Information processing apparatus, calculation method, and positioning system for calculating integer bias

An information processing apparatus including a GPS reception unit that receives a radio wave from a satellite and a processing unit that calculates an integer bias between a first reference station and the information processing apparatus on a basis of the radio wave from the satellite. The processing unit acquires an inter-reference-station integer bias between a second reference station different from the first reference station and the first reference station. The processing unit calculates an integer bias between the information processing apparatus and the second reference station on a basis of the integer bias between the first reference station and the information processing apparatus, and the inter-reference-station integer bias between the first reference station and the second reference station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase of International Patent Application No. PCT/JP2016/082869 filed on Nov. 4, 2016 which claims priority benefit of Japanese Patent Application No. JP 2016-012912 filed in the Japan Patent Office on Jan. 27, 2016. Each of the above-referenced applications is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to an information processing apparatus, a calculation method, and a positioning system.

BACKGROUND ART

In recent years, attention has been paid to interferometric positioning in which the phases of radio waves (carriers) from a GPS satellite are measured between two spots including a reference station whose position is known and an unknown spot whose position is unknown, and the measured observation value is used for positioning. In interferometric positioning, a path difference of carriers between the two spots is obtained, and the relative position of the unknown spot from the reference station is calculated to measure the position of the unknown spot. The accuracy of measuring distance with carrier phases is high, and it is possible in interferometric positioning to perform positioning with accuracies of approximately several millimeters to several centimeters.

Patent Literature 1 discloses a vehicle including a GPS reception unit as a positioning apparatus that performs the above-described interferometric positioning. The vehicle disclosed in Patent Literature 1 is classified into a reference vehicle and a non-reference vehicle. The non-reference vehicle uses interferometric positioning to calculate the relative position with respect to the reference vehicle.

CITATION LIST

Patent Literature

DISCLOSURE OF INVENTION

Technical Problem

A positioning apparatus as disclosed in Patent Literature 1 uses only an observation value of a specific reference station to perform interferometric positioning. Such a positioning apparatus makes a complicated calculation to decide (i.e., initialize) an integer bias when the positioning apparatus moves to switch the reference station for interferometric positioning.

The present disclosure then proposes a novel and improved information processing apparatus, calculation method, and positioning system capable of calculating an integer bias according to a simple calculation when the information processing apparatus switches reference stations.

Solution to Problem

According to the present disclosure, there is provided an information processing apparatus including: a GPS reception unit configured to receive a radio wave from a satellite; and a processing unit configured to calculate an integer bias between a first reference station and the information processing apparatus on a basis of the radio wave from the satellite. The processing unit acquires an inter-reference-station integer bias between a second reference station different from the first reference station and the first reference station. The processing unit calculates an integer bias between the information processing apparatus and the second reference station on a basis of the integer bias between the first reference station and the information processing apparatus, and the inter-reference-station integer bias between the first reference station and the second reference station.

Advantageous Effects of Invention

As described above, according to the present disclosure, it is possible to calculate an integer bias according to a simple calculation when an information processing apparatus switches reference stations.

MODE(S) FOR CARRYING OUT THE INVENTION

Note that description will be made in the following order.

0. Principle of Interferometric Positioning

1. Method of Calculating Integer Bias

2. Example of System Configuration

3. Configuration of Mobile Station

4. Operation Example in which Mobile Station Switches Reference Stations

5. Operation Example in which Mobile Station Verifies Inter-Reference-Station Integer Bias

6. Another System Configuration of the Present Disclosure

7. Supplemental Information

0. Principle of Interferometric Positioning

FIG. 1is a diagram illustrating the principle of interferometric positioning.FIG. 1illustrates a GPS satellite100, a reference station200whose position is known, and a mobile station300whose position is unknown. Note that the mobile station300is an example of an information processing apparatus that receives radio waves from the GPS satellite100for positioning. The reference station200and the mobile station300respectively include GPS reception units202and302that receive radio waves from the GPS satellite100.

The GPS satellite100makes predetermined orbits, and the position of the GPS satellite100is known. The GPS satellite100transmits radio waves of an L1 band (1575.42 MHz) and an L2 band (1227.6 MHz). The reference station200and the mobile station300use the GPS reception units202and302to observe the radio waves transmitted from the GPS satellite100, and observe the carrier phases and the pseudorange (distance obtained by adding an error to the true distance from the GPS satellite100to the GPS reception units202and302).

