Re: [Discuss-gnuradio] Channel model - the identity channel

[Raj Bhattacharjea]

Thanks for the hints for where to look and why this happens from a code perspective. I don't think it makes sense from a semantic perspective (if the user says taps=1, she should get the unity gain delay free channel) but I'm guessing "patches are welcome" is the appropriate response to this minor usability issue.

On Tuesday, June 28, 2016, Andrej Rode <address@hidden> wrote:
> Hey Raj,
>
> > introduces a delay that can be corrected by applying the taps [0,0,0,1].
> > See the attached flowgraph that subtracts the signals before and after
> > the channel model; if you let taps = 1, the two signals don't cancel. If
> > you use taps = [0,0,0,1], they do.
>
> The delay you are seeing is introduced by the fractional_resapmler
> inside the channel_model block. The FIR filter inside the fractional
> resampler needs to build up and therefore introduces a initial delay of
> three samples.
>
> If you want to know more about the insides of the channel model I
> suggest you look at the sources [0][1] yourself.
>
> Greetings,
> Andrej
>
> [0] ./gr-channels/lib/channel_model_impl.cc
> [1] ./gr-channels/lib/channel_model_impl.h


--

Raj Bhattacharjea, PhD

Georgia Tech Research Institute

Information and Communications Laboratory

http://www.prism.gatech.edu/~rb288/

404.407.6622