123300281 Truyen Hinh Ky Thuat So

7/29/2019 123300281 Truyen Hinh Ky Thuat So

1/79

Chng III: TRUYN HNH K THUT S

Bi 1: c im truyn hnh s

1. Gii thiu chung

TH s l hthngtruyn hnh m ttc cc thitbttongun,lutr,x l, truyndn, thu tn hiutruyn hnh uda trn cng nghkthuts. Trong , tn hiu TH l cc dy xung vung ngvi ccchui bt dliunh phn 0, 1.

Cng nghtruyn hnh sangbclthmnhtuyti so vi cngnghtngt. Trong tng lai gn,truyn hnh thgiistintisha hon ton.

TH s ra i c tnh kthpvitruyn hnh tngt: c thsdngcc thitbucuitngtsn c.

uimca THs:

Tn hius t nhycmvi cc dng mo xy ra trn ngtruyn.

C khnng pht hinli v sa sai.


2/79

Tnh anng v linh hot trong qu trnh x l tn hiu.

Hiuqusdng ti nguyn tns v c khnng truynnhiuchngtrnh trn mt knh RF.

Tnh phn cp: c thc truynmtchng trnh c phn gii caoduy nhthocmt vi chng trnh c phn gii tiu chun.

Khnngtinhiudng thng tin khc nhau.

Titkimnnglng,vi cng mt cng sut pht, dinph sng lnhn

cng ngh tng t. Cng sut my pht schbng 1/4 cng sut mypht tngt.

Truyn hnh svi cng nghmngntn (SFN) c thtitkimcti nguyn tns.

D dng thch nghi vi cc bc pht trin tip theo sang truyn hnh phn gii cao hoc pht thanh vichtlng CD trong tng lai.

Th trngadng, c khnng cung cpnhiu loi hnh dchv. Honton c khnng ho nhp vo xa l thng tin.


3/79

S khi

Bin i AD, DA.

Nn v gii nn.

M ha v gii m ha knh

iu ch v gii iu ch s.

Knh thng tin: V tuyn v hu tuyn.

BiniA/D

BiniD/A

NnGhpknh

Tchknh gii

nn

M haknh

Gii mha knh

iuch

Giiiuch

Knhthng

tin

Thit b pht

Thit b thu

Tn hiu

truyn hnh

analog

Tn hiu

truyn hnhanalog


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2. c im ca TH s

Yu cuvbngtnlnhn: V dh NTSC tn hiutnghp cbngtn 4.2 MHz, khi s ha tn s ly mu 4fSC: 14,4 MHz x 8bit/mu =

115,2 Mbit/s, rngbngtnkhong 58 MHz. Bin php khcphc nntn hius.

Tl tn hiu trn tp m S/N: cao hnnhiu so vi tn hiutngt. ivi tn hiusnhiu l cc bit lickhcphcbngmch sa li. Khic qu nhiu bit li,snhhngcanhiuc lm gimbng cchche li,ts S/N cahthngsgimrt t hoc khng i. ngha: cim c ch cho vicsnxutchng trnh truyn hnh vi cc chcnng

bin tpphctp,cnnhiulnc v ghi, victruyn tn hiu qua nhiuchngcngcthchinrtthunlivi tn hius m khng lm suygimchtlng tn hiu hnh.

Mo phi tuyn: Tn hius khngbnhhngbi mo phi tuyn trongqu trnh x l v truyndn.


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Gi thnh v phc tp: vi s pht trin ca nghnh cng nghiptruyn thng s v cng nghip my tnh v cng nghmch tch hp. Githnh rhn v phctpgimdn.

X l tn hius: dung lng lu tr ln, tc chp x l tng,dngchng trnh truyn hnh, nn, m habomt,chuynichun

Khongcch gia cc trm ng knh: Tn hiu s cho php cc trmtruyn hnh ng knh thchinmtkhong cch gn nhau hnnhiuso vih thng tng t m khng bnhiu. Mtphn v tn hius t

chunhhngcanhiung knh, mtphn l do khnng thay thxung ho v xung ngbbng cc t m, ni m hthngtngt gyra nhiulnnht.

Hin tng Ghosts (bng ma):Hin tng ny xy ra trong h thngtng t do tn hiu truyn n my thu theo nhiu ng. Vic trnh

nhiung knh cahthngscng lm gimihintng ny trongtruyn hnh s.


