Relative position detection system, relative position detection method, and position information transmission device

Abstract

To provide a relative position detection system which is installed on a cliff or the like, operates for a long period of time by a battery, and can realize positional accuracy of about several centimeters.SOLUTION: A relative position detection system 1 includes: computing means 6; a receiving base station 5 connected to the computing means 6 through a communication line; a plurality of position information transmitters 2A and 2B each of which acquires an instantaneous value of a carrier wave phase of a radio wave transmitted from a plurality of GNSS satellites at predetermined sampling timing synchronized with GNSS time, and wirelessly transmits the acquired instantaneous value of the carrier wave phase to the receiving base station 5, thereby transmits the instantaneous value of the carrier phase to the computing means 6; and satellite information acquiring means 4 which is connected to the computing means 6 through the communication line and acquires satellite orbit information of the GNSS satellite and transmits the satellite orbit information to the computing means 6, where the computing means 6 detects relative positions of the plurality of position information transmitting devices 2A and 2B by using the instantaneous value of the carrier phase and the satellite orbit information.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a relative position detection system, a relative position detection method, and a position information transmission device.

Background Art

[0002] In dangerous areas where disasters such as landslides are likely to occur, a ground monitoring system using GPS (Global Positioning System) or GNSS (Global Navigation Satellite System) has been proposed to monitor slight displacements of the ground and structures. Here, GPS represents a satellite system operated by the United States, and GNSS is a term representing artificial satellite systems launched by countries including the United States, Japan, Europe, China, etc. In the present invention, the description will be unified using the term GNSS, but it is needless to say that the present invention can be applied to GPS.

[0003] The GNSS position detection method can be broadly classified into two types: a method for detecting the code phase and a method for detecting the carrier phase. The method for detecting the code phase is widely and commonly used, such as in car navigation. Since the code signal sent from a GNSS satellite changes at about 1 MHz, the position on the earth can be determined with an error of several meters to several tens of meters. On the other hand, the method for detecting the carrier phase can obtain much higher accuracy (less than several centimeters) by detecting the carrier frequency (1.5 GHz).

[0004] The present invention relates to a relative position detection system and a relative position detection method that enable detection of landslides, earth and sand collapses, etc. by detecting the carrier phase of radio waves sent from GNSS satellites and detecting slight displacements of the ground and structures, and a position information transmission device that transmits the carrier phase of radio waves sent from GNSS satellites.

[0005] Two known GNSS receiving methods for detecting carrier phase are static and kinematic. The static method achieves ultra-high precision (error of a few millimeters) and is used in surveying, but requires continuous observation of the carrier phase. As a result, it consumes a lot of power and cannot be used to detect landslides and mudslides in locations where commercial power is not supplied.

[0006] The kinematic method enables highly accurate relative position detection (error of a few centimeters) by transmitting the integrated value of the carrier wave phase every second. For example, Patent Document 1 describes a method in which radio waves transmitted by a GNSS satellite are received, the integrated value of the carrier wave phase is counted, and transmitted to a center at regular intervals, where the center determines the reception point position (baseline vector) based on the received integrated value of the phase.

[0007] To detect landslides and mudslides using this kinematic method, it is necessary to continuously transmit carrier phase integration values ​​from multiple satellites without interruption. This requires a transmission rate of at least 1 kbps, but a problem has been that the network is often not in place at locations prone to landslides and mudslides, making it impossible to apply in such cases. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 3532267 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Therefore, the present invention aims to provide a relative position detection system, a relative position detection method, and a position information transmission device that can be installed on cliffs or similar terrain, operate for extended periods using batteries, and achieve positional accuracy of several centimeters. [Means for solving the problem]

[0010] [1] The relative position detection system 1 of the present invention includes a calculation means 6, a receiving base station 5 connected to the calculation means 6 by a communication line, a plurality of position information transmitting devices 2A, 2B each which acquire instantaneous values ​​of carrier phase of radio waves transmitted from a plurality of GNSS (Global Navigation Satellite System) satellites at a predetermined sampling timing synchronized with GNSS time, and transmit the acquired instantaneous values ​​of carrier phase to the receiving base station by wireless transmission, thereby transmitting the instantaneous values ​​of carrier phase to the calculation means 6, and a satellite information acquisition means 4 connected to the calculation means by a communication line which acquires satellite orbit information of GNSS satellites and transmits the acquired satellite orbit information to the calculation means 6, wherein the calculation means 6 is a relative position detection system 1 which detects the relative positions of the plurality of position information transmitting devices using the instantaneous values ​​of carrier phase and the satellite orbit information.

[0011] [2] In the relative position detection system 1 of the present invention, it is preferable that the calculation means 6 detects the relative positions of the plurality of position information transmitting devices 2A, 2B using a double phase difference calculation of the carrier phase.

[0012] [3] In the relative position detection system 1 of the present invention, it is preferable that the transmission rate from the plurality of position information transmitting devices 2A, 2B to the receiving base station 5 is lower than the transmission rate from the satellite information acquisition means 4 to the calculation means 6.

[0013] [4] In the relative position detection system 1 of the present invention, it is preferable that the wireless transmission from the plurality of position information transmitting devices 2A, 2B to the receiving base station 5 is performed by LPWA (Low Power Wide Area) wireless communication means that is capable of long-distance communication and has low power consumption.

[0014] [5] In the relative position detection system 1 of the present invention, it is preferable that the interval of the predetermined sampling timing (SEC00) is set to 1 minute or more.

[0015] [6] The relative position detection method of the present invention is a relative position detection method which involves acquiring instantaneous values ​​of carrier phases of radio waves transmitted from multiple GNSS satellites at multiple measurement points at a predetermined sampling timing synchronized with GNSS time, transmitting the acquired instantaneous values ​​of carrier phases to a calculation means by communication means including at least wireless transmission, acquiring satellite orbit information of multiple GNSS satellites, transmitting the acquired satellite orbit information to the calculation means, and in the calculation means detecting the relative position between the multiple measurement points using the instantaneous values ​​of carrier phases and the satellite orbit information.

