GNSS Navigation Method, Terminal, Integrated Navigation System, and Storage Medium

Abstract

The present invention provides a GNSS navigation method, a terminal, an integrated navigation system, and a storage medium. The GNSS navigation method includes: selecting valid observations based on a basic rejection scheme and an auxiliary rejection scheme, wherein the auxiliary rejection scheme depends on the INS navigation result; calculating a predicted value of the current epoch parameter based on the INS navigation result; calculating a floating-point solution of the estimated value of the current epoch parameter according to the selected valid observations and the predicted value of the current epoch parameter; and performing integer ambiguity fixing based on the floating-point solution of the estimated value of the current epoch parameter and its estimation error to obtain a fixed solution of the estimated value of the current epoch parameter. In this way, the accuracy and reliability of GNSS navigation are improved.

Description

Technical Field

[0001] The present invention relates to the field of positioning and navigation, and particularly to a GNSS navigation method, a GNSS navigation terminal, an integrated navigation system, and a storage medium. Background Art

[0002] The Global Navigation Satellite System (GNSS) can provide all-weather real-time positioning, navigation, and timing services for global users. The core constellations include the US GPS (Global Positioning System), China's Beidou Navigation Satellite System (BDS), the EU's Galileo, and Russia's GLONASS. Without the assistance of augmentation information, the pseudo-range single-point positioning accuracy of an independent single-system GNSS is about 5 meters. To meet the requirements for high-precision positioning in fields such as surveying and mapping, autonomous driving, and deformation monitoring, it is necessary to correct the original GNSS measurement errors to achieve centimeter- or even millimeter-level positioning. At the user end, the Real Time Kinematic (RTK) technology is the most widely used and technically mature GNSS navigation and positioning technology. The RTK technology uses two receivers (or navigation terminals) that simultaneously receive GNSS satellite signals, eliminates the systematic errors at the satellite end and the receiving end through real-time differential methods, and greatly reduces the errors related to the propagation path, thereby realizing the functions of high-precision positioning, speed measurement, and timing.

[0003] Although GNSS technology has many advantages, GNSS satellite signals are vulnerable to interference or occlusion. In environments where GNSS satellite signals are severely attenuated, such as in areas with tree cover, urban canyons, tunnels, etc., the quality of GNSS satellite signals deteriorates sharply, making it impossible to achieve high-precision positioning. In such scenarios, relying solely on a single GNSS system cannot complete real-time high-precision navigation tasks. Usually, multiple sensors are required for integrated navigation to compensate for the deficiencies of GNSS navigation. An integrated navigation system is a system that combines multiple sensors to perform functions such as navigation and positioning. It can effectively overcome the disadvantages of a single system and leverage the advantages of each system, thereby improving the accuracy, stability, and reliability of navigation and providing more effective navigation information to users. The combination of an Inertial Navigation System (INS) and a GNSS system is the most commonly used integrated system. The INS system is a completely autonomous three-dimensional dead reckoning navigation system that does not rely on the external environment, and has advantages such as complete autonomy, no external transmitted signals, high sampling frequency, and output of attitude information. Due to its good autonomy and high short-term accuracy, the INS system can effectively make up for the deficiencies of GNSS navigation in occluded or interfered environments. At the same time, the GNSS system can output high-precision navigation information, provide initialization information for the INS system, and can provide real-time high-precision correction information to the INS system in real time to prevent the errors of the INS system from gradually accumulating over time and improve the usability of the INS.

[0004] In the process of system combination, according to different information adopted by RTK, the RTK / INS combination mode is divided into loose combination, tight combination and deep combination. In the loose combination, the navigation information calculated by the RTK system is output to the INS system. The INS system uses the difference between the predicted information and the navigation information output by the RTK system as the observation quantity to estimate parameters such as position, speed and attitude, and obtains the combined navigation result in the loose combination mode. RTK is the most mature and widely used technology in the GNSS system. In the loose combination mode, the RTK system and the INS system are independent of each other. The combined system has high reliability and is easy to implement, which is the most widely used combination method at present. Although the loose combination mode has many advantages, due to the relatively simple combination method, the performance of the combined navigation is relatively limited. The tight combination is a combination method that uses the observations of the RTK system and the predicted information of the INS system as observations for overall solution. Compared with the loose combination, in the case of tight combination, the predicted information of the INS system is directly fused with the observations of the RTK system, which can effectively improve the RTK navigation performance in the satellite signal occlusion environment. Since the RTK system and the INS system are solved as a system, the abnormal results of the INS system will directly affect the RTK system, resulting in lower overall reliability of the system. The deep combination is the fusion of the RTK system and the INS system at the hardware level. Due to the large implementation difficulty, complex use and low reliability level, it is rarely used in actual engineering applications. Summary of the Invention

[0005] The purpose of the present invention is to provide a GNSS navigation method, a GNSS navigation terminal, a combined navigation system and a storage medium, which assist GNSS navigation according to the INS navigation result, so as to achieve high-precision, high-stability and high-reliability navigation.

[0006] To achieve the object of the invention, according to one aspect of the present invention, there is provided a GNSS navigation method. When an INS navigation result is received and the INS navigation result is available, it includes: selecting valid observations based on a basic rejection scheme and an auxiliary rejection scheme, wherein the auxiliary rejection scheme depends on the INS navigation result; calculating a predicted value of the current epoch parameter based on the INS navigation result, and calculating a prediction error of the predicted value of the current epoch parameter based on an estimation error of an estimated value of the previous epoch parameter; calculating a floating-point solution of the estimated value of the current epoch parameter according to the selected valid observations and the predicted value of the current epoch parameter, and calculating an estimation error of the floating-point solution of the estimated value of the current epoch parameter based on the prediction error of the predicted value of the current epoch parameter; and performing integer ambiguity fixing according to the floating-point solution of the estimated value of the current epoch parameter and its estimation error to obtain a fixed solution of the estimated value of the current epoch parameter and its estimation error, wherein the GNSS navigation result includes time, the floating-point solution or the fixed solution of the estimated value of the current epoch parameter and its estimation error, and the parameters include one or more of speed and position.

[0007] According to another aspect of the present invention, there is provided a GNSS navigation terminal, which receives the INS navigation result of an INS navigation terminal. When the INS navigation result is received and the INS navigation result is available, the GNSS navigation terminal performs the following operations: selecting valid observations based on a basic rejection scheme and an auxiliary rejection scheme, wherein the auxiliary rejection scheme depends on the INS navigation result; calculating a predicted value of the current epoch parameter based on the INS navigation result, and calculating a prediction error of the predicted value of the current epoch parameter based on an estimation error of an estimated value of the previous epoch parameter; calculating a floating-point solution of the estimated value of the current epoch parameter according to the selected valid observations and the predicted value of the current epoch parameter, and calculating an estimation error of the floating-point solution of the estimated value of the current epoch parameter based on the prediction error of the predicted value of the current epoch parameter; and performing integer ambiguity fixing according to the floating-point solution of the estimated value of the current epoch parameter and its estimation error to obtain a fixed solution of the estimated value of the current epoch parameter and its estimation error, wherein the GNSS navigation result includes time, the floating-point solution or the fixed solution of the estimated value of the current epoch parameter and its estimation error, and the parameters include one or more of speed and position.

