Patent Description:
A new class of safety systems, referred to as advanced driver assistance systems (ADAS), has been introduced into automobiles to reduce human operation error. These systems are enabled by smart sensors based primarily on millimeter-wave automotive radars. The proliferation of such assistance systems, which may provide functionality such as rear-view facing cameras, electronic stability control, and vision-based pedestrian detection systems, has been enabled in part by improvements in microcontroller and sensor technologies. Enhanced embedded radar-based solutions are enabling complementary safety features for ADAS designers.

In an automotive radar system, one or more radar sensors may be used to detect obstacles around the vehicle and the speeds of the detected objects relative to the vehicle. A processing unit in the radar system may determine the appropriate action needed, e.g., to avoid a collision or to reduce collateral damage, based on signals generated by the radar sensors. Current automotive radar systems are capable of detecting objects and obstacles around a vehicle, the position of any detected objects and obstacles relative to the vehicle, and the speed of any detected objects and obstacles relative to the vehicle. For example, via the processing unit, the radar system may alert the vehicle driver about potential danger, prevent a collision by controlling the vehicle in a dangerous situation, take over partial control of the vehicle, or assist the driver with parking the vehicle.

Automotive radar systems are required to meet the functional safety specifications of International Standard <NUM> titled "Road Vehicles - Functional Safety. " ISO <NUM> defines functional safety as the absence of unreasonable risk caused by malfunctioning behavior of electrical/electronic systems. Functional safety in automotive radar is the prevention of harm to humans due to failure of components in the radar. For automotive radar, the radar should be known to be functioning appropriately within a fault tolerant time interval of approximately <NUM> milliseconds (ms). Thus, while the vehicle is operating, a failure in any part of the radar that would lead to a degraded signal-to-noise ratio (SNR) or false detection of presence or position of obstacles should be detected, and an appropriate response performed within approximately <NUM>. <CIT> discloses an imbalance correction of in-phase and quadrature phase return signals. <CIT> relates to a radarsensor for vehicles. <CIT> relates to a millimeter wave pulsed radar system.

In described examples, a radar system includes: a receive channel including a complex baseband; and a processor coupled to the receive channel to receive a first plurality of digital intermediate frequency (IF) samples from an in-band (I) channel of the complex baseband and a corresponding second plurality of digital IF samples from a quadrature (Q) channel of the complex baseband. The processor is configured to execute instructions to compute at least one failure metric based on the first plurality of digital IF samples and the second plurality of digital IF samples.

In at least one example, a method for failure detection in a radar system includes receiving a first plurality of digital intermediate frequency (IF) samples from an in-band (I) channel of a complex baseband of a receive channel of the radar system and a corresponding second plurality of digital IF samples from a quadrature (Q) channel of the complex baseband, computing at least one failure metric based on the first plurality of digital IF samples and the second plurality of digital IF samples, and determining whether a failure has occurred based on the at least one failure metric. The invention further relates to the following items:.

In the drawings, like elements are denoted by like reference numerals for consistency.

Example embodiments provide for functional safety monitoring in the receive channel(s) of a radar system as the radar system is used, e.g., in an operating vehicle. More specifically, in various embodiments, performance of components in each complex baseband in the radar system is monitored by computing one or more failure metrics based on signals generated in the I (in-band) channel and the Q (quadrature) channel of each complex baseband. The failure metrics are computed during normal operation of the radar system without disrupting the primary radar function. The failure metrics may be one or more of the ratio of energy of the received signals in the I channel and the Q channel of a complex baseband, the cross-correlation between the received signals in the I channel and the Q channel of a complex baseband, and the spectral content in the image band.

Embodiments are described herein in reference to frequency modulated continuous wave (FMCW) radar. An FMCW radar transmits, via one or more transmit antennas, a radio frequency (RF) frequency ramp referred to as a chirp. Further, multiple chirps may be transmitted in a unit referred to as a frame. The transmitted chirps are reflected from any objects in the field of view (FOV) of the radar and are received by one or more receive antennas. The received signal for each receive antenna is down-converted to an intermediate frequency (IF) signal and then digitized. After the digitized data for an entire frame is received, the data is processed to detect any objects in the FOV and to identify the range, velocity and angle of arrival of detected objects.

