JPH08146110A - Location measuring unit - Google Patents

Abstract

PURPOSE: To determine the location of a moving body in a comparatively confined area on the ground (a local area) using a comparatively small-scale device. CONSTITUTION: At least three or more of fixed stations 2, 3, 4 are established at different locations on the ground, and further a fixed station 6 equipped with only a transmitter is established on the ground. A moving body existing in an area surrounded by the respective fixed stations and/or in the vicinity of the area is equipped with a transmitter having only a transmitting function, or is made to carry the same. When the moving bodies are plural, the signals transmitted from the respective moving bodies are to be their own signals for distinguishing the respective moving bodies from each other. Since the transmitters of the respective moving bodies are equipped with no time register, the signals remitted from the transmitters include no time data. The location of the moving body can be obtained from the respective arriving times of the signals from the moving body and the fixed station 6 measured by the fixed stations 2, 3, 4, and from the already known locations of the fixed stations 2, 3, 4, 6, no synchronizing the respective stations in time is required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position measuring system for positioning the position of a moving body within a relatively limited area (local wear) on the ground using a relatively small-scale device.

[0002]

2. Description of the Related Art The most popular method for determining the position on the ground at present is GPS. This is 3 or more in different orbits that orbit the earth (for positioning of moving objects on the ground)
The microwave emitted from the satellite is received by the mobile body on the ground, the pseudo distance between the mobile body and each satellite is calculated, and the position of the mobile body is determined by calculation.

At this time, the mobile body does not have a transmitting function, but has a receiving function for receiving microwaves, a code synchronizing function for measuring a pseudo distance from each satellite, and a code for decoding information from the satellites. Has a message decoding function and a calculation processing function for calculating and determining the position. The positioning system based on 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. These have a master station and two or more slave stations installed at fixed points on the earth, and emit pulses from each master station and each slave station (each slave station receives a pulse from the master station and then emits a pulse),
A mobile station such as a ship receives a pulse from each station, measures the arrival time difference of the pulses, and calculates the position of itself (mobile station) from the time difference. In this case as well, like the GPS, the mobile body does not have a transmission function, but has a reception function for receiving pulses and a calculation processing function for measuring the arrival time difference of the pulses.

In the above-mentioned GPS and Loran C systems, both mobile units have a position measuring device having a receiving function, a calculating function, etc., and determine the position of the self (mobile unit) by themselves. Such a method is convenient as a positioning method for a moving object that moves in a wide area on the earth.

However, when the GPS or Loran C method is used for positioning a large number of moving bodies in a limited area on the ground, each moving body is equipped with the position measuring device as described above or is carried. But there is a problem with this. That is, since the above-mentioned position measuring device is relatively large in size due to its complicated function and is expensive, it is generally installed in a large number of moving objects within a limited area or carried by a person. There is a drawback that the cost becomes too high, and there is a problem that it is too large especially when carried by a person.

[0007] In order to solve such problems,
A method called an inverse GPS method has been proposed as a positioning system for a large number of moving objects within a limited area on the ground.
FIG. 5 shows a schematic diagram of the reverse GPS system. In FIG. 5, 1 is a moving body, and 2 to 5 are fixed stations (sign posts). Reverse GPS
In the system, contrary to the GPS system, the mobile unit 1 does not have a receiving function but only a transmitting function, and transmits a unique signal.
At that 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 that the mobile unit 1 itself has. In the reverse GPS system, a plurality of fixed stations 2 to 5 are installed at different positions on the ground, and each fixed station does not have a transmission function contrary to the function of GPS satellites, but has a reception function. There is.

In FIG. 5, the times at which the fixed stations 2 to 5 receive the signal transmitted by the mobile unit 1 are T ₁ , T ₂ , T ₃ and T _{4 respectively.}
When the position of the moving body _{1 (P x, P y,} P z) is the position of each fixed station _{2~5 (X 1, Y 1,} Z 1), (X 2, Y 2,
Z ₂ ), (X ₃ , Y ₃ , Z ₃ ), and (X ₄ , Y ₄ , Z ₄ ) are related by the following equation.

