Satellite signal receiving device and program

Abstract

To perform positioning and time synchronization by GNSS with good accuracy, even when a satellite signal reception environment is bad.SOLUTION: A satellite signal receiver comprises a signal selection unit that selects a prescribed number of satellite signals on the basis of the reception quality of satellite signals received by a GNSS antenna, and a measurement unit that executes positioning or time synchronization using the prescribed number of satellite signals selected by the signal selection unit. The signal selection unit selects a satellite signal the reception quality of which is best from all of the satellite signals received, and selects all satellite signals the reception quality of which are better than a lower limit that is defined as equivalent to the value of the best reception quality minus a prescribed value.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] The present invention relates to a technology for performing highly accurate positioning and time synchronization using a Global Navigation Satellite System (GNSS). [Background technology]

[0002] In recent years, GNSS positioning and time synchronization have been used in a wide range of applications.

[0003] In GNSS-based positioning and time synchronization, the positioning and time synchronization processes are performed using GNSS satellite signals (hereinafter, satellite signals) received by a GNSS antenna.

[0004] There are cases where structures around the installation location of the GNSS antenna block line-of-sight reception of satellite signals. In such cases, the satellite signals are not received at the required signal strength by the GNSS antenna, or are received as invisible satellite signals due to multipath reflection and diffraction by structures around the installation location of the GNSS antenna. As a result, the positioning performance and time synchronization performance of the GNSS are degraded. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Tsukagoshi et al. "Position Estimation for Autonomous Mobile Robot Navigation in Promenade Environments Using Open Source GNSS Library" Transactions of the Society of Instrument and Control Engineers, Vol. 52, No. 5, 276 / 283 (2016) Summary of the Invention [Problem to be solved by the invention]

[0006] In order to improve the accuracy of GNSS positioning and time synchronization, it is important to receive as many visible satellite signals as possible in line of sight and to effectively exclude invisible satellite signals that cannot be received in line of sight, which have a significant impact on degradation of accuracy, from the satellite signals used for positioning and time synchronization.

[0007] The present invention has been made in consideration of the above-mentioned points, and aims to provide a technology that enables appropriate selection of satellite signals and accurate GNSS-based positioning and time synchronization even when the satellite signal reception environment is poor. [Means for solving the problem]

[0008] According to the disclosed technology, a signal selection unit that selects a predetermined number of satellite signals based on reception quality of the satellite signals received by a GNSS antenna; a measurement unit that performs positioning or time synchronization using a predetermined number of satellite signals selected by the signal selection unit, the signal selection unit selects the satellite signal with the best reception quality from all received satellite signals, and sets a lower limit to a value obtained by subtracting a predetermined value from the best reception quality, and selects all satellite signals with reception quality lower than the lower limit. A satellite signal receiving device, When the total number of the satellite signal with the best reception quality and all satellite signals with reception quality better than the lower limit is less than the predetermined number, the signal selection unit selects satellite signals with reception quality equal to or lower than the lower limit using reception quality obtained by adding a premium corresponding to the priority of the GNSS type to the reception quality of the satellite signals with reception quality equal to or lower than the lower limit, so that the total number of selected satellite signals becomes the predetermined number. A satellite signal receiving device is provided. Effect of the Invention

[0009] According to the disclosed technology, a technology is provided that enables accurate positioning and time synchronization using GNSS even when the satellite signal reception environment is poor. [Brief description of the drawings]

[0010] [Figure 1] 1 is a configuration diagram of a measurement device according to an embodiment of the present invention. [Diagram 2] FIG. 11 is a diagram showing an example of a processing procedure related to selection of a satellite signal. [Diagram 3]FIG. 11 is a diagram illustrating an example of setting parameters. [Figure 4] FIG. 11 is a diagram illustrating an example of setting a GNSS bias value. [Diagram 5] FIG. 13 is a diagram illustrating an example of setting an elevation angle bias value. [Figure 6] FIG. 13 is a diagram illustrating an example of setting GNSS priority levels. [Figure 7] FIG. 11 is a diagram showing a processing procedure relating to setting of a bias value. [Figure 8] FIG. 13 is a diagram showing the maximum CNR value for each group. [Figure 9] FIG. 13 is a diagram illustrating an example of curve fitting. [Figure 10] FIG. 11 is a diagram illustrating an example of bias value setting. [Figure 11] FIG. 2 is a diagram showing how a satellite signal is incident on and reflected from a wall of a building. [Figure 12] FIG. 2 is a diagram showing how a satellite signal is incident on and reflected from a wall of a building. [Figure 13] FIG. 13 is a diagram showing an example of setting a dCNR value depending on an elevation angle. [Figure 14] FIG. 11 is a diagram showing an example of a processing procedure related to selection of a satellite signal. [Figure 15] FIG. 11 is a diagram illustrating an example of setting parameters. [Figure 16] FIG. 11 is a diagram showing a processing procedure relating to setting of a bias value. [Figure 17] FIG. 11 is a diagram illustrating an example of bias value setting. [Figure 18] FIG. 1 is a diagram showing an example of actual measurement of reception characteristics in the L1 band. [Figure 19] FIG. 1 is a diagram showing an example of actual measurement of reception characteristics in the L2 band. [Figure 20] FIG. 2 illustrates an example of a hardware configuration of the apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment.

[0012] (Details of the problem, summary of the embodiment) In recent years, navigation satellite systems other than GPS, such as GLONASS, Galileo, BeiDou, and QZSS, have become available, and the number of satellites is increasing.

[0013] As mentioned above, in order to improve the accuracy of GNSS positioning and time synchronization, it is important to receive as many visible satellite signals as possible in line of sight and to effectively exclude invisible satellite signals that cannot be received in line of sight and which have a significant impact on degradation of accuracy from the satellite signals used for positioning and time synchronization.

[0014] A conventional method for eliminating invisible satellite signals is known as a CNR masking method, which eliminates satellite signals with a CNR (Carrier-to-Noise Ratio) below a preset threshold from received satellite signals.

