Ionospheric delay and clock error correction method and system based on two-way earth-space hetero-frequency signals

Abstract

The application discloses an ionospheric delay and clock difference correction method and system based on a space-ground bidirectional hetero-frequency signal, relates to the technical fields of navigation and positioning, space measurement and control and space-ground time service, and can obtain corrected pseudo-range observations and carrier phase observations without depending on real-time ionospheric model parameters input by other external systems and without increasing space-ground bidirectional measurement system resources. A pseudo-range and carrier phase extraction module extracts and corrects pseudo-range and carrier phase in the bidirectional measurement stage of a space-ground bidirectional measurement system, and obtains corrected pseudo-range observations and carrier phase observations. A carrier phase ambiguity determination module determines carrier phase ambiguity according to positioning results provided by an external navigation system and known ground station coordinates. Then, a spacecraft keeps continuous signal tracking on a ground station i, and carrier phase ambiguity is updated in real time. An ionospheric delay and clock difference estimation module estimates the total amount of electrons on an uplink and downlink signal transmission path and space-ground clock difference, and obtains bidirectional distance.

Description

Technical Field

[0001] This invention relates to the fields of navigation and positioning, aerospace telemetry and control, and space-to-ground time service, specifically to a method and system for ionospheric delay and clock error correction based on two-way different frequency signals between space and ground. Background Technology

[0002] In applications such as navigation and positioning, aerospace telemetry and control, and space-to-ground time synchronization, two-way measurements across the ionosphere are indispensable. Two-way measurement systems transmit phase-modulated signals and employ a carrier-phase-based two-way measurement mode. Because the signal transmission passes through the atmospheric ionosphere, the free electrons and ions in the ionosphere alter the signal propagation speed, causing a shift in the measurement phase. Furthermore, clock bias in two-way measurement systems further exacerbates the phase shift, degrading the accuracy of two-way measurements. Therefore, accurate estimation of ionospheric delay and clock bias is crucial for high-precision two-way measurements.

[0003] Conventional ionospheric correction methods are mainly divided into model-based methods and co-directional dual-frequency methods. Model-based methods establish mathematical models based on the ionospheric delay characteristics, such as Klobuchar, Bent, and NeQuick. Ionospheric delay correction based on mathematical models relies on real-time ionospheric model parameters input from other external systems to calculate the ionospheric delay, thus it cannot work independently. In the co-directional dual-frequency method, the two-way measurement system simultaneously transmits and receives two frequency signals. Due to the diffuse nature of the ionosphere, different frequency signals will produce different delays when passing through the same ionosphere. Therefore, the observations of the two-way signals can be weighted and combined to remove the influence of ionospheric delay. However, this method requires simultaneous transmission and reception of two signals, resulting in high resource overhead. Furthermore, neither the model-based method nor the co-directional dual-frequency method can directly eliminate the ionospheric clock bias; additional clock bias estimation steps are required to achieve high-precision two-way measurements.

[0004] Therefore, how to achieve high-precision bidirectional measurement without relying on ionospheric model parameters input from other external systems and without increasing the resources of the space-ground bidirectional measurement system is an urgent problem to be solved. Summary of the Invention

[0005] In view of this, the present invention provides a method and system for ionospheric delay and clock bias correction based on two-way heterogeneous signals from the ground and space. It can operate independently without relying on real-time ionospheric model parameters input from other external systems, and does not increase the resources of the two-way measurement system from the ground and space. It has better robustness and a wider range of application scenarios.

[0006] To achieve the above objectives, the present invention provides an ionospheric delay and clock bias correction system based on two-way heterogeneous signals from the ground and space, used to correct ionospheric delay and clock bias in a two-way measurement system from the ground and space; the system includes a pseudo-moment and carrier phase extraction module, a carrier phase ambiguity determination module, and an ionospheric delay and clock bias estimation module;

[0007] The two-way measurement system consists of multiple ground stations with known clock differences between them and spacecraft.

[0008] The pseudo-moment and carrier phase extraction module is used in the two-way measurement phase between the ground station and the spacecraft in a two-way measurement system to extract and correct pseudo-moments and carrier phases, respectively obtaining corrected pseudo-moment observations and carrier phase observations. The corrected pseudo-moment observations include the uplink pseudorange ρ between the ground station and the spacecraft. u and downlink pseudorange ρ d The corrected carrier phase observations include the uplink carrier phase φ obtained from spacecraft sampling. u and the downlink carrier phase φ obtained by ground station sampling d .

[0009] The carrier phase ambiguity determination module, based on the positioning results provided by the external navigation system and the known ground station coordinates, calculates the true uplink distance R between ground station i and the spacecraft. u and the actual downlink distance R d And resolve the carrier phase ambiguity, including the uplink carrier ambiguity N. u and downlink carrier ambiguity N d The spacecraft then maintains continuous signal tracking of ground station i and updates the carrier phase ambiguity in real time; the carrier phase ambiguity N is then... u N d The corrected pseudorange observation ρ u ρ d and the corrected carrier phase observation φ u φ d The data is then sent to the ionospheric delay and clock bias estimation module for estimation.

