System and method for detecting fall of person

Abstract

The invention relates to a system for detecting a fall of a person. The system includes a fixed sensor located at a fixed position relative to the person and a wearable sensor worn by the person, which can report a fall of the person independently of one another. Further, the system includes a line-of-sight detection unit configured to determine whether the wearable sensor is within a line-of-sight of the fixed sensor. To detect a fall of a person, a fall detection unit of the system takes into account a fall report as provided by one or both of a fixed sensor and a wearable sensor. Further, in order to detect a fall, the fall detection unit takes into account the presence or absence of a line of sight between the wearable sensor and the fixed sensor. Thereby, it is possible to increase the reliability of detecting a fall, in particular in the case where only one of the wearable sensor and the fixed sensor reports a fall.

Description

Technical Field

[0001] The invention relates to a system and a method for detecting a fall of a person. Furthermore, the invention relates to a computer program for detecting a fall of a person and to a non-transitory computer-readable data medium storing the computer program. Background Art

[0002] Since falling is one of the main health threats to the elderly, fall detection systems that can detect a person's fall and provide an alarm accordingly are often used. For example, in the article "Wearable Fall Detection System Using Barometric Pressure Sensors and Machine Learning", SENSORCOMM 2019: The Thirteenth International Conference on Sensor Technologies and Applications, ISBN: 978-1-61208-744-3, Y. Sun et al. raised the problem of detecting short falls, such as falling from a bed or chair when an elderly person is trying to get up. In order to reduce the number of false alarms, Y. Sun et al. suggested using a first pressure sensor attached to a waist belt and a second pressure sensor attached to a person's shoes, where the second pressure sensor is used as a reference sensor.

[0003] However, it remains desirable to further improve the reliability of systems and methods for detecting a person's falls.

[0004] LI HAOBO et al. disclose preliminary results on multisensory recognition and fall detection of daily indoor activities to monitor the well-being of older adults at risk of physical and cognitive chronic health conditions. Five different sensors—continuous wave (CW) radar, frequency modulated CW (FMCW) radar, and an inertial measurement unit including an accelerometer, gyroscope, and magnetometer—were used to simultaneously collect data from 20 subjects performing 10 activities. Rather than using all available sensors, it is more efficient and economical to select a subset of them to maximize classification accuracy and avoid unnecessary computation to process information when it is not significant. Each individual sensor and several sensor combinations were trained with a quadratic kernel support vector machine classifier. Summary of the invention

[0005] The invention is based on the object of providing a system, a method and a computer program for detecting a fall of a person. In particular, with the system, the method and the computer program it should be possible to reliably detect a fall of a person and at the same time reduce the number of false alarms. Thus, with the system, the method and the computer program the number of false positive or missed alarms should be relatively low, while real falls should be detected with high accuracy.

[0006] According to the present invention, a system for detecting a person's fall is provided, which comprises a fixed sensor, a wearable sensor, a sight line detection unit, a fall detection unit and an output unit.

[0007] The fixed sensor is configured to provide a first sensor signal indicating a person falling. The wearable sensor is configured to provide a second sensor signal indicating a person falling. The sight line detection unit is configured to determine whether the wearable sensor is within the sight line of the fixed sensor and provide a sight line signal indicating whether the wearable sensor is within the sight line of the fixed sensor. The fall detection unit is configured to detect a person falling based on a) the sight line signal and b) the first sensor signal and / or the second sensor signal. In addition, the output unit is configured to provide an output signal indicating whether a person falling has been detected.

[0008] The present invention is based on the recognition that it may be advantageous to use a combination of wearable sensors and fixed sensors to detect a fall of a person. Wearable sensors may have the advantage that they are always with the person and can therefore detect falls wherever the person goes, i.e. also outdoors. On the other hand, wearable sensors, in particular wearable sensors around the wrist, may provide a relatively large number of false alarms, because certain movements other than real falls are detected as falls. With fixed sensors, it may be possible to detect a fall of a person within the field of view of the fixed sensor. When combining wearable sensors with fixed sensors in a hybrid fall detection system, it may be possible to benefit from the various advantages associated with each of the fixed and wearable sensors. Thereby, it may be possible to improve the reliability of fall detection.

[0009] However, in a hybrid fall detection system, there may be a situation where only one of the wearable and fixed sensors detects a fall. In this case, one must decide whether a true fall has occurred or whether a false alarm has been triggered.

[0010] With the system according to the invention, the reliability of detecting a real fall can be improved while reducing the number of false alarms and / or missed alarms, because a line of sight detection unit is employed, which determines whether the wearable sensor is within the line of sight of the fixed sensor. The presence or absence of a line of sight can be used as an additional parameter for evaluating whether a real fall has actually occurred. Assuming that both the wearable sensor and the fixed sensor report a fall, and the wearable sensor is also within the line of sight of the fixed sensor, it may be possible to determine with increased certainty that a real fall has actually occurred. However, if only one of the wearable sensor and the fixed sensor reports a fall, and the wearable sensor is within the line of sight of the fixed sensor, it may be determined as a false alarm, because the one sensor that did not report the fall should be in a situation where the fall should have actually been detected. However, if only one of the wearable sensor and the fixed sensor reports a fall, and the wearable sensor is not within the line of sight of the fixed sensor, it may be determined as a real fall, because the corresponding other sensor that did not report the fall may not have actually detected the fall.

[0011] Therefore, the presence or absence of line of sight can be used as an additional parameter for evaluating and thereby improving the reliability of fall detection achieved by the system.With the system, it may therefore be possible to reduce the number of false positive alarms and / or missed negative alarms while detecting real falls with a relatively high degree of accuracy.

[0012] In the system, the output signal provided by the output unit may indicate a certain probability that a fall has occurred. For example, with reference to the situation explained above, in the case where a wearable sensor and a fixed sensor report a fall and the wearable sensor is within the line of sight of the fixed sensor, the output signal may indicate a higher probability that a fall has occurred than in the case where only one of the wearable sensor and the fixed sensor reports a fall and the wearable sensor is within the line of sight of the fixed sensor. Thus, it may be possible to adapt further strategies for elderly care more accurately to the actual risk of a person falling.

