Method for operating a radar device comprising several radar sensors and motor vehicle

Abstract

A method for operating a radar device (2) comprising a plurality of radar sensors (3, 4, 5) and a control unit (6) connected to the radar sensors (3, 4, 5), wherein the radar device (2) at least partially detects an environment of the radar device (2), and wherein the radar sensors (3, 4, 5) are each configured to transmit at least one transmission signal in a frequency band (9, 10, 11) within an overall frequency band, wherein the overall frequency bands of the respective radar sensors (3, 4, 5) at least partially overlap, the radar sensors (3, 4, 5) each transmit the at least one transmission signal in a time window, and the respective start times for the transmission are predetermined by the control unit (6), wherein the time window of a first of the radar sensors (3) and the time window of a second of the radar sensors (4) partially overlap in an overlap time period,wherein, during the overlap period, the frequency band (9) of the first radar sensor (3) is reduced by at least one restriction frequency section as a function of a restriction rule, and the frequency band (10) of the second radar sensor (4) is restricted such that the restricted frequency band (10) of the second radar sensor (4) does not overlap with the restricted frequency band (9) of the first radar sensor (3), wherein the restricted frequency band (10) of the second radar sensor (4) lies at least partially within the restriction frequency section, wherein the radar device (2) determines the restriction rule as a function of the detected environment.

Description

The invention relates to a method for operating a radar device comprising a plurality of radar sensors and a control unit connected to the radar sensors, wherein a surrounding area of the radar device is at least partially detected by the radar device and wherein the radar sensors are each designed to emit at least one transmission signal in a frequency band within an overall frequency band, wherein the overall frequency bands of the respective radar sensors at least partially overlap, the radar sensors each transmit the at least one transmission signal in a time window and the respective start times for the transmission are predefined by the control unit. The invention further relates to a motor vehicle.Modern motor vehicles generally provide a multiplicity of assistance systems which assist the driver by means of a partially automated driving mode and / or at least temporarily take over the motor vehicle control in a fully automated driving mode. The assistance systems used for partially automated or automated driving operation often operate on the basis of data which are generated by radar systems of the motor vehicle. For this purpose, a motor vehicle can contain a plurality of different radars for different functions, for example a long-range radar (long-range radar) for detecting objects at distances of up to 300 m, a mid-range radar (mid-range radar) for detecting objects at distances of up to 150 m, a short-range radar (short-range radar) and / or a plurality of corner radars (corner radars) in order in particular to detect the near field within a few meters around the motor vehicle with a 360° detection range and to be able to provide a parking aid, for example.The different radar systems may occupy at least partially different frequency bands. A long-range radar and / or a medium-range radar can each operate, for example, in the 77 GHz frequency range and the corner radars can operate, for example, in the 24 GHz frequency range. In addition to different frequency ranges, the modulation methods used for the individual radars, for example slow chirp, fast chirp or pulse doppler, can also differ. By selecting different frequency ranges and / or different modulation methods, it is possible to separate the individual radar data also in the case of at least partially overlapping reception ranges within the scope of a data evaluation, so that the occurrence of interference between the individual radar systems can be avoided.Various methods for operating radar sensors of a radar device comprising a plurality of radar sensors are known from the prior art.DE 10 2005 056 800 A1 describes a method for operating a radar system of a motor vehicle. The radar system comprises at least one first sensor module and at least one further sensor module, wherein a detection range of the first sensor module overlaps at least partially with a detection range of the second sensor module. In a monitoring mode, the first sensor module receives a transmission signal transmitted by the further sensor module in order to obtain information about the operating state of the further sensor module. Depending on this operating state, the sensor module can be synchronized with the operation of the further sensor module.US 2016 / 0109568 A1 describes a radar system having a plurality of radar sensors, each of which includes an individual control device.The data of received radar waves can be evaluated by the control devices of the radar sensors. A central evaluation device connected to the respective radar sensors performs a common evaluation of the data detected by the radar sensors, it being possible for the transmission operation of the individual radar sensors to be synchronized via the common evaluation device.DE 10 2016 004 305 A1 discloses a motor vehicle having a plurality of radar sensors arranged in different installation positions. The radar sensors can each be operated as transmitters and / or as receivers, wherein at least one first radar sensor for transmitting a transmission signal and at least one second radar sensor different from the first radar sensor for receiving a reflection signal of the transmission signal are controlled by a control device. The control device then ascertains at least one piece of sensor information describing the surroundings of the motor vehicle as a function of the transmission signal of the first radar sensor and the reflection signal received by the second radar sensor.By providing the 77 GHz frequency band for automotive applications and by the clear advantage exhibited by the use of frequency-modulated continuous wave (FMCW) radars compared to other modulation techniques, it is desirable that as many radar sensors as possible in a motor vehicle can be operated in this frequency band and with this modulation technique. Operating a plurality of radar sensors in at least partially overlapping frequency ranges