INTERFERENCE MITIGATION IN AUTOMOTIVE RADAR SYSTEMS BY ARTIFICIAL DOPPLER MODULATION

Abstract

A method of operating an automotive radar system that includes a radar transmitter unit for transmitting radar waveforms towards a scene, a radar receiving unit for receiving radar waveforms that have been reflected by a target in the scene, and an evaluation and control unit for decoding range-Doppler information from the received waveforms. The method includes: transmitting a first sequence of radar waveforms (x.sub.Tx) and a second sequence of radar waveforms ({tilde over (x)}.sub.Tx,k) towards the scene that differs from the first transmitted sequence of radar waveforms (x.sub.Tx) by predetermined phase shifts (.sub.k) such that each radar waveform ({tilde over (x)}.sub.Tx,k) of the second sequence has a different predetermined phase shift (.sub.k). First range-Doppler information and second range-Doppler information are decoded. Deviations of the second range-Doppler information from the first range-Doppler information are compared to at least one predetermined deviation value. Based on the results of the comparing, a potential interference condition is identified.

Claims

1. A method of operating an automotive radar system for avoiding interference by other radar systems, the automotive radar system including: a radar transmitter unit that is configured to transmit radar waveforms (x.sub.Tx, {tilde over (x)}.sub.Tx,) having a radar carrier frequency towards a scene, a radar receiving unit that is configured for receiving radar waveforms (x.sub.Rx, {tilde over (x)}.sub.Rx) that have been transmitted by the radar transmitter unit and have been reflected by a target in the scene, and an evaluation and control unit that is configured for decoding range-Doppler information from the radar waveforms (x.sub.Rx, {tilde over (x)}.sub.Rx) received by the radar receiving unit, the method comprising steps of: transmitting a first sequence of radar waveforms (x.sub.Tx) towards a scene, receiving first radar waveforms (x.sub.Rx) that have been reflected by a target hit by the transmitted first sequence of radar waveforms (x.sub.Tx), decoding first range-Doppler information from the received first radar waveforms (x.sub.Rx), transmitting at least a second sequence of radar waveforms ({tilde over (x)}.sub.Tx,k) towards the scene that differs from the first transmitted sequence of radar waveforms (x.sub.Tx) by predetermined phase shifts (.sub.k) such that each radar waveform ({tilde over (x)}.sub.Tx,k) of the second sequence has a different predetermined phase shift (.sub.k), receiving second radar waveforms ({tilde over (x)}.sub.Rx,k) that have been reflected by the target hit by the transmitted second sequence of radar waveforms ({tilde over (x)}.sub.Tx,k), decoding second range-Doppler information from the received second radar waveforms ({tilde over (x)}.sub.Rx,k), comparing deviations of the second range-Doppler information from the first range-Doppler information to at least one predetermined deviation value, and based on the results of the comparing, identifying a potential interference condition.

2. The method as claimed in claim 1, wherein the predetermined phase shifts (.sub.k) are based on a Doppler frequency (f.sub.) derived from a predetermined velocity () relative to a target and the radar carrier frequency.

3. The method as claimed in claim 2, wherein the predetermined velocity () is randomly selected from a predetermined range of velocities.

4. The method as claimed in claim 1, wherein the steps of transmitting a sequence of radar waveforms include transmitting a plurality of consecutive radar waveforms (x.sub.Tx, {tilde over (x)}.sub.Tx,k) of identical duration ().

5. The method as claimed in claim 1, wherein the steps of decoding the first range-Doppler information and the second range-Doppler information comprises sorting the respective range-Doppler information into a plurality of range gates and a plurality of Doppler bins, and the step of comparing deviations comprises comparing a mutual shift between the range-Doppler information along the respective plurality of Doppler bins.

6. The method as claimed in claim 1, wherein the steps of decoding include dechirping the received radar waveforms (x.sub.Rx, {tilde over (x)}.sub.Rx,k) and carrying out either a fast Fourier transform or a correlation analysis at the dechirped radar waveforms.

7. The method as claimed in claim 1, wherein the steps of transmitting sequences of radar waveforms (x.sub.Tx, {tilde over (x)}.sub.Tx,k) towards the scene comprises transmitting frequency-modulated or phase-modulated continuous radar waves towards the scene.

