Method for transmitting correction information in a satellite navigation system

Abstract

To continue positioning calculation regardless of the presence or absence of a correction signal and to shorten an initial position calculation time in a satellite navigation system.SOLUTION: In a satellite navigation system including a GPS in United States and a quasi-zenith satellite system in Japan, in a wide-area differential GPS for generating and transmitting correction information on a clock error, a position error, and the like of a navigation satellite, the correction information is transmitted via a communication line different from a wireless correction signal from the satellite, so that positioning calculation is continued regardless of whether or not the correction signal is shielded in a user station, and the correction information transmitted in the past is repeatedly transmitted together with the latest correction information, so that an initial position calculation time (TTFF) in the user station is shortened.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for transmitting correction information in a satellite navigation system. [Background technology]

[0002] Satellite navigation systems that use satellites to measure position are collectively called GNSS (Global Navigation Satellite System), and a representative example is the US-based GPS (Global Positioning System). GNSS generally uses a receiver to receive positioning signals transmitted by satellites called navigation satellites, and calculates the receiver's position by measuring the distance between the navigation satellite and the receiver. The receiver that determines the position is called a user receiver or user station. The error between the determined position and the true position is called the positioning error.

[0003] To calculate the receiver's position, it is necessary to know the position of the navigation satellite that is transmitting the positioning signal, and the orbital information required for this is transmitted by the navigation satellite itself by superimposing it on the positioning signal. Because the orbital information is created by prediction, it contains an error of several meters, which causes positioning errors when calculating the receiver's position.

[0004] The timing at which a navigation satellite transmits a positioning signal is predetermined, and the navigation satellite transmits the positioning signal based on the time of its own clock. This clock is a highly accurate atomic clock, and information about the slight gain or loss of the clock is also superimposed on the positioning signal. However, even with this information, there is still an error equivalent to a few meters in distance, which becomes a factor in positioning errors when calculating the receiver's position.

[0005] In the case of GPS, for example, navigation satellites transmit their own orbital information and clock information superimposed on positioning signals, repeatedly at a 30-second cycle. GNSS navigation satellites other than GPS also repeatedly transmit similar information at their own specific cycles. Generally, the error detection codes attached to the orbital information and clock information do not have sufficient error detection capabilities, so receivers may receive this information twice and confirm that the information received each time matches before using it for positioning calculations.

[0006] Before reaching the ground, a positioning signal passes through the ionosphere and troposphere above, and delays occur as the radio signal passes through each of these regions. These delays are called the ionospheric propagation delay and the troposphere propagation delay, respectively. Therefore, when this radio signal is used as a positioning signal, these ionospheric propagation delay and troposphere propagation delay become a cause of positioning errors. The magnitude of the ionospheric propagation delay and the troposphere propagation delay converted into distance are called the ionospheric propagation delay and the troposphere delay, respectively.

[0007] On the other hand, by installing a receiver at a fixed reference station on the ground and using the distance measured by this to create correction information for distance measurement errors caused by ionospheric propagation delays, tropospheric propagation delays, etc., and transmitting this information to the user, the distance measured at the user station is corrected based on the correction information, thereby improving the position measurement accuracy (called positioning accuracy) at the user station. This method is called Differential GPS (DGPS). When correction information is transmitted using a radio signal, the radio signal is called a correction signal.

[0008] The exact location of the reference station used in DGPS must be known in advance in order to generate correction information. This is obtained as coordinate values ​​by measuring the antenna position of the reference station. Any measurement error at the reference station is reflected in the correction information as a positioning error at the user station.

[0009] DGPS corrections are usually transmitted repeatedly to allow user stations to start receiving them at any time. Also, because the transmission format of corrections is fixed, invalid corrections may be included along with valid corrections.

[0010] There are several specific methods of DGPS, one of which is called Wide Area Differential GPS (WADGPS). In this method, distances measured by a reference station are used to generate correction information for each cause of positioning error, such as the navigation satellite's clock error, the navigation satellite's position error, ionospheric propagation delay, and tropospheric propagation delay, and this information is then transmitted to the user station. Since each of these error causes manifests itself differently as distance measurement errors depending on the user station's location, the user station calculates the correction value it should use from the correction information according to its approximate location and uses it for correction.

