Reception device, reception method, and program

Abstract

The purpose of the present disclosure is to effectively eliminate an unnecessary invisible satellite signal when receiving a satellite signal in a fixed and installed state.　In view of the above, the present disclosure provides a reception device for receiving a satellite signal in a fixed state and performing positioning or time synchronization, the reception device having a mask setting unit that estimates the satellite signal as a visible satellite signal when the signal strength of the satellite signal is equal to or greater than a first threshold value and a delay time from a reference value of the reception time of the satellite signal is equal to or less than a second threshold value, and updates a satellite signal reception mask indicating an elevation angle threshold value for each direction on the basis of the position of a first visible satellite signal, which has an elevation angle equal to or less than the elevation angle threshold value in the satellite signal reception mask, among the positions of visible satellite signals in a sky plot at a prescribed time epoch.

Description

Receiving device, receiving method, and program

[0001] The present disclosure relates to a method for effectively eliminating invisible satellite signals blocked by surrounding structures when receiving GNSS signals (satellite signals) using a fixed antenna.

[0002] Global Navigation Satellite Systems (GNSS) are used in outdoor environments to measure the absolute position of objects and synchronize time with high precision. In addition to GPS (USA), other navigation satellite systems, such as GLONASS (Russia), Galileo (Europe), BeiDou (China), QZSS (Japan), and NAVIC (India), are also in operation in various countries, and the number of available navigation satellites is increasing. By correcting the clock bias (time error) between satellite systems, satellite positioning (hereinafter referred to as "positioning") and satellite time synchronization (hereinafter referred to as "time synchronization") can be performed using multi-constellation GNSS (hereinafter referred to as "multi-GNSS"), which uses a mixture of satellite signals from multiple navigation satellite systems. Increasing the number of satellites used for positioning and time synchronization improves the availability of positioning and time synchronization in environments where GNSS signals (also referred to as "satellite signals") are difficult to receive. Here, a "difficult reception environment" refers to a reception environment in which there are buildings or other structures that block satellite signals around the satellite signal reception position. In such a difficult reception environment, there are two main factors that cause the accuracy of positioning and time synchronization to deteriorate.

[0003] One factor is that structures reduce the open space area in the sky, reducing the number of satellites from which satellite signals can be received as direct waves (visible satellites or LOS (Line-of-sight) satellites), and biasing the geometric positions of visible satellites in the line-of-sight area.The degree to which the number of satellites and their positions in the sky affect the accuracy of positioning and time synchronization can be quantitatively estimated using an index called DOP (Dilution of Precision).

[0004] The second factor is the effect of multipath, where satellite signals are reflected or diffracted by structures before reaching the receiving position. There are two types of multipath: multipath of visible satellite signals accompanied by direct waves, and multipath of satellites without direct waves (invisible satellites or NLOS (Non Line-of-sight) satellites). The latter has a greater impact on the degradation of positioning accuracy or time synchronization accuracy. This is because, while the effect of multipath when a GNSS signal receiving antenna (hereinafter referred to as "GNSS antenna") receives visible satellite signals can be effectively removed by signal processing in the correlator inside the GNSS signal receiving device, the propagation delay associated with the reflection or diffraction of invisible satellite signals directly causes errors in the pseudorange measurement of the satellite signals.

[0005] In mobile communication systems using Time Division Duplex (TDD), which multiplexes downlink signals from base stations to terminals and uplink signals from terminals to base stations on the time axis, highly accurate synchronization of the transmission and reception timing of communication frames at each base station is required to suppress interference between base stations. Since synchronization is required not only between base stations of the same carrier but also between base stations of different carriers, absolute time synchronization using GNSS signals is used instead of relative timing synchronization between base stations. Urban areas with high mobile communication traffic demand generally have a higher density of base stations. However, when synchronizing the time of base stations in such areas, there are often challenges, such as limited open space for receiving GNSS signals due to surrounding structures and the reception of multipath signals, which can degrade the accuracy of time synchronization.

