JP2008107160A - Satellite radio wave receiver for mobile unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect whether multipath has occurred with high precision. <P>SOLUTION: The satellite radio wave receiver for a mobile unit includes a threshold range setting means 140 for setting a range which is derived on the basis of measurement or estimation and is taken by a correlation peak value P<SB>CA</SB>under a condition in which multipath is absent to be a first threshold range and setting a range which is derived on the basis of measurement or estimation and is taken by the phase deviation amount Δϕ of the code phase of a replica pseudo-noise code with respect to the code phase of a pseudo-noise code under the same condition to be a second threshold range, a decision means 142 for deciding whether the calculated correlation peak value and deviation amount of the code phase for a received satellite signal are within the first threshold range and the second threshold range set by the threshold range setting means, respectively, and a multipath detection means 144 for determining that multipath has occurred when at least either one of the calculated correlation peak value and deviation amount of the code phase is not within each of the threshold ranges. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention calculates the pseudo distance between a satellite and a mobile object by performing a correlation value calculation using a replica pseudo noise code generated inside the pseudo noise code carried on the radio wave from the satellite. The present invention relates to a mobile satellite radio wave receiver to be calculated.

Conventionally, when detecting the phase of a pseudo-noise code from a pseudo-noise code or a modulated signal modulated by a pseudo-noise code, even if a reflected wave by multipath is superimposed on the direct wave, the pseudo-noise code by the direct wave A technique for making it possible to correctly detect the phase is known (see, for example, Patent Document 1).
JP 2001-36429 A

  By the way, when the reflected wave by the multipath is superimposed on the direct wave, it is difficult to correctly detect the phase of the pseudo noise code by the direct wave, and the phase of the pseudo noise code cannot be detected correctly. In this case, an error occurs in the calculated pseudo distance. On the other hand, when a multipath occurs, a countermeasure may be considered in which the calculated pseudo distance is temporarily not used for positioning, but in order to realize this, whether or not the multipath has occurred is determined. It is necessary to detect with high accuracy.

  Therefore, an object of the present invention is to provide a satellite radio wave receiver for a mobile body that can accurately detect whether or not a multipath has occurred.

In order to achieve the above object, according to a first aspect of the present invention, code synchronization is performed by performing a correlation value calculation on a pseudo-noise code carried on a radio wave from a satellite using a replica pseudo-noise code generated internally. That is, a satellite radio wave receiver for a mobile object that calculates a pseudo distance between the satellite and the mobile object,
A range derived based on actual measurement or estimation, and a range that can be taken by the correlation peak value in a situation where there is no multipath is set as the first threshold range, and the range derived based on actual measurement or estimation A threshold range setting means for setting a possible range of the phase shift amount of the code phase of the replica pseudo noise code with respect to the code phase of the pseudo noise code under the same condition as a second threshold range;
It is determined whether or not the correlation peak value calculated for the received satellite signal and the code phase shift amount are within the first threshold range and the second threshold range set by the threshold range setting means, respectively. Determination means to perform,
Multipath detection means for determining that multipath has occurred when it is determined that at least one of the calculated correlation peak value and code phase shift amount is not within the respective threshold ranges. It is characterized by that.

A second invention is the satellite radio wave receiver according to the first invention,
In the threshold range setting means, the first threshold range and the second threshold range are set based on a variance value of the correlation peak value calculated from past observation data and a variance value of the deviation amount of the code phase. It is characterized by that. Thereby, the first threshold range and the second threshold range can be adapted during actual operation.

A third invention is the satellite radio wave receiver according to the second invention,
The variance value is calculated using observation data obtained when the moving object is located at a position where the number of observable satellites is equal to or greater than a predetermined value and the possibility of multipath occurrence is low, among past observation data. It is characterized by that. Thereby, the first threshold range and the second threshold range can be set appropriately.

A third invention is the satellite radio wave receiver according to the third invention,
The position where the possibility of the occurrence of multipath is low includes an open area where there is no surrounding building that may cause multipath.

  ADVANTAGE OF THE INVENTION According to this invention, the satellite radio wave receiver for mobile bodies which can detect accurately whether the multipath generate | occur | produced is obtained.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a system configuration diagram showing an overall configuration of a GPS (Global Positioning System) to which a satellite radio wave receiver according to the present invention is applied. As shown in FIG. 1, the GPS includes a GPS satellite 10 that orbits the earth and a mobile station 30 that is located on the earth and can move on the earth. Here, it is assumed that the mobile station 30 is a vehicle. However, the mobile station 30 includes an information terminal such as a motorcycle, a railway, a ship, an aircraft, a hawk lift, a robot, and a mobile phone that moves as a person moves.

  The GPS satellite 10 always broadcasts navigation messages toward the earth. The navigation message includes satellite orbit information (ephemeris and almanac) regarding the corresponding GPS satellite 10, a clock correction value, and an ionosphere correction coefficient. The navigation message is spread by the C / A code, is carried on the L1 wave (frequency: 1575.42 MHz), and is constantly broadcast toward the earth. The L1 wave is a combined wave of a Sin wave modulated with a C / A code and a Cos wave modulated with a P code (Precision Code), and is orthogonally modulated. The C / A code and the P code are pseudo noise codes, and are code strings in which -1 and 1 are irregularly arranged periodically.

