iBSS mode SNR stats & rant about multi-card interference

From: Eric Johanson (hostap_at_cubesearch.com)
Date: 2002-06-04 02:55:06 UTC

Hi there,

I have some questions regarding the iBSS mode support on the hostap mode drivers (and all wireless drivers, for that point).

When acting as a BSS mode client, you can see the sig, noise, 'quality', and SNR. All of the drivers support different methods of accessing this information (proc, iwconfig, iwpriv, etc).

I've seen some stuff posted about seeing the clients currently connected when in master BSS mode (via hostap in /proc/net/prism2/wlan). I'm not sure if you can see the SNR, etc.

However, when in iBSS (adhoc) mode, it's not clear to me how to access this information, or even how to read it if you have more than one client connected. In our testing, the hostap driver is one of the best around; I'm hoping that there is some method of seeing this via one method or another.

This feature would be very useful to us folks in seattle; we (try to) use iBSS for all of our p2p links. The problem is that we can't tune[aim] the antenna, unless we can see SNR numbers.

Also, I would like to report that the driver works well with the dlink DWL520 cards, which runs cooler and produces much less stray RF than most (all?) of the pcmcia based cards. The DWL520 is ideal for a multi-radio setup, as you won't have quite the interference between the cards. In our testing, if you have two (or more) pcmcia cards in pci->pcmcia bridges, you'll impact your speed by about 30%, even with 'correct' channel separation. EG:

card 1 (channel 1)
card 2 (channel 6)
card 3 (channel 11)

Under that model, if any of the cards are at full TX/RX, it will impact the transfer speed of the cards next to it by about 30%. This is using lucent silver cards in pci-> pcmcia bridges, so I don't know if the same numbers apply with prism2 based cards. With the DWL520 cards, this number decreases quite a bit - I don't have numbers handy, but it was hardly noticeable. In both cases, the cards had been connected to around 10' of lmr400, connected to 14dbi yagi antennas pointed away from each other at a distance of about 10feet.

Anyway, sorry for the random rant, I hope somebody finds this information useful. I'm interested to see if other folks have seen the simalar issues with mutli-card setups. But really, I just want to see iBSS mode SNR stats. :)

Jouni, keep up the great work on the driver. I want to get bumper stickers that say "HostAP solved all of my wlan problems".

Kindest Regards,

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