Method for determining at least one object information item of at least one target object which is sensed with a radar system, in particular of a vehicle, radar system and driver assistance system

Abstract

A method for determining at least one object information item of at least one target object (18) which is sensed with a radar system (12), in particular of a vehicle (10), a radar system (12) and a driver assistance system (20) are described. In the method, transmission signals (32a, 32b) are transmitted into a monitoring range (14) of the radar system (12) with at least one transmitter (26a, 26b). Echoes, which are reflected at the at least one target object (18), of the transmission signals (32a, 32b) are received as received signals (34a, 34b) with at least one receiver (30), and if necessary are converted into a form which can be used by an electronic control and/or evaluation device (28). The received signals (34a, 34b) are subjected to at least one multi-dimensional discrete Fourier transformation. At least one target signal is determined from the result of the at least one Fourier transformation. At least one object information item is determined from the at least one target signal. At the transmitter end, at least one first transmission signal (32a) and at least one second transmission signal (32b) are generated from a frequency-modulated continuous wave signal. The at least one second transmission signal (32b) is encoded by means of phase modulation with respect to the at least one first transmission signal (32a), with the result that an at least temporary signal orthogonality between the at least one first transmission signal (32a) and the at least one second transmission signal (32b) is obtained. The at least one first transmission signal (32a) is emitted with at least one first transmitter (26a), and the at least one second transmission signal (32b) is emitted with at least one second transmitter (26b), simultaneously into the monitoring range (14) of the radar system (12). The at least one second transmission signal (32b) is emitted with regular transmission pauses of a predefined length.

Claims

1. A method for determining at least one object information item of at least one target object which is sensed with a radar system of a vehicle, the method comprising: transmitting transmission signals into a monitoring range of the radar system with at least one transmitter; receiving echoes of the transmission signals, which are reflected at the at least one target object, as received signals with at least one receiver; and converting the received signals into a form useable by an electronic control and/or evaluation device; wherein the received signals are subjected to at least one multi-dimensional discrete Fourier transformation, determining at least one target signal from the result of the at least one Fourier transformation; determining at least one object information item from the at least one target signal; and generating, at the transmitter end, at least one first transmission signal and at least one second transmission signal from a frequency-modulated continuous wave signal, wherein the at least one second transmission signal is encoded by phase modulation with respect to the at least one first transmission signal, with the result that an at least temporary signal orthogonality between the at least one first transmission signal and the at least one second transmission signal is obtained, wherein the at least one first transmission signal is emitted with at least one first transmitter, and the at least one second transmission signal is emitted with at least one second transmitter, simultaneously into the monitoring range of the radar system, wherein the at least one second transmission signal is emitted with regular transmission pauses of a predefined length; and wherein for at least one target spectrum value: a difference between the complex-valued amplitudes (s(k, l)) of the cells which are associated with this target spectrum value and have the lowest Doppler value (l) and the third-lowest Doppler value (l) is formed, and the absolute value of this difference is squared and assigned to a first comparison value (X.sub.0), and a difference between the complex-valued amplitudes (s(k, l)) of the cells which are associated with this target spectrum value (az.sub.k,lt) and have the second-lowest Doppler value (l) and the highest Doppler value (l) is formed, and the absolute value of this difference is squared and assigned to a second comparison value (X.sub.1), the comparison values (X.sub.0, X.sub.1) are compared and the signals which are associated with the cells from whose amplitudes (s(k, l)) the lower of the two comparison values (X.sub.0, X.sub.1) is formed are validated as the two target signals which originate from the at least one second transmission signal, for the same target object, the absolute values of the amplitudes (s(k, l)) of the cells which are not used to form the lowest comparison value (X.sub.0, X.sub.1) are compared, and the signal which is associated with the cell with the largest amplitude (s(k, l)) in absolute terms is validated for the same target object as the target signal which originates from the at least one first transmission signal.

2. The method according to claim 1, wherein at the receiver end a multiplicity of target signals is determined from the result of the at least one multi-dimensional discrete Fourier transformation, wherein one of the target signals for each physically present target object corresponds to the at least one first transmission signal, and two target signals correspond to the at least one second transmission signal.

