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
|
/* -*- c++ -*- */
/*
* Copyright 2013 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.
*/
#ifndef INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H
#define INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H
#include <digital/api.h>
#include <gnuradio/block.h>
namespace gr {
namespace digital {
/*!
* \brief Estimate channel and coarse frequency offset for OFDM from preambles
* \ingroup ofdm_blk
* \ingroup synchronizers_blk
*
* \details
* Input: OFDM symbols (in frequency domain). The first one (or two) symbols are expected
* to be synchronisation symbols, which are used to estimate the coarse freq offset
* and the initial equalizer taps (these symbols are removed from the stream).
* The following \p n_data_symbols are passed through unmodified (the actual equalisation
* must be done elsewhere).
* Output: The data symbols, without the synchronisation symbols.
* The first data symbol passed through has two tags:
* 'ofdm_sync_carr_offset' (integer), the coarse frequency offset as number of carriers,
* and 'ofdm_sync_eq_taps' (complex vector).
* Any tags attached to the synchronisation symbols are attached to the first data
* symbol. All other tags are propagated normally.
*
* This block assumes the frequency offset is even (i.e. an integer multiple of 2).
*
* [1] Schmidl, T.M. and Cox, D.C., "Robust frequency and timing synchronization for OFDM",
* Communications, IEEE Transactions on, 1997.
* [2] K.D. Kammeyer, "Nachrichtenuebertragung," Chapter. 16.3.2.
*/
class DIGITAL_API ofdm_chanest_vcvc : virtual public block
{
public:
typedef boost::shared_ptr<ofdm_chanest_vcvc> sptr;
/*
* \param sync_symbol1 First synchronisation symbol in the frequency domain. Its length must be
* the FFT length. For Schmidl & Cox synchronisation, every second sub-carrier
* has to be zero.
* \param sync_symbol2 Second synchronisation symbol in the frequency domain. Must be equal to
* the FFT length, or zero length if only one synchronisation symbol is used.
* Using this symbol is how synchronisation is described in [1]. Leaving this
* empty forces us to interpolate the equalizer taps.
* If you are using an unusual sub-carrier configuration (e.g. because of OFDMA),
* this sync symbol is used to identify the active sub-carriers. If you only
* have one synchronisation symbol, set the active sub-carriers to a non-zero
* value in here, and also set \p force_one_sync_symbol parameter to true.
* \param n_data_symbols The number of data symbols following each set of synchronisation symbols.
* Must be at least 1.
* \param eq_noise_red_len If non-zero, noise reduction for the equalizer taps is done according
* to [2]. In this case, it is the channel influence time in number of
* samples. A good value is usually the length of the cyclic prefix.
* \param max_carr_offset Limit the number of sub-carriers the frequency offset can maximally be.
* Leave this zero to try all possibilities.
* \param force_one_sync_symbol See \p sync_symbol2.
*/
static sptr make(
const std::vector<gr_complex> &sync_symbol1,
const std::vector<gr_complex> &sync_symbol2,
int n_data_symbols,
int eq_noise_red_len=0,
int max_carr_offset=-1,
bool force_one_sync_symbol=false
);
};
} // namespace digital
} // namespace gr
#endif /* INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H */
|