and using the same modulation method has the disadvantage that interference can occur to an increased extent between the individual radar sensors, so that detection of the surroundings of a motor vehicle or the like is made more difficult. The interference increases the noise level for the individual radar sensors, which results in a reduction in the maximum possible distance for detecting objects in the environment of the motor vehicle and can have the effect that a separation of the different data generated by the individual radar sensors is no longer possible reliably during their evaluation.In order to avoid interference, different multiplexing methods are known in principle. In so-called time multiplexing, the radar sensors are operated in such a way that they do not transmit simultaneously, so that only one radar sensor is transmitting at a given point in time, or waves transmitted and reflected by this radar sensor are detected. This method has the disadvantage that, in the case of a large number of radar sensors, the duration of the individual detection cycles overall results in a very long time period until a radar sensor can measure again. This is disadvantageous in particular for detecting the environment of a motor vehicle, since the position of individual objects in the environment of the motor vehicle can continuously change and should therefore be checked as often as possible by a new measurement.Another method for multiplexing is so-called frequency multiplexing, in which the radar sensors transmit simultaneously, but the available frequency band is divided into different subbands which are assigned to one of the radar sensors in each case and which do not overlap. This method has the disadvantage that the bandwidth available for the respective radar sensors is limited to the subbands allocated to them in each case, as a result of which their detection properties are likewise limited.DE 102018 201 303 A1 discloses a method for operating a plurality of radar sensors of a vehicle in at least partially spatially coincident detection ranges and in a common frequency space. The sensors each transmit along a frequency ramp, wherein the different frequency ramps of the sensors are selected such that a frequency gap f 2- f 1 arises at any point in time between the respective transmission frequencies, e.g. f 1 and f 2. The transmitting sensors each have the same transmission frequency band, but differ with respect to the starting points in time or the starting frequencies of the individual ramps, so that overall, an interleaved emission of the radar sensors results.EP 1 826 586 A1 discloses an automotive radar system and describes that, in order to avoid interference between different radar sensors on different vehicles, a different carrier frequency of the radar sensor modulation can be selected if interference with the signal of a radar sensor of another vehicle occurs. Besides, as a changeable modulation state, a modulation manner, an orientation of the polarization direction of the transmitted wave, a transmission cycle, and / or a modulation code are further described.The object of the invention is therefore to specify an improved method for operating a radar device comprising a plurality of radar sensors, which method avoids the occurrence of interference and at the same time restricts the detection properties of the radar sensors as little as possible.To achieve this object, in a method of the type mentioned at the beginning, the invention provides for the time window of a first of the radar sensors and the time window of a second of the radar sensors to partially overlap in an overlap time segment, wherein during the overlap time segment, the frequency band of the first radar sensor is reduced by at least one restriction frequency segment as a function of a restriction rule, and the frequency band of the second radar sensor is restricted in such a way that the restricted frequency band of the second radar sensor does not overlap with the restricted frequency band of the first radar sensor, wherein the restricted frequency band of the second radar sensor is at least partially within the restriction frequency segment, wherein the radar device ascertains the restriction rule as a function of the detected environment.Because the total frequency bands of the respective radar sensors at least partially overlap and also the time windows in which the radar sensors each transmit partially overlap in the overlap time segment, the disadvantages of pure time multiplexing and those of pure frequency multiplexing can be overcome. By transmitting in at least partially overlapping frequency bands, it is advantageously possible to avoid having to assign to each of the radar sensors a single subband which does not overlap with other subbands. Due to the partial temporal overlap of the time windows in which the radar sensors each transmit, it is advantageously made possible for the radar sensors to be able to measure one after the other in a more rapid sequence than would be the case with a pure time multiplexing without temporal overlap.In order to avoid the occurrence of interference in the overlap time interval in which the time window of the first radar sensor and the time window of the second radar sensor overlap, on account of the likewise at least partially overlapping total frequency bands, the frequency band of the first radar sensor is reduced by at least one limiting frequency interval on the basis of the total frequency band of the first radar sensor in the method according to the invention. The frequency band of the second radar sensor is also limited in the overlap time segment on the basis of the total frequency band of the second radar sensor. The limitation of the frequency band of the first radar sensor and the limitation of the frequency band of the second radar sensor are effected in this case as a function of a restriction rule. Furthermore, the limiting of the frequency bands is carried out in such a way that the limited frequency band of the second radar sensor does not overlap with the limited frequency band of the first radar sensor, wherein the limited frequency band of the second radar sensor is at least partially within the limiting frequency section.In other words, the second radar sensor transmits in the overlap period at least partially within the restriction frequency range cut from the frequency band of the first radar sensor by the restriction. For this purpose, the frequency band of the second radar sensor is limited in