METHOD IN A RADAR SYSTEM, RADAR SYSTEM OR DEVICE OF A RADAR SYSTEM

Description

[0001] The invention relates to a method in a radar system, a radar system, and a device of a radar system. In particular, this applies to a radar arrangement with distributed transmitting / receiving units,

[0002] In radar technology, a distinction is made between primary radars and secondary radars. Primary radar refers to radar systems that passively analyze reflected signal echoes from previously transmitted high-frequency signals. In secondary radar, the high-frequency signals previously transmitted by a first radar unit are received by a second radar unit. The second radar unit then actively transmits a response signal back to the first radar unit. Secondary radars are sometimes also called transponder systems, with the first radar unit often being referred to as the base station and the second radar unit as the transponder. A primary radar receives and processes its own self-transmitted signal, while a secondary radar receives and processes an external signal generated by another unit.

[0003] Synthetic aperture (SA) radar techniques are known for both radar imaging and transponder location. Common techniques and implementations can be found, for example, in the textbook "Inverse Synthetic Aperture Radar Imaging with Matlab Algorithms," chapters 3 and 4, or in R. Miesen, F. Kirsch, and M. Vossiek, "UHF RFID Localization Based on Synthetic Apertures," IEEE Transactions on Automation Science and Engineering, vol. 10, no. 3, pp. 807-815, July 2013, or in G. Li, R. Ebelt, and M. Vossiek, "A Novel Sequential Monte Carlo Method Based Synthetic Aperture Reconstruction Approach for Real-Time 3D Wireless Local Positioning," Frequenz: Journal of RF-Engineering and Telecommunications, vol. 66, no. 11-12, pp. 363-371, Nov. 2012. SA processes are also known from, for example, US 7948431 B2, US 8299959 B2 and the prior art presented in these documents.

[0004] It is generally known that SA methods can be implemented with all coherent waveforms, for example, electromagnetic waveforms in the radar domain. In the field of radar sensor technology, this is usually referred to as SAR (Synthetic Aperture Radar), SDRS (Software-Defined Radar Sensors), or MIMO (multiple input multiple output) radar.

[0005] Even signals from wave sources whose path and coherence are unknown to the receiver can be processed using SA methods if a signal is formed from signals received at at least two spatially separated locations. This signal no longer describes an absolute phase but rather phase differences between the signals. This approach is also known as radar interferometry or, for the field of radiometry, is described in Ruf, CS; Swift, CT; Tanner, AB; and Le Vine, DM, "Interferometric synthetic aperture microwave radiometry for the remote sensing of the Earth," Geoscience and Remote Sensing, IEEE Transactions on, vol. 26, no. 5, pp. 597, 611, September 1988. However, even with these methods, it is required that the signals received at at least two spatially separated locations are received by coherent receivers in order to be able to determine the phase differences between the at least two signals.However, with only two receiving locations, it is not possible to determine a distance to the wave source using such methods.

[0006] A variety of secondary radar methods are also known, as described, for example, in US 7940743 B2, in Stelzer, A., Fischer, A., Vossiek, M.: "A New Technology for Precise Position Measurement-LPM", Microwave Symposium Digest, 2004, IEEE MTT-S International, Vol. 2, 6-11, June 2004, pp. 655-658, or in R. Gierlich, J. Huttner, A. Ziroff, and M. Huemer, "Indoor positioning utilizing fractional-N PLL synthesizer and multi-channel base stations", Wireless Technology, 2008, EuWiT 2008, European Conference on, 2008, pp. 49-52.

[0007] In the field of radar radiolocation and communications technology, it is also known to separate the signals from multiple transmitters using multiplexing. Code-time or frequency-division multiplexing are common multiplexing methods. For example, Roehr, S.; Gulden, P.; and Vossiek, M., "Precise Distance and Velocity Measurement for Real-Time Locating in Multipath Environments Using a Frequency-Modulated Continuous-Wave Secondary Radar Approach," Microwave Theory and Techniques, IEEE Transactions on, vol. 56, no. 10, pp. 2329, 2339, Oct. 2008, demonstrate how multiplexing can be implemented with FMCW signals (FMCW: Frequency Modulated Continuous Wave). Sturm, Christian, et al. "Spectrally interleaved multi-carrier signals for radar network applications and multi-input multi-output radar" IET Radar, Sonar & Navigation, 2013, 7th year, no. 3, pp. 261-269 and in GUTIERREZ DEL ARROYO, Jose R.; JACKSON, Julie Ann; TEMPLE, Michael A."Receive signal processing for OFDM-based radar imaging" In: Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on. IEEE, 2013, pp. 2775-2779, OFDM signals (OFDM: Orthogonal Frequency-Division Multiplexing) are used for multiplexing.

[0008] Radar methods that use so-called multi-ramp FMCW signals for distance and speed measurement are known, e.g. from: Afi, F.; Vossiek, M., "Detection of weak moving targets based on 2-D range-Doppler FMCW radar Fourier processing", German Microwave Conference, 2010 , pp. 214, 217, 15-17, March 2010, and from the prior art cited therein as well as from US0201400221 1 1A1.

[0009] Secondary radar methods and secondary radar arrangements are well known from Scheiblhofer, Stefan, et al., "Performance analysis of cooperative FMCW radar, distance measurement systems", In: Microwave Symposium Digest, 2008 IEEE MTT-S International. IEEE, 2008, pp. 121-124 and Roehr, S.; Gulden, P.; Vossiek, M., "Precise Distance and Velocity Measurement for Real Time Locating in Multipath Environments Using a Frequency-Modulated Continuous-Wave Secondary Radar Approach", Microwave Theory and Techniques, IEEE Transactions on, vol. 56, no. 10, pp. 2329, 2339, Oct. 2008. These methods are based either on non-coherent synchronization or on transmitting the difference in frequency between the down-converted signals. Both methods are therefore not suitable for coherent distance measurement and as a basis for SAR methods.

[0010] The object of the invention is to propose an alternative method and system arrangement that enables coherent distance measurement between units. The aim is to provide the necessary elements for coherent distance measurement between two units. In particular, this should enable highly accurate distance measurement between secondary radar units and, for radar in general, enable the synthesis of larger apertures and / or a higher achievable resolution.

[0011] This object is achieved by a method in a radar system having the features of patent claim 1, a radar system according to claim 12, or a device of a radar system having the features of patent claim 16. Advantageous embodiments are the subject of dependent claims.

[0012] Accordingly, in general terms, a method is disclosed in a radar system in which a first signal is generated in a first non-coherent transceiver unit and is transmitted, in particular broadcast, via a path, a first signal is generated in a further, in particular second, non-coherent transceiver unit and is transmitted, in particular broadcast, via the path, a comparison signal is formed in the first transceiver unit from its first signal and from such a first signal received by the further transceiver unit via the path, and a further comparison signal is formed in the further transceiver unit from its first signal and from such a first signal received by the first transceiver unit via the path, wherein the further comparison signal is transmitted, in particular communicated, from the further transceiver unit to the first transceiver unit.

[0013] The term "first signal," instead of simply "signal," serves in particular as a conceptual distinction from comparison signals and comparison-comparison signals. Such a comparison signal corresponds in particular to a comparison signal generated in a first comparison stage in one of the two transmitting / receiving units, wherein the comparison signal of at least one of the two transmitting / receiving units is transmitted to at least the other of the transmitting / receiving units.

[0014] Insofar as the terms "second", "further" or "other" are used, this serves in particular to distinguish a signal or a component in or from a first such transmitting-receiving unit from at least one corresponding signal or a corresponding component of at least a second such transmitting-receiving unit, which cooperates with the first such transmitting-receiving unit for the purpose of carrying out the method or as a system component.

[0015] The path is in particular an air interface over which the signals and comparison signals are sent or transmitted and received by means of antennas.

[0016] If calculations, evaluations, or other process steps are performed in the transmitting / receiving unit, this also includes a possibly physically independent evaluation device connected to the transmitting / receiving unit. For example, the transmitting / receiving unit can be designed as an arrangement comprising, in particular, one or more antennas with a few signal-generating or signal-processing components, while other components such as the signal comparison units or an evaluation device are connected to such an arrangement as structurally independent components. If components are used, these can, if technically feasible, be designed as so-called hardware comprising processing components and / or implemented as signal or data processing steps executed entirely or partially in a processor.

[0017] This advantageously enables improved data processing in the first transmitting / receiving unit, since the comparison signal transmitted into this first transmitting / receiving unit comprises information content or data, in particular about a clock or phase and frequency state of the other transmitting / receiving unit, and thus a coherence or a signal appearing coherent can be reconstructed and evaluated for a signal in the transmitting / receiving unit or an evaluation device connected to it.

[0018] Another advantage is that determining the comparison signal results in a signal with a lower frequency, which requires fewer sampling points for unambiguous representation. This makes it easier to transmit the information contained therein to the other transmitting / receiving unit(s). Especially for signals in the frequency range above 1 GHz, the lower sampling rate for the comparison signal is very advantageous for technical implementation and is therefore desirable. Another advantage is the reduction in memory requirements due to the smaller data volume.

[0019] One embodiment consists in forming a comparison / comparison signal from this comparison signal and the further comparison signal. Such a comparison / comparison signal corresponds, in particular, to a signal generated in a second comparison stage in one of the two transceiver units from two such comparison signals, wherein the comparison signal originates, in particular, from the transceiver unit itself, and the other comparison signal used for comparison was transmitted from another transceiver unit. Such a comparison / comparison signal, in particular in a secondary radar system, is a signal with properties of a signal that can otherwise be generated with a primary radar system.

