Biological information detection system, biological information detection method, and program

Abstract

Provided are a biological information generation system, a biological information generation method, and a program that make it possible to accurately measure biological information such as the respiration rate and heart rate of a subject. A Doppler sensor control unit (30) controls the position of a Doppler sensor (15) such that the Doppler sensor (15) is disposed at one of a plurality of predetermined candidate positions. A reliability calculation unit (36) calculates, for at least one candidate position, the reliability of biological information obtained from Doppler data indicating a measurement result measured by the Doppler sensor (15) disposed at the candidate position, on the basis of the Doppler data. A determination unit (38) determines the measurement position from among the plurality of candidate positions on the basis of the reliability calculated for the at least one candidate position. The biological information generation unit (40) repeatedly executes processing for generating biological information of the measurement subject on the basis of Doppler data indicating a measurement result measured by the Doppler sensor (15) disposed at the measurement position.

Description

Title of Invention: BIOLOGICAL INFORMATION DETECTION SYSTEM, BIOLOGICAL INFORMATION DETECTION METHOD, AND PROGRAM Technical Field The present invention relates to a biological information detection system, a biological information detection method, and a program, and more particularly, to a system for detecting biological information of a person to be measured based on a Doppler signal. Background Art Various systems for measuring biological information, such as a respiratory rate or a heart rate, of a person to be measured who is on a bed have been considered. To give an example of such systems, in Patent Literature 1, there is described a sensor system which performs non-contact sensing of biological information by a plurality of Doppler sensors attached to a bed. In addition, in Patent Literature 2, there is described a monitoring system which determines whether respiration or a pulse deviates from a normal state based on information acquired from a Doppler sensor arranged below a bed or on a ceiling. Citation List Patent Literature [Patent Literature 1] JP 2020-18861 A [Patent Literature 2] JP 2020-113016 A Summary of Invention Technical Problem In the technologies as described in Patent Literature 1 and Patent Literature 2, the Doppler sensor is fixed, and hence the biological information, such as the respiratory rate or the heart rate, of the person to be measured may fail to be accurately measured depending on a position and a posture of the person to be measured. The present invention has been made in view of the abovementioned problem, and has an object to provide a biological information detection system, a biological information detection method, and a program with which biological information, such as a respiratory rate or a heart rate, of a person to be measured is measurable with accuracy. Solution to Problem (1) According to one embodiment of the present invention, there is provided a biological information detection system including: Doppler sensor control means for controlling a position of a Doppler sensor such that the Doppler sensor is arranged at any one of a plurality of candidate positions determined in advance; reliability level calculation means for calculating, for at least one of the plurality of candidate positions, based on Doppler data indicating a measurement result obtained by the Doppler sensor arranged at candidate position, a reliability level of biological information obtained from the Doppler data; measurement position determination means for determining a measurement position from among the plurality of candidate positions based on the reliability level calculated for the at least one of the plurality of candidate positions; and biological information generation means for repeatedly executing processing of generating the biological information of a person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor arranged at the measurement position. (2) The biological information detection system according to Item (1) may further include measurement condition determination means for determining whether the calculated reliability level satisfies a given measurement condition, the biological information detection system may be configured to repeatedly cause the measurement condition determination means to determine whether the calculated reliability level satisfies the given measurement condition, and cause the Doppler sensor control means to move the Doppler sensor to another of the plurality of candidate positions in response to the calculated reliability level failing to satisfy the given measurement condition, until the calculated reliability level satisfies the given measurement condition, and the measurement position determination means may be configured to determine, as the measurement position, one of the plurality of candidate positions at which the calculated reliability level satisfies the given measurement condition. (3) In the biological information detection system according to Item (1), the reliability level calculation means may be configured to calculate the reliability level for each of all the plurality of candidate positions, and the measurement position determination means may be configured to determine, as the measurement position, one of the plurality of candidate positions having the highest calculated reliability level. (4) The biological information detection system according to any one of Items (1) to (3) may further include change condition determination means for determining whether the reliability level of the latest generated biological information satisfies a given change condition in a situation in which the processing of generating the biological information of the person to be measured is repeatedly executed, and the Doppler sensor control means may be configured to change the position of the Doppler sensor in response to the reliability level of the latest biological information satisfying the given change condition. (5) In the biological information detection system according to any one of Items (1) to (3), for each of a plurality of Doppler sensors, a plurality of the candidate positions associated with the each of the plurality of Doppler sensors may be determined in advance, the Doppler sensor control means may be configured to control, for each of the plurality of Doppler sensors, the position of the Doppler sensor such that the Doppler sensor is arranged at any one of the plurality of the candidate positions associated with the Doppler sensor, the measurement position determination means may be configured to determine a measurement Doppler sensor from among the plurality of Doppler sensors and determine the measurement position from among the plurality of the candidate positions associated with the measurement Doppler sensor, and the biological information generation means may be configured to repeatedly execute the processing of generating the biological information based on the Doppler data indicating the measurement result obtained by the measurement Doppler sensor arranged at the measurement position. (6) The biological information detection system according to Item (5) may further include change condition determination means for determining whether the reliability level of the latest generated biological information satisfies a given change condition in a situation in which the processing of generating the biological information of the person to be measured is repeatedly executed, the measurement position determination means may be configured to re-determine, when the reliability level of the latest biological information satisfies the given change condition, the measurement Doppler sensor from among the plurality of Doppler sensors and re-determine the measurement position from among the plurality of candidate positions associated with the measurement Doppler sensor, and the biological information generation means may be configured to repeatedly execute, after the measurement Doppler sensor and the measurement position are re-determined, the processing of generating the biological information based on the Doppler data indicating the measurement result obtained by the re-determined measurement Doppler sensor arranged at the re-determined measurement position. (7) In the biological information detection system according to Item (6), the measurement position determination means may be configured to determine a heart rate Doppler sensor from among the plurality of Doppler sensors and determine a heart rate measurement position from among the plurality of the candidate positions associated with the heart rate Doppler sensor, the measurement position determination means may be configured to determine a respiratory rate Doppler sensor from among the plurality of Doppler sensors and determine a respiratory rate measurement position from among the plurality of the candidate positions associated with the respiratory rate Doppler sensor, the respiratory rate Doppler sensor may be a Doppler sensor different from the heart rate Doppler sensor, the biological information generation means may be configured to repeatedly execute processing of generating a heart rate of the person to be measured based on the Doppler data indicating the measurement result obtained by the heart rate Doppler sensor arranged at the heart rate measurement position, and the biological information generation means may be configured to repeatedly execute processing of generating a respiratory rate of the person to be measured based on the Doppler data indicating the measurement result obtained by the respiratory rate Doppler sensor arranged at the respiratory rate measurement position. (8) The biological information detection system according to Item (7) may further include: heart rate measurement change condition determination means for determining whether the reliability level of the latest generated heart rate satisfies a given heart rate measurement change condition; and respiratory rate measurement change condition determination means for determining whether the reliability level of the latest generated respiratory rate satisfies a given respiratory rate measurement change condition, the measurement position determination means may be configured to re-determine the heart rate Doppler sensor from among the Doppler sensors other than the respiratory rate Doppler sensor and re-determine the heart rate measurement position from among the plurality of the candidate positions associated with the heart rate Doppler sensor when the reliability level of the latest heart rate satisfies the given heart rate measurement change condition, the measurement position determination means may be configured to re-determine the respiratory rate Doppler sensor from among the Doppler sensors other than the heart rate Doppler sensor and redetermine the respiratory rate measurement position from among the plurality of the candidate positions associated with the respiratory rate Doppler sensor when the reliability level of the latest respiratory rate satisfies the given respiratory rate measurement change condition, the biological information generation means may be configured to repeatedly execute, after the heart rate Doppler sensor and the heart rate measurement position are re-determined, the processing of generating the heart rate based on the Doppler data indicating the measurement result obtained by the re-determined heart rate Doppler sensor arranged at the re-determined heart rate measurement position, and the biological information generation means may be configured to repeatedly execute, after the respiratory rate Doppler sensor and the respiratory rate measurement position are re-determined, the processing of generating the respiratory rate based on the Doppler data indicating the measurement result obtained by the re-determined respiratory rate Doppler sensor arranged at the re-determined respiratory rate measurement position. (9) The biological information detection system according to any one of Items (5) to (8) may further include Doppler sensor selection means for selecting, from among the plurality of Doppler sensors, a plurality of Doppler sensors based on a position of the person to be measured, and the measurement position determination means may be configured to determine the measurement Doppler sensor from among the selected plurality of Doppler sensors. (10) In the biological information detection system according to any one of Items (1) to (9), the Doppler sensor control means may be configured to control