[opendtv] Re: Specs flap is mobile TVs next test
- From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 12 Mar 2006 16:23:13 -0500
Tom Barry wrote:
>What confuses me is that the broadcasters, who supposedly
>detest the interactive mobile guys, do not instead want to
>use a form of broadcasting that could easily be received on
>a normal portable phone, without subscription.
I'm not sure what the broadcasters really think. Some people on here make it
sound like everyone, including broadcasters, is hell-bent on forcing all
their customers on some sort of subscription scheme. But I'm skeptical about
these opinions.
Others will use that as another opportunity to complain about the fact that
you can't transmit DVB-H along with 8-VSB on the same frequency channel,
even though it's far from certain that any broadcaster anywhere in the world
would be doing that, or that DVB-H will be the choice for mobile service to
handhleds in the first place. It looks like DMB-T will be a strong
contender, and of course neither that nor MediaFlo can be transmitted on
DVB-T bands.
And also, there's no reason why broadcasters can't also serve interactive
mobile customers, if they have a mind to. They can always charge for the
interactive aspects. (You pay x if you to send in your vote in that game
show.)
>My daughters cell phone also happens to have an FM radio for
>which no special fees are required. That feature just happened
>to be in her model. While I realize the cell phone providers
>might not be particularly pleased to provide normal OTA TV
>reception it seems some cell phone CE manufacturers would be
>happy to include it if passable reception could be expected.
Passable reception is not the most difficult problem anymore, I don't think.
The toughest problem will be power requirements for receivers. I mean, power
draw at the receiver.
The reception problem can be addressed with some simple arithmetic. Once you
have developed receivers which are sensitive and tolerate echo well, and in
spite of your continued skepticism this has happened to a large degree
already (e.g. the Samsung Gemini chip), the other pieces of the reception
puzzle are signal margin needed and transmitted power available, comparing
analog FM with ATSC.
Signal margins for mono FM reception with the best receivers are lower than
for 8-VSB, from numbers Audio magazine used to report back when (~12 dB C/N
for the best of them IIRC). That lower margin applies for fairly noisy
mono-only reception. Might be good enough for cell phones. Who could tell
the difference? So FM might have the edge there, by 3 dB or so.
The antenna is very inefficient for VHF or UHF, but UHF would have the edge
there. I'm not sure what the cell phone uses as FM antenna. Could it be the
cable to an earphone? Anyway, I'd give TV the edge there, for UHF stations
anyway.
Tranmsitted power gives FM the edge. FM transmitters are limited to 50 KW
ERP, correct? If you look at the difference in channel width, that 50 KW
would equate to 1.8 MW ERP for TV. So here, DTT is at a disadvantage,
especially the DTT transmitters currently at 50 KW or thereabouts. They
would be just about out of the question.
Then there's the digital cliff. Any analog reception will be easier, no
matter which of the currently available digital schemes you can mention, in
terms of graceful degradation.
So I think all in all, 8-VSB to cell phones is not impossible, except for
the power drain issue. That will be solved in time. Ditto for any other
digital transmission to tiny devices, which isn't specifically designed for
tiny devices (and doesn't make big tradeoffs to favor tiny device
reception).
>I wonder it if would be royalties issue?
The best we have been able to determine on this open forum, royalties for
ATSC receivers amount to $15 total, for MPEG and 8-VSB together. That isn't
much when you look at what these cell phones actually cost to the service
provider (not necessarily what the subscribers see as an initial cost to
them, of course).
Bert
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