Method for operating a radar

Abstract

A method for operating a pulsed mmWave radar device, the method comprising: by a radar controller, determining a set of measurement distances distributed over a measurement distance range; and for each measurement distance: performing a radar measurement comprising transmitting a number of radar pulses and obtaining radar return data from radar return signals resulting from the transmitted number of radar pulses, and performing signal averaging over the radar return data, thereby obtaining averaged radar return data for the respective measurement distance; wherein the number of radar pulses for each measurement distance of the set of measurement distances is determined by the radar controller such that the number is an increasing function of measurement distance.

Description

[0001] P1633WW00 1

[0002] METHOD FOR OPERATING A RADAR

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to a method for operating a radar, and a radar device.

[0005] BACKGROUND

[0006] There is a growing interest in radar technology enabling short range and high precision measurements in industrial, medical, security as well as consumer applications. Non-limiting example applications include ranging and positioning, presence and gesture detection, and investigation of material properties such as thickness, size, dielectric properties, material composition etc.

[0007] In pulse-based radar systems the send time may be kept short, which in turn enables a lower power consumption. Ultra- wideband, UWB, pulses (e.g. with a bandwidth of a few GHz or more) may as an example allow pulse durations in the order of nanoseconds, hundreds of picoseconds or shorter. In a pulse-based radar system a radar pulse (“wavelet”) is transmitted to be reflected off a radar target, wherein the reflected radar pulse is received and analyzed, e.g. to determine a time-of-flight of the radar pulse, and / or other characteristics of the reflected pulse such as amplitude and phase. Pulse-based radar systems operating in the millimetre band, or mmWave band, (herein considered to correspond to the spectrum extending from 30 GHz to 300 GHz) are of particular interest as the short wavelength of mmWave radar pulses facilitates high accuracy measurements in short range applications.

[0008] Document EP 1048960 discloses a different type of pulsed radar distance measurement, referred to as equivalent time sampling (ETS). In this technique, a train of pulses is used to generate a reflection echo in “extended time”. Each reflected pulse will always be mixed with a corresponding transmission pulse to form one sample of the time domain echo. By increasing the PRF, the resolution of the echo will increase.

[0009] SUMMARY

[0010] In some radar applications, radar measurements need to be performed over a range of distances, e.g., to detect targets at different distances from the radar. For a pulsed-based radar, this may be achieved by performing a “range sweep” comprising transmitting a burst of radar pulses, and evaluating radar responses from a plurality of distances over the range of distances. It is an object of the present invention to provide improved approaches and devices for pulsed mmWave radar measurements, facilitating performing radar measurements over a range of distances in a precise and energy efficient manner. Further or alternative objects may be understood from the following.

[0011] According to a first aspect of the present invention, there is provided a method for operating a pulsed mmWave radar device, the method comprising:P1633WW00 2

[0012] by a radar controller, determining a set of measurement distances distributed over a measurement distance range; and

[0013] for each measurement distance:

[0014] performing a radar measurement comprising transmitting a number of radar pulses and obtaining radar return data from radar return signals resulting from the transmitted number of radar pulses, and

[0015] performing signal averaging over the radar return data, thereby obtaining averaged radar return data for the respective measurement distance;

[0016] wherein the number of radar pulses for each measurement distance of the set of measurement distances is determined by the radar controller such that the number is an increasing function of measurement distance.

[0017] Varying the number of radar pulses transmitted for each measurement distance in accordance with the method of the first aspect allows the transmitted radar energy to be efficiently distributed over the distance range spanned by the radar measurements / range sweep. Since the energy of a transmitted radar pulse is diluted as the radar pulse propagates to and from a target, the signal-to-noise ratio (SNR) will decrease at greater target distances. Increasing the number of radar pulses transmitted for greater measurement distances and performing signal averaging over the return data obtained for each measurement distance allows the decreased SNR to be compensated for throughout the range sweep by reducing the noise level as a function of measurement distance. In particular, this may be achieved without varying the energy of each transmitted radar pulse in dependence on the measurement distance. Thus, the transmitted radar pulses may have substantially the same energy, i.e., be of substantially equal energy.

[0018] Moreover, whereas transmitting the same number of radar pulses for each measurement distance leads to SNR loss at increasing measurement distances, it may further result in unnecessarily high SNR at closer measurement distances, and thus prolonged sampling times and increased power consumption. In contrast, by determining the respective number of radar pulses to be transmitted for each respective measurement distance of the set of measurement distances as an increasing function of measurement distance, this issue may be mitigated since a smaller number of radar pulses may be used at closer measurement distances than at greater measurement distances.

[0019] The set of numbers or radar pulses to be transmitted for each measurement distance of the set of measurement distances may in the following be referred to as the pulse distribution set.

[0020] In the present disclosure, the term “radar pulse” is used to refer to an electromagnetic oscillating signal having a carrier frequency (the center frequency of the radar pulse) and a limited temporal extension. Each pulse may include a plurality of oscillations orP1633WW00 3

[0021] periods, in accordance with the carrier / center frequency of the wavelet. The term “radar wavelet” may be used as a synonym to “radar pulse”.

[0022] The signal averaging performed over the respective radar return pulse data obtained in each respective radar measurement, may involve summing corresponding samples from a set of sub-measurements of the respective radar measurement, and dividing the summed samples by the number of sub-measurements of the respective radar measurement. By increasing the number of transmitted pulses, it will be possible to complete more submeasurements, so that the average of these sub-measurements becomes more reliable.

[0023] In some embodiments, each sub-measurement comprises obtaining an I / Q sample, wherein, for each respective radar measurement, the signal averaging involves summing the I / Q samples from the set of sub-measurements of the respective radar measurement and dividing the summed I / Q samples by the number of sub-measurements of the respective radar measurement.

[0024] It is noted that, according to the method of the first aspect, it is the number of pulses that is important for a given measurement, and not the pulse repetition frequency (PRF). Although it is conceivable to have varying PRF for different measurement distances, for a given measurement application the radar pulses may advantageously be transmitted at constant PRF.

[0025] In some embodiments, the radar measurements for the set of measurement distances are performed successively.

[0026] This may facilitate configuration of the radar for performing the range sweep, and limit the amount of reconfiguration of the radar needed between successive radar pulse transmissions.

[0027] In some embodiments, the radar measurements are performed in sequence, starting with a minimum measurement distance and ending with a maximum measurement distance of the set of measurement distances, or vice versa.

[0028] The range sweep may thus be conducted in order of increasing or decreasing measurement distance.

[0029] In some embodiments, the set of measurement distances comprises a number of measurement distances with a spacing of less than half a wavelength of a carrier frequency of the radar pulses.

[0030] Aliasing of the averaged radar return data may thereby be avoided.

[0031] In some embodiments, each sub-measurement comprises: transmitting the radar pulse, receiving a signal comprising a radar return pulse resulting from the transmitted radar pulse, and obtaining radar return data from a portion of the received signal within a range window corresponding to the respective measurement distance.P1633WW00 4

[0032] Hence, the relevant portion of the received signal, corresponding to each respective measurement distance, may be extracted by gating the received signal using a range window (“range gate”) corresponding to the respective measurement distance.

[0033] In some embodiments, the method further comprises determining, by the radar controller, a set of measurement configurations, wherein a measurement configuration is determined for each measurement distance of the set of measurement distances, and wherein determining each measurement configuration comprises determining a delay setting for the range window corresponding to the measurement distance.

[0034] The radar controller may hence configure a delay setting for each range window / range gate. The delay setting for each respective range window may in particular be determined as the round delay trip delay corresponding to the measurement distance associated with the respective range window.

[0035] In some embodiments, the method further comprises, prior to performing each radar measurement, configuring the radar according to the associated measurement configuration, comprising configuring the radar to use the delay setting for the range window corresponding to the respective measurement distance, and subsequently performing the radar measurement.

