Radar sensor and method of operating a radar sensor

Abstract

A radar sensor has a radar transmitter controlled to operate cyclically, wherein each cycle comprises a sequence of frames and the frames each have an associated (fixed) duty cycle. A signal from a receiver of the radar sensor is interpreted to detect possible motion. A motion confirmation mode is then used to provide a more accurate motion signal. This duty cycle variation enables the power consumption to be reduced but without reducing the detection range, because periods of large duty cycle (for large range detection) are maintained.

Description

[0001] Radar sensor and method of operating a radar sensor

[0002] FIELD OF THE INVENTION

[0003] This invention relates to radar sensors, for example for motion sensing in order to detect the presence (and optionally also movement characteristics) of an object or person. The detection is used for automating control of an apparatus.

[0004] BACKGROUND OF THE INVENTION

[0005] The use of motion sensing is well-known for controlling an apparatus. For example, motion sensing, in order to provide presence detection, is used for controlling lighting systems, alarm systems, camera and security systems, and smart home devices.

[0006] The most common low-cost motion detectors use passive infrared (PIR) sensors. Radar sensors are more sensitive than PIR sensors and thus can give improved performance. However, radar sensors, as active RF devices, consume significantly more power than PIR sensors. This is a major limitation in the use of radar sensors to replace PIR sensors, especially for applications with a tight power budget (e.g., solar or battery solutions).

[0007] It is also more and more important to minimize the power consumption of Internet of Things (loT) devices, such as sensors in lighting products, not only during a standby mode but also during normal operation, in order to achieve better efficiency. In the case of lighting systems, a particular lighting efficiency (Im / W) is needed to meet certain energy labels (e.g., Class A).

[0008] It is known that a pulsed operation can reduce the power consumption of radar sensors. A simple illustration of a pulsed operation for a radar sensor is shown in Figure 1, which plots the operating voltage of the radar transmitter over time. The radar sensor, especially its radio transmitter, works in a intermittent, periodic, mode. In each period, having a pulse repetition time 10, the radar sensor works only for a fraction of the whole period, i.e., the duration of the pulse width 12.

[0009] The duty cycle of the pulsed operation is defined as the ratio (e.g., as a percentage) of the pulse width 12 to the pulse repetition time 10: Pulse width

[0010] Duty cycle = - —;— Pulse repetition time

[0011] The actual power consumption of the radar sensor depends on the duty cycle of the pulsed operation:

[0012] ^actual Pew Duty cycle

[0013] Pew is the power consumption when the radar sensor works in continuous mode.

[0014] The duty cycle determines not only the power consumption, but also the radar signal quality which in turn determines the maximum detection range of the radar sensor. In a certain range, the lower the duty cycle, the smaller the detection range.

[0015] Existing solutions set the duty cycle based on the maximum detection range to ensure the radar sensor performs as required. As a result, the reduction in power consumption of the radar is limited by its maximum detection range.

[0016] It is desirable that the power consumption of the radar sensor can be further reduced while still ensuring a desired maximum detection range.

[0017] JP2006 / 226847 discloses a radar sensor with different duty cycles applied at different times.

[0018] US2020064445A1 relates to smartphone-based power-efficient radar processing and memory provisioning for detecting gestures. Different sequences are designed to configure the radar system differently. Each sequence is associated with a different power mode and the progression from the first sequence to the last sequence incrementally increase power consumption within the radar system.

[0019] CN108684101A discloses a system comprising an object movement detection module, a microprocessor unit (MCU) and brightness / color adjustable LED lamps. The object movement detection module adopts Doppler radar technology, and generates a high- electric level signal when motion is detected. After receiving the high-electric level signal, the MCU adjusts the brightness and color of the LED lamps by changing the duty ratio of PWM signals and / or on / off of PWM signals.

[0020] US2023041835A1 discloses a method for exposure level estimation, including transmitting radar signals for object detection and communication signals for wireless communication operations. The method also includes identifying a location of an object relative to the electronic device within a first time duration based on the radar signals, the first time duration including a previous time until a current time. The method further includes determining a radio frequency (RF) exposure measurement associated with the object based on the location of the object over the first time duration. Additionally, the method includes determining a power density budget over a second time duration based on a comparison of the RF exposure measurement to an RF exposure threshold, the second time duration including the current time until a future time. The method also includes modifying the wireless communication operations for the second time duration based on the power density budget.

[0021] SUMMARY OF THE INVENTION

[0022] The invention is defined by the claims.

