Position measurement device, position measurement method, and program recording medium

A position measurement device which includes: a storage unit that stores area information for setting a first region along a boundary of the specific area; an area setting unit that acquires the area information from the storage unit and sets the first region on the basis of the acquired area information; and a position measurement unit that acquires the first region from the area setting unit, sets the acquired first region as a verification region, measures the position of the object located in the verification region, and updates the area information stored in the storage unit.

This application is a National Stage Entry of PCT/JP2018/023050 filed on Jun. 18, 2018, which claims priority from Japanese Patent Application 2017-120117 filed on Jun. 20, 2017, the contents of all of which are incorporated herein by reference, in their entirety.

TECHNICAL FIELD

The present invention relates to a position measurement device, a position measurement method, and a program which measure a position of a target.

BACKGROUND ART

There is a technique of receiving a reflected wave of an electromagnetic wave transmitted toward a range including a specific area, and performing, by using the received reflected wave, position measurement of a target located in the specific area. For example, presence or absence of a target can be determined by scanning a reflected wave for each section uniquely determined by a distance and an angle from an antenna which transmits and receives an electromagnetic wave, and measuring spectral intensity of the section. Generally, in position measurement of a target in a specific area, all sections covering the whole specific area are scanned.

NPL 1 discloses a tracking technique of scanning all sections of a specific area, and, when a target is discovered, performing position measurement by restricting a scan range to a region including the target. The technique of NPL 1 performs position measurement for all sections in a specific area with low frequency, and, when a target is discovered at a certain scan opportunity, performs position measurement with high frequency at a next scan opportunity, mainly for a region to which the target seems to move.

PTL 1 discloses a radar device which uses beat signals acquired from a plurality of antennas, and detects a target at a plurality of detection angles. The device of PTL 1 selects a target for calculation from detected targets, and changes, based on position information of the target for calculation, an interval between some detection angles among a plurality of detection angles at which a target is detected next, in such a way as to be different from an interval between other detection angles. The device of PTL 1 enables to set a small interval between inspection angles of an angle range requiring detailed sensing, and set a large interval between other inspection angles, and therefore, enables to improve detection accuracy of a target, and shorten a detection time of the target.

CITATION LIST

Patent Literature

Non Patent Literature

SUMMARY OF INVENTION

Technical Problem

A general position measurement technique has a problem that detection of spectral intensity is performed in all sections in a specific area, and therefore, a scan time becomes long.

In contrast, the techniques of NPL 1 and PTL 1 enable to shorten a scan time by restricting a scan range to a target in a specific area. However, the techniques of NPL 1 and PTL 1 scan all sections of the specific area until discovering a target, and therefore, it takes time to discover a target newly entering the specific area. In other words, the techniques of NPL 1 and PTL 1 have a problem of, when a target newly enters a specific area, being unable to measure a position of the target in the specific area in real time.

In order to solve the problem described above, an object of the present invention is to provide a position measurement device which enables to shorten a time required for detecting a target entering a specific area, and perform position measurement of the target located in the specific area in real time.

Solution to Problem

A position measurement device according to one aspect of the present invention includes: a storage means for storing area information for setting a first region along a boundary of a specific area; an area setting means for acquiring the area information from the storage means, and setting the first region, based on the acquired area information; and a position measurement means for acquiring the first region from the area setting means, setting the acquired first region to a verification region, performing position measurement of a target located in the verification region, and updating the area information stored in the storage means.

A position measurement method according to one aspect of the present invention includes: setting a first region, based on area information acquired from a storage means for storing the area information for setting the first region along a boundary of a specific area; setting the first region to a verification region; performing position measurement of a target located in the verification region; and updating the area information stored in the storage means.

A program according to one aspect of the present invention causes a computer to execute: processing of setting a first region, based on area information acquired from a storage means for storing the area information for setting the first region along a boundary of a specific area; processing of setting the first region to a verification region; processing of performing position measurement of a target located in the verification region; and processing of updating the area information stored in the storage means.

Advantageous Effects of Invention

According to the present invention, it becomes possible to provide a position measurement device which enables to shorten a time required for detecting a target entering a specific area, and perform position measurement of the target located in the specific area in real time.

EXAMPLE EMBODIMENT

Example embodiments of the present invention will be described below by using the drawings. However, limitation being technically preferable in order to implement the present invention is placed on example embodiments described below, but does not limit the scope of the invention to the description below. Note that, in all the drawings used for description of the example embodiments below, the same reference sign is given to a similar part, unless there is a particular reason. Moreover, in the example embodiments below, a repeated description may be omitted in relation to a similar configuration and operation.

First Example Embodiment

First, a position measurement device according to a first example embodiment of the present invention is described with reference to the drawings. The position measurement device according to the present example embodiment measures a position of a target in a specific area by transmitting an electromagnetic wave to a range including the specific area where position measurement of a target is performed, and receiving and then analyzing a reflected wave of the transmitted electromagnetic wave.

FIG.1is a block diagram illustrating a configuration of a position measurement device1according to the present example embodiment. As inFIG.1, the position measurement device1includes a signal transmission unit11, a signal reception unit12, a beat signal generation unit13, an information storage unit14, an area setting unit15, and a position measurement unit17.

The signal transmission unit11generates a transmission signal transmitted toward a measurement target area via a transmission antenna. The signal transmission unit11outputs the generated transmission signal to the transmission antenna and the beat signal generation unit13. A generation signal generated by the signal transmission unit11is transmitted toward the measurement target area via at least one transmission antenna. For example, the signal transmission unit11generates a pulse wave, a continuous wave, and a frequency modulated continuous wave (hereinafter, FMCW), as a transmission signal. An example using the FMCW is described below.

The signal reception unit12receives, as a reception signal, a reflected wave of a transmission signal via at least one reception antenna. The signal reception unit12outputs the received reception signal to the beat signal generation unit13. When there are a plurality of reception antennas, the signal reception unit12separately outputs, to the beat signal generation unit13, reception signals each acquired from each reception antenna.

The beat signal generation unit13acquires a transmission signal from the signal transmission unit11, and acquires a reception signal from the signal reception unit12. The beat signal generation unit13generates an intermediate frequency signal (hereinafter, an IF signal) by synthesizing the acquired transmission signal and the reception signal. The beat signal generation unit13outputs the generated IF signal to the position measurement unit17.

When there are a plurality of transmission antennas or reception antennas, the beat signal generation unit13synthesizes a transmission signal and a reception signal for each pair of a transmission antenna and a reception antenna. For example, when transmission antennas are configured by Tx1and Tx2and reception antennas are configured by Rx1and Rx2, four pairs of (Tx1, Rx1), (Tx1, Rx2), (Tx2, Rx1), and (Tx2, Rx2) are formed. In this case, the beat signal generation unit13generates an IF signal for each of the four pairs.

The information storage unit14(also referred to as a storage unit) stores information (hereinafter, area information) for calculating a step-in area (also referred to as a first region). Moreover, the information storage unit14stores information (hereinafter, target information) for calculating a tracking area (also referred to as a second region). Note that, when no tracking area is set, the information storage unit14may store area information.

The step-in area is a region set along a boundary of a specific area. Note that, although an example of setting a step-in area inside a boundary of a specific area is described in the present example embodiment, a step-in area may be set outside a boundary of a specific area. Moreover, a step-in area may be a fixed region, or may be a region which dynamically changes in shape and area each time position measurement is performed.

A tracking area is a range in which a target is estimated, based on a past position measurement result, to be located in current position measurement. A tracking area may be set in a range of a fixed distance from a past target position, or may be set in a range in which a distance from a target position dynamically changes.

