JP2024055231A - Relative position detection system, relative position detection method, and phase detection device - Google Patents

Abstract

[Problem] To provide a relative position detection system and relative position detection method that enable high-precision positioning with an error of about a few centimeters using radio waves from GNSS satellites. Also provided is a phase detection device that realizes carrier phase detection with low power consumption. [Solution] The relative position detection system and relative position detection method of the present invention realize high-precision positioning by detecting instantaneous values of carrier phase at a time that precisely matches a specified UTC time, and calculating evaluation indexes using the instantaneous values for all possible combinations of satellite pairs. Also, the phase detection device of the present invention realizes carrier phase sampling that matches UTC time while consuming low power by correcting the sampling time of the carrier phase to obtain the instantaneous value of the carrier phase. [Selected Figure] Figure 2

Description

The present invention relates to a relative position detection system, a relative position detection method, and a phase detection device.

In dangerous areas where disasters such as landslides are likely to occur, ground monitoring systems using GPS (Global Positioning System) or GNSS (Global Navigation Satellite System) have been proposed to monitor slight displacements of the ground and structures. Here, GPS is the term for the artificial satellite system operated by the United States, and GNSS is the term for the artificial satellite system launched by countries such as the United States, Japan, Europe, and China. In this invention, we will explain it in a unified manner using GNSS, but it goes without saying that the invention can also be applied to GPS.

GNSS position detection methods can be broadly divided into two categories: methods that detect code information and methods that detect the carrier phase. The method that detects code information is widely used in car navigation and other applications. The code information sent from GNSS satellites changes at approximately 1 MHz, so it is possible to know the position on Earth (latitude, longitude, and altitude) with an accuracy of a few meters to about 10 meters.

The code information can detect not only the position but also the exact time (GPS time). For example, many commercially available GNSS receivers provide a pulse (1PPS) synchronized with GPS time. 1PPS is a time pulse that matches GPS time with a high degree of accuracy, with an error of about 10 nanoseconds, no matter where the GNSS receiver is located on Earth.

By correcting for leap seconds, GPS time can be converted to UTC (Coordinated Universal Time), which is common throughout the world. By adding 9 hours to UTC, it can be converted to Japan Standard Time (JST). In the following explanations, we will assume that the GNSS receiver detects UTC, but UTC can also be interpreted as GPS time or JST.

When higher positioning accuracy than that provided by code information is required, a method of detecting the carrier phase is used. It is known that by using a high-frequency carrier (approximately 1.5 GHz), it is possible to perform positioning with a high degree of accuracy, with an error of less than a few centimeters. Methods for detecting the carrier phase include RTK (Real-Time-Kinematic) or carrier phase relative positioning, and devices equipped with RTK are commercially available.

For example, Patent Document 1 discloses a carrier phase relative positioning device in which multiple antennas are installed on a moving body and at a fixed position, radio waves are received from multiple GNSS satellites, a double phase difference is calculated, an integer bias N is determined, and then a vector (relative position vector) between the moving body and the fixed position is estimated.

As described in Patent Document 1, the conventional carrier phase positioning method (hereinafter referred to as the conventional method) is a positioning method in which a single reference satellite (hereinafter referred to as the reference satellite) is determined to determine the double phase difference. This conventional method has the following three problems (1) to (3). (1) Since an integrated value (integrated phase) of the carrier phase detected from the radio waves of each satellite is required, the amount of information is large and positioning calculations are difficult. (2) If the radio waves from the reference satellite are lost, the integer bias N must be calculated again, which may interrupt positioning. (3) If noise is mixed into the carrier phase detected from the reference satellite, the positioning error increases.

Patent Document 2 discloses a device that acquires the carrier phase as an instantaneous value at a predetermined sampling timing synchronized with UTC and performs positioning. The device disclosed in Patent Document 2 can solve the problems (1) and (2) mentioned above.

However, even the device described in Patent Document 2 cannot solve the problem in (3). In addition, the device described in Patent Document 2 must sample the carrier phase in precise agreement with UTC, which creates a new problem of high power consumption because the operating frequency of the GNSS receiver must be increased.

Patent No. 3532267 JP 2022-112022 A

The present invention therefore aims to provide a relative position detection system and a relative position detection method that are a positioning method using carrier phase and that can achieve highly accurate and stable positioning even when radio waves from some satellites are interrupted or when the noise level of the carrier phase is high. It also aims to provide a phase detection device that can achieve such a relative position detection system and relative position detection method with low power consumption.