  Currently, 24 GPS satellites 10 orbit the earth at an altitude of about 20,000 km, and each of the four GPS satellites 10 is evenly arranged on six orbiting earth surfaces inclined by 55 degrees. ing. Therefore, as long as the sky is open, at least five GPS satellites 10 can be observed at any time on the earth.

  The mobile station 30 is equipped with a GPS receiver 1 as a satellite radio wave receiver. The GPS receiver 1 measures the position of the mobile station 30 based on the satellite signal from the GPS satellite 10, as will be described in detail below.

FIG. 2 is a schematic system configuration diagram showing an embodiment of the GPS receiver 1 mounted on the mobile station 30 of FIG. In FIG. 2, only _one GPS satellite 10 ₁ (subscript is a satellite identification number) is shown in order to avoid complication of explanation. Signal processing relating satellite signal from the GPS satellite 10 ₁ is a signal processing is substantially the same as about the satellite signals from the other GPS satellites ₁₀ 2, 10 _3, etc.. Therefore, in the following, unless otherwise stated, the description will be continued assuming a signal processing according to the GPS satellite 10 _1. The signal processing described below is executed in parallel (simultaneously) on the satellite signals from the observable GPS satellites 10 ₁ , 10 ₂ , 10 _{3 and the} like.

  As shown in FIG. 2, the GPS receiver 1 of the present embodiment includes a GPS antenna 20, a high frequency circuit 22, an A / D (analog-to-digital) conversion circuit 24, a signal processing circuit 100, an INS sensor. 26, various sensors 28, a map DB (database) 29, and a calculation unit 32. The calculation unit 32 includes a signal processing circuit 100 and a positioning calculation circuit 200.

GPS antenna 20 receives a hygienic signal transmitted from the GPS satellite 10 _1, the voltage signal satellite signal received (in this example, frequency 1.5 GHz) is converted to. A voltage signal of 1.5 GHz is referred to as an RF (radio frequency) signal.

  The high-frequency circuit 22 amplifies a weak RF signal supplied via the GPS antenna 20 to a level at which A / D conversion can be performed later, and at the same time, an intermediate frequency (typically 1 MHz to 20 MHz). A signal obtained by down-converting the RF signal in this way is referred to as an IF (Intermediate frequency) signal.

  The A / D conversion circuit 24 converts the IF signal (analog signal) supplied from the high frequency circuit 22 into a digital IF signal so that digital signal processing can be performed.

The signal processing circuit 100, the digital IF signal supplied from the A / D conversion circuit 24 C / A code synchronization performs (described later), takes out a navigation message, the pseudo between the GPS satellite 10 ₁ and the mobile station 30 Calculate the distance. The calculation method of the pseudo distance will be described in detail later. The pseudoranges, unlike true distance between the GPS satellite 10 ₁ and the mobile station 30 includes an error due to clock error (clock bias) and radio wave propagation velocity changes.

Here, the pseudorange ρ with respect to the GPS satellite 10 ₁ is expressed as follows.
ρ = c · τ _u + b Formula (1)
Here, c is the speed of light, b is an error component, and mainly corresponds to a distance error due to a clock error. tau _u indicates the travel time from the GPS satellite 10 ₁ and the mobile station 30 (GPS antenna 20).

Positioning calculation circuit 200, based on the satellite orbit information and the current time of the navigation message to calculate the GPS satellite 10 _1, the current position in the world coordinate system _{(X 1, Y 1, Z} 1). Since the GPS satellite 101 is _one of artificial satellites, its movement is limited to a certain plane (orbital plane) including the center of gravity of the earth. Further, the trajectory of the GPS satellites 10 ₁ are elliptic motion to one focus global centroid, by sequentially numerical equations of Kepler, can be calculated GPS satellite 10 ₁ in position on the track surface. The position of the GPS satellite 10 _{1 (X 1,} Y 1, _{Z 1),} taking into account that the GPS satellite 10 ₁ of the raceway surface and the equatorial plane of the world coordinate system is in rotational relationship, in orbit plane obtained by 3-dimensional rotational coordinate transformation of the position of the GPS satellite 10 _1. As shown in FIG. 3, the world coordinate system is defined by an X axis and a Y axis that are orthogonal to each other in the equator plane with the center of gravity of the earth as the origin, and a Z axis that is orthogonal to both axes.