The area setting unit15acquires area information with reference to the information storage unit14, and sets a step-in area along a boundary of a specific area using the acquired area information. The area setting unit15outputs the set step-in area to the position measurement unit17. Moreover, the area setting unit15sets a tracking area for performing position measurement of a target being tracked. The area setting unit15outputs the set tracking area to the position measurement unit17. Note that, when only a target located in a step-in area is targeted for detection, the area setting unit15may not set a tracking area.

As inFIG.2, the area setting unit15includes a step-in area setting unit151(also referred to as a first region setting unit), and a tracking area setting unit153(also referred to as a second region setting unit). The step-in area setting unit151refers to the information storage unit14, and sets a step-in area having any width from a boundary of a specific area. The tracking area setting unit153refers to the information storage unit14, and sets a tracking area for performing position measurement of a target being tracked. Note that, when only a target located in a step-in area is targeted for detection, the tracking area setting unit153may be omitted.

The position measurement unit17has a first function of setting a scan area. The position measurement unit17gives the step-in area setting unit151an instruction to acquire a step-in area, and acquires the step-in area from the step-in area setting unit151. Moreover, the position measurement unit17gives the tracking area setting unit153an instruction to acquire a tracking area, and acquires the tracking area from the tracking area setting unit153. The position measurement unit17sets, to a scan area (also referred to as a verification region), a region combining a tracking area and a step-in area. Note that, when only a target located in a step-in area is targeted for detection, the position measurement unit17gives the area setting unit15which does not include the tracking area setting unit153, an instruction to acquire a tracking area. When only a target located in a step-in area is targeted for detection, the position measurement unit17sets the step-in area to a scan area.

Moreover, the position measurement unit17has a second function of performing position measurement in a scan area. The position measurement unit17acquires an IF signal from the beat signal generation unit13, performs position measurement of a scan area, based on the acquired IF signal, and calculates a position spectrum of a section in the scan area.

Furthermore, the position measurement unit17has a third function of updating information in the information storage unit14. The position measurement unit17determines, based on the calculated position spectrum, whether a target is located in an area, and updates, according to a determination result, information held in the information storage unit14.

The above is the description of an overview of the components of the position measurement device1according to the present example embodiment. Note that a configuration (referred to as an intermediate signal generation unit) combining the signal transmission unit11, the signal reception unit12, and the beat signal generation unit13inside a broken line inFIG.1may be configured outside without being included in the position measurement device1. In this case, the position measurement device1may receive an IF signal generated by an intermediate signal generation unit configured outside.

Here, a measurement target area to which a transmission signal is transmitted from the position measurement device1is described.FIG.3is a conceptual diagram for describing a measurement target area A11of the position measurement device1. A specific area A12, a step-in area A13, an internal area A14, and a tracking area A15are set inside the measurement target area A11.

In the example ofFIG.3, a target111and a target112are located inside the specific area A12. The target111is a target whose position is already measured in previous position measurement. On the other hand, the target112is a target which has been located outside the specific area A12in previous position measurement, but newly entered the specific area A12in current position measurement.

The measurement target area A11(inside a fan shape of a full line) is a region in which the position measurement device1is able to perform position measurement of a target by a reflected wave of an electromagnetic wave received via an antenna.

The specific area A12(inside a rectangular shape of a broken line) is a region set within a range of the measurement target area A11in order for the position measurement device1to perform position measurement of a target.

The step-in area A13(a region between the rectangular shape of the broken line and a rectangular shape of a full line) is a region set along a boundary of the specific area A12. In the example ofFIG.3, the step-in area A13is set inside the boundary of the specific area A12. Note that, as long as a target entering the specific area A12can be detected, the step-in area A13may be set in a part including outside of the boundary of the specific area A12.

The internal area A14(inside the rectangular shape of the full line) is a region included in the specific area A12and set inside the step-in area A13.

The tracking area A15(inside a circular shape of a full line) is a region in which a target is estimated, based on a previous scan result, to be located at current scan timing.

In the present example embodiment, position measurement of all targets located inside the specific area A12is enabled by performing position measurement of a scan area including the step-in area A13and the tracking area A15. In the present example embodiment, a region being a scan target is limited, and therefore, position measurement of a target can be performed in a short time as compared with a scheme which scans all regions of the specific area A12.

Now, characteristic components of the position measurement device1according to the present example embodiment are described in detail. In relation to the area setting unit15, description is given below separately for the step-in area setting unit151and the tracking area setting unit153.

First, the information storage unit14is described.FIG.4is a table (an information table140) indicating one example of information held by the information storage unit14. The information storage unit14holds information including area information and target information.

Area information is information used in order to set the step-in area A13. The information table140inFIG.4includes, as one example of the area information, a specific area coordinate, a step-in coordinate, and a step-in width. Note that, when the step-in area A13is set at width from the boundary of the specific area A12, only a step-in range may be included as area information. Moreover, when a width of a step-in area dynamically changes, it is preferable that the information storage unit14holds a target speed and a previous scan time (a previous position measurement time) as area information.

A specific area coordinate is a coordinate indicating a range of the specific area A12. In the example ofFIG.3, coordinates (x1, y1), (x2, y2), (x3, y3), and (x4, y4) of four vertexes of the specific area A12represented by the rectangular shape of the broken line are set as specific area coordinates. Note that, when the specific area A12is not rectangular, a coordinate indicating a shape of the specific area A12may be designated as a specific area coordinate. Note that information representing a shape of the specific area A12may be not a coordinate but a mathematical expression.

When width of the step-in area A13is a fixed value, a step-in coordinate is a coordinate for calculating the width of the step-in area A13. In the example ofFIG.3, coordinates (x5, y5), (x6, y6), (x7, y7), and (x8, y8) of four vertexes of the internal area A14represented by the rectangular shape of the full line are step-in coordinates. On the other hand, when width of the step-in area A13dynamically changes, the width is set using a target speed and a previous scan time.

Target information is information used in order to calculate a tracking area. InFIG.4, a target identifier and a target position are included in target information.

A target identifier is an identifier uniquely allocated to an individual target. A target identifier is used in order to determine which target has exited when information relating to a target that has exited to outside of the specific area A12is deleted. Note that, when information about a target determined to be located inside the specific area A12in the past is preserved, a target identifier may be omitted. From now on, it is assumed that information relating to a target that has exited to the outside of the specific area A12is deleted, and an example of using a target identifier is described.

A target position is a coordinate indicating a position of a target. A target position is linked with a target identifier uniquely allocated to an individual target.

For example, when the target111given a target identifier “111” is located at (x9, y9), and the target112given a target identifier “112” is located at (x10, y10), a target position and a target identifier are held as inFIG.4.

When the tracking area A15is in a fixed range from a target position, the information storage unit14stores a tracking range in addition to a target position and a target identifier. Moreover, when the tracking area A15dynamically changes, the information storage unit14stores a target speed and a previous scan time. Note that, when a plurality of targets are located inside the specific area A12, and a target speed of each target is different, the information storage unit14stores a target speed of each target.

Additionally, a tracking area may be set based on a movement prediction model of a target. In this case, the information storage unit14stores information relating to movement prediction model generation. For example, information relating to movement prediction model generation includes position information, a measurement time, and the like of a target in the past.

The above is the detailed description of the information storage unit14. Note that a step-in coordinate, a step-in range, a target speed, and a tracking range may be predetermined fixed values, or may be values input via a non-illustrated user interface (UI).

Next, the step-in area setting unit151is described. The step-in area setting unit151acquires area information from the information storage unit14. The step-in area setting unit151sets a step-in area, based on the acquired area information, and outputs the set step-in area to the position measurement unit17.

When a step-in area is fixed, the step-in area setting unit151acquires, as area information, a specific area coordinate and at least either a step-in coordinate or a step-in range from the information storage unit14. The step-in area setting unit151sets a step-in area, based on the acquired area information.

