A vehicle radar system arranged for reducing interference

DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to a vehicle radar system comprising at least one transceiver arrangement arranged to generate and transmit radar signals, and to receive reflected radar signals. The transceiver arrangement comprises an ADC (Analogue to Digital Converter) arrangement that is arranged to output a digital IF (Intermediate Freguency) signal in a time domain to a DSP (Digital Signal Processor) arrangement.

Many vehicle radar systems comprise radar transceivers that are arranged for generating radar signals that are transmitted, reflected and received by means of appropriate antennas comprised in the radar system. The radar signals may for example be in the form of FMCW (Freguency Modulated Continuous Wave) signals where freguency chirps signals are formed in a well-known manner.

In a multi-radar environment, other radars can create interference with each other when the freguency chirps cross, or come close to each other. This exhibits itself as a burst of interference somewhere within the received signal during one or more of the chirp signals. This problem becomes apparent when the received analogue signal has been converted to a digital signal and typically is processed by the radar system using one or more FFT (Fast Fourier Transform) processing steps which converts the digital time domain into a freguency domain.

If the interference is present in one or more of the chirp signals, the noise floor will be raised since the noise is spread across all freguencies. This raising of the noise floor has the effect of reducing the range of the radar, which of course is undesirable.

EP 1672379 describes identifying a block of digital samples that has elevated noise levels, and deleting that block. However, this has a negative effect of also raising the noise floor by the creation of sidelobes following the FFT processing . US 6191726 describes removing interference after converting the digital signals to the freguency domain and filtering using an FIR (Finite Impulse Response) filter. However, this approach also has the effect of damaging the desired signal. Us 2015/0260828 describes using interpolation for removing interference. However, a more accurate result is desired.

It is therefore desired to provide a vehicle radar system that is able to provide removal of interference that provides more accurate results than described previously.

The object of the present disclosure is thus to provide a vehicle radar system that is able to provide removal of interference that provides more accurate results than described previously.

This object is achieved by means of a vehicle radar system comprising at least one transceiver arrangement arranged to generate and transmit radar signals, and to receive reflected radar signals, where the transmitted radar signals have been reflected by one or more objects. The transceiver arrangement) comprises an ADC (Analogue to Digital Converter) arrangement that is arranged to output a digital IF (Intermediate Freguency) signal in a time domain to a DSP (Digital Signal Processor) arrangement that is adapted for radar signal processing . first DSP function is arranged to:

- Identify and retain sample points of the digital IF signal in a spectral domain with signal components that exceed a certain level threshold, such that an approximation signal is formed in the time domain.

- Identify possible sections of the digital IF signal in the time domain that exhibit interference exceeding an interference threshold.

- Determine whether or not to replace such sections with eguivalent sections of the approximation signal.

- If applicable, replace such sections with eguivalent sections of the approximation signal.

This object is also achieved by means of a method for a radar system, where the method comprises:

Generating and transmitting radar signals.

Receiving reflected radar signals, where the transmitted radar signals have been reflected by one or more objects.

Outputting a digital IF (Intermediate Freguency) signal in a time domain.

Identifying and retaining sample points of the digital IF signal in a spectral domain with signal components that exceed a certain level threshold, such that an approximation signal is formed in the time domain.

Identifying possible sections of the digital IF signal in the time domain that exhibit interference exceeding an interference threshold.

Determining whether or not to replace such sections with eguivalent sections of the approximation signal.

If applicable, replacing such sections with eguivalent sections of the approximation signal. According to an example, the first DSP function is arranged to set all other sample points to zero when the approximation signal is formed.

According to another example, the first DSP function comprises an FFT (Fast Fourier Transform) module, a threshold module, an inverse FFT module, an approximation module and a detection and repair module .

The FFT module is arranged to transform the digital IF signal to the spectral domain.

The threshold module is arranged to identify and retain sample points with signal components that exceed a certain level threshold, while all other sample points are set to zero.

The inverse FFT module is arranged to transform a spectral repair signal output from the threshold module to the time domain .

The approximation module is arranged to output an approximation signal

The detection and repair module is arranged to identify possible sections of the digital IF signal that exhibit interference exceeding an interference threshold, to determine whether or not to replace such sections with eguivalent sections of the approximation signal, and, if applicable, to replace such sections with eguivalent sections of the approximation signal.

Other examples are disclosed in the dependent claims.