3. The method according to claim 1, wherein the result of the at least one multi-dimensional Fourier transformation is implemented as a range Doppler matrix for a uniqueness range with respect to a Doppler dimension, wherein the range Doppler matrix is composed of cells which are each characterized by a Doppler value (l) and a range value (k) and have a complex-valued amplitude (s(k, l)) which characterizes a signal intensity, wherein: the range Doppler matrix is divided into four sub-matrices (TM) with the same extent with respect to the Doppler dimension, for each range value (k) the absolute values of the amplitudes (s(k, l)) of the cells of the sub-matrices (TM) which each correspond in priority with respect to their Doppler value (l) are combined to form a respective spectrum value, from the spectrum values those values are determined which are above a predefined threshold and are detected as targets spectrum values which are associated with a respective target signal.

4. The method according to claim 1, wherein at least one object information item is determined from at least one validated target signal.

5. The method according to claim 1, wherein the target spectrum values are determined from the spectrum values by at least one detection algorithm.

6. The method according to claim 1, wherein length of the transmission pauses of the at least one second transmission signal are predefined as a period length or integral multiple of the period length of the at least one first transmission signal.

7. The method according to claim 1, wherein in the course of the determination of at least one object information item a phase difference between at least two validated target signals is determined.

8. The method according to claim 1, wherein at least one multi-dimensional discrete Fourier transformation is executed as a fast Fourier transformation.

9. The method according to claim 1, wherein a regularly alternating pattern is applied to at least one transmission signal.

10. The method according to claim 1, wherein at least one transmission signal with a constant phase and/or at least one transmission signal with a changing phase are/is emitted.

11. The method according to claim 1, wherein a phase change between 0° and 180° is applied to at least one transmission signal after each frequency ramp of the frequency-modulated continuous wave signal.

12. A radar system of a vehicle, for determining at least one object information item of at least one target object, comprising: at least one transmitter for transmitting transmission signals into a monitoring range; at least one receiver for receiving echoes, which are reflected at the at least one target object, of the transmission signals as received signals; and at least one control and/or evaluation device comprising means for determining at least one target signal from at least one multi-dimensional discrete Fourier transformation of the received signals and for determining at least one object information item from at least one target signal wherein the at least one control and/or evaluation unit further comprises means for carrying out the method according to claim 1.

13. A driver assistance system of a vehicle, comprising at least one electronic control device for controlling functional devices of the vehicle on the basis of object information which is made available by at least one radar system; and at least one radar system for determining at least one object information item of at least one target object, wherein the at least one radar system has at least one transmitter for transmitting transmission signals into a monitoring range, at least one receiver for receiving echoes, which are reflected at the at least one target object, of the transmission signals as received signals, and at least one control and/or evaluation device comprising means for determining at least one target signal from at least one multi-dimensional discrete Fourier transformation of the received signals and for determining at least one object information item from at least one target signal, wherein the at least one control and/or evaluation unit has means for carrying out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, features and details of the invention are apparent from the following description, in which an exemplary embodiment of the invention will be explained in more detail with reference to the drawing. A person skilled in the art will also expediently consider individually the features which have been disclosed in the drawing, the description and the claims in combination and combine them to form further meaningful combinations. In the drawing:

(2) FIG. 1 shows a motor vehicle with a driver assistance system and a radar system for monitoring a monitoring range ahead of the motor vehicle in the direction of travel;

(3) FIG. 2 shows a functional illustration of the motor vehicle with the driver assistance system and the radar system from FIG. 1;

(4) FIG. 3 shows a frequency/time diagram of a first transmission signal of a first transmitter of the radar system from FIGS. 1 and 2;

(5) FIG. 4 shows a frequency/time diagram of a second transmission signal of a second transmitter of the radar system from FIGS. 1 and 2;

(6) FIG. 5 shows a range Doppler diagram with target signals which have been acquired from received signals of the first transmission signal and of the second transmission signal from FIGS. 3 and 4 which have been reflected at three target objects;

(7) FIG. 6 shows an amplitude absolute-valued Doppler diagram of the target signals from FIG. 5, which are located in the same range gate;

(8) FIG. 7 shows a spectrum matrix which can be acquired from the amplitudes of the cells in accordance with the range Doppler diagram from FIG. 5;

(9) FIG. 8 shows calculations of, for example, four spectrum values of the spectrum matrix from FIG. 7; and

(10) FIG. 9 shows the spectrum matrix from FIG. 7, which contains, for example, the spectrum values from the calculations from FIG. 8.

