Method for operating a Doppler multiplexing method in radar networks

Abstract

Method for operating a Doppler multiplexing method (DDM) in multiple-input-multiple-output (MIMO) radar networks, wherein uniquely coded signals are transmitted by means of Doppler multiplexing (DDM) from at least one first (Rad 1 ) and a second radar (Rad 2 ) from a MIMO radar network are convolved with the respective DDM codes and the signals are determined which have a unique assignment to a radar (Rad 1 , wheel 2 ). The uniquely assigned signals are then determined for their occurrence in the monostatic paths, the bistatic path, and their occurrence in all paths using a search algorithm, enabling robust MIMO angle estimation over an arbitrary aperture.

Description

[0001] The invention relates to a method for angle estimation based on signals from a multiple-input-multiple-output radar network (MIMO) operated using the Doppler division multiplexing (DMM) method.

[0002] In particular, the invention relates to a method for operating a Doppler multiplex method in radar networks used in driver assistance systems of motor vehicles for environmental detection. State of the art

[0003] Modern radar systems, particularly for driver assistance systems in motor vehicles, are designed as multiple-input-multiple-output (MIMO) radar networks and comprise a plurality of transmitters (Tx) and receivers (Rx). To separate and identify a larger number of transmitters on the receiving side, such radar networks can be operated using Doppler Division Multiplexing (DDM). This prevents an extension of the minimum measurement time required to separate the transmitters on the receiving side, as would occur, for example, in a radar network operated using Time Division Multiple Access (TDM). DE 10 2020 202 500 A1 describes a TDM method with a reduction in the required minimum measurement time. The DDM method also allows the transmission power and thus the emitted energy to be increased proportionally to the measurement time.This results in an improved signal-to-noise ratio during data processing, which in turn enables an extended range.

[0004] The application of Doppler multiplexing in radar networks presents a particular challenge. It must be considered that, due to the spatial distance between individual radar devices, different radial velocities and distances to the same target can be measured. This leads to distortion of the Doppler multiplexing code. This impairs the decoding and analysis of the data, particularly with regard to angle estimation when using multiple input and output channels (MIMO). This problem can significantly impair the efficiency of a radar network.

[0005] To improve transmitter identification, the respective transmitted signals can be pre-encoded for each transmitter using a phase shift, allowing the received signals to be assigned to a transmitter based on their phase shift. Such a method is described, for example, in US 2022 / 0171049 A1. Disclosure of the invention

[0006] It is an object of the invention to provide a method which allows a robust decoding of the code of a Doppler multiplex method within a radar network and thus enables an accurate angle estimation.

[0007] This object is achieved according to the invention with the method specified in claim 1.

[0008] The inventive method for operating a Doppler multiplexing (DDM) method in multiple-input-multiple-output (MIMO) radar networks comprises the steps: Generating and transmitting coded signals by Doppler multiplexing to at least a first and a second radar from a MIMO radar network, each radar comprising at least a transmitter and a receiver, and the coded signals having a respective DDM code that uniquely identifies each radar; Reception and processing of reflected signals for digital processing and conversion into distance-Doppler velocity matrices; Threshold detection for each distance-Doppler matrix to determine cells with potential signals from the respective radar, whereby the threshold detection binary transforms the signals; Convolution of the respective potential binary signals with each of the unique DDM codes and unique assignment of the respective signals to one of the radars,

[0009] Determining the uniquely assigned signals in the bistatic path whose signal parameters overlap for each radar, and determining the uniquely assigned signals in the monostatic path for each radar, whereby the signals of the respective monostatic path differ from the signals of the bistatic path;

[0010] Determination of the signals that have been uniquely assigned in both the bistatic path and each monostatic path, whereby signals of the monostatic paths are determined starting from the respective signal of the bistatic path, and MIMO angle estimation with full aperture of a virtual MIMO array formed from the signals uniquely assigned in all paths.

[0011] According to a preferred embodiment, the method further comprises the steps of determining the signals that were assigned only in the bistatic path; MIMO angle estimation with the bistatic aperture of the first and second radars and / or the method further comprises the steps of determining the signals that were assigned only in one of the monostatic paths; MIMO angle estimation with at least one of the monostatic aperture of the first radar and the monostatic aperture of the second radar.

[0012] The radar network may include more than two radars, with each DDM code uniquely identifying the respective radar.