[0008] According to another aspect of the present invention, the present invention provides a combined navigation system, which includes: an INS navigation terminal; a GNSS navigation terminal connected to the INS navigation terminal, wherein the GNSS navigation terminal performs GNSS navigation to obtain a GNSS navigation result and transmits the GNSS navigation result to the INS navigation terminal, and the INS navigation terminal performs INS navigation according to the GNSS navigation result to obtain an INS navigation result and transmits the INS navigation result to the GNSS navigation terminal; the GNSS navigation terminal is the GNSS navigation terminal described above.

[0009] According to still another aspect of the present invention, the present invention provides a storage medium, which stores program instructions therein, and the program instructions are executed to implement the above-mentioned GNSS navigation method.

[0010] Compared with the prior art, the present invention uses the INS navigation result to assist in GNSS navigation, so as to achieve high-precision, high-stability and high-reliability navigation. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic structural diagram of the combined navigation system in an embodiment of the present invention;

[0012] Figure 2 It is a schematic flow diagram of the GNSS navigation method executed by the GNSS navigation terminal in an embodiment of the present invention;

[0013] Figure 3 It is a structural block diagram of the INS navigation terminal in an embodiment of the present invention;

[0014] Figure 4 It is a schematic flow diagram of the INS navigation method executed by the INS navigation terminal in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following will, in conjunction with the accompanying drawings and preferred embodiments, describe in detail the specific implementation manners, structures, features and their effects of the present invention.

[0016] The present invention aims to solve the problems of low fusion positioning accuracy, poor stability and reliability of the RTK / INS system. By optimizing the physical fusion mode and data fusion mode of RTK / INS, a stable, reliable and high-performance RTK / INS combined navigation system is proposed. RTK / INS combined navigation is widely used in many fields, but the traditional combination mode has always been unable to achieve high precision, high stability and high reliability. Therefore, optimizing the combination mode of RTK / INS and improving the overall performance of the system are crucial for the wide application of the combined navigation system.

[0017] Figure 1 This is a schematic structural diagram of the integrated navigation system 100 in an embodiment of the present invention. As Figure 1 shown, the integrated navigation system 100 includes an INS navigation terminal 110 and a GNSS navigation terminal 120 connected to the INS navigation terminal 110. The INS navigation terminal 110 is a navigation terminal based on inertial navigation system technology, and can also be referred to as an inertial navigation terminal, an INS positioning terminal, an INS navigation system, an INS system, etc. It is used to perform inertial navigation to obtain an INS navigation result. The INS navigation result includes one or more of attitude, velocity, position, and time. The GNSS navigation terminal 120 is a navigation terminal based on global satellite navigation system technology, and can also be referred to as a satellite navigation terminal, a GNSS positioning terminal, etc. It is used to perform satellite navigation to obtain a GNSS navigation result. The GNSS navigation result includes one or more of velocity, position, and time. In a preferred embodiment, the GNSS navigation terminal 120 is an RTK navigation terminal, and the GNSS navigation result is an RTK navigation result.

[0018] The INS navigation terminal 110 and the GNSS navigation terminal 120 are independent of each other, and data bidirectional communication is realized between the two through a physical interface. Specifically, the INS navigation terminal 110 includes an I / O interface (i.e., input / output interface) 111, and the GNSS navigation terminal 120 includes an I / O interface (i.e., input / output interface) 121. The I / O interface 111 establishes a communication connection with the I / O interface 121. The GNSS navigation terminal 120 transmits the GNSS navigation result to the INS navigation terminal 110 in real time through the I / O interface, and the INS navigation terminal 110 transmits the INS navigation result to the GNSS navigation terminal 120 in real time through the I / O interface. Different from the existing integrated navigation system, in the integrated navigation system 100 of the present invention, the GNSS navigation terminal 120 will assist in GNSS navigation according to the INS navigation result received in real time, so as to effectively improve the accuracy, stability, and reliability of GNSS navigation.

[0019] Figure 2 This is a schematic flowchart of the GNSS navigation method executed by the GNSS navigation terminal 120 in an embodiment of the present invention. As Figure 2 shown, the GNSS navigation method 200 includes the following steps.

[0020] Step 210, the GNSS navigation terminal 120 receives the INS navigation result of the INS navigation terminal 110. The INS navigation result of the INS navigation terminal 110 will be transmitted to the GNSS navigation terminal 120 in real time.

[0021] Step 220: Determine whether the INS navigation result is received and whether the received INS navigation result is available.

[0022] If the INS navigation result is not received or the INS navigation result is unavailable, the no-branch guides the GNSS navigation method 200 to 260, thereby performing conventional GNSS navigation, that is, the existing GNSS navigation. If the INS navigation result is received and the INS navigation result is available, the yes-branch guides the GNSS navigation method 200 to 230, thereby assisting GNSS navigation with the INS navigation result. In one embodiment, the INS navigation result includes an availability identifier, and based on the identifier, it is determined whether the INS navigation result is available.

[0023] Step 260: Select valid observations based on a basic rejection scheme.

[0024] It should be noted that the receiver of the GNSS navigation terminal 210 receives various observations. Since this part is a conventional technique, it is not reflected in Figure 2 Among them, the observations include pseudorange observations, carrier observations, and Doppler observations. However, some of the observations may have gross errors, that is, some observations may be abnormal and need to be rejected. It should be noted that the carrier observations are in units of weeks, and the gross error in the carrier observations is called a cycle slip. In other words, it is necessary to select valid observations from the observations, that is, observations without gross errors or cycle slips. Specifically, it is necessary to reject the pseudorange observations with gross errors, the carrier observations with cycle slips, and the Doppler observations with gross errors respectively, to obtain valid pseudorange observations, carrier observations, and Doppler observations.

[0025] In one embodiment, the basic rejection scheme is: according to the distribution of the residuals of the observations among the residuals of all observations, reject the observations that do not satisfy the probability distribution. This basic rejection scheme has a large relationship with factors such as the accuracy of the prior information, the stochastic model, and the geometric distribution of the observed satellites, and the actual effect is sometimes not ideal.

[0026] The step of selecting valid observations, or rather, the step of rejecting observations with gross errors, can also be referred to as the step of data preprocessing.

[0027] Step 270: Calculate the predicted value of the current epoch parameter based on the estimated value of the previous epoch parameter, and calculate the prediction error of the predicted value of the current epoch parameter based on the estimation error of the estimated value of the previous epoch parameter. The parameters include position, velocity, integer ambiguity, etc.