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Bi 2: S ha tn hiu truyn hnh

1. Giithiu chung

Chuyni tn hiutruyn hnh tngt thnh tn hius(gi l s ha tn

hiutruyn hnh). C haiphngthc: Sha trctip tn hiu video mu tnghp (Composite Signal):

Tc bit u ra thp.

Tn hiu video stnghp cn mang y cc nhcimca tn hiu videotngt,nht l hintng can nhiu chi-mu.

Sha ring cc tn hiu video thnhphn (Component Signal): Cc tn hiu video thnhphn: tn hiu chi EY, 2 hiu mu ER-Y v EB-Y; hoc

cc tn hiu mu cbn: ER, EG, EBcngthitruyn theo thi gian hocghp knh theo thi gian.

Tc dng bit ln.

Khcphcc cc nhcimca tn hius video tnghp. Khngphthuc vo dnghtruyn hnh mu PAL, NTSC, SECAM nn to

thunli cho vic trao i cc chng trnh truyn hnh, tinti xy dngmtchun chung vtruyn hnh s cho ton thgii.

Quctkhuyn co sdng hnh thcbini ny.


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2.Sha tnhiu video mutnghp

tinti xu hngchun ho cho cc thitb Video s,ngi ta ara hai tiu chunvtnslymu l fSA = 4fSC NTSC v 4fSCPAL tns

lymubng 4 lntns sng mang mu v sdng 8 bit hoc 10 bit biu din cc mu.

a. Tn hiu videostnghp tiuchun 4fSCNTSC

Cc thamscbn:

Tn hiu vo NTSC

+ Tng s mu trn mt dngvideo+ S mu trn mt dng video tchcc+ Tn s ly mu

+ Cu trc ly mu+ Cc mu+ S bt lng t

910768 14f

sc- 14,32818 MHZ

Trc giao+330, +1320, +2310,

+303010 bit/mu


8/79

Cu trc lymu:

Khong cch ly mu

trng vinh bin cc

tn hiu EI & EQ.

Smu trn 1 dng:

NSA=FSA/FH=4FSC/FH=

4x3.58MHz/15750Hz=910.

Trong : 768 mu cho

dng video tch cc; 142mu cho ngb dng.


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Thang lng t:

Quan h gia mc video tng t v thang lng t ng vi m ha 10 bit.


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Cu trc dng s:

Quan h gia dng tng t v dng s.


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Cu trc mnh s:

Quan h gia mnhtngt v mnh s.


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b. Tn hiu video s tng hp tiu chun 4fSCPAL

Cc tham s c bn:

Tn hiu vo PAL

+ Tng s mu cho mt dng

+ S mu trn mt dng tch cc

+ Tn s ly mu

+ Cc mu

+ Cu trc ly mu

+ S bt lng t ho

1135

948

4fsc - 17,734475 MHz

+450; +1350; +2250; +3150

Cu trc trc giao

8 hoc 10 bit cho mt mu


13/79

Cu trc ly mu:

Khong cch lymuti 45, 135, 225, 315 , khngphinhlnnht.VD: sc mu vng c bin ln nht 0.934V nhng mu ln nht ch0,886V.


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Thang lng t:

Quan h gia mc video tng t v thang lng t ng vi m ha 10 bit.


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Cu trc dng s:

Quan h gia dng tng t v dng s.


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Cu trc mnh s:

Khong xa mnh smnh 1: dng 623 n

dng 5. Khong xa mnh s

mnh 2: dng 310 ndng 317.


17/79

3. Sha tnhiu video thnhphn

a. Tn hiu thnhphnsha v tnslymu:

Theo chun CCIR 601: cc tn hiu thnhphncs ha gm tn hiu

chi EY, 2 hiuhiu mu ER-Y v EB-Y Tn s ly mu tn hiu chi l 13,5 MHz c chn sao cho l mt s

nguyn lntns dng fH cho c hai tiu chun 525 v 625 dng:

FSA=13,5 MHz = 864 x fHivi tiu chun 625 (fH = 15625 Hz).

FSA=13,5 MHz = 858 x fHivi tiu chun 525 (fH = 15750 Hz).

