Patent Publication Number: US-2022233103-A1

Title: Estimation device and estimation method

Description:
TECHNICAL FIELD 
     The present disclosure relates to an estimation device and an estimation method that radiate a wireless signal to a living body and receive a reflection signal therefrom to identify the living body or estimate the orientation of the living body. 
     BACKGROUND ART 
     Technologies have been known for radiating a wireless signal to a living body and receiving a reflection signal therefrom to identify/estimate the living body or estimate the orientation of the living body (see, for example, Patent Literature (PTL) 1 and PTL 2). PTL 1 discloses a device that estimates the driver of an automobile by radiating electromagnetic waves to the driver and extracting the heartbeats and heat sound signals, using reflected waves from the driver. PTL 2 discloses a method of measuring the heart rate of the driver of an automobile, who is a test subject, using a plurality of transmitter-receivers. 
     Another example is PTL 3 that discloses a device that measures patterns of 360-degree radiation to the test subject, using a plurality of antennas. Further another example is PTL 4 that discloses an identification device that identifies an individual using a plurality of antennas disposed near the test subject. 
     Further another example is PTL 5 that discloses an estimation device that estimates the orientation of a living body, using a plurality of antennas disposed near the test subject. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] Japanese Unexamined Patent Application Publication No. 2015-042293 
         [PTL 2] Japanese Unexamined Patent Application Publication No. 2009-055997 
         [PTL 3] Japanese Unexamined Patent Application Publication No. 2007-325621 
         [PTL 4] Japanese Unexamined Patent Application Publication No. 2019-93104 
         [PTL 5] Japanese Unexamined Patent Application Publication No. 2019-211458 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In many cases, identification of a living body or estimation of the orientation of the living body utilizing electromagnetic waves are performed under a condition that a person to be measured and antennas are located relatively close to each other as shown in PTL 1, PTL 2, PTL 4, and PTL 5. 
     That the test subject and the antennas need to be located close to each other is unlikely to be a problem for the identification of an individual in a narrow area such as a driver&#39;s seat and an individual room. Such limitation, however, poses a problem that individual identification is hard to be performed in a situation in daily life, etc. 
     The present disclosure has been conceived in view of the above circumstances, and its aim is to provide an estimation device and an estimation method capable of identifying a living body or estimating the orientation of the living body by use of electromagnetic waves even under a condition that a test subject and antennas are spaced apart from each other in, for example, an indoor place. 
     Solution to Problem 
     The estimation device according to an aspect of the present disclosure is: an estimation device that identifies a living body or estimates an orientation of the living body, the estimation device including: M transmission antenna elements each transmitting a first transmission signal to a predetermined range that includes a first living body, where M is an integer greater than or equal to 1; N receivers disposed to surround the predetermined range, where N is an integer greater than or equal to 3, the N receivers each including a reception antenna element that receives, over a predetermined period, a first reception signal that is the first transmission signal reflected by the first living body; a memory that stores training signals which are (M×N) second reception signals obtained by causing each of the N receivers to preliminarily receive a second reception signal that is a second transmission signal transmitted from each of the M transmission antenna elements and reflected by a second living body; a first vector calculator that calculates a first vector for each of the training signals and each of (M×N) first reception signals by respective predetermined methods, the (M×N) first reception signals being obtained by the N receivers each receiving the first reception signal; and an estimator that calculates a plurality of correlation coefficients from the first vectors and identifies the first living body or estimates an orientation of the first living body by a predetermined method, using the plurality of correlation coefficients calculated. 
     These general and specific aspects may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or any combination of systems, methods, integrated circuits, computer programs, or computer-readable recording media. 
     Advantageous Effects of Invention 
     The estimation device according to the present disclosure is capable of identifying a living body or estimating the orientation of the living body by use of electromagnetic waves even under a condition that a test subject and antennas are spaced apart from each other in, for example, an indoor place. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram showing an exemplary configuration of an estimation device according to the embodiment. 
         FIG. 2  is a diagram showing an example of the training signal shown in  FIG. 1 . 
         FIG. 3  is a configuration diagram showing an exemplary detailed configuration of the circuit shown in  FIG. 1 . 
         FIG. 4  is a flowchart of an exemplary operation performed by the estimation device according to the embodiment. 
         FIG. 5  is a flowchart of an exemplary detailed operation of step S 11  according to the embodiment. 
         FIG. 6  is a flowchart of an exemplary detailed operation of step S 13  according to the embodiment. 
         FIG. 7  is a diagram showing the environment used for a test that uses the estimation device according to the embodiment. 
         FIG. 8  is a diagram showing exemplary propagation channels calculated from reception signals received in the environment shown in  FIG. 7 . 
         FIG. 9  is a diagram showing an exemplary result of correlation calculation performed after calculating first vectors of the propagation channels shown in  FIG. 8 . 
         FIG. 10  is a diagram showing an exemplary data correctness for three persons. 
         FIG. 11  is a diagram showing the configuration of PTL 1. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     (Underlying Knowledge Forming Basis of the Present Disclosure) 
     In PTL 1 and PTL 2, electromagnetic waves are radiated to a person seated in the driver&#39;s seat of an automobile to measure reflected waves from the person. Subsequently, computation is performed on the measurement result to measure the heartbeats or heat sounds, and then a temporal correlation of the measured heartbeats or heart sounds is obtained to identify the living body. 
     However, PTL 1 has a problem, as described above, that its method is operable only in a limited environment, such as a narrow space like the driver&#39;s seat, where the positions of the test subject and the antennas are identifiable. For this reason, in a situation in daily life such as an indoor place, identification of a living body or estimation of the orientation of the living body is required to be performed under a condition that the antennas and the test subject are spaced apart from each other, with a flexibility given to the positional relationship between the antennas and the test subject. 
     The inventors have spent much time to study the foregoing problem to find the points described below that are required for the identification of a living body or estimation of the orientation of the living body by use of electromagnetic waves, even under a condition that the test subject and the antennas are spaced apart from each other such as in an indoor place. That is to say, antenna elements are disposed around the room in which a target individual to be identified is active to transmit transmission waves from various directions and receive reflected waves and scattered waves in various directions, thereby obtaining reception signals capturing a larger number of features of the living body. 
     The reception signals vary, to no small extent, depending on the distance between the living body and an antenna or the orientation or posture of the living body. As such, to identify the living body or estimate the orientation of the living body, training data needs to be obtained while estimating the position or posture of the living body from the reception signals and the position or posture of the living body is stored as an identified position. At this time, the intensity of reception signals is relatively high when the distance between the antenna and the test subject is sufficiently short as in the background arts such as in PTL 1 and PTL 2, and thus the identification of an individual or the estimation of the orientation of the living body is feasible. However, when the identification of the living body is performed using electromagnetic waves in an indoor place, etc. where the test subject and the antennas are spaced apart from each other, the intensity of reception signals becomes low due to distance attenuation. This makes it hard to distinguish between the reception signals and noise floor, thus reducing the accuracy of identifying the individual or estimating the orientation of the living body. 
     In view of the above, the inventors have found that it is possible to know whether the living body to be measured is present in the training data or to accurately identify the orientation of such living body in the following manner, even in an area such as a housing space: decompose a correlation matrix into eigenvalues; reorder the result in order of eigenvalues; extract channels that include many vital components and remove DC components therefrom; and calculate a correlation with the training data after the test subject makes the same posture in the identified position. 
     The estimation device according to an aspect of the present disclosure is an estimation device that identifies a living body or estimates an orientation of the living body, the estimation device including: M transmission antenna elements each transmitting a first transmission signal to a predetermined range that includes a first living body, where M is an integer greater than or equal to 1; N receivers disposed to surround the predetermined range, where N is an integer greater than or equal to 3, the N receivers each including a reception antenna element that receives, over a predetermined period, a first reception signal that is the first transmission signal reflected by the first living body; a memory that stores training signals which are (M×N) second reception signals obtained by causing each of the N receivers to preliminarily receive a second reception signal that is a second transmission signal transmitted from each of the M transmission antenna elements and reflected by a second living body; a first vector calculator that calculates a first vector for each of the training signals and each of (M×N) first reception signals by respective predetermined methods, the (M×N) first reception signals being obtained by the N receivers each receiving the first reception signal; and an estimator that calculates a plurality of correlation coefficients from the first vectors and identifies the first living body or estimates an orientation of the first living body by a predetermined method, using the plurality of correlation coefficients calculated. Note that the first vectors correspond to, for example, a training first vector and a test first vector. The estimator corresponds to, for example, the circuit. 
     With this, it is possible to calculate a plurality of correlation coefficients from the training signals and the first reception signals that are measurement signals obtained from the reception antenna elements disposed around the first living body. Subsequently, depending on whether the maximum value of the plurality of correlation coefficients exceeds a threshold, it is possible to estimate whether the first living body and the second living body that is included in the training data are in the same orientation. Alternatively, it is possible to authenticate the living body by identifying whether the first living body and the second living body that is included in the training data are identical. 
     For example, the first vector calculator may include: a second matrix calculator that calculates a second matrix from the first reception signals; a decomposer that decomposes the second matrix by a predetermined method and reorders elements of the second matrix by a predetermined method, and calculate the first vectors, using the elements of the second matrix that have been reordered and the training signals or the first reception signals. 
     For example, the decomposer may decompose the second matrix into eigenvalues and reorder, in descending order, the eigenvalues that are diagonal elements. 
     For example, the decomposer may decompose the second matrix into singular values and reorder, in descending order, the singular values that are diagonal elements. 
     For example, the first vector calculator may remove, by a predetermined method, a DC component from the first vectors calculated. 
     For example, the estimator may calculate, by a predetermined method, a total number of correlation functions to be used among a plurality of correlation matrices and calculate a total sum of correlation matrices for an amount equivalent to the total number of correlation functions to be used. 
     For example, to estimate an orientation of the first living body, the estimator may store training signals for respective orientations of a living body, and estimate, as the orientation of the first living body, an orientation of one of the training signals that corresponds to a maximum of the total sum of the plurality of correlation matrices. 
