A Dual PVT Calculation Method with Redundant Backup between Beidou B1I and B3I Signals

Abstract

The present invention relates to a dual PVT calculation method in which Beidou B1I and B3I signals are mutually redundant backups, belonging to the field of satellite navigation technology. This method improves stability and real-time performance by setting an additional least squares filter and Kalman filter, and ensures the consistency of the system state and reduces the computing power consumption caused by dual calculations by reasonably designing the state quantities and other system parameters that can be reused between the two filters.

Description

Technical Field

[0001] The present invention belongs to the technical field of satellite navigation, and relates to a dual PVT calculation method in which the Beidou B1I and B3I signals are mutually redundant backups. Background Art

[0002] The open service signal B3I of the Beidou satellite navigation system is a ranging signal in the B3 frequency band broadcast by Beidou-2 and Beidou-3 satellites. It, together with the B1I and B2I open service signals, constitutes the "three-frequency service" signal system of Beidou. The interface control document (ICD) of B3I was officially released on the Beidou official website in February 2018. It is noted in the Beidou ICD that the code length of B3I is 10230, while the code length of B1I is 2046. Therefore, directly capturing B3I will significantly consume more baseband resources. The carriers, pseudo-codes, and navigation data of the B3I and B1I signals broadcast by the same satellite have the same starting point. Therefore, software algorithms usually utilize the coherent characteristics of the two signals to achieve aided acquisition of the B3I signal with a 5-fold code length, so as to reduce the time consumption of direct capture of B3I. For dual-frequency users, the functions of B3I are mainly reflected in: 1) serving as a redundant backup for the B1I signal; 2) using the dual-frequency ionospheric-free combination method to correct the ionospheric delay effect and improve the positioning accuracy.

[0003] Currently, the PVT algorithm usually selects the raw observables generated by one of the B1I or B3I signals according to the user interface and enters the solution process. One defect of this method is that since B1I and B3I occupy different tracking channels and their respective integration completion (dump) timestamps are different, in the case of no dump time synchronization, when switching between the B1 / B3 positioning modes, the pseudo-range observables generated by B3 and the pseudo-range observables generated by B1 will have a large difference in value due to different timestamps, resulting in a poor coincidence between the predicted observation value and the actual observation value of the Kalman filter. The system tends to misjudge the newly incoming observables as incorrect observables and reject them, resulting in a significant reduction in the number of satellites used for filter solution and causing accuracy loss (that is, the complete replacement of B3I will cause the system state to be disordered). At the same time, when the B1 frequency band is significantly interfered with and the B3 frequency band is intact, due to the lag of the single KF filter RAIM algorithm in determining the faulty satellite, it is very easy for the output result error of the KF filter to be too large in one or some time elements, and the (normal) B3I observables do not form a replacement in time.

[0004] Therefore, there is an urgent need for a dual PVT algorithm in which the Beidou B1I and B3I signals are mutually redundant backups to solve the above-mentioned stability problem and real-time problem. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a dual PVT (Position, Velocity and Time) calculation method in which Beidou B1I and B3I signals are mutually redundant backups, by setting an additional least squares filter and a Kalman filter to solve the stability problem and real-time problem in the prior art, and by reasonably designing the reusable state quantities and other system parameters between the two filters to ensure the consistency of the system state and reduce the computing power consumption caused by double calculation.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A dual PVT (Position, Velocity and Time) calculation method in which Beidou B1I and B3I signals are mutually redundant backups, specifically including the following steps:

[0008] S1: Define two sets of Kalman filters KF B1 、KF B3 , and define state quantities Var B1 、Var B3 respectively in the filters according to the PVA or PV model; where KF B1 、KF B3 are respectively used to process the raw observations from the B1I signal and the raw observations from the B3I signal;

[0009] S2: Set a B3I acquisition mechanism in the baseband part that combines direct acquisition of B3I with frequency point traction of B1I to acquire B3I;