<FIG> is a block diagram of an example frequency modulated continuous wave (FMCW) radar system with a complex baseband in the receive channel. In this example, the FMCW radar system includes a local oscillator generator (LO Gen) <NUM>, a transmit channel <NUM>, a receive channel <NUM>, and a digital signal processor (DSP) <NUM>. The LO generator <NUM> is configured to generate a frequency modulated radio frequency (RF) signal for transmission via the transmit channel <NUM>. The transmit channel includes a power amplifier (PA) <NUM> coupled to the LO generator <NUM> to receive and amplify the RF signal and a transmit antenna <NUM> coupled to the PA to receive the amplified signal for transmission.

The receive channel <NUM> includes a receive antenna <NUM> to receive a reflected transmitted RF signal, a low-noise amplifier (LNA) <NUM> coupled to the receive antenna <NUM> to receive and amplify the received RF signal, and a complex baseband coupled to the LNA <NUM> to receive the amplified received RF signal. The complex baseband includes an I channel and a Q channel. Each channel includes a mixer <NUM>, <NUM> coupled to the LNA <NUM> to receive the signal. Each mixer <NUM>,<NUM> is also coupled to the LO generator <NUM> to receive the original RF signal. In particular, the mixer <NUM> in the I channel receives the signal in-phase, and the mixer <NUM> in the Q channel receives the signal ninety degrees out of phase. The mixers <NUM>, <NUM> mix the input signals to generate respective I and Q IF signals. Each mixer <NUM>, <NUM> serves as a down converter that generates an output signal with a frequency equal to the difference between the frequency of the inputs received from the LNA <NUM> and the LO generator <NUM>.

In each channel, an intermediate frequency (IF) amplifier <NUM>, <NUM> is coupled to the respective mixer <NUM>, <NUM> to receive the respective IF signal. For example, each IF amplifier <NUM>, <NUM> may include a baseband bandpass filter for filtering the IF signal and a variable gain amplifier (VGA) for amplifying the filtered IF signal. An analog-to-digital converter (ADC) <NUM>, <NUM> is coupled to each IF amplifier <NUM>, <NUM> to receive and convert respective analog I and Q IF signals to digital signals. Each ADC <NUM>, <NUM> is also coupled to a digital signal processor (DSP) <NUM> to provide the digital signals to the DSP <NUM> for FMCW radar signal processing. The DSP <NUM> may also be programmed to execute instructions implementing an embodiment of the failure detection method of <FIG>. As described in more detail in reference to <FIG>, the DSP may be used to compute one or more failure metrics using the samples received from the complex baseband. The failure metric or metrics can then be used to detect failures, if any, of components in the complex baseband.

<FIG> is a flow diagram of a method for failure detection using a complex baseband of an FMCW radar system. The method is described assuming a single complex baseband in single receive channel. For radar systems with multiple receivers, each having a complex baseband, the method may be performed for each complex baseband. Initially, digital I and Q IF samples for a frame of chirps are received <NUM> from the I and Q channels of the complex baseband. The DC (direct current) offsets of the signal from the I channel and the signal from the Q channel are then computed <NUM>. The respective DC offsets may be computed as the average of the samples from the respective channel.

An energy ratio failure metric M<NUM> is then computed <NUM>. The energy ratio failure metric is the ratio of energy of the received signals in the I channel and the Q channel. The expectation is that this failure metric should be close to unity. Some failures can be detected by checking whether this failure metric is significantly different from unity. The failure metric may be computed by <MAT> where E{. } denotes expectation, i.e., the mean squared energy of the samples from the respective I or Q channel. For example, E{|I|<NUM>} is computed by <MAT> where n is the number of I samples. E{|Q|<NUM>} is similarly computed. While not specifically shown, the respective DC offset is subtracted from each sample before this failure metric is computed.

