JP5413118B2 - Positioning system - Google Patents

Description

  The present invention relates to a mobile positioning system using GNSS, and more particularly to a positioning system that can dispose of satellites used for positioning.

  A positioning method using GNSS (Global Navigation Satellite System) called GPS (US), Galileo (Europe), or Glonass (Russia) is known. In this positioning method, if the radio wave receiving device from the satellite can capture a predetermined number or more of the radio waves of the artificial satellites, sufficient accuracy can be obtained practically. However, the error included in the position of the receiving device measured by GNSS cannot be made zero with respect to the actual position of the receiving device (for example, a vehicle). For example, the receiving device can supplement about 10 satellites, but if radio waves received from many satellites are used for positioning, the error may increase. In particular, in an urban area, a multipath in which radio waves are reflected on a building tends to occur before the radio waves arrive at a receiving device from a satellite. When multipath occurs, a relatively large error is often included (for example, ˜100 m).

  Thus, a technique for reducing the influence of multipath has been considered (see, for example, Patent Document 1). Patent Document 1 compares the electric field strength of radio waves received by a right-hand polarized antenna and a left-hand polarized antenna for the purpose of reducing positioning position errors even in a multipath environment. A GNSS receiver that selects radio waves used for positioning is disclosed.

JP 2009-186415 A

  However, the technique disclosed in Patent Document 1 has a problem that the radio wave used for positioning cannot be selected by estimating the reliability of the received radio wave. For this reason, the GNSS receiver described in Patent Document 1 may actually discard radio waves even when a positioning position with little error is obtained.

  In view of the above problems, an object of the present invention is to provide a positioning system that improves the accuracy of a positioned position in consideration of the reliability of received radio waves.

In view of the above problems, the present invention provides an observation distance calculation means for calculating an observation distance between a vehicle and a satellite from an arrival time of radio waves received from the satellite, and a movement amount vector of the satellite for a predetermined time based on position information received from the satellite. Satellite movement vector estimation means for estimating the vehicle, gradient estimation means for estimating the gradient of the link on which the vehicle is traveling, and a vehicle movement vector for estimating the vehicle movement amount vector for a predetermined time from the vehicle movement direction and the gradient. An estimation unit; a distance change amount estimation unit that calculates a magnitude of a difference vector between the movement amount vector of the satellite and the movement amount vector of the vehicle; Obtain the amount of change in the observation distance over time, and compare it with the amount of change in the estimated distance to estimate the reliability of the radio wave received from the satellite, and the radio wave received from the satellite according to the reliability And management, to provide a positioning system and having a, a positioning means for estimating the position of the vehicle.

  In consideration of the reliability of the received radio wave, it is possible to provide a positioning system that improves the accuracy of the positioned position.

It is an example of the figure for demonstrating the outline of a positioning system. It is an example of the functional block diagram of a positioning system. It is an example of the figure which illustrates the gradient calculation method of the method 1 typically.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is an example of a diagram for explaining an outline of the positioning system 100 of the present embodiment. The features of the positioning system 100 of this embodiment are as follows.
(1) From the movement amount vector of the satellite 12 and the movement amount vector of the vehicle 11, the positioning system 100 estimates the amount of change in the pseudo distance between the satellite 12 and the vehicle 11.
(2) The positioning system 100 observes the observation distance between the satellite 12 and the vehicle 11.
(3) The amount of change in the pseudorange and the amount of change in the observation distance are compared, and the reliability of the radio wave received from the satellite 12 is estimated.

  As a result of the estimation, if the difference between the change amount of the pseudo distance and the change amount of the observation distance is large, the radio wave received from the satellite 12 is likely to be affected by the multipath, and the positioning system 100 is not used for positioning. . When the positioning system 100 receives a multipath radio wave, a position error equivalent to a multipath error (a time delay through which the radio wave passes through the multipath) is generated, depending on the arrangement of the satellites 12. Even if radio waves received from other satellites 12 do not pass through multipath, if there is at least one satellite 12 that has received radio waves via multipath, the position of vehicle 11 is greatly deviated from the true value. . Therefore, the position of the vehicle 11 can be determined with high accuracy by excluding the multipath from the positioning calculation.

