GNU Radio C++ API Reference: corr_est_cc.h Source File

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corr_est_cc.h
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1/* -*- c++ -*- */
2/*
3 * Copyright 2015 Free Software Foundation, Inc.
4 *
5 * This file is part of GNU Radio
6 *
7 * SPDX-License-Identifier: GPL-3.0-or-later
8 *
9 */
10
11#ifndef INCLUDED_DIGITAL_CORR_EST_CC_CC_H
12#define INCLUDED_DIGITAL_CORR_EST_CC_CC_H
13
14#include <gnuradio/digital/api.h>
15#include <gnuradio/sync_block.h>
16
17namespace gr {
18namespace digital {
19
20/*!
21 * \brief Correlate stream with a pre-defined sequence and estimate peak
22 * \ingroup synchronizers_blk
23 *
24 * \details
25 * Input:
26 * \li Stream of complex samples.
27 *
28 * Output:
29 * \li Output stream that just passes the input complex samples
30 * \li tag 'phase_est': estimate of phase offset
31 * \li tag 'time_est': estimate of symbol timing offset
32 * \li tag 'corr_est': the correlation value of the estimates
33 * \li tag 'amp_est': 1 over the estimated amplitude
34 * \li tag 'corr_start': the start sample of the correlation and the value
35 *
36 * \li Optional 2nd output stream providing the advanced correlator output
37 *
38 * This block is designed to search for a sync word by correlation
39 * and uses the results of the correlation to get a time and phase
40 * offset estimate. These estimates are passed downstream as
41 * stream tags for use by follow-on synchronization blocks.
42 *
43 * The sync word is provided as a set of symbols after being
44 * filtered by a baseband matched filter.
45 *
46 * The phase_est tag can be used by downstream blocks to adjust
47 * their phase estimator/correction loops, and is currently
48 * implemented by the gr::digital::costas_loop_cc block.
49 *
50 * The time_est tag can be used to adjust the sampling timing
51 * estimate of any downstream synchronization blocks and is
52 * currently implemented by the gr::digital::pfb_clock_sync_ccf
53 * block.
54 *
55 * The caller must provide a "time_est" and "phase_est" tag
56 * marking delay from the start of the correlated signal segment,
57 * in order to mark the proper point in the sync word for
58 * downstream synchronization blocks. Generally this block cannot
59 * know where the actual sync word symbols are located relative to
60 * "corr_start", given that some modulations have pulses with
61 * intentional ISI. The user should manually examine the primary
62 * output and the "corr_start" tag position to determine the
63 * required tag delay settings for the particular modulation,
64 * sync word, and downstream blocks used.
65 *
66 * For a discussion of the properties of complex correlations,
67 * with respect to signal processing, see:
68 * Marple, Jr., S. L., "Estimating Group Delay and Phase Delay
69 * via Discrete-Time 'Analytic' Cross-Correlation, _IEEE_Transcations_
70 * _on_Signal_Processing_, Volume 47, No. 9, September 1999
71 *
72 */
73 typedef enum {
74 THRESHOLD_DYNAMIC,
75 THRESHOLD_ABSOLUTE,
76} tm_type;
77
78 class DIGITAL_API corr_est_cc : virtual public sync_block
79{
80public:
81 typedef std::shared_ptr<corr_est_cc> sptr;
82
83 /*!
84 * Make a block that correlates against the \p symbols vector
85 * and outputs a phase and symbol timing estimate.
86 *
87 * \param symbols Set of symbols to correlate against (e.g., a
88 * sync word).
89 * \param sps Samples per symbol
90 * \param mark_delay tag marking delay in samples after the
91 * corr_start tag
92 * \param threshold Threshold of correlator.
93 * The meaning of this parameter depends on the threshold
94 * method used. For DYNAMIC threshold method, this
95 * parameter is actually 1 - Probability of False
96 * Alarm (under some inaccurate assumptions). The
97 * code performs the check
98 * |r[k]|^2 + |r[k+1]|^2 <> -log(1-threshold)*2*E,
99 * where r[k] is the correlated incoming signal,
100 * and E is the average sample energy of the
101 * correlated signal. For ABSOLUTE threshold method,
102 * this parameter sets the threshold to a fraction
103 * of the maximum squared autocorrelation. The code
104 * performs the check |r[k]|^2 <> threshold * R^2,
105 * where R is the precomputed max autocorrelation
106 * of the given sync word. Default is 0.9
107 * \param threshold_method Method for computing threshold.
108 */
109 static sptr make(const std::vector<gr_complex>& symbols,
110 float sps,
111 unsigned int mark_delay,
112 float threshold = 0.9,
113 tm_type threshold_method = THRESHOLD_ABSOLUTE);
114
115 virtual std::vector<gr_complex> symbols() const = 0;
116 virtual void set_symbols(const std::vector<gr_complex>& symbols) = 0;
117
118 virtual unsigned int mark_delay() const = 0;
119 virtual void set_mark_delay(unsigned int mark_delay) = 0;
120
121 virtual float threshold() const = 0;
122 virtual void set_threshold(float threshold) = 0;
123};
124
125} // namespace digital
126} // namespace gr
127
128#endif /* INCLUDED_DIGITAL_CORR_EST_CC_H */
gr::digital::corr_est_cc
Definition corr_est_cc.h:79
gr::digital::corr_est_cc::mark_delay
virtual unsigned int mark_delay() const =0
gr::digital::corr_est_cc::set_mark_delay
virtual void set_mark_delay(unsigned int mark_delay)=0
gr::digital::corr_est_cc::make
static sptr make(const std::vector< gr_complex > &symbols, float sps, unsigned int mark_delay, float threshold=0.9, tm_type threshold_method=THRESHOLD_ABSOLUTE)
gr::digital::corr_est_cc::threshold
virtual float threshold() const =0
gr::digital::corr_est_cc::sptr
std::shared_ptr< corr_est_cc > sptr
Definition corr_est_cc.h:81
gr::digital::corr_est_cc::set_symbols
virtual void set_symbols(const std::vector< gr_complex > &symbols)=0
gr::digital::corr_est_cc::symbols
virtual std::vector< gr_complex > symbols() const =0
gr::digital::corr_est_cc::set_threshold
virtual void set_threshold(float threshold)=0
gr::sync_block::sync_block
sync_block(void)
Definition sync_block.h:28
api.h
DIGITAL_API
#define DIGITAL_API
Definition gr-digital/include/gnuradio/digital/api.h:18
gr::digital::tm_type
tm_type
Correlate stream with a pre-defined sequence and estimate peak.
Definition corr_est_cc.h:73
gr::digital::THRESHOLD_ABSOLUTE
@ THRESHOLD_ABSOLUTE
Definition corr_est_cc.h:75
gr::digital::THRESHOLD_DYNAMIC
@ THRESHOLD_DYNAMIC
Definition corr_est_cc.h:74
gr::digital
Definition adaptive_algorithm.h:22
gr
GNU Radio logging wrapper.
Definition basic_block.h:29
sync_block.h