Detection method and detection device for abnormality of receiving signal, and ship system using detection method and detection device for abnormality of receiving signal

Abstract

To suppress erroneous determination even when a minute variation or offset occurs in a path difference, to accurately detect an abnormal GNSS signal without omission.SOLUTION: A path difference determination unit 52 is configured to: perform, at a predetermined interval, a path difference determination process of comparing, with a first path difference threshold, a path difference indicator, which indicates a difference in paths, of GNSS signals transmitted from a plurality of GNSS satellites to a plurality of GNSS antennas 3A, 3B, and 3 to determine whether or not an arrival direction of the GNSS signals is normal based on the comparison result; and, when the arrival direction of the GNSS signal of at least one GNSS satellite is determined to be abnormal in the determination process performed in the previous cycle, perform, on all the satellites, the path difference determination process for a next cycle using a second path difference threshold that is set so that the arrival direction is more likely to be determined to be abnormal than the first path difference threshold.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a technique for detecting abnormalities in received signals in GNSS (Global Navigation Satellite System).

Background Art

[0002] In GNSS such as GPS (Global Positioning System) that measures the position of a moving object using GNSS signals transmitted from satellites, there is damage in that false GNSS signals are transmitted from transmission sources such as satellites and ground stations, and the GNSS receiver that has received the false GNSS signal is caused to measure an incorrect position. To prevent such damage, a technique for determining the authenticity of the satellite that transmitted the GNSS signal is known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses receiving GNSS signals transmitted from a plurality of satellites by a plurality of antennas, and determining that the GNSS signal is abnormal when the path difference (the difference in the carrier phase of the GNSS signal) representing the difference in the paths from the satellite that transmitted the GNSS signal to each of the plurality of antennas is equal to or less than a predetermined path difference threshold. That is, since the path differences of GNSS signals transmitted by impersonating a plurality of satellites from the same transmission source are the same, it can be determined that the transmission source of the GNSS signal determined to be abnormal is suspected of being a false satellite (hereinafter, this technique is also referred to as path difference coincidence detection).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the travel path difference consistency detection, when the time synchronization between a plurality of receivers that receive GNSS signals via antennas is insufficient, when multipath or noise occurs in the GNSS signals, or when the Doppler frequency of the GNSS signals varies for each satellite due to differences such as the orbiting direction of each satellite, minute variations or offsets may occur in the travel path difference under the influence. The travel path difference consistency detection is executed at a predetermined cycle. However, if minute variations or offsets occur in the travel path difference, a satellite classified as having a travel path difference anomaly because the travel path difference was less than or equal to a predetermined travel path difference threshold (i.e., the travel path difference was consistent) in the determination of the previous cycle may have a travel path difference greater than the predetermined travel path difference threshold due to minute variations or offsets in the next cycle's determination (i.e., the travel path difference is inconsistent), and there is a possibility of misjudging it as a normal GNSS signal. To suppress such misjudgments, the travel path difference threshold may be relaxed by taking into account in advance the minute variations or offsets that occur in the travel path difference (i.e., set to a large value). However, if the travel path difference threshold is relaxed, misjudgments may occur when there are no minute variations or offsets in the travel path difference.

[0006] Also, in the travel path difference consistency detection, when an anomaly is detected in a certain type of GNSS satellite system (e.g., GPS), there is a high possibility that an anomaly will also be detected in other types of satellite systems (e.g., GLONASS, Galileo, etc.). Therefore, in the travel path difference consistency detection, there is a risk of missed anomaly detection if only individual countermeasures are taken for satellites determined to be suspicious of being false satellites.

[0007] Therefore, an object of the present invention is to provide a method and apparatus for detecting anomalies in received signals that can suppress misjudgments even when minute variations or offsets occur in the travel path difference and accurately and without omission detect abnormal GNSS signals.

Means for Solving the Problem

[0008] In order to solve the above problems, a method for detecting an abnormality in a received signal according to the present invention receives GNSS signals transmitted from a plurality of satellites via a plurality of antennas, compares a path difference index representing a difference in paths from the satellites that transmitted the GNSS signals to each of the plurality of antennas with a predetermined path difference threshold value, and executes, at a predetermined period, a process of determining whether the arrival direction of the GNSS signal is normal based on a comparison result between the path difference index and the predetermined path difference threshold value. When at least one of the satellites is determined to have an abnormal arrival direction of the GNSS signal in the determination executed in the immediately preceding period, for all satellites, the determination in the next period is executed using a second path difference threshold value set to make it easier to determine that the arrival direction is abnormal, rather than the predetermined path difference threshold value. This is the gist of the invention.

[0009] In the method for detecting an abnormality in a received signal according to the present invention, when all of the satellites determined to have an abnormal arrival direction of the GNSS signal are determined to have a normal arrival direction of the GNSS signal using the second path difference threshold value, the determination in the next period may be executed using the predetermined path difference threshold value.

[0010] In the method for detecting an abnormality in a received signal according to the present invention, it may be determined whether the arrival direction of the GNSS signal is normal based on the path difference index for each type of satellite system to which the satellite belongs.

[0011] In the method for detecting an abnormality in a received signal according to the present invention, the abnormal state of the satellite determined to be abnormal may be maintained for a predetermined time.

[0012] In the method for detecting an abnormality in a received signal according to the present invention, when it is determined that the arrival direction of the GNSS signal is normal when the arrival direction of the GNSS signal is determined to be abnormal for a plurality of satellites and the abnormal state is maintained, or when a predetermined time has elapsed since the state where the arrival direction of the GNSS signal is determined to be normal, the abnormal state for the plurality of satellites may be released.

[0013] The method for detecting an abnormality in a received signal according to the present invention may be such that, according to the number of satellites determined to be abnormal, the number of reception channel allocations for satellites having a different frequency band from the satellites determined to be abnormal is changed.

[0014] The method for detecting an abnormality in a received signal according to the present invention executes a first determination process for determining whether the GNSS signal is normal at a predetermined period. When it is determined in the first determination process that all of the GNSS signals are normal, the position calculated based on the GNSS signal is output. When it is determined in the first determination process that some or all of the GNSS signals are not normal, a second determination process is executed to determine whether a position can be calculated based only on the GNSS signals determined to be normal during the processing of the first determination process. When it is determined in the second determination process that a position can be calculated, the position calculated based only on the GNSS signals determined to be normal during the processing of the first determination process is output. When it is determined in the second determination process that a position cannot be calculated, a position estimated by adding a change amount measured by a sensor capable of measuring at least acceleration and angular velocity to the most recent position among the positions calculated based only on the GNSS signals determined to be normal before the processing of the first determination process is output, or a message indicating that the position cannot be measured is output.

[0015] The method for detecting an abnormality in a received signal according to the present invention, when it is determined in the second determination process that a position cannot be calculated, executes a third determination process for determining whether the difference between the position calculated based on the GNSS signal and the position estimated in the second determination process is equal to or greater than a predetermined threshold. When it is determined in the third determination process that the difference is equal to or greater than the predetermined threshold, the estimated position is output, or the message is output. When it is determined in the third determination process that the difference is less than the predetermined threshold, the position calculated based on the GNSS signal is output.

[0016] The method for detecting an abnormality in a received signal according to the present invention executes a first determination process for determining whether the GNSS signal is normal at a predetermined period. When it is determined in the first determination process that all of the GNSS signals are normal, the time calculated based on the GNSS signal is output. When it is determined in the first determination process that some or all of the GNSS signals are not normal, a second determination process is executed to determine whether a time can be calculated based only on the GNSS signals determined to be normal during the processing of the first determination process. When it is determined in the second determination process that a time can be calculated, the time calculated based only on the GNSS signals determined to be normal during the processing of the first determination process is output. When it is determined in the second determination process that a time cannot be calculated, a time estimated by adding the elapsed time measured by the internal clock to the most recent time among the times calculated based only on the GNSS signals determined to be normal before the processing of the first determination process is output.

[0017] The method for detecting an abnormality in a received signal according to the present invention, when it is determined in the second determination process that a time cannot be calculated, executes a third determination process for determining whether the difference between the time calculated based on the GNSS signal and the time estimated in the second determination process is equal to or greater than a predetermined threshold. When it is determined in the third determination process that the difference is equal to or greater than the predetermined threshold, the estimated time is output. When it is determined in the third determination process that the difference is less than the predetermined threshold, the time calculated based on the GNSS signal is output.

[0018] The method for detecting an abnormality in a received signal according to the present invention determines that the GNSS signal is in an unstable reception situation and there may be an abnormality in the GNSS signal when at least one of the following cases occurs: the number of satellites determined to have a normal arrival direction of the GNSS signal based on the travel path difference index is less than a predetermined threshold for determining that the GNSS signal is normal based on the travel path difference index; the number of satellites determined to have an abnormal arrival direction of the GNSS signal based on the travel path difference index is within a predetermined range; at least one of the positioning positions of the plurality of antennas has not been calculated; and the standard deviation of the positioning distances between the plurality of antennas calculated using the positioning positions of the plurality of antennas is greater than a predetermined threshold.

[0019] Further, there is provided a ship system using the method for detecting an abnormality in a received signal according to the present invention, in which a first ship and a second ship are communicably connected. The first ship includes position measuring means for measuring the position of its own ship based on the GNSS signal, and an abnormality detection unit for detecting an abnormality in the GNSS signal. The second ship is capable of acquiring the position of the first ship measured by the position measuring means, and is capable of acquiring the fact that an abnormality has been detected by the abnormality detection unit when an abnormality is detected. This is a ship system characterized by the above.

[0020] The ship system may be configured such that the second ship includes position information utilization calculation means for performing calculations using the position of the first ship measured by the position measuring means, and when it is acquired that an abnormality has been detected in the first ship, the position information utilization calculation means invalidates the position of the first ship measured by the position measuring means, or proposes to the user to invalidate it.

[0021] A ship system using the method for detecting abnormality of a received signal according to the present invention, the ship comprising position measuring means for measuring the position of the own ship based on the GNSS signal, and an abnormality detection unit for detecting an abnormality of the GNSS signal, wherein the ship transmits own ship information including the position of the own ship measured by the position measuring means to another ship, and when an abnormality is detected by the abnormality detection unit, transmission of the own ship information to the other ship is invalidated, or the user is proposed to invalidate it. This is a ship system characterized by the above.

[0022] The ship system may be provided with position information utilization calculation means for performing calculations using the position of the own ship measured by the position measuring means on the ship, and when an abnormality is detected by the abnormality detection unit, the position of the own ship measured by the position measuring means in the position information utilization calculation means is invalidated, or the user is proposed to invalidate it.

[0023] A ship system using the method for detecting abnormality of a received signal according to the present invention, wherein a first ship and a second ship are communicably connected, and the first ship and the second ship are provided with position measuring means for measuring the position of the own ship based on the GNSS signal, and the position of the own ship measured by the position measuring means is transmitted to another ship. The first ship is provided with an abnormality detection unit for detecting an abnormality of the GNSS signal. When an abnormality is detected by the abnormality detection unit and the position difference between the position of the own ship measured by the position measuring means at the time of the abnormality detection and the position of the second ship is less than a predetermined threshold value, it is determined that the position of the second ship is abnormal. This is a ship system characterized by the above.

[0024] The ship system may be such that the first ship is provided with position information utilization calculation means for performing calculations using the position of the second ship, and when it is determined that the position of the second ship is abnormal, the position of the second ship in the position information utilization calculation means is invalidated, or the user is proposed to invalidate it.

[0025] Also, a receiving signal abnormality detection device according to the present invention includes a receiving unit that receives GNSS signals transmitted from a plurality of satellites via a plurality of antennas, a path difference index representing a difference in paths from the satellites that transmitted the GNSS signals to each of the plurality of antennas, and a predetermined path difference threshold value, and compares the path difference index with the predetermined path difference threshold value, and executes, at a predetermined period, a process of determining whether the arrival direction of the GNSS signal is normal based on a comparison result between the path difference index and the predetermined path difference threshold value. The path difference determination unit, when at least one of the satellites is determined in the determination executed in the immediately preceding period that the arrival direction of the GNSS signal is not normal, executes the determination in the next period for all the satellites using a second path difference threshold value set so as to be more likely to be determined that the arrival direction is not normal than the predetermined path difference threshold value.

[0026] The receiving signal abnormality detection device according to the present invention may be configured such that when all of the satellites determined to have an abnormal arrival direction of the GNSS signal are determined to have a normal arrival direction of the GNSS signal using the second path difference threshold value, the determination in the next period is executed using the predetermined path difference threshold value.

[0027] The receiving signal abnormality detection device according to the present invention may be configured to determine whether the arrival direction of the GNSS signal is normal based on the path difference index for each type of satellite system to which the satellite belongs.

[0028] The receiving signal abnormality detection device according to the present invention may be configured such that a non-normal state of a satellite determined to be non-normal is maintained for a predetermined time.

[0029] When it is determined that the arrival direction of the GNSS signal is not normal for a plurality of satellites and the abnormal state is maintained, when it is determined that the arrival direction of the GNSS signal is normal, or when a predetermined time has elapsed since the state where it is determined that the arrival direction of the GNSS signal is normal, the abnormal state for the plurality of satellites may be released.

[0030] The reception signal abnormality detection device according to the present invention may be configured such that the number of reception channel allocations for satellites having a different frequency band from the satellites determined to be abnormal changes according to the number of satellites determined to be abnormal.

[0031] The reception signal abnormality detection device according to the present invention includes an abnormality detection unit that executes a first determination process for determining whether the GNSS signal is normal at a predetermined cycle, and an output information adjustment unit that adjusts information to be output. When it is determined in the first determination process that all of the GNSS signals are normal, the output information adjustment unit outputs a position calculated based on the GNSS signal. When it is determined in the first determination process that some or all of the GNSS signals are not normal, a second determination process is executed to determine whether a position can be calculated based only on the GNSS signals determined to be normal during the processing of the first determination process. When it is determined in the second determination process that a position can be calculated, the output information adjustment unit outputs a position calculated based only on the GNSS signals determined to be normal during the processing of the first determination process. When it is determined in the second determination process that a position cannot be calculated, the output information adjustment unit outputs a position estimated by adding a change amount measured by a sensor capable of measuring at least acceleration and angular velocity to the most recent position among the positions calculated based only on the GNSS signals determined to be normal before the processing of the first determination process, or outputs a message indicating that the position cannot be measured.

[0032] When the output information adjustment unit determines that the position cannot be calculated in the second determination process, the abnormal detection device for the received signal according to the present invention executes a third determination process for determining whether the difference between the position calculated based on the GNSS signal and the position estimated in the second determination process is equal to or greater than a predetermined threshold value. When it is determined in the third determination process that the difference is equal to or greater than the predetermined threshold value, the estimated position may be output, or the message may be output. When it is determined in the third determination process that the difference is less than the predetermined threshold value, the position calculated based on the GNSS signal may be output.

[0033] The abnormal detection device for the received signal according to the present invention includes an abnormal detection unit that executes a first determination process for determining whether the GNSS signal is normal at a predetermined cycle, and an output information adjustment unit that adjusts information to be output. When it is determined in the first determination process that all of the GNSS signals are normal, the output information adjustment unit outputs the time calculated based on the GNSS signal. When it is determined in the first determination process that some or all of the GNSS signals are not normal, the output information adjustment unit executes a second determination process for determining whether a time can be calculated based only on the GNSS signals determined to be normal during the process of the first determination process. When it is determined in the second determination process that a time can be calculated, the output information adjustment unit outputs the time calculated based only on the GNSS signals determined to be normal during the process of the first determination process. When it is determined in the second determination process that a time cannot be calculated, the output information adjustment unit outputs the time estimated by adding the elapsed time measured by the internal clock to the most recent time among the times calculated based only on the GNSS signals determined to be normal before the process of the first determination process.

[0034] In the receiving signal abnormality detection device according to the present invention, when it is determined in the second determination process that the output information adjustment unit cannot calculate the time, the third determination process is executed to determine whether the difference between the time calculated based on the GNSS signal and the time estimated in the second determination process is equal to or greater than a predetermined threshold. When it is determined in the third determination process that the difference is equal to or greater than the predetermined threshold, the estimated time is output. When it is determined in the third determination process that the difference is less than the predetermined threshold, the time calculated based on the GNSS signal may be output.

[0035] In the receiving signal abnormality detection device according to the present invention, when the number of satellites determined to have a normal arrival direction of the GNSS signal based on the travel path difference index is less than a predetermined threshold for determining that the GNSS signal is normal based on the travel path difference index, when the number of satellites determined to have an abnormal arrival direction of the GNSS signal based on the travel path difference index is within a predetermined range, when at least one positioning position of the plurality of antennas has not been calculated, and when the standard deviation of the positioning distances between the plurality of antennas calculated using the positioning positions of the plurality of antennas is greater than a predetermined threshold, in at least one of these cases, there may be provided means for determining that the GNSS signal is in an unstable reception state and that an abnormality may have occurred in the GNSS signal.

[0036] Furthermore, there is provided a ship system using the receiving signal abnormality detection device according to the present invention, in which a first ship and a second ship are communicably connected. The first ship includes position measuring means for measuring its own ship's position based on the GNSS signal and an abnormality detection unit for detecting an abnormality in the GNSS signal. The second ship is capable of acquiring the position of the first ship measured by the position measuring means and, when an abnormality is detected by the abnormality detection unit, is capable of acquiring that fact. This is a ship system characterized by the above.

[0037] The ship system may be configured such that the second ship is provided with position information utilization calculation means for performing calculations using the position of the first ship measured by the position measurement means, and when it is determined that an abnormality has occurred in the first ship, the position information utilization calculation means invalidates the position of the first ship measured by the position measurement means, or proposes to the user to invalidate the position.

[0038] Also, a ship system using the reception signal abnormality detection device according to the present invention, comprising: a ship provided with position measurement means for measuring the position of the ship itself based on the GNSS signal; and an abnormality detection unit for detecting an abnormality in the GNSS signal, wherein the ship transmits ship information including the position of the ship itself measured by the position measurement means to another ship, and when an abnormality is detected by the abnormality detection unit, transmission of the ship information to the other ship is invalidated, or the user is proposed to invalidate the transmission.

[0039] The ship system may be configured such that the ship is provided with position information utilization calculation means for performing calculations using the position of the ship itself measured by the position measurement means, and when an abnormality is detected by the abnormality detection unit, the position information utilization calculation means invalidates the position of the ship itself measured by the position measurement means, or proposes to the user to invalidate the position.