[1] The relative position detection system of the present invention comprises a plurality of antennas (2A, 2B), phase detection devices (3A, 3B) connected to each of the plurality of antennas (2A, 2B) for receiving radio waves from a plurality of GNSS satellites (Sat1, Sat2, Sat3, Sat4) and detecting instantaneous values of carrier phases (φA(1), φA(2), φA(3), φA(4)) and (φB(1), φB(2), φB(3), φB(4)), and a positioning means (4) for positioning a relative position vector P' between the plurality of antennas (3A and 3B) using the instantaneous values of the carrier phases, and the positioning means (4) calculates the difference in the instantaneous values of the carrier phases for a satellite pair (n, r) consisting of two satellites extracted from the plurality of GNSS satellites. The relative position detection system (1) is characterized by including a double phase difference calculation means (44) that calculates the double phase difference θ(n,r) to obtain the double phase difference θ(n,r), a satellite position information acquisition means (43) that acquires the satellite position of the GNSS satellite, an evaluation means (42) that uses the double phase difference θ(n,r) and the satellite position to obtain an evaluation index E(n,r,P') of the relative position vector P', and a comprehensive evaluation means (41) that integrates the evaluation index E(n,r,P') for the different satellite pairs (n,r) to calculate a comprehensive evaluation index Energy(P').

[2] In the relative position detection system of the present invention, it is preferable that the evaluation means (42) includes a lattice vector calculation means for determining a lattice vector k(n,r) related to the satellite pair (n,r), a theoretical double difference calculation means for calculating the inner product of the lattice vector k(n,r) and the relative position vector P' to determine a theoretical double phase difference Φ(n,r,P'), and a phase difference evaluation means (426) for evaluating the difference between the theoretical double phase difference Φ(n,r,P') and the double phase difference θ(n,r) and outputting the evaluation index E(n,r,P').

[3] In the relative position detection system of the present invention, it is preferable that the overall evaluation by the overall evaluation means (41) uses an evaluation index E(n,r,P') for all possible combinations of satellite pairs (n,r).

[4] In the relative position detection system of the present invention, it is preferable that the instantaneous value of the carrier phase has a change range of 2π radians.

[5] The relative position detection method of the present invention is a relative position detection method that receives radio waves from multiple GNSS satellites using multiple phase detection devices respectively connected to multiple antennas, detects instantaneous values of carrier phases, and uses the instantaneous values of carrier phases to position a relative position vector between the antennas, characterized in that the positioning includes: determining a double phase difference using the instantaneous values of the carrier phase for a satellite pair (n, r), acquiring the satellite positions of the multiple GNSS satellites; determining an evaluation index for the relative position vector P' using the double phase difference θ(n, r) and the satellite positions; and comprehensively evaluating the evaluation indexes for the multiple satellite pairs to obtain the relative position vector as the positioning result.

[6] The phase detection device (3) of the present invention includes a satellite signal receiving unit (31) that receives radio waves transmitted from a plurality of GNSS satellites and detects the carrier phase θ(n), carrier offset frequency Dp(n), code information, and pseudorange Pr(n) of the plurality of GNSS satellites (n) at device time (Tr);
a time error acquisition unit (32) that calculates an error (Δ(n)) in the device time using the code information and the pseudorange Pr(n);
an instantaneous phase calculation unit (33) that corrects the carrier phase θ(n) using the carrier offset frequency Dp(n) and the device time error (Δ(n)) obtained from the multiple satellite signal receiving units to calculate an instantaneous value φ(n) of the carrier phase at a predetermined time (Ts);
and a data transmission section (35) that transmits the instantaneous value φ(n) of the carrier phase.

[7] In the phase detection device (3) of the present invention, it is preferable that the instantaneous phase calculation unit (33) limits the instantaneous value φ(n) of the carrier phase to a range of 0 to 2π radians.

[8] In the phase detection device (3) of the present invention, it is preferable that the data transmission unit (35) transmits position information (latitude, longitude, altitude) detected from the code information in addition to the instantaneous value φ(n) of the carrier phase.

The relative position detection system and relative position detection method of the present invention use the carrier phase obtained from the phase detection device to determine an evaluation index for each satellite pair, and detect the relative position by integrating the evaluation indexes obtained from many satellite pairs. Therefore, it is possible to provide a relative position detection system and relative position detection method that can achieve highly accurate and stable positioning even when radio waves from some satellites are interrupted or when the noise level of the carrier phase is high.

The phase detection device of the present invention also includes a satellite signal receiving unit that detects the carrier phase, carrier offset frequency, code information, and pseudo distance of multiple GNSS satellites at device time, and uses the carrier offset frequency, code information, and pseudo distance obtained from the multiple satellite signal receiving units to correct the carrier phase and calculate the instantaneous value of the carrier phase at a specified time. As a result, the operating frequency of the satellite signal receiving unit can be kept low, making it possible to realize a phase detection device that consumes even less power than conventional devices.

