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1.2. K thut pht thanh s
Nhng nm gn y k thut s nhanh chng lm thay i cch thc sn
xut, phn phi chng trnh pht thanh. Cc nh lm pht thanh u t rt nhiu
vo vic s ho khu vc sn xut v phn phi chng trnh pht thanh. V by gi,
thi k chuyn hng trong khu vc pht sng v ang din ra si ng. Do s pht
trin nhanh chng ca k thut s, ti thi k hi t cc k thut thng tin lin lc,
k thut pht sng v k thut my tnh.
1.2.1. Tnh hnh pht trin ca pht thanh s
hu ht cc nc Chu u, vic th nghim pht thanh s trn mt t ang
c trin khai. Ngi ta d nh trong mt vi nm ti pht thanh s s ng mt vai
tr ng k v s dn thay th cho kiu pht thanh truyn thng. Sau y l mt s t
liu tham kho v tin trnh ang din ra trn th gii.
Hip hi pht thanh Chu u (EBU) chnh thc trnh ln hip hi vin
thng quc t (ITU) tiu chun pht thanh s - EUREKA 147 gi tt l pht thanh
DAB l tiu chun s p dng trn phm vi ton Chu u. Hin nay ti Chu u nhiu
quc gia hon thnh giai on th nghim pht thanh s v bt u thi k hot
ng chnh thc ca cc dch v ny. Ngoi Chu u, mt s nc khc nh Canada,
Singapore, i loan, Australia cng a h thng pht thanh s theo tiu chun E-
147 vo khai thc chnh thc.
Sau tiu chun E147 tiu chun pht thanh s DRM - pht thanh s trn cc
bng tn nh hn 30 MHz c t chc ITU thng qua vo thng 4/2001 v ti
thng 9/2001 t chc v tiu chun ETSTI ban hnh tiu chun ny. Sau khi ban
hnh tiu chun s tin hnh pht th nghim nm 2002 v nm 2003 chnh thc a
vo hot ng pht thanh s theo chun DRM.
Ngi M i theo hng khc vi Chu u. Ngi ta ang nghin cu chun
IBOC - (In Band On Channel) pht thanh s trn cc bng tn cho FM v AM truyn
thng. Tuy khi xng kh sm nhng nm ca thp nin 90 nhng hin nay tt c
cn trong giai on nghin cu th nghim.
Ngi Nht a ra mt tiu chun cho mnh l tiu chun pht thanh s
trn mt t ISDB-T. y l tiu chun dng chung cho pht thanh v truyn hnh,
2
trong ISDB-T bng hp 9429 KHz hoc 1,3 MHz) cho pht thanh. Th nghim
pht thanh s theo tiu chun ny c tin hnh ti Nht v cho kt qu kh quan.
Ngi Hn Quc a ra mt tiu chun pht thanh s a phng tin DMB.
y l tiu chun dng chung cho pht thanh v truyn hnh s s dng cc thit b thu
l in thoi di ng. K thut ca pht thanh s DMB pht trin da trn s cht lc
nhng u im ca k thut DAB v hon ton tng thch vi DAB. Vi chun pht
thanh s ny th ngi Hn Quc gii quyt c vn my thu thanh s. Hin
nay tiu chun ny c tin hnh pht ti Hn Quc v mt s nc v cho kt
qu rt kh quan. y l mt chun mi nhng ang c rt nhiu nc quan tm v
th nghim.
Trong thi gian qua ngi ta c nhiu n lc thc y tin trnh pht trin
pht thanh s. So vi truyn hnh s, pht thanh s c nhiu vn kh khn hn.
Ngay ti thi im ny, trn th gii vn cn tip tc nghin cu v DSB. Trong khi
c khong 230 triu ngi trn hnh tinh c th s dng dch v DAB (Pht
thanh s theo chun E 147) vi 400 cc dch v khc nhau. Gi thnh my thu l vn
chnh lm chm tin trnh pht trin DSB. Hin nay trn th trng c khong 16
loi my thu khc nhau theo chun E-147. cc bng mch my thu PCI l hng pht
trin ca cc nh sn xut my thu.
Hip hi ABU trong thi gian qua cng c nhiu n lc h tr cc nc
trong khu vc pht trin DSB. t chc nhiu hi tho v thnh lp nhiu nhm
cng tc, phn tch lp chin lc pht trin. i TNVN cng ang nghin cu v la
chn tiu chun pht thanh s cho Vit Nam, hin nay i ting Ni Vit Nam ang
pht th nghim pht thanh s DRM.
Cho n nay, nhp pht trin cng ngh pht thanh s khng c nh mong
i. Th trng my thu thanh s l mt ro cn ln cho qu trnh pht trin pht thanh
s. Bn cnh , do c nhng xu hng v mc hon thin cng ngh khc nhau
nn tnh hnh trin khai pht thanh s cng din ra khc nhau gia cc nc trn th
gii v trong khu vc. Sau y l mt s thng tin cp nht v vic ng dng pht
thanh s ti mt s nc khu vc Chu - Thi Bnh Dng theo t liu ABU.
