KR102031838B1 - Method and apparatus for processing differential information of global navigation satellite system - Google Patents

Abstract

Receiving satellite data from at least one reference station receiving a satellite signal, generating correction information using the received data, and transmitting the generated correction information to a user device over a data link; A method of processing correction information of a system (Global Navigation Satellite System, GNSS) is disclosed.
Also, receiving the correction information from the central processing device, determining whether the valid information has elapsed, and if the valid time has elapsed, first location information of the user device immediately before the valid time has elapsed by using the correction information. And generating correction information of the Global Navigation Satellite System (GNSS) in the user device, which generates second position information of the current time point after the valid time of the user device has elapsed by using the carrier phase integration. A method of generating location information of is disclosed.

Description

Apparatus and method for processing correction information of satellite navigation system {METHOD AND APPARATUS FOR PROCESSING DIFFERENTIAL INFORMATION OF GLOBAL NAVIGATION SATELLITE SYSTEM}

The present disclosure provides an apparatus and method for processing correction information of a satellite navigation system.

The Global Navigation Satellite System (GNSS) is a satellite navigation system that provides precise location information on Earth using satellites regardless of the weather, and includes the United States GPS (Global Positioning System) and Russian GLONASS (GLObal NAvigation Satellite System). The location information of the GNSS has an error with respect to the true value. The error factors include satellite clock and orbit error, ionospheric delay error, convective delay error, multipath error, receiver signal tracking error, and noise. GNSS location information is calculated by applying triangulation method to the distance measurement data for each satellite.

Differential GPS (DGPS) is a method for reducing such an error, and the positional accuracy can be improved by generating correction information using a reference station having a true value and then removing the error.

Differential satellite navigation is classified into narrow differential satellite and wide-area satellite navigation according to the correction information generation method. Narrow-band differential satellite navigation generates and corrects the error of each satellite as one term based on the true value. The wide-area differential satellite navigation classifies each error component and corrects it by several terms, and compensates by measuring the clock / orbit error and ionospheric delay error of the satellite, respectively. Since the global differential satellite navigation compensates for each error term independently, the effective range of the correction information is as large as several hundred Km.

On the other hand, in order to improve the position measurement accuracy in the satellite, the differential satellite navigation needs to provide correction information using a separate data link. These data links include the Ground Based Augmentation System (GBAS) using the grounded RF modem and the Satellite Based Augmentation System (SBAS) using the geostationary satellite. In addition, the correction information has a valid time, since the error information does not match the actual time after the valid time. Therefore, it can be used only for a certain time after receiving correction information.

An apparatus and method for processing correction information of a satellite navigation system are provided. The technical problem to be achieved by the present embodiment is not limited to the technical problems as described above, and further technical problems can be inferred from the following embodiments.

As a technical means for achieving the above technical problem, a first aspect of the present disclosure, the step of receiving data from at least one reference station for receiving a satellite signal; Generating correction information using the received data; And transmitting the generated correction information to a user device without passing through a data link. The method may include a method for processing correction information of a global navigation satellite system (GNSS) in a central processing device. .

In addition, preprocessing the received data; And generating correction information by using the pre-processed data.

In addition, a method of sequentially generating correction information regarding an ionospheric delay error and correction information about an orbit and a clock error of a satellite may be provided.

A second aspect of the disclosure includes receiving the correction information from a central processing device; Determining whether the valid time of the correction information has elapsed; Generating first location information of the user device immediately before the valid time elapses using the correction information when the valid time elapses; And generating second position information of a current time point after the effective time elapses of the user device by applying a carrier phase integration technique to the first position information of the user device. A method of generating location information of a user device may be provided by processing correction information of a Satellite System (GNSS).

The method may include generating location information of a current time point of the user device by using the correction information when the valid time has not elapsed.

In addition, receiving carrier phase data; Calculating an amount of change in position of the user device by integrating the received carrier phase data; And outputting the second position of the user device using the calculated position change amount and the first position information of the user device.

The method may also include receiving the correction information directly from the central processing device without going through a data link.

In addition, the carrier phase data, (here, Is the satellite location, Is the receiver location, Is the line of sight between the satellite and the receiver, Is a satellite positioning error, Is an ionospheric delay error, Is the convective delay error, Is a satellite clock error, Receiver error, RF frequency wavelength of the GNSS signal, Is an unknown, Is the carrier phase data Can be provided.

