A TUTORIAL ON DTTB BY Amrit Pal Singh,ASE,DDK Jalandhar SOON DD IS GOING TO LAUNCH DTTB SERVICE THROUGH OUT THE NATION BUT IN PHASED MANNER. 1
REQUEST READERS ARE REQUESTED TO SEND THEIR VALUABLE SUGGESTIONS TO IMPROVE THE PRESENTATION FURTHER. amritpalsingh@sify.com Phone: 9417895270 2
WHAT DTTB IS?DIGITAL TERRESTRIAL TELEVISION BROADCASTING 3
HOW TO RECEIVE DTTB TRANSMISSION 4
BENEFITS OF DTTB TRANSMISSION IMROVED RECEPTION AND PICTURE QUALITY OVER ANALOGUE TRANSMISION NO GHOST CLEAR PICTURES SHARPER PICTURES SUPPORTS HIGH DEFINITION TV AND INTERACTIVE MULTIMEDIA SERVICES CARRIES MORE CONTENT IN SAME BANDWIDTH 4-8 CHANNELS IN STANDARD DEFINITION USING MPEG-2 8-16 CHANNELS IN STANDARD DEFINITION USING MPEG-4 PART 10AVC 5
BENEFITS OF DTTB TRANSMISSION LOWER TRANSMISSION POWER WILL COVER THE SAME DISTANCE SUPPORTS MOBILE TV, PORTABLE TV AND FIXED TV RECEPTION BETTER USE OF FREQUENCY SPECTRUM CAN RELEASE VALUABLE SPECTRUM FOR OTHER PURPOSES AUXILLIARY DATA CAN BE TRANSMITTED MULTIPLE AUDIO CHANNELS CAN BE TRANSMITTED 6
BENEFITS OF DTTB TRANSMISSION 7
BENEFITS OF DTTB TRANSMISSION 8
BENEFITS OF DTTB TRANSMISSION 9
BENEFITS OF DTTB TRANSMISSION 10
BENEFITS OF DTTB TRANSMISSION 11
BENEFITS OF DTTB TRANSMISSION 12
BENEFITS OF DTTB TRANSMISSION 13
BENEFITS OF DTTB TRANSMISSION 14
STANDARDS AVAILABLE FOR DTTB ATSC:ADVANCED TELEVISION SYSTEM COMMITTEE DVB-T :DIGITAL VIDEO BROADCAST TERRESTRIAL ISDB:INTEGRATED SERVICE FOR DIGITAL BROADCAST T-DMB:TERRESTRIAL DIGITAL MULTIMEDIA BRODCASTING 15
ATSC DEVELPOD IN USA. DEPLOYED IN USA,CANADA,SOUTH KOREA,TAIWAN USES SINGLE CARRIER MODULATION TECHNIQUE KNOWN AS-8VSB NOT SUITABLE FOR MOBILE RECEPTION NOT ADOPTED WIDELY NOT SUITABLE FOR SFN MAXIMUM PAYLOAD DATA RATE 19.39MBPS IN 6 MHZ CHANNEL 16
DVB DEVELPOED IN EUROPE USES MULTICARRIER MODULATION SYSTEM : COFDM SUITABLE FOR FIXED,PORTABLE AND MOBILE RECEPTION WIDELY DEPLOYED IN WORLD MAXIMUM PAYLOAD DATA RATE AVAILABLE IS 31.56MBPS IN 8MHZ CHANNEL 17
ISDB DEVELPOD AND DEPLOYED IN JAPAN USES SEGMENTED COFDM BETTER SUITABLE FOR MOBILE RECEPTION ISDB-T SEPARATES 6MHZ CHANNEL INTO 13 SEGMENTS EACH SEGMENT BEING 429KHZ NOT WIDELY DEPLOYED. DEPLOYED ONLY IN JAPAN AND BRAZIL MAXIMUM PAYLOAD DATA RATE IS 23.2MBPS IN 6 MHZ CHANNEL 18
COMPARISON OF STANDARDS ITEM ATSC ISDB-T DVB-T TRANSMISSION BANDWIDTH SINGLE CARRIER 8VSB MULTIPLE CARRIER OFDM EACH SUITABLE FOR 6,7,8 MHZ MODULATION ERROR CONTROL CHARACTERISTICS PROPOSING COUNTRY 8VSB REED SOLOMEN+TRELLIS CODE ADVANCED ANALOGUE BASED FORMAT MORE REBUST IN AWGN CHANNEL HIGHER SPECTAL EFFICIENCY LOWER PEAK TO AVERAGE POWER RATIO REBUST TO IMPULSIVE AND PHASE NOISE NOT SUITABLE FOR MOBILE RECEPTION AND SFN USA DQPSK,QPSK,16QAM,64 QAM REED SOLOMEN CODE + CONVOLUTIONAL CODE SUITABLE FOR SFN SUITABLE FOR MOBILE RECEPTION HIGHLY IMMUNE TO LONGER DELAYS AND MULTIPATH GHOSTS JAPAN QPSK,16QAM,64QAM EUROPE 19