In general, in interferometric positioning, the reference station200transmits the observed observation values (carrier phase and pseudorange) and positional information of the reference station200to the mobile station300. The mobile station300uses the observation values of the reference station200and the observation values observed by the mobile station300itself to calculate the relative position of the mobile station300with respect to the reference station200. The position of the mobile station300is hereby measured. With reference toFIG. 1, the following describes the principle of interferometric positioning in more detail.

The dashed line illustrated inFIG. 1represents an equidistant plane from the GPS satellite100. L ofFIG. 1means a path difference between the path between the GPS satellite100and the GPS reception unit202of the reference station200, and the path between the GPS satellite100and the GPS reception unit302of the mobile station300. The path difference L illustrated inFIG. 1is the sum of the length of an integer number of cycles of a carrier of the GPS satellite100and the length of the fraction corresponding to a phase angle θ. Here, the number of cycles of carriers included between the GPS satellite100and the GPS reception units202and302is generally referred to as integer bias.

In interferometric positioning, carrier phases can be measured by the GPS reception units202and302, and obtaining an integer bias is thus the same as obtaining a path difference. To obtain this integer bias, as described above, the GPS reception units202and302respectively included in the reference station200and the mobile station300observe radio waves from the same GPS satellite100. Using the respective observation values from the GPS satellite100which are observed by the reference station200and the mobile station300, the mobile station300then calculates an integer bias. In addition, the mobile station300uses the calculated integer bias to obtain the baseline vector illustrated by an arrow inFIG. 1. According to this baseline vector, the relative position of the mobile station300with respect to the reference station200is obtained.

Note that, as the wavelength of the carriers of the GPS satellite100, the above-described L1 band has a wavelength of 19 cm, and the L2 band has a wavelength of 24 cm. The GPS reception units202and302have high accuracy of observing carrier phases. It is possible in interferometric positioning to perform positioning with carriers having such wavelength with accuracies of approximately several millimeters to several centimeters.

Interferometric positioning includes static positioning that is performed when the mobile station300is in a static state, and kinematic positioning that is performed when the mobile station300is in a dynamic state. The present disclosure chiefly describes kinematic positioning. In kinematic positioning, the mobile station300decides (i.e., initializes) an integer bias when beginning an observation, and performs positioning in a short time while the mobile station300is moving. The mobile station300moves, so that the mobile station300switches the reference stations200in accordance with a situation. The mobile station300then performs initialization whenever switching the reference stations200.

1. Method of Calculating Integer Bias

The above describes the basic principle of interferometric positioning. The following describes a method of calculating the above-described integer bias. Note that a calculation method is shown here in which the algorithm of the Kalman filter is applied, and kinematic positioning is performed.FIG. 2is a diagram illustrating two GPS satellites including a GPS satellite i102and a GPS satellite j104, the reference station200, and the mobile station300. In general, a carrier phase ΦAifrom the GPS satellite i102which is observed by the mobile station300is expressed as follows.
[Math. 1]
ΦAi=λ−1rAi+BAi−I+T+(δA−δi)  (1)

Here, a subscript A means the mobile station300, and rAirepresents the geometric distance (true distance) between the GPS satellite i102and the mobile station300. In addition, I represents an ionospheric delay. T represents a tropospheric delay. δArepresents a clock error of the GPS reception unit302. δirepresents a clock error of the GPS satellite i102. In addition, λ represents the wavelength of a carrier from the GPS satellite i102. BAirepresents an integer bias.

Next, a single phase difference is calculated from a formula (1) to cancel the ionospheric delay I, the tropospheric delay T, and the clock error δAof a receiver. The single phase difference is a difference between the carrier phases measured by the mobile station300from the GPS satellite i102and the GPS satellite j104. It is then preferable to select a GPS satellite having a large angle of elevation as viewed from the mobile station300as the GPS satellite i102.

