CN114779285A - Precise orbit determination method based on microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver - Google Patents
Precise orbit determination method based on microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver Download PDFInfo
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- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
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- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
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- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/33—Multimode operation in different systems which transmit time stamped messages, e.g. GPS/GLONASS
Abstract
The invention discloses a precise orbit determination method based on a microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver, which comprises the following steps: (1) selecting a low-power-consumption radio frequency front-end chip, and designing a corresponding radio frequency front-end link; (2) designing a guide capture module, and entering the guide capture modules L2C and B3I after blind capture of L1C/A and B1I is completed; (3) according to a low-orbit micro-nano satellite high-dynamic operation scene, a tracking loop model is built; (4) acquiring original measurement data of a GNSS receiver, and performing precise orbit determination by adopting an EKF algorithm and a constraint dynamics method based on an L1C/A, L2C double-frequency civil code non-difference observation value; (5) and processing by adopting a fixed interval smoothing method to obtain a final smooth precise orbit determination result. The invention effectively meets the microminiaturization and low power consumption of the satellite-borne GNSS receiver and orbit determination system under the high dynamic operation scene of the micro-nano low orbit satellite; and a high-precision tracking algorithm based on L1C/A, L2C dual frequency is designed for the first time by using GPS raw data output by a receiver.
Description
Technical Field
The invention relates to the field of satellite navigation, in particular to a precise orbit determination method based on a micro-miniature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver.
Background
The micro-nano satellite can provide very limited power consumption, and the satellite GNSS receiver and the orbit determination system are required to meet the requirements of microminiaturization and low power consumption while achieving higher orbit determination precision. Although the single-frequency measurement type GNSS receiver can meet the power consumption requirement, the dual-frequency carrier phase observed quantity with millimeter-level precision cannot be constructed, and the orbit determination precision can only reach several decimeters.
Chinese patent publication No. CN102540204A discloses a single-chip dual-frequency global satellite navigation receiver, which divides a global satellite navigation signal into two frequency intervals that are mirror image signals, respectively receives the global satellite navigation signal in each frequency interval through two receiving channels on the same chip, and the two receiving channels share the same two frequency synthesizers, thereby realizing the simultaneous reception of the dual-frequency satellite navigation signal.
However, the power consumption of the dual-frequency measurement type satellite-borne GPS receiver is usually over 10W, and obviously, the dual-frequency measurement type satellite-borne GPS receiver is not suitable for micro-nano satellites. Therefore, in order to realize centimeter-level orbit determination precision on the micro-nano satellite, the micro-miniature low-power-consumption technical bottleneck of a dual-frequency measurement type satellite-borne GNSS receiver needs to be broken through urgently, and a corresponding orbit determination algorithm is realized.
At present, two schemes of a microminiaturized dual-frequency measurement type satellite-borne GNSS receiver are mainly adopted, namely the GNSS receiver adopting Micro-Electro-Mechanical System (MEMS) technology and the GNSS receiver adopting unencrypted civil code signals. Compared with the traditional receiver, the MEMS receiver has obvious power consumption advantages, the MEMS dual-frequency GPS receiver adopted by the APOD-A satellite carries out dual-frequency measurement based on L1C/A and L2P signals, and the power consumption is less than 3W. However, due to the fact that square loss exists when the semi-codeless technology is used for tracking the L2P signal, the carrier-to-noise ratio of the actually obtained L2 signal is obviously lower than that of L1, and in-orbit measurement shows that the average tracking star number (5.1) of L2 is less than half of the average tracking star number (10.7) of L1. Therefore, although the highest possible cm-level orbit determination accuracy of the APOD-A satellite based on the MEMS dual-frequency GPS receiver is achieved, the stability is poor, and the orbit determination accuracy of part of observation dates can only reach 3-7 dm.