[0006] Another application using fixed GNSS antennas is to measure the displacement of a GNSS antenna fixed to a building using GNSS-based precision positioning technology for the purpose of maintaining the building's facilities.However, even in such applications, the reception environment for GNSS signals is degraded by surrounding buildings in urban areas, which can cause a problem of degraded positioning accuracy.

[0007] In environments where GNSS signals are difficult to receive due to the presence of structures around the receiving position, one effective way to prevent deterioration in the accuracy of positioning or time synchronization using GNSS signals is to select visible satellite signals within line of sight as the satellite signals to be used and exclude invisible satellite signals that are not within line of sight.

[0008] For applications requiring stationary reception of GNSS signals, such as time synchronization for mobile communication base stations or facility maintenance, a fixed-position antenna (hereafter referred to as a "GNSS antenna") is used. One method involves identifying the boundary between the sky and the structure on a sky image captured by a fisheye lens installed at the receiving position (the phase center of the GNSS antenna) with its optical axis facing the zenith. Then, a corresponding satellite signal reception mask profile is set. A "satellite signal reception mask" is a rule for excluding satellite signals not used for positioning or time synchronization from received satellite signals. For example, the mask profile sets the elevation angle at the boundary between the structure and the sky in each direction as the elevation angle threshold for excluding received satellite signals. Satellite signals with an elevation angle below the threshold are considered invisible and are not used.

[0009] Instead of capturing sky images, there is also a method of processing data from a sky plot (sky map) showing the location of structures using three-dimensional geospatial information, specifically three-dimensional building data, to generate a mask profile.

[0010] Naohiro Tada et al., "Technological Development for Expanding the Application Range of High-Precision Satellite Positioning in Outdoor 3D Space," Geospatial Information Authority of Japan Bulletin 2018 No. 130

[0011] However, the above-mentioned method of generating a mask profile based on geospatial information of sky images and structures around the receiving position has the problem that it requires a lot of time and effort to generate the mask profile. Also, errors in the alignment of the optical axis of the fisheye lens of the camera when capturing the sky image, errors in identifying the orientation of the captured image, and errors in the two-dimensional position and height data of buildings in the three-dimensional building data lead to errors in setting the mask profile and ultimately errors in determining invisible satellites.

[0012] On the other hand, a method that does not use geospatial information about sky images or structures around the receiving location involves receiving satellite signals from a stationary position for a long period of time, estimating whether the satellite signal is visible or invisible from the received satellite signal strength, and then estimating the boundary between the structure and the sky image based on the collected azimuth and elevation data of visible or invisible satellites. However, when an invisible satellite signal with a low elevation angle reflects off the vertical wall of a building or other structure, the reflection coefficient is large, and in some cases the signal strength of the received signal is high even if the satellite is invisible. For this reason, setting a threshold for the signal strength of the received signal does not necessarily enable accurate determination of whether the satellite signal is visible or invisible.

[0013] The present disclosure has been made to solve the above-mentioned problems, and aims to effectively eliminate unnecessary invisible satellite signals when receiving satellite signals in a fixed installation.

[0014] In order to achieve the above object, the disclosure of claim 1 is a receiving device that receives satellite signals in a fixed state and performs positioning or time synchronization, and that estimates the satellite signal as a visible satellite signal when the signal strength of the satellite signal is equal to or greater than a first threshold and the delay time from a reference value of the reception time of the satellite signal is equal to or less than a second threshold, and that has a mask setting unit that updates the satellite signal reception mask based on the position of a first visible satellite signal that is equal to or less than an elevation angle threshold in a satellite signal reception mask that indicates an elevation angle threshold for each direction, among the positions of the visible satellite signals in a sky plot, at a predetermined time epoch.

[0015] As described above, the present invention has the effect of effectively eliminating unnecessary invisible satellite signals.

