Signal processing system, sensor system, signal processing method and program

Abstract

The problem to be overcome by the present invention is to provide a signal processing system, a sensor system, a signal processing method and a program, all of which are configured or designed to accurately judge the properties of an object. The signal processing system (2) according to the present invention includes a difference calculation unit (23) and a judgment unit (24). The difference calculation unit (23) uses a sensor signal (Y1) of a reference timing and a plurality of sensor signals (Y1) of a plurality of comparison timings offset relative to the reference timing. The difference calculation unit (23) generates the respective differences between the sensor signal (Y1) of the reference timing and the plurality of sensor signals (Y1) of the plurality of comparison timings as a plurality of differential signals, and obtains the respective amplitudes of the plurality of differential signals as a plurality of differential values. The judgment unit (24) obtains an evaluation value based on the plurality of differential values, and judges the properties of the object (9) by using the evaluation value.

Description

Technical Field

[0001] The present invention relates to a signal processing system, a sensor system, a signal processing method and a program. Background Art

[0002] Patent Document 1 discloses a body motion signal processing device for sensing the condition of a person bathing in a bathroom based on a reflected wave obtained by irradiating the bathroom with microwaves (radio waves).

[0003] The body motion signal processing device transmits radio waves in the bathroom, receives the radio waves reflected in the bathroom as a received signal, and detects a body motion signal representing the movement of the subject's body based on the received signal. Then, the body motion signal processing device compares the amplitude value of the signal corresponding to the body motion area component included in the received signal detected when the subject (i.e., the person who is about to take a bath) is not in the bathroom with the amplitude value of the body motion signal detected when the subject is taking a bath in the bathroom, thereby detecting the body movement of the subject in the bathroom (for example, represented by his or her heart rate and breathing). In addition, the body motion signal processing device sends a notification as an alarm according to the subject's condition when necessary.

[0004] A signal processing system such as the above-mentioned body motion signal processing device is required to more accurately judge the attributes of an object such as a person.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2017 / 149923 Summary of the invention

[0008] An object of the present invention is to provide a signal processing system, a sensor system, a signal processing method, and a program, all of which are configured or designed to accurately determine the attributes of an object.

[0009] A signal processing system according to one aspect of the present invention receives a sensor signal from a radio wave sensor that emits radio waves as transmission waves and receives radio waves reflected from an object as reception waves, the sensor signal including information about the distance between the radio wave sensor and the object. The signal processing system includes a difference calculation unit and a judgment unit. The difference calculation unit uses a sensor signal of a reference timing and a plurality of sensor signals of a plurality of comparison timings offset relative to the reference timing. The difference calculation unit generates a plurality of differential signals as respective differences between the sensor signal of the reference timing and the plurality of sensor signals of the plurality of comparison timings, and obtains the respective amplitudes of the plurality of differential signals as a plurality of differential values. The judgment unit obtains an evaluation value based on the plurality of differential values, and judges the property of the object by using the evaluation value.

[0010] A sensor system according to another aspect of the present invention includes: the above-mentioned signal processing system; and the radio wave sensor.

[0011] A signal processing method according to another aspect of the present invention includes receiving a sensor signal from a radio wave sensor that emits radio waves as transmission waves and receives radio waves reflected from an object as reception waves, the sensor signal including information about the distance between the radio wave sensor and the object. The signal processing method includes a difference calculation step and a judgment step. The difference calculation step includes using a sensor signal of a reference timing and a plurality of sensor signals of a plurality of comparison timings offset relative to the reference timing. The difference calculation step includes generating a plurality of differential signals as respective differences between the sensor signal of the reference timing and the plurality of sensor signals of the plurality of comparison timings, and obtaining the respective amplitudes of the plurality of differential signals as a plurality of differential values. The judgment step includes obtaining an evaluation value based on the plurality of differential values, and judging the property of the object by using the evaluation value.

[0012] A program according to still another aspect of the present invention is designed to cause a computer system to perform the above-mentioned signal processing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a block diagram illustrating a sensor system including a signal processing system according to a first embodiment;

[0014] Figure 2 is a block diagram illustrating a radio wave sensor according to a first embodiment;

[0015] Figure 3 is a waveform diagram showing a phase difference between an I component and a Q component of a sensor signal in the first embodiment;

[0016] Figure 4A shows a trace of a first differential signal in the IQ plane according to the first embodiment;

[0017] Figure 4 B shows the trajectory of the second differential signal in the IQ plane;

[0018] Figure 5 A shows a trace of another first differential signal in the IQ plane according to the first embodiment;

[0019] Figure 5 B shows the trace of another second differential signal in the IQ plane;

[0020] Figure 6 A shows a trace of a further first differential signal in the IQ plane according to the first embodiment;

[0021] Figure 6 B shows a trace of yet another second differential signal in the IQ plane;

[0022] Figure 7 A shows a trace of yet another first differential signal in the IQ plane according to the first embodiment;

[0023] Figure 7 B shows a trace of yet another second differential signal in the IQ plane;

[0024] Figure 8 A and Figure 8 B each shows how the evaluation value in the first embodiment changes over time;

[0025] Fig. 9 A and Fig. 9 B each shows how the evaluation value in the first embodiment changes over time;

[0026] Fig.10 A and Fig.10 B each shows how the evaluation value in the first embodiment changes over time;

[0027] Fig.11 A and Fig.11 B each shows how the evaluation value in the first embodiment changes over time;

[0028] Fig.12 A and Fig.12 B each shows how the evaluation value in the first embodiment changes over time;

[0029] Fig.13 is a flowchart showing how the signal processing system in the first embodiment operates;

[0030] Fig.14 is a block diagram illustrating a sensor system including a signal processing system according to a first modification example of the first embodiment;

[0031] Fig.15 is a plan view illustrating how the determination area may be set in the first modification example of the first embodiment;

[0032] Fig.16 is a block diagram illustrating a sensor system including a signal processing system according to a second embodiment;

[0033] Fig.17 is a plan view illustrating how the determination area may be set in the second embodiment;

[0034] Fig.18 How to perform distance determination processing according to the second embodiment is shown;

[0035] Fig.19 A is a diagram plotting a set of distance data according to the second embodiment;

[0036] Fig.19 B is a diagram showing how the index in the second embodiment changes over time;

[0037] Fig. 20 How to perform the index calculation process in the second embodiment;

[0038] Fig.21 A is a diagram plotting another set of distance data according to the second embodiment;

[0039] Fig.21 B is a graph showing how another indicator in the second embodiment changes over time;

[0040] Fig. 22 A is a diagram plotting yet another set of distance data according to the second embodiment;

[0041] Fig. 22 B is a diagram showing how another indicator in the second embodiment changes over time;

[0042] Fig.23 A and Fig.23 B are graphs each showing how still another indicator in the second embodiment changes over time;

[0043] Fig.24 A. Fig.24 B and Fig.24 C are graphs each showing how still another indicator in the second embodiment changes with time; and

[0044] Fig.25 is a flowchart showing how the signal processing system in the second embodiment operates. DETAILED DESCRIPTION

[0045] The present invention generally relates to a signal processing system, a sensor system, a signal processing method and a program. More particularly, the present invention relates to the following signal processing system, a sensor system, a signal processing method and a program, all of which are configured or designed to determine the properties of an object by using a radio wave sensor.

[0046] Note that the embodiments and modifications thereof to be described below are merely typical embodiments and modifications among the various embodiments and modifications of the present invention, and should not be construed as limiting. On the contrary, these typical embodiments and modifications may be easily modified in various ways according to design selection or any other factors without departing from the true spirit and scope of the present invention.

[0047] (1) First Embodiment

[0048] (1.1) Overview of sensor system

[0049] Figure 1 A sensor system A1 including the signal processing system 2 according to the first embodiment is exemplified.

[0050] The sensor system A1 includes a radio wave sensor 1 and a signal processing system 2. The signal processing system 2 according to the present embodiment is implemented as a signal processor.

[0051] The radio wave sensor 1 emits radio waves as transmission waves 101 within the irradiation area R1 , receives radio waves reflected from the object 9 within the irradiation area R1 as reception waves 102 , and outputs a sensor signal Y0 including information on the distance L between the radio wave sensor 1 and the object 9 .

[0052] The signal processing system 2 determines the attribute of the object 9 by performing signal processing on the sensor signal Y0 supplied from the radio wave sensor 1 .

[0053] The distance L to the object 9 changes not only due to the movement of the object 9 but also due to the movement of only a part of the object 9. For example, if the object 9 is a person, the sensor signal Y0 including the information related to the distance L is signal-processed, which makes it possible to derive information related to the movement of the person, which includes not only information related to his or her movement but also biometric information such as his or her breathing rate, heart rate, and pulse, etc. That is, if the object 9 is a person, examples of the attributes of the object 9 include the presence of the person, his or her movement speed, his or her position, and biometric information.

[0054] (1.2) Radio wave sensor

[0055] The radio wave sensor 1 according to the present embodiment is a frequency modulated continuous wave (FMCW) radio wave sensor. Figure 2As shown, the radio wave sensor 1 includes a transceiver 1a, a transmitting antenna 1b and a receiving antenna 1c. The transceiver 1a transmits a transmission wave 101 whose frequency (transmission frequency) changes over time via the transmitting antenna 1b, and receives a receiving wave 102 whose frequency (receiving frequency) changes over time via the receiving antenna 1c. Then, the transceiver 1a generates a beat signal whose frequency (beat frequency) is equal to the frequency difference between the transmission frequency and the receiving frequency as the sensor signal Y0. The signal processing system 2 receives the sensor signal Y0 from the radio wave sensor 1, and can determine the distance to the object 9 based on the beat frequency of the sensor signal Y0. Note that the transmission wave 101 is preferably a microwave. In particular, the transmission wave 101 preferably has a frequency of 24.15 GHz. However, the transmission wave 101 does not have to be a microwave, but may also be a millimeter wave, and the frequency of the transmission wave 101 is not limited to any specific value.