[0013] The wearable sensor may preferably be worn on a person. The wearable sensor may be or may include an accelerometer, and the second sensor signal may represent an acceleration indicating a person falling. Additionally or alternatively, the wearable sensor may be or may include a velocity sensor, and the second sensor signal may represent a velocity indicating a person falling. Additionally or alternatively, the wearable sensor may be or may include a position sensor, and the second sensor signal may represent a change in position of the person indicating a person falling. Additionally or alternatively, the wearable sensor may be or may include an air pressure sensor, and the second sensor signal may represent a change in height indicating a person falling. The wearable sensor may provide the second sensor signal if a certain threshold associated with the corresponding parameter is exceeded. For example, if the wearable sensor is an accelerometer, the second sensor signal may be provided if an acceleration above a predefined acceleration threshold is detected. The wearable sensor may alternatively be configured to provide the second sensor signal continuously, for example after a predefined time interval. The received second sensor signal may be analyzed, for example, by the fall detection unit for detecting a fall.

[0014] The second sensor signal may be provided with or may include a timestamp associated with a certain moment when a certain parameter has been exceeded, for example when a predefined threshold has been exceeded. For example, at a certain moment, a certain speed has been detected to be above a predefined speed threshold and is therefore considered to indicate a fall.

[0015] However, it may also be possible that the second sensor signal represents the evolution or trajectory of a certain parameter over time. For example, the second sensor signal may represent a change in the detected position over time, which may indicate a fall of the person. For example, the position may be continuously monitored and, using the fall detection unit, a fall of the person may be detected based on the evolution of the position of the person.

[0016] The fall detection unit may be or may include a processor or a processing unit configured to process the first sensor signal, the second sensor signal and the line of sight signal. In particular, the processor or the processing unit may be or may include a digital signal processor, a central processing unit of a computer, a microprocessor, a multi-core processor and / or a field programmable gate array (FPGA).

[0017] The line of sight detection unit may be implemented by the same processor or processing unit as the fall detection unit, or may be implemented by an external processor or processing unit. The fall detection unit and the line of sight detection unit are preferably configured to exchange line of sight signals, thereby having a transmitter at the line of sight detection unit and a receiver at the fall detection unit. The line of sight detection unit and / or the fall detection unit may further comprise a receiver for receiving the first sensor signal and / or the second sensor signal. Therefore, the wearable sensor and the fixed sensor preferably comprise a transmitter for providing the first sensor signal and the second sensor signal. The first sensor signal and the second sensor signal and the line of sight signal may be provided wirelessly or by wire.

[0018] Preferably, the fall detection unit of the system is configured to detect a fall of a person if the line of sight signal indicates that the wearable sensor is within the line of sight of the fixed sensor and at least one of the first sensor signal and the second sensor signal indicates that the person has fallen. In some cases, it may be advantageous to always detect a fall if at least one of the wearable sensor and the fixed sensor reports that the person has fallen. In this case, an alarm may be triggered whenever any of the wearable sensor or the fixed sensor indicates that the person has fallen.

[0019] Alternatively, the fall detection unit of the system may be configured to detect a fall of a person only if the line of sight signal indicates that the wearable sensor is within the line of sight of the fixed sensor and both the first sensor signal and the second sensor signal indicate that the person has fallen. In this case, a fall may be detected with improved reliability and in particular with a reduced number of false alarms.

[0020] Alternatively, the fall detection unit of the system may be configured to detect a fall of the person if the line of sight signal indicates that the wearable sensor is not within the line of sight of the fixed sensor and at least one of the first sensor signal and the second sensor signal indicates that the person has fallen. This may be advantageous in the event that the wearable sensor loses line of sight to the fixed sensor. It may then be advantageous to rely only on the wearable sensor and the fixed sensor, respectively, so that for detecting a fall it may be sufficient if only one of the wearable sensor and the fixed sensor reports that the person has fallen.

[0021] Preferably, the line of sight detection unit is configured to repeatedly determine whether the wearable sensor is within the line of sight of the fixed sensor at predefined time intervals. For example, the line of sight signal may be provided after each time interval, or only if a predefined situation is additionally detected. Such a predefined situation may be detected using an accelerometer detecting a sudden acceleration, an air pressure sensor detecting a sudden change in altitude, or a position sensor detecting a sudden change in position. The time interval for providing the line of sight signal may be dynamically adjusted. For example, the frequency of providing the line of sight signal may be increased if a predefined situation is detected. Thereby, it is possible to determine whether the wearable sensor is within the line of sight of the fixed sensor multiple times during a certain time span, for example during a fall.

[0022] The fall detection unit may be configured to detect a fall using a single line of sight signal associated with one of the predefined time intervals, or using several line of sight signals associated with two or more predefined time intervals. Using more than one line of sight signal to determine whether a fall has occurred may further increase the reliability of the fall detection. For example, during a fall, line of sight may be lost at some time. In this case, the fall detection unit may use this condition of lost line of sight to evaluate the reliability of the first and second sensor signals. Thus, in order to detect a fall of a person, the fall detection unit may be configured to take into account the moment when line of sight is lost. If line of sight has been present during most of the detected falls, loss of line of sight may indicate that something covered the wearable sensor after the fall, such as himself / herself, or furniture, etc.

[0023] Additionally or alternatively, the line of sight detection unit may be configured to determine whether the wearable sensor is within the line of sight of the fixed sensor if at least one of the first sensor signal and the second sensor signal indicates that the person has fallen. In this case, the determination of the presence or absence of a line of sight between the wearable sensor and the fixed sensor is triggered by at least one of the first sensor signal and the second sensor signal indicating that the person has fallen. Thus, the line of sight detection unit may be configured to determine whether the wearable sensor is within the line of sight of the fixed sensor upon receiving the first sensor signal and / or the second sensor signal indicating that the person has fallen.

[0024] If the line of sight detection unit is configured to take into account at least one fixed object in the field of view of the fixed sensor, it may be advantageous to determine whether the wearable sensor is within the line of sight of the fixed sensor. The fixed object may be within the line of sight of the wearable sensor and the fixed sensor, thereby preventing the line of sight detection unit from detecting the presence of the line of sight of the wearable sensor and the fixed sensor. For example, there may be some furniture in the field of view of the fixed sensor, and the line of sight of the wearable sensor and the fixed sensor may be blocked by the fixed object. The line of sight detection unit may be configured to provide a corresponding line of sight signal indicating that the line of sight is blocked by the fixed object. When the corresponding line of sight signal indicating that the line of sight is blocked by the fixed object is received, the fall detection unit may be configured to detect a fall of a person without relying on the presence of the line of sight. In this case, it may be sufficient to detect that a person has fallen if at least one of the wearable sensor and the fixed sensor reports that the person has fallen.

