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Re: UTC nastygram on BPL



On Thu, Jun 24, 2004 at 11:35:28PM -0700, Emily Clarke wrote:
>
> I apologize for the length of this post (or as some may see it - a
> rant.)  BPL is a complex technical, political and corporate issue.  So I
> felt it important to speak about the entire issue, not small parts of it.
...
>
> BPL is presumably a spread spectrum technology of which I know much about.

Actually, BPL is not SS, if it was proper SS we'd not be moaning about it
at all. With the right chirping frequency and algorithm, all that would
have happened, is the noise floor would have gone up slightly and that
would have been it. Maybe an entire db.

> While I can't divulge why, before I retired from the defense industry, I
> spent a lot of time developing it. I spent many hours in front of spectrum

Heh. I have done defense industry. Held the security clearance etc.
Have the T shirt with the bullet holes and blood. I Hated it.
Never again. I can talk about it in generality but not specifics.

> analyzers looking at, tweaking it, and analyzing it's characteristics. So I
> am very familiar with the concept and it's implementation. At least from a
> signal characteristics point of view.

We were only DF'ing it. ;-)

There are several different competing technologies for BPL.

It appears, at least one of the variants is using a form of
multi-carrier adaptive modulation. This is quite similar to what they
use on DSL and cable and was originally proposed by Telebit. Before
the "superior" V.34bis etc.

Basically, many many carriers are used, each carrying some of the data load.
DSP is used to sample the BER of each carrier, and as BER goes up
that carrier moves from QAM down to PSK. Or back up to QAM as BER goes down.
(or more.  I am not sure how many points are in the trellis at the highest tbh)

This was done, I am quite sure, to save money. The BPL proponents
could use DSL chip sets instead of developing much more expensive SS.
Thereby keeping the cost of the modem down.

With true SS the right chirping rate and algorithm is used to spread
the signal throughout the entire spectrum, so to normal receivers,
it appears as pure gaussian noise.

> So what to do?

The NTIA are doing it. Unlike the ARRL which I agree, has fumbled
the ball badly, they have put together constructive criticisms that
if you read *carefully* mitigiate BPL quite well. If you read their
paper carefully, the suggested cleaning up of the lines they suggest
will only result in the power companies installing fibre instead.
It would be cheaper.

Well done NTIA.

- Diane VA3DB
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