CN116685265A

CN116685265A - Detection system and method for detecting movement of an object

Info

Publication number: CN116685265A
Application number: CN202280009243.4A
Authority: CN
Inventors: F·皮尔曼; P·戴克斯勒
Original assignee: Signify Holding BV
Current assignee: Signify Holding BV
Priority date: 2021-01-07
Filing date: 2022-01-04
Publication date: 2023-09-01

Abstract

The present invention relates to a detection system for detecting a movement of an object by using at least two devices adapted to transmit and receive radio frequency signals. The system (110) comprises: a control unit (111) for controlling the at least two devices such that at least one of the at least two devices is a transmitting device (120) transmitting a radio frequency signal having a frequency of the transmission signal and such that at least one of the at least two devices is a receiving device (130) receiving the radio frequency signal, the radio frequency signal being indicative of a reflection of the transmitted radio frequency signal of the object; a signal frequency providing unit (112) for providing a transmission signal frequency at which the radio frequency signal has been transmitted; and a detection unit (113) for detecting a movement of the object by performing passive Doppler sensing based on the received radio frequency signal and the provided transmission signal frequency.

Description

Detection system and method for detecting movement of an object

Technical Field

The present invention relates to a detection system, method and computer program for detecting a movement of an object.

Background

Today, networks using multiple devices in home and office applications use radio frequency sensing to detect movement of objects are of increasing interest. The basic idea of radio frequency is that network devices (including e.g. luminaires, smart switches, smart application devices, etc.) form a radio network by frequently exchanging messages, wherein the amplitude of the messages is then monitored and compared with e.g. a baseline signal to determine changes in the environment of the network device. For example, these changes may be interpreted as movements of a person, inactivity of a person, changes in the state of an object (such as opening or closing of a door), and the like. However, monitoring the amplitude of the exchanged messages is a complex and error-prone process, which often results in false or false-positive results, e.g. in false detection of persons in the room. Because radio frequency sensing is often used to control functions of network devices (e.g., lighting functions), inaccurate radio frequency sensing results cause interference in network device applications and are highly undesirable. It would therefore be advantageous to provide a motion detection system for a network of network devices that allows for higher accuracy.

Disclosure of Invention

It is an object of the invention to provide a detection system, a method and a computer program that allow an improved detection of a movement of an object in the environment of the detection system.

In a first aspect of the present invention a detection system for detecting a movement of an object by using at least two devices adapted to transmit and receive radio frequency signals is presented, wherein the system comprises a) a control unit for controlling the at least two devices such that at least one of the at least two devices is a transmitting device transmitting radio frequency signals having a transmit signal frequency and such that at least one of the at least two devices is a receiving device receiving radio frequency signals, the radio frequency signals being indicative of a reflection of the transmitted radio frequency signals of the object, b) a signal frequency providing unit for providing a transmit signal frequency at which the radio frequency signals have been transmitted, and c) a detection unit for detecting a movement of the object by performing passive Doppler (passive Doppler) sensing based on the received radio frequency signals and the provided transmit signal frequency.

Since the detection unit is adapted to detect the movement of the object by performing passive doppler sensing based on the received radio frequency signal transmitted by one of the at least two devices and received by the other of the at least two devices and the provided transmission signal frequency, passive doppler sensing may be performed based on knowledge of the transmission signal frequency, i.e. without having to determine the transmission signal frequency from the received radio frequency signal itself. This allows the motion to be detected with high accuracy using radio frequency signals. Thus, the detection system allows for improved motion detection.

A detection system for detecting movement of an object utilizes at least two devices adapted to transmit and receive radio frequency signals. The object may refer to, for example, a living being or an object, in particular to a moving living being or object. Biological may refer to a human or an animal; and the object may refer to any object, for example to a robotic household appliance or door. In a preferred embodiment, the detection system is adapted to detect movements of a human being in the vicinity of the at least two devices. Typically, a simple object (such as a robotic cleaner in a room) provides a simple doppler signal, i.e. the object has only one velocity. More complex objects or living beings include more complex doppler signals because different parts of the complex object or living beings typically move in different directions at different speeds. These more complex doppler signals can also be considered doppler features and allow easy differentiation between different objects and their behaviour.

Preferably, the two devices are network devices that are part of a network formed by at least the two network devices. However, the network may also comprise more than two network devices, wherein in this case the detection system may utilize all network devices or only a part of the network devices as at least two network devices for performing the motion detection. The network of network devices is typically formed by the communication of network devices with each other, wherein the communication of network devices of the network may be based on any known communication protocol, such as WiFi communication protocol, zigBee communication protocol, bluetooth communication protocol, etc. It is therefore preferred that the two devices, preferably network devices, comprise a network device communication unit, wherein the network device communication unit is adapted to transmit and receive wireless signals, in particular radio frequency signals, and/or wired signals. For example, the network device communication unit may comprise a network device transceiver for receiving and transmitting radio frequency signals, or a transmitter for transmitting radio frequency signals and a receiver for receiving radio frequency signals. In particular, the at least two devices may be intelligent network devices, i.e. any device comprising a communication unit for transmitting and receiving wireless signals, in particular radio frequency signals, but which otherwise fulfil the functions of a corresponding legacy device. For example, such intelligent network devices may be intelligent home devices, in which case the corresponding legacy functionality may be that of legacy home devices (e.g. lighting devices or home appliances). In a preferred embodiment, the at least two devices are referred to as smart light modules, smart plugs or smart switches.

The detection system may be part of a network comprising at least two devices, e.g. by being provided as software or hardware in one of the network devices or distributed over a plurality of network devices communicating with each other. However, the detection system may also be a stand-alone system or part of one or more devices that are not part of the network but may communicate with at least one device that is preferably part of the network. For example, the detection system may be provided as software running on a handheld computing device or in another network, which software may communicate with the network or at least one device that is preferably part of the network, for example via a gateway. If the at least two devices are not part of the network, the detection system may be provided as part of one of the at least two devices (e.g. as software or hardware provided in one of the at least two devices) and may be adapted to communicate with two of the at least two devices via a wired or wireless communication protocol. Further, also in this case, the detection system may be a stand-alone system provided external to the at least two devices, e.g. on a handheld computing device, a network solution, or any other computing device adapted to communicate with the at least two devices.

The control unit is adapted to control at least two devices. Furthermore, if more than two devices are provided, e.g. as part of a network of a plurality of network devices, the control unit may be adapted to control all or part of these devices. In general, the control unit may be adapted to control the at least two devices by sending control commands to the at least two devices, which control commands, when executed by the at least two devices, result in providing the functionality of the at least two devices indicated by the control commands.

