JP4492295B2 - Time synchronization system - Google Patents

Description

  The present invention relates to a time synchronization system that enables synchronization with a reference time, a terminal device, a terminal device control method, a terminal device control program, and a computer-readable recording medium that records the terminal device control program. is there.

Conventionally, a positioning system that measures the current position of a GPS receiver by using, for example, a GPS (Global Positioning System) that is a satellite navigation system has been put into practical use. In this positioning system, the distance between the GPS satellite and the GPS receiver (hereinafter referred to as a pseudo-range) is determined from the time difference between the time when the satellite signal is transmitted from the GPS satellite and the time when the GPS receiver receives the satellite signal. ) To calculate the current position based on a plurality of pseudo distances.
Therefore, in the above-described positioning system, it is desirable that the GPS receiver is synchronized with the time used by the GPS satellite (hereinafter referred to as GPS time) in order to improve the positioning accuracy and shorten the positioning calculation time. It is.
On the other hand, a technique has been proposed in which a mobile phone is synchronized with GPS time by receiving a signal from a base station synchronized with GPS time (for example, Patent Document 1).
JP-T-2004-507186 (FIG. 5 etc.)

  However, even if the accurate GPS time is put on the signal from the base station, the time at which the mobile phone receives the signal from the base station by the signal transmission time until the signal arrives from the base station to the mobile phone. There is a discrepancy between the correct GPS time.

  Accordingly, the present invention provides a time synchronization system and a terminal device that can accurately calculate a signal propagation delay time from a reference time information providing device that transmits a signal with a reference time and synchronize with the reference time. An object of the present invention is to provide a terminal device control method, a terminal device control program, and a computer-readable recording medium recording the terminal device control program.

  According to the first aspect, the object is to provide a reference time information providing device that provides reference time information indicating a reference time, a terminal device that can communicate with the reference time information providing device, and a device that can communicate with the terminal device. A propagation delay information providing device, wherein the propagation delay information providing device is a distance between the reference time information providing device and the propagation delay information providing device, and / or the reference time. Propagation delay information storing means for storing propagation delay information indicating a time until a signal arrives at the propagation delay information providing apparatus from the information providing apparatus, and the terminal apparatus receives the reference time from the reference time information providing apparatus. Reference time information receiving means for receiving information, propagation delay information receiving means for receiving the propagation delay information from the propagation delay information providing apparatus, reference time information and the propagation delay information A correction reference time information generating means for correcting the reference time information to generate correction reference time information, and a terminal time correction for correcting the time of the terminal clock inside the terminal device based on the correction reference time information. And a time synchronization system characterized by comprising:

  According to the configuration of the first invention, the terminal device can receive the reference time information from the reference time information providing device by the reference time information receiving means. However, if the time of the terminal clock is corrected using the reference time information as it is, an error corresponding to a propagation delay of the reference time information is generated, and the time of the terminal clock cannot be accurately set to the reference time. Note that matching the times generated by different devices with each other is hereinafter referred to as time synchronization.

  Therefore, the terminal device further includes the propagation delay information receiving unit and the correction reference time information generating unit. The propagation delay information receiving means can receive the propagation delay information. The propagation delay information includes a distance between the reference time information providing apparatus and the propagation delay information providing apparatus and / or a signal from the reference time information providing apparatus until the signal reaches the propagation delay information providing apparatus. It is information indicating time. For example, if the calculation is performed by dividing the distance between the reference time information providing device and the propagation delay information providing device by the speed of light, the error for the propagation delay can be calculated. The time until the signal reaches the propagation delay information providing apparatus indicates the error of the above-described propagation delay as it is.

Then, the terminal device can generate the corrected reference time information by correcting the reference time information based on the reference time information and the propagation delay information by the corrected reference time information generating means. The corrected reference time information is information indicating, for example, a time obtained by delaying the transmission time of the reference time indicated by the reference time information by the above-described propagation delay. That is, it shows the true reference time when the terminal device receives the reference time information.
Therefore, the terminal device corrects the time of the terminal clock when the reference time information is received by the terminal time correction unit based on the correction reference time information, thereby correcting the time of the terminal clock. It can be synchronized to the time.
Accordingly, it is possible to accurately calculate the signal propagation delay time from the reference time information providing apparatus that transmits the signal with the reference time and synchronize with the reference time.

  According to a second aspect of the present invention, there is provided a reference time information receiving means for receiving the reference time information from a reference time information providing apparatus that provides reference time information indicating a reference time, and a communication with the reference time information providing apparatus. A signal arrives from the possible propagation delay information providing device to the distance between the reference time information providing device and the propagation delay information providing device and / or from the reference time information providing device to the propagation delay information providing device. A propagation delay information receiving means for receiving propagation delay information indicating a time until, and a correction reference that generates correction reference time information by correcting the reference time information based on the reference time information and the propagation delay information A terminal device comprising: time information generating means; and terminal time correcting means for correcting the time of the terminal clock inside the terminal device based on the correction reference time information. It is achieved by.

  According to the configuration of the second invention, the terminal device accurately determines the propagation delay time of the signal from the reference time information providing device that transmits the signal carrying the reference time, as in the configuration of the first invention. It can be calculated and synchronized with the reference time.

  According to a third invention, in the configuration of the second invention, the time accuracy of the terminal clock corrected by the terminal time correction means based on the signal frequency of the reference time information providing device and the unit signal of the terminal clock is obtained. It has the time precision maintenance means to maintain, It is characterized by the above-mentioned.

  According to the configuration of the third invention, since the terminal device has the time accuracy maintaining means, the terminal time correction means once sets the terminal clock inside the terminal device based on the correction reference time information. When the time is corrected, the time of the terminal clock can be maintained in synchronization with the reference time without newly acquiring the reference time information from the reference time information providing apparatus.