(11) In the figures, identical structural elements are provided with the same reference numerals.

EMBODIMENT(S) OF THE INVENTION

(12) FIG. 1 illustrates a motor vehicle 10 in the form of a passenger vehicle in front view. The motor vehicle 10 has a radar system 12. The radar system 12 is arranged, for example, in the front bumper of the motor vehicle 10. All components of the radar system 12, for example a plurality of transmitters and receivers, can be contained, for example, combined in a single radar sensor. The radar system 12 can be used to monitor a monitoring region 14, shown in FIG. 2, in the driving direction 16 in front of the motor vehicle 10 for objects 18. The radar system 12 can also be arranged and oriented differently at another location on the motor vehicle 10. The objects 18 can be, for example, other vehicles, persons, obstacles, uneven portions of the roadway, for example potholes or rocks, roadway boundaries or the like. In FIG. 2, an object 18 is indicated, for example, as a chequered rectangle. Otherwise, FIG. 2 is merely a functional diagram of some of the components of the motor vehicle 10 and of the radar system 12, which diagram does not serve for spatial orientation.

(13) The radar system 12 is configured as a frequency-modulated continuous wave radar. Frequency-modulated continuous wave radar systems are also referred to in specialist circles as FMCW (frequency modulated continuous wave) radar systems. The radar 12 can be used, for example, to determine a distance, a direction and a speed of the object 18 relative to the motor vehicle 10.

(14) The radar system 12 is part of a driver assistance system 20 or can at least be connected thereto. For example, the driver assistance system 20 can be used to support a driver of the motor vehicle 10. For example, the motor vehicle 10 can drive and park or exit parking spaces at least partially autonomously using the driver assistance system 20. The driver assistance system 20 can be used to influence driving functions of the motor vehicle 10, for example engine control, a braking function, or a steering function, or to output notices or warning signals. To this end, the driver assistance system 20 is connected in a regulating and/or controlling fashion to function devices 22. FIG. 2 illustrates by way of example two function devices 22. The function devices 22 can be, for example, an engine control system, a brake system, a steering system, a chassis control system or a signal output system.

(15) The driver assistance system 20 includes an electronic control device 24, with which corresponding electronic control and regulation signals can be transmitted to the function devices 22 and/or be received and processed thereby.

(16) The radar system 12 comprises, for example, a first transmitter 26a, a second transmitter 26b, an electronic control and evaluation device 28 and a receiver 30. The transmitters 26a and 26b are implemented, for example, with a radar sensor which contains, for example, a chip with the two integrated transmitters 26a and 26b. The transmitters 26a and 26b are each connected to a separate transmission antenna. For example, the—here three—transmission antennas are arranged at a distance of a few millimetres.

(17) The control and evaluation device 28 has a signal-transmitting connection to the control device 24. The control device 24 can be used to perform open-loop/closed-control of the driving functions of the motor vehicle 10 in accordance with object information of the radar system 12. It is not essential for the invention whether electrical/electronic control and/or evaluation devices, such as for example the control device 24, the control and evaluation device 28, an engine control device of the motor vehicle 10, or the like, are integrated into one or more components or assemblies or realized at least partially as decentralized components or assemblies.

(18) The respective transmission antennas of the transmitters 26a and 26b are, for example, of identical design. The transmitters 26a and 26b can be used to transmit respective transmission signals 32a and 32b, in each case at a constantly changing frequency into the monitoring range 14. The transmission signals 32a and 32b are reflected at the object 18 and sent back as corresponding received signals 34a and 34b to the receiver 30 and received therewith. According to a further method described below, the distance, the direction and the speed of the object 18 relative to the motor vehicle 10 are determined from the received signals 34a and 34b with the control and evaluation device 28.