[0036] This enables the number of radar pulses of a given radar measurement and radar measurement distance to be transmitted in rapid succession, without reconfigurations between successive radar transmissions of the given radar measurement.

[0037] In some embodiments, determining the number of sub-measurements for each measurement distance comprises, by the radar controller:

[0038] obtaining configuration information indicating the number of sub-measurements for a maximum measurement distance of the measurement distance range, and determining the number of sub-measurements for each respective measurement distance based on the number of sub-measurements for the maximum measurement distance and a scaling factor for the respective measurement distance, wherein the scaling factor is based on a fraction of the respective measurement distance and the maximum measurement distance.

[0039] Hence, given configuration information indicating the number of radar pulses to be transmitted for the maximum measurement distance in the measurement distance range, the number of radar pulses to be transmitted for the remaining (shorter) measurement distances of the measurement distance range may be efficiently and conveniently determined such that the number is an increasing function of measurement distance.

[0040] In some embodiments, the number of sub-measurements of each radar measurement is determined by the radar controller such that the number is a step-wise increasing function of measurement distance, the function defining a set of levels of numbers of radar pulses and an interval of measurement distances mapped to each level.P1633WW00 5

[0041] Hence, the set of measurement distances may be partitioned into a number of subsets of measurement distances, wherein each subset is assigned the same number of radar pulses (i.e., given by the level). Thus, instead of storing one number (i.e., one value indicating the number of sub-measurements) per measurement distance, only one number per subset needs to be stored. The amount of memory required to store the numbers or radar pulses to transmit may hence be reduced.

[0042] In some embodiments, each radar measurement comprises for each respective transmitted radar pulse:

[0043] generating a reference pulse,

[0044] receiving a received signal comprising the radar return pulse corresponding to the transmitted radar pulse,

[0045] mixing the received signal and the reference pulse to obtain a mixing product, and

[0046] integrating the mixing product to obtain an integrated mixing product; wherein obtaining the radar return data of the radar measurement comprises deriving a number of samples from the integrated mixing products obtained in the radar measurement.

[0047] This amounts to, what may be referred to as, a “time-diluted measurement approach”. Compared to a direct sampling of single radar pulse, a time-diluted sampling approach may lower the demands on the speed and accuracy of the acquisition circuitry of the radar sensor. Conversely, a time-diluted sampling approach may allow use of higher-frequency radar signals.

[0048] In the time-diluted measurement approach, the measurement distance may be determined by controlling a delay (i.e., timing offset) between the transmission of the radar pulse and the respective reference pulse. The method may comprise determining, by the radar controller, a set of measurement configurations, wherein a measurement configuration is determined for each measurement distance of the set of measurement distances, and wherein determining each measurement configuration comprises determining a setting of a delay (timing offset) between transmitting the radar pulse and generating the respective reference pulse. Hence, the reference pulse and the delay setting may here correspond to the above-mentioned range window / range gate and its associated delay setting.

[0049] In the present disclosure, the term “mixing” refers to RF mixing / frequency mixing (e.g., by a mixer) of two signals (e.g. a received radar pulse and a reference pulse) to obtain a mixing product.

[0050] In the present disclosure, the term “integrating” refers to an integration (e.g. by an integrator) of a signal (e.g. the mixing product of the received radar pulse and the reference pulse) to obtain a time integral of the signal (e.g. an integrated mixing product). The integration hence converts the mixing product of each measurement into a respectiveP1633WW00 6

[0051] integrated mixing product. The integrated mixing product may in particular be a DC signal. The respective mixing product may be integrated over its full duration. That is, the time period during which the mixing product is accumulated (e.g. by the integrator) may cover the full duration of the mixing product. The radar return data for the may accordingly be obtained by deriving samples from the integrated mixing products of the radar measurement.

[0052] In some embodiments, the radar return data for each radar measurement indicates an amplitude and / or a phase for the measurement distance. Thus, one or more of amplitude and phase information may be obtained from the radar measurements.

[0053] In some embodiments, the transmitted radar pulses of each radar measurement have substantially the same energy.

[0054] More specifically, the radar pulses may be substantially identical radar pulses e.g., in terms of amplitude and waveform. Identical transmitted radar pulses enable phase-coherent radar measurements, such that there is phase-coherence (a constant predetermined phase-relationship) between sequentially transmitted radar pulses. This may facilitate signal processing and increase measurement accuracy.

[0055] Analogous to the transmitted radar pulses, in embodiments comprising the time-diluted measurement approach set out above, the reference pulses may further be identical to each other, e.g., in terms of amplitude and waveform. The reference pulses may further be identical to the transmitted radar pulses. Accordingly, each sub-measurement may comprise: generating and transmitting a respective instance of the radar pulse, generating a respective instance of the reference pulse, receiving a respective received signal comprising the respective radar return pulse corresponding to the respective instance of the transmitted radar pulse, and mixing and integrating the respective received signal and the respective instance of the reference pulse to obtain a respective integrated mixing product.

[0056] In some embodiments, the method further comprises thresholding the averaged radar return data, the thresholding comprising comparing the averaged radar return data obtained for each measurement distance to a threshold varying over the measurement distance range.

[0057] Since the number of transmitted radar pulses of each sub-measurement is a function of measurement distance, the noise level (as a consequence of the signal averaging) will also be a function of measurement distance. Thus, by using a distance-varying threshold, a reliable thresholding of the averaged radar return data may be achieved.

[0058] In some embodiments, the method further comprises:

[0059] normalizing the averaged radar return data with a noise estimate varying over the measurement distance range to obtain noise-normalized averaged return data; and thresholding the noise-normalized averaged return data, the thresholding comprising comparing the noise-normalized averaged radar return data obtained for each measurement distance to a common threshold.P1633WW00 7

[0060] By normalizing the averaged radar return data with a distance-varying noise estimate, the above-mentioned distance-variable noise level may be compensated for, such that thresholding may be performed using a common / fixed threshold.

[0061] According to a second aspect of the present invention, there is provided a radar device configured to implement the method according to the first aspect, or any embodiments any one of the preceding claims

[0062] In general, any embodiment, feature, effect or advantage discussed in connection with the first aspect applies correspondingly to the second aspect.

[0063] BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The above, as well as additional objects, aspects, embodiments, features and effects of the present disclosure, may be better understood through the following illustrative and nonlimiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.

[0065] Fig. 1 is a block diagram of a radar device according to some embodiments. Fig. 2 is a flow chart of a method for operating a radar according to some embodiments.

[0066] Fig. 3 is a flow chart showing sub-steps of the step of performing a radar measurement in Fig. 2.

[0067] Fig. 4-5 are schematic diagrammatic depictions of a range sweep, according to various examples.

[0068] Fig. 6 is a block diagram of a further radar device according to some embodiments.

[0069] Fig. 7 is a schematic timing diagram of a radar measurement according to a time-diluted sampling approach.

[0070] Fig. 8 is a diagrammatic depiction of a set of measurement distances partitioned into a number of subsets of measurement distances, each subset being associated with a respective number of radar pulses to be transmitted.

[0071] Fig. 9 is a diagram of SNR variations over measurement distance for a case where the SNR loss is fully compensated and partially compensated, respectively.