When performing positioning calculations using the phase detection device of the present invention, the amount of information transmitted to the positioning calculation unit can be small. Therefore, in this invention, a long-distance wireless transmission system such as LPWA (Low Power Wide Area) can be applied as a means of transmitting information from the phase detection device. In this case, the phase detection device of the present invention can be installed in the mountains where mobile phones are out of range, making it possible to detect landslides in the mountains.

FIG. 1 is a conceptual explanatory diagram of high-precision positioning using a carrier phase according to a conventional method. 1 shows an example of the configuration of a relative position detection system 1A of the present invention. 4 is a flowchart showing a positioning calculation of a positioning means 4A of the present invention. 13 is a flowchart of a calculation (step S6) for determining an evaluation index by the evaluation means 42 of the present invention. 2 shows an example of the configuration of an evaluation means 42 used in the relative position detection system 1A. 2 is a configuration example of a phase detection device 3 of the present invention. 2 shows an example of the configuration of an instantaneous phase calculation unit 33 constituting the phase detection device 3. 13 is a diagram showing a schematic representation of an internal signal waveform of an instantaneous phase calculation unit 33. FIG. 4 is a diagram showing an example of a format of a payload transmitted by the phase detection device 3 of the present invention. 13 shows the results of a simulation performed to confirm the relative position detection method of the present invention. 13 shows the results of a simulation performed to confirm the relative position detection method of the present invention. 13 shows the results of an experiment conducted to experimentally confirm the relative position detection method of the present invention. 13 is a configuration example of a relative position detection system 1B according to a second embodiment. 13 is a configuration example of a phase detection device 3 in the third embodiment. 13 is a diagram showing an example of a format of a payload transmitted by a phase detection device 3 in the fourth embodiment.

<Outline of the relative position detection method of the present invention>
The outline of the present invention will be explained in comparison with the conventional method. In the following, satellite numbers will be written in parentheses. For example, "satellite number n" will be written as "(n)" and "reference satellite r" will be written as "(r)". In addition, for each of the two antennas and phase detection devices, one will be written as A and the other as B. For example, the instantaneous value of the carrier phase of GNSS satellite Sat1 detected by phase detection device 2A will be written as φA(1). In addition, an example will be explained in which four GNSS satellites (Sat1 to Sat4) can be received, but it is also possible to receive radio waves from more GNSS satellites. In the following, the number of received GNSS satellites will be written as M.

[Conventional method]
FIG. 1 is a diagram for explaining a high-precision positioning detection method using carrier phase as exemplified in Patent Document 1. Radio waves from four GNSS satellites (Sat1 to SAt4) in the sky are received by two antennas (2A and 2B) and converted into electrical signals. Here, antenna 2A is installed at a reference position. Phase detection devices (3A and 3B) are connected to the two antennas, respectively, and GNSS reception is performed by the phase detection devices, and the carrier phases (ΩA(1), ΩA(2), ΩA(3), ΩA(4)) and (ΩB(1), ΩB(2), ΩB(3), ΩB(4)) of each satellite are detected. Positioning means 4 uses this carrier phase to determine the relative position to antenna 2B placed at an unknown location and outputs a relative position vector P'. Hereinafter, the distance R between the two antennas may also be called the "baseline length."

The positioning means 4 is composed of an RTK calculation unit 49 that performs positioning calculations, a dual phase difference calculation means 44, and a communication means 46.

The double phase difference calculation means 44 outputs the double phase difference θ(n,r) from the carrier phase obtained from the reference satellite (r) and other satellites (n). This calculation removes various disturbances, such as changes in propagation delay in the ionosphere. When the reference satellite is (r = 1), three pairs of double phase differences (θ(2,1), θ(3,1), θ(4,1)) are obtained. The RTK calculation unit 49 uses these three pairs of double phase differences to perform positioning.

If the distances from the satellite (n) to the antennas 2A and 2B are RA(n) and RB(n), the integer bias is N(n), and the carrier wavelength (approximately 19 cm) is λ, the three sets of double phase differences are expressed by the following equation 1.

In the conventional method, it is necessary to use the same reference satellite (i.e., the underlined terms in Equation 1 must be the same). For this reason, when radio waves are received from M satellites, the simultaneous equations in Equation 1 become M-1. The number of unknowns exceeds the number of equations, and Equation 1 cannot be solved in this state.

In the conventional method, the carrier phase is acquired at different times, and multiple sets of simultaneous equations of Equation 1 are prepared to perform positioning calculations. Since the carrier phases acquired at different times are used, an "accumulated phase" is used, which is the time-integrated carrier phase. This accumulated phase has the disadvantage that it contains a large amount of information, requiring high-speed communication.

In addition, with the conventional method, an integer bias is calculated for one reference satellite, so if the reference satellite's signal is strongly affected by noise, the positioning results can fluctuate significantly. Furthermore, with the conventional method, if the reference satellite cannot be received, the integer bias must be calculated again, which can cause positioning to be interrupted.

Next, we will explain embodiment 1 of the present invention.

