Hi Maksim, > I sent a lot of different signals using USRP + gnu radio "specially > with flat characteristic in frequency domain" but I notice some > strange behavior, that the received signals has some spikes. For > example, I attached OFDM signal mentioned this behavior in red.
I believe what we're looking at is the time domain magnitude of an OFDM signal in complex baseband, right? signal In that case, I'm not surprised -- OFDM classically has what is typically called a Peak-Average-Power-Ratio (PAPR) problem . Since you know how OFDM works: Assume you feed it a symbol vector of /all the same symbols/. What does the time domain signal look like? Considering that, these spikes aren't even really high; eyeballing the average power during OFDM transmissionto be around digital 0.15, a maximum peak of three times that isn't really what I'd even consider a spike -- it's not even 5dB higher than the avarage; and considering the noise floor seems to be somewhere around 0.005, your receiver doesn't even need 20dB of dynamic range. > Is it because of some properties of USRP? I doubt that; unless you're driving your USRP's frontend's amplifier very hard, you should have 20dB spurious-free dynamic range without problem. Best regards, Marcus On 23.10.2015 15:19, scott tiger wrote: > Thank you very much Tom and Marcus for your response. > One another question: > I sent a lot of different signals using USRP + gnu radio "specially > with flat characteristic in frequency domain" but I notice some > strange behavior, that the received signals has some spikes. For > example, I attached OFDM signal mentioned this behavior in red. Is it > because of some properties of USRP? > > P.S. the signal sent using a short cable as an environment, so the > received signal should be approximately the same as the transmitted. > > Thank you for your reply > Best regards > Maksim > > > On Thu, Oct 15, 2015 at 4:43 PM, Marcus Müller > <[email protected] <mailto:[email protected]>> wrote: > > Hi Tom, hi Maksim, > > problem being that afaik we don't have stuff to parse the metadata > file sink data to something matlabby. But maybe I'm wrong and > someone already went and did the specific task of using the python > module[1] to first parse the file and then the segment headers, > and push them into a matlab-compatible storage format. > > Best regards, > Marcus > > [1] from gnuradio.blocks import parse_file_metadata > > On 10/15/2015 04:20 PM, Tom Rondeau wrote: >> On Thu, Oct 15, 2015 at 7:54 AM, Marcus Müller >> <[email protected] <mailto:[email protected]>> wrote: >> >> Hi Maksim, >> >> you're right, the raw sample data can't contain any sideband >> information such as to what the USRP was tuned to. >> Maybe you just want to use the "tag debug" block to print out >> the sample offsets at which an rx_freq tag was seen, and >> parse that textual information. >> >> Best regards, >> Marcus >> >> >> On 10/15/2015 12:13 PM, scott tiger wrote: >>> Dear all, >>> I tried to implement the frequency hopping and I did it, But >>> I have one problem. After stored the signal in dat file and >>> tried to separate the frequencies in matlab "it is imposible >>> to do that". >>> Can you tell me please if there is some block in GNUradio >>> which can I use to store the changing frequency to be >>> comparable whith the received signal to cut the received >>> signal according to the generated frequency? >>> >>> >>> Thank you for any advice >>> Maksim >> >> >> I'd recommend the file mete sink: >> >> http://gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1file__meta__sink.html >> >> You can read about the file metadata format here: >> http://gnuradio.org/doc/doxygen/page_metadata.html >> >> Tom >> > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] <mailto:[email protected]> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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