Patent ID: 12253590

EXAMPLE EMBODIMENT

Example Embodiment

An object detection apparatus, an object detection method, and a program according to an example embodiment of the present invention will be described hereinafter with reference toFIGS.1to17. In each of the drawings described below, identical or corresponding parts are indicated by the same reference signs, and descriptions thereof will not be repeated.

Apparatus Configuration

First, the overall configuration of the object detection apparatus according to the present example embodiment will be described with reference toFIG.1.FIG.1is a block diagram illustrating the overall configuration of the object detection apparatus according to the example embodiment of the present invention.

An object detection apparatus1000according to the present example embodiment illustrated inFIG.1is an apparatus for detecting an object to be detected (called a “target object” hereinafter)1003using radio waves, and is what is known as an imaging apparatus. As illustrated inFIG.1, the object detection apparatus1000includes a transmission unit1101, a reception unit1102, and a processing device1211. Additionally, in the example illustrated inFIG.1,1005indicates a plane on which the target object1003is placed (called a “target object placement plane” hereinafter).

The transmission unit1101includes a transmission antenna, and uses the transmission antenna to emit a radio wave1002serving as a transmission signal toward the target object1003present on the target object placement plane1005. The reception unit1102includes a reception antenna, and uses the reception antenna to receive a radio wave1004reflected by the target object1003as a reception signal. The reception unit1102further generates, from the received reception signal, an intermediate frequency signal (called an “IF signal” hereinafter).

Specifically, in the example illustrated inFIG.1, the transmission unit1101outputs the transmission signal via a terminal1208toward the reception unit1102. The reception unit1102generates an IF signal by mixing the radio wave (reception signal)1004that has been reflected by the target object1003and the transmission signal output via the terminal1208. Additionally, the reception unit1102outputs the generated IF signal to the processing device1211.

Additionally, in the example illustrated inFIG.1, a transmission/reception device1001includes the transmission unit1101and the reception unit1102. Furthermore, although only one each of the transmission unit1101and the reception unit1102are illustrated in the example inFIG.1, there may actually be a plurality of transmission units1101and reception units1102. If there are a plurality of transmission units1101and reception units1102, each of the transmission units1101corresponds to one of the reception units1102.

The processing device1211first calculates a distribution of the amplitudes of the radio wave reflected by the target object1003(called a “reflection amplitude distribution” hereinafter) on the basis of the placement of the transmission antenna, the position of the reception antenna, the frequency of the radio wave1002emitted from the transmission antenna, and the IF signal. Then, the processing device1211corrects the calculated reflection amplitude distribution using a correction operator calculated from a point spread function (PSF) indicating the characteristics of the transmission unit1101and the reception unit1102.

In this manner, in the present example embodiment, by applying the correction operator to the reflection amplitude distribution of the target object1003obtained from measurements by transmitting and receiving radio waves, a true reflection amplitude distribution, unweighted by PSF, is calculated. Therefore, according to the present example embodiment, the range of positions over which the target object1003can be detected can be expanded and a higher resolution of detection can be achieved compared to typical imaging apparatuses (object detection apparatuses) using radio waves. In other words, according to the present example embodiment, the range of positions that can be detected can be expanded and the resolution can be increased, which improves the detection accuracy, while avoiding an increase in the size of the aperture, which is a cause of higher costs in the apparatus and a drop in the ease of installation.

The configuration of the transmission/reception device1001of the object detection apparatus1000according to the present first example embodiment will be described in more detail next with reference toFIGS.2to4in addition toFIG.1.FIG.2is a diagram illustrating the specific configurations of the transmission unit and the reception unit in the object detection apparatus according to the example embodiment of the present invention.FIG.3is a diagram illustrating another example of the specific configurations of the transmission unit and the reception unit in the object detection apparatus according to the example embodiment of the present invention.

As illustrated inFIG.2, according to the present first example embodiment, in the transmission/reception device1001, the transmission unit1101includes an oscillator1201and a transmission antenna1202. The reception unit1102includes a reception antenna1203, a mixer1204, and an interface circuit1205. Furthermore, as illustrated inFIG.1, the transmission unit1101and the reception unit1102are connected by a terminal1208.

In the transmission unit1101, the oscillator1201generates an RF signal (radio wave). The RF signal generated by the oscillator1201is transmitted as a transmission signal from the transmission antenna1202and emitted to the target object1003. The radio wave1004reflected by the target object1003is received by the reception antenna1203in the reception unit1102.

The mixer1204generates an IF signal by mixing the RF signal input from the oscillator1201via the terminal1208with the radio wave received by the reception antenna1203(the reception signal). The IF signal generated by the mixer1204is transmitted to the processing device1211via the interface circuit1205.

The interface circuit1205has a function for converting the IF signal, which is an analog signal, into a digital signal that can be handled by the processing device1211, and then outputting the obtained digital signal to the processing device1211.

Additionally, in the example illustrated inFIG.2, one transmission unit1101includes a single transmission antenna1202, but the present example embodiment is not limited thereto. An example in which one transmission unit1101includes a plurality of transmission antennas1202will be described with reference toFIG.3.