Ph tn hiu chi lymutns 13,5 MHz vph tn hiumulymutns 6.75 MHz.


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b. Cc chun lymu: C nhiuchun lymu tn hiu video thnh phn,im khc nhau chyu l tllymu vphng php lymu tn hiuchi v cc tn hiu mu.

Tiu chun 4:4:4

Tn hiu chi EY, 2 hiu mu ER-Y v EB-Yc lymu trn ttc cc

dng tch ccca tn hiu video. VD h PAL: 625 dng (576 dng tch cc) x 720 ct,lymu 10 bit theo

chun 4:4:4, tc bit u ra:

Tc bit = (720 (EY )+720 (ER-Y )+ 720 (EB-Y)) mu x 576 dng x 10 bit/mu

x 25nh/s = 311 Mbps


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Tiu chun 4:2:2

C 4 lnlymu chi EY, c hai lnlymu cc hiu mu ER-Y v EB-Y .

Khi gii m mu imnhch lymu chi s lymu hai tn hiumucaimnhtrc.

VD: H PAL lymuchun 4:2:2, 10bit/mu th tc bit u ra:

Tc bit = (720 (EY )+360 (ER-Y )+ 360 (EB-Y)) mu x 576 dng x 10 bit/mux 25 nh/s = 207 Mbps.

-> Tc bit gim


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Tiu chun 4:2:0

Lymu chi EY trn ttc cc dng, c cch mtimnh li lymucho chmt tn hiu mu.

Tn hiu mu cly xen k theo tng dng VD: dng n lymu ER-Y thdng n+1 lymu EB-Y.

VD: H PAL lymuchun 4:2:0, 10bit/mu th tc bit u ra:Tc bit = (720 (EY )+180 (ER-Y )+ 180 (EB-Y)) mu x 576 dng x 10 bit/mu

x 25 nh/s = 155,5 Mbps.-> Tc bit gim


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Tiu chun 4:1:1

Lymu chi EY trn ttc cc dng, c 4 mu EYlilymu hai tn hiumu ER-Y v EB-Ymtln.

Khi gii m mu 3 imnh sau c suy ra timnhu. VD: H PAL lymuchun 4:1:1, 10bit/mu th tc bit u ra:

Tc bit = (720 (EY )+180 (ER-Y )+ 180 (EB-Y)) mu x 576 dng x 10 bit/mux 25 nh/s = 155,5 Mbps.

-> Tc bitbngvichun 4:2:0.


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c. Thang lng t

Quan h tn hiu chi tng t EYv cc mc lng t.


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Quan h tn hiu hiu mu tng t ER-Yv cc mc lng t.


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Quan h tn hiu hiu mu tng t EB-Yv cc mc lng t.


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d. Cu trc ly mu

Ly mu thi gian xa dng h 625/50


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Ly mu xa mnh h 625/50


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Bi 3: Nn tn hiu video (Digital video compression)1. Mc ch nn

Gim tc bit u ra nhm gim rng bng tn cn thit truyn ti

(bandwidth reduction)

Application Data RateUncompressed Compressed

Video Conference

352 x 240 @ 15 fps 30.4 Mbps 64 - 768 kbps

CD-ROM Digital Video

352 x 240 @ 30 fps 60.8 Mbps 1.5 - 4 Mbps

Broadcast Video

720 x 480 @ 30 fps 248.8 Mbps 3 - 8 Mbps

HDTV

1280 x 720 @ 60 fps 1.33 Gbps 20 Mbps


28/79

V dvi tn hiu HDTV:

Bnchtca nn Video l mt qu trnh trong dliubiudinlngthng tin ca mt nh hoc nhiu nh c gimbtbng cch loibnhngsliudtha trong tn hiu Video.

dthadliu (data redundancy):l trung tm trong nn nhs. dthadliu khngphi l mt khi nimtrutng m l mtthct c thnhlngcbng ton hc. Dthav khng gian (spatial redundancy). Dthavthigian (temporal redundancy).

High-Definition Television (HDTV)- 1920x1080

- 30 frames per second (full motion)- 8 bits for each three primary colors (RGB)Total 1.5 Gb/sec!

Cable TV: each cable channel is 6 MHz- Max data rate of 19.2 Mb/sec- Reduced to 18 Mb/sec w/audio + control Compression rate must be ~ 80:1!


