A remote calibration method and system for frequency standards based on the NTP protocol

Abstract

This invention discloses a method and system for remote calibration of frequency standards based on the NTP protocol. The method includes the following steps: S1, the NTP protocol server reads a first frequency standard signal that meets the accuracy requirements as a reference frequency signal and initializes the local time; the calibration device reads a second frequency standard signal to be calibrated as a reference frequency signal, counts the time using the nominal value of the second frequency, and completes initialization; S2, the calibration device transmits messages with the server through the NTP protocol transceiver module, records the transmission and reception timestamps, calculates the clock offset, and adjusts the local time to complete synchronization; S3, the calibration device repeats message transmission at a preset period, calculates the clock offset and network round-trip delay round by round, and obtains a plural sample; S4, abnormal samples are removed based on the network round-trip delay, and linear fitting is performed on the retained samples. The negative value of the fitting slope is taken as the relative frequency deviation of the second frequency standard. This invention utilizes the NTP protocol for remote calibration of frequency standards, which can significantly reduce the cost of calibration compared to satellite and fiber optic remote calibration technologies.

Description

Technical Field

[0001] This invention belongs to the field of frequency standard calibration technology, and specifically refers to a remote calibration method and system for frequency standards based on the NTP protocol. Background Technology

[0002] With the rapid development of information technology, measuring instruments and testing equipment are evolving towards intelligence, high precision, and networking. As the "time and frequency heart" of equipment, frequency standards are playing an increasingly crucial role. At the same time, because the performance of frequency standards is affected by environmental factors and aging, regular metrological calibration has become a necessary step to ensure the accuracy of equipment measurements and the reliable operation of the system.

[0003] Currently, frequency standard calibration traditionally requires transporting the frequency standard to a laboratory, which is inefficient and costly. While remote calibration technologies, primarily targeting high-precision frequency standards, include satellite and fiber optic remote calibration, these methods are expensive due to the high cost of equipment and links. Furthermore, NTP protocol frequency standard calibration is highly susceptible to network fluctuations, resulting in relatively low accuracy. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned problems in the prior art and to provide a method and system for remote calibration of frequency standards based on the NTP protocol, which improves the accuracy of remote calibration of frequency standards based on the NTP protocol through algorithm optimization.

[0005] The specific technical solution adopted in this invention is as follows:

[0006] In a first aspect, the present invention provides a remote calibration method for frequency standards based on the NTP protocol, comprising:

[0007] S1. The NTP protocol server reads the frequency signal output of the first frequency standard that meets the preset accuracy requirements as its own reference frequency signal and initializes the local time; the calibration device reads the frequency signal output of the calibrated second frequency standard as its own reference frequency signal and counts the time using the nominal value of the second frequency standard to complete the initialization.

[0008] S2. The calibration device sends a synchronization request message to the NTP protocol server through the NTP protocol transceiver module, and receives the response message sent back by the NTP protocol server in response to the received request through the NTP protocol transceiver module, thus completing one round of message transmission operation. The calibration device records the message transmission and reception timestamps of the calibration device and the NTP protocol server in this round of message transmission operation, then calculates the clock offset between the two and adjusts the local time of the calibration device to complete time synchronization.

[0009] S3. After time synchronization is completed, the calibration equipment continues to repeat the message transmission operation according to the preset sampling period. Based on the message transmission and reception timestamp information recorded in each round of message transmission operation, the clock offset and network round-trip delay between the calibration equipment and the NTP protocol server are calculated round by round to obtain the time T2 when the synchronization request message is received by the NTP protocol server, the clock offset TD, and the network round-trip delay T. delay The plural sample constituted;

[0010] S4. Using network round-trip delay as an anomaly screening indicator, outliers are removed from the tuple samples obtained in all message transmission operation rounds. The retained tuple samples are used as fitting data. The time T2 when the synchronization request message of the NTP protocol server is received is used as the independent variable and the clock offset TD is used as the dependent variable for linear fitting. The negative value of the slope obtained by fitting is used as the relative frequency deviation of the second frequency standard.