- Australia
3
T ngy 17 thng 11 nm 2003, ton b mng pht thanh thng mi Sydney
cng cc i pht thanh cng ng nh ABC v SBS bt u pht thanh s trn
bng III ca di tn VHF theo tiu chun Eureka- 147. Vic th nghim cng ngh
pht thanh s ti c c tin hnh cch y 5 nm do mt vi i pht thanh thng
mi v i ABC thc hin trn bng tn L.
D n pht thanh s Sydney l d n pht thanh s u tin c thc hin trn
hai knh truyn hnh trong bng III ca ph tn VHF. Vic th nghim ny cho php
so snh cht lng truyn dn trong bng L v bng III cng nh phn ng ca khch
hng v cc nh lm qung co i vi cng ngh v cc loi my thu mi.
Trong giai on th nghim thit lp mt cng xooc-xiom gi l Digital
Radio Broadcasting Australia Pty Ltd (DRBA) s hu h thng truyn dn s ca
Sydney v chu trch nhim i vi vic qun l ghp knh. i tc chin lc trong
giai on th nghim bao gm cc nh sn xut my thu nh: Alpine Electronics; Pure
Digital; Factum Electronics AB v Blaupunkt; hng chuyn bn l Harvey Norman;
hng qung co Universal McCann; cc nh cung cp c s h tng nh Radio Scape,
BSA, Comsyst, RFS v TXA.
Cc nh cng nghip ang thng tho vi chnh ph v chnh sch thng nht
trong gii thiu v ph cp pht thanh s trong c nc trn c s mt m hnh thng
nht.
- Brunei
i pht thanh truyn hnh Brunei RTB (Radio Television Brunei) bt u
pht th nghim dch v DAB-T t cui nm 2001 da trn tiu chun Eureka- 147.
Hin nay dch v bao gm 5 knh FM pht ng thi. H lp mt my pht DAB
T 300W pht trn knh 12B. Giai on pht trin th nghim c vng ph sng ti a
khong 60Km. Tnh ti thi im hin nay, vn cha c mt k hoch no m rng
vng th nghim ra trn khp c nc. Tuy nhin RTB vn tip tc n lc cung
cp, a k thut cng ngh ny ti tt c mi ngi.
- Trung Quc
Trung Quc bt u th nghim cng ngh DAB ln u tin vo nm 1995. Ba
trm pht Eureka-147 u tin (Mng mt tn s SFN) c pht sng vo ngy
15 thng 12 nm 1996 ti 3 khu vc Foshan, Guangzhou v Zhongshan ti tnh Qung
4
ng. i pht sng Foshan l trung tm x l tn hiu ca mng ny. N cn cung
cp cc thnh phn ho v hnh nh theo thi gian thc. Vng ph sng DAB ca
mng mt tn s ny vo khong 8% din tch ca tnh Qung ng, phc v cho
khong 1,3465 triu ngi. Mng mt tn s th hai c thit lp ti Beijing,
Tianjing v Langfang vo thng 5 nm 2000. Hai mng mt tn s ny hin nay vn
ang hot ng th nghim v cung cp chng trnh m thanh DAB. Trung Quc
thay i tn s pht t 85Mhz sang tn s 209,936Mhz vo nm 1998. Hu nh cc
my thu DAB hin c Trung Quc u c sn xut ti i Loan v Nht Bn. Ti
nay mi ch bn c vi chic my thu, do gi thnh my thu qu cao. Mt s cng ty
a phng tin c nh pht trin my thu DMB (Digital Multimedia Broadcasting)
v thit b truyn dn da trn cng ngh MPEG-4. Thng 4 nm 2004, ti cuc hp
hi ng chung hng nm Hng Chu, Trung Quc, i pht thanh quc t Trung
Quc v i pht thanh quc gia Trung Quc ng h pht DRM trong di sng
trung v sng ngn. Trung Quc cn mong mun tham gia vo h thng pht trn ton
cu. Trung Quc tin hnh pht th nghim cng ngh DRM Zhejiang s dng
bng tn sng trung v sng ngn.
- ng Timor
Dch v pht thanh cng cng ca Timor Leste gn y vn cha c bt k k
hoch no ng dng pht thanh s. ng Timor vn ang giai on bt u ca vic
xy dng mt h thng truyn dn tng t ca quc gia cho c pht thanh v truyn
hnh, v c gng vt qua cc th thch ch yu nh l kh nng k thut, cc vn
v in, nhin liu v cc vn v hu cn khc.
- Hng Kng
Cc pht thanh v cng ngh thng tin Hng Kng TBB (Information
Technology and Broadcasting Bureau) nay i tn thnh CTB (Communications
and Technology Brand) pht hnh phiu tham kho kin v pht thanh s mt t
vo ngy 1 thng 12 nm 2000 Hng Kng trong vng 3 thng. Qua phiu tham
kho cho thy vn k thut i vi vic th nghim DAB c tnh kh thi, nhng v
mt thng mi c th khng th ng vng c trong giai on ny. Cng qua
phiu tham kho, nhiu ngi cho rng chnh ph nn xem xt, cn nhc cc ng dng
hp dn ca dch v DAB khi tim nng th trng ca n tr nn r nt hn.
