RU2717098C1 - Two-frequency phase method of determining signals delay of a navigation satellite system in the ionosphere - Google Patents

Abstract

FIELD: satellite navigation.

SUBSTANCE: invention relates to satellite navigation and is intended to determine delay of signals of global navigation satellite systems (GNSS) in ionosphere using two-frequency navigation equipment of consumer (NAC). Said result is achieved due to that, first, when calculating vertical (zenith) delay of signals of the navigation satellite system and inclined signal delays in the ionosphere of each visible NSC, increments of the inclined factor and phase pseudo-ranges measured in the ranges L1 and L2 are used, on the time interval M limited by the permissible error value of approximation of the measured increments by a linear relationship, then the slope delay of the signal in the ionosphere for each j-th NSC is calculated.

EFFECT: high accuracy of navigation measurements owing to reduced error in estimating delay of signals of navigation satellite systems in the ionosphere.

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Description

The present invention relates to the field of satellite navigation and is intended to determine the delay of signals of global navigation satellite systems (GNSS) in the ionosphere using dual-frequency consumer navigation equipment (NAL).

The widespread use of modern global navigation satellite systems GLONASS and GPS leads to the need to improve the accuracy of navigation measurements. A great influence on the error of navigation measurements using signals from the global navigation satellite systems GLONASS and GPS is exerted by the conditions for the passage of signals from navigation spacecraft (NSC) in the atmosphere.

As studies show, the ionosphere has the greatest impact on the signals of the GLONASS and GPS. The magnitude of the signal delay in the ionosphere depends on solar activity, seasonal and daily variations in the electron concentration, elevation angle and azimuth of the satellite and on the latitude and longitude of the signal reception point.

There is a method in which to find the ionospheric delay of a signal, a code pseudorange difference measured from signals in different frequency ranges [1] is used. In this method, it is required to calibrate the delay difference when passing signals along the NAP paths for L1 and L2. To calibrate the NAP, it is necessary to determine the delay difference of the L1 and L2 signals in the satellite, antenna, and receiver path. The determination of these values is a long and laborious process that requires the use of additional equipment.

The use in the method of the difference of code pseudorange, which have a random error at the level of 1-2 meters, leads to an increase in the error in determining the ionospheric delay of the signal.

In addition to the two-frequency code method, a single-frequency method for determining the ionospheric delay of a signal is described, described in RF patent No. 2208809 [2] where the difference of the increments of the code and phase pseudorange is used to determine the ionospheric delay of the signal. The algorithm for finding the ionospheric delay of the signal is divided into two stages. At the first stage, the vertical (zenith) delay of the signal in the ionosphere is estimated, and at the second, the vertical (zenith) delay is recalculated into the inclined one using the display function describing the dependence of the signal delay in the ionosphere on the elevation angle of the satellite. As in the previous method, the disadvantage is the use in the calculations of code pseudorange with increased random error. An additional factor determining the error of this method is the use of a mathematical model of the ionosphere as a mapping function with a lack of accuracy approximating the dependence of the signal delay in the ionosphere on the elevation angle of the satellite.

Closest to the claimed invention is a method for determining the delay of the signals of a navigation satellite system in the ionosphere [3], in which the source data is not code pseudorange, but pseudorange measured by the phase of the carrier frequency of the signal in the ranges L1 and L2. The determination of the ionospheric delay by this method is also divided into two stages. At the first stage, the increments of the phase pseudorange for the time between the current and previous measurements are estimated, then the difference between the obtained increments is calculated and the vertical (zenith) delay of the navigation signal of the satellite system in the ionosphere is determined by the formula:

- накопленное значениеWhere

- accumulated value

oblique factor for the jth NKA;

i - current time, s;

j is the number of the navigation spacecraft, j = 1,2, ..., n is the filtration coefficient, 0 <k <1;

N {i) is the number of navigation spacecraft visible at the current moment of time i;

- приращение наклонного фактора;

- increment of the inclined factor;

- наклонный фактор;

- inclined factor;

R _e is the radius of the Earth, m;

h is the average height of the ionospheric layer, m;

y ^j (i) is the elevation angle of the jth satellite, deg;

