CN114584136A - GNSS-based high-stability crystal oscillator taming and maintaining system and method - Google Patents
GNSS-based high-stability crystal oscillator taming and maintaining system and method Download PDFInfo
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- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
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Abstract
The invention discloses a GNSS-based high-stability crystal oscillator taming and maintaining system and method, which comprises a GNSS receiver board card and an OCXO crystal oscillator FPGA, wherein the second pulse signal output ends of the GNSS receiver board card and the FPGA are connected to a phase difference measuring module, the output end of the phase difference measuring module is connected to a processor, the output end of the processor is connected to a D/A conversion module, the output end of the D/A conversion module is connected to the OCXO crystal oscillator through a signal conditioning circuit, the second pulse signal of the OCXO crystal oscillator is output after being subjected to frequency division through the FPGA, and the OCXO crystal oscillator is connected with a temperature sensor. The invention can realize the automatic maintenance of the crystal oscillator frequency.
Description
Technical Field
The invention belongs to the technical field of Beidou time service, and particularly relates to a high-stability crystal oscillator taming and maintaining system and method based on GNSS (global navigation satellite system), which are used for obtaining high-precision time service for rapid crystal oscillator taming of a Beidou product and improving the crystal oscillator taming and maintaining precision of the Beidou product.
Background
Yang dust (2016) of the university of rocket force engineering is used for predicting the frequency drift amount of the crystal oscillator losing GPS signals by establishing an aging model of the crystal oscillator, regarding temperature as acceleration stress, introducing model parameters, estimating diffusion parameters of the model by using historical data through a maximum likelihood estimation method and estimating drift parameters through Kalman filtering, thereby completing the compensation of the system frequency. However, the model cannot distinguish the frequency influence of aging and temperature on the crystal oscillator, and cannot accurately predict when the system temperature is high.
The Bayan (2011) of the Seisan electronics technology university uses a 1PPS signal to lock the OCXO, and uses a holding algorithm of the OCXO to ensure that the crystal oscillator can maintain higher frequency accuracy within a certain time after the GPS signal fails, and the accuracy is maintained to be 1 multiplied by 10 < -10 > within 3 hours after the GPS signal fails. But the frequency accuracy of the system shows a monotonous descending trend when the system is maintained, which shows that the algorithm has limited compensation for the aging of the crystal oscillator.
The OCXO-based LTE base station clock system retention algorithm is realized by the stangar of china university (2014), a parameter estimation value of a crystal oscillator is obtained by using a recursive least square method with a forgetting factor, when a GPS receiver is in a retention state, the system obtains voltage control data of an oven controlled crystal oscillator by using a linear model, the oven controlled crystal oscillator is continuously calibrated, and after 12-hour training, the even second error of the system is 600ns, but the aging rate-frequency characteristic of the crystal oscillator is not considered, and a perfect prediction model is not established.
The first-order frequency standard such as a hydrogen clock and a cesium clock has high frequency accuracy and stability, but has high requirements on the environment due to large volume, high price and high requirement on the environment; on the contrary, the price of the secondary frequency standard is low, the requirement on the environment is general, the short-term stability is good, but the frequency accuracy and the long-term frequency stability are poor. Therefore, the advantages of the two are combined to improve the frequency accuracy and the long-term stability of the secondary frequency standard under the condition of having minimum influence on the short-term stability of the frequency of the secondary frequency standard; at present, a receiver is mainly used for locking a local crystal oscillator by utilizing a standard 1PPS signal output after processing a satellite signal, if the satellite signal is lost, the crystal oscillator is in a non-calibration state, the frequency accuracy of the crystal oscillator cannot be maintained at the moment, and the frequency accuracy error is gradually increased under the influence of aging.
[1] Poplar dust, huchanghua, plum blossom rose. GPS calibration crystal oscillator type frequency source frequency conservation method based on Wiener process [ J ] chinese test, 2016, 42 (06): 14-18.
[2] The corvavus eye-skin, the OCXO self-adaptation taming and keeping technology research [ D ]. Western Ann electronic technology university, 2011.
[3] Wu pinrong.lte base station clock system maintenance algorithm based on OCXO studies [ D ]. south china university, 2014.