[0010] The ionospheric delay and clock bias estimation module, based on the calculated carrier phase ambiguity N, u N d ; Corrected pseudorange observation ρ u ρ d and the corrected carrier phase observation φ u φ d The total amount of electrons and the clock difference between the ground and the uplink signal transmission paths are estimated to obtain the bidirectional distance.

[0011] Furthermore, during a two-way measurement phase of the space-ground two-way measurement system, ground station i transmits at frequency f at time t1.u The uplink signal, via the uplink true distance R u The signal was then received by the spacecraft, at which point the spacecraft's time was t2 + δt, where δt represents the time difference between Earth and space. After receiving the uplink signal from the ground station, the spacecraft transmitted the signal at frequency f. d The downlink signal is sent to the ground station; the downlink signal passes through the downlink true distance R d It was then received by ground station i, at which point the ground station time was t3;

[0012] The ionospheric delay and clock bias estimation module observes the uplink pseudorange ρ between the ground station and the spacecraft based on the transmission and reception times of the ground station and the spacecraft. u and downlink pseudorange ρ d ;

[0013] The observation equation is as follows:

[0014] ρ u =R u +I u +δt+τ u +T+ε u (1)

[0015] ρ d =R d +I d -δt+τ d +T+ε d (2)

[0016] Where R u R d Representing the true distances of the uplink and downlink respectively; I u I d These represent the uplink and downlink ionospheric delays, respectively; τ u τ d These represent the uplink and downlink signal processing device delays, respectively; T represents the tropospheric delay; ε u and ε d Represents observation noise;

[0017] The upward and downward signal paths are basically overlapping, and the total electron TEC is equal on both the upward and downward paths;

[0018] Taking advantage of the diffuse nature of the ionosphere, the uplink and downlink ionospheric delay errors have the following relationship:

[0019]

[0020] Where N e This represents the total number of electrons along the path.

[0021] Uplink carrier phase φ obtained from spacecraft sampling u and the downlink carrier phase φ obtained by ground station samplingd for:

[0022] λ u φ u =R u -I u +δt+τ u +T+λ u N u (4)

[0023] λ d φ d =R d -I d -δt+τ d +T+λ d N d (5)

[0024] Where λ u , λ d These represent the uplink and downlink signal wavelengths, respectively; N u N d Represents the integer ambiguity of uplink and downlink signal carriers;

[0025] The pseudorange and carrier phase observation results of the uplink and downlink signals are converted; the equipment delay error τ is calibrated in advance. u τ d And it is removed from the observations; the tropospheric delay error T has a relatively small impact and is usually corrected by the model; the true range R of the uplink and downlink u R d The relationship is derived by combining signal transmission delay, the relative elevation angle between the spacecraft and the ground station, and the Earth's rotation speed. The result is...

[0026]

[0027] Where B represents the latitude of the spacecraft, which can be extrapolated from the spacecraft positioning results of the previous epoch; θ represents the spacecraft's pitch angle relative to the ground station, and θ represents the spacecraft's azimuth angle relative to the ground station. From this, the true uplink and downlink distances R are obtained. u and R d The transformation relationship;

[0028] After eliminating equipment delay, tropospheric delay, and uplink / downlink true range asymmetry, the corrected pseudorange and carrier phase observations are obtained.

[0029]

[0030]

[0031]

[0032]

[0033] Furthermore, the ionospheric delay and clock bias estimation module uses the calculated carrier integer ambiguity N... u N d ; Corrected pseudorange observation ρ u ρ d and the corrected carrier phase observation φ u φ d The total amount of electrons and the clock difference between the ground and the uplink signal transmission paths are estimated, and the true value of the bidirectional distance R is obtained.

[0034] Let z = [R, N] e ,δt] T If the variable to be estimated is represented by , then the ionospheric delay and clock bias estimation module uses the following method for estimation:

[0035]

[0036] in

[0037]

[0038] The total number of electrons N along the signal transmission path is obtained. e After obtaining the estimation results, the uplink and downlink ionospheric delays are estimated according to formula (3), thereby removing the ionospheric delay and the clock difference between the ground and the sky from the uplink and downlink observations.

