JP4334104B2 - Car navigation system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a GPS navigation system and a car navigation apparatus that uses GPS as a positioning means.
[0002]
[Prior art]
The car navigation device includes a GPS receiver and a vehicle position determination unit that determines a vehicle position based on a GPS positioning solution and other sensor inputs. Here, the GPS receiver measures the distance (pseudo distance) between the GPS satellite and the GPS receiver itself by tracking the GPS signal transmitted from the GPS satellite and acquiring GPS data, and simultaneously measures the distance. A positioning operation is executed geometrically based on pseudoranges for a plurality of GPS satellites. Further, the GPS receiver calculates the moving speed and traveling direction of the vehicle by measuring the change rate of the carrier frequency of each GPS satellite signal (Doppler measurement), and outputs these calculation results as a GPS output message.
[0003]
At this time, when the number of satellites being tracked is three, the two-dimensional positioning is calculated using latitude and lightness as positions, and when the number of satellites is four or more, the three-dimensional positioning is calculated using latitude, longitude, and altitude as positions. Done. Here, the number of GPS signals that the GPS receiver can simultaneously capture (that is, the number of GPS satellites) is determined by the number of channels of the GPS receiver.
[0004]
On the other hand, the vehicle position determination unit executes an algorithm that rationally determines the vehicle position based on dead reckoning, map matching, and a GPS receiver positioning solution.
[0005]
The GPS signal is a C / A code having an L1 frequency (about 1.575 GHz) that is open to the public. Further, in GPS positioning using a C / A code, the positioning solution is estimated to have an error of about 100 m due to a plurality of error factors. The largest error factor is SA (Selective Availability). Besides this, ionospheric delay error, tropospheric delay error, satellite orbit information error, satellite clock error, multipath error, and GPS receiver thermal noise. There are errors due to this.
[0006]
In order to remove such errors in GPS positioning and improve the accuracy of GPS positioning, a system called DGPS (Differential GPS) is used. With DGPS, it is possible to remove or reduce pseudorange errors caused by SA errors, ionospheric delay errors, tropospheric delay errors, satellite orbit information errors, and satellite clock errors. DGPS broadcasts information such as pseudo-range correction values from a ground reference station, and improves the accuracy of GPS positioning solutions by receiving this broadcast with a car navigation device or the like. Currently, this broadcast is intended for car navigation. Are broadcast by FM multiplexing.
[0007]
The car navigation device corresponding to the above DGPS includes a DARC FM multiplexed DGPS receiver as an internal unit or an external unit separately from the GPS receiver and the vehicle position determination unit. The own vehicle position determination unit inside the car navigation device receives the pseudorange correction value received by the DARC FM multiplexed DGPS receiver and sends the pseudorange correction value to the GPS receiver. The calculation unit in the GPS receiver This correction value is applied to the position calculation. That is, in order to support DGPS as a car navigation device, it is necessary to mount a receiver other than a GPS receiver such as a DARC FM multiplex DGPS receiver in the device, and physical burden and cost burden for that purpose Is a problem.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and provides a GPS receiver that obtains information such as a pseudo-range correction value and outputs a highly accurate positioning solution that reflects the correction value. It is an object of the present invention to provide a car navigation device capable of obtaining a highly accurate GPS positioning solution without providing a receiver.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the car navigation device according to claim 1 is based on a GPS (Global Positioning System) signal and an SBAS (Satellite Based Augmentation System) signal, and includes an error included in the GPS positioning solution. A GPS receiver that generates information, a speed sensor that outputs the speed of the host vehicle, an angular speed sensor that outputs an angular speed of the host vehicle, dead reckoning based on outputs from the speed sensor and the angular speed sensor, and position information and The dead reckoning means for generating the error information included in the position information, the error information included in the GPS positioning solution and the error information included in the position information obtained from the dead reckoning means are compared, and the GPS positioning solution and the position information Of these, navigation calculation means for determining the one with the smaller error as the vehicle position is provided .
[0010]
Among the signals processed by the RF processing means, GPS data is extracted by the GPS correlation processing means and calculation means, and SBAS messages are extracted by the SBAS correlation processing means and calculation means.
[0011]
Furthermore, position information with a smaller error among the position information obtained by the GPS positioning solution and dead reckoning can be adopted as the vehicle position.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a block diagram of a GPS receiver according to the present invention. The SBAS compatible GPS receiver 10 is configured to receive an SBAS signal in order to obtain a highly accurate positioning solution. SBAS is a GPS augmentation system that uses geostationary satellites. The contents of SBAS will be described next.
