On Thu, Jun 21, 2012 at 5:39 PM, Lukasz <zmiel...@poczta.onet.pl> wrote: > Hi, >
> I'm observing following behaviour (I don't have good radio background, so > please > correct me if I'm wrong): > it seems that device (eg. sony xperia x10 with Android and TI wlan chip; other > devices behave in similar way) is sending probe requests on different > channels. That's correct > If my AP is configured on channel 11, it will also receive probe requests sent > on channel 10, but with lower signal level. That's also correct, you're observing "adjacent channel interference" which means if a device that has a really strong signal (or is really close) sends a packet on a channel adjacent to the one your radio is tuned to, you'll hear it anyway, with a low signal. Check the graphs on https://en.wikipedia.org/wiki/IEEE_802.11#Channels_and_international_compatibility > > As I undesrstand it, rssi values around 20 correspond to frames sent on > channel > on which my AP is configured (11 in that case) and values above 60 correspond > to > probe requests sent at channel 10 (reg. domain is set to 11 channels on > device). > Is that correct interpretation? Correct. I've seen more extreme cases (that same attenuation of 40 db between channel as far apart as 1 and 11) > > Is there any way to filter out frames received on other channels (so I only > receive frames from channel on which my AP is configured)? Thresholding the > signal level won't be a good solution: I won't be able to distinguish frames > received on different channel from frames received from device which is far > away. Filtering in time is also tricky as it involves finding out interval in > which device is performing scans. > > Maybe it's possible to somehow narrow down the width of rx band? I can't speak at the radio/driver level since i'm not a programmer, but maybe you can dissect the packet on a higher layer: on wireshark I can see the probes include a tag (set by the sending device) with the channel the probe was sent. the fieldname in wireshark is "wlan_mgt.ds.current_channel" and it's located on a tag with "wlan_mgt.tag.number"=3 It may not be the easiest way (you have to dissect the probe bytes) but you'll have no doubt that's the channel the probe was originally sent in. just my 2c Good luck! and please post any interesting results :) Guido _______________________________________________ ath9k-devel mailing list ath9k-devel@lists.ath9k.org https://lists.ath9k.org/mailman/listinfo/ath9k-devel