[0040] Also, a ship system using the reception signal abnormality detection device according to the present invention, wherein a first ship and a second ship are communicably connected, the first ship and the second ship are each provided with position measurement means for measuring the position of the ship itself based on the GNSS signal, the position of the ship itself measured by the position measurement means is transmitted to the other ship, the first ship is provided with an abnormality detection unit for detecting an abnormality in the GNSS signal, and when an abnormality is detected by the abnormality detection unit and the position difference between the position of the ship itself measured by the position measurement means at the time of the abnormality detection and the position of the second ship is less than a predetermined threshold, it is determined that the position of the second ship is abnormal.

[0041] The ship system may be provided with position information utilization calculation means for the first ship to perform calculations using the position of the second ship. When it is determined that the position of the second ship is abnormal, the position of the second ship may be invalidated in the position information utilization calculation means, or a proposal may be made to the user to invalidate it.

Effect of the Invention

[0042] According to the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to this invention, when at least one of the satellites is determined to have an abnormal arrival direction of the GNSS signal in the determination executed in the immediately preceding cycle, for all satellites, the determination in the next cycle is executed using a second travel difference threshold value set so that it is more likely to be determined that the arrival direction is abnormal than a predetermined travel difference threshold value. Therefore, even when interference such as transmitting a false GNSS signal is performed against a plurality of types of satellite systems of GNSS, it is possible to accurately and without omission detect an abnormal GNSS signal without increasing the risk of false determination caused by minute variations or offsets occurring in the travel difference.

[0043] According to the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to this invention, when it is determined that part or all of the GNSS signals are abnormal, a determination process is performed as to whether a position can be calculated based only on the GNSS signals determined to be normal. When a position cannot be calculated based only on the GNSS signals determined to be normal, a position estimated by adding the change amount measured by an inertial device (a sensor capable of measuring acceleration and angular velocity) to the most recent position among the positions calculated based only on the GNSS signals determined to be normal is output. Thus, it becomes possible to provide appropriate position information to the outside (other devices, services, etc.). Also, when a position cannot be calculated based only on the GNSS signals determined to be normal, at least a message indicating that the position cannot be measured is output, so that it is possible to surely prevent incorrect position information based on abnormal received signals from being used outside (other devices, services, etc.).

[0044] According to the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to the present invention, when it is not possible to calculate a position based only on GNSS signals determined to be normal, the position calculated based on GNSS signals including GNSS signals determined to be abnormal is compared with the position estimated to be normal, that is, the most recent position among the positions calculated based only on GNSS signals determined to be normal, and the amount of change measured by the inertial device is added to the estimated position, and it is determined whether the difference is equal to or greater than a predetermined threshold value to adjust the output information. Therefore, it is possible to provide more appropriate and effective position information to the outside (other devices, services, etc.).

[0045] According to the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to the present invention, when it is determined that part or all of the GNSS signals are not normal, a determination process is performed to determine whether it is possible to calculate the time based only on GNSS signals determined to be normal. When it is not possible to calculate the time based only on GNSS signals determined to be normal, the time estimated by adding the elapsed time measured by the internal clock to the most recent time among the times calculated based only on GNSS signals determined to be normal is output. Therefore, it is possible to provide appropriate time information to the outside (other devices, services, etc.).

[0046] According to the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to the present invention, when it is not possible to calculate the time based only on GNSS signals determined to be normal, the time calculated based on GNSS signals including GNSS signals determined to be abnormal is compared with the time estimated to be normal, that is, the time estimated by adding the elapsed time measured by the internal clock to the most recent time among the times calculated based only on GNSS signals determined to be normal, and it is determined whether the difference is equal to or greater than a predetermined threshold value to adjust the output information. Therefore, it is possible to output more appropriate and effective time information to the outside (other devices, services, etc.).

[0047] According to the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to the present invention, since it is possible to detect a situation where reception of GNSS signals is unstable, it is possible to grasp the abnormality of GNSS signals at the stage of possibility. Even when the detection of the abnormality is delayed, it is possible to prevent the output of incorrect information (such as position and time) based on false GNSS signals, and to improve the reliability of the received signal abnormality detection process.

[0048] According to the ship system using the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to the present invention, since the second ship can know that an abnormality of GNSS signals has been detected on the first ship, it is possible to prevent damage caused by false GNSS signals from affecting its own ship, and to improve the safety of navigation.

[0049] According to the ship system using the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to the present invention, the second ship invalidates (proposes to the user) the incorrect position of the first ship measured based on false GNSS signals in the position information utilization calculation means that performs calculation processing using the position of the first ship. Therefore, it is possible to more surely prevent damage caused by false GNSS signals from affecting its own ship, and to improve the safety of navigation.

[0050] According to the ship system using the method for detecting abnormality of a received signal and the apparatus for detecting abnormality of a received signal according to the present invention, when a ship detects an abnormality of GNSS signals on its own ship, it invalidates (proposes to the user) the transmission of its own ship information including the position of its own ship measured based on false GNSS signals to other ships. Therefore, it is possible to prevent damage caused by false GNSS signals from affecting surrounding ships, and to improve the safety of navigation.

[0051] According to the method for detecting an abnormality in a received signal and the ship system using the apparatus for detecting an abnormality in a received signal according to the present invention, when a ship detects an abnormality in a GNSS signal on its own ship, the ship invalidates (proposes to the user) an incorrect position of its own ship measured based on a false GNSS signal in the position information utilization calculation means that performs calculation processing using the position of its own ship. Therefore, it is possible to more reliably prevent damage caused by false GNSS signals from spreading to surrounding ships and improve the safety of navigation.

[0052] According to the method for detecting an abnormality in a received signal and the ship system using the apparatus for detecting an abnormality in a received signal according to the present invention, when a first ship receives a false GNSS signal, the first ship can determine whether the position of a second ship is abnormal. Therefore, it is possible to detect whether the second ship is receiving the false GNSS signal, and ultimately, it is possible to improve the safety of navigation.

[0053] According to the method for detecting an abnormality in a received signal and the ship system using the apparatus for detecting an abnormality in a received signal according to the present invention, the first ship invalidates (proposes to the user) the position of the second ship determined to be abnormal in the position information utilization calculation means that performs calculation processing using the position of the second ship. Therefore, it is possible to reduce damage caused by false GNSS signals and improve the safety of navigation.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0055] Hereinafter, the present invention will be described based on the illustrated embodiments. In this embodiment, a case where the apparatus for detecting an abnormality in a received signal according to the present invention is incorporated in a GNSS compass will be described as an example.

[0056] (Embodiment 1) (Overall Configuration of GNSS Compass) FIG. 1 is a functional block diagram showing a schematic configuration of a GNSS compass 1 according to an embodiment, including an apparatus for detecting an abnormality in a received signal according to the present invention. The GNSS compass 1 is used, for example, when mounted on a moving body such as a ship, a vehicle, and an aircraft.

[0057] The GNSS compass 1 according to the embodiment has a function of receiving satellite signals / positioning signals (referred to as "GNSS signals") transmitted from a plurality of satellites (referred to as "GNSS satellites") used in GNSS (Global Navigation Satellite System) and detecting an abnormality in the GNSS signals that are received signals in GNSS, and a function of calculating the position of its own device and the like. The GNSS compass 1 mainly includes a control unit 2, a GNSS antenna 3, a GNSS receiver 4, an abnormality detection unit 5, and a positioning unit 6. Each part constituting the GNSS compass 1 is connected so as to be able to transmit and receive signals via a bus and communicate with each other.

[0058] Examples of satellite systems included in GNSS are GPS (Global Positioning System, Global Positioning Satellite), GLONASS (GLObal NAvigation Satellite System), Galileo, BDS (BeiDou navigation satellite System), and the like.

[0059] Each of the plurality of GNSS satellites transmits, as radio waves, a GNSS signal including ephemeris, which is data indicating the current position of the GNSS satellite itself. The GNSS signals transmitted from each of the plurality of GNSS satellites also include information indicating the time when the GNSS satellite transmitted the GNSS signal as radio waves.

[0060] The control unit 2 has a function of controlling the operations of each part constituting the GNSS compass 1, and is configured as a device having a central processing unit (CPU: abbreviated from Central Processing Unit) that performs arithmetic processing involved in, for example, detection of abnormalities in GNSS signals and calculations such as the position of the GNSS compass 1.

[0061] The control unit 2 also has a function of serving as a storage area for storing and storing programs, various information, and data used when the central processing unit (CPU) performs arithmetic processing involved in detecting abnormalities in GNSS signals and calculating the position of the GNSS compass 1, etc., or serving as a work area for temporarily storing data and information generated when the central processing unit (CPU) performs the arithmetic processing. It is configured as a device having at least one of, for example, a ROM (abbreviated from Read Only Memory), which is a read-only storage device, a RAM (abbreviated from Random Access Memory), which is a readable and writable storage device, and a hard disk.

[0062] The control unit 2 controls the start, content, and end of the processing of each part constituting the GNSS compass 1 according to a control program by causing the central processing unit (CPU) to execute a program (referred to as a "control program") for controlling the operation of the GNSS compass 1.

[0063] The GNSS receiver unit 4 is a device for receiving GNSS signals transmitted from a plurality of GNSS satellites S_i (where i is a unique number for each satellite to distinguish the plurality of GNSS satellites from each other), and is composed of at least two GNSS receivers each equipped with a GNSS antenna 3. In this embodiment, the GNSS receiver unit 4 is composed of three GNSS receivers 4A, 4B, and 4C. The GNSS receiver 4A is equipped with a GNSS antenna 3A, the GNSS receiver 4B is equipped with a GNSS antenna 3B, and the GNSS receiver 4C is equipped with a GNSS antenna 3C.

[0064] The three GNSS antennas 3A, 3B, and 3C are arranged and fixed on the moving body on which the GNSS compass 1 is mounted, being spaced apart from each other at a predetermined interval. In this embodiment, the three GNSS antennas 3A, 3B, and 3C are arranged at the positions of the vertices of an equilateral triangle (see Fig. 2).

[0065] The line segments connecting the GNSS antennas 3A, 3B, and 3C to each other are called "baselines". The dimensions of the baselines, which are the distances between the GNSS antennas 3A, 3B, and 3C, are known as the design values of the arrangement of the GNSS antennas 3A, 3B, and 3C. In this embodiment, the dimensions of the baseline AB between the GNSS antenna 3A and the GNSS antenna 3B, the dimensions of the baseline BC between the GNSS antenna 3B and the GNSS antenna 3C, and the dimensions of the baseline AC between the GNSS antenna 3A and the GNSS antenna 3C are all known. The dimensions of the baselines, which are the distances between the GNSS antennas 3A, 3B, and 3C, are set to be one wavelength or more (usually about several wavelengths) in order to avoid interference between the GNSS antennas 3A, 3B, and 3C.

[0066] Each of the GNSS receivers 4A, 4B, and 4C receives the GNSS signals transmitted from each of the GNSS satellites S_i via the GNSS antennas 3A, 3B, and 3C, converts them into electrical signals (especially digital signals), and outputs them.

[0067] The GNSS signal is sequentially transmitted from the GNSS satellite S_i as a radio wave (referred to as the "GNSS radio wave") superimposed on a carrier wave. Each of the GNSS receivers 4A, 4B, and 4C receives the GNSS radio wave, demodulates the GNSS radio wave, and extracts the GNSS signal. Then, the GNSS signal is output from the GNSS receiving unit 4.

[0068] By executing a control program by the central processing unit (CPU) of the control unit 2, an abnormality detection unit 5 and a positioning unit 6 are configured within the control unit 2.

[0069] The abnormality detection unit 5 is a device for detecting an abnormality in the GNSS signal output from the GNSS receiving unit 4 and outputting a detection result.

[0070] The positioning unit 6 is a device for calculating and outputting positioning information using the GNSS signal output from the GNSS receiving unit 4.

[0071] Although the positioning information calculated by the positioning unit 6 is not limited to specific items, for example, at least one of the position, orientation, and attitude of the own vehicle (e.g., rolling, pitching, turning rate (ROT)) can be mentioned. Since well-known techniques can be applied to the calculation process of the positioning information by the positioning unit 6 and this invention is not limited to specific items, methods, etc., a detailed description will be omitted.

[0072] Based on the detection result of the abnormality of the GNSS signal output from the abnormality detection unit 5, the positioning unit 6 determines the GNSS satellite S_i to be excluded from the satellite group used in the calculation process of the positioning information (in other words, determines the GNSS satellite S_i used in the calculation process of the positioning information).

[0073] (Processing content of the abnormality detection unit) The method for detecting an abnormality in a received signal according to the embodiment receives GNSS signals transmitted from a plurality of GNSS satellites S_i via a plurality of GNSS antennas 3A, 3B, and 3C, and determines whether the arrival direction of the GNSS signal is normal based on an index representing the difference in the paths from the GNSS satellite S_i that transmitted the GNSS signal to each of the plurality of GNSS antennas 3A, 3B, and 3C.

[0074] Also, the GNSS compass 1 according to the embodiment including a device for detecting an abnormality in a received signal as a device for implementing the above method for detecting an abnormality in a received signal receives GNSS signals transmitted from a plurality of GNSS satellites S_i via a plurality of GNSS antennas 3A, 3B, and 3C, and has a path difference determination unit 52 that determines whether the arrival direction of the GNSS signal is normal based on an index representing the difference in the paths from the GNSS satellite S_i that transmitted the GNSS signal to each of the plurality of GNSS antennas 3A, 3B, and 3C, and a positioning unit 6 that calculates positioning information, and determines the GNSS satellite S_i to be used in the calculation process of the positioning information by the positioning unit 6 based on the determination result of whether the arrival direction of the GNSS signal is normal.

[0075] The abnormality detection unit 5 is a device for detecting an abnormality in a GNSS signal. It receives the input of the GNSS signal for each GNSS satellite S_i output from the GNSS receiving unit 4 (which is composed of three GNSS receivers 4A, 4B, and 4C each having a GNSS antenna 3 (specifically, any one of 3A, 3B, and 3C)) at a predetermined period, and executes an arithmetic process (referred to as an "abnormality detection arithmetic process") for detecting an abnormality in the GNSS signal that is a received signal in GNSS based on the GNSS signal. The abnormality detection arithmetic process may be executed at the predetermined period in accordance with the predetermined period when the GNSS signal is output from the GNSS receiving unit 4, or may be executed at a period different from the predetermined period.

[0076] The abnormality detection unit 5 includes a path difference calculation unit 51 and a path difference determination unit 52.

[0077] The travel path difference calculation unit 51 receives the input of the GNSS signals for each GNSS satellite Si output from the GNSS receiver unit 4, and calculates the difference in the travel paths from the GNSS satellite Si to each of the GNSS antennas 3A, 3B, and 3C using the information of the GNSS signals. The processing performed by the travel path difference calculation unit 51 and the travel path difference determination unit 52 is referred to as "travel path difference determination processing".

[0078] For each GNSS satellite Si, the travel path difference calculation unit 51 calculates the difference (absolute value) in the travel paths from the GNSS satellite Si to each of the GNSS antennas 3A, 3B, and 3C, which is caused by the plurality of GNSS antennas 3A, 3B, and 3C being arranged at a predetermined interval from each other, for each pair of the GNSS antennas 3A, 3B, and 3C, that is, for each combination of two GNSS antennas 3.

[0079] FIG. 3 is a diagram for explaining the travel path difference. Although the travel path difference is actually obtained in three dimensions, it is explained in two dimensions in FIG. 3 for the purpose of explaining the principle of the travel path difference. In the example shown in FIG. 3, the difference in the travel paths from each of the GNSS satellites S1 and S2 to the GNSS antenna 3A and the travel path to the GNSS antenna 3B (that is, the travel path difference between the GNSS antenna 3A and the GNSS antenna 3B) is taken up and explained.

[0080] The difference C1AB in the travel paths from the GNSS satellite S1 to the GNSS antenna 3A and the travel path to the GNSS antenna 3B is expressed as in the following formula 1, and the difference C2AB in the travel paths from the GNSS satellite S2 to the GNSS antenna 3A and the travel path to the GNSS antenna 3B is expressed as in the following formula 2 (see FIG. 3(A)). (Equation 1) C1AB = LAB × cos(θ1) (Equation 2) C2AB = LAB × cos(θ2) Here, LAB: The dimension of the baseline AB between the GNSS antenna 3A and the GNSS antenna 3B θ1: The elevation angle of the GNSS satellite S1 θ2: The elevation angle of the GNSS satellite S2

[0081] The difference C_1AB between the path from GNSS satellite S_1 represented by the above formula (1) to GNSS antenna 3A and the path to GNSS antenna 3B is calculated according to the following formula (3). Also, the difference C_2AB between the path from GNSS satellite S_2 represented by the above formula (2) to GNSS antenna 3A and the path to GNSS antenna 3B is calculated according to the following formula (4). (Equation 3) C_1AB = λ_1×(N_1+P_1AB) (Equation 4) C_2AB = λ_2×(N_2+P_2AB) Herein,[[]] λ_1: Wavelength of the carrier wave of the GNSS radio wave of GNSS satellite S_1 λ_2: Wavelength of the carrier wave of the GNSS radio wave of GNSS satellite S_2 N_1: Integer value bias (cycle or more) of the GNSS radio wave of GNSS satellite S_1 N_2: Integer value bias (cycle or more) of the GNSS radio wave of GNSS satellite S_2 P_1AB: Single difference between antennas of the GNSS radio wave of GNSS satellite S_1 (less than cycle) P_2AB: Single difference between antennas of the GNSS radio wave of GNSS satellite S_2 (less than cycle)

[0082] The single difference P_iXY between antennas for GNSS satellite S_i (where X and Y are antenna symbols for distinguishing a plurality of GNSS antennas 3 from each other and X≠Y; the same applies hereinafter) is the difference in the carrier phase integration value of one GNSS satellite S_i with respect to two GNSS antennas 3 (in the example shown in FIG. 3, GNSS antenna 3A and GNSS antenna 3B).

[0083] The path difference calculation unit 51 calculates the difference C_iXY between the path from GNSS satellite S_i to GNSS antenna X and the path to GNSS antenna Y for each combination of two GNSS antennas 3 for each GNSS satellite S_i.

[0084] Next, the travel path difference determination unit 52 determines whether the travel path difference C_iXY for each GNSS satellite S_i calculated by the travel path difference calculation unit 51 and for each combination of the two GNSS antennas 3 is normal.

[0085] Here, in the example shown in FIG. 3, since the GNSS satellite S_1 and the GNSS satellite S_2 usually exist at mutually different spatial positions, the elevation angles θ_1 and θ_2 of each satellite as seen from the GNSS compass 1 (specifically, the GNSS antenna 3) are mutually different. And since the elevation angle θ_1 of the GNSS satellite S_1 and the elevation angle θ_2 of the GNSS satellite S_2 are mutually different, the travel path difference C_1AB for the GNSS satellite S_1 and the travel path difference C_2AB for the GNSS satellite S_2 are mutually different (see FIG. 3(A) and the above equations (1) and (2)).

