/* -*- c++ -*- */
/*
* Copyright 2004,2007,2011 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_MPSK_RECEIVER_CC_H
#define INCLUDED_DIGITAL_MPSK_RECEIVER_CC_H
#include <gruel/attributes.h>
#include <gr_block.h>
#include <gr_complex.h>
#include <fstream>
class gri_mmse_fir_interpolator_cc;
class digital_mpsk_receiver_cc;
typedef boost::shared_ptr<digital_mpsk_receiver_cc> digital_mpsk_receiver_cc_sptr;
// public constructor
digital_mpsk_receiver_cc_sptr
digital_make_mpsk_receiver_cc (unsigned int M, float theta,
float alpha, float beta,
float fmin, float fmax,
float mu, float gain_mu,
float omega, float gain_omega, float omega_rel);
/*!
* \brief This block takes care of receiving M-PSK modulated signals through phase, frequency, and symbol
* synchronization.
* \ingroup sync_blk
* \ingroup demod_blk
*
* This block takes care of receiving M-PSK modulated signals through phase, frequency, and symbol
* synchronization. It performs carrier frequency and phase locking as well as symbol timing recovery.
* It works with (D)BPSK, (D)QPSK, and (D)8PSK as tested currently. It should also work for OQPSK and
* PI/4 DQPSK.
*
* The phase and frequency synchronization are based on a Costas loop that finds the error of the incoming
* signal point compared to its nearest constellation point. The frequency and phase of the NCO are
* updated according to this error. There are optimized phase error detectors for BPSK and QPSK, but 8PSK
* is done using a brute-force computation of the constellation points to find the minimum.
*
* The symbol synchronization is done using a modified Mueller and Muller circuit from the paper:
*
* G. R. Danesfahani, T.G. Jeans, "Optimisation of modified Mueller and Muller
* algorithm," Electronics Letters, Vol. 31, no. 13, 22 June 1995, pp. 1032 - 1033.
*
* This circuit interpolates the downconverted sample (using the NCO developed by the Costas loop)
* every mu samples, then it finds the sampling error based on this and the past symbols and the decision
* made on the samples. Like the phase error detector, there are optimized decision algorithms for BPSK
* and QPKS, but 8PSK uses another brute force computation against all possible symbols. The modifications
* to the M&M used here reduce self-noise.
*
*/
class digital_mpsk_receiver_cc : public gr_block
{
public:
~digital_mpsk_receiver_cc ();
void forecast(int noutput_items, gr_vector_int &ninput_items_required);
int general_work (int noutput_items,
gr_vector_int &ninput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items);
// Member functions related to the symbol tracking portion of the receiver
//! (M&M) Returns current value of mu
float mu() const { return d_mu;}
//! (M&M) Returns current value of omega
float omega() const { return d_omega;}
//! (M&M) Returns mu gain factor
float gain_mu() const { return d_gain_mu;}
//! (M&M) Returns omega gain factor
float gain_omega() const { return d_gain_omega;}
//! (M&M) Sets value of mu
void set_mu (float mu) { d_mu = mu; }
//! (M&M) Sets value of omega and its min and max values
void set_omega (float omega) {
d_omega = omega;
d_min_omega = omega*(1.0 - d_omega_rel);
d_max_omega = omega*(1.0 + d_omega_rel);
d_omega_mid = 0.5*(d_min_omega+d_max_omega);
}
//! (M&M) Sets value for mu gain factor
void set_gain_mu (float gain_mu) { d_gain_mu = gain_mu; }
//! (M&M) Sets value for omega gain factor
void set_gain_omega (float gain_omega) { d_gain_omega = gain_omega; }
// Member function related to the phase/frequency tracking portion of the receiver
//! (CL) Returns the value for alpha (the phase gain term)
float alpha() const { return d_alpha; }
//! (CL) Returns the value of beta (the frequency gain term)
float beta() const { return d_beta; }
//! (CL) Returns the current value of the frequency of the NCO in the Costas loop
float freq() const { return d_freq; }
//! (CL) Returns the current value of the phase of the NCO in the Costal loop
float phase() const { return d_phase; }
//! (CL) Sets the value for alpha (the phase gain term)
void set_alpha(float alpha) { d_alpha = alpha; }
//! (CL) Setss the value of beta (the frequency gain term)
void set_beta(float beta) { d_beta = beta; }
//! (CL) Sets the current value of the frequency of the NCO in the Costas loop
void set_freq(float freq) { d_freq = freq; }
//! (CL) Setss the current value of the phase of the NCO in the Costal loop
void set_phase(float phase) { d_phase = phase; }
protected:
/*!
* \brief Constructor to synchronize incoming M-PSK symbols
*
* \param M modulation order of the M-PSK modulation
* \param theta any constant phase rotation from the real axis of the constellation
* \param alpha gain parameter to adjust the phase in the Costas loop (~0.01)
* \param beta gain parameter to adjust the frequency in the Costas loop (~alpha^2/4)
* \param fmin minimum normalized frequency value the loop can achieve
* \param fmax maximum normalized frequency value the loop can achieve
* \param mu initial parameter for the interpolator [0,1]
* \param gain_mu gain parameter of the M&M error signal to adjust mu (~0.05)
* \param omega initial value for the number of symbols between samples (~number of samples/symbol)
* \param gain_omega gain parameter to adjust omega based on the error (~omega^2/4)
* \param omega_rel sets the maximum (omega*(1+omega_rel)) and minimum (omega*(1+omega_rel)) omega (~0.005)
*
* The constructor also chooses which phase detector and decision maker to use in the work loop based on the
* value of M.