In the example inFIG.3, the transmission unit1101includes one oscillator1201and a plurality of transmission antennas1202. The transmission unit1101also includes a variable phase shifter1206which is provided for each of the transmission antennas1202. Each transmission antenna1202is connected to the oscillator1201via a corresponding variable phase shifter1206. Each variable phase shifter1206controls the directivity of the transmission antenna1202by controlling the phase of the transmission signal supplied from the oscillator1201to each of the transmission antennas1202.

In the example illustrated inFIG.3, the transmission unit1101can also supply RF signals from the oscillator1201to the plurality of transmission antennas1202through time division. In this case, the variable phase shifter1206need not be provided in the transmission unit1101.

The specific configuration of the object detection apparatus according to the present example embodiment will be described in detail next with reference toFIGS.4and5, with comparison to the configuration of a conventional object detection apparatus.FIG.4is a block diagram illustrating the specific configuration of the object detection apparatus according to the example embodiment of the present invention.FIG.5is a block diagram illustrating the specific configuration of the conventional object detection apparatus.

As illustrated inFIG.4, in the object detection apparatus1000according to the present example embodiment, the processing device1211includes an amplitude calculation unit1301, an antenna placement/RF frequency input unit1302, a PSF calculation unit1303, a correction operator calculation unit1304, and a corrected amplitude calculation unit1305. Additionally, in the present example embodiment, the processing device1211actually includes a computer, and each unit is constructed by the computer. This point will be described later.

The antenna placement/RF frequency input unit1302obtains, from the exterior, information such as the placement of the transmission antenna1202, the placement of the reception antenna1203, and the frequency of the radio wave1002emitted from the transmission antenna1202(the RF frequency). The antenna placement/RF frequency input unit1302inputs the obtained information to the PSF calculation unit1303and the amplitude calculation unit1301.

The PSF calculation unit1303calculates the PSF (point spread function) on the basis of the information input by the antenna placement/RF frequency input unit1302. The correction operator calculation unit1304calculates the correction operator on the basis of the PSF calculated by the PSF calculation unit1303. The correction operator is used to calculate the true reflection amplitude distribution, as described above.

The amplitude calculation unit1301is activated when the transmission unit1101emits the radio wave1002and the reception unit1102receives the radio wave1004. The amplitude calculation unit1301then calculates the reflection amplitude distribution on the basis of the information input by the antenna placement/RF frequency input unit1302and the IF signal generated by the reception unit1102.

Upon the reflection amplitude distribution being calculated by the amplitude calculation unit1301, the corrected amplitude calculation unit1305corrects the reflection amplitude distribution using the correction operator calculated by the correction operator calculation unit1304. The corrected amplitude calculation unit1305then outputs the corrected reflection amplitude distribution as a corrected amplitude.

On the other hand, as illustrated inFIG.5, a conventional object detection apparatus2000includes the transmission/reception device1001and a processing device2001like the object detection apparatus1000illustrated inFIG.4, but differs from the object detection apparatus1000in terms of the configuration of the processing device2001.

Specifically, as illustrated inFIG.5, in the conventional object detection apparatus2000, the processing device2001includes only the amplitude calculation unit1301and the antenna placement/RF frequency input unit1302. As such, the conventional object detection apparatus2000cannot correct the reflection amplitude distribution, and therefore has a problem in that the range of positions in which the object to be detected can be detected is limited, and a problem in that the desired resolution cannot be achieved and the detection accuracy is therefore poor, as described above.

Apparatus Operations

Operations of the object detection apparatus1000according to the example embodiment of the present invention will be described next with reference toFIG.6.FIG.6is a flowchart illustrating operations by the object detection apparatus according to the example embodiment of the present invention. The following descriptions will refer toFIGS.1to4as appropriate. In the present example embodiment, an object detection method is realized by causing the object detection apparatus1000to operate. As such, the following descriptions of the operations of the object detection apparatus1000will be given in place of descriptions of the object detection method according to the present first example embodiment.

As illustrated inFIG.6, the antenna placement/RF frequency input unit1302first obtains the information such as the placement of the transmission antenna1202, the placement of the reception antenna1203, and the frequency of the radio wave (the transmission signal) transmitted from the transmission antenna1202(the RF frequency). The antenna placement/RF frequency input unit1302then inputs the obtained information, i.e., the antenna placements and the RF frequency settings, to the PSF calculation unit1303and the amplitude calculation unit1301(step A1).

Next, the PSF calculation unit1303calculates the PSF (point spread function) of the object detection apparatus1000on the basis of the information input in step A1(the placement of the transmission antenna1202, the placement of the reception antenna1203, and the RF frequency) (step A2). Step A2will be described in greater detail later.

Next, the correction operator calculation unit1304calculates the correction operator using the point spread function (step A3). As will be described later, the correction operator is an operator for back-calculating the true reflection amplitude distribution of the target object1003from the radio wave amplitude distribution of the reflected wave obtained by the amplitude calculation unit1301.