Positioning calculation circuit 200, the calculation result of the satellite position, based on the calculation result of the pseudo-range supplied from the signal processing circuit 100, the position of the moving body _{30 (X u, Y u,} Z u) were positioning, e.g. Output to the navigation system as shown in FIG. The position of the moving body 30 may be derived on the principle of triangulation using the respective pseudoranges and satellite positions obtained for the three GPS satellites 10. In this case, since the pseudo distance includes a clock error as described above, the clock error component is removed using the pseudo distance and the satellite position obtained for the fourth GPS satellite 10. Note that the positioning method of the position of the moving body 30 is not limited to the single positioning as described above, but may be interference positioning (a method in which received data at a fixed station installed at a known point is used in combination). In the case of interference positioning, the position of the moving body 30 is measured using a single phase difference or a double phase difference of pseudo distances obtained by the fixed station and the moving body 30 as described above.

  The positioning calculation circuit 200 includes various sensors 28 such as an INS (inertial navigation system) sensor 26, a vehicle speed sensor, a rudder angle sensor, an azimuth meter, etc. The positioning result may be corrected using information from (database) 29. The INS sensor 26 may include a gyro sensor and a G (acceleration) sensor. For example, the positioning calculation circuit 200 may correct the positioning result by map matching using the map information from the map DB 29, or while the satellite signal cannot be received such as during tunnel traveling, the INS sensor 26 and various sensors. 28, position information of the moving body 30 (position information by inertial navigation) may be generated based on the movement mode of the moving body 30 estimated based on H.28. For example, the speed vector (Vx, Vy) of the vehicle (moving body 30) is based on the body coordinate system (see FIG. 3) with the vehicle body as a reference, so that the positioning calculation circuit 200 uses the speed vector (Vx, Vy). ) To the world coordinate system via the local coordinate system. Normally, rotational transformation of coordinates can be realized by using Euler angles, but transformation from the body coordinate system to the local coordinate system may be realized only by the yaw angle ψ assuming that the roll angle and the pitch angle are small (however, Of course, it is possible to consider the roll angle and the pitch angle, or to ignore the yaw angle.) The conversion from the local coordinate system to the world coordinate system is realized by conversion using the longitude and latitude of the vehicle position.

  Next, a detailed configuration of the above-described signal processing circuit 100 will be described.

FIG. 4 is a diagram showing functional blocks that schematically represent the main functions of the signal processing circuit 100. Hereinafter, to avoid complicating the description, it will be described as a representative signal processing relating satellite signals from one single GPS satellite 10 ₁ (1-channel signal processing). The signal processing described below is executed in parallel (simultaneously) with respect to the satellite signals from the observable GPS satellites 10 ₁ , 10 ₂ , 10 _3, etc. for each observation period (for example, 1 ms).

As shown in FIG. 4, the signal processing circuit 100 has a DDL (Delay-Locked).
(Loop) 110, PLL (Phase-Locked Loop) 120, and filter 130. The signal processing circuit 100 also includes a correlation peak value calculation unit 119, a threshold range setting unit 140, a determination unit 142, and a multipath detection unit 144. The threshold range setting unit 140, the determination unit 142, and the multipath detection unit 144 may be realized by an appropriate processor or microcomputer such as a DSP (Digital Signal Processor). The other part of the signal processing circuit 100 may be realized by a logic circuit configured by an IC. Note that these hardware configuration classifications are merely examples.

  The DDL 110 includes a cross-correlation calculation units 111 and 112, a phase advancement unit 113, a phase delay unit 114, a phase shift calculation unit 115, a phase correction amount calculation unit 116, a replica C / A code generation unit 117, and a pseudo distance calculation unit 118. including.

The replica C / A code generation unit 117 generates a replica C / A code. The replica C / A code with respect to the C / A code, which is put on the satellite signals from the GPS satellites 10 _1, + 1, the arrangement of -1 is the same code.

The replica C / A code generated by the replica C / A code generation unit 117 is input to the cross correlation calculation unit 111 via the phase advancement unit 113. That is, an early replica code is input to the cross correlation calculation unit 111. In the phase advancer 113, the replica C / A code is advanced by a predetermined phase. Let the phase advance amount advanced by the phase advancer 113 be θ ₁ .

  In addition, the digital correlation signal is input to the cross-correlation calculation unit 111 after being multiplied by a replica carrier generated by the PLL 120 by a mixer (not shown).

The cross-correlation calculation unit 111 calculates a correlation value (Early correlation value E _CA ) using the input digital IF signal and the Early replica code of the phase advance amount θ ₁ . The Early correlation value E _CA is calculated by the following equation, for example.
Early correlation value E _CA = Σ {(digital IF) × (Early replica code)}
The replica C / A code generated by the replica C / A code generation unit 117 is input to the cross correlation calculation unit 112 via the phase delay unit 114. That is, the late replica code is input to the cross-correlation calculation unit 112. In the phase delay unit 114, the replica C / A code is delayed by a predetermined phase. The phase delay amount delayed by the phase delay unit 114 is the same as the phase advance amount θ ₁ but has a different sign.

  Further, the digital correlation signal is input to the cross-correlation calculation unit 112 after being multiplied by a replica carrier generated by the PLL 120 by a mixer (not shown).