As another approach for a microminiaturized GNSS orbit determination technology, compared with a P code, the power consumption of a GNSS receiver can be obviously reduced by adopting an civil code signal which is not subjected to encryption processing and has a lower code rate. The GPS civil signal is supplemented with the L2C signal and the L5 signal on the basis of the fully supported L1C/A signal. The number of current GPS satellites broadcasting L2C signals reaches 23, and the dual-frequency orbit determination navigation function based on L1C/A and L2C can be basically supported. The power consumption of the digital processing circuit is proportional to the clock frequency, so that the GPS receiver based on the L1C/A and L2C double-frequency civil codes has obvious advantages in power consumption. Therefore, from the perspective of system stability and power consumption, it is imperative to design a new GPS receiver to meet the application requirements of the micro-nano satellite.
Disclosure of Invention
The invention provides a precise orbit determination method based on a microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver, which realizes high-sensitivity capture of L1C/A, L2C, B1I and B3I and high-stability tracking in a high dynamic environment under the condition of meeting the requirement of microminiaturization of low power consumption, and effectively solves the problem of overlarge power consumption of the traditional double-frequency measurement satellite-borne GNSS receiver.
A precise orbit determination method based on a microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver comprises the following steps:
(1) selecting a low-power-consumption radio frequency front-end chip and designing a corresponding radio frequency front-end link;
(2) designing a guide capture module, and entering the L2C and B3I guide capture modules after blind capture of L1C/A and B1I is completed;
(3) according to a low-orbit micro-nano satellite high-dynamic operation scene, a tracking loop model is built;
(4) acquiring original measurement data of a GNSS receiver, and performing precise orbit determination by adopting an EKF algorithm and a constraint dynamics method based on an L1C/A, L2C double-frequency civil code non-difference observation value;
(5) and processing by adopting a fixed interval smoothing method to obtain a final smooth precise orbit determination result.
The strategy for reducing power consumption in the method comprises the steps that a radio frequency front end with low power consumption and a baseband signal processing part are adopted to guide and capture GPS L2C and B3I by adopting GPS L1C/A and B1I; the method adopts FLL and PLL to appoint time to carry out loop opening to realize rapid carrier loop drawing; and finally, designing a precise orbit determination algorithm by adopting an EKF algorithm and a constraint dynamics method based on the L1C/A, L2C double-frequency civil code non-difference observed value, and processing by adopting a fixed interval smoothing method to smooth the precise orbit determination result of the GPS.
In the step (1), the radio frequency front-end link is specifically as follows:
after receiving the navigation signal, the radio frequency front end sequentially passes through a four-frequency-point band-pass filter, a low-noise amplifier and a power divider, and realizes the shunting of the radio frequency signal input to four frequency points by a single antenna through the power divider; and each path of radio frequency signal is transmitted to a corresponding low-power-consumption radio frequency front-end chip after passing through the primary filter, the amplifier and the secondary filter in sequence.
Further, the low-power-consumption radio frequency front end chip adopts a radio frequency front end chip MAX2771 to cover the frequency points L1 and L2 of the GPS and the frequency points B1 and B3 of the Beidou system respectively.
In the step (2), the workflow of the guidance capture module is as follows:
searching in a range of +/-2 chips near the chip phase obtained by blind acquisition of the L1C/A signal, and performing multiple conversion on the carrier frequency obtained by blind acquisition of the L1C/A signal to obtain the carrier frequency of a corresponding satellite GPS L2C signal;
similarly, searching is carried out in the range of +/-2 chips near the chip phase obtained by blind acquisition of the B1I signal, and the carrier frequency of the corresponding satellite Beidou B3I signal is obtained by carrying out multiple conversion on the carrier frequency obtained by blind acquisition of the B1I.
In the step (3), the tracking loop model uses a structural mode of pulling a PLL by the FLL, and the FLL and the PLL open the loop by using a mode of appointing time, namely: and for the FLL, the energy of the FLL is not judged, the PLL is automatically started only after a period of fixed time, the FLL and the PLL simultaneously perform signal tracking, a tracking channel judges the energy output of the PLL, and the lock losing is judged if the energy value of the FLL is smaller than a threshold value.