[0020] One embodiment consists in that the comparison comparison signal, in which the two comparison signals are processed together - in particular conjugated complex multiplied - corresponds to a comparison signal generated with a coherent radar system.

[0021] In particular, a method can thus be carried out in a radar system in which a comparison-comparison signal is formed in that a comparison signal is formed in a first non-coherent transmitting-receiving unit from a first signal generated by the first non-coherent transmitting-receiving unit itself and from a first signal generated in a further, in particular second non-coherent transmitting-receiving unit and transmitted, in particular emitted, via a path, and subsequently the comparison-comparison signal is formed from this comparison signal and a further comparison signal, wherein the further comparison signal is formed in a corresponding manner in the further transmitting-receiving unit from such a first signal generated in the second non-coherent transmitting-receiving unit and such a first signal received in the second non-coherent transmitting-receiving unit from the first transmitting-receiving unit and is transmitted, in particular communicated, to the first transmitting-receiving unit.

[0022] In particular, a method can thus be carried out in a radar system in which a comparison comparison signal is formed by generating a first signal in a first non-coherent transmitting-receiving unit and forming a comparison signal from the first signal and from a first signal received by a further, in particular second, non-coherent transmitting-receiving unit, wherein the first signal is generated by the further transmitting-receiving unit and sent, in particular broadcast, to the first transmitting-receiving unit via a path, a further comparison signal is formed in a corresponding manner in the further transmitting-receiving unit from such a first signal generated therein and such a first signal of the first transmitting-receiving unit received therein via the path and transmitted to the first transmitting-receiving unit,in particular is communicated and the comparison comparison signal is formed from this comparison signal and the further comparison signal.,

[0023] In particular, a method can thus be carried out in a distributed radar system with at least two spatially spaced transmitting / receiving units as radar units, in which the transmitting / receiving units each have a signal generator, wherein the signal generators generate signals which are mutually exchanged between the radar units and wherein the transmitting / receiving units have communication means, wherein with the communication means at least one of the comparison signals of a transmitting / receiving unit in which it was formed is transmitted to at least one other transmitting / receiving unit and wherein at least one of the transmitting / receiving units has a second orfurther comparison unit and the determined comparison signals of the two first comparison units of the two transmitting-receiving units are fed to this second comparison unit and at least one mixing process or a correlation is carried out in this second comparison unit and thus a comparison-comparison signal is formed in such a way that a feature of this comparison-comparison signal is proportional to the signal propagation time that a signal requires for the path between the transmitting-receiving units, wherein the feature is the phase or the phase curve or the frequency of the comparison signal or the position of a pulse-shaped signal maximum in the comparison signal.

[0024] This procedure, or an arrangement implementing it, is advantageous for highly accurate distance measurement between secondary radar units. This procedure, or an arrangement implementing it, is advantageous according to a further embodiment in order to enable a larger aperture and a higher achievable resolution for radar in general. For larger apertures, a technically simpler implementation of an array is advantageous, since, in particular, the previously necessary complex distribution of high-frequency signals is no longer required.

[0025] One embodiment consists in that at least one of the comparison signal, the further comparison signal or the comparison-comparison signal is formed by at least one of mixing or correlation.

[0026] Preferably, at least one mixing process is performed in a further comparison unit or the second comparison process, thus forming a comparison-comparison signal, and a signal is determined or calculated from this comparison-comparison signal using a Fourier transformation. From this determined or calculated signal, a distance and / or a spatial position and / or a speed of an object or of a second radar unit used as a transceiver unit is determined.

[0027] Preferably, at least one comparison / comparison signal is formed in a further comparison unit or the second comparison process, and at least one phase or phase value and / or at least one frequency value is determined from this comparison / comparison signal using a Fourier transformation. In particular, a distance and / or speed value is determined, in particular calculated, using at least one of these phase or frequency values.

[0028] Instead of mixing or in addition to it, correlation can be used.

[0029] One embodiment is that at least one such further comparison signal is transmitted between the transmitting-receiving units as at least one of data, a signal containing data or a signal containing data that can be reconstructed.

[0030] This ensures that the data content of the comparison signal is received uncorrupted or can be reconstructed at the receiver. When comparing the comparison signals, corruption or interference that could arise from signal corruption during the transmission of the data contained in the signal is thus avoided. Thus, what is transmitted or communicated is, in particular, data as such, especially digital data, whereby such data can be transmitted both via transmission using an antenna into the vicinity of the antenna and via a cable. Another advantage is that in this case, in particular, only necessary parts of the signal need be transmitted or the signal can be transmitted in compressed / preprocessed form, thus lowering the data rate requirements for communication.

[0031] One embodiment consists in transmitting at least one of the first signals as a transmission signal over the path configured as an air interface. The transmission of the first signals can thus be carried out in the usual way by emitting or radiating a radar signal as an analog signal into the vicinity of the transmitting antenna using a transmitting antenna.

[0032] One embodiment consists in coordinating the times for transmitting the first signals in such a way that the first signals at least partially overlap in time. This results in a pre-synchronization of the transmitting / receiving units transmitting the first signals in particular so that the signals overlap, in particular by at least a quarter of their signal length or modulation duration, preferably by more than a half of their signal length or modulation duration. Advantageously, such an implementation requires a lower bandwidth, which must be taken into account when generating the signals and when dimensioning the required components. In addition, the range is improved because both signals are present over a longer period of time.

[0033] One embodiment consists in that a signal propagation time required by such a first signal for the path between the transmitting / receiving units is determined from at least one comparison comparison signal by analyzing at least one of a phase or a phase value, a frequency, an amplitude curve or a phase curve of the comparison comparison signal.

[0034] In particular, the distance between the participating transmit / receive units can be determined from the signal propagation time. Methods for determining the signal propagation time include, for example, frequencies using spectral analysis, in particular Fourier transformation; phase values can be determined analytically or using Fourier transformation; an amplitude curve from an amplitude-time diagram; and / or a phase curve from a phase-time diagram. In particular, a phase, a frequency, an amplitude curve, a phase curve of the reference-comparison signal, or a position of a pulse-shaped signal maximum in the reference-comparison signal are deterministically determined using the signal propagation time.

[0035] In the second comparison process, a correlation process is performed, thereby forming a comparison-comparison signal, and at least one pulse-shaped signal maximum or pulse is detected in this comparison-comparison signal. Subsequently, the temporal position of the pulse in the comparison signal or a phase value or frequency of at least one detected pulse is determined, and at least one of these previously determined position, phase, or frequency values is used to calculate a distance or speed value.

[0036] One embodiment involves generating and transmitting at least one of the first signals as an FMCW or OFDM modulated signal. FMCW-modulated signals enable particularly simple evaluation of the comparison signal via a Fourier transform. Furthermore, due to their principle, they are particularly well-suited for distance measurement, as their time-frequency relationship is particularly well-known. Furthermore, FMCW signals can be generated with little technical effort. OFDM signals are particularly advantageous for communications systems. They thus enable advantageous integration of the method into communications systems.

[0037] One embodiment involves generating and transmitting at least one of the first signals as a multi-ramp signal. This advantageously results in good speed determination and target separation.

[0038] One embodiment consists in that a plurality of comparison comparison signals, which are measured one after the other in time by at least two transmitting-receiving units, of which at least one of the transmitting-receiving units is moving, are determined and at least one of a distance, a position, a speed or the presence of one of the transmitting-receiving units or the presence of such a transmitting-receiving unit or at least one of a distance, a position, a speed relative to an object or the presence of an object is determined using a synthetic aperture method.

[0039] For example, the distance between the transmitting / receiving units is measured along the direct path, as with secondary radar, thus determining the distance between the two units. The distance between the transmitting / receiving units can also be determined or measured using a reflection from an object as a passive target. With the known position of the units, the distance and position of the object can then be determined.

[0040] Furthermore, in general terms, a radar system is disclosed in which at least one first non-coherent transceiver unit is designed to generate a first signal and to transmit it, in particular to emit it, via a path, at least one further, in particular second non-coherent transceiver unit is designed to generate a first signal and to transmit it, in particular to emit it, via the path, the first transceiver unit is designed to form a comparison signal from its first signal and from a first signal received from the further transceiver unit via the path, the further transceiver unit is designed to form a further comparison signal from its first signal and from a first signal received from the first transceiver unit via the path, and the further comparison signal is transmitted, in particular communicated, from the further transceiver unit to the first transceiver unit.

[0041] One embodiment is that in the radar system a comparison comparison signal is formed from this comparison signal and the further comparison signal.

[0042] One embodiment consists in the radar system with three or more spatially spaced transmitting / receiving units, in which a distance, a position, a speed or the presence of one of the transmitting / receiving units or the presence of such a transmitting / receiving unit or at least one of a distance, a position, a speed relative to an object or the presence of an object is determined from two or more comparison comparison signals which are measured with more than two pairs of two of the spatially spaced transmitting / receiving units.

[0043] The arrangement thus creates aperture matrices, the evaluation of which allows the angle of incidence to be determined. Alternatively, an aperture can be scanned with only one transmit-receive unit, and the angle of incidence can then be determined using a synthetic aperture method.

[0044] One embodiment is the radar system in which the first transceiver unit and at least one such further transceiver unit and / or an evaluation device are configured to carry out such a method. Such an evaluation device is in particular a component of one or both transceiver units or is connected to one or more such transceiver units.

