WO2010073113A1

WO2010073113A1 - Gnss receiver and positioning method

Info

Publication number: WO2010073113A1
Application number: PCT/IB2009/007881
Authority: WO
Inventors: Naoto Hasegawa; Hideaki Tampo
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2008-12-26
Filing date: 2009-12-23
Publication date: 2010-07-01
Also published as: WO2010073113A8; JP2010151725A

Abstract

A GNSS receiver includes an observation data computation portion (104) that obtains observation data; a position calculation portion (108) that calculates a position of the GNSS satellite; a position estimation portion (112) that estimates a position of the GNSS receiver, based on information other than a positioning signal; an observation data estimation portion (114) that estimates the observation data, based on the calculated position of the GNSS satellite, and the estimated position of the GNSS receiver; a receiver error estimation portion (118) that estimates a receiver error; an observation data error estimation portion (106) that estimates a common error in the observation data, based on the estimated receiver error, and estimates an error in the observation data, based on the observation data, the estimated observation data, and the common error; and a positioning computation portion (116) that performs the positioning computation using the observation data whose error is equal to or smaller than a predetermined threshold value.

Description

GNSS RECEIVER AND POSITIONING METHOD

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a GNSS receiver and a positioning method, which determine a position and a velocity by receiving signals from orbiting satellites for GNSS.

2. Description of the Related Art

[0002] A Global Navigation Satellite System (GNSS) is a navigation system in which three navigation satellites (i.e., orbiting satellites for GNSS) (hereinafter, referred to as "GNSS satellites") are acquired by a GNSS receiver provided in an airplane to determine ranges from the GNSS satellites, and a clock time is set using a signal from the fourth GNSS satellite. Thus, the three-dimensional position of the flying airplane is determined. The GNSS includes a Global Positioning system (GPS), GALILEO, and Glonass.

[0003] For example, the GNSS receiver is provided in a movable object, and determines the position and velocity of the movable object. For example, the GNSS receiver determines ranges (pseudoranges) from the plurality of GNSS satellites to the GNSS receiver by receiving radio waves from the plurality of GNSS satellites. Thus, the GNSS receiver performs positioning, that is, determines the position and velocity of the movable object in which the GNSS receiver is provided, based on the determined pseudoranges. The signal emitted from the GNSS satellite reaches the GNSS receiver at a time point later than a time point at which the signal is emitted by a time required to transmit the radio wave from the GNSS satellite to the GNSS receiver. Accordingly, by determining the times required to transmit the radio waves from the plurality of GNSS satellites to the GNSS receiver, it is possible to determine the position of the GNSS receiver by positioning computation. For example, a range determination portion of the GNSS receiver determines the ranges (pseudoranges) from the GNSS satellites to the GNSS receiver using the radio waves emitted from the GNSS satellites. A positioning computation portion determines the position of the GNSS receiver, based on the ranges determined by the range determination portion.

[0004] The GNSS receiver may receive a reflected wave that reaches the GNSS receiver after reflected from a building or the like, in addition to a direct wave that reaches the GNSS receiver through a path that connects the GNSS satellite directly to the GNSS receiver. The phenomenon, in which the radio wave emitted from the GNSS satellite reaches the GNSS receiver through two or more paths, is referred to as "multipath phenomenon". When the GNSS receiver determines the pseudorange based on the reflected wave instead of the direct wave, an error in the pseudorange is larger than an error in the pseudorange determined based on the direct wave, because it takes longer time for the reflected wave to reach the GNSS receiver than for the direct wave to reach the GNSS receiver.

[0005] For example, in a GPS receiver, a correlation between a signal received from a GPS satellite and a replica signal is determined, and the pseudorange is determined based on the position of a correlation peak. When the pseudoranges are determined based on the signals received from a plurality of GPS satellites in the multipath environment, correlation values between the received signals and the replica signals greatly vary, because the received signals include the reflected waves. Because the correlation values between the received signals and the replica signals greatly vary, the pseudoranges greatly vary. As a result, an error in the positioning result is large. [0006] For example, Japanese Patent Application Publication No.

2001-264409 (JP-A-2001-264409) describes a method in which a positioning computation is performed using only signals from satellites corresponding to Doppler shift amounts that are different from estimated Doppler shift amounts by values smaller than a threshold value. The estimated Doppler shift amounts are calculated by a so-called Inertial Navigation System (INS) using outputs from a gyro sensor, a vehicle speed sensor, and the like.

[0007] The GNSS receiver obtains various data, such as outputs from the gyro sensor and the vehicle speed sensor. However, the precisions of the obtained data are not determined. If observation data with low precisions are used in the positioning computation, the precision of the result obtained by the positioning computation is low (i.e., the precisions of the determined position and the determined velocity are low)

SUMMARY OF THE INVENTION

[0008] The invention provides a GNSS receiver and a positioning method, which improves positioning accuracy.

[0009] A first aspect of the invention relates to a Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on a positioning signal transmitted from a GNSS satellite. The GNSS receiver includes an observation data computation portion that obtains observation data to be observed by the GNSS receiver, using a code included in the positioning signal transmitted from the GNSS satellite; a position calculation portion that calculates a position of the GNSS satellite, based on orbit information included in the positioning signal transmitted from the GNSS satellite; a position estimation portion that estimates a position of the GNSS receiver, based on information other than the positioning signal; an observation data estimation portion that estimates the observation data, based on the position of the GNSS satellite calculated by the position calculation portion, and the position of the GNSS receiver estimated by the position estimation portion; a receiver error estimation portion that estimates a receiver error that is an error in the GNSS receiver; an observation data error estimation portion that estimates a common error in the observation data due to the receiver error, based on the estimated receiver error that is estimated by the receiver error estimation portion, and estimates an error in the observation data, based on the observation data obtained by the observation data computation portion, the estimated observation data that is estimated by the observation data estimation portion, and the common error; and a positioning computation portion that performs the positioning computation using the observation data whose error is equal to or smaller than a predetermined threshold value.

[0010] In the above-described aspect, the position calculation portion may calculate the position and velocity of the GNSS satellite, based on the orbit information included in the positioning signal transmitted from the GNSS satellite; the position estimation portion may estimate the position and velocity of the GNSS receiver, based on the information other than the positioning signal; and the observation data estimation portion may estimate the observation data, based on the position and velocity of the GNSS satellite calculated by the position calculation portion, and the position and velocity of the GNSS receiver estimated by the position estimation portion. [0011] In the above-described aspect, the observation data may include at least one of a pseudorange, a rate of change in the pseudorange, and an amount of change in the pseudorange.

[0012] In the above-described aspect, the receiver error estimation portion may estimate the error in the observation data based on a previous error in the observation data, and may correct the estimated error in the observation data based on a result of the positioning computation performed by the positioning computation portion.

[0013] In the above-described aspect, the receiver error estimation portion may correct the error in the observation data, based on an error and a differential value of the error calculated based on results of a position computation and a velocity computation performed by the positioning computation portion.

[0014] In the above-described aspect, the receiver error estimation portion may estimate the receiver error based on a previous receiver error, and may correct the estimated receiver error based on a result of the positioning computation performed by the positioning computation portion.

[0015] In the above-described aspect, the receiver error estimation portion may estimate the receiver error and a differential value of the receiver error, and may correct the estimated receiver error based on results of a position computation and a velocity computation performed by the positioning computation portion.

[0016] In the above-described aspect, the receiver error may include a clock error.

[0017] In the above-described aspect, the information other than the positioning signal may include information from at least one of an acceleration sensor, an angular acceleration sensor, and a geomagnetic sensor; and the position estimation portion may estimate the position of the GNSS receiver by inertial navigation.

[0018] The GNSS receiver according to the above-described aspect may further include a map database, and the position estimation portion may estimate the position of the GNSS receiver by performing map-matching using the map database.

[0019] A second aspect of the invention relates to a Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on positioning signals transmitted from a plurality of GNSS satellites. The GNSS receiver includes an observation data computation portion that obtains observation data relating to each of the GNSS satellites, using a code included in the positioning signal transmitted from the corresponding GNSS satellite; a position calculation portion that calculates a position of each of the GNSS satellites, based on orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; a position estimation portion that estimates a position of the GNSS receiver, based on information other than the positioning signals; an observation data estimation portion that estimates the observation data relating to each of the GNSS satellites, based on the position of the corresponding GNSS satellite calculated by the position calculation portion, and the position of the GNSS receiver estimated by the position estimation portion; a receiver error estimation portion that estimates a receiver error that is an error in the GNSS receiver; an observation data error estimation portion that estimates a common error in the observation data due to the receiver error, based on the estimated receiver error that is estimated by the receiver error estimation portion, and estimates an error in the observation data, based on the observation data obtained by the observation data computation portion, the estimated observation data that is estimated by the observation data estimation portion, and the common error, wherein the observation data error estimation portion selects combinations of the GNSS satellites acquired by the GNSS receiver; the observation data error estimation portion estimates a positioning error that is to occur when the positioning computation is performed using each of the selected combinations of the GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites, and arrangement of the GNSS satellites; and the observation data error estimation portion selects the GNSS satellites to be used in the positioning computation, based on at least one of i) the estimated errors in the observation data relating to the GNSS satellites and ii) the estimated positioning errors relating to the selected combinations of the GNSS satellites; and a positioning computation portion that performs the positioning computation using the GNSS satellites selected by the observation data error estimation portion. [0020] A third aspect of the invention relates to a Global Navigation

Satellite System (GNSS) receiver that performs a positioning computation based on positioning signals transmitted from a plurality of GNSS satellites. The GNSS receiver includes an observation data computation portion that obtains observation data relating to each of the GNSS satellites, using a code included in the positioning signal transmitted from the corresponding GNSS satellite; a position calculation portion that calculates a position of each of the GNSS satellites, based on orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; a position estimation portion that estimates a position of the GNSS receiver, based on information other than the positioning signals; an observation data estimation portion that estimates the observation data relating to each of the GNSS satellites, based on the position of the corresponding GNSS satellite calculated by the position calculation portion, and the position of the GNSS receiver estimated by the position estimation portion; an observation data precision estimation portion that estimates a precision of the observation data relating to each of the GNSS satellites, based on the observation data obtained by the observation data computation portion and the corresponding estimated observation data that is estimated by the observation data estimation portion, wherein the observation data precision estimation portion selects combinations of the observation data with precisions equal to or higher than a first predetermined threshold value, calculates a Dilution of Precision (DOP) value relating to each of the selected combinations, selects at least one combination of the observation data based on the calculated DOP values, calculates a Horizontal Dilution of Precision (HDOP) value relating to each of the at least one combination selected based on the calculated DOP values, and selects the combination of the observation data corresponding to a smallest HDOP value; and a positioning computation portion that performs the positioning computation using the combination of the observation data corresponding to the smallest HDOP value.