  According to a fourth aspect of the invention, there is provided Doppler deviation detecting means for detecting a Doppler deviation generated in a signal frequency of the reference time information providing device due to relative movement between the terminal device and the reference time information providing device. And when the Doppler deviation is detected, the time of the terminal clock is corrected again by the reference time information receiving means, the propagation delay information receiving means, the corrected reference time information generating means, and the terminal time correcting means. It is the structure which carries out.

According to the structure of 4th invention, the said terminal device can detect the Doppler deviation produced by the relative movement of the said terminal device and the said reference time information provision apparatus by the said Doppler deviation detection means. When the Doppler deviation occurs, the signal frequency of the reference time information providing device varies, so the signal frequency of the reference time information providing device cannot be used as a reference, and the time of the terminal clock The accuracy cannot be maintained. The Doppler bias means a frequency shift due to the Doppler effect.
Therefore, when the terminal device detects the Doppler deviation, the terminal device corrects the time of the terminal clock again.
Thereby, it can be ensured that the time of the terminal clock is synchronized with the reference time.

  According to a fifth aspect of the present invention, in any one of the second to fourth aspects of the present invention, there is provided positioning means for positioning a current position based on a position related signal from a position information satellite, and the reference time is the position information. A configuration for performing the positioning based on the position-related signals of the number of satellites that is one less than the normal number of satellites of the position information satellite required for positioning when synchronized with the time used by the satellite; It is characterized by becoming.

According to the configuration of the fifth aspect of the invention, when the reference time is synchronized with the time used by the position information satellite, the terminal device uses the normal number of position information satellites necessary for positioning. However, it is possible to perform the positioning based on the position-related signals of the number of satellites that is one less.
The normal number of satellites necessary for the positioning is four or more in the case of three-dimensional positioning and three or more in the case of two-dimensional positioning. However, one of the position information satellites is used to calculate the time used by the position information satellite. Therefore, if the terminal device is synchronized with the time used by the location information satellite, the number of the location information satellites used for the positioning may be one less.
In this regard, when the reference time is synchronized with the time used by the position information satellite, the number of terminal devices that can be synchronized with the reference time is, for example, three in the case of three-dimensional positioning. In the case of dimensional positioning, for example, the current position can be measured based on the position-related signals from two position information satellites, and as a result, the time required for positioning the current position can be shortened. .

  According to a sixth aspect of the present invention, there is provided a reference time information receiving step in which the terminal device receives the reference time information from a reference time information providing device that provides reference time information indicating a reference time. From the propagation delay information providing apparatus communicable with the reference time information providing apparatus, the distance between the reference time information providing apparatus and the propagation delay information providing apparatus, and / or the propagation from the reference time information providing apparatus. A propagation delay information receiving step for receiving propagation delay information indicating a time until a signal arrives at the delay information providing device, and the terminal device determines the reference time based on the reference time information and the propagation delay information. A correction reference time information generation step for correcting the information to generate correction reference time information; and the terminal device is connected to an end of the terminal device based on the correction reference time information. It is achieved by the control method of the terminal apparatus characterized by having a terminal time correction step of correcting the time of the clock.

  According to the configuration of the sixth invention, similarly to the configuration of the second invention, the terminal device accurately determines the propagation delay time of the signal from the reference time information providing device that transmits the signal with the reference time. It can be calculated and synchronized with the reference time.

  According to a seventh aspect of the present invention, there is provided a reference time information receiving step in which a terminal device receives the reference time information from a reference time information providing device that provides reference time information indicating a reference time. The distance between the reference time information providing apparatus and the propagation delay information providing apparatus and / or the reference time information providing apparatus from the propagation delay information providing apparatus capable of communicating with the reference time information providing apparatus. Propagation delay information receiving step for receiving propagation delay information indicating a time until a signal arrives at the propagation delay information providing device from the terminal device, based on the reference time information and the propagation delay information, A correction reference time information generation step for correcting the reference time information to generate correction reference time information, and the terminal device based on the correction reference time information, The terminal time correction step of correcting the time of the end device inside the terminal clock, is achieved by the control program of the terminal device, characterized in that for the execution.

  According to an eighth aspect of the present invention, there is provided a reference time information receiving step in which a terminal device receives the reference time information from a reference time information providing device that provides reference time information indicating a reference time to a computer. The distance between the reference time information providing apparatus and the propagation delay information providing apparatus and / or the reference time information providing apparatus from the propagation delay information providing apparatus capable of communicating with the reference time information providing apparatus. Propagation delay information receiving step for receiving propagation delay information indicating a time until a signal arrives at the propagation delay information providing device from the terminal device, based on the reference time information and the propagation delay information, A correction reference time information generation step for correcting the reference time information to generate correction reference time information, and the terminal device based on the correction reference time information, It is accomplished by a computer-readable recording medium a control program of the terminal device, characterized in that to execute a terminal time correction step of correcting the time of the end device inside the terminal clock, a.

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
The embodiments described below are preferred specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention is particularly limited in the following description. Unless otherwise stated, the present invention is not limited to these embodiments.

FIG. 1 is a schematic diagram showing a time synchronization system 10 and the like according to an embodiment of the present invention.
As shown in FIG. 1, the time synchronization system 10 includes base stations 20A, 20B, 20C, and 20D. The base station 20A and the like provide the reference time information indicating the reference time to the terminal 60. That is, the base station 20A and the like are an example of a reference time information providing apparatus. The reference time provided by the base station 20A or the like is obtained by receiving, for example, signals S1, S2, S3, and S4 that are position-related signals from GPS satellites 12a, 12b, 12c, and 12d that are position information satellites. It is synchronized with the time used by the satellite 12a and the like (hereinafter referred to as GPS time).

As shown in FIG. 1, the time synchronization system 10 includes a terminal 60. The terminal 60 includes a terminal communication device 70 and can communicate with the base station 20A and the like. This terminal 60 is an example of a terminal device.
The terminal 60 also includes a terminal GPS device 76 for positioning the current position based on the signal S1 from the GPS satellite 12a or the like. This terminal GPS device 76 is an example of positioning means.

