CN116660944A - A method and system for GPS occultation observation based on Beidou satellite signals - Google Patents

Abstract

The invention relates to the technical field of GNSS radio occultation atmospheric detection, in particular to a method and system for GPS occultation observation based on Beidou satellite signals. The method of the present invention includes: capturing, tracking and positioning the receiver through the signal received by the GNSS occultation receiver, obtaining the time and position information of the GNSS occultation receiver under the time-space coordinates of the Beidou satellite system, and then converting the Beidou positioning result into GPS positioning As a result, the GPS satellite position is calculated according to the GPS positioning results, and the GPS occultation prediction and occultation capture tracking are realized based on the GPS satellite position, and the GPS occultation observation is completed. A system for GPS occultation observation using Beidou satellite signals of the present invention includes three parts: a radio frequency front end, an FPGA end and an ARM end. The present invention does not need to separately allocate positioning channel resources to the GPS system, thereby saving system resources and computing time.

Description

A method and system for GPS occultation observation based on Beidou satellite signals

technical field

The invention relates to the technical field of GNSS radio occultation atmospheric detection, in particular to a method and system for GPS occultation observation based on Beidou satellite signals.

Background technique

GNSS (Global Navigation Satellite System, Global Navigation Satellite System) occultation observer is used for occultation remote sensing detection, which can provide global, all-weather, high vertical resolution atmospheric profile information, and has a wide range of applications in meteorology, astronomy, etc. , and the current GNSS occultation observation system is developing in the direction of low-cost miniaturization and high integration. Such miniature GNSS occultation observers often use low-cost components, and their hardware calculations and resources are limited. For example, If the traditional occultation tracking method is directly applied to this kind of observatory, it may cause excessive computation, insufficient resources, and the instrument cannot operate normally.

When traditional methods are used for GPS (Global Positioning System, Global Positioning System) and Beidou occultation observations, it is necessary to first use the positioning antenna to capture, track and decode the GPS and Beidou signals, and then use the GNSS occultation receiver, GPS satellites, and Beidou The satellite performs positioning calculation, and then predicts the occultation event according to the relative position of the receiver, GPS satellite and Beidou satellite, and predicts its pseudo-range phase and carrier frequency and puts it into the tracking loop to realize fine tracking. In this process, the GNSS occultation receiver is often required to track and calculate the positioning of the GPS and Beidou dual systems respectively, which takes a lot of time and resources to process the positioning calculation results, and there is a gap between the actual GPS and the Beidou system. The fixed time and coordinate conversion relationship can be converted to each other through algorithms, and repeated calculations cause a lot of waste of time and resources.

Contents of the invention

The purpose of the present invention is to solve the problems existing in the existing traditional methods. Considering that there is a fixed conversion relationship between GPS and the Beidou system in practice, the present invention proposes to use the Beidou system alone for positioning calculation, and then convert the Beidou positioning results into GPS positioning results, and calculate GPS satellite positions based on the results, so as to realize GPS occultation prediction, capture and tracking, and complete GPS occultation event observation. This method can remove the GPS positioning calculation module from the system, and only retain a small number of GPS channels to receive GPS satellite ephemeris/almanac information, thereby saving hardware resources and improving system operation efficiency; The autonomous and controllable navigation system can provide reliable positioning services, so after adopting the method, the reliability and safety of the overall receiver will be significantly improved.

In order to achieve the above object, the present invention is achieved through the following technical solutions.

The present invention proposes a method for GPS occultation observation based on Beidou satellite signals, the method comprising:

The signal received by the GNSS occultation receiver is used to capture, track and locate the receiver, obtain the time and position information of the GNSS occultation receiver under the time-space coordinates of the Beidou satellite system, and then convert the Beidou positioning results into GPS positioning results, and based on GPS Based on the positioning results, the GPS satellite position is calculated, and based on the GPS satellite position, the GPS occultation prediction and occultation capture tracking are realized, and the GPS occultation observation is completed.

As one of the improvements of the above technical solution, the method specifically includes:

Step 1. Receive the positioning radio frequency analog signal through the positioning antenna of the GNSS occultation receiver and process to obtain the positioning intermediate frequency digital signal;

Step 2. Correlate the positioning intermediate frequency digital signal with the local code and carrier of the Beidou satellite system, obtain the correlation peak value, capture and track each satellite of the Beidou system, measure the pseudo-range of each satellite of the Beidou system, and obtain the real-time satellite information of each satellite of the Beidou system Almanac or almanac and BDT-GNSS time synchronization parameters; and calculate the position of GNSS occultation receiver according to Beidou satellite pseudo-range information, ephemeris or almanac information;

