Patent Description:
Techniques and apparatuses are described that implement a smart-device-based radar system capable of performing symmetric Doppler interference mitigation. The radar system employs symmetric Doppler interference mitigation to filter one or more interference artifacts. An interference artifact can occur due to vibration of the radar system or vibration of other objects that are observed by the radar system. Due to the back and forth motion of the vibration, the interference artifact has both a positive and negative range rate. As such, the interference artifact contributes to amplitudes of both positive and negative Doppler bins of a range-Doppler map generated by the radar system. These amplitudes are approximately symmetric across the Doppler spectrum for one or more range bins. If the interference artifact is not filtered, some radar systems may generate a false detection (or a false alarm) based on the interference artifact or be unable to detect a desired object that is obscured by the interference artifact. A false detection or false alarm represents an erroneous detection that does not correspond to an object of interest. In general, an interference artifact refers any type of noise or interference that presents an approximately symmetric amplitude across the Doppler spectrum.

Symmetric Doppler interference mitigation exploits the symmetric amplitude contributions of the interference artifact across the Doppler spectrum to attenuate the interference artifact. This filtering operation incorporates the interference artifact within the noise floor, without significantly attenuating reflections from the desired object. Symmetric Doppler interference mitigation can be performed on each radar frame (e.g., each chirp) without a priori knowledge about the frequency or amplitude of the vibration. In this way, the radar system can filter interference artifacts that are generated from a variety of different types of vibrations. An ability of the symmetric Doppler interference mitigation to attenuate the interference artifact is also independent of the Doppler sampling frequency and whether or not aliasing occurs. By filtering the interference artifacts, the radar system produces fewer false detections in the presence of vibrations and can detect objects that would otherwise be masked by the interference artifact.

Preferred embodiments are found in the dependent claims.

Apparatuses for and techniques implementing a smart-device-based radar system capable of performing symmetric Doppler interference mitigation are described with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components:.

Integrating a radar system within an electronic device can be challenging. One such challenge involves size or layout constraints of the electronic device, which may limit where the radar can be placed relative to other components within the electronic device. In some cases, an operation of the component causes the radar system to vibrate (e.g., move back and forth across one or more dimensions). A speaker, for instance, can generate an audible sound that causes the radar to vibrate with a frequency that is dependent on the frequency of the audible sound and with an amplitude that is dependent on a volume of the speaker. Additionally or alternatively, the electronic device, which houses the radar system, may vibrate due to external forces. These vibrations can occur as a user walks with the electronic device or rides in a vehicle (e.g., a car, a bus, a train, or a plane).

Due to the vibrations, the radar system observes one or more interference artifacts within a received radar signal. To the radar system, the interference artifact can appear to be one or more moving objects. It can be challenging for the radar system to distinguish between an object of interest (e.g., a desired object) within the external environment and the interference artifact. As such, the radar system may generate one or more false detections based on the interference artifact, which increases the radar system's false-alarm rate and degrades the performance of the radar system. Sometimes the interference artifact can mask the desired object and prevent the radar system from detecting the object.

In other cases, the radar system observes objects that are vibrating. These objects can be internal or external to the electronic device. Sometimes multipath causes the radar system to observe an interference artifact associated with the vibrating object at a range that is farther than the range to the vibrating object. The interference artifact associated with the vibrating object can similarly result in a false detection and mask other desired objects.

Some techniques may try to reduce the occurrence of interference artifacts by isolating the radar system from internal components within the electronic device that cause the radar system to vibrate. However, this may increase cost of the electronic device and increase a footprint of the radar system. In some cases, this may result in the radar system being placed in a sub-optimal location that makes it challenging for the radar system to perform its intended function, such as detecting the user. In other cases, it may not be possible to isolate the radar system from the internal component due to size or layout constraints of the electronic device.

Other techniques may limit a field of view of the radar system to reduce a likelihood of the radar system observing components within the electronic device that vibrate. However, this technique also limits the volume of space in which the radar system can detect a desired object. As such, effective operation of the radar system is limited.

In contrast, this document describes techniques and devices that implement a smart-device-based radar system capable of performing symmetric Doppler interference mitigation. The radar system employs symmetric Doppler interference mitigation to filter one or more interference artifacts. An interference artifact can occur due to vibration of the radar system or vibration of other objects that are observed by the radar system. Due to the back and forth motion of the vibration, the interference artifact has both a positive and negative range rate. As such, the interference artifact contributes to amplitudes of both positive and negative Doppler bins of a range-Doppler map generated by the radar system. These amplitudes are approximately symmetric across the Doppler spectrum for one or more range bins. If the interference artifact is not filtered, some radar systems may generate a false detection (or a false alarm) based on the interference artifact or be unable to detect a desired object that is obscured by the interference artifact. A false detection or false alarm represents an erroneous detection that does not correspond to an object of interest. In general, an interference artifact refers any type of noise or interference that presents an approximately symmetric amplitude across the Doppler spectrum.

<FIG> is an illustration of example environments <NUM>-<NUM> to <NUM>-<NUM> in which techniques using, and an apparatus including, a smart-device-based radar system capable of performing symmetric Doppler interference mitigation may be embodied. In the depicted environments <NUM>-<NUM> to <NUM>-<NUM>, a smart device <NUM> includes a radar system <NUM> capable of detecting one or more objects (e.g., users) in the presence of one or more interference artifacts. As described above, an interference artifact has an approximately symmetric Doppler response. The smart device <NUM> is shown to be a smartphone in environments <NUM>-<NUM> to <NUM>-<NUM>.

In the environments <NUM>-<NUM> to <NUM>-<NUM>, the radar system <NUM> observes one or more interference artifacts. These interference artifacts can appear due to an operation of a component within the smart device <NUM> causing the radar system <NUM> to vibrate, external forces causing the radar system <NUM> to vibrate, or the radar system <NUM> observing another vibrating object that is internal or external to the smart device <NUM>. Generally, a vibration refers to a back and forth motion across one or more dimensions. This motion can repeat over time with an amplitude that decays or remains relatively steady.

In the environment <NUM>-<NUM>, the smart device <NUM> produces an audible sound. The audible sound can be a single tone, a ring tone, an alarm bell, or music, for instance. While the audible sound is produced, a user makes a reach gesture, which decreases a distance between the smart device <NUM> and the user's hand. Although the audible sound causes the radar system <NUM> to vibrate, the radar system <NUM> uses symmetric Doppler interference mitigation to filter the interference artifact generated by the audible sound. By filtering the interference artifact, the radar system <NUM> can detect the reach gesture. Responsive to detecting the reach gesture, the smart device <NUM> can dynamically adjust a volume of the audible sound based on the distance between the user's hand and the radar system <NUM>.

In some implementations, the radar system can analyze the interference artifact prior to filtering the interference artifact. For example, the radar system <NUM> can analyze the interference artifact to recognize the type of audible sound produced. This can include identifying the genre of music, recognizing a particular artist, or identifying a title of a song. The radar system <NUM> can provide information to the smart device <NUM>, which can display the information to the user. In this manner, the radar system <NUM> can analyze the frequency and amplitude of its vibrations to perform music recognition.

In environment <NUM>-<NUM>, the user makes a swipe gesture by moving a hand above the smart device <NUM> along a horizontal dimension (e.g., from a left side of the smart device <NUM> to a right side of the smart device <NUM>). While the gesture is performed, the table vibrates due to the user placing their mug on the table. Although this causes the smart device <NUM>, and therefore the radar system <NUM>, to vibrate, the radar system <NUM> uses symmetric Doppler interference mitigation to filter the resulting interference artifact and detect the swipe gesture. Responsive to detecting the swipe gesture, the smart device <NUM> displays new content to the user. In environments <NUM>-<NUM> and <NUM>-<NUM>, the user performs a gesture using an appendage or body part. Alternatively, the user can perform a gesture using a stylus, a hand-held object, a ring, or any type of material that can reflect radar signals.

The radar system <NUM> can also recognize other types of gestures or motions not shown in <FIG>. Example types of gestures include a knob-turning gesture in which a user curls their fingers to grip an imaginary doorknob and rotate their fingers and hand in a clockwise or counter-clockwise fashion to mimic an action of turning the imaginary doorknob. Another example type of gesture includes a spindle-twisting gesture, which a user performs by rubbing a thumb and at least one other finger together.

The gestures can be two-dimensional, such as those used with touch-sensitive displays (e.g., a two-finger pinch, a two-finger spread, or a tap). The gestures can also be three-dimensional, such as many sign-language gestures, e.g., those of American Sign Language (ASL) and other sign languages worldwide. Upon detecting each of these gestures, the smart device <NUM> can perform an action, such as display new content, move a cursor, activate one or more sensors, open an application, and so forth. In this way, the radar system <NUM> provides touch-free control of the smart device <NUM>.

