SWIG related problem with new filter function

GNU Radio
1

Hi,
Based on gr_firdes.cc/gr_firdes.h/gfr_firdes.i I developed a similar
class
to generate filter taps for a Raised Cosine filter. The following is the
SWIG interface file and the C++ header with .cc file containing the
algorithm for the static function declared in the header. The
compilation
goes without errors but when I import in Python environment I do not see
this function being imported. It seems like SWIG doesn’t see the
definition
of the member functin ‘raised_cosine’.

SWIG INTERFACE

%{
#include “dsss_firdes.h”
%}

GR_SWIG_BLOCK_MAGIC(dsss,firdes);
class dsss_firdes
{
public:
static std::vector raised_cosine(double gain, double
sampling_freq,
double symbol_rate, double alpha, int ntaps);
};

C++ HEADER
class dsss_firdes {
public:
static std::vector raised_cosine (double gain, double
sampling_freq, double symbol_rate, double alpha, int ntaps);
};

Thanks

2

On Fri, Jul 1, 2011 at 8:36 AM, John A. [email protected] wrote:

};

Are you doing this in your own top-level block (dsss from the looks of
it)
or under a current GNU Radio directory like gnuradio-core where the
gr_firdes currently is?

You haven’t mentioned adding anything to the Makefile so that it is
built
properly. If you are working under gnuradio-core/src/lib/general, you’ll
also want to add your .h and .i files to general.i so that it get’s
compiled.

Also, just curious, what application are you interested in that requires
a
raised cosine filter? And couldn’t you just create a root raised cosine
filter and convolve the the taps against themselves to make the raised
cosine taps?

Tom

3

Hi Tom,

Are you doing this in your own top-level block (dsss from the looks of it)
or under a current GNU Radio directory like gnuradio-core where the
gr_firdes currently is?

Yes, I am doing this in my own top-level directory named ‘dsss’
(abbreviation for direct sequence spread spectrum)

You haven’t mentioned adding anything to the Makefile so that it is built
properly. If you are working under gnuradio-core/src/lib/general, you’ll
also want to add your .h and .i files to general.i so that it get’s
compiled.

I added the names to Makefile.am like I added the remaining names of
files.
The Makefile.am has been adapted from howto-write-a-block. The C++ part
gets
compiled without any problem but when importing in python it throws an
undefined_variable_dsss_firdes_Z*** type of error, which according to my
previous experience occurs with wrong SWIG interface problem. I am
pretty
sure I am having a SWIG related issue here.

Also, just curious, what application are you interested in that requires a
raised cosine filter? And couldn’t you just create a root raised cosine
filter and convolve the the taps against themselves to make the raised
cosine taps?

I am developing a BPSK based Direct sequence spread spectrum Tx/Rx and
at
the transmitter i wanted to use a raised cosine filter when
interpolating
from symbol to N samples before sending it to the USRP. I am not sure if
this is the preferred method but I haven’t found any documentation
related
to DSSS that mentions pulse-shaping.

4

On Sun, Jul 3, 2011 at 3:25 AM, John A. [email protected] wrote:

undefined_variable_dsss_firdes_Z*** type of error, which according to my
previous experience occurs with wrong SWIG interface problem. I am pretty
sure I am having a SWIG related issue here.

Ok, it sounds like you are doing everything correctly. In my
experience
with this stuff, it usually comes down to a small typo somewhere. You
can
post your files here (.i, .h, and Makefile) so others to maybe have a
look
to see if there’s anything incorrect in them.

to DSSS that mentions pulse-shaping.

Tom

There is definitely some work on pulse shaping of DSSS systems. I
believe,
though, that they all use root raised cosine filters. This is done at
both
the transmitter and receiver so that the received signal has gone
through
two root raised cosine filters to make the raised cosine filter, which
is a
Nyquist filter.

Tom

5

John,
Did you ever figure out your problem with this? It looks like what you
are
doing is ok. The gr_firdes.i file uses the %rename function, so is it
possible you aren’t seeing your raised cosine code because you are
expecting
it under a different name?

If you do dir(dsss), what do you get?

Tom

6

Here are all the related files.

C++ header

  • dsss_firdes.h *

#ifndef DSSS_FIRDES_H
#define DSSS_FIRDES_H

#include
#include

class dsss_firdes {
public:
dsss_firdes();

static std::vector raised_cosine (double gain, double
sampling_freq,
double symbol_rate, double alpha, int ntaps);
};

#endif

C++ Source file -

  • dsss_firdes.cc *

#include “dsss_firdes.h”
#include

using std::vector;

// Raised Cosine Filter

vector
dsss_firdes::raised_cosine (double gain, double sampling_freq, double
symbol_rate, double alpha, int ntaps)
{
ntaps |= 1; // ensure that ntaps is odd

double spb = sampling_freq/symbol_rate; // samples per bit/symbol
vector taps(ntaps);
double scale = 0;
for(int i=0;i<ntaps;i++)
{
double x1,x2,rc1;
double xindx = i - ntaps/2;
x1 = M_PI * xindx/spb;
x2 = 1-(4alphaalpha*(xindx/spb)*(xindx/spb));

  if(i == ntaps/2){
        taps[i] = 1;
        continue;
   }
  if(fabs(x2) < 0.000001){ // manage rounding errors. treat 0.000001

as
zero
x2 = 8alpha(xindx/spb)(xindx/spb);
rc1 = sin(x1)sin(alphax1)/x2;
}
else{
rc1 = (sin(x1)cos(alphax1))/(x1x2);
}
taps[i] = rc1;
scale += taps[i];
}

  for(int i=0;i<ntaps;i++){
       taps[i] = taps[i] * gain / scale;
    }
  return taps;

}

SWIG interface
** dsss.i **

%include “gnuradio.i”

%{
#include “dsss_firdes.h”
%}

//GR_SWIG_BLOCK_MAGIC(dsss,firdes);
class dsss_firdes
{
public:
static std::vector raised_cosine(double gain, double
sampling_freq,
double symbol_rate, double alpha, int ntaps);
};

  • Makefile.am *

include $(top_srcdir)/Makefile.common

C/C++ headers get installed in ${prefix}/include/gnuradio

grinclude_HEADERS = dsss_firdes.h

###################################

SWIG Python interface and library

TOP_SWIG_IFILES = dsss.i

Install so that they end up available as:

import gnuradio.dsss

This ends up at:

${prefix}/lib/python${python_version}/site-packages/gnuradio

dsss_pythondir_category = gnuradio

additional sources for the SWIG-generated library

dsss_la_swig_sources = dsss_firdes.cc

include $(top_srcdir)/Makefile.swig

add some of the variables generated inside the Makefile.swig.gen

BUILT_SOURCES = $(swig_built_sources)

Do not distribute the output of SWIG

no_dist_files = $(swig_built_sources)