     With this, it is possible to accurately identify whether the training data includes a living body that is in the same orientation as that of the living body to be measured, even in an area such as a housing space. 
     For example, to identify the first living body, the estimator may store training signals in a same orientation for each living body, and estimate, as a living body identical to the first living body, one of the training signals that corresponds to a maximum of the total sum of the plurality of correlation matrices. 
     With this, it is possible to accurately identify whether the training data includes the living body to be measured, even in an area such as a housing space. 
     Also, the living body position estimation method according to an aspect of the present disclosure is an estimation method performed by an estimation device that identifies a living body or estimates an orientation of the living body, wherein the estimation device includes: M transmission antenna elements each transmitting a first transmission signal to a predetermined range that includes a first living body, where M is an integer greater than or equal to 1; N receivers disposed to surround the predetermined range, where N is an integer greater than or equal to 3, the N receivers each including a reception antenna element that receives, over a predetermined period, a first reception signal that is the first transmission signal reflected by the first living body; and a memory that stores training signals which are (M×N) second reception signals obtained by causing each of the N receivers to preliminarily receive a second reception signal that is a second transmission signal transmitted from each of the M transmission antenna elements and reflected by a second living body; wherein the estimation method includes: calculating a first vector for each of the training signals and (M×N) first reception signals by respective predetermined methods, the (M×N) first reception signals being obtained by the N receivers each receiving the first reception signal; and calculating a plurality of correlation coefficients from the first vectors and identifying the first living body or estimating an orientation of the first living body by a predetermined method, using the plurality of correlation coefficients calculated. 
     Note that these general and specific aspects may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or any combination of systems, methods, integrated circuits, computer programs, or computer-readable recording media. 
     Hereinafter, a certain exemplary embodiment is described in greater detail with reference to the accompanying Drawings. The exemplary embodiment described below shows a general or specific example. The numerical values, shapes, materials, elements, the arrangement and connection of the elements, steps, the processing order of the steps etc. shown in the following exemplary embodiment are mere examples, and therefore do not limit the scope of the appended Claims and their equivalents. Therefore, among the elements in the following exemplary embodiment, those not recited in any one of the independent claims are described as optional elements. Also, in the specification and the drawings, elements having substantially the same functional configuration are assigned the same reference marks and are not described to avoid redundancy. 
     Embodiment 
     [Configuration of Estimation Device  10 A] 
       FIG. 1  is a configuration diagram showing an exemplary configuration of estimation device  10 A according to the embodiment.  FIG. 2  is a diagram showing an example of training signal  42  shown in  FIG. 1 .  FIG. 3  is a configuration diagram showing an exemplary detailed configuration of circuit  40  shown in  FIG. 1 . 
     Estimation device  10 A according to the present disclosure includes: M transmission antenna elements, where M is an integer greater than or equal to 1; N receivers each including a reception antenna element, where N is an integer greater than or equal to 3; circuit  40 ; and memory  41 . 
     Each of the M transmission antenna elements transmits a transmission signal to predetermined range A 1  that includes living body  50 . The transmission signal is a high-frequency signal such as microwaves generated by a transmitter, etc. 
     Living body  50  is, for example, a person. Living body  50 , which is a target to be estimated by estimation device  10 A, is a living body to be authenticated or whose orientation is to be estimated. 
     Predetermined range A 1  is a preliminarily defined range of a space that includes living body  50 . Stated differently, predetermined range A 1  is a space used by estimation device  10 A to estimate living body  50 . 
     Each of the M transmission antenna elements transmits, for example, a first transmission signal to predetermined range A 1  that includes a first living body, which is living body  50  to be measured. Each of the M transmission antenna elements also transmits a second transmission signal to predetermined range A 1  that includes a second living body, which is known living body  50  serving as training data. 
     The N receivers, each including a reception antenna element, are disposed to surround predetermined range A 1 . Using the reception antenna element, each of the N receivers receives, over a predetermined period, reception signals each including a reflection signal which is a transmission signal reflected by living body  50 . For example, using the reception antenna element, each of the N receivers receives, over predetermined period T, first reception signals each including a reflection signal, which is a first transmission signal reflected by the first living body. Also, for example, using the reception antenna element, each of the N receivers receives training signals each being a second reception signal including a reflection signal, which is a second transmission signal reflected by the second living body, over a period that is K times longer than predetermined period T, where K is 2 or greater. 
     As shown in  FIG. 1 , estimation device  10 A in the present embodiment includes, for example, eight transmitter-receivers  30 A to  30 H, circuit  40 , and memory  41 . Stated differently, the M transmission antenna elements and the N receivers may be configured as eight transmitter-receivers  30 A to  30 H. Note that the number of the transmitter-receivers is not limited to be eight. 
     [Transmitter-Receivers  30 A to  30 H] 
     In the present embodiment, eight transmitter-receivers  30 A to  30 H are disposed around predetermined range A 1 . Each of eight transmitter-receivers  30 A to  30 H transmits a transmission signal to predetermined range A 1  that includes living body  50  such as a person, thereby receiving a reception signal that includes a reflection signal reflected by living body  50 . Eight transmitter-receivers  30 A to  30 H may be disposed, for example, in a circular form at even intervals, or outside of predetermined range A 1 . 
     As shown in  FIG. 1 , transmitter-receivers  30 A to  30 H include corresponding antenna elements  31 A to  31 H. Using antenna elements  31 A to  31 H, transmitter-receivers  30 A to  30 H transmit transmission signals to predetermined range A 1 . More specifically, using antenna elements  31 A to  31 H, transmitter-receivers  30 A to  30 H emit microwaves as transmission signals to living body  50  such as a person. Note that transmitter-receivers  30 A to  30 H may transmit, using antenna elements  31 A to  31 H, unmodulated transmission signals or transmission signals that have undergone modulation processing. 
     To transmit modulated transmission signals, each of transmitter-receivers  30 A to  30 H may further include a circuit for performing modulation processing. 
     Using antenna elements  31 A to  31 H, transmitter-receivers  30 A to  30 H also receive, over a predetermined period, reception signals that include reflection signals, which are transmission signals reflected by living body  50 . Transmitter-receivers  30 A to  30 H output the received reception signals to circuit  40 . Note that each of transmitter-receivers  30 A to  30 H may include a circuit for processing the reception signals. In this case, each of transmitter-receivers  30 A to  30 H may transform the received reception signals into low-frequency signals by frequency transform. Note that each of transmitter-receivers  30 A to  30 H may demodulate the reception signals. 
     Subsequently, each of transmitter-receivers  30 A to  30 H outputs, to circuit  40 , the signals obtained by frequency transform and/or demodulation processing. 
     In an example shown in  FIG. 1 , estimation device  10 A includes eight transmitter-receivers  30 A to  30 H, which are transmitters and receivers having four antenna elements commonly used for transmission and reception, but the configuration of estimation device  10 A is not limited to this. The number of transmitter-receivers  30 A to  30 H is not limited to eight, and thus may be, for example, N, where N is an integer greater than or equal to 3. Also, transmitters with M transmission antenna elements, where M is an integer greater than or equal to 1, and receivers with N reception antenna elements may be separately provided. 
     [Memory  41 ] 
     Memory  41  is an auxiliary storage device that includes a nonvolatile storage region. Examples of memory  41  include read only memory (ROM), a flash memory, a hard disk drive (HDD). Memory  41  stores, for example, information used for various processes of operating estimation device  10 A. 
     As shown in  FIG. 1 , memory  41  stores training signals  42 . Training signals  42  are signal waveforms preliminarily obtained for the second living body, which is known living body  50  that is (present) in predetermined range A 1 . More specifically, training signals  42  are (M×N) second reception signals, which is derived by multiplying M by N. Such (M×N) second reception signals are obtained by causing the N receivers to preliminarily receive second reception signals each including a reflection signal that is a second transmission signal transmitted from each of the M transmission antenna elements to the second living body and reflected by the second living body. Here, training signals  42  may be (M×N) second reception signals obtained by the N receivers preliminarily receiving second reception signals over a period that is K times longer than the predetermined period, where K is greater than or equal to 2. 
     In the present embodiment, the M transmission antenna elements and the N receivers include eight transmitter-receivers  30 A to  30 H as shown in  FIG. 1 . With reference to  FIG. 2 , an example of training signal  42  in such case will be described. Training signals  42  shown in  FIG. 2  are exemplary reception signals received by a single receiver during a measurement period. 
     Training signals  42  shown in  FIG. 2  are time response waveforms of a plurality of reception signals obtained by transmitter-receivers  30 A to  30 H preliminarily receiving reception signals that include reflection signals transmitted from antenna elements  31 A to  31 H to known living body  50  (second living body) present in predetermined range A 1  and reflected from the surface of such second living body  50 . Stated differently, training signals  42  shown in  FIG. 2  represent the intensity of a plurality of reception signals obtained by transmitter-receivers  30 A to  30 H preliminarily receiving reception signals that include reflection signals during the measurement period. Here, the measurement period is a period that is K times longer than the foregoing predetermined period, where K is 2 or greater. Non-limiting examples of the measurement period is 120 seconds [s]. The measurement period is simply required to be longer than or equal to the heartbeat cycle of a person, and thus may be 3 seconds [s], 10 seconds [s], 30 seconds [s], etc. 
     Note that training signal  42  may be preliminarily obtained for each of a plurality of known second living bodies. In this case, each of a plurality of training signals  42  that correspond to a plurality of known second living bodies may be stored in memory  41  in association with estimation information used to estimate the corresponding second living body. 
     [Circuit  40 ] 
     Circuit  40 , which is an estimator, performs various processes of operating estimation device  10 A. Circuit  40  includes, for example, a processor that executes a control program and a volatile storage region (main storage device) used as a work area in executing the control program. The storage region is, for example, a random-access memory (RAM). 
     Circuit  40  temporarily stores the first reception signals obtained from the respective N receivers in the storage region for a predetermined period. Circuit  40  may temporarily store the phases and amplitudes of the first reception signals in such storage region for a predetermined period. In the present embodiment, circuit  40  temporarily stores the reception signals obtained from the respective transmitter-receivers  30 A to  30 H in the storage region for a predetermined period. 
     Note that circuit  40  may include a dedicated circuit for performing various processes of operating estimation device  10 A. Stated differently, circuit  40  may be a circuit for performing software processing or may be a circuit for performing hardware processing. Circuit  40  may also include a nonvolatile storage region. 
     The following describes a functional configuration of circuit  40 . 
     As shown in  FIG. 3 , circuit  40  includes first vector calculator  410 , DC remover  411 , and estimator  412 . Note that DC remover  411  is not essential. 
     &lt;First Vector Calculator  410 &gt; 
     More specifically, using the reception signals stored in the storage region of circuit  40  and the training signals stored in memory  41 , first vector calculator  410  first calculates a propagation channel of each of the reception signals and each of the training signals: 
     