[0015] However, since the CNR value of a satellite signal depends on factors such as the antenna gain, the receiver sensitivity, the cable loss between the antenna and receiver, and the type of satellite, it is difficult to set an optimal threshold value.

[0016] In addition, with the CNR masking method, if an interference signal is mixed into the signal bandwidth of a satellite signal, the CNR value of the satellite signal drops overall, and there is a risk that the satellite signal will be lost due to the CNR mask, making positioning and time synchronization impossible. Such interference signals include intentionally generated GNSS jamming (disturbing) signals, as well as noise generated by equipment and interference signals from other communication systems.

[0017] In this embodiment, in order to receive many visible satellite signals that can be received in line of sight and effectively exclude invisible satellite signals that cannot be received in line of sight and have a significant effect on deterioration of accuracy from the satellite signals used for positioning and time synchronization, a satellite signal suitable for use in positioning and time synchronization is selected according to the procedure described below, which assumes a multi-GNSS environment in which a large number of visible satellites can be secured. This procedure uses the reception quality of the satellite signal as the basis for selection, and makes it possible to select a satellite signal that is free of the effects of individual characteristics of the antenna and receiver and interference signals.

[0018] A specific example of the configuration and operation of this embodiment will be described in detail below. In the process described below, CNR is used as an index of reception quality, but an index of reception quality other than CNR may be used. In this embodiment, the "satellite signal" when "selecting a satellite signal" is linked to the GNSS satellite that transmits the satellite signal. For example, if GNSS satellite A, GNSS satellite B, and GNSS satellite C are three different arbitrary GNSS satellites, selecting three satellite signals means selecting the satellite signal from GNSS satellite A, the satellite signal from GNSS satellite B, and the satellite signal from GNSS satellite C.

[0019] In addition, in this embodiment, the elevation angle dependency and the GNSS type / frequency band dependency are taken into consideration when normalizing the CNR value. Here, the GNSS type means the type of navigation satellite system such as GPS or GLONASS. The reason for taking the elevation angle dependency into consideration is that the smaller the elevation angle of the satellite, the longer the propagation path in the troposphere close to the earth's surface becomes, and the more the satellite signal tends to attenuate. The reason for taking the GNSS type dependency into consideration is that the signal frequency and transmission power differ depending on the GNSS type, which causes a difference in the CNR value. Furthermore, even for the same GNSS type, the CNR value differs depending on the frequency band of the signal (L1 band, L2 band, L5 band, etc. in the case of GPS). It is also possible to take into consideration either the elevation angle dependency or the GNSS type / frequency band dependency.

[0020] A first embodiment and a second embodiment will be described below. Regarding the second embodiment, differences from the first embodiment will be mainly described. ------------------First embodiment--------------------------------

[0021] (Device configuration) 1 shows an example of the configuration of a measurement device 100 according to this embodiment. The measurement device 100 according to this embodiment includes a GNSS antenna 110, a signal receiving unit 120, a signal selecting unit 130, a measurement unit 140, an output unit 150, a signal data storage unit 160, a bias value setting unit 170, and a bias value storage unit 180. Note that the measurement device 100 is a device that receives and processes satellite signals, and may be called a "satellite signal receiving device."

[0022] The GNSS antenna 110 receives radio waves transmitted from orbiting GNSS satellites and converts the radio waves into electrical signals, which may be referred to as "satellite signals."

[0023] The GNSS antenna 110 and the signal receiving unit 120 are connected by a cable, and the satellite signal is sent to the signal receiving unit 120 via the cable. If the distance between the GNSS antenna 110 and the signal receiving unit 120 is long, an amplifier may be provided between the GNSS antenna 110 and the signal receiving unit 120.

[0024] The signal receiving unit 120 receives a satellite signal, measures the CNR, and identifies the type of the GNSS satellite that is the transmission source of the received satellite signal. In addition, the elevation angle is measured using satellite orbit information (e.g., almanac, ephemeris). The satellite orbit information may be acquired from the navigation message of the satellite signal, or may be acquired from other means (e.g., a server on a network). The signal receiving unit 120 sends the identification information (a code such as a PRN number) of the received satellite signal, the elevation angle of the satellite signal, the CNR, and the satellite type to the signal selecting unit 130. In addition, the signal receiving unit 120 stores the identification information, elevation angle, CNR, and satellite type of each received satellite signal in the signal data storage unit 160. The elevation angle is the angle between the line of sight and the horizontal plane when viewing the GNSS satellite that is the transmission source of the satellite signal from the reception point of the satellite signal (i.e., the GNSS antenna). For example, when the GNSS satellite is at the zenith, its elevation angle is 90°.

[0025] The types of GNSS satellites covered in this embodiment are GPS, GLONASS, Galileo, BeiDou, and QZSS. However, these are merely examples, and there may be more or less types than these.

[0026] The signal selection unit 130 selects a satellite signal to be used for positioning and time synchronization from among the multiple received satellite signals. The selection procedure will be described later.

[0027] The measurement unit 140 calculates time information that is highly accurately synchronized with the absolute time by performing time synchronization using a satellite signal transmitted from a GNSS satellite equipped with an atomic clock that is precisely managed with respect to the absolute time. The absolute time here is, for example, Coordinated Universal Time (UTC). Note that the measurement unit 140 may perform only one of positioning and time synchronization.

[0028] From the received satellite signal, the absolute time at which the satellite signal was transmitted from the GNSS satellite can be known. However, unless the propagation time from the GNSS satellite to the position of the GNSS antenna 110 is measured and the time offset value Δt between the time of the measurement unit 140 and the time of the satellite is corrected, accurate absolute time cannot be obtained at the receiving position.

[0029] Therefore, the measurement unit 140 performs positioning and time synchronization simultaneously by calculating four parameters, namely, three-dimensional coordinate information (x, y, z) of the reception position and a time offset (Δt) by code positioning using satellite signals from, for example, four or more GNSS satellites. The measurement unit 140 may perform carrier phase positioning in addition to code positioning.