  As shown in FIG. 1, the time synchronization system 10 includes an IC tag 40. The IC tag 40 is disposed on a sign 52 attached to the utility pole 50, for example. The IC tag 40 can communicate with a terminal 60 having a terminal tag reader 72 for communicating with the IC tag 40. The IC tag 40 is an example of a propagation delay information providing device.

The terminal 60 is a mobile phone, PHS (Personal Handy-phone System), PDA (Personal Digital Assistance _), or the like, but is not limited thereto.
Further, the number of base stations 20A and the like is not limited to four, and the number of GPS satellites 12a and the like is not limited to four.

Unlike the present embodiment, the IC tag 40 is not limited to the sign 52 of the utility pole 50, but may be installed near a traffic light, a traffic sign, a sidewalk, a store, the entrance of a station, or the like.
Also, unlike the present embodiment, terminal 60 may be configured to be able to perform base station positioning (TDOA: Time difference of Arrival) instead of GPS positioning.

(Main hardware configuration of base station 20A)
FIG. 2 is a schematic diagram showing the main hardware configuration of the base station 20A.
Note that the main hardware configuration of the base stations 20B, 20C, and 20D is the same as that of the base station 20A, and thus the description thereof is omitted.
As shown in FIG. 2, the base station 20 </ b> A has a computer, and the computer has a bus 22.

  The bus 22 is connected to a CPU (Central Processing Unit) 24, a storage device 26, an external storage device 28, and the like. The storage device 26 is, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory). The external storage device 28 is, for example, an HD (Hard Disk).

The bus 22 is connected to an input device 30 for inputting various information.
The bus 22 includes a base station communication device 32 for communicating with the terminal 60, a base station clock 34 for generating reference time information, a base station for receiving a signal S1 and the like from the GPS satellite 12a, etc. A GPS device 36 is connected.
Further, a base station display device 38 for displaying various information and the like is connected to the bus 22.

(Hardware configuration of IC tag 40)
FIG. 3 is a schematic diagram showing a hardware configuration of the IC tag 40.
The IC tag 40 has a tag main body 40a made of vinyl chloride or the like, and an IC chip 40b is disposed on the tag main body 40a.

  The IC tag 40 includes an IC (integrated circuit) chip 40b and an antenna unit 40c that transmits and receives information by being in non-contact and close proximity. Since this IC tag 40 uses RFID (Radio Frequency Identification: automatic recognition using radio), it is configured such that information can be exchanged by exchanging radio waves without contact by the antenna unit 40c. Yes.

The antenna unit 40 c receives the IC tag excitation signal from the terminal tag reader 72 of the terminal 60 in FIG. 1 and transmits a response signal to the terminal tag reader 72.
The communicable distance of the IC tag 40 is approximately within 3 meters (m) although it depends on the radio wave intensity from the terminal tag reader 72. Therefore, when the terminal 60 is communicating with the IC tag 40, the position of the terminal 60 is substantially equal to the position of the IC tag 40.

  Since the IC tag 40 is composed of an IC, it can be miniaturized. Specifically, the size of the IC tag 40 is extremely small as compared with the sign 52, for example, the front and back surfaces having a side of 0.5 millimeters (mm) to 1.0 millimeters (mm), and smaller dimensions. It is the flat rectangular parallelepiped which has a side surface.

(Main hardware configuration of terminal 60)
FIG. 4 is a schematic diagram showing the main hardware configuration of the terminal 60.
As shown in FIG. 4, the terminal 60 has a computer, and the computer has a bus 62.
A CPU 64, a storage device 66, and the like are connected to the bus 62.

The bus 62 is connected to an input device 68 for inputting various information.
In addition, a terminal communication device 70 for communicating with the base station 20A and the like, a terminal tag reader 72, a terminal clock 74, a terminal GPS device 76, and a terminal display device 78 for displaying various information are connected to the bus 62. ing.
The terminal clock 74 is an example of a terminal clock inside the terminal 60.

(Main software configuration of base station 20A)
FIG. 5 is a schematic diagram showing a main software configuration of the base station 20A.
Note that the main software configuration of the base stations 20B, 20C, and 20D is the same as that of the base station 20A, and thus the description thereof is omitted.
As shown in FIG. 5, the base station 20A includes a base station control unit 100 that controls each unit, a base station communication unit 102 corresponding to the base station communication device 32 in FIG. 2, and a base station corresponding to the base station clock 34 in FIG. The time generation unit 104 and the base station GPS unit 106 corresponding to the base station GPS device 36 of FIG.

  As illustrated in FIG. 5, the base station 20A includes a base station first storage unit 110 that stores various programs and a base station second storage unit 150 that stores various types of information.

  As illustrated in FIG. 5, the base station 20 </ b> A stores a reference time information generation program 112 in the base station first storage unit 110. The reference time information generation program 112 is information for the base station control unit 100 to generate the reference time information 152 generated by the base station time generation unit 104.

FIG. 6 is a schematic diagram illustrating an example of the reference time information 152.
As shown in FIG. 6, the reference time information 152 includes a base station ID 152a that is an identification code of the base station 20 itself, and a transmission time 152b. The transmission time 152b is, for example, the time t1 of the moment when the marker 152c arranged at the front end portion of the reference time information 152 of one unit (also called one packet or one frame) is transmitted with the base station ID 152a and the transmission time information 152b.
As shown in FIG. 6, since the marker 152c is arranged at the packet boundary, the reference time information 152 is also the moment of transmission of the packet boundary (packet boundary time).
The time generated by the base station time generation unit 104 is synchronized with the GPS time based on the signal S1 and the like from the GPS satellite 12a received by the base station GPS unit 106. Therefore, t1 which is the transmission time 152b is also synchronized with the GPS time.