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2. Nn da trn gimdthav khng gian (Spatial Redundancy):

Cc imnh ln cn nhau trong mt nhhoc cc nh lin tip nhau th

tngt nhau hoc khc nhau rt t, ta chcn thng tin vs khc nhau ny.


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Chuyn thnhphnlymu video t ER, EG, EB sang EY, ER-Y, EB-Y : Mtngi km nhycmvi cc tn hiu mu.

Chia bc nh lm cc Macro Blocks (16x16 pixels) gm 4 Blocks, miBlockgm 8x8 pixels.

Bini cosin rirc DCT (Discrete Cosine Transformation).

Nn khng gian c thc hinbi php bin i DCT trn Block 8x8pixels da trn phn tch Fourier, trong tn hiucbiudindng sin vcos,binidliudidng bin thnh dliudidngtns.

Saubini DCT, cc gi trca blockcspxp theo thtt tri quaphi v t trn xungdivi cc thnhphntnstngdn: t 1 chiu DCn thnh phn xoay chiu cao nht AC. Sbin i gi tr bin (chnhlch) theo hng no cng ln th gi tr AC theo hng cng cao.

Lngt ha

Bn thn phpbini DCT khng nn dliu

Qu trnh lngt ha v m ha sau DCT thchin nn data.


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Zig-Zag Scan,

Run-length

coding

Quantization

major reduction

controls quality

Intra-Frame

Encoded


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M ha chuyn i khi (Block Transform Encoding)

Run-lengthCode

HuffmanCode

DCT

Zig-zag Quantize

011010001011101...


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Qu trnh nn

So snh vi qu trnh gii nn

DC component139 144 149 153

144 151 153 156

150 155 160 163

159 161 162 160

original image

DCT

1260 -1 -12 -5

-23 -17 -6 -3

-11 -9 -2 2

-7 -2 0 1

AC components

Quantize

79 0 -1 0

-2 -1 0 0

-1 -1 0 0

0 0 0 0

zigzag79 0 -2 -1 -1 -1 0 0 -1 0 0 0 0 0 0 0

run-length

code

0 79

1 -2

0 -10 -1

0 -1

2 -1

0 0

Huffman

code10011011100011...

139 144 149 153

144 151 153 156

150 155 160 163

159 161 162 160

144 146 149 152

156 150 152 154

155 156 157 158

160 161 161 162

original block reconstructed block

-5 -2 0 1

-4 1 1 2

-5 -1 3 5

-1 0 1 -2

errors


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Mt s vn :

Khi no th vic gim d tha v khng giangim hiu qu?

Tr li: Khi bc nh c phn gii cao hoc phim c hnh nh v mu scbin i nhanh. Nu nn s lm gim cht lng nh.

V d :

Original (63 kb)

Low (7kb)

Very Low (4 kb)


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3. Nn da trn gim d tha v thi gian (Temporal Redundancy):

Cc nh lin tip nhau c hnh nh mu sc tng t nhau. C d thathng tin.

950 951 952


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C ng theo thi gian


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Gim s d tha v thi gian:

D on b chuyn ng (Motion Compensated Prediction): D on nhhin ti da trn cc nh c m ha trc .


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Vector chuyn ng (Motion Vector):


39/79

S khi b nn video (video compression encoder)


40/79

S khi b gii nn video (video compression decoder)


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Nhm nh GOP (Group Of Pictures)

Cc loinh:

nh loi I ( Intra-picture): L nh c m ho c lp, nh I c cha

ngdliu ti toli tonb hnh nh v chng cto thnhbngthng tin cachmtnh, nh I cho php truy cpngu nhin, tuy nhintctln nn thpnht.

nhloi P (Predicted - Picture): L nh m ho c b chuynngtnhI hocnh P pha trc(nhdontrc), nh P cung cp cc hs nn

cao hnnh I. nhloi B (Bidiretional Predcited-picture): L nhc m ho sdng

b chuynngtnh I v nh P pha trc v pha sau (nhdon haichiu), nh B c tl nn cao nht.

Cu trc ca GOP:


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GOP mlunbtubngmtnh I v kt thc mtnhtrcnh I tiptheo.

