Hi Carlos, I just realized that maybe the core problem here is that I don't really understand what you're trying to do -- could you explain what this system will be used for, and why you need that particular sampling rate etc?
Best regards, Marcus On 11/28/2014 05:59 PM, Marcus Müller wrote: > Hello Carlos, > > I don't really think that what you built really reflects what you're > trying to achieve: I thought you needed a really small delay in time > domain, and a sampling rate conversion from 10MHz to 10.23MHz. > > Why are you doing a delay in frequency domain? That will simply be a > frequency shift in time domain, which you could easily realize (and with > much smaller computational error) by multiplying with a complex sine in > time domain. > > I don't really understand what you mean with "small variable delay in > the receiver": Do you mean your system is not somehow synchronized? > > Best regards, > Marcus Müller > > On 11/28/2014 05:16 PM, Carlos Alberto Ruiz Naranjo wrote: >> 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 >>>>>>> >>>>>>> _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
