Re: [Discuss-gnuradio] FM multipath fading simulation issue

[Marcus Müller]

Hi Konrad,

Sooo I remember both blog entries on [1] and [2] regarding the flat/Rayleigh fading model. There were fixes to the models in GR, so if you're using those, be sure to use a recent version of GR!

Also, as so often, you're right, the public docs of the freq.-selective fading channel model [3] are a bit too sparse. But to be really brutally honest with you here: since you're writing a thesis on this, looking into the source code would've been a good idea; so let me point you to that quickly [4]. If I skim this correctly it's basically a tapped delay line model made up from multiple flat faders! I think the blog posts I referred to are the right thing to look at when understanding those.

Note that I really think the documentation isn't quite sufficient here – soooo if you'd want to research how these channel models exactly work, and write up a couple lines of prose about that, you could get eternal fame by extending the documentation here! That would be really appreciated (also, if you happen to let's say incorporate an extensive discussion of channel models in your thesis, and make that thesis publicly available, it'd be totally ok and even appreciated if you'd cite your thesis in what short documentation makes sense in the API docs).

Best regards,
Marcus


[1] http://oshearesearch.com
[2] https://www.bastibl.net
[3] http://gnuradio.org/doc/doxygen/classgr_1_1channels_1_1selective__fading__model.html
[4] https://github.com/gnuradio/gnuradio/blob/master/gr-channels/lib/selective_fading_model_impl.cc

On 08/05/2016 11:31 AM, Konrad Puchalski wrote:

Hi there,

 

I work at a company that develope tuner modules.I am a student and want to simulate mulitpath fading for fm broadcast signals. That is my thesis.

The model/scenario should work like this:

 

Imagine that the transmitter is locatetd and 0 kilometer. The car (or receiver) is driving infront the transmitter in a distance X a continuous circle

At this point there would be a LOS so only the doppler effect would affect the received signal.

 

Additionaly I want to define a point where the signal will be reflected. So LOS-Path + NLOS-Path.

My Signal source have to be a 1kHz Tone, FM modulated and with a deviation of 22.5kHz.

 

As far as I can see, GnuRadio has two fading models. "Fading Model" and the "Frequency Selective Fading Model".

What does these models actually contain? I think that the meaning of this model is not clear enough for me.

Fading effect occure because of multipath signal propagation. So I would assume to have a parameter where I can tell the block how much paths I want and how long is the time delay betweet the several paths.

 

Talking about the doppler effect there are two different equations: One for the case that the receiver is moving away from the transmitter and one for the case when it is moving towards the transmitter.

The normalized max. Doppler is a static function, so how does itdistinguish between the directions of movement? How does it affect the signal?

 

When I select the NLOS Model: How many paths do the model actually simulate? Just one and I have to use n blocks for n paths ?

 

Can't I simulate a simple fading by adding a source and the same source but delayed together ??

 

Mayby someone can help me with this issue?

Or is my approach completely wrong ?

 

Attached you find my flowgraph.

 

 

Thank you very much!

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