Method and device for detecting abnormality in received signal

Abstract

To suppress erroneous determination and accurately detect an abnormal GNSS signal even when minor variations or offsets occur in a path difference.SOLUTION: A path difference determination unit 54 executes determination processing of a path difference of comparing a path difference indicator which represents a difference in paths of GNSS signals transmitted from multiple GNSS satellites to multiple GNSS antennas 3A, 3B, 3C with a first path difference threshold and determining whether or not the arrival direction of the GNSS signal is normal on the basis of the comparison result in a prescribed cycle; and executes determination processing of the path difference in the next cycle by using a second path difference threshold that is set to make it easier to determine the arrival direction as abnormal compared to the first path difference threshold regarding the GNSS satellite whose arrival direction of the GNSS signal is determined to be abnormal in the determination processing of the path difference executed in the immediately previous cycle.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technique for detecting anomalies in signals received in a Global Navigation Satellite System (GNSS). [Background technology]

[0002] In GNSS such as GPS (Global Positioning System), which measures the position of a moving object using GNSS signals transmitted from satellites, there has been a problem in which a false GNSS signal is transmitted from a transmitting source such as a satellite or a ground station, causing a GNSS receiving device that receives the false GNSS signal to measure an incorrect position. To prevent such damage, a technique is known for determining whether a satellite that transmitted a GNSS signal is genuine (for example, see Patent Document 1).

[0003] In Patent Document 1, GNSS signals transmitted from multiple satellites are received by multiple antennas, and the GNSS signals are determined to be abnormal if the path difference (difference in carrier phase of the GNSS signals) indicating the difference in the path from the satellite that transmitted the GNSS signal to each of the multiple antennas is equal to or less than a predetermined path difference threshold. In other words, since GNSS signals transmitted from the same source disguised as multiple satellites have the same path difference, the source of a GNSS signal determined to be abnormal can be determined to be suspected of being a fake satellite (hereinafter, this technology is also referred to as path difference matching detection). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4803862 Summary of the Invention [Problem to be solved by the invention]

[0005] In path difference match detection, minute variations or offsets in the path difference may occur due to the influence of insufficient time synchronization between multiple receivers receiving GNSS signals via antennas, multipath or noise in the GNSS signal, or differences in the Doppler frequency of the GNSS signal for each satellite due to differences in the orbital direction of each satellite, etc. The path difference match detection is performed at a predetermined cycle, but if minute variations or offsets occur in the path difference, a satellite that was classified as having a path difference equal to or less than a predetermined path difference threshold (i.e., path difference match) in the judgment of the previous cycle may have a path difference greater than the predetermined path difference threshold (i.e., path difference mismatch) due to minute variations or offsets in the judgment of the next cycle, and may be erroneously determined to be a normal GNSS signal. To prevent such erroneous judgments, the path difference threshold can be relaxed (i.e., set to a large value) by taking into account minute variations and offsets in the path difference in advance. However, if the path difference threshold is relaxed, erroneous judgments will occur when there are no minute variations or offsets in the path difference.

[0006] Therefore, an object of the present invention is to provide a method and device for detecting abnormalities in a received signal that can suppress erroneous judgments even when slight variations or offsets occur in the path difference and accurately detect abnormal GNSS signals. [Means for solving the problem]

[0007] In order to solve the above problem, the method for detecting abnormalities in a received signal of the present invention receives GNSS signals transmitted from multiple satellites via multiple antennas, compares a path difference indicator indicating the difference in paths from the satellite that transmitted the GNSS signals to each of the multiple antennas with a predetermined path difference threshold, and performs a process at a predetermined cycle to determine whether the arrival direction of the GNSS signal is normal or not based on the comparison result between the path difference indicator and the predetermined path difference threshold, and for a satellite for which the arrival direction of the GNSS signal was determined to be abnormal in the determination performed in the previous cycle, performs the determination in the next cycle using a second path difference threshold set so that the arrival direction is more likely to be determined to be abnormal than the predetermined path difference threshold.

[0008] The method for detecting abnormalities in a received signal according to the present invention may be such that, for a satellite belonging to the same type of satellite system as the satellite for which the arrival direction of the GNSS signal was determined to be abnormal in the determination performed in the previous cycle, the determination in the next cycle is performed using the second path difference threshold.

[0009] The method for detecting abnormalities in a received signal according to the present invention may be such that, if the determination performed in the previous cycle determines that the arrival direction of the GNSS signal for at least one of the satellites is not normal, the determination in the next cycle is performed for all satellites using the second path difference threshold.

[0010] The method for detecting an abnormality in a received signal according to the present invention may further determine whether or not the transmission time of the GNSS signal contained in the GNSS signal is normal based on a comparison between the transmission time of the GNSS signal and a predetermined reference transmission time.

[0011] The method for detecting an abnormality in a received signal according to the present invention may further include determining whether or not the pseudorange of the satellite that transmitted the GNSS signal is normal based on a comparison between the pseudorange of the satellite and a pseudorange of a predetermined reference satellite.

[0012] The method for detecting abnormalities in a received signal according to the present invention may be such that, for a satellite in which the arrival direction of the GNSS signal is determined to be abnormal, when the arrival direction of the GNSS signal is determined to be normal using the second path difference threshold, the satellite performs the determination for the next period using the predetermined path difference threshold.

[0013] The method for detecting an abnormality in a received signal according to the present invention may determine whether or not the direction of arrival of the GNSS signal is normal based on the path difference index for each type of satellite system to which the satellite belongs.

[0014] The method for detecting an abnormality in a received signal according to the present invention may be such that the reference transmission time for the satellite that transmitted the GNSS signal is a transmission time contained in a GNSS signal transmitted from the satellite in the past.

[0015] The method for detecting an abnormality in a received signal according to the present invention may be such that the reference transmission time for the satellite that transmitted the GNSS signal is a transmission time included in a GNSS signal transmitted from another satellite.

[0016] The method for detecting an abnormality in a received signal according to the present invention may be arranged to maintain the abnormal state of a satellite determined to be abnormal for a predetermined period of time.

[0017] The method for detecting abnormalities in a received signal of the present invention may include canceling the abnormal state for a plurality of satellites when the arrival direction of the GNSS signal is determined to be abnormal and the abnormal state is maintained, and when the arrival direction of the GNSS signal is determined to be normal, or when the state in which the arrival direction of the GNSS signal is determined to be normal has elapsed for a predetermined time.

[0018] The method for detecting abnormalities in a received signal of the present invention may include canceling the abnormal state for a satellite determined to be abnormal when the abnormal state for the satellite determined to be abnormal is maintained and the transmission time of the GNSS signal is determined to be normal, or when a predetermined time has elapsed during which the transmission time of the GNSS signal has been determined to be normal.

[0019] The method for detecting abnormalities in a received signal according to the present invention may vary the number of receiving channels allocated to satellites having a different frequency band from the satellites determined to be abnormal, depending on the number of satellites determined to be abnormal.

[0020] The method for detecting an abnormality in a received signal according to the present invention may include executing a first determination process at a predetermined interval to determine whether the GNSS signals are normal, and if it is determined in the first determination process that all of the GNSS signals are normal, outputting a position calculated based on the GNSS signals, and if it is determined in the first determination process that some or all of the GNSS signals are not normal, executing a second determination process to determine whether a position can be calculated based only on the GNSS signals determined to be normal at the time of processing the first determination process, and if it is determined in the second determination process that the position can be calculated, outputting a position calculated based only on the GNSS signals determined to be normal at the time of processing the first determination process, and if it is determined in the second determination process that the position cannot be calculated, outputting a position estimated by adding an amount of change measured by a sensor capable of measuring at least acceleration and angular velocity to the closest position among positions calculated based only on GNSS signals determined to be normal before processing the first determination process, or outputting a message indicating that the position cannot be measured.

[0021] The method for detecting an abnormality in a received signal of the present invention may, when it is determined in the second determination process that the position cannot be calculated, execute a third determination process to determine whether or not the difference between the position calculated based on the GNSS signal and the position estimated in the second determination process is greater than or equal to a predetermined threshold, and when it is determined in the third determination process that the difference is greater than or equal to the predetermined threshold, output the estimated position or output the message, and when it is determined in the third determination process that the difference is less than the predetermined threshold, output the position calculated based on the GNSS signal.

[0022] The method for detecting an abnormality in a received signal according to the present invention may include executing a first determination process at a predetermined interval to determine whether the GNSS signals are normal, and if it is determined in the first determination process that all of the GNSS signals are normal, outputting a time calculated based on the GNSS signals, and if it is determined in the first determination process that some or all of the GNSS signals are not normal, executing a second determination process to determine whether the time can be calculated based only on the GNSS signals determined to be normal during the first determination process, and if it is determined in the second determination process that the time can be calculated, outputting the time calculated based only on the GNSS signals determined to be normal during the first determination process, and if it is determined in the second determination process that the time cannot be calculated, outputting a time estimated by adding an elapsed time measured by an internal clock to the most recent time calculated based only on the GNSS signals determined to be normal before the first determination process.

[0023] The method for detecting an abnormality in a received signal of the present invention may, when it is determined in the second determination process that the time cannot be calculated, execute a third determination process to determine whether the difference between the time calculated based on the GNSS signal and the time estimated in the second determination process is greater than or equal to a predetermined threshold, output the estimated time if it is determined in the third determination process that the difference is greater than or equal to the predetermined threshold, and output the time calculated based on the GNSS signal if it is determined in the third determination process that the difference is less than the predetermined threshold.

[0024] The method for detecting abnormalities in a received signal of the present invention may determine that the GNSS signal is in an unstable reception state and that there is a possibility that an abnormality has occurred in the GNSS signal in at least one of the following cases: the number of satellites for which the arrival direction of the GNSS signal is determined to be normal based on the path difference indicator is less than a predetermined threshold for determining that the GNSS signal is normal based on the path difference indicator; the number of satellites for which the arrival direction of the GNSS signal is determined to be abnormal based on the path difference indicator is within a predetermined range; the positioning position of at least one of the multiple antennas has not been calculated; and the standard deviation of the positioning distances between the multiple antennas calculated using the positioning positions of the multiple antennas is greater than a predetermined threshold.

[0025] In addition, the received signal abnormality detection device of the present invention comprises a receiving unit that receives GNSS signals transmitted from multiple satellites via multiple antennas, and a path difference determination unit that performs a process at a predetermined cycle to compare a path difference index indicating the difference in paths from the satellite that transmitted the GNSS signal to each of the multiple antennas with a predetermined path difference threshold and determine whether the arrival direction of the GNSS signal is normal or not based on the comparison result between the path difference index and the predetermined path difference threshold, wherein the path difference determination unit performs the determination in the next cycle for a satellite for which the arrival direction of the GNSS signal was determined to be abnormal in the determination performed in the immediately previous 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 predetermined path difference threshold.

[0026] The device for detecting abnormalities in a received signal of the present invention may be configured so that, for a satellite belonging to the same type of satellite system as the satellite for which the arrival direction of the GNSS signal was determined to be abnormal in the determination performed in the previous cycle, the path difference determination unit performs the determination in the next cycle using the second path difference threshold.

[0027] The received signal abnormality detection device of the present invention may be configured so that, when the path difference determination unit determines that the arrival direction of the GNSS signal of at least one of the satellites is not normal in the determination performed in the previous cycle, the path difference determination unit performs the determination in the next cycle for all satellites using the second path difference threshold.

[0028] The received signal abnormality detection device of the present invention may further have a transmission time determination unit that determines whether the transmission time of the GNSS signal is normal or not based on a comparison between the transmission time of the GNSS signal contained in the GNSS signal and a predetermined reference transmission time, and may determine a satellite to be used in the calculation process of the positioning information by the positioning unit based on the determination result of whether the transmission time of the GNSS signal is normal or not and the determination result of whether the arrival direction of the GNSS signal is normal or not.

[0029] The received signal abnormality detection device of the present invention may further have a pseudodistance determination unit that determines whether the pseudodistance of the satellite that transmitted the GNSS signal is normal or not based on a comparison between the pseudodistance of the satellite and a predetermined reference satellite, and may determine the satellite to be used in the calculation process of the positioning information by the positioning unit based on the determination result of whether the arrival direction of the GNSS signal is normal or not and the determination result of whether the pseudodistance of the satellite is normal or not.

[0030] The received signal abnormality detection device of the present invention may be configured so that, for a satellite in which the arrival direction of the GNSS signal is determined to be abnormal, when the arrival direction of the GNSS signal is determined to be normal using the second path difference threshold, the determination for the next cycle is performed using the predetermined path difference threshold.

[0031] The received signal abnormality detection device according to the present invention may determine whether or not 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.

[0032] The received signal abnormality detection device of the present invention may be configured so that the reference transmission time for the satellite that transmitted the GNSS signal is a transmission time contained in a GNSS signal transmitted from the satellite in the past.

[0033] The received signal abnormality detection device of the present invention may be configured so that the reference transmission time for the satellite that transmitted the GNSS signal is a transmission time included in a GNSS signal transmitted from another satellite.

[0034] The received signal abnormality detection device according to the present invention may be configured so that the abnormal state of a satellite that has been determined to be abnormal is maintained for a predetermined period of time.

[0035] The received signal abnormality detection device of the present invention may be configured to cancel the abnormal state for a plurality of satellites when the arrival direction of the GNSS signal is determined to be abnormal and the abnormal state is maintained, and when the arrival direction of the GNSS signal is determined to be normal, or when a predetermined time has elapsed during which the arrival direction of the GNSS signal has been determined to be normal.

[0036] The received signal abnormality detection device of the present invention may be configured to cancel the abnormal state for a satellite determined to be abnormal when the transmission time of the GNSS signal is determined to be normal while the abnormal state for the satellite determined to be abnormal is maintained, or when a predetermined time has elapsed during which the transmission time of the GNSS signal has been determined to be normal.

[0037] The device for detecting abnormalities in received signals according to the present invention may be configured to change the number of receiving channel allocations of satellites having a different frequency band from the satellites determined to be abnormal in accordance with the number of satellites determined to be abnormal.

[0038] The received signal abnormality detection device of the present invention comprises an abnormality detection unit that executes a first determination process at a predetermined period to determine whether the GNSS signals are normal or not, and an output information adjustment unit that adjusts the information to be output, and 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 signals, and 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 to determine whether a position can be calculated based only on the GNSS signals determined to be normal at the time of the first determination process, and when it is determined in the second determination process that the position can be calculated, the output information adjustment unit outputs a position calculated based only on the GNSS signals determined to be normal at the time of the first determination process, and when it is determined in the second determination process that the position cannot be calculated, the output information adjustment unit may output a position estimated by adding an amount of change measured by a sensor capable of measuring at least acceleration and angular velocity to the closest position among positions calculated based only on the GNSS signals determined to be normal before the time of the first determination process, or output a message indicating that the position cannot be measured.