Disclosure of Invention
The invention aims to provide a high-stability crystal oscillator taming and maintaining system and a high-stability crystal oscillator taming and maintaining method based on GNSS (global navigation satellite system), so as to overcome the defects of the prior art; in the crystal oscillator maintaining stage (when the GNSS signal is lost), the crystal oscillator frequency error compensation amount is predicted according to the model in the disciplined stage, so that the accuracy and the stability of the crystal oscillator output frequency are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
high stable crystal oscillator taming and keeping system based on GNSS, including GNSS receiver integrated circuit board and OCXO crystal oscillator FPGA, GNSS receiver integrated circuit board and FPGA's pulse per second signal output is connected to phase difference measurement module, phase difference measurement module's output is connected to the treater, the output of treater is connected to DA conversion module, DA conversion module's output is connected to OCXO crystal oscillator through signal conditioning circuit, OCXO crystal oscillator's pulse per second signal passes through FPGA frequency division back output, be connected with temperature sensor on the OCXO crystal oscillator.
Further, the processor employs an STM32 processor.
Further, the temperature sensor adopts DS18B 20.
Further, the D/a conversion module employs a DAC 1220.
Further, two IIR filters are arranged in the processor and are respectively used for filtering aging influence factors and temperature influence factors in the phase difference.
The high-stability crystal oscillator taming and maintaining method based on the GNSS comprises two working modes: locking the taming mode and the out-of-lock keeping mode;
when the GNSS receiver board card normally outputs the second pulse signal, the GNSS receiver board card is in a locking discipline mode, the phase difference measuring module is used for measuring the phase difference between the second pulse signal of the GNSS receiver board card and the second pulse signal of the OCXO crystal oscillator, the frequency deviation of the OCXO crystal oscillator is calculated through the phase difference, the frequency deviation of the OCXO crystal oscillator is converted into the digital quantity of the crystal oscillator control voltage, the crystal oscillator control voltage is obtained through the D/A conversion module, the output frequency of the OCXO crystal oscillator is calibrated in real time, the working time and the temperature sensor value of the OCXO crystal oscillator are recorded at the same time, and the temperature frequency characteristic and the aging frequency characteristic of the OCXO crystal oscillator are modeled;
when the GNSS receiver board card cannot normally output a pulse per second signal, switching to an unlocking maintaining mode, if the modeling is completed, predicting the OCXO crystal oscillator frequency deviation by using a model established in the locking discipline mode, compensating the OCXO crystal oscillator output frequency, and realizing the automatic maintenance of the OCXO crystal oscillator frequency; if the modeling is not completed, calculating the sliding average value of the latest frequency deviations to compensate the output frequency of the OCXO crystal oscillator, and realizing the automatic maintenance of the OCXO crystal oscillator frequency.
Further, the phase difference measuring module is used for measuring the phase difference between the GNSS receiver board second pulse signal and the OCXO crystal oscillator second pulse signal, and the frequency deviation of the OCXO crystal oscillator is calculated through the phase difference, specifically:
the phase difference measurement module carries out phase difference measurement on a pulse per second signal output by the GNSS receiver board card and an OCXO crystal oscillator pulse per second signal obtained through FPGA frequency division, then carries out filtering on a phase difference measurement value in the processor, and calculates the OCXO crystal oscillator frequency deviation by utilizing the filtered phase difference:
wherein, Δ f is the frequency deviation of OCXO crystal oscillator, f0And the nominal frequency of the OCXO crystal oscillator, delta T is the phase difference after filtering, and tau is the sampling interval of the phase difference measuring module.
Further, the frequency deviation of the OCXO crystal oscillator is converted into a digital quantity of the crystal oscillator control voltage, and then the crystal oscillator control voltage is obtained through the D/a conversion module to calibrate the OCXO crystal oscillator output frequency in real time, specifically:
according to the frequency deviation of the OCXO crystal oscillator, the digital quantity of the crystal oscillator control voltage is calculated by utilizing the voltage-controlled sensitivity coefficient K of the OCXO crystal oscillator, and then the digital quantity is converted into the crystal oscillator control voltage U which is equal to U through a D/A conversion module0And + delta f/K, so as to realize real-time calibration of the output frequency of the OCXO crystal oscillator.