[0013] Each radar can comprise multiple transmitters, with the DDM code comprising unique phase shifts of the signals from each transmitter of the respective radar. A unique phase shift leads to an assignment of the measured signals to the respective transmitter, as no transmitter provides the same Doppler velocity bin of a distance-Doppler velocity matrix for a target with the same speed. Distance-Doppler velocity matrices sort the received signals into dedicated areas (bins) according to their speed and distance. This enables a unique reconstruction of the target's velocity even without joint evaluation of the DDM codes of all radars in the radar network.For example, the phase shifts can be disjoint; further, for example, the phase shifts can be relatively prime and include relatively prime differences in the phase shifts between the transmitters of the respective radar, or any combination thereof. The DDM codes of the individual radars differ from one another in such a way that they uniquely identify each radar, i.e., no DDM code is identical to another. When using radars with only one transmitter each, the DDM codes correspond to unique phase shifts between the transmitters of the respective radars.

[0014] The determination of the signals which have been uniquely assigned in both the bistatic path and each monostatic path is carried out using a search algorithm starting from the respective signal of the bistatic path.

[0015] The signals that have been uniquely assigned in both the bistatic path and each monostatic path can be determined by means of a point-symmetric search starting from the respective signal of the bistatic path.

[0016] The search range of a point-symmetric search can be extended by one bin for each dimension from zero bins to the maximum possible deviation.

[0017] The method can be implemented using linear frequency modulated chirps or exponential frequency modulated chirps or stepped frequency modulated chirps as sequential transmit signals.

[0018] The maximum possible deviation can be adjusted to match the distance-dependent frequencies in a stepped frequency-modulated sequential frequency modulation.

[0019] A preferred development of the invention therefore comprises implementing the method according to a time division multiplex (TDM) scheme. In this scheme, the respective DDM codes of the first radar and the second radar are swapped in a first and a second time slot of the time division multiplex scheme. The method is executed for the first time slot and the second time slot, and the results of the respective time slots are compared with one another, taking into account only those signals that are identical for each time slot. Identical signals are those signals whose parameters are identical for the respective bins of the distance-Doppler velocity matrices. The embodiment assumes that the first and second radars transmit with the same number of transmitters.

[0020] Further preferably, the results of the first and second time windows are compared before the MIMO angle estimation step, and this is only carried out for considered signals.

[0021] The time interval between the time windows is only a few microseconds, so the signal parameters in both time windows are approximately the same and can be output as equal bins by transforming them into distance-Doppler velocity matrices. Thus, two adjacent time windows produce the same results for correctly assigned signals.

[0022] Such a refinement has the advantage of reducing the incidence of false-positive measurements, where a DDM code is randomly generated from reflected echoes of signals from individual radars, but these originate from different measured targets. This results in a pseudo-signal that is not based on a single measured target. These false-positive measurements can be eliminated by the process steps "Determination of the uniquely assigned signals in the bistatic path (BP)" and "Determination of the signals that are present in both the bistatic path (BP) and each monostatic path (MP). 1 , MP 2 ) were clearly assigned" cannot always be avoided, or are not always detected by these steps. In particular, in the step of "determining the signals which are only present in one of the monostatic paths (MP 1 , MP 2)" it is not always clear whether it is a signal formed only in the monostatic path or whether it is an artifact from multiple signals from different measured targets. False-positive detections are largely prevented by the preferential further training, since the pseudo-signals formed randomly from reflected echoes from different measured targets would have to form for each of the DDM codes to be taken into account.

[0023] When implementing these embodiments of the invention in a radar network with more than two radars, the DDM codes of the individual radars can be swapped in pairs for each of two time windows. This can be done consistently for all time windows, or the DDM codes can be swapped for each of two previously determined or randomly selected radars for each of two time windows. The DDM codes of the plurality of radars can also be shifted by one radar for each time window, whereby this shift must be taken into account during the evaluation.

[0024] The MIMO angle estimation of the considered data is advantageously performed with a correction for the velocity-dependent phase differences for each time window. This is easily possible using known methods.

[0025] The invention further comprises a radar network with at least a first and a second radar. The method according to one of the preferred embodiments or refinements is implemented with the radar network. Each radar therefore comprises at least one transmitter and one receiver, which can be embodied as conventional radar antennas and can be further configured such that each transmitter is simultaneously a receiver.