Type SizeCompression

---------------------

I 18 KB 7:1

P 6 KB 20:1

B 2.5 KB 50:1

Avg 4.8 KB 27:1

-------------------

T l nn ph thucvo t ls lngnhB, P trong mi GOP


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Mt s vn :

Khi no d tha v thi gian gim hiu qu?

Tr li: - Khi nhiu cnh thay i trong nh.

- Di chuyn tc cao


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4. Cc chun nn video hin ti

STANDARD APPLICATION BIT RATE

JPEG Continuous-tone still-imagecompression Variable

H.261 (1990) Video telephony andteleconferencing over ISDN

p x 64 kb/s

MPEG-1 (1991) Video on digital storage media(CD-ROM)

1.5 Mb/s

MPEG-2 (1993) Digital Television > 2 Mb/s

H.263 (1995) Video telephony over PSTN < 33.6 kb/s

MPEG-4 (1993) Object-based coding,synthetic content, interactivity

Variable

H.264 (2003)

Advanced VideoCoding Standard

From Low bitrate coding to HDencoding, HD-DVD,Surveillance, Videoconferencing.

Variable


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Chun nn H261 (1990): Truyn video hai chiu thi gian thc,ngdng trong thoi video v hi

ngh video.

Chunlymu 4:2:0. H.261 htrtc bit p*64 kbps (p=1..30). CIF: CommonIntermediate FormatQCIF: Quarter CIF.

Sdngnh I v P (cha c nh B).


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Bi 4: iu ch tn hiu truyn hnh s

DVB: Digital Video Broadcast

DVB-S: Satellite

DVB-C: Cable

DVB-T: Terrestrial


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1. S khi h thng truyn hnh s DVB (Digital Video Broadcast)

S tng qut pha pht/thu ca DVB


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Pha thu:

Tn hiu RF t mi trngtruyndni vobitnxung IF. VD:

DVB-S: Ku: 10,7 12,75 GHz qua b LNC (Low Noise Converter)

chuynxung IF1: 9502175 MHz, sau khi lachn knh tiptcitnxung IF 2: 480 MHz.

BVB-C v DVB-T: Chuyn t RF: 47 860 MHz xung trung tn IF36,15 MHz.

Giiiuchtngng: COFDM (T), QAM (C), QPSK (S) khiphhai tn hiu I, Q.

Bini ADC, Lc,nhdng lid liu (sysbol remapping), thc hinqu trnh sali, khiphcli cc gi truynti PES 188 byte.

Giingu nhin ha, v tch knh theo yu cungisdng.

Gii nn MPEG2 video v audio cachng trnh mong mun.


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S b thu DVB-T (set top box)

2 i i h t h h


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2. cimcaiuchtruyn hnh s DVB-S:

Khong cch truynln 36 000 Km, suy hao v nhiungtruynln. Cng xut pht nh, tn hiun anten thu mttrtyu, C/N nh Chnphng php iuch QPSK cho ts C/N ln,vibngtnrng2736 MHz (analog FM angtnti).

DVB-C:

Khong cch truynnh,nhiunh,ts C/N ln >30dB. Chunhhngcahintngvng (echoes) tn hiu dophnxti cc

node trong mng, tuy nhin nhhng ny nh.-> Chnphng php iuch 16 - 256 QAM, bng tnhp 6 8 MHz(analog AM)

DVB-T: Khong cch truynnh, cng sut pht ln. nhhng nghim trngbihintngang.

-> Chnphng php iuch COFDM,bngtnhp 68 MHz.


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iuch bin trc giao QAM (Quadarture Amplitude Modulation):

Cc phng php iuchs ASK, FSK: hiusutbng thng km, yucu nng cao tc bit trnbngtn cho trc.

Phng php iuch QAM: ban ungdng cho iuch tn hiu mutrong h NTSC 1954. Sau ng dng cho iu ch s nng cao hiu sutbng thng.

Skhiiuch v giiiuch QAM:


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u vo n bit, n/2 bit cho mi knh I, Q.

Ta c thbiudinstrng thi (symbol) tngng trn mtphng I & Qgi l chm sao (Constellation). Miim l mt ngi sao (star) tngngvi 1 symbol biudin cc bit.

Chm sao QPSK (4-QAM)

2 bits/symbol.