Further, the recording of the working time and the temperature sensor value of the OCXO crystal oscillator models the temperature frequency characteristic and the aging frequency characteristic of the OCXO crystal oscillator, specifically:
establishing a mathematical model between the working time and the frequency deviation of the crystal oscillator and a mathematical model between the temperature and the frequency deviation of the crystal oscillator;
the mathematical model between the crystal oscillator working time and the frequency deviation is as follows:
ft(t)＝a0+a1t+ε(t)
wherein t is the working time of the crystal oscillator, ft(t) is the crystal oscillator frequency deviation caused by aging, [ epsilon ] (t) is the aging influence part of the random crystal oscillator frequency deviation and the measurement error, a0For aging part of the initial frequency offset, a1Is the aging factor;
the mathematical model between the crystal oscillator temperature and the frequency error is as follows:
fT(T)＝b0+b1T+υ(T)
wherein T is the crystal oscillation temperature fT(T) is the temperature-induced crystal oscillator frequency deviation, upsilon (T) is the temperature influence part of the random crystal oscillator frequency deviation and the measurement error, and b0For the temperature part of the initial frequency shift, b1Is the temperature coefficient;
two IIR filters arranged in a processor separate out the aging influence part of the crystal oscillator frequency random deviation and the measurement error and the temperature influence part of the crystal oscillator frequency random deviation and the measurement error in the phase difference data, and calculate to obtain the frequency deviation fT(T) and ft(t) obtaining a parameter a by fitting the frequency deviation with temperature and time information, respectively0And a1And parameter b0And b1Thereby establishing a temperature frequency characteristic model and an aging frequency characteristic model.
Further, the parameter a is obtained by fitting the frequency deviation with temperature and time information respectively0And a1And parameter b0And b1The method specifically comprises the following steps:
respectively fitting parameters a of the temperature frequency characteristic model by adopting a recursive least square method with forgetting factors0And a1And aging frequency characteristic modelParameter b0And b1The recursive least squares with forgetting factor formula is as follows:
wherein, the k time represents the k recursion,
represents the estimated value of the model parameter at the k time, y (k) is the observed quantity of the frequency error,
the observed quantity of the temperature or the crystal oscillator time at the moment k-1, K (k) is a gain vector, P (k) is a covariance matrix, and lambda epsilon (0,1) is a forgetting factor;
for the aging frequency characteristic model:
for the temperature frequency characteristic model:
by simulating the above formulaParameter a of resultant temperature frequency characteristic model0And a1And parameter b of aging frequency characteristic model0And b1。
Compared with the prior art, the invention has the following beneficial technical effects:
the crystal oscillator is acclimated through a pulse per second signal of GNSS, the working time and temperature of the crystal oscillator are recorded, and the calculation and prediction of a temperature coefficient and an aging coefficient are completed by utilizing a recursive least square method with a forgetting factor; and when no second pulse signal (GNSS signal failure) exists, calculating the crystal oscillator frequency offset compensation quantity by utilizing the predicted aging coefficient and temperature coefficient, and realizing automatic maintenance of the crystal oscillator frequency.
The crystal oscillator taming and maintaining mode is tested by building a test platform, and the result shows that: after rapid domestication, the frequency accuracy of the crystal oscillator is improved to 5.5 multiplied by 10 < -11 > from 2.2 multiplied by 10 < -8 >, which is improved by nearly three orders of magnitude. After the GNSS signal is disconnected, the phase difference drift of the crystal oscillator within 24 hours is about 4ms, and the performance of the crystal oscillator is improved by about three orders of magnitude relative to 1900ms when the crystal oscillator is in free drift.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a schematic diagram of a GNSS-based high-stability crystal oscillator taming and maintenance system according to the present invention;
FIG. 2 is a flowchart illustrating a GNSS-based high-stability crystal oscillator taming and maintaining method according to the present invention;
FIG. 3 is a connection diagram for testing the PPS precision of the Beidou time service terminal 1 in the embodiment of the invention.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples.
