mirror of https://github.com/gnss-sdr/gnss-sdr
82 lines
2.5 KiB
C++
82 lines
2.5 KiB
C++
/*!
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* \file tracking_2nd_PLL_filter.cc
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* \brief Implementation of a 2nd order PLL filter for tracking carrier loop.
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* \author Javier Arribas, 2011. jarribas(at)cttc.es
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*
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* Class that implements 2 order PLL filter for tracking carrier loop. The algorithm
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* is described in:
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* K.Borre, D.M.Akos, N.Bertelsen, P.Rinder, and S.~H.~Jensen, A Software-Defined
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* GPS and Galileo Receiver. A Single-Frequency Approach,
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* Birkhauser, 2007, Applied and Numerical Harmonic Analysis.
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*
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* -----------------------------------------------------------------------------
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*
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* GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
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* This file is part of GNSS-SDR.
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*
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* Copyright (C) 2010-2020 (see AUTHORS file for a list of contributors)
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* SPDX-License-Identifier: GPL-3.0-or-later
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*
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* -----------------------------------------------------------------------------
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*/
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#include "tracking_2nd_PLL_filter.h"
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void Tracking_2nd_PLL_filter::calculate_lopp_coef(float* tau1, float* tau2, float lbw, float zeta, float k)
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{
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// Solve natural frequency
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const float Wn = lbw * 8.0F * zeta / (4.0F * zeta * zeta + 1.0F);
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// solve for t1 & t2
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*tau1 = k / (Wn * Wn);
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*tau2 = 2.0F * zeta / Wn;
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}
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void Tracking_2nd_PLL_filter::set_PLL_BW(float pll_bw_hz)
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{
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// Calculate filter coefficient values
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d_pllnoisebandwidth = pll_bw_hz;
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calculate_lopp_coef(&d_tau1_carr, &d_tau2_carr, d_pllnoisebandwidth, d_plldampingratio, 0.25); // Calculate filter coefficient values
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}
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void Tracking_2nd_PLL_filter::initialize()
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{
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// carrier/Costas loop parameters
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d_old_carr_nco = 0.0;
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d_old_carr_error = 0.0;
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}
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/*
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* PLL second order IIR filter
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* Req Input in [Hz/Ti]
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* The output is in [Hz/s].
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*/
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float Tracking_2nd_PLL_filter::get_carrier_nco(float PLL_discriminator)
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{
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float carr_nco = d_old_carr_nco + (d_tau2_carr / d_tau1_carr) * (PLL_discriminator - d_old_carr_error) + (PLL_discriminator + d_old_carr_error) * (d_pdi_carr / (2.0F * d_tau1_carr));
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d_old_carr_nco = carr_nco;
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d_old_carr_error = PLL_discriminator;
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return carr_nco;
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}
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Tracking_2nd_PLL_filter::Tracking_2nd_PLL_filter(float pdi_carr) : d_pdi_carr(pdi_carr),
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d_plldampingratio(0.7)
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{
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}
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Tracking_2nd_PLL_filter::Tracking_2nd_PLL_filter() : d_pdi_carr(0.001),
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d_plldampingratio(0.7)
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{
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}
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void Tracking_2nd_PLL_filter::set_pdi(float pdi_carr)
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{
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d_pdi_carr = pdi_carr; // Summation interval for code
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}
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