[0072] DETAILED DESCRIPTION

[0073] Fig. 1 is a block diagram of a radar device 100, hereinafter termed radar 100. The radar 100 comprises a transmitter 104 (transmitter circuit) and a receiver 106 (receiver circuit). The transmitter 104 is configured to generate and transmit radar pulses Tx. The receiver 106 is configured to receive a return signal S comprising radar return pulses Rx. The radar 100 further comprises a radar controller 102 coupled to the transmitter 104 and the receiver 106 and configured to control the operation of the transmitter 104 and the receiver 106.P1633WW00 8

[0074] The transmiter 104 and the receiver 106 are configured to transmit / receive the radar pulses Tx / Rx via an antenna or antenna arrangement 108 of the radar 100. In the illustrated example, the antenna 108 is shared by the transmitter 104 and the receiver 106. For example, the transmiter 104 and the receiver 106 may as shown be coupled to the antenna 108 via a selector 109 for selectively coupling either the transmiter 104 or the receiver 106 to the antenna 108. However, it is also possible to employ separate antennas for the transmiter 104 and the receiver 106. The antenna(s) 108 may for example comprise a directional antenna, such as a dipole antenna, a Yagi antenna or a phased array antenna. A reflector such as a hom reflector and / or a dielectric lens may be arranged in connection with the antenna 108 to improve the directionality of the radar pulses Tx / Rx. Also, omnidirectional antennas are possible.

[0075] The radar 100 is configured as a pulsed mmWave radar, meaning that the transmitter 104 is configured to generate and transmit the radar signals in the form of radar pulses Tx having a carrier frequency in the mmWave band (30 GHz to 300 GHz). The radar 100 may in particular be configured as a mmWave UWB radar, wherein the transmiter 104 may be configured to generate and transmit mmWave UWB radar pulses Tx. The term UWB pulse or UWB signal may here be defined as an antenna transmission for which the emited signal bandwidth exceeds the lesser of 500 MHz or 20% of the center frequency. UWB radar pulses Tx may for example have a bandwidth of about 7 GHz to about 14 GHz (e.g., measured at full width half maximum (FWHM)). Non-limiting examples of frequency bands which the radar pulses Tx may occupy include 57-71 GHz, 57-64 GHz or 77-81 GHz. While such pulses may enable high accuracy measurements in short range applications, the approaches disclosed herein are envisaged to have a more general applicability and thus be used in conjunction with radar pulses of higher or lower carrier frequencies, as well narrower or wider bandwidths.

[0076] The radar 100 may be a phase-coherent radar, meaning that the transmiter 104 is configured to generate and transmit the radar pulses Tx in a phase-coherent manner. Thus, the transmiter 104 may generate instances of radar pulses Tx with a well-defined phase relationship (e.g., a same initial phase). For example, the transmiter 104 may (e.g., in each radar measurement) generate identical instances of a radar pulse Tx (in terms of initial phase, carrier frequency and duration).

[0077] An example implementation of a transmiter capable of generating phase-coherent mmWave UWB radar pulses is described in WO2012 / 163403 Al, in particular on page 11 line 22 to page 12 line 14. This implementation offers a low-complexity method for generating UWB mmWave radar pulses with a well-defined and fixed initial phase, carrier frequency and duration. The radar pulse generation (e.g., mmWave pulses or mmWave UWB pulses) may however also be realized using other oscillator configurations, for example, by a pulse generator relying on negative differential conductance (e.g. provided by a cross-coupledP1633WW00 9

[0078] differential pair) or positive feedback, where it is possible to start and quench the oscillations rapidly. Further example implementations include passing a continuous oscillation through a switchable amplifier, filtering of a baseband pulse, up-conversion of a baseband pulse, or using digital gates to create the desired waveform, as per se is known to the person skilled in the art.

[0079] During operation of the radar 100, the radar pulses Tx may be transmitted towards a radar target, schematically indicated by reference sign 10. A radar pulse Tx may be reflected by the radar target 10 and received by the receiver 106 as a received signal comprising a radar return pulse Rx resulting from the radar pulse Tx (i.e., a reflection of the transmitted radar pulses Tx reflected off the radar target 10 and received by the antenna 108). In the following, the reflection of a transmitted radar pulse Tx comprised in a received signal may referred to as a radar return pulse Rx. That is, “a radar return pulse Rx” designates the span or portion of a received signal comprising the reflected signal energy of a transmitted (and then reflected) radar pulse Tx.

[0080] In Fig. 1 the radar target 10 is merely schematically shown. As may be appreciated, the type of radar target 10 is in practice dependent on the application of the radar 100. In a gesture detection application, the radar target 10 may be a hand or a finger of a user locate in relative proximity to an electronic device (e.g. a tablet computer, a laptop computer, a media player, a smart watch, headphones or some other electronic device implementing a radar-based contactless user interaction). In an autonomous robot application (e.g. a cleaning robot, a lawn mower robot, a drone), the radar target 10 may be a structure such as a wall or some obstacle whose presence and / or position may be relevant for a movement decision by the autonomous robot. In a surface scanning application, the radar target 10 may be a surface of interest (e.g. a surface traversed by a robot). These examples of applications and radar targets are however merely non-limiting examples and many other types of applications and radar targets 10 are possible.

[0081] The operations of the receiver 106 will be described in further detail in the below, but may on a general level comprise receiving and processing of radar return pulses Rx. For instance, a signal comprising a radar return pulse Rx may be received (e.g., via the antenna 108) and sampled by the receiver 106 to produce radar samples. The receiver 106 may comprise one or more analog-to-digital converters (ADC) for sampling the received signal to obtain radar samples, as well as one or more filtering stages, sample buffers, variable gain amplifiers for adapting (e.g. amplifying or attenuating) the signal level of the received signal to the dynamic range of the ADC(s), and / or other conventional receiver circuitry facilitating processing of pulse signals. The radar return pulses Rx may be sampled using any suitable technique, such as direct / real-time sampling of each radar return pulse Rx, or, as further described below, by time-diluted sampling of a sequence of radar return pulses Rx. The radar samples define radar return data which may further be processed to measureP1633WW00 10

[0082] parameters such as time-of-flight, amplitude and / or phase. The processing of the radar return data may be performed by a radar signal processor 110 coupled to, or comprised in, the receiver 106. The radar signal processor 110 may for example be implemented by a digital signal processor (DSP). While the radar signal processor 110 here is illustrated as a block separate from the receiver 106, the radar signal processor 110 may also be comprised in, i.e., form part of, the receiver 106.

[0083] To facilitate the radar measurements, the receiver 106 may employ a range window for gating the received signal, in Fig. 1 schematically illustrated by a rectangular window W. Thus, the receiver 106 may, upon receiving a signal comprising a radar return pulse Rx resulting from a transmitted radar pulse Tx, gate the received signal with the range window W, and sample the windowed portion of the received signal. By varying the relative timing (i.e., timing offset or delay) of the range window W with respect to the transmission of the radar pulse Tx, a temporal portion of the received signal S corresponding to a measurement distance of interest may thus be selected, i.e., filtered out. Further, signal contributions from reflecting surfaces located at distances different from the measurement distance of interest defined by the range window W, including noise, may be discarded. The relative timing of the range window W and the radar pulse Tx may be controlled by the radar controller 102. For example, the radar controller 102 may include timing circuitry configured to generate first and second trigger signals with a controllable delay, the first trigger signal triggering the transmitter 104 to generate and transmit a radar pulse Tx and the second trigger signal triggering the receiver 106 to generate a range window W. The duration (width) of the range window W may be set based on the duration (width) of the transmit radar pulses Tx. For example, the duration of the range window W may be set to meet or exceed an expected duration of a radar return pulse Rx, or be shorter such that the receiver 106 may filter out and sample only a portion (e.g., one a or more periods) of a radar return pulse Rx. Examples of range windows include a Hanning window, a trapezoidal window or a raised cosine window, a rectangular window, or some other suitable window shape.

[0084] The radar controller 102 and the radar signal processor 110 may each be implemented in dedicated circuitry, an application-specific integrated circuit (ASICs) or field-programmable gate arrays (FPGAs). Combined hardware-software implementations are also possible, such as a processor device (e.g., one or more microprocessors) in combination with a computer-readable medium (e.g., non-transitory computer-readable medium) storing instructions for causing the processor device to perform operations of the radar controller 102 and / or radar signal processor 110.

