Here are all the related files.
C++ header
***************
* dsss_firdes.h *
***************
#ifndef _DSSS_FIRDES_H_
#define _DSSS_FIRDES_H_
#include <vector>
#include <cmath>
class dsss_firdes {
public:
dsss_firdes();
static std::vector<float> 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 <stdexcept>
using std::vector;
// Raised Cosine Filter
vector<float>
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<float> 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-(4*alpha*alpha*(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 = 8*alpha*(xindx/spb)*(xindx/spb);
rc1 = sin(x1)*sin(alpha*x1)/x2;
}
else{
rc1 = (sin(x1)*cos(alpha*x1))/(x1*x2);
}
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<float> 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)
On Sun, Jul 3, 2011 at 10:33 AM, Tom Rondeau <[email protected]> wrote:
> On Sun, Jul 3, 2011 at 3:25 AM, John Andrews <[email protected]> wrote:
>
>> 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.
>>
>
> 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.
>
>
>> 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.
>>
>>>
>>> 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
>
>
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