In environment <NUM>-<NUM>, the user walks with the smart device <NUM>. Although the smart device <NUM> vibrates with each step the user takes, the radar system <NUM> uses symmetric Doppler interference mitigation to filter the resulting interference artifact. In this way, the radar system <NUM> avoids producing false detections based on the interference artifact. Additionally, if a haptic sensor within the smart device <NUM> activates, the symmetric Doppler interference mitigation can also filter an interference artifact resulting from the haptic sensor to further avoid additional false detections.

In environment <NUM>-<NUM>, the user interacts with the smart device <NUM> while in a moving vehicle. Although rough roads may cause the vehicle to vibrate, the radar system <NUM> uses symmetric Doppler interference mitigation to filter an interference artifact resulting from vibration of the walls of the vehicle or vibration of the radar system <NUM> itself. If the smart device <NUM> includes a piezoelectric touch screen, the radar system <NUM> can also use symmetric Doppler interference mitigation to filter an interference artifact resulting from the user interacting with the touch screen.

The radar system <NUM> can perform other types of operations besides gesture recognition or object detection. For example, the radar system <NUM> can determine one or more characteristics of an object (e.g., location, movement, or composition), generate a three-dimensional map of a surrounding environment for contextual awareness, detect and track multiple users to enable both users to interact with the smart device <NUM>, and perform human vital-sign detection.

Some implementations of the radar system <NUM> are particularly advantageous as applied in the context of smart devices <NUM>, for which there is a convergence of issues. This can include a need for limitations in a spacing and layout of the radar system <NUM> and low power. Exemplary overall lateral dimensions of the smart device <NUM> can be, for example, approximately eight centimeters by approximately fifteen centimeters. Exemplary footprints of the radar system <NUM> can be even more limited, such as approximately four millimeters by six millimeters with antennas included. Exemplary power consumption of the radar system <NUM> may be on the order of a few milliwatts to tens of milliwatts (e.g., between approximately two milliwatts and twenty milliwatts). The requirement of such a limited footprint and power consumption for the radar system <NUM> enables the smart device <NUM> to include other desirable features in a space-limited package (e.g., a camera sensor, a fingerprint sensor, a display, and so forth). The smart device <NUM> and the radar system <NUM> are further described with respect to <FIG>.

<FIG> illustrates the radar system <NUM> as part of the smart device <NUM>. The smart device <NUM> is illustrated with various non-limiting example devices including a desktop computer <NUM>-<NUM>, a tablet <NUM>-<NUM>, a laptop <NUM>-<NUM>, a television <NUM>-<NUM>, a computing watch <NUM>-<NUM>, computing glasses <NUM>-<NUM>, a gaming system <NUM>-<NUM>, a microwave <NUM>-<NUM>, and a vehicle <NUM>-<NUM>. Other devices may also be used, such as a home service device, a smart speaker, a smart thermostat, a security camera, a baby monitor, a Wi-Fi™ router, a drone, a trackpad, a drawing pad, a netbook, an e-reader, a home-automation and control system, a wall display, and another home appliance. Note that the smart device <NUM> can be wearable, non-wearable but mobile, or relatively immobile (e.g., desktops and appliances). The radar system <NUM> can be used as a stand-alone radar system or used with, or embedded within, many different smart devices <NUM> or peripherals, such as in control panels that control home appliances and systems, in automobiles to control internal functions (e.g., volume, cruise control, or even driving of the car), or as an attachment to a laptop computer to control computing applications on the laptop.

The smart device <NUM> includes one or more computer processors <NUM> and computer-readable media <NUM>, which includes memory media and storage media. Applications and/or an operating system (not shown) embodied as computer-readable instructions on the computer-readable media <NUM> can be executed by the computer processor <NUM> to provide some of the functionalities described herein. The computer-readable media <NUM> also includes a radar-based application <NUM>, which uses radar data generated by the radar system <NUM> to perform a function, such as presence detection, gesture-based touch-free control, collision avoidance for autonomous driving, human vital-sign notification, and so forth.

The smart device <NUM> can also include a network interface <NUM> for communicating data over wired, wireless, or optical networks. For example, the network interface <NUM> may communicate data over a local-area-network (LAN), a wireless local-area-network (WLAN), a personal-area-network (PAN), a wire-area-network (WAN), an intranet, the Internet, a peer-to-peer network, point-to-point network, a mesh network, and the like. The smart device <NUM> may also include a display (not shown).

The radar system <NUM> includes a communication interface <NUM> to transmit the radar data to a remote device, though this need not be used when the radar system <NUM> is integrated within the smart device <NUM>. In general, the radar data provided by the communication interface <NUM> is in a format usable by the radar-based application <NUM>.

The radar system <NUM> also includes at least one antenna array <NUM> and at least one transceiver <NUM> to transmit and receive radar signals. The antenna array <NUM> includes at least one transmit antenna element and at least one receive antenna element. In some situations, the antenna array <NUM> includes multiple transmit antenna elements to implement a multiple-input multiple-output (MIMO) radar capable of transmitting multiple distinct waveforms at a given time (e.g., a different waveform per transmit antenna element). The antenna elements can be circularly polarized, horizontally polarized, vertically polarized, or a combination thereof.

In some implementations, the antenna array <NUM> includes two or more receive antenna elements for digital beamforming. The receive antenna elements of the antenna array <NUM> can be positioned in a one-dimensional shape (e.g., a line) or a two-dimensional shape (e.g., a rectangular arrangement, a triangular arrangement, or an "L" shape arrangement) for implementations that include three or more receive antenna elements. The one-dimensional shape enables the radar system <NUM> to measure one angular dimension (e.g., an azimuth or an elevation) while the two-dimensional shape enables the radar system <NUM> to measure two angular dimensions (e.g., to determine both an azimuth angle and an elevation angle of the object <NUM>). An element spacing associated with the receive antenna elements can be less than, greater than, or equal to half a center wavelength of the radar signal.

Using the antenna array <NUM>, the radar system <NUM> can form beams that are steered or un-steered, wide or narrow, or shaped (e.g., hemisphere, cube, fan, cone, cylinder). The steering and shaping can be achieved through analog beamforming or digital beamforming. The one or more transmitting antenna elements can have, for instance, an un-steered omnidirectional radiation pattern or can produce a wide steerable beam to illuminate a large volume of space. To achieve target angular accuracies and angular resolutions, the receiving antenna elements can be used to generate hundreds or thousands of narrow steered beams with digital beamforming. In this way, the radar system <NUM> can efficiently monitor an external environment and detect one or more users.

The transceiver <NUM> includes circuitry and logic for transmitting and receiving radar signals via the antenna array <NUM>. Components of the transceiver <NUM> can include amplifiers, mixers, switches, analog-to-digital converters, or filters for conditioning the radar signals. The transceiver <NUM> also includes logic to perform in-phase/quadrature (I/Q) operations, such as modulation or demodulation. A variety of modulations can be used, including linear frequency modulations, triangular frequency modulations, stepped frequency modulations, or phase modulations. Alternatively, the transceiver <NUM> can produce radar signals having a relatively constant frequency or a single tone. The transceiver <NUM> can be configured to support continuous-wave or pulsed radar operations.

A frequency spectrum (e.g., range of frequencies) that the transceiver <NUM> uses to generate the radar signals can encompass frequencies between <NUM> and <NUM> gigahertz (GHz), between <NUM> and <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, or at approximately <NUM>. In some cases, the frequency spectrum can be divided into multiple sub-spectrums that have similar or different bandwidths. The bandwidths can be on the order of <NUM> megahertz (MHz), <NUM>, <NUM>, and so forth. Different frequency sub-spectrums may include, for example, frequencies between approximately <NUM> and <NUM>, <NUM> and <NUM>, or <NUM> and <NUM>. Although the example frequency sub-spectrums described above are contiguous, other frequency sub-spectrums may not be contiguous. To achieve coherence, multiple frequency sub-spectrums (contiguous or not) that have a same bandwidth may be used by the transceiver <NUM> to generate multiple radar signals, which are transmitted simultaneously or separated in time. In some situations, multiple contiguous frequency sub-spectrums may be used to transmit a single radar signal, thereby enabling the radar signal to have a wide bandwidth.

The radar system <NUM> also includes one or more system processors <NUM> and a system media <NUM> (e.g., one or more computer-readable storage media). The system media <NUM> optionally includes a hardware-abstraction module <NUM>. The system media <NUM> also includes an interference mitigation module <NUM>. The hardware-abstraction module <NUM> and the interference mitigation module <NUM> can be implemented using hardware, software, firmware, or a combination thereof. In this example, the system processor <NUM> implements the hardware-abstraction module <NUM> and the interference mitigation module <NUM>. Together, the hardware-abstraction module <NUM> and the interference mitigation module <NUM> enable the system processor <NUM> to process responses from the receive antenna elements in the antenna array <NUM> to detect a user, determine a position of the object, and/or recognize a gesture performed by the user.

In an alternative implementation (not shown), the hardware-abstraction module <NUM> and the interference mitigation module <NUM> are included within the computer-readable media <NUM> and implemented by the computer processor <NUM>. This enables the radar system <NUM> to provide the smart device <NUM> raw data via the communication interface <NUM> such that the computer processor <NUM> can process the raw data for the radar-based application <NUM>.