an orientation of the Doppler sensor such that an emission direction of a microwave is any one of a plurality of candidate directions determined in advance, the reliability level calculation means may be configured to calculate, for at least one of the plurality of candidate directions, a reliability level of the biological information obtained from the Doppler data based on the Doppler data indicating the measurement result obtained by the Doppler sensor emitting the microwave in the candidate direction, the biological information detection system may further include measurement direction determination means for determining a measurement direction from among the plurality of candidate directions based on the reliability level calculated for the at least one of the plurality of candidate directions, and the biological information generation means may be configured to generate the biological information of the person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor controlled such that the emission direction of the microwave is the measurement direction. (11) In the biological information detection system according to any one of Items (1) to (10), the Doppler sensor control means may be configured to control the Doppler sensor such that an emission polarization plane direction of a microwave is any one of a plurality of candidate polarization plane directions determined in advance, the reliability level calculation means may be configured to calculate, for the at least one of the plurality of candidate polarization plane directions, a reliability level of the biological information obtained from the Doppler data based on the Doppler data indicating the measurement result obtained by the Doppler sensor emitting the microwave having the candidate polarization plane direction as the emission polarization plane direction, the biological information detection system may further include measurement polarization plane direction determination means for determining a measurement polarization plane direction from among the plurality of candidate polarization plane directions based on the reliability level calculated for the at least one of the plurality of candidate polarization plane directions, and the biological information generation means may be configured to generate the biological information of the person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor controlled such that the emission polarization plane direction of the microwave is the measurement polarization plane direction. (12) The biological information detection system according to any one of Items (1) to (11) may further include body movement determination means for determining whether a body movement of the person to be measured has occurred, and the biological information generation means may be configured to suspend generation of the biological information in response to determining that the body movement of the person to be measured has occurred, and in a situation in which the generation of the biological information is suspended, resume the generation of the biological information in response to determining that the body movement of the person to be measured has not occurred. (13) The biological information detection system according to any one of Items (1) to (12) may further include frequency spectrum generation means for generating a frequency spectrum based on the Doppler data, and the reliability level calculation means may be configured to calculate, as the reliability level, an amplitude ratio between a largest peak and a second largest peak included in the frequency spectrum. (14) According to one embodiment of the present invention, there is provided a biological information detection method including the steps of: controlling a position of a Doppler sensor such that the Doppler sensor is arranged at any one of a plurality of candidate positions determined in advance; calculating, for at least one of the plurality of candidate positions, based on Doppler data indicating a measurement result obtained by the Doppler sensor arranged at the candidate position, a reliability level of biological information obtained from the Doppler data; determining a measurement position from among the plurality of candidate positions based on the reliability level calculated for the at least one of the plurality of candidate positions; and repeatedly executing processing of generating the biological information of a person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor arranged at the measurement position. (15) According to one embodiment of the present invention, there is provided a program for causing a computer to execute the steps of: controlling a position of a Doppler sensor such that the Doppler sensor is arranged at any one of a plurality of candidate positions determined in advance; calculating, for at least one of the plurality of candidate positions, based on Doppler data indicating a measurement result obtained by the Doppler sensor arranged at the candidate position, a reliability level of biological information obtained from the Doppler data; determining a measurement position from among the plurality of candidate positions based on the reliability level calculated for the at least one of the plurality of candidate positions; and repeatedly executing processing of generating the biological information of a person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor arranged at the measurement position. The program may be stored in a computer-readable information storage medium. Advantageous Effects of Invention According to the present invention, the biological information, such as a respiratory rate or a heart rate, of the person to be measured is measurable with accuracy. Brief Description of Drawings FIG. 1 is a configuration diagram of a biological information detection system according to an embodiment of the present invention. FIG. 2A is a diagram for schematically illustrating an example of a Doppler sensor illustrated in FIG. 1. FIG. 2B is a diagram for schematically illustrating the example of the Doppler sensor illustrated in FIG. 1. FIG. 2C is a diagram for schematically illustrating the example of the Doppler sensor illustrated in FIG. 1. FIG. 2D is a diagram for schematically illustrating the example of the Doppler sensor illustrated in FIG. 1. FIG. 2E is a diagram for schematically illustrating the example of the Doppler sensor illustrated in FIG. 1. FIG. 2F is a diagram for schematically illustrating the example of the Doppler sensor illustrated in FIG. 1. FIG. 3 is a functional block diagram of a computer in the embodiment of the present invention. FIG. 4 is a graph for showing an example of a frequency spectrum. FIG. 5 is a diagram for illustrating an example of estimation of a position of a person to be measured. FIG. 6A is a flow chart for illustrating an example of a flow of processing performed by the computer in the embodiment of the present invention. FIG. 6B is a flow chart for illustrating the example of the flow of the processing performed by the computer in the embodiment of the present invention. FIG. 7 is a flow chart for illustrating an example of a flow of processing performed by the computer in the embodiment of the present invention. Description of Embodiments Now, an embodiment of the present invention is described in detail with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a biological information detection system 1 according to the embodiment of the present invention. As illustrated in the figure, the biological information detection system 1 includes a computer 10, a Doppler sensor unit 12, and a plurality of load sensors 14. The Doppler sensor unit 12 includes a plurality of Doppler sensors 15 (see FIG. 2A to FIG. 2F). Here, the Doppler sensor unit 12 includes, for example, six Doppler sensors 15. Further, the biological information detection system 1 includes four load sensors 14 (14a to 14d). In this embodiment, a ball screw 18 is attached to a headboard of a bed 16, and the Doppler sensor 15 is supported by the ball screw 18 (see FIG. 2A to FIG. 2F). In this embodiment, the ball screw 18 is arranged to extend in an up-down direction along a headboard surface of the bed 16. The Doppler sensor 15 is movable along the headboard surface of the bed 16. That is, the Doppler sensor 15 is movable in the up-down direction along an extending direction of the ball screw 18. The up-down direction along the headboard surface may be a substantially vertical direction. In this embodiment, for example, any one of the Doppler sensors 15 emits a microwave toward a heart of a person to be measured sleeping on the bed 16, the microwave is reflected by the heart of the person to be measured, and each Doppler sensor 15 receives the reflected wave. Then, the Doppler sensor 15 generates a Doppler signal indicating a movement of the heart accompanying a heartbeat from the reflected wave, and outputs Doppler data obtained by digitizing the Doppler signal. With the Doppler effect, the reflected wave is shifted in frequency, and a heart rate of the person to be measured can be obtained by observing the frequency shift. Further, any one of the Doppler sensors 15 emits a microwave toward a chest of the person to be measured sleeping on the bed 16, the microwave is reflected by the chest of the person to be measured, and each Doppler sensor 15 receives the reflected wave. The Doppler sensor 15 generates a Doppler signal indicating a movement of the chest accompanying respiration from the reflected wave, and outputs Doppler data obtained by digitizing the Doppler signal. With the Doppler effect, the reflected wave is shifted in frequency, and a respiratory rate of the person to be measured can be obtained by observing the frequency shift. The reflected wave is detected by quadrature detection as a Doppler signal including an I signal being an in-phase component with respect to the transmitted wave and a Q signal being a quadrature component with respect to the transmitted wave, and is output to the computer 10 in a digital form. The Doppler signal input to the computer 10 is time-series data, and indicates an amplitude at each time (I component and Q component). In this embodiment, the Doppler sensor 15 that measures the heart rate and the Doppler sensor 15 that measures the respiratory rate may be separate Doppler sensors 15, or the Doppler sensor 15 that measures the heart rate and the Doppler sensor 15 that measures the respiratory rate may be the same Doppler sensor 15. For example, when the heart rate is accurately measured in a predetermined frequency range (for example, near 1.25 Hz) associated with the heart rate and the respiratory rate is accurately measured in a predetermined frequency range (for example, near 0.3 Hz) associated with the respiratory rate based on a measurement result obtained by a certain Doppler sensor 15, both the measurement of the heart rate and the measurement of the respiratory rate may be performed by the Doppler sensor 15. The load sensor 14 is located below a position of the person to be measured in a situation in which the person to be measured is on the bed 16. As illustrated in FIG. 1, the load sensor 14 may be provided on each of four legs of the bed 16. Each load sensor 14 outputs load data indicating a measurement result of a load applied to the load sensor 14. The computer 10 may be formed of a publicly-known computer including, for example, a CPU, a memory, an input device, and a display. Further, the computer 10 generates the biological information (here, for example, heart rate and respiratory rate) of the person to be measured based on the Doppler signal output from each Doppler sensor 15. Further, the biological information detection system 1 according to this embodiment includes 18 stepping motors 20 that operate in accordance with a control signal received from the computer 10. Six stepping motors 20a among the 18 stepping motors 20 are connected to the mutually different ball screws 18, respectively. The stepping motor 20a connected to the ball screw 18 moves the Doppler sensor 15 in the up-down direction by controlling rotation of the ball screw 18. Six stepping motors 20b among the 18 stepping motors 20 are provided in housings of the Doppler sensors 15, respectively. The stepping motor 20b provided in the housing of the Doppler sensor 15 controls rotation of the Doppler sensor 15 in one direction (for example, the up-down direction). Six stepping motors 20c among the 18 stepping motors 20 are connected to antennas included in the Doppler sensors 15, respectively. The stepping motor 20c connected to the antenna can control an orientation of the antenna. FIG. 3 is a functional block diagram of the computer 10 in the embodiment of the present invention. As illustrated in the