[OLSR-users] Double radio mesh and OLSR

Jim Thompson (spam-protected)
Fri Apr 8 22:44:46 CEST 2005

John Clark wrote:

> Henrion Benjamin wrote:
>> Jim Thompson <(spam-protected)> [050408]:
>>> Unfortunately, it is highly unlikely that you will "avoid 
>>> interference" here, since the selectivity of
>>> common 802.11 radios is not high enough to prevent severe ACI.
>>> Now, if you were to move them to different *bands*, then you might 
>>> have something, then again, you might introduce enough hysteresis 
>>> that things really break.   
>> I was thinking to use two different types of antennas, one in Hpol and
>> the other in Vpol. For instance, a slotted waveguide and a simple
>> colinear.
> I have not had time to test things out, but in the near future I'll be 
> setting up a system with
> 3 wifi cards, and attendent antennas. I have however, set up several 
> of these boxes to have
> an active wifi card on one antenna, and one of the cards be a 
> 'monitor' for the traffic on a
> particular channel, and have seen packets on other channels, when I've 
> just had several pairs
> operating on different channels. The antennas are the 'short' 20-25 
> cm. and placed about 10 cm
> appart from each other.
> Since I'm setting up an ad-hoc network, I can 'fix' things by making 
> each network on the respective
> channels a different IBSS, and while packets will be received, they'll 
> be ignored. This does not
> prevent lower bandwith due to collisions, etc, but at least the 
> packets will be filltered out early.

In this situation, the incoming SNR is high enough to set CCA, so there 
won't be any "collisions", at least, not by the nearby stations/APs.

Its when the signal isn't high enough to set CCA, but still high enough 
to destroy the channel vector that the real damage begins.

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