Methods for reducing Doppler ambiguities when evaluating multiple modulation cycles

Abstract

The invention relates to a method for operating a radar sensor or radar network, comprising the steps of: transmitting at least three frames of frequency-modulated radar signals, each with a defined frame duration and a plurality of frequency-modulated radar signals per frame, wherein the transmission includes a defined pause between each pair of frames, wherein the frame duration and / or the pause duration are selected such that the center times of the frames are non-equidistant relative to each other; receiving and processing reflected signals; and jointly evaluating multiple frames.

Description

[0001] The invention relates to a method for operating a radar sensor or radar network to reduce ambiguities during the joint evaluation of multiple frames of radar signals. The invention further relates to a radar sensor and a radar network for carrying out such a method. State of the art

[0002] Radar systems for measuring the distance, relative speed, and angle of targets are increasingly used in motor vehicles for safety and comfort functions as part of driver assistance systems. The accuracy of radar measurements and their resolution of relative speeds are playing an increasingly important role, as driver assistance systems and autonomous driving functions require the most precise possible environmental perception.

[0003] Radar sensors used in driver assistance systems in motor vehicles often employ modulation techniques that frequency-modulate the signals using a chirp method. Another commonly used modulation technique is orthogonal frequency division multiplexing (OFDM), in which the frequency band is divided into several orthogonal subchannels. In both methods, a radar signal can be transmitted with a sequence of signals for sampling (frames) followed by a pause without signals. In a chirp sequence method, a frame is formed by a sequence of multiple chirp signals, while in an OFDM method, it is formed by transmitting multiple OFDM symbols.

[0004] In radar measurements, the resolution of the relative velocity Δv of the radar system depends on the measurement duration Tf, whereby Δv=c2f0∗Tf This applies. Here, c denotes the speed of light and f0 the center frequency of the corresponding radar modulation. High resolution is advantageous because it allows for the detection of as many targets as possible and the separation of even small differences or changes in relative velocity. The maximum measurement duration Tf is limited; depending on the application, it is restricted by requirements such as the maximum permissible latency until result output and the maximum unambiguously measurable relative velocity, but can also be limited by other factors such as thermal conditions. The maximum measurement duration Tf also limits the maximum duration of the frames. Therefore, a combined evaluation of several frames or entire measurement cycles can significantly increase the effective measurement duration. This also significantly improves the resolution of the relative velocity compared to the evaluation of a single measurement cycle.However, the pauses between frames lead to ambiguities in determining the relative speed. These arise from undersampling in the Doppler effect. Without a clear speed determination, incorrect assessments of the vehicle's surroundings can occur, impairing the effectiveness of the safety functions of a driver assistance system. This is particularly true in the context of collision avoidance, adaptive cruise control, and lane keeping assist systems. Disclosure of the invention

[0005] The object of the invention is therefore to create a method for operating a radar sensor or radar network that enables high resolution and unambiguous speed determination.

[0006] Advantageous embodiments and further developments of the invention are set out in the dependent claims.

[0007] A method according to the invention for operating a radar sensor or radar network comprises the following steps: Transmission of at least three frames of frequency-modulated radar signals, each with a defined frame duration and a plurality of frequency-modulated radar signals per frame, wherein the transmission includes a defined pause between each pair of frames, wherein the frame duration and / or the pause duration are selected such that the center times of the frames are non-equidistant relative to each other; reception and processing of reflected signals; joint evaluation of multiple frames.

[0008] The frame durations and / or pause durations are chosen such that the time offsets between the midpoints of any two consecutive frames are different. For example, the frame durations and / or pause durations are chosen such that the time offset between the midpoints of a first and a second frame differs from the time offset between the midpoints of the first and a third frame, or from the time offset between the midpoints of the second and a third frame. In particular, the frame durations and / or pause durations are chosen such that the evaluation of multiple frames in the interframe relative velocity spectrum does not yield any velocity hypotheses with identical power levels.

[0009] The method according to the invention suppresses ambiguities in determining relative velocity in such a way that an unambiguous velocity determination of a target is possible, whereby no velocity hypotheses with an identical high power level occur in the evaluation of multiple frames within the frame-spanning relative velocity spectrum. The method according to the invention therefore enables high resolution over long measurement durations across multiple frames and simultaneously ensures an unambiguous velocity determination. Multiple frames are, for example, two to eight frames.

