Patent Description:
In automotive radar systems, it is desirable to detect when the radar sensor is blocked by debris, such as dirt, snow, ice, etc. Sensor blockage or radar blockage attenuates the transmitted and received signal such that objects in the field of view are no longer detectable. It is also important to alert the driver when the sensor is blocked so that the driver does not rely on the radar system while a sensor is blocked, and so that the driver can intervene and clear the debris from the sensor to restore performance of the system.

Declaring a sensor blockage based on the absence of radar signal processing detections is a relatively straightforward means of determining sensor blockage with minimal additional processing time or resources. One drawback of this approach is that it is difficult to distinguish the blocked case from the case in which there are relatively few or no objects large enough to create detections in the field of view of a sensor that is not blocked and is functioning properly. This situation can occur, for example, when the automobile in which the system is operating is passing through a desert or along a bridge or causeway surrounded by water.

<CIT> discloses an automotive radar system and method wherein a plurality of range-Doppler maps for the region are generated from digital data signals, and the plurality of range-Doppler maps are averaged to generate an averaged range-Doppler map.

<CIT> describes a method for detecting blocked state of radar device in e.g. dead angle monitoring system, of a car. The method involves analyzing a portion of a reception signal, and detecting blocked state of radar devices based on analysis.

<CIT> describes a system with a controller, antenna, and method for detecting obstruction and misalignment of a ground vehicle radar having an antenna configured to detect objects in a first direction. The system characterized as being substantially parallel to a horizontal plane about the ground vehicle, and detect objects in a second direction characterized as being toward a roadway surface proximate to the ground vehicle. The second direction radar return from the roadway is expected to have certain characteristics. If the characteristics are outside of a predetermined window, then obstruction and/or misalignment of the first direction and the second direction is likely, and so the radar may not reliably detect an object in the first direction, such as a vehicle in an adjacent lane.

<CIT> describes a radar apparatus of the present invention is a radar apparatus for detecting an object around a vehicle, which comprises a transmitter section for radiating a frequency modulated, transmitted wave a receiver section for receiving a radio wave re-radiated from an object exposed to the transmitted wave. Mixing the radio wave received with part of the transmitted wave to obtain beat signals. A signal processing section for analyzing frequencies of the beat signals to detect the object around the vehicle. The radar apparatus is arranged to set a first threshold value and a second threshold value higher than the first threshold value as to signal levels of a frequency spectrum of the beat signals. The signal processing section is arranged to detect the object around the vehicle, using a beat frequency of a signal level over the second threshold value, and to compare the frequency spectrum with the first threshold value in a predetermined frequency range to determine whether there is dirt on the transmitter section or on the receiver section.

According to one aspect, a radar system is provided according to accompanying claim <NUM>. According to a second aspect, a radar detection method is provided according to accompanying claim <NUM>. Optional features are provided according to the accompanying dependent claims.

The present disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the present disclosure, in which like reference numerals represent similar parts throughout the several views of the drawings.

Automotive radar is designed for active safety, and to provide a continuous level of safety, the radar must be able to detect if it is functioning according to specifications. If the radar is blocked by mud or snow or other obscurants, then the radar performance may be significantly degraded, and the user should be alerted. In some configurations, it would be desirable to include a secondary radar sensor dedicated to monitoring the physical state of the primary radar. However, due to considerations of cost and physical space, this approach is considered impractical. Therefore, according to the present disclosure, the radar system itself is configured to detect whether it is blocked and to report blockage to the user/operator. According to the present disclosure, an approach to detecting blockage, concluding whether the radar is blocked or unblocked, and reporting radar sensor blockage is described in detail.

It should be noted that the exemplary radar system claimed and described in detail herein has a central frequency of approximately <NUM> with an elevation beam width of approximately <NUM>° FWHM (full-width half-maximum). In some exemplary embodiments, the radar sensor is typically mounted about <NUM> above the road.

