802.11 Beacon frame transmitter - mobile devices

GNU Radio
1

Greetings

After creating beacon frames transmitter based on usrp i decided to
check
its performance. Im sending a beacon frames and correctly decoding it by
my
wlan card (in monitor mode - screen attached).

http://gnuradio.4.n7.nabble.com/file/n51215/beacon.png

Any ideas why i cant find this network on any mobile device (smartphone,
laptop)?

Best,

Ernest

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2

Can’t remember exactly but is there some form of CRC checking with the
beacon? Because in monitor mode, CRC checking is typically disabled.
R

3

I think yes. Rest of 802.11 beacon in my area also have CRC (while in
monitor
mode - Windows Network Monitor).

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4

Any ideas why i cant find this network on any mobile device (smartphone,
laptop)?

It is probably the difference between passive vs active scanning. To
save time and consequently power, most battery powered wifi devices
use active scanning where the station sends a probe request and
expects to get a probe response from the AP (or beaconing device).

Typical dwell times in active scanning are 20-40ms / channel while
passive (listen only) scans are usually more like 110 ms / channel,
since the default beacon interval of many APs is 100ms.

If you have linux on your laptop, you might try ‘iw wlan0 scan freq
$FREQ passive’

Jason

5

So, following your idea, after waiting a larger period of time, passive
scanning should “catch” my beacon right? (becouse when entering new
area, or
getting in range of unknown AP, there are no information to send direct
probe request by mobile device).

I think that mobile device is performing some kind of “check” that wlan
card
in monitor mode don’t, rather than im facing active/passive scanning
problem.

Best

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