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Chm sao 64-QAM,

6 bits/symbol

Sau khi thc hinbin

i DA, hai tn hiuanalog I & Q a vo iu

bin ring bit vi hai

sng mang trc giao.


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3. iuch trong DVBS v DVBC

Mi quan hgia BER (Bit Error Ratio) v SNR trong iukin l tngiviiuch QAM:

Nhnthyrngvi cng BER, QPSK cho SNRlnhn 12dB so vi 64QAM.


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Da vo cimv mi trngtruyncngnhhiu sutbng thng ti

a c thtc,ng thi qua thnghim thc t ta a ra lachn

phng php iuch:

DVB-S: QPSKvi 2 bits/symbol.

DVB-C: 64-QAM vi 6 bits/symbol.

Vi DVB-T: Do nhhng nghim trngbiang, bin nbthu bini, BER lnhnmc cho php. Nn khng sdng QAM

cho DVB-T.


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nhhngcanhiunvicgiiiuch QAM:

Chm sao u ra cabgiiiuch QPSK trong u thu v tinh:

Chm sao QPSK vi nhiu trong DVB-S


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Chm sao u ra ca b gii iu ch 64-QAM trong u thu cp:

Nu S/N ln hn mc cho php, b gii iu ch s khng phn bit cim trong chm sao vi cc im ln cn n -> sai li symbol.

Chm sao 64-QAM vi

nhiu S/N=23dB


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Vi TH cp, ngoi nhhngnhiu trn ngtruyn cn c nhhngcahin tngvng tn hiu trong mng. ISI (Inter-Symbol Interference)rtln nn khng th phnbit cc im ln cn.

Trong u thu DVB-T sdngblngt ha vngtng thch khiphcli chm sao tngi chnh xc.

Constell ation of 64-QAM with echoes Constell ation of 64-QAM withechoes after equal izing


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4. iu ch trong DVB-T

Sdngiuch phn chia theo tnstrc giao m ha COFDM (CodedOrthogonal Frequency Division Modulation):

Phn chiabngtnssdng thnh nhiubnghp,mibnghp l mtsng mang con iu ha v cc sng mang ny l trc giao vi nhau (hngnghn sng mang).

Dng bt d liu tc cao s phn chia thnh cc lung tc bt thphn,milungsciuchbi cc sng mang trc giao.

Tnh trc giao: nhphca sng mang ny tngngvi gi tr khngtrongphca cc sng mang khc.

Ph OFDM vi s sng mang N=5


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Chu k biu tng Ts: thi gian truyn i 1 symbol.

1/Ts: l khong cch tn s gia hai sng mang con lin tip.

Ph OFDM vi s sng mang N=32

S d COFDM i i h h


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Sdng COFDM trit tiu nhhngcaang:

ivihthngn sng mang (QAM): my thu scgnggiiiuchdliubng cch kim tra ttc thng tin nhnc lin quan n symbolth n kc thng tin thu trctipln thng tin thu c do tr.

gim ISI th phi gim tc symbol ngha l khong cch pht 2symbol lin tip (Tsymbol)philnhnrtnhiu so vithi gian trlnnhtTdelay -> gim tc bit -> khcphcbng s dng nhiu sng mangOFDM.

Tdelay>>Tsymbol Tdelay


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Sdngnhiu sng mang trc giao: Khi chu k s dng li ca mtsng mang con l rtln. Chu k ny lnhnrtnhiu so vithi gian trlnnhtca symbol. Do thi gian x l cho cng mt sng mang vicc trca n stng ln -> gim ISI.

Chn thm khongbo v GI (Guard Interval): Nu khong t hp thuc tri di theo 2 symbol th khng ch c nhiu ca cng sng mang(ISI) m cn cnhiu xuyn sng mang (ICI). trnh iu ny chng tachn thm khongbov gip mbo cc thng tin tnghp l ntcng mt symbol v xuthincnh.

GI c chn phnucathi gian ca 1 symbol.

GI l copy caoncui symbol vi 1 khongthi gianbng 1/4, 1/8,1/16, 1/32 ca 1 symbol.

T hi th kh kh b


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Tn hiu a ng thu c khng c khong bo v:

?? ?? ??