such a way that it at least partially encompasses the limiting frequency section cut off from the first frequency band and also does not overlap with the remaining, limited frequency band of the first radar sensor. This advantageously enables the radar sensors to transmit with limited and non-overlapping frequency bands in the overlap time interval, whereas the radar sensors can transmit with an unlimited frequency band, i.e., with their respective total frequency band, outside the overlap time interval, in which either only the first radar sensor or only the second radar sensor transmits.The invention is based on the idea that, for the operation of a radar sensor without any significant functional restriction, the total frequency band does not have to be available at all times of the transmission of a radar sensor, as long as there are at least temporal subareas during the transmission in which the total frequency band is available. By generating the overlap time interval in which at least two radar sensors are transmitting simultaneously, it is achieved that radar sensors of a radar device comprising a plurality of radar sensors, which radar sensors measure cyclically one after the other, can measure more quickly again, since the transmission of the second radar sensor is already commenced again before the time window of the first radar sensor has expired. This reduces the duration which lies between two transmission processes of a radar sensor, as a result of which a function of the radar device, for example a detection of the environment by means of the radar device, can be improved.It is possible in particular for there to be more than one first and more than one second radar sensor, wherein a plurality of first or a plurality of second radar sensors each transmit simultaneously and their frequency bands are each restricted identically. This is possible, for example, if the detection ranges of the two first radar sensors do not overlap with one another, but in each case overlap with the detection range of a second radar sensor, so that interference between the second radar sensor and each of the two first radar sensors is avoided by the restriction according to the method according to the invention. This also applies accordingly to scenarios in which a plurality of first and also a plurality of second radar sensors are present.The first radar sensor may transmit both upstream of the second radar sensor and downstream of the second radar sensor. The only decisive factor for the method according to the present invention is that the time window in which the first radar sensor transmits and the time window in which the second radar sensor transmits partially overlap in the overlap time segment. The overlap time interval is shorter than each of the two time windows, so that consequently both a time range in which only the first radar sensor is transmitting and a time range in which only the second radar sensor is transmitting exist.The frequency bands of the first and second radar sensors are not limited at least temporarily outside the overlap time interval, so that the radar sensors can transmit at least temporarily outside the overlap time interval in each case in their overall frequency band predefined as a function of their design. The limiting of the frequency band of the first radar sensor and the frequency band of the second radar sensor in the overlap time interval can be understood as a complementary limiting, since the limiting frequency interval, which is no longer available to the first radar sensor for transmission due to the limiting, is at least partially available to the second radar sensor for transmission.The method according to the invention has the advantage that at no time does two radar sensors transmit with overlapping frequency bands or with overlapping time windows. In this way, interference between the radar sensors of the radar device, in particular in the case of radar sensors having at least partially spatially overlapping detection ranges, can be advantageously avoided. The partially overlapping time windows furthermore advantageously result in a faster sequence of the transmission signals than in a time division multiplex method. Furthermore, the in particular only temporary frequency band restriction in the overlap time interval allows transmission at least partially with a greater bandwidth outside the overlap time interval than would be possible in a pure frequency multiplex method. In radar sensors which can emit more than one transmission signal, such as in multimode radar sensors, for example, all transmission signals can be transmitted within the respective, at least temporarily restricted frequency band of the radar sensor.The control unit, which specifies the respective start times for the transmission of the radar sensors, can generate a synchronous transmission of the transmission signals of the radar sensors and / or a defined time offset between the individual time windows. The control unit may be a separate control unit connected to the radar sensors of the radar device. It is also possible for the control unit to be a component of at least one of the radar sensors, this radar sensor being connected to the other radar sensors of the radar device, so that the respective starting instants can also be predefined by the control unit for the further radar sensors of the radar device.In a preferred embodiment of the invention, provision can be made for radar sensors to be used which each transmit within the same total frequency band. In radar sensors, the total frequency band in which they can transmit or receive is generally predefined as a function of the design. Furthermore, defined frequency bands are provided or prescribed for specific applications. The method according to the invention advantageously makes it possible for two radar sensors to be able to transmit at least temporarily in each case in a frequency band which corresponds to the total frequency band available for their function, with the result that radar sensors of the same design can advantageously also be used for a plurality of radar sensors assigned to different functions. In particular, it is made possible that a plurality of radar sensors operable within a total frequency band preferred for a plurality of functions can be used. Outside the overlap time interval, transmission in a frequency band corresponding to the complete available total frequency band of each radar sensor is possible.According to the invention, it can be provided that the