[0085] While not expressly shown in Fig. 1, the radar 100 may further comprise circuits and functional blocks for supporting and facilitating operating the radar 100. For example, the radar 100 may comprise a communication interface (e.g., a serial or parallel bus) coupled to the radar controller 102 to enable communication with external devices or controllers, forP1633WW00 11

[0086] instance to output measurement data, status data, and / or receive configuration information. The radar 100 may further comprise a memory section, e.g., comprising anon-volatile memory for storing configuration information, settings, and / or instructions implementing various operations of the radar 100.

[0087] A method 200 for operating the radar 100, in particular to perform a range sweep, will now be described in further detail with reference to the flow chart of Fig. 2.

[0088] At step S202, the radar controller 102 determines a set of measurement distances distributed over a measurement distance range. The measurement distance range may in the following be denoted R and be defined by a minimum measurement distance and a maximum measurement distance, i.e., R = [Rmin, Rmax], The measurement distance ranged defines the range of distances from the radar 100 in which radar measurements of the range sweep are to be performed. In other words, the measurement distance range R defines the range across which the range sweep (range scan) is to be performed. The measurement distance range R may for example be represented in units of length (e.g., meters or millimeters), but may also be represented in terms of minimum and maximum round trip delay and thus in units of time (e.g., in seconds, milliseconds, picoseconds). The set of measurement distances may in the following be denoted!) = {dl, d2, d3, ... dM}, where the measurement distances dl, d2, etc. of the set D are ordered in sequence of increasing values. The measurement distance dl may thus be equal to the minimum measurement distance Rmin and the measurement distance dM may be equal to the maximum measurement distance Rmax.

[0089] The radar controller 102 may at the optional step S201 obtain range information indicating the measurement distance range R. The range information may for example form part of configuration information transferred, stored, or otherwise available to the radar controller 102. For example, the range information may form part of user-defined sensor configuration information, input to the radar controller 102 during configuration of the radar 100 for an intended measurement application. The configuration information may for example be input from an external device such as a computer, via a communication interface of the radar 100. The range information, or the measurement distance ranged, may alternatively be predetermined and stored (e.g., as non-volatile data) in a memory section of the radar 100. The radar controller 102 may thus at step S202, based on the range information, determine the set of measurement distances D.

[0090] For example, the radar controller 102 may based on the range information, and one or more further parameters, determine a set of measurement distances D distributed across the measurement distance range R. The one or more further parameters may include a number of measurement distances M to be distributed across the measurement distance range R. The number may like the range information form part of user-defined sensor configuration information. However, the number M may also be predetermined parameter, or determined dynamically based on factors such as an amount of available memory of the radarP1633WW00 12

[0091] 100 for storing instructions and radar return data, a maximum time for conducting the range sweep, etc. The radar controller 102 may upon determining the set of measurement distances D further take into account distribution information, indicating a desired distribution of the set of measurement distances Z), e.g., an equidistant spacing or a variable spacing (e.g., different spacings in different sub-ranges of the measurement distance range). For example, in some applications it may be desirable to have a closer spacing in one or more sub-ranges of interest than in other sub-ranges. The distribution information may form part of user-defined sensor configuration information. The distribution information may however also be predetermined. As a further example, the radar controller 102 may be configured to determine the set of measurement distances D to be equidistant.

[0092] According to a further example, omitting step S201, the set of measurement distances D may be determined by being transferred to the radar controller 102, or retrieved as predetermined data by the radar controller 102 from a memory section. This implementation may for example be useful where the radar 100 is to be statically configured to a specific measurement application, with no need for dynamic adaptation of the set of measurement distances D.

[0093] Subsequent to, or in parallel with, determining the set of measurement distances Z), the radar controller 102 may further determine a set of measurement configurations, one measurement configuration for each measurement distance of the set D (e.g., in total M measurement configurations). Each measurement configuration is thus associated with a respective measurement distance of the set D and defines a configuration of the radar 100 to be used for subsequently performing the radar measurement for the respective measurement distance. Where the radar 100 employs a range window W, as set out above, determining a measurement configuration for a respective measurement distance may comprise determining a delay setting for the range window W corresponding to the respective measurement distance.

[0094] Subsequent to determining the set of measurement distances D at step S202, the method 200 proceeds at step S203 to determine the number of radar pulse Tx to be transmitted (hereinafter termed “Tx pulses”) for each measurement distance of the set D. The number of Tx pulses determined for a given measurement distance di of the set D (where i = 1, 2, ... AZ is the index of the given measurement distance) may in the following be denoted ni. Thus, the determined number of Tx pulses for measurement distance dl is nJ, the determined number of Tx pulses for measurement distance d2 is n2, and so on. The determined set of numbers nJ, n2, etc., may in the following be referred to as the pulse distribution set A. The determined set of numbers of Tx pulses / pulse distribution set A may define configuration information for the range sweep (e.g., together with the above-mentioned measurement configurations) and be stored by the radar controller 102 to be used while performing the range sweep, discussed below.P1633WW00 13

[0095] In accordance with the present disclosure, the radar controller 102 determines the pulse distribution set Vso as to efficiently distribute the transmitted radar energy between the respective measurement distances of the set of measurement distances D. More specifically, the radar controller 102 determines the respective number of Tx pulses to be transmitted for each respective measurement distance of the set D as an increasing function of measurement distance. As discussed above, by determining the number of Tx pulses ni in this manner, the radar measurements may be adapted to, when combined with signal averaging, compensate for the SNR loss of radar return pulses Rx seen at increasing measurement distances during the range sweep. More specifically, by increasing the number ni of Tx pulses for measurement distance di relative to measurement distance dj (j=i-l and thus the number of Rx pulses sampled and averaged for measurement distance di, the noise level may be reduced so as to compensate for the reduced signal level as the measurement distance is increased from dj to di. The dependence on received signal level (or equivalently received power) may be calculated using the radar equation (chosen in dependence on the type of radar target), as per se is well-known in the art. Thus, for a given reduction in signal level or power between two measurement distances dj to di, the number ni of Tx pulses needed to compensate (e.g., within a predetermined target tolerance) for the given reduction after signal averaging (i.e., by reducing the noise level / power) may be determined.

[0096] Fig. 4 shows a first example of a pulse distribution set N for a range sweep, that may be determined by the radar controller 102. For ease of illustration, the pulse distribution set N is by way of example shown for five measurement distances dl to d5 which, without loss of generality, are shown to be substantially uniformly spaced. The number ni of Tx pulses to transmit for each measurement distance di is in Fig. 4 schematically indicated by a corresponding number of blocks. In the illustrated example, the number of Tx pulses increases by way of example by a factor of two between successive measurement distances. The number ni of the pulse distribution set N thus varies according to a strictly increasing function of measurement distance d.

[0097] Fig. 5 shows a further example of a pulse distribution set N for a range sweep. The shown pulse distribution set N is similar to the distribution of Fig. 4, however differs in that the pulse distribution set N defines the same number of radar pulses for two measurement distances, e.g., nl = n2. Thus, as exemplified by Fig. 5, the number ni of the pulse distribution set N may vary according to a non-strictly monotonically increasing function of measurement distance d.

[0098] It is to be noted that the examples of Fig. 4-5 merely are illustrative and that pulse distribution sets N of other forms also are possible. For example, the number of measurement distances M of the setZ) may in many applications be considerably greater than M = 5, such as 100, 1000 or more. Further, the number ni of the pulse distribution set N may vary according to different functions over different sub-ranges (i.e., intervals) of theP1633WW00 14

[0099] measurement distance range R, such as be strictly increasing over one or more sub-ranges and be constant over other sub-ranges (i.e., piecewise strictly increasing).