[0030] The measurement unit 140 outputs time information based on this absolute time and location information that is the positioning result via the output unit 150. For example, if the measurement device 100 is a base station in a mobile network, the base station can use the time information synchronized with the absolute time to, for example, match the time slot configuration (arrangement) of the uplink and downlink signals of a TDD (Time Division Duplex) signal frame with an adjacent base station (synchronized with the absolute time) and then synchronize the transmission timing of the signal frame, thereby transmitting a TDD signal without interfering with the adjacent base station.

[0031] The bias value setting unit 170 sets (calculates) a bias value using the satellite signal data stored in the signal data storage unit 160, and stores the set bias value in the bias value storage unit 180. The bias value stored in the bias value storage unit 180 is used in the satellite signal selection process in the signal selection unit 130. The bias value setting operation by the bias value setting unit 170 will be described in detail later.

[0032] The measuring device 100 in this embodiment may be a single, physically integrated device, or may be a device in which several functional units are physically separated and the separated functional units are connected via a network.

[0033] In addition, the measurement device 100 may include all of the functions shown in FIG. 1, or some of the functions (e.g., the signal selection unit 130 and the measurement unit 140) may be provided on a network (e.g., on the cloud), and the remaining functions may be installed in and used by the measurement device 100.

[0034] For example, satellite signal selection and positioning calculation may be performed on the cloud by outputting observation data from the signal receiving unit 120 provided in the measuring device 100 and transmitting the observation data to a device consisting of a signal selecting unit 130 and a measuring unit 140 provided on the cloud. In this case, the measuring unit 140 on the cloud returns the positioning calculation result to the output unit 150.

[0035] Furthermore, a device consisting of "signal data storage unit 160 and bias value setting unit 170" in measuring device 100 may be provided on a network (eg, on the cloud), and the remaining functions may be installed in measuring device 100 and used.

[0036] For example, the signal receiving unit 120 in the measuring device 100 outputs observation data, stores the observation data in the signal data storage unit 160 provided on the cloud, and the bias value setting unit 170 provided on the cloud sets the bias value using the stored data. In this case, the bias value is returned from the bias value setting unit 170 on the cloud to the bias value storage unit 180.

[0037] (Example of operation of signal selection unit 130) Next, an example of the operation of the signal selection unit 130 will be described in detail following the procedure of the flowchart shown in Fig. 2. In describing the procedure, Figs. 3 to 6 will also be referenced.

[0038] First, the setting parameters used in the procedure will be described with reference to Fig. 3. As shown in Fig. 3, CNR0 is the maximum CNR value of all received satellite signals in the L1 band. dCNR is a parameter that determines the selection range of satellite signals. N0 is the number of selected satellite signals. Note that reception in the L1 band is just one example.

[0039] In S101 of FIG. 2, the signal selection unit 130 normalizes the CNR values of all satellite signals received in the L1 band, taking into account the GNSS type and elevation angle dependency. Specifically, normalization is performed by adding the GNSS bias value and the elevation angle bias value preset by the bias value setting unit 170 to the CNR value obtained by observation.

[0040] FIG. 4 shows an example of setting the GNSS bias value, and FIG. 5 shows an example of setting the elevation angle bias value. These bias values are stored in the bias value storage unit 180.

[0041] For example, assuming that the CNR value obtained by observing a certain satellite signal is 30 dB-Hz, the elevation angle is 30°, and the satellite type is GLO (GLONASS), the signal selection unit 130 sets the CNR value after correction (after normalization) of the satellite signal to 30 + 4 + 2 = 36 dB-Hz. Hereafter, the CNR value means the CNR value after normalization.

[0042] In S102 of FIG. 2, the signal selection unit 130 selects the satellite signal with the largest CNR value from all the satellite signals received in the L1 band, and records its CNR value as CNR0. Here, it is assumed as a precondition that there is at least one visible satellite signal.

[0043] In S103, the signal selection unit 130 sets a value smaller than CNR0 by dCNR (e.g., 10 dB) as the lower limit of CNR for the CNR value (CNR0) of the satellite signal selected in S102, and selects the satellite signals that meet the conditions from the received satellite signals. That is, the signal selection unit 130 selects all satellite signals that satisfy CNR0 - dCNR < CNR < CNR0 from all the satellite signals received in the L1 band.

[0044] In S104, the signal selection unit 130 determines whether the number of satellite signals selected in S102 and S103 is equal to or greater than a preset minimum number of selected satellite signals (N0). If the determination result in S104 is Yes, the signal selection process by the signal selection unit 130 ends. The signal selection unit 130 notifies the measurement unit 140 of the identification information (code such as a PRN number) of the selected satellite signal, and the measurement unit 140 performs positioning and time synchronization using the selected satellite signal.

[0045] If the determination result in S104 is No, that is, if the number of satellite signals selected in S102 and S103 is less than the preset minimum number of selectable satellite signals (N0), the process proceeds to S105.

[0046] In S105, the signal selection unit 130 selects satellite signals in order from the satellite signal with the next highest CNR value whose CNR value is less than "CNR0-dCNR" based on the preset priority order of GNSS types, and compensates for the total number of selected satellite signals to be N0.

[0047] An example of setting the priority order of GNSS types is shown in Fig. 6. The setting values ​​of the priority order of GNSS types are also stored in the bias value storage unit 180, and the signal selection unit 130 refers to the setting values ​​stored in the bias value storage unit 180. Fig. 6 shows that GPS has the highest priority order, and GLO (GLONASS) has the lowest priority order.

[0048] Here, we will explain the selection based on the priority order of GNSS types. For each type of GNSS satellite, there is a difference (clock bias) in the time accuracy based on the absolute time of the clock operating the satellite. When selecting a substitute satellite signal in S105, the reliability of the GNSS, including the clock bias, is taken into consideration.

[0049] For example, GPS and QZSS are navigation satellite systems whose time is perfectly synchronized with each other and whose clock bias is small, so they can be classified as Category 1, Galileo as Category 2, and GLONASS and BeiDou as Category 3. Based on such categorization, the priorities are set as shown in Figure 6.

[0050] One example of a method for selecting alternative satellite signals that takes into account the priority order based on reliability as described above is to set a premium (value added) to the CNR value according to the priority order (or reliability category), and then select the required number of satellite signals starting with the satellite signals with the highest CNR values.

