JPH08129061A - Position measuring system - Google Patents

Abstract

PURPOSE: To provide a relatively small and inexpensive position measuring system for a moving body present in a relatively restricted local area. CONSTITUTION: A transmitter 1a having only a transmission function is set in a moving body 1. Transmission signals from the moving body 1 are proper to the moving body 1, not including time data. At least three fixed stations 2-4 are equipped with receivers 2a-4a, respectively. The receivers 2a-4a have time-measuring means 2b-4b to measure the time T1 -T3 when the transmission signals are received. The time-measuring means are synchronized in operation by time-synchronizing means 2c-4c for achieving the time synchronization of fixed stations. The position (Px , Py ) of the moving body 1 is calculated from time differences (T1 -T2 ), (T2 -T3 ) by a position-calculating means 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioning system for positioning the position of a moving body within a relatively limited area (local area) on the ground using a relatively small device, and more Specifically, without using a large-scale positioning system such as Loran C or GPS, there are at least three fixed stations installed on the ground and a mobile body (mobile station) carrying only a transmitter, The present invention relates to a positioning system that determines the position of a moving body.

[0002]

2. Description of the Related Art The most popular method for determining the position on the ground at present is GPS. This is because the microwaves emitted from three or more satellites in different orbits around the earth (in the case of positioning of a moving body on the ground) are received by the moving body on the ground, and the pseudo range between the moving body and each satellite is received. Is calculated and the position of the moving body is determined by calculation. At that time, the mobile body does not have a transmission function, but a reception function for receiving microwaves, a code synchronization function for measuring the pseudo range with each satellite, and a message for decoding information from the satellites. It has a decoding function and a calculation processing function for calculating and determining the position. The positioning system by GPS is mainly used for positioning of automobiles, ships and aircrafts as a civilian application.

Loran C is a positioning system mainly used for positioning ships on the sea rather than on the ground. This installs a master station and two or more slave stations at fixed points on the earth,
The master station and each slave station emit a pulse (each slave station receives a pulse from the master station and then emits a pulse), and the mobile station such as a ship receives the pulse of each station and measures the arrival time difference of the pulse, The position of itself (mobile station) is calculated from the time difference. Also in this case, the mobile body does not have a transmitting function like the GPS, and a receiving function for receiving a pulse, a circuit for measuring a difference in arrival time of pulses, and a calculation processing function for calculating and determining a position. have.

In each of the above-mentioned GPS and Loran C systems, both mobile units have a position measuring device having a reception function, a calculation function, etc., and determine the position of the self (mobile unit) by themselves. It was Such a method is convenient as a positioning method for a moving body that moves in a wide area on the earth. However, when positioning a large number of moving bodies within a limited area on the ground, it is quite problematic to have each moving body carry the position measuring device as described above and use the GPS or Loran C method. is there. Since the above-mentioned position measuring device is relatively large and expensive due to its complicated function, such a position measuring device can be used for a large number of moving objects (for example, people) within a limited area on the ground. This is because carrying the cellphone has the drawback of being too expensive overall.

Therefore, a method called an inverse GPS method has been proposed as a positioning system for a mobile body within a limited area on the ground. FIG. 4 shows a schematic diagram of the reverse GPS system. In the figure, 1 is a moving body, and 2 to 5 are fixed stations (signposts 2 to 5). In the reverse GPS method, contrary to the GPS method, the mobile unit 1 does not have a receiving function but has only a transmitting function,
Send a unique signal. At this time, the mobile unit 1 is characterized by transmitting a unique signal for identifying itself from other mobile units and at the same time transmitting the time T _{0 of the} clock held by the mobile unit 1 itself. In the reverse GPS method, a plurality of fixed stations (signposts) 2, 3, 4, 5 are installed at different positions on the ground, and each fixed station does not have a transmission function contrary to the GPS satellite function. It has a receiving function.
In FIG. 4, the time when each of the fixed stations 2, 3, 4, and 5 received the signal transmitted by the mobile 1 is T ₁ , T ₂ , and
If T ₃ and T ₄ are set, the position of the moving body 1 (P _x , P _y , P _z )
Is the position of each fixed station 2, 3, 4, 5 (X ₁ , Y ₁ ,
Z ₁ ), (X ₂ , Y ₂ , Z ₂ ), (X ₃ , Y ₃ , Z ₃ ),
(X ₄ , Y ₄ , Z ₄ ) and the following relation.