COMPARISON OF STANDARDS ITEM ATSC ISDB-T DVB-T INTERLEAVIN G BITS/SYMBOL YES YES YES FREQUENCY NO YES YES TIME NO YES NO PAY LOAD DATA RATE FOR 6 MHZ CHANNEL 19.39 Mbps 3.65-23.2 Mbps 3.69-23.5 Mbps 20
COMPARISON OF STANDARDS ITEM ATSC ISDB-T DVB-T HDTV, SD TV FIXED RECEPTION YES YES YES DATA BROADCASTING POSSIBLE INSERVICE POSSIBLE SFN IMPOSSIBLE YES YES HDTV MOBILE RECEPTION IMPOSSIBLE GOOD POSSIBLE PORTABLE RECEPTION BY CELL PHONE IMPOSSIBLE GOOD POSSIBLE INTERNET ACCESS NOT GOOD GOOD POSSIBLE 21
STANDARD FOR INDIA DVB-T AS IT IS WIDELY DEPLOYED THROUGH OUT THE WORLD 22
KEY FEATURES OF DVB-T HIGHLY IMMUNE TO MULTIPATH REFLECTIONS NO.OF CARRIERS :2K AND 8K,4K FOR DVB-H SERVICE GUARD INTERVAL: ¼,1/8,1/16,1/32 MODULATONS:QPSK,16QAM AND 64QAM 23
KEY FEATURES OF DVB-T FEC:CONCATENATED REED SOLOMEN AND CONVOLUTIONAL CODES WITH OUTER AND INNER INTERLEAVERS CONVOLUTIONAL CODES 1/2,2/3,3/4,5/6,7/8 COMPATIBLE FOR MPEG2 AND MPEG4 AVC SUITABLE FOR SD AND HD TELEVISION SUITABLE FOR SINGLE FREQUENCY NETWORK (SFN)IN ADDITION TO MULTI FREQUENCY NETWORK(MFN) 24
KEY FEATURES OF DVB-T SUITABLE FOR HIERARCHIAL AND NON HIERARCHIAL MODULATIONS SUITABLE FOR FIXED TV,INDOOR PORTABLE TV, OUTDOOR PORTABLE TV AND HANDHELD MOBILE TV HIGHLY FLEXIBLE SYSTEM SUITABLE FOR 6MHZ,7MHZ AND 8 MHZ CHANNEL BANDWIDTH NET DATA RATE AVAILABLE FOR PAYLOAD 31.67 MBPS 25
KEY FEATURES OF DVB-T HIGHLY MATURED STANDARD LOW COST SET TOP BOXES 26
STANDARDS ADOPTED BY NATIONS 27
KEY TECHNOLOGIES USED COMPRESSION MPEG2-INEFFICIENT AND OUTDATED MPEG4 PART 10- TWICE EFFICIENT TO MPEG2 AND FUTURISTIC O COFDM- ALL THE STANDARDS FOR DTTB EXCEPT ATSC ARE BASED ON COFDM 28
PROBLEMS FACED IN TERRESTRIAL TRANSMISSION MULTIPATH RECEPTION RESULTING: GHOST IN PICTURE NOISE INTERFERENCE FROM IC ENGINES,CARS ETC RESULTING: IMPULSE INTERFERENCE VARIABLE PATH ATTENUATION RESULTING: FADING CO CHANNEL AND ADJACENT CHANNEL INTERFERENCE RESULTING :POOR PICTURE QUALITY. DOPPLER EFFECT 29
MULTIPATH REFLECTIONS 30
MULTIPATH REFLECTIONS 31
MULTIPATH REFLECTIONS IN SINGLE CARRIER MODULATION,MULTIPATH REFLECTIONS CAUSES INTER SYMBOL INTERFERENCE KNOWN AS ISI, RESULTING POOR PICTURE QUALITY 32
THEN HOW TO CONTROL ISI? INCREASE THE TIME INTERVAL BETWEEN TRANSMITTED SYMBOLS.THAT REDUCES THE SYMBOL RATE. INSERT A GUARD INTERVAL BETWEEN ADJACENT SYMBOLS IN COFDM THE BIT STREAM TO BE TRANSMITTED IS DISTRIBUTED OVER CLOSELY SPACED INDIVIDUAL SUB CARRIERS 33
SOLUTION FOR ALL PROBLEMS? COFDM A MAGIC COFDM - Orthogonal Carriers 34
COFDM 35
OFDM BASED ON SPREADIND DATA OVER LARGE NO.OF CLOSELY SPACED CARRIERS EACH CARRIER MODULATED AT LOW BIT RATE IN FDM THE CARRIERS ARE INDIVIDUALLY FILTERED TO AVOID OVERLAPPING. SO THERE IS NO ISI. BUT THE SCHEME IS SPECTRALLY INEFFICEINT 36
