JP4207766B2 - Relative positioning system - Google Patents

Description

  The present invention obtains correction information based on GPS information received from the satellite at the actual reference station, sends the correction information into the cover area by the antenna station, and the mobile station receives the GPS information received from the satellite and the antenna station. The present invention relates to a relative positioning system configured to perform relative positioning of its own position based on received correction information.

As a positioning system used for land use, marine use, and aeronautical use, a relative positioning system using one-way communication such as so-called D-GPS and RTK-GPS has been considered (for example, see Patent Document 1). In this system, using satellite observation information (GPS information) at a plurality of real reference stations whose positions are known, correction information (differential information) of the reference point is generated using the antenna station as a reference point, and FM, for example, is transmitted from the antenna station. The correction information is transmitted (one-way communication) using multiplex broadcasting. The mobile station receives the correction information, corrects the GPS information received by itself based on the correction information, and performs positioning.
JP 2002-318273 A

  In the relative positioning system (D-GPS) as described above, the positioning accuracy can be improved as compared with the single positioning (absolute positioning). There is a situation where the positional accuracy deteriorates as the distance between the two increases. Therefore, in order to further improve the positioning accuracy, it is necessary to set the reference points at intervals as short as possible. However, in the conventional system, the construction of the reference points is limited by the number of physically existing antenna stations. Therefore, in order to set a large number of reference points at short intervals, the number of antenna stations is increased accordingly. An additional installation must be made, resulting in poor feasibility.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a relative positioning system capable of improving positioning accuracy while reducing the number of antenna stations that transmit correction information.

To achieve the above object, the relative positioning system of the present invention calculates correction information at each virtual reference point set in the coverage area of the antenna station based on GPS information received from the satellite at the actual reference point. Correction information generating means is provided, and the antenna station is configured to send correction information at a plurality of virtual reference points calculated by the correction information generating means into the cover area, and the mobile station is sent from the antenna station. The correction information relating to the virtual reference point located in the vicinity of the own station position among the plurality of correction information is selectively used to perform relative positioning, and the estimation between the own station and the virtual reference point is performed. distance Dn, and, to that based on both the difference δTn the time information correction information of the virtual reference point corresponding to the current time, multiplied by the weighting constant the distance Dn, As the index A which is a sum of the multiplied by the weighting constant serial time difference δTn is minimized, characterized in was configured to select a virtual reference point using the correction information at that time (claim 1 invention).

In the present invention, a large number of virtual reference points can be set at short intervals within the coverage area of one antenna station, and correction information relating to the large number of virtual reference points can be transmitted from the antenna station. it can. The mobile station can perform positioning with sufficiently high accuracy by performing relative positioning selectively using correction information relating to a virtual reference point located in the vicinity of the own station position. As a result, according to the present invention, it is possible to obtain an excellent effect that the positioning accuracy can be improved while reducing the number of antenna stations that transmit correction information.
When the mobile station selects the virtual reference point using the correction information, if the correction information is all the latest data, the virtual reference point with the shortest distance may be selected. However, if there is a difference in the update time of the correction information between the virtual reference points, there is a risk that relatively old correction information may be used, so the virtual reference point with the closest distance is always selected. Is not always good. Therefore, the mobile station is determined based on both the estimated distance Dn between the own station and the virtual reference point and the difference δTn between the current time and the time information of the correction information of the corresponding virtual reference point. If the virtual reference point using the correction information is selected so that the index A consisting of the sum of Dn multiplied by the weighting constant and the time difference δTn multiplied by the weighting constant is minimized. This makes it possible to use correction information that is a virtual reference point that is close to the position of the own station and that is relatively new, and can further improve the reliability of positioning.

At this time, the correction information generating means can be configured to generate correction information at each virtual reference point by linear interpolation based on GPS information at three or more real reference stations. As a result, the correction information at a large number of virtual reference points can be generated with sufficient certainty.
Here, the correction information that can be transmitted from one antenna station per unit time is limited by the data rate. Therefore, the correction information regarding all the virtual reference points in the cover area cannot always be transmitted at the same time. The number of correction information that can be sent is considered to be limited. As countermeasures, the following measures can be taken.

