Hi Marcus, I spent a week doing tests and do not know what can be the fault. Did you see any mistake? [1] If I transmit the signal with no delay (signal -> FFT -> IFFT -> USRP) I have a small variable delay unwanted in the receiver.
Greetings. [1] Now use powers of two in the FFT lenght (128,256...) 2014-11-19 14:57 GMT+01:00 Carlos Alberto Ruiz Naranjo < carlosruiznara...@gmail.com>: > *** The bandwidth of the signal is 4 MHz. > > > > Greetings, > Carlos Alberto Ruiz Naranjo. > > Área de Aviónica y Sistemas No Tripulados/Avionics and Unmanned Systems > Department > > Parque Tecnológico y Aeronáutico de Andalucía > C/ Wilbur y Orville Wright, 17-19-21 > 41309 La Rinconada > Sevilla (Spain) > (+34) 954179002 > http://www.catec.aero/ > > 2014-11-19 9:03 GMT+01:00 Carlos Alberto Ruiz Naranjo < > carlosruiznara...@gmail.com>: > >> Hello! >> >> I have done the fractional delay block ( http://pastebin.com/cEDfTh9m ). >> Have you seen some error? I have used the proposed filter in "Closed >> Form Variable Fractional Time Delay Using FFT" [1][2] >> This is my flowgraph: >> >> >> >> >> - My signal sample rate is 10230000 samples per second and I want a >> variable delay of 1ns of precision. What is the relationship between the >> maximum precision of fractional delay and the length of the FFT? What is >> the limit? >> >> - Is it a problem the fractional resampler of 1.023? Can it distort my >> signal? [3] >> >> >> Greetings, >> Carlos Alberto Ruiz Naranjo. >> >> Área de Aviónica y Sistemas No Tripulados/Avionics and Unmanned Systems >> Department >> >> Parque Tecnológico y Aeronáutico de Andalucía >> C/ Wilbur y Orville Wright, 17-19-21 >> 41309 La Rinconada >> Sevilla (Spain) >> (+34) 954179002 >> http://www.catec.aero/ >> >> >> >> >> >> >> [1] >> https://www.deepdyve.com/lp/institute-of-electrical-and-electronics-engineers/comments-on-closed-form-variable-fractional-time-delay-using-fft-tNk7X6CH9c >> [2] http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6171834 >> [3] I use the fractional resampler because I can't put a sample rate of >> 10230000 in the USRP block. >> >> >> >> >> 2014-11-17 14:26 GMT+01:00 Marcus Müller <marcus.muel...@ettus.com>: >> >>> Hi Carlos, >>> yes, your formular looks correct, scalar multiplication aside. >>> >>> Regarding your problem: >>> It's not a problem, it's a feature :) >>> you're using window functions in your FFT, that's what's changing your >>> signal. >>> The FFT is but an implementation of the DFT (discrete fourier >>> transform), which is, considering the input as element of a >>> n_fft-dimensional vector space, is but a base change, and thus has an >>> inverse -- the IDFT (incarnated by the IFFT). >>> >>> what you see is something like the norm of the square of the window >>> function; use "rectangular" to avoid this. >>> >>> Greetings, >>> Marcus >>> >>> On 11/17/2014 12:23 PM, Carlos Alberto Ruiz Naranjo wrote: >>> > I have some questions about FFT method. >>> > >>> > - I have done a test with my signal ( [Signal] -> [FFT] -> [IFFT] -> >>> [Signal] >>> > ) and I have a problem with the spectrum (central lobe): >>> > >>> > >>> > >>> > >>> > >>> > - To insert a delay I multiply the FFT by [1], right? >>> > >>> > Can I insert a delay (no variable) if I multiply the FFT by GNURadio >>> sine >>> > complex block? >>> > >>> > >>> > >>> > >>> > Greetings, >>> > Carlos Alberto Ruiz Naranjo. >>> > >>> > Área de Aviónica y Sistemas No Tripulados/Avionics and Unmanned Systems >>> > Department >>> > >>> > Parque Tecnológico y Aeronáutico de Andalucía >>> > C/ Wilbur y Orville Wright, 17-19-21 >>> > 41309 La Rinconada >>> > Sevilla (Spain) >>> > (+34) 954179002 >>> > http://www.catec.aero/ >>> > >>> > >>> > [1] N: length of FFT, m: delay, k: position >>> > >>> > >>> > >>> > 2014-11-12 15:32 GMT+01:00 Marcus Müller <marcus.muel...@ettus.com>: >>> > >>> >> well, yes, you could, but that sounds ugly: >>> >> 1. a sample rate of 1e9Hz implies --for complex float-- a memory >>> >> consumption of 1e9*8B~=8GB per second... >>> >> 2. unwieldy fractional resampling, because 10.23e6 and 1e9 don't have >>> a >>> >> very large common divisor; you'll be interpolating by a factor of >>> 100000 >>> >> just to decimate by 1023... That is effectively just very very many >>> samples >>> >> in-between. >>> >> 3. you're sampling at 10.23MS/s, but you want to do something with a >>> >> temporal resolution of 10 times that rate; that's a phase shift, for >>> sure, >>> >> but I'm afraid that it sounds like you're trying to harm Nyquist in >>> some >>> >> way or another. >>> >> >>> >> When were talking on how to simulate delay introduced by radar range >>> in >>> >> GNU Radio, a wise[1] elder[2] told me to do time shifting in frequency >>> >> domain: >>> >> >>> >> The idea is that a time shift corresponds to frequency shift in >>> frequency >>> >> domain, so you can, within the spectral precision defined by the >>> length of >>> >> your DFT, have arbitrary shifts by doing [time >>> signal]->[DFT]->[multiply >>> >> with complex sine]->[IDFT] . Note that, due to the circular nature of >>> the >>> >> DFT, this will distort the first samples of the output. >>> >> >>> >> Greetings, >>> >> Marcus >>> >> >>> >> [1] one might consider him wise >>> >> [2] not really an elder >>> >> >>> >> >>> >> On 11/12/2014 02:50 PM, Carlos Alberto Ruiz Naranjo wrote: >>> >> >>> >> Hello, >>> >> >>> >> I have in my project a sample rate of 10.23 million samples per >>> second and >>> >> I need to delay the signal +-1ns. With GNURadio block delay I can >>> delay the >>> >> signal 97.75ns (1 / 10,230,000 -> + - one sample). >>> >> >>> >> Could I use the fractional resampler block to enter a variable >>> >> fractional delay? >>> >> Has anyone implemented a fractional delay block? >>> >> >>> >> Thank you. >>> >> >>> >> >>> >> >>> >> >>> >> _______________________________________________ >>> >> Discuss-gnuradio mailing listDiscuss-gnuradio@gnu.orghttps:// >>> lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >> >>> >> >>> >> >>> >> _______________________________________________ >>> >> Discuss-gnuradio mailing list >>> >> Discuss-gnuradio@gnu.org >>> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >> >>> >> >>> >>> >> >
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