FIG. 3is a diagram illustrating an example of the relationship between the positions of two GPS satellites106and108and the position of the mobile station300. The GPS satellite106represents a satellite having a relatively larger angle of elevation as viewed from the mobile station300than that of the GPS satellite108. As understood fromFIG. 3, a comparison between the distance between the mobile station300and the GPS satellite106and the distance between the mobile station300and the GPS satellite108shows that the distance between the mobile station300and the GPS satellite106is shorter. In this way, as a satellite has a larger angle of elevation as viewed from the mobile station300, the distance of the ionosphere and the troposphere to be passed becomes shorter. Accordingly, the ionospheric delay I and the tropospheric delay T decrease. Therefore, in the case where observations are made in the reference station200and the mobile station300with a common GPS satellite, it is preferable to select a GPS satellite having a larger angle of elevation.

The method of calculating an integer bias will be described with reference toFIG. 2again. A single phase difference ΦAijbetween the GPS satellite i102and the GPS satellite j104described above is expressed with the following formula.

As understood from a formula (2), the single phase difference between the GPS satellite i102and the GPS satellite j104cancels a clock error on the receiver side. However, the single phase difference between the GPS satellite i102and the GPS satellite j104does not cancel clock errors on the GPS satellite sides. Therefore, to eliminate the clock errors on the GPS satellite sides, the double phase difference between the mobile station300and the reference station200is calculated.

The double phase difference ΦABijdescribed above is expressed with the following formula.

[Math.⁢3]ΦABij=⁢ΦABi-ΦABj=⁢λ-1⁡(rABi-rABj)+BABij(3)
Here, a subscript B means the reference station200. In addition, M double phase differences are defined. M is less by one than K that is the number of GPS satellites used for positioning.

When the M double phase differences are defined as described above, a formula (3) above defines independent equations at time t as follows.

The left side and the right side of each equation in a formula (4) above are calculated to define a matrix zn(observation errors at time tn) as follows.

Next, the relationship between the position of the mobile station300at the time tnand the position of the mobile station300at time tn+1is expressed with the amounts Δx, Δy, and Δz of correction as follows.

Here, x(tn+1), y(tn+1), and z(tn+1) mean the coordinates of the mobile station300at the time tn+1. x(tn), y(tn), and z(tn) mean the coordinates of the mobile station300at the time tn.

In addition, similarly, the relationship between the value of an integer bias at the time tnand the value of an integer bias at the time tn+1is expressed with the integer bias's amount ΔB of correction as follows.

When, with regard to the sight line direction from the mobile station300to a satellite, if the position of the GPS satellite i102is taken to be xi(ximeans the coordinates of the GPS satellite i102), and the position of the mobile station300is taken to be xA(xAmeans the coordinates of the mobile station300), a unit vector eAiis defined as follows.

In addition, when eAidefined in a formula (8) is used for each GPS satellite used for positioning, a matrix H is defined as follows.

According to the formula described above, znwhen t=n holds is expressed as follows.

Here, I represents an identity matrix.

In addition, when the algorithm of the Kalman filter is applied to a formula (10) described above, the formula (10) is expressed with the following formula.

Here, P represents a covariance matrix of state variables. R represents a covariance matrix of observation errors. In this way, the amounts Δx and ΔB of correction which are calculated by applying the algorithm of the Kalman filter are real numbers, and called Float solutions.

To convert the acquired Float solutions into integers (which are called Int solutions), Least-square Ambiguity Decorrelation Adjustment Method (LAMBDA Method) is typically used.

As described above, in interferometric positioning, the mobile station300that is an unknown spot uses the single phase difference and double phase difference between carriers to calculate an integer bias. The mobile station300can then perform kinematic positioning by using the calculated integer bias.

2. Example of System Configuration

The above describes the principle of interferometric positioning and the method of calculating an integer bias in detail. The following describes an example of a system configuration according to an embodiment of the present disclosure. In the present embodiment, an information processing apparatus will be described that receives radio waves from a satellite and performs information processing. Note that examples of the information processing apparatus include the mobile station300as illustrated inFIG. 4which performs positioning while moving.

The system according to the present embodiment includes the GPS satellite100, the reference station200whose position is known, the mobile station300, a network400, and a server500. As described above, the GPS satellite100similarly emits radio waves. The reference station200and the mobile station300receive the radio waves emitted from the GPS satellite100. The network400conveys information from the reference station200or the mobile station300. The network400may be, for example, a public network such as the Internet, or a network such as a mobile telephone network which includes a wireless interface.

