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

Abstract

The present application relates to GNSS radio occultation atmospheric sounding technical field, especially in kind based on big dipper satellite signal carries out GPS occultation observation method and system.The present application method includes: through the signal received by GNASS occultation receiver is captured and tracked positioning receiver, obtains GNSS occultation receiver in big dipper satellite system space-time coordinate under the time and position information, after big dipper positioning result is converted into GPS positioning result, and according to GPS positioning result, the position of GPS satellite is solved, GPS occultation prediction and occultation capture tracking are realized based on GPS satellite position, and GPS occultation observation is completed.The system of one kind for carrying out GPS occultation observation of the present application based on big dipper satellite signal includes three parts of radio frequency front end, FPGA end and ARM end.The present application need not be separately assigned positioning channel resource for GPS system, saves system resource, saves operation time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of GNSS radio occultation atmospheric sounding technology, and particularly relates to a method and system for GPS occultation observation based on Beidou satellite signals. BACKGROUND

[0002] GNSS (Global Navigation Satellite System) occultation observation instrument is used for occultation remote sensing detection, and can provide global, all-weather and high vertical resolution atmospheric profile information, and has a wide application in meteorology, astronomy and the like. At present, GNSS occultation observation systems develop towards low cost miniaturization and high integration. Such mini GNSS occultation observation instruments often use low-cost components, and the hardware operation amount and resources are limited. If the traditional occultation tracking method is directly applied to such observation instruments, the operation amount may be excessive, the resources may be insufficient, and the instrument may not be able to normally operate.

[0003] In the traditional method, when GPS (Global Positioning System) and Beidou occultation observation are performed, the GPS and Beidou signals are first captured, tracked and decoded by using a positioning antenna, and then the GNSS occultation receiver, GPS satellite and Beidou satellite are positioned and solved. Then, the relative positions of the receiver and the GPS satellite and the Beidou satellite are predicted, and the pseudorange phase and carrier frequency are predicted and placed in the tracking loop to realize fine tracking. In this process, the GNSS occultation receiver needs to realize tracking and positioning solution of the GPS and Beidou double systems respectively, and needs to occupy a large amount of time and resources to process the positioning solution results. However, there is a fixed time and coordinate conversion relationship between the actual GPS and Beidou systems, which can be converted by algorithm. The repeated calculation causes a large waste of time and resources. SUMMARY

[0004] The present application aims to solve the problems in the existing traditional method. Considering that there is a fixed conversion relationship between the GPS and Beidou systems in practice, the present application proposes to use the Beidou system alone for positioning solution, and then convert the Beidou positioning result into a GPS positioning result, and solve the GPS satellite position according to the result, so as to realize GPS occultation prediction, capture and tracking, and complete GPS occultation event observation. This method can eliminate the GPS positioning solution module from the system, and only keep a small number of GPS channels to receive GPS satellite ephemeris / almanac information, so as to save hardware resources and improve system operation efficiency. Moreover, the Beidou system is a self-controllable navigation system with complete intellectual property rights of China, and can provide reliable positioning services. Therefore, after using the present method, the reliability and safety of the overall receiver will be obviously improved.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution.

[0006] This invention proposes a method for GPS occultation observation based on BeiDou satellite signals, the method comprising:

[0007] The receiver is captured, tracked, and positioned by receiving signals from a GNSS occultation receiver. The time and position information of the GNSS occultation receiver in the spatiotemporal coordinates of the BeiDou satellite system is obtained. Then, the BeiDou positioning result is converted into a GPS positioning result, and the GPS satellite position is calculated based on the GPS positioning result. GPS occultation prediction and occultation capture and tracking are realized based on the GPS satellite position, thus completing the GPS occultation observation.

[0008] As one improvement to the above technical solution, the method specifically includes:

[0009] Step 1. Receive the positioning radio frequency analog signal through the positioning antenna of the GNSS occultation receiver and process it to obtain the positioning intermediate frequency digital signal;

[0010] Step 2. Correlate the positioning intermediate frequency digital signal with the local code and carrier of the BeiDou satellite system to obtain the correlation peak value, acquire and track each satellite of the BeiDou system, measure the pseudorange of each satellite of the BeiDou system, obtain the real-time ephemeris or almanac and BDT-GNSS time synchronization parameters of each satellite of the BeiDou system; and calculate the position of the GNSS occultation receiver based on the pseudorange information and ephemeris or almanac information of the BeiDou satellites.

