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] <mailto:[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: > 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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