[0011] As a preferred embodiment of the first aspect above, the NTP protocol server receives the Global Navigation Satellite System (GNSS) time signal through the timing antenna and performs time synchronization, thereby completing the initialization of the local time.

[0012] As a preferred embodiment of the first aspect mentioned above, the message transmission timestamp information to be recorded during each round of message transmission operation includes the time T1 for sending the synchronization request message of the calibration device, the time T2 for receiving the synchronization request message of the NTP protocol server, the time T3 for sending the response message of the NTP protocol server, and the time T4 for receiving the response message of the calibration device in this round of message transmission operation.

[0013] As a preferred option of the first aspect mentioned above, the clock offset TD corresponding to each round of message transmission operation is calculated as TD = ((T2-T1) + (T3-T4)) / 2.

[0014] As a preferred embodiment of the first aspect mentioned above, the network round-trip delay T corresponding to each round of message transmission operation is... delay The calculation formula is T delay = (T2-T1)+(T4-T3).

[0015] As a preferred option of the first aspect mentioned above, when removing outliers from tuple samples, the network round-trip delay of all tuple samples is screened for outliers using the Laida criterion. If the network round-trip delay of a tuple sample is an outlier, the entire tuple sample is removed.

[0016] As a preferred embodiment of the first aspect above, the linear fitting employs the least squares linear fitting method.

[0017] Secondly, the present invention provides a frequency standard remote calibration system based on the NTP protocol, which is used to implement the frequency standard remote calibration method based on the NTP protocol as described in any of the first aspects above. The system includes a first frequency standard, an NTP protocol server, a second frequency standard, an NTP protocol transceiver module, and a calibration device including a processing module and a storage module. The NTP protocol server is electrically connected to the first frequency standard and can acquire the frequency signal output of the first frequency standard. The calibration device is electrically connected to the second frequency standard and can acquire the frequency signal output of the second frequency standard. The calibration device is electrically connected to the NTP protocol transceiver module, and the NTP protocol transceiver module establishes a communication connection with the NTP protocol server through a network.

[0018] As a preferred embodiment of the second aspect above, the NTP protocol server is connected to a timing antenna, and through the timing antenna, it establishes a communication connection with the Global Navigation Satellite System, enabling it to receive time signals from the Global Navigation Satellite System.

[0019] As a preferred embodiment of the second aspect above, the relative frequency deviation of the first frequency standard is at least one order of magnitude smaller than that of the second frequency standard.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. This invention utilizes the NTP protocol for remote calibration of frequency standards, which can significantly reduce the cost of calibration compared to satellite and fiber optic remote calibration technologies.

[0022] 2. This invention utilizes a high-precision time and frequency standard frequency signal output as the frequency reference for the NTP protocol server, enabling the system to maintain normal operation even when no GNSS signal is received, thus improving the system's robustness.

[0023] 3. Since the processing module in the calibration equipment has limited accuracy in timestamp generation, this invention utilizes preliminary time synchronization to reduce the time deviation between the processing module and the NTP protocol server, thereby improving the accuracy of timestamps and the relative frequency deviation calibration accuracy.

[0024] 4. This invention utilizes abnormal network round-trip delay T delay Using NTP protocol as a screening criterion to remove abnormal sample data and reduce the impact of network fluctuations on calibration results can improve the accuracy of remote calibration of frequency standards. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the steps of a remote calibration method for frequency standards based on the NTP protocol.

[0026] Figure 2This is a schematic diagram of one form of the frequency standard remote calibration system based on the NTP protocol of the present invention;

[0027] Figure 3 This is a schematic diagram of another form of the frequency standard remote calibration system based on the NTP protocol of the present invention;

[0028] Figure 4 Network round-trip delay T delay Data distribution chart of T1 (vertical axis) and T2 (horizontal axis);

[0029] Figure 5 This is a data distribution graph showing the time difference TD (vertical axis) and T2 (horizontal axis). Detailed Implementation

[0030] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0031] In the description of this invention, it should be understood that when an element is considered to be "connected" to another element, it can be a direct connection to the other element or an indirect connection, i.e., there is an intermediate element. Conversely, when an element is said to be "directly" connected to another element, there is no intermediate element.