Step 3. Correlate the positioning intermediate frequency digital signal with the local pseudocode and carrier of each GPS satellite to obtain a correlation peak value, and capture and track each GPS satellite, measure the GPS satellite pseudo-range, and obtain the real-time ephemeris or almanac of each GPS satellite;

Step 4. According to the BDT-GNSS time synchronization information and the Beidou time information measured at the current moment, the conversion relationship between the Beidou system and the GPS system is used to calculate the GPS time at the current moment, and according to the ephemeris or almanac of each GPS satellite and the conversion The obtained GPS time information calculates the real-time position of each GPS satellite;

Step 5. According to the obtained GNSS occultation receiver position and each GPS satellite position, judge whether each GPS satellite is in an occultation state, and generate a GPS occultation prediction table;

Step 6. According to the GPS occultation prediction table obtained in step 5, update the occultation event status and complete the GPS occultation observation.

As one of the improvements of the above-mentioned technical solution, in the step 3, the real-time ephemeris or almanac of each GPS satellite is obtained, including:

When the real-time ephemeris or almanac of a certain GPS satellite is acquired, the tracking channel resource occupied by the satellite is released, so as to receive the real-time ephemeris or almanac of other GPS satellites.

As one of the improvements of the above-mentioned technical solution, in the step 4, the calculation formula of the GPS time _tGPS at the current moment is:

t _GPS ＝t _BD -Δt _Systems

Among them, Δt _Systems is the difference between the time seconds of the Beidou system and the time seconds of the GPS system at the current moment, and the calculation formula is:

Δt _Systems ＝A _0BGTO +A _1BGTO [t _BD -t _0BGTO +604800(WN-WN _BGTO )]+A _2BGTO [t _BD -t _0BGTO +604800(WN-WN _BGTO )] ²

Among them, A _0BGTO , A _1BGTO , A _2BGTO and WN _BGTO are BDT-GNSS time synchronization parameter broadcast parameters, t _BD is the current Beidou time second, and WN is the current Beidou time week.

As one of the improvements of the above technical solution, the step 5 specifically includes:

Step 5-1. Calculate the elevation angle Elev, the tangent point height T _ph and the relative azimuth angle R _AZM of each GPS satellite per second according to the obtained GNSS occultation receiver position and each GPS satellite position, and make the following judgments:

When the star elevation angle Elev, the tangent point height T _ph and the relative azimuth angle R _AZM are all within the range of the occultation judgment setting conditions, it is an effective occultation event;

When any one of the star elevation angle Elev, the tangent point height T _ph and the relative azimuth angle R _AZM is not within the range of the occultation judgment setting conditions, it is a failed occultation event;

Step 5-2. Update the GPS occultation event prediction table for this second according to the occultation event of the last second Medium; Simultaneously cache the last second GPS occultation event to the last second GPS occultation event prediction table /> middle.

As one of the improvements of the above technical solution, the step 6 specifically includes:

Step 6-1. According to the prediction table of GPS occultation events in this second and last-second GPS occultation event prediction table/> Make a difference between the status identifiers of each GPS satellite occultation event in the current second and the last second, and judge according to the result of the difference, specifically:

When the difference result of the satellite is 1, it means that the satellite occultation event in this second is a new GPS occultation event;

When the difference result of the satellite is -1, it means that the satellite occultation event in this second is a failed GPS occultation event;

When the difference result of the satellite is 0, further judge whether the satellite occultation event of this second is a valid GPS occultation event, if the satellite occultation event of this second is a valid GPS occultation event, it means that the satellite occultation event of this second The event is an existing occultation event; if the satellite occultation event in this second is an invalid GPS occultation event, it means that there is no occultation event in this second.

Step 6-2. Update the occultation event status according to the judgment result, and complete the GPS occultation observation, specifically:

When it is judged that the GPS satellite occultation event is a new occultation event, it is further judged whether there is an idle GPS occultation tracking channel: if it exists, the new occultation event is assigned to this channel, and the occultation event capture and tracking are started. Collect occultation observation data; if there is no free channel, keep the new mark for the occultation event until there is a free channel allocated for it or the occultation event expires;

When it is judged as a failed occultation event, stop receiving the occultation event, release and initialize the GPS occultation tracking channel, set it as idle, and wait for new occultation events to be used;

When it is judged as an existing occultation event, keep track of the occultation event and continue to collect occultation data.