[0011] The clock error of a navigation satellite appears as a uniform distance measurement error regardless of the location of the user station. The position error of a navigation satellite appears as a distance measurement error due to the dot product with the line of sight when the navigation satellite is viewed from the user station. The ionospheric propagation delay appears as a distance measurement error due to the integral of the density distribution in the ionosphere on the path from which the ranging signal transmitted by the navigation satellite reaches the user station. The tropospheric propagation delay appears as a distance measurement error due to the integral of the refractive index of the atmosphere on the path from which the ranging signal transmitted by the navigation satellite reaches the user station. In other words, except for the clock error of the navigation satellite, the distance measurement error appears differently depending on the location of the user station.

[0012] It is known that the amount of ionospheric propagation delay is inversely proportional to the square of the frequency. Therefore, if a reference station measures distances using positioning signals of multiple frequencies, the amount of ionospheric propagation delay can be calculated from those distances. Alternatively, if a reference station or user station measures distances using positioning signals of multiple frequencies, the distance from which the amount of ionospheric propagation delay has been removed can be obtained by linearly combining the results of those measurements.

[0013] WADGPS is characterized by the generation of correction information for each cause of positioning error, but when simply referred to as DGPS, it is common for the method to use distance measurement errors as correction information directly, rather than generating correction information for each cause of positioning error. To distinguish this method from WADGPS, it is sometimes called Local Area DGPS (LADGPS). While WADGPS is characterized by its ability to provide service over a wide geographical area, LADGPS generally has an advantage in terms of positioning accuracy when the service area is not that wide. Generally, LADGPS is used only when the service area is approximately 10 km or less.

[0014] In the WADGPS system in which user stations are equipped with receivers compatible with one frequency of positioning signals (called "single-frequency WADGPS"), the ionospheric propagation delay must be transmitted as part of the correction information, so the reference station measures distance using positioning signals of multiple frequencies, and the master station calculates the ionospheric propagation delay over the service area and stores it in a specified transmission format.

[0015] In the WADGPS system where user stations are equipped with receivers compatible with two frequencies of positioning signals (called "dual-frequency WADGPS"), the correction information does not include ionospheric propagation delay. Both the reference station and user station measure distance using positioning signals of multiple frequencies, and the distance excluding ionospheric propagation delay is obtained as a linear combination of these measurement results.

[0016] In WADGPS, correction information generated by the master station is transmitted to user stations via some kind of communication line. When this communication line is constructed using a satellite, the satellite is called a correction information distribution satellite, and the radio signal used for transmission is called a correction signal. Because WADGPS provides correction information that can be used over a wide geographical area, it is common for the service to be provided to a large number of user stations.

[0017] As a practical example of WADGPS, SBAS (Satellite-Based Augmentation System) has been standardized for aircraft. The SBAS standard for single-frequency WADGPS is called "L1 SBAS," and the SBAS standard for dual-frequency WADGPS is called "L5 SBAS."

[0018] The SBAS standard specifies the transmission format of correction information, and correction information is transmitted from a correction information distribution satellite after containing correction information for each cause of positioning error, such as the clock error of the navigation satellite, the position error of the navigation satellite, and in L1 SBAS, ionospheric propagation delay. Note that tropospheric propagation delay can be corrected with sufficient accuracy using a tropospheric propagation delay model, so it is not included in the transmission format of the SBAS standard, and correction is made using a tropospheric propagation delay model predetermined by both the master station and the user station. A correction information distribution satellite under the SBAS standard is called an SBAS satellite. WADGPS based on the SBAS standard is simply called SBAS.

[0019] As explained in

[0009] , in SBAS, it is necessary to allow user stations to start receiving the correction information at any timing, so the correction information is transmitted repeatedly. Also, since the transmission format of SBAS is determined by the SBAS standard, invalid correction information may be included along with valid correction information.