BRIEF HISTORY OF COFDM-1 GREW OUT OF MULTI CARRIER MODULATION (MCM) USED IN MILITARY HF RADIO IN LATE 1950 DIVIDES STREAM INTO SEVERAL PARALLEL BIT STREAMS BIT STREAMS USED TO MODULATE SEVERAL CARRIERS 37
BRIEF HISTORY OF COFDM-2 TIME DOMAIN SIGNAL USED TO ENSURE SUBCARRIER ORTHOGONALITY NO NEED FOR STEEP BAND PASS FILTER SUB CARRIER SPECTRUM ALLOWED TO OVERLAP POPULAR IN 1980 & USED IN DAB COFDM + QPSK 38
COFDM EVERY WHERE DVB-T DVB-T2 DAB ISDB-T DRM WIFI MEDIA FLO DMB-T DVB-C2 EXCEPT ATSC 39
FREQUENCY DIVISION MULTIPLEXING 40
MODULATION 41
FREQUENCY DIVISION MULTIPLEXING 42
COFDM FUNCTIONAL BLOCKS 43
DVB-T FRAMING STRUCTURE OFDM SYMBOL TIME DOMAIN Ts OFDM FRAME Tf OFDM SUPER FRAME GUARD INTERVAL USEFUL INTERVAL 0 67 t Tu t 4 X OFDM FRAMES t 44
OFDM SIGNAL TIME DOMAIN SIGNAL OF OFDM WAVE FREQUENCY DOMAIN SIGNAL OF OFDM WAVE CARRIER 1 + CARRIER 2 f1 + + f2 + + CARRIER K + + = + = fk TRANSMISSION SIGNAL GI ACTIVE SYMBOL DURATION OFDM SYMBOL f1, f2, f3, fk MAGNITUDE SPECTRUM FREQUENCY 45
WHAT COFDM IS ANY WAY? C+O + FDM CODED +ORTHOGONAL + FREQUENCY DIVISION MULTIPLEXING CODED : BECAUSE DATA STREAM IS FEC CODED AND ERROR PROTECTED ORTHOGONAL:SUB CARRIERS ARE PLACED 90DEG APART SO THEY DONOT INTERFERE WITH EACH OTHER FDM : BECAUSE NUMBER OF SUB CARRIERS ARE 2K,4K OR 8K AND ARE FREQUENCY DIVISION MULTIPLEXED 46
COFDM COFDM MAPS THE BINARY INFORMATION OVER SEVERAL THOUSAND CLOSLY SPACED ORTHOGONAL SUB CARRIERS WHICH CARRY PORTION OF DATA STREAM SUCH THAT ECHOS DUE TO MULTIPATH REFLECTIONS ONLY AFFECT FEW OF SUB CARRIERS NOT THE ENTIRE DATA STREAM 47
COFDM THE EFFECTED SYMBOLS ARE RECOVERED BY ERROR CORRECTION DECODING IN THE RECIEVERS. 48
COFDM EACH OF SUB CARRIER IS VECTOR MODULATED EMPLOYING ONE OF MODULATING TECHNIQUE QPSK 16QAM 64QAM 49
COFDM ALL SUB CARRIERS ARE SPACED APART BY CONSTANT INTERVAL Δf 50
COFDM-NUMBER OF SUB CARRIERS IN DVB-T NUMBER OF SUB CARRIERS IN DVB-T STANDARD 2K FOR 2048 POINTS IFFT 8K FOR 8192 POINTS IFFT 4K FOR 4096 POINTS IFFT (DVB-H SERVICE ONLY) 51
COFDM-DOES ALL SUB CARRIERS CARRY PAYLOAD AND ARE TRANSMITTED NO THEY HAVE TO CARRY FOLLOWING CATEGORIES OF DATA PAY LOAD CARRIERS WITH FIXED POSITION INACTIVE CARRIERS WITH FIXED POSITION CONTINUAL PILOTS WITH FIXED POSITION SCATTERED PILOTS WITH CHANGING POSITION TPS CARRIERS WITH FIXED POSITIONS 52
COFDM-ACTUAL NO. OF SUB CARRIERS IN 2K MODE TOTAL NO. OF SUB CARRIERS TRANSMITTED 1705 CARRIERS FOR PAY LOAD -1512 CARRIERS AS PILOTS FOR SYNCHRONIZATION 176 CARRIERS FOR TPS-17 REMAINING CARRIERS ARE SET TO ZERO TPS-TRANSMISSION PARAMETER SIGNALLING 53