The cross-correlation calculation unit 112 calculates a correlation value (Late correlation value L _CA ) using the input digital IF signal and the Late replica code of the phase delay amount −θ ₁ . The Late correlation value L _CA is calculated by the following equation, for example.
Late correlation value L _CA1 = Σ {(digital IF) × (Late replica code)}
In this way, the cross-correlation calculation units 111 and 112 execute the correlation value calculation with the correlator interval d ₁ (also referred to as “spacing”) being 2θ ₁ . The Early correlation value E _CA and the Late correlation value L _CA calculated by the cross correlation calculation units 111 and 112 are input to the phase shift calculation unit 115.

The phase shift calculation unit 115 calculates the degree of phase shift between the digital IF signal and the replica C / A code generated by the replica C / A code generation unit 117. That is, the phase shift calculation unit 115 calculates (estimates) the phase shift amount Δφ of the replica C / A code with respect to the received C / A code. The phase shift amount Δφ of the replica C / A code is calculated by the following equation, for example.
(Phase shift amount Δφ) = (E _CA −L _CA ) / 2 (E _CA + L _CA )
The phase shift amount Δφ thus calculated is input to the phase correction amount calculation unit 116, a threshold range setting unit 140, which will be described later, and the determination unit 142.

In the phase correction amount calculation unit 116, an appropriate phase correction amount is calculated so as to eliminate the phase shift amount Δφ. An appropriate phase correction amount is calculated, for example, according to the following arithmetic expression.
(Phase correction amount) = (P gain) × (phase shift amount Δφ) + (I gain) × Σ (phase shift amount Δφ)
This equation is an equation representing feedback control using PI control, and the P gain and the I gain are experimentally determined from the balance between variation and response, respectively. The phase correction amount calculated in this way is input to the replica C / A code generation unit 117.

  In the replica C / A code generation unit 117, the phase of the generated replica C / A code is corrected by the phase correction amount calculated by the phase correction amount calculation unit 116. That is, the tracking point of the replica C / A code is corrected. The replica C / A code thus generated is input to the cross-correlation calculation units 111 and 112 via the phase advance unit 113 and the phase delay unit 114 as described above, and the pseudo distance calculation unit 118 and the correlation peak value calculation unit. 119 is input. In the cross-correlation calculators 111 and 112, the replica C / A code generated in this way is used for correlation value calculation for the IF digital signal input in the next observation cycle.

The pseudo distance calculation unit 118 calculates the pseudo distance ρ ′ _CA based on the replica C / A code generated by the replica C / A code generation unit 117 using, for example, the following expression. In addition, as a meaning of a code, “′” added to the pseudo distance ρ _CA indicates that a filtering process described later is not executed, and “ _CA ” indicates a pseudo distance calculated based on the C / A code. Indicates ρ.
ρ ′ _CA = N _CA × 300
_{Here, N CA} corresponds to the number of bits of the C / A code between the GPS satellite 10 ₁ and the mobile station 30, the phase and C / A code replica generated by the replica C / A code generating unit 117 It is calculated based on a receiver clock inside the receiver 1. The numerical value 300 is derived from the fact that the C / A code has a 1-bit length of 1 μs and a length corresponding to 1 bit of about 300 m (1 μs × light speed). A signal representing the pseudo distance ρ ′ _CA calculated in this way is input from the DDL 110 to the filter 130.

In the PLL 120, the Doppler frequency change Δf _{L1 of} the Doppler-shifted received carrier wave (received carrier) is measured using a carrier replica signal generated inside. The measurement method of the Doppler frequency change amount Δf _L1 may be realized by a correlation value calculation using an internally generated replica carrier. The digital IF signal input to the PLL 12 is obtained by multiplying the replica C / A code supplied from the DDL 110 by a mixer (not shown). A signal representing the Doppler frequency change amount Δf _L from the PLL 120 is input to the filter 130.

In the filter 130, filter processing of the pseudo distance ρ ′ _CA is executed using the Doppler frequency change amount Δf _L. The filter process may be a process called carrier smoothing known in this field, and can be realized using a hatch filter or a Kalman filter. A signal representing the pseudo distance ρ _CA after the filter processing is supplied to the positioning calculation circuit 200 (see FIG. 2) and used for the positioning calculation of the position of the moving body 30.

  The correlation peak value calculation unit 119 receives the replica C / A code generated by the replica C / A code generation unit 117. That is, the Prompt replica code is input to the correlation peak value calculation unit 119. The correlation peak value calculation unit 119 receives the digital IF signal after being multiplied by a replica carrier generated by the PLL 120 by a mixer (not shown).

The correlation peak value calculation unit 119 calculates a correlation peak value using the input digital IF signal and a Prompt replica code with a phase delay amount of zero. The correlation peak value _PCA is calculated by the following formula, for example.
Correlation peak value P _CA = Σ {(digital IF) × (Prompt replica code)}
Note that the correlation peak value _PCA is a value calculated under the assumption that the tracking of the C / A code is accurately performed, as is clear from the above formula, and the peak of the actual correlation value. It may be different from the value. Signal representing the correlation peak value P _CA from correlation peak value calculation unit 119 is input to a threshold range setting unit 140 and the judging unit 142.