       
         
           
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     to be obtained when a multiple-input and multiple-output (MIMO) array antenna that includes receiver K R , transmitter K T , M r  reception antenna elements, and M t  transmission antenna elements is disposed around living body  50  is represented as shown in Expression 1 and Expression 2: 
     
       
         
           
             
               
                 
                   
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     In Expression 1 and Expression 2, K R  and K T  represent a receiver number and a transmitter number, respectively, and M r  and M t  represent the antenna element number of each receiver and each transmitter, respectively. 
     
       
         
           
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     represents a complex channel response from the M t -th antenna of transmitter K T  to the M r -th antenna of receiver K R , where t represents the observation time. 
     Subsequently, first vector calculator  410  calculates a frequency response matrix shown in Math. 7 of the propagation channels 
     
       
         
           
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     is represented as in Expression 3. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       9 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         F 
                         
                           ( 
                           
                             
                               k 
                               R 
                             
                             ⁢ 
                             
                               k 
                               T 
                             
                           
                           ) 
                         
                       
                       ⁡ 
                       
                         ( 
                         ω 
                         ) 
                       
                     
                     = 
                     
                       ( 
                       
                         
                           
                             
                               
                                 f 
                                 11 
                                 
                                   ( 
                                   
                                     
                                       k 
                                       R 
                                     
                                     ⁢ 
                                     
                                       k 
                                       T 
                                     
                                   
                                   ) 
                                 
                               
                               ⁡ 
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                           
                           
                             … 
                           
                           
                             
                               
                                 f 
                                 
                                   1 
                                   ⁢ 
                                   
                                     M 
                                     t 
                                   
                                 
                                 
                                   ( 
                                   
                                     
                                       k 
                                       R 
                                     
                                     ⁢ 
                                     
                                       k 
                                       T 
                                     
                                   
                                   ) 
                                 
                               
                               ⁡ 
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                           
                         
                         
                           
                             ⋮ 
                           
                           
                             ⋱ 
                           
                           
                             ⋮ 
                           
                         
                         
                           
                             
                               
                                 f 
                                 
                                   
                                     M 
                                     r 
                                   
                                   ⁢ 
                                   1 
                                 
                                 
                                   ( 
                                   
                                     
                                       k 
                                       R 
                                     
                                     ⁢ 
                                     
                                       k 
                                       T 
                                     
                                   
                                   ) 
                                 
                               
                               ⁡ 
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                           
                           
                             … 
                           
                           
                             
                               
                                 f 
                                 
                                   
                                     M 
                                     r 
                                   
                                   ⁢ 
                                   
                                     M 
                                     t 
                                   
                                 
                                 
                                   ( 
                                   
                                     
                                       k 
                                       R 
                                     
                                     ⁢ 
                                     
                                       k 
                                       T 
                                     
                                   
                                   ) 
                                 
                               
                               ⁡ 
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
     Here, ω is a frequency range corresponding to the living body. 
     Subsequently, first vector calculator  410  converts the propagation channels 
     
       
         
           
             [ 
             
               Math 
               . 
               
                   
               
               ⁢ 
               10 
             
             ] 
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               H 
               ⁡ 
               
                 ( 
                 t 
                 ) 
               
             
           
         
       
     
     and the frequency response matrix 
     
       
         
           
             [ 
             
               Math 
               . 
               
                   
               
               ⁢ 
               11 
             
             ] 
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               F 
               ⁡ 
               
                 ( 
                 ω 
                 ) 
               
             
           
         
       
     
     into vectors: 
     
       
         
           
             [ 
             
               Math 
               . 
               
                   
               
               ⁢ 
               12 
             
             ] 
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               
                 vec 
                 ⁢ 
                 
                   { 
                   
                     H 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   } 
                 
               
               , 
               
                 vec 
                 ⁢ 
                 
                   { 
                   
                     F 
                     ⁡ 
                     
                       ( 
                       ω 
                       ) 
                     
                   
                   } 
                 
               
             
           
         
       
     
     
       
         
           
             [ 
             
               Math 
               . 
               