[0039] The received signal abnormality detection device of the present invention may be configured so that, when the output information adjustment unit determines in the second determination process that the position cannot be calculated, it executes a third determination process to determine whether the difference between the position calculated based on the GNSS signal and the position estimated in the second determination process is greater than or equal to a predetermined threshold, and when it is determined in the third determination process that the difference is greater than or equal to the predetermined threshold, it outputs the estimated position or outputs the message, and when it is determined in the third determination process that the difference is less than the predetermined threshold, it outputs the position calculated based on the GNSS signal.

[0040] The received signal abnormality detection device of the present invention comprises an abnormality detection unit that executes a first determination process at a predetermined period to determine whether the GNSS signals are normal or not, and an output information adjustment unit that adjusts the information to be output, and when it is determined in the first determination process that all of the GNSS signals are normal, the output information adjustment unit outputs a time calculated based on the GNSS signals, and 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 to determine whether the time can be calculated based only on the GNSS signals determined to be normal at the time of the first determination process, and when it is determined in the second determination process that the time can be calculated, the output information adjustment unit outputs the time calculated based only on the GNSS signals determined to be normal at the time of the first determination process, and when it is determined in the second determination process that the time cannot be calculated, the output information adjustment unit outputs a time estimated by adding the elapsed time measured by an internal clock to the most recent time calculated based only on the GNSS signals determined to be normal before the time of the first determination process.

[0041] The received signal abnormality detection device of the present invention may be configured so that, when the output information adjustment unit determines that the time cannot be calculated in the second determination process, it executes a third determination process to determine whether the difference between the time calculated based on the GNSS signal and the time estimated in the second determination process is greater than or equal to a predetermined threshold, and when it determines in the third determination process that the difference is greater than or equal to the predetermined threshold, it outputs the estimated time, and when it determines in the third determination process that the difference is less than the predetermined threshold, it outputs the time calculated based on the GNSS signal.

[0042] The received signal abnormality detection device of the present invention may have a means for determining that the GNSS signal is in an unstable reception state and that an abnormality may have occurred in the GNSS signal in at least one of the following cases: the number of satellites for which the arrival direction of the GNSS signal is determined to be normal based on the path difference indicator is less than a predetermined threshold for determining that the GNSS signal is normal based on the path difference indicator; the number of satellites for which the arrival direction of the GNSS signal is determined to be abnormal based on the path difference indicator is within a predetermined range; the positioning position of at least one of the multiple antennas has not been calculated; and the standard deviation of the positioning distances between the multiple antennas calculated using the positioning positions of the multiple antennas is greater than a predetermined threshold. Effect of the Invention

[0043] According to the method and device for detecting abnormalities in a received signal of the present invention, for a satellite for which the arrival direction of a GNSS signal was determined to be abnormal in the determination performed in the previous cycle, the determination in the next cycle is performed using a second path difference threshold that is set so that the arrival direction is more likely to be determined to be abnormal than a predetermined path difference threshold.This makes it possible to suppress erroneous determinations caused by minute variations or offsets in the path difference and to accurately detect abnormal GNSS signals.

[0044] According to the method and device for detecting abnormalities in a received signal of the present invention, for a satellite belonging to the same type of satellite system as a satellite for which the arrival direction of a GNSS signal was determined to be abnormal in the determination performed in the previous cycle, the determination in the next cycle is performed using a second path difference threshold that is set to make it easier to determine that the arrival direction is abnormal than a predetermined path difference threshold.Therefore, even if interference is occurring such as transmitting false GNSS signals to a specific type of satellite system, it is possible to detect abnormalities in the received signal in that satellite system without missing anything, without increasing the risk of erroneous determination.

[0045] According to the method and device for detecting abnormalities in a received signal of the present invention, if the arrival direction of the GNSS signal for at least one satellite is determined to be abnormal in the determination performed in the previous cycle, 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 abnormal than a predetermined path difference threshold.Therefore, even if interference is occurring, such as transmitting false GNSS signals to multiple types of GNSS satellite systems, it is possible to detect abnormal GNSS signals without increasing the risk of erroneous determination.

[0046] According to the method and device for detecting abnormalities in a received signal of the present invention, abnormalities in the transmission time of the GNSS signal are detected, as well as abnormalities in the path difference (the direction of arrival of the GNSS signal) from the satellite to each of the multiple antennas. Therefore, abnormalities in the path difference can be detected more reliably in the GNSS signal, but since the processing is performed on GNSS signals transmitted from multiple satellites, detection may be delayed. On the other hand, abnormalities in the transmission time are processed independently for each satellite, so detection can be performed immediately. By combining the processing for determining the transmission time and the processing for determining the path difference, abnormalities in the received signal in the GNSS can be detected in a mutually complementary manner, thereby improving the reliability of the processing for detecting abnormalities in the received signal in the GNSS.

[0047] According to the method and device for detecting abnormalities in a received signal of the present invention, if abnormalities in the pseudorange of a satellite are further detected, it is possible to more reliably detect abnormalities in the received signal in the GNSS by further combining it with a pseudorange judgment process, thereby further improving the reliability of the process for detecting abnormalities in the received signal in the GNSS.

[0048] According to the method and device for detecting abnormality in a received signal of the present invention, when it is determined that a part or all of the GNSS signals are abnormal, a process for determining whether or not a position can be calculated based only on the GNSS signals determined to be normal is performed, and when the position cannot be calculated based only on the GNSS signals determined to be normal, an estimated position is output by adding a change amount measured by an inertial device (a sensor capable of measuring acceleration and angular velocity) to the nearest position among the positions calculated based only on the GNSS signals determined to be normal, so that appropriate position information can be provided to the outside (other devices, services, etc.). Also, when the position cannot be calculated based only on the GNSS signals determined to be normal, a message indicating that at least the position cannot be measured is output, so that it is possible to reliably prevent erroneous position information based on abnormal received signals from being used by the outside (other devices, services, etc.).

[0049] According to the method and device for detecting abnormalities in a received signal of the present invention, when a position cannot be calculated based only on GNSS signals determined to be normal, a position calculated based on GNSS signals including GNSS signals determined to be abnormal is compared with a position estimated to be normal, i.e., a position estimated by adding the amount of change measured by the inertial device to the most recent position calculated based only on GNSS signals determined to be normal, and the output information is adjusted based on whether the difference is greater than or equal to a predetermined threshold, making it possible to provide more appropriate and useful position information to the outside (other devices, services, etc.).

[0050] According to the method and device for detecting abnormalities in a received signal of the present invention, when it is determined that some or all of the GNSS signals are abnormal, a determination process is performed to determine whether the time can be calculated based only on the GNSS signals determined to be normal, and if the time cannot be calculated based only on the GNSS signals determined to be normal, an estimated time is output by adding the elapsed time measured by the internal clock to the most recent time calculated based only on the GNSS signals determined to be normal, making it possible to provide appropriate time information to the outside (other devices, services, etc.).

[0051] According to the method and device for detecting abnormalities in a received signal of the present invention, when the time cannot be calculated 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, i.e., the most recent time calculated based only on GNSS signals determined to be normal, and the output information is adjusted based on whether the difference is greater than or equal to a predetermined threshold value, thereby making it possible to output more appropriate and useful time information to the outside (other devices, services, etc.).

[0052] According to the method and device for detecting an abnormality in a received signal of the present invention, it is possible to detect a situation in which the reception of a GNSS signal is unstable, so that an abnormality in the GNSS signal can be grasped at the possibility stage. Even if the detection of the abnormality is delayed, it is possible to prevent the output of erroneous information (such as position and time) based on a false GNSS signal, thereby improving the reliability of the abnormality detection process in the received signal. [Brief description of the drawings]

[0053] [Figure 1] FIG. 1 is a functional block diagram showing a schematic configuration of a GNSS compass according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing the arrangement of multiple GNSS antennas in the GNSS compass of FIG. 1. [Diagram 3] FIG. 3 is a diagram for explaining the path difference between the GNSS antennas in FIG. 2. [Figure 4] 4 is a flowchart showing a procedure of a process of determining a path difference performed by a path difference determining unit in FIG. 1 by switching between a first path difference threshold value and a second path difference threshold value. [Diagram 5] 13 is a flowchart showing a procedure of a process of determining a trajectory difference performed by switching between a first trajectory difference threshold and a second trajectory difference threshold in a trajectory difference determination unit of a GNSS compass according to a second embodiment. [Figure 6] 13 is a flowchart showing a procedure of a process of determining a trajectory difference performed by switching between a first trajectory difference threshold and a second trajectory difference threshold in a trajectory difference determination unit of a GNSS compass according to a third embodiment. [Figure 7] FIG. 11 is a functional block diagram showing a schematic configuration of a GNSS compass according to fourth and fifth embodiments. [Figure 8] 13 is a flowchart showing a procedure of an output information adjustment process performed in the control unit of the GNSS compass according to the fourth embodiment. [Figure 9] 13 is a flowchart showing a procedure of an output information adjustment process performed in a control unit of a GNSS compass according to a fifth embodiment. [Figure 10] FIG. 13 is a functional block diagram showing a schematic configuration of a GNSS compass according to a sixth embodiment. [Figure 11] FIG. 11 is a diagram for explaining an example of an unstable reception period. [Figure 12] FIG. 11 is a diagram for explaining an example of an unstable reception period. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiments. In the embodiments, a received signal abnormality detection device according to the present invention will be described as being incorporated in a GNSS compass.

[0055] (Embodiment 1) (Overall configuration of GNSS compass) 1 is a functional block diagram showing a schematic configuration of a GNSS compass 1 according to a first embodiment, which includes a detection device for detecting an abnormality in a received signal according to the present invention. The GNSS compass 1 is mounted on a moving object such as a ship, a vehicle, or an aircraft for use.

[0056] The GNSS compass 1 according to this embodiment has a function of receiving satellite signals / positioning signals (called "GNSS signals") transmitted from each of a plurality of satellites (called "GNSS satellites") used in the GNSS (Global Navigation Satellite System; global positioning satellite system), detecting abnormalities in the GNSS signals, which are received signals in the GNSS, and calculating the position of the aircraft, etc., and mainly has a control unit 2, a GNSS antenna 3, a GNSS receiver 4, an abnormality detector 5, and a positioning unit 6. The components constituting the GNSS compass 1 are connected so as to be able to transmit and receive signals via a bus and communicate information with each other.

[0057] Satellite systems included in GNSS include GPS (Global Positioning System, short for Global Positioning Satellite), GLONASS (Global NAvigation Satellite System), Galileo, and BDS (BeiDou navigation satellite System).

[0058] Each of the multiple GNSS satellites transmits a GNSS signal including an ephemeris, which is data indicating the current position of the GNSS satellite, as radio waves. The GNSS signal transmitted from each of the multiple GNSS satellites also includes information indicating the time when the GNSS satellite transmitted the GNSS signal as radio waves.

[0059] The control unit 2 has the function of controlling the operation of each part that makes up the GNSS compass 1, and is configured as a device having a central processing unit (CPU: short for Central Processing Unit) that performs calculations related to, for example, detecting abnormalities in the GNSS signal and calculating the position of the GNSS compass 1.

[0060] The control unit 2 also has the function of serving as a memory area for storing programs, various information, and data used by the central processing unit (CPU) when performing arithmetic processing such as detecting anomalies in the GNSS signal and calculating the position of the GNSS compass 1, and as a working area for temporarily storing data and information generated when the central processing unit (CPU) performs the arithmetic processing, and is configured as a device having at least one of, for example, a ROM (short for Read Only Memory), which is a read-only memory device, a RAM (short for Random Access Memory), which is a readable and writable memory device, and a hard disk.

[0061] The control unit 2 coordinates and controls the start, content, and end of processing of each part that makes up the GNSS compass 1 in accordance with a program (called the "control program") for controlling the operation of the GNSS compass 1 by having the central processing unit (CPU) execute the control program.

[0062] The GNSS receiver unit 4 is a device for receiving GNSS signals transmitted from each of multiple GNSS satellites S_i (where i is a number unique to each satellite for distinguishing and identifying the multiple GNSS satellites from one another), 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, with the GNSS receiver 4A equipped with a GNSS antenna 3A, the GNSS receiver 4B equipped with a GNSS antenna 3B, and the GNSS receiver 4C equipped with a GNSS antenna 3C.

[0063] The three GNSS antennas 3A, 3B, and 3C are fixed at predetermined intervals on a mobile object on which the GNSS compass 1 is mounted. In this embodiment, the three GNSS antennas 3A, 3B, and 3C are disposed at the vertices of an equilateral triangle (see FIG. 2).

[0064] The line segment connecting the GNSS antennas 3A, 3B, and 3C is called a "baseline." The dimensions of the baseline, which is the distance between the GNSS antennas 3A, 3B, and 3C, are known as design values ​​for 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 baseline, which is the distance between the GNSS antennas 3A, 3B, and 3C, are set to one wavelength or more (usually, about several wavelengths) to avoid interference between the GNSS antennas 3A, 3B, and 3C.

[0065] Each of the GNSS receivers 4A, 4B, 4C receives a GNSS signal transmitted from a respective GNSS satellite S_i via a GNSS antenna 3A, 3B, 3C, converts the signal into an electrical signal (particularly, a digital signal), and outputs the electrical signal.

[0066] The GNSS signal is superimposed on a carrier wave and transmitted successively from the GNSS satellite S_i as a radio wave (called a "GNSS radio wave"). Each of the GNSS receivers 4A, 4B, and 4C receives the GNSS radio wave and demodulates the GNSS radio wave to extract the GNSS signal. The GNSS signal is then output from the GNSS receiver 4.

[0067] An abnormality detection section 5 and a positioning section 6 are configured in the control unit 2 by a central processing unit (CPU) of the control unit 2 executing the control program.

[0068] The abnormality detection unit 5 is a device for detecting an abnormality in the GNSS signal output from the GNSS reception unit 4 and outputting the detection result.

[0069] The positioning unit 6 is a device for calculating and outputting positioning information using the GNSS signal output from the GNSS receiving unit 4.

[0070] The positioning information calculated by the positioning unit 6 is not limited to a specific item, but may include, for example, at least one of the aircraft's position, direction, and attitude (for example, rolling, pitching, rate of turn (ROT)), etc. The calculation process of the positioning information by the positioning unit 6 may use well-known technology, and the present invention is not limited to a specific item or method, so a detailed description will be omitted.