- накопленное значение наклонной задержки навигационного спутникового сигнала в ионосфере, м;

- the accumulated value of the oblique delay of the navigation satellite signal in the ionosphere, m;

- приращение наклонной задержки навигационного спутникового сигнала в ионосфере, м;

- increment of the oblique delay of the navigation satellite signal in the ionosphere, m;

f ₁ , f ₂ - carrier frequency for the frequency range L1 and L2, respectively, Hz;

- приращение фазовой псевдодальности, измеренной на несущей частоте f₁, м;

- increment of the phase pseudorange measured at the carrier frequency f ₁ , m;

- приращение фазовой псевдодальности,

- increment of phase pseudorange,

measured at the carrier frequency f ₂ , m

At the second stage, the vertical (zenith) delay of the signal in the ionosphere is converted into the oblique delay of the navigation signal of the satellite system in the ionosphere for each visible satellite, using the mathematical model of the ionosphere according to the formula:

Used in the prototype, the concept of an inclined factor corresponds to the concept of a mapping function used in the single-frequency method [2] (the expressions for their definition coincide).

The found oblique signal delay has an error due to the error in determining the vertical delay of the navigation signal of the satellite system in the ionosphere and the error of the mathematical model of the ionosphere approximating the dependence of the signal delay in the ionosphere on the elevation angle of the satellite.

The basis of the invention is the task of improving the accuracy of navigation measurements, by reducing the error in determining the delay of the signals of the navigation satellite system in the ionosphere.

The problem is solved in that in the method for determining the delay of the signals of the navigation satellite system in the ionosphere, which measure the phase pseudorange and calculate their increments at two carrier frequencies, calculate the difference between the received increments, and the oblique delay of the signals of the navigation satellite system in the ionosphere for each visible satellite determined by the formula, including the calculation of the vertical (zenith) delay of the signals of the navigation satellite system in the ionosphere and the inclined factor, taking into account In order to calculate the mathematical model of the ionosphere, according to the invention, first, when calculating the vertical (zenith) delay of the navigation satellite system signals and the oblique signal delays in the ionosphere of each visible satellite, increments of the oblique factor and phase pseudorange measured in the ranges L1 and L2 over a time interval M limited permissible value of the approximation error of the measured increments by a linear dependence (for example, 30 seconds):

- приращение наклонного фактора;

- increment of the inclined factor;

- приращение фазовой псевдодальности, измеренной на несущей частоте f₁, м;

- increment of the phase pseudorange measured at the carrier frequency f ₁ , m;

- приращение фазовой псевдодальности, измеренной на несущей частоте f₂, м;

- increment of the phase pseudorange measured at the carrier frequency f ₂ , m;

then calculate the oblique delay of the signal in the ionosphere for each y-th spacecraft by the formula:

где i>М;

where i>M;

i - current time, s;

j is the number of the currently visible navigation spacecraft, j = 1, 2, ..., n;

i _n - the initial moment of time for tracking the signal of the jth satellite;

- приращение наклонной задержки навигационного спутникового сигнала j-го НКА в ионосфере, м;

- increment of the oblique delay of the navigation satellite signal of the jth satellite in the ionosphere, m;

- оценка значения ионосферной задержки сигнала, сформированная на начальном этапе слежения за сигналом j-го НКА с учетом значения угла места спутника и оценки вертикальной задержки сигналов навигационной спутниковой системы в ионосфере, сформированной к моменту начала слежения за сигналом j-го НКА;

- estimation of the ionospheric delay of the signal generated at the initial stage of tracking the signal of the jth satellite, taking into account the elevation angle of the satellite and estimating the vertical delay of the signals of the navigation satellite system in the ionosphere, formed by the time the tracking of the signal of the jth satellite is started;

OF ^j (γ ^j (i _n )) is the oblique factor of the jth satellite at the initial time;

γ ^j (i _n ) is the elevation angle of the spacecraft at the initial time, deg.

In FIG. 1 is a structural diagram of consumer navigation equipment, and FIG. 2 shows a block diagram of an algorithm that implements the proposed method of phase two-frequency determination of the delay of the signals of a navigation satellite system in the ionosphere.

