JPH08170983A - Fixed station for differential global positioning system and navigation system using the same - Google Patents

Abstract

PURPOSE: To transmit error information for differential GPS of a large quantity at a high speed to a mobile unit by using an FM broadcasting. CONSTITUTION: A reference station 10 in a base station 100 calculates the error of a position measured value obtained by receiving a radiowave from a GPS satellite from a true position. Fixed station information including the calculated error information and health information of all GPS satellites is minimum- transition-keying-modulated by using 75kHz subcarrier by an organizer and a modulator 14, and transmitted to a mobile unit 200 via an FM transmitter 16 and an antenna 18. The fixed station information is demodulated by the FM multiplex receiver 22 of the unit 200, and output to a DGPS receiver 20. The receiver 20 corrects the error information for transmitting the measured position value calculated based on the radiowave from the GPS satellite, and calculates the true position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed station for a differential global positioning system and a navigation system using the same, and more particularly to a system using FM multiplex broadcasting.

[0002]

2. Description of the Related Art In recent years, a global positioning system (GPS) has been used which receives radio waves from a plurality of artificial satellites orbited around the earth and detects the reception position. From each satellite, its orbital data is multiplied by a pseudo-random (PRN) code to spread the spectrum, and the carrier is phase-modulated with the spread signal, and the signal from the i-satellite is received on the earth. ,
From the difference T between the reception time of the PRN code and the transmission time of the PRN code and the propagation velocity C of the radio wave, the distance between the i satellite and the reception point can be calculated. However, since the time error E of the GPS receiver is actually included, this distance CT is a pseudo distance. Since the unknowns are the reception points (X, Y, Z) and the time error E, these values can be known by receiving the radio waves from the four satellites.

However, when positioning is performed using a C / A code that is generally released as the PRN code, the PR
100m due to N code time resolution and human error
It is said that some distance error occurs.

Therefore, conventionally, an error in the positioning value by GPS at a fixed point whose true position is known or its correction value is notified to the moving point, and the positioning value is corrected based on the correction value at the moving point. Has proposed a differential GPS (hereinafter referred to as DGPS) that improves accuracy.

For example, in Japanese Utility Model Laid-Open No. 6-16888, a GPS positioning value (Xs, Ys, Z is determined by a fixed station whose true position is known.
error (correction value) ΔX = Xo−Xs ΔY = Yo−Ys ΔZ = Zo−Zs with respect to the true position (Xo, Yo, Zo) of A configuration is disclosed in which RDS data is organized as fixed station information, multiplexed from an antenna to FM broadcasting, and transmitted to a mobile body. Here, RDS (Radio
Data System) is a method for multiplexing digital data on a 57 kHz subcarrier of FM broadcasting using BPSK (two-phase phase shift keying), and is an FM multiplexing method that is mainly used in Europe and the United States.

[0006]

However, the RDS
The method has a problem in that the data transmission speed is relatively slow and the number of data that can be transmitted within a fixed time is limited. Therefore, for example, even when the health information indicating the functional state of the used GPS satellite is added to the fixed station information to be transmitted, the limited G
If only the health information of the PS satellite can be sent (specifically, the health information of only the GPS satellite that sends the error information), and the visible GPS satellites are different before and after traveling through a long tunnel,
When the GPS satellite has a malfunction after passing through the tunnel, there is a problem that positioning is performed based on an erroneous radio wave from the GPS satellite until the health information of the GPS satellite is received next time.

The present invention has been made in view of the above problems of the prior art, and an object thereof is a DGPS for which the data transmission speed can be made higher than that of the RDS system and therefore more fixed station information can be transmitted to a mobile body. It is to provide a fixed station and a navigation system using the fixed station.

[0008]

In order to achieve the above object, a fixed station for DGPS according to claim 1 is a positioning means for receiving a radio wave from an artificial satellite to measure the position, and a positioning means for obtaining the position. In the fixed station for DGPS, which comprises an error calculating means for calculating an error between the obtained position and a known true position, and a transmitting means for transmitting fixed station information including the calculated error information, the transmitting means comprises: Station information of FM broadcast 76
It is characterized in that it is transmitted by a minimum transition keying modulation method using a kHz subcarrier.

