Object detection apparatus, object detection method, and computer-readable recording medium

1. An object detection apparatus for detecting an object with radio waves, the object detection apparatus comprising:

a transmission unit configured to emit a radio wave as a transmission signal toward the object;

a reception unit configured to receive, through a plurality of receiving antennas, radio waves reflected by the object as reception signals, and to generate, for each reception signal received by the respective plurality of receiving antennas, based on the reception signals, an intermediate frequency signal, wherein the reception unit includes a reference receiving antenna and a measurement receiving antenna; and

an arithmetic unit configured to decide sampling times so as to suppress generation of a virtual image by a beam pattern obtained by synthesizing the respective intermediate frequency signals, and execute sampling on a first intermediate frequency signal generated from a reception signal received by the measurement receiving antenna and a second intermediate frequency signal generated from a reception signal received by the reference receiving antenna,

based on obtained sample values, normalize the intermediate frequency signal generated from the reception signal received by the measurement receiving antenna according to the intermediate frequency signal generated from the reception signal received by the reference receiving antenna, and generates a normalized intermediate frequency signal as the intermediate frequency signal for position detection, and

calculate an evaluation function that represents a position distribution of the object from the normalized intermediate frequency signal, and based on the evaluation function, detects the position and shape of the object.

2. The object detection apparatus according to claim 1 ,

wherein the arithmetic unit is configured to:

execute processing to limit the position of the object to be detected, on the intermediate frequency signal generated from the reception signal received by the measurement receiving antenna and the intermediate frequency signal generated from the reception signal received by the reference receiving antenna, and

execute the sampling based on the intermediate frequency signal on which the processing has been executed.

3. The object detection apparatus according to claim 1 ,

wherein the arithmetic unit is configured to:

calculate a correlation matrix from the normalized intermediate frequency signal; and

calculate the evaluation function from the correlation matrix.

4. The object detection apparatus according to claim 3 ,

wherein the measurement receiving antenna is included in a plurality of measurement receiving antennas, and the plurality of measurement receiving antennas are arranged in each of at least two directions with respect to the position of the reference receiving antenna, and

the arithmetic unit is configured to:

generate, for each direction, the normalized intermediate frequency signal from the measurement receiving antenna installed in the corresponding direction;

further, calculate the correlation matrix from a direct product of the normalized intermediate frequency signal generated for each direction; and

calculate the evaluation function that represents a multidimensional position distribution of the object from the correlation matrix.

5. The object detection apparatus according to claim 3 ,

wherein the normalized intermediate frequency signal is included in a plurality of normalized intermediate frequency signals,

the arithmetic unit is further configured to:

select a plurality of ranges of the normalized intermediate frequency signal;

calculate the correlation matrix from the respective plurality of normalized intermediate frequency signals for which the plurality of ranges are prescribed, and further, from an average of the correlation matrix; and

calculate the evaluation function that represents a position distribution of the object.

6. The object detection apparatus according to claim 1 ,

wherein the transmission unit is configured emit a radio wave whose frequency changes over time toward the object as the transmission signal, and

the reception unit is configured mix the transmission signal with the reception signal received by each of the receiving antennas to generate the intermediate frequency signal.

7. The object detection apparatus according to claim 6 ,

wherein a plurality of the receiving antennas are provided, and

an interval between the receiving antennas adjacent to each other is set to be no more than an upper limit value determined by a minimum value and a maximum value of the frequency of the transmission signal.

8. An object detection method, performed by an object detection apparatus, for detecting an object with radio waves, the object detection method comprising:

emitting a radio wave as a transmission signal toward the object;

receiving, through a plurality of receiving antennas, radio waves reflected by the object as reception signals, and generating, for each reception signal received by the respective plurality of receiving antennas, based on the reception signals, an intermediate frequency signal, wherein a reference receiving antenna and a measurement receiving antenna are used as the receiving antennas;

deciding sampling times so as to suppress generation of a virtual image by a beam pattern obtained by synthesizing the respective intermediate frequency signals, and performing sampling on the intermediate frequency signals at the decided sampling times wherein the sampling is executed on a first intermediate frequency signal generated from a reception signal received by the measurement receiving antenna and a second intermediate frequency signal generated from a reception signal received by the reference receiving antenna, and

based on obtained sample values, the intermediate frequency signal generated from the reception signal received by the measurement receiving antenna is normalized according to the intermediate frequency signal generated from the reception signal received by the reference receiving antenna, and a normalized intermediate frequency signal is generated as the intermediate frequency signal for position detection, and

when the object is detected, an evaluation function that represents a position distribution of the object is calculated from the normalized intermediate frequency signal, and based on the evaluation function, the position and shape of the object are detected.