[0010] According to a preferred embodiment of the invention, the frequency-modulated radar signals are modulated using a chirp sequence method or an orthogonal frequency division multiplex (OFDM) method. For example, each frame comprises a plurality of chirp signals or a plurality of OFDM symbols.

[0011] According to a preferred embodiment of the invention, each pair of frames differs in at least one parameter of their frequency-modulated radar signals. This ensures that the measurements of the individual frames are uncorrelated and, for example, that errors do not recur over cycles. The processing or evaluation method takes the parameter deviation into account. If the modulation method is a chirp sequence method, the chirp signals of two consecutive frames preferably differ in at least one of the following parameters: the sign of the slope of the chirp signals; the sign of the change in the center frequency of the individual chirp signals within a frame; the bandwidth of the chirp signals; the magnitude of the change in the center frequency; the ramp timing. For example, the center frequency of the chirp signals within a frame can increase or decrease.Changing the frames in at least one parameter of the signals can also be used to divide the frames between multiple radar sensors when using a radar system, and to uniquely identify the sensors during evaluation.

[0012] According to a preferred embodiment of the invention, each pair of frames differs in at least one parameter of their frequency-modulated radar signals, the differences being implemented such that the total bandwidth used is increased across the measurement cycles. Thus, in addition to improved speed separation capability, improved distance separation capability can also be achieved. Δd=c2BW to be obtained. Here, BW indicates the total bandwidth used and c the speed of light.

[0013] According to a preferred embodiment of the invention, the frequency-modulated radar signals of a frame are arranged non-equidistantly in time. This includes the temporal interleaving of at least two subsequences within a frame. Such interleaving makes it possible to determine an unambiguous speed with a correspondingly coarser resolution of the relative speed simply by evaluating the signals of a single frame. Furthermore, the non-equidistant arrangement of the signals within a frame allows the frame length to be adjusted, thereby enabling the midpoints of several frames to be arranged non-equidistantly relative to each other.

[0014] According to a preferred embodiment of the invention, the joint evaluation comprises the evaluation of the received signals of several frames and the creation of a distance-Doppler velocity spectrum (range Doppler) taking into account the movement of at least one target detected by the signals.

[0015] The joint evaluation can involve the evaluation of all received signals from multiple frames. The consideration of the movement of at least one target detected by the signals is achieved, for example, by compensating for changes in distance (range migration). The joint evaluation enables the creation of a very finely resolved distance-Doppler velocity spectrum, whereby ambiguities in the measured relative velocity of each target are suppressed by a transmission scheme according to the invention. A joint evaluation requires only one joint evaluation step.

[0016] According to a preferred embodiment of the invention, the joint evaluation comprises preprocessing the received signals of individual frames and subsequent cross-frame evaluation. The preprocessing includes a one-dimensional frequency analysis of each received radar signal or a two-dimensional frequency analysis of each received radar signal, wherein the first dimension is the frequency per signal and the second dimension is the frequency across the signals of a frame.

[0017] Such a frequency analysis is performed, for example, using a fast Fourier transform. The preprocessing and frame-spanning evaluation can be carried out on separate components of the radar system. Since frame-spanning evaluation requires increased computing capacity due to the large number of signals to be analyzed, if performed on a radar sensor, it must have a corresponding configuration and the necessary processing power. This increases the cost of the radar sensor and can—depending on the design—lead to heat dissipation problems. Separating the components allows, for example, frame-spanning evaluation to be performed on a central control unit or a central processing unit.This is particularly advantageous when the method is implemented on a MIMO (Multiple-Input-Multiple-Output) radar network, as a central control unit or a central computing unit can thus perform the frame-spanning evaluation of several radar sensors.

[0018] Preprocessing using one- or two-dimensional frequency analysis enables the detection of targets captured by the signals that exhibit a sufficiently distinct relative velocity or a sufficient difference in relative velocity. However, the resolution is limited; for example, relative velocity can be resolved to an accuracy of 0.05 m / s, meaning that targets with a smaller difference in relative velocity can no longer be distinguished, or that a small change in the relative velocity of a target is no longer detected. The results of the preprocessing calculations can be used for cross-frame analysis, thereby reducing the computational effort required for this.

[0019] According to a preferred embodiment of the invention, the cross-frame evaluation comprises a one-dimensional frequency analysis of the received signals of several frames taking into account the expected phase shifts, a coherent superposition of the preprocessing results, and a search for at least one global maximum in the superimposed results.