[0016] 1 is a diagram illustrating the configuration of a receiving device according to an embodiment; and FIG. 2 is a diagram illustrating the electrical hardware configuration of a receiving device according to an embodiment. (a) is a diagram illustrating a sky plot in which an initial mask is set, and (b) is a diagram illustrating a mask profile in this case. (a) is a diagram illustrating an example of setting an initial mask when a structure is present in a specific azimuth, and (b) is a diagram illustrating a mask profile in this case. (b) is a diagram illustrating an example of a sky plot in which the azimuth division value is set to 45°. (c) is a flowchart illustrating the processing or operation of a receiving device. (a) is a diagram illustrating an example of a sky plot showing satellite signals in an initial positioning calculation process (S11), and (b) is a diagram illustrating an example of a sky plot showing satellite signals in a visible satellite signal estimation process (S12). (a) is a diagram illustrating an example of a sky plot showing satellite signals in an initial time epoch process (S13), and (b) is a diagram illustrating an example of a sky plot showing satellite signals in a next time epoch process (S14).

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0018] [Configuration diagram of receiving device] In this embodiment, when receiving satellite signals in a stationary state using a fixedly installed GNSS antenna 31 in a reception environment where there are surrounding structures that block satellite signals, the receiving device 3 automatically generates a satellite signal reception mask to effectively exclude invisible satellite signals from the satellite signals used for positioning or time synchronization.

[0019] First, the configuration of the receiving device of this embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing the configuration of the receiving device of this embodiment.

[0020] As shown in FIG. 1, the receiving device 3 includes a parameter storage unit 30, a GNSS antenna 31, a satellite signal receiving unit 32, a mask setting unit 33, a positioning and time synchronization calculation unit 34, and an output unit 35.

[0021] (Parameter Storage Unit) The parameter storage unit 30 is realized by a RAM 303 or an SSD 304, which will be described later, and stores therein each parameter used by the mask setting unit 33. Each parameter is set by the user via an input device 308, which will be described later, or the like.

[0022] (GNSS Antenna) The GNSS antenna 31 is an antenna for receiving GNSS signals (satellite signals). In this embodiment, it is assumed that the GNSS antenna 31 is installed in a fixed position and receives satellite signals while stationary. The satellite signals received by the GNSS antenna 31 are input to the satellite signal receiving unit 32 via a signal transmission medium such as a coaxial cable. An RF signal amplifier may be inserted between the GNSS antenna 31 and the satellite signal receiving unit 32 to compensate for propagation loss of the GNSS signals due to the cable. Furthermore, when performing time synchronization, parameters such as the cable length and the effective relative dielectric constant of the transmission line medium are measured in advance before installing the GNSS antenna 31 in order to correct the propagation time of the cable between the GNSS antenna 31 and the satellite signal receiving unit 32.

[0023] (Satellite Signal Reception Unit) The satellite signal reception unit 32 is composed of circuits such as an analog front-end unit that processes high-frequency signals and a baseband signal processing unit, and outputs observation data such as satellite type, satellite number such as SVN (Space Vehicle Number), elevation angle, azimuth angle, and signal strength obtained from the navigation message in the received satellite signal to the mask setting unit 33. In addition to this observation data, it also outputs observation data such as the pseudorange, Doppler shift, and carrier phase of the satellite signal to the positioning and time synchronization calculation unit 34. The input and output of satellite signals is repeated at regular intervals (e.g., every second). Hereinafter, a certain time (timing) at which a series of data is obtained in the satellite signal reception unit 32 will be referred to as a "time epoch."

[0024] (Mask setting unit) The mask setting unit 33 automatically updates the mask profile of the satellite signal reception mask using processing described below, based on data received from the satellite signal reception unit 32. The mask profile is given, for example, by an elevation angle threshold for each azimuth. The mask setting unit 33 reads each parameter from the parameter storage unit 30 as necessary.