[0056] Specifically, the transceiver 1a using the FMCW method repeatedly performs a sweep process in which the frequency of the transmission wave 101 (i.e., the transmission frequency) is alternately increased and then decreased multiple times. According to the sweep process, the transmission frequency increases by the sweep frequency width Δfa during the sweep time Ta. The transceiver 1a receives the reflected wave within a time 2L / C (where C is the speed of light) after emitting the transmission wave 101. The frequency of the reflected wave (i.e., the receiving frequency) also changes with the passage of time like the transmission frequency. Then, the transceiver 1a generates a beat signal having a frequency (beat frequency) fb equal to the frequency difference between the transmission frequency and the receiving frequency, and outputs the beat signal as the sensor signal Y0. The beat frequency fb is given by fb=[(Δfa·2L) / (C·Ta)]. Therefore, the distance L to the object 9 is expressed by the following formula (1).

[0057] L=(fb·C·Ta) / (2·Δfa) (1)

[0058] Then, the radio wave sensor 1 outputs an IQ signal including an in-phase component and a quadrature component as a sensor signal Y0 (i.e., a beat signal having a frequency fb). In the following description, the in-phase component will sometimes be referred to as an "I component" below, and the quadrature component will sometimes be referred to as a "Q component" below.

[0059] (1.3) Signal processing system (signal processor)

[0060] (1.3.1) Overview of signal processing system

[0061] like Figure 1 As shown, the signal processing system 2 includes a preprocessing unit 21 , a storage unit 22 , a difference calculation unit 23 , a judgment unit 24 and an output unit 25 .

[0062] The preprocessing unit 21 has an amplification function of amplifying the sensor signal Y0 and an AD conversion function of converting the sensor signal Y0 into a digital signal. The preprocessing unit 21 stores the digital sensor signal Y1 thus amplified in the storage unit 22. The sensor signal Y1 is a signal obtained by performing an amplification process and an AD conversion process on the sensor signal Y0, and is a signal substantially the same as the sensor signal Y0. Therefore, each of the sensor signal Y0 and the sensor signal Y1 can be regarded as a sensor signal including information related to the distance L to the object 9. Alternatively, the radio wave sensor 1 may include the preprocessing unit 21. In this case, the sensor signal Y1 supplied from the radio wave sensor 1 is stored in the storage unit 22.

[0063] The storage unit 22 stores the history of the sensor signal Y1. That is, the storage unit 22 stores the plurality of sensor signals Y1 generated by the preprocessing unit 21 in chronological order. The history of the sensor signal Y1 indicates the change of the sensor signal Y1 during a predetermined period of time in the past.

[0064] The difference calculation unit 23 generates a plurality of difference signals ΔY based on the history of the sensor signal Y1 stored in the storage unit 22 and obtains respective amplitudes of the plurality of difference signals ΔY as a plurality of difference values ​​ΔZ. The difference calculation unit 23 will be described in detail later.

[0065] The judgment unit 24 obtains an evaluation value based on the plurality of differential values ​​ΔZ, and judges the attribute of the object 9 by using the evaluation value. Examples of the attribute of the object 9 include the type of the object 9, the presence or absence of the object 9, its movement speed, position, and movement. The judgment unit 24 will be described in further detail later.

[0066] The output unit 25 outputs the decision made by the judgment unit 24 to the notification system 3. The communication between the output unit 25 and the notification system 3 is established by wired communication via a communication line or wireless communication using a wireless signal. The wired communication can be established, for example, via a twisted pair, a dedicated communication line, or a LAN (Local Area Network) cable. The wireless communication can be in accordance with a protocol such as Or wireless communication of a standard such as a low-power radio standard (eg, designated low-power radio) that does not require a license, or wireless communication such as infrared communication.

[0067] The above-mentioned signal processing system 2 preferably includes a computer system. The computer system may include a processor and a memory as its main hardware components. At least some functions of the signal processing system 2 according to the present invention may be performed by causing the processor to execute a program stored in the memory of the computer system. The program may be pre-stored in the memory of the computer system. Alternatively, the program may also be downloaded via a telecommunication line, or distributed after being recorded in some non-temporary storage media such as a memory card, an optical disk, or a hard disk drive (any of which is readable by the computer system). The processor of the computer system may be implemented as a single or multiple electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). As used herein, "integrated circuits" such as IC or LSI are referred to by different names according to the degree of their integration. Examples of integrated circuits include system LSI, very large-scale integrated circuits (VLSI) and ultra-large-scale integrated circuits (ULSI). Optionally, a field programmable gate array (FPGA) to be programmed after manufacturing the LSI or a logic device that allows the reconfiguration of the connection or circuit section inside the LSI to be reconfigured may also be used as a processor. These electronic circuits may be integrated together on a single chip or distributed on multiple chips, whichever is appropriate. These multiple chips can be gathered together in a single device or distributed in multiple devices without limitation. As used herein, a "computer system" includes a microcontroller comprising one or more processors and one or more memories. Therefore, a microcontroller can also be implemented as one or more electronic circuits including semiconductor integrated circuits or large-scale integrated circuits.

[0068] In addition, the computer system may also be a system composed of a single computer or multiple computers. For example, at least some functions of the preprocessing unit 21, the storage unit 22, the difference calculation unit 23, the judgment unit 24 and the output unit 25 may also be implemented as a cloud computing system.

[0069] The notification system 3 includes at least one of a server, a personal computer, a dedicated terminal, a smartphone, and a tablet computer, and performs a notification operation or an alarm operation based on a decision made by the judgment unit 24 .

[0070] (1.3.2) Signal processing

[0071] In the present embodiment, the signal processing system 2 includes a difference calculation unit 23 and a judgment unit 24 , and judges whether the object 9 is a person as an attribute of the object 9 within the irradiation region R1 .

[0072] The radio wave sensor 1 is set in a room, and emits a transmission wave 101 to an irradiation area R1 in the room. In the room, electrical appliances (such as an electric fan and a robot vacuum cleaner) and movable devices such as curtains are arranged as exemplary objects 9. In addition, a person as an exemplary object 9 enters and leaves the irradiation area R1. In this case, for the signal processing system 2, the person is a detection target, and the movable device is an interference object other than the detection target.

[0073] (Difference calculation unit)

[0074] The difference calculation unit 23 generates a plurality of difference signals ΔY, and obtains the respective amplitudes of the plurality of difference signals ΔY as a plurality of difference values ​​ΔZ. Each difference signal ΔY is a difference signal between a pair of sensor signals Y1 of two different timings, and is a signal from which a signal component caused by the stationary object 9, a signal component caused by background noise, and other signal components are removed.

[0075] If the object 9 is a person, the movement of the person caused by his or her breathing changes the respective amplitudes of the I component and the Q component of the sensor signal Y1 (or Y0 ) and the phase difference between the I component and the Q component. Figure 3 The waveform X1 shows the phase difference between the I component and the Q component of the sensor signal Y1. Figure 3 As shown, waveform X1 pulsates with a breathing cycle T0. Figure 3 , a reference timing t0, a first comparison timing t1 which is a previous timing relative to the reference timing t0, and a second comparison timing t2 which is earlier than the first comparison timing t1 are shown. The second comparison timing t2 is a timing which is earlier than the reference timing t0 by a time length which is equal to or greater than 1 / 4 of one respiratory cycle T0 and equal to or less than half of one respiratory cycle T0. That is, the time length of the time period T2 between the reference timing t0 and the second comparison timing t2 is greater than the time length of the time period T1 between the reference timing t0 and the first comparison timing t1. In addition, in Figure 3 The width ΔH2 of the change in the waveform X1 during the time period T2 shown (hereinafter referred to as "change width ΔH2") is larger than that during the period T2. Figure 3 The width ΔH1 of the change in the waveform X1 during the time period T1 shown (hereinafter referred to as "change width ΔH1"). The change width ΔH1 is obtained by subtracting the amplitude of the waveform X1 at the first comparison timing t1 from the amplitude of the waveform X1 at the reference timing t0. The change width ΔH2 is obtained by subtracting the amplitude of the waveform X1 at the second comparison timing t2 from the amplitude of the waveform X1 at the reference timing t0.

[0076] That is, assuming that the sensor signal Y1 at timing tn is represented by Y1(tn), if the object 9 is a person, the difference between the sensor signal Y1(t0) and the sensor signal Y1(t2) tends to be greater than the difference between the sensor signal Y1(t0) and the sensor signal Y1(t1).

[0077] Therefore, the differential signal ΔY between the sensor signal Y1(t0) and the sensor signal Y1(t1) will be referred to as the "first differential signal ΔY(t0, t1)" below, and the differential signal ΔY between the sensor signal Y1(t0) and the sensor signal Y1(t2) will be referred to as the "second differential signal ΔY(t0, t2)" below. The first differential signal ΔY(t0, t1) is given by [Y1(t0)-Y1(t1)]. The second differential signal ΔY(t0, t2) is given by [Y1(t0)-Y1(t2)].

[0078] Alternatively, the difference calculation unit 23 may generate a difference signal ΔY in the frequency domain by performing a fast Fourier transform (FFT) or a discrete cosine transform (DCT) on the difference signal ΔY in the time domain. In this case, the first difference signal ΔY(t0, t1) will be a signal in the frequency domain generated by performing an FFT or DCT on [Y1(t0)–Y1(t1)]. The second difference signal ΔY(t0, t2) will be a signal in the frequency domain generated by performing an FFT or DCT on [Y1(t0)–Y1(t2)]. The first difference signal ΔY(t0, t1) and the second difference signal ΔY(t0, t2) in the frequency domain are each represented by a complex number.