[0100] As an illustrative non-limiting example, in a low-power distance ranging measurement application (e.g., utilizing a battery-powered radar 100), the measurement distance range may span from about 0 to 20 meters and a spacing of the measurement distances may be about 0.25 cm (thus allowing the full measurement distance range to be covered without gaps). A non-limiting example of such an application is level-monitoring in a silo. As another non-limiting example, where power consumption, measurement time and frequency are of less consideration, even smaller measurement spacings may be used, e.g., less than 0.1 cm.

[0101] An example of an equation that may be used by the radar controller 102 to determine a pulse distribution set N for a range sweep is:

[0102] ni = nmax * (di / Rmax)x(Eq. 1)

[0103] where nmax is the number of Tx pulses to be transmitted at the maximum measurement distance Rmax. which according to the notation introduced above gives that nmax = nM and Rmax = dM. The number nmax may be indicated as part of the above-mentioned configuration information (e.g., and thus be user-supplied). The further parameter x is a model parameter which is set in dependence on the SNR loss as a function of measuring distance. The value of the parameter x may be set for the given measurement application and is a positive value greater than 1, typically in a range from 2 to 4. Theoretically, to obtain a uniform SNR throughout the measurement distance range R. x may be set to 4 assuming a generic radar target 10 with an at least approximately isotropic re-radiation pattern (such as smaller point-like objects) and set to 2 for a larger planar radar target 10 (such as a water or floor surface, a wall, or other planar structure). By varying x between 2 and 4, Eq. 1 may be adapted to the shapes and sizes of radar targets expected in a given application. Using Eq. 1, the radar controller 102 may thus in a computationally efficient and straightforward manner determine the number of Tx pulses for each respective measurement distance of the set of measurement distances D based on the number of radar pulses (nmax) for the maximum measurement distance (Rmax) and a scaling factor for the respective measurement distance based on a fraction of the respective measurement distance di and the maximum measurement distance Rmax.

[0104] With an appropriate value of x, Eq. 1 enables determining an ideal, or at least approximately ideal, pulse distribution set N in the sense that an expected SNR loss may be compensated at all measurement distances of the set D, such that a uniform, or close to uniform SNR may be obtained throughout the measurement distance range R. While this may be desirable from the point of view of optimizing measurement accuracy, in some scenarios,P1633WW00 15

[0105] such as where the number of measurement distances M is great relative to available memory resources of the radar controller 102, storing a respective number ni for each measurement distance di may be infeasible. In such scenarios, the radar controller 102 may use Eq. 1 as a starting point, to determine an initial (“ideal”) pulse distribution set N, and subsequently determine a compressed or sparse representation of the initial pulse distribution set N to reduce memory utilization, e.g., by assigning the same number ni of Tx pulses to sub-ranges of consecutive measurement distances di. An implementation of this approach will now be discussed with reference to Fig. 8-9.

[0106] Fig. 8 shows a first pulse distribution set N’ (dashed line) and a second pulse distribution set N” (dotted line). The first pulse distribution set N’ corresponds to an “ideal” pulse distribution set determined according to Eq. 1. The second pulse distribution set N” is in contrast determined such that the number ni is a step-wise increasing function of measurement distance di (dotted line). The step-wise function defines a set of levels of numbers of Tx pulses to be transmitted, and an interval (sub-range) of measurement distances mapped to each level. For example, the levels may be determined such that the SNR increase when transitioning from one level of the step-wise function to a next may be the same for all levels (assuming the measurement distance is the same). Thus, the second pulse distribution set N” in a sense corresponds to a quantization of the first pulse distribution set N’. This reduces the amount of memory required to store the second pulse distribution set N” compared to the first pulse distribution set N’ since only one number per sub-range needs to be stored.

[0107] A compact representation of the second pulse distribution set N” may be to store each level together with the index i at which the next level should be applied. The levels together with the indices may be stored as a table. The number of levels may be based on an amount of memory available for storing the configuration information. The radar controller 102 may dynamically (i.e., at run-time) determine the number of levels based on an available memory. Thereby, the table representing the second pulse distribution set N” may be determined to fit within the available memory, creating a controlled way of varying the number of transmit pulses Tx for any number of measurement distances of the set D (i.e., any M).

[0108] Fig. 9 shows SNR variations over measurement distance for the first and second pulse distribution sets N’ and N”. As may be seen, the quantization of the number of Tx pulses to transmit n into the smaller number of levels of the second pulse distribution set N” the results in an SNR which varies about the constant / uniform SNR provided by the first pulse distribution set N’. However, the SNR variation may be controlled and thus limited to an acceptable level via the number of levels.

[0109] In view of the above, it is noted that in some measurement applications, a high measurement precision, and thus a uniform SNR, is desired. However, the tolerance for SNRP1633WW00 16

[0110] variations over a measurement distance range may, in practice, vary for different measurement applications. That is, some measurement applications may be less sensitive to a decreasing SNR at increasing measurement distances than others. In any case, the approaches set out above enables the number or Tx pulses to be scaled to compensate for the SNR loss to a desired degree.

[0111] Now returning to the flow chart of Fig. 2, subsequent to determining the pulse distribution set N at step S203, the method 200 proceeds at step S204 to perform the range sweep. The radar controller 102 accordingly causes the radar 100 (including the transmitter 102 and the receiver 104) to perform a radar measurement for each measurement distance dl, d2, etc. of the set of measurement distances D. The radar measurements are performed in succession. The radar measurements may be performed in sequence, starting with the minimum measurement distance dl and ending with the maximum measurement distance dM. The radar measurements may also proceed by starting with the maximum measurement distance dM and ending with the minimum measurement distance dl. Performing the radar measurements in sequence in this manner (i.e., minimum to maximum measurement distance, or vice versa) may simplify the control loop and facilitate the obtaining and processing of the resulting radar return data. However, performing the radar measurements in other orders are also possible. For instance, where a sub-range of the measurement distance range R is of relatively greater interest, the radar measurements within this sub-range may be performed first, and thereafter the radar measurements for the remaining parts of the distance range R may be performed. Regardless of the ordering of the radar measurements, each radar measurement comprises a number of sub-steps, as shown in the flowchart of Fig. 3.

[0112] At step S2041, the radar controller 102 causes the radar transmitter 104 to transmit the number of Tx pulses ni determined for the respective measurement distance di of the setZ). To illustrate with reference to Fig. 4, nl = 2 Tx pulses for measurement distance dl . n2 = 4 Tx pulses for measurement distance d2. n3 = 8 Tx pulses for measurement distance d3, and so on. The transmit power of each Tx pulse may be substantially equal, such that the Tx pulses have substantially the same energy. The Tx pulses may in particular be transmitted as phase-coherent and substantially identical pulses, e.g. in terms of amplitude and waveform.

[0113] The Tx pulses may be transmitted at a given pulse repetition frequency (PRF), and as indicated in figure 4 the PRF may be constant for all measurement distances. On the other hand, the PRF of the Tx pulses may vary for different measurement applications. For example, in applications where a high measurement rate is needed, the PRF may be 1-100 MHz or greater, such as in a range from 10 MHz to 50 MHz. In applications involving great measurement distances, a lower measurement rate may be useful. Otherwise, a higher measurement rate may be useful to limit the overall measurement time and power

[0114] consumption.P1633WW00 17

[0115] At step S2042, the radar controller 102 causes the receiver 106 to obtain radar return signal data (hereinafter termed “return data” and denoted “rdata ”) from the return signal S comprising the radar returns pulses Rx (hereinafter termed “Rx pulse”) resulting from the ni transmitted Tx pulses transmitted for the measurement distance di.