[0010] S3: Independently demodulate the B3I and B1I message data, perform sub-frame synchronization code search and BCH check on the demodulated data, and assemble them into D1 / D2 data frames. Before the new sub-frame of the B3I signal is passed into the PVT module to update the ephemeris information, poll the B1I tracking channels. If the satellite corresponding to B3I has entered the sub-frame synchronization state in the corresponding channel of B1I, then do not pass the B3I data frame into the PVT module;

[0011] S4: The PVT module receives the B1I and B3I raw observation information transmitted from the baseband, including pseudorange, (phase) Doppler, carrier-to-noise ratio, satellite transmission time, etc.;

[0012] S5: Before the observations at any frequency point enable the system to perform the first positioning, take the observations with more satellites, calculate the mean value of the positions of all satellites, use this mean value as a rough estimate of the user's current position, and bring it into the least squares filters of B1I and B3I as the iterative starting point for position calculation;

[0013] S6: Perform least squares filtering on the B1I observables and B3I observables respectively. If both output the first positioning information at the same time epoch, transmit the positioning information to the corresponding Kalman filters respectively to initialize the state variables. If one of the least squares filters outputs the first positioning result earlier than the other least squares filter, transmit the first positioning result to the two Kalman filters KF B1 、KF B3 to initialize all state variables;

[0014] S7: Divide the clock offset of the first solution result by the speed of light, add it to the current local system time, and adjust the baseband PPS circuit. At this time, the receiver is in the time service state;

[0015] S8: Configure the positioning mode according to the user interface information; if the user interface does not configure a specific positioning mode, adopt an adaptive method to optimize the PVT results output by KF B1 、KF B3 ;

[0016] S9: Use the satellite-based fault detection and exclusion algorithm (FDE) based on receiver autonomous integrity monitoring (RAIM) to obtain the integrity observables and error observables at the current time epoch, and use the signal correlation between the B1I and B3I signals to achieve cross-assistance of the baseband tracking loop; use the loop parameters of B3I to perform loss-of-lock reacquisition on the B1I signal.

[0017] Furthermore, in step S2, for any Beidou-2 / Beidou-3 satellite, if its B1I signal is successfully captured and enters the stable tracking state, and the B3I signal it broadcasts has not been captured by the B3I direct capture module, then calculate the Doppler shift Dopp B1 and the pseudo-code phase value of the corresponding B3I signal according to the Doppler shift of B1I, B3 and directly open the tracking channel.

[0018] Furthermore, in step S2, the specific method of frequency point traction is as follows: calculate the carrier Doppler shift and carrier NCO frequency control word of B3I according to the ratio of the nominal carrier frequencies of B3I and B1I; calculate the pseudo-code Doppler shift and pseudo-code NCO frequency control word of B3I according to the ratio relationship between the carrier frequency and the pseudo-code frequency; calculate the pseudo-code phase of B3I according to the pseudo-code phase of B1I, and configure the digital front end with the carrier NCO frequency control word, pseudo-code NCO frequency control word and pseudo-code phase and directly open the B3I tracking channel; the calculation formulas used are:

[0019] M B3_code =(f B3_code_nominal -dopp B1 ×f​B3 2 / (f B1 ×M B3_code_nominal ))*2 n / f s

[0020] M B3_carrier =(dopp B1 )×(f B3 / f B1 )×2 n / f s

[0021]

[0022] Among them, M B3_code represents the frequency control word of the B3 pseudo-code NCO, f B3_code_nominal represents the B3I pseudo-code rate, f B3 and f B1 respectively represent the B3I and B1I nominal carrier frequencies, dopp B1 represents the Doppler value of B1I, f s represents the operating frequency of the tracking circuit, n represents the carrier NCO bit width, M B3_code_nominal represents the nominal frequency of the B3I pseudo-code NCO, M B3_carrier represents the frequency control word of the satellite carrier tracking loop, represents the pseudo-code phase value of B1I, L B3_code represents the double B3I code length; dt represents the difference in the timestamp when the integration between the B1I and B3I tracking channels of the same satellite is completed.