The position of the reference station200is known. The reference station200includes an apparatus that can measure a carrier phase from the GPS satellite100. For example, the reference station200may be a structure such as a building, a traffic light, or a base station in a mobile telephone network which includes an apparatus that can measure a carrier phase from the GPS satellite100and is installed in the city. In addition, the reference station200may also be an electronic reference point installed by Geospatial Information Authority of Japan. Note thatFIG. 4illustrates only one reference station200. However, a plurality of reference stations are installed in this system.

In addition, the mobile station300is illustrated as a vehicle inFIG. 4. However, in the present embodiment, the mobile station300is not limited to a vehicle. The mobile station300may be an apparatus such as a mobile phone or a game console which can be carried by a person. In addition, the mobile station300may be a ship. As long as the mobile station300is an apparatus that includes an apparatus which can measure a carrier phase from the GPS satellite100, and is movable, the mobile station300may be any apparatus.

In addition, the mobile station300receives information regarding the observation values (carrier phase and pseudorange) of the reference station200and the position of the reference station200via the network400, and uses the information from the reference station200and an observation value obtained by the mobile station300itself measuring radio waves from the GPS satellite100to perform interferometric positioning.

The server500receives the observation values observed by the reference station200from the reference station200via the network400. In addition, the server500is configured to use the observation values received from the reference station200to calculate information used for positioning performed by the mobile station300. The server500is configured to transmit the information used for positioning to the mobile station300via the network400.

3. Configuration of Mobile Station

The above describes the configuration example of the system according to an embodiment of the present disclosure. Next, the configuration of the mobile station300will be described in detail with reference toFIG. 5. The mobile station300includes the GPS reception unit302, a processing unit304, and a communication unit310.

The GPS reception unit302receives radio waves from the GPS satellite100, and sends information regarding the radio waves received from the GPS satellite100to the processing unit304. The communication unit310is an apparatus used to wirelessly communicate with another apparatus. The communication unit310receives information regarding the observation values observed by the reference station200and the position of the reference station200from the reference station200via the network400, and sends the received information to the processing unit304. The communication unit310may be a transceiver used for a wireless LAN such as Bluetooth (registered trademark) or Wi-Fi, or a mobile telephone network such as Long Term Evolution (LTE).

In addition, the processing unit304includes an integer bias estimation unit306and a positioning unit308. The integer bias estimation unit306estimates an integer bias on the basis of observation values based on radio waves received by the GPS reception unit302from a satellite and various kinds of information received from the communication unit310. The positioning unit308performs positioning on the basis of the integer bias calculated by the integer bias estimation unit306.

4. Operation Example in Which Mobile Station Switches Reference Stations

The above describes the configuration examples of the system and the mobile station300according to the present embodiment. The following describes an operation example in which the mobile station300switches the reference stations200for positioning.

FIG. 6is a diagram illustrating the overview of the case where the mobile station300switches reference stations from a reference station A204serving as a switching source to a reference station B206serving as a switching destination. InFIG. 6, i and j represent GPS satellites. The subscript A represents the reference station A204serving as a switching source. The subscript B represents the reference station B206serving as a switching destination. In addition, a subscript R represents the mobile station300.

First, the mobile station300performs kinematic positioning on the basis of the reference station A204serving as a switching source. The integer bias estimation unit306of the mobile station300then estimates an integer bias BARijbetween the reference station A204serving as a switching source and the mobile station300. In addition, the reference station A204serving as a switching source continuously transmits an observation value BAijto the server500. In addition, similarly, the reference station B206serving as a switching destination continuously transmits an observation value BBijto the server500.

Next, the mobile station300moves, and the mobile station300gets farther from the reference station A204serving as a switching source. Meanwhile, once the mobile station300comes closer to the reference station B206serving as a switching destination, the mobile station300switches the reference stations. In general, in interferometric positioning, the positioning accuracy becomes higher as the distance between the mobile station300and a reference station becomes shorter. This is because, once the distance between the mobile station300and a reference station becomes longer, the propagation status of radio waves received by the mobile station300from the GPS satellite100becomes considerably different from the propagation status of radio waves received by the mobile station300from the GPS satellite100. This difference in propagation status reduces the effects of cancelling an ionospheric delay and a tropospheric delay described above, resulting in a greater positioning error. It is thus preferable for the mobile station300to perform kinematic positioning on the basis of a closer reference station.

InFIG. 6, as described above, when the mobile station300comes closer to the reference station B206serving as a switching destination, the mobile station300performs kinematic positioning on the basis of the reference station B206serving as a switching destination. The mobile station300then calculates BBRijthat is an integer bias between the mobile station300and the reference station B206serving as a switching destination.