When a step-in coordinate is used, the step-in area setting unit151sets, to a step-in area, a region between a range set by the step-in coordinate and a range set by the specific area coordinate. On the other hand, when a step-in range is used, the step-in area setting unit151sets, to a step-in area, a region having a width of the step-in range from a boundary of the specific area coordinate.

When a step-in area dynamically changes, the step-in area setting unit151acquires a specific area coordinate, a target speed, and a previous scan time from the information storage unit14. In this case, the step-in area setting unit151updates the previous scan time held in the information storage unit14to a current time. The step-in area setting unit151calculates a step-in area range Rstep-inby applying, to Equation 1, a target speed V and a difference time Tdifffrom the previous scan time to the current time. Note that, in Equation 1, α is a constant.
Rstep-in=α×V×Tdiff(1)

As in Equation 1, the step-in area range Rstep-inis a value being proportional to the target speed V and the difference time Tdiff. A part from the boundary of the specific area A12to the step-in area range Rstep-inis a step-in area Astep-in.

The above is the detailed description of the step-in area setting unit151.

Next, the tracking area setting unit153is described. The tracking area setting unit153acquires target information from the information storage unit14. The tracking area setting unit153sets a tracking area, based on the target information acquired from the information storage unit14, and outputs the set tracking area to the position measurement unit17.

When a tracking area is fixed, the tracking area setting unit153acquires a target position and a tracking range from the information storage unit14, and sets a tracking area. In relation to the target111inFIG.4, the tracking area setting unit153acquires a target position (x9, y9) and a tracking range (5 m), and sets a range with a radius of 5 m around the target position (x9, y9) to a tracking area.

When a tracking area dynamically changes, the tracking area setting unit153acquires, as target information, a target position, the target speed V, and a previous scan time. The tracking area setting unit153sets a tracking area, based on the acquired target information. In this case, in relation to the target111inFIG.4, the tracking area setting unit153updates the previous scan time to a current time. The tracking area setting unit153calculates a tracking range Rtrackingby applying, to Equation 2, the target speed V and a difference time Tdifffrom the previous scan time to the current time. Note that, in Equation 2, β is a constant.
Rtracking=β×V×Tdiff(2)

A tracking area set for the target111is a region with the radius Rtrackingaround the target position (x9, y9). The tracking range Rtrackingis a value being proportional to the target speed V and the difference time Tdiff. Note that a tracking area is not limited to a circular shape. For example, the tracking range Rtrackingmay be set by using a Kalman filter or the like, based on movement prediction of a target. When the Kalman filter is used, the tracking area setting unit153performs movement prediction by acquiring, from the information storage unit14, past position information of a target and information of a time in which the target is present at the position, and sets a tracking area.

For example, when the number of targets being tracked is N, the tracking area setting unit153performs calculation of Equation 2 in relation to each target (N is a natural number). Then, the tracking area setting unit153sets, to a tracking area Atracking, a union of tracking areas Atracking_neach set for each target by Equation 3 (n is a natural number).
Atracking=Atracking_1∪Atracking_2∪ . . . ∪Atracking_N(3)

The above is the detailed description of the tracking area setting unit153.

Next, the position measurement unit17is described. The position measurement unit17includes the following three functions.

The first function of the position measurement unit17is a function of setting a scan area. The position measurement unit17sets a scan area using a step-in area acquired from the step-in area setting unit151, and a tracking area acquired from the tracking area setting unit153.

The position measurement unit17calculates a scan area Ascanby the following Equation 4 or 5 using an acquired step-in area Astep-inand a tracking area Atracking. Note that, in Equation 5, Ainterestindicates the whole specific area A12.
Ascan=Astep-in∪Atracking(4)
Ascan=Astep-in∪(Atracking∩Ainterest)  (5)

Equation 4 adds a condition that a region outside the specific area A12is also designated as the scan area Ascanwhen the tracking area Atrackingincludes outside of the specific area A12. On the other hand, Equation 5 adds a condition that a region outside the specific area A12is not designated as the scan area Ascanwhen the tracking area Atrackingincludes the outside of the specific area A12.

The second function of the position measurement unit17is a function of performing position measurement in a scan area. The position measurement unit17performs position measurement in a scan area using an IF signal acquired from the beat signal generation unit13. A section in the scan area Ascanis a range included in a set in Expression 6, among sections U (rscan, θscan) represented by a distance rscanand an angle θscan.
{U(rscan,θscan)|(rscan×cos θscan,rscan×sin θscan)∈Ascan}  (6)

In the example ofFIG.3, a section U1is a section inside the step-in area A13indicated by a distance r and an angle θ.

From now on, a method of calculating spectral intensity of a section U (rscan, θscan) as a position spectrum is illustrated.

First, in order to calculate spectral intensity of a section, the position measurement unit17calculates a spectrum (hereinafter, a range spectrum) from the position measurement device1to a target. When the FMCW is applied, the position measurement unit17calculates a range spectrum Prangeby Fourier-transforming an IF signal IFsignal(Equation 7).FIG.5is one example of a graph illustrating a relation between a difference frequency ΔF calculated by use of Equation 7, and spectral intensity.
Prange=FFT(IFsignal)  (7)

FIG.6is a graph for describing a mechanism of performing position measurement by applying the FMCW. The position measurement unit17calculates a distance r to a target by applying, to Equation 8, the difference frequency ΔF, a sweep time Tsweep, a frequency bandwidth BW, and a parameter of light speed c.

Next, the position measurement unit17calculates a position spectrum of a section by calculating a spectrum of an angle of a target at any distance from the position measurement unit17. The position measurement unit17detects a direction of the target located at the distance r, by implementing a direction-of-arrival estimation method for a range spectrum Prange(r) of a distance from a reception antenna to the target. Moreover, the position measurement unit17may implement, by using Equation 8, a direction-of-arrival estimation method for a range spectrum of the difference frequency ΔF associated with the distance r.

An example of using a beamformer method as the direction-of-arrival estimation method is described below. Note that Capon or a linear prediction method may be used as the direction-of-arrival estimation method. Moreover, multiple signal classification (MUSIC) may be used as the direction-of-arrival estimation method. Further, estimation of signal parameters via rotational invariance techniques (ESPRIT) may be used as the direction-of-arrival estimation method.

The position measurement unit17uses a weight vector a(θ) expressed by Equation 9, in order to direct a main lobe of an array antenna to the angle θ. Note that, in Equation 9, T indicates a transposed matrix, j indicates an imaginary unit, λ indicates a wavelength of a central frequency, K indicates the number of elements of a reception antenna, and d1indicates a distance from a reference point of a device to a position of an i-th element.

The position measurement unit17calculates, as a position spectrum, spectral intensity Pposition(r, θ) at the distance r and the angle θ, by using Equation 10. Note that the position measurement unit17may calculate 0 in a range satisfying the condition of Expression 6. In Equation 10, H represents a conjugate transposed matrix. Moreover, in Equation 10, a correlation matrix Rxx(r) is calculated from the range spectrum Prange(r) of any difference frequency component ΔF received from a plurality of reception antennas. Any difference frequency component ΔF is equivalent to any distance.

FIG.7is one example of a result of performing direction-of-arrival estimation using a range spectrum at a distance r1calculated by applying a difference frequency component ΔF1exceeding a threshold value inFIG.5to Equation 8. The position measurement unit17performs position measurement of a target by calculating a position spectrum Pposition(r, θ) using Equation 10, for the distance rscanand the angle θscansatisfying the condition of Expression 6. As above, the position measurement unit17calculates the spectral intensity Pposition(r, θ) in the section U (rscan, θscan) represented by a distance and an angle.

A scan area being a union of a tracking area and a step-in area does not include an internal area, and therefore, has a small area as compared with a specific area. Thus, the number of sections calculated by using Equation 10 is reduced, and a time required for position measurement is shortened by calculating within a range of a scan area, rather than calculating over the whole specific area including the internal area.