[0011] Step 3. Correlate the positioning intermediate frequency digital signal with the local pseudocode and carrier of each GPS satellite to obtain the correlation peak value, and acquire and track each GPS satellite, measure the pseudorange of the GPS satellite, and obtain the real-time ephemeris or almanac of each GPS satellite.

[0012] Step 4. Based on the BDT-GNSS time synchronization information and the BeiDou time information measured at the current time, use the conversion relationship between the BeiDou system and the GPS system to calculate the current GPS time, and calculate the real-time position of each GPS satellite based on the ephemeris or almanac of each GPS satellite and the converted GPS time information.

[0013] Step 5. Based on the obtained GNSS occultation receiver position and the position of each GPS satellite, determine whether each GPS satellite is in an occultation state and generate a GPS occultation prediction table;

[0014] Step 6. Based on the GPS occultation prediction table obtained in Step 5, update the occultation event status and complete the GPS occultation observation.

[0015] As one of the improvements of the above technical solutions, in the step 3, the real-time ephemeris or almanac of each GPS satellite is acquired, including:

[0016] 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 that the real-time ephemeris or almanac of the remaining GPS satellites is received.

[0017] As one of the improvements of the above technical solutions, in the step 4, the GPS time t GPS at the current moment is calculated according to the following formula:

[0018] t GPS =t BD -Δt Systems

[0019] Wherein, Δt Systems is the difference between the Beidou system time second at the current moment and the GPS system time second, and the calculation formula is as follows:

[0020] 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

[0021] Wherein, A 0BGTO , A 1BGTO , A 2BGTO and WN BGTO are BDT-GNSS time synchronization parameter broadcast parameters, t BD is the Beidou time second at the current moment, and WN is the current Beidou time week.

[0022] As one of the improvements of the above technical solutions, the step 5 specifically includes:

[0023] Step 5-1. According to the obtained GNSS occultation receiver position and the position of each GPS satellite, the elevation angle Elev, the tangent height T ph and the relative azimuth angle R AZM of each GPS satellite per second are calculated, and the following judgment is made:

[0024] When the elevation angle Elev, the tangent height T ph and the relative azimuth angle R AZM are all within the set condition range of the occultation judgment, it is an effective occultation event;

[0025] When any one of the elevation angle E, the tangent point height T ph and the relative azimuth angle R AZM is not within the range of the occultation judgment setting condition, it is an invalid occultation event;

[0026] Step 5-2. Update the current second GPS occultation event prediction table according to the last second occultation event; and cache the last second GPS occultation event into the last second GPS occultation event prediction table at the same time.

[0027] As one of the improvements of the above technical solutions, the step 6 specifically includes:

[0028] Step 6-1. Subtract the current second GPS occultation event prediction table and the last second GPS occultation event prediction table to obtain the satellite difference result, and make a judgment according to the difference result, specifically:

[0029] When the satellite difference result is 1, it indicates that the current second satellite occultation event is a new GPS occultation event;

[0030] When the satellite difference result is -1, it indicates that the current second satellite occultation event is an invalid GPS occultation event;

[0031] When the satellite difference result is 0, further judge whether the current second satellite occultation event is a valid GPS occultation event, if the current second satellite occultation event is a valid GPS occultation event, it indicates that the current second satellite occultation event is an existing occultation event; if the current second satellite occultation event is an invalid GPS occultation event, it indicates that there is no occultation event for the current second satellite.

[0032] Step 6-2. Update the occultation event state according to the judgment result to complete the GPS occultation observation, specifically:

[0033] When it is judged that the GPS satellite occultation event is a new occultation event, further judge whether there is an idle GPS occultation tracking channel: if there is, assign the new occultation event to the channel, start the occultation event capture tracking, and collect the occultation observation data; if there is no idle channel, keep the new occultation event marker until there is an idle channel for it to be assigned or the occultation event is invalid;

[0034] When it is judged to be an invalid occultation event, stop receiving the occultation event, release and initialize the GPS occultation tracking channel, and set it to idle, waiting for the use of the subsequent new occultation event;

[0035] When it is judged to be an existing occultation event, keep tracking the occultation event and continuously collect the occultation data.

