applematt
23-06-2007, 02:15 PM
Who Has the Most Room for HDTV?
-------- -- Terrestrial -- Satellite -- Satellite
Bandwidth - 6 MHz - 24 MHz - 36 MHz
Modulation - 8 VSB - QPSK -QPSK
Bit Rate - 19.39 Mbps -27 Mbps -40.44 Mbps 2
Satellite providers also have similar compression challenges.
Transponder space (the satellite-located transmission systems) is so expensive that compression is required for everything. Popular channels are typically encoded at 15 Mbps or more before they go to the satellite operators. Depending on the available satellite bandwidth (could be 24 MHz or 36 MHz, which yields 27 Mbps and 40.44 Mbps of bandwidth respectively), satellite operators can compress these 15Mbps signals down to 13.5 Mbps, so they can cram two or three HDTV streams on these satellite signals,
respectively.
Who’s required to do what?
Your over-the-air digital TV broadcaster only has 6 MHz (19.39 Mbps) of bandwidth
over which it can send its TV signals. It can fill this in anyway it chooses, combining
such broadcasts as HDTV, ****, weather images, and even FM broadcasts onto
one bandwidth stream. The FCC, through its DTV rules, has said broadcasters must
transmit one standard-definition digital-TV signal — 480i — and has not said anything
about requiring HDTV.
So TV stations have to make some economic decisions about how best to use that
signal. In one chunk of 6MHz bandwidth, a broadcaster could send one full-quality,
720p 60-frame-per-second (fps) HDTV program; or, two shows, one (say) for a 720p
or 1080i HDTV show and one 480i **** show, both at 30 fps; or, four 480i **** 30
fps shows. How a station mixes and matches its signals depends as much on its
technology as its positioning in the market.
-------- -- Terrestrial -- Satellite -- Satellite
Bandwidth - 6 MHz - 24 MHz - 36 MHz
Modulation - 8 VSB - QPSK -QPSK
Bit Rate - 19.39 Mbps -27 Mbps -40.44 Mbps 2
Satellite providers also have similar compression challenges.
Transponder space (the satellite-located transmission systems) is so expensive that compression is required for everything. Popular channels are typically encoded at 15 Mbps or more before they go to the satellite operators. Depending on the available satellite bandwidth (could be 24 MHz or 36 MHz, which yields 27 Mbps and 40.44 Mbps of bandwidth respectively), satellite operators can compress these 15Mbps signals down to 13.5 Mbps, so they can cram two or three HDTV streams on these satellite signals,
respectively.
Who’s required to do what?
Your over-the-air digital TV broadcaster only has 6 MHz (19.39 Mbps) of bandwidth
over which it can send its TV signals. It can fill this in anyway it chooses, combining
such broadcasts as HDTV, ****, weather images, and even FM broadcasts onto
one bandwidth stream. The FCC, through its DTV rules, has said broadcasters must
transmit one standard-definition digital-TV signal — 480i — and has not said anything
about requiring HDTV.
So TV stations have to make some economic decisions about how best to use that
signal. In one chunk of 6MHz bandwidth, a broadcaster could send one full-quality,
720p 60-frame-per-second (fps) HDTV program; or, two shows, one (say) for a 720p
or 1080i HDTV show and one 480i **** show, both at 30 fps; or, four 480i **** 30
fps shows. How a station mixes and matches its signals depends as much on its
technology as its positioning in the market.