The hardware-abstraction module <NUM> transforms raw data provided by the transceiver <NUM> into hardware-agnostic radar data, which can be processed by the interference mitigation module <NUM>. In particular, the hardware-abstraction module <NUM> conforms complex radar data from a variety of different types of radar signals to an expected input of the interference mitigation module <NUM>. This enables the interference mitigation module 222to process different types of radar signals received by the radar system <NUM>, including those that utilize different modulations schemes for frequency-modulated continuous-wave radar, phase-modulated spread spectrum radar, or impulse radar. The hardware-abstraction module <NUM> can also normalize complex radar data from radar signals with different center frequencies, bandwidths, transmit power levels, or pulsewidths.

Additionally, the hardware-abstraction module <NUM> conforms complex radar data generated using different hardware architectures. Different hardware architectures can include different antenna arrays <NUM> positioned on different surfaces of the smart device <NUM> or different sets of antenna elements within an antenna array <NUM>. By using the hardware-abstraction module <NUM>, the interference mitigation module <NUM> can process complex radar data generated by different sets of antenna elements with different gains, different sets of antenna elements of various quantities, or different sets of antenna elements with different antenna element spacings.

By using the hardware-abstraction module <NUM>, the interference mitigation module <NUM> can operate in radar systems <NUM> with different limitations that affect the available radar modulation schemes, transmission parameters, or types of hardware architectures. The hardware-abstraction module <NUM> is further described with respect to <FIG>.

The interference mitigation module <NUM> filters the hardware-agnostic radar data to attenuate one or more interference artifacts resulting from vibration of the radar system <NUM> or vibration of other objects detected by the radar system <NUM>. Due to the back and forth motion of the vibration, the interference artifact has both a positive and negative range rate. As such, the interference artifact contributes to amplitudes across both positive and negative Doppler bins of a range-Doppler map generated by the radar system. In contrast, most desired objects contribute to amplitudes across either positive or negative Doppler bins. In other words, the amplitudes resulting from the interference artifact are approximately symmetric across the Doppler bins, whereas the amplitudes resulting from the desired object are one-sided and not symmetrical. The interference mitigation module <NUM> exploits this difference to attenuate the interference artifact without significantly attenuating the desired object. In some cases, the interference mitigation module <NUM> can also analyze and adjust phase information within the range-Doppler map to mitigate the effects of the interference artifact. The interference mitigation module <NUM> is further described with respect to <FIG>.

The interference mitigation module <NUM> produces filtered radar data, which can be further analyzed by the system processor <NUM>. For example, the system processor <NUM> can process the filtered radar data to generate radar-application data for the radar-based application <NUM>. Example types of radar-application data include a position of a user, movement of the user, a type of gesture performed by the user, a measured vital-sign of the user, a collision alert, or characteristics of an object.

<FIG> illustrates an example location of the radar system <NUM> relative to other components within the smart device <NUM>. In this example, the smart device <NUM> is shown to be a smartphone <NUM>-<NUM>. An exterior of the smartphone <NUM>-<NUM> includes an exterior housing <NUM> and an exterior viewing panel <NUM>. As an example, the exterior housing <NUM> has a vertical height of approximately <NUM> millimeters (mm), a horizontal length of approximately <NUM>, and a width of approximately <NUM>. The exterior housing <NUM> can be composed of metal material, for instance.

The exterior viewing panel <NUM> forms an exterior face of the smartphone <NUM>-<NUM> and has a vertical height of approximately <NUM> and a horizontal length of approximately <NUM>. The exterior viewing panel <NUM> includes cut-outs for various components that are positioned within an interior of the smartphone <NUM>-<NUM> (e.g., positioned beneath the exterior viewing panel <NUM>). These components are further described below.

The exterior viewing panel <NUM> can be formed using various types of glass or plastics that are found within display screens. In some implementations, the exterior viewing panel <NUM> has a dielectric constant (e.g., a relative permittivity) between approximately four and ten, which attenuates or distorts radar signals. As such, the exterior viewing panel <NUM> is opaque or semi-transparent to a radar signal and can cause a portion of a transmitted or received radar signal to be reflected.

At least a portion of the radar system <NUM>, such as an integrated circuit that includes the antenna array <NUM> and the transceiver <NUM>, is positioned beneath the exterior viewing panel <NUM> and near an edge of the smartphone <NUM>-<NUM>. As an example, the integrated circuit has a vertical height of approximately <NUM>, a horizontal length of approximately <NUM>, and a thickness of approximately <NUM> (within +/- <NUM> along each dimension). These dimensions enable the integrated circuit to fit between the exterior housing <NUM> and a display element <NUM>. The vertical height of the integrated circuit can be similar to other components that are positioned near the edge of the smartphone <NUM>-<NUM> so as to avoid reducing a size of the display element <NUM>.

In this example implementation, the antenna array <NUM> is oriented towards (e.g., faces) the exterior viewing panel <NUM>. As such, the integrated circuit radiates through the exterior viewing panel <NUM> (e.g., transmits and receives the radar signals that propagate through the exterior viewing panel <NUM>). If the exterior viewing panel <NUM> behaves as an attenuator, the radar system <NUM> can adjust a frequency or a steering angle of a transmitted radar signal to mitigate the effects of the attenuator instead of increasing transmit power. As such, the radar system <NUM> can realize enhanced accuracy and longer ranges for detecting the user without increasing power consumption.

The display element <NUM> displays images that are viewed through the exterior viewing panel <NUM>. As shown, the antenna array <NUM> of the radar system <NUM> is oriented towards (e.g., faces) a same direction as the display element <NUM> such that the radar integrated circuit <NUM> transmits radar signals towards a user that is looking at the display element <NUM>.

In this example, the integrated circuit transmits and receives radar signals with frequencies between approximately <NUM> and <NUM>. This mitigates electromagnetic interference with a wireless communication system of the smartphone <NUM>-<NUM>, which uses frequencies below <NUM>, for instance. Transmitting and receiving radar signals with millimeter wavelengths further enables the integrated circuit to realize the above footprint.

A depicted interior of the smartphone <NUM>-<NUM> includes the integrated circuit of the radar system <NUM>, the display element <NUM>, an infrared sensor <NUM>, a speaker <NUM>, a proximity sensor <NUM>, an ambient light sensor <NUM>, a camera <NUM>, and another infrared sensor <NUM>. The integrated circuit of the radar system <NUM>, the infrared sensor <NUM>, the speaker <NUM>, the proximity sensor <NUM>, the ambient light sensor <NUM>, the camera <NUM>, and the infrared sensor <NUM> are positioned beneath an upper portion of the exterior viewing panel <NUM>. The display element <NUM> is positioned beneath the lower portion of the exterior viewing panel <NUM>. In this example, a distance between a top edge of the display element <NUM> and a top edge of the exterior viewing panel <NUM> (DGD) is approximately <NUM>.

The infrared sensors <NUM> and <NUM> can be used for facial recognition. To conserve power, the infrared sensors <NUM> and <NUM> operate in an off-state when not in use. However, a warm-up sequence associated with transitioning the infrared sensors <NUM> and <NUM> from the off-state to an on-state can require a significant amount of time, such as a half-second or more. This can cause a delay in execution of the facial recognition. To reduce this time delay, the radar system <NUM> proactively detects the user reaching towards or approaching the smartphone <NUM>-<NUM> and initiates the warm-up sequence prior to the user touching the smartphone <NUM>-<NUM>. As such, the infrared sensors <NUM> and <NUM> can be in the on-state sooner and reduce a time the user waits for the facial recognition to complete.

In this example, the integrated circuit of the radar system <NUM> is positioned between the infrared sensor <NUM> and the speaker <NUM>. A distance between the integrated circuit and the speaker <NUM> (DSR) is approximately <NUM> or less. As such, the radar system <NUM> is within close proximity to the speaker <NUM> and can vibrate while the speaker <NUM> produces audible sounds. By using symmetric Doppler interference mitigation, the radar system <NUM> can operate while the speaker <NUM> is producing the audible sounds without increasing the false-alarm rate.

<FIG> illustrates an example operation of the radar system <NUM>. In the depicted configuration, the radar system <NUM> is implemented as a frequency-modulated continuous-wave radar. However, other types of radar architectures can be implemented, as described above with respect to <FIG>. In environment <NUM>, a user <NUM> is located at a particular slant range <NUM> from the radar system <NUM>. To detect the user <NUM>, the radar system <NUM> transmits a radar transmit signal <NUM>. At least a portion of the radar transmit signal <NUM> is reflected by the user <NUM>. This reflected portion represents a radar receive signal <NUM>. The radar system <NUM> receives the radar receive signal <NUM> and processes the radar receive signal <NUM> to extract data for the radar-based application <NUM>. As depicted, an amplitude of the radar receive signal <NUM> is smaller than an amplitude of the radar transmit signal <NUM> due to losses incurred during propagation and reflection.