FIG. 1 will be described in detail. The vehicle 11 travels on a link between the nodes N2 and N1 from the node N1 toward the node N2. The position of the vehicle 11 at time t is V _t , and the position of the vehicle 11 at time t + 1 is V _{t + 1} .

In the case of GPS, the satellite 12 orbits around the earth in about 12 hours over the altitude of about 20200 km. There are six orbits, and four or more satellites 12 orbit around each orbit, so that the positioning system 100 can always supplement four or more satellites 12 at any location on the earth. The position of the same satellite 12 at time t is _St , and the position at time t + 1 is _{St + 1} .

The time interval from time t to time t + 1 is not particularly limited, but it is a time that the vehicle 11 is traveling on the same link in order to obtain a three-dimensional movement amount vector of the vehicle 11 as will be described later. preferable. The movement amount vector of the satellite 12 from time t to time t + 1 is m _s , and the movement amount vector of the vehicle 11 is m _v .

  The vector e is a unit vector when the vehicle 11 is viewed from the satellite 12 (hereinafter referred to as a line-of-sight vector). Since the distance between the vehicle 11 and the satellite 12 is long, the line-of-sight vector e may not change in a short time. The size of the line-of-sight vector e is “1”.

  FIG. 2 shows an example of a functional block diagram of the positioning system 100. The positioning system 100 of this embodiment is mounted on, for example, a navigation device. Each functional block in FIG. 2 is realized by a CPU of a computer of the navigation apparatus executing a program or an IC circuit.

  The GNSS signal receiving unit 21 receives radio waves transmitted from the satellite 12. A GPS will be described as an example. The GNSS signal receiving unit 21 converts the received radio wave into digital data, and demodulates the C / A code by comparing with a C / A code unique to each satellite. Therefore, the positioning system 100 can specify the satellite 12 at this time. The C / A code includes navigation message data. In the case of GPS, navigation message data includes satellite clock correction data, ephemeris data, ionosphere correction parameters, UTC correction parameters, satellite 12 health information, almanac data, and the like. The almanac data is orbit information regarding all the satellites 12 in the orbit, and the ephemeris data includes accurate position information of each satellite 12 and time information when the signal is emitted.

The observation distance calculation unit 22 calculates an observation distance ρ between the vehicle 11 and the satellite 12. The observation distance calculation unit 22 synchronizes the time of the clock held for each satellite 12 and multiplies the time interval between the time information when the satellite 12 emits radio waves and the current time by the speed at which the radio waves reach the atmosphere. Thus, the observation distance ρ between the vehicle 11 and the satellite 12 is calculated. The observation distance at time t is ρ _t , and the observation distance at time t + 1 is ρ _{t + 1} .

The interval between time t and time t + 1 is predetermined (for example, 1 to several seconds). The observation distance calculation unit 22 calculates the observation distances ρ _t and ρ _{t + 1} between the vehicle 11 and the satellite 12 periodically or when the GNSS signal reception unit 21 supplements the new satellite 12, for example. Here, since the time t and the time t + 1 are used for the timing of calculating the movement vector m _s of the satellite 12 and the movement vector m _v of the vehicle 11, the observation distance calculator 22 calculates the observation distance ρ _t . The satellite position calculation unit 23, the satellite movement vector estimation unit 24, the gradient estimation unit 26, and the vehicle movement vector estimation unit 27 are notified of the calculated timing and the timing at which the observation distance ρ _{t + 1} is calculated.

The satellite position calculation unit 23 calculates the position of the satellite 12. Since the position information of the satellite 12 is included in the ephemeris data, the position information can be used as it is. The satellite position calculation unit 23 converts the position information into values applicable to the positioning system 100, such as converting the ephemeris data coordinate system (WGS-84) to the Japanese geodetic system. The position of the satellite 12 at time t is _St , and the position of the satellite 12 at time t + 1 is _{St + 1} .

The satellite movement vector estimation unit 24 estimates the movement amount vector m _s of the satellite 12 from the positions S _t and S _{t + 1} of the satellite 12. From the vector connecting the position S _{t + 1} the origin and the satellite 12 of a predetermined (e.g., Japanese geodetic system) coordinate system, a vector obtained by subtracting the vector connecting the position S _t of the origin and the satellite 12 is in movement quantity vector m _s of the satellite 12 is there.