Next, in the transmission/reception device1001, the transmission unit1101emits the radio wave1002serving as the transmission signal toward the target object1003(step A4). At the same time as the emission of the radio wave1002serving as the transmission signal, the transmission unit1101outputs the transmission signal to the reception unit1102via the terminal1208.

Next, in the transmission/reception device1001, the reception unit1102receives, through the reception antenna1203, the radio wave reflected by the target object1003as the reception signal (step A5).

Next, in the transmission/reception device1001, the reception unit1102generates the IF signal by mixing the transmission signal output from the transmission unit1101in step A4with the reception signal received in step A5(step A6).

Next, the amplitude calculation unit1301calculates the amplitude distribution of the radio wave reflected by the target object1003(the reflection amplitude distribution) on the basis of the information input in step A1(the placement of the transmission antenna1202, the placement of the reception antenna1203, and the RF frequency) and the IF signal generated in step A6(step A7).

Next, the corrected amplitude calculation unit1305corrects the reflection amplitude distribution of the reflected wave, calculated in step A7, using the correction operator calculated in step A3(step A8). Through this, the true reflection amplitude distribution of the target object1003can be calculated. Additionally, the corrected amplitude calculation unit1305outputs the corrected reflection amplitude distribution as a corrected amplitude.

Note that steps A1to A3are processes independent from measurement, while steps A4to A8are processes linked to measurement (the emission and reception of radio waves). Accordingly, steps A1to A3need only be performed once before measurement as long as the placement of the transmission antenna1202, the placement of the reception antenna1203, and the RF frequency of the transmission signal are not changed. On the other hand, steps A4to A8are executed with each measurement. Steps A4to A8need not be executed sequentially, after the execution of steps A1to A3.

Here, for comparison, operations by the conventional object detection apparatus2000illustrated inFIG.5will be described with reference toFIG.7.FIG.7is a flowchart illustrating operations by the conventional object detection apparatus.

As illustrated inFIG.7, of steps A1to A8illustrated inFIG.6, the conventional object detection apparatus2000executes only steps A1, A4, A5, and A7. In other words, as can be seen fromFIG.7, steps A2, A3, and A6are not executed by the conventional object detection apparatus, and these steps correspond to characteristic processing in the present example embodiment.

Of the steps A1through A7illustrated inFIG.6, steps A2, A3, A7, and A8, which are performed by the processing device1211, will be described in detail below.

Step A2

Operations by the PSF calculation unit1303in step A2will be described. The PSF calculation unit1303calculates a PSF(r,ro) of the object detection apparatus1000on the basis of the information output from the antenna placement/RF frequency input unit1302, i.e., the placement of the transmission antenna1202, the placement of the reception antenna1203, and the information of the RF frequency of the transmission signal transmitted from the transmission antenna1202.

The PSF(r,ro) is given by a radio wave amplitude distribution P(r) of the reflected wave from the target object1003when the target object1003is present only at one point at a position ro. rois the position where the target object1003is present. The PSF(r,ro) can be calculated in advance by determining the placement of the transmission antenna1202, the placement of the reception antenna1203, an RF frequency f, and a range of positions to be scanned (called a “scanning position” hereinafter) r. Note that “scanning position r” means a position where the radio wave reflected by the target object1003is received (the position of the reception antenna).

If the reflection amplitude distribution at the position roof the target object1003is given as σ(ro), the relationship between a reflection amplitude distribution P(r) of the reflected wave from the target object1003obtained through measurement and a true reflection amplitude distribution σ(ro) of the target object1003is given by the following Expression 1.
P(r)=Bσ(ro)  Expression 1

In the above Expression 1, a matrix B is a PSF matrix. The PSF matrix is a matrix obtained by setting the scanning position r to be constant in each row, setting the position roof the target object1003to be constant in each column, and furthermore arranging PSF(r,ro) as elements.

Note that complex values may be set as the reflection amplitude distribution P(r) of the reflected wave from the target object1003obtained through measurement, the PSF matrix B, and the true reflection amplitude distribution σ(ro) of the target object1003.

Step A3

Operations by the correction operator calculation unit1304in step A3will be described next. The correction operator calculation unit1304calculates a correction operator B†for back-calculating the true reflection amplitude distribution σ(ro) of the target object1003from the reflection amplitude distribution P(r) of the reflected wave obtained by the amplitude calculation unit1301, on the basis of the relationship in the above Expression 1.

Specifically, the correction operator calculation unit1304follows the sequence described hereinafter to generate a regularized pseudoinverse matrix of B, rather than an inverse matrix of the PSF matrix B, as the correction operator B†in order to achieve numerical stability. First, the correction operator calculation unit1304performs singular value decomposition of the PSF matrix B using the following Expression 2.
B=UΣVHExpression 2

In the above Expression 2, U and V are unitary matrices. Σ is a diagonal matrix having singular values as components. The matrix Σ with all elements below a regularization parameter γ set to zero and the nonzero elements set to their reciprocals is taken as Σ†. In this case, the correction operator B†is calculated by the following Expression 3.
B†=VΣ†UHExpression 3
Step A7

Operations by the amplitude calculation unit1301in step A7will be described next. The beamformer method can be given as one example of a method for calculating the reflection amplitude distribution of the reflected wave from the target object1003. A processing sequence using the beamformer method will be described below.

