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control_loop.h
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/* -*- c++ -*- */
/*
* Copyright 2011,2013 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* SPDX-License-Identifier: GPL-3.0-or-later
*
*/
#ifndef GR_BLOCKS_CONTROL_LOOP
#define GR_BLOCKS_CONTROL_LOOP
#include <gnuradio/blocks/api.h>
#include <gnuradio/math.h>
namespace gr {
namespace blocks {
/*!
* \brief A second-order control loop implementation class.
*
* \details
* This class implements a second order control loop and is
* intended to act as a parent class to blocks which need a control
* loop (e.g., gr::digital::costas_loop_cc,
* gr::analog::pll_refout_cc, etc.). It takes in a loop bandwidth
* as well as a max and min frequency and provides the functions
* that control the update of the loop.
*
* The loop works of alpha and beta gains. These gains are
* calculated using the input loop bandwidth and a pre-set damping
* factor. The damping factor can be changed using the
* #set_damping_factor after the block is
* constructed. The alpha and beta values can be set using their
* respective #set_alpha or #set_beta functions if very precise
* control over these is required.
*
* The class tracks both phase and frequency of a signal based on
* an error signal. The error calculation is unique for each
* algorithm and is calculated externally and passed to the
* advance_loop function, which uses this to update its phase and
* frequency estimates.
*
* This class also provides the functions #phase_wrap and
* #frequency_limit to easily keep the phase and frequency
* estimates within our set bounds (phase_wrap keeps it within
* +/-2pi).
*/
class BLOCKS_API control_loop
{
protected:
float d_phase, d_freq;
float d_max_freq, d_min_freq;
float d_damping, d_loop_bw;
float d_alpha, d_beta;
public:
control_loop(void) {}
control_loop(float loop_bw, float max_freq, float min_freq);
virtual ~control_loop();
/*! \brief Update the system gains from the loop bandwidth and damping factor.
*
* \details
* This function updates the system gains based on the loop
* bandwidth and damping factor of the system. These two
* factors can be set separately through their own set
* functions.
*/
void update_gains();
/*! \brief Advance the control loop based on the current gain
* settings and the inputted error signal.
*/
void advance_loop(float error)
{
d_freq = d_freq + d_beta * error;
d_phase = d_phase + d_freq + d_alpha * error;
}
/*! \brief Keep the phase between -2pi and 2pi.
*
* \details
* This function keeps the phase between -2pi and 2pi. If the
* phase is greater than 2pi by d, it wraps around to be -2pi+d;
* similarly if it is less than -2pi by d, it wraps around to
* 2pi-d.
*
* This function should be called after advance_loop to keep the
* phase in a good operating region. It is set as a separate
* method in case another way is desired as this is fairly
* heavy-handed.
*/
void phase_wrap()
{
while (d_phase > (2 * GR_M_PI))
d_phase -= 2 * GR_M_PI;
while (d_phase < (-2 * GR_M_PI))
d_phase += 2 * GR_M_PI;
}
/*! \brief Keep the frequency between d_min_freq and d_max_freq.
*
* \details
* This function keeps the frequency between d_min_freq and
* d_max_freq. If the frequency is greater than d_max_freq, it
* is set to d_max_freq. If the frequency is less than
* d_min_freq, it is set to d_min_freq.
*
* This function should be called after advance_loop to keep the
* frequency in the specified region. It is set as a separate
* method in case another way is desired as this is fairly
* heavy-handed.
*/
void frequency_limit()
{
if (d_freq > d_max_freq)
d_freq = d_max_freq;
else if (d_freq < d_min_freq)
d_freq = d_min_freq;
}
/*******************************************************************
* SET FUNCTIONS
*******************************************************************/
/*!
* \brief Set the loop bandwidth.
*
* \details
* Set the loop filter's bandwidth to \p bw. This should be
* between 2*pi/200 and 2*pi/100 (in rads/samp). It must also be
* a positive number.
*
* When a new damping factor is set, the gains, alpha and beta,
* of the loop are recalculated by a call to update_gains().