[0021] A fourth aspect of the invention relates to a positioning method in a Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on a positioning signal transmitted from a GNSS satellite. The positioning method includes obtaining observation data to be observed by the GNSS receiver, using a code included in the positioning signal transmitted from the GNSS satellite; calculating a position of the GNSS satellite, based on orbit information included in the positioning signal transmitted from the GNSS satellite; estimating a position of the GNSS receiver, based on information other than the positioning signal; estimating the observation data, based on the calculated position of the GNSS satellite, and the estimated position of the GNSS receiver; estimating a receiver error that is an error in the GNSS receiver; estimating a common error in the observation data due to the receiver error, based on the estimated receiver error, and estimating an error in the observation data, based on the observation data, the estimated observation data, and the common error; and performing the positioning computation using the observation data whose error is equal to or smaller than a predetermined threshold value. [0022] A fifth aspect of the invention relates to a positioning method in a

Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on positioning signals transmitted from a plurality of GNSS satellites. The positioning method includes obtaining observation data relating to each of the GNSS satellites, using a code included in the positioning signal transmitted from the corresponding GNSS satellite; calculating a position of each of the GNSS satellites, based on orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; estimating a position of the GNSS receiver, based on information other than the positioning signals; estimating the observation data relating to each of the GNSS satellites, based on the calculated position of the corresponding GNSS satellite, and the estimated position of the GNSS receiver; estimating a receiver error that is an error in the GNSS receiver; estimating a common error in the observation data due to the receiver error, based on the estimated receiver error, and estimating an error in the observation data, based on the observation data, the estimated observation data, and the common error; selecting combinations of the GNSS satellites acquired by the GNSS receiver; estimating a positioning error that is to occur when the positioning computation is performed using each of the selected combinations of the GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites, and arrangement of the GNSS satellites; selecting the GNSS satellites to be used in the positioning computation, based on at least one of i) the estimated errors in the observation data relating to the GNSS satellites and ii) the estimated positioning errors relating to the selected combinations of the GNSS satellites; and performing the positioning computation using the selected GNSS satellites.

[0023] A sixth aspect of the invention relates to a positioning method in a Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on positioning signals transmitted from a plurality of GNSS satellites. The positioning method includes obtaining observation data relating to each of the GNSS satellites, using a code included in the positioning signal transmitted from the corresponding GNSS satellite; calculating a position of each of the GNSS satellites, based on orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; estimating a position of the GNSS receiver, based on information other than the positioning signals; estimating the observation data relating to each of the GNSS satellites, based on the calculated position of the corresponding GNSS satellite, and the estimated position of the GNSS receiver; estimating a precision of the observation data relating to each of the GNSS satellites, based on the observation data and the corresponding estimated observation data; selecting combinations of the observation data with precisions equal to or higher than a first predetermined threshold value; calculating a Dilution of Precision (DOP) value relating to each of the selected combinations; selecting at least one combination of the observation data based on the calculated DOP values; calculating a Horizontal Dilution of Precision (HDOP) value relating to each of the at least one combination selected based on the calculated DOP values; selecting the combination of the observation data corresponding to a smallest HDOP value; and performing the positioning computation using the combination of the observation data corresponding to the smallest HDOP value.

[0024] The GNSS receiver and the positioning method according to the above-described aspects improve the positioning accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: FIG. 1 is a functional block diagram of a GNSS receiver according to a first embodiment of the invention;

FIG. 2 is a flowchart showing operation of the GNSS receiver according to the first embodiment of the invention; FIG. 3 is a flowchart showing the operation of the GNSS receiver according to the first embodiment of the invention;

FIG. 4 is a flowchart showing the operation of the GNSS receiver according to the first embodiment of the invention;

FIG. 5 is a flowchart showing operation of a GNSS receiver according to a second embodiment of the invention;

FIG. 6 is a flowchart showing the operation of the GNSS receiver according to the second embodiment of the invention;

FIG. 7 is a flowchart showing the operation of the GNSS receiver according to the second embodiment of the invention; FIG. 8 is a flowchart showing the operation of the GNSS receiver according to the second embodiment of the invention;

FIG. 9 is a flowchart showing operation of a GNSS receiver according to a fourth embodiment of the invention;

FIG. 10 is a functional block diagram of a GNSS receiver according to a sixth embodiment of the invention;

FIGS. 11 A and 11 B show a functional block diagram of the GNSS receiver according to the sixth embodiment of the invention;

FIG. 12 is a flowchart showing operation of the GNSS receiver according to the sixth embodiment of the invention; FIG. 13 is a flowchart showing the operation of the GNSS receiver according to the sixth embodiment of the invention;

FIG. 14 is a flowchart showing the operation of the GNSS receiver according to the sixth embodiment of the invention;

FIG. 15 is a flowchart showing the operation of the GNSS receiver according to the sixth embodiment of the invention;

FIG. 16 is a flowchart showing the operation of the GNSS receiver according to the sixth embodiment of the invention; and

FIG. 17 is a flowchart showing the operation of the GNSS receiver according to the sixth embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0026] Embodiments of the invention will be described with reference to the drawings. [0027] In all the drawings illustrating the embodiments, portions having the same function are denoted by the same reference numeral, and the repeated description thereof will be omitted. [First embodiment] [System] [0028] A Global Navigation Satellite System (GNSS) includes GNSS satellites that revolve around the Earth, and a GNSS receiver 100 that is positioned on the Earth, and moves on the Earth. In the embodiment, a Global Positioning System (GPS) will be described as an example of the GNSS system. However, the invention may be applied to Global Navigation Satellite Systems other than the GPS. [0029] Each of the GNSS satellites constantly broadcasts a navigation message (i.e., a satellite signal) to the Earth. The navigation message includes orbit information on the orbit of the corresponding GNSS satellite (i.e., Ephemeris and Almanac), a clock correction value, and an ionospheric correction coefficient. The navigation message is spread using a coarse/acquisition code (i.e., C/A code), and is carried on a Ll carrier (frequency: 1575.42 MHz). Thus, the navigation message is constantly broadcast toward the Earth. The Ll carrier is a composite wave of a sine wave modulated by the C/A code and a cosine wave modulated by a Precision code (i.e., P code), and is a quadrature-modulated wave. Each of the C/A code and the P code is a pseudo noise code, and is a code string in which -1 and 1 are arranged irregularly and periodically.

[0030] The twenty-four GPS satellites revolve around the Earth at an altitude of approximately 20,000 km in the sky. The four GPS satellites are evenly disposed on each of six orbital planes around the Earth. The orbital planes are inclined by 55 degrees relative to each other. Accordingly, at least five GPS satellites are constantly observed at any place on the Earth as long as the place is open to the sky.

[0031] The GNSS receiver 100 is provided in, for example, a movable object. Examples of the movable object include a vehicle, a two-wheeled motor vehicle, a train, a ship, an airplane, a robot, and an information terminal that is moved by movement of a human, such as a mobile terminal.

[0032] Observation data obtained by the GNSS receiver 100 includes various errors. However, in the GNSS receiver 100, the errors cannot be completely removed. Accordingly, the precision of a positioning result decreases. Particularly, the error due to the multipath phenomenon may be extremely large, for example, approximately 100 m. [GNSS receiver]

[0033] The GNSS receiver 100 according to the embodiment estimates the position and velocity of the GNSS receiver 100 based on data other than observation data obtained from the radio waves transmitted from the GNSS satellites. Then, the GNSS receiver 100 estimates the observation data to be obtained from the radio wave transmitted from the GNSS satellite, based on the estimated position and estimated velocity of the GNSS receiver 100 and the position and velocity of the

GNSS satellite obtained from the positioning signal transmitted from the GNSS satellite. Then, the GNSS receiver 100 determines the precision of the observation data based on the observation data and the estimated observation data.

[0034] When the GNSS receiver 100 determines the precision of the observation data, the GNSS receiver 100 estimates an error that is inevitably included in the observation data due to the characteristics of the GNSS receiver 100 (hereinafter, the error will be referred to as "a common error"). By estimating the common error, it is possible to improve the accuracy of estimating the error in the observation data.

[0035] The GNSS receiver 100 performs a positioning computation using the GNSS satellites other than the GNSS satellite corresponding to the observation data with a low precision. By performing the positioning computation using the

GNSS satellites other than the GNSS satellite corresponding to the observation data with a low precision, it is possible to improve the precision of the positioning result.

[0036] The observation data includes, for example, a pseudorange, a Doppler frequency, and an Accumulated Doppler Range (ADR). It is possible to obtain the pseudorange, the Doppler frequency, and the Accumulated Doppler Range (ADR) relating to each satellite acquired by the GNSS receiver 100. The observation data may include other data.

[0037] FIG. 1 shows the GNSS receiver according to the embodiment. [0038] The GNSS receiver 100 includes an antenna 102, a positioning signal receiving portion 104 (that may be regarded as the observation data computation portion according to the invention), an observation data precision determination portion 106 (that may be regarded as the observation data error estimation portion and the observation data precision determination portion according to the invention), a satellite position velocity calculation portion 108 (that may be regarded as the position calculation portion according to the invention), sensors 1 10, a receiver position velocity estimation portion 112 (that may be regarded as the position estimation portion according to the invention), an observation data estimation portion 114 (that may be regarded as the observation data estimation portion according to the invention), a positioning computation portion 116 (that may be regarded as the positioning computation portion according to the invention), and a receiver clock error estimation portion 118 (that may be regarded as the receiver error estimation portion according to the invention).

[0039] The antenna 102 receives the radio waves from GNSS satellites 50 (501 and 5O₂). Although FIG. 2 shows the two GNSS satellites, the positioning computation is generally performed based on the positioning signals transmitted from four or more GNSS satellites.

[0040] The positioning signal receiving portion 104 is connected to the antenna 102. The positioning signal receiving portion 104 receives the positioning signals from the GNSS satellites 50 via the antenna 102. The positioning signal receiving portion 104 extracts the navigation message using a C/A code generated in the positioning signal receiving portion 104. More specifically, the positioning signal receiving portion 104 synchronizes a replica C/A code signal with the C/A code in the Ll band by shifting the phase of the replica C/A code signal with respect to the phase of the C/A code in the Ll band. Thus, the positioning signal receiving portion 104 extracts the navigation message. The positioning signal receiving portion 104 extracts the orbit information on the orbit of the satellite included in the navigation message. For example, the replica C/A code may be synchronized with the received C/A code by tracking the phase at which a correlation value between the replica C/A code and the received C/A code is the maximum value (i.e., a peak value), using a Delay-Locked Loop (DLL). The positioning signal receiving portion 104 inputs the information on the orbit, which has been extracted, to the satellite position velocity calculation portion 108. [0041] Also, the positioning signal receiving portion 104 inputs the observation data to the observation data precision determination portion 106. For example, the observation data may include the pseudorange, the Doppler frequency, and the ADR. The positioning signal receiving portion 104 tracks the radio wave transmitted from each of the acquired GNSS satellites by tracking the code phase at which the correlation value between the replica C/A code signal and the received C/A code is the maximum value. The positioning signal receiving portion 104 calculates the pseudorange based on the result of the correlation process. The positioning signal receiving portion 104 may output, as the pseudorange, the code phase at which the correlation value between the replica C/A code signal and the received C/A code is the maximum value.

[0042J Also, the positioning signal receiving portion 104 determines a rate of change in the pseudorange (hereinafter, referred to as "pseudorange change rate").

The pseudorange change rate corresponds to the Doppler frequency of the carrier that carries the positioning signal. The pseudorange change rate is used to calculate the velocity at which the GNSS receiver 100 moves.

[0043] Also, the positioning signal receiving portion 104 calculates the Accumulated Doppler Range (ADR). The positioning signal receiving portion 104 may calculate the ADR by determining the amount of change in the pseudorange, or may calculate the ADR by integrating the Doppler frequency. The ADR is mainly used to smooth the pseudorange, and to calculate the amount of movement. The positioning signal receiving portion 104 inputs the pseudorange, the pseudorange change rate, and the ADR, to the observation data precision determination portion 106. [0044] The satellite position velocity calculation portion 108 is connected to the positioning signal receiving portion 104. The satellite position velocity calculation portion 108 calculates a current position of the GNSS receiver 100 in a world coordinate system, based on the information on the orbit, which is input to the satellite position velocity calculation portion 108 by the positioning signal receiving portion 104. Because the GNSS satellite is one of man-made satellites, the movement of the GNSS satellite is confined to a certain plane (orbital plane) that includes the gravity center of the Earth. The orbit of the GNSS satellite is an ellipse with one focus at the gravity center of the Earth. The position of the GNSS satellite in the orbital plane is calculated by sequential numerical solution of the Kepler's equation. Also, the position of the GNSS satellite is determined by three-dimensional rotational coordinate transformation of the position of the GNSS satellite in the orbital plane, taking into account that there is a rotational relation between the orbital plane of the GNSS satellite and the equatorial plane in the world coordinate system. In the world coordinate system, the gravity center of the Earth is an original point. The world coordinate system is defined by an X-axis and a Y-axis that are orthogonal to each other in the equatorial plane, and a Z-axis that is orthogonal to the X-axis and the Y-axis. The satellite position velocity calculation portion 108 derives the movement velocity of the GNSS satellite, based on the position of the GNSS satellite. The satellite position velocity calculation portion 108 inputs the position and movement velocity of the GNSS satellite, to the observation data estimation portion 114.

