Positioning system, positioning device, communication base station, control method, and recording medium storing program

A communication base station includes a propagation time evaluation section which determines whether or not a propagation time required for a communication radio wave to propagate between the communication base station and a positioning device is within a predetermined allowable time range, a code phase calculation section which calculates a code phase of each satellite signal, a difference calculation section which calculates a difference between the code phase calculated by the communication base station and a positioning-side code phase, a difference evaluation section which determines whether or not the difference is within a multipath range which is a difference range when the positioning-side code phase is affected by a multipath, a correction value transmission section which transmits the code phase calculated by the communication base station to the positioning device when the difference evaluation section has determined that the difference is within the multipath range, and the like.

Japanese Patent Application No. 2006-198758 filed on Jul. 20, 2006 and Japanese Patent Application No. 2006-198921 filed on Jul. 21, 2006, are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a positioning system which locates the present position using satellite signals from positioning satellites.

A positioning system has been used in practice which locates the present position of a positioning device utilizing a satellite positioning system (SPS) which is a navigation system utilizing satellites (see JP-A-10-339772 and the like).

The positioning device may receive a radio wave from the satellite in a state in which an indirect wave (hereinafter called “multipath wave”), which occurs when the radio wave is reflected by a building or the like, interferes with a direct wave. The multipath wave reaches the positioning device after a delay due to reflection by a building or the like. When the multipath wave interferes with the direct wave, the correlation peak value varies, whereby a large error occurs in positioning calculations. In this specification, an environment in which a multipath easily occurs is called a multipath environment.

In order to solve the above problem, technology has been proposed for a positioning device integrated in a portable telephone in which the positioning device utilizes the position of a communication base station when the positioning device has determined that the position of the communication base station is more accurate than the position calculated using satellite radio waves (e.g. JP-A-2006-109355).

The code phase of a coarse and acquisition (C/A) code calculated by the communication base station may be used as the code phase at the positioning device.

However, since the position of the communication base station is fixed, the position output according to the technology disclosed in JP-A-2006-109355 may be inconvenient when the positioning device integrated in a portable telephone moves.

Moreover, since the code phase of the C/A code calculated by the communication base station should differ from the true code phase at the position of the positioning device, the accuracy of the located position may deteriorate when uniformly using the code phase at the communication base station as the code phase at the positioning device merely based on the situation in which the positioning device can communicate with the communication base station.

SUMMARY

According to one aspect of the invention, there is provided a communication base station which can communicate with a positioning device which locates a position using satellite signals from a plurality of positioning satellites and is located at a fixed position, the communication base station comprising:

a propagation time calculation section which calculates a propagation time required for a communication radio wave to propagate between the communication base station and the positioning device;

a propagation time evaluation section which determines whether or not the propagation time is within a predetermined allowable time range;

a satellite signal reception section which receives the satellite signals;

a code phase calculation section which calculates a code phase of each of the satellite signals;

a positioning-side code phase reception section which receives a positioning-side code phase which is a code phase of each of the satellite signals calculated by the positioning device;

a difference calculation section which calculates a difference between the code phase calculated by the code phase calculation section and the positioning-side code phase received from the positioning device;

a difference evaluation section which determines whether or not the difference is within a multipath range which is a difference range when the positioning-side code phase is affected by a multipath; and

a correction value transmission section which transmits the code phase calculated by the communication base station to the positioning device when the difference evaluation section has determined that the difference is within the multipath range.

According to another aspect of the invention, there is provided a positioning device which can communicate with a communication base station located at a fixed position and locates a position using satellite signals from a plurality of positioning satellites, when the communication base station has determined that a propagation time required for a communication radio wave to propagate between the communication base station and the positioning device is within a predetermined allowable time range, and has calculated a difference between a code phase calculated by the communication base station based on the received satellite signal and a positioning-side code phase which is a code phase of each of the satellite signals calculated by the positioning device, and the difference is within a multipath range which is a difference range when the positioning-side code phase is affected by a multipath, the positioning device receiving the code phase calculated by the communication base station and locating a position using the code phase calculated by the communication base station and the positioning-side code phase.

According to a further aspect of the invention, there is provided a positioning system comprising a positioning device which locates a position using satellite signals from a plurality of positioning satellites and a communication base station which can communicate with the positioning device,

the communication base station including:

an initial position calculation section which calculates an initial position of the positioning device;

a code phase calculation section which calculates a code phase of the satellite signal at a position of the communication base station;

an estimated difference calculation section which estimates a difference between the code phase calculated by the code phase calculation section and a code phase of the satellite signal on assumption that the communication base station is located at the initial position as an estimated difference;

an estimated code phase calculation section which estimates the code phase on assumption that the communication base station is located at the initial position as an estimated code phase based on the code phase calculated by the code phase calculation section and the estimated difference; and

a subsidiary information transmission section which transmits the initial position and the estimated code phase to the positioning device; and

the positioning device including:

a terminal code phase calculation section which calculates a code phase at a position of the positioning device as a terminal code phase based on the satellite signal;

a code phase difference calculation section which calculates a code phase difference between the estimated code phase and the terminal code phase; and

a positioning section which locates a position using the estimated code phase or the terminal code phase depending on the code phase difference.

According to still another aspect of the invention, there is provided a positioning device which locates a position using satellite signals from a plurality of positioning satellites, the positioning device comprising:

a base station position information acquisition section which acquires base station position information from a communication base station which can communicate with the positioning device, the base station position information indicating a position of the communication base station;

a transmission direction information acquisition section which acquires transmission direction information indicating a transmission direction of a communication radio wave transmitted from the communication base station to the positioning device;

a base station code phase acquisition section which acquires a base station code phase from the communication base station, the base station code phase being a code phase at a position of the communication base station calculated by the communication base station based on the satellite signal;

a propagation time calculation section which calculates a propagation time required for a communication radio wave to propagate between the communication base station and the positioning device;

an initial position calculation section which calculates an initial position of the positioning device based on the position of the communication base station, the transmission direction, and the propagation time;

an estimated difference calculation section which estimates a difference between the code phase at the position of the communication base station and a code phase of the satellite signal at the initial position as an estimated difference;

an estimated code phase calculation section which estimates the code phase at the initial position as an estimated code phase based on the base station code phase and the estimated difference;

a terminal code phase calculation section which calculates a code phase at a position of the positioning device as a terminal code phase based on the satellite signal;

a code phase difference calculation section which calculates a code phase difference between the estimated code phase and the terminal code phase; and

a positioning section which locates a position using the estimated code phase or the terminal code phase depending on the code phase difference.

According to a still further aspect of the invention, there is provided a positioning device which locates a position using satellite signals from a plurality of positioning satellites, the positioning device comprising:

a base station position information acquisition section which acquires base station position information from a communication base station which can communicate with the positioning device, the base station position information indicating a position of the communication base station;

a base station code phase acquisition section which acquires a base station code phase from the communication base station, the base station code phase being a code phase at a position of the communication base station calculated by the communication base station based on the satellite signal;

an initial position calculation section which calculates an initial position utilizing communication radio waves from a plurality of the communication base stations;

an estimated difference calculation section which estimates a difference between the code phase at the position of the communication base station and a code phase of the satellite signal at the initial position as an estimated difference;

an estimated code phase calculation section which estimates the code phase at the initial position as an estimated code phase based on the base station code phase and the estimated difference;

a terminal code phase calculation section which calculates a code phase at a position of the positioning device as a terminal code phase based on the satellite signal;

a code phase difference calculation section which calculates a code phase difference between the estimated code phase and the terminal code phase; and

a positioning section which locates a position using the estimated code phase or the terminal code phase depending on the code phase difference.

DETAILED DESCRIPTION OF THE EMBODIMENT

The invention may realize a communication base station which provides a code phase at the communication base station to a positioning device which can communicate with the communication base station only when a condition is satisfied whereby it is appropriate for the positioning device to use the code phase at the communication base station.

The invention may also allow occurrence of a multipath to be determined and the position to be accurately located when a multipath occurs in comparison with the case of using the code phase at the communication base station.

According to one embodiment of the invention, there is provided a communication base station which can communicate with a positioning device which locates a position using satellite signals from a plurality of positioning satellites and is located at a fixed position, the communication base station comprising:

a propagation time calculation section which calculates a propagation time required for a communication radio wave to propagate between the communication base station and the positioning device;

a propagation time evaluation section which determines whether or not the propagation time is within a predetermined allowable time range;

a satellite signal reception section which receives the satellite signals;

a code phase calculation section which calculates a code phase of each of the satellite signals;

a positioning-side code phase reception section which receives a positioning-side code phase which is a code phase of each of the satellite signals calculated by the positioning device;

a difference calculation section which calculates a difference between the code phase calculated by the code phase calculation section and the positioning-side code phase received from the positioning device;

a difference evaluation section which determines whether or not the difference is within a multipath range which is a difference range when the positioning-side code phase is affected by a multipath; and

a correction value transmission section which transmits the code phase calculated by the communication base station to the positioning device when the difference evaluation section has determined that the difference is within the multipath range.