[0036] The application further provides a system for GPS occultation observation based on Beidou satellite signals, which comprises:

[0037] a radio frequency front-end module, configured to process a positioning radio frequency signal received by a GNSS occultation receiver positioning antenna to obtain a positioning intermediate frequency digital signal;

[0038] a signal processing module, configured to correlate the positioning intermediate frequency digital signal with a local code and a carrier of the Beidou satellite system, obtain a correlation peak, capture and track each satellite of the Beidou system, measure pseudoranges of the satellites of the Beidou system, obtain real-time ephemeris or almanac of the satellites of the Beidou system and BDT-GNSS time synchronization parameters, and calculate a position of the GNSS occultation receiver according to the pseudorange information of the satellites of the Beidou system and the ephemeris or almanac information; and further configured to correlate the positioning intermediate frequency digital signal with a local pseudorange and a carrier of a GPS satellite to obtain a correlation peak, capture and track each GPS satellite, measure pseudoranges of the GPS satellites, and obtain real-time ephemeris or almanac of the GPS satellites.

[0039] a conversion module, configured to calculate a GPS time at a current time according to the BDT-GNSS time synchronization information and the Beidou time information measured at the current time, and calculate real-time positions of the GPS satellites according to the ephemeris or almanac of the GPS satellites and the converted GPS time information.

[0040] an occultation sampling module, configured to determine whether each GPS satellite is in an occultation state according to the position of the GNSS occultation receiver and the positions of the GPS satellites, and generate a GPS occultation prediction table; and further configured to update an occultation event state according to the GPS occultation prediction table, and complete GPS occultation observation.

[0041] As one of the improvements of the above technical solutions, the signal processing module comprises:

[0042] a Beidou signal processing unit, configured to correlate the positioning intermediate frequency digital signal with a local code and a carrier of the Beidou satellite system, obtain a correlation peak, capture and track each satellite of the Beidou system, measure pseudoranges of the satellites of the Beidou system, obtain real-time ephemeris or almanac of the satellites of the Beidou system and BDT-GNSS time synchronization parameters, and calculate a position of the GNSS occultation receiver according to the pseudorange information of the satellites of the Beidou system and the ephemeris or almanac information; and

[0043] a GPS signal processing unit, configured to correlate the positioning intermediate frequency digital signal with a local pseudorange and a carrier of a GPS satellite to obtain a correlation peak, capture and track each GPS satellite, measure pseudoranges of the GPS satellites, and obtain real-time ephemeris or almanac of the GPS satellites.

[0044] As one of the improvements of the above technical solutions, the signal processing module is realized based on an FPGA chip.

[0045] As one of the improvements of the above technical solutions, the conversion module and the occultation sampling module are realized based on an ARM chip.

[0046] Compared with the prior art, the present application has the following advantages:

[0047] 1. The method for calculating GPS position information by using Beidou positioning results proposed in the present application does not reduce the performance of an observation instrument, does not need to separately allocate positioning channel resources to a GPS system, reduces the steps for calculating GPS positioning results in a traditional receiver, saves system resources, saves operation time, and the saved time / space can be allocated to Beidou positioning tracking / occultation observation, thereby improving positioning accuracy and the number of occultation event observations; and the Beidou system has complete independent intellectual property rights and is more secure and controllable.

[0048] 2. Compared with the method for separately calculating the positioning results of the GPS and Beidou systems in a traditional method, the method proposed in the present application is simple and effective and does not need to be changed in hardware. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 A flowchart of a method for GPS occultation observation by using Beidou satellite signals is proposed in the present application.

[0050] Figure 2 A system structure diagram of a system for GPS occultation observation by using Beidou satellite signals is proposed in the present application. DETAILED DESCRIPTION

[0051] The present application proposes a method for GPS occultation observation based on Beidou satellite signals in a micro GNSS occultation observation system. This method uses Beidou direct signal tracking and positioning to calculate the position of a receiver, and calculates GPS occultation events by receiving GPS ephemeris / almanac information, thereby realizing GPS occultation event tracking and observation based on Beidou positioning. This method fully utilizes the mutual compatibility of Beidou and GPS signals, reduces the system resource consumption required for GPS direct signal positioning, reduces the dependence of a receiver system on GPS signals, is helpful for the design goals of low resource, low power consumption and high integration of a micro GNSS occultation observation system, can be applied to the field of micro GNSS occultation observation, and has wide application prospects. This method has a simple and clear design structure, is suitable for a micro GNSS occultation receiver, and does not need to be changed in special hardware.

[0052] The technical solutions of the present application will be described in detail below with reference to the drawings and embodiments.

[0053] Embodiment 1

[0054] As Figure 1 shown, a method flow chart for GPS occultation observation using Beidou satellite signals is proposed.

[0055] The method proposed includes the following steps:

[0056] (1) Beidou signal positioning solution

[0057] The signal received by the front-end radio frequency unit is down-converted to the positioning antenna, so as to capture, track and solve the ephemeris / almanac of the Beidou positioning signal, calculate the receiver position and the Beidou satellite position.