[0045] The sensors 110 input information other than the GNSS information obtained by the GNSS, to the receiver position velocity estimation portion 112. The sensors 110 include, for example, an acceleration sensor, an angular acceleration sensor, a geomagnetic sensor (a direction sensor). The sensors 110 may obtain data required to determine the position of the GNSS receiver 100 without using the radio waves transmitted from the GNSS satellites 50. For example, the sensors 110 input, to the receiver position velocity estimation portion 112, acceleration detected by the acceleration sensor, angular acceleration detected by the angular acceleration sensor, and a direction detected by the geomagnetic sensor.

[0046] The receiver position velocity estimation portion 112 estimates the position and velocity of the GNSS receiver 100, based on the information input to the receiver position velocity estimation portion 112 by the sensors 110. The receiver position velocity estimation portion 112 may determine the velocity of the GNSS receiver 100 by integrating the acceleration detected by the acceleration sensor, and may determine the movement distance of the GNSS receiver 100 by integrating the velocity. The receiver position velocity estimation portion 112 may be an inertial navigation device. The receiver position velocity estimation portion 112 may perform map-matching using the movement velocity and the direction detected by the geomagnetic sensor. When the map-matching is performed, map data is input to the receiver position velocity estimation portion 112. The receiver position velocity estimation portion 112 inputs the estimated position and estimated velocity of the GNSS receiver 100, to the observation data estimation portion 114.

[0047] The observation data estimation portion 114 is connected to the satellite position velocity calculation portion 108 and the receiver position velocity estimation portion 112. The observation data estimation portion 114 estimates the observation data, based on the position and velocity of the satellite input to the observation data estimation portion 114 by the satellite position velocity calculation portion 108, and the estimated position and estimated velocity of the GNSS receiver 100 estimated by the receiver position velocity estimation portion 112.

[0048] The observation data estimation portion 114 estimates the pseudorange based on the position of each GNSS satellite 50 and the position of the GNSS receiver 100. Also, the observation data estimation portion 114 calculates the pseudorange change rate. The observation data estimation portion 114 calculates the ADR by integrating the pseudorange change rate. The observation data estimation portion 114 inputs the estimated observation data to the observation data precision determination portion 106.

[0049] The observation data precision determination portion 106 is connected to the positioning signal receiving portion 104 and the observation data estimation portion 114. The observation data precision determination portion 106 determines the precision of the observation data, based on the observation data input to the observation data precision determination portion 106 by the positioning signal receiving portion 104, and the estimated observation data input to the observation data precision determination portion 106 by the observation data estimation portion 114. More specifically, the observation data precision determination portion 106 estimates the error in the observation data. The observation data precision determination portion 106 may estimate the error in the observation data by removing the estimated observation data and the common error from the observation data. The common error may be an error which is caused due to a clock error in the GNSS receiver 100, and which is commonly included in any observation data. If the error in the observation data is smaller than a predetermined threshold value, the observation data precision determination portion 106 inputs the observation data to the positioning computation portion 116. If the error in the observation data is equal to or larger than the predetermined threshold value, the observation data precision determination portion 106 does not input the observation data to the positioning computation portion 116.

[0050] The positioning computation portion 116 is connected to the observation data precision determination portion 106. The positioning computation portion 116 performs the positioning computation using the observation data input to the positioning computation portion 116 by the observation data precision determination portion 106. For example, the observation data precision determination portion 106 inputs the pseudorange with a high precision to the positioning computation portion 116. The positioning computation portion 116 may derive the position of the GNSS receiver 100 according to the principle of the triangulation, using the pseudoranges to the three GNSS satellites 50 and the positions of the three GNSS satellites 50. In this case, the clock error component may be removed using the pseudorange to the fourth GNSS satellite 50 and the position of the fourth GNSS satellite 50. The positioning computation portion 116 derives the movement velocity of the GNSS receiver 100 by determining the rate of change in the position of the GNSS receiver 100 based on the derived position of the GNSS receiver 100. The positioning computation portion 116 outputs the derived position and derived movement velocity of the GNSS receiver 100. The positioning computation portion 116 inputs the derived position and derived movement velocity of the GNSS receiver 100, to the receiver clock error estimation portion 118. [0051] The method of determining the position of the GNSS receiver 100 is not limited to the point positioning method. As the method of determining the position of the GNSS receiver 100, an interferometric positioning method (i.e., a method in which data received at a fixed station installed at a known point is also used) may be employed. In the interferometric positioning method, the position of the GNSS receiver 100 is determined using, for example, a single difference or a double difference between the pseudoranges obtained at the fixed station and the GNSS receiver 100.

[0052] The receiver clock error estimation portion 118 is connected to the positioning computation portion 116 and the observation data precision determination portion 106. The receiver clock error estimation portion 118 estimates the clock error in the GNSS receiver 100. For example, the receiver clock error estimation portion 118 estimates the clock error in the GNSS receiver 100 and the differential value of the clock error, using a previous clock error that is determined in an immediately preceding routine, and a Kalman filter. It may be necessary to add a bias term, depending on the GNSS receiver 100. As the Kalman filter, a first-order Markov model for the differential value of the receiver clock error may be used. The receiver clock error estimation portion 118 inputs the estimated receiver clock error to the observation data precision determination portion 106. [0053] The case, in which when the precision of the observation data is determined in the GNSS receiver 100, the clock error is estimated as an example of the common error that is inevitably included in the observation data due to the characteristics of the GNSS receiver 100, will be described. However, errors other than the clock error may be estimated. [Positioning method]

[0054] FIG. 2 shows a positioning method in the GNSS receiver 100 according to the embodiment.

[0055] The GNSS receiver 100 estimates the receiver clock error using the model and the previous clock error (step S202). More specifically, the receiver clock error estimation portion 118 estimates the receiver clock error and the differential value of the receiver clock error, using the previous receiver clock error and the Kalman filter. The receiver clock error estimation portion 118 inputs the estimated receiver clock error to the observation data precision determination portion 106. [0056] The GNSS receiver 100 performs a position computation (step S204). The observation data precision determination portion 106 determines a common error in the pseudorange due to the receiver clock error, based on the estimated receiver clock error input to the observation data precision determination portion 106 by the receiver clock error estimation portion 118. Then, the observation data precision determination portion 106 estimates an error in the pseudorange (hereinafter, may be referred to as "pseudorange error") by removing an estimated pseudorange included in the estimated observation data input to the observation data precision determination portion 106 by the observation data estimation portion 114 and the common error in the pseudorange due to the receiver clock error, from the pseudorange included in the observation data input to the observation data precision determination portion 106 by the positioning signal receiving portion 104. If the estimated pseudorange error is smaller than a predetermined threshold value, the observation data precision determination portion 106 determines that the pseudorange is usable for the positioning computation. The observation data precision determination portion 106 inputs the pseudorange, which is determined to be usable for the positioning computation, to the positioning computation portion 116. The positioning computation portion 116 performs the position computation using the pseudorange input to the positioning computation portion 116 by the observation data precision determination portion 106.

[0057] The GNSS receiver 100 performs a velocity computation (step S206). The observation data precision determination portion 106 determines a common error in the pseudorange change rate due to the receiver clock error, based on the estimated receiver clock error input to the observation data precision determination portion 106 by the receiver clock error estimation portion 118. The observation data precision determination portion 106 estimates an error in the pseudorange change rate (hereinafter, may be referred to as "pseudorange change rate error") by removing the estimated pseudorange change rate included in the estimated observation data input to the observation data precision determination portion 106 by the observation data estimation portion 114 and the common error in the pseudorange change rate due to the receiver clock error, from the pseudorange change rate included in the observation data input to the observation data precision determination portion 106 by the positioning signal receiving portion 104. If the estimated pseudorange change rate error is smaller than a predetermined threshold value, the observation data precision determination portion 106 determines that the pseudorange change rate is usable for the velocity computation. The observation data precision determination portion 106 inputs the pseudorange change rate, which is determined to be usable for the positioning computation, to the positioning computation portion 116. The positioning computation portion 116 performs the velocity computation using the pseudorange change rate input to the positioning computation portion 116 by the observation data precision determination portion 106.

[0058] The GNSS receiver 100 estimates the receiver clock error using the model and the previous clock error (step S208). The receiver clock error estimation portion 118 corrects the estimated receiver clock error, based on the position and the velocity determined by the positioning computation portion 116.

[0059] FIG. 3 shows a position computation method in the GNSS receiver 100 according to the embodiment. [0060] Step S304 to step S310 are steps in a loop (step S302 and step

S312) performed for each of the acquired GNSS satellites.

[0061] The GNSS receiver 100 estimates the pseudorange error (step S304). The observation data precision determination portion 106 determines a common error "s" in the pseudorange due to the receiver clock error, based on the estimated receiver clock error input to the observation data precision determination portion 106 by the receiver clock error estimation portion 118. The observation data precision determination portion 106 estimates a pseudorange error ε_p, based on a pseudorange p included in the observation data input to the observation data precision determination portion 106 by the positioning signal receiving portion 104, an estimated pseudorange "r" included in the estimated observation data input to the observation data precision determination portion 106 by the observation data estimation portion 114, and the common error "s" in the pseudorange due to the receiver clock error. For example, the pseudorange error ε_p is estimated using the equation ε_p = p - r - s.

[0062] The GNSS receiver 100 determines whether the pseudorange error ε_p estimated in step S304 is smaller than the predetermined threshold value (step S306). The observation data precision determination portion 106 determines whether the pseudorange error ε_p is smaller than the predetermined threshold value (ε_p < the predetermined threshold value).

[0063] If the pseudorange error ε_p is smaller than the predetermined threshold value (YES in step S306), a usable flag for the pseudorange is turned on to indicate that the pseudorange is usable (step S308). More specifically, if the pseudorange error ε_p is smaller than the predetermined threshold value, the observation data precision determination portion 106 turns on the usable flag for the pseudorange p corresponding to the pseudorange error ε_p.

[0064] If the pseudorange error ε_p is equal to or larger than the predetermined threshold value (NO in step S306), the usable flag for the pseudorange is turned off (step S310). More specifically, if the pseudorange error ε_p is equal to or larger than the predetermined threshold value, the observation data precision determination portion 106 turns off the usable flag for the pseudorange p corresponding to the pseudorange error ε_p.

[0065] The GNSS receiver 100 computes the position of the GNSS receiver 100 using the pseudoranges for which the usable flag is turned on in step S308 (step S314). The observation data precision determination portion 106 inputs the pseudoranges for which the usable flag is turned on, to the positioning computation portion 116. The positioning computation portion 116 computes the position of the GNSS receiver 100 using the pseudoranges input to the positioning computation portion 116. [0066] FIG. 4 shows a velocity computation method in the GNSS receiver 100 according to the embodiment.