[0028] In a specific embodiment, first, according to formula (1), the predicted value of the current epoch parameter is calculated based on the estimated value (or filtered value, i.e., the solution result of the previous epoch parameter) of the previous epoch parameter:

[0029]

[0030] where k represents the previous epoch and k + 1 represents the current epoch, represents the estimated value of the previous epoch parameter, and the parameter is usually parameters such as position and velocity, represents the predicted value of the current epoch parameter (or the parameter to be estimated), and Φ k+1,k represents the state transition matrix of the parameter.

[0031] Then, according to the estimation error of the estimated value of the previous epoch parameter, the prediction error of the predicted value of the current epoch parameter is calculated:

[0032]

[0033] where P k represents the estimation error of the estimated value of the previous epoch parameter (specifically the variance - standard deviation matrix), and P k+1,k represents the prediction error of the predicted value of the current epoch parameter (specifically the variance - standard deviation matrix), Q k represents the process noise, and Γ k represents the coefficient matrix of the process noise.

[0034] Step 280: Calculate the floating - point solution of the estimated value of the current epoch parameter based on the selected valid observations and the predicted value of the current epoch parameter, and calculate the estimation error of the floating - point solution of the estimated value of the current epoch parameter based on the prediction error of the predicted value of the current epoch parameter.

[0035] In one embodiment, the floating - point solution of the estimated value of the current epoch parameter is calculated according to the following formula (3):

[0036]

[0037] where L k+1 represents the selected valid observations, H k+1 represents the design matrix of the current epoch observations, and K k+1 represents the filtering gain matrix of the current epoch;

[0038] where the filtering gain matrix K of the current epoch k+1 , is the weight of the estimated variance in the total variance (estimated variance and observation variance), and its formula (4) is as follows:

[0039]

[0040] where H k+1 represents the design matrix of the current epoch observations, K k+1 represents the filtering gain matrix of the current epoch, and R k+1 represents the stochastic model of the observations.

[0041] In one embodiment, the estimation error of the estimated value of the current epoch parameters is calculated according to the following formula (5):

[0042] P k+1 = (E - K k+1 H k+1 )P k+1,k (5)

[0043] where E represents the identity matrix, and P k+1 represents the estimation error of the estimated value of the current epoch parameters.

[0044] In the state update model, the parameter matrix and the state transition matrix Φ k+1,k are respectively as follows:

[0045]

[0046]

[0047] where dt represents the time difference between epochs, X, Y, and Z respectively represent the components of the position in the X, Y, and Z axes of the coordinate system among the parameters to be estimated, V X , V Y , V Z respectively represent the components of the velocity in the X, Y, and Z axes of the coordinate system among the parameters to be estimated, and N represents the vector of integer ambiguity parameters.

[0048] Step 290, perform integer ambiguity fixing based on the floating-point solution of the estimated value of the current epoch parameters and its estimation error, and obtain the fixed solution of the estimated value of the current epoch parameters and its estimation error.

[0049] The floating-point solution or fixed solution of the estimated value of the current epoch parameters and its estimation error can be part of the GNSS navigation result. If there is a fixed solution, the fixed solution is output; if there is no fixed solution, the floating-point solution is output. The GNSS navigation result includes time, velocity, and position.

[0050] Steps 260 - 290 can be existing GNSS navigation algorithms (such as RTK technology), so they are not described in detail here. Step 260 is the preprocessing step of the observations. Steps 270 - 280 are two models of Kalman filtering, namely the prediction model and the observation model. Step 290 is the integer ambiguity fixation. Currently, the most commonly used method for integer ambiguity fixation is the lambda method.

[0051] Step 230, select valid observations based on the basic rejection scheme and the auxiliary rejection scheme, where the auxiliary rejection scheme depends on the INS navigation result.

[0052] Since the observations include pseudorange observations, carrier observations, and Doppler observations, and since the Doppler observations are used to calculate the instantaneous velocity, the characteristics between epochs of the INS cannot be applied to the preprocessing of Doppler observation data. Therefore, this step 230 specifically includes: selecting valid pseudorange observations based on the basic rejection scheme and the auxiliary rejection scheme; selecting valid carrier observations based on the basic rejection scheme and the auxiliary rejection scheme; and selecting valid Doppler observations based on the basic rejection scheme.

[0053] The basic rejection scheme is the same as the basic rejection scheme in step 260 above. In other words, step 230 will not only select valid observations based on the basic rejection scheme like step 260, but also further select valid observations based on the auxiliary rejection scheme, so as to obtain more accurate and reliable observations. Therefore, the auxiliary rejection scheme is only carried out when the INS navigation result is available. The traditional basic rejection scheme is not affected by whether the INS navigation result is available. It is equivalent to adding a reliable rejection mechanism on the basis of the conventional processing mechanism when the INS navigation result is available, improving the accuracy and reliability of the observation rejection.

[0054] In one embodiment, the auxiliary rejection scheme is: calculate the satellite - earth distance between the previous and next epochs according to the position in the INS navigation result; calculate the a posteriori residual of the pseudorange observation according to the satellite - earth distance between the previous and next epochs. If the a posteriori residual of the pseudorange is greater than the product of the accuracy of the pseudorange observation and a predetermined coefficient, it is considered that the pseudorange observation has a gross error and needs to be rejected, otherwise the pseudorange observation is considered valid; calculate the a posteriori residual of the carrier observation according to the satellite - earth distance between the previous and next epochs. If the a posteriori residual of the carrier observation is greater than the product of the accuracy of the carrier observation and a predetermined coefficient, it is considered that the carrier observation has a cycle slip and needs to be rejected, otherwise the carrier observation is considered valid.

[0055] More specifically, calculate the a posteriori residual of the pseudorange observation according to the following formula:

[0056]

[0057] In the formula,

[0058]

[0059] where ρ is the satellite-earth distance between the satellite and the satellite signal receiver (i.e., the navigation terminal), (X s , Y s , Z s ) respectively represent the three-dimensional position of the satellite in the coordinate system, and (X r , Y r , Z r ) respectively represent the three-dimensional position of the receiver in the coordinate system.

[0060] where c is the speed of light, is the clock error variation of the satellite clock, is the satellite-earth distance between two consecutive epochs, P represents the pseudorange observation value, is the double-difference pseudorange observation value of the pseudorange observation value; the derivation process and principle of the formula (6) are as follows.

[0061] Taking the previous epoch as the base station and the current epoch as the rover with accurate position for baseline solution. The observation equation of a single satellite pseudorange is as follows:

[0062] P = ρ + Ion + Trop + cdt i + cdt j + ε (7)

[0063] In the formula, P represents the pseudorange observation value, ρ represents the satellite-earth distance between the satellite and the satellite signal receiver, Ion represents the ionospheric delay error, Trop represents the tropospheric delay error, cdt i represents the clock error of the receiver, cdt j represents the clock error of the satellite, and ε represents the random error of the observation value.

[0064] First, perform inter-satellite differencing on the pseudorange observation value to obtain the inter-satellite single difference

[0065] ΔP = Δρ + ΔIon + ΔTrop + cΔdt j + Δε (8)

[0066] In the formula, Δ represents the inter-satellite single difference.