[0006]

[Number 1] ^{_{√ (X 1 -P x) 2}} + (Y 1 -P y) 2 + (Z 1 -P z) 2 = C (T 1 -T 0 + △ t) (1) √ (X 2 _{^{-P x) 2 + (Y 2}} -P y) 2 + (Z 2 -P z) 2 = C (T 2 -T 0 + △ t) (2) √ (X 3 -P x) 2 + (Y ^{_{3 -P y) 2 + (Z}} 3 -P z) 2 = C (T 3 -T 0 + △ t) (3) √ (X 4 -P x) 2 + (Y 4 -P y) 2 + ( Z ₄ −P _z ) ² = C (T ₄ −T ₀ + Δt) (4) where C is the electromagnetic wave velocity and Δt is the offset of the clock of the mobile unit 1 with respect to the clock of the fixed station. (1)-(4)
By solving the equations simultaneously, the unknowns (P _x , P _y ,
P _z ) and Δt are obtained, and the position of the moving body 1 can be determined. Regarding the inverse GPS system, for example, "Local Positioning System by spread spectrum communication system"
One study ”, IEICE Technical Report SST 92-91, March 1993.

[0007]

As described above, there is a problem in using the GPS or Loran C system for positioning a large number of moving objects within a limited area on the ground. In GPS and Loran C, since the moving body itself determines the position of itself, the moving body must carry a position measuring device including a large-scale circuit. However, such position-measuring devices are relatively large and expensive. Therefore, carrying such a position-measuring device with a large number of moving bodies in the area has a drawback that the cost is too high as a whole. Another problem is that the positioning accuracy is too poor with GPS or Loran C for positioning within a limited area. The positioning accuracy is about 100 m for GPS and about several 100 m for Loran C. Such accuracy is too poor to determine the position of the moving body within a limited area within a few kilometers. Therefore, also in that respect, it is difficult to use GPS or Loran C.

On the other hand, the above-mentioned reverse GPS system is a system in which the mobile body carries only the transmitter, so that it is lower in cost than GPS and Loran C, and more suitable for positioning the mobile body in a limited area. This is a suitable method. However, such an inverse GPS system also has drawbacks. In the reverse GPS method, not only the mobile unit transmits a unique signal for identifying itself from other mobile units, but also the mobile unit needs to have its own clock and transmit its own time as information. . The fact that the mobile body has such a clock and needs to send the information makes the circuit of the transmitter carried by the mobile body more complicated, and thus the cost of the transmitter becomes higher and the miniaturization becomes difficult. There is a drawback that Also, on the fixed station side,
Since a circuit for decoding the time information transmitted from the mobile body from the transmission signal is required, the receiving circuit becomes complicated and the cost increases.

An object of the present invention is to provide a positioning system for determining the position of a moving body within a relatively limited area (local area) on the ground by using a relatively small scale device. .

[0010]

In order to achieve the above-mentioned object, the positioning system of the present invention includes at least one mobile station equipped with transmitting means for transmitting a unique position measurement signal having no time information, and At least three fixed stations that receive position measurement signals, time measuring means that measures the reception time of the signals from the reception signals of each fixed station, and the position of the mobile station from the measured reception times of the fixed stations. It is characterized by including position calculating means for calculating and time synchronization means between fixed stations for synchronizing the time measuring operation of the time measuring means.