[0032] In the description of this invention, it should be understood that the terms "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0033] like Figure 1 As shown, in a preferred embodiment of the present invention, a remote calibration method for a frequency standard based on the NTP protocol is provided, which includes steps S1 to S4. The purpose of this remote calibration method for a frequency standard based on the NTP protocol is to measure the relative frequency deviation between a calibrated frequency standard and a high-precision frequency standard, so as to evaluate the frequency accuracy of the calibrated frequency standard or correct its deviation. The specific implementation of each step is described in detail below.

[0034] S1, NTP protocol server 2 reads the frequency signal output of the first frequency standard 1 that meets the preset accuracy requirements as its own reference frequency signal and initializes the local time; calibration device reads the frequency signal output of the calibrated second frequency standard 4 as its own reference frequency signal and counts the time using the nominal frequency value of the second frequency standard 4 to complete the initialization.

[0035] It should be noted that the specific accuracy of the first frequency standard 1 mentioned above can be determined according to actual calibration needs; theoretically, the higher the accuracy, the better. Generally speaking, the relative frequency deviation of the first frequency standard 1 should be at least one order of magnitude smaller than that of the second frequency standard 4.

[0036] It should be noted that in step S1 above, the local time of the NTP protocol server 2 is used as a relative time reference in subsequent calculations. Therefore, when initializing the local time, an initial running time can be directly set, which theoretically will not affect the relative frequency deviation finally calculated by this invention. Of course, if it is necessary to assign an accurate local time to the NTP protocol server 2, the NTP protocol server 2 receives the GNSS time signal from the Global Navigation Satellite System through the timing antenna 3 and performs time synchronization, thereby completing the initialization of the local time.

[0037] It should be noted that the nominal frequency value of the second frequency standard 4 is the nominal frequency of the second frequency standard 4 itself, which can be determined by the data marked on its instruction manual or nameplate.

[0038] S2. The calibration device sends a synchronization request message to the NTP protocol server 2 through the NTP protocol transceiver module 6, and receives the response message sent back by the NTP protocol server 2 in response to the received request through the NTP protocol transceiver module 6, thus completing one round of message transmission operation. The calibration device records the message transmission and reception timestamps of the calibration device and the NTP protocol server 2 in this round of message transmission operation, then calculates the clock offset between the two and adjusts the local time of the calibration device to complete time synchronization.

[0039] It should be noted that the aforementioned calibration equipment generally includes a processing module 5 and a storage module 7. The processing module 5 is responsible for processing signals and data, while the storage module 7 is responsible for storing the data and the computer programs that perform the relevant signal and data processing functions. The calibration equipment can be implemented using a microcontroller or a host computer; the specific form is not limited and can be selected according to the actual scenario. Furthermore, the specific form of the aforementioned NTP protocol transceiver module 6 is not limited, as long as it can establish a message transmission and reception protocol between the calibration equipment and the NTP protocol server 2, enabling message communication between the two.

[0040] To calculate the clock offset and network round-trip delay between the calibration device and NTP protocol server 2, the message transmission and reception timestamp information to be recorded during each round of message transmission operations by the calibration device and NTP protocol server 2 includes the following: the time T1 when the calibration device sends the synchronization request message, the time T2 when the NTP protocol server 2 receives the synchronization request message, the time T3 when the NTP protocol server 2 sends the response message, and the time T4 when the calibration device receives the response message. The time T1 and T4 can be collected locally on the calibration device, while the time T2 and T3 need to be collected from the NTP protocol server 2.

[0041] For ease of description, the clock offset is denoted as TD and the network round-trip delay is denoted as T in this invention. delay Therefore, based on the timestamps T1, T2, T3, and T4 collected in each round of message transmission, the clock offset TD and network round-trip delay T corresponding to this round of message transmission can be calculated using the following two formulas. delay ,in:

[0042] The clock offset TD is calculated as TD = ((T2-T1) + (T3-T4)) / 2.

[0043] Network round-trip latency T delay The calculation formula is T delay = (T2-T1)+(T4-T3).

