Energy efficient micro-doppler radar technology

Abstract

A first wireless device (300) is operated by performing (201) a first procedure and a second procedure (205, 207). The first procedure (201) includes causing (201) the first wireless device (300) to transmit a first radar signal having a first configuration of signal properties; and receiving (201) one or more reflections of the first radar signal. The second procedure (205, 207) includes using (205) at least the one or more reflections of the first radar signal as a basis for determining a second configuration of signal properties, wherein the first configuration of signal properties differs from the second configuration of signal properties; causing (207) a second radar signal to be transmitted, wherein the second radar signal has the second configuration of signal properties; receiving (207) one or more reflections of the second radar signal; and obtaining (209) micro-Doppler information at least from the one or more reflections of the second radar signal.

Description

[0001] P111310W001

[0002] -1-

[0003] ENERGY EFFICIENT MICRO-DOPPLER RADAR TECHNOLOGY

[0004] BACKGROUND

[0005] The present invention relates to radar technology, more particularly to radar technology that employs micro-Doppler processing, and even more particularly to radar technology that employs energy efficient micro-Doppler processing.

[0006] Some or all of the following abbreviations are used in this specification:

[0007] Abbreviation Explanation

[0008] BW Bandwidth

[0009] CW Continuous Wave

[0010] EM Electromagnetic

[0011] FFT Fast Fourier Transform

[0012] FMCW Frequency Modulated Continuous Wave

[0013] ML Machine Learning

[0014] NB Narrowband

[0015] RF Radio Frequency

[0016] SFCW Stepped Frequency Continuous Wave

[0017] SINR Signal plus Interference and Noise Ratio

[0018] SNR Signal to Noise Ratio

[0019] STFT Short Time Fourier Transform

[0020] TX Transmission

[0021] TXR Transmitter / Receiver

[0022] WB Wideband

[0023] A multitude of well established, radar-based approaches are available for detecting the presence of an object and its overall location and movement characteristics. Conventional radar sensing may be used to identify object range, direction, and size based on reflected signal characteristics, and its speed and direction of movement can be detected based on the Doppler shift and spread of the received reflection signal.

[0024] Conventional radar schemes may use any of a number of different signal designs, such as: P111310W001

[0025] -2-

[0026] Continuous Wave (CW): In CW radar, a continuous radio frequency (RF) signal is transmitted and continuously emitted by the radar antenna. Radar sensing in this instance is based on measuring the Doppler shift caused by moving objects. CW radar lacks range information and relies solely on Doppler frequency shift as a basis for measuring velocity.

[0027] - Frequency Modulated Continuous Wave (FMCW): FMCW radar equipment transmits a continuous wave with a frequency that varies linearly over time. By comparing the transmitted and received signals, FMCW radar measures the range to the target based on the frequency difference between a frequency of a currently transmitted signal and the frequency of the received reflection signal (which difference corresponds to how much time it took between transmission of the radar signal and receipt of its reflection). FMCW also provides velocity information based on the detected Doppler shift that is present in the received reflection signal.

[0028] OFDM: Coded radar, often implemented using Orthogonal Frequency Division Multiplexing (OFDM), uses coded waveforms for transmission. An OFDM radar transmits a burst of data made up of multiple frequencies, like WiFi. The same OFDM signal can be used to transmit data like a communication system alongside radar functions.

[0029] Stepped Frequency Continuous Wave (SFCW): SFCW radar is similar to FMCW radar but operates by transmitting a series of discrete frequencies instead of a continuously varying frequency. This discrete frequency hopping enables better range resolution and immunity to certain types of interference.

[0030] - Pulsed Radar: Consists of short bursts or pulses of electromagnetic (EM) energy that are transmitted from the radar antenna. These pulses are typically of high power and short duration. After transmitting a pulse, the radar system waits for a brief period, known as the “listening” or “dwell” time, during which it listens for the return echoes from targets. The round-trip time of these echoes provides information about the range to the target.

[0031] Each of these radar transceiver schemes has its own advantages and applications, depending on factors such as required range, resolution, velocity measurement accuracy, and susceptibility to interference.

[0032] A radar sensing system can operate in a monostatic fashion, an arrangement in which the same unit both transmits a radar signal and receives the reflected signals. Alternatively bi-static P111310W001

[0033] -3- or multi-static operation can be used, in which transmitting and receiving are performed by different devices.

[0034] It is possible to use radar sensing to obtain even more detailed information about an object and thereby identify, for example, what type of object it is and / or what type of activity it is engaged in. This type of sensing relies on micro-Doppler (herein abbreviated as “pDoppler”) signatures. In some instances, time-Doppler signatures are detected, depicting variations in detailed Doppler frequency components over time. The overall object pattern is collected during an extended observation window and the pattern may contain periodic / cyclo-stationary elements. An example time-Doppler signature 100 of a walking person is shown in Figure 1 A. Due to the different velocities of the person’s torso, arm, and foot, each of these produces its own distinct Doppler signature, which is clearly evident in the figure.

[0035] 2 v

[0036] The Doppler shift as a function of object part movement can be expressed as Fd= Ft— , and the subject velocity is estimated as v , where:

[0037] - Fa'. Doppler frequency

[0038] - Ft. Carrier (transmitter) frequency

[0039] - v. Doppler velocity

[0040] - c. speed of light

[0041] When a radar signal with a non-negligible relative bandwidth (BW) is used and the Doppler estimation is based on the center frequency, the relative error, which creates smearing in the frequency domain, is given by (where, A denotes an amount of error). AFt may be caused by signal BW, hardware imperfections, and the like. The Doppler resolution improves for higher values of Ft. For example, an analysis has shown that Ff=30 GHz enables a person’s arm to be detected whereas Ff=10 GHz leads to smearing that hides the arm details.