  The positioning system 100 has a map DB (DataBase) 25. The map DB 25 stores road map information such as road networks and intersections in association with latitude and longitude. The map DB 25 is a table-like database in which nodes (points where roads and roads intersect, for example, intersections) corresponding to actual road networks are associated with links (roads connecting nodes and nodes). Note that the positioning system 100 may download a part or the whole of the map DB 25 from the server according to the position and the traveling direction of the vehicle 11.

The gradient estimation unit 26 estimates the gradient of the link on which the vehicle 11 is traveling. In this embodiment, the gradient can be calculated by two methods.
Method 1: A method of calculating from the acceleration acquired from the rotation of the wheel and the observation value of the acceleration sensor.
FIG. 3 is an example of a diagram schematically illustrating the gradient calculation method of Method 1. The vehicle 11 travels on a link having a gradient θ. The gradient estimation unit 26 calculates the acceleration _aw from the temporal change in the vehicle speed detected by the vehicle speed sensor. When the link has no gradient, the acceleration _aw and the acceleration a detected by the acceleration sensor are equal.

However, when the gradient θ is positive, the acceleration a decreases with the gradient θ (when the gradient θ is negative, the acceleration a increases with the gradient θ). The acceleration corresponding to this gradient θ is assumed to be g _x . Therefore, the following equation holds.
a = a _w −g _x
As shown in the figure, the acceleration g _x can be expressed as follows from the gravitational acceleration g and the gradient θ.
g _x = g · sin θ
Therefore, the acceleration a can be expressed as follows.
a = a _w −g · sin θ
Therefore, the gradient θ can be expressed by the following equation.
θ = arcsin {(a _w −a) / g}
Method 2: A method of accumulating altitude information of each node in the map DB 25 and calculating the link gradient using the altitude information of the end of the link.

  The gradient estimation unit 26 registers the altitude (that is, altitude information h) of the position information in the map DB 25 when the position information (three-dimensional) of the vehicle 11 is acquired at the node. This position information is the position calculated by the positioning calculation unit 32. Since the altitude information h has low accuracy, a plurality of N of altitude information h at the node are accumulated, and the gradient estimation unit 26 sets the average <h> as the altitude of the node.

なお、Ｎの数が少ない内は、平均＜ｈ＞の精度が低いおそれがあるので、Ｎは所定の閾値をこえてから勾配を求めてもよい。

Since the accuracy of the average <h> may be low when the number of N is small, the gradient may be obtained after N exceeds a predetermined threshold.

  Since the link length is registered in the map DB 25, the gradient estimation unit 26 calculates the gradient θ by dividing the difference in altitude between two nodes sandwiching the link by the link length. According to the method 2, the gradient θ can be obtained without an acceleration sensor, and the reliability of the satellite 12 can be determined. In addition, when using the altitude information registered in map DB25 for calculation of a gradient, the position of the vehicle 11 needs to be specified on the link.

Vehicle movement vector estimating unit 27 calculates a movement quantity vector m _v of the vehicle 11. The direction of the movement amount vector m _v can be obtained from the direction of the link registered in the map DB 25 and the gradient θ estimated by the gradient estimation unit 26. The amount of movement can be obtained from the vehicle speed or the movement distance detected by the vehicle speed sensor. Therefore, the movement amount vector m _v can be obtained without specifying the position V _t of the vehicle 11 at time _t and the position V _t + 1 of the vehicle 11 at time t + 1.

Incidentally, the direction of the links registered in the map DB 25, when used for the estimation of the movement quantity vector m _v, it is necessary to position of the vehicle 11 is identified on the link. The yaw angle detected by the yaw rate sensor may be used without using the link direction registered in the map DB 25.

  The line-of-sight vector estimation unit 29 estimates the line-of-sight vector e from the position of the satellite 12 and the approximate position of the vehicle 11. As described above, since the line-of-sight vector e does not change in a short time, the position of the vehicle 11 may be approximate (for example, the position finally measured by the positioning calculation unit 32). The line-of-sight vector estimation unit 29 calculates the line-of-sight vector e by subtracting a vector connecting the origin and the position of the satellite 12 from a vector connecting the origin of the coordinate system and the approximate position of the vehicle 11 to obtain a unit length.

The pseudo distance change estimation unit 28 estimates the pseudo distance change Δρ * from the movement vector m _s of the satellite 12, the movement vector m _v of the vehicle 11, and the line-of-sight vector e.