[0016] [7] In the relative position detection method of the present invention, it is preferable to detect the relative positions of the plurality of position information transmitting devices 2A, 2B using a double phase difference calculation of the carrier phase.

[0017] [8] In the relative position detection method of the present invention, it is preferable that the transmission rate of the wireless transmission is lower than the transmission rate of the satellite information.

[0018] [9] In the relative position detection method of the present invention, it is preferable to use LPWA (Low Power Wide Area) wireless communication means that is capable of long-distance communication and has low power consumption for wireless transmission.

[0019]

[10] In the relative position detection method of the present invention, it is preferable that the interval between the predetermined sampling timings (SEC00) is 1 minute or more.

[0020]

[11] In the relative position detection method of the present invention, the relative positions of the plurality of measurement points are represented by a three-dimensional relative distance vector P calculated using the GNSS antenna of a reference measurement point among the two measurement points as the starting point and the GNNS antenna of the other measurement point among the two measurement points as the ending point. Preferably, the relative distance vector P is calculated by estimating a three-dimensional estimated relative distance vector Re as an estimated value of the relative distance vector, calculating an error evaluation value E which is an index for evaluating position error from the estimated estimated relative distance vector Re, determining the estimated relative distance vector that minimizes the error evaluation value E, and outputting the determined estimated relative distance vector as the relative distance vector P.

[0021]

[12] In the relative position detection method of the present invention, it is preferable to obtain a double phase difference φ(n) from the instantaneous value of the carrier phase, obtain an estimated double phase difference φ“(n) based on the estimated relative distance vector Re, and calculate the error evaluation value E according to the difference between the double phase difference φ(n) and the estimated double phase difference φ“(n).

[0022]

[13] In the relative position detection method of the present invention, the estimated double phase difference φ″(n) calculates the position information of the plurality of GNSS satellites at the predetermined sampling timing using the satellite orbit information of the plurality of GNSS satellites. When one of the plurality of GNSS satellites is used as a reference satellite, the reference satellite position coordinates (X(0), Y(0), Z(0)) of the reference satellite are extracted from the position information of the plurality of GNSS satellites, and the position coordinates (X(n), Y(n), Z(n)) of each satellite other than the reference satellite are extracted from the position information of the GNSS satellites. The position coordinates (Xr, Yr, Zr) of the reference measurement point are obtained, and the wave number vector k(n) is calculated from the reference satellite position coordinates (X(0), Y(0), Z(0)), the position coordinates (X(n), Y(n), Z(n)) of each satellite n, and the position coordinates (Xr, Yr, Zr) of the reference measurement point. The estimated double phase difference φ′(n) is preferably obtained by performing an inner product operation between the wave number vector k(n) and the estimated relative distance vector Re, and applying a remainder operation with 2π as the modulus to the estimated double phase difference φ′(n).

[0023]

[14] The position information transmission device 2 of the present invention includes a satellite signal receiving unit 221 that receives radio waves transmitted from a plurality of GNSS satellites and outputs the carrier phase and satellite orbit information included in the radio waves, an arithmetic unit 23 that detects GNSS time information from the satellite orbit information, a sampling unit 25 that samples the carrier phase output from the satellite signal receiving unit 221 at a predetermined sampling timing to obtain an instantaneous value of the carrier phase, and a wireless communication unit 26 that wirelessly transmits the instantaneous value of the carrier phase obtained by the sampling unit 25. The position information transmission device 2 is synchronized with the GNSS time information at the predetermined sampling timing.

[0024]

[15] In the position information transmission device 2 of the present invention, it is preferable that the predetermined sampling timing is a predetermined time determined by the GNSS time information.

[0025]

[16] In the position information transmitting device 2 of the present invention, it is preferable that the wireless communication unit 26 wirelessly transmits the instantaneous value of the carrier phase by means of LPWA (Low Power Wide Area) wireless communication that enables long-distance communication and low power consumption.

[0026]

[17] In the position information transmitting device 2 of the present invention, it is preferable that the interval of the predetermined sampling timing (SEC00) is 1 minute or more.

Advantages of the Invention

[0027] According to the relative position detection system, relative position detection method, and position information transmitting device of the present invention, the instantaneous value of the carrier phase acquired at sampling timing synchronized with the GNSS time is obtained from the position information transmitting device, and satellite information is obtained from a separately provided GNSS receiver (satellite information acquisition means). Using these instantaneous values of the carrier phase and satellite information, the relative positions of a plurality of position information transmitting devices can be detected. Therefore, in the position information transmitting device, it is only necessary to acquire and transmit the instantaneous value of the carrier phase at an extremely low sampling rate (for example, once per minute). Thus, highly accurate position detection using the carrier phase can be performed with extremely low power consumption, and for example, it becomes possible to operate with a battery. Also, since it is possible to make the amount of information transmitted wirelessly extremely small, by using a low-power and long-distance wireless transmission system such as LPWA, it can be installed in the mountains where a conventional mobile phone goes out of service area, and it becomes possible to detect landslides in the mountains. As a result, according to the present invention, it is possible to provide a relative position detection system, relative position detection method, and position information transmitting device that can be installed on cliffs or the like, operate with a battery for a long time, and still achieve a position accuracy of about several centimeters.

