Re: [Discuss-gnuradio] IEEE 802.15.4 on USRP N210

[Sebastian Bader]

Hi Marius,

Thanks for the quick reply. First of all I get a communication now.
When I set the sample rate to 4M then it works. Any idea why? Could it
have something to do with the 2M data rate? But shouldn't it then work
with every sample rate > 4M, which it doesn't? See more info below.

> I don't really understand what you're trying to archive, but here's a
> stack for 802.15.4:
> http://wiesel.ece.utah.edu/redmine/projects/gr-ieee802-15-4/wiki

The first step to my goal was to get a communication going between
USRP N210 devices and regular wireless sensor nodes, such as TelosB,
etc. I have seen the stack you mentioned, but it is pretty similar to
the UCLA stack with some extra features. Here, as well as with the
UCLA stack some modifications are needed to make them work with N210s
and the UHD driver.

> How did you change the frequencies? If you change the center-frequency
> on a FFT your USRP2 <-> PC communication breaks down? What is the
> decimation?

Sorry for that, probably I wasn't clear here. The frequency change had
nothing to do with the FFT. The FFT I just did to see whether I
actually get something from my sensor nodes and what might be the
reason why I can receive from another N210, but not from a sensor
node.
The frequency change is done in the python script directly, i.e., in
the setup of the USRP device. The original code has 2,475 GHz as its
center frequency (which is channel 25 in the 802.15.4). When I have
two N210s with that frequency, they do communicate. When I change the
frequency to another channel (by changing the center frequency on both
devices), they do not communicate any longer.

> To demodulate you need at least 2 * the frequency of the channel. So
> in case of 802.15.4 something like 5 MS/s should be sufficient.

I thought the same. As soon as it should be over 2* it should be good.
Thus the test with a rather high sampling rate. Strange is that two
N210s can communicate with a 1M sample rate as long as both devices
have the same sample rate. Now the combination sensor node - N210
works only with 4M. Any idea what might be the reason.

> I actually finished a project on 802.15.4 and used USRP2s with the
> WIESEL stack to analyze a real-time sensor network. I'll commit some
> stuff quite soon (this week). E. g. a complete demod and mod path in
> GRC. Most stuff is in German though. :)

Let me know when you have some code or report work done on that. The
language should not be an issue :)

Regards,
Sebastian