[0079] In addition, the difference calculation unit 23 can divide the entire frequency range in the frequency domain into multiple frequency cells, and can use the signal components in one specific frequency cell or multiple specific frequency cells as the difference signal ΔY. Using the signal components in (one or more than one) specific frequency cells as the difference signal ΔY enables the judgment unit 24 to judge the properties of the object 9 by focusing only on the object 9 that exists at the specific distance L or within the specific distance L range.

[0080] The difference calculation unit 23 obtains a first difference signal ΔY ( t0 , t1 ) and a second difference signal ΔY ( t0 , t2 ) in each regular calculation period (which is a period sufficiently shorter than one breathing period T0 ). Figure 4 A shows, on the IQ plane, a locus of a first differential signal ΔY ( t0 , t1 ) obtained in each calculation cycle in a case where the subject 9 is a person sleeping in a bed (hereinafter referred to as “sleeping person”). Figure 4B shows the trajectory of the second differential signal ΔY(t0, t2) obtained in each calculation cycle when the object 9 is a sleeping person on the IQ plane. The first differential signal ΔY(t0, t1) and the second differential signal ΔY(t0, t2) change around the points of I=0 and Q=0, and the trajectory of the second differential signal ΔY(t0, t2) is distributed in a wider range than the trajectory of the first differential signal ΔY(t0, t1). Then, the difference calculation unit 23 obtains the average value (i.e., the time average value) of the amplitude of the first differential signal ΔY(t0, t1) per predetermined time as the first differential value ΔZ1. In addition, the difference calculation unit 23 also obtains the average value (i.e., the time average value) of the amplitude of the second differential signal ΔY(t0, t2) per predetermined time as the second differential value ΔZ2. In this case, the second differential value ΔZ2 becomes significantly larger than the first differential value ΔZ1. In this example, the time length of the period T1 is assumed to be 50 msec, and the time length of the period T2 is assumed to be 500 msec.

[0081] In addition, the amplitude of the first differential signal ΔY(t0, t1) is the amplitude of each of the I component and the Q component of the first differential signal ΔY(t0, t1), the amplitude of only the I component of the first differential signal ΔY(t0, t1), or the amplitude of only the Q component of the first differential signal ΔY(t0, t1). Similarly, the amplitude of the second differential signal ΔY(t0, t2) is the amplitude of each of the I component and the Q component of the second differential signal ΔY(t0, t2), the amplitude of only the I component of the second differential signal ΔY(t0, t2), or the amplitude of only the Q component of the second differential signal ΔY(t0, t2).

[0082] Note that if the breathing rate of a sleeping person is to be detected, the time period T2 is preferably set to a value falling within the range from 500 msec to 7 sec. On the other hand, if the breathing rate of an awake person 91 is to be detected, the time periods T1, T2 are set to have a shorter time length. However, it is preferred to set the respective time lengths of the time periods T1, T2 according to, for example, the person as the detection target or the movement of the person as the detection target.

[0083] On the other hand, if the object 9 is a curtain, then Figure 5 As shown in FIGS. 5A and 5B , the trajectory of the first differential signal ΔY(t0, t1) and the trajectory of the second differential signal ΔY(t0, t2) are distributed in substantially the same range. As a result, the first differential value ΔZ1 and the second differential value ΔZ2 are approximately equal to each other.

[0084] Furthermore, if the object 9 is a swinging electric fan, then Figure 6As shown in FIGS. 6A and 6B , the trajectory of the second differential signal ΔY(t0, t2) is distributed in a slightly wider range than the trajectory of the first differential signal ΔY(t0, t1). As a result, the second differential value ΔZ2 becomes slightly larger than the first differential value ΔZ1.

[0085] On the other hand, if the object 9 is a fan without swing, then Figure 7 As shown in FIGS. 7A and 7B , the trajectory of the first differential signal ΔY(t0, t1) and the trajectory of the second differential signal ΔY(t0, t2) are distributed in substantially the same range. As a result, the first differential value ΔZ1 and the second differential value ΔZ2 are approximately equal to each other.

[0086] Optionally, the difference calculation unit 23 may obtain the effective value (i.e., root mean square (RMS)) of the amplitude of the first differential signal ΔY(t0, t1) as the first differential value ΔZ1, and obtain the RMS of the amplitude of the second differential signal ΔY(t0, t2) as the second differential value ΔZ2. Alternatively, the difference calculation unit 23 may obtain the standard deviation of the amplitude of the first differential signal ΔY(t0, t1) as the first differential value ΔZ1, and may obtain the standard deviation of the amplitude of the second differential signal ΔY(t0, t2) as the second differential value ΔZ2. Alternatively, the difference calculation unit 23 may also obtain the first differential value ΔZ1 and the second differential value ΔZ2 after passing the time functions of the first differential signal ΔY(t0, t1) and the second differential signal ΔY(t0, t2) through a filter such as a low-pass filter.

[0087] (Judgment Unit)

[0088] The determination unit 24 includes a target determination unit 241 .

[0089] The target judgment unit 241 obtains the evaluation value Ga based on the first difference value ΔZ1 and the second difference value ΔZ2, and judges the attribute of the object 9 by using the evaluation value Ga. In the present embodiment, the target judgment unit 241 judges whether the object 9 is a person as the attribute of the object 9.

[0090] The target judgment unit 241 preferably obtains the evaluation value Ga by using the ratio [ΔZ2 / ΔZ1] of the second difference value ΔZ2 to the first difference value ΔZ1. Using the ratio [ΔZ2 / ΔZ1] makes the evaluation value Ga a relative value (ie, a normalized value), thereby helping to improve the accuracy of the judgment process.

[0091] For example, the target judgment unit 241 obtains the evaluation value Ga1 by the following formula (2) as the evaluation value Ga. The evaluation value Ga1 obtained by the formula (2) becomes greater than 1 when the object 9 is a person, but becomes approximately equal to 1 when the object 9 is an interference object such as a curtain or an electric fan.

[0092] Ga1=ΔZ2 / ΔZ1 (2)

[0093] Alternatively, the target judgment unit 241 obtains the evaluation value Ga2 by the following formula (3) as the evaluation value Ga. The evaluation value Ga2 obtained by formula (3) is close to 1 when the object 9 is a person, and is close to 0 when the object 9 is an interference object such as a curtain or an electric fan.

[0094] Ga2=1–ΔZ1 / ΔZ2 (3)

[0095] Figure 8 A and Figure 8 B. Fig. 9 A and Fig. 9 B. Fig.10 A and Fig.10 B. Fig.11 A and Fig.11 B and Fig.12 A and Fig.12 B each shows how the evaluation value Ga2 changes with time. Figure 8 A. Fig. 9 A. Fig.10 A. Fig.11 A and Fig.12 The evaluation value Ga2 shown in each of A is obtained based on the first differential value ΔZ1 which is the RMS of the amplitude of the first differential signal ΔY (t0, t1) and the second differential value ΔZ2 which is the RMS of the amplitude of the second differential signal ΔY (t0, t2). Figure 8 B. Fig. 9 B. Fig.10 B. Fig.11 B and Fig.12 The evaluation value Ga2 shown in each of B is obtained based on the first difference value ΔZ1 which is the standard deviation of the amplitude of the first difference signal ΔY ( t0 , t1 ) and the second difference value ΔZ2 which is the standard deviation of the amplitude of the second difference signal ΔY ( t0 , t2 ).

[0096] also, Figure 8 A and Figure 8 B. Fig. 9 A and Fig. 9 B. Fig.10 A and Fig.10 B. Fig.11 A and Fig.11 B and Fig.12 A and Fig.12 Ka1 and Ka2 shown in each of B are evaluation thresholds to be compared with the associated evaluation value Ga2. In the present embodiment, the evaluation threshold Ka1 is set to 0.5, and the evaluation threshold Ka2 is set to 0.1.

[0097] Figure 8 A and Figure 8 B shows how the evaluation value Ga2 changes over time in the case where the subject 9 is a person sitting still. Figure 8 A and Figure 8 In B, the evaluation value Ga2 is close to 1 and remains equal to or greater than the evaluation threshold Ka1 for a long period of time.

[0098] Fig. 9 A and Fig. 9 B shows how the evaluation value Ga2 changes over time when the object 9 is a curtain. In this case, the curtain flutters in the wind, for example, causing the evaluation value Ga2 to increase more easily. However, one cycle of the curtain fluttering is different from one breathing cycle T0 of a person. Therefore, the respective time lengths of the time periods T1, T2 are set to be the same as one breathing cycle T0 of a person (see Figure 3 ) can reduce the excessive increase of the evaluation value Ga2 when the object 9 is a curtain. Fig. 9 A and Fig. 9 In B, the evaluation value Ga2 remains smaller than the evaluation threshold Ka1 and equal to or larger than the evaluation threshold Ka2 for a relatively long period of time.

[0099] Fig.10 A and Fig.10 B shows how the evaluation value Ga2 changes over time when the object 9 is a swinging electric fan. In this case, the swinging of the electric fan causes the evaluation value Ga2 to increase more easily. However, one cycle of the swinging of the electric fan is different from one breathing cycle T0 of a person. Therefore, the time lengths of the time periods T1 and T2 are set to be the same as one breathing cycle T0 of a person (see Figure 3 ) can reduce the excessive increase of the evaluation value Ga2 when the object 9 is a swinging electric fan. Fig.10 A and Fig.10 In B, the evaluation value Ga2 remains smaller than the evaluation threshold Ka1 and equal to or larger than the evaluation threshold Ka2 for a relatively long period of time.

[0100] Fig.11 A and Fig.11 B shows how the evaluation value Ga2 changes over time when the object 9 is an electric fan that does not swing (ie, is fixed). In this case, the electric fan does not swing so that the evaluation value Ga2 is less than Fig.10 A and Fig.10 The evaluation value Ga2 in B. Fig.11 A and Fig.11 In B, the evaluation value Ga2 remains smaller than the evaluation threshold Ka2 for a relatively long period of time.