  As illustrated in FIG. 5, the base station 20 </ b> A stores a reference time information transmission program 114 in the base station first storage unit 110. The reference time information transmission program 114 is information for the base station control unit 100 to transmit the reference time information 152 to the terminal 60 that has requested the reference time information 152.

Note that, unlike the present embodiment, the reference time information 152 may indicate the transmission time of the immediately preceding frame instead of the transmission time of the marker 152c.
Unlike the present embodiment, the base station 20A does not transmit the reference time information 152 in response to a request from the terminal 60, but transmits the reference time information 152 at regular intervals such as every 30 seconds (s). May be transmitted automatically. In this case, the terminal 60 needs to have a broadcast receiver such as an FM receiver for receiving the reference time information 152 transmitted periodically.

(About software configuration of IC tag 40)
FIG. 7 is a schematic diagram showing a main software configuration of the IC tag 40.
As shown in FIG. 7, the IC tag 40 transmits an excitation signal receiving unit 200 that receives an excitation signal from the terminal tag reader 72 of the terminal 60 of FIG. 1 and a response signal based on the distance information 206 to the terminal tag reader 72. The response signal transmission unit 202 is provided.

  The IC tag 40 also has an information storage file 204 that stores distance information 206. The distance information 206 is an example of propagation delay information, and the information storage file 204 is an example of propagation delay information storage means.

FIG. 8 is a schematic diagram illustrating an example of the distance information 206.
As shown in FIG. 8, the distance information 206 is information indicating a base station ID for identifying each base station 20A, 20B, 20C and 20D and a distance corresponding to each base station ID. The distance indicated by the distance information 206 is information indicating the distance between each base station 20A and the like and the IC tag 40.

Unlike the present embodiment, the distance information 206 is not the distance between the plurality of base stations 20A and the like and the IC tag 40, but is the base station closest to the position of the IC tag 40, for example, the base station 20A and the IC Only the distance to the tag 40 may be indicated.
Further, unlike the present embodiment, instead of the distance information 206, the time until a signal (radio wave) reaches the IC tag 40 from each base station 20A or the like or the base station closest to the position of the IC tag 40 is shown. You may do it.

(About the software configuration of the terminal 60)
FIG. 9 is a schematic diagram illustrating a main software configuration of the terminal 60.
9, the terminal 60 includes a terminal control unit 300 that controls each unit, a terminal communication unit 302 that corresponds to the terminal communication device 70 in FIG. 4, a terminal tag reader unit 304 that corresponds to the terminal tag reader 72 in FIG. Terminal time generation unit 306 corresponding to the terminal clock 74 of FIG. 4, a terminal GPS unit 308 corresponding to the terminal GPS device 76 of FIG.

As illustrated in FIG. 9, the terminal 60 stores a reference time information acquisition program 312 in the terminal first storage unit 310. The reference time information acquisition program 312 is information for the terminal control unit 300 to acquire the reference time information 152 (see FIG. 6) from the base station 20A or the like. That is, the reference time information acquisition program 312 and the terminal control unit 300 are examples of reference time information acquisition means.
Specifically, the terminal control unit 300 receives the reference time information 152 by the terminal communication unit 302 according to the reference time information acquisition program 312 and stores it in the terminal second storage unit 350 as the terminal-side reference time information 352.

FIG. 10 is a schematic diagram showing the terminal-side reference time information 352 and the like.
As shown in FIG. 10, the terminal side reference time information 352 includes, for example, the base station ID of the base station 20A that has received the reference time information 152 and the marker 152c of the reference time information 152 (see FIG. 6). Is information indicating transmission time information t1 that is the time at which is transmitted.

As illustrated in FIG. 9, the terminal 60 stores a marker reception time information generation program 314 in the terminal first storage unit 310. The marker reception time information generation program 314 is information for generating the marker reception time information 354 indicating the time at which the terminal control unit 300 receives the marker 152c of the reference time information 152. The time at which the marker 152c is received is measured by the terminal clock 74 corresponding to the terminal time generation unit 306. The marker reception time information 354 is information indicating the time t2 at the moment when the marker 152c measured by the terminal clock 74 is received, as shown in FIG.
The terminal control unit 300 stores the generated marker reception time information 354 in the terminal second storage unit 350.

Here, the terminal 60 does not correct the time generated by the terminal clock 74 using the transmission time t1 and the marker reception time t2 as they are. If the transmission time t1 is used as it is, an error corresponding to a propagation delay until the reference time information 152 arrives at the terminal 60 from the base station 20A occurs, and the time of the terminal clock 74 can be accurately adjusted to the reference time of the base station 20A. It is not possible.
Therefore, the terminal 60 further has the following configuration.

  As illustrated in FIG. 9, the terminal 60 stores a distance information acquisition program 316 in the terminal first storage unit 310. The distance information acquisition program 316 is information for the terminal control unit 300 to acquire the distance information 206 (see FIG. 7) from the IC tag 40 (see FIG. 1). That is, the distance information acquisition program 316 and the terminal control unit 300 are examples of propagation delay information acquisition means.

  Specifically, the terminal control unit 300 receives the distance information 206 by the terminal tag reader unit 304 in accordance with the distance information acquisition program 316 and stores it in the terminal second storage unit 350 as the terminal side distance information 356.

As shown in FIG. 10C, the terminal-side distance information 356 is a distance between the base station 20A and the IC tag 40 when the terminal 60 acquires the reference time information 152 from the base station 20A. It is information indicating 5 kilometers (km).
As described above, the communicable distance of the IC tag 40 is approximately within 3 meters (m), so that the position of the terminal 60 in communication with the IC tag 40 is substantially equal to the position of the IC tag 40. Therefore, for example, the distance of 5 kilometers (km) shown in the terminal-side distance information 356 is also the distance between the base station 20A and the terminal 60.

