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Re: Re: QRM ON 2.4 GIG



>I just copy pulsating  QRM when operating on AO-40 today. It was a local

802.11b access points (base stations) transmit periodic beacons, even
when no data traffic is being sent. I believe this is done 10
times/sec, though I am not sure if this exact rate is specified by the
standard or if it can vary with the implementation.

Beacons announce the base station's presence and identity to new
mobile nodes. They also notify nodes already associated with that base
station when packets are queued for them.

This lets an idle mobile node "sleep" (i.e., turn its receiver off to
save battery power) without missing traffic. It only need wake up for
(some fraction of) the beacon transmissions, and if the beacon does
not list traffic for that station it can go right back to sleep.

This suggests that a modulation and coding scheme designed to deal
with periodic, pulsed interference would be a good defensive measure
for use on S-band satellite downlinks.

Phil
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