A third aspect of the present disclosure includes a communication unit for receiving data from at least one reference station for receiving satellite signals; And a correction information generator configured to generate correction information using the received data, wherein the communication unit transmits the generated correction information to a user device without using a data link. A central processing device for processing correction information to be used in a Satellite System (GNSS) may be provided.

A fourth aspect of the present disclosure, the communication unit for receiving the correction information from the central processing device; And determining whether the correction time has elapsed, and when the valid time has elapsed, generating first position information of the user device immediately before the valid time has elapsed by using the correction information, and performing carrier phase integration By using the correction information of the Global Navigation Satellite System (GNSS), including; user device location information generation unit for generating second location information of the current time point after the effective time of the user device has elapsed using; A user device for generating location information of the user device may be provided.

A fifth aspect of the present disclosure can provide a computer readable recording medium having recorded thereon a program for executing the methods of the first and second aspects on a computer.

1 is an exemplary diagram for describing an overall operation of processing correction information of a satellite navigation system according to an embodiment.
2 is a diagram illustrating an example of processing correction information in a central processing device, according to an exemplary embodiment.
3 is a flowchart of a method of processing correction information, according to an exemplary embodiment.
4 is a flowchart of a method of generating correction information in a central processing device according to an embodiment.
5 is a diagram illustrating an example of processing correction information in a central processing device and a user device according to an exemplary embodiment.
6 is a flowchart of a method of generating location information of a user device by processing correction information, according to an exemplary embodiment.

The phrases “in some embodiments” or “in one embodiment” appearing in various places in the specification are not necessarily all referring to the same embodiment.

Some embodiments of the present disclosure may be represented by functional block configurations and various processing steps. Some or all of these functional blocks may be implemented in various numbers of hardware and / or software configurations that perform particular functions. For example, the functional blocks of the present disclosure may be implemented by one or more microprocessors or by circuit configurations for a given function. In addition, for example, the functional blocks of the present disclosure may be implemented in various programming or scripting languages. The functional blocks may be implemented in algorithms running on one or more processors. In addition, the present disclosure may employ the prior art for electronic configuration, signal processing, and / or data processing. Terms such as "mechanism", "element", "means" and "configuration" may be used widely and are not limited to mechanical and physical configurations. In addition, the “…” described in the specification. Wealth ”,“… Module ”means a unit for processing at least one function or operation, which may be implemented in hardware or software, or a combination of hardware and software.

In addition, the connecting lines or connecting members between the components shown in the drawings are merely illustrative of functional connections and / or physical or circuit connections. In an actual device, the connections between components may be represented by various functional connections, physical connections, or circuit connections that are replaceable or added.

Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings.

1 is an exemplary diagram for describing an overall operation of processing correction information of a satellite navigation system according to an embodiment.

Referring to FIG. 1, each of at least one reference station 20 may receive satellite signals from a plurality of GNSS satellites 30 in a global navigation satellite system (GNSS). The satellite signal received from the GNSS satellite 30 may include data for generating correction information and location information.

For example, the correction information may include correction information about clock / orbit error, ionospheric delay error, convective delay error, satellite position error, etc. of the satellite, and the position information may include GPS (Global Positioning System) coordinates. This is not restrictive. Meanwhile, the at least one reference station 20 may be a wide range reference station, but is not limited thereto.

The central processing device 10 may generate correction information of the user device 40 by using the data received from the at least one reference station 20. The location information of the user device 40 generated in the satellite navigation system may have an error compared with the location value of the actual user device 40, and the central processing device 10 may receive data received from the reference station 20. The error can be compensated by generating correction information. For example, the central processing device 10 uses the data received from the reference station 20 to generate correction information for the clock / orbit error, ionospheric delay error, convective delay error, satellite position error, etc. of the satellite. Error can be compensated. Various correction information generated by the central processing device 10 may then be used by the user device 40 to generate location information of the user device 40 itself.

The user device 40 may generate location information of the user device 40 by using the correction information received from the central processing device 10. In one embodiment, the user device 40 applies the distance measurement data, which is a measurement result of the distance of the user device 40 with respect to each GNSS satellite 30, to a triangulation method to apply the location information of the user device 40 itself. Can be generated. The distance measurement data considering the correction information for compensating for various errors may be expressed by the following equation.

