CN109061689B - Satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance - Google Patents

Satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance Download PDF

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CN109061689B
CN109061689B CN201810634418.6A CN201810634418A CN109061689B CN 109061689 B CN109061689 B CN 109061689B CN 201810634418 A CN201810634418 A CN 201810634418A CN 109061689 B CN109061689 B CN 109061689B
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gnss
satellite
signal
receiver
gnss receiver
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CN109061689A (en
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张蓬
蒙艳松
张攀
王登峰
杨克元
王延光
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Xian Institute of Space Radio Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • 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
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • 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
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/27—Acquisition or tracking or demodulation of signals transmitted by the system creating, predicting or correcting ephemeris or almanac data within the receiver

Abstract

A satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance comprises the following steps: (1) preparing input data of the GNSS receiver; (2) performing orbit dynamics recursion of the GNSS receiver in the motion state; (3) calculating t1The estimated value of the emission time of all signals reaching the GNSS receiver at the moment and the position and the speed of the corresponding GNSS satellite under an ECI system; (4) calculating auxiliary information; (5) signal synchronization is aided. The invention can greatly reduce the time required by GNSS signal synchronization, thereby improving the overall navigation performance of the satellite-borne GNSS receiver.

Description

Satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance
Technical Field
The invention relates to a satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance, and belongs to the technical field of satellite autonomous navigation.
Background
The satellite-borne GNSS has the advantages of high autonomy, high positioning precision, small volume and power consumption and the like. Unlike terrestrial application scenarios, the on-board GNSS receiver faces more challenging signal processing requirements. For low orbit users and large elliptic orbit users, the Doppler search range of the GNSS signals is dozens of KHz, which is larger than 8KHz applied to the ground; because the receiver flies around the ground at a high speed, the visible GNSS satellites in the visual field range of the receiver change rapidly, and the average available time of a single GNSS satellite is far lower than that of a ground scene; for a large elliptic orbit user, the GNSS signal has a larger signal power dynamic range due to receiving the signals of the sidelobe of the GNSS satellite transmitting antenna. Under the condition that in-orbit real-time auxiliary information does not exist, the GNSS signal capturing module needs to sequentially traverse and search all GNSS satellites, Doppler ranges and code time delays; after the signal acquisition is successful, the GNSS signal synchronization can be completed only by continuing the operations of bit synchronization and frame synchronization, which is inefficient.
The existing satellite-borne GNSS receiver auxiliary method mainly performs satellite searching list and signal code phase and Doppler acquisition assistance, and rarely relates to information synchronization assistance. However, the frame synchronization process and the bit synchronization process may consume at least tens of seconds, and especially for medium and high-rail users, since the power of the received GNSS signal may be very low, it is necessary to accumulate for a long time to obtain a bit edge and extract the header and time information of the navigation message by multiple loop accumulation, and skipping the bit synchronization and the frame synchronization process may greatly reduce the signal synchronization time and increase the success probability of the signal synchronization. In addition, the existing GNSS receiver assistance method does not use the predicted signal reception power to adjust the pre-detection integration duration used for signal acquisition, so that the receiver can only set the pre-detection integration duration according to the highest acquisition sensitivity of the receiver, and the signal acquisition time is wasted for GNSS signals with higher reception power.
Document 1: in patent "a satellite-borne aided GPS method and system based on dynamic orbit extrapolation" (patent number: CN201510443835.9 publication date 2015/10/28), a satellite-borne aided GPS method based on dynamic orbit extrapolation is introduced, which comprises 4 steps: 1) performing orbit position extrapolation according to a low-orbit satellite dynamic model and a latest positioning result of the satellite-borne GPS receiver under a J2000.0 coordinate system, acquiring an extrapolated position of the satellite-borne GPS receiver and converting the extrapolated position into an ECEF coordinate system; 2) calculating and acquiring the positions of all GPS satellites in an ECEF coordinate system according to the effective GPS almanac; 3) calculating the pitch angles of all GPS satellites to the satellite-borne GPS receiver at the same epoch, judging whether each GPS satellite is visible to the satellite-borne GPS receiver, sequencing all GPS satellites according to the visibility probability, and acquiring a sequenced GPS satellite PRN number list; 4) and carrying out GPS satellite priority configuration on a capturing channel of the satellite-borne GPS receiver according to the GPS satellite PRN number list.
Document 2: an assisted GPS rapid search method based on dynamic orbit extrapolation is introduced in a thesis (telemetering and remote control) Vol.37, No.1,2014, wherein a satellite orbit motion rule is taken as auxiliary information, the approximate position of a satellite-borne GPS receiver is predicted based on the dynamic orbit extrapolation, and then whether a GPS satellite is visible to the satellite-borne GPS receiver is judged in real time by calculating a pitch angle. The satellite-borne GPS receiver can preferentially capture visible GPS satellites, thereby reducing the capturing times and shortening the positioning time.