[0025] Preferably, the system further comprises an external light source operably connected to the fall detection unit and configured to provide a light signal. The wearable sensor may comprise a light sensor configured to detect the light signal provided by the external light source. The line of sight detection unit may be configured to determine that the wearable sensor is within the line of sight of the fixed sensor if the wearable sensor has detected the light signal emitted by the external light source with its light sensor. For example, the line of sight detection unit may be configured to determine whether the wearable sensor is within the line of sight of the fixed sensor upon receiving a light detection signal provided by the light sensor indicating that the light signal has been detected.

[0026] Preferably, the external light source is located near or close to the fixed sensor. If one of the sensors indicates a fall, the external light source may be controlled to emit a light signal to check whether the wearable sensor is within the line of sight of the fixed sensor, thereby evaluating the reliability of the fall detection. For example, the fall detection unit and / or the line of sight detection unit may be configured to control the external light source to emit a light signal if one of the first sensor signal and the second sensor signal indicates a person has fallen. Alternatively or additionally, the fall detection unit and / or the line of sight detection unit may be configured to control the external light source to repeatedly emit light after a predefined time interval to repeatedly check whether the wearable sensor is within the line of sight of the fixed sensor.

[0027] As an alternative or in addition to the external light source, the fixed sensor may include an integrated light source configured to emit a light signal. The wearable sensor may include a light sensor configured to detect the light signal. The line of sight detection unit may be configured to determine that the wearable sensor is within the line of sight of the fixed sensor if the wearable sensor has detected a light signal emitted by the integrated light source with its light sensor.

[0028] When an integrated light source with a fixed sensor is used in addition to or as an alternative to an external light source, detection of the presence of a line of sight may be improved because the light signal is emitted directly from the location of the fixed sensor. Thus, the light signal may be emitted directly along a virtual line of sight axis that virtually connects the wearable sensor and the fixed sensor.

[0029] The fall detection unit and / or the sight line detection unit may be configured to control the integrated light source to emit a light signal if one of the first sensor signal and the second sensor signal indicates that a person has fallen. Alternatively or additionally, the fall detection unit and / or the sight line detection unit may be configured to control the external light source to repeatedly emit light after a predefined time interval to repeatedly check whether the wearable sensor is within the sight line of the fixed sensor.

[0030] The light signal provided by the external light source and / or the integrated light source may be a flash signal, an infrared light signal or a coded light signal. A flash signal, an infrared light signal or a coded light signal is preferred to reliably distinguish the light signal from ambient light.

[0031] The system may further include an optional navigation system including a plurality of beacons configured to communicate with the wearable sensor to determine a relative position of the wearable sensor using the navigation system. The line of sight detection unit may be configured to determine whether the wearable sensor is within a line of sight of the fixed sensor based on the tracked position of the wearable sensor and the known position of the fixed sensor.

[0032] In such a system, the beacons may establish a tracking environment in which the wearable sensor moves and exchanges signals with the beacons for position detection. The navigation system may be an indoor navigation system installed in the same room or area as the fixed sensor. The line of sight detection unit may be configured to consider a fixed object located in the field of view of the fixed sensor for determining whether the wearable sensor is within the line of sight of the fixed sensor based on the tracked position of the wearable sensor by means of the beacon and the known position of the fixed sensor.

[0033] When a navigation system including multiple beacons is used, the wearable sensor is preferably configured to communicate with the beacons of the navigation system by means of ultra-wideband (UWB) communication, radio frequency identification (RFID) communication, near field communication (NFC), Bluetooth communication and / or visible light communication (VLC) to determine the relative position of the wearable sensor. The wearable sensor can be equipped with a UWB tag, an RFID tag, an NFC tag, a Bluetooth tag and / or a VLC sensor. The wearable sensor can also be configured to actively determine its position based on communication with the beacon and provide a position signal to the position detection system for further processing.

[0034] As an alternative or in addition to the navigation system including a plurality of beacons, the system may include a position detection system including at least one position sensor located at the wearable sensor and configured to track the position of the wearable sensor relative to the fixed sensor using the position detection system. The line of sight detection unit may be configured to determine whether the wearable sensor is within the line of sight of the fixed sensor based on the tracked position of the wearable sensor and the known position of the fixed sensor.

[0035] If a position detection system including at least one position sensor located at a wearable sensor is used, beacons distributed in the tracking area may not be used, but the wearable sensor communicates directly with the position detection system. The position sensor may be an active or passive sensor that communicates directly with the position detection system. For example, the position sensor may include an optical sensor such as an LED that emits light indicating the position of the wearable sensor. The emitted light may be captured by the position detection system. Additionally or alternatively, the position sensor may include one or more sensor coils, and the position detection system may be configured to generate an oscillating magnetic field for inducing a voltage signal in the sensor coil. The position detection system may analyze the voltage signal to determine the relative position of the wearable sensor.

[0036] The position detection system including at least one position sensor located at the wearable sensor may be an indoor position detection system installed in the same room or area as the fixed sensor. It may be beneficial to equip the fixed sensor with an additional position sensor to determine the position of the fixed sensor using the position detection system. Alternatively, the position of the fixed sensor may be provided to the position detection system in advance. For example, the position of the fixed sensor may be known in advance in the coordinate system of the position detection system to allow the wearable sensor to be tracked relative to the fixed sensor. Based on the positions of the wearable sensor and the fixed sensor as provided by the position detection system, the line of sight detection unit may determine whether the wearable sensor is within the line of sight of the fixed sensor. Thus, the line of sight detection unit may be configured to take into account a fixed object that is located in the field of view of the fixed sensor for determining whether the wearable sensor is within the line of sight of the fixed sensor.

[0037] Preferably, the fixed sensor is or includes a radar. Using the radar, the fixed sensor can sense the field of view where a person may be present. The radar can be a monostatic frequency modulated continuous wave (FMCW) radar or a WIFI-based bistatic radar. The wearable sensor can be or can be included in the following: a smart watch, a neck-worn sensor, a ring sensor, a head-worn sensor, an ear-worn sensor, or a wrist-worn sensor.