[Embodiment 1]
An example of the configuration of a relative position detection system 1A of the present invention is shown in Fig. 2. As in the conventional example, radio waves from four satellites (Sat1 to Sat4) are converted into electrical signals by two antennas (2A and 2B), the carrier phase is detected by phase detectors (3A and 3B), and the positioning means 4 outputs a relative position vector P' between the antennas (2A, 2B).

In the present invention, the positioning means 4 is composed of a comprehensive evaluation means 41, an evaluation means 42, a satellite position information acquisition means 43, a double phase difference calculation means 44, a system controller 45, and a communication means 46. The operation of each means will be described later using Figures 3 and 4.

The two phase detection devices 3A and 3B each sample the carrier phase at a timing synchronized with UTC, and output the instantaneous values of the carrier phase φA(n) and φB(n). (Hereinafter, the instantaneous value of the carrier phase synchronized with UTC in this way will be referred to as the "instantaneous phase.") The phase detection devices 3A and 3B each transmit the instantaneous phase to the positioning means 4 via the communication means 46. In many cases, the communication means 46 is realized by a wireless communication device, but it is also possible to use a communication device with a wired connection such as a coaxial cable.

The double phase difference calculation means 44 calculates the double phase difference θ(n,r) from the instantaneous phases φA(n) and φB(n), the satellite position information acquisition means 43 obtains the satellite position, and the evaluation means 42 calculates an evaluation index using this information (double phase difference, satellite position, and estimated relative position vector P' described below). The overall evaluation means 41 adds the evaluation index obtained for the positioning pair (n,r) to the overall evaluation index. The estimated relative position vector P' that minimizes the overall evaluation index is searched for and output as the positioning result.

Figure 3 is a flowchart of the positioning calculation controlled by the system controller 45. The details of the positioning calculation will be explained below with reference to Figure 3.

[Step S0]
In step S0, the system controller 45 obtains instantaneous values φA(n) and φB(n) of the carrier phase obtained from the communication means 46.

[Step S1]
In step S1, the system controller 45 sets the search center position vector P0. When used to detect disasters such as landslides, the installation positions of the antennas 2A and 2B are approximately known. The center position vector P0 can be determined by subtracting the position coordinates of the two antennas. The positioning in this embodiment searches three-dimensionally with this center position vector P0 as the center.

[Step S2]
Next, in step S2, the system controller 45 adds an offset vector to the central position vector P0 to provisionally determine an estimated relative position vector P'.

In the following explanation, the estimated relative position vector P' is expressed in polar coordinates (R, α, β). That is, R is the distance between the antennas, α is the azimuth angle relative to the north-south line, and β is the elevation angle in the vertical direction.

The estimated relative position vector P' is the sum of the central position vector (R0, α0, β0) and the offset vector (ΔR, Δα, Δβ) as shown in the following equation 2.
The system controller 45 searches for an optimal value of the estimated relative position vector P' by determining an overall evaluation index Energy(P') described below while changing the offset vector.

[Step S3]
In step S3, the system controller 45 sequentially extracts all possible combinations of satellite pairs. For example, when four GNSS satellites (Sat1 to Sat4) are received, there are six possible satellite pairs as shown in the following formula 2. In step S3, these six possible satellite pairs are sequentially extracted.

As shown in Equation 1, the conventional method only uses three combinations: (2,1), (3,1), and (4,1). Therefore, in the conventional method, the carrier phase obtained from the reference satellite (r=1) is evaluated using three equations, while the carrier phases obtained from satellites 2, 3, and 4 are only used once. In contrast, our method uses all combinations (six combinations), enabling highly accurate positioning by evaluating the information obtained from all satellites equally.

[Step S4]
Next, in step S4, the double phase difference calculation means 44 performs the difference calculation of Equation 4 for the satellite pair (n, r) to obtain the double phase difference θ(n, r).

[Step S5]
Next, in step S5, the satellite position information acquisition means 43 acquires the position (X(n), Y(n), Z(n)) of each satellite. Specifically, the satellite position (X(n), Y(n), Z(n)) is obtained by solving the Kepler equation using the satellite orbit information (ephemeris) Ep. Here, the satellite orbit information Ep is broadcast as code information from each satellite, so it can be obtained by installing a commercially available GNSS receiver and receiving satellite radio waves. Alternatively, the satellite orbit information Ep can be downloaded from an Internet server published by the Geospatial Information Authority of Japan or the like.

[Step S6]
In step S6, the evaluation means 42 performs the evaluation index calculation shown in Fig. 5 using the three types of information explained so far (double phase difference, satellite position, and estimated relative position vector P') to obtain the evaluation index E(n, r, P'). The evaluation index is an index that indicates the accuracy of the estimated relative position vector P'. In an ideal state without noise, when the estimated relative position vector P' has a correct value, the evaluation index becomes "0".