[0039] Furthermore, in the ionospheric delay and clock bias estimation module, if the following situation exists: the spacecraft loses carrier tracking lock on ground station i, resulting in the loss of carrier phase ambiguity, then the space-to-ground clock bias information calculated by continuously tracking the ground station with other carriers is used to adjust the uplink and downlink carrier phase ambiguity of ground station i and the total electron quantity N on the signal transmission path. e Estimate the values ​​to achieve high-precision bidirectional measurement with ground station i; let x = [R, N] e N u N d ] T Let x represent the variable to be estimated. Then, the estimation method for x is as follows:

[0040]

[0041] in

[0042]

[0043] This determines the total number of electrons N along the signal transmission path. e And the carrier integer ambiguity, to obtain the total number of electrons N on the signal transmission path. eAfter estimating the results, the uplink and downlink ionospheric delays are calculated according to formula (3), thereby removing the ionospheric delays and the clock difference between the ground and the sky from the uplink and downlink observations.

[0044] Another embodiment of the present invention provides a method for ionospheric delay and clock bias correction based on bidirectional frequency signals from Earth and space, comprising the following steps:

[0045] The two-way measurement system consists of multiple ground stations with known clock differences between them and spacecraft.

[0046] Step 1: During the two-way measurement phase of the ground station and spacecraft in the space-ground two-way measurement system, pseudo-moments and carrier phases are extracted and corrected to obtain corrected pseudo-moment and carrier phase observations. The corrected pseudo-moment observations include the uplink pseudorange ρ between the ground station and the spacecraft. u and downlink pseudorange ρ d The corrected carrier phase observations include the uplink carrier phase φ obtained from spacecraft sampling. u and the downlink carrier phase φ obtained by ground station sampling d .

[0047] Step 2: Based on the positioning results provided by the external navigation system and the known ground station coordinates, calculate the true uplink distance R between ground station i and the spacecraft. u and the actual downlink distance R d And resolve the carrier phase ambiguity, including the uplink carrier ambiguity N. u and downlink carrier ambiguity N d The spacecraft then maintained continuous signal tracking of ground station i and updated the carrier phase ambiguity in real time.

[0048] Step 3: Calculate the carrier phase ambiguity N u N d ; Corrected pseudorange observation ρ u ρ d and the corrected carrier phase observation φ u φ d The total amount of electrons and the clock difference between the ground and the uplink signal transmission paths are estimated to obtain the bidirectional distance.

[0049] Furthermore, during a two-way measurement phase of the space-ground two-way measurement system, ground station i transmits at frequency f at time t1. u The uplink signal, via the uplink true distance R u The signal was then received by the spacecraft, at which point the spacecraft's time was t2 + δt, where δt represents the time difference between Earth and space. After receiving the uplink signal from the ground station, the spacecraft transmitted the signal at frequency f. d The downlink signal is sent to the ground station; the downlink signal passes through the downlink true distance R dIt was then received by ground station i, at which point the ground station time was t3;

[0050] Step one, specifically:

[0051] The uplink pseudorange ρ between the ground station and the spacecraft was observed from the launch and reception times of the ground station and the spacecraft. u and downlink pseudorange ρ d ;

[0052] The observation equation is as follows:

[0053] ρ u =R u +I u +δt+τ u +T+ε u (1)

[0054] ρ d =R d +I d -δt+τ d +T+ε d (2) Where R u R d Representing the true distances of the uplink and downlink respectively; I u I d These represent the uplink and downlink ionospheric delays, respectively; τ u τ d These represent the uplink and downlink signal processing device delays, respectively; T represents the tropospheric delay; ε u and ε d Represents observation noise;

[0055] The upward and downward signal paths are basically overlapping, and the total electron TEC is equal on both the upward and downward paths;

[0056] Taking advantage of the diffuse nature of the ionosphere, the uplink and downlink ionospheric delay errors have the following relationship:

[0057]

[0058] Where N e This represents the total number of electrons along the path.

[0059] Uplink carrier phase φ obtained from spacecraft sampling u and the downlink carrier phase φ obtained by ground station sampling d for:

[0060] λ u φ u =R u -I u +δt+τ u +T+λ u N u (4)

[0061] λ d φ d =R d -I d -δt+τ d +T+λ d N d (5)

[0062] Where λ u , λ d These represent the uplink and downlink signal wavelengths, respectively; N u N d Represents the integer ambiguity of uplink and downlink signal carriers;

[0063] The pseudorange and carrier phase observation results of the uplink and downlink signals are converted; the equipment delay error τ is calibrated in advance. u τ d And it is removed from the observations; the tropospheric delay error T has a relatively small impact and is usually corrected by the model; the true range R of the uplink and downlink u R d The relationship is derived by combining signal transmission delay, the relative elevation angle between the spacecraft and the ground station, and the Earth's rotation speed. The result is...

[0064]

[0065] Where B represents the latitude of the spacecraft, which can be extrapolated from the spacecraft positioning results of the previous epoch; θ represents the spacecraft's pitch angle relative to the ground station, and θ represents the spacecraft's azimuth angle relative to the ground station. From this, the true uplink and downlink distances R are obtained. u and R d The transformation relationship;

[0066] After eliminating equipment delay, tropospheric delay, and uplink / downlink true range asymmetry, the corrected pseudorange and carrier phase observations are obtained:

[0067]

[0068]

[0069]

[0070]

[0071] Furthermore, step three specifically involves:

[0072] The calculated carrier integer ambiguity N u N d ; Corrected pseudorange observation ρ u ρ dand the corrected carrier phase observation φ u φ d The total amount of electrons and the clock difference between the ground and the earth are estimated on the uplink and downlink signal transmission paths, and the bidirectional distance is obtained.