5
- n
n l mt trong cc quc gia khc chp nhn h thng Eureka- 147 nh l
h thng pht thanh cho tng lai. i pht thanh cng cng AIR (All India Radio)
bt u pht th nghim u n DAB ti New Delhi t thng 4 nm 1997.
Trong nm 2004, AIR pht dch v DAB th nghim vi my pht c cng
sut l 1KW Delhi. Chng trnh pht gm 6 knh Stereo, ngoi ra cn c cc dch
v cho PAD v d liu. Chng trnh th nghim DAB s m rng Chennai,
Mumbai v Kolkata vo nm 2005-2006.
- Iran
IRIB l t chc pht thanh quc gia duy nht khuyn khch pht thanh s. Bn
cnh vic pht DRM, IRIB cn xem xt h thng DAB Eureka-147 trn bng III v
bng L. Th nghim trn h thng DRM c thc hin vo u nm 2001 da trn
m phng my tnh. N c tin hnh bi mt vi my tnh m phng cng vic ca
b iu ch, my pht v my thu khi tiu chun DRM c thit lp vo thng 9 nm
2001. u nm 2004, mt b exiter th nghim cng c pht trin da trn m
phng my tnh. Kim tra truyn dn ca h thng DRM, s dng kt hp my pht
cng sut thp v cao, c thc hin thnh cng vo nm 2004. IRIB ang c k
hoch pht trin h thng phn cng DRM y , bao gm cc thnh phn my ch,
b iu ch, my pht tng thch vi DRM cng sut ln v h thng iu khin,
kim sot lin quan.
- Nht Bn
K t thng 4 nm 1999, ti 11 vng Nht Bn tin hnh vic kim tra,
nh gi kh nng thc hin ca h thng ISDB-T. ISDB-T l cng ngh trong lnh
vc pht sng cho c truyn hnh v pht thanh s vi kh nng pht bng thng rng
ln bng thng hp. Nhng kim tra nh gi ny bao gm: Pht s liu pht thanh,
truyn hnh, cc dch v khn cp v a phng tin di ng, EPG, truyn hnh tr tin
v cc dch v theo yu cu khc. Theo k hoch vo nm 2006, ISDB-T s ph sng
ton b Nht Bn, v nh vy truyn hnh tng t s c th ngng pht vo nm
2010.
DRP (The Digital Radio Promotion Association) pht th nghim pht thanh
s Nht Bn v ngy 10 thng 10 nm 2003 trn bng III ca di tn VHF. Vng ph
6
sng hin nay bao gm Tokyo v Osaka. Thng 2 nm 2004, NHK a ra dch v
d bo thi tit theo nhiu ngn ng. Dch v pht thanh ny c da trn c s mt
h thng t ng dch v c d liu v thi tit theo ting Nht Bn, Hn Quc, Anh
v Trung Quc.
Tm nhn 1, l nh cung cp thit b lin lc v dch v pht thanh v tinh, cho
hng chng trnh v tinh s tr tin trn knh Sky Perfect TV, dch v in thoi
Tu-Ka s v lin lc v tuyn ti tt c khch hng Nht Bn t ngy 1 thng 2 nm
2002. Chng trnh Sky Perfect TV cung cp hn 194 knh truyn hnh v 106 knh
pht thanh s.
Trn y l tnh hnh pht trin pht thanh s mt s nc trong khu vc
Chu - Thi Bnh Dng. Ngoi ra cn nhiu nc khc trn th gii cng v
ang trin khai pht thanh s, c th tnh hnh pht trin DAB ca mt s nc nh
sau:
Anh Ph 60% dn s Gia nm 1998
Thu in Ph 75% dn s u nm 1998
c Ph 37% dn s Cui nm 1997
H Lan Ph 45% dn s Gia nm 1998
Nauy Ph 60% dn s Cui nm 1998
Ph 60% dn s Cui nm 1999
Canada Ph 35% dn s Cui nm 1998
1.2.2. Nhng u, nhc im ca pht thanh s so vi pht thanh truyn thng.
- Pht thanh s khc phc c nhc im ca pht thanh truyn thng nh
can nhiu, mo pha inh trong truyn sng, giao thoa c bit gii quyt c s cht
chi ca di tn s.
- Pht thanh s t cht lng m thanh tng ng vi a CD, hn hn cc
h thng pht thanh truyn thng k c pht thanh FM Stereo. N cung cp cho ngi
nghe cht lng m thanh nh nhau vi my thu c nh, trn xe t, hoc bng my
xch tay. Pht thanh s cho ta kh nng khng nhng truyn i m thanh cht lng
tng ng vi a CD, m cn truyn d liu di dng vn bn, nh, hnh. Lc
my thu thanh s tr thnh phng tin a chc nng gip con ngi tip nhn nhiu
loi thng tin khc nhau.
7
- H thng pht thanh s bng tn thp cung cp kh nng ph sng pht thanh
trn mt vng rng ln, khng ch trn phm vi mt quc gia m thm ch trn na
qu a cu. phc v trn phm vi rng ln ny, h thng ch cn n mt trm
pht cng sut va phi, iu ny tng chng ch c th thc hin v cng vi s
pht trin th pht thanh s c nhng u im hn pht thanh truyn thng l :
- mo tn s ca pht thanh s t hn pht thanh truyn thng.