Further, in order to achieve the above object, the fixed station for DGPS according to claim 2 is the fixed station for differential global positioning system according to claim 1, wherein the transmitting means includes a plurality of pieces of fixed station information. It is characterized in that the error information of eight artificial satellites is included in two data packets transmitted in each transmission frame.

In order to achieve the above object, the fixed station for DGPS according to claim 3 is the fixed station for differential global positioning system according to claim 1, wherein the fixed station information includes the error information. Is characterized in that different data areas include an ID code that makes a cycle through six repetitions that can identify each of six consecutive transmission frames, and information about the latitude, longitude, and altitude of the fixed station.

In order to achieve the above object, the fixed station for DGPS according to claim 4 is the DGPS fixed station according to claim 1.
In the fixed station for use, the fixed station information includes health information of all artificial satellites in a data area different from the error information.

In order to achieve the above object, the fixed station for DGPS according to claim 5 is the DGPS fixed station according to claim 4.
In the fixed station for health, the health information of the artificial satellite is characterized by allocating the health information of each satellite to each bit of the data area.

In order to achieve the above object, the fixed station for DGPS according to claim 6 is the DGPS according to claim 1.
In the fixed station for use, the transmitting means alternately transmits new and old error information for a predetermined time with respect to the artificial satellite in which the ephemeris switching has occurred.

Further, in order to achieve the above object, the navigation system according to claim 7 is a navigation system according to claim 1 or claim 2 or claim 3 or claim 4 or claim 5.
Alternatively, a receiving unit for receiving the FM broadcast transmitted from the DGPS fixed station according to claim 6, a demodulating unit for demodulating fixed station information included in the received signal, and a position measured by receiving radio waves from an artificial satellite. And a position calculating unit that calculates a true position based on the demodulated error information and the position obtained by the second positioning unit.

[0015]

The present invention is based on the FM developed by NHK (registered trademark).
DARC (Data Radio), which is one of multiple broadcasts
The correction value data for DGPS is transmitted by FM broadcasting using the Channel: trademark system. DAR
C ™ uses LMSK (L, which uses a 76 kHz subcarrier and controls multiple levels according to a stereo audio signal.
ever Controlled Minimum S
This is a Hift Keying method, and high-speed transmission of 16 kbps is possible. Therefore, by using this DARC, error information of many satellites can be efficiently transmitted as fixed station information.

As will be described later, in the DARC system, each transmission frame is composed of 272 blocks in 5 seconds, and each block has a data packet or a parity packet. In the present invention, 2 of each transmission frame is used.
The error information of eight GPS satellites is sent out using one data packet. Usually, the number of GPS satellites that can be seen in the sky, that is, the number of GPS satellites that can be received is eight or less. Therefore, by incorporating the error information of eight GPS satellites in one transmission frame, the error information can be efficiently sent.

The error information of eight or more GPS satellites and other accompanying information are transmitted in the next transmission frame, and transmission of all fixed station information is completed in six consecutive transmission frames. An ID code is attached to these 6 consecutive transmission frames so that they can be identified. Further, by transmitting the position information of the fixed station itself together with the error information, it is possible to correct the positioning value with higher accuracy. Becomes

The advantage of the DARC system is that a large amount of data can be transmitted at high speed, and by utilizing this, the health information of all GPS satellites can be transmitted.
The health information of the GPS satellite is information indicating whether or not the GPS satellite is functioning normally, and the base station detects the health information included in the radio wave from the GPS satellite or determines the functional state of the GPS satellite. Judge and send. In the conventional method, the error information itself accompanies the health information (for example, when the correction value data are all 1 in an unhealth state, etc.), in the present invention, the health information of the GPS satellite is a GPS satellite that requires the error information. Not only this, all the GPS satellites are assigned to each bit of a data area different from the error information data area and transmitted. Therefore, for example, when a 12-bit data area is secured, the health information of 12 GPS satellites in total can be transmitted.