[0073] Let z = [R, N] e ,δt] T If the variable to be estimated is represented by , then the ionospheric delay and clock bias estimation module uses the following method for estimation:

[0074]

[0075] in

[0076]

[0077] The total number of electrons N along the signal transmission path is obtained. e After obtaining the estimation results, the uplink and downlink ionospheric delays are estimated according to formula (3), thereby removing the ionospheric delay and the clock difference between the ground and the sky from the uplink and downlink observations.

[0078] Furthermore, in step three, if the following situation exists: the spacecraft loses carrier tracking lock on ground station i, resulting in the loss of carrier phase ambiguity, then the space-to-ground clock difference information calculated by continuously tracking the ground station with other carriers is used to correct the uplink and downlink carrier phase ambiguity of ground station i and the total electronic quantity N on the signal transmission path. e Estimate the values ​​to achieve high-precision bidirectional measurement with ground station i; let x = [R, N] e N u N d ] T Let x represent the variable to be estimated. Then, the estimation method for x is as follows:

[0079]

[0080] in

[0081]

[0082] This determines the total number of electrons N along the signal transmission path. e And the carrier integer ambiguity, to obtain the total number of electrons N on the signal transmission path. e After estimating the results, the uplink and downlink ionospheric delays are calculated according to formula (3), thereby removing the ionospheric delays and the clock difference between the ground and the sky from the uplink and downlink observations.

[0083] Beneficial effects:

[0084] This invention is applicable to two-way measurement systems between ground and space. It utilizes uplink signals transmitted from ground stations and downlink signals transmitted from spacecraft. By measuring the pseudorange and carrier phase information of the uplink and downlink signals, and taking advantage of the characteristics of the ionospheric dispersion medium, it corrects the ionospheric delay and the clock difference between ground and space along the signal transmission path. Compared with conventional model methods, the proposed method does not rely on real-time ionospheric model parameters input from other external systems and can operate independently. Compared with the co-directional dual-frequency method, the proposed method only requires the two-way measurement system to transmit and receive one signal simultaneously, without increasing the resources of the two-way measurement system, and has a wider range of application scenarios. Attached Figure Description

[0085] Figure 1 for. Figure 1 Flowchart of an ionospheric delay and clock bias correction method based on two-way heterogeneous signals from Earth and space.

[0086] Figure 2 for. Figure 2 Schematic diagram of two-way measurement between ground and sky

[0087] Among them, 1-, 2- Detailed Implementation

[0088] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0089] In a two-way measurement system between ground and space, ground stations and spacecraft transmit bidirectional measurement signals at different frequencies. Utilizing the diffuse nature of the ionosphere, simultaneous estimation of ionospheric delay and clock bias between ground and space can be achieved. This invention proposes a method for ionospheric delay and clock bias correction based on bidirectional, different-frequency signals between ground and space. The two-way measurement system requires only one receiving channel and one transmitting channel to jointly estimate and correct ionospheric delay and clock bias, achieving high-precision two-way measurement. Compared to model-based methods, the proposed method does not rely on real-time ionospheric model parameters input from other external systems, exhibiting independence and autonomy. Compared to the co-directional dual-frequency method, the proposed method only requires simultaneous transmission and reception of one signal, without increasing the resources of the two-way measurement system.

[0090] Example 1:

[0091] The embodiments of the present invention include an ionospheric delay and clock bias correction system based on bidirectional frequency signals from the ground and the sky, and an ionospheric delay and clock bias correction method based on the system based on bidirectional frequency signals from the ground and the sky.

[0092] The ionospheric delay and clock bias correction system based on bidirectional frequency signals from Earth and space provided by this invention has the following structural block diagram: Figure 1 As shown, it includes a pseudorange and carrier phase extraction module, a carrier phase ambiguity determination module, and an ionospheric delay and clock bias estimation module.

[0093] Pseudorange and carrier phase extraction module:

[0094] Without loss of generality, a two-way measurement system is described as follows: A two-way measurement system consists of multiple ground stations with known clock differences between them and a spacecraft. During a single two-way measurement, ground station i transmits at time t1 at a frequency of f. u The uplink signal, via the uplink true distance R u The signal was subsequently received by the spacecraft, at which point the spacecraft's time was t2 + δt, where δt represents the time difference between Earth and space. After receiving the uplink signal from the ground station, the spacecraft transmitted at frequency f. d The downlink signal is sent to the ground station. The signal travels through the downlink true distance R. d It was then received by ground station i, at which point the ground station time was t3. A schematic diagram of the two-way measurement between ground and space is shown below. Figure 2 As shown.