[0071] Based on the detection result of an abnormality in the GNSS signal output from the abnormality detection unit 5, the positioning unit 6 determines a GNSS satellite S_i to be excluded from the group of satellites used in the calculation process of the positioning information (in other words, determines the GNSS satellite S_i to be used in the calculation process of the positioning information).

[0072] (Processing contents of the abnormality detection unit) The method for detecting abnormalities in a received signal in accordance with an embodiment includes receiving GNSS signals transmitted from multiple GNSS satellites S_i via multiple GNSS antennas 3A, 3B, and 3C, determining whether the transmission time of the GNSS signal contained in the GNSS signal is normal based on a comparison between the transmission time of the GNSS signal contained in the GNSS signal and a predetermined reference transmission time, determining whether the pseudo-distance ρ_i of the GNSS satellite S_i that transmitted the GNSS signal is normal based on a comparison between the pseudo-distance ρ_i of the GNSS satellite S_i that transmitted the GNSS signal and the pseudo-distance ρr of a predetermined reference satellite Sr, and determining whether the arrival direction of the GNSS signal is normal based on an index representing the difference in the path from the GNSS satellite S_i that transmitted the GNSS signal to each of the multiple GNSS antennas 3A, 3B, and 3C.

[0073] A GNSS compass 1 according to an embodiment including a received signal abnormality detection device as equipment for implementing the above-mentioned received signal abnormality detection method includes a GNSS receiver 4 that receives GNSS signals transmitted from a plurality of GNSS satellites S_i via a plurality of GNSS antennas 3A, 3B, 3C, a transmission time determination unit 51 that determines whether or not the transmission time of the GNSS signal is normal based on a comparison between the transmission time of the GNSS signal contained in the GNSS signal and a predetermined reference transmission time, and a pseudorange ρ_i of the GNSS satellite S_i that transmitted the GNSS signal and a pseudorange ρr of a predetermined reference satellite Sr. The system includes a pseudo-distance determination unit 52 which determines whether the distance ρ_i is normal or not, a path difference determination unit 54 which determines whether the direction of arrival of the GNSS signal is normal or not based on an index which indicates the difference in the path from the GNSS satellite S_i which transmitted the GNSS signal to each of the multiple GNSS antennas 3A, 3B, 3C, and a positioning unit 6 which calculates positioning information, and the GNSS satellite S_i to be used in the calculation process of the positioning information by the positioning unit 6 is determined based on the determination result of whether the transmission time of the GNSS signal is normal or not, the determination result of whether the direction of arrival of the GNSS signal is normal or not, and the determination result of whether the pseudo-distance ρ_i of the GNSS satellite S_i is normal or not.

[0074] The anomaly detection unit 5 is a device for detecting anomalies in the GNSS signal, and receives an input of a GNSS signal for each GNSS satellite S_i output at a predetermined period from the GNSS receiving unit 4 (note that this is composed of three GNSS receivers 4A, 4B, 4C, each of which has a GNSS antenna 3 (specifically, one of 3A, 3B, 3C)), and executes a calculation process (referred to as an "anomaly detection calculation process") for detecting an anomaly in the GNSS signal, which is a signal received in the GNSS, based on the GNSS signal. The anomaly detection calculation process may be executed at a predetermined period in accordance with the predetermined period in which the GNSS signal is output from the GNSS receiving unit 4, or may be executed at a period different from the predetermined period.

[0075] The abnormality detection unit 5 includes a transmission time determination unit 51, a pseudo distance determination unit 52, a path difference calculation unit 53, and a path difference determination unit .

[0076] The transmission time determination unit 51 receives the GNSS signal for each GNSS satellite S_i output from the GNSS receiver 4 and determines whether the transmission time of the GNSS signal is normal or not. The process performed by the transmission time determination unit 51 is called a "transmission time determination process."

[0077] The transmission time determination unit 51 determines, for each GNSS satellite S_i, whether or not the absolute value of the difference between the transmission time of the GNSS signal contained in the GNSS signal and a predetermined reference transmission time is equal to or greater than a predetermined time difference threshold.

[0078] The reference transmission time may be set for each GNSS satellite S_i, or may be set as a common time for all GNSS satellites S_i.

[0079] When the reference transmission time is set for each GNSS satellite S_i, the reference transmission time for the GNSS satellite S_i may be the transmission time contained in a GNSS signal previously transmitted from the GNSS satellite S_i, which was acquired and stored, plus the elapsed time from the time the GNSS signal was received.

[0080] The elapsed time is measured, for example, by mounting a temperature compensated crystal oscillator (TCXO: an abbreviation for Temperature Compensated Crystal Oscillators) in the GNSS receiver 4 as a measuring device for the elapsed time. In this case, the elapsed time may be corrected taking into consideration an error in the measuring device for the elapsed time (for example, the temperature compensated crystal oscillator) that changes over time and a deviation in the Doppler shift of the GNSS satellite S_i. The Doppler shift is calculated as the frequency difference between the carrier frequency of the GNSS radio wave transmitted from the GNSS satellite S_i and the reception frequency at the GNSS receiver 4 (specifically, the GNSS receivers 4A, 4B, 4C) that occurs due to the Doppler effect.

[0081] When determining whether the transmission time of the GNSS signal is normal or not (that is, in the process of determining the transmission time), only the decimal part of the transmission time of the GNSS signal may be used.

[0082] The time difference threshold is not limited to a specific value, and is appropriately set to an appropriate value, taking into consideration, for example, errors that are expected to occur due to mechanical errors, etc. When a time obtained by adding an elapsed time to a transmission time previously acquired for a GNSS satellite S_i is used as the reference transmission time for the GNSS satellite S_i, the time difference threshold may be set to a value within a range of, for example, about 1 to 3 milliseconds.

[0083] When the absolute value of the difference between the transmission time of the GNSS signal contained in the GNSS signal and the reference transmission time is greater than or equal to a time difference threshold, the transmission time determination unit 51 determines that the transmission time of the GNSS signal is abnormal and classifies the GNSS satellite S_i that transmitted the GNSS signal as having a transmission time abnormality.

[0084] On the other hand, when the reference transmission time is set as a common one for all GNSS satellites S_i, the transmission time of the GNSS signal contained in the GNSS signal transmitted from another GNSS satellite S_j (where j is a number unique to each satellite for distinguishing and identifying a plurality of GNSS satellites from one another, and i ≠ j; the same applies below) may be used as the reference transmission time for the GNSS satellite S_i. As the other GNSS satellite S_j, for example, the satellite with the largest satellite elevation angle is selected from the plurality of GNSS satellites S_i from which the GNSS signal is received by the GNSS receiver 4 at the time of execution of the (or most recent) abnormality detection calculation process.

[0085] In this case, the transmission time determination unit 51 determines, for each GNSS satellite S_i, whether or not the absolute value of the difference between the transmission time of the GNSS signal contained in the GNSS signal transmitted from the GNSS satellite S_i and the reception time of the GNSS signal and the difference between the transmission time of the GNSS signal contained in the GNSS signal transmitted from another GNSS satellite S_j and the reception time of the GNSS signal is equal to or greater than a predetermined time difference threshold. The reception time of the GNSS signal is identified by the clock function / time information held by the GNSS receiver 4. The clock function / time information held by the GNSS receiver 4 is supplied from, for example, a temperature compensated crystal oscillator (TCXO) mounted on the GNSS receiver 4 as a device common to the multiple GNSS receivers 4A, 4B, and 4C.

[0086] When the transmission time of a GNSS signal included in the GNSS signal transmitted from another GNSS satellite S_j is used as the reference transmission time for the GNSS satellite S_i, the time difference threshold may be set to a different value according to the combination of the type of satellite system (e.g., GPS, GLONASS, BDS) included in the GNSS of the GNSS satellite S_i and the type of GNSS of the other GNSS satellite S_j. For example, in the case of a combination of GPS, the time difference threshold may be set to any value in the range of about 20 to 30 milliseconds, and in the case of a combination of GPS and BDS, the time difference threshold may be set to any value in the range of about 90 to 110 milliseconds.

[0087] When the absolute value of the difference between the transmission time of a GNSS signal contained in a GNSS signal transmitted from a GNSS satellite S_i and the reception time of the GNSS signal and the difference between the transmission time of a GNSS signal contained in a GNSS signal transmitted from another GNSS satellite S_j and the reception time of the GNSS signal is greater than or equal to a time difference threshold, the transmission time determination unit 51 determines that the transmission time of the GNSS signal transmitted from the GNSS satellite S_i is abnormal, and classifies the GNSS satellite S_i that transmitted the GNSS signal as having a transmission time abnormality.

[0088] Then, the transmission time determination unit 51 outputs information about the GNSS satellite S_i that has been classified as having an abnormal transmission time to the positioning unit 6 as satellite information having an abnormal transmission time.

[0089] Next, the pseudo distance determination unit 52 receives the GNSS signal for each GNSS satellite S_i output from the GNSS receiver 4, and determines whether the pseudo distance of the GNSS satellite S_i that transmitted the GNSS signal is normal or not. The process performed by the pseudo distance determination unit 52 is called the "pseudo distance determination process."

[0090] The pseudorange is the propagation distance of the GNSS signal transmitted from the GNSS satellite S_i and received via the GNSS antenna 3, and is a distance determined from the difference between the time the received GNSS signal (in other words, the GNSS radio wave) is transmitted from the GNSS satellite S_i and the time it is received via the GNSS antenna 3 (in other words, the propagation time of the GNSS signal).

[0091] The pseudorange ρ_i of GNSS satellite S_i is calculated by multiplying the difference between the time when a GNSS signal (GNSS radio wave) is transmitted from GNSS satellite S_i and the time when the GNSS signal (GNSS radio wave) is received via GNSS antenna 3 by the propagation speed of radio waves (specifically, the speed of light).

[0092] The time when the GNSS signal is transmitted from the GNSS satellite S_i is included in the GNSS signal. The time when the GNSS signal is received via the GNSS antenna 3 is determined by the clock function / time information held by the GNSS receiver 4. The clock function / time information held by the GNSS receiver 4 is supplied from, for example, a temperature compensated crystal oscillator (TCXO) mounted on the GNSS receiver 4 as a device common to the multiple GNSS receivers 4A, 4B, 4C. The propagation time of the GNSS signal, which corresponds to the difference between the time when the GNSS signal is transmitted and the time when it is received, may be determined based on the phase shift of the C / A code. The C / A code is a code unique to each GNSS satellite S_i, and functions as information indicating the transmission source.

[0093] The pseudo-distance determination unit 52 determines, for each GNSS satellite S_i, whether or not the absolute value of the difference between the pseudo-distance ρ_i of the GNSS satellite S_i and the pseudo-distance ρr of a predetermined reference satellite Sr is greater than a predetermined pseudo-distance difference threshold. As the reference satellite Sr, for example, the satellite with the largest satellite elevation angle is selected from among the multiple GNSS satellites S_i from which the GNSS signal is received by the GNSS receiver 4 at the time of execution of the corresponding (or most recent) abnormality detection calculation process.

[0094] The pseudorange difference threshold is not limited to a specific value, and is appropriately set to an appropriate value, for example, taking into consideration the maximum value expected as the difference in pseudorange between GNSS satellites when the orbits of the GNSS satellites are assumed. The pseudorange difference threshold may be set to any value within a range of, for example, about 1 to 2 km.

[0095] When the absolute value of the difference between the pseudorange ρ_i of the GNSS satellite S_i and the pseudorange ρr of the reference satellite Sr is greater than a pseudorange difference threshold, the pseudorange determination unit 52 determines that the pseudorange of the GNSS satellite S_i is abnormal and classifies the GNSS satellite S_i as having an abnormal pseudorange.

[0096] The pseudodistance determination unit 52 may classify the GNSS satellite S_i as having an abnormal pseudodistance when the absolute value of the difference between the pseudodistance ρ_i of the GNSS satellite S_i and the pseudodistance ρr of the reference satellite Sr is greater than the pseudodistance difference threshold, and also when the signal strength / reception strength of the GNSS signal transmitted from the GNSS satellite S_i is higher than a predetermined threshold.

[0097] Then, the pseudorange determining unit 52 outputs information about the GNSS satellite S_i classified as having an abnormal pseudorange to the positioning unit 6 as satellite information having an abnormal pseudorange.

[0098] Next, the path difference calculation unit 53 receives the GNSS signal for each GNSS satellite S_i output from the GNSS receiver 4, and calculates the difference in the path from the GNSS satellite S_i to each of the GNSS antennas 3A, 3B, 3C using information on the GNSS signal. The process performed by the path difference calculation unit 53 and the path difference determination unit 54 is called the "path difference determination process."

[0099] The path difference calculation unit 53 calculates the path difference (absolute value) from the GNSS satellite S_i to each GNSS antenna 3A, 3B, 3C, which arises for each GNSS satellite S_i due to the multiple GNSS antennas 3A, 3B, 3C being arranged at a predetermined interval from each other, for each GNSS antenna 3A, 3B, 3C, i.e., for each combination of two GNSS antennas 3.

[0100] Fig. 3 is a diagram for explaining the path difference. The path difference is actually calculated three-dimensionally, but Fig. 3 explains it in two dimensions to explain the principle of the path difference. In the example shown in Fig. 3, the difference between the path to the GNSS antenna 3A and the path to the GNSS antenna 3B (i.e., the path difference between the GNSS antenna 3A and the GNSS antenna 3B) for each of the GNSS satellites S_1 and S_2 will be explained.