Brief Description of the Drawings

[0028] [Figure 1] It is a configuration diagram of a GNSS position information transmitting device 40 according to the conventional method 1. [Figure 2] It is a configuration diagram of a GNSS position information transmitting device 41 according to the conventional method 2. [Figure 3] This is a schematic diagram illustrating the difference between the instantaneous value and the integrated phase of the carrier wave. [Figure 4] This is an experimental configuration diagram of the integrated phase detection method. [Figure 5] These are the experimental results of the integrated phase detection method. [Figure 6] This is a configuration diagram of the location information transmission device 2 according to Embodiment 1. [Figure 7] This figure shows the payload configuration of the LPWA wireless signal transmitted by the location information transmission device 2 according to Embodiment 1. [Figure 8] This is a configuration diagram of the relative position detection system 1 according to Embodiment 1. [Figure 9] This figure shows a relative position detection method using the relative position detection system 1 according to Embodiment 1. [Figure 10] This figure illustrates the relative position detection method according to Embodiment 2 using the relative position detection system 1 according to Embodiment 1. [Figure 11] This is an explanatory diagram illustrating the calculation method of the calculation server 6 in the relative position detection system according to Embodiment 2. [Figure 12] This figure shows an example of two GNSS antennas, A1 and B1, being installed at a predetermined distance on the roof of a two-story building for the purpose of conducting an experiment. [Figure 13] This figure shows the measurement results of the relative distance R obtained through the experiment. [Figure 14] This figure shows the measurement results of the horizontal azimuth angle α with respect to the north-south line L1 and the vertical angle β with respect to the horizontal plane L2, obtained through experiments. [Modes for carrying out the invention]

[0029] The present invention will be explained below in comparison with conventional methods using embodiments shown in the figures. First, the conventional method will be described.

[0030] [Conventional Method 1] Figure 1 is a diagram of the configuration of a GNSS position information transmission device 40 according to Conventional Method 1. The GNSS position information transmission device 40 is a GNSS position information transmission device that detects code signals (code phase information), and is a typical GNSS position information transmission device installed in car navigation systems, etc. Since it is publicly known technology, it will be explained in a simplified manner. The antenna 20 receives radio waves from each GNSS satellite, and the satellite signal receiving unit 221 receives the code phase information and satellite orbit information (ephemeris) of each satellite, which are provided to the calculation unit 23. The front end 21 filters out the weak received signals, amplifies them, converts them into low-frequency signals (IQ signals), and supplies them to multiple satellite receiving units 221. The satellite receiving unit 221 consists of a synchronization unit, a random number generation unit, a despreader unit, a decoding unit, etc. (not shown), and outputs the code phase information and satellite orbit information of each satellite.

[0031] The calculation unit 23 determines the satellite position (X(n), Y(n), Z(n)) of each satellite from the satellite orbit information and the distance (pseudo-distance) between each satellite and the receiving point from the code phase information. The calculation unit 23 solves a system of equations formed from the positions of four or more satellites and the pseudo-distance to output the position of the receiving point (Xr, Yr, Zr) and the accurate GNSS time. It outputs a "1PPS" signal, for example, once per second, as a pulse that precisely matches the GNSS time.

[0032] Incidentally, since the modulation frequency of the code signal is approximately 1 MHz, the position (Xr, Yr, Zr) detected by the device shown in Figure 1 contains a measurement error of several meters to tens of meters. This is insufficient accuracy for the purpose of detecting slight displacements of the ground or structures, which is the target of this invention, and therefore it cannot be used for that purpose.

[0033] [Conventional Method 2] Figure 2 is a diagram of the configuration of the GNSS position information transmission device 41 according to the conventional method 2. The GNSS position information transmission device 41 is a position information transmission device that detects the carrier wave phase. Since the carrier wave frequency (1.5 GHz) is significantly higher than the modulation frequency (approximately 1 MHz), high accuracy with an error of several centimeters can be achieved. In Figure 2, the satellite signal receiving unit 221 outputs the carrier wave phase (φ1, φ2, ..., φM) of each satellite in addition to the code phase information and satellite orbit information. The carrier wave phase is a signal that changes in the range from -π to π, and a "phase jump" occurs each time a phase boundary is crossed. Therefore, the phase integration unit 222 integrates the carrier wave phases and outputs the integrated phase (φs(1), φs(2), ..., φs(M)). By using an integrated phase, the effect of "phase jump" can be reduced.

[0034] Figure 3 is a schematic diagram illustrating the difference between the instantaneous value and the integrated phase of the carrier wave phase. In the example shown in Figure 3, assuming that the measurement of the carrier wave phase begins at time t=0, the instantaneous value φ(n) and integrated phase φs(n) of the nth satellite's carrier wave phase at time t=T are schematically shown. In Figure 3, the instantaneous value φ(n) of the carrier wave phase folds between +π and -π, so at time t=T, φ(n)=0, and it is not possible to determine how much the phase has rotated since the start of observation. In contrast, the integrated phase φs(n) at time t=T is 7π, indicating that the phase has rotated 3 times since the start of observation, and there has also been a phase shift of π.

[0035] The integrated phases (φs(1), φs(2), ..., φs(M)) are held by a latch 25 every second. Since each integrated phase is an integrated value over one second, it contains more than 30 bits of information. These integrated phases are transmitted from the antenna 27 by the wireless communication unit 26. As this is a known technique, details are omitted, but in high-precision relative position detection using carrier phase, the integrated phases (φs(1), φs(2), ..., φs(M)) are received by a receiving device (not shown), the phase difference is calculated between different receiving devices, and then the phase difference between different satellites is calculated. This operation, which calculates the phase difference twice, is called double-difference phase calculation, and it removes the effects of the ionosphere and frequency shifts of the receiving devices. Finally, the phase uncertainty that is an integer multiple of 2π is removed and high-precision position information is output. The phase uncertainty that is an integer multiple of 2π is generally called the "integer bias N". Conventional method 2 presents the challenge of accurately determining the value of this integer bias N for each received satellite.

[0036] Figure 4 is an experimental configuration diagram of the integrated phase detection method. Figure 5 shows the experimental results of the integrated phase detection method. In Figure 4, the GNSS position information transmitter 41B was initially installed at location A. Here, location A is 1 m away from the location (reference position) where the GNSS position information transmitter 41A was placed. In this experiment, the installation location of 41B was shifted by 10 cm every 20 seconds, moving from A→B→C→D→E→F→G.