The radar transmit signal <NUM> includes a sequence of chirps <NUM>-<NUM> to <NUM>-N, where N represents a positive integer greater than one. The radar system <NUM> can transmit the chirps <NUM>-<NUM> to <NUM>-N in a continuous burst or transmit the chirps <NUM>-<NUM> to <NUM>-N as time-separated pulses, as further described with respect to <FIG>. A duration of each chirp <NUM>-<NUM> to <NUM>-N can be on the order of tens or thousands of microseconds (e.g., between approximately <NUM> microseconds (µs) and <NUM> milliseconds (ms)), for instance.

Individual frequencies of the chirps <NUM>-<NUM> to <NUM>-N can increase or decrease over time. In the depicted example, the radar system <NUM> employs a two-slope cycle (e.g., triangular frequency modulation) to linearly increase and linearly decrease the frequencies of the chirps <NUM>-<NUM> to <NUM>-N over time. The two-slope cycle enables the radar system <NUM> to measure the Doppler frequency shift caused by motion of the user <NUM>. In general, transmission characteristics of the chirps <NUM>-<NUM> to <NUM>-N (e.g., bandwidth, center frequency, duration, and transmit power) can be tailored to achieve a particular detection range, range resolution, or doppler sensitivity for detecting one or more characteristics the user <NUM> or one or more actions performed by the user <NUM>.

At the radar system <NUM>, the radar receive signal <NUM> represents a delayed version of the radar transmit signal <NUM>. The amount of delay is proportional to the slant range <NUM> (e.g., distance) from the antenna array <NUM> of the radar system <NUM> to the user <NUM>. In particular, this delay represents a summation of a time it takes for the radar transmit signal <NUM> to propagate from the radar system <NUM> to the user <NUM> and a time it takes for the radar receive signal <NUM> to propagate from the user <NUM> to the radar system <NUM>. If the user <NUM> and/or the radar system <NUM> is moving, the radar receive signal <NUM> is shifted in frequency relative to the radar transmit signal <NUM> due to the Doppler effect. In other words, characteristics of the radar receive signal <NUM> are dependent upon motion of the hand and/or motion of the radar system <NUM>. Similar to the radar transmit signal <NUM>, the radar receive signal <NUM> is composed of one or more of the chirps <NUM>-<NUM> to <NUM>-N.

The multiple chirps <NUM>-<NUM> to <NUM>-N enable the radar system <NUM> to make multiple observations of the user <NUM> over a predetermined time period. A radar framing structure determines a timing of the chirps <NUM>-<NUM> to <NUM>-N, as further described with respect to <FIG>.

<FIG> illustrates an example radar framing structure <NUM> for detecting a frame-of-reference change using machine learning. In the depicted configuration, the radar framing structure <NUM> includes three different types of frames. At a top level, the radar framing structure <NUM> includes a sequence of main frames <NUM>, which can be in the active state or the inactive state. Generally speaking, the active state consumes a larger amount of power relative to the inactive state. At an intermediate level, the radar framing structure <NUM> includes a sequence of feature frames <NUM>, which can similarly be in the active state or the inactive state. Different types of feature frames <NUM> include a pulse-mode feature frame <NUM> (shown at the bottom-left of <FIG>) and a burst-mode feature frame <NUM> (shown at the bottom-right of <FIG>). At a low level, the radar framing structure <NUM> includes a sequence of radar frames (RF) <NUM>, which can also be in the active state or the inactive state.

The radar system <NUM> transmits and receives a radar signal during an active radar frame <NUM>. In some situations, the radar frames <NUM> are individually analyzed for basic radar operations, such as search and track, clutter map generation, user location determination, and so forth. Radar data collected during each active radar frame <NUM> can be saved to a buffer after completion of the radar frame <NUM> or provided directly to the system processor <NUM> of <FIG>.

The radar system <NUM> analyzes the radar data across multiple radar frames <NUM> (e.g., across a group of radar frames <NUM> associated with an active feature frame <NUM>) to identify a particular feature. Example types of features include a particular type of motion, a motion associated with a particular appendage (e.g., a hand or individual fingers), and a feature associated with different portions of the gesture. To detect a change in the radar system <NUM>'s frame of reference or recognize a gesture performed by the user <NUM> during an active main frame <NUM>, the radar system <NUM> analyzes the radar data associated with one or more active feature frames <NUM>.

A duration of the main frame <NUM> may be on the order of milliseconds or seconds (e.g., between approximately <NUM> and <NUM> seconds (s)). After active main frames <NUM>-<NUM> and <NUM>-<NUM> occur, the radar system <NUM> is inactive, as shown by inactive main frames <NUM>-<NUM> and <NUM>-<NUM>. A duration of the inactive main frames <NUM>-<NUM> and <NUM>-<NUM> is characterized by a deep sleep time <NUM>, which may be on the order of tens of milliseconds or more (e.g., greater than <NUM>). In an example implementation, the radar system <NUM> turns off all of the active components (e.g., an amplifier, an active filter, a voltage-controlled oscillator (VCO), a voltage-controlled buffer, a multiplexer, an analog-to-digital converter, a phase-lock loop (PLL) or a crystal oscillator) within the transceiver <NUM> to conserve power during the deep sleep time <NUM>.

In the depicted radar framing structure <NUM>, each main frame <NUM> includes K feature frames <NUM>, where K is a positive integer. If the main frame <NUM> is in the inactive state, all of the feature frames <NUM> associated with that main frame <NUM> are also in the inactive state. In contrast, an active main frame <NUM> includes J active feature frames <NUM> and K-J inactive feature frames <NUM>, where J is a positive integer that is less than or equal to K. A quantity of feature frames <NUM> can be adjusted based on a complexity of the environment or a complexity of a gesture. For example, a main frame <NUM> can include a few to a hundred feature frames <NUM> (e.g., K may equal <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>). A duration of each feature frame <NUM> may be on the order of milliseconds (e.g., between approximately <NUM> and <NUM>).

To conserve power, the active feature frames <NUM>-<NUM> to <NUM>-J occur prior to the inactive feature frames <NUM>-(J+<NUM>) to <NUM>-K. A duration of the inactive feature frames <NUM>-(J+<NUM>) to <NUM>-K is characterized by a sleep time <NUM>. In this way, the inactive feature frames <NUM>-(J+<NUM>) to <NUM>-K are consecutively executed such that the radar system <NUM> can be in a powered-down state for a longer duration relative to other techniques that may interleave the inactive feature frames <NUM>-(J+<NUM>) to <NUM>-K with the active feature frames <NUM>-<NUM> to <NUM>-J. Generally speaking, increasing a duration of the sleep time <NUM> enables the radar system <NUM> to turn off components within the transceiver <NUM> that require longer start-up times.

Each feature frame <NUM> includes L radar frames <NUM>, where L is a positive integer that may or may not be equal to J or K. In some implementations, a quantity of radar frames <NUM> may vary across different feature frames <NUM> and may comprise a few frames or hundreds of frames (e.g., L may equal <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>). A duration of a radar frame <NUM> may be on the order of tens or thousands of microseconds (e.g., between approximately <NUM> and <NUM>). The radar frames <NUM> within a particular feature frame <NUM> can be customized for a predetermined detection range, range resolution, or doppler sensitivity, which facilitates detection of a particular feature or gesture. For example, the radar frames <NUM> may utilize a particular type of modulation, bandwidth, frequency, transmit power, or timing. If the feature frame <NUM> is in the inactive state, all of the radar frames <NUM> associated with that feature frame <NUM> are also in the inactive state.

The pulse-mode feature frame <NUM> and the burst-mode feature frame <NUM> include different sequences of radar frames <NUM>. Generally speaking, the radar frames <NUM> within an active pulse-mode feature frame <NUM> transmit pulses that are separated in time by a predetermined amount. This disperses observations over time, which can make it easier for the radar system <NUM> to detect the frame-of-reference change due to larger changes in the observed chirps <NUM>-<NUM> to <NUM>-N within the pulse-mode feature frame <NUM> relative to the burst-mode feature frame <NUM>. In contrast, the radar frames <NUM> within an active burst-mode feature frame <NUM> transmit pulses continuously across a portion of the burst-mode feature frame <NUM> (e.g., the pulses are not separated by a predetermined amount of time). This enables an active-burst-mode feature frame <NUM> to consume less power than the pulse-mode feature frame <NUM> by turning off a larger quantity of components, including those with longer start-up times, as further described below.

Within each active pulse-mode feature frame <NUM>, the sequence of radar frames <NUM> alternates between the active state and the inactive state. Each active radar frame <NUM> transmits a chirp <NUM> (e.g., a pulse), which is illustrated by a triangle. A duration of the chirp <NUM> is characterized by an active time <NUM>. During the active time <NUM>, components within the transceiver <NUM> are powered-on. During a short-idle time <NUM>, which includes the remaining time within the active radar frame <NUM> and a duration of the following inactive radar frame <NUM>, the radar system <NUM> conserves power by turning off one or more active components within the transceiver <NUM> that have a start-up time within a duration of the short-idle time <NUM>.