[0101] The difference C_1AB between the path from GNSS satellite S_1 to GNSS antenna 3A and the path to GNSS antenna 3B is expressed as the following formula 1, and the difference C_2AB between the path from GNSS satellite S_2 to GNSS antenna 3A and the path to GNSS antenna 3B is expressed as the following formula 2 (see Figure 3(A)). (Math 1) C_1AB = L_AB×cos(θ_1) (Math 2) C_2AB = L_AB×cos(θ_2) Here, L_AB: Dimension of baseline AB between GNSS antenna 3A and GNSS antenna 3B θ_1: Elevation angle of GNSS satellite S_1 θ_2: Elevation angle of GNSS satellite S_2

[0102] The difference C_1AB between the path from the GNSS satellite S_1 to the GNSS antenna 3A and the path to the GNSS antenna 3B, expressed as the above formula 1, is calculated according to the following formula 3. Moreover, the difference C_2AB between the path from the GNSS satellite S_2 to the GNSS antenna 3A and the path to the GNSS antenna 3B, expressed as the above formula 2, is calculated according to the following formula 4. (Math 3) C_1AB = λ_1×(N_1+P_1AB) (Math. 4) C_2AB = λ_2×(N_2+P_2AB) Here, λ_1: The wavelength of the GNSS radio wave carrier of GNSS satellite S_1 λ_2: The wavelength of the GNSS radio wave carrier of GNSS satellite S_2 N_1: Integer bias (one or more cycles) of the GNSS signal from GNSS satellite S_1 N_2: Integer bias (one or more cycles) of the GNSS signal from GNSS satellite S_2 P_1AB: Single difference between antennas of GNSS radio waves from GNSS satellite S_1 (less than a cycle) P_2AB: Single difference between antennas of GNSS radio waves from GNSS satellite S_2 (less than a cycle)

[0103] The inter-antenna single difference P_iXY for GNSS satellite S_i (where X, Y are antenna symbols for distinguishing and identifying multiple GNSS antennas 3 from each other, and X≠Y; same below) is the difference between the carrier phase integrated values ​​of one GNSS satellite S_i for two GNSS antennas 3 (in the example shown in Figure 3, GNSS antenna 3A and GNSS antenna 3B).

[0104] The path difference calculation unit 53 calculates the difference C_iXY between the path from the GNSS satellite S_i to the GNSS antenna X and the path to the GNSS antenna Y for each GNSS satellite S_i and each combination of two GNSS antennas 3 .

[0105] Next, the path difference determination unit 54 determines whether the path difference C_iXY for each GNSS satellite S_i and each combination of two GNSS antennas 3 calculated by the path difference calculation unit 53 is normal or not.

[0106] 3, GNSS satellite S_1 and GNSS satellite S_2 are usually located at different spatial positions, so that the elevation angles θ_1 and θ_2 of the satellites as viewed from the GNSS compass 1 (specifically, the GNSS antenna 3) are different from each other. And, because the elevation angle θ_1 of the GNSS satellite S_1 and the elevation angle θ_2 of the GNSS satellite S_2 are different from each other, the path difference C_1AB for the GNSS satellite S_1 and the path difference C_2AB for the GNSS satellite S_2 are different from each other (see FIG. 3(A) and the above formulas 1 and 2).

[0107] In contrast, when GNSS satellite S_1 and GNSS satellite S_2 are both present in the same spatial position, the elevation angles θ_1 and θ_2 of the satellites as viewed from the GNSS compass 1 (specifically, the GNSS antenna 3) are the same (see FIG. 3B). When the elevation angles θ_1 and θ_2 of the GNSS satellite S_1 and S_2 are the same, the path difference C_1AB for the GNSS satellite S_1 and the path difference C_2AB for the GNSS satellite S_2 are the same (see Equations 1 and 2 above).

[0108] A case in which 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 may be, for example, a case in which a signal including the positioning information and orbit information of multiple GNSS satellites is transmitted from a single transmitting antenna, in other words, a case in which multiple GNSS signals are transmitted from a single transmitting antenna (in other words, the same location; including an antenna station installed on the ground) while making it appear that GNSS signals (in other words, GNSS radio waves) are transmitted from multiple GNSS satellites, that is, a case in which multiple false GNSS signals are transmitted from a single transmitting antenna / same location. In this regard, the "GNSS signals transmitted from multiple GNSS satellites S_i" in this invention includes signals transmitted from a single transmitting antenna / same location while making it appear that GNSS signals are transmitted from multiple GNSS satellites S_i.

[0109] Therefore, the path difference determination unit 54 compares the difference (path difference index) between the path differences (absolute values) C_iXY for multiple GNSS satellites S_i with a predetermined path difference threshold (hereinafter referred to as the first path difference threshold), and performs a process (path difference determination process) at a predetermined period to determine whether the arrival direction of the GNSS signal is normal or not based on the comparison result.

[0110] More specifically, the path difference determination unit 54 calculates the difference (path difference index) between the maximum and minimum values ​​of the path differences (absolute values) C_iXY for the multiple GNSS satellites S_i for each space between two GNSS antennas 3, that is, for each combination of two GNSS antennas 3, and when the calculated path difference index is less than or equal to the first path difference threshold, it classifies the multiple GNSS satellites S_i as having an abnormal direction of arrival of the GNSS signal.

[0111] In addition, for satellites whose arrival direction of the GNSS signal was determined to be abnormal in the path difference determination process executed in the immediately preceding cycle (i.e., satellites classified as having a path difference), the path difference determination unit 54 executes the path difference determination process for the next cycle using a second path difference threshold value that is set to make it easier to determine that the arrival direction is abnormal than the first path difference threshold value.

[0112] Here, the second path difference threshold set so that the arrival direction is more likely to be determined to be abnormal than the first path difference threshold is a threshold having a value greater than the first path difference threshold, and the relationship between the first path difference threshold and the second path difference threshold is "first path difference threshold<second path difference threshold." According to this, even if minute variations or offsets occur in the path difference due to influences such as insufficient time synchronization between receivers, occurrence of multipath or noise in the GNSS signal, or differences in the Doppler frequency of the GNSS signal for each satellite due to differences in the orbital direction of each satellite, by performing the path difference determination process using the second path difference threshold set so that the arrival direction is more likely to be determined to be abnormal, it is possible to prevent a GNSS signal that should actually be determined to be abnormal from being erroneously determined to be normal.

[0113] The path difference threshold is not limited to a specific value, and is appropriately set to an appropriate value, taking into consideration errors assumed to occur due to mechanical errors, etc., even if multiple GNSS signals are actually transmitted from a single transmitting antenna / the same point. The second path difference threshold is set to a value larger than the first path difference threshold by identifying minute variations and offsets occurring in the path difference based on the time synchronization accuracy of the GNSS receivers 4A, 4B, 4C, the frequency and amount of multipath or noise occurrence, changes in the Doppler frequency of the GNSS signal, individual differences between GNSS compasses 1, etc., and is appropriately set to a value larger than the first path difference threshold so as not to be affected by these.

[0114] Here, the operation of the above-mentioned path difference determination process will be described with reference to the flowchart shown in Fig. 4. The path difference determination unit 54 receives the path difference C_iXY between the GNSS antenna XY of the GNSS satellite S_i for each combination of two GNSS antennas out of the three GNSS antennas 3A, 3B, 3C (in other words, for each baseline AB, BC, AC) output from the path difference calculation unit 53 at the time of the process. The path difference determination unit 54 finds the difference between the maximum and minimum values ​​(path difference index) of the path differences C_iXY between the GNSS antennas XY of the input GNSS satellite S_i, and performs the following process.

[0115] The path difference determination unit 54 checks whether or not the two GNSS satellites used in calculating the path difference index are GNSS satellites classified as having a path difference in the path difference determination process of the immediately preceding cycle (step S1).

[0116] If the path difference determination unit 54 determines that the GNSS satellites are not classified as having a path difference in step S1 (NO in step S1), it determines whether the path difference index is equal to or smaller than a first path difference threshold (step S2). If the path difference index is equal to or smaller than the first path difference threshold (YES in step S2), it classifies the two GNSS satellites S_i as having an abnormal direction of arrival of the GNSS signal (step S3).

[0117] In step S1 of the next cycle, the path difference determination unit 54 checks whether the GNSS satellite used to calculate the path difference index is a GNSS satellite classified as a path difference index in the determination of the immediately preceding cycle, and if it is confirmed that the GNSS satellite is classified as a path difference index (YES in step S1), it checks whether the path difference index is equal to or smaller than the second path difference threshold (step S4). If the path difference index is equal to or smaller than the second path difference threshold (YES in step S4), it classifies the two GNSS satellites S_i as having an abnormal GNSS signal arrival direction (step S3).

[0118] Furthermore, when it is determined in step S4 that the path difference index is greater than the second path difference threshold (NO in step S4), the two GNSS satellites S_i are classified as having normal path differences, assuming that the arrival direction of the GNSS signals from those two GNSS satellites S_i is normal (step S5).

[0119] For the two GNSS satellites S_i classified as having normal path differences in step S5, it is determined whether or not the path difference indicator is equal to or smaller than the first path difference threshold in the path difference determination process in the next cycle (steps S1, S2).

[0120] In this way, by appropriately switching between the first path difference threshold and the second path difference threshold to perform the path difference determination process, it is possible to suppress erroneous determinations caused by minute variations and offsets in the path difference and to accurately detect abnormal GNSS signals.

[0121] A lower limit of the number of satellites may be set when determining that the direction of arrival of the GNSS signal is abnormal for a plurality of GNSS satellites S_i. For example, when the difference between the maximum and minimum values ​​of the path differences C_iXY for two GNSS satellites S_i is equal to or less than the path difference threshold, the two GNSS satellites S_i may not be classified as path difference, whereas when the difference between the maximum and minimum values ​​of the path differences C_iXY for three or more GNSS satellites S_i is equal to or less than the path difference threshold, the three or more GNSS satellites S_i may be classified as path difference. In this case, the lower limit of the number of satellites is not limited to a specific value, but may be set to any value within a range of, for example, about 3 to 5.

[0122] The multiple GNSS satellites S_i used in determining the path difference anomaly may all belong to the same type of satellite system, and the path difference anomaly may be determined for each type of satellite system to which the satellite belongs, i.e., GPS, GLONASS, BDS, etc. For example, when the difference between the maximum and minimum values ​​of the path differences for two GPS satellites is equal to or less than the path difference threshold, the two GPS satellites may not be classified as path difference anomalies, whereas when the difference between the maximum and minimum values ​​of the path differences for three or more GPS satellites is equal to or less than the path difference threshold, the three or more GPS satellites may be classified as path difference anomalies. In this case, the lower limit of the number of satellites is not limited to a specific value, but may be set to any value within a range of, for example, about 3 to 5.

[0123] Here, when multiple GNSS satellites S_i are present at different spatial positions, the inter-antenna single differences P_iXY for the multiple GNSS satellites S_i are usually different from each other, whereas when multiple GNSS signals are transmitted from a single transmitting antenna / the same point, the inter-antenna single differences P_iXY for the multiple GNSS satellites S_i are the same. Therefore, in the process of determining the path 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 formulas 3 and 4).

[0124] It is also conceivable that the antenna single differences P_1AB and P_2AB for the two GNSS satellites S_1 and S_2 happen to be the same even though the GNSS satellites S_1 and S_2 are located at different spatial positions and the path difference C_1AB for the GNSS satellite S_1 and the path difference C_2AB for the GNSS satellite S_2 are actually different. However, since the GNSS satellites S_1 and S_2 are moving, the above state does not continue for a long time (for example, more than a few seconds). In addition, since the baseline direction is different for each GNSS antenna 3, for example, even if the antenna single differences P_1AB and P_2AB for the two GNSS satellites S_1 and S_2 happen to be the same in the combination of the GNSS antenna 3A and the GNSS antenna 3B, the antenna single differences P_1AB and P_2AC for the two GNSS satellites S_1 and S_2 do not become the same in the combination of the GNSS antenna 3A and the GNSS antenna 3C.

[0125] When verifying the inter-antenna single differences P_iXY for multiple GNSS satellites S_i, the path difference determination unit 54 compares the difference (path difference index) between the inter-antenna single differences (absolute values) P_iXY for the multiple GNSS satellites S_i with a predetermined path difference threshold (hereinafter referred to as the first path difference threshold), and performs a process (path difference determination process) at a predetermined period to determine whether the arrival direction of the GNSS signal is normal or not based on the comparison result.

[0126] More specifically, the path difference determination unit 54 calculates the difference (path difference index) between the maximum and minimum values ​​of the inter-antenna single differences (absolute values) P_iXY for the multiple GNSS satellites S_i for each space between GNSS antennas 3, that is, for each combination of two GNSS antennas 3, and when the calculated path difference index is less than or equal to the first path difference threshold, it classifies the multiple GNSS satellites S_i as having an abnormal direction of arrival of the GNSS signal.

[0127] In addition, for satellites whose arrival direction of the GNSS signal was determined to be abnormal in the path difference determination process executed in the immediately preceding cycle (i.e., satellites classified as having a path difference), the path difference determination unit 54 executes the path difference determination process for the next cycle using a second path difference threshold value that is set to make it easier to determine that the arrival direction is abnormal than the first path difference threshold value.

[0128] Here, the second path difference threshold is set so that the arrival direction is more likely to be determined to be abnormal than the first path difference threshold, and is a threshold having a value greater than the first path difference threshold, and the relationship between the first path difference threshold and the second path difference threshold is "first path difference threshold<second path difference threshold."

[0129] In this case, the first path difference threshold is also not limited to a specific value, and is appropriately set to an appropriate value, taking into consideration errors assumed to occur due to mechanical errors, etc., even if multiple GNSS signals are actually transmitted from a single transmitting antenna / the same point. The second path difference threshold is appropriately set to a value larger than the first path difference threshold by identifying minute variations and offsets occurring in the path difference based on the time synchronization accuracy of the GNSS receivers 4A, 4B, 4C, the frequency and amount of multipath or noise occurrence, changes in the Doppler frequency of the GNSS signal, individual differences between GNSS compasses 1, etc., and not being affected by these.

[0130] In addition, the processing procedure when using the difference between the inter-antenna single differences (absolute values) P_iXY for multiple GNSS satellites S_i as the path difference threshold and performing the path difference determination process is similar to the flowchart shown in Figure 4, so a detailed explanation is omitted.

[0131] In this way, by appropriately switching between the first path difference threshold and the second path difference threshold to perform the path difference determination process, it is possible to suppress erroneous determinations caused by minute variations or offsets in the path difference.

[0132] As described above, the path difference C_iXY and the single difference between antennas P_iXY for GNSS satellite S_i, which represent the path difference from GNSS satellite S_i to each GNSS antenna 3A, 3B, and 3C and are used in the process of determining the path difference for each GNSS satellite S_i, are called the "path difference index."

[0133] Then, the path difference determination unit 54 outputs information about the GNSS satellite S_i classified as having a path difference abnormality (in other words, an abnormality in the direction of arrival of the GNSS signal) to the positioning unit 6 as satellite information about a path difference abnormality.

[0134] In each of the above judgment processes, a GNSS satellite S_i that is classified as having an abnormal transmission time, a GNSS satellite S_i that is classified as having an abnormal pseudorange, and a GNSS satellite S_i that is classified as having an abnormal path difference are excluded from the group of satellites used in the calculation process of 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 positioning information by the positioning unit 6.