[0020] An example of an L1 SBAS is the MSAS (Michibiki-Based Satellite Augmentation System) operated by the Japan Civil Aviation Bureau. [Prior art documents] [Patent documents]

[0021] [Patent Document 1] US Patent Application Publication No. 2020 / 0274814 [Non-patent literature]

[0022] [Non-Patent Document 1] Takahiro Yamamoto, Masahito Mogamiya, "Cloud-based Michibiki centimeter-level positioning receiver," NAVIGATION, No. 210, pp. 10-15, October 2019 [Non-patent document 2] A. Favenza et al., “A Cloud-based Approach to GNSS Augmentation for Navigation Services,” IEEE ACM 7th Intl. Conf. Utility and Cloud Computing, December 2014. Summary of the Invention [Problem to be solved by the invention]

[0023] In WADGPS, correction information generated by the master station is transmitted to user stations via some kind of communication line. In the case of the SBAS standard, the SBAS satellite, which distributes correction information, transmits an SBAS signal in a format similar to the positioning signal of a GPS satellite as a correction signal. The SBAS signal transmits one SBAS message consisting of 250 bits per second. The correction information contained in the SBAS message has a set validity period.

[0024] Geostationary satellites are used as SBAS satellites. In Japan, geostationary satellites are always visible in a fixed position in the southern sky. If the SBAS signal is blocked by an obstacle or other obstruction, the user station will no longer be able to receive correction information, and once the validity period of the correction information received just before the blockage has expired, the correction information can no longer be applied to all navigation satellites in use.

[0025] SBAS messages include those that transmit the satellite's clock error, satellite position error, and ionospheric propagation delay, and are distinguished by the message type number included in the message, which ranges from 0 to 63. There is no specific order in which messages are transmitted, but they generally form a transmission cycle that takes 120 seconds to complete.

[0026] A user station collects multiple SBAS messages and begins applying correction information once all the messages necessary to perform positioning calculations that apply the correction information are collected. The time from when a user station starts operation until it starts outputting its position with the correction information applied is called TTFF (Time to First Fix). The components of TTFF are: (a) the time it takes for the user station to acquire and start tracking the navigation satellite's positioning signal, (b) the time it takes to extract the navigation satellite's orbital information and clock information from the navigation satellite's positioning signal, and (c) the time it takes for the SBAS messages necessary to perform positioning calculations that apply the correction information to be collected, with (c) usually being the dominant factor.

[0027] Therefore, TTFF is determined by the transmission order of SBAS messages and the configuration of the transmission cycle, but generally requires approximately 30 to 120 seconds. TTFF also varies depending on the timing at which the user station begins operation, so it is generally discussed as an expected value. Because the expected TTFF value is determined by the transmission order of SBAS messages, there is no room for improvement on the user receiver side as long as the SBAS signal is received and used.

[0028] Even if the SBAS signal is blocked, the user station will no longer be able to apply the corrections once the validity period of the corrections received immediately before the blockage has expired. However, if the SBAS signal returns before that, the application of the corrections can be resumed immediately. If the SBAS signal returns after the validity periods of all corrections have expired, the same concept as TTFF can be applied. If the SBAS signal returns somewhere in between these two cases, i.e., when the validity periods of some corrections have expired, the time until all SBAS messages necessary to perform positioning calculations that apply the corrections are available will be between 0 and TTFF.

[0029] As described above, in WADGPS, the TTFF and the time required for the correction signal to recover from obstruction are determined by the order in which the correction information is transmitted. The object of the present invention is to reduce these times regardless of the order in which the correction information is transmitted. [Means for solving the problem]

[0030] WADGPS correction information is not received at user stations from correction information distribution satellites, but rather by providing a distribution station that receives correction signals and transmitting them using ground-based communication lines. In this case, the distribution station Since SBAS signals are not blocked, SBAS messages can be transmitted to user stations at all times. With this configuration, user stations can continue positioning calculations using correction information, regardless of whether the SBAS signals are blocked or not, as long as they can receive the navigation satellite's positioning signals.