In particular, the control unit is adapted to control at least one of the at least two devices such that it acts as a transmitting device for transmitting radio frequency signals having a transmission signal frequency. The transmit signal frequency may refer to a frequency or a range of frequencies. Furthermore, the control unit may be adapted to control the sensing device such that more than one radio frequency signal is transmitted, each radio frequency signal having a different sensing signal frequency. In particular, the transmitted radio frequency signals are transmitted at a transmission signal frequency that lies within a predetermined signal frequency range, for example, within a signal frequency range defined by the ZigBee standard of 2.4GHz, or within a frequency range of WiFi standard communications that lies within a frequency range of about 2.5GHz, 50GHz, or even 60 GHz. Within such a predefined frequency range, the control unit may be adapted to control the transmitting device such that it transmits radio frequency signals having a specific transmission signal frequency selected from the available range. However, the radio frequency signal having the transmission signal frequency transmitted by the transmission device may also be predetermined, for example, by the hardware of the transmission device or by a rule provided within the transmission device, so that in this case the control unit controls the transmission device by causing the transmission device to transmit only the radio frequency signal having the transmission signal frequency indicated by the transmission device itself. If the at least two devices refer to network devices, it is preferred that the transmitting network device is adapted to utilize its network device communication unit, in particular a transmitter of the network device communication unit, for transmitting radio frequency signals having the frequency of the transmission signal. However, if the transmitting network device includes a network device communication unit adapted for only wired network communication or for only network communication in another range than the radio frequency range, the network device may include an additional unit for transmitting radio frequency signals. In a preferred embodiment, the radio frequency signals transmitted by the transmitting device refer to communication signals within the network, i.e. signals for communication between network devices.

The control unit is further adapted to control at least one of the at least two devices to act as a receiving device receiving a radio frequency signal indicative of a reflection of the transmitted radio frequency signal of the object. In particular, the control unit may be adapted to control the receiving device such that it monitors signals received within a predetermined frequency range within which reflection of the transmitted radio frequency signal (in particular when reflected by the object) is expected. Preferably, if the receiving device refers to a network device, the receiving device receives the reflected radio frequency signal with a network device communication unit, in particular a receiver of the network device communication unit. However, the receiving device may also comprise a dedicated receiving unit which is not part of the network device communication unit for receiving the reflected radio frequency signals. The transmitting device and the receiving device are typically not referred to the same device of the at least two devices. Thus, if only two devices are used, one of the two devices is a transmitting device and the other of the two devices is a receiving device. In particular, at least two devices are independent of each other and are not provided at the same location. Preferably, the transmitting device and the receiving device are provided with a certain predetermined distance from each other, wherein the distance is preferably greater than 1m, more preferably greater than 2m. Thus, in a preferred embodiment, the control of the at least two devices by the control unit comprises selecting which of the at least two devices acts as a transmitting device and which of the at least two devices acts as a receiving device. In particular, if more than two devices (i.e., multiple devices) are provided, the selecting may include selecting one or more of the devices to act as a transmitting device and selecting one or more of the devices to act as a receiving device based on, for example, the locations of the multiple devices, characteristics of the multiple devices (e.g., whether the devices include radio frequency transmit and/or receive units), and/or availability of the devices, etc. The control unit is thus generally adapted to control the formation of a pair of devices, wherein one of such a pair of devices is regarded as a transmitting device of the pair and the other device is regarded as a receiving device of the pair. However, overlapping of such pairs may also be considered so that, for example, one device acts as a transmitting device in one device pair and as a receiving device in another device pair, or so that the transmitting device is the same for different device pairs but the receiving device is different for each pair. In the last case, all pairs of devices comprising the same transmitting device may be considered to form a device group. The pairs or groups of devices may be distinguished by distinguishing the signals transmitted by the transmitting devices of each pair or group of devices. For example, the control unit may be adapted to control each transmitting device of the pair or group of devices to transmit radio frequency signals at different times or by using different transmit signal frequencies.

In general, the control unit may be adapted to control the transmitting device and/or the receiving device in a scanning mode, wherein the scanning mode allows for a directional scanning of at least a portion of the sensing area. Preferably, in the scanning mode, the control unit is adapted to control the sensing device and/or the receiving device to perform directional transmission and/or reception. For example, using known orientation methods, the sensing device may be controlled to subsequently direct radio frequency signals to different areas of the room to systematically scan for the presence of motion in the room. However, in other embodiments, the control unit may be adapted to control the transmitting device and/or the receiving device to perform non-directional transmission, in particular to transmit and/or receive signals in/from multiple directions simultaneously.

Furthermore, the detection system comprises a signal frequency providing unit for providing a transmission signal frequency at which the radio frequency signal has been transmitted. The signal frequency providing unit may be, for example, a storage unit storing the transmission signal frequency (the transmission signal frequency is, for example, a predetermined transmission signal frequency), or may be connected to a storage unit storing the transmission signal frequency. The signal frequency providing unit may also be adapted as a receiving unit for receiving the transmission signal frequency, e.g. from a control unit controlling the transmitting device or from the transmitting device itself, and then providing the received transmission signal frequency. For example, the transmitting device may be adapted to monitor and provide a transmission signal frequency of the radio frequency signal transmitted by itself, and to provide the transmission signal frequency to the signal frequency providing unit to provide the transmission signal frequency. In particular, the signal frequency providing unit may be part of the transmitting device and may then be adapted to communicate with the detection unit to provide the transmitted signal frequency. In general, for all embodiments, if the control unit controls more than one transmitting device, the signal frequency providing unit may be adapted to provide the transmission signal frequency of each transmitting device, in particular in case the transmitting devices use different transmission signal frequencies.

The detection unit is then adapted to detect the movement of the object by performing passive doppler sensing based on the received radio frequency signal and the provided transmission signal frequency. Typically, passive doppler sensing involves performing doppler analysis on a received signal, wherein the receiver of the signal is different from the transmitter, i.e. wherein the transmitter is provided at a different location than the receiver of the signal. In the present invention, passive doppler sensing is based not only on received radio frequency signals, but also on knowledge of the frequency of the transmitted signals, i.e. knowledge of the transmitted radio frequency signals. This has the following advantages: a complex and error-prone analysis of the received radio frequency signal for extracting the transmit signal frequency from the received radio frequency signal may be omitted. In particular, based on the received radio frequency signal and the provided transmit signal frequency, a known Doppler analysis may be performed. Doppler analysis is based on the following principle: the frequency of the wave reflected from the moving object will vary depending on the speed of the moving object. Thus, by providing the received radio frequency signal and the provided transmission signal frequency to the detection unit, the detection unit may determine whether the received radio frequency signal comprises at least one signal portion having a frequency that is offset with respect to the provided transmission signal frequency, which frequency is indicative of the presence of a movement of the object. In order to detect the movement of the object based on the received radio frequency signal and the provided frequency of the transmission signal, the detection unit may be adapted to extract the frequency shift from the received radio frequency signal indicative of the movement of the object (i.e. to perform a doppler analysis), such as a signal frequency analysis method, a signal mixing method, etc., using any known software or hardware solution. Furthermore, the detection unit is preferably adapted to distinguish between biological and simple objects, e.g. based on the complexity of the doppler analysis results. For example, for a simple object, the result typically includes only one velocity, while for a living being, the result is expected to result in more than one determined velocity, i.e., a velocity signature. The detection unit may then be adapted to further analyze the velocity characteristics, e.g. to determine the identity, average velocity, respiratory movement, direction of movement, etc. of the living being based on the velocity characteristics. For example, the detection unit may be adapted to determine in the spectrum of the received signal whether more than one doppler shift can be found, and may determine that this is indicative of the presence of living beings.

