JP2001099910A - RTK / GPS-IMU combined positioning method - Google Patents

Abstract

(57) [Summary] (With correction) [Problem] An RTK / RTK that determines a minimum search space without omission of an integer-valued bias solution even when GPS satellite reception is interrupted
A GPS-IMU combined positioning method is provided. A mobile station having a GPS receiving section, a GPS correction data receiving section, an RTK side position calculating section, and an IMU,
In the RTK / GPS-IMU combined positioning method using a reference station and an RTK-IMU combined positioning device comprising a plurality of GPS satellites, when determining the integer bias when the interruption of the transmission wave of the GPS satellite or the reference station is recovered, , A search space is set with the output position of the IMU as the center position, and the error variance of the position is set as a radius around the center position, and the integer value bias is selected from among the integer value bias candidates having a solution in the search space. RTK / GP to decide
S-IMU combined positioning method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an RTK / GPS.
The present invention relates to an IMU combined positioning method, and particularly to an RTK / GPS-IMU combined positioning method in which re-initialization is easy.

[0002]

2. Description of the Related Art RTK / GPS-IMU with reference to FIG.
A conventional example of the combined positioning device will be described very simply. The reference station 10 transmits GPS satellite data obtained from each GPS satellite via the transmitting antenna 101 as GPS correction data.

The GPS receiver 142 of the mobile station 14
The GPS satellite data transmitted from the PS satellite is received via the antenna unit 15 and acquired. The GPS correction data receiving unit 143 receives and obtains the GPS correction data transmitted from the reference station 10 via the reception antenna 16. RT
The K positioning calculation unit 141 sets a combination candidate of an integer bias in the search space based on a certain search space stored in the ROM, and determines an integer bias from these. Then, the current position is estimated based on the integer bias. The RTK positioning calculation unit 141 also performs a positioning calculation based on the GPS satellite data obtained by the GPS receiving unit 142 and the GPS correction data obtained by the GPS correction data receiving unit 143. RTK
The positioning calculation unit 141 outputs the estimated current position and other data. The operation of the RTK / GPS-IMU combined positioning device will be described in detail below in order.

The reference station 10 receives each radio wave transmitted from the GPS satellites 12 and 13 and measures the phase difference Δφ _{S23 of the} carrier. Then, in the mobile station 14, the same set of GPS satellites out of the normally required four GPS satellites, for example, the GPS satellite 12 and the GPS
Each radio wave transmitted from the satellite 13 is received, and the phase difference Δφ _{M23 of the} carrier is measured. The phase difference between these two phase differences (Δφ _S23 −Δφ _M23 ) is obtained, and this is called a double phase difference. Here, one GPS satellite is used as a reference GPS.
And the other three GPS satellites as subordinate GPS satellites, and the position of the mobile station 14 is determined by calculating the double phase difference for each set of the reference GPS satellite and the three subordinate GPS satellites. You can know. Hereinafter, a description will be given using mathematical expressions.

When the reference GPS satellite S _M and the three subordinate GPS satellites S _S1 , S _S2 , and S _S3 are viewed from the reference station 10, the direction cosines are C _M , C _S1 , C _S2 , and C _S3 , respectively. Reference station 1
_Assuming that a position vector from 0 to the mobile station 14 is r, the reference GPS satellite S _M and the subordinate GPS satellite S _Si (i = 1, 2,
Double difference DDfai _i obtained by a set of 3) can be expressed by the following equation.

DDφ ₁ = r (C _S1 −C _M ) DDφ ₂ = r (C _S2 −C _M ) DDφ ₃ = r (C _S3 −C _M ) By solving these three equations for r, the mobile station 14 The position can be determined. In this case, the double phase difference is 3
The same value is obtained for every integral multiple of 60 °. This uncertain integer value is called an integer value bias or ambiguity. This positioning device is well known and commonly used as an RTK / GPS positioning device. The navigation device shown in FIG.
This is an RTK / GPS-IMU combined positioning device configured by using an inertial navigation device IMU, which is another navigation device, in combination with a TK / GPS positioning device.