figure, the computer 10 includes a Doppler sensor control module 30, a Doppler data acquisition module 32, a frequency spectrum generation module 34, a reliability level calculation module 36, a determination module 38, a biological information generation module 40, a biological information storage module 42, a change condition determination module 44, a load data acquisition module 46, a body movement determination module 48, a personto-be-measured position estimation module 50, and a Doppler sensor selection module 52. Those functional blocks are implemented by executing a signal processing program and a control program in the computer 10. The signal processing program and the control program may be stored in various computer-readable information storage media such as a semiconductor memory, and loaded into the computer 10 from the media. In another case, the programs may be downloaded onto the computer 10 through a data communication line such as the Internet. The Doppler sensor control module 30 controls a position of the Doppler sensor 15 such that the Doppler sensor 15 is arranged at any one of a plurality of candidate positions determined in advance, for example. Here, for each of the plurality of (for example, six) Doppler sensors 15, a plurality of candidate positions associated with the Doppler sensor 15 may be determined in advance. Then, the Doppler sensor control module 30 may control the position of each of the plurality of Doppler sensors 15 such that the Doppler sensor 15 is arranged at any one of the plurality of candidate positions associated with the Doppler sensor 15. For example, the Doppler sensor control module 30 outputs a control signal corresponding to a target position of the Doppler sensor 15 connected to the ball screw 18, to the stepping motor 20a connected to the ball screw 18. The ball screw 18 may rotate with the stepping motor 20a rotating in accordance with the control signal, and as a result, the Doppler sensor 15 may be arranged at the target position. For example, the plurality of candidate positions may be determined in advance at intervals of five centimeters along the extending direction (for example, the up-down direction) of the ball screw 18. The Doppler sensor 15 may be arranged at any one of the candidate positions set at intervals of five centimeters. As another example, a predetermined number of (for example, three) heights such as a first height, a second height, and a third height in descending order of height may be determined in advance. In this case, a position at the first height, a position at the second height, and a position at the third height correspond to the plurality of candidate positions, respectively. The Doppler sensor 15 may be controlled to be located at any one of the first height, the second height, or the third height. FIG. 2A is an illustration of an example of a state in which the Doppler sensor 15 is controlled to be located at the first height. FIG. 2B is an illustration of an example of a state in which the Doppler sensor 15 is controlled to be located at the second height. FIG. 2C is an illustration of an example of a state in which the Doppler sensor 15 is controlled to be located at the third height. Here, any one of the candidate positions may also be at a height of 300 mm above a surface of a mattress placed on the bed 16. Further, in this embodiment, threshold values (for example, an upper limit and a lower limit of the height) may be set for a position at which the Doppler sensor 15 can be arranged. In addition, the Doppler sensor 15 may be arranged in a range not exceeding the threshold values (a range equal to or more than the lower limit and equal to or less than the upper limit). The Doppler sensor control module 30 may also control an orientation of the Doppler sensor 15 such that an emission direction of a microwave is any one of a plurality of candidate directions determined in advance. Here, for each of the plurality of (for example, six) Doppler sensors 15, a plurality of candidate directions associated with the Doppler sensor 15 may be determined in advance. Then, the Doppler sensor control module 30 may control the orientation of each of the plurality of Doppler sensors 15 such that the emission direction of the microwave is any one of the plurality of candidate directions associated with the Doppler sensor 15. For example, the Doppler sensor control module 30 outputs a control signal corresponding to a target emission direction of the microwave emitted by the Doppler sensor 15 to the stepping motor 20b provided in the housing of the Doppler sensor 15. Then, with the stepping motor 20b rotating in accordance with the control signal, the emission direction of the microwave emitted by the Doppler sensor 15 may become the target emission direction. For example, as illustrated in FIG. 2A, FIG. 2D, FIG. 2E, and FIG. 2F, it may be possible to perform orientation control of the Doppler sensor 15 such that the emission direction of the microwave emitted by the Doppler sensor 15 is oriented in any one of a front direction (see FIG. 2A), a direction downward by 10 degrees with respect to the front direction (see FIG. 2D), a direction downward by 20 degrees with respect to the front direction (see FIG. 2E), or a direction downward by 30 degrees with respect to the front direction (see FIG. 2F). In this case, the front direction, the direction downward by 10 degrees with respect to the front direction, the direction downward by 20 degrees with respect to the front direction, and the direction downward by 30 degrees with respect to the front direction correspond to the plurality of candidate directions, respectively. Further, the Doppler sensor control module 30 may control the Doppler sensor 15 such that a polarization plane direction of an emitted microwave (hereinafter referred to as "emission polarization plane direction of the microwave") is any one of a plurality of candidate polarization plane directions determined in advance. Here, for each of the plurality of (for example, six) Doppler sensors 15, a plurality of candidate polarization plane directions associated with the Doppler sensor 15 may be determined in advance. Then, the Doppler sensor control module 30 may control each of the plurality of Doppler sensors 15 such that the emission polarization plane direction of the microwave is any one of the plurality of candidate polarization plane directions associated with the Doppler sensor 15. For example, the Doppler sensor control module 30 outputs a control signal corresponding to a target emission polarization plane direction of the microwave emitted by the Doppler sensor 15 to the stepping motor 20c connected to the antenna included in the Doppler sensor 15. Then, the antenna may rotate with the stepping motor 20c rotating in accordance with the control signal, and as a result, the emission polarization plane direction of the microwave emitted by the Doppler sensor 15 may become the target emission polarization plane direction. Here, for example, the Doppler sensor 15 may be controlled such that the emission polarization plane direction is any one of a horizontal direction (0 degrees) or a vertical direction (90 degrees). In this case, the horizontal direction and the vertical direction correspond to the plurality of emission polarization plane directions, respectively. In this embodiment, the position of the Doppler sensor 15 (the height in the above-mentioned example), the emission direction of the microwave emitted by the Doppler sensor 15, and the emission polarization plane direction of the microwave emitted by the Doppler sensor 15 described above can be independently controlled for each of the six Doppler sensors 15. The Doppler data acquisition module 32 acquires, for each of the six Doppler sensors 15, Doppler data indicating a measurement result obtained by the Doppler sensor 15 in a certain period. The frequency spectrum generation module 34 generates a frequency spectrum based on the Doppler data acquired by the Doppler data acquisition module 32, for example. FIG. 4 shows an example of the generated frequency spectrum. The frequency spectrum generation module 34 executes, for example, fast Fourier transform (FFT) on Doppler data input thereto, to thereby convert the Doppler data into a frequency spectrum. Here, data of the I signal and data of the Q signal may each be converted into a frequency spectrum, for example. For example, the reliability level calculation module 36 calculates, for at least one candidate position, a reliability level of the biological information obtained from the Doppler sensor 15 based on the Doppler data indicating the measurement result obtained by the Doppler sensor 15 arranged at the candidate position. The reliability level calculation module 36 may calculate, for at least one candidate direction, the reliability level of the biological information obtained from the Doppler sensor 15 based on the Doppler data indicating the measurement result obtained by the Doppler sensor 15 emitting the microwave in the candidate direction. The reliability level calculation module 36 may calculate, for at least one candidate polarization plane direction, the reliability level of the biological information obtained from the Doppler sensor 15 based on the Doppler data indicating the measurement result obtained by the Doppler sensor 15 emitting the microwave having the candidate polarization plane direction as the emission polarization plane direction. As described above, when there are three degrees of freedom of the position, the emission direction, and the emission polarization plane direction for each Doppler sensor 15, the reliability level associated with a combination of a certain Doppler sensor 15, a certain position, a certain emission direction, and a certain emission polarization plane direction may be calculated based on the Doppler data indicating the measurement result of the certain Doppler sensor 15 in a case in which the microwave having the certain emission polarization plane direction is emitted in the certain emission direction from the certain Doppler sensor 15 arranged at the certain position. Here, for example, the reliability level calculation module 36 may calculate an amplitude at a largest peak and an amplitude at a second largest peak included in the frequency spectrum generated based on the Doppler data. In the example of FIG. 4, a largest peak P1 and a second largest peak P2 are shown. Then, the reliability level calculation module 36 may calculate, as the reliability level, an amplitude ratio between the amplitude at the largest peak P1 and the amplitude at the second largest peak P2 included in the frequency spectrum, that is, an amplitude ratio obtained by dividing the amplitude at the largest peak P1 by the amplitude at the second largest peak P2. The determination module 38 determines, from among a plurality of candidate positions, a measurement position that is the position of the Doppler sensor 15 when the biological information is generated, based on the reliability level calculated for at least one candidate position, for example. Here, the determination module 38 may determine a measurement Doppler sensor from among the plurality of Doppler sensors 15, and determine the measurement position from among a plurality of candidate positions associated with the measurement Doppler sensor. Further, the determination module 38 may determine, from among the plurality of candidate directions, a measurement direction that is an emission direction of a microwave when the biological information is generated, based on the reliability level calculated for at least one candidate direction. Further, the determination module 38 may determine a measurement polarization plane direction that is an emission polarization plane direction of a microwave when the biological information is generated from among a plurality of candidate polarization plane directions based on the reliability level calculated for at least one candidate polarization plane direction. Details of the determination of the measurement position, the measurement direction, and the measurement polarization plane direction are described later. Further, in this embodiment, a heart rate Doppler sensor for measuring a heart rate and a respiratory rate Doppler sensor for measuring a respiratory rate may be determined. Here, as described above, the heart rate Doppler sensor may be the same Doppler sensor 15 as the respiratory rate Doppler sensor, or may be a Doppler sensor 15 different from the respiratory rate Doppler sensor. Then, a heart rate measurement position may be determined from among a plurality of candidate positions associated with the heart rate Doppler sensor. Further, a heart rate measurement direction may be determined from