(19) Alternatively, in an exemplary embodiment which is not shown, the transmitters 26a and 26b and the receiver 30, for example the antennas thereof, can be arranged spatially distant from one another. The transmitters 26a and 26b and the receiver 30, or the respective antennas, can be arranged in a different way, for example at different heights and/or at different distances and/or with a different arrangement and/or at a different location.

(20) The method for determining object information of objects 18 which are sensed with the radar system 12 is explained by way of example below with reference to FIGS. 3 to 9.

(21) In the method, the control and evaluation device 28 is used to actuate the transmitters 26a and 26b in such a way that the first transmission signal 32a is transmitted with the first transmitter 26a, and the second transmission signal 32b is transmitted with the second transmitter 26b, simultaneously into the monitoring range 14. The transmission signals 32a and 32b are generated from, for example, the same frequency-modulated continuous wave signal and are composed of a plurality of what are referred to as chirps, which occur successively. The second transmission signal 32b is also encoded with respect to the first transmission signal 32a by means of phase modulation in the form of binary shift keying, in such a way that a signal orthogonality between the first transmission signal 32a and the second transmission signal 32b is achieved.

(22) FIG. 3 shows a frequency/time diagram for the first transmission signal 32a. The frequency f is plotted on the ordinate axis, and the time t on the abscissa axis. The chirps are shown here in each case as frequency ramps. The successive chirps of the first transmission signal 32a each have the same phase position, that is to say each shifted by 0° in respect of their phase. The first transmission signal 32a is therefore emitted with a constant phase. Overall, 128 such chips are emitted, for example, during a measurement. The number of chirps specifies a uniqueness range which is 128 here.

(23) FIG. 4 shows a frequency/time diagram, comparable with FIG. 3, of the second transmission signal 32b. The second transmission signal 32b is emitted in an analogous fashion to the first transmission signal 32a on the basis of successive chirps, but here with a transmission pause after each emitted chirp. The length of the transmission pause corresponds to the length of a chirp. Moreover, the successive chirps are implemented with a phase change, specifically between 0° and 180°, and therefore with a regularly alternating pattern.

(24) The receiver 30 is used to receive the echoes, reflected at the object 18, of the transmission signals 32a and 32b as received signals 34a and 34b, and converted into a form which can be used by the control/evaluation device 28.

(25) The received signals 34a and 34b are subjected to a two-dimensional fast Fourier transformation with corresponding means of the control/evaluation device 28.

(26) Target signals ZS, corresponding to the transmission signals 32a and 32b, of physically present target objects and their respective complex-valued amplitudes are obtained from the result of the two-dimensional discrete Fourier transformation. A target object is a part of the object 18. A plurality of target objects can originate from the same object 18 or from different objects. One time signal ZS per target object corresponds to the first transmission signal 32a. Owing to the shifting of the phase position and of the transmission pauses of the second transmission signal 32b, two target signals ZS per target object correspond after the Fourier transformation. Therefore, three target signals ZS correspond overall to each target object. In this context, the target signals ZS from the second transmission signal 32b are shifted by half the uniqueness range with respect one another in the Doppler dimension and by ¼ or ¾ of the uniqueness range with respect to the target signal ZS from the first transmission signal 32a. In addition, for the same target object the amplitudes of the target signals ZS from the second transmission signal 32b are identical in respect of absolute value and phase, that is to say the complex values, and are lower in absolute value than the amplitude of the target signal ZS from the first transmission signal 32a, provided that the transmission signals 32a and 32b are emitted with the same power.

(27) In FIG. 5, for example the target signals ZS are each indicated in a range Doppler matrix with a cross. The range gates correspond here to so-called “range bins” or distance intervals. The range Doppler matrix comprises, for example, 256 range gates. The Doppler gates correspond to what are referred to as relative speed gates or “Doppler bins”.

(28) In the present exemplary embodiment, the uniqueness range in the Doppler dimension corresponds to the number of chirps and is 128 Doppler gates, as already mentioned above. The range Doppler matrix therefore comprises, for example, 128 Doppler gates. The range Doppler matrix is composed of cells which characterized by a range value k and a Doppler value l, and has a complex-valued amplitude s(k, l). The absolute value of the amplitude s(k, l) characterizes the intensity of any signal in the cell or, if no signal is received, the noise there.