                   
               
               ⁢ 
               13 
             
             ] 
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               
                 vec 
                 ⁢ 
                 
                   { 
                   
                     H 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   } 
                 
               
               , 
               
                 vec 
                 ⁢ 
                 
                   { 
                   
                     F 
                     ⁡ 
                     
                       ( 
                       ω 
                       ) 
                     
                   
                   } 
                 
               
             
           
         
       
     
     are represented as shown in Expression 4 and Expression 5, respectively, where T represents transpose. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       14 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     vec 
                     ⁢ 
                     
                       { 
                       
                         
                           H 
                           
                             ( 
                             
                               
                                 k 
                                 R 
                               
                               ⁢ 
                               
                                 k 
                                 T 
                               
                             
                             ) 
                           
                         
                         ⁡ 
                         
                           ( 
                           ω 
                           ) 
                         
                       
                       } 
                     
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               h 
                               11 
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           … 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             
                               h 
                               
                                 
                                   M 
                                   r 
                                 
                                 ⁢ 
                                 1 
                               
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                         
                         , 
                         … 
                         ⁢ 
                         
                             
                         
                         , 
                         
                           
                             
                               h 
                               
                                 1 
                                 ⁢ 
                                 
                                   M 
                                   t 
                                 
                               
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           … 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             
                               h 
                               
                                 
                                   M 
                                   r 
                                 
                                 ⁢ 
                                 
                                   M 
                                   t 
                                 
                               
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                         
                       
                       ] 
                     
                     T 
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       15 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     vec 
                     ⁢ 
                     
                       { 
                       
                         
                           F 
                           
                             ( 
                             
                               
                                 k 
                                 R 
                               
                               ⁢ 
                               
                                 k 
                                 T 
                               
                             
                             ) 
                           
                         
                         ⁡ 
                         
                           ( 
                           ω 
                           ) 
                         
                       
                       } 
                     
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               f 
                               11 
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           … 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             
                               f 
                               
                                 
                                   M 
                                   r 
                                 
                                 ⁢ 
                                 1 
                               
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                         
                         , 
                         … 
                         ⁢ 
                         
                             
                         
                         , 
                         
                           
                             
                               f 
                               
                                 1 
                                 ⁢ 
                                 
                                   M 
                                   t 
                                 
                               
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           … 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             
                               f 
                               
                                 
                                   M 
                                   r 
                                 
                                 ⁢ 
                                 
                                   M 
                                   t 
                                 
                               
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                         
                       
                       ] 
                     
                     T 
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ) 
                 
               
             
           
         
       
     
     Subsequently, first vector calculator  410  calculates a second matrix shown in Math. 17 from the vector matrix: 
     
       
         
           
             
               
                 
                   vec 
                   ⁢ 
                   
                     { 
                     
                       F 
                       ⁡ 
                       
                         ( 
                         ω 
                         ) 
                       
                     
                     } 
                   
                 
               
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                     ⁢ 
                     16 
                   
                   ] 
                 
               
             
             
               
                 R 
               
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                     ⁢ 
                     17 
                   
                   ] 
                 
               
             
           
         
       
     
     The second matrix 
     
       
         
           
             [ 
             
               Math 
               . 
               
                   
               
               ⁢ 
               18 
             
             ] 
           
         
       
       
         
           
             
                 
             
             ⁢ 
             R 
           
         
       
     
     is represented as shown in Expression 6, where E[{ }{ }] is an ensemble average. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       19 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     R 
                     
                       ( 
                       
                         
                           k 
                           R 
                         
                         ⁢ 
                         
                           k 
                           T 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     E 
                     ⁡ 
                     
                       [ 
                       
                         vec 
                         ⁢ 
                         
                           { 
                           
                             
                               F 
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                             ⁡ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                           } 
                         
                         ⁢ 
                         vec 
                         ⁢ 
                         
                           { 
                           
                             
                               
                                 ( 
                                 
                                   F 
                                   
                                     ( 
                                     
                                       
                                         k 
                                         R 
                                       
                                       ⁢ 
                                       
                                         k 
                                         T 
                                       
                                     
                                     ) 
                                   
                                 
                                 ) 
                               
                               H 
                             
                             ⁢ 
                             
                               ( 
                               ω 
                               ) 
                             
                           
                           } 
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ) 
                 
               
             
           
         
       
     
     First vector calculator  410  then performs eigenvalue decomposition on the second matrix: 
         R   [Math. 20]
 
     The eigenvalue decomposition is represented as shown in Expression 7, Expression 8, and Expression 9, where H represents complex conjugate transpose. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       21 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     R 
                     
                       ( 
                       
                         
                           k 
                           R 
                         
                         ⁢ 
                         
                           k 
                           T 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       U 
                       
                         ( 
                         
                           
                             k 
                             R 
                           
                           ⁢ 
                           
                             k 
                             T 
                           
                         
                         ) 
                       
                     
                     ⁢ 
                     
                       
                         
                           Λ 
                           
                             ( 
                             
                               
                                 k 
                                 R 
                               
                               ⁢ 
                               
                                 k 
                                 T 
                               
                             
                             ) 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             U 
                             
                               ( 
                               
                                 
                                   k 
                                   R 
                                 
                                 ⁢ 
                                 
                                   k 
                                   T 
                                 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                       H 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       22 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       Λ 
                       
                         ( 
                         
                           
                             k 
                             R 
                           
                           ⁢ 
                           
                             k 
                             T 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       diag 
                       ⁡ 
                       
                         [ 
                         
                           
                             λ 
                             1 
                             
                               ( 
                               
                                 
                                   k 
                                   R 
                                 
                                 ⁢ 
                                 
                                   k 
                                   T 
                                 
                               
                               ) 
                             
                           
                           , 
                           … 
                           ⁢ 
                           
                               
                           
                           , 
                           
                             λ 
                             L 
                             
                               ( 
                               
                                 
                                   k 
                                   R 
                                 
                                 ⁢ 
                                 
                                   k 
                                   T 
                                 
                               
                               ) 
                             
                           
                           , 
                           … 
                           ⁢ 
                           
                               
                           
                           , 
                           
                             λ 
                             
                               
                                 M 
                                 r 
                               
                               ⁢ 
                               
                                 M 
                                 t 
                               
                             
                             
                               ( 
                               
                                 
                                   k 
                                   R 
                                 
                                 ⁢ 
                                 
                                   k 
                                   T 
                                 
                               
                               ) 
                             
                           
                         
                         ] 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         ∴ 
                         
                           
                             λ 
                             1 
                           
                           ≥ 
                           
                             λ 
                             2 
                           
                           ≥ 
                           
                               
                           
                           ⁢ 
                           … 
                         
                       
                       ⁢ 
                       
                           
                       
                       , 
                       
                         
                           
                             λ 
                             L 
                           
                           &gt; 
                           
                             λ 
                             
                               L 
                               + 
                               1 
                             
                           
                         
                         = 
                         
                           … 
                           = 
                           
                             λ 
                             
                               
                                 M 
                                 R 
                               
                               ⁢ 
                               
                                 M 
                                 T 
                               
                             
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       23 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     U 
                     1 
                     
                       ( 
                       
                         
                           k 
                           R 
                         
                         ⁢ 
                         
                           k 
                           T 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     [ 
                     
                       
                         
                           u 
                           1 
                           
                             ( 
                             
                               
                                 k 
                                 R 
                               
                               ⁢ 
                               
                                 k 
                                 T 
                               
                             
                             ) 
                           
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         … 
                       
                       ⁢ 
                       
                           
                       
                       , 
                       
                         u 
                         L 
                         
                           ( 
                           
                             
                               k 
                               R 
                             
                             ⁢ 
                             
                               k 
                               T 
                             
                           
                           ) 
                         
                       
                       , 
                       … 
                       ⁢ 
                       
                           
                       
                       , 
                       
                         u 
                         
                           
                             M 
                             r 
                           
                           ⁢ 
                           
                             M 
                             t 
                           
                         
                         
                           ( 
                           
                             
                               k 
                               R 
                             
                             ⁢ 
                             
                               k 
                               T 
                             
                           
                           ) 
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     9 
                   
                   ) 
                 
               
             
           
         
       
     
     Here, 
     
       
         
           
             [ 
             
               Math 
               . 
               
                   
               
               ⁢ 
               24 
             
             ] 
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               Λ 
               
                 ( 
                 
                   
                     k 
                     R 
                   
                   ⁢ 
                   
                     k 
                     T 
                   
                 
                 ) 
               
             
           
         
       
     
     represents each diagonal element of the eigenvalues, and 
     
       
         
           
             [ 
             
               Math 
               . 
               
                   
               
               ⁢ 
               25 
             
             ] 
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               U 
               
                 ( 
                 
                   
                     k 
                     R 
                   
                   ⁢ 
                   
                     k 
                     T 
                   
                 
                 ) 
               
             
           
         
       
     
     represents the eigenvector corresponding to an eigenvalue. 
     Using each eigenvector 
     
       
         
           
             [ 
             
               Math 
               . 
               