The present invention also proposes a system for GPS occultation observation based on Beidou satellite signals, the system comprising:

The radio frequency front-end module is used to process the positioning radio frequency signal received by the positioning antenna of the GNSS occultation receiver to obtain the positioning intermediate frequency digital signal;

The signal processing module is used to correlate the positioning intermediate frequency digital signal with the local code and carrier of the Beidou satellite system, obtain the correlation peak, capture and track each satellite of the Beidou system, measure the pseudo-range of each satellite of the Beidou system, and obtain each satellite of the Beidou system The real-time ephemeris or almanac and BDT-GNSS time synchronization parameters, and calculate the position of GNSS occultation receiver according to the Beidou satellite pseudo-range information, ephemeris or almanac information; it is also used to combine the positioning intermediate frequency digital signal with the GPS satellite local pseudocode, Correlate the carrier to obtain the correlation peak, and capture and track each GPS satellite, measure the pseudo-range of each GPS satellite, and obtain the real-time ephemeris or almanac of each GPS satellite;

The conversion module, according to the BDT-GNSS time synchronization information and the Beidou time information measured at the current time, uses the conversion relationship between the Beidou system and the GPS system to calculate the GPS time at the current time, and according to the ephemeris or almanac of each GPS satellite and the conversion The obtained GPS time information calculates the real-time position of each GPS satellite; and

The occultation sampling module is used to determine whether each GPS satellite is in an occultation state according to the obtained GNSS occultation receiver position and each GPS satellite position, and to generate a GPS occultation prediction table; it is also used to, according to the GPS occultation prediction table, Update the status of the occultation event and complete the GPS occultation observation.

As one of the improvements of the above technical solution, the signal processing module includes:

The Beidou signal processing unit is used to correlate the positioning intermediate frequency digital signal with the local code and carrier of the Beidou satellite system, obtain the correlation peak value, capture and track the Beidou satellite, measure the pseudo-range of the Beidou satellite, and obtain the real-time ephemeris or ephemeris of the Beidou satellite Almanac and BDT-GNSS time synchronization parameters, and calculate GNSS occultation receiver position based on Beidou satellite pseudorange information, ephemeris or almanac information; and

The GPS signal processing unit is used to correlate the positioning intermediate frequency digital signal with the local pseudocode and carrier of the GPS satellite to obtain the correlation peak value, and capture and track each GPS satellite, measure the pseudo-range of each GPS satellite, and obtain the real-time ephemeris of each GPS satellite or almanac.

As one of the improvements of the above technical solution, the signal processing module is realized based on FPGA chip.

As one of the improvements of the above technical solution, the conversion module and the occultation sampling module are implemented based on an ARM chip.

Compared with the prior art, the present invention has the advantages of:

1. The method for calculating GPS position information using Beidou positioning results proposed by the present invention does not need to allocate positioning channel resources to the GPS system without reducing the performance of the observer, which reduces the steps of traditional receivers for calculating GPS positioning results and saves System resources save computing time, and the saved time/space can be allocated to Beidou positioning tracking/occultation observations, thereby improving positioning accuracy and the number of occultation event observations; and the Beidou system has completely independent intellectual property rights, which is more secure and controllable ;

2. Compared with the method of separately calculating the positioning results of the GPS and Beidou systems in the traditional method, the method proposed by the present invention is simple and effective, and does not require hardware modification.

Description of drawings

Fig. 1 is a kind of method flowchart that adopts Beidou satellite signal to carry out GPS occultation observation that the present invention proposes;

FIG. 2 is a structural diagram of a system for GPS occultation observation using Beidou satellite signals proposed by the present invention.

Detailed ways

The invention proposes a method for GPS occultation observation based on Beidou satellite signals in a miniature GNSS occultation observation system. This method uses the Beidou direct signal for tracking and positioning, calculates the location of the receiver, and calculates the GPS occultation event by receiving the GPS ephemeris/almanac information, so as to realize the tracking and observation of GPS occultation events based on Beidou positioning. This method makes full use of the mutual compatibility between Beidou and GPS signals, reduces the system resource consumption required for GPS direct signal positioning, reduces the dependence of the receiver system on GPS signals, and contributes to the low-resource and low-power miniature GNSS occultation observation system. It can be applied to the field of miniature GNSS occultation observation and has broad application prospects. The design structure of this method is simple and clear, and it is suitable for miniature GNSS occultation receivers without special hardware modification.

The technical solutions of the present invention will be described in detail below in conjunction with the drawings and embodiments.

Example 1

As shown in FIG. 1 , it is a flow chart of a method for GPS occultation observation using Beidou satellite signals proposed by the present invention.

The method that the present invention proposes comprises the following steps:

(1) Beidou signal positioning solution

The positioning antenna signal received by the front-end radio frequency unit is down-converted, so as to capture, track, and solve the ephemeris/almanac of the Beidou positioning signal, and calculate the position of the receiver and the position of the Beidou satellite.

(2) Prediction of Beidou occultation events

According to the position of the receiver and the position of the Beidou satellite calculated by the solution, it is judged whether the Beidou occultation condition is triggered, and the Beidou occultation event prediction table is generated accordingly.