COFDM-ACTUAL NO. OF SUB CARRIERS IN 8K MODE TOTAL NO. OF SUB CARRIERS TRANSMITTED 6817 CARRIERS FOR PAY LOAD -6048 CARRIERS AS PILOTS FOR SYNCHRONIZATION 701 CARRIERS FOR TPS- 68 REMAINING CARRIERS ARE SET TO ZERO TPS-TRANSMISSION PARAMETER SIGNALLING 54
COMPARING 2K AND 8K MODE Sr.No. 2K MODE 8K MODE 1. No. OF CARRIERS 1705 6817 2. PAYLOAD CARRIERS 1512 6048 3. CONTINUAL PILOT 45,2.6% OF 1705 177,2.6% OF 6817 4. SCATTERED PILOTS 131,8% OF 1705 524,8% OF 6817 5. TPS CARRIER 17 68 55
DVB-T SYSTEM PARAMETERS IFFT SAMPLING FREQUENCY DVB-T SIGNAL BANDWIDTH SPECTRUM OCCUPIED BY 8,7 AND 6MHZ DVB-T CHANNELS DATA RATE SIGNAL LEVEL OF INDIVIDUAL CARRIER GUARD INTERVAL USEFUL SYMBOL PERIOD TOTAL SYMBOL PERIOD 56
IFFT SAMPLING FREQUENCY ELEMENTRY TIME ELEMENT FOR 8MHZ BANDWIDTH T=Tu/N=7/64 µsec F sampling ifft 8mhz 1/T =64/7 MHZ Tu=USEFUL SYMBOL PERIOD N=FFT SIZE 2048 FOR 2K MODE 8192 FOR 8K MODE 57
USEFUL SYMBOL DURATION IN 2K MODE FOR 8MHZ CHANNEL-Tu T=Tu/N 7/64=Tu/2048 Tu=7/64*2048 =224µsec 58
USEFUL SYMBOL DURATION IN 8K MODE FOR 8 MHZ Tu T=Tu/N 7/64=Tu/8192 Tu=7/64*8192 =896µsec 59
SUB CARRIER SPACING IN 2K MODE FOR 8MHZ CHANNEL-Δf Δf=1/Tu =1/224, Tu=224µsec =4464 Hz 60
SUB CARRIER SPACING IN 8K MODE FOR 8MHZ CHANNEL-Δf Δf=1/Tu =1/896, Tu=896µsec =1116 Hz 61
INTER SYMBOL INTERFERENCE 62
GUARD INTERVAL Tg GURAD INTERVAL IS THE UN-UTILISED SPACE BETWEEN TWO ADJACENT SYMBOLS. GUARD INTERVAL IS USED TO ELEMINATE THE INTER SYMBOL INTERFERENCE BETWEEN ADJACENT SYMBOLS DUE TO MULTIPATH ECHOS MORE THE GUARD INTERVAL MORE THE PROTECTION FROM INTER SYMBOL INTERFERENCE POPULARLY KNOWN AS ISI GUARD INTERVAL MUST BE LONGER THAN LONGEST ECHO DELAY TIME END PORTION OF NEXT SYMBOL IS REPLICATED IN PREVIOUS GUARD INTERVAL G.I. IS CHOOSEN DEPENDING UPON NATURE OF TERRAIN 63
GUARD INTERVAL Tg G.I. IS NECESSARY EVIL AS IT CONSUMES LOT OF DATA CAPACITY GI OF ¼ GIVES MORE PROTECTION FROM ISI AND GI OF 1/32 GIVES LEAST PROTECTION FROM ISI. 64
GUARD INTERVAL IN 2K MODE FOR 8MHZ CHANNEL-Tg DVB-T SPECIFEIES G.I. OF ¼,1/8/1/16 AND 1/32 OF USEFUL SYMBOL DURATION G.I. ¼ 224/4=56µsec 1/8 224/8=28µsec 1/16 224/16=14µsec 1/32 224/32=7µsec 65
TOTAL SYMBOL DUARTION IN 2K MODE FOR 8MHZ CHANNEL-Ts Ts=Tu+Tg FOR G.I. ¼ Ts=224+56=280µsec 1/8 Ts=224+28=252µsec 1/16Ts=224+14=238µsec 1/32Ts=224+7=231µsec 66
SYMBOL FREQUENCY/RATE IN 2K MODE 8 MHZ CHANNEL FOR G.I. ¼ 1/280=3.5714KHZ 1/8 1/252=3.9683KHZ 1/16 1/238=4.2017KHZ 1/32 1/231=4.3290KHZ 67
BANDWIDTH UTILIZED IN 2K MODE FOR 8MHZ CHANNEL BWdvb-t=NUMBER OF CARRIERS USED*SUB CARRIER SPACING =1705*4464 =7.611MHZ BANDWIDTH OF 200KHZ ON EACH SIDE OF 8MHZ CHANNEL IS LEFT UNUSED 68
GUARD INTERVAL IN 8K MODE FOR 8MHZ CHANNEL-Tg DVB-T SPECIFEIES G.I. OF ¼,1/8/1/16 AND 1/32 OF USEFUL SYMBOL DURATION G.I. ¼ 896/4=224µsec 1/8 896/8=112µsec 1/16 896/16=56µsec 1/32 224/32=28µsec 69