According to this configuration, the communication base station can determine whether or not the propagation time is within the allowable time range using the propagation time evaluation section. Therefore, the communication base station can identify whether or not the positioning device is positioned close to the communication base station in addition to whether or not the positioning device is positioned in the communication area (cell) of the communication base station.

The communication base station can calculate the difference between the code phase calculated by the communication base station and the positioning-side code phase using the difference calculation section. Since the true positions of the communication base station and the positioning device usually differ even if the communication base station is close to the positioning device, the difference may include the difference due to the difference in true position, the difference due to an error caused by a factor other than a multipath, and the difference due to an error caused by a multipath.

The communication base station can determine whether or not the difference is within the multipath range using the difference evaluation section. Specifically, the communication base station can determine not only whether or not a difference exists between the code phase calculated by the communication base station and the positioning-side code phase, but also whether or not the difference is within the multipath range.

Since the communication base station includes the correction value transmission section, the communication base station can transmit the code phase calculated by the communication base station to the positioning device when the difference evaluation section has determined that the difference is within the multipath range.

Since the communication base station can identify whether or not the positioning device is positioned close to the communication base station, the communication base station can transmit the code phase calculated by the communication base station to the positioning device when the communication base station has determined that the condition is satisfied whereby the positioning device is positioned close the communication base station and the difference is within the multipath range. When the condition is satisfied whereby the positioning device is positioned extremely close the communication base station, the positioning-side code phase should be almost the same as the code phase calculated by the communication base station if the positioning-side code phase is not affected by a multipath. Therefore, it is appropriate for the positioning device to locate the position using the code phase calculated by the communication base station. It is also appropriate for the positioning device to locate the position using the code phase calculated by the nearby communication base station instead of the positioning-side code phase calculated by the positioning device using a multipath signal. Specifically, the positioning accuracy of the positioning device is likely to be improved.

This allows the code phase at the base station to be provided to the positioning device which can communicate with the communication base station only when the condition is satisfied whereby it is appropriate for the positioning device to use the code phase at the base station.

In the communication base station, the allowable time range may be specified as a time range when the communication base station and the positioning device are so close that positions of the communication base station and the positioning device are considered to be almost identical.

In the communication base station, the multipath range may be specified taking into account a distance corresponding to the allowable time range and a calculation error of the positioning-side code phase.

According to this configuration, the communication base station can reliably determine whether or not the positioning-side code phase is affected by a multipath.

According to one embodiment of the invention, there is provided a method of controlling a communication base station which can communicate with a positioning device which locates a position using satellite signals from a plurality of positioning satellites and is located at a fixed position, the method comprising:

calculating a propagation time required for a communication radio wave to propagate between the communication base station and the positioning device;

determining whether or not the propagation time is within a predetermined allowable time range;

receiving the satellite signals;

calculating a code phase of each of the satellite signals;

receiving a positioning-side code phase which is a code phase of each of the satellite signals calculated by the positioning device;

calculating a difference between the code phase calculated by the communication base station and the positioning-side code phase received from the positioning device;

determining whether or not the difference is within a multipath range which is a difference range when the positioning-side code phase is affected by a multipath; and

transmitting the code phase calculated by the communication base station to the positioning device when the difference has been determined to be within the multipath range.

According to this configuration, the code phase at the base station can be provided to the positioning device which can communicate with the communication base station only when the condition is satisfied whereby it is appropriate for the positioning device to use the code phase at the base station.

According to one embodiment of the invention, there is provided a computer-readable recording medium storing a program for causing a computer included in a communication base station, which can communicate with a positioning device which locates a position using satellite signals from a plurality of positioning satellites and is located at a fixed position, to execute the above method.

According to one embodiment of the invention, there is provided a positioning device which can communicate with a communication base station located at a fixed position and locates a position using satellite signals from a plurality of positioning satellites, when the communication base station has determined that a propagation time required for a communication radio wave to propagate between the communication base station and the positioning device is within a predetermined allowable time range, and has calculated a difference between a code phase calculated by the communication base station based on the received satellite signal and a positioning-side code phase which is a code phase of each of the satellite signals calculated by the positioning device, and the difference is within a multipath range which is a difference range when the positioning-side code phase is affected by a multipath, the positioning device receiving the code phase calculated by the communication base station and locating a position using the code phase calculated by the communication base station and the positioning-side code phase.

According to this configuration, the positioning device can receive the code phase at the base station and locate the position using the received code phase only when the condition is satisfied whereby it is appropriate for the positioning device to use the code phase at the base station.

According to one embodiment of the invention, there is provided a positioning system comprising a positioning device which locates a position using satellite signals from a plurality of positioning satellites and a communication base station which can communicate with the positioning device,

the communication base station including:

an initial position calculation section which calculates an initial position of the positioning device;

a code phase calculation section which calculates a code phase of the satellite signal at a position of the communication base station;

an estimated difference calculation section which estimates a difference between the code phase calculated by the code phase calculation section and a code phase of the satellite signal on assumption that the communication base station is located at the initial position as an estimated difference;

an estimated code phase calculation section which estimates the code phase on assumption that the communication base station is located at the initial position as an estimated code phase based on the code phase calculated by the code phase calculation section and the estimated difference; and

a subsidiary information transmission section which transmits the initial position and the estimated code phase to the positioning device; and

the positioning device including:

a terminal code phase calculation section which calculates a code phase at a position of the positioning device as a terminal code phase based on the satellite signal;

a code phase difference calculation section which calculates a code phase difference between the estimated code phase and the terminal code phase; and

a positioning section which locates a position using the estimated code phase or the terminal code phase depending on the code phase difference.

According to this configuration, the communication base station can calculate the initial position of the positioning device. The communication base station can calculate the estimated difference.

The communication base station can calculate the estimated code phase at the initial position based on the code phase calculated based on the received satellite signal and the estimated difference. The positioning device can calculate the code phase difference between the estimated code phase and the terminal code phase. Since the positioning device can estimate the Doppler shift of the carrier carrying the satellite signal using the initial position, the positioning device can efficiently receive the satellite signal and promptly calculate the terminal code phase.

The positioning device can locate the position using the estimated code phase or the terminal code phase depending on the code phase difference.

For example, the positioning device can locate the position using the estimated code phase when the code phase difference is large enough to indicate occurrence of a multipath. The estimated code phase is not the code phase at the communication base station, but is the code phase estimated to be the code phase at the initial position of the positioning device. Therefore, the estimated code phase is closer to the true code phase of the positioning device than the code phase at the communication base station.

Therefore, the positioning system allows occurrence of a multipath to be determined and the position to be accurately located when a multipath occurs in comparison with the case of using the code phase at the communication base station.

In the positioning system, the initial position calculation section of the communication base station may calculate the initial position of the positioning device based on the position of the communication base station, a propagation time required for a communication radio wave to propagate between the communication base station and the positioning device, and a transmission direction of the communication radio wave.

According to one embodiment of the invention, there is provided a positioning device which locates a position using satellite signals from a plurality of positioning satellites, the positioning device comprising:

a base station position information acquisition section which acquires base station position information from a communication base station which can communicate with the positioning device, the base station position information indicating a position of the communication base station;

a transmission direction information acquisition section which acquires transmission direction information indicating a transmission direction of a communication radio wave transmitted from the communication base station to the positioning device;

a base station code phase acquisition section which acquires a base station code phase from the communication base station, the base station code phase being a code phase at a position of the communication base station calculated by the communication base station based on the satellite signal;

a propagation time calculation section which calculates a propagation time required for a communication radio wave to propagate between the communication base station and the positioning device;

an initial position calculation section which calculates an initial position of the positioning device based on the position of the communication base station, the transmission direction, and the propagation time;

an estimated difference calculation section which estimates a difference between the code phase at the position of the communication base station and a code phase of the satellite signal at the initial position as an estimated difference;

an estimated code phase calculation section which estimates the code phase at the initial position as an estimated code phase based on the base station code phase and the estimated difference;

a terminal code phase calculation section which calculates a code phase at a position of the positioning device as a terminal code phase based on the satellite signal;

a code phase difference calculation section which calculates a code phase difference between the estimated code phase and the terminal code phase; and

a positioning section which locates a position using the estimated code phase or the terminal code phase depending on the code phase difference.

According to this configuration, the positioning device can calculate the initial position. Therefore, since the positioning device can estimate the Doppler shift of the carrier carrying the satellite signal using the initial position, the positioning device can efficiently receive the satellite signal. The positioning device can calculate the estimated difference. The positioning device can calculate the estimated code phase. The positioning device can also calculate the code phase difference between the estimated code phase and the terminal code phase.

The positioning device can locate the position using the estimated code phase or the terminal code phase depending on the code phase difference.