Assume that the IF signal obtained through an nth antenna of the reception antenna1203, when the radio wave1002of the frequency f is transmitted from an mth antenna of the transmission antenna1202, is denoted as s(m,n,f). In the following, u=(m,n,f) is set, and s(m,n,f) is denoted as s(u). The reflection amplitude distribution of the target object1003at position r is set to σ(r). Assuming that the IF signal s(u) and the reflection amplitude distribution σ(ro) at the position roof the target object1003are column vectors, the two can be related by a direction matrix A as follows, as indicated by Expression 4 below.
s(u)=Aσ(r)  Expression 4

Additionally, the elements of the direction matrix A are given by a(u,r), indicated by the following Expression 5.
a(u,r)=exp[−j2πf/c·(RTX(m,r)+RRX(n,r))]  Expression 5

Here, RTX(m,r) is the distance from the mth antenna of the transmission antenna1202to the position r. RRX(n,r) is the distance from the nth antenna of the reception antenna1203to the position r. The direction matrix A is configured by placing the elements a(u,r) with u=(m,n,f) constant in each row and the position r constant in each column. The direction matrix A can be calculated in advance by determining the placement of the transmission antenna1202, the placement of the reception antenna1203, the transmission frequency f, and the range of positions r to be scanned.

In the beamformer method, the reflection amplitude distribution P(r) of the reflected wave from the target object1003is calculated from the IF signal s(u) obtained through measurement and the direction matrix A calculated in advance, through the following Expression 6. In the following Expression 6, the superscript H of the matrix A represents a complex conjugate.
P(r)=AHs(u)  Expression 6

In the present example embodiment, the reflection amplitude distribution P(r) of the reflected wave from the target object1003may be calculated on the basis of the beamformer method as described above, but the calculation may be performed on the basis of another method.

Step A8

Operations by the corrected amplitude calculation unit1305in step A8will be described next. The corrected amplitude calculation unit1305corrects the reflection amplitude distribution P(r) of the reflected wave, calculated by the amplitude calculation unit1301, on the basis of the correction operator B†calculated by the correction operator calculation unit1304. Through this, the true reflection amplitude distribution σ(ro) of the target object1003can be calculated. Specifically, the corrected amplitude calculation unit1305calculates the true reflection amplitude distribution σ(ro) of the target object1003on the basis of the following Expression 7.
σ(ro)=B†P(r)  Expression 7

Additionally, the corrected amplitude calculation unit1305outputs the calculated true reflection amplitude distribution σ(ro) as a corrected amplitude. Furthermore, the corrected amplitude calculation unit1305can also output the corrected amplitude calculated in step A8as an image expressing the reflection amplitude distribution of the reflected wave from the target object1003.

Here, the aperture plane of the object detection apparatus according to the present example embodiment and the aperture plane of the conventional object detection apparatus will be compared with reference toFIGS.8and9.FIG.8is a diagram illustrating a positional relationship between the aperture plane of the conventional object detection apparatus illustrated inFIG.5and a space in which a target object can be detected.FIG.9is a diagram illustrating a positional relationship between the aperture plane of the object detection apparatus according to the example embodiment of the present invention and a space in which a target object can be detected.

FIG.8illustrates a positional relationship between the aperture plane207of the conventional object detection apparatus illustrated inFIG.5, a region directly facing the aperture plane207(called a “directly-facing region” hereinafter)1402, the target object1003, and a space in which the target object1003can be detected (called a “detection space” hereinafter)1400. As illustrated inFIG.8, in the conventional object detection apparatus, the detection space1400in which the target object1003can be detected is limited to a space surrounded by the aperture plane207and the directly-facing region1402, as described in the section on the problem to be solved by the invention. Specifically, in the example inFIG.8, the detection space1400is constructed as a parallelepiped taking the aperture plane207and the directly-facing region1402as two opposing faces.

FIG.9illustrates a positional relationship between an aperture plane1401of the object detection apparatus1000according to the present example embodiment, the directly-facing region1402directly facing the aperture plane1401, the target object1003, and the space in which the target object1003can be detected (the detection space)1400. The aperture plane1401is constructed by the transmission antenna1202and the reception antenna1203illustrated inFIG.2orFIG.3.

As illustrated inFIG.9, in the present example embodiment, the detection space1400of the target object1003is a space larger than a parallelepiped taking the aperture plane1401and the directly-facing region1402as two opposing faces, unlike the example inFIG.8. In the example inFIG.9, the detection space1400is a space which includes the outer space of the parallelepiped taking the aperture plane1401and the directly-facing region1402as the two opposing faces. In other words, according to the object detection apparatus1000in the present example embodiment, the target object1003can also be detected at positions beyond the range of the aperture plane1401. Note that this point will be described in greater detail later.

First Variation

A first variation on the object detection apparatus1000according to the present example embodiment will be described next with reference toFIG.10.FIG.10is a diagram illustrating functions of the object detection apparatus according to a first variation on the example embodiment of the present invention.