[0031] Furthermore, by repeatedly transmitting previously transmitted correction information along with the latest correction information, the user station will immediately have all the messages necessary to perform positioning calculations that apply the correction information, thereby shortening the TTFF.

[0032] In addition, by using a one-way communication line to distribute correction information to user stations, it is possible to adopt a broadcast communication line in which multiple receivers receive data. This includes multicast communication in IP networks. Generally, one-way communication lines are easier to establish communication in poor communication environments than two-way communication lines.

[0033] Since SBAS signals do not contain information that identifies user stations, and there is no mechanism for identifying user stations, SBAS correction information can be used by anyone. Therefore, even if correction information that has been transmitted in the past is repeatedly transmitted, there is no particular problem from a security standpoint, since the information is being retransmitted in a state that anyone can use.

[0034] Patent Document 1 describes an invention in which a server provides transmission parameters that optimize the procedure for broadcasting assistance data to solve the problem that existing correction systems do not always properly determine transmission parameters for assistance data and that the division of roles between the server, network device, and terminal device is unclear, resulting in inefficient broadcast procedures for assistance data. In this invention, communication between the server and network device aligns the types and transmission frequency of assistance data that the server can provide with the types and transmission frequency of assistance data that the network device can receive and process. Similar processing is also performed between the network device and terminal device, allowing only highly necessary information to be transmitted according to each device's resources. The server in this invention provides the correction information.

[0035] The invention of Patent Document 1 requires two-way communication, but the present invention requires only one-way communication. Furthermore, even if the invention of Patent Document 1 is applied to SBAS messages, the same correction information as that transmitted in the past is not repeatedly transmitted, and the latest correction information for each cause of positioning error is not transmitted each time a transmission is made. Therefore, the messages required to perform positioning calculations that apply correction information at the user station are not immediately available, and the TTFF cannot be shortened.

[0036] Non-Patent Document 1 describes a method for transmitting correction information from a cloud server to a user station via a communication line separate from the quasi-zenith satellite system, in relation to the CLAS (Centimeter-Level Augmentation Service) service of the quasi-zenith satellite system, which can be considered a type of WADGPS. It also describes how, in the event that this communication is interrupted, the time required to recover from the communication interruption can be shortened by transmitting correction information going back in time.

[0037] However, the purpose of the method in Non-Patent Document 1 is to reduce the amount of data communication by not transmitting RAW data (this is the name given to the detailed distance information obtained by the user station through measurements) from the user station to the cloud server, and correction information is distributed over the communication line only when requested by the user station. Under normal conditions, the user station receives and uses correction signals from the quasi-zenith satellite, so correction information is not obtained over the communication line unless the quasi-zenith satellite is blocked. While this method can reduce the amount of data transmission of correction information over the communication line, it cannot be implemented unless the communication line is bidirectional. Furthermore, since a request for transmission of correction information to the cloud server is made only after determining that the quasi-zenith satellite is blocked, there is a risk of a long response time. Furthermore, Non-Patent Document 1 does not disclose the timing at which the user station requests the cloud server to distribute correction information, or the specific correction information that the cloud server transmits to the user station when responding to a request from the user station, and these are unclear.

[0038] Furthermore, the function of distributing correction information retroactively is limited to cases where communication is interrupted. Communication occurs only when a user station requests the cloud server to send correction information, so this function also requires a two-way communication line. Past correction information is sent in batches for 60 seconds, which includes redundant correction information, and therefore takes a long time to send the data.

[0039] Since a two-way communication line is used, it takes time for the round-trip communication. Also, since the cloud server may be required to handle multiple user stations, it is necessary to manage them and respond to all requests from each user station.

[0040] Non-Patent Document 2 describes a method for performing SBAS calculation processing on a cloud server rather than on a user station. In this case, distance information obtained by measurement by the user station is transmitted to the cloud server via a communication line, and calculation processing is performed on the cloud server, which has the advantage of reducing power consumption on the user station side.