[Step S7]
In step S7, the overall evaluation means 41 adds the above-mentioned evaluation index E(n, r, P') to the overall evaluation index Ex(P').

[Step S8]
In step S8, the system controller 45 judges whether the calculations in steps S3 to S7 have been performed for all possible positioning pairs (n, r). If there are any remaining positioning pairs, the process returns to step S3, and an evaluation index calculation is performed for the new positioning pairs. If it is judged that the processing for all positioning pairs (n, r) has been completed, the process proceeds to step S9. At this point, the overall evaluation index Ex(P') expressed by the following formula 5 has been obtained.

[Step S9]
In step S9, the system controller 45 judges whether or not the overall evaluation index Ex(P') has been calculated for all possible estimated relative position vectors P'. If any P' remains for which the overall evaluation index has not been calculated, the process returns to step S2, where a new offset vector (ΔR, Δα, Δβ) is added to the central position vector P0 to update the estimated relative position vector P', and the process of calculating the overall evaluation index is restarted. When the overall evaluation index Ex(P') has been calculated for all estimated relative position vectors P', the process proceeds to step S10.

[Step S20]
In step S10, the system controller 45 outputs the estimated relative position vector P' that minimizes the overall evaluation index Ex(P') as the positioning result, and the positioning calculation is completed.

[Evaluation index calculation]
The evaluation means 42 performs the evaluation index calculation to obtain the evaluation index E(n, r, P') in steps S61 to S65 of Fig. 4. Hereinafter, these steps will be described in order.
[Step S61]
First, in step S61, the coordinates (Xa, Ya, Za) of the reference position where the antenna 2A is placed are obtained by converting the latitude and longitude of the reference position into a geocentric rectangular coordinate system.

[Step S62]
In step S61, a direction vector v(n) from the reference position (Xa, Ya, Za) to the coordinates (X(n), Y(n), Z(n)) of the satellite (n) is calculated using the following formula 6. A direction vector v(r) is calculated in the same manner for the reference satellite (r).

Here, the magnitude of the direction vector v(n) is normalized by the distance r(n) calculated by the following equation 7.

[Step S63]
In step S63, the grid vector k(n,r) is calculated by subtracting the direction vector v(r) to the reference satellite (r) from the direction vector v(n) to the satellite (n) according to the following equation 8.
The lattice vector k(n,r) represents the interference fringes formed by the radio waves of two satellites (n,r). The spacing Λ(n,r) of these interference fringes can be calculated using the following formula 9.
Here, η(n,r) is the angle made by satellite (n) and satellite (r) extracted as a satellite pair. Please note that in the positioning method of the present invention, the period of the lattice vector differs depending on the satellite selected as a pair. For example, when η is 30 degrees, the spacing Λ of the interference fringes is 37 cm, which is larger than the wavelength λ. (In conventional methods, the period is a constant value λ regardless of the satellite.)

[Step S64]
In step S64, the theoretical double phase difference Φ(n, r, P′) is calculated by the inner product of the lattice vector and the estimated relative position vector P′ using the following equation 10.

[Step S65]
The theoretical double phase difference obtained by the above processing and the actually measured double phase difference are both phase information. Therefore, in step S65, the difference between the two pieces of phase information is evaluated as in the following formula 11. That is, the difference is calculated as two phasors to obtain the evaluation index E(n, r, P').

When the distance between the relative position vector P and the estimated relative position vector P' is the shortest, the evaluation index E(n,r,P') in the above formula should be the smallest.

Figure 5 shows an example of the configuration of the evaluation means 42. In step S62, the evaluation means 42 performs the calculation of equation 6 using the subtractor 420 and divider 422 to obtain the direction vector v(n). Similarly, the subtractor 421 and divider 423 calculate the direction vector v(r). In step S63, the lattice vector calculator 424 performs the calculation of equation 8 to obtain the lattice vector k(n,r). In step S64, the inner product calculator 425 calculates the inner product of the lattice vector k(n,r) shown in equation 10 and the estimated relative position vector P' to obtain the theoretical double phase difference Φ(n,r,P'). In step S65, the phasor difference calculator 426 calculates the difference between the double phase difference shown in equation 11 and the theoretical double phase difference to obtain the evaluation index E(n,r,P').

As explained above, the relative position detection method of the present invention does not use the integer bias calculated in the conventional method. Therefore, the positioning calculation can be completed with a single measurement. It is also not necessary to calculate the integrated phase by integrating the phase, as is done in the conventional method, and it is possible to limit the range of change in the instantaneous phase to 0 to 2π. As a result, the phase detection device 3 of the present invention can reduce the amount of information transmitted to the positioning means 4.