8. An automotive radar system, comprising: a radar transmitter unit that is configured to transmit at least a sequence of radar waveforms (x.sub.Tx) towards a scene according to a first predetermined pattern, the radar waveforms having a radar carrier frequency, a radar receiving unit that is configured for receiving radar waveforms (x.sub.Rx) that have been transmitted by the radar transmitter unit and have been reflected by a target in the scene, an evaluation and control unit that is configured for decoding range-Doppler information from the radar waveforms (x.sub.Rx) received by the radar receiving unit, wherein the radar transmitter unit is further configured to transmit, at predetermined points in time and/or in predetermined time intervals, a sequence of radar waveforms ({tilde over (x)}.sub.Tx) according to a second predetermined pattern that differs from the first predetermined pattern by predetermined phase shifts (.sub.k) such that each radar waveform ({tilde over (x)}.sub.Tx,k) of the second sequence has a different predetermined phase shift (.sub.k), and wherein: the evaluation and control unit is configured to: decode first range-Doppler information from radar waveforms (x.sub.Rx) received after reflection of the sequence of radar waveforms (x.sub.Tx) according to the first predetermined pattern at the target, decode second range-Doppler information from radar waveforms ({tilde over (x)}.sub.Rx,k) received after reflection of the sequence of radar waveforms ({tilde over (x)}.sub.Tx,k) according to the second predetermined pattern at the target, compare deviations of the first range-Doppler information from the second range-Doppler information to at least one predetermined deviation value, and identify, based on the result of the comparison, a potential interference condition.

9. The automotive radar system as claimed in claim 8, further comprising pluralities of range gates and pluralities of Doppler bins for sorting the decoded first range-Doppler information and the decoded second range-Doppler information, wherein deviations of the first range-Doppler information from the second range-Doppler information are indicated by mutual shifting of activated positions along the pluralities of Doppler bins.

10. The automotive radar system as claimed in claim 8, wherein the radar transmitter unit and the radar receiving unit form an integral part of a transceiver unit.

11. The automotive radar system as claimed in claim 8, wherein the evaluation and control unit comprises a processor unit and a digital data memory unit to which the processor unit has data access.

12. A software module for controlling automatic execution of the method as claimed in claim 1, wherein each of the transmitting, receiving, decoding, and comparing steps to be conducted are converted into a program code of the software module, wherein the program code is implementable in a digital data memory unit of the automotive radar system or a separate control unit and is executable by a processor unit of the automotive radar system or a separate control unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

[0050] FIG. 1 schematically illustrates a configuration of an automotive radar system in accordance with the invention and targets in a scene, and

[0051] FIG. 2 is a flowchart of an embodiment of a method in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0052] FIG. 1 schematically illustrates a configuration of an automotive radar system 10 in accordance with an embodiment of the invention and targets 26, 28 of a scene. The automotive radar system 10 is designed as a frequency-modulated continuous wave (FMCW) radar system and is installable in a vehicle such as a passenger car (not shown).

[0053] The automotive radar system 10 comprises a radar transmitter unit 12, a radar receiving unit 16 and an evaluation and control unit 20 that is connected by data links to both the radar transmitter unit 12 and the radar receiving unit 16.

[0054] The radar transmitter unit 12 includes a radar transmit antenna 14 that is directed towards the scene. The radar receiving unit 16 includes a radar receiving antenna 18 that is also directed towards the scene. The radar transmit antenna 14 and the radar receiving antenna 18 are co-located in a monostatic arrangement, which is indicated in FIG. 1 by use of a combined symbol. In this specific embodiment, the radar transmitter unit 12 and the radar receiving unit 16 form an integral part of a transceiver unit. In other embodiments, the radar transmitter unit 12 and the radar receiving unit 16 may be designed as separate units. The evaluation and control unit 20 comprises a processor unit 22 and a digital data memory unit 24 to which the processor unit 22 has data access.

[0055] Controlled by the evaluation and control unit 20, the radar transmitter unit 12 is configured to transmit a sequence of radar waveforms x.sub.Tx to the scene. The sequence of radar waveforms x.sub.Tx is formed according to a first predetermined pattern, which is given by consecutively transmitted radar waveforms x.sub.Tx of a predefined duration . The individual transmitted radar waveforms x.sub.Tx have a radar carrier frequency of about 77.0 GHz that is triangle wave frequency-modulated.