[0026] The features described can, of course, be combined with each other as desired, provided this is technically possible. Character description

[0027] Preferred embodiments of the invention are explained in more detail below with reference to the figures. They show: Fig. 1 a schematic representation of a radar system which is operated with the method according to the invention; Fig. 2 distance-Doppler velocity matrices with examples of DDM codes; Fig. 3 an overview of the steps of a first embodiment of the method; Fig. 4 the evaluation of the measurement results obtained according to the first embodiment of the method; Fig. 5 an example of a signal assigned in all paths; Fig. 6 shows a time diagram of a time-division multiplex method of a preferred development of the method according to the invention; Fig. 7 the implementation of the procedure according to the preferred further training.

[0028] Fig. 1 shows a schematic representation of a radar system 10 which is operated with the method according to the invention. The radar system 10 is arranged here, for example, on a vehicle F and comprises a first radar wheel 1 and a second radar wheel 2 Each radar wheel includes 1 , wheel 2at least one transmitter (Tx, not shown) and one receiver (Rx, not shown). The transmitter can also be a receiver, or the transmitter and receiver can be implemented as separate antennas. Preferably, each radar comprises multiple transmitters and receivers.

[0029] The radar wheel 1 and bike 2 are arranged with their reference points at a distance d. The radar system 10 detects in Fig. 1 a point target P, which moves with the relative velocity v. The distance d of the radars Rad 1 , wheel 2 to each other leads to different measured radial velocities v 1 , v 2 and different distances R 1 , R 2 to the point target P.

[0030] By combining each transmitter with each receiver, a virtual array of virtual channels can be created, which is based on the addition of the signal propagation times from the transmitter to the point target and from the point target to the receiver. This allows for an increase in the aperture and thus the resolution of the radar system 10. This requires a clear assignment of the received signals to the transmitters, which is possible using a DDM method.

[0031] The method assumes that speed v and distance R are approximately identical for all virtual channels of a radar. Thus, with radar 1 (Rad 1 ) with distance R 1 and speed v 1 and with Radar 2 (Rad 2 ) with distance R 2 and speed v 2 : v1=v2 and R1=R2.

[0032] In the measured bistatic path (BP), i.e. the reception of a signal with a receiver that is not the transmitter at the same time, the speed is: vmix=v1+v22, and the distance Rmix=R1+R22. .

[0033] It is assumed that v 1 ≧ v mix ≧ v 2 and R1 ≧ R mix ≧ R 2 .

[0034] It is clear to the expert that the distance and speed of the monostatic paths (MP 1 , MP 2 ) (transmitter is also receiver) of the radars may deviate upwards or downwards from the parameters of the bistatic path. Therefore, the following applies: Δv=|v1−v2|2and ΔR=|R1−R2|2

[0035] For ΔR, ΔR max ∈ [0; d / 2] as the upper limit of this deviation, where d is the distance between the reference points of both radars. For most detected targets, Δv is max ∈ [0; v lim / 2], where there is no theoretical upper limit. v lim is therefore defined as a limit value and corresponds to a limit value below which the majority of the measured speeds lie.

[0036] For unambiguous assignment, the respective DDM code (DC 1 , DC 2 ) for each radar (wheel 1 , wheel 2 ) with multiple transmitters, unique phase shifts of the signals of each transmitter (Tx) of the respective radar (Rad 1 , wheel 2 ). In particular, the DMM code can include relatively prime differences in the phase shifts between the transmitters of the respective radar. For example, the two differences in the phase shifts of two transmitters of a radar can be relatively prime.

[0037] Fig. Figure 2a shows a distance-Doppler velocity matrix a) which represents an example of such a DDM code. The radar identified by the DDM code comprises two transmitters Tx 1 and Tx 2 . The signals from the transmitter Tx 1 and Tx2 are coded in such a way that they are disjointly phase-shifted. From Tx 1 on Tx 2 leads the difference in phase shifts between two consecutive signals to 5 / 8 of the maximum speed v max . And from Tx 2 on Tx 1 leads the difference of the phase shifts between two consecutive signals and taking into account the periodic continuation to 3 / 8 of the maximum speed v maxTherefore, the differences in the phase shifts are relatively prime to each other, and the DDM code is unique. Due to the periodic continuation or ring array structure in Doppler dimensions, each measurement and subsequent convolution with the DDM code results in a unique velocity, and thus also a unique assignment of the measured velocity to a transmitter (Tx).