- Tn hiu a vo pht thanh s c th a nhiu knh v cng mt dng
chuyn ti (Khi ghp knh dng chuyn ti).
Ngi ta khuyn ngh vi cc di tn s sau s ph hp cho my thu DSB dn dng
(c nh, di ng xch tay, trn t):
Bng L (1,452 GHz-1,492 GHz)
S (2,310 GHz-2,360 GHz)
VHF Band 3 (174-240 MHz)
Bng FM (87-108 MHz)
Bng AM < 30 MHz
Cc bng tn cao hn s b nh hng ca thi tit nn c suy hao ln do ch
phc v cho cng vic truyn tn hiu gc t Studio n cc i pht sng thng qua
cc thit b thu pht c nh.
Vic qun l, phn b di thng trn cc bng tn L & S cho pht thanh Digital
c th gii nht tr quy nh theo WARC' 92 (WARC l vit tt ca World
Aministrative Radio Conference)
V mt cng ngh, hin nay k thut x l tn hiu m thanh s t nhiu
thnh tu mi, iu c minh chng bng s ra i ca hng lot gii php x l
nn tn hiu v hng lot cc tiu chun qui nh cho truyn dn v pht sng c
ban hnh.
8
1.2.3. Pht thanh s chun DAB (Digital Audio Broadcating)
Cho n nay mi ngi u tha nhn mt thc t l s song song cng tn ti
mt s tiu chun v pht thanh s. La chn tiu chun l cng vic ca mi quc
gia, trong c cc t chc quc t ch ng vai tr h tr.
Hin nay c mt s tiu chun pht thanh DSB c thng qua hoc v ang
th nghim trn th gii:
+ EUREKA 147 Digital Audio Broadcasting (DAB).
+ Digital Radio Mondiale (DRM).
+ IBOC US Digital Radio (IDAB, DRE).
+ ISDB T (Japan).
+ Wold space.
1.2.3.1 S khi h thng pht DAB
Tiu chun ny do EBU ca Chu u a ra v c ITU cng nhn l tiu
chun cho pht thanh s (1992). H thng lm vic di tn s t 30 MHz n 3 GHz.
- Hnh 1.a l s khi my pht thanh s theo tiu chun E147
1. M ha ngun
- Khi m ha ngun thc hin x l tn hiu m thanh s theo chun nn
MPEG-1 Layer-2 v MPEG-2 Layer-2. Vi tc bit c th thay i d dng t 8 Kps
n 384 Kbps.
- Truyn d liu: c th truyn cc lung data ring bit hoc ng gi.
M
ho
knh
Ghp
knh
Ghp
knh
dng
truyn ti OFDM
Trn tn
Ghp
knh
gi
M
ho
knh
M
ho
ngun
Tn hiu DAB
f=1,5MHz
Thng tin dch v
Thng tin ghp knh
Tn hiu Audio
Data
Hnh 1.a: S my pht thanh s chun DAB
Tn s Radio
9
- Truyn cc d liu lin quan n chng trnh PAD (Programme Associated
Data) bng cch gn vo lung d liu m thanh. Tc thp nht l 667bps v c th
thay i theo m tn hiu m thanh c s dng.
- Truy cp d liu c iu kin CA (Conditional Access) phc v cho cc
mc ch thng mi.
- Truyn thng tin dch v SI (Service Information): Thng tin gip cho ngi
s dng la chn chng trnh. Ngoi ra SI cn lin kt vi cc dch v trong phm vi
cng mt knh tn hiu tng hp v cc dch v ca cc tn hiu tng hp (Esemble)
khc, ng thi c th lin kt vi cc nh cng cp dch v trn FM hoc AM.
2. M ho knh.
D liu ca chng trnh c tri ra, xp xp theo m v chn theo thi gian.
tri d liu ra thnh cc chui bt ngu nhin mang ni dung tng ng cn c d
liu sp xp tn hiu DAB. Vi phng php ny vic s dng cc b khuch i cng
sut t hiu qu cao. M sp xp thc hin x l bng cch a thm cc d liu ph
gip cho my thu nhn bit v loi tr tt cc sai st do truyn dn. i vi tn hiu
m thanh, mt vi thnh phn trong khung m thanh t b nh hng bi sai st truyn
dn hn cc thnh phn khc cho nn c th gim s lng d liu ph. Ch ny
gi l chng sai st khng cn bng Unequal Error Protection (UEP).
3. iu ch OFDM v cc ch truyn dn:
S dng phng thc iu ch OFDM yu cu vic truyn dn d liu vi tc
cao ph hp cho cc my thu di ng, xch tay v c nh, c bit l trong mi
trng truyn sng phc tp. Kiu iu ch ny c thc hin bng cch chia thng
tin ra thnh nhiu khong nh, s dng sng mang ring bit m ho, sau a
chng vo knh truyn dn.