[0067] Then, perform epoch-to-epoch differencing. According to the above, regarding the observation value of the previous epoch as the reference station, which is equivalent to station-to-station differencing, thus forming the double-difference observation value as follows:

[0068]

[0069] Since the ionospheric and tropospheric errors after double differencing are greatly weakened and can be ignored, Equation (9) is simplified to obtain the following formula (10):

[0070]

[0071] When the INS navigation result is available, the accuracy of the relative position between INS epochs reaches the centimeter level. The relative position between epochs provided by INS can be considered as the true value, and the satellite-earth distance between the previous and subsequent epochs can be accurately calculated based on the position in the INS navigation result Therefore, the satellite-earth distance between epochs is a known observed value. The above equation only needs to estimate the clock error variation of the satellite clock

[0072] By transforming the formula (10), the a posteriori residual of the pseudorange observation value is obtained as follows:

[0073]

[0074] It can be seen from the above equation that if there is a gross error in the pseudorange observation value of the current epoch, the a posteriori residual will deteriorate accordingly

[0075] In one example, three times the accuracy of the pseudorange observation value is taken as the threshold for the occurrence of gross errors. That is,

[0076]

[0077] In the formula, ρ represents the accuracy of the pseudorange observation value. When the a posteriori residual exceeds 3σ, it is considered that there is a gross error in the pseudorange observation value and it is excluded, otherwise it is considered that there is no gross error in the pseudorange observation value. In this example, the predetermined coefficient is 3. In other examples, the predetermined coefficient can be other values

[0078] This method is equivalent to performing short baseline analysis with known positions. The double difference residuals can accurately reflect the error situation of the observed values, and can effectively exclude the gross errors existing in the pseudorange observation values

[0079] More specifically, the a posteriori residual of the carrier observation value is calculated according to the following formula

[0080] where c is the speed of light, is the clock error variation of the satellite clock, ρ is the satellite-earth distance between the satellite and the satellite signal receiver, is the satellite-earth distance between the previous and subsequent epochs, λ represents the circumference of the carrier observation value, represents the carrier observation value in units of weeks

[0081] The derivation process and principle of the formula (11) are as follows

[0082] The carrier observation value is in units of weeks. The gross error in the carrier observation value is called a cycle slip. The method of cycle slip detection also utilizes the characteristic of high relative position accuracy between INS epochs. Through the double difference between epochs, it is determined whether there is a cycle slip.

[0083] The single carrier observation equation is as follows:

[0084]

[0085] In the formula, λ represents the circumference of the carrier observation value, represents the carrier observation value in units of weeks, ρ represents the satellite-earth distance between the satellite and the receiving end, Ion represents the ionospheric delay error, Trop represents the tropospheric delay error, N represents the integer cycle ambiguity in the carrier in units of weeks, cdt i represents the clock error of the receiving end, cdt j represents the clock error of the satellite end, and ε represents the random error of the observation value.

[0086] First, perform an inter-satellite difference on the carrier observation value to obtain an inter-satellite single difference

[0087]

[0088] Then, perform a difference between epochs. Since the integer cycle ambiguity values of the previous and subsequent epochs are the same, when performing the difference between epochs, the parameter of the integer cycle ambiguity is eliminated, and the result is as follows:

[0089]

[0090] Since the ionospheric and tropospheric errors after the double difference are greatly weakened and can be ignored, the simplified equation (14) is as follows:

[0091]

[0092] Similarly, the relative position between epochs provided by INS can be considered as the true value, and the satellite-earth distance between the previous and subsequent epochs can be calculated according to the position in the INS navigation result The above equation only needs to estimate the change amount of the clock error of the satellite clock

[0093] By transforming the formula (15), the a posteriori residual equation of the carrier observation value is obtained as follows,

[0094]

[0095] In the above equation, according to the a posteriori residuals of the carrier observations, it can be determined whether there are gross errors or cycle slips in the carrier observations. If there is a cycle slip in the carrier observations at the current epoch, the integer ambiguity value between epochs will change, and this result will also be reflected in the a posteriori residuals of the carrier.

[0096] Similarly, in one example, three times the accuracy of the carrier observations is taken as the threshold for the occurrence of cycle slips. That is,

[0097]

[0098] In the formula, σ represents the accuracy of the carrier observations. When the a posteriori residuals exceed 3σ, it is considered that a cycle slip has occurred in the carrier observations and they are removed. Otherwise, it is considered that no cycle slip has occurred in the carrier observations. In this example, the predetermined coefficient is 3. In other examples, the predetermined coefficient can be other values.

[0099] Step 240: Determine whether the observation environment is poor or the movement change of the carrier is large. If so, that is, the observation environment is poor or the movement change of the carrier is large, go to step 250. If not, that is, the observation environment is good and the movement change of the carrier is small, then go to step 270 and enter the conventional GNSS navigation.

[0100] The prediction model of the Kalman filter is a motion prediction model designed according to Newton's laws of motion. The speed and position in the parameters are the instantaneous results of the previous epoch, so the motion state of the receiver cannot be accurately described. To express the inaccuracy brought by the motion model, the prediction error includes process noise. When the speed of the previous epoch is inaccurate or the movement change between carrier epochs is too large, at this time, the accuracy of the prediction model of the Kalman filter will be greatly reduced. If the process noise is less than the error of the prediction model, it may lead to abnormal filtering or even divergence. Therefore, steps 240 and 250 are added in the present invention.

[0101] Wherein the carrier is a device carrying the INS navigation terminal 110 and the GNSS navigation terminal 120. In other words, the INS navigation terminal 110 and the GNSS navigation terminal 120 are arranged on the same carrier. The observation environment is judged by the rejection rate of the observations, and the movement change of the carrier is judged by the change amount of the heading between the previous and current epochs.

[0102] In one embodiment, if the rejection rate of the observations is higher than the predetermined rejection threshold, it is considered that the observation environment is poor. Otherwise, it is considered that the observation environment is good.

[0103] First, define the ratio of the rejected observations in the total observations as the rejection rate. Generally, the better the observation environment, the higher the accuracy of the observations, and the smaller the probability of observations with gross errors. The more observations are rejected, the worse the observation environment, and the less reliable the calculated result.

[0104] The mathematical expression of the rejection rate of observations is as follows:

[0105]

[0106] In the formula, α represents the rejection rate of observations, f1 represents the number of rejected observations, and f represents the total number of observations.

[0107] In an example, the predetermined rejection threshold is 0.3, that is, when α exceeds 0.3, it can be considered that the observation environment is poor, otherwise it is considered that the observation environment is good. Of course, the predetermined rejection threshold can also be other values.

[0108] Therefore, when the observation environment is poor, the INS navigation result can be used for motion prediction in Kalman filtering, rather than the GNSS navigation result of the previous epoch for motion prediction in Kalman filtering. The motion prediction in Kalman filtering corresponds to step 270.