In the positioning system of the present invention, the transmitting means is configured to generate a signal obtained by modulating a carrier signal with a PN code as the position measuring signal, and the time measuring means includes a convolver, and the convolver includes the convolver. May be configured so that the above-mentioned signal and the reference signal modulated by the time-inverted PN code of the transmission side PN code are input.

Further, different PN codes may be assigned to the respective mobile stations, and the time measuring means may switch the code pattern of the receiving side PN code.

[0013]

In the positioning system of the present invention, the position measurement signal from the mobile station (moving body) is received by each fixed station, and the reception time of each is measured. The position of the mobile station is calculated from each reception time, and the time measurement operation of each fixed station is synchronized. In this case, when the transmission / reception system is configured by the spread spectrum system, time measurement is performed based on the correlation output of the convolver. When different PN codes are assigned to each mobile station, the receiving side PN code pattern is switched correspondingly.

[0014]

Embodiments of the present invention shown in the drawings will be described below.
An embodiment of the positioning system of the present invention is shown in FIG. In the present invention, at least three fixed stations 2, 3, 4 and the position calculation means 5 are installed at different positions on the ground. Also,
The mobile 1 existing in the area surrounded by each fixed station and the area around the fixed station carries a transmitter 1a having only a transmitting function as a transmitting means. In FIG. 1, 1 is shown as a moving body 1.
Although only one is shown, a plurality of moving bodies may exist. In that case, each mobile unit carries only one transmitter. At that time, the signal transmitted from the transmitter of each mobile body is a unique signal for distinguishing each mobile body from other mobile bodies. For example, the frequency of the transmission signal is changed for each mobile body or the modulation code is changed. Shall be changed.
However, unlike the conventional reverse GPS system (FIG. 4), in the present invention, each mobile body does not have a clock, and the signal transmitted from the transmitter 1a is only the unique signal as described above. It is assumed that the time of each mobile unit is not transmitted unlike the method. That is, the difference between the present invention and the conventional reverse GPS system is that each mobile body does not have a clock and does not transmit time information in the present invention.

Each of the fixed stations 2, 3 and 4 of the present invention has receivers 2a to 4 for receiving the signal transmitted from the mobile unit 1.
a is installed respectively. Further, it is assumed that each receiver is provided with time measuring means 2b to 4b for measuring the time when the receiver of each fixed station receives the signal transmitted from the mobile unit 1. At that time, the time measuring means of each receiver is adjusted so as to be time-synchronized with each other, and therefore has fixed station time synchronization means 2c to 4c.

In the present invention constructed as described above, the position (P _x , P _y ) of the moving body 1 is determined as follows. The signals transmitted from the mobile unit 1 are transmitted at positions (X ₁ , Y ₁ ), (X
_2, Y _2), when the (X _3, Y _3, respectively T ₁ the received time in the receiver 2a~4a fixed stations 2, 3, 4 in), T _2, T _3, for each receiver Since the time measuring means 2b to 4b are synchronized with each other, the following equation holds.

(2) √ (P_x-X₁)²+ (P_y-Y₁)²−√ (P_x-X₂)²+ (P_y-Y₂)² = C ・ (T₁-T₂) (5) √ (P_x-X₂)²+ (P_y-Y₂)²−√ (P_x-X₃)²+ (P_y-Y₃)²  = C ・ (T₂-T₃(6) Here, C is the velocity of the electromagnetic wave. Equations (5) and (6)
An unknown position (P_x, P_y)
Can be In terms of drawing, the time difference (T₁−
T₂), (T₂-T₃), (T₁-T₃) Each constant curve is
Each becomes a hyperbola, so draw three hyperbolas and intersect
Unknown position (P_x, P_y) Can be asked.
Such a method is the hyperbolic navigation used in Loran C.
And the position calculating means 5 in the present invention.
Then, an arithmetic circuit for carrying out the above-described method may be used,
It's not particularly difficult.

