[opendtv] Re: Every ATSC receiver sold prior to 5th generation is non-functional?
- From: Richard Hollandsworth <holl_ands@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 13 Feb 2006 21:09:14 -0800 (PST)
CORRECTION: 5 to 20 usec delay corresponds to 1 to 4 mile delta distance (oops,
slipped a decimal).
<holl_ands>
==================================================
Richard Hollandsworth <holl_ands@xxxxxxxxx> wrote: Just like ATSC today, it's a
probabilistic game.....it's not all or nothing,
As a SFN channel is turned on, a certain percentage of users who used to have
good reception will suffer from unacceptable multipath (which can come and go).
If the signal strength from multiple towers are both strong, then the
probabiity of problems rises.
The relative distance to the two towers is also a factor, since it is the
DELTA delay that pushes the equalizer to it's extremes. (Delta is about 10
miles for 5 usec delay and 40 miles for 20 usec delay).
Of course, normal multipath will be on top of this, but nearby multipath (under
1 mile) has been found to be the predominant problem in suburban environments.
In urban environments, reflections off of skyscrapers is more of a problem with
much longer delays corresponding to the path length deltas.
So if a user is more or less equidistant between two SFN towers, then the
arrival times for the signals are fairly close together....well within the
range of current equalizers.
If the signal strength from one tower is say 15-20 dB above the other, then
perhaps even 3rd Gen ATSC Receivers would suffer minimal degradation, other
than the current mess-o-multipath.
SFN (Distributed Transmission) tests will need to be conducted with 3rd and 4th
Gen Receivers, collecting statistics across a fairly large number of users
before we'll know whether this is the promised BIG IMPROVEMENT or yet another
reason some people will simply find it too much of a hassle to make OTA ATSC
work.....
I'm hoping it improves reception for a much larger number of people than are
adversely affected....statistically speaking.....personally, they better not
screw up my meager reception any worse than it is already....
=============================================
"Stephen W. Long" wrote: See comments below
At 05:04 PM 2/13/2006 -0800, you wrote:
>Bert wrote:
>>As Doug says, such low power repeaters can also be used
>>with 8-VSB, as shown in Ottawa, but you need decent
>>receivers which accept pre-echo. They exist. Just not on
>>store shelves. Why not on store shelves?
>
>The ATSC A/111 standard and the companion A/110A Recommended Practice,
>address the uses of 8VSB SFNs and Repeaters. One major station group is
>currently testing this concept in a relatively large market but findings are
>yet to be published. As you say, this requires 5th Gen type receiver
>hardware to be successful, which seemingly can only be obtained thru the
>purchase of a new DTV set.
So, every ATSC receiver sold prior to 5th generation is non-functional?
As I recall, while I was personally being attacked by organizations
supporting 8VSB, one of the objections to switching to a COFDM based system
was that such a switch would disenfranchise "all" (all 1000 of them I
guess) of the previously sold ATSC receivers. So the weakness of the ATSC
8VSB design requires a 5th generation receiver, that no one is selling yet.
Hmmm. Is the scent of a class action lawsuit in the wind to compensate
all of the consumers of ATSC receivers that are 4th generation or older?
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