<FIG> includes a schematic block diagram of an automotive radar system <NUM> for processing automobile radar signals, in accordance with some exemplary embodiments. Referring to <FIG>, system <NUM> includes a radar sensor module <NUM>, which processes radar transmit and receive signals which are compatible with the radar detection and monitoring system in the host automobile. Radar module <NUM> generates and transmits radar signals into the region adjacent to the host vehicle that is being monitored by the radar system Generation and transmission of signals is accomplished by RF signal generator <NUM>, radar transmit circuitry <NUM> and transmit antenna <NUM>. Radar transmit circuitry <NUM> generally includes any circuitry required to generate the signals transmitted via transmit antenna <NUM>, such as pulse shaping circuitry, transmit trigger circuitry, RF switch circuitry, or any other appropriate transmit circuitry used by the radar system.

Radar module <NUM> also receives returning radar signals at radar receive circuitry <NUM> via receive antenna <NUM>. Radar receive circuitry <NUM> generally includes any circuitry required to process the signals received via receive antenna <NUM>, such as pulse shaping circuitry, receive trigger circuitry, RF switch circuitry, or any other appropriate receive circuitry used by the radar system In some exemplary embodiments, the received signals processed by radar receive circuitry <NUM> are forwarded to phase shifter circuitry <NUM>, which generates two signals having a predetermined phase difference. These two signals, referred to as an inphase (I) signal and a quadrature (Q) signal, are mixed with an RF signal from RF signal generator <NUM> by mixers <NUM> and <NUM>, respectively. The resulting difference signals are further filtered as required by filtering circuitry <NUM> to generate baseband I and Q signals, labeled "I" and "Q" in <FIG>. The baseband I and Q signals are digitized by analog-to-digital converter circuitry (ADC) <NUM>.

In automobile radar systems, these digitized I and Q baseband signals are processed by a processor <NUM>, which can include such circuitry as a digital signal processor (DSP), associated memory, associated I/O circuitry, communication bus circuitry, and any other circuitry required for carrying out any processing functions of system <NUM> and/or radar sensor <NUM>. In some exemplary embodiments, the radar module <NUM> transmits and receives radar sweeps, i.e., frequency-modulated (FM) chirps, at a rate of approximately <NUM>. In some exemplary embodiments, processor <NUM> can perform processing such as a fast Fourier Transform (FFT) to generate Doppler range-plus-velocity (RV) bins for each sweep, which include range, bearing and velocity information for radar detection of clutter. It will be understood that other sweep rates can be used. As used herein, the term "clutter" refers to any target or physical object that may return a radar signal resulting in a radar detection. These Doppler RV bins of radar clutter data are processed according to the detailed description herein to identify when the sensor is blocked.

According to the present disclosure, radar system <NUM> determines whether system <NUM> is detecting other automobiles and stationary objects in the region being monitored. If the radar is detecting clutter objects, e.g., other vehicles, poles, guardrails, road surface, etc., then the blockage state may be set to unblocked or clear. However, the converse is not necessarily true. That is, if the radar is not detecting clutter, it cannot necessarily be concluded that the radar is blocked. Instead, it is considered that the automobile could be in the desert scenario where there is little clutter. It should be noted that, according to the present disclosure, environments having little radar clutter may include a desert, or other regions such as a large parking lot with no features, a large snow-covered area, a bridge or causeway adjacent to a body of water, or a grassy landscape.

According to the present disclosure, it is recognized that, in different environments, detections of environmental clutter, such as stationary ground clutter, e.g., poles, guardrails, road surface, etc., will have different signatures. Accordingly, observations of clutter detections are analyzed to identify and distinguish the environments in which the system is operating, such that a reliable determination of sensor blockage can be generated. Clutter observations are analyzed using multiple approaches, and the results are fused to generate a conclusion as to whether the sensor is clear or blocked.