The third function of the position measurement unit17is a function of updating information in the information storage unit14. The position measurement unit17determines, by using calculated spectral intensity, whether a target is located inside an area, and updates information in the information storage unit14according to a determination result. For example, when spectral intensity in a certain section exceeds a preset threshold value, the position measurement unit17determines that a target is located in the section.

InFIG.5, spectral intensity of a spectrum having a peak at difference frequency ΔF1exceeds a threshold value. Moreover, inFIG.7, spectral intensity exceeds a threshold value at angles θ1and θ2, in relation to the distance r1calculated by using the difference frequency ΔF1. In other words, the position measurement unit17determines that targets are located at positions of coordinates indicated by (r1cos θ1, r1sin θ1) and (r1cos θ2, r1sin θ2).

When a target is detected in a scan area, the position measurement unit17updates or newly registers position information of the target held in the information storage unit14.

When newly registering position information (target position) of the target in the information storage unit14, the position measurement unit17registers the position information in association with an identifier (target identifier). An identifier may be attached in any way as long as a target being tracked can be identified. For example, the position measurement unit17uses a monotonously increasing numeral as an identifier.

On the other hand, in relation to a target which is not detected in a scan area, the position measurement unit17deletes information about the target from the information storage unit14. In the present function, the position measurement unit17deletes information about all targets from the information storage unit14, when no target is detected in a scan area. Moreover, when at least one target is detected in a scan area, the position measurement unit17deletes or updates information held in the information storage unit14, after determining whether or not a target currently being tracked is located inside a specific area. Further, when determining that a target for which a tracking area is set is located outside the area, the position measurement unit17deletes information about the target from the information storage unit14.

Herein, a method of determining that a target is located outside the specific area A12is described by use ofFIG.8. InFIG.8, a target113is located in the step-in area A13, and a part of the tracking area A15set in line with the target113includes outside of the specific area A12. An area being the tracking area A15and being outside the specific area A12is a region which may not be set to a scan area, as described by using Equations 4 and 5.

In a case of performing position measurement for the whole tracking area A15(Equation 4), the position measurement unit17determines that the target113is outside the specific area A12, when a position of the target113is outside the specific area A12.

On the other hand, in a case of not performing position measurement for a region being the tracking area A15and being outside the specific area A12(Equation 5), the position measurement unit17determines that a position of a target is outside the specific area A12, when no target is detected in the tracking area A15.

The above is the description of details of the components of the position measurement device1according to the present example embodiment. Note that, although a two-dimensional coordinate system is used in the above description in order to simplify the description, the scheme according to the present example embodiment may replace the two-dimensional coordinate system with a two-dimensional polar coordinate illustrated inFIG.9or a three-dimensional coordinate system illustrated inFIG.10. In the example ofFIG.9, a position indicated by (X, Y) in the two-dimensional coordinate system is indicated by (r cos θ, r sin θ) in the two-dimensional polar coordinate. Moreover, in the example ofFIG.10, a position indicated by (X, Y, −Z) in the three-dimensional coordinate system is indicated by (R sin θ1cos θ2, R sin θ1sin θ2, −R cos θ1) in a three-dimensional polar coordinate. Note that, although an example in which an antenna is located at an origin of each coordinate system is illustrated in each ofFIGS.9and10, an origin of each coordinate system may be set at a position other than a position of the antenna.

Next, an operation of the position measurement device1according to the present example embodiment is described with reference to the drawings.FIG.11is a flowchart for describing the operation of the position measurement device1. Note that, although a component of the position measurement device1is designated as an operation agent below, the position measurement device1itself may be designated as an operation agent.

The flowchart inFIG.11illustrates processing from a point of receiving a reflected wave of an electromagnetic wave sent toward a measurement target area to a point of performing position measurement of a target using a signal of the reflected wave. The processing in the flowchart inFIG.11may be regularly executed, or may be irregularly executed. For example, the position measurement device1repeatedly executes the processing in the flowchart inFIG.11every second.

InFIG.11, first, the beat signal generation unit13generates an IF signal by mixing, for each pair of transmission/reception antennas, a transmission signal generated by the signal transmission unit11with a reception signal received by the signal reception unit12(step S11). The beat signal generation unit13outputs the generated IF signal to the position measurement unit17.

Next, the step-in area setting unit151acquires area information from the information storage unit14in response to a request from the position measurement unit17, and sets a step-in area, based on the acquired area information (step S12). The step-in area setting unit151outputs the set step-in area to the position measurement unit17.

When a set step-in area is fixed, the step-in area setting unit151is able to set a step-in area as follows. For example, the step-in area setting unit151acquires specific area coordinates and a step-in coordinates inFIG.4, and sets, to a step-in area, a region between a line connecting the specific area coordinates and a line connecting the step-in coordinates. Moreover, for example, the step-in area setting unit151acquires specific area coordinates and a step-in range inFIG.4, and sets, to a step-in area, a region within the step-in range from a line connecting the specific area coordinates.

When a step-in area dynamically changes, the step-in area setting unit151is able to set a step-in area as follows. For example, the step-in area setting unit151acquires specific area coordinates, a target speed, and a previous scan time inFIG.4, determines width from a line connecting the specific area coordinates using an elapsed time from previous scan, and the target speed, and sets a step-in area. The step-in area setting unit151calculates a step-in area range by applying, to Equation 1, the target speed, and a difference time between the previous scan time and a current time. Then, the step-in area setting unit151updates all scan times in the information storage unit14to the current time.

Next, the tracking area setting unit153acquires target information from the information storage unit14in response to a request from the position measurement unit17, and sets a tracking area (step S13). The tracking area setting unit153outputs the set tracking area to the position measurement unit17. Note that a target identifier associated with a target position may be acquired from the information storage unit14and then output to the position measurement unit17by the tracking area setting unit153, or may be acquired from the information storage unit14by the position measurement unit17.

When a tracking area is fixed, for example, the tracking area setting unit153acquires a target position and a tracking range inFIG.4. Then, the tracking area setting unit153sets, to a tracking area, a region in a circle with a radius of the tracking range around the target position.

When a tracking area dynamically changes, the tracking area setting unit153is able to set a tracking area as follows. For example, the tracking area setting unit153acquires a target position, a target speed, and a previous scan time inFIG.4, and determines a tracking range from an elapsed time from previous scan, and the target speed. Then, the tracking area setting unit153sets, to a tracking area, a region in a circle with a radius of the tracking range around the target position.

The tracking area setting unit153calculates a tracking range by applying, to Equation 2, the target speed, and a difference time between the previous scan time and the current time. Moreover, for example, the tracking area setting unit153is able to set a tracking area also by acquiring, from the information storage unit14, past position information of a target and information of a time at which the target has been present at the position, and performing movement prediction based on a movement prediction model. When the number of targets being tracked is N, the tracking area setting unit153sets a tracking area in relation to each target, and sets, to a tracking area, a union of tracking areas each set in relation to each target.

Next, the position measurement unit17sets a scan area to be a scan target, by use of the step-in area acquired from the step-in area setting unit151, and the tracking area acquired from the tracking area setting unit153(step S14). The position measurement unit17calculates a scan area by applying the step-in area and the tracking area to Equation 4 or 5.

Next, the position measurement unit17performs position measurement for all sections inside the scan area, and determines whether a target is located inside the specific area A12(step S15). The position measurement unit17calculates a position spectrum by use of Equation 10, for all the sections inside the scan area, by using the condition of Expression 6. The position measurement unit17determines that a target is located in a section in which intensity of a position spectrum exceeds a threshold value.

When determining that a target is located inside the specific area A12(Yes in step S15), the position measurement unit17registers position information (target position) of the target in the information storage unit14(step S16). Note that, in relation to a newly detected target, the position measurement unit17registers an identifier (target identifier) of the target in the information storage unit14in association with the position information.