[0037] Figure 5 shows the results of calculating the integrated phase output from the GNSS position information transmitter 41B, using the GNSS position information transmitter 41A as the reference position and the GNSS satellite 3B as the reference satellite, and then performing a double-difference phase calculation. As can be seen from Figure 5, it can be seen that a movement of 10 cm at 20-second intervals is detected with high accuracy. Furthermore, it can be seen that by using integrated phase in this way, even if the phase difference exceeds the range of ±π, it can be detected as a continuous waveform.

[0038] To achieve high-precision position detection using carrier phase, however, the wireless transmitter 26 must transmit integrated phases (φs(1), φs(2), ..., φs(M)) every second. Assuming each integrated phase is 30 bits and the number of satellites M is 6, the wireless communication unit 26 requires a transmission rate of 180 bps. In reality, there is redundancy such as headers and error correction, requiring several times that transmission rate (for example, 1 kbps). This transmission rate could be easily achieved if a mobile phone network were used, but wireless devices using mobile phone networks have the problem of high power consumption, and furthermore, there are many places such as mountainous areas where mobile phone networks cannot be used.

[0039] Incidentally, LPWA (Low Power Wide Area) wireless communication has the advantage of being usable even in mountainous areas due to its long communication range, and also has the advantage of low power consumption. However, the amount of data that can be transmitted with LPWA is small, for example, about 128 bits per minute. Converted to a transmission rate, this is 2 bps, which is two orders of magnitude lower than the 180 bps required for the transmission of integrated phase. A GNSS position information transmission device that can detect carrier phase and bridge this two-order-of-magnitude difference is desired.

[0040] Next, embodiments of the present invention will be described. [Embodiment 1] Figure 6 is a configuration diagram of the position information transmission device 2 according to Embodiment 1. The position information transmission device 2, which is installed at multiple measurement points, receives radio waves from GNSS satellites using the receiving antenna 20 as shown in Figure 6, and the satellite signal processing unit 22 performs GNSS reception processing. The front end 21 extracts the weak received signal with a filter, amplifies it, converts it into a low-frequency signal, and supplies it to multiple satellite signal receiving units 221. The satellite signal receiving units 221 output code phase information, satellite orbit information, and carrier phase (φ1, φ2, , φM). The calculation unit 23 calculates the position (Xr, Yr, Zr) where the receiving antenna 20 is placed and the accurate GNSS time. In the implementation of the present invention, it is assumed that the carrier frequency transmitted from the GNSS satellite is approximately 1.5 GHz.

[0041] The latch (sampling means) 25 samples (acquires) the carrier phase (φ1, φ2, ..., φM) at the timing of 00 seconds every minute of GNSS time (sampling timing SEC00). The sampling timing SEC00 can be created, for example, by dividing a pulse (1 PPS pulse) once per second by 60 in synchronization with the GNSS time. Here, the value sampled by the latch 25 is the instantaneous value of the carrier phase, not the integrated value.

[0042] In other words, the latch 25 obtains the instantaneous value of the carrier phase by sampling the carrier phase (φ1, φ2, ..., φM) output from the satellite signal receiving unit 221 at a predetermined sampling timing (sampling timing SEC00). The "instantaneous value of the carrier phase" obtained by sampling the carrier phase (φ1, φ2, ..., φM) is to be distinguished from the carrier phase (φ1, φ2, ..., φM) by adding parentheses around the subscripts φ1, φ(2), ..., φ(M), such as "φ(1), φ(2), ..., φ(M)".

[0043] The instantaneous values ​​of the carrier phase (φ(1), φ(2), ..., φ(M)) sampled by latch 25 are then wirelessly transmitted by wireless communication unit 26. Since the timing of latching the instantaneous values ​​of the carrier phase is precisely determined by GNSS time, the calculation server (calculation means) 6, described later, can achieve high-precision relative position detection.

[0044] Figure 7 shows the payload configuration of the LPWA radio signal transmitted by the position information transmission device 2 according to Embodiment 1. The first two bytes are the header, which sets information such as the ID number of the position information transmission device 2 and the battery voltage. The remaining 14 bytes set two bytes of information obtained from up to seven satellites (satellite number (6 bits), CNR (2 bits), carrier phase (8 bits)). This CNR is an index representing the carrier strength and corresponds to the Carrier to Noise Ratio in English. Here, in order to compress the amount of information during transmission, the CNR is simplified and only two bits are transmitted. That is, "11" is transmitted when the CNR is good, and "10" or "01" is transmitted when it is moderate. If no satellite is received, the CNR is set to "00".

[0045] Figure 8 is a diagram showing the configuration of the relative position detection system 1 according to Embodiment 1. As shown in Figure 8, the relative position detection system 1 is configured using two of the above-mentioned position information transmitting devices 2. When the two position information transmitting devices 2 are described separately, they may be referred to as position information transmitting device 2A and position information transmitting device 2B. These position information transmitting devices 2A and 2B are installed at two measurement points. Specifically, position information transmitting device 2A is installed in a location with bedrock or similar material where there is no risk of landslides. On the other hand, position information transmitting device 2B is installed in a location where positional displacement may occur due to precursory phenomena of landslides. By accurately measuring the relative distance from position information transmitting device 2A to position information transmitting device 2B, precursory phenomena such as landslides can be detected.

[0046] As described above, the position information transmitting devices 2A and 2B receive radio waves from the GNSS satellite 3, set the instantaneous carrier phase value of each satellite as a payload, and transmit it as LPWA radio to the receiving base station 5 installed at the foot of the mountain. The receiving base station 5 transmits the payload sent from the position information transmitting device 2 to the computing server (computation means) 6 located in the cloud. The satellite orbit information acquisition means (GNSS receiver) 4 is composed of a commercially available GNSS receiver or the like, and receives satellite orbit information (ephemeris) from the radio waves of the GNSS satellite and transmits it to the computing server 6. With the satellite orbit information provided by the GNSS receiver 4, the computing server 6 can accurately determine the positions of all satellites.