[0051] For example, in the example of FIG. 6, the premium for priority 1 is 5, the premium for priority 2 is 4, the premium for priority 3 is 3, the premium for priority 4 is 2, and the premium for priority 5 is 1.

[0052] As an example, assume that N0 is 5, and three satellite signals have been selected in S102 and S103. If satellite signals having a CNR value less than "CNR0-dCNR" include satellite signal 1 (CNR value=26 dB-Hz, premium=1), satellite signal 2 (CNR value=25 dB-Hz, premium=3), and satellite signal 3 (CNR value=24 dB-Hz, premium=5), then in S105 signal selection unit 130 selects satellite signal 3 and satellite signal 2 whose CNR values ​​including premium are 29 dB-Hz and 28 dB-Hz.

[0053] (Example of bias value setting) Next, an example of an operation for setting a bias value will be described in detail along the procedure of the flowchart shown in Fig. 7. In describing the procedure, Figs. 8 to 10 will also be referred to.

[0054] In S201, satellite signal data is continuously collected by the signal receiving unit 120. Regarding the length of time for collection, in an open sky environment, collection for 24 hours is sufficient. In other reception environments, continuous collection for a longer period is necessary. Data may be collected as needed and the bias value may be updated.

[0055] In S202, the collected satellite signal data is stored in the signal data storage unit 160 as a set of (GNSS type, elevation angle, CNR value).

[0056] In S203, the bias value setting unit 170 divides the data of the same GNSS type into groups for each elevation angle range based on the satellite signal data stored in the signal data storage unit 160, and extracts the maximum CNR value for each group.

[0057] An example of the process of S203 for a certain GNSS type is shown in Fig. 8. In the example of Fig. 8, the elevation angles are grouped into 0° to 15°, 15° to 30°, 30° to 45°, 45° to 60°, 60° to 75°, and 75° to 90°, and the maximum CNR value of each group is extracted.

[0058] In S204, the bias value setting unit 170 applies curve fitting to the extracted maximum value data, for example, by a nonlinear least squares method. In S205, the bias value setting unit 170 repeats the curve fitting several times, excluding the largest outlier. An example of S204 and S205 for the GNSS type shown in FIG. 8 is shown in FIG. 9.

[0059] In S206, the bias value setting unit 170 generates a fitting function for each GNSS type, and in S207, sets a bias value for the GNSS type and elevation angle using the fitting function for each GNSS type. An example of S206 and S207 is shown in Fig. 10. As shown in Fig. 10, for each GNSS type, a larger bias value is set as the elevation angle becomes smaller. Also, in the example of Fig. 10, bias values ​​are set in the order of GNSS-C>GNSS-B>GNSS-A between the GNSS types.

[0060] (About the dCNR setting value) Next, the dCNR setting value (called dCNR value) will be described. As described in S103 of FIG. 2, the dCNR value is a parameter that determines the range of CNR values ​​for selecting satellite signals. The dCNR value may be a fixed value that does not depend on the elevation angle of the satellite signal, but an example in which the dCNR value is determined depending on the elevation angle of the satellite signal will be described below. The example described here is an example assuming a case in which the reflecting surface of a satellite signal is a vertical wall surface (concrete or glass) of a building, such as in an urban area.

[0061] Figure 11 shows how a satellite signal with a high elevation angle is incident on and reflected by a vertical wall of a building, and Figure 12 shows how a satellite signal with a low elevation angle is incident on and reflected by a vertical wall of a building. As shown in Figures 11 and 12, the angle of incidence of a satellite signal with a low elevation angle on a vertical wall of a building is larger than the angle of incidence of a satellite signal with a high elevation angle on a vertical wall of a building.

[0062] Because the reflectivity of a satellite signal from the vertical walls of a building depends on the angle of incidence, it is expected that a satellite signal with a low elevation angle will have a relatively higher reflectivity (the reflected signal strength will be greater) than a satellite signal with a high elevation angle.

[0063] Therefore, giving the dCNR value an elevation angle dependency is effective in selecting visible / invisible satellites. Fig. 13 shows an example of setting the dCNR value given the elevation angle dependency. As shown in Fig. 13, the dCNR value is set so that it increases as the elevation angle of the satellite signal increases. Such a setting value having the elevation angle dependency may be stored in the bias value storage unit 180 in the form of a function corresponding to the curve in Fig. 13, for example, or may be stored in the bias value storage unit 180 in the form of a table that holds the dCNR value for each elevation angle (for example, in 5° increments).

[0064] In S103 described above, when determining whether the CNR value of a certain satellite signal satisfies "CNR0 - dCNR < CNR < CNR0", the signal selection unit 130 refers to the bias value storage unit 180 to obtain the dCNR value corresponding to the elevation angle of the satellite signal, and uses the dCNR value to determine whether "CNR0 - dCNR < CNR < CNR0" is satisfied.

[0065] Also, in the selection of supplementary satellite signals in S105 described above, when determining whether the CNR value of a certain satellite signal is less than or equal to "CNR0 - dCNR", the signal selection unit 130 refers to the bias value storage unit 180 to obtain the dCNR value corresponding to the elevation angle of the satellite signal, and uses the dCNR value to determine whether it is less than or equal to "CNR0 - dCNR".

[0066] In the determination of whether to select a satellite signal by "CNR0 - dCNR < CNR < CNR0", since the dCNR value of a satellite signal with a lower elevation angle is smaller than that of a satellite signal with a higher elevation angle, the range of "CNR0 - dCNR < CNR < CNR0" is narrower for a satellite signal with a lower elevation angle than for a satellite signal with a higher elevation angle. That is, a more stringent filtering is performed on a satellite signal with a lower elevation angle than on a satellite signal with a higher elevation angle. The reason for making the dCNR value have an elevation angle dependence so that a more stringent filtering is performed on a satellite signal with a lower elevation angle than on a satellite signal with a higher elevation angle will be explained below.

