gr_pn_correlator_cc.cc

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/* -*- c++ -*- */
/*
 * Copyright 2007 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 3, 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., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <gr_pn_correlator_cc.h>
#include <gr_io_signature.h>

gr_pn_correlator_cc_sptr
gr_make_pn_correlator_cc(int degree, int mask, int seed)
{
  return gr_pn_correlator_cc_sptr (new gr_pn_correlator_cc(degree, mask, seed));
}

gr_pn_correlator_cc::gr_pn_correlator_cc(int degree, int mask, int seed)
  : gr_sync_decimator ("pn_correlator_cc",
		       gr_make_io_signature (1, 1, sizeof(gr_complex)),
		       gr_make_io_signature (1, 1, sizeof(gr_complex)),
		       (unsigned int)((1ULL << degree)-1)) // PN code length
{
  d_len = (unsigned int)((1ULL << degree)-1);
  if (mask == 0)
    mask = gri_glfsr::glfsr_mask(degree);
  d_reference = new gri_glfsr(mask, seed);
  for (int i = 0; i < d_len; i++)	// initialize to last value in sequence
    d_pn = 2.0*d_reference->next_bit()-1.0;
}

gr_pn_correlator_cc::~gr_pn_correlator_cc()
{
  delete d_reference;
}

int
gr_pn_correlator_cc::work(int noutput_items,
			  gr_vector_const_void_star &input_items,
			  gr_vector_void_star &output_items)
{
  const gr_complex *in = (const gr_complex *) input_items[0];
  gr_complex *out = (gr_complex *) output_items[0];
  gr_complex sum;

  for (int i = 0; i < noutput_items; i++) {
    sum = 0.0;

    for (int j = 0; j < d_len; j++) {
      if (j != 0)		            // retard PN generator one sample per period
	d_pn = 2.0*d_reference->next_bit()-1.0; // no conditionals
      sum += *in++ * d_pn;
    }

    *out++ = sum*gr_complex(1.0/d_len, 0.0);
  }

  return noutput_items;
}