restriction rule comprises a time-dependent restriction function, wherein the frequency band of the first radar sensor is restricted by at least one time-dependent restriction frequency section during the overlap time section as a function of the restriction information.The use of a time-dependent restriction function as a restriction rule achieves the advantage that no invariable division between the frequency bands takes place within the overlap time interval, but that a time-dependent restriction which can be adapted during the time profile of the overlap time interval can be carried out. Due to the time-dependent restriction within the overlap time interval, the division of the frequency bands can be adapted by the restriction, for example, to the measurement method of one or more of the radar sensors and / or to a modulation method used by one or more of the radar sensors, so that an effect of the restriction of the respective frequency band on the function of the radar sensor, i.e., on its detection properties, can advantageously be kept as low as possible.The time-dependent restriction function allows the at least one restriction frequency section, which is omitted from the first radar sensor by the restriction, to be configured in a time-dependent manner and to represent at least a part of the restricted frequency band of the second radar sensor, which is added by the restriction, for example, by a reduction in its restriction. In particular, the restriction of the frequency band of the second radar sensor may likewise be time-dependent. It can be provided that the frequency band of the first radar sensor is limited with a restriction that increases in the overlap time interval according to the restriction function, wherein a restriction of the frequency band of the second radar sensor is reduced over the overlap time interval, in particular according to the restricted frequency band of the first radar sensor, so that sections continuously omitted from the first frequency band by the restriction are at least partially added to the second restricted frequency band. The restriction rule can comprise one or more, in particular sectionally defined, restriction functions which define a restriction in particular for the entire duration of an overlap time section.In a preferred configuration of the invention, it can be provided that the restriction function is or comprises a linear function, wherein the frequency band of the first radar sensor is at least partially reduced according to the linear function during the overlap time interval and a restriction of the frequency band of the second radar sensor is at least partially reduced according to the linear function during the overlap time interval. The linear function can in this case comprise in particular at least one function defined in regions, which describes a straight line running within the restriction time section. For a plurality of successive overlap periods, a restriction can be effected in each case according to the same linear function. It is also possible for overlap periods following one another in time to be restricted in each case according to different restriction functions.According to the invention, it can be provided that the limiting function comprises a frequency gap and / or a time gap, wherein the frequency bands of the radar sensors in the overlap time segment are separated from one another by the frequency gap and / or the time gap. Due to the limitation in the overlap time interval carried out according to the invention, the frequency bands are also time-dependent at least in regions. By providing a frequency gap and / or a time gap, a distance between the limited frequency band of a first radar sensor and the limited frequency band of a second radar sensor can be achieved in terms of time or frequency. By providing a frequency gap, it is possible to cause the frequency bands of the radar sensors to be spaced apart from one another by the value of the frequency gap at the same time within the overlap period. Accordingly, the time gap can cause the frequency bands of the radar sensors in the overlap time interval to be separated from one another by the value of the time gap with respect to a same frequency. The value of the frequency gap and the value of the time gap can be understood here as a line width of the limiting function, by means of which, given a predefined scaling on the time and frequency axis, a time gap and a frequency gap, that is to say a distance between the frequency bands of the first and second radar sensors, which frequency bands are likewise plotted over the time axis and the frequency axis, are defined.In a preferred embodiment of the invention, provision can be made for radar sensors to be used whose total frequency bands are in a range between 76 GHz and 81 GHz inclusive, in particular between 76 GHz and 77 GHz inclusive. In radar sensors configured in this way, it may furthermore be provided according to the invention that a value between 1 MHz and 20 MHz inclusive, in particular between 5 MHz and 10 MHz, is used as the value of the frequency gap and / or that a value between 0.1 ms and 10 ms inclusive, in particular a value of 1 ms, is used as the value of the time gap. Compared with the entire bandwidth or with the entire time duration of a time window in which the radar sensors transmit, the frequency gap or the time gap represents only an extremely small restriction. By providing the frequency gap and / or the time gap, the interference between the respective radar sensors can be further reduced, since a border-side direct bordering of the limited frequency bands is avoided. Furthermore, it is also possible to compensate for small time fluctuations during the synchronization of the transmission times of the radar sensors, since, owing to the time gap and the frequency gap, overlapping of the limited frequency bands is avoided even if the intended transmission time deviates slightly. In principle, it is possible to use the method according to the invention also in radar sensors transmitting in other total frequency ranges. The value of the frequency gap and / or the value of the time gap can be adjusted in particular depending on the total frequency range of the radar sensors used in each case.According to the invention, it can be provided that at least the first radar sensor and the second radar sensor, in particular all radar sensors of the radar device, transmit cyclically one after the other, wherein the time windows of two consecutive