[0058] (2) Beidou occultation event prediction

[0059] According to the calculated receiver position and the position of the Beidou satellite, it is judged whether the Beidou occultation condition is triggered, and a Beidou occultation event prediction table is generated accordingly.

[0060] (3) Beidou occultation event capture and tracking

[0061] According to the Beidou occultation event prediction table obtained in step (2), the Beidou occultation event table state is updated, if it is a new occultation event, a channel is allocated for tracking; if it is a failed occultation event, the channel is released and the observation is ended.

[0062] (4) Beidou occultation data packaging and sending

[0063] The Beidou occultation observation data is packaged every second, and the carrier phase, pseudorange, I / Q path integral value and other information are stored, transmitted through LVDS, and used for subsequent occultation inversion calculation.

[0064] (5) Obtain GPS ephemeris / almanac

[0065] The GPS signal is received through 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 given to other GPS satellites without ephemeris / almanac for use.

[0066] (6) Convert Beidou positioning result to GPS positioning result

[0067] According to the BDT-GNSS time synchronization information in the GNSS occultation receiver and the Beidou time information measured at the current time, the conversion relationship between the Beidou system and the GPS system is used to calculate the GPS time at the current time, and the GPS satellite real-time position is calculated according to the received GPS ephemeris / almanac in step (5) and the converted GPS time information.

[0068] (7) GPS occultation event prediction

[0069] 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.

[0070] (8) GPS occultation event capture and tracking

[0071] According to the Beidou occultation event prediction table obtained in step (7), the occultation event state is updated, if it is a new occultation event, a channel is allocated for tracking, if it is a failed occultation event, the channel is released, and the observation is ended.

[0072] (9) Beidou occultation data packaging and sending

[0073] The Beidou occultation observation data is packaged every second, and information such as carrier phase, pseudorange, I / Q path integral value is stored, and is sent to the star service system through the LVDS interface, and is used for subsequent occultation inversion calculation after being received by the ground station.

[0074] Specifically,

[0075] In step (1), the positioning antenna receives the positioning signal, the front-end radio frequency unit down-converts the received radio frequency signal to obtain an analog intermediate frequency signal, and the AD sampling module converts it into an intermediate frequency digital signal, the digital signal is input into the baseband board FPGA, and the baseband board generates the local code and carrier of the Beidou system, and the capture result is transmitted to the ARM end to obtain the correlation peak value, so as to further realize capture, tracking, and electric text decoding; then, the Beidou satellite pseudorange information, time information, and ephemeris / almanac information measured are used to calculate the position of the GNSS occultation receiver in the Beidou coordinate system and the position of the Beidou satellite, and the carrier, pseudocode phase and other information of each Beidou satellite are calculated according to the position of the Beidou satellite and the position of the GNSS occultation receiver, which are used for subsequent occultation prediction and occultation capture.

[0076] In step (2), the elevation angle, azimuth angle, tangent height, and relative azimuth angle of the Beidou satellite are calculated every second according to the GNSS receiver position and the Beidou satellite position calculated at the current time on the ARM end, the above information is used to judge the occultation condition of each Beidou satellite, the occultation event judgment result is written into the occultation event prediction table TblBDp of the current second, and the Beidou occultation event generated in the last second is stored in the occultation event prediction table TblBDe of the last second.

[0077] In step (3), the Beidou occultation event prediction tables TblBDp and TblBDe of the current second and the last second generated in step (2) are compared to determine new, existing and failed occultation events, the new occultation event is allocated to the occultation tracking observation channel, and the failed occultation event is deleted from the tracking channel.

[0078] Step (4) includes: packing the Beidou occultation event measurement results in the current second every second, and transmitting the results to the star service processing system buffer through the LVDS interface at the end of the second.

[0079] Step (5) includes: correlating the intermediate frequency signal transmitted to the baseband board FPGA end after A / D conversion in step (1) with the local pseudo code and carrier of the GPS satellite, obtaining the correlation peak value, and capturing and tracking the GPS satellite to measure the pseudo range and receive the ephemeris and almanac of the GPS satellite.

[0080] Step (6) includes: converting the Beidou system time information obtained in step (1) to GPS system at the ARM end. Specifically, it includes: analyzing the BDT-GNSS time synchronization (BGTO) information broadcast by the Beidou III satellite, and using the information algorithm to convert the current Beidou time calculated by the GNSS occultation receiver to GPS time; converting the GNSS receiver position in the Beidou coordinate system calculated by the Beidou system to the geocentric inertial coordinate system, and using the positioning information, the GPS satellite ephemeris almanac information obtained in step (5), and the GPS time converted above to calculate the positions of each GPS satellite, which is used for GPS occultation prediction in step (7).