TOTAL SYMBOL DUARTION IN 8K MODE FOR 8MHZ CHANNEL-Ts Ts=Tu+Tg FOR G.I. ¼ Ts=896+224=1120µsec 1/8 Ts=896+112=1008µsec 1/16Ts=896+56=952µsec 1/32Ts=896+28=924µsec 70
SYMBOL FREQUENCY/RATE IN 8K MODE 8 MHZ CHANNEL FOR G.I. ¼ 1/1120=0.8929KHZ 1/8 1/1008=0.9920KHZ 1/16 1/952=1.0504KHZ 1/32 1/924=1.0823KHZ 71
BANDWIDTH UTILIZED IN 8K MODE FOR 8MHZ CHANNEL BWdvb-t=NUMBER OF CARRIERS USED*SUB CARRIER SPACING =6817*1116 =7.607MHZ BANDWIDTH OF 200KHZ ON EACH SIDE OF 8MHZ CHANNEL IS LEFT UNUSED 72
BANDWIDTH USED IN 2K AND 8K MODE SAME BANDWIDTH IS USED IN 2K AND 8K MODE 7.61MHZ 73
GROSS DATA AVAILABLE FOR 8MHZ CHANNEL GROSS DATA RATE AVAILABLE=SYMBOL RATE OFDM*No OF PAYLOAD SUB CARRIERS*BITS PER SYMBOL EXAMPLE: MODE 2K,GI 1/32,MOD 64QAM SYMBOL RATE FROM SLIDE NO.49-4.329KSPS 74
GROSS DATA AVAILABLE FOR 8MHZ CHANNEL =4.329*1512*6 =39.273MBPS 75
NET DATA RATE AVAILABLE FOR 8MHZ CHANNEL DEPENDS UPON REED SOLOMON AND CONVOLUTIONAL CODE USED NET DATA RATE AVAILABLE=GROSS DATA RATE AVAILABLE*188/204*CODE RATE EXAMPLE: 39.273*188/204*7/8 =31.66 MBPS 76
GROSS DATA AVAILABLE IN 8MHZ CHANNEL FOR VARIOUS SCHEMES MODUL ATION 2K MODE GUARD INTERVAL 8K MODE GUARD INTERVAL 1/4 1/8 1/16 1/32 1/4 1/8 1/16 1/32 QPSK 10.8 12.0 12.7 13.0 9 10.8 12.0 12.7 13.0 9 16QAM 21.6 24.0 25.4 1 26.1 82 21.6 24.0 25.4 1 26.1 82 64QAM 32.4 36.0 38.1 1 39.2 7 32.4 36.0 38.1 1 39.2 7 77
NET DATA AVAILABLE IN 8MHZ CHANNEL FOR VARIOUS SCHEMES MODULATI ON FEC CODE RATE 2K MODE GUARD INTERVAL 1/4 1/8 1/16 1/32 8K MODE GUARD INTERVAL 1/4 1/8 1/16 1/32 QPSK 1/2 4.97 5.52 5.85 6.03 4.97 5.52 5.85 6.03 QPSK 2/3 6.63 7.37 7.80 8.04 6.63 7.37 7.80 8.04 QPSK 3/4 7.46 8.29 8.78 9.04 7.46 8.29 8.78 9.04 QPSK 5/6 8.29 9.21 9.75 10.05 8.29 9.21 9.75 10.05 QPSK 7/8 8.70 9.67 10.24 10.55 8.70 9.67 10.24 10.55 78
NET DATA AVAILABLE IN 8MHZ CHANNEL FOR VARIOUS SCHEMES MODULA TION FEC CODE RATE 2K MODE GUARD INTERVAL 1/4 1/8 1/16 1/32 8K MODE GUARD INTERVAL 1/4 1/8 1/16 1/32 16QAM 1/2 9.95 11.05 11.7 12.06 9.95 11.05 11.7 12.06 16QAM 2/3 13.27 14.74 15.61 16.08 13.27 14.74 15.61 16.08 16QAM 3/4 14.92 16.58 17.56 18.09 14.92 16.58 17.56 18.09 16QAM 5/6 16.58 18.43 19.51 20.1 16.58 18.43 19.51 20.10 16QAM 7/8 17.41 19.35 20.49 21.11 17.41 19.35 20.49 21.11 79
NET DATA AVAILABLE IN 8MHZ CHANNEL FOR VARIOUS SCHEMES MODULA TION FEC CODE RATE 2K MODE GUARD INTERVAL 1/4 1/8 1/16 1/32 8K MODE GUARD INTERVAL 1/4 1/8 1/16 1/32 64QAM 1/2 14.92 16.58 17.56 18.09 14.92 16.58 17.56 18.09 64QAM 2/3 19.90 22.11 23.41 24.12 19.90 22.11 23.41 24.12 64QAM 3/4 22.39 24.88 26.34 27.14 22.39 24.88 26.34 27.14 64QAM 5/6 24.88 27.64 29.27 30.16 24.88 27.64 29.27 30.16 64QAM 7/8 26.12 29.02 30.73 31.66 26.12 29.02 30.73 31.66 80
2K VS 8K MODE 8K MODE HAS EXACTLY 4 TIMES AS MANY PAYLOAD CARRIERS AS 2K MODE IN 2K MODE SYMBOL RATE IS 4 TIMES TO THAT OF 8K MODE SO BOTH THE MODES WILL HAVE SAME DATA RATE FOR SAME TRANSMISSION PARAMETERS 81
