh cht lng cao v mt s dch v truyn d liu.

Nhng nhc im ca tiu chun E147: Cho ti lc ny c th nhn thy ro cn ln nht cho vic pht trin tiu chun ny l my thu,v gi vn cn cao so vi my thu thng thng. Cc dch v gia tng mi cha thc s hp dn ngi nghe. iu ny c th thy qua vic pht trin DAB c vi mng FM hin c hot ng rt hiu qu v c nhiu cc dch v nh RDS hay chng trnh v giao thng. Mt vn khc l bng tn s: Vi cng ngh ny, pht thanh s s dng vng tn s m truyn hnh analog s dng. Tuy nhin, hin nay truyn hnh s, truyn hnh qua v tinh v truyn hnh cp ang pht trin rt mnh, cc bng tn ny s dn c gii phng cho pht thanh s dng. Phi u t my pht v ng ten mi. C th s dng li c s h tng nh h thng ct anten.3. PHT THANH S THEO TIU CHUN IBOC HD RADIO v DRM Cc tiu chun ny khng s dng cc bng thng mi, s dng li bng thng ca pht thanh analog v tn dng ti a kh nng ti s dng cc c s h tng hin c. Giai on chuyn tip s din ra t t, pht s song song vi pht analog.3.1.Tiu chun IBOC-HD Radio:M ch chng s dng bng tn s sng AM MW v FM c sn pht s. Cng ngh ny c gi tt l IBOC (In Band On Chanel). Tn mi hin nay l HD-Radio (High Definition Radio). Rong giai on chuyn tip mt chng trnh pht thanh di dng dng analog v digital s c cng mt my pht pht i. My thu thu c c hai loi tn hiu, tn hiu analog ng vai tr d phng cho tn hiu digital v mc sng mang ca tn hiu digital thp hn ca tn hiu analog 30dB. Khi chuyn sang hon ton pht s c th pht 4 chng trnh mono trn mt knh v pht mt s dch v d liu. Cht lng ca tn hiu AM s bng cht lng tn hiu FM analog v tn hiu FM s gn bng cht lng CD. Cng ngh IBOC c y ban h thng radio quc gia ca M (National Radio Systems Committee- NRSC) tiu chun ha thng 9.2005 (NRSC-5-A In-band/on-channel Digital Radio Broadcasting Standard).3.2.Nhng u nhc im ca cng ngh IBOCu im:+ Cht lng chng trnh c nng cao. Khc phc c hin tng nhiu do phn x nhiu tia.+ Khng yu cu bng tn mi cho pht thanh s. S dng li ph tn cho pht thanh FM v AM.+C kh nng s dng li c my pht, anten. Ch cn u t ci tin chuyn sang pht thanh s trong giai on chuyn tip.+ Gim chi ph khai thc mc d c s dng cc thit b c+ C th m thm cc dch v mi k c dch v truyn d liu+ Trong giai on chuyn tip, my thu s thu c hai loi tn hiu analog v digital (theo l thuyt v hin nay cha c my thu trn th trng)+ Trong giai on qu s lm vic theo ch simulcast cho nn thun li cho ngi nghe.Nhng nhc im ca cng ngh IBOC-HD Radio: Cng ngh HD radio ch c s dng ti m, cho n thi im ny ch c mt vi quc gia ( Brasil, Philippin, Thy s) bt u th nghim. Nc lng ging canada chn cng ngh truyn hnh s ca m nhng li chn cng ngh E 147 ca chu u cho pht thanh. iu ny c lin quan n vn my pht v my thu: Nu theo cng ngh ny s phi hon ton ph thuc vo cc nh cung cp my pht ca m, y l iu m t ai chp nhn. Gi c my thu ph thuc vo s lng my sn xut ra. Nu ch b hp trong th trng nc m th gi my thu s cao hn nhng sn phm khc c s lng tiu th nhiu hn cc th trng khc. Cho n ht qu I/2006, mi d kin c mt s chng loi my thu bn v u tuner vi gi r nht l 300$. Ch yu hin nay vn ch l my thu trn xe t trong cc model xe t 2006 ca hai hng xe sang trng l BMW v Mercedes Benz. Cht lng m thanh khng cao nh cht lng ca tiu chun E 147. Tuy giai on chuyn i t analog sang digital din ra mt cch t t, nhng giai on chuyn i ngi nghe phi chp nhn cht lng gim i nu s dng bng thng c cho mt knh pht c hai dch v analog v digital. Vn can nhiu gia cc knh i vi sng trung vn cn l mt tn ti ang tip tc nghin cu khc phc. Do tc bt thp cho nn dch v gia tng cng hn ch hn so vi tiu chun E147. Hin nay ngi ta cha nghin cu n kh nng thit lp mng mt tn s. i vi i pht thanh quc gia vic thit lp mng mt tn s l iu v cng quan trng v phm vi ph sng rt rng. C c mng mt tn s s rt thun li cho ngi nghe khi phi di chuyn t vng ny sang vng khc.3.3. Tiu chun DRMTiu chun ETSI TS 101 980 (2001- 09)- Pht thanh s trn bng tn nh hn 30MHz c th gi tt l tiu chun DRM.Hin nay DRM c a vo khai thc chnh thc. Hin trn th gii c trn 1500 i pht sng ngn ang hot ng, v vy DRM s l mt hng rt ng quan tm.DRM s dng cng ngh COFDM, tn hiu m thanh nn MPEG AAC kt hp vi mt s k thut nn khc nh SPR, MPEG 4CELP, HVXC. Hin nay cc nh ch to linh kin in t ang ht sc l lc ch to chip mi s dng cho my thu vi gi thnh thp. Mt trong nhng tiu ch ca tiu chun ny l my thu, my pht gi thnh thp, cht lng m thanh cao. Tuy nhin cho ti thi im ny cha c my thu thanh thng phm.3.3.1.H thng DRM H thng DRM c thit k thay th pht thanh AM analog hin nay. Ngoi ra h thng cn c thit k sao cho cc dch v pht thanh s cng tn ti vi cc dch v pht thanh analog trong khong thi gian chuyn i. Nh vy qu trnh chuyn sang cng ngh s s c tin hnh theo nhiu pha v din ra mt cch t t, khng c s t bin. Khc vi mt s cng ngh pht thanh s khc, h thng DRM c thit k sao cho c th s dng li my pht AM analog sau khi c s ci tin nht nh. iu ny ht sc c ngha v mt kinh t v s gim chi ph u t cho cc i pht thanh khi chuyn sang cng ngh s.

