Re: [Discuss-gnuradio] really need suggestions for operating on big blocks of data

[Vincenzo Pellegrini]

Yes Achilleas, the explanation is very clear and useful.
I'll probably go this way.

just two questions:
Yesterday night, I think Ive succeded in passing vector input to my
block, and collecting vector output from it.
so now I do think that I could also perform permutation this way (i.e.
operating ona a big single item rather than on many bytes flowing in and
out). this eases a bit the process, in consideration of the fact that my
interleaver is made up of two parts, one being called the "bit
interleaver" and another called "sybmbol interleaver", both involving
also some demultiplexing of the serial input stream.

so my first question is: 
is permuting vector coefficients a wise way to perform interleaving? /
does the block you were telling me about internally implement anything
like this?

the second is: can I expect a 8 MHz wide (2048 carriers) OFDM signal to
travel safely over the USB2.0 bus (I recall its bandwidth is exactly 8
complex Msps @16 bits) and be interpolated the right way by the USRP?

very many thanks
vincenzo

On Tue, 2007-05-29 at 17:47 -0400, Achilleas Anastasopoulos wrote:
> Vincenzo,
> 
> what you want is already implemented in gnuradio.
> Take a look at the following classes/blocks in gr-trellis:
> interleaver.h/i/cc
> trellis_permutation.h/i/cc
> 
> Brief summary:
> 1) generate a text file (see below) describing your permutation (or have 
> your favorite program generate it automatically)
> 2) Instantiate an "interleaver" object with this file
> 3) instantiate two "permutation" blocks (one for
> the interleaver and one for the deinterleaver) in your code.
> 
> Eg,
> ----
> interleaver=trellis.interleaver("myfile.txt")
> inter = trellis.permutation(interleaver.K(),interleaver.INTER(),1,1)
> deinter = trellis.permutation(interleaver.K(),interleaver.DEINTER(),1,1)
> ----
> 
> the meaning of the last two parameters can be seen from looking at
> the above files/examples, but in your case (where you interleave bytes)
> should be just 1 and 1.
> 
> 
> the text file has the following format (in your case):
> 6048   (the size of the permutation)
> 3 1 0 5 .... (N numbers in {0,1,...,6047} describing what goes where)
> 
> eg, if I want to permute 5 items at a time you would generate the 
> following file:
> 5
> 4 3 2 1 0
> (this will just reverse the order of incoming symbols, ie
> the first becomes fifth, the second fourth, etc).
> 
> I hope this is clear. Let me know if you have any problems with this,
> Achilleas
> 
> 
> Vincenzo Pellegrini wrote:
> > Thanks Achilleas Thanks Eric,
> > 
> > Yes Achilleas, what you have described is right exactly what I need.
> > the constant permutation is indeed a vector hard coded in my block.
> > 
> > my problem is that I could neither set the step of the cycle
> > 
> > for (int i = 0; i < noutput_items; i+= STEP){
> > 
> > as far as 1512, nor as far as 6048.. (well'if I do it runs but the
> > output has no meaning)
> > 
> > another thing I've tried is to demultiplex my input stream into many
> > output streams in order to do interleaving among them, but I don't think
> > it's a good idea.. and actually works only as far as 1512.
> > 
> > Yesterday I realized how to do that by passing just big vectors to my
> > block but I'm still failing to get it to work on vectors longer than
> > 1512 bytes.. :)
> > 
> > what I'm working upon is a dvbt transmitter, as described in 
> > http://www.com-tech.it/downloads/en_300744.pdf
> > 
> > I'm (slowly, because I also have to keep up with my academic duties)
> > climbing up the functional block chain towards the aerial.. :D
> > 
> > so where I think I am now is the Inner Interleaver..
> > 
> > very many thank for listening
> > 
> > vincenzo
> > 
> > On Tue, 2007-05-29 at 10:48 -0400, Achilleas Anastasopoulos wrote:
> > 
> >>vincenzo,
> >>
> >>let me make sure I understand what you want to implement:
> >>
> >>You want a block that processes N=6048 BYTES at a time.
> >>The input is x1,x2,x3....,xN
> >>and the output is another N=6048 bytes which are a
> >>permutation of the input block, ie,
> >>y1,y2,....,yN
> >>such that
> >>y(i)=x(permutation(i)).
> >>Next time another block of N BYTES is input and permuted in the same 
> >>way, etc...
> >>The "permutation" function is prespecified and constant
> >>throughout the operation.
> >>
> >>Is this correct?
> >>
> >>If not, could you please specify exactly the functionality
> >>you want to implement.
> >>
> >>Achilleas
> > 
> > 
> > 
>