2K VS 8K MODE 8K MODE IS RECOMMENDED FOR SINGLE FREQUENCY NETWORK. 2K MODE IS RECOMMENDED FOR MULTI FREQUENCY NETWORK BANDWIDTH CONSUMED BY BOTH MODE IS SAME. 8K MODE IS MORE RESILIENT TO MULTIPATH REFLECTIONS. 82
PILOT SIGNALS CONTINUAL PILOTS O ALWAYS IN THE SAME POSITION WITHIN COFDM SYMBOL O 45 IN 2K MODE AND 177 IN 8K MODE O TRANSMITTED AT INCREASED POWER LEVEL O USED TO ESTIMATE CHANNEL CHARACTERISTICS AND MAKE CORRECTION 83
PILOT SIGNAL SCATTERED PILOTS LOCATED AS A PRE DEFINED PATTERN EQUAL NO PER SYMBOL 131 IN 2K MODE AND 524 IN 8K MODE TRANSMITTED AT INCREASED POWER LEVELS USED IN CONJUCTION WITH CONTINUAL PILOTS TO ESTIMATE CHANNEL ERRORS 84
TRANSMISSION PARAMETER SIGNALLING (TPS) CARRIED BY TPS PILOT CARRIERS USED TO CONVEY INFORMATION ABOUT GUARD INTERVAL,MODULATION, CODE RATE,2K/8K MODE,HIERARCHIAL INFORMATION,FRAME NUMBER WITHIN SUPER FRAME TPS IS TRANSMITTED USING DBPSK OF THE TPS PILOTS OVER 68 CONSEQUTIVE SYMBOLS CORRESPONDING TO OFDM FRAME DBPSK IS USED DUE ITS RUGGEDNESS 85
COMPATIBILITY FOR 6MHZ AND 7MHZ CHANNELS DVB-T IS COMPATIBLE WITH 6 AND 7 MHZ CHANNELS WHERE EVER REQUIRED BUT WITH REDUCED DATA CAPACITY IN PROPORTION TO CHANNEL BANDWIDTH. 86
FEC EMPLOYED IN DVB-T REED SOLOMEN CODE AS OUTER CODE OUTER INTERLEAVER CONVOLUTIONAL CODING INNER INTERLEAVER 87
FEC-OUTER CODE-REED SOLOMEN CODE IT IS A BLOCK CODE ADDES 16 PARITY BYTES TO ORIGINAL 188 DATA BYTES MAKING PACKET LENGTH OF 204 BYTES INCREASING OVERHEADS CAPABLE OF CORRECTING EIGHT ERRORED BYTES PER TRANSPORT PACKET OPERATES OVER INDIVIDUAL PACKETS CAPABLE OF REDUCING BER FROM 2X10 4 TO 2X10 11 FOR QEF DECODING BANDWIDTH OVERHEAD IS 8% 88
ERROR BURSTS ERROR DOES NOT OCCURE IN SINGLE BIT BUT IN MANY SUCCESSIVE BITS KNOWN AS ERROR BURSTS EFFECTS HUNDREDS OF BITS RS CODE CANNOT CORRECT MORE THAN 8 ERRORED BYTES IN A TS PACKET SO INTERLEAVER INSERTS UPTO 2244 BYTES FROM OTHER TS PACKETS THAT SPREADS ERRORS BRINGING UNDER THE CONTROL OF RS CODE 89
FEC-OUTER INTERLEAVER(BYTE WISE) O ALSO KNOWN AS FORNEY CONVOLUTIONAL INTERLEAVER IS USED TO PROTECT MPEG STREAM FROM BURSTY NOISE AND ERRORS TAKES 12 TS PACKETS IN PARALLEL AND FEED A BYTE INTO CYCLIC BUFFER INCREASES EFFIECIENCY OF R-S CODE 90
FEC-INNER CODE- CONVOLUTIONAL CODE 1.IT IS A BIT LEVEL CODE 2.PROVIDES A SECOND LAYER OF FORWARD ERROR CORRECTION. 3.TARGET BER IN RECEIVER AFTER ERROR CORRECTION IS 10-11, CORRESPONDING TO ROUGHLY ONE UNCORRECTED ERROR PER HOUR. 4.TARGET BER 10 4 CAN BE ACHIEVED WITH CHANNEL BER<10-2. 5.CHOICE OF CODE RATES OF 1/2, 2/3, 3/4, 5/6, 7/8 ALLOWS TRADING OF BANDWIDTH AND ERROR PERFORMANCE. 91