  That is, first, it is desirable to sufficiently increase the positioning accuracy in urban areas where traffic is crowded or in traffic areas, but in the neighborhood, high positioning accuracy is not required in practice. Therefore, the virtual reference points are set relatively densely in urban areas and traffic junctions and relatively coarsely set in remote areas (the invention of claim 3). The update frequency can be reduced (invention of claim 4). According to these, since the amount of correction information in the remote area can be relatively small, a sufficient amount of correction information that is important is transmitted while suppressing the amount of data to be transmitted as a whole. Will be able to.

  Further, the antenna station may be configured to transmit correction information at a plurality of virtual reference points in a time division manner (invention of claim 5). As a result, even if the amount of correction information that can be transmitted per unit time is small, correction information relating to a large number of virtual reference points as a whole can be transmitted. Furthermore, at this time, the sending order of the correction information of each virtual reference point within the coverage area of the antenna station can be set so as to circulate while connecting the virtual reference points separated as much as possible (invention of claim 6), According to this, since the correction information of each virtual reference point is sequentially transmitted in a distributed form, even when the mobile station cannot receive the correction information of the best (closest) virtual reference point at a certain timing. Then, it is possible to perform positioning by receiving the correction information of the suboptimal virtual reference point, and it is possible to prevent inconvenience that the correction information of the virtual reference point far from the own station position must be used.

By the way, even if the mobile station side receives all the correction information of a large number of virtual reference points, it takes a long time just to receive the correction information, or reception for receiving other information. Since a separate machine is required, there is a problem that the burden on the hardware configuration is increased.
Therefore, when the correction information is transmitted from the antenna station in a time-sharing manner as described above, the program information for guiding the timing and channel at which the correction information at each virtual reference point is transmitted by the antenna station. It can be set as the structure sent out (invention of Claim 7). According to this, when the mobile station receives the program information in advance, it is possible to know the timing and channel for receiving the necessary virtual reference point correction information, and only when the necessary information is transmitted. The correction information can be received by operating the receiver. Therefore, it is possible to simplify the hardware configuration and improve the efficiency of receiving correction information.

Further, in the mobile station, from both the distance Dn between the own station and the virtual reference point using the correction information and the difference δTn between the current time and the time information of the correction information of the corresponding virtual reference point, Accuracy information indicating accuracy can be calculated and output together with positioning information (invention of claim 8). According to this, it is possible to inform the user of the accuracy with which the obtained positioning result was obtained, in other words, how much it may be different from the actual information, which is useful for the user. Can be provided.
In the present invention, the index A used when the mobile station selects the virtual reference point using the correction information can be calculated by the following equation, where a and c are weighting constants. If the value of δTn is within a constant b seconds, all the terms of (δTn−b) can be handled as 0 (the invention of claim 9).
Index A = Dn * a + (δTn−b) * c

Hereinafter, with the first embodiment of the present invention will be described with reference to FIGS. First, FIG. 2 schematically shows the overall configuration of the relative positioning system according to the present embodiment. Here, a plurality of GPS satellites 1 orbit around the satellite orbit over the earth, and GPS information such as time information and navigation messages is transmitted as radio signals. On the other hand, a plurality of actual reference stations 2, a correction information generation center 3 that functions as correction information generation means, and a plurality of antenna stations 4 are provided on the ground. Further, in the present embodiment, a vehicle (automobile) moving on land is taken as a specific example as the mobile station 5 that performs positioning of its own position using this system.