[0081] Step (7) includes: judging the GNSS occultation receiver position calculated in step (1) and the GPS satellite position calculated in step (6) every second at the ARM end, calculating the elevation angle, azimuth angle, tangent height, relative azimuth angle, predicted carrier frequency, code phase and other information of the GPS satellite, judging the GPS satellite occultation condition through the above information, writing the occultation event judgment result into the occultation event prediction table TblGPSp of the current second, and storing the occultation event generated in the last second into the occultation event prediction table TblGPSe of the last second.

[0082] Step (8) includes: comparing the GPS occultation event prediction tables TblGPSp and TblGPSe of the current second and the last second generated in step (7), determining the new, existing and invalid GPS occultation events, assigning the new occultation event to the GPS occultation tracking observation channel, inputting the predicted carrier frequency and code phase information of the GPS satellite corresponding to the occultation event to start occultation observation, and deleting the invalid occultation event from the tracking channel.

[0083] Step (9) includes: packing the GPS occultation event measurement results in the current second every second, and transmitting the results to the star service processing system buffer through the LVDS interface at the end of the second; and transmitting the Beidou occultation measurement results together to the ground system through the ground station for subsequent inversion calculation.

[0084] Embodiment 2

[0085] The application provides a system for GPS occultation observation by using Beidou satellite signals, which comprises a radio frequency front end module, a signal processing module, a conversion module and an occultation sampling module.

[0086] The radio frequency front end module is used for processing the positioning radio frequency signals received by the GNSS occultation receiver positioning antenna to obtain positioning intermediate frequency digital signals.

[0087] The signal processing module comprises a Beidou signal processing unit and a GPS signal processing unit. The Beidou signal processing unit is used for correlating the positioning intermediate frequency digital signals with the local codes and carriers of the Beidou satellite system, obtaining correlation peaks, capturing and tracking the Beidou satellites, measuring the Beidou satellite pseudo distances, obtaining the real-time ephemeris or almanac of the Beidou satellites and BDT-GNSS time synchronization parameters, and calculating the position of the GNSS occultation receiver according to the Beidou satellite pseudo distance information, ephemeris or almanac information. The GPS signal processing unit is used for correlating the positioning intermediate frequency digital signals with the local pseudo codes and carriers of the GPS satellites to obtain correlation peaks, capturing and tracking each GPS satellite, measuring the pseudo distances of each GPS satellite, and obtaining the real-time ephemeris or almanac of each GPS satellite.

[0088] The conversion module is used for calculating the GPS time at the current moment by using the conversion relationship between the Beidou system and the GPS system according to the BDT-GNSS time synchronization information and the Beidou time information measured at the current moment, and calculating the real-time positions of each GPS satellite according to the ephemeris or almanac of each GPS satellite and the converted GPS time information.

[0089] The occultation sampling module is used for judging whether each GPS satellite is in an occultation state according to the obtained position of the GNSS occultation receiver and the positions of each GPS satellite, and generating a GPS occultation prediction table. The occultation sampling module is also used for updating the occultation event state according to the GPS occultation prediction table, and completing the GPS occultation observation.

[0090] The signal processing module is realized based on an FPGA chip, and the conversion module and the occultation sampling module are realized based on an ARM chip.

[0091] Figure 2 The application provides a system for GPS occultation observation by using Beidou satellite signals, which comprises a radio frequency front end module, a signal processing module, a conversion module and an occultation sampling module.

[0092] In order to make the purpose and technical scheme of the application clearer, the application provides a method for GPS occultation observation based on Beidou satellite signals in a micro GNSS occultation observation system.

[0093] The GNSS occultation observation instrument structure according to the present application is shown in Figure 2 The GNSS occultation observation instrument structure according to the present application is shown in

[0094] The GNSS occultation observation instrument is taken as an example for description according to the received Beidou signal being a Beidou third-generation B1C signal and the GPS signal being a GPS L1 signal. Both signal carrier frequencies are 1575.42Mhz. First, the positioning antenna receives the signal of the frequency point and performs filtering and down-conversion to obtain an intermediate frequency signal, which is input to the baseband FPGA end. Then, the analog intermediate frequency signal is converted into a digital intermediate frequency signal r IF .