FEC-INNER INTERLEAVER (FREQUENCY) SPLITS TS INTO 2 STREAMS FOR QPSK SPLITS TS INTO 4 STREAMS FOR 16 QAM SPLITS TS INTO 6 STREAMS FOR 64QAM BLOCK SIZE IS 126BITS,I=12 FOR 2K SYSTEM=1512 BITS SYMBOL INTERLEAVER TAKES 1512 BITS FROM INTERLAEVER 92
SYMBOL INTERLEAVER IN 2K MODE 12 GROUPS OF 126 INTERLEAVED DATA WORDS (1512 BITS) ARE COMBINED TO DATA GROUP IN 8K MODE 48 GROUPS OF 126 INTERLEAVED DATA WORDS (6048 BITS) ARE COMBINED TO DATA GROUP DATA GROUPS ARE INTERLEAVED BY SYMBOL INTERLEAVER TO GENERATE COFDM SYMBOL LEAVES THE SUB CARRIERS FREE FOR DIFFERENT TYPES PILOTS 93
FEC CHAIN 94
GRAY CODE MAPPING-QPSK 95
GRAY CODE MAPPING- 16QAM 96
GRAY CODE MAPPING-64QAM 97
HIERARCHIAL MODULATION ALLOWS TO TRANSMIT TWO DIGITAL DATA STREAMS VIA ONE TRANSMITTER LOW PRIORITY STREAM- LP STREAM & HIGH PRIORITY STREAM-HP STREAM 98
LP STREAM HIGH DATE RATE REQUIRES HIGHER C/No SUITABLE FOR FIXED TV RECEPTION 99
HP STREAM LOW DATA RATE REQUIRES LOWER C/No VERY REBUST SUITABLE FOR MOBILE RECEPTION 100
QPSK IN 64QAM 101
QPSK IN 16QAM 102
APPLICATIONS OF HIERARCHIAL MODULATION 1.TRANSMIT SERVICES TO FIXED AND PORTABLE TV AT SAME TIME 2.TRANSMIT SERVICES TO FIXED AND MOBLIE TV AT SAME TIME 3.TRANSMIT SD TV AND HD TV AT SAME TIME 103
HIERARCHIAL CHAIN 104
DVB-T TRANSMITTER CHAIN 105
ENERGY DISPERSAL PREVENTS THE GENERATION OF UNMODULATED CARRIERS BY MODULATOR ENSURES ADEQUATE BINARY TRANSITIONS PSEUDO RANDOM BINARY SEQUENCE (PRBS) IS USED IN ENERGY DISPERSAL 106
DATA SCRAMBLING INITIALIZATION SEQUENCE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ENABLE 1 RANDOMIZED DATA OUTPUT DATA INPUT 107
DATA SCRAMBLING PSEUDO RANDOM BINARY SEQUENCE ( PRBS) ENERGY DISPERSAL ENSURES ADEQUATE BINARY TRANSITIONS 108
MAPPER MAPPER MODULATES ENCODED TS ONTO QPSK,16QAM OR 64QAM CONSTELLATIONS BOTH HIERARCHIAL AND NON HIERARCHIAL MODULATIONS ARE SUPPORTED 109
FRAME ADAPTATION INSERTION OF PILOT CARRIERS USED FOR SYNCHRONISATION AND CHANNEL EASTIMATION INSERTION OF TPS CARRIERS 110
COFDM PERFORMS IFFT WITH 2K OR 8K SUB CARRIERS 111
GUARD INTERVAL INSERTION INSERTS G.I TO REDUCE ISI 112
D/A INTERPOLATES THE COFDM SIGNAL PRODUCING ANALOG SIGNAL 113
RF FRONT END SHIFTS BASE BAND IQ SIGNALS TO PROPER CARRIER FREQUENCY 114
DVB-T RECIEVER CHAIN 115
COVERAGE AREA OF DVB-T TRANSMITTER 116
DVB-T2,NEW 2 nd GENERATION STANDARD DEVELPOD FOR POST ANALOGUE SWITCH OFF BASED ON PROVEN COFDM STANDARD BASED ON FULLY DEVELPOED STANDARD DVB-S2 STANDARD BASED ON NEW ERROR CORRECTION AND MODULATION SCHEMES. EMPLOYS LDPC CODE INSTEAD OF CONVOLUTIONAL CODE EMPLOYS BCH CODE INSTEAD OF REED SOLOMEN CODE EXPECTED TO PROVIDE 30-50% MORE DATA IN SAME BANDWIDTH AND SAME RECEPTION CONDITIONS 117