Here, the server500uses the observation value BAijreceived from the reference station A204serving as a switching source and the observation value BBijreceived from the reference station B206serving as a switching destination to calculate an inter-reference-station integer BABijbias between the reference station A204serving as a switching source and the reference station B206serving as a switching destination in accordance with the following formula. The server500then transmits the calculated inter-reference-station integer bias BABijto the mobile station300.
[Math. 12]
BABij=BAij−BBij(12)

The mobile station300receives and acquires the inter-reference-station integer bias BABijfrom the server500via the communication unit310. The integer bias estimation unit306uses the acquired inter-reference-station integer bias BABijand the already calculated integer bias BARijbetween the mobile station300and the reference station A204serving as a switching source to calculate an integer bias BBRijbetween the mobile station300and the reference station B206serving as a switching destination as follows.
[Math. 13]
BBRij=BARij−BABij(13)

In this way, the mobile station300sets the calculated integer bias between the mobile station300and the reference station B206serving as a switching destination as an initial value. The mobile station300then uses the observation value of the reference station B206serving as a switching destination which is received from the server500, and the observation value observed by the GPS reception unit302of the mobile station300to perform kinematic positioning with the reference station B206.

As described above, the integer bias estimation unit306calculates the integer bias BBRijbetween the mobile station300and the reference station B206serving as a switching destination. The positioning unit308uses the calculated integer bias BBRijto perform kinematic positioning. In this way, the mobile station300uses the inter-reference-station integer bias BABijto eliminate the necessity of initialization when switching the reference stations.

The above describes the overview of the operation of the system according to the present embodiment. With reference toFIG. 7, the following describes the above-described operation in detail. In S100, the reference station A204that is a reference station serving as a switching source transmits an observation value BAijto the server500. Similarly, in S102, the reference station B206that is a reference station serving as a switching destination transmits an observation value BBijto the server500. In addition, in S104, the mobile station300receives radio waves of a satellite with the GPS reception unit302, and acquires an observation value.

Next, in S106, the server500transmits the observation value EAijof the reference station A204to the mobile station300. In S108, the mobile station300uses the observation value acquired in S104and the observation value EAijof the reference station A204which is received from the server500, and performs kinematic positioning.

Next, in S110, the mobile station300transmits the current location of the mobile station300to the server500. In S112, the server500, which receives the current location of the mobile station300, searches a plurality of installed reference stations for a reference station in the vicinity of the mobile station300. Here, in the case where the reference station A204is the closest reference station to the mobile station300, the server500performs no operation. Meanwhile, in the case where the mobile station300moves afterward, and the server500determines on the basis of the current location of the mobile station300received after the mobile station300moves that the closest reference station to the mobile station300is the reference station B206, the server500performs the operation of S114.

In S114, the server500uses the observation value BAijof the reference station A204and the observation value BBijof the reference station B206to calculate an inter-reference-station integer bias BABijbetween the reference station A204and the reference station B206. In S116, the server500then transmits the calculated inter-reference-station integer bias BABijand the observation value BBijof the reference station B206to the mobile station300.

The mobile station300, which receives the inter-reference-station integer bias BABijfrom the server500, recognizes that the closest reference station is changed from the reference station A204to the reference station B206. Next, in S118, the mobile station300receives radio waves of a satellite with the GPS reception unit302to acquire an observation value. In S120, the mobile station300then calculates an integer bias BBRijbetween the mobile station300and the reference station B206on the basis of a formula (13) described above, and performs kinematic positioning in cooperation with the reference station B206with the integer bias BBRijset as an initial value.

As described above, the mobile station300according to the present embodiment uses the inter-reference-station integer bias BABijto eliminate the necessity of initialization when switching the reference stations. This allows for prompt positioning, and the mobile station300does not have to perform a complicated calculation for initialization. Further, the mobile station300can perform positioning with the closest reference station, and thus stably calculate an accurate integer bias and perform accurate positioning.

5. Operation Example in Which Mobile Station Verifies Inter-Reference-Station IntegeR Bias

The above describes the operation example in which an inter-reference-station integer bias is used, and the mobile station300performs kinematic positioning. The following describes an operation example in which the mobile station300verifies this inter-reference-station integer bias.