[0086] On the other hand, when both the GNSS satellite S_1 and the GNSS satellite S_2 exist at the same spatial position, the elevation angles θ_1 and θ_2 of each satellite as seen from the GNSS compass 1 (specifically, the GNSS antenna 3) become the same (see FIG. 3(B)). And when the elevation angle θ_1 of the GNSS satellite S_1 and the elevation angle θ_2 of the GNSS satellite S_2 are the same, the travel path difference C_1AB for the GNSS satellite S_1 and the travel path difference C_2AB for the GNSS satellite S_2 become the same (see the above equations (1) and (2)).

[0087] As an example of the case where the elevation angle θ_1 of the GNSS satellite S_1 and the elevation angle θ_2 of the GNSS satellite S_2 are the same, for example, a signal including the positioning information and orbital information of a plurality of GNSS satellites may be transmitted from a single transmitting antenna. In other words, it is conceivable that a plurality of GNSS signals (in other words, GNSS radio waves) are transmitted from a plurality of GNSS satellites but appear to be transmitted from a single transmitting antenna (in other words, the same location; including the antenna station installed on the ground). That is, there is a case where a plurality of false GNSS signals are transmitted from a single transmitting antenna / the same location. In this regard, the "GNSS signals transmitted from a plurality of GNSS satellites S_i" in the present invention includes signals transmitted from a single transmitting antenna / the same location while appearing to be transmitted from a plurality of GNSS satellites S_i.

[0088] Therefore, the travel difference determination unit 52 compares the difference (travel difference index) between the travel differences (absolute values) C_iXY for a plurality of GNSS satellites S_i with a predetermined travel difference threshold (hereinafter referred to as the first travel difference threshold), and based on the comparison result, determines whether the arrival direction of the GNSS signal is normal (travel difference determination process) at a predetermined cycle.

[0089] More specifically, the travel difference determination unit 52 calculates, for each pair of GNSS antennas 3, that is, for each combination of two GNSS antennas 3, the difference (travel difference index) between the maximum value and the minimum value of the travel differences (absolute values) C_iXY for a plurality of GNSS satellites S_i. When the obtained travel difference index is less than or equal to the first travel difference threshold, the plurality of GNSS satellites S_i are classified as having an abnormal travel difference on the grounds that the arrival direction of the GNSS signal is abnormal.

[0090] Further, when there is at least one satellite (i.e., a satellite classified as a travel path difference anomaly) for which it was determined that the arrival direction of the GNSS signal was not normal in the travel path difference determination process executed in the previous cycle, for all satellites, the travel path difference determination process for the next cycle is executed using a second travel path difference threshold value set so that it is more likely to be determined that the arrival direction is not normal than the first travel path difference threshold value.

[0091] Here, the second travel path difference threshold value set so that it is more likely to be determined that the arrival direction is not normal than the first travel path difference threshold value is a threshold value having a value larger than the first travel path difference threshold value, and the relationship between the first travel path difference threshold value and the second travel path difference threshold value is "the first travel path difference threshold value < the second travel path difference threshold value". According to this, even when there are minute variations or offsets in the travel path difference due to insufficient time synchronization between receivers, multi-path or noise in the GNSS signal, or differences in the Doppler frequency of the GNSS signal for each satellite due to differences such as the orbiting direction of each satellite, etc., by executing the travel path difference determination process using the second travel path difference threshold value set so that it is more likely to be determined that the arrival direction is not normal, it is possible to suppress the GNSS signal that should originally be determined as abnormal from being erroneously determined as normal.

[0092] The travel path difference threshold value is not limited to a specific value. For example, even if multiple GNSS signals are actually transmitted from a single transmission antenna / the same location, after considering errors that are assumed to occur due to mechanical errors, etc., it is appropriately set to an appropriate value. Also, the second travel path difference threshold value is based on the time synchronization accuracy of the GNSS receivers 4A, 4B, 4C, the occurrence frequency and amount of multi-path or noise, the change in the Doppler frequency of the GNSS signal, the individual differences for each GNSS compass 1, etc., to identify minute variations or offsets that occur in the travel path difference, and is appropriately set to a value larger than the first travel path difference threshold value so as not to be affected by these.

[0093] Here, the operation of the above road path difference determination process will be described based on the flowchart shown in FIG. 4. The road path difference determination unit 52 receives, for each combination of two of the three GNSS antennas 3A, 3B, and 3C (in other words, for each of the baselines AB, BC, and AC), the input of the road path difference C_iXY between the GNSS antennas X - Y of the respective GNSS satellite S_i from the road path difference calculation unit 51 at the time of the said process. The road path difference determination unit 52 obtains the difference (road path difference index) between the maximum value and the minimum value among the road path differences C_iXY between the GNSS antennas X - Y of the input GNSS satellite S_i, and performs the following process.

[0094] The road path difference determination unit 52 checks whether there is a GNSS satellite classified as having an abnormal road path difference in the road path difference determination process of the previous cycle (step S1).

[0095] If the road path difference determination unit 52 can confirm in step S1 that there is no GNSS satellite classified as having an abnormal road path difference (NO in step S1), it determines whether the road path difference index is less than or equal to the first road path difference threshold for the two GNSS satellites used in calculating the road path difference index (step S2). When the road path difference index is less than or equal to the first road path difference threshold (YES in step S2), the two GNSS satellites S_i are classified as having an abnormal arrival direction of the GNSS signal, and the two GNSS satellites S_i are classified as having an abnormal road path difference (step S3).

[0096] In step S1 of the next cycle, the road path difference determination unit 52 checks whether there is a GNSS satellite classified as having an abnormal road path difference in the determination of the previous cycle. If it can be confirmed that there is a GNSS satellite classified as having an abnormal road path difference (YES in step S1), it determines whether the road path difference index is less than or equal to the second road path difference threshold for the two GNSS satellites used in calculating the road path difference index (step S4). When the road path difference index is less than or equal to the second road path difference threshold (YES in step S4), the two GNSS satellites S_i are classified as having an abnormal arrival direction of the GNSS signal, and the two GNSS satellites S_i are classified as having an abnormal road path difference (step S3).

[0097] Also, in the determination of step S4, when the travel path difference index is greater than the second travel path difference threshold (NO in step S4), the two GNSS satellites S_i are classified as having a normal arrival direction of the GNSS signal, and the two GNSS satellites S_i are classified as having a normal travel path difference (step S5).

[0098] When there is no GNSS satellite S_i that was classified as having an abnormal travel path difference in the previous cycle among the two GNSS satellites S_i classified as having a normal travel path difference in step S5, it is determined whether the travel path difference index is less than or equal to the first travel path difference threshold (steps S1, S2). On the other hand, when there is a GNSS satellite S_i that was classified as having an abnormal travel path difference in the previous cycle among the two GNSS satellites S_i classified as having a normal travel path difference in step S5, in the determination process of the travel path difference in the next cycle, it is determined whether the travel path difference index is less than or equal to the second travel path difference threshold (step S4).

[0099] In this way, by appropriately switching between the first travel path difference threshold and the second travel path difference threshold to perform the determination process of the travel path difference, it is possible to suppress misjudgments caused by minute variations or offsets in the travel path difference, and to accurately and without omission detect abnormal GNSS signals.

[0100] When determining that the arrival directions of the GNSS signals of a plurality of GNSS satellites S_i are abnormal, the lower limit of the number of satellites may be set. For example, when the difference between the maximum value and the minimum value of the travel path differences C_iXY of the two GNSS satellites S_i is less than or equal to the travel path difference threshold, the two GNSS satellites S_i are not classified as having an abnormal travel path difference, while when the difference between the maximum value and the minimum value of the travel path differences C_iXY of three or more GNSS satellites S_i is less than or equal to the travel path difference threshold, the three or more GNSS satellites S_i may be classified as having an abnormal travel path difference. Although the lower limit of the number of satellites in this case is not limited to a specific value, it is considered that it may be set to any value in the range of about 3 to 5, for example.

[0101] When determining the abnormal travel difference, all of the multiple GNSS satellites S_i belong to the same type of satellite system, and the abnormal travel difference may be determined for each type of satellite system to which the satellites belong, that is, for each of GPS, GLONASS, BDS, etc. For example, when the difference between the maximum value and the minimum value among the travel differences of two GPS satellites is less than or equal to the travel difference threshold, the two GPS satellites are not classified as having an abnormal travel difference. On the other hand, when the difference between the maximum value and the minimum value among the travel differences of three or more GPS satellites is less than or equal to the travel difference threshold, the three or more GPS satellites may be classified as having an abnormal travel difference. Although the lower limit of the number of satellites in this case is not limited to a specific value, it is considered that it may be set to any value within a range of about 3 to 5, for example.

[0102] Here, when the multiple GNSS satellites S_i are present at mutually different spatial positions, the inter-antenna single differences P_iXY for the multiple GNSS satellites S_i are usually different from each other. In contrast, when multiple GNSS signals are transmitted from a single transmitting antenna / the same location, the inter-antenna single differences P_iXY for the multiple GNSS satellites S_i are the same. Therefore, in the determination process of the travel difference for each GNSS satellite S_i, the inter-antenna single differences P_iXY for the multiple GNSS satellites S_i may be verified (see the above equations 3 and 4).

[0103] Note that even though GNSS satellite S_1 and GNSS satellite S_2 are at different spatial positions and the path difference C_1AB for GNSS satellite S_1 and the path difference C_2AB for GNSS satellite S_2 are actually different, it is conceivable that the single differences P_1AB and P_2AB between the antennas for the two GNSS satellites S_1 and S_2 happen to be the same. However, since GNSS satellites S_1 and S_2 are moving, the above state will not last long (for example, for more than several seconds). Also, since the directions of the baselines are different for each pair of GNSS antennas 3, even if the single differences P_1AB and P_2AB between the antennas for the two GNSS satellites S_1 and S_2 happen to be the same in the combination of GNSS antenna 3A and GNSS antenna 3B, the single differences P_1AB and P_2AC between the antennas for the two GNSS satellites S_1 and S_2 will not be the same in the combination of GNSS antenna 3A and GNSS antenna 3C.

[0104] When verifying the single differences P_iXY between the antennas for a plurality of GNSS satellites S_i, the path difference determination unit 52 compares the difference (path difference index) between the single differences (absolute values) P_iXY between the antennas for the plurality of GNSS satellites S_i and a predetermined path difference threshold (hereinafter referred to as the first path difference threshold), and based on the comparison result, executes a process (path difference determination process) for determining whether the arrival direction of the GNSS signal is normal at a predetermined cycle.

[0105] More specifically, the path difference determination unit 52 obtains, for each pair of GNSS antennas 3, that is, for each combination of two GNSS antennas 3, the difference (path difference index) between the maximum value and the minimum value among the single differences (absolute values) P_iXY between the antennas for the plurality of GNSS satellites S_i. When the obtained path difference index is less than or equal to the first path difference threshold, the plurality of GNSS satellites S_i are classified as having an abnormal path difference on the assumption that the arrival direction of the GNSS signal for the plurality of GNSS satellites S_i is abnormal.

[0106] In addition, when there is at least one satellite for which it was determined that the arrival direction of the GNSS signal was not normal in the travel path difference determination process executed in the previous cycle (i.e., a satellite classified as having an abnormal travel path difference), for all satellites, the travel path difference determination process for the next cycle is executed using a second travel path difference threshold value that is set so that it is more likely to be determined that the arrival direction is not normal than the first travel path difference threshold value.

[0107] Here, the second travel path difference threshold value that is set so that it is more likely to be determined that the arrival direction is not normal than the first travel path difference threshold value is a threshold value having a value larger than the first travel path difference threshold value, and the relationship between the first travel path difference threshold value and the second travel path difference threshold value is "first travel path difference threshold value < second travel path difference threshold value".

[0108] In this case, the first travel path difference threshold value is not limited to a specific value either. For example, even if multiple GNSS signals are actually transmitted from a single transmitting antenna / the same location, an appropriate value is appropriately set after considering errors that are assumed to occur due to mechanical errors, etc. Also, the second travel path difference threshold value is based on the time synchronization accuracy of the GNSS receivers 4A, 4B, and 4C, the occurrence frequency and amount of multipath or noise, the change in the Doppler frequency of the GNSS signal, the individual differences of each GNSS compass 1, etc., to identify minute variations and offsets that occur in the travel path difference, and is appropriately set to a value larger than the first travel path difference threshold value so as not to be affected by these.

[0109] Note that when using the difference between the inter-antenna single differences (absolute values) P_iXY for a plurality of GNSS satellites S_i as the travel path difference threshold value and performing the travel path difference determination process, the processing procedure is the same as the flowchart shown in FIG. 4, so detailed description is omitted.

[0110] In this way, by appropriately switching between the first travel path difference threshold value and the second travel path difference threshold value and performing the travel path difference determination process, it is possible to suppress false determinations caused by minute variations and offsets that occur in the travel path difference.

[0111] As described above, the difference in the paths from GNSS satellite \(S_i\) to each GNSS antenna 3A, 3B, and 3C, which is used in the determination process of the path difference for each GNSS satellite \(S_i\), such as the path difference \(C_{iXY}\) for GNSS satellite \(S_i\) and the single difference \(P_{iXY}\) between antennas, is called the "path difference index".

[0112] Then, the path difference determination unit 52 outputs the information regarding GNSS satellite \(S_i\) classified as having a path difference anomaly (in other words, an anomaly in the arrival direction of the GNSS signal) to the positioning unit 6 as satellite information with a path difference anomaly.

[0113] In the above determination process, GNSS satellite \(S_i\) classified as having a path difference anomaly is excluded from the satellite group used in the calculation process of the positioning information by the positioning unit 6, and the GNSS signal transmitted from the excluded GNSS satellite \(S_i\) is not used in the calculation process of the positioning information by the positioning unit 6.

[0114] It may be set whether to exclude GNSS satellite \(S_i\) classified as having a path difference anomaly for each item of the positioning information calculated by the positioning unit 6 (specifically, the position, azimuth, and attitude of the own vehicle, etc.). For example, as an example for explanation only, when calculating the position of the own vehicle, GNSS satellite \(S_i\) classified as having a path difference anomaly may not be excluded, and when calculating the azimuth and attitude of the own vehicle, it may be excluded.

[0115] GNSS satellite \(S_i\) classified as having a path difference anomaly (in other words, GNSS satellite \(S_i\) determined to be abnormal) may be such that the state classified as the above anomaly (in other words, the above abnormal state) is maintained for a predetermined anomaly holding time (and the above determination process is not performed while the state classified as the above anomaly is maintained).

[0116] The abnormal holding time is not limited to a specific time length. For example, after considering avoiding a situation where the number of normal (in other words, used for the calculation process of the positioning information by the positioning unit 6) GNSS satellites S_i extremely decreases, or ensuring the possibility of capturing normal GNSS satellites S_i accompanying the movement of the mobile body equipped with the GNSS compass 1, it is appropriately set to an appropriate time length. The abnormal holding time may be set to zero. In this case, that is, the determination process of the travel difference for each GNSS satellite S_i is performed every time the abnormality detection calculation process is executed.

[0117] When the state classified as abnormal is maintained for the abnormal holding time, the GNSS satellite S_i classified as having a travel difference abnormality may be removed from the abnormality classification immediately after the elapse of the abnormal holding time and be made a satellite for receiving GNSS signals (and a satellite targeted for the above determination process). Or, when it is determined that the state during the abnormal holding time is a state not classified as abnormal (a state where the arrival direction of the GNSS signal is normal), it may be immediately removed from the abnormality classification and be made a satellite for receiving GNSS signals (and a satellite targeted for the above determination process). Or, when the state where it is determined that the arrival direction of the GNSS signal is normal during the abnormal holding time has elapsed for a predetermined time (that is, when it has been maintained for a predetermined normal continuation time), it may be removed from the abnormality classification and be made a satellite for receiving GNSS signals (and a satellite targeted for the above determination process).

[0118] The normal continuation time is not limited to a specific time length. For example, after considering avoiding a situation where the number of normal (in other words, used for the calculation process of the positioning information by the positioning unit 6) GNSS satellites S_i extremely decreases, it is appropriately set to an appropriate time length.

[0119] When in a state classified as a travel difference anomaly, and for a plurality of GNSS satellites \(S_i\) in a state classified as a travel difference anomaly, when the difference between the travel differences (absolute values) \(C_iXY\) of the plurality of GNSS satellites \(S_i\) becomes greater than the travel difference threshold value, it may be determined that the travel difference anomaly for the plurality of GNSS satellites \(S_i\) has been resolved, and the plurality of GNSS satellites \(S_i\) may be removed from the classification of travel difference anomaly (in other words, the abnormal state of the plurality of GNSS satellites \(S_i\) is released).

[0120] An output device (not shown) equipped with, for example, a monitor and a speaker, which is attached to the GNSS compass 1, may be provided so that when a travel difference anomaly occurs, an alarm screen is displayed on the monitor of the output device or an alarm is issued from the speaker of the output device to notify the user. Also, other devices that use GNSS signals (for example, radar, inertial navigation devices) may be notified that a travel difference anomaly has occurred.

[0121] When the number of GNSS satellites \(S_i\) classified as having a travel difference anomaly is large and the number of GNSS satellites \(S_i\) used in the calculation process of the positioning information by the positioning unit 6 is small, the number of received channel allocations for satellites whose types of GNSS (that is, different frequency bands) are different from those of the GNSS satellites \(S_i\) classified as the anomaly may be increased. That is, according to the number of GNSS satellites \(S_i\) classified as the anomaly, the number of received channel allocations for satellites whose frequency bands are different from those of the GNSS satellites \(S_i\) classified as the anomaly may be changed.

[0122] For example, as the specification of the GNSS receiving unit 4, when types of a plurality of GNSS satellite systems (for example, GPS, GLONASS, BDS) share and are allocated to the same receiving channel and there is a limit to the number of satellites to be allocated, when there are no GNSS satellites \(S_i\) classified as having a travel difference anomaly, many GNSS satellites \(S_i\) that prioritize the accuracy of the calculation of the positioning information by the positioning unit 6 are allocated, while when there are many GNSS satellites \(S_i\) classified as having a travel difference anomaly, many GNSS satellites \(S_i\) that can prioritize the continuation of the calculation of the positioning information by the positioning unit 6 may be allocated.