For example, the positioning device can locate the position using the estimated code phase when the code phase difference is large enough to indicate occurrence of a multipath. The estimated code phase is not the code phase at the communication base station, but is the code phase estimated to be the code phase at the initial position of the positioning device. Therefore, the estimated code phase is closer to the true code phase of the positioning device than the code phase at the communication base station. Therefore, the positioning device can determine occurrence of a multipath and accurately locate the position when a multipath occurs in comparison with the case of using the code phase at the communication base station.

According to one embodiment of the invention, there is provided a positioning device which locates a position using satellite signals from a plurality of positioning satellites, the positioning device comprising:

a base station position information acquisition section which acquires base station position information from a communication base station which can communicate with the positioning device, the base station position information indicating a position of the communication base station;

a base station code phase acquisition section which acquires a base station code phase from the communication base station, the base station code phase being a code phase at a position of the communication base station calculated by the communication base station based on the satellite signal;

an initial position calculation section which calculates an initial position utilizing communication radio waves from a plurality of the communication base stations;

an estimated difference calculation section which estimates a difference between the code phase at the position of the communication base station and a code phase of the satellite signal at the initial position as an estimated difference;

an estimated code phase calculation section which estimates the code phase at the initial position as an estimated code phase based on the base station code phase and the estimated difference;

a terminal code phase calculation section which calculates a code phase at a position of the positioning device as a terminal code phase based on the satellite signal;

a code phase difference calculation section which calculates a code phase difference between the estimated code phase and the terminal code phase; and

a positioning section which locates a position using the estimated code phase or the terminal code phase depending on the code phase difference.

According to this configuration, since the positioning device can calculate the initial position using the communication radio waves from the communication base stations, the positioning device can determine occurrence of a multipath and accurately locate the position when a multipath occurs in comparison with the case of using the code phase at the communication base station.

According to one embodiment of the invention, there is provided a method of controlling a communication base station which can communicate with a positioning device which locates a position using satellite signals from a plurality of positioning satellites, the method comprising:

calculating an initial position of the positioning device;

calculating a code phase of the satellite signal;

estimating a difference between the calculated code phase and a code phase of the satellite signal calculated on assumption that the communication base station is located at the initial position as an estimated difference;

estimating the code phase of the satellite signal on assumption that the communication base station is located at the initial position as an estimated code phase based on the calculated code phase and the estimated difference; and

transmitting the initial position and the estimated code phase to the positioning device.

According to this configuration, the communication base station can transmit the initial position and the estimated code phase to the positioning device. Therefore, the positioning device can calculate the code phase difference between the terminal code phase calculated based on the received satellite signal and the estimated code phase and locate the position using the estimated code phase or the terminal code phase depending on the code phase difference.

This allows occurrence of a multipath to be determined and the position to be accurately located when a multipath occurs in comparison with the case of using the code phase at the communication base station.

According to one embodiment of the invention, there is provided a computer-readable recording medium storing a program for causing a computer included in a communication base station, which can communicate with a positioning device which locates a position using satellite signals from a plurality of positioning satellites, to execute the above method.

Preferred embodiments of the invention are described below in detail with reference to the drawings and the like.

The following embodiments illustrate specific preferred examples of the invention and are provided with various technologically preferred limitations. Note that the scope of the invention is not limited to the following embodiments (modes or aspects) unless otherwise indicated.

FIG. 1is a schematic view showing a positioning system10according to one embodiment of the invention.

As shown inFIG. 1, the positioning system10includes global positioning system (GPS) satellites12a,12b,12c,12d,12e, and12f. The GPS satellites12aand the like can respectively transmit radio waves S1, S2, S3, S4, S5, and S6. The GPS satellites12aand the like exemplify a positioning satellite.

The positioning satellite is not limited to the GPS satellite, but may be a satellite generally used in a satellite positioning system (SPS). The SPS includes the Galileo, a quasi-zenith satellite, and the like in addition to the GPS.

The radio waves S1and the like carry various codes. A C/A code is one of such codes. The C/A code is a signal having a bit rate of 1.023 Mbps and a bit length of 1023 bits (=1 msec). The C/A code includes 1023 chips. The C/A code exemplifies a satellite signal.

The positioning system10includes a terminal20A and a terminal20B. The terminal20A and the terminal20B are generically called a terminal20.

The terminal20is a portable telephone having a positioning function, and can locate the present position using the C/A code. The terminal20exemplifies a positioning device.

The terminal20can specify the code phases (phases) of the C/A codes from three or more different GPS satellites12aand the like to calculate the pseudo-range between each of the GPS satellites12aand the like and the terminal20, and locate the present position using the calculated pseudo-ranges, for example.

FIG. 2is a schematic view showing an example of a positioning method.

As shown inFIG. 2, it may be considered that the C/A codes continuously line up between the GPS satellite12aand the terminal20, for example. Since the distance between the GPS satellite12aand the terminal20is not necessarily a multiple of the length (about 300 kilometers (km)) of the C/A code, a code fraction C/Aa may exist. Specifically, a portion of a multiple of the C/A code and a fraction portion may exist between the GPS satellite12aand the terminal20. The total length of the portion of a multiple of the C/A code and the fraction portion is the pseudo-range. The terminal20locates the position using the pseudo-ranges for three or more GPS satellites12aand the like.

In this specification, the fraction portion C/Aa of the C/A code is called a code phase (phase). The code phase may be indicated by the number of the chip of the 1023 chips of the C/A code, or may be converted into distance, for example.

The position of the GPS satellite12ain the orbit can be calculated using an ephemeris. The ephemeris is information carried on the radio waves S1and the like and indicating the precise orbit of each of the GPS satellites12aand the like. The portion of a multiple of the C/A code can be specified by calculating the distance between the position of the GPS satellite12ain the orbit and an initial position Q0(not shown), for example. Since the length of the C/A code is about 300 kilometers (km), the position error of the initial position Q0must be 150 kilometers (km) or less.

The terminal20performs a correlation process including a coherent process and an incoherent process.

When the coherent time of the coherent process is 5 msec, the terminal20calculates the correlation value of the C/A code synchronously accumulated over 5 msec and a C/A code replica and the like. The correlated code phase and the correlation value are output as a result of the coherent process.

In the incoherent process, the terminal20calculates the correlation cumulative value (incoherent value) by accumulating the correlation values as the coherent results.

The code phase at which the correlation cumulative value becomes maximum is the code fraction C/Aa.

The positioning system10also includes a base station40. The base station40can communicate with the terminal20. The base station40is a communication base station in a portable telephone system, and is located at a fixed position. The coordinates of the fixed position are known. The fixed position at which the base station40is located is an open sky environment in which no obstacle exists around the base station40. Therefore, the base station40can receive the radio wave S3from the GPS satellite12cas a direct wave r1, for example. The base station40exemplifies a communication base station.

The base station40can arbitrate communication between the terminal20and another terminal through a dedicated line65.

The base station40includes a GPS receiver42, and can receive the radio waves S1and the like from the GPS satellites12aand the like.

The base station40can calculate the code phase of the C/A code. The base station40transmits and receives communication radio waves using four antennas54a,54b,54c, and54d, for example. The four antennas54aand the like respectively transmit the communication radio waves in four different directions such as the north, south, east, and west, and receive the communication radio waves from the terminal20. The transmission direction of the communication radio wave is also called a cell sector.

The base station40can identify the direction of the antenna through which the base station40transmits the communication radio wave to the terminal20which communicates with the base station40.

When no obstacle exists around the terminal20such as in the case of the position of the terminal20A, the radio wave S3reaches the terminal20A as a direct wave r2, for example.

When obstacles such as buildings13A and13B exist around the terminal20such as in the case of the position of the terminal20B, the radio wave S3is reflected by the building13B and reaches the terminal20B as an indirect wave (multipath wave) r3, for example.

Since the propagation path of the multipath wave r3is longer than that of the direct wave, the terminal20B calculates the code phase to be longer than that of the direct wave. As a result, the accuracy of the located position deteriorates.

The base station40can assist the terminal20B to locate the position with high accuracy by transmitting the code phase calculated by the base station40in order to correct the code phase calculated by the terminal20B under the influence of the multipath only when the code phase calculated based on the received direct wave r1and the period of time (round trip time (RTT)) required for the communication radio wave to make a round trip between the base station40and the terminal20satisfy specific necessary conditions.

Since the propagation velocity of the communication radio wave is known (speed of light), the base station40can calculate the distance d between the base station40and the terminal20B using the RTT.

The base station40transmits and receives the communication radio waves using four antennas (not shown), for example. The four antennas respectively transmit the communication radio waves in four different directions such as the north, south, east, and west, and receive the communication radio waves from the terminal20. The base station40can identify the direction of the antenna through which the terminal20receives the communication radio wave from the base station40.

Two embodiments relating to the above-described schematic configuration are given below. A positioning system1010according to a first embodiment and a positioning system2010according to a second embodiment correspond to the positioning system10in the above-described schematic configuration. A terminal1020according to the first embodiment and a terminal2020according to the second embodiment correspond to the terminal20in the above-described schematic configuration. A base station1040according to the first embodiment and a base station2040according to the second embodiment correspond to the base station40in the above-described schematic configuration.