(29) In the exemplary embodiment shown, the target signals ZS of three target objects are determined In this context, the target signals ZS which are located at the same range gate with the same range value, that is to say at the same distance from the radar system 12, correspond to the same target object.

(30) The assignment of the target signals ZS to the transmission signals 32a and 32b and to the corresponding target objects occurs first in the manner explained below. However, for the sake of better comprehension, the respective designations will already be introduced now. The target signals are designated by “ZS1”, “ZS2” and “ZS3”, in a corresponding way to the target objects. The target signals ZS which originate from the first transmission signal 32a are additionally characterized by “TX1”. The target signals ZS which correspond to the second transmission signal 32b are additionally designated by “TX21” or “TX22”, wherein “TX21” corresponds to the first target signal and “TX22” corresponds to the second target signal of the second transmission signal 32b. For example, the target signal which corresponds to the second target object and originates from the first transmission signal 32a has the designation “ZS2.sub.TX1”. Correspondingly, the target signals which correspond to the second target object and originate from the second transmission signal 32b have the designations “ZS2.sub.TX21” and “ZS2.sub.TX22”.

(31) In FIG. 5, the three target signals ZS which are associated with the same target object are each surrounded with a dotted ellipse to make them easily recognizable. The target signals ZS1 which are associated with the first target object have the same range value, for example 32, and in addition the three target signals ZS1 have the Doppler values 0, 32 and 64. The target signals ZS2 which are associated with the second target object have the same range value, for example 96. In addition, the three target signals ZS2 have the Doppler values 0, 32 and 96. The target signals ZS3 which are associated with the third target object have the same range value, for example 192. In addition, the three target signals ZS3 have the Doppler values 16, 48 and 80.

(32) FIG. 6 shows, for example, the target signals ZS2.sub.TX1, ZS2.sub.TX21 and ZS2.sub.TX22, which are associated with the second target object, in an amplitude absolute-value Doppler diagram. For the sake of better comprehension, the absolute value of the amplitude of the strongest target signal ZS2.sub.TX1 is standardized to 1. For example, the amplitudes can be specified as attenuation. In this case, for example the amplitudes of the target signals ZS2.sub.TX21 and ZS2.sub.TX22 from the second transmission signal 32b may be 6 dB smaller than the amplitude of the target signal ZS2.sub.TX1 from the first transmission signal 32a.

(33) In the text which follows it is explained how the target signals ZS are assigned to the corresponding transmission signals 32a and 32b and validated.

(34) The range Doppler matrix is divided into sub-matrices TM0, TM1, TM2 and TM3 with the same extent in the Doppler dimension. In this context, the number of sub-matrices TM is calculated from the quotient of the number of Doppler gates of the uniqueness range and the smallest possible Doppler interval between target signals ZS originating from the first transmission signal 32a and the second transmission signal 32b, of the same target object. In the case of the exemplary uniqueness range of 128 Doppler gates and a smallest possible Doppler interval of 32 Doppler gates, the range Doppler matrix is divided into four sub-matrices TM0, TM1, TM2 and TM3, each with the extent of 32 Doppler gates.

(35) For each range value k the absolute values of the amplitudes s of the cells of the sub-matrices TM0, TM1, TM2 and TM3 which each correspond in priority with respect to their Doppler value l are combined to form a respective spectrum value a.sub.k,lt. In other words, the respective cells of the sub-matrices TM0, TM1, TM2 and TM3 with the lowest Doppler value l are combined, those cells with the second-lowest Doppler value l are combined and those cells with the third-lowest Doppler value l are combined etc. In order to determine the spectrum values a.sub.k,lt, the absolute values of the amplitudes s of the respective cells are advantageously added and the result squared. This is done according to the following formula:
a.sub.k,lt=(|s.sub.0(k,lt)|+|s.sub.1(k,lt+32)|+|s.sub.2(k,lt+64)|+|s.sub.3(k,lt+96)|).sup.2