[0023] Furthermore, in step S8, when the positioning mode is not configured in the user interface, the adaptive mode is defaultly adopted to optimize the PVT result, specifically including:

[0024] S801: Select the priority as solution valid flag > Doppler residual > number of satellites in view. In this state, the B3I and B1I signals are redundant backups of each other;

[0025] S802: Use the selected PVT result to update the receiver status, specifically including: Since the output system time information will participate in the baseband control inside the navigation receiver, it is necessary to fixedly select the time information output by one of the KF B1 or KF B3 to time the system; at the same time, after the adjustment of the whole second, since the system is in the zero clock offset state, to prevent numerical instability of the Kalman filter, it is necessary to correct the clock offset state variables of KF B1 and KF B3 as follows:

[0026] b nonref =bnonref -b ref

[0027] b ref = 0

[0028] where b ref is the system clock error under the reference time base, and b nonref is the system clock error between any other GNSS time base and the reference time base.

[0029] Furthermore, in step S9, the signal correlation between B1I and B3I signals is used to achieve cross-assistance of the baseband tracking loop, specifically including: at any time element, KF B1 the velocity measurement Doppler residual is re B1 , the set of satellites for solution is SV B1 , KF B3 the velocity measurement Doppler residual is re B3 , the set of satellites for solution is SV B3 , then the following carrier PLL and carrier FLL correction algorithms can be adopted:

[0030] If re B1 < t dopp , SV i ∈ SV B1 , then M B3_carrier = dopp B1 × (f B3 / f B1 ) × 2 n / f s , where t dopp is the preset Doppler residual threshold, SV i is the sub-frame synchronized Beidou satellite in a stable tracking state, M B3_carrier is the frequency control word of the satellite SV i carrier tracking loop, dopp B1 is the Doppler value of B1I, (f B3 / f B1 ) is the ratio of the nominal carrier frequencies of B3I and B1I, n is the carrier NCO bit width, and f s is the operating frequency of the tracking circuit;

[0031] Similarly, if re B3 < t dopp , SV i ∈ SV B3 , then M B1_carrier = (dopp B3 ) × (f B1 / f B3 ) × 2 n / fs , where dopp B3 is the Doppler value of B3I of the same satellite B3I.

[0032] Furthermore, in step S9, the loop parameters of B3I are used to relock and recapture the B1I signal, specifically including: if re B3 <t prange , SV i ∈SV B3 , and the tracking channel loop of the B1I signal of SV i is unlocked, then the loop parameters of B3I are derived by the method of step S2. Due to the time consumption of the dual PVT algorithm program, the loop parameters of B3I calculated by this unlock and recapture algorithm will lag in time. It is necessary to predict the current state of the B3I signal using the carrier Doppler change rate of the B1I signal, calculate the updated loop parameters and turn on the B3I tracking channel; where t prange represents a preset pseudorange residual threshold.

[0033] The beneficial effects of the present invention are as follows: The present invention solves the stability problem and real-time problem of the prior art by setting an additional least squares filter and a Kalman filter; and by reasonably designing the reusable state variables and other system parameters between the two filters, the consistency of the system state is ensured, and the computing power consumption caused by double calculation is reduced. The dual PVT algorithm included in the method of the present invention can make the B1I and B3I signals of Beidou form a more perfect and real-time redundant backup for each other.

[0034] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0036] Figure 1 is a flowchart of a dual PVT calculation method for Beidou B1I and B3I signals to form a redundant backup for each other;

[0037] Figure 2 is a block diagram of the implementation of B3I direct capture combined with B1I traction to capture B3I in the present invention;

[0038] Figure 3 is a dual PVT flowchart of B1I and B3I forming a redundant backup for each other in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0040] See also Figures 1 to 3 , Figure 1 The present invention proposes a dual PVT algorithm for BeiDou B1I and BeiDou B3I signals to serve as redundant backups for each other. Figure 1 As shown, specifically including the following:

[0041] (1) The intermediate frequency (IF) signal output by the receiver's RF first enters the direct acquisition modules of B1I and B3I. These modules perform a three-dimensional search of the IF signal's carrier Doppler, pseudo-code phase, and satellite PRN without any auxiliary information. Because the B3I code length is five times that of the B1I, and given limited hardware resources, the software typically configures multiple rounds of pseudo-code phase searches to complete acquisition, significantly increasing acquisition time. Therefore, the receiver prioritizes capturing the B1I signal, which takes less time.