                   
               
               ⁢ 
               26 
             
             ] 
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               U 
               
                 ( 
                 
                   
                     k 
                     R 
                   
                   ⁢ 
                   
                     k 
                     T 
                   
                 
                 ) 
               
             
           
         
       
     
     and 
     
       
         
           
             
               
                 
                   vec 
                   ⁢ 
                   
                     { 
                     
                       H 
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     } 
                   
                 
               
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                     ⁢ 
                     27 
                   
                   ] 
                 
               
             
           
         
       
     
     in Expression 4, first vector calculator  410  calculates first vectors: 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       28 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     y 
                     
                       ( 
                       
                         
                           k 
                           R 
                         
                         ⁢ 
                         
                           k 
                           T 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               y 
                               1 
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                         
                           
                             ⋮ 
                           
                         
                         
                           
                             
                               y 
                               
                                 
                                   M 
                                   r 
                                 
                                 ⁢ 
                                 
                                   M 
                                   t 
                                 
                               
                               
                                 ( 
                                 
                                   
                                     k 
                                     R 
                                   
                                   ⁢ 
                                   
                                     k 
                                     T 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                       ) 
                     
                     = 
                     
                       ( 
                       
                         
                           
                             
                               
                                 
                                   ( 
                                   
                                     u 
                                     1 
                                     
                                       ( 
                                       
                                         
                                           k 
                                           R 
                                         
                                         ⁢ 
                                         
                                           k 
                                           T 
                                         
                                       
                                       ) 
                                     
                                   
                                   ) 
                                 
                                 H 
                               
                               ⁢ 
                               vec 
                               ⁢ 
                               
                                 { 
                                 
                                   
                                     H 
                                     
                                       ( 
                                       
                                         
                                           k 
                                           R 
                                         
                                         ⁢ 
                                         
                                           k 
                                           T 
                                         
                                       
                                       ) 
                                     
                                   
                                   ⁡ 
                                   
                                     ( 
                                     t 
                                     ) 
                                   
                                 
                                 } 
                               
                             
                           
                         
                         
                           
                             ⋮ 
                           
                         
                         
                           
                             
                               
                                 
                                   ( 
                                   
                                     u 
                                     
                                       
                                         M 
                                         r 
                                       
                                       ⁢ 
                                       
                                         M 
                                         t 
                                       
                                     
                                     
                                       ( 
                                       
                                         
                                           k 
                                           R 
                                         
                                         ⁢ 
                                         
                                           k 
                                           T 
                                         
                                       
                                       ) 
                                     
                                   
                                   ) 
                                 
                                 H 
                               
                               ⁢ 
                               vec 
                               ⁢ 
                               
                                 { 
                                 
                                   
                                     H 
                                     
                                       ( 
                                       
                                         
                                           k 
                                           R 
                                         
                                         ⁢ 
                                         
                                           k 
                                           T 
                                         
                                       
                                       ) 
                                     
                                   
                                   ⁡ 
                                   
                                     ( 
                                     t 
                                     ) 
                                   
                                 
                                 } 
                               
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ) 
                 
               
             
           
         
       
     
     &lt;DC Remover  411 &gt; 
     DC remover  411  calculates DC-removed first vectors by removing, from the first vectors of the reception signals and the training signals shown in Expression 10, the DC components that are noise components not required for the estimation of living body  50 . DC remover  411  may store the calculated DC-removed first vectors in memory  41  or in the storage region of circuit  40 . 
     DC remover  411  removes the direct current (DC) components from the first vectors by, for example, a method shown in Expression 11. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       29 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       y 
                       
                         D 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         C 
                       
                       
                         ( 
                         
                           
                             k 
                             R 
                           
                           ⁢ 
                           
                             k 
                             T 
                           
                         
                         ) 
                       
                     
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         y 
                         
                           ( 
                           
                             
                               k 
                               R 
                             
                             ⁢ 
                             
                               k 
                               T 
                             
                           
                           ) 
                         
                       
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     - 
                     
                       
                         ∑ 
                         
                           k 
                           = 
                           0 
                         
                         
                           N 
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         
                           
                             y 
                             
                               ( 
                               
                                 
                                   k 
                                   R 
                                 
                                 ⁢ 
                                 
                                   k 
                                   T 
                                 
                               
                               ) 
                             
                           
                           ⁡ 
                           
                             ( 
                             k 
                             ) 
                           
                         
                         / 
                         N 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     11 
                   
                   ) 
                 
               
             
           
         
       
     
     &lt;Estimator  412 &gt; 
     Estimator  412  calculates correlation coefficients by removing the DC components from the first vectors calculated from the reception signals 
     
       
         
           
             
               
                 
                   
                     y 
                     
                       T 
                       L 
                     
                     
                       ( 
                       
                         
                           k 
                           R 
                         
                         ⁢ 
                         
                           k 
                           T 
                         
                       
                       ) 
                     
                   
                   ⁡ 
                   
                     ( 
                     t 
                     ) 
                   
                 
               
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                     ⁢ 
                     30 
                   
                   ] 
                 
               
             
           
         
       
     
     and the first vectors calculated from the training signals 
     
       
         
           
             
               
                 
                   
                     y 
                     
                       D 
                       L 
                     
                     
                       ( 
                       
                         
                           k 
                           R 
                         
                         ⁢ 
                         
                           k 
                           T 
                         
                       
                       ) 
                     
                   
                   ⁡ 
                   
                     ( 
                     t 
                     ) 
                   
                 
               
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                     ⁢ 
                     31 
                   
                   ] 
                 
               
             
           
         
       
     
     and then applying the following resultants to Expression 12: 
     
       
         
           
             
               
                 
                   
                     
                       y 
                       
                         D 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           C_T 
                           L 
                         
                       
                       
                         ( 
                         
                           
                             k 
                             R 
                           
                           ⁢ 
                           
                             k 
                             T 
                           
                         
                         ) 
                       
                     
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   , 
                   
                     
                       y 
                       
                         D 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           C_D 
                           L 
                         
                       
                       
                         ( 
                         
                           
                             k 
                             R 
                           
                           ⁢ 
                           
                             k 
                             T 
                           
                         
                         ) 
                       
                     
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                     ⁢ 
                     32 
                   
                   ] 
                 
               
             
           
         
       
     
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       33 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ρ 
                     ⁡ 
                     
                       ( 
                       
                         t 
                         , 
                         L 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             
                               ∑ 
                               
                                 k 
                                 = 
                                 0 
                               
                               
                                 
                                   N 
                                   T 
                                 
                                 - 
                                 1 
                               
                             
                             ⁢ 
                             
                               
                                 ∑ 
                                 
                                   
                                     k 
                                     T 
                                   
                                   = 
                                   0 
                                 
                                 
                                   K 
                                   T 
                                 
                               
                               ⁢ 
                               
                                 ∑ 
                                 
                                   
                                     k 
                                     R 
                                   
                                   = 
                                   1 
                                 
                                 
                                   K 
                                   R 
                                 
                               
                             
                           
                         
                       
                       
                         
                           
                              
                             
                               
                                 
                                   y 
                                   
                                     D 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       C_T 
                                       L 
                                     
                                   
                                   
                                     ( 
                                     
                                       
                                         k 
                                         R 
                                       
                                       ⁢ 
                                       
                                         k 
                                         T 
                                       
                                     
                                     ) 
                                   
                                 
                                 ⁡ 
                                 
                                   ( 
                                   k 
                                   ) 
                                 
                               
                               ⁢ 
                               
                                 
                                   ( 
                                   
                                     
                                       y 
                                       
                                         D 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         
                                           C_T 
                                           L 
                                         
                                       
                                       
                                         ( 
                                         
                                           
                                             k 
                                             R 
                                           
                                           ⁢ 
                                           
                                             k 
                                             T 
                                           
                                         
                                         ) 
                                       
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         k 
                                         + 
                                         
                                           
                                             F 
                                             s 
                                           
                                           ⁢ 
                                           t 
                                         
                                       
                                       ) 
                                     
                                   
                                   ) 
                                 
                                 * 
                               
                             
                              
                           
                         
                       
                     
                     
                       
                         
                           
                             
                               
                                 ∑ 
                                 
                                   k 
                                   = 
                                   0 
                                 
                                 
                                   
                                     N 
                                     T 
                                   
                                   - 
                                   1 
                                 
                               
                               ⁢ 
                               
                                 
                                   ∑ 
                                   
                                     
                                       k 
                                       T 
                                     
                                     = 
                                     0 
                                   
                                   
                                     K 
                                     T 
                                   
                                 
                                 ⁢ 
                                 
                                   ∑ 
                                   
                                     
                                       k 
                                       R 
                                     
                                     = 
                                     1 
                                   
                                   
                                     K 
                                     R 
                                   
                                 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   
                                     
                                       
                                          
                                         
                                           
                                             y 
                                             
                                               D 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               
                                                 C_T 
                                                 L 
                                               
                                             
                                             