  As shown in FIG. 8, when the distance information 206 of the IC tag 40 includes the distances between the plurality of base stations 20A to 20D, the terminal 60 includes the distances between the plurality of base stations 20A and the like. The information 206 is received, and only the distance corresponding to the base station 20A is selected using the base station ID of the base station 20A and stored in the terminal second storage unit 350 as the terminal-side distance information 356.

  As illustrated in FIG. 9, the terminal 60 stores a delay time information generation program 318 in the terminal first storage unit 310. The delay time information generation program 318 causes the terminal control unit 300 to generate delay time information 358 indicating the time required for the signal (radio wave) from the base station 20A to travel the distance indicated by the terminal-side distance information 356. Information.

FIG. 11 is a schematic diagram showing the delay time information 358 and the like.
The propagation speed of radio waves is 300,000 kilometers per second (km / s). Therefore, according to the delay time information generation program 318, the terminal control unit 300 divides 5 kilometers (km) indicated by the terminal-side distance information 356 (see FIG. 10C) by 300,000 kilometers (km / s) per second. As a result, delay time information 358 indicating n seconds (s) is generated.
The terminal control unit 300 stores the generated delay time information 358 in the terminal second storage unit 350.

  Unlike the present embodiment, the information storage file 204 (see FIG. 7) of the IC tag 40 has a time (delay) required for a signal (radio wave) to travel the distance between the base station 20A and the IC tag 40. Terminal 60 acquires information indicating the delay time from the IC tag and uses it as delay time information 358 as it is.

  As illustrated in FIG. 9, the terminal 60 stores a modified transmission time information generation program 320 in the terminal first storage unit 310. In the modified transmission time information generation program 320, the terminal control unit 300 causes the transmission time t1 (see FIG. 10A) indicated in the terminal-side reference time information 352 to be the delay time n indicated in the delay time information 358 (FIG. 11 ( This is information for generating correction transmission time information 360 (see FIG. 11 (b)) based on (a). The corrected transmission time information 360 is an example of correction reference time information. The modified transmission time information generation program 320 and the terminal control unit 300 are an example of correction reference time information generation means.

Specifically, the terminal control unit delays the transmission time t1 by the delay time n in accordance with the modified transmission time information generation program 320, and the modified transmission time information 360 (see FIG. 11B) indicating the modified transmission time t1 + n. Generate. Since the corrected reference time information 360 is generated based on the accurate transmission time t1 and the accurate delay time n, an accurate reference at the moment when the terminal 60 receives the marker 152c of the reference time information 152 from the base station 20A. Indicates the time.
The terminal control unit 300 stores the generated modified transmission time information 360 in the terminal second storage unit 350.

  As illustrated in FIG. 9, the terminal 60 stores a terminal clock correction value information generation program 322 in the terminal first storage unit 310. The terminal clock correction value information generation program 322 includes terminal clock correction value information indicating a correction value for the terminal control unit 300 to correct the time of the terminal clock 74 based on the marker reception time information 354 and the corrected transmission time information 360. This is information for generating 362.

As described above, the marker reception time information 354 indicates the time when the terminal clock 74 measures the instant at which the terminal 60 received the marker 152c of the reference time information 152 from the base station 20A.
On the other hand, as described above, the corrected transmission time information 360 indicates an accurate reference time at the moment when the terminal 60 receives the marker 152c of the reference time information 152 from the base station 20A.
Therefore, the difference t2− (t1 + n) between the marker reception time t2 (see FIG. 10B) shown in the marker reception time information 354 and the corrected transmission time t1 + n (see FIG. 11B) shown in the corrected transmission time information 360. ) Is the terminal clock correction value.
Therefore, the terminal control unit 300 performs the terminal clock correction value information 362 indicating the terminal clock correction value t2- (t1 + n) based on the marker reception time information 354 and the corrected transmission time information 360 according to the terminal clock correction value information generation program 322. (See FIG. 11C).
The terminal control unit 300 stores the generated terminal clock correction value information 362 in the terminal second storage unit 350.

As illustrated in FIG. 9, the terminal 60 stores a terminal clock correction program 324 in the terminal first storage unit 310. The terminal clock correction program 324 is information for the terminal control unit 300 to correct the time generated by the terminal clock 74 based on the terminal clock correction value information 362.
For example, if the terminal clock correction value is a plus (+) value, the time of the terminal clock 74 is advanced from the reference time of the base station 20A, so the terminal control unit 300 follows the terminal clock correction program 324 in accordance with the terminal clock correction program 324. A process of delaying by the time indicated by the correction value is performed. Specifically, in the process of generating the basic frequency of the terminal clock 74, for example, in the process of converting the frequency generated by a crystal oscillator (not shown) into time, processing such as changing the conversion rate is performed.
On the other hand, if the terminal clock correction value is a minus (−) value, the time of the terminal clock 74 is delayed from the reference time of the base station 20A, so the terminal control unit 300 follows the terminal clock correction program 324. The time of the terminal clock 74 is advanced by the time indicated by the terminal clock correction value.
The terminal clock correction value information generation program 320, the terminal clock correction program 324, and the terminal control unit 300 described above are examples of terminal time correction means.

  As described above, the terminal 60 can accurately calculate the reference time information 152 from the base station 20A and the propagation delay time of the signal carrying the reference time information 152, and can synchronize with the reference time.

As illustrated in FIG. 9, the terminal 60 stores a terminal positioning program 326 in the terminal first storage unit 310. The terminal positioning program 326 is information for the terminal control unit 300 to determine the minimum necessary number of GPS satellites 12a and the like necessary for positioning the current position.
Specifically, based on the terminal positioning program 326, the terminal control unit 300, when the time of the terminal clock 74 is synchronized with the reference time of the base station 20A or the like, normal GPS satellites 12a and the like necessary for positioning The minimum necessary number is determined so that positioning is performed based on the signal S1 or the like of the number of satellites one less than the number of satellites.