[0042] In more advanced radar receivers, such as when the Doppler estimation is based on frequency offset hypothesis testing, the signal BW need not have an impact on the frequency resolution.

[0043] The signal BW has no impact on time-resolution. In the limit, it bounds time resolution, but this is not an issue for pDoppler variations on the 0.1-10 Hz time scale.

[0044] In another type of solutions, a range-Doppler signature may be estimated. For a given time instant, each pDoppler contribution can be further separated in terms of range. An exemplary range-Doppler signature 103 of a walking person is shown in Figure IB. Aside from P111310W001

[0045] -4- differences in reflection signal energy and pDoppler signature, the signal reflections from the person’s torso, hand, and foot are further distinguishable from one another by having different ranges. When considered in combination, these different measures lead to a more confident estimation of what is being detected.

[0046] As expected, higher BW yields higher range resolution, which can be used for such things as gait detail analysis, isolation of different body parts, and identifying whether a person has a gun. Range resolution of 0.2 m suffices for sensing a foot, whereas centimeter-level range resolution is needed for sensing a hand.

[0047] As mentioned above, for baseline Doppler estimation, the higher BW also proportionally reduces frequency resolution because it increases the maximum Doppler shift error (i.e., due to larger max AF). This can be mitigated by aggregating over multiple NB channels, or by using an advanced receiver (e.g., hypothesis-based correlation detection).

[0048] The estimated pDoppler signatures may be used as, for example, input to ML models trained to distinguish different signature patterns and map them to different object types and their movement types, in order to complete the identification task.

[0049] Methods for analyzing captured data in two or more steps have been disclosed in the literature, wherein one or more features or information elements in captured pDoppler data are extracted in a first step and based on classification of such first feature, a second in-depth analysis of same or more of the captured data is then performed. See, for example, X. Guo, C. S. Ng, E. de Jong and A. B. Smits, “Micro-Doppler Based Mini-UAV Detection with Low-Cost Distributed Radar in Dense Urban Environment,” 2019 16th European Radar Conference (EuRADf Paris, France, 2019, pp. 189-192; Ma, B., Eguiazarian, K., & Chen, B., “Low Resolution Radar Target Classification Using Vision Transformer Based on Micro-Doppler Signatures,” IEEE Sensors Journal, Vol. 23, No. 22, 2023, p. 28474 - 28485; and M. Jahangir, B. I. Ahmad and C. J. Baker, “Robust Drone Classification Using Two-Stage Decision Trees and Results from SESAR S AFIR Trials,” 2020 IEEE International Radar Conference (RADAR), Washington, DC, USA, 2020, pp. 636-641.

[0050] Conventional technology is problematic in several respects, especially if a device with a limited power supply is to be used for sensing (e.g., a mobile communications device). For example, many radar-based applications require estimating both macroscopic object location (range, direction, speed) and finer details of the object. As an example, this information might be needed for purposes of object identification, where pDoppler signatures may be utilized. P111310W001

[0051] -5-

[0052] For initial object detection using convention radar functionality, a WB signal is typically used that provides satisfactory range resolution based on the main reflection (with a relatively “large” radar cross-section) from the object, even when a mobile device with limited power is used for radar operation.

[0053] However, if a pDoppler signature is also desired for object identification, the device transmission power is limited, much lower than for example a car radar, and the received signal SNR reflected from smaller parts of the object may be too low to reliably estimate smaller details of the pDoppler signature.

[0054] In CN109557535A and the related US2022252712A1, a two-stage radar procedure is described in which a first radar signal is used for ranging and a second radar signal is used for pDoppler characterization of the object. However, when the radar is implemented in a handset, the permissible energy consumption of the device is limited. Therefore, routinely performing additional radar transmission for signature detection, as in the above-referenced publication, is not desirable since it has an adverse effect on the battery life of the device.

[0055] There is therefore a need for technology that addresses the above and / or related problems (e.g., a need for technology that enables a pDoppler signature to be obtained having sufficient detail to detect a desired object while minimizing device energy consumption).

[0056] SUMMARY

[0057] It should be emphasized that the terms “comprises” and “comprising”, when used in this specification, are taken to specify the presence of stated features, integers, steps or components; but the use of these terms does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0058] Moreover, reference letters may be provided in some instances (e.g., in the claims and summary) to facilitate identification of various steps and / or elements. However, the use of reference letters is not intended to impute or suggest that the so-referenced steps and / or elements are to be performed or operated in any particular order.

[0059] In accordance with one aspect of the present invention, the foregoing and other objects are achieved in technology (e.g., methods, apparatuses, nontransitory computer readable storage media, program means) that enable a first wireless device to use radar to sense its environment and obtain micro-Doppler information from the sensing.

[0060] In an aspect of some but not necessarily all inventive embodiments, obtaining the microDoppler information comprises performing a first procedure that comprises: causing the first P111310W001

[0061] -6- wireless device to transmit a first radar signal having a first configuration of signal properties; and receiving one or more reflections of the first radar signal. Inventive embodiments also include the first wireless device performing a second procedure that comprises: using at least the one or more reflections of the first radar signal as a basis for determining a second configuration of signal properties, wherein the first configuration of signal properties differs from the second configuration of signal properties; causing a second radar signal to be transmitted, wherein the second radar signal has the second configuration of signal properties; receiving one or more reflections of the second radar signal; and obtaining micro-Doppler information at least from the one or more reflections of the second radar signal.

[0062] In another aspect of some but not necessarily all inventive embodiments, obtaining the micro-Doppler information comprises using one or more reflections of an earlier radar signal as another basis for determining the second configuration of signal properties.