A number of advantages are obtained by means of the present disclosure. Mainly, a vehicle radar system is provided that is able to provide removal of interference such that the interference level after FFT processing is at a lower level than previously. This results in reduced range reduction of the radar system due to the overlap of signals. Further, the removal of interference reduces the potential for false targets being found at the target identification stage. BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described more in detail with reference to the appended drawings, where:

Figure 1 shows a schematic top view of a vehicle;

Figure 2 shows a simplified schematic of a vehicle radar system;

Figure 3 shows an example of an FMCW chirp signal;

Figure 4 shows a simplified schematic of a first DSP function that is arranged for interference removal;

Figure 5 shows three graphs of digital IF signals; and

Figure 6 shows a flowchart for methods according to the present disclosure.

DETAILED DESCRIPTION

Figure 1 schematically shows a top view of a vehicle 1 arranged to run on a road 2 in a direction D, where the vehicle 1 comprises a vehicle radar system 3 which is arranged to distinguish and/or resolve single targets from the surroundings by transmitting signals 4 and receiving reflected signals 5 and using a Doppler effect in a previously well- known manner.

The vehicle radar system 3 thus comprises a radar transceiver arrangement 7 and is arranged to provide azimuth angle, radial velocity of possible target objects 6 by simultaneously sampling and analyzing phase and amplitude of the received signals 5. The distance to said target objects 6 is according to some aspect also acguired. The radar signals may for example be in the form of FMCW (Freguency Modulated Continuous Wave) Doppler signals operating at 77 GHz, so-called chirp signals .

With reference also to Figure 2, the vehicle radar system 3 comprises a transceiver arrangement 7 that is arranged for generating and transmitting sweep signals in the form of FMCW chirp signals 4, and to receive reflected signals 5, where the transmitted chirp signals 4 have been reflected by an object 6.

The transceiver arrangement 7 comprises a transmitter 8 with a transmit antenna arrangement 14, a receiver 9 with a receiver antenna arrangement 16, an Analog to Digital Converter (ADC) arrangement 10 and sampling and timing arrangement 11.

As shown in Figure 3, a transmitted chirp signal 4 is in the form of a continuous sinusoid where the output freguency F _ou t varies from a first freguency f start to a second freguency f _s to _P over the course of a ramp r, where each chirp signal 4 comprises repeating cycles of a plurality of freguency ramps r. There the magnitude of the first freguency f start falls below the magnitude of the second freguency f _s to _P .

A cycle for a chirp signal 4 lasts for a certain cycle time t _c , each ramp r lasts a certain ramp time t _r , having a ramp period time tT. Between two consecutive ramps of the chirp signal 4 there is a delay time tD. Referring back to Figure 2, the reflected signals 5 are received by the receiver 9 via the receiver antenna arrangement 16. The received signals 5, thus constituted by reflected radar echoes, are then mixed with the transmitted chirp signals 4 in the receiver 9. This may be a single channel mixer, or a two channel mixer comprising both in-phase and guadrature components. In this way, an IF (Intermediate Freguency) signal 17 is acguired, which may be real or, in the case of guadrature mixer, imaginary. The IF signal 17 is filtered in an IF filter 18 such that a filtered IF signal 19 is acguired.

The difference freguency of the filtered IF signal 19 relates to the target distance and is transferred to the corresponding ADC arrangement 10, where the filtered IF signal 19 is sampled at a certain predetermined sampling freguency f _s and converted to a digital IF signal 20 comprising sample points in a previously known manner, the sampling freguency f _s being provided in the form of a sampling and timing signal 21 produced by the sampling and timing arrangement 11 that is connected to the ADC arrangement 10.

The ADC arrangement 10 is connected to a DSP arrangement 12 that is adapted for radar signal processing in first DSP function 12a and a second DSP function 12b.

According to the present disclosure, with reference also to Figure 4, the first DSP function 12a is arranged for signal repair and comprises an FFT (Fast Fourier Transform) module 27, a threshold module 28, an inverse FFT module 29, a buffer module 30 for storing the approximation signal and a detection and repair module 31. As indicated with dashed lines, the first DSP function 12a optionally comprises a first optional pre-processing module 32. The optional pre-processing module 32 will be discussed more later. The detection and repair module 31 is arranged to detect the samples that have incurred interference and this may be accomplished by using a high pass filter and threshold detection process.

The input digital IF signal 20 is transformed to a freguency domain by the FFT module 27, and the acguired digital spectral signal 34 is processed in the threshold module 28. The threshold module 28 is arranged to identify and retain sample points with signal components that exceed a certain level threshold, while all other sample points are set to zero . The threshold module 28 is arranged to output a spectral repair signal 35 that is fed into the inverse FFT module 29 that is arranged to transform the spectral repair signal 35 back to the time domain. A resulting output repair signal 45 is fed into the buffer module 30 that is arranged to output an approximation signal 36 that is fed into the detection and repair module 31. The buffer module 30 comprises a storage buffer and is arranged to enable a necessary block, or necessary blocks, of the signal to be replaced in the detection and repair module 31.