The number of normal satellites required for positioning is four or more in the case of three-dimensional positioning, and three or more in the case of two-dimensional positioning. However, one of these GPS satellites is used for calculating GPS time. Therefore, if the terminal 60 is synchronized with the GPS time, the number of GPS satellites 12a and the like used for positioning may be one less.
As described above, since the reference time of the base station 20A and the like is synchronized with the GPS time, the number of terminals 60 synchronized with the reference time is, for example, three in the case of three-dimensional positioning, and in the case of two-dimensional positioning. For example, the current position can be measured based on the signals S1 from the two GPS satellites 12a and the like, and as a result, the time required for positioning the current position can be shortened.
Unlike this embodiment, if the number of satellites used for positioning is not reduced by one, GPS satellites that should be used for GPS time calculation are used to calculate latitude, longitude, and altitude. Therefore, positioning accuracy can be improved.

The above is the configuration of the time synchronization system 10 according to the present embodiment. Hereinafter, an example of the operation will be mainly described with reference to FIG.
FIG. 12 is a schematic flowchart showing an operation example of the time synchronization system 10 according to the present embodiment.
The terminal 60 will be described below on the assumption that it is connected to the base station 20A.

First, the terminal 60 receives the reference time information 152 (see FIG. 6) from the connected base station 20A (step ST1 in FIG. 12). This step ST1 is an example of a reference time information acquisition step. The reference time information 152 includes a base station ID 152a, a transmission time 152b, and a marker 152c. The terminal 60 stores the acquired reference time information 152 as terminal-side reference time information 352 (see FIG. 10A) in the terminal second storage unit 350 (see FIG. 9).

  Subsequently, the terminal 60 receives distance information 206 (see FIG. 8) from the IC tag 40 (step ST2). This step ST2 is an example of a propagation delay information acquisition step. Since the position of the terminal 60 in communication with the IC tag 40 is substantially equal to the position of the IC tag 40, the distance between the base station 20A and the IC tag 40 indicated by the distance information 206 is the current position of the base station 20A and the terminal 60. It is also the distance. The terminal 60 stores the distance between the base station 20A and the current position in the terminal second storage unit 350 (see FIG. 9) as terminal-side distance information 356 (see FIG. 10C).

Subsequently, the terminal 60 determines whether or not the terminal side distance information 356 indicating the distance from the current position to the base station 20A has been acquired (step ST3), and can acquire the terminal side distance information 356. If it is determined that it has been completed, the process proceeds to step ST4.
In step ST4, the terminal 60 generates delay time information 358 (see FIG. 11A) based on the terminal-side distance information 356.

  Subsequently, the terminal 60 generates the corrected transmission time information 360 (see FIG. 11B) based on the transmission time included in the terminal-side reference time information 352 and the delay time indicated by the delay time information 358 (step ST5). ). This step ST5 is an example of a correction reference time information generation step.

Subsequently, the terminal 60 corrects the time of the terminal clock 74 based on the corrected transmission time information 360 (step ST6). This step ST6 is an example of a terminal time correction step.
In step ST6, the difference between the marker reception time t2 shown in the marker reception time information 354 (see FIG. 10B) and the correction transmission time t1 + n shown in the correction transmission time information 360 (see FIG. 11B). Terminal clock correction value information 362 (see FIG. 11C) indicating t2- (t1 + n) is generated, and the time of the terminal clock 74 is corrected based on the terminal clock correction value information 362.

  In step ST3 described above, when the terminal 60 determines that the terminal-side distance information 356 has not been acquired, it is based on the transmission time t1 of the terminal-side reference time information 352 (see FIG. 10A). Then, the time of the terminal clock 74 is corrected (step ST41). The transmission time t1 does not indicate the correct reference time at the moment when the marker 152c is received. Therefore, although the positioning by the terminal GPS device 76 takes time, since the accurate time can be acquired when the positioning by the terminal GPS device 76 is finished, the terminal 60 is based on the accurate GPS time acquired by the positioning, The time of the terminal clock 74 can be corrected.

The terminal 60 periodically performs the above-described step ST1 and the like.
This timing depends on the accuracy (clock accuracy) error tolerance of the terminal clock 74. For example, the tolerance is 0.01 ppm (parts per million), and 0 until 24 hours (h) elapses. If the clock accuracy does not cause an error of 0.01 ppm, the above-described step ST1 and the like are performed every 24 hours (h). For example, the allowable range of the error in the clock accuracy is defined by the range in which the terminal GPS device 76 can perform positioning with one fewer satellites than the number of satellites necessary for normal positioning. This range is, for example, 0.01 ppm.

  Unlike the present embodiment, the timing at which terminal 60 executes step ST1 is, for example, detected that terminal 60 has shifted from the coverage of base station 20A to the coverage of base station 20B (so-called hands-over). It is also good when you do.

This embodiment is particularly effective for GPS positioning, as will be described below.
In order to perform quick positioning with a GPS receiver incorporated in a device such as a mobile phone, a navigation message of GPS satellites, an approximate position, and an accurate time are required. For example, if the time is shifted by 1 millisecond (ms), the propagation speed of the radio wave is 300,000 kilometers (km / s) per second, and therefore appears as an error of 300 kilometers (km). When the time is shifted by 1 microsecond (μs), an error of 300 meters (m) appears.
In GPS positioning, a signal transmitted from a GPS satellite includes a parameter indicating time and a parameter indicating the orbit position of the GPS satellite. If the approximate position of the GPS receiver is known, signals from a plurality of GPS satellites can be obtained. By solving simultaneous equations based on, it is possible to estimate the exact time and position. In order to solve this equation, it is necessary to receive signals from at least four GPS satellites for three-dimensional positioning.
Here, when accurate time is held in advance, the calculation can be performed with signals from at least three GPS satellites. This is because when a signal from a GPS satellite is obstructed by a building in an urban area or the like, only a small number of GPS satellites can be observed. Therefore, time synchronization is greatly affected by the GPS receiver that performs GPS positioning. It will be a merit.
This also affects the positioning accuracy. In particular, the single-point positioning with a GPS receiver has a great influence on the positioning accuracy. Here, single-point positioning is a method used by mobile devices, such as starting a GPS receiver, performing positioning once, and stopping the GPS receiver, and corrects positioning accuracy unlike continuous positioning. However, it is generally a method with lower positioning accuracy than continuous positioning.
According to the present embodiment, since time synchronization in terminal 60 can be performed accurately, positioning can be performed with high accuracy even in single positioning.

