/* -*- 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 #include #include #include #include #include class gri_mmse_fir_interpolator_cc; class digital_mpsk_receiver_cc; typedef boost::shared_ptr digital_mpsk_receiver_cc_sptr; // public constructor DIGITAL_API digital_mpsk_receiver_cc_sptr digital_make_mpsk_receiver_cc (unsigned int M, float theta, float loop_bw, 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 * \ingroup digital * * 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_API digital_mpsk_receiver_cc : public gr_block, public gri_control_loop { 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); //! Returns the modulation order (M) currently set float modulation_order() const { return d_M; } //! Returns current value of theta float theta() const { return d_theta; } //! Returns current value of mu float mu() const { return d_mu; } //! Returns current value of omega float omega() const { return d_omega; } //! Returns mu gain factor float gain_mu() const { return d_gain_mu; } //! Returns omega gain factor float gain_omega() const { return d_gain_omega; } //! Returns the relative omega limit float gain_omega_rel() const {return d_omega_rel; } //! Sets the modulation order (M) currently void set_modulation_order(unsigned int M); //! Sets value of theta void set_theta(float theta) { d_theta = theta; } //! Sets value of mu void set_mu (float mu) { d_mu = mu; } //! 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); } //! Sets value for mu gain factor void set_gain_mu (float gain_mu) { d_gain_mu = gain_mu; } //! Sets value for omega gain factor void set_gain_omega (float gain_omega) { d_gain_omega = gain_omega; } //! Sets the relative omega limit and resets omega min/max values void set_gain_omega_rel(float omega_rel); 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 loop_bw Loop bandwidth to set gains of phase/freq tracking loop * \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 loop_bw, 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; /*! * \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 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_API digital_mpsk_receiver_cc_sptr digital_make_mpsk_receiver_cc (unsigned int M, float theta, float loop_bw, float fmin, float fmax, float mu, float gain_mu, float omega, float gain_omega, float omega_rel); }; #endif