At 10:27 AM -0500 11/13/06, Manfredi, Albert E wrote:
There is also NOTHING you can do for legacy DVB-T receivers to take advantage of DVB-H, or to take advantage of HDTV. And yet, no one would argue that DVB-H and HDTV are incompatible with DVB-T. They are, instead, compatible post-facto additions to the standard.
NO. HDTV was fully defined in the DVB standards from day one. MPEG-4 is an addition, but it fits with NO OTHER CHANGES to the standard. As people keep telling you Bert, the Europeans made the logical decision to START with SDTV, then migrate to HDTV in the future.
This IS NOT as A-VSB it to ATSC. A-VSB is a completely new modulation scheme that happens to be backward compatible to 8-VSB (i.e. it does not break legacy receivers). And it takes a bandwidth toll if you want to use it to improve reception, while you can transmit HDTV bits with DVB without any change to the receivers.
In Europe, in order to maintain compatibility with SDTV sets and not reduce SD programming choices, HDTV is having to be transmitted on new dedicated frequencies. Which in practice means that HDTV choices will be more scarce. And in order to fit HDTV in the multiplexes, a reduction of robustness is going to be required, as the HDTV multiplexes go to 64-QAM vs the 16-QAM used for SD.
Sounds like good decision making to me. As countries in Europe are recovering analog spectrum, they can now use it to deliver a new HD service alongside the existing SDTV service. They can also move to 8K carrier schemes for the HD service, which will improve the bandwidth throughput. And, over time they can reduce SD choice as more HD content becomes available, OR they can allocate more bandwidth to portable/handheld services is this is the direction the market wants to go. In each case there is no change to the transmitters, other than dialing in the desired operating mode(s).
Over here, the HDTV choices are already available, but the more robust options are not yet. So, opposite what Euro DTT is doing, the US model started with HDTV and then adds the robust modes, potentially usable for SD streams.
Robust options are becoming available, however, not from ATSC broadcasters. Given the politics involved, my guess is that full powered broadcasters will NOT use A-VSB in the U.S., as they would need to field their own receivers and promote the service. They won't even do this for ATSC.
STS 1/4 rate is "worst case" in the sense that it removes more legacy 8-VSB compatible bandwidth than any other A-VSB mode.
Actually this is a variable. There are four modes for SRS and a bunch of modes for STS. 1/4 rate delivers less (1/2) payload than 1/2 rate for the same loss of bits. But SRS can use more bits at the higher insertion rates.
SRS, instead, can be tuned to whatever level of robustness you want. Add one byte at a time of training sequence, if you want, until you achieve the required robustness. And the remining payload remains compatible with legacy receivers. It is intellectually dishonest, there is no other word for it, to pretend that A-VSB is incompatible with 8-VSB.
Call it what you want Bert. It is still a major change for broadcasters that will require entirely new receivers to obtain the benefits, and if used, will reduce the payload available to legacy receivers.
The real question, however, remains...Is it worth it, versus moving to other alternatives that may provide services that the majority of U.S. viewers will ACTUALLY USE.
Sorry Bert, but keeping highly valuable spectrum resources tied up so that a tiny percentage of the U.S. viewing audience can enjoy HDTV broadcasts via legacy receivers is nearly as badly broken as Social Security.
Talk about false economy... Regards Craig ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways:- Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org
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