[0025] The updated state of the satellite signal reception mask, together with the received satellite signals, is displayed on a sky plot (sky chart) by a display device 307, such as a display described below. A "sky plot" is a diagram for displaying positions in the sky, with radial lines indicating azimuth angles and concentric circles indicating elevation angles drawn on a circle centered at the zenith and with the horizon as its outer periphery.

[0026] (Positioning and Time Synchronization Calculation Unit) The positioning and time synchronization calculation unit 34 receives observation data from the satellite signal reception unit 32, selects the satellite signal to be used for positioning and time synchronization based on the mask profile of the satellite signal reception mask input from the mask setting unit 33, and then performs positioning and time synchronization calculations. The positioning and time synchronization calculation unit 34 has a function to correct the time bias between each GNSS and is multi-GNSS compatible. Positioning calculations are performed using the code positioning method or the carrier phase positioning method. For time synchronization, time information synchronized with UTC (Coordinated Universal Time) is output, with the propagation delay of the GNSS signal compensated for in the transmission path from the GNSS antenna 31 to the satellite signal reception unit 32.

[0027] (Output Unit) The output unit 35 outputs the results of the positioning and time synchronization calculations to an external device. The GNSS solutions resulting from the positioning calculations are output in, for example, the NMEA (National Marine Electronics Association) 0183 format. The results of the time synchronization calculations are output as a timing signal such as a 1 PPS (Pulse Per Second) signal synchronized to the exact second of UTC, or as data of a time synchronization protocol of a packet communication network such as PTP (Precision Time Protocol) or NTP (Network Time Protocol).

[0028] [Electrical Configuration of Receiving Device] Fig. 2 is a diagram showing the electrical hardware configuration of the receiving device. Note that all or part of the configuration shown in Fig. 1 may be realized by executing the following program, or may be realized by a circuit or the like.

[0029] As shown in FIG. 2, the receiving device 3 is a computer and includes a CPU 301, a ROM 302, a RAM 303, an SSD 304, an external device connection I / F (Interface) 305, a network I / F 306, a display device 307, an input device 308, a media I / F 309, and a bus line 310.

[0030] Of these, the CPU 301 controls the overall operation of the receiving device 3. The ROM 302 stores programs such as IPL used to drive the CPU 301. The RAM 303 is used as a work area for the CPU 301.

[0031] The SSD 304 reads or writes various data under the control of the CPU 301. Note that instead of the SSD 304, a hard disk drive (HDD) may be used.

[0032] The external device connection I / F 305 is an interface for connecting various external devices, such as a display, a speaker, a keyboard, a mouse, a USB memory, and a printer.

[0033] The network I / F 306 is an interface for performing data communication via a communication network such as the Internet.

[0034] The display device 307 is a type of display means that displays various images, such as a liquid crystal display or an organic electroluminescence (EL) display. An example of the display device 307 is a display.

[0035] The input device 308 is a type of input means for selecting and executing various instructions, selecting a processing target, moving a cursor, etc. An example of the input device 308 is a pointing device.

[0036] The media I / F 309 controls reading and writing (storing) of data from and to a recording medium 309m such as a flash memory, etc. The recording medium 309m includes DVDs and Blu-ray Discs (registered trademarks).

[0037] The bus line 310 is an address bus, a data bus, etc. for electrically connecting the components such as the CPU 301 shown in FIG.

[0038] [Processing or Operation of the Embodiment] Next, an outline of the processing or operation of the present embodiment will be described. This embodiment is premised on the assumption that the GNSS antenna 31 is installed in a fixed manner and is applied to a reception environment in which there are permanent structures that block satellite signals around the reception position of GNSS signals (satellite signals), but there is open space at least near the zenith. In such a reception environment, the receiving device 3 of this embodiment automatically generates a satellite signal reception mask that effectively excludes invisible satellites, thereby suppressing deterioration in the accuracy of positioning and time synchronization.