[0116] Assuming a radar target 10 (or other reflecting surface) reflecting the Tx pulses towards the receiver 106 is present within the transmission and reception lobe of the radar 100, the receiver 106 may, for each Tx pulse transmitted for the measurement distance di, receive a return signal S comprising an Rx pulse and sample (by the ADC) a portion of the received signal S corresponding to the measurement distance di. Where the radar target 10 (or other reflecting surface) is present at the measurement distance di, the sampled portion will include an Rx pulse resulting from the Tx pulse. Where no radar target (or other reflecting surface) is present at the measurement distance di, the sampled portion will be absent from an Rx pulse (and may thus include only measurement noise). In applications where measuring the phase and / or frequency of Rx pulses is desired, the received signal may be sampled at least at twice the carrier frequency of the Tx pulses, to avoid aliasing. In applications where, for instance, only amplitude is of interest (e.g., in a simple presence detector), a lower sampling rate may suffice.

[0117] Prior to performing each respective radar measurement, the radar controller 102 may configure the radar 100 (e.g., the transmitter 104 and the receiver 106) according to the associated measurement configuration determined for the respective measurement distance di. The configuration may comprise providing an instruction or other control signal to the transmitter 106 regarding the number of Tx pulses to be transmitted in the respective radar measurement. Where the radar 100 employs a range window W, as discussed above, the configuration may further comprise controlling the delay setting of the range window W in accordance with the delay setting indicated by the configuration information determined for the measurement distance di. Thus, for each Tx pulse, the receiver 106 may receive a signal S comprising the Rx pulse, and sampling the portion of the received signal S within the range window W corresponding the respective measurement distance di. The range window W may thus in other words define a sampling window for the receiver 106.

[0118] The combination of a transmission of a Tx pulse and the subsequent sampling of the received signal S may be referred to as a sub-measurement of the radar measurement. Thus, a radar measurement for measurement distance di comprises ni sub-measurements.

[0119] The receiver 106 may obtain (e.g., collect / aggregate and store) the samples sampled by the receiver 106 in the radar measurement (i.e., in each sub-measurement) as the return data rdata of / for the radar measurement for the measurement distance di. It is also possible to apply pre-processing to the samples and obtain the pre-processed samples as the return data rdata. The pre-processing may for example comprise performing demodulation (e.g., I / Q demodulation) on the samples of each sub-measurement of the radar measurement.P1633WW00 18

[0120] Thus, the receiver 106 may estimate I / Q samples (e.g., I / Q samples of sampled Rx pulses), wherein the return data rdata may be obtained as the estimated I / Q samples.

[0121] While Fig. 3 shows steps S2041 and S2042 as sequential steps, it is to be noted that the steps are performed in an interleaved or alternating fashion, such that each transmission of a Tx pulse is followed by sampling of a received signal S (e.g., comprising an Rx pulse resulting from a reflection of the Tx pulse). In short range applications suitable for mmWave measurements, the spacing between successive Tx pulses may typically be orders of magnitude longer than the round trip delay to the radar target 10, meaning that the Rx pulse resulting from one Tx pulse always will received by the receiver 106 prior to the transmitter 104 transmitting the next Tx pulse.

[0122] Subsequent to performing each sub-measurement of respective radar measurement, the method 200 proceeds at step S2043 to perform signal averaging over the return data rdata, thereby obtaining averaged radar return data (denoted “avg rdata ”) for the radar measurement and the respective measurement distance di. The receiver 106 may input the return data rdata to the radar signal processor 110 (e.g., DSP) wherein the radar signal processor 110 performs the signal averaging to determine the averaged return data avg rdata. The signal averaging may be performed upon completing each sub-measurement of a respective radar measurement, or only after completing all radar measurements. The signal averaging may comprise summing corresponding samples (or I / Q samples) from each of the sub-measurements of the radar measurement and dividing the summed samples by the number of sub-measurements (i.e., the number of Tx pulses ni) of the radar measurement. For example, the return data rdata may be stored in ni vectors wherein the ni vectors may be summed (element-wise) and divided by ni. Assuming the noise is uncorrelated and has a zero mean, and that the ni Rx pulses sampled for a given measurement distance di are identical, the signal averaging results in an of SNR avg = ni * SNR, where SNR is the SNR that would be obtained for a single sub-measurement (a single Rx pulse) at measurement distance di.

[0123] Once the radar measurement for each measurement distance di of the set D have been performed, the range sweep has been completed. Thus, averaged return data avg rdata has been obtained for each radar measurement / measurement distance di of the set D. The averaged return data avg rdata may be stored in a memory section of the radar 100 and / or subjected to further signal processing. The averaged return data avg rdata (e.g., subsequent to further signal processing, such as thresholding, discussed below) may be output (e.g., via a communication interface of the radar 100) to an external device for storage and / or further processing.

[0124] One example of processing that may be applied to the averaged return data avg rdata is a thresholding operation. Thus, the radar signal processor 110 may as shown in Fig. 2 at optional step S205 of the method 200 compare the averaged return data avg rdata obtained for each measurement distance to a threshold to obtain thresholded averaged returnP1633WW00 19

[0125] data (hereinafter termed “thresholded data” and denoted “th avg rdata ”). The thresholding may comprise setting the value of samples of the averaged return data avg rdata which fall below the threshold to zero. The thresholding may also comprise selectively forwarding the samples of the averaged return data avg rdata meeting or exceeding the threshold to subsequent post-processing, thus ignoring or discarding samples not meeting the threshold.

[0126] As discussed above, owing to the compensation of the SNR loss enabled by the method 200, the noise level will vary (i.e., decrease) across the measurement distance range R. Thus, to enable a reliable thresholding of the averaged return data avg rdata, the thresholding may utilize a threshold having a value varying over the measurement distance range. For example, the threshold Th may be defined as Th = {Thi, Th2, ... ThM} wherein Thi = ThO / m, where Thi is a predetermined base threshold value (e.g., for a zero measurement distance) and oi is a scaling factor being a function of ni. Thus, thresholding the averaged return data avg rdata may comprise comparing the avg rdata for each measurement distance di to Thi. To illustrate, in the idealized example above, where SNR avg = ni * SNR, the scaling factor may be oi = sqrt(ni) (assuming the thresholding is done in signal level domain). As an alternative to a distance-varying threshold, the radar signal processor 110 may instead normalize the averaged return data avg rdata with a noise estimate (analogous to z) varying over the measurement distance range to obtain noise-normalized averaged return data.

[0127] Subsequently, thresholding may be applied to the noise-normalized averaged return data by comparing the noise-normalized averaged radar return data obtained for each measurement distance to a common threshold (analogous to ThO).

[0128] Fig. 6 is a block diagram of a further radar device 300. The radar (device) 300 generally corresponds to the radar 100 of Fig. 1 and accordingly comprises a transmitter 310 and a receiver 320. The discussion of the transmitter 102 above applies correspondingly to the transmitter 310. Accordingly, the transmitter 310 may comprise a pulse generator 312 (which also may be termed wavelet generator 312) configured to generate and transmit radar signals in the form of mmWave pulses, such as mmWave UWB pulses, which also in this example may be referred to as Tx pulses. The pulse generator 312 may be configured to generate each Tx pulse with a same waveform and amplitude, such that multiple mutually phase-coherent instances of Tx pulses may be generated at temporally spaced measurement occasions. This enables obtaining phase-coherent radar return data from multiple measurements, and hence facilitates the time-diluted measurement approach to be further described below. The receiver 320 comprises a reference pulse generator 322 corresponding to the pulse generator 312. The (reference) pulse generator 322 is configured to generate reference pulses Ref. The aforementioned properties of the transmitted radar pulses Tx may apply correspondingly to the reference pulses Ref. Accordingly, the reference pulses Ref may be radio-frequency pulses, e.g. UWB mmWave pulses. The pulse generator 322 may like the pulse generator 312 be configured to generate each reference pulse Ref with a same waveform and magnitude, suchP1633WW00 20

[0129] that reference pulses Ref generated at temporally spaced measurement occasions may present mutual phase-coherence. The radar pulses Tx and the reference pulses Ref may further be generated to present the same waveform and magnitude. In other words, the radar pulses Tx may be substantially identical to the reference pulses Ref. This enables the receiver 320 to implement matched filter detection of received radar pulses Rx during operation, as will be further described below. Although a matched filter implementation may provide improved signal-to-noise performance, it is in principle possible to obtain representative measurements also using Ref pulses not matching the Tx pulses, e.g. Ref pulses and Tx pulses with different envelopes but with matching carrier / center frequency.