(3) Beidou occultation event capture and tracking

According to the Beidou occultation event prediction table obtained in step (2), update the state of the Beidou occultation event table, if it is a new occultation event, allocate a channel for tracking; if it is a failed occultation event, release its channel, End observation.

(4) Beidou occultation data packaged and sent

The Beidou occultation observation data is packaged every second, and its carrier phase, pseudorange, I/Q channel integral value and other information are stored, and transmitted through LVDS for subsequent occultation inversion calculations.

(5) Get GPS ephemeris/almanac

The GPS signal is received by the positioning antenna signal, so as to obtain the real-time ephemeris/almanac of each GPS satellite. After the acquisition is completed, the channel occupied by the satellite is released, and the channel is used by other GPS satellites that have not obtained the ephemeris/almanac.

(6) Convert Beidou positioning results to GPS positioning results

According to the BDT-GNSS time synchronization information in the message received by the GNSS occultation receiver and the Beidou time information measured at the current moment, the GPS time at the current moment is calculated by using the conversion relationship between the Beidou system and the GPS system, and according to the step (5 ) from the received GPS ephemeris/almanac and the converted GPS time information to calculate the real-time position of the GPS satellites.

(7) Prediction of GPS occultation events

According to the GPS system position and the GPS satellite position calculated in step (6), it is judged whether each GPS satellite is in an occultation state, and a GPS occultation prediction table is generated.

(8) GPS occultation event capture and tracking

According to the Beidou occultation event prediction table obtained in step (7), update the status of the occultation event. If it is a new occultation event, allocate a channel for tracking; if it is a failed occultation event, release its channel and end the observation .

(9) Beidou occultation data packaged and sent

Pack the Beidou occultation observation data every second, store its carrier phase, pseudo-range, I/Q channel integral value and other information, send it to the star system through the LVDS interface, and use it for subsequent occultation inversion calculations after being received by the ground station .

specifically,

Step (1) includes: receiving the positioning signal through the positioning antenna, using the front-end radio frequency unit to down-convert the received radio frequency signal to obtain an analog intermediate frequency signal, and converting it into an intermediate frequency digital signal through the AD sampling module, and inputting the digital signal to the baseband board FPGA is used to correlate with the baseband board to generate the local code and carrier of the Beidou system, and transmit the capture result to the ARM end to obtain the correlation peak, so as to further realize capture, tracking, and decryption of the message; then, according to the measured Beidou satellite pseudo-range information, time Information and ephemeris/almanac information to calculate the position of the GNSS occultation receiver in the Beidou coordinate system and the position of the Beidou satellite, and calculate various information such as the carrier wave of each Beidou satellite and the pseudo-code phase according to the position of the Beidou satellite and the position of the GNSS occultation receiver , for subsequent occultation prediction and occultation capture.

Step (2) includes: calculate the elevation angle, azimuth angle, tangent point height and relative azimuth angle of the Beidou satellite according to the GNSS receiver position and the Beidou satellite position calculated at the current moment at the ARM end every second, and use the above information To judge the occultation conditions of each Beidou satellite, write the occultation event judgment result into the current second occultation event prediction table TblBDp, and at the same time, store the Beidou occultation event generated in the previous second into the previous second occultation event prediction table In TblBDe.

Step (3) includes: comparing the Beidou occultation event prediction tables TblBDp and TblBDe generated in step (2) for the current second and the previous second, to determine the new, existing and invalid occultation events, and to add new occultation events to The star event is assigned to the occultation tracking observation channel, and the invalid occultation event is deleted from the tracking channel.

Step (4) includes: packing the measurement results of the Beidou occultation event within the current second every second, and transmitting the results to the cache of the star affairs processing system through the LVDS interface at the end of the second.

In step (5), include: after the A/D conversion in the step (1), the intermediate frequency signal that is passed into the FPGA end of the baseband board is correlated with the local pseudocode and carrier of the GPS satellite to obtain a correlation peak value, and the GPS satellite is captured and tracked, Measure pseudo-range, receive ephemeris and almanac of GPS satellites.

The step (6) includes: converting the Beidou system time information obtained in the step (1) to the GPS system at the ARM end. Specifically, it includes: analyzing the BDT-GNSS time synchronization (BGTO) information broadcast by the Beidou three-generation satellite, and using the information algorithm to convert the current Beidou time calculated by the GNSS occultation receiver to GPS time; the Beidou coordinate system calculated by the Beidou system The lower GNSS receiver position is converted into the earth-centered inertial coordinate system, and the GPS satellite ephemeris information obtained in the positioning information and the step (5) and the above-mentioned converted GPS time are used to calculate each GPS satellite position for use in the step (7) Medium GPS occultation prediction.