(36) Here, “k” is the respective distance value between 0 and 256. “lt” is a running parameter for the Doppler values l. “lt” runs from 0 to 32, that is to say over the extent of a sub-matrix TM in the Doppler dimension. s.sub.0 corresponds to the respective complex-valued amplitude in the cell of the lowest sub-matrix TM0 in FIG. 5, extending between the Doppler values 0 and 32. S.sub.1 corresponds to the respective complex-valued amplitude in the cell of the second-lowest sub-matrix TM1 in FIG. 5, which extends between the Doppler values 32 and 64. S.sub.2 corresponds to the respective complex-valued amplitude in the cell of the third sub-matrix TM2 in FIG. 5, extending between the Doppler values 64 and 96. S.sub.3 corresponds to the respective complex-valued amplitude in the cell of the uppermost sub-matrix TM3 in FIG. 5, extending between the Doppler values 96 and 128.

(37) The spectrum values a.sub.k,lt obtained thereby can be presented in a 32×256 spectrum matrix (a.sub.k,lt,), as indicated in FIG. 7. In this context, for the sake of better comprehension only four of the spectrum values a.sub.k,lt are designated, for example.

(38) For example, calculations for four of the spectrum values a.sub.k,lt are shown in FIG. 8. Anticipating the result, for the sake of simple explanation the amplitudes s of cells in which target signals ZS are located are surrounded by dotted ellipses and provided with the corresponding designations. The amplitudes s which are not marked by ellipses merely have noise. The corresponding spectrum matrix (a.sub.k,lt,) is illustrated in FIG. 9. In this context, for the sake of better clarity, the spectrum values a.sub.k,lt which are calculated by way of example and those which have already been illustrated in FIG. 7 are shown.

(39) From all the spectrum values a.sub.k,lt, for example those which are above a predefined threshold and are detected as being target spectrum values which are associated with a respective target signal ZS1, ZS2 and ZS3 are determined, for example, with a detection algorithm for determining a constant false alarm rate (CFAR). In the present example, these are the spectrum values a.sub.32,0, a.sub.96,0, and a.sub.192,16, which, for the sake of better comprehension, are designated in the text which follows as target spectrum values az.sub.32,0, az.sub.96,0, and az.sub.192,16.

(40) For each target spectrum value az.sub.k,lt, the complex-valued amplitudes s.sub.0(k,lt), s.sub.1(k,lt+32), s.sub.2(k,lt+64) and s.sub.3(k,lt+96) of the cells which give rise to this target spectrum value az.sub.k,lt and which have the same range value k are combined in pairs according to the following formulas to form respective comparison values X.sub.0 and X.sub.1.
X.sub.0=|s.sub.0−s.sub.2|.sup.2
X.sub.1=|s.sub.1−s.sub.3|.sup.2

(41) Here, a difference is formed between the complex-valued amplitude so of the cell which is associated with the respective target spectrum value az and which has the lowest Doppler value l and the complex-valued amplitude s.sub.2 of the cells associated with the target spectrum value az and has the third-lowest Doppler value l. The absolute value of the difference is squared and assigned to a first comparison value X.sub.0. In addition, a difference is formed between the complex-valued amplitude s.sub.1 of the cell which is associated with the same target spectrum value az and which has the second-lowest Doppler value l and the complex-valued amplitude s.sub.3 of the cell which is associated with the target spectrum value az and has the highest Doppler value l. The absolute value of the difference is squared and assigned to a second comparison value X.sub.1.

(42) In the text which follows, this is carried out by way of example for the second target object with the range value k=32. In the example, the target spectrum value az.sub.96,0 with the amplitudes s.sub.0(96,0), s.sub.1(96,32), s.sub.2(96,64) and s.sub.3(96,96) corresponds to the second target object. For example, the following correspond:
X.sub.0,Target2=|s.sub.0(96,0)−s.sub.2(96,64)|.sup.2
X.sub.1,Target2=|s.sub.1(96,32)−s.sub.3(96,96)|.sup.2

(43) In the text which follows, in line with the Doppler amplitude diagram for FIG. 6, for the sake of easier calculation it is assumed, for example, that a cell with a target signal ZS1.sub.TX1, which originates from the first transmission signal 32a has the standardized amplitude s(k, l)=1. The cells with the target signals ZS1.sub.TX21 and ZS1.sub.TX22, which originate from the second transmission signal 32b, have, for example, the standardized amplitude s(k, l)=0.5. The cells without a target signal have, for example, amplitudes of, on average, approximately s(k, l)=0.2. Cells without a target signal generally have noise.