transmission signals each overlap in an overlap time interval, wherein during each overlap time interval the frequency bands of the radar sensors transmitting the overlapping transmission signals are limited depending on the restriction rule. The radar sensors transmitting cyclically one after the other can be operated by the control unit with synchronous starting times or with a defined time offset between the starting times. It is also possible, in particular, for a third radar sensor and / or further radar sensors to transmit cyclically one after the other in addition to the first radar sensor and the second radar sensor. In particular, all radar sensors of the radar device can transmit cyclically one after the other. In a third radar sensor that is also provided, the order 1-2-3-1-2-3, etc., may be used as the transmission order, for example. In the case of more than three radar sensors transmitting cyclically one after the other and / or in the case of more than three groups of radar sensors transmitting cyclically one after the other, further transmission sequences can correspondingly also be used.Regardless of the number of radar sensors transmitting cyclically one after the other, one of the radar sensors can always be understood as a first radar sensor and one of the radar sensors as a second radar sensor in the sense of the invention. This means that in the case of the radar sensors transmitting cyclically one after the other there is in each case an overlap of a time window at the beginning of the time window of a radar sensor and an overlap at the end of the time window of each radar sensor. Between the two overlap time segments there is also a range in each case in which the relevant radar sensor can transmit without limiting its frequency band and without overlapping with the frequency band of a further radar sensor. It is also possible for there to be a plurality of first, a plurality of second and / or a plurality of further radar sensors which are arranged, for example, in such a way that their detection ranges do not overlap. This enables the plurality of first and / or plurality of further radar sensors to be able to transmit simultaneously as a group in each case. In this case, in particular for each radar sensor of a group, the same restriction of its frequency band within an overlap time interval can be carried out.In a preferred embodiment of the invention, it can be provided that the radar sensors are each operated as continuous wave radar, in particular as frequency-modulated continuous wave radar (FMCW radar), Doppler radar and / or pulsed noise radar. For this purpose, it may be provided that the radar sensors are each designed as a continuous wave radar, an FMCW radar, a Doppler radar or a pulsed noise radar. The use of radar sensors which can be operated, for example, as FMCW radar or are designed as FMCW radar has the advantage that, due to the limitation of the frequency bands in the overlap time interval provided according to the invention, advantageously in the case of a radar operated as FMCW radar, no or only very little impairment of its operation occurs due to the frequency limitation in the overlap time interval, since, due to the modulation method used, the entire bandwidth of the available total frequency band is not used, at least partially, within a time window, depending on time. This effect can also occur accordingly in other types of radar and can be used with comparable advantage.According to the invention, it is provided that a surrounding area of the radar device is at least partially detected by the radar device, wherein the radar device determines the restriction rule as a function of the detected surrounding area. The restriction rule can be determined by at least one of the radar sensors and / or by the control unit. In this case, a restriction function and / or a value of a frequency gap and / or a value of a time gap can be determined and used as a restriction rule. In this way, it is made possible for the restriction rule to be adapted in each case to different operating situations of the individual radar sensors arising from the respectively currently prevailing environment of the motor vehicle. Depending on the current environment of the motor vehicle, different modes of operation of the radar sensors may result, which can be taken into account by ascertaining the restriction rule as a function of the detected environment.For a motor vehicle according to the invention, it is provided that it comprises a radar device having a plurality of radar sensors and a control unit connected to the radar sensors, wherein the control unit is configured to carry out a method according to one of the preceding claims.All the advantages and embodiments described above with respect to the method according to the invention also apply accordingly to the motor vehicle according to the invention.According to the invention, it may be provided that the radar sensors comprise at least one long-range radar sensor, one long-range radar sensor and / or one short-range radar sensor, and / or that the radar sensors each comprise a radar sensor arranged in an interior of the motor vehicle, in particular a radar sensor for driver observation and / or a radar sensor for gesture detection. Radar sensors detecting for a surrounding area of the motor vehicle, such as far-range radar sensors, mid-range radar sensors and / or after-range radar sensors, such as corner-area radar sensors, for example, may result in spatially at least partially overlapping detection ranges, in which the radar sensors may advantageously be operated by the method according to the invention for reducing and / or avoiding interference. At least two radar sensors arranged in an interior of a motor vehicle may also have at least partially overlapping detection ranges, so that these radar sensors may also be advantageously operated using the method according to the present invention. The radar sensors arranged in an interior of the motor vehicle may be, for example, radar sensors for driver observation and / or radar sensors for gesture detection.Further advantages and embodiments of the invention result from the exemplary embodiments described below and on the basis of the drawings. These are schematic representations and show: FIG. 1 shows an exemplary embodiment of a motor vehicle according to the invention, FIG. 2 shows a first diagram in which the frequency characteristics of a plurality of radar sensors are shown over time, and FIG. 3 shows a second diagram