Good morning!
I started writing a small signal processing block (OFDM transmitter) and ran
into some problems.
My starting point was the well written gr-how-to-write-a-block tutorial.
I have, let's say, 1536 input samples and want to produce 1800 output
samples with my block. When I run my code with small values
(say fft size of 32) I get valid OFDM symbols but a lot of zeros in
between. When I uses higher values either the scheduler quits
(
sched: <gr_block ofdm_tx_vcc (0)> is
requesting more input data
than we can provide.
)
or even the buffer can't be allocated. This makes me sure that there is
a programming mistake on my part, but I can't seem to find it.
I would be thankful if somebody could point out my mistake? The main
files are attached, a modified gr-how-to-build-a-block can be found here:
http://www.1c3.de/gr-dab.tar.bz2 .
Yet another question: Can blocks somehow interchange values? I would
like to write two blocks, one that estimates a frequency offset and
another one that compensates it (simple modulation). Or do I have to
do that in one block?
Jens
/* -*- c++ -*- */
%feature("autodoc", "1"); // generate python docstrings
%include "exception.i"
%import "gnuradio.i" // the common stuff
%{
#include "gnuradio_swig_bug_workaround.h" // mandatory bug fix
#include "ofdm_tx_cc.h"
#include <stdexcept>
%}
// ----------------------------------------------------------------
/*
* First arg is the package prefix.
* Second arg is the name of the class minus the prefix.
*
* This does some behind-the-scenes magic so we can
* access howto_square_ff from python as howto.square_ff
*/
GR_SWIG_BLOCK_MAGIC(ofdm,tx_cc);
ofdm_tx_cc_sptr ofdm_do_tx_cc (int ofdm_sym_len, int gi_len, int fft_len);
class ofdm_tx_cc : public gr_sync_block
{
private:
ofdm_tx_cc (int ofdm_sym_len, int gi_len, int fft_len);
};
/* -*- c++ -*- */
/*
* Copyright 2004 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/*
* config.h is generated by configure. It contains the results
* of probing for features, options etc. It should be the first
* file included in your .cc file.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <ofdm_tx_cc.h>
#include <gr_io_signature.h>
#include <gri_fft.h>
#include <math.h>
/*
* Create a new instance of gr_ofdm_tx_cc and return
* a boost shared_ptr. This is effectively the public constructor.
*/
ofdm_tx_cc_sptr
ofdm_do_tx_cc (int ofdm_sym_len, int gi_len, int fft_len)
{
return ofdm_tx_cc_sptr (new ofdm_tx_cc (ofdm_sym_len, gi_len, fft_len));
}
/*
* Specify constraints on number of input and output streams.
* This info is used to construct the input and output signatures
* (2nd & 3rd args to gr_block's constructor). The input and
* output signatures are used by the runtime system to
* check that a valid number and type of inputs and outputs
* are connected to this block. In this case, we accept
* only 1 input and 1 output.
*/
static const int MIN_IN = 1; // mininum number of input streams
static const int MAX_IN = 1; // maximum number of input streams
static const int MIN_OUT = 1; // minimum number of output streams
static const int MAX_OUT = 1; // maximum number of output streams
/*
* The private constructor
* Takes length of OFDM symbol (including guard interval) and guard interval length as
* arguments. Variable FFT length and subcarrier selection mask is implemented later.
*/
ofdm_tx_cc::ofdm_tx_cc (int ofdm_sym_len, int gi_len, int fft_len)
: gr_block ("ofdm_tx_vcc",
gr_make_io_signature (MIN_IN, MAX_IN, (ofdm_sym_len-gi_len)*sizeof(gr_complex)),
gr_make_io_signature (MIN_OUT, MAX_OUT, ofdm_sym_len * sizeof(gr_complex)))
{
d_ofdm_sym_len = ofdm_sym_len;
d_gi_len = gi_len;
d_fft_len = ofdm_sym_len-gi_len; // FIXME: not yet implemented
// OFDM symbols can't be split, contrain request size
set_output_multiple(d_ofdm_sym_len);
// set approximate out rate
set_relative_rate((double)(d_ofdm_sym_len) / (double)(d_ofdm_sym_len-d_gi_len));
d_fft = new gri_fft_complex(d_fft_len, true);
}
/*
* Our virtual destructor.
*/
ofdm_tx_cc::~ofdm_tx_cc ()
{
delete d_fft;
}
/*
* Implementation of gr_block::forecast() - estimate the number of input samples, if we are asked to
* output noutput_items samples.
*/
void
ofdm_tx_cc::forecast (int noutput_items, gr_vector_int &ninput_items_required)
{
// noutput_items should be a multiple of d_ofdm_sym_len (see constructor)
assert ((noutput_items % d_ofdm_sym_len) == 0);
int nblocks = noutput_items / d_ofdm_sym_len;
int input_required = nblocks * (d_ofdm_sym_len-d_gi_len);
unsigned ninputs = ninput_items_required.size();
for (unsigned int i = 0; i < ninputs; i++)
ninput_items_required[i] = input_required;
}
/*
* Here the actual work is done - "d_ofdm_sym_len-d_gi_len" complex samples are consumed and
* "d_ofdm_sym_len" samples are written.