Both documents 1 and 2 use a dynamic extrapolation method for generating a visible satellite list, and auxiliary information such as doppler information and code delay is used to shorten the acquisition time of the GPS signal. But the method described does not assist bit/frame synchronization with a priori information. For GNSS signals of general strength, the time overhead of bit synchronization and frame synchronization is tens of seconds, and for weak GNSS signals, the time overhead of bit synchronization and frame synchronization can reach several minutes, and even the time overhead of bit synchronization and frame synchronization can not be successful, which becomes a bottleneck of GNSS signal synchronization.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method overcomes the defects of the prior art and provides a satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance.
The technical solution of the invention is as follows:
a satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance comprises the following steps:
(1) input data preparation for a GNSS receiver, including the GNSS receiver at a previous time t0The effective navigation result, the GNSS receiver almanac information, the GNSS satellite transmitting antenna gain directional diagram and the GNSS receiver receiving antenna gain directional diagram;
(2) performing orbit dynamics recursion of GNSS receiver in motion state to obtain t1Position of time GNSS receiver under geocentric inertial system
Figure GDA0002565760590000031
And velocity
Figure GDA0002565760590000032
(3) From GNSS receiver at t1The motion state of the moment and GNSS almanac information, calculating t1Transmission of signals all arriving at the GNSS receiver at the momentEstimation of time of flight
Figure GDA0002565760590000033
And corresponding GNSS satellite positions under ECI system
Figure GDA0002565760590000034
Speed of rotation
Figure GDA0002565760590000035
(4) And (3) auxiliary information calculation: position under ECI system using GNSS satellites
Figure GDA0002565760590000036
Speed of rotation
Figure GDA0002565760590000037
And position of GNSS receiver under inertial system
Figure GDA0002565760590000038
Speed of rotation
Figure GDA0002565760590000039
The calculating the auxiliary information specifically comprises: the method comprises the following steps of (1) obtaining a GNSS visible satellite list, a GNSS signal time delay, a GNSS signal Doppler, a GNSS signal receiving power, a partial pseudo range ambiguity and a full pseudo range;
(5) signal synchronization assistance: narrowing the search range of the satellites according to the GNSS visible satellite list; reducing a two-dimensional searching range during code phase and frequency capturing of the GNSS signals according to the GNSS signal time delay and the GNSS signal Doppler; optimizing the pre-check integral duration used for capturing the GNSS signals and the search sequence of the satellites according to the GNSS signal receiving power; and omitting a bit synchronization/frame synchronization process according to the partial pseudo range ambiguity and the full pseudo range, and directly entering a signal synchronization state after the GNSS signal code phase and frequency acquisition is finished.
GNSS receiver at last moment t0Including the ECEF-based position
Figure GDA00025657605900000310
Speed of rotation
Figure GDA00025657605900000311
Clock difference bu(t0) And clock speed
Figure GDA00025657605900000312
The ECEF system refers to the earth-centered earth-fixed coordinate system.
The GNSS receiver almanac information is demodulated by GNSS navigation messages or injected into the receiver for static storage prior to satellite transmission.
And the GNSS satellite transmitting antenna gain directional diagram and the GNSS receiver receiving antenna gain directional diagram are solidified and stored in a GNSS receiver memory.
Step (2) of carrying out GNSS receiver motion state orbit dynamics recursion to obtain t1Position of time GNSS receiver under geocentric inertial system
Figure GDA00025657605900000313
And velocity
Figure GDA00025657605900000314
The method specifically comprises the following steps:
firstly, the position of the GNSS receiver under the ECEF system
Figure GDA0002565760590000041
And velocity
Figure GDA0002565760590000042
Converting to ECI to obtain position
Figure GDA0002565760590000043
And velocity
Figure GDA0002565760590000044
Then, the acceleration calculated by the orbital mechanics model is used for carrying out numerical integration operation, and the integration duration is t1-t0To obtain t1Position of a time-of-day GNSS receiver under inertial system
Figure GDA0002565760590000045
And velocity
Figure GDA0002565760590000046
Figure GDA0002565760590000047
Figure GDA0002565760590000048
Wherein the content of the first and second substances,
Figure GDA0002565760590000049
representing orbital perturbation acceleration.
In the step (3)
Figure GDA00025657605900000410
Is shown at t1The time reaches the emission time of the jth GNSS satellite signal at the GNSS receiver.