[0038] The system can optionally be further improved in that each of the fixed sensor and the wearable sensor includes an air pressure sensor for detecting the height above the floor based on absolute air pressure. The fall detection unit can be configured to detect a person's fall based on the detected heights of the fixed sensor and the wearable sensor. Therefore, the detected heights of the fixed sensor and the wearable sensor can be used as an additional parameter of the line of sight to increase the reliability of detecting a person's fall. For example, if a sudden change in height is detected using the air pressure sensor, the fall detection unit can detect the fall even if the line of sight signal indicates a lack of line of sight between the wearable sensor and the fixed sensor. The air pressure sensor of the fixed sensor can therefore be used as a reference sensor. In addition, an inertial measurement unit (IMU) can be included in the wearable sensor.

[0039] The present invention also relates to a method for detecting a person falling. The method comprises the following steps:

[0040] - receiving a first sensor signal from a fixed sensor indicating that a person has fallen, and / or

[0041] - receiving a second sensor signal from a wearable sensor indicating that the person has fallen, and

[0042] - determine if the wearable sensor is within the line of sight of the fixed sensor,

[0043] - provide a line-of-sight signal indicating whether the wearable sensor is within the line of sight of the fixed sensor,

[0044] - detecting a person falling down based on a) the line of sight signal and b) the first sensor signal and / or the second sensor signal, and

[0045] -Provide an output signal indicating whether a person fall has been detected.

[0046] The method may be performed using the above-described system for detecting a fall of a person.

[0047] The method may include the step of receiving a first sensor signal from a fixed sensor indicating that a person has fallen, but does not include the step of receiving a second sensor signal from a wearable sensor indicating that a person has fallen. Alternatively, the method may include both the step of receiving a first sensor signal from a fixed sensor indicating that a person has fallen and the step of receiving a second sensor signal from a wearable sensor indicating that a person has fallen.

[0048] The invention also relates to a computer program for detecting a fall of a person, the computer program comprising instructions for performing the steps of the above method when run on a computer.The computer program may be stored on a non-transitory computer-readable data medium.

[0049] According to one aspect, an object is to provide a system, method and computer program for monitoring a person. Monitoring may include fall detection. In one example, the system includes: a fixed sensor configured to provide a first sensor signal indicating a monitoring state of the person; a wearable sensor configured to provide a second sensor signal indicating a monitoring state of the person; a line of sight detection unit configured to determine whether the wearable sensor is within the line of sight of the fixed sensor and provide a line of sight signal indicating whether the wearable sensor is within the line of sight of the fixed sensor; a monitoring detection unit configured to detect the monitoring state of the person based on a) the line of sight signal and b) the first sensor signal and / or the second sensor signal; and (optionally) an output unit configured to provide an output signal indicating the monitoring state of the person.

[0050] In this aspect, monitoring may include detecting a person's fall, vital signs such as a person's heart rate, breathing, or any other monitoring related to a person's health / care, or characteristics such as a person's presence, movement, activity. The monitoring state includes the output of the monitoring, such as whether a fall, heart rate, activity, etc. has been detected. It should be understood that this aspect of the invention may also be any combination of a dependent claim or the above embodiments with the corresponding independent claim, for example, a fall detection unit may be understood as a monitoring detection unit.

[0051] It shall be understood that the heating system of claim 1, the method of claim 13, the use of the heating element of claim 13, and the computer program of claim 14 have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0052] It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or the above-described embodiments with the respective independent claim.

[0053] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In the following drawings:

[0055] Figure 1 A system for detecting a fall of a person is shown;

[0056] Figure 2 A system for detecting a fall of a person is shown, the system comprising an external light source and a wearable sensor having a light sensor;

[0057] Figure 3 A system is shown that includes an indoor navigation system that includes a plurality of beacons for determining relative positions of wearable sensors worn by a person;

[0058] Figure 4 A system is shown that includes a position detection system configured to provide position information representing a relative position of a wearable sensor to determine whether the wearable sensor is within a line of sight of a fixed sensor;

[0059] Figure 5 A flow chart representing a method for detecting a fall of a person is shown. DETAILED DESCRIPTION

[0060] Figure 1 A system 100 for detecting a fall of a person 102 is shown (not part of the system). The person 102 wears a smartwatch including a wearable sensor 104. The wearable sensor 104 is on the person 102 and can therefore detect a fall of the person 102 wherever the person 102 goes. In order to detect a fall of the person 102, the wearable sensor 104 includes an accelerometer configured to detect acceleration. The wearable sensor 104 is configured to provide a second sensor signal 106 indicating whether a fall has occurred, for example representing the detected acceleration. In particular, the wearable sensor 104 can be configured to provide the second sensor signal 106 if the detected acceleration is above a predefined acceleration threshold. In the event that the detected acceleration is above the predefined threshold, the wearable sensor 104 therefore reports the fall of the person 102 by providing the second sensor signal 106 indicating the fall.

[0061] Alternatively, the second sensor signal 106 may be provided continuously (e.g., at predefined time intervals), and the analysis of the second sensor signal 106 may be performed external to the wearable sensor 104. For example, the fall detection unit 108 may be used to analyze the second sensor signal 106. The analysis of the second sensor signal 106 may include a comparison with a threshold value (e.g., a predefined acceleration threshold value) for identifying a fall of the person 102.

[0062] In addition to or as an alternative to the accelerometer, the wearable sensor may include a velocity sensor configured to measure the velocity of person 102 , a position sensor configured to measure a change in position of person 102 , or a barometric pressure sensor configured to detect a change in altitude of person 102 .

[0063] The system 100 is a hybrid fall detection system that includes fixed sensors 110 in addition to wearable sensors 104. The fixed sensors 110 have the following advantages: The fixed sensors 110 do not provide positive alarms that falsely indicate a fall of the person 102 triggered by certain movements of the person 102 that might be interpreted as a fall by the wearable sensors 104. For example, if the wearable sensors are included in a smartwatch, a quick movement of the arm might be falsely interpreted as a fall by the wearable sensors. However, the fixed sensors 110 might have a limited field of view, and the person 102 might walk out of the field of view such that the fixed sensors 110 can no longer detect a fall of the person 102.