(44) The following amplitudes are obtained for the second target object:
s.sub.0(96,0)=1
s.sub.1(96,32)=0.5
s.sub.2(96,64)=0.2
s.sub.3(96,96)=0.5

(45) The following is obtained for the comparison values X.sub.0,Target2 and X.sub.1,Target2:
X.sub.0,Target2=|1−0.2|.sup.2=0.8
X.sub.1,Target2=|0.5−0.5|.sup.2=0

(46) The comparison values X.sub.0 and X.sub.1 are compared. The signals which are associated with the cells from whose amplitudes the lower of the two comparison values X.sub.0 or X.sub.1 is formed are validated as the two target signals ZS.sub.TX21 and ZS.sub.TX22 which originate from the second transmission signal 32b for the same target object.

(47) In the example, the lower comparison value is X.sub.1,Target2. The comparison value X.sub.1,Target2 was formed from the amplitudes s.sub.1(96,32) and s.sub.3(96,96). Therefore, the signals which are associated with the cells (96, 32) and (96, 96) of the range Doppler matrix are validated as the two target signals ZS2.sub.TX21 and ZS2.sub.TX22 of the second target object from the second transmission signal 32b.

(48) Subsequently, the absolute values of the amplitudes s.sub.0(96,0) and s.sub.2(96,64) of the cells (96,0) and (96,64), which are not used to form the lower comparison value X.sub.1,Target2 are compared. The target signal which is associated with the amplitude which is the largest in absolute value is validated as the target signal for the target object which originates from the first transmission signal 32a. The absolute value of the amplitude |s.sub.0(96,0)|=1 is larger than the absolute value of the amplitude |s.sub.2(96,64)|=0.2. Therefore, the target signal which is associated with the cell (96,0) with the higher absolute value of the amplitude s.sub.0(96,0) than the target signal ZS2.sub.TX1 for the second target object which originates from the first transmission signal 32a is validated.

(49) Object information of the second target object, for example a speed, a directional angle and a distance of the target object relative to the radar system 12 are determined from the validated target signals ZS2.sub.TX1, ZS2.sub.TX21 and ZS2.sub.TX22.

(50) Since the first transmission signal 32a is not encoded and is shifted in its phase, the Doppler value l which is associated with the first target signal 38a can be considered to be the correct Doppler value, and the correct relative speed of the second target object can be derived therefrom.

(51) To determine a directional angle, a phase difference D between the validated target signals ZS2.sub.TX1, ZS2.sub.TX21 and ZS2.sub.TX22 is determined. The phase difference D can be determined from the validated target amplitudes s.sub.TX1, s.sub.TX21 and s.sub.TX22, for example by means of the following mathematical operation:
D=s.sub.TX1*conj(s.sub.TX21+s.sub.TX22)
where D and the amplitudes s.sub.TX1, s.sub.TX21 and s.sub.TX22 are complex numbers and where “conj” stands for “for “complex-conjugate”. The phase of the variable D then corresponds to the phase difference between the target signals.

(52) In the selected example, the following mathematical relationship is accordingly obtained:
D=s.sub.0(96,0)*conj(s.sub.1(96,32)+s.sub.3(96,96))

(53) The method steps which are explained by way of example on the basis of the second target object are correspondingly carried out for the first target object and third target object. In this way, the corresponding target signals ZS1.sub.TX1, ZS1.sub.TX21, ZS1.sub.TX22 and respectively ZS3.sub.TX1, ZS3.sub.TX21, ZS3.sub.TX22 are also validated for the other target objects, and the corresponding object information determined from said signals.

(54) The entire method is carried out cyclically, with the result that the monitoring range 14 is monitored continuously for objects 18, and correspondingly sensed objects 18 can be tracked.

(55) The invention can also be used with a radar system 12 with more than one receiver 30. When, for example, two receivers are used, a three-dimensional fast Fourier transmission can be carried out instead of a two-dimensional fast Fourier transformation.