In an embodiment, the control unit is further adapted to: controlling the at least two devices such that each of the at least two devices acts as a transmitting device, each transmitting device transmitting a radio frequency signal having a different signal frequency; and controlling the at least two devices such that each device acts as a receiving device to receive a reflection of a transmitted radio frequency signal of an object corresponding to the transmitted radio frequency signal of the respective other device, wherein the detection unit is adapted to perform passive doppler sensing based on the received radio frequency signal. Thus, in this embodiment, the control unit is adapted to control the devices available as transmitting devices and receiving devices such that the device pairs or groups are formed as overlapping device pairs or groups. In particular, in this embodiment, a device group may be defined for each device capable of acting as a transmitting device, wherein the device group then comprises the device acting as a transmitting device and all other devices capable of receiving as receiving devices the reflected radio frequency signals of the transmitting device. Thus, a transmitting device that is also able to receive radio frequency signals acts as a transmitting device in its own group and as a receiving device in other groups. The detection unit is then adapted to perform passive doppler sensing, i.e. doppler analysis, based on the received radio frequency signals. For example, the detection device may be adapted to perform passive doppler sensing for each group independent of each other, preferably based on the results of doppler analysis of all pairs of the group. However, the detection unit may also be adapted to perform passive doppler sensing using radio frequency signals received from different groups. For example, the detection unit may be adapted to compare the results of passive doppler sensing performed by different pairs of one group or by different groups with each other and apply a logic rule to the comparison to determine whether the results do relate to movement of an object, in particular a human being, or are caused by other reasons, such as noise, vibrations of the device itself, etc. In particular, in order to reduce the influence of vibrations on the motion detection, e.g. caused by processes within the device or in the device environment, it is preferred that the detection unit is adapted to compare the passive doppler sensing results of all pairs of devices, wherein the receiving device of one pair is the transmitting device of the other pair and vice versa. Thus, passive doppler sensing results, preferably based on different transmit signal frequencies and corresponding to substantially the same detection region (in particular, the region between two devices forming two device pairs), may be compared, and a logic rule may be applied to the comparison to determine whether the detection result is caused by movement of the object. For example, if the passive doppler sensing results indicate that the object is moving at different speeds, the detection results are likely not caused by moving objects, but are likely caused by noise, for example.

In an embodiment, the control unit is adapted to control the transmitting device to detect a radio frequency signal resulting from a reflection of a transmitted radio frequency signal transmitted by itself, and wherein the detection unit is adapted to monitor the detected radio frequency signal and to detect the movement of the object further based on the monitored radio frequency signal. In particular, the transmitting device is adapted to monitor the radio frequency signal resulting from the reflection of the transmitted radio frequency signal transmitted by itself, which is not reflected by the object. The signal frequency providing unit may then be further adapted to provide the detected radio frequency signal to the detection unit. The detection unit is then adapted to monitor the detected radio frequency signal detected by the transmitting device. Monitoring may include, for example, determining a temporal change in the detected radio frequency signal. In particular, a sudden (i.e. within a predetermined short time frame) occurrence of a change may indicate an event that should be considered when detecting the movement of the object. Preferably, the detection unit is adapted to monitor the detected radio frequency signal by monitoring the frequency of occurrence in the detected radio frequency signal. In particular, it is preferred that the detection unit identifies a narrow frequency band in the spectrum of the detected radio frequency signal, i.e. a signal in a frequency range smaller than a predetermined range, preferably a speed variation of 20cm/s, more preferably 10cm/s, according to a doppler relation. Such narrow frequencies are typically the result of vibrations of the transmitting device itself or the environment of the transmitting device. Thus, when the application of the detection system is intended to detect a movement of an object, preferably a human being, it is preferred that the detection unit is adapted to use the identified narrow frequency range to filter out the identified narrow frequency range in the received radio frequency signal, since it is contemplated that the received radio frequency signal also comprises frequencies in the identified narrow frequency band, i.e. shows an excitation in the frequency spectrum, which excitation, however, is likely not caused by the movement of the object. The detection unit is then adapted to determine the movement of the object by performing passive doppler sensing based on the filtered received radio frequency signal.

In an embodiment, the detection unit is adapted to: determining an excitation within a frequency range in a frequency spectrum of the received radio frequency signal, wherein the excitation is substantially constant over a predetermined period of time; and performing passive doppler sensing based on the received radio frequency signal by filtering out a frequency range in the spectrum of the received radio frequency signal. Since it is expected that the movement of an object, in particular a human being, is not constant over a long period of time, excitation over a frequency range that is substantially constant over a long period of time is likely not caused by movement of the object, but by vibrations in the environment or by noise, for example. Based on the application of the detection system, it is preferred that the predetermined period of time is determined, for example, according to a time scale of the movement expected by the movement of the object that should be detected. For example, if the object whose movement should be detected is a human being, the predetermined period of time may refer to a few minutes (e.g. 3 or 4 minutes), because it is highly unlikely that the movement of a human being, for example, in a small room does not change during such a period of time. Thus, it is possible to observe that a substantially constant excitation in the received radio frequency signal, i.e. an excitation that is constant over a predetermined range of more than a few minutes, is not likely to be caused by the movement of the object and can be filtered out. In this context, the term "substantially constant" refers to an excitation that occurs at the same frequency or frequency range during a predetermined period of time, the amplitude of which is not below a noise threshold.

In a preferred embodiment, the detection unit may be adapted to determine the occurrence of an excitation in a frequency range narrower than a predetermined frequency range, and to perform passive doppler sensing based on the received radio frequency signal by filtering out the narrow frequency range in the spectrum of the received radio frequency signal. In particular, if the motion of the object that should be detected refers to the motion of a human being, it may be expected that the excitation in the frequency range of the received radio frequency signal caused by the moving human being expands or blurs over a wide frequency range, e.g. as different parts of the human body move at different speeds like arms and legs move at different speeds than the human torso. Thus, the excitation of the received radio frequency signal occurring in a very narrow frequency range is likely not caused by the movement of a human being or indeed any living being, but by vibrations of mechanical parts in the environment of the transmitting device or the receiving device. Preferably, the predetermined frequency range refers to a velocity variation of 20cm/s, more preferably 10cm/s, according to the Doppler relationship. Thus, by filtering out the excitation, which is likely to be caused by the motion source (which should not be detected with respect to the application of the detection system), or any kind of noise in the environment of the detection system, the accuracy of the motion detection can be improved, especially in view of the specific application of the detection system.

In one embodiment, the detection unit is adapted to determine an I channel and a Q channel based on the received radio frequency signal and to perform passive doppler sensing based on the I channel and the Q channel.