[0064] The fixed sensor 110 includes a radar that is a monostatic FMCW radar. Alternatively, the fixed sensor 110 may include a Wi-Fi-based bistatic radar. In the event that the fixed sensor 110 detects a fall of the person 102, it provides a first sensor signal 112 indicating the fall. Alternatively, the fixed sensor may continuously provide the first sensor signal 112, and analysis of the first sensor signal 112 may be performed at the fall detection unit 108. Based on the first sensor signal 112, the fall detection unit 108 may extract features indicating a fall of the person 102, and determine whether a real fall of the person 102 has occurred based on the extracted features.

[0065] When the wearable sensor 104 and the fixed sensor 110 are used in combination, a situation may arise where only one of the sensors 104, 110 reports a fall of the person 102. In this case, the system 100 needs to determine whether a real fall has occurred, or whether the report of the fall is a false alarm. In order to make this determination, it is advantageous to know the spatial relationship between the wearable sensor 104 and the fixed sensor 110. In particular, it may be advantageous to know the position of the wearable sensor 104 relative to the fixed sensor 110. If the wearable sensor 104 is within the line of sight 114 of the fixed sensor 110, and only one of the two sensors 104, 110 reports a fall, it may be more likely that the report of the fall is a false alarm. In addition, if the wearable sensor 104 is not within the line of sight 114 of the fixed sensor 110, and only one of the two sensors 104, 110 reports a fall, it may be more likely that a real fall has actually occurred.

[0066] In order to analyze the spatial relationship between the wearable sensor 104 and the fixed sensor 110, the system 100 includes a line of sight detection unit 116, which is configured to determine whether the wearable sensor 104 is within the line of sight 114 of the fixed sensor 110. The detection of the line of sight 114 can be achieved in various ways. For example, as shown in FIG. Figure 2As described in detail, the line of sight 114 can be detected using a light source external to or integrated into the fixed sensor 110, and if the wearable sensor 104 is within the line of sight 114 of the fixed sensor 110, the light source is configured to provide a light signal that can be detected by a light sensor included in the wearable sensor 104. Additionally or alternatively, as described in reference Figure 3 and Figure 4 As described in detail, a navigation system or a position detection system can be used to track the position of the wearable sensor 104 relative to the fixed sensor 110, respectively.

[0067] The line of sight detection unit 116 is configured to provide a line of sight signal 118 indicating whether the wearable sensor 104 is within the line of sight 114 of the fixed sensor 110. The line of sight detection unit 116 may provide the line of sight signal 118 continuously (e.g., at predefined time intervals), and may indicate the absence or presence of the line of sight 114 for each time interval. Alternatively, the line of sight detection unit 116 may provide the line of sight signal 118 only in the event that at least one of the wearable sensor 104 and the fixed sensor 110 reports a fall of the person 102. For example, in the event that at least one of the wearable sensor 104 and the fixed sensor 110 reports a fall of the person 102, the fall detection unit 108 may trigger the line of sight detection unit 116 to check for the presence of the line of sight 114.

[0068] The fall detection unit 108 of the system may receive the line of sight signal 118 from the line of sight detection unit 116, and decide for or against a fall of the person 102 based on the line of sight signal 118 and the fall of the person 102 reported by at least one of the wearable sensor 104 and the fixed sensor 110. The result of the decision made by the fall detection unit 108 may be provided to the output unit 120 of the system, which is configured to provide an output signal 122 indicating whether a fall of the person 102 has been detected. Based on whether the output signal 122 indicates a fall of the person 102, further actions may be triggered, for example, an alarm may be activated to notify about the fall of the person 102. The output signal 122 may also indicate the probability that a real fall has occurred. Based on the provided probability, further actions may be triggered. For example, if the probability that a real fall has occurred is higher than a predefined probability threshold, an alarm may be activated accordingly. The output signal 122 may also be received by a device having a display for visualizing a message indicating the probability that a real fall has occurred. The user of the device may then decide whether further actions are required based on the provided message.

[0069] Figure 2 A system 200 is shown for detecting a fall of a person 202 (not part of the system). Figure 1The system 100 described, the system 200 includes a wearable sensor 204. Similar to the wearable sensor 104, the wearable sensor 204 can be included in a smart watch or similar device worn by the person 202. The wearable sensor 202 can even be implanted under the skin of the person 202. The wearable sensor 204 includes an air pressure sensor 206 for detecting the height above the floor based on the absolute air pressure. The change in height above the floor as detected by the air pressure sensor 206 can indicate a fall of the person 202. The wearable sensor 204 is configured to provide a second sensor signal 208 indicating a fall of the person 204, for example representing the height above the floor detected by the air pressure sensor 206. In addition to the air pressure sensor 206, the wearable sensor 204 may include an accelerometer, a velocity sensor, or a position sensor for detecting a fall of the person 202.

[0070] In addition to the air pressure sensor 206, the wearable sensor 204 includes a light sensor 210 configured to detect a light signal 212 to determine whether the wearable sensor 204 is within a line of sight 214 of a fixed sensor 216 of the system. The light sensor 210 can be a semiconductor-based photodetector, such as a photodiode or a phototransistor. When the light signal 212 is detected with the light sensor 210, the wearable sensor 204 can provide a light detection signal 218 indicating whether the light signal 212 has been detected. The light signal 212 can be a visible flash or an infrared signal or a coded light.

[0071] In operation of the system 200, the light signal 212 may be provided by an external light source 220, which is preferably located at or at least close to the fixed sensor 216. Instead of the external light source 220, an integrated light source integrated into the fixed sensor 216 may be used. It is particularly preferred that the external light source 220 or, alternatively, the integrated light source is located at the same location as the fixed sensor 216 or at least close to the fixed sensor 216. Thus, if the light sensor 210 detects the light signal 212 from the external or integrated light source, it may be assumed that the wearable sensor 204 is within the line of sight 214 of the fixed sensor 216. This assumption may be valid because the light signal 212 approximately propagates along a virtual line of sight axis that virtually connects the wearable sensor 204 and the fixed sensor 216.