Cho php thit lp mng mt tn s do x l iu ch tn hiu COFDM (Coded
Orthogonal Frequeney Division Multiplex).
Hin ti EUREKA 147 a ra bn ch khc nhau p dng trong tng
trng hp c th:
- Ch I: Thch hp cho mng ph sng trn mt t do mt tn s trn bng
VHF, c kh nng ln nht cch ly cc i pht.
10
- Ch II: Thch hp cho s dng mng mt tn s khong gia bng L v
cho pht thanh khu vc s dng mt i pht. khong tn s cch ly gia cc i pht
ln cho nn s phn bit thng tin gia cc i pht cao v cho php s dng anten
hu hng.
- Ch III: Thch hp vi phng thc truyn qua cp, qua v tinh, ph sng
mt t cho vng lm. Do c th lm vic ti cc tn s ti 3 GHz phc v tt cho
thu di ng. Phng thc ny cho php di pha ln nht.
- Ch IV: Cng p dng cho bng L, cho php dn cch khng gian gia cc
i pht trong mng mt tn s ln. ng thi t b nh hng khi thu trn xe t chy
vi tc cao.
4. Thit lp mng:
Mng mu thit lp theo tiu chun EUREKA 147 (Hnh 7.2).
Trong cc chng trnh c tch hp li nh b dn knh theo cu trc hai
tng:
- Tng 1: Cc nh cung cp dch v pht thanh trn mng phi thc hin:
+ M ho m thanh.
+ D liu lin quan n chng trnh (PAD).
+ Thng tin dch v.
+ Thng tin cho iu khin v trng thi.
+ Cc dch v d liu c lp.
11
- Tng 2: Thc hin tng hp chung bao gm:
+ Thit lp lung d liu a dch v cho DAB, tr cc thng tin a thm ti
my pht.
+ a thm thng tin h tr cho iu khin v trng thi.
Mt trong nhng c im chnh ca b dn knh DAB l d dng thay i li
tn s phi hp gia cc chng trnh v cc nh cung cp khc nhau khi cn thit.
- Tng 3: my pht DAB
1.2.3.2 S khi my thu DAB
Chng trnh m ho m thanh
To ra PAD
Chng trnh gn nhn dch v
Dn knh
Dch v pht thanh
M ho d liu ng gi
Dch v thng tin
Dn knh
Dch v cho
gi d liu
Cc dch v khc
Dn knh chung
Thng tin
dch v
Giao din iu khin dn knh
My pht
DAB
Nhn dng tn hiu
pht
Tng 1 Tng 2 Tng 3
Hnh 1.b: Mng mu thit lp theo chun EUREKA 147
12
1.2.4 Pht thanh s DRM (Digital Radio Mondiale)
p ng nhng rng buc trong pht thanh trong cc knh di tn di 30
MHz, tc bit cho m ho ngun nm trong khong t 8 Kbit/s (Vi cc knh c
rng ph tn thp) ti 20 Kbit/s (Vi knh HF tiu chun) v ti a l ti 48 Kbit/s
(Gp knh).
K thut m ho m thanh kiu MPEG 4 AAC (Advanced Audio Coding) c
cc cng c chng li cao dng chung cho c pht thanh mono v Stereo (V d hot
ng vi tc 20 Kbit/s).
iu ch kiu QAM.
* Di y l s khi my pht thanh s theo tiu chun DRM.
D lu ph
Gii iu ch
OFDM
Mch v o
(Tuner)
Gii m Audio
Giao din ng-i s dng
Gii m knh
Antena
VXL
D liu m thanh
Bus iu khin
Gii m Data FIC
D Liu
Bo v BT
Cao
Bo v BT
Cao
nh
X
IU CH
OFDM
Trn
Tn
Tin M
ho
Tin m
ho
Tn hiu
DRM
M ho
ngun
Ghp
knh
Phn tn
nng lng
M
ho
knh
DL m
thanh
Ci
xen
Phn tn
nng lng
M
ho
knh
Phn tn
nng lng
M
ho
knh
Thng tin m t dich v
Thng tin truy
nhp knh nhanh
Bo v BT
Cao
M ho
ngun
MSC
FAC
SC
SDC
D Liu Pht
Pilot
Hnh 1.c: S khi my pht thanh s theo tiu chun DRM
13
1.2.5 Pht thanh s chun DMB (Digital Multimedia Broadcasting)
DMB l tiu chun do h thng pht thanh truyn hnh Hn Quc KBS gii
thiu. Phng n ny c cc chuyn gia trong lnh vc truyn thng rt quan tm,
c th ni y l bc t ph v cng ngh pht thanh trong lnh vc truyn thng i
chng hin nay. Vi s ra i ca cng ngh mi c bit l cng ngh DMB, ranh
gii gia pht thanh truyn hnh truyn thng v pht truyn thng a phng tin s
b xo m.
