I'm not sure about DOCR's (but not my area). From Doug Lung's report:
--------quote------------
While a single-channel distributed transmission system offers the most
flexibility and the best performance, it requires distributing
programming to each site through a microwave or fiber connection.
Digital on-channel repeaters, or DOCRs, appear to be much simpler, since
they receive the primary station off-air and retransmit it on the same
channel, eliminating the need for the microwave or fiber connections.
--------quote------------
But I'm of the school that says we will soon have very fast fiber
connecting all important (worth paying money) fixed locations in this
country anyway. OTA TV will be for portable/mobile. In that world
Digital On-channel repeaters might have less value compared to the
single channel distributed system. But again, I have zero credentials
in this area.
Is it really certain that DOCR's create enough pre-echo to trash legacy
receivers?
Anyway, the transition is taking so long that nobody may care by the
time it's done, at least if we don't finish it soon. Otherwise we can
wait for my own vision of fiber to everywhere coupled with WiFi/UWB from
the nodes giving us all our broadband/HDTV/Phone/3D/Smellyvision.
I'm still very skeptical ATSC will ever be sufficient but I'm also still
very convinced we no choice but to get on with it now to just find out
(or prove it).
- Tom
Bob Miller wrote:
> On 11/14/06, Tom Barry <trbarry@xxxxxxxxxxx> wrote:
>
>> Yes, I agree, for the 8vsb transition we should "stay the course" and
>> show one way or the other in 2009 exactly how well the current ATSC
>> standard can work. We are down to only a couple years now, so let's
>> just do it.
>>
>> Then, in 2010, we can re-evaluate and grade how well we have done
>> compared with the rest of the world. If Bert is correct then by that
>> time we should have compatible ATSC converters for $50 that work fine
>> with rabbit ears. Hopefully we will also have VCR/PVR's that allow us
>> the expected functionality with OTA. The market will either provide or
>> ATSC will get voted off the island and we can then do something else.
>>
>> Practically anything is preferable to further delay.
>>
>> - Tom
>>
> Anything is preferable to further delay. The delay is the modulation.
> Yes anything is preferable to further delay. Lets get rid of the
> modulation.
>
> i.e. We need DOCR's. If you accept that and you accept that legacy
> receivers DELAY for an INDEFINITE time any use of DOCRs then you
> accept that 8-VSB as limited by legacy receivers is responsible for
> the DELAY.
>
> Or do you suggest that we go ahead and build DOCRs that trash legacy
> receiver reception? If so the legacy receiver holy cow situation goes
> away and we should consider switching to a new modulation and codec.
>
> Or do we wait to build these necessary DOCRs till we find a way of
> making them work with legacy receivers? That sounds like DELAY.
> Possibly an infinite one.
>
> If you believe as I do that manufacturers, retailers and therefore
> consumers are not very interested in participating in the OTA
> transition because of reception problems with 8-VSB then the
> modulation is the DELAY. If you don't accept that fact then you have
> to explain in convoluted twisted logic why LG sells COFDM receivers in
> OZ with 19 million people but can't make money selling 8-VSB receivers
> in the US a market of 300 million people. even with the advantage of
> owning IP royalty rights for 8-VSB.
>
> Bob Miller
>
>
>
>
>
>
>
> Bob Miller
>
>>
>> Bob Miller wrote:
>> > My point, Doug Lung's point was that legacy receivers are a problem
>> > when designing DOCRs. Even if 5th gen receivers work perfect with
>> > DOCRs the legacy receivers hold back their use.
>> >
>> > Until you can design a DOCRs that will work with legacy receivers you
>> > can't use DOCRs based on the legacy receiver is holy theory.
>> >
>> > But you need DOCRs for a successful DTV HDTV transition according to
>> Doug.
>> >
>> > Catchy 22.
>> >
>> > Legacy receivers are bad. But you can't get rid of them and they are
>> > increasing in numbers everyday. What to do what to do.
>> >
>> > I guess we are just stuck with a dead OTA. But above all we must stay
>> > the course.
>> >
>> > Bob Miller
>> >
>> > On 11/13/06, Albert Manfredi <bert22306@xxxxxxxxxxx> wrote:
>> >
>> >> Bob Miller wrote:
>> >>
>> >> >One other little problem with legacy receivers and the
>> >> >future/present needs of the US DTV spectum.
>> >> >
>> >> >Doug Lung in "China's new DTV Standard and DOCRs" brings
>> >> >up the troubling need for DOCRs. He thinks they are required
>> >> >for a successful OTA HDTV future.
>> >>
>> >> For the record, I didn't buy your other arguments, but we've been over
>> >> them
>> >> time and time again.
>> >>
>> >> What you need for digital OCRs is a reasonable amount of pre-echo
>> >> tolerance,
>> >> where the amount of pre-echo tolerance you have is proportional to how
>> >> much
>> >> power the OCR can transmit, compared with the power density in that
>> >> location
>> >> generated by the main transmitter. This is the same consideration you
>> >> have
>> >> to give to SFNs that use unsynchronized transmitter.
>> >>
>> >> The safe way to design this sort of network is to use what the French
>> >> call
>> >> the umbrella configuration. The big stick is used for the bulk of
>> >> coverage
>> >> (e.g. the Eiffel Tower), and the OCRs are low powered enough that
>> they do
>> >> not interfere with each other and don't radiate so far that the main
>> >> transmitter will create what looks like strong pre-echo many usec
>> >> prior to
>> >> the repeated signal.
>> >>
>> >> The 5th gen receivers can stand strong pre-echo out to roughly 15
>> usec or
>> >> so, realistically, which means that beyond 3 miles from the OCR, you
>> >> really
>> >> want that repeated signal to become weak compared with the main
>> >> transmitter's signal. That's so the main transmitter will again
>> seem like
>> >> the dominant signal, and the OCR will create a benign post-echo. As
>> the
>> >> relative power of the pre-echo drops, 5th gen receivers can tolerate
>> >> quite a
>> >> bit of pre-echo. Like -50 usec.
>> >>
>> >> The CRC demoed these in Ottawa, using the LG 5th gen demod. They
>> got good
>> >> results with two OCRs creating coverage that overlapped with the main
>> >> transmitter, which is not half bad.
>> >>
>> >> Yes, this is a strong suit of COFDM -- pre-echo tolerance --
>> although 1st
>> >> and 2nd generation DVB-T receivers (according to the French CSA
>> document
>> >>
>> >> http://www.csa.fr/pdf/Rapport-GT2-Aspects_Radiofrequence_de_la_TNT.pdf
>> >>
>> >> Section 2.3.1.5) also had trouble with pre-echo tolerance.
>> >>
>> >> It is of course not unreasonable to expect that as time goes by, as
>> >> things
>> >> change, people will require STBs even if they own an integrated set.
>> >> We have
>> >> discussed this many times too. If AVC is introduced, for example. I
>> think
>> >> OCRs or gap fillers can be used with 8-VSB, and would be easiest to
>> >> implement when terrain masks the main transmitter's signal. Like in a
>> >> valley. Using directional antennas with the OCR helps too. No matter
>> >> 8-VSB
>> >> or COFDM, designing a solid multi-transmitter single channel network
>> >> in no
>> >> trivial task.
>> >>
>> >> Bert
>> >>
>> >> _________________________________________________________________
>> >> Try the next generation of search with Windows Live Search today!
>> >>
>>
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>>
>> >>
>> >>
>> >>
>> >>
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>> --
>> Tom Barry trbarry@xxxxxxxxxxx
>> Find my resume and video filters at www.trbarry.com
>>
>>
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Find my resume and video filters at www.trbarry.com
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