[0038] Fig. Figure 2b shows such a measurement after threshold detection, which allows a binary transformation and a representation as a distance-Doppler velocity matrix. In the distance-Doppler velocity matrix b), convolution with the DDM code results from Fig. 2a a unique speed v est which also determines the assignment of the radars Tx 1 , Tx 2 to the corresponding bins. In other words, the unique speed of the target is 3 / 8 v maxwhich, when convolved with the DDM code, results in a measured speed of 3 / 8 v max for Tx 1 and a measured speed of 3 / 8 v max for Tx 2 results.

[0039] A contrary example is in Fig. 2c. The DDM code of the two transmitters Tx 1 and Tx 2 is not unique, since the differences in the phase shifts between the transmitters are not coprime, but provides a measurement as in Fig. 2d shows ambiguous results. Thus, no unambiguous determination of the velocity v est possible and also a clear assignment of the transmitter Tx 1 and Tx 2 to the measured bins is not possible without comparison with the measured velocities of the entire radar system. This slows down the evaluation of the measurements and represents a disadvantage that is solved by the method according to the invention.

[0040] Fig. Figure 3 shows an overview of the first steps of a first embodiment of the method before the evaluation steps. In step S1, for each radar wheel 1 , wheel 2 of the radar network operated with the method generates uniquely coded signals that the respective radar wheel 1 , wheel 2 This can be achieved, for example, by means of a unique phase shift of the signals from the individual transmitters of each radar, as described above. In step S2, each radar transmits the 1 , wheel 2 specifically coded signals and receives all reflected signals within its angular range. These are then processed for digital processing and converted into distance-Doppler velocity matrices (step S3).

[0041] Using threshold detection performed in step S4, the detected signals are binary transformed and assigned the values ​​0 and 1, respectively. For example, a threshold value of an amplitude at a frequency representing the Doppler velocity is used. This allows potential signals to be filtered out and signals with too low an amplitude to be excluded. The thus binary-transformed and filtered distance-Doppler velocity matrices are then evaluated (step S5).

[0042] Such an evaluation shows Fig. 4. In step S5.1, the data in as in Fig. 4 generated distance-Doppler velocity matrices (Range-Doppler matrix, RDM) of the respective radars Rad 1 , wheel 2 These binary distance-Doppler velocity matrices are compared in step S5.2 with each of the unique DDM codes DC 1 , DC 2of the two radars, here the distance-Doppler velocity matrix of Rad 1 with the DDM code DC 1 and the DDM code DC 2 and the distance-Doppler velocity matrix of Rad 2 also with the DDM code DC 1 and the DDM code DC 2 . As in Fig. As shown in Figure 2, for each signal, the unique DDM codes result in exactly one speed v est and a unique assignment of the radar that transmitted the coded signal underlying the measured signal. Each of the potential signals in each distance-Doppler velocity matrix is ​​assigned a corresponding velocity v est and assigned to a radar.

[0043] Subsequently, in step S5.3, the uniquely assigned signals are determined which were measured in the bistatic path (BP) and whose signal parameters (R est and v est) overlap for each radar (Rmix and v mix ), ie the signals are for each radar wheel 1 , wheel 2 identical. That is, the signal parameters (R est and v est ) are located in the same bins in the distance-Doppler velocity matrix for each radar, pointing to the same location. This increases the robustness of the method.

[0044] Likewise, in step S5.4, the uniquely assigned signals measured in the monostatic paths are determined. For example, the convolution of the distance-Doppler velocity matrix of radar Rad 1 with the DDM code DC 1 from bike 1 the signals which are in the monostatic path MP 1 from bike 1 are trained.

[0045] To enable a MIMO angle estimation over the full virtual aperture, in step S5.5 the signals are determined which are present in both the bistatic path (BP) and each monostatic path (MP1 , MP 2 ) have been uniquely assigned. The determination is carried out using a search algorithm. This searches for the respective signal of the bistatic path (R mix and v mix ) Signals of the monostatic pathways (R x , v x ). As described, the deviation of the signals of the respective monostatic path Δv=|v1−v2|2 and ΔR=|R1−R2|2, where the limits of this deviation are defined as ΔR max ∈ [0; d / 2] and Δv max E [0; v lim / 2] are defined as upper limits. The search algorithm searches starting from the point R est , v est in the distance-Doppler velocity matrix by means of a point-symmetric search for the signals of the monostatic paths (R x , v x ). The search range is, for example, for each dimension from zero bins to the maximum possible deviation (ΔR max , Δv max) are each extended by one bin.

