Satellite signal receiving device, satellite signal selection method, and program

Abstract

A satellite signal reception device according to the present invention is provided with: a signal selection unit that selects a prescribed number of satellite signals on the basis of the reception quality of a satellite signal received by a GNSS antenna; and a measurement unit that performs positioning by using the prescribed number of satellite signals selected by the signal selection unit and determines an initial estimated position. The signal selection unit selects a plurality of satellite signals to be used for positioning or time synchronization, on the basis of a comparison result obtained by comparing a reception time when a satellite signal is expected to be received at the initial estimated position as a direct wave with the actual reception time of the satellite signal.

Description

Technical Field

[0001] The present invention relates to a technique for highly accurately performing positioning and time synchronization by GNSS (Global Navigation Satellite System).

Background Art

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

[0003] In positioning and time synchronization by GNSS, processing of positioning and time synchronization is executed using GNSS satellite signals (hereinafter referred to as satellite signals) received by a GNSS antenna.

[0004] When the reception of satellite signals in a line-of-sight state is blocked by structures or the like existing around the installation position of the GNSS antenna, the satellite signals may not be received at a signal strength required by the GNSS antenna, or may be received as invisible satellite signals due to multipath reflected and diffracted by structures or the like existing around the installation position of the GNSS antenna. As a result, the positioning performance and time synchronization performance by GNSS deteriorate.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0007] The present invention has been made in view of the above points, and an object thereof is to provide a technology that enables appropriate selection of satellite signals and accurate positioning and time synchronization by GNSS even when the reception environment of the satellite signals is not good.

Means for Solving the Problems

[0008] According to the disclosed technology, a signal selection unit that selects a predetermined number of satellite signals based on the reception quality of the satellite signals received by a GNSS antenna, a measurement unit that performs positioning using the predetermined number of satellite signals selected by the signal selection unit and determines an initial estimated position, are provided. The signal selection unit selects a plurality of satellite signals to be used for positioning or time synchronization based on a comparison result obtained by comparing an expected reception time when the satellite signal is received as a direct wave at the initial estimated position with an actual reception time of the satellite signal. A satellite signal receiving device, Based on the comparison result, the signal selection unit rejects a satellite signal that is actually received with a delay time equal to or greater than a threshold value from the reception time expected when received as a direct wave at the initial estimated position, updates the initial estimated position with the coordinate values obtained by positioning using a plurality of satellite signals excluding the rejected satellite signal, repeats the process based on the comparison result using the updated initial estimated position, and when a predetermined end condition is satisfied, ends the repeated process, The signal selection unit decreases the threshold value every time the process is repeated, The predetermined end condition is that the difference between the initial estimated position before update and the initial estimated position after update becomes equal to or less than a preset value A satellite signal receiving device is provided.

Effects of the Invention

[0009] According to the disclosed technology, a technology is provided that enables accurate positioning and time synchronization by GNSS even when the reception environment of the satellite signals is not good.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described with reference to the drawings. The embodiments described below are merely examples, and the embodiments to which the present invention is applied are not limited to the following embodiments.

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

[0013] As described above, in order to improve the accuracy of positioning and time synchronization by GNSS, it is important to receive as many visible satellite signals that can be received in a line-of-sight state, and to effectively exclude non-visible satellite signals that cannot be received in a line-of-sight state and have a great impact on the deterioration of accuracy from the satellite signals used for positioning and time synchronization.

[0014] As a conventional method for excluding non-visible satellite signals, a C / N0 (Carrier-To-Noise Power Density) mask method is known, which excludes satellite signals with a C / N0 value below a preset threshold from the received satellite signals.

[0015] However, since the C / N0 value of satellite signals depends on factors such as the antenna gain, the receiver sensitivity, the cable loss between the antenna and the receiver, and the satellite type, it is difficult to set an optimal threshold.

[0016] In addition, in the C / N0 mask method, when interference signals are mixed into the signal bandwidth of satellite signals, the C / N0 value of the satellite signals decreases overall, and as a result of losing satellite signals due to the C / N0 mask, there is a risk that positioning and time synchronization cannot be achieved. Such interference signals include, in addition to intentionally generated GNSS jamming signals, noise generated by devices and interference signals from other communication systems.

[0017] In the present embodiment, in order to effectively exclude invisible satellite signals that cannot be received in the line-of-sight state, which have a large impact on the deterioration of accuracy, from the satellite signals used for positioning and time synchronization, while receiving many visible satellite signals that can be received in the line-of-sight state, after assuming a multi-GNSS environment in which a large number of visible satellites can be ensured, the following-described procedure is used to select satellite signals suitable for use in positioning and time synchronization. Although the intensity (reception quality) of the received satellite signals is used as the basis for selection in this procedure, it enables the selection of satellite signals while taking into account the individual characteristics of the antenna and receiver and the influence of interference signals.

[0018] Also, in this procedure, visible satellite signals are preferentially selected. When the number of visible satellites is small, invisible satellites with a small influence on accuracy deterioration and a small propagation delay in addition to the visible satellites are selected.

[0019] Hereinafter, examples of the configuration and operation in the embodiments of the present invention will be described in detail. In the processes described below, the C / N0 value is used as an index of reception quality, but an index of reception quality other than the C / N0 value may also be used. Also, in the present embodiment, the "satellite signal" when "selecting a satellite signal" is assumed to be associated with the GNSS satellite that is the transmission source of the satellite signal. For example, assuming that 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.

[0020] (Device Configuration) FIG. 1 shows a configuration example of the measuring device 100 in the embodiment of the present invention. The measuring device 100 in the present embodiment includes a GNSS antenna 110, a signal receiving unit 120, a signal selection 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 measuring device 100 is a device that receives and processes satellite signals, and this may be referred to as a "satellite signal receiving device."

[0021] The GNSS antenna 110 receives radio waves transmitted from GNSS satellites in orbit and converts the radio waves into electrical signals. This electrical signal may also be referred to as a "satellite signal."

[0022] 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 through the cable. When 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.

[0023] The signal receiving unit 120 receives satellite signals, measures the C / N0 value, and identifies the type of GNSS satellite that is the transmission source of the received satellite signal. In addition, using the orbital information of the satellite (e.g., almanac, ephemeris), the elevation angle is measured. The orbital information of the satellite may be obtained from the navigation message of the satellite signal, or may be obtained from other means (e.g., a server on the network). The signal receiving unit 120 sends the identification information (code such as PRN number) of the received satellite signal, the elevation angle of the satellite signal, the C / N0 value, and the satellite type to the signal selection unit 130. In addition, the signal receiving unit 120 stores the identification information, elevation angle, C / N0 value, and satellite type for each received satellite signal in the signal data storage unit 160. Note that the elevation angle is the angle formed between the line of sight when looking at 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) and the horizontal plane. For example, when the GNSS satellite is at the zenith, the elevation angle is 90°.