Step (7) includes: judge according to the GNSS occultation receiver position calculated in step (1) and the GPS satellite position calculated in step (6) at the ARM end every second, calculate the elevation angle, azimuth angle, cut Point height, relative azimuth, predicted carrier frequency, code phase and other information, judge the GPS satellite occultation conditions based on the above information, write the occultation event judgment result into the current second occultation event prediction table TblGPSp, and at the same time, write The occultation events generated in the last second are stored in the previous second occultation event prediction table TblGPSe.

Step (8) includes: according to the GPS occultation event prediction table TblGPSp and TblGPSe generated in step (7) in this second and the previous second are compared to determine new, existing and invalid GPS occultation events, and add The occultation event is assigned to the GPS occultation tracking observation channel, and the predicted carrier frequency and code phase information of the GPS satellite corresponding to the occultation event is input to start the occultation observation, and the invalid occultation event is deleted from the tracking channel.

Step (9) includes: packaging the measurement results of GPS occultation events within this second every second, and transmitting the results to the cache of the star affairs processing system through the LVDS interface at the end of the second; and passing the ground station together with the Beidou occultation measurement results It is transmitted to the ground system for subsequent inversion calculations.

Example 2

A system for GPS occultation observation using Beidou satellite signals proposed by the present invention includes: a radio frequency front-end module, a signal processing module, a conversion module and an occultation sampling module.

The radio frequency front-end module is used to process the positioning radio frequency signal received by the positioning antenna of the GNSS occultation receiver to obtain the positioning intermediate frequency digital signal;

The signal processing module includes: Beidou signal processing unit and GPS signal processing unit; Beidou signal processing unit is used to correlate the positioning intermediate frequency digital signal with the local code and carrier of the Beidou satellite system, obtain the correlation peak value, and capture and track the Beidou satellite , measure the Beidou satellite pseudo-range, obtain the real-time ephemeris or almanac and BDT-GNSS time synchronization parameters of the Beidou satellite, and calculate the position of the GNSS occultation receiver according to the Beidou satellite pseudo-range information, ephemeris or almanac information; the GPS signal processing unit, It is used to correlate the positioning intermediate frequency digital signal with the local pseudocode and carrier of the GPS satellite to obtain the correlation peak, and capture and track each GPS satellite, measure the pseudo-range of each GPS satellite, and obtain the real-time ephemeris or almanac of each GPS satellite.

The conversion module, according to the BDT-GNSS time synchronization information and the Beidou time information measured at the current time, uses the conversion relationship between the Beidou system and the GPS system to calculate the GPS time at the current time, and according to the ephemeris or almanac of each GPS satellite and the conversion The obtained GPS time information calculates the real-time position of each GPS satellite;

The occultation sampling module is used to determine whether each GPS satellite is in an occultation state according to the obtained GNSS occultation receiver position and each GPS satellite position, and to generate a GPS occultation prediction table; it is also used to, according to the GPS occultation prediction table, Update the status of the occultation event and complete the GPS occultation observation.

Among them, the signal processing module is implemented based on FPGA chip, and the conversion module and occultation sampling module are implemented based on ARM chip.

Fig. 2 is a design block diagram of a system for GPS occultation observation using Beidou satellite signals (hereinafter referred to as GNSS occultation observer) provided in Embodiment 2 of the present invention, including three parts: a radio frequency front end, an FPGA end and an ARM end.

In order to make the purpose and technical solution of the present invention clearer, a method for GPS occultation observation based on Beidou satellite signals in a micro GNSS occultation observation system proposed by the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

The structure of the GNSS occultation observer of the present invention is shown in Figure 2, which consists of three parts: a radio frequency front end, a baseband board FPGA and a baseband board ARM. The RF front-end includes a positioning antenna module, a forward occultation antenna module and a backward occultation antenna module; in order to miniaturize the receiver, the baseband board FPGA and the baseband board ARM can be implemented using SOC integrated chips.

The GNSS occultation observer takes the Beidou signal received as the B1C signal of the third generation of Beidou and the GPS signal as the GPS L1 signal as an example. The carrier frequency of the two signals is 1575.42Mhz. First, the positioning antenna receives the signal at this frequency point and performs filtering and down-conversion to obtain an intermediate frequency signal, which is input to the baseband FPGA terminal, and then the analog intermediate frequency signal is converted to Digital intermediate frequency signal r _IF .