FIG. 8is a schematic diagram illustrating the operation for the mobile station300to verify an inter-reference-station integer bias. As described above, the reference station A204and the reference station B206transmit the observation values BAijand BBijto the server500. In addition, the server500transmits the received observation values BAijand BBijto the mobile station300.

The mobile station300uses the observation values BAijand BBijreceived from the server500to perform kinematic positioning with the reference station A204and the reference station B206, and obtains integer biases between both reference stations and the mobile station300. That is, the positioning unit308of the mobile station300performs kinematic positioning with both reference stations to calculate the integer bias BARijbetween the reference station A204and the mobile station300, and the integer bias BBRijbetween the reference station B206and the mobile station300.

The integer bias estimation unit306then uses the calculated integer biases BARijand BBRijbetween the respective reference stations and the mobile station300to calculate the above-described inter-reference-station integer bias BABijin accordance with the following formula.
[Math. 14]
BARij−BBRij=BABij(14)

In this way, the mobile station300performs kinematic positioning with the two of the reference station A204and the reference station B206, and verifies the inter-reference-station integer bias from the calculated integer biases, which makes it possible to improve the accuracy of the inter-reference-station integer bias. In addition, the improved accuracy of the inter-reference-station integer bias improves the accuracy of kinematic positioning that is finally performed by the mobile station300.

FIG. 9is a sequence diagram in which the above-described inter-reference-station integer bias is verified. As described above, in S200and S202, the reference station A204and the reference station B206continuously transmit observation values to the server500. In addition, in S204, the mobile station300receives radio waves from the GPS satellite100with the GPS reception unit302to acquire an observation value.

Next, in S206, the server500transmits the respective observation values received from the reference station A204and the reference station B206to the mobile station300. In addition, in S208, the mobile station300uses the received observation values to perform kinematic positioning with the reference station A204and the reference station B206. In S210, the mobile station300then calculates an inter-reference-station integer bias on the basis of a formula (14), and verifies the inter-reference-station integer bias with the inter-reference-station integer bias received from the server500.

Note that positioning may be performed in S208between the reference station A204and the reference station B206, and the mobile station300in parallel or at different timing. Performing positioning at different timing distributes the calculation load on the positioning unit308of the mobile station300. At this time, to improve the verification and positioning accuracy, the mobile station300may store an observation value observed by the mobile station300in a storage unit, and use the observation value observed by the mobile station300for verification and positioning at the same time as the received observation values of the reference stations.

6. Another System Configuration of the Present Disclosure

The above describes one example of the system configuration according to the present disclosure.FIG. 10describes another example of the system configuration according to the present disclosure. Specifically, in another system configuration, a reference station C602, a reference station D604, and a reference station E606illustrated inFIG. 10emit radio waves from themselves. In addition, for example, each of reference stations602,604, and606is configured to emit radio waves including information for identifying each of the reference stations602,604, and606. Circles702,704, and706illustrated by dashed lines inFIG. 10represent areas that radio waves reach from the respective reference stations602,604, and606. These areas represented by the circles702,704, and706are herein defined as radio wave arrival areas of the respective reference stations602,604, and606.

Here, an interface of radio waves emitted from a reference station may be an interface used for a wireless LAN such as Bluetooth (registered trademark) or Wi-Fi, or a mobile telephone network such as Long Term Evolution (LTE).

According to this system configuration, the mobile station300observes the radio wave strength from each of the reference stations602,604, and606with the communication unit310. At this time, if each of the reference stations602,604, and606emits radio waves with the same strength, the mobile station300can determine, by observing this radio wave strength, which reference station is the closest reference station among a plurality of reference stations.

More specifically, inFIG. 10, the mobile station300falls within the radio wave arrival areas702,704, and706of the respective reference stations602,604, and606. The communication unit310of the mobile station300measures the radio wave strength of radio waves from each of the reference stations602,604, and606, and sends the measured radio wave strength to the processing unit304as reception strength. The processing unit304estimates the closest reference station from the mobile station300on the basis of the reception strength received by the communication unit310. In addition, the mobile station300may estimate the distance from the mobile station300to each of the reference stations602,604, and606on the basis of the reception strength received by the communication unit310. Note that, in the example ofFIG. 10, the communication unit310receives radio waves having the greatest radio wave strength from the reference station E606.

