[opendtv] Re: 20060912 Twang's Tuesday Tribune (Mark's Monday Memo)

  • From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Thu, 14 Sep 2006 21:09:38 -0400

Mark Schubin wrote:

I have, thus far, been to about a dozen flats around the UK where
people are using indoor antennas for DTT reception. They range
from five flats in London to two in Edinburgh, one in Bristol, and
one out in the boonies of Sussex.

Only one had any reception problems, and that was a ground-floor
flat in London on a narrow street with a first-generation box in
1999. It had some slight breakup when a truck came down the
street.

And you didn't compare this with, say, an LG 5th gen or Samsung Gemini system.

Here's what the numbers say SHOULD happen, assuming the same spectral efficiency. And this is why I'd like to see some real test results from China.

The COFDM receivers will work under a wider range of multipath scenarios. So they will appear more robust than even the Samsung Gemini, but not by a whole lot. (The Gemini goes out to +60 usec, which is about like COFDM at 1/16 GI. But not as good as COFDM under strong pre-echo.)

But when the multipath is within the limits of the 8-VSB demod, the 8-VSB receiver should be able to decode a weaker signal successfully.

If you're in severe multipath, even Brazil E, a good VSB receiver should work well. Brazil E is three equal strength paths, 1 usec apart. If you spread out the Brazil E echoes more and more, eventually the COFDM receiver will do better.

Similarly, if you have no diversity antennas, COFDM will do better with deep nulls. With diversity antennas, 8-VSB will catch up some and perhaps even beat COFDM, again depending on the echo range.

And for plain old long range reception, where multipath is usually too weak to be an issue, 8-VSB should do better by several dB. Then again, this last part was even true with 1st gen 8-VSB, as Sinclair found out. Should be better now.

Bert

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