As a result, in the mobile body which receives the FM radio wave from the fixed station and corrects the GPS positioning, whether the GPS satellite is in the health state or the unhealth state even if the GPS satellite to be received changes. Since it can be known in advance, positioning is not performed based on incorrect orbit data from GPS satellites in an unhealthy state.

Further, according to the present invention, in order to cope with the switching of the ephemeris (orbit detailed parameter of the GPS satellite) at regular time intervals, new and old error information is alternately transmitted within a predetermined time after the ephemeris switching occurs. In the mobile body that receives the FM broadcast from the base station, the positioning value calculated based on the radio wave from the GPS satellite is received from the base station.
Although the true current position is calculated by correcting with the error information included in the M broadcast, there is a delay between the time when the radio wave from the GPS satellite is received and the time when the error information sent from the base station is received. Therefore, for example, at time t1, G
Orbit data is received from the PS satellite S, the ephemeris of the GPS satellite S is switched at time t2, and
Considering the case where the error information sent from the base station in 3 is received, the data used for positioning by the mobile is based on the old ephemeris, while the error information sent from the base station is based on the new ephemeris. However, the moving object cannot correct the positioning value using this error information, and the error information based on the old ephemeris is necessary. Therefore, in the present invention, old and new error information is alternately transmitted,
Positioning value correction on the mobile side is possible.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall system configuration of this embodiment. This system includes a fixed base station 100 and a mobile unit 200. The base station 100 includes a fixed reference station 10, a composer 12, a modulator 14, an FM transmitter 16 and an F transmitter.
The mobile unit 200 is configured to include the M station transmitting antenna 18.
Includes a GPS antenna, a DGPS receiver 20 and an FM multiplex receiver 22. The fixed reference station 10 constitutes error calculation means of the fixed station, and the knitting device 12 and the modulator 1
4. The FM transmitter 16 and the FM station transmitting antenna constitute the transmitting means of the fixed station. The reference station 10 receives radio waves from GPS satellites to measure its own position, and calculates an error between the positioning data and the true position. As will be described later, in this embodiment, the correction value data is ΔX = Xo−Xs, ΔY.
= Yo−Ys, ΔZ = Zo−Zs, not the difference between the pseudo distance and the true distance between each GPS satellite and the reference station. Further, the reference station 10 detects the functional states of all the satellites and outputs them to the knitting machine 12 as health information. The knitting device 12 inputs the correction value data and the health information from the reference station 10 and formats them into DARC data for FM multiplexing as described later. The modulator 14 modulates the DARC data from the knitting device 12 by the minimum transition keying modulation method using a 76 kHz subcarrier and also modulates a normal FM audio signal, and the FM transmitter 16 and the transmission antenna 18 perform FM multiplex broadcasting. Send.

The FM broadcast from the base station 100 is transmitted to the mobile unit 2.
No. 00 FM multiplex receiver 22 demodulates a normal FM audio signal, and 76 kHz subcarriers are separated by a filter to demodulate fixed station information.
It is output to the S receiver 20. DGPS receiver 20
Corrects the positioning value based on the positioning value based on the GPS radio wave received by the GPS antenna, the correction value data and the health information included in the fixed station information input from the FM multiplex receiver 22, and calculates the true position. .

The correction value data as the error information and the DARC format of the health information will be described in detail below.

The DARC transmission frame structure is shown in FIG. One frame is composed of 272 blocks, and one frame is transmitted in 5 seconds. Each block is
It has a data packet or a parity packet, and the data packet is composed of 190 bits including CRC data. However, the actual information amount of the data packet is 144 bits excluding the prefix and the like. In such a transmission frame structure, fixed station information including correction value data and health information is transmitted using two data packets in one frame. That is, 144 × 2 = 288 bits / 5 seconds.