[Number 1] ^{_{{(X 1 -P x) 2}} + (Y 1 -P y) 2 + (Z 1 -P z) 2} 1/2 = C (T 1 -T 0 + △ t) (1) ^{_{{(X 2 -P x) 2}} + (Y 2 -P y) 2 + (Z 2 -P z) 2} 1/2 = C (T 2 -T 0 + △ t) (2) {(X 3 _{^{-P x) 2 + (Y 3}} -P y) 2 + (Z 3 -P z) 2} 1/2 = C (T 3 -T 0 + △ t) (3) {(X 4 -P x) _{^{2 + (Y 4 -P y)}} 2 + (Z 4 -P z) 2} 1/2 = C (T 4 -T 0 + △ t) (4) where, C is the electromagnetic wave speed, △ t is fixed It is the offset of the clock of the mobile unit 1 with respect to the clock of the station.

The unknowns (P _x , P _y , P _z ) and Δt are obtained by solving the above equations (1) to (4) simultaneously.
The position of the mobile 1 can be determined. In addition, reverse GP
As a document relating to the S system, for example, “A study of Local Positioning System by spread spectrum communication system”;
Confidential technique SST 92-91, March 1993.

[0010]

As described above (expensive and relatively large size), the positioning of a large number of moving objects within a limited area on the ground is performed by the method utilizing GPS or Loran C. In addition to the disadvantage of the need for a position finder and the cost of the entire system becoming too high accordingly, the positioning accuracy is low in the method using GPS or Loran C for "positioning within a limited area". There was a problem of passing.

That is, the positioning accuracy of GPS is 100 m.
The amount is about several hundred US in Loran C. With such accuracy, the accuracy is too low to determine the position of the moving body within a limited area within a few kilometer US.
It is difficult to perform accurate positioning within the “limited area” using S or Loran C.

On the other hand, in the above-described reverse GPS system, the mobile body is equipped with only a transmitter or is carried by the GPS.
It can be said that the system can be configured at a lower cost than the system using Loran C, and is suitable for positioning a moving object in a “limited area”. There is such a problem.

In the reverse GPS system, the mobile body not only transmits a unique signal for identifying itself from other mobile bodies, but also has a clock (timekeeping mechanism) provided on the mobile body itself to inform the time of the mobile body itself. Need to send as. The cost of the transmitter increases because the mobile unit equipped with such a clock and transmitting the time of the mobile unit itself as information complicates the circuit of the transmitter that is installed in the mobile unit or carried by the mobile unit. In addition to the above, it is difficult to reduce the size required especially for mobile phones. In addition, the fixed station also needs a circuit for decoding the time information transmitted from the mobile unit, which complicates the receiving circuit and increases the cost. Further, an important problem in the above-mentioned reverse GPS system is that the fixed stations (see FIG. 5) must be time-synchronized.

This means that if the fixed stations are not synchronized with each other, the measurement times of T _{1 to} T _{4 in} the above-mentioned formulas (1) to (4) include offsets that differ between the fixed stations. And the correct position ( _Px , _Py , _Pz ) of the mobile station cannot be determined. Therefore, it is necessary to establish time synchronization between fixed stations, but advanced technology is required to establish time synchronization so that the position of a mobile station can be more accurately determined by the inverse GPS method, and therefore expensive time is required. There is a problem that a synchronizing circuit is required. For example, in order to determine the position with a position accuracy of about 1 m, in the GPS method, it is necessary to perform time synchronization between each fixed station with an accuracy of 3 ns (nanosecond) to 4 ns, but synchronization between each fixed station is performed in nanosecond units. To achieve this, a time synchronization circuit consisting of a highly accurate clock and a complicated circuit is required.

The present invention solves the above problems of the conventional method,
An object of the present invention is to provide a position measurement system for determining the position of a moving body within a relatively limited area (local area) on the ground using a relatively small-scale device.

[0016]

In order to achieve the above object, the position measuring system of the first invention comprises a mobile station which transmits a first reference signal and a second mobile station which is different from the first reference signal. A first fixed station that transmits a reference signal, and at least three second fixed stations that receive the first reference signal and the second reference signal, respectively, and each second fixed station is a mobile station. And a time measuring means for measuring the arrival time of the signal from the first fixed station, and the difference between the arrival times of the signals from the mobile station and the first fixed station, which are measured by the respective time measuring means, and It is characterized in that the position of the mobile station is determined based on the positions of the first and second fixed stations.

According to a second invention, in the position measuring system of the first invention, the communication system between the mobile station and the first fixed station and the second fixed station is a spread spectrum communication system, and the mobile station is unique. The mobile station is a plurality of mobile stations to which the PN code is assigned, and the time measuring means of the second fixed station is a time measuring means configured to be able to switch the code pattern of the receiving side PN code.