In the threshold value range setting section 140, a range that can be taken of the correlation peak value P _CA within multipath no status is set as the first threshold range. Further, in the threshold range setting unit 140, a range that can be taken by the phase shift amount Δφ in a situation where there is no multipath is set as the second threshold range.

Specifically, the threshold range setting unit 140 calculates the average value and the variance σ _{P of} the correlation peak value P _CA based on the N number of observation data obtained under a situation where there is no multipath. The The first threshold value range is set as the mean value ± 3 [sigma] _P. Similarly, the threshold range setting unit 140 calculates the average value and the variance σ _{Δφ of the} phase shift amount Δφ based on the N number of observation data obtained under the situation where there is no multipath. The second threshold range is set as an average value ± 3σ _Δφ . In the threshold range setting unit 140, the first threshold range and the second threshold range are periodically changed based on observation data obtained during actual operation. This is because the appropriate threshold range is affected by weather conditions, hardware configuration characteristic differences (for example, characteristic differences due to differences in GPS antenna 20 and individual high-frequency circuit 22), hardware configuration deterioration over time, and the like. Because it changes. The threshold range change timing in the threshold range setting unit 140 and the observation data acquisition method in a situation where there is no multipath will be described later.

The decision unit 142, by using the first threshold value range set in the threshold range setting unit 140, whether the current observation cycle correlation peak value P _CA obtained at is within a first threshold range is determined. The determination result is output to the multipath detection unit 144. Further, the determination unit 142 determines whether or not the phase shift amount Δφ obtained in the current observation period is within the second threshold range using the second threshold range set by the threshold range setting unit 140. . The determination result is output to the multipath detection unit 144.

The multipath detection unit 144 determines whether a multipath has occurred based on the above-described two types of determination results from the determination unit 142. Specifically, in the multi-path detector 144, the determination of the correlation peak value P _CA obtained by this observation period is not within the first threshold range, and a phase shift amount Δφ obtained in the current observation period When at least one of the determinations that it is not within the second threshold range is supplied from the determination unit 142, it is determined that multipath has occurred. The determination of the correlation peak value P _CA obtained by this observation period is not within the first threshold range, and the determination of the phase shift amount Δφ obtained in the current observation period is not within the second threshold range It may be determined that multipath has occurred when at least one of the above is continuously supplied from the determination unit 142 at a predetermined number of processing cycles.

When it is determined that multipath has occurred, the multipath detection unit 144 generates a signal indicating this (hereinafter referred to as multipath detection signal). The multipath detection signal may be supplied to, for example, the positioning calculation circuit 200 (see FIG. 2) and used for the positioning calculation of the position of the moving body 30. In this case, the positioning calculation circuit 200, without using the pseudorange [rho _CA for GPS satellites 10 ₁ multipath is detected, the positioning operation can be performed. Alternatively, the positioning calculation circuit 200, without using the pseudorange [rho _CA for GPS satellites 10 ₁ multipath is detected, based on information from the positioning result and the INS sensor 26 of the multi-path detection before the positioning calculation circuit 200 The positioning calculation may be performed using the estimated pseudorange (pseudorange derived by inertial navigation). Alternatively, when the multipath detection unit 144 evaluates the possibility of occurrence of multipaths, the positioning calculation may be performed with a weighting coefficient according to the possibility of occurrence of multipaths. In this case, the weighting coefficient may be set to, for example, 0.8 when the possibility of occurrence of multipath is low, and the weighting coefficient may be set to, for example, 0.2 when occurrence of multipath is certain. The possibility of occurrence of multipath may be evaluated based on how much the correlation peak value _PCA and the phase shift amount Δφ are approximated or deviated from the respective threshold ranges.

  FIG. 5 is a conceptual diagram for explaining the above-described multipath detection method. In FIG. 5, the horizontal axis represents the code phase of the CA code, and the vertical axis represents the correlation value. In FIG. 5, a two-dimensional threshold region defined by the first threshold range and the second threshold range is indicated by hatching.

In situations where multibus has not occurred, it means that only the direct wave from the GPS satellite 10 ₁ is received, as indicated by the straight line of the direct wave in FIG. 5, the symmetrical around the correlation peak value The correlation value characteristic is shown. On the other hand, when a multibus occurs, a reflected wave having a correlation peak value is received with a code phase shifted from the code phase of the correlation peak value related to the direct wave, as shown by a straight line of the reflected wave in FIG. The Therefore, when a multibus occurs, a combined wave of a direct wave and a reflected wave as shown by the straight line of the received wave in FIG. 5 is received. In the example shown in FIG. 5, the reflected wave has an upward convex correlation value characteristic, but may have a downward convex correlation value characteristic. Anyway, if the multi-bus has occurred, the correlation characteristic of the reception wave, the correlation peaks of the direct wave is not clearly appear, and it becomes difficult to detect the code phase correlating peak value P _CA. As a result, the phase shift amount Δφ can change greatly. Further, when a multibus occurs, the correlation peak value of the received wave greatly changes with respect to the correlation peak value in a situation where the multibus does not occur.

