[opendtv] Re: Letter to TV Technology
- From: "Bob Miller" <robmxa@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 8 Oct 2007 19:56:38 -0400
On 10/8/07, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx> wrote:
> Bob Miller wrote:
>
> > Most countries don't have mandated receivers for instance.
> > The US does.
>
> All that means is that some TV customers will be surprised when their
> TVs suddenly quit working. There is no nagic going on here. If analog TV
> goes off, either you plan ahead by creating transition mechanisms, or
> you have to deal with more last-minute problems.
>
> > In the article Hoffman rights ...
> >
> > "Time marches on, technology advances, and today's ATSC
> > receivers deal with such conditions quite capably. So
> > capably, in fact, that we are contemplating the possibility
> > of implementing single frequency network (SFN) television
> > broadcasting in the United States."
> >
> > He seems to be saying that the latest 8-VSB receiver
> > capability makes possible the contemplation of using SFN's
> > with 8-VSB.
>
> You haven't been paying attention, then, because this has been covered
> on many occasions.
>
> It's true that better receivers help in making SFNs work, but MOSTLY
> this is true for passively synchronized SFNs. That's why, for example,
> the CRC demoed their gap fillers working in Ottawa, with the LG 5th gen
> receivers. These gap fillers depended on receivers with good pre-echo
> tolerance, and the 4th and 5th gen receivers were the first ones to
> provide this capability.
>
> The innovation that made true SFNs possible with 8-VSB, i.e. more than
> just gap fillers, is the one we have talked about here for a long time,
> Bob. It is cheap, effective, transmitter synchronization. It is A/110.
> Obviously, better receivers will also help, because propagation paths
> are often quirky. However there never was anything IMPOSSIBLE about SFNs
> with 8-VSB.
>
> In short, that is what the TV Technology article should have emphasized.
>
> > DVB-T which was chosen by Hong Kong earlier was replaced
> > by DTMB after they tested the two BTW.
>
> And DTMB uses training sequences and powerful equalizers, and actually
> dials back the inherent echo tolerance of COFDM. It not only replaces
> the GI with a training sequence, but it also goes "backwards" from 8K to
> 4K mode, or even a single carrier mode, further impacting negatively on
> COFDM's inherent echo tolerance.
>
> So it simply brings together all the bags of tricks that have evolved
> since the early 1990s, to provide a system that is at the same time
> robust and spectrally efficient.
>
> With transmitter synchronization for SFNs, and better equalizers as well
> as schemes such as A-VSB for the low bitrate streams, 8T-VSB can have
> its life extended. Which is the only way to go when deploying new
> systems like this. You don't stop and start from scratch every time
> someone has a good idea.
>
> Bert
>
I have never been wed to any particular aspect of any modulation other
than does it work and is it the best. We debated 4K for at least 2
years and Europe almost had a third 4K version of DVB-T. Seems they
may go to 4K for DVB-T2.
You know that bridge that fell down in Minneapolis? A lot of people
would be better off if someone with a better idea had been listened
to, if they had stopped and started over from scratch before ever
building it or even tearing it down and starting from scratch at any
point since it was built.
Same with 8-VSB. The US public would be better off if we stopped 8-VSB
now, or had stopped it at any point up till now or at any point in its
feeble life going forward.
But I am not asking for that. Only asking to allow another modulation
to co-exist. It is trivial to add another modulation capability to
receivers today. And those new receivers could also handle MPEG4 or
VP7. Since we are willing to write off legacy receivers lots of things
should be possible.
In fact the only time anyone seriously worried about legacy receivers
was when there were very few of them and it was a convenient argument
against allowing COFDM. Now that there are lots of legacy receivers
those who still are proponents of 8-VSB are not worried about the
threat of another modulation being considered and will have no problem
making them obsolete.
Bob Miller
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