An active burst-mode feature frame <NUM> includes P active radar frames <NUM> and L-P inactive radar frames <NUM>, where P is a positive integer that is less than or equal to L. To conserve power, the active radar frames <NUM>-<NUM> to <NUM>-P occur prior to the inactive radar frames <NUM>-(P+<NUM>) to <NUM>-L. A duration of the inactive radar frames <NUM>-(P+<NUM>) to <NUM>-L is characterized by a long-idle time <NUM>. By grouping the inactive radar frames <NUM>-(P+<NUM>) to <NUM>-L together, the radar system <NUM> can be in a powered-down state for a longer duration relative to the short-idle time <NUM> that occurs during the pulse-mode feature frame <NUM>. Additionally, the radar system <NUM> can turn off additional components within the transceiver <NUM> that have start-up times that are longer than the short-idle time <NUM> and shorter than the long-idle time <NUM>.

Each active radar frame <NUM> within an active burst-mode feature frame <NUM> transmits a portion of the chirp <NUM>. In this example, the active radar frames <NUM>-<NUM> to <NUM>-P alternate between transmitting a portion of the chirp <NUM> that increases in frequency and a portion of the chirp <NUM> that decreases in frequency.

The radar framing structure <NUM> enables power to be conserved through adjustable duty cycles within each frame type. A first duty cycle <NUM> is based on a quantity of active feature frames <NUM> (J) relative to a total quantity of feature frames <NUM> (K). A second duty cycle <NUM> is based on a quantity of active radar frames <NUM> (e.g., L/<NUM> or P) relative to a total quantity of radar frames <NUM> (L). A third duty cycle <NUM> is based on a duration of the chirp <NUM> relative to a duration of a radar frame <NUM>.

Consider an example radar framing structure <NUM> for a power state that consumes approximately <NUM> milliwatts (mW) of power and has a main-frame update rate between approximately <NUM> and <NUM> hertz (Hz). In this example, the radar framing structure <NUM> includes a main frame <NUM> with a duration between approximately <NUM> and <NUM> second. The main frame <NUM> includes thirty-one pulse-mode feature frames <NUM> (e.g., K is equal to <NUM>). One of the thirty-one pulse-mode feature frames <NUM> is in the active state. This results in the duty cycle <NUM> being approximately equal to <NUM>%. A duration of each pulse-mode feature frame <NUM> is between approximately <NUM> and <NUM>. Each pulse-mode feature frame <NUM> is composed of eight radar frames <NUM> (e.g., L is equal to <NUM>). Within the active pulse-mode feature frame <NUM>, all eight radar frames <NUM> are in the active state. This results in the duty cycle <NUM> being equal to <NUM>%. A duration of each radar frame <NUM> is between approximately <NUM> and <NUM>. An active time <NUM> within each of the active radar frames <NUM> is between approximately <NUM> and <NUM>. As such, the resulting duty cycle <NUM> is approximately <NUM>%. This example radar framing structure <NUM> has been found to yield good performance results. These good performance results are in terms of good frame-of-reference detection, gesture recognition, and presence detection while also yielding good power efficiency results in the application context of a handheld smartphone in a low-power state. Generation of the radar transmit signal <NUM> (of <FIG>) and the processing of the radar receive signal <NUM> (of <FIG>) are further described with respect to <FIG>.

<FIG> illustrates an example antenna array <NUM> and an example transceiver <NUM> of the radar system <NUM>. In the depicted configuration, the transceiver <NUM> includes a transmitter <NUM> and a receiver <NUM>. The transmitter <NUM> includes at least one voltage-controlled oscillator <NUM> and at least one power amplifier <NUM>. The receiver <NUM> includes at least two receive channels <NUM>-<NUM> to <NUM>-M, where M is a positive integer greater than one. Each receive channel <NUM>-<NUM> to <NUM>-M includes at least one low-noise amplifier <NUM>, at least one mixer <NUM>, at least one filter <NUM>, and at least one analog-to-digital converter <NUM>.

The antenna array <NUM> includes at least one transmit antenna element <NUM> and at least two receive antenna elements <NUM>-<NUM> to <NUM>-M. The transmit antenna element <NUM> is coupled to the transmitter <NUM>. The receive antenna elements <NUM>-<NUM> to <NUM>-M are respectively coupled to the receive channels <NUM>-<NUM> to <NUM>-M. Although the radar system <NUM> of <FIG> is shown to include multiple receive antenna elements <NUM>-<NUM> to <NUM>-M and multiple receive channels <NUM>-<NUM> to <NUM>-M, the described techniques for symmetric Doppler interference mitigation can also be applied to radar systems <NUM> that utilize a single receive antenna element <NUM> and a single receive channel <NUM>.

During transmission, the voltage-controlled oscillator <NUM> generates a frequency-modulated radar signal <NUM> at radio frequencies. The power amplifier <NUM> amplifies the frequency-modulated radar signal <NUM> for transmission via the transmit antenna element <NUM>. The transmitted frequency-modulated radar signal <NUM> is represented by the radar transmit signal <NUM>, which can include multiple chirps <NUM>-<NUM> to <NUM>-N based on the radar framing structure <NUM> of <FIG>. As an example, the radar transmit signal <NUM> is generated according to the burst-mode feature frame <NUM> of <FIG> and includes <NUM> chirps <NUM> (e.g., N equals <NUM>).

During reception, each receive antenna element <NUM>-<NUM> to <NUM>-M receives a version of the radar receive signal <NUM>-<NUM> to <NUM>-M. In general, relative phase differences between these versions of the radar receive signals <NUM>-<NUM> to <NUM>-M are due to differences in locations of the receive antenna elements <NUM>-<NUM> to <NUM>-M. Within each receive channel <NUM>-<NUM> to <NUM>-M, the low-noise amplifier <NUM> amplifies the radar receive signal <NUM>, and the mixer <NUM> mixes the amplified radar receive signal <NUM> with the frequency-modulated radar signal <NUM>. In particular, the mixer performs a beating operation, which downconverts and demodulates the radar receive signal <NUM> to generate a beat signal <NUM>.

A frequency of the beat signal <NUM> represents a frequency difference between the frequency-modulated radar signal <NUM> and the radar receive signal <NUM>, which is proportional to the slant range <NUM> of <FIG>. Although not shown, the beat signal <NUM> can include multiple frequencies, which represents reflections from different portions of the user <NUM> (e.g., different fingers, different portions of a hand, or different body parts). In some cases, these different portions move at different speeds, move in different directions, or are positioned at different slant ranges relative to the radar system <NUM>.

The filter <NUM> filters the beat signal <NUM>, and the analog-to-digital converter <NUM> digitizes the filtered beat signal <NUM>. The receive channels <NUM>-<NUM> to <NUM>-M respectively generate digital beat signals <NUM>-<NUM> to <NUM>-M, which are provided to the system processor <NUM> for processing. The receive channels <NUM>-<NUM> to <NUM>-M of the transceiver <NUM> are coupled to the system processor <NUM>, as shown in <FIG>.

<FIG> illustrates an example scheme implemented by the radar system <NUM> for performing symmetric Doppler interference mitigation. In the depicted configuration, the system processor <NUM> implements the hardware-abstraction module <NUM> and the interference mitigation module <NUM>. The system processor <NUM> is connected to the receive channels <NUM>-<NUM> to <NUM>-M. The system processor <NUM> can also communicate with the computer processor <NUM>. Although not shown, the hardware-abstraction module <NUM> and/or the interference mitigation module <NUM> can be implemented by the computer processor <NUM>.

In this example, the hardware-abstraction module <NUM> accepts the digital beat signals <NUM>-<NUM> to <NUM>-M from the receive channels <NUM>-<NUM> to <NUM>-M. The digital beat signals <NUM>-<NUM> to <NUM>-M represent raw or unprocessed complex radar data. The hardware-abstraction module <NUM> performs one or more operations to generate hardware-agnostic radar data <NUM>-<NUM> to <NUM>-M based on digital beat signals <NUM>-<NUM> to <NUM>-M. The hardware-abstraction module <NUM> transforms the complex radar data provided by the digital beat signals <NUM>-<NUM> to <NUM>-M into a form that is expected by the interference mitigation module <NUM>. In some cases, the hardware-abstraction module <NUM> normalizes amplitudes associated with different transmit power levels or transforms the complex radar data into a frequency-domain representation.

The hardware-agnostic radar data <NUM>-<NUM> to <NUM>-M can include magnitude information or both magnitude and phase information (e.g., in-phase and quadrature components). The hardware-agnostic radar data <NUM>-<NUM> to <NUM>-M includes range-Doppler maps for each receive channel <NUM>-<NUM> to <NUM>-M and for a particular active feature frame <NUM>, as further described with respect to <FIG> and <FIG>.