[0072] Therefore, the sight line detection unit 222 of the system can use the detection of the light signal 212 using the light sensor 210 to determine the absence or presence of the support sight line 214. If the sight line detection unit 222 receives the light detection signal 218 indicating the presence of the sight line 214 from the wearable sensor 200, the sight line detection unit 222 can provide a sight line signal 224 indicating the presence of the sight line 214 between the wearable sensor 204 and the fixed sensor 216.

[0073] The fixed sensor 216 includes a radar, which is a bistatic radar based on Wi-Fi. Alternatively, the radar may be a monostatic FMCW radar or the like. In the event that the fixed sensor detects a fall of the person 202, the fixed sensor 216 may provide a first sensor signal 228 indicating the fall. The first sensor signal 228 may also be provided repeatedly after a predefined time interval, and the analysis of the first sensor signal 228 may be performed externally, for example by a fall detection unit 230 of the system. In addition to the radar, the fixed sensor 216 includes an air pressure sensor 226, which serves as a reference sensor for the air pressure sensor 206 included by the wearable sensor 204. Thus, the height above the floor as detected by the air pressure sensor 206 of the wearable sensor 204 may be compared with the height detected by the air pressure sensor 226 of the fixed sensor 216. For example, a change in height of the wearable sensor 204 may be determined relative to the reference height provided by the air pressure sensor 226 of the fixed sensor 216.

[0074] The fall detection unit 230 is configured to detect a fall of the person 202 using the first sensor signal 228 and / or the second sensor signal 208 in addition to the line of sight signal 224. In addition, the fall detection unit 230 may use a reference height as measured by the air pressure sensor 226 of the fixed sensor 216. In particular, upon receiving the first sensor signal 228 or the second sensor signal 208, the fall detection unit 230 may trigger the line of sight detection unit 222 to provide a line of sight signal 224, which indicates the absence or presence of the line of sight 214 between the wearable sensor 204 and the fixed sensor 216. When triggered to provide the line of sight signal 224, the line of sight detection unit 222 may trigger the external light source 220 to emit the light signal 212. In the event that the light sensor 210 detects the light signal 212 and the wearable sensor 204 provides the corresponding light detection signal 218 to the line of sight detection unit 222, the line of sight detection unit 222 provides the line of sight signal 224 to the fall detection unit 230, which indicates the presence of the line of sight 214. In this case, the fall detection unit 230 may require both the wearable sensor 204 and the fixed sensor 216 to report a fall of the person 200 in order to detect a real fall. If the line of sight detection unit does not receive a light detection signal, then after a predefined time span, the line of sight detection unit 224 may provide a line of sight signal indicating that there is no line of sight 214. For example, if the line of sight detection unit 224 reports that there is no line of sight 214, then if only one of the wearable sensor 204 and the fixed sensor 216 reports a fall, then the fall detection unit 230 may determine that the supporting person 200 has fallen. Based on the determination of whether a fall has occurred as provided by the fall detection unit 230, the output unit 232 of the system may provide an output signal 234 indicating whether a fall has been detected.

[0075] Figure 3 A system 300 (not part of the system) for detecting a fall of a person 302 is shown. The system 300 includes an indoor navigation system 304, which includes a plurality of beacons 306 for determining the relative position of a wearable sensor 308 worn by the person 302. The indoor navigation system 304 is used to determine the absence or presence of a line of sight 310 between the wearable sensor 308 and the fixed sensor 314 by means of a line of sight detection unit 312. The indoor navigation system 304 may also be connected to a reference Figure 1 The navigation system 304 may also be used in addition to or instead of an external or integrated light source to emit a light signal that may be used as described in reference Figure 2 The wearable sensor described includes a light sensor capture.

[0076] The beacons 306 are distributed over the area where the person 302 moves. For example, the beacons 306 can be attached to a wall, a ceiling, or furniture, etc. The beacons 306 are configured to transmit beacon signals 316 that can be received by the wearable sensor 308. For example, the wearable sensor 308 may include a tag configured to detect the beacon signal 316 provided by the beacon 306. The beacon 306 is configured to communicate via Bluetooth and may be a Bluetooth low energy (BLE) beacon. Alternatively, the beacon 306 may be configured to communicate by means of UWB communication, RFID communication, NFC communication, or VLC communication. Therefore, the tag of the wearable sensor configured to communicate with the beacon 306 is a Bluetooth tag, but when a different communication protocol is used, it may be a UWB tag, an RFID tag, an NFC tag, or a VLC tag.

[0077] The wearable sensor 308 may be configured to determine its location based on communication with the beacon 306 and provide a location signal to the indoor navigation system 304. Alternatively, the wearable sensor 308 may be configured to preferably wirelessly transmit location data based on communication with the beacon, and the indoor navigation system 304 may be configured to determine the location of the wearable sensor based on the provided location data. The indoor navigation system 304 may track the location of the wearable sensor 308 and provide the tracked location 318 to the system line of sight detection unit 312. The relative location of the fixed sensor 314 may be provided a priori to the line of sight detection unit 312, or may be determined by the indoor navigation system 304 and provided to the line of sight detection unit 312. Based on the tracked location 318 and the known location of the fixed sensor 314, the line of sight detection unit 312 may determine whether the wearable sensor 308 is within the line of sight 310 of the fixed sensor 314. The line of sight detection unit 312 may provide a line of sight signal 320 indicating the absence or presence of the line of sight 310.

[0078] The wearable sensor 308 of the system 300 includes a speed sensor and is configured to report a fall of the person 302 if the speed sensor senses a speed above a predefined speed threshold. As an alternative or in addition to the speed sensor, the wearable sensor 308 may include a speed sensor as described in reference Figure 2 The air pressure sensor described in Figure 1 The wearable sensor 308 of the described system 100 includes an accelerometer. Additionally or alternatively, the wearable sensor 308 may also include a position sensor. In the event that the speed sensor detects a speed above a predefined threshold, or alternatively, repeatedly provides the detected speed at predefined time intervals, the wearable sensor 308 may provide a second sensor signal 322 indicating a fall of the person 302.

[0079] Fixed sensors 314 include radars, which may be, for example, Figure 1 The monostatic FMCV radar described, or for example as in reference Figure 2 The Wi-Fi based bistatic radar described above. Upon detecting a fall or continuously at predefined time intervals, the fixed sensor 314 may provide a first sensor signal 324 indicating a fall of the person 302 .