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention uses the recursive least square method with forgetting factors to model the aging frequency characteristic and the temperature frequency characteristic of the crystal oscillator, and uses two IIR filters to separate the aging influence factor and the temperature influence factor. In the crystal oscillator taming stage, modeling the aging frequency characteristic and the temperature frequency characteristic of the crystal oscillator; in the crystal oscillator maintaining stage (when the GNSS signal is lost), the crystal oscillator frequency error compensation amount is predicted according to the model in the disciplined stage, so that the accuracy and the stability of the crystal oscillator output frequency are improved.
When the GNSS receiver locks the satellite signal and outputs 1PPS signal through the GNSS receiver board card, the OCXO crystal oscillator is in a locking acclimation stage. And at the moment, the phase difference between the PPS signal of the GNSS receiver board card 1 and the second pulse signal of the OCXO crystal oscillator is measured by a counter in the measurement of a phase difference measurement module to calculate the frequency deviation of the OCXO crystal oscillator, the frequency deviation of the OCXO crystal oscillator is converted into the digital quantity of the crystal oscillator control voltage, and the crystal oscillator control voltage is obtained through D/A conversion to calibrate the crystal oscillator output frequency in real time. And simultaneously recording the working time of the crystal oscillator and the value of the temperature sensor, and completing modeling on the temperature frequency characteristic and the aging frequency characteristic of the crystal oscillator by adopting a recursive least square method with forgetting factors. When the GNSS receiver is affected by interference or other factors and cannot normally output 1PPS signals, the crystal oscillator is in a holding stage, the model established in the disciplining stage is used for predicting the frequency deviation of the crystal oscillator, and the output frequency of the crystal oscillator is compensated, so that the automatic holding of the crystal oscillator frequency is realized.
As shown in fig. 1, a counter of the phase difference measurement module measures a phase difference between a 1PPS second pulse signal output by the GNSS time service positioning receiver and a crystal oscillator second pulse signal obtained by frequency division by the FPGA, and then a kalman filtering algorithm is run in an STM32 to filter the phase difference measurement value to eliminate the jitter of the GNSS second pulse signal. The formula for calculating the frequency deviation of the phase difference is as follows:
wherein, Δ f is the frequency deviation of OCXO crystal oscillator, f0And the nominal frequency of the OCXO crystal oscillator, delta T is the phase difference after filtering, and tau is the sampling interval of the phase difference measuring module.
The frequency deviation of the crystal oscillator can be obtained according to the phase difference and the nominal frequency, the digital quantity of the crystal oscillator control voltage is calculated by utilizing the voltage-controlled sensitivity coefficient K of the crystal oscillator, and then the digital quantity is converted into the crystal oscillator control voltage U which is U through the DAC12200And + delta f/K, thereby realizing the real-time adjustment of the crystal oscillator frequency. The crystal oscillator is aged slowly, the aging index is usually the annual aging rate, such as +/-0.05 ppm (part per Million), and the daily aging rate is approximately constant. A mathematical model between the crystal oscillator operating time and the frequency error can be established:
ft(t)＝a0+a1t+ε(t) (2)
wherein t is the working time of the crystal oscillator, ft(t) is the crystal oscillator frequency error caused by aging, [ epsilon ] (t) is the aging influence part of the random deviation and measurement error of the crystal oscillator frequency, a0For aging part of the initial frequency offset, a1Is the aging factor.
The mathematical model between the crystal oscillator temperature and the frequency error is as follows:
fT(T)＝b0+b1T+υ(T) (3)
wherein T is the crystal oscillation temperature fT(T) is the temperature-induced crystal oscillator frequency error, upsilon (T) is the temperature influence part of the random crystal oscillator frequency deviation and the measurement error, and b0For the temperature part of the initial frequency shift, b1Is the temperature coefficient.
When the crystal oscillator is in a disciplined state, the system automatically records the working time and the environmental temperature of the crystal oscillator, separates a change part caused by temperature and a change part caused by aging in the phase difference data through an IIR filter, and calculates to obtain a frequency difference fT(T) and ft(t) of (d). Fitting the frequency difference with temperature and time information respectively to obtain a in the formula (2)0、a1Parameter and b in formula (3)0、b1Parameters, thereby establishing a temperature model and an aging model. The invention adopts a recursive least square method with forgetting factors to respectively fit the temperature model parameters and the aging model parameters, and the recursive least square formula with the forgetting factors is as follows:
wherein, the k time represents the k recursion,
represents the estimated value of the model parameter at the k time, y (k) is the observed quantity of the frequency error,
and the observed quantity of the temperature or the crystal oscillation time at the moment k-1, K (k) is a gain vector, P (k) is a covariance matrix, and lambda epsilon (0,1) is a forgetting factor.