In Equation 1, Is the satellite location, Is the receiver location, Is the line of sight between the satellite and the receiver, Is a satellite positioning error, Is an ionospheric delay error, Is the convective delay error, Is a satellite clock error, Receiver error, Means errors such as multipath and signal tracking.

On the other hand, a separate data link (not shown) is required to obtain more accurate correction information. Data links (not shown) include a Ground Based Augmentation System (GBAS) using an RF modem on the ground and a Satellite Based Augmentation System (SBAS) using a geostationary satellite. However, a data link (not shown) using an RF modem or geostationary satellite on the ground is expensive, requires separate facilities or equipment, and maintains complex operation.

According to the present disclosure, the central processing device 10 generates correction information using data received from the reference station 20, and generates the correction information without using a separate data link (not shown). 10, directly to the user device 40. By directly transmitting the generated correction information from the central processing device 10 to the user device 40 without using a separate data link (not shown), a change in hardware can be minimized and only a change in software can be possible.

In addition, since the condition for measuring the position of the user device 40 changes over time, the correction information generated using the data received from the reference station 20 is valid only for a certain time. The time at which the correction information generated as described above can be effectively used is called an effective time of the correction information. After the effective time, the correction information may be different from the actual value.

According to the present disclosure, the current position information of the user device 40 may be generated by using the correction information generated by using the carrier integrator method even after the valid time. In addition, by using the carrier integrator method, the application time of precision differential satellite navigation can be maximized, and it can be effectively applied to the ultra-precision strike weapon system.

In one embodiment, the user device may be an induced weapon, but is not limited thereto.

2 is a diagram illustrating an example of processing correction information in a central processing device, according to an exemplary embodiment.

Referring to FIG. 2, the central processing device 10 may include a communication unit 11 and a correction information generation unit 12. In the central processing device 10 shown in FIG. 2, only components related to the embodiment are shown. Thus, it will be understood by those skilled in the art that other general purpose components may be further included in addition to the components shown in FIG.

The reference station 20 may receive a satellite signal from the GNSS satellite 30. Satellite signals include refraction by ionospheric and convective layers passing from the GNSS satellite 30 to the reference station 20 on the ground, errors in the position and time of satellites estimated from the ground, and radio waves reflected by surrounding obstacles. An error component due to a multipath, which is a reception phenomenon, may be included to reduce positional accuracy.

The communication unit 11 of the central processing device 10 may receive data based on satellite signals from the reference station 20. The data received from the reference station 20 may include information for generating correction information.

The communication unit 11 may include one or more components that enable communication between the central processing device 10 and the reference station 20 and the user device 40. For example, the communication unit 11 may include a short range communication unit, a mobile communication unit, and a broadcast receiving unit.

The short-range wireless communication unit includes a Bluetooth communication unit, a BLE (Bluetooth Low Energy) communication unit, a near field communication unit (Near Field Communication unit), a WLAN (Wi-Fi) communication unit, a Zigbee communication unit, an infrared ray (IrDA) It may include, but is not limited to, a Data Association (W Association) communication unit, a WFD (Wi-Fi Direct) communication unit, an ultra wideband (UWB) communication unit, an Ant + communication unit, and the like.

The mobile communication unit transmits and receives a radio signal with at least one of a base station, an external terminal, and a server on a mobile communication network. Here, the wireless signal may include various types of data according to transmission and reception of a voice call signal, a video call call signal, or a text / multimedia message.

The broadcast receiver receives a broadcast signal and / or broadcast related information from the outside through a broadcast channel. The broadcast channel may include a satellite channel and a terrestrial channel.

The correction information generator 12 of the central processing device 10 may generate correction information for compensating for an error by using the data received from the communication unit 11. For example, the central processing device 10 uses the data received from the reference station 20 to generate correction information for the clock / orbit error, ionospheric delay error, convective delay error, satellite position error, etc. of the satellite. Error can be compensated.

