Energy detector

GNU Radio
1

HI ALL

I’m trying to implement ENERGY DETECTOR using gnu radio.
Is there any library or modules to help. Especially when implementing
energy
detection we need to estimate the awgn.
I’ve searched in
http://gnuradio.org/doc/doxygen/
but i cannot find any relative information.

regards,

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2

I implemented an energy detector on the GNU Radio by using a GPU at my
old
job.

We used an FFT based method which is not uncommon. What you do is FFT
the
data and then compute the PSD. Do this in overlapping blocks (e.g.
12.5%,
50%, etc). You could optionally use a window too. Then, with the PSDs,
you
create a long term average (LTA) and a short term average (STA). The
STA
might be 4 PSDs and the LTA might be 10 PSDs. Given the LTA, you set a
threshold so many dB about it (e.g. 3dB). Call this threshold the noise
riding threshold (NRT). Finally, to detect energy, given the NRT, you
find
places where the STA is greater than the NRT…that’s where you have
an
energy. You can get a coarse center frequency and bandwidth by
examining
which PSD bins cross the NRT.

Depending on your environment, you may find that you have lots of
isolated,
single-bin crossing due to noise. You can just filter these by saying
an
“energy” must have a minimum of 5 consecutive bins. Or, you can write
an
algorithm to combine bins. Say you have this, where C is a crossing:
C_C_CC__

You can filter this to get:
CCCCCC__

-Isaac

abbasi9999 wrote:

regards,

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3

On 12/9/2009 7:49 AM, abbasi9999 wrote:

This can all be done using the usrp_spectrum_sense script or even
looking at usrp_fft to see how this is done. One way to estimate the
noise is have a known “quiet time” where you measure the energy of the
channel and use a threshold derived from that as the signal detection
threshold.

Tim

4

Thanks for the reply>
I’ve already checked usrp_spectrum_sense.
I have two points:

  1. usrp_fft: does this file still exist ? because i cannot find it. but
    i
    think, it just give you the same results as usrp_spectrum_sense without
    tuning the frequency band.
  2. You meant by using “quiet time”, is to use the same method of
    estimating
    the signal power (using fft), However, use it when you are sure that
    there
    is no signal (can we consider this in Cognitive Radio systems??).

thanks

Newman, Timothy wrote:

but i cannot find any relative information.
Tim

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