Next, the form of the signal transmitted from the transmitter carried by the mobile unit 1 of the present invention will be described. The signal transmitted from the transmitter must be capable of detecting the arrival time of the signal at the receivers of the fixed stations 2, 3 and 4. As the transmission signal for that purpose, it is possible to use one of the pulses used in Loran C. However, when a pulse wave is used as the transmission signal, the frequency band used becomes too wide and there is a possibility that it cannot be used under the Radio Law. In addition, the transmitter requires a large amount of power to transmit a pulse wave from a transmitter, which requires a large capacity battery to be used as a power source, which may make the transmitter unsuitable for carrying. Therefore, as a powerful form of the signal transmitted by the transmitter of the mobile unit 1, the carrier is modulated by the pseudo noise code (PN code) as shown in FIG. 2 by the spread spectrum method as used in GPS. It is desirable to use signals. In FIG. 2A, 21
Is a PN code generator (PNG), 22 is a carrier signal generator, and 23 is a modulator. The signal modulated by the PN code can limit the band to a certain width, and can solve the problems of the Radio Law. Also, if the types of PN codes are changed using the same band, the interference of signals with each other can be made extremely small. Therefore, a unique PN code is assigned to each mobile of a large number of mobiles within the area, and each mobile Can be identified. Therefore, it is desirable to use a signal in which the carrier is modulated by the PN code as the signal transmitted from the mobile body in the present invention.

Next, the time measuring means for detecting the arrival time by receiving the transmission wave (spread spectrum signal) from the moving body by the receivers of the fixed stations 2, 3, 4 will be described. Here, a case where a signal obtained by modulating a carrier with a PN code is used as a transmission wave as described above will be described. When the PN code is used as a signal, in order to detect the arrival time at the receiver side, the input PN code and the PN code at the receiver side must be correlated and the time point at which the correlation peak is obtained must be detected. . As a method of obtaining such correlation, D
There are a method using LL, a method using a matched filter, and a method using a convolver. Of these, DLL
The method using can be used when the modulated waves by the PN code are continuously input. However, it is more realistic that the signal transmitted from the transmitter of the mobile unit 1 is transmitted intermittently after a certain period of time, rather than as a continuous wave, in order to save the electric power consumption of the mobile unit. It is thought that there are many.
Therefore, in the case of such an intermittent wave, it is difficult to use the DLL. Therefore, considering a case where an intermittent wave is transmitted, a matched filter and a convolver can be given as candidates for correlation. Among them, the matched filter has a problem that correlation can be obtained only in the case of a specific PN code pattern. Therefore, when different types of PN codes are transmitted from a large number of mobile bodies, it is necessary for the fixed station to prepare as many matched filters as the number of types of PN codes. It is not realistic in terms of circuit scale and cost. Therefore, the use of a convolver is the most effective means of obtaining correlation in the receiver of the fixed station.

FIG. 2B shows an example of a basic circuit configuration when a convolver is used as the time measuring means in the receiver according to the present invention. In the figure, the fixed station 2 includes a bandpass filter (BPF) 6, amplifiers 7 and 13, and local oscillators 9 and 1.
1, mixers 8 and 12, convolver 10, detector 14,
A time counting unit 2b including a time difference measuring unit 15 is provided. The other fixed stations have the same configuration.