[0067] Assuming that the reflecting surface of the satellite signal in the urban area is the vertical wall surface (concrete or glass) of a building, the satellite signal with a low elevation angle will be in a state close to total reflection, and the difference between the signal intensity of the reflected satellite signal and the signal intensity when received as a direct wave without obstacles (the reference signal intensity normalized by the bias values in FIGS. 4 and 5) will be small.

[0068] That is, for low-elevation satellite signals, the optical path length of the medium that attenuates the signal strength, such as the ionosphere and the troposphere, becomes longer, so the signal strength when received as a direct wave becomes smaller. On the other hand, since the decrease in the signal strength when reflected by a building is small, it is necessary to reduce the dCNR value and perform filtering more strictly to remove the multipath signal (reflected wave) of the invisible satellite signal. For high-elevation satellites, the opposite is true, expanding the range of "CNR0 - dCNR < CNR < CNR0" and making them easier to select.

[0069] Note that giving the dCNR value an elevation dependency such that the dCNR value increases as the elevation of the satellite signal increases is just an example. Depending on the environment, it may be appropriate to give the dCNR value a different elevation dependency.

[0070] It is also conceivable to perform satellite selection for each satellite type unit, but this is not done. The reasons are as follows.

[0071] In the technology according to the present invention, it is premised that at least one visible satellite exists. When satellite selection is performed for each satellite type unit, if there is no visible satellite in a certain satellite type, the reference CNR value (CNR0) may become an inappropriate value, and the accuracy of satellite selection may deteriorate. If all satellite types are targeted as in the first and second embodiments, the probability of at least one visible satellite existing increases. ―――――――――――Second Embodiment―――――――――――

[0072] Next, the second embodiment will be described. The second embodiment is different from the first embodiment in that the measuring device 100 selects satellite signals for each frequency band. That is, in the first embodiment, satellite signal selection was performed targeting only the L1 band as an example, but in the second embodiment, satellite signal selection is performed for each of the plurality of frequency bands output by each satellite.

[0073] The effect of the invention can be achieved by the technique described in the first embodiment. The second embodiment is a variation of the embodiment of the invention. In the second embodiment, the reason for selecting a satellite signal for each frequency band is as follows.

[0074] Since each satellite outputs signals in multiple frequency bands, from the perspective of selecting a satellite suitable for positioning based on the satellite's position (visible / invisible), if the visibility of a satellite can be accurately determined using a satellite signal in any one frequency band, there is no need to select a satellite using signals in each of the multiple frequency bands.

[0075] However, in reality, it is not guaranteed that visibility can be determined 100% accurately. Also, the reception characteristics of antennas and receivers and the state of interference signals may differ for each frequency band, and selecting satellite signals from multiple frequency bands may result in the selection of a combination of satellite signals that is more suitable for positioning calculations.

[0076] In positioning calculations, different satellite signals can be used for each frequency band. Since different satellites support different frequency bands (for example, the GPS L5 frequency band is only compatible with some satellites), by selecting satellite signals individually for each frequency band, it is possible to expand the variation of policy settings for positioning calculations (such as changing the N0 value for each frequency band).

[0077] (Device configuration) The device configuration of the measuring device 100 in the second embodiment is the same as that in the first embodiment, as shown in Fig. 1. The operation of each unit is also basically the same as in the first embodiment, but differs from the first embodiment in that an operation is performed to select a satellite signal for each frequency band.

[0078] That is, the signal receiving unit 120 sends the identification information (a code such as a PRN number) of the received satellite signal, the elevation angle of the satellite signal, the CNR, and the satellite type to the signal selecting unit 130 for each frequency band. Furthermore, the signal receiving unit 120 stores the identification information, elevation angle, CNR, and satellite type of each received satellite signal for each frequency band in the signal data storage unit 160. In this embodiment, the L1 band and the L2 band are targeted as the multiple frequency bands. However, the use of the L1 band and the L2 band is an example, and the L5 band may be used in addition to these, or a frequency band other than the L1 band, the L2 band, and the L5 band may be used.

[0079] (Example of operation of signal selection unit 130) Next, an example of the operation of the signal selection unit 130 in the second embodiment will be described. Fig. 14 is a flowchart showing the operation of the signal selection unit 130. Although the flow is basically the same as that in the first embodiment shown in Fig. 2, the second embodiment differs from the first embodiment in that the flow of Fig. 14 is repeated for each frequency band, and in S113 (corresponding to S103 in Fig. 2), it is determined whether the minimum CNR value in the frequency band being processed is satisfied. Note that Fig. 14 shows the processing for the L1 band in the repetition for each frequency band, as an example.

[0080] First, the setting parameters used in the procedure of the second embodiment will be described with reference to Fig. 15. As shown in Fig. 15, L1 is the minimum CNR value of the selected satellite in the L1 band. dCNR L1 is a parameter that determines the selection range of L1 band satellite signals. 0L1 is the number of selected satellite signals in the L1 band. Similar parameters are set for the L2 band. If you use other frequency bands, you can set parameters for each frequency band. For example, in the L5 band, CNR L5 Set the following:

[0081] First, for the L1 band, the process of the flow in FIG. 14 is executed. The processes of S101 and S102 are the same as those in the first embodiment. However, in the second embodiment, bias values as shown in FIGS. 4 and 5 are set for each frequency band, and in the normalization process of S101, normalization is performed using the bias value corresponding to the frequency band being processed. In S102, the satellite signal with the largest CNR value is selected from all the satellite signals received in the corresponding frequency band (initially the L1 band), and its CNR value is recorded as CNR0.

[0082] In S113, the signal selection unit 130 sets a value that is dCNR L1 (e.g., 10 dB) smaller than the CNR value (CNR0) of the satellite signal selected in S102 as the lower limit of CNR, and selects satellite signals that meet the conditions from the received satellite signals. Here, the signal selection unit 130 selects, from all the satellite signals received in the L1 band, all satellite signals that satisfy CNR0 - dCNR L1 < CNR < CNR0 and also satisfy L1 < CNR.