  The actual reference station 2 includes a GPS receiver, and is accurately measured and installed at a fixed position (electronic reference point) where the latitude, longitude, and altitude are known. In this case, as shown in FIG. 1, a plurality of actual reference stations 2 are arranged at appropriate intervals (for example, about 50 km to 100 km). The GPS receiver of each real reference station 2 captures four appropriate GPS satellites 1 and receives GPS information from them. Each real reference station 2 is connected to the correction information generation center 3 via a line 6 such as a dedicated line or the Internet network, and transmits the received GPS information to the correction information generation center 3 in real time. . In the following description, when it is necessary to distinguish a plurality (five) of the actual reference stations 2 illustrated in FIG. 1, (R1) to (R5) are added after the reference numeral 2 to distinguish them.

  The correction information generation center 3 includes a computer and data communication means, and detects an error component in each actual reference station 2 from the GPS information sent from each actual reference station 2 and the accurate position of each actual reference station 2. In addition, as will be described in detail later, a plurality of virtual reference points V are set in the cover area of the antenna station 4, and error information at each virtual reference point V is calculated to generate correction information. Yes. The correction information generation center 3 is connected to a plurality of antenna stations 4 via a line 7 such as a dedicated line or the Internet network, and transmits the generated correction information to the corresponding antenna station 4.

  In this case, the antenna station 4 is composed of, for example, an FM multiplex broadcasting station, and a plurality of antenna stations 4 are arranged at an appropriate interval (for example, about 50 km to 100 km) as shown in FIG. These antenna stations 4 transmit normal broadcast programs as FM broadcast waves in the cover area, and multiplex them to transmit correction information at each virtual reference point V. In the following, when it is necessary to distinguish a plurality of (two) antenna stations 4 shown in FIG. 1, (A1) and (A2) are added after the reference numeral 4, and In FIG. 1, the cover area of antenna station 4 (A1) (circular range indicated by a broken line) is indicated by the reference numeral A101, and the cover area of antenna station 4 (A2) is indicated by the reference numeral A102. Yes.

  The mobile station 5 includes a GPS receiver 8. FIG. 3 schematically shows the electrical configuration of the GPS receiver 8. The GPS receiver 8 is a GPS antenna 9 that receives GPS information from the GPS satellite 1, and a GPS- that processes the received signal. An RF (Radio Frequency) unit 10 and a GPS-BB (Base Band) unit 11, an FM antenna 12 that receives FM broadcast waves from the antenna station (FM multiple broadcasting station) 4, and an FM-RF unit that processes the received signal 13 and the FM-BB unit 14, the application CPU 15, an operation unit 16 for a user to input various operations, and a display unit 17 for performing various displays including positioning results.

  At this time, the application CPU 15 includes a memory and the like, and performs positioning (relative positioning) of the current position of the own station by its software configuration (execution of the control program). As will be described in detail later, this positioning is executed based on GPS information received from the same four GPS satellites 1 captured by the actual reference station 2 and correction information received from the antenna station 4. The positioning result is output to the display unit 17. The received correction information is stored in the memory of the application CPU 15. The positioning result is used for vehicle navigation, for example.

  In the present embodiment, as described above, the correction information generation center 3 sets a plurality of virtual reference points V in each cover area of the plurality of antenna stations 4, and errors in the respective virtual reference points V. The correction information is generated by calculating the component. As a specific example, as shown in FIG. 1, with respect to the cover area A101 of the antenna station 4 (A1), as shown by a black triangle in the figure, a plurality (in this case, 14) of virtual reference points V101 to V114. Are set to be distributed substantially evenly (at equal intervals).

  The correction information related to each virtual reference point V101 to V114 is based on GPS information obtained from each real reference station 2 in real time, and three or more real reference stations 2 (in this case, for example, arranged so as to surround the cover area A101) It is calculated by linear interpolation from error components (correction information) of actual reference station 2 (R1) to actual reference station 2 (R4). The correction information of the virtual reference points V101 to V114 generated in this way is transmitted from the correction information generation center 3 to the corresponding antenna station 4 (A1), and from the antenna station 4 (A1) in the cover area A101. Is sent out. At this time, as shown in FIG. 4, the correction information includes position information (latitude and longitude data) and time information (time when the correction information is generated) of the corresponding virtual reference point V. Yes.