As shown in the figure, when the convolver 10 is used, two input terminals 10a, 1 of the convolver 10 are used.
On one side of 0b, a BPF 6, an amplifier 7, a local oscillator 9,
The mixer 8 inputs the modulated wave by the PN code transmitted from the mobile body, and inputs the reference signal in which the carrier is modulated by the bar PN code generated by the PN code generator 16 to the other input terminal of the convolver. To configure. However, the bar PN generated by the PN code generator 16
The code needs to be a bar PN code obtained by time-reversing the PN code transmitted from the mobile body. By doing so with the reference signal, the convolver 10 can take the correlation between the PN code transmitted from the mobile and the bar PN code of the fixed station, and the resulting correlation signal output is detected by the detector 14. The time difference measuring unit 15 can detect the transmission time T ₁ of the signal from the mobile unit 1 from the occurrence time. In the present invention, the input signal input to the convolver (the signal transmitted from the moving body) and the generation timing of the bar PN code generated from the PN code generator 16 are adjusted so as to have the relationship shown in FIG. To be done. The feature of FIG. 3 is that the PN code bars PN generated in each fixed station are synchronized in time so that they occur at the same time. Such time synchronization of the PN code is performed by the fixed station time synchronization unit 2c of FIG. 2 (b). In this way, the reference signal is time-synchronized between the fixed stations because the fixed base stations have the same reference time and the signal transmitted from the mobile station is received by each fixed station (T _{1 in} FIG. 3). , T ₂ , T ₃ ) are correctly detected. If the PN code is not time synchronized,
It will be apparent that the reference time of each fixed station is different and the arrival time of the signal transmitted from the mobile to each fixed station cannot be measured correctly.

As described above, when the convolver is used in the present invention, it is necessary to synchronize the fixed stations with each other when generating the PN code. However, if you pay attention to that point,
The code pattern of the PN code of the reference signal can be switched at any time. It is preferable that the PN code generator 16 of FIG. 2 not only generate a constant bar PN code but can switch the code pattern of the bar PN code in time. It is well known that such switching of the PN code can be easily performed using ordinary digital circuit technology. When the PN code of the reference signal of the convolver is switched as described above, the convolver outputs a large correlation output only when the PN code in the time-reversed relationship of the PN signal is input, and therefore it is used to identify the moving body. can do. That is, as described above, when there are a large number of moving objects, a unique PN code can be assigned to each moving object, but by switching the code pattern of the PN code of the convolver reference signal in time, PN that has a time-reversal relationship with it
Only the code can be discriminated (from the magnitude of the correlation output), which makes it possible to temporally identify the mobile body corresponding to each PN code.

As described above, the use of the convolver in the present invention has an advantage that not only positioning can be performed even when an intermittent wave is transmitted from a moving body, but also the moving body can be easily identified.

[0023]

As described above, according to the present invention,
A relatively limited area on the ground (local area) compared to conventional GPS, Loran C, or reverse GPS
Positioning of a moving body inside can be performed by a smaller scale and lower cost device. As an application example of the present invention, the position of a person in an amusement center, a ski resort, a golf course, or the like can be detected, and the present invention can be applied to search for a lost child and prevent danger. It can also be applied to positioning and control of mobile devices in farms and factories.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration example of a transmission means and a receiver of a mobile unit and a fixed station in the above embodiment.

FIG. 3 is a diagram showing a convolver timing of each receiver of FIG. 2;

FIG. 4 is a block diagram showing a conventional reverse GPS positioning system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mobile 2-4 Fixed station 2a-4a Receiver 2b-4b Time measurement means 2c-4c Time synchronization means 5 Position calculation means

Claims (3)

[Claims] 1. At least one mobile station provided with a transmission means for transmitting a unique position measurement signal having no time information, at least three fixed stations receiving the position measurement signal, and each fixed station. Time measurement means for measuring the reception time of the signal from the received signal, position calculation means for calculating the position of the mobile station from the measured reception time of the fixed station, and time measurement operation of the time measurement means A positioning system comprising: time synchronization means between fixed stations; 2. The transmitting means is configured to generate a signal obtained by modulating a carrier signal with a PN code as the position measuring signal, and the time measuring means includes a convolver, and the convolver transmits the signal together with the signal. The positioning system according to claim 1, wherein the side PN code and a reference signal modulated by a time-inverted PN code are input. 3. The positioning according to claim 2, wherein different PN codes are assigned to the respective mobile stations, and the time measuring means is configured to be able to switch the code pattern of the receiving side PN code. system.