[0013]
The above-described DGPS is an effective system when the user (GPS receiver) is within a certain distance range from the reference station, and the distance is generally about 200 km. On the other hand, SBAS, which is scheduled for maintenance for aircraft, is a system that covers a range of several thousand km. SBAS is a wide-area reinforcement system that uses geostationary satellites in GNSS, an aircraft navigation system based on GPS and GLONASS, and is planned to be used as WAAS in the US, EGNOS in the EU (European Union), and MSAS in Japan. . SBAS estimates the satellite clock error, satellite orbit information error, and ionospheric delay error including errors due to SA as independent information based on the data of the reference stations installed over a wide area. It can be applied in a wide range as error data.
The abbreviations used here are defined below.
GLONASS: Global Orbiting Navigation Satellite
GNSS: Global Navigation Satellite System
WAAS: Wide Area Augmentation System
EGNOS: European Geostationary Navigation Overlay Service
MSAS: MTSAT Satellite-based Augmentation System
[0014]
The SBAS signal uses a C / A code having the same L1 frequency as GPS, and the data transmission rate from the GPS satellite is 50 bps, whereas the information transmission rate is 250 bps (data transmission rate 500 bps). The point is different. The SBAS signal format is based on the Minimum Operational Performance Standard (MOPS) DO-229 APPENDIX A: Wide Area Augmentation established by the Special Committee (SC-159) of the United States Aeronautical Radio Technical Committee (RTCA). Complies with System Signal Specification.
[0015]
Hereinafter, the operation of the SBAS-compatible GPS receiver 10 will be described in detail with reference to FIG. As shown in FIG. 1, the SBAS compatible GPS receiver 10 down-converts the signal captured by the antenna 5, and a GPS digital correlation that performs a correlation operation on the GPS signal from the output signal of the RF unit 21. The processing unit 22 controls the SBAS digital correlation processing unit 51, the GPS digital correlation processing unit 22, and the SBAS digital correlation processing unit 51 that perform correlation calculation on the SBAS signal from the output signal of the RF processing unit 21, and these correlation processing units It is comprised by the positioning calculating part 23 which performs a positioning calculation based on the output from. In FIG. 1, four GPS digital correlation processing units 22 are shown. The number of GPS digital correlation processing units 22 corresponds to the number of GPS satellites that can be captured simultaneously. It can be changed.
[0016]
In FIG. 1, a portion relating to GPS signal processing, which includes the GPS antenna 5, the RF unit 21, the GPS digital correlation processing unit 22, and the positioning calculation unit 23, is a conventional GPS receiver that does not involve SBAS signal processing. It is the same as the configuration of. That is, the SBAS-compatible GPS receiver 10 receives from the SBAS digital correlation processing unit 52 that receives the same signal as the signal input to the GPS digital correlation processing unit 22, the GPS digital correlation processing unit 22, and the SBAS digital correlation processing unit 51. This configuration is characterized in that it includes a positioning calculation unit 23 to which a correlation processing output is input.
[0017]
In FIG. 1, the GPS signal is processed as follows. A GPS signal having a carrier frequency of 1575.42 MHz captured by the GPS antenna 5 is sent to the RF unit 21. In the RF unit 21, the synthesizer 33 generates a local oscillation frequency based on the oscillation frequency of the reference clock 34. The down-converter 31 mixes the frequency of the GPS signal input from the antenna 5 and the local oscillation frequency, and down-converts the GPS signal to an intermediate frequency signal (drops the frequency). The GPS signal converted to the intermediate frequency is converted to a digital signal by the A / D converter 32 and output to the GPS digital correlation processing unit 22.
[0018]
In the carrier correlation unit 35 of the GPS digital correlation unit 22, the input signal from the A / D converter 32 and the carrier frequency signal generated by the carrier NCO 37 are multiplied and integrated, and a correlation value is calculated. Further, the output signal of the carrier correlation unit 35 is sent to the PRN code (pseudo-random code) correlation unit 36, and is multiplied and integrated with the PRN code signal generated by the code NCO 39 and the PRN code generation unit 38, thereby The correlation value between the output signal of the carrier correlation unit 35 and the PRN code signal is calculated. The PRN code generated here is a PRN code unique to the GPS satellite to be captured.