[0130] In the illustrated example, the transmitter 310 is coupled to a transmit antenna 314 and the receiver 320 is coupled to a receive antenna 324. However, a shared transmit / receive antenna configuration is also possible, e.g., as discussed above with reference to the radar 100.

[0131] The receiver 320 comprises a mixer 326. The mixer 326 is configured to perform mixing of a pair of input signals and output the resulting mixing product M. A first input of the mixer 326 is coupled to the input port of the receiver 320 (coupled to receiver antenna 324). A second input of the mixer 326 is coupled to an output of the pulse generator 322. Hence, in response to a received signal S (e.g., comprising an Rx pulse) and a Ref pulse being applied to the mixer inputs, the mixer 326 outputs the instantaneous mixing product. Where a Ref pulse received at the second input presents a temporal overlap with an Rx pulse received at the first input, the mixing product M will also be a pulse comprising the product of the overlapping portions of the Rx and Ref pulses. Passive as well as active, balanced or unbalanced mixer implementations are possible, e.g. a Gilbert cell, a diode mixer or a passive field-effect transistor mixer.

[0132] The receiver 320 further comprises an integrator 327. The integrator 327 is configured to integrate the mixing product M to output an integrated mixing product I. An input of the integrator 327 is coupled to the output of the mixer 326. The mixing product M, which for overlapping Rx and Ref input pulses will be an AC signal, may hence be converted to a DC signal. The integrator 327 may be implemented by a capacitor, or an integrating OP-amp. An integration time of the integrator 327 should be equal to or greater than a maximum expected duration of the (pulsed) mixing product M. While in the illustrated example, the receiver 320 comprises separate mixing and integrating circuit elements 326, 327, it is also possible to realize the mixing and integration of received signal S and the Ref pulse in a common circuit portion or element providing, simultaneously, the mixing and integration function, e.g. a capacitive mixing circuit element or portion.

[0133] The receiver 320 further comprises a sampling circuit which in the illustrated example is implemented as an ADC 328. An input of the ADC 328 is coupled to the output of the integrator 327. The ADC 328 is configured to convert a DC-level integrated mixingP1633WW00 21

[0134] product I accumulated by the integrator 328 to a corresponding digital sample x. Although not shown in Fig. 6, the radar 300 may, as discussed with reference to the radar 100, comprise additional circuitry for adapting (e.g. amplifying or attenuating) the integrated mixing product I prior to the ADC 328, to optimize the output level of the integrator 327 with respect to the dynamic range of the ADC 328.

[0135] The radar 300 (e.g., the receiver 320) further comprises a radar signal processor which in the illustrated example is implemented by a digital signal processor (DSP) 330. An input of the DSP 330 is coupled to an output of the ADC 328. As further described below, the DSP 330 is configured to perform (e.g., among others) signal averaging of radar return data obtained by the receiver 320 during a range sweep.

[0136] The radar 300 comprises a radar controller 302 for controlling the operations of the transmitter 310 and receiver 320. To orchestrate the generation and transmission of the Tx pulses and the generation of the Ref pulses, the radar controller 302 includes a timing circuit configured to output a first trigger Tx trig to the radar pulse generator 312 for triggering generation of a radar pulse Tx. The timing circuit is further configured to output a second trigger Refytrig to the pulse generator 322 for triggering generation of a reference pulse Ref. The timing circuit is configured to output the second trigger Refytrig with a controllable / programmable delay after the first trigger Tx trig. In other words, the timing circuit may delay the output of the second trigger with respect to the output of the first trigger by a controllable delay time. The first and second triggers Tx trig, Refytrig may for example be formed by a rising edge or a falling edge of a (digital) pulse.

[0137] The pulse generator 312 of the transmitter 310 is in turn configured to generate a Tx pulse in response to receiving the first trigger Tx_trig. Correspondingly, the pulse generator 322 of the receiver 320 is configured to generate a reference pulse Ref in response to receiving the second trigger Refytrig.

[0138] The timing circuit may operate on basis of a reference clock CLK, e.g. provided by a voltage-controlled oscillator (VCO) or some other conventional clock source of the radar device 100, or an external clock source. The timing circuit may comprise counter circuitry configured to output the first trigger Tx_trig and the second trigger Refytrig after a respective number of clock edges of the clock CLK. Higher precision delay control may be obtained by distributing the clock signal into a first path associated with the first trigger generation Tx_trig and a second path associated with the second trigger generation Refytrig. A delay line (e.g. a tapped delay line or other digital or continuous delay circuit) may be provided in one of the first or second path to provide fine delay control between the respective clock signals propagating along the first and second paths. By way of example, state of the art delay circuits, such as tapped delay lines, may enable variable delay control with a resolution / step-size of about 0.5 ps or less. It is also possible to use separate and synchronized clocks sources for controlling the generation of the first and second triggers Tx_trig, Refytrig.P1633WW00 22

[0139] The operation of the radar 300 will now be described with further reference to Fig. 7 showing a schematic timing diagram of a single radar measurement which may form the basis for the method 200 discussed with reference to Fig. 2-3. In particular, the measurement approach illustrated in the timing diagram may be comprised in single submeasurement of a given radar measurement of the method 200.

[0140] Responsive to a first trigger Tx_trig, a Tx pulse is generated by the pulse generator 312 and transmitted by the transmitter 310 towards the radar target 10. The receiver 320 receives a signal S comprising an Rx pulse corresponding to a reflection of the Tx pulse by radar target 10 (or other reflecting surface). The mixer 326 mixes the received signal S with a Ref pulse to obtain a mixing product M. The mixing product M is integrated by the integrator 327 to obtain an integrated mixing product I. The integrated mixing product I is sampled by ADC 328 to produce a digital sample x for the sub-measurement.

[0141] As discussed above, the radar 300 may generate the Ref pulse with a variable delay time (T) with respect to the Tx pulse. The temporal alignment / timing offset (5) between the Rx pulse and the Ref pulse at the mixer 326 is accordingly a function of the round-trip delay (RTD) of the Tx pulse and the delay time T. AS may be appreciated, the RTD depends on the distance to the radar target 10. Under the constraint that the RTD does not change, an instantaneous phase relationship between the Rx pulse and the Ref pulse during mixing, and hence the instantaneous mixing product M, may accordingly be varied deterministically between successive radar measurements by varying the delay time T. The integrated mixing product I and the digital counterpart x of each sub-measurement thus corresponds to a value or sample of a cross-correlation between the Rx pulse and the Ref pulse, as a function of the delay T.

[0142] Accordingly, the radar 300 may perform a range sweep as discussed with reference to the radar 100 and the method 200 of Fig. 2, with the difference that each respective measurement distance di of the set D here corresponds to a respective delay setting TI between the Ref pulse and the Tx pulse (i. e. , as determined by the controllable delay between the first and second triggers Tx_trig, Ref trig).

[0143] Thus, a measurement configuration including a delay setting for the timing circuit may be determined for each measurement distance di of the range sweep. In applications where measuring the phase and / or frequency of Rx pulses is desired, at least a subset of the measurement distances di may be distributed with a spacing of less than half a wavelength of the carrier frequency of the Tx pulses. Each sub-measurement of a respective radar measurement results in a respective digital sample x of the integrated mixing product I obtained for the delay setting zi. Thus, each sub-measurement according to the time-diluted sampling approach comprises: generating and transmitting a respective Tx pulse, generating a respective Ref pulse, receiving a respective received signal S comprising the respective Rx pulse corresponding to the respective Tx pulse, mixing and integrating the respective receivedP1633WW00 23

[0144] signal S and the respective Ref pulse to obtain a respective integrated mixing product I, and sampling the respective integrated mixing product I to obtain a digital sample x.