For the aging frequency characteristic model:
for the temperature frequency characteristic model:
when the GNSS receiver 1PPS signal is lost, the crystal oscillator is in a hold state. And (3) respectively calculating frequency errors by combining the temperature measurement value and the crystal oscillator working time and obtaining an aging model formula (2) and a temperature model formula (3) through recursive least square fitting with forgetting factors, and accumulating the frequency errors to be used as crystal oscillator offset compensation quantity, so that the output frequency of the crystal oscillator can still keep a certain accuracy within a certain time.
As shown in fig. 2, the whole crystal oscillator taming and maintaining system is powered on and initialized, the single chip microcomputer STM32 is initialized firstly, the working modes mainly include a clock, a serial port and an I/O port, and then the DAC1220 is reset and the register thereof is configured, so that the DAC1220 works in a 20-bit self-calibration state. After the initialization is completed, it is necessary to wait for the output frequency of the crystal oscillator to be stable, and the output power of the crystal oscillator is about 1.5W at this time. STM32 receives the phase difference data from serial port 1 at timing 1s and performs Kalman filtering. It is also necessary to feed the phase difference data into IIR1 and IIR2 digital filters. IIR1 is used for separating high-frequency variation parts caused by temperature variation in phase difference data, and the bandwidth is designed to be 3 mHz. IIR2 is used for separating the low-frequency change part caused by aging in the phase difference data, and the bandwidth is designed to be 0.03 mHz. And respectively carrying out temperature model training and aging model training on the data after IIR1 and IIR2 filtering. And when the GNSS signal exists, converting the phase difference after Kalman filtering from the formula (1) into frequency deviation, converting the frequency deviation into a voltage control word, and inputting the voltage control word into a DA (digital-to-analog) to convert the voltage control word into crystal oscillator control voltage. And meanwhile, calculating a 100-point sliding average value of the frequency deviation, and taking the frequency deviation as a final crystal oscillator frequency compensation value when the whole training model is not stable but the GNSS signal is invalid.
And after the training is finished, if the GNSS signal is not lost, continuing the training, if the GNSS signal is lost, entering a holding mode, predicting the frequency drift trend of the crystal oscillator according to the model obtained by the training, calculating the frequency deviation compensation quantity of the crystal oscillator, converting the frequency deviation compensation quantity into control voltage, and adjusting the output frequency of the crystal oscillator in real time.
Examples
The Beidou positioning time service terminal with the time service function has the advantages that the 1PPS output rising edge and the falling edge can be set, the pulse width is adjustable, and the precision is better than 50ns (1 sigma).
The 1PPS accuracy testing equipment is connected according to the figure 3. The atomic clock provides a 10MHz frequency scale signal to the navigation signal simulator, the navigation signal simulator simulates a satellite signal, the power level of an output signal of the satellite signal simulator is set to be-125 dBm, the simulated satellite signal is accessed to a measured position time service terminal through a radio frequency line, the observation height cut-off angle of the positioning time service terminal is set to be 10 degrees, the number of observable effective satellites is guaranteed to be more than 8, and the simulated position time service terminal is still at a certain known point.
The navigation signal simulator and the positioning time service terminal simultaneously output 1PPS to a time interval counter to obtain no less than 1000 time intervals. And counting 1PPS rising edge difference values output by the navigation signal simulator and the positioning time service terminal, sequencing from small to large, and taking an Mth 66.7% value as a 1PPS precision test result, wherein M is the total time interval number.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: although the present invention has been described in detail with reference to the above embodiments, those skilled in the art will appreciate that various changes, modifications and equivalents can be made in the embodiments of the invention without departing from the scope of the invention as defined by the appended claims.