In the step (4), the specific process of performing precise orbit determination by adopting an EKF algorithm and a constraint kinetics method is as follows:
(4-1) EKF filter initialization: at the initial epoch t0Initializing receiver position, speed and clock error by using a least square method single-point positioning result, initializing carrier phase observed quantity ambiguity by using pseudo range and carrier phase observed quantity, initializing orbit dynamics model parameters and initializing a corresponding state covariance matrix;
(4-2) time update: using an orbit dynamics model to recur the state quantity of the filter from the last epoch to the current epoch, and updating a state covariance matrix;
(4-3) pretreatment of observation data: carrying out gross error detection and cycle slip detection on the observation data;
(4-4) measurement update: updating the filtering state quantity by using a double-frequency deionization layer combination or a single-frequency GRAPHIC combination, and updating a state covariance matrix at the same time;
and (4-5) entering the next epoch, and operating the steps (4-2) to (4-4).
In the step (5), the specific process of adopting the fixed interval smoothing method for processing is as follows:
forward filtering: performing precise orbit determination calculation in the sequence from the observation initial epoch to the observation end epoch, and storing the filter state estimation result X at each timei,fwdAnd corresponding state covariance matrix Pi,fwd；
Backward filtering: performing precise orbit determination calculation according to the sequence from the observation ending epoch to the observation initial epoch, and storing the filter state estimation result X at each momenti,bckAnd corresponding state covariance matrix Pi,bck；
And (3) weighted combination: determining the weight of the forward filtering and backward filtering results of each epoch according to the covariance matrix, and carrying out weighted combination as shown in the following formula to obtain a final result Xi,smo：
In the formula (I), the compound is shown in the specification,
and
representing the respective state covariance matrix Pi,fwdAnd Pi,bckThe inverse matrix of (c).
Compared with the prior art, the invention has the following beneficial effects:
1. the invention provides a design of a dual-mode four-frequency GNSS receiver under microminiature and low power consumption constraints on a micro-nano satellite platform, wherein a GPS mode of the receiver is designed based on L1C/A and L2C dual-frequency civil code signals, a radio frequency front end and a navigation antenna of a microminiaturized receiver are adopted, the weight is only 150g, the power consumption is only 3.5W, the weight and the power consumption are far lower than those of a traditional high-performance dual-frequency measurement type satellite-borne GPS receiver, and the microminiaturized application requirements of a micro-nano satellite can be well met.
2. The invention designs a corresponding precise orbit determination algorithm based on the L1C/A, L2C double-frequency civil code non-difference observation value, the orbit determination precision reaches centimeter level, and the method is used for carrying out double-frequency precise orbit determination by using the L2C frequency point for the first time in the current public research.
3. The invention is compatible with the BD mode, can receive and process the frequency points B1I and B3I of the Beidou navigation system, and provides theoretical and practical basis for verifying the orbit determination and navigation of the BD system by a satellite-borne receiver.
Drawings
FIG. 1 is a schematic diagram of a radio frequency front end link according to the present invention;
FIG. 2 shows a loop simulation result according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a state transition matrix according to the present invention;
FIG. 4 is a flow chart of a precision tracking algorithm in accordance with the present invention;
FIG. 5 is a flowchart of a fixed interval smoothing method according to the present invention;
FIG. 6 shows the result of the GPS precise orbit determination algorithm (data A) in the embodiment of the present invention;
FIG. 7 shows the result of the GPS precise orbit determination algorithm (data B) in the embodiment of the present invention.
Detailed Description
The invention will be described in further detail below with reference to the drawings and examples, which are intended to facilitate the understanding of the invention without limiting it in any way.
In the invention, a low-power-consumption radio-frequency front-end chip is selected, a corresponding radio-frequency front-end link is designed, and as shown in figure 1, after the radio-frequency front-end chip receives a navigation signal received by a satellite-borne microstrip antenna, the radio-frequency front-end chip firstly passes through a band-pass filter, so that the insertion loss is very small, and the better noise coefficient of the radio-frequency front-end is ensured. Then, a low noise amplifier LNA is adopted for signal amplification, radio frequency signals input to four frequency points by a single antenna are branched by a power divider, then, specific filters are selected for the central frequency and the bandwidth of each frequency point, and the redundancy design of gain is carried out. Before the signal is sent to the radio frequency front end chip, a first-stage filter is added to suppress the image signal before mixing.