[0095] The uplink pseudorange ρ between the ground station and the spacecraft can be observed from the launch and reception times of the ground station and the spacecraft. u and downlink pseudorange ρ d The observation equation is as follows:

[0096] ρ u =R u +I u +δt+τ u +T+ε u (1)

[0097] ρ d =R d +I d -δt+τ d +T+ε d (2)

[0098] Where R u R d Representing the true distances of the uplink and downlink respectively; I u I d These represent the uplink and downlink ionospheric delays, respectively; τ u τ d These represent the uplink and downlink signal processing device delays, respectively; T represents the tropospheric delay; ε u ε d This represents observation noise.

[0099] Considering that the uplink and downlink signal paths are essentially overlapping, the total electron concentration (TEC) on both paths can be assumed to be equal. Utilizing the diffuse nature of the ionosphere, the uplink and downlink ionospheric delay errors have the following relationship:

[0100]

[0101] Where N eThis represents the total number of electrons along the path.

[0102] Uplink carrier phase φ obtained from spacecraft sampling u and the downlink carrier phase φ obtained by ground station sampling d It can be represented as:

[0103] λ u φ u =R u -I u +δt+τ u +T+λ u N u (4)

[0104] λ d φ d =R d -I d -δt+τ d +T+λ d N d (5)

[0105] Where λ u , λ d These represent the uplink and downlink signal wavelengths, respectively. N u N d This represents the integer ambiguity of the uplink and downlink signal carriers.

[0106] The pseudorange and carrier phase observation results of the uplink and downlink signals are converted. Equipment delay error τ u τ d Calibration can be performed in advance, allowing for the elimination of errors from observations. Tropospheric delay error T has a relatively small impact and is typically corrected using a model. The true ranges R for uplink and downlink... u R d The relationship can be derived by combining signal transmission delay, relative elevation angle between spacecraft and ground station, and Earth's rotation speed. The result is...

[0107]

[0108] Where B represents the latitude of the spacecraft, which can be extrapolated from the spacecraft positioning results of the previous epoch. θ represents the spacecraft's pitch angle relative to the ground station, and θ represents the spacecraft's azimuth angle relative to the ground station. From this, the true uplink and downlink ranges R can be obtained. u and R d The transformation relationship.

[0109] After eliminating equipment delay, tropospheric delay, and uplink / downlink true range asymmetry, the corrected pseudorange and carrier phase observations can be obtained.

[0110]

[0111]

[0112]

[0113]

[0114] This shows that once the carrier integer ambiguity N... u and N d It is confirmed that ionospheric delay and clock bias can be calculated simultaneously.

[0115] Carrier phase ambiguity determination module:

[0116] When pseudorange observation noise is low, carrier phase integer ambiguity can be directly determined using pseudorange observation results. However, pseudorange observation noise is usually high, so using pseudorange to determine carrier integer ambiguity has a large error. When positioning can be performed using other external navigation systems (such as Global Navigation Satellite System (GNSS) or Inertial Navigation System), the uplink true distance R between ground station i and the spacecraft can be calculated by using the precise positioning results provided by the external navigation system and the known ground station coordinates. u and the actual downlink distance R d The spacecraft then continuously tracks the signal from ground station i and updates the carrier phase integer ambiguity in real time.

[0117] The carrier phase integer ambiguity, the corrected pseudorange, and the carrier phase observations are fed into the ionospheric delay and clock bias estimation module for estimation.

[0118] Ionospheric delay and clock bias estimation module:

[0119] The calculated carrier integer ambiguity N u N d ; Corrected pseudorange observation ρ u ρ d and the corrected carrier phase observation φ u φ d This allows estimation of the total number of electrons and the clock difference between the ground and upstream sides along the uplink and downlink signal transmission paths, yielding the true bidirectional distance R. Let z = [R, N] e ,δt] T If we represent the variable to be estimated, then the estimation method is as follows:

[0120]

[0121] in

[0122]

[0123] The total number of electrons N along the signal transmission path is obtained.e After obtaining the estimation results, the uplink and downlink ionospheric delays can be estimated according to formula (3). This allows the ionospheric delay and the clock difference between the ground and space stations to be eliminated from the uplink and downlink observations, thus achieving high-precision two-way measurements between the ground and space stations.

[0124] Furthermore, if the spacecraft loses carrier tracking lock on ground station i, resulting in the loss of integer ambiguity, the clock difference information between the ground station and the uplink and downlink carriers, calculated by continuously tracking other carriers, can be used to correct the integer ambiguity of the uplink and downlink carriers of ground station i, as well as the total electronic quantity N on the signal transmission path. e An estimation is performed to achieve high-precision bidirectional measurement with ground station i. Let x = [R, N] e N u N d ] T Let x represent the variable to be estimated. Then, the estimation method for x is as follows:

[0125]

[0126] in

[0127]

[0128] This allows us to determine the total number of electrons N along the signal transmission path and the carrier integer ambiguity. We then obtain the...