Hnh 9 : S khi h thng DRMB gii m audio v d liu s to ra cc nh dng d liu ph hp. Cc d liu sau b gii mc th bao gm hai phn vi cp bo v khc nhau. B tng hp tn hiu s t hp li theo nh dng xc nh trong khung truyn dn phn tn nng lng (energy dispersal) trnh kh nng c s u u khng mong mun trong tn hiu truyn dn. B m knh (channel encoder) s a vo d liu mt s bt ngu nhin, theo qui cch nht nh thc hin bo v d liu v sa li; v thc hin phn b cc thng tin m ha digital vo cc phn t QAM. Nhng sng mang c bn cha cc thng tin s c a i iu ch ti my pht. Cc phn t c b tr tri ra theo trnh t thi gian, theo mt h thng nht nh, ti phn thu d liu s c khi phc li. Nh , tn hiu c bo ton, khng b suy gim do hin tng pha inh nhanh. Tn hiu Pilot c tc dng cung cp cho my thu nhng tn hiu chun k c pha, bin nh s tin hnh gii m tn hiu. B to tn hiu OFDM s phn b cc phn t QAM vo ma trn thi gian-tn s. OFDM l tp hp cc sng mang ph, mi sng mang ph l tn hiu hnh sin vi tn s, bin nht nh trong mt khong thi gian ngn. Trong trng hp DRM OFDM chim di thng l 10kHz s c t 88 n 226 sng mang ph. S lng sng mang ph ph thuc vo ch truyn dn. B iu ch s bin i cc tn hiu i din cho OFDM sang tn hiu analog a i pht sng. i vi my pht sng AM khng tuyn tnh, tn hiu s c phn chia thnh hai: tn hiu bin (A) v tn hiu Pha (PRF). Tn hiu"A" a ti u vo ca b iu ch m tn, tn hiu PRF a ti u vo ca ch sng. Vi my pht AM tuyn tnh, tn hiu OFDM s a thng vo u vo m tn ca my pht. 3.3.2.Ch truyn dn H thng DRM c thit k vi 4 ch truyn dn khc nhau. Trong tng ch li c s phi hp gia s lng QAM, tc bt t c n nh truyn dn theo iu kin truyn sng v vng phc v.