In particular, the detection unit may determine the I channel by multiplying the received radio frequency signal by a signal comprising the provided transmission signal frequency and the Q channel by multiplying the received radio frequency signal again by a signal comprising the provided transmission signal frequency (wherein one of the two signals is phase shifted, e.g. by 90 °), thereby determining the I channel and the Q channel. Preferably, the detection unit is then adapted to construct a complex signal from the Q channel and the I channel, wherein the I channel refers to the imaginary part of the complex signal and the Q channel refers to the real part of the complex signal. The complex signal is then preferably used to detect the movement of the object. In particular, it is preferred that the spectrum of the complex signal is determined by the detection unit, for example by performing a fourier transformation of the complex signal and by detecting the movement of the object based on the spectrum of the complex signal. For example, a complex signal of such a construction may show a positive frequency and a negative frequency in the frequency spectrum, wherein an excitation in the positive frequency indicates a movement with a movement component towards the receiving device, and a negative frequency indicates a movement with a movement component away from the receiving device. However, the exact relationship between motion and the determined frequency depends on the phase shift used to construct the Q channel. In general, the construction of the complex signal allows not only an accurate determination of the speed of movement of the object, but also at least an accurate determination of the direction of movement of the object relative to the receiving device, independently of the exact phase shift used. Furthermore, in complex signals (in particular in the spectrum of complex signals), movements that are not caused by objects (in particular humans) but are caused by vibrations in the device environment, for example, can be distinguished even more clearly. In particular, noise caused by vibrations in the environment results in excitation in the spectrum of complex signals in both positive and negative frequencies, as vibrations comprise two motion components. In contrast, a general movement of an object (like a human) comprises a more fixed direction and thus only results in excitation in positive or negative frequencies. It is therefore preferred that the detection unit is adapted to identify an excitation in the frequency spectrum of the complex signal caused by the vibration, e.g. because the excitation is present in both positive and negative frequencies, thereby filtering the frequency range in which the excitation occurs from the received radio frequency signal, and to base the doppler analysis on the filtered received radio frequency signal. In this case, it is noted that respiratory movements of a person that is not otherwise moving may also be considered vibrations, and thus may be detected by monitoring positive and negative frequencies using the above-described method.

In an embodiment, the control unit is further adapted to control the transmitting device to transmit an additional radio frequency signal having a signal frequency different from the frequency of the transmitted signal, and to control the receiving device to receive the additional radio frequency signal resulting from the reflection of the additional radio frequency signal from the object, wherein the detection unit is further adapted to perform passive doppler sensing based on the additional received radio frequency signal. Thus, in this embodiment, each transmitting device controlled by the control unit is adapted to transmit two radio frequency signals having different transmission signal frequencies, such that each receiving device controlled by the control unit can receive two radio frequency signals that have been reflected from the object based on the two different transmitted radio frequency signals. Since the doppler effect, i.e. the frequency shift due to motion in the reflected radio frequency signal, is frequency dependent for moving objects, different frequency shifts can be found in two different received radio frequency signals according to the principle of the doppler effect. In general, the transmission signal frequency providing unit is in this case adapted to provide the two transmission signal frequencies to the detection unit.

In a preferred embodiment, the detection unit is adapted to perform passive doppler sensing further based on the additionally received radio frequency signal by comparing the additionally received radio frequency signal with the received radio frequency signal. Preferably, the comparison refers to subtracting an additional received radio frequency signal from the received radio frequency signal in the frequency domain, wherein the detection unit is adapted to detect the motion based on the signal resulting from the subtraction. In general, due to the principle of the doppler effect, the real motion of an object results in excitation in different frequency ranges of two different received radio frequency signals, whereas noise caused by vibrations in, for example, the device environment typically results in excitation in a frequency range independent of the frequency of the transmitted signal. Thus, by subtracting the two received radio frequency signals from each other, frequency excitations lying in the same frequency range can be removed, and then the detection unit can apply a doppler analysis to the signal resulting from the subtraction that does not contain excitations in the frequency range caused by noise. In another preferred embodiment, the detection unit may be adapted to perform passive doppler sensing by performing doppler analysis on two received radio frequency signals independent of each other with a respective transmission signal frequency provided for each signal. The detection unit may then be adapted to compare the results of the two independent doppler analyses to perform passive doppler sensing. For example, if there is a real moving object (e.g., a human being), each of the two independent Doppler analyses will result in substantially the same determined velocity for that object. However, if the result of the doppler analysis is caused by noise, it is likely that a different velocity is determined in each individual doppler analysis, which indicates that the corresponding signal is not caused by a real moving object, but may be caused by noise or vibration. Thus, the detection unit may be adapted to apply a logic rule to the comparison of the two results from the two independent doppler analyses to perform passive doppler sensing. The logic rules may be predetermined or may be learning rules learned by the detection unit, e.g. during a training phase, wherein the detection unit is faced with different environmental scenarios and the desired result of the passive doppler sensing is also provided as input to the detection unit (e.g. provided by the user), and the detection unit is then adapted to learn the logic rules that can be applied to realize the desired result of the passive doppler sensing using known machine learning algorithms. Thus, it is preferable that the comparison means that doppler analysis is performed on two signals independent of each other, and the results of the doppler analysis are compared in terms of consistency.

In one embodiment, performing doppler analysis includes applying a threshold filter to the received radio frequency signal in the frequency domain. In particular, the received radio frequency signal may be provided in the frequency domain, for example by applying a Fast Fourier Transform (FFT). In the frequency domain, the received radio frequency signal may optionally be further modified, for example by squaring the received radio frequency signal. The threshold value may then be predetermined, for example based on calibration measurements or experience, and provided to a threshold filter. The threshold filter then increases all signal portions of the received radio frequency signal that lie above a predetermined threshold in the frequency domain and decreases all signal portions of the received radio frequency signal that lie outside the threshold in the frequency domain. The decreasing and increasing may be based on predetermined values that are increased or decreased, respectively, may refer to an application function (e.g., a scaling function) that depends on the difference between the signal portion and the threshold, and so on. The movement may then be determined based on the filtered received radio frequency signal. Such filtering allows a more accurate determination of the movement.

In an embodiment the control unit is adapted to control the transmitting device such that two radio frequency signals with different transmit signal frequencies, e.g. 2.4GHz and 5.8GHz, are utilized. In this embodiment, the performance of the doppler sensing may comprise determining a confidence vector for the motion, e.g. the detection unit may comprise dedicated logic comprising the confidence vector for the motion. Each component of the vector describes the probability of motion relative to the receiving device over a range of speeds. Preferably, the confidence vector is updated every 100ms by analyzing the received radio frequency signals originating from two different transmitted signals, here from 2.4GHz and 5.8GHz frequency signals. For both transmit signal frequencies, the detection unit may be adapted to perform the following as part of the doppler analysis. A low pass filter having a predetermined cut-off frequency of, for example, 120Hz is provided to each received radio frequency signal, after which the signal is sampled at a predetermined sampling frequency (for example, at 240 Hz). The detection unit is then adapted to calculate a short fast fourier transform yielding a spectrum using the last received 256 samples every 100 ms. The spectrum is then a set of domains, where each domain contains a frequency range that can be mapped to a relative velocity range that can be mapped to a confidence vector for the motion. The detection unit may thus be adapted to subsequently use the frequency spectrum by squaring the amplitude of the frequency spectrum to construct the power spectrum. For each domain in the power spectrum whose value is above the selected threshold, the corresponding component of the confidence vector may then be increased. For each domain in the power spectrum whose value is below the selected threshold, the corresponding component of the confidence vector may then be reduced. The detection unit is then adapted to determine that a motion is detected when the maximum of all components exceeds 0.5 after the confidence vector has been updated, otherwise the detection unit is adapted to determine that no motion is present.