[0024] The types of GNSS satellites targeted in this embodiment are GPS, GLONASS, Galileo, BeiDou, QZSS, and NAVIC. However, these are examples, and there may be more or fewer types than these.

[0025] The signal selection unit 130 selects satellite signals to be used for positioning and time synchronization from among the received multiple satellite signals. The selection procedure will be described later.

[0026] The measurement unit 140 calculates time information that is highly accurately time-synchronized with absolute time by performing time synchronization using satellite signals transmitted from GNSS satellites equipped with atomic clocks whose time is precisely managed with respect to absolute time. Here, the absolute time is, for example, Coordinated Universal Time (UTC). Note that the measurement unit 140 may perform only one of positioning and time synchronization.

[0027] Although the absolute time when the satellite signal was transmitted from the GNSS satellite can be known from the received satellite signal, accurate absolute time cannot be obtained at the reception position 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.

[0028] Therefore, the measurement unit 140 simultaneously performs positioning and time synchronization by calculating four parameters, i.e., the three-dimensional coordinate information (x, y, z) of the reception position and the 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 (interferometric positioning) in addition to code positioning.

[0029] The measurement unit 140 outputs time information based on this absolute time and position information which is the positioning result via the output unit 150. For example, if the measuring device 100 is a base station in a mobile network, the base station uses time information synchronized with the absolute time to, for example, match the time slot configurations of the uplink and downlink signals of the TDD (Time Division Duplex) signal frame with those of an adjacent base station (which is also synchronized with the absolute time), and then synchronize the transmission timing of the signal frame, so as to be able to transmit the TDD signal without interfering with the adjacent base station.

[0030] The bias value setting unit 170 uses the satellite signal data stored in the signal data storage unit 160 to set (calculate) a bias value, 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 for the selection process of satellite signals in the signal selection unit 130. Details of the bias value setting operation by the bias value setting unit 170 will be described later.

[0031] The measuring device 100 in the present embodiment may be a physically integrated single device, or may be a device in which several functional units are physically separated and the separated multiple functional units are connected by a network.

[0032] Also, the measuring device 100 may include all the functions shown in FIG. 1, or some functions (for example, the signal selection unit 130 and the measurement unit 140) may be provided on the network (for example, on the cloud), and the remaining functions may be installed in the measuring device 100 and used.

[0033] For example, observation data may be output from the signal receiving unit 120 provided in the measuring device 100 and transmitted to a device composed of "the signal selection unit 130 and the measurement unit 140" provided on the cloud, so that satellite signal selection and positioning calculation are performed on the cloud. In this case, the positioning calculation result is returned from the measurement unit 140 on the cloud to the output unit 150.

[0034] Alternatively, a device consisting of "signal data storage unit 160 and bias value setting unit 170" in the measuring device 100 may be provided on a network (e.g., on the cloud), and the remaining functions may be mounted on the measuring device 100 and used.

[0035] For example, observation data is output from the signal reception unit 120 provided in the measuring device 100, the observation data is stored in the signal data storage unit 160 provided on the cloud, and the bias value setting unit 170 provided on the cloud sets a 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.

[0036] (Processing content for satellite signal selection) Next, the operation of the measuring device 100 for satellite signal selection (particularly the operations of the signal selection unit 130 and the measurement unit 140) will be described. The measuring device 100 performs satellite signal selection processing in the procedures of (1) initial estimated position determination processing, (2) satellite selection processing, and (3) missing satellite selection processing. The outline of each processing is as follows.

[0037] (1) The initial estimated position determination processing is a process of determining an initial estimated position that serves as a reference when performing satellite selection.

[0038] (2) The satellite selection processing is a process of selecting, in addition to LOS (Line Of Sight) satellite signals, NLOS (Non Line Of Sight) satellite signals with small delays by comparing the estimated reception time and the actual reception time at the initial estimated position.

[0039] (3) The missing satellite selection processing is a process of additionally selecting satellites to suppress deterioration of positioning and time synchronization accuracy due to deterioration of the DOP (Dilution Of Precision) value when the number of selected satellite signals is small.

[0040] Hereinafter, each of (1) initial estimated position determination processing, (2) satellite selection processing, and (3) missing satellite selection processing will be described with reference to flowcharts.

[0041] The meanings of the symbols of the parameters used here are as follows. A specific example of the satellite signal selection process in the initial estimation positioning process will be described later, and the parameters used in that specific example will be explained again in that specific example.

[0042] dCN0: The maximum value of the difference between the maximum value of the C / N0 value of the received satellite signal and the C / N0 value of the satellite signal selected in the initial estimation position process N0: The minimum number of satellite signals selected in the initial estimation positioning process dT: The threshold of the delay time from the expected reception time at the initial estimation position in the satellite selection process N s : The maximum number of times the initial estimation position is updated in the satellite selection process dp: The threshold of the difference between the initial estimation positions before and after the update for determining the completion in the satellite selection process N1: The minimum number of satellite signals selected in the missing satellite selection process <(1) Initial Estimation Positioning Process> Referring to the flowchart of FIG. 2, the initial estimation positioning process will be described.

[0043] In S1-1, the signal selection unit 130 extracts the satellite signal with the largest C / N0 value from the plurality of satellite signals received by the signal reception unit 120.

[0044] In S1-2, the signal selection unit 130 selects, from the plurality of satellite signals, the satellite signals whose difference in C / N0 value from the largest C / N0 value extracted in S1-1 is less than or equal to a preset value (dCN0).

[0045] In S1-3, when the number of satellite signals selected in S1-1 and S1-2 is less than the preset minimum number of satellite signals (N0), the signal selection unit 130 complements the satellite signals from the satellite signals with a larger C / N0 value (next point) until the minimum number of satellite signals (N0) is reached.

[0046] In S1-4, the measurement unit 140 determines the initial estimated position of the measurement device 100 by code positioning using the satellite signals selected in S1-1 to S1-3. Note that, as the positioning method, a positioning method other than code positioning may be used. The same applies to the steps of performing code positioning in the subsequent processing.