First Embodiment

The first embodiment is described below.

(Main Hardware Configuration of Terminal1020)

FIG. 3is a schematic view showing the main hardware configuration of the terminal1020.

As shown inFIG. 3, the terminal1020includes a bus1022.

A central processing unit (CPU)1024, a storage device1026, and the like are connected with the bus1022. The storage device1026is a random access memory (RAM), a read only memory (ROM), or the like.

An input device1028for inputting various types of information and the like, a power supply device1030, a communication device1032, and a GPS device1034are also connected with the bus1022. The terminal1020can receive the radio waves S1and the like using the GPS device1034.

A display device1036for displaying various types of information is also connected with the bus1022.

(Main Hardware Configuration of Base Station1040)

FIG. 4is a schematic view showing the main hardware configuration of the base station1040.

As shown inFIG. 4, the base station1040includes a bus1042.

A CPU1044, a storage device1046, an external storage device1048, and the like are connected with the bus1042. The external storage device1048is a hard disk drive (HDD) or the like.

An input device1050for inputting various types of information and the like, a power supply device1052, a communication device1054, a GPS device1056, a display device1058, and a clock1060are also connected with the bus1042.

The base station1040can identify one of four antennas through which a specific terminal1020transmits and receives the communication radio wave.

The base station1040can measure the RTT (seeFIG. 1) using the clock1060.

(Main Software Configuration of Terminal1020)

FIG. 5is a schematic view showing the main software configuration of the terminal1020.

As shown inFIG. 5, the terminal1020includes a terminal control section1100which controls each section, a communication section1102corresponding to the communication device1032shown inFIG. 3, a GPS section1104corresponding to the GPS device1034, a display section1106corresponding to the display device1036, and the like.

The terminal1020also includes a first storage section1110which stores various programs, and a second storage section1150which stores various types of information.

As shown inFIG. 5, the terminal1020stores satellite orbital information1152in the second storage section1150. The satellite orbital information1152includes an almanac1152aand an ephemeris1152b.

The almanac1152ais information indicating the approximate orbits of all of the GPS satellites12aand the like (seeFIG. 1). The almanac1152acan be acquired by decoding any of the waves S1and the like from the GPS satellites12aand the like.

The ephemeris1152bis information indicating the precise orbit of each of the GPS satellites12aand the like (seeFIG. 1). For example, when acquiring the ephemeris1152bof the GPS satellite12a, it is necessary to receive and decode the waves S1from the GPS satellite12a.

The terminal1020utilizes the satellite orbital information1152for positioning.

As shown inFIG. 5, the terminal1020stores a satellite signal reception program1112in the first storage section1110. The satellite signal reception program1112is a program for causing the control section1100to receive the radio waves S1and the like from the GPS satellites12aand the like.

In more detail, the control section1100determines the GPS satellites12aand the like which can be observed at the present time referring to the almanac1152a, and receives the radio waves S1and the like from the observable GPS satellites12aand the like. In this case, the position of the base station1040is used as the reference position of the terminal1020, for example. The terminal1020can acquire information indicating the position of the base station1040from the base station1040with which the terminal1020communicates.

As shown inFIG. 5, the terminal1020stores a code phase calculation program1114in the first storage section1110. The code phase calculation program1114is a program for causing the terminal control section1100to calculate the code phase of the C/A code in units of the GPS satellites12aand the like.

For example, the terminal control section1100calculates a code phase CPm1of the GPS satellite12a, a code phase CPm2of the GPS satellite12b, a code phase CPm3of the GPS satellite12c, and a code phase CPm4of the GPS satellite12d.

The terminal control section1100stores code phase information1154indicating the code phases CPm1and the like in the second storage section1150. The code phases CPm1and the like are generically called a terminal code phase CPm.

As shown inFIG. 5, the terminal1020stores a code phase transmission program1116in the first storage section1110. The code phase transmission program1116is a program for causing the terminal control section1100to transmit the code phase information1154to the base station1040.

As shown inFIG. 5, the terminal1020stores a correction information reception program1118in the first storage section1110. The correction information reception program1118is a program for causing the terminal control section1100to receive a base station code phase CPb from the base station1040.

The base station code phase CPb is information provided by the base station1040when the radio wave S1or the like received by the terminal1020is a multipath wave.

The terminal control section1100stores correction information1156indicating the base station code phase CPb in the second storage section1150.

As shown inFIG. 5, the terminal1020stores a positioning program1120in the first storage section1110. The positioning program1120is a program for causing the terminal control section1100to locate the present position using the code phase information1154and the correction information1156.

FIG. 6is a view illustrative of the process based on the positioning program1120.

As shown inFIG. 6, when the terminal1020has received the base station code phase CPb3for only the GPS satellite12c, for example, the terminal control section1100uses the code phases CPm1, CPm2, and CPm4calculated by the terminal1020for the GPS satellites12a,12b, and12d. The terminal control section1100uses the base station code phase CPb3for the GPS satellite12cinstead of the code phase CPm3.

The terminal control section1100locates the present position using the code phases CPm1, CPm2, CPm4, and CPb3, and calculates a located position P.

The terminal control section1100stores located position information1158indicating the calculated located position P in the second storage section1150.

As shown inFIG. 5, the terminal1020stores a located position output program1122in the first storage section1110. The located position output program1122is a program for causing the terminal control section1100to display the located position P on the display device1036(seeFIG. 3).

(Main Software Configuration of Base Station1040)

FIG. 7is a schematic view showing the main software configuration of the base station1040.

As shown inFIG. 7, the base station1040includes a control section1200which controls each section, a communication section1202corresponding to the communication device1054shown inFIG. 4, a GPS section1204corresponding to the GPS device1056, a display section1206corresponding to the display device1058, a clock section1208corresponding to the clock1060, and the like.

The base station1040also includes a first storage section1210which stores various programs, and a second storage section1250which stores various types of information.

As shown inFIG. 7, the base station1040stores satellite orbital information1252in the second storage section1250. The satellite orbital information1252includes an almanac1252aand an ephemeris1252b.

As shown inFIG. 7, the base station1040stores an RTT calculation program1212in the first storage section1210. The RTT calculation program1212is a program for causing the control section1200to calculate a propagation time (RTT) required for the communication radio wave to propagate between the base station1040and the terminal1020. The RTT calculation program1212and the control section1200exemplify a propagation time calculation section.

In more detail, the control section1200transmits a specific frame (hereinafter called “base station frame”) to the terminal1020, and receives a frame (hereinafter called “terminal frame”) transmitted from the terminal1020corresponding to the base station frame. The control section1200calculates the RTT by measuring the transmission time of the specific base station frame and the reception time of the terminal frame corresponding to the base station frame using the clock section1208.

As described above, the control section1200calculates the round trip time (RTT) required for the communication radio wave to make a round trip between the base station1040and the terminal1020.

The control section1200stores RTT information1254indicating the calculated RTT in the second storage section1250.

As shown inFIG. 7, the base station1040stores an RTT evaluation program1214in the first storage section1210. The RTT evaluation program1214is a program for causing the control section1200to determine whether or not the RTT is equal to or less than a predetermined time threshold value α. The time threshold value α is 0.7 microseconds (μm), for example. A time range equal to or less than the time threshold value α exemplifies an allowable time range. The RTT evaluation program1214and the control section1200exemplify a propagation time evaluation section.

The time threshold value α is specified as a period of time by which the control section1200determines that the terminal1020is located in the communication area (also called “cell”) of the base station1040and is sufficiently close to the base station1040. In other words, the time range indicated by the time threshold value α is specified as a time range when the base station1040and the terminal1020are so close that the positions of the base station1040and the terminal1020are considered to be almost identical.

When the RTT is 0.7 microseconds (μm), the period of time required for the communication radio wave to reach the terminal1020from the base station1040is 0.35 (0.7/2) microseconds (μm). Since the communication radio wave propagates at the speed of light (about 299792.456 m/ms), the distance between the base station1040and the terminal1020is about 105 meters (m). The above distance is specified as a distance appropriate for the base station1040to transmit the calculated code phase to the terminal1020and the terminal1020to locate the position using the code phase calculated by the base station1040when the base station1040has determined that the code phase calculated by the terminal1020is affected by a multipath as a result of a comparison between the code phase calculated by the base station1040and the code phase calculated by the terminal1020, as described later.

As shown inFIG. 7, the base station1040stores a satellite signal reception program1216in the first storage section1210. The satellite signal reception program1216is a program for causing the control section1200to receive the radio waves S1and the like from the GPS satellites12aand the like. The satellite signal reception program1216and the control section1200exemplify a satellite signal reception section.

The satellite signal reception program1216is the same as the satellite signal reception program1112of the terminal1020(seeFIG. 5).