For the radio frequency front end chip, the receiver designed by the invention adopts a radio frequency front end chip MAX2771 specially used for satellite navigation, and covers the frequency points L1 and L2 of a GPS and the frequency points B1 and B3 of a Beidou system. The main advantages of the radio frequency front-end chip include:
1. the chip adopts SiGe BiCMOS technology, can provide extremely low power consumption and has lower noise coefficient; 2. the chip has an Automatic Gain Control (AGC) function and supports a dynamic gain range of 59 dB; 3. the precision of the chip local oscillator frequency synthesizer can reach +/-30 Hz, and the accuracy of digital intermediate frequency is greatly improved; 4. the chip has 1-3 bit adjustable ADC quantization digit, and if the 3bit quantization digit is adopted, the power consumption of the whole machine can be reduced under the condition that the sensitivity of the radio frequency front end is almost not lost.
The blind capture of L1C/A and B1I is completed and then the blind capture enters a guide capture module, and the module is an optimized design aiming at signal capture of GPS L2C and Beidou B3I, so that the dynamic power consumption of a receiver can be greatly reduced. Searching in the range of +/-2 chips near the chip phase obtained by blind acquisition of the GPS L1C/A signal, and obtaining the carrier frequency of the corresponding satellite GPS L2C signal by performing multiple conversion on the carrier frequency obtained by blind acquisition of the GPS L1C/A signal.
The specific implementation method of the GPS L1C/A signal guide auxiliary GPS L2C signal is as follows:
1. each sample point of the local pseudo random code is input to the PN buffer and buffered sequentially in 4096 columns and 20 rows, where 20 rows represent the unknown 20ms initial phase ambiguity of the GPS L2C CM code signal and 4096 columns correspond to the sample point offset.
2. Because the sampling clock of the GPS L2C is 4.096MHz, about 15 sampling points correspond to +/-2 chips, after the GPS L1C/A signal blind acquisition is completed, a chip phase starting column for guiding L2C to acquire is determined, then 15 columns of data are read in sequence, sampling point offset within ms is completed, and the data are sent to a correlator.
3. After the correlator completes parallel correlation operation, the result is sent to a non-coherent integrator to complete integration and peak value judgment, namely, the determination of 20ms ambiguity and the capture of code phase within ms are completed.
In addition, the pseudo code length of the Beidou B3I signal is 10230bit, the receiver also conducts guiding capture on the Beidou B3I signal through the Beidou B1I signal, the method is similar to the method for guiding capture on the GPS L2C signal through the GPS L1C/A signal, and the unique difference is that the PN buffer is changed into a 1-row 20460-column structure.
For pico-nano satellite formation, the dynamic characteristic is large, a large error exists between a rough carrier frequency value obtained by capturing and the carrier frequency of an actual received signal, and at the moment, the carrier phase of the received signal is tracked by directly using a PLL (phase locked loop) with certain difficulty. Therefore, the tracking loop model built by the invention uses the structure mode of FLL pulling PLL. The method comprises the following steps:
the FLL and the PLL of the invention adopt the mode of appointed time to carry out loop opening, namely: and for the FLL, the energy of the FLL is not judged, the PLL is automatically started only after a period of fixed time, the FLL and the PLL simultaneously perform signal tracking, a tracking channel judges the energy output of the PLL, and the lock losing is judged if the energy value of the FLL is smaller than a threshold value. The appointed time and the energy threshold value of the loop opening are selected by means of combination of prediction and multiple actual measurement.
In a GNSS receiver tracking loop model, values of an I branch and a Q branch output after integration in a PLL are I (t) and Q (t), respectively, and P in FLLdotAnd PcrossIs the output value I of the ith epoch I, Q wayp(k) And Qp(k) The complex vector r obtained by combinationp(k) Complex vector r combined with k-1 epochp(k-1) the result of conjugate multiplication represents dot multiplication and cross multiplication, respectively. The integral values output after coherent integration of the leading path and the lagging path in the DLL are respectively IE、QEAnd IL、QLThe signal power values are respectively PEAnd PL。
The tracking performance of a receiver is simulated by adopting the structure of an FLL traction PLL, a discriminator of a tracking loop in a table 1 and proper loop parameters, and the actual error condition of the receiver under different signal-to-noise ratios is mainly analyzed.
