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Add a Doppler prediction method to Ephemeris objects

This commit is contained in:
Carles Fernandez 2022-03-19 10:57:33 +01:00
parent feaab97c3d
commit 9af3e6c125
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2 changed files with 187 additions and 33 deletions
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204
src/core/system_parameters/gnss_ephemeris.cc
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@ -17,10 +17,156 @@
#include "gnss_ephemeris.h"
#include "MATH_CONSTANTS.h"
#include "gnss_frequencies.h"
#include <algorithm>
#include <cmath>
#include <functional>
#include <numeric>
#include <vector>
double Gnss_Ephemeris::sv_clock_drift(double transmitTime)
{
const double dt = check_t(transmitTime - this->toc);
this->dtr = sv_clock_relativistic_term(transmitTime);
this->satClkDrift = this->af0 + this->af1 * dt + this->af2 * (dt * dt) + this->dtr;
return this->satClkDrift;
}
double Gnss_Ephemeris::predicted_doppler(double rx_time_s,
double lat,
double lon,
double h,
double ve,
double vn,
double vu,
int band) const
{
const double RE_WGS84 = 6378137.0; //!< earth semimajor axis (WGS84) (m)
const double FE_WGS84 = (1.0 / 298.257223563); //!< earth flattening (WGS84)
const double lat_rad = lat * D2R;
const double lon_rad = lon * D2R;
const double sinp = sin(lat_rad);
const double cosp = cos(lat_rad);
const double sinl = sin(lon_rad);
const double cosl = cos(lon_rad);
const double e2 = FE_WGS84 * (2.0 - FE_WGS84);
const double v = RE_WGS84 / std::sqrt(1.0 - e2 * sinp * sinp);
// Position in EFEF
const std::vector<double> pos_rx = {(v + h) * cosp * cosl, (v + h) * cosp * sinl, (v * (1.0 - e2) + h) * sinp};
// Velovity in EFEF
const double t = cosp * vu - sinp * vn;
const std::vector<double> vel_rx = {cosl * t - sinl * ve, sinl * t + cosl * ve, sinp * vu + cosp * vn};
std::array<double, 7> sat_pos_vel = {0};
satellitePosVelComputation(rx_time_s, sat_pos_vel);
const std::vector<double> pos_sat = {sat_pos_vel[0], sat_pos_vel[1], sat_pos_vel[2]};
const std::vector<double> vel_sat = {sat_pos_vel[3], sat_pos_vel[4], sat_pos_vel[5]};
std::vector<double> x_sr = pos_sat;
std::transform(x_sr.begin(), x_sr.end(), pos_rx.begin(), x_sr.begin(), std::minus<double>()); // pos_sat - pos_rx
const double norm_x_sr = std::sqrt(std::inner_product(x_sr.begin(), x_sr.end(), x_sr.begin(), 0.0)); // Euclidean norm
std::vector<double> v_sr = vel_sat;
std::transform(v_sr.begin(), v_sr.end(), vel_rx.begin(), v_sr.begin(), std::minus<double>()); // vel_sat - vel_rx
const double radial_vel = std::inner_product(v_sr.begin(), v_sr.end(), x_sr.begin(), 0.0) / norm_x_sr;
const double predicted_doppler_normalized = -(radial_vel / SPEED_OF_LIGHT_M_S);
double predicted_doppler = 0.0;
if (this->System == 'E') // Galileo
{
if (band == 1)
{
predicted_doppler = predicted_doppler_normalized * FREQ1;
}
else if (band == 5)
{
predicted_doppler = predicted_doppler_normalized * FREQ5;
}
else if (band == 6)
{
predicted_doppler = predicted_doppler_normalized * FREQ6;
}
else if (band == 7)
{
predicted_doppler = predicted_doppler_normalized * FREQ7;
}
else if (band == 8)
{