[0109] In actual operation, it is usually only necessary to judge the degree of change in the movement of the carrier according to the change in the heading. If the change amount of the heading between the previous and current epochs exceeds the predetermined change threshold, it is considered that the movement of the carrier changes greatly, otherwise, it is considered that the movement of the carrier changes slightly, where the change amount of the heading between the previous and current epochs is calculated according to the attitude in the INS navigation result.

[0110] The change in the heading of the carrier between the previous and current epochs is as follows:

[0111] ΔJ = J k+1 -J k

[0112] In the formula, ΔJ represents the change amount of the heading between the previous and current epochs, J k+1 represents the heading value of the current epoch, and J k represents the heading value of the previous epoch. When the absolute value of the change amount of the heading between the previous and current epochs exceeds the predetermined change threshold, such as 30 degrees, it is considered that the movement of the carrier changes greatly at this time.

[0113] When the movement of the carrier changes greatly, that is, when the attitude changes greatly, the motion prediction is performed according to the speed of the previous epoch, and its prediction error will be much larger than the process error in the state update model. At this time, the INS navigation result can be used for motion prediction in Kalman filtering.

[0114] Of course, in some embodiments, step 240 may not be set, and after step 230, the GNSS navigation method 200 directly jumps to step 250.

[0115] Step 250: Calculate the predicted value of the current epoch parameter based on the INS navigation result, and calculate the prediction error of the predicted value of the current epoch parameter based on the estimation error of the estimated value of the previous epoch parameter.

[0116] As described above, in the case where the observation environment is poor or the carrier motion changes greatly, the motion prediction in step 270 may be inaccurate and unreliable. Therefore, step 250 is adopted in the present invention to replace step 270.

[0117] In one embodiment, calculating the predicted value of the current epoch parameter based on the INS navigation result includes: calculating the INS average speed during the period from the previous epoch to the current epoch based on the speed in the INS navigation result, and calculating the predicted value of the current epoch position based on the INS average speed and the time difference between the previous epoch and the current epoch; using the speed of the current epoch in the INS navigation result to replace the predicted value of the current epoch speed.

[0118] The following formula is used to calculate the INS average speed during the period from the previous epoch to the current epoch:

[0119]

[0120] In the formula, represents the calculated INS average speed, V k+1 represents the INS speed of the current epoch, V k represents the INS speed of the previous epoch.

[0121] Calculate the predicted value of the current epoch position based on the INS average speed and the time difference between the previous epoch and the current epoch:

[0122]

[0123] In the formula, S k+1,k represents the position of the current epoch predicted according to the INS average speed, corresponding to the three-dimensional coordinates of (X, Y, Z). dt is the time difference between epochs. It can be seen from this formula that using the average speed for state update is equivalent to using the trapezoidal area method to calculate the integral of the speed from the previous epoch to the current epoch, which can accurately describe the motion model of the carrier.

[0124] The specific method for calculating the prediction error of the predicted value of the current epoch parameter based on the estimation error of the estimated value of the previous epoch parameter in step 250 still adopts the corresponding specific calculation method in step 270, which will not be repeated here.

[0125] Figure 3 This is a structural block diagram of the INS navigation terminal 110 in an embodiment of the present invention. In addition to the I / O interface, the INS navigation terminal 110 further includes an inertial measurement unit 112, an inertial navigation module 113, and a combined navigation module 114.

[0126] Figure 4 This is a schematic flowchart of the INS navigation method 300 executed by the INS navigation terminal 110 in an embodiment of the present invention. As Figure 3 shown, the INS navigation method 300 includes the following steps.

[0127] Step 310, the inertial measurement unit 112 acquires inertial measurement data, corrects the inertial measurement data based on the sensor error obtained by feedback to obtain corrected inertial measurement data, and outputs the corrected or uncorrected inertial measurement data.

[0128] Step 320, the inertial navigation module 113 calculates the attitude, velocity, and position based on the inertial measurement data output by the inertial measurement unit, corrects the calculated attitude, velocity, and position based on the state error obtained by feedback to obtain corrected attitude, velocity, and position, and outputs the corrected or uncorrected attitude, velocity, and position.

[0129] Step 330, the combined navigation module 114 performs combined navigation based on the attitude, velocity, and position output by the inertial navigation module and the GNSS navigation result to obtain the INS navigation result, sensor error, and state error, feeds the sensor error back to the inertial measurement unit 112, and feeds the state error back to the inertial navigation module 113. The INS navigation result includes one or more of attitude, velocity, position, and time.

[0130] In an embodiment, the update frequency of the GNSS navigation result is lower than the update frequency of the INS navigation result. The update frequency of the INS navigation result can generally reach 100 hz or even higher, and the update frequency of the GNSS navigation result is lower, generally 1 - 10 hz.

[0131] Due to the difference in the update frequencies of the two sets of data, the integrated navigation algorithm and the inertial navigation algorithm are two independent tasks. After the integrated navigation algorithm is solved, the sensor error and the state error are output to the inertial measurement unit 112 and the inertial navigation module 113. Generally, the sensor error and the state error are relatively stable in a short period of time and do not need to be updated frequently. When receiving the GNSS navigation result, the integrated navigation module 113 performs integrated navigation based on the attitude, velocity, and position output by the inertial navigation module and the GNSS navigation result to obtain the INS navigation result, the sensor error, and the state error. When not receiving the GNSS navigation result, the integrated navigation module 113 directly outputs the attitude, velocity, and position output by the inertial navigation module 112 as the INS navigation result.

[0132] When receiving the sensor error feedback from the integrated navigation module 113, the inertial measurement unit 112 corrects the inertial measurement data based on the sensor error obtained from the feedback to obtain the corrected inertial measurement data. When not receiving the sensor error feedback from the integrated navigation module, the inertial measurement unit 112 corrects the inertial measurement data based on the historical sensor error obtained from the feedback or does not correct the inertial measurement data. The sensor error is relatively stable in a short period of time, and there are significant differences in the errors of different sensors. Therefore, the available time length of the historical sensor error is related to the characteristics of the sensor. When receiving the state error feedback from the integrated navigation module 113, the inertial navigation module 112 corrects the calculated attitude, velocity, and position based on the state error obtained from the feedback. When not receiving the state error feedback from the integrated navigation module 113, the inertial navigation module 112 corrects the calculated attitude, velocity, and position based on the historical state error obtained from the feedback, or does not correct the calculated attitude, velocity, and position. Similarly, the state error is relatively stable in a short period of time. Therefore, the available time length of the historical state error is related to the characteristics of the sensor.

[0133] Before step 310, the INS navigation method 300 further includes the following step: performing the initialization work of the INS navigation terminal 110.

