I received the signal in gnu radio sink, then take the file and divide it into 128 length sequences"because I used 128 IFFT in the transmitter". I made FFT to get the signal in frequency domain. Finally, I plotted the results.
Best regards Maksim On Tue, Oct 27, 2015 at 12:14 PM, scott tiger <thekiller.sc...@gmail.com> wrote: > I received the signal in gnu radio sink, then take the file and divide it > into 128 length sequences"because I used 128 IFFT in the transmitter". I > made FFT to get the signal in frequency domain. Finally, I plotted the > results. > > Best regards > Maksim > > On Tue, Oct 27, 2015 at 12:08 PM, Marcus Müller <marcus.muel...@ettus.com> > wrote: > >> That's what I don't understand – how did you put them together? >> >> I saved the received signal in a file, then I did further steps in matlab >> (FFT, gathering ...). >> >> What **are** those steps? >> >> >> On 10/27/2015 12:02 PM, scott tiger wrote: >> >> Hi Marcus >> of course in gnu, I used a band pass filter. But I have spikes in the >> center frequency of the signal. >> >> >> That's what I don't understand – how did you put them together? >> >> I saved the received signal in a file, then I did further steps in matlab >> (FFT, gathering ...). >> >> Best regards >> Maksim >> >> On Tue, Oct 27, 2015 at 10:50 AM, Marcus Müller <marcus.muel...@ettus.com >> > wrote: >> >>> Hi Maksim, >>> >>> In the receiver I made FFT and plot the correspond figure. >>> >>> So, that's pretty clearly frequency domain of the receive signal, right? >>> So that might answer your question regarding DC offset: If there is DC >>> offset, you'd see a constant spike at the center frequency. That's not >>> really the case here, if I understand correctly. >>> >>> The last figure which I sent it is the signal in the frequency domain >>> which are repeated with each transmission "I put them all together to >>> compare them." >>> >>> That's what I don't understand – how did you put them together? >>> >>> Best regards, >>> Marcus >>> >>> >>> >>> >>> On 10/27/2015 10:44 AM, scott tiger wrote: >>> >>> Hi Marcus, >>> Y-Axis is the amplitude "abs(of the complex signal)". >>> X-Axis is not pure frequency domain or time domain, because the figure >>> is drown from follow: >>> I generate ZC sequence "its amplitude equals to 1 in frequency domain" >>> then I made IFFT and transmit the signal using USRP. The environment is a >>> cable. I received the signal from another antenna of the same USRP. In the >>> receiver I made FFT and plot the correspond figure. Since, I am the source >>> file in the transmitter transmit the signal many times"repeat activated". >>> The last figure which I sent it is the signal in the frequency domain which >>> are repeated with each transmission "I put them all together to compare >>> them." >>> I attached the same figure with more explanation "each black block is >>> the signal in the frequency domain", but block 1 .....n is the same signal >>> transmitted in different times. >>> >>> Thank you for your reply >>> Best regards >>> Maksim >>> >>> >>> On Mon, Oct 26, 2015 at 4:47 PM, Marcus Müller <marcus.muel...@ettus.com >>> > wrote: >>> >>>> Hi Maksim, >>>> >>>> Could you keep this on the mailing list? >>>> >>>> I don't fully understand: >>>> >>>> > In fact, the figure shows repeated OFDM signal, each of it in >>>> frequency domain. >>>> >>>> So you take the OFDM signal, and shift it in frequency domain, and then >>>> have N identical OFDM signals transmitted at the same time? >>>> Can you clearly state what your X-Axis and what you Y-Axis are? >>>> >>>> >>>> For example, I transmitted a zadoff-chu sequence which has a flat >>>> characteristic in frequency domain. The environment was a short cable with >>>> attenuation. The received signal also showed in frequency domain. >>>> I attached it also "the figure shows the repeated sequences 2Mhz >>>> bandwidth in frequency domain". What I am curious about are spikes which >>>> appear usually in the center frequency? I thought may it is related some >>>> how with dc offset in USRP. >>>> >>>> >>>> I don't understand this graph: >>>> [image: Maksim] >>>> >>>> What is the X-Axis, what is the Y-Axis? >>>> >>>> Maybe you meant that you take values from a Zadoff-Chu sequence, IFFT >>>> them, thus generating an OFDM signal (which, by the way, is also a ZC >>>> sequence), add guard intervals and transmit them? >>>> >>>> >>>> >>>> I attached it also "the figure shows the repeated sequences 2Mhz >>>> bandwidth in frequency domain". What I am curious about are spikes which >>>> appear usually in the center frequency? I thought may it is related some >>>> how with dc offset in USRP. >>>> >>>> I'm really getting intrigued by what you observe :) but we'll really >>>> have to understand the graphs, which at this point, I'm afraid, I don't. >>>> >>>> Best regards, >>>> Marcus >>>> >>>> >>> >>> >> >> >
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