Re: [Discuss-gnuradio] Spectrum Sensing

[Johannes Demel]

Hi Nikita,

so basically what you want is a couple of calculated FFTs per second. These are then sent to the web service and delivered to who ever connects to it.

Let's assume every USRP has its own flowgraph. Then The thing to do is, receive samples, convert them to a vector with the size of your FFT, use a 'Keep one in N' block to decimate the number of FFTs per second and feed the output to a FFT block. Then pass your results around as you like.

Happy hacking

Johannes

On Tue, Dec 17, 2013 at 11:26 AM, Nikita Sharakhov <address@hidden> wrote:

Hi Johannes,

 

Here are some more details.  I am building a web service, which returns spectrum data (the amount of energy at different frequencies) for a USRP, like so:

 

http://128.173.221.40/WebServices/SpectrumAPIfineGrain.php?node=49&frq=2000000000

 

The script behind this data service calls a python program to calculate the spectrum and write the results to a text file.  Here is my goal:  I would like to find an alternative to the python program.

 

This data is visualized in a web application:

 

http://filebox.vt.edu/users/sharni/Radio/new.html

 

clicking on a node visualizes the spectrum for the USRP.  The RAND button toggles between fake and real data.  Currently the data is not accurate.

 

Thanks,

 

Nikita

 

 

From: Johannes Demel [mailto:address@hidden]
Sent: Tuesday, December 17, 2013 12:30 PM
To: Nikita Sharakhov
Cc: address@hidden

Subject: Re: [Discuss-gnuradio] Spectrum Sensing

 

Hi Nikita,

In order to answer your question we need more information on what you want to do exactly. gr-fosphor takes all unprocessed samples and does everything on the GPU. Calculating spectrum, graphical output etc. As far as I know there isn't a way to get the samples back from the GPU.

Cheers

Johannes

 

On Mon, Dec 16, 2013 at 8:12 PM, Nikita Sharakhov <address@hidden> wrote:

Hi Johannes,

 

Thanks for the answer!  I am building my own web-based GUI, so I just need a script that just writes the spectrum data to a text file or to standard command-line output.  Is that possible with gr-fosphor?  Is there any other software that I should look at?

 

Best regards,

 

Nikita

 

From: Johannes Demel [mailto:address@hidden]
Sent: Monday, December 16, 2013 10:58 PM
To: Nikita Sharakhov
Subject: Re: [Discuss-gnuradio] Spectrum Sensing

 

Hi Nikita,

'uhd_fft' is only a graphical frontend for your flowgraph. It contains a WX FFT Sink and some information about your setup. The WX FFT Sink itself seems to be so fast because it only calculates about 10 FFTs per second. All the other input samples are simply dropped. If you want to have a real real-time GUI take a look at gr-fosphor.

If a few snapshots of the spectrum per second are sufficient for you, think about a keeping only a tiny fraction of your input samples. This will speed things up. On the other hand, if you want to calculate a FFT for all samples, look at the FFT block. BTW: the output of the FFT block would be the 'raw samples' you were asking for.

Happy hacking

Johannes

 

On Mon, Dec 16, 2013 at 8:03 AM, Nikita Sharakhov <address@hidden> wrote:

I would like to do spectrum sensing with GNU radio. Is there a good way to get the raw output from uhd_fft.py (the value for each frequency)? I would like to do this programatically (with code), rather than through a GUI.

I have tried doing spectrum sensing with usrp_spectrum_sense.py, and this script has questionable accuracy and seems to be much slower than uhd_fft.py.

Thanks!

 

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