[0039] <Initial Settings> First, a description will be given of parameters that are initially set for the mask setting unit 33. The initial parameters set in the mask setting unit 33 are "initial mask," "azimuth division," "signal strength threshold," and "time residual threshold."

[0040] The "initial mask" is the initial value of the satellite signal reception mask, and the mask profile is given as an example of the elevation angle threshold for each azimuth. Figure 3(a) shows an example of a sky plot in which an initial mask m1 has been set. The elevation angle threshold for each azimuth is a constant value (70°), and the shape of the initial mask m1 on the sky plot in this case is a circle (only the thick line portion) indicated by the thick line that gives the elevation angle threshold. Figure 3(a) shows the initial mask m1 that takes into account three structures a, b, and c. Figure 3(b) shows the mask profile at that time.

[0041] The initial mask m1 is set to have an elevation angle that is larger than the maximum elevation angle of surrounding structures a, b, and c in the sky when looking up at the zenith from the receiving position, with some margin, as shown in FIG. 3(a).

[0042] FIG. 4(a) shows an example of a sky plot in which an initial mask m1' is set when a structure is present in a specific azimuth. The elevation threshold for azimuths between 0° and 179° is a constant value (70°), and the elevation threshold for azimuths between 180° and 359° is a constant value (20°). In this case, the shape of the initial mask m1' is shown by a small semicircle (azimuths between 0° and 179°: only the thick line portion) and a large semicircle (azimuths between 180° and 359°: only the thick line portion). FIG. 4(a) shows an initial mask m1' that takes into account a single wide structure d. FIG. 4(b) shows the mask profile at that time. Note that while FIGS. 3(a) and 4(a) show the positions of structures on the sky plot for reference purposes only, in this embodiment, it is not necessary to actually capture a sky image using a fisheye lens or the like and determine the exact elevation angle of the boundary between the sky and the structure; the initial mask can be set based solely on a rough guide.

[0043] "Azimuth division" is a parameter that determines the granularity of azimuth division when updating the satellite signal reception mask, and can be set to any angle. Figure 5 shows an example of a sky plot with the azimuth division value set to 45°. In urban canyon environments, the structures that block satellite signals are mainly buildings. However, in cases where there are narrow open spaces in the azimuth between buildings, setting the azimuth division value to a small value allows for the creation of a satellite signal reception mask that is more suited to the shape of the structures.

[0044] The "signal strength threshold" is a signal strength threshold parameter used to determine whether a received satellite signal is a visible satellite signal. For example, the carrier-to-noise density ratio (C / N0) (unit: dB-Hz) is used. The C / N0 value depends on the gain of the GNSS antenna 31 used, the reception sensitivity of the satellite signal receiving unit 32, the propagation loss of the cable connecting the GNSS antenna 31 and the satellite signal receiving unit 32, and other factors. For example, 45 dB-Hz is set as a value that indicates a high probability of being a visible satellite signal. A satellite signal with a carrier-to-noise density ratio greater than this is determined to be a visible satellite signal. The "signal strength threshold" may be a constant value or a function of the elevation angle of the satellite signal. Furthermore, the "signal strength threshold" may be set as a relative value (unit: dB) based on the satellite signal reception status, rather than as an absolute value of the signal strength of the received signal, such as the C / N0 value. For example, the C / N0 value of the satellite signal with the highest signal strength among the satellite signals received by the receiving device 3 may be set as a reference value, and the difference in signal strength (unit: dB) from this value may be set as a threshold. Satellite signals with a difference value equal to or less than the threshold are determined to be visible satellite signals. In this case, the "signal strength threshold" (signal strength difference) may be a constant value or a function of the elevation angle of the satellite signal. Furthermore, the "signal strength threshold" may be set individually for each GNSS satellite system. Note that the signal strength threshold is an example of a first threshold.