[0047] The calculation server 6 calculates the relative distance R using a calculation described later. It is known that when a landslide occurs, the relative distance changes slowly, and eventually the landslide occurs when it exceeds a certain value. Therefore, the calculation server 6 determines that the risk of a landslide is increasing when the relative distance exceeds a predetermined value. When the risk is high, the calculation server 6 prompts residents to evacuate by displaying a warning on the smartphone 7.

[0048] Figure 9 is a diagram illustrating a relative position detection method using the relative position detection system 1 according to Embodiment 1. The method for calculating relative distance will be explained using Figure 9. In this calculation, one of the received GNSS satellites is designated as the reference satellite and its satellite number is set to "0". The difference calculation shown in [Equation 1] and [Equation 2] below is performed on the instantaneous values ​​of the carrier phase obtained from the reference satellite and the satellite number n. Note that "instantaneous value of carrier phase" may also be written as "instantaneous phase". [Formula 1] φAr(n)=φA(n) - φA(0) [Formula 2] φBr(n)=φB(n) - φB(0) In [Equation 1] and [Equation 2], φA(n) is the instantaneous phase obtained by the latch 25 of the position information transmitting device 2A after receiving radio waves from satellite number n, and φB(n) is the instantaneous phase obtained by the latch 25 of the position information transmitting device 2B after receiving radio waves in the same manner.

[0049] Next, using the position information transmitter 2A as the reference position, the double phase difference φd(n) of the carrier wave phase is determined by the following [Equation 3]. [Formula 3] φd(n)=φBr(n) - φAr(n) The relationship between the double phase difference φd(n) obtained in [Equation 3] above and the relative distance is shown in [Equation 4] below. Since the range of change of the relative distance is known, [Equation 4] can be solved by applying the least squares method to multiple satellites n. [Formula 4] 2πN(n)+φd(n)=R×(2π / λ)×{cosθ(n)-cosθ(0))} In [Equation 4], N(n) is an integer and represents the phase uncertainty with respect to satellite number n. λ is the wavelength of the carrier wave, θ(0) is the angle between the direction vector R and the direction vector from position information transmitter 2A to reference satellite (0), and θ(n) is the angle between the direction vector R and the direction vector from position information transmitter 2B to satellite n.

[0050] Here, the direction vector R is the vector from the coordinates (Xr, Yr, Zr) of the position information transmitter 2A to a virtual point (Xt, Yt, Zt) set in the assumed direction of movement of the position information transmitter 2B. Also, the direction vector to satellite n is the vector from the coordinates (Xr, Yr, Zr) of the position information transmitter 2A to the position of satellite n (X(n), Y(n), Z(n)). The position of each GNSS satellite can be determined by applying Kepler's equations to the satellite orbit information (ephemeris).

[0051] In the above explanation, to avoid complexity, we assumed that the direction of movement due to the landslide was known in advance and explained only the length R of the movement direction vector R. However, as shown in Embodiment 2 described later, by considering a three-dimensional movement direction vector P and applying the same process to correspond to the three-dimensional movement direction, it is possible to further broaden the scope of application. Also, in the above [Equation 4], the integer N(n) representing the phase uncertainty differs for each satellite, and since the integer N(n) must be determined for each satellite, the amount of computation increases. Errors may occur if the estimation of the integer N(n) is incorrect.

[0052] [Embodiment 2] Figure 10 is a diagram illustrating a relative position detection method according to Embodiment 2 using the relative position detection system 1 according to Embodiment 1. In Embodiment 2, a three-dimensional relative distance vector P is obtained by a calculation described later. As shown in Figure 10, the relative distance vector P is a three-dimensional vector that starts from the GNSS antenna of the position information transmitting device 2A and ends at the GNNS antenna of the position information transmitting device 2B, and represents the relative positions of the two position information transmitting devices 2A and 2B.

[0053] Figure 10 shows that the relative distance vector P can be decomposed into three components. The relative distance vector P can be expressed in polar coordinates (R, α, β), which consists of the relative distance R between A and B, the angle α on the horizontal plane with respect to the north-south line L1 connecting south and north (let's call this the horizontal azimuth angle with respect to the north-south line L1), and the vertical angle β with respect to the horizontal plane L2. Although the relative distance vector P can also be expressed using a Cartesian coordinate system instead of polar coordinates, we will use polar coordinates (R, α, β) consistently in the following explanation.

[0054] When a landslide occurs, not only does the relative distance R slowly increase, but the vertical angle β also changes. Depending on the cliff structure, it may also move horizontally (the horizontal azimuth angle α also changes). Therefore, the calculation server 6 calculates the relative distance vector P at predetermined intervals, and determines that the risk of a landslide has increased when the changes in the relative distance R, horizontal azimuth angle α, and vertical angle β exceed predetermined values. Similar to Embodiment 1 described above, the calculation server 6 can prompt residents to evacuate by displaying a warning on the smartphone 7.

[0055] The calculation server 6 performs the following calculations (steps S1 to S12) to obtain the relative distance vector P. Figure 11 is an explanatory diagram illustrating the calculation method of the calculation server 6 in the relative position detection system according to Embodiment 2. When explaining steps S1 and beyond, refer to Figure 11 as needed. Note that the relative position detection system according to Embodiment 2 has the same system configuration as the relative position detection system 1 according to Embodiment 1.

[0056] [Step S1] First, in step S1, the instantaneous value of the carrier phase of each satellite (n) transmitted by LPWA, i.e., the instantaneous phase φ(n), is subjected to a two-stage difference calculation as described in [Equation 3] to obtain the double phase difference φd(n).

[0057] [Step S2] In step S2, using the satellite orbit information (ephemeris) provided by the GNSS receiver 4, the reference satellite position coordinates (X(0),Y(0),Z(0)) of the reference satellite (0) and the position coordinates (X(n),Y(n),Z(n)) of each satellite (n) other than the reference satellite (0) are determined. In the following, "reference satellite position coordinates (X(0),Y(0),Z(0))" may be written as "reference satellite position coordinates (X(0),Y(0),Z(0))", and "position coordinates (X(n),Y(n),Z(n))" may be written as "each satellite position coordinates (X(n),Y(n),Z(n))".