[0047] Note that, for S1-1 to S1-3, more detailed examples will be described later as the first embodiment and the second embodiment.

[0048] <(2) Satellite Selection Process> Next, with reference to the flowchart of FIG. 3, the satellite selection process will be described.

[0049] In S2-1, the signal selection unit 130 compares the expected reception time and the actual reception time when each satellite signal is received as a direct wave by the signal reception unit 120 at the initial estimated position, on the premise that the clock bias of the receiver (measurement device 100) and the time bias between satellite systems are corrected during the code positioning in S1-4.

[0050] Regarding the expected reception time when a satellite signal is received as a direct wave, it can be calculated from the straight-line distance between the satellite position of the transmission source of the satellite signal calculated from the orbit information and the initial estimated position. The actual reception time may be measured by any of the signal reception unit 120, the signal selection unit 130, and the measurement unit 140.

[0051] In S2-2, the signal selection unit 130 rejects the satellite signals whose actual reception time is delayed by dT or more than the reception time at the initial estimated position expected by the comparison in S2-1.

[0052] For example, let dT be X [ns]. Assuming that the expected reception time of satellite signal A is T and the actual reception time of satellite signal A is T + X + 1 [ns], since the delay time is X + 1 (dT or more), satellite signal A is rejected.

[0053] In S2-3, the measurement unit 140 performs code positioning on a plurality of satellite signals received by the signal reception unit 120, excluding the satellite signals rejected in S2-2, and updates the initial estimated position of the measuring device 100 with the obtained coordinate values.

[0054] In S2-4, (1) when the number of satellite signals selected in S2-3 is less than 4 (in other words, when the number of selected satellites is less than 4), (2) when the vector difference between the initial estimated positions before and after the update is less than or equal to a preset value (dp), (3) when the preset number of calculations (N s ) is reached, if any of these conditions are met, the calculation is terminated. If none of (1) to (3) are met, S2-1 to S2-3 are repeated. Note that the conditions for terminating the calculation are not limited to (1) to (3).

[0055] Regarding the above (2), for example, if the position after the update of the initial estimated position at the nth time is x n (vector representing the position), and the position after the update of the initial estimated position at the (n + 1)th time is x n+1 , in the case where |x n - x n+1 | is less than or equal to dp[m], the calculation is terminated.

[0056] In the repeated processing of S2-1 to S2-3, the dT value may be decreased each time. For example, in the first calculation of S2-2, dT = X [ns], and in the nth (n is an integer of 2 or more) calculation of S2-2, it may be set that dT = X - (n - 1)×Δ (Δ is a positive real number, provided that dT>0). By such processing, dT becomes smaller each time, so the number of rejected satellite signals increases, and it becomes easier to select satellite signals with a smaller delay from the more expected reception times.

[0057] <(3) Missing Satellite Selection Process> Next, referring to the flowchart of FIG. 4, the missing satellite selection process will be described.

[0058] In S3-1, when the number of satellite signals selected at the time of completion of the calculation in S2-4 is smaller than a preset number (N1), the signal selection unit 130 compares the delay times among a plurality of non-selected satellite signals that are selection candidates in order to select supplementary satellite signals to make up the number to reach this number. The delay time is the difference between the reception time expected when the satellite signal is received as a direct wave at the initial estimated position and the actual reception time, which is the object of comparison with dT in S2-2. Regarding the delay time of each non-selected satellite signal, the value measured and calculated in the last S2-2 of the repetition may be used, or the value newly measured and calculated at this time of S3-1 using the initial estimated position at the time of completion of the calculation in S2-4 may be used.

[0059] In S3-2, the signal selection unit 130 compares the DOP values when adding the satellite signal with the smallest delay time and the satellite signal with the second smallest delay time selected in S3-1 to the satellite signals selected at the time of completion of the calculation in S2-4, and selects the satellite signal with the smaller cost value calculated by the delay time and the DOP value as the satellite signal to be added.

[0060] For example, assume that satellite signal A, satellite signal B, and satellite signal C are selected at the time of completion of the calculation in S2-4. In S3-2, assume that satellite signal D is selected as the satellite signal with the smallest delay time, and satellite signal E is selected as the satellite signal with the second smallest delay time.

[0061] Here, assume that the delay time of satellite signal D is 2, the delay time of satellite signal E is 3, the DOP value of "satellite signal A, satellite signal B, satellite signal C, satellite signal D" is 7, and the DOP value of "satellite signal A, satellite signal B, satellite signal C, satellite signal E" is 4. If the cost value is "delay time × DOP value", the cost value of "satellite signal A, satellite signal B, satellite signal C, satellite signal D" is 2×7 = 14, and the cost value of "satellite signal A, satellite signal B, satellite signal C, satellite signal E" is 3×4 = 12. Therefore, in this case, satellite signal E is selected as the satellite signal to be added.

[0062] Also, a premium for satellite type may be set for the cost value. Here, the GNSS type means the type of a navigation satellite system such as GPS or GLONASS. For example, when the priority of satellites is set as shown in FIG. 9 described later, the higher the priority (the smaller the numerical value of the priority), the smaller the value is given as the premium of the cost value.

[0063] For example, in the example of FIG. 9, the premium for priority 1 is set to 1, the premium for priority 2 is set to 2, the premium for priority 3 is set to 3, the premium for priority 4 is set to 4, and the premium for priority 5 is set to 5.

[0064] In the above examples of satellite signals D and E, if the premium of satellite signal D is 1 and the premium of satellite signal E is 4, the cost value of "satellite signal A, satellite signal B, satellite signal C, satellite signal D" is 2×7 + 1 = 15, and the cost value of "satellite signal A, satellite signal B, satellite signal C, satellite signal E" is 3×4 + 4 = 16. Therefore, in this case, satellite signal D is selected as the additional satellite signal.

[0065] In S3-3, the signal selection unit 130 determines whether the number of satellite signals has reached a preset number (N1). If not, the processes of S3-1 and S3-2 are repeated. At this time of repetition, processing is performed on satellite signals excluding those for which addition has already been determined.

[0066] In S3-3, when the number of satellite signals has reached the preset number (N1), the calculation is terminated, and for example, positioning and time synchronization are performed using the selected satellite signals.

[0067] (Specific example of processing in initial estimated positioning processing) Hereinafter, as a specific operation example of the measurement device 100, a specific example of the procedure for selecting satellite signals in the above-described initial estimated positioning processing will be described.