[0067] Step S404 to step S410 are steps in a loop (step S402 and step S412) performed for each of the acquired GNSS satellites. [0068] The GNSS receiver 100 estimates a pseudorange change rate error

(i.e., a Doppler frequency error) ε_d (step S404). The observation data precision determination portion 106 determines a common error in the pseudorange change rate due to the receiver clock error, based on the estimated receiver clock error input to the observation data precision determination portion 106 by the receiver clock error estimation portion 118. The observation data precision determination portion 106 estimates a pseudorange change rate error ε_d, based on a pseudorange change rate "d" included in the observation data input to the observation data precision determination portion 106 by the positioning signal receiving portion 104, an estimated pseudorange change rate r dot included in the estimated observation data input to the observation data precision determination portion 106 by the observation data estimation portion 114, and the common error s dot in the pseudorange change rate due to the receiver clock error. For example, the pseudorange change rate error εa is determined using the equation, ε_d = d - r dot - s dot.

[0069] The GNSS receiver 100 determines whether the pseudorange change rate error ε_d estimated in step S404 is smaller than the predetermined threshold value (step S406). More specifically, the observation data precision determination portion 106 determines whether the pseudorange change rate error εd is smaller than the predetermined threshold value (ε_d < the predetermined threshold value). [0070] If the pseudorange change rate error E_d is smaller than the predetermined threshold value (YES in step S406), the observation data precision determination portion 106 turns on the usable flag for the pseudorange change rate "d" corresponding to the pseudorange change rate error εd.

[0071] If the pseudorange change rate error ε_d is equal to or larger than the predetermined threshold value (NO in step S406), the usable flag is turned off (step S410). More specifically, if the pseudorange change rate error ε_d is equal to or larger than the predetermined threshold value, the observation data precision determination portion 106 turns off the usable flag for the pseudorange change rate "d" corresponding to the pseudorange change rate error εd.

[0072] The GNSS receiver 100 computes the velocity of the GNSS receiver 100 using the pseudorange change rates for which the usable flag is turned on in step S408 (step S414). The observation data precision determination portion 106 inputs the pseudorange change rates for which the usable flag is turned on, to the positioning computation portion 116. The positioning computation portion 116 computes the velocity of the GNSS receiver 100 using the pseudorange change rates input to the positioning computation portion 116.

[0073] According to the embodiment, the position computation is performed using the pseudoranges having the pseudorange errors smaller than the predetermined threshold value. Therefore, it is possible to improve the accuracy of the position computation. Because pseudorange error is estimated taking into account the common error in the pseudorange due to the receiver clock error, it is possible to more accurately estimate the pseudorange error.

[0074] According to the embodiment, the velocity computation is performed using the pseudorange change rates having the pseudorange change rate errors smaller than the predeteπnined threshold value. Therefore, it is possible to improve the accuracy of the velocity computation. Because the pseudorange change rate is estimated taking into account the common error in the pseudorange change rate due to the receiver clock error, it is possible to more accurately estimate the pseudorange change rate error. [Second embodiment]

[0075] A GNSS receiver according to a second embodiment of the invention will be described.

[0076] In the GNSS receiver 100 according to the second embodiment, a method of selecting the pseudoranges and the pseudorange change rates used in the positioning computation is different from that in the above-described GNSS receiver according to the first embodiment. The GNSS receiver 100 estimates a positioning error relating to each of possible combinations of the acquired GNSS satellites among all the combinations of the acquired GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites and arrangement of the GNSS satellites. Then, the GNSS receiver 100 performs the positioning computation using the combination of the GNSS satellite corresponding to the smallest estimated positioning error. [0077] The observation data estimation portion 114 inputs, to the observation data precision determination portion 106, the estimated observation data and the position and velocity of the GNSS satellite.

[0078] The observation data precision determination portion 106 determines the errors in the observation data (including the pseudorange error and the pseudorange change rate error) relating to each of the GNSS satellites using the above-described method. Then, the observation data precision determination portion 106 estimates the positioning errors that are to occur when the position computation and the velocity computation are performed using each of the possible combinations of the acquired GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites, and the positions of the GNSS satellites. The observation data precision determination portion 106 may estimate the positioning errors relating to each of all the combinations of the acquired GNSS satellites. The observation data precision determination portion 106 determines that the position computation should be performed using the pseudoranges corresponding to the smallest estimated positioning error, and the velocity computation should be performed using the pseudorange change rates corresponding to the smallest estimated positioning error. The observation data precision determination portion 106 inputs the pseudoranges and the pseudorange change rates to be used in the positioning computation, to the positioning computation portion 116.

[0079J FIG. 5 shows a positioning method in the GNSS receiver 100 according to the embodiment.

[0080] The GNSS receiver 100 estimates the receiver clock error using the model and the previous clock error (step S502). The observation data precision determination portion 106 determines the common error in the pseudorange due to the receiver clock error, based on the estimated receiver clock error input to the observation data precision determination portion 106 by the receiver clock error estimation portion 118. The receiver clock error estimation portion 118 estimates the receiver clock error and the differential value of the receiver clock error, using the previous receiver clock error and the Kalman filter. The receiver clock error estimation portion 118 inputs the estimated receiver clock error to the observation data precision determination portion 106.

[0081] The GNSS receiver 100 estimates the pseudorange error (step S504). The observation data precision determination portion 106 estimates the common error, based on the estimated receiver clock error. Then, the observation data precision determination portion 106 estimates the pseudorange error by removing the estimated pseudorange and the common error from the pseudorange.

[0082] The GNSS receiver 100 estimates the pseudorange change rate error (step S506). The observation data precision determination portion 106 determines the common error in the pseudorange change rate due to the receiver clock error, based on the estimated receiver clock error input to the observation data precision determination portion 106 by the receiver clock error estimation portion 118. The observation data precision determination portion 106 estimates the pseudorange change rate error by removing the estimated pseudorange change rate and the common error, from the pseudorange change rate.

[0083] The GNSS receiver 100 performs the position computation (step S508). The observation data precision determination portion 106 estimates a positioning error ε<i) relating to each of the possible combinations of the GNSS satellites, based on the positions of the GNSS satellites and the pseudorange errors relating to the GNSS satellites. In this case, "i" is an integer number in a range of 1 to N (N is an integer number larger than 0), and represents an identifier used to identify each combination of the GNSS satellites. For example, the observation data precision determination portion 106 may determine the positioning error using the equation (1) described below. ε_(l) = (H¹H)-' H^τε_p (1)

[0084] In the equation (1), H represents a design matrix of an observation equation in the positioning computation, and ε_p is a vector of the estimated pseudorange error. ε_p is represented by the equation (2) described below. εp ⁼ [ ^εpi ^εp2 ^■" ε_Pm ] (2)

[0085] In the equation (2), m represents the number of the GNSS satellites used in the positioning computation. T indicates a transposed matrix.

[0086] The observation data precision determination portion 106 inputs, to the positioning computation portion 116, the pseudoranges corresponding to the smallest estimated positioning error among the estimated positioning errors relating to the combinations of the GNSS satellites. The positioning computation portion

116 performs the positioning computation using the pseudoranges input to the positioning computation portion 116 by the observation data precision determination portion 106.

[0087] The GNSS receiver 100 performs the velocity computation (step S510). The observation data precision determination portion 106 estimates a positioning error S(,₎ relating to each of possible combinations of the GNSS satellites, based on the pseudorange change rate errors relating to the GNSS satellites, and the positions of the GNSS satellites. In this case, "i" is an integer number in a range of 1 to N (N is an integer number larger than 0), and represents an identifier used to identify each combination of the GNSS satellites. For example, the observation data precision determination portion 106 may determine the positioning error using the equation (1) described below. ε_(l) = (H^τH)-Η^τε_d (3)

[0088] In the equation (3), H represents the design matrix of the observation equation in the positioning computation, and εj is a vector of the estimated pseudorange change rate error, εj is represented by the equation (4) described below. εd = [ εdi εd2 - ε_dm ]^τ (4)

[0089] In the equation (4), m represents the number of the GNSS satellites used in the positioning computation. T indicates the transposed matrix.

[0090] The observation data precision determination portion 106 inputs, to the positioning computation portion 116, the pseudorange change rates corresponding, to the smallest estimated positioning error among the estimated positioning errors relating to the combinations of the GNSS satellites. The positioning computation portion 116 performs the velocity computation using the pseudorange change rates input to the positioning computation portion 116 by the observation data precision determination portion 106.

[0091] The GNSS receiver 100 estimates the receiver clock error using the model and the previous clock error (step S512). The receiver clock error estimation portion 118 corrects the estimated receiver clock error based on the position and velocity of the GNSS receiver 100 determined by the positioning computation portion 116.

[0092] FIG. 6 shows a method of estimating the pseudorange error in the GNSS receiver 100 according to the embodiment.

[0093] Step S604 is a step in a loop (step S602 and step S606) performed for each of the acquired GNSS satellites. [0094] The GNSS receiver 100 estimates the pseudorange error (step S604).

The observation data precision determination portion 106 determines the common error, based on the estimated receiver clock error input to the observation data precision determination portion 106 by the receiver clock error estimation portion 118. For example, the observation data precision determination portion 106 determines the common error "s" in the pseudorange due to the receiver clock error. The observation data precision determination portion 106 estimates the pseudorange error ε_p, based on the pseudorange p included in the observation data input to the observation data precision determination portion 106 by the positioning signal receiving portion 104, the estimated pseudorange "r" included in the estimated observation data input to the observation data precision determination portion 106 by the observation data estimation portion 114, and the common error "s" in the pseudorange due to the receiver clock error. For example, the pseudorange error ε_p is estimated using the equation, ε_p = p - r - s. [0095] FIG. 7 shows a method of estimating the pseudorange change rate error in the GNSS receiver 100 according to the embodiment.

[0096) Step S704 is a step in a loop (step S702 and step S706) performed for each of the GNSS satellites.

[0097] The GNSS receiver 100 estimates the pseudorange change rate error (step S704). The observation data precision determination portion 106 determines the common error, based on the estimated receiver clock error input to the observation data precision determination portion 106 by the receiver clock error estimation portion 118. For example, the observation data precision determination portion 106 determines the common error s dot in the pseudorange change rate due to the receiver clock error. The observation data precision determination portion 106 estimates the pseudorange change rate error εa based on the pseudorange change rate "d" included in the observation data input to the observation data precision determination portion 106 by the positioning signal receiving portion 104, the estimated pseudorange change rate r dot included in the estimated observation data input to the observation data precision determination portion 106 by the positioning signal receiving portion 104, and the common error s dot in the pseudorange change rate due to the receiver clock error. For example, the pseudorange change rate error εa is estimated using the equation, εa = d - r dot - s dot.

[0098] FIG. 8 shows a position/velocity computation method in the GNSS receiver 100 according to the embodiment.

[0099] The GNSS receiver 100 selects possible combinations of the GNSS satellites to be used in the positioning computation, from among the GNSS satellites acquired by the GNSS receiver 100 (step S802). The observation data precision determination portion 106 estimates the positioning error that is to occur when the positioning computation is performed using each of the possible combinations of the acquired GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites and the positions of the GNSS satellites. The observation data precision determination portion 106 may estimate the positioning error relating to each of all the combinations of the acquired GNSS satellites. The identifier "i" is assigned to each of the combinations of the GNSS satellites.

[0100] Step S806 is a step in a loop (step S804 and step S808) performed for each of the combinations of the GNSS satellites.

[0101] The GNSS receiver 100 estimates the positioning error that is to occur when the positioning computation is performed (step S806). The positioning computation includes the position computation (i.e., the computation for determining the position of the GNSS receiver 100) and the velocity computation (i.e., the computation for determining the velocity of the GNSS receiver 100). The observation data precision determination portion 106 estimates the positioning error S₍i) relating to the combination "i" of the GNSS satellites, based on the positions of the GNSS satellites and the estimated errors in the observation data. The observation data may include the pseudorange and the pseudorange change rate. In this case, "i" is an integer number in a range of 1 to N (N is an integer number larger than 0), and represents an identifier used to identify each combination of the GNSS satellites. For example, the observation data precision determination portion 106 may determine the error in the position, using the above-described equation (1). Also, for example, the observation data precision determination portion 106 may determine the error in the velocity, using the above-described equation (3).