[0101] Fig.12 A and Fig.12B shows how the evaluation value Ga2 changes over time when there is no object 9 in the irradiation region R1. That is, the evaluation value Ga2 is a value representing background noise. Fig.12 A and Fig.12 In B, the evaluation value Ga2 remains smaller than the evaluation threshold Ka2 for a relatively long period of time.

[0102] The target judgment unit 241 according to the present embodiment judges the possibility that the object 9 is a detection target in three stages by comparing the evaluation value Ga2 with two evaluation threshold values ​​Ka1 , Ka2 .

[0103] As a decision in the first stage, when the evaluation value Ga2 is found to be equal to or greater than the evaluation threshold Ka1, the target judgment unit 241 judges that at least a person should exist as the object 9 within the irradiation area R1. That is, if the evaluation value Ga2 is equal to or greater than the evaluation threshold Ka1, at least a person should exist as the object 9 within the irradiation area R1. However, it is unclear whether there are any interfering objects as the object 9 within the irradiation area R1. Note that when the evaluation value Ga2 is found to remain equal to or greater than the evaluation threshold Ka1 for a predetermined time or longer, the target judgment unit 241 preferably judges that at least a person should exist within the irradiation area R1.

[0104] As a decision in the second stage, when the evaluation value Ga2 is found to be less than the evaluation threshold Ka1 and equal to or greater than the evaluation threshold Ka2, the target judgment unit 241 judges that at least an interfering object should exist as the object 9 within the irradiation area R1. That is, if the evaluation value Ga2 is less than the evaluation threshold Ka1 and equal to or greater than the evaluation threshold Ka2, then an interfering object should exist as the object 9 within the irradiation area R1. However, it is unclear whether there is any person as the object 9 within the irradiation area R1. Note that when the evaluation value Ga2 is found to remain less than the evaluation threshold Ka1 and equal to or greater than the evaluation threshold Ka2 for a predetermined time or longer, the target judgment unit 241 preferably judges that at least an interfering object should exist within the irradiation area R1.

[0105] As a decision in the third stage, when the evaluation value Ga2 is found to be smaller than the evaluation threshold Ka2, the target judgment unit 241 judges that a person and an interfering object should not exist in the irradiation area R1 as the object 9. That is, if the evaluation value Ga2 is smaller than the evaluation threshold Ka2, a person and an interfering object should not exist in the irradiation area R1 as the object 9. Note that when the evaluation value Ga2 is found to remain smaller than the evaluation threshold Ka2 for a predetermined time or longer, the target judgment unit 241 preferably judges that a person or an interfering object should not exist in the irradiation area R1.

[0106] It is assumed that the body motion signal processing device of Patent Document 1 cited above is a comparative example. In the comparative example, the amplitude value of the body motion signal component of the received signal to be detected when there is no person in the irradiation area R1 and the amplitude value of the body motion signal detected when there is a person in the irradiation area R1 are compared with each other to detect the body motion (such as heart rate or breathing rate, etc.) of the person in the irradiation area R1. According to such a comparative example, in the case where the evaluation value Ga2 is less than the evaluation threshold Ka1 and is equal to or greater than the evaluation threshold Ka2, it is highly likely that a decision is made that a person should be present in the irradiation area R1.

[0107] On the other hand, the sensor system A1 and the signal processing system 2 according to the present embodiment compare the evaluation value Ga2 with the evaluation threshold values ​​Ka1 and Ka2, thereby more accurately determining whether the object 9 present in the irradiation area R1 is a person or an interference object. That is, the sensor system A1 and the signal processing system 2 can determine the attributes of the object 9 with sufficient accuracy.

[0108] (1.3.3) Signal processing method

[0109] The signal processing method according to this embodiment can be summarized as follows: Fig.13 Flowchart shown.

[0110] Fig.13 The signal processing method shown includes a receiving step S1, a storing step S2, a difference calculating step S3, an evaluation value calculating step S4, and a judging step S5.

[0111] In the receiving step S1 , the pre-processing unit 21 receives the sensor signal Y0 from the radio wave sensor 1 .

[0112] In the storing step S2 , the storage unit 22 stores the history of the sensor signal Y1 using the sensor signal Y0 that has been amplified and AD-converted by the pre-processing unit 21 as the sensor signal Y1 .

[0113] In the difference calculation step S3, the difference calculation unit 23 generates a first difference signal ΔY (t0, t1) and a second difference signal ΔY (t0, t2) as a plurality of difference signals ΔY based on the history of the sensor signal Y1 stored in the storage unit 22. Then, the difference calculation unit 23 obtains the amplitude of the first difference signal ΔY (t0, t1) as a first difference value ΔZ1. In addition, the difference calculation unit 23 obtains the amplitude of the second difference signal ΔY (t0, t2) as a second difference value ΔZ2.

[0114] In the evaluation value calculation step S4 , the target judgment unit 241 (judgment unit 24 ) obtains the evaluation value Ga by using the ratio [ΔZ2 / ΔZ1 ] of the second difference value ΔZ2 to the first difference value ΔZ1 .

[0115] In the judgment step S5 , the target judgment unit 241 (judgment unit 24 ) uses the evaluation value Ga to judge whether the object 9 is a person.

[0116] The program stored in the memory of the computer system is preferably designed to cause the processor to perform the above-mentioned signal processing method.

[0117] The signal processing method and program described above also enable accurate judgment of whether the subject 9 is a person as a detection target.

[0118] (1.4) Notification system

[0119] The output unit 25 transmits the decision made by the target judgment unit 241 to the notification system 3. The notification system 3 notifies the administrator of the decision made by the target judgment unit 241 in the form of at least one of an image and a sound.

[0120] Examples of such a notification system 3 include a notification system operated by a business operator who provides a service of watching a designated person as the exemplary object 9. In this case, the person designated as the detection target may be, for example, an elderly person who is a resident of a welfare facility, an elderly person who uses a day care service center, an elderly person who lives alone, or an elderly person who lives in a residence that provides services for the elderly.

[0121] If the state of absence of a person in irradiation area R1 continues for a predetermined period of time or longer, notification system 3 notifies a predetermined terminal device that the person designated as the detection target is absent. This enables an administrator or family members of the elderly to take appropriate actions when notified of the absence of the person designated as the detection target.

[0122] Note that the person being the detection target need not be an elderly person, but may be, for example, a child using a nursery or a patient hospitalized in a medical institution. That is, the age, gender, or any other attribute of the person designated as the detection target is not limited to any specific one.

[0123] (1.5) First Modification

[0124] In the signal processing system 2 according to the above-described first embodiment, if the evaluation value Ga2 is smaller than the evaluation threshold Ka1 and equal to or larger than the evaluation threshold Ka2, it is unclear whether a person exists as the object 9 within the irradiation region R1.

[0125] Therefore, in order to more accurately determine whether the object 9 is a person as a detection target, Fig.14As shown, the judgment unit 24 according to the present modification further includes a distance judgment unit 242. The distance judgment unit 242 determines the distance L to the object 9 as a distance judgment value based on the frequency spectrum (frequency distribution) of the second differential signal ΔY (t0, t2). The target judgment unit 241 performs a judgment process for judging whether the object 9 is a person based on the distance judgment value obtained by the distance judgment unit 242.

[0126] In addition, the signal processing system 2 pre-sets the directivity of at least one of the transmitting antenna 1b and the receiving antenna 1c of the radio wave sensor 1 according to the object 9 as the detection target, thereby limiting the irradiation area R1 of the radio wave according to the object 9 as the detection target. Specifically, the directivity of at least one of the transmitting antenna 1b and the receiving antenna 1c of the radio wave sensor 1 is set so that the irradiation area R1 includes an area where a person is highly likely to exist, but does not include an area where a person is unlikely to exist.

[0127] The target judgment unit 241 preferably regards a certain area in the irradiation area R1 where a person is highly likely to exist as a judgment area, and judges whether the object 9 is a person based only on the received wave reflected from the object 9 in the judgment area. That is, the target judgment unit 241 limits the judgment area, thereby reducing the influence of the interfering object compared to the influence of the person. As a result, this can reduce the possibility of failing to detect a person in the judgment area.

[0128] For example, Fig.15 How to set the judgment area is illustrated. In this example, it is assumed that a person 91 lying on a rectangular parallelepiped bed 8 is an object 9 as a detection target. Curtains 92 are arranged as the object 9 at both ends along the length of the bed 8 (i.e., at both longitudinal ends) and at one end along the width of the bed 8 (i.e., at one lateral end).

[0129] In this case, the radio wave sensor 1 is placed adjacent to the person 91. Specifically, the radio wave sensor 1 may be placed, for example, on the headboard of the bed 8 or on a wall adjacent to the headboard of the bed 8. The directivity of the radio wave sensor 1 is set to a teardrop shape so that the irradiation area R1 viewed vertically covers the bed 8 as much as possible and covers the curtain 92 as little as possible.

[0130] The target judgment unit 241 defines an area in the irradiation area R1 where the distance L is less than the distance threshold L0 as a non-judgment area R10. In addition, the target judgment unit 241 defines an area in the irradiation area R1 where the distance L is equal to or greater than the distance threshold L0 but less than the distance threshold L1 as a judgment area R11. Furthermore, the target judgment unit 241 defines an area in the irradiation area R1 where the distance L is equal to or greater than the distance threshold L1 but less than the distance threshold L2 as a judgment area R12. Furthermore, the target judgment unit 241 defines an area in the irradiation area R1 where the distance L is equal to or greater than the distance threshold L2 as a non-judgment area R13. Note that the distance threshold L0 is a distance L that is too close to the radio wave sensor 1 to cover the person 91. The distance threshold L1 is a distance L that covers the upper half of the body of the person 91 but hardly covers the lower half of his or her body. The distance threshold L2 is a value approximately equal to the total length of the bed 8 along its longitudinal axis.