The input digital IF signal 20 is also fed directly into the detection and repair module 31. The detection and repair module 31 is arranged to identify possible sections of the digital IF signal 20 that exhibit interference exceeding an interference threshold, and to determine whether or not to replace such sections with eguivalent sections of the approximation signal 36 that is available from the buffer module 30. The detection and repair module 31 is arranged to output a repaired digital IF signal 20' to the second DSP function 12b that is adapted for radar signal processing, for example by means of a windowing and range FFT function to convert the digital IF signal 20 to a range domain, and a Doppler FFT to combine the results from successive chirp signal ramps, or other suitable Doppler radar cycles, into the Doppler domain. This results in an output 44 comprising Range-Doppler matrices that are transferred for further processing, which is not further discussed here, many examples of such further processing being well-known in the art.

The second DSP function 12b is well-known and its functionality is well-known in the art and is therefore described in less detail than the first DSP function 12a. The first DSP function 12a and the second DSP function 12b may very well be practically implemented in one and the same signal processor arrangement in the DSP arrangement 12, or, alternatively, in different signal processor arrangements in the DSP arrangement 12.

More in detail, the digital spectral signal 34 is constituted by a complex vector that represents the targets at amplitude peaks, where each amplitude peak position corresponds to the freguency (or range) . Without interference, the amplitude level of the digital spectral signal 34 between the amplitude peaks will be low, corresponding to a noise floor. However, when bursts of interference occur in the time domain, the noise floor rises up, thus hiding the weaker targets that were detectable previously. The larger targets, still having amplitude that exceeds the amplitude of the noise floor, are still detectable. The complex vector of the digital spectral signal 34 is used to identify the largest targets, i.e. the signal components that have an amplitude level that exceeds said certain level threshold. All parts between these signal components are set to zero, mainly containing noise.

Then, after the inverse FFT, the acguired output repair signal 45 only contains information of the largest targets, and thus lacks information about the smaller targets. Therefore, the detection and repair module 31 is arranged to keep as much of the original digital IF signal 20 as possible, since it contain the signal from the smaller targets as well. But where the digital IF signal 20 is determined to contain interference, this section of the digital IF signal 20 is deleted and the eguivalent signal section from the approximation signal 36 is inserted instead to form the repaired digital IF signal 20' . There may be an additional smoothing within the detection and repair module 31 that is arranged to remove any discontinuities in sections of the signal bordering the transition from original signal to replaced signal but this is not essential.

This means that when the processing starts at the second DSP function 12b, most targets are present in the repaired digital IF signal 20' . Only in those sections that are determined to contain interference, there is only information about the larger targets, so the energy/information about the smaller targets is slightly reduced, but they end up being much more present than when the noise burst is left in the original digital IF signal 20, without repair. As mentioned previously, those sections of the digital IF signal 20 that are determined to contain interference are those that are determined to exhibit interference exceeding an interference threshold, This is illustrated in Figure 5, where three graphs 39, 40, 41 are shown, all graphs 39, 40, 41 showing amplitude A on their y-axis and time t on their x-axis. A first graph 39 shows the original digital IF signal 20 with a period of interference 37. A second graph 40 shows the approximation signal 36, and a third graph 41 shows the repaired digital IF signal 20' where the period of interference 37 from the first graph has been removed and the eguivalent signal section 38 from the approximation signal 36 has been inserted instead.

The repaired digital IF signal 20' thus comprises the original digital IF signal 20 without the deleted portions, and the eguivalent portions of the approximation signal 36 are inserted instead of the deleted portions . Only one such deleted portion 37 is shown in the example with reference to Figure 5, but in practice each radar cycle may comprise one or more such portions that may have originated from one or more external interference sources . As indicated in Figure 1, the vehicle 1 comprises a safety control unit 42 and safety means 43, for example an emergency braking system and/or an alarm signal device. The safety control unit 42 is arranged to control the safety means 43 in dependence of input from the radar system 3. According to an aspect, the output 44 of the second DSP function 12b constitutes input to the safety control unit 42.

According to Figure 6, the present disclosure relates to a method comprising:

46: Generating and transmitting radar signals 4.