Claims (10)
1. High stable crystal oscillator taming and keeping system based on GNSS, its characterized in that, including GNSS receiver integrated circuit board and OCXO crystal oscillator FPGA, GNSS receiver integrated circuit board and FPGA's pulse per second signal output is connected to phase difference measurement module, phase difference measurement module's output is connected to the treater, the output of treater is connected to DA conversion module, DA conversion module's output is connected to OCXO crystal oscillator through signal conditioning circuit, OCXO crystal oscillator's pulse per second signal passes through FPGA frequency division back output, be connected with temperature sensor on the OCXO crystal oscillator.
2. The GNSS based high stability crystal oscillator taming and maintenance system of claim 1 wherein said processor employs an STM32 processor.
3. The GNSS based high-stability crystal oscillator taming and maintenance system of claim 1, wherein said temperature sensor employs DS18B 20.
4. The GNSS-based high-stability crystal oscillator taming and maintenance system of claim 1 wherein the D/A conversion module employs a DAC 1220.
5. The GNSS based high-stability crystal oscillator taming and maintenance system according to claim 1, wherein two IIR filters are provided in said processor, said two IIR filters being configured to filter aging-affecting factors and temperature-affecting factors out of phase difference, respectively.
6. The GNSS-based high-stability crystal oscillator taming and maintaining method adopts the GNSS-based high-stability crystal oscillator taming and maintaining system as claimed in any one of claims 1 to 5, and is characterized by comprising two working modes: locking the taming mode and the out-of-lock keeping mode;
when the GNSS receiver board card normally outputs the second pulse signal, the GNSS receiver board card is in a locking discipline mode, the phase difference measuring module is used for measuring the phase difference between the second pulse signal of the GNSS receiver board card and the second pulse signal of the OCXO crystal oscillator, the frequency deviation of the OCXO crystal oscillator is calculated through the phase difference, the frequency deviation of the OCXO crystal oscillator is converted into the digital quantity of the crystal oscillator control voltage, the crystal oscillator control voltage is obtained through the D/A conversion module, the output frequency of the OCXO crystal oscillator is calibrated in real time, the working time and the temperature sensor value of the OCXO crystal oscillator are recorded at the same time, and the temperature frequency characteristic and the aging frequency characteristic of the OCXO crystal oscillator are modeled;
when the GNSS receiver board card cannot normally output the second pulse signal, switching to an unlocking maintenance mode, if the modeling is completed, predicting the OCXO crystal oscillator frequency deviation by using a model established in the locking disciplined mode, compensating the OCXO crystal oscillator output frequency, and realizing the automatic maintenance of the OCXO crystal oscillator frequency; if the modeling is not completed, calculating the sliding average value of the latest frequency deviations to compensate the output frequency of the OCXO crystal oscillator, and realizing the automatic maintenance of the OCXO crystal oscillator frequency.
7. The GNSS-based high-stability crystal oscillator taming and maintaining method according to claim 6, wherein the phase difference measuring module is used for measuring the phase difference between the GNSS receiver board second pulse signal and the OCXO crystal oscillator second pulse signal, and calculating the frequency deviation of the OCXO crystal oscillator from the phase difference, specifically:
the phase difference measurement module carries out phase difference measurement on a pulse per second signal output by the GNSS receiver board card and an OCXO crystal oscillator pulse per second signal obtained through FPGA frequency division, then carries out filtering on a phase difference measurement value in the processor, and calculates the OCXO crystal oscillator frequency deviation by utilizing the filtered phase difference:
wherein, Δ f is the frequency deviation of OCXO crystal oscillator, f0And the nominal frequency of the OCXO crystal oscillator, delta T is the phase difference after filtering, and tau is the sampling interval of the phase difference measuring module.
8. The GNSS-based high-stability crystal oscillator taming and maintaining method according to claim 7, wherein the method comprises the steps of converting the frequency deviation of the OCXO crystal oscillator into a digital quantity of a crystal oscillator control voltage, obtaining the crystal oscillator control voltage through a D/a conversion module, and calibrating the OCXO crystal oscillator output frequency in real time, specifically:
according to the frequency deviation of the OCXO crystal oscillator, the digital quantity of the crystal oscillator control voltage is calculated by utilizing the voltage-controlled sensitivity coefficient K of the OCXO crystal oscillator, and then the digital quantity is converted into the crystal oscillator control voltage U which is equal to U through a D/A conversion module0And + delta f/K to realize the real-time calibration of the output frequency of the OCXO crystal oscillator.