*
* \param bw (float) new bandwidth
*/
virtual void set_loop_bandwidth(float bw);
/*!
* \brief Set the loop damping factor.
*
* \details
* Set the loop filter's damping factor to \p df. The damping
* factor should be sqrt(2)/2.0 for critically damped systems.
* Set it to anything else only if you know what you are
* doing. It must be a number between 0 and 1.
*
* When a new damping factor is set, the gains, alpha and beta,
* of the loop are recalculated by a call to update_gains().
*
* \param df (float) new damping factor
*/
void set_damping_factor(float df);
/*!
* \brief Set the loop gain alpha.
*
* \details
* Sets the loop filter's alpha gain parameter.
*
* This value should really only be set by adjusting the loop
* bandwidth and damping factor.
*
* \param alpha (float) new alpha gain
*/
void set_alpha(float alpha);
/*!
* \brief Set the loop gain beta.
*
* \details
* Sets the loop filter's beta gain parameter.
*
* This value should really only be set by adjusting the loop
* bandwidth and damping factor.
*
* \param beta (float) new beta gain
*/
void set_beta(float beta);
/*!
* \brief Set the control loop's frequency.
*
* \details
* Sets the control loop's frequency. While this is normally
* updated by the inner loop of the algorithm, it could be
* useful to manually initialize, set, or reset this under
* certain circumstances.
*
* \param freq (float) new frequency
*/
void set_frequency(float freq);
/*!
* \brief Set the control loop's phase.
*
* \details
* Sets the control loop's phase. While this is normally
* updated by the inner loop of the algorithm, it could be
* useful to manually initialize, set, or reset this under
* certain circumstances.
*
* \param phase (float) new phase
*/
void set_phase(float phase);
/*!
* \brief Set the control loop's maximum frequency.
*
* \details
* Set the maximum frequency the control loop can track.
*
* \param freq (float) new max frequency
*/
void set_max_freq(float freq);
/*!
* \brief Set the control loop's minimum frequency.
*
* \details
* Set the minimum frequency the control loop can track.
*
* \param freq (float) new min frequency
*/
void set_min_freq(float freq);
/*******************************************************************
* GET FUNCTIONS
*******************************************************************/
/*!
* \brief Returns the loop bandwidth.
*/
float get_loop_bandwidth() const;
/*!
* \brief Returns the loop damping factor.
*/
float get_damping_factor() const;
/*!
* \brief Returns the loop gain alpha.
*/
float get_alpha() const;
/*!
* \brief Returns the loop gain beta.
*/
float get_beta() const;
/*!
* \brief Get the control loop's frequency estimate.
*/
float get_frequency() const;
/*!
* \brief Get the control loop's phase estimate.
*/
float get_phase() const;
/*!
* \brief Get the control loop's maximum frequency.
*/
float get_max_freq() const;
/*!
* \brief Get the control loop's minimum frequency.
*/
float get_min_freq() const;
};
// This is a table of tanh(x) for x in [-2, 2] used in tanh_lut.
