This is my network topology:
A<--B-->C
To exclude Interference between antennas I replicated the same experiments with
two soekris instead of one.
Specifically, I use the same antenna placement but I sobstituted the second
wireless card of B with
another dedicated soekris
A<--B
D-->C
In this scenario I achieved a per flow throughput of about 24-25 Mbps. So there
isn't interference between antennas.
To excluded interference between wireless cards I repeated the same experiment
of the first scenario using a PC equipped with
an Athlon 64 processor (2043.086 MHz processor with 1GB of memory). I put both
the wireless cards into two contiguous PCI slots
using two miniPCI to PCI single Slot Adapter so that the wireless cards are
about 1-2 cm from each other. Also in this case
both the wireless cards are able to work simultaneously and I obtained a per
flow throughput of about 24-25Mbps.
I also opened the case of the soekris B and D of the second scenario and I
bring the wireless card of soekris B near to the wireless card of soekris D
(varying their relative position ). Also in this case I obtained a per flow
throughput of about 24-25Mbps.
Consequently, I think that the problem is related to the madwifi driver or to
the soekris board.
> David Young wrote:
>/ On Fri, Jul 25, 2008 at 03:50:17PM +0200, Emilio Ancillotti wrote:
/>>/ Hi there,
/>>/
/>>/ I have a problem using my soekris 4801 with two miniPCI wireless cards
/>>/ (R52H High Power Mikrotik 802.11a/b/g mPCI).
/>>/
/>>/ The problem is the following. When each wireless card works alone
/>>/ I have not problem, and I obtain a throughput of about 24-25Mbps.
/>>/ However, when both cards work simultaneously, the per flow throughput
/>>/ of each cards is reduce of about 40%, even if the two wireless cards
/>>/ use different channels (1 and 11).
/>/
/>/ Are the antennas very close? Within a foot of each other? When the
/>/ antennas of the two radios are very close, they may interfere with each
/>/ other, even at opposite ends of the 2.4GHz ISM band. It is also possible
/>/ that two radios in the same box will interfere at the intermediate
/>/ frequency (IF). Jim Thompson has written about the various ways that
/>/ two colocated radios can interfere, even on so-called "non-overlapping"
/>/ 802.11 channels. A Google search will probably turn up his discussion
/>/ of the issues.
/>/
/
So then to the users here organize their networks to avoid radio contention?
My immediate thought would be to use limit units to 1 radio each and
connect a pair of units through a small switch, but that sounds like an
expensive messy hack.
Comments?
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