[0045] The "time residual threshold" is a threshold for the delay from a reference value of the reception time of a satellite signal at an estimated reception position (described below), and is set to, for example, 50 nanoseconds. Here, the "reference value of reception time" is the time at which the satellite signal is assumed to arrive as a direct wave at the estimated reception position. The "time residual threshold" is set for the purpose of eliminating satellite signals from invisible satellites that arrive at the reception position with a propagation delay due to reflection or diffraction, and is used together with the "signal strength threshold" to determine whether a received satellite signal is a visible satellite signal or an invisible satellite signal. The time residual threshold is an example of a second threshold.

[0046] <Processing or Operation of Receiving Device> Next, the processing or operation of the receiving device will be described using Figures 6 to 8. Figure 6 is a flowchart showing the processing or operation of the receiving device. Note that processes S11 to S13 in Figure 6 show processing using satellite signals received by the receiving device 3 in the initial time epoch. Process S14 shows processing using GNSS signals (satellite signals) received by the receiving device 3 in the next time epoch. Process S15 shows processing using GNSS signals received by the receiving device 3 in a further time epoch.

[0047] 7(a) is a diagram showing an example of a sky plot showing satellite signals in the initial positioning calculation process (S11), and FIG. 7(b) is a diagram showing an example of a sky plot showing satellite signals in the visible satellite signal estimation process (S12). FIG. 8(a) is a diagram showing an example of a sky plot showing satellite signals in the initial time epoch process (S13), and FIG. 8(b) is a diagram showing an example of a sky plot showing satellite signals in the next time epoch process (S14).

[0048] S11: Initial Positioning Calculation Processing The mask setting unit 33 performs initial positioning calculations using all of the satellite signals whose received satellite signal strengths clear (or exceed) the "signal strength threshold" and all of the satellite signals that clear the initial mask m1 (white circles on the sky plot in FIG. 7A ), and determines the initial value of the estimated reception position. This embodiment is based on the premise that the GNSS antenna 31 will be used without the installer measuring the exact position (latitude and longitude) of the GNSS antenna 31 (phase center). Therefore, the true value of the position of the GNSS antenna 31 (phase center) is unknowable. In this sense, the position of the GNSS antenna 31 (phase center) calculated by the initial positioning calculation is referred to as the initial value of the "estimated" reception position. The "estimated" reception position is updated in subsequent processing. If the number of satellite signals is less than four, which is required for positioning calculations, the initial positioning calculations for that time epoch are postponed, and the initial positioning calculations are performed in a time epoch in which the number of satellite signals becomes four or more due to movement of satellite positions in the sky.

[0049] S12: Visible Satellite Signal Estimation Process The mask setting unit 33 estimates as visible satellite signals those satellite signals whose received satellite signal strength is equal to or greater than the "signal strength threshold" and whose time residual (delay time from the reference value of the reception time) at the initial value of the estimated reception position determined in process S11 is equal to or less than the "time residual threshold." Since invisible satellite signals that involve reflection or diffraction arrive at the estimated reception position with a delay from the reference value compared to visible satellite signals, satellites estimated to be invisible based on the "time residual threshold" are selectively excluded (rejected) from the sky plot. The white triangles in Figure 7(b) indicate excluded satellite signals.

[0050] The mask setting unit 33 performs positioning calculations using the visible satellite signals estimated by the above-described process and the satellite signals with the initial mask m1 cleared, and updates the estimated reception position from the initial value. If the number of satellite signals is less than the four required for positioning calculations, the mask setting unit 33 postpones updating the estimated reception position from the initial value in that time epoch, and instead performs the initial value update process in a time epoch when the number of satellite signals becomes four or more due to movement of satellite positions in the sky. The initial value update process in that time epoch may be repeated several times. An upper limit on the number of process repetitions may be set in advance, or the convergence of the reception position estimation process may be determined by the amount of change in the estimated reception position before and after the update being equal to or less than a predetermined threshold.