predicted_doppler = predicted_doppler_normalized * FREQ8;
}
else
{
predicted_doppler = 0.0;
}
}
else if (this->System == 'G') // GPS
{
if (band == 1)
{
predicted_doppler = predicted_doppler_normalized * FREQ1;
}
else if (band == 2)
{
predicted_doppler = predicted_doppler_normalized * FREQ2;
}
else if (band == 5)
{
predicted_doppler = predicted_doppler_normalized * FREQ5;
}
else
{
predicted_doppler = 0.0;
}
}
else if (this->System == 'B') // Beidou
{
if (band == 1)
{
predicted_doppler = predicted_doppler_normalized * FREQ1_BDS;
}
else if (band == 2)
{
predicted_doppler = predicted_doppler_normalized * FREQ2_BDS;
}
else if (band == 3)
{
predicted_doppler = predicted_doppler_normalized * FREQ3_BDS;
}
else
{
predicted_doppler = 0.0;
}
}
else
{
predicted_doppler = 0.0;
}
return predicted_doppler;
}
void Gnss_Ephemeris::satellitePosition(double transmitTime)
{
std::array<double, 7> pos_vel_dtr = {0};
satellitePosVelComputation(transmitTime, pos_vel_dtr);
this->satpos_X = pos_vel_dtr[0];
this->satpos_Y = pos_vel_dtr[1];
this->satpos_Z = pos_vel_dtr[2];
this->satvel_X = pos_vel_dtr[3];
this->satvel_Y = pos_vel_dtr[4];
this->satvel_Z = pos_vel_dtr[5];
this->dtr = pos_vel_dtr[6];
}
void Gnss_Ephemeris::satellitePosVelComputation(double transmitTime, std::array<double, 7>& pos_vel_dtr) const
{
// Restore semi-major axis
const double a = this->sqrtA * this->sqrtA;
@ -128,45 +274,53 @@ void Gnss_Ephemeris::satellitePosition(double transmitTime)
// --- Compute satellite coordinates in Earth-fixed coordinates
const double xprime = r * cuk;
const double yprime = r * suk;
this->satpos_X = xprime * cok - yprime * cik * sok;
this->satpos_Y = xprime * sok + yprime * cik * cok; // ********NOTE: in GALILEO ICD this expression is not correct because it has minus (- sin(u) * r * cos(i) * cos(Omega)) instead of plus
this->satpos_Z = yprime * sik;
pos_vel_dtr[0] = xprime * cok - yprime * cik * sok;
pos_vel_dtr[1] = xprime * sok + yprime * cik * cok; // ********NOTE: in GALILEO ICD this expression is not correct because it has minus (- sin(u) * r * cos(i) * cos(Omega)) instead of plus
pos_vel_dtr[2] = yprime * sik;
// Satellite's velocity. Can be useful for Vector Tracking loops
const double xpkdot = rkdot * cuk - yprime * ukdot;
const double ypkdot = rkdot * suk + xprime * ukdot;
const double tmp = ypkdot * cik - this->satpos_Z * ikdot;
const double tmp = ypkdot * cik - pos_vel_dtr[2] * ikdot;
this->satvel_X = -Omega_dot * this->satpos_Y + xpkdot * cok - tmp * sok;
this->satvel_Y = Omega_dot * this->satpos_X + xpkdot * sok + tmp * cok;
this->satvel_Z = yprime * cik * ikdot + ypkdot * sik;
pos_vel_dtr[3] = -Omega_dot * pos_vel_dtr[1] + xpkdot * cok - tmp * sok;
pos_vel_dtr[4] = Omega_dot * pos_vel_dtr[0] + xpkdot * sok + tmp * cok;
pos_vel_dtr[5] = yprime * cik * ikdot + ypkdot * sik;
// Time from ephemeris reference clock
tk = check_t(transmitTime - this->toc);
this->dtr = this->af0 + this->af1 * tk + this->af2 * tk * tk;
pos_vel_dtr[6] = this->af0 + this->af1 * tk + this->af2 * tk * tk;
if (this->System == 'E')
{
this->dtr -= 2.0 * sqrt(GALILEO_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