Bng1.Chtruyndn

ChCh iu chQAM(nQAM)rngbng thng(kHz)McchsdngBngtn

A16,644,5,5,9,10,18,20Sngt,choaphngKhuvc,trndiLWvMW.Sngngnbng26MHz,choaphngtrongtmnhnthy.

B16,644,5,5,9,10,18,20Sngtrichoingoi,phsngqucgiatrnMWvSW.

C16,6410,20Sngtricnantoncaophsngingoi,trnbngSW.

D16,6410,20Sngtricnantoncaophsngqucgia,trnbngSW.

3.3.3. Cht lng m thanh m bo kt hp gia cht lng m thanh v s lng cc dch v trongmt knh DRM ngi ta a ra 3 ch m ha m thanh khc nhau, ph thuc vo tc bt, cht lng v loi dch v:AAC - cho cht lng cao nht, CELP-Code Excited Linear Predictive v HVXC-Harmonic Vector eXcitition, Coding p dng trong cc trng hp tc bt thp, s dng ch yu cho ting ni, khng dng cho m nhc.Ngoi ra ngi ta cn c th nng cao cht lng chung cho c ba kiu m ho nu trn khi s dng m ha SBR- Spectral Band Replication.

Hnh 11: S khi b m ha m thanh3.3.4. Simulcast - pht ng thi cc dch v analog v digital Simulcast l mt trong nhng kh nng ca h thng DRM c cc nh cung cp dch v pht thanh quan tm. Trng hp y l trn tn s ang pht dch v analog s pht thm dch v digital vi cng ni dung chng trnh.Simulcast c th thc hin theo hai cch: - S dng mt my pht v anten pht c hai tn hiu analog v digital (cng chung ni dung chng trnh) - Lp t thm my pht DRM cng sut nh cng tn s vi my pht analog hin c, pht chung h thng anten vi my pht analog. S la chn ny kinh t hn phng n 1 trong trng hp my pht analog hin c phi ci tin rt nhiu pht DRM. - pht ng thi tn hiu digital v analog m khng c s can nhiu v m bo cht lng m thanh ta s dng thm ph tn s ca knh ln cn, tn hiu analog 9 kHz v 4,5 kHz ,digital pha bin di tn hiu analog 9 kHz v 9 kHz,digital pha bin di hai bin (DSB) tn hiu analog 9 kHz v 9 kHz digital pha bin trn.