[0051] S13: Satellite signal reception mask update process A (processing at initial time epoch) The mask setting unit 33 updates the satellite signal reception mask (here, initial mask m1) based on the positions of specific visible satellite signals estimated in process S12 whose elevation angles are equal to or less than the elevation angle threshold in initial mask m1, to generate a satellite signal reception mask m2. As shown in FIG. 8( a), the satellite signal reception mask m2 has a shape that combines line segments connecting the endpoints p1 and p2 of the initial mask m1 within a specific area on the sky plot that is divided in azimuth to the position P1 of a visible satellite signal within the specific area that are closest in azimuth. Note that position P1 of the visible satellite signal is an example of the position of the first visible satellite signal.

[0052] S14: Process B for updating the satellite signal reception mask (processing in the time epoch next to the initial time epoch) In the next time epoch, the satellite position on the sky plot will move along its orbit, but visible satellites will be estimated again by processes S11 and S12. The next time epoch is an example of a second time epoch.

[0053] As shown in Figure 8(b), the mask setting unit 33 adds the newly estimated position P2, etc. of the visible satellite signal in the current time epoch (the black circle in Figure 8(b)) to the position P1, etc. of the visible satellite signal in the previous time epoch, and updates the satellite signal reception mask m2 using the same procedure as in step S13 to generate a satellite signal reception mask m3. Note that position P2 of the visible satellite signal is an example of the position of the second visible satellite signal.

[0054] Furthermore, if the position of a visible satellite signal newly estimated by the mask setting unit 33 has a larger elevation angle than the position of a visible satellite signal in the same direction estimated in the previous time epoch, the mask setting unit 33 does not update the portion of the satellite signal reception mask that indicates the newly estimated position of the visible satellite signal from the previously estimated position of the visible satellite signal. Note that the satellite orbit is shown by a dashed dotted line in Figure 8(b). Furthermore, if the initial time epoch is a "predetermined time epoch," the next time epoch is an example of a "time epoch after the predetermined time epoch."

[0055] The mask setting unit 33 updates the estimated reception position using the satellite signal that last cleared the satellite signal reception mask and the visible satellite signals. If the number of satellite signals is less than four, which is required for positioning calculations, the mask setting unit 33 postpones updating the estimated reception position in that time epoch, and instead performs the update process for the estimated reception position in a time epoch when the number of satellite signals becomes four or more due to movement of satellite positions in the sky.

[0056] S15: Satellite signal reception mask update process C (processing in subsequent time epochs) The mask setting unit 33 repeats process S14 over time in subsequent time epochs, updates the satellite signal reception mask with satellite signals that are newly estimated to be visible satellites, and updates the estimated reception position using the satellite signals that have cleared the satellite signal reception mask. Note that if the initial time epoch or the next time epoch is a "predetermined time epoch," the subsequent time epoch is an example of a "time epoch after the predetermined time epoch."

[0057] By repeating the process of step S15 over time, the region of the elevation angle below the boundary given by the satellite signal reception mask on the sky plot gradually becomes smaller and gradually approaches the boundary between the sky and the structure.

[0058] S16: Calculation of positioning and time synchronization The mask setting unit 33 executes the above process after startup of the receiving device, and after a certain time epoch has passed, the positioning and time synchronization calculation unit 34 uses the satellite signal from which the satellite signal reception mask m3 has been cleared for positioning and time synchronization. Note that the mask setting unit 33 may fix the mask profile at the point in time during update process C when it determines that the change in the mask profile (threshold value for each direction) of the satellite signal reception mask before and after the update is equal to or less than the change threshold value and has converged, and may not perform visible satellite determination in subsequent time epochs, but may use the satellite signal from which the satellite signal reception mask has been cleared (selected by the mask) for positioning and time synchronization.

[0059] When the positioning and time synchronization calculation unit 34 performs time synchronization, if it determines that convergence has occurred based on the amount of change in the mask profile (threshold value for each direction) of the satellite signal reception mask before and after updating, or the amount of change in the estimated reception position before and after updating, it fixes the estimated reception position at that time as the true value of the reception position, and in subsequent time epochs, it can continue ``time synchronization'' using satellite signals from at least one satellite that has cleared the satellite signal reception mask.

