This application is a National Stage Entry of PCT/JP2018/007883 filed on Mar. 1, 2018, which claims priority from Japanese Patent Application 2017-087605 filed on Apr. 26, 2017, the contents of all of which are incorporated herein by reference, in their entirety.

TECHNICAL FIELD

The present invention relates to an object detection apparatus and an object detection method for detecting an object using radio waves, and also relates to a computer-readable recording medium that stores a program for realizing the object detection apparatus and the object detection method.

BACKGROUND ART

Recent years has seen monitoring apparatus that use a radar being installed for the purpose of monitoring railroad crossings and intersections. For example, Patent Document 1 discloses a monitoring apparatus (railroad crossing protective apparatus) that uses an obstacle detection method of a reflection type utilizing radar waves. The monitoring apparatus disclosed in Patent Document 1 determines whether an obstacle is present or not present in a monitoring area.

However, since the monitoring apparatus disclosed in Patent Document 1 only has a function of determining whether an obstacle is present or not present in the monitoring area, obtainable information is insufficient in terms of monitoring of an area. That is to say, a distinction between an object whose presence in the monitoring area is problematic and other objects cannot be made simply by detecting the presence of a target object. For this reason, the monitoring apparatus disclosed in Patent Document 1 has a problem in making an erroneous warning, that is, an unnecessary warning is issued when a safe object enters the monitoring area.

To avoid the aforementioned problem of an erroneous warning being made, it is necessary to not only detect the presence of a target object, but to also determine the type of the target object and identify the behavior thereof to determine whether the presence of this target object in the monitoring area is safe or dangerous.

For this reason, Patent Document 2 and Patent Document 3 disclose a monitoring apparatus that measures the size or dimensions of a target object using a radar in order to identify the type of the target object. Specifically, the monitoring apparatus disclosed in Patent Document 2 makes radar waves turn on a horizontal plane to irradiate an entire railroad crossing with the radar waves, and forms a cross-sectional railroad crossing image using reflected waves that have reflected off an obstacle in the railroad crossing. Also, the monitoring apparatus disclosed in Patent Document 2 performs image processing on the obtained cross-sectional railroad crossing image to accurately recognize the size of the obstacle, and correctly identifies whether the obstacle is an automobile or a pedestrian or the like.

The monitoring apparatus disclosed in Patent Document 3 is installed at an intersection, and detects the position, speed, dimensions, and moving direction of an object that is present at the intersection and an object approaching the intersection, using a radar sensor. Note that the objects may include vehicles and people, who are vulnerable road users.

As a radar method for measuring the distance between a target object and the monitoring apparatus, the FMCW (Frequency Modulated Continuous Wave) method, in which transmitted waves with a continuously changing frequency are emitted, is often used. The distance resolution achieved by the FMCW method is given as c/(2BW), where the frequency bandwidth of an RF transmission signal is denoted as BW, and the light velocity is denoted as c. Also, for example, Patent Document 4 discloses that the MUSIC (Multiple Signal Classification method) is applied, as a means for increasing the distance resolution achieved by the FMCW method from c/(2BW), to signal processing in a radar using the FMCW method.

LIST OF PRIOR ART DOCUMENTS

Patent Document

Patent Document 1: Japanese Patent Laid-Open Publication No. 2001-051056

Patent Document 2: Japanese Patent Laid-Open Publication No. 2001-130412

Patent Document 3: Japanese Patent Laid-Open Publication No. 2016-122439

Patent Document 4: Japanese Patent Laid-Open Publication No. H10-031065

SUMMARY OF INVENTION

Problems to be Solved by the Invention

The monitoring apparatus disclosed in the aforementioned Patent Documents 2 and 3 identify the type of a target object based on the size or dimensions of the target object as described above, but a problem arises in that an error may occur in the identification. This is due to the fact that the size and dimensions of a target object that can be measured by a radar depend on the size or dimensions of the target object as seen by the radar. That is to say, the size or dimensions of the same target object as seen by the radar may change depending on the orientation or position of the target object, and thus, incorrect identification may occur.

For example, the size or dimensions of a target object as seen by a radar changes between a state where a person is standing, a state where a person is crouching down, and a state where a person is lying down. For this reason, it is difficult for a monitoring apparatus to identify that all of these target objects are people. Thus, there is a demand for a technology that enables more accurate identification of the type and behavior of a target object using a radar.

An example object of the invention is to solve the foregoing problems and provide an object detection apparatus, an object detection method, and a computer-readable recording medium that enable identification of an object without being affected by the state of the object.

Means for Solving the Problems

To achieve the above-stated example object, an object detection apparatus according to an example aspect of the invention is an object detection apparatus for detecting an object using radio waves, including:

an emitting unit configured to emit an RF transmission signal obtained by sweeping a frequency in every period;

a receiving unit configured to receive, if the RF transmission signal emitted by the emitting unit is reflected off the object, the RF transmission signal reflected off the object as an RF reception signal;

an IF signal generating unit configured to generate, in every period, a complex IF signal based on a signal obtained by mixing the RF transmission signal with the RF reception signal;

a position detecting unit configured to detect a position of the object based on an evaluation function generated based on the complex IF signal generated in every period; and a displacement detecting unit configured to detect a displacement of the object based on the position of the object detected by the position detecting unit and a phase of complex reflectance of the object calculated based on the complex IF signal.

To achieve the above-stated object, an object detection method according to an example aspect of the invention is an object detection method for detecting an object using radio waves, including:

(a) a step of emitting an RF transmission signal obtained by sweeping a frequency in every period;

(b) a step of receiving, if the RF transmission signal emitted in the (a) step is reflected off the object, the RF transmission signal reflected off the object as an RF reception signal;

(c) a step of generating, in every period, a complex IF signal based on a signal obtained by mixing the RF transmission signal with the RF reception signal;

(d) a step of detecting a position of the object based on an evaluation function generated based on the complex IF signal generated in every period; and

(e) a step of detecting a displacement of the object based on the position of the object detected in the (d) step and a phase of complex reflectance of the object calculated based on the complex IF signal.

Furthermore, to achieve the above-stated object, a computer-readable recording medium according to an example aspect of the invention is a computer-readable recording medium in an object detection apparatus including:

an emitting unit configured to emit an RF transmission signal obtained by sweeping a frequency in every period; a receiving unit configured to receive, if the RF transmission signal emitted by the emitting unit is reflected off an object, the RF transmission signal reflected off the object as an RF reception signal; an IF signal generating unit configured to generate, in every period, a complex IF signal based on a signal obtained by mixing the RF transmission signal with the RF reception signal; and a processor, the recording medium storing a program including a command to cause the processor to perform:

(a) a step of detecting a position of the object based on an evaluation function generated based on the complex IF signal generated in every period; and

(b) a step of detecting a displacement of the object based on the position of the object detected in the (a) step and a phase of complex reflectance of the object calculated based on the complex IF signal.

Advantageous Effects of the Invention

As described above, according to the invention, an object can be identified without being affected by the state of the object.