In an embodiment, the detection unit is further adapted to perform radio frequency sensing based on the amplitude of the received signal, wherein the detection unit is adapted to perform passive doppler sensing based on a sensing result determined for at least one of the at least two devices and/or based on a device state of at least one of the at least two devices, instead of or in addition to radio frequency sensing. In particular, the detection unit may be adapted to perform radio frequency sensing using known radio frequency algorithms, as described for example in WO 2020/043606 A1. Preferably, the detection unit is adapted to apply a predetermined logic rule to decide, based on the result of the radio frequency sensing, whether passive doppler sensing should be performed, for example, within a predetermined period of time as an alternative or in addition to the radio frequency sensing. The predetermined logic rules may be applicable to the application of the system and may depend on the situation. For example, the detection unit may be adapted to generally perform radio frequency sensing, and if the detection unit determines that the result of the radio frequency sensing may not be reliable (i.e. may not meet a predetermined quality criterion), the detection unit may be adapted to additionally perform passive doppler sensing (e.g. as described in the embodiments above) to verify the result of the radio frequency sensing. In another example, if at least one device is in a sleep state, e.g. when it is not expected that a person will be present in the area during night time, the detection unit may be adapted to apply passive doppler sensing (instead of radio frequency sensing) from time to detect motion in the area, wherein if the passive doppler sensing detects motion, the detection unit may be adapted to additionally initiate the performance of radio frequency sensing, e.g. by waking up the device, to obtain more information about the determined motion in the area.

In an embodiment two pairs of devices are used for detecting motion, wherein the control unit is adapted to control each pair of devices such that each pair of devices comprises at least a transmitting device and a receiving device, wherein the control unit is further adapted to control the transmitting device and the receiving device such that radio frequency signals of different frequencies are used for passive doppler sensing by the two pairs of devices, wherein the detection unit is adapted to perform passive doppler sensing for each pair of devices independently and to further detect motion based on a comparison of the resulting detection results. In particular, it is preferred that the detected motion refers to a small movement or vibration of the object. In this context, micro-movements are defined as movements of small size and/or time, wherein "small" in this context means a size of less than 10cm and a time of less than 1 minute. For example, small movements may refer to periodic movements of the human body, such as respiratory movements or heartbeat movements. Thus, in this embodiment, it is preferable that the system is specifically adapted such that the movement of the object refers to detecting a vibration movement or a minute movement of the object. In many of the above embodiments, it is preferable to eliminate these vibrations or small movements from the motion detection of the object. However, in other applications, it may be advantageous to specifically detect vibrations, for example, in the case of machine monitoring for monitoring machine functions, where vibrations of the machine are generally indicative of a change in state within the machine. Therefore, the principles discussed above in relation to removing vibrations can now also be applied to adapt the detection unit to detect vibrations or small movements of the object.

In one embodiment, the result of the motion detection is used to control the function of the device. For example, it is preferable that the device refers to a lighting device, and the lighting function is controlled based on motion detection. However, other functions may also or instead be controlled by the results of motion detection performed by the system.

In one aspect of the invention a detection method for detecting a movement of an object by using at least two devices adapted to transmit and receive radio frequency signals is proposed, wherein the method comprises a) controlling the at least two devices such that at least one of the at least two devices is a transmitting device transmitting radio frequency signals having a transmit signal frequency and such that at least one of the at least two devices is a receiving device receiving radio frequency signals, the radio frequency signals being indicative of a reflection of the transmitted radio frequency signals of the object, b) providing the transmit signal frequency at which the radio frequency signals have been transmitted, and c) detecting the movement of the object by performing passive doppler sensing based on the received radio frequency signals and the provided transmit signal frequency.

In a further aspect of the invention a computer program product for detecting motion is presented, wherein the computer program product comprises program code means for causing a detection system according to claim 1 to perform a detection method according to claim 14.

It will be appreciated that the detection system as described above, the method as described above and the computer program as described above have similar and/or identical preferred embodiments, in particular as defined in the dependent claims.

It is to be understood that the preferred embodiments of the invention may also be any combination of the dependent claims or the above embodiments with the corresponding independent claims.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

Drawings

In the following figures:

FIG. 1 schematically and exemplarily shows two radio frequency devices for use in a detection system controlling the radio frequency devices, and

fig. 2 schematically and exemplarily shows a detection method for detecting a movement of an object.

Detailed Description

Fig. 1 schematically and exemplarily shows two radio frequency devices 120, 130 and a detection system 110. Preferably, the radio frequency device 120, 130 is part of a network formed by at least two radio frequency devices 120, 130, wherein optionally the network comprises additional radio frequency devices not shown in fig. 1, which additional radio frequency devices may also be controlled by the detection system 110. However, for a better overview, the principles of the present invention are described below with respect to only the two radio frequency devices 120, 130 shown in fig. 1, and these explained principles may then also be applied to systems comprising more than two radio frequency devices 120, 130. It is particularly noted here that the two radio frequency devices 120, 130 refer to completely different devices and are not located in the same location, but are provided with a distance from each other of preferably more than 1 m, more preferably more than 3 m.

The detection system 110 may be a stand-alone system in communicative contact with at least two radio frequency devices 120, 130; or may be provided as part of one of the at least two radio frequency devices 120, 130, such as within a housing or as part of software and/or hardware provided in one of the at least two devices 120, 130. Preferably, if at least two of the radio frequency devices 120, 130 are part of a network, the detection system is also part of the network (e.g., as part of one of the devices of the network) or distributed over multiple devices of the network. In this case, the communication between the detection system 110 and the at least two devices 120, 130 and optionally the other network devices may be part of a general network communication, i.e. messages from and to the detection system 110 are sent as part of a communication protocol used by the network.

The detection system 110 includes a control unit 111, a signal frequency providing unit 112, and a detection unit 113. The control unit 111 is adapted to control the radio frequency device 120 and the radio frequency device 130. In particular, the control unit 111 is adapted to control the radio frequency device 120 to act as a transmitting device for transmitting a radio frequency signal 121 having a transmit signal frequency. Furthermore, the control unit 111 is adapted to control the radio frequency device 130 to act as a receiving device for receiving a radio frequency signal 131, which radio frequency signal 131 is the result of a reflection of the radio frequency signal 121 from the object, in this case the person 140 moving in the direction 141. Due to the doppler effect, the reflected signal 131 received by the radio frequency device 130 comprises information about the movement 141 of the person 140, in particular the signal 131 reflected from the person 140 has undergone a frequency shift with respect to the transmitted radio frequency signal 121. The transmitted radio frequency signal 121 is preferably also transmitted as part of a general network communication, i.e. refers to a general network communication signal comprising e.g. a message for another network device. However, the transmitted radio frequency signal 121 may also be a dedicated signal that is transmitted only for motion detection.

The signal frequency providing unit 112 is adapted to provide a transmitted signal frequency of the transmitted radio frequency signal 121. In particular, the detection system 110 communicates with the radio frequency device 120 serving as a transmission device, so that the radio frequency device 120 can provide information about the transmission signal frequency to the signal frequency providing unit 112. For example, the signal frequency providing unit 112 may be adapted to initiate communication of the radio frequency device 120, preferably via a network communication signal comprising the transmission signal frequency. However, in other embodiments, the radio frequency device 120 acting as a transmitting device may be adapted to provide the transmitting signal frequency to the signal frequency providing unit 112 by itself, or the transmitting signal frequency may be predetermined and stored on a memory from which the signal frequency providing unit 112 may read the transmitting signal frequency. The signal frequency providing unit 112 is then adapted to provide the transmission signal frequency to the detection unit 113.