[0042] To further reduce the total time required to complete a round of acquisition of all satellites' B1I and B3I signals, a frequency-pushing method can be used to bypass the direct acquisition module and directly open the B3I tracking channel for any successfully acquired satellite Svi when its tracking loop is closed and the corresponding B3I signal has not yet been acquired.

[0043] The specific method of frequency pulling is as follows: the carrier Doppler shift and carrier NCO frequency control word of B3I are calculated based on the ratio of the nominal carrier frequencies of B3I and B1I; the pseudo-code Doppler shift and pseudo-code NCO frequency control word of B3I are calculated based on the proportional relationship between the carrier frequency and the pseudo-code frequency; the pseudo-code phase of B3I is calculated based on the pseudo-code phase of B1I, and the carrier NCO frequency control word, pseudo-code NCO frequency control word and pseudo-code phase are used to configure the digital front end and directly open the B3I tracking channel; the calculation formula used is:

[0044] M B3_code =(f B3_code_nominal -dopp B1 ×f B3 2 / (f B1 ×M B3_code_nominal ))*2 n / f s

[0045] M B3_carrier = (dopp B1 ) × (f B3 / f B1 ) × 2 n / f s

[0046]

[0047] Wherein, M B3_code represents the frequency control word of the B3 pseudo-code NCO, f B3_code_nominal represents the B3I pseudo-code rate, f B3 and f B1 respectively represent the B3I and B1I nominal carrier frequencies, dopp B1 represents the Doppler value of B1I, f s represents the operating frequency of the tracking circuit, n represents the carrier NCO bit width, M B3_code_nominal represents the nominal frequency of the B3I pseudo-code NCO, M B3_carrier represents the frequency control word of the satellite carrier tracking loop, represents the pseudo-code phase value of B1I, L B3_code represents the double B3I code length; dt represents the difference in time stamps when the integration between the B1I and B3I tracking channels of the same satellite is completed.

[0048] There are various methods for determining the closure of the tracking loop. For example: 1) The carrier-to-noise ratio CN0 of the signal ≥ 30, in bit synchronization, and the phase difference shown by the carrier PLL is constantly less than 15°; 2) The carrier-to-noise ratio CN0 of the signal ≥ 30, and the signal TOW word is successfully read.

[0049] (2) Since the navigation messages of B1I and B3I are exactly the same, the dual signals broadcast by the same satellite share the same ephemeris. After the receiver is powered on and the signal enters the stable tracking state, the satellite position and velocity (PV), ionospheric, tropospheric correction values, and original observables such as Doppler, pseudorange, and carrier-to-noise ratio calculated using the ephemeris start to be sent to the PVT module at the frequency f configured by the user interface.

[0050] (3) At any solution epoch, the least squares filter and the Kalman filter are respectively used to solve the observables. The functions of the former are: 1) Initialize the state variables of the Kalman filter at the first solution moment; 2) When the Kalman filter diverges and the least squares result is valid, use the least squares result to reset the Kalman filter and output the PVT information generated by the least squares to the user side.

[0051] The Kalman filters in this embodiment all adopt the PVA model, and the set of state variables is {x, y, z, v x , v y, v z , α x , α y , α z ,, cd}, and their corresponding meanings are the xyz-axis coordinates, xyz-axis velocities, xyz-axis accelerations, clock error vectors (including the system clock error and the clock errors between other satellite system time bases and the reference satellite system time base), and clock drifts in the ECEF coordinate system.

[0052] First, set two sets of least squares filters LS B1 , LS B3 , and two sets of Kalman filters KF B1 , KF B3 , to process the observables from B1I signals and B3I signals respectively. After the receiver is powered on, the baseband starts to generate the original observables of B1I. Once at a certain epoch t i1 , the complete ephemeris is read and the number of observables is sufficient, the least squares filter LS B1 outputs the first positioning result under B1I, and uses this result to initialize the state variables x, y, z, v B1 of KF x , v y , v z ,, cd. At the next epoch t i2 , the velocity measurement result of LS B1 and the velocity measurement result at t i1 are differenced to obtain the acceleration, and the state variables α B1 of KF x , α y , α z are initialized. In subsequent epochs, KF B1 enters the working state of state prediction - state solution.