(Second Embodiment)
Next, a second embodiment will be described.
Since the configuration of the time synchronization system 10A (see FIG. 1) in the second embodiment has many configurations in common with the time synchronization system 10 in the first embodiment, the common parts have the same reference numerals, etc. The description will be omitted, and the difference will be mainly described below.

FIG. 13 is a schematic diagram showing a main hardware configuration of a terminal 60A used in the time synchronization system 10A.
As illustrated in FIG. 13, the terminal 60 </ b> A includes a carrier frequency counter 80. The carrier frequency counter 80 is a device for measuring the carrier signal frequency of a signal from the base station 20A or the like for each one-second pulse transmitted from the terminal clock 74. The carrier signal frequency is an example of a signal frequency, and the 1-second pulse signal transmitted from the terminal clock 74 is an example of a unit signal.

FIG. 14 is a schematic diagram illustrating a main software configuration of the terminal 60A.
As illustrated in FIG. 14, the terminal 60 </ b> A stores a 1-second pulse error measurement program 328 in the terminal first storage unit 310. The 1-second pulse error measurement program 328 is information for the terminal control unit 300 to measure the carrier signal frequency from the base station 20A or the like based on the transmission interval of the 1-second pulse signal transmitted from the terminal clock 74. .

As illustrated in FIG. 14, the terminal 60 </ b> A stores a terminal clock error correction program 330 in the terminal first storage unit 310. The terminal clock error correction program 330 is the time of the terminal clock 74 corrected by the terminal clock correction program 324 by the terminal control unit 300 based on the carrier signal frequency from the base station 20A or the like and the 1 second pulse signal of the terminal clock 74. This is information for maintaining the accuracy of. That is, the terminal clock error correction program 330 and the terminal control unit 300 are examples of time accuracy maintaining means.
If the carrier signal frequency from the base station 20A or the like is stable at 1.5 gigahertz (GHz), for example, it is 1.5 based on 1 second (s) of the terminal clock 74 that is the internal clock of the terminal 60A. If a carrier signal that is not gigahertz (GHz) is detected, it can be considered that the terminal clock 74 has caused an error or jitter.
Here, the error of the terminal clock 74 means an amount that deviates from an expected value due to a change in characteristics or temperature of an element such as a crystal resonator that generates the fundamental frequency of the terminal clock 74 in advance. This is a gentle change.
On the other hand, jitter is a sudden shift during the operation of the element, and is an unstable operation without regularity or vibration that occurs once every 10,000 times, for example.

  Therefore, the terminal control unit 300, for example, based on 1 second (s) of the terminal clock 74, the carrier signal frequency from the base station 20A is a frequency that is 1 / 10,000th (%) higher than 1.5 gigahertz (GHz). If so, it is considered that the transmission frequency of the terminal clock 74 is shifted by that amount. Then, the terminal control unit 300 includes a terminal time generation unit 306 so that the terminal clock 74 transmits a 1-second pulse at a frequency that is 1 / 10,000 (%) higher than the carrier signal frequency of 1.5 GHz (GHz). Modify the time generation function.

  Therefore, once the terminal control unit 300 corrects the time of the terminal clock 74 by the terminal clock correction program 324 or the like, the terminal does not newly acquire the reference time information 152 (see FIG. 5) from the base station 20A or the like. The time of the clock 74 can be maintained in synchronization with the reference time.

  Unlike the present embodiment, the carrier signal frequency from the base station 20A or the like may be lower, for example, an intermediate frequency, or a signal frequency from a stable frequency generator other than the base station 20A or the like. May be used to maintain the accuracy of the time of the terminal clock 74 once corrected.

As illustrated in FIG. 14, the terminal 60 </ b> A stores a Doppler bias detection program 332 in the terminal first storage unit 310. The Doppler deviation detection program 332 is information for the terminal control unit 300 to detect the Doppler deviation generated in the carrier signal frequency from the base station 20A due to the relative movement between the terminal 60A and the base station 20A, for example. That is, the Doppler deviation detection program 332 and the terminal control unit 300 are examples of Doppler deviation detection means.
For example, the terminal 60A detects the Doppler bias by detecting that the terminal 60A has moved from the cover range of the base station 20A to the cover range of the base station 20B (hands over). The occurrence of a hands-over means that the terminal 60A has moved relative to the base station 20A and the base station 20B at fixed positions, and therefore detects a Doppler bias through the detection of a hands-over. It can be done.
Further, when the terminal control unit 300 detects the Doppler deviation of the carrier signal frequency of the base station 20A or the like based on the Doppler deviation detection program 332, the reference time information acquisition program 312, the marker reception time information generation program 314, the distance The time of the terminal clock 74 is corrected again by the information acquisition program 316, the delay time information generation program 318, the modified transmission time information generation program 320, the terminal clock correction value information generation program 322, and the terminal clock correction program 324. .

When the Doppler deviation occurs in the carrier signal frequency from the base station 20A or the like, the carrier signal frequency itself fluctuates. Therefore, the time accuracy of the terminal clock 74 is maintained with reference to the carrier signal frequency of the base station 20A or the like. I can't.
Therefore, when the terminal 60A detects the Doppler bias, the terminal 60A corrects the time of the terminal clock 74 again.
Thereby, it can be ensured that the time of the terminal clock 74 is synchronized with the reference time of the base station 20A or the like.