[0058] [Step S3] In step S3, the location where the reference position information transmitting device 2A is installed (reference measurement point) is determined as the receiving point position coordinates (Xr, Yr, Zr).

[0059] [Step S4] In step S4, the direction vector e(n) is calculated from the receiving point coordinates (Xr, Yr, Zr) to each satellite position coordinate (X(n), Y(n), Z(n)). Similarly, the direction vector from the receiving point coordinates (Xr, Yr, Zr) to the reference satellite position coordinates (X(0), Y(0), Z(0)) is calculated as e(0). Here, the direction vector is a vector that points only to the direction component, and its magnitude is normalized to "1".

[0060] [Step S5] In step S5, the computing server 6 obtains the wave vector k(n) = e(n) - e(0) by subtracting the direction vector e(0) toward the reference satellite (0) from the direction vector e(n). Here, the equiphase surfaces of the double phase difference φd(n) are formed in a direction perpendicular to the wave vector k(n). Also, the spacing of the double phase difference φd(n) is inversely proportional to the magnitude of the wave vector k(n).

[0061] [Step S6] In step S6, the computing server 6 determines a three-dimensional estimated relative distance vector Re as an estimated value of the relative distance vector P, as shown in [Equation 5] below. [Formula 5] Re=(R'+ΔR,α'+Δα, β'+Δβ) In [Equation 5] above, (R', α', β') is the initial vector used as the starting point for the calculation. Since the displacement due to the landslide is a slow movement, the relative distance vector P is expected to be not significantly different from the initial vector (R', α', β'). Therefore, the initial vector (R', α', β') can be determined by pre-measuring the position of the receiving point B. Alternatively, the relative distance vector P measured a few minutes earlier can be used as the initial vector (R', α', β').

[0062] The value we want to find in the following calculations is the combination of (ΔR, Δα, Δβ) that minimizes the distance between the estimated relative distance vector Re and the relative distance vector P. Since the positional change due to a landslide starts slowly, it is expected that this (ΔR, Δα, Δβ) will be a small value when precursory phenomena of a landslide occur.

[0063] [Step S7] In step S7, the calculation server 6 scans the values ​​of (ΔR, Δα, Δβ). For example, for ΔR, it scans from ΔR = -0.5m to ΔR = +0.5m in 1mm increments (1000 combinations), for Δα, it scans from Δα = -30 degrees to +30 degrees in 0.5 degree increments (120 combinations), and for Δβ, it scans from Δβ = -15 degrees to +15 degrees in 0.5 degree increments (60 combinations). The total number of scan combinations is 1000 × 120 × 60 = 7,200,000.

[0064] By applying various methods for finding the optimal value, the total number of combinations scanned can be reduced, thereby shortening the computation time. In Embodiment 2, the simplification of the calculation is not described, and the following explanation assumes that all combinations are scanned.

[0065] [Step S8] In step S8, the computing server 6 calculates the estimated double phase difference φ'd(n) shown in [Equation 6] below by calculating the inner product of the estimated relative distance vector Re and the wave vector k(n) that have been estimated by the scan. [Formula 6] φ'd(n)=(2π / λ)×{Re·k(n)} In [Equation 6], the "·" in Re·k(n) within {} represents the dot product of the two vectors Re and k(n).

[0066] The calculations performed by the computation server 6 described above are schematically illustrated in Figure 11 as vectors. Specifically, at receiving point A, the direction vectors e(0) and e(n) of the reference satellite (0) and satellite (n) are calculated, and the wave vector k(n) is obtained by subtracting the two direction vectors. An equiphase surface with a double phase difference φd(n) is formed in a direction orthogonal to the wave vector k(n). The relative distance vector P is a three-dimensional vector extending from receiving point A to receiving point B, which is located at an unknown location. Near receiving point B, the estimated relative distance vector Re extends to the estimated receiving point B'.

[0067] If we consider the case where receiving point B is at the position of estimated receiving point B', the estimated double phase difference observed at that time is φ'd(n) determined by [Equation 6] above.

[0068] Therefore, by searching for the estimated receiving point B' that minimizes the difference between the double phase difference φd(n) observed from the instantaneous phase transmitted via LPWA and the estimated double phase difference φ'd(n), we can determine that this point is closest to the coordinates of the desired receiving point B.

[0069] However, as mentioned earlier, the instantaneous phase transmitted by LPWA is folded into the range from +π to -π, so the value of the double phase difference φd(n) is similarly folded. In contrast, the estimated double phase difference φ'd(n) is obtained by performing the operation [Equation 6] on the estimated relative distance vector Re, so it is not folded and may be a value that far exceeds π, for example. Therefore, step S9 below is performed.

[0070] [Step S9] In step S9, the calculation server 6 performs the calculation shown in [Equation 7] below and applies a modulo operation modulo 2π to the estimated double phase difference φ'd(n) to fold it into the range from +π to -π. [Formula 7] φ“d(n)=mod{φ'd(n),2π}

[0071] When the distance between the estimated receiving point B' and receiving point B is shortest, the double phase difference φ“d(n) obtained by [Equation]7 is close to the value of the double phase difference φd(n).

[0072] Here, when comparing the double phase difference φ“d(n) shown in [Equation 7] above with the double phase difference φd(n) shown in [Equation 3], it is necessary to consider a phase jump of 2π. For example, if we simply subtract φ“d(n) = 0.9π and φd(n) = -0.9π, we get φ“d(n) - φd(n) = 1.8π. However, in this example, the correct phase difference is 0.2π. Thus, simple subtraction is not possible, so some ingenuity is required to find the phase difference. Therefore, we perform the following step S10.