[0083] In S104, the signal selection unit 130 determines whether the number of satellite signals selected in S102 and S103 is equal to or greater than a preset minimum number of selected satellite signals (N 0L1 ). If the determination result of S104 is Yes, the signal selection process by the signal selection unit 130 for the L1 band ends. The signal selection unit 130 notifies the measurement unit 140 of the identification information (codes such as PRN numbers) of the selected satellite signals, and the measurement unit 140 performs positioning and time synchronization using the selected satellite signals.

[0084] The signal selection unit 130 executes the process of the flow in FIG. 14 for the next frequency band (e.g., the L2 band).

[0085] If the determination result of S104 is No, that is, if the number of satellite signals selected in S102 and S103 is less than the preset minimum number of selected satellite signals (N 0L1 ), the process proceeds to S105.

[0086] The process of S105 may be the same as the process described in the first embodiment. That is, in S105, the signal selection unit 130 selects satellite signals in descending order of CNR value from the satellite signal with the next largest CNR value that is equal to or less than "CNR0-dCNR" based on the preset priority order of GNSS types (e.g., FIG. 6), until the total number of selected satellite signals reaches N 0L1 Compensate so that it becomes.

[0087] 6 may be set for each frequency band. In this case, the signal selection unit 130 selects a satellite signal using the priority order corresponding to the frequency band being processed.

[0088] As in the first embodiment, a method for selecting alternative satellite signals taking into account priority based on reliability can be used in which a premium (value added) is set to the CNR value according to the priority (or reliability category), and the required number of satellite signals is selected in order starting from the satellite signal with the highest CNR value.

[0089] For example, in the example of FIG. 6, the premium for priority 1 is 5, the premium for priority 2 is 4, the premium for priority 3 is 3, the premium for priority 4 is 2, and the premium for priority 5 is 1.

[0090] As an example, 0L1 is 5, and three satellite signals are selected in S102 and S103. L1 " If the satellite signals with CNR values ​​below this are satellite signal 1 (CNR value = 26 dB-Hz, premium = 1), satellite signal 2 (CNR value = 25 dB-Hz, premium = 3), and satellite signal 3 (CNR value = 24 dB-Hz, premium = 5), in S105 signal selection unit 130 selects satellite signal 3 and satellite signal 2 whose CNR values ​​including the premium are 29 dB-Hz and 28 dB-Hz.

[0091] When S105 ends, the signal selection unit 130 notifies the measurement unit 140 of the identification information (a code such as a PRN number) of the selected satellite signal, and the measurement unit 140 performs positioning and time synchronization using the selected satellite signal.

[0092] The signal selection unit 130 executes the process of the flow in FIG. 14 for the next frequency band (for example, the L2 band).

[0093] In the above example, positioning and time synchronization are performed using a selected satellite signal for each frequency band, but positioning and time synchronization may also be performed using satellite signals of multiple frequency bands based on a satellite signal selected in a specific frequency band.

[0094] For example, by executing the flow of Figure 14 for each of the L1 band and the L2 band, if satellite signals 1, 2, 3, and 4 are selected in the L1 band and satellite signals 5, 6, 7, and 8 are selected in the L2 band, the DOP (Dilution of Precision) values ​​of satellite signals 1, 2, 3, and 4 may be compared with the DOP values ​​of satellite signals 5, 6, 7, and 8, and the satellite signal of the frequency band with the smaller DOP value may be selected, and positioning and time synchronization may be performed using the L1 band and L2 band signals.

[0095] (Variations in the method of selecting alternate satellite signals) Another example of the selection of an alternate satellite signal in S105 will be described. The signal selection unit 130 may select an alternate satellite signal taking into consideration the DOP value. For example, the signal selection unit 130 selects satellite signals A, B, and C in descending order of the satellite signal with the next largest CNR value that is equal to or less than "CNR0-dCNR" as correction satellite signal candidates, calculates the DOP value when the alternate satellite candidates A, B, and C are each added to the satellite signal already selected, and selects the satellite signal with the smallest DOP value.

[0096] For example, if the satellite signals already selected at the time of S104 are satellite signals 1, 2, and 3, then the DOP values ​​of "satellite signals 1, 2, 3, A," "satellite signals 1, 2, 3, B," and "satellite signals 1, 2, 3, C" are calculated. If the DOP value of "satellite signals 1, 2, 3, A" is the smallest, then "satellite signals 1, 2, 3, A" is selected. If the number of satellites to be selected is greater than 4, the above process can be repeated until that number of satellites is reached.

[0097] Here, the alternative satellite signal selection method described in the first embodiment is referred to as selection method 1, and the above method using the DOP value is referred to as selection method 2. The signal selection unit 130 may select an alternative satellite signal by a combination of selection methods 1 and 2.

[0098] As an example of a combination, selection method 1 is used to select alternate satellite signals, and selection method 2 is then performed on each of the selected satellite signals to select satellite signals with smaller DOP values.

[0099] Also, for example, a cost value (evaluation value) may be set as an expected value representing the degree of improvement in positioning accuracy by the satellite signal selected based on selection methods 1 and 2, and the satellite signal for which the total cost value (evaluation value) of selection methods 1 and 2 is the smallest may be selected as the alternative satellite signal. For example, assume that satellite signals A and B are selected as candidates for the alternative satellite signal by a combination of selection methods 1 and 2. For example, assume that the CNR value of satellite signal A is 30 dB-Hz, the CNR value of satellite signal B is 28 dB-Hz, the DOP value when satellite signal A is selected is 5, and the DOP value when satellite signal B is selected is 4. If the total cost value (evaluation value) of selection methods 1 and 2 is set as the DOP value / CNR value, the cost values ​​of satellite signals A and B are 1 / 6 and 1 / 7, respectively, and satellite signal B is smaller than satellite signal A, so satellite signal B is selected as the alternative satellite signal.

[0100] (Example of bias value setting) In the second embodiment, the bias value setting operation executed by bias value setting unit 170 is basically the same as the bias value setting operation in the first embodiment, but the second embodiment differs from the first embodiment in that a bias value is set for each frequency band.

[0101] 16 shows a flowchart of the bias value setting operation in the second embodiment. In S201, the signal receiving unit 120 continuously collects satellite signal data for each frequency band.