[0044] However, it should be noted that step S2 above completes the first round of message transmission operations. The purpose of this operation is to use the timestamps T1, T2, T3, and T4 collected during this round of transmission to calculate the clock offset TD. This calculated clock offset TD is then used to adjust the local time of the calibration device, thus achieving time synchronization. Assuming the local time of the calibration device before adjustment is T0, then the adjusted local time of the calibration device is T = T0 + TD.

[0045] S3. After time synchronization is completed, the calibration equipment continues to repeat the message transmission operation according to the preset sampling period. Based on the message transmission and reception timestamp information recorded in each round of message transmission operation, the clock offset and network round-trip delay between the calibration equipment and NTP protocol server 2 are calculated round by round to obtain the time T2 when the synchronization request message is received by NTP protocol server 2, the clock offset TD, and the network round-trip delay T. delay The plural sample constitutes the sample.

[0046] It should be noted that the above-mentioned preset sampling period can be set according to actual needs. For example, with a sampling period of 1 second, the calibration device will continuously perform multivariate sample data sampling operations according to this period until a sufficient sample size is obtained for subsequent fitting.

[0047] S4. Using network round-trip delay as an anomaly screening indicator, outliers are removed from the tuple samples obtained in all message transmission operation rounds. The retained tuple samples are used as fitting data. The time T2 when the synchronization request message of NTP protocol server 2 is received is used as the independent variable and the clock offset TD is used as the dependent variable for linear fitting. The negative value of the slope obtained by fitting is used as the relative frequency deviation of the second frequency standard 4.

[0048] It should be noted that outlier removal algorithms can be varied when performing outlier removal on multivariate samples, such as the commonly used Laida criterion and Grubbs criterion, or the Dixon criterion, Chauville criterion, t-test, F-test, etc. In the embodiments of this invention, it is recommended to use the Laida criterion to screen for outliers in the network round-trip delay of all multivariate samples. If the network round-trip delay of a multivariate sample is an outlier, the entire multivariate sample is removed and will not participate in subsequent linear fitting. After removing the outlier multivariate samples, the remaining multivariate samples can be used as fitting data for linear fitting. The linear fitting function can be expressed as TD = k*T² + b, where k is the slope and b is the bias. In the embodiments of this invention, the linear fitting can use the least squares linear fitting method. The coefficient k obtained by fitting is negative and can be used as the relative frequency deviation of the second frequency standard 4, that is, the relative frequency deviation of the second frequency standard 4 is -k.

[0049] In addition, to implement the NTP protocol-based remote calibration method for frequency standards shown in S1 to S4 above, this invention also provides an NTP protocol-based remote calibration system for frequency standards. For example... Figure 2 As shown, the system includes a first frequency standard 1, an NTP protocol server 2, a second frequency standard 4, an NTP protocol transceiver module 6, and a calibration device including a processing module 5 and a storage module 7. The NTP protocol server 2 is electrically connected to the first frequency standard 1 and can collect the frequency signal output of the first frequency standard 1. The calibration device is electrically connected to the second frequency standard 4 and can collect the frequency signal output of the second frequency standard. The calibration device is electrically connected to the NTP protocol transceiver module 6, and the NTP protocol transceiver module 6 establishes a communication connection with the NTP protocol server 2 through a network.

[0050] As mentioned earlier, if the local time initialization of NTP protocol server 2 does not require Global Navigation Satellite System (GNSS) assistance, then it can be directly used. Figure 2The system shown is sufficient. If the local time initialization of NTP protocol server 2 requires the assistance of Global Navigation Satellite System (GNSS), then NTP protocol server 2 can be further connected to timing antenna 3. Through timing antenna 3, a communication connection can be established with the Global Navigation Satellite System (GNSS), enabling it to receive GNSS time signals. The system at this point is as follows: Figure 3 As shown.

[0051] To better understand the technical effects achievable by the present invention, a specific embodiment is provided below to demonstrate the specific calibration effect of the above-mentioned frequency standard remote calibration method and system based on the NTP protocol.

[0052] Example

[0053] In this embodiment, based on such Figure 3 The frequency standard remote calibration system based on the NTP protocol is shown. The specific steps of the frequency standard remote calibration method based on the NTP protocol are as follows:

[0054] Step 1: NTP Protocol Server 2 Initialization Operation: NTP Protocol Server 2 uses the frequency signal output of High Precision Frequency Standard 1 as the reference frequency signal, and receives the Global Navigation Satellite System (GNSS) time signal through the timing antenna 3 to perform local time synchronization.