  In the same way, the cover area A102 of the antenna station 4 (A2) is also configured so that the plurality of virtual reference points V201 to V2mm are substantially evenly (substantially equidistant) as indicated by the hatched triangles in FIG. For example, each correction information is calculated by linear interpolation from four error components (correction information) of the actual reference station 2 (R2) to the actual reference station 2 (R5). Then, the correction information is sent to the antenna station 4 (A2) and sent into the cover area A102.

  Here, the correction information that can be transmitted from one antenna station 4 per unit time (for example, every second) is limited by the data rate, and there is a situation in which correction information regarding all the virtual reference points V in the cover area cannot be transmitted at a time. is there. Therefore, in the present embodiment, the antenna station 4 is configured to transmit correction information at a plurality of virtual reference points V in a time division manner. At this time, the correction information for each virtual reference point V in the cover area of the antenna station 4 is sent in the order of circulation while connecting the virtual reference points V separated as much as possible. Specifically, in the cover area A101 shown in FIG. 1, the transmission order is virtual reference points V101, V110, V108, V104, V112, V103,.

  Then, as will be described in the following description of the operation (flowchart description), the mobile station 5 (GPS receiver 8) is included in a plurality of correction information transmitted from the antenna station 4 within the cover area where the own station exists. The relative positioning is performed by selectively using the correction information regarding the virtual reference point V located in the vicinity of the own station position. At this time, in this embodiment, based on both the estimated distance D between the own station and the virtual reference point V, and the difference δT between the current time and the time information of the correction information of the corresponding virtual reference point V. Thus, the virtual reference point V using the correction information is selected. Furthermore, in this embodiment, the GPS receiver 8 includes the distance D between the local station and the virtual reference point V using the correction information, and the time information of the correction information of the current virtual time and the corresponding virtual reference point V. Accuracy information indicating the accuracy of positioning is calculated from both of the difference δT, and is output together with the positioning result (displayed on the display unit 17).

  Next, the operation of the above configuration will be described with reference to FIG. The flowchart of FIG. 5 shows the processing procedure of the positioning of the own station in the mobile station 5 (GPS receiver 8). First, in step S1, it is determined whether or not the current time information exists in the GPS receiver 8 itself. If the time information does not exist (No in step S1), GPS is used in the next step S2. Independent positioning (positioning without using correction information) is executed, and the own station position is calculated (updated). At this time, time information is acquired from the GPS information received together. When single positioning is performed in this way, the process proceeds to step S9 described later.

  On the other hand, if the time information exists (Yes in step S1), the time information in the correction information stored in the memory is compared with the current time in step S3, and there is a difference greater than the threshold value. The correction information data (that is, old) is deleted. In the next step S4, it is determined whether or not the correction information exists (is left) in the memory. If the correction information does not exist (No in step S4), the process proceeds to step S2 and single positioning is executed. The If the correction information exists (Yes in step S4), it is determined in step S5 whether the local station position information exists.

Here, when the local station position information exists (Yes in step S5), a process of selecting a virtual reference point V (correction information to be used for relative positioning) is executed in step S6. In the present embodiment, the one that minimizes the next index A is selected from a plurality of correction information (see FIG. 4) stored in the memory.
Index A = Dn * a + (δTn−b) * c
Where Dn is the distance between the virtual reference point V and the local station position, δTn is the difference between the current time and the time information of the correction information, the subscript n is the number of the correction information, and a and c are weighting constants. . The constant b is set to 3 seconds, for example, and if the time difference of δTn is within 3 seconds, all the terms (δTn−b) are handled as 0.

  By selecting the correction information of the virtual reference point V that minimizes the index A in this manner, it is possible to use correction information that is a virtual reference point V that is close to the local station position and that is relatively new. Become. For example, if the position of the mobile station 5 is a position indicated by a double circle in FIG. 1, the correction information of the virtual reference point V104 is selected. At this time, if the local station location information does not exist at the beginning of use (No in step S5), in step S7, an appropriate one of the correction information (for example, the correction information with the latest time information). Is selected. Even in this case, correction information at any one of the virtual reference points V in the cover area where the own station position exists is used.

