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/* -*- c++ -*- */
/*
* Copyright 2006-2008,2010,2011 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 <digital_ofdm_frame_acquisition.h>
#include <gr_io_signature.h>
#include <gr_expj.h>
#include <gr_math.h>
#include <cstdio>
#define VERBOSE 0
#define M_TWOPI (2*M_PI)
#define MAX_NUM_SYMBOLS 1000
digital_ofdm_frame_acquisition_sptr
digital_make_ofdm_frame_acquisition (unsigned int occupied_carriers,
unsigned int fft_length,
unsigned int cplen,
const std::vector<gr_complex> &known_symbol,
unsigned int max_fft_shift_len)
{
return gnuradio::get_initial_sptr(new digital_ofdm_frame_acquisition (occupied_carriers, fft_length, cplen,
known_symbol, max_fft_shift_len));
}
digital_ofdm_frame_acquisition::digital_ofdm_frame_acquisition (unsigned occupied_carriers,
unsigned int fft_length,
unsigned int cplen,
const std::vector<gr_complex> &known_symbol,
unsigned int max_fft_shift_len)
: gr_block ("ofdm_frame_acquisition",
gr_make_io_signature2 (2, 2, sizeof(gr_complex)*fft_length, sizeof(char)*fft_length),
gr_make_io_signature2 (2, 2, sizeof(gr_complex)*occupied_carriers, sizeof(char))),
d_occupied_carriers(occupied_carriers),
d_fft_length(fft_length),
d_cplen(cplen),
d_freq_shift_len(max_fft_shift_len),
d_known_symbol(known_symbol),
d_coarse_freq(0),
d_phase_count(0)
{
d_symbol_phase_diff.resize(d_fft_length);
d_known_phase_diff.resize(d_occupied_carriers);
d_hestimate.resize(d_occupied_carriers);
unsigned int i = 0, j = 0;
std::fill(d_known_phase_diff.begin(), d_known_phase_diff.end(), 0);
for(i = 0; i < d_known_symbol.size()-2; i+=2) {
d_known_phase_diff[i] = norm(d_known_symbol[i] - d_known_symbol[i+2]);
}
d_phase_lut = new gr_complex[(2*d_freq_shift_len+1) * MAX_NUM_SYMBOLS];
for(i = 0; i <= 2*d_freq_shift_len; i++) {
for(j = 0; j < MAX_NUM_SYMBOLS; j++) {
d_phase_lut[j + i*MAX_NUM_SYMBOLS] = gr_expj(-M_TWOPI*d_cplen/d_fft_length*(i-d_freq_shift_len)*j);
}
}
}
digital_ofdm_frame_acquisition::~digital_ofdm_frame_acquisition(void)
{
delete [] d_phase_lut;
}
void
digital_ofdm_frame_acquisition::forecast (int noutput_items, gr_vector_int &ninput_items_required)
{
unsigned ninputs = ninput_items_required.size ();
for (unsigned i = 0; i < ninputs; i++)
ninput_items_required[i] = 1;
}
gr_complex
digital_ofdm_frame_acquisition::coarse_freq_comp(int freq_delta, int symbol_count)
{
// return gr_complex(cos(-M_TWOPI*freq_delta*d_cplen/d_fft_length*symbol_count),
// sin(-M_TWOPI*freq_delta*d_cplen/d_fft_length*symbol_count));
return gr_expj(-M_TWOPI*freq_delta*d_cplen/d_fft_length*symbol_count);
//return d_phase_lut[MAX_NUM_SYMBOLS * (d_freq_shift_len + freq_delta) + symbol_count];
}
void
digital_ofdm_frame_acquisition::correlate(const gr_complex *symbol, int zeros_on_left)
{
unsigned int i,j;
std::fill(d_symbol_phase_diff.begin(), d_symbol_phase_diff.end(), 0);
for(i = 0; i < d_fft_length-2; i++) {
d_symbol_phase_diff[i] = norm(symbol[i] - symbol[i+2]);
}
// sweep through all possible/allowed frequency offsets and select the best
int index = 0;
float max = 0, sum=0;
for(i = zeros_on_left - d_freq_shift_len; i < zeros_on_left + d_freq_shift_len; i++) {
sum = 0;
for(j = 0; j < d_occupied_carriers; j++) {
sum += (d_known_phase_diff[j] * d_symbol_phase_diff[i+j]);
}
if(sum > max) {
max = sum;
index = i;
}
}
// set the coarse frequency offset relative to the edge of the occupied tones
d_coarse_freq = index - zeros_on_left;
}
void
digital_ofdm_frame_acquisition::calculate_equalizer(const gr_complex *symbol, int zeros_on_left)
{
unsigned int i=0;
// Set first tap of equalizer
d_hestimate[0] = d_known_symbol[0] /
(coarse_freq_comp(d_coarse_freq,1)*symbol[zeros_on_left+d_coarse_freq]);
// set every even tap based on known symbol
// linearly interpolate between set carriers to set zero-filled carriers
// FIXME: is this the best way to set this?
for(i = 2; i < d_occupied_carriers; i+=2) {
d_hestimate[i] = d_known_symbol[i] /
(coarse_freq_comp(d_coarse_freq,1)*(symbol[i+zeros_on_left+d_coarse_freq]));
d_hestimate[i-1] = (d_hestimate[i] + d_hestimate[i-2]) / gr_complex(2.0, 0.0);
}
// with even number of carriers; last equalizer tap is wrong
if(!(d_occupied_carriers & 1)) {
d_hestimate[d_occupied_carriers-1] = d_hestimate[d_occupied_carriers-2];
}
if(VERBOSE) {
fprintf(stderr, "Equalizer setting:\n");
for(i = 0; i < d_occupied_carriers; i++) {
gr_complex sym = coarse_freq_comp(d_coarse_freq,1)*symbol[i+zeros_on_left+d_coarse_freq];
gr_complex output = sym * d_hestimate[i];
fprintf(stderr, "sym: %+.4f + j%+.4f ks: %+.4f + j%+.4f eq: %+.4f + j%+.4f ==> %+.4f + j%+.4f\n",
sym .real(), sym.imag(),
d_known_symbol[i].real(), d_known_symbol[i].imag(),
d_hestimate[i].real(), d_hestimate[i].imag(),
output.real(), output.imag());
}
fprintf(stderr, "\n");
}
}
int
digital_ofdm_frame_acquisition::general_work(int noutput_items,
gr_vector_int &ninput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
const gr_complex *symbol = (const gr_complex *)input_items[0];
const char *signal_in = (const char *)input_items[1];
gr_complex *out = (gr_complex *) output_items[0];
char *signal_out = (char *) output_items[1];
int unoccupied_carriers = d_fft_length - d_occupied_carriers;
int zeros_on_left = (int)ceil(unoccupied_carriers/2.0);
if(signal_in[0]) {
d_phase_count = 1;
correlate(symbol, zeros_on_left);
calculate_equalizer(symbol, zeros_on_left);
signal_out[0] = 1;
}
else {
signal_out[0] = 0;
}
for(unsigned int i = 0; i < d_occupied_carriers; i++) {
out[i] = d_hestimate[i]*coarse_freq_comp(d_coarse_freq,d_phase_count)
*symbol[i+zeros_on_left+d_coarse_freq];
}
d_phase_count++;
if(d_phase_count == MAX_NUM_SYMBOLS) {
d_phase_count = 1;
}
consume_each(1);
return 1;
}
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