[0019]
Further, the carrier NCO 37 and the code NCO 39 are connected to the positioning calculation unit 23 by a carrier tracking loop 43 and a code tracking loop 42, respectively. The positioning calculation unit 23 feedback-controls the frequency and phase of the carrier frequency signal generated by the carrier NCO 37 so that the amplitude value of the GPS correlation processing output 41 is maximized, and is generated by the code NCO 39 and the PRN code generation unit 38. The frequency and phase of the PRN code signal to be fed back are controlled. By these feedback controls, the GPS signal is tracked and further inverse spectrum spread to the original narrowband modulation signal.
[0020]
The positioning calculation unit 23 demodulates the signal from the GPS correlation processing output 41 to extract GPS data, and corrects the pseudo distance with the correction value obtained from the SBAS signal, as described later, and executes the positioning calculation. Note that the GPS digital correlation processing units 22 are provided as many as the number of GPS satellites that perform simultaneous acquisition (four channels in the figure), and the respective correlation processing outputs are sent to the positioning calculation unit 23.
[0021]
In FIG. 1, the SBAS signal is processed as follows. As described above, since the SBAS signal is a C / A code having the same L1 frequency as the GPS signal, the GPS antenna 5 and the RF unit 21 for the GPS digital correlation processing unit 22 are shared as shown in FIG. Yes. The SBAS signal is processed as described above without being distinguished from the GPS signal by the RF unit 21, and is converted into an intermediate frequency signal.
[0022]
The SBAS channel / digital correlation processing unit 51 is configured to achieve the same function as the GPS digital correlation processing unit 22. In the SBAS carrier correlation unit 35 ′, the output value from the RF unit 21 and the signal of the carrier frequency generated by the SBAS carrier NCO 37 ′ are multiplied and integrated to calculate the correlation value. Further, the output signal of the SBAS carrier correlation unit 35 ′ is sent to the SBASPRN code correlation unit 36 ′, and is multiplied and integrated with the PRN code signal generated by the SBAS code NCO 39 ′ and the SBASPRN code generation unit 38 ′. Thus, the correlation value between the output signal of the SBAS carrier correlator 35 ′ and the signal of the PRN code output from the SBASPRN code generator 38 ′ is calculated. The PRN code generated here is a PRN code unique to the SBAS geostationary satellite to be captured.
[0023]
The SBAS normally uses one geostationary satellite, and it is sufficient that one SBAS digital correlation processing unit 51 is provided. If multiple SBAS signals from, for example, two geostationary satellites are acquired simultaneously, two SBAS channel / digital correlation processing units 51 may be provided to form a receiver.
[0024]
The SBAS channel correlation processing output 52 is output to the positioning calculation unit 23. The SBAS carrier NCO 37 'and the SBAS code NCO 39' are connected to the positioning calculation unit 23 by a carrier tracking loop 43 'and a code tracking loop 42', respectively. The positioning calculation unit 23 performs feedback control of the frequency and phase of the carrier frequency signal generated by the SBAS carrier NCO 37 ′ so that the amplitude value of the SBAS channel correlation processing output 52 becomes maximum, and also includes the SBAS code NCO 39 ′ and the SBASPRN code. The frequency and phase of the PRN code signal generated by the generation unit 38 ′ are feedback-controlled. By these feedback controls, the SBAS signal is tracked and further subjected to inverse spread spectrum to the original narrowband modulation signal.
[0025]
Further, the positioning calculation unit 23 demodulates the signal from the signal of the SBAS channel correlation processing output 52 according to the SBAS data transmission rate (500 bps), and acquires the SBAS message. The positioning calculation unit 23 performs a positioning calculation by reflecting the correction value for the pseudo distance included in the acquired SBAS message, thereby sending a highly accurate positioning solution reflecting the correction data by SBAS as the GPS output message 3. Is possible.
[0026]
The positioning calculation unit 23 acquires the SBAS message, and outputs one or more information (information obtained from the SBAS) of the following 1) to 7) as the GPS message 3 from the information included in the message. To do.
1) Information on whether correction by SBAS is applied 2) Information on UDRE (User Differential Range Error) 3) Information on UDRE degradation coefficient (change rate) 4) Elapsed time since last correction application 5) Ionospheric delay 6) Horizontal plane error when SBAS is applied (specified by 2drms or 3σ)
7) Three-dimensional error when SBAS is applied (specified by 2σ or 3σ)
[0027]
Note that the error information of 6) or 7) is not directly included in the SBAS message, and the positioning calculation unit 23 uses the information of 2) to 5) to convert the information. . For example, UDRE indicates an error value (an error value as completeness information) that cannot be removed even by applying SBAS for a pseudorange, and this error value is expressed in a horizontal plane (two dimensions) or 3 according to a geometric principle. Information of 6) or 7) is obtained by converting into a value on a dimensional space. In this case, the error in 6) in the horizontal plane may be defined by 3σ (σ: standard deviation) of the error value as the completeness information, or may be defined by 2drms which means the horizontal radius of the error. . The three-dimensional error in the above 7) may be defined by 2σ of the error value as the integrity information or may be defined by 3σ. The information obtained from these SBAS makes it possible to know whether or not the correction by SBAS is applied to the GPS positioning solution included in the GPS output message 3, and provides a highly accurate GPS positioning solution in the application of SBAS. It is possible to accurately estimate the degree of error included.
