Tutorial on the Grand Alliance HDTV System FCC Field Operations Bureau July 27, 1994 Robert Hopkins ATSC 27 July 1994 1
Tutorial on the Grand Alliance HDTV System Background on USA HDTV Why there is a Grand Alliance Basic Grand Alliance HDTV System specifications Tutorial using block diagrams of Grand Alliance HDTV System Issues for FCC Field Operations Bureau 27 July 1994 2
Background on USA HDTV ATSC formed in 1982 FCC Advisory Committee on Advanced Television Service formed in 1987 Over 20 proposals for ATV broadcasting First digital HDTV proposal in 1990 Field narrowed to four digital HDTV and one analog HDTV proposals Proposals tested during 1991 and 1992 27 July 1994 3
No Single Winner from Testing Four digital HDTV systems were found superior to the analog system Each digital HDTV system had some superior characteristics No one digital HDTV system was considered to have overall superiority 27 July 1994 4
Why There Is a Grand Alliance The Advisory Committee suggested the four digital HDTV proponents get together in a Grand Alliance combining the best parts of each system. On May 24, 1993 the Digital HDTV Grand Alliance was formed. 27 July 1994 5
Grand Alliance (GA) Members AT&T David Sarnoff Research Center General Instrument MIT Philips North America Thomson Consumer Electronics Zenith Electronics Corporation 27 July 1994 6
Basic GA Specifications Video formats: 1280 (H) x 720 (V) progressive scan at 60 Hz, 30 Hz, and 24 Hz 1920 (H) x 1080 (V) interlaced scan at 60 Hz, progressive scan at 30 Hz and 24 Hz Vertical rates also at 59.94 Hz, 29.97 Hz, and 23.98 Hz. Video compression: MPEG-2 (Main Profile at High Level) Audio compression: Dolby AC-3 Transport: MPEG-2 Transport Stream RF modulation 8-VSB 27 July 1994 7
Grand Alliance Encoder Video source Audio source Ancillary data Video compressor Audio compressor M u l t i p l e x e r Modulator RF output 27 July 1994 8
Video Compression Encoder Video input Pre-processer New picture S Difference picture DCT Quantizer Previous picture Predicted picture Inverse quantizer Motion estimator Motion compensated predictor Picture memory S Inverse DCT Motion vectors Encoded coefficients Control data Entropy encoder Buffer fullness Buffer Packetizer PES packets 27 July 1994 9
Motion Prediction Blocks 1 2 3 4 1 2 3 4 5 6 7 8 5 6 7 8 9 10 12 9 10 11 12 11 14 13 15 16 13 14 15 16 Blocks of previous picture used to predict new picture. Previous picture after using motion vectors to adjust block positions. 27 July 1994 10
DCT Coefficients DC coefficient DC coefficient Zigzag scan Alternate zigzag scan 27 July 1994 11
Coded Video Sequence Backward motion prediction Forward motion prediction B I B P B P B P B P B P B I B Display order 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Transmission order 2 1 4 3 6 5 8 7 10 9 12 11 14 13 16 Intra coded picture Bidirectionally coded picture Predictively coded picture 27 July 1994 12
Video Compression Decoder Inverse quantizer Inverse DCT S New picture Video output PES packets Encoded coefficients De-packetizer Rate Buffer Predicted picture Entropy decoder Motion compensated predictor Motion vectors Picture memory Previous picture Control data 27 July 1994 13
AC-3 Audio Encoder Ideal bit allocator Bit allocation supervisor Bit allocation side information PCM audio in TDAC transform filter bank Mantissas Quantizer Bit allocation Multiplexer Encoded AC-3 bit stream Core bit allocator Spectral envelope decoder Exponents Spectral envelope encoder Spectral envelope 27 July 1994 14
AC-3 Audio Decoder Inverse quantizer Mantissas Encoded AC-3 bit stream Demultiplexer Bit allocation side information Core bit allocator Bit allocation Inverse TDAC filter bank PCM audio out Spectral envelope Spectral envelope decoder Exponents 27 July 1994 15
MPEG-2 Packets Video data Audio data Video encoder Audio encoder Packetizer Packetizer Video PES packets Audio PES packets Program stream multiplexer MPEG-2 Program Stream packets Ancillary data A Packetizer Transport stream MPEG-2 Transport Stream packets multiplexer Program Stream packets are designed for relatively error-free environments. Transport Stream packets are designed for environments where errors are likely. The Grand Alliance HDTV System uses Transport Stream packets. 27 July 1994 16
System Level Multiplex Studio A Video PES packets Audio PES packets MUX Program A Transport stream Ancillary data A MUX System level multiplex Studio B Video PES packets Audio PES packets MUX Program B Transport stream Ancillary data B 27 July 1994 17
VSB Data Frame 4 832 symbols 1 Field sync #1 312 segments 1 S e g m e n t Data + FEC Field sync #2 48.6 ms 312 segments s y n c Data + FEC 1 segment = 77.7 µs 27 July 1994 18
VSB Transmitter Data Data randomizer Reed-Solomon encoder Data interleaver Trellis encoder Segment sync Multiplexer Pilot insertion VSB modulator RF upconverter Field sync 27 July 1994 19
Grand Alliance VSB Receiver Tuner IF filter & synchronous detector NTSC rejection filter Equalizer Phase tracker Sync & timing Trellis decoder Data de-interleaver Reed-Solomon decoder Data de-randomizer Data 27 July 1994 20
Grand Alliance VSB Equalizer Input symbols S 78 tap filter S Equalized symbols Slicer 177 tap filter Field sync Coefficients Filter coefficient calculator Training sequence Rejection comb in/out 27 July 1994 21
FCC Field Operations Bureau Issues Co-channel and adjacent channel interference into NTSC will increase slightly. The visual effect will be the same as if the signal got weaker more snow. Interference into digital HDTV will not affect pictures and sound, but it will cause the digital HDTV threshold signal level to increase. This is true for co-channel interference, adjacent channel interference, electrical interference, ghosts, etc. 27 July 1994 22
FOB Issues (continued) Propagation effects will be the same as they are for NTSC (for example, inversion layers). People who buy HDTV will pay more money; they will put up good antennas; and they will expect fast resolution of interference problems. 27 July 1994 23
FOB Issues (concluded) Anticipate Advisory Committee recommendation to FCC in Spring 1995. Anticipate FCC Rules by end of 1995. Anticipate some digital HDTV on-the-air in 1998. TV monitoring equipment in trucks and in field offices will need to be in place. So, budget now! 27 July 1994 24