pos_vel_dtr[6] -= 2.0 * sqrt(GALILEO_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
}
else if (this->System == 'B')
{
this->dtr -= 2.0 * sqrt(BEIDOU_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
pos_vel_dtr[6] -= 2.0 * sqrt(BEIDOU_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
}
else
{
this->dtr -= 2.0 * sqrt(GPS_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
pos_vel_dtr[6] -= 2.0 * sqrt(GPS_GM * a) * this->ecc * sek / (SPEED_OF_LIGHT_M_S * SPEED_OF_LIGHT_M_S);
}
}
double Gnss_Ephemeris::sv_clock_drift(double transmitTime)
double Gnss_Ephemeris::check_t(double time) const
{
const double dt = check_t(transmitTime - this->toc);
this->dtr = sv_clock_relativistic_term(transmitTime);
this->satClkDrift = this->af0 + this->af1 * dt + this->af2 * (dt * dt) + this->dtr;
return this->satClkDrift;
const double half_week = 302400.0; // seconds
double corrTime = time;
if (time > half_week)
{
corrTime = time - 2.0 * half_week;
}
else if (time < -half_week)
{
corrTime = time + 2.0 * half_week;
}
return corrTime;
}
@ -184,7 +338,7 @@ double Gnss_Ephemeris::sv_clock_relativistic_term(double transmitTime) const
{
n0 = sqrt(GALILEO_GM / (a * a * a));
}
else if (this->System == 'E')
else if (this->System == 'B')
{
n0 = sqrt(BEIDOU_GM / (a * a * a));
}
@ -235,19 +389,3 @@ double Gnss_Ephemeris::sv_clock_relativistic_term(double transmitTime) const
}
return dtr_;
}
double Gnss_Ephemeris::check_t(double time) const
{
const double half_week = 302400.0; // seconds
double corrTime = time;
if (time > half_week)
{
corrTime = time - 2.0 * half_week;
}
else if (time < -half_week)
{
corrTime = time + 2.0 * half_week;
}
return corrTime;
}

16
src/core/system_parameters/gnss_ephemeris.h
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@ -19,6 +19,7 @@
#ifndef GNSS_SDR_GNSS_EPHEMERIS_H
#define GNSS_SDR_GNSS_EPHEMERIS_H
#include <array>
#include <cstdint>
/*!
@ -36,6 +37,20 @@ public:
*/
double sv_clock_drift(double transmitTime);
/*!
* \brief Computes prediction of the Doppler shift for a given time and receiver's position and velocity.
* @param[in] rx_time_s Time of Week in seconds
* @param[in] lat Receiver's latitude in degrees
* @param[in] lon Receiver's longitude in degrees
* @param[in] h Receiver's height in meters
* @param[in] ve Receiver's velocity in the East direction [m/s]
* @param[in] vn Receiver's velocity in the North direction [m/s]
* @param[in] vu Receiver's velocity in the Up direction [m/s]
* @param[in] band Signal band for which the Doppler will be computed
* (1: L1 C/A, E1B, BI1; 2: L2C, BI2; 3: BI3; 5: L5/E5a; 6: E6B; 7: E5b; 8: E5a+E5b)
*/
double predicted_doppler(double rx_time_s, double lat, double lon, double h, double ve, double vn, double vu, int band) const;
void satellitePosition(double transmitTime); //!< Computes the ECEF SV coordinates and ECEF velocity
uint32_t PRN{}; //!< SV ID
@ -83,6 +98,7 @@ protected:
char System{}; //!< Character ID of the GNSS system. 'G': GPS. 'E': Galileo. 'B': BeiDou
private:
void satellitePosVelComputation(double transmitTime, std::array<double, 7>& pos_vel_dtr) const;
double check_t(double time) const;
double sv_clock_relativistic_term(double transmitTime) const;
};