DVB-T2,NEW 2 nd GENERATION STANDARD CAN EMPLOY UPTO 256QAM AND 32K TO PROVIDE DATA CAPACITY OF 35.9Mbps USE OF HIGHER ORDER MODULATION NEEDS MORE POWERFUL FEC PILOT STRUCTURE CARRIER IS MODIFIED TO REDUCE THE OVERHEADS FROM 8 % TO 1 % 16 K AND 32 K MODES ARE AVAILABLE MAXIMUM GUARD INTERVAL IS 500 µsec THAT IMPROVES S/N BEST SUITABLE FOR NATION WIDE SFN 118
DVB-T2 BENEFITS MUCH BETTER FLEXIBLE SYSTEM DUE TO NEW ERROR CORRECTION CODES CAPABLE OF DELIVERING UPTO 3 HD TV INSTEAD OF ONE HDTV IN DVB-T CAPABLE OF DELIVERING TO MOBILE RECIEVERS IN MORE EFFICENT WAY AT HIGHER DATA RATE REDUCES PEAK TO AVERAGE POWER RATIO THAT HELPS TO TRANSMIT MORE POWER FROM SAME TRANSMITTER 119
DVB-T2 BENEFITS STILL IN ITS CHILDHOOD NEEDS TIME TO MATURE EQUIPMENT IS VERY COSTLY COMPARED TO STANDARD DVB-T 120
COMPARING DVB-T2 WITH DVB-T DVB-T DVB-T2 FEC MODULATIONS CONVOLUTIONAL + REED SOLOMEN CODE ½,2/3,3/4,5/6,7/8 QPSK,16QAM,64QAM LDPC+BCH ½,3/5,2/3,3/4,4/5,5/6 QPSK,16QAM,64QAM,256QAM GUARD INTERVALS FFT SIZE ¼,1/8,1/16,1/32 2K,8K ¼,19/256,1/8,19/128,1/16,1/ 32, 1/128 1K,2K,4K,8K,16K,32K SCATTERED PILOTS CONTINUAL PILOTS 8% OF TOTAL 2.6% OF TOTAL 1%,2%,4%,8% OF TOTAL 0.35% OF TOTAL 121
GENERIC DTTB TRANSMITTER CHAIN 122
GENERIC DTTB TRANSMITTER CHAIN A DVB-T TRANSMITTER MODULATES THE ASI TS SIGNAL OVER AT IF OF 36.15 MHZ USING CODFM MODULATION SCHEME. THE MODULATED IF IS UPCONVERTED TO DESIRED CHANNEL FOR TRANSMISSION. THE UPCONVERTED SIGNAL IS SUITABLY AMPLIFIED IN POWER AMPLIFIERS THE AMPLIFIED OUTPUT IS PASSED THROUGH CAVITY BAND PASS FILTER TO AVOID INTERFERENCE WITH ADJACENT CHANNEL 123
POWER AMPLIFIERS PAs ARE THE HEART OF ANY DVB-T TRANSMITTER PEAK TO AVERAGE POWER RATIO (PAR) IN DVB-T TRANSMISSION IS AROUND 15-17dB. THEY NEED TO BE HIGHLY LINEAR THAN THE EXISTING POWER AMPLIFIERS FOR ANALOGUE TRANSMISSION TO DEAL WITH WITH HIGHER PAR SO POWER AMPLIFIERS BUILT WITH LD-MOSFETs AND IOT ARE ONLY SUITABLE FOR DVB-T TRANSMISSSION PAs BUILT WITH BIPOLAR TRANSISTORS AND NORMAL MOSFETS ARE NOT SUITABLE FOR DVB-T TRANSMISSION 124
MANUFACTURES OF SOURCE CODING EQUIPMENT ENCODERS BASED ON MPEG2 & MPEG4 AND MULTIPLEXER TANDBERG SCOPUS GRASS VALLEY HARRIS ENVIVO AND MANY OTHERS 125
ENCODERS AND MULTIPLEXERS 126
MANUFACTURES OF TRANSMITTERS NEC SOLID STATE R&S- SOLID STATE HARRIS- SOLID STATE AND IOT THOMCAST- SOLID STATE AND IOT TOSHIBA- SOLID STATE AXCERA- SOLID STATE AND IOT PLISCH- SOLID STATE AND DOZON OF ITALIAN COMPANIES 127
DTTB TRANSMITTERS FROM VARIOUS MANUFACTURERS 128
SET TOP BOXES ARE USED TO RECEIVE THE COFDM SIGNAL,DEMODULATE THEM AND DECODE THEM USING EITHER MPEG2 OR MPEG4 DECODER OUTPUTS THROUGH CCVS,COMPONENT VIDEO,HDMI & SCART RECEPTION ALSO POSSIBLE FOR PERSONAL COMPUTERS AND LAP TOPS USING DVB-T PCI,PCMCIA CARDS AND DVB-T USB2 CARDS 129
SET TOP BOX 130
REFERENCES WWW.DVB.ORG.UK WWW.DTG.ORG WWW.DIGITAG.ORG WWW.EBU.ORG WWW.ETSI.ORG TRAINING MATERIAL FROM STI(T) 131