[0129] e

[0130] After estimating the total number of electrons N along the signal transmission path, the uplink and downlink can be calculated using formula (3).

[0131] e

[0132] Ionospheric delay. This allows ionospheric delay and ground-to-ground clock bias to be eliminated from uplink and downlink observations, enabling high-precision two-way ground-to-ground measurements.

[0133] Example 2:

[0134] Another embodiment of the present invention provides a method for ionospheric delay and clock bias correction based on bidirectional frequency signals from Earth and space, characterized by comprising the following steps:

[0135] The two-way measurement system consists of multiple ground stations with known clock differences between them and spacecraft.

[0136] Step 1: During the two-way measurement phase of the ground station and spacecraft in the space-ground two-way measurement system, pseudo-moments and carrier phases are extracted and corrected to obtain corrected pseudo-moment and carrier phase observations. The corrected pseudo-moment observations include the uplink pseudorange ρ between the ground station and the spacecraft. u and downlink pseudorange ρ dThe corrected carrier phase observations include the uplink carrier phase φ obtained from spacecraft sampling. u and the downlink carrier phase φ obtained by ground station sampling d During a two-way measurement phase of the space-ground two-way measurement system, ground station i transmits at frequency f at time t1. u The uplink signal, via the uplink true distance R u The signal was then received by the spacecraft, at which point the spacecraft's time was t2 + δt, where δt represents the time difference between Earth and space. After receiving the uplink signal from the ground station, the spacecraft transmitted the signal at frequency f. d The downlink signal is sent to the ground station; the downlink signal passes through the downlink true distance R d It was then received by ground station i, at which point the ground station time was t3;

[0137] Step one, specifically:

[0138] The uplink pseudorange ρ between the ground station and the spacecraft was observed from the launch and reception times of the ground station and the spacecraft. u and downlink pseudorange ρ d ;

[0139] The observation equation is as follows:

[0140] ρ u =R u +I u +δt+τ u +T+ε u (1)

[0141] ρ d =R d +I d -δt+τ d +T+ε d (2)

[0142] Where R u R d Representing the true distances of the uplink and downlink respectively; I u I d These represent the uplink and downlink ionospheric delays, respectively; τ u τ d These represent the uplink and downlink signal processing device delays, respectively; T represents the tropospheric delay; ε u and ε d Represents observation noise;

[0143] The upward and downward signal paths are basically overlapping, and the total electron TEC is equal on both the upward and downward paths;

[0144] Taking advantage of the diffuse nature of the ionosphere, the uplink and downlink ionospheric delay errors have the following relationship:

[0145]

[0146] Where N e This represents the total number of electrons along the path.

[0147] Uplink carrier phase φ obtained from spacecraft sampling u and the downlink carrier phase φ obtained by ground station sampling d for:

[0148] λ u φ u =R u -I u +δt+τ u +T+λ u N u (4)

[0149] λ d φ d =R d -I d -δt+τ d +T+λ d N d (5)

[0150] Where λ u , λ d These represent the uplink and downlink signal wavelengths, respectively; N u N d Represents the integer ambiguity of uplink and downlink signal carriers;

[0151] The pseudorange and carrier phase observation results of the uplink and downlink signals are converted; the equipment delay error τ is calibrated in advance. u τ d And it is removed from the observations; the tropospheric delay error T has a relatively small impact and is usually corrected by the model; the true range R of the uplink and downlink u R d The relationship is derived by combining signal transmission delay, the relative elevation angle between the spacecraft and the ground station, and the Earth's rotation speed. The result is...

[0152] Where B represents the latitude of the spacecraft, which can be extrapolated from the spacecraft positioning results of the previous epoch; θ represents the spacecraft's pitch angle relative to the ground station, and θ represents the spacecraft's azimuth angle relative to the ground station. From this, the true uplink and downlink distances R are obtained. u and R d The transformation relationship;

[0153] After eliminating equipment delay, tropospheric delay, and uplink / downlink true range asymmetry, the corrected pseudorange and carrier phase observations are obtained:

[0154]

[0155]

[0156]

[0157]

[0158] Step 2: Based on the positioning results provided by the external navigation system and the known ground station coordinates, calculate the true uplink distance R between ground station i and the spacecraft. u and the actual downlink distance R d And resolve the carrier phase ambiguity, including the uplink carrier ambiguity N. u and downlink carrier ambiguity N d The spacecraft then maintained continuous signal tracking of ground station i and updated the carrier phase ambiguity in real time.