9. The GNSS-based high-stability crystal oscillator taming and maintaining method according to claim 7, wherein the recording of the operating time and the temperature sensor value of the OCXO crystal oscillator models the temperature frequency characteristic and the aging frequency characteristic of the OCXO crystal oscillator, and specifically includes:
establishing a mathematical model between the working time and the frequency deviation of the crystal oscillator and a mathematical model between the temperature and the frequency deviation of the crystal oscillator;
the mathematical model between the crystal oscillator working time and the frequency deviation is as follows:
ft(t)＝a0+a1t+ε(t)
wherein t is the working time of the crystal oscillator, ft(t) is the crystal oscillator frequency deviation caused by aging, [ epsilon ] (t) is the aging influence part of the random crystal oscillator frequency deviation and the measurement error, a0For aging part of the initial frequency offset, a1Is the aging factor;
the mathematical model between the crystal oscillator temperature and the frequency error is as follows:
fT(T)＝b0+b1T+υ(T)
wherein T is the crystal oscillation temperature fT(T) is crystal oscillator frequency deviation caused by temperature, upsilon (T) is temperature influence part of crystal oscillator frequency random deviation and measurement error, b0For the temperature part of the initial frequency shift, b1Is the temperature coefficient;
the aging influence part of the random deviation of the crystal oscillator frequency and the measurement error in the phase difference data and the temperature influence of the random deviation of the crystal oscillator frequency and the measurement error are separated by two IIR filters arranged in a processorPart, calculating to obtain frequency deviation fT(T) and ft(t) obtaining a parameter a by fitting the frequency deviation with temperature and time information, respectively0And a1And parameter b0And b1Thereby establishing a temperature frequency characteristic model and an aging frequency characteristic model.
10. The GNSS-based high-stability crystal oscillator taming and maintenance method of claim 9, wherein the parameter a is obtained by fitting frequency deviation with temperature and time information respectively0And a1And parameter b0And b1The method specifically comprises the following steps:
respectively fitting parameters a of the temperature frequency characteristic model by adopting a recursive least square method with forgetting factors0And a1And parameter b of aging frequency characteristic model0And b1The recursive least squares with forgetting factor formula is as follows:
wherein, the k time represents the k recursion,
represents the estimated value of the model parameter at the k time, y (k) is the observed quantity of the frequency error,
is observed quantity of temperature or crystal oscillation time at the moment k-1, K (k) is gain vector, P (k) is covariance matrix, and lambda epsilon (0,1) is forgettingA factor;
for the aging frequency characteristic model:
for the temperature frequency characteristic model:
fitting parameter a of temperature frequency characteristic model by the above formula0And a1And parameter b of aging frequency characteristic model0And b1。
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115079558A (en) * | 2022-06-16 | 2022-09-20 | 成都迅翼卫通科技有限公司 | Time service and keeping time method based on special synchronous chip |
| CN115134203A (en) * | 2022-06-27 | 2022-09-30 | 国网青海省电力公司信息通信公司 | Signal processing method and device and electronic equipment |
| CN115134904A (en) * | 2022-06-27 | 2022-09-30 | 国网青海省电力公司信息通信公司 | Signal processing method, signal processing device, electronic equipment and computer readable storage medium |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115079558A (en) * | 2022-06-16 | 2022-09-20 | 成都迅翼卫通科技有限公司 | Time service and keeping time method based on special synchronous chip |
| CN115134203A (en) * | 2022-06-27 | 2022-09-30 | 国网青海省电力公司信息通信公司 | Signal processing method and device and electronic equipment |
| CN115134904A (en) * | 2022-06-27 | 2022-09-30 | 国网青海省电力公司信息通信公司 | Signal processing method, signal processing device, electronic equipment and computer readable storage medium |
| CN115134203B (en) * | 2022-06-27 | 2024-04-09 | 国网青海省电力公司信息通信公司 | Signal processing method and device and electronic equipment |
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