[0056] The radar receiving unit 16 is configured for receiving radar waveforms that have been transmitted by the radar transmitter unit 12 and have been reflected by at least one of the targets 26, 28 in the scene. Signals generated by the radar receiving unit 16 are transferred to the evaluation and control unit 20 via the data link. The evaluation and control unit 20 is configured for decoding range-Doppler information from radar waveforms x.sub.Rx received by the radar receiving unit 16 and continually processes received radar waveform excerpts x.sub.Rx of duration . The radar receiving unit 16 comprises pluralities of range gates and pluralities of Doppler bins (not shown) for sorting the decoded range-Doppler information.

[0057] The received radar waveform excerpts x.sub.Rx are transformed in order to decode spatial information of the reflecting target 26, 28. This can formally be expressed by a mapping T(x.sub.Rx)=x.sub.a. In this specific embodiment, the transform T is given by a subsequent application of a dechirp algorithm and a fast Fourier transform (FFT). In an alternative embodiment, in which the automotive radar system may be designed as a phase-modulated continuous wave (PMCW) radar system, the transform may be given by a subsequent application of a dechirp algorithm and a correlation analysis.

[0058] In order to decode the Doppler frequency, the spatial decoding is repeated for a plurality of N times, wherein N is a power of 2 selected between 128 and 1024. That is, a sequence of transformed signals

T(x.sub.Rx,1)=x.sub.a,1;T(x.sub.Rx,2)=x.sub.a,2; . . . ;T(x.sub.Rx,N)=x.sub.a,N

is recorded for Doppler decoding.

[0059] Controlled by the evaluation and control unit 20, the radar transmitter unit 12 is configured to transmit, at predetermined points in time that are timely spaced by a multiple of N.Math., a sequence of radar waveforms {tilde over (x)}.sub.Tx,k according to a second predetermined pattern that differs from the first predetermined pattern by predetermined phase shifts .sub.k such that each radar waveform {tilde over (x)}.sub.Tx,k of the second sequence has a different predetermined phase shift .sub.k. The sequence of radar waveforms {tilde over (x)}.sub.Tx,k according to the second predetermined pattern is transmitted in lieu of the sequence of radar waveforms x.sub.Tx according to the first predetermined pattern.

[0060] The sequence of radar waveforms {tilde over (x)}.sub.Tx,k according to the second predetermined pattern can be expressed as

e.sup.2i.Math..sup.k.Math.x.sub.Tx for k=1,2, . . . ,N

[0061] In one approach, the predetermined phase shifts .sub.k are based on a Doppler frequency f.sub. derived from a predetermined relative velocity that is randomly selected from a predetermined range of velocities, which in this specific embodiment is a range between 0.5 m/s and 10.0 m/s for parking purposes, and is randomly selected as a velocity of 1.0 m/s, between the automotive radar system 10 and the target 26, 28, and the radar carrier frequency.

[0062] For a fixed relative velocity between the automotive radar system 10 and the target 26, 28, hence a fixed Doppler shift, the above transform undergoes a phase shift corresponding to the Doppler frequency f.sub.

x.sub.a,ke.sup.2i.Math.f.sup..sup..Math.k.Math..Math.x.sub.a,1 for k=1,2, . . . ,N

[0063] The various Doppler shifts present in the radar-illuminated scene superimpose in the range gates and Doppler bins. Hence, the spatial information can be divided in separated Doppler bins by means of the FFT of length N in the single range gates.

[0064] In other words, transmission of the sequence of radar waveforms {tilde over (x)}.sub.Tx,k according to the second predetermined pattern results in a predefined shift of the spatial information in the Doppler bins with respect to the transmission of the sequence of radar waveforms x.sub.Tx according to the first predetermined pattern.

[0065] In the following, an embodiment of a method of operating the automotive radar system 10 pursuant to FIG. 1 for avoiding interference by other radar systems will be described. A flowchart of the method is provided in FIG. 2. In preparation of operating the automotive radar system 10, it shall be understood that all involved units and devices are in an operational state and configured as illustrated in FIG. 1.