Hnh 123.3.5. Gii php ph sng Mng mt tn s -SFN (Single Frequency Network) Thit lp mng gm nhiu my pht, pht cng ni dung chng trnh v trn cng mt tn s. Trong mng s c nhng vng thu c tn hiu t t nht mt i pht tr ln. Khi tnh ton thit lp mng ngi ta phi tnh ton sao cho tr v thi gian gia cc tn hiu nh hn khong an ton ca khung d liu.Trong trng hp ny tn hiu thu c c th kho hn tn hiu ca mt i pht ti. Nu cng tc thit k mng c tin hnh cn thn, c th thit lp mng mt tn s trn phm vi ph sng quc gia. u vit ca mng mt tn s l tit kim c ph tn s. "Nhc im" l kh phc tp trong phn thit k. Mng s dng nhiu tn s- MFN. Khc vi pht thanh AM analog, pht thanh AM s cho php trong khi thu chng trnh, my thu c th chuyn v thu tn s khc c cht lng tt hn, tt nhin phi pht cng mt ni dung. Trong nhm d liu SDC c cha danh sch cc tn s cng pht mt ni dung chng trnh. Khi tn hiu thu bng thng 9 kHz cho pht thanh analog digital c khng tt, theo danh sch my thu t ng chn tn s c cht lng sng cao hn. Chc nng ny khng ch b hp trong phm vi pht thanh s. Hin nay pht thanh FM nhiu nc c pht dch v RDS, trong cng c danh sch cc tn s pht cng ni dung chng trnh. Khi ngi thu i ra khi vng ph sng FM my thu t ng chuyn sang thu DRM, vi iu kin my thu thanh l loi a nng thu c c AM, FM analog v AM digital. Tng t nh vy my thu ang thu tn hiu DRM c th t ng chuyn sang thu tn hiu FM khi tn hiu tt hn. Trong pht thanh i ngoi trn bng sng ngn, ngi ta hay pht mt ni dung chng trnh trn nhiu tn s, hoc tn s pht c th thay i theo gi trong ngy. Trong trng hp ny my thu s t ng chuyn v tn s thch hp theo danh sch cc tn s m my thu thu c . 3.3.6. Th nghim pht thanh s trn bng sng trung. (Kt qu pht th nghim cng ngh DRM - tiu chun ETSI TS 101 980 V1.1.1 (2001-9) trn bng tn sng trung, s dng my pht sng DX 10kW analog) Thng 6 nm 2003 hng lot cc i pht thanh ln trn th gii nh BBC, VOA, DW a dch v pht thanh s DRM trn di sng ngn vo hot ng chnh thc. Cht lng thu tt, vt tri so vi pht thanh analog. Nm 2004 Trung Quc ngi ta cng th nghim pht thanh s DRM trn di sng trung, ci tin my pht DX cho pht DRM. Cng trong nm 2004 ti Hng kng cng tin hnh pht th nghim nh gi cht lng ca pht thanh DRM trn bng sng trung. Ngy 10/5/2004 ti Bangkok chnh thc pht th nghim pht thanh s trn bng tn sng trung. D n pht th nghim do i pht thanh quc gia Thi Lan-NBT kt hp vi Hip hi pht thanh truyn hnh chu Thi Bnh Dng-ABU, t chc DRM, hng VT Merlin (Anh), hng Harris (M) v i pht thanh i ngoi c (DW) thc hin. T 27 n 29.4 .2005, ti Wellington, New Zealand tin hnh th nghim DRM ci tin my pht ca Thales. Cui thng 7.2005, ti ng Hi Vit nam cng tin hnh th nghim DRM trn c s ci tin my pht 200kW ca Harris.3.3.7.Nhng u nhc im ca tiu chun DRM: u im:+ Cht lng chng trnh c nng cao. Khc phc c hin tng nhiu do phn x nhiu tia. + Khng yu cu bng tn mi cho pht thanh s. + C kh nng s dng li c my pht , anten. Ch cn u t v ci tin chuyn sang pht thanh s trong giai on chuyn tip. + Gim chi ph khai thc mc d c s dng cc thit b c. + C th m thm cc dch v mi k c dch v truyn d liu. + Vng ph sng rng ln, c kh nng ph sng tm xa khi s dng bng sng ngn. iu ny c bit quan trng v hu ht cc i pht sng i ngoi hin nay u s dng sng ngn. y l tiu chun pht thanh s duy nht hin nay cho sng ngn. + Gim chi ph khai thc (in nng) mc d c s dng cc thit b c. + C th m rng thm cc dch v mi k c dch v truyn d liu. + My thu c thit k thu c tn hiu analog v tn hiu digital.

Nhc im: Cng ging nh HD radio cht lng m thanh khng cao nh cng ngh E 147 ca chu u. Hin mi ang nghin cu dng cho band FM.

Hng 3: Pht thanh s qua v tinh c nhc im l phc v thu c nh l chnh cho nn phi thit lp trm pht li mt t cho cc my thu di ng. Pht thanh s qua v tinh ph thuc rt nhiu vo qu v tinh c dng.Hng 4: Pht thanh s theo tiu chun nht bn ISDB-T, n c th truyn i cc dch v multimedia nh HDTV,SDTV,DSB v mobile multimedia trong tn hiu audio c m ha theo chun MPEG 2 AAC( ISO/IEC13818 7.

TI LIU THAM KHO[1]. Din n NFC, nfc-rofum.org, thng 12 nm 2013[2]. Din n tinh t. tinhte.vn/communication, thng 12 nm 2013[3].Din n tailieu.vn . Trang wed tailieu.vn, thng 12 nm 2013[4].Bo co tng kt khoa hc k thut v ng dng v pht trin pht thanh s- TS on Vit Trung.-20051