[0159] Step 3: Calculate the carrier phase ambiguity N u N d ; Corrected pseudorange observation ρ u ρ d and the corrected carrier phase observation φ u φ d The total amount of electrons and the clock difference between the ground and the uplink signal transmission paths are estimated to obtain the bidirectional distance.

[0160] Step three, specifically:

[0161] The calculated carrier integer ambiguity N u N d ; Corrected pseudorange observation ρ u ρ d and the corrected carrier phase observation φ u φ d The total amount of electrons and the clock difference between the ground and the earth are estimated on the uplink and downlink signal transmission paths, and the bidirectional distance is obtained.

[0162] Let z = [R, N] e ,δt] T If the variable to be estimated is represented by , then the ionospheric delay and clock bias estimation module uses the following method for estimation:

[0163]

[0164] in

[0165]

[0166] The total number of electrons N along the signal transmission path is obtained. eAfter obtaining the estimation results, the uplink and downlink ionospheric delays are estimated according to formula (3), thereby removing the ionospheric delay and the clock difference between the ground and the sky from the uplink and downlink observations.

[0167] 8. The ionospheric delay and clock bias correction system based on two-way heterogeneous frequency signals between space and ground as described in claim 7, characterized in that, in step three, if the following situation exists: the spacecraft loses carrier tracking lock on ground station i, resulting in the loss of carrier phase ambiguity, then the space-ground clock bias information calculated by continuously tracking the ground station with other carriers is used to correct the uplink and downlink carrier phase ambiguity of ground station i and the total electron quantity N on the signal transmission path. e Estimate the values ​​to achieve high-precision bidirectional measurement with ground station i; let x = [R, N] e N u N d ] T Let x represent the variable to be estimated. Then, the estimation method for x is as follows:

[0168]

[0169] in

[0170]

[0171] This determines the total number of electrons N along the signal transmission path. e And the carrier integer ambiguity, to obtain the total number of electrons N on the signal transmission path. e After estimating the results, the uplink and downlink ionospheric delays are calculated according to formula (3), thereby removing the ionospheric delays and the clock difference between the ground and the sky from the uplink and downlink observations.