After obtaining the intermediate frequency signal r _IF , generate the local carrier and Beidou B1C local pseudo code on the FPGA side, correlate it with the r _IF , strip the B1C pseudo code and carrier information in the intermediate frequency signal, and send the processed signal to the ARM end, Obtain the correlation peak value to realize the capture, put the capture result into the positioning tracking loop, and then obtain the I/Q channel integration result according to the integration time, realize stable tracking and obtain the Beidou B-CNAV1 message information through the I/Q channel integration identification, and extract from it The time parameter is saved along with parameters such as ephemeris, almanac and BDT-GNSS time synchronization information. After calculating the system time parameters SOH (second count within an hour), HOW (hour count within a week) and WN (whole week count), the Beidou time at the current moment can be obtained, and the ephemeris, almanac and various error corrections can be extracted from the message Quantity and other parameters, so as to solve the position of the GNSS occultation observer and the positions of each Beidou satellite constellation.

After the position calculation is completed, the Beidou occultation event prediction can be carried out. According to the position calculation results of the GNSS occultation observer and the Beidou satellite constellation, the elevation angle Elev of each Beidou satellite per second, the height of the tangent point T _ph and Relative azimuth R _AZM , if the three are within the range of conditions in Table 1, it is considered to be a valid occultation event, otherwise it is a failed occultation event, and it is updated to the current Beidou occultation event prediction table Tbl _BDp according to the upper occultation event ; and cache the last second Beidou occultation event into the last second Beidou occultation event prediction table Tbl _BDe .

Table 1 Judgment table of occultation range

After obtaining the prediction results of Beidou occultation events, the difference between the prediction table of Beidou occultation events before and after seconds can be determined to determine the new, existing and invalid occultation events in this second:

According to the judgment result of the above occultation event, perform the following operations:

· Added occultation events

First judge whether there is an idle Beidou occultation tracking channel, if so, assign new occultation events to this channel, start occultation event capture and tracking, and collect occultation observation data; if there is no idle channel, keep this occultation event The star event is marked as new and tracking is not enabled until a free channel is allocated for it or the occultation event expires.

·Existing occultation events

Keep track and keep collecting occultation data.

Failed occultation events

If there is no occultation event in the occultation channel in the occultation prediction table, the occultation event will be considered invalid, and the reception of the occultation event will be stopped at this time, the Beidou occultation channel will be released and initialized, and the channel status will be set to Free for future occultation events.

· No occultation events

Do nothing.

After the occultation event judgment operation is completed, new occultation events are captured, and existing occultation events are kept tracked, and information such as carrier phase, I/Q channel integration, carrier-to-noise ratio, and pseudorange is collected, and buffered at a rate of 100Hz , and pack it according to the time stamp, and send it to the star system through the bus.

For the GPS system, the intermediate frequency signal r _IF is correlated with the local carrier and GPS L1C/A code on the FPGA side, and the correlation results are sent to the ARM side to realize the tracking of the GPS direct signal and obtain the GPS ephemeris/almanac information.

According to the BDT-GNSS time synchronization parameter part of the Beidou B-CNAV1 message information, the resolved Beidou time can be converted into GPS time:

Δt _Systems ＝A _0BGTO +A _1BGTO [t _BD -t _0BGTO +604800(WN-WN _BGTO )]+A _2BGTO [t _BD -t _0BGTO +604800(WN-WN _BGTO )] ²

Among them, A _0BGTO ~ A _2BGTO and WN _BGTO are BDT-GNSS time synchronization parameter broadcast parameters, t _BD is the current Beidou time second, WN is the current Beidou time week, and the calculated Δt _Systems is the current Beidou system time second and GPS system The difference in time seconds, so the GPS system time seconds can be calculated as

t _GPS ＝t _BD -Δt _Systems

Using the above conversion relationship, it is possible to obtain the GPS time and seconds at the current time without parsing the GPS message, and use the Beidou system to calculate the position information of the GNSS occultation observer and the GPS ephemeris, and calculate the position information of the GPS satellite constellation for GPS occultation predictions.

Similar to the Beidou occultation prediction method, the GNSS occultation observer calculates the elevation angle Elev, tangent point height T _ph and relative azimuth angle R _AZM of each GPS satellite per second. If the three are within the range of the table conditions, it is considered valid An occultation event, otherwise it is a failed occultation event, updated to the current second GPS occultation event prediction table Tbl _GPSp according to the last occultation event; and cache the last second GPS occultation event to the last second GPS occultation event prediction table Tbl _GPSe .

Doing the same difference for GPS occultation events, we can get the operation situation of GPS occultation events:

For the judgment result of the above occultation event, the remaining operations are the same as those of the Beidou occultation event, and the received observation information is packaged and saved at a rate of 100 Hz.

After receiving the Beidou and GPS occultation data per second, the star system caches them and downloads them to the ground receiving station in due course for subsequent inversion.

