JP2001281320A - Car navigation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a car navigation system capable of improving the use efficiency of a GPS regardless of the presence or absence of SA operation. SOLUTION: A deviation computing unit finds and stores a difference between an own vehicle position estimation result based on map matching and a GPS positioning solution so as to find a mean value. According to the comparison between the mean value calculated by the deviation computing unit and a predetermined value, existence/absence of SA operation is determined, and according to the existence/absence of the SA operation determined in this process, UERE is switched and 2 drms is computed so as to be used as an error estimation value to the GPS positioning solution. Because the existence/absence of the SA operation is reflected on the error estimation value of the GPS positioning, solution, the GPS use efficiency can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in GPS utilization efficiency in a car navigation system.

[0002]

2. Description of the Related Art A GPS signal received by a GPS receiver mounted on a general car navigation system is a C / A code of L1 frequency (about 1.575 GHz) which is open to the public. This C / A code includes SA (Selective Availabili) for the satellite clock inside the GPS satellite.
ty) is added. GPS
If such a SA is operated in
It is generally estimated that the distance to a GPS satellite obtained by measuring a GPS signal by a receiver (this distance is called a pseudorange) includes an error of 20 m to 30 m in some cases. On the other hand, the error of the pseudo distance when the SA is not operated is smaller by one digit than that when the SA is operated.

FIG. 3 shows a configuration of a car navigation system according to the prior art. In FIG. 3, the GPS receiver 2 converts the GPS satellite signals into Ephemeris.
GPS data such as GPS data is extracted and the pseudorange is measured to perform GPS positioning calculation, and the GPS positioning solution and other information are
Output as PS output message 3. NAVI_CP
A dead reckoning calculation unit in U1 is provided from a certain point (base point) based on an output signal from the gyro sensor 12 that outputs a DC voltage proportional to the angular velocity in the turning direction of the vehicle and the speed pulse 13. Is calculated to estimate the current position, and the estimation result (DR positioning result) is output to the positioning filter 23 as the dead reckoning output 22.

The positioning filter 23 calculates an error estimation value for each of the GPS positioning solution and the DR positioning result from the information included in the GPS output message 3 and the information regarding the accuracy of the dead-reckoning sensor included in the dead-reckoning output 22. . Furthermore, based on each error estimate,
After weighting each positioning result, a mixing operation is performed, and the positioning solution is output as a positioning filter output 24.

[0005] In the map matching calculation section 25, the trajectory of the own vehicle indicated by the positioning solution received from the positioning filter 23,
By comparing the characteristics of the map data obtained from the digital map 11, the position having the highest rationality as the own vehicle position is estimated,
The estimated position 26 is output. The estimated position 26 is used as information for displaying the position of the vehicle on the display device of the car navigation system, and is fed back to the dead reckoning calculation unit 21 as a base point for trajectory calculation.

[0006] The positioning filter 23 calculates 2 drms (distance root means square) defined by the following equation, and uses it as an error estimation value for the GPS positioning solution. 2drms = 2 × UERE × HDOP Here, HDOP (Horizontal Dilution Of Precision)
n) is an index for estimating the GPS positioning solution accuracy in the horizontal direction (latitude and longitude directions), and is calculated by a geometric calculation from the arrangement of GPS satellites used for the GPS positioning calculation. URE (User Equivalent Range
Error) is the square of each error factor of satellite orbit error, satellite clock error including SA influence, ionospheric delay error, tropospheric delay error, multipath error, and receiver noise error in GPS pseudorange measurement. Sum,
It is a value determined theoretically and empirically.

According to a commonly used example, the UE
The value of RE is 20.6 m when SA operation is performed, and 5.3 m when SA operation is not performed. Where HDOP =
When calculated as 2.0, 2drms is 82.2 m when SA operation is performed and 21.2 m when SA operation is not performed. As described above, the value of 2drms greatly changes depending on whether SA operation is performed.

[0008]

In calculating 2drms, it is necessary to determine the URE in advance. On the other hand, since the operation of the SA is arbitrarily performed by the administrator of the SA operation, the car navigation system recognizes in advance the presence or absence of the SA operation, and
It cannot be reflected in the calculation of ms. Therefore, if the SA operation is not performed, the above-described positioning filter 23 uses the URE with the SA operation and performs 2 drm.
When s is calculated, the error estimation value of the GPS positioning solution becomes extremely larger than the actual error value. As a result, the weighting for the GPS positioning solution in the mixing operation in the positioning filter 23 is reduced, and the GPS utilization efficiency as a car navigation system is significantly impaired.