The interference mitigation module <NUM> generates filtered radar data <NUM> based on the hardware-agnostic radar data <NUM>-<NUM> to <NUM>-M. The filtered radar data <NUM> includes filtered range-Doppler maps with interference artifacts that have been attenuated. The filtered radar data <NUM> can be provided to other modules within the radar system <NUM>, such as a gesture-recognition module, a presence-detection module, a collision-avoidance module, a vital-sign measurement module, and so forth. These modules produce radar-application data <NUM>, which is provided to the radar-based application <NUM> of <FIG>. Operation of the hardware-abstraction module <NUM> is further described with respect to <FIG>.

<FIG> illustrates an example hardware-abstraction module <NUM> for performing symmetric Doppler interference mitigation. In the depicted configuration, the hardware-abstraction module <NUM> includes a pre-processing stage <NUM> and a signal-transformation stage <NUM>. The pre-processing stage <NUM> operates on each chirp <NUM>-<NUM> to <NUM>-N within the digital beat signals <NUM>-<NUM> to <NUM>-M. In other words, the pre-processing stage <NUM> performs an operation for each active radar frame <NUM>. In this example, the pre-processing stage <NUM> includes M one-dimensional (1D) Fast-Fourier Transform (FFT) modules, which respectively process the digital beat signals <NUM>-<NUM> to <NUM>-M. Other types of modules that perform similar operations are also possible, such as a Fourier Transform module.

For simplicity, the hardware-abstraction module <NUM> is shown to process a digital beat signal <NUM>-<NUM> associated with the receive channel <NUM>-<NUM>. The digital beat signal <NUM>-<NUM> includes the chirps <NUM>-<NUM> to <NUM>-M, which are time-domain signals. The chirps <NUM>-<NUM> to <NUM>-M are passed to a one-dimensional FFT module <NUM>-<NUM> in an order in which they are received and processed by the transceiver <NUM>. Assuming the radar receive signals <NUM>-<NUM> to <NUM>-M include <NUM> chirps <NUM>-<NUM> to <NUM>-N (e.g., N equals <NUM>), the one-dimensional FFT module <NUM>-<NUM> performs <NUM> FFT operations to generate pre-processed complex radar data per chirp <NUM>-<NUM>.

The signal-transformation stage <NUM> operates on the sequence of chirps <NUM>-<NUM> to <NUM>-M within each of the digital beat signals <NUM>-<NUM> to <NUM>-M. In other words, the signal-transformation stage <NUM> performs an operation for each active feature frame <NUM>. In this example, the signal-transformation stage <NUM> includes M buffers and M two-dimensional (2D) FFT modules. For simplicity, the signal-transformation stage <NUM> is shown to include a buffer <NUM>-<NUM> and a two-dimensional FFT module <NUM>-<NUM>.

The buffer <NUM>-<NUM> stores a first portion of the pre-processed complex radar data <NUM>-<NUM>, which is associated with the first chirp <NUM>-<NUM>. The one-dimensional FFT module <NUM>-<NUM> continues to process subsequent chirps <NUM>-<NUM> to <NUM>-N, and the buffer <NUM>-<NUM> continues to store the corresponding portions of the pre-processed complex radar data <NUM>-<NUM>. This process continues until the buffer <NUM>-<NUM> stores a last portion of the pre-processed complex radar data <NUM>-<NUM>, which is associated with the chirp <NUM>-M.

At this point, the buffer <NUM>-<NUM> stores pre-processed complex radar data associated with a particular feature frame <NUM>-<NUM>. The pre-processed complex radar data per feature frame <NUM>-<NUM> represents magnitude information (as shown) and phase information (not shown) across different chirps <NUM>-<NUM> to <NUM>-N and across different range bins <NUM>-<NUM> to <NUM>-A, where A represents a positive integer.

The two-dimensional FFT <NUM>-<NUM> accepts the pre-processed complex radar data per feature frame <NUM>-<NUM> and performs a two-dimensional FFT operation to form the hardware-agnostic radar data <NUM>-<NUM>, which represents a range-Doppler map <NUM>. The range-Doppler map <NUM> includes complex radar data for the range bins <NUM>-<NUM> to <NUM>-A and Doppler bins <NUM>-<NUM> to <NUM>-B, where B represents a positive integer. In other words, each range bin <NUM>-<NUM> to <NUM>-A and Doppler bin <NUM>-<NUM> to <NUM>-B includes a complex number with real and imaginary parts that together represent magnitude and phase information. The quantity of range bins <NUM>-<NUM> to <NUM>-A can be on the order of tens or hundreds, such as <NUM> or <NUM> (e.g., A equals <NUM> or <NUM>). The quantity of Doppler bins can be on the order of tens or hundreds, such as <NUM>, <NUM>, or <NUM> (e.g., B equals <NUM>, <NUM>, or <NUM>). As described above with respect to <FIG> and <FIG>, the range-Doppler map <NUM> can include an interference artifact, as further described with respect to <FIG>.

<FIG> illustrates an example range-Doppler map <NUM> for performing symmetric Doppler interference mitigation. In this example, the amplitude (or magnitude) information of the hardware-agnostic radar data <NUM> is illustrated with different patterns. Larger amplitudes are represented with patterns that have a larger percentage of black. Smaller amplitudes are represented with patterns that have a smaller percentage of black (e.g., a higher percentage of white). Although not shown, the range-Doppler map <NUM> can also include phase information.

Each range bin <NUM> and Doppler bin <NUM> contains amplitude information for a particular range interval and Doppler frequency interval. The range bins <NUM> are labeled from <NUM> to A. The Doppler bins <NUM> are labeled from -B/<NUM> to <NUM> to B/<NUM>. The zero Doppler bin <NUM> includes amplitude information for objects that have a Doppler frequency of <NUM> or a Doppler frequency equal to a multiple of the pulse repetition frequency (PRF). The ± B/<NUM> bins include amplitude information for objects that have a Doppler frequency of ± PRF/<NUM>.

In this example, the radar receive signal <NUM> includes reflections from a hand <NUM> of the user <NUM> (of <FIG>) and reflections from a body <NUM> of the user <NUM>. The hand <NUM> and the body <NUM> have a medium-low amplitudes at different range bins <NUM>. In this case, the body <NUM> is relatively stationary and appears within the zero and negative one Doppler bins <NUM>. The hand <NUM> appears within the negative two and negative one Doppler bins <NUM>. In most situations, the desired object (or user <NUM>) contributes to amplitudes within a few Doppler bins <NUM> that are either on the positive side or the negative side of the Doppler spectrum. As such, a plot of the amplitude of the object is one-sided and not symmetrical across the Doppler bins <NUM> for the range bin <NUM> corresponding to the slant range <NUM> to the object. For example, at <NUM>, the amplitude response of one of the range bins that includes the hand <NUM> has a single peak within the negative Doppler bins <NUM> and no peak within the positive Doppler bins <NUM>.

The radar receive signal <NUM> also includes an interference artifact <NUM> due to vibration of the radar system <NUM>, vibration of a component within the smart device <NUM>, or vibration of an obj ect within the external environment. Due to the back and forth motion of the vibration, the interference artifact <NUM> contributes to amplitudes of both positive and negative Doppler bins, such as the negative two and positive two Doppler bins <NUM>. An amplitude of the interference artifact <NUM> is also approximately symmetric for one or more range bins <NUM>. An example amplitude plot of the interference artifact <NUM> for the first range bin <NUM> is shown at <NUM>. Note that an amplitude of the interference artifact <NUM> is greater than an amplitude of the hand <NUM> in this example.

As shown at <NUM>, the amplitude of the interference artifact <NUM> is approximately symmetric across the Doppler bins <NUM>. In other words, a peak at one of the positive Doppler bins <NUM> corresponds, or essentially corresponds, to another peak at one of the negative Doppler bins <NUM>. In this example, a peak occurs at the positive two Doppler bin <NUM> and a corresponding peak, or essentially corresponding peak, occurs at the negative one Doppler bin <NUM>. As described, the corresponding positive and negative Doppler bins <NUM> do not have to be exactly the same (e.g., the highest part of the peaks do not have to occur within the positive two and negative two Doppler bins <NUM> or the positive one and negative one Doppler bins <NUM>). Instead, the corresponding positive and negative Doppler bins <NUM> can be within some window depending on the resolution of the Doppler bins <NUM> (e.g., within two Doppler bins <NUM> of the opposite Doppler bin <NUM>, within three Doppler bins <NUM> of the opposite Doppler bin <NUM>, and so forth). This interval can include a quantity of Doppler bins <NUM> that represent a fraction of the pulse-repetition frequency, such as less than ten percent or less than twenty percent, for example. In some cases, the amplitudes of these peaks are approximately equal to each other (e.g., within ten to twenty percent of each other or less).

In another example not shown, the amplitude of the interference artifact <NUM> is symmetric across the Doppler bins <NUM>. In other words, a peak occurs at one of the positive Doppler bins <NUM> (e.g., the positive one Doppler bin <NUM>) and another peak occurs at a corresponding negative Doppler bin <NUM> (e.g., the negative one Doppler bin <NUM>).