[0063] In yet another aspect of some but not necessarily all inventive embodiments, obtaining the micro-Doppler information comprises estimating a signal to noise ratio of the one or more reflections of the first radar signal; performing the second procedure only if the estimated signal to noise ratio is below a predetermined threshold; and when the estimated signal to noise ratio is above the predetermined threshold, using the one or more reflections of the first radar signal for micro-Doppler radar processing.

[0064] In still another aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises the second radar signal being transmitted from the first wireless device. In an aspect of some but not necessarily all alternative embodiments, the second configuration of signal properties comprises the second radar signal being transmitted from a second device.

[0065] In another aspect of some but not necessarily all inventive embodiments, the first configuration of signal properties comprises the first radar signal being one of a wideband pulse; a wideband continuous wave signal; a coded signal implemented using Orthogonal Frequency Division Multiplexing; and a Frequency Modulated Continuous Wave signal.

[0066] In yet another aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises the second radar signal being a narrowband signal.

[0067] In still another aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises the second radar signal being one of P111310W001

[0068] -7- a single tone; a Frequency Modulated Continuous Wave, FMCW, chirp; an instantaneous state of an FMCW signal; and an instantaneous frequency state of an FMCW sweep used as the first radar signal.

[0069] In another aspect of some but not necessarily all inventive embodiments, causing the first wireless device to transmit the first radar signal comprises causing the first wireless device to transmit the first radar signal as a directed beam having a first beamwidth; and causing the second radar signal to be transmitted comprises causing the second radar signal to be transmitted as a directed beam having a second beamwidth that is narrower than the first beamwidth.

[0070] In yet another aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises sweeping a beam of the second radar signal. In some but not necessarily all such embodiments, sweeping the beam of the second radar signal comprises sweeping the beam of the second radar signal at a period that is faster than a period of a micro-Doppler signature to be measured.

[0071] In an aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises causing the second radar signal to be transmitted a plurality of times, wherein the micro-Doppler information is obtained additionally from reflections received from the plurality of second radar signal transmissions. In some but not necessarily all such embodiments, for each of the plurality of times, the second radar signal is caused to be transmitted over a different narrow beam direction.

[0072] In still another aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises causing the second radar signal to be transmitted a plurality of times with each transmission of the second radar signal being in a different narrow beam direction; and producing a set of filtered reflections by filtering out received reflections that have a signal power less than a threshold power level, wherein the micro-Doppler information is obtained additionally from the set of filtered reflections from the plurality of second radar signal transmissions.

[0073] In another aspect of some but not necessarily all inventive embodiments, receiving the one or more reflections of the second radar signal comprises producing a set of accumulated reflections by accumulating received reflections from each of a plurality of second radar signal transmissions, wherein the micro-Doppler information is obtained additionally from the set of accumulated reflections. In some but not necessarily all such embodiments, the plurality of time instances are adjacent time instants that occur during an observation window that is shorter than P111310W001

[0074] -8- a period of a micro-Doppler signature. Alternatively, the plurality of time instances are offset from one another by a period of a micro-Doppler signature.

[0075] In yet another aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises causing the second radar signal to be transmitted in a direction of a static object.

[0076] In still another aspect of some but not necessarily all inventive embodiments, obtaining the micro-Doppler information comprises selecting a frequency to be used when transmitting the second radar signal based on one or both of a required micro-Doppler signature type and a micro-Doppler signature resolution.

[0077] In another aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises one or more range parameters selected for use in a first range to be sensed.

[0078] In yet another aspect of some but not necessarily all inventive embodiments, obtaining the micro-Doppler information comprises the second configuration of signal properties comprises a frequency selected to achieve a predetermined level of Doppler resolution.

[0079] In still another aspect of some but not necessarily all inventive embodiments, the second configuration of signal properties comprises a polarization orientation of the second radar signal.

[0080] In another aspect of some but not necessarily all inventive embodiments, obtaining the micro-Doppler information comprises using the one or more reflections of the second radar signal as a basis for estimating a period of a micro-Doppler signature. In an aspect of some but not necessarily all such embodiments, using the one or more reflections of the second radar signal as the basis for estimating the period of the micro-Doppler signature comprises performing a frequency analysis of a strongest Doppler component in the one or more reflections of the second radar signal.

[0081] In yet another aspect of some but not necessarily all inventive embodiments, using at least the one or more reflections of the first radar signal as the basis for determining the second configuration of signal properties comprises using at least the one or more reflections of the first radar signal as the basis for determining a configuration that will do one or more of the following: achieve a predetermined micro-Doppler range resolution; achieve a predetermined frequency resolution; detect an object in the presence of clutter; P111310W001

[0082] -9- sense an object located at a predetermined distance from a transmitting antenna of the second radar signal; sense an object having a predetermined size; sense a predetermined cross-sectional size of an object; and satisfy power management requirements.

[0083] In still another aspect of some but not necessarily all inventive embodiments, obtaining the micro-Doppler information comprises deriving, from the one or more reflections of the first radar signal, one or more of: a range of a sensed object relative to a radar transmitter antenna; a direction of a sensed object relative to the radar transmitter antenna; an angle of a sensed object relative to the radar transmitter antenna; and a presence of clutter in a sensed area.

[0084] In another aspect of some but not necessarily all inventive embodiments, the second configuration specifies one or more of: a bandwidth adaptation; a beam scan adaptation; a scanning duration; a scanning repetition to be performed; a scanning repetition rate; and a type of scanning to be performed.

[0085] BRIEF DESCRIPTION OF THE DRAWINGS

[0086] The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which:

[0087] Figure 1 A is an illustration of a time-Doppler signature.

[0088] Figure IB is an illustration of a range-Doppler signature.

[0089] Figure 2 is, in one respect, a flowchart of actions performed by a device that performs detailed radar sensing in a power efficient way in accordance with some but not necessarily all inventive embodiments.