On the other hand, when determining that a target is located outside the specific area A12(No in step S15), the position measurement unit17deletes information about the target from the information storage unit14(step S17). Specifically, the position measurement unit17deletes, from the information storage unit14, position information of a target coinciding with an identifier (target identifier) of the target determined to be located outside the specific area A12, together with the identifier.

The above is the description of the operation of the position measurement device1according to the present example embodiment.

As above, the position measurement device according to the present example embodiment executes position measurement in relation to a scan area including a tracking area and a step-in area of a target already detected in previous position measurement. Thus, the position measurement device according to the present example embodiment is able to thoroughly detect, in a step-in area, a target entering a specific area, while tracking a target located inside the specific area.

With a general scheme, position measurement is performed for all sections of a specific area. On the other hand, the scheme according to the present example embodiment reduces a region to be scanned, by restricting to a tracking area and a step-in area and thus performing position measurement, and therefore, is able to shorten a required time of a scan.

In other words, according to the present example embodiment, a first advantageous effect that a scan time can be shortened can be acquired. A reason for this is that position measurement is performed in a step-in area set along an inner periphery of a boundary of a specific area, and therefore, processing is completed in a short time as compared with a case where position measurement is performed for all sections of the specific area.

Furthermore, according to the present example embodiment, a second advantageous effect that a target entering a specific area can be detected in real time can be acquired. A reason for this is that a target entering a specific area can be thoroughly detected in a step-in area.

Herein, a related art of the scheme according to the present example embodiment is described with reference to the drawings.

FIG.12is an example of receiving a reflected wave of an electromagnetic wave transmitted from a transmission/reception antenna10, and scanning all sections of the specific area A12. A scheme inFIG.12is able to determine presence or absence of the target111by scanning each section U uniquely determined by a distance R and an angle θ from the transmission/reception antenna10, and measuring spectral intensity of the section U. The example ofFIG.12has a time to scan all sections of the specific area A12. For example, assuming that the number of sections included in the specific area A12is Nsection, and a scan time required for position measurement for one section is Tscan, a total scan time Ttotalis calculated by Equation 11.
Ttotal=Nsection×Tscan(11)

In this way, the scheme inFIG.12scans all sections of the specific area A12, and therefore, requires time to detect the target112entering the specific area A12within one position measurement time (total scan time Ttotal).

FIG.13is an example of, when performing position measurement for all sections of a specific area with the scheme inFIG.12and then detecting the target111, tracking the detected target111. In the example ofFIG.13, all sections inside the specific area A12are scanned by low-frequency position measurement. Then, when the target111is detected inside the specific area, a range (the tracking area A15) in which the target111is estimated to move is tracked by high-frequency position measurement in next position measurement.

A scheme inFIG.13enables to shorten a scan time by tracking the target111with concentration. However, the scheme inFIG.13does not enable to measure, in real time, a position of a target entering the specific area A12in a period of tracking the target111with concentration.

Moreover, the scheme inFIG.13scans all sections inside the specific area A12by low-frequency position measurement, and therefore, when a wait time of position measurement is prolonged too much, detection of a target entering the specific area A12during the wait time is delayed.

Further, the schemes inFIGS.12and13enables to increase measurement accuracy of position measurement by setting a fine interval between distance measurement and angle measurement. However, scanning too finely increases the number of sections to be scanned, and prolongs a required time for scanning.

The scheme according to the present example embodiment sets a step-in area in line with a boundary of a specific area, and performs position measurement of a target in the step-in area. Since a target always passes through the step-in area when entering the specific area, a target entering the specific area can be thoroughly detected. Moreover, in the scheme according to the present example embodiment, a target can be certainly detected in a step-in area by providing the step-in area in line with a distance in which the target moves in a scan time interval. Moreover, the scheme according to the present example embodiment enables to shorten a required time for position measurement by scanning a section inside a step-in area with concentration. In other words, the present example embodiment enables to shorten a scan time by performing position measurement of a limited scan area while tracking a detected target.

Second Example Embodiment

Next, a position measurement device according to a second example embodiment of the present invention is described with reference to the drawings. The present example embodiment is different from the first example embodiment in including a pre-scan function of measuring at least either a distance or a direction of a target.

FIG.14is a block diagram illustrating a configuration of a position measurement device2according to the present example embodiment. As inFIG.14, the position measurement device2includes a signal transmission unit21, a signal reception unit22, a beat signal generation unit23, an information storage unit24, an area setting unit25, a pre-scan unit26, and a position measurement unit27.

The signal transmission unit21, the signal reception unit22, the information storage unit24, and the area setting unit25are similar to the corresponding components of the position measurement device1according to the first example embodiment, and therefore, description thereof is omitted.

The beat signal generation unit23is similar to the component of the position measurement device1, but is different from the position measurement device1in outputting a generated IF signal to the pre-scan unit26.

The pre-scan unit26performs at least either distance measurement or direction measurement before position measurement by the position measurement unit27, and determines whether a target is located inside the specific area.

When a target is detected in a specific area, the pre-scan unit26outputs a range spectrum or an IF signal to the position measurement unit27. Note that, when a target is detected in a specific area, the pre-scan unit26may output distance information and direction information of the target to the position measurement unit27, in addition to a range spectrum or an IF signal.

On the other hand, when no target is detected in a specific area, the pre-scan unit26deletes target information held in the information storage unit24.

As inFIG.15, the pre-scan unit26includes a distance measurement unit261which measures a distance to a target, and a direction measurement unit263which measures a direction of a target.

The distance measurement unit261measures a distance to a target, and determines whether the target is located inside a specific area.

When a target is detected in a specific area, the distance measurement unit261outputs an IF signal or a range spectrum to the position measurement unit27. In this instance, the distance measurement unit261may output acquired distance information of the target to the position measurement unit27. Note that the distance information of the target may have a plurality of candidates. On the other hand, when no target is detected in a specific area, the distance measurement unit261deletes information about the target held in the information storage unit24.

For example, the distance measurement unit261calculates a range spectrum by use of Equation 7. The distance measurement unit261determines presence or absence of a target by determining whether or not the acquired spectrum has a peak exceeding a set threshold value. When a distance r calculated using Equation 8 has a value indicating inside of a specific area Ainterestwith regard to a difference frequency ΔF having spectral intensity exceeding a threshold value, the distance measurement unit261outputs a range spectrum Prange(r) of the difference frequency ΔF to the position measurement unit27. Note that the distance measurement unit261determines whether the distance r is inside the specific area, by whether the distance r is included in a set in Expression 12.
{U(rinterest,θinterest)|(rinterest×cos θinterest,rinterest×sin θinterest)∈Ainterest}  (12)

From now on, it is assumed that the distance r associated with difference frequencies ΔF1to ΔFMof a range spectrum exceeding a threshold value is a set represented by Expression 13 (M is a natural number).
{rpeak1,rpeak2, . . . ,rpeakM}  (13)

The distance measurement unit261outputs the set of Expression 13 and the range spectrum Prange(r) to the position measurement unit27.

The direction measurement unit263performs direction-of-arrival estimation for an IF signal, measures a direction of a target from an acquired angle spectrum, and determines whether a target is located inside a specific area.

When a target detects a target inside a specific area, the direction measurement unit263outputs an IF signal to the position measurement unit27. On the other hand, when no target is detected in a specific area, the direction measurement unit263deletes target information held in the information storage unit24, in a way similar to the distance measurement unit261. In this instance, the direction measurement unit263may output acquired direction information of the target to the position measurement unit27. Note that the direction information of the target may have a plurality of candidates.