[Configuration of Phase Detection Device]
6 shows the configuration of a phase detection device 3 according to an embodiment of the present invention. The phase detection devices 3, installed at multiple measurement points, receive satellite radio waves obtained by the receiving antennas 2, detect the instantaneous phases (φ(1), φ(2), φ(3), φ(M)) of the carrier waves at predetermined times Ts, and transmit the instantaneous phases to the positioning means 4 by the data transmission unit 35.

The phase detection device 3 is composed of a front end 30, a satellite signal receiving unit 31, a time error acquisition unit 32, an instantaneous phase calculation unit 33, a timing generation means 34, a data transmission unit 35, and an antenna 36. Of these, the satellite signal receiving unit 31 and the instantaneous phase calculation unit 33 are each installed for each satellite. Although only satellite (n) is illustrated in FIG. 6, in reality the same signal processing is performed for each of the M satellites.

In FIG. 6, the front end 30 uses a filter to extract the weak signal captured by the antenna 2, amplifies it, converts it into a low-frequency signal, and supplies it to multiple satellite signal receivers 31. The satellite signal receiver 31 outputs the code information (n) of each satellite (n), the pseudorange Pr(n), the carrier phase Ω(n), and the carrier frequency offset Dp(n). Of these, the frequency offset Dp(n) is generally called the "Doppler frequency." The time error acquisition unit 32 uses the code information (n) to perform GNSS reception processing and obtains the position (X(n), Y(n), Z(n)) of each satellite (n) and the position (Xa, Ya, Za) of the receiving antenna 2. The time error acquisition unit 32 uses this information to obtain the time error Δ(n) of the radio wave received from each satellite (n) using the following equation 12 and outputs it.
Here, Range(n) represents the distance from each satellite (n) to the receiving antenna 2, Cv represents the speed of light, and Satellite_Delay(n) represents the transmission delay time of each satellite (n). Satellite_Delay(n) can be calculated from the code information of each satellite (n).

The timing generating means 34 is composed of a crystal oscillator, a counter, etc., and supplies an operating clock to the satellite signal receiving unit 31. Since the power consumption of the satellite signal receiving unit 31 increases in proportion to the operating clock frequency, it is desirable to use an operating clock with as low a frequency as possible. Commercially available GNSS receivers use a low frequency such as 1 kHz. The timing generating means 34 also counts the operating clock and outputs the device time Tr. The device time Tr includes a time error in the period of the operating clock (the reciprocal of the frequency). (When the operating clock is 1 kHz, an error of up to 1 ms is included). The device time Tr also includes a time error due to the time it takes for the radio waves from each satellite to reach the antenna 2.

The multiple instantaneous phase calculation units 33 then correct the effect of the time error contained in the carrier phase Ω(n) sampled at the device time Tr, and output the corrected phase to the carrier phase at a specific time Ts (i.e., the instantaneous phase φ(n)).

7 is a block diagram showing the configuration of the instantaneous phase calculation unit 33. A correction time detection means 331 calculates and outputs a phase correction time δ from a predetermined time Ts that coincides with UTC, the device time Tr, and a time error Δ(n) according to the following formula 13.

As a result of the above, the phase correction means 332 obtains the instantaneous phase φ(n) according to the following equation 14.
Here, the function mod represents the modulo 2π operation.

Figure 8 shows a schematic diagram of the processed waveform of the instantaneous phase calculation unit 33. If the carrier wave has the waveform shown in (A), then the carrier phase φ shown in (B) is detected from a phase detection circuit (not shown) inside the satellite signal reception unit 31. This carrier phase is folded into the range of 0 to 2π, so by adding 2π every time it changes from 2π to 0, the integrated phase Ω shown in (C) is obtained. The goal is to sample the integrated phase Ω at a specified time Ts, but since the operating clock frequency cannot be increased in order to reduce power consumption, actual sampling involves a time error. The sampling time with a time error is shown diagrammatically as Tr. Here, the frequency offset Dp(n) represents the slope of the integrated phase Ω.

The correction calculation in Equation 14 approximates and corrects the integrated phase as a linear change with a slope of Dp(n) to obtain the instantaneous phase φ(n) at a given time Ts. Of course, it is also possible to further improve accuracy by approximating the integrated phase with a higher-order polynomial.

The phase detection device 3 shown in FIG. 6 outputs the instantaneous phases (φ(1) to φ(M)) of all satellites (Sat1 to SatM) to the data transmission unit 35. The data transmission unit 35 wirelessly transmits the instantaneous phases to the positioning means 4 via the antenna 36, and the positioning means 4 is configured to perform the positioning calculation described above.

Figure 9 shows an example of the payload information structure transmitted by the phase detection device 3. In this figure, the first two bytes are the header, which consists of an ID number (8 bits) previously assigned to the phase detection device 3, remaining battery power (4 bits), and the number of satellites M that were successfully received (4 bits).