[0045] In particular, a device of a radar system is preferred, in particular for carrying out such a method and / or in such a radar system, wherein the device is designed as a first non-coherent transmitting-receiving unit - in particular first non-coherent transmitting-receiving unit - and has a signal generator and at least one antenna, which are designed to generate a first signal and to transmit it, in particular to radiate it, via a path, has an arrangement which is designed to form a comparison signal from the first signal and from such a first signal received by a further transceiver unit via the path and at least one of an interface which is designed to transmit, in particular to communicate, the comparison signal to the further transceiver unit or an interface which is designed to receive such a further comparison signal generated by the further transceiver unit by means of transmission, in particular communication, in the first transceiver unit.

[0046] One embodiment consists in a device with a further comparison unit which forms a comparison comparison signal from the comparison signal formed in the same transmitting-receiving unit and the comparison signal transmitted to this transmitting-receiving unit.

[0047] The arrangement that outputs the comparison signal and the comparison unit are designed, in particular, as a mixer or correlator. Thus, processing, in particular a correlation process, is performed. From the ultimately formed comparison signal, the distance, position, or speed of an object or of this transmitting / receiving unit is determined.

[0048] One embodiment consists in a device in which the at least one interface is a data interface. This enables the first comparison signal to be transmitted as data—in particular as a data signal containing digital data—between the transmitting / receiving units.

[0049] One embodiment consists in a device in which a filter is arranged between the arrangement which outputs the comparison signal and the further comparison unit which forms the comparison comparison signal, wherein the filter applies the comparison signal to the comparison unit, wherein the filter does not apply a further comparison signal formed in the arrangement upstream of the filter and suppresses the comparison signal formed in the upstream arrangement or provides it at a terminal.

[0050] This allows the additional comparison signal, which is generated by a back reflection from the transmitting antenna of the transceiver unit to its receiving antenna, to be either kept away from the additional comparison unit or made available at a separate output or connection for further processing. Such an arrangement is particularly advantageous when using CW signals and takes into account passive radar content generated by back or cross reflection.

[0051] One embodiment consists in a device which has a plurality of receiving antennas which are spatially spaced apart from one another and to which an arrangement is assigned in each case which is designed to form a comparison signal from the first signal and from such a first signal received by such a further transmitting-receiving unit via the path.

[0052] This creates a coherent multi-channel receiver that simulates a spatial aperture that generates a plurality of comparison signals by measuring or transmitting the first signals and enables corresponding evaluations of, for example, the angular positions of the devices relative to one another and / or in space.

[0053] Thus, a method for generating coherent radar signals with multiple incoherently operating transmit / receive units and arrangements for implementing the method are particularly preferred, as are novel distributed radar systems for positioning and imaging using the method and arrangements. Coherence is achieved in particular through post-processing of the various signals.

[0054] The problem is solved in particular by forming measurement signals in a distributed radar system consisting of at least two radar units whose sources are not coherent with one another in such a way that the phase of the signals thus formed is proportional to the signal propagation time of the measurement signals exchanged between the radar units, as is otherwise only the case with coherent radar units. The preferred methods and arrangements enable novel, high-performance distributed radar systems with multiple non-coherent transceiver units that are suitable both for locating and imaging passively reflecting objects and for locating other non-coherent transceiver units. In these distributed radar systems with multiple non-coherent transceiver units, SA methods are also particularly applicable.

[0055] This represents a crucial improvement, since, as explained, SA methods actually require coherent transmit / receive units. The preferred methods make it possible, in particular, to generate large synthetic apertures with multiple spatially distributed transmit / receive units without the need to supply the multiple units with a common coherent radio-frequency reference signal, as is usually the case. By eliminating the radio-frequency lines for distributing the radio-frequency reference signal, the costs and complexity of such arrangements are significantly reduced.

[0056] In the area of secondary radar, the arrangement also increases the achievable accuracy of position, movement and speed measurements, as coherent signals are now available.

[0057] Exemplary embodiments are explained in more detail below with reference to the drawings. In the various figures, the same reference numerals are used for identical or similarly acting method steps, signals, components, and the like, so that reference is also made to the explanations for other figures in this regard. In particular, differences from the explanations for other, particularly the preceding, figures are preferably described. They show: Fig. 1 schematically shows a structure of two non-coherent transmit / receive units and their interactions and signal processing; Fig. 2 schematically shows a structure of two non-coherent transmit / receive units and their interactions and signal processing when using CW radar signals (CW: continuous wave); Fig. 3 an arrangement of several such non-coherent transmit / receive units to form a MIMO arrangement for measuring passively reflecting objects to locate an object or to image an object scene; Fig. 4 an arrangement of several such non-coherent transmit / receive units to form a MIMO arrangement for measuring between actively reflecting non-coherent transmit / receive units to locate at least one further non-coherent transmit / receive unit; Fig. 5 a recording situation for secondary radar aperture synthesis; Fig. 6 a recording situation for an inverse secondary radar aperture synthesis; Fig.Fig. 7 shows an arrangement for measuring an angle between two non-coherent transmitting / receiving units relative to the second antenna plane; Fig. 8 shows an arrangement for measuring an angle between two non-coherent transmitting / receiving units relative to the first antenna plane; Fig. 9 shows an arrangement for measuring an angle between an object and a first of two non-coherent transmitting / receiving units or for locating an object or for imaging an object scene; and Fig. 10 shows an exemplary FMCW multi-ramp signal.

[0058] Fig. 1 schematically shows a structure of two non-coherent transceiver units NKSE1, NKSE2 and their preferred interactions and signal processing as components of a distributed radar system to illustrate an exemplary, preferred basic structure. In the following, the term transceiver unit NKSE1, NKSE2 always refers to a non-coherent transceiver unit NKSE1, NKSE2.

[0059] The two transceiver units NKSE1, NKSE2 are arranged spatially separated. The transceiver units NKSE1, NKSE2 exchange signals with each other, including signals containing information or data, via a path SP, which is designed, in particular, as an air interface. In one of the transceiver units NKSE1, NKSE2, in addition to signals transmitted directly from the other transceiver unit NKSE2, NKSE1, indirectly transmitted signals are also received, which were subject to reflection from an object along the path SP.

[0060] For an application of a preferred method, a preferred arrangement consists of at least two similarly constructed transmitting-receiving units NKSE1, NKSE2.

[0061] In a first of the at least two transceiver units NKSE1, NKSE2, a signal generator SigGen1 generates a first signal sigTX1. This first signal sigTX1 is split into two paths via a signal splitter. The first signal sigTX1 is emitted from the first transceiver unit NKSE1 via an antenna TA1 configured as a transmitting antenna via one of the paths. The first signal sigTX1 is fed to a signal comparison unit SigComp1 via the other path. The signal generator uses, in particular, a clock source or an oscillator or an oscillator signal.

[0062] The second or a further one of the at least two transceiver units NSKE2 receives the signal emitted by the first transceiver unit NSKE1 via an antenna RA2 configured as a receiving antenna and feeds it as a first received signal sigRX21 to a signal comparison unit SigComp2. In this second or further transceiver unit NSKE2, a signal generator SigGen2 generates a further first signal sigTX2. This further first signal sigTX2 is also split, in particular split via a signal splitter, and fed via one path to the signal comparison unit SigComp2. The further first signal sigTX2 is emitted via a second path via an antenna TA2 configured as a transmitting antenna.

[0063] The first transmitting / receiving unit NSKE1 receives the signal emitted by the second or further transmitting / receiving unit NSKE2 via an antenna RA1 designed as a receiving antenna and feeds this as a first received signal sigRX12 to the signal comparison unit SigComp1 of the first transmitting / receiving unit NSKE1.

[0064] According to one variant, the respective first signal sigTX1, sigTX2 can be decoupled from the path between the signal generator SigGen1, SigGen2 and the antenna TA1, TA2, for example, via a directional coupler. It is also possible to transmit the first signal sigTX1, sigTX2 via the antenna TA1, TA2 connected as the transmitting antenna and to receive it via the additional antenna RA1, RA2 connected as the receiving antenna and to apply it to the signal comparison unit SigComp1, SigComp2. Furthermore, it is possible to transmit the first signal sigTX1, sigTX2 via the antenna TA1, TA2 connected as the transmitting antenna and to receive it via the same antenna additionally connected as the receiving antenna on the same path, to decouple it and apply it to the signal comparison unit SigComp1, SigComp2.

[0065] Preferably, frequency-modulated signals are used as such first signals sigTX1 or sigTX2. In particular, linear frequency-modulated signals (FMCW: frequency modulated continuous wave), stepped frequency-modulated signals (FSCW: frequency stepped continuous wave), frequency-shift keyed signals (FSK: frequency shift keying), signals with frequency hops (FHOP: frequency hop), or signals using orthogonal frequency-division multiplexing (OFDM) are preferred signal and / or modulation forms. However, all other signal forms with so-called good correlation properties, as are generally known in radar technology, such as noise signals, pseudo-random pulse sequences with amplitudes or phase modulation, such as Barker, M, Gold, or Kasami sequences, or polyphase codes, can also be used.It is particularly advantageous for the simultaneous operation of multiple transceiver units NKSE1, NSKE2 if, for multiplexing multiple transceiver units NKSE-N with a number N of transceiver units NKSE-N with N > 1 signal forms are selected with which a set of N orthogonally modulated signals sigTX1, sigTX2, ... sigTXN can be formed. Thus, each first signal sigTX1, sigTX2, ... formed in one of the transceiver units NKSE1, NSKE2, ... NSKE-N can be separated from the first received signals formed in one of the other transceiver units NKSE1, NSKE2, ... NSKE-N, even during simultaneous reception. In particular, the number N can thus also be greater than two.