FIG. 3 shows a transmission format of fixed station information in two data packets (288 bits) in one frame. Bit positions 1 to 3 are bits of the data ID, and 000 to 1 also serve as a sequential number.
It increments in sequence between 01. Therefore, fixed station information that does not fit in two data packets is transmitted using data packets having consecutive data IDs within the frame in the next 5 seconds, and transmission of all data is completed in a maximum of 6 frames and 30 seconds. Bit position 2 is time correction T
, And the value is determined based on the time when the correction value data was obtained by the reference station 10. Specifically, when the time when the correction value data was obtained is an even time, it is "0",
It becomes '1' at odd time. The value of this time correction bit allows the DGPS receiver 20 of the mobile unit 200 to correct the time delay with the base station 100. Bit positions 5 to 276 are bits of the correction value data, and eight G
34 bits are allocated to each PS satellite.
That is, the correction value data of the first GPS satellite is assigned to bit positions 5 to 38, the correction value data of the second GPS satellite is assigned to bit positions 39 to 72, and the correction value of the third GPS satellite is corrected. Value data is assigned to bit positions 73 to 106, and so on for the eighth G
The correction value data of the PS satellite is assigned (see FIG. 4). Generally, the number of GPS satellites that can be observed at one point on the earth is 8 or less at 95% of the time, so
Generally, sufficient correction value data can be sent in one frame. Bit positions 277 to 288 are bits of communication data, and health information of all GPS satellites is assigned to this data area.

As described above, the transmission format of 288 bits of two data packets in one frame is composed of a data ID which is a code that makes a cycle every six frames, correction value data of eight GPS satellites, and communication data. , When actually transmitted as FM multiplex radio waves,
It is sent from the LSB (least significant bit) in 8-bit units,
Specifically, 8, 7, 6, 5, 4, 3, 2, 1, 16,
15, 14, 13, 12, 11, 10, 9, 24, 2
It is transmitted in the order of 3, 22, 21, ....

FIG. 5 shows the contents of the correction value data of each satellite. The correction value data is the scale factor SF
(1 bit), user differential range error UDRE (2 bits), satellite IDSt. ID (5
Bit), a pseudo distance correction value PRC (11 bits), a distance change rate correction value RRC (7 bits), and an issue of data IODE (8 bits). SF is PR
It shows the order of C and RRC, and UDRE is
It represents the accuracy of the true position obtained using the correction value data. The ID represents the GPS satellite number.
Further, PRC is a correction value of the pseudo distance from each GPS satellite, and this is based on the pseudo distance between the GPS satellite and the reference station 10 calculated based on the radio wave received from each GPS satellite, and the true position of the reference station 10. It is the difference in the distance from the GPS satellite calculated by That is, as described above, the correction value data calculated by the base station is the GPS positioning value (Xs, Ys, Z
s) error ΔX, Δ with respect to the true position (Xo, Yo, Zo)
Although Y and ΔZ can be calculated as an error between the pseudo distance and the true distance between the base station and each GPS satellite, in the present embodiment, the error of the pseudo distance for each GPS satellite is corrected data. To send as. RRC represents the rate of change of the correction value, and the correction value at any time is interpolated by the DGPS receiver 20 based on PRC and this RRC. IODE is a code that each GPS satellite adds to its orbital data. By receiving orbital data with the same code by the DGPS receiver 20, correction based on the same orbital data used by the reference station 10 is possible. Become.