in which the frequency bands of a plurality of radar sensors are shown over time.FIG. 1 shows an exemplary embodiment of a motor vehicle 1 according to the invention. Motor vehicle 1 includes a radar device 2 and a first radar sensor 3, a second radar sensor 4, two third radar sensors 5, and a control unit 6. Alternatively, the control unit 6 can be designed as a component of one of the radar sensors 3, 4, 5, wherein the radar sensor having the control unit 6 is connected to the further radar sensors of the radar device 2. The connection 7 can be designed, for example, as an electrical or optical line. Via the electrical line 7, the control unit 6 can specify the respective start times for transmission by the individual radar sensors 3, 4, 5, with the result that the radar sensors 3, 4, 5 can be synchronized by the control unit 6.Radar sensors 3, 4, 5 of motor vehicle 1 are each designed as a frequency-modulated continuous wave radar (FMCW radar) and are also provided to transmit or receive in a total frequency band between 76 GHz and 81 GHz inclusive. The first radar sensor 3 is used as a long-range radar sensor (long-range radar sensor). The second radar sensor 4 forms a mid-range radar sensor (mid-range radar sensor) and the two third radar sensors 5 each form a short-range sensor (short-range radar sensor) designed as a corner-region radar sensor (corner radar sensor), by means of which a short range around the motor vehicle 1 can be detected.The detection ranges (not shown) of the radar sensors 3, 4, 5 partially overlap in this case, wherein interference may occur in the case of simultaneous transmission due to the configuration of the radar sensors 3, 4, 5 for transmission in the same overall frequency band. In order to avoid and / or to reduce interference which occurs, the control unit 6 is designed to carry out a method according to the invention, which is explained in detail below.FIG. 2 shows a first diagram 8 which is used to explain an exemplary embodiment of a method according to the invention. In diagram 8, the time t is plotted on the abscissa and the frequency f on the ordinate. Furthermore, three frequency bands 9, 10, 11 are shown, which are assigned to radar sensors 3, 4, 5 of motor vehicle 1. Frequency band 9 is the frequency band of first radar sensor 3, frequency band 10 is the frequency band of second radar sensor 4, and frequency band 11 is the frequency band of each of radar sensors 5.In the exemplary illustration in FIG. 2, the time window of the second radar sensor and thus also the frequency band 10 begins at the time t 1 and the time window of the third radar sensors and thus also their frequency band 11 begins at the time t 3. Furthermore, the time window of first radar sensor 3 and thus also its frequency band 9 ends at time t 2 and the time window of second radar sensor 4 ends at time t 4. Between the time windows of the radar sensors 3, 4, 5 and thus also between their frequency bands 9, 10, 11, an overlap time interval is formed in each case, in which the frequency bands of two radar sensors transmitting successively at least partially overlap. The overlap time interval in which the frequency band 9 of the first radar sensor 3 overlaps with the frequency band 10 of the second radar sensor 4 extends in FIG. 2 between the times t 1 and t 2. Accordingly, the overlap time interval extends in that the frequency band 10 of the second radar sensor 4 overlaps with the frequency band 11 of the third radar sensors 5 between the times t 3 and t 4.The frequency bands 9, 10, 11 are each within the same total frequency band which extends between the frequencies f 0 and f 1. Within the first overlap time interval, i.e. between the times t 1 and t 2, the frequency band 9 of the first radar sensor 3 is limited as a function of a restriction rule. The restriction rule comprises a time-dependent restriction function 12, which is a linear function in the present case. This is defined in each case for the individual overlap time segments and is shown in FIG. 2 in each case as a line with increased line thickness. According to the restriction function 12, i.e. according to the line shown, the frequency band 9 of the first radar sensor 3 extending from f 0 to f 1 is restricted within the overlap time interval between t 1 and t 2. This means that at each time t i within the overlap time interval, only a limited frequency band which extends between f 0 and f i is available to the first radar sensor 3. The restriction frequency portion away from the frequency band 9 from the total frequency band by the restriction function thus extends from f i to f 1. at each time t i within the overlap time portion.Furthermore, in the overlap time interval between t 1 and t 2 the frequency band 10 of the second radar sensor 4 is also limited, wherein the limitation is likewise effected as a function of the limitation function 12. The frequency band 10 of the second radar sensor 4 is limited in such a way that the frequency band 10 begins at the frequency f 1 at the time t 1 and then extends continuously as far as the end of the overlap time interval in each case at a time t i within the overlap time interval from f i to f 1. The frequency band 10 of the second radar sensor 4 thus comprises the limiting frequency section of the first radar sensor 3 within the overlap time interval between t 1 and t 2 At the time t 2, i.e. at the end of the overlap time interval, the frequency band 10 of the second radar sensor 10 is no longer limited and it extends from f 0 to f 1.In the time range between t 2 and t 3 the frequency band 10 of the second radar sensor 4 is likewise unlimited and therefore corresponds to the total frequency band of the second radar sensor 4. in the subsequent overlap time interval between the points in time t 3 and t 4 there is once again a restriction of the second frequency band 10 and of the frequency band 11 of the third radar sensors 3, in order to avoid an overlap of the frequency bands 10, 11 also in the second overlap time interval between the points in time t 3 and t 4 analogously to the first overlap time interval t 1 and t 2. In this case, in the overlap time interval between the times t 3 and t 4 the frequency band 10 of the second radar sensor 4 is limited in accordance with the frequency band 9 of the first radar sensor 3 in the overlap time interval between t 1 and t 2. Similarly, frequency band 11 of third radar sensors 5 in the overlap time interval between points in time t 3 and t 4 is limited, as is frequency band 10 of second