[Discuss-gnuradio] How to integrate a specific number of vectors element-wise in gnuradio?

[Eskil Varenius]

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