[0135] It may be set as to which of the abnormalities, transmission time abnormality, pseudo distance abnormality, and course difference abnormality, GNSS satellites S_i classified as such should be excluded for each item of positioning information calculated by the positioning unit 6 (specifically, the position, orientation, and attitude of the aircraft itself, etc.). For example, as an example for the purpose of explanation only, when calculating the position of the aircraft itself, GNSS satellites S_i classified as such should be excluded, whereas GNSS satellites S_i classified as such should be excluded as such should be excluded as such should be excluded as such should be excluded as such should be excluded, and when calculating the orientation and attitude of the aircraft itself, GNSS satellites S_i classified as such should be excluded as such should be excluded as such should be excluded.

[0136] A GNSS satellite S_i that is classified as having (any of) a transmission time abnormality, a pseudorange abnormality, and / or a path difference abnormality (in other words, a GNSS satellite S_i that is determined to be abnormal) may be configured to maintain the state classified as abnormal (in other words, the abnormal state) for a predetermined abnormality retention time (and the determination process is not performed while the state classified as abnormal is maintained).

[0137] The abnormality holding time is not limited to a specific time length, and is appropriately set to an appropriate time length, taking into consideration, for example, avoiding a situation in which the number of normal GNSS satellites S_i (in other words, used in the calculation process of positioning information by the positioning unit 6) is extremely reduced and ensuring the possibility of capturing normal GNSS satellites S_i as the mobile body on which the GNSS compass 1 is mounted moves. The abnormality holding time may be set to zero. In this case, the process of determining the transmission time, the process of determining the pseudorange, and the process of determining the path difference for each GNSS satellite S_i are performed every time the abnormality detection calculation process is executed.

[0138] The abnormality hold time may be set for each type of abnormality. That is, the abnormality hold time may be set to the same time length for cases classified as transmission time abnormality, pseudo distance abnormality, and path difference abnormality, or may be set to different time lengths.

[0139] When a state classified as abnormal is maintained for the abnormality holding time, the GNSS satellite S_i classified as (any of) transmission time abnormality, pseudo distance abnormality, and path difference abnormality may be immediately removed from the abnormality classification after the abnormality holding time has elapsed and made into a satellite that is a target for receiving the GNSS signal (and a target satellite for each of the above-mentioned determination processes). Alternatively, when it is determined that the state is not classified as abnormal (the arrival direction of the GNSS signal is normal) during the abnormality holding time, the satellite may be immediately removed from the abnormality classification and made into a satellite that is a target for receiving the GNSS signal (and a target satellite for each of the above-mentioned determination processes). Alternatively, when a predetermined time has elapsed during the abnormality holding time in which the arrival direction of the GNSS signal is determined to be normal (i.e., when the normality is maintained for a predetermined duration), the satellite may be removed from the abnormality classification and made into a satellite that is a target for receiving the GNSS signal (and a target satellite for each of the above-mentioned determination processes).

[0140] The normal continuation time is not limited to a specific length of time, but is set to an appropriate length of time, for example, while taking into consideration a situation in which the number of normal GNSS satellites S_i (in other words, those used in the calculation processing of positioning information by the positioning unit 6) is drastically reduced.

[0141] The normal duration may be set for each type of anomaly, i.e., the normal duration may be set to the same time length for cases classified as transmission time anomaly, pseudo range anomaly, and path difference anomaly, or may be set to different time lengths.

[0142] In a state where a GNSS satellite S_i is classified as a transmission time anomaly, a pseudo distance anomaly, or a path difference anomaly (any one of them), if the absolute value of the difference between the transmission time of the GNSS signal contained in the GNSS signal transmitted from the GNSS satellite S_i and the reference transmission time becomes less than a time difference threshold, it may be determined that the anomaly for the GNSS satellite S_i has been resolved, and the GNSS satellite S_i may be removed from the anomaly classification (in other words, the anomaly state of the GNSS satellite S_i may be released). In addition, in a state where multiple GNSS satellites S_i are classified as path differences, if the difference between the path differences (absolute values) C_iXY for the multiple GNSS satellites S_i becomes greater than a path difference threshold, it may be determined that the path difference anomaly for the multiple GNSS satellites S_i has been resolved, and the multiple GNSS satellites S_i may be removed from the path difference anomaly classification (in other words, the anomaly state of the multiple GNSS satellites S_i may be released).

[0143] An output device (not shown) including, for example, a monitor and a speaker may be provided in association with the GNSS compass 1, and the occurrence of (any of) a transmission time anomaly, a pseudo-distance anomaly, and a path difference anomaly may be notified to a user by displaying an alarm screen on the monitor of the output device or issuing an alarm from the speaker of the output device. Also, the occurrence of (any of) a transmission time anomaly, a pseudo-distance anomaly, and a path difference anomaly may be notified to other devices (for example, radar, inertial navigation system) that use the GNSS signal.

[0144] When the number of GNSS satellites S_i classified as being abnormal in transmission time, abnormal in pseudo distance, or abnormal in path difference (among any of them) is large and the number of GNSS satellites S_i used in the calculation process of positioning information by the positioning unit 6 is reduced, the number of reception channels allocated to satellites of a different GNSS type (i.e., different frequency band) from the GNSS satellites S_i classified as abnormal may be increased. In other words, the number of reception channels allocated to satellites of a different frequency band from the GNSS satellites S_i classified as abnormal may be changed according to the number of GNSS satellites S_i classified as abnormal.

[0145] For example, if the specifications of the GNSS receiver unit 4 allow multiple types of GNSS satellite systems (e.g., GPS, GLONASS, BDS) to be shared and assigned to the same receiving channel and there is a limit to the number of satellites that can be assigned, then when there is no GNSS satellite S_i classified as having a transmission time anomaly, pseudo distance anomaly, or path difference anomaly (any of the above), many GNSS satellites S_i may be assigned that prioritize the accuracy of the calculation of positioning information by the positioning unit 6, and on the other hand, when there are many GNSS satellites S_i classified as having a transmission time anomaly, pseudo distance anomaly, or path difference anomaly (any of the above), many GNSS satellites S_i may be assigned that can prioritize the continuation of the calculation of positioning information by the positioning unit 6.

[0146] When the number of GNSS satellites S_i classified as transmission time anomaly, pseudo distance anomaly, and / or path difference anomaly is large and the number of GNSS satellites S_i used in the positioning information calculation process by the positioning unit 6 is small, and thus a state in which the positioning unit 6 is unable to perform the positioning information calculation process continues for a predetermined time or more, as a fail-safe, the GNSS satellites S_i classified as abnormal may be removed from the abnormal classification and made into satellites from which GNSS signals are received (and which are the targets of the above-mentioned determination processes). In this case, information (e.g., a flag) indicating that the GNSS satellites S_i are classified as transmission time anomaly, pseudo distance anomaly, and / or path difference anomaly may be added to the GNSS signal output from the GNSS receiver 4.

[0147] As described above, according to the method for detecting abnormalities in a received signal and the GNSS compass 1 of this embodiment, transmission time abnormalities and pseudo distance abnormalities are detected, as well as path difference abnormalities (in other words, abnormalities in the direction of arrival of the GNSS signal). Therefore, path difference abnormalities can be detected more reliably as GNSS signal abnormalities are processed on GNSS signals transmitted from multiple GNSS satellites S_i, but detection may be delayed because the processing is performed on GNSS signals transmitted from multiple GNSS satellites S_i. On the other hand, transmission time abnormalities and pseudo distance abnormalities are processed independently for each GNSS satellite S_i, so detection can be performed immediately. By combining the processing for determining the transmission time and pseudo distance with the processing for determining the path difference, abnormalities in the received signal in the GNSS can be detected in a mutually complementary manner, thereby improving the reliability of the processing for detecting abnormalities in the received signal in the GNSS.

[0148] (Embodiment 2) Next, a method for detecting an abnormality in a received signal and a GNSS compass 1 according to a second embodiment of the present invention will be described. Note that the same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

[0149] In the first embodiment, for a satellite whose arrival direction of a GNSS signal is determined to be abnormal in the path difference determination process executed in the immediately preceding cycle, the path difference determination process for the next cycle is executed using a second path difference threshold set so that the arrival direction is more likely to be determined to be abnormal than the first path difference threshold. However, interference such as transmitting false GNSS signals is often performed not on an individual satellite basis but on a satellite system (e.g., GPS, GLONASS, BDS) basis. Therefore, there is a risk that an abnormality will be missed if only individual measures are taken against satellites determined to be suspected of being false satellites in the path difference determination process.

[0150] In order to solve the above problem, in the method for detecting an abnormality in a received signal and the GNSS compass 1 according to the present embodiment, when determining a path difference abnormality, the path difference determination process for the next period is performed using a second path difference threshold set so that the arrival direction is more likely to be determined to be abnormal than the first path difference threshold, not only for a satellite determined to have an abnormal arrival direction of a GNSS signal in the path difference determination process performed in the previous period (i.e., a satellite classified as having a path difference abnormality), but also for satellites belonging to the same type of satellite system as the satellite. Specifically, for example, if a GPS satellite was classified as having a path difference abnormality in the determination in the previous period, the path difference determination process for the next period is performed using the second path difference threshold for all GPS satellites. In this respect, the present embodiment differs from the first embodiment.

[0151] FIG. 5 is a flowchart showing a procedure of a process of determining a trajectory difference performed by switching between a first trajectory difference threshold and a second trajectory difference threshold in the trajectory difference determination unit 54 of the GNSS compass 1 according to this embodiment.

[0152] The path difference determination unit 54 checks whether the two GNSS satellites used to calculate the path difference index belong to the same type of satellite system as the GNSS satellite classified as having a path difference in the path difference determination process of the previous cycle (step S1a).

[0153] If the path difference determination unit 54 determines that the GNSS satellites do not belong to the same type of satellite system as the GNSS satellites classified as path difference-insensitive in step S1a (NO in step S1a), it determines whether the path difference index is equal to or smaller than a first path difference threshold (step S2). If the path difference index is equal to or smaller than the first path difference threshold (YES in step S2), it classifies the two GNSS satellites S_i as path difference-insensitive, determining that the arrival direction of the GNSS signal from the two GNSS satellites S_i is abnormal (step S3).

[0154] In step S1a of the next cycle, the path difference determination unit 54 checks whether the GNSS satellite used to calculate the path difference index belongs to the same type of satellite system as the GNSS satellite classified as a path difference error in the determination of the previous cycle, and if it is confirmed that the GNSS satellite belongs to the same type of satellite system as the GNSS satellite classified as a path difference error (YES in step S1a), it determines whether the path difference index is equal to or smaller than the second path difference threshold (step S4). If the path difference index is equal to or smaller than the second path difference threshold (YES in step S4), it classifies the two GNSS satellites S_i as having an abnormal GNSS signal arrival direction (step S3).

[0155] Furthermore, when it is determined in step S4 that the path difference index is greater than the second path difference threshold (NO in step S4), the two GNSS satellites S_i are classified as having normal path differences, assuming that the arrival direction of the GNSS signals from those two GNSS satellites S_i is normal (step S5).

[0156] For the two GNSS satellites S_i classified as having a normal path difference in step S5, if a GNSS satellite belonging to the same type of satellite system as the GNSS satellite S_i is not classified as having a path difference in the immediately preceding cycle, it is determined whether or not the path difference index is equal to or less than the first path difference threshold in the path difference determination process for the next cycle (steps S1a, S2). On the other hand, for the two GNSS satellites S_i classified as having a normal path difference in step S5, if a GNSS satellite belonging to the same type of satellite system as the GNSS satellite S_i is classified as having a path difference in the immediately preceding cycle, it is determined whether or not the path difference index is equal to or less than the second path difference threshold in the path difference determination process for the next cycle (step S4).

[0157] As described above, according to the method for detecting abnormalities in a received signal and the GNSS compass 1 of this embodiment, for satellites belonging to the same type of satellite system as a satellite for which the arrival direction of a GNSS signal was determined to be abnormal in the determination performed in the previous cycle, the determination in the next cycle is performed using the 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.Therefore, even if interference is occurring with a specific type of satellite system, such as by transmitting false GNSS signals, it is possible to detect abnormalities in the received signal in that satellite system without missing anything, without increasing the risk of erroneous determination.

[0158] (Embodiment 3) Next, a method for detecting an abnormality in a received signal and a GNSS compass 1 according to a third embodiment of the present invention will be described. Note that the same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

[0159] In the second embodiment, the path difference determination process for the next period is performed using a second path difference threshold value set so that the arrival direction of a satellite belonging to the same type of satellite system as a satellite determined to have an abnormal GNSS signal arrival direction in the path difference determination process executed in the immediately preceding period is determined to be abnormal, compared to the first path difference threshold value. However, when interference such as transmitting a false GNSS signal is performed on a certain type of GNSS satellite system (e.g., GPS), it is highly likely that interference is also performed on other types of satellite systems (e.g., GLONASS, Galileo, etc.). Therefore, there is a risk of anomaly detection being missed if only measures are taken against satellites belonging to the same type of satellite system as a satellite determined to be suspected of being a false satellite in the path difference determination process.

[0160] In order to solve the above problem, in the method for detecting an abnormality in a received signal and the GNSS compass 1 according to the present embodiment, when determining a path difference abnormality, if it is determined in the determination performed in the immediately preceding cycle that the arrival direction of the GNSS signal of at least one satellite is not normal, the determination process of the path difference in the next cycle is performed using the second path difference threshold value set so that the arrival direction is more likely to be determined to be abnormal than the first path difference threshold value for all satellites. Specifically, for example, if a GPS satellite was classified as having a path difference in the determination in the immediately preceding cycle, the determination process of the path difference in the next cycle is performed using the second path difference threshold value for all satellites, such as all GLONASS satellites, all Galileo satellites, and all BDS satellites, as well as all GPS satellites. In this respect, the present embodiment differs from the first and second embodiments.

[0161] FIG. 6 is a flowchart showing a procedure of a process of determining a trajectory difference performed by switching between the first trajectory difference threshold and the second trajectory difference threshold in the trajectory difference determining unit 54 of the GNSS compass 1 according to this embodiment.

[0162] The path difference determination unit 54 checks whether or not there is a GNSS satellite that has been classified as a path difference in the path difference determination process of the immediately preceding cycle (step S1b).

[0163] If it is confirmed that there is no GNSS satellite classified as having a path difference in step S1b (NO in step S1b), the path difference determination unit 54 determines whether the path difference index of the two GNSS satellites used in calculating the path difference index is equal to or smaller than a first path difference threshold (step S2). If the path difference index is equal to or smaller than the first path difference threshold (YES in step S2), it classifies the two GNSS satellites S_i as having an abnormal direction of arrival of the GNSS signal (step S3).