[0123] When the number of GNSS satellites Si classified as having abnormal travel differences is large and the number of GNSS satellites Si used in the calculation process of the positioning information by the positioning unit 6 is small, and the state where the calculation process of the positioning information by the positioning unit 6 cannot be performed continues for a predetermined time or more, for fail-safe, the GNSS satellites Si classified as the above abnormalities may be removed from the above classification of abnormalities and be set as satellites to receive GNSS signals (and satellites that are the target of the above determination process). In this case, information (for example, a flag) indicating that it is a GNSS satellite Si classified as having an abnormal travel difference may be added to the GNSS signal output from the GNSS receiving unit 4.

[0124] As described above, according to the method for detecting an abnormality in a received signal and the GNSS compass 1 according to the present embodiment, when at least one of the satellites is determined to have an abnormal arrival direction of the GNSS signal in the determination executed in the previous cycle, for all satellites, the determination in the next cycle is executed using a second travel difference threshold value set so as to be more likely to be determined to have an abnormal arrival direction than a predetermined travel difference threshold value. Therefore, even when interference such as transmitting a false GNSS signal is performed on a plurality of types of GNSS satellite systems of GNSS, it is possible to suppress false determination caused by minute variations and offsets occurring in the travel difference, and to accurately and without omission detect an abnormal GNSS signal.

[0125] (Embodiment 2) Next, a method for detecting an abnormality in a received signal and the GNSS compass 1 according to Embodiment 2 of the present invention will be described. Regarding the same configuration as in Embodiment 1, the same reference numerals will be used and detailed description will be omitted.

[0126] In Embodiment 1, when it is determined that the GNSS signal from the GNSS satellite is abnormal, a countermeasure method of not using the GNSS signal for calculations such as position is taken. However, the specific calculation method for positions and the like when it is determined that the GNSS signal from the GNSS satellite is abnormal has not been sufficiently studied.

[0127] Therefore, the method for detecting abnormalities in received signals and the GNSS compass 1 according to the present embodiment are intended to be able to calculate appropriate position information and time information and provide them to the outside (other devices, services, etc.) when it is determined that part or all of the GNSS signals from GNSS satellites are not normal. In particular, an output information adjustment unit 7 is provided to adjust the position information and time information output to the outside (other devices, services, etc.) according to the results of each determination process in the abnormality detection unit 5. In this regard, the present embodiment is different from the first embodiment.

[0128] FIG. 5 is a functional block diagram showing a schematic configuration of the GNSS compass according to the present embodiment. Here, the output information adjustment unit 7 is a device for adjusting the position information and time information output to the outside (other devices, services, etc.) according to the detection result of the abnormality of the GNSS signal output from the abnormality detection unit 5. Further, the inertial device 8 (sensor) is mainly composed of a gyro sensor (angular velocity sensor) and an acceleration sensor, and is a device for calculating position information such as attitude angle, velocity, and position by integrating inertial information such as angular velocity and acceleration obtained from these sensors.

[0129] FIG. 6 is a flowchart showing the processing procedure in the GNSS compass 1 according to the present embodiment and mainly the output information adjustment process performed in the output information adjustment unit 7.

[0130] FIG. 6(A) is a flowchart showing the adjustment process of the position information as the output information. First, the positioning unit 6 calculates the position of the own device based on the GNSS signals for each GNSS satellite S_i output from the GNSS reception unit 4 at a predetermined cycle and outputs it to the output information adjustment unit 7 (step S11a).

[0131] The inertial device 8 calculates position information (such as attitude angle, velocity, and position) using a gyro sensor and an acceleration sensor and outputs it to the output information adjustment unit 7 (step S12a).

[0132] And when, in the first determination process performed by the abnormality detection unit 5, a determination result that part or all of the GNSS signals transmitted from the GNSS satellite S_i is not normal is output (step S13a: Yes), the output information adjustment unit 7 performs a second determination process to determine whether it is possible to calculate the position based only on the GNSS signals determined to be normal during the process of the first determination process (step S14a). Whether it is possible to calculate the position based on the GNSS signals (GNSS positioning) is determined by the number of GNSS satellites S_i that transmit normal GNSS signals. Generally, GNSS positioning is considered possible if there are about 3 to 4 or more GNSS satellites S_i that transmit normal GNSS signals.

[0133] In the second determination process, when it is determined that GNSS positioning is not possible (step S14a: No), the output information adjustment unit 7 generally outputs, as the position of the own vehicle, the position estimated by adding the change amount measured by the inertial device 8 to the latest (most recent) position among the positions calculated based only on the GNSS signals determined to be normal before the process of the first determination process (step S15a). Here, the change amount measured by the inertial device 8 specifically means the change amount of the speed from the most recent GNSS positioning time when the position could be calculated based only on the GNSS signals determined to be normal to the time of the first determination process. Also, the estimated position is stored in the control unit 2 (RAM) as the most recent position information.

[0134] Regarding the process in step S15a, a specific example will be given for explanation. GNSS signals are transmitted from a plurality of GNSS satellites S_i every α seconds. In the first determination process, it is determined that all the GNSS signals transmitted for the nth time at time t are normal. However, in the first determination process, it is determined that some or all of the GNSS signals transmitted for the (n + 1)th time at time (t + α) are not normal. In the second determination process, it is assumed that it is determined that the position cannot be calculated based only on the GNSS signals determined to be normal among the plurality of GNSS signals transmitted for the (n + 1)th time at time (t + α). In this case, "the most recent (latest) position among the positions calculated based only on the GNSS signals determined to be normal before the processing time of the first determination process" becomes the position Gl(n) calculated based on the GNSS signals transmitted for the nth time from the GNSS satellite S_i, and "the change amount measured by the inertial device 8" is the amount I(t + α) - I(t) obtained by subtracting the measured position I(t) of the inertial device 8 at time t from the measured position I(t + α) of the inertial device 8 at time (t + α), that is, the change amount v(α) of the speed v in α seconds. Therefore, the output information adjustment unit 7 outputs the estimated position Gl(n) + v(α) (obtained by adding the change amount v(α) (the change amount of the speed v in α seconds) to the position Gl(n)) as the position of the own vehicle (step S15a). Then, this estimated position Gl(n) + v(α) is stored in the control unit 2 (RAM) as the latest position information.

[0135] However, since the calculation process of the change amount in the inertial device 8 is an integration process, errors accumulate over time and no longer show accurate values. Therefore, when the error of the change amount output from the inertial device 8 becomes large, the output information adjustment unit 7 outputs, as an exception, a message indicating that the position of the own vehicle cannot be measured (step S15a).

[0136] On one hand, when a determination result that all GNSS signals transmitted from GNSS satellite S_i are normal is output from the abnormality detection unit 5 in the first determination process (step S13a: No), and when it is determined that GNSS positioning is possible based only on the GNSS signals determined to be normal in the second determination process (step S14a: Yes), the output information adjustment unit 7 outputs, as the position of the own vehicle, the position calculated based only on the GNSS signals determined to be normal during the processing of the first determination process (step S16a). And at this timing, the change amount measured by the inertial device 8 is added to the latest position information stored in the control unit 2 (RAM), that is, the latest position among the positions calculated based only on the GNSS signals determined to be normal, and the estimated position (Gl(n) + v(α) in the above example) is calibrated with the position information based on the GNSS signal (step S17a).

[0137] FIG. 6(B) is a flowchart showing the procedure of the adjustment process of the time information as the output information. First, the GNSS receiver 4 calculates the time based on the GNSS signals for each GNSS satellite S_i output at a predetermined cycle, and outputs it to the output information adjustment unit 7 (step S11b).

[0138] Also, the GNSS receiver 4 updates the internal clock with, for example, a temperature-compensated crystal oscillator (TCXO) (mounted on the GNSS receiver 4), and outputs the time of the internal clock to the output information adjustment unit 7 (step S12b).

[0139] When, in the first determination process performed by the abnormality detection unit 5, a determination result that part or all of the GNSS signals transmitted from the GNSS satellite S_i is not normal is output (step S13b: Yes), a second determination process is performed to determine whether it is possible to calculate the time based only on the GNSS signals determined to be normal during the process of the first determination process (step S14b). Whether it is possible to calculate the time based on the GNSS signals is determined by the number of GNSS satellites transmitting normal GNSS signals. Generally, if there are about two or more GNSS satellites S_i transmitting normal GNSS signals, it is considered possible to calculate the time based on the GNSS signals.

[0140] In the second determination process, when it is determined that it is not possible to calculate the time based on the GNSS signals (step S14b: No), the output information adjustment unit 7 outputs, as the time of the own device, the time estimated by adding the elapsed time measured by the internal clock to the most recent time among the times calculated based only on the GNSS signals determined to be normal before the process of the first determination process (step S15b). Here, the elapsed time measured by the internal clock specifically means the elapsed time from the most recent time when the time could be calculated based only on the GNSS signals determined to be normal to the time during the process of the first determination process. Also, the estimated time is stored in the control unit 2 (RAM) as the most recent time information.

[0141] Regarding the process in step S15b, a specific example will be given for explanation. GNSS signals are transmitted from a plurality of GNSS satellites S_i every α seconds. In the first determination process, it is determined that all the GNSS signals transmitted for the nth time at time t are normal. However, in the first determination process, it is determined that some or all of the GNSS signals transmitted for the (n + 1)th time at time (t + α) are not normal. And in the second determination process, it is determined that the time cannot be calculated based only on the GNSS signals determined to be normal among the plurality of GNSS signals transmitted for the (n + 1)th time at time (t + α). In this case, "the most recent time among the times calculated based only on the GNSS signals determined to be normal before the process of the first determination process" becomes the time Gt(n) calculated based on the GNSS signals transmitted for the nth time from the GNSS satellite S_i. Therefore, the output information adjustment unit 7 outputs the time Gt(n)+α estimated by adding the elapsed time (α) measured by the internal clock at time Gt(n) as the time of its own device (step S15b). And this estimated time Gt(n)+α is stored in the control unit 2 (RAM) as the most recent time information.

[0142] On the other hand, when the determination result that all the GNSS signals transmitted from the GNSS satellite S_i are normal is output from the abnormality detection unit 5 in the first determination process (step S13b: No), and when it is determined in the second determination process that the time can be calculated based only on the GNSS signals determined to be normal (step S14b: Yes), the output information adjustment unit 7 outputs the time calculated based only on the GNSS signals determined to be normal at the time of the process of the first determination process as the time of its own device (step S16b). And at this timing, the time of the internal clock of the GNSS reception unit 4 is calibrated by the time based on the GNSS signal (step S17b).

[0143] According to the method for detecting abnormality of a received signal and the GNSS compass 1 according to this embodiment, when it is determined that part or all of the GNSS signals are not normal, a determination process is performed to determine whether a position can be calculated based only on the GNSS signals determined to be normal. When a position cannot be calculated based only on the GNSS signals determined to be normal, a position estimated by adding the change amount measured by the inertial device 8 to the most recent position among the positions calculated based only on the GNSS signals determined to be normal is output. Therefore, it is possible to provide appropriate position information to the outside (other devices, services, etc.). Further, when a position cannot be calculated based only on the GNSS signals determined to be normal, at least a message indicating that the position cannot be measured is output, so that it is possible to surely prevent incorrect position information based on abnormal received signals from being used outside (other devices, services, etc.).

[0144] Also, according to the method for detecting abnormality of a received signal and the GNSS compass 1 according to this embodiment, when it is determined that part or all of the GNSS signals are not normal, a determination process is performed to determine whether a time can be calculated based only on the GNSS signals determined to be normal. When a time cannot be calculated based only on the GNSS signals determined to be normal, a time estimated by adding the elapsed time measured by the internal clock to the most recent time among the times calculated based only on the GNSS signals determined to be normal is output. Therefore, it is possible to provide appropriate time information to the outside (other devices, services, etc.).

[0145] (Embodiment 3) Next, the method for detecting abnormality of a received signal and the GNSS compass 1 according to Embodiment 3 of the present invention will be described. Note that the same components as those in Embodiment 1 will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0146] In Embodiment 3, when it is not possible to calculate the position and time based only on the GNSS signals determined to be normal, the difference between the position and time calculated based on the GNSS signals including the GNSS signals determined to be abnormal and the position and time estimated to be normal is compared, and then the output information is adjusted, which is different from Embodiment 2.

[0147] FIG. 5 is a functional block diagram showing a schematic configuration of the GNSS compass according to the present embodiment, and FIG. 7 is a flowchart showing a processing procedure in the GNSS compass 1 according to the present embodiment and a procedure of output information adjustment processing mainly performed in the output information adjustment unit 7.

[0148] FIG. 7(A) is a flowchart showing a procedure for adjusting the position information as output information. First, the positioning unit 6 calculates the position of the own vehicle based on the GNSS signals for each GNSS satellite S_i output from the GNSS receiving unit 4 at a predetermined cycle, and outputs it to the output information adjustment unit 7 (step S11a).

[0149] The inertial device 8 calculates position information (attitude angle, velocity, position, etc.) using a gyro sensor and an acceleration sensor, and outputs it to the output information adjustment unit 7 (step S12a).

[0150] When, in the first determination process performed by the abnormality detection unit 5, a determination result that part or all of the GNSS signals transmitted from the GNSS satellite S_i is not normal is output (step S13a: Yes), the output information adjustment unit 7 performs a second determination process to determine whether it is possible to calculate the position based only on the GNSS signals determined to be normal during the process of the first determination process (step S14a). When it is determined in the second determination process that GNSS positioning is not possible (step S14a: No), the output information adjustment unit 7 compares the position calculated based on the GNSS signals including the GNSS signals determined to be not normal with the position estimated by adding the change amount measured by the inertial device 8 to the most recent (latest) position among the positions calculated based only on the GNSS signals determined to be normal before the process of the first determination process, and calculates the difference between the two (step S18a). Then, when the difference is equal to or greater than a predetermined threshold (step S18a: Yes), in principle, the estimated position is output as the position of the own vehicle, and as an exception, a message indicating that the position of the own vehicle cannot be measured is output (step S15a). Note that the estimated position is stored in the control unit 2 (RAM) as the most recent position information.

[0151] For the processes in steps S18a and S5a, specific examples will be given for explanation. Similar to the example of the first embodiment, GNSS signals are transmitted from a plurality of GNSS satellites S_i every α seconds, and it is determined in the first determination process that all the GNSS signals transmitted for the nth time at time t are normal. However, it is determined in the first determination process that some or all of the GNSS signals transmitted for the (n + 1)th time at time (t + α) are not normal. In the second determination process, it is determined that the position cannot be calculated based only on the GNSS signals determined to be normal among the plurality of GNSS signals transmitted for the (n + 1)th time at time (t + α). In this case, "the most recent (latest) position among the positions calculated based only on the GNSS signals determined to be normal before the time of the first determination process" becomes the position Gl(n) calculated based on the GNSS signals transmitted for the nth time from the GNSS satellite S_i, and "the change amount measured by the inertial device 8" is the amount I(t + α) - I(t) obtained by subtracting the measured position I(t) of the inertial device 8 at time t from the measured position I(t + α) of the inertial device 8 at time (t + α), that is, the change amount v(α) of the velocity v during α seconds. Therefore, the estimated position is Gl(n) + v(α). On the other hand, the position calculated based on the (n + 1)th GNSS signal including the GNSS signals determined to be abnormal is Gl(n + 1). Thus, the output information adjustment unit 7 compares the estimated position Gl(n) + v(α) with the position Gl(n + 1) calculated based on the (n + 1)th GNSS signal and calculates the difference between the two (step S18a). When the difference is equal to or greater than a predetermined threshold (step S18a: Yes), in principle, the output information adjustment unit 7 outputs the estimated position Gl(n) + v(α) as the position of the own vehicle, and as an exception, outputs a message indicating that the position of the own vehicle cannot be measured (step S15a). Note that this estimated position Gl(n) + v(α) is stored in the control unit 2 (RAM) as the latest position information.

[0152] Here, the predetermined threshold is not particularly limited and can be set as appropriate. For example, it can be considered to be set to 10 to 100 m.

[0153] On the other hand, when a determination result that the GNSS signal transmitted from the GNSS satellite S_i is normal is output from the abnormality detection unit 5 in the first determination process (step S13a: No), when it is determined that GNSS positioning is possible based only on the GNSS signals determined to be normal in the second determination process (step S14a: Yes), and when the difference is less than a predetermined threshold (step S18a: No), the output information adjustment unit 7 outputs the position calculated based on the GNSS signal as the position of the own vehicle (step S16a). Here, when the difference is less than the predetermined threshold (step S18a: No), the position calculated based on the GNSS signal including the GNSS signal determined to be abnormal (position Gl(n + 1) in the above example) will be output as the position of the own vehicle. However, when the difference is less than the threshold, using the position calculated based on the GNSS signal including the GNSS signal determined to be abnormal externally (such as other vehicles or services) is considered to have little risk of causing problems such as malfunction. And at this timing, the change amount measured by the inertial device 8 in the latest position information stored in the control unit 2 (RAM), that is, the latest position among the positions calculated based only on the GNSS signals determined to be normal, is added to correct the position estimated by adding (Gl(n) + v(α) in the above example) with the position information based on the GNSS signal (step S17a).

[0154] FIG. 7(B) is a flowchart showing the procedure of the adjustment process of the time information as output information. First, the GNSS receiver 4 calculates the time based on the GNSS signals for each GNSS satellite S_i output at a predetermined cycle and outputs it to the output information adjustment unit 7 (step S11b).

[0155] Also, the GNSS receiver 4 updates the internal clock with, for example, a temperature-compensated crystal oscillator (TCXO) (mounted on the GNSS receiver 4) and outputs the time of the internal clock to the output information adjustment unit 7 (step S12b).

[0156] When a determination result that part or all of the GNSS signals transmitted from the GNSS satellite S_i is not normal is output in the first determination process performed by the abnormality detection unit 5 (step S13b: Yes), the output information adjustment unit 7 performs a second determination process to determine whether it is possible to calculate the time based only on the GNSS signals determined to be normal during the process of the first determination process (step S14b). When it is determined in the second determination process that it is not possible to calculate the time based on the GNSS signals (step S14b: No), the output information adjustment unit 7 compares the time calculated based on the GNSS signals including the GNSS signals determined to be not normal with the time estimated by adding the elapsed time measured by the internal clock to the most recent (latest) time among the times calculated based only on the GNSS signals determined to be normal before the process of the first determination process, and calculates the difference between the two (step S18b). When the difference is equal to or greater than a predetermined threshold (step S18b: Yes), the estimated time is output as the time of the own device (step S15b). Note that the estimated time is stored in the control unit 2 (RAM) as the most recent time information.