[0028]
By installing the SBAS-compatible GPS receiver 10 described above, the car navigation device can use not only the result of the positioning solution by GPS but also the information obtained from the SBAS when determining the position of the vehicle. It becomes. FIG. 2 shows the configuration of a car navigation apparatus equipped with the SBAS-compatible GPS receiver 10.
[0029]
In FIG. 2, NAVI_CPU 1 determines its own vehicle position based on dead reckoning, map matching, and GPS positioning solution, and performs all processes necessary as a car navigation device such as route calculation from the current position to the destination. CPU for performing. The speed pulse 13 is a pulse signal whose frequency changes in proportion to the traveling speed of the automobile, and can be extracted from most automobiles. The gyro 12 outputs a DC voltage corresponding to the angular velocity in the turning direction of the automobile. The digital map 11 is obtained by converting a map mainly composed of roads into digital data, and is usually packaged as a medium such as a CD-ROM or a DVD-ROM.
[0030]
The NAVI_CPU 1 is connected to the SBAS-compatible GPS receiver 10 and acquires information obtained from the above-described SBAS together with the GPS positioning solution. Further, the gyro 12 and the speed pulse 13 input to the NAVI_CPU 1 are used for dead reckoning (dead reckoning navigation). In addition, as a sensor for dead reckoning, a technique using a geomagnetic sensor or other sensors is also known, and the car navigation apparatus 20 may be configured to use such a sensor. Information contained in the digital map 11 is used for displaying a map on a display device (not shown) and also for performing map matching.
[0031]
The NAVI_CPU 1 obtains from the above-mentioned SBAS as an estimated error value of the GPS positioning solution in a scene where it is determined which position information of the position obtained from the sensor for dead reckoning or the GPS positioning solution is more reliable. Among the information to be obtained, for example, the error in the horizontal plane of the above 6) is used, and an estimated value of the error included in the sensor output for dead reckoning is obtained by a method specific to each sensor, and each estimated error value is used as a comparison value. It is possible to employ position information with a smaller error estimate as the vehicle position.
[0032]
【The invention's effect】
As described above, according to the SBAS-compatible GPS receiver according to claim 1, the pseudo-range correction value by SBAS is acquired, and a high-accuracy GPS positioning solution is output and information obtained from SBAS is output. It becomes possible. In addition, according to the car navigation device of the second aspect, it is possible to obtain a high-accuracy GPS positioning solution and determine the vehicle position based on the positioning solution without providing a DARC FM multiplex receiver. It is. Furthermore, according to the car navigation apparatus of the third aspect, it is possible to construct and execute a navigation algorithm that effectively uses information obtained from SBAS.
[Brief description of the drawings]
FIG. 1 is an internal block diagram of a SBAS compatible GPS receiver according to the present invention.
FIG. 2 is a block diagram of a car navigation device equipped with an SBAS-compatible GPS receiver.
[Explanation of symbols]
1 NAVI_CPU
5 GPS antenna 10 SBAS compatible GPS receiver 11 Digital map 12 Gyro 13 Speed pulse 20 Car navigation device 21 RF unit 22 Digital correlation processing unit 23 Positioning calculation unit 51 SBAS channel digital correlation processing unit

Claims (1)

A GPS receiver that generates a GPS positioning solution and error information included in the GPS positioning solution based on a GPS (Global Positioning System) signal and an SBAS (Satellite Based Augmentation System) signal;
A speed sensor that outputs the speed of the vehicle,
An angular velocity sensor that outputs an angular velocity of the vehicle;
Dead reckoning means for performing dead reckoning based on outputs from the velocity sensor and the angular velocity sensor, and generating position information and error information included in the position information;
The error information included in the GPS positioning solution is compared with the error information included in the position information obtained from the dead reckoning means, and the smaller one of the GPS positioning solution and the position information is determined as the vehicle position. Navigation calculation means to determine;
A car navigation device comprising:

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