[0164] In step S1b of the next cycle, the path difference determination unit 54 checks whether or not there is a GNSS satellite that was classified as a path difference error in the determination of the immediately preceding cycle, and if it is confirmed that there is a GNSS satellite that was classified as a path difference error (YES in step S1b), it determines whether or not the path difference index of the two GNSS satellites used in calculating the path difference index is equal to or less than the second path difference threshold (step S4). If the path difference index is equal to or less than the second path difference threshold (YES in step S4), it classifies the two GNSS satellites S_i as having an abnormal GNSS signal arrival direction (step S3).

[0165] Furthermore, when it is determined in step S4 that the path difference index is greater than the second path difference threshold (NO in step S4), the two GNSS satellites S_i are classified as having normal path differences, assuming that the arrival direction of the GNSS signals from those two GNSS satellites S_i is normal (step S5).

[0166] For the two GNSS satellites S_i classified as having normal path differences in step S5, if there is no GNSS satellite S_i classified as having normal path differences in the immediately preceding cycle, it is determined whether or not the path difference indicator is equal to or less than the first path difference threshold in the path difference determination process for the next cycle (steps S1b, S2). On the other hand, for the two GNSS satellites S_i classified as having normal path differences in step S5, if there is a GNSS satellite S_i classified as having normal path differences in the immediately preceding cycle, it is determined whether or not the path difference indicator is equal to or less than the second path difference threshold in the path difference determination process for the next cycle (step S4).

[0167] As described above, according to the method for detecting abnormalities in a received signal and the GNSS compass 1 of this embodiment, if the arrival direction of the GNSS signal for at least one satellite is determined to be abnormal in the determination performed in the previous cycle, 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 abnormal than a predetermined path difference threshold.Therefore, even if interference is occurring, such as transmitting false GNSS signals to multiple types of GNSS satellite systems, it is possible to detect abnormal GNSS signals without increasing the risk of erroneous determination.

[0168] (Embodiment 4) Next, a method for detecting an abnormality in a received signal and a GNSS compass 1 according to a fourth embodiment of the present invention will be described. Note that the same components as those in the first embodiment are designated by the same reference numerals and detailed descriptions thereof will be omitted.

[0169] In the first embodiment, when a GNSS signal from a GNSS satellite is determined to be abnormal, the GNSS signal is not used to calculate a position, etc. However, a specific method for calculating a position, etc. when a GNSS signal from a GNSS satellite is determined to be abnormal has not been fully considered.

[0170] Therefore, the method for detecting an abnormality in a received signal and the GNSS compass 1 according to this embodiment aim to make it possible to calculate appropriate position information and time information and provide it to the outside (other devices, services, etc.) when it is determined that a part or all of the GNSS signals from a GNSS satellite are abnormal. In particular, an output information adjustment unit 7 is provided to adjust the position information and time information to be output to the outside (other devices, services, etc.) according to the results of each determination process in the abnormality detection unit 5. In this respect, this embodiment differs from the first embodiment.

[0171] 7 is a functional block diagram showing a schematic configuration of a GNSS compass according to this embodiment. Here, the output information adjustment unit 7 is a device for adjusting the position information and time information to be output to the outside (other devices, services, etc.) according to the detection result of an abnormality in the GNSS signal output from the abnormality detection unit 5. Also, 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.

[0172] FIG. 8 is a flowchart showing the processing procedure in the GNSS compass 1 according to this embodiment, and also showing the procedure of the output information adjustment processing performed mainly in the output information adjustment unit 7.

[0173] 8A is a flowchart showing the procedure of the adjustment process of the position information as the output information. First, the positioning unit 6 calculates its own position based on the GNSS signal for each GNSS satellite S_i output from the GNSS receiving unit 4 at a predetermined period, and outputs it to the output information adjustment unit 7 (step S11a).

[0174] The inertial device 8 calculates position information (attitude angle, speed, position, etc.) using a gyro sensor and an acceleration sensor, and outputs the information to the output information adjustment unit 7 (step S12a).

[0175] Then, when the first determination process performed in the abnormality detection unit 5 outputs a determination result that some or all of the GNSS signals transmitted from the GNSS satellites S_i are not normal (step S13a: Yes), the output information adjustment unit 7 performs a second determination process (step S14a) to determine whether or not it is possible to calculate the position based on only the GNSS signals determined to be normal during the first determination process. Whether or not it is possible to calculate the position based on the GNSS signals (GNSS positioning) depends on the number of GNSS satellites S_i that transmit normal GNSS signals, and generally, it is considered that GNSS positioning is possible if there are about 3 to 4 or more GNSS satellites S_i that transmit normal GNSS signals.

[0176] If it is determined in the second determination process that GNSS positioning is not possible (step S14a: No), the output information adjustment unit 7 outputs, as the position of the aircraft itself, a position estimated by adding the amount of change measured by the inertial device 8 to the most recent (latest) position among positions calculated based only on GNSS signals determined to be normal before the first determination process (step S15a). Here, the amount of change measured by the inertial device 8 specifically means the amount of change in speed from the most recent GNSS positioning when the position could be calculated based only on GNSS signals determined to be normal to the time of the first determination process. In addition, the estimated position is stored in the control unit 2 (RAM) as the most recent position information.

[0177] The process in step S15a will be described with a specific example. It is assumed that GNSS signals are transmitted from multiple GNSS satellites S_i every α seconds, and the first determination process determines that all of the GNSS signals transmitted for the nth time at time t are normal, but the first determination process determines that some or all of the GNSS signals transmitted for the (n+1)th time at time (t+α) are not normal, and the second determination process determines that the position cannot be calculated based only on the GNSS signals determined to be normal among the multiple 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 signal determined to be normal before the first determination process" is the position Gl(n) calculated based on the GNSS signal transmitted from the GNSS satellite S_i for the nth time, 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 for α seconds. Therefore, the output information adjustment unit 7 outputs the position Gl(n)+v(α) estimated by adding the change amount v(α) (the change amount of the speed v for α seconds) to the position Gl(n) as the position of the aircraft (step S15a). Then, this estimated position Gl(n)+v(α) is stored in the control unit 2 (RAM) as the most recent position information.

[0178] However, since the calculation process of the amount of change in the inertial device 8 is an integrating process, errors accumulate over time and the value is no longer accurate. Therefore, when the error in the amount of change output from the inertial device 8 becomes large, the output information adjustment unit 7 exceptionally outputs a message indicating that the position of the aircraft cannot be measured (step S15a).

[0179] On the other hand, when the anomaly detection unit 5 outputs a result of the first determination process that all GNSS signals transmitted from the GNSS satellite S_i are normal (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 the position calculated based only on the GNSS signals determined to be normal in the first determination process as the position of the aircraft (step S16a). Then, at this timing, the position (in the above example, Gl(n)+v(α)) estimated by adding the amount of change measured by the inertial device 8 to the most recent position information stored in the control unit 2 (RAM), that is, the most recent position among the positions calculated based only on the GNSS signals determined to be normal, is calibrated by the position information based on the GNSS signals (step S17a).

[0180] 8B is a flowchart showing the procedure for adjusting the time information as output information. First, the GNSS receiver 4 calculates the time based on the GNSS signal for each GNSS satellite S_i output at a predetermined interval, and outputs the time to the output information adjuster 7 (step S11b).

[0181] Furthermore, the GNSS receiver 4 updates its internal clock using, for example, a temperature compensated crystal oscillator (TCXO) (mounted in the GNSS receiver 4), and outputs the time of the internal clock to the output information adjuster 7 (step S12b).

[0182] Then, if the first determination process performed in the abnormality detection unit 5 outputs a determination result that some or all of the GNSS signals transmitted from the GNSS satellite S_i are not normal (step S13b: Yes), a second determination process is performed to determine whether or not it is possible to calculate the time based only on the GNSS signals determined to be normal in the first determination process (step S14b). Whether or not it is possible to calculate the time based on the GNSS signals depends on the number of GNSS satellites transmitting normal GNSS signals, and generally, it is considered possible to calculate the time based on the GNSS signals if there are about 2 to 4 or more GNSS satellites S_i transmitting normal GNSS signals.

[0183] If it is determined in the second determination process that the time cannot be calculated based on the GNSS signal (step S14b: No), the output information adjustment unit 7 outputs the estimated time as the time of the aircraft by adding the elapsed time measured by the internal clock to the most recent time calculated based only on the GNSS signal determined to be normal before 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 signal determined to be normal to the time when the first determination process was performed. The estimated time is stored in the control unit 2 (RAM) as the most recent time information.

[0184] The process in step S15b will be described with a specific example. It is assumed that GNSS signals are transmitted from multiple GNSS satellites S_i every α seconds, and all GNSS signals transmitted for the nth time at time t are determined to be normal in the first determination process, but some or all of the GNSS signals transmitted for the (n+1)th time at time (t+α) are determined to be abnormal in the first determination process, and it is determined in the second determination process that the time cannot be calculated based only on the GNSS signals determined to be normal among the multiple 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 first determination process" is the time Gt(n) calculated based on the GNSS signal transmitted for the nth time from the GNSS satellite S_i, so the output information adjustment unit 7 outputs the estimated time Gt(n)+α as the time of the aircraft itself by adding the elapsed time (α) measured by the internal clock to the time Gt(n) (step S15b). Then, this estimated time Gt(n)+α is stored in the control unit 2 (RAM) as the most recent time information.

[0185] On the other hand, if the anomaly detection unit 5 outputs a determination result that all GNSS signals transmitted from the GNSS satellite S_i are normal in the first determination process (step S13b: No), and if 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), the output information adjustment unit 7 outputs the time calculated based only on the GNSS signals determined to be normal in the first determination process as the time of its own aircraft (step S16b). Then, at this timing, the time of the internal clock of the GNSS receiver 4 is calibrated to the time based on the GNSS signals (step S17b).

[0186] According to the method for detecting an abnormality in a received signal and the GNSS compass 1 of this embodiment, when it is determined that a part or all of the GNSS signals are abnormal, a determination process is performed as to whether or not the position can be calculated based only on the GNSS signals determined to be normal, and when the position cannot be calculated based only on the GNSS signals determined to be normal, an estimated position is output by adding the amount of change measured by the inertial device 8 to the nearest position among the positions calculated based only on the GNSS signals determined to be normal, so that it is possible to provide appropriate position information to the outside (other devices, services, etc.). In addition, when the position cannot be calculated based only on the GNSS signals determined to be normal, a message indicating that at least the position cannot be measured is output, so that it is possible to reliably prevent erroneous position information based on an abnormal received signal from being used by the outside (other devices, services, etc.).

[0187] In addition, according to the method for detecting abnormalities in a received signal and the GNSS compass 1 of this embodiment, when it is determined that some or all of the GNSS signals are abnormal, a determination process is performed to determine whether the time can be calculated based only on the GNSS signals determined to be normal, and if the time cannot be calculated based only on the GNSS signals determined to be normal, an estimated time is output by adding the elapsed time measured by the internal clock to the most recent time calculated based only on the GNSS signals determined to be normal, making it possible to provide appropriate time information to the outside (other devices, services, etc.).

[0188] (Embodiment 5) Next, a method for detecting an abnormality in a received signal and a GNSS compass 1 according to a fifth embodiment of the present invention will be described. Note that the same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

[0189] The fifth embodiment differs from the fourth embodiment in that, when the position and time cannot be calculated based only on GNSS signals determined to be normal, the output information is adjusted after comparing the difference between the position and time calculated based on GNSS signals including GNSS signals determined to be abnormal and the position and time assumed to be normal.

[0190] FIG. 7 is a functional block diagram showing a schematic configuration of a GNSS compass according to this embodiment, and FIG. 9 is a flowchart showing a processing procedure in the GNSS compass 1 according to this embodiment, and also showing the procedure of output information adjustment processing performed mainly in the output information adjustment unit 7.

[0191] 9A is a flowchart showing the procedure of the adjustment process of the position information as the output information. First, the positioning unit 6 calculates its own position based on the GNSS signal for each GNSS satellite S_i output from the GNSS receiving unit 4 at a predetermined period, and outputs it to the output information adjustment unit 7 (step S11a).

[0192] The inertial device 8 calculates position information (attitude angle, speed, position, etc.) using a gyro sensor and an acceleration sensor, and outputs the information to the output information adjustment unit 7 (step S12a).

[0193] Then, when the first determination process performed in the abnormality detection unit 5 outputs a determination result that some or all of the GNSS signals transmitted from the GNSS satellite S_i are not normal (step S13a: Yes), the output information adjustment unit 7 performs a second determination process to determine whether or not the position can be calculated based only on the GNSS signals determined to be normal during the first determination process (step S14a). When the second determination process determines 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 abnormal with the position estimated by adding the amount of change 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 before the first determination process, and calculates the difference between the two (step S18a). If the difference is equal to or greater than a predetermined threshold (step S18a: Yes), the estimated position is output as the position of the aircraft as a rule, and as an exception, a message is output indicating that the position of the aircraft cannot be measured (step S15a).The estimated position is stored in the control unit 2 (RAM) as the most recent position information.

[0194] The processing in steps S18a and S5a will be described with a specific example. As in the example of the first embodiment, it is assumed that GNSS signals are transmitted from a plurality of GNSS satellites S_i every α seconds, and all of the GNSS signals transmitted for the nth time at time t are determined to be normal in the first determination processing, but some or all of the GNSS signals transmitted for the (n+1)th time at time (t+α) are determined to be abnormal in the first determination processing, and it is determined in the second determination processing 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 positions calculated based only on GNSS signals determined to be normal before the first determination process" is the position Gl(n) calculated based on the GNSS signal transmitted from the GNSS satellite S_i for the nth time, 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) - that is, the change amount v(α) of the speed v during α seconds, so 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 signal determined to be abnormal is Gl(n+1). Therefore, 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 them (step S18a). If the difference is equal to or greater than a predetermined threshold (step S18a: Yes), the output information adjustment unit 7 outputs the estimated position Gl(n)+v(α) as the aircraft's position in principle, and outputs a message indicating that the aircraft's position cannot be measured as an exception (step S15a). The estimated position Gl(n)+v(α) is stored in the control unit 2 (RAM) as the most recent position information.

[0195] Here, the predetermined threshold value is not particularly limited and may be set appropriately, but may be set to, for example, 10 to 100 m.