among a plurality of candidate directions associated with the heart rate Doppler sensor. Further, a heart rate measurement polarization plane direction may be determined from among a plurality of candidate polarization plane directions associated with the heart rate Doppler sensor. Then, a respiratory rate measurement position may be determined from among a plurality of candidate positions associated with the respiratory rate Doppler sensor. Further, a respiratory rate measurement direction may be determined from among a plurality of candidate directions associated with the respiratory rate Doppler sensor. Further, a respiratory rate measurement polarization plane direction may be determined from among a plurality of candidate polarization plane directions associated with the respiratory rate Doppler sensor. The biological information generation module 40 generates biological information of the person to be measured based on Doppler data indicating a measurement result obtained by the Doppler sensor 15 arranged at the measurement position, for example. Here, the biological information generation module 40 may repeatedly execute processing of generating the biological information of the person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor 15 arranged at the measurement position. Further, the biological information generation module 40 may repeatedly execute processing of generating the biological information based on the Doppler data indicating the measurement result obtained by the measurement Doppler sensor arranged at the measurement position. For example, processing of generating the heart rate of the person to be measured based on the Doppler data indicating the measurement result obtained by the heart rate Doppler sensor arranged at the heart rate measurement position may be repeatedly executed. Further, processing of generating the respiratory rate of the person to be measured based on the Doppler data indicating the measurement result obtained by the respiratory rate Doppler sensor arranged at the respiratory rate measurement position may be repeatedly executed. For example, in response to determination of the measurement Doppler sensor, the measurement position, the measurement direction, and the measurement polarization plane direction, acquisition of the Doppler data in a certain period, generation of the frequency spectrum based on the Doppler data, and generation of the biological information associated with the period based on the frequency spectrum may be repeatedly executed. For example, the biological information generation module 40 identifies a spectrum peak in a first frequency range (for example, near 0.3 Hz) corresponding to respiration in the frequency spectrum based on the Doppler data indicating the measurement result obtained by the respiratory rate Doppler sensor, and calculates the respiratory rate from a frequency corresponding to the peak. For example, the biological information generation module 40 may calculate the respiratory rate per minute by multiplying the frequency (in Hertz) of the spectrum peak by 60. Further, for example, the biological information generation module 40 identifies a spectrum peak in a second frequency range (for example, near 1.25 Hz) corresponding to the heartbeat in the frequency spectrum based on the Doppler data indicating the measurement result obtained by the heart rate Doppler sensor, and calculates the heart rate from a frequency corresponding to the peak. For example, the biological information generation module 40 may calculate the heart rate per minute by multiplying the frequency (in Hertz) of the spectrum peak by 60. The respiratory rate and the heart rate calculated in this manner are stored in the biological information storage module 42. In this manner, time-series data of the respiratory rate and the heart rate is stored in the biological information storage module 42. For example, the change condition determination module 44 determines whether a reliability level of the latest generated biological information satisfies a given change condition in a situation in which the processing of generating the biological information of the person to be measured is repeatedly executed. Here, whether the change condition is satisfied may be determined for each of the heart rate and the respiratory rate. That is, the change condition determination module 44 may determine whether a reliability level of the latest generated heart rate satisfies a given heart rate measurement change condition. Further, the change condition determination module 44 may determine whether a reliability level of the latest generated respiratory rate satisfies a given respiratory rate measurement change condition. As an example of the change condition, there is a condition that the reliability level becomes equal to or less than a predetermined threshold value. Here, a threshold value relating to the heart rate measurement change condition and a threshold value relating to the respiratory rate measurement change condition may be the same or different. Then, in response to the reliability level of the latest biological information satisfying the change condition, for example, the determination module 38 re-determines the measurement position from among the plurality of candidate positions, and the Doppler sensor control module 30 changes the position of the Doppler sensor 15 to the measurement position re-determined from among the plurality of candidate positions. Here, in response to the reliability level of the latest biological information satisfying the change condition, the determination module 38 may re-determine the measurement Doppler sensor from among the plurality of Doppler sensors 15, and redetermine the measurement position from among a plurality of candidate positions associated with the measurement Doppler sensor. In this case, the same Doppler sensor 15 as the measurement Doppler sensor when the reliability level of the latest biological information satisfies the change condition may be re-determined as the measurement Doppler sensor, or a Doppler sensor 15 different from the measurement Doppler sensor when the reliability level of the latest biological information satisfies the change condition may be re-determined as the measurement Doppler sensor. Further, when the reliability level of the latest heart rate satisfies the heart rate measurement change condition, the heart rate Doppler sensor may be re-determined from among the Doppler sensors 15 other than the respiratory rate Doppler sensor, and the heart rate measurement position may be redetermined from among a plurality of candidate positions associated with the heart rate Doppler sensor. In this case, generation of the respiratory rate by the respiratory rate Doppler sensor may be continued without changing the respiratory rate Doppler sensor. Further, when the reliability level of the latest respiratory rate satisfies the respiratory rate measurement change condition, the respiratory rate Doppler sensor may be redetermined from among the Doppler sensors 15 other than the heart rate Doppler sensor, and the respiratory rate measurement position may be re-determined from among a plurality of candidate positions associated with the respiratory rate Doppler sensor. In this case, generation of the heart rate by the heart rate Doppler sensor may be continued without changing the heart rate Doppler sensor. Then, after the position of the Doppler sensor 15 is changed to the re-determined measurement position, the biological information generation module 40 may repeatedly execute processing of generating the biological information based on the Doppler data indicating the measurement result obtained by the Doppler sensor 15 at the measurement position after the change. Here, after the measurement Doppler sensor and the measurement position are re-determined, the biological information generation module 40 may repeatedly execute processing of generating the biological information based on the Doppler data indicating the measurement result obtained by the re-determined measurement Doppler sensor arranged at the redetermined measurement position. Further, after the heart rate Doppler sensor and the heart rate measurement position are re-determined, processing of generating the heart rate based on the Doppler data indicating the measurement result obtained by the re-determined heart rate Doppler sensor arranged at the re-determined heart rate measurement position may be repeatedly executed. Further, after the respiratory rate Doppler sensor and the respiratory rate measurement position are re-determined, processing of generating the respiratory rate based on the Doppler data indicating the measurement result obtained by the re-determined respiratory rate Doppler sensor arranged at the re-determined respiratory rate measurement position may be repeatedly executed. In the above description, the measurement position is redetermined in response to the reliability level satisfying the change condition. Similarly, the measurement direction and the measurement polarization plane direction may be re-determined. Then, the measurement direction may be changed to the redetermined measurement direction, and the measurement polarization plane direction may be changed to the re-determined measurement polarization plane direction. The load data acquisition module 46 acquires load data indicating a measurement result of a load applied to a plurality of (for example, four) load sensors 14, for example. Here, the load data output from each of the plurality of (for example, four) load sensors 14 may be acquired at predetermined time intervals. The body movement determination module 48 determines whether a body movement of the person to be measured has occurred, for example. Here, the body movement determination module 48 may calculate a total weight based on the load data acquired from the respective four load sensors 14 at predetermined time intervals, and generate total weight data indicating the calculated total weight. For example, the total weight data indicating a total value of measurement results of loads applied to the respective four load sensors 14 may be generated. Then, the body movement determination module 48 may determine whether the body movement of the person to be measured has occurred based on a magnitude of fluctuation in a value indicated by the total weight data. Here, for example, the body movement determination module 48 may determine whether the body movement of the person to be measured has occurred every time a determination timing, which arrives at a time interval longer than the time interval at which the total weight data is generated, arrives. Here, a period between two consecutive determination timings is referred to as "body movement determination period." Then, a maximum value or a minimum value of the value of the total weight data generated in a specific body movement determination period may be identified. Then, an average value of the values of the total weight data generated in a body movement determination period immediately preceding the specific body movement determination period may be identified. Then, when a difference between the maximum value identified for the body movement determination period and the average value identified for the body movement determination period immediately preceding the specific body movement determination period is equal to or more than a predetermined value, it may be determined that the body movement of the person to be measured has occurred in the body movement determination period. Further, when a difference between the minimum value identified for the body movement determination period and the average value identified for the body movement determination period immediately preceding the specific body movement determination period is equal to or more than a predetermined value, it may be determined that the body movement of the person to be measured has occurred in the body movement determination period. Then, when neither condition is satisfied, it may be determined that the body movement of the person to be measured has not occurred in the body movement determination period. A method of determining whether the body movement of the person to be measured has occurred is not limited to this method. Then, in response to determining that the body movement of the person to be measured has occurred, the biological information generation module 40 may suspend generation of the biological information. Then, in response to determining that the body movement of the person to be measured has not occurred in a situation in which the generation of the biological information is suspended, the biological information generation module 40 may resume the generation of the biological