[0020] The one-dimensional frequency analysis of the received signals from multiple frames, or across the time offsets of multiple frames, enables the creation of a very finely resolved range-Doppler spectrum, taking into account the motion of at least one target detected by the signals. For example, targets that differ in their relative velocity by less than 0.05 m / s, or exhibit such a small change in their relative velocity, can be separated. By using a transmission scheme according to the invention, ambiguities in the determined relative velocity of each target arising from undersampling in the Doppler effect are suppressed. Likewise, a model for the phase shifts between frames expected due to the time offsets is established for the relevant relative velocity range.In this case, if the preprocessing only includes a one-dimensional frequency analysis, the cross-frame evaluation can include a two-dimensional frequency analysis of the received signals from multiple frames.

[0021] Coherent superposition involves superimposing the results of the preprocessing, taking into account the created model and thus the expected phase shifts, with the results of the cycle-spanning evaluation. For example, the results of a two-dimensional frequency analysis of the signals from the individual frames in the preprocessing are coherently superimposed with the results of a one-dimensional frequency analysis of the received signals across multiple frames. Subsequently, a global maximum or several local maxima are identified in the superimposed result. This significantly improves the resolution of the relative velocity and enables a precise resolution of the relative velocity spectrum.

[0022] According to a preferred embodiment of the invention, the frequency-modulated radar signals are modulated in a radar multiplexing method and the method is designed to operate a multiple-input multiple-output (MIMO) radar sensor or radar network.

[0023] This allows the described advantages of the method according to the invention to be combined with the advantages of a MIMO radar sensor or MIMO radar network. The radar multiplexing method can, for example, be a time-division multiplexing scheme or a frequency-division multiplexing scheme; for example, the multiplexing scheme can be a time-division multiplexing (TDM) scheme or it can use Doppler division multiplexing (DDM) codes as the scheme.

[0024] The invention further comprises a radar sensor with which the inventive method is carried out according to any of the embodiments described above. The radar sensor is, for example, configured to perform the complete joint evaluation of several frames. The radar sensor includes, for example, storage means configured to store the received signals of the several frames to be jointly evaluated and to make them available for evaluation.

[0025] The invention further comprises a radar network comprising at least a first and a second radar sensor, with which the method according to the invention is carried out according to any of the embodiments described above. The radar sensors can each be the radar sensor described above. The radar network can further comprise a central processing unit on which at least the frame-spanning evaluation is performed. The radar sensors are configured to communicate with the central processing unit. The central processing unit can also be configured to perform at least part of the processing of reflected signals and the complete joint evaluation of multiple frames.

[0026] The subject matter of the invention is not limited to the features of the individual embodiments but can also include any technically possible combination of the described embodiments that falls under the main claim.

[0027] The following section explains an exemplary embodiment in more detail with reference to the drawing. The drawing shows: Fig. Figure 1 shows a time-frequency scheme of a state-of-the-art chirp sequence method; Fig. Figure 2 shows a relative velocity spectrum with ambiguous results according to a time-frequency scheme of Fig. 1; Fig. Figure 3 shows a time-frequency scheme according to a first embodiment of the invention; Fig. Figure 4 shows a relative velocity spectrum with unambiguous results according to a time-frequency scheme of the first embodiment of the invention; Fig. Figure 5 shows a time-frequency scheme according to a second embodiment of the invention; Fig. Figure 6 shows a time-frequency scheme according to a third embodiment of the invention; Fig. Figure 7 shows a time-frequency scheme according to a fourth embodiment of the invention; Fig. Figure 8 shows the steps of the inventive method according to one of the first to fourth embodiments.

[0028] In Fig. Figure 1 shows a state-of-the-art time-frequency scheme. It depicts the transmission of signals in a sequence of frames S1, S2, S3 (hereinafter referred to as Sx), each representing a sampling of three chirp radar signals 10 with increasing frequency. The chirp signals 10 in each frame Sx are arranged with the same frequency, the same frequency rise from f1 to f2, and the same spacing between them. Each frame Sx has a defined measurement duration Tf, with a pause P1, P2 (hereinafter referred to as Px) without chirp signals of a defined length Tp between each frame Sx.