The consumer’s navigation equipment includes the following units: antenna, radio path (RT), frequency synthesizer, analog-to-digital converter (ADC) unit, reference generator (OG), and digital signal processing unit (DSP). Moreover, the digital signal processing unit comprises a primary signal processing unit (PIC) and a secondary signal processing unit (VOS).

A navigation signal from the satellite is fed to the RT unit from the antenna, where it is summed with the local oscillator frequency and divided into 2 channels. The filtered and amplified signal is fed to a two-channel ADC, clocked by the clock frequency of the frequency synthesizer, where the received signal is digitized. The obtained digital samples are sent to the input of the POS block to determine the main navigation parameters - code and phase pseudorange, satellite elevation angle, amplitude, etc. The BOC block receives navigation parameters, where an algorithm for calculating the ionospheric delay of the signal of each visible signal to the current one can be implemented the time of the satellite according to the block diagram shown in FIG. 2.

The initial data for calculating the oblique delay of the signal in the ionosphere are the satellite elevation angle, pseudorange measured by the phase of the signal carrier, and the oblique factor (operand 1). The phase pseudorange at frequencies L1 L2 and the slope factor of each j-th satellite are described by the following expressions:

- дальность до j-ого НКА;

- фазовая неоднозначность;

Where

- range to the j-th NKA;

- phase ambiguity;

- длина волны;

- задержка сигнала j-го НКА в ионосфере;

- wavelength;

- signal delay of the jth satellite in the ionosphere;

- задержка сигнала j-ого НКА в тропосфере; τ - расхождение шкалы времени НАЛ относительно шкалы времени систем ГЛОНАСС или GPS;

- случайная погрешность; с - скорость распространения радиоволн в вакууме;

- угол места j-го НКА; R_e - радиус Земли; h - средняя высота ионосферного слоя; i - текущий момент времени.

- signal delay of the jth satellite in the troposphere; τ is the discrepancy of the NAL timeline relative to the time scale of GLONASS or GPS systems;

- random error; C is the speed of propagation of radio waves in a vacuum;

- elevation angle of the j-th spacecraft; R _e is the radius of the Earth; h is the average height of the ionospheric layer; i is the current time.

In the next step, initialize the variable k (operand 2) and check the condition for ending the cycle, where N (i) is the number of navigation spacecraft visible at the current time moment i (operand 3).

To calculate the increments of phase pseudorange and the increment of the oblique factor, in the time interval M, it is necessary to write the initial data to the buffer, where j is the number of the currently visible navigation spacecraft (operand 4). After recording, an increase in the size of the buffer occurs (operand 5) and it is necessary to check the condition that the buffer size is equal to the value M (operand 6). If the conditions are not met, increment to (operand 7) and read the next value of y (operand 8), in the opposite case, increments of phase pseudorange and increment of the slope factor (operand 9) are calculated. The increments of the phase pseudorange and the increment of the oblique factor are calculated by the following expressions:

Next, the increment of the inclined delay (7) (operand 10) is calculated and the algorithm is repeated until the loop condition (operand 3) becomes false.

As soon as the condition of the cycle becomes false, they go on to execute the next cycle, where the variable k is reset (operand 11) and begin to check the condition for ending the cycle (operand 12). This cycle is responsible for the rejection of satellites for which the increment of the oblique delay was not calculated. For rejection, the condition of equal buffer size and M value (operand 13) is responsible. If the condition is false, then increment k (operand 14) and read the next value j (operand 15), otherwise, the obtained data is substituted into the function of calculating the vertical delay (operand 16) and repeat the algorithm until the loop condition (operand 12) will become false.

In the next step, the variable k is reset (operand 17) and the condition for ending the loop (operand 18) is checked. If the condition is false, then the condition of equality of the buffer size and the value of M is checked (operand 19). If the result is false, increment to (operand 20) and read the next value j (operand 21), and if the result is true, check the initial moment of time for tracking the signal (operand 22). If the current time is the initial time of signal tracking, then the estimate of the initial value of the ionospheric delay of the signal (operand 24) (formula 8) is calculated, otherwise the oblique delay of the signal in the ionosphere (operand 23) is calculated (formula 9). After calculation, the algorithm is repeated until the loop condition (operand 18) becomes false.