radar sensor 4 in the overlap time interval between t 1 and t 2 is limited.It can be provided that the limiting function comprises a frequency gap or a time gap, wherein the limited frequency bands 9, 10 of the radar sensors 3, 4 in the overlap time interval between t 1 and t 2 or the limited frequency bands 10, 11 of the radar sensors 4, 5 in the overlap time interval between t 3 and t 4 are respectively separated from one another by the frequency gap and / or the time gap. The frequency gap and the time gap can be understood as a line width of the restriction function 12, by which a value for the frequency gap and a value for the time gap are defined with respect to a predefined scaling of the abscissa and ordinate.This line width of the limiting function 12 achieves the effect that a distance corresponding to the value of the frequency gap arises between the frequency band 9 and the frequency band 10 at the illustrated time t i in the frequency range. Accordingly, with respect to the frequency f i shown, a time gap arises which arises from the line width of the restriction function 12 and which also space the frequency band 9 and the frequency band 10 from one another in terms of time.For the total frequency bands of radar sensors 3, 4, 5 running between 76 GHz and 81 GHz inclusive in the present example, a value between 1 MHz and 20 MHz inclusive, in particular between 5 MHz and 10 MHz, can be used as the value of the frequency gap. As the value of the time gap, a value between 0.1 ms and 10 ms inclusive, in particular a value of 1 ms, can be used.As can be seen from FIG. 2, the method according to the invention achieves the effect that the second radar sensor 4 can transmit in the frequency band 10 between the times t 1 and t 4 which is partially restricted in each case in the overlap time segments, without an overlap occurring with the frequency band 9 of the first radar sensor 3, the time window of which only ends at the time t 2. Furthermore, no overlap arises with the frequency band 11 of the third radar sensors 5, whose time window for transmission already begins at the time t 3. This advantageously reduces interference occurring between radar sensors 3, 4, 5.Radar sensors 3, 4, 5 may transmit in particular cyclically one after the other, so that after the time window in which third radar sensors 5 transmit in frequency band 11, a new overlap time segment with a further time window of first radar sensor 3 arises. In this overlap time interval, not shown in FIG. 2, too, a restriction can be carried out, for example, according to the first overlap time interval between t 1 and t 2 or the second overlap time interval between t 3 and t 4 respectively.By operating the radar sensors 3, 4, 5 in each case as a frequency-modulated continuous wave radar, the restrictions which arise as a result of the restriction of the frequency bands available in each case in the overlap time segments can be advantageously reduced, with the result that no or only a slight functional impairment of the radar sensors 3, 4, 5 occurs.In addition to using a same restriction rule for different overlap periods, it is possible that different restriction rules are used for different overlap periods. This is illustrated by way of example in a second diagram 16 in FIG. 3. In the first overlap time segment between the times t 1 and t 2 the limitation of the first frequency band 9 and the limitation of the second frequency band 10 take place as a function of a limitation function which comprises a step function 13 and a linear function 14. At the time t 1 a restriction according to the step function 13 takes place first until the time t a, wherein from the time t a a restriction according to the linear function 14 until the time t 2 is carried out.In contrast, in the second overlap time segment between the times t 3 and t 4 the frequency band 10 of the second radar sensor 4 and the frequency band 11 of the third radar sensors 5 are limited according to a restriction rule which comprises only one step function 15.It is possible that different restriction functions composed of a plurality of step functions and / or a plurality of linear functions, for example with different slopes, are used for different overlap periods. In particular, it is provided that an evaluation of the environment of the motor vehicle 1 takes place by the control unit 6 of the motor vehicle 1 on the basis of the information detected by the radar sensors 3, 4, 5, wherein a restriction rule for the radar sensors 3, 4, 5 is determined in each case as a function of the current environment of the motor vehicle 1. This makes it possible for the restriction in the overlap time segments to take place in each case in accordance with the currently prevailing requirements for the operation of the individual radar sensors 3, 4, 5, with the result that, as a result of the restrictions on the frequency bands in the overlap time segments, there is no or only a slight impairment of the function of the operation of the radar sensors.The value of a frequency gap and / or the value of a time gap or a corresponding line width of a restriction function can also be determined as a function of environmental information describing the environment of the motor vehicle and thus be adapted to currently prevailing states. The restriction rule determined by the control unit 6 can then be transmitted by the control unit 6 for example via the connections 7 to the radar sensors 3, 4, 5 and taken into account by these in addition to the likewise predefined start times for the transmission.It is possible for the motor vehicle to comprise more than the radar sensors 3, 4, 5 shown. Analogously to the exemplary embodiments illustrated above on the basis of the three frequency bands 9, 10, 11, it is also possible for the overlap periods which arise in each case to be restricted in the respective overlap periods when further radar sensors are used according to a restriction rule.In addition to the two third radar sensors 5, two or more first radar sensors 3 and / or two or more second radar sensors 4 may also be provided, which, for example, each transmit in the same time windows with a frequency band limited in the same way. It is also possible for the first radar sensor 3, the second radar sensor 4 and / or the third radar sensors 5 to be radar sensors arranged in an interior of the motor vehicle 1. Radar sensors 3, 4, 5 may be used, for example, for monitoring a driver and / or for gesture detection, for example, as part of gesture control.