[0131] Therefore, the judgment area R11 is an area that covers the upper half of the body of the person 91 on the bed 8 but does not cover any curtains 92, and in which the possibility of detecting an interfering object is low. The judgment area R12 is an area that covers the lower half of the body of the person 91 on the bed 8 and in which one edge contacts one of the curtains 92. However, the curtains 92 have little effect on the edge of the judgment area R12.

[0132] When it is found that the distance judgment value obtained by the distance judgment unit 242 based on the second differential signal ΔY (t0, t2) is equal to or greater than the distance threshold value L0 and less than the distance threshold value L2, the target judgment unit 241 performs a judgment process using the first differential signal ΔY (t0, t1) and the second differential signal ΔY (t0, t2). Specifically, the target judgment unit 241 obtains the evaluation value Ga based on the ratio [ΔZ2 / ΔZ1] of the second differential value ΔZ2 of the second differential signal ΔY (t0, t2) and the first differential value ΔZ1 of the first differential signal ΔY (t0, t1), and performs a judgment process using the evaluation value Ga. In other words, the target judgment unit 241 judges whether the object 9 is a person only for the object 9 existing in any one of the judgment areas R11, R12. This can reduce the possibility that the target judgment unit 241 mistakenly regards an interfering object such as a curtain 92 as a person 91 or mistakenly regards a person 91 as an interfering object 9 such as a curtain 92.

[0133] (1.6) Second Modification

[0134] Furthermore, in the first embodiment, the target judgment unit 241 may judge whether the object 9 is a detection target by comparing the evaluation value Ga with at least one evaluation threshold value.

[0135] For example, the target judgment unit 241 may judge whether the object 9 is a detection target in two stages by comparing the evaluation value Ga with a single evaluation threshold. Alternatively, the target judgment unit 241 may judge whether the object 9 is a detection target in four stages by comparing the evaluation value Ga with three evaluation thresholds.

[0136] (2) Second Embodiment

[0137] (2.1) Signal processing

[0138] Fig.16 A sensor system A2 including a signal processing system 2A according to a second embodiment is illustrated. In the following description, any constituent element in the second embodiment having the same function as the corresponding part of the above-mentioned first embodiment will be designated by the same reference numeral as the corresponding part, and its description will be omitted here.

[0139] In order to accurately determine the property of the object 9 as the detection target, the signal processing system 2A pre-sets the directivity of at least one of the transmitting antenna 1b and the receiving antenna 1c of the radio wave sensor 1 according to the object 9 as the detection target, thereby Fig.17 As shown, the irradiation area R1 of the radio wave is limited according to the object 9 as the detection target. Specifically, the directivity of at least one of the transmitting antenna 1b and the receiving antenna 1c of the radio wave sensor 1 is set so that the irradiation area R1 includes an area where the person 91 is highly likely to exist, but does not include an area where the person 91 is unlikely to exist.

[0140] In addition, the determination unit 24 of the signal processing system 2A includes a distance determination unit 243 and a target determination unit 244 .

[0141] The distance judgment unit 243 detects that the peak of the signal strength in the spectrum of the second differential signal ΔY (t0, t2) becomes equal to or greater than the peak threshold value Kb1 (see Fig.18 ) as the peak frequency fp. In addition, the distance judgment unit 243 also judges the distance L as the attribute of the object 9 based on the peak frequency fp (that is, obtains the distance judgment value). Whenever the distance judgment unit 243 judges the distance L, the distance judgment unit 243 generates data related to the distance judgment value as distance data.

[0142] Specifically, as distance measurement preprocessing, the distance judgment unit 243 converts the second differential signal ΔY(t0, t2) as a signal in the time domain into a second differential signal ΔY(f) as a signal in the frequency domain by performing FFT or DCT on the second differential signal ΔY(t0, t2).

[0143] Fig.18An exemplary second difference signal ΔY(f) is shown. As a distance determination process, the distance determination unit 243 compares the signal strength of the second difference signal ΔY(f) with a peak threshold Kb1. Then, as a distance determination process, the distance determination unit 243 extracts a peak frequency fp at which the signal strength of the second difference signal ΔY(f) reaches a peak within a range equal to or greater than the peak threshold Kb1. The peak frequency fp corresponds to the beat frequency fb (see Equation (1)). Therefore, the distance determination unit 243 can clearly obtain the distance L by substituting the peak frequency fp into the beat frequency fb in Equation (1).

[0144] Next, as shown Fig.17 the target determination unit 244 defines a determination region R21 as a region where the person 91 in the irradiation region R1 is most likely to exist. As a re-evaluation process, the target determination unit 244 extracts distance data generated from the received wave reflected by the object 9 within the determination region R21. That is, the target determination unit 244 restricts the determination region R21, thereby reducing the influence of the interfering object 93 compared to the influence of the person 91. As a result, this can reduce the possibility of failing to detect the person 91 in the determination region R21.

[0145] Specifically, as shown Fig.17 a person 91 lying on a bed 8 having a rectangular parallelepiped shape is assumed to be the object 9 to be detected. In Fig.17 the radio wave sensor 1 is placed beside the head of the person 91. In addition, it is assumed that the interfering object 93 faces the radio wave sensor 1 in a state where the person 91 is disposed between the radio wave sensor 1 and the interfering object 93. In this case, the distance between the radio wave sensor 1 and the interfering object 93 is longer than the distance between the radio wave sensor 1 and the person 91.

[0146] Therefore, the target determination unit 244 presets distance thresholds L10, L11, where the distance thresholds L10, L11 satisfy L10 < L11. The target determination unit 244 defines a region in the irradiation region R1 where the distance L is less than the distance threshold L10 as a non-determination region R20. In addition, the target determination unit 244 defines a region in the irradiation region R1 where the distance L is equal to or greater than the distance threshold L10 but less than the distance threshold L11 as a determination region R21. Further, the target determination unit 24 defines a region in the irradiation region R1 where the distance L is equal to or greater than the distance threshold L11 as a non-determination region R22. Note that the distance threshold L10 is a distance L that is too close to the radio wave sensor 1 to cover the person 91. The distance threshold L11 is a value approximately equal to the total length of the bed 8 along its longitudinal axis.

[0147] The target determination unit 244 determines whether the distance determination value is equal to or greater than the distance threshold L10 and less than the distance threshold L11 by comparing the distance determination value with the distance thresholds L10 and L11.

[0148] Specifically, Fig.19 A is a graph in which distance data Da corresponding to a large number of distance judgment values ​​obtained by the distance judgment unit 243 in each calculation cycle are plotted along the time axis. Fig.19 In A, time period Tb1 is a time period when the person 91 is not on the bed 8. Time period Tb2 after time period Tb1 is a time period when the person 91 lies face up on the bed 8. Time period Tb3 after time period Tb2 is a time period when the person 91 is not on the bed 8. Fig.19 The distance data Da including a large number of distance judgment values ​​shown in A includes in combination the distance data Da1 generated by the person 91 and the distance data Da2 generated by the interference object. Therefore, the target judgment unit 244 extracts only the distance data Da having a distance judgment value equal to or greater than the distance threshold value L10 and less than the distance threshold value L11 from the distance data Da including a large number of distance judgment values ​​as the distance data Da1 generated by the person 91.

[0149] Next, the target judgment unit 244 performs an index calculation process by obtaining an index based on the density of the distance data Da1 per predetermined time using the distance data Da1 thus extracted. The index is a value indicating the possibility that the object 9 is the person 91. In the present embodiment, the larger the index, the more likely the object 9 is the person 91.

[0150] Specifically, Fig. 20 As shown, the target judgment unit 244 sets an evaluation window W1 with a time length of a predetermined time Tw within a range equal to or greater than the distance threshold L10 and less than the distance threshold L11. That is, the distance data Da included in the evaluation window W1 is the distance data Da2, and the number of distance judgment values ​​of the distance data Da included in the evaluation window W1 corresponds to the density of the distance data Da2 per predetermined time Tw. The target judgment unit 244 obtains the number of distance judgment values ​​of the distance data Da included in the evaluation window W1 (that is, the density of the distance data Da2 per predetermined time Tw) as an index. The target judgment unit 244 shifts the evaluation window W1 by a predetermined sliding time as time passes, and obtains the index each time the target judgment unit 244 shifts the evaluation window W1.

[0151] Fig.19 B shows the Fig.19The index obtained by the distance data Da2 shown in A. The index in the time period Tb2 in which the person 91 lies face up on the bed 8 is greater than the index in each of the time periods Tb1 and Tb3 in which the person 91 is not on the bed 8. Therefore, the target judgment unit 244 performs judgment processing by comparing the index with a predetermined index threshold value Kc1. When it is found that the index remains equal to or greater than the index threshold value Kc1 for a predetermined period of time or longer, the target judgment unit 244 judges that the person 91 should be present in the judgment area R21.

[0152] Fig.21 A is a graph of another set of distance data Da plotted along the time axis. Fig.21 In A, the time period Tb11 is a time period during which the person 91 is not on the bed 8. The time period Tb12 after the time period Tb11 is a time period during which the person 91 is lying on the bed 8 on his side. The time period Tb13 after the time period Tb12 is a time period during which the person 91 is not on the bed 8. If the person 91 is lying on the bed 8 on his side, the transmission wave 101 (see FIG. 101 ) emitted from the radio wave sensor 1 is greater than that in the case where the person 91 is lying on the bed 8 with his face up. Figure 1 ) is more likely to be reflected from the back of person 91. That is, this reduces the possibility that his or her movement caused by the breathing of person 91 is reflected in the received wave 102. However, in the present embodiment, the index in the time period Tb12 in which person 91 lies on the side on the bed 8 is greater than the index in any of the time periods Tb11 and Tb13 in which person 91 is not on the bed 8. This enables the target judgment unit 244 to judge that person 91 should be present in the judgment area R21 in the time period Tb12 by comparing the index with the index threshold value Kc1.