[0023] According to examples in accordance with an aspect of the invention, there is provided a radar sensor comprising: a radar transmitter for transmitting radar pulses; a radar receiver for receiving the radar pulses after reflection from a monitoring area of the radar sensor; and a controller for controlling the timing of operation of the radar transmitter, wherein the controller is configured, during a scan mode, to: control the radar transmitter to operate cyclically, wherein each cycle comprises a sequence of frames; during each frame, control the radar transmitter to transmit a set of radar pulses with an associated duty cycle for that frame; and interpret a signal from the radar receiver to detect possible motion, wherein the controller is configured, in response to a detection of possible motion during the scan mode, to update the cyclic operation of the radar transmitter to provide a motion confirmation mode.

[0024] In this way, a radar sensor is operated with pulsed operation but with a varied duty cycle in a scan mode. This duty cycle variation enables the power consumption to be reduced but without reducing the detection range, because periods of large duty cycle (for long range detection) are maintained. A maximum duty cycle used by the system corresponds to a maximum detection range as required by the application. In addition, duty cycles which are smaller than this maximum duty cycle are used as part of the cyclic operation in the scan mode. Each frame for example has sufficient pulses to identify a possible motion within the corresponding detection range.

[0025] In response to a detection of possible motion in the scan mode, the controller updates the cyclic operation of the radar transmitter to provide a motion confirmation mode. In this way, the scan mode may be used simply to detect possible motion, and a verification can then take place using a motion confirmation mode which is selected for detection in the appropriate distance range. Thus, when the radar sensor detects a possible motion from the data samples of a frame of the scan mode with a particular duty cycle, a new varied duty cycle scheme is used to quickly confirm if the possible motion is a valid motion.

[0026] Each cycle of the scan mode for example comprises a sequence of frames with duty cycle that increases over time in a stepwise manner. This provides a simple control approach, with a stepped increment in duty cycle over the duration of the periodic cycle. This means the scanning starts with the smallest detection range. It means that a lowest power consumption is used initially. If this is sufficient to enable motion detection, it means the motion can be detected in a most power efficient manner. Only if no motion is detected, does a larger range sensing (with larger duty cycle and hence larger power consumption) need to be applied.

[0027] Each cycle of the scan mode for example comprises frames with duty cycles ranging from a minimum duty cycle in the range 0.1% to 1% (e.g., 0.5%) to a maximum duty cycle in the range 3% to 10%. (e.g., 5%). There may for example be five frames per cycle. The set of radar pulses of each frame for example comprises between 16 and 128 pulses (e.g., 64 pulses). Each frame (of the scan mode and the motion compensation mode) for example has a duration of between 50ms and 100ms.

[0028] During the motion confirmation mode, one or more cycles are preferably provided, each comprising frames having at least the duty cycle corresponding to the frame of the scan mode during which motion was detected.

[0029] The motion confirmation mode may again be a stepped stair-shaped scheme, but the cycle (or cycles) only contains the duty cycle at which motion was detected during the scan mode and duty cycles which are larger. The motion confirmation mode may be used for one or more cycles until a valid motion is confirmed or not confirmed. The sensor then returns to the scan mode.

[0030] The controller is for example configured to: start the motion confirmation mode immediately following the frame of the scan mode during which the motion was detected; and set the first frame of the motion confirmation mode with the same duty cycle as the frame of the scan mode during which motion was detected.

[0031] Thus, as soon as possible motion is detected, the duty cycle is repeated as the start of the motion confirmatory mode.

[0032] The invention also provides a method of operating a radar sensor, comprising: controlling a radar transmitter of the radar sensor to operate cyclically during a scan mode, wherein each cycle comprises a sequence of frames; during each frame of the scan mode, controlling the radar transmitter to transmit a set of radar pulses with an associated duty cycle for that frame and receiving the radar pulses at a radar receiver after reflection from a monitoring area of the radar sensor; interpreting a signal from the radar receiver to detect possible motion during the scan mode; and in response to a detection of motion in the scan mode, updating the cyclic operation of the radar transmitter to provide a motion confirmation mode.

[0033] This provides the method of operation of the radar sensor as defined above.

[0034] Each cycle of the scan mode for example comprises frames with duty cycles ranging from a minimum duty cycle in the range 0.1% to 1% to a maximum duty cycle in the range 3% to 20%.

[0035] The invention also provides a computer program comprising computer program code which is adapted, when said program is run on a computer, to implement the method defined above.