[0068] In the following description of specific examples, when normalizing the C / N0 value, the elevation angle dependency and the GNSS type / frequency band dependency are taken into consideration. Here, the GNSS type means the type of navigation satellite system such as GPS or GLONASS. The reason for considering the elevation angle dependency is that the propagation path in the troposphere closer to the surface becomes longer as the elevation angle of the satellite decreases, and the satellite signal tends to be more attenuated. The reason for considering the GNSS type dependency is that the signal frequency and transmission power differ depending on the GNSS type, resulting in a difference in the C / N0 value. Furthermore, even for the same GNSS type, the C / N0 value varies depending on the signal frequency band (in the case of GPS, L1 band, L2 band, L5 band, etc.). Note that it is also possible to consider only one of the elevation angle dependency and the GNSS type / frequency band dependency.

[0069] Hereinafter, as a specific example of the satellite selection procedure in the initial estimated position determination process, a first embodiment and a second embodiment will be described. Regarding the second embodiment, the parts different from the first embodiment will be mainly described.

[0070] ―――――――――――First Embodiment―――――――――――

[0071] (Operation Example of Signal Selection Unit 130 in the First Embodiment) An operation example of the signal selection unit 130 in the first embodiment will be described in detail according to the procedure of the flowchart shown in FIG. 5. In the description of the procedure, FIGS. 6 to 9 are also referred to.

[0072] First, referring to FIG. 6, the setting parameters used in the procedure will be described. As shown in FIG. 6, CN 0max is the maximum value of the C / N0 values of all received satellite signals in the L1 band. dCN0 is a parameter that determines the selection range of satellite signals. Specifically, it is the maximum value of the difference between the maximum value of the C / N0 values of the received satellite signals and the C / N0 values of the satellite signals selected in the initial estimated position process. N0 is the number of selected satellite signals. Specifically, it is the minimum number of satellite signals selected in the initial estimated position determination process. Note that in the first embodiment, reception is performed in the L1 band, but reception in the L1 band is just an example.

[0073] In S101 of FIG. 5, the signal selection unit 130 normalizes the C / N0 values of all satellite signals received in the L1 band in consideration of 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 C / N0 value obtained by observation.

[0074] An example of the setting of the GNSS bias value is shown in FIG. 7, and an example of the setting of the elevation angle bias value is shown in FIG. 8. These bias values are stored in the bias value storage unit 180.

[0075] For example, assuming that the C / N0 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 corrected (normalized) C / N0 value of the satellite signal to 30 + 4 + 2 = 36 dB-Hz. Hereafter, the C / N0 value means the normalized C / N0 value.

[0076] In S102 of FIG. 5, the signal selection unit 130 selects the satellite signal with the largest C / N0 value from all the satellite signals received in the L1 band, and records its C / N0 value as CN 0max Note that here, it is assumed as a precondition that there is at least one visible satellite signal.

[0077] In S103, the signal selection unit 130 sets a value smaller than dCN0 (e.g., 10 dB) from CN as the lower limit of C / N0 for the C / N0 value (C / N0) 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 0max -dCN0 < C / N0 < CN 0max from all the satellite signals received in the L1 band. 0max

[0078] 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 (codes such as PRN numbers) of the selected satellite signals, so that the measurement unit 140 can perform positioning and time synchronization using the selected satellite signals.

[0079] 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 selected satellite signals (N0), the process proceeds to S105.

[0080] In S105, the signal selection unit 130 selects satellite signals in order from the satellite signals with a C / N0 value less than or equal to "CN 0max -dCN0" and the next highest C / N0 value, and fills in the selection so that the total number of selected satellite signals becomes N0.

[0081] Fig. 9 shows an example of setting the priority order of GNSS types. 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. In Fig. 9, it is shown that the priority of GPS is the highest and the priority of GLO (GLONASS) is the lowest.

[0082] Here, the selection based on the priority order of GNSS types will be described. 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 the missing satellite signals in S105, it is considered to select them in consideration of the reliability of GNSS including the clock bias.

[0083] For example, GPS and QZSS are navigation satellite systems with their times completely synchronized with each other and a small clock bias. Therefore, they can be classified in the form that Category 1 and Category 2 are Galileo, and Category 3 is GLONASS and BeiDou. Based on such categorization, a priority setting as shown in FIG. 9 is made.

[0084] As a method for selecting a supplementary satellite signal considering the priority based on the reliability as described above, as an example, a premium (added value, unit: dB) is set for the C / N0 value according to the priority (or category of reliability), and the required number is sequentially selected from the satellite signals with the highest C / N0 value.

[0085] For example, in the example of FIG. 9, the premium for Priority 1 is set to 5, the premium for Priority 2 is set to 4, the premium for Priority 3 is set to 3, the premium for Priority 4 is set to 2, and the premium for Priority 5 is set to 1.

[0086] As an example, assuming N0 is 5 and three satellite signals are selected in S102 and S103. Also, as satellite signals having C / N0 values of "CN 0max - dCN0" or less, if there are Satellite Signal 1 (C / N0 value = 26 dB-Hz, premium = 1), Satellite Signal 2 (C / N0 value = 25 dB-Hz, premium = 3), and Satellite Signal 3 (C / N0 value = 24 dB-Hz, premium = 5), then in S105, the signal selection unit 130 selects Satellite Signal 3 and Satellite Signal 2 with C / N0 values of 29 dB-Hz and 28 dB-Hz after adding the premium.

[0087] (Operation example regarding bias value setting) Next, an operation example for setting the bias value will be described in detail according to the procedure of the flowchart shown in FIG. 10. Refer to FIGS. 11 to 13 during the description of the procedure.

[0088] In S201, the signal receiving unit 120 continuously collects satellite signal data. Regarding the length of the collection time, in an open sky environment, continuous collection for 24 hours is sufficient. In other receiving environments, longer continuous collection is required. Data can be collected at any time, and the bias value can be updated accordingly.

[0089] In S202, the collected satellite signal data is stored in the signal data storage unit 160 as a set of (GNSS type, elevation angle, C / N0 value).

[0090] In S203, based on the satellite signal data stored in the signal data storage unit 160, the bias value setting unit 170 groups the data for the same GNSS type according to the elevation angle range, and extracts the maximum value of the C / N0 value for each group.

[0091] FIG. 11 shows an example of the process of S203 for a certain GNSS type. In the example of FIG. 11, the elevation angles are grouped into 0° - 15°, 15° - 30°, 30° - 45°, 45° - 60°, 60° - 75°, and 75° - 90°, and the maximum value of the C / N0 value for each group is extracted.