From GNSS receiver at t1The motion state of the moment and GNSS almanac information, calculating t1Estimation of the emission time of all signals arriving at a GNSS receiver
Figure GDA00025657605900000411
And corresponding GNSS satellite positions under ECI system
Figure GDA00025657605900000412
Speed of rotation
Figure GDA00025657605900000413
The method specifically comprises the following steps:
step 3.1: using t1Initialization
Figure GDA00025657605900000414
The number of juxtaposed iterations m is 0,
Figure GDA00025657605900000415
step 3.2: calculating the estimated value of the distance between the GNSS satellite j and the GNSS receiver at the signal emission moment
Figure GDA00025657605900000416
Figure GDA00025657605900000417
Wherein the content of the first and second substances,
Figure GDA00025657605900000418
calculating by using a GNSS almanac;
step 3.3: calculating an estimate of the propagation time of a signal
Figure GDA00025657605900000419
Figure GDA00025657605900000420
Wherein c is the speed of light;
step 3.4: updating estimated value of GNSS satellite j emission time
Figure GDA00025657605900000421
Figure GDA00025657605900000422
Step 3.5: calculating iteration times m plus 1, if m is less than 3, returning to the step 2, otherwise, continuing to execute;
step 3.6: use of
Figure GDA0002565760590000051
And GNSS almanac calculation position
Figure GDA0002565760590000052
And velocity
Figure GDA0002565760590000053
And (6) ending.
The step (4) uses the position of the GNSS satellite under ECI system
Figure GDA0002565760590000054
Speed of rotation
Figure GDA0002565760590000055
And position of GNSS receiver under inertial system
Figure GDA0002565760590000056
Speed of rotation
Figure GDA0002565760590000057
The auxiliary information is calculated, and specifically:
step 4.1: visible star list calculation: by GNSS satellite position
Figure GDA0002565760590000058
And GNSS receiver position
Figure GDA0002565760590000059
Determining whether the GNSS satellite signals are invisible due to the earth occlusion, thereby determining a visible satellite list;
step 4.2: and (3) GNSS signal time delay calculation: by GNSS satellite position
Figure GDA00025657605900000510
GNSS receiver position
Figure GDA00025657605900000511
And the satellite clock bias b of GNSSj(t1) Clock parameter b of receiveru(t0) And
Figure GDA00025657605900000512
performing a received signal delay τjAnd calculating, wherein the mathematical expression is as follows:
Figure GDA00025657605900000513
wherein, bj(t1) Calculating by using a GNSS almanac;
step 4.3: GNSS signal Doppler calculation: by GNSS satellite position
Figure GDA00025657605900000514
Speed of rotation
Figure GDA00025657605900000515
GNSS receiver position
Figure GDA00025657605900000516
Speed of rotation
Figure GDA00025657605900000517
GNSS clock drift rate
Figure GDA00025657605900000518
And clock drift rate of the receiver
Figure GDA00025657605900000519
Calculating the Doppler of the GNSS signal, wherein a specific mathematical expression is as follows:
Figure GDA00025657605900000520
wherein f iscarrIndicating the GNSS carrier frequency, c the speed of light,
Figure GDA00025657605900000521
calculating by using a GNSS almanac;
step 4.4: GNSS signal received power PoAnd (3) calculating: through the GNSS signal space transmission distance R, the transmitting antenna gain LTXGain L of receiving antennaRXAnd calculating, wherein the specific mathematical expression is as follows:
Figure GDA0002565760590000061
wherein, PICDIs the minimum received power, O, of the earth surface of the GNSS signal given by the ICD fileGIs the global offset, R, of the GNSS emission signal given by the ICD file0Is the distance between the receiver and the GNSS satellite when the minimum power on the earth's surface is received;
GNSS signal space transmission distance RjPosition calculation by GNSS receiver and GNSS satellites:
Figure GDA0002565760590000062
LTX，LRXthe function of the pitch angle theta of the sight position vector at a GNSS satellite transmitting antenna and the pitch angle beta of a GNSS receiver receiving antenna is obtained by looking up a table after the pitch angle theta and the pitch angle beta are solved; the calculation formula of angle beta and angle theta is as follows:
Figure GDA0002565760590000063
Figure GDA0002565760590000064
step 4.5: partial pseudorange ambiguity and full pseudorange calculation:
firstly, calculating partial pseudo range ambiguity N:
Figure GDA0002565760590000065
where round () denotes a rounding calculation, fsfracA measurement range representing a portion of the pseudorange; partial pseudoranges, fs, for GPS L1C/A signals without frame sync and bit syncfrac1ms × speed of light;
partial pseudoranges, fs, not synchronized by framesfracThe full pseudorange p can then be recovered at 20ms x speed of lightfull：
ρfull＝N×fsfrac+ρfrac
When signal is delayed by taujThe absolute value of the error is less than
Figure GDA0002565760590000071
The recovered full pseudorange is correct and the signal delay τjThe error means: signal delay taujThe difference between the calculated value and the true value of (d);
calculating the GNSS signal emission time through the full pseudo range and the GNSS receiver local sampling time:
Figure GDA0002565760590000072
the judgment criterion of the step (4.1) is as follows: if the angle alpha is less than the angle beta, the corresponding GNSS satellite is not shielded; the angle alpha represents an included angle between a connecting line of the receiver and an ECEF system origin and a tangent line of the earth surface passing through the receiver, and the angle beta represents an included angle between the connecting line of the receiver and the ECEF system origin and a sight position vector of the GNSS satellite j; the mathematical expressions of α and β are:
Figure GDA0002565760590000073
Figure GDA0002565760590000074
wherein R isearthRepresenting the radius of the earth.