[0134] The initialization process is a process in which the INS navigation terminal 110 determines the initial position, velocity, and attitude of the INS navigation terminal 110 based on the GNSS navigation results output by the GNSS navigation terminal 120. This process is a rough process and does not require a very high accuracy of the initialization results. Since the initialization of the INS navigation terminal 110 requires the application of the GNSS navigation results, it is included in the integrated navigation algorithm. When the INS navigation terminal 110 has not completed initialization, only the initialization work is carried out. After initialization is completed, the subsequent steps 310, 320, and 330 are performed. After initialization is completed, the initialization work is no longer executed, unless the GNSS navigation terminal 120 is locked out for a long time, resulting in a large attitude deviation in the INS navigation results.

[0135] In steps 310 and 320, after obtaining the inertial measurement data (specific force and angular velocity), attitude update, specific force conversion, velocity update, and position update are performed. Since this part of the algorithm is relatively mature, it will not be elaborated here.

[0136] Since the vehicle coordinate system and the navigation coordinate system are determined based on information such as the position and attitude of the vehicle, there must be certain errors. In addition, after the INS navigation terminal 110 completes initialization, there must also be a certain accuracy. These factors will all cause certain errors in the results of the navigation algorithm. When there is a state error feedback of the integrated navigation algorithm, corrections are made to the attitude, position, velocity, and other information of the navigation results; when there is no state error feedback of the integrated navigation algorithm, historical feedback information is used for correction or no correction is made.

[0137] The integrated navigation algorithm in step 330 is only performed when the RTK navigation results are updated. Usually, the update frequency of the INS navigation results is relatively high, generally up to 100 Hz or even higher. The update frequency of the RTK navigation results is relatively low, generally 1 - 10 Hz. Due to the difference in the frequencies of the two sets of data, the integrated navigation algorithm and the inertial navigation algorithm are two independent tasks. After the integrated navigation algorithm is solved, the feedback information is output to the inertial navigation part in step 320, and the inertial navigation uses the error feedback according to the situation. Generally, the sensor errors and state errors are relatively stable in a short period of time and do not require frequent updates. Therefore, the integrated navigation plays a role in correcting the raw data errors and state parameter errors of the inertial navigation algorithm, and the result of the inertial navigation algorithm is the result output by the INS.

[0138] The integrated navigation module 114 adopts an integrated navigation algorithm. The integrated navigation algorithm uses Kalman filtering to fuse the GNSS navigation results and the navigation results of the inertial navigation algorithm. In the state update model, the parameters estimated by the integrated navigation algorithm are as follows:

[0139]

[0140] Wherein, δr represents the INS position error, δv represents the INS velocity error, φ represents the INS attitude error, b g represents the angular velocity zero bias, b a represents the acceleration zero bias. All parameters are vectors including the X, Y, and Z axes in the coordinate system.

[0141] In the observation equation, the observation value of the integrated navigation is:

[0142] r INS = r RTK + δ RTK-INS

[0143] Wherein, r INS represents the position and velocity information of the INS, r RTK represents the position and velocity information of the GNSS, δ RTK-INS represents the total error of the INS and the GNSS.

[0144] Preferably, the GNSS navigation terminal is an RTK navigation terminal, and the GNSS navigation is RTK navigation. The present invention is based on a loose combination of physical fusion mode, making full use of the relevant information of the RTK navigation terminal and the INS navigation terminal to improve the performance and reliability of the integrated navigation system. The principle is as follows: The RTK navigation terminal and the INS navigation terminal are connected through a physical interface, and the systems are independent of each other, ensuring the reliability of the overall system. Different from the traditional loose combination that only requires the INS navigation terminal to receive the calculation result (i.e., the RTK navigation result) of the RTK navigation terminal, the present invention requires two-way communication between the RTK navigation terminal and the INS navigation terminal, that is, not only does the INS navigation terminal use the calculation result of the RTK navigation terminal for integrated navigation, but also the RTK navigation terminal uses the calculation result of the INS navigation terminal for calculation. This fusion mode retains the physical fusion mode of the loose combination, and uses the calculation result of the INS navigation terminal to assist RTK calculation to improve performance, and at the same time can realize the plug-and-play function. In the plug-and-play function, there are two cases: First, when the RTK navigation terminal is not inserted into the INS navigation terminal, only normal RTK calculation is performed; Second, when the RTK navigation terminal is inserted into the INS navigation terminal, the RTK navigation terminal and the INS navigation terminal communicate with each other through a physical connection to realize the integrated navigation of the two systems of the RTK navigation terminal and the INS navigation terminal. When the RTK navigation terminal receives the calculation result of the INS navigation terminal, the calculation result of the INS navigation terminal is used for two purposes. One is to detect the quality of GNSS raw observation data according to the high short-term prediction accuracy of the INS; the other is to compensate the inaccurate RTK speed with the high-precision INS speed, which can effectively improve the accuracy of the prediction model of the RTK navigation terminal. Through the above fusion mode, the reliability of the loose combination can be effectively inherited, the plug-and-play function of the INS navigation terminal can be realized, the calculation result of the INS navigation terminal is used to improve the data preprocessing (observation value selection) and the accuracy of the prediction model of the RTK navigation terminal, and the navigation accuracy and reliability of the RTK navigation terminal can be effectively improved. When the INS navigation terminal is inserted, the INS navigation terminal performs integrated navigation calculation according to the real-time calculation result of the RTK navigation terminal, and corrects the original data error and state parameter error of the INS navigation terminal in real time to prevent the error accumulation of the INS navigation terminal from causing the calculation error to increase continuously.

[0145] Compared with the traditional RTK / INS combination scheme, the combination scheme in the present invention has the following advantages: 1. The RTK navigation terminal and the INS navigation terminal are independent of each other, and the plug-and-play function is realized through a physical interface, ensuring the stability and reliability of the system; 2. The real-time INS solution result (i.e., the INS navigation result) is used for RTK solution. By utilizing the high position accuracy of the INS at adjacent epochs, the correctness of pseudorange gross error detection and carrier cycle slip detection is improved, ensuring the accuracy of the observation model in filtering; 3. By utilizing the high velocity accuracy of the INS, the average velocity between INS epochs is calculated to replace the unreliable RTK velocity, improving the accuracy of the prediction model; 4. The solution result provided by the INS navigation terminal is used for data preprocessing and state model of the RTK navigation terminal, improving the performance and reliability of the RTK navigation terminal without affecting the RTK navigation terminal, ensuring the stability and reliability of the RTK navigation terminal during operation. 5. The INS navigation terminal performs integrated navigation solution based on the solution result (RTK navigation result) of the RTK navigation terminal. According to the original data and state parameter correction information calculated by the integrated navigation, it is used for INS solution to correct the INS solution result in real time, ensuring the overall performance, stability and reliability of the INS navigation terminal.

[0146] According to another aspect of the present invention, the present invention provides a computing device, which includes a processor and a memory. Program instructions are stored in the memory, and these program instructions are executed by the processor to implement the above GNSS navigation method 200.

[0147] According to still another aspect of the present invention, the present invention provides a storage medium, in which program instructions are stored, and these program instructions are executed to implement the above GNSS navigation method 200.

[0148] In this document, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion. In addition to the listed elements, it may also include other elements not specifically listed.

