/* -*- c++ -*- */
/*
* Copyright (C) 2017 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_SYMBOL_SYNC_FF_H
#define INCLUDED_DIGITAL_SYMBOL_SYNC_FF_H
#include <gnuradio/digital/api.h>
#include <gnuradio/block.h>
#include <gnuradio/digital/timing_error_detector_type.h>
#include <gnuradio/digital/constellation.h>
#include <gnuradio/digital/interpolating_resampler_type.h>
namespace gr {
namespace digital {
/*!
* \brief Symbol Synchronizer block with float input, float output.
* \ingroup synchronizers_blk
*
* \details
* This implements a discrete-time error-tracking synchronizer.
*
* For this block to work properly, the input stream must meet the
* following requirements:
*
* 1. if not using the PFB Matched Filter interpolator, and using
* a non-CPM timing error detector, the input pulses must have peaks
* (not flat), which usually can be implemented by using a matched
* filter before this block.
*
* 2. for decision directed timing error detectors, the input pulses
* should nominally match the normalized slicer constellation, which
* is normalized to an average symbol magnitude of 1.0 over the entire
* constellation.
*/
class DIGITAL_API symbol_sync_ff : virtual public block
{
public:
// gr::digital::symbol_sync_ff::sptr
typedef boost::shared_ptr<symbol_sync_ff> sptr;
/*!
* Make a Symbol Synchronizer block.
*
* \details
* This implements a discrete-time error-tracking synchronizer.
*
* For this block to work properly, the input stream must meet the
* following requirements:
*
* 1. if not using the PFB Matched Filter interpolator, and using
* a non-CPM timing error detector, the input pulses must have peaks
* (not flat), which usually can be implemented by using a matched
* filter before this block.
*
* 2. for decision directed timing error detectors, the input pulses
* should nominally match the normalized slicer constellation, which
* is normalized to an average symbol magnitude of 1.0 over the entire
* constellation.
*
* \param detector_type
* The enumerated type of timing error detector to use.
* See enum ted_type for a list of possible types.
*
* \param sps
* User specified nominal clock period in samples per symbol.
*
* \param loop_bw
* Approximate normailzed loop bandwidth of the symbol clock tracking
* loop. It should nominally be close to 0, but greater than 0. If
* unsure, start with a number around 2*pi*0.040, and experiment to find
* the value that works best for your situation.
*
* \param damping_factor
* Damping factor of the symbol clock tracking loop.
* Damping < 1.0f is an under-damped loop.
* Damping = 1.0f/sqrt(2.0f) is a maximally flat loop response.
* Damping = 1.0f is a critically-damped loop.
* Damping > 1.0f is an over-damped loop.
*
* \param ted_gain
* Expected gain of the timing error detector, given the TED in use
* and the anticipated input amplitude, pulse shape, and Es/No.
* This value is the slope of the TED's S-curve at timing offset tau = 0.
* This value is normally computed by the user analytically or by
* simulation in a tool outside of GNURadio.
* This value must be correct for the loop filter gains to be computed
* properly from the desired input loop bandwidth and damping factor.
*
* \param max_deviation
* Maximum absolute deviation of the average clock period estimate
* from the user specified nominal clock period in samples per symbol.
*
* \param osps
* The number of output samples per symbol (default=1).
*
* \param slicer
* A constellation obj shared pointer that will be used by
* decision directed timing error detectors to make decisions.
* I.e. the timing error detector will use this constellation
* as a slicer, if the particular algorithm needs sliced
* symbols.
*
* \param interp_type
* The enumerated type of interpolating resampler to use.
* See the interpolating resampler type enum for a list of possible types.
*
* \param n_filters
* The number of arms in the polyphase filterbank of the interpolating
* resampler, if using an interpolating resampler that uses a PFB.
*
* \param taps
* The prototype filter for the polyphase filterbank of the interpolating
* resampler, if using an interpolating resampler that uses a PFB.
*/
static sptr make(enum ted_type detector_type,
float sps,
float loop_bw,
float damping_factor = 1.0f,
float ted_gain = 1.0f,
float max_deviation = 1.5f,
int osps = 1,
constellation_sptr slicer = constellation_sptr(),
ir_type interp_type = IR_MMSE_8TAP,
int n_filters = 128,
const std::vector<float> &taps = std::vector<float>());
/*!
* \brief Returns the normalized approximate loop bandwidth.
*
* \details
* See the documentation for set_loop_bandwidth() for more details.
*
* Note that if set_alpha() or set_beta() were called to directly
* set gains, the value returned by this method will be inaccurate/stale.
*/
virtual float loop_bandwidth() const = 0;
/*!
* \brief Returns the loop damping factor.
*
* \details
* See the documentation for set_damping_factor() for more details.
*
* Note that if set_alpha() or set_beta() were called to directly
* set gains, the value returned by this method will be inaccurate/stale.