[0090] Figure 3 is a block diagram of an exemplary wireless device with radar capability and having an exemplary controller that causes any and / or all of the herein-described and illustrated actions associated with the device to be performed. P111310W001

[0091] -10-

[0092] DETAILED DESCRIPTION

[0093] The various features of the invention will now be described with reference to the figures, in which like parts are identified with the same reference characters.

[0094] The various aspects of the invention will now be described in greater detail in connection with a number of exemplary embodiments. To facilitate an understanding of the invention, many aspects of the invention are described in terms of sequences of actions to be performed by elements of a computer system or other hardware capable of executing programmed instructions. It will be recognized that in each of the embodiments, the various actions could be performed by specialized circuits (e.g., analog and / or discrete logic gates interconnected to perform a specialized function), by one or more processors programmed with a suitable set of instructions, or by a combination of both. The term “circuitry configured to” perform one or more described actions is used herein to refer to any such embodiment (i.e., one or more specialized circuits alone, one or more programmed processors, or any combination of these). Moreover, the invention can additionally be considered to be embodied entirely within any form of non- transitory computer readable carrier, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein. Thus, the various aspects of the invention may be embodied in many different forms, and all such forms are contemplated to be within the scope of the invention. For each of the various aspects of the invention, any such form of embodiments as described above may be referred to herein as “logic configured to” perform a described action, or alternatively as “logic that” performs a described action.

[0095] An aspect of some inventive embodiments involves a first radar sensing to detect one or more objects followed, at least under some circumstances, by a second radar sensing to acquire pDoppler information. The two radar transmissions can use different radar transmission schemes, where the pDoppler transmission characteristics is adapted based on the first detection and ranging results.

[0096] In some instances, the first object detection may be performed using conventional, wide- beam radar, where the SNR for the large radar cross-section is sufficient. Then, pDoppler detection is performed using a second, modified radar scheme configured to increase the received radar signal SINR. As a nonlimiting example, the modified radar signaling scheme may use a signal that allows energy focusing (e.g., using narrower BW, scanning with narrower beams, extended scan duration to allow time-averaging, etc.). P111310W001

[0097] -11-

[0098] In some but not necessarily all embodiments, the second, pDoppler-oriented scan is performed conditionally, for example only if the object segment return signal quality (based on parameters like TX power, object distance, target radar cross-section, etc.) is below a threshold. The second signal parameters and the receiver processing for the pDoppler scan may be adapted based on the above parameters determined from the first scan.

[0099] These and other aspects of various inventive embodiments are now described in further detail in the following.

[0100] Figure 2 is, in one respect, a flowchart of actions performed by a device that performs detailed radar sensing in a power efficient way in accordance with some but not necessarily all inventive embodiments. In other respects, the blocks depicted in Figure 2 can also be considered to represent means 200 (e.g., hardwired or programmable circuitry or other processing means) for carrying out the described actions.

[0101] As shown beginning in Figure 2, the process includes a device (e.g., a wireless device that incorporates radar functionality) performing a first radar measurement to detect and locate the object (step 201). This first sensing may be performed by conventional radar technology. Known techniques may be used for estimating the range and spatial direction of the object (e.g., by scanning an area of interest using multiple radar beam configurations. For example, a wideband signal having a short time duration, and transmitted in relatively wide beams in order to minimize the scan time and to obtain good range resolution.

[0102] Receiver algorithms used for receiving the reflections may also be conventional (e.g., correlation processing of the wideband signal for each beam direction to find the location hypotheses returning highest reflected power).

[0103] The received first signal reflection may be recorded / stored for further processing (e.g., possible pDoppler estimation).

[0104] In decision block 203, the received first signal reflection is assessed to determine whether the first signal reflection is of sufficient quality for use in a pDoppler signature estimation. If there is no need for a second measurement (“No” path out of decision block 203), then processing skips ahead to step 209 (described below).

[0105] In this exemplary embodiment, assessing the received first signal reflection as called for in decision block 203 can be understood to refer to the first radar signal reflection obtained in step 201. However, as used herein, the term “first radar signal reflection” is interpreted more broadly, so that assessing the first radar signal reflection can, in some instances, refer to the current / most recent first radar measurement, and in other instances can include assessments of P111310W001

[0106] -12- one or more past / previously made “first” radar measurements. To illustrate this point, and without limitation, a wireless device may choose to not obtain pDoppler signatures in all directions and ranges, but instead to obtain these only in particular areas, and to make the assessment based on a number of most recent first measurements. Then multiple such measurement would reveal if the current scene could be a candidate for further pDoppler analysis (together with historical analysis, for example, whether this new object is in a certain area, and avoiding performing pDoppler measurements on swaying trees or bushes regularly).

[0107] Assessing whether a second measurement is required takes into consideration characteristics of the first reflection signal compared to characteristics needed to obtain a required pDoppler signature type and resolution. The assessment can be made in a number of different ways. Various non-limiting exemplary embodiments include one or more of the following:

[0108] - Determining whether the estimated / expected pDoppler reflection SNR is above a threshold, indicating that the first signal reflection is of sufficient quality for use detecting patterns corresponding to small parts of the object. Otherwise, a second radar measurement is indicated. An estimated / expected pDoppler reflection SNR can be obtained by, for example, adding predetermined correction factors to the SNR of the first signal reflection, where the correction factor may depend on, for example and without limitation, one or more of object type, object distance, pDoppler processing algorithm, and the like.

[0109] - Detecting whether the distance to the sensed object is above a threshold distance, resulting in the reflected signal’s SNR being below a threshold for a nominal TX power and object part radar cross-section. If the object’s distance is above the threshold distance, then the second radar measurement is deemed necessary.

