1

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.