FIG. 6 shows the format of communication data assigned to bit positions 277-288. Health information of all GPS satellites is assigned to the area of this communication data, and the communication data in one frame is 12 bits, and the health information of each GPS satellite is assigned to each bit. For example, the health information of the first to twelfth GPS satellites is assigned to the communication data of the data packet of ID = 000 in the first frame, and the data of ID = 001 5 seconds after the second frame is assigned. Health information of the 13th to 24th GPS satellites is assigned to the communication data of the packet, and ID = 0 after 5 seconds after the third frame.
The health information of the 25th to 32nd GPS satellites is assigned to the communication data of 10 data packets (currently, the GPS satellites orbit the earth 6
There are a total of 24 on each orbital surface, but here 3
2). The health information of each GPS satellite is 1 bit, and "0" represents health (normal) and "1" represents unhealth (abnormal). Therefore, '00100000000
The case of 0'indicates that the third GPS satellite is in an unhealth state. Note that the fourth frame ID = 01
The health information of the fixed station 100 is assigned to the communication data of the first data packet, and the other communication data of the fifth frame and the sixth frame are reserved. Here, the reference station 1 in the fixed station 100
The information of the true position of 0, that is, the information of the latitude, the longitude and the altitude is assigned, and the position information of the fixed station is notified to the mobile body 200 together with the correction value data and the health information. The distance over which the radio wave from the GPS satellite propagates in the ionosphere greatly differs when the fixed station and the moving body are separated, so the accuracy of the positioning value correction on the moving body side decreases as the distance between the fixed station and the moving body increases. Therefore, by notifying the position information of the fixed station to the moving body in this way and estimating the influence of the distance by the DGPS receiver 20 on the moving body side, it is possible to reduce the deterioration of the correction accuracy.

Thus, in this embodiment, one frame 5
Correction value data and 1 for 8 satellites at 288 bits per second
The health information of two satellites is transmitted, and the transmission of all the correction data is completed in 30 seconds for 6 frames. However, the orbit detailed parameters (ephemeris) transmitted from each GPS satellite are switched at regular intervals. . Therefore, it is necessary for the base station 100 to send the correction value data of each GPS satellite to the mobile body in response to the ephemeris switching.

However, the correction value data is calculated for the time when the orbit data of the satellite is received by the mobile unit 200 and the orbit data received by the base station 100, and the correction value data is transmitted to the mobile unit 200 to receive the correction value data. Since there is a time lag at the time, the correction value data based on the old ephemeris may be required on the mobile body 200 side within a predetermined time after the ephemeris switching occurs.

Therefore, in the present embodiment, even when such ephemeris switching occurs, not only the correction value data based on the new ephemeris but also the correction value data based on the old ephemeris are transmitted from the base station 100. .

7 to 9 show a data format transmitted from the fixed station 100 when the ephemeris is switched. FIG. 7 shows a case where there are eight visible GPS satellites in the base station and the ephemeris switching occurs in the second GPS satellite and the third GPS satellite among them. In the data packet of ID = 000 in the first 5 seconds, the correction value data based on the old ephemeris is transmitted. The correction value data based on the new ephemeris is sent in the data packet of ID = 001 in the next 5 seconds. The correction value data based on the old ephemeris is sent again in the data packet of ID = 010 in the next 5 seconds, and the correction value data based on the new ephemeris is sent in the data packet of ID = 011 in the next 5 seconds. Thereafter, similarly, correction value data based on the old ephemeris and correction value data based on the new ephemeris are alternately transmitted, and new and old data are transmitted every 10 seconds. Therefore, the moving body 200
In the DGPS receiver 20, the correction value data is normally obtained every 5 seconds, but it is set to 1 when the ephemeris is switched.
It will be obtained every 0 seconds, but in such a short time, sufficient accuracy (10 m or less) can be obtained for practical use.

On the other hand, FIG. 8 shows 10 visible GPS satellites at the base station, of which the second GPS satellite and the third GPS satellite are
This is the case when the ephemeris switching occurs in the satellite. In this case, the correction value data of the GPS satellites cannot be sent in one frame, and the correction value data of the remaining two GPS satellites will be sent in the next frame. Therefore, the normal G
When the correction value data of the PS satellite can be sent every 5 seconds,
It may be possible to send it out after 10 seconds. When the ephemeris switching occurs, the old and new correction value data are alternately transmitted, so that there are cases where the old and new data can be transmitted after 10 seconds and cases where they can be transmitted after 15 seconds.

FIG. 9 shows 12 visible GPS satellites at the base station.
This is the worst case in which ephemeris switching occurs in all GPS satellites. In this case, since the old and new correction value data are alternately sent, the old and new correction value data are sent every 15 seconds.

As described above, in the case of FIGS. 8 and 9, the time interval at which the correction data is obtained becomes a maximum of 15 seconds when the ephemeris is switched, but it rarely occurs in the cases of FIGS. 8 and 9 and is practically used. I think there is no problem.

