Re: [Discuss-gnuradio] Fractional delay in fractional resampler block

[Carlos Alberto Ruiz Naranjo]

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 <address@hidden>:

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.

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