[0080] Based on at least one of the first sensor signal 324 and the second sensor signal 322 and using the line of sight signal 320, the fall detection unit 328 of the system is configured to detect a fall of the person 302, for example, as described with reference to Figure 1 and Figure 2 The fall detection unit of the described system 100 or system 200 may then be described. The output unit 330 of the system may then provide an output signal 332 indicating whether the fall detection unit 328 has detected a fall.

[0081] Figure 4 A system 400 (not part of the system) for detecting a fall of a person 402 is shown. The system 400 includes a position detection system 406 configured to provide position information 408 representing a relative position of a wearable sensor 404 to determine whether the wearable sensor 404 is within a line of sight 410 of a fixed sensor 412. The position detection system 406 can be used in addition to or instead of an indoor navigation system, for example, as described with respect to Figure 3 The position detection system 406 may also be used in addition to or instead of an external or integrated light source configured to emit a light signal as described in reference Figure 2 The position detection system 406 can also be used with the light sensor detection of the wearable sensor described in the reference Figure 1 The system 100 described is used in conjunction with.

[0082] The position detection system 406 is an electromagnetic position detection system including a field generator configured to generate an oscillating magnetic field 416. The wearable sensor 404 includes a position sensor 414, which includes at least one sensor coil. The oscillating magnetic field 416 can induce a voltage in the sensor coil of the position sensor 414, and the wearable sensor 404 can provide a position detection signal representing the induced voltage. Since the induced voltage depends on the distance to the magnetic field generator and also on the orientation of the sensor coil within the oscillating magnetic field, the relative position of the wearable sensor can be determined based on the induced voltage. Based on the position detection signal provided by the position sensor, the position detection system 406 can determine the relative position of the wearable sensor 404. Optionally, the fixed sensor 412 can also be equipped with a position sensor, so that the position detection system 406 can also determine the relative position of the fixed sensor 412. Alternatively, the relative position of the fixed sensor can be known a priori, for example as a coordinate in the coordinate system of the position detection system. As an alternative to an electromagnetic position detection system, the position detection system 406 may be an optical position detection system, and the position sensor 414 may include one or more light emitting diodes (LEDs) or the like that emit light, based on which the position detection system 406 may determine the relative position of the wearable sensor 404. Alternatively, the position sensor 414 may include a light detector for detecting light provided by one or more light sources for position detection.

[0083] In particular, when using an optical position detection system, it may be possible to employ a plurality of modulated LEDs as light sources, which are distributed in a room or over an area in which a person moves. For example, the LED may be part of or comprised by one or more luminaires, or attached to one or more power sockets, etc. A person may wear a position sensor, for example, as part of a wearable sensor, for example, on the person's wrist. The position sensor may then sense the modulated light emitted by the distributed LEDs with a light detector for determining the relative position of the position sensor based on the modulation of the detected light. For example, the position sensor may comprise a combination of a segmented photodiode and an aperture, for example in combination with a processing electronic device, which is configured to identify the modulation of the light emission of the distributed LEDs. Thereby, it is possible to detect the position of the wearable sensor, which in turn may be used to determine whether the wearable sensor is within the line of sight of the fixed sensor.

[0084] Alternatively, it may be possible to employ multiple position sensors that are distributed in a room or over an area where a person moves. Preferably, the relative positions of the distributed position sensors are known. For example, the position sensor may be attached to or be part of a luminaire and / or power socket, etc. In this case, a modulated LED may be worn on a person, preferably as part of a wearable sensor, to emit modulated light that can be detected by multiple distributed position sensors to detect the position of the wearable sensor relative to the distributed position sensors. Based on the relative position of the modulated LED worn on the person, it may be possible to determine whether the wearable sensor is within the line of sight of the fixed sensor.

[0085] In addition to the position sensor 414, the wearable sensor 404 may include, for example, Figure 2 The pressure sensor described, or for example as reference Figure 2 accelerometer described, or for example as reference Figure 3 The wearable sensor 404 is configured to provide a second sensor signal 418 indicating the fall of the person 402. The fixed sensor 412 includes a radar that can be a monostatic FMCW radar or a Wi-Fi based bistatic radar. When the fall of the person 402 is detected, the fixed sensor 412 provides a first sensor signal 420 indicating the fall.

[0086] Based on the position information 408 representing the relative position of the wearable sensor 404 as tracked by the position detection system 406 and the known relative position of the fixed sensor 412, the line of sight detection unit 422 of the system can determine whether the wearable sensor 404 is within the line of sight 410 of the fixed sensor 412. After checking the line of sight 410, the line of sight detection unit 422 can provide a line of sight detection signal 424 indicating the presence or absence of the line of sight.

[0087] The fall detection unit 426 of the system may determine the likelihood that a real fall of the person 402 has occurred using the provided line of sight signal 424 and at least one of the first sensor signal 420 and the second sensor signal 418 indicating a fall of the person 402. The result of the fall detection performed by the fall detection unit 426 may then be transmitted to the output unit 428, which is configured to provide an output signal 430 indicative of the result.

[0088] Figure 5 A flow chart showing a method for detecting a fall of a person is shown. The method described below can be used, for example, as described in reference Figure 1 The system 100 described in reference Figure 2 The system 200 described in reference Figure 3The system 300 described herein or using reference Figure 4 The system 400 described is implemented.

[0089] In particular, the method can be implemented by means of a computer program comprising instructions for performing the method steps when running on a computer. The computer can be part of the system 100, the system 200, the system 300 or the system 400. For example, the computer can include or implement the functionality of the sight detection unit and / or the fall detection unit and / or the output unit as described above with respect to the systems 100, 200, 300 and / or 400.

[0090] In the method, a first sensor signal indicating that a person has fallen is received from a fixed sensor, preferably comprising a radar (step S1). As an alternative or in addition to receiving the first sensor signal, in the method, a second sensor signal indicating that a person has fallen is received from a wearable sensor, which may be part of a smart watch or the like worn by the person (step S2). In addition to receiving the first sensor signal and / or the second sensor signal, it is determined whether the wearable sensor is within the line of sight of the fixed sensor (step S3). Determining whether the wearable sensor is within the line of sight of the fixed sensor may be achieved using an external or integrated light source for emitting light signals and a light sensor of the wearable sensor, as described with respect to Figure 2 Alternatively or additionally, line of sight may be used as described with respect to Figure 3 The navigation system described and / or by using the reference Figure 4 The position detection system described is determined.