[0092] In S204, the bias value setting unit 170 applies curve fitting to the extracted maximum value data, for example, by the non - linear least squares method. In S205, the bias value setting unit 170 repeats the curve fitting excluding the largest outlier several times. Examples of S204 and S205 for the GNSS type shown in FIG. 11 are shown in FIG. 12.

[0093] In S206, the bias value setting unit 170 generates a fitting function for each GNSS type. In S207, the bias value for GNSS type - elevation angle is set by the fitting function of each GNSS type. Examples of S206 and S207 are shown in FIG. 13. As shown in FIG. 13, for any GNSS type, the smaller the elevation angle, the larger the bias value set. Also, in the example of FIG. 13, among the GNSS types, the bias values are set in the order of GNSS - C > GNSS - B > GNSS - A.

[0094] (Regarding the setting value of dCN0) Next, the setting value of dCN0 (referred to as the dCN0 value) will be described. As explained in S103 of FIG. 5, the dCN0 value is a parameter that determines the range of the C / N0 value for selecting satellite signals. The dCN0 value may be a fixed value independent of the elevation angle of the satellite signal. However, below, an example of determining the dCN0 value depending on the elevation angle of the satellite signal will be described. The example described here is an example assuming a case where the reflecting surface of the satellite signal is the vertical wall surface (concrete or glass) of a building, such as in an urban area.

[0095] FIG. 14 shows the state where a satellite signal with a high elevation angle is incident on and reflected by the vertical wall surface of a building, and FIG. 15 shows the state where a satellite signal with a low elevation angle is incident on and reflected by the vertical wall surface of a building. As shown in FIGS. 14 and 15, the incident angle at which a satellite signal with a low elevation angle is incident on the vertical wall surface of a building is larger than the incident angle at which a satellite signal with a high elevation angle is incident on the vertical wall surface of a building.

[0096] Since the reflectivity of the satellite signal by the vertical wall surface of the building depends on the incident angle, it is expected that the satellite signal with a low elevation angle has a relatively large reflectivity (large signal intensity of the reflected wave) compared to the satellite signal with a high elevation angle.

[0097] Therefore, giving the dCN0 value an elevation angle dependency is effective in visible / invisible satellite selection. FIG. 16 shows an example of setting the dCN0 value with an elevation angle dependency. As shown in FIG. 16, the dCN0 value is set to increase as the elevation angle of the satellite signal increases. Such a set value with an 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. 16, or may be stored in the bias value storage unit 180 in the form of a table holding the dCN0 value for each elevation angle (for example, in 5° increments).

[0098] In S103 described above, the signal selection unit 130 determines that the C / N0 value of a certain satellite signal is "CN 0max -dCN0 < C / N0 < CN 0maxWhen determining whether the condition " is satisfied, the bias value storage unit 180 is referred to, the dCN0 value corresponding to the elevation angle of the satellite signal is obtained, and the "CN 0max -dCN0 < C / N0 < CN 0max " is determined whether it is satisfied using the obtained dCN0 value.

[0099] Also, in the satellite signal selection for supplementing the above-mentioned S105, when the signal selection unit 130 determines whether the C / N0 value of a certain satellite signal is less than or equal to "CN 0max -dCN0", the bias value storage unit 180 is referred to, the dCN0 value corresponding to the elevation angle of the satellite signal is obtained, and it is determined whether it is less than or equal to "CN 0max -dCN0" using the obtained dCN0 value.

[0100] "CN 0max -dCN0 < C / N0 < CN 0max " In the determination of whether to select a satellite signal, since the dCN0 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 "CN 0max -dCN0 < C / N0 < CN 0max " is narrower for a satellite signal with a lower 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 dCN0 value have an elevation angle dependency 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 is explained below.

[0101] 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 is 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 the presence of obstacles (the reference signal intensity normalized by the bias value in FIGS. 7 and 8) becomes small.

[0102] That is, for low-elevation satellite signals, since the optical path length of the medium that attenuates the signal strength, such as the ionosphere and the troposphere, becomes longer, 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, in order to remove the multipath signal (reflected wave) of the invisible satellite signal, it is necessary to reduce the dCN0 value and perform filtering more strictly. For high-elevation satellites, the opposite is true, and the range of " 0max -dCN0 < C / N0 < CN 0max " is widened to make it easier to be selected.

[0103] Note that giving elevation dependence so that the dCN0 value increases as the elevation angle of the satellite signal increases is an example. Depending on the environment, it may be appropriate to give a different elevation dependence to the dCN0 value.

[0104] Note that although it is conceivable to perform satellite selection for each satellite type unit, it is not done. The reasons are as follows.

[0105] 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 C / N0 value (CN 0max ) 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 the existence of at least one visible satellite is improved.

[0106] ―――――――――――Second Embodiment―――――――――――

[0107] 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 is 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.

[0108] Note that the effects of the invention can be achieved by the technology described in the first embodiment. The second embodiment is a variation of the embodiments of the invention. The reasons for selecting satellite signals for each frequency band in the second embodiment are as follows.

[0109] Since each satellite outputs signals in a plurality of frequency bands, from the perspective of selecting satellites suitable for positioning based on the position (visible / invisible) of the satellite, if the visibility / invisibility of the satellite can be accurately determined by the satellite signal in any one frequency band, there is no need to select satellites using the signals in each of the plurality of frequency bands.

[0110] However, in reality, it is not guaranteed that the visibility / invisibility can be determined with 100% accuracy. Also, the reception characteristics of the antenna-receiver and the state of interference signal mixing may vary for each frequency band, and by selecting satellite signals for each of the plurality of frequency bands, it may be possible to select a combination of satellite signals more suitable for positioning calculations.

[0111] In positioning calculations, different satellite signals can be used for each frequency band. Since the frequency bands supported by satellites are different (for example, the L5 frequency band of GPS is supported by only some satellites), by individually selecting satellite signals for each frequency band, the variations in the policy settings of positioning calculations (such as changing the N0 value for each frequency band) can be expanded.

[0112] The device configuration of the measuring device 100 in the second embodiment is the same as the device configuration in the first embodiment, as shown in FIG. 1. The operations of each part are also basically the same as those in the first embodiment, but it is different from the first embodiment in that it performs operations for selecting satellite signals for each frequency band.

