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 <[email protected]> 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 <[email protected]> > 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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