[0102] The GNSS receiver 100 performs the positioning computation using the combination of the GNSS satellites corresponding to the smallest estimated positioning error (step S810). The observation data precision determination portion 106 inputs, to the positioning computation portion 116, the observation data corresponding to the smallest estimated positioning error, among all the estimated positioning errors. The positioning computation portion 116 performs the position computation and/or the velocity computation using the observation data input to the positioning computation portion 116 by the observation data precision determination portion 106.

[0103] According to the embodiment, the positioning error relating to each of possible combinations of the GNSS satellites is estimated. The positioning computation is performed using the combination corresponding to the smallest estimated positioning error. Therefore, it is possible to improve the accuracy of the position computation and the velocity computation. [Third embodiment] [0104] A GNSS receiver according to a third embodiment of the invention will be described.

[0105] In the GNSS receiver 100 according to the third embodiment, a method of selecting the pseudoranges and the pseudorange change rates to be used in the positioning computation is different from that in the above-described GNSS receiver. The GNSS receiver 100 according to the third embodiment selects combinations of the GNSS satellites so that a variation in the estimated error in the observation data in each of the selected combinations is small. Then, the GNSS receiver 100 estimates the positioning error relating to each of the selected combinations of the GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites and the arrangement of the GNSS satellites. Then, the GNSS receiver 100 performs the positioning computation using the pseudoranges and the pseudorange change rates corresponding to the combination of the GNSS satellites corresponding to the smallest estimated positioning error. [0106] The observation data estimation portion 114 inputs, to the observation data precision determination portion 106, the estimated observation data and the positions and velocities of the GNSS satellites.

[0107] The observation data precision determination portion 106 determines the errors in the observation data using the above-described methods. The observation data includes the pseudorange error and the pseudorange change rate error. The observation data precision determination portion 106 selects combinations of the GNSS satellites so that the variation in the estimated error in the observation data in each of the selected combinations of the GNSS satellites is equal to or smaller than a predetermined threshold value. Then, the observation data precision determination portion 106 estimates the positioning error that is to occur when the positioning computation is performed, based on the estimated errors in the observation data relating to each of the selected combinations of the GNSS satellites, and the positions of the GNSS satellites. Then, the observation data precision determination portion 106 determines that the positioning computation should be performed using the combination of the GNSS satellites corresponding to the smallest estimated positioning error. The observation data precision determination portion 106 inputs the observation data to be used in the positioning computation, to the positioning computation portion 116. [0108] The positioning method in the GNSS receiver 100 according to the third embodiment is different from the positioning method described with reference to FIG. 5 to FIG. 8 in a process in step S802.

[0109] In step S802, the GNSS receiver 100 selects combinations of the GNSS satellites so that the variation in the estimated error in the observation data in each of the selected combinations of the GNSS satellites is small, based on the estimated errors in the observation data relating to the GNSS satellites. Then, the GNSS receiver 100 estimates the positioning error, based on the estimated errors in the observation data relating to each of the selected combinations of the GNSS satellites, and the positions of the GNSS satellites. For example, if the GNSS receiver 100 acquires eight GNSS satellites, the GNSS receiver 100 selects combinations of the GNSS satellites so that the variation in the estimated error in the observation data in each of the selected combinations is small, while increasing the number of the GNSS satellites to be used in the positioning computation, from four to eight. Then, the GNSS receiver 100 estimates the positioning error relating to each of the selected combinations. The GNSS receiver 100 performs the positioning computation using the combination of the GNSS satellites corresponding to the smallest estimated positioning error.

[0110] According to the third embodiment, the combinations of the GNSS satellites are selected so that the variation in the estimated error in the observation data in each of the selected combinations of the GNSS satellites is small. Then, the positioning error relating to each of the selected combinations of the GNSS satellites is estimated. Thus, it is possible to reduce the amount of computation required to estimate the positioning errors. [Fourth embodiment]

[0111] A GNSS receiver according to a fourth embodiment of the invention will be described.

[0112] The GNSS receiver 100 according to the fourth embodiment is the same as the GNSS receiver according to each of the first to third embodiments. However, in the GNSS receiver 100 according to the fourth embodiment, a process, which is executed after selecting the GNSS satellites to be used in the positioning computation, is different from that in the GNSS receiver according to each of the first to third embodiments. If all the estimated errors in the observation data relating to all the acquired GNSS satellites are equal to or larger than a predetermined threshold value, the GNSS receiver 100 uses all the acquired GNSS satellites in the positioning computation. That is, if all the estimated errors in the observation data relating to all the acquired GNSS satellites are equal to or larger than the predetermined threshold value, the GNSS receiver 100 resets the selection of the GNSS satellites to be used in the positioning computation. [0113] A positioning method in the GNSS receiver according to the fourth embodiment is the same as the positioning method described with reference to FIG. 5.

[0114] A method of estimating the pseudorange error in the GNSS receiver 100 according to the fourth embodiment is the same as the method of estimating the pseudorange error described with reference to FIG. 6.

[0115] A method of estimating the pseudorange change rate error in the GNSS receiver 100 according to the fourth embodiment is the same as the method of estimating the pseudorange change rate error described with reference to FIG. 7. [0116] FIG. 9 shows a position/velocity computation method in the GNSS receiver 100 according to the fourth embodiment.

[0117] The GNSS receiver 100 selects possible combinations of the GNSS satellites to be used in the positioning computation, from among the GNSS satellites acquired by the GNSS receiver 100 (step S902). For example, the GNSS receiver 100 estimates the positioning error that is to occur when the positioning computation is performed using each of the possible combinations of the acquired GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites and the positions of the GNSS satellites. The GNSS receiver 100 may estimate the positioning error that is to occur when the positioning computation is performed using each of all the combinations of the acquired GNSS satellites. Also, for example, the GNSS receiver 100 may select combinations of the GNSS satellites so that the variation in the estimated error in the observation data in each of the selected combinations is small. Then, the GNSS receiver 100 may estimate the positioning error relating to each of the selected combinations of the GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites and the positions of the GNSS satellites. The identifier "i" is assigned to each of the combinations of the GNSS satellites.

[0118] Step S906 is a step in a loop (step S904 and S908) performed for each combination "i" of the GNSS satellites. [0119] The GNSS receiver 100 estimates the positioning error that is to occur when the positioning computation is performed (step S906). The positioning computation includes the position computation and the velocity computation. The observation data precision determination portion 106 estimates the positioning error 8₍₀ relating to the combination "i" of the GNSS satellites, based on the positions of the GNSS satellites and the estimated errors in the observation data relating to the GNSS satellites. The observation data includes the pseudorange and the pseudorange change rate. In this case, "i" is an integer number in a range of 1 to N (N is an integer number larger than 0), and represents an identifier used to identify each combination of the GNSS satellites.

[0120] The GNSS receiver 100 determines whether to reset the selection of the combinations of the GNSS satellites (step S910). The GNSS receiver 100 determines whether all the estimated errors in the observation data relating to all the acquired GNSS satellites are equal to or larger than the predetermined threshold value. If all the estimated errors in the observation data relating to all the acquired GNSS satellites are equal to or larger than the predetermined threshold value, the GNSS receiver 100 determines that the selection of the combinations of the GNSS satellites should be reset.

[0121] If the GNSS receiver 100 determines that the selection of the combinations of the GNSS satellites should be reset (YES in step S910), the GNSS receiver 100 determines that the positioning computation should be performed using all the acquired GNSS satellites, that is, the GNSS receiver 100 selects all the acquired GNSS satellites (step S912). The observation data precision determination portion 106 inputs the observation data corresponding to all the estimated positioning errors, to the positioning computation portion 116. If the GNSS receiver 100 determines that the selection of the combinations of the GNSS satellites should not be reset (NO in step S910), the GNSS receiver 100 determines that the positioning computation should be performed using the combination of the GNSS satellites corresponding to the smallest estimated positioning error, that is, the GNSS receiver 100 selects the combination of the GNSS satellites corresponding to the smallest estimated positioning error (step S914). The observation data precision determination portion 106 inputs, to the positioning computation portion 116, the observation data corresponding to the smallest estimated positioning error among all the estimated positioning errors.

[0122] The GNSS receiver 100 computes the position or the velocity of the GNSS receiver 100 (step S916). More specifically, the positioning computation portion 116 computes the position or the velocity of the GNSS receiver 100 using the observation data input to the positioning computation portion 116 by the observation data precision determination portion 106.

[0123] According to the embodiment, it is determined whether all the estimated errors in the observation data relating to all the acquired GNSS satellites are larger than the predetermined threshold value. If all the estimated errors in the observation data relating to all the acquired GNSS satellites are larger than the predetermined threshold value, all the acquired GNSS satellites are used. If at least one of the estimated errors in the observation data relating to all the acquired GNSS satellites is smaller than the predetermined threshold value, the combination of the GNSS satellites corresponding to the smallest estimated positioning error is used. Thus, the number of the GNSS satellites to be used in the positioning computation is changed based on the estimated errors in the observation data relating to all the GNSS satellites. Accordingly, the positioning computation is performed using all the acquired GNSS satellites, or using the combination of the GNSS satellites corresponding to the smallest estimated positioning error. Thus, it is possible to improve the accuracy of the position computation and the velocity computation. [Fifth embodiment]

[0124] A GNSS receiver according to a fifth embodiment will be described.

[0125] The GNSS receiver 100 according to the fifth embodiment is the same as the GNSS receiver according to each of the first to third embodiments. However, in the GNSS receiver 100 according to the fifth embodiment, a process, which is executed after selecting the GNSS satellites to be used in the positioning computation, is different from that in the GNSS receiver according to each of the first to third embodiments. If the average value of absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is equal to or larger than a predetermined threshold value, the GNSS receiver 100 uses all the acquired GNSS satellites in the positioning computation. That is, if the average value of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is equal to or larger than the predetermined threshold value, the GNSS receiver 100 resets the selection of the GNSS satellites to be used in the positioning computation.

[0126] A positioning method in the GNSS receiver according to the fifth embodiment is the same as the positioning method described with reference to FIG. 5. [0127] A method of estimating the pseudorange error in the GNSS receiver

100 according to the fifth embodiment is the same as the method of estimating the pseudorange error described with reference to FIG. 6.

[0128] A method of estimating the pseudorange change rate error in the GNSS receiver 100 according to the fifth embodiment is the same as the method of estimating the pseudorange change rate error described with reference to FIG. 7.

[0129] A position/velocity computation method in the GNSS receiver 100 according to the fifth embodiment is different from the position/velocity computation method described with reference to FIG. 9, in a process in step S910. [0130] In step S910, the GNSS receiver 100 determines whether to reset the selection of the combinations of the GNSS satellites. The GNSS receiver 100 determines whether the average value of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is equal to or larger than the predetermined threshold value. If the average value of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is equal to or larger than the predetermined threshold value, the GNSS receiver 100 determines that the selection of the combinations of the GNSS satellites should be reset. If the average value of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is smaller than the predetermined threshold value, the GNSS receiver 100 determines that the selection of the combinations of the GNSS satellites should not be reset.

[0131] According to the embodiment, it is determined whether the average of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is equal to or larger than the predetermined threshold value. If the average of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is equal to or larger than the predetermined threshold value, all the acquired GNSS satellites are used. If the average of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is smaller than the predetermined threshold value, the combination of the GNSS satellites corresponding to the smallest estimated positioning error is used. Thus, the number of the GNSS satellites to be used in the positioning computation is changed based on the average value of the absolute values of the estimated errors in the observation data. Accordingly, the positioning computation is performed using all the acquired GNSS satellites, or using the GNSS satellites corresponding to the smallest estimated positioning error when the average of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is smaller than the predetermined threshold value. Thus, it is possible to improve the accuracy of the position computation and the velocity computation. [Sixth embodiment]

[0132] A GNSS receiver according to a sixth embodiment of the invention will be described.