[0036] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0039] Fig. 1 shows a pulsed operation of a radar sensor;

[0040] Fig. 2 shows a radar sensor which may be controlled in accordance with the invention;

[0041] Fig. 3 shows a variable duty cycle scheme;

[0042] Fig. 4 shows the scan mode of Figure 3 in more detail; Fig. 5 shows one example of the radar switching between two varied duty cycle schemes; and

[0043] Fig. 6 shows the method employed by the radar sensor.

[0044] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The invention will be described with reference to the Figures.

[0046] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0047] The invention provides a radar sensor having a radar transmitter controlled to operate cyclically, wherein each cycle comprises a sequence of frames and the frames each have an associated (fixed) duty cycle. A signal from a receiver of the radar sensor is interpreted to detect possible motion. A motion confirmation mode is then used to provide a more accurate motion signal. The duty cycle variation enables the power consumption to be reduced but without reducing the detection range, because periods of large duty cycle (for large range detection) are maintained.

[0048] Figure 2 shows a radar sensor which may be controlled in accordance with the invention.

[0049] The radar sensor comprises a radar transmitter 20 for transmitting radar pulses and a radar receiver 22 for receiving the radar pulses after reflection from a monitoring area of the radar sensor. A controller 24 is used for controlling the timing of operation of the radar transmitter. The interpretation of the radar receiver signals is synchronized with the radar transmitter operation.

[0050] In one example, the controller 24 may also function as a lighting system controller which controls a lighting arrangement 26. Thus, the lighting is controlled (in known manner) based on motion detection, in order to identify the presence of a moving object. The moving object to be detected may be a person or animal or it may be a vehicle in the case of a street lighting application. However, the invention may be applied to any apparatus which is controlled using motion detection.

[0051] The invention relates to the control of the duty cycle of the radar sensor (as explained with reference to Figure 1), and does not change the underlying conceptual method of motion detection. As a result, the motion detection concept will not be described in detail.

[0052] In brief, a radar sensor determines Doppler frequency shifts based on phase difference measurements (between the transmitted and received signals), to detect a moving object, and optionally also an object's speed and direction. The radar sensor operates in the micro wave band.

[0053] This invention is based on operating the radar sensor in a pulsed operation but with a varied duty cycle to further reduce the power consumption without reducing its detection range.

[0054] Firstly, a maximum duty cycle (Dmax) is identified corresponding to the maximum detection range as required by the application. Then, several duty cycles which are smaller than Dmax are further determined. For example, if Dmaxis 5%, examples of other possible duty cycles could be 3%, 2%, 1%, 0.5%.

[0055] During the pulsed operation, instead of using a fixed duty cycle, the radar sensor adopts a varied duty cycle scheme to form a scan mode, such as a stair-shaped scheme as illustrated by Figure 3, which plots the duty cycle over time.

[0056] In one cycle 30, the radar sensor increases the duty cycle gradually from a minimum value (Dmin) to the maximum value (Dmax). One step of the stair is termed a frame 32.

[0057] Each frame 32 contains multiple pulses (e.g., 64) with the same duty cycle.

[0058] The pulses in each individual frame should be able to generate enough data samples for the radar sensor to determine if there is a possible motion within the corresponding detection range. A typical duration of one frame is around 50-100ms. One cycle contains multiple frames.

[0059] The example of Figure 3 has five frames 32 per cycle 30, for example with the duty cycles listed above. More generally, the duty cycles may range from a minimum duty cycle in the range 0.1% to 1% to a maximum duty cycle in the range 3% to 10%.

[0060] The scan pattern shown in Figure 3 may be considered to be a scan mode, and it is employed while there is no detected motion.

[0061] Figure 4 shows the scan mode in more detail.

[0062] The overall cycle 30 has five frames. The first frame 40a has a 0.5% duty cycle, the second frame 40b has a 1.0% duty cycle, the third frame 40c has a 2% duty cycle, the fourth frame 40d has a 3% duty cycle and the fifth frame 40e has a 5% duty cycle. All frames have 64 pulses in this example.

[0063] By way of example, with a 1kHz sampling rate, one frame containing 64 pulses (i.e., data samples) has a duration of 64ms. Then the overall duration of one cycle is 320ms.

[0064] Within each cycle, the duty cycle increases gradually as well as the detection range of the radar sensor. By using this varied duty cycle scheme, the actual power consumption is reduced from 5% to 2.3% compared to a constant 5% duty cycle.