[0073] [Step S10] As step S10, for example, the difference in phase between φ“d(n) and φd(n) is evaluated by performing the following calculation [Equation 8]. [Formula 8] F(n) = {cosφ“d(n) - cosφd(n)} 2 +{sinφ“d(n)-sinφd(n)} 2

[0074] [Step S11] Finally, in step S11, the calculation shown in [Equation 9] below is performed to sum up all evaluation results from satellite number 1 to satellite number M, and an error evaluation value E, which serves as an index for positional error evaluation, is obtained.

number

[0075] As explained above, the optimal estimated value of the relative distance vector P can be obtained using the instantaneous values ​​of the carrier phase (φ(1), φ(2), ..., φ(M)). Since the instantaneous values ​​of the carrier phase contain little information, it is possible to detect precursory phenomena of landslides using low-rate, low-power wireless communication technologies such as LPWA.

[0076] Next, I will explain the experiments conducted by the inventor. Figure 12 shows an example of two GNSS antennas A1 and B1 being installed at a predetermined distance on the roof of a two-story building for the experiment. As shown in Figure 12, two GNSS antennas A1 and B1 were installed on the roof of a two-story building at a distance of 1.6 m, and these antennas A1 and B1 (see Figure 12) were connected to two self-made GNSS receivers (not shown).

[0077] Then, signals from six GNSS satellites were received every five minutes, and at five-minute intervals according to GNSS time, the carrier phase from the six GNSS satellites was sampled to obtain the instantaneous value of the carrier phase (instantaneous phase) and transmitted to a personal computer (PC). On the PC, the double phase difference and difference direction vector were calculated for the instantaneous phase of each GNSS satellite, and the relative position (R, α, β) that best matched the calculated double phase difference was searched for and determined. Here, R is the relative distance between antenna A1 and antenna B1, α is the horizontal azimuth angle with respect to the north-south line L1 (see Figure 12(b)), and β is the vertical angle β with respect to the horizontal plane L2 (see Figure 12(a)). Here, R = 1.6 m (measured value using a tape measure), α = 19 degrees (angle determined from the map), and β = 0 degrees (see Figure 12). Note that the illustration of the double phase difference obtained for each GNSS satellite is omitted.

[0078] Figure 13 shows the measurement results of the relative distance R obtained from the experiment. Here, the results are shown from nine measurements taken every 5 minutes from 18:00 (18:00) to 18:40 (18:40) on October 1, 2021. In conducting these measurements, it was assumed that the relative distance R was in the range of 1m to 2m, the horizontal azimuth angle α was in the range of ±30 degrees, and the vertical angle β was in the range of ±15 degrees, and the search was conducted within these ranges.

[0079] According to the measurement results of the relative distance R shown in Figure 13, the average value from 18:00 to 18:40, measured every 5 minutes, was 1.591m, and the maximum error from this average value was 1.02cm at 18:05. As a result, a result was obtained that agreed with the measured value of 1.6m with high accuracy.

[0080] Figure 14 shows the experimental results of the horizontal azimuth angle α with respect to the north-south line L1 and the vertical angle β with respect to the horizontal plane L2. As shown in Figure 13, the average value of the horizontal azimuth angle α with respect to the north-south line L1 from 18:00 to 18:40, measured every 5 minutes, was 20 degrees. This result shows a high degree of agreement with the measured value of 19 degrees for the horizontal azimuth angle α with respect to the north-south line L1. On the other hand, the average value of the vertical angle β with respect to the horizontal plane L, measured every 5 minutes from 18:00 to 18:40, was 2.5 degrees, although there was some error. This result shows a relatively high degree of agreement with the measured value of 0 degrees for the vertical angle β with respect to the horizontal plane L2.

[0081] The experimental results above confirm that relative position detection using instantaneous values ​​of carrier phase is feasible. By performing relative position detection using instantaneous values ​​of carrier phase in this way, it becomes possible to transmit instantaneous values ​​of carrier phase using wireless transmission systems such as LPWA. Therefore, it becomes possible to perform high-precision position detection using carrier phase with extremely low power consumption, and for example, it becomes possible to operate on batteries. Consequently, it becomes possible to install a position information transmission device in mountainous areas where conventional mobile phones have no signal, to detect landslides in the mountains, and moreover, it can operate for a long period of time on batteries and achieve a position accuracy of a few centimeters.

[0082] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, the following modifications are also possible.

[0083] (1) In the embodiments described above, it was assumed that the carrier frequency transmitted from the GNSS satellite is approximately 1.5 GHz. However, since there are GNSS satellites that use carrier frequencies other than 1.5 GHz, such as 1.2 GHz, applying the present invention using two types of carrier frequencies, 1.5 GHz and 1.2 GHz, will enable even higher precision measurements.

[0084] (2) In the embodiments described above, the example given was that a GNSS receiver 4 is installed as the satellite information acquisition means 4 for acquiring satellite orbit information (ephemeris). However, satellite orbit information (ephemeris) can also be acquired, for example, from a web server on the internet. Therefore, to acquire satellite orbit information (ephemeris), not only a GNSS receiver 4 but also satellite information acquisition means including a web server connected to the internet can be used. For this reason, "satellite information acquisition means 4" includes a GNSS receiver and a web server connected to the internet. [Explanation of Symbols]

[0085] 1...Relative position detection system, 2(2A,2B)...Position information transmission device (measurement point), 3(3A,3B,3C)...GNSS satellite, 4...GNSS receiver (means for acquiring satellite information), 5...Receiving base station, 6...Computation server (means for calculation), 7...Smartphone, 20...Receiving antenna, 21...Front end, 22...Satellite signal processing unit, 23...Calculation unit, 25...Latch (sampling means), 26...Wireless transmission unit, 27...LPWA transmitting antenna, 221...Satellite signal receiving unit, φ1,φ2,...,φM...Carrier phase, φ(1),φ(2),...,φ(M)...Instantaneous value of carrier phase (instantaneous phase)