[0172] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for ionospheric delay and clock error correction based on two-way earth-space dual-frequency signals, characterized in that, The application relates to ionospheric delay and clock error correction for a space-ground two-way measurement system; the system comprises a pseudo-range and carrier phase extraction module, a carrier phase ambiguity determination module and an ionospheric delay and clock error estimation module; The space-ground two-way measurement system is composed of multiple ground stations and a spacecraft, and clock differences among the ground stations are known; The pseudo-moment and carrier phase extraction module is used to extract and correct pseudo-moments and carrier phases during the two-way measurement phase of the ground station and spacecraft in the two-way measurement system, respectively obtaining corrected pseudo-moment observations and carrier phase observations. The corrected pseudo-moment observations include the uplink pseudorange between the ground station and the spacecraft. and downlink pseudorange The corrected carrier phase observations include the uplink carrier phase sampled by the spacecraft. and downlink carrier phase obtained from ground station sampling ; The carrier phase ambiguity determination module, based on the positioning results provided by the external navigation system and the known ground station coordinates, reverse-engineers the coordinates of the ground station. i The actual ascent distance of the spacecraft and the actual downlink distance And resolve carrier phase ambiguity, including uplink carrier ambiguity. and downlink carrier ambiguity The spacecraft then maintained its position relative to the ground station. i Continuous signal tracking and real-time updates of carrier phase ambiguity; [The text abruptly ends here, likely due to an incomplete sentence or a formatting error.] , Corrected pseudorange observations , and the corrected carrier phase observations , The signal is sent to the ionospheric delay and clock bias estimation module for estimation; The ionosphere delay and clock error estimation module is used for estimating the total number of electrons on the uplink and downlink signal transmission paths and the clock error between the ground and the satellite to obtain the two-way range. , ; the corrected pseudorange observation , ; and the corrected carrier phase observation , ; During one bidirectional measurement phase of the aforementioned two-way measurement system, the ground station i exist The transmission frequency at any given time is The uplink signal, via the uplink true distance It was subsequently received by the spacecraft, at which point the spacecraft time was [time missing]. ,in Represents the time difference between Earth and space; after the spacecraft receives the uplink signal from the ground station, it transmits at a frequency of... The downlink signal is sent to the ground station; the downlink signal passes through the downlink true distance. Later by ground station i Received, at this time the ground station time is ; The ionospheric delay and clock bias estimation module observes the uplink pseudorange between the ground station and the spacecraft based on the transmission and reception times of the ground station and the spacecraft. and downlink pseudorange ; An observation equation is as follows: （1） （2） wherein , respectively represent the uplink and downlink true ranges; , respectively represent the uplink and downlink ionospheric delays; , respectively represent the uplink and downlink signal processing device delays; represents the tropospheric delay; and represents the observation noise; Upstream and downstream signal paths are basically coincident, and the total electron content TEC on the upstream and downstream paths is equal; By using the ionospheric dispersion medium characteristics, the ionospheric delay error of the upstream and downstream signals has the following size relationship: （3） wherein is the total amount of electrons on the path; The uplink carrier phase sampled by the spacecraft and the downlink carrier phase sampled by the ground station are: （4） （5） wherein , represent uplink and downlink signal wavelengths, respectively; , represent uplink and downlink signal carrier integer ambiguities, respectively; The upstream and downstream signal pseudo-range and carrier phase observation results are converted; Calibrate equipment delay error in advance , , Troposphere delay error has little effect, usually corrected by model; relationship between uplink and downlink true range , , Deduce the result by combining signal transmission delay, relative elevation angle between spacecraft and ground station, and earth rotation speed （6） wherein represents the spacecraft latitude, which can be extrapolated from the previous epoch spacecraft positioning result; represents the spacecraft elevation angle relative to the ground station, represents the spacecraft azimuth angle relative to the ground station, from which the uplink and downlink true ranges are obtained and the conversion relationship; After removing device delay, tropospheric delay and upstream and downstream true distance asymmetry factors, corrected pseudo-range and carrier phase observations are obtained （7） （8） （9） （10）。 2. The ionospheric delay and clock error correction method based on the two-way earth-space dual-frequency signals, characterized in that, The method comprises the following steps: The space-ground two-way measurement system is composed of multiple ground stations and a spacecraft, and clock differences among the ground stations are known; Step one: in the two-way measurement stage of the ground station and the spacecraft in the sky-ground two-way measurement system, pseudo-range and carrier phase are extracted and corrected, and corrected pseudo-range observations and carrier phase observations are obtained, the corrected pseudo-range observations include uplink pseudo-range and downlink pseudo-range of the ground station and the spacecraft, and the corrected carrier phase observations include uplink carrier phase sampled by the spacecraft and downlink carrier phase sampled by the ground station; Step two: according to the positioning result provided by the external navigation system and the known ground station coordinates, the real distance between the ground station and the spacecraft is deduced i and the real distance of the spacecraft downward , and the carrier phase ambiguity is solved, including the uplink carrier ambiguity and the downlink carrier ambiguity ; then the spacecraft keeps continuous signal tracking of the ground station i , and updates the carrier phase ambiguity in real time; Step three: resolving the ambiguity of carrier phase from the resolved carrier phase ambiguity , ; corrected pseudo-range observation , and corrected carrier phase observation , , estimating the total amount of electrons on the uplink and downlink signal transmission path, the clock difference between the satellite and the ground, and obtaining the two-way range; During one bidirectional measurement phase of the aforementioned two-way measurement system, the ground station i exist The transmission frequency at any given time is The uplink signal, via the uplink true distance It was subsequently received by the spacecraft, at which point the spacecraft time was [time missing]. ,in Represents the time difference between Earth and space; after the spacecraft receives the uplink signal from the ground station, it transmits at a frequency of... The downlink signal is sent to the ground station; the downlink signal passes through the downlink true distance. Later by ground station i Received, at this time the ground station time is ; The step one is specifically: The uplink pseudorange between the ground station and the spacecraft was observed based on the launch and reception times of the ground station and the spacecraft. and downlink pseudorange ; An observation equation is as follows: （1） （2） wherein , respectively represent the uplink and downlink true ranges; , respectively represent the uplink and downlink ionospheric delays; , respectively represent the uplink and downlink signal processing device delays; represents the tropospheric delay; and represents the observation noise; Upstream and downstream signal paths are basically coincident, and the total electron content TEC on the upstream and downstream paths is equal; By using the ionospheric dispersion medium characteristics, the ionospheric delay error of the upstream and downstream signals has the following size relationship: （3） wherein is the total amount of electrons on the path; The uplink carrier phase sampled by the spacecraft and the downlink carrier phase sampled by the ground station is: （4） （5） wherein , represent uplink and downlink signal wavelengths, respectively; , represent uplink and downlink signal carrier integer ambiguities, respectively; The upstream and downstream signal pseudo-range and carrier phase observation results are converted; Pre-calibrate equipment delay error , And removed from the observations; tropospheric delay error The impact is relatively small and is usually corrected by the model; uplink and downlink true distances , The relationship is derived by combining signal transmission delay, the relative elevation angle between the spacecraft and the ground station, and the Earth's rotation speed. The result is... （6） wherein represents the spacecraft latitude, which can be extrapolated from the previous epoch spacecraft positioning result; represents the spacecraft elevation angle relative to the ground station, represents the spacecraft azimuth angle relative to the ground station, from which the uplink and downlink true ranges are obtained and the conversion relationship; After removing device delay, tropospheric delay and upstream and downstream true distance asymmetry factors, corrected pseudo-range and carrier phase observations are obtained （7） （8） （9） （10）。

Images