Claims

Method for operating a radar device (2) comprising a plurality of radar sensors (3, 4, 5) and a control unit (6) connected to the radar sensors (3, 4, 5), wherein a surrounding area of the radar device (2) is at least partially detected by the radar device (2), and wherein the radar sensors (3, 4, 5) are each designed to emit at least one transmission signal in a frequency band (9, 10, 11) within an overall frequency band, wherein the overall frequency bands of the respective radar sensors (3, 4, 5) at least partially overlap, the radar sensors (3, 4, 5) each transmit the at least one transmission signal in a time window and the respective start times for the transmission are predefined by the control unit (6), wherein the time window of a first of the radar sensors (3) and the time window of a second of the radar sensors (4) partially overlap in an overlap time section, wherein during the overlap time interval, the frequency band (9) of the first radar sensor (3) is reduced by at least one limiting frequency interval as a function of a limiting rule and the frequency band (10) of the second radar sensor (4) is limited in such a way that the limited frequency band (10) of the second radar sensor (4) does not overlap with the limited frequency band (9) of the first radar sensor (3), wherein the limited frequency band (10) of the second radar sensor (4) is at least partially within the limiting frequency interval, wherein the radar device (2) determines the limiting rule as a function of the detected environment.Method according to Claim 1, characterized in that radar sensors (3, 4, 5) are used which each transmit within the same total frequency band.Method according to Claim 1 or 2, characterized in that the restriction rule comprises a time-dependent restriction function (12), wherein the frequency band (9) of the first radar sensor (3) is restricted by at least one time-dependent restriction frequency section during the overlap time section as a function of the restriction function (12).Method according to Claim 3, characterized in that the restriction function (12) is or comprises a linear function, wherein the frequency band (9) of the first radar sensor (3) is at least partially reduced according to the linear function during the overlap time interval and a restriction of the frequency band (10) of the second radar sensor (4) is at least partially reduced according to the linear function during the overlap time interval.Method according to either of Claims 3 and 4, characterized in that the limiting function (12) comprises a frequency gap and / or a time gap, the frequency bands (9, 10, 11) of the radar sensors (3, 4, 5) being separated from one another in the overlap time section by the frequency gap and / or the time gap.Method according to one of the preceding claims, characterized in that radar sensors (3, 4, 5) are used whose total frequency bands are in a range between 76 Ghz inclusive to 81 GHz inclusive, in particular between 76 GHz and 77 GHz inclusive.Method according to claims 5 and 6, characterised in that a value between 1 MHz and 20 MHz, in particular between 5 MHz and 10 MHz, is used as the value of the frequency gap and / or that a value between 0.1 ms and 10 ms, in particular a value of 1 ms, is used as the value of the time gap.Method according to one of the preceding claims, characterized in that at least the first radar sensor (3) and the second radar sensor (4), in particular all the radar sensors (3, 4, 5) of the radar device (2), transmit cyclically one after the other, wherein the time windows of two successive transmission signals each overlap in an overlap time interval, wherein during each overlap time interval the frequency bands (9, 10, 11) of the radar sensors (3, 4, 5) transmitting the overlapping transmission signals are limited as a function of the restriction rule.Method according to one of the preceding claims, characterized in that the radar sensors (3, 4, 5) are each operated as continuous-wave radar, in particular as frequency-modulated continuous-wave radar, Doppler radar and / or pulsed-noise radar.Motor vehicle comprising a radar device (2) having a plurality of radar sensors (3, 4, 5) and a control unit (6) connected to the radar sensors (3, 4, 5), wherein the control unit (6) is configured to carry out a method according to one of the preceding claims.Motor vehicle according to Claim 10, characterized in that the radar sensors (3, 4, 5) comprise at least one long-range radar sensor, one long-range radar sensor and / or one short-range radar sensor, and / or in that the radar sensors (3, 4, 5) each comprise a radar sensor arranged in an interior of the motor vehicle (1), in particular a radar sensor for driver observation and / or a radar sensor for gesture detection.

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