[0110] - The angle or direction to the object, in relation to the device orientation (e.g., in relation to the device antenna array directivity in that direction).

[0111] - Assessing the amount of transmission power either used or available for use when transmitting first radar signal. Transmission power can be constrained due to, for example, regulations or network constraints on permissible transmission powers, the wireless device’s battery status, and the like. The less power, the greater the need for a second transmission. P111310W001

[0112] -13-

[0113] - Assessing the expected characteristics of the part of the object that is to be sensed (e.g., its size, material, and expected radar cross-section). Any aspect that would reduce the quality of the received reflection motivates performance of a second transmission.

[0114] - Detecting the presence of clutter in the direction of the object.

[0115] With continued reference to Figure 2, if it is decided that a second sensing will be required in order for a pDoppler analysis to be performed (“Yes” path out of decision block 203), the device determines (step 205) a second signal configuration to be used for the second radar sensing, with the second parameters being based on the estimated environment and object details, where the estimation may be based on properties of the first radar signal reflection, and based on the required pDoppler signature type and resolution. The signal configuration may include the signal type (e.g., a single tone, FMCW / chirp or an instantaneous state of a FMCW signal, a BLUETOOTH® signal, etc.), signal bandwidth, beam sweep type (e.g., beam width, the number of beams, dwell / sweep times, etc.), other spatial parameters, time duration, number of transmissions, and the like. These aspects are described further below.

[0116] In some but not necessarily all embodiments, the configuration of the second signal is predetermined and used whenever the second radar sensing is to be performed.

[0117] After determining the parameters for configuring the second radar signal, the device then performs the second radar measurement to obtain a pDoppler characterization of the object (step 207) (i.e., transmission of the second radar signal and reception of the second radar signal reflections, both using a transmitter and receiver configured in accordance with configuration parameters determined in step 205).

[0118] Afterwards, the signal obtained from the first or second radar measurement is analyzed (step 209) to obtain pDoppler information (e.g., a pDoppler signature). Receiver processing for the second radar reflection signal may differ from processing performed on the first radar signal reflection in order to utilize the different characteristics of the second radar reflection signals, such as its spatial and temporal features, and also to reduce the impact of bandwidth on frequency resolution. Additional details are provided in a section below.

[0119] In an aspect of some but not necessarily all embodiments, if a criterion for requiring performance of the second measurement is fulfilled but the device does not have sufficient power or signaling capability to achieve a sufficient SNR in the second measurement, the device may ask a second device to perform the second radar signal transmission for pDoppler signature detection in a bi-static mode. P111310W001

[0120] -14-

[0121] Further aspects of pDoppler signal adaptation will now be discussed. As mentioned above, the second radar signal is configured based on reflections of the first radar signal. More particularly, the device adapts the radar signal used for pDoppler characterization based on the expected signal energy reflected from the smaller parts of the object. The evaluation of detectable signal energy / SNR may in turn be based on the measured object distance, radar crosssection of a sub-object (i.e., part of an object), and usable transmission power (including device power amplifier, regulations, the impact of interference creation in the NW, etc.).

[0122] The estimation of required signal energy / SNR may be based on required pDoppler signature type and resolution. The second radar signal may be a frequency-optimized signal and a range-optimized signal, adapting the bandwidth and time-span of the radar signal correspondingly. In one non-limiting example, the signal may have a wider bandwidth if a high range resolution of the Doppler signature is desired, and a narrower bandwidth if a higher Doppler frequency resolution is required.

[0123] The adaptation of the second radar signal may include configuring the radar signal type and bandwidth, radar beam width and scan pattern, radar scan duration and averaging mode, pDoppler signature mode (time-Doppler, or range-Doppler slices), combining frequency resolution and range resolution scans, and the like. In some examples of the second radar transmission, the device extends / expands the range of frequencies over which sensing is performed by performing stepped continuous wave transmissions (or any kind of stepped narrowband waveform of the transmitter design), thus not only making it possible to adjust spatial (beamforming) and time (dwell duration) characteristics of the pDoppler information, but also increasing the frequency range.

[0124] In another aspect of some but not necessarily all embodiments, the device uses the received signal energy and / or signal SNR from a first radar sensing (“SNR1”) of a potential object of interest for which the pDoppler signature is desired and its estimated distance from that sensing to estimate the radar cross-section of the object of interest. It may then use the expected feature size of the object (e.g., its estimated proportional size within the object as a whole) and the required SNR for pDoppler analysis (“SNR2target”) to determine the required beam width reduction or time repetitions, or the degree of bandwidth reduction (e.g., approximated by a factor R=SNR2target / SNRl, to obtain the required SNR).

[0125] In another aspect of some but not necessarily all embodiments, the device selects a second signal configuration that results in the shortest pDoppler scan time. For example, if the type of pDoppler analysis does not require high range resolution, the device may select a P111310W001

[0126] -15- bandwidth reduction by a factor, R, and use a relatively wide beam and short time duration. If, on the other hand, a high range resolution is required, the device may then keep the maximum available bandwidth and reduce the beam width or increase the time sequence duration by the factor R.

[0127] In another aspect of some but not necessarily all embodiments, the second signaling scheme may include transmitting the second radar signal in a direction of a static object to achieve object illumination from additional directions via reflections. It may also include selecting a suitable polarization orientation of the second radar signal to maximize the reflected signal energy and maximize the effective radar cross-section.

[0128] In another aspect of some but not necessarily all embodiments, if an FMCW / OFDM type radar is implemented for ranging in the first measurement, then using a stepped frequency CW signal in the second measurement adds the possibility of also examining the target pDoppler signature at multiple frequencies.