It should be noted that the above implementation examples are only a preferred implementation of GPS occultation observation based on Beidou satellite signals in a miniature GNSS occultation observation system provided by the present invention, and this preferred implementation is not intended to limit the protection of the present invention. range. All algorithms and their corresponding system designs disclosed in the present invention can be intercepted in various combinations or replaced by features with the same or similar purpose and effect. It should be pointed out that for those skilled in the art, without departing from the principle and spirit of the present invention, various improvements and changes can also be made, such as adding, deleting, replacing or merging certain steps or functions unit/module, and these improvements and changes are also within the protection scope of the present invention.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent replacements to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all of them should be included in the scope of the present invention. within the scope of the claims.

Claims (10)

1. A method for performing GPS occultation observation based on beidou satellite signals, the method comprising:

the method comprises the steps of capturing, tracking and positioning a receiver through signals received by a GNSS occultation receiver, obtaining time and position information of the GNSS occultation receiver under space-time coordinates of a Beidou satellite system, converting Beidou positioning results into GPS positioning results, resolving GPS satellite positions according to the GPS positioning results, realizing GPS occultation prediction and occultation capturing and tracking based on the GPS satellite positions, and completing GPS occultation observation.

2. The method for performing GPS occultation observation based on Beidou satellite signals according to claim 1, which is characterized by specifically comprising the following steps:

step 1, receiving and processing a positioning radio frequency analog signal through a positioning antenna of a GNSS occultation receiver to obtain a positioning intermediate frequency digital signal;

step 2, correlating the positioning intermediate frequency digital signal with a local code and a carrier wave of a Beidou satellite system, acquiring a correlation peak value, capturing and tracking each satellite of the Beidou satellite system, measuring the pseudo range of each satellite of the Beidou satellite system, and acquiring real-time ephemeris or almanac and BDT-GNSS time synchronization parameters of each satellite of the Beidou satellite system; calculating the position of the GNSS occultation receiver according to the Beidou satellite pseudo-range information, ephemeris or almanac information;

step 3, correlating the positioning intermediate frequency digital signals with the local pseudo codes and carriers of all GPS satellites to obtain correlation peaks, capturing and tracking all GPS satellites, measuring the pseudo range of the GPS satellites, and obtaining the real-time ephemeris or almanac of all GPS satellites;

step 4, calculating GPS time at the current moment by utilizing a conversion relation between a Beidou system and a GPS system according to BDT-GNSS time synchronization information and Beidou time information obtained by measuring the current moment, and calculating real-time positions of all GPS satellites according to ephemeris or almanac of all GPS satellites and the GPS time information obtained by conversion;

step 5, judging whether each GPS satellite is in a satellite-masking state according to the obtained GNSS satellite-masking receiver position and each GPS satellite position, and generating a GPS satellite-masking prediction table;

and step 6, updating the satellite-occulting event state according to the GPS satellite-occulting prediction table obtained in the step 5, and completing GPS satellite-occulting observation.

3. The method for performing GPS occultation observation based on Beidou satellite signals according to claim 2, wherein in the step 3, acquiring real-time ephemeris or almanac of each GPS satellite includes:

when the real-time ephemeris or almanac of a certain GPS satellite is obtained, the tracking channel resources occupied by the satellite are released, so that the real-time ephemeris or almanac of the other GPS satellites is received.

4. The method for performing GPS occultation observation based on Beidou satellite signals according to claim 2, wherein in the step 4, the current moment GPS time t _GPS The calculation formula of (2) is as follows:

t _GPS ＝t _BD -t _Systems

wherein t is _Systems The calculation formula is as follows for the difference between the Beidou system time second and the GPS system time second at the current moment:

t _Systems ＝A _0BGTO +A _1BGTO [t _BD -t _0BGTO +604800(WN-WN _BGTO )]+A _2BGTO [t _BD -t _0BGTO +604800(WN-WN _BGTO )] ²

wherein A is _0BGTO 、A _1BGTO 、A _2BGTO And WN _BGTO Are BDT-GNSS time synchronization parameter broadcasting parameters, t _BD And WN is the current Beidou moment and week.

5. The method for performing GPS occultation observation based on the beidou satellite signal according to claim 2, wherein the step 5 specifically includes:

step 5-1, calculating elevation angle Elev and tangential point height T of each GPS satellite per second according to the obtained position of the GNSS occultation receiver and the positions of each GPS satellite _ph Relative azimuth R _AZM And makes the following judgment:

elevation angle of star Elev, tangent point height T _ph Relative azimuth R _AZM When the satellite-masking judgment conditions are within the range of the satellite-masking judgment setting conditions, the satellite-masking judgment conditions are effective satellite-masking events;

elevation angle of star Elev, tangent point height T _ph And relative azimuth R _AZM If any one of the two is not in the range of the occultation judging and setting conditions, the occultation event is a failure occultation event;

step 5-2. Occultation according to last secondGPS occultation event prediction table for updating event to present secondIn (a) and (b); meanwhile, the GPS occultation event prediction table from last second GPS occultation event to last second GPS occultation event is buffered +.>Is a kind of medium.

