"seaweedsteve" <seaweedsteve@gmail.com> hath wroth:

>OK. So....if I understand correctly, it's not so much that 802.11B is
>effectively more powerful than G, but that the different forms of
>modulation simply yield different power measurements ?

Yep, that's about it. AM modulation causes the average power to
decrease somewhat.

>A bit of the old "apples to oranges"?

Nope. Just specmanship. The FCC specs are for average power. If
they were for peak power, the two power ratings would be roughly
equal. There's also RMS power (heating power), which is there just to
confuse everyone.

>In any case, is it true that operating in B can allow decent
>connections (albeit slow) at increased distances?

Yes. But think of what you're doing. It takes roughly 13 times
longer to send a packet at 1Mbit/sec than at 11Mbits/sec. You're
occupying 13 times the air time (transmission time) sending this one
packet. If I assume a nearby microwave oven raising havoc, I suspect
that there's a 100% chance that the 1Mbit/sec transmission will get
clobbered and need to be repeated. It might never arrive. However,
the 11Mbit/sec will get clobbered less often, and some of the data
will arrive, even though the error rate is horrendous. This also
applies to multipath and co-channel interference. Going slow is NOT a
general cure for reliability issues.

I suggest you read:
<http://pdos.csail.mit.edu/roofnet/doku.php?id=interesting>
which is a report on the MIT Roofnet mesh mess. Mesh is the worst
case topology, where interference is epidemic. Note the relationship
between speed and probability of delivering packets. It's quite
illuminating.

I tend to lock the speed of my access points at the slower OFDM
speeds. This has the side effect of rejecting all 802.11b connections
on SOME (not all) access points. However, It's the most reliable
compromise I've found between range and retransmissions. However, it
does not work for all conditions and I've had to go back to the more
common "automatic" speed settings on two hot spots.

>1) Given a required connection speed of say, 9-11Mbps?
>
>2) Simply comparing lowest fallback in each; 1-2 Mbps in B to ...9
>Mbps in G?

Sorry. I don't understand the question. In a perfect world, faster
is better up to the limit of the fade margin. In a real world,
interference seems to be the prime motivator, and that requires a much
more complex model. For example, fragmentation threshold and flow
control work nicely for reducing the effects of interference and
hidden transmitters. In other words, there's no simple answer to
determining the optimum speed setting.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558