The detection unit 113 is adapted to detect the movement of the person 140 by performing passive doppler sensing based on the received radio frequency signal 131 and the provided transmission signal frequency. Passive doppler sensing includes at least doppler analysis based on the received radio frequency signal 131 and the provided transmit signal frequency. For example, the detection unit 113 may be adapted to multiply the electronic representation of the received radio frequency signal 131 with an electronic representation of a periodic signal having the frequency of the transmitted signal via hardware or software. Optionally, a low pass filter may also be provided on the resulting multiplied signal such that the filtered signal only comprises frequencies below a predetermined frequency threshold. Mathematically, multiplication and low pass filtering of a signal may be considered to determine the difference between two input signals, where the excitation in the non-zero frequency range in the resulting signal is due to the Doppler effect of the moving person 140 on the transmitted radio frequency signal 121. In the first approximation, the excitation frequency may be considered to be proportional to the relative velocity of the moving person 140 (directed proportional). Thus, from the excitation frequency, the movement 141 and even the speed of the person 140 can be determined. However, the detection unit 113 may also be adapted to include more complex analysis methods into the passive doppler sensing. For example, detection unit 131 may also utilize the I and Q channels to determine the doppler shift caused by movement 141 of person 140.

Some additional more detailed embodiments and applications of the detection system 110 are described below. In the following embodiments, at least two devices are part of a network of network devices that may be controlled by a control unit. Generally, the network may be based on different network communication protocols, such as WiFi, bluetooth, zigbee, etc.

In one embodiment, the network refers to, for example, a WiFi (e.g., 2.4 GHz) network. In this case, the control unit may be adapted to control the network device to transmit radio frequency signals in the ultra wideband frequency range on non-overlapping frequencies. This non-overlapping may be achieved by using available channels, but may also be achieved by using disparate frequencies (e.g., 2.4GHz and 60GHz of WiFi communication protocols). Furthermore, the detection unit may be provided with the frequency of the transmission signal of all network devices, i.e. the frequency channel used. However, if the detection unit is part of each network device, the detection unit of the network device may be provided with only the transmission signal frequency of the neighboring network device. With passive doppler sensing, the detection unit (optionally, each detection unit of each network device independently) may then attempt to sense motion, for example, by finding a non-zero frequency component in the product of the received radio frequency signal and the signal having the corresponding transmit signal frequency. Furthermore, the detection unit may be adapted to identify possible noise sources (such as vibrations), which may be manifested as narrow frequency range excitations in the received radio frequency signal, for example, and which are typically caused by mechanical vibrations or electromagnetic interference. The identification of noise in the received radio frequency signal may be based on monitoring a low frequency spectrum of the transmitted radio frequency signal that is not reflected by the object. In particular, each network device may also receive a radio frequency signal generated by its own transmitted signal, which is not reflected by the object. The excitation frequencies in these monitored signals with a narrow frequency range, which frequently occur suddenly in the monitored signals, can then be identified. Thus, in passive doppler sensing, such frequencies may then be ignored by the detection unit. Additionally or alternatively, the monitoring of the vibrations may be achieved by the detection unit by analyzing the doppler spectrum of the received radio frequency signal. Constant narrow frequency excitation-i.e. not moving in the spectrum for more than e.g. 500 ms-can then be identified as vibration and filtered out for doppler sensing. Furthermore, the detection unit may be adapted to employ two channels, i.e. channels c1 (t) and c2 (t), referring to I-channels and Q-channels, which are phase shifted, e.g. 90 °. From these channels, the detection unit may be adapted to construct a new signal s (t) =c1 (t) + i c2 (t), where i is an imaginary number. Based on the complex fourier transform of the new signal, doppler sensing may be performed, for example, by subtracting the positive spectrum from the negative spectrum of the complex fourier transform and performing doppler analysis on the result.

In one embodiment, the network may be further adapted to perform radio frequency sensing, for example, by exchanging short network messages and by monitoring amplitude variations of these messages, which are indicative of time variations in the environment. In this case, the detection may be adapted to double confirm the result of the radio frequency sensing by a temporary handover of the passive doppler sensing. This has the following benefits: the default mode of operation of the network device is standby power friendly.

In one embodiment, the network may also be adapted to utilize 5.8GHz multi-channels. For example, the control unit may be adapted to provide a trigger signal or to cause one of the network devices to provide a trigger signal, wherein based on the trigger signal the network device is adapted to transmit two radio frequency signals, one in the 5.8GHz range and one in the 24GHz range. The detection unit may then be adapted to analyze the two spectra of the received signal and subtract the overlapping portions. The insight in this embodiment is that the motion signal typically occurs in different parts of the frequency spectrum and will therefore still be present in the resulting frequency spectrum. In contrast, vibrations occur in both spectra at similar frequencies and will therefore be counteracted by subtraction in the resulting spectra. In general, the detection device may be adapted to assign a lower transmission signal frequency (e.g., 2.4 GHz) to the transmission device expected to suffer more vibration (e.g., due to being located near the vibration source), and to assign a higher transmission signal frequency (e.g., 60 GHz) to the transmission device expected to suffer less vibration.

The presence of vibration or protruding (spike) in the received signal is sometimes related to the period of temperature change and is a result of the expansion and/or contraction of the mechanical elements of the network device. This occurs especially when the lamp is on or off, if the network device comprises a lighting function. In general, when the lamp has just been turned on, movement due to vibration or false positive detection of presence is not very problematic, since someone should be present anyway. However, such a detected false alarm is undesirable when the lamp has just been turned off. Thus, in order to avoid false positive detection in the passive doppler sensing result or the radio frequency sensing result, the detection unit may be adapted to start with either of the two sensing methods and then to additionally perform the other only during difficult off periods (e.g. 0 to 30 minutes after the lamp has been turned off) to maximize the robustness of the detection to vibrations and to achieve a fully standby power system.

In one embodiment, rather than attempting to avoid the effects of vibration, it may be desirable to specifically detect vibration of an object. In this case, the detection unit may be adapted to control the transmitting device to transmit a radio frequency signal having a transmission signal frequency that is sensitive to mechanical vibrations of the transmitting device itself and/or of the object in its field of view. For example, the lighting device may thus be used to monitor vibration of heating, ventilation and air conditioning (HVAC) equipment near an office ceiling. In this example, a sudden increase in vibration of the HVAC equipment may cause vibration of nearby lighting equipment and indicate an impending HVAC equipment failure. The above-described system may then be used to monitor such vibration events. In another exemplary application, the detection device may be adapted to employ passive Doppler sensing, optionally with additional radio frequency sensing, to monitor the activation time of the machine (e.g., conveyor belt), and also, for example, to monitor changes in machine vibration patterns indicative of impending damage to machine components. Based on such monitoring, maintenance may be proactively scheduled to avoid more serious damage to the machine and unplanned downtime.