[0129] Turning the discussion now to aspects relating to receiver processing, if a narrow-beam reception strategy is used, multiple narrow beam directions may be swept (either over time using multiple scans or simultaneously using, e.g., digital / hybrid receiver beam forming) and detection results accumulated over the multiple directions. Beams with a received signal level below a threshold may be omitted from accumulation. If the Doppler component can be detected in a given beam direction, then the presence of Doppler components in that direction can be used as an additional inclusion criterion. The sweep period may be much shorter than the signature period.

[0130] The received signal may be temporally accumulated. If a (non-coherent) accumulation window is comparable to the signature period, a 1-D signature may be obtained. If multiple (coherent) accumulation windows are used, each much shorter than the signature period, then a 2-D signature may be obtained.

[0131] Further (non-coherent) accumulation may be performed per-time-index, with spacing equal to the pDoppler signature period of a moving object to be detected (where the moving object is known to typically have a repetitive movement pattern with a typical repetition rate - for example a human stride or bicycle pedal rotation). The period may be estimated based on frequency analysis (e.g., FFT peak), further ensuring (e.g., via STFT techniques) that the period is stable.

[0132] Figure 3 is a block diagram of a wireless device 300 with radar capability. In this exemplary embodiment, transmission and reception are performed by a configurable transceiver P111310W001

[0133] -16-

[0134] 311. The wireless device 300 also comprises a controller 301 configured to cause the wireless device 300 to carry out any combination of the various actions described herein. In particular, the controller 301 includes circuitry configured to carry out any one or any combination of the various functions described herein. Such circuitry could, for example, be entirely hard-wired circuitry (e.g., one or more Application Specific Integrated Circuits - “ASICs”). Depicted in the exemplary embodiment of Figure 3, however, is programmable circuitry, comprising a processor 303 coupled to one or more memory devices 305 (e.g., Random Access Memory, Magnetic Disc Drives, Optical Disk Drives, Read Only Memory, etc.) and to an interface 307 that enables bidirectional communication with other elements of a device as described above. A complete list of possible other elements is beyond the scope of this description.

[0135] The memory device(s) 305 store program means 309 (e.g., a set of processor instructions) configured to cause the processor 303 to control other device elements so as to carry out any of the aspects described herein. The memory device(s) 305 may also store data (not shown) representing various constant and variable parameters as may be needed by the processor 303 and / or as may be generated when carrying out its functions such as those specified by the program means 309.

[0136] Since pDoppler based sensing and signal processing may be complex, it can impose a relatively high amount of additional energy consumption in legacy solutions. Embodiments consistent with aspects of the invention provide a number of advantages over conventional technology. For example, the two-step scanning procedure of the various inventive embodiments enables robust and accurate detection of object location and range, and additionally obtains a more detailed pDoppler signature in an energy-efficient and time-efficient manner.

[0137] Also, since the resolution of the second radar sensing, and the corresponding duration, for a general radar scene setup is higher than the sensing performed in the first radar sensing, some embodiments of the technology provide a savings compared to technology in which the only sensing that is performed covers an entire scene and is configured to satisfy pDoppler requirements.

[0138] In some embodiments, a further advantage is that, when the scenario permits, the technology uses the first step signal also for pDoppler signature acquisition, which allows omitting the second step and eliminating related energy cost and detection latency. It thus provides savings compared to always performing the second radar sensing after the first radar sensing in a non-adaptive manner. P111310W001

[0139] -17-

[0140] Still further, if the second step is necessary, using the first radar sensing result to configure the second signal to use the largest viable beam width, largest bandwidth, or shortest time sequence minimizes the related energy cost and detection latency. It thus provides savings compared to always performing the second radar sensing with a fixed, worst-case signal configuration in a non-adaptive manner.

[0141] When the radar is operating close to its maximum power while it is active, and the resolution is controlled by bandwidth, beam width, or time sequence / repetition adaptation, the energy consumption cost is then proportional to the total duration of the second signal transmission. The invention has been described with reference to particular embodiments. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the embodiment described above. Thus, the described embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is further illustrated by the appended claims, rather than only by the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein.

Claims

P111310W001-18-CLAIMS:

1. A method of operating a first wireless device (300), the method comprising: performing (201) a first procedure that comprises: causing (201) the first wireless device (300) to transmit a first radar signal having a first configuration of signal properties; and receiving (201) one or more reflections of the first radar signal; and performing a second procedure (205, 207) that comprises: using (205) at least the one or more reflections of the first radar signal as a basis for determining a second configuration of signal properties, wherein the first configuration of signal properties differs from the second configuration of signal properties; causing (207) a second radar signal to be transmitted, wherein the second radar signal has the second configuration of signal properties; receiving (207) one or more reflections of the second radar signal; and obtaining (209) micro-Doppler information at least from the one or more reflections of the second radar signal.

2. The method of claim 1, comprising: using one or more reflections of an earlier radar signal as another basis for determining the second configuration of signal properties.

3. The method of claim 1 or claim 2, comprising: estimating a signal to noise ratio of the one or more reflections of the first radar signal; performing the second procedure only if (203) the estimated signal to noise ratio is below a predetermined threshold; and when the estimated signal to noise ratio is above the predetermined threshold, using the one or more reflections of the first radar signal for micro-Doppler radar processing.

4. The method of any one of the previous claims, wherein the second configuration of signal properties comprises the second radar signal being transmitted from the first wireless device (300).

5. The method of any one of claims 1 through 3, wherein the second configuration of signal properties comprises the second radar signal being transmitted from a second device.P111310W001-19-6. The method of any one of the previous claims, wherein the first configuration of signal properties comprises the first radar signal being one of: a wideband pulse; a wideband continuous wave signal; a coded signal implemented using Orthogonal Frequency Division Multiplexing; and a Frequency Modulated Continuous Wave signal.

7. The method of any one of the previous claims, wherein the second configuration of signal properties comprises the second radar signal being a narrowband signal.