[0065] When the radar sensor detects a possible motion from the data samples of one frame of the scan mode (with a certain duty cycle e.g., DM), it will follow a new varied duty cycle scheme. This is termed a motion confirmation mode.

[0066] This motion confirmation mode is used to confirm if the possible motion is a valid motion. The motion confirmation mode also uses a stepped frame-by-frame adjustment of the duty cycle, but each frame only contains the duty cycle DM at which motion was detected during the scan mode, or a duty cycle larger than DM.

[0067] The radar sensor works with the new motion confirmation mode for one or more cycles until a valid motion is confirmed or not confirmed, then it is changed back to the scan mode with each cycle containing all the duty cycles.

[0068] By having an additional motion confirmation mode, the frames during the scan mode can be short enough that they only need to detect a possible motion event. Detection using a short frame will enable motion to be detected, but with a reduced confidence. Thus, the detection may relate to other factors such as noise (i.e. there may be false positive detections).

[0069] In particular, in the scan mode, loose criteria may be endorsed to make sure all suspected motion will be identified to ensure no detections are missed. The short frame in the scan mode can also provide more agile response to a motion in the long range.

[0070] In the confirmation mode, tighter criteria may be used to filter out motions that do not want to be detected. For example, a radar sensor that is placed in an outdoor environment may detect the swing of trees or leaves in the scan mode, but these can be removed in the confirmation mode using a suitable sensing algorithm. Thus, the confirmation mode may be used to help reduce false positives so that only true positive results are ultimately reported. In this way, the overall cycle period during the scan mode can be kept as short as possible so that the full depth range is interrogated with sufficiently fast repetition rate, and movements at any location within the overall maximum range will not be missed. Thus, a minimal desired response time can still be guaranteed.

[0071] The duration of the confirmation mode for example depends on the complexity of the detection algorithm and the acceptable response time to confirm a valid detection. Generally, the confirmation mode for example lasts from a few hundred milliseconds to a few seconds (normally <5s).

[0072] In this way, the power consumption of the radar is minimized while the maximum detection range and the minimal response time are both guaranteed.

[0073] Figure 5 shows one example of the radar switching between the scan mode and two examples of the motion confirmation modes during its operation.

[0074] The radar sensor by default works in pulsed scan mode to detect any possible motions.

[0075] Once a possible motion is detected within a certain frame with a certain duty cycle (e.g., DM), the sensor immediately switches to the motion confirmation mode to quickly confirm whether the possible motion is a valid motion or not. The radar sensor keeps working with the motion confirmation mode for one or more cycles until a valid motion is confirmed or not confirmed, then it will change back to the scan mode. If a valid motion is confirmed, a motion call is generated by the radar sensor.

[0076] As shown in Figure 5, in a first example, a possible motion is detected in the third frame 50a (with 2% duty cycle) of the second cycle. The radar sensor is then switched to the motion confirmation mode. In this mode, the cycle contains only three duty cycles: 2%, 3% and 5%.

[0077] As shown, the motion confirmation mode starts immediately following the frame 50a of the scan mode during which the motion was detected. It starts with a repeat of the same duty cycle (2% in this example) as the frame 50a of the scan mode during which motion was detected.

[0078] In this example, with just one cycle of the motion confirmation mode (as there are now three frames during which the motion will be detected), the sensor has completed the confirmation.

[0079] Motion based signal processing is performed to confirm the motion.

[0080] In the second example, a possible motion is detected in fourth frame 50b (with 3% duty cycle) of the first cycle. The radar sensor is switched to the motion confirmation mode with each cycle containing only two duty cycles: 3% and 5%. The confirmation of the valid motion has in this example taken two motion confirmation mode cycles (because after the first cycle there have been only three frames during which the motion could be confirmed.

[0081] Figure 6 shows the method employed by the radar sensor.

[0082] In step 60, the sensor is operated in the scan mode. As described above, this involves operating cyclically with a sequence of frames, and during each frame a set of radar pulses is transmitted with an associated duty cycle for that frame, wherein the cycle comprises frames with duty cycles that increase over time in a stepwise manner.

[0083] In step 62 it is determined from a radar sensor signal analysis if a possible motion has been detected. This analysis takes place during each frame.

[0084] For a typical low-power signal processing approach, the signal would be collected for each pulse and buffered until the end of the frame. Then one round of signal processing can be carried out on a whole frame of data. The motion detection thus typically takes place at the end of each frame.

[0085] If no motion is sensed, the scan mode continues.