[0066] The signal comparison units SigComp1, SigComp2 compare the first signal sigTX1 or sigTX2 applied to them, respectively, and the first received signal sigRX12 or sigRX21, respectively, and each form a particular first comparison signal sigC12 or sigC21. In particular, the phase and / or time profile of these comparison signals sigC12, C21 is predetermined by the time, frequency, and / or phase difference of the corresponding first signals sigTX1 or sigTX2 and the corresponding first received signals sigRX12 or sigRX21, respectively, and is optionally determined.According to the invention, the phase and / or time profile of the comparison signal sigC12 of the first transmitting / receiving unit NKSE1 is determined and ascertainable by the time, frequency and / or phase difference of the first signal sigTX1 and the first received signal sigRX12 in the first transmitting / receiving unit NKSE1, and the phase and / or time profile of the comparison signal sigC21 of the second or further transmitting / receiving unit NKSE2 is determined and ascertainable by the time, frequency and / or phase difference of the first signal sigTX2 and the first received signal sigRX21 in the second transmitting / receiving unit NKSE2.

[0067] Such signal comparison units SigComp1 or SigComp2 preferably comprise a so-called mixer when using frequency-modulated signals, or a correlator when using phase- and amplitude-modulated or pulse-shaped signals to form the comparison signal sigC12 or sigC21. In the mixer, the two signals are multiplied entirely or in sections, and in the correlator, they are correlated entirely or in sections. The combined use of mixer and correlator is also feasible.

[0068] The comparison signal sigC21 of the second or further transceiver unit NKSE2 is transmitted via a data interface CommTX, CommRX of the second transceiver unit NKSE2 to a data interface CommTX, CommRX of the first transceiver unit NKSE1 and is fed to a further signal comparison unit SigComp12 in the first transceiver unit NKSE1. The comparison signal sigC21 is preferably digitized and then transmitted via the interfaces configured as digital interfaces. The interface between the data interfaces CommTX, CommRX can be implemented wirelessly as a radio interface, in particular via the path SP between them, or via a line or wired connection. The comparison signal sigC12 formed in the first transceiver unit NKSE1 is fed as a further signal to the further signal comparison unit SigComp12 in the first transceiver unit NKSE1.

[0069] The further signal comparison unit SigComp12 compares the comparison signals sigC12 and sigC21 applied to it and forms a comparison-comparison signal sigCC12. In particular, its phase or its amplitude and / or phase characteristic is determined or optionally ascertained by the signal propagation time required by a signal for the path from the first transceiver unit NKSE1 to the second and / or further transceiver unit NKSE2 or from the second and / or further transceiver unit NKSE2 to the first transceiver unit NKSE1. For this purpose, the further signal comparison unit SigComp12 preferably comprises a mixer and / or a correlator for forming the comparison-comparison signal sigCC12. The comparison signal sigC12 is preferably supplied to the further signal comparison unit SigComp12 in digitized form, and the signal comparison is preferably carried out by means of digital signal processing.

[0070] The comparison comparison signal sigCC21 is thus formed in particular in that, in a first step, a comparison signal sigC12 is formed in the first transmitting-receiving unit NKSE1 from a first signal sigTX1 generated by the first transmitting-receiving unit NKSE1 itself and from a first signal sigTX2 generated in the second or a further transmitting-receiving unit NKSE2 and transmitted via the path SP, and subsequently, in a second step, the comparison comparison signal sigCC21 is formed from this first comparison signal sigC21 and a further first comparison signal sigC21, wherein beforehand the further first comparison signal sigC21 is formed in a corresponding manner in the other transmitting-receiving unit NKSE2 from its first signal sigTX2 and the first signal sigTX1 received in it via the path SP from the first transmitting-receiving unit NKSE1 and is transmitted in particular as a data signal.

[0071] Whether the signal sigTX1 emitted by the antenna TA1 of one transceiver unit NKSE1 travels directly to the antenna RA2, which is configured as the receiving antenna, or is reflected by an object and then reaches the antenna RA2, which is configured as the receiving antenna, of the other transceiver unit NKSE2, is initially irrelevant. The transmission path from one antenna TA1 to the other antenna RA2 can generally be described, as is common in systems theory, by a channel transfer function or the so-called channel impulse response. The method described here makes particular use of the fact that the signal sigTX2 emitted by the antenna TA2 used for transmission is transmitted to the antenna RA1 via the same channel as before in the opposite direction from the antenna TA1 used for transmission of one transceiver unit NKSE1 to the antenna RA2 used for reception of the other transceiver unit NKSE2.The commonly known technical term for the particularly required equality of the channel transfer functions in both transmission directions is so-called channel reciprocity. Those skilled in the art will know that channel reciprocity can be assumed if the antennas TA1 and RA1 are located at the same location, or if only one antenna is used for transmitting and receiving in one transceiver unit NKSE1, and if, in addition, the antennas TA2 and RA2 of the other transceiver unit NKSE2 are located at the same location, or if only one antenna is used for transmitting and receiving in the other transceiver unit NKSE2. A particularly sufficient approximate channel reciprocity can also be assumed if both the antennas TA1, RA1 of one transmitting-receiving unit NKSE1 and the antennas TA2, RA2 of at least one other transmitting-receiving unit NKSE2 are arranged very closely adjacent to each other.By very close proximity we mean that the spatial sampling theorem is observed, e.g. the distance for antennas with an aperture angle of 180° is half the wavelength or for a distance of 90° it is one wavelength.

[0072] In the at least one other transceiver unit NKSE2, a comparison comparison signal sigCC21 can be formed in a manner similar to how a comparison comparison signal sigCC12 was formed in the above-described transceiver unit NKSE1. However, with channel reciprocity, the information that can be extracted from the comparison comparison signals sigCC21 and sigCC12 is identical. Therefore, it is usually sufficient to form only one of the two comparison comparison signals.

[0073] Optionally, by a corresponding procedure, the comparison signal sigC12 of the first transceiver unit NKSE1 can be transmitted via the or a data interface CommTX, CommRX of the first transceiver unit NKSE1 to the or a data interface CommTX, CommRX of the second and / or further transceiver unit NKSE2 and applied to a further signal comparison unit SigComp21 of this second and / or further transceiver unit NKSE2. The comparison signal sigC21 formed in this transceiver unit NKSE2 is supplied as a further signal to the further signal comparison unit SigComp21 in the second and / or further transceiver unit NKSE2. A comparison comparison signal sigCC21 is thus also formed with the further signal comparison unit SigComp21.

[0074] Using an exemplary embodiment shown in Fig. 2 is illustrated, a basic function and a basic structure of a suitable non-coherent transmitting-receiving unit will now be explained by way of example.

[0075] For the sake of simple mathematical representation, the signal generators are initially assumed to be sinusoidal signal generators. Mathematically, the generated CW signals (CW = continuous wave) are each represented as a complex-valued sinusoidal continuous wave signal at a fixed angular frequency ω1 or ω2 of the exemplary transmit / receive units NKSE1, NSKE2. A continuous wave signal is, in particular, a signal that is continuously transmitted at a constant frequency over a period of time. A transfer of this signal representation to real-valued signals is known as such. The first signals sigTX1, sigTX2 of the two transmit / receive units NKSE1, NSKE2, assumed to be CW transmit signals, are defined as follows, depending on time t: sigTX 1 = e j ω 1 t − T 01 + φ 1 und sigTX 2 = e j ω 2 t − T 02 + φ 2

[0076] The start times of the signals sigTX1, sigTX2 are T01 and T02, respectively, and phases φ1 and φ2 are arbitrary zero phase angles, i.e., angles at time t = 0. For time-limited signals, the start times of the signals are preferably chosen such that the two signals sigTX1, sigTX2 overlap significantly. Let T be a time duration of the two signals sigTX1, sigTX2, and ΔT12 be the absolute value of the difference between the start times T01 and T02, respectively. Preferably, the time duration T is much greater than the absolute value of the difference ΔT12, advantageously at least 10 times greater. If this is not the case, the transmitting / receiving units NKSE1, NKSE2 are equipped with devices designed to store the transmitted and received signals sigTX1, sigTX2, sigRX21, sigRX12 in order to compare them offline following a signal transmission.

[0077] One of the transmit / receive units NKSE1 transmits the first signal sigTX1. This signal is transmitted to at least one other of the transmit / receive units NKSE2, where it is received as the signal sigRX21. The transmitted signal can also be reflected off an object and returned to the transmitting unit NKSE1, where it is received as the signal sigRX11. Consequently, the following applies to the signal that has not yet been downconverted: sigRX 21 = e j ω 1 t − T 01 − τ 12 + φ 1 + φ 12 and sigRX 11 = e j ω 1 t − T 01 − τ 11 + φ 1 + φ 11 , where τ12 represents a propagation time of the signal from one, in particular the first, of the transmitting / receiving units NKSE1 to the other, in particular the second, of the transmitting / receiving units NKSE2, and τ11 represents a propagation time of the signal from one, in particular the first, of the transmitting / receiving units NKSE1 to an object and back to itself. Phases φ12 and φ11, in particular, take into account all constant system- and reflection-related phase shifts that may occur.