According to the RTK / GPS-IMU combined positioning device described above, highly accurate positioning can be performed by using the positioning device in combination. However, during positioning, any one of the radio waves arriving from the four GPS satellites is interrupted, or the communication that takes a double phase difference between the reference station and the mobile station is interrupted, so that the GPS positioning can be performed. Without, G
A case occurs where the PS position output cannot be obtained. The interruption of radio waves arriving from GPS satellites is caused by RTK / GPS-IMU
This occurs when the mobile station using the combined positioning device cannot receive GPS satellite information, such as when entering a road under a tunnel-shaped roof. The interruption of communication between the reference station and the mobile station occurs due to the environment around the reference station and the mobile station, radio interference, and various other reasons.

[0008] If any of the radio waves arriving from the four GPS satellites or the communication that takes the double phase difference between the reference station and the mobile station is interrupted, even if the communication is interrupted for a short time. , The integer bias needs to be determined again. here,
Determining the integer value bias is called initial setting. Then, when the mobile station 14 equipped with the RTK / GPS-IMU combined positioning device is working or traveling, the GPS satellite information is interrupted and positioning calculation cannot be performed.
Performing initial setting when satellite information can be received again is called re-initializing. However, the candidates for the integer value bias are usually as large as about 100,000 sets.
It takes about 1 to 3 minutes. Depending on the mobile station, the time of about 1 to 3 minutes becomes a problem. During the execution of the integer value bias determination processing, the mobile station stops moving or moves while the current position is in an indeterminate state. I will have to do it.

Hybrid positioning by the RTK / GPS-IMU combined positioning apparatus shown in FIG. 4 will be described with reference to FIG. In the RTK / GPS-IMU combined positioning device, the RTK / GPS operates with the integer value bias determined, and the RTK / GPS operates.
K-positioning to generate GPS position output and IMU14
0 also operates to start IMU combined hybrid positioning to generate IMU position output. The position output filter 1411 of the RTK positioning calculation unit 141 has a GPS position output
Input both the MU position output and IM from the GPS position output.
The IMU 14 generates a sensor error by subtracting the U position output.
It returns to 0 and outputs an error variance matrix at a position indicating the variation of the error. IMU 140 is a position output filter 1
The current position corrected based on the sensor error returned from 411 is calculated and output. Here, the error dispersion and the position error dispersion will be described just in case. The error variance of the position means the position output by GPS satellite positioning and IM
This is a statistical value indicating how much the difference in position output due to U positioning varies. In this hybrid positioning, the position output by the GPS satellite positioning is assumed to be an accurate output, and the difference between this and the position output by the hybrid positioning is estimated to be the output error of the hybrid positioning. Thereby, the expression of error dispersion of position is adopted. Instead of the error variance of the position, it may be simply expressed as the variance of the position. The variance value is calculated in the process of estimating the error.

A case where RTK / GPS positioning cannot be performed will be described with reference to FIG.
As described above, even if the RTK / GPS positioning cannot be performed for various reasons, the IMU 140 continues to operate. The position output filter 1411 receives only the position output of the continuously operating IMU 140, executes the calculation of the current position based on the input, estimates the current position, and outputs the estimated value of the GPS satellite. The current position. In this case, the sensor error is set to a fixed value. Further, calculation of a search space, in other words, calculation of an integer value bias, is executed based on the error variance matrix obtained by the position output filter 1411 and the output position obtained by the IMU 140.

Next, re-initialization will be described with reference to FIG. G that can receive GPS satellite information
When the number of PS satellites returns to the number required to perform a fix, an integer bias is determined and reinitialization calculations are performed. Even during this calculation, the IMU 140 operates and keeps outputting the position. When the integer value bias is determined, the process returns to the hybrid positioning with IMU in FIG.

FIG. 7 is a flowchart for explaining the operation of FIG. When RTK positioning cannot be performed for various reasons, positioning is performed only by the IMU. As a result, when the position of the mobile station 14 is determined, the position and each of the GPS satellites 1 that have been used for GPS positioning up to that time are determined.
The distances to 2 and 13 are calculated, and the wave numbers and phases of the carrier waves of the radio waves of the GPS satellites 12 and 13 at the calculated distance are calculated (S1). Next, it is checked whether or not it has returned to a state where positioning by GPS radio waves can be executed (S2). If recovered, GP received
A double phase difference is measured for the S satellite wave. 2 obtained from this measurement value and the positioning result of the IMU immediately before it.
The difference of the heavy phase difference is rounded off, rounded down, rounded up, and other processing is performed to estimate a search space, that is, an integer value bias (S3). If not, the process returns to step (S2). Next, the search space is narrowed down. In other words, the integer bias candidates are narrowed down to a number of about ± 1 to 2 (S4). The test is repeated for these integer value bias candidates (S5). Determine the correct integer bias value.
After the determination of the integer value bias, the RTK positioning using the bias is restored, and the hybrid positioning using the IMU is executed (S6).