[0113] That is, the signal reception unit 120 sends, for each frequency band, the identification information (codes such as PRN numbers) of the received satellite signal, the elevation angle of the satellite signal, the C / N0 value, and the satellite type to the signal selection unit 130. Also, the signal reception unit 120 stores, for each frequency band, the identification information, elevation angle, C / N0 value, and satellite type of each received satellite signal in the signal data storage unit 160. In the present embodiment, the L1 band and the L2 band are targeted as a plurality of frequency bands. However, using the L1 band and the L2 band is an example, and in addition to these, the L5 band may be used, or frequency bands other than the L1 band, L2 band, and L5 band may be used.

[0114] (Operation example of the signal selection unit 130 in the second embodiment) Next, an operation example of the signal selection unit 130 in the second embodiment will be described. FIG. 17 is a flowchart showing the operation of the signal selection unit 130. Basically, it is the same as the flow in the first embodiment shown in FIG. 5, but in the second embodiment, the flow of FIG. 17 is repeated for each frequency band, and in S113 (corresponding to S103 in FIG. 5), it is different from the first embodiment in that it determines whether the minimum C / N0 value in the frequency band being processed is satisfied. Note that FIG. 17 shows, as an example, the processing for the L1 band in the repetition for each frequency band.

[0115] First, with reference to FIG. 18, the setting parameters used in the procedure of the second embodiment will be described. As shown in FIG. 18, CN 0L1 is the minimum C / N0 value of the selected satellite in the L1 band. dCN 0L1 is a parameter for determining the selection range of the satellite signal in the L1 band (corresponding to dCN0 described above). N 0L1 is the number of selected satellite signals in the L1 band. Similar parameters are set for the L2 band. When using other frequency bands, parameters may be set for each frequency band. For example, for the L5 band, CN 0L5 etc. are set.

[0116] First, for the L1 band, the process of the flow in FIG. 17 is executed. The processes of S101 and S102 are the same as those in the first embodiment. However, in the second embodiment, a bias value as shown in FIGS. 7 and 8 is 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 C / N0 value is selected from all the satellite signals received in the corresponding frequency band (initially the L1 band), and its C / N0 value is recorded as CN 0max and recorded as such.

[0117] In S113, the signal selection unit 130, for the C / N0 value (CN 0max ) of the satellite signal selected in S102, uses a value smaller than CN 0max by dCN 0L1 (e.g., 10 dB) as the lower limit of C / N0, and selects satellite signals that meet the conditions from the received satellite signals. Here, the signal selection unit 130 selects all satellite signals from the satellite signals received in the L1 band that satisfy CN 0max -dCN 0L1 <C / N0 < CN 0max and satisfy CN 0L1 <C / N0.

[0118] 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, so that the measurement unit 140 can perform positioning and time synchronization using the selected satellite signals.

[0119] The signal selection unit 130 executes the process of the flow in FIG. 17 for the next frequency band (e.g., the L2 band).

[0120] If the determination result of S104 is No, that is, the number of satellite signals selected in S102 and S103 is less than the preset minimum number of selected satellite signals (N0L1 ) If it is less, proceed to S105.

[0121] 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, based on the preset priority order of GNSS types (e.g., Fig. 9), when the C / N0 value is "CN 0max -dCN 0L1 " or less, selects satellite signals in order from the satellite signal with the next highest C / N0 value, and fills in so that the total number of selected satellite signals is N 0L1 becomes.

[0122] Note that the priority order setting as shown in Fig. 9 may be determined for each frequency band. In that case, the signal selection unit 130 selects satellite signals using the priority order corresponding to the frequency band being processed.

[0123] Similar to the first embodiment, as a method for selecting supplementary satellite signals considering the priority order based on reliability, a method can be used in which a premium (added value) is set for the C / N0 value according to the priority order (or category of reliability), and the required number is sequentially selected from the satellite signal with the highest C / N0 value.

[0124] For example, in the example of Fig. 9, 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.

[0125] As an example, assuming N 0L1 is 5, and assuming that 3 satellite signals are selected in S102 and S103. Also, as satellite signals having a C / N0 value of "CN 0max -dCN 0L1 " or less, there are satellite signal 1 (C / N0 value = 26 dB-Hz, premium = 1), satellite signal 2 (C / N0 value = 25 dB-Hz, premium = 3), and satellite signal 3 (C / N0 value = 24 dB-Hz, premium = 5). Then, in S105, the signal selection unit 130 selects satellite signal 3 and satellite signal 2 whose C / N0 values with the premium added are 29 dB-Hz and 28 dB-Hz.

[0126] When S105 ends, the signal selection unit 130 notifies the measurement unit 140 of the identification information (codes such as PRN numbers) of the selected satellite signal, so that the measurement unit 140 can perform positioning and time synchronization using the selected satellite signal.

[0127] The signal selection unit 130 executes the processing of the flow in FIG. 17 for the next frequency band (for example, L2 band).

[0128] In the above example, positioning and time synchronization are performed using the selected satellite signal for each frequency band. However, positioning and time synchronization using satellite signals in a plurality of frequency bands based on the satellite signal selected in a specific frequency band may also be performed.

[0129] For example, by executing the flow of FIG. 17 in each of the L1 band and the L2 band, when satellite signals 1, 2, 3, 4 are selected in the L1 band and satellite signals 5, 6, 7, 8 are selected in the L2 band, the DOP (Dilution of Precision) values of satellite signals 1, 2, 3, 4 and the DOP values of satellite signals 5, 6, 7, 8 are compared, and the satellite signals in the frequency band with the smaller DOP value are selected, and positioning and time synchronization using the signals in the L1 band and the L2 band may be performed.

[0130] (Variations of the method for selecting missing satellite signals) In the first embodiment and the second embodiment, other examples of the selection of the missing satellite signal in S105 will be described. The signal selection unit 130 may select the missing satellite signal in consideration of the DOP value. For example, the signal selection unit 130 selects satellite signals A, B, and C in order from the satellite signal with the next highest C / N0 value when the C / N0 value is "CN 0max -dCN0" or less as candidates for the missing satellite signal, calculates the DOP value when adding the missing satellite candidates A, B, and C to the already selected satellite signals respectively, and selects the satellite signal with the smallest DOP value.

[0131] For example, assuming that the satellite signals already selected at the time of S104 are satellite signals 1, 2, and 3, calculate the DOP values of "satellite signals 1, 2, 3, A", "satellite signals 1, 2, 3, B", and "satellite signals 1, 2, 3, C" respectively. If the DOP value of "satellite signals 1, 2, 3, A" is the smallest, then select "satellite signals 1, 2, 3, A". If the number of satellites to be selected is greater than 4, the above process may be repeated until the number of satellites is reached.