  In the next step S8, relative positioning using the selected correction information is executed, and the own station position is calculated (updated). This relative positioning is performed by correcting the GPS information obtained from the four GPS satellites 1 using the correction information. At this time, the correction information regarding the virtual reference point V located in the vicinity of the own station position. By using n, it is possible to perform positioning with sufficiently high accuracy. The positioning result (local station position) is displayed on the display unit 17, for example.

  In step S9, accuracy information indicating the accuracy of positioning is calculated. This accuracy information is obtained from both the distance D between the local station position and the virtual reference point V using the correction information, and the difference δT between the current time and the time information of the correction information of the corresponding virtual reference point V. The smaller the distance D and the smaller the time difference δT, the higher the accuracy (for example, several cm to several m). In the case of single positioning (step S2), the accuracy is considerably inferior (for example, the accuracy is about 100 m), and when correction information is appropriately selected (step S7), the accuracy is slightly inferior (for example, 10 m). The following. The calculated accuracy information is also displayed on the display unit 17, for example.

  In step S10, correction information reception processing for receiving correction information transmitted from the antenna station 4 is executed. The received correction information is written in the memory, but when new correction information related to the same virtual reference point V is received, the correction information is rewritten. Thereafter, the processing from step S3 is repeated.

  By the way, in this embodiment, as described above, the correction information that can be transmitted from one antenna station 4 per unit time (for example, every second) is limited by the data rate. The correction information at the reference point V is transmitted in a time-sharing manner, and the correction information is transmitted in an order that circulates while connecting the virtual reference points V separated as much as possible.

  As a result, even if the amount of correction information that can be transmitted per unit time in the antenna station 4 is small, correction information relating to a large number of virtual reference points V in the cover area as a whole can be transmitted. Moreover, since the correction information of each virtual reference point V is sequentially transmitted in a distributed form, even when the mobile station 5 has not received the correction information of the best (closest) virtual reference point V at a certain timing, In other words, positioning can be performed using the correction information of the suboptimal virtual reference point V, and the inconvenience of having to use the correction information of the virtual reference point V far from the own station position can be prevented. It is.

  As described above, according to the present embodiment, the correction information at the virtual reference point V set in a plurality of coverage areas of one antenna station 4 is calculated by the correction information generation center 3 and transmitted from the corresponding antenna station 4. Since the mobile station 5 is configured to selectively use the correction information related to the virtual reference point V located in the vicinity of the own station position among the plurality of correction information, the mobile station 5 performs the relative positioning. Unlike a D-GPS that has one antenna station as a reference point, it is possible to set a large number of virtual reference points V at short intervals within the coverage area of one antenna station 4. As a result, it is possible to obtain an excellent effect that the positioning accuracy can be improved while reducing the number of antenna stations 4 that transmit correction information.

  In particular, in this embodiment, correction information is transmitted from the antenna station 4 at a plurality of virtual reference points V in a time-sharing manner and the transmission order is devised, so the number of correction information that can be transmitted simultaneously is It is possible to cover defects with limitations. Further, in this embodiment, when the mobile station 5 selects the virtual reference point V using the correction information, the estimated distance D between the own station and the virtual reference point V and the virtual reference corresponding to the current time. Since the selection is made on the basis of both the difference δT from the time information of the correction information of the point V, the reliability of positioning can be further improved. Furthermore, in the present embodiment, since the accuracy information indicating the accuracy of positioning is calculated and output together with the positioning information, it is possible to obtain an advantage that information useful for the user can be provided. .

  In the above-described embodiment (description of the flowchart), the index A is used to select the correction information (virtual reference point V) (step S6 in FIG. 5). Only the distance D between them may be used to select the correction information of the virtual reference point V located closest (the value of D is the smallest). In addition, when the local station position information does not exist, an appropriate one is selected from the correction information (step S7 in FIG. 5), but the average value of the correction information in the cover area is calculated, A method of using the result as correction information is also conceivable. Correction information on the center position of the cover area (position of the antenna station 4) may be used.