[0046] Fig. Figure 5 shows such a signal. The bistatic signal (R mix , v mix ) is formed in the bistatic path BP and the monostatic signals (R 1 , v 1 ; R 2 , v 2 ) are each point-symmetric around the bistatic signal in their distance-Doppler velocity matrix. They have a deviation of one distance bin (ΔR) and two velocity bins (Δv). The search algorithm, for example, first searches for the monostatic signals in the bins directly surrounding the bistatic signal and then expands its search area by one bin at a time, thereby detecting the monostatic signals (R 1 , v 1 ; R 2 , v 2 ) of the radar wheel 1 , wheel 2 and recognizes the point symmetry.

[0047] In the present case, the deviation is small, but the search algorithm also takes into account the periodic continuation or ring array structure in Doppler dimension in order to correctly assign the monostatic signals to the bistatic signal.

[0048] The determination of the signals assigned only in the monostatic path in step S5.4 can alternatively also be carried out via step S5.5, whereby all monostatic signals are determined which are not assigned in all paths or which are not assigned in the bistatic path.

[0049] Furthermore, in step S5.7, the signals that are only assigned in the bistatic path can be determined.

[0050] By fully assigning the signals to the respective radars or the respective transmitters and receivers, a MIMO angle estimation can then be performed using the signals assigned in all paths over the full virtual aperture (step S5.8). This leads to improved angular resolution and thus to more accurate results. Additionally or alternatively, a MIMO angle estimation can be performed with each of the monostatic apertures of the first radar Rad. 1 , the monostatic aperture of the second radar wheel 2 and the bistatic aperture of the first and second radar Rad 1 , wheel 2 can be performed as required. The Doppler velocity is output with full unambiguousness.

[0051] A preferred development of the invention comprises the assignment of the method to a scheme of a time division multiplex method (TDM).

[0052] Fig. Figure 6 shows such a preferred development of the method with an assignment of the method to a time-division multiplexing (TDM) scheme. The TDM scheme has several time slots Z, which in this case are divided into a first and a second time slot Z 1 and Z 2 which are carried out alternately. The invention is of course not limited to two time windows, but can comprise any technically feasible number of time windows. Each radar wheel 1 , wheel 2 In each time slot, the receiver transmits a signal encoded with a unique DDM code as described above. The DDM code used is DC 1 , DC 2 for the radars Rad 1 , wheel 2 for each of the two time windows Z 1 , Z 2 exchanged. In the first time window Z 1 is the signal from Rad 1 with the DDM code DC 1coded and the signal from Rad 2 with the DDM code DC 2 . In the second time window Z 2 is the signal from Rad 1 with the DDM code DC 2 coded and the signal from Rad 2 with the DDM code DC 1 . The time windows Z 1 , Z 2 are executed alternately during the time-division multiplexing process. The swap is therefore repeated for each time slot.

[0053] Fig. Figure 7 shows the implementation of the preferred further development of the method. Fig. 3 and Fig. The steps described in section 4 and not shown individually here also apply to the preferred further training. The difference lies in steps S1 and S6. In step 1, the signals for wheel 1 and bike 2 with their respective DDM code DC 1 , DC 2 encoded, whereby this encoding is as Fig. 6 described for each of the time windows Z1 , Z 2 In step S6, the assigned signals from each of steps S5.3 to S5.7 are compared based on their parameters (R x , v x ) and only those signals that are identical for each of the time windows are selected. Step S5.8 is then performed only with this selected data, eliminating false-positive measurements since, as described, the probability that these are identical in both time windows is extremely low. This further increases the robustness of the method. For example, it is also possible to perform step S5.8 before step S6 and to further process only those values ​​from the MIMO angle estimates of both time windows that correspond to the signals selected in step S6.