The partial pseudoranges are defined as: measuring a pseudo range value with integer pseudo code period ambiguity when a GNSS signal bit edge or a navigation message header is not synchronized; using predicted signal time delays taujAnd a partial pseudorange ρfracAnd (4) recovering an accurate pseudo range value without ambiguity, namely a full pseudo range through calculation.
Compared with the prior art, the invention has the beneficial effects that:
(1) the method predicts the ambiguity of partial pseudo range and the launching time of GNSS signals on the basis of the orbit dynamics model extrapolation GNSS receiver motion state. Therefore, the signal frame synchronization and bit synchronization processes can be skipped, and the time overhead of signal synchronization is greatly reduced. Especially for high-orbit users, due to the fact that the received GNSS signals are extremely low in power, long-time accumulation is needed to obtain bit edges, navigation message frame headers and time information are extracted in a multi-cycle accumulation mode, and skipping over the processes of bit synchronization and frame synchronization can greatly reduce signal synchronization time and increase signal synchronization success probability.
(2) According to the method, the receiving power of each visible GNSS satellite is predicted according to the geometric relation between the receiver position extrapolated by the orbit dynamics model and the GNSS satellite, the satellite selection strategy is optimized and captured according to the prediction result, and the satellite selection efficiency is improved.
Drawings
FIG. 1 is a schematic diagram of a GNSS visible satellite;
FIG. 2 is a schematic diagram of GNSS signal transmission and reception gain calculation;
FIG. 3 is a diagram illustrating simulation test results.
Detailed Description
The satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance provided by the invention can be used for carrying out signal synchronization real-time assistance on the satellite-borne GNSS receiver, and the specific content of the assistance comprises the following steps:
1. and (5) satellite searching assistance. The method comprises the steps of setting a satellite searching range by using auxiliary GNSS visible satellite list information, eliminating invisible satellites and reducing time overhead for capturing the invisible satellites; the auxiliary receiving power is used, the priority of the satellite to be searched is set, and the satellite with stronger power is searched preferentially, so that a receiver can quickly capture a high-quality signal, and the usability of the GNSS is enhanced;
2. signal acquisition assistance. The auxiliary Doppler and time delay information is used for setting a Doppler and code phase two-dimensional searching range of a received signal, and a searching area is reduced; setting a pre-detection integral time by using auxiliary received power information, and dynamically selecting the pre-detection integral length of signals with different powers, so that the single acquisition time is shortened on the premise of ensuring the acquisition performance;
3. and information synchronization assistance. And (4) carrying out a partial pseudo range algorithm by using the auxiliary partial pseudo range ambiguity, and accurately acquiring the full pseudo range and the GNSS signal transmitting time under the condition that the position of a bit edge and the position of a navigation message frame head are unknown. Thereby allowing the receiver to directly complete signal synchronization without going through bit synchronization and frame synchronization processes, extracting correct measurement values, and reducing signal synchronization time.
Compared with the document 1 (patent "a satellite-borne aided GPS method and system based on dynamic orbit extrapolation (patent number: CN201510443835.9 publication date 2015/10/28)) and the document 2 (satellite-borne aided GPS fast search method based on dynamic orbit extrapolation (telemetering remote control) (Vol.37, No.1,2014)), the method introduced in the invention not only assists in the satellite search range and the code delay/Doppler two-dimensional capture range, but also differs from the following steps:
1. implementing part of the pseudorange algorithm using the predicted pseudorange ambiguity, thereby allowing the pseudorange to be directly output by skipping two time-consuming steps of bit synchronization and frame synchronization;
2. and predicting the receiving power of the signal to be captured, and dynamically setting the star searching priority and the pre-detection integral duration according to the receiving power. Therefore, the time required by signal synchronization is greatly reduced, and particularly for medium and high-orbit GNSS users with high GNSS signal receiving power fluctuation, the performance improvement is particularly remarkable.
The invention discloses a GNSS receiver signal synchronization method based on orbital dynamics assistance, which comprises the following steps:
step 1: GNSS receiver input data preparation.
Preparing the GNSS receiver at the last time t0Including the lower position of ECEF system (Earth-center-earth-fixed coordinate system)
Figure GDA0002565760590000091
And velocity
Figure GDA0002565760590000092
Clock difference bu(t0) Clock speed
Figure GDA0002565760590000093
And the like; preparation of valid GNSS receiver almanac information (including clock parameters) that can be demodulated via GNSS navigation messages, or in the satelliteInjecting the satellite into a receiver for static storage before satellite transmission; and preparing a GNSS satellite transmitting antenna gain directional diagram and a GNSS receiver receiving antenna gain directional diagram, and solidifying and storing the GNSS satellite transmitting antenna gain directional diagram and the GNSS receiver receiving antenna gain directional diagram in a GNSS receiver memory.