[0145] Analogous to the discussion of the receiver 106 and step S2042 of Fig. 3, the receiver 320 may thus obtain, for each measurement distance di of the setZ), radar return data rdata comprising ni digital samples x. Further, at step S2043, the radar signal processor / DSP 330 of the radar 300 may perform signal averaging of the return data rdata to obtain averaged return data avg rdata for each radar measurement. The signal averaging may comprise summing the samples x from each of the sub-measurements of the radar measurement and dividing the summed samples by the number of sub-measurements ni of the radar measurement. The averaged return data avg rdata may be stored in a memory section of the radar 300 and / or subjected to further signal processing. For instance, the DSP 330 may perform I / Q demodulation of the averaged return data avg rdata. Additionally, or alternatively, the DSP 330 may at step S205 apply thresholding to the averaged (and optionally I / Q demodulated) return data avg rdata (e.g., as set out above using either a distance-variable threshold or a fixed threshold after performing noise-normalization of the data avg rdata). The averaged return data avg rdata (e.g., subsequent to further signal processing) may be output (e.g., via a communication interface of the radar 300) to an external device for storage and / or further processing.

[0146] According to a time-diluted approach, the rate at which samples x of the crosscorrelation are obtained is not dictated by the carrier frequency of the Tx pulses. Rather, the samples x may be obtained at a rate dependent on the PRF of the transmitter 310.

[0147] In the illustrated example, the transmitter 310 and the receiver 320 comprise respective pulse generators 312, 322. Using different pulse generators for the transmitter 310 and the receiver 320 may be advantageous in that a timing of the Tx pulses and Ref pulses conveniently may be controlled independently from one another, among others enabling Tx and Ref pulses to be generated with a temporal overlap. Moreover, timing control may be facilitated since delaying of the actual pulses (Tx and Rel) may be avoided, which may facilitate precise delay control. However, implementations comprising a single pulse generator shared by the transmitter 310 and the receiver 320 are also possible. A single pulse generator implementation may implement delay control by providing separate triggers to the pulse generator for generating the radar pulse Tx and the reference pulse Ref, and a switch for directing the respective pulses to the transmitter 310 or receiver 320. Alternatively, a single pulse may be generated and distributed into both a transmit branch and a reference branch. The transmit branch may provide the Tx pulses as input to the transmitter 310. The reference branch may comprise delay circuitry for delaying Ref pulse so as to provide a reference pulse Ref delayed with respect to the Tx pulse, as input to the receiver 320.

[0148] In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art,P1633WW00 24

[0149] other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.

[0150] For instance, while in the illustrated examples of above, the radar devices 100, 300 each comprise a co-located transmitter-receiver pair, the approaches set out herein may also be used by a radar device comprising a transmitter and receiver arranged in separate spaced apart units.

Claims

P1633WW00 25CLAIMS1. A method for operating a pulsed mmWave radar device (100, 300), the method comprising:by a radar controller (102, 302), determining (S202) a set of measurement distances distributed over a measurement distance range; andfor each measurement distance:performing (S204) a radar measurement comprising transmitting (S2041) a number of radar pulses and obtaining (S2042) radar return data from radar return signals resulting from the transmitted number of radar pulses, andperforming signal averaging (S2043) over the radar return data, thereby obtaining averaged radar return data for the respective measurement distance;wherein the number of radar pulses for each measurement distance of the set of measurement distances is determined (S203) by the radar controller (102, 302) such that the number is an increasing function of measurement distance.

2. The method according to claim 1, wherein the signal averaging involves summing corresponding samples from a set of sub-measurements of the radar measurement and dividing the summed samples by the number of sub-measurements of the radar measurement.

3. The method according to claim 1 or 2, wherein the radar pulses are transmitted at constant pulse repetition frequency, PRF.

4. The method according to any one of the preceding claims, wherein the radar measurements for the set of measurement distances are performed successively.

5. The method according to any one of the preceding claims, wherein the set of measurement distances comprises a number of measurement distances with a spacing of less than half a wavelength of a carrier frequency of the radar pulses.

6. The method according to any one of the preceding claims, wherein each radar measurement comprises: for each transmitted radar pulse (Tx), receiving a signal (S) comprising a radar return pulse (Rx) resulting from the transmitted radar pulse (Tx), and obtaining radar return data from a portion of the received signal (S) within a range window (W) corresponding to the respective measurement distance.

7. The method according to claim 6, further comprising determining, by the radar controller (102), a set of measurement configurations,P1633WW00 26wherein a measurement configuration is determined for each measurement distance of the set of measurement distances, andwherein determining each measurement configuration comprises determining a delay setting for the range window (W) corresponding to the measurement distance.

8. The method according to claim 7, further comprising, prior to performing each radar measurement, configuring the radar (100) according to the associated measurement configuration, comprising configuring the radar (100) to use the delay setting for the range window (W) corresponding to the respective measurement distance, and subsequently performing the radar measurement.

9. The method according to any one of the preceding claims, wherein determining the number of radar pulses (Tx) for each measurement distance comprises, by the radar controller (102):obtaining configuration information indicating the number of radar pulses (Tx) for a maximum measurement distance of the measurement distance range, and determining the number of radar pulses (Tx) for each respective measurement distance based on the number of radar pulses for the maximum measurement distance and a scaling factor for the respective measurement distance, wherein the scaling factor is based on a fraction of the respective measurement distance and the maximum measurement distance.

10. The method according to any one of the preceding claims, wherein the number of radar pulses (Tx) of each set radar measurement is determined by the radar controller (102) such that the number is a step-wise increasing function of measurement distance, the function defining a set of levels of numbers of radar pulses and an interval of measurement distances mapped to each level.

11. The method according to any of the preceding claims, wherein each radar measurement comprises for each respective transmitted radar pulse (Tx):generating a reference pulse (Rel),receiving a received signal (S) comprising the radar return pulse (Rx) corresponding to the transmitted radar pulse (Tx),mixing the received signal (S) and the reference pulse (Rel) to obtain a mixing product (M), andintegrating the mixing product to obtain an integrated mixing product (I); wherein obtaining the radar return data of the radar measurement comprises deriving a number of samples from the integrated mixing products (I) obtained in the radar measurement.P1633WW00 2712. The method according to any one of the preceding claims, wherein the radar return data for each radar measurement indicates an amplitude and / or a phase for the measurement distance.

13. The method according to any one of the preceding claims, wherein the transmitted radar pulses of each radar measurement have substantially the same energy.

14. The method according to any one of the preceding claims, further comprising thresholding (S205) the averaged radar return data, the thresholding comprising comparing the averaged radar return data obtained for each measurement distance to a threshold varying over the measurement distance range.

15. The method according to any one of the preceding claims, further comprising:normalizing the averaged radar return data with a noise estimate varying over the measurement distance range to obtain noise-normalized averaged return data; and thresholding the noise-normalized averaged return data, the thresholding comprising comparing the noise-normalized averaged radar return data obtained for each measurement distance to a common threshold.

16. A radar device (100, 300) configured to implement the method according to any one of the preceding claims.

17. The radar device according to claim 16, comprising:a transmitter (104) for transmitting (S2041) a number of radar pulses;a receiver (106) for obtaining (S2042) radar return data from radar return signals resulting from the transmitted number of radar pulses; anda radar signal processor (110) for performing signal averaging (S2043) over the radar return data, thereby obtaining averaged radar return data;a radar controller (102) for determining (S202) a set of measurement distances distributed over a measurement distance range, and to control the transmitter (104) such that the number of radar pulses transmitted for each measurement distance of the set of measurement distances is an increasing function of measurement distance.

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