information. The person-to-be-measured position estimation module 50 estimates a position of the person to be measured on the bed 16, for example. The person-to-be-measured position estimation module 50 may estimate the position of the person to be measured on the bed 16 based on the load data acquired from the four load sensors 14 at predetermined time intervals. For example, as illustrated in FIG. 5, it is assumed that a direction from left to right when viewed from above the bed 16 such that the headboard of the bed 16 is the upper side is a positive direction of an X-axis, and a direction from top to bottom when viewed from above the bed 16 such that the headboard of the bed 16 is the upper side is a positive direction of a Y-axis. It is assumed that coordinates of respective centers of the load sensors 14a, 14b, 14c, and 14d are (0, 0), (1, 0), (0, 1), and (1, 1). In addition, it is assumed that the latest measurement results of loads obtained by the load sensor 14a, the load sensor 14b, the load sensor 14c, and the load sensor 14d are "a", "b", "c", and "d", respectively. In this case, coordinate values (x, y) of the position of the person to be measured may be calculated by mathematical expressions of "x=(b+d) / (a+b+c+d)" and "y=(c+d) / (a+b+c+d)." A method of estimating the position of the person to be measured is not limited to this method. The Doppler sensor selection module 52 selects a plurality of Doppler sensors from among the plurality of Doppler sensors 15 based on the position of the person to be measured. For example, a predetermined number of (for example, four) Doppler sensors 15 close to the estimated position of the person to be measured may be selected. Then, when the selection of the Doppler sensors 15 is performed, the determination module 38 may determine the measurement Doppler sensor from among the selected plurality of Doppler sensors 15. Further, in this case, the reliability level calculation module 36 may calculate the abovementioned reliability level only for the selected plurality of Doppler sensors 15. Now, an example of a flow of measurement position determination processing is described with reference to flow charts illustrated as an example in FIG. 6A and FIG. 6B. In the processing illustrated in this processing example, it is assumed that each of the six Doppler sensors 15 is arranged at a predetermined initial position that is any one of a plurality of candidate positions. First, the Doppler data acquisition module 32 operates each of the six Doppler sensors 15 for a predetermined time, and acquires Doppler data indicating a measurement result obtained by the Doppler sensor 15 during the predetermined time (Step S101). Then, the frequency spectrum generation module 34 generates, for each of the six pieces of Doppler data acquired in the processing step illustrated in Step S101, a frequency spectrum based on the piece of Doppler data (Step S102). Then, the reliability level calculation module 36 calculates a reliability level (Step S103). Here, for example, the above-mentioned reliability level in a predetermined frequency range (for example, in a predetermined frequency range near 1.25 Hz) associated with the heart rate is calculated for each of the six frequency spectra generated in the processing step illustrated in Step S102. A reliability level calculated from a frequency spectrum based on Doppler data indicating a measurement result obtained by the Doppler sensor 15 is hereinafter referred to as "reliability level corresponding to the Doppler sensor 15." Then, the determination module 38 determines whether a predetermined measurement condition (heart rate measurement condition) is satisfied for each of the six reliability levels calculated in the processing step illustrated in Step S103 (Step S104). Here, for example, whether the amplitude ratio, which is the calculated reliability level, is larger than a predetermined value may be determined. Then, the determination module 38 determines whether at least one Doppler sensor 15 corresponding to the reliability level satisfying the heart rate measurement condition is present (Step S105). When such a Doppler sensor 15 is present (Step S105: Y), any one of the Doppler sensors 15 corresponding to the reliability level satisfying the heart rate measurement condition is determined as the heart rate Doppler sensor, and the candidate position at which the heart rate Doppler sensor is arranged is determined as the heart rate measurement position (Step S106). Here, for example, the Doppler sensor 15 corresponding to the highest reliability level (for example, the largest amplitude ratio) may be determined as the heart rate Doppler sensor. When such a Doppler sensor 15 is not present (Step S105: N), the body movement determination module 48 determines presence or absence of a body movement, and when it is determined that there is a body movement, waits until it is determined that there is no body movement (Step S107). When it is determined that there is no body movement, the Doppler sensor control module 30 changes the position of at least one Doppler sensor 15 (Step S108), and the process returns to the processing step illustrated in Step S101. In this case, the positions of all the Doppler sensors 15 may be changed. Further, in this case, a height of the Doppler sensor 15 may be changed downward by five centimeters in consideration of the fact that the heart rate tends to be accurately measurable as the Doppler sensor 15 becomes closer to the person to be measured. When the heart rate Doppler sensor and the heart rate measurement position are determined in the processing step illustrated in Step S106, the reliability level calculation module 36 calculates the reliability level (Step S109). Here, for example, the above-mentioned reliability level in a predetermined frequency range (for example, in a predetermined frequency range near 0.3 Hz) associated with the respiratory rate is calculated for the frequency spectrum based on the Doppler data of the heart rate Doppler sensor generated in the processing step illustrated in Step S102. Then, the determination module 38 determines whether the reliability level calculated in the processing step illustrated in Step S109 satisfies a predetermined measurement condition (respiratory rate measurement condition) (Step S110). Here, for example, whether the amplitude ratio that is the calculated reliability level is larger than a predetermined value may be determined. The respiratory rate measurement condition may be the same as or different from the heart rate measurement condition. When the respiratory rate measurement condition is satisfied (Step S110: Y), the heart rate Doppler sensor is also determined as the respiratory rate Doppler sensor, and the candidate position at which the respiratory rate Doppler sensor is arranged is also determined as the respiratory rate measurement position (Step S111). Then, the processing illustrated in this processing example is ended. When the respiratory rate measurement condition is not satisfied (Step S110: N), the reliability level calculation module 36 calculates the reliability level (Step S112). Here, for example, the above-mentioned reliability level in the predetermined frequency range associated with the respiratory rate is calculated for each of the frequency spectra generated in the processing step illustrated in Step S102 of the Doppler sensors 15 (for example, five Doppler sensors 15) other than the heart rate Doppler sensor. Then, the determination module 38 determines whether the predetermined respiratory rate measurement condition is satisfied for each of the five reliability levels calculated in the processing step illustrated in Step S112 (Step S113). Here, for example, whether the amplitude ratio that is the calculated reliability level is larger than a predetermined value may be determined. As described above, the respiratory rate measurement condition may be the same as or different from the heart rate measurement condition. The respiratory rate measurement condition in the processing step illustrated in Step S110 and the respiratory rate measurement condition in the processing step illustrated in Step S113 may be the same or different. Then, the determination module 38 determines whether at least one Doppler sensor 15 corresponding to the reliability level satisfying the respiratory rate measurement condition in the processing step illustrated in Step S113 is present (Step S114). When such a Doppler sensor 15 is present (Step S114: Y), any one of the Doppler sensors 15 corresponding to the reliability level satisfying the respiratory rate measurement condition is determined as the respiratory rate Doppler sensor, and the candidate position at which the respiratory rate Doppler sensor is arranged is determined as the respiratory rate measurement position (Step S115). Here, for example, the Doppler sensor 15 corresponding to the highest reliability level (for example, the largest amplitude ratio) may be determined as the respiratory rate Doppler sensor. Then, the processing illustrated in this processing example is ended. When such a Doppler sensor 15 is not present (Step S114: N), the Doppler sensor control module 30 changes the position of at least one Doppler sensor 15 among the Doppler sensors 15 other than the heart rate Doppler sensor (Step S116). In this case, the positions of all the Doppler sensors 15 (for example, five Doppler sensors 15) other than the heart rate Doppler sensor may be changed. In this case, the height of the Doppler sensor 15 may be changed upward by five centimeters in consideration of the fact that the respiratory rate tends to be accurately measurable by measuring a wide range. Then, for each of the five Doppler sensors 15 other than the heart rate Doppler sensor, the Doppler data acquisition module 32 operates the Doppler sensor 15 for a predetermined time, and acquires the Doppler data indicating the measurement result obtained by the Doppler sensor 15 during the predetermined time (Step S117). Then, the frequency spectrum generation module 34 generates, for each of the five pieces of Doppler data acquired in the processing step illustrated in Step S117, a frequency spectrum based on the piece of Doppler data (Step S118). Then, the process returns to the processing step illustrated in Step S112. Here, for example, the reliability level is calculated for each of the frequency spectra generated in the processing step illustrated in Step S118. In the processing example illustrated in FIG. 6A and FIG. 6B, the heart rate Doppler sensor and the heart rate measurement position are determined, and then the respiratory rate Doppler sensor and the respiratory rate measurement position are determined, in consideration of the fact that the heartbeat has a small amount of displacement and it is thus difficult to detect the heartbeat. Here, the respiratory rate Doppler sensor and the respiratory rate measurement position may be determined first, and then the heart rate Doppler sensor and the heart rate measurement position may be determined. Further, when the position of the Doppler sensor 15 reaches a threshold value, the Doppler sensor control module 30 may change the position of the Doppler sensor 15 to an initial position. As illustrated in FIG. 6A and FIG. 6B, determining whether the calculated reliability level satisfies the measurement condition and moving the Doppler sensor 15 to another candidate position in response to the calculated reliability level not satisfying the measurement condition may be repeated until the calculated reliability level satisfies the measurement condition. Then, the candidate position at which the calculated reliability level satisfies the measurement condition may be determined as the measurement position. Further, in this embodiment, the reliability level calculation module 36 may calculate the reliability level for each of all the candidate positions. Then, the determination module 38 may determine the candidate position having the highest calculated reliability level as the measurement position. For example, the reliability level calculation module 36 may calculate the reliability levels in a round-robin manner for all combinations of the Doppler sensors 15, the candidate positions, the candidate directions, and the candidate polarization plane directions. For example, it is assumed that there are six Doppler sensors 15. It is assumed that there are three candidate positions (the first height, the second height, and the third height). It is assumed that there are four candidate directions (the front direction, the direction downward by 10 degrees with respect to the front direction, the direction downward by 20 degrees with respect to the front direction, and the direction downward by 30 degrees with