Claims

1. Calculation means and A receiving base station connected to the calculation means via a communication line, Multiple position information transmitting devices each acquire instantaneous values ​​of carrier phases of radio waves transmitted from multiple GNSS (Global Navigation Satellite System) satellites at a predetermined sampling timing synchronized with GNSS time, and transmit the acquired instantaneous values ​​of carrier phases to the receiving base station wirelessly, thereby transmitting the instantaneous values ​​of carrier phases to the calculation means. The system includes a satellite information acquisition means connected to the calculation means via a communication line, which acquires satellite orbit information of a GNSS satellite and transmits the acquired satellite orbit information to the calculation means, The calculation means is a relative position detection system characterized by detecting the relative positions of the plurality of position information transmitting devices using the instantaneous value of the carrier phase and the satellite orbit information, The relative positions of multiple measurement points are, It is represented by a three-dimensional relative distance vector P calculated using the GNSS antenna of the reference measurement point among the two measurement points in the aforementioned plurality of measurement points as the starting point and the GNSS antenna of the other measurement point among the two measurement points as the ending point. The aforementioned calculation means is As an estimated value of the relative distance vector, a three-dimensional estimated relative distance vector Re is estimated, The wave vector k(n) is calculated using the reference satellite position information (X(0), Y(0), Z(0)) of a reference satellite among multiple GNSS satellites, the position information (X(n), Y(n), Z(n)) of each satellite among the multiple GNSS satellites other than the reference satellite, and the position coordinates (Xr, Yr, Zr) of the reference measurement point. Based on the dot product calculation between the wave vector k(n) and the estimated relative distance vector Re, the estimated double phase difference φ''(n) is obtained. The double phase difference φ(n) is obtained from the instantaneous value of the carrier phase. An error evaluation value E is calculated based on the difference between the aforementioned double phase difference φ(n) and the estimated double phase difference φ''(n). The estimated relative distance vector that minimizes the error evaluation value E is determined, and the determined estimated relative distance vector is output as the relative distance vector P. Relative position detection system.

2. The relative position detection system according to claim 1, characterized in that the transmission rate from the plurality of position information transmitting devices to the receiving base station is slower than the transmission rate from the satellite information acquisition means to the calculation means.

3. The relative position detection system according to claim 1 or 2, characterized in that the wireless transmission from the plurality of position information transmitting devices to the receiving base station is performed by LPWA (Low Power Wide Area) wireless communication means that is capable of long-distance communication and has low power consumption.

4. The relative position detection system according to any one of claims 1 to 3, characterized in that the interval of the predetermined sampling timing is set to one minute or more.

5. At multiple measurement points, instantaneous values ​​of the carrier phase of radio waves transmitted from multiple GNSS satellites are acquired at a predetermined sampling timing synchronized with GNSS time, and the acquired instantaneous values ​​of the carrier phase are transmitted to a calculation means by communication means including at least wireless transmission. The system acquires satellite orbit information of multiple GNSS satellites and transmits the acquired satellite orbit information to the calculation means. The calculation means is characterized by detecting the relative positions between the plurality of measurement points using the instantaneous value of the carrier phase and the satellite orbit information, The relative positions of the aforementioned multiple measurement points are, It is represented by a three-dimensional relative distance vector P calculated using the GNSS antenna of the reference measurement point among the two measurement points in the aforementioned plurality of measurement points as the starting point and the GNSS antenna of the other measurement point among the two measurement points as the ending point. The aforementioned calculation means is As an estimated value of the relative distance vector, a three-dimensional estimated relative distance vector Re is estimated, The wave vector k(n) is calculated using the reference satellite position information (X(0), Y(0), Z(0)) of the reference satellite among the multiple GNSS satellites, the position information (X(n), Y(n), Z(n)) of each satellite among the multiple GNSS satellites other than the reference satellite, and the position coordinates (Xr, Yr, Zr) of the reference measurement point. Based on the dot product calculation between the wave vector k(n) and the estimated relative distance vector Re, the estimated double phase difference φ''(n) is obtained. The double phase difference φ(n) is obtained from the instantaneous value of the carrier phase. An error evaluation value E is calculated based on the difference between the aforementioned double phase difference φ(n) and the estimated double phase difference φ''(n). The estimated relative distance vector Re that minimizes the error evaluation value E is determined, and the determined estimated relative distance vector is output as the relative distance vector P. A method for detecting relative position.

6. The relative position detection method according to claim 5, characterized in that the transmission rate of the wireless transmission is slower than the transmission rate of the satellite information.

7. The relative position detection method according to claim 5 or 6, characterized in that the wireless transmission uses LPWA (Low Power Wide Area) wireless communication means capable of long-distance communication and low power consumption.

8. The relative position detection method according to any one of 5 to 7, characterized in that the interval of the predetermined sampling timing is one minute or more.

9. The estimated double phase difference φ''(n) is, Using the satellite orbit information of the plurality of GNSS satellites, the position information of the plurality of GNSS satellites at the predetermined sampling timing is calculated. When one of the aforementioned multiple GNSS satellites is designated as the reference satellite, the reference satellite position coordinates (X(0), Y(0), Z(0)) are extracted from the position information of the multiple GNSS satellites, and the position coordinates (X(n), Y(n), Z(n)) of each satellite other than the reference satellite are extracted from the position information of the GNSS satellites. Determine the position coordinates (Xr, Yr, Zr) of the aforementioned reference measurement point. The wave vector k(n) is calculated using the reference satellite position coordinates (X(0), Y(0), Z(0)), the position coordinates of each satellite n (X(n), Y(n), Z(n)), and the position coordinates of the reference measurement point (Xr, Yr, Zr). The relative position detection method according to claim 5, characterized in that an estimated double phase difference φ'(n) is obtained by performing an inner product operation between the wave vector k(n) and the estimated relative distance vector Re, and the relative position is determined by applying a modulo operation modulo 2π to the estimated double phase difference φ'(n).

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