In the present embodiment, when a multibus occurs in the current observation cycle, attention is paid to the fact that the correlation peak value P _CA and the phase shift amount Δφ in the current observation cycle change greatly compared to the previous observation cycle. As shown in FIG. 5, a two-dimensional threshold region (two-dimensional threshold region defined by the first threshold range and the second threshold range) defined by the correlation peak value _PCA and the phase shift amount Δφ is obtained. When the correlation peak value _PCA and the phase shift amount Δφ in the current observation period deviate from the threshold region, it is determined that multibus has occurred. Thereby, the presence or absence of the multibus can be accurately determined.

  Next, a preferred specific example of a method for updating a two-dimensional threshold region (first threshold range and second threshold range) by the threshold range setting unit 140 will be described.

  FIG. 6 is a flowchart showing a threshold area updating method realized by the threshold range setting unit 140. The following processing routine is executed at a predetermined processing cycle.

  In step 100, it is determined whether or not the weather around the current mobile object 30 is good. This determination may be realized based on various sensors mounted on the moving body 30 such as a rain sensor or a sunshine sensor, or based on weather information obtained through communication from an external information providing center. It may be realized. If the weather is good, the process proceeds to step 110; otherwise, the process proceeds to step 105.

  In step 105, the continuous observation data number M is initialized to zero. As can be understood from the following description, the number M of continuous observation data corresponds to the number of processing cycles when a situation where it is estimated that no multibus has occurred is continuing.

  In step 110, it is determined whether or not the current position of the moving body 30 belongs to the open area. An open area is an area where there are no surrounding buildings that can cause multipath. For example, a region where high-rise buildings exist in the vicinity is a typical example of a region that is not an open region. An area where there are no high-rise buildings and the sky is open is a typical example of an open area. More specifically, the open area includes an area where fields and vacant areas spread, an area where low-rise houses are scattered, and an area where there are no large buildings on the highway on a high position from the ground. Whether or not it belongs to an open area may typically be determined based on the position information of the moving body 30 and the map information in the map DB 29. In this case, in the map information of the map DB 29, an open area may be registered in advance based on building information. The position information of the moving body 30 may be based on the positioning result of the positioning calculation circuit 200. If the current position of the moving body 30 belongs to the open area, the process proceeds to step 120. Otherwise, the process proceeds to step 105.

In step 120, the number of currently observable GPS satellites 10 ₁ is equal to or more than a predetermined number is determined. The predetermined number may be 10, for example. Further, the number of observable GPS satellites 10 ₁ good as that only GPS satellite 10 ₁ reception sensitivity is good is counted. If the number of currently observable GPS satellites 10 ₁ is equal to or larger than a predetermined number, the process proceeds to step 130, otherwise, the process proceeds to step 105.

  In step 130, the continuous observation data number M is incremented. The initial value of the continuous observation data number M is zero, and the continuous observation data number M is incremented by 1 each time the conditions of the steps 100, 110, and 120 are satisfied in a continuous processing cycle. Note that the counter of the number M of continuously observed data may have a filter that holds the counter value even when the conditions of steps 100, 110, and 120 are not satisfied in a temporary short cycle.

  In step 140, it is determined whether the continuous observation data number M is equal to or greater than a predetermined value. The predetermined value depends on the processing cycle of this processing, but may be a value corresponding to observation data for 100 ms (N = 100), for example.

In step 150, the two-dimensional threshold region (first threshold range and second threshold range) is updated using the observation data acquired under the condition where the conditions of steps 100, 110, and 120 are satisfied. The That is, as described above, the first threshold range may be updated based on the average value and the variance σ _P of the correlation peak value P _CA calculated under the condition where the conditions of the steps 100, 110, and 120 are satisfied. . Similarly, the second threshold range may be updated based on the average value of the phase shift amount Δφ and the variance σ _Δφ calculated under the condition where the conditions of steps 100, 110, and 120 are satisfied.

  As described above, according to the processing shown in FIG. 6, it is possible to accurately estimate the situation where no multibus has occurred and update the two-dimensional threshold area during actual operation. Even when the correlation value characteristic changes, an appropriate two-dimensional threshold region can be set accordingly.

  Note that the process shown in FIG. 6 may be executed, for example, during one trip from when the ignition switch is turned on to when it is turned off until one threshold region update process is realized. In this case, depending on the case, the condition may not be satisfied during one trip and the update may not be performed once. Alternatively, the process shown in FIG. 6 may be executed every certain period (for example, every week or every month).

  According to the present embodiment described above, the following excellent effects are exhibited.

As described above, the presence or absence of the multibus is detected using the two-dimensional threshold region (first threshold range and second threshold range) defined by the correlation peak value _PCA and the phase shift amount Δφ. Detection accuracy can be increased.