respect to the front direction). It is assumed that there are two candidate polarization plane directions (the horizontal direction and the vertical direction). In this case, while the control is being performed by the Doppler sensor control module 30, the reliability level calculation module 36 may sequentially calculate the reliability levels for all of 144 (6*3*4*2) combinations. For example, the Doppler sensor 15, the candidate position, the candidate direction, and the candidate polarization plane direction in the combination having the highest calculated reliability level may be determined as the measurement Doppler sensor, the measurement position, the measurement direction, and the measurement polarization plane direction, respectively. Then, the Doppler sensor control module 30 may perform control such that the measurement Doppler sensor is located at the measurement position and the microwave having the measurement polarization plane direction as the polarization plane direction is emitted in the measurement direction. Then, the biological information generation module 40 may start generating the biological information by the measurement Doppler sensor. In this case, the combination having the highest calculated reliability level may be determined for each of the heartbeat and the respiration. Then, the Doppler sensor 15, the candidate position, the candidate direction, and the candidate polarization plane direction in the combination having the highest reliability level for the heartbeat may be determined as the heart rate Doppler sensor, the heart rate measurement position, the heart rate measurement direction, and the heart rate measurement polarization plane direction, respectively. Further, the Doppler sensor 15, the candidate position, the candidate direction, and the candidate polarization plane direction in the combination having the highest reliability level for the respiration may be determined as the respiratory rate Doppler sensor, the respiratory rate measurement position, the respiratory rate measurement direction, and the respiratory rate measurement polarization plane direction, respectively. Next, an example of a flow of processing of changing the measurement position, the measurement direction, and the measurement polarization plane direction is described with reference to a flow chart illustrated as an example in FIG. 7. In this processing example, every time the biological information of the person to be measured is generated for each of the heart rate and the respiratory rate, the change condition determination module 44 determines whether the reliability level of the latest biological information satisfies a given change condition (Step S201). Here, for example, when it is determined that the respiratory rate satisfies the respiratory rate measurement change condition (Step S201: Y), the Doppler sensor control module 30 changes the respiratory rate measurement polarization plane direction of the respiratory rate Doppler sensor (Step S202). Then, the change condition determination module 44 determines again, for the respiratory rate Doppler sensor, whether the respiratory rate measurement change condition is satisfied (Step S203). When the respiratory rate measurement change condition is not satisfied (Step S203: N), the process returns to the processing step illustrated in Step S201. When the respiratory rate measurement change condition is satisfied (Step S203: Y), the Doppler sensor control module 30 initializes the respiratory rate measurement polarization plane direction of the respiratory rate Doppler sensor (Step S204). In this processing example, for example, it is assumed that the horizontal direction is determined in advance as an initial value of the respiratory rate measurement polarization plane direction. In this case, the respiratory rate measurement polarization plane direction of the respiratory rate Doppler sensor is set to the horizontal direction. Then, the Doppler sensor control module 30 changes the respiratory rate measurement direction of the respiratory rate Doppler sensor (Step S205). Here, for example, the respiratory rate measurement direction is changed by 10 degrees to face the position of the person to be measured estimated by the personto-be-measured position estimation module 50. Then, the change condition determination module 44 determines again, for the respiratory rate Doppler sensor, whether the respiratory rate measurement change condition is satisfied (Step S206). When the respiratory rate measurement change condition is not satisfied (Step S206: N), the process returns to the processing step illustrated in Step S201. When the respiratory rate measurement change condition is satisfied (Step S206: Y), the Doppler sensor control module 30 determines whether the measurement direction has reached a threshold value (for example, the front direction, or the direction downward by 30 degrees with respect to the front direction) (Step S207). When the threshold value is not reached (Step S207: N), the process returns to the processing step illustrated in Step S205. When the threshold value is reached (Step S207: Y), the Doppler sensor control module 30 initializes the respiratory rate measurement direction of the respiratory rate Doppler sensor (Step S208). In this processing example, for example, it is assumed that the front direction is determined in advance as an initial value of the respiratory rate measurement direction. In this case, the respiratory rate measurement direction of the respiratory rate Doppler sensor is set to the front direction. Then, the Doppler sensor control module 30 changes the respiratory rate measurement position of the respiratory rate Doppler sensor (Step S209). Here, for example, the height of the respiratory rate Doppler sensor may be changed upward by five centimeters. Then, the change condition determination module 44 determines again, for the respiratory rate Doppler sensor, whether the respiratory rate measurement change condition is satisfied (Step S210). When the respiratory rate measurement change condition is not satisfied (Step S210: N), the process returns to the processing step illustrated in Step S201. When the respiratory rate measurement change condition is satisfied (Step S210: Y), the Doppler sensor control module 30 determines whether the respiratory rate measurement position has reached a threshold value (Step S211). Here, for example, whether the respiratory rate measurement position of the Doppler sensor 15 has reached a position determined in advance is determined. When the threshold value is not reached (Step S211: N), the process returns to the processing step illustrated in Step S202. When the threshold value is reached (Step S211: Y), the Doppler sensor control module 30 initializes the respiratory rate measurement position, the respiratory rate measurement direction, and the respiratory rate measurement polarization plane direction (Step S212), and the process returns to the processing step illustrated in Step S201. Here, for example, the respiratory rate measurement position may be set to a predetermined initial position, the respiratory rate measurement direction may be set to the front direction, and the respiratory rate measurement polarization plane direction may be set to the horizontal direction. In this processing example, in the processing step illustrated in Step S212, the determination module 38 may redetermine the respiratory rate Doppler sensor from among the respiratory rate Doppler sensor and the four Doppler sensors 15 other than the heart rate Doppler sensor, re-determine the respiratory rate measurement position from among candidate positions associated with the re-determined respiratory rate Doppler sensor, re-determine the respiratory rate measurement direction from among candidate directions associated with the re-determined respiratory rate Doppler sensor, and re-determine the respiratory rate measurement polarization plane direction from among candidate polarization plane directions associated with the re-determined respiratory rate Doppler sensor. The processing of re-determining the respiratory rate Doppler sensor, the respiratory rate measurement position, the respiratory rate measurement direction, and the respiratory rate measurement polarization plane direction may be, for example, the same processing as the above-mentioned processing of determining the respiratory rate Doppler sensor, the respiratory rate measurement position, the respiratory rate measurement direction, and the respiratory rate measurement polarization plane direction. Then, the Doppler sensor control module 30 may control such that the respiratory rate Doppler sensor is located at the re-determined measurement position and the microwave having the re-determined measurement polarization plane direction as the polarization plane direction of the respiratory rate Doppler sensor is emitted in the re-determined measurement direction. Then, the biological information generation module 40 may start generating the respiratory rate by the respiratory rate Doppler sensor. Further, the reliability level calculation module 36 may calculate, for the four Doppler sensors 15, the reliability levels in a round-robin manner for all combinations of the four Doppler sensors 15, the candidate positions, the candidate directions, and the candidate polarization plane directions. Then, the determination module 38 may re-determine the Doppler sensor 15, the candidate position, the candidate direction, and the candidate polarization plane direction in the combination having the highest calculated reliability level as the respiratory rate Doppler sensor, the respiratory rate measurement position, the respiratory rate measurement direction, and the respiratory rate measurement polarization plane direction, respectively. When it is determined that the heart rate satisfies the heart rate measurement change condition in the processing step illustrated in Step S201, the heart rate Doppler sensor, the heart rate measurement position, the heart rate measurement direction, and the heart rate measurement polarization plane direction may be re-determined by executing the same processing as the processing described above. In this embodiment, the measurement position and the like of the Doppler sensor 15 are controllable, and the biological information is generated based on the Doppler data measured at the measurement position determined based on the reliability level. Thus, according to this embodiment, it is possible to accurately measure the biological information, such as the respiratory rate or the heart rate, of the person to be measured regardless of the position and the posture of the person to be measured. In this embodiment, the ball screw 18 is not required to extend in the up-down direction, and may extend in a left-right direction. The Doppler sensor 15 may be movable in one direction (for example, the left-right direction) different from the up-down direction. The Doppler sensor 15 may be movable in both the up-down direction and the left-right direction. The Doppler sensor 15 may be movable in any direction on a given surface. Further, in this embodiment, the Doppler sensor 15 may be movable along a given surface other than the headboard surface of the bed 16. For example, the ball screw 18 may be provided on a wall surface of a room in which the bed 16 is placed. The Doppler sensor 15 may be movable along the wall surface of the room in which the bed 16 is placed. Further, the position and the number of the load sensors 14 are not limited to those illustrated in FIG. 1. An acceleration sensor may be provided on the mattress, and the body movement determination module 48 may determine whether the body movement has occurred based on a measurement result obtained by the acceleration sensor. Further, the position and the orientation of the Doppler sensor 15 are not limited to the position and the orientation described above. For example, the Doppler sensor 15 may be attached to a ceiling. Further, the number of the Doppler sensors 15 included in the biological information detection system 1 is not limited to six. For example, the number of the Doppler sensors 15 included in the biological information detection system 1 may be one. Further, the position of the Doppler sensor 15, the emission direction of the microwave, and the emission polarization plane direction of the microwave are not required to be automatically controlled in accordance with instructions of a program. For example, a person such as an operator may be capable of manually controlling the position of the Doppler sensor 15, the emission direction of the microwave, and the emission polarization plane direction of the microwave by performing operation input to the computer 10.