TABLE 1
Figure 2 shows the doppler difference, carrier phase error, pseudorange error and 1ms instantaneous I/Q-path correlation after the tracking loop has stabilized at-26 dB signal to noise ratio.
Based on this, the measurement errors of the tracking loop at input SNR of-24 dB, -22dB, -20dB, -18dB, -16dB are continuously analyzed in 2dB steps, as shown in Table 2.
TABLE 2
| Input signal-to-noise ratio (dB) | -26 | -24 | -22 | -20 | -18 | -16 |
| Mean square error of carrier phase error (mm) | 3.59 | 3.25 | 2.83 | 2.34 | 1.85 | 1.47 |
| Mean square error of carrier frequency error (Hz) | 3.83 | 3.12 | 2.16 | 1.68 | 1.29 | 1.02 |
| Mean square error of code phase error (m) | 1.687 | 1.470 | 1.320 | 1.160 | 1.031 | 0.832 |
It can be seen from table 2 that the error of the loop is continuously reduced with the increase of the signal-to-noise ratio, and after the loop parameters are reasonably selected, the accuracies of the carrier phase, the carrier frequency and the code phase of the receiver are all at a higher level. In addition, the stability of the tracking loop is good, which shows that the receiver tracking loop designed by the invention has stable architecture, and the loop parameters selected aiming at the micro-nano satellite formation running environment are reliable.
After the original GPS measurement data of the GNSS receiver is obtained, a corresponding precise orbit determination algorithm is designed based on the L1C/A, L2C double-frequency civil code non-difference observation value.
To eliminate the effect of ionospheric delay errors, the main source of observation data errors, dual-frequency GPS generally employs a dual-frequency ionospheric-elimination combined observation model, a dual-frequency pseudorange-elimination ionospheric combination (hereinafter abbreviated IFP) and a dual-frequency carrier-phase-elimination ionospheric combination (hereinafter abbreviated IFL):
the observation vector of the dual-frequency GPS precision orbit determination observation model (IFP + IFL) can be expressed as:
wherein n is the number of usable stars in the observation data in double frequency.
The IFL combined observations include unknown ambiguities, which can be initialized according to equation (4):
bIF,0＝LIF-PIF (4)
wherein b isIF,0Combine the initial values of the ambiguities for the IFL.
The filtering state quantity of the low-orbit satellite GPS precise orbit determination algorithm based on the EKF algorithm and the constraint dynamics method is as follows:
X＝{r,v,D,dtr,B} (5)
wherein r and v are respectively a position vector and a velocity vector of the low-orbit satellite receiver in an ECEF coordinate system, D is a parameter to be estimated of the dynamic model, and dt isrAnd B is the carrier phase observation ambiguity vector.
D＝{Cd,Cr,aR,aT,aN} (6)
CdIs the coefficient of atmospheric resistance, CrIs the solar radiation pressure coefficient, aR,aT,aNRadial, lateral and normal empirical accelerations, respectively.
The filter state quantity state transition matrix can be expressed as:
wherein 1 denotes the receiver clock difference dtrKeeping the carrier phase ambiguity vector B unchanged in the time updating process, wherein 1 represents that the carrier phase ambiguity vector B keeps unchanged in the time updating process, and phiYIs a filter state quantity r, v, Cd,Cr,aR,aT,aNThe corresponding state transition matrix is structured as shown in fig. 3.
Φr,vA state transition matrix, S, corresponding to the filter state quantities r, vr,vFor the sensitive matrix, the two matrices can be obtained by solving the variational equation by using a numerical integration method. The numerical integration method adopted by the invention is a 4-order Runge-Kutta method. The process noise matrix and the observation noise matrix can be obtained by calculation according to prior information provided by an algorithm initialization process, and the design matrix is a partial derivative of an observation model function to the filtering state quantity.