The present invention has been made in view of the above problems, and has as its object to provide a car navigation system capable of improving GPS use efficiency regardless of whether SA operation is performed.

[0010]

A car navigation system according to the present invention comprises a judging means for judging the presence / absence of SA operation and a changing means for changing an error estimation value for a GPS positioning solution based on the judgment result by the judging means. Prepare. With this configuration, it is possible to obtain an accurate error estimation value for the GPS positioning solution regardless of the presence or absence of SA operation.

In this case, the determination means includes a deviation calculating unit for calculating an average value of a difference between the result of the vehicle position estimation by map matching and the GPS positioning solution, and a difference between the average value calculated by the deviation calculating unit and a predetermined value. It can be configured by a determination unit that determines the presence or absence of SA operation by comparing. Since the accuracy of the GPS positioning solution is monitored by the deviation calculation unit,
When the accuracy of the GPS positioning solution is increased, it is determined that there is no SA operation, and it is possible to set an error estimation value according to the determination.

Also, it is determined whether or not there is SA operation in the GPS, and the UER is changed according to the result of the determination to change 2drm.
GP that reflects the presence or absence of SA operation by calculating s
It is possible to obtain an error estimate for the S positioning solution.
Accordingly, by estimating the position of the own vehicle using the error estimation value obtained here, a car navigation algorithm that can increase the GPS use efficiency regardless of the presence or absence of SA operation is constructed.

In this case, it is possible to determine the presence or absence of SA operation by calculating the average value of the difference between the own vehicle position estimation result by map matching and the GPS positioning solution, and comparing the average value with a predetermined value.

[0014]

FIG. 1 shows the configuration of a car navigation system according to the present invention. FIG. 2 is a flowchart showing a process of calculating 2 drms in the NAVI_CPU 10 of FIG. In FIG. 1,
Portions that are the same as the functions in the prior art shown in FIG. 3 are denoted by the same reference numerals.

The car navigation system 100 shown in FIG.
In the positioning filter 33, the information contained in the GPS output message 3 and the information about the accuracy of the dead-reckoning sensor contained in the dead-reckoning output 22 are used to calculate G
An error estimation value is calculated for each of the PS positioning solution and the DR positioning result. Further, based on each error estimation value, each positioning result is weighted, and then a mixing operation is performed, and the solution is output as a positioning filter output 34. At this time, the positioning filter 33 outputs 2drm as the estimated error value for the GPS positioning solution obtained from the GPS receiver 2.
Calculate s. The 2d calculated by the positioning filter 33
Details of rms will be described later.

The map matching calculation unit 25 compares the trajectory of the own vehicle indicated by the positioning solution received from the positioning filter 33 with the characteristics of the map data obtained from the digital map 11 and determines the most reasonable position as the own vehicle position. Estimate high position,
Output as the estimated position 36.

The operation of the deviation calculator 31 and the positioning filter 33 will be described with reference to FIG. The deviation calculator 31 calculates the GPS positioning solution sent from the GPS receiver 2 at a predetermined time interval and the estimated position 3 calculated based on the GPS positioning solution and output from the map matching calculator 25.
From 6, the difference between the respective positioning results is obtained. Here, since each positioning result is expressed as coordinates of latitude and longitude, in the calculation of the difference, the difference between the coordinates indicated by each latitude and longitude is calculated as a linear distance (DEV).

The calculation and storage of the DEV are performed in the HD
OP is equal to or less than a predetermined value (DOPref) and GPS
It is executed only when the number of GPS satellites (SATnum) used in the calculation of the positioning solution is equal to or larger than a predetermined number (Nsat) and the value of the estimated position 36 is determined to be valid. (S201). That is, S201
In, by setting the number of GPS satellites used for the GPS positioning calculation and the conditions for HDOP depending on the arrangement of the GPS satellites, it is possible to calculate and store a DEV with a predetermined accuracy or higher. The information as to whether the estimated position 36 is valid is obtained from the map matching calculation unit 2.
5 to the deviation calculation unit 31. Also, HDO
Each information of P and SATnum is a GPS output message 3
Obtained from

Next, the deviation calculator 31 stores the stored D
Average value (DEV) for a fixed number of samples (N) of EV
(mean) is calculated (S202). DEVmean
Is output to the positioning filter 33 as a deviation calculation unit output 32.