[0196] On the other hand, when the abnormality detection unit 5 outputs a determination result that the GNSS signal transmitted from the GNSS satellite S_i is normal in the first determination process (step S13a: No), when it is determined that GNSS positioning is possible based only on the GNSS signal 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 aircraft (step S16a). Here, when the difference is less than a 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) is output as the position of the own aircraft, but when the difference is less than the threshold, even if the position calculated based on the GNSS signal including the GNSS signal determined to be abnormal is used externally (such as another aircraft or a service), there is little risk of malfunction or other problems occurring, and therefore it is considered that there is no problem. Then, at this timing, the most recent position information stored in the control unit 2 (RAM), i.e., the most recent position among the positions calculated based only on the GNSS signals determined to be normal, is added to the change amount measured by the inertial device 8 to estimate the position (in the above example, Gl(n)+v(α)), and the estimated position is calibrated using the position information based on the GNSS signals (step S17a).

[0197] 9B is a flowchart showing the procedure for adjusting the time information as output information. First, the GNSS receiver 4 calculates the time based on the GNSS signal for each GNSS satellite S_i output at a predetermined interval, and outputs the time to the output information adjuster 7 (step S11b).

[0198] Furthermore, the GNSS receiver 4 updates its internal clock using, for example, a temperature compensated crystal oscillator (TCXO) (mounted in the GNSS receiver 4), and outputs the time of the internal clock to the output information adjuster 7 (step S12b).

[0199] Then, when the first determination process performed by the abnormality detection unit 5 outputs a determination result that some or all of the GNSS signals transmitted from the GNSS satellite S_i are not normal (step S13b: Yes), the output information adjustment unit 7 performs a second determination process to determine whether or not it is possible to calculate the time based only on the GNSS signals determined to be normal during 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 abnormal with 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 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 aircraft (step S15b). The estimated time is stored in the control unit 2 (RAM) as the most recent time information.

[0200] The processing in steps S18b and S5b will be described with a specific example. As in the example of the first embodiment, assume that GNSS signals are transmitted from multiple GNSS satellites S_i every α seconds, and that all GNSS signals transmitted for the nth time at time t are determined to be normal in the first determination processing, but that some or all of the GNSS signals transmitted for the (n+1)th time at time (t+α) are determined to be abnormal in the first determination processing, and that it is determined in the second determination processing that the time cannot be calculated based only on the GNSS signals determined to be normal among the multiple GNSS signals transmitted for the (n+1)th time at time (t+α). In this case, the "most recent (latest) time among the times calculated based only on the GNSS signals determined to be normal before the first determination processing" is the time Gt(n) calculated based on the GNSS signal transmitted for the nth time from the GNSS satellite S_i, and 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 signal determined to be abnormal is Gt(n+1). Therefore, 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 them (step S18b). If 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 aircraft (step S15b). This estimated time Gt(n)+α is stored in the control unit 2 (RAM) as the most recent time information.

[0201] Here, the specified threshold value is not particularly limited and may be set as appropriate; for example, when the GNSS compass 1 is powered on (i.e., when the time calibration of step S17b is being performed), it may be set to approximately 2 to 10 seconds, and when the GNSS compass 1 is not powered on (i.e., when the time calibration of step S17b is not being performed), it may be set to approximately 30 to 200 seconds.

[0202] On the other hand, when the abnormality detection unit 5 outputs a result of the first determination process that the GNSS signal transmitted from the GNSS satellite S_i is normal (step S13b: No), when it is determined that the time can be calculated based only on the GNSS signal 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 aircraft (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)) is output as the time of the own aircraft, but when the difference is less than the threshold, there is little risk of malfunction or other problems occurring even if the time calculated based on the GNSS signal including the GNSS signal determined to be abnormal is used externally (such as another aircraft or a service), so it is considered that there is no problem. At this timing, the time of the internal clock of the GNSS receiver 4 is calibrated with the time based on the GNSS signal (step S17b).

[0203] According to the method for detecting abnormalities in a received signal and the GNSS compass 1 of this embodiment, when a position cannot be calculated based only on GNSS signals determined to be normal, a position calculated based on GNSS signals including GNSS signals determined to be abnormal is compared with a position estimated by adding the amount of change measured by the inertial device 8 to the closest position among positions calculated based only on GNSS signals determined to be normal, and the output information is adjusted based on whether or not the difference is greater than or equal to a predetermined threshold, making it possible to provide more appropriate and useful position information to the outside (other devices, services, etc.).

[0204] In addition, according to the method for detecting abnormalities in a received signal and the GNSS compass 1 of this embodiment, when the time cannot be calculated 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 presumed to be normal, i.e., the most recent time calculated based only on GNSS signals determined to be normal, and the time presumed by adding the elapsed time measured by the internal clock, and the output information is adjusted based on whether or not the difference is greater than or equal to a predetermined threshold, making it possible to output more appropriate and valid time information to the outside (other devices, services, etc.).

[0205] (Embodiment 6) Next, a method for detecting an abnormality in a received signal and a GNSS compass 1 according to a sixth embodiment of the present invention will be described. Note that the same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

[0206] In the first embodiment, as a detection condition for an abnormality in the received signal, it is required that all or many of the GNSS receivers 4A, 4B, and 4C detect an abnormality in the received signal. However, when the reception of the GNSS signal by the GNSS receivers 4A, 4B, and 4C is unstable, the detection of the abnormality may be delayed or may not be performed. For example, when the GNSS receivers 4A, 4B, and 4C are far from the source of the false GNSS signal and receive a weak signal (FIG. 11A), or when the false GNSS signal and the true GNSS signal are mixed and both signals are transmitted (FIG. 11B), the satellite information that can be received by each of the GNSS receivers 4A, 4B, and 4C is different, so that the detection of the abnormality may be delayed, and as a result, erroneous information (such as position and time) of the false GNSS signal may be used ("unstable reception period 1" in FIG. 12). In addition, when the GNSS receivers 4A, 4B, and 4C are in an obstructed environment, or when the processing timing between the GNSS receivers 4A, 4B, and 4C is asynchronous and there is a difference in tracking satellite information, etc., the GNSS receivers 4A, 4B, and 4C cannot receive the GNSS signal during that period, so that the detection of an abnormality is delayed, and as a result, there is a risk of using erroneous information (such as position and time) of the fake GNSS signal. Furthermore, after the GNSS receivers 4A, 4B, and 4C move out of the influence of the fake GNSS signal or after the fake GNSS signal stops broadcasting, and before the GNSS receivers 4A, 4B, and 4C stabilize tracking to the true GNSS signal, an abnormality is no longer detected, but at this time, erroneous information (such as position and time) of the fake GNSS signal remains in the GNSS receivers 4A, 4B, and 4C, and there is a risk of using the erroneous information prematurely ("unstable reception period 2" in FIG. 12).

[0207] Therefore, the method for detecting an abnormality in a received signal and the GNSS compass 1 according to this embodiment make it possible to detect a situation in which the reception of a GNSS signal is unstable (unstable reception period), in which detection of an abnormality in a received signal is delayed or not detected at all. Specifically, an unstable reception period detection unit 9 is provided, and a situation in which the reception of a GNSS signal is unstable (unstable reception period) is detected based on the determination result output from the abnormality detection unit 5 and the determination result output from the positioning unit 6. In this respect, this embodiment differs from the first embodiment.

[0208] 10 is a functional block diagram showing a schematic configuration of a GNSS compass according to this embodiment. Here, the abnormality detection unit 5 further includes an abnormality determination unit 55, and the positioning unit 6 includes a positioning number determination unit 61 and a standard deviation determination unit 62. Also, the unstable reception period detection unit 9 is a device for detecting a situation in which the reception of the GNSS signal is unstable (unstable reception period) based on the determination result output from the abnormality detection unit 5 and the determination result output from the positioning unit 6.

[0209] In this embodiment, the path difference determination unit 54 outputs information about the GNSS satellite S_i classified as having a path difference abnormality (in other words, an abnormality in the direction of arrival of the GNSS signal) to the abnormality determination unit 55 as satellite information having a path difference abnormality.

[0210] On the other hand, when the path difference index is greater than a predetermined path difference threshold, the path difference determination unit 54 determines that the arrival direction of the GNSS signal for the multiple GNSS satellites S_i is normal, and outputs information about the GNSS satellite S_i classified as having a normal path difference (in other words, a normal arrival direction of the GNSS signal) to the reception unstable period detection unit 9 as satellite information having a normal path difference.

[0211] The abnormality determination unit 55 receives information about the GNSS satellite S_i classified according to the course difference output from the course difference determination unit 54, and determines whether or not an abnormality has occurred in the GNSS signal.

[0212] Specifically, the abnormality judgment unit 55 counts the number of GNSS satellites S_i classified as having a course difference based on information about the GNSS satellites S_i classified as having a course difference output from the course difference judgment unit 54, and judges whether the number is within a predetermined range.

[0213] The predetermined range is not limited to a specific value, and is appropriately set to an appropriate value, taking into consideration the number of GNSS satellites expected when GNSS signals from multiple GNSS satellites are transmitted from a single transmitting antenna / the same point, etc. The predetermined range may be set to a value of, for example, about 2 to 3.

[0214] The abnormality determination unit 55 determines that an abnormality has occurred in the GNSS signal when the number of GNSS satellites S_i classified as path difference abnormal is greater than the predetermined range (e.g., 4 or more). On the other hand, when the number of GNSS satellites S_i classified as path difference abnormal is within the predetermined range (e.g., 2 to 3), it outputs information that the number of GNSS satellites S_i classified as path difference abnormal (in other words, GNSS signal arrival direction abnormality) is within the predetermined range to the reception unstable period detection unit 9. Note that when the number of GNSS satellites S_i classified as path difference abnormal is less than the predetermined range (e.g., 0 or 1), it may be determined that the GNSS signal is normal.

[0215] If it is determined that an abnormality has occurred in the GNSS signal, an abnormality state is reached, and, for example, the GNSS satellite S_i classified as having a trajectory difference may be excluded from the group of satellites used in the calculation processing of positioning information (specifically, the aircraft's position, orientation, and attitude, etc.) by the positioning unit 6, and the GNSS signal transmitted from the excluded GNSS satellite S_i may not be used in the calculation processing of positioning information by the positioning unit 6.

[0216] In addition, in the positioning unit 6 in this embodiment, the positioning number determination unit 61 receives input of the positioning positions for each GNSS antenna (3A, 3B, 3C) for the position calculation antenna, and determines whether the positioning positions for each of the three GNSS antennas 3A, 3B, 3C have been calculated.

[0217] If the positioning position of at least one of the three GNSS antennas 3A, 3B, 3C has not been calculated, in other words, if the number of position calculation antennas is 0 to 2, the positioning number determination unit 61 outputs information that the number of position calculation antennas is 0 to 2, i.e., information that there is an antenna for which the positioning position has not been calculated (non-positioning), to the reception unstable period detection unit 9.

[0218] 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.

[0219] When the standard deviation determination unit 62 receives the positioning positions of each of the three GNSS antennas 3A, 3B, 3C output from the positioning number determination unit 61, it uses the positioning positions to calculate the positioning distance between each of the three GNSS antennas 3A, 3B, 3C, that is, for each combination of two GNSS antennas (any two of 3A, 3B, 3C).

[0220] Specifically, three positioning distances are calculated: 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. The positioning position is specifically the latitude, longitude, and altitude, and the positioning distance is the length of a line segment connecting three-dimensional coordinates.

[0221] The standard deviation determination unit 62 then calculates the standard deviation (referred to as the "standard deviation of the inter-antenna positioning distances") of the positioning distances between each of the three GNSS antennas 3A, 3B, and 3C, that is, the positioning distances for each combination of two GNSS antennas (any two of 3A, 3B, and 3C), and determines whether the standard deviation of the inter-antenna positioning distances is greater than a predetermined threshold (deviation threshold).

[0222] The deviation threshold is not limited to a specific value, and is appropriately set to an appropriate value, taking into consideration, for example, the baseline dimension, which is the distance between the GNSS antennas 3A, 3B, and 3C (which is known as a design value for the arrangement of the GNSS antennas 3A, 3B, and 3C) and the positioning error that is assumed to occur due to mechanical error even in a normal state. The deviation threshold may be set to any value within a range of, for example, about 100 to 600 m.

[0223] If the standard deviation of the inter-antenna positioning distance is below the deviation threshold, it is assumed that no abnormality has occurred in the GNSS signal, so, for example, the positioning unit 6 may calculate the average value of the positioning positions of each of the three GNSS antennas 3A, 3B, and 3C and output this average value as the current position of the GNSS compass 1.

[0224] On the other hand, if the standard deviation of the inter-antenna positioning distance is greater than the deviation threshold, the standard deviation determining unit 62 outputs to the unstable reception period detecting unit 9 information that the standard deviation of the inter-antenna positioning distance is greater than the deviation threshold.

[0225] (Processing contents of reception unstable period detection part) The unstable reception period detection unit 9 detects an unstable reception period based on the judgment results output from the abnormality detection unit 5 (i.e., the judgment result as to whether the arrival direction of the GNSS signal is normal or not, and the judgment result as to whether an abnormality has occurred in the GNSS signal or not) and the judgment results output from the positioning unit 6 (i.e., the judgment result as to whether the positioning position has been calculated or not, and the judgment result as to whether the standard deviation is greater than a predetermined threshold value or not).

[0226] Specifically, when any of the following four criteria is met, the unstable reception period detection unit 9 determines that the GNSS signal is in an unstable reception state and that there is a possibility that an abnormality has occurred in the GNSS signal.

[0227] First, the reception unstable period detection unit 9 receives information about GNSS satellites S_i classified as having normal path differences from the path difference determination unit 54, calculates the number of GNSS satellites S_i, and determines whether the number is greater than or equal to a predetermined threshold (normality determination threshold) for determining that the GNSS signal is normal based on the path difference index.

[0228] The normality determination threshold is not limited to a specific value, and is appropriately set to an appropriate value, for example, taking into consideration the number of GNSS satellites expected when GNSS signals from multiple GNSS satellites are transmitted from a single transmitting antenna / the same point. The normality determination threshold may be set to any value within a range of, for example, about 3 to 5.

[0229] The unstable reception period detection unit 9 determines that the GNSS signal is normal when the number of GNSS satellites S_i classified as having normal path differences is greater than or equal to the normal judgment threshold, and determines that the GNSS signal is in an unstable reception state and there is a possibility that an abnormality has occurred in the GNSS signal when the number is less than the normal judgment threshold.

[0230] Secondly, the unstable reception period detection unit 9 receives information from the abnormality judgment unit 55 that the number of GNSS satellites S_i classified as having a path difference abnormality (in other words, an abnormality in the arrival direction of the GNSS signal) is within a predetermined range, and determines that the GNSS signal is in an unstable reception state and that there is a possibility that an abnormality has occurred in the GNSS signal.