Claims

1. A biological information detection system, comprising:Doppler sensor control means for controlling a position of a Doppler sensor such that the Doppler sensor is arranged at any one of a plurality of candidate positions determined in advance;reliability level calculation means for calculating, for at least one of the plurality of candidate positions, based on Doppler data indicating a measurement result obtained by the Doppler sensor arranged at the candidate position, a reliability level of biological information obtained from the Doppler data;measurement position determination means for determining a measurement position from among the plurality of candidate positions based on the reliability level calculated for the at least one of the plurality of candidate positions; andbiological information generation means for repeatedly executing processing of generating the biological information of a person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor arranged at the measurement position.

2. The biological information detection system according to claim 1, further comprising measurement condition determination means for determining whether the calculated reliability level satisfies a given measurement condition,wherein the biological information detection system is configured to repeatedly cause the measurement conditiondetermination means to determine whether the calculatedreliability level satisfies the given measurement condition, and cause the Doppler sensor control means to move the Doppler sensor to another of the plurality of candidate positions in response to the calculated reliability level failing to satisfy the given measurement condition, until the calculated reliability level satisfies the given measurement condition, andwherein the measurement position determination means is configured to determine, as the measurement position, one of the plurality of candidate positions at which the calculated reliability level satisfies the given measurement condition.

3. The biological information detection system according to claim 1,wherein the reliability level calculation means is configured to calculate the reliability level for each of all the plurality of candidate positions, andwherein the measurement position determination means is configured to determine, as the measurement position, one of the plurality of candidate positions having the highest calculated reliability level.