The correction information generation unit 12 of the central processing device 10 may be manufactured in the form of at least one hardware chip and mounted on the central processing device 10. For example, the correction information generator 12 may be manufactured in the form of a dedicated hardware chip for generating correction information, or may be formed of an existing general purpose processor (eg, CPU or application processor) or graphics dedicated processor (eg, GPU). It may be manufactured in part and mounted on the above-described central processing device 10.

The communication unit 11 of the central processing device 10 may transmit various correction information generated by the correction information generation unit 12 to the user device 40.

3 is a flowchart of a method of processing correction information, according to an exemplary embodiment.

Referring to FIG. 3, in operation 310, the central processing device 10 may receive data from at least one reference station 20 that receives satellite signals. The data received from the reference station 20 may include information for generating correction information.

In operation 320, the CPU 10 may generate correction information using the data received from the at least one reference station 20. For example, the central processing device 10 uses the data received from the reference station 20 to generate correction information for the clock / orbit error, ionospheric delay error, convective delay error, satellite position error, etc. of the satellite. Error can be compensated.

In operation 330, the CPU 10 may transmit the generated correction information directly to the user device 40 without passing through the data link.

4 is a flowchart of a method of generating correction information in a central processing device according to an embodiment.

Referring to FIG. 4, in operation 410, the central processing device 10 may receive data from at least one reference station 20 that receives satellite signals from the GNSS satellite 30. The at least one reference station 20 may be a wide area reference station and the central processing device 10 may receive and control data of the widespread reference station.

In operation 420, the central processing device 10 may preprocess data received from the at least one reference station 20. In one embodiment, the central processing device 10 uses the data received from the reference station 20 to determine the validity of the measurements, to detect carrier phase errors and to reduce noise, to reduce the GNSS receiver clock errors of the multiple reference stations 20. Compensation can be performed. On the other hand, the preprocessing process performed in the central processing device 10 is not limited thereto. The preprocessed data may be applied to the generation of ionospheric error correction information using the dual frequency in step 430.

In operation 430, the CPU 10 may generate correction information regarding an ionospheric delay error. Correction information for the ionospheric delay error may be measured using a dual frequency. A number of precise measurements that have undergone the preprocessing of step 420 may be used.

In operation 440, the CPU 10 may generate correction information about the satellite clock / orbit error. When the correction information for the ionospheric delay error is generated in step 430, the CPU 10 may calculate the clock / orbit error of the GNSS satellite 30 inversely as the remaining error after removing the ionospheric delay error. The clock / orbit error of the GNSS satellite 30 is the next largest error component after the ionospheric delay error, and the central processing device 10 applies the position of the ground station that is accurately positioned on the Kalman filter to apply the clock of the GNSS satellite 30. Correction information can be generated against orbital errors.

In operation 450, the CPU 10 may generate correction information for the remaining errors except for the ionospheric delay and the satellite clock / orbit error. For example, the central processing device 10 may generate correction information for convective delay error, multipath error, receiver signal tracking error, and noise, but the type of error is not limited thereto.

In steps 430 and 440, correction information for the ionospheric delay error, which is the largest error in the satellite navigation system, and correction information for the clock / orbit error of the GNSS satellite are generated. Compensation information for the ionospheric delay error and correction information for the clock / orbit error of the GNSS satellite may be compensated for, and then compensation for the remaining error may be generated.

The global correction information generated through steps 410 to 450 may be directly transmitted to the user device 40. The user device 40 may generate accurate position information of the user device 40 by using the wide area correction information.

For example, the global correction information generated through the steps 410 to 450 in the central processing device 10 may launch or control guided weapons or the like without going through a separate data link (eg, GBAS, SBAS, etc.). Can be delivered directly to the user device 40, such as a fire control device. In addition, the correction information may be finally updated immediately before firing the guided weapon or the like from the fire control apparatus.

Data links (not shown) using terrestrial RF modems or geostationary satellites are expensive, require separate facilities or equipment, and are complex to maintain. On the other hand, transmitting the correction information generated by the central processing device 10 directly to the user device 40 without passing through the data link may be possible by minimizing changes in hardware and only by changing software.

5 is a diagram illustrating an example of processing correction information in a central processing device and a user device according to an exemplary embodiment.

Hereinafter, the content overlapping with FIG. 2 will be omitted for convenience.

