mirror of https://github.com/gnss-sdr/gnss-sdr
142 lines
5.0 KiB
C++
142 lines
5.0 KiB
C++
/*!
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* \file CN_estimators.cc
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* \brief Library with a set of Carrier to Noise estimators and lock detectors.
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* SNV_CN0 is a Carrier-to-Noise (CN0) estimator based on the Signal-to-Noise Variance (SNV) estimator [1].
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*
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* Carrier lock detector using normalised estimate of the cosine
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* of twice the carrier phase error [2].
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*
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*
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* [1] Marco Pini, Emanuela Falletti and Maurizio Fantino, "Performance
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* Evaluation of C/N0 Estimators using a Real Time GNSS Software Receiver,"
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* IEEE 10th International Symposium on Spread Spectrum Techniques and
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* Applications, pp.28-30, August 2008.
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*
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*
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*
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* [2] Van Dierendonck, A.J. (1996), Global Positioning System: Theory and
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* Applications,
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* Volume I, Chapter 8: GPS Receivers, AJ Systems, Los Altos, CA 94024.
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* Inc.: 329-407.
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*
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*
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* \author Javier Arribas, 2011. jarribas(at)cttc.es
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*
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*
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* -------------------------------------------------------------------------
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*
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* Copyright (C) 2010-2011 (see AUTHORS file for a list of contributors)
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*
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* GNSS-SDR is a software defined Global Navigation
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* Satellite Systems receiver
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*
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* This file is part of GNSS-SDR.
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*
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* GNSS-SDR is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* at your option) any later version.
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*
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* GNSS-SDR is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNSS-SDR. If not, see <http://www.gnu.org/licenses/>.
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*
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* -------------------------------------------------------------------------
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*/
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#include "CN_estimators.h"
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#include "GPS_L1_CA.h"
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#include <gnuradio/gr_complex.h>
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#include <math.h>
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/*!
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* Signal-to-Noise (SNR) (\f$\rho\f$) estimator using the Signal-to-Noise Variance (SNV) estimator:
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* \f{equation}
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* \hat{\rho}=\frac{\hat{P}_s}{\hat{P}_n}=\frac{\hat{P}_s}{\hat{P}_{tot}-\hat{P}_s},
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* \f}
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* 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,
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* \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,
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* \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.
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*
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* The SNR value is converted to CN0 [dB-Hz], taking to account the receiver bandwidth and the PRN code gain, using the following formula:
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* \f{equation}
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* CN0_{dB}=10*log(\hat{\rho})+10*log(\frac{f_s}{2})-10*log(L_{PRN}),
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* \f}
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* where \f$f_s\f$ is the sampling frequency and \f$L_{PRN}\f$ is the PRN sequence length.
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*/
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float gps_l1_ca_CN0_SNV(gr_complex* Prompt_buffer, int length, long fs_in)
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{
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// estimate CN0 using buffered values
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// MATLAB CODE
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//Psig=((1/N)*sum(abs(imag(x((n-N+1):n)))))^2;
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//Ptot=(1/N)*sum(abs(x((n-N+1):n)).^2);
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//SNR_SNV(count)=Psig/(Ptot-Psig);
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//CN0_SNV_dB=10*log10(SNR_SNV)+10*log10(BW)-10*log10(PRN_length);
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float SNR, SNR_dB_Hz;
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float tmp_abs_I,tmp_abs_Q;
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float Psig,Ptot;
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//float M2,M4;
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Psig=0;
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Ptot=0;
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for (int i=0;i<length;i++)
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{
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tmp_abs_I=std::abs(Prompt_buffer[i].imag());
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tmp_abs_Q=std::abs(Prompt_buffer[i].real());
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Psig+=tmp_abs_I;
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Ptot+=Prompt_buffer[i].imag()*Prompt_buffer[i].imag()+Prompt_buffer[i].real()*Prompt_buffer[i].real();
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}
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Psig=Psig/(float)length;
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Psig=Psig*Psig;
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SNR=Psig/(Ptot/(float)length-Psig);
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SNR_dB_Hz=10*log10(SNR)+10*log10(fs_in/2)-10*log10(GPS_L1_CA_CODE_LENGTH_CHIPS);
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return SNR_dB_Hz;
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}
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/*!
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* The Carrier Phase Lock Detector block uses the normalised estimate of the cosine of twice the carrier phase error is given by
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* \f{equation}
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* C2\phi=\frac{NBD}{NBP},
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* \f}
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* where \f$NBD=(\sum^{N-1}_{i=0}|Im(Pc(i))|)^2+(\sum^{N-1}_{i=0}|Re(Pc(i))|)^2\f$,
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* \f$NBP=\sum^{N-1}_{i=0}Im(Pc(i))^2-\sum^{N-1}_{i=0}Re(Pc(i))^2\f$, and
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* \f$Pc(i)\f$ is the prompt correlator output for the sample index i.
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*/
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float carrier_lock_detector(gr_complex* Prompt_buffer, int length)
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{
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/*!
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* \todo Code lock detector
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*/
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// estimate using buffered values
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// MATLAB CODE
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// lock detector operation
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//NBD=sum(abs(imag(x((n-N+1):n))))^2 + sum(abs(real(x((n-N+1):n))))^2;
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//NBP=sum(imag(x((n-N+1):n)).^2) - sum(real(x((n-N+1):n)).^2);
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//LOCK(count)=NBD/NBP;
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float tmp_abs_I,tmp_abs_Q;
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float tmp_sum_abs_I,tmp_sum_abs_Q;
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float tmp_sum_sqr_I,tmp_sum_sqr_Q;
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tmp_sum_abs_I=0;
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tmp_sum_abs_Q=0;
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tmp_sum_sqr_I=0;
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tmp_sum_sqr_Q=0;
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float NBD,NBP;
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for (int i=0;i<length;i++)
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{
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tmp_abs_I=std::abs(Prompt_buffer[i].imag());
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tmp_abs_Q=std::abs(Prompt_buffer[i].real());
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tmp_sum_abs_I+=tmp_abs_I;
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tmp_sum_abs_Q+=tmp_abs_Q;
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tmp_sum_sqr_I+=(Prompt_buffer[i].imag()*Prompt_buffer[i].imag());
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tmp_sum_sqr_Q+=(Prompt_buffer[i].real()*Prompt_buffer[i].real());
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}
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NBD=tmp_sum_abs_I*tmp_sum_abs_I+tmp_sum_abs_Q*tmp_sum_abs_Q;
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NBP=tmp_sum_sqr_I-tmp_sum_sqr_Q;
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return NBD/NBP;
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}
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