Path 1

Path 2

Path 3

Combined

antenna

input

(Path

1+2+3)

"Blank

screen"

Perfcect

picture

TV

CAM

DVB-

T

TRX

Path1

Path

2

Path3

Invalid data within

symbol duration

Invalid data within

symbol duration

Invalid data within

symbol duration

Tn hiu a ng thu c c khong bo v:


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Tn hiu a ng thu c c khong bo v:

??????

Path 1

Path 2

Path 3

Combined

antenna

input

(Path

1+2+3)

Perfcect

picture

Perfcect

picture

TV

CAM

DVB-

T

TRX

Path1

Path

2

Path

3

Valid data for symbol

duration


duration


duration

T d COFDM + GI t it ti


66/79

Tc dng ca COFDM + GI: trit tiu a ng

Analogue television and multipath

Perfcect

pictureTV CAM

Analogue

TV

TRX

PerfcectpicturePerfcectpicturePerfcectpicture

Directpath

Refle

ctionn

o.1

Refle

ction

no.

2


67/79

Digital television (COFDM) and multipath

Perfcectpicture

Perfcect

pictureTV CAM

DVB-T

TRX

Directpath

Refle

ction

no.1

Refle

ction

no.

2


68/79

M hnh nguyn l iu ch COFDM:

Hai ch 2K v 8K tng ng vi s lng sng mang 1705 v 6817 trnbng tn 8 MHz.

Number of carriers:

2K: 1.705

8K: 6.817

Carrier 1 Carrier 2 Carrier 3 Carrier nCarrier n-1Carrier n-2

spacing

8K: 1.1kHz

2K: 4.4kHz

Mapper

(Data, TPS

and Pilots)

+

+

+

+

OFDM spectrum

Carrier 1

Carrier n

AM

AM

Carrier

OSC90 deg+

DAC

DAC

Composite waveform

equal to the sum off

all 6817 / 1705 carriers

10111001

10101000

11101100

11111101

00010011

00000010

01000110

01010111

h d hi i l i


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COFDM thc t s dng IFFT: chip vi x l vi DSP

Bin i FFT v IFFT

S&H

and

A/D conv.

FFT

processor

Re

Im

f1 f2 f3 f4 f5 f6 f7

f

f

f8

T

S1 S2 S3 S4 S5 S6 S7 S8

Discrete frequency

components of the

waveform

0

0

F = sample freq. / number of samples

IFFT

processor

Re

Im

Discrete frequency

components of the

waveformT

S1 S2 S3 S4 S5 S6 S7 S8

f1 f2 f3 f4 f5 f6 f7

f

f

f8

0

0

D/A conv.

For COFDM the input to

the IFFT is the real and

imaginary values for each

of the carriers in the

COFDM symbol

iu ch COFDM dng IFFT:


70/79

iu ch COFDM dng IFFT:

TS adaptation &

Energy

dispersal

Outer

Coder and

Interleaver

Inner

Coder and

Interleaver

MapperIFFT

IF or

RF

converter

MPEG-2

TS

OFDM

carrier

IFFT

Re 1,2,3....1.705 (6.817)

Im 1,2,3....1.705 (6.817)

I

Q

+

Baseband

I+Q

1: The complete set of Re and Im values (one pair per carrier)

is stored in the IFFT processor.

2: The frequency components of the spectrum (the individual

carriers) are then transferred to the time domain (a

waveform in time) by the IFFT

C d DVB T

s224 s896


71/79

Cc mode trong DVB-T

Tham s Mode 2K Mode 8K

S lng sng mang con

rng symbol c ch(TU)

Khong cch sng mang (1/TU)

Bng thng

Khong bo v

Phng thc iu ch

Tl m

1705

224us

4464hz

7.61Mhz

T/4, T/8, T/12

QPSK, 16-64QAM

1/2, 2/3, 3/4, 5/6, 7/8

6817

869us

1116Hz

7.61Mhz

T/4, T/8

QPSK, 16-64QAM

1/2, 2/3, 3/4, 5/6, 7/8

Exercise: Calculation of the useful bit-rate in a common DVB-T transmission example (UK


72/79

Exercise: Calculation of the useful bit rate in a common DVB T transmission example (UKcase):

8MHz channel;

2K mode (8K or 2K is unimportant for the bit-rate);

modulation: 64-QAM; guard interval: 1/32;

code rate: 2/3.

