/*!
 * \file lock_detectors.h
 * \brief Interface of a library with a set of code and carrier phase lock detectors.
 *
 * SNV_CN0 is a Carrier-to-Noise (CN0) estimator
 * based on the Signal-to-Noise Variance (SNV) estimator [1].
 * Carrier lock detector using normalised estimate of the cosine
 * of twice the carrier phase error [2].
 *
 * [1] Marco Pini, Emanuela Falletti and Maurizio Fantino, "Performance
 * Evaluation of C/N0 Estimators using a Real Time GNSS Software Receiver,"
 * IEEE 10th International Symposium on Spread Spectrum Techniques and
 * Applications, pp.28-30, August 2008.
 *
 * [2] Van Dierendonck, A.J. (1996), Global Positioning System: Theory and
 * Applications,
 * Volume I, Chapter 8: GPS Receivers, AJ Systems, Los Altos, CA 94024.
 * Inc.: 329-407.
 * \authors <ul>
 *          <li> Javier Arribas, 2011. jarribas(at)cttc.es
 *          <li> Luis Esteve, 2012. luis(at)epsilon-formacion.com
 *          </ul>
 * -------------------------------------------------------------------------
 *
 * Copyright (C) 2010-2018  (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 <https://www.gnu.org/licenses/>.
 *
 * -------------------------------------------------------------------------
 */

#ifndef GNSS_SDR_LOCK_DETECTORS_H_
#define GNSS_SDR_LOCK_DETECTORS_H_

#include <gnuradio/gr_complex.h>


/*! \brief CN0_SNV is a Carrier-to-Noise (CN0) estimator
 * based on the Signal-to-Noise Variance (SNV) estimator
 *
 * Signal-to-Noise (SNR) (\f$\rho\f$) estimator using the Signal-to-Noise Variance (SNV) estimator:
 * \f{equation}
 *  \hat{\rho}=\frac{\hat{P}_s}{\hat{P}_n}=\frac{\hat{P}_s}{\hat{P}_{tot}-\hat{P}_s},
 * \f}
 *  where \f$\hat{P}_s=\left(\frac{1}{N}\sum^{N-1}_{i=0}|Re(Pc(i))|\right)^2\f$ is the estimation of the signal power,
 * \f$\hat{P}_{tot}=\frac{1}{N}\sum^{N-1}_{i=0}|Pc(i)|^2\f$ is the estimator of the total power, \f$|\cdot|\f$ is the absolute value,
 * \f$Re(\cdot)\f$ stands for the real part of the value, and \f$Pc(i)\f$ is the prompt correlator output for the sample index i.
 *
 * The SNR value is converted to CN0 [dB-Hz], taking to account the coherent integration time, using the following formula:
 * \f{equation}
 *     CN0_{dB}=10*log(\hat{\rho})-10*log(2 * T_{int}),
 * \f}
 * where \f$T_{int}\f$ is the coherent integration time, in seconds.
 * Ref: Marco Pini, Emanuela Falletti and Maurizio Fantino, "Performance
 * Evaluation of C/N0 Estimators using a Real Time GNSS Software Receiver,"
 * IEEE 10th International Symposium on Spread Spectrum Techniques and
 * Applications, pp.28-30, August 2008.
 */
float cn0_svn_estimator(const gr_complex* Prompt_buffer, int length, double coh_integration_time_s);


/*! \brief A carrier lock detector
 *
 * The Carrier Phase Lock Detector block uses the estimate of the cosine of twice the carrier phase error is given by
 * \f{equation}
 *     C2\phi=\frac{NBD}{NBP},
 * \f}
 *  where \f$NBD=(\sum^{N-1}_{i=0}|Im(Pc(i))|)^2+(\sum^{N-1}_{i=0}|Re(Pc(i))|)^2\f$,
 *  \f$NBP=\sum^{N-1}_{i=0}Im(Pc(i))^2-\sum^{N-1}_{i=0}Re(Pc(i))^2\f$, and
 *  \f$Pc(i)\f$ is the prompt correlator output for the sample index i.
 * Ref: Van Dierendonck, A.J. (1996), Global Positioning System: Theory and
 * Applications,
 * Volume I, Chapter 8: GPS Receivers, AJ Systems, Los Altos, CA 94024.
 * Inc.: 329-407.
 */
float carrier_lock_detector(gr_complex* Prompt_buffer, int length);

#endif