[0132] Here, the missing satellite signal selection method described in the first embodiment is defined as selection method 1, and the above method using the DOP value is defined as selection method 2. The signal selection unit 130 may select the missing satellite signal in combination with selection methods 1 and 2.

[0133] As an example of the combination, by using selection method 1, select the missing satellite signal, and for each of the selected satellite signals, implement selection method 2 to select the satellite signal with a small DOP value.

[0134] Also, for example, set a cost value (evaluation value) with the improvement degree of the positioning accuracy by the satellite signals selected based on selection methods 1 and 2 as the expected value, and select the satellite signal with the minimum total cost value (evaluation value) of selection methods 1 and 2 as the missing satellite signal. For example, assume that satellite signal A and satellite signal B are selected as candidates for the missing satellite signal by the combination of selection methods 1 and 2. For example, the C / N0 value of satellite signal A is 30 dB-Hz, the C / N0 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. When setting the total cost value (evaluation value) of selection methods 1 and 2 as "DOP value ÷ (C / N0 value)", the cost values of satellite signals A and B are 1 / 6 and 1 / 7 respectively. Since the cost value of satellite signal B is smaller than that of satellite signal A, satellite signal B is selected as the missing satellite signal.

[0135] (Operation example regarding bias value setting) In the second embodiment, the bias value setting operation executed by the bias value setting unit 170 is basically the same as the bias value setting operation in the first embodiment. However, in the second embodiment, it is different from the first embodiment in that the bias value is set for each frequency band.

[0136] FIG. 19 shows a flowchart of the bias value setting operation in the second embodiment. In S201, the signal reception unit 120 continuously collects satellite signal data for each frequency band.

[0137] 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, C / N0 value).

[0138] In S213, the bias value setting unit 170 groups the data for the same GNSS type and frequency band based on the satellite signal data stored in the signal data storage unit 160 for each range of elevation angles, and extracts the maximum value of the C / N0 value for each group. The processing example is as described with reference to FIG. 8.

[0139] In S204, the bias value setting unit 170 applies curve fitting to the extracted maximum value data by means of the non-linear least squares method or the like. In S205, the bias value setting unit 170 repeats the curve fitting excluding the largest outlier several times. The examples of S204 and S205 for the GNSS type shown in FIG. 11 are as shown in FIG. 12.

[0140] In S206, the bias value setting unit 170 generates a fitting function for each GNSS type, and in S207, sets the bias value for the GNSS type and elevation angle according to the fitting function of each GNSS type. An example of S206 and S207 for the L1 band is shown in FIG. 20.

[0141] As described above, in the second embodiment, a bias value is set for each frequency band of each satellite signal (e.g., L1 band, L2 band, L5 band in the case of GPS) with respect to the GNSS satellite type. This is because the reception characteristics of the satellite signal depend not only on the GNSS satellite type and elevation angle but also on the frequency band of the satellite signal. Note that a bias value based only on the GNSS satellite type and frequency band may be set without using the elevation angle.

[0142] Measured examples of the differences in reception characteristics depending on the frequency band for the combination of the same GNSS antenna and GNSS receiver are shown in FIGS. 21 and 22. FIG. 21 shows the L1 signal of GPS, and FIG. 22 shows the L2 signal of GPS. In both FIGS. 21 and 22, the horizontal axis is the elevation angle (°), and the vertical axis is the C / N0 value (dB-Hz).

[0143] (Variations regarding bias value setting) Even for the same GNSS type, there are cases where the transmitted signal output differs for individual satellites. For example, the transmitted 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.

[0144] For example, when the transmitted signal intensity of satellite A is smaller than that of other satellites of the same GNSS type, there are cases where the received signal intensity becomes small and it is not selected even when received as a direct wave. In that case, for the satellite signal during normalization, correction is performed by adding an individual bias value to the reception quality. The individual bias value is applied in addition to the GNSS bias value and elevation angle bias value shown in FIGS. 7 and 8. Alternatively, for the satellite signal to which the individual bias value is applied, only the individual bias value may be applied without applying the GNSS bias value and elevation angle bias value. Alternatively, for the satellite signal to which the individual bias value is applied, the elevation angle bias value and the individual bias value may be applied without applying the GNSS bias value.

[0145] Regarding which satellite of which GNSS type to set an individual bias value for, for example, in advance, for each GNSS type and each satellite, measure the received signal strength, store the measured value in the signal data storage unit 160, and the bias value setting unit 170 selects a satellite in which the same event as the above satellite A occurs, and sets an individual bias value for the selected satellite.

[0146] Also, the individual bias value for a specific satellite may be applied to cases other than the case related to the transmission signal output like the above satellite A.

[0147] (Regarding the set value of dCN0) Regarding the dCN0 value for each frequency band in the second embodiment (that is, the dCN 0L1 value, the dCN 0L2 value, etc.), as described with reference to FIGS. 14 and 15, a dCN0 value with elevation angle dependence may be set. In this case, for example, set a dCN0 value with elevation angle dependence as shown in FIG. 16 for each frequency band.

[0148] (Operation when the number of satellite signals available for positioning is less than the set value of the minimum number of satellite signals) To perform positioning and time synchronization using navigation satellite signals, it is necessary to receive at least 4 satellite signals. However, the number of satellite signals available for positioning and time synchronization is significantly reduced due to structures existing around the reception position of the satellite signals, and the number of satellite signals available for positioning and time synchronization is less than the minimum number of satellite signals N0 selected in the initial estimated positioning process, or less than the minimum number of satellite signals N1 selected in the supplementary satellite selection process. In this case, as operations of the measurement device 100, for example, there are options such as (1) not outputting a positioning solution, (2) outputting a positioning solution using available satellite signals. Regarding which of these operations to perform, it may be switched by setting in advance.

[0149] (Example of hardware configuration) FIG. 23 is a diagram showing a hardware configuration example of a computer that can be used as the measurement device 100 in the present embodiment. The computer may be a physical device or a virtual machine on the cloud.

[0150] The computers in FIG. 23 each have 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, etc., which are mutually connected by a bus B. Note that the GNSS antenna 110 is not shown in FIG. 20. The GNSS antenna 110 is connected to the interface device 1005, for example.