[0054] Although the unambiguous range of the speed of the method for unambiguous speed determination in the second embodiment is initially reduced by a factor of 2 due to the alternately executed time windows, such a disadvantage can be compensated for by a corresponding implementation of the TDM method in a known manner. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 202 500 A1

[0003] US 2022 / 0171049 A1

[0005]

Claims

[1] A method for operating a Doppler multiplexing (DDM) method in multiple-input-multiple-output (MIMO) radar networks, comprising the steps Generating and transmitting coded signals by Doppler multiplexing (DDM) to at least a first (Rad 1 ) and a second radar (Rad 2 ) from a MIMO radar network, where each radar (Rad 1 , wheel 2 ) comprises at least one transmitter and one receiver and wherein the coded signals have a respective DDM code (DC 1 , DC 2 ) that each radar (rad 1 , wheel 2 ) clearly identified; Reception and processing of reflected signals for digital processing and conversion into distance-Doppler velocity matrices; Threshold detection for each distance-Doppler matrix to determine cells with potential signals from the respective radar (Rad 1 , wheel 2), where the threshold detection transforms the signals into binary; Convolution of the respective potential binary signals with each of the unique DDM codes and unique assignment of the respective signals to one of the radars (Rad 1 , wheel 2 ), Determination of the uniquely assigned signals in the bistatic path (BP), whose signal parameters overlap for each radar, and determination of the uniquely assigned signals in the monostatic path (MP 1 , MP 2 ) for each radar (wheel 1 , wheel 2 ), whereby the signals of the respective monostatic path (MP 1 , MP 2 ) deviate from the signals of the bistatic path; Determination of the signals which are present in both the bistatic path (BP) and each monostatic path (MP 1 , MP 2) were clearly assigned, whereby starting from the respective signal of the bistatic path (BP) the signals of the monostatic paths (MP 1 , MP 2 ) and Full aperture MIMO angle estimation of a virtual MIMO array formed from the uniquely assigned signals in all paths. [2] The method of claim 1, further comprising the steps of: Determination of the signals that were assigned only in the bistatic path (BP); MIMO angle estimation using the bistatic aperture of the first and second radar (Rad 1 , wheel 2 ) and / or further comprehensively the steps: Determination of the signals which are only present in one of the monostatic paths (MP 1 , MP 2 ) were assigned; MIMO angle estimation with at least one of the monostatic apertures of the first radar (Rad 1 ), monostatic aperture of the second radar (Rad2 ). [3] Method according to one of the preceding claims, wherein each radar comprises a plurality of transmitters (Tx) and the respective DDM code (DC 1 , DC 2 ) unique phase shifts of the signals of each transmitter (Tx) of the respective radar (Rad 1 , wheel 2 ) includes. [4] Method according to one of the preceding claims, wherein the signals which are transmitted in both the bistatic path (BP) and each monostatic path (MP 1 , MP 2 ) were uniquely assigned, can be determined by means of a point-symmetric search starting from the respective signal of the bistatic path (BP). [5] Method according to claim 4, wherein the search range of the point-symmetric search is extended by one bin for each dimension from zero bins to the maximum possible deviation. [6] Method according to one of the preceding claims, wherein the method is carried out by means of linear frequency modulated chirps or exponential frequency modulated chirps or stepped frequency modulated chirps as sequential transmission signals. [7] Method according to one of the preceding claims, wherein the method is carried out according to a time division multiplexing (TDM) scheme and the respective DDM codes (DC 1 , DC 2 ) of the first radar (Rad 1 ) and the second radar (Rad 2 ) in a first and a second time window (Z 1 , Z 2 ) and the procedure for the first time window (Z 1 ) and the second time window (Z 2 ) is carried out; the results are compared and only signals are taken into account that are valid for each time window (Z 1 , Z 2 ) are identical. [8] Method according to claim 7, wherein the results of the first and second time windows (Z 1 , Z 2 ) are compared before the MIMO angle estimation step and this is only carried out for considered signals. [9] A method according to any one of the preceding claims 1 to 6, wherein the radar network comprises more than two radars and wherein each DDM code uniquely identifies the respective radar. [10] Method according to one of claims 7 or 8 in conjunction with claim 9, wherein the DDM codes of the individual radars for each of two time windows (Z 1 , Z 2 ) are exchanged in pairs. [11] Radar network with at least a first and a second radar, in which the method according to one of claims 1 to 10 is implemented.

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