In one embodiment, the control unit may be adapted to select the transmitting device and the receiving device such that two different pairs of devices are assigned to monitor the moving environment, wherein the two pairs of devices have overlapping sensing fields of view. The control unit may for example control the first pair such that it uses a transmission signal frequency in the 5GHz WiFi range, while controlling the second pair such that it uses a transmission signal frequency in the 60GHz WiFi range. The detection unit may then be adapted to perform passive doppler sensing based on the two pairs of received signals, e.g. in order to perform fall detection of e.g. people or packages in a warehouse. A fall is generally characterized by an acceleration of 1g followed by a deceleration of about-5 g. By monitoring the target area simultaneously at two different frequencies, it is possible to monitor fall detection and to monitor the presence of a person. For example, the detection unit may be adapted to use a 5.8GHz signal for fall detection, as falling of objects often results in a large frequency difference, which is visible in the spectrum of the received signal of the 5.8GHz device pair. In order to monitor the presence of a human, for example by sensing respiration, the detection unit may be adapted to utilize a higher frequency which tends to provide a higher resolution spectrum. And when rigid objects fall to the floor they will vibrate briefly after a hard impact against the floor. The detection unit may thus also be adapted to monitor vibrations of an object that has just fallen from, for example, a warehouse pallet/forklift, to evaluate the strength with which the object has hit the floor.

Fig. 2 schematically and exemplarily shows a method for detecting a movement of an object. The method 200 includes a first step 210: controlling at least two radio frequency devices (e.g., radio frequency devices 120, 130 shown in fig. 1) such that at least one of the at least two devices is a transmitting device that transmits a radio frequency signal (e.g., radio frequency signal 121) having a transmit signal frequency; and such that at least one of the at least two radio frequency devices 120, 130 is a receiving device that receives radio frequency signals (e.g., radio frequency signal 131) resulting from reflections of the transmitted radio frequency signals of the subject. In a further step 220, the method comprises providing a transmit signal frequency at which the radio frequency signal has been transmitted, for example for use in a next step 230. In step 230, the motion of the object is detected, for example, by performing passive doppler sensing based on the received radio frequency signal and the provided transmit signal frequency, in accordance with the principles explained above.

Some general principles will be explained below. Radio frequency sensing is an increasingly interesting technology. The basic idea is that a system of radio frequency devices exchanges messages whose amplitude is monitored. Any change in amplitude is indicative of a change in the environment in the vicinity of the transmitter radio frequency device and the receiver radio frequency device. The radio frequency sensing may utilize standard wireless radio frequency devices. For example, zigBee devices mostly use 2.4GHz signals, although the ZigBee standard can also be implemented at 868 MHz. Many modern WiFi devices now use both 2.4GHz and 5GHz signals, and even after a few years will use 60GHz WiFi signals.

In recent years, so-called passive doppler sensing has been developed. This technique is challenging because one needs to identify both the signal from the moving object and the carrier frequency in the signal. However, the advantage of using passive doppler detection compared to standard radio frequency detection is the rich information that can be obtained.

In general, the higher the frequency (i.e., the shorter the wavelength), the more susceptible the sensing system that uses radio frequency signals to mechanically vibrate the transmitting device or the receiving device. For example, mechanical vibrations from blinds, e.g., luminaires as network devices, can severely impact the performance of mass market 5.8GHz radio frequency sensors. Thus, when using radio frequency sensing, there is a need to carefully design the sensing algorithm, where robustness to vibrations is taken into account. Furthermore, it is known that conventional preventative maintenance solves 18% of machine problems, while 82% of machines fail due to random or unknown factors. The prior art also teaches that 82% of the unknown factors are preferably identified by continuous monitoring of the machine and addressed with predictive maintenance. It is known that many times the motor itself within the machine is an early indicator when there is a risk of unplanned shutdown. It is known that vibration and temperature sensors, among other things, reveal the state of an electric motor, for example for a conveyor belt. In order to track motor operation 24 hours a day, based on the above-described invention, it is suggested to employ vibration sensing with a detection system as described above to determine, for example, an average total usage time of the machine, which is helpful in understanding the threshold for preventive or periodic maintenance. For example, using the obtained data, a threshold value that can result in 2500 hours of use is still acceptable, but preventive maintenance should be scheduled at 2000 hours to limit the risk of unplanned outages. In particular, the detection system as described above may be used to monitor vibration of a machine without the need to directly attach a vibration sensor to the machine. For example, by carefully monitoring vibration frequencies and patterns, a baseline of motor state may be established, and ultimately motor health may be estimated. For example, for several months, the vibration level of the motor remains consistent with a predetermined baseline, so that maintenance is not required. However, eventually the vibration frequency and/or amplitude starts to increase, for example, because the motor components have worn down and become thinner. Based on the difference from the baseline, it may be determined that the motor component needs to be replaced as soon as possible.

In another application, the detection system may be used for automatic lighting control. The requirements for automatic lighting control are often very stringent. Turning on the light when someone is entering should be quick, but turning on the light when no person is there (i.e. false alarm) is highly undesirable. In some applications, the activation of the lights also has a safety element, for example, in a multi-aisle warehouse, turning on the lights at the intersection between two islets alerts that a forklift is approaching the intersection. Furthermore, if in most applications radio frequency sensing is applied to the lighting control, the sensing performance depends on the lamp state itself, e.g. when the lamp is turned off, false alarms are highly undesirable as it leads to a very noticeable malfunction (i.e. malfunction) of the system. The above-described invention allows to overcome these problems by providing passive doppler sensing for controlling the illumination system in addition to or instead of radio frequency sensing.

Preferably, for passive Doppler transmission, two different transmit signal frequencies (e.g., 2.4GHz WiFi and 5GHz WiFi) are used to eliminate false triggers due to vibration, as described in detail above. In particular, it may be advantageous to use two transmitted signal frequencies in applications that are expected to be subject to strong vibration, such as where an office troffer is installed in a system ceiling near HVAC ducting, or where a suspended light fixture in a warehouse is placed near heavy machinery. Furthermore, in addition to vibrations of the transmitting device and/or the receiving device itself, vibrations of objects within the field of view of the sensing system may also cause false triggers. This can also be solved by using two different frequencies as the transmission signal frequency as described above.

Furthermore, to allow reducing the effects of vibrations, the detection system as described above may be adapted to control the network device system (e.g. the lighting system) and may be adapted to apply passive doppler sensing which ignores the narrow frequency excitation if the network device system is in an off state. In this case the detection unit may be adapted to filter the received signal, e.g. by using the I-channel and the Q-channel, and to subtract the positive frequency from the negative frequency. Preferably, in the illumination system, passive doppler sensing is applied by the detection unit in the off-state and/or only after the radio frequency sensing has observed a trigger, such as the presence of a person. In one embodiment, two different frequency carriers (i.e., two different transmit signal frequencies) are used for passive doppler sensing and a comparison is made between the two signals to identify vibrations present in the device or in the field of view being sensed. The comparison may be performed in the frequency domain and the resulting spectrum may be subtracted. The frequency at which the vibrations occur is not dependent on the carrier frequency, whereas the doppler effect is dependent on the carrier frequency. Thus, by subtracting the resulting spectrum, vibrations can be removed from the signal, but the true motion is preserved. Additionally or alternatively, the comparison may be made in the time domain by comparing the energy present in the two channels. Further motion analysis is only performed if both channels are sufficiently above a predetermined threshold.