[0018]

With the above structure, the position measuring system according to the first aspect of the invention is different from the conventional reverse GPS system in that the position of the moving body is 3
Arrival times of the first reference signal from the mobile and the second reference signal from the first fixed station and the known first fixed station position and at least 3 It can be determined from the positions of the two second fixed stations.
That is, the position measurement system does not require time synchronization between the fixed stations, and the first reference signal transmitted from the mobile body does not include time data.

The position measuring system of the second invention further comprises:
Since the time measuring means in the second fixed station is configured to be able to switch the code pattern of the PN code on the receiving side, the transmission signals from the mobile stations are discriminated from the transmission signals from the plurality of mobile stations, and the respective transmission signals are discriminated from each other. The arrival times of the signal from the mobile station and the second reference signal from the first fixed station and the known first fixed station position and at least three second fixed station positions respectively mobile station The position of can be calculated.

[0020]

1 is a diagram showing one embodiment of the position measuring system of the present invention, and FIG. 2 is a diagram showing a configuration example of the fixed station in FIG. In the position measuring system of the present invention, at least three fixed stations 2, 3 and 4 are installed at different positions on the ground, and the fixed station 6 having only a transmitter is installed on the ground.

Further, the area surrounded by each fixed station and / or the mobile body existing around the area is equipped with or carries a transmitter having only a transmitting function. In FIG. 1, only the moving body 1 is shown for the sake of explanation, but there may be a plurality of moving bodies. When there are a plurality of moving bodies, each moving body is equipped with a transmitter having only a transmitting function, or To carry.

When there are a plurality of moving bodies, the signal transmitted from the transmitter of each moving body is a unique signal for distinguishing each moving body from other moving bodies. For example, for each moving body, It is assumed that the frequency of the transmission signal is changed or the modulation code is changed. However, unlike the above-mentioned conventional reverse GPS system (see FIG. 5), in the present invention, the transmitter of each mobile body does not have a timekeeping mechanism such as a clock, and the signal transmitted from the transmitter is unique to the above-mentioned. It is only a signal, and the time data by the clock mechanism of the transmitter of each mobile body is not transmitted.

That is, the first difference between the present invention and the conventional reverse GPS system is that the transmitter of each mobile body does not have a timekeeping mechanism in the present invention, and the transmission signal does not include time information. In addition, the fixed station 6 having only a transmitter does not have a time counting mechanism, the transmission signal does not include time information, and is used to identify each mobile unit and each fixed station 2, 3, 4. The point is that it only contains a unique signal.

The second difference between the present invention and the conventional reverse GPS system is that, in the present invention, unlike the reverse GPS system, the fixed station 6 equipped with only the above-mentioned transmitter is fixed stations 2, 3, and 4. Other than that, one is installed. In addition, each fixed station 2,
2, 3 and 4 are receivers 2a for receiving the respective signals transmitted from the mobile unit 1 and the fixed station 6, as shown in FIG.
3a and 4a are provided respectively, and the receivers 2a, 3a and 4a each have a time difference between the time when the signal from the mobile unit 1 and the signal from the fixed station 6 are received by the respective receivers. Time measuring means 2b, 3b, 4 for measuring
b is provided.

The third difference between the present invention and the conventional reverse GPS system is that the present invention does not require time synchronization between fixed stations as in the reverse GPS system. The receivers 2a, 3a, 4a of the respective fixed stations 2, 3, 4 are provided with time measuring means 2b, 3b, 4b for measuring the time difference at the time of reception by the respective receivers. The point is that the time measuring means does not need to be time-synchronized like the time measuring means used in the conventional inverse GPS receiver.

In the position measuring system of the present invention configured as described above, the position (P _x , P _y ) of the moving body 1 is determined as follows.

FIG. 3 is a time chart showing the arrival time of the received signal in the fixed stations 2 and 3 of FIG. 1 as an example. In FIG. 3, the oscillator at the position (S _x , S _y ) is now. The time when the signal 7 from the fixed station 6 having only one and the signal 8 from the mobile 1 are received by the fixed station 2 at the position (X ₁ , Y ₁ ) respectively is T _1S and T _1P, and similarly, The times at which the signal 7 from the fixed station 6 and the signal 8 from the mobile 1 are received by the fixed station 3 located at the position (X ₂ , Y ₂ ) are T _2S and T _2P .