8. The method of claim 7, wherein the second configuration of signal properties comprises the second radar signal being one of: a single tone; a Frequency Modulated Continuous Wave, FMCW, chirp; an instantaneous state of an FMCW signal; and an instantaneous frequency state of an FMCW sweep used as the first radar signal.

9. The method of any one of the previous claims, wherein: causing (201) the first wireless device (300) to transmit the first radar signal comprises causing (201) the first wireless device (300) to transmit the first radar signal as a directed beam having a first beamwidth; and causing (207) the second radar signal to be transmitted comprises causing (207) the second radar signal to be transmitted as a directed beam having a second beamwidth that is narrower than the first beamwidth.

10. The method of any one of the previous claims, wherein the second configuration of signal properties comprises sweeping a beam of the second radar signal.

11. The method of claim 10, wherein sweeping the beam of the second radar signal comprises sweeping the beam of the second radar signal at a period that is faster than a period of a micro-Doppler signature to be measured.P111310W001-20-12. The method of any one of claims 1 through 9, wherein the second configuration of signal properties comprises: causing (207) the second radar signal to be transmitted a plurality of times, wherein the micro-Doppler information is obtained (209) additionally from reflections received from the plurality of second radar signal transmissions.

13. The method of claim 12, wherein for each of the plurality of times, the second radar signal is caused to be transmitted over a different narrow beam direction.

14. The method of any one of claims 1 through 11, wherein the second configuration of signal properties comprises: causing (207) the second radar signal to be transmitted a plurality of times with each transmission of the second radar signal being in a different narrow beam direction; and producing a set of filtered reflections by filtering out received reflections that have a signal power less than a threshold power level, wherein the micro-Doppler information (209) is obtained additionally from the set of filtered reflections from the plurality of second radar signal transmissions.

15. The method of any one of claims 1 through 11, wherein receiving the one or more reflections of the second radar signal comprises: producing a set of accumulated reflections by accumulating received reflections from each of a plurality of second radar signal transmissions, wherein the micro-Doppler information (209) is obtained additionally from the set of accumulated reflections.

16. The method of claim 15, wherein the plurality of time instances are adjacent time instants that occur during an observation window that is shorter than a period of a micro-Doppler signature.

17. The method of claim 15, wherein the plurality of time instances are offset from one another by a period of a micro-Doppler signature.P111310W001-21-18. The method of any one of the previous claims, wherein the second configuration of signal properties comprises: causing (207) the second radar signal to be transmitted in a direction of a static object.

19. The method of any one of the previous claims, comprising: selecting a frequency to be used when transmitting the second radar signal based on one or both of a required micro-Doppler signature type and a micro-Doppler signature resolution.

20. The method of any one of the previous claims, wherein the second configuration of signal properties comprises: one or more range parameters selected for use in a first range to be sensed.

21. The method of any one of the previous claims, wherein the second configuration of signal properties comprises: a frequency selected to achieve a predetermined level of Doppler resolution.

22. The method of any one of the previous claims, wherein the second configuration of signal properties comprises: a polarization orientation of the second radar signal.

23. The method of any one of the previous claims, comprising: using the one or more reflections of the second radar signal as a basis for estimating a period of a micro-Doppler signature.

24. The method of claim 23, wherein using the one or more reflections of the second radar signal as the basis for estimating the period of the micro-Doppler signature comprises: performing a frequency analysis of a strongest Doppler component in the one or more reflections of the second radar signal.

25. The method of any one of the previous claims, wherein using at least the one or more reflections of the first radar signal as the basis for determining the second configuration of signal properties comprises using at least the one or more reflections of the first radar signal as the basis for determining a configuration that will do one or more of the following:P111310W001-22- achieve a predetermined micro-Doppler range resolution; achieve a predetermined frequency resolution; detect an object in the presence of clutter; sense an object located at a predetermined distance from a transmitting antenna of the second radar signal; sense an object having a predetermined size; sense a predetermined cross-sectional size of an object; and satisfy power management requirements.

26. The method of any one of the previous claims, comprising: deriving, from the one or more reflections of the first radar signal, one or more of: a range of a sensed object relative to a radar transmitter antenna; a direction of a sensed object relative to the radar transmitter antenna; an angle of a sensed object relative to the radar transmitter antenna; and a presence of clutter in a sensed area.

27. The method of any one of the previous claims, wherein the second configuration specifies one or more of: a bandwidth adaptation; a beam scan adaptation; a scanning duration; a scanning repetition to be performed; a scanning repetition rate; and a type of scanning to be performed.

28. A computer program (309) comprising instructions that, when executed by at least one processor (303), causes the at least one processor (303) to carry out the method according to any one of claims 1 through 27.

29. A carrier comprising the computer program (309) of claim 23, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a non-transitory computer readable storage medium (305).P111310W001-23-30. An apparatus of a wireless device (300), wherein the apparatus is configured to cause the wireless device (300) to perform: performing (201) a first procedure that comprises: causing (201) the first wireless device (300) to transmit a first radar signal having a first configuration of signal properties; and receiving (201) one or more reflections of the first radar signal; and performing a second procedure (205, 207) that comprises: using (205) at least the one or more reflections of the first radar signal as a basis for determining a second configuration of signal properties, wherein the first configuration of signal properties differs from the second configuration of signal properties; causing (207) a second radar signal to be transmitted, wherein the second radar signal has the second configuration of signal properties; receiving (207) one or more reflections of the second radar signal; and obtaining (209) micro-Doppler information at least from the one or more reflections of the second radar signal.

31. The apparatus of claim 30, comprising: using one or more reflections of an earlier radar signal as another basis for determining the second configuration of signal properties.