[0151] A program for realizing the processing on the computer is provided by a recording medium 1001 such as a CD-ROM or a memory card, for example. When the recording medium 1001 storing the program is set in the drive device 1000, the program is installed from the recording medium 1001 via the drive device 1000 into the auxiliary storage device 1002. However, the program does not necessarily have to be installed from the recording medium 1001, and it may be downloaded from another computer via a network. The auxiliary storage device 1002 stores the installed program and also stores necessary files, data, etc.

[0152] When an instruction to start the program is given, the memory device 1003 reads out and stores the program from the auxiliary storage device 1002. The CPU 1004 realizes the functions related to the measurement device 100 according to 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), etc. according to the program. The input device 1007 is composed of a keyboard, a mouse, buttons, or a touch panel, etc., and is used to input various operation instructions. The output device 1008 outputs the calculation result.

[0153] (Effects of Embodiment) As described above, according to the embodiment of the present invention, a visible satellite signal can be selected from received satellite signals with high accuracy without depending on the characteristics of a receiver or an antenna. Thereby, the positioning accuracy in a poor reception environment can be improved. In addition, the influence of interference signals in satellite selection can be reduced.

[0154] (Supplementary Note) In the present embodiment, at least a measurement device, a measurement method, and a program described in each of the following items are provided. (Item 1) A signal selection unit that selects a predetermined number of satellite signals based on the reception quality of satellite signals received by a GNSS antenna, a measurement unit that performs positioning using the predetermined number of satellite signals selected by the signal selection unit and determines an initial estimated position, and the signal selection unit selects a plurality of satellite signals to be used for positioning or time synchronization based on a comparison result of comparing an expected reception time when the satellite signal is received as a direct wave at the initial estimated position with an actual reception time of the satellite signal Satellite signal receiving device. (Item 2) Based on the comparison result, the signal selection unit rejects a satellite signal actually received with a delay time equal to or longer than a threshold value from an expected reception time when received as a direct wave at the initial estimated position The satellite signal receiving device according to Item 1. (Item 3) The measurement unit performs positioning using a plurality of satellite signals excluding the rejected satellite signal, and updates the initial estimated position with the obtained coordinate values The satellite signal receiving device according to Item 2. (Item 4) The signal selection unit updates the initial estimated position, repeats the process based on the comparison result using the updated initial estimated position, and ends the repeated process when a predetermined end condition is satisfied The satellite signal receiving device according to Item 3. (Item 5) When the number of selected satellite signals at the time of completion of the repeated process is smaller than a preset number, the signal selection unit compares delay times among a plurality of non-selected satellite signals, and determines a non-selected satellite signal to be added to the selected satellite signals based on the DOP value when the non-selected satellite signal with a smaller delay time is added to the selected satellite signals. The satellite signal receiving device according to Item 4. (Item 6) A satellite signal selection method executed by a satellite signal receiving device, selecting a predetermined number of satellite signals based on the reception quality of the satellite signals received by a GNSS antenna; performing positioning using the predetermined number of satellite signals and determining an initial estimated position; selecting a plurality of satellite signals to be used for positioning or time synchronization based on a comparison result of comparing an expected reception time when a satellite signal is received as a direct wave at the initial estimated position with an actual reception time of the satellite signal; A satellite signal selection method comprising: (Item 7) A program for causing a computer to function as each part in the satellite signal receiving device according to any one of Items 1 to 5.

[0155] As described above, the present embodiment has been described, but the present invention is not limited to such a specific embodiment, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

[0156] This patent application claims priority based on International Patent Application PCT / JP2022 / 000721 filed on January 12, 2022, and incorporates the entire contents of International Patent Application PCT / JP2022 / 000721 into this application.

Description of Reference Numerals

[0157] 100 Measuring device 110 GNSS antenna 120 Signal receiving unit 130 Signal Selection Unit 140 Measurement Unit 150 Output Unit 160 Signal Data Storage Unit 170 Bias Value Setting Unit 180 Bias Value Storage Unit 1000 Drive Device 1001 Recording Medium 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 the reception quality of satellite signals received by a GNSS antenna; A measurement unit that performs positioning using the predetermined number of satellite signals selected by the signal selection unit and determines an initial estimated position. The satellite signal receiving device includes: The signal selection unit is a satellite signal receiving device that selects a plurality of satellite signals for positioning or time synchronization based on a comparison result obtained by comparing an expected reception time when a satellite signal is received as a direct wave at an initial estimated position with an actual reception time of the satellite signal. Based on the comparison result, the signal selection unit rejects a satellite signal that is actually received with a delay time equal to or greater than a threshold value from the expected reception time when received as a direct wave at the initial estimated position, updates the initial estimated position with coordinate values obtained by positioning using a plurality of satellite signals excluding the rejected satellite signal, repeats the process based on the comparison result using the updated initial estimated position, and ends the repeated process when a predetermined end condition is satisfied. The signal selection unit decreases the threshold value each time the process is repeated. The predetermined end condition is that the difference between the initial estimated position before update and the initial estimated position after update becomes equal to or less than a preset value. Satellite signal receiving device.

2. When the number of selected satellite signals at the time of ending the repeated process is smaller than a preset number, the signal selection unit compares the delay times among a plurality of non-selected satellite signals and determines a non-selected satellite signal to be added to the selected satellite signals based on the DOP value when the non-selected satellite signal with the smallest delay time is added to the selected satellite signals. The satellite signal receiving device according to claim 1.

3. A satellite signal selection method executed by a satellite signal receiving device, the method comprising: Selecting a predetermined number of satellite signals based on the reception quality of satellite signals received by a GNSS antenna; Performing positioning using the predetermined number of satellite signals and determining an initial estimated position; Selecting a plurality of satellite signals for positioning or time synchronization based on a comparison result obtained by comparing an expected reception time when a satellite signal is received as a direct wave at an initial estimated position with an actual reception time of the satellite signal. The satellite signal selection method includes: Based on the comparison result, the satellite signal receiving device rejects a satellite signal that is actually received with a delay time equal to or greater than a threshold value from the reception time expected when received as a direct wave at the initial estimated position, updates the initial estimated position with the coordinate value obtained by positioning using a plurality of satellite signals excluding the rejected satellite signal, and repeats the process based on the comparison result using the updated initial estimated position. When a predetermined end condition is satisfied, the repeated process is terminated. The satellite signal receiving device decreases the threshold value every time the process is repeated. The predetermined end condition is that the difference between the initial estimated position before update and the initial estimated position after update is equal to or less than a preset value. Satellite signal selection method.

4. A program for causing a computer to function as each part in the satellite signal receiving device according to claim 1 or 2.

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