[0133] FIG. 10 shows a functional block diagram of the GNSS receiver 100 according to the sixth embodiment. The GNSS receiver 100 according to the sixth embodiment is different from the GNSS receiver according to each of the first to fifth embodiments in that the GNSS receiver 100 according to the sixth embodiment does not include the receiver clock error estimation portion 118.

[0134] FIGS. HA and HB show in detail the observation data estimation portion 114 and the observation data precision determination portion 106 of the GNSS receiver 100 shown in FIG. 10. The observation data estimation portion 114 includes a pseudorange estimation portion 1142, a Doppler frequency estimation portion 1144, and an ADR estimation portion 1146. The observation data precision determination portion 106 includes a pseudorange precision determination portion 1062, a Doppler frequency precision determination portion 1064, an ADR precision determination portion 1066, Dilution of Precision (DOP) calculation portions 1068 (1068i, IO68₂, and IO68₃), and a data selection portion 1070.

[0135] The pseudorange estimation portion 1142 is connected to the satellite position velocity calculation portion 108 and the receiver position velocity estimation portion 112. The pseudorange estimation portion 1142 estimates the pseudorange based on the position and velocity of the satellite input to the pseudorange estimation portion 1142 by the satellite position velocity calculation portion 108, and the estimated position and estimated velocity of the GNSS receiver 100 input to the pseudorange estimation portion 1142 by the receiver position velocity estimation portion 112. The pseudorange estimation portion 1142 inputs the estimated pseudorange to the pseudorange precision determination portion 1062.

[0136] The Doppler frequency estimation portion 1144 is connected to the satellite position velocity calculation portion 108 and the receiver position velocity estimation portion 112. The Doppler frequency estimation portion 1144 estimates the Doppler frequency based on the position and the velocity of the satellite input to the Doppler frequency estimation portion 1144 by the satellite position velocity calculation portion 108, and the estimated position and estimated velocity of the GNSS receiver 100 input to the Doppler frequency estimation portion 1144 by the receiver position velocity estimation portion 112. The Doppler frequency estimation portion 1144 inputs the estimated Doppler frequency to the Doppler frequency precision determination portion 1064.

[0137] The ADR estimation portion 1146 is connected to the satellite position velocity calculation portion 108 and the receiver position velocity estimation portion 112. The ADR estimation portion 1146 estimates the ADR based on the position and velocity of the satellite input to the ADR estimation portion 1146 by the satellite position velocity calculation portion 108, and the estimated position and velocity of the GNSS receiver 100 input to the ADR estimation portion 1146 by the receiver position velocity estimation portion 112. The ADR estimation portion 1146 inputs the estimated ADR to the ADR precision determination portion 1066.

[0138] The pseudorange precision determination portion 1062 is connected to the positioning signal receiving portion 104 and the pseudorange estimation portion 1142. The pseudorange precision determination portion 1062 determines the precision of the pseudorange, based on the pseudorange included in the observation data input to the pseudorange precision determination portion 1062 by the positioning signal receiving portion 104, and the estimated pseudorange input to the pseudorange precision determination portion 1062 by the pseudorange estimation portion 1142. The pseudorange precision determination portion 1062 inputs the pseudorange with a precision equal to or higher than a predetermined threshold value, to the DOP calculation portion 1068|. The predetermined threshold value is a value that makes it possible to determine whether the precision of the pseudorange is high.

[0139] The Doppler frequency precision determination portion 1064 is connected to the positioning signal receiving portion 104 and the Doppler frequency estimation portion 1144. The Doppler frequency precision determination portion 1064 determines the precision of the Doppler frequency, based on the Doppler frequency included in the observation data input to the Doppler frequency precision determination portion 1064 by the positioning signal receiving portion 104, and the estimated Doppler frequency input to the Doppler frequency precision determination portion 1064 by the Doppler frequency estimation portion 1144. The Doppler frequency precision determination portion 1064 inputs the Doppler frequency with a precision equal to or higher than a predetermined threshold value, to the DOP calculation portion IO68₂. The predetermined threshold value is a value that makes it possible to determine whether the precision of the Doppler frequency is high.

[0140] The ADR precision determination portion 1066 is connected to the positioning signal receiving portion 104 and the ADR estimation portion 1146. The ADR precision determination portion 1066 determines the precision of the ADR, based on the ADR included in the observation data input to the ADR precision determination portion 1066 by the positioning signal receiving portion 104, and the estimated ADR input to the ADR precision determination portion 1066 by the ADR estimation portion 1146. The ADR precision determination portion 1066 inputs the ADR with a precision equal to or higher than a predetermined threshold value, to the DOP calculation portion IO68₃. The predetermined threshold value is a value that makes it possible to determine whether the precision of the estimated ADR is high.

[0141] The DOP calculation portion 1068] is connected to the pseudorange precision determination portion 1062. The DOP calculation portion IO68₁ calculates DOP values relating to possible combinations of the pseudoranges, based on the pseudoranges with high precisions input to the DOP calculation portion IO68₁ by the pseudorange precision determination portion 1062. The DOP calculation portion IO68₁ selects at least one combination of the pseudoranges corresponding to the smallest DOP value, and determines Horizontal Dilution of Precision (HDOP) value(s) and Vertical Dilution of Precision (VDOP) value(s) relating to the determined combination(s) of the pseudoranges. The DOP calculation portion 1068₁ inputs, to the data selection portion 1070, the combination(s) of the pseudoranges corresponding to the smallest DOP value, the HDOP value(s), and the VDOP value(s).

[0142] The DOP calculation portion IO68₂ is connected to the Doppler frequency precision deteπnination portion 1064. The DOP calculation portion IO682 calculates the DOP values relating to possible combinations of the Doppler frequencies, based on the Doppler frequencies with high precisions input to the DOP calculation portion 1068₂ by the Doppler frequency precision determination portion 1064. The DOP calculation portion 1068₂ selects at least one combination of the Doppler frequencies corresponding to the smallest DOP value, and determines the HDOP value(s) and the VDOP value(s) relating to the determined combination(s) of the Doppler frequencies. The DOP calculation portion 1068₂ inputs, to the data selection portion 1070, the combination(s) of the Doppler frequencies corresponding to the smallest DOP value, the HDOP value(s), and the VDOP value(s).

[0143] The DOP calculation portion IO683 is connected to the ADR precision determination portion 1066. The DOP calculation portion IO68₃ calculates the DOP values relating to possible combinations of the ADRs, based on the ADRs with high precisions input to the DOP calculation portion IO68₃ by the ADR precision determination portion 1066. The DOP calculation portion IO68₃ selects at least one combination of the ADRs corresponding to the smallest DOP value, and determines the HDOP value(s) and the VDOP value(s) relating to the determined combination(s) of the ADRs. The DOP calculation portion IO68₃ inputs, to the data selection portion 1070, the combination(s) of the ADRs corresponding to the smallest DOP value, the HDOP value(s), and the VDOP value(s).

[0144] The data selection portion 1070 is connected to the DOP calculation portion IO68₁, the DOP calculation portion 1068₂, and the DOP calculation portion IO68₃. The DOP calculation portion IO68₁ inputs the combination(s) of the pseudoranges corresponding to the smallest DOP value, the HDOP value(s), and the VDOP value(s), to the data selection portion 1070. The DOP calculation portion IO68₂ inputs the combination(s) of the Doppler frequencies corresponding to the smallest DOP value, the HDOP value(s), and the VDOP value(s), to the data selection portion 1070. The DOP calculation portion IO68₃ inputs the combination(s) of the ADRs corresponding to the smallest DOP value, the HDOP value(s), and the VDOP value(s), to the data selection portion 1070. The data selection portion 1070 selects the smallest HDOP value from among the HDOP values input to the data selection portion 1070 by the DOP calculation portion IO68₁. The data selection portion 1070 determines whether the selected HDOP value is equal to or smaller than a predetermined threshold value. If the selected HDOP value is equal to or smaller than the predetermined threshold value, the data selection portion 1070 determines that three-dimensional positioning should be performed. If the selected HDOP value is larger than the predetermined threshold value, the data selection portion 1070 determines that two-dimensional positioning should be performed. The data selection portion 1070 inputs, to the positioning computation portion 116, the pseudoranges corresponding to the selected HDOP value, and a signal indicating that the two-dimensional positioning should be performed or a signal indicating that the three-dimensional positioning should be performed.

[0145] The data selection portion 1070 may select the smallest HDOP value among the HDOP values input to the data selection portion 1070 by the DOP calculation portion 1068₂, or may select the smallest HDOP value among the HDOP values input to the data selection portion 1070 by the DOP calculation portion IO68₃. The data selection portion 1070 determines whether the selected HDOP value is equal to or smaller than the predetermined threshold value. If the selected HDOP value is equal to or smaller than the predetermined threshold value, the data selection portion 1070 determines that the three-dimensional positioning should be performed. If the selected HDOP value is larger than the predetermined threshold value, the data selection portion 1070 determines that the two-dimensional positioning should be performed. The data selection portion 1070 inputs, for example, the pseudoranges corresponding to the selected HDOP value, and the signal indicating that the two-dimensional positioning should be performed, or the signal indicating that the three-dimensional positioning should be performed, to the positioning computation portion 116.

[0146] The positioning computation portion 116 performs the two-dimensional positioning or the three-dimensional positioning, based on, for example, the pseudoranges input to the 116 by the data selection portion 1070, and the signal indicating that the two-dimensional positioning or the three-dimensional positioning should be performed.

[0147] FIG. 12 shows an example of processes executed by the DOP calculation portion IO68₁ of the GNSS receiver 100 according to the embodiment.

[0148] Step S 1204 to step S 1206 are steps in a loop (step S 1202 and step S 1208) performed for the acquired GNSS satellites.

[0149] The GNSS receiver 100 selects the pseudoranges with high precisions (step S 1204). More specifically, the DOP calculation portion IO68₁ selects the pseudoranges with high precisions input to the DOP calculation portion IO681 by the pseudorange precision determination portion 1062. [0150] The GNSS receiver 100 calculates the DOP values relating to the possible combinations of the pseudoranges selected in step S 1204 (step S 1206). More specifically, the DOP calculation portion IO68₁ calculates the DOP values relating to the possible combinations of the selected pseudoranges.

[0151] FIG. 13 shows an example of processes executed by the DOP calculation portion IO68₂ of the GNSS receiver 100 according to the embodiment.

[0152] Step S 1304 to step S 1306 are steps in a loop (step S 1302 and step S 1308) performed for the acquired GNSS satellites.

[0153] The GNSS receiver 100 selects the Doppler frequencies with high precisions (step S 1304). More specifically, the DOP calculation portion IO682 selects the Doppler frequencies with high precisions input to the DOP calculation portion IO68₂ by the Doppler frequency precision determination portion 1064.

[0154] The GNSS receiver 100 calculates the DOP values relating to the possible combinations of the Doppler frequencies selected in step S 1304 (step S 1306). More specifically, the DOP calculation portion 1068₂ calculates the DOP values relating to the possible combinations of the selected Doppler frequencies.

[0155] FIG. 14 shows an example of processes executed by the DOP calculation portion IO68₃ of the GNSS receiver 100 according to the embodiment.

[0156] Step S 1404 to step S 1406 are steps in a loop (step S 1402 and step S 1408) performed for the acquired GNSS satellites.

[0157] The GNSS receiver 100 selects the ADRs with high precisions (step S 1404). More specifically, the DOP calculation portion IO68₃ selects the ADRs with high precisions input to the DOP calculation portion IO68₃ by the ADR precision determination portion 1066. [0158] The GNSS receiver 100 calculates the DOP values relating to possible combinations of the ADRs selected in step S 1404 (step S 1406). More specifically, the DOP calculation portion IO68₃ calculates the DOP values relating to the possible combinations of the selected ADRs.