In the case where the processing unit304estimates the distance to a reference station on the basis of the reception strength, the distance from the mobile station300to the respective reference stations602,604, and606which is estimated by the processing unit304is represented as L1, L2, and L3 inFIG. 10. The processing unit304determines on the basis of the reception strength received by the communication unit310that the distance L3 to the reference station E606is the shortest. The processing unit304then acquires information for identifying the reference station E606from radio waves emitted from the reference station E606.

Next, the mobile station300transmits this information for identifying the reference station E606to the server500. The server500, which receives the information for identifying the reference station E606, recognizes the reference station E606as a reference station serving as the next switching destination on the basis of this identification information. The server500then calculates an inter-reference-station integer bias with the reference station E606recognized as a reference station serving as a switching destination, and transmits the calculated inter-reference-station integer bias to the mobile station300.

The mobile station300, which receives the inter-reference-station integer bias, uses the received inter-reference-station integer bias to calculate an integer bias between the mobile station300and the reference station E606on the basis of a formula (12). Such a configuration allows the mobile station300to switch reference stations without initialization. In addition, the mobile station300can perform positioning with the closest reference station, and thus stably calculate an accurate integer bias. This allows the mobile station300to perform accurate positioning.

According to the configuration described above, the mobile station300calculates the closest reference station from the radio wave strength of radio waves emitted from reference stations, and thus the mobile station300does not have to transmit the current location, which corresponds to S110ofFIG. 7. In addition, the server500does not have to search for a reference station in the vicinity of the mobile station300, which corresponds to S112ofFIG. 7, because the mobile station300issues a notification of a reference station serving as a switching destination. Configured in this way, the mobile station300and the server500have less processing loads.

The above describes the example in which each of the reference stations602,604, and606emits radio waves including information for identifying the reference station. However, the reference station may emit radio waves including information indicating the position of the reference station in addition to the information for identifying the reference station.

According to such a configuration, the mobile station300can calculate the straight-line distance from the mobile station300to the reference station from the position of the mobile station300and the received position of the reference station. Such a configuration allows the mobile station300to calculate the distance from the mobile station300to the reference station without relying on the radio wave strength. Accordingly, it is possible to more accurately determine the closest reference station.

Note that, in the example of this system, the configuration that an observation value observed by each reference station is broadcast may be adopted. If the system is configured in this way, for example, the broadcast observation value can be received by the mobile station300, and the integer bias estimation unit306can calculate and acquire an inter-reference-station integer bias. Using this inter-reference-station integer bias calculated by the integer bias estimation unit306, the integer bias estimation unit306may calculate an integer bias between the reference station serving as a switching destination and the mobile station300. According to such a configuration, a heavy load is imposed on the processing unit304of the mobile station300, but there is no need to use the server500as the system. Accordingly, the system configuration can be made simpler.

7. Supplemental Information

For example, inFIG. 9, an inter-reference-station integer bias may be verified by the server500. The mobile station300then transmits an observation value acquired in S204to the server500. The server500, which receives the observation value from the mobile station300, also uses observation values received from the reference station A204and the reference station B206to calculate integer biases between the reference station A204and the reference station B206, and the mobile station300.

The server500can then verify the inter-reference-station integer bias on the basis of the calculated integer biases between the reference station A204and the reference station B206, and the mobile station300. In this case, the mobile station300just transmits observation values, and thus the mobile station300has less processing loads on the processing unit304. Therefore, in the mobile station300having limited capacity in general, it is possible to reduce processing loads and leave the processing to the server500having enormous capacity.

In addition, in the case where a reference station used by the mobile station300chiefly includes not a public, but unique system, an inter-reference-station integer bias may be verified with the released observation value of an electronic reference point installed by Geospatial Information Authority of Japan. Such a configuration improves the accuracy of the inter-reference-station integer bias described above, and allows the mobile station300to perform accurate positioning.

In addition, the server500may calculate inter-reference-station integer biases of various combinations of reference stations, and broadcast the calculated inter-reference-station integer biases of the various combinations of reference stations. For example, in the case where the mobile station300selects the closest reference station on the basis of the reception strength of radio waves emitted from reference stations, the mobile station300may receive a broadcast inter-reference-station integer bias. The mobile station300then receives the broadcast inter-reference-station integer bias with the communication unit310, and stores the broadcast inter-reference-station integer bias in the storage unit or the like. When switching reference stations, the mobile station300may then select an inter-reference-station integer bias between a reference station serving as a switching source and a reference station serving as a switching destination from the inter-reference-station integer biases stored in the storage unit, and use the inter-reference-station integer bias to perform kinematic positioning. Configured in this way, the mobile station300does not have to transmit the current position to the server500. In addition, the positioning unit308can perform positioning according to an extremely simple calculation.