                                               ( 
                                               
                                                 
                                                   k 
                                                   R 
                                                 
                                                 ⁢ 
                                                 
                                                   k 
                                                   T 
                                                 
                                               
                                               ) 
                                             
                                           
                                           ⁡ 
                                           
                                             ( 
                                             k 
                                             ) 
                                           
                                         
                                          
                                       
                                       2 
                                     
                                     ⁢ 
                                     
                                       
                                         ∑ 
                                         
                                           k 
                                           = 
                                           0 
                                         
                                         
                                           
                                             N 
                                             T 
                                           
                                           - 
                                           1 
                                         
                                       
                                       ⁢ 
                                       
                                         
                                           ∑ 
                                           
                                             
                                               k 
                                               T 
                                             
                                             = 
                                             0 
                                           
                                           
                                             K 
                                             T 
                                           
                                         
                                         ⁢ 
                                         
                                           ∑ 
                                           
                                             
                                               k 
                                               R 
                                             
                                             = 
                                             1 
                                           
                                           
                                             K 
                                             R 
                                           
                                         
                                       
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                        
                                       
                                         
                                           y 
                                           
                                             D 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             
                                               C_T 
                                               L 
                                             
                                           
                                           
                                             ( 
                                             
                                               
                                                 k 
                                                 R 
                                               
                                               ⁢ 
                                               
                                                 k 
                                                 T 
                                               
                                             
                                             ) 
                                           
                                         
                                         ⁡ 
                                         
                                           ( 
                                           
                                             k 
                                             + 
                                             
                                               
                                                 F 
                                                 s 
                                               
                                               ⁢ 
                                               t 
                                             
                                           
                                           ) 
                                         
                                       
                                        
                                     
                                     2 
                                   
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     12 
                   
                   ) 
                 
               
             
           
         
       
     
     Here, * represents complex conjugate. 
     Here, t represents the training data observation time, L represents a random eigenvalue number, NT represents the number of samples of test data reception signals, ND represents the number of samples of training signals, and FS represents the sampling frequency. 
     Here, Expression 13 and Expression 14 may be used to calculate correlation coefficients. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       34 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ρ 
                     ⁡ 
                     
                       ( 
                       
                         t 
                         , 
                         L 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             
                               ∑ 
                               
                                 
                                   k 
                                   T 
                                 
                                 = 
                                 0 
                               
                               
                                 K 
                                 T 
                               
                             
                             ⁢ 
                             
                               ∑ 
                               
                                 
                                   k 
                                   R 
                                 
                                 = 
                                 1 
                               
                               
                                 K 
                                 R 
                               
                             
                           
                         
                       
                       
                         
                           
                              
                             
                               
                                 ∑ 
                                 
                                   k 
                                   = 
                                   0 
                                 
                                 
                                   
                                     N 
                                     T 
                                   
                                   - 
                                   1 
                                 
                               
                               ⁢ 
                               
                                 
                                   
                                     y 
                                     
                                       D 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       
                                         C_T 
                                         L 
                                       
                                     
                                     
                                       ( 
                                       
                                         
                                           k 
                                           R 
                                         
                                         ⁢ 
                                         
                                           k 
                                           T 
                                         
                                       
                                       ) 
                                     
                                   
                                   ⁡ 
                                   
                                     ( 
                                     k 
                                     ) 
                                   
                                 
                                 ⁢ 
                                 
                                   
                                     ( 
                                     
                                       
                                         y 
                                         
                                           D 
                                           ⁢ 
                                           
                                               
                                           
                                           ⁢ 
                                           
                                             C_T 
                                             L 
                                           
                                         
                                         
                                           ( 
                                           
                                             
                                               k 
                                               R 
                                             
                                             ⁢ 
                                             
                                               k 
                                               T 
                                             
                                           
                                           ) 
                                         
                                       
                                       ⁡ 
                                       
                                         ( 
                                         
                                           k 
                                           + 
                                           
                                             
                                               F 
                                               s 
                                             
                                             ⁢ 
                                             t 
                                           
                                         
                                         ) 
                                       
                                     
                                     ) 
                                   
                                   * 
                                 
                               
                             
                              
                           
                         
                       
                     
                     
                       
                         
                           
                             
                               
                                 ∑ 
                                 
                                   k 
                                   = 
                                   0 
                                 
                                 
                                   
                                     N 
                                     T 
                                   
                                   - 
                                   1 
                                 
                               
                               ⁢ 
                               
                                 
                                   ∑ 
                                   
                                     
                                       k 
                                       T 
                                     
                                     = 
                                     0 
                                   
                                   
                                     K 
                                     T 
                                   
                                 
                                 ⁢ 
                                 
                                   ∑ 
                                   
                                     
                                       k 
                                       R 
                                     
                                     = 
                                     1 
                                   
                                   
                                     K 
                                     R 
                                   
                                 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   
                                     
                                       
                                          
                                         
                                           
                                             y 
                                             
                                               D 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               
                                                 C_T 
                                                 L 
                                               
                                             
                                             
                                               ( 
                                               
                                                 
                                                   k 
                                                   R 
                                                 
                                                 ⁢ 
                                                 
                                                   k 
                                                   T 
                                                 
                                               
                                               ) 
                                             
                                           
                                           ⁡ 
                                           
                                             ( 
                                             k 
                                             ) 
                                           
                                         
                                          
                                       
                                       2 
                                     
                                     ⁢ 
                                     
                                       
                                         ∑ 
                                         
                                           k 
                                           = 
                                           0 
                                         
                                         
                                           
                                             N 
                                             T 
                                           
                                           - 
                                           1 
                                         
                                       
                                       ⁢ 
                                       
                                         
                                           ∑ 
                                           
                                             
                                               k 
                                               T 
                                             
                                             = 
                                             0 
                                           
                                           
                                             K 
                                             T 
                                           
                                         
                                         ⁢ 
                                         
                                           ∑ 
                                           
                                             
                                               k 
                                               R 
                                             
                                             = 
                                             1 
                                           
                                           
                                             K 
                                             R 
                                           
                                         
                                       
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                        
                                       
                                         
                                           y 
                                           
                                             D 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             
                                               C_T 
                                               L 
                                             
                                           
                                           
                                             ( 
                                             
                                               
                                                 k 
                                                 R 
                                               
                                               ⁢ 
                                               
                                                 k 
                                                 T 
                                               
                                             
                                             ) 
                                           
                                         
                                         ⁡ 
                                         
                                           ( 
                                           
                                             k 
                                             + 
                                             
                                               
                                                 F 
                                                 s 
                                               
                                               ⁢ 
                                               t 
                                             
                                           
                                           ) 
                                         
                                       
                                        
                                     
                                     2 
                                   
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     13 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       35 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ρ 
                     ⁡ 
                     
                       ( 
                       
                         t 
                         , 
                         L 
                       
                       ) 
                     
                   
                   = 
                   
                     
                        
                       
                         
                           
                             
                               
                                 ∑ 
                                 
                                   
                                     k 
                                     T 
                                   
                                   = 
                                   0 
                                 
                                 
                                   K 
                                   T 
                                 
                               
                               ⁢ 
                               
                                 
                                   ∑ 
                                   
                                     
                                       k 
                                       R 
                                     
                                     = 
                                     0 
                                   
                                   
                                     K 
                                     R 
                                   
                                 
                                 ⁢ 
                                 
                                   ∑ 
                                   
                                     k 
                                     = 
                                     0 
                                   
                                   
                                     
                                       N 
                                       T 
                                     
                                     - 
                                     1 
                                   
                                 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   y 
                                   
                                     D 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       C_T 
                                       L 
                                     
                                   
                                   
                                     ( 
                                     
                                       
                                         k 
                                         R 
                                       
                                       ⁢ 
                                       
                                         k 
                                         T 
                                       
                                     
                                     ) 
                                   
                                 
                                 ⁡ 
                                 
                                   ( 
                                   k 
                                   ) 
                                 
                               
                               ⁢ 
                               
                                 
                                   ( 
                                   
                                     
                                       y 
                                       
                                         D 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         
                                           C_T 
                                           L 
                                         
                                       
                                       
                                         ( 
                                         
                                           
                                             k 
                                             R 
                                           
                                           ⁢ 
                                           
                                             k 
                                             T 
                                           
                                         
                                         ) 
                                       
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         k 
                                         + 
                                         
                                           
                                             F 
                                             s 
                                           
                                           ⁢ 
                                           t 
                                         
                                       
                                       ) 
                                     
                                   
                                   ) 
                                 
                                 * 
                               
                             
                           
                         
                       
                        
                     
                     
                       
                         
                           
                             
                               
                                 ∑ 
                                 
                                   k 
                                   = 
                                   0 
                                 
                                 
                                   