Cng ngh DMB thc cht l s pht trin mi ca phng thc pht thanh qua
di ng vi vic cung cp hnh nh cht lng cao, m thanh s v cc d liu ht sc
a dng km theo. DMB l s cht lc cc im mnh ca h thng pht thanh s
EUREKA 147 v hon ton tng thch vi h thng DAB ca Chu u. Di y l
bng thng k cht lng v cng ngh ca DMB cho tng loi tn hiu:
Loi T.
hiu
Cht lng Cng ngh
Audio Stereo cht lng gn CD (BER 10-4) MUSICAM (MPEG-1, 2 Layer 2
Video
(DMB)
Video Mn hnh 7 QVGA
(320x240@30 hnh /giy)
MPEG- 4 AVC
Audio Stereo cht lng FM MPEG- 4 BSAC
D
liu
Nhiu ng dng khc MPEG- 4 BIFS
Mux Audio/Video/Data MPEG- 4 SL, TS
Knh
thu
Di ng, th ( BER 10-8) RS (204, 188) Conv..Byte
Interleave
D liu EPG, bn tin, thi tit, chng khon,
bn tin giao thng
PAD, NPAD, TDC, MOT, BWS,
Slice show
DMB c thit k cung cp dch v a phng tin nhm n i tng
khch hng di ng. Vi h thng DMB, khch hng c th thu c cc chng
trnh truyn hnh, pht thanh v cc dch v d liu khc khi di chuyn vi tc cao
nh trn t, tu ho, xe inDo c pht trin t h thng pht thanh s E147
14
nn vic thit lp h thng DRM tng i n gin, ch cn b xung thm thit b m
ho video v h thng thit b pht thanh s E147 hin c.
T chc TU Media v SK Telecom pht DMB v tinh (DMB-S) vo ngy 1
thng 9 nm 2004 trong khi chnh ph d nh pht DMB mt t ( DMB-T) vo cui
nm 2004 hoc u nm 2005. DMB-S l dch v da trn c s thu bao ph sng
ton quc, trong khi DMB l dch v min ph. Mi giy php DMB-S cho php cung
cp 11 dch v hnh nh, 25 dch v m thanh v 3 dch v d liu vi d n l
500.000 thu bao trong nm th nht v tip tc ti 8 triu thu bao trong vng 5 nm
ti. Cc cng ty Pers Tsl, FreeSat, Samsung v TBK Electronic pht trin cc my
thu, Module DAB v DRM.
Vi s pht trin nhanh chng ca in thoi di ng v my tnh c nhn, ngi
ta hy vng rng pht thanh s vi cng ngh DMB s c iu kin pht trin nhanh
chng.
1.3. H thng AM/FM vi IN- BAND/ON- CHANNEL (IBOC).
Do thiu ht v bng thng, khng th b tr tn s mi cho dch v DSB nh
Chu u (Chun EUREKA 147). Hoa K a ra h thng IBOC, nhm xy dng h
thng pht thanh DSB mt t dng ph tn ca pht thanh AM v FM analog. H
thng IBOC tng thch vi tn hiu analog ang s dng IBOC cho php truyn ng
thi c m thanh analog, digital v d liu trn ph tn c ca analog. Khi c s
giao thoa khng mong mun gia cc tn hiu analog v tn hiu digital, cn loi tr
vn ny.
H thng my pht
DAB (E147)
H thng my pht
DAB (E147)
TS
Mux
M ho
Video Video
M ho
Video
Audio
Data
RS
Encoder
Conv.
Interleaver
Knh pht thanh (MUSICAM)
Knh d liu
Audio
Data
Hnh 1.d: S khi h thng DMB (E147)
RF
15
Quy nh mi nht ca IBOC, p dng chun nn MPEG- 2AAC.
- i vi bng FM:
+ IBOC cho php trn cng mt tn s pht ng thi chng trnh Audio
digital v Audio analog.
+ Tc m m thanh 96kbps hoc 128 kbps.
+ K thut iu ch OFDM.
+ Tc truyn d liu > 64 Kbps trong :
Vi d liu lin quan n chng trnh (PAD) l 8 kbps :
D liu ph: B gii hn bi qu trnh m ho Audio l t 2 n 32 kbps.
D liu chun a vo l 64 Kbps (D liu c phn b).
- i vi bng AM:
+ Bng tn vi di thng ca RF 30KHz.
+ Tc m Audio 48-32-16 Kbps.
H thng IBOC tri qua hai giai on pht trin c bn.
1. Thi k 1994 1996: Giai on pht trin u tin. Thi k ny h thng a
ra 4 vn v thng s ( 3 cho FM, 1 cho AM) l:
+ V FM:
AT & T/LUCENT/AMATI
USA DR FM-1
USA DR FM- 2
+ V AM: 1st GENERATION a ra phn b li tn s cho pht DAB.
Tuy nhin c 4 vn trn u khng thch hp vi pht thanh DAB. iu ny
c khc phc trong giai on 2.
2. T nm 1997 n nay, trn c s k tha nhng thnh tu m giai on 1 t
c, IBOC pht trin cc k thut mi, c bit l vic p dng chun nn MPEG
2AAC. IBOC a ra khuyn ngh v c Digital Radio Express chp thun
th nghim. Vo thng 1/1998, t chc USA Digital Radio ( USADR) ng cho
pht trin IBOC nhng theo yu cu ring ca mnh. Giai on ny c tn l Next
generation IBOC.