[0055] Step 2: Initialization of the processing module 5 of the calibration equipment: The processing module 5 uses the frequency signal output of the calibrated frequency standard 4 as the reference frequency signal, and performs time counting based on the nominal frequency value of the calibrated frequency standard 4.

[0056] Step 3: Preliminary time synchronization operation of the processing module 5 of the calibration equipment: The processing module 5 sends a synchronization request message to the NTP protocol server 2 through the NTP protocol transceiver module 6. The message includes the local time T1 of the processing module 5 when the synchronization request message is sent. When the NTP protocol server 2 receives the synchronization request message, it records its own local time T2. After processing the received request, the NTP protocol server 2 sends a response message at its local time T3, which includes three timestamps: T1, T2, and T3. In addition, the processing module 5 receives the response message through the NTP protocol transceiver module 6 and records the local time T4 when the response message is received. The processing module 5 uses the four timestamps T1, T2, T3, and T4 to calculate the time difference between the local time of the processing module 5 and the NTP protocol server 2, i.e., the clock offset TD. The formula for the clock offset TD is as follows (1):

[0057] TD=((T2-T1)+(T3-T4)) / 2 (1)

[0058] Processing module 5 adjusts its local time according to the clock offset TD to synchronize with the time of NTP protocol server 2. Assume the local time before adjustment by processing module 5 is T0, and the adjusted local time is T = T0 + TD.

[0059] Step 4: The processing module 5 of the calibration device continuously performs data sampling operations: In this embodiment, the processing module 5 uses a sampling period of 12 seconds and continuously performs message transmission operations according to the operation in step 4. Each round of message transmission operations can obtain four timestamps: T1, T2, T3, and T4. The clock offset TD between the local time of the processing module 5 and the NTP protocol server 2 is calculated according to formula 1. The network round-trip delay Tdelay is calculated according to formula (2).

[0060] Tdelay=(T2-T1)+(T4-T3) (2)

[0061] In this embodiment, sampling is performed continuously for 2.8 days, and then corresponding calculations are performed based on these collected timestamps. The sampling data of each round is recorded in the storage module 7 in the form of tuple samples (T2, TD, Tdelay).

[0062] Step 5: Abnormal data removal operation: In order to reduce the impact of network fluctuations on calibration results, the processing module 5 uses the Raida criterion to identify abnormal network round-trip delays Tdelay. If an abnormal Tdelay is identified, the tuple sample (T2, TD, Tdelay) corresponding to the network round-trip delay Tdelay is removed.

[0063] Step 6: Calculate the relative frequency deviation of the calibrated frequency standard 4. Based on the linear relationship between the clock offset TD and the time T2 when the synchronization request message of the NTP protocol server 2 is received, the relative frequency deviation of the calibrated frequency standard 4 is finally calculated using the least squares linear fitting method.

[0064] In this embodiment, the original data has a total of 19,475 data points. After anomaly identification of abnormal network round-trip delay Tdelay using the Raida criterion, 73 abnormal samples were identified. Figure 4 This demonstrates the network round-trip delay T corresponding to samples with Tdelay anomalies identified from the raw data when using network round-trip delay Tdelay for anomaly identification. delay -T2 distribution, while Figure 5 This shows the T values ​​corresponding to the samples with T-delay anomalies identified from the raw data. D -T² distribution. Finally, based on the 19402 samples after removing outliers, the function TD = k*T² + b was fitted, yielding a relative frequency deviation of 7.8932 × 10⁻⁶. -6The relative frequency deviation obtained by directly fitting a total of 19,475 original data points was 7.9013 × 10⁻⁶. -6 This demonstrates that the outlier removal operation of the present invention can improve the measurement accuracy of relative frequency deviation.