[0078] The other transceiver unit, NKSE2, transmits its signal sigTX2. This signal is transmitted to the first of the transceiver units, NKSE1, where it is received as the signal sigRX12. However, the signal can also be reflected by objects and returned to the other transceiver unit, NKSE2, where it is transmitted, and is received as the signal sigRX22. Consequently, the following applies: sigRX 12 = e j ω 2 t − T 02 − τ 21 + φ 2 + φ 21 and sigRX 22 = e j ω 2 t − T 02 − τ 22 + φ 2 + φ 22 , where τ21 represents a propagation time of the signal from the other, in particular second, of the transmitting / receiving units NKSE2 to the one, in particular first, of the transmitting / receiving units NKSE1, and τ22 represents a propagation time of the signal from the other transmitting / receiving unit NKSE2 to an object and back again. With channel reciprocity, the propagation times τ21 and τ12 are equal, which is assumed below. Phases or phase values φ21 and φ22 take into account, in particular, all constant system- and reflection-related phase shifts that may occur. With channel reciprocity, the phases φ21 and φ12 are equal, which is assumed below for the sake of simplicity.

[0079] The signal comparison units SigComp1, SigComp2 are implemented as mixers in the exemplary embodiment. They downmix the received signals sigRX21, sigRX11 and sigRX12, sigRX22 into a low-frequency frequency band. As such, it is generally known that a mixing process can be expressed in systems theory as a multiplication, or a downmixing of two complex

[0080] Sinusoidal signals are multiplied by the complex conjugate (* = symbol for conjugation) of one of the signals. Therefore, the following applies: sigC 11 = sigTX 1 ⋅ sigRX 11 * = ⋅ e j ω 1 t − T 01 + φ 1 ⋅ e − j ω 1 t − T 01 − τ 11 + φ 1 + φ 11 = e j ω 1 τ 11 + φ 11 , as well as: sigC 21 = sigTX 2 ⋅ sigRX 21 * = e j ω 2 t − T 02 + φ 2 ⋅ e − j ω 1 t − T 01 − τ 12 + φ 1 + φ 12 = e j ω 2 t − T 02 − ω 1 t − T 01 − τ 12 + φ 2 − φ 1 − φ 12 sigC 22 = sigTX 2 ⋅ sigRX 22 * = ⋅ e j ω 2 t − T 02 + φ 2 ⋅ e − j ω 2 t − T 02 − τ 22 + φ 2 + φ 22 = e j ω 2 τ 22 + φ 22

[0081] In the signal comparison unit SigComp1 of the first transmitting-receiving unit NKSE1, the comparison signal sigC12 is formed from the signal SigTX1 of the first transmitting-receiving unit NKSE1 and the signal sigRX12 of the other transmitting-receiving unit NKSE2 received therein, and a comparison signal sigC11 is formed from the signal SigTX1 of the first transmitting-receiving unit NKSE1 and the reflected signal sigRX11 received therein. In the signal comparison unit SigComp2 of the other, in particular second, transmitting-receiving unit NKSE2, the comparison signal sigC21 is formed from the signal SigTX2 of this transmitting-receiving unit NKSE2 and the signal sigRX21 of the other, first transmitting-receiving unit NKSE1 received therein, and a comparison signal sigC22 is formed from the signal SigTX2 of the second transmitting-receiving unit NKSE2 and the reflected signal sigRX22 received therein.

[0082] To ensure that the comparison signals sigC12 and sigC11 or the comparison signals sigC21 and sigC22 can be easily separated from one another, i.e., in particular, to enable multiplex operation, the angular frequency ω1 of one transceiver unit NKSE1 is preferably selected to be different from the frequency ω2 of the other transceiver unit NKSE2. A frequency offset |Δ12| = |ω1-ω2| should preferably be selected to be greater than zero but not too large. The latter is useful in order to avoid unnecessarily increasing the bandwidth of the comparison signal, particularly for components such as an analog-to-digital converter ADC, a filter FLT, the additional signal comparison unit SigComp12, and the data interfaces CommTX and CommRX. In particular, the frequency offset |Δ12| should be smaller than the current, for example, 20 MHz, which is the usual operating frequency.The bandwidth of the down-converted comparison signal corresponds to the frequencies contained in the signal, in particular the range from zero to the highest frequency contained in the comparison signal.

[0083] Such analog-to-digital converters (ADCs) are connected downstream of the signal comparison units SigComp1 and SigComp2. Depending on the design, such a filter (FLT) or the data interfaces CommTX and CommRX are connected downstream of the analog-to-digital converters (ADCs). Such a filter (FLT) is connected upstream of the additional signal comparison unit SigComp12. The additional signal comparison unit SigComp12 is again designed, for example, as a mixer (MIX).

[0084] The additional signal comparison unit SigComp12, connected between the filter FLT and the receiving data interface CommRX, receives the comparison signal sigC12 from the filter FLT. This comparison signal is formed from the signal sigTX1 generated in this transceiver unit NKSE1 and the signal sigRX12 received from the other transceiver unit NKSE2 via the path SP. Furthermore, the additional signal comparison unit SigComp12 receives the signal sigC21 transmitted by the other transceiver unit NKSE2 from the data interface CommRX.

[0085] Optionally, the FLT filter provides the comparison signal sigC11, which was generated by back reflection, for further processing. Optionally, the CommRX data interface provides the transmitted comparison signal sigC22, which was generated by back reflection in the other transceiver unit NKSE2 and was transmitted along with the signal, for further processing.

[0086] If more than two non-coherent transmit / receive units NKSEi with i = 1, 2, ... N are used, the signals of all transmit / receive units NKSEi are operated in multiplex mode. In the illustrated embodiment, for a third non-coherent transmit / receive unit, the following applies for the respective frequency offset, for example, that |Δ12| ≠ |Δ13| ≠ |Δ23| and |Δ12| ≠ 0, |Δ13| ≠ 0, |Δ23| ≠ 0.

[0087] If complex modulated signals, such as FMCW, FSK, FSCW, or OFDM signals, are used as the signals sigTX1 or sigTX2 generated by the transceiver units, these signals sigTX1 or sigTX2 are preferably modulated in such a way that they are multiplexable, i.e., all transmitted signals generated by the transceiver units can be separated after reception in a transceiver unit and assigned to the respective transceiver unit that transmitted a signal. Conventional code, frequency, and time-division multiplexing methods are particularly applicable for signal separation.

[0088] The comparison signals sigC11, sigC22, which are created from signals generated, transmitted, and reflected back by one of the transceiver units, represent, in particular, conventional CW radar signals when used, for example, with FMCW modulated transmission signals, in particular when considered individually, conventional FMCW radar signals. The components and their arrangement for obtaining these comparison signals sigC11, sigC22 correspond, in particular, to a conventional CW radar. Therefore, it is known as such how CW radar systems are constructed and how CW radar signals are processed and how, when using multiple signal frequencies, the distance and speed to multiple targets can be determined using FMCW, FSK, FHOP, or OFDM radar methods.

[0089] In particular, both comparison signals sigC22, sigC21 of the first signal comparison unit SigComp2 in the second transceiver unit NKSE2 are transmitted via the CommTX, CommRX interfaces to the first transceiver unit NKSE1, in particular, and further processed there. Optionally, it is also possible to transmit the two corresponding comparison signals sigC11, sigC12, which are generated in the first transceiver unit NKSE1, in particular, in a similar manner to the other, in particular second, transceiver unit NKSE2, and process them there. For the sake of clarity, this option and the components required for it are not shown in the exemplary embodiment.

[0090] As previously described, a particularly preferred approach involves feeding the comparison signals sigC21 and sigC12 transmitted in this way to at least one further signal comparison unit SigComp12. In the example, the further signal comparison unit SigCom12, in particular in the first transmitting / receiving unit NKSE1, is designed, in particular, as a mixer that processes, in particular multiplies, the comparison signal sigC21 obtained by transmission and the comparison signal sigC12 formed in this transmitting / receiving unit NKSE1. The comparison result, in particular the mixing result, is obtained using the phase values φ12 = φ21: sigCC 12 = sigC 12 ⋅ sigC 21 = e j ω 1 t − T 01 − ω 2 t − T 02 − τ 12 + φ 1 − φ 2 − φ 21 ⋅ e j ω 2 t − T 02 − ω 1 t − T 01 − τ 12 + φ 2 − φ 1 − φ 12 ⇒ sigCC 12 = e − j ω 1 + ω 2 τ 12 − 2 φ 12

[0091] As can be seen, after the second comparison process, this comparison signal sigCC12 also corresponds in form to a signal from a conventional CW radar, since the phase of the signal is proportional to the signal's propagation time τ12. Through the reciprocal measurement and further signal comparison, it is possible to compensate, in particular, for all unknown components of the initially incoherent signals. In this way, a radar signal is created similar to that of a coherent radar, even though the two non-coherent transmit / receive units NKSE1, NKSE2 are used for the measurement.

[0092] Since the form of the comparison signal sigCC12 also corresponds to a conventional CW radar signal, the known FMCW, FSK, FHOP, or OFDM radar methods can also be applied when using multiple signal frequencies to determine the distance between the two non-coherent transceiver units NKSE1, NKSE2 and the relative speed between them. FMCW, FSK, FHOP, or OFDM radar methods are known as such in the field of radar technology and are applicable to the transmitted first signals sigTX1, sigTX2.

[0093] If the transmitting / receiving units NKSE1, NKSE2 are at an unknown distance from each other or if they are moving with an unknown relative speed to each other, the distance and speed of the transmitting / receiving units to each other can be determined, as explained, by evaluating the comparison signal sigCC12, which is determined at several frequencies, provided that the signals between the transmitting / receiving units are exchanged directly via a line of sight.

