Subject: Re: multiple wireless cards
Newsgroups: gmane.linux.drivers.madwifi.devel
Date: 2008-07-19 23:28:35 GMT (24 weeks, 6 days, 3 hours and 46 minutes ago)
Hi Emilio,
I agree with Eric. Multiple radios inside a single node cause interference even if
they are on orthogonal channels due to radiation leakage, board crosstalk and
small antenna separation. You may have to shield the wireless cards or increase
the separation between antennae. You should take a look at this paper for similar
observations
http://www.pittsburgh.intel-research.net/~kpapagia/papers/winmee05_robinson.pdf
Ashish
--
"For humans, honesty is a matter of degree. Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep engineers away from customers, romantic interests, and other people who can't handle the truth."
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I agree with Eric. Multiple radios inside a single node cause interference even if
they are on orthogonal channels due to radiation leakage, board crosstalk and
small antenna separation. You may have to shield the wireless cards or increase
the separation between antennae. You should take a look at this paper for similar
observations
http://www.pittsburgh.intel-research.net/~kpapagia/papers/winmee05_robinson.pdf
Ashish
On Sat, Jul 19, 2008 at 4:10 PM, Eric W Anderson <Eric.Anderson <at> colorado.edu> wrote:
Hi Emilio,
You may just be experiencing plain old-fashioned interference. Two
WiFi devices operating that close to each other at the same time are
pretty much guaranteed to step on each other. Even with the channel
separation between 1 and 11, the amount of power bleeding over is
probably enough to induce packet loss. That's an issue even when both
cards are purely transmitting because of backoff and/or lost ACKs.
Try it with different cards and/or different drivers and see what
happens.
Eric
Thus spake emilio ancillotti (emilio.ancillotti <at> iit.cnr.it):--
> Hi there,
>
> I have a problem using 2 Atheros based wireless cards at the same time.
> Secifically, when each card works alone the driver works fine. However,
> when both cards work simultaneously, the per flow throughput of each
> cards is reduce of about 30-40%, even if the two wireless cards use
> different channels (1 and 11).
> My testbed consisted of a soekris 4801 with 2 R52H High Power Mikrotik
> 802.11a/b/g mPCI adapter runnig the madwifi 0.9.4 and the linux kernel
> 2.6.22.
> To see the throughput reduction I opened two outgoing asimptotic UDP
> flows (using the iperf tool) between the soekris board and two laptop.
> The two wireless cards worked in ad-hoc mode and I used 54Mbps as the
> wireless transmission rate (I disable the autorate alghoritm).
>
> Has anyone experienced the same problem?
>
> I would be really grateful if anyone shared his experience relative to
> my question.
>
> Regards,
> Emilio Ancillotti
>
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