gnss-sdr/src/algorithms/tracking/libs/tracking_discriminators.cc

/*!
 * \file tracking_discriminators.cc
 * \brief Library with a set of code tracking and carrier tracking discriminators that is used by the tracking algorithms
 * \author Javier Arribas, 2011. jarribas(at)cttc.es
 *
 *
 * -------------------------------------------------------------------------
 *
 * Copyright (C) 2010-2011  (see AUTHORS file for a list of contributors)
 *
 * GNSS-SDR is a software defined Global Navigation
 *          Satellite Systems receiver
 *
 * This file is part of GNSS-SDR.
 *
 * GNSS-SDR 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 of the License, or
 * at your option) any later version.
 *
 * GNSS-SDR 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 GNSS-SDR. If not, see <http://www.gnu.org/licenses/>.
 *
 * -------------------------------------------------------------------------
 */

#include "tracking_discriminators.h"
#include <math.h>

//  All the outputs are in RADIANS
/*!
 * FLL four quadrant arctan discriminator:
 * \f{equation}
 * 	\frac{\phi_2-\phi_1}{t_2-t1}=\frac{ATAN2(cross,dot)}{t_1-t_2},
 * \f}
 * where \f$cross=I_{PS1}Q_{PS2}-I_{PS2}Q_{PS1}\f$ and \f$dot=I_{PS1}I_{PS2}+Q_{PS1}Q_{PS2}\f$,
 * \f$I_{PS1},Q_{PS1}\f$ are the inphase and quadrature prompt correlator outputs respectively at sample time \f$t_1\f$, and
 * \f$I_{PS2},Q_{PS2}\f$ are the inphase and quadrature prompt correlator outputs respectively at sample time \f$t_2\f$. The output is in [radians/second].
 */

float fll_four_quadrant_atan(gr_complex prompt_s1, gr_complex prompt_s2,float t1, float t2)
{
	float cross,dot;
	dot=prompt_s1.imag()*prompt_s2.imag()+prompt_s1.real()*prompt_s2.real();
	cross=prompt_s1.imag()*prompt_s2.real()-prompt_s2.imag()*prompt_s1.real();
	return atan2(cross,dot)/(t2-t1);
}

/*!
 * PLL four quadrant arctan discriminator:
 * \f{equation}
 * 	\phi=ATAN2(Q_{PS},I_{PS}),
 * \f}
 * where \f$I_{PS1},Q_{PS1}\f$ are the inphase and quadrature prompt correlator outputs respectively. The output is in [radians].
 */
float pll_four_quadrant_atan(gr_complex prompt_s1)
{
	return atan2(prompt_s1.real(),prompt_s1.imag());
}

/*!
 * PLL Costas loop two quadrant arctan discriminator:
 * \f{equation}
 * 	\phi=ATAN\left(\frac{Q_{PS}}{I_{PS}}\right),
 * \f}
 * where \f$I_{PS1},Q_{PS1}\f$ are the inphase and quadrature prompt correlator outputs respectively. The output is in [radians].
 */

float pll_cloop_two_quadrant_atan(gr_complex prompt_s1)
{
	if (prompt_s1.imag()!=0.0)
	{
		return atan(prompt_s1.real()/prompt_s1.imag());
	}else{
		return 0;
	}
}
/*!
 * DLL Noncoherent Early minus Late envelope normalized discriminator:
 * \f{equation}
 * 	error=\frac{E-L}{E+L},
 * \f}
 * where \f$E=\sqrt{I_{ES}^2,Q_{ES}^2}\f$ is the Early correlator output absolute value and
 * \f$L=\sqrt{I_{LS}^2,Q_{LS}^2}\f$ is the Late correlator output absolute value. The output is in [chips].
 */
float dll_nc_e_minus_l_normalized(gr_complex early_s1, gr_complex late_s1)
{
	float P_early, P_late;
	P_early=std::abs(early_s1);
	P_late=std::abs(late_s1);
	return (P_early-P_late)/((P_early+P_late));
}