The flow of the precise orbit determination algorithm is shown in fig. 4, and includes:
step 1.EKF filter initialization: at an initial epoch t0Receiver position, velocity and clock error are initialized using least squares single point positioning results, carrier phase observations are initialized using pseudoranges and carrier phase observationsMeasuring ambiguity, initializing orbit dynamics model parameters, and initializing a corresponding state covariance matrix.
Meanwhile, the method adopts a fixed interval smoothing method to smooth the GPS precision orbit determination result. The fixed interval smoothing algorithm obtains a smoothed result by weighting the forward result and the backward result, as shown in fig. 5, the specific flow is as follows:
forward filtering: performing precise orbit determination settlement according to the sequence from the observation starting epoch to the observation ending epoch, and storing the filtering state estimation result X at each momenti,fwdAnd corresponding state covariance matrix Pi,fwd。
Backward filtering: performing precision orbit determination settlement according to the sequence from the observation ending epoch to the observation starting epoch, and storing the filter state estimation result X at each momenti,bckAnd corresponding state covariance matrix Pi,bck。
And (3) weighted combination: determining weights for the forward filtering and backward filtering results of each epoch according to the covariance matrix, and performing weighted combination according to the formula (8) to obtain a final result:
in the formula (I), the compound is shown in the specification,
and
representing the respective state covariance matrix Pi,fwdAnd Pi,bckThe inverse matrix of (c).
The dual-mode four-frequency GNSS receiver is verified by a precise orbit determination algorithm by adopting a semi-physical simulation platform, a navigation signal simulator of a Casebron GSS9000 model is used for generating GPS L1C/A and GPS L2C dual-frequency civil code signals, and GPS measurement data in the dual-mode four-frequency GNSS receiver is used. The orbit scene is set to a low orbit satellite orbit. The simulator uses the Klobuchar ionosphere model to generate ionospheric delays.
Wherein TEC represents the number of electrons per square meter; fcIs the carrier frequency; and E is an observation elevation angle.
Two groups of GPS observation data are acquired by using a semi-physical simulation platform and the dual-mode four-frequency GNSS receiver, wherein the two groups of GPS observation data are named as data A and data B respectively, and the duration of each group of data is about 24 hours. And (3) respectively adopting a self-developed GPS precise orbit determination algorithm to carry out precise orbit determination verification on the data A and the data B, wherein the precise orbit determination result is shown in figures 6 and 7, a 3 sigma statistical method is adopted, and the precise orbit determination precision statistics is shown in table 3.
TABLE 3
From the above results, the microminiature low-power consumption dual-mode four-frequency GNSS receiver and the self-grinding GPS precise orbit determination algorithm can realize centimeter-level precise orbit determination, and the precision of the precise orbit determination is about 8-9 cm; the precision orbit determination precision of the MEMS satellite-borne GPS receiver is approximately equivalent to that of the APOD-A satellite MEMS, but the precision orbit determination precision has obvious advantages in L2 star number and orbit determination stability.
The embodiments described above are intended to illustrate the technical solutions and advantages of the present invention, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the present invention.
Claims (8)
1. A precise orbit determination method based on a microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver is characterized by comprising the following steps:
(1) selecting a low-power-consumption radio frequency front-end chip, and designing a corresponding radio frequency front-end link;
(2) designing a guide capture module, and entering the guide capture modules L2C and B3I after blind capture of L1C/A and B1I is completed;
(3) building a tracking loop model according to a high dynamic operation scene of the low-orbit micro-nano satellite;
(4) acquiring original measurement data of a GNSS receiver, and performing precise orbit determination by adopting an EKF algorithm and a constraint dynamics method based on an L1C/A, L2C double-frequency civil code non-difference observation value;
(5) and processing by adopting a fixed interval smoothing method to obtain a final smooth precise orbit determination result.
2. The precise orbit determination method based on the microminiature low-power-consumption satellite-borne dual-mode quad-band GNSS receiver, as claimed in claim 1, wherein in the step (1), the RF front-end link is specifically as follows:
after receiving the navigation signal, the radio frequency front end sequentially passes through a four-frequency-point band-pass filter, a low-noise amplifier and a power divider, and realizes the shunting of the radio frequency signal input to four frequency points by a single antenna through the power divider; and each path of radio frequency signal passes through the primary filter, the amplifier and the secondary filter in turn and then is transmitted to the corresponding low-power radio frequency front-end chip.