As shown inFIG. 7, the base station1040stores a code phase calculation program1218in the first storage section1210. The code phase calculation program1218is a program for causing the control section1200to calculate the code phase of the C/A code in units of the GPS satellites12aand the like. The code phase calculation program1218and the control section1200exemplify a code phase calculation section.

For example, the control section1200calculates a code phase CPb1of the GPS satellite12a, a code phase CPb2of the GPS satellite12b, a code phase CPb3of the GPS satellite12c, and a code phase CPb4of the GPS satellite12d.

When the RTT is equal to or less than the predetermined time threshold value α, the distance between the base station1040and the terminal1020is very short. Therefore, the base station1040can receive the radio waves S1and the like from the GPS satellites12aand the like almost the same as the GPS satellites12aand the like used by the terminal1020to calculate the code phases, and calculate the code phases.

Since the base station1040receives the radio waves S1and the like in an open sky environment (i.e., the reception state of the radio waves S1and the like is good), the code phases CPb1and the like are not affected by a multipath and have an extremely high accuracy. The code phases CPb1and the like are generically called a code phase CPb.

The control section1200stores code phase information1258indicating the code phases CPb1and the like in the second storage section1250.

As shown inFIG. 7, the base station1040stores a terminal code phase reception program1220in the first storage section1210. The terminal code phase reception program1220is a program for causing the control section1200to receive the terminal code phase information1154(seeFIG. 5) from the terminal1020. The terminal code phase reception program1220and the control section1200exemplify a positioning-side code phase reception section.

The control section1200stores the received terminal code phase information1154in the second storage section1250as the terminal code phase information1258.

As shown inFIG. 7, the base station1040stores a code phase difference calculation program1222in the first storage section1210. The code phase difference calculation program1222is a program for causing the control section1200to calculate a difference CPdif between the base station code phase CPb1or the like and the terminal code phase CPm1or the like. The difference CPdif exemplifies a difference. The code phase difference calculation program1222and the control section1200exemplify a difference calculation section.

FIG. 8is a view illustrative of the process based on the code phase difference calculation program1222.

FIG. 8schematically shows a code phase comparison.

The control section1200calculates the difference CPdif in units of the GPS satellites12aand the like. For example, the control section1200calculates the difference between the base station code phase CPb1of the GPS satellite12aand the terminal code phase CPm1of the GPS satellite12a. As shown inFIG. 8, the control section1200calculates the difference CPdif in chips such as c1chips or c2chips. The chip is a basic unit forming the C/A code.

The control section1200stores code phase difference information1260indicating the calculated difference CPdif in the second storage section1250.

As shown inFIG. 7, the base station1040stores a code phase difference evaluation program1224in the first storage section1210. The code phase difference evaluation program1224is a program for causing the control section1200to determine whether or not the difference CPdif is equal to or greater than a threshold value β. The threshold value β is one chip, for example. When the difference CPdif is equal to or greater than the threshold value β, the terminal side code phase used to calculate the difference CPdif may be affected by a multipath. In other words, a difference range equal to or greater than the threshold value β is specified as a difference range when the terminal side code phase is affected by a multipath.

A range equal to or greater than the threshold value β exemplifies a difference range. The code phase difference evaluation program1224and the control section1200exemplify a difference evaluation section.

When the control section1200has determined that the RTT is equal to or less than the threshold value α based on the RTT evaluation program, the control section1200operates based on the satellite signal reception program1216, the code phase calculation program1218, the terminal code phase reception program1220, the code phase difference calculation program1222, and the code phase difference evaluation program1224.

As shown inFIG. 7, the base station1040stores a correction value transmission program1226in the first storage section1210. The correction value transmission program1226is a program for causing the control section1200to transmit the base station code phase CPb1or the like of the corresponding GPS satellite12aor the like to the terminal1020when the control section1200has determined that the difference CPdif is equal to or greater than the threshold value β. The correction value transmission program1226and the control section1200exemplify a correction value transmission section.

The positioning system1010is configured as described above.

As described above, the base station1040can determine whether or not the RTT is equal to or less than the threshold value α. Therefore, the base station1040can identify whether or not the terminal1020is close to the base station1040in addition to whether or not the terminal1020is positioned in the communication area (cell) of the base station1040.

The base station1040can calculate the difference CPdif between the code phase CPb calculated by the base station1040and the terminal code phase CPm. Since the true positions of the base station1040and the terminal1020usually differ even if the base station1040is close to the terminal1020, the difference CPdif includes the difference due to the difference in true position, the difference due to an error caused by a factor other than a multipath, and the difference due to an error caused by a multipath.

When the base station1040has determined that the difference CPdif is equal to or greater than the threshold value β, the base station1040can transmit the code phase CPb calculated by the base station1040to the terminal1020.

Since the base station1040can identify whether or not the terminal1020is positioned close to the base station1040, as described above, the base station1040can transmit the base station code phase CPb1or the like to the terminal1020when the base station1040has determined that the condition is satisfied whereby the terminal1020is positioned very close to the base station1040and that the difference CPdif is equal to or greater than the threshold value β. When the condition is satisfied whereby the terminal1020is positioned very close to the base station1040, the terminal code phase CPm should be almost the same as the base station code phase CPb when the terminal code phase CPm is not affected by a multipath. Therefore, it is appropriate for the terminal1020to use the base station code phase CPb for positioning. It is also appropriate for the terminal1020to locate the position using the base station code phase CPb calculated by the nearby base station1040instead of the terminal code phase CPm calculated by the terminal1020using a multipath signal. Specifically, the positioning accuracy of the terminal1020is likely to be improved.

This allows the base station1040to provide the base station code phase CPb to the terminal1020which can communicate with the base station1040only when the condition is satisfied whereby it is appropriate for the terminal1020to use the base station code phase CPb.

The configuration of the positioning system1010according to this embodiment has been described above. An operation example of the positioning system1010is described below mainly usingFIG. 9.

FIG. 9is a schematic flowchart showing an operation example of the positioning system1010.

The base station1040calculates the RTT between the base station1040and the terminal1020(step STA1inFIG. 9). The step STA1exemplifies a propagation time calculation step.

The base station1040determines whether or not the RTT is equal to or less than the threshold value α (step STA2). The step STA2exemplifies a propagation time evaluation step.

When the base station1040has determined that the RTT is equal to or less than the threshold value α, the base station1040receives the radio waves S1and the like (step STA3). The step STA3exemplifies a satellite signal reception step.

The base station1040receives the terminal code phase CPm from the terminal1020(step STA5). The step STA5exemplifies a positioning-side code phase reception step.

The base station1040calculates the code phase difference CPdif (step STA6). The step STA6exemplifies a difference calculation step.

The base station1040determines whether or not at least one code phase difference CPdif is equal to or greater than the threshold value β (step STA7). The step STA7exemplifies a difference evaluation step.

When the base station1040has determined that at least one code phase difference CPdif is equal to or greater than the threshold value β, the base station1040transmits the base station code phase CPb1or the like of the corresponding GPS satellite12aor the like to the terminal1020(step STA8). The step STA8exemplifies a correction value transmission step.

The terminal corrects the terminal code phase CPm1or the like of the GPS satellite12aor the like corresponding to the base station code phase CPb1or the like with the base station code phase CPb1(step STA9).

The terminal1020locates the position (step STA10). In the step STA10, the terminal1020locates the position using the base station code phase CPb for the GPS satellite for which the base station code phase CPb has been received, and locates the position using the terminal code phase CPm for the GPS satellite for which the base station code phase CPb has not been received.

The terminal1020outputs the located position P (step STA11).

When the base station1040has determined that the RTT is greater than the time threshold value α in the step STA2, the base station1040notifies the terminal1020that the base station1040does not transmit the base station code phase CPb.

When a code phase difference CPdif equal to or greater than the threshold value β does not exist in the step STA7, the base station1040also notifies the terminal1020that the base station1040does not transmit the base station code phase CPb.

The base station1040can provide the base station code phase CPb to the terminal1020which can communicate with the base station1040only when the condition is satisfied whereby it is appropriate for the terminal1020to use the base station code phase CPb.

The terminal1020can accurately locate the position using the base station code phase CPb for the GPS satellite for which the base station code phase CPb has been received and using the terminal code phase CPm for the GPS satellite for which the base station code phase CPb has not been received.

A program for controlling a communication base station may be provided which causes a computer to execute the propagation time calculation step, the propagation time evaluation step, the satellite signal reception step, the code phase calculation step, the positioning-side code phase reception step, the difference calculation step, the difference evaluation step, and the correction value transmission step, and the like of the above-described operation example.

A computer-readable recording medium or the like may also be provided which stores such a program for controlling a communication base station or the like.

A program storage medium used to install the program for controlling a communication base station or the like in a computer to allow the program or the like to be executable by the computer may be implemented by a package medium such as a flexible disk such as a floppy disk®, a compact disk read only memory (CD-ROM), a compact disk-recordable (CD-R), a compact disk-rewritable (CD-RW), or a digital versatile disk (DVD), a semiconductor memory, a magnetic disk, or a magnetooptical disk in which the program is stored temporarily or permanently, or the like.