Referring to FIG. 5, the central processing device 10 may include a communication unit 11 and a correction information generation unit 12, and the user device 40 may include the communication unit 41 and the correction information generation unit 42. It may include. Only components related to the embodiment are shown in the central processing device 10 and the user device 40 shown in FIG. 5. Accordingly, it will be understood by those skilled in the art that other general purpose components may be further included in addition to the components shown in FIG. 5.

The reference station 20 may receive a satellite signal from the GNSS satellite 30. In addition, the communication unit 11 of the central processing device 10 may receive data based on satellite signals from the reference station 20. In addition, the correction information generation unit 12 of the central processing device 10 may generate correction information that can compensate for an error using the data received from the communication unit 11. In addition, the communication unit 11 of the central processing device 10 may transmit various correction information generated by the correction information generation unit 12 to the user device 40.

The communication unit 41 of the user device 40 may receive the correction information from the central processing device 10. For example, the communication unit 41 of the user device 40 may receive correction information regarding a clock / orbit error, an ionospheric delay error, a convective delay error, a position error of the satellite, and the like from the central processing device 10. have.

The user device location information generation unit 42 of the user device 40 may generate location information of the user device 40 by compensating for an error using the correction information received from the central processing device 10.

For example, the user device 40 may generate distance measurement data of the user device 40 for each GNSS satellite 30 by substituting the correction information received from the central processing device 10 in Equation 1 described above. Can be. The user device 40 may generate location information of the user device 40 by applying the generated ranging data to a triangulation method.

On the other hand, since the condition for measuring the position of the user device 40 changes over time, the correction information generated using the data received from the reference station 20 is valid only for a certain time. The time at which the correction information generated as described above can be effectively used is called an effective time of the correction information. After the effective time, the correction information may be different from the actual value. The user device location information generation unit 42 of the user device 40 may apply a technique that can effectively use correction information received directly from the central processing device 10 even after a valid time without going through a separate data link. . A technique that can effectively use the correction information even after the valid time will be described later with reference to FIG. 6.

6 is a flowchart of a method of generating location information of a user device by processing correction information, according to an exemplary embodiment.

Referring to FIG. 6, in operation 610, the communication unit 41 of the user device 40 may receive correction information from the central processing device 10. For example, the communication unit 41 of the user device 40 may receive correction information regarding a clock / orbit error, an ionospheric delay error, a convective delay error, a position error of the satellite, and the like from the central processing device 10. have.

In operation 620, the user device location information generation unit 42 of the user device 40 may determine whether the valid time of the correction information received from the central processing device 10 has elapsed.

If it is determined in step 620 that the valid time of the correction information has not elapsed, the flow proceeds to step 650.

In operation 650, the user device location information generator 42 of the user device 40 may generate location information of the real time user device using the correction information without updating the correction information received from the central processing device 10. Can be. The user device location information generator 42 of the user device 40 may generate location information of the user device 40 by compensating for an error using the correction information received from the central processing device 10.

If it is determined in step 620 that the valid time of the correction information has elapsed, the flow proceeds to step 630.

In operation 630, the user device location information generator 42 of the user device 40 may apply an additional technique to effectively use the correction information received from the central processing device 10. In one embodiment, the user device location information generation unit 42 may determine the location of the user device 40 immediately before the valid time elapses using the correction information received from the central processing device 10. The user device location information generation unit 42 may store the location of the user device 40 immediately before the valid time elapses using the correction information in a memory (not shown) of the user device 40.

In operation 640, the user device location information generator 42 of the user device 40 may apply the carrier phase integration scheme to generate location information of the current time point after the valid time of the user device 40 elapses. The carrier phase data used in the carrier phase integration technique is precise data with a very small measurement error in cm.

In one embodiment, carrier phase data May be represented by the following equation.

In Equation 2, Is the satellite location, Is the receiver location, Is the line of sight between the satellite and the receiver, Is a satellite positioning error, Is an ionospheric delay error, Is the convective delay error, Is a satellite clock error, Receiver error, The RF frequency wavelength of the GNSS signal (0.19m for GPS), Is an unknown, Is the carrier phase data Indicates a measurement error.

The above-mentioned distance measurement data Equation 1 and carrier phase data for The difference from Equation 2 is that the ionospheric error code is negative and there is an unknown term indicating the repetition of the RF frequency period.