A cross correlation failure metric M<NUM> is also computed <NUM>. The cross correlation failure metric measures the cross-correlation between the signals received in the I and Q channels. The expectation is that this failure metric should be close to zero. Some failures can be detected by checking whether this failure metric is significantly different from zero. The failure metric may be computed by <MAT> where E{|I|<NUM>} and E{|Q|<NUM>} are computed as described hereinabove, and E{IQ} is computed by <MAT> where n is the number I sample and Q samples. While not specifically shown, the respective DC offset is subtracted from each sample before this failure metric is computed.

An image band spectral content failure metric M<NUM> is also computed <NUM>. The term "image band" refers to the mirror frequency spectrum of the actual beat frequency (in-band) spectrum. In a functional FMCW radar, peaks corresponding to detected objects should exist on only one side of the spectrum. Some failures can be detected by checking for excess content in the image band. More specifically, in the absence of component failure, the image band spectrum should only include thermal noise. Thus, some failures can be detected by checking for excess or unexpected (spurious) signal content in the image band, i.e., signal content that is not representative of thermal noise. The value of this failure metric is set to indicate whether spurious content exists in the image band.

For example, the failure metric may be computed as a ratio of the energy in the image band to the thermal or overall noise level of the receive channel. Any suitable technique may be used to compute this failure metric. For example, in some embodiments, the failure metric may be computed by computing the complex fast Fourier transform (FFT) of I+jQ sample data and comparing the image band bins, i.e., the negative FFT bins, to a thermal noise energy threshold. Spurious content in the image band is indicated if any of the image band bins exceeds the threshold and the value of M<NUM> is set accordingly. In some embodiments, the failure metric may be computed by passing the complex I+jQ data through a filter to extract only the image band content and the energy of the filtered samples (containing the image band signal) is used as the metric. In this latter case, the filtered samples are compared with a thermal noise energy threshold to detect excess or unexpected signal content in the image band.

For example, the value of the thermal noise energy threshold may be determined empirically or using probability analysis calculations, such that in absence of any failure, very little chance exists that a sample including random thermal noise exceeds the threshold. The expected thermal noise level of a receive channel may be determined, such as based on production tests, by observing the ADC output samples during functional operation, or by using special calibration modes of operation in which the receive channel is operated with the transmit channel (TX) turned off, or the receive channel (RX) is operated in an internal TX-to-RX loopback test mode.

In some embodiments, the spectral content failure metric may be computed in sub-bands within the image band, thus allowing any spurious content (spikes) in the image band to be detected more accurately. Accordingly, the thermal noise in each sub-band would be smaller and hence the spurious content can be detected more easily. In such embodiments, a different thermal noise threshold may be needed for each sub-band as the amount of thermal noise in each sub-band may vary. The expected thermal noise level in each sub-band may be determined as described hereinabove for the entire image band.

Interference from another radar, e.g., the radar of an on-coming vehicle, can also cause failure detection when using the image band spectral content failure metric. This may be desired or undesired, depending on the application. If the presence of interference is to be treated as detection of a failure failure, then the image band spectral content failure metric can be used without modification. However, if only a permanent failure in the receive chain circuitry should be treated as detection of a failure, then the image band spectral content metric should be conditionally ignored whenever presence of interference from another radar is suspected. Such interference from another radar is typically a transient phenomenon, affecting only a few samples in a chirp. For example, the presence of interference can be detected as a temporary spike in the time domain I and Q samples received. Also, for example, a temporary spike in the time domain samples may be determined as a function of the root mean square (also referred to as the quadratic mean) of either the I or Q time domain samples. If interference is detected, the image band spectral content failure metric may be ignored. For example, the failure metric M<NUM> may be set to indicate no spurious content, even if the metric computation indicated spurious content.

Interference from another radar should affect both the I channel and Q channel similarly. In some embodiments, if interference is detected in the time domain samples, the time domain samples corresponding to the temporary spike in each of the I channel and the Q channel may be compared to a spike detection threshold. If one channel shows a spike and the other does not, then a failure of the complex baseband may be indicated, e.g., the failure metric M<NUM> may be set to indicate spurious content despite the fact interference was detected. For example, the value of the spike detection threshold may be determined empirically or using probability analysis calculations, such that in absence of any failure, very little chance exists that a sample exceeds the threshold.