Preferably, passive doppler sensing is performed during the cooling phase of the device. During the cooling phase of the device, the microwave carrier frequency emitted by the device may interfere with nearby radio frequency sensors due to carrier offset. Thus, while the first pair of lights means to have different carrier frequencies (i.e., transmit signal frequencies), the adjacent second pair of lights perform sensing within the radio frequency range, the carrier frequencies of the first pair of lights change due to temperature changes of the first pair of lights, and may become the same frequency as the carrier frequencies of the second pair of lights. Thus, the sensing of the first pair of light and the second pair of light may interfere with each other. However, this can only occur on one channel (i.e., the transmit signal frequency) at the time. Thus, performing passive doppler sensing based on a plurality of different transmit signal frequencies can help identify and avoid this problem. This embodiment can also be applied to the start-up phase of the device.

In one embodiment, it is preferred that if the function of the device (e.g., the lamp) has been off for a significant amount of time (e.g., more than 30 minutes), the transmission of the radio frequency signal is turned off to save energy and reduce unwanted wireless smoke.

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.

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.

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.

The processes performed by one or several units or devices (e.g., control of at least two devices, provision of transmitted radio frequency signals, and detection of motion, etc.) may be performed by any other number of units or devices. These processes may be implemented as program code means of a computer program and/or as dedicated hardware.

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

Any reference signs in the claims shall not be construed as limiting the scope.

The present invention relates to a detection system for detecting a movement of an object by using at least two devices adapted to transmit and receive radio frequency signals. The system comprises: a control unit for controlling the at least two devices such that at least one of the at least two devices is a transmitting device that transmits a radio frequency signal having a transmission signal frequency, and such that at least one of the at least two devices is a receiving device that receives a radio frequency signal indicating a reflection of the transmitted radio frequency signal of the object; a signal frequency providing unit for providing a transmission signal frequency at which the radio frequency signal has been transmitted; and a detection unit for detecting a motion of the object by performing passive Doppler sensing based on the received radio frequency signal and the provided transmission signal frequency.

Claims

1. A detection system for detecting a motion (141) of an object (140) by using at least two devices (120, 130) adapted to transmit and receive radio frequency signals (121, 131), wherein the system (110) comprises:

a control unit (111) for controlling the at least two devices (120, 130) such that at least one of the at least two devices (120, 130) is a transmitting device (120) transmitting a radio frequency signal (121) having a transmission signal frequency, and such that at least one of the at least two devices (120, 130) is a receiving device (130) receiving a radio frequency signal (131), the radio frequency signal (131) being indicative of a reflection of the transmitted radio frequency signal of the object (140),

A signal frequency providing unit (112) for providing the transmission signal frequency at which the radio frequency signal (121) has been transmitted, and

a detection unit (113) for detecting a movement (141) of the object (140) by performing passive Doppler sensing based on the received radio frequency signal (131) and the provided transmission signal frequency,

wherein the detection unit (113) is adapted to: determining an excitation in a frequency range in a frequency spectrum of the received radio frequency signal (131), wherein the excitation is substantially constant over a predetermined period of time; and performing the passive doppler sensing based on the received radio frequency signal (131) by filtering out a frequency range in the spectrum of the received radio frequency signal (131).

2. The detection system according to claim 1, wherein the control unit (111) is further adapted to: controlling the at least two devices (120, 130) such that each of the at least two devices (120, 130) acts as a transmitting device (120), each transmitting device (120) transmitting a radio frequency signal (121) having a different signal frequency; and controlling the at least two devices (120, 130) such that each device acts as a receiving device (130) to receive a radio frequency signal (131), the radio frequency signal (131) being indicative of a reflection of a transmitted radio frequency signal (121) of an object (140) corresponding to the transmitted radio frequency signal (121) of the respective other device, wherein the detection unit (113) is adapted to perform passive doppler sensing based on the received radio frequency signal (131).

3. The detection system according to any one of claims 1 and 2, wherein the control unit (111) is adapted to control the transmitting device (120) to detect a radio frequency signal resulting from a reflection of the transmitted radio frequency signal (121) transmitted by itself, and wherein the detection unit (113) is adapted to monitor the detected radio frequency signal and to detect the movement (141) of the object (140) also based on the monitored radio frequency signal.

4. The system according to any of the preceding claims, wherein the detection unit (113) is adapted to determine an I channel and a Q channel based on the received radio frequency signal (131) and to perform the passive doppler sensing based on the I channel and the Q channel.

5. The detection system according to any one of the preceding claims, wherein the control unit (111) is further adapted to control the transmitting device (120) to transmit an additional radio frequency signal having a signal frequency different from the signal frequency and to control the receiving device (130) to receive an additional radio frequency signal resulting from a reflection of the additional radio frequency signal from the object (140), and wherein the detection unit (113) is further adapted to perform the passive doppler sensing based on the additional received radio frequency signal.

6. The detection system according to claim 5, wherein the detection unit (113) is adapted to perform the passive doppler sensing further based on the additional received radio frequency signal by comparing the additional received radio frequency signal with the received radio frequency signal (131).

7. The system according to claim 6, wherein the comparing refers to subtracting the additionally received radio frequency signal (131) from the received radio frequency signal in the frequency domain, wherein the detection unit (113) is adapted to detect the motion (141) based on the signal resulting from the subtracting.

8. The system of claim 6, wherein the comparing refers to performing doppler analysis on two signals independent of each other and comparing the results of the doppler analysis in terms of consistency.

9. The system according to any of the preceding claims, wherein the detection unit (113) is further adapted to perform radio frequency sensing based on the amplitude of the received signal, and wherein the detection unit (113) is adapted to perform passive doppler sensing based on a sensing result determined for at least one of the at least two devices (120, 130) and/or based on a device state of at least one of the at least two devices (120, 130) instead of or in addition to radio frequency sensing.

10. The system according to any of the preceding claims, wherein two pairs of devices are used for detecting motion, wherein the control unit (111) is adapted to control each pair of devices such that each pair of devices comprises at least a transmitting device and a receiving device, wherein the control unit (111) is further adapted to control the transmitting device and the receiving device such that radio frequency signals of different frequencies are used for passive doppler sensing by the two pairs of devices, wherein the detection unit (113) is adapted to perform the passive doppler sensing on each pair of devices independently and to further detect motion based on a comparison of the resulting detection results.

11. The system of claim 10, wherein the detected motion is a small movement or vibration of the object.

12. A system according to any one of the preceding claims, wherein the result of the motion detection is used to control the function of the device.

13. A detection method for detecting a movement of an object by using at least two devices adapted to transmit and receive radio frequency signals, wherein the method (200) comprises:

controlling (210) the at least two devices such that at least one of the at least two devices is a transmitting device transmitting a radio frequency signal having a frequency of the transmitted signal, and such that at least one of the at least two devices is a receiving device receiving a radio frequency signal, the radio frequency signal being indicative of a reflection of the transmitted radio frequency signal of the object,

Providing (220) the transmit signal frequency at which the radio frequency signal has been transmitted, and

detecting (230) a motion of the object by performing passive doppler sensing based on the received radio frequency signal and the provided transmit signal frequency,

wherein the method further comprises determining an excitation within a frequency range in the frequency spectrum of the received radio frequency signal (131), wherein the excitation is substantially constant over a predetermined period of time, and performing the passive doppler sensing based on the received radio frequency signal (131) by filtering out the frequency range in the frequency spectrum of the received radio frequency signal (131).

14. A computer program product for detecting motion, wherein the computer program product comprises program code means for causing a detection system according to claim 1 to perform the detection method according to claim 13.