[opendtv] Re: The "real" problem with OFDM in the U.S.
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 16 Mar 2005 17:41:33 -0500
Craig Birkmaier wrote:
> No, Bert, this is not true. Ubiquitous coverage
> comes from the delivery of the INTENDED signals
> for the market in which the viewer lives,
Sorry, Craig, but RF propagation is what it is. Pattern
overlap is also used in the French DTT scheme, to assure
ubiquitous coverage. You simply cannot design a
practical system with sharp coverage contours, no matter
how much you would want to have this be the case.
This is true at any scale you care to examine. With big
sticks, small sticks, cell phone towers, or IEEE 802.11
microsticks in hot spots.
You're just repeating dogma here. Give me any coverage
contour you care to hypothesize that does NOT include
overlap, and I'll show you holes in coverage, and a
house planted right in that hole that won't have a
usable signal (in populated parts of the world).
> > Where does someone who lives in Aberdeen, Havre de
> > Grace, or even Elkton MD get his TV signal from, Craig?
> > Why should a Baltimore or Philadelphia station owner
> > NOT want to cover those communities?
>
> According to the market coverage maps the answer is
> Baltimore.
Thank you. Now, if you were to deploy small sticks in an
SFN for Baltimore TV stations, to achieve your desired
super-sharp contours, just exactly how many towers do
you expect you would need to cover a 50-60 mile radius
with the kind of sharp coverage contours you want?
The German answer was two tall sticks with 180 or 200 KW
each, for that sort of coverage. And that assumes outdoor
receiving antenna beyond 12-14 miles from the towers, and
roofmount (high gain) beyond 27 mile range. That does not
give any semblance of sharp pattern, but at least it uses
just one frequency. Very similar to our big sticks.
The French answer is multiple translators, each low power,
with overlapping coverage patterns. That provides good
coverage but uses more frequencies. Same problem, smaller
scale. The first translator west of Paris is under 30 miles
from the Eiffel Tower.
If you still don't believe this, say so, and I will copy
the table for you to see. I'm trying to force you to see
reality here, Craig.
> The battle lines are drawn over who gets the placement
> on cable systems (or DBS local-into-local) when the cable
> system can place an antenna on a big tower and receive
> duplicated services from several markets. If the cable
> system is inside the grade B countours for a station,
> there is no debate - they get carriage. If the cable
> system is "between markets," they may carry signals from
> multiple markets, or they may negotiate with a station
> from one market or another for carriage.
All of which suggests that OTA stations want to achieve the
widest possible coverage, *even* for their cable carriage
negotiations. So I ask you again: what are the practical
ways of achieving this? Not practiced marketese answers
here, not rehearsed dogma, but real-world.
> As I mentioned previously, the area you live is somewhat
> unique, since it lies between two markets that have huge
> overlaps; this is the exception, not the rule.
That's the crux of my diagreement! It's not unique at all.
Up and down the East and West Coasts, Gulf Coast, that's
the RULE. There are no unpopulated areas between markets.
And once again, even in other parts of the world, ubiquitous
coverage is required. Check out the map of the French DTT
coverage. It tries to be uniform. There is no wilderness
there, Craig. Overlapping patterns of translators.
Overlapping patterns of big sticks. Overlapping patterns
of individual small-scale two or three-tower SFNs. What's
the difference? It's a matter of tradeoffs ALWAYS.
Ubiquitous coverage means overlapping patterns. Big sticks,
with occasional assistance from gap fillers, are a
reasonable approach, when the markets are huge.
Bert
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