[0095] After obtaining the intermediate frequency signal r IF , the local carrier and Beidou B1C local pseudo code are generated at the FPGA end, which are correlated with r IF , the B1C pseudo code and carrier information in the intermediate frequency signal are stripped, the processed signal is sent to the ARM end, the correlation peak value is obtained to realize capture, the capture result is placed into the positioning tracking loop, the I / Q path integration result is obtained according to the integration time, the Beidou B-CNAV1 message information is obtained through the I / Q path integration after stable tracking, the time parameters and ephemeris, almanac and BDT-GNSS time synchronization information are extracted from the message information, and the parameters are saved. After calculating the system time parameters SOH (second count in hour), HOW (hour count in week) and WN (whole week count), the current Beidou time can be obtained, and the ephemeris, almanac and various error correction quantities are extracted from the message information, so as to solve the position of the GNSS occultation observation instrument and the position of each Beidou satellite constellation.

[0096] After completing the position solution, the Beidou occultation event prediction can be performed. According to the position solution results of the GNSS occultation observation instrument and the Beidou satellite constellation, the elevation angle E ph , the tangent point height T AZM and the relative azimuth angle R AZM of each Beidou satellite per second can be calculated. If the three are within the condition range of Table 1, it is considered as a valid occultation event, otherwise it is an invalid occultation event. The above occultation event is updated to the Beidou occultation event prediction table Tbl BDp of the current second according to the above occultation event, and the above-second Beidou occultation event is cached into the Beidou occultation event prediction table Tbl BDe of the above second.

[0097] Table 1: Occultation range judgment table

[0098]

[0099] After obtaining the prediction result of BDS occultation event, the prediction table of BDS occultation event in the previous and next seconds is subtracted, so as to determine the newly added, existing and invalid occultation events in the current second:

[0100]

[0101] According to the above judgment result of occultation event, the following operations are performed:

[0102] ·Newly added occultation event

[0103] First, it is judged whether there is an idle BDS occultation tracking channel. If there is, the newly added occultation event is allocated to the channel, and the occultation event capture tracking is started to collect occultation observation data. If there is no idle channel, the occultation event is marked as newly added and tracking is not started until there is an idle channel for allocation or the occultation event is invalid.

[0104] ·Existing occultation event

[0105] The tracking is maintained, and the occultation data is continuously collected.

[0106] ·Invalid occultation event

[0107] If the occultation event existing in the occultation channel is not in the occultation prediction table, it is considered that the occultation event is invalid, at which time the occultation event is stopped to be received, the BDS occultation channel is released and initialized, and the channel state is set to idle so as to be used by the newly added occultation event later.

[0108] ·No occultation event

[0109] No operation is performed.

[0110] After the judgment operation of the occultation event is completed, the newly added occultation event is captured, the existing occultation event is tracked, and the carrier phase, I / Q path integral, carrier-to-noise ratio and pseudo-range information are collected, which are cached at a rate of 100 Hz and packaged according to the time stamp, and then sent to the star service system through the bus.

[0111] For the GPS system, the intermediate frequency signal r IF The correlation is performed between the intermediate frequency signal and the local carrier and GPS L1C / A code at the FPGA end, and the correlation result is sent to the ARM end to realize the tracking of the GPS direct signal and obtain the GPS ephemeris / almanac information.

[0112] According to the BDT-GNSS time synchronization parameter part in the BDS B-CNAV1 message information, the BDS time solved can be converted into GPS time:

[0113] 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

[0114] wherein A 0BGTO ~A 2BGTO and WN BGTO are BDT-GNSS time synchronization parameter broadcast parameters, t BD is the current moment BDT time second, WN is the current BDT time week, the calculated Δt Systems is the difference between the current moment BDT system time second and GPS system time second, so the GPS system time second can be calculated as

[0115] t GPS =t BD -Δt Systems

[0116] Using the above conversion relationship, the current moment GPS time second can be obtained without analyzing the GPS electric text, and the position information of the GNSS occultation observation instrument and the GPS ephemeris can be calculated using the BDT system, and the GPS satellite constellation position information is calculated for GPS occultation prediction.

[0117] Similar to the BDT occultation prediction method, the GNSS occultation observation instrument calculates the elevation angle E ph , the tangent point height T AZM and the relative azimuth angle R AZM of each GPS satellite per second, if all of them are within the table condition range, it is considered as a valid occultation event, otherwise it is an invalid occultation event, and the above occultation event is updated to the current second GPS occultation event prediction table Tbl GPSp , and the last second GPS occultation event is cached in the last second GPS occultation event prediction table Tbl GPSe .