[0060] Furthermore, since this embodiment is based on the premise that the structures blocking the satellite signals are artificial buildings, the mask setting unit 33 estimates that the area above the elevation angle of a satellite determined to be visible at a certain time epoch is open space, and updates the satellite signal reception mask.

[0061] As described above, when receiving satellite signals in a fixed installation, it is possible to effectively eliminate invisible satellite signals by automatically generating a satellite signal reception mask, thereby suppressing deterioration of positioning accuracy or time synchronization accuracy over time.

[0062] Furthermore, automatic generation of the satellite signal reception mask can be achieved not only by starting up the receiving device 3 after installation and executing steps S11 to S16, but also by resetting the receiving device 3 and repeating the steps from startup if the environment of the surrounding structures changes, thereby enabling adaptive processing in response to changes in the reception environment.

[0063] [Supplementary Note] The present invention is not limited to the above-described embodiment, and various modifications and applications are possible, for example, as shown below.

[0064] (1) The receiving device 3 can be realized by a computer and a program, but this program can also be recorded on a (non-transitory) recording medium or provided via a communication network such as the Internet.

[0065] (2) The CPU 301 (microprocessor) may be a single or multiple processors.

[0066] 3 Receiving device 30 Parameter storage unit 31 GNSS antenna 32 Satellite signal receiving unit 33 Mask setting unit 34 Positioning and time synchronization calculation unit 35 Output unit

Claims

1. A receiving device that receives satellite signals in a fixed state to perform positioning or time synchronization, the receiving device having a mask setting unit that estimates the satellite signal to be a visible satellite signal when the signal strength of the satellite signal is equal to or greater than a first threshold and the delay time from a reference value of the reception time of the satellite signal is equal to or less than a second threshold, and updates the satellite signal reception mask based on the position of a first visible satellite signal that is equal to or less than an elevation angle threshold in a satellite signal reception mask that indicates an elevation angle threshold for each direction, among the positions of the visible satellite signals in a sky plot, at a specified time epoch.

2. The receiving device described in claim 1, wherein the mask setting unit updates the updated satellite signal reception mask based on the position of a second visible satellite signal among the positions of the visible satellite signals, which is in the same orientation as the position of the first visible satellite signal and is equal to or less than the elevation angle threshold, in a time epoch after the specified time epoch.

3. The receiving device described in claim 2, wherein the mask setting unit does not update the portion of the satellite signal reception mask from the position of the first visible satellite signal to the position of the second visible satellite signal when the position of the second visible satellite signal has a larger elevation angle than the position of the first visible satellite signal.

4. The receiving device described in claim 1, wherein the mask setting unit updates the satellite signal reception mask so that it has a shape formed by joining the line segments connecting the end points of the satellite signal reception mask before the update within a specified area divided in azimuth on the sky plot and the positions of visible satellite signals within the specified area that are closest in azimuth.

5. A receiving device as described in claim 2 or 3, wherein the mask setting unit fixes the mask profile when it is determined that the change in the mask profile of the satellite signal reception mask before and after the update falls below a change threshold and has converged.

6. A receiving method executed by a receiving device that receives satellite signals in a fixed state and performs positioning or time synchronization, wherein, when the signal strength of the satellite signal is equal to or greater than a first threshold and the delay time from a reference value of the reception time of the satellite signal is equal to or less than a second threshold, the satellite signal is estimated to be a visible satellite signal, and a mask setting process is executed to update the satellite signal reception mask based on the position of a first visible satellite signal that is equal to or less than an elevation angle threshold in a satellite signal reception mask that indicates an elevation angle threshold for each direction, among the positions of the visible satellite signals in a sky plot, at a predetermined time epoch.

7. A program for causing a computer to execute the method according to claim 6.

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