[0149] In this document, the front, back, up, down and other orientation words are defined based on the positions of the components in the drawings and the positions of the components relative to each other, only for the sake of clarity and convenience in expressing the technical solution. It should be understood that the use of the orientation words should not limit the scope of protection requested by this application.

[0150] Without conflict, the above embodiments and the features in the embodiments in this document can be combined with each other.

[0151] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A GNSS navigation method, characterized in that, When the INS navigation result is received and available, it includes: Selecting valid observations based on a basic rejection scheme and an auxiliary rejection scheme, where the auxiliary rejection scheme depends on the INS navigation result; Calculating the predicted value of the current epoch parameters based on the INS navigation result, and calculating the prediction error of the predicted value of the current epoch parameters based on the estimation error of the estimated value of the previous epoch parameters; Calculating the floating-point solution of the estimated value of the current epoch parameters according to the selected valid observations and the predicted value of the current epoch parameters, and calculating the estimation error of the floating-point solution of the estimated value of the current epoch parameters based on the prediction error of the predicted value of the current epoch parameters; and Performing integer ambiguity fixing according to the floating-point solution of the estimated value of the current epoch parameters and its estimation error to obtain the fixed solution of the estimated value of the current epoch parameters and its estimation error, where the GNSS navigation result includes time, the floating-point solution or fixed solution of the estimated value of the current epoch parameters and its estimation error, and the parameters include one or more of speed and position; The observations include pseudorange observations, carrier observations, and Doppler observations; The basic rejection scheme is: according to the distribution of the residuals of the observations among the residuals of all observations, rejecting the observations that do not satisfy the probability distribution; The auxiliary rejection scheme is: calculating the satellite-earth distance between the previous and current epochs according to the position in the INS navigation result; calculating the a posteriori residual of the pseudorange observation according to the satellite-earth distance between the previous and current epochs. If the a posteriori residual of the pseudorange observation is greater than the product of the accuracy of the pseudorange observation and a predetermined coefficient, it is considered that the pseudorange observation has a gross error and needs to be rejected, otherwise the pseudorange observation is considered valid; calculating the a posteriori residual of the carrier observation according to the satellite-earth distance between the previous and current epochs. If the a posteriori residual of the carrier observation is greater than the product of the accuracy of the carrier observation and a predetermined coefficient, it is considered that the carrier observation has a cycle slip and needs to be rejected, otherwise the carrier observation is considered valid.

2. The GNSS navigation method according to claim 1, characterized in that, When the INS navigation result is not received or the INS navigation result is unavailable, it further includes: Selecting valid observations based on the basic rejection scheme; Calculating the predicted value of the current epoch parameters according to the estimated value of the previous epoch parameters, and calculating the prediction error of the predicted value of the current epoch parameters based on the estimation error of the estimated value of the previous epoch parameters; Calculating the floating-point solution of the estimated value of the current epoch parameters according to the selected valid observations and the predicted value of the current epoch parameters, and calculating the estimation error of the floating-point solution of the estimated value of the current epoch parameters based on the prediction error of the predicted value of the current epoch parameters; and Performing integer ambiguity fixing according to the floating-point solution of the estimated value of the current epoch parameters and its estimation error to obtain the fixed solution of the estimated value of the current epoch parameters and its estimation error.

3. The GNSS navigation method according to claim 1, characterized in that, When the INS navigation result is received and available, the GNSS navigation method further includes: Judging whether the observation environment is poor or the carrier motion change is large. If so, that is, the observation environment is poor or the carrier motion change is large, then calculate the predicted value of the current epoch parameters based on the INS navigation result and perform subsequent operations; If the answer is no, i.e., the observation environment is good and the carrier motion change is small, calculate the predicted value of the current epoch parameters based on the estimated value of the previous epoch parameters, and perform subsequent operations. If the rejection rate of the observation values is higher than the predetermined rejection threshold, it is considered that the observation environment is poor; otherwise, it is considered that the observation environment is good. If the change in the heading between the previous and current epochs exceeds the predetermined change threshold, it is considered that the carrier motion change is large; otherwise, it is considered that the carrier motion change is small, where the change in the heading between the previous and current epochs is calculated based on the attitude in the INS navigation result. The INS navigation result includes an availability flag, and based on this flag, it is determined whether the INS navigation result is available. The rejection rate of the observation values is the ratio of the number of rejected observation values to the total number of observation values.

4. The GNSS navigation method according to claim 1, characterized in that, The calculation of the predicted value of the current epoch parameters based on the INS navigation result includes: Calculate the INS average velocity from the previous epoch to the current epoch based on the velocity in the INS navigation result, and calculate the predicted value of the current epoch position based on the INS average velocity and the time difference between the previous and current epochs. Use the velocity of the current epoch in the INS navigation result to replace the predicted value of the current epoch velocity.

5. The GNSS navigation method according to claim 1, characterized in that, Selecting valid observation values based on the basic rejection scheme and the auxiliary rejection scheme based on the INS navigation result includes: Selecting valid pseudorange observation values based on the basic rejection scheme and the auxiliary rejection scheme. Selecting valid carrier observation values based on the basic rejection scheme and the auxiliary rejection scheme; and Selecting valid Doppler observation values based on the basic rejection scheme.

6. A GNSS navigation terminal, which receives the INS navigation result of an INS navigation terminal, characterized in that, When the INS navigation result is received and the INS navigation result is available, the GNSS navigation terminal performs the following operations: Select valid observation values based on the basic rejection scheme and the auxiliary rejection scheme, where the auxiliary rejection scheme depends on the INS navigation result. Calculate the predicted value of the current epoch parameters based on the INS navigation result, and calculate the prediction error of the predicted value of the current epoch parameters based on the estimation error of the estimated value of the previous epoch parameters. Calculate the floating-point solution of the estimated value of the current epoch parameters based on the selected valid observation values and the predicted value of the current epoch parameters, and calculate the estimation error of the floating-point solution of the estimated value of the current epoch parameters based on the prediction error of the predicted value of the current epoch parameters; and Perform integer ambiguity resolution based on the floating-point solution of the estimated value of the current epoch parameters and its estimation error to obtain the fixed solution of the estimated value of the current epoch parameters and its estimation error, where the GNSS navigation result includes time, the floating-point solution or fixed solution of the estimated value of the current epoch parameters and its estimation error, and the parameters include one or more of velocity and position. The observation values include pseudorange observation values, carrier observation values, and Doppler observation values. The basic rejection scheme is: according to the distribution of the residuals of the observation values among the residuals of all observation values, reject the observation values that do not satisfy the probability distribution. The auxiliary rejection scheme is as follows: calculate the satellite-earth distance between the previous and current epochs based on the position in the INS navigation result; calculate the a posteriori residual of the pseudorange observation value based on the satellite-earth distance between the previous and current epochs. If the a posteriori residual of the pseudorange observation value is greater than the product of the accuracy of the pseudorange observation value and a predetermined coefficient, it is considered that the pseudorange observation value has a gross error and needs to be rejected. Otherwise, it is considered that the pseudorange observation value is valid; calculate the a posteriori residual of the carrier observation value based on the satellite-earth distance between the previous and current epochs. If the a posteriori residual of the carrier observation value is greater than the product of the accuracy of the carrier observation value and a predetermined coefficient, it is considered that the carrier observation value has a cycle slip and needs to be rejected. Otherwise, it is considered that the carrier observation value is valid.