3. The precise orbit determination method based on the microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver, as recited in claim 2, wherein the low-power-consumption radio frequency front-end chip adopts a radio frequency front-end chip MAX2771, and covers the frequency points L1 and L2 of the GPS and the frequency points B1 and B3 of the Beidou system, respectively.
4. The precise orbit determination method based on the microminiature low-power-consumption satellite-borne dual-mode quad-band GNSS receiver as claimed in claim 1, wherein in the step (2), the working process of the guided capture module is as follows:
searching in a range of +/-2 chips near the chip phase obtained by blind acquisition of the L1C/A signal, and performing multiple conversion on the carrier frequency obtained by blind acquisition of the L1C/A signal to obtain the carrier frequency of a corresponding satellite GPS L2C signal;
similarly, searching is carried out in the range of +/-2 chips near the chip phase obtained by blind acquisition of the B1I signal, and the carrier frequency of the corresponding Beidou B3I satellite signal is obtained by carrying out multiple conversion on the carrier frequency obtained by blind acquisition of the B1I.
5. The precise orbit determination method based on the microminiature low-power-consumption satellite-borne dual-mode quad-frequency GNSS receiver, as claimed in claim 1, wherein in the step (3), the tracking loop model uses FLL to pull the structure mode of PLL, and FLL and PLL adopt the appointed time mode to open the loop, that is: and for the FLL, the energy of the FLL is not judged, the PLL is automatically started only after a period of fixed time, the FLL and the PLL simultaneously perform signal tracking at the same time, a tracking channel judges the energy output of the PLL, and if the energy value of the PLL is smaller than a threshold value, the lock losing is judged.
6. The precise orbit determination method based on the microminiature low-power-consumption satellite-borne dual-mode quad-band GNSS receiver as claimed in claim 1, wherein in the step (4), the precise orbit determination is carried out by adopting an EKF algorithm and a constraint dynamics method in the following specific processes:
(4-1) EKF filter initialization: at an initial epoch t0Initializing the position, the speed and the clock error of a receiver by using a least square method single-point positioning result, initializing the ambiguity of a carrier phase observed quantity by using a pseudo range and the carrier phase observed quantity, initializing a track dynamics model parameter and initializing a corresponding state covariance matrix;
(4-2) time update: using a track dynamics model to recur the state quantity of the filter from the last epoch to the current epoch, and updating a state covariance matrix;
(4-3) pretreatment of observation data: performing gross error detection and cycle slip detection on the observation data;
(4-4) measurement update: updating the filtering state quantity by using a double-frequency deionization layer combination or a single-frequency GRAPHIC combination, and updating a state covariance matrix at the same time;
and (4-5) entering the next epoch, and operating the steps (4-2) to (4-4).
7. The precise orbit determination method based on the microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver as claimed in claim 1, wherein in the step (5), the specific process of adopting the fixed interval smoothing method for processing is as follows:
forward filtering: performing precise orbit determination calculation in the sequence from the observation initial epoch to the observation end epoch, and storing the filter state estimation result X at each timei,fwdAnd corresponding state covariance matrix Pi,fwd；
Backward filtering: performing precise orbit determination calculation in the sequence from the observation end epoch to the observation initial epoch, and storing the filter state estimation result X at each timei,bckAnd corresponding state covariance matrix Pi,bck；
And (3) weighted combination: determining the weight of the results of forward filtering and backward filtering of each epoch according to the covariance matrix, and performing weighted combination to obtain the final result Xi,smo。
8. The precise orbit determination method based on the microminiature low-power-consumption satellite-borne dual-mode four-frequency GNSS receiver as claimed in claim 7, wherein the final result X is obtained by weighted combinationi,smoThe formula of (1) is as follows:
in the formula (I), the compound is shown in the specification,
and
representing respectively the state covariance matrix Pi,fwdAnd Pi,bckThe inverse matrix of (c).
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