[0157] Regarding the processes in steps S18b and S5b, a specific example will be given for explanation. Similar to the example of Embodiment 1, GNSS signals are transmitted from a plurality of GNSS satellites S_i every α seconds. In the first determination process, it is determined that all the GNSS signals transmitted for the nth time at time t are normal. However, in the first determination process, it is determined that some or all of the GNSS signals transmitted for the (n + 1)th time at time (t + α) are not normal. In the second determination process, it is assumed that it is determined that the time cannot be calculated based only on the GNSS signals determined to be normal among the plurality of GNSS signals transmitted for the (n + 1)th time at time (t + α). In this case, the "latest (newest) time among the times calculated based only on the GNSS signals determined to be normal before the processing time of the first determination process" is the time Gt(n) calculated based on the GNSS signals transmitted for the nth time from the GNSS satellite S_i. Therefore, the time estimated by adding the elapsed time (α) measured by the internal clock is Gt(n)+α. On the other hand, the time calculated based on the (n + 1)th GNSS signal including the GNSS signals determined to be not normal is Gt(n + 1). Thus, the output information adjustment unit 7 compares the estimated time Gt(n)+α with the time Gt(n + 1) calculated based on the (n + 1)th GNSS signal, and calculates the difference between the two (step S18b). Then, when the difference is equal to or greater than a predetermined threshold (step S18b: Yes), the estimated time Gt(n)+α is output as the time of the own device (step S15b). This estimated time Gt(n)+α is stored in the control unit 2 (RAM) as the latest time information.

[0158] Here, the predetermined threshold is not particularly limited and can be set as appropriate. For example, when the power of the GNSS compass 1 is on (that is, when the time calibration in step S17b is being executed), it can be set to about 2 to 10 seconds. When the power of the GNSS compass 1 is off (that is, when the time calibration in step S17b is not being executed), it can be set to about 30 to 200 seconds.

[0159] On the other hand, when a determination result that the GNSS signal transmitted from the GNSS satellite S_i is normal is output from the abnormality detection unit 5 in the first determination process (step S13b: No), when it is determined that the time can be calculated based only on the GNSS signals determined to be normal in the second determination process (step S14b: Yes), and when the difference is less than a predetermined threshold (step S18b: No), the output information adjustment unit 7 outputs the time calculated based on the GNSS signal as the time of the own device (step S16b). Here, when the difference is less than the predetermined threshold (step S18b: No), the time calculated based on the GNSS signal including the GNSS signal determined to be abnormal (in the above example, the time Gt(n + 1)) will be output as the time of the own device. However, when the difference is less than the threshold, using the time calculated based on the GNSS signal including the GNSS signal determined to be abnormal externally (such as other devices or services) is considered to have little risk of causing problems such as malfunction. And at this timing, the time of the internal clock of the GNSS receiver 4 is calibrated by the time based on the GNSS signal (step S17b).

[0160] According to the method for detecting abnormality of the received signal and the GNSS compass 1 according to this embodiment, when the position cannot be calculated based only on the GNSS signals determined to be normal, the position calculated based on the GNSS signal including the GNSS signal determined to be abnormal is compared with the position estimated to be normal, that is, the position estimated by adding the change amount measured by the inertial device 8 to the closest position among the positions calculated based only on the GNSS signals determined to be normal, and it is determined whether the difference is equal to or greater than a predetermined threshold to adjust the output information. Therefore, it is possible to provide more appropriate and effective position information to the outside (such as other devices or services).

[0161] Also, according to the method for detecting abnormality of the received signal and the GNSS compass 1 according to this embodiment, when the time cannot be calculated based only on the GNSS signals determined to be normal, the time calculated based on the GNSS signals including the GNSS signals determined to be abnormal is compared with the time estimated to be normal, that is, the most recent time among the times calculated based only on the GNSS signals determined to be normal, and the time estimated by adding the elapsed time measured by the internal clock is compared. Then, it is determined whether the difference is equal to or greater than a predetermined threshold value, and the output information is adjusted. Therefore, it is possible to output more appropriate and effective time information to the outside (other devices, services, etc.).

[0162] (Embodiment 4) Next, the method for detecting abnormality of the received signal and the GNSS compass 1 according to Embodiment 4 of the present invention will be described. Regarding the same configuration as in Embodiment 1, the detailed description will be omitted by using the same reference numerals.

[0163] In Embodiment 1, as a detection condition for an abnormality in a received signal, it is necessary that the abnormality in the received signal is detected by all or many of the GNSS receivers 4A, 4B, and 4C. However, when the reception of GNSS signals by the GNSS receivers 4A, 4B, and 4C is unstable, the detection of an abnormality may be delayed or the abnormality may not be detected. For example, when the GNSS receivers 4A, 4B, and 4C are far from the radiation source of the false GNSS signal and receive weak signals (Fig. 9A), or when the false GNSS signal and the true GNSS signal are mixed and both signals are transmitted (Fig. 9B), etc., since the satellite information that can be received differs for each of the GNSS receivers 4A, 4B, and 4C, the detection of an abnormality is delayed, and as a result, there is a risk of using incorrect information (such as position and time) of the false GNSS signal ("Reception instability period 1" in Fig. 10). Also, when the GNSS receivers 4A, 4B, and 4C are in a shielding environment, or when there are differences in the processing timings between the GNSS receivers 4A, 4B, and 4C and differences occur in tracking satellite information, etc., during that period, since the GNSS receivers 4A, 4B, and 4C cannot receive GNSS signals, the detection of an abnormality is delayed, and as a result, there is a risk of using incorrect information (such as position and time) of the false GNSS signal. Furthermore, after the GNSS receivers 4A, 4B, and 4C have moved out of the influence of the false GNSS signal or after the false GNSS signal has stopped transmitting, before the GNSS receivers 4A, 4B, and 4C become stable in tracking the true GNSS signal, no abnormality is detected anymore, but at this time, incorrect information (such as position and time) of the false GNSS signal remains in the GNSS receivers 4A, 4B, and 4C, and there is a risk of using that incorrect information prematurely ("Reception instability period 2" in Fig. 10).

[0164] Therefore, the method for detecting an abnormality in a received signal and the GNSS compass 1 according to the present embodiment can detect a situation (reception instability period) where the reception of GNSS signals is unstable, such that the detection of an abnormality in the received signal is delayed or the abnormality is not detected. Specifically, a reception instability period detection unit 9 is provided to detect a situation (reception instability period) where the reception of GNSS signals is unstable based on the determination result output from the abnormality detection unit 5 and the determination result output from the positioning unit 6. In this regard, the present embodiment is different from Embodiment 1.

[0165] Figure 8 is a functional block diagram showing a schematic configuration of the GNSS compass according to the present embodiment. Here, the abnormality detection unit 5 further includes an abnormality determination unit 53, and the positioning unit 6 includes a positioning number determination unit 61 and a standard deviation determination unit 62. Further, the reception instability period detection unit 9 is a device for detecting a situation (reception instability period) in which the reception of GNSS signals is unstable based on the determination result output from the abnormality detection unit 5 and the determination result output from the positioning unit 6.

[0166] In the present embodiment, the travel path difference determination unit 52 outputs information on the GNSS satellite S_i classified as a travel path difference abnormality (in other words, an abnormality in the arrival direction of the GNSS signal) to the abnormality determination unit 53 as satellite information on the travel path difference abnormality.

[0167] On the other hand, when the travel path difference index is greater than a predetermined travel path difference threshold, the travel path difference determination unit 52 determines that the arrival directions of the GNSS signals of the plurality of GNSS satellites S_i are normal, and classifies the information on the GNSS satellites S_i as a normal travel path difference (in other words, a normal arrival direction of the GNSS signal) and outputs it to the reception instability period detection unit 9 as satellite information on the normal travel path difference.

[0168] The abnormality determination unit 53 receives the input of information on the GNSS satellite S_i classified as a travel path difference abnormality output from the travel path difference determination unit 52, and determines whether an abnormality has occurred in the GNSS signal.

[0169] Specifically, the abnormality determination unit 53 counts the number of GNSS satellites S_i classified as a travel path difference abnormality based on the information on the GNSS satellite S_i classified as a travel path difference abnormality output from the travel path difference determination unit 52, and determines whether the number is within a predetermined range.

[0170] The predetermined range is not limited to a specific value. For example, when GNSS signals of multiple GNSS satellites are transmitted from a single transmitting antenna / the same location, the number of GNSS satellites assumed is considered, and then an appropriate value is set as appropriate. The predetermined range may be set to a value of about 2 to 3, for example.

[0171] When the number of GNSS satellites S_i classified as traveling path anomalies is greater than the number within the predetermined range (for example, when it is 4 or more), the abnormality determination unit 53 determines that an abnormality has occurred in the GNSS signal. On the other hand, when the number of GNSS satellites S_i classified as traveling path anomalies is within the predetermined range (for example, when it is 2 to 3), it outputs information indicating that the number of GNSS satellites S_i classified as traveling path anomalies (in other words, arrival direction anomaly of the GNSS signal) is within the predetermined range to the reception instability detection unit 9. Note that when the number of GNSS satellites S_i classified as traveling path anomalies is less than the number within the predetermined range (for example, when it is 0 or 1), it may be determined that the GNSS signal is normal.

[0172] When it is determined that an abnormality has occurred in the GNSS signal, it enters an abnormal state. For example, the GNSS satellites S_i classified as traveling path anomalies are excluded from the group of satellites used in the calculation process of the positioning information (specifically, the position, orientation, and attitude of the own vehicle, etc.) by the positioning unit 6, and the GNSS signals transmitted from the excluded GNSS satellites S_i may not be used in the calculation process of the positioning information by the positioning unit 6.

[0173] Also, in the positioning unit 6 in this embodiment, the positioning number determination unit 61 receives the input of the positioning positions for each of the GNSS antennas (3A, 3B, 3C) of the position calculation antenna, and determines whether the positioning positions of the three GNSS antennas 3A, 3B, and 3C have been calculated.

[0174] When the positioning position of at least one of the three GNSS antennas 3A, 3B, and 3C has not been calculated, in other words, when the number of antennas for position calculation is 0 to 2, the positioning number determination unit 61 outputs information indicating that the number of antennas for position calculation is 0 to 2, that is, information indicating that there is an antenna for which the positioning position has not been calculated (non-positioning) to the reception instability detection unit 9.

[0175] On the other hand, when the positioning positions of each of the three GNSS antennas 3A, 3B, and 3C have been calculated, the positioning number determination unit 61 outputs the positioning positions of each of the three GNSS antennas 3A, 3B, and 3C to the standard deviation determination unit 62.

[0176] When the standard deviation determination unit 62 receives the input of the positioning positions of each of the three GNSS antennas 3A, 3B, and 3C output from the positioning number determination unit 61, it uses the positioning positions to calculate the positioning distances between each pair of the three GNSS antennas 3A, 3B, and 3C, that is, for each combination of two GNSS antennas (any two of 3A, 3B, and 3C).

[0177] Specifically, three positioning distances, namely the positioning distance between GNSS antenna 3A and GNSS antenna 3B, the positioning distance between GNSS antenna 3B and GNSS antenna 3C, and the positioning distance between GNSS antenna 3A and GNSS antenna 3C, are calculated. The positioning position is specifically latitude, longitude, and altitude, and the positioning distance is the length of the line segment connecting the three-dimensional coordinates.

[0178] Subsequently, the standard deviation determination unit 62 calculates the standard deviation of the positioning distances between each pair of the three GNSS antennas 3A, 3B, and 3C, that is, the standard deviation of the positioning distances for each combination of two GNSS antennas (any two of 3A, 3B, and 3C) (referred to as the "standard deviation of the positioning distances between antennas"), and determines whether the standard deviation of the positioning distances between antennas is greater than a predetermined threshold value (deviation threshold value).

[0179] The deviation threshold is not limited to a specific value. For example, it is set to an appropriate value after considering factors such as the dimension of the baseline, which is the distance between GNSS antennas 3A, 3B, and 3C (where the design values of the arrangements of each GNSS antenna 3A, 3B, and 3C are known), and the positioning error that is assumed to occur due to mechanical errors even in a normal state. The deviation threshold can be set to an appropriate value as appropriate, for example, to any value within the range of about 100 to 600 m.

[0180] When the standard deviation of the positioning distance between antennas is less than or equal to the deviation threshold, it is considered that there is no abnormality in the GNSS signal. For example, the positioning unit 6 may calculate the average value of the positioning positions of the three GNSS antennas 3A, 3B, and 3C and output the average value as the current position of the GNSS compass 1.

[0181] On the other hand, when the standard deviation of the positioning distance between antennas is greater than the deviation threshold, the standard deviation determination unit 62 outputs information indicating that the standard deviation of the positioning distance between antennas is greater than the deviation threshold to the reception instability regular detection unit 9.

[0182] (Processing content of the reception instability regular detection unit) The reception instability regular detection unit 9 performs detection of reception instability regularly based on the determination results output from the abnormality detection unit 5 (that is, the determination result of whether the arrival direction of the GNSS signal is normal and the determination result of whether an abnormality has occurred in the GNSS signal) and the determination results output from the positioning unit 6 (that is, the determination result of whether the positioning position has been calculated and the determination result of whether the standard deviation is greater than a predetermined threshold).

[0183] Specifically, the reception instability regular detection unit 9 determines that the GNSS signal is in an unstable reception state and there may be an abnormality in the GNSS signal when any of the following four judgment criteria is met.

[0184] First, the reception instability periodic detection unit 9 receives, from the travel path difference determination unit 52, information regarding the GNSS satellite S_i classified as having a normal travel path difference, calculates the number of such GNSS satellites S_i, and determines whether or not the number is equal to or greater than a predetermined threshold value (normal determination threshold value) for determining that the GNSS signal is normal based on the travel path difference index.

[0185] The normal determination threshold value is not limited to a specific value. For example, when GNSS signals of a plurality of GNSS satellites are transmitted from a single transmission antenna / the same location, the number of GNSS satellites assumed is considered, and then an appropriate value is set as appropriate. The normal determination threshold value may be set to any value in the range of about 3 to 5, for example.

[0186] When the number of GNSS satellites S_i classified as having a normal travel path difference is equal to or greater than the normal determination threshold value, the reception instability periodic detection unit 9 determines that the GNSS signal is normal. When the number is less than the normal determination threshold value, it determines that the GNSS signal is in an unstable reception state and there may be an abnormality in the GNSS signal.

[0187] Second, the reception instability periodic detection unit 9 receives, from the abnormality determination unit 53, information indicating that the number of GNSS satellites S_i classified as having an abnormal travel path difference (in other words, an abnormal arrival direction of the GNSS signal) is within a predetermined range, and determines that the GNSS signal is in an unstable reception state and there may be an abnormality in the GNSS signal.

[0188] Third, the reception instability periodic detection unit 9 receives, from the positioning number determination unit 61, information indicating that the number of positioning antennas is 0 to 2, that is, information indicating that there is an antenna for which the positioning position has not been calculated (non-positioning), and determines that the GNSS signal is in an unstable reception state and there may be an abnormality in the GNSS signal.

[0189] Fourthly, when the reception instability period detection unit 9 receives from the standard deviation determination unit 62 information that the standard deviation of the positioning distances between antennas is greater than the deviation threshold value, it determines that the GNSS signal is in a state of unstable reception and that there may be an abnormality in the GNSS signal.

[0190] In any one of the above four determination criteria, when it is determined that the GNSS signal is in a state of unstable reception and that there may be an abnormality in the GNSS signal, the reception instability period detection unit 9 causes the positioning unit 6 not to use the positioning position and GNSS time calculated from the GNSS signal in the calculation process of the positioning information.

[0191] As described above, according to the method for detecting an abnormality in a received signal and the GNSS compass 1 according to the present embodiment, since it is possible to detect a situation where the reception of the GNSS signal is unstable, it is possible to grasp the abnormality of the GNSS signal at the stage of possibility. Even when the detection of the abnormality is delayed, it is possible to prevent the output of incorrect information (such as position and time) based on a false GNSS signal, and to improve the reliability of the abnormality detection process of the received signal.

[0192] (Embodiment 5) Next, a method for detecting an abnormality in a received signal and a ship system using the GNSS compass 1 according to Embodiment 5 of the present invention will be described. Regarding the same configurations as in Embodiments 1 to 4, detailed descriptions will be omitted by using the same reference numerals.

[0193] As described above, in recent years, there has been damage caused by transmitting an abnormal signal from a transmission source such as a satellite or a ground station and causing a GNSS receiver that has received this abnormal signal to measure an incorrect position. In order to prevent such damage, various technologies have been developed (see, for example, Patent Document 1, Japanese Patent Application Laid-Open No. 2023-155130, and Japanese Patent Application Laid-Open No. 2024-515652).

[0194] Vessels navigating on the sea are also vulnerable to such spoofed GNSS signals. For example, if a GNSS receiver installed on a certain vessel X receives a spoofed GNSS signal and calculates an incorrect positioning location from that spoofed GNSS signal, the Automatic Identification System (AIS) installed on vessel X will adopt the incorrect positioning location calculated from that spoofed GNSS signal as the position of its own vessel and transmit it to other vessels, etc. as the position information of its own vessel. In that case, vessels navigating around vessel X will display the incorrect position of vessel X received via AIS, as well as the speed, course, etc. based on the incorrect position of vessel X on an Electronic Chart Display and Information System (ECDIS), or the ECDIS will output a false collision warning based on the incorrect position of vessel X, thus hindering safe navigation. Therefore, as the popularization of automatic operation of vessels through labor-saving and remote control from land progresses, it is necessary to construct a system to reduce the damage caused by spoofed GNSS signals.

[0195] Therefore, in this embodiment, a ship system according to Embodiments 1 to 4, which is a method for detecting abnormalities in received signals and uses a GNSS compass 1, is provided. When a ship receiving a spoofed GNSS signal exists in the vicinity, this ship system can prevent the damage caused by that spoofed GNSS signal from affecting the own ship.

[0196] FIG. 11 is a block diagram showing the schematic configuration of a ship system 10X according to an embodiment of the present invention. The ship system 10X according to this embodiment mainly includes a first ship 20AX, a second ship 20BX, and an onshore server 30. Here, the first ship 20AX and the second ship 20BX are communicably connected via an AIS, which will be described later. Also, the first ship 20AX, the second ship 20BX, and the onshore server 30 are communicably connected via a communication satellite 40 such as an Inmarsat (registered trademark) satellite.

