ATSC Digital Television
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Transcript of ATSC Digital Television
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ATSC Digital Television Advanced Television Systems Committee standards for broadcast digital television
Presented by Andrew Sonnek
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Objectives of DTV Increase picture resolution by up to 5x Support AC-3 5.1 channel audio (standard of
Dolby Digital) Maximize bandwidth allocation by using
complex video and audio compression Reduce the bit rate by a factor of 50 or higher Preserve the high level of quality required for
the application
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DTV Picture Resolution Standards
Vertical Lines
Horizontal Pixels
Aspect Ratio
Picture Rate
Standard Definition 480 640 4:3 60I, 60P,
30P, 24PStandard Definition 480 704 16:9 60I, 60P,
30P, 24PExtended Definition 720 1280 16:9 60P,
30P, 24PHigh Definition 1080 1920 16:9 60I, 30P,
24P
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Uncompressed VideoAssuming 480p @ 30 frames/sec.
* See: ftp://ftp.jacweb.jvc.com/jvcpro/justbitsfree.pdf
Y720 pixels /
linex
480 lines / frame
x30
frames / sec
x8
bits / pixel
= 83 Mbps
CRCB 360 x 480 x 30 x 16 = 83 Mbps166
Mbps
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The ChallengeThe ATSC allocates 6 MHz for a single
channelSo…
Over the air 6 MHz =~ 19 MbpsOver coaxial Cable TV line =~ 38 Mbps
From our last calculations…Uncompressed 480p signal = 166 Mbps!!
When in distress… compress!
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Video CompressionFilm mode encoding – encoder
recognizes a film source of less than 60 fps and will only encode at a rate of 30 fps or 24 fps
Uses source-adaptive processing – maximize compression techniques depending on spatial resolution, temporal resolution, and scanning rate.
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Video Compression Uses the MPEG-2 compression layers as a
basis for the DTV compression standard Because of limitations of MPEG-2 standard,
the DTV standard is only based on MPEG-2 standards. A DTV compressed video stream is NOT an MPEG-2 video stream so a MPEG-2 decoder will not decode DTV signals
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Audio Compression Audio is compressed using the AC-3 (Digital
Audio Compression Level 3) Standard developed by Dolby Labs. AC-3 is commonly known as Dolby Digital.
AC-3 supports 1 mono channel to 5.1 channels per service with multi service support up to 640 kbps total
Frequency range from 20Hz – 20kHz Sample rate of 48kHz @ 16 bits/sample
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DTV SubsystemsBased on International Telecommunications Union – Task Group 11/3
Diagram from ATSC Doc A/54
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Source Coding and Compression SubsystemResponsible for minimizing the number
of bits needed to represent the video, audio, and control data through:
- Video compression- Audio compression- Encoding ancillary data
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Ancillary Data Includes:
- Control data- Conditional access control- Audio & video associated data
such as closed captioning- Independent program services- Program guides- Text based emergency messages
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Service Multiplex and Transport SubsystemBased on the MPEG standard for fixed-
length transport stream packetizationResponsible for multiplexing all video,
audio, and ancillary data streams, creating one data stream compatible with terrestrial and cable transmission, and inserting local programming using flags
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Advantages of MPEG Transport Standards Easy to detect and correct errors while
broadcasting moderately long fixed-length packets over air or cable
Can accommodate video, audio, and data Expandable for future services Operational with other media and standards Packets can be easily partitioned for transfer
in a link layer that supports ATM transmission
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PID (Packet Identifier) Used in the packet header to identify
separate audio, video, and data packets in a multiplexed stream.
Do not need to be specified in advance! Allows for the allocation for the entire channel
so data to be sent in bursts e.g. – send out an encryption key to thousands of subscribers of a pay-per-view at one time or download program related software to a “smart receiver”
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Transport Packet
4 Byte Header Data
Variable length Adaptation Header
188 Byte Packet
Header includes – synchronization bit, PID, error handling counter
Adaptation Header can include – blank bits for packet sizing, keys for conditional access control, and local programming flags
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RF/Transmission SubsystemResponsible for:
- Channel coding- Modulation
Channel coding inserts additional data for the receiver to reconstruct the original data stream
Modulation converts the digital data stream into a transmittable signal
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High Data Rate ModeTwice the bandwidth as terrestrial modeDivides the amplitude into more data
levelsDoes not work as well over long
distancesTerrestrial mode used for most over-
the-air broadcasts
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Sub-channels6 MHz frequency can be divided up into
at most 4 sub-channelsUsed to broadcast multiple
programming options or multimedia channels
Good for programming that does not require high resolutions