7. The GNSS navigation terminal according to claim 6, wherein, When the INS navigation result is not received or the INS navigation result is unavailable, the GNSS navigation terminal performs the following operations: Select valid observations based on the basic rejection scheme; Calculate the predicted value of the current epoch parameter based on the estimated value of the previous epoch parameter, and calculate the prediction error of the predicted value of the current epoch parameter based on the estimation error of the estimated value of the previous epoch parameter; Calculate the floating-point solution of the estimated value of the current epoch parameter based on the selected valid observations and the predicted value of the current epoch parameter, and calculate the estimation error of the floating-point solution of the estimated value of the current epoch parameter based on the prediction error of the predicted value of the current epoch parameter; and Perform integer ambiguity resolution based on the floating-point solution of the estimated value of the current epoch parameter and its estimation error to obtain the fixed solution of the estimated value of the current epoch parameter and its estimation error.

8. The GNSS navigation terminal according to claim 6, wherein, When the INS navigation result is received and the INS navigation result is available, the GNSS navigation terminal also performs the following operations: Judge whether the observation environment is poor or the change in the carrier motion is large. If so, that is, the observation environment is poor or the change in the carrier motion is large, then calculate the predicted value of the current epoch parameter based on the INS navigation result and perform subsequent operations; If not, that is, the observation environment is good and the change in the carrier motion is small, then calculate the predicted value of the current epoch parameter based on the estimated value of the previous epoch parameter and perform subsequent operations.

9. The GNSS navigation terminal according to claim 8, wherein, If the rejection rate of the observations is higher than a predetermined rejection threshold, it is considered that the observation environment is poor. Otherwise, it is considered that the observation environment is good; If the change in the heading between the previous and current epochs exceeds a predetermined change threshold, it is considered that the change in the carrier motion is large. Otherwise, it is considered that the change in the carrier motion is small, where the change in the heading between the previous and current epochs is calculated based on the attitude in the INS navigation result. The INS navigation result includes an availability flag, and it is determined whether the INS navigation result is available based on the flag. The rejection rate of the observations is the ratio of the number of rejected observations to the total number of observations.

10. The GNSS navigation terminal according to claim 6, wherein, The calculation of the predicted value of the current epoch parameter based on the INS navigation result includes: Calculate the INS average speed from the previous epoch to the current epoch based on the speed in the INS navigation result, and calculate the predicted value of the current epoch position based on the INS average speed and the time difference between the previous and current epochs; Use the speed of the current epoch in the INS navigation result to replace the predicted value of the current epoch speed.

11. The GNSS navigation terminal according to claim 6, wherein, Selecting valid observations based on the basic rejection scheme and the auxiliary rejection scheme based on the INS navigation result includes: Selecting valid pseudorange observations based on the basic rejection scheme and the auxiliary rejection scheme; Selecting valid carrier observations based on the basic rejection scheme and the auxiliary rejection scheme; and Selecting valid Doppler observations based on the basic rejection scheme.

12. The GNSS navigation terminal according to claim 11, wherein, Calculate the a posteriori residual of the pseudorange observation according to the following formula :[[-]] In the formula Among them, ρ is the satellite-ground distance between the satellite and the satellite signal receiver, (X s , Y s , Z s ) respectively represent the three-dimensional position of the satellite in the coordinate system, (X r , Y r , Z r ) respectively represent the three-dimensional position of the receiver in the coordinate system, where c is the speed of light, is the clock error variation of the satellite clock, is the satellite-earth distance between two consecutive epochs, P represents the pseudorange observation, is the double-difference pseudorange observation of the pseudorange observation; Calculate the a posteriori residual of the carrier observation according to the following formula : where λ represents the wavelength of the carrier observation, representing the carrier observation in cycles.

13. A combined navigation system, characterized in that, It includes: INS navigation terminal; A GNSS navigation terminal connected to the INS navigation terminal, wherein the GNSS navigation terminal performs GNSS navigation to obtain a GNSS navigation result, and transmits the GNSS navigation result to the INS navigation terminal. The INS navigation terminal performs INS navigation based on the GNSS navigation result to obtain an INS navigation result, and transmits the INS navigation result to the GNSS navigation terminal; The GNSS navigation terminal is the GNSS navigation terminal according to any one of claims 6-12.

14. The combined navigation system according to claim 13, characterized in that, The INS navigation terminal includes: An inertial measurement unit that acquires inertial measurement data, corrects the inertial measurement data based on the sensor error obtained by feedback to obtain corrected inertial measurement data, and outputs the corrected or uncorrected inertial measurement data; An inertial navigation module that calculates attitude, velocity, and position based on the inertial measurement data output by the inertial measurement unit, and corrects the calculated attitude, velocity, and position based on the state error obtained by feedback to obtain corrected attitude, velocity, and position, and outputs the corrected or uncorrected attitude, velocity, and position; A combined navigation module that performs combined navigation based on the attitude, velocity, and position output by the inertial navigation module and the GNSS navigation result to obtain an INS navigation result, a sensor error, and a state error, and feeds back the sensor error to the inertial measurement unit and the state error to the inertial navigation module. The INS navigation result includes one or more of attitude, velocity, position, and time.

15. The combined navigation system according to claim 14, characterized in that, The update frequency of the GNSS navigation result is lower than the update frequency of the INS navigation result. When receiving the GNSS navigation result, the combined navigation module performs combined navigation based on the attitude, velocity, and position output by the inertial navigation module and the GNSS navigation result to obtain an INS navigation result, a sensor error, and a state error, When the GNSS navigation result is not received, the combined navigation module directly outputs the attitude, velocity, and position output by the inertial navigation module as the INS navigation result.

16. The combined navigation system according to claim 14, characterized in that, When receiving the sensor error feedback from the combined navigation module, the inertial measurement unit corrects the inertial measurement data based on the sensor error obtained by feedback to obtain corrected inertial measurement data. When not receiving the sensor error feedback from the combined navigation module, the inertial measurement unit corrects the inertial measurement data based on the historical sensor error obtained by feedback or does not correct the inertial measurement data; When receiving the state error feedback from the integrated navigation module, the inertial navigation module corrects the calculated attitude, velocity, and position based on the state error obtained from the feedback. When not receiving the state error feedback from the integrated navigation module, the inertial navigation module corrects the calculated attitude, velocity, and position based on the historical state error obtained from the feedback, or does not correct the calculated attitude, velocity, and position.

17. A storage medium, in which program instructions are stored, and the program instructions are executed to implement the GNSS navigation method according to any one of claims 1-5.

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