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Re: [Discuss-gnuradio] anyone implement the Raleigh fadingmodel/multi-p


From: Richard Clarke
Subject: Re: [Discuss-gnuradio] anyone implement the Raleigh fadingmodel/multi-path?
Date: Wed, 30 Jan 2008 13:53:56 +1300
User-agent: Thunderbird 2.0.0.9 (Windows/20071031)

OK, I'll look at gathering up all relevant code and documentation and see what hosting options I have at this end. When I've got this sorted I'll post a link to the location of the files. In the meantime a little additional detail, taken from some of the comments in one of the header files. It will be great to progress this module such that multiple delayed paths can be implemented at the C++ level without requiring python to handle the delays.

*------------------------------------------------------------------
/*

This class implements a flat Rayleigh Fading Simulator based on Christos Komninakis work referred to in his paper "A Fast and Accurate Rayleigh Fading Simulator" (http://www.ee.ucla.edu/~chkomn/). Some analysis has been carried out by myself confirming that his algorithm is similar to the Rayleigh model available within Matlab "rayleighchan()".


Inputs

- seed: the random channel seed (e.g. -115).
- fdT: Discrete Doppler Rate (small positive fraction, e.g. 0.001 - 0.2), where fd is the Doppler fade frequency and 1/T is the sample rate of the channel. Note that the current implementation only supports rational fractions of 0.2. To accommodate other values the IIR filter needs to re-designed using Matlab (please reefer to the paper mentioned above for details). - pwr: the square root power of the resulting fading waveform (e.g. pwr = 5 would produce a fading waveform with an output power of 25). - flag_indep: Determines whether individual blocks processed by the channel should be treated as independent blocks or as one continuous block. 1 if blocks are independent, 0 if continuous across blocks.

Jonas Hodel
01/02/07
*/ *---------------------------------------------------------------

Cheers
Richard
(Please note: I have no control over the signature attached to the bottom of this email, sorry! ;-)

George Nychis wrote:
Hi Richard,

This would be great! I have great use for this, and I'm sure many others would too. Did he generate any documentation showing his evaluation of his implementation, and any details of it? (like a final research paper).

Could you make this code publicly available to the list so that we can review its implementation and discuss integrating it in to the code base? We could work on integrating the multiple paths in to the C++ block and making it flexible.

If you host it for us, it won't undergo just one set of eyes, but many sets of eyes on the list :) But make sure to link to it, rather than send an attachment because of list restrictions. Then we can put it in a features branch within the SVN repository to work on it if needed.

Thank you!
George


Richard Clarke wrote:
Hi George,

I have had a Summer student doing some work on this (a year ago now). He implemented a GNU Radio module that can do Rayleigh channel simulation. He based it on a particular paper (I'd have to look it up) for the implementation. He verified the statistical performance of his implementation against the Matlab Rayleigh channel model and against theory and found it to be a close match. I'm not entirely convinced of the delayed multiple path aspects of the design/implementation but haven't had time to look into it further. In fact as it stands I believe the GNU Radio module (at C++ level) only handles a single flat fading path and doing multiple delayed paths is done at the python module level and which invokes multiple instances of the Flat fading Rayleigh C++ GNU Radio module.

I'd welcome another set of eyes and someone more experienced than I am with GNU Radio to help finish off this potentially very useful addition to the GNU Radio code base.

Cheers
Richard



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