32. The apparatus of claim 30 or claim 31, comprising: estimating a signal to noise ratio of the one or more reflections of the first radar signal; performing the second procedure only if (203) the estimated signal to noise ratio is below a predetermined threshold; and when the estimated signal to noise ratio is above the predetermined threshold, using the one or more reflections of the first radar signal for micro-Doppler radar processing.

33. The apparatus of any one of claims 30 through 32, wherein the second configuration of signal properties comprises the second radar signal being transmitted from the first wireless device (300).

34. The apparatus of any one of claims 30 through 32, wherein the second configuration of signal properties comprises the second radar signal being transmitted from a second device.P111310W001-24-35. The apparatus of any one of claims 30 through 34, wherein the first configuration of signal properties comprises the first radar signal being one of: a wideband pulse; a wideband continuous wave signal; a coded signal implemented using Orthogonal Frequency Division Multiplexing; and a Frequency Modulated Continuous Wave signal.36 The apparatus of any one of claims 30 through 35, wherein the second configuration of signal properties comprises the second radar signal being a narrowband signal.

37. The apparatus of claim 36, wherein the second configuration of signal properties comprises the second radar signal being one of: a single tone; a Frequency Modulated Continuous Wave, FMCW, chirp; an instantaneous state of an FMCW signal; and an instantaneous frequency state of an FMCW sweep used as the first radar signal.

38. The apparatus of any one of claims 30 through 37, wherein: causing (201) the first wireless device (300) to transmit the first radar signal comprises causing (201) the first wireless device (300) to transmit the first radar signal as a directed beam having a first beamwidth; and causing (207) the second radar signal to be transmitted comprises causing (207) the second radar signal to be transmitted as a directed beam having a second beamwidth that is narrower than the first beamwidth.

39. The apparatus of any one of claims 30 through 38, wherein the second configuration of signal properties comprises sweeping a beam of the second radar signal.

40. The apparatus of claim 39, wherein sweeping the beam of the second radar signal comprises sweeping the beam of the second radar signal at a period that is faster than a period of a micro-Doppler signature to be measured.P111310W001-25-41. The apparatus of any one of claims 30 through 38, wherein the second configuration of signal properties comprises: causing (207) the second radar signal to be transmitted a plurality of times, wherein the micro-Doppler information is obtained (209) additionally from reflections received from the plurality of second radar signal transmissions.

42. The apparatus of claim 41, wherein for each of the plurality of times, the second radar signal is caused to be transmitted over a different narrow beam direction.

43. The apparatus of any one of claims 30 through 40, wherein the second configuration of signal properties comprises: causing (207) the second radar signal to be transmitted a plurality of times with each transmission of the second radar signal being in a different narrow beam direction; and producing a set of filtered reflections by filtering out received reflections that have a signal power less than a threshold power level, wherein the micro-Doppler information (209) is obtained additionally from the set of filtered reflections from the plurality of second radar signal transmissions.

44. The apparatus of any one of claims 30 through 40, wherein receiving the one or more reflections of the second radar signal comprises: producing a set of accumulated reflections by accumulating received reflections from each of a plurality of second radar signal transmissions, wherein the micro-Doppler information (209) is obtained additionally from the set of accumulated reflections.

45. The apparatus of claim 44, wherein the plurality of time instances are adjacent time instants that occur during an observation window that is shorter than a period of a micro-Doppler signature.

46. The apparatus of claim 44, wherein the plurality of time instances are offset from one another by a period of a micro-Doppler signature.P111310W001-26-47. The apparatus of any one of claims 30 through 46, wherein the second configuration of signal properties comprises: causing (207) the second radar signal to be transmitted in a direction of a static object.

48. The apparatus of any one of claims 30 through 47, comprising: selecting a frequency to be used when transmitting the second radar signal based on one or both of a required micro-Doppler signature type and a micro-Doppler signature resolution.

49. The apparatus of any one of claims 30 through 48, wherein the second configuration of signal properties comprises: one or more range parameters selected for use in a first range to be sensed.

50. The apparatus of any one of claims 30 through 49, wherein the second configuration of signal properties comprises: a frequency selected to achieve a predetermined level of Doppler resolution.

51. The apparatus of any one of claims 30 through 50, wherein the second configuration of signal properties comprises: a polarization orientation of the second radar signal.

52. The apparatus of any one of claims 30 through 51, comprising: using the one or more reflections of the second radar signal as a basis for estimating a period of a micro-Doppler signature.

53. The apparatus of claim 52, wherein using the one or more reflections of the second radar signal as the basis for estimating the period of the micro-Doppler signature comprises: performing a frequency analysis of a strongest Doppler component in the one or more reflections of the second radar signal.

54. The apparatus of any one of claims 30 through 53, wherein using at least the one or more reflections of the first radar signal as the basis for determining the second configuration of signal properties comprises using at least the one or more reflections of the first radar signal as the basis for determining a configuration that will do one or more of the following:P111310W001-27- achieve a predetermined micro-Doppler range resolution; achieve a predetermined frequency resolution; detect an object in the presence of clutter; sense an object located at a predetermined distance from a transmitting antenna of the second radar signal; sense an object having a predetermined size; sense a predetermined cross-sectional size of an object; and satisfy power management requirements.

55. The apparatus of any one of claims 30 through 54, comprising: deriving, from the one or more reflections of the first radar signal, one or more of: a range of a sensed object relative to a radar transmitter antenna; a direction of a sensed object relative to the radar transmitter antenna; an angle of a sensed object relative to the radar transmitter antenna; and a presence of clutter in a sensed area.

56. The apparatus of any one of claims 30 through 55, wherein the second configuration specifies one or more of: a bandwidth adaptation; a beam scan adaptation; a scanning duration; a scanning repetition to be performed; a scanning repetition rate; and a type of scanning to be performed.

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