[0118] Similarly, the difference between the GPS occultation events can be obtained as follows:

[0119]

[0120] According to the above occultation event judgment result, the remaining operation is the same as that of the BDT occultation event, and the received observation information is packaged and saved at a rate of 100 Hz.

[0121] After the satellite system receives the BDT and GPS occultation data information per second, it is cached and downloaded to the ground receiving station in time for subsequent inversion.

[0122] It should be noted that the above embodiment is only a preferred embodiment of the application, and is not intended to limit the scope of the application. All algorithms and corresponding system designs disclosed in the application can be combined or replaced by features with the same or similar purposes and effects. It should be noted that those skilled in the art can make various improvements and changes without departing from the principles and spirit of the application, such as adding, deleting, replacing or merging certain steps or functional units / modules, and these improvements and changes are within the scope of the application.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the application and are not limiting. Although the application is described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the application do not deviate from the spirit and scope of the application, and should be covered in the scope of the claims of the application.

Claims

1. A method for GPS occultation observation based on Beidou satellite signals, the method comprising: acquiring time and position information of a GNSS occultation receiver in a Beidou satellite system space-time coordinate by capturing, tracking and positioning of the receiver through signals received by the GNSS occultation receiver, then converting the Beidou positioning result into a GPS positioning result, calculating GPS satellite positions according to the GPS positioning result, realizing GPS occultation prediction and occultation capture tracking based on the GPS satellite positions, and completing GPS occultation observation; wherein the method specifically comprises: Step 1. Receiving a positioning radio frequency analog signal through a positioning antenna of the GNSS occultation receiver and processing the positioning radio frequency analog signal to obtain a positioning intermediate frequency digital signal; Step 2. Correlating the positioning intermediate frequency digital signal with local codes and carriers of the Beidou satellite system to obtain correlation peaks, capturing and tracking each satellite of the Beidou system, measuring pseudoranges of each satellite of the Beidou system, obtaining real-time ephemeris or almanac and BDT-GNSS time synchronization parameters of each satellite of the Beidou system, and calculating a position of the GNSS occultation receiver according to the Beidou satellite pseudorange information, ephemeris or almanac information; Step 3. Correlating the positioning intermediate frequency digital signal with local pseudocodes and carriers of each GPS satellite to obtain correlation peaks, capturing and tracking each GPS satellite, measuring GPS satellite pseudoranges, and obtaining real-time ephemeris or almanac of each GPS satellite; Step 4. Calculating a current GPS time using a conversion relationship between the Beidou system and the GPS system according to BDT-GNSS time synchronization information and Beidou time information measured at the current time, and calculating real-time positions of each GPS satellite according to ephemeris or almanac of each GPS satellite and the converted GPS time information; Step 5. Judging whether each GPS satellite is in an occultation state according to the obtained position of the GNSS occultation receiver and the positions of each GPS satellite, and generating a GPS occultation prediction table; Step 6. Updating an occultation event state according to the GPS occultation prediction table obtained in Step 5, and completing GPS occultation observation. 2.The method of claim 1, wherein, In Step 3, the real-time ephemeris or almanac of each GPS satellite comprises: When the real-time ephemeris or almanac of a certain GPS satellite is obtained, releasing tracking channel resources occupied by the satellite, so as to receive real-time ephemeris or almanac of the remaining GPS satellites. 3.The method of claim 1, wherein, In step 4, the current time GPS time t GPS The calculation formula is: t GPS = t BD - Δt Systems Where Δt Systems is the difference between the current time of the Beidou system and the GPS system, and the calculation formula is as follows: 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 Wherein, A 0BGTO , A 1BGTO , A 2BGTO , and WN BGTO are all BDT-GNSS time synchronization parameter broadcast parameters, t BD is the current BDT time second, and WN is the current BDT time week.

4. The method of claim 1, wherein, In Step 5, the method specifically comprises: Step 5-1. Calculate the elevation angle E and the tangent height T of each GPS satellite for each second from the obtained GNSS occultation receiver position and the position of each GPS satellite ph and the relative azimuth angle R AZM and make the following determination: When the 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 condition, it is an effective occultation event. When any one of the 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 condition, it is a failed occultation event. Step 5-2. Update the current GPS occultation event prediction table according to the previous second occultation event in the mean time cache the previous second GPS occultation event into the previous second GPS occultation event prediction table .