[0029] According to the time-frequency scheme, in a state-of-the-art method, frames Sx are sampled by transmitting signals 10 and receiving corresponding reflected signals, with the frames Sx being interrupted by pauses Px. The time-frequency scheme is not limited to the number of frames; however, a pause Px occurs after each frame Sx. The pause after frame S3 is not shown here. Thus, the combination of a frame Sx with a subsequent pause Px forms a measurement cycle Z1, Z2 (hereinafter referred to as Zx), meaning the scheme comprises a plurality of identical measurement cycles Z1, Z2. Here, ΔT = Tf + Tp applies. For example, if Tf is 20 ms and Tp is 20 ms, then ΔT = 40 ms. Here, ΔT describes the interval between the midpoint 12 of one frame Sx and the midpoint 12 of another frame Sx.Due to the identical length Tf of the frames Sx and the identical lengths Tp of the pauses Px, the midpoints 12 of the frames Sx are equidistant from each other.

[0030] By jointly evaluating several frames Sx or measurement cycles Zx to increase the effective measurement duration and the resulting improved resolution, the following occurs as in Fig. 2 presented to ambiguous results regarding velocity hypotheses.

[0031] Fig. Figure 2 shows a relative velocity spectrum with ambiguous results after the joint evaluation of several frames according to a time-frequency scheme. Fig. 1. Here, the sampled frames are evaluated and displayed across frames, or in other words, the measurement cycles are evaluated and displayed across cycles. The true relative velocity of a measured example target v trueThe power level is 0 m / s. Due to the pauses Px between the frames Sx, undersampling in the Doppler effect leads to ambiguous results. This means there are multiple velocity hypotheses with the same power level in the range of 0 dB, -0.05 m / s, 0 m / s, and 0.05 m / s. Therefore, a clear determination of the actual relative velocity of the target is no longer possible.

[0032] Fig. Figure 3 shows a time-frequency scheme (hereinafter referred to as scheme) according to a first embodiment of the invention. The scheme comprises the transmission of signals in a plurality of frames S1, S2, S3 (hereinafter referred to as Sx), each of which includes three chirp radar signals 10 with increasing frequency. The chirp signals 10 are arranged in each frame Sx with the same frequency and the same frequency rise from f1 to f2, and at the same intervals between them. Each frame Sx has a defined measurement duration Tf, with a pause P1, P2 (hereinafter referred to as Px) without chirp signals 10 following each frame. The defined lengths Tp1, Tp2 of the pauses P1, P2 are different, with Tp1 ≠ Tp2. This results in different ΔT values: ΔT12 and ΔT23. Here, ΔT12 indicates the distance between the midpoints 12 of frames S1 and S2, and ΔT23 indicates the distance between the midpoints 12 of frames S2 and S3.Due to the different lengths of the pauses Px, ΔT12 ≠ ΔT23. This means that the midpoints 12 of the frames Sx are not equidistant from each other.

[0033] In the first embodiment shown, the duration of the pauses Px is selected such that the midpoints 12 of each pair of consecutive frames Sx have different time offsets ΔT. The embodiment also includes further frames Sx not shown here, wherein the pauses Px are selected such that the aforementioned condition is met between each pair of adjacent frames Sx, meaning that the midpoints 12 of the frames Sx are not equidistant from one another. For example, the embodiment also includes pauses Px selected such that no pause Px is the same as any other pause Px, i.e., that no two intervals of the midpoints 12 of the frames Sx are the same. This enables evaluation across a large number of frames Sx or measurement cycles Zx without yielding ambiguous results from an evaluation across frames or cycles.

[0034] Fig. Figure 4 shows a relative velocity spectrum with unambiguous results after the joint evaluation of the received signals of several frames, which were arranged according to a time-frequency scheme as described in Fig. 3. The illustrated embodiment was transmitted. Here, the sampled frames are evaluated and displayed across frames, or in other words, the measurement cycles are evaluated and displayed across cycles. The true relative velocity of a measured example target v true The velocity is 0 = m / s. Due to the different lengths Tp1, Tp2 of the pauses Px between the frames Sx and the resulting non-equidistant arrangement of the midpoints 12, the ambiguities caused by undersampling in the Doppler effect can be suppressed. Therefore, only one velocity hypothesis exists in the region of a power level of 0 dB, and the one in Fig. 2 presented velocity hypotheses which do not v trueThe corresponding values ​​are significantly below the power level of v true , for example in the range of -8 dB. This allows for an unambiguous determination of the relative velocity with a simultaneously fine resolution of the relative velocity in the range of less than 0.05 m / s.