[0197] The first ship 20AX mainly includes a GNSS compass (position measuring means, abnormality detection unit) 1A, an AIS 202A, and a control unit 203A. The second ship 20BX mainly includes an AIS 202B, a control unit 203B, and an ECDIS (position information utilization calculation means) 204B. The first ship 20AX may additionally include an ECDIS, and the second ship 20BX may additionally include a GNSS compass. Here, the AIS 202A of the first ship 20AX and the AIS 202B of the second ship 20BX are communicably connected by international VHF (VHF radio waves) as described later. Note that components with the same number generally have the same function and configuration, and the symbols "A" and "B" following the number are attached to distinguish whether the component belongs to the first ship 20AX or the second ship 20BX.

[0198] As the GNSS compass 1A, any of the GNSS compasses described in Embodiments 1 to 4 is used, so the details are omitted.

[0199] AIS (Automatic Identification System) 202A and 202B are devices for automatically identifying the movements of ships using international VHF (VHF radio waves), and their basic configuration is the same as that of existing AISs that are obligatorily installed on ships meeting certain criteria according to the SOLAS Convention (abbreviation for International Convention for the Safety of Life at Sea; international convention for the safety of life at sea).

[0200] The AIS 202B of the second ship 20BX is communicably connected to the AIS 202A of the first ship 20AX via international VHF (VHF radio waves), and receives information regarding the first ship 20AX from the AIS 202A (specifically, information such as the ship's identification number (MMSI number), ship name, position, course, speed, destination, etc., hereinafter also referred to as "AIS information"). The position information included in the AIS information of the first ship 20AX is the position of the first ship 20AX measured by the positioning unit 6A of the GNSS compass 1A provided on the first ship 20AX. That is, the second ship 20BX can acquire the position of the first ship 20AX measured by the positioning unit 6A of the GNSS compass 1A via the AIS 202A and the AIS 202B. Therefore, if the first ship 20AX is receiving a false GNSS signal, the position included in the AIS information of the first ship 20AX, as well as the course and speed calculated based on the position, are predicted to be incorrect.

[0201] The position of the first ship 20AX obtained by the AIS 202B of the second ship 20BX from the AIS 202A of the first ship 20AX is displayed on the display unit 2041B of the ECDIS 204B described later, and is used for arithmetic processing for alarm output in the alarm output unit 2042B.

[0202] The control unit 203A of the first ship 20AX is a device mainly having functions of controlling the GNSS compass 1A and the AIS 202A, and the control unit 203B of the second ship 20BX is a device mainly having functions of controlling the AIS 202B and the ECDIS 204B.

[0203] The ECDIS (Electronic Chart Display and Information System) 204B provided on the second ship 20BX is a device that integrates geographical information from nautical electronic charts, position information such as the position, azimuth, and speed of the ship, and information from various devices mounted on the ship and displays it on a screen, and has a function of outputting an alarm when the own ship approaches another ship or approaches a shoal or a quay wall, etc. Its basic configuration is the same as that of an existing ECDIS that is obligatorily installed on ships that meet certain criteria according to the SOLAS Convention.

[0204] ECDIS204B is a device that performs calculations using the position of the first ship 20AX, and mainly includes a display unit 2041B and an alarm output unit 2042B.

[0205] The display unit 2041B is a device for displaying various information. Specifically, as shown in FIG. 13, it displays the position of the second ship 20BX (own ship) and the position of the first ship 20AX (other ship). Here, the position of the second ship 20BX (own ship) is the position obtained from the AIS202B. For example, when the second ship 20BX is equipped with a GNSS compass, it may be the position measured by its positioning unit. Also, the position of the first ship 20AX (other ship) is the position of the first ship 20AX obtained by the AIS202B from the AIS202A, and is the position measured by the positioning unit 6A of the GNSS compass 1A of the first ship 20AX.

[0206] That is, the display unit 2041B of the ECDIS204B displays the position of the first ship 20AX measured by the positioning unit 6A of the GNSS compass 1A on the screen. Therefore, when the positioning unit 6A of the GNSS compass 1A calculates the position of the first ship 20AX based on a false GNSS signal, an incorrect position of the first ship 20AX ("AIS position (error) of the first ship 20AX" in FIG. 13) will be displayed on the display unit 2041B of the ECDIS204B. For this reason, as will be described later, when the second ship 20BX obtains, via the land server 30, that an abnormality in the GNSS signal has been detected by the abnormality detection unit 5A of the first ship 20AX, the second ship 20BX invalidates (proposes to the user) the position of the first ship 20AX obtained by the AIS202B from the AIS202A and measured by the positioning unit 6A of the GNSS compass 1A in the display unit 2041B, that is, does not display it (proposes to the user). In this case, the second ship 20BX may also not display (proposes to the user) not only the position of the first ship 20AX but also all other AIS information (speed, course, etc.) regarding the first ship 20AX obtained from the AIS202A in the display unit 2041B.

[0207] The alarm output unit 2042B is a device for outputting an alarm to notify of the risk of collision with a ship or the like. Specifically, based on the position of the second ship 20BX (own ship) and the position of the first ship 20AX (other ship), it determines whether there is a risk of collision between the two ships and outputs an alarm. Here, the position of the second ship 20BX (own ship) is the position obtained from the AIS 202B. For example, if the second ship 20BX is equipped with a GNSS compass, it may be the position measured by its positioning unit. Also, the position of the first ship 20AX (other ship) is the position of the first ship 20AX obtained by the AIS 202B from the AIS 202A, and is the position measured by the positioning unit 6A of the GNSS compass 1A of the first ship 20AX.

[0208] That is, the warning output unit 2042B of the ECDIS 204B outputs a warning using the position of the first ship 20AX measured by the positioning unit 6A of the GNSS compass 1A. Therefore, if the positioning unit 6A of the GNSS compass 1A calculates the position of the first ship 20AX based on a false GNSS signal, the determination of whether there is a risk of collision between the two ships will be based on the incorrect position of the first ship 20AX, and there is a risk that a false warning will be output because a collision will be determined even though the two ships are not actually approaching each other (and therefore there is no need to take action) (see FIG. 13). Therefore, as will be described later, when the second vessel 20BX receives information via the land server 30 that the anomaly detection unit 5A of the first vessel 20AX has detected an anomaly in the GNSS signal, the alarm output unit 2042B determines whether to output an alarm by invalidating (or suggesting to the user that) the position of the first vessel 20AX acquired by the AIS 202B from the AIS 202A and measured by the positioning unit 6A of the GNSS compass 1A, i.e., by not using (or suggesting to the user that) the position of the first vessel 20AX in the collision prediction calculation. In this case, the second vessel 20BX may be configured to not use (or suggest to the user that) not only the position of the first vessel 20AX but also all other AIS information (speed, course, etc.) related to the first vessel 20AX acquired from the AIS 202A in the collision prediction calculation in the alarm output unit 2042B.

[0209] The alarm output by the alarm output unit 2042B may be displayed as a message or a symbol on the display unit 2041B, or may be output as a sound such as a buzzer.

[0210] The land server 30 is a device communicatively connected to the first ship 20AX and the second ship 20BX via a communication satellite 40, and is provided on a land-based management computer or the like. The land server 30 receives various information uploaded from devices mounted on the first ship 20AX and the second ship 20BX, and transmits necessary information to the devices mounted on the first ship 20AX and the second ship 20BX and performs management based on the received information.

[0211] When information indicating that an abnormality has been detected in the GNSS signal is uploaded from the first ship 20AX, the onshore server 30 used in this embodiment particularly uplinks that information to the communication satellite 40 together with the MMSI number of the first ship 20AX, so that the second ship 20BX can downlink the MMSI number of the first ship 20AX and the information indicating that an abnormality has been detected in the GNSS signal in the first ship 20AX from the communication satellite 40. That is, the second ship 20BX can acquire, via the onshore server 30, information indicating that an abnormality has been detected in the GNSS signal by the abnormality detection unit 5A of the first ship 20AX. Note that the onshore server 30 may directly perform the uplink of information to the communication satellite 40 and the downlink from the communication satellite 40, or may perform them via a maritime station (a radio station installed on land for communicating with ships on the ocean) that is communicably connected to the onshore server 30 via a public line.

[0212] Next, the operation and action of the ship system 10X of this embodiment will be described with reference to FIG. 12.

[0213] First, when the abnormality detection unit 5A of the GNSS compass 1A provided in the first ship 20AX detects an abnormality in the GNSS signal (step S101X), the first ship 20AX uploads, via the communication satellite 40, information indicating that "an abnormality in the GNSS signal has been detected" and its own MMSI number to the onshore server 30 (step S102X). The process of step S102X is, in more detail, performed by the first ship 20AX uplinking information indicating that "an abnormality in the GNSS signal has been detected" and the MMSI number to the communication satellite 40, and the onshore server 30 downlinking them from the communication satellite 40. Also, as a method of transmitting information indicating that "an abnormality in the GNSS signal has been detected", for example, it may be decided that when an abnormality in the GNSS signal is detected, the "abnormal signal detection flag" is set to 1, and when no abnormality in the GNSS signal is detected, the "abnormal signal detection flag" is set to 0 (zero), and when an abnormality in the GNSS signal is detected, it may be transmitted by setting the "abnormal signal detection flag" to 1.

[0214] Next, the onshore server 30 uplinks information that "an abnormality in the GNSS signal has been detected" (for example, "abnormal signal detection flag" 1) and the MMSI number of the first ship 20AX to the communication satellite 40 on the first ship 20AX (step S103X), and the second ship 20BX downlinks them from the communication satellite 40 (step S104X). In other words, the second ship 20BX downloads information that "an abnormality in the GNSS signal has been detected" (for example, "abnormal signal detection flag" 1) and the MMSI number of the first ship 20AX from the onshore server 30 via the communication satellite 40 (steps S103X, S104X). In this way, the second ship 20BX obtains the fact that an abnormality in the GNSS signal has been detected on the first ship 20AX.

[0215] On the other hand, the first ship 20AX measures its own position with the positioning unit 6A of the GNSS compass 1A (step S105X). The position of the first ship 20AX measured here is based on the GNSS signal in which an abnormality has been detected, so it is predicted to indicate an incorrect position.

[0216] Next, the AIS 202A of the first ship 20AX transmits the position of its own ship measured in this way to the AIS 202B of the second ship 20BX by international VHF (VHF radio wave) (step S106X). In other words, the second ship 20BX obtains the position of the first ship 20AX via the AIS 202A and the AIS 202B (step S106X).

[0217] Next, based on the information about the first ship 20AX (information indicating that an abnormality in the GNSS signal was detected) downloaded from the onshore server 30, the second ship 20BX determines that the position of the first ship 20AX acquired by the AIS 202B is incorrect, and invalidates (proposes to the user to do so) the position of the first ship 20AX in the ECDIS 204B (step S107X). Specifically, "invalidating" means, for example, not displaying the incorrect position of the first ship 20AX on the display unit 2041B of the ECDIS 204B, or not using the incorrect position of the first ship 20AX when the alarm output unit 2042B determines the risk of collision between the first ship 20AX and the second ship 20BX. Thereby, damage caused by false GNSS signals can be reduced. Note that the second ship 20BX may invalidate (not display or not use) all other AIS information (speed, course, etc.) regarding the first ship 20AX obtained from the AIS 202A in addition to the position of the first ship 20AX in the ECDIS 204B.

[0218] If the second ship 20BX downloads from the onshore server 30 via the communication satellite 40 information that the first ship 20AX "does not detect an abnormality in the GNSS signal" (for example, "abnormal signal detection flag" 0), the second ship 20BX may resume using the AIS information regarding the first ship 20AX in the ECDIS 204B.

[0219] Also, when the second ship 20BX downloads from the onshore server 30 via the communication satellite 40 information that the first ship 20AX "detected an abnormality in the GNSS signal" (for example, "abnormal signal detection flag" 1), in order to notify the user that the own ship may have received AIS information including incorrect information regarding the first ship 20AX, the second ship 20BX may output a screen popup, buzzer, alert, etc.

[0220] As described above, according to the ship system 10X according to this embodiment, the second ship 20BX can be informed when an abnormality in the GNSS signal is detected in the first ship 20AX. Therefore, it is possible to prevent damage caused by a false GNSS signal from affecting the own ship and improve the safety of navigation.

[0221] Moreover, the second ship 20BX prevents the display unit 2041B and the alarm output unit 2042B of the ECDIS 204B that perform arithmetic processing using the position of the first ship 20AX from displaying or using (and proposing to the user) the incorrect position of the first ship 20AX measured based on a false GNSS signal. Therefore, it is possible to more reliably prevent damage caused by a false GNSS signal from affecting the own ship and improve the safety of navigation.

[0222] (Embodiment 6) Next, a method for detecting an abnormality in a received signal and a ship system using the GNSS compass 1 according to Embodiment 6 of the present invention will be described. For configurations similar to those in Embodiments 1 to 5, the same reference numerals are used and detailed descriptions are omitted.

[0223] In Embodiment 5, the purpose is to prevent damage caused by a false GNSS signal from affecting the own ship when surrounding ships receive a false GNSS signal. However, it is also possible to assume a case where the own ship receives a false GNSS signal.

[0224] Therefore, in the present embodiment, a ship system is provided that uses the method for detecting an abnormality in a received signal and the GNSS compass 1 according to Embodiments 1 to 4, and can prevent damage caused by a false GNSS signal from affecting surrounding ships when the own ship receives a false GNSS signal.

[0225] FIG. 14 is a block diagram showing a schematic configuration of a ship system 10Y according to an embodiment of the present invention. The ship system 10Y according to this embodiment mainly includes a ship (own ship) 20Y and another ship 20Y'. Here, the ship (own ship) 20Y and the other ship 20Y' are communicably connected via an AIS described later.

[0226] The ship (own ship) 20Y mainly includes a GNSS compass (position measurement means, abnormality detection unit) 1, an AIS 202, a control unit 203, and an ECDIS (position information utilization calculation means) 204, and the other ship 20Y' mainly includes an AIS 202'. The other ship 20Y' may additionally include a GNSS compass, a control unit, and an ECDIS. Here, the AIS 202 of the ship (own ship) 20Y and the AIS 202' of the other ship 20Y' are communicably connected by international VHF (VHF radio waves) as described later. Note that the AIS 202 and the AIS 202' are assumed to have the same function and configuration.

[0227] As the GNSS compass 1, any of the GNSS compasses described in Embodiments 1 to 4 is used, and thus details are omitted.

[0228] The AIS 202 of the ship (own ship) 20Y is communicably connected to the AIS 202' of another ship 20Y' via international VHF (VHF radio waves), and transmits own ship information (AIS information) to the AIS 202'. The position information included in the AIS information of the ship (own ship) 20Y is the position of the own ship measured by the positioning unit 6 of the GNSS compass 1. That is, the ship (own ship) 20Y transmits, via the AIS 202 and the AIS 202', own ship information (AIS information) including the position of the own ship measured by the positioning unit 6 of the GNSS compass 1 to the other ship 20Y'. Therefore, when the ship (own ship) 20Y receives a false GNSS signal, the position of the own ship included in the own ship information (AIS information) is predicted to be incorrect. Therefore, when the abnormality detection unit 5 detects an abnormality in the GNSS signal, the ship (own ship) 20Y invalidates (proposes to the user) the transmission of own ship information (AIS information) including the position of the own ship measured by the positioning unit 6 of the GNSS compass 1 to the other ship 20Y'. Specifically, for example, the ship (own ship) 20Y does not transmit own ship information (AIS information) to the other ship 20Y' via the AIS 202, or transmits after replacing the position of the own ship with "non-positioning".

[0229] The control unit 203 is a device mainly having a function of controlling the GNSS compass 1, the AIS 202, and the ECDIS 204.

[0230] The ECDIS 204 is a device that performs calculations using the position of the ship (own ship) 20Y, and mainly includes a display unit 2041 and an alarm output unit 2042.

[0231] The display unit 2041 is a device for displaying various information. Specifically, as shown in FIG. 16, it displays the position of the ship (own ship) 20Y and the position of the other ship 20Y'. Here, the position of the ship (own ship) 20Y is the position measured by the positioning unit 6 of the GNSS compass 1. Also, the position of the other ship 20Y' is the position obtained from the AIS 202'. For example, if the other ship 20Y' is equipped with a GNSS compass, it may be the position measured by its positioning unit.

[0232] That is, the display unit 2041 of the ECDIS 204 displays the position of the ship (own ship) 20Y measured by the positioning unit 6 of the GNSS compass 1 on the screen. Therefore, when the positioning unit 6 of the GNSS compass 1 calculates the position of the ship (own ship) 20Y based on a false GNSS signal, an incorrect position of the ship (own ship) 20Y ("AIS position (error) of the ship (own ship) 20Y" in FIG. 16) will be displayed on the display unit 2041 of the ECDIS 204. Therefore, when the abnormality detection unit 5 detects an abnormality in the GNSS signal, the ship (own ship) 20Y invalidates (proposes to the user) the position of the own ship measured by the positioning unit 6 of the GNSS compass 1 on the display unit 2041, that is, does not display it (proposes to the user) on the display unit 2041. In this case, the ship (own ship) 20Y may also not display (proposes to the user) all the own ship information (AIS information) including the position of the own ship on the display unit 2041.

[0233] The alarm output unit 2042 is a device for outputting an alarm to notify of the risk of collision with a ship or the like. Specifically, based on the position of the ship (own ship) 20Y and the position of another ship 20Y', it determines whether there is a risk of collision between the two ships and outputs an alarm. Here, the position of the ship (own ship) 20Y is the position measured by the positioning unit 6 of the GNSS compass 1. Also, the position of the other ship 20Y' is the position of the other ship 20Y' obtained by the AIS 202 from the AIS 202'. For example, when the other ship 20Y' is equipped with a GNSS compass, it may be the position measured by its positioning unit.

[0234] That is, the alarm output unit 2042 of the ECDIS 204 outputs an alarm using the position of the ship (own ship) 20Y measured by the positioning unit 6 of the GNSS compass 1. Therefore, when the positioning unit 6 of the GNSS compass 1 calculates the position of the ship (own ship) 20Y based on a false GNSS signal, it is determined whether there is a risk of collision between the two ships based on the incorrect position of the ship (own ship) 20Y. As a result, there is a possibility that a false alarm will be output because it is determined that there is a collision even though the two ships are not actually approaching (therefore, there is no need to avoid the course) (see Fig. 16). Therefore, when the abnormality detection unit 5 of the GNSS compass 1 detects an abnormality in the GNSS signal, the ship (own ship) 20Y invalidates (proposes to the user) the position of the own ship measured by the positioning unit 6 of the GNSS compass 1 in the determination process of the alarm output by the alarm output unit 2042, that is, does not use it for the calculation of collision prediction (proposes to the user). In this case, the ship (own ship) 20Y may also not use (proposes to the user) all the own ship information (AIS information) including the position of the own ship for the calculation of collision prediction in the alarm output unit 2042.