[0066] In order to be able to carry out the method automatically and in a controlled way, the evaluation and control unit 10 comprises a software module 30 (FIG. 1). The method steps to be conducted are converted into a program code of the software module 30. The program code is implemented in the digital data memory unit 24 of the evaluation and control unit 20 and is executable by the processor unit 22 of the evaluation and control unit 20.

[0067] All predetermined/predefined values, thresholds and tolerance margins mentioned herein such as phase shifts, range of relative velocity, deviation value, radar waveform duration etc. reside in the digital data memory unit 24 of the evaluation and control unit 20 and can readily be retrieved by the processor unit 22 of the evaluation and control unit 20.

[0068] Referring now to FIG. 2, in a first step 32 of the method a first sequence of N radar waveforms x.sub.Tx,1, x.sub.Tx,2, . . . , x.sub.Tx,N according to the first predetermined pattern is transmitted over time N.Math. towards the scene.

[0069] In a next step 34 of the method, first radar waveform excerpts x.sub.Rx,1, x.sub.Rx,2, . . . , x.sub.Rx,N, each one of duration Z, are received that have been reflected by the target 26, 28 hit by the transmitted first sequence of radar waveforms x.sub.Tx. In another step 36, a first range-Doppler information is decoded as described before from the received first radar waveform excerpts x.sub.Rx,1, x.sub.Rx,2, . . . , x.sub.Rx,N. As an interim result of the step 36 of decoding, transformed signals T(x.sub.Rx,1)=x.sub.a,1; T(x.sub.Rx,2)=x.sub.a2; . . . ; T(x.sub.Rx,N)=x.sub.a,N are generated, which represent N times the range information of the reflecting target 26, 28. The first range-Doppler information is derived by applying the FFT of length N over the single range gates. Then, in another step 38 of the method, a second sequence of radar waveforms {tilde over (x)}.sub.Tx,k:=e.sup.2i.Math.f.sup..sup..Math..Math.x.sub.Tx,1; e.sup.2i.Math.f.sup..sup..Math.2.Math.x.sub.Tx,2; . . . ; e.sup.2i.Math.f.sup..sup..Math.N.Math.x.sub.Tx,N is transmitted to the scene according to the second predetermined pattern, differing from the first predetermined pattern by the predetermined phase shifts 2i.Math.f.sub.k, which are based on the Doppler frequency f.sub. derived from the randomly selected predetermined relative velocity of 1.0 m/s.

[0070] In a next step 40, second radar waveform excerpts {tilde over (x)}.sub.Rx,1, {tilde over (x)}.sub.Rx,2, . . . , {tilde over (x)}.sub.Rx,N of duration are received that have been reflected by the target 26, 28 hit by the transmitted second sequence of radar waveforms {tilde over (x)}.sub.Tx,k. In another step 42, a second range-Doppler information is decoded as described before from the received second radar waveform excerpts {tilde over (x)}.sub.Rx,1, {tilde over (x)}.sub.Rx,2, . . . , {tilde over (x)}.sub.Rx,N. As an interim result of the step 42 of decoding, transformed signals T({tilde over (x)}.sub.Rx,1)={tilde over (x)}.sub.a,1; T({tilde over (x)}.sub.Rx,2)={tilde over (x)}.sub.a,2; . . . ; T({tilde over (x)}.sub.Rx,N)={tilde over (x)}.sub.a,N are generated, which represent N times the range information of the hit target 26, 28. The second range-Doppler information is derived by applying the FFT of length N over the single range gates.

[0071] With respect to the first range-Doppler information, the second range-Doppler information is shifted along the Doppler bins in Doppler dimension by the velocity , which is a predetermined value.

[0072] A deviation of the second range-Doppler information from the first range-Doppler information is given by the shift along the Doppler bins by the predetermined velocity . This deviation is compared to a predetermined deviation value for a shift along the Doppler bins in a next step 44 of the method.

[0073] In another step 46 of the method, based on the results of the step of comparing 44, a potential interference condition is identified in case that the result of the comparison is negative, and ghost targets are identified. In case that the deviation is equal to the predetermined deviation value within predefined margins of tolerance, targets are identified as being properly detected and regular operation of the automotive radar system 10 can be confirmed, for instance by sending an appropriate information to an electronic control unit of the vehicle.

[0074] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0075] Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality, which is meant to express a quantity of at least two. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.