Vn ca IBOC phi gii quyt l giao thoa gia cc thnh phn vi tn hiu
Radio, vn ny c gii quyt EUREKA 147.
16
Khi gii quyt vn giao thoa tn hiu, ph tn s 18Khz (20Khz) i vi AM
v 200Khz i vi FM ca pht thanh tng t hin nay l khng thch hp. Tuy nhin
h thng Next generation IBOC s dng th thut x l theo thi gian Time
diversity t c tnh thch hp vi ph tn quy nh ca Analog. iu ny
tng kh nng khc phc s tc ng qua li gia cc thnh phn tn hiu v s tc
nghn khi truyn tn hiu trong mt khong thi gian ngn t 1-5s. USADR s dng
Time diversity cho chn m sa sai nhm loi tr kh nng giao thoa ca tn hiu
Audio.
Mt khc khi pht ng thi c analog v digital s c s h tr ging nh
Time diversity l: nu chng trnh digital c li th my thu c th ly tn hiu
m thanh ca chng trnh analog chn vo do s khng xy ra mt tn hiu.
Hin ti IBOC ang c u th bng tn FM.
1.4 BST - OFDM ISDB (Japan).
Tiu chun ny c khuyn ngh bi NHK (Japan) nhm ng dng cho pht
cc tn hiu hnh nh, m thanh v truyn d liu di rng qua v tinh, pht trn mt
t v qua cp. Cc c im c bn ca tiu chun ny nh sau:
- i vi pht sng trn mt t, ISDB ch trng phn b di tn s thnh cc
ph vi Segment c di thng 432 KHz.
- p dng iu ch OFDM nn cho php xy dng mng ph sng dng mt
tn s.
phi hp hot ng gia pht thanh, truyn hnh s v mng vin thng,
Nht a ra giao din trao i d liu theo chun MPEG - 2 dn knh tn hiu,
c bit s dng iu ch OFDM vi kiu iu ch s QPSK, DQPSK, 16 QAM v
64QAM.
Tn hiu truyn dn c t chc vo mt s nhm trong khi OFDM (Gi l
Segment c di thng 432 KHz). Cc tn hiu ng b v cc thng s truyn dn
nh dng iu ch v xc nh li c th ch ra tng segment cho mi nhm segment
OFDM, v vy n c th t ti 4 mc phn cp (Layer) khc nhau cho vic thit k
trong knh.
H thng ny vi cc chc nng c gii thiu nhm m bo cc dch v
pht thanh, truyn hnh linh hot th hin nh sau:
17
* C th pht truyn hnh c phn gii cao.
* Cung cp cc dch v a phng tin v cc dch v lin kt.
* C th s dng thit b thu di ng vi cht lng m thanh, hnh nh v d
liu cao.
* Nh cc Layers m vic truyn dn cc tn hiu c th thc hin ng thi
trn 1 knh phc v cho cc thit b thu di ng v c nh.
H thng c khuyn ngh ny a ra gii thng chun l 5,6 Mhz v thm
mt vng 432Khz, nn tng cng l 6 Mhz. Tuy nhin, n c th ko di ti 7 n 8
Mhz m khng gp bt k kh khn g v khi ch vic thm cc segment.
Trong hnh 1.e gii thiu 3 dng truyn v thu tn hiu nh sau:
1. Cc my thu nh di ng vi b gii m OFDM 5,6 MHz v mn hnh hin
th nh SDTV.
2. My thu tch hp vi b gii iu ch OFDM 5,6 MHz dnh cho HDTV, c
th thu tt c cc dch v.
3. My thu xch tay hoc b ti vi b gii m OFDM 432 KHz dng cho cc
dch v m thanh v d liu.
1.5 H thng Worldspace ( ITU R digital system D).
5,6Mhz
My thu a h
HDTV SDTV for mobile Stereo SDTV for mobile Stereo
.. .. ..
5,6Mhz
My thu di ng
432Khz
My thu thanh xch tay
Segment
Interleaving Interleaving Interleaving
Hnh 1.e: Cc dng truyn v thu tn hiu ca BST
18
Worldspace s dng h thng 3 v tinh a tnh AFRISTAR (21E), ASIASTAR
(105E), MERICASTAR (95W) ph sng 3 vng rng ln Chu Phi, Chu v Chu
M :
+ Mi v tinh c 3 bp hng (Becam) ring.
+ Mi Becam ph sng c 14 n 28 triu km2.
+ Mi Becam c hai b pht p (Transponder) : 1 s dng, 1 iu ch
vi lung d liu theo kiu QPSK.
+ Mi sng mang truyn i 96 knh (tc 16 Kbps mt knh) s dng thut
ton nn MPEG - Layer 3. Tu thuc yu cu c th v cht lng ca m thanh cc
knh ny c th tng hp t tc 128Kbps.
+ Vic x l d liu 96 knh c s thnh lung d liu bit kiu TDM c th
c thc hin trm mt t hoc trn v tinh.