6. The method for performing GPS occultation observation based on Beidou satellite signals according to claim 5, wherein the step 6 specifically includes:

step 6-1. According to the GPS occultation event prediction table of this secondAnd last second GPS occultation event prediction table +.>The satellite occultation event state identifiers of the GPS satellites in the present second and the last second are subjected to difference, and judgment is carried out according to the difference result, specifically:

when the satellite difference result is 1, the satellite occultation event is a newly added GPS occultation event in the second;

when the satellite difference result is-1, the satellite occultation event is a failure GPS occultation event in the second;

when the satellite difference result is 0, further judging whether the satellite occultation event of the second is an effective GPS occultation event, if the satellite occultation event of the second is an effective GPS occultation event, indicating that the satellite occultation event of the second is an existing occultation event; if the satellite occultation event is an invalid GPS occultation event, indicating that the satellite does not have the occultation event in the second;

step 6-2, updating the state of the occultation event according to the judging result to finish GPS occultation observation, specifically comprising the following steps:

when judging that the GPS satellite occultation event is a newly added occultation event, further judging whether an idle GPS occultation tracking channel exists or not: if yes, distributing the newly added occultation event into the channel, starting occultation event capturing and tracking, and collecting occultation observation data; if the idle channel does not exist, the new mark of the occultation event is kept until the idle channel distributes the idle channel or the occultation event is invalid;

when judging that the satellite occultation event is invalid, stopping receiving the satellite occultation event, releasing and initializing the GPS satellite occultation tracking channel, setting the GPS satellite occultation tracking channel to be idle, and waiting for newly adding the satellite occultation event for use;

and when judging that the existing occultation event exists, keeping tracking the occultation event, and continuously collecting occultation data.

7. A system for performing GPS occultation observation based on beidou satellite signals, the system comprising:

the radio frequency front end module is used for processing the positioning radio frequency signals received by the positioning antenna of the GNSS occultation receiver to obtain positioning intermediate frequency digital signals;

the signal processing module is used for correlating the positioning intermediate frequency digital signal with a local code and a carrier wave of the Beidou satellite system, acquiring a correlation peak value, capturing and tracking each satellite of the Beidou satellite system, measuring the pseudo range of each satellite of the Beidou satellite system, acquiring real-time ephemeris or almanac and BDT-GNSS time synchronization parameters of each satellite of the Beidou satellite system, and calculating the position of the GNSS occultation receiver according to the pseudo range information, ephemeris or almanac information of the Beidou satellite; the method is also used for correlating the positioning intermediate frequency digital signals with GPS satellite local pseudo codes and carriers to obtain correlation peaks, capturing and tracking each GPS satellite, measuring each GPS satellite pseudo range and obtaining real-time ephemeris or almanac of each GPS satellite;

the conversion module is used for calculating GPS time at the current moment by utilizing the conversion relation between a Beidou system and a GPS system according to BDT-GNSS time synchronization information and Beidou time information obtained by measuring the current moment, and calculating the real-time position of each GPS satellite according to each GPS satellite ephemeris or almanac and the GPS time information obtained by conversion; and

the occultation sampling module is used for judging whether each GPS satellite is in an occultation state according to the obtained GNSS occultation receiver position and each GPS satellite position and generating a GPS occultation prediction table; and the satellite occultation state updating module is also used for updating the satellite occultation event state according to the GPS satellite occultation prediction table to finish GPS satellite occultation observation.

8. The system for performing GPS occultation observation based on Beidou satellite signals of claim 7, wherein the signal processing module includes:

the Beidou signal processing unit is used for correlating the positioning intermediate frequency digital signal with a local code and a carrier wave of a Beidou satellite system, acquiring a correlation peak value, capturing and tracking a Beidou satellite, measuring a Beidou satellite pseudo-range, acquiring real-time ephemeris or almanac and BDT-GNSS time synchronization parameters of the Beidou satellite, and calculating the position of the GNSS occultation receiver according to the Beidou satellite pseudo-range information, the ephemeris or almanac information; and

and the GPS signal processing unit is used for correlating the positioning intermediate frequency digital signal with a GPS satellite local pseudo code and a carrier wave to obtain a correlation peak value, capturing and tracking each GPS satellite, measuring the pseudo range of each GPS satellite and obtaining the real-time ephemeris or almanac of each GPS satellite.

9. The system for performing GPS occultation observation based on Beidou satellite signals according to claim 7, wherein the signal processing module is realized based on an FPGA chip.

10. The system for performing GPS occultation observation based on Beidou satellite signals according to claim 7, wherein the conversion module and the occultation sampling module are realized based on ARM chips.