[0159] Each of FIG. 15 and FIG. 16 shows an example of processes executed by the DOP calculation portion IO68₁ of the GNSS receiver 100 according to the embodiment.

[0160] In FIG. 15, the DOP calculation portion IO68₁ selects the pseudoranges with high precisions relating to possible combinations of the four or more GNSS satellites among the acquired GNSS satellites. Then, the DOP calculation portion IO68₁ calculates the DOP values based on the pseudoranges, and selects the appropriate combinations based on the calculated DOP values.

[0161] Step S1504 to step S1508 are steps in a loop (step S1502 and step Sl 510) performed for the acquired GNSS satellites.

[0162] The GNSS receiver 100 selects the pseudoranges with high precisions (step S 1504). More specifically, the DOP calculation portion IO681 selects the pseudoranges input to the DOP calculation portion IO68₁ by the pseudorange precision determination portion 1062.

[0163] The GNSS receiver 100 calculates the DOP value relating to each of possible combinations of the pseudoranges selected in step S 1504 (step S 1506). More specifically, the DOP calculation portion IO68₁ calculates the DOP value relating to each of the possible combinations of the selected pseudoranges.

[0164] In the GNSS receiver 100, residuals of DOP values and the DOP values are stored (step S 1508). More specifically, the DOP calculation portion 1068₁ calculates the average value of the calculated DOP values, and calculates the residual of each DOP value from the average value. Then, in the DOP calculation portion IO68₁, the residuals and the DOP values are temporarily stored.

[0165] The GNSS receiver 100 selects the combination(s) of the pseudoranges corresponding to the smallest value among values obtained by multiplying the residuals by the respective DOP values (i.e., by the residuals x the respective DOP values) (step Sl 512). More specifically, the DOP calculation portion IO68₁ calculates the values by multiplying the residuals by the respective DOP values, based on the residuals and the DOP values that are temporarily stored. Then, the DOP calculation portion IO68₁ selects the combination(s) of the pseudoranges corresponding to the smallest value among the values obtained by multiplying the residuals by the respective DOP values.

[0166] In FIG. 16, first, the DOP calculation portion IO68₁ selects the pseudoranges with high precisions relating to a possible combination of the four GNSS satellites among the acquired GNSS satellites. Then, the DOP calculation portion 1068] calculates the DOP value based on the pseudoranges. If a value obtained by multiplying a residual of the DOP value by the DOP value is equal to or smaller than a predetermined threshold value, the DOP calculation portion IO681 selects the four GNSS satellites. If the value obtained by multiplying the residual by the DOP value is larger than the predetermined threshold value, the DOP calculation portion 1068₁ performs the same processes for the other combinations of the four GNSS satellites. If the value obtained by multiplying the residual by the DOP value relating to each of the other combinations of the four GNSS satellites is larger than the predetermined threshold value, the DOP calculation portion IO68₁ performs the same processes for each of the other combinations of the increased number of GNSS satellites.

[0167] Step S 1604 to step S 1608 are steps in a loop (step S 1602 and step S 1610) performed for the acquired GNSS satellites.

[0168] The GNSS receiver 100 selects the pseudoranges with high precisions (step S 1604). More specifically, the DOP calculation portion 1068| selects the pseudoranges with high precisions input to the DOP calculation portion 10681 by the pseudorange precision determination portion 1062.

[0169] The GNSS receiver 100 calculates the DOP values relating to possible combinations of the pseudoranges selected in S 1604 (step S 1606). More specifically, the DOP calculation portion 1068i calculates the DOP values relating to the possible combinations of the selected pseudoranges.

[0170] The GNSS receiver 100 determines the average value of the calculated DOP values, and determines the residual of each DOP value from the average value. The GNSS receiver 100 determines whether the value obtained by multiplying each residual by the corresponding DOP value is equal to or smaller than the predetermined threshold value (step S 1608). More specifically, the DOP calculation portion 1068₁ determines the average value of the calculated DOP values, and determines the residual of each DOP value from the average value. Then, the

DOP calculation portion IO68₁ determines whether the value obtained by multiplying each residual by the corresponding DOP value is equal to or smaller than the predetermined threshold value (step S 1608).

[0171] If the value obtained by multiplying the residual by the corresponding DOP value is equal to or smaller than the predetermined threshold value (YES in step S 1608), the GNSS receiver 100 determines that the combination of the GNSS satellites corresponding to the DOP value should be used in the positioning computation. More specifically, if the value obtained by multiplying the residual by the corresponding DOP value is equal to or smaller than the predetermined threshold value (YES in step S 1608), the DOP calculation portion 1068₁ determines that the combination of the pseudoranges corresponding to the DOP value should be used in the positioning computation. The DOP calculation portion 1068| inputs the combination of the pseudoranges to the data selection portion 1070.

[0172] If the value obtained by multiplying the residual by the corresponding DOP value is larger than the predetermined threshold value (NO in step S 1608), the GNSS receiver 100 performs the processes in step S 1604 to step S 1608 for the other combinations.

[0173] FIG. 17 shows an example of processes performed by the data selection portion 1070 of the GNSS receiver 100. [0174] The GNSS receiver 100 selects the combination of the pseudoranges corresponding to the smallest HDOP value among the HDOP values relating to the combinations of the pseudoranges (step S 1702). More specifically, the data selection portion 1070 selects the pseudoranges corresponding to the smallest HDOP value, based on the HDOP values input to the data selection portion 1070 by the DOP calculation portion 1068|. The data selection portion 1070 may select the Doppler frequencies corresponding to the smallest HDOP value, or the ADRs corresponding to the smallest HDOP value.

[0175] The GNSS receiver 100 determines whether the HDOP value relating to the pseudoranges (or the Doppler frequencies or the ADRs) selected in step S 1702 is equal to or smaller than the predetermined threshold value (step S 1704). More specifically, the data selection portion 1070 determines whether the HDOP value relating to the selected pseudoranges (or the selected Doppler frequencies or the selected ADRs) is equal to or smaller than the predetermined threshold value. [0176] If the HDOP value is equal to or smaller than the predetermined threshold value (YES in step S 1704), the GNSS receiver 100 deteπnines that the three-dimensional positioning should be performed (step S 1706). More specifically, if the HDOP value relating to the selected pseudoranges (or the selected Doppler frequencies or the selected ADRs) is equal to or smaller than the predetermined threshold value, the data selection portion 1070 determines that the three-dimensional positioning should be performed.

[0177] If the HDOP value is larger than the predetermined threshold value (NO in step S 1704), the GNSS 100 determines that the two-dimensional positioning should be performed (step S 1708). More specifically, if the HDOP value relating to the selected pseudoranges (or the selected Doppler frequencies or the selected ADRs) is larger than the predetermined threshold value, the data selection portion 1070 determines that the two-dimensional positioning should be performed.

[0178] According to the embodiment, the positioning computation is performed using the appropriate combination of the GNSS satellites selected from among the combinations of the four or more GNSS satellites acquired by the GNSS receiver 100, based on the DOP values. The four GNSS satellites make it possible to perform the positioning computation. Thus, it is possible to improve the accuracy of the position computation and the velocity computation. [0179] According to the embodiment, first, the DOP values relating to combinations of the four GNSS satellites are sequentially determined. The four GNSS satellites make it possible to perform the positioning computation. Then, while increasing the number of the GNSS satellites included in each combination, the DOP values relating to the combinations of the increased number of the GNSS satellites are sequentially determined. When the DOP value satisfies the predetermined characteristic condition, the positioning computation is performed using the combination of the GNSS satellites corresponding to the DOP value. Accordingly, it is possible to improve the processing speed while ensuring the high accuracy of the position computation and the velocity computation. [0180] For the sake of convenience in the explanation and for the sake of facilitating understanding, the description has been made using specific examples of numerical values. However, unless otherwise specified, the numerical values are simply exemplary values, and any appropriate values may be used.

[0181] While the invention has been described with reference to specific embodiments thereof, it is to be understood that the embodiments are simply exemplary embodiments, and it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. For the sake of convenience in the explanation, the apparatus according to the embodiments of the invention has been described using the functional block diagrams. However, the apparatus may be implemented by hardware, software, or the combination of hardware and software. The invention is not limited to the above-described embodiments, and the invention is intended to cover various modifications.

Claims

CLAIMS:

1. A Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on a positioning signal transmitted from a GNSS satellite, comprising: an observation data computation portion that obtains observation data to be observed by the GNSS receiver, using a code included in the positioning signal transmitted from the GNSS satellite; a position calculation portion that calculates a position of the GNSS satellite, based on orbit information included in the positioning signal transmitted from the GNSS satellite; a position estimation portion that estimates a position of the GNSS receiver, based on information other than the positioning signal; an observation data estimation portion that estimates the observation data, based on the position of the GNSS satellite calculated by the position calculation portion, and the position of the GNSS receiver estimated by the position estimation portion; a receiver error estimation portion that estimates a receiver error that is an error in the GNSS receiver; an observation data error estimation portion that estimates a common error in the observation data due to the receiver error, based on the estimated receiver error that is estimated by the receiver error estimation portion, and estimates an error in the observation data, based on the observation data obtained by the observation data computation portion, the estimated observation data that is estimated by the observation data estimation portion, and the common error; and a positioning computation portion that performs the positioning computation using the observation data whose error is equal to or smaller than a predetermined threshold value.

2. The GNSS receiver according to claim 1, wherein the position calculation portion calculates the position and velocity of the GNSS satellite, based on the orbit information included in the positioning signal transmitted from the GNSS satellite; the position estimation portion estimates the position and velocity of the

GNSS receiver, based on the information other than the positioning signal; and the observation data estimation portion estimates the observation data, based on the position and velocity of the GNSS satellite calculated by the position calculation portion, and the position and velocity of the GNSS receiver estimated by the position estimation portion.

3. The GNSS receiver according to claim 1 or 2, wherein the observation data includes at least one of a pseudorange, a rate of change in the pseudorange, and an amount of change in the pseudorange.

4. The GNSS receiver according to any one of claims 1 to 3, wherein the receiver error estimation portion estimates the error in the observation data based on a previous error in the observation data, and corrects the estimated error in the observation data based on a result of the positioning computation performed by the positioning computation portion.

5. The GNSS receiver according to claim 4, wherein the receiver error estimation portion corrects the error in the observation data, based on an error and a differential value of the error calculated based on results of a position computation and a velocity computation performed by the positioning computation portion.

6. The GNSS receiver according to any one of claims 1 to 3, wherein the receiver error estimation portion estimates the receiver error based on a previous receiver error, and corrects the estimated receiver error based on a result of the positioning computation performed by the positioning computation portion.

7. The GNSS receiver according to claim 6, wherein the receiver error estimation portion estimates the receiver error and a differential value of the receiver error, and corrects the estimated receiver error based on results of a position computation and a velocity computation performed by the positioning computation portion.

8. The GNSS receiver according to claim 1, wherein the receiver error includes a clock error.

9. The GNSS receiver according to claim 1, wherein the information other than the positioning signal includes information from at least one of an acceleration sensor, an angular acceleration sensor, and a geomagnetic sensor; and the position estimation portion estimates the position of the GNSS receiver by inertial navigation.

10. The GNSS receiver according to claim 1, further comprising a map database, wherein the position estimation portion estimates the position of the GNSS receiver by performing map-matching using the map database.