Δρ * = − (m _s −m _v ) · e (1)
Since the direction of (m _s −m _v ) and the line-of-sight vector e differ by approximately 180 degrees, the length of (m _s −m _v ) is obtained when the inner product of both is negative. The length of (m _s −m _v ) is the distance between the satellite 12 and the vehicle 11 at time t + 1 when the distance between the satellite 12 and the vehicle 11 at time t is used as a reference.

The satellite reliability calculation unit 31 calculates the reliability of the satellite ₁₂ from the observation distance change Δρ (= ρ _{t + 1} −ρ _t ) obtained from the observation distances ρ _t and ρ _{t + 1} and the pseudo distance change Δρ *. To do. The observation distances ρ _t and ρ _{t + 1} may include multipath effects, whereas the pseudo-range change Δρ * does not include multipath effects (the movement vector m _s of the satellite 12 is digital data). Calculated from the above). Therefore, when Δρ and Δρ * are significantly different, it can be estimated that the observation distance includes an error represented by a multipath.

The satellite reliability calculation unit 31 calculates the reliability r from the following equation, for example.
r = Δρ−Δρ * (2)
Note that the calculation method of the reliability r is an example, and “r = (Δρ−Δρ *) / Δρ *”, “r = Δρ / Δρ *”, “r = 1 / (Δρ−Δρ *)”, etc. Good.

  The positioning calculation unit 32 determines the reliability of the satellite 12 based on the reliability r, and measures the position of the vehicle 11. According to Equation (2), the greater the value, the lower the reliability. Therefore, for example, when the reliability r is greater than the threshold, the positioning calculation unit 32 does not use the radio wave received from the satellite 12 for positioning. In this case, the influence of the multipath on the position of the vehicle 11 can be made zero. Alternatively, the positioning calculation unit 32 may calculate the position of the vehicle 11 by giving a weight to the observation distance ρ calculated from the radio wave received from the satellite 12 according to the reliability r. In this case, the influence of the multipath on the position of the vehicle 11 can be reduced according to the degree of multipath.

  In addition, when the reliability r is larger than the threshold, the positioning calculation unit 32 does not use the radio wave received from the satellite 12 for positioning. When the reliability is equal to or less than the threshold, the positioning calculation unit 32 weights the observation distance ρ according to the reliability r. The position of the vehicle 11 may be calculated.

  The positioning calculation unit 32 excludes any satellites 12 to be excluded, and finally supplements four or more satellites 12 to calculate the distance to each satellite 12. Then, the position (latitude / longitude / altitude) of the vehicle 11 measured from the radio wave is determined by obtaining the intersection of the surfaces of three spheres centered on at least three satellites 12. If only three satellites 12 can be captured, the positioning calculation unit 32 calculates only the latitude and longitude.

  According to the positioning system 100 of the present embodiment, radio waves received by multipath are not used for positioning calculation or the influence can be reduced, so that the accuracy of the position of the vehicle 11 can be improved.

21 GNSS signal reception unit 22 Observation distance calculation unit 23 Satellite position calculation unit 24 Satellite movement vector estimation unit 25 Map DB
26 Gradient estimation unit 27 Vehicle movement vector estimation unit 28 Pseudo distance change estimation unit 29 Gaze vector estimation unit 31 Satellite reliability calculation unit 32 Positioning calculation unit 100 Positioning system

Claims (1)

Observation distance calculation means for calculating the observation distance between the vehicle and the satellite from the arrival time of the radio wave received from the satellite,
Satellite movement vector estimation means for estimating a movement vector of a satellite for a predetermined time based on position information received from the satellite;
Gradient estimation means for estimating the gradient of the link on which the vehicle is traveling;
Vehicle movement vector estimation means for estimating a movement vector of the vehicle for the predetermined time from the vehicle movement direction and the gradient;
A distance change amount estimation means for calculating a magnitude of a difference vector between the movement amount vector of the satellite and the movement amount vector of the vehicle, and estimating an amount of change in the estimated distance between the satellite and the vehicle;
A reliability estimation means for obtaining a variation in the observation distance for the predetermined time and estimating a reliability of radio waves received from a satellite in comparison with the variation in the estimated distance;
And positioning means for processing radio waves received from a satellite according to the reliability and estimating a position of the vehicle.

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