[0153] Fig. 22 A is a graph plotting the distance data Da obtained when only an interfering object such as a curtain exists in the judgment area R21 along the time axis. In this case, the index becomes smaller than the index threshold Kc1. This enables the target judgment unit 244 to judge that the person 91 should not be in the judgment area R21 by comparing the index with the index threshold Kc1.

[0154] Fig.23 A shows an index obtained when the person 91 lies face up in the middle of the bed 8. In this case, the index becomes larger than the index threshold Kc1. This enables the target judgment unit 244 to judge that the person 91 should be present in the judgment area R21 by comparing the index with the index threshold Kc1.

[0155] Fig.23B shows an index obtained when the person 91 sits at the end of the bed 8. In this case, the index becomes larger than the index threshold Kc1. This enables the target judgment unit 244 to judge that the person 91 should be present in the judgment area R21 by comparing the index with the index threshold Kc1.

[0156] Fig.24 A shows that in the non-judgment area R20 (see Fig.17 ) is an index obtained when there is a curtain as the object 9. In this case, the index becomes smaller than the index threshold Kc1. This enables the target judgment unit 244 to judge that the person 91 should not be in the judgment area R21 by comparing the index with the index threshold Kc1.

[0157] Fig.24 B shows that in the non-judgment area R22 (see Fig.17 ) is an index obtained when there is a curtain as the object 9. In this case, the index becomes smaller than the index threshold Kc1. This enables the target judgment unit 244 to judge that the person 91 should not be in the judgment area R21 by comparing the index with the index threshold Kc1.

[0158] Fig.24 C shows that in the non-judgment area R22 (see Fig.17 ) is an index obtained when there is a swinging electric fan as the object 9. In this case, the index becomes smaller than the index threshold Kc1. This enables the target judgment unit 244 to judge that the person 91 should not be in the judgment area R21 by comparing the index with the index threshold Kc1.

[0159] As can be seen from the above description, the sensor system A2 and the signal processing system 2A according to the present embodiment can accurately determine whether the object 9 existing in the irradiation area R1 is a person 91 by comparing the index with the index threshold Kc1.

[0160] (2.2) Adjustment of peak detection sensitivity

[0161] The distance judgment unit 243 detects that the peak of the signal strength in the spectrum of the second differential signal ΔY (t0, t2) becomes equal to or greater than the peak threshold value Kb1 (see Fig.18 ) as the peak frequency fp. However, the signal strength of the sensor signal Y1 (Y0) sometimes changes. Therefore, if the signal strength of the sensor signal Y1 (Y0) is relatively low, it is difficult for the distance judgment unit 243 to detect the peak frequency fp. That is, if the signal strength of the sensor signal Y1 (Y0) is relatively low, the sensitivity of the peak detection of the distance judgment unit 243 becomes relatively low, thereby making the sensitivity of the person detection by the target judgment unit 244 relatively low.

[0162] Therefore, the distance judgment unit 243 changes the sensitivity of the peak detection using the distance judgment unit 243 itself based on the evaluation value Ga, thereby adjusting the sensitivity of the peak detection so that the sensitivity can fall within a predetermined range. This enables the distance judgment unit 243 to detect the peak frequency fp even if the signal strength of the sensor signal Y1 (Y0) is relatively low. Therefore, the sensor system A2 and the signal processing system 2A can accurately judge the distance L to the object 9. That is, the judgment unit 24 according to the present embodiment can also accurately judge the attribute of the object 9 by using the evaluation value Ga.

[0163] (2.2.1) First Example of Sensitivity Adjustment

[0164] For example, the distance judgment unit 243 may continuously or stepwise change the peak threshold Kb1 based on the evaluation value Ga1 (see formula (2)). In this case, the larger the evaluation value Ga1 is, the more significantly the distance judgment unit 243 increases the peak threshold Kb1. The smaller the evaluation value Ga1 is, the more significantly the distance judgment unit 243 decreases the peak threshold Kb1.

[0165] Alternatively, the distance judgment unit 243 may also continuously or stepwise change the peak threshold Kb1 based on the evaluation value Ga2 (see formula (3)). In this case, the smaller the evaluation value Ga2 is, the more significantly the distance judgment unit 243 increases the peak threshold Kb1. The larger the evaluation value Ga2 is, the more significantly the distance judgment unit 243 decreases the peak threshold Kb1.

[0166] The distance determination unit 243 changes the peak threshold Kb1 so that the sensitivity of peak detection can fall within a predetermined range.

[0167] (2.2.2) Second Example of Sensitivity Adjustment

[0168] For example, the difference calculation unit 23 can amplify each of the sensor signals Y1(t0), Y1(t1) and Y1(t2) with an amplification factor based on the evaluation value Ga1 (see formula (2)). In this case, the larger the evaluation value Ga1 is, the more significantly the difference calculation unit 23 reduces the amplification factor. The smaller the evaluation value Ga1 is, the more significantly the difference calculation unit 23 increases the amplification factor. That is, the difference calculation unit 23 changes the signal strengths of the sensor signals Y1(t0), Y1(t1) and Y1(t2) based on the evaluation value Ga1. Note that the difference calculation unit 23 can not only set the amplification factor to 1 or more, but also set the amplification factor to less than 1.

[0169] Alternatively, the difference calculation unit 23 may also amplify each of the sensor signals Y1(t0), Y1(t1) and Y1(t2) with an amplification factor based on the evaluation value Ga2 (see formula (3)). In this case, the smaller the evaluation value Ga2 is, the more significantly the difference calculation unit 23 reduces the amplification factor. The smaller the evaluation value Ga2 is, the more significantly the difference calculation unit 23 increases the amplification factor. That is, the difference calculation unit 23 changes the signal strengths of the sensor signals Y1(t0), Y1(t1) and Y1(t2) based on the evaluation value Ga2. Note that the difference calculation unit 23 may not only set the amplification factor to 1 or more, but may also set the amplification factor to less than 1.

[0170] The difference calculation unit 23 enables the sensitivity of peak detection to fall within a predetermined range by changing the respective signal intensities of the sensor signals Y1 ( t0 ), Y1 ( t1 ), and Y1 ( t2 ).

[0171] (2.3) Signal processing method

[0172] The signal processing method according to this embodiment can be summarized as follows: Fig.25 Flowchart shown.

[0173] Fig.25 The signal processing method shown includes a difference evaluation step S11, a sensitivity adjustment step S12, a distance measurement preprocessing step S13, a distance judgment step S14, a re-evaluation step S15, an index calculation step S16 and a target judgment step S17.

[0174] The difference evaluation step S11 includes the receiving step S1, the storing step S2, the difference calculating step S3, and the evaluation value calculating step S4 according to the first embodiment (see Fig.13 ). Specifically, in the difference evaluation step S11, the target judgment unit 241 (judgment unit 24) obtains the evaluation value Ga by using the [ΔZ2 / ΔZ1] ratio of the second difference value ΔZ2 to the first difference value ΔZ1.

[0175] In the sensitivity adjustment step S12, the distance judgment unit 243 adjusts the sensitivity of the peak detection by changing the peak threshold value Kb1 according to the evaluation value Ga. Alternatively, in the sensitivity adjustment step S12, the difference calculation unit 23 adjusts the sensitivity of the peak detection by changing the respective signal strengths of the sensor signals Y1(t0), Y1(t1), Y1(t2) according to the evaluation value Ga.

[0176] In the distance measurement preprocessing step S13, the distance judgment unit 243 converts the second differential signal ΔY(t0, t2) as a signal in the time domain into a second differential signal ΔY(f) as a signal in the frequency domain by performing FFT or DCT on the second differential signal ΔY(t0, t2).

[0177] In the distance judgment step S14, the distance judgment unit 243 compares the signal strength of the second differential signal ΔY(f) with the peak threshold Kb1, thereby extracting the peak frequency fp at which the signal strength of the second differential signal ΔY(f) reaches a peak value within a range equal to or greater than the peak threshold Kb1.

[0178] In the re-evaluation step S15, the target judgment unit 244 extracts the judgment area R21 (see Fig.17 ) is the distance data Da1 generated by the received wave reflected by the object 9 within.

[0179] In the index calculation step S16 , the target judgment unit 244 uses the extracted distance data Da1 to obtain an index based on the density per predetermined time of the distance data Da1 .

[0180] In the target judgment step S17, the target judgment unit 244 compares the index with a predetermined index threshold Kc1. When the index is found to remain equal to or greater than the index threshold Kc1 for a predetermined time or longer, the target judgment unit 244 judges that the person 91 should exist in the judgment area R21.

[0181] The program stored in the memory of the computer system is preferably designed to cause the processor to perform the above-mentioned signal processing method.

[0182] The signal processing method and program described above also enable the attributes of the object 9 to be accurately determined.

[0183] (3) Other Modifications

[0184] The above-described signal processing system obtains the evaluation value Ga by using the respective differential values ​​(i.e., the first differential value ΔZ1 and the second differential value ΔZ2) of the two differential signals (i.e., the first differential signal ΔY(t0, t1) and the second differential signal ΔY(t0, t2)). However, the signal processing system may obtain the evaluation value Ga by using the respective differential values ​​of three or more differential signals.

[0185] Alternatively, a ratio ΔZ1 / ΔZ2 of the first differential value ΔZ1 to the second differential value ΔZ2 may be used instead of the above-described ratio ΔZ2 / ΔZ1 .