  Also, by updating the two-dimensional threshold area during actual operation, it is possible to maintain good multibus detection accuracy even when the correlation value characteristics change due to, for example, deterioration of the hardware configuration over time. be able to. In addition, since the situation where the multibus does not occur is accurately estimated and the two-dimensional threshold area is updated during actual operation, the two-dimensional threshold area can be appropriately changed.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

For example, in the above embodiment, as the correlation peak value P _CA, although derived the correlation peak value P _CA by actual measurement, based on the pseudo distance is derived by the inertial navigation based on information from the INS sensor 26 guess it may derive correlation peak value P _CA by. In this case, the correlation value of the code phase corresponding to pseudo-range derived by the inertial navigation may be used as the correlation peak value P _CA speculative. The pseudo-range ρ _estimation by inertial navigation may be a geometric distance between the GPS satellite 101 and the GPS receiver ₁ derived by inertial navigation. For example, as shown in the following equation, A distance obtained by adding a clock error ρ _err to the distance may be used.
ρ _guess = sqrt {(X _{u estimate} (i) −X ₁ (i)) ² + (Y _{u estimate} (i) −Y ₁ (i)) ² + (Z _{u estimate} (i) −Z ₁ (i) ² } + ρ _err
Here, the estimated position [X _{u estimation} (i), Yu _estimation (i), Z _{u estimation} (i)] is a positioning result derived by inertial navigation, and positioning in the previous observation cycle (i−1). position of the mobile station 30 is a positioning result of the arithmetic circuit _{200 [X u (i-1} ), Y u (i-1), Z u (i-1)] and the previous observation period from INS sensor 26 (i -1) to the current observation cycle (i) and the movement information of the mobile station 30 is calculated. The clock error ρ _err may be calculated by the following equation, for example.
ρ ′ _err = ρ _CA (i−1) −sqrt {(X _u (i−1) −X ₁ (i−1)) ² + (Y _u (i−1) −Y ₁ (i−1)) ^{_{2 + (Z u (i-}} 1) -Z 1 (i-1)) 2} equation (1)
ρ _err = 1 / n × Σρ ′ _err equation (2)
In the above-described embodiment, the actually measured phase shift amount Δφ is derived as the phase shift amount Δφ. However, the phase shift is estimated based on the pseudorange derived by inertial navigation based on information from the INS sensor 26. The deviation amount Δφ may be derived. In this case, a code phase corresponding to the pseudoranges derived by inertial navigation, the difference between the code phase correlating peak value P _CA may be used as a phase shift amount Δφ speculative.

In the above-described embodiment, the second threshold range is set for the phase shift amount Δφ. Instead, the same second threshold range is set for a parameter substantially equivalent to the phase shift amount Δφ. May be set. For example, a similar second threshold range may be set for the above-described phase correction amount calculated based on the phase shift amount Δφ. A similar second threshold range may be set for the change rate of the phase shift amount Δφ (change amount of the phase shift amount Δφ per unit time). This utilizes the fact that the rate of change of the phase shift amount Δφ takes a large value when a multibus occurs. Further, the Doppler frequency change Delta] f _L, based on the speed of light c and the known carrier frequency _{f L} (1575.42 MHz), the relative speed [Delta] V between the GPS satellite 10 ₁ and the mobile 30, for example, Δf _L = ΔV · f with _L / _(c-ΔV) relationship, calculated for each observation cycle, from the pseudorange [rho _'CA, pseudorange change amount between observation cycle (amount of relative movement of the moving body 30 with respect to the GPS satellite 10 ₁ And equivalent to the time integral value of ΔV) is derived, and a pseudo distance ρ ″ _CA obtained by subtracting is derived, and the change amount or change rate of the pseudo distance ρ ″ _CA for each observation period (pseudo distance ρ ″ per unit time) against _CA amount of change) may be set the same second threshold range. in this case, the pseudorange [rho _"CA, instead of pseudorange [rho _{'CA, guess} pseudorange [rho by inertial navigation above May be derived using

Further, in the above embodiment, setting the first threshold range of similar for it are set the first threshold value range with respect to the correlation peak value P _CA, correlation peak value P _CA and substantially equivalent parameters May be. For example, it may be set a second threshold range of similar for the rate of change of the correlation peak value P _CA (change amount of the phase shift amount Δφ per unit time). This, for the rate of change of the correlation peak P _CA, in which multi-bus is utilized to be a large value when generated.

In the above-described embodiment, the presence / absence of multipath is determined by threshold determination for the correlation peak value _PCA and the phase shift amount Δφ. However, in combination with other multipath detection methods, multipath detection accuracy is improved. Is also possible. For example, in addition to the above threshold determination result, the vehicle position (or pseudorange) derived by inertial navigation based on information from the INS sensor 26 and the vehicle position (or pseudorange) derived by satellite navigation described above. When the difference is larger than a predetermined value, it may be determined that a multipath is detected. This utilizes the fact that the vehicle position derived by inertial navigation is not affected by multipath, unlike the vehicle position derived by satellite navigation described above.