In the present first variation, the corrected amplitude calculation unit1305of the processing device1211first divides a specific region or a specific space where the target object1003is present into a plurality of parts. Then, the corrected amplitude calculation unit1305corrects the amplitude distribution for each part obtained by the division (called “partial space” hereinafter), using this partial space as a defining region.

Specifically,FIG.10illustrates the aperture plane1401of the object detection apparatus1000, and the detection space1400in which the target object1003can be detected, according to the present example embodiment. The true reflection amplitude distribution σ(ro) and the reflection amplitude distribution P(r) are calculated in this detection space1400. Here, the number of target objects1003in the detection space1400is denoted as N, the amount of calculation required to calculate the corrected amplitude using the above Expression 7 is denoted as O(N2).

Additionally, like the example inFIG.9,FIG.10illustrates the aperture plane1401of the object detection apparatus1000and the detection space1400. In the example inFIG.10, the detection space1400is divided into Kxparts in an x-axis direction, Kyparts in a y-axis direction, and Kzparts in a z-axis direction. In other words, inFIG.10, the corrected amplitude calculation unit1305divides the detection space1400into K partial spaces, with K=KxKyKz.

In this manner, according to the present first variation, the detection space1400is divided into K partial spaces, and thus the amount of calculation of the above Expression 7 per partial space is O((N/K)2). Additionally, the detection space1400contains K partial spaces, and thus the amount of calculation of the above Expression 7 for the detection space1400as a whole is O(N2/K). In other words, if the detection space1400is divided into K partial spaces, as in the present first variation, the amount of calculation is reduced by a factor of 1/K compared to a case where the detection space1400is not divided. Accordingly, in step A8, it is preferable that the correction process using the above Expression 7 be executed after dividing the detection space1400into a plurality of partial spaces.

Second Variation

A second variation on the object detection apparatus1000according to the present example embodiment will be described next with reference toFIG.11.FIG.11is a block diagram illustrating the configuration of object detection apparatus according to the second variation on the example embodiment of the present invention.

In the present second variation, the object detection apparatus1000is connected to an external separate processing device1212. Additionally, in the present second variation, unlike the processing device1211illustrated inFIG.4, the processing device1211does not include the antenna placement/RF frequency input unit1302, the PSF calculation unit1303, and the correction operator calculation unit1304, and instead includes a correction operator input unit1306. In the present second variation, the correction operator input unit1306is included as an interface for the processing device1211with respect to the separate processing device1212. In the present second variation, like the processing device1211illustrated inFIG.4, the processing device1211includes the amplitude calculation unit1301and the corrected amplitude calculation unit1305.

On the other hand, as illustrated inFIG.11, the external separate processing device1212includes the antenna placement/RF frequency input unit1302, the PSF calculation unit1303, and the correction operator calculation unit1304. Accordingly, in the present variation, the information of the placement of the transmission antenna1202, the placement of the reception antenna1203, and the frequency (RF frequency) of the radio wave1002emitted from the transmission antenna1202is obtained by the separate processing device1212.

The obtained information is then input to the amplitude calculation unit1301of the processing device1211from the separate processing device1212. The calculation of the PSF and the calculation of the correction operator based on the PSF are performed in the separate processing device1212, and the correction operator is input to the correction operator input unit1306of the processing device1211from the separate processing device1212. In this case, the correction operator input unit1306inputs the correction operator, which has been input by the separate processing device1212, to the corrected amplitude calculation unit1305.

According to this configuration, in the present second variation, the processing independent from the measurement (steps A1to A3) among the steps A1to A8illustrated inFIG.6are executed by the external separate processing device1212. On the other hand, the processing related to measurement (steps A4to A8) is executed by the processing device1211of the object detection apparatus1000.

Additionally, in the present second variation, the processing independent from the measurement (steps A1to A3) is executed only once by the separate processing device1212before the processing related to the measurement (steps A4to A8) is executed by the processing device1211. The processing device1211then executes the processing related to measurement (steps A4to A8) with each measurement.

In this manner, according to the present second variation, the processing independent from measurement (steps A1to A3), which takes a comparatively long processing time, is performed by a processing device separate from the object detection apparatus1000. As such, according to the present second variation, the processing load on the object detection apparatus1000is lightened, and the processing time is shortened.

Effects of the Example Embodiment

Effects of the present example embodiment will be described hereinafter with reference toFIGS.12to16.

FIG.12is a diagram illustrating a positional relationship between the object detection apparatus according to the example embodiment of the present invention and an object to be detected. The aperture plane1401formed by the transmission antenna1202and the reception antenna1203of the object detection apparatus1000, the directly-facing region1402directly facing the aperture plane1401, and the target object1003are illustrated inFIG.12.

In the conventional object detection apparatus, as described in the section on the problem to be solved by the invention, the position at which the target object1003can be detected is limited to the detection space1400surrounded by the aperture plane1401and the directly-facing region1402as illustrated inFIG.12(seeFIG.8). In the example inFIG.12as well, the detection space1400is constructed as a parallelepiped taking the aperture plane207and the directly-facing region1402as two opposing faces.