[0186] In addition, the object 9 serving as the detection target does not have to be a person 91, but may be, for example, an animal such as a dog or a cat, a robot, a machine having a moving part, a movable machine, an electrical device having a moving part, or a movable electrical device, etc.

[0187] Alternatively, the signal processing system may also use as a differential signal the difference between the sensor signal Y0 in the case where the object 9 is a person 91 as a detection target and the sensor signal Y0 in the case where the object 9 is an interfering object 93. That is, the signal processing system can also achieve the same advantages as those described above by using the differential signal between the multiple sensor signals Y0 shifted from each other along the time axis, instead of using the differential signal between the multiple sensor signals Y0 regarding mutually different objects 9.

[0188] Furthermore, the radio wave sensor 1 does not need to be an FMCW radio wave sensor as long as the radio wave sensor 1 can measure the distance to the object 9. Alternatively, the radio wave sensor 1 may also be a binary frequency shift keying (FSK) radio wave sensor.

[0189] Optionally, the above-mentioned embodiments and their modifications may be appropriately combined and adopted.

[0190] (4) Summary

[0191] A signal processing system (2, 2A) according to a first aspect of a typical embodiment receives a sensor signal (Y0) including information about a distance (L) between the radio wave sensor (1) and an object (9) from a radio wave sensor (1). The radio wave sensor (1) emits a radio wave as a transmission wave (101) and receives a radio wave reflected from the object (9) as a reception wave (102). The signal processing system (2, 2A) includes a difference calculation unit (23) and a judgment unit (24). The difference calculation unit (23) uses a sensor signal (Y1 (t0)) of a reference timing (t0) and a plurality of sensor signals (Y1 (t1), Y1 (t2)) of a plurality of comparison timings (t1, t2) offset from the reference timing (t0). The difference calculation unit (23) generates the respective differences between the sensor signal (Y1(t0)) of the reference timing (t0) and the plurality of sensor signals (Y1(t1), Y1(t2)) of the plurality of comparison timings (t1, t2) as a plurality of differential signals (ΔY(t0, t1), ΔY(t0, t2)), and obtains the respective amplitudes of the plurality of differential signals (ΔY(t0, t1), ΔY(t0, t2)) as a plurality of differential values ​​(ΔZ, ΔZ1, ΔZ2). The judgment unit (24) obtains the evaluation values ​​(Ga, Ga1, Ga2) based on the plurality of differential values ​​(ΔZ, ΔZ1, ΔZ2), and judges the attribute of the object (9) by using the evaluation values ​​(Ga, Ga1, Ga2).

[0192] The signal processing system (2, 2A) having such a configuration can accurately determine the attributes of the object (9).

[0193] In the signal processing system (2, 2A) according to the second aspect of the exemplary embodiment which can be implemented in combination with the first aspect, each of the plurality of comparison timings (t1, t2) is preferably earlier than the reference timing (t0).

[0194] The signal processing system (2, 2A) having such a configuration can accurately determine the attributes of the object (9).

[0195] In the signal processing system (2, 2A) of the third aspect according to the typical embodiment, which can be implemented in combination with the first aspect or the second aspect, each differential value among the multiple differential values ​​(ΔZ, ΔZ1, ΔZ2) is preferably an average value, an effective value (RMS value) or a standard deviation of each amplitude of the multiple differential signals (ΔY(t0, t1), ΔY(t0, t2)).

[0196] The signal processing system (2, 2A) having such a configuration can obtain the respective amplitudes of the plurality of differential signals (ΔY(t0, t1), ΔY(t0, t2)) as specific values.

[0197] In the signal processing system (2, 2A) of the fourth aspect according to the typical embodiment which can be implemented in combination with any one of the first to third aspects, the judgment unit (24) preferably uses the ratio (ΔZ2 / ΔZ1, ΔZ1 / ΔZ2) of multiple differential values ​​(ΔZ1, ΔZ2) as the evaluation value (Ga, Ga1, Ga2).

[0198] The signal processing system (2, 2A) having such a configuration can obtain the evaluation values ​​(Ga, Ga1, Ga2) as relative values, thereby improving the accuracy of the judgment process.

[0199] In the signal processing system (2) according to the fifth aspect of the exemplary embodiment which can be implemented in combination with any one of the first to fourth aspects, the judgment unit (24) preferably includes a target judgment unit (241). The target judgment unit (241) uses the evaluation value (Ga, Ga1, Ga2) to judge whether the object (9) is a predetermined detection target (91) as an attribute of the object (9).

[0200] The signal processing system (2) having such a configuration can judge whether the object (9) is a detection target (91) by directly using the evaluation values ​​(Ga, Ga1, Ga2).

[0201] In the signal processing system (2) of the sixth aspect according to the typical embodiment which can be implemented in combination with the fifth aspect, the target judgment unit (241) preferably judges whether the object (9) is a predetermined detection target (91) by comparing the evaluation value (Ga, Ga1, Ga2) with at least one evaluation threshold (Ka1, Ka2).

[0202] The signal processing system (2) having such a configuration can judge whether the object (9) is a detection target (91) by directly using the evaluation values ​​(Ga, Ga1, Ga2).

[0203] In the signal processing system (2) according to the seventh aspect of the typical embodiment which can be implemented in combination with the sixth aspect, at least one evaluation threshold (Ka1, Ka2) includes a plurality of evaluation thresholds (Ka1, Ka2). The target judgment unit (241) preferably judges the possibility that the object (9) is the detection target (91) in three stages by comparing the evaluation value (Ga, Ga1, Ga2) with two evaluation thresholds among the plurality of evaluation thresholds (Ka1, Ka2).

[0204] The signal processing system (2) having such a configuration can judge the possibility that the object (9) is the detection target (91) in three stages by directly using the evaluation values ​​(Ga, Ga1, Ga2).

[0205] In the signal processing system (2A) of the eighth aspect according to the typical embodiment which can be implemented in combination with any one of the first aspect to the fourth aspect, the sensor signal (Y0) is preferably a signal whose frequency changes according to the distance (L). The judgment unit (24) preferably includes a distance judgment unit (243). The distance judgment unit (243) preferably detects the frequency at which the peak of the signal intensity becomes equal to or greater than the peak threshold value (Kb1) in the frequency spectrum of at least one differential signal of the plurality of differential signals (ΔY(t0, t1), ΔY(t0, t2)) as the peak frequency (fp), and judges the distance (L) as the attribute of the object (9) based on the peak frequency (fp). The distance judgment unit (243) changes the peak threshold value (Kb1) according to the evaluation value (Ga, Ga1, Ga2).

[0206] The signal processing system (2A) having such a configuration can accurately judge the distance (L) to the object (9).

[0207] In the signal processing system (2A) of the ninth aspect according to the typical embodiment which can be implemented in combination with any one of the first aspect to the fourth aspect, the sensor signal (Y0) is preferably a signal whose frequency changes according to the distance (L). The judgment unit (24) preferably includes a distance judgment unit (243). The distance judgment unit (243) detects the frequency at which the peak of the signal intensity becomes equal to or greater than the peak threshold value (Kb1) in the frequency spectrum of at least one differential signal of the plurality of differential signals (ΔY(t0, t1), ΔY(t0, t2)) as the peak frequency (fp), and judges the distance (L) as the attribute of the object (9) based on the peak frequency (fp). The difference calculation unit (23) changes the signal intensity of the sensor signal (Y1(t0)) of the reference timing (t0) and the signal intensity of the plurality of sensor signals (Y1(t1), Y1(t2)) of the plurality of comparison timings (t1, t2) based on the evaluation value (Ga, Ga1, Ga2).

[0208] The signal processing system (2A) having such a configuration can accurately determine the distance (L) to the object (9).

[0209] In the signal processing system (2A) of the tenth aspect according to the typical embodiment that can be implemented in combination with the eighth aspect or the ninth aspect, the judgment unit (24) preferably also includes a target judgment unit (244), which is used to judge whether the object (9) is a predetermined detection target (91) as an attribute of the object (9). Each time the distance judgment unit (243) judges the distance (L), the distance judgment unit (243) generates distance data (Da). The target judgment unit (244) judges whether the object (9) is a predetermined detection target (91) by obtaining an index of the density of each predetermined time (Tw) based on the distance data (Da) and comparing the index with an index threshold (Kc1).

[0210] The signal processing system (2A) having such a configuration can accurately determine whether the object (9) is a detection target (91).

[0211] In the signal processing system (2, 2A) of the eleventh aspect according to the typical embodiment which can be implemented in combination with the fifth aspect, the sixth aspect, the seventh aspect or the tenth aspect, the target judgment unit (241, 244) preferably judges whether the object (9) is a predetermined detection target (91) only for an object (9) whose distance (L) relative to the radio wave sensor (1) falls within a predetermined range.

[0212] The signal processing system (2, 2A) having such a configuration can accurately determine whether the object (9) is a detection target (91) by reducing the influence of the interfering object (93).

[0213] In the signal processing system (2, 2A) of the twelfth aspect according to the typical embodiment which can be implemented in combination with any one of the first to eleventh aspects, the difference calculation unit (23) preferably sets two of the multiple comparison timings as two comparison timings (t1, t2). The difference calculation unit (23) generates the respective differences between the sensor signal (Y1(t0)) of the reference timing (t0) and the two sensor signals (Y1(t1), Y1(t2)) of the two comparison timings (t1, t2) among the multiple sensor signals as two differential signals (ΔY(t0, t1), ΔY(t0, t2)). Then, the difference calculation unit (23) obtains the respective amplitudes of the two differential signals (ΔY(t0, t1), ΔY(t0, t2)) as two differential values ​​(ΔZ1, ΔZ2).

[0214] The signal processing system (2, 2A) having such a configuration can accurately determine the attributes of the object (9).