[0053] Similarly, use LS B3 to initialize all the state variables of KF j1 at the initial epoch t j2 , t B3 with the positioning result, and make KF B3 enter the working state of state prediction - state solution.

[0054] After the above steps, the receiver is in the "dual PVT" state, and the PVT results from KF B1 and KF B3 are output at any epoch when the satellite search is normal. At this time, the positioning information output to the user terminal needs to be optimized from the two results.

[0055] (4) Since the output system time information will participate in the baseband control inside the navigation receiver, it is necessary to fixedly select KF B1 or KFB3 The time information output by one of the filters is used to time the system. At the same time, after the adjustment of the whole second, since the system is in a zero clock error state, in order to prevent numerical instability of the Kalman filter, it is necessary to perform the following corrections on the clock error state variables of KF B1 and KF B3 :

[0056] b nonref = b nonref - b ref ,

[0057] b ref = 0,

[0058] where b ref is the system clock error under the reference time base, and b nonref is the system clock error between any other GNSS time base and the reference time base.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A dual PVT calculation method with Beidou B1I and B3I signals being mutually redundant backups, characterized in that, The method specifically includes the following steps: S1: Define two sets of Kalman filters KF B1 and KF B3 , and define the state variables Var B1 and Var B3 respectively in the filters according to the PVA or PV model; Among them, KF B1 and KF B3 are used to process the original observations from the B1I signal and the original observations from the B3I signal respectively; S2: Set up a B3I acquisition mechanism that combines direct acquisition of B3I with B1I signal traction for B3I acquisition in the baseband part; S3: Independently demodulate the B3I and B1I message data, search for the sub-frame synchronization code and perform BCH check on the demodulated data, and assemble them into D1 / D2 data frames. Before the new sub-frame of the B3I signal is input into the PVT module to update the ephemeris information, poll the B1I tracking channels. If the satellite corresponding to B3I has entered the sub-frame synchronization state in the corresponding channel of B1I, then do not input the B3I data frame into the PVT module; S4: The PVT module receives the original measurement information of B1I and B3I transmitted from the baseband, including pseudorange, Doppler, carrier-to-noise ratio, and satellite transmission time; S5: Before the system performs the first positioning with the measurements at any frequency point, select the measurements with more satellites, calculate the mean value of the positions of all satellites, use this mean value as a rough estimate of the user's current position, and input it into the least-squares filters of B1I and B3I as the iterative starting point for position calculation; S6: Perform least squares filtering on the B1I observable and the B3I observable respectively. If both output the first positioning information at the same time epoch, the positioning information is respectively passed into the corresponding Kalman filters to initialize the state variables; if one of the least squares filters outputs the first positioning result earlier than the other least squares filter, the first positioning result is passed into the two Kalman filters KF B1 and KF B3 to initialize all state variables; S7: Divide the clock error of the first calculation result by the speed of light, add it to the current local system time, and adjust the baseband PPS circuit. At this time, the receiver is in the time service state; S8: Configure the positioning mode according to the user interface information; if the positioning mode is not configured in the user interface, an adaptive method is used to optimize the PVT results output by KF B1 、KF B3 ; S9: Use the satellite-based fault detection and exclusion algorithm based on receiver autonomous integrity monitoring to obtain the intact measurements and error measurements at the current epoch, and use the signal correlation between the B1I and B3I signals to achieve cross-assistance for the baseband tracking loop; use the loop parameters of B3I to perform relocking and reacquisition on the B1I signal.

2. The dual PVT calculation method according to claim 1, wherein In step S2, for any Beidou-2 / Beidou-3 satellite, if its B1I signal is successfully captured and enters the stable tracking state, and the B3I signal broadcast by it has not been captured by the B3I direct capture module, then the Doppler shift Dopp B1 and the pseudo-code phase value are used to calculate the Doppler shift Dopp B3 and the pseudo-code phase of the corresponding B3I signal, and the tracking channel is directly opened.