[0094] Fig. 3 shows a possible arrangement of several non-coherent transmitting-receiving units NKSE1, NKSE2, ... NKSE-N in a measuring situation for locating or imaging an object O. The transmitting-receiving units NKSE1, NKSE2, ... NKSE-N each have a known position p 1 , p 2 , ... p N . A particularly common evaluation device P receives, in particular, comparison signals sigCC11, sigCC12, sigCC13, sigCC22, sigCC21, sigCC23, ... sigCC33, sigCC31, sigCC32 from the transmitting / receiving units NKSE1, NKSE2, ... NKSE-N for further processing. The comparison comparison signals sigCC11, sigCC12, sigCC13, sigCC22, sigCC21, sigCC23, .... sigCC33, sigCC31, sigCC32 cover combinations of more than two of the transmitting-receiving units NKSE1, NKSE2, ... NKSE-N, in particular all possible combinations of all of the transmitting-receiving units NKSE1, NKSE2, ... NKSE-N which result from such an arrangement.

[0095] If the transmitting / receiving units NKSE1, NKSE2 are at a constant and known distance from one another and if they jointly irradiate an object O with their transmitted signals, a distance or a length of the signal transmission path can be determined or ascertained in a manner comparable to the reflected comparison signals sigC11 and sigC22 according to the above embodiment, and a relative speed to the object O can be determined or ascertained as with the comparison comparison signal sigCC12.

[0096] Thus, by evaluating the two or more comparison signals sigC11, sigC22, which are formed due to back reflections, and the comparison-comparison signal sigCC12, a length of the signal transmission path can be determined. For example, with an omnidirectional antenna, the distance values derived from the comparison signals sigC11, sigC22, which are formed due to back reflections, thus provide a circular path on which the object O may be located, and the comparison-comparison signal sigCC12 provides a hyperbola. Using multilateration methods known as such, the position of the object O can be determined, in particular relative to the positions of the transceiver units NKSE1, NKSE2. By using additional transceiver units NKSE-N, the positioning accuracy is improved, and an improved multi-target capability is achieved.

[0097] The deviations between the phase values φ11, φ22, and φ12 are usually constant, but not necessarily known. However, if the deviations between the phase values φ11, φ22, and φ12 are known, e.g., from a calibration measurement, the signals sigC11, sigC22, which are formed due to back reflections, and the reference signal sigCC12 can also be compared with regard to their phases. This then allows very precise angle measurements, particularly using phase monopulse or interferometric methods, as well as the application of so-called reconstructive imaging methods, such as SAR reconstruction methods or broadband holography. Reconstructive methods are also known as digital beamforming or diffraction tomography. For reconstruction methods, it is advantageous to use a larger number—e.g., N—of transmit / receive units.The advantage of applying the preferred method here is that not only can the phase values φ11, φ22, ..., φNN of N unilateral / monostatic measurement paths be determined, as would be usual with distributed, non-coherent radars, but also, in particular, the phase values φ12, φ13, ..., φ1N, φ23, φ24, ... φ2N, ..., φN-1N of cross-transmission paths are included in the evaluation, which drastically increases the measurement information. With appropriate selection of antenna positions in so-called sparse arrays, it is possible to achieve good reconstruction results with relatively few transmit / receive units.

[0098] Fig. 4 shows a possible arrangement of several non-coherent transceiver units NKSE1, NKSE3, ..., NKSE-N to form a MIMO secondary radar in a measurement situation for locating at least one further non-coherent transceiver unit NKSE2. In the example, the N-1 positions p 1 ,p 3 , ... p N of the transmitting-receiving units NKSE1, NKSE3, ... NKSE-N. The position p 2 of the further or other, in particular second transmitting-receiving unit NKSE 2 is initially unknown.

[0099] Using the preferred method, the distance from each of the transmitting / receiving units NKSE1, NKSE3, ..., NKSE-N to another of the transmitting / receiving units NKSE1, NKSE3, ..., NKSE-N can be determined. In the exemplary embodiment, for example, the comparison / comparison signal sigCC12, using the signals sigTX1, sigTX2 generated in the first and second of these transmitting / receiving units NKSE1, NKSE2, provides the distance between the first transmitting / receiving unit NKSE1 and the second transmitting / receiving unit NKSE2, and the third transmitting / receiving unit NKSE3 and, for example, the Nth transmitting / receiving unit NKSE-N each also provide a distance value to the second transmitting / receiving unit NKSE2. The position of the second transceiver unit NKSE2 can thus be determined using known multilateration methods. The positioning accuracy is improved by using additional, appropriately arranged transceiver units.

[0100] The deviations of the phase values φ12, φ32 to φN2 from one another are usually constant, but not necessarily known. However, if the deviations of the phase values are known, which can be ensured, for example, by calibration, then according to a preferred embodiment, for example, the comparison signals sigC12, sigC32, which are formed on the basis of one signal generated in the transceiver unit NKSE1, NKSE3 and one signal generated by the other, in particular second, transceiver unit NKSE2, and the comparison signal sigCCN2, which is formed on the basis of signals, for example, from the Nth transceiver unit NKSE-N and the second transceiver unit NKSE2, are also compared with regard to their phases or phase values φ12, φ32 to φN2.This allows for very precise angle measurements using phase monopulse or interferometric methods, as well as the application of so-called reconstructive positioning methods, such as SAR reconstruction methods or broadband holography. Alternatively, such a procedure can also be implemented, for example, by operating each transceiver unit with at least two receive channels and using their transmit and transmission signals. This allows the angle of arrival of the signals in the transceiver unit to be determined by evaluating the phase differences between the channels.

[0101] Suitable SAR methods for locating a transponder are known, for example, from the documents cited in the introduction. Due to the preferred method and arrangement described here, such methods for locating a transponder can no longer be applied only to so-called backscatter transponders, which are characterized by the fact that a radar signal is reflected from a transponder with a coherent carrier phase modulation. Transmission to other transponder systems is now also possible, even if transponders with their own signal source usually respond non-coherently. The method described now makes it possible, in particular, to determine a phase value φ12, φ32, ..., φN2 that is proportional to the respective distance between the two interacting incoherent or non-coherent transceiver units.Therefore, all localization and reconstruction methods known from primary radar technology and from the localization of backscatter transponders are applicable. Compared to backscatter transponder systems, transponder systems with the non-coherent transceiver units described here have the advantage that their range can be significantly greater, in particular, and more complex multiplexing methods can be applied.

[0102] The preferred method can be used particularly advantageously if, during a measurement between two non-coherent transmitting / receiving units NKSE1, NKSE2, at least one of the transmitting / receiving units NKSE1 is moving and a relative movement between the transmitting / receiving units NKSE1, NKSE2 is determined by an assisting sensor, e.g., an inertial sensor, an odometer, or other motion-measuring device. An exemplary SAR measurement situation is shown in Fig. 5 with a recording situation for secondary radar aperture synthesis. Since a measurement between two transmit-receive units NKSE1, NKSE2 using the method described here generates a signal whose phase is proportional to the distance between the transmit-receive units NKSE1, NKSE2, the synthetic aperture methods (SAR) and inverse synthetic aperture methods (ISAR), known as such in radar technology, are applicable.

[0103] A particular first transmitting-receiving unit NKSE1 moves at a time t starting from a position p 1 ( t ) at a speed v 1 not equal to zero along a trajectory and performs multiple measurements during the journey to the other, in particular the second transmitting-receiving unit NKSE 2 according to the method described here. The second transmitting-receiving unit NKSE 2 is located, for example, at a position p 2 ( t ) at a speed v1 equals zero. In particular, a comparison signal sigCC12 from these two transceiver units NKSE1, NKSE2 is used for evaluation. Using a holographic reconstruction algorithm, as known as such from the documents cited above, it is then possible to determine the position of the second transceiver unit NKSE2 relative to the first transceiver unit NKSE1 with high precision. The method and arrangement shown are therefore particularly suitable for the highly precise location of vehicle witnesses, such as motor vehicles, aircraft, rail vehicles, mobile robots, autonomous vehicles, etc. The first transceiver unit NKSE1 is located, for example, on the vehicle, and further transceiver units NKSE2, etc. are located as waymarks at known positions. If the vehicle moves, the first transceiver unit NKSE1 can determine its relative position to the other transceiver units NKSE2 etc.according to an SA procedure and thus determine their own position in the coordinate system of the waypoints.

[0104] Fig. 6 shows an exemplary measurement or recording situation for inverse secondary radar aperture synthesis. A second transmitting-receiving unit NKSE2 moves at a time t from a position p 2 ( t ) at a speed v 2 not equal to zero along a trajectory and performs multiple measurements during the movement according to the preferred method with at least one further, in particular first, transmitting-receiving unit NKSE1. Using, for example, an inertial platform, the second transmitting-receiving unit NKSE2 also determines the course of the trajectory and transmits it by radio to the first transmitting-receiving unit NKSE1, which in particular remains at a fixed position. p 1 ( t ) and a speed v1 equals zero. In this case, an inertial platform is understood to be, in particular, an arrangement of acceleration and angular velocity sensors, preferably each designed with three axes. In particular, a comparison comparison signal sigCC12 from these two transceiver units NKSE1, NKSE2 is used for evaluation. Using a holographic reconstruction algorithm, as described as such in the documents cited in the introduction, the position of the second transceiver unit NKSE2 relative to the first transceiver unit NKSE1 is then determined with particular high precision. The method and arrangement shown are therefore particularly suitable for locating mobile objects equipped with a transponder with such a non-coherent transceiver unit, or in particular for locating end effectors of robots or, for example, crane booms or load handling equipment equipped in this way.If several stationary transceiver units are used to determine the position of a mobile transceiver unit, the positioning method referred to in the documents mentioned above as "multilateral inverse synthetic aperture secondary radar" is used with particular advantage.