  Unlike the present embodiment, the terminal 60A does not hands over Doppler bias, but has a PLL (Phase Locked Loop) in the terminal 60A, and causes Doppler bias due to PLL shift. You may make it detect.

  Also, unlike the present embodiment, when the error or jitter of the terminal clock 74 is outside the allowable range, the terminal 60A performs the above-described step ST1 etc. every 300 seconds (s), for example. Also good. If the error or jitter is greater than 0.3 pM (ppm), for example, the 1-second pulse on the terminal clock 74 side cannot be referred to as the time reference, so that the accuracy of the corrected time can be maintained. It is not possible. In this regard, if the above-described step ST1 is periodically performed when the error or jitter of the terminal clock 74 is outside the allowable range, the time of the terminal clock 74 is periodically corrected and maintained at the reference time. You can continue. Such a configuration is particularly effective when the terminal clock 74 has no temperature compensation circuit.

As a method of time synchronization, there is generally a method in which a terminal is connected to a network and keeps the time by inquiring the time from an accurate time source. According to this method, it is possible to measure the delay with the time source in the inquiry procedure, but since this delay is not necessarily constant depending on the network through which the inquiry procedure passes, it is not possible to keep the time of the terminal accurate. Have difficulty.
In addition, there is a method in which a delay time (that is, a pseudorange in GPS positioning) is calculated and precisely synchronized with a time source based on an atomic clock by GPS positioning or the like. However, depending on environmental conditions such as the inside of the building and underground, the terminal cannot always perform GPS positioning, and it is difficult to keep the time accurate.
In this regard, for example, the terminal 60A according to the present embodiment receives accurate reference time information 152 from the base station 20A or the like as long as it can communicate with the base station 20A or the like. Then, for example, distance information 206 indicating the distance to the base station 20A is received from the IC tag 40 located in the vicinity of the terminal 60A, and the delay time is accurately calculated by dividing the distance indicated by the distance information 206 by the speed of light. can do. Then, based on the terminal-side reference time information 352 and the delay time information 358, the transmission time can be corrected and the accurate reception time of the reference time information 152 can be calculated.
That is, the terminal 60A can know the distance to the base station 20A, for example, without performing GPS positioning, and can obtain and maintain an accurate time by taking into account the propagation delay derived from the distance. Can do.

(About programs and computer-readable recording media)
A terminal device control program for causing a computer to execute the reference time information reception step, the propagation delay information reception step, the correction reference time information generation step, the terminal time correction step, and the like of the above-described operation example can be provided.
Moreover, it can also be set as the computer-readable recording medium etc. which recorded the control program etc. of such a terminal device.

  A program storage medium used for installing the control program of the terminal device in the computer and making it executable by the computer is, for example, a floppy disk such as a floppy (registered trademark), a CD-ROM (Compact Disc Read Only). Semiconductor memory in which programs are temporarily or permanently stored as well as package media such as Memory, CD-R (Compact Disc-Recordable), CD-RW (Compact Disc-Rewriterable), DVD (Digital Versatile Disc), etc. It can be realized with a magnetic disk or a magneto-optical disk.

  The present invention is not limited to the embodiments described above. Furthermore, the above-described embodiments may be combined with each other.

It is the schematic which shows the time synchronization system which concerns on embodiment of this invention. It is the schematic which shows the main hardware constitutions of a base station. It is the schematic which shows the hardware constitutions of IC tag. It is the schematic which shows the main hardware constitutions of a terminal. It is the schematic which shows the main software structures of a base station. It is the schematic which shows an example of reference | standard time information. It is the schematic which shows the main software structures of an IC tag. It is the schematic which shows an example of distance information. It is the schematic which shows the main software structures of a terminal. It is the schematic which shows terminal side reference time information etc. It is the schematic which shows delay time information etc. It is a schematic flowchart which shows the operation example of a time synchronous system. It is the schematic which shows the main hardware constitutions of a terminal. It is the schematic which shows the main software structures of a terminal.

Explanation of symbols

  10, 10A ... time synchronization system, 12a, 12b, 12c, 12d ... GPS satellite, 20A, 20B, 20C, 20D ... base station, 40 ... IC tag, 60 ... terminal, 70 ... Terminal communication device, 72 ... Terminal tag reader, 76 ... Terminal GPS device, 312 ... Reference time information acquisition program, 314 ... Marker reception time information generation program, 316 ... Distance information acquisition Program, 318 ... Delay time information generation program, 320 ... Modified transmission time information generation program, 322 ... Terminal clock correction value information generation program, 324 ... Terminal clock correction program

Claims (1)

A reference time information providing device for providing reference time information indicating a reference time;
A terminal device capable of communicating with the reference time information providing device;
A propagation delay information providing device capable of communicating with the terminal device;
A time synchronization system comprising:
The propagation delay information providing device is a distance between the reference time information providing device and the propagation delay information providing device and / or a signal from the reference time information providing device until the signal reaches the propagation delay information providing device. Propagation delay information storage means for storing propagation delay information indicating time,
The terminal device
Reference time information receiving means for receiving the reference time information from the reference time information providing device;
Propagation delay information receiving means for receiving the propagation delay information from the propagation delay information providing device;
Correction reference time information generating means for correcting the reference time information and generating corrected reference time information based on the reference time information and the propagation delay information;
Terminal time correction means for correcting the time of the terminal clock inside the terminal device based on the correction reference time information;
Time accuracy maintaining means for maintaining the accuracy of the time of the terminal clock corrected by the terminal time correction means based on the signal frequency of the reference time information providing device and the unit signal of the terminal clock;
A Doppler deviation detecting means for detecting a Doppler deviation generated in a signal frequency of the reference time information providing device due to relative movement between the terminal device and the reference time information providing device;
When the Doppler deviation is detected, the time of the terminal clock is corrected again by the reference time information receiving means, the propagation delay information receiving means, the previous correction reference time information generating means, and the terminal time information correcting means.
A time synchronization system characterized by that .

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