In the present invention, as shown in FIG.
Since the times of the receivers 3 and 4 are not time-synchronized, there is an offset (Δt _{0 in} FIG. 3) between the fixed stations at the starting point of time, but in the position measuring system of the present invention, the offset as described above is used. It is possible to accurately determine the position of the moving body even if there is between fixed stations. The position determining method will be described below.

In FIG. 1, the difference in distance between the fixed station 6 having only a transmitter and the fixed stations 2 and 3 is the time when the signal sent from the fixed station 6 reaches the fixed station 2. Although it is equal to the difference between the arrival time at the fixed station 3 and the velocity C of the electromagnetic wave, there is a time offset of Δt ₀ between the fixed station 2 and the fixed station 3 as shown in FIG. Considering this, the following formula is established.

## EQU00002 ## {(X₂-S_x)²+ (Y₂-S_y)²｝^1/2 -{(X₁-S_x)²+ (Y₁-S_y)²｝^1/2  = C {(T_2S-△ t₀) -T_1S} (5)

Similarly, the distance difference between the mobile unit 1 and the fixed station 2 and the fixed station 3, the time when the signal sent from the mobile unit 1 reaches the fixed station 2 and the time when the signal reaches the fixed station 3. The following equation holds between the differences of.

Equation 3] ^{_{{(X 2 -P x) 2}} + (Y 2 -P y) 2} 1/2 - {(X 1 -P x) 2 + (Y 1 -P y) 2} 1/2 = C {(T _2P −Δt ₀ ) −T _1P } (6)

When Δt ₀ is eliminated from the equations (5) and (6), the following equation holds.

Equation 4] _{[{(X 2 -S x)} 2 + (Y 2 -S y) 2} 1/2 - {(X 1 -S x) 2 + (Y 1 -S y) 2} 1/2 _{] - [{(X 2 -P} x) 2 + (Y 2 -P y) 2} 1/2 - {(X 1 -P x) 2 + (Y 1 -P y) 2} 1/2] = C {( _T2S - _T2P )-( _T1S - _T1P )} (7)

Equation (7) does not include the time offset Δt ₀ between the fixed stations 2 and 3, and the arrival time difference (T _2P -T _2S ) of each signal measured by the clock mechanism of the fixed stations 2 and 3 and (T _1S −
The relational expression of the unknown position (P _x , P _y ) is shown by T _1P ).

That is, in the position measuring system of the present invention, it is not necessary to synchronize the time of the clock mechanism between the fixed stations, and each arrival time of each signal transmitted from the fixed station 6 having only the transmitter and the mobile unit 1. Can be independently measured by the clock mechanism of each fixed station, and the position of the mobile body 1 can be obtained from the difference in arrival times.

In addition, in order to actually find the position (P _x , P _y ) of the moving body 1 in the position measuring system of the present invention, in addition to the above-mentioned equation (7), the fixed station 3 (position (X ₂ , Y ₂ )) And fixed station 4
A relational expression between the distance difference measured at (position (X ₃ , Y ₃ )) and the arrival time is required. The relational expression is given by the following expression (8) in the same manner as the procedure for obtaining the expression (7).

Equation 5] _{[{(X 3 -S x)} 2 + (Y 3 -S y) 2} 1/2 - {(X 2 -S x) 2 + (Y 2 -S y) 2} 1/2 _{] - [{(X 3 -P} x) 2 + (Y 3 -P y) 2} 1/2 - {(X 2 -P x) 2 + (Y 2 -P y) 2} 1/2] = C {( _T3S - _T3P )-( _T2S - _T2P )} (8) where _T3S and _T3P are signals from the fixed station 6 and the mobile unit 1.
It is the time when the fixed station 4 receives the signals from the respective stations.

In the above equations (7) and (8), positions (X ₁ , Y ₁ ), (X ₂ , Y ₂ ), (X ₃ , Y ₃ ), (S _x ,
S _y ) is a fixed value and is known. Further, the times (T _1S , T _1P ), (T _2S , T _2P ), (T _3S , T _3P ) are also times obtained from the measurement values of the fixed stations 2, 3, 4 respectively. Therefore, the position (P _x , P _y ) of the moving body 1 composed of two unknowns can be calculated by simulating the equations (7) and (8).