  Next, a second embodiment (corresponding to claim 7) of the present invention will be described with reference to FIGS. Note that the same parts as those in the first embodiment are omitted from the illustration and detailed description, and the reference numerals are also used in common, and only differences from the first embodiment will be described below. The second embodiment differs from the first embodiment in that the antenna station 4 guides the timing and channel at which the correction information at each virtual reference point V is sent together with the correction information. The program information is transmitted.

  FIG. 6 schematically shows a configuration example of this program information. This program information indicates which correction reference information of which virtual reference point V out of each virtual reference point V in the cover area covered by the antenna station 4 will be transmitted at which timing (time) and in which channel. The list shows the position coordinates (latitude, longitude) of each virtual reference point V, transmission time (indicated by 0, 1, 2,...), And transmission channel number (in this case, frequency division) 3 including data of # 1 to # 3). This program information is transmitted from the antenna station 4 periodically (for example, every 60 seconds).

  On the other hand, the mobile station 5 (GPS receiver 8) receives the program information, and based on the program information, the virtual reference point V necessary for relative positioning (the distance D from the own station position is shortest). The receiver is controlled so as to receive only the correction information regarding the antenna station 4 from the antenna station 4. The flowchart of FIG. 7 shows the procedure of the correction information reception process executed by the mobile station 5 (GPS receiver 8) at that time.

  That is, first, in step S11, it is determined whether or not program information exists. If the program information does not exist (not received) (No in step S11), the process proceeds to step S15 described later. If the program information exists (Yes in step S11), the transmission time and the transmission channel number of the correction information of the virtual reference point V to be acquired are read from the program information in step S12. In step S13, it is determined whether or not the current time matches the transmission time. If the current time does not match the transmission time (No in step S13), the reception process is terminated.

  If the current time matches the transmission time (Yes in step S13), the reception channel is set to match the transmission channel number in step S14, and then, in step S15, from the antenna station 4 The correction information being sent is received, and the received correction information is stored in the memory. Thereby, the correction information regarding the required virtual reference point V can be acquired, and highly accurate relative positioning can be performed using the correction information.

  According to this configuration, when the mobile station 5 receives the program information in advance, it is possible to know the timing and channel for receiving the necessary correction information of the virtual reference point V, and the necessary correction information is transmitted. The correction information can be received only by operating the receiver. Accordingly, when the mobile station 5 receives all the correction information of a large number of virtual reference points V, it takes a lot of time just to receive the correction information, or other information (for example, VICS information). Since a separate receiver for receiving the signal is required, it is possible to eliminate the problem of increasing the burden on the hardware configuration and simplify the hardware configuration of the mobile station 5 (GPS receiver 8). In addition, it is possible to improve the efficiency of receiving correction information.

The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
In other words, as a contrivance to limit the correction information that can be sent out per unit time from one antenna station, virtual reference points are set relatively densely in urban areas and traffic areas and relatively roughly in remote areas. (Corresponding to claim 3) or lower the update frequency of correction information in remote areas than in urban areas (for example, every second in urban areas and every 5 seconds in remote areas) (claim) 4).

  In this case, it is desirable to sufficiently increase the positioning accuracy in urban areas where roads are densely packed or in traffic areas. However, in highlands, high positioning accuracy is not required in practice. The amount of correction information can be made relatively small, and a sufficient amount of important correction information can be transmitted while suppressing the amount of data to be transmitted as a whole.

  Further, the correction information generation center 3 (correction information generation means) may be provided integrally with the antenna station 4 or may be provided integrally with the actual reference station 2. In this case, the correction information generation center 3 may not be connected to the plurality of antenna stations 4, and one correction information generation center 3 may be provided for each antenna station 4. In short, the correction information generation center 3 may physically exist anywhere.