11. A Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on positioning signals transmitted from a plurality of GNSS satellites, comprising: an observation data computation portion that obtains observation data relating to each of the GNSS satellites, using a code included in the positioning signal transmitted from the corresponding GNSS satellite; a position calculation portion that calculates a position of each of the GNSS satellites, based on orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; a position estimation portion that estimates a position of the GNSS receiver, based on information other than the positioning signals; an observation data estimation portion that estimates the observation data relating to each of the GNSS satellites, based on the position of the corresponding GNSS satellite calculated by the position calculation portion, and the position of the GNSS receiver estimated by the position estimation portion; a receiver error estimation portion that estimates a receiver error that is an error in the GNSS receiver; an observation data error estimation portion that estimates a common error in the observation data due to the receiver error, based on the estimated receiver error that is estimated by the receiver error estimation portion, and estimates an error in the observation data, based on the observation data obtained by the observation data computation portion, the estimated observation data that is estimated by the observation data estimation portion, and the common error, wherein the observation data error estimation portion selects combinations of the GNSS satellites acquired by the GNSS receiver; the observation data error estimation portion estimates a positioning error that is to occur when the positioning computation is performed using each of the selected combinations of the GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites, and arrangement of the GNSS satellites; and the observation data error estimation portion selects the GNSS satellites to be used in the positioning computation, based on at least one of i) the estimated errors in the observation data relating to the GNSS satellites and ii) the estimated positioning errors relating to the selected combinations of the GNSS satellites; and a positioning computation portion that performs the positioning computation using the GNSS satellites selected by the observation data error estimation portion.

12. The GNSS receiver according to claim 11, wherein the position calculation portion calculates the position and velocity of each of the GNSS satellites, based on the orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; the position estimation portion estimates the position and velocity of the GNSS receiver, based on the information other than the positioning signals; and the observation data estimation portion estimates the observation data relating to each of the GNSS satellites, based on the position and velocity of the corresponding GNSS satellite calculated by the position calculation portion, and the position and velocity of the GNSS receiver estimated by the position estimation portion.

13. The GNSS receiver according to claim 11 or 12, wherein the observation data includes at least one of a pseudorange, a rate of change in the pseudorange, and an amount of change in the pseudorange.

14. The GNSS receiver according to any one of claims 11 to 13, wherein the observation data error estimation portion selects possible combinations of the acquired GNSS satellites, estimates the positioning error relating to each of the selected combinations of the GNSS satellites, and selects the combination of the GNSS satellites corresponding to a smallest estimated positioning error; and the positioning computation portion performs the positioning computation using the selected combination of the GNSS satellites corresponding to the smallest estimated positioning error.

15. The GNSS receiver according to any one of claims 11 to 13, wherein the observation data error estimation portion selects combinations of the acquired GNSS satellites so that a variation in the estimated error in the observation data in each of the selected combinations is equal to or smaller than a first predetermined threshold value, estimates the positioning error relating to each of the selected combinations of the GNSS satellites, and selects the combination of the GNSS satellites corresponding to a smallest estimated positioning error; and the positioning computation portion performs the positioning computation using the selected combination of the GNSS satellites corresponding to the smallest estimated positioning error.

16. The GNSS receiver according to any one of claims 11 to 13, wherein after the observation data error estimation portion selects the combinations of the GNSS satellites acquired by the GNSS receiver, and estimates the positioning error relating to each of the selected combinations of the acquired GNSS satellites, the observation data error estimation portion determines whether all the estimated errors in the observation data relating to all the acquired GNSS satellites are equal to or larger than a second predetermined threshold value; if the observation data error estimation portion determines that all the estimated errors in the observation data relating to all the acquired GNSS satellites are equal to or larger than the second predetermined threshold value, the observation data error estimation portion resets selection of the combinations of the GNSS satellites, and selects all the acquired GNSS satellites, and the positioning computation portion performs the positioning computation using all the acquired GNSS satellites; and if the observation data error estimation portion determines that at least one of the estimated errors in the observation data relating to all the acquired GNSS satellites is smaller than the second predetermined threshold value, the observation data error estimation portion selects the combination of the GNSS satellites corresponding to a smallest estimated positioning error, and the positioning computation portion performs the positioning computation using the selected combination of the GNSS satellites corresponding to the smallest estimated positioning error.

17. The GNSS receiver according to any one of claims 11 to 13, wherein after the observation data error estimation portion selects the combinations of the GNSS satellites acquired by the GNSS receiver, and estimates the positioning error relating to each of the selected combinations of the acquired GNSS satellites, the observation data error estimation portion determines whether an average value of absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is equal to or larger than a third predetermined threshold value; if the observation data error estimation portion determines that the average value of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is equal to or larger than the third predetermined threshold value, the observation data error estimation portion resets selection of the combinations of the GNSS satellites, and selects all the acquired GNSS satellites, and the positioning computation portion performs the positioning computation using all the acquired GNSS satellites; and if the observation data error estimation portion determines that the average value of the absolute values of the estimated errors in the observation data relating to all the acquired GNSS satellites is smaller than the third predetermined threshold value, the observation data error estimation portion selects the combination of the GNSS satellites corresponding to a smallest estimated positioning error, and the positioning computation portion performs the positioning computation using the selected combination of the GNSS satellites corresponding to the smallest estimated positioning error.

18. A Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on positioning signals transmitted from a plurality of GNSS satellites, comprising: an observation data computation portion that obtains observation data relating to each of the GNSS satellites, using a code included in the positioning signal transmitted from the corresponding GNSS satellite; a position calculation portion that calculates a position of each of the

GNSS satellites, based on orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; a position estimation portion that estimates a position of the GNSS receiver, based on information other than the positioning signals; an observation data estimation portion that estimates the observation data relating to each of the GNSS satellites, based on the position of the corresponding GNSS satellite calculated by the position calculation portion, and the position of the GNSS receiver estimated by the position estimation portion; an observation data precision estimation portion that estimates a precision of the observation data relating to each of the GNSS satellites, based on the observation data obtained by the observation data computation portion and the corresponding estimated observation data that is estimated by the observation data estimation portion, wherein the observation data precision estimation portion selects combinations of the observation data with precisions equal to or higher than a first predetermined threshold value, calculates a Dilution of Precision (DOP) value relating to each of the selected combinations, selects at least one combination of the observation data based on the calculated DOP values, calculates a Horizontal Dilution of Precision (HDOP) value relating to each of the at least one combination selected based on the calculated DOP values, and selects the combination of the observation data corresponding to a smallest HDOP value; and a positioning computation portion that performs the positioning computation using the combination of the observation data corresponding to the smallest HDOP value.

19. The GNSS receiver according to claim 18 wherein, the position calculation portion calculates the position and velocity of each of the GNSS satellites, based on the orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; the position estimation portion estimates the position and velocity of the

GNSS receiver, based on the information other than the positioning signals; and the observation data estimation portion estimates the observation data relating to each of the GNSS satellites, based on the position and velocity of the corresponding GNSS satellite calculated by the position calculation portion, and the position and velocity of the GNSS receiver estimated by the position estimation portion.

20. The GNSS receiver according to claim 18 or 19, wherein the observation data includes at least one of a pseudorange, a rate of change in the pseudorange, and an amount of change in the pseudorange.

21. The GNSS receiver according to any one of claims 18 to 20, wherein when the observation data precision estimation portion selects the at least one combination of the observation data based on the DOP values, the observation data precision estimation portion selects the at least one combination of the observation data corresponding to the smallest DOP value.

22. The GNSS receiver according to any one of claims 18 to 20, wherein when the observation data precision estimation portion selects the at least one combination of the observation data based on the DOP values, the observation data precision estimation portion calculates an average value of the DOP values, calculates a residual of each of the DOP values from the average value, and selects the at least one combination of the observation data corresponding to the smallest value among values obtained by multiplying the residuals by the respective DOP values.

23. The GNSS receiver according to any one of claims 18 to 20, wherein when the observation data precision estimation portion selects the at least one combination of the observation data based on the DOP values, the observation data precision estimation portion calculates an average value of the DOP values, calculates a residual of each of the DOP values from the average value, determines whether each of values obtained by multiplying the residuals by the respective DOP values is equal to or smaller than a second predetermined threshold value, and selects the combination of the observation data corresponding to the obtained value equal to or smaller than the second predetermined threshold value.

24. The GNSS receiver according to any one of claims 18 to 23, wherein the observation data precision estimation portion determines whether the smallest HDOP value is equal to or smaller than a third predetermined threshold value; if the observation data precision estimation portion determines that the smallest HDOP value is equal to or smaller than the third predetermined threshold value, the observation data precision estimation portion determines that three-dimensional positioning should be performed; and if the observation data precision estimation portion determines that the smallest HDOP value is larger than the third predetermined threshold value, the observation data precision estimation portion determines that two-dimensional positioning should be performed.

25. A positioning method in a Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on a positioning signal transmitted from a GNSS satellite, comprising: obtaining observation data to be observed by the GNSS receiver, using a code included in the positioning signal transmitted from the GNSS satellite; calculating a position of the GNSS satellite, based on orbit information included in the positioning signal transmitted from the GNSS satellite; estimating a position of the GNSS receiver, based on information other than the positioning signal; estimating the observation data, based on the calculated position of the GNSS satellite, and the estimated position of the GNSS receiver; estimating a receiver error that is an error in the GNSS receiver; estimating a common error in the observation data due to the receiver error, based on the estimated receiver error, and estimating an error in the observation data, based on the observation data, the estimated observation data, and the common error; and performing the positioning computation using the observation data whose error is equal to or smaller than a predetermined threshold value.

26. A positioning method in a Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on positioning signals transmitted from a plurality of GNSS satellites, comprising: obtaining observation data relating to each of the GNSS satellites, using a code included in the positioning signal transmitted from the corresponding GNSS satellite; calculating a position of each of the GNSS satellites, based on orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; estimating a position of the GNSS receiver, based on information other than the positioning signals; estimating the observation data relating to each of the GNSS satellites, based on the calculated position of the corresponding GNSS satellite, and the estimated position of the GNSS receiver; estimating a receiver error that is an error in the GNSS receiver; estimating a common error in the observation data due to the receiver error, based on the estimated receiver error, and estimating an error in the observation data, based on the observation data, the estimated observation data, and the common error; selecting combinations of the GNSS satellites acquired by the GNSS receiver; estimating a positioning error that is to occur when the positioning computation is performed using each of the selected combinations of the GNSS satellites, based on the estimated errors in the observation data relating to the GNSS satellites, and arrangement of the GNSS satellites; selecting the GNSS satellites to be used in the positioning computation, based on at least one of i) the estimated errors in the observation data relating to the GNSS satellites and ii) the estimated positioning errors relating to the selected combinations of the GNSS satellites; and performing the positioning computation using the selected GNSS satellites.

27. A positioning method in a Global Navigation Satellite System (GNSS) receiver that performs a positioning computation based on positioning signals transmitted from a plurality of GNSS satellites, comprising: obtaining observation data relating to each of the GNSS satellites, using a code included in the positioning signal transmitted from the corresponding GNSS satellite; calculating a position of each of the GNSS satellites, based on orbit information included in the positioning signal transmitted from the corresponding GNSS satellite; estimating a position of the GNSS receiver, based on information other than the positioning signals; estimating the observation data relating to each of the GNSS satellites, based on the calculated position of the corresponding GNSS satellite, and the estimated position of the GNSS receiver; estimating a precision of the observation data relating to each of the GNSS satellites, based on the observation data and the corresponding estimated observation data; selecting combinations of the observation data with precisions equal to or higher than a first predetermined threshold value; calculating a Dilution of Precision (DOP) value relating to each of the selected combinations; selecting at least one combination of the observation data based on the calculated DOP values; calculating a Horizontal Dilution of Precision (HDOP) value relating to each of the at least one combination selected based on the calculated DOP values; selecting the combination of the observation data corresponding to a smallest HDOP value; and performing the positioning computation using the combination of the observation data corresponding to the smallest HDOP value.