Vic truyn tn hiu ln v tinh ca nh cung cp chng trnh thng qua trm
up-link. Tu thuc vo khong cch ti v tinh, ngi ta s xc nh cng sut pht c
th. sp xp cc chng trnh khc nhau, trm up-link s dng vic phn chia theo
tn s FDMA (cc chng trnh c pht i trn cc tn s khc nhau). Trn v tinh
c cc b phn x l tn hiu thu pht cc chng trnh tr li mt t vi phng
thc phn chia theo thi gian TDMA.
Mt s c im c bn ca Woldspace:
- Tiu chun ny s dng chun nn MPEG-2.5 Layer3.
- S dng iu ch tn hiu DQPSK (Differentia Quadrature Phase Shift
Keying).
- Tc truyn trong khong: 16Kbps ca knh (c bn) n 128 Kbps (ln
nht). m bo cht lng m thanh khc nhau (tt hn AM, FM mono, gn nh CD).
- Kh nng truyn ln nht ca mi sng mang l 1.5Mbps.
- Vic dn knh c th thc hin mt t hoc trn v tinh nh cc Hub. Mi
Beam c mt Hub.
- Uplink tn hiu phn b theo tn s FDMA.
- Downlink tn hiu theo thi gian TDMA.
- Di tn s cho uplink l bng X (7025 n 7075 MHz).
19
- Di tn quy nh cho downlink l bng L vi ph tn 40MHz t 1452 ti
1492 MHz.
- Gc ngng uplink nh nht khong 100.
- Gc ngng downlink tnh theo ng knh ca mi bp hng l 60.
1.6 Digital AM (SW and MW Replcement)
Hin ti c hai nhm t chc xem xt tin ti thit lp tiu chun duy nht cho
digital AM l:
- Pht thanh digital bng hp NADIB (Narow Band Digital Broadcasting) ca
Chu u.
- DRM (Digital Radio Modiale) l t chc do nhiu nh pht thanh v hng sn
xut thnh lp.
Thc hin tng chuyn t pht thanh analog sang digital, hin nay c 4 t
chc a khuyn ngh xem xt cng nhn lm tiu chun chung:
- SKYWAVE2000 ca Thomcast.
- T2MTELEFUNKEN- Multicast.
- JPL/VOA- (ITU- R System B development).
- IBOC.
Trong IBOC mi a tiu chun nhng cha c xem xt. Hin nay hng
pht trin nhm a ra tiu chun chung l ca 3 t chc cn li.
SKYWAVE2000 v T2M c xt n giai on chuyn giao gia pht thanh
analog sang digital th hin ch l gi nguyn ph tn giao cho pht AM, nhng
thu hp di tn tn hiu analog ci thm tn hiu s. Lm nh vy tn hiu pht i s
gm c tn hiu analog v digital.
Tuy nhin cch x l tn hiu ca hai h thng rt khc nhau. SKYWAVE2000
tn hiu digital iu bin vi nhiu sng mang, thc hin iu ch song song, cn gii
php ca T2M l dng mt sng mang ph iu ch tn hiu digital sau mi a
chn vo ph analog, n thc hin iu ch mt sng mang digital s dng APSK.
T thy rng SKYWAVE2000 pht trin ph hp vi phng thc pht
analog SSB. T2M c th cho php pht analog AM cng vi mt hoc hai knh digital
c cng ni dung hoc mt s chng trnh digital c ni dung khc, hoc tng hp
hai knh thnh mt chng trnh digital cht lng cao.
20
H thng JPL/VOA (ITU-R digital system B) cho bng AM
21
Hnh 1.f miu t ph tn tn hiu ca Skywave2000 ch pht ng thi
analog v digital.
2. Tiu chun ca T2M Telefunken.
- Cho php pht ng thi hai chng trnh Analog v Digital.
- C th cho php lm vic theo cc ch :
+ Pht analog + 2 knh digital.
+ Pht analog + 1 knh digital bin thp.
+ Pht analog + 1 knh digital bin trn.
+ Pht thanh hon ton digital.
- Tiu chun m ho m thanh MPEG - 2 Layer3.
- Cho php s dng my thu hin c.
- Kh nng truyn d liu: 1000bps.
- Khi pht hon ton digital t gii thng l 6Khz i vi Mono v 2X4Khz i
vi STEREO.
- iu ch ni tip.
- Ph tn hiu ca T2M theo cc ch pht khc nhau nh sau:
4Kbps
8Kbps
208bps
Tn hiu tng t
Tn hiu s ho
3.5Khz 3 Khz 1.5 Khz
4.5Khz
Khz 10 10 10 10 10 5
5
Digital Analog
Hnh 1.f: Ph tn tn hiu ca Skywave2000 ch pht ng thi analog v digital
Hnh 1.g: Ph tn hiu ca T2M theo cc ch pht khc nhau
22
3. Tiu chun JBL/VOA ca Hoa k.
- Ch cho php pht hon ton digital.
- Phn b di thng 10KHz cho pht digital trn cc bng sng ngn.
- t cht lng m thanh vi ph tn 10KHz, tnh n vic hiu chnh mc
giao thoa.
- Tng s thng tin (m thanh v d liu) c th truyn 32Kbps.
- Phng thc x l tn hiu tng t T2M.