In addition, such a calculation is performed by the position calculating means which is composed of a calculation circuit of a management station (which may be either an independent station or a fixed station) of the position measurement system. The measured values (T _1S , T _1P ),
(T _2S , T _2P ), (T _3S , T _3P ), and the known value (X ₁ ,
Y ₁ ), (X ₂ , Y ₂ ), (X ₃ , Y ₃ ), (S _x , S _y ) can be obtained, and the transmission of information from the fixed stations 2, 3, 4 to the management station is local. It is also possible to use a communication line such as the Internet.

As described above, according to the present invention, the position of the mobile unit can be easily determined without time synchronization between the fixed stations. Therefore, unlike the conventional reverse GPS system, a highly accurate timekeeping mechanism and a time synchronization circuit are unnecessary. Thereby, the positioning system can be configured at a lower cost as a whole.

Next, the form of the signal transmitted from the mobile unit 1 when the mobile unit 1 carries the portable oscillator according to the present invention and the signal transmitted from the fixed station 6 having only the oscillator will be described. .

The signals transmitted from the transmitters of the mobile unit 1 and fixed station 6 must be such that the arrival times of the signals can be detected by the receivers of the fixed stations 2, 3 and 4. As such a transmission signal, it is also possible to use one of the pulses used in Loran C. However, when a pulse wave is used as a transmission signal, the frequency band used may be too wide to be used under the Radio Law. Further, the mobile body 1 requires a large amount of power to transmit the pulse wave from the above-mentioned portable oscillator, and requires a battery having a large capacity as a power source, which may not be suitable for carrying.

Therefore, as a desirable form of the signal transmitted by the transmitters of the mobile unit 1 and the fixed station 6, a signal obtained by modulating a carrier with a pseudo noise code (hereinafter referred to as PN code) as used in GPS (such as Such signals are spread spectrum signals).

That is, since the signals modulated by the PN code can limit the band to a certain width, the problem in the Radio Law can be solved, and if the type of the PN code is changed by using the same band, mutual interference of signals occurs. Can be made extremely small, so that PNs unique to a large number of moving objects in the area and one fixed station 6 can be obtained.
By assigning a code, the fixed stations 2, 3 and 4 can identify a plurality of mobile units and the fixed station 6. Therefore, the signal transmitted from the mobile unit and the fixed station 6 is preferably a signal obtained by modulating the carrier with a PN code.

FIG. 4 shows the mobile unit 1 and the fixed station 6 in FIG.
4A is a block diagram showing an example of the configuration of the transmitter and the receivers of the fixed stations 2, 3 and 4, and FIG. 4A shows an example of the configuration of the transmitter of the mobile unit and the fixed station 6.

In FIG. 4A, 21 is a PN code generator (P
NG), 22 is a carrier signal generator, and 23 is a modulator, and a unique PN code is assigned to the mobile body.
The transmitter of the mobile unit generates a PN code assigned to the mobile unit from the PN code generator (PNG) 21, modulates the PN code by the carrier from the carrier signal generator 22, and spreads and transmits it from the transmission antenna. . Similarly, the transmitter of the fixed station 6 also has a unique P other than the PN code assigned to each mobile from the PN code generator (PNG) 21.
An N code is generated, the PN code is modulated by the carrier from the carrier signal generator 22, and spread transmission is performed from the transmission antenna.

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 and 4 will be described. Here, the signal in which the carrier is modulated by the PN code as described above will be described. When the PN code is used as a signal, the input P is detected in order to detect the arrival time at the receiver side.
The N code and the PN code on the receiving side must be correlated to detect the time point at which the correlation peak is obtained. As a method of obtaining such correlation, there are a method using a DLL, a method using a matched filter, and a method using a convolver.

Of these, the method using the DLL can be used when the modulated waves by the PN code are continuously input. However, in the position measurement system, the signal from the mobile transmitter may be transmitted intermittently after a certain period of time instead of the continuous wave in order to save the power consumption due to the radio wave transmission of the mobile. D when an intermittent wave is transmitted
Matched filters or convolvers are better than LL. Among them, the matched filter can correlate only a specific PN code pattern. Therefore, if a matched filter is used, if a large number of mobiles transmit different types of PN codes, the PN code is transmitted to each fixed station. This means that it is necessary to equip as many matched filters as there are types, which is not realistic from the viewpoint of line scale and cost.

On the other hand, when the convolver is used, the above-mentioned inconvenience does not occur. Therefore, the arrival time is detected on the receiver side, the input PN code and the PN code on the receiving side are correlated, and the correlation is calculated. It is desirable to use a convolver to detect when the peak is obtained.