Specifically, according to the present disclosure, detection data in the Doppler RV bins can be subjected to multiple, e.g., three, analyses. These analyses include an immediate detection analysis, a temporal averaging analysis and an RV averaging analysis. The immediate detection analysis is analogous to normal radar detection processing, in which clutter detections are characterized by relatively strong radar returns. Such clutter includes a passing automobile or a ground-stationary object, such as a light pole. The temporal averaging analysis focuses on clutter at constant RV values, such as roadside barriers, e.g., guardrails, which have weak radar returns. The RV averaging analysis focuses on temporally changing clutter at indistinct ranges, such as could occur in clutter-sparse environments, such as a desert, landscapes with rolling hills, bodies of water, etc..

<FIG>, <FIG> and <FIG> are waveform diagrams illustrating the immediate detection analysis, temporal averaging analysis and RV averaging analysis, respectively, for detection of radar sensor blockage. In each diagram, waveforms are plotted representing radar returns from successive sweeps. Each plotted waveform represents the FFT of an FM chirp radar sweep. Each plotted waveform shows radar reflective clutter as peaks positioned on the horizontal RV axis, representing the sum of the clutter object range and the clutter object velocity relative to the radar sensor, which is a known property of FM chirp radar.

Referring to <FIG>, which illustrates immediate detection analysis of the disclosure, six radar returns 100a through <NUM> are illustrated. Each of the returns is compared to a clutter threshold. Where the return waveform exceeds the clutter threshold, the return is concluded to identify a clutter object. For example, returns 100c and 100d are associated with a strong reflecting clutter object, which produces tall peaks in the returns, which peaks are shown to exceed their respective immediate clutter thresholds 101c and 101d. These strong returns result in a positive clutter indication being generated by the immediate detection analysis. Because of the positive clutter indication, it can be concluded that the sensor is not blocked.

Referring to <FIG>, which illustrates temporal averaging analysis of the disclosure, return waveforms 102a through 102f include no peaks tall enough to exceed their respective immediate clutter thresholds. As a result, the immediate detection analysis does not yield a clutter detection. In waveforms 102a through 102f, relatively small peaks 107a through 107f, respectively, indicate a weak stationary clutter, which is largely obscured by noise. An example of such a stationary clutter object could be a barrier, e.g., a concrete wall along the road, which is a constant distance from the moving host vehicle. Since the distance to the barrier is not changing, it has zero velocity relative to the radar sensor, and the radar signal from the barrier shows up at one RV location determined by the distance, i.e., range, to the barrier. According to the present disclosure, the temporal averaging analysis is used for such a situation to combine many radar returns, including returns 102a through 102f, from multiple respective sweeps, to produce a clear signal from the weak clutter. This combined signal is illustrated schematically as waveform <NUM> of <FIG>. As a result of the combination of many returns, the combined return <NUM> includes a combined peak <NUM>, which is more pronounced than the peaks of the individual waveforms 102a through 102f. As a result, the temporal averaging or combination results in better discrimination of this clutter against background noise compared to what is obtained with the immediate detection analysis by itself. A high variation of the averaged data across RV values, as quantified by the standard deviation, provides a positive clutter indication, and it can be concluded that the sensor is not blocked.

Referring to <FIG>, which illustrates temporal averaging analysis of the disclosure, return waveform <NUM> changes strength as a function of time. In this scenario, there may be no distinct clutter objects present. An example of this situation is a landscape of gently changing radar reflectivity without distinct clutter objects at specific ranges. According to the present disclosure, an RV interval of data for each radar sweep is averaged. The result of this averaging is a value 105a illustrated in <FIG>. Referring to <FIG>, this same value 105b is stored with a sequence of RV averages from radar sweeps at other times. As illustrated in <FIG>, a high temporal variation of the averages from different sweeps, as quantified by their standard deviation, provides a positive clutter indication, and it can be concluded that the sensor is not blocked.

According to the present disclosure, the results of the immediate detection analysis, temporal averaging analysis and RV averaging analysis are fused to generate an overall result regarding possible blockage of the radar sensor. The results are logically "OR'ed" such that if any of the three analyses generates a clutter detection, then it can be concluded that the sensor is not blocked. Conversely, if none of the three analyses generates a clutter detection, then it can be concluded that the sensor is blocked.