*/
virtual float damping_factor() const = 0;
/*!
* \brief Returns the user provided expected gain of the Timing Error
* Detector.
*
* \details
* See the documentation for set_ted_gain() for more details.
*/
virtual float ted_gain() const = 0;
/*!
* \brief Returns the PI filter proportional gain, alpha.
*
* \details
* See the documentation for set_alpha() for more details.
*/
virtual float alpha() const = 0;
/*!
* \brief Returns the PI filter integral gain, beta.
*
* \details
* See the documentation for set_beta() for more details.
*/
virtual float beta() const = 0;
/*!
* \brief Set the normalized approximate loop bandwidth.
*
* \details
* Set the normalized approximate loop bandwidth.
* Useful values are usually close to 0.0, e.g. 2*pi*0.045.
*
* It should be a small positive number, corresponding to the normalized
* natural radian frequency of the loop as digital low-pass filter that is
* filtering the clock phase/timing error.
*
* Technically this parameter corresponds to the natural radian frequency
* of the 2nd order loop transfer function (scaled by Fs),
* which is the radius of the pole locations in the s-plane of an
* underdamped analog 2nd order system.
*
* The input parameter corresponds to omega_n_norm in the following
* relation:
*
* omega_n_norm = omega_n*T = 2*pi*f_n*T = 2*pi*f_n_norm
*
* where T is the period of the clock being estimated by this
* clock tracking loop, and omega_n is the natural radian frequency
* of the 2nd order loop transfer function.
*
* When a new loop bandwidth is set, the gains, alpha and beta,
* of the loop are automatically recalculated.
*
* \param omega_n_norm normalized approximate loop bandwidth
*/
virtual void set_loop_bandwidth (float omega_n_norm) = 0;
/*!
* \brief Set the loop damping factor.
*
* \details
* Set the damping factor of the loop.
* Damping in the range (0.0, 1.0) yields an under-damped loop.
* Damping in the range (1.0, Inf) yields an over-damped loop.
* Damping equal to 1.0 yields a crtically-damped loop.
* Damping equal to 1.0/sqrt(2.0) yields a maximally flat
* loop filter response.
*
* Damping factor of the 2nd order loop transfer function.
* When a new damping factor is set, the gains, alpha and beta,
* of the loop are automatcally recalculated.
*
* \param zeta loop damping factor
*/
virtual void set_damping_factor (float zeta) = 0;
/*!
* \brief Set the expected gain of the Timing Error Detector.
*
* \details
* Sets the expected gain of the timing error detector, given the TED in
* use and the anticipated input amplitude, pulse shape, and Es/No.
* This value is the slope of the TED's S-curve at timing offset tau = 0.
* This value is normally computed by the user analytically or by
* simulation in a tool outside of GNURadio.
* This value must be correct for the loop filter gains to be computed
* properly from the desired input loop bandwidth and damping factor.
*
* When a new ted_gain is set, the gains, alpha and beta,
* of the loop are automatcally recalculated.
*
* \param ted_gain expected gain of the timing error detector
*/
virtual void set_ted_gain (float ted_gain) = 0;
/*!
* \brief Set the PI filter proportional gain, alpha.
*
* \details
* Sets the PI filter proportional gain, alpha.
* This gain directly mutliplies the clock phase/timing error
* term in the PI filter when advancing the loop.
* It most directly affects the instantaneous clock period estimate,
* T_inst, and instantaneous clock phase estimate, tau.
*
* This value would normally be adjusted by setting the loop
* bandwidth and damping factor. However,
* it can be set here directly if desired.
*
* Setting this parameter directly is probably only feasible if
* the user is directly observing the estimates of average clock
* period and instantaneous clock period over time in response to
* an impulsive change in the input stream (i.e. watching the loop
* transient behavior at the start of a data burst).
*
* \param alpha PI filter proportional gain
*/
virtual void set_alpha (float alpha) = 0;
/*!
* \brief Set the PI filter integral gain, beta.
*
* \details
* Sets the PI filter integral gain, beta.
* This gain is used when integrating the clock phase/timing error
* term in the PI filter when advancing the loop.
* It most directly affects the average clock period estimate,
* T_avg.
*
* This value would normally be adjusted by setting the loop
* bandwidth and damping factor. However,
* it can be set here directly if desired.
*
* Setting this parameter directly is probably only feasible if
* the user is directly observing the estimates of average clock
* period and instantaneous clock period over time in response to
* an impulsive change in the input stream (i.e. watching the loop
* transient behavior at the start of a data burst).
*
* \param beta PI filter integral gain
*/
virtual void set_beta (float beta) = 0;
};
} /* namespace digital */
} /* namespace gr */
#endif /* INCLUDED_DIGITAL_SYMBOL_SYNC_FF_H */