Referring to <FIG>, after the failure metrics are computed, the failure metrics are used to determine <NUM> whether a failure has occurred in the complex baseband. For example, the energy ratio failure metric M<NUM> may be compared to a threshold to determine if the metric is sufficiently close to unity. Similarly, the cross correlation failure metric M<NUM> may be compared to a threshold to determine if the metric is sufficiently close to zero. For example, each threshold may be determined empirically or using probability analysis calculations, such that in absence of any failure, little chance exists that the corresponding metric exceeds the threshold. Further, the value of the image band spectral content failure metric M<NUM> may checked to see if spurious content was detected in the image band. If any one of these failure metrics indicates a failure, then a failure of the radar system has occurred.

The method described hereinabove is executed during normal operation of the radar system. Given that the complex baseband(s) of the radar system are operating correctly, the failure metrics confirm absence of failures (of the types the failure metrics are designed to detect). Further, the failure metrics are robust to various normal operating conditions. For example, if no objects are in the FOV of the radar system, the received signal will be thermal noise, which for a correctly operating radar system (after compensating for any IQ mismatch) will satisfy M<NUM> ≅ <NUM> and M<NUM> ≅ <NUM> and M<NUM> will show no spurious spectral content. In another example, if one or more objects are in the FOV of the radar system, the received signal will contain beat frequency tone(s) corresponding to the object or objects, which should be on one side of the complex baseband spectrum. A correctly operating radar system (after compensating for any IQ mismatch) will satisfy M<NUM> ≅ <NUM> and M<NUM> ≅ <NUM> and M<NUM> will show no spurious spectral content.

Tables <NUM>-<NUM> illustrate the simulated results of using the failure metrics in four example failure cases in four example scenarios. Table <NUM> illustrates simulated failure detection results for each failure metric when a gain drop (failure) occurs in an I channel by <NUM> dB, using a threshold of 2dB for M<NUM>. Table <NUM> illustrates simulated failure detection results for each failure metric when a phase change (failure) occurs in a Q channel by <NUM> degrees. Table <NUM> illustrates simulated failure detection results for each failure metric when a Q channel fails such that only noise is coming out of the channel at a level similar to the thermal noise level. Table <NUM> illustrates simulated failure detection results when a Q channel fails such that only noise is coming out of the channel at a level similar to the I channel overall power (signal + noise).

<FIG> is a block diagram of an example frequency modulated continuous wave (FMCW) radar system <NUM> configured to perform failure detection using the complex basebands of the receive channels of the radar system during normal operation in a vehicle. The example FMCW radar system <NUM> includes a radar system-on-a-chip (SOC) <NUM>, a processing unit <NUM>, and a network interface <NUM>. An example architecture of the radar SOC <NUM> is described in reference to <FIG>.

The radar SOC <NUM> is coupled to the processing unit <NUM> via a high speed serial interface. In another embodiment, the processing unit <NUM> may be integrated inside the radar SOC <NUM>. As described in more detail in reference to <FIG>, the radar SOC <NUM> includes multiple receive channels, each having a complex baseband that generates a pair of digital I and Q IF signals (alternatively referred to as dechirped signals, beat signals, or raw radar signals) that are provided to the processing unit <NUM> via the high speed serial interface.

The processing unit <NUM> includes functionality to perform radar signal processing, such as processing the received radar signals to determine distance, velocity and angle of any detected objects. The processing unit <NUM> may also include functionality to perform post processing of the information about the detected objects, such as tracking objects and determining rate and direction of movement. Further, the processing unit <NUM> includes functionality to perform failure detection using each pair of digital I and Q IF signals. More specifically, the processing unit <NUM> includes functionality to compute one or more of the metrics described hereinabove, according to an embodiment of the method of <FIG> for each complex baseband in the radar SOC <NUM> based on the digital I and Q IF signals generated in the complex baseband. Further, the processing unit <NUM> includes functionality to cause a radar failure to be indicated to an operator of the vehicle via the network interface <NUM> based on the computed metric(s).