[0013]

[Problems to be Solved by the Invention] RTK / GPS-IM
The first method of re-initializing the U-combined positioning device is a high-speed initial setting method called on-the-fly in which the determination of the integer value bias, that is, the estimation of the current position is performed while the mobile station is moving. . This first method involves moving a GPS satellite, G
This is performed by using information such as pseudo-range, carrier wave phase and wide-lane using two-frequency beats, which are information of PS satellites, and other information comprehensively. As a result, it is possible to efficiently narrow down the integer value bias candidates, and it is possible to select a correct candidate from among a small number of candidates. However, in this first method of reinitialization, when the reinitialization is started, the state where the measurement position is incorrect or unknown continues for several minutes. In the case of the configuration using only GPS satellites, since the influence of the carrier wave phase error is large, the search space becomes large, and at least 1 to 3 is required before the integer value bias is determined.
It takes about a minute. In order to obtain accurate measurement values, it is necessary to use expensive components. Also,
If the traveling vehicle equipped with the RTK / GPS-IMU combined positioning device needs to be re-initialized while working or traveling, since the exact current position is unknown, the operation is stopped or the current position is lost. The work will be continued or run with inaccuracy. Furthermore, in this case, the RTK positioning device must be of a two-frequency type.

In a second method of re-initialization, an error of the IMU is obtained in advance at the time of a momentary interruption of the GPS satellite reception, and the size of the search space is set to a certain fixed value in a descending manner. This second method can cope with the momentary interruption of the GPS satellite reception, but if the interruption of the GPS satellite reception continues for a certain length of time, the error in the position output of the IMU becomes large and is determined in advance. In some cases, it may not be possible to re-initialize when the user leaves the search space. In addition, GPS
The time at which satellite reception is interrupted cannot be predicted. If the search space is set small, an incorrect solution can be obtained without including the solution of the integer value bias candidate in the search space, so that the search space must be set large. As a result, the arithmetic processing time required until the determination of the integer value bias increases, which is against the demand for speeding up the determination of the integer value bias.

The present invention provides an RTK / GPS-IMU combined positioning method that determines a minimum search space without omission of an integer-valued bias solution even when GPS satellite reception is interrupted.

[0016]

Means for Solving the Problems A GPS receiving section and a GPS
A mobile station 14 having an IMU, a reference station 10, a plurality of GPS satellites 1
In the RTK / GPS-IMU combined positioning method using the RTK-IMU combined positioning device comprising 1, 12, and 13, when determining the integer bias when the interruption of the transmission wave of the GPS satellite or the reference station is recovered, the coordinates are determined as follows. A search space is set with the output position of the IMU as a center position and a radius of error variance of the position centered on the center position, and an integer bias is determined from integer bias candidates having a solution in the search space. RTK / GPS-IM
The U combined positioning method was configured.

[0017]

An embodiment of the present invention will be described with reference to FIG. In FIG. 1, members common to those in the conventional example are denoted by common reference numerals. G of mobile station 14
The PS receiver 142 receives the GP transmitted from each GPS satellite.
S satellite data is received via the antenna unit 15 and acquired.

The reference station 10 receives G signals obtained from each GPS satellite.
The PS satellite data is transmitted via the transmission antenna 101 as GPS correction data. GPS correction data receiving unit 14
3 receives and acquires the GPS correction data via the receiving antenna 16. The error estimator 144 calculates the GPS position output output from the RTK positioning calculator 141 and the IMU1
40, and input the IMU position output from the GPS position output by the position output filter 1411.
The IMU 14 generates a sensor error by subtracting the U position output.
It returns to 0 and outputs an error variance matrix at a position indicating a variation in error to the search space setting unit 145. IMU14
“0” calculates and outputs the current position corrected based on the sensor error fed back from the position output filter 1411.