In the first example embodiment, the correlation matrix Rxx(r) is acquired by using the range spectrum Prange(r) having any distance r. In the present example embodiment, a correlation matrix Rxxis calculated by use of an IF signal. Specifically, the direction measurement unit263calculates an angle spectrum Pangle(θ) by applying the correlation matrix Rxxto Equation 14, by using a beamformer method being a direction-of-arrival estimation method. Note that the direction measurement unit263may use a direction-of-arrival estimation method other than the beamformer method, as in the first example embodiment. Note that θ may be in a range satisfying the condition of Expression 12.

The direction measurement unit263determines presence or absence of a target in a specific area by determining whether a spectrum acquired by Equation 14 exceeds a threshold value.

From now on, it is assumed that an angle θ of an angle spectrum exceeding a threshold value is included in a set represented by Expression 15 (N is a natural number).
{θpeak1,θpeak2, . . . ,θpeakN}  (15)

The direction measurement unit263outputs the set of Expression 15 and the IF signal to the position measurement unit27.

Next, the position measurement unit27is described. The position measurement unit27includes three functions. Note that a first and third functions of the position measurement unit27are similar to those in the first example embodiment, and therefore, description thereof is omitted.

A second function of the position measurement unit27is a function of inputting an IF signal or a range spectrum from the pre-scan unit26, and performing position measurement of a scan area by use of the input IF signal or range spectrum. Note that, when inputting an IF signal, the second function of the position measurement unit27is the same as the second function of the position measurement unit27in the first example embodiment.

When acquiring distance information or direction information of a target from the pre-scan unit26, the position measurement unit27may calculate only a position spectrum regarding a distance included in the set of Expression 13 or a direction included in the set of Expression 15, at a time of calculating a position spectrum by using Equation 10.

As one example, a case where the distance measurement unit261detects a target in a region at a distance r from the position measurement device2is described. In this instance, the position measurement unit27acquires a range spectrum Prange(r) having a distance r, from the distance measurement unit261. The position measurement unit27calculates a correlation matrix Rxx(r) by using the range spectrum Prange(r), and calculates a position spectrum Pposition(r, θ) by using Equation 10. On the other hand, the position measurement unit27does not calculate a position spectrum in relation to a region which is not at the distance r in the scan area.

Herein, a measurement target area to which a transmission signal is transmitted from the position measurement device2is described.FIG.16is an example of performing distance measurement as a pre-scan, andFIG.17is an example of performing direction measurement as a pre-scan.

FIG.16is a conceptual diagram for describing a measurement target area A21of the position measurement device2when distance measurement is performed as a pre-scan. Inside the measurement target area A21, a specific area A22, a step-in area A23, an internal area A24, a tracking area A25, a pre-scan area A26, and a position measurement area A27are set. Note that the specific area A22, the step-in area A23, the internal area A24, and the tracking area A25are similar to those in the first example embodiment, and therefore, description thereof is omitted.

In the example ofFIG.16, a target211and a target212are located inside the specific area A22. The target211is a target whose position is already measured in previous position measurement. On the other hand, the target212is a target which has been located outside the specific area A22in the previous position measurement, but newly entered the specific area A22in current position measurement.

InFIG.16, a region in a range at a distance including the specific area A22in the measurement target area A21is designated as the pre-scan area A26. The distance measurement unit261detects a target located in the pre-scan area A26, and calculates a distance between the target and the position measurement device2.

Furthermore, inFIG.16, the target212is located in a place at a distance r1from the position measurement device2. The position measurement unit27performs position measurement with regard to a region (the position measurement area A27) at the distance r1from the position measurement device2, in the scan area combining the step-in area A23and the tracking area A25.

FIG.17is a conceptual diagram for describing the measurement target area A21of the position measurement device2when direction measurement is performed as a pre-scan. Inside the measurement target area A21, a specific area A22, a step-in area A23, an internal area A24, a tracking area A25, a pre-scan area A28, and a pre-scan area A29are set. Note that the specific area A22, the step-in area A23, the internal area A24, and the tracking area A25are similar to those in the example ofFIG.16, and therefore, description thereof is omitted. Additionally, in the example ofFIG.17, a target211and a target212are located inside the specific area A22, as in the example ofFIG.16.

In the example ofFIG.17, a target located in a region (being the same as the measurement target area A21) in a range at a distance including the specific area A22in the measurement target area A21is detected, and a direction of the target from the position measurement device2can be detected. InFIG.17, the target212is located in a direction at an angle θ1from the position measurement device2. The position measurement unit27performs position measurement with regard to a direction region (the pre-scan area A28and the pre-scan area A29) at the angle θ1, in the scan area combining the step-in area A23and the tracking area A25, and therefore, a required time for position measurement is shortened.

Next, an operation of the position measurement device2according to the present example embodiment is described with reference to the drawings.FIG.18is a flowchart for describing the operation of the position measurement device2. Note that, although a component of the position measurement device2is designated as an operation agent below, the position measurement device2itself may be designated as an operation agent.

The flowchart inFIG.18illustrates processing from a point of receiving a reflected wave of an electromagnetic wave sent toward a measurement target area to a point of performing position measurement of a target by using a signal of the reflected wave, as in the first example embodiment. The processing illustrated by the flowchart inFIG.18is repeated appropriately.

InFIG.18, first, the beat signal generation unit23generates an IF signal by mixing, for each pair of transmission/reception antennas, a transmission signal generated by the signal transmission unit21with a reception signal received by the signal reception unit22(step S21). The beat signal generation unit23outputs the generated IF signal to the pre-scan unit26.

Next, the pre-scan unit26determines whether a target is located inside a specific area (step S22). When a target is detected inside the specific area (Yes in step S22), the operation proceeds to step S23. On the other hand, when no target is detected inside the specific area (No in step S22), the operation proceeds to step S28, and target information is deleted from the information storage unit24(step S28).

When direction measurement is performed as a pre-scan in step S22, the pre-scan unit26calculates a range spectrum using Equation 7. The pre-scan unit26checks presence or absence of a target inside the specific area by whether a peak of the calculated spectrum exceeds a threshold value.

When following two conditions are satisfied (equivalent to Yes in step S22), the pre-scan unit26outputs the IF signal or the range spectrum Prange(r) to the position measurement unit27. A first condition is a condition that spectral intensity exceeds a threshold value at a difference frequency ΔF of the range spectrum. The second condition is a condition that a distance r associated with the ΔF acquired by Equation 8 is a value indicating inside of the specific area Ainterest. In this instance, the pre-scan unit26may output distance information of a target to the position measurement unit27.

Furthermore, when direction measurement is performed as a pre-scan in step S22, the pre-scan unit26performs direction-of-arrival estimation for the IF signal, and measures a direction from an acquired angle spectrum to a target. The pre-scan unit26calculates a correlation matrix Rxxby using the IF signal, and calculates an angle spectrum Pangle(θ) by applying the calculated correlation matrix Rxxto Equation 14.

The pre-scan unit26checks presence or absence of a target inside the specific area A22by whether a peak of the calculated spectrum exceeds a threshold value.

When determining, by the direction measurement, that a target is present inside the specific area A22(equivalent to Yes in step S22), the pre-scan unit26outputs the IF signal to the position measurement unit27.

In this instance, the pre-scan unit26may output direction information of the target to the position measurement unit27.

As in the first example embodiment, the area setting unit25acquires area information from the information storage unit24in response to a request from the position measurement unit27, and sets a step-in area, based on the acquired area information (step S23). The area setting unit25outputs the set step-in area to the position measurement unit27.

Furthermore, as in the first example embodiment, the area setting unit25acquires target information from the information storage unit24in response to a request from the position measurement unit27, and sets a tracking area (step S24). The area setting unit25outputs the set tracking area to the position measurement unit27.