The first embodiment has been described above. Note that the control section1200of the base station1040may transmit the RTT information1254(see FIG.7) and the code phase information1256to the terminal1020, and the terminal1020may calculate the code phase difference CPdif, differing from this embodiment.

Second Embodiment

A second embodiment is described below.

(Main Hardware Configuration of Base Station2040)

FIG. 10is a schematic view showing the main hardware configuration of a base station2040.

As shown inFIG. 10, the base station2040includes a bus2042.

A central processing unit (CPU)2044, a storage device2046, an external storage device2048, and the like are connected with the bus2042. The storage device2046is a random access memory (RAM), a read only memory (ROM), or the like. The external storage device2048is a hard disk drive (HDD) or the like.

An input device2050for inputting various types of information and the like, a power supply device2052, a communication device2054, a GPS device2056, a display device2058, and a clock2060are also connected with the bus2042.

The base station2040can measure the round trip time (RTT) (seeFIG. 1) using the clock2060. The RTT is the period of time required for the communication radio wave to make a round trip between the base station2040and a terminal2020. The half of the RTT is the propagation time required for the communication radio wave to propagate between the base station2040and the terminal2020.

(Main Hardware Configuration of Terminal2020)

FIG. 11is a schematic view showing the main hardware configuration of the terminal2020.

As shown inFIG. 11, the terminal2020includes a bus2022.

A CPU2024, a storage device2026, and the like are connected with the bus2022.

An input device2028for inputting various types of information and the like, a power supply device2030, a communication device2032, and a GPS device2034are also connected with the bus2022. The terminal2020can receive the radio waves S1and the like using the GPS device2034.

A display device2036for displaying various types of information is also connected with the bus2022.

(Main Software Configuration of Base Station2040)

FIG. 12is a schematic view showing the main software configuration of the base station2040.

As shown inFIG. 12, the base station2040includes a control section2200which controls each section, a communication section2202corresponding to the communication device2054shown inFIG. 10, a GPS section2204corresponding to the GPS device2056, a display section2206corresponding to the display device2058, a clock section2208corresponding to the clock2060, and the like.

The base station2040also includes a first storage section2210which stores various programs, and a second storage section2250which stores various types of information.

As shown inFIG. 12, the base station2040stores satellite orbital information2252in the second storage section2250. The satellite orbital information2252includes an almanac2252aand an ephemeris2252b. The almanac2252ais information indicating the approximate orbits of all of the GPS satellites12aand the like (seeFIG. 1). The almanac2252acan be acquired by decoding any of the signals carried on the radio waves S1and the like from the GPS satellites12aand the like.

The ephemeris2252bis information indicating the precise orbit of each of the GPS satellites12aand the like (seeFIG. 1). For example, when acquiring the ephemeris2252bof the GPS satellite12a, it is necessary to receive and decode the radio wave S1from the GPS satellite12a.

As shown inFIG. 12, the base station2040stores base station position information2254in the second storage section2250. The base station position information2254is information indicating the position of the base station2040located at a fixed position by means of latitude, longitude, and height.

As shown inFIG. 12, the base station2040stores an RTT calculation program2212in the first storage section2210. The RTT calculation program2212is a program for causing the control section2200to calculate the propagation time (RTT) required for the communication radio wave to propagate between the base station2040and the terminal2020. The RTT calculation program2212and the control section2200exemplify a propagation time calculation section.

In more detail, the control section2200transmits a specific frame (hereinafter called “base station frame”) to the terminal2020, and receives a frame (hereinafter called “terminal frame”) transmitted from the terminal2020corresponding to the base station frame. The control section2200calculates the RTT by measuring the transmission time of the specific base station frame and the reception time of the terminal frame corresponding to the base station frame using the clock section2208.

As described above, the control section2200calculates the round trip time (RTT) required for the communication radio wave to make a round trip between the base station2040and the terminal2020.

The control section2200stores RTT information2256indicating the calculated RTT in the second storage section2250.

As shown inFIG. 12, the base station2040stores a transmission direction information acquisition program2214in the first storage section2210. The transmission direction information acquisition program2214is a program for causing the control section2200to acquire information indicating the transmission direction of the communication radio wave transmitted to the terminal2020which communicates with the base station2040.

In more detail, the control section2200specifies the transmission direction by specifying one of the antennas54aand the like used to transmit the communication radio wave to the terminal2020. As the transmission direction, the north is indicated by 0 degrees, the east is indicated by 90 degrees, the south is indicated by 180 degrees, and the west is indicated by 270 degrees.

The control section2200stores transmission direction information2258indicating the transmission direction in the second storage section2250.

As shown inFIG. 12, the base station2040stores a satellite signal reception program2216in the first storage section2210. The satellite signal reception program2216is a program for causing the control section2200to receive the radio waves S1and the like from the GPS satellites12aand the like.

In more detail, the control section2200determines the GPS satellites12aand the like which can be observed at the present time referring to the almanac2252a, and receives the radio waves S1and the like from the observable GPS satellites12aand the like. In this case, a base station position Pb is used as the reference position of the base station2040.

As shown inFIG. 12, the base station2040stores a code phase calculation program2218in the first storage section2210. The code phase calculation program2218is a program for causing the control section2200to calculate the code phase of the C/A code in units of the GPS satellites12aand the like.

For example, the control section2200calculates the code phase CPb1of the GPS satellite12a, the code phase CPb2of the GPS satellite12b, the code phase CPb3of the GPS satellite12c, and the code phase CPb4of the GPS satellite12d.

Since the base station2040receives the radio waves S1and the like in an open sky environment (i.e., the reception state of the radio waves S1and the like is good), the code phases CPb1and the like are not affected by a multipath and have an extremely high accuracy. The code phases CPb1and the like are generically called a code phase CPb.

The control section2200stores code phase information2260indicating the code phases CPb1and the like in the second storage section2250.

As shown inFIG. 12, the base station2040stores an initial position calculation program2220in the first storage section2210. The initial position calculation program2220is a program for causing the control section2200to calculate an initial position Pip of the terminal2020. The initial position calculation program2220and the control section2200exemplify an initial position calculation section.

The terminal2020uses the initial position Pip as an initial estimated position when locating the position. The terminal2020uses the initial position Pip when calculating the observable GPS satellites12aand the like or calculating the Doppler shift of the radio waves S1and the like from the GPS satellites12aand the like, for example.

FIG. 13is a view illustrative of the process based on the initial position calculation program2220.

The control section2200calculates the distance d between the base station2040and the terminal2020according to an expression1shown inFIG. 13. Since the propagation time required for the communication radio wave to propagate from the base station2040to the terminal2020is half of the RTT, the distance d can be calculated by multiplying the half of the RTT by the propagation velocity (speed of light) of the communication radio wave.

The control section2200calculates the position apart from the base station position Pb by the distance d in the transmission direction θ as the initial position Pip. Since the transmission direction θ is two-dimensional, a height Zb of the base station position Pb is used as the height of the initial position Pip.

The control section2200stores initial position information2262indicating the calculated initial position Pip (Xip, Yip, Zip) in the second storage section2250. The height Zip is equal to the height Zb of the base station position Pb, as described above.

As shown inFIG. 12, the base station2040stores an estimated difference calculation program2222in the first storage section2210. The estimated difference calculation program2222is a program for causing the control section2200to calculate the estimated difference CPdif between the code phase of a specific GPS satellite at the base station2040and the code phase at the initial position Pip of the terminal2020. The estimated difference calculation program2222and the control section2200exemplify an estimated difference calculation section.

FIG. 14is a view illustrative of the process based on the estimated difference calculation program2222.

The control section2200calculates an estimated difference Timedif in delay time according to an expression2shown inFIG. 14. The control section2200calculates the satellite position Ps (Xs, Ys, Zs) of the GPS satellite12ain the orbit at the present time referring to the ephemeris2252b, for example. The control section2200calculates the difference between the distance between the satellite position Ps and the base station position Pb and the distance between the satellite position Ps and the initial position Pip of the terminal2020. The control section2200calculates the estimated difference Timedif in delay time by dividing the difference in distance by the propagation velocity (speed of light) of the radio waves S1and the like. The unit for the estimated difference Timedif is milliseconds (msec).

The C/A code is a signal having a bit rate of 1.023 Mbps and a bit length of 1023 bits (=1 msec), as described above. Therefore, the estimated difference CPdif can be calculated by multiplying the estimated difference Timedif by 1023.

The control section2200stores estimated difference information2264indicating the calculated estimated difference CPdif in the second storage section2250.

As shown inFIG. 12, the base station2040stores an estimated code phase calculation program2224in the first storage section2210. The estimated code phase calculation program2224is a program for causing the control section2200to calculate an estimated code phase CPip based on the estimated difference CPdif and the base station code phase CPb or the like calculated based on the received radio wave S1or the like. The estimated code phase CPip exemplifies an estimated code phase.