The processing unit <NUM> may include any suitable processor or combination of processors as needed for the processing throughput of the application using the radar data. For example, the processing unit <NUM> may include a digital signal processor (DSP), a microcontroller (MCU), an SOC combining both DSP and MCU processing, or a field programmable gate array (FPGA) and a DSP.

The processing unit <NUM> may provide control information as needed to one or more electronic control units in the vehicle via the network interface <NUM>. Electronic control unit (ECU) is a generic term for any embedded system in a vehicle that controls one or more the electrical system or subsystems in the vehicle. Example types of ECU include electronic/engine control module (ECM), power train control module (PCM), transmission control module (TCM), brake control module (BCM or EBCM), central control module (CCM), central timing module (CTM), general electronic module (GEM), body control module (BCM), and suspension control module (SCM).

The network interface <NUM> may implement any suitable protocol, such as the controller area network (CAN) protocol, the FlexRay protocol, or Ethernet protocol.

<FIG> is a block diagram of an example radar SOC <NUM>. The radar SOC <NUM> may include multiple transmit channels <NUM> for transmitting FMCW signals and multiple receive channels <NUM> for receiving the reflected transmitted signals. The transmit channels <NUM> are identical and include a power amplifier <NUM>, <NUM> to amplify the transmitted signal and antenna. A receive channel includes a suitable receiver and antenna. Further, each of the receive channels <NUM> are identical and include a low-noise amplifier (LNA) <NUM>, <NUM> to amplify the received signal coupled to a complex baseband.

Each complex baseband includes a quadrature mixer <NUM>, <NUM> to mix the signal generated by transmission generation circuitry in the SOC <NUM> with the received signal to generate analog I and Q IF signals, a pair of baseband bandpass filters <NUM>, <NUM> for filtering respective analog I and Q IF signals signal, a pair of variable gain amplifiers <NUM>, <NUM> for amplifying respective filtered analog I and Q IF signals, and a pair of analog-to-digital converters <NUM>, <NUM> for converting respective analog I and Q IF signals to digital I and Q IF signals. The quadrature mixer <NUM> serves as a down converter that generates output signals with a frequency equal to the difference between the frequency of the inputs received from the low-noise amplifier and the transmission generation circuitry, both of which are radio frequency (RF) signals. The bandpass filter, VGA, and ADC of a receive channel may be collectively referred to as a baseband chain or baseband filter chain. Further, the bandpass filter and VGA may be collectively referred to as an IF amplifier.

The receive channels <NUM> are coupled to the digital front end (DFE) component <NUM> to provide the digital I and Q IF signals to the DFE <NUM>. The DFE <NUM> may include functionality to perform decimation filtering on the digital I and Q IF signals to reduce the data transfer rate. The DFE <NUM> may also perform other operations on the digital IF signals, e.g., digital compensation of non-idealities in the receive channels, such as inter-RX gain imbalance non-ideality, inter-RX phase imbalance non-ideality and the like. The DFE <NUM> is coupled to the high speed serial interface (I/F) <NUM> to transfer decimated digital I And Q IF signals to the processing unit <NUM>.

The serial peripheral interface (SPI) <NUM> provides an interface for communication with the processing unit <NUM>. For example, the processing unit <NUM> may use the SPI <NUM> to send control information (such as timing and frequencies of chirps, output power level, and triggering of monitoring functions) to the control module <NUM>.

The control module <NUM> includes functionality to control the operation of the radar SOC <NUM>. For example, the control module <NUM> may include a buffer to store output samples of the DFE <NUM>, an FFT (fast Fourier transform) engine to compute spectral information of the buffer contents, and an MCU that executes firmware to control the operation of the radar SOC <NUM>.