This problem occurs because, in the conventional object detection apparatus, the reflected waves from a target object1003outside the detection space1400are weaker than reflected waves from a target object1003inside the detection space1400, which makes it difficult to detect a target object1003outside the detection space1400.

In other words, the reflection amplitude distribution P(r) of the reflected wave from the target object1003is obtained as a result of interference of the reflection amplitude distribution σ(ro), weighted by the PSF matrix B, as indicated by Expression 1 above. Accordingly, in the conventional object detection apparatus, even if the true reflection amplitude distribution σ(ro) of the target object1003has no amplitude difference between the inside and the outside of the detection space1400, as a result of the interference of the reflection amplitude distribution σ(ro) weighted by the PSF matrix B, the reflection amplitude becomes stronger inside the detection space1400and the amplitude becomes weaker outside, causing the image to disappear.

A result of a conventional object detection apparatus imaging the reflection amplitude distribution P(r) of the reflected wave from the target object1003using the beamformer method, when the target object1003bridges the inside and outside of the detection space1400(seeFIG.12), will be described with reference toFIG.13.FIG.13is a diagram illustrating an example of an image of an object, located bridging the inside and outside of a detection space, that is detected by the conventional object detection apparatus. As illustrated inFIG.13, the reflection amplitude distribution P(r) of the reflected wave from the target object1003has a strong amplitude inside the detection space1400. However, outside the detection space1400, the amplitude weakens and the image disappears.

On the other hand, according to the present example embodiment, an effect is achieved in which the target object1003can be detected even when the target object1003is located outside the detection space1400. The reason for this is that in the present example embodiment, it is not the radio wave amplitude distribution P(r), which is weighted by the PSF matrix B and has an amplitude difference between the inside and outside of the detection space1400, but the true reflection amplitude distribution σ(ro) of the target object1003, which is unweighted by the PSF matrix B, that is ultimately output.

A result of the object detection apparatus1000according to the present example embodiment imaging the reflection amplitude distribution P(r) of the reflected wave from the target object1003using the beamformer method, when the target object1003bridges the inside and outside of the detection space1400(seeFIG.12), will be described with reference toFIG.14.FIG.14is a diagram illustrating an example of an image of an object, located bridging the inside and outside of a detection space, that is detected by the object detection apparatus according to the example embodiment of the present invention.

In the example inFIG.14, the reflection amplitude distribution P(r) of the reflected wave from the target object1003is calculated by the amplitude calculation unit1301, and the calculated reflection amplitude distribution is corrected by the corrected amplitude calculation unit1305using the correction operator obtained by the correction operator calculation unit1304. As a result, the true reflection amplitude distribution σ(ro) of the target object1003is obtained as a corrected image. As illustrated inFIG.14, according to the object detection apparatus1000of the present example embodiment, unlike the conventional object detection apparatus, an image of a target object1003bridging the inside and the outside of the detection space1440is obtained.

In this manner, in the present example embodiment, the target object1003which can be detected need not be located inside the detection space1400, and the location thereof is not limited to a range restricted by the aperture plane1401. Therefore, according to the present example embodiment, there is no need to increase the size of the aperture plane1401in order to expand the range over which the target object1003can be detected, which makes it unnecessary to increase the size of the object detection apparatus1000, and the ease of installation of the object detection apparatus1000is also not impaired.

In addition, in the present example embodiment, because there is no need to increase the size of the object detection apparatus1000, there is no need to increase the number of transmission antennas1202, the number of reception antennas1203, and the number of transceivers accordingly. As a result, according to the present example embodiment, the detection range can be expanded without increasing the cost.

Furthermore, the object detection apparatus1000according to the present example embodiment has an effect of achieving a higher resolution than the conventional object detection apparatus. In the conventional object detection apparatus, an image distributed wider than the true reflection amplitude distribution σ(ro) of the target object1003due to the influence of the PSF, which represents the spread of points, is obtained as the reflection amplitude distribution P(r), as indicated by the above Expression 1. On the other hand, in the object detection apparatus according to the present example embodiment, the final output is the true reflection amplitude distribution σ(ro) of the target object1003, from which the effect of PSF representing the spread of points is eliminated, and thus the resolution is improved compared to the conventional object detection apparatus.

Here, the resolution of the object detection apparatus according to the present example embodiment and the resolution of the conventional object detection apparatus will be compared and described, with reference toFIGS.15and16.FIG.15is a diagram illustrating an example of an image of an object detected by the conventional object detection apparatus.FIG.16is a diagram illustrating an example of an image of an object detected by the object detection apparatus according to the example embodiment of the present invention. InFIGS.15and16, the target object1003to be detected is a quadrangle having four holes. Additionally, the images illustrated inFIGS.15and16indicate results of imaging the radio wave amplitude distribution P(r) of the reflected wave from the target object1003.