Step 2: and (4) performing orbit dynamics recursion on the motion state of the GNSS receiver.
Orbit dynamics models are commonly used to determine and predict the orbital position and velocity of satellites. The method models various orbit perturbation factors acting on the spacecraft, and carries out integral operation on acceleration caused by perturbation force to recur the motion state of the spacecraft. The main factors of the orbit dynamics model include the earth gravitational field, the three-body attraction caused by the moon and the sun, the atmospheric resistance, the solar radiation pressure and the like. Using an orbit dynamics model to carry out motion state recursion, firstly, the position of the GNSS receiver under an ECEF system
Figure GDA0002565760590000094
And velocity
Figure GDA0002565760590000095
Converting to under the earth's center inertial system (ECI) to obtain the position
Figure GDA0002565760590000096
And velocity
Figure GDA0002565760590000097
Then, the acceleration calculated by the orbital mechanics model is used for carrying out numerical integration operation, and the integration duration is t1-t0To obtain t1Position of a time-of-day GNSS receiver under inertial system
Figure GDA0002565760590000098
And velocity
Figure GDA0002565760590000099
Figure GDA00025657605900000910
Figure GDA0002565760590000101
Wherein the content of the first and second substances,
Figure GDA0002565760590000102
representing orbital perturbation acceleration.
And step 3: and calculating the motion state of the GNSS satellite.
Assuming all GNSS satellites are visible, using the GNSS receiver at t1The motion state of the moment and GNSS almanac information, calculating t1Estimation of the emission time of all signals arriving at a GNSS receiver
Figure GDA0002565760590000103
Is shown at t1The transmission time of the jth GNSS satellite signal reaching the GNSS receiver), and the corresponding position of the GNSS satellite under the ECI system
Figure GDA0002565760590000104
And velocity
Figure GDA0002565760590000105
The step 3 further comprises the following steps:
step 3.1: using t1Initialization
Figure GDA0002565760590000106
With the number of juxtaposed iterations m of 0
Figure GDA0002565760590000107
Step 3.2: calculating the estimated value of the distance between the GNSS satellite j and the GNSS receiver at the signal emission moment
Figure GDA0002565760590000108
Figure GDA0002565760590000109
Wherein the content of the first and second substances,
Figure GDA00025657605900001010
using GNSS almanac calculations.
Step 3.3: calculating an estimate of the propagation time of a signal
Figure GDA00025657605900001011
Figure GDA00025657605900001012
Where c is the speed of light.
Step 3.4: updating estimated value of GNSS satellite j emission time
Figure GDA00025657605900001013
Figure GDA00025657605900001014
Step 3.5: calculating iteration times m plus 1, if m is less than 3, returning to the step 2, otherwise, continuing to execute;
step 3.6: use of
Figure GDA00025657605900001015
And GNSS almanac calculation position
Figure GDA00025657605900001016
And velocity
Figure GDA00025657605900001017
And (6) ending.
And 4, step 4: and (4) auxiliary information calculation.
Position under ECI system using GNSS satellites
Figure GDA0002565760590000111
And velocity
Figure GDA0002565760590000112
And position of GNSS receiver under inertial system
Figure GDA0002565760590000113
And velocity
Figure GDA0002565760590000114
The calculating the auxiliary information specifically comprises: the method comprises the steps of GNSS visible satellite list, GNSS signal time delay, GNSS signal Doppler, GNSS signal receiving power, partial pseudo range ambiguity and full pseudo range.
The step 4 further comprises the following steps:
step 4.1: visible star list calculation. FIG. 1 is a schematic diagram of GNSS visible satellites for determining positions of GNSS satellites
Figure GDA0002565760590000115
And GNSS receiver position
Figure GDA0002565760590000116
The GNSS satellite signals are determined to be invisible due to being obscured by the earth. If < alpha < beta, the corresponding GNSS satellite is not shielded. The angle alpha represents an included angle between a connecting line of the receiver and an ECEF system origin and a tangent line of the earth surface passing through the receiver, and the angle beta represents an included angle between the connecting line of the receiver and the ECEF system origin and a sight position vector of the GNSS satellite j. The mathematical expressions of α and β are:
Figure GDA0002565760590000117
Figure GDA0002565760590000118
wherein R isearthRepresenting the radius of the earth.
Step 4.2: and (4) calculating the time delay of the GNSS signal. By GNSS satellite position
Figure GDA0002565760590000119
GNSS receiver position
Figure GDA00025657605900001110
And the satellite clock bias b of GNSSj(t1) Clock parameter b of receiveru(t0) And
Figure GDA00025657605900001111
performing a received signal delay τjAnd calculating, wherein the mathematical expression is as follows:
Figure GDA00025657605900001112
wherein, bj(t1) Using GNSS almanac calculations.