The second half of the payload information is the instantaneous phase detected from each satellite. That is, a total of 16 bits are assigned to each satellite: satellite number (6 bits), CNR (2 bits), and instantaneous phase (8 bits). Here, CNR (Carrier to Noise Ratio) is an index of carrier strength, and is set to "11" when the radio wave strength from the satellite is strong and good instantaneous phase is expected, and "10" or "01" when it is moderate. If the satellite cannot be received, the CNR is set to "00".

In the payload information configuration example of Figure 9, the instantaneous phase and header obtained from a maximum of seven (M=7) satellites can be combined into a 128-bit payload. If ELTRES is adopted as the LPWA wireless communication, the payload that can be transmitted in one transmission is 128 bits, so the payload information of Figure 9 can be transmitted in one transmission. (ELTRES is a registered trademark of Sony Corporation). As the amount of information transmitted by the instantaneous phase is thus small, the present invention can be applied to LPWA wireless.

[Verification by simulation]
A simulation was performed to verify the principle, and is introduced below. In this simulation, we assumed that the baseline length R = 1.6 m, and that the instantaneous phases were obtained from a total of seven (M = 7) GNSS satellites. Since the number of satellites is M = 7, the total number of combinations of satellite pairs is 21 (7C2).

Figure 10 shows plots of the evaluation indices for three types of satellite pairs (2,1), (3,1), and (3,2) by changing the baseline length R. It can be confirmed that all three evaluation indices (A), (B), and (C) show the minimum value "0" at the correct baseline length (R = 1.6 m). In addition, the evaluation index E(3,2) for satellite pair (3,2) has a period of more than 2 m. For this satellite pair, since the period of the evaluation index is long, it is possible that accurate positioning can be performed even if the moving distance of antenna 2B becomes large. On the other hand, since the evaluation index E(3,2) changes gradually, it is possible that the variation in the positioning results will increase due to the influence of noise.

The evaluation indices obtained from all 21 satellite pairs were then added together, and the overall evaluation index Ex(R) was plotted, as shown in Figure 11. It was found that the overall evaluation index Ex(R) was 0 only at the correct baseline length (R = 1.6 m), confirming that the relative position detection method of the present invention is correct.

[Experimental confirmation]
Antennas 2A and 2B were installed on the roof of a building, 9.55 m apart, and the results of measuring the baseline length R using the present invention are shown in Figure 12. In this experiment, a total of nine GNSS satellites were received (M=9). The total number of satellite pair combinations was large, at 36 (=9C2). Looking at the results in Figure 12, the overall evaluation index Ex(R) became almost zero when the baseline length reached the correct 9.55 m, and positioning was performed correctly. This confirmed the suitability of the positioning method of the present invention.

[Embodiment 2]
In the above-described embodiment 1, the assumed application was to detect disasters such as landslides, so the central position vector P0 could be determined assuming that the installation positions of the antennas 2A and 2B were approximately known. However, there are also application examples other than disaster detection, and in such cases, it is assumed that the positions of the antennas 2A and 2B are not known in advance. Therefore, an example in which the positions of the antennas 2A and 2B are obtained by code positioning will be described below as embodiment 2. Note that the description of the same parts as embodiment 1 will be omitted.

Figure 13 is a configuration example of a relative position detection system 1B according to embodiment 2. As in embodiment 1, the instantaneous phase is detected by phase detection devices (3A and 3B), and the positioning means 4 outputs a relative position vector P' between the antennas (2A, 2B). In embodiment 2, the two phase detection devices (3A and 3B) perform code positioning, and obtain the coordinates (latitude, longitude, and altitude) of the approximate positions of the antennas 2A and 2B, which are transmitted to the positioning means 4. The positioning means 4 converts these coordinates into a geocentric orthogonal coordinate system, and is able to estimate the central position vector P0 from the relative positions of the two antennas. As a result, it is no longer necessary to know the positions of the antennas 2A and 2B in advance, and this can be applied to, for example, positioning of moving objects.

Figure 14 shows an example of the configuration of the phase detection device 3 according to the second embodiment. The time error acquisition unit 32 performs code positioning and sends information on the latitude, longitude, and altitude of the antenna 2 to the data transmission unit 35. Using the latitude, longitude, and altitude information sent from the data transmission unit 35, the positioning means 4 can obtain the central position vector P0.

Figure 15 shows an example of the configuration of payload information transmitted by the phase detection device 2 according to the second embodiment. The first 78 bits are a header, which includes an ID number (8 bits) followed by information on the latitude (24 bits), longitude (24 bits) and altitude (12 bits) of the positioned antenna 2. Using 24 bits for the latitude and longitude information makes it possible to specify the position of antenna 2 anywhere on Earth with an accuracy of a few meters.