In the positioning filter 33, DEVmean is compared with a predetermined threshold value Xref, and DEVm is calculated.
If ean is smaller than Xref, it is determined that the accuracy of the GPS positioning solution has been increased and the SA is not operated (S203: YES). In this case, a value (UEREoff; for example,
5.3m) is substituted (S204), and 2drms is calculated using the URE (S206). Meanwhile, DEV
If mean is equal to or greater than Xref, it is determined that the accuracy of the GPS positioning solution has decreased and that SA operation is being performed (S203: NO). In this case, the value when the SA operation is performed is set as the variable URE (UEREon; for example, 20.6 m).
Is substituted (S205), and 2drm is used by using this UERE.
s is calculated (S206). Note that the calculation of 2drms in S206 is performed according to the following definition: 2drms = 2 × UERE × HDOP.

The 2drms calculated in S206 is compared with the error estimation value for the dead reckoning positioning result in the positioning filter 33 as an error estimation value for the GPS positioning solution, and is used for weighting the GPS positioning solution. Is done.

In the above description, the value used as a criterion for changing the URE is Xref as one value.
However, for example, in the determination of S203, it is determined whether the previous UER is UREon or UREof
f, and UREon to U
Xref for EREoff and UEREoff
It is also possible to set Xref to a different value when used in the case of changing to UERon (that is, to provide Xref with hysteresis) to suppress frequent switching of URE.

[0023]

As described above, according to the present invention,
In the car navigation system, it is possible to change the error estimation value (2 drms) for the GPS positioning solution according to the operation status of SA in GPS. Thus, the positioning filter correctly weights the GPS positioning solution, and the use efficiency of the GPS positioning solution is increased. That is, without being affected by the operation status of SA,
It is possible to realize a car navigation system and a car navigation algorithm that can improve GPS use efficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram of a car navigation system according to the present invention.

FIG. 2 is a flowchart showing a process of calculating 2drms in the car navigation system of the present invention.

FIG. 3 is a block diagram of a car navigation system according to the related art.

[Explanation of symbols]

 Reference Signs List 1 NAVI_CPU1 2 GPS receiver 3 GPS output message 10 NAVI_CPU 11 Digital map 12 Gyro 13 Speed pulse 21 Dead reckoning operation unit 23 Positioning filter 25 Map matching operation unit 31 Deviation operation unit 33 Positioning filter 100 Car navigation system

Claims (6)

[Claims] 1. GPS (Global Positioning System)
A car navigation system, comprising: a judgment unit for judging the presence or absence of SA (Selective Availability) operation in the above, and a change unit for changing an error estimation value for a GPS positioning solution based on a judgment result by the judgment unit. . 2. A deviation calculation unit for calculating an average value of a difference between a result of estimating a position of the vehicle by map matching and a GPS positioning solution, and comparing the average value with a predetermined value for SA operation. The car navigation system according to claim 1, further comprising: a determination unit configured to determine presence / absence. 3. Determine the presence or absence of SA operation in the GPS, and, based on the result of the determination, determine a UER (User Equivalent Ra).
2ge by switching nge Error (user equivalent side distance error)
ms (distance root mean square),
GPS in car navigation system characterized by
Calculation method of error estimation value for positioning solution. 4. The method according to claim 1, wherein an average value of a difference between the own vehicle position estimation result by the map matching and the GPS positioning solution is obtained, and the presence or absence of SA operation is determined by comparing the average value with a predetermined value. A method for calculating an error estimation value for a GPS positioning solution in the car navigation system according to claim 3. 5. A GP according to claim 3 or claim 4.
A method for estimating the position of the own vehicle in a car navigation system, comprising estimating the position of the own vehicle using a method of calculating an error estimation value for the S positioning solution. 6. A storage medium storing the method according to claim 3 as a program to be read and executed by a CPU in a car navigation system.