[0065] The embodiments described above are merely some preferred implementations of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A remote calibration method for frequency standards based on the NTP protocol, characterized in that, include: S1. The NTP protocol server reads the frequency signal output of the first frequency standard that meets the preset accuracy requirements as its own reference frequency signal and initializes the local time. The calibration equipment reads the output frequency signal of the second frequency standard to be calibrated as its own reference frequency signal, and performs time counting with the nominal value of the second frequency standard to complete the initialization. S2. The calibration device sends a synchronization request message to the NTP protocol server through the NTP protocol transceiver module, and receives the response message sent back by the NTP protocol server in response to the received request through the NTP protocol transceiver module, thus completing one round of message transmission operation. The calibration device records the message transmission and reception timestamps of the calibration device and the NTP protocol server in this round of message transmission operation, then calculates the clock offset between the two and adjusts the local time of the calibration device to complete time synchronization. S3, after completing the time synchronization, the calibration device continues to repeatedly perform the packet transmission operation according to the preset sampling period, and calculates the clock offset and the network round-trip delay between the calibration device and the NTP protocol server round by round according to the packet transmission time stamp information recorded in each round of packet transmission operation, to obtain the synchronization request packet receiving time T2, the clock offset TD and the network round-trip delay T delay a plurality of tuples S4. Using network round-trip delay as an anomaly screening indicator, outliers are removed from the tuple samples obtained in all message transmission operation rounds. The retained tuple samples are used as fitting data. The time T2 when the synchronization request message of the NTP protocol server is received is used as the independent variable and the clock offset TD is used as the dependent variable for linear fitting. The negative value of the slope obtained by fitting is used as the relative frequency deviation of the second frequency standard.

2. The remote calibration method for frequency standards based on the NTP protocol as described in claim 1, characterized in that, The NTP protocol server receives the time signal from the Global Navigation Satellite System via the timing antenna and performs time synchronization, thereby completing the initialization of the local time.

3. The remote calibration method for frequency standards based on the NTP protocol as described in claim 1, characterized in that, During each round of message transmission operations, the message sending and receiving timestamp information that needs to be recorded includes the time T1 when the synchronization request message of the calibration device is sent, the time T2 when the synchronization request message of the NTP protocol server is received, the time T3 when the response message of the NTP protocol server is sent, and the time T4 when the response message of the calibration device is received.

4. The remote calibration method for frequency standards based on the NTP protocol as described in claim 3, characterized in that, The clock offset TD corresponding to each round of message transmission operation is calculated as TD = ((T2-T1) + (T3-T4)) / 2.

5. The remote calibration method for frequency standards based on the NTP protocol as described in claim 3, characterized in that, The network round-trip delay T corresponding to each round of message transmission operation delay The calculation formula is T delay = (T2-T1)+(T4-T3).

6. The remote calibration method for frequency standards based on the NTP protocol as described in claim 1, characterized in that, When removing outliers from tuple samples, the network round-trip delay of all tuple samples is screened for outliers using the Laida criterion. If the network round-trip delay of a tuple sample is an outlier, the entire tuple sample is removed.

7. The remote calibration method for frequency standards based on the NTP protocol as described in claim 1, characterized in that, The linear fitting method used is the least squares linear fitting method.

8. A remote calibration system for frequency standards based on the NTP protocol, characterized in that, To implement the remote calibration method for frequency standards based on the NTP protocol as described in any one of claims 1 to 7, the system includes a first frequency standard, an NTP protocol server, a second frequency standard, an NTP protocol transceiver module, and a calibration device including a processing module and a storage module; the NTP protocol server is electrically connected to the first frequency standard and can acquire the frequency signal output of the first frequency standard; the calibration device is electrically connected to the second frequency standard and can acquire the frequency signal output of the second frequency standard; the calibration device is electrically connected to the NTP protocol transceiver module, and the NTP protocol transceiver module establishes a communication connection with the NTP protocol server through a network.

9. The frequency standard remote calibration system based on the NTP protocol as described in claim 8, characterized in that, The NTP protocol server is connected to a timing antenna, which establishes a communication connection with the Global Navigation Satellite System (GNSS) and can receive GNSS time signals.

10. The frequency standard remote calibration system based on the NTP protocol as described in claim 8, characterized in that, The relative frequency deviation of the first frequency standard is at least one order of magnitude smaller than that of the second frequency standard.

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