[opendtv] Re: (No Date: Tue, 28 Sep 2004 10:30:37 -0400

  • From: "John Willkie" <johnwillkie@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Thu, 14 Oct 2004 19:41:21 -0700

Frank, I'm sorry that I wasn't clear.

For each virtual channel emitted in the 8-VSB, there is a modulation mode
parameter.  There are provisions in A/65 for analog and digital services,
and NTSC and 8/16 VSB modulation.  In ATSC A/81 (satellite ATSC) there are
provisions for a variety of modulation modes.  No provision for COFDM.

You asserted that COFDM could have been permitted without any change in
PSIP. I challenged that.

The problem is symmetrical: there is no provision in DVB-SI for NTSC or 8/16
VSB.

So, they both don't recognize the other.  To make COFDM useful in TV sets
that also support VSB, there has to be common ground in the metadata
schemes, beyond MPEG-2 SI (PAT) and PSI (PMTs).  I also am unaware of any
way at the MPEG-2 level to signal modulation mode -- that's effectively
"user private" with the users being DVB and ATSC.

Sinclair was advocating back then dual-mode TV sets.  That would have
required -- without the systems recognizing one another -- two different
EPGs.  Or, maybe EPGs should be optional?

I've had an exchange with a very knowledgeable engineer on the CE side about
the contortions required at transmit and receiver to make PSIP-E work in the
E-VSB environment.  Transmitting COFDM and ATSC in side by side transmitters
might be easy, but I suspect that implementing dual or unified EPGs in dual
mode DTV sets would be almost as difficult, if not more so.

One item immediately comes to mind: with PSIP, the EITs are three hours
long, ending at 12:00 GMT and every three hours thereafter.  That's so the
sets can deal with the changes all at once.  I do not believe that DVB-SI
matches up like that, at least in sync with PSIP.

Remember, these dual mode sets were to be on the market within six months.
If it had been accepted by the FCC -- despite the best intentions of Nat
Ostroff, Mark Aitken, Dermot and others, I suspect we'd just about now see
fully standards-compliant dual mode receivers on the market.

If only this had been pushed circa mid-1994, we might be in a good place
now.  Unfortunately, the push came half a decade later, after FCC had
embedded 8-VSB into their rules, and Congress had effectively cemented
terrestrial 8-VSB DTV into law.



-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx
[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Eory Frank-p22212
Sent: Thursday, October 14, 2004 5:35 PM
To: 'opendtv@xxxxxxxxxxxxx'
Subject: [opendtv] Re: (No Date: Tue, 28 Sep 2004 10:30:37 -0400


From: "John Willkie" <johnwillkie@xxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Date: Thu, 14 Oct 2004 14:21:06 -0700

>As to who talks about what here, I am corrected.  (I suspect that you are
>missing a "not" in the last sentence, but I was able to discern a
>correction.)

You're right. I meant to say you are NOT the only one who has publicly
discussed the influence of patents and IP licensing in the various
modulation wars that have been fought as far back as the 1920s.

>But, how much do those COFDM silicon assemblies that handle HD cost
compared
>to 8-VSB?  Shouldn't we compare apples to apples?

HD has nothing to do with it. Either modulation scheme can carry enough
megabits per second in 6 MHz to support HDTV. What you should be asking is
'how much does a COFDM demod cost compared to an 8-VSB demod'? The
difference in silicon area between the two is quite dramatic. So is the
power dissipation. Silicon area directly goes to cost, but power also
indirectly affects cost because a power-hungry IP core limits the level of
integration that is achievable in an SoC.

Bert is fond of invoking Moore's Law to argue that in time, the cost
differences due to silicon area between COFDM and 8-VSB will be in the
noise. But Moore's Law doesn't apply to power dissipation. In fact, the
power problem keeps getting worse as CMOS geometries continue to shrink. The
desktop PC solution to this problem -- a massive heatsink & fan -- will
never fly in the CE world.

Cost has both a silicon component and a licensing component. Even if we give
LG the benefit of the doubt and say their terms will be about the same as
the DVB licensing terms, 8-VSB still has a cost disadvantage.

>As to permitting COFDM would not have required any change in PSIP:  I guess
>I have an unfair advantage, being that I only really know about metadata.
>However, I've looked extensively at the DVB-SI spec, and I know PSIP and
>PMCP innately.  If you can find a way to unambiguously define a COFDM
>transport stream in PSIP or PMCP, could you point me to it?  If you know of
>a way to unambiguously define an ATSC transport stream in DVB-SI, you might
>want to point me to that.

What do you mean a "COFDM transport stream" or an "ATSC transport stream"?
Both ATSC and DVB-T use MPEG-2 transport streams. Even with a non-8-VSB
modulation scheme, the transport parser, video decoder, audio decoder, PSIP
processor, etc. would see the same 188 byte MPEG-2 TS packets that they see
now from an 8-VSB demod. You're getting hung up on differences between ATSC
& DVB-T regarding what goes into those TS packets, and I'm saying those
contents wouldn't have to change just because the modulation was
(hypothetically) changed. A "COFDM ATSC" system could still be ATSC in every
respect, except for the modulation.

But of course this is all water under the bridge. The decision was made and
so we move on and make the best of it. But that doesn't mean we can't look
back and speculate about how things might have been different if it had gone
the other way.

The real irony is that two of the reasons COFDM was rejected by ACATS were
(a) it was believed it was still in the R&D stage, not yet ready for
deployment; and (b) it was believed that the large FFT sizes would require
too much silicon to make a cost-effective solution. Considering the earlier
and still much larger volume shipments of DVB-T receivers relative to ATSC
receivers, and considering the dramatically smaller silicon area & power of
DVB-T demods vs. ATSC demods, points (a) & (b) above turned out to be 180
degrees out of phase with reality.

-- Frank


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