The payload in Figure 15 has a total length of 142 bits when the number of satellites, M, is 4. When the number of satellites increases to M=11, the length of the payload becomes 254 bits. Since the amount of data that can be sent at one time with ELTRES is 128 bits, it is necessary to send it in two parts, but this is still a usable amount of information.

The configuration of the present invention has been described above, but it is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the gist of the present invention. For example, the following modifications are also possible.

In the above embodiment, the unit of instantaneous phase has been described as radians. However, by dividing the instantaneous phase by the constant 2π, one rotation of the phase can also be used as the unit. In this case, the instantaneous phase changes in the range from 0 to 1.

In the above embodiment, all possible combinations of satellite pairs are used. For example, when the number of satellites M = 9, two satellites are selected from the nine satellites to create a satellite pair, so the total number of possible combinations of satellite pairs is 36 (9C2). It is not necessarily necessary to use "all" of the 36 combinations, and it is possible to exclude some of them. For example, the angle η between the satellite pairs can be checked, and only satellite pairs with a large η can be excluded from positioning. Alternatively, only satellites with large noise can be determined from the CNR and excluded.

In the above embodiment, the estimated relative position vector P' that minimizes the overall evaluation index Ex(P') is output as the positioning result. However, for example, it is also possible to obtain an estimated relative position vector P1' that minimizes the overall evaluation index Ex(P') and an estimated relative position vector P2' that minimizes the overall evaluation index Ex(P'), and output either P1' or P2' as the positioning result using other information such as the movement status of antenna 2B.

In the above embodiment, the carrier frequency transmitted from the satellite was described as approximately 1.5 GHz, but there are also satellites that use a 1.2 GHz carrier. By applying the present invention using two types of carrier waves, 1.5 GHz and 1.2 GHz, even more accurate measurements can be made.

Claims (8)

A plurality of antennas;
a phase detection device connected to each of the plurality of antennas, for receiving radio waves from a plurality of GNSS satellites and detecting an instantaneous value of a carrier phase;
a positioning means for measuring a relative position vector between the plurality of antennas by using the instantaneous value of the carrier phase,
The positioning means (4)
a double phase difference calculation means for calculating a difference between instantaneous values of the carrier phase for a satellite pair consisting of two satellites extracted from the plurality of GNSS satellites to obtain a double phase difference;
A satellite position information acquisition means for acquiring the satellite positions of the GNSS satellites;
an evaluation means for calculating an evaluation index of the relative position vector using the dual phase difference and the satellite position;
A relative position detection system comprising: a comprehensive evaluation means for integrating the evaluation indexes relating to different satellite pairs to calculate a comprehensive evaluation index. The evaluation means includes:
A lattice vector calculation means for calculating a lattice vector relating to the satellite pair;
a theoretical double difference calculation means for calculating an inner product of the lattice vector and the relative position vector to obtain a theoretical double phase difference;
2. The relative position detection system according to claim 1, further comprising a phase difference evaluation means for evaluating a difference between said theoretical double phase difference and said double phase difference, and outputting said evaluation index. The relative position detection system according to claim 1 or 2, characterized in that the overall evaluation by the overall evaluation means uses evaluation indices for all possible combinations of satellite pairs. The relative position detection system according to claim 1 or 2, characterized in that the instantaneous value of the carrier phase has a change width within a range of 2π radians. A relative position detection method (4) for receiving radio waves from a plurality of GNSS satellites using a plurality of phase detection devices respectively connected to a plurality of antennas, detecting instantaneous values of carrier phases, and locating a relative position vector P between the antennas using the instantaneous values of the carrier phases, comprising:
The positioning is
determining a dual phase difference using the instantaneous values of carrier phase for the satellite pair;
Acquire satellite positions of the plurality of GNSS satellites;
determining an evaluation index for the relative position vector using the dual phase difference and the satellite position;
A relative position detection method, comprising: comprehensively evaluating the evaluation indexes for a plurality of the satellite pairs to obtain the relative position vector as a positioning result. a satellite signal receiving unit that receives radio waves transmitted from a plurality of GNSS satellites and detects carrier phases, carrier offset frequencies, code information, and pseudoranges of the plurality of GNSS satellites at device time;
a time error acquisition unit that calculates an error in the device time using the code information and the pseudorange;
an instantaneous phase calculation unit that corrects the carrier phase using the carrier offset frequencies and the device time error obtained from the plurality of satellite signal receiving units to calculate an instantaneous value of the carrier phase at a predetermined time;
and a data transmission section for transmitting the instantaneous value of the carrier wave phase. The phase detection device according to claim 6, characterized in that the instantaneous phase calculation unit limits the instantaneous value of the carrier phase to a range of 0 to 2π radians. The phase detection device according to claim 6 or 7, characterized in that the data transmission unit transmits position information (latitude, longitude, altitude) detected from the code information in addition to the instantaneous value of the carrier phase.