As illustrated inFIG.15, the conventional object detection apparatus has a low resolution, and thus fails to detect the holes present in the target object1003. On the other hand, in the present example embodiment, the reflection amplitude distribution P(r) of the reflected wave from the target object1003is corrected by the correction operator and calculated as the true reflection amplitude distribution σ(ro). Accordingly, as illustrated inFIG.16, with the object detection apparatus1000according to the example embodiment of the present invention, the resolution is improved compared to the conventional apparatus and as a result, the four holes present in the target object1003are detected successfully. In this manner, according to the present example embodiment, a higher resolution is achieved than in the conventional system, and thus an effect in which the accuracy of detecting the target object1003is improved can be achieved.

Program

A program according to the present example embodiment may be any program that causes the computer included in the processing device1211to execute steps A1to A3and A7to A8illustrated inFIG.6. The object detection apparatus1000and the object detection method according to the present example embodiment can be implemented by installing the program in the computer and executing the program. In this case, a processor of the computer performs processing by functioning as the amplitude calculation unit1301, the antenna placement/RF frequency input unit1302, the PSF calculation unit1303, the correction operator calculation unit1304, and the corrected amplitude calculation unit1305of the processing device1211.

The program according to the present example embodiment may be executed by a computer system constructed from a plurality of computers. In this case, for example, the respective computers may function as one of the amplitude calculation unit1301, the antenna placement/RF frequency input unit1302, the PSF calculation unit1303, the correction operator calculation unit1304, and the corrected amplitude calculation unit1305of the processing device1211.

Here, the computer that implements the processing device1211of the object detection apparatus1000by executing the program according to the present example embodiment will be described with reference toFIG.17.FIG.17is a block diagram illustrating an example of the computer implementing the processing device of the object detection apparatus according to the example embodiment of the present invention.

As illustrated inFIG.17, a computer110includes a CPU (Central Processing Unit)111, main memory112, a storage device113, an input interface114, a display controller115, a data reader/writer116, and a communication interface117. These units are connected by a bus121so as to be capable of data communication with each other. Note that in addition to, or instead of, the CPU111, the computer110may include a GPU (Graphics Processing Unit) or a FPGA (Field-Programmable Gate Array).

The CPU111loads the program (code) according to the present example embodiment, which is stored in the storage device113, into the main memory112, and executes the program according to a prescribed sequence, thereby carrying out various types of operations. The main memory112is typically a volatile storage device such as DRAM (Dynamic Random Access Memory) or the like. The program according to the present example embodiment is stored in a computer-readable recording medium120and provided in such a state. Note that the program according to the present example embodiment may be distributed over the Internet, which is connected via the communication interface117.

In addition to a hard disk drive, a semiconductor storage device such as Flash memory or the like can be given as a specific example of the storage device113. The input interface114facilitates data transfer between the CPU111and an input device118such as a keyboard and a mouse. The display controller115can be connected to a display device119, and controls displays made in the display device119.

The data reader/writer116facilitates data transfer between the CPU111and the recording medium120, reads out programs from the recording medium120, and writes results of processing performed by the computer110into the recording medium120. The communication interface117facilitates data exchange between the CPU111and other computers.

A generic semiconductor storage device such as CF (Compact Flash (registered trademark)), SD (Secure Digital), or the like, a magnetic recording medium such as a flexible disk or the like, an optical recording medium such as a CD-ROM (Compact Disk Read Only Memory) or the like, and so on can be given as specific examples of the recording medium120.

Note that the processing device1211of the object detection apparatus1000according to the present example embodiment can also be implemented using hardware corresponding to the respective units, instead of a computer in which a program is installed. Furthermore, the processing device1211of the object detection apparatus1000may be partially implemented by a program, with the remaining parts realized by hardware.

All or parts of the above-described example embodiments can be expressed as Supplementary Note 1 to Supplementary Note 15, described hereinafter, but are not intended to be limited to the following descriptions.

Supplementary Note 1

An object detection apparatus for detecting an object using radio waves, the apparatus including:

a transmission unit, including a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna;

a reception unit, including a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received; and

a processing device,

wherein the processing device:

calculates an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal, and

furthermore, corrects the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.

Supplementary Note 2

The object detection apparatus according to Supplementary Note 1,

wherein the processing device calculates the point spread function on the basis of the placement of the transmission antenna, the placement of the reception antenna, and the frequency of the radio wave emitted from the transmission antenna, calculates the correction operator on the basis of the point spread function calculated, and corrects the amplitude distribution using the correction operator calculated.

Supplementary Note 3

The object detection apparatus according to Supplementary Note 2,

wherein the processing device calculates a pseudoinverse matrix of a matrix that takes the point spread function as an element, and corrects the amplitude distribution using, as the correction operator, the pseudoinverse matrix calculated.

Supplementary Note 4

The object detection apparatus according to Supplementary Note 1,

wherein the processing device accepts an input of the correction operator from outside, and corrects the amplitude distribution using the correction operator for which the input is accepted.

Supplementary Note 5

The object detection apparatus according to any one of Supplementary Notes 1 to 4,

wherein the processing device divides a specific region or a specific space in which the object is present into a plurality of parts, and corrects the amplitude distribution for each of the parts obtained from the dividing using the parts as defining regions.