In other examples not shown, the interference artifact <NUM> can contribute to the amplitudes of all of the Doppler bins <NUM>. Sometimes, some frequency components of the interference artifact <NUM> that are greater than half of the pulse repetition frequency experience aliasing. As an example, the pulse repetition frequency of the radar system <NUM> can be approximately two kilohertz. In this case, a portion of the interference artifact <NUM> can wrap around the Doppler spectrum and encompass both the ± B/<NUM> Doppler bins <NUM> and ± <NUM> Doppler bins <NUM>. In some cases, the interference artifact <NUM> is observed across multiple range bins <NUM>. The quantity of range bins <NUM> depends on the range bin resolution and interactions between the radar signals and an interior of the smart device <NUM>. As an example, the interference artifact <NUM> can space across multiple range bins <NUM> that represent a range that is less than or equal to <NUM> centimeters (cm).

The interference mitigation module <NUM> exploits the symmetric amplitude of the interference artifact <NUM> across the Doppler bins <NUM> to attenuate the interference artifact <NUM> without significantly attenuating desired objects, such as the hand <NUM> or the body <NUM>, as further described with respect to <FIG>.

<FIG> illustrates an example implementation of a interference mitigation module <NUM> for symmetric Doppler interference mitigation. In the example, the interference mitigation module <NUM> includes a noise floor estimation module <NUM>, a comparison module <NUM>, and a noise-floor scaling module <NUM>. The interference mitigation module <NUM> can optionally include a bypass module <NUM> and a residual noise filter module <NUM> to further improve symmetric Doppler interference mitigation.

During operation, the interference mitigation module <NUM> receives at least one range-Doppler map <NUM>, such as the range-Doppler map <NUM> of <FIG>. Although not shown, the interference mitigation module <NUM> can sequentially or concurrently process multiple range-Doppler maps <NUM>, such as those that correspond to the different receive channels <NUM>-<NUM> to <NUM>-M. Similar operations that are described with respect to the range-Doppler map <NUM> are applied to the remaining range-Doppler maps <NUM>.

During operation, the noise floor estimation module <NUM> analyzes the range-Doppler map <NUM> to produce a noise-floor estimate <NUM>. In some cases, the noise floor estimation module <NUM> determines the noise-floor estimate <NUM> based on a particular set of range bins <NUM> and Doppler bins <NUM>. These range bins <NUM> and Doppler bins <NUM> can exclude those that are likely to be affected by the interference artifact <NUM> or other stationary objects.

Consider <FIG>, which illustrates example regions within the range-Doppler map <NUM> (of <FIG>) for estimating a noise level. In particular, a first noise-estimation window <NUM>-<NUM> and a second noise-estimation window <NUM>-<NUM> identify range bins <NUM> and Doppler bins <NUM> for generating the noise-floor estimate <NUM>. In this case, the noise-estimation windows <NUM>-<NUM> and <NUM>-<NUM> do not include the Doppler bins <NUM> associated with stationary objects or objects with range rates that appear in the low Doppler bins <NUM> (e.g., the <NUM> and ± <NUM> Doppler bins <NUM>). Additionally, the noise-estimation windows <NUM>-<NUM> to <NUM>-<NUM> avoid a first few range bins <NUM> in which the interference artifact <NUM> may be present. As an example, the noise-estimation windows <NUM>-<NUM> to <NUM>-<NUM> do not include range bins <NUM> that represent slant ranges <NUM> that are less than <NUM>.

In some cases, one or more of the noise-estimation windows <NUM>-<NUM> or <NUM>-<NUM> include a bin associated with one or more desired objects. However, due to the large number of bins that are not associated with a desired object, inclusion of a desired object, such as the hand <NUM> within the noise-estimation window <NUM>-<NUM>, does not significantly impact the noise-floor estimate <NUM>.

The noise floor estimation module <NUM> computes an average amplitude of the bins within the noise-estimation windows <NUM>-<NUM> and <NUM>-<NUM> to determine the noise-floor estimate <NUM>. In other cases, the noise floor estimation module <NUM> computes a noise-floor estimate <NUM> for each bin by computing a local average (e.g., averaging the amplitude of each bin with its neighboring bins).

Returning to <FIG>, the bypass module <NUM> analyzes the range-Doppler map <NUM> to determine whether or not a desired object contributes to a peak at the zero Doppler bin <NUM> or the neighboring ± <NUM> Doppler bins <NUM>. If a desired object is detected, the bypass module <NUM> provides a bypass indicator <NUM> to the comparison module <NUM>, which directs the comparison module <NUM> to not filter the low Doppler bins <NUM>, such as the ± <NUM> Doppler bins <NUM>. Alternatively, if the bypass module <NUM> determines that there is not a desired object within the low Doppler bins <NUM>, the bypass indicator <NUM> directs the comparison module <NUM> to filter the low Doppler bins <NUM>.

The bypass module <NUM> makes this determination by analyzing a shape of a peak within the zero and ± <NUM> Doppler bins <NUM>. If the bypass module <NUM> detects a single peak within these bins, the bypass module <NUM> determines that a desired object is present. Alternatively, if the bypass module <NUM> detects two peaks across any of these bins, the bypass module <NUM> determines that a desired object is not present. If a desired object is not present, the comparison module <NUM> applies a filter that attenuates the detected peaks. Otherwise, if a desired object is present, the comparison module <NUM> does not apply the filter.

The comparison module <NUM> compares amplitudes of the positive Doppler bins <NUM> to amplitudes of the corresponding negative Doppler bins <NUM> for each range bin <NUM>. The comparison module <NUM> scales an amplitude of a first positive Doppler bin <NUM> (e.g., the positive one Doppler bin) by an amplitude of the corresponding first negative Doppler bin <NUM> (e.g., the negative one Doppler bin). This process continues for other Doppler bins <NUM> such that the amplitudes of the positive two, three. B/<NUM> Doppler bins <NUM> are scaled by amplitudes of the corresponding negative two, negative three. -B/<NUM> Doppler bins <NUM>.

Amplitudes of the negative Doppler bins <NUM> are similarly adjusted. The first negative Doppler bin <NUM> (e.g., negative one Doppler bin) is scaled by the original amplitude of the first positive Doppler bin <NUM> (e.g., the positive one Doppler bin). Note that if the bypass indicator <NUM> indicates that a desired object is present within the low Doppler bins <NUM> (e.g., the zero Doppler bin, the positive one Doppler bin, and the negative one Doppler bin), the comparison module <NUM> does not adjust the amplitude of these bins <NUM>.

This filtering operation is further characterized by Equations <NUM> and <NUM>, which computes the scaled amplitudes of a positive Doppler bin or a negative Doppler bin: <MAT> <MAT> where Âp[x] represents the scaled amplitude of a positive "x" Doppler bin, Ân[x] represents the scaled amplitude of a negative "x" Doppler bin, Ap[x] represents the original amplitude of the positive "x" Doppler bin, and An[x] represents the original amplitude of the negative "x" Doppler bin.

Other operations can alternatively be performed by the comparison module <NUM>. In a not claimed example, the comparison module <NUM> can perform a subtraction operation to determine the difference in amplitudes between the corresponding Doppler bins <NUM>. In this case, the comparison module <NUM> decreases an amplitude of the positive one Doppler bin <NUM> by the amplitude of the negative one Doppler bin <NUM>, and similarly decreases the amplitude of the negative one Doppler bin <NUM> by the original amplitude of the positive one Doppler bin <NUM>.

In general, the operation performed by the comparison module <NUM> exploits the symmetric property of the interference artifact <NUM> to attenuate the interference artifact <NUM> and produce the scaled range-Doppler map <NUM>. Because the desired object (e.g., the hand <NUM> or the body <NUM>) is not symmetric across the Doppler spectrum, the amplitude of the desired object is scaled by a value that is representative of the noise floor. Because this value is significantly smaller than the peak amplitude of the interference artifact, the scaled amplitude of the interference artifact <NUM> can become smaller than the scaled amplitude of the desired object within the scaled range-Doppler map <NUM>.

To reduce the scaling of the desired object, the noise-floor scaling module <NUM> multiplies the scaled range-Doppler map <NUM> by the noise-floor estimate <NUM>. This causes the Doppler bins <NUM> associated with the interference artifact <NUM> to have amplitudes that are approximately equal to the noise floor. The amplitudes associated with the body <NUM> or the hand <NUM>, however, remain relatively unchanged as the noise floor estimate <NUM> is approximately equal to the value by which the comparison module <NUM> scaled the desired object. The resulting output of the noise-floor scaling module <NUM> is a filtered range-Doppler map <NUM>.

In some implementations, the residual noise filter module <NUM> can further process the filtered range-Doppler map <NUM> to remove noise that results due to the operations performed by the comparison module <NUM> and the noise-floor scaling module <NUM>. This can include providing a filter that smooths the amplitudes across the range bins <NUM> and/or Doppler bins <NUM>. The residual noise filter module <NUM> can be implemented as a low-pass filter, a median filter, a filter that operates across one dimension (e.g., operates on the range bins <NUM> or the Doppler bins <NUM>), a filter that operates on two dimensions (e.g., operates on both the range bins <NUM> and the Doppler bins <NUM>), or some combination thereof.