                                     N 
                                     T 
                                   
                                   - 
                                   1 
                                 
                               
                               ⁢ 
                               
                                 
                                   ∑ 
                                   
                                     
                                       k 
                                       T 
                                     
                                     = 
                                     0 
                                   
                                   
                                     K 
                                     T 
                                   
                                 
                                 ⁢ 
                                 
                                   ∑ 
                                   
                                     
                                       k 
                                       R 
                                     
                                     = 
                                     1 
                                   
                                   
                                     K 
                                     R 
                                   
                                 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   
                                     
                                       
                                          
                                         
                                           
                                             y 
                                             
                                               D 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               
                                                 C_T 
                                                 L 
                                               
                                             
                                             
                                               ( 
                                               
                                                 
                                                   k 
                                                   R 
                                                 
                                                 ⁢ 
                                                 
                                                   k 
                                                   T 
                                                 
                                               
                                               ) 
                                             
                                           
                                           ⁡ 
                                           
                                             ( 
                                             k 
                                             ) 
                                           
                                         
                                          
                                       
                                       2 
                                     
                                     ⁢ 
                                     
                                       
                                         ∑ 
                                         
                                           k 
                                           = 
                                           0 
                                         
                                         
                                           
                                             N 
                                             T 
                                           
                                           - 
                                           1 
                                         
                                       
                                       ⁢ 
                                       
                                         
                                           ∑ 
                                           
                                             
                                               k 
                                               T 
                                             
                                             = 
                                             0 
                                           
                                           
                                             K 
                                             T 
                                           
                                         
                                         ⁢ 
                                         
                                           ∑ 
                                           
                                             
                                               k 
                                               R 
                                             
                                             = 
                                             1 
                                           
                                           
                                             K 
                                             R 
                                           
                                         
                                       
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                        
                                       
                                         
                                           y 
                                           
                                             D 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             
                                               C_T 
                                               L 
                                             
                                           
                                           
                                             ( 
                                             
                                               
                                                 k 
                                                 R 
                                               
                                               ⁢ 
                                               
                                                 k 
                                                 T 
                                               
                                             
                                             ) 
                                           
                                         
                                         ⁡ 
                                         
                                           ( 
                                           
                                             k 
                                             + 
                                             
                                               
                                                 F 
                                                 s 
                                               
                                               ⁢ 
                                               t 
                                             
                                           
                                           ) 
                                         
                                       
                                        
                                     
                                     2 
                                   
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     14 
                   
                   ) 
                 
               
             
           
         
       
     
     Subsequently, estimator  412  calculates the maximum value in time t direction for each eigenvalue L as shown in Expression 15. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       36 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       ρ 
                       ⁡ 
                       
                         ( 
                         L 
                         ) 
                       
                     
                     max 
                   
                   = 
                   
                     max 
                     ⁡ 
                     
                       ( 
                       
                         ρ 
                         ⁡ 
                         
                           ( 
                           
                             t 
                             , 
                             L 
                           
                           ) 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     15 
                   
                   ) 
                 
               
             
           
         
       
     
     Subsequently, estimator  412  adds the maximum values of the respective eigenvalues for the number of the used eigenvalues as shown in Expression 16. Estimator  412  performs the process shown in Expression 16 for each item of training data stored, and estimates the training data that gives the largest S as a correct living body. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       37 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   S 
                   = 
                   
                     
                       ∑ 
                       
                         L 
                         = 
                         1 
                       
                       
                         L 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         ′ 
                       
                     
                     ⁢ 
                     
                       
                         ρ 
                         ⁡ 
                         
                           ( 
                           L 
                           ) 
                         
                       
                       max 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     16 
                   
                   ) 
                 
               
             
           
         
       
     
     Here, instead of using Expression 16, a coefficient may be applied to each eigenvalue as shown in Expression 17: 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       38 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   S 
                   = 
                   
                     
                       ∑ 
                       
                         L 
                         = 
                         1 
                       
                       
                         L 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         ′ 
                       
                     
                     ⁢ 
                     
                       
                         1 
                         
                           L 
                           α 
                         
                       
                       ⁢ 
                       
                         
                           ρ 
                           ⁡ 
                           
                             ( 
                             L 
                             ) 
                           
                         
                         max 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     17 
                   
                   ) 
                 
               
             
           
         
       
     
