Re: [Discuss-gnuradio] 802.11 and Bluetooth

[Eric Blossom]

On Wed, Dec 06, 2006 at 12:01:03AM -0500, Tom Rondeau wrote:
> I've seen a number of questions about these issues in the past couple of
> days, so I'm addressing this from my own knowledge.
> 
> Can we detect Bluetooth and WiFi with GNU Radio?
> 
> I'm making two assumptions: we're using the USRP and WiFi/802.11 is
> specifically addressing 802.11a/b/g.
> 
> The answer is no. The bandwidth is too large for the system to currently
> handle. If you tune the GNU Radio to the center frequency of an 802.11
> channel, you'll see what looks like a rise in the noise floor (and, under
> these conditions, it really is a rise in the noise) when there is a
> transmission.
> 
> Bluetooth signals hop from 2.402 - 2.480 MHz; 79 1 MHz channels at a rate of
> 1600 hops per second. The GNU Radio cannot look a the entire band all at
> once, so if you look at a particular slice (~4 MHz) of spectrum, you might
> catch a glimpse of a signal every now and then, unless you can plug in the
> right frequency hopping sequence (I think I have both MATLAB and C++ code to
> do this, buried somewhere, but then you'd need the master address (easy) and
> its clock (difficult) to do it; and I'm not sure if the USRP's can change
> frequency and settle fast enough for this).
> 
> If you have some 1 or 2 Mbps 802.11 devices to use, the BBN guys have done
> work on receiving those (search the list, it's been addressed a number of
> times in the past).
> 
> Hope this clears a bit up,
> Tom

Actually, I think you should be able to detect Bluetooth without too
much trouble.  If you just stare at a single point in the spectrum you
should be able to reliably detect 7 1 MHz channel's worth of data.

IIRC the hopping sequence is known, and thus you should be able to
determine if what you are seeing is bluetooth or not, even though you
are seeing only 7 out of 79 channels.

Eric