How to capture raw signal from wireless router?

Question

I have seen several projects now which derive novel spatial information from radio data collected from a typical wireless router:

http://wisee.cs.washington.edu/

http://www.extremetech.com/extreme/133936-using-wifi-to-see-through-walls

The idea of using a wireless router as a sort of passive radar is fantastic.

I am very interested in experimenting with data collected from a wireless router myself, but there is little information on how to go about actually interfacing with a wireless router and getting a raw stream of information collected by the device. Similar questions have been asked on here before, but I am yet to see a satisfactory answer.

I don't have the rep points necessary to link to the other questions but see:

'Capture Raw Signal from WiFi card as You Would a Sound Card'

'raw wifi “signal data” access'

I am looking for a solution that would let me use a low-cost device such as the oh so common WRT54G wireless router. If your answer involves custom radio hardware, you needn't bother posting.

Answer 1

As far as I know, the only option using a commodity hardware is to use Intel 5300 Wifi card. You can get the complex CSI (amplitude and phase info therein) from the three antenna on it from a sample of subcarriers (OFDM). You can take a look at this site:

http://dhalperi.github.io/linux-80211n-csitool/

Answer 2

If you read the wisee research paper you will find the platform they use for the system, it is USRP N210 from Ettus plus GNU radio software. So it is not your usual WiFi AP they are using but the SDR solution this question also hints about.

WiFi devices are build to handle physical layer in silicon and the monitor mode is the best thing you can get without going the SDR path. You can get quite a lot of information from it - the radiotap header contains for example received signal strength and receiving antenna information. But if you really want to explore physical layer of WiFi then commodity hardware is not going to cut it.