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Re: [Discuss-gnuradio] Rayleigh fading simulator

From: Nasi
Subject: Re: [Discuss-gnuradio] Rayleigh fading simulator
Date: Fri, 07 Mar 2014 15:11:37 +0400

Hi Richard,

Thanks a lot!

Statistical validation can be correct for different Doppler implementations in general.
However the way they add Doppler shifts is different.

I took your code and implemented in matlab and compared with jakes model of matlab's rayleighchan function.
There is a big mismatch in how they add Doppler shift from sample to sample. May be this is an interpolation/filter issue.
This happens when I add Doppler shift in a deterministic way. I keep the phase constant and time coherent.
After that I take a look at the Doppler shift that the methods add. As an input I take ones to see the difference.

You know better than me how Doppler is added from sample to sample.
Especially, for a short time period (coherent time) within one OFDM symbol the Doppler shift is linear.
At least we can assume that it is almost linear which we should not feel the difference too much.
Classical Doppler models like Jakes model would represent this property.

Now I am trying to test it in reality and find out how it is added to the input data from sample to sample.
And which model is better to take into account. I need it since I am trying to compensate it back in the receiver as a part of my research work.

I will appreciate your comments on this.


Четверг, 6 марта 2014, 8:56 +13:00 от Richard Clarke <address@hidden>:
Hi Nasi,

when I checked the fading models supplied in GNU Radio 3.7 the other week they seemed to be generating nasty glitches in their output. You could instead take a look at 'my' custom block for doing simple single path configurable doppler Rayleigh fading. The output of this has been statistically validated against the theoretical Rayleigh distribution. I can provide further details of the validations that have been done if required. There is a version of the block for both GNURadio 3.6 and 3.7 API's. This block works fine when instantiated singly, however if you try and build a multipath fading model out of it by instantiating more than one of these blocks (with delays) at the python level then the whole thing tends to seg fault, for as yet undetermined reasons.

You are welcome to give it a try however.

Here is the link to the GNU Radio 3.7 version of the block, https://github.com/hawk2050/gr-rccBlocks

Feedback welcome


On 3 March 2014 06:25, Nasi <address@hidden> wrote:

it is so simple, I try to explain again:

my question is how you add Doppler to the channel (the code)?

Different people add it in a different way like using FIR or IIR filters. So, I am wondering if you used IIR filter or FIR. If you know of course, how you coded it?

Воскресенье, 2 марта 2014, 15:26 +01:00 от Martin Braun <address@hidden>:

On 03/01/2014 04:35 PM, Nasi wrote:
> Helo all,
> I need your help for simulation of the Rayleigh fading.
> I know that I can use GNURADIO channel models, but I need to know how
> they simulated.
> For example I am looking into the 'fading_model_impl.cc' in channel
> models of GNURADIO.
> Can someone tell me how this is simulated?

Can you specify what you want to do? I don't understand the question.
If you connect this block to your signal, it will "simulate" the channel.

> I heard some people also developed it on their own, but I am not sure if
> that is available and supported by you.

Developed their own what? Channels?
You can configure these channels to different types of scenarios.


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