[0231] Thirdly, the unstable reception period detection unit 9 receives information from the positioning number determination unit 61 that the number of position calculation antennas is 0 to 2, i.e., information 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 that there is a possibility that an abnormality has occurred in the GNSS signal.

[0232] Fourth, the unstable reception period detection unit 9 receives information from the standard deviation determination unit 62 that the standard deviation of the inter-antenna positioning distance is greater than the deviation threshold, and determines that the GNSS signal is in an unstable reception state and that there is a possibility that an abnormality has occurred in the GNSS signal.

[0233] If it is determined that the GNSS signal is in an unstable reception state and there is a possibility that an abnormality is occurring in the GNSS signal based on any one of the above four judgment criteria, the unstable reception period detection unit 9 will prevent the positioning unit 6 from using the positioning position and GNSS time calculated from the GNSS signal in the calculation process of positioning information.

[0234] As described above, the method for detecting an abnormality in a received signal and the GNSS compass 1 of this embodiment can detect situations in which GNSS signal reception is unstable, making it possible to grasp an abnormality in the GNSS signal at the possibility stage. Even if the detection of an abnormality is delayed, it is possible to prevent the output of erroneous information (such as position and time) based on a false GNSS signal, thereby improving the reliability of the abnormality detection process in the received signal.

[0235] Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there are design changes and the like within the scope of the gist of the present invention, they are included in the present invention.

[0236] For example, in the above embodiment, the method for detecting abnormalities in a received signal according to the present invention is implemented in a GNSS compass 1 whose schematic configuration is shown in Figure 1 (in other words, the device for detecting abnormalities in a received signal according to the present invention is incorporated into the GNSS compass 1), but the equipment / device to which the method for detecting abnormalities in a received signal according to the present invention is applied or the device for detecting abnormalities 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 Figure 1, and the method for detecting abnormalities in a received signal according to the present invention may be applied or the device for detecting abnormalities in a received signal according to the present invention may be incorporated into a GNSS compass having another configuration, and the method for detecting abnormalities in a received signal according to the present invention may be applied to other types of equipment or devices that use GNSS, and the device for detecting abnormalities in a received signal according to the present invention may be incorporated into other types of equipment or devices that use GNSS.

[0237] Furthermore, in the above embodiment, the pseudo distance determination unit 52 is provided to perform the pseudo distance determination process, but the pseudo distance determination process is not essential to this invention. Even in this case, the transmission time determination process by the transmission time determination unit 51 is performed, and since processing is performed independently for each GNSS satellite S_i, detection can be performed in real time, and by combining the transmission time determination process and the path difference determination process, anomalies in the GNSS reception signal can be detected in a mutually complementary manner, thereby improving the reliability of the detection process of anomalies in the GNSS reception signal. [Explanation of symbols]

[0238] 1 GNSS compass 2. Control unit 3 GNSS antennas 3A, 3B, 3C GNSS antennas 4 GNSS receiver 4A, 4B, 4C GNSS receiver 5. Anomaly detection section 51 Transmission time determination unit 52 Pseudo-range determination unit 53 Path difference calculation section 54 Path difference determination section 55 Abnormality determination section 6 Positioning unit 61 Positioning number determination unit 62 Standard deviation determination section 7 Output information adjustment section 8 Inertial devices (sensors) 9 Unstable reception period detection unit (means)

Claims

1. receiving GNSS signals transmitted from a plurality of satellites via a plurality of antennas, comparing a path difference indicator representing a difference in a 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 or not the arrival direction of the GNSS signals is normal based on a comparison result between the path difference indicator and the predetermined path difference threshold at a predetermined cycle; The satellite in which the arrival direction of the GNSS signal is determined to be abnormal in the determination performed in the immediately preceding period performs the determination in the next period using a second path difference threshold value that is set so that the arrival direction is more likely to be determined to be abnormal than the predetermined path difference threshold value.

2. A method for detecting an abnormality in a received signal.

2. a satellite belonging to the same type of satellite system as the satellite for which the arrival direction of the GNSS signal was determined to be abnormal in the determination performed in the immediately preceding period, performs the determination in the next period using the second path difference threshold value; 2. The method for detecting an abnormality in a received signal according to claim 1.

3. When it is determined in the determination performed in the immediately preceding period that the arrival direction of the GNSS signal of at least one of the satellites is not normal, the determination in the next period is performed for all satellites using the second path difference threshold value.

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

4. and further determining whether the transmission time of the GNSS signal is normal based on a comparison between a transmission time of the GNSS signal included in the GNSS signal and a predetermined reference transmission time.

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

5. and determining whether the pseudorange of the satellite that transmitted the GNSS signal is normal based on a comparison between the pseudorange of the satellite and a pseudorange of a predetermined reference satellite.

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

6. When the arrival direction of the GNSS signal of the satellite is determined to be abnormal and the arrival direction of the GNSS signal of the satellite is determined to be normal using the second path difference threshold, the satellite performs the determination of the next period using the predetermined path difference threshold.

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

7. determining whether the arrival direction of the GNSS signal is normal or not based on the path difference index 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.

8. the reference transmission time for the satellite that transmitted the GNSS signal is a transmission time included in a GNSS signal previously transmitted from the satellite; 5. The method for detecting an abnormality in a received signal according to claim 4.

9. the reference transmission time for the satellite that transmitted the GNSS signal is a transmission time included in a GNSS signal transmitted from another satellite; 5. The method for detecting an abnormality in a received signal according to claim 4.

10. maintaining the abnormal state of the satellite determined to be abnormal for a predetermined period of time; 6. The method for detecting an abnormality in a received signal according to claim 1.

11. when the arrival direction of the GNSS signal is determined to be normal for a plurality of satellites and the abnormal state is maintained after the arrival direction of the GNSS signal is determined to be abnormal, or when a predetermined time has elapsed since the state in which the arrival direction of the GNSS signal is determined to be normal, canceling the abnormal state for the plurality of satellites; 6. The method for detecting an abnormality in a received signal according to claim 1.

12. when the transmission time of the GNSS signal is determined to be normal while the abnormal state of the satellite determined to be abnormal is maintained, or when a predetermined time has elapsed during which the transmission time of the GNSS signal has been determined to be normal, canceling the abnormal state of the satellite determined to be abnormal.

5. The method for detecting an abnormality in a received signal according to claim 4.

13. changing the number of reception channels allocated to 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; 6. The method for detecting an abnormality in a received signal according to claim 1.

14. A first determination process is executed at a predetermined interval to determine whether the GNSS signal is normal; When it is determined in the first determination process that all of the GNSS signals are normal, a 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 or not a position can be calculated based only on the GNSS signals determined to be normal in the first determination process; When it is determined in the second determination process that the position can be calculated, a position calculated based only on the GNSS signals determined to be normal in the first determination process is output; If it is determined in the second determination process that the position cannot be calculated, an estimated position is output by adding an amount of change measured by a sensor capable of measuring at least acceleration and angular velocity to the closest position among positions calculated based only on GNSS signals determined to be normal before the first determination process, or a message is output to indicate that the position cannot be measured.

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

15. When it is determined in the second determination process that the position cannot be calculated, a third determination process is executed to determine whether or not a 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, outputting the estimated position or outputting the message; 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.

15. The method for detecting an abnormality in a received signal according to claim 14.

16. A first determination process is executed at a predetermined interval to determine whether the GNSS signal is normal; When it is determined that all of the GNSS signals are normal in the first determination process, a 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 or not the time can be calculated based only on the GNSS signals determined to be normal in the first determination process; When it is determined in the second determination process that the time can be calculated, the time calculated based only on the GNSS signal determined to be normal in the first determination process is output; If it is determined in the second determination process that the time cannot be calculated, an estimated time is output by adding the elapsed time measured by the internal clock to the most recent time calculated based only on the GNSS signal determined to be normal before the first determination process.

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

17. If it is determined in the second determination process that the time cannot be calculated, a third determination process is executed to determine whether or not a 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, the estimated time is output; When it is determined in the third determination process that the difference is less than the predetermined threshold, a time calculated based on the GNSS signal is output.

17. The method for detecting an abnormality in a received signal according to claim 16.

18. If the number of satellites for which the arrival direction of the GNSS signal is determined to be normal based on the path difference indicator is less than a predetermined threshold for determining that the GNSS signal is normal based on the path difference indicator, When the number of satellites for which the arrival direction of the GNSS signal is determined to be abnormal based on the path difference indicator is within a predetermined range, if a positioning position of at least one of the plurality of antennas has not been calculated; and a 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, the GNSS signal is determined to be in an unstable reception state and an abnormality may be occurring in the GNSS signal.

6. A method for detecting an abnormality in a received signal according to claim 1.

19. 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 of comparing a path difference index indicating 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 determining 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 at a predetermined cycle; the path difference determination unit performs the determination in the next period using a second path difference threshold value that is set so that the arrival direction of the satellite determined to be abnormal in the determination performed in the immediately previous period is more likely to be determined to be abnormal than the predetermined path difference threshold value; 2. A detection device for detecting an abnormality in a received signal.

20. the path difference determination unit performs the determination in the next period using the second path difference threshold value for a satellite belonging to the same type of satellite system as the satellite for which the arrival direction of the GNSS signal was determined to be abnormal in the determination performed in the immediately previous period; 20. The apparatus for detecting an abnormality in a received signal according to claim 19.

21. 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 previous period, the path difference determination unit performs the determination in the next period for all satellites using the second path difference threshold value.

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

22. and a transmission time determination unit that determines whether the transmission time of the GNSS signal is normal based on a comparison between the transmission time of the GNSS signal included in the GNSS signal and a predetermined reference transmission time.

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

23. a pseudorange determining unit that determines whether the pseudorange of the satellite that transmitted the GNSS signal is normal or not based on a comparison between the pseudorange of the satellite and a pseudorange of a predetermined reference satellite; 20. The apparatus for detecting an abnormality in a received signal according to claim 19.

24. When the arrival direction of the GNSS signal of the satellite is determined to be abnormal and the arrival direction of the GNSS signal of the satellite is determined to be normal using the second path difference threshold, the satellite performs the determination of the next period using the predetermined path difference threshold.

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

25. determining whether the arrival direction of the GNSS signal is normal or not based on the path difference index for each type of the satellite system to which the satellite belongs; 20. The apparatus for detecting an abnormality in a received signal according to claim 19.

26. the reference transmission time for the satellite that transmitted the GNSS signal is a transmission time included in a GNSS signal previously transmitted from the satellite; 23. The apparatus for detecting an abnormality in a received signal according to claim 22.

27. the reference transmission time for the satellite that transmitted the GNSS signal is a transmission time included in a GNSS signal transmitted from another satellite; 23. The apparatus for detecting an abnormality in a received signal according to claim 22.

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

24. The device for detecting an abnormality in a received signal according to claim 19.

29. when the arrival direction of the GNSS signal is determined to be normal for a plurality of satellites and the abnormal state is maintained after the arrival direction of the GNSS signal is determined to be abnormal, or when a predetermined time has elapsed since the state in which the arrival direction of the GNSS signal is determined to be normal, canceling the abnormal state for the plurality of satellites; 24. The device for detecting an abnormality in a received signal according to claim 19.

30. when the transmission time of the GNSS signal is determined to be normal while the abnormal state of the satellite determined to be abnormal is maintained, or when a predetermined time has elapsed during which the transmission time of the GNSS signal has been determined to be normal, canceling the abnormal state of the satellite determined to be abnormal.

23. The apparatus for detecting an abnormality in a received signal according to claim 22.

31. According to the number of satellites determined to be abnormal, the number of reception channels allocated to satellites having a frequency band different from that of the satellites determined to be abnormal is changed.

24. The device for detecting an abnormality in a received signal according to claim 19.

32. an abnormality detection unit that executes a first determination process for determining whether the GNSS signal is normal or not at a predetermined cycle; an output information adjustment unit that adjusts the information to be output; The output information adjustment unit When it is determined in the first determination process that all of the GNSS signals are normal, a 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 or not a position can be calculated based only on the GNSS signals determined to be normal in the first determination process; When it is determined in the second determination process that the position can be calculated, a position calculated based only on the GNSS signals determined to be normal in the first determination process is output; If it is determined in the second determination process that the position cannot be calculated, an estimated position is output by adding an amount of change measured by a sensor capable of measuring at least acceleration and angular velocity to the closest position among positions calculated based only on GNSS signals determined to be normal before the first determination process, or a message is output to indicate that the position cannot be measured.

24. An apparatus for detecting an abnormality in a received signal according to claim 19.

33. When it is determined in the second determination process that the position cannot be calculated, the output information adjustment unit executes a third determination process to determine whether or not a 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, outputting the estimated position or outputting the message; 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.

33. The apparatus for detecting an abnormality in a received signal according to claim 32.

34. an abnormality detection unit that executes a first determination process for determining whether the GNSS signal is normal or not at a predetermined cycle; an output information adjustment unit that adjusts the information to be output; The output information adjustment unit When it is determined that all of the GNSS signals are normal in the first determination process, a 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 or not the time can be calculated based only on the GNSS signals determined to be normal in the first determination process; When it is determined in the second determination process that the time can be calculated, the time calculated based only on the GNSS signal determined to be normal in the first determination process is output; If it is determined in the second determination process that the time cannot be calculated, an estimated time is output by adding the elapsed time measured by the internal clock to the most recent time calculated based only on the GNSS signal determined to be normal before the first determination process.

24. The device for detecting an abnormality in a received signal according to claim 19.

35. When it is determined that the time cannot be calculated in the second determination process, the output information adjustment unit executes a third determination process to determine whether or not a 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, the estimated time is output; When it is determined in the third determination process that the difference is less than the predetermined threshold, a time calculated based on the GNSS signal is output.

35. The apparatus for detecting an abnormality in a received signal according to claim 34.

36. If the number of satellites for which the arrival direction of the GNSS signal is determined to be normal based on the path difference indicator is less than a predetermined threshold for determining that the GNSS signal is normal based on the path difference indicator, When the number of satellites for which the arrival direction of the GNSS signal is determined to be abnormal based on the path difference indicator is within a predetermined range, if a positioning position of at least one of the plurality of antennas has not been calculated; and a means for determining that the GNSS signal is in an unstable reception state and that there is a possibility that an abnormality has occurred in the GNSS signal in at least one of the cases where a 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; 24. The device for detecting an abnormality in a received signal according to claim 19.

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