[0235] Next, the operation and action of the ship system 10Y of this embodiment will be described with reference to Fig. 15.

[0236] First, the abnormality detection unit 5 of the GNSS compass 1 provided on the ship (own ship) 20Y detects an abnormality in the GNSS signal (step S101Y).

[0237] On the other hand, the ship (own ship) 20Y measures the position of the own ship with the positioning unit 6 of the GNSS compass 1 (step S102Y). The position of the ship (own ship) 20Y measured here is a position measured based on the GNSS signal in which an abnormality has been detected, and is predicted to indicate an incorrect position.

[0238] Therefore, the AIS 202 of the ship (own ship) 20Y invalidates (proposes to the user) the transmission of the own ship information (AIS information) including the incorrect position of the own ship measured by the positioning unit 6 of the GNSS compass 1 to other ships 20Y'. "Invalidating the transmission" specifically means, for example, setting the position of the own ship included in the own ship information (AIS information) as "not positioned" and then transmitting the own ship information (AIS information) to other ships 20Y' (AIS 202') by international VHF (VHF radio waves) (step S103Y), or not transmitting the own ship information (AIS information) to other ships 20Y'. Thereby, the ship (own ship) 20Y can prevent the damage caused by the false GNSS signal from affecting other ships.

[0239] Furthermore, the ship (own ship) 20Y invalidates (proposes to the user) the incorrect position of the own ship measured by the positioning unit 6 of the GNSS compass 1 in the ECDIS 204 (step S104Y). "Invalidating" specifically means, for example, not displaying the incorrect position of the own ship on the display unit 2041 of the ECDIS 204, or not using the incorrect position of the own ship when the alarm output unit 2042 determines the risk of collision between the ship (own ship) 20Y and other ships 20Y'. Thereby, it is possible to more reliably prevent the damage caused by the false GNSS signal from affecting other ships. Note that the ship (own ship) 20Y may also invalidate (not display or not use) all other own ship information (AIS information) (speed, course, etc.) obtained from the AIS 202 in addition to the position of the own ship in the ECDIS 204.

[0240] When the abnormality detection unit 5 no longer detects an abnormality in the GNSS signal, the ship (own ship) 20Y may resume the use of the own ship information (AIS information) including the position of the own ship in the ECDIS 204.

[0241] As described above, according to the ship system 10Y according to this embodiment, when the ship (own ship) 20Y detects an abnormality in the GNSS signal on its own, it invalidates (proposes to the user) the transmission of its own ship information (AIS information) including the position of the own ship measured based on the false GNSS signal to other ships 20Y'. Therefore, it is possible to prevent the damage caused by the false GNSS signal from spreading to surrounding ships and improve the safety of navigation.

[0242] Moreover, when the ship (own ship) 20Y detects an abnormality in the GNSS signal on its own, it does not display or use (proposes to the user) the incorrect position of the own ship measured based on the false GNSS signal on the display unit 2041 or the alarm output unit 2042 of the ECDIS 204 that performs arithmetic processing using the position of the own ship. Therefore, it is possible to more reliably prevent the damage caused by the false GNSS signal from spreading to surrounding ships and improve the safety of navigation.

[0243] (Embodiment 7) Next, a method for detecting an abnormality in a received signal and a ship system using the GNSS compass 1 according to Embodiment 7 of the present invention will be described. For the same configurations as in Embodiments 1 to 6, the same reference numerals will be used and detailed descriptions will be omitted.

[0244] In Embodiment 5, the purpose is to prevent the own ship from being affected by the false GNSS signal when surrounding ships receive the false GNSS signal. In Embodiment 6, the purpose is to prevent the damage caused by the false GNSS signal from spreading to surrounding ships when the own ship receives the false GNSS signal. However, it can be assumed that when the own ship receives the false GNSS signal, surrounding ships may also receive the same false GNSS signal.

[0245] Therefore, in the present embodiment, a ship system using the method for detecting an abnormality in a received signal according to Embodiments 1 to 4 and the GNSS compass 1 is provided, which can detect whether surrounding ships also receive the false GNSS signal when the own ship receives the false GNSS signal.

[0246] FIG. 17 is a block diagram showing a schematic configuration of a ship system 10Z according to an embodiment of the present invention. The ship system 10Z according to this embodiment mainly includes a first ship 20AZ and a second ship 20BZ. Here, the first ship 20AZ and the second ship 20BZ are communicably connected via an AIS described later.

[0247] The first ship 20AZ mainly includes a GNSS compass (position measuring means, abnormality detecting unit) 1A, an AIS 202A, a control unit 203A, an ECDIS (position information utilization calculation means) 204A, and a determination unit 205A. The second ship 20BZ mainly includes a GNSS compass (position measuring means) 1B, an AIS 202B, and a control unit 203B. The second ship 20BZ may additionally include a determination unit and an ECDIS. Here, the AIS 202A of the first ship 20AZ and the AIS 202B of the second ship 20BZ are communicably connected by international VHF (VHF radio wave) as described later. In addition, components with the same number generally have the same function and configuration, and the symbols "A" and "B" following the number are attached to distinguish whether the component belongs to the first ship 20AZ or the second ship 20BZ.

[0248] As the GNSS compasses 1A and 1B, any of the GNSS compasses described in Embodiments 1 to 4 are used, so the details are omitted.

[0249] The AIS 202A of the first ship 20AZ and the AIS 202B of the second ship 20BZ are communicably connected by international VHF (VHF radio waves) and transmit and receive information (AIS information) regarding the first ship 20AZ or the second ship 20BZ. The position information included in the AIS information of the first ship 20AZ is the position of the first ship 20AZ measured by the positioning unit 6A of the GNSS compass 1A provided on the first ship 20AZ, and the position information included in the AIS information of the second ship 20BZ is the position of the second ship 20BZ measured by the positioning unit 6B of the GNSS compass 1B provided on the second ship 20BZ. That is, the first ship 20AZ transmits its own position measured by the positioning unit 6A of the GNSS compass 1A to the second ship 20BZ via the AIS 202A and the AIS 202B, and the second ship 20BZ transmits its own position measured by the positioning unit 6B of the GNSS compass 1B to the first ship 20AZ via the AIS 202A and the AIS 202B. The position of the second ship 20BZ received by the first ship 20AZ is sent to the ECDIS 204A, displayed on the display unit 2041A, and used for arithmetic processing for alarm output in the alarm output unit 2042A.

[0250] When the abnormality detection unit 5A of the first ship 20AZ detects an abnormality in the GNSS signal, the first ship 20AZ stores its own position measured by the positioning unit 6A of the GNSS compass 1A in, for example, a memory (not shown), and sends it to the determination unit 205A described later in order to perform a determination process as to whether the position of the second ship 20BZ is abnormal. When the abnormality detection unit 5A detects an abnormality in the GNSS signal, since the position of the first ship 20AZ is predicted to be incorrect, it may not be used except for use in this determination process. That is, in the AIS 202A, the AIS information including the position of the own ship may not be transmitted to the second ship 20BZ, or the position of the own ship included in the AIS information may be set to "non-positioning" and then the AIS information may be transmitted to the second ship 20BZ. In the ECDIS 204A, the position of the own ship may not be displayed on the display unit 2041A and may not be used for arithmetic processing for alarm output in the alarm output unit 2042A.

[0251] Further, when the abnormality detection unit 5A of the first ship 20AZ detects an abnormality in the GNSS signal, the position of the second ship 20BZ at the time of abnormality detection included in the AIS information of the second ship 20BZ is stored, for example, in a memory (not shown), and is sent to a determination unit 205A described later in order to perform a determination process as to whether the position of the second ship 20BZ is abnormal.

[0252] The control unit 203A of the first ship 20AZ is a device mainly having a function of controlling the GNSS compass 1A, the AIS 202A, the ECDIS 204A, and the determination unit 205A, and the control unit 203B of the second ship 20BZ is a device mainly having a function of controlling the GNSS compass 1B and the AIS 202B.

[0253] The ECDIS 204A is a device that performs calculations using the position of the second ship 20BZ, and mainly includes a display unit 2041A and an alarm output unit 2042A.

[0254] The display unit 2041A is a device for displaying various information. Specifically, as shown in FIG. 19, it displays the position of the first ship 20AZ (own ship) and the position of the second ship 20BZ (other ship). Here, the position of the first ship 20AZ (own ship) is the position measured by the positioning unit 6A of the GNSS compass 1A, and the position of the second ship 20BZ (other ship) is the position of the second ship 20BZ obtained by the AIS 202A from the AIS 202B, which is the position measured by the positioning unit 6B of the GNSS compass 1B of the second ship 20BZ.

[0255] That is, the display unit 2041A of the ECDIS 204A displays on the screen the position of the first ship 20AZ measured by the positioning unit 6A of the GNSS compass 1A and the position of the second ship 20BZ measured by the positioning unit 6B of the GNSS compass 1B. Therefore, when the positioning unit 6A of the GNSS compass 1A calculates the position of the first ship 20AZ based on a false GNSS signal, an incorrect position of the first ship 20AZ (the "AIS position (error) of the first ship 20AZ" in FIG. 19) is displayed on the display unit 2041A of the ECDIS 204A. When the position of the second ship 20BZ obtained by the AIS 202A from the AIS 202B is abnormal (that is, when the positioning unit 6B of the GNSS compass 1B calculates the position of the second ship 20BZ based on its false GNSS signal), an incorrect position of the second ship 20BZ (the "AIS position (error) of the second ship 20BZ" in FIG. 19) is displayed on the display unit 2041A of the ECDIS 204A. Therefore, as will be described later, when the first ship 20AZ determines that the position of the second ship 20BZ is abnormal when detecting an abnormality in the GNSS signal on its own ship, the first ship 20AZ invalidates (proposes to the user) the position of the second ship 20BZ obtained by the AIS 202A from the AIS 202B, that is, does not display it (proposes to the user) on the display unit 2041A. At that time, the first ship 20AZ may also not display its own incorrect position on the display unit 2041A. Further, the first ship 20AZ may not display (proposes to the user) on the display unit 2041A not only the position of the second ship 20BZ but also all other AIS information (speed, course, etc.) regarding the second ship 20BZ obtained from the AIS 202B.

[0256] The alarm output unit 2042A is a device for outputting an alarm to notify of the risk of collision with a ship or the like. Specifically, based on the position of the first ship 20AZ (own ship) and the position of the second ship 20BZ (other ship), it determines whether there is a risk of collision between the two ships and outputs an alarm. Here, the position of the first ship 20AZ (own ship) is the position measured by the positioning unit 6A of the GNSS compass 1A, and the position of the second ship 20BZ (other ship) is the position obtained by the AIS 202A from the AIS 202B and is the position measured by the positioning unit 6B of the GNSS compass 1B.

[0257] That is, the alarm output unit 2042A of the ECDIS 204A outputs an alarm using the position of the first ship 20AZ measured by the positioning unit 6A of the GNSS compass 1A and the position of the second ship 20BZ measured by the positioning unit 6B of the GNSS compass 1B. Therefore, when the positioning unit 6A of the GNSS compass 1A calculates the position of the first ship 20AZ based on a false GNSS signal, or when the position of the second ship 20BZ obtained by the AIS 202A from the AIS 202B is abnormal (that is, when the positioning unit 6B of the GNSS compass 1B calculates the position of the second ship 20BZ based on that false GNSS signal), it is determined whether there is a risk of collision between the two ships based on the incorrect positions of the first ship 20AZ and the second ship 20BZ. As a result, there is a possibility that a false alarm will be output by determining a collision even though the two ships are not actually approaching (therefore, there is no need to avoid the course) (see Fig. 19). Therefore, as will be described later, when the first ship 20AZ determines that the position of the second ship 20BZ is abnormal when detecting an abnormality in the GNSS signal on its own ship, in the determination process of the alarm output by the alarm output unit 2042A, the AIS 202A invalidates (proposes to the user) the position of the second ship 20BZ obtained from the AIS 202B, that is, does not use it (proposes to the user) for the calculation of collision prediction. At that time, the first ship 20AZ may also not use its own incorrect position in the determination process of the alarm output by the alarm output unit 2042A. In addition, the first ship 20AZ may, in the alarm output unit 2042A, not use (propose to the user) not only the position of the second ship 20BZ but also all other AIS information (speed, course, etc.) regarding the second ship 20BZ obtained from the AIS 202B for the calculation of collision prediction.

[0258] The determination unit 205A provided on the first ship 20AZ is a device for determining whether the position of the second ship 20BZ is abnormal (incorrect) when the own ship is receiving a false GNSS signal, and detecting whether the second ship 20BZ is also receiving a false GNSS signal.

[0259] In the case where both the first ship 20AZ and the second ship 20BZ are receiving a false GNSS signal, it is assumed that the intensity of the false GNSS signal is strong enough to reach both ships. In such a case, it is considered that on the display unit 2041A of the ECDIS 204A, the first ship 20AZ and the second ship 20BZ are displayed in a state of approaching each other (with a small positional difference) (refer to "AIS position (false) of the first ship 20AZ" and "AIS position (false) of the second ship 20BZ" in FIG. 19). Therefore, the determination unit 205A performs the above determination based on this positional difference.

[0260] Specifically, the determination process in the determination unit 205A is performed as follows. First, when the anomaly detection unit 5A detects an anomaly in the GNSS signal, the determination unit 205A obtains the position of the first ship 20AZ measured at the time of the anomaly detection from the positioning unit 6A, and obtains the position of the second ship 20BZ (included in the AIS information) at the time of the anomaly detection via the AIS 202B and the AIS 202A. Here, since an anomaly in the GNSS signal has been detected in the first ship 20AZ, the position of the first ship 20AZ is predicted to be incorrect (refer to "AIS position (false) of the first ship 20AZ" in FIG. 19).

[0261] Next, the determination unit 205A calculates the difference (positional difference) between the obtained position of the first ship 20AZ and the position of the second ship 20BZ. When the positional difference is less than a predetermined threshold Th, it is determined that the position of the second ship 20BZ is abnormal (incorrect) (refer to "AIS device (false) of the second ship 20BZ" in FIG. 19), and it is judged that the second ship 20BZ is also receiving the false GNSS signal. As the predetermined threshold, when there are a plurality of ships on the sea, it may be set to a distance between ships that cannot actually be assumed. Specifically, a value considering the ship size of the own ship can be set, for example, a range circle with a radius of about (half of the total length of the own ship + 20 to 30 m) from the center of gravity of the own ship can be considered. The circle shown in FIG. 19 indicates the range within this threshold Th.

[0262] On the other hand, when the determination unit 205A determines that the position difference is equal to or greater than a predetermined threshold Th, it determines that the position of the second ship 20BZ is normal (correct) (refer to "AIS device (correct) of the second ship 20BZ" in FIG. 19), and determines that the second ship 20BZ is not receiving its false GNSS signal.

[0263] In addition, when the determination unit 205A determines that the position of the second ship 20BZ is abnormal (incorrect), in order to confirm the actual position of the second ship 20BZ, a target detection method such as a radar or a camera other than AIS may be used.

[0264] Next, the operation and action of the ship system 10Z of this embodiment will be described with reference to FIG. 18.

[0265] First, the abnormality detection unit 5A of the GNSS compass 1A provided on the first ship 20AZ detects an abnormality in the GNSS signal (step S101Z).

[0266] Next, the first ship 20AZ measures its own position with the positioning unit 6A of the GNSS compass 1A, for example, stores it in a memory (not shown), and then sends it to the determination unit 205A (step S102Z). Since the measured position of the first ship 20AZ is based on the GNSS signal in which an abnormality has been detected, it is predicted to indicate an incorrect position. Therefore, the first ship 20AZ may not use the above-mentioned position of its own ship except for using it in the determination process in the determination unit 205A (that is, it may not be transmitted to other ships via the AIS202A, may not be displayed on the display unit 2041A of the ECDIS204A, or may not be used by the alarm output unit 2042A).

[0267] 0]]On the other hand, the second ship 20BZ measures its own position with the positioning unit 6B of the GNSS compass 1B (step S103Z), and transmits the measured position of its own ship to the first ship 20AZ (AIS202A) via the AIS202B (step S104Z).

[0268] Next, the first ship 20AZ performs a determination process for determining whether the position of the second ship 20BZ is abnormal using the position of its own ship sent from the positioning unit 6A and the position of the second ship 20BZ received via the AIS 202A in the determination unit 205A (step S105Z).

[0269] Specifically, the determination unit 205A calculates the difference (position difference) between the position of the first ship 20AZ and the position of the second ship 20BZ. If the position difference is less than a predetermined threshold Th, it is determined that the position of the second ship 20BZ is abnormal (incorrect) (Yes in step S105Z), and it is judged that the second ship 20BZ is also receiving a false GNSS signal. In this case, the first ship 20AZ invalidates (proposes to the user to do so) the position of the second ship 20BZ in the ECDIS 204A (step S106Z). "Invalidate" specifically means, for example, not displaying the incorrect position of the second ship 20BZ on the display unit 2041A of the ECDIS 204A, or not using the incorrect position of the second ship 20BZ when the alarm output unit 2042A determines the risk of collision between the first ship 20AZ and the second ship 20BZ. Thereby, damage caused by false GNSS signals can be reduced. Note that the first ship 20AZ may invalidate (not display or not use) not only the position of the second ship 20BZ in the ECDIS 204A but also all other AIS information (speed, course, etc.) regarding the second ship 20BZ obtained from the AIS 202B.

[0270] On the other hand, when the positional difference between the position of the first ship 20AZ and the position of the second ship 20BZ is equal to or greater than a predetermined threshold value Th, the determination unit 205A determines that the position of the second ship 20BZ is not abnormal (correct) (No in step S105Z), and determines that the second ship 20BZ is not receiving a false GNSS signal. In this case, the first ship 20AZ validates the position of the second ship 20BZ in the ECDIS 204A (step S107Z). Specifically, "validating" means displaying the position of the second ship 20BZ on the display unit 2041A of the ECDIS 204A. Note that even if the position of the second ship 20BZ is not abnormal, since the position of the first ship 20AZ is abnormal, it is considered that the warning output unit 2042A cannot correctly determine the risk of collision between the first ship 20AZ and the second ship 20BZ.

[0271] As described above, according to the ship system 10Z according to this embodiment, the first ship 20AZ can determine whether the position of the second ship 20BZ is abnormal when the own ship receives a false GNSS signal. Therefore, it is possible to detect whether the second ship 20BZ is receiving the false GNSS signal, and by extension, it is possible to improve the safety of navigation.