Search space setting section 145 obtains the IMU position output output from IMU 140 and obtains the error variance matrix of the position output from error estimating section 144. Here, with respect to the coordinates, a search space is set with the output position of the IMU as the center position and the error variance of the position as a radius around the center position. RTK positioning calculation unit 141
Acquires the search space set by the search space setting unit 145, sets candidates for combinations of integer biases in the search space, and determines an integer bias from these. Then, the current position is estimated based on the integer bias. The RTK positioning calculation section 141 also stores the GPS satellite data acquired by the GPS
The positioning calculation is performed based on the GPS correction data acquired by the S correction data receiving unit 143. RTK positioning calculation unit 1
41 outputs the estimated current position and other data to the error estimating unit 144.

Here, referring again to FIG. 5, the RTK
In general, the GPS-IMU combined positioning device uses the IMU in which the RTK / GPS operates with the integer value bias determined, generates the GPS position output by performing the RTK positioning, and also operates the IMU 140 to generate the IMU position output. I'm doing hybrid positioning. That is, the position output filter 1411 which is a navigation filter formed in the RTK positioning calculation unit 141 of the mobile station 14 receives both the GPS position output and the IMU position output, and subtracts the IMU position output from the GPS position output. An error is generated and fed back to the IMU 140, and an error variance matrix indicating the error variation is output.
The IMU 140 continuously calculates and outputs the corrected current position based on the sensor error fed back from the position output filter 1411.

Referring to FIG. 6A, a case where RTK positioning cannot be performed will be described. As described above, the IMU 140 continues to operate even when the RTK positioning by the GPS satellites cannot be performed. In this case, the position output filter 1411 receives only the position output of the continuously operating IMU 140, executes the calculation of the current position of the GPS satellite based on the input, and estimates the current position by the IMU 140. I have. In this case, the sensor error is set to a fixed value. Furthermore,
Based on the error variance matrix obtained by the position output filter 1411 and the output position obtained by the IMU 140, calculation of a search space, in other words, calculation of an integer value bias is executed. The GPS satellites 12 and 13 are reacquired and the GP
Until the S-satellite information is sufficiently received by the GPS receiving unit 142, that is, a sufficient number of GPs
The IMU 140 performs a single position output until the S satellites are aligned, and based on this, the position output filter 1411 continues to calculate the position error variance.

Here, a sufficient number of G's for RTK positioning
When the PS satellites are ready, reinitialization is started in the following order. (1) Referring to FIG. 2A, for the XYZ rectangular coordinates, the output position of the IMU 140 is set as the center position, and the center position is set as the center (X ₀ , Y ₀ , Z ₀ ), and the error variance of the position is set to the radius. A three-dimensional space is set as R. That is, XY
The allowable values and the allowable ranges of the XYZ three-direction components of the error variance of the position in the Z rectangular coordinates are set. 3-dimensional space is expressed by ^{_{(X-X 0) 2 +}} (Y-Y 0) 2 + (Z-Z 0) 2 ≦ R 2. The internal area including the spherical surface is a search space in which the search space is set.

In this case, the space set by the position error variance changes depending on the environment. For example, in the case of the mobile station 14 moving on a plane, the space is set by fixing the height direction. (Second) A combination of integer value biases, that is, a search space is determined in the space set by (First).
Here, the center position obtained by the IMU140 positioning and G
From the PS satellite information, a combination of integer value biases at the center of the search space is calculated. The elements of this combination of integer value biases are changed by integers, and if the position indicated by the changed combination is within the three-dimensional space set by (first), this is left as a candidate for the integer value bias.

[0024] In the following, this will be specifically described. When the positioning is not completed, the integer value bias for each acquired GPS satellite is unknown. That is, as for the integer value bias of each GPS satellite, a large number of integer value biases for each GPS satellite are listed as candidates for the correct answer. Normally, when the integer bias is determined, the distance between the GPS receiver and each GPS satellite can be determined, so that the position of the GPS receiver can be determined. Conversely, combinations of integer-valued biases N ₁ , N ₂ , N ₃ ,... N _i indicating a certain position, here the closest position calculated backward from the IMU position
Can be determined. Since the bias value usually becomes a real value when calculated backward, it is rounded, rounded down, rounded up or otherwise rounded to an integer value, the position is determined, and this is used as a combination of the integer value bias closest to the center position. Generally, when obtaining a position by GPS positioning, 4
More than one GPS satellite needs to be acquired. Similarly, in RTK / GPS positioning using carrier phase, 4K
More than one GPS satellite needs to be acquired. Since the description will be complicated when the three dimensions are described, the two dimensions using three GPS satellites will be described below with reference to FIG. 2B.