47: Receiving reflected radar signals 5, where the transmitted radar signals 4 have been reflected by one or more objects 6. 48: Outputting a digital IF signal 20 in a time domain. 49: Identifying and retaining sample points of the digital IF signal 20 in a spectral domain with signal components that exceed a certain level threshold such that an approximation signal 36 is formed in the time domain.

51: Identifying possible sections 37 of the digital IF signal 20 in the time domain that exhibit interference exceeding an interference threshold.

52: Determining whether or not to replace such sections 37 with eguivalent sections 38 of the approximation signal 36. 53: If applicable, replacing such sections 37 with eguivalent sections 38 of the approximation signal 36.

According to an example, the method comprises:

50: Setting all other sample points to zero when forming the approximation signal 36.

For the above method, the digital IF signal 20 in the time domain is processed in a parallel manner; one part is processed such that the approximation signal 36 is formed in the time domain, and one part is examined for possible interference sections, where parts of the approximation signal 36 is used to replace such interference sections where applicable. The result is a repaired digital IF signal 20' . The present disclosure is not limited to the examples above, but may vary freely within the scope of the appended claims. For example, the radar system may be implemented in any type of vehicle such as cars, trucks, buses, boats and aircraft as well as fixed radars such as those monitoring traffic flow, marine environments, aircraft landing or presence of pedestrians .

The radar transceiver 7 is adapted for any suitable type of Doppler radar. There may be any number of radar transceivers 7 in the vehicle radar system 3, and they may be arranged for transmission and signals in any suitable direction. The plurality of sensing sectors or sensing bins may thus be directed in other desirable directions, such as rearwards or at the sides of the vehicle 1.

If the digital IF signal 20 is determined to not contain any interference and/or it is determined to not replace sections of the digital IF signal 20 with the approximation signal 36, the repaired digital IF signal 20' is identical to the digital IF signal 20. The term "repaired" does in this context not indicate that an actual reparation has occurred, but that a reparation has been possible. The FFT module 27 and the inverse FFT module 29 may be comprised in one and the same FFT calculation module. According to some aspects, the inverse FFT module 29 is arranged for a discrete inverse FFT that only provides the necessary signal estimation sample points as instructed by the detection and repair module 31, thus avoiding the need for a full inverse FFT. The range FFT and Doppler FFT described may be performed in any suitable FFT calculation module.

The ADC arrangement 10 and DSP arrangement 12 should be interpreted as having a corresponding ADC and DSP functionality, and may each be constituted by a plurality of separate components. Alternatively, each ADC arrangement may be comprised in one ADC chip, and each DSP arrangement may be comprised in one DSP chip, or even combined in one common chip .

According to an aspect, each antenna arrangement 14, 16 comprises one or more antennas, where each antenna may be constituted by one antenna element or by an array of antenna elements. The number of antenna arrangements, antennas within each antenna arrangement, IF signals and corresponding receiver (RX) channels may vary. According to an aspect, this means that if a radar system 3 such as the one described above comprises a plurality of simultaneous parallel receiver (RX) channels, these enable estimation of target azimuth angle. In such cases, it is possible to analyze the signal of only one RX channel in order to identify which ADC samples that have suffered the interference .

Since the other RX channels are sampled simultaneously, the same ADC block of ADC samples during a radar cycle will suffer interference. This can be used to simplify the processing.

The FFT module 27, which is arranged for transforming the digital IF signal 20 to the freguency domain, is according to some aspects also able to operate more efficiently when analyzing multiple RX channels in parallel, since the signal on each channel would typically comprise targets of similar ranges. The important differences between the RX channels would be the amplitude and phase of the signal at certain ranges. Therefore having performed a full FFT on a first channel, and the peak search in the threshold module 28, it may be possible to perform a discrete Fourier Transform at only the spectral freguencies identified from the first channel for all subseguent channels . If the ADC signal is real, according to some aspect, the inverse FFT module 29 is arranged for an inverse discrete cosine transform. This is particularly appealing if the number of samples suffering interference is small compared to the total length of the ADC samples of a radar cycle. According to an aspect, the optional pre-processing module 32 is arranged to reduce the noise floor in a first stage. This could be performed by multiplying the signal by 2 ^Λ Ν and discarding the overflow bits, such that the interference would appear clipped but the original signal is unchanged. Alternatively, the replacement module 31 could be arranged to replace the interference samples with value 0. The pre ^¬ processing module 32 has the benefit of lowering the noise floor slightly at the digital spectral signal 34 such that the threshold applied at the threshold module 28 could be lower, and the approximation signal 36 could comprise weaker targets.