static float tanh_lut_table[256] = {
-0.96402758, -0.96290241, -0.96174273, -0.96054753, -0.95931576, -0.95804636,
-0.95673822, -0.95539023, -0.95400122, -0.95257001, -0.95109539, -0.9495761,
-0.94801087, -0.94639839, -0.94473732, -0.94302627, -0.94126385, -0.93944862,
-0.93757908, -0.93565374, -0.93367104, -0.93162941, -0.92952723, -0.92736284,
-0.92513456, -0.92284066, -0.92047938, -0.91804891, -0.91554743, -0.91297305,
-0.91032388, -0.90759795, -0.9047933, -0.90190789, -0.89893968, -0.89588656,
-0.89274642, -0.88951709, -0.88619637, -0.88278203, -0.87927182, -0.87566342,
-0.87195453, -0.86814278, -0.86422579, -0.86020115, -0.85606642, -0.85181914,
-0.84745683, -0.84297699, -0.83837709, -0.83365461, -0.82880699, -0.82383167,
-0.81872609, -0.81348767, -0.80811385, -0.80260204, -0.7969497, -0.79115425,
-0.78521317, -0.77912392, -0.772884, -0.76649093, -0.75994227, -0.75323562,
-0.74636859, -0.73933889, -0.73214422, -0.7247824, -0.71725127, -0.70954876,
-0.70167287, -0.6936217, -0.68539341, -0.67698629, -0.66839871, -0.65962916,
-0.65067625, -0.64153871, -0.6322154, -0.62270534, -0.61300768, -0.60312171,
-0.59304692, -0.58278295, -0.57232959, -0.56168685, -0.55085493, -0.53983419,
-0.52862523, -0.51722883, -0.50564601, -0.49387799, -0.48192623, -0.46979241,
-0.45747844, -0.44498647, -0.4323189, -0.41947836, -0.40646773, -0.39329014,
-0.37994896, -0.36644782, -0.35279057, -0.33898135, -0.32502449, -0.31092459,
-0.2966865, -0.28231527, -0.26781621, -0.25319481, -0.23845682, -0.22360817,
-0.208655, -0.19360362, -0.17846056, -0.16323249, -0.14792623, -0.13254879,
-0.11710727, -0.10160892, -0.08606109, -0.07047123, -0.05484686, -0.0391956,
-0.02352507, -0.00784298, 0.00784298, 0.02352507, 0.0391956, 0.05484686,
0.07047123, 0.08606109, 0.10160892, 0.11710727, 0.13254879, 0.14792623,
0.16323249, 0.17846056, 0.19360362, 0.208655, 0.22360817, 0.23845682,
0.25319481, 0.26781621, 0.28231527, 0.2966865, 0.31092459, 0.32502449,
0.33898135, 0.35279057, 0.36644782, 0.37994896, 0.39329014, 0.40646773,
0.41947836, 0.4323189, 0.44498647, 0.45747844, 0.46979241, 0.48192623,
0.49387799, 0.50564601, 0.51722883, 0.52862523, 0.53983419, 0.55085493,
0.56168685, 0.57232959, 0.58278295, 0.59304692, 0.60312171, 0.61300768,
0.62270534, 0.6322154, 0.64153871, 0.65067625, 0.65962916, 0.66839871,
0.67698629, 0.68539341, 0.6936217, 0.70167287, 0.70954876, 0.71725127,
0.7247824, 0.73214422, 0.73933889, 0.74636859, 0.75323562, 0.75994227,
0.76649093, 0.772884, 0.77912392, 0.78521317, 0.79115425, 0.7969497,
0.80260204, 0.80811385, 0.81348767, 0.81872609, 0.82383167, 0.82880699,
0.83365461, 0.83837709, 0.84297699, 0.84745683, 0.85181914, 0.85606642,
0.86020115, 0.86422579, 0.86814278, 0.87195453, 0.87566342, 0.87927182,
0.88278203, 0.88619637, 0.88951709, 0.89274642, 0.89588656, 0.89893968,
0.90190789, 0.9047933, 0.90759795, 0.91032388, 0.91297305, 0.91554743,
0.91804891, 0.92047938, 0.92284066, 0.92513456, 0.92736284, 0.92952723,
0.93162941, 0.93367104, 0.93565374, 0.93757908, 0.93944862, 0.94126385,
0.94302627, 0.94473732, 0.94639839, 0.94801087, 0.9495761, 0.95109539,
0.95257001, 0.95400122, 0.95539023, 0.95673822, 0.95804636, 0.95931576,
0.96054753, 0.96174273, 0.96290241, 0.96402758
};
/*!
* A look-up table (LUT) tanh calculation. This function returns an
* estimate to tanh(x) based on a 256-point LUT between -2 and
* 2. If x < -2, it returns -1; if > 2, it returns 1.
*
* This LUT form of the tanh is "hidden" in this code because it
* is likely too coarse an estimate for any real uses of a
* tanh. It is useful, however, in certain control loop
* applications where the input is expected to be within these
* bounds and the noise will be greater than the quanitzation of
* this small LUT. For more accurate forms of tanh, see
* volk_32f_tanh_32f.