[0041] According to the method of Non-Patent Document 2, since there is no need for the user station to receive the SBAS signal, as long as the positioning signal from the navigation satellite can be received, the cloud server can continue to perform positioning calculations applying correction information, regardless of whether the SBAS signal is blocked or not. Non-Patent Document 2 does not mention TTFF, but if the cloud server stores SBAS messages and then applies them, TTFF can be improved.

[0042] However, the method in Non-Patent Document 2 requires the transmission of distance information from the user station to the cloud server and the transmission of calculation results from the cloud server to the user station, so it requires a two-way communication line and also requires time for round-trip communication. Furthermore, the cloud server is expected to provide services to multiple user stations, and it must manage them and respond to all requests from each user station, requiring a large-scale computing capacity proportional to the number of user stations it supports.

[0043] Incidentally, if the geographical area covered by the service is not too wide, LADGPS generally has an advantage over WADGPS in terms of positioning accuracy. The equipment for receiving SBAS signals is similar to the reference station equipment for LADGPS, and both systems primarily consist of an antenna and a satellite navigation receiver. Given these circumstances, those skilled in the art would likely consider it a natural design to configure LADGPS rather than WADGPS, provided that the user station can obtain correction information via a communication line. With LADGPS, the TTFF is generally short, provided the line speed is sufficient.

[0044] However, since SBAS is now in stable operation, if WADGPS is configured by receiving SBAS signals, it can provide services over a wide geographical area. Also, as long as WADGPS is acceptable in terms of positioning accuracy, it has the advantage of eliminating the need to measure the positions of reference stations, which is required for LADGPS.

[0045] The invention of claim 1 is a method for transmitting correction information in a satellite navigation system comprising a plurality of navigation satellites that transmit positioning signals, a user station that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distance between them, a correction information distribution satellite that distributes correction information according to factors of positioning error such as clock error and position error of the plurality of navigation satellites and ionospheric propagation delay, and a distribution station that receives the correction information distributed by the correction information distribution satellite, wherein the distribution station has a unidirectional communication line connecting to the user station, the distribution station stores the correction information received from the correction information distribution satellite, and when transmitting the correction information to the user station via the communication line, the distribution station transmits only the latest correction information from the stored correction information according to the factor of positioning error each time.

[0046] The invention of claim 2 is a method for transmitting correction information in a satellite navigation system, characterized in that, in the invention described in claim 1, when transmitting only the latest correction information for each cause of the positioning error, invalid correction information is omitted from the correction information and only valid correction information is transmitted. [Effects of the Invention]

[0047] Since the invention according to claim 1 is configured as described above, the user station does not need to receive the SBAS signal, and therefore, regardless of whether the SBAS signal is blocked at the user station, as long as the positioning signal from the navigation satellite can be received, the positioning calculation applying the correction information can be continued. Furthermore, since the SBAS messages required to execute the positioning calculation applying the correction information are immediately available at the user station, the TTFF can be shortened.

[0048] The invention of claim 2 is configured as described above, and in addition to the effect of the invention of claim 1, it is possible to further reduce the amount of data transmission related to the transmission of correction information. [Brief explanation of the drawings]

[0049] [Figure 1]1 is a schematic diagram illustrating a first embodiment of the present invention, for explaining a method for transmitting correction information in a satellite navigation system according to claims 1 and 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0050] Specific embodiments of the present invention will be described in detail below with reference to the drawings. [Example]

[0051] This invention Example The following will be described in detail with reference to FIG. 1. FIG. Example 1 is a schematic diagram illustrating a method for transmitting correction information in a satellite navigation system according to claims 1 and 2 of the present invention.

[0052] The SBAS satellite 1 transmits correction information by SBAS signals. The correction information is stored in a predetermined transmission format as an SBAS message, and one SBAS message is transmitted per second.

[0053] The distribution station 11 is connected to the communication line 3 via a data transmitter 16 and can transmit data to the communication line.

[0054] The distribution station 11 receives the SBAS signal transmitted by the SBAS satellite 1 with an antenna 12, and an RF reception processing circuit 13 executes reception processing.