FIG. 15is a view illustrative of the process based on the estimated code phase calculation program2224.

When an angle of elevation ELVb of a specific GPS satellite at the base station position Pb is larger than an angle of elevation ELVip at the initial position Pip, the control section2200calculates the estimated code phase CPip by adding the estimated difference CPdif to the base station code phase CPb according to an expression4A. When the angle of elevation ELVb is larger than the angle of elevation ELVip, the distance between a specific satellite and the base station2040is shorter than the distance between the satellite and the terminal2020. Therefore, the sign of the estimated difference CPdif becomes positive.

When the angle of elevation ELVb of a specific GPS satellite at the base station position Pb is smaller than the angle of elevation ELVip at the initial position Pip, the control section2200calculates the estimated code phase CPip by subtracting the estimated difference CPdif from the base station code phase CPb according to an expression4B. When the angle of elevation ELVb is smaller than the angle of elevation ELVip, the distance between a specific satellite and the base station2040is longer than the distance between the satellite and the terminal2020. Therefore, the sign of the estimated difference CPdif becomes negative.

The control section2200stores the calculated estimated code phase CPip in the second storage section2250. Note that the sign of the estimated difference CPdif may be determined during the calculation process according to the expression2shown inFIG. 14, differing from this embodiment. Specifically, since the difference between the distance between a specific GPS satellite and the base station position Pb and the distance between the GPS satellite and the terminal2020is calculated during the calculation process according to the expression2shown inFIG. 14, these distances can be compared. When the distance between a specific GPS satellite and the base station position Pb is longer than the distance between the GPS satellite and the terminal2020, the sign of the estimated difference CPdif becomes negative. On the other hand, when the distance between a specific GPS satellite and the base station position Pb is shorter than the distance between the GPS satellite and the terminal2020, the sign of the estimated difference CPdif becomes positive.

As shown inFIG. 12, the base station2040stores a subsidiary information transmission program2226in the first storage section2210. The subsidiary information transmission program2226is a program for causing the control section2200to transmit the initial position information2262and the estimated code phase information2266to the terminal2020. The subsidiary information transmission program2226and the control section2200exemplify a subsidiary information transmission section.

The main software configuration of the base station2040has been described above.

The main software configuration of the terminal2020is described below.

(Main Software Configuration of Terminal2020)

FIG. 16is a schematic view showing the main software configuration of the terminal2020.

As shown inFIG. 16, the terminal1020includes a terminal control section2100which controls each section, a communication section2102corresponding to the communication device2032shown inFIG. 11, a GPS section2104corresponding to the GPS device2034, a display section2106corresponding to the display device2036, and the like.

The terminal2020also includes a first storage section2110which stores various programs, and a second storage section2150which stores various types of information.

As shown inFIG. 16, the terminal2020stores satellite orbital information2152in the second storage section2150. The satellite orbital information2152includes an almanac2152aand an ephemeris2152b.

The terminal2020utilizes the satellite orbital information2152for positioning.

As shown inFIG. 16, the terminal2020stores a satellite signal reception program2112in the first storage section2110. The satellite signal reception program2112is a program for causing the terminal control section2100to receive the radio waves S1and the like from the GPS satellites12aand the like.

The satellite signal reception program2112is the same as the satellite signal reception program2216of the base station2040except that the terminal control section2100uses the initial position Pip as the initial position for receiving the radio waves S1and the like. Specifically, the terminal control section2100uses the initial position Pip as the initial position for calculating the observable GPS satellites12aand the like, and also uses the initial position Pip for calculating the reception frequencies of the radio waves from the GPS satellites12aand the like. The reception frequency includes the Doppler shift.

As shown inFIG. 16, the terminal2020stores a code phase calculation program2114in the first storage section2110. The code phase calculation program2114is a program for causing the terminal control section2100to receive the radio waves S1and the like and calculate the code phase of the C/A code in units of the GPS satellites12aand the like. The code phase calculation program2114and the terminal control section2100exemplify a terminal code phase calculation section.

For example, the terminal control section2100calculates the code phase CPm1of the GPS satellite12a, the code phase CPm2of the GPS satellite12b, the code phase CPm3of the GPS satellite12c, and the code phase CPm4of the GPS satellite12d.

The terminal control section2100stores code phase information2154indicating the code phases CPm1and the like in the second storage section2150. The code phases CPm1and the like are generically called a terminal code phase CPm.

As shown inFIG. 16, the terminal2020stores a subsidiary information reception program2116in the first storage section2110. The subsidiary information reception program2116is a program for causing the terminal control section2100to receive the initial position information2262(seeFIG. 12) and the estimated code phase information2266(seeFIG. 12) from the base station2040.

The terminal control section2100stores the received initial position information2262in the second storage section2150as initial position information2156. The terminal control section2100stores the received estimated code phase information2266in the second storage section2150as estimated code phase information2158.

As shown inFIG. 16, the terminal2020stores a code phase difference calculation program2118in the first storage section2110. The code phase difference calculation program2118is a program for causing the terminal control section2100to calculate the code phase difference CPer between the estimated code phase CPip and the terminal code phase CPm. The code phase difference CPer exemplifies a code phase difference. The code phase difference calculation program2118and the terminal control section2100exemplify a code phase difference calculation section.

FIGS. 17A and 17Bare views illustrative of the process based on the code phase difference calculation program2118.

As shown inFIG. 17A, the terminal control section2100calculates the code phase difference CPer by calculating the difference between the estimated code phase CPip and the terminal code phase CPm and indicating the difference by the absolute value according to an expression5.

As shown inFIG. 17B, the terminal control section2100calculates the code phase difference CPer in units of the GPS satellites12aand the like. For example, the code phase difference Cpera of the GPS satellite12ais c1chips, and the code phase difference Cperb of the GPS satellite12bis c2chips.

The terminal control section2100stores code phase difference information2160indicating the calculated code phase difference CPper in the second storage section2150.

As shown inFIG. 16, the terminal2020stores a positioning program2120in the first storage section2110. The positioning program2120is a program for causing the terminal control section2100to locate the position using the estimated code phase CPip or the terminal code phase CPm depending on the code phase difference CPer. The positioning program2120and the terminal control section2100exemplify a positioning section.

FIGS. 18A and 18Bare views illustrative of the process based on the positioning program2120.

As shown inFIG. 18A, the terminal control section2100uses the terminal code phase CPm for a satellite of which the code phase difference Cper is less than a threshold value α. When the code phase difference Cper is less than the threshold value α, it is considered that the radio wave S1or the like from the GPS satellite is not a multipath wave. Therefore, the terminal control section2100uses the terminal code phase CPm calculated based on the actually received signal S1or the like. The threshold value α is specified as a value which allows occurrence of a multipath to be determined depending on the accuracy of the initial position Pip.

The threshold value α according to this embodiment is two chips, for example. The C/A code includes 1023 chips. When the estimated code phase CPip and the terminal code phase CPm differ by two chips or more, the terminal control section2100determines that the terminal code phase CPm is calculated using a multipath signal.

The threshold value α may be set to be smaller as the accuracy of the initial position Pip becomes higher. Since the initial position Pip is specified by the RTT and the transmission direction of the communication radio wave, the accuracy of the initial position Pip increases as the transmission direction is more accurately identified. Therefore, the threshold value α may be set at 1.5 chips when the number of transmission directions is eight (north, northeast, east, southeast, south, southwest, west, and northwest), and may be set at 1 chip when the number of transmission directions is sixteen, differing from this embodiment. Whether or not the terminal code phase CPm is affected by a multipath can be more accurately determined as the accuracy of the initial position Pip increases and the threshold value α decreases.

On the other hand, the terminal control section2100uses the estimated code phase CPip for a satellite of which the code phase difference Cper is equal to or greater than the threshold value α. When the code phase difference Cper is equal to or greater than the threshold value α, it is considered that the radio wave S1or the like from the GPS satellite is a multipath wave. Therefore, the terminal control section2100uses the estimated code phase CPip.

For example, when the terminal control section2100locates the position using the GPS satellites12a,12b,12c, and12dand only the code phase difference CPer corresponding to the GPS satellite12cis equal to or greater than the threshold value α, the terminal control section2100locates the position using the terminal code phases CPma, CPmb, and CPmd and the estimated code phase CPipc, as shown inFIG. 18B.

The terminal control section2100stores located position information2162indicating the calculated located position P1in the second storage section2150.

As shown inFIG. 16, the terminal2020stores a located position output program2122in the first storage section2110. The located position output program2122is a program for causing the terminal control section2100to display the located position P1on the display device2036(seeFIG. 11).

The positioning system2010is configured as described above.

As described above, the base station2040can calculate the initial position Pip of the terminal2020.

The base station2040can calculate the estimated difference CPdif.

The base station2040can calculate the estimated code phase CPip at the initial position Pip of the terminal2020based on the code phase CPb calculated based on the radio wave S1or the like and the estimated difference CPdif.

