Dear Gnuradio enthusiasts,
Short version:
Does someone have a good approach to average a specific (but large)
number of vectors together element-wise with the exactly same relative
weight? Say I want the two vectors [1,2,3,3] and [1,2,3,4] coming one
after another giving the output [1,2,3,3.5] - is there any block
available that does this and if so: how? (In reality I will have many
more vectors and elements though).
Long version:
I'm building an application for radio astronomy using Gnuradio and the
USRP. I think I have hit a point where I have to write my own custom
blocks for gnuradio to accomplish what I want, but before I dive into
that I want to ask you as well if you have already solved this current
problem of mine. I have tried to google this extensively and gotten
closer and closer but without finding exactly what I need. I have
played with the Gnuradio-companion and find it very helpful. I have
some python experience but not much C++, hence my hesitation to dive
into the custom block writing before I made sure no-one has already
solved this.
The grand plan is as follows:
1) Use an USRP to recieve a signal, I know how.
2) Divide the stream of samples into vectors, I know how.
3) Take the FFT of the vectors one by one, I know how.
4) Average the vectors coming from the FFT together element-wise. I
don't know how.
5) Save the averaged vector to a file, I know how.
What I cannot solve is step 4: I need to take the N vectors (each of
size M) coming from the FFT-block and sum them together element-wise
to produce one vector of size M.
I found Jonathan Corgans interesting reply to a similar question on
"How to integrate a vector signal" at
http://lists.gnu.org/archive/html/discuss-gnuradio/2007-04/msg00146.html
where Jonathan advises to use the gr.single_pole_iir_filter_xx block
with a parameter 0<alpha <1. It seems to me that such an approach
works well if one wants to average "a couple" of vectors, and also if
you want to apply weights to the averaging. But, if I want to average
Exactly say 1027 vectors together with Exactly the same weight to all
of them, it seems to me that I cannot use the single_pole_iir_filter.
Am I mistaken? At least I have not managed to make it do what I want.
Perhaps this is the solution and I'm just confused by the signal
processing language which I'm not used to yet (I have a more
theoretical physics/math background).
I found Jonathan Corgans entries from 2006 on vector addition in
Gnuradio,
http://lists.gnu.org/archive/html/patch-gnuradio/2006-06/msg00002.html
and I can use the adder in Gnuradio companion. So, in principle I
could split my vectors in N streams, convert each stream to a vector
again, feed them to a vector adder with N inputs and then get the
output I want. But it seems suboptimal to have to deal with this
splitting step to N inputs. I just want to add the vectors element-wise.
I found the simple_ra package which claims to do things for radio
astronomy very similar to what I want to do
(https://www.cgran.org/wiki/simple_ra#ProjectDescription). But, the
unfortunately I have not found any extensive documentation of the code
and I have not yet managed to understand if I can extract a solution
to my problem from there. To use part of the simple_ra package
functionality as a black-box is unfortunately no option since I have
similar projects in mind if I solve this one, but they would not be
related to radio astronomy.
Hence my question: Does someone have a good approach to average a
specific (but large) number of vectors together element-wise with the
exactly same relative weight? Say I want the two vectors [1,2,3,3] and
[1,2,3,4] coming one after another giving the output [1,2,3,3.5] - is
there any block available that does this and if so: how?
Best regards,
Eskil Varenius
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I'm curious as to why, in radio astronomy, you need to be able to
control the number of FFTs you average together. Since nature isn't
nearly so
exacting as, for example, telecommunications, in that regard.
The "code" in simple_ra is produced by a .grc flow-graph. The .grc
flow-graph is shipped with the code, and such flow-graphs are very-nearly
self-documenting. There's also a README that comes with it. Since
I maintain simple_ra as a very-much part-time time, and I have a handful
of *other* applications I support/maintain, and I'm the
maintainer/author of build-gnuradio, I haven't had time to write more
extensive documentation.
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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