*/
digital_mpsk_receiver_cc (unsigned int M, float theta,
float alpha, float beta,
float fmin, float fmax,
float mu, float gain_mu,
float omega, float gain_omega, float omega_rel);
void make_constellation();
void mm_sampler(const gr_complex symbol);
void mm_error_tracking(gr_complex sample);
void phase_error_tracking(gr_complex sample);
/*!
* \brief Phase error detector for MPSK modulations.
*
* \param sample the I&Q sample from which to determine the phase error
*
* This function determines the phase error for any MPSK signal by creating a set of PSK constellation points
* and doing a brute-force search to see which point minimizes the Euclidean distance. This point is then used
* to derotate the sample to the real-axis and a atan (using the fast approximation function) to determine the
* phase difference between the incoming sample and the real constellation point
*
* This should be cleaned up and made more efficient.
*
* \returns the approximated phase error.
*/
float phase_error_detector_generic(gr_complex sample) const; // generic for M but more costly
/*!
* \brief Phase error detector for BPSK modulation.
*
* \param sample the I&Q sample from which to determine the phase error
*
* This function determines the phase error using a simple BPSK phase error detector by multiplying the real
* and imaginary (the error signal) components together. As the imaginary part goes to 0, so does this error.
*
* \returns the approximated phase error.
*/
float phase_error_detector_bpsk(gr_complex sample) const; // optimized for BPSK
/*!
* \brief Phase error detector for QPSK modulation.
*
* \param sample the I&Q sample from which to determine the phase error
*
* This function determines the phase error using the limiter approach in a standard 4th order Costas loop
*
* \returns the approximated phase error.
*/
float phase_error_detector_qpsk(gr_complex sample) const;
/*!
* \brief Decision maker for a generic MPSK constellation.
*
* \param sample the baseband I&Q sample from which to make the decision
*
* This decision maker is a generic implementation that does a brute-force search
* for the constellation point that minimizes the error between it and the incoming signal.
*
* \returns the index to d_constellation that minimizes the error/
*/
unsigned int decision_generic(gr_complex sample) const;
/*!
* \brief Decision maker for BPSK constellation.
*
* \param sample the baseband I&Q sample from which to make the decision
*
* This decision maker is a simple slicer function that makes a decision on the symbol based on its
* placement on the real axis of greater than 0 or less than 0; the quadrature component is always 0.
*
* \returns the index to d_constellation that minimizes the error/
*/
unsigned int decision_bpsk(gr_complex sample) const;
/*!
* \brief Decision maker for QPSK constellation.
*
* \param sample the baseband I&Q sample from which to make the decision
*
* This decision maker is a simple slicer function that makes a decision on the symbol based on its
* placement versus both axes and returns which quadrant the symbol is in.
*
* \returns the index to d_constellation that minimizes the error/
*/
unsigned int decision_qpsk(gr_complex sample) const;
private:
unsigned int d_M;
float d_theta;
// Members related to carrier and phase tracking
float d_alpha;
float d_beta;
float d_freq, d_max_freq, d_min_freq;
float d_phase;
/*!
* \brief Decision maker function pointer
*
* \param sample the baseband I&Q sample from which to make the decision
*
* This is a function pointer that is set in the constructor to point to the proper decision function
* for the specified constellation order.
*
* \return index into d_constellation point that is the closest to the recieved sample
*/
unsigned int (digital_mpsk_receiver_cc::*d_decision)(gr_complex sample) const; // pointer to decision function
std::vector<gr_complex> d_constellation;
unsigned int d_current_const_point;
// Members related to symbol timing
float d_mu, d_gain_mu;
float d_omega, d_gain_omega, d_omega_rel, d_max_omega, d_min_omega, d_omega_mid;
gr_complex d_p_2T, d_p_1T, d_p_0T;
gr_complex d_c_2T, d_c_1T, d_c_0T;
/*!
* \brief Phase error detector function pointer
*
* \param sample the I&Q sample from which to determine the phase error
*
* This is a function pointer that is set in the constructor to point to the proper phase error detector
* function for the specified constellation order.
*/
float (digital_mpsk_receiver_cc::*d_phase_error_detector)(gr_complex sample) const;
//! get interpolated value
gri_mmse_fir_interpolator_cc *d_interp;
//! delay line length.
static const unsigned int DLLEN = 8;
//! delay line plus some length for overflow protection
__GR_ATTR_ALIGNED(8) gr_complex d_dl[2*DLLEN];
//! index to delay line
unsigned int d_dl_idx;
friend digital_mpsk_receiver_cc_sptr
digital_make_mpsk_receiver_cc (unsigned int M, float theta,
float alpha, float beta,
float fmin, float fmax,
float mu, float gain_mu,
float omega, float gain_omega, float omega_rel);
};
#endif