As described above, in the present embodiment, the correction value data of old and new ephemeris are alternately transmitted for 3 to 5 minutes, so the DGPS receiver 20 of the mobile unit 200
The positioning value can be surely corrected based on the orbit data from the GPS satellite in which the ephemeris has been switched.

[0038]

As described above, according to the first to seventh aspects of the present invention, since a large amount of error information for DGPS can be transmitted at high speed, the efficiency of DGPS can be improved. You can

Further, since the fixed station information includes health information of all GPS satellites, G in the unhealthy state is included.
Positioning is not performed based on erroneous orbital data from PS satellites, and reliability can be further improved.

Further, even when the ephemeris of the GPS satellite is switched, not only the error information based on the new ephemeris is immediately transmitted, but the error information based on the old ephemeris is alternately transmitted within a predetermined time, so that the mobile unit It is possible to prevent erroneous correction due to the time difference between the reception time of the GPS radio wave and the reception time of the FM radio wave from the fixed station, and correct the positioning value.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a transmission format of the embodiment.

FIG. 3 is an explanatory diagram of a data packet format of the embodiment.

FIG. 4 is an explanatory diagram of data contents of a data packet of the embodiment.

FIG. 5 is an explanatory diagram of contents of correction data according to the embodiment.

FIG. 6 is an explanatory diagram of a format of communication data according to the embodiment.

FIG. 7 is an explanatory diagram of a transmission format when switching ephemeris according to the same embodiment.

FIG. 8 is an explanatory diagram of another transmission format when switching the ephemeris according to the same embodiment.

FIG. 9 is an explanatory diagram of another transmission format when switching the ephemeris according to the same embodiment.

[Explanation of symbols]

10 reference station, 12 trainer, 14 modulator, 16 transmitter, 18 transmitting antenna, 20 DGPS receiver,
22 FM multiplex receiver, 100 base station, 200 mobile.

Claims (7)

[Claims] 1. A positioning means for receiving a radio wave from an artificial satellite to measure a position, an error calculating means for calculating an error between the position obtained by this positioning means and a known true position, and the calculated error. A fixed station for a differential global positioning system, comprising: a transmitting unit that transmits fixed station information including information, wherein the transmitting unit transmits the fixed station information to an FM broadcast of 76 kHz.
A fixed station for a differential global positioning system, characterized by transmitting with a minimum transition keying modulation method using z subcarriers. 2. The fixed station for a differential global positioning system according to claim 1, wherein the transmitting means transmits the fixed station information in a plurality of transmission frames, and two data packets in each transmission frame are transmitted. Fixed station for differential global positioning system, characterized in that it contains error information for each satellite. 3. The fixed station for a differential global positioning system according to claim 1, wherein in the fixed station information, six consecutive transmission frames can be identified in a data area different from the error information. A fixed station for a differential global positioning system, characterized in that it includes an ID code that repeats one cycle and information about the latitude, longitude, and altitude of the fixed station. 4. The fixed station for a differential global positioning system according to claim 1, wherein the fixed station information includes health information of all artificial satellites in a data area different from the error information. Fixed station for differential global positioning system. 5. The fixed station for a differential global positioning system according to claim 4, wherein the health information of the artificial satellite is assigned to each bit of the data area. Fixed station for global positioning system. 6. The fixed station for a differential global positioning system according to claim 1, wherein the transmitting means alternately transmits old and new error information for a predetermined time with respect to an artificial satellite in which ephemeris switching has occurred. Fixed station for differential global positioning system. 7. Claim 1 or claim 2 or claim 3.
Alternatively, a receiving unit that receives the FM broadcast transmitted from the fixed station for the differential global positioning system according to claim 4, 5 or 6, and a demodulating unit that demodulates the fixed station information included in the received signal. A second positioning means for receiving a radio wave from an artificial satellite and measuring a position; and a position calculating means for calculating a true position based on the demodulated error information and the position obtained by the second positioning means. Navigation system characterized by.