The programmable timing engine <NUM> includes functionality to receive chirp parameter values for a sequence of chirps in a radar frame from the control module <NUM> and to generate chirp control signals that control the transmission and reception of the chirps in a frame based on the parameter values. For example, the chirp parameters are defined by the radar system architecture and may include a transmitter enable parameter for indicating which transmitters to enable, a chirp frequency start value, a chirp frequency slope, a chirp duration, indicators of when the transmit channels should transmit and when the DFE output digital should be collected for further radar processing, etc. One or more of these parameters may be programmable.

The radio frequency synthesizer (SYNTH) <NUM> includes functionality to generate FMCW signals for transmission based on chirp control signals from the timing engine <NUM>. In some embodiments, the SYNTH <NUM> includes a phase locked loop (PLL) with a voltage controlled oscillator (VCO).

The clock multiplier <NUM> increases the frequency of the transmission signal (LO signal) to the LO frequency of the mixers <NUM>, <NUM>. The clean-up PLL (phase locked loop) <NUM> operates to increase the frequency of the signal of an external low frequency reference clock (not shown) to the frequency of the SYNTH <NUM> and to filter the reference clock phase noise out of the clock signal.

The clock multiplier <NUM>, synthesizer <NUM>, timing generator <NUM>, and clean up PLL <NUM> are an example of transmission generation circuitry. The transmission generation circuitry generates a radio frequency (RF) signal as input to the transmit channels and as input to the quadrature mixers in the receive channels via the clock multiplier. The output of the transmission generation circuitry may be referred to as the LO (local oscillator) signal or the FMCW signal.

Example embodiments are described herein in which the metrics are computed at the frame level. In some embodiments, the metrics are computed for each chirp in a frame or for sequences of chirps in a frame.

In another example, embodiments are described herein in which all three metrics are computed. In some embodiments, one metric is computed or any two of the metrics are computed.

In another example, embodiments are described herein in which the computation of the metrics and the failure determination is performed in a processor external to a radar SOC. In some embodiments, the computation of the metrics is performed by a processor on the radar SOC, and the results are communicated to a processor external to the SOC for failure determination, and both the computation of the metrics and the failure determination are performed by a processor on the SOC, with a failure indication communicated to a processor external to the SOC.

In another example, one or more of the components in a complex baseband may differ from those described herein.

In another example, embodiments are described herein in reference to FMCW radar, but embodiments are possible for other types of radar modulation.

In another example, some embodiments are described herein in which the radar system is an embedded radar system in a vehicle, but embodiments are possible for other applications of embedded radar systems, such as surveillance and security applications, maneuvering a robot in a factory or warehouse, and industrial fluid level sensing.

In this description, method steps may be shown and/or described in a sequential fashion, but one or more of the steps shown in the drawings and/or described herein may be performed concurrently, may be combined, and/or may be performed in a different order. Accordingly, embodiments are not limited to the specific ordering of steps shown in the drawings and/or described herein.

Software instructions implementing all or portions of methods described herein may be initially stored in a computer-readable medium and loaded and executed by a processor. In some cases, the software instructions may be distributed via removable computer readable media, via a transmission path from computer readable media on another digital system, etc. Examples of computer-readable media include non-writable storage media such as read-only memory devices, writable storage media such as disks, flash memory, memory, or a combination thereof.

Claim 1:
A radar system comprising:
a receive channel (<NUM>) comprising a complex baseband; and
a processor (<NUM>) coupled to the receive channel (<NUM>) and configured to receive a first plurality of digital intermediate frequency IF samples from an in-band I channel of the complex baseband and a corresponding second plurality of digital IF samples from a quadrature Q channel of the complex baseband, wherein the processor (<NUM>) is configured to execute instructions to compute at least one failure metric a) by checking for signal content in an image band in excess of thermal noise, or b) based on a ratio of energy in the first plurality of digital IF samples and the second plurality of digital IF samples, or c) a measure of cross-correlation between the first plurality of digital IF samples and the second plurality of digital IF samples;
wherein the failure metric is computed in order to detect a functional safety failure in the radar system during normal operation of the radar system without disrupting the primary radar function.