<FIG> includes a top-level logical flow diagram illustrating steps in a method of detecting radar sensor blockage, according to an exemplary embodiments. Referring to <FIG>, FM radar sweep data collection and conditioning, including FFT processing is performed in step <NUM>. The data for the sweeps, as illustrated and described above in connection with <FIG>, is analyzed to generate clutter detections is step <NUM>. This clutter detection processing receives the individual predetermined detection thresholds and compares the processed sweep data to the thresholds as described above. The results of the three analyses are logically OR'ed, such that a positive detection by any of the analyses results in a conclusion of a clutter detection. This OR'ed clutter result is input to blockage logic <NUM> to determine whether a blockage declaration should be issued.

<FIG> includes a logical flow diagram of steps in FM data collection and conditioning <NUM> illustrated in <FIG>, according to some exemplary embodiments. Referring to <FIG>, the FM chirp data is received and processed at step <NUM>, the processing including mean subtraction, I-Q calibration correction, beamforming and other data processing and conditioning. Next, in step <NUM>, further processing of the FM data, including complex FFT, is performed. Those of ordinary skill in the art will recognize the operations in steps <NUM>, <NUM> and <NUM> as traditional radar processing operations whose purpose is to provide Doppler radar detections. The operations in step <NUM> condition the radar data in preparation for the FFT operation in step <NUM>. The operations in step <NUM> provide an array of bins containing complex-valued Doppler signals and convert them to real-valued Doppler detection magnitudes. Those of ordinary skill in the art will recognize the array of bins is indexed by the range-plus-velocity (RV) of detected clutter in the radar data, where velocities are measured radially with respect to the radar transmitter/receiver. In step <NUM>, weighting is performed on the data in each RV bin. In some exemplary embodiments, data from certain predetermined RV bins is emphasized by weighting, and data from other predetermined RV bins is deemphasized by weighting. For example, in some exemplary embodiments, data from low-valued RV bins are deemphasized by weighting, and data from high-valued RV bins are emphasized by weighting. The conditioned RV data, including weighted Doppler radar detections in an array of RV bins, is forwarded to clutter detection <NUM>.

<FIG> includes a logical flow diagram of steps in clutter detection <NUM> illustrated in <FIG>, according to some exemplary embodiments. Referring to <FIG>, the conditioned RV data is received at the three independent analyses described herein, namely, the immediate detection analysis, indicated by line <NUM>, the temporal averaging analysis <NUM>, and the RV averaging analysis <NUM>.

Continuing to refer to <FIG>, as described above in connection with <FIG>, for the immediate detection analysis, the sweep data at <NUM> is compared to the predetermined threshold, illustrated for two sweeps as 101c and 101d, in threshold comparison processing <NUM>. In some embodiments, a standard deviation of the sweep data is computed in a moving time window as data for successive sweeps is received. The standard deviation is compared to a predetermined threshold standard deviation. If the threshold is exceeded, then a clutter detection signal is issued and transmitted to OR processing <NUM>.

Continuing to refer to <FIG>, as described above in connection with <FIG>, the temporal averaging analysis <NUM> is sensitive to small clutter signals that are unchanging over time. The analysis maintains temporal averaged array of clutter signals at different RV bins. Each new radar sweep provides signals in an array at different RV bins, which is combined with the temporal averaged array. In some exemplary embodiments, each new array of signals is combined with the temporal averaged array to produce a fading-memory temporal average, and this average is preserved from one sweep to the next. The feedback path <NUM> indicates the preservation of the temporal average information from one radar sweep to the next radar sweep. The variation of these averages across RV bins is used to indicate the presence of a clutter object, for example, the object indicated by peaks 107a-107f in <FIG>.

In some exemplary embodiments, the variations in the average <NUM>, computed by a standard deviation of values across RV bins, can be compared to a predetermined clutter threshold in threshold comparison processing <NUM>. If the threshold is exceeded, then a clutter detection signal is issued and transmitted to OR processing <NUM>.