[0086] If possible motion is sensed, the motion confirmation mode is entered in step 64.

[0087] If motion is confirmed in step 66, a motion call is made in step 68, typically to control an apparatus according to the detected motion, For example, a lighting system may be configured to turn on due to motion detection, indicating the presence of a moving person or vehicle.

[0088] If the possible motion is not confirmed in step 66, the scan mode is resumed. 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.

[0089] Functions implemented by a processor may be implemented by a single processor or by multiple separate processing units which may together be considered to constitute a "processor". Such processing units may in some cases be remote from each other and communicate with each other in a wired or wireless manner.

[0090] 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. A computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied 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. If the term "adapted to" is used in the claims or description, it is noted the term

[0091] "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa.

[0092] Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A radar sensor comprising: a radar transmitter (20) for transmitting radar pulses; a radar receiver (22) for receiving the radar pulses after reflection from a monitoring area of the radar sensor; and a controller (24) for controlling the timing of operation of the radar transmitter, wherein the controller is configured, during a scan mode, to: control the radar transmitter to operate cyclically, wherein each cycle (30) comprises a sequence of frames (32) with duty cycles that increase over time from one frame to another in a stepwise manner; during each frame (32), control the radar transmitter to transmit a set of radar pulses with an associated duty cycle for that frame; and interpret a signal from the radar receiver to detect possible motion, wherein the controller is configured, in response to a detection of possible motion during the scan mode, to update the cyclic operation of the radar transmitter to provide a motion confirmation mode, which uses a stepped frame-by-frame adjustment of the duty cycle and each frame only contains the duty cycle DM at which motion was detected during the scan mode, or a duty cycle larger than DM.

2. The radar sensor of claim 1, wherein each cycle of the scan mode comprises frames with duty cycles ranging from a minimum duty cycle in the range 0.1% to 1% to a maximum duty cycle in the range 3% to 10%.

3. The radar sensor of any one of claims 1 to 2, wherein each frame has a duration of between 50ms and 100ms.

4. The radar sensor of any one of claims 1 to 3, wherein during the motion confirmation mode, one or more cycles are provided, each comprising frames having at leastthe duty cycle corresponding to the frame of the scan mode during which possible motion was detected.

5. The radar sensor of claim 4, wherein the controller is configured to: start the motion confirmation mode immediately following the frame of the scan mode during which the motion was detected; and set the first frame of the motion confirmation mode with the same duty cycle as the frame of the scan mode during which motion was detected.

6. The radar sensor of any one of claims 1 to 5, wherein the controller is configured to perform the motion confirmation mode until the detected motion is confirmed or not confirmed.

7. A lighting system, comprising: a lighting arrangement; a lighting controller; and the radar sensor of any one of claims 1 to 6 for providing a confirmed motion detection signal to the lighting controller.

8. A method of operating a radar sensor, comprising:(60) controlling a radar transmitter of the radar sensor to operate cyclically during a scan mode, wherein each cycle comprises a sequence of frames with duty cycles that increase over time from one frame to another in a stepwise manner; during each frame of the scan mode, controlling the radar transmitter to transmit a set of radar pulses with an associated duty cycle for that frame and receiving the radar pulses at a radar receiver after reflection from a monitoring area of the radar sensor;(62) interpreting a signal from the radar receiver to detect possible motion during the scan mode; and in response to a detection of motion, updating the cyclic operation of the radar transmitter to provide a motion confirmation mode (64), which uses a stepped frame-by- frame adjustment of the duty cycle and each frame only contains the duty cycle DM at which motion was detected during the scan mode, or a duty cycle larger than DM.

9. The method of claim 8, wherein each cycle of the scan mode comprises frames with duty cycles ranging from a minimum duty cycle in the range 0.1% to 1% to a maximum duty cycle in the range 3% to 10%.

10. The method of claim 9, comprising, during the motion confirmation mode, providing one or more cycles with frames having at least the duty cycle corresponding to the frame of the scan mode during which motion was detected.

11. The method of claim 10, comprising starting the motion confirmation mode immediately following the frame during which the motion was detected during the scan mode, and the first frame of the motion confirmation mode has the same duty cycle as the frame of the scan mode during which motion was detected.

12. The method of any one of claims 8 to 11, comprising performing the motion confirmation mode operation until the detected motion is confirmed or not confirmed.

13. A computer program comprising computer program code which is adapted, when said program is run on a computer, to implement the method of any one of claims 8 to

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