As in the first example embodiment, the position measurement unit27acquires the step-in area and the tracking area from the area setting unit25. As in the first example embodiment, the position measurement unit27sets a scan area to be a scan target, by using the acquired step-in area and tracking area (step S25).

The position measurement unit27calculates position spectrums for all sections of the scan area by using the IF signal or range spectrum acquired from the pre-scan unit26, and determines whether a target is located inside the specific area A22(step S26). In this instance, the position measurement unit27may perform position measurement exclusively for a section coinciding with the distance information or the direction information of the target being an input from the pre-scan unit26.

When determining that a target is located inside the specific area A22(Yes in step S26), the position measurement unit27registers position information (target position) of the target in the information storage unit24, as in the first example embodiment (step S27).

On the other hand, when determining that a target is located outside the specific area A22(No in step S26), the position measurement unit27deletes information about the target from the information storage unit24(step S28).

The above is the description of the operation of the position measurement device2according to the present example embodiment.

As above, in the present example embodiment, position measurement is not performed when no target is detected in a pre-scan. In other words, in the present example embodiment, when a target is located inside a specific area, a distance or a direction of the target is calculated by a pre-scan, and position measurement is performed in the position measurement unit in relation to a limited distance or direction in a scan area. Thus, according to the present example embodiment, a scan time can be shortened by reducing unnecessary position measurement, as compared with the first example embodiment.

Third Example Embodiment

Next, a position measurement device according to a third example embodiment of the present invention is described with reference to the drawings. The position measurement device according to the present example embodiment is different from that according to the first example embodiment in including a pre-scan function of measuring either a distance or a direction of a target located in a step-in area, and in skipping position measurement itself when no target is detected in a pre-scan.

FIG.19is a block diagram illustrating a configuration of a position measurement device3according to the present example embodiment. As inFIG.19, the position measurement device3includes a pre-scan unit36, in addition to a signal transmission unit31, a signal reception unit32, a beat signal generation unit33, an information storage unit34, an area setting unit35, and a position measurement unit37.

The signal transmission unit31, the signal reception unit32, and the information storage unit34are similar to components of the position measurement device1according to the first example embodiment, and therefore, description thereof is omitted.

The beat signal generation unit33is similar to the component of the position measurement device1, but is different from the position measurement device1in outputting a generated IF signal to the pre-scan unit36.

The area setting unit35is similar to the component of the position measurement device1, but is different from the position measurement device1in outputting a step-in area to the pre-scan unit36.

The pre-scan unit36acquires a step-in area from the area setting unit35. The pre-scan unit36separates the acquired step-in area into a distance measurement area for pre-scanning by distance measurement, and a direction measurement area for pre-scanning by direction measurement. Note that a step-in area is equivalent to a sum of a distance measurement area and a direction measurement area.

Then, the pre-scan unit36performs, before position measurement by the position measurement unit37, distance measurement in relation to a distance measurement area and direction measurement in relation to a direction measurement area, and determines whether a target is located inside the step-in area.

When a target is detected in the step-in area, the pre-scan unit36outputs a range spectrum or an IF signal to the position measurement unit37. Note that, when a target is detected in the step-in area, the pre-scan unit36may output distance information or direction information of the target to the position measurement unit37, in addition to a range spectrum or an IF signal.

On the other hand, when no target is detected inside the step-in area, the pre-scan unit36deletes target information held in the information storage unit34.

Herein, a detailed configuration of the pre-scan unit36is described. As inFIG.20, the pre-scan unit36includes a distance measurement unit361, a direction measurement unit363, and an area assignment unit365.

The distance measurement unit361acquires an IF signal from the beat signal generation unit33. The distance measurement unit361performs distance measurement in relation to a distance measurement area assigned by the area assignment unit365, and determines whether a target is located inside the distance measurement area.

The distance measurement unit361outputs a range spectrum to the position measurement unit37regardless of whether a target is located inside the distance measurement area. In this instance, the distance measurement unit361may output information relating to a distance of a target to the position measurement unit37. Assuming that a distance measurement area assigned by the area assignment unit365is Ah_step-in, whether a distance r is in a scan range can be determined by whether the distance r is included in a set of Expression 16.
{U(rh_step-in)|(rh_step-in×cos θ,rh_step-in×sin θ)∈Ah_step-in}  (16)

The direction measurement unit363acquires an IF signal from the beat signal generation unit33. The direction measurement unit363performs direction measurement in relation to a direction measurement area assigned by the area assignment unit365, and determines whether a target is located inside the direction measurement area.

The direction measurement unit363outputs the IF signal to the position measurement unit37regardless of whether a target is located inside the direction measurement area. In this instance, the direction measurement unit363may output information relating to a direction of a target to the position measurement unit37. Assuming that a direction measurement area assigned by the area assignment unit365is Av_step-in, whether a direction θ is in a scan range can be determined by whether the direction θ is included in a set of Expression 17.
{U(θv_step-in)|(r×cos θv_step-in,r×sin θv_step-in)∈Av_step-in}  (17)

The area assignment unit365(also referred to as an assignment unit) acquires a step-in area from the area setting unit35, and separates the step-in area into a distance measurement area and a direction measurement area. The area assignment unit365outputs the distance measurement area to the distance measurement unit361, and outputs the direction measurement area to the direction measurement unit363.

Next, the position measurement unit37is described. The position measurement unit37includes following three functions. Note that a first and third functions of the position measurement unit37are similar to those in the first example embodiment, and therefore, description thereof is omitted.

A second function of the position measurement unit37is a function of inputting an IF signal or a range spectrum from the pre-scan unit26, and performing position measurement of a scan area by using the input IF signal or range spectrum, as in the second example embodiment. However, in the present example embodiment, when no target is detected by the pre-scan unit36, position measurement may be performed in a new scan area Anew_scanin which a step-in area Astep-inis removed from a scan area Ascan, as in Equation 18. Moreover, an area obtained by removing the distance measurement area and the direction measurement area from the scan area Ascanmay be designated as the new scan area Anew_scan.
Anew_scan=Ascan∩Astep-in(18)

Herein, a measurement target area to which a transmission signal is transmitted from the position measurement device3is described.FIG.21is a conceptual diagram for describing a measurement target area A31targeted for measurement by the position measurement device3. Inside the measurement target area A31, a specific area A32, a distance measurement area A33, a direction measurement area A34, a tracking area A35, a scan range A36, and a scan range A37are set. The distance measurement area A33and the direction measurement area A34configure a step-in area. Note that the specific area A32and the tracking area A35are similar to those in the first example embodiment, and therefore, description thereof is omitted.

In the example ofFIG.21, a target311located inside the specific area A32. The target311is a target whose position is already measured in previous position measurement.

The area assignment unit365outputs the distance measurement area A33in the step-in area to the distance measurement unit361. The distance measurement unit361pre-scans a scan range including the distance measurement area A33by distance measurement. InFIG.21, the scan range A36is a range scanned in order to cover the distance measurement area A33. The distance measurement unit361outputs a range spectrum of the pre-scanned scan range A36to the position measurement unit37.

Furthermore, the area assignment unit365outputs the direction measurement area A34in the step-in area to the direction measurement unit363. The direction measurement unit363pre-scans, by direction measurement, a range including the direction measurement area A34in the step-in area. InFIG.21, the scan range A37is a range scanned in order to cover the direction measurement area A34. The direction measurement unit363outputs an IF signal of the pre-scanned scan range A37to the position measurement unit37.

Note that, in the example ofFIG.21, a target is located in neither the distance measurement area A33nor the direction measurement area A34, and therefore, position measurement may be performed for the tracking area A35of the target311.

Next, an operation of the position measurement device3according to the present example embodiment is described with reference to the drawings.FIG.22is a flowchart for describing the operation of the position measurement device3. Note that, although a component of the position measurement device3is designated as an operation agent below, the position measurement device3itself may be designated as an operation agent.