[0105] The following figures show possible further designs of such non-coherent transmitting-receiving units.

[0106] Fig. 7 shows an arrangement for measuring an angle between two non-coherent transmitting-receiving units NKSE1, NKSE2 relative to an antenna plane, in particular with a plurality of antennas RA2,1, RA2,2, RA2,3 switched for reception. A first of the transmitting-receiving units NKSE1 is in particular comparable to the first transmitting-receiving unit NKSE1 from Fig. 2 constructed, whereby a filter is not shown or is omitted entirely. A communication interface CommRX for receiving a signal from the other, in particular second, transceiver unit NKSE2 is optionally configured such that it can receive a comparison signal which is transmitted by the second transceiver unit NKSE2 with an antenna CA2 designed for transmission via an air interface.

[0107] The second transceiver unit NKSE2 also has a signal generator SigGen2, whose generated signal sigTX2 is transmitted via an antenna TA2 and also coupled out. In the second transceiver unit NKSE2, the multiple, e.g. three, antennas RA2,1, RA2,2, RA2,3 connected for reception each have a downstream signal comparison unit SigComp2, which is designed, for example, as a mixer. The generated signal sigTX2 is also applied to these signal comparison units SigComp2 for mixing with the received signal from the antenna. The mixed signals are each transmitted directly or, in particular, each applied to a downstream analog-to-digital converter and applied to the communication interface CommTRX for transmission to the other transceiver unit NKSE1. For example, this communication interface CommTRX is equipped with the antenna CA2 for transmission via the air interface.

[0108] Three or more comparison signals sigC21,1, sigC21,2, sigC21,3 are thus transmitted to the first transceiver unit NKSE1, with the comparison signals sigC21,1, sigC21,2, sigC21,3 each being assigned to a different receiving location within the second transceiver unit NKSE. In the first transceiver unit NKSE1, preferably several comparison signals sigCC121, sigCC122, ... sigCC12N are formed and provided or evaluated for evaluation.

[0109] By using multiple coherently coupled receiving antennas in a transmitting / receiving unit NKSE2, it is possible to determine not only the distance and speed between two transmitting / receiving units NKSE1, NKSE2, but also their angle to each other. How the angle of incidence of a wave can be determined using multiple coherent receiving channels is known per se. With the arrangement according to Fig. 7 In particular, the angle between two transmitting-receiving units NKSE1, NKSE2 relative to the antenna plane of the transmitting-receiving unit NKSE2 with the plurality of antennas RA2,1, RA2,2, RA2,3 is also determined.

[0110] With an order according to Fig. 8 the angle between two non-coherent transmitting-receiving units NKSE1, NKSE2 relative to an antenna plane of the first transmitting-receiving unit NKSE1 can be determined.

[0111] In this example, the first of the transmitting-receiving units NKSE1 is particularly comparable to the second transmitting-receiving unit NKSE2 from Fig. 7 constructed, in particular, with a plurality of antennas RA1,1, RA1,2, RA1,3 switched for reception. An arrangement of signal comparison units SigComp1 is connected downstream of these, each of which has a mixer for each antenna RA1,1, RA1,2, RA1,3. Each of these signal comparison units SigComp2 is supplied with one of the received signals from one of the antennas and additionally with the signal sigTX1 generated in the first transceiver unit NKSE1 for mixing. The signals generated by the mixers are each applied as comparison signals to a downstream analog-to-digital converter ADC1, ADC2, or ADCN and, after conversion or directly, to a signal comparison unit SigComp12. The signal comparison unit SigComp12 is also supplied with a signal received via a communication interface CommTRX or data received via this interface, which contains a comparison signal sigC21 received from the second transceiver unit NKSE2.The signal comparison unit SigComp12 generates in particular several comparison signals sigCC112, sigCC122, ... sigCC1N2, which are provided or evaluated for evaluation.

[0112] For example, the communication interface CommTRX is equipped with an antenna CA1 for receiving via the air interface. Similarly, the second transceiver unit NKSE2 has a communication interface CommTRX equipped with an antenna CA2 for transmitting via the air interface. The second transceiver unit NKSE2 is otherwise similar to the second transceiver unit NKSE2 from Fig. 2 Another difference is that the second transmitting-receiving unit NKSE2 is made of Fig. 8 a filter FLT, which is connected between the analog-digital converter ADC and the communication interface CommTRX and only allows the comparison signal to pass to the communication interface CommTRX, which is generated from the comparison of its own generated signal sigTX2 and a signal sigRX21 received by the first transceiver unit NKSE1.

[0113] If, according to a further embodiment, several antennas connected for reception are formed in both non-coherent transmit / receive units, the angle between the transmit / receive units and the tilt of the two antenna planes relative to each other can be determined. Alternatively or additionally, it would also be possible, for example, to use several coherent transmission channels.

[0114] Such an arrangement with several non-coherent transmitting-receiving units arranged in parallel is also advantageous for measuring objects O as passive radar targets. Fig. 9 shows an example of a measurement arrangement with two non-coherent transmit-receive units NKSE1, NKSE2 on a non-cooperative target, including an angle measurement. The transmit-receive units NKSE1, NKSE2 are arranged as shown in Fig. 8 However, the first transmitted signals sigTX1 and sigTX2 are directed at object O, from which the signals are reflected to the corresponding antennas RA1,1 RA1,2, ... RA1,N and RA2, respectively. With this arrangement, in addition to the distance according to one of the previous methods, an angle of arrival can also be estimated using the phase differences and combined with the distance. To solve an internal calibration problem, each transmit / receive unit can also be equipped with a so-called backscatter, which is used to calibrate the receive channels.

[0115] It is particularly advantageous for distance and speed measurement to use so-called multi-ramp FMCW signals as the measurement signal or by the respective signal generator SigGen1, SigGen2 as its signal sigTX1, sigTX2. Fig. 10shows exemplary FMCW multi-ramp signals, which are generated as a first signal sigTX1,1, sigTX1,2, ..., SigTX1,K or sigTX2,1, sigTX2,2, ..., SigTX2,K by the signal generator SigGen1, SigGen2 as its signal sigTX1 of the first or other / second transceiver units NKSE1, NSKE2 of the preceding figures. In these multi-ramp FMCW signals, a number of preferably K identically FMCW-modulated signals sigTX1,1; sigTX1,2; ... sigTX1,K or sigTX2,1; sigTX2,2; ... sigTX2,K are transmitted at a preferably fixed time interval. For multiplexing, the multi-ramp FMCW signals are transmitted in the transmitter / receiver units involved in a measurement with either a slight time or frequency offset. "Slight" refers specifically to a time delay of no more than 10% of the measurement ramp duration or the equivalent frequency offset in the time-frequency diagram.

[0116] As described, the preferential mutual exchange of signals results in an FMCW measurement signal for each individual FMCW ramp. This results in a total of K FMCW measurement signals. These are then preferably arranged into a matrix as reference signals sigCC12,1; sigCC12,2; ..., sigCC12,K. This data matrix, when arranged row by row, has the following form: sigCC 12 Mat = sigCC 12 , 1 sigCC 12 , 2 ⋮ sigCC 12 , K .

[0117] If a two-dimensional Fourier transformation is applied to this matrix, a so-called range-Doppler diagram is created, from which the distance and speed between the non-coherent transmit-receive units NKSE can be determined very precisely.

[0118] To improve the coordination of the signal generators in the distributed transceiver units, it may be useful to synchronize the signal sources in the stations or the devices with non-coherent transceiver units by exchanging radio signals before performing the measurement procedures described as preferred, with regard to frequency / clock rate and time offset. This is because inexpensive oscillators can deviate significantly from the nominal value or drift with temperature changes. A deviation in the clock generators in the signal sources causes, for example, a scaling of all frequency values and time durations, which can distort the signal modulation and the time base of the digitized signals, in particular, and subsequently lead to erroneous comparison results.For synchronizing the non-coherent transceiver units, a method according to US 8,108,558 B2 "Circuit arrangement and method for synchronization of clocks in a network" or a method according to US 7,940,743 B2 "Method and device for the synchronization of radio stations and a time-synchronous radio bus system" are suitable, for example. In particular, for synchronizing the non-coherent transceiver units, it is advantageous to apply the method from US 7,940,743 B2 to the comparison signals sigC21 and sigC12, respectively. In particular, it is advantageous to exchange at least two FMCW radar signals with at least two sweep rates (sweep rate: change in signal frequency per unit time) that differ in magnitude or sign.A preferred embodiment uses at least two FMCW radar signals, wherein in one of these FMWC signals the frequency increases over time, which corresponds to a positive sweep rate, and in another FMCW signal the frequency decreases over time, which corresponds to a negative sweep rate.

[0119] In particular, further combinations of the various design elements shown in the various figures or mentioned as alternatives to those described can be realized.

[0120] A further possible embodiment could be, for example, a pre-selection of an interesting range of the comparison signals sigC21, sigC12 and a transmission of only this range via the communication device instead of transmitting a complete comparison signal. Accordingly, the term "comparison signal" also includes a partial comparison signal, as long as it still contains sufficient data content to determine a comparison signal. In such a case, an index value can optionally be transmitted, indicating which range of the comparison signal was transmitted. Transmission of multiple ranges or sections of such a comparison signal is also feasible.

[0121] According to a further embodiment, transmitting the comparison signals also includes transmitting the spectra instead of the actually generated comparison signals and / or transmitting spectra in sections. In particular, it is also possible to form a spectrum of the two comparison signals or to perform a complex conjugate multiplication at the spectral level to form the comparison-comparison signal.