[0272] Moreover, the first ship 20AZ does not display or use (proposes to the user) the position of the second ship 20BZ determined to be abnormal in the display unit 2041A or the warning output unit 2042A of the ECDIS 204A that performs arithmetic processing using the position of the second ship 20BZ. Therefore, it is possible to reduce the damage caused by false GNSS signals and improve the safety of navigation.

[0273] The embodiments of the present invention have been described above. However, the specific configuration is not limited to the above embodiments, and even if there are design changes and the like within the scope that does not depart from the gist of the present invention, they are included in the present invention.

[0274] For example, in the above-described embodiment, the method for detecting an abnormality in a received signal according to the present invention is implemented in the GNSS compass 1 whose schematic configuration is shown in FIG. 1 (in other words, the apparatus for detecting an abnormality in a received signal according to the present invention is incorporated in the GNSS compass 1). However, the device / apparatus in which the method for detecting an abnormality in a received signal according to the present invention is applied or the apparatus for detecting an abnormality in a received signal according to the present invention is incorporated is not limited to the GNSS compass 1 whose schematic configuration is shown in FIG. 1. The method for detecting an abnormality in a received signal according to the present invention may be applied to a GNSS compass having another configuration or the apparatus for detecting an abnormality in a received signal according to the present invention may be incorporated therein. Further, the method for detecting an abnormality in a received signal according to the present invention may be applied to other types of devices / apparatuses that utilize GNSS, or the apparatus for detecting an abnormality in a received signal according to the present invention may be incorporated in other types of devices / apparatuses that utilize GNSS.

[0275] Also, in the ship system according to the above-described embodiment, ECDIS is exemplified as the position information utilization calculation means. However, any means other than ECDIS may be used as long as it performs calculations using position information. Further, in the ship system according to the above-described embodiment, two ships are assumed. However, three or more ships may exist.

Explanation of Reference Numerals

[0276] 1 GNSS compass 2 Control unit 3 GNSS antenna 3A, 3B, 3C GNSS antennas 4 GNSS receiving unit 4A, 4B, 4C GNSS receivers 5 Abnormality detection unit 51 Course difference calculation unit 52 Course difference determination unit 53 Abnormality determination unit 6 Positioning unit 61 Positioning number determination unit 62 Standard deviation determination unit 7 Output information adjustment unit 8 Inertial device (sensor) 9 Reception Instability Detection Unit (Means) 10X, 10Y, 10Z Ship System 20AX, 20AZ First Ship 20BX, 20BZ Second Ship 20Y Ship (Own Ship) 20Y’ Other Ship 202, 202’, 202A, 202B AIS 203, 203A, 203B Control Unit 204, 204A, 204B ECDIS (Position Information Utilization Calculation Means) 2041, 2041A, 2041B Display Unit (Position Information Utilization Calculation Means) 2042, 2042A, 2042B Alarm Output Unit (Position Information Utilization Calculation Means) 205A Judgment Unit 30 Onshore Server 40 Communication Satellite

Claims

1. receiving GNSS signals transmitted from a plurality of satellites via a plurality of antennas, comparing a path difference index representing a difference in path from the satellite that transmitted the GNSS signals to each of the plurality of antennas with a predetermined path difference threshold, and determining whether the direction of arrival of the GNSS signals is normal or not based on the comparison result between the path difference index and the predetermined path difference threshold at a predetermined cycle; If it is determined in the determination performed in the immediately preceding cycle that the arrival direction of the GNSS signal from at least one of the satellites is not normal, the determination for the next cycle is performed for all satellites using a second path difference threshold that is set so that the arrival direction is more likely to be determined to be not normal than the predetermined path difference threshold. A method for detecting an abnormality in a received signal.

2. When it is determined that the arrival direction of the GNSS signal from all of the satellites for which it has been determined that the arrival direction of the GNSS signal is not normal using the second path difference threshold, the determination for the next cycle is performed using the predetermined path difference threshold.

2. The method for detecting an abnormality in a received signal according to claim 1.

3. determining whether the direction of arrival of the GNSS signal is normal based on the path difference indicator for each type of the satellite system to which the satellite belongs; 2. The method for detecting an abnormality in a received signal according to claim 1.

4. Maintaining the abnormal state of the satellite determined to be abnormal for a predetermined period of time; 2. The method for detecting an abnormality in a received signal according to claim 1.

5. When the arrival direction of the GNSS signal is determined to be abnormal for a plurality of satellites and the abnormal state is maintained, if the arrival direction of the GNSS signal is determined to be normal, or if a predetermined time has elapsed since the state in which the arrival direction of the GNSS signal is determined to be normal, the abnormal state for the plurality of satellites is released.

2. The method for detecting an abnormality in a received signal according to claim 1.

6. changing the number of assigned reception channels for satellites having a frequency band different from that of the satellites determined to be abnormal, according to the number of satellites determined to be abnormal; 2. The method for detecting an abnormality in a received signal according to claim 1.

7. A first determination process for determining whether the GNSS signal is normal is executed at a predetermined interval; When it is determined in the first determination process that all of the GNSS signals are normal, the position calculated based on the GNSS signals is output. When it is determined in the first determination process that some or all of the GNSS signals are not normal, a second determination process is executed to determine whether a position can be calculated based only on the GNSS signals determined to be normal during the processing of the first determination process. When it is determined in the second determination process that a position can be calculated, the position calculated based only on the GNSS signals determined to be normal during the processing of the first determination process is output. When it is determined in the second determination process that a position cannot be calculated, a position estimated by adding the change amount measured by a sensor capable of measuring at least acceleration and angular velocity to the most recent position among the positions calculated based only on the GNSS signals determined to be normal before the processing of the first determination process is output, or a message indicating that the position cannot be measured is output. The method for detecting an abnormality of a received signal according to claim 1, characterized in that.

8. When it is determined in the second determination process that a position cannot be calculated, a third determination process is executed to determine whether the difference between the position calculated based on the GNSS signals and the position estimated in the second determination process is equal to or greater than a predetermined threshold. When it is determined in the third determination process that the difference is equal to or greater than the predetermined threshold, the estimated position is output, or the message is output. When it is determined in the third determination process that the difference is less than the predetermined threshold, the position calculated based on the GNSS signals is output. The method for detecting an abnormality of a received signal according to claim 7, characterized in that.

9. The first determination process for determining whether the GNSS signals are normal is executed at a predetermined period. When it is determined in the first determination process that all of the GNSS signals are normal, the time calculated based on the GNSS signals is output. When it is determined in the first determination process that some or all of the GNSS signals are not normal, a second determination process is executed to determine whether a time can be calculated based only on the GNSS signals determined to be normal during the processing of the first determination process. When it is determined in the second determination process that the time can be calculated, output the time calculated based only on the GNSS signals determined to be normal during the processing of the first determination process. When it is determined in the second determination process that the time cannot be calculated, output the time estimated by adding the elapsed time measured by the internal clock to the most recent time among the times calculated based only on the GNSS signals determined to be normal before the processing of the first determination process. The method for detecting an abnormality of a received signal according to claim 1, characterized in that.

10. When it is determined in the second determination process that the time cannot be calculated, execute a third determination process for determining whether or not the difference between the time calculated based on the GNSS signal and the time estimated in the second determination process is equal to or greater than a predetermined threshold value. When it is determined in the third determination process that the difference is equal to or greater than the predetermined threshold value, output the estimated time. When it is determined in the third determination process that the difference is less than the predetermined threshold value, output the time calculated based on the GNSS signal. The method for detecting an abnormality of a received signal according to claim 9, characterized in that.

11. When the number of satellites determined to have a normal arrival direction of the GNSS signal based on the travel path difference index is less than a predetermined threshold value for determining that the GNSS signal is normal based on the travel path difference index. When the number of satellites determined to have an abnormal arrival direction of the GNSS signal based on the travel path difference index is within a predetermined range. When at least one of the positioning positions of the plurality of antennas has not been calculated, and When the standard deviation of the positioning distances between the plurality of antennas calculated using the positioning positions of the plurality of antennas is greater than a predetermined threshold value, in at least one of the cases, it is determined that the GNSS signal is in an unstable reception state and there may be an abnormality in the GNSS signal. The method for detecting an abnormality of a received signal according to claim 1, characterized in that.

12. A ship system using the method for detecting an abnormality of a received signal according to claim 1, wherein A first ship and a second ship are communicably connected. The first ship includes a position measuring means for measuring the position of the ship itself based on the GNSS signal, and an abnormality detecting unit for detecting an abnormality of the GNSS signal. The second ship is capable of acquiring the position of the first ship measured by the position measuring means, and is capable of acquiring that fact when an abnormality is detected by the abnormality detection unit. A ship system characterized by this.

13. The second ship is provided with position information utilization calculation means for performing calculations using the position of the first ship measured by the position measuring means, when it is acquired that the abnormality has been detected in the first ship, invalidates the position of the first ship measured by the position measuring means in the position information utilization calculation means, or proposes to the user to invalidate it. The ship system according to claim 12, characterized by this.

14. A ship system using the method for detecting an abnormality in a received signal according to claim 1, wherein the ship is provided with position measuring means for measuring its own position based on the GNSS signal, and an abnormality detection unit for detecting an abnormality in the GNSS signal, the ship transmits its own ship information including its own position measured by the position measuring means to another ship, and when an abnormality is detected by the abnormality detection unit, invalidates the transmission of the own ship information to the other ship, or proposes to the user to invalidate it. A ship system characterized by this.

15. The ship is provided with position information utilization calculation means for performing calculations using its own position measured by the position measuring means, when an abnormality is detected by the abnormality detection unit, invalidates the position of the ship itself measured by the position measuring means in the position information utilization calculation means, or proposes to the user to invalidate it. The ship system according to claim 14, characterized by this.

16. A ship system using the method for detecting an abnormality in a received signal according to claim 1, wherein a first ship and a second ship are communicably connected, the first ship and the second ship are provided with position measuring means for measuring their own positions based on the GNSS signal, and transmit their own positions measured by the position measuring means to another ship, the first ship is provided with an abnormality detection unit for detecting an abnormality in the GNSS signal, and when an abnormality is detected by the abnormality detection unit and the positional difference between the position of the ship itself measured by the position measuring means at the time of the abnormality detection and the position of the second ship is less than a predetermined threshold value, it is determined that the position of the second ship is abnormal. A ship system characterized by this.

17. The first ship a position information utilization calculation means for performing calculations using the position of the second ship; When it is determined that the position of the second vessel is abnormal, the position information utilization calculation means invalidates the position of the second vessel or suggests to the user that the position be invalidated.

17. A marine vessel system according to claim 16.

18. a receiving unit that receives GNSS signals transmitted from a plurality of satellites via a plurality of antennas; a path difference determination unit that performs a process at a predetermined cycle to compare a path difference index that indicates a difference in a path from the satellite that transmitted the GNSS signal to each of the plurality of antennas with a predetermined path difference threshold, and determines whether or not the arrival direction of the GNSS signal is normal based on a comparison result between the path difference index and the predetermined path difference threshold, When it is determined that the arrival direction of the GNSS signal of at least one of the satellites is not normal in the determination performed in the immediately preceding cycle, the path difference determination unit performs the determination in the next cycle for all satellites using a second path difference threshold value that is set so that the arrival direction is more likely to be determined to be not normal than the predetermined path difference threshold value.

2. A detection device for detecting abnormalities in a received signal.

19. When it is determined that the arrival direction of the GNSS signal from all of the satellites for which it has been determined that the arrival direction of the GNSS signal is not normal using the second path difference threshold, the determination for the next cycle is performed using the predetermined path difference threshold.

19. The apparatus for detecting an abnormality in a received signal according to claim 18.

20. determining whether the direction of arrival of the GNSS signal is normal based on the path difference indicator for each type of the satellite system to which the satellite belongs; 19. The apparatus for detecting an abnormality in a received signal according to claim 18.

21. The abnormal state of the satellite determined to be abnormal is maintained for a predetermined time period.

19. The apparatus for detecting an abnormality in a received signal according to claim 18.

22. When the arrival direction of the GNSS signal is determined to be abnormal for a plurality of satellites and the abnormal state is maintained, if the arrival direction of the GNSS signal is determined to be normal, or if a predetermined time has elapsed since the state in which the arrival direction of the GNSS signal is determined to be normal, the abnormal state for the plurality of satellites is released. The receiving signal abnormality detection device according to claim 18, characterized in that...

23. The number of receiving channel allocations for satellites determined to be abnormal and satellites having different frequency bands changes according to the number of satellites determined not to be normal. The receiving signal abnormality detection device according to claim 18, characterized in that...

24. An abnormality detection unit that executes a first determination process for determining whether the GNSS signal is normal at a predetermined cycle, An output information adjustment unit that adjusts the output information, and The output information adjustment unit, When it is determined in the first determination process that all of the GNSS signals are normal, outputs the position calculated based on the GNSS signal, When it is determined in the first determination process that some or all of the GNSS signals are not normal, executes a second determination process for determining whether a position can be calculated based only on the GNSS signals determined to be normal during the processing of the first determination process, When it is determined in the second determination process that a position can be calculated, outputs the position calculated based only on the GNSS signals determined to be normal during the processing of the first determination process, When it is determined in the second determination process that a position cannot be calculated, outputs the position estimated by adding the change amount measured by at least a sensor capable of measuring acceleration and angular velocity to the most recent position among the positions calculated based only on the GNSS signals determined to be normal before the processing of the first determination process, or outputs a message indicating that the position cannot be measured. The receiving signal abnormality detection device according to claim 18, characterized in that...

25. When it is determined in the second determination process that a position cannot be calculated, the output information adjustment unit executes a third determination process for determining whether the difference between the position calculated based on the GNSS signal and the position estimated in the second determination process is equal to or greater than a predetermined threshold value, When it is determined in the third determination process that the difference is equal to or greater than the predetermined threshold value, outputs the estimated position or outputs the message, When it is determined in the third determination process that the difference is less than the predetermined threshold value, outputs the position calculated based on the GNSS signal. The receiving signal abnormality detection device according to claim 24, characterized in that...

26. An abnormality detection unit that executes a first determination process for determining whether or not the GNSS signal is normal at a predetermined cycle, and an output information adjustment unit that adjusts the output information, wherein the output information adjustment unit, when it is determined in the first determination process that all of the GNSS signals are normal, outputs the time calculated based on the GNSS signal, when it is determined in the first determination process that some or all of the GNSS signals are not normal, executes a second determination process for determining whether or not a time can be calculated based only on the GNSS signals determined to be normal during the process of the first determination process, when it is determined in the second determination process that a time can be calculated, outputs the time calculated based only on the GNSS signals determined to be normal during the process of the first determination process, when it is determined in the second determination process that a time cannot be calculated, outputs a time estimated by adding the elapsed time measured by the internal clock to the most recent time among the times calculated based only on the GNSS signals determined to be normal before the process of the first determination process, The reception signal abnormality detection device according to claim 18, characterized in that.

27. When it is determined in the second determination process that a time cannot be calculated, the output information adjustment unit executes a third determination process for determining whether or not the difference between the time calculated based on the GNSS signal and the time estimated in the second determination process is equal to or greater than a predetermined threshold value, when it is determined in the third determination process that the difference is equal to or greater than the predetermined threshold value, outputs the estimated time, when it is determined in the third determination process that the difference is less than the predetermined threshold value, outputs the time calculated based on the GNSS signal, The reception signal abnormality detection device according to claim 26, characterized in that.

28. when the number of satellites determined to have a normal arrival direction of the GNSS signal based on the travel path difference index is less than a predetermined threshold for determining that the GNSS signal is normal based on the travel path difference index, when the number of satellites determined to have an abnormal arrival direction of the GNSS signal based on the travel path difference index is within a predetermined range, when at least one positioning position of the plurality of antennas has not been calculated, and, When the standard deviation of the positioning distances between each of the plurality of antennas, calculated using the positioning positions of the plurality of antennas, is greater than a predetermined threshold value, in at least one case, it is determined that the GNSS signal is in an unstable reception situation and there may be an abnormality in the GNSS signal, and there is means for making such a determination. The reception signal abnormality detection device according to claim 18, characterized by the above.

29. A ship system using the reception signal abnormality detection device according to claim 18, wherein a first ship and a second ship are communicably connected, the first ship includes position measurement means for measuring its own ship's position based on the GNSS signal and an abnormality detection unit for detecting an abnormality in the GNSS signal, the second ship can acquire the position of the first ship measured by the position measurement means, and can acquire the fact that an abnormality has been detected by the abnormality detection unit when an abnormality is detected, A ship system characterized by the above.

30. The second ship includes position information utilization calculation means for performing calculations using the position of the first ship measured by the position measurement means, when it is acquired that an abnormality has been detected in the first ship, the position information utilization calculation means invalidates the position of the first ship measured by the position measurement means, or proposes to the user to invalidate it, The ship system according to claim 29, characterized by the above.

31. A ship system using the reception signal abnormality detection device according to claim 18, wherein a ship includes position measurement means for measuring its own ship's position based on the GNSS signal and an abnormality detection unit for detecting an abnormality in the GNSS signal, the ship transmits its own ship information including its own ship's position measured by the position measurement means to another ship, and when an abnormality is detected by the abnormality detection unit, invalidates the transmission of the own ship information to the other ship, or proposes to the user to invalidate it, A ship system characterized by the above.

32. The ship includes position information utilization calculation means for performing calculations using the position of the ship measured by the position measurement means, when an abnormality is detected by the abnormality detection unit, the position information utilization calculation means invalidates the position of the ship measured by the position measurement means, or proposes to the user to invalidate it, The ship system according to claim 31, characterized by the above.

33. A ship system using the apparatus for detecting abnormality of a received signal according to claim 18, wherein a first ship and a second ship are communicably connected; the first ship and the second ship are each provided with position measuring means for measuring the position of its own ship based on the GNSS signal, and transmits the position of its own ship measured by the position measuring means to the other ship; the first ship is provided with an abnormality detecting unit for detecting an abnormality of the GNSS signal, and when an abnormality is detected by the abnormality detecting unit and the position difference between the position of its own ship measured by the position measuring means at the time of the abnormality detection and the position of the second ship is less than a predetermined threshold value, it is determined that the position of the second ship is abnormal; a ship system characterized by the above.

34. The first ship is provided with position information utilization calculation means for performing calculations using the position of the second ship, and when it is determined that the position of the second ship is abnormal, invalidates the position of the second ship in the position information utilization calculation means or proposes to the user to invalidate the position; a ship system according to claim 33, characterized by the above.

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