Step 4.3: and calculating the Doppler of the GNSS signals. By GNSS satellite position
Figure GDA00025657605900001113
And velocity
Figure GDA00025657605900001114
GNSS receiver position
Figure GDA00025657605900001115
And velocity
Figure GDA00025657605900001116
And clock drift rate of GNSS
Figure GDA00025657605900001117
Clock drift rate of receiver
Figure GDA00025657605900001118
And calculating, wherein the specific mathematical expression is as follows:
Figure GDA0002565760590000121
wherein f iscarrIndicating the GNSS carrier frequency, c the speed of light,
Figure GDA0002565760590000122
using GNSS almanac calculations.
Step 4.4: and calculating the GNSS signal receiving power. Through the GNSS signal space transmission distance R, the transmitting antenna gain LTXGain L of receiving antennaRXAnd calculating, wherein the specific mathematical expression is as follows:
Figure GDA0002565760590000123
wherein, PICDIs the minimum received power, O, of the earth surface of the GNSS signal given by the ICD fileGIs the global offset, R, of the GNSS emission signal given by the ICD file0Is the distance between the receiver and the GNSS satellites at minimum power reception from the earth's surface.
GNSS signal space transmission distance RjPosition calculation by GNSS receiver and GNSS satellites:
Figure GDA0002565760590000124
FIG. 2 is a schematic diagram of GNSS signal transmit and receive gain calculation, LTX，LRXThe function of the pitch angle theta of the sight position vector at the GNSS satellite transmitting antenna and the pitch angle beta of the GNSS receiver receiving antenna can be obtained by looking up a table after the pitch angle theta and the pitch angle beta are solved. The calculation of angle beta is the same as that in the step 4.1, and the calculation formula of angle theta is as follows:
Figure GDA0002565760590000125
step 4.5: partial pseudorange ambiguity and full pseudorange calculation. The partial pseudoranges are defined as: and measuring the pseudo range value with integer pseudo code period ambiguity when the GNSS signal bit edge or the navigation message header is not synchronized. The predicted signal delay τ may be usedjAnd a partial pseudorange ρfracThe exact unambiguous pseudorange values (called full pseudoranges) are recovered by calculation, as well as the time of transmission of the signal. First of all, calculatePseudo range ambiguity N:
Figure GDA0002565760590000131
where round () denotes a rounding calculation, fsfracRepresenting the measurement range of the partial pseudoranges. Partial pseudoranges, fs, for GPS L1C/A signals without frame sync and bit syncfrac1ms × speed of light; partial pseudoranges, fs, not synchronized by framesfrac20ms x speed of light. Full pseudoranges may then be recovered:
ρfull＝N×fsfrac+ρfrac
as long as signal delay tau is guaranteedjThe absolute value of the error is less than
Figure GDA0002565760590000132
The full pseudoranges recovered are guaranteed to be correct. The full pseudorange and the GNSS receiver local sample time together may calculate the GNSS signal launch time:
Figure GDA0002565760590000133
and 5: signal synchronization assistance: narrowing the search range of the satellites according to the GNSS visible satellite list; reducing a two-dimensional searching range during code phase and frequency capturing of the GNSS signals according to the GNSS signal time delay and the GNSS signal Doppler; optimizing the pre-check integral duration used for capturing the GNSS signals and the search sequence of the satellites according to the GNSS signal receiving power; and omitting a bit synchronization/frame synchronization process according to the partial pseudo range ambiguity and the full pseudo range, and directly entering a signal synchronization state after the GNSS signal code phase and frequency acquisition is finished.
The signal synchronization method introduced by the invention and the methods introduced in the documents 1 and 2 are subjected to hardware simulation test, a large elliptical orbit is selected in a test scene, and the height of the test arc orbit is about 36 kilometres. As shown in fig. 3, it can be seen from the test results that the synchronization performance of the GNSS satellite is significantly improved by using the method of the present invention. In the test arc segment, the method disclosed by the invention can be used for performing synchronous operation on average 1.5332 GNSS satellites more than the method disclosed in the literature. The invention can greatly reduce the time required by GNSS signal synchronization, thereby improving the overall navigation performance of the satellite-borne GNSS receiver.