Claims

1. Method in a radar system, in which - in a first non-coherent transceiver unit (NKSE1), a first signal (sigTX1) is generated and transmitted, in particular emitted, via a path (SP), - a first signal (sigTX2) is generated in a further, in particular second non-coherent transceiver unit (NKSE2) and transmitted, in particular emitted, via the path (SP), - in the first transceiver unit (NKSE1), a comparison signal (sigC12) is formed from its first signal (sigTX1) and from such a first signal (sigTX2) received from the further transceiver unit (NKSE2) via the path (SP), wherein the phase and / or time course of the comparison signal (sigC12) is determined and ascertainable by the time, frequency and / or phase difference of the first signal (sigTX1) of the first transceiver unit (NKSE1) and of the first signal (sigTX2) received from the further transceiver unit (NKSE2) in the first transceiver unit (NKSE1), and - in the further transceiver unit (NKSE2), a further comparison signal (sigC21) is formed from its first signal (sigTX2) and from such a first signal (sigTX1) received from the first transceiver unit (NKSE1) via the path (SP), wherein the phase and / or time course of the further comparison signal (sigC21) is determined or ascertainable by the time, frequency and / or phase difference of the first signal (sigTX2) of the further transceiver unit (NKSE2) and of the first signal (sigTX1) received from the first transceiver unit (NKSE1) in the further transceiver unit (NKSE2), - wherein the further comparison signal (sigC21) is transmitted, in particular communicated, from the further transceiver unit (NKSE2) to the first transceiver unit (NKSE1).

2. Method according to claim 1, in which a comparison-comparison signal (sigCC21; sigCC12) is formed from this comparison signal (sigC12) and the further comparison signal (sigC21).

3. Method according to claim 2, in which the comparison-comparison signal (sigCC21; sigCC12), by processing the two comparison signals (sigC12, sigC21) with each other, in particular by conjugate complex multiplication, corresponds to a comparison signal generated by a coherent radar system.

4. Method according to a preceding claim, in which at least one of the comparison signal (sigC12), the further comparison signal (sigC21) or the comparison-comparison signal (sigCC21; sigCC12) is formed by at least one of mixing or correlation.

5. Method according to a preceding claim, in which at least one such further comparison signal (sigC21; sigC12) is transmitted between the transceiver units (NKSE2; NKSE1) as at least one of data, a signal containing data, or a signal containing data in a reconstructable form.

6. Method according to a preceding claim, in which at least one of the first signals (sigTX1, sigTX2) is transmitted as a transmission signal via the path (SP) designed as an air interface.

7. Method according to a preceding claim, in which the times for transmitting the first signals (sigTX1, sigTX2) are coordinated such that the first signals (sigTX1, sigTX2) overlap at least partially in time.

8. Method according to one of claims 2 to 7, in which a signal propagation time (τ12) required by such a first signal (sigTX1, sigTX2) for the path between the transceiver units (NKSE1, NKSE2) is determined from at least one comparison-comparison signal (sigCC21; sigCC12), by analyzing at least one of a phase or a phase value (φ12, φ 13, ..., φ 1N, φ22, φ23, φ24, ... φ2N, ..., φN-1N), a frequency, an amplitude course or a phase course of the comparison-comparison signal (sigCC12).

9. Method according to a preceding claim, in which at least one of the first signals (sigTX1, sigTX2) is generated and transmitted as an FMCW or OFDM modulated signal.

10. Method according to a preceding claim, in which at least one of the first signals (sigTX1, sigTX2) is generated and transmitted as a multi-ramp signal.

11. Method according to a preceding claim, in which - multiple comparison-comparison signals (sigCC12) are measured in succession with at least two transceiver units (NKSE1, NKSE2), of which at least one of the transceiver units (NKSE1, NKSE2) is in motion, and - using a synthetic aperture method, at least one of a distance, a position, a speed or the presence of one of the transceiver units (NKSE2, NKSE1) or the presence of such transceiver units (NKSE2, NKSE1) or at least one of a distance, a position a speed relative to an object (O) or the presence of an object (O) is determined.

12. Radar system, in which - at least one first non-coherent transceiver unit (NKSE1) is designed to generate a first signal (sigTX1) and transmit it via a path (SP), in particular to emit it, - at least one further, in particular second non-coherent transceiver unit (NKSE2) is designed to generate a first signal (sigTX2) and transmit it, in particular emit it, via the path (SP), - the first transceiver unit (NKSE1) is designed to form a comparison signal (sigC12) from its first signal (sigTX1) and from such a first signal (sigTX2) received from the further transceiver unit (NKSE2) via the path (SP), wherein the phase and / or time course of the comparison signal (sigC12) is determined or ascertainable by the time, frequency and / or phase difference of the first signal (sigTX1) of the first transceiver unit (NKSE1) and of the first signal (sigTX2) received from the further transceiver unit (NKSE2) in the first transceiver unit (NKSE1), - the further transceiver unit (NKSE2) is designed to form a further comparison signal (sigC21) from its first signal (sigTX2) and from such a first signal (sigTX1) received from the first transceiver unit (NKSE1) via the path (SP), wherein the phase and / or time course of the further comparison signal (sigC21) is determined or ascertainable by the time, frequency and / or phase difference of the first signal (sigTX2) of the further transceiver unit (NKSE2) and of the first signal (sigTX1) received from the first transceiver unit (NKSE1) in the further transceiver unit (NKSE2), and - the further comparison signal (sigC21) is transmitted, in particular communicated, from the further transceiver unit (NKSE2) to the first transceiver unit (NKSE1).

13. Radar system according to claim 12, in which a comparison-comparison signal (sigCC21; sigCC12) is formed from this comparison signal (sigC12) and the further comparison signal (sigC21).

14. Radar system according to claim 12 or 13 with three or more spatially separated transceiver units (NKSE1, NKSE2, NKSE3, NKSE-N), in which from two or more comparison-comparison signals (sigCC12, sigCC12, sigCC13, sigCC22, sigCC32) which are measured with more than two pairs of two of the spatially separated transceiver units (NKSE1, NKSE2; NKSE-N, NKSE2) each, a distance, a position, a speed or the presence of one of the transceiver units (NKSE2, NKSE1) or the presence of one such transceiver unit (NKSE2, NKSE1) or at least one of a distance, a position, a speed relative to an object (O) or the presence of an object (O) is determined.

15. Radar system according to one of claims 12 to 14, in which the first transceiver unit (NKSE1) and at least one such further transceiver unit (NKSE2) and / or an evaluation device (P) are designed to carry out a method according to one of the preceding claims.

16. Device of a radar system, in particular for carrying out a method according to one of claims 1 to 11 and / or in a radar system according to one of claims 12 to 15, wherein the device - is designed as a first non-coherent transceiver unit (NKSE1), in particular a first non-coherent transceiver unit (NKSE1), and - has a signal generator and at least one antenna (TA1; RA1) which are designed to generate a first signal (sigTX1) and transmit it via a path (SP), in particular to emit it, - has an arrangement which is designed to form a comparison signal (sigC12) from the first signal (sigTX1) and from such a first signal (sigTX2) received from a further transceiver unit (NKSE2) via the path (SP), - and at least one of - an interface (CommTX) which is designed to transmit the comparison signal (sigC12) to the further transceiver unit (NKSE2), in particular to communicate it, wherein the phase and / or time course of the comparison signal (sigC12) is determined or ascertainable by the time, frequency and / or phase difference of the first signal (sigTX1) of the first transceiver unit (NKSE1) and of the first signal (sigTX2) received from the further transceiver unit (NKSE2) in the first transceiver unit (NKSE1), or - an interface (CommRX) which is designed to receive a further such comparison signal (sigC21) generated by the further transceiver unit (NKSE2) by means of transmission, in particular communication, in the first transceiver unit (NKSE1), wherein the phase and / or time course of the further comparison signal (sigC21) is determined or ascertainable by the time, frequency and / or phase difference of the first signal (sigTX2) of the further transceiver unit (NKSE2) and of the first signal (sigTX1) received from the first transceiver unit (NKSE1) in the further transceiver unit (NKSE2).

17. Device according to claim 16, having a further comparison unit (sigComp12) which forms a comparison-comparison signal (sigCC12) from the comparison signal (sigC12) formed in the same transceiver unit (NKSE1) and the comparison signal (sigC21) transmitted to this transceiver unit (NKSE1).

18. Device according to claim 16 or 17, in which the at least one interface (CommTX, CommRX) is a data interface.

19. Device according to one of claims 16 to 18, in which a filter (FLT) is arranged between the arrangement that outputs the comparison signal (sigC12) and the further comparison unit (sigComp12) which forms the comparison-comparison signal (sigCC12), wherein the filter (FLT) applies the comparison signal (sigC12) to the comparison unit (sigComp12), wherein the filter (FLT) does not apply a further comparison signal (sigC11) formed in the arrangement upstream of the filter (FLT) and suppresses the comparison signal (sigC11) formed in the upstream arrangement or makes it available at a connection.

20. Device according to one of claims 16 to 19, comprising a plurality of spatially separated receiving antennas (RA1,1, ..., RA1,N; RA2,1, RA2,N), each of which is assigned an arrangement that is designed to form in each case a comparison signal (sigC21,1, sigC21,2, sigC21,3) from the first signal (sigTX2) and from one such first signal (sigTX1) received from such a further transceiver unit (NKSE2) via the path (SP).