[0055] The message decoder 14 receives the necessary signals from the RF receiving processing circuit 13 , decodes the SBAS messages, and delivers them to the storage device 15 and the data transmitter 16 .

[0056] The data transmitter 16 transmits past SBAS messages stored in the storage device 15 to the communication line 3 in addition to the latest SBAS message received from the message decoder 14. This transmission process is performed, for example, every time the latest SBAS message is obtained.

[0057] Each of the navigation satellites 2 (2a, 2b, etc.) transmits a positioning signal.

[0058] The user station 21 is connected to the communication line 3 via a data receiver 24 and can receive data from the communication line.

[0059] The user station 21 receives the positioning signals transmitted by the navigation satellites 2 (2a, 2b, . . . ) with an antenna 22, and an RF reception processing circuit 23 executes reception processing.

[0060] The positioning calculation unit 25 receives the necessary signals from the RF reception processing circuit 23 and calculates the position of the user receiver from information on the distance to the navigation satellites 2 (2a, 2b, etc.). At this time, it applies the SBAS message received by the data receiver 24, applies correction information, and then performs position calculation. The obtained calculation result is output as position information 26.

[0061] [Table 1]

[0062] Table 1 summarizes the maximum transmission interval and validity period for correction information actually transmitted by MSAS, the SBAS operated by Japan. Correction information regarding the satellite clock and satellite position is provided for each satellite, and correction information for multiple satellites is contained in a single SBAS message. The ionospheric vertical delay is provided as a value at a grid point called an IGP (Ionospheric Grid Point), which is located every 5 degrees of latitude and longitude, and a maximum of 15 IGP delays can be contained in a single SBAS message. The maximum transmission interval is the maximum time between SBAS transmissions of the correction information. The validity period is the time interval until the correction information becomes unusable; user stations can use the correction information within the validity period after receiving it. In the SBAS standard, the validity period is set longer than the maximum transmission interval, essentially twice as long, to take into account the possibility that user stations may miss some SBAS messages.

[0063] In SBAS, a validity period is set for correction information, and a user station can use that correction information within the validity period after receiving the correction information. Therefore, when the distribution station 11 transmits past SBAS messages stored in the storage device 15 to the communication line 3, it can limit the transmission to only SBAS messages within the validity period. Furthermore, since the validity period of correction information in SBAS is basically twice the maximum transmission interval, at any given time, there are two or more pieces of correction information within their validity period. Therefore, if only the most recent SBAS message for each cause of positioning error is transmitted from among the stored SBAS messages, the amount of data transmission can be reduced to less than half compared to transmitting all SBAS messages within their validity period.

[0064] Furthermore, invalid correction information may be omitted from the latest SBAS message, and only valid correction information may be transmitted, further reducing the amount of data transmitted.

[0065] Next, the operation will be explained with reference to FIG.

[0066] The user station 21 has the function of receiving the positioning signal transmitted by the navigation satellite 2 (2a, 2b, etc.) and measuring the distance from the navigation satellite to the user station. Since the measured distance contains various error factors, when the position of the user station is calculated using the measured distance, this results in a positioning error.

[0067] In contrast, when correction information from SBAS is applied, SBAS, which is one type of WADGPS, provides wide-area correction, so the user station can correct positioning errors and obtain a highly accurate position.

[0068] In this invention, the distribution station 11 transmits previously transmitted correction information in addition to the latest SBAS correction information to the user station via the communication line 3. Therefore, the user station does not need to receive the SBAS signal, and as long as it can receive the positioning signal from the navigation satellite, it can continue positioning calculations applying the correction information, regardless of whether the SBAS signal is blocked at the user station. Furthermore, the user station immediately obtains the SBAS messages necessary to perform positioning calculations applying the correction information, thereby shortening the TTFF.

[0069] When the distribution station 11 transmits past SBAS messages stored in the storage device 15 to the communication line 3, it transmits only the most recent SBAS messages from the stored SBAS messages according to the cause of the positioning error, thereby reducing the amount of data transmission to less than half compared to transmitting all SBAS messages within the validity period.

