> 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 <mailto: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 <mailto: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: >> 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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