In the above-described embodiment, as a preferred embodiment, the two-dimensional threshold region (first threshold range and second threshold range) is updated as appropriate. However, the first threshold range and the second threshold range are multipath. It may be a fixed value determined in advance based on observation data observed under no circumstances. In this case, the threshold range setting unit 140 may read and set the stored fixed value, and various inputs (correlation peak value _PCA and phase shift amount Δφ) to the threshold range setting unit 140 are unnecessary.

  In addition, as a preferable example, the process shown in FIG. 6 is performed based on observation data acquired during the time when three conditions (the conditions of steps 100, 110, and 120) are satisfied for a predetermined time. The dimension threshold region is updated. For example, if any one of the above-mentioned step 100 and the above-mentioned steps 110 and 120 or two conditions (combinations are arbitrary) are continuously satisfied for a predetermined time, they are acquired in the meantime. The two-dimensional threshold area may be updated based on the observed data.

Alternatively, other conditions may be added in addition to the three conditions (the conditions of the above steps 100, 110, and 120), or in addition to any one or two of these conditions. For example, even in a situation where multibus does not occur, the calculated pseudorange ρ ′ _CA or ρ _CA converges in consideration of the fact that the thermal noise is superimposed on the digital IF signal and the correlation value varies. It may be added as another condition. Whether or not the pseudo distance ρ ′ _CA or ρ _CA has converged is determined by substituting the pseudo distance ρ ″ _CA obtained by subtracting the pseudo distance variation between the observation periods from the pseudo distance ρ ′ _{CA for} each observation period. It may be determined based on whether or not the pseudo distance ρ ″ _CA is within a predetermined degree of variation.

  In the above-described embodiment, an example in which the present invention is applied to the GPS has been described. However, the present invention can also be applied to a satellite system below the GPS, for example, another GNSS (Global Navigation Satellite System) such as Galileo. is there.

Further, although the C / A code is used in the above-described embodiment, the present invention similarly determines the pseudorange ρ with respect to the GPS satellite 10 based on the P code of the L1 wave and / or the P code of the L2 wave. The present invention can also be applied to a configuration for calculation. In the case of a P code, since it is encrypted with a W code, when performing P code synchronization, the P code may be extracted by a DLL using a cross correlation method. Pseudorange [rho based on P-code _'P, by measuring whether M _P bit of P code as P code GPS satellite 10 ₁ is 0-th bit is received at the mobile station 30, [rho' It can be determined as _P = _MP × 30.

1 is a system configuration diagram showing an overall configuration of a GPS to which a satellite radio wave receiver according to the present invention is applied. FIG. 2 is a schematic system configuration diagram showing an embodiment of a satellite radio wave receiver mounted on the mobile station 30 of FIG. 1. It is a figure which shows the relationship between a world coordinate system and a local coordinate system, and the relationship between a local coordinate system and a body coordinate. 2 is a functional block diagram showing main functions of a signal processing circuit 100. FIG. It is a conceptual diagram for demonstrating the multipath detection method. 5 is a flowchart illustrating a threshold area update method realized by a threshold range setting unit 140.

Explanation of symbols

1 GPS receiver 10 GPS satellite 20 GPS antenna 22 High frequency circuit 24 A / D conversion circuit 26 INS sensor 28 Various sensors 29 Map DB
DESCRIPTION OF SYMBOLS 30 Mobile body 32 Calculation part 100 Signal processing circuit 119 Correlation peak value calculation part 140 Threshold range setting part 142 Judgment part 144 Multipath detection part 110 DDL
120 PLL
130 Filter 200 Positioning calculation circuit

Claims (4)

The pseudo-distance between the satellite and the mobile object is obtained by performing correlation value calculation using the replica pseudo-noise code generated internally for the pseudo-noise code carried on the radio wave from the satellite and performing code synchronization. A satellite radio receiver for a mobile object that calculates
A range derived based on actual measurement or estimation, and a range that can be taken by the correlation peak value in a situation where there is no multipath is set as the first threshold range, and the range derived based on actual measurement or estimation A threshold range setting means for setting a possible range of the phase shift amount of the code phase of the replica pseudo noise code with respect to the code phase of the pseudo noise code under the same condition as a second threshold range;
It is determined whether or not the correlation peak value calculated for the received satellite signal and the code phase shift amount are within the first threshold range and the second threshold range set by the threshold range setting means, respectively. Determination means to perform,
Multipath detection means for determining that multipath has occurred when it is determined that at least one of the calculated correlation peak value and code phase shift amount is not within the respective threshold ranges. A satellite radio wave receiver.   In the threshold range setting means, the first threshold range and the second threshold range are set based on a variance value of the correlation peak value calculated from past observation data and a variance value of the deviation amount of the code phase. The satellite radio wave receiver according to claim 1.   The variance value is calculated using observation data obtained when the moving object is located at a position where the number of observable satellites is equal to or greater than a predetermined value and the possibility of multipath occurrence is low, among past observation data. The satellite radio wave receiver according to claim 2.   The satellite radio wave receiver according to claim 3, wherein the position where the possibility of occurrence of multipath is low includes an open area where there is no surrounding building that may cause multipath.

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