[0035] Fig. Figure 5 shows a time-frequency scheme (hereinafter referred to as the scheme) according to a second embodiment of the invention. The scheme comprises the transmission of signals in a plurality of frames S1, S2, S3 (hereinafter referred to as Sx), each of which includes three chirp radar signals 10 with increasing frequencies. The chirp signals 10 are arranged in each frame Sx with the same frequency increase from f1 to f2 and the same spacing between them. The transmitted signals 10 of the frames Sx vary with respect to at least one parameter. In the present embodiment, frame S1 includes an increasing center frequency of the chirp signals 10 within the frame. Frame S2 includes a constant center frequency of the chirp signals 10 within the frame. And frame S3 includes a decreasing center frequency of the chirp signals 10 within the frame. Each frame Sx has the same defined measurement duration Tf. The pauses Px correspond in their execution to the pauses of the in Fig. The characteristics described in the 3 diagrams shown also apply here and are not repeated. Due to the execution of the pauses Px, the midpoints 12 of the frames Sx are not equidistant from each other. Therefore, the corresponding to Fig. The three described advantages of unambiguous speed determination can also be realized here.

[0036] By changing at least one parameter of the frames Sx relative to each other—here, as described, different changes in the center frequency across the chirp signals 10—the measurements of the individual measurement cycles Zx become uncorrelated. This makes it possible to distinguish the reflected signals of the frames Sx, whereby the joint evaluation of several frames Sx naturally takes the differences in the parameters into account. When the method is implemented with multiple radar sensors and the time-frequency sequence is distributed among the radar sensors, it is possible to distinguish between the sensors that emitted the corresponding signals. The embodiment is not limited to the illustrated variation of the change in the center frequency but also includes any other change in the parameters of the frames relative to each other.Such a change could be, for example, a modification of the sign of the slope of the chirp signals; the sign of the change in the center frequency of the individual chirp signals within a frame; the bandwidth of the chirp signals; the magnitude of the change in the center frequency; or the ramp timing. These modifications can be combined in any way such that the chirp signals 10 from two consecutive frames Sx differ in at least one of the parameters, and / or that all frames Sx of the embodiment differ from all other frames Sx in at least one parameter. These modifications can also be used to increase the total utilized bandwidth (BW) across the measurement cycles, thus achieving not only improved velocity separation but also improved distance separation. Δd=c2BW receives.

[0037] Fig. Figure 6 shows a time-frequency scheme (hereinafter referred to as the scheme) according to a third embodiment of the invention. The scheme comprises the transmission of signals in a plurality of frames S1, S2, S3 (hereinafter referred to as Sx), each of which contains three chirp radar signals 10 with increasing frequency. The chirp signals 10 have the same frequency rise from f1 to f2 in each frame Sx and are arranged at equal intervals. The intervals of the chirp signals 10 between the frames Sx vary. Thus, the frames S1, S2, S3 have different defined lengths Tf1, Tf2, Tf3, where Tf1 ≠ Tf2 ≠ Tf3. The lengths Tp of the pauses P1, P2 (hereinafter referred to as Px) are identical, where Tp1 = Tp2.

[0038] Due to the different lengths of the frames Sx, different ΔT values ​​result: ΔT12 and ΔT23, where ΔT12 ≠ ΔT23. Here, ΔT12 represents the distance between the midpoints 12 of frames S1 and S2, and ΔT23 represents the distance between the midpoints 12 of frames S2 and S3. Therefore, the midpoints 12 of the frames Sx are not equidistant from each other, and the corresponding values ​​are... Fig. The three described advantages of unambiguous speed determination can also be realized here.

[0039] Fig. Figure 7 shows a time-frequency scheme (hereinafter referred to as scheme) according to a fourth embodiment of the invention. This embodiment represents a combination of the elements shown in Fig. 3, Fig. 5 and Fig. The embodiments shown in Figure 6 are described. The scheme comprises the transmission of signals in a plurality of frames S1, S2, S3 (hereinafter referred to as Sx), each of which contains three chirp radar signals 10 with increasing frequency. The chirp signals 10 are arranged in each frame Sx with the same frequency increase from f1 to f2 and identical spacing between them within the frame. The frames Sx vary from each other in at least one parameter, as described above. Fig. 5 described. Likewise, the intervals of the chirp signals 10 between the frames Sx vary as described. Fig. 6 described. Thus, frames S1, S2, S3 have different defined lengths Tf1, Tf2, Tf3, where Tf1 ≠ Tf2 ≠ Tf3. Likewise, the defined lengths Tp of the rests P1, P2 (hereinafter referred to as Px) are different, as described below. Fig. 3 described, where Tp1 ≠ Tp2.