Thus, the proposed method allows you to determine the oblique delay of the signal in the ionosphere for each satellite without error in the mathematical model of the ionosphere, approximating the dependence of the signal delay in the ionosphere on the elevation angle of the satellite.

The use of phase pseudorange increments over a certain time interval limited by the permissible error of approximation of the measured increments by a linear dependence allows one to detect disturbances in the continuity of tracking the phase of the carrier frequency of the satellite and eliminate the “jumps” in phase cycles caused by this, thereby reducing the random error in measuring increments of phase pseudoranges, which accordingly, it reduces the error in determining the vertical (anti-aircraft) delay of the signal in the ionosphere.

In addition, the formation of current estimates of the inclined ionospheric delay for each satellite as the sum of the initial value and the integral of the changes in the ionospheric delay of the signal, calculated from the difference in the increments of the phase pseudorange in the ranges L1 and L2, makes it possible to determine the change in the ionospheric delay of the signal for each satellite with the smallest error, which and excludes from the error in determining the current value of the slant delay of the signal in the ionosphere the error component due to the error of the ionosphere model An experiment approximating the dependence of the signal delay in the ionosphere on the elevation angle of a satellite.

In the claimed method, as well as in the prototype, the systematic error due to the delay of the signal in the paths of the NAP is eliminated due to the use of phase increments of the corresponding measurements.

LITERATURE

1. Global satellite navigation system GLONASS / Ed. Kharisova V.N., Perova A.I., Boldina V.A. - M .: IPRZhR, 1999 .-- 560 s.

2. Pat. RU 2208809, IPC ⁷ G01S 5/02, G01S 1/32, Н04В 7/185. The method of single-frequency determination of the delay of the signals of the navigation satellite system in the ionosphere / Kazantsev M.Yu., Kokorin V.I., Fateev Yu.L .; applicant GOU VPO Krasnoyarsk State Technical University. - No. 2002104727/09; declared 02.21.2002. publ. 07/20/2003.

3. Pat. RU 2584243 C1, MKP G01S 19/04. A method for determining the delay of the signals of a navigation satellite system in the ionosphere / Kurnosov A.S., Fateev Yu.L .; applicant Federal State Autonomous Educational Institution of Higher Professional Education "Siberian Federal University". - No. 20155110269/07; declared 03/23/2015. publ. 05/25/2016, Bull. No. 14 (prototype).

Claims (14)

The method for determining the delay of the signals of the navigation satellite system in the ionosphere, by which phase pseudorange is measured and their increments are calculated at two carrier frequencies, the difference between the obtained increments is calculated, and the oblique delay of the signals of the navigation satellite system in the ionosphere for each visible satellite is determined by the formula including the calculation of the vertical (anti-aircraft) delay of the signals of the navigation satellite system in the ionosphere and the inclined factor taking into account the mathematical model of the ionosphere, characterized in that, first, when calculating the vertical (zenith) delay of the navigation satellite system signals and the oblique signal delays in the ionosphere of each visible satellite, increments of the oblique factor and phase pseudorange measured in the ranges L1 and L2 are used, on the time interval M, limited by the permissible approximation error measured increments by a linear relationship, for example, 30 seconds:

- increment of the inclined factor;

- increment of the phase pseudorange measured at the carrier frequency f ₁ , m;

- increment of the phase pseudorange measured at the carrier frequency f ₂ , m; then calculate the oblique delay of the signal in the ionosphere for each j-th spacecraft by the formula:

where i>M; i - current time, s; j is the number of the currently visible navigation spacecraft, j = 1,2, ..., n; i _n - the initial moment of time for tracking the signal of the jth satellite;

- increment of the oblique delay of the navigation satellite signal of the jth satellite in the ionosphere, m;

- estimation of the ionospheric delay of the signal, formed at the initial stage of tracking the signal of the jth satellite, taking into account the elevation angle of the satellite and estimating the vertical delay of the signals of the navigation satellite system in the ionosphere, formed by the time the tracking of the signal of the jth satellite is started;

- the oblique factor of the j-th spacecraft at the initial time; γ ^j (i _n ) is the elevation angle of the spacecraft at the initial time, deg.

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