The terminal2020can calculate the code phase difference CPer between the estimated code phase CPip and the terminal code phase CPm. Since the terminal2020can estimate the Doppler shift of the radio wave S1or the like carrying the C/A code using the initial position Pip, the terminal2020can efficiently receive the C/A code and promptly calculate the terminal code phase CPm.

The terminal2020can locate the position using the estimated code phase CPip or the terminal code phase CPm depending on the code phase difference CPer.

For example, the terminal2020can locate the position using the estimated code phase CPip when the code phase difference CPer is large enough to indicate occurrence of a multipath. The estimated code phase CPip is not the code phase at the base station2040, but is the code phase estimated to be the code phase at the initial position Pip of the terminal2020. Specifically, the initial position Pip is closer to the true position of the terminal2020than the position of the base station2040.

Therefore, the estimated code phase CPip is closer to the true code phase of the terminal2020than the base station code phase CPb.

Therefore, the positioning system2020allows occurrence of a multipath to be determined and the position to be accurately located when a multipath occurs in comparison with the case of using the code phase at the communication base station. Moreover, since the initial position Pip is closer to the true position of the terminal2020than the position of the base station2040, the calculation result of the positioning calculations is rapidly obtained. Specifically, the time to first fix (TTFF) is reduced.

The configuration of the positioning system2010according to this embodiment has been described above. An operation example of the positioning system2010is described below mainly usingFIGS. 19 and 20.

FIGS. 19 and 20are schematic flowcharts showing an operation example of the positioning system2010.

The base station2040calculates the RTT between the base station2040and the terminal2020(step STB1inFIG. 19). The base station2040acquires the transmission direction information (step STB2).

The base station2040receives the radio waves S1and the like and calculates the code phases CPb (step STB3).

The base station2040calculates the initial position Pip of the terminal2020based on the base station position Pb, the RTT, and the transmission direction (step STB4). The step STB4exemplifies an initial position calculation step.

The base station2040calculates the estimated difference CPdif between the code phase at the base station position Pb and the code phase at the initial position Pip (step STB5). The step STB5exemplifies an estimated difference calculation step.

The base station2040calculates the estimated code phase CPip at the initial position Pip based on the base station code phase CPb and the estimated difference CPdif (step STB6). The step STB6exemplifies an estimated code phase calculation step.

The base station2040transmits the initial position information2262(seeFIG. 12) and the estimated code phase information2266(seeFIG. 12) to the terminal2020(step STB7). The step STB7exemplifies a subsidiary information transmission step.

The terminal2020receives the initial position information2262and the estimated code phase information2266from the base station2040(step STB8inFIG. 20). The terminal2020stores the initial position information2262and the estimated code phase information2266in the second storage section2150as the initial position information2156and the estimated code phase information2158.

The terminal2020receives the C/A code carried on the radio wave S1or the like using the initial position Pip (step STB9).

The terminal2020calculates the terminal code phase CPm (step STB10).

The terminal2020calculates the code phase difference CPer between the estimated code phase CPip and the terminal code phase CPm (step STB11).

The terminal2020locates the position using the estimated code phase CPip for a satellite of which the code phase difference CPer is equal to or greater than the threshold value α and using the terminal code phase CPm for a satellite of which the code phase difference CPer is less than the threshold value α (step STB12).

The terminal2020then outputs the located position P1(step STB13).

The above steps allow occurrence of a multipath to be determined and the position to be accurately located when a multipath occurs in comparison with the case of using the code phase at the communication base station.

Modification of Second Embodiment

A modification of the second embodiment is described below.

A terminal2020X and a base station2040according to the modification of the second embodiment are mainly configured in the same manner as the terminal2020and the base station2040according to the second embodiment. Therefore, the same sections are indicated by the same symbols, and description thereof is omitted. The following description mainly focuses on the differences from the terminal2020and the base station2040according to the second embodiment.

In the modification of the second embodiment, the terminal2020X has most of the functions of the base station2040according to the second embodiment. This allows occurrence of a multipath to be determined and the position to be accurately located when a multipath occurs in comparison with the case of using the code phase at the communication base station without modifying the communication base station to a large extent.

FIG. 21is a schematic view showing the main software configuration of the base station2040X.

As shown inFIG. 21, the base station2040X does not include the RTT calculation program2212, the initial position calculation program2220, the estimated difference calculation program2222, the estimated code phase calculation program2224, and the subsidiary information transmission program2226, differing from the base station2040according to the second embodiment (seeFIG. 12).

The base station2040X stores a basic information transmission program2228in the first storage section2150. The basic information transmission program2228is a program for causing the control section2200to transmit the base station position information2254, the transmission direction information2258, and the code phase information2260to the terminal2020X.

FIG. 22is a schematic view showing the main software configuration of the terminal2020X.

As shown inFIG. 22, the terminal2020X does not include the subsidiary information reception program2116, differing from the terminal2020according to the second embodiment (seeFIG. 16).

The terminal2020X stores a basic information reception program2124in the first storage section2150. The basic information reception program2124is a program for causing the terminal control section2100to receive the base station position information2254, the transmission direction information2258, and the code phase information2260from the base station2040X. The basic information reception program2124and the terminal control section2100exemplify a base station position information acquisition section, a transmission direction acquisition section, and a base station code phase acquisition section.

The terminal control section2100stores the base station position Pb included in the base station position information2254, the transmission direction included in the transmission direction information2258, and the base station code phase CPb included in the code phase information2260in the second storage section2150as basic information2164.

As shown inFIG. 22, the terminal2020X stores an RTT calculation program2126in the first storage section2150. The RTT calculation program2126is the same as the RTT calculation program2212of the base station2040(seeFIG. 12). The RTT calculation program2126and the terminal control section2100exemplify a propagation time calculation section.

In more detail, the terminal control section2100transmits a specific frame (hereinafter called “terminal frame”) to the base station2040X, and receives a frame (hereinafter called “base station frame”) transmitted from the base station2040X corresponding to the terminal frame. The terminal control section2100calculates the time RTT by measuring the transmission time of the specific terminal frame and the reception time of the base station frame corresponding to the terminal frame.

As shown inFIG. 22, the terminal2020X stores an initial position calculation program2128in the first storage section2150. The initial position calculation program2128is the same as the initial position calculation program2220of the base station2040(seeFIG. 12). The initial position calculation program2128and the terminal control section2100exemplify an initial position calculation section.

The terminal control section2100stores initial position information2166indicating the calculated initial position Pip in the second storage section2150.

Note that the terminal control section2100may receive signals from a plurality of base stations2040X and calculate the initial position Pip based on the received signals, differing from this modification.

As shown inFIG. 22, the terminal2020X stores an estimated difference calculation program2130in the first storage section2150. The estimated difference calculation program2130is the same as the estimated difference calculation program2222of the base station2040(seeFIG. 12). The estimated difference calculation program2130and the terminal control section2100exemplify an estimated difference calculation section.

The terminal control section2100stores estimated difference information2168indicating the calculated estimated difference CPdif in the second storage section2150.

As shown inFIG. 22, the terminal2020X stores an estimated code phase calculation program2132in the first storage section2150. The estimated code phase calculation program2132is the same as the estimated code phase calculation program2224of the base station2040(seeFIG. 12). The estimated code phase calculation program2132and the terminal control section2100exemplify an estimated code phase calculation section.

The terminal control section2100stores estimated code phase information2170indicating the calculated estimated code phase CPip in the second storage section2150.

In the modification of the second embodiment, the terminal2020X calculates the initial position Pip and the estimated code phase CPip, as described above.

A program for controlling a communication base station may be provided which causes a computer to execute the initial position calculation step, the estimated difference calculation step, the estimated code phase calculation step, the subsidiary information transmission step, and the like of the above-described operation example.

A computer-readable recording medium or the like may also be provided which stores such a program for controlling a communication base station or the like.

A program storage medium used to install the program for controlling a communication base station or the like in a computer to allow the program and the like to be executable by the computer may be implemented by a package medium such as a flexible disk such as a floppy disk®, a compact disk read only memory (CD-ROM), a compact disk-recordable (CD-R), a compact disk-rewritable (CD-RW), or a digital versatile disk (DVD), a semiconductor memory, a magnetic disk, or a magnetooptical disk in which the program is stored temporarily or permanently, or the like.

The second embodiment has been described above. Note that various modifications and variations may be made.

For example, the base station2040may receive the terminal code phase CPm from the terminal2020, calculate the code phase difference CPer, and compare the code phase difference CPer with the threshold value α, differing from the second embodiment. The base station2040may transmit the terminal code phase CPm or the estimated code phase CPip used for positioning to the terminal2020.

Although two embodiments have been described above, the invention is not limited to the above two embodiments. The above embodiments may be configured in combination.

Although only some embodiments of the invention have been described above in detail, those skilled in the art would readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, such modifications are intended to be included within the scope of the invention.