1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
|
/* -*- 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 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.
*/
/*
* 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 <stdio.h>
#include <gnuradio/io_signature.h>
#include "ofdm_coarse_frequency_correct_impl.h"
#include <gnuradio/expj.h>
#define M_TWOPI (2*M_PI)
namespace gr {
namespace dab {
ofdm_coarse_frequency_correct::sptr
ofdm_coarse_frequency_correct::make(unsigned int fft_length, unsigned int num_carriers, unsigned int cp_length)
{
return gnuradio::get_initial_sptr
(new ofdm_coarse_frequency_correct_impl(fft_length, num_carriers, cp_length));
}
ofdm_coarse_frequency_correct_impl::ofdm_coarse_frequency_correct_impl(unsigned int fft_length, unsigned int num_carriers, unsigned int cp_length)
: gr::sync_block("ofdm_coarse_frequency_correct",
gr::io_signature::make (1, 1, sizeof(gr_complex)*fft_length),
gr::io_signature::make (1, 1, sizeof(gr_complex)*num_carriers)),
d_fft_length(fft_length), d_num_carriers(num_carriers), d_cp_length(cp_length),
d_symbol_num(0), d_freq_offset(0), d_delta_f(0)
{
d_zeros_on_left = (d_fft_length-d_num_carriers)/2;
set_tag_propagation_policy(TPP_ONE_TO_ONE);
}
float
ofdm_coarse_frequency_correct_impl::mag_squared(const gr_complex sample) {
const float __x = sample.real();
const float __y = sample.imag();
return __x * __x + __y * __y;
}
void
ofdm_coarse_frequency_correct_impl::correlate_energy(const gr_complex *symbol)
{
unsigned int i, index;
double sum=0, max=0;
/* energy based correlation - note that DAB uses a zero central carrier -
* we always sum up the energy for all carriers except DC; this is however
* only done for the first offset; for the others, the diff is calculated
*/
/* offset 0 */
for (i=0; i<d_num_carriers+1; i++) {
if (i != d_num_carriers/2)
sum+=(double)mag_squared(symbol[i]);
}
max = sum;
index = 0;
/* other offsets */
for (i=1; i<d_fft_length-d_num_carriers; i++) {
/* diff on left side */
sum -= (double)mag_squared(symbol[i-1]);
/* diff for zero carrier */
sum += (double)mag_squared(symbol[i+d_num_carriers/2-1]);
sum -= (double)mag_squared(symbol[i+d_num_carriers/2]);
/* diff on rigth side */
sum += (double)mag_squared(symbol[i+d_num_carriers]);
/* new max found? */
if (sum > max) {
max = sum;
index = i;
}
}
d_freq_offset = index;
}
int
ofdm_coarse_frequency_correct_impl::work(int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
unsigned int i;
gr_complex phase_offset_correct;
/* partially adapted from gr_ofdm_frame_acquisition.cc
however:
- energy based offset frequency estimation instead of using the pilot symbol
- correlation in linear time instead of sqare
- only magnitude equalisation (phase equalisation is unnecessery, because of the diff_phasor later in the chain)
- calculation of the magnitude scale factors is done in the same step as the calculation of the energy for the freq. offset estimation -> very efficient :)
*/
const gr_complex *iptr = (const gr_complex *) input_items[0];
gr_complex *optr = (gr_complex *) output_items[0];
// This block is only handling one item at a time, so we only need to check one:
std::vector<tag_t> tags;
get_tags_in_range(tags, 0, nitems_read(0), nitems_read(0) + 1, pmt::mp("first"));
bool tag_now = false;
for(int i=0;i<tags.size();i++) {
int current;
current = tags[i].offset - nitems_read(0);
if (current == 0) tag_now = true;
}
if (tag_now) { // Stream tag was found
correlate_energy(iptr);
d_delta_f = d_freq_offset+d_num_carriers/2-d_fft_length/2;
// fprintf(stderr, "cfs: coarse freq. offset (subcarriers): %d\n", d_delta_f);
d_symbol_num = 0;
} else {
d_symbol_num++;
}
/* correct phase offset from removing cp */
/* could be done after diff phasor, then it would be the same offset for each symbol; but its hardly much of an overhead */
phase_offset_correct = gr_expj(-M_TWOPI*(float)d_delta_f*(float)d_cp_length/(float)d_fft_length * (float)d_symbol_num);
for (i=0;i<d_num_carriers/2;i++) {
optr[i] = iptr[d_freq_offset+i]*phase_offset_correct;
}
for (i=d_num_carriers/2;i<d_num_carriers;i++) {
optr[i] = iptr[d_freq_offset+i+1]*phase_offset_correct;
}
return 1;
}
}
}
|