*/
static inline float tanhf_lut(float x)
{
if (x > 2)
return 1;
else if (x <= -2)
return -1;
else {
int index = 128 + 64 * x;
return tanh_lut_table[index];
}
}
} /* namespace blocks */
} /* namespace gr */
#endif /* GR_BLOCKS_CONTROL_LOOP */
gr::blocks::control_loop
A second-order control loop implementation class.
Definition control_loop.h:51
gr::blocks::control_loop::get_damping_factor
float get_damping_factor() const
Returns the loop damping factor.
gr::blocks::control_loop::~control_loop
virtual ~control_loop()
gr::blocks::control_loop::set_beta
void set_beta(float beta)
Set the loop gain beta.
gr::blocks::control_loop::set_min_freq
void set_min_freq(float freq)
Set the control loop's minimum frequency.
gr::blocks::control_loop::get_min_freq
float get_min_freq() const
Get the control loop's minimum frequency.
gr::blocks::control_loop::get_phase
float get_phase() const
Get the control loop's phase estimate.
gr::blocks::control_loop::frequency_limit
void frequency_limit()
Keep the frequency between d_min_freq and d_max_freq.
Definition control_loop.h:116
gr::blocks::control_loop::d_damping
float d_damping
Definition control_loop.h:55
gr::blocks::control_loop::get_loop_bandwidth
float get_loop_bandwidth() const
Returns the loop bandwidth.
gr::blocks::control_loop::control_loop
control_loop(float loop_bw, float max_freq, float min_freq)
gr::blocks::control_loop::phase_wrap
void phase_wrap()
Keep the phase between -2pi and 2pi.
Definition control_loop.h:95
gr::blocks::control_loop::d_freq
float d_freq
Definition control_loop.h:53
gr::blocks::control_loop::get_frequency
float get_frequency() const
Get the control loop's frequency estimate.
gr::blocks::control_loop::control_loop
control_loop(void)
Definition control_loop.h:59
gr::blocks::control_loop::get_alpha
float get_alpha() const
Returns the loop gain alpha.
gr::blocks::control_loop::d_alpha
float d_alpha
Definition control_loop.h:56
gr::blocks::control_loop::set_frequency
void set_frequency(float freq)
Set the control loop's frequency.
gr::blocks::control_loop::get_beta
float get_beta() const
Returns the loop gain beta.
gr::blocks::control_loop::set_alpha
void set_alpha(float alpha)
Set the loop gain alpha.
gr::blocks::control_loop::advance_loop
void advance_loop(float error)
Advance the control loop based on the current gain settings and the inputted error signal.
Definition control_loop.h:76
gr::blocks::control_loop::d_max_freq
float d_max_freq
Definition control_loop.h:54
gr::blocks::control_loop::set_damping_factor
void set_damping_factor(float df)
Set the loop damping factor.
gr::blocks::control_loop::update_gains
void update_gains()
Update the system gains from the loop bandwidth and damping factor.
gr::blocks::control_loop::set_loop_bandwidth
virtual void set_loop_bandwidth(float bw)
Set the loop bandwidth.
gr::blocks::control_loop::set_phase
void set_phase(float phase)
Set the control loop's phase.
gr::blocks::control_loop::get_max_freq
float get_max_freq() const
Get the control loop's maximum frequency.
gr::blocks::control_loop::set_max_freq
void set_max_freq(float freq)
Set the control loop's maximum frequency.
api.h
BLOCKS_API
#define BLOCKS_API
Definition gr-blocks/include/gnuradio/blocks/api.h:18
math.h
GR_M_PI
#define GR_M_PI
Definition math.h:32
gr::blocks::tanh_lut_table
static float tanh_lut_table[256]
Definition control_loop.h:278
gr::blocks::tanhf_lut
static float tanhf_lut(float x)
Definition control_loop.h:337
gr
GNU Radio logging wrapper.
Definition basic_block.h:29