The distance R _i between the GPS receiver and each GPS satellite is: R ₁ = Φ ₁ + kλ R ₂ = Φ ₂ + mλ R ₃ = Φ ₃ + nλ where Φ: length k by carrier phase measurement, k: m, n: integer value bias value λ: wavelength It can be seen that the bias combination closest to the center position, that is, the reference combination is (k, m, n). Each element k,
m and n are changed by integers, and the combination of the integer value biases included in the circle among the combinations of the integer value biases set at the position of the intersection indicated by the white circle o is correct G
Since it may indicate the PS satellite position, this is left as a candidate for the integer value bias. These candidates are called a search space. These candidates are immediately real space,
Since it represents a position in the earth fixed coordinate space or the NEH coordinate space, this space is referred to as a search space as a space for searching for a correct answer.

Reinitialization is started in the obtained search space. Even during the reinitialization, the position output of the IMU 140 is continuously performed. FIG. 3 is a flowchart of the operation of the RTK / GPS-IMU combined positioning device. (S1) The RTK / GPS-IMU combined positioning device is activated, and the positioning process is started. (S2) A process for confirming the operation state of the RTK positioning device is started.

(S3) With the integer value bias determined, the RTK / GPS-IMU combined positioning device determines whether or not it is in the RTK positioning state. If YES, (S1
Go to 1). If NO, the process proceeds to (S4). (S11) It is determined whether the IMU is in the output state. If YES, the process proceeds to (S12). If NO, the process proceeds to (S14).

(S12) The calculation of the position output filter of the IMU is started. (S13) The RTK-IMU combined positioning operation is started. (S14) The IMU is not in the output state, and the positioning operation of the RTK alone is started. (S4) In (S3), it is determined whether the IMU is not in the RTK positioning state but in the output state. YES
If, the process proceeds to (S5). If NO,
Move to (S10).

(S5) In (S4), the IMU is set to Y
In the output state of ES and without the RTK observation value,
The calculation of the position output filter of the MU is started. (S6) The output position of the IMU is set as the center position. (S7) A search space is set with the output position of the IMU as the center position and the error variance of the position as the radius.

(S8) It is checked whether the number of GPS satellites is 5 or more. (S9) If the number of GPS satellites is 5 or more in (S8), the process proceeds to an integer value bias determination process, and then returns to the RTK positioning device operation state confirmation process (S2). In (S8), if the number of GPS satellites is 4 or less, it is determined whether or not it is in the RTK positioning state (S3).
Return to.

[0031]

As described above, according to the present invention, the search space is limited to a three-dimensional space whose radius is the error variance of the position, so that the search space is set down. The search space can be set smaller than in the conventional example. As a result, even if the GPS satellite information is interrupted for a certain short period of time, re-initialization can be performed at a high speed due to the small search space, so that accurate position measurement can be performed almost continuously. By the way, if the error dispersion of the position is about the wavelength of the carrier, the integer value bias candidates can be narrowed down to almost one, and the reinitialization is set to 1
The epoch, that is, the processing can be completed within one data output interval.

[Brief description of the drawings]

FIG. 1 illustrates an embodiment.

FIG. 2 is a view for explaining setting of a search space and searching for a candidate for an integer value bias.

FIG. 3 is a flowchart of the operation of the embodiment.

FIG. 4 is a diagram illustrating a conventional example.

FIG. 5 is a diagram simply illustrating hybrid positioning.

FIG. 6 is a diagram illustrating reinitialization.

FIG. 7 is a flowchart of the operation of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Reference station 12, 13 GPS satellite 14 Mobile station 140 IMU 141 RTK positioning calculation part 1411 Position output filter 142 GPS reception part 15 Antenna part 101 Transmission antenna 143 GPS correction data reception part 16 Receiving antenna 144 Error estimation part 145 Search space setting part

Claims (1)

[Claims] 1. An RTK / GPS using a GPS receiving unit, a GPS correction data receiving unit, an RTK positioning calculating unit, a mobile station having an IMU, a reference station, and an RTK-IMU combined positioning device including a plurality of GPS satellites. In the IMU combined positioning method, when determining the integer bias when the interruption of the transmission radio wave of the GPS satellite or the reference station is recovered, the coordinates are determined by I
An output position of the MU is set as a center position, a search space is set with the error variance of the position as a radius around the center position, and an integer bias is determined from the integer bias candidates having a solution in the search space. RTK · G characterized by the following
PS-IMU combined positioning method.