FIG. 4 (b) is a block diagram showing the basic configuration when a convolver is used for the receiver of the fixed station.
6 is a BPF (band pass filter), 7 and 13 are amplifiers, 9 and 11 are local oscillators, 8 and 12 are mixers, 10
Is a convolver, 14 is a detector, and 15 is a time measuring unit. Further, in this embodiment, the convolver 10 and the local oscillator 1 are used.
1, the mixer 12, the amplifier 13, the wave detector 14, and the time measuring unit 15 constitute time measuring means.

As shown in FIG. 4B, the convolver 10
When using, the two input terminals 10a of the convolver,
The input terminal 10a of the 10b has a BPF 6, an amplifier 7,
A modulated wave by the PN code transmitted from the mobile unit by the local oscillator 9 and the mixer 8 is input, and a bar PN code (PN code generated by the PN code generator 16 is input to the other input terminal 10b of the convolver 10. Is a time-reversed signal), and a reference signal in which a carrier is modulated is input.

By setting the reference code as such, the convolver 10 can take the correlation between the PN code transmitted from the mobile unit and the bar PN code of the fixed station, and the resultant correlation output signal is detected by the detector 14 Then, the time measuring unit 15 can detect the transmission time T _1S of the signal from the moving body 1 from the detected time. Here, by switching the code pattern of the PN code of the reference signal at an arbitrary time point, the transmission time T _1S of signals from a plurality of moving bodies and the transmission time T _PS of signals from the fixed station 6 are similarly measured by the time measuring unit. It can be detected at 15.

That is, the PN code generator 1 of FIG.
It is desirable that 6 not only generate a constant bar PN code but can switch the code pattern of the bar PN code in time. Further, it is well known that such PN code switching can be easily performed by using ordinary digital circuit technology.

When the PN code of the reference signal of the convolver is switched as described above, the convolver produces a large correlation output only when the PN code having a time-reversal relationship with the PN code is input, and this is used to identify the moving body. can do. In other words, when there are a plurality of mobiles as described above, a unique PN code is assigned to each mobile and the code pattern of the PN code that is the reference signal of the convolver is temporally switched in the receiver of the fixed station. By this, only the PN code having a time-reversal relationship with the reference signal can be discriminated (from the magnitude of the correlation output).
The mobile body corresponding to the code can be identified.

As an application example of the present invention, it can be used for searching for a lost child or detecting danger such as detecting the position of a person at an amusement center, a ski resort, a golf course, or the like, and a mobile device at a farm or factory. It can also be used for positioning and control such as.

[0053]

As described above, according to the present invention, compared with the conventional GPS system, Loran C, or reverse GPS system, the movement of a moving object within a relatively limited area (local area) on the ground can be achieved. Positioning can be achieved with a smaller, lower cost device.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a position measuring system of the present invention.

FIG. 2 is a diagram showing a configuration example of a fixed station in FIG.

FIG. 3 is a time chart showing a state of arrival time of a received signal in the fixed stations 2 and 3 of FIG. 1 as an example.

4 is a block diagram showing a configuration example of a transmitter and a receiver of a mobile body and a fixed station in FIG.

FIG. 5 is a schematic diagram of an inverse GPS system as a conventional technique.

[Explanation of symbols]

 1 mobile (mobile station) 2, 3, 4 fixed station (second fixed station) 6 fixed station (first fixed station) 2a, 3a, 4a receiver 2b, 3b, 4b time measuring means 10 convolver (time Measuring means) 11 Local oscillator (time measuring means) 12 Mixer (time measuring means) 14 Detector (time measuring means) 15 Time measuring section (time measuring means)

Claims (2)

[Claims] 1. A mobile station transmitting a first reference signal, a first fixed station transmitting a second reference signal different from the first reference signal, the first reference signal and the second reference signal. At least three second fixed stations each receiving a reference signal, the time for each second fixed station to measure the arrival times of signals from the mobile station and the first fixed station, respectively. A measuring unit, and a difference in arrival time of signals from the mobile station and the first fixed station, which are respectively measured by the time measuring units, and
A position measuring system characterized in that the position of the mobile station is determined based on the position of the second fixed station. 2. The position measuring system according to claim 1,
The communication method between the mobile station and the first fixed station and the second fixed station is a spread spectrum communication method, and the mobile station is a plurality of mobile stations to which a unique PN code is assigned, and the second fixed station The position measuring system, wherein the time measuring unit is a time measuring unit configured to be able to switch the code pattern of the PN code on the receiving side.