*/
int
ofdm_tx_cc::general_work (int noutput_items,
gr_vector_int &ninput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
// pointers to data
const gr_complex *in = (const gr_complex *) input_items[0];
gr_complex *out = (gr_complex *) output_items[0];
int out_count=0; // counts the number of written complex samples
int in_count=0; // counts number of samples consumed
printf("available in (samples): %i\n", ninput_items[0]);
printf("requested out (samples): %i\n", noutput_items);
while(out_count<noutput_items)
{
memcpy(d_fft->get_inbuf(), in, d_fft_len*sizeof(gr_complex)); // copy to input buffer
d_fft->execute(); // compute fft
// cyclic prefix is repetition of the end in the beginning
memcpy(out, d_fft->get_outbuf()+(d_fft_len-d_gi_len), d_gi_len*sizeof(gr_complex)); // guard interval; last argument of memcpy is length in bytes
memcpy(out+d_gi_len, d_fft->get_outbuf(), d_fft_len*sizeof(gr_complex)); // copy data
// increase pointers, counters
in += d_ofdm_sym_len-d_gi_len;
out += d_ofdm_sym_len;
out_count += d_ofdm_sym_len;
in_count += d_ofdm_sym_len-d_gi_len;
}
// noutput_items should always be a multiple of d_ofdm_sym_len, so the assert shouldn't fail now
assert (out_count == noutput_items);
// Tell runtime system how many input items we consumed.
consume_each(in_count);
// Tell runtime system how many output items we produced.
return out_count;
}
/* -*- c++ -*- */
/*
* Copyright 2004 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#ifndef INCLUDED_OFDM_TX_CC_H
#define INCLUDED_OFDM_TX_CC_H
#include <gr_block.h>
class gri_fft_complex;
class ofdm_tx_cc;
/*
* We use boost::shared_ptr's instead of raw pointers for all access
* to gr_blocks (and many other data structures). The shared_ptr gets
* us transparent reference counting, which greatly simplifies storage
* management issues. This is especially helpful in our hybrid
* C++ / Python system.
*
* See http://www.boost.org/libs/smart_ptr/smart_ptr.htm
*
* As a convention, the _sptr suffix indicates a boost::shared_ptr
*/
typedef boost::shared_ptr<ofdm_tx_cc> ofdm_tx_cc_sptr;
/*!
* \brief Return a shared_ptr to a new instance of howto_square2_ff.
*
* To avoid accidental use of raw pointers, howto_square2_ff's
* constructor is private. howto_make_square2_ff is the public
* interface for creating new instances.
*/
ofdm_tx_cc_sptr ofdm_do_tx_cc ();
/*!
* \brief OFDM transmitter.
* \ingroup block
*
* A simple OFDM transmitter block.
*/
class ofdm_tx_cc : public gr_block
{
private:
// The friend declaration allows ofdm_do_tx_cc to
// access the private constructor.
friend ofdm_tx_cc_sptr ofdm_do_tx_cc (int ofdm_sym_len, int gi_len, int fft_len);
ofdm_tx_cc (int ofdm_sym_len, int gi_len, int fft_len); // private constructor
unsigned int d_ofdm_sym_len;
unsigned int d_gi_len;
unsigned int d_fft_len;
gri_fft_complex *d_fft;
public:
~ofdm_tx_cc (); // public destructor
// Where all the action really happens
int general_work (int noutput_items,
gr_vector_int &ninput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items);
void forecast(int noutput_items, gr_vector_int &ninput_items_required);
};
#endif /* INCLUDED_OFDM_TX_H */
#!/usr/bin/env python
#
# Copyright 2004 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2, or (at your option)
# any later version.
#
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING. If not, write to
# the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
# Boston, MA 02111-1307, USA.
#
from gnuradio import gr, gr_unittest
import ofdm, inspect
class qa_ofdm (gr_unittest.TestCase):
def setUp (self):
self.fg = gr.flow_graph ()
def tearDown (self):
self.fg = None
def test_001_square_ff (self):
fft_len = 32 # fails for higher values (eg. 512)
gi_len = 4
ofdm_sym_len = fft_len+gi_len;
ofdm_tx = ofdm.ofdm_do_tx_cc (ofdm_sym_len, gi_len, 0)
print ofdm_tx.output_multiple()
print ofdm_tx.relative_rate()
s2p = gr.serial_to_parallel (gr.sizeof_gr_complex, fft_len)
p2s = gr.parallel_to_serial (gr.sizeof_gr_complex, ofdm_sym_len)
dst = gr.file_sink(gr.sizeof_gr_complex, "ofdm_sym_out")
SNR=10
src = gr.noise_source_c(gr.GR_GAUSSIAN, pow(10.0,-SNR/20.0))
self.fg.connect(src, s2p)
self.fg.connect(s2p, ofdm_tx)
self.fg.connect(ofdm_tx, p2s)
self.fg.connect(p2s, dst)
self.fg.run()
if __name__ == '__main__':
gr_unittest.main ()
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