Continuing to refer to <FIG>, as described above in connection with <FIG>, the RV averaging analysis <NUM> and <NUM> is sensitive to radar returns that change strength over time, even in the absence of distinctly identifiable clutter objects. The Doppler signals from a set of RV bins are averaged, and the averaged data 105a, referred to herein as the RV average, is observed over many sweeps to identify variations over time. Over time, these RV averages 105b are maintained in memory, referred to herein as temporal stack <NUM>. Over time, returns for each new sweep are averaged over the set of RV bins, and the RV average is appended to the stack. In some exemplary embodiments, this stack is maintained in a first-in-first-out (FIFO) configuration such that, after the stack is full at a predetermined number of sweeps, e.g., <NUM> sweeps, as each new sweep is received, the RV average is appended to the stack, and the RV average from the oldest sweep is removed from the stack. The feedback path <NUM> indicates the preservation of the temporal stack information from one radar sweep to the next radar sweep. The stack of RV averages is analyzed for temporal variability. A standard deviation measuring variability can be computed across the temporal stack and can be compared to a predetermined threshold in threshold comparison processing <NUM>. If the threshold is exceeded, then a clutter detection signal is issued and transmitted to OR processing <NUM>.

OR processing <NUM> receives signals indicative of indications generated by immediate detection analysis, temporal averaging analysis and RV averaging analysis. If any of these indications is active/true, then OR processing generates an active/true clutter signal.

In general, if any of the analyses described herein results in a detection clutter detection, then it can be concluded from the results of the OR processing <NUM> that the sensor is not blocked. However, according to the present disclosure, the blockage or non-blockage conclusion is determined based on reduction or elimination of errors in the conclusion, using blockage detection logic <NUM>. <FIG> includes a logical flow diagram of steps in blockage detection logic <NUM> illustrated in <FIG>, according to some exemplary embodiments.

Referring to <FIG>, the clutter signal is received at a decision block <NUM>. If the clutter signal is low, i.e., inactive or false, then clutter is not detected, and a low count is incremented in step <NUM>. To increase confidence in a blockage conclusion in the absence of clutter detections, a predetermined minimum number of cycles, i.e., sweeps, without a clutter detection is required before a notification of sensor blockage is issued. To that end, in decision block <NUM>, a determination is made as to whether the minimum number of cycles without a clutter detection has been reached. In the particular exemplary embodiment illustrated in <FIG>, the minimum number of cycles is <NUM>. It will be understood that other minimums can be selected. If the minimum has not been reached, then flow returns to decision block <NUM>, where the next sweep is analyzed. If the minimum has been reached, then a sensor blockage is indicated in step <NUM>.

In decision block <NUM>, if the clutter signal is high, i.e., active or true, then clutter is detected, and a high count is incremented in step <NUM>. To increase confidence in a non-blockage conclusion in the presence of clutter detections, a predetermined minimum number of cycles, i.e., sweeps, with a clutter detection present is required before a notification of sensor non-blockage is issued. To that end, in decision block <NUM>, a determination is made as to whether the minimum number of cycles with a clutter detection has been reached. In the particular exemplary embodiment illustrated in <FIG>, the minimum number of cycles is two. It will be understood that other minimums can be selected. If the minimum has not been reached, then flow returns to decision block <NUM>, where the next sweep is analyzed. If the minimum has been reached, then a sensor non-blockage is indicated in step <NUM>.

In the exemplary embodiment illustrated in <FIG>, a hysteresis characteristic of the blockage and non-blockage notifications is included. In general, under the hysteresis feature processing <NUM>, a new notification state, i.e., blockage or non-blockage, must be maintained for a predetermined period of time before the notification state can be toggled again. In some exemplary embodiments, that predetermined period of time can be set at approximately <NUM> seconds. Other periods of time can be used. A timer in hysteresis feature processing <NUM> checks the timer to determine whether the predetermined hysteresis time period has expired. When blockage or non-blockage notifications are issued in blocks <NUM> and <NUM>, respectively, if the hysteresis timing characteristic is met, then the appropriate final blockage or non- blockage notification is issued.

<FIG> include timing diagrams illustrating timing of signals associated with the radar sensor blockage detection, according to some exemplary embodiments.