The interference mitigation module <NUM> is also not limited to only analyzing and adjusting the amplitude of the range-Doppler map <NUM>. In some implementations, the interference mitigation module <NUM> additionally operates on the phase information within the range-Doppler map <NUM>. Consider an example in which the interference artifact <NUM> causes the phases of the positive Doppler bins and phases of the negative Doppler bins to be in-phase or out of phase. In this case, the interference mitigation module <NUM> can recognize this characteristic to determine whether or not the interference artifact <NUM> is present. If the interference artifact <NUM> is present, the interference mitigation module <NUM> activates the comparison module <NUM> to filter the interference artifact <NUM>. Otherwise, the filtering operation is bypassed so that the system processor <NUM> operates on the range-Doppler map <NUM> instead of the filtered range-Doppler map <NUM>. In some cases, the interference mitigation module <NUM> can analyze the phase information to determine an amount to suppress the interference artifact <NUM>.

In some cases, the interference mitigation module <NUM> operates on a portion of the range bins <NUM>. If the interference artifact <NUM> is likely to appear within a particular set of range bins <NUM>, for instance, the interference mitigation module <NUM> can perform the actions described above for this set of range bins <NUM> and not process the remaining range bins <NUM>. As an example, the set of range bins <NUM> can include the first five range bins <NUM>, the first seven range bins <NUM>, or the first ten range bins <NUM>. This can increase efficiency of the interference mitigation module <NUM> and enable the interference mitigation module <NUM> to operate on range-Doppler maps <NUM> that have a large quantity of range bins <NUM> and/or Doppler bins <NUM>.

<FIG> depicts an example method <NUM> for performing operations of a smart-device-based radar system capable of symmetric Doppler interference mitigation. Method <NUM> is shown as sets of operations (or acts) performed but not necessarily limited to the order or combinations in which the operations are shown herein. In portions of the following discussion, reference may be made to the environment <NUM>-<NUM> to <NUM>-<NUM> of <FIG>, and entities detailed in <FIG> or <FIG>, reference to which is made for example only.

At <NUM>, a radar transmit signal is transmitted using an antenna array of a radar system. For example, the radar system <NUM> uses at least one transmit antenna element <NUM> to transmit the radar transmit signal <NUM>, as shown in <FIG>. In some implementations, the radar transmit signal <NUM> includes multiple chirps <NUM>-<NUM> to <NUM>-N, whose frequencies are modulated, as shown in <FIG>.

At <NUM>, a radar receive signal is received using the antenna array. The radar receive signal includes an interference artifact and a version of the radar transmit signal that is reflected by at least one object. For example, the radar system <NUM> uses at least one receive antenna element <NUM> to receive a version of the radar receive signal <NUM> that is reflected by the user <NUM>, as shown in <FIG> and <FIG>. The radar receive signal <NUM> can also include the interference artifact <NUM> shown in <FIG>. The interference artifact <NUM> occurs due to vibration of the radar system <NUM> or vibration of other objects detected by the radar system <NUM>.

At <NUM>, a range-Doppler map is generated based on the radar receive signal. The interference artifact contributes to amplitudes of both positive and negative Doppler bins of the range-Doppler map for at least one range bin. For example, the hardware-abstraction module <NUM> generates the range-Doppler map <NUM>, as shown in <FIG>. Across at least one range bin <NUM> within the range-Doppler map <NUM> (e.g., such as the first range bin <NUM>), the interference artifact <NUM> contributes to amplitudes of both positive and negative Doppler bins <NUM>, such as the ± <NUM>, ± <NUM>, and ± <NUM> Doppler bins <NUM>. In particular, the interference artifact <NUM> has an approximately symmetric amplitude across the Doppler bins <NUM>, as shown at <NUM>.

At <NUM> the interference artifact within the range-Doppler map is filtered to attenuate the interference artifact and generate a filtered range-Doppler map. The interference mitigation module <NUM> filters the range-Doppler map <NUM> to attenuate the interference artifact <NUM> and generate the filtered range-Doppler map <NUM>, as shown in <FIG>.

At <NUM>, the filtered range-Doppler map is analyzed to detect the at least one object. For example, the system processor <NUM> analyzes the filtered range-Doppler map <NUM> to detect the at least one object. The system processor <NUM> can further determine one or more characteristics about the object, such as the object's relative position (e.g., range, azimuth and/or elevation), movement, or composition. The system processor <NUM> can also recognize a gesture performed by a user, measure a vital-sign of the user, provide collision avoidance, and so forth.

<FIG> illustrates various components of an example computing system <NUM> that can be implemented as any type of client, server, and/or computing device as described with reference to the previous <FIG> to implement symmetric Doppler interference mitigation.

The computing system <NUM> includes communication devices <NUM> that enable wired and/or wireless communication of device data <NUM> (e.g., received data, data that is being received, data scheduled for broadcast, or data packets of the data). Although not shown, the communication devices <NUM> or the computing system <NUM> can include one or more radar systems <NUM>. The device data <NUM> or other device content can include configuration settings of the device, media content stored on the device, and/or information associated with a user <NUM> of the device. Media content stored on the computing system <NUM> can include any type of audio, video, and/or image data. The computing system <NUM> includes one or more data inputs <NUM> via which any type of data, media content, and/or inputs can be received, such as human utterances, the radar-based application <NUM>, user-selectable inputs (explicit or implicit), messages, music, television media content, recorded video content, and any other type of audio, video, and/or image data received from any content and/or data source.

The computing system <NUM> also includes communication interfaces <NUM>, which can be implemented as any one or more of a serial and/or parallel interface, a wireless interface, any type of network interface, a modem, and as any other type of communication interface. The communication interfaces <NUM> provide a connection and/or communication links between the computing system <NUM> and a communication network by which other electronic, computing, and communication devices communicate data with the computing system <NUM>.

The computing system <NUM> includes one or more processors <NUM> (e.g., any of microprocessors, controllers, and the like), which process various computer-executable instructions to control the operation of the computing system <NUM> and to enable techniques for, or in which can be embodied, gesture recognition in the presence of saturation. Alternatively or in addition, the computing system <NUM> can be implemented with any one or combination of hardware, firmware, or fixed logic circuitry that is implemented in connection with processing and control circuits which are generally identified at <NUM>. Although not shown, the computing system <NUM> can include a system bus or data transfer system that couples the various components within the device. A system bus can include any one or combination of different bus structures, such as a memory bus or memory controller, a peripheral bus, a universal serial bus, and/or a processor or local bus that utilizes any of a variety of bus architectures.

The computing system <NUM> also includes a computer-readable media <NUM>, such as one or more memory devices that enable persistent and/or non-transitory data storage (i.e., in contrast to mere signal transmission), examples of which include random access memory (RAM), non-volatile memory (e.g., any one or more of a read-only memory (ROM), flash memory, EPROM, EEPROM, etc.), and a disk storage device. The disk storage device may be implemented as any type of magnetic or optical storage device, such as a hard disk drive, a recordable and/or rewriteable compact disc (CD), any type of a digital versatile disc (DVD), and the like. The computing system <NUM> can also include a mass storage media device (storage media) <NUM>.

The computer-readable media <NUM> provides data storage mechanisms to store the device data <NUM>, as well as various device applications <NUM> and any other types of information and/or data related to operational aspects of the computing system <NUM>. For example, an operating system <NUM> can be maintained as a computer application with the computer-readable media <NUM> and executed on the processors <NUM>. The device applications <NUM> may include a device manager, such as any form of a control application, software application, signal-processing and control module, code that is native to a particular device, a hardware abstraction layer for a particular device, and so on.

The device applications <NUM> also include any system components, engines, or managers to implement symmetric Doppler interference mitigation. In this example, the device applications <NUM> includes the radar-based application <NUM> and the interference mitigation module <NUM> of <FIG>.

Claim 1:
A method performed by a radar system, wherein the radar system is embedded within a smart device, the method comprising:
transmitting (<NUM>) a radar transmit signal using an antenna array of the radar system;
receiving (<NUM>) a radar receive signal using the antenna array, the radar receive signal including an interference artifact and a version of the radar transmit signal that is reflected by at least one object, wherein the smart device includes a first component positioned within an interior of the smart device, and wherein the interference artifact represents at least vibration of the at least one first component;
generating (<NUM>) a range-Doppler map based on the radar receive signal, the interference artifact contributing to amplitudes of both positive and negative Doppler bins of the range-Doppler map for at least one range bin;
filtering (<NUM>) the interference artifact within the range-Doppler map to attenuate the interference artifact and generate a filtered range-Doppler map, wherein the filtering of the interference artifact within the range-Doppler map comprises:
producing a scaled range-Doppler map by:
scaling amplitudes of the positive Doppler bins by amplitudes of corresponding negative Doppler bins for each range bin of the range-Doppler map, and
scaling amplitudes of the negative Doppler bins by the amplitudes of the corresponding positive Doppler bins for each range bin of the range-Doppler map; and
analyzing (<NUM>) the filtered range-Doppler map to detect the at least one object.