     Here, training data that is obtained by changing the orientations of the living body enables the estimation of the orientation of the living body. Meanwhile, training data on different living bodies that is recorded with the orientations of the living bodies fixed enables the identification of the living body. 
     As described above, estimation device  10 A shown in  FIG. 1  is capable of estimating living body  50  by circuit  40  that processes the reception signals received by transmitter-receivers  30 A to  30 H. 
     [Operation of Estimation Device  10 A] 
     The following describes an operation performed by estimation device  10 A with the above configuration.  FIG. 4  is a flowchart of an exemplary operation performed by estimation device  10 A according to the embodiment.  FIG. 5  is a flowchart of an operation performed by first vector calculator  410  of estimation device  10 A according to the embodiment.  FIG. 6  is a flowchart of an operation performed by estimator  412  of estimation device  10 A according to the embodiment. 
     First, estimation device  10 A transmits M transmission signals and receives N reception signals (S 10 ). More specifically, using the M transmission antenna elements, which is derived from (transmitter K T )×(the number of transmission antenna elements M t ), estimation device  10 A transmits first transmission signals to predetermined range A 1  that includes the first living body. Subsequently, using the reception antenna element of each of the N receivers, which is derived from (receiver K R )×(the number of reception antennas M r ), estimation device  10 A receives, over a predetermined period, first reception signals each including a reflection signal that is the first transmission signal reflected by the first living body. In the present embodiment, transmitter-receivers  30 A to  30 H cause antenna elements  31 A to  31 H to transmit transmission signals to predetermined range A 1  in a state that the first living body, which is living body  50  to be estimated, is located inside of predetermined range A 1 . 
     Using antenna elements  31 A to  31 H, transmitter-receivers  30 A to  30 H receive, over the predetermined period, first reception signals each including a reflection signal that is the first transmission signal reflected by the first living body. 
     Here,  FIG. 7  is a diagram showing the environment in which an estimation test was conducted using estimation device  10 A which is an example in the present embodiment.  FIG. 8  is a diagram showing exemplary propagation channels calculated from the reception signals received in the environment shown in  FIG. 7 . 
     As shown in  FIG. 7 , in the estimation test in the present embodiment, estimation device  10 A uses four transmitter-receivers that correspond to transmitter-receivers  30 B,  30 D,  30 F, and  30 H. Here, there may be eight receivers and transmitters as shown in  FIG. 1 , four receivers and transmitters, or any numbers greater than or equal to 2. 
     The four transmitter-receivers are disposed at the four vertices of a square with the side length of four meters (m), with test subject  50   a  located at the center. In the estimation test, test subject  50   a  corresponds to living body  50  to be estimated, i.e., the first living body. Also, four-element rectangular patch antennas are used as the reception antenna elements and the transmission antenna elements that correspond to antenna elements  31 B to  31 H. 
     More specifically, each of the eight reception antenna elements included in the four transmitter-receivers is a rectangular patch antenna located at the height of 0.9 m from the floor. Each of the eight transmission antenna elements included in the four transmitter-receivers is located one wavelength immediately above the microwaves of the corresponding reception antenna element. Here, the transmission antenna and the reception antenna may be a single antenna, or may be separately used. 
     Subsequently, estimation device  10 A calculates first vectors from the first reception signals obtained in step S 10  and training signals  42  stored in memory  41  (S 11 ). A detailed process included in step S 11  is shown in  FIG. 5 . 
     First, estimation device  10 A reads, from memory  41 , training signals  42 , which are (M×N) second reception signals obtained by the N receivers preliminarily receiving reflection signals that are the second transmission signals transmitted from the M transmission antenna elements to the second living body, which is known living body  50 , and reflected by the second living body. 
     Subsequently, estimation device  10 A calculates a second matrix each from the first reception signals obtained in step S 10  and training signals  42  read from memory  41  (S 20 ). 
     Then, estimation device  10 A performs eigenvalue decomposition on the second matrices (S 21 ), and reorders the resulting eigenvalues in descending order of diagonal elements to calculate first vectors (S 22 ). In the present embodiment, circuit  40  calculates the first vectors for both the first reception signals and training signals  42 . Note that the present description uses eigenvalue decomposition in step S 21 , but singular value decomposition may be performed on the second matrices to calculate first vectors on the basis of the resulting singular values. In this case, the first vectors may be calculated as singular vectors by reordering singular values in descending order, or as eigenvectors. 
     Returning to  FIG. 4 , estimation device  10 A then removes DC components from the first vectors of both the first reception signals and training signals  42  obtained in step S 11  (S 12 ). 
     Subsequently, estimation device  10 A estimates the living body, using the first vectors of both the first reception signals and training signals  42  from which DC components have been removed in step S 12  (S 13 ). A detailed process included in step S 13  is shown in  FIG. 6 . 
     Estimation device  10 A calculates a correlation coefficient for each eigenvalue, using the first vectors of both the first reception signals and training signals  42  (S 30 ).  FIG. 9  shows correlation coefficients calculated for the respective eigenvalues. The first vectors are reordered in descending order of eigenvalues, such as a first eigenvalue and a second eigenvalue. As such, it is known from  FIG. 9  that the degree of correlation is higher with a larger eigenvalue and lower with a smaller eigenvalue. 
     Subsequently, estimation device  10 A determines the maximum value in temporal direction for each eigenvalue, and further calculates a total sum of the maximum values of the respective eigenvalues for the number of the used eigenvalues determined by a predetermined method (S 31 ). Here, the number of the used eigenvalues may be, for example, on the order of two-thirds (⅔) of the total number of eigenvalues, such as eight and nine. Alternatively, eigenvalues may be selected which are greater than or equal to the average of correlation coefficients of the respective eigenvalues, or eigenvalues may be selected whose difference between the maximum and minimum values of the correlation coefficients is greater than or equal to a certain value. 
     Further, to calculate a total sum of the maximum values of the used eigenvalues, a total sum of the maximum values may be simply calculated or may be calculated using eigenvalues that have been sloped on eigenvalue basis. 
     Here, to slope eigenvalues on eigenvalue basis, slope coefficient α may be 1.7 or may be another coefficient.  FIG. 10  shows the result of estimating the orientations of three living bodies as test subjects in an estimation test conducted by estimation device  10 A shown in  FIG. 7 . The result shows that an average correctness is 75% or higher regardless of the positions where the three test subjects stand. 
     Subsequently, estimation device  10 A performs living body estimation (S 32 ). For the estimation of the orientation of a living body, estimation device  10 A measures a training signal for each orientation of the living body, and estimates that the orientation that corresponds to the largest maximum value among those of the used eigenvalues is the orientation of the living body. For living body identification, estimation device  10 A measures training signals in the same orientation that are located in a plurality of positions, measures a first signal of the second living body in the same orientation as the orientation in which the training signals have been obtained, calculates the maximum values of the used eigenvalues, and estimates that the training signal that corresponds to the largest maximum value among those of the used eigenvalues is the living body identified. At this time, the training signal that corresponds to the largest maximum value among the maximum values of the used eigenvalues may be estimated as the living body to be identified or the training signal that corresponds to an eigenvalue greater than or equal to a threshold may be estimated as the living body to be identified. 
     [Effect, Etc.] 
     In the environment used for a recognition test as shown in  FIG. 7 , estimation device  10 A as an example of the present disclosure transmits transmission waves from transmitters or the antenna elements of the receivers disposed, for example, at four positions around living body  50 , and receives reception signals. Subsequently, estimation device  10 A: calculates second matrices from the training signals stored in memory  41  and the reception signals from living body  50  to be authenticated, which is test subject  50   a ; performs eigenvalue decomposition; reorders the resulting eigenvalues in descending order; calculates a first vector for each of the eigenvalues; removes the DC components from the first vectors; and calculates a temporal correlation of the first vectors by sliding correlation calculation. 
     First vectors having larger eigenvalues include a larger number of living body components. As such, it is possible to raise the signal-to-noise ratio of the living body components by narrowing down eigenvalues to be used. 
     Here, when test subject  50   a  and known living body  50  included in a training signal match, i.e., when known living body  50  and test subject  50   a  are in the same orientation, or when known living body  50  and test subject  50   a  are the same person in the same orientation, the maximum value of the correlation coefficients of sliding correlation becomes large. Meanwhile, when test subject  50   a  and known living body  50  included in a training signal are different, i.e., when known living body  50  and test subject  50   a  are in different orientations, or when known living body  50  and test subject  50   a  are different persons in the same orientation, the maximum value of the correlation coefficients of sliding correlation becomes small. 
     With this, it is possible for estimation device  10 A to determine whether test subject  50   a  is in the same orientation as the orientation of known living body  50  included in a training signal, or whether test subject  50   a  and known living body  50  are the same living body, on the basis of the maximum value of the correlation coefficients calculated by sliding correlation calculation. 
     The reception signals obtained by the antenna elements of estimation device  10 A are DC-biased. The DC bias is vulnerable to an individual difference of estimation device  10 A and a delicate positional difference of living body  50 , thus affecting an estimation rate. In view of this, estimation device  10 A according to the present embodiment uses reception signals from which DC components have been removed to calculate a plurality of correlation coefficients. This improves the estimation rate. 
     As described above, estimation device  10 A according to the present embodiment is capable of calculating a first vector on an eigenvalue basis from the training signals and the first reception signals that are measurement signals obtained from the reception antenna elements disposed around the first living body, and calculating a plurality of correlation coefficients by use of a selected number of values to be used. With this, it is possible to estimate the orientation of the living body and identifying an individual even under a condition that the living body and the antennas are relatively distant from each other and the signal-to-noise ratio of the living components is poor. 
     Further, it is possible to authenticate the living body by estimating whether the first living body and the second living body included in training data are in the same orientation or whether the first living body and the second living body are the same person in the same orientation, depending on whether the maximum value of a plurality of correlation coefficients exceeds a threshold. 
     Also, estimation device  10 A according to the present embodiment removes the DC components from the first vectors by a predetermined method to calculate correlation coefficients. With this, it is possible to reduce from the reception signals the DC components, which are noise components not required for living body estimation, thus enabling the estimation of the living body to be effectively performed in a short time. 
     Further, estimation device  10 A according to the present embodiment is capable of estimating living body  50 , such as a person, by use of wireless signals such as microwaves. Stated differently, estimation device  10 A according to the present embodiment is capable of estimating living body  50  such as a person, without needing to analyze images captured by a camera, etc. This thus enables the estimation of a person, while protecting the privacy of such person. 
     Each of the elements in the foregoing embodiment may be configured in the form of an exclusive hardware product, or may be realized by executing a software program suitable for the element. Each of the elements may be realized by means of a program executing unit, such as a CPU and a processor, reading and executing the software program recorded on a recording medium such as a hard disk or a semiconductor memory. Here, the software program for realizing the estimation device and so forth according to the foregoing embodiment are a program described below. 
     Stated differently, such program is a program that causes a computer to execute an estimation method performed by an estimation device that identifies a living body or estimates an orientation of the living body, wherein the estimation device includes: M transmission antenna elements each transmitting a first transmission signal to a predetermined range that includes a first living body, where M is an integer greater than or equal to 1; N receivers disposed to surround the predetermined range, where N is an integer greater than or equal to 3, the N receivers each including a reception antenna element that receives, over a predetermined period, a first reception signal that is the first transmission signal reflected by the first living body; and a memory that stores training signals which are (M×N) second reception signals obtained by causing each of the N receivers to preliminarily receive a second reception signal that is a second transmission signal transmitted from each of the M transmission antenna elements and reflected by a second living body; wherein the estimation method includes: calculating a first vector for each of the training signals and (M×N) first reception signals by respective predetermined methods, the (M×N) first reception signals being obtained by the N receivers each receiving the first reception signal; and calculating a plurality of correlation coefficients from the first vectors and identifying the first living body or estimating an orientation of the first living body by a predetermined method, using the plurality of correlation coefficients calculated. 
     The estimation device and others according to one or more aspects of the present disclosure have been described above on the basis of the embodiment, but the present disclosure is not limited to the embodiment. The present disclosure also includes a variation achieved by making various modifications to the embodiment that can be conceived by those skilled in the art without departing from the essence of the present disclosure and an embodiment achieved by combining elements included in different embodiments. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable for use as an estimation device and an estimation method for estimating a living body by use of wireless signals. In particular, the present disclosure is applicable for use as: an estimation device included in a home appliance that performs control in accordance with a living body, a surveillance device that detects the intrusion of a living body, and so forth; and an estimation method. 
     REFERENCE SIGNS LIST 
     
         
           10 A estimation device 
           30 A- 30 H transmitter-receiver 
           31 A- 31 H antenna element 
           40  circuit 
           41  memory 
           42  training signal 
           50  living body 
           50   a  test subject 
           410  first vector calculator 
           411  DC remover 
           412  estimator