According to some aspects, when forming the approximation signal 36, it is not necessary to set all other sample points to zero when sample points of the digital IF signal 20 in a spectral domain with signal components that exceed a certain level threshold have been identified and retained. This is due to that since the interference zones are identified, they do not need to set to be zero.

The vehicle radar system 3 according to the above is thus arranged to operate in the presence of external interference sources using a certain signal repair procedure in accordance with the present disclosure. The signal repair procedure comprises detecting the sections of the ADC signal that have incurred the interference, and replacing just those sections with an approximation signal, maintaining small target information with minimal side-lobe creation. The approximation signal is derived using an FFT process on the original signal and removing interference manually by a thresholding technigue . Generally, the present disclosure relates to a vehicle radar system 3 comprising at least one transceiver arrangement 7 arranged to generate and transmit radar signals 4, and to receive reflected radar signals 5, where the transmitted radar signals 4 have been reflected by one or more objects 6, where the transceiver arrangement 7 comprises an ADC (Analogue to Digital Converter) arrangement 10 that is arranged to output a digital IF (Intermediate Freguency) signal 20 in a time domain to a DSP (Digital Signal Processor) arrangement 12 that is adapted for radar signal processing. A first DSP function 12a is arranged to:

- identify and retain sample points of the digital IF signal 20 in a spectral domain with signal components that exceed a certain level threshold, such that an approximation signal 36 is formed in the time domain,

- identify possible sections 37 of the digital IF signal 20 in the time domain that exhibit interference exceeding an interference threshold,

- determine whether or not to replace such sections 37 with eguivalent sections 38 of the approximation signal 36, and

- if applicable, replace such sections 37 with eguivalent sections 38 of the approximation signal 36. According to an example, the first DSP function 12a is arranged to set all other sample points to zero when the approximation signal 36 is formed.

According to an example, the first DSP function 12a comprises an FFT (Fast Fourier Transform) module 27, a threshold module 28, an inverse FFT module 29, an approximation module 30 and a detection and repair module 31, where:

- the FFT module 27 is arranged to transform the digital IF signal 20 from the time domain to the spectral domain, - the threshold module 28 is arranged to identify and retain sample points with signal components that exceed a certain level threshold, while all other sample points are set to zero,

- the inverse FFT module 29 is arranged to transform a spectral repair signal 35 output from the threshold module 28 to the time domain,

- the approximation module 30 is arranged to output an approximation signal 36, and

- the detection and repair module 31 is arranged to identify possible sections 37 of the digital IF signal 20 in the time domain that exhibit interference exceeding an interference threshold, to determine whether or not to replace such sections 37 with eguivalent sections 38 of the approximation signal 36, and, if applicable, to replace such sections 37 with eguivalent sections 38 of the approximation signal 36.

According to an example, the detection and repair module 31 is arranged to output a repaired digital IF signal 20' to a second DSP function 12b that is adapted for radar signal processing by means of a range FFT to convert the repaired digital IF signal 20' to a range domain, and a Doppler FFT to combine the results from successive Doppler radar cycles into the Doppler domain.

According to an example, the radar system 3 comprises a plurality of simultaneous parallel receiver channels, where the radar system 3 is arranged to identify possible sections 37 of the digital IF signal 20 in the time domain that exhibit interference exceeding an interference threshold for only one receiver channel. Generally, the present disclosure also relates to a method for a radar system 3, where the method comprises:

46: generating and transmitting radar signals 4;

47: receiving reflected radar signals 5, where the transmitted radar signals 4 have been reflected by one or more objects 6; and

48: outputting a digital IF (Intermediate Freguency) signal 20 in a time domain;

49: identifying and retaining sample points of the digital IF signal 20 in a spectral domain with signal components that exceed a certain level threshold, such that an approximation signal 36 is formed in the time domain;

51: identifying possible sections 37 of the digital IF signal 20 in the time domain that exhibit interference exceeding an interference threshold,

52: determining whether or not to replace such sections 37 with eguivalent sections 38 of the approximation signal 36, and

53: if applicable, replacing such sections 37 with eguivalent sections 38 of the approximation signal 36.

According to an example, the method comprises:

50: setting all other sample points to zero when forming the approximation signal 36.

According to an example, the method further comprises outputting a repaired digital IF signal 20' for radar signal processing by converting the repaired digital IF signal 20' to a range domain, and combining the results from successive Doppler radar cycles into the Doppler domain.

According to an example, the method comprises identifying possible sections 37 of the digital IF signal 20 in the time domain that exhibit interference exceeding an interference threshold for only one receiver channel where the radar system 3 uses a plurality of simultaneous parallel receiver channels.