[0070] To confirm that data transmission volume can be reduced, we provide an example of tallying the number of the most recent SBAS messages within their validity period, broken down by the cause of positioning error. Looking at messages sent by MSAS, an SBAS operated by Japan, for the single day of August 7, 2022, we calculated the number of such messages at any given time during the day, finding an average of 38.3, a minimum of 33, and a maximum of 44 (1,375 bytes). The number of SBAS messages within their validity period at any given time during the same day was an average of 156.6, a minimum of 132, and a maximum of 177, so data transmission volume has been reduced to less than half this amount.

[0071] Furthermore, when transmitting correction information, if invalid correction information is omitted from the latest SBAS message and only valid correction information is transmitted, the amount of data transmitted can be further reduced.

[0072] To confirm that data transmission volume can be further reduced, we present an example in which the most recent SBAS messages within their validity period were extracted for each cause of positioning error, and the required number of bits was calculated when invalid correction information was omitted. For the one day of August 7, 2022, we looked at messages sent by MSAS, an SBAS operated by Japan, and calculated the required number of bits at any given time during the day. The average was 4,305.2 bits, the minimum was 3,159 bits, and the maximum was 5,533 bits. The maximum data volume was approximately 692 bytes, further reducing data transmission volume compared to

[0074] .

[0073] In addition, in FIG. 1, the storage device 15 and the data transmitter 16 are housed inside the distribution station 11, but the storage device and the data transmitter may be separated and installed outside the distribution station. [Industrial Applicability]

[0074] The method for transmitting correction information in a satellite navigation system of this invention can be used to transmit correction information in WADGPS. In WADGPS, the TTFF (time to first fix) at a user station and the time required for recovery from correction signal obstruction are determined by the order in which the correction information is transmitted. However, with the transmission method of the present invention, the user station does not need to receive the correction signal, so as long as it can receive the positioning signal from the navigation satellite, it can continue positioning calculations applying the correction information, regardless of whether the correction signal is obstructed at the user station. Furthermore, the user station immediately has the correction information necessary to perform positioning calculations applying the correction information, thereby shortening the TTFF. [Explanation of symbols]

[0075] 1 SBAS satellite 2(2a,2b...) Navigation satellite 3. Communication lines 11 Broadcasting Stations 12 Antenna 13 RF receiving processing circuit 14 Message Decoder 15 Storage device 16 Data Transmitter 21 User Station 22 Antenna 23 RF receiving processing circuit 24 Data Receiver 25 Positioning calculation unit 26 Position Output

Claims

1. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a correction information distribution satellite that distributes correction information according to factors of positioning errors such as clock errors, position errors, and ionospheric propagation delays of the plurality of navigation satellites; In a satellite navigation system including a distribution station that receives correction information distributed by the correction information distribution satellite, the distribution station is provided with a one-way communication line connected to the user station; the distribution station stores the correction information received from the correction information distribution satellite; When transmitting the correction information to the user station via the communication line, the distribution station A method for transmitting correction information in a satellite navigation system, characterized in that, each time a transmission is made, only the most recent correction information for each cause of positioning error is transmitted from among the stored correction information.

2. When transmitting only the latest correction information for each cause of the positioning error, 2. The method for transmitting correction information in a satellite navigation system according to claim 1, wherein invalid correction information is omitted from the correction information and only valid correction information is transmitted.

3. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system having a master station that generates correction information for each cause of positioning error, such as clock error, position error, and ionospheric propagation delay, of the plurality of navigation satellites using the distances measured by the reference station, the master station has a one-way communication line connected to the user station; The master station stores the generated correction information, When transmitting the correction information to the user station via the communication line, the master station A method for transmitting correction information in a satellite navigation system, characterized in that, each time a transmission is made, only the most recent correction information for each cause of positioning error is transmitted from among the stored correction information.

4. When transmitting only the latest correction information for each cause of the positioning error, 4. The method for transmitting correction information in a satellite navigation system according to claim 3, wherein invalid correction information is omitted from the correction information and only valid correction information is transmitted.

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