[opendtv] Re: COFDM and equalization
- From: Doug McDonald <dtvmcdonald@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 20 Apr 2004 06:35:55 -0700 (PDT)
--- Eory Frank-p22212 <Frank.Eory@xxxxxxxxxxxx> wrote:
> Henry Baker wrote:
>
> But the plain-vanilla approach works well and has a
> relatively modest hardware (silicon area) cost. It
> is not the "magic" of the equalizer that makes this
> so, but the brilliant signal structure -- pilots and
> guard interval -- that allow a simple,
> straightforward equalizer approach to perform
> acceptably well for most channels. The system was
> designed to allow a low-cost simple approach to
> "just work."
This is a good statement of COFDM as used in TV.
Basically, it is designed with ineffiencies
(i.e. "guard interval " and "pilots" that make
it easy to receive in moderately good cases with
simple
hardware. "Easy" is the good part ... inefficiencies
are the bad part: at the same bitrate, it requires
much more power than a single carrier system,
especially peak power. We are talking three times the
power at the bitrate of US DTV. This is
really true, and DESPITE THE LIES OF THE COFDM
PROPONENTS LIKE BOB MILLER AND THE BBC, it actually
shows up in the real world. Our town is an
excellent example: we are right on the boundary
of a certain Fox dtv station, and 3 dB really
does make a big difference: people on the
east side of town seem to be unable, normally,
to get it: but with a 0.5 dB NF preamp I have tried
at a couple of places, instead of a 4 dB NF preamp,
they get it. Thus, 3 dB more transmitter power
and it would work ... and with COFDM, the
edge would move about 4 miles west: to the edge
of town, and very very few would get it. Thus,
POWER REALLY DOES MATTER, and our town shows why
we made the right choice.
Doug McDonald
=====
Doug McDonald
my last name at scs dot uiuc dot edu, not here at Yahoo, please
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