  In addition, the antenna station 4 is not limited to the FM multiplex broadcasting station, and may be an AM station, a television broadcasting station, a broadcasting satellite (stationary satellite, quasi-zenith satellite), or the like, or specialized for transmitting correction information. It may be a station. Further, the system of the present invention can be used not only for land (for automobiles and pedestrians) but also for marine and aeronautical purposes (the mobile station 5 is a ship or an aircraft). Furthermore, various modifications can be made to the hardware configuration, software configuration, and the like of the GPS receiver 8, and the present invention can be implemented with appropriate modifications without departing from the scope of the invention.

The 1st Example of this invention is a figure which shows the example of arrangement | positioning of a real reference station, an antenna station, and a virtual reference point The figure which shows schematically the whole structure of the system which concerns on a present Example. Block diagram schematically showing the electrical configuration of a GPS receiver of a mobile station The figure which shows the composition of correction information Flow chart showing processing procedure of relative positioning in mobile station The figure which shows the 2nd Example of this invention and shows the structure of program information It is a flowchart which shows the process sequence of correction information reception in a mobile station.

Explanation of symbols

In the drawings, 1 is a GPS satellite, 2 is an actual reference station, 3 is a correction information generation center (correction information generation means), 4 is an antenna station, 5 is a mobile station, 8 is a GPS receiver, 15 is an application CPU, and 17 is a display. , V is a virtual reference point, and A101 and A102 are cover areas.

Claims (9)

The correction information is obtained based on the GPS information received from the satellite at the actual reference station, and the correction information is transmitted into the cover area by the antenna station, and the mobile station receives the GPS information received from the satellite and the correction received from the antenna station. A relative positioning system configured to perform relative positioning of its own position based on information,
Based on GPS information received from the satellite in the real reference station, comprising correction information generating means for calculating correction information at each virtual reference point set in the cover area,
The antenna station sends correction information at a plurality of virtual reference points calculated by the correction information generating means into the cover area,
The mobile station is configured to perform relative positioning by selectively using correction information regarding a virtual reference point located in the vicinity of the own station position among a plurality of correction information transmitted from the antenna station, The distance Dn is multiplied by a weighting constant based on both the estimated distance Dn between the own station and the virtual reference point and the difference δTn between the current time and the time information of the correction information of the corresponding virtual reference point. And a virtual reference point using the correction information is selected so that an index A consisting of the sum of the time difference δTn multiplied by a weighting constant is minimized .   The relative positioning system according to claim 1, wherein the correction information generation unit generates correction information at each virtual reference point by linear interpolation based on GPS information at three or more actual reference stations.   3. The relative positioning system according to claim 1, wherein the virtual reference points are set relatively densely in urban areas and traffic areas and relatively coarsely in remote areas.   4. The relative positioning system according to claim 1, wherein the correction information generation unit lowers the update frequency of the correction information in a remote area as compared with an urban area. 5.   5. The relative positioning system according to claim 1, wherein the antenna station performs transmission of correction information at a plurality of virtual reference points in a time division manner.   6. The relative positioning according to claim 5, wherein the antenna station sets the order in which correction information of each virtual reference point in the coverage area is transmitted so as to circulate while connecting the virtual reference points separated as much as possible. system.   7. The relative positioning system according to claim 5, wherein the antenna station transmits program information for guiding a timing and a channel at which correction information at each virtual reference point is transmitted. The mobile station determines the positioning accuracy from both the distance Dn between the local station and the virtual reference point using the correction information, and the difference δTn between the current time and the time information of the correction information of the corresponding virtual reference point. The relative positioning system according to any one of claims 1 to 7, characterized in that accuracy information indicating ??? is calculated and output together with positioning information. The index A when the mobile station selects a virtual reference point using the correction information is calculated by the following formula, where a and c are weighting constants, and the time difference δTn is within a constant b seconds. If there is, the relative positioning system according to any one of claims 1 to 8, wherein (δTn-b) is treated as all 0 terms.
Index A = Dn * a + (δTn−b) * c

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