9. The object detection method according to claim 8 ,

wherein when the intermediate frequency signals for position detection are generated,

processing to limit the position of the object to be detected is executed on the intermediate frequency signal generated from the reception signal received by the measurement receiving antenna and the intermediate frequency signal generated from the reception signal received by the reference receiving antenna, and

the sampling is executed based on the intermediate frequency signal on which the processing has been executed.

10. The object detection method according to claim 8 ,

wherein when the object is detected, a correlation matrix is calculated from the normalized intermediate frequency signal, and the evaluation function is calculated from the correlation matrix.

11. The object detection method according to claim 10 ,

wherein the measurement receiving antenna is included in a plurality of measurement receiving antennas, and the plurality of measurement receiving antennas are arranged in each of at least two directions with respect to the position of the reference receiving antenna, and

when the intermediate frequency signals for position detection are generated, for each direction, the normalized intermediate frequency signal is generated from the measurement receiving antenna installed in the corresponding direction, and

when the object is detected, the correlation matrix is calculated from a direct product of the normalized intermediate frequency signal generated for each direction, and then the evaluation function that represents a multidimensional position distribution of the object is calculated from the correlation matrix.

12. The object detection method according to claim 10 ,

wherein the normalized intermediate frequency signal is included in a plurality of normalized intermediate frequency signals,

when the object is detected, a plurality of ranges of the normalized intermediate frequency signal are selected, the correlation matrix is calculated from the respective plurality of normalized intermediate frequency signals for which the plurality of ranges are prescribed, and further, from an average of the correlation matrix, the evaluation function that represents a position distribution of the object is calculated.

13. A non-transitory computer-readable recording medium including,

in an object detection apparatus including a transmission unit configured to emit a radio wave as a transmission signal toward an object, a reception unit configured to receive, through a plurality of receiving antennas, radio waves reflected by the object as reception signals, and to generate, for each reception signal received by the respective plurality of receiving antennas, based on the reception signals, an intermediate frequency signal, and a computer, wherein the reception unit includes a reference receiving antenna and a measurement receiving antenna as the receiving antenna,

a program recorded on the non-transitory computer-readable recording medium, the program including instructions that cause the computer to carry out:

deciding sampling times so as to suppress generation of a virtual image by a beam pattern obtained by synthesizing the respective intermediate frequency signals, and performing sampling on the intermediate frequency signals at the decided sampling times wherein the sampling is executed on a first intermediate frequency signal generated from a reception signal received by the measurement receiving antenna and a second intermediate frequency signal generated from a reception signal received by the reference receiving antenna, and

based on obtained sample values, the intermediate frequency signal generated from the reception signal received by the measurement receiving antenna is normalized according to the intermediate frequency signal generated from the reception signal received by the reference receiving antenna, and a normalized intermediate frequency signal is generated as the intermediate frequency signal for position detection, and

when the object is detected, an evaluation function that represents a position distribution of the object is calculated from the normalized intermediate frequency signal, and based on the evaluation function, the position and shape of the object are detected.

14. The non-transitory computer-readable recording medium according to claim 13 ,

wherein when the intermediate frequency signals for position detection are generated,

processing to limit the position of the object to be detected is executed on the intermediate frequency signal generated from the reception signal received by the measurement receiving antenna and the intermediate frequency signal generated from the reception signal received by the reference receiving antenna, and

the sampling is executed based on the intermediate frequency signal on which the processing has been executed.

15. The non-transitory computer-readable recording medium according to claim 13 ,

wherein when the object is detected, a correlation matrix is calculated from the normalized intermediate frequency signal, and the evaluation function is calculated from the correlation matrix.

16. The non-transitory computer-readable recording medium according to claim 15 ,

wherein the measurement receiving antenna is included in a plurality of measurement receiving antennas, and the plurality of measurement receiving antennas are arranged in each of at least two directions with respect to the position of the reference receiving antenna, and

when the intermediate frequency signals for position detection are generated, for each direction, the normalized intermediate frequency signal is generated from the measurement receiving antenna installed in the corresponding direction, and

when the object is detected, the correlation matrix is calculated from a direct product of the normalized intermediate frequency signal generated for each direction, and then the evaluation function that represents a multidimensional position distribution of the object is calculated from the correlation matrix.

17. The non-transitory computer-readable recording medium according to claim 15 ,

wherein the normalized intermediate frequency signal is included in a plurality of normalized intermediate frequency signals,

when the object is detected, a plurality of ranges of the normalized intermediate frequency signal are selected, the correlation matrix is calculated from the respective plurality of normalized intermediate frequency signals for which the plurality of ranges are prescribed, and further, from an average of the correlation matrix, the evaluation function that represents a position distribution of the object is calculated.