Claims (10)

1. A satellite-borne GNSS receiver signal synchronization method based on orbital dynamics assistance is characterized by comprising the following steps:
(1) input data preparation for a GNSS receiver, including the GNSS receiver at a previous time t0The effective navigation result, the GNSS receiver almanac information, the GNSS satellite transmitting antenna gain directional diagram and the GNSS receiver receiving antenna gain directional diagram;
(2) performing orbit dynamics recursion of GNSS receiver in motion state to obtain t1Position of time GNSS receiver under geocentric inertial system
Figure FDA0002565760580000011
And velocity
Figure FDA0002565760580000012
(3) From GNSS receiver at t1The motion state of the moment and GNSS almanac information, calculating t1Estimation of the emission time of all signals arriving at a GNSS receiver
Figure FDA0002565760580000013
And corresponding GNSS satellite positions under ECI system
Figure FDA0002565760580000014
Speed of rotation
Figure FDA0002565760580000015
(4) And (3) auxiliary information calculation: position under ECI system using GNSS satellites
Figure FDA0002565760580000016
Speed of rotation
Figure FDA0002565760580000017
And position of GNSS receiver under inertial system
Figure FDA0002565760580000018
Speed of rotation
Figure FDA0002565760580000019
The calculating the auxiliary information specifically comprises: the method comprises the following steps of (1) obtaining a GNSS visible satellite list, a GNSS signal time delay, a GNSS signal Doppler, a GNSS signal receiving power, a partial pseudo range ambiguity and a full pseudo range;
(5) signal synchronization assistance: narrowing the search range of the satellites according to the GNSS visible satellite list; reducing a two-dimensional searching range during code phase and frequency capturing of the GNSS signals according to the GNSS signal time delay and the GNSS signal Doppler; optimizing the pre-check integral duration used for capturing the GNSS signals and the search sequence of the satellites according to the GNSS signal receiving power; and omitting a bit synchronization/frame synchronization process according to the partial pseudo range ambiguity and the full pseudo range, and directly entering a signal synchronization state after the GNSS signal code phase and frequency acquisition is finished.
2. The method according to claim 1, wherein the method comprises the following steps: GNSS receiver at last moment t0Including the ECEF-based position
Figure FDA00025657605800000110
Speed of rotation
Figure FDA00025657605800000111
Clock difference bu(t0) And clock speed
Figure FDA00025657605800000112
The ECEF system refers to the earth-centered earth-fixed coordinate system.
3. The method according to claim 1, wherein the method comprises the following steps: the GNSS receiver almanac information is demodulated by GNSS navigation messages or injected into the receiver for static storage prior to satellite transmission.
4. The method according to claim 1, wherein the method comprises the following steps: and the GNSS satellite transmitting antenna gain directional diagram and the GNSS receiver receiving antenna gain directional diagram are solidified and stored in a GNSS receiver memory.
5. The method according to claim 1, wherein the method comprises the following steps: step (2) of carrying out GNSS receiver motion state orbit dynamics recursion to obtain t1Position of time GNSS receiver under geocentric inertial system
Figure FDA0002565760580000021
And velocity
Figure FDA0002565760580000022
The method specifically comprises the following steps:
firstly, the position of the GNSS receiver under the ECEF system
Figure FDA0002565760580000023
And velocity
Figure FDA0002565760580000024
Converting to ECI to obtain position
Figure FDA0002565760580000025
And velocity
Figure FDA0002565760580000026
Then using the acceleration calculated by the orbit mechanics model to carry out numerical valueIntegral operation with integral duration t1-t0To obtain t1Position of a time-of-day GNSS receiver under inertial system
Figure FDA0002565760580000027
And velocity
Figure FDA0002565760580000028
Figure FDA0002565760580000029
Figure FDA00025657605800000210
Wherein the content of the first and second substances,
Figure FDA00025657605800000211
representing orbital perturbation acceleration.
6. The method according to claim 1, wherein the method comprises the following steps: in the step (3)
Figure FDA00025657605800000212
Is shown at t1The time reaches the emission time of the jth GNSS satellite signal at the GNSS receiver.
7. The method according to claim 1 or 6, wherein the method comprises the following steps:
from GNSS receiver at t1The motion state of the moment and GNSS almanac information, calculating t1Estimation of the emission time of all signals arriving at a GNSS receiver
Figure FDA00025657605800000213
And corresponding GNSS satellite in ECIPosition under tether
Figure FDA00025657605800000214
Speed of rotation
Figure FDA00025657605800000215
The method specifically comprises the following steps:
step 3.1: using t1Initialization
Figure FDA0002565760580000031
The number of juxtaposed iterations m is 0,
Figure FDA0002565760580000032
step 3.2: calculating the estimated value of the distance between the GNSS satellite j and the GNSS receiver at the signal emission moment
Figure FDA0002565760580000033
Figure FDA0002565760580000034
Wherein the content of the first and second substances,
Figure FDA0002565760580000035
calculating by using a GNSS almanac;
step 3.3: calculating an estimate of the propagation time of a signal
Figure FDA0002565760580000036
Figure FDA0002565760580000037
Wherein c is the speed of light;
step 3.4: updating estimated value of GNSS satellite j emission time
Figure FDA0002565760580000038
Figure FDA0002565760580000039
Step 3.5: calculating iteration times m plus 1, if m is less than 3, returning to the step 2, otherwise, continuing to execute;
step 3.6: use of
Figure FDA00025657605800000310
And GNSS almanac calculation position
Figure FDA00025657605800000311
And velocity
Figure FDA00025657605800000312
And (6) ending.