We have 1705 useful carriers modulated in 64-QAM (6 bits/symbol) with a symbol frequencyof 4464.286 Hz, which gives a bitrate of:

151264464.286 = 40.500 Mb/s

The bit-rate calculation must take into account the guard interval (i.e., 32/33 with = 1/32) andthe channel coding overheads (i.e., 2/3 for puncturing and 188/204 for RS coding), thereforethe useful bit-rate:

4050031/322/3188/204 = 24.128 Mb/s

This bit-rate, depending on the trade-off between picture quality and number of programs perchannel chosen by the broadcaster, allows transmission of four to six TV programs.

Depending on the trade-off between robustness and bit-rate chosen by the broadcaster (or thebroadcasting regulation authority), the DVB-T system can carry the following minimum andmaximum bitrates in an 8MHz channel:

Minimum bit-rate: 4.98 Mb/s (QPSK modulation, guard interval 1/4, code rate 1/2)

Maximum bit-rate: 31.67 Mb/s (64-QAM, guard interval 1/32, code rate 7/8)

One can see that the bit-rate can vary in a ratio from 1 to more than 6!

Phn chia knh truyn:


73/79

Phn chia knh truyn:

time

fre

quency

Channel

Bandwidth

f requency

sub-band

t ime

segment

T h


74/79

T chc sng mang:

time

frequency

Channel

Bandwidth

sub-carr iers

OFDM symbo l

OFDM symbo l

Kh b


75/79

Khong bo v:

time

frequency

Channel

Bandwidth

Used

part

duration

Guard

Interval

duration

OFDM

symbolduration

ng b: H thng DVB T s dng cc sng mang "pilot" tri u n trong


76/79

ngb: Hthng DVB-T sdng cc sng mang pilot , triun trongknh truyndn,ng vai tr lm cc imnhdungb.

Khc vi sng mang cc chng trnh, cc pilot khng iuch QAM, m chiuch BPSKvimc cng sutlnhn 2,5 dB so vi cc sng mang khc.Hnh 6biudin phnb sng mang pilot rirc v lin tcvi mc cng sut

lnhn cc sng mang dliu 2,5 dB.

time

frequency

Channel

Bandwidth

DVB-T Transmission Frame

Boosted pilot

Cc pilot (sng mang) lin tc: bao gm 177 pilot vi 8K v 45 pilot vi


77/79

Cc pilot (sng mang) lin tc: bao gm 177 pilot vi 8K, v 45 pilot vi2K. Cc pilot ny c v tr cnh trong di tn 8MHz v cnh trongbiu chm sao u thu sa li tn s, t ng iu chnh tn s(AFC) sali pha.

Cc pilot (sng mang) rirc (phn tn): bao gm 524 pilot vi 8K, v 131pilot vi 2K c v tr cnh trongbiu chm sao. Chng khng c v trcnh trong mintns,nhngctriu trong di thng 8MHz. Bnmy thu khi nhnc cc thng tin t cc pilot ny stngiuchnhtc"png knh" ttnht v thchinvichiuchnh(nucn).

Mang d liu:


78/79

Mang d liu:

time

GUARD

intervall

USED PART

of the symbol

USEFUL DATA

PROTECTED DATA

GUARD INTERVALL INSERTION

OFDMSYMBOL

DURATIONfrequ

ency

0

110

1

(PILOTs NOT REPRESENTED )

Hin nay trn thgiitnti song song ba tiu chuntruyn hnh s. l:


79/79

ATSC (Advanced Television System Commitee) caM.

iu bin ct 8VSB (Vestigal Side Band). Khng c khnng thu di ng,khng chngcang v khng thitlpmngntn.

DVB-T (Digital Video Broadcasting) ca Chu u.

ISDB-T (Intergrated service Digital Broadcast) caNht.

Ging nhau: usdngiuch COFDM. C khnng thu di ng,chngang v thitlpmngntn.

Khc nhau: ISDB-T sdng ghp xen thi gian.

Phn on vng tns cho cc dchv khc nhau: 10 khong cho dchv video v 3 khong cho dchv audio.

Khng tng thch vi DVB-S v DVB-C.

123300281 Truyen Hinh Ky Thuat So

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Transcript of 123300281 Truyen Hinh Ky Thuat So