Re: [Discuss-gnuradio] Impulse response in DVB-T, someboby knows how to calculate?

[Federico 'Larroca' La Rocca]

Hi,

If you want the channel impulse response you may simply perform an IFFT on the channel frequency response estimated by the equalizer of gr-dtv/dvbt (don't forget to "shift" it, so that it starts at 0 and ends at 2\pi). I think this is performed by the block "Demod Reference Signals", but it does not output the estimated channel. However, modifications should be relatively simple once you dig a little bit into the code and understand what you are looking for. You may look at the corresponding blocks at gr-isdbt ("Sync and Channel Estimation") to look for ideas on how to achieve this.

best

Federico

2016-10-02 20:03 GMT-03:00 Tom Rondeau <address@hidden>:

On Sun, Oct 2, 2016 at 2:40 PM, Cinaed Simson <address@hidden> wrote:

On 10/01/2016 04:46 PM, Juan Antonio wrote:
> Hello, someone would know how to calculate the impulse response of a
> COFDM, DVB-T channel with an SDR device?
>
> Thank you in advance
>
>

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An inverse DFT on a sinc function in the frequency domain yields a sine
function in the time domain. And a DFT on the sine function in the time
domain yields a sinc function in the frequency domain.

No, the DFT of a sine function is an impulse. More formally, a Dirac delta function.

The sinc function is the result of a truncated sine wave where the sine wave is multiplied by a square wave. The DFT of a square wave is a sinc, so with a truncated sine wave in the time domain, you are convolving a sinc with a delta function in the frequency domain.

Tom

 

I presume the "C" in COFDM means to chop up the bandwidth into carriers
such that the sinc function in one channel hits nulls in the other
channels.

Piece of cake in theory.

There's a gr-dvbt project on github

  https://github.com/BogdanDIA/gr-dvbt

I don't know anything about it - I don't even know if it works.

-- Cinaed

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