[0215] In the signal processing system (2, 2A) of the thirteenth aspect according to the typical embodiment which can be implemented in combination with the twelfth aspect, the two comparison timings (t1, t2) are preferably a first comparison timing (T1) and a second comparison timing (T2). The first comparison timing (t1) is closer to the reference timing (t0) than the second comparison timing (t2). The time length between the reference timing (t0) and the second comparison timing (t2) is equal to or greater than 1 / 4 of one breathing cycle of a person.

[0216] The signal processing system (2, 2A) having such a configuration can accurately determine the attributes of a person (91) serving as a detection target.

[0217] A sensor system (A1, A2) according to a fourteenth aspect of the typical embodiment includes: the signal processing system (2, 2A) according to any one of the first to thirteenth aspects; and a radio wave sensor (1).

[0218] The sensor system (A1, A2) having such a configuration can accurately determine the properties of an object (9).

[0219] In the sensor system (A1, A2) of the fifteenth aspect according to the typical embodiment which can be implemented in combination with the fourteenth aspect, the radio wave sensor (1) includes: a transmitting antenna (1b) for emitting a transmission wave (101); and a receiving antenna (1c) for receiving a reception wave (102). At least one of the transmitting antenna (1b) and the receiving antenna (1c) preferably has directivity.

[0220] The sensor system (A1, A2) having such a configuration can accurately determine the properties of the object (9) by reducing the influence of the interfering object (93).

[0221] A signal processing method according to a sixteenth aspect of a typical embodiment includes: receiving a sensor signal (Y0) including information about a distance (L) between the radio wave sensor (1) and an object (9) from a radio wave sensor (1). The radio wave sensor (1) emits a radio wave as a transmission wave (101), and receives a radio wave reflected from the object (9) as a reception wave (102). The signal processing method includes a difference calculation step (S3) and a judgment step (S5, S14). The difference calculation step (S3) includes: using a sensor signal (Y1 (t0)) of a reference timing (t0) and a plurality of sensor signals (Y1 (t1), Y1 (t2)) of a plurality of comparison timings (t1, t2) offset relative to the reference timing (t0). The difference calculation step (S3) includes: generating respective differences between a sensor signal (Y1(t0)) of a reference timing (t0) and a plurality of sensor signals (Y1(t1), Y1(t2)) of a plurality of comparison timings (t1, t2) as a plurality of differential signals (ΔY(t0, t1), ΔY(t0, t2)), and obtaining respective amplitudes of the plurality of differential signals (ΔY(t0, t1), ΔY(t0, t2)) as a plurality of differential values ​​(ΔZ, ΔZ1, ΔZ2). The judgment step (S5, S14) includes: obtaining evaluation values ​​(Ga, Ga1, Ga2) based on the plurality of differential values ​​(ΔZ, ΔZ1, ΔZ2), and judging the properties of the object (9) by using the evaluation values ​​(Ga, Ga1, Ga2).

[0222] The signal processing method enables accurate determination of the properties of the object (9).

[0223] The program according to the seventeenth aspect of the exemplary embodiment is designed to cause a computer system to perform the signal processing method according to the sixteenth aspect.

[0224] This procedure enables accurate determination of the properties of the object (9).

[0225] Description of Reference Numerals

[0226] 1 Radio wave sensor

[0227] 1b Transmitting antenna

[0228] 1c Receiving antenna

[0229] 101 Send Wave

[0230] 102 Receiving Wave

[0231] 2,2A Signal Processing System

[0232] 23 Difference calculation unit

[0233] 24 Judgment Unit

[0234] 243 Distance Judgment Unit

[0235] 244 Target Judgment Unit

[0236] 9 Objects

[0237] 91 people (detection target)

[0238] L distance

[0239] Y0,Y1(t0),Y1(t1),Y1(t2) sensor signals

[0240] t0 reference timing

[0241] t1 First comparison timing (comparison timing)

[0242] t2 Second comparison timing (comparison timing)

[0243] ΔY(t0,t1),ΔY(t0,t2) differential signal

[0244] ΔZ, ΔZ1, ΔZ2 difference value

[0245] Ga,Ga1,Ga2 evaluation value

[0246] Ka1,Ka2 evaluation thresholds

[0247] Kb1 peak threshold

[0248] Kc1 indicator threshold

[0249] fp peak frequency

[0250] Da distance data

[0251] Tw Scheduled time

[0252] S3 difference calculation steps

[0253] S5 Judgment Steps

[0254] S14 Distance determination step (determination step)

Claims

1. A signal processing system configured to receive a sensor signal from a radio wave sensor, the radio wave sensor being configured to emit radio waves as transmission waves and receive radio waves reflected from an object as reception waves, the sensor signal including information about a distance between the radio wave sensor and the object, the signal processing system comprising: a difference calculation unit configured to use a sensor signal of a reference timing and a plurality of sensor signals of a plurality of comparison timings shifted with respect to the reference timing to generate a plurality of difference signals as respective differences between the sensor signal of the reference timing and the plurality of sensor signals of the plurality of comparison timings, the time differences between the reference timing and the plurality of comparison timings being different from each other, and to obtain respective amplitudes of the plurality of difference signals as a plurality of difference values; as well as A judgment unit is configured to obtain an evaluation value based on the plurality of difference values, and to judge a property of the object by using the evaluation value.

2. The signal processing system according to claim 1, wherein: Each of the plurality of comparison timings is earlier than the reference timing.

3. The signal processing system according to claim 1 or 2, wherein: Each of the plurality of differential values ​​is an average value, an effective value, or a standard deviation of each amplitude of the plurality of differential signals.

4. The signal processing system according to claim 1 or 2, wherein: The determination unit is configured to use a ratio of the plurality of difference values ​​as the evaluation value.

5. The signal processing system according to claim 1 or 2, wherein: The judgment unit includes a target judgment unit configured to use the evaluation value to judge whether the object is a predetermined detection target as an attribute of the object.

6. The signal processing system according to claim 5, wherein: The target judgment unit is configured to judge whether the object is a predetermined detection target by comparing the evaluation value with at least one evaluation threshold.

7. The signal processing system according to claim 6, wherein: The at least one evaluation threshold comprises a plurality of evaluation thresholds, and The target judgment unit is configured to judge the possibility that the object is a detection target in three stages by comparing the evaluation value with two evaluation thresholds among the plurality of evaluation thresholds.

8. The signal processing system according to claim 1 or 2, wherein: The sensor signal is a signal whose frequency varies according to the distance, The judging unit includes a distance judging unit configured to detect a frequency at which a peak of signal strength becomes equal to or greater than a peak threshold value in a frequency spectrum of at least one of the plurality of differential signals as a peak frequency, and to judge the distance as a property of the object based on the peak frequency, and The distance determination unit is configured to change the peak threshold value according to the evaluation value.

9. The signal processing system according to claim 1 or 2, wherein: The sensor signal is a signal whose frequency varies according to the distance, The judging unit includes a distance judging unit configured to detect a frequency at which a peak of signal strength becomes equal to or greater than a peak threshold value in a frequency spectrum of at least one of the plurality of differential signals as a peak frequency, and to judge the distance as a property of the object based on the peak frequency, and The difference calculation unit is configured to change the signal strength of the sensor signal at the reference timing and the signal strengths of the plurality of sensor signals at the plurality of comparison timings based on the evaluation value.

10. The signal processing system according to claim 8, wherein: The judging unit further includes a target judging unit configured to judge whether the object is a predetermined detection target as an attribute of the object. The distance determination unit is configured to generate distance data each time the distance determination unit determines the distance, and The target judgment unit is configured to judge whether the object is a predetermined detection target by obtaining an index of density per predetermined time based on the distance data and comparing the index with an index threshold.

11. The signal processing system according to claim 5, wherein: The target judgment unit is configured to judge whether or not the object is a predetermined detection target only for an object whose distance relative to the radio wave sensor falls within a predetermined range.

12. The signal processing system according to claim 1 or 2, wherein: The difference calculation unit is configured to set two of the multiple comparison timings as two comparison timings, generate two differential signals as respective differences between the sensor signal of the reference timing and the two sensor signals of the two comparison timings among the multiple sensor signals, and obtain respective amplitudes of the two differential signals as two differential values.

13. The signal processing system according to claim 12, wherein: The two comparison timings are a first comparison timing and a second comparison timing, The first comparison timing is closer to the reference timing than the second comparison timing, and The time length between the reference timing and the second comparison timing is equal to or greater than 1 / 4 of one breathing cycle of a person.

14. A sensor system comprising: The signal processing system according to any one of claims 1 to 13; as well as The radio wave sensor.

15. The sensor system of claim 14, wherein: The radio wave sensor includes: a transmitting antenna configured to emit the transmitting wave; and a receiving antenna configured to receive the receiving wave, and At least one of the transmitting antenna and the receiving antenna has directivity.

16. A signal processing method, comprising receiving a sensor signal from a radio wave sensor, the radio wave sensor being configured to emit radio waves as transmission waves and receive radio waves reflected from an object as reception waves, the sensor signal comprising information related to a distance between the radio wave sensor and the object, the signal processing method comprising: a difference calculating step for using a sensor signal at a reference timing and a plurality of sensor signals at a plurality of comparison timings shifted relative to the reference timing to generate a plurality of difference signals as respective differences between the sensor signal at the reference timing and the plurality of sensor signals at the plurality of comparison timings, the time differences between the reference timing and the plurality of comparison timings being different from each other, and obtaining respective amplitudes of the plurality of difference signals as a plurality of difference values; as well as A judging step of obtaining an evaluation value based on the plurality of differential values ​​and judging a property of the object by using the evaluation value. 17 . A non-transitory storage medium storing a program designed to cause a computer system to perform the signal processing method according to claim 16 .

18. A computer program product comprising a program designed to cause a computer system to perform the signal processing method according to claim 16.

Images