5. The method of claim 4, wherein, In Step 6, the method specifically comprises: Step 6-1. According to the GPS Occultation Event Prediction Table of this second and the GPS Occultation Event Prediction Table of the last second Differ the status identifiers of each GPS satellite occultation event of this second and the last second, and make a judgment according to the result of the difference, specifically as follows: When the satellite difference result is 1, it indicates that the satellite occultation event in the current second is a new GPS occultation event; When the satellite difference result is -1, it indicates that the satellite occultation event in the current second is an invalid GPS occultation event; When the satellite difference result is 0, it further judges whether the satellite occultation event in the current second is a valid GPS occultation event, if the satellite occultation event in the current second is a valid GPS occultation event, it indicates that the satellite occultation event in the current second is an existing occultation event, and if the satellite occultation event in the current second is an invalid GPS occultation event, it indicates that there is no satellite occultation event in the current second; Step 6-2. Updating the occultation event state according to the judgment result, and completing GPS occultation observation, specifically comprising: When the GPS satellite occultation event is determined to be a new occultation event, it is further determined whether there is a free GPS occultation tracking channel: if there is, the new occultation event is assigned to the channel, occultation event capture tracking is started, and occultation observation data is collected; if there is no free channel, the new occultation event flag is kept until a free channel is assigned to it or the occultation event is invalidated; When the GPS satellite occultation event is determined to be a new occultation event, it is further determined whether there is a free GPS occultation tracking channel: if there is, the new occultation event is assigned to the channel, occultation event capture tracking is started, and occultation observation data is collected; if there is no free channel, the new occultation event flag is kept until a free channel is assigned to it or the occultation event is invalidated; When the GPS satellite occultation event is determined to be a new occultation event, it is further determined whether there is a free GPS occultation tracking channel: if there is, the new occultation event is assigned to the channel, occultation event capture tracking is started, and occultation observation data is collected; if there is no free channel, the new occultation event flag is kept until a free channel is assigned to it or the occultation event is invalidated; 6. A system for GPS occultation observation based on Beidou satellite signals, the system comprising: a radio frequency front-end module for processing a positioning radio frequency signal received by a GNSS occultation receiver positioning antenna to obtain a positioning intermediate frequency digital signal; a signal processing module for correlating the positioning intermediate frequency digital signal with local codes and carriers of a Beidou satellite system, obtaining correlation peaks, capturing and tracking each satellite of the Beidou system, measuring pseudoranges of each satellite of the Beidou system, obtaining real-time ephemeris or almanac of each satellite of the Beidou system and BDT-GNSS time synchronization parameters, and calculating a GNSS occultation receiver position according to Beidou satellite pseudorange information, ephemeris or almanac information; the signal processing module is also configured to correlate the positioning intermediate frequency digital signal with local pseudocodes and carriers of GPS satellites to obtain correlation peaks, capture and track each GPS satellite, measure pseudoranges of each GPS satellite, and obtain real-time ephemeris or almanac of each GPS satellite; a conversion module configured to calculate a current GPS time according to BDT-GNSS time synchronization information and Beidou time information measured at the current time, using a conversion relationship between the Beidou system and the GPS system, and calculate real-time positions of each GPS satellite according to ephemeris or almanac of each GPS satellite and the converted GPS time information; and an occultation sampling module configured to determine whether each GPS satellite is in an occultation state according to the obtained GNSS occultation receiver position and positions of each GPS satellite, and generate a GPS occultation prediction table; the occultation sampling module is also configured to update an occultation event state according to the GPS occultation prediction table, and complete GPS occultation observation.

7. The system for GPS occultation observation based on Beidou satellite signals according to claim 6, characterized in that, The signal processing module comprises: a Beidou signal processing unit configured to correlate the positioning intermediate frequency digital signal with local codes and carriers of a Beidou satellite system, obtain correlation peaks, capture and track each satellite of the Beidou system, measure pseudoranges of each satellite of the Beidou system, obtain real-time ephemeris or almanac of each satellite of the Beidou system and BDT-GNSS time synchronization parameters, and calculate a GNSS occultation receiver position according to Beidou satellite pseudorange information, ephemeris or almanac information; and a GPS signal processing unit configured to correlate the positioning intermediate frequency digital signal with local pseudocodes and carriers of GPS satellites to obtain correlation peaks, capture and track each GPS satellite, measure pseudoranges of each GPS satellite, and obtain real-time ephemeris or almanac of each GPS satellite.

8. The system for GPS occultation observation based on Beidou satellite signals according to claim 6, characterized in that, The signal processing module is implemented based on an FPGA chip.

9. The system for GPS occultation observation based on Beidou satellite signals according to claim 6, characterized in that, The conversion module and the occultation sampling module are realized based on an ARM chip.

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