Supplementary Note 6

An object detection method for detecting an object using radio waves, the method including,

in an object detection apparatus including a transmission unit, having a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna, and a reception unit, having a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received:

(a) a step of calculating an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal; and

(b) a step of correcting the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.

Supplementary Note 7

The object detection method according to Supplementary Note 6, further including:

in the object detection apparatus, (c) a step of calculating the point spread function on the basis of the placement of the transmission antenna, the placement of the reception antenna, and the frequency of the radio wave emitted from the transmission antenna, and calculating the correction operator on the basis of the point spread function calculated,

wherein in the (b) step, the amplitude distribution is corrected using the correction operator calculated.

Supplementary Note 8

The object detection method according to Supplementary Note 7,

wherein in the (c) step, a pseudoinverse matrix of a matrix that takes the point spread function as an element is calculated as the correction operator, and

in the (b) step, the amplitude distribution is corrected using the pseudoinverse matrix.

Supplementary Note 9

The object detection method according to Supplementary Note 6,

wherein in the (b) step, an input of the correction operator from outside is accepted, and the amplitude distribution is corrected using the correction operator for which the input is accepted.

Supplementary Note 10

The object detection method according to any one of Supplementary Notes 6 to 9,

wherein in the (b) step, a specific region or a specific space in which the object is present is divided into a plurality of parts, and the amplitude distribution is corrected for each of the parts obtained from the dividing using the parts as defining regions.

Supplementary Note 11

A computer-readable recording medium in which is recorded a program for using a computer to detect an object using radio waves, the program including commands for causing the computer to execute,

in an object detection apparatus including a transmission unit, having a transmission antenna, configured to emit a radio wave toward the object using the transmission antenna, and a reception unit, having a reception antenna, configured to receive the radio wave reflected by the object as a reception signal and generate an intermediate frequency signal from the reception signal received:

(a) a step of calculating an amplitude distribution of the radio wave reflected by the object on the basis of a placement of the transmission antenna, a placement of the reception antenna, a frequency of the radio wave emitted from the transmission antenna, and the intermediate frequency signal; and

(b) a step of correcting the amplitude distribution calculated, using a correction operator calculated from a point spread function indicating characteristics of the transmission unit and the reception unit.

Supplementary Note 12

The computer-readable recording medium according to Supplementary Note 11,

wherein the program further includes commands for causing the computer to execute:

(c) a step of calculating the point spread function on the basis of the placement of the transmission antenna, the placement of the reception antenna, and the frequency of the radio wave emitted from the transmission antenna, and calculating the correction operator on the basis of the point spread function calculated,

wherein in the (b) step, the amplitude distribution is corrected using the correction operator calculated.

Supplementary Note 13

The computer-readable recording medium according to Supplementary Note 12,

wherein in the (c) step, a pseudoinverse matrix of a matrix that takes the point spread function as an element is calculated as the correction operator, and

in the (b) step, the amplitude distribution is corrected using the pseudoinverse matrix.

Supplementary Note 14

The computer-readable recording medium according to Supplementary Note 11,

wherein in the (b) step, an input of the correction operator from outside is accepted, and the amplitude distribution is corrected using the correction operator for which the input is accepted.

Supplementary Note 15

The computer-readable recording medium according to any one of Supplementary Notes 11 to 14,

wherein in the (b) step, a specific region or a specific space in which the object is present is divided into a plurality of parts, and the amplitude distribution is corrected for each of the parts obtained from the dividing using the parts as defining regions.

The configuration of a preferred embodiment of the present invention has been described thus far. However, the content disclosed in the above-described Patent Document and so on can be incorporated into the present invention by reference. Many changes and variations on the example embodiment are possible on the basis of that basic technical spirit, without departing from the scope of the overall disclosure of the present invention (including the scope of the patent claims). Additionally, various elements disclosed can be combined or selected in a variety of ways without departing from the scope of the patent claims of the present invention. In other words, the present invention includes various modifications and variations that can be carried out by one skilled in the art according to the overall disclosure and technical spirit including the scope of the patent claims.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, an increase in the size and cost of the apparatus can be suppressed while expanding the range of positions for an object to be detected and improving the resolution. The present invention is useful in imaging apparatuses, remote sensing apparatuses, and the like that detect objects using radio waves.

REFERENCE SIGNS LIST

110Computer111CPU112Main memory113Storage device114Input interface115Display controller116Data reader/writer117Communication interface118Input device119Display device120Recording medium121Bus1000Object detection apparatus1001Transmission/reception device1002Radio wave (transmission signal)1003Target object (object to be detected)1004Radio wave (reception signal)1005Target object placement plane1101Transmission unit1102Reception unit1201Oscillator1202Transmission antenna1203Reception antenna1204Mixer1205Interface circuit1206Variable phase shifter1208Terminal1211Processing device1301Amplitude calculation unit1302Antenna placement/RF frequency input unit1303PSF (point spread function) calculation unit1304Correction operator calculation unit1305Corrected amplitude calculation unit1306Correction operator input unit1400Detection space1401Aperture plane1402Directly-facing region