Hi all, Thank you Marcus for your kind reply.
My original intention is to test whether there are signal transmission in a certain spectrum band. So at first I want to use energy detection and other methods to test which band has signal, and then compare the probability of detection in different SNR. I store the samples in /out.dat, cos I want to use the sample to calculate the detection probability.(But now I don’t know how to get detection probability, I wonder whether I can use the data to calculate it.) Thanks, Yan From: discuss-gnuradio-bounces+eexyh22=nottingham.ac...@gnu.org [mailto:discuss-gnuradio-bounces+eexyh22=nottingham.ac...@gnu.org] On Behalf Of Marcus Müller Sent: 12 February 2016 11:52 To: discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] The threshold of energy detection Hi Yan, The threshold block converts your signal to 1 if you've been above the "high" value, unless it has fallen below "low" again. Everywhere else, it's 0. See the "documentation" tab in the block properties, or the GNU Radio doxygen manual [1]. But: Parseval's theorem states that energy in frequency and in time domain are directly proportional, so your stream to vector -> FFT->complex to mag²-> vector to stream>moving average can simply be replaced with a complex to mag²->moving average if detecting the average energy in your signal is all you want , which seems probable, seeing that length(average)≈length(FFT). I'm not quite sure what your original intention was when storing (FFT->mag²->average) samples in test_sensor/out.dat; the signal after moving averaging is neither really frequency nor time domain. Out of curiosity: what do you want with that data? There's very valid applications for frequency domain filters (a moving average is actually but a low pass FIR filter, in principle), but the convolution that filtering usually means is often replaced with a multiplication in time domain, which is much less CPU-intense and mathematically equivalent! Best regards, Marcus [1] https://gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1threshold__ff.html#details ¹ For new applications, I recommend Qt rather than WX -- the latter isn't going to be around forever. On 12.02.2016 12:02, Yan Huang wrote: Hi all, I’m using USRP B210 to do spectrum sensing, and the flow graph as attached file. It can get a result that there is a peak at 5.8 GHz which is the receiving signal frequency. But if I change the Moving Average block to a threshold, there is no output like previous one. I want to ask how can I get a result have a peak at 5.8 GHz in frequency domain using threshold. I can only get 1 or 0 in time domain not in frequency domain. Is there anyone can give me some advice? Thanks in advance. Yours Sincerely Yan This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org<mailto:Discuss-gnuradio@gnu.org> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.
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