Note that the scope of the present disclosure includes a computer program for causing the processing unit304including the integer bias estimation unit306and the positioning unit308to operate as described above. In addition, there may be provided a storage medium having such a program stored therein.

As described above, according to an embodiment of the present disclosure, the mobile station300acquires an inter-reference-station integer bias between a reference station serving as a switching source and a reference station serving as a switching destination, and calculates an integer bias between the reference station serving as a switching destination and the mobile station300. Such a configuration allows the mobile station300to switch reference stations without initialization. Note that, as understood from the above-described embodiment, an inter-reference-station integer bias may be received and acquired from another apparatus, and also calculated by the mobile station300and acquired.

In addition, a reference station serving as a switching destination is selected from a plurality of installed reference stations on the basis of information regarding the current location which is transmitted from the mobile station300or the reception strength of radio waves that are received by the mobile station300and emitted from each reference station. Such a configuration allows the mobile station300to perform positioning with the closest reference station, and thus stably calculate an accurate integer bias. This allows the mobile station300to perform accurate positioning.

An information processing apparatus including:

a GPS reception unit configured to receive a radio wave from a satellite; and

a processing unit configured to calculate an integer bias between a first reference station and the information processing apparatus on a basis of the radio wave from the satellite, in which

the processing unit acquires an inter-reference-station integer bias between a second reference station different from the first reference station and the first reference station, and

the processing unit calculates an integer bias between the information processing apparatus and the second reference station on a basis of the integer bias between the first reference station and the information processing apparatus, and the inter-reference-station integer bias between the first reference station and the second reference station.

The information processing apparatus according to (1), further including:

a communication unit configured to transmit a signal, in which

the communication unit transmits a position of the information processing apparatus to a server that selects the second reference station.

The information processing apparatus according to (2), in which

the second reference station is located at a position closest to the information processing apparatus among a plurality of reference stations.

The information processing apparatus according to (1), further including:

a communication unit configured to receive a radio wave emitted from the second reference station, in which

the processing unit selects the second reference station on a basis of reception strength of the radio wave emitted from the second reference station.

The information processing apparatus according to (4), in which

the processing unit selects a reference station having greatest reception strength of a radio wave from a plurality of reference stations as the second reference station.

the processing unit performs kinematic positioning in cooperation with the first reference station or the second reference station.

the processing unit further calculates the integer bias between the second reference station and the information processing apparatus on the basis of the radio wave from the satellite,

the processing unit calculates an inter-reference-station integer bias on a basis of the integer bias between the first reference station and the information processing apparatus, and the integer bias between the second reference station and the information processing apparatus, and

the processing unit verifies the received inter-reference-station integer bias on a basis of the calculated inter-reference-station bias.

A calculation method including:

receiving a radio wave from a satellite;

calculating an integer bias between a first reference station and an information processing apparatus on a basis of the radio wave from the satellite;

acquiring an inter-reference-station integer bias between a second reference station different from the first reference station and the first reference station; and

calculating an integer bias between the information processing apparatus and the second reference station on a basis of the integer bias between the first reference station and the information processing apparatus, and the inter-reference-station integer bias between the first reference station and the second reference station.

A positioning system including:

a first reference station whose position is known and a second reference station different from the first reference station, the first reference station receiving a radio wave from a satellite; and

an information processing apparatus configured to perform positioning on a basis of the radio wave from the satellite, in which

the information processing apparatus includesa GPS reception unit configured to receive the radio wave from the satellite, anda processing unit configured to calculate an integer bias between the first reference station and the information processing apparatus on the basis of the radio wave from the satellite,

the processing unit acquires an inter-reference-station integer bias between the first reference station and the second reference station, and

the processing unit calculates an integer bias between the information processing apparatus and the second reference station on a basis of the integer bias between the first reference station and the information processing apparatus, and the inter-reference-station integer bias between the first reference station and the second reference station.

REFERENCE SIGNS LIST