On Apr 25, 2006, at 10:46 AM, Matt Thompson wrote:
Hi,
I was wondering if anyone has experienced this, and/or knows a
resolution.
When I turn on a GE 2.4GHz Analog cordless phone, there is
absolutely no
communication between two Tmote sky modules (CC2420 Radio). 802.11
does
not seem to interfere,
802.11 does interfere, depending on the two channels used. But 802.11
might not be using the channel heavily, and its signal might be
strong enough to cause the nodes to backoff in their CSMA. This is a
trace
nor does a set of old Radio Shack 2.4GHz wireless
video senders, although I have not yet tried all channels. I can
avoid
the cordless phone interference by using channel 26 on the motes, but
this is not a permanent solution.
I think the issue is that the phones use an analog signal rather than
packets. Therefore they just transmit: there's no CSMA, etc.
I don't think there's a perfect solution to this problem. E.g., even
if you figure out that channel C is OK, then someone might turn on a
device which interferes significantly with C. There's little you can
do to a serious jammer. It becomes especially difficult because nodes
might not hear the same things, and so while transmitter X thinks
channel Y is OK, there's an interferer next to receiver Z that out-
shouts everyone else. Synchronization/frequency hopping can give
diversity, but if a large number of the frequencies experience
interference, you need to adjust, etc.
Phil
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