4. The biological information detection system according to claim 1, further comprising change condition determination means for determining whether the reliability level of the latest generated biological information satisfies a given change condition in a situation in which the processing of generatingthe biological information of the person to be measured is repeatedly executed,wherein the Doppler sensor control means is configured to change the position of the Doppler sensor in response to the reliability level of the latest biological information satisfying the given change condition.

5. The biological information detection system according to claim 1,wherein, for each of a plurality of Doppler sensors, a plurality of the candidate positions associated with the each of the plurality of Doppler sensors are determined in advance,wherein the Doppler sensor control means is configured to control, for each of the plurality of Doppler sensors, the position of the Doppler sensor such that the Doppler sensor is arranged at any one of the plurality of the candidate positions associated with the Doppler sensor,wherein the measurement position determination means is configured to determine a measurement Doppler sensor from among the plurality of Doppler sensors and determine the measurement position from among the plurality of the candidate positions associated with the measurement Doppler sensor, andwherein the biological information generation means is configured to repeatedly execute the processing of generating the biological information based on the Doppler data indicating the measurement result obtained by the measurement Doppler sensor arranged at the measurement position.

6. The biological information detection system according to claim 5, further comprising change condition determination means for determining whether the reliability level of the latest generated biological information satisfies a given change condition in a situation in which the processing of generating the biological information of the person to be measured is repeatedly executed,wherein the measurement position determination means is configured to re-determine, when the reliability level of the latest biological information satisfies the given change condition, the measurement Doppler sensor from among the plurality of Doppler sensors and re-determine the measurement position from among the plurality of candidate positions associated with the measurement Doppler sensor, andwherein the biological information generation means is configured to repeatedly execute, after the measurement Doppler sensor and the measurement position are re-determined, the processing of generating the biological information based on the Doppler data indicating the measurement result obtained by the re-determined measurement Doppler sensor arranged at the redetermined measurement position.

7. The biological information detection system according to claim 6,wherein the measurement position determination means is configured to determine a heart rate Doppler sensor from among the plurality of Doppler sensors and determine a heart ratemeasurement position from among the plurality of the candidate positions associated with the heart rate Doppler sensor,wherein the measurement position determination means is configured to determine a respiratory rate Doppler sensor from among the plurality of Doppler sensors and determine a respiratory rate measurement position from among the plurality of the candidate positions associated with the respiratory rate Doppler sensor,wherein the respiratory rate Doppler sensor is a Doppler sensor different from the heart rate Doppler sensor,wherein the biological information generation means is configured to repeatedly execute processing of generating a heart rate of the person to be measured based on the Doppler data indicating the measurement result obtained by the heart rate Doppler sensor arranged at the heart rate measurement position, andwherein the biological information generation means is configured to repeatedly execute processing of generating a respiratory rate of the person to be measured based on the Doppler data indicating the measurement result obtained by the respiratory rate Doppler sensor arranged at the respiratory rate measurement position.

8. The biological information detection system according to claim 7, further comprising:heart rate measurement change condition determination means for determining whether the reliability level of the latestgenerated heart rate satisfies a given heart rate measurement change condition; andrespiratory rate measurement change condition determination means for determining whether the reliability level of the latest generated respiratory rate satisfies a given respiratory rate measurement change condition,wherein the measurement position determination means is configured to re-determine the heart rate Doppler sensor from among the Doppler sensors other than the respiratory rate Doppler sensor and re-determine the heart rate measurement position from among the plurality of the candidate positions associated with the heart rate Doppler sensor when the reliability level of the latest heart rate satisfies the given heart rate measurement change condition,wherein the measurement position determination means is configured to re-determine the respiratory rate Doppler sensor from among the Doppler sensors other than the heart rate Doppler sensor and re-determine the respiratory rate measurement position from among the plurality of the candidate positions associated with the respiratory rate Doppler sensor when the reliability level of the latest respiratory rate satisfies the given respiratory rate measurement change condition,wherein the biological information generation means is configured to repeatedly execute, after the heart rate Doppler sensor and the heart rate measurement position are redetermined, the processing of generating the heart rate based on the Doppler data indicating the measurement result obtained bythe re-determined heart rate Doppler sensor arranged at the redetermined heart rate measurement position, andwherein the biological information generation means is configured to repeatedly execute, after the respiratory rate Doppler sensor and the respiratory rate measurement position are re-determined, the processing of generating the respiratory rate based on the Doppler data indicating the measurement result obtained by the re-determined respiratory rate Doppler sensor arranged at the re-determined respiratory rate measurement position.

9. The biological information detection system according to claim 5, further comprising Doppler sensor selection means for selecting, from among the plurality of Doppler sensors, a plurality of Doppler sensors based on a position of the person to be measured,wherein the measurement position determination means is configured to determine the measurement Doppler sensor from among the selected plurality of Doppler sensors.

10. The biological information detection system according to claim 1,wherein the Doppler sensor control means is configured to control an orientation of the Doppler sensor such that an emission direction of a microwave is any one of a plurality of candidate directions determined in advance,wherein the reliability level calculation means isconfigured to calculate, for at least one of the plurality of candidate directions, a reliability level of the biological information obtained from the Doppler data based on the Doppler data indicating the measurement result obtained by the Doppler sensor emitting the microwave in the candidate direction,wherein the biological information detection system further comprises measurement direction determination means for determining a measurement direction from among the plurality of candidate directions based on the reliability level calculated for the at least one of the plurality of candidate directions, andwherein the biological information generation means is configured to generate the biological information of the person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor controlled such that the emission direction of the microwave is the measurement direction.

11. The biological information detection system according to claim 1,wherein the Doppler sensor control means is configured to control the Doppler sensor such that an emission polarization plane direction of a microwave is any one of a plurality of candidate polarization plane directions determined in advance,wherein the reliability level calculation means is configured to calculate, for at least one of the plurality of candidate polarization plane directions, a reliability level ofthe biological information obtained from the Doppler data based on the Doppler data indicating the measurement result obtained by the Doppler sensor emitting the microwave having the candidate polarization plane direction as the emission polarization plane direction,wherein the biological information detection system further comprises measurement polarization plane direction determination means for determining a measurement polarization plane direction from among the plurality of candidate polarization plane directions based on the reliability level calculated for the at least one of the plurality of candidate polarization plane directions, andwherein the biological information generation means is configured to generate the biological information of the person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor controlled such that the emission polarization plane direction of the microwave is the measurement polarization plane direction.

12. The biological information detection system according to claim 1, further comprising body movement determination means for determining whether a body movement of the person to be measured has occurred,wherein the biological information generation means is configured to suspend generation of the biological information in response to determining that the body movement of the person to be measured has occurred, and in a situation in which thegeneration of the biological information is suspended, resume the generation of the biological information in response to determining that the body movement of the person to be measured has not occurred.

13. The biological information detection system according to claim 1, further comprising frequency spectrum generation means for generating a frequency spectrum based on the Doppler data,wherein the reliability level calculation means is configured to calculate, as the reliability level, an amplitude ratio between a largest peak and a second largest peak included in the frequency spectrum.

14. A biological information detection method, comprising the steps of:controlling a position of a Doppler sensor such that the Doppler sensor is arranged at any one of a plurality of candidate positions determined in advance;calculating, for at least one of the plurality of candidate positions, based on Doppler data indicating a measurement result obtained by the Doppler sensor arranged at the candidate position, a reliability level of biological information obtained from the Doppler data;determining a measurement position from among the plurality of candidate positions based on the reliability level calculated for the at least one of the plurality of candidatepositions; andrepeatedly executing processing of generating the biological information of a person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor arranged at the measurement position.

15. A program for causing a computer to execute the steps of:controlling a position of a Doppler sensor such that the Doppler sensor is arranged at any one of a plurality of candidate positions determined in advance;calculating, for at least one of the plurality of candidate positions, based on Doppler data indicating a measurement result obtained by the Doppler sensor arranged at the candidate position, a reliability level of biological information obtained from the Doppler data;determining a measurement position from among the plurality of candidate positions based on the reliability level calculated for the at least one of the plurality of candidate positions; andrepeatedly executing processing of generating the biological information of a person to be measured based on the Doppler data indicating the measurement result obtained by the Doppler sensor arranged at the measurement position.

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