The flowchart inFIG.22illustrates processing from a point of receiving a reflected wave of an electromagnetic wave sent toward a measurement target area to a point of performing position measurement of a target by use of a signal of the reflected wave, as in the first example embodiment. The processing in the flowchart inFIG.22is repeated appropriately.

InFIG.22, first, the beat signal generation unit33generates an IF signal by mixing, for each pair of transmission/reception antennas, a transmission signal generated by the signal transmission unit31with a reception signal received by the signal reception unit32(step S301). The beat signal generation unit33outputs the generated IF signal to the pre-scan unit36.

Next, the area setting unit35acquires area information from the information storage unit34in response to a request from the pre-scan unit36, and sets a step-in area, based on the acquired area information (step S302). The area setting unit35outputs the set step-in area to the pre-scan unit36.

Next, the area assignment unit365of the pre-scan unit36separates, into a distance measurement area and a direction measurement area, the step-in area acquired from the area setting unit35(step S303). The area assignment unit365outputs the distance measurement area to the distance measurement unit361, and outputs the direction measurement area to the direction measurement unit363.

Next, the pre-scan unit36determines whether or not a target is located inside a step-in area configured by the distance measurement area and the direction measurement area (step S304). The pre-scan unit36outputs a range spectrum and an IF signal to the position measurement unit37.

When detecting a target inside the step-in area (Yes in step S304), the pre-scan unit36notifies the position measurement unit37that the target is detected (the operation proceeds to step S307). When receiving the notification from the pre-scan unit36, the position measurement unit37requests the area setting unit35to acquire the step-in area and a tracking area.

On the other hand, when no target is detected inside the step-in area (No in step S304), target information is deleted from the information storage unit34(step S305).

When the target information is deleted from the information storage unit34in step S305, the pre-scan unit36refers to target information in the information storage unit34, and checks presence or absence of a target being tracked (step S306). When a target being tracked is present (Yes in step S306), the pre-scan unit36outputs an IF signal to the position measurement unit37(the operation proceeds to step S307). On the other hand, when no target being tracked is present (No in step S306), the processing along the flowchart inFIG.22is finished.

The area setting unit35acquires area information from the information storage unit34in response to a request from the position measurement unit37, and sets a step-in area, based on the acquired area information (step S307). The area setting unit35outputs the set step-in area to the position measurement unit37. Note that, when information about a step-in area is output from the pre-scan unit36to the position measurement unit37, step S307may be omitted.

The area setting unit35acquires target information from the information storage unit34in response to a request from the position measurement unit37, and sets a tracking area (step S308). The area setting unit35outputs the set tracking area to the position measurement unit37.

The position measurement unit37acquires the step-in area and the tracking area from the area setting unit35. The position measurement unit37sets a scan area to be a scan target, by using the acquired step-in area and tracking area (step309).

The position measurement unit37calculates position spectrums for all sections of the scan area by using the IF signal or range spectrum acquired from the pre-scan unit36, and determines whether a target is located inside the specific area (step S310). However, when a tracking target is detected in step S306(Yes in step S306), the position measurement unit37may perform position measurement only in a new scan area.

When determining that a target is located inside a specific area (Yes in step S310), the position measurement unit37registers position information (target position) of the target in the information storage unit34(step S311).

On the other hand, when determining that a target is located outside the specific area (No in step S310), the position measurement unit37deletes information about the target from the information storage unit34(step S312).

The above is the description of the operation of the position measurement device3according to the present example embodiment.

As above, in the present example embodiment, position measurement is not performed when no target is detected in a step-in area by the pre-scan unit, in contrast to the second example embodiment. In other words, in the second example embodiment, position measurement is performed when a target is present inside a specific area, whereas, in the present example embodiment, position measurement is not performed unless the distance measurement unit and the position measurement unit sense a target even when a target is present inside a particular area. Thus, according to the present example embodiment, a scan time can be shortened by further reducing unnecessary position measurement, as compared with the second example embodiment.

Herein, a hardware configuration which executes processing by the position measurement device according to each example embodiment of the present invention is described by citing an information processing device90inFIG.23as one example. Note that the information processing device90inFIG.23is a configuration example for executing processing by the position measurement device according to each example embodiment, and does not limit the scope of the present invention.

As inFIG.23, the information processing device90includes a processor91, a main storage device92, an auxiliary storage device93, an input/output interface95, and a communication interface96. InFIG.23, an interface is abbreviated as an I/F. The processor91, the main storage device92, the auxiliary storage device93, the input/output interface95, and the communication interface96are data-communicably connected to one another via a bus99. Moreover, the processor91, the main storage device92, the auxiliary storage device93, and the input/output interface95are connected to a network such as the Internet or an intranet via the communication interface96.

The processor91extracts a program stored in the auxiliary storage device93or the like into the main storage device92, and executes the extracted program. In the present example embodiment, a configuration using a software program installed in the information processing device90may be provided. The processor91executes processing by the position measurement device according to the present example embodiment.

The main storage device92has a region where a program is deployed. The main storage device92may be a volatile memory such as a dynamic random access memory (DRAM). Moreover, a non-volatile memory such as a magnetoresistive random access memory (MRAM) may be configured and added as the main storage device92.

The auxiliary storage device93stores various data. The auxiliary storage device93is configured by a local disk such as a hard disk or a flash memory. Note that the main storage device92may be configured in such a way as to store various data, and the auxiliary storage device93may be omitted.

The input/output interface95is an interface for connecting the information processing device90and peripheral equipment. The communication interface96is an interface for connecting to an external system or device through a network such as the Internet or an intranet, based on a standard or a specification. The input/output interface95and the communication interface96may be formed into a common interface as an interface for connecting to external device.

The information processing device90may be configured in such a way that input equipment such as a keyboard, a mouse, and a touch panel is connected to the information processing device90as required. The input equipment is used for input of information and setting. Note that, when a touch panel is used as input equipment, a display screen of display equipment may be configured in such a way as to double as an interface of the input equipment. Data communication between the processor91and input equipment may be mediated by the input/output interface95.

Furthermore, the information processing device90may be equipped with display equipment for displaying information. When being equipped with display equipment, the information processing device90preferably include a display control device (not illustrated) for controlling display of the display equipment. The display equipment may be connected to the information processing device90via the input/output interface95.

Still further, the information processing device90may be equipped with a disk drive as required. The disk drive is connected to the bus99. Between the processor91and a non-illustrated recording medium (program recording medium), the disk drive mediates reading of data and a program from the recording medium, writing of a processing result of the information processing device90into the recording medium, and the like. The recording medium can be implemented by an optical recording medium such as a compact disc (CD) or a digital versatile disc (DVD). Additionally, the recording medium may be implemented by a semiconductor recording medium such as a universal serial bus (USB) memory or a secure digital (SD) card, a magnetic recording medium such as a flexible disk, or another recording medium.

The above is one example of a hardware configuration for enabling the position measurement device according to each example embodiment of the present invention. Note that the hardware configuration inFIG.23is one example of a hardware configuration for executing arithmetic processing by the position measurement device according to each example embodiment, and does not limit the scope of the present invention. Moreover, a program which causes a computer to execute processing relating to the position measurement device according to each example embodiment also falls within the scope of the present invention. Further, a program recording medium recording a program according to each example embodiment also falls within the scope of the present invention.

The components of the position measurement device according to each example embodiment can be combined in any way. Moreover, each component of the position measurement device according to each example embodiment may be implemented by software, or may be implemented by a circuit.

While the present invention has been described above with reference to the example embodiments, the present invention is not limited to the above-described example embodiments. Various changes which can be understood by a person skilled in the art can be made to a configuration and details of the present invention within the scope of the present invention.

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-120117, filed on Jun. 20, 2017, the disclosure of which is incorporated herein in its entirety by reference.

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