[0102] In S212, the collected satellite signal data is stored in the signal data storage unit 160 as a set of (GNSS type, frequency band, elevation angle, CNR value).

[0103] In S213, the bias value setting unit 170 groups data of the same GNSS type and frequency band for each elevation angle range based on the satellite signal data stored in the signal data storage unit 160, and extracts the maximum CNR value for each group. An example of this process is as described with reference to FIG.

[0104] In S204, the bias value setting unit 170 applies curve fitting to the extracted maximum value data by a nonlinear least squares method or the like. In S205, the bias value setting unit 170 repeats the curve fitting several times, excluding the largest outlier. An example of S204 and S205 for the GNSS type shown in FIG. 8 is as shown in FIG. 9.

[0105] In S206, the bias value setting unit 170 generates a fitting function for each GNSS type, and in S207, sets a bias value for the GNSS type and elevation angle using the fitting function for each GNSS type. An example of S206 and S207 for the L1 band is shown in FIG.

[0106] As described above, in the second embodiment, a bias value is set for each satellite signal frequency band for the GNSS satellite type (for example, L1 band, L2 band, and L5 band for GPS). This is because the satellite signal reception characteristics depend on the frequency band of the satellite signal as well as the GNSS satellite type and elevation angle. Note that a bias value may be set based only on the GNSS satellite type and frequency band without using the elevation angle.

[0107] Figures 18 and 19 show actual measurement examples of the difference in reception characteristics depending on the frequency band for the same combination of GNSS antenna and GNSS receiver. Figure 18 shows the GPS L1 signal, and Figure 19 shows the GPS L2 signal. In both Figures 18 and 19, the horizontal axis is the elevation angle (°) and the vertical axis is the CNR (SNR) value (dB-Hz).

[0108] (Variations regarding bias value settings) Even for the same GNSS type, the transmission signal output may differ depending on the individual satellite. For example, the transmission signal output may differ depending on the satellite orbit (GEO / IGSO / MEO). In that case, a bias value may be set for each individual satellite.

[0109] For example, if the transmitted signal strength of satellite A is weaker than the signal strength of other satellites of the same GNSS type, the received signal strength may be weak and the satellite may not be selected even if it is received as a direct wave. In such a case, a correction is performed by adding an individual bias value to the reception quality of the satellite signal during normalization. The individual bias value is applied in addition to the GNSS bias value and elevation bias value shown in Figures 4 and 5. Alternatively, for satellite signals to which an individual bias value is applied, only the individual bias value may be applied without applying the GNSS bias value and elevation bias value. Alternatively, for satellite signals to which an individual bias value is applied, the elevation bias value and individual bias value may be applied without applying the GNSS bias value.

[0110] Regarding which GNSS type and which satellite to set an individual bias value for, for example, the received signal strength is measured in advance for each GNSS type and each satellite, the measurement values ​​are stored in the signal data storage unit 160, and the bias value setting unit 170 selects a satellite for which an event similar to that of satellite A described above occurs, and sets an individual bias value for the selected satellite.

[0111] Also, individual bias values ​​for particular satellites may be applied in cases other than those involving transmitted signal power, such as satellite A above.

[0112] (About the dCNR setting value) Regarding the dCNR value for each frequency band in the second embodiment, a dCNR value having an elevation angle dependency may be set as described with reference to Figures 11 and 12. In this case, for example, a dCNR value having an elevation angle dependency as shown in Figure 13 is set for each frequency band.

[0113] (Hardware configuration example) 20 is a diagram showing an example of the hardware configuration of a computer that can be used as the measuring device 100 in the first and second embodiments. The computer may be a computer as a physical device, or may be a virtual machine on the cloud.

[0114] The computer in Fig. 20 includes a drive device 1000, an auxiliary storage device 1002, a memory device 1003, a CPU 1004, an interface device 1005, a display device 1006, an input device 1007, and an output device 1008, which are all connected to each other via a bus B. Note that the GNSS antenna 110 is not shown in Fig. 20. The GNSS antenna 110 is connected to, for example, the interface device 1005.

[0115] The program for realizing the processing on the computer is provided by a recording medium 1001 such as a CD-ROM or a memory card. When the recording medium 1001 storing the program is set in the drive device 1000, the program is installed from the recording medium 1001 to the auxiliary storage device 1002 via the drive device 1000. However, the program does not necessarily have to be installed from the recording medium 1001, but may be downloaded from another computer via a network. The auxiliary storage device 1002 stores the installed program as well as necessary files, data, etc.

[0116] The memory device 1003 reads out and stores the program from the auxiliary storage device 1002 when an instruction to start the program is received. The CPU 1004 realizes functions related to the measuring device 100 in accordance with the program stored in the memory device 1003. The interface device 1005 is used as an interface for connecting to the GNSS antenna 110. The display device 1006 displays a GUI (Graphical User Interface) or the like according to a program. The input device 1007 is composed of a keyboard and mouse, buttons, a touch panel, or the like, and is used to input various operation instructions. The output device 1008 outputs the results of calculations.

[0117] (Effects of the embodiment) As described above, according to the first and second embodiments of the present invention, a reference value for reception quality (CNR0) is measured to reflect fluctuations in reception quality due to the characteristics of the equipment used and the superposition of interference signals, and satellite signals are selected taking into account reception quality due to satellite type and elevation angle, thereby making it possible to perform accurate GNSS-based positioning and time synchronization even when the satellite signal reception environment is poor.