3. The dual PVT calculation method according to claim 1, characterized in that In step S2, the specific method of frequency point traction is: calculate the carrier Doppler frequency shift and carrier NCO frequency control word of B3I according to the ratio of the nominal carrier frequencies of B3I and B1I; calculate the pseudocode Doppler frequency shift and pseudocode NCO frequency control word of B3I according to the ratio relationship between the carrier frequency and the pseudocode frequency; Calculate the pseudocode phase of B3I according to the pseudocode phase of B1I, and configure the digital front end with the carrier NCO frequency control word, pseudocode NCO frequency control word, and pseudocode phase and directly turn on the B3I tracking channel; the calculation formula used is: M B3_code = (f B3_code_nominal -dopp B1 × f B3 2 / (f B1 × M B3_code_nominal )) * 2 n / f s M B3_carrier = (dopp B1 ) × (f B3 / f B1 ) × 2 n / f s Among them, M B3_code represents the frequency control word of the B3 pseudo-code NCO, f B3_code_nominal represents the B3I pseudo-code rate, f B3 and f B1 respectively represent the B3I and B1I nominal carrier frequencies, dopp B1 represents the Doppler value of B1I, f s represents the operating frequency of the tracking circuit, n represents the carrier NCO bit width, M B3_code_nominal represents the nominal frequency of the B3I pseudo-code NCO, M B3_carrier represents the frequency control word of the satellite carrier tracking loop, represents the pseudo-code phase value of B1I, L B3_code represents the double B3I code length; dt represents the difference in the time stamps when the integration between the B1I and B3I tracking channels of the same satellite is completed.

4. The dual PVT calculation method according to claim 1, wherein In step S8, when the positioning mode is not configured in the user interface, an adaptive mode is adopted to optimize the PVT result, specifically including: S801: Select the priority as solution valid flag > Doppler residual > number of satellites in view; S802: Update the receiver status using the selected PVT results, specifically including: fixedly select KF B1 or KF B3 Use the time information output by one of the filters to time the system; at the same time, after the adjustment of the whole second, correct the clock error state variables of KF B1 and KF B3 as follows: b nonref = b nonref -b ref b ref ＝0 where b ref is the system clock error under the reference time base, and b nonref is the system clock error between any other GNSS time base and the reference time base.

5. The dual-PVT calculation method according to claim 3, wherein In step S9, cross-assistance of the baseband tracking loop is achieved by using the signal correlation between the B1I and B3I signals, which specifically includes: at any time element, KF B1 The velocity Doppler residual is re B1 , and the set of satellites for solution is SV B1 , KF B3 The velocity Doppler residual is re B3 , and the set of satellites for solution is SV B3 , then the following carrier PLL and carrier FLL correction algorithms are adopted: If re B1 <t dopp , SV i ∈SV B1 , then M B3 _carrier = dopp B1 ×(f B3 / f B1 )×2 n / f s , where t dopp is the preset Doppler residual threshold, SV i is the sub-frame synchronized BeiDou satellite in a stable tracking state, M B3_carrier is the frequency control word of the satellite SV i carrier tracking loop, dopp B1 is the Doppler value of B1I, (f B3 / f B1 ) is the ratio of the nominal carrier frequencies of B3I and B1I, n is the carrier NCO bit width, f s is the operating frequency of the tracking circuit; Similarly, if re B3 <t dopp , SV i ∈SV B3 , then M B1 _carrier = (dopp B3 ) × (f B1 / f B3 ) × 2 n / f s , where dopp B3 is the Doppler value of the same satellite B3I.

6. The dual PVT calculation method according to claim 5, wherein, In step S9, the B1I signal is relocked and reacquired using the loop parameters of B3I, which specifically includes: if re B3 <t prange , SV i ∈SV B3 , and the loop of the B1I signal tracking channel with SV i is unlocked, then the loop parameters of B3I are derived using the method of step S2, the current state of the B3I signal is predicted using the carrier Doppler change rate of the B1I signal, the updated loop parameters are calculated, and the B3I tracking channel is enabled; where t prange represents a preset pseudorange residual threshold.

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