Re: [Discuss-gnuradio] How to speed up spectrum sensing?

[devin kelly]

Well if you're sensing a 40 MHz band you have to retune.  The largest band you can sense without retuning is about 25 MHz.

Also I would try higher FFT sizes, like 1024, 2048, or 4096.  Watch your CPU load when you run your script, your processor probably isn't slowing you down even with large FFT sizes.  

I highly suggest you look at tune delay and dwell delay, manipulating those can really speed up your sensing times.  The tune delay you can only set to be so low without corrupting your data.  However, the dwell delay you can set to be as low as one sweep, it all depends on how much averaging you want to do.  Look at the code where it deals with the delay times.

Also, just how fast do you need this to be?  You should be able to do thousands of sweeps in less than a second if I remember correctly.

Devin

On Thu, May 26, 2011 at 8:59 PM, Yang <address@hidden> wrote:

Thank you for replying.

I have already tried different fft size (256, 128, 32, etc) but as you said it did not change my sensing time. I also change my decimation but no luck too.

I intend to sense a broad band, say, 20M or 40M. But it seems this script costs too much time working. Should I retune or not? Because if I do not it only sense a very narrow band.

-- 
Yang
Sent with Sparrow

On 2011年5月27日星期五 at 上午4:15, devin kelly wrote:

Changing the fft size won't change your sensing time that much unless the machine you're using is really slow or the fft size is outrageous.  What fft sizes are you using?

What will affect your sensing time more is the sampling/decimation rate you sent, the tune delay, and the dwell delay.  Be careful when changing the tune delay, if it is too short your data will be corrupted.

Look at the usrp_spectrum_sense.py code and try this:

$ python usrp_spectrum_sense.py --help

Also, since you're only trying to look at a narrow band, usrp_spectrum_sense.py isn't for you. This script is really for looking at different bands and different times, but you really only need to look at one band.  Basically, you never need to retune and a lot of that script does is retune.

Devin

On Sat, May 14, 2011 at 8:11 AM, Alexander Chemeris <address@hidden> wrote:

On Fri, May 13, 2011 at 14:25, Tom Rondeau <address@hidden> wrote:
> On Fri, May 13, 2011 at 11:12 AM, Yang <address@hidden> wrote:
>>
>> Hi all,
>> I am working on the implementation of dynamic spectrum access with
>> gnuradio and usrp2. I modified usrp_spectrum_sense for usrp2 to do the
>> sensing job. However, I find the sensing speed is intolerably slow, which is
>> about 1s for 1MHz.
>
> Yang,
> Considering that the USRP2 can sample 25 MHz, you should be able to capture
> that bandwidth instantaneously.

Note, that while USRP2 can sample 25MHz, you probably can't receive
that much in your PC. I'm working with USRP N210 and having troubles
with receiving even 16 MSPS.

--
Regards,
Alexander Chemeris.

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