[0118] (Summary of the embodiment) In the present embodiment, at least the measurement device, the measurement method, and the program described in the following items are provided. (Section 1) a signal selection unit that selects a predetermined number of satellite signals based on reception quality of the satellite signals received by the GNSS antenna; a measurement unit that performs positioning or time synchronization using a predetermined number of satellite signals selected by the signal selection unit; A satellite signal receiving device comprising: (Section 2) The signal selection unit normalizes reception quality measured from the received satellite signals based on the GNSS type, frequency band, or elevation angle of the satellite signals, and selects the predetermined number of satellite signals using the normalized reception quality. 2. A satellite signal receiving device as described in item 1. (Section 3) The signal selection unit performs the normalization by adding a bias value that is set in advance based on a GNSS type or an elevation angle of the satellite signal to the reception quality measured from the received satellite signal. 3. A satellite signal receiving device as defined in claim 2. (Section 4) a bias value setting unit that obtains a fitting function for the elevation angle and reception quality for each GNSS type and frequency band based on the GNSS type, frequency band, elevation angle, and reception quality of the collected satellite signal, and sets the bias value using the obtained fitting function 4. A satellite signal receiving device according to claim 3, comprising: (Section 5) The signal selection unit normalizes reception quality of a satellite signal received from a specific satellite by adding a preset individual bias value for the specific satellite, and selects the predetermined number of satellite signals using the normalized reception quality. 5. A satellite signal receiving device according to claim 1. (Section 6) The signal selection unit selects the satellite signal with the best reception quality from all received satellite signals, and sets a lower limit to a value obtained by subtracting a predetermined value from the best reception quality, and selects all satellite signals with reception quality lower than the lower limit. 6. A satellite signal receiving device according to any one of claims 1 to 5. (Section 7) The signal selection unit selects the satellite signal with the best reception quality from all received satellite signals, and selects all satellite signals whose reception quality is better than a lower limit obtained by subtracting a predetermined value from the best reception quality and also better than a preset minimum reception quality, with the lower limit being a value obtained by subtracting a predetermined value from the best reception quality. 6. A satellite signal receiving device according to any one of claims 1 to 5. (Section 8) When determining whether to select a certain satellite signal, the signal selection unit uses a value that depends on the elevation angle of the satellite signal as the predetermined value. 8. A satellite signal receiving device according to claim 6 or 7. (Section 9) When the total number of the satellite signal with the best reception quality and all satellite signals with reception quality better than the lower limit is less than the predetermined number, the signal selection unit selects satellite signals with reception quality equal to or lower than the lower limit based on the priority order of GNSS types so that the total number of selected satellite signals becomes the predetermined number. 9. A satellite signal receiving device according to any one of claims 1 to 8. (Section 10) When the total number of the satellite signal with the best reception quality and all satellite signals with reception quality better than the lower limit is less than the predetermined number, the signal selection unit selects satellite signals with reception quality equal to or lower than the lower limit based on a DOP value so that the total number of selected satellite signals becomes the predetermined number. 10. A satellite signal receiving device according to any one of claims 6 to 9. (Section 11) A satellite signal processing method executed by a satellite signal receiving device, comprising: a signal selection step of selecting a predetermined number of satellite signals based on reception quality of the satellite signals received by the GNSS antenna; a measurement step of performing positioning or time synchronization using a predetermined number of satellite signals selected by the signal selection step; A satellite signal processing method comprising: (Section 12) A program for causing a computer to function as each unit in a satellite signal receiving device according to any one of claims 1 to 10.

[0119] Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims.

[0120] This patent application claims priority to international application PCT / JP2020 / 043044, filed on November 18, 2020, and international application PCT / JP2021 / 020391, filed on May 28, 2021, and the entire contents of international application PCT / JP2020 / 043044 and international application PCT / JP2021 / 020391 are incorporated herein by reference. [Explanation of symbols]

[0121] 100 Measuring Equipment 110 GNSS antenna 120 Signal receiving unit 130 Signal selection section 140 Measurement section 150 Output section 160 Signal data storage unit 170 Bias value setting section 180 Bias value storage section 1000 Drive Device 1001 Recording media 1002 Auxiliary storage device 1003 Memory device 1004 CPU 1005 Interface device 1006 Display device 1007 Input Device 1008 Output device

Claims

1. a signal selection unit that selects a predetermined number of satellite signals based on reception quality of the satellite signals received by the GNSS antenna; a measurement unit that performs positioning or time synchronization using a predetermined number of satellite signals selected by the signal selection unit, the signal selection unit selects the satellite signal with the best reception quality from all received satellite signals, and selects all satellite signals with reception quality lower than a lower limit obtained by subtracting a predetermined value from the best reception quality, When the total number of the satellite signal with the best reception quality and all satellite signals with reception quality better than the lower limit is less than the predetermined number, the signal selection unit selects satellite signals with reception quality equal to or lower than the lower limit using reception quality obtained by adding a premium corresponding to the priority order of the GNSS type to the reception quality of the satellite signals with reception quality equal to or lower than the lower limit, so that the total number of selected satellite signals becomes the predetermined number. Satellite signal receiving device.

2. a signal selection unit that selects a predetermined number of satellite signals based on reception quality of the satellite signals received by the GNSS antenna; a measurement unit that performs positioning or time synchronization using a predetermined number of satellite signals selected by the signal selection unit, the signal selection unit selects the satellite signal with the best reception quality from among all received satellite signals, and selects all satellite signals whose reception quality is better than a lower limit obtained by subtracting a predetermined value from the best reception quality and whose reception quality is better than a preset minimum reception quality, When the total number of the satellite signal with the best reception quality and all satellite signals with reception quality better than the lower limit is less than the predetermined number, the signal selection unit selects satellite signals with reception quality equal to or lower than the lower limit using reception quality obtained by adding a premium corresponding to the priority order of the GNSS type to the reception quality of the satellite signals with reception quality equal to or lower than the lower limit, so that the total number of selected satellite signals becomes the predetermined number. Satellite signal receiving device.

3. When determining whether to select a certain satellite signal, the signal selection unit uses a value that depends on the elevation angle of the satellite signal as the predetermined value.

3. A satellite signal receiving device according to claim 1 or 2.

4. When the total number of the satellite signal with the best reception quality and all satellite signals with reception quality better than the lower limit is less than the predetermined number, the signal selection unit selects satellite signals with reception quality equal to or lower than the lower limit based on a DOP value such that the total number of selected satellite signals becomes the predetermined number.

4. A satellite signal receiving device according to claim 1.

5. A program for causing a computer to function as each unit in the satellite signal receiving device according to any one of claims 1 to 4.

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