Carrier phase data Indicating a measurement error of Is very small since it is an error measuring the phase within one wavelength (for example, 0.19 m). In addition, integrating the carrier phase data represents an amount of change in the position of the user device 40 for a specific time. Since the integration error increases with time, but most of the terms in Equation 2 change slowly, the magnitude of the integration error is several tens of minutes. Very small below cm On the other hand, the result of integrating the carrier phase data may be the relative position change of the user device 40 for a specific time.

The user device position information generation unit 42 stores position and carrier phase data of the user device 40 immediately before the effective time elapses. Using the result of integrating, the location information of the current time may be generated after the valid time of the user device 40 elapses.

The user device 40 applies the carrier integrator method to the position information of the user device 40 generated by using the existing correction information even after the valid time of the correction information has passed through steps 610 to 640, thereby enabling precise differential satellite navigation. The application time can be maximized and it can be effectively applied to ultra-precision strike weapon systems.

The embodiments may also be implemented in the form of a recording medium including instructions executable by a computer, such as a program module executed by the computer. Computer readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. In addition, computer readable media may include both computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically includes computer readable instructions, data structures, other data in modulated data signals such as program modules, or other transmission mechanisms, and includes any information delivery media.

Further, in this specification, “unit” may be a hardware component such as a processor or a circuit, and / or a software component executed by a hardware component such as a processor.

The foregoing description of the specification is intended to be illustrative, and it is understood that those skilled in the art can easily modify the present invention into other specific forms without changing the technical spirit or essential features of the present invention. Could be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present embodiment is indicated by the following claims rather than the above description, and should be construed as including all changes or modifications derived from the meaning and scope of the claims and their equivalents.

Claims (11)

A method for generating location information of a user device by processing correction information of a global navigation satellite system (GNSS) in a user device,
Receiving the correction information from a central processing device;
Determining whether the valid time of the correction information has elapsed;
Generating first location information of the user device immediately before the valid time elapses using the correction information when the valid time elapses; And
Generating second position information of a current time point after the valid time elapses of the user device by using the first position information of the user device and a carrier phase integration technique;
Including, the method. The method of claim 1,
Determining whether the valid time of the correction information has elapsed,
Generating location information of a current time point of the user device using the correction information when the valid time has not elapsed;
Including, the method. The method of claim 1,
Generating the second location information,
Receiving carrier phase data;
Calculating an amount of change in position of the user device by integrating the received carrier phase data; And
Generating the second position information of the user device using the calculated position change amount and the first position information of the user device;
Including, the method. The method of claim 1,
Receiving the correction information,
Receiving the correction information directly from the central processing device without at least one of a ground based reinforcement system and a satellite based reinforcement system;
Including, the method. The method of claim 3, wherein
The carrier phase data is, (here, Is the satellite location, Is the receiver location, Is the line of sight between the satellite and the receiver, Is a satellite positioning error, Is an ionospheric delay error, Is the convective delay error, Is a satellite clock error, Receiver error, RF frequency wavelength of the GNSS signal, Is an unknown, Is the carrier phase data It is calculated by the measurement error of). The method of claim 1,
The method,
Receiving data from at least one reference station receiving satellite signals at the central processing device;
Generating correction information using the received data; And
Transmitting the generated correction information to a user device without at least one of a ground-based reinforcement system and a satellite-based reinforcement system;
Further comprising, the method. The method of claim 6,
Generating the correction information,
Preprocessing the received data; And
Generating correction information using the preprocessed data;
Including, the method. The method of claim 6,
Generating the correction information,
Sequentially generating correction information about an ionospheric delay error and correction information about an orbit and a clock error of a satellite;
Including, the method. In the user device for generating the location information of the user device using the correction information of the Global Navigation Satellite System (GNSS),
A communication unit for receiving the correction information from a central processing device; And
It is determined whether the valid time of the correction information has elapsed, and when the valid time has elapsed, first position information of the user device immediately before the valid time elapses is generated using the correction information, and the carrier phase integration is generated. A user device location information generation unit configured to generate second location information of a current time point after the valid time elapses of the user device;
The user device comprising a. A computer-readable recording medium having recorded thereon a program for executing the method of claim 1 on a computer. delete