Specifically, <FIG> illustrates exemplary timing waveforms for a clutter detection signal generated according to immediate detection threshold comparison processing <NUM>, a clutter detection signal generated according to temporal averaging threshold comparison processing <NUM>, a clutter detection signal generated according to RV averaging threshold comparison processing <NUM>, and the resulting "OR'ed" clutter signal from OR processing <NUM>. <FIG> illustrates exemplary timing waveforms for the "OR'ed" clutter signal from OR processing <NUM>, the low count generated in step <NUM> of <FIG>, the high count generated in step <NUM> of <FIG>, and the blockage notification signal generated according to the present disclosure.

Hence, according to the embodiments, multiple averaging approaches to clutter detection are used to detect low-amplitude clutter objects that would otherwise be hidden below the detection threshold. With two or more approaches, the approach provides the flexibility to set thresholds independently for each approach to respond to different types of clutter. Since different averaging approaches are sensitive to different types of clutter, the independent thresholds can be raised to minimize false clutter detections in blocked situations.

<FIG> includes a schematic perspective view of an automobile <NUM>, equipped with one or more radar systems <NUM>, including one or more radar sensor modules <NUM>, described herein in detail, according to exemplary embodiments. Referring to <FIG>, it should be noted that, although only a single radar sensor module <NUM> is illustrated, it will be understood that multiple radar sensor modules <NUM> according to the exemplary embodiments can be used in automobile <NUM>. Also, for simplicity of illustration, radar sensor module <NUM> is illustrated as being mounted on or in the front section of automobile <NUM>. It will also be understood that one or more radar sensor modules <NUM> can be mounted at various locations on automobile <NUM>, including at the rear of automobile <NUM>.

<FIG> includes a schematic top view of automobile <NUM> equipped with two radar sensor modules <NUM>, as described above in detail, according to exemplary embodiments. In the particular embodiments illustrated in <FIG>, a first radar sensor module <NUM> is connected via a bus <NUM>, which in some embodiments can be a standard automotive controller area network (CAN) bus, to a first CAN bus electronic control unit (ECU) 58A. Detections generated by the processing described herein in detail in radar sensor module <NUM> can be reported to ECU 58A, which processes the detections and can provide detection alerts via CAN bus <NUM>. Similarly, in some exemplary embodiments, a second radar sensor module <NUM> is connected via CAN bus <NUM> to a second CAN bus electronic control unit (ECU) 58B. Detections generated by the radar processing described herein in detail in radar sensor module <NUM> can be reported to ECU 58B, which processes the detections and can provide detection alerts via CAN bus <NUM>. It should be noted that this configuration is exemplary only, and that many other automobile radar system configurations within automobile <NUM> can be implemented. For example, a single ECU can be used instead of multiple ECUs. Also, the separate ECUs can be omitted altogether.

Claim 1:
A radar system (<NUM>) in a movable host system, the radar system comprising:
a radar detector (<NUM>) for transmitting radar signals into a region over a plurality of sweeps, detecting reflected returning radar signals for each of the plurality of sweeps, and converting the reflected returning radar signals into digital data signals; and
a processor (<NUM>) for receiving the digital data signals and processing the digital data signals to detect environmental clutter objects in the region,
characterized in that
the processing comprises at least
(i) an immediate detection process by which the digital data signals are compared to a clutter threshold and a first signal indicative of presence of a first clutter object is generated if the digital data signals exceed the clutter threshold,
(ii) a time-averaging process by which data for each of a plurality of range-plus-velocity (RV) bins is analyzed over multiple sweeps to generate a second signal indicative of presence of a second clutter object, and
(iii) an RV-averaging process independent of the time-averaging process by which data for a plurality of RV values within each sweep are combined to form RV averages for each sweep and the RV averages for a plurality of sweeps are analyzed over multiple sweeps to generate a third signal indicative of presence of a third clutter object, wherein
the processor applies the first, second and third signals to a logical OR process to generate a fourth signal indicating that the radar detector is not blocked if any of the first, second or third clutter objects is present.