[0040] The combination of the different lengths Tf1, Tf2, Tf3 of frames S1, S2, S3 with the different lengths Tp1, Tp2 of rests P1, P2 also results in different ΔT values: ΔT12 and ΔT23. Here, ΔT12 represents the interval between the midpoints 12 of frames S1 and S2, and ΔT23 represents the interval between the midpoints 12 of frames S2 and S3. Therefore, the midpoints 12 of frames S1, S2, and S3 are not equidistant from each other, and the corresponding values ​​are... Fig. The three described advantages of unambiguous speed determination can also be realized here. By changing at least one parameter of the frames relative to each other – here, as described, the different changes in the center frequency across the chirp signals 10 of a frame Sx – the measurements of the individual measurement cycles Zx are uncorrelated and encompass the Fig. 5 described advantages.

[0041] Fig.Figure 8 shows the steps of the method according to the invention, based on one of the first to fourth embodiments. Step S1 comprises transmitting at least three frames of frequency-modulated radar signals according to a time-frequency scheme of one of the described embodiments or of any embodiment falling within the claims. The frames each have a defined duration and are separated by a pause of defined length. The midpoints of the frames are arranged non-equidistantly relative to each other by the selection of a corresponding time-frequency scheme.

[0042] In step S2, reflected signals are received and processed. This is done in the usual way, depending on the radar system used. For example, the signals are demodulated analogously and then made available for evaluation by an analog-to-digital converter.

[0043] In step S3, the received signals are evaluated, whereby the evaluation can include a joint evaluation of the received signals from several frames and the creation of a distance-Doppler velocity spectrum. This evaluation can include prior preprocessing of the received signals from individual frames and subsequent cross-frame evaluation according to the embodiments described above.

[0044] The described embodiments and those illustrated in the figures can, of course, be combined with one another in any way, provided this is technically feasible. This includes, in particular, combining variations in the lengths Tf and Tp with changes to the frames relative to each other in at least one parameter. The invention is therefore not limited to the illustrated embodiments but encompasses any combination of embodiments falling under the claims.

Claims

[1] Method for operating a radar sensor or radar network, comprising the steps: Emitting at least three frames (S1, S2, S3) of frequency-modulated radar signals (10) each with a defined duration (Tf1, Tf2, Tf3) of a frame (S1, S2, S3) and a plurality of frequency-modulated radar signals (10) per frame (S1, S2, S3), wherein the transmission includes a defined pause (P1, P2) between each two frames (S1, S2, S3), wherein the duration (Tf1, Tf2, Tf3) of the frames and / or the duration (Tp1, Tp2) of the pauses (P1, P2) are selected such that the midpoints (12) of the frames (S1, S2, S3) are not equidistant from each other; reception and processing of reflected signals; joint evaluation of several frames (S1, S2, S3). [2] Method according to one of the preceding claims, wherein the frequency-modulated radar signals (10) are modulated in a chirp sequence method or an orthogonal frequency division multiplexing method. [3] Method according to one of the preceding claims, wherein each pair of frames (S1, S2, S3) differ in at least one parameter of their frequency-modulated radar signals (10). [4] Method according to one of the preceding claims, wherein the frequency-modulated radar signals (10) of a frame (S1, S2, S3) are arranged non-equidistant to each other in time. [5] Method according to one of the preceding claims, wherein the joint evaluation comprises the evaluation of the received signals of several frames (S1, S2, S3) and the creation of a distance-Doppler velocity spectrum taking into account the motion of at least one target detected by the signals. [6] Method according to any of the preceding claims, wherein the joint evaluation comprises preprocessing the received signals of individual frames (S1, S2, S3) and subsequent cross-frame evaluation; wherein the preprocessing comprises a one-dimensional frequency analysis of each received radar signal or a two-dimensional frequency analysis, wherein the first dimension comprises the frequency per signal and the second dimension comprises the frequency across the signals of a frame (S1, S2, S3). [7] Method according to claim 6, wherein the cross-frame evaluation comprises a one-dimensional frequency analysis of the received signals of several frames (S1, S2, S3) taking into account the expected phase shifts, a coherent superposition of the preprocessing results and a search for at least one local or global maximum in the superimposed results. [8] Method according to one of the preceding claims, wherein the frequency-modulated radar signals (10) are modulated in a radar multiplexing method and wherein the method is designed to operate a multiple-input multiple-output (MIMO) radar sensor or radar network. [9] Radar sensor with which the method according to one of the preceding claims is carried out. [10] Radar network comprising at least a first and a second radar sensor with which the method according to claim 8 is carried out.

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