8. The method according to claim 1, wherein the method comprises the following steps: the step (4) uses the position of the GNSS satellite under ECI system
Figure FDA00025657605800000313
Speed of rotation
Figure FDA00025657605800000314
And position of GNSS receiver under inertial system
Figure FDA00025657605800000315
Speed of rotation
Figure FDA00025657605800000316
The auxiliary information is calculated, and specifically:
step 4.1: visible star list calculation: by GNSS satellite position
Figure FDA00025657605800000317
And GNSS receiver position
Figure FDA00025657605800000318
Determining whether the GNSS satellite signals are invisible due to the earth occlusion, thereby determining a visible satellite list;
step 4.2: and (3) GNSS signal time delay calculation: by GNSS satellite position
Figure FDA00025657605800000319
GNSS receiver position
Figure FDA00025657605800000320
And the satellite clock bias b of GNSSj(t1) Clock parameter b of receiveru(t0) And
Figure FDA0002565760580000041
performing a received signal delay τjAnd calculating, wherein the mathematical expression is as follows:
Figure FDA0002565760580000042
wherein, bj(t1) Calculating by using a GNSS almanac;
step 4.3: GNSS signal Doppler calculation: by GNSS satellite position
Figure FDA0002565760580000043
Speed of rotation
Figure FDA0002565760580000044
GNSS receiver position
Figure FDA0002565760580000045
Speed of rotation
Figure FDA0002565760580000046
GNSS clock drift rate
Figure FDA0002565760580000047
And clock drift rate of the receiver
Figure FDA0002565760580000048
Calculating the Doppler of the GNSS signal, wherein a specific mathematical expression is as follows:
Figure FDA0002565760580000049
wherein f iscarrIndicating the GNSS carrier frequency, c the speed of light,
Figure FDA00025657605800000410
calculating by using a GNSS almanac;
step 4.4: GNSS signal received power PoAnd (3) calculating: through the GNSS signal space transmission distance R, the transmitting antenna gain LTXGain L of receiving antennaRXAnd calculating, wherein the specific mathematical expression is as follows:
Figure FDA00025657605800000411
wherein, PICDIs the minimum received power, O, of the earth surface of the GNSS signal given by the ICD fileGIs the global offset, R, of the GNSS emission signal given by the ICD file0Is the distance between the receiver and the GNSS satellite when the minimum power on the earth's surface is received;
GNSS signal space transmission distance RjPosition calculation by GNSS receiver and GNSS satellites:
Figure FDA00025657605800000412
LTX，LRXthe function of the pitch angle theta of the sight position vector at a GNSS satellite transmitting antenna and the pitch angle beta of a GNSS receiver receiving antenna is obtained by looking up a table after the pitch angle theta and the pitch angle beta are solved; the angle beta is smaller than the sum of the angles beta,the calculation formula of the angle theta is as follows:
Figure FDA0002565760580000051
Figure FDA0002565760580000052
step 4.5: partial pseudorange ambiguity and full pseudorange calculation:
firstly, calculating partial pseudo range ambiguity N:
Figure FDA0002565760580000053
where round () denotes a rounding calculation, fsfracA measurement range representing a portion of the pseudorange; partial pseudoranges, fs, for GPS L1C/A signals without frame sync and bit syncfrac1ms × speed of light; partial pseudoranges, fs, not synchronized by framesfracThe full pseudorange p can then be recovered at 20ms x speed of lightfull：
ρfull＝N×fsfrac+ρfrac
When signal is delayed by taujThe absolute value of the error is less than
Figure FDA0002565760580000054
The recovered full pseudorange is correct and the signal delay τjThe error means: signal delay taujThe difference between the calculated value and the true value of (d);
calculating the GNSS signal emission time through the full pseudo range and the GNSS receiver local sampling time:
Figure FDA0002565760580000055
9. the method according to claim 8, wherein the orbit dynamics assistance-based satellite-borne GNSS receiver signal synchronization method comprises: the judgment criterion of the step (4.1) is as follows: if the angle alpha is less than the angle beta, the corresponding GNSS satellite is not shielded; the angle alpha represents an included angle between a connecting line of the receiver and an ECEF system origin and a tangent line of the earth surface passing through the receiver, and the angle beta represents an included angle between the connecting line of the receiver and the ECEF system origin and a sight position vector of the GNSS satellite j; the mathematical expressions of α and β are:
Figure FDA0002565760580000061
Figure FDA0002565760580000062
wherein R isearthRepresenting the radius of the earth.
10. The method according to claim 8, wherein the orbit dynamics assistance-based satellite-borne GNSS receiver signal synchronization method comprises: the partial pseudoranges are defined as: measuring a pseudo range value with integer pseudo code period ambiguity when a GNSS signal bit edge or a navigation message header is not synchronized; using predicted signal time delays taujAnd a partial pseudorange ρfracAnd (4) recovering an accurate pseudo range value without ambiguity, namely a full pseudo range through calculation.
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