[0091] After determining whether the wearable sensor is within the line of sight of the fixed sensor, a line of sight signal is provided, which indicates the absence or presence of the line of sight (step S4). Using the line of sight signal and the first sensor signal and / or the second sensor signal, for example, using, for example, as reference Figure 1 , Figure 2 , Figure 3 or Figure 4 The fall detection unit described above detects a fall of a person (step S5). Subsequently, an output signal indicating whether a fall of a person has been detected is provided (step S6).

[0092] In summary, the present invention relates to a system for detecting a fall of a person. The system comprises a fixed sensor located at a fixed position relative to the person and a wearable sensor worn by the person, which two sensors can report a fall of the person independently of each other. Furthermore, the system comprises a line of sight detection unit, which is configured to determine whether the wearable sensor is within the line of sight of the fixed sensor. For detecting a fall of the person, the fall detection unit of the system takes into account a fall report as provided by one or both of the fixed sensor and the wearable sensor. Furthermore, for detecting a fall, the fall detection unit takes into account the absence or presence of a line of sight between the wearable sensor and the fixed sensor. Thereby, it is possible to increase the reliability of detecting a fall, in particular in cases where only one of the wearable sensor and the fixed sensor reports a fall.

[0093] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0094] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0095] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0096] The processes performed by one or several units or devices (e.g., the following processing: receiving the first and second sensor signals, determining the line of sight, detecting a person's fall, etc.) may be performed by any other number of units or devices. These processes (in particular, detecting a person's fall according to the method for detecting a person's fall performed by the fall detection system) may be implemented as program code means of a computer program and / or as dedicated hardware.

[0097] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided together with or as a part of other hardware; but may also be distributed in other forms, such as via the Internet, or other wired or wireless telecommunication systems.

[0098] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A system for detecting a person falling, the system comprising: - a fixed sensor configured to provide a first sensor signal indicative of a person falling; - a wearable sensor configured to provide a second sensor signal indicative of a person falling; a line of sight detection unit configured to determine whether the wearable sensor is within the line of sight of the fixed sensor and to provide a line of sight signal indicating whether the wearable sensor is within the line of sight of the fixed sensor; - a fall detection unit configured to detect a fall of a person based on a) the line of sight signal and b) the first sensor signal and / or the second sensor signal; as well as - an output unit configured to provide an output signal indicating whether a fall of a person has been detected.

2. The system of claim 1 , wherein the fall detection unit is configured to detect a fall of the person if the line of sight signal indicates that the wearable sensor is within the line of sight of the fixed sensor and at least one of the first sensor signal and the second sensor signal indicates that the person has fallen.

3. The system according to claim 1 or 2, wherein the line of sight detection unit is configured to repeatedly determine whether the wearable sensor is within the line of sight of the fixed sensor at predefined time intervals.

4. The system of claim 1 or 2, wherein the line of sight detection unit is configured to determine whether the wearable sensor is within the line of sight of the fixed sensor if at least one of the first sensor signal and the second sensor signal indicates that the person has fallen.

5. System according to at least one of the preceding claims, wherein for determining whether the wearable sensor is within the line of sight of the fixed sensor, the line of sight detection unit is configured to take into account at least one fixed object within the field of view of the fixed sensor.

6. The system according to at least one of the preceding claims, further comprising an external light source operably connected to the fall detection unit and located near the fixed sensor, wherein the wearable sensor comprises a light sensor configured to detect light signals, and wherein the line of sight detection unit is configured to determine that the wearable sensor is within the line of sight of the fixed sensor if the wearable sensor has detected a light signal emitted by the external light source with its light sensor.

7. A system according to at least one of the preceding claims, wherein the fixed sensor comprises an integrated light source, the wearable sensor comprises a light sensor configured to detect light signals, and wherein the line of sight detection unit is configured to determine that the wearable sensor is within the line of sight of the fixed sensor if the wearable sensor has detected a light signal emitted by the integrated light source with its light sensor.

8. The system according to at least one of the preceding claims, further comprising a navigation system, the navigation system comprising a plurality of beacons configured to communicate with the wearable sensor to determine the relative position of the wearable sensor using the navigation system, wherein the line of sight detection unit is configured to determine whether the wearable sensor is within the line of sight of the fixed sensor based on the tracked position of the wearable sensor and the known position of the fixed sensor.

9. The system of claim 8, wherein the wearable sensor is configured to communicate with a beacon of the navigation system by means of ultra-wideband communication, radio frequency identification communication, near field communication, Bluetooth communication, or visible light communication.

10. The system according to at least one of the preceding claims, further comprising a position detection system, the position detection system comprising at least one position sensor, the at least one position sensor being located at the wearable sensor and configured to track the position of the wearable sensor relative to the fixed sensor using the position detection system, and wherein the line of sight detection unit is configured to determine whether the wearable sensor is within the line of sight of the fixed sensor based on the tracked position of the wearable sensor and the known position of the fixed sensor.

11. The system according to at least one of the preceding claims, wherein the fixed sensor is or comprises a radar.

12. The system according to at least one of the preceding claims, wherein each of the fixed sensor and the wearable sensor comprises an air pressure sensor for detecting a height above a floor based on absolute air pressure, and wherein the fall detection unit is configured to detect a fall of a person based on the detected heights of the fixed sensor and the wearable sensor.

13. A computer-implemented method for detecting a fall of a person, the method comprising: - receiving a first sensor signal from a fixed sensor indicating that a person has fallen, and / or - receiving a second sensor signal from a wearable sensor indicating that the person has fallen, and - determine if the wearable sensor is within the line of sight of the fixed sensor, - provide a line-of-sight signal indicating whether the wearable sensor is within the line of sight of the fixed sensor, - detecting a person falling down based on a) the line of sight signal and b) the first sensor signal and / or the second sensor signal, and -Provide an output signal indicating whether a person fall has been detected.

14. A computer program for detecting a fall of a person, the computer program comprising instructions for performing the steps of the method according to claim 13 when run on a computer.

15. A non-transitory computer-readable data medium storing a computer program according to claim 14.

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