METHOD FOR LOW-INTERFERENCE OPERATION OF A PLURALITY OF RADAR SENSORS

Abstract

A method for low-interference operation of a plurality of radar sensors, which are installed in different vehicles and each emit a transmission signal in an operating range, which is characterized by at least one of the following parameters: frequency, coding, activity time window. Each radar sensor is assigned an operating range according to at least one degree of freedom of movement of the vehicle, in which the radar sensor is installed.

Claims

1-10. (canceled)

11. A method for low-interference operation of a plurality of radar sensors, which are installed in different respective vehicles and each emit a transmission signal in an operating range, which is characterized by at least one of the following parameters: frequency, coding, activity time window, the method comprising: assigning each respective radar sensor of the radar sensors a respective operating range according to at least one degree of freedom of movement of the respective vehicle, in which the respective radar sensor is installed.

12. The method as recited in claim 11, wherein the operating ranges differ from each other in a position of a frequency band, in which the respective radar sensor transmits and receives.

13. The radar sensor as recited in claim 11, wherein the radar sensors transmit coded signals, and the operating ranges differ from each other with regard to code symbols used for coding.

14. The method as recited in claim 11, wherein the radar sensors are synchronized with each other by a universal time signal, and the respective operating ranges differ in a position of activity time windows, in which the radar sensor transmits and/or receives.

15. The method as recited in claim 11, wherein the position of each respective vehicle is measured in a global coordinate system, and at least one degree of freedom, which is determinative for the assigning of the operating ranges, is a spatial coordinate of the respective vehicle in the global coordinate system.

16. The method as recited in claim 15, wherein each respective radar sensor receives information about a road currently traveled on by the respective vehicle, from an independent onboard navigation system of the respective vehicle, each road is assigned a directional parameter for each direction of travel, and the operating ranges of each respective radar sensor are selected as a function of the directional parameter.

17. The method as recited in claim 15, wherein the degree of freedom, which is determinative for the assignment of the operating ranges, is an orientation of the respective vehicle with regard to a cardinal direction.

18. The method as recited in claim 16, wherein the operating ranges are assigned to the individual radar sensors as a function of an orientation of the respective radar sensor with regard to the respective vehicle.

19. The method as recited in claim 17, wherein each operating range is characterized by a continuously varying parameter, and the operating ranges are assigned to each radar sensor according to a function, which assigns a value of the parameter to an angle, which indicates an orientation of the respective radar sensor with respect to the cardinal direction.

20. The method as recited in claim 19, wherein the operating ranges are assigned in such a manner, that for each pair of radar sensors, which are installed in two different vehicles, and whose spatial orientations are opposed to each other, the respective operating ranges of the two radar sensors are different from each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows a sketch of a traffic situation for explaining the method of the present invention.

[0022] FIG. 2 shows a matrix for representing interference to be expected between radar sensors in the traffic situation shown in FIG. 1.

[0023] FIG. 3 shows an example of assigning frequency bands to the radar sensors shown in FIG. 1.

[0024] FIG. 4 shows a digital map of a navigation system, including assignment rules for the frequency bands of the radar sensors.

[0025] FIG. 5 shows frequency-time graphs for illustrating synchronization of activity time windows in the case of two radar sensors.

[0026] FIG. 6 shows a wind rose for explaining another specific embodiment of the method according to an example embodiment of the present invention.

[0027] FIG. 7 shows an example of orientation-dependent assignment of frequency bands for a radar sensor.

[0028] FIG. 8 shows a graph of frequency band overlap in the method according to FIGS. 6 and 7.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0029] A traffic situation, in which three vehicles 1, 2, 3 travel on a road 4 that has one traffic lane 5, 6 for each direction of travel, is shown in FIG. 1. Vehicles 1 and 2 travel in the same direction in traffic lane 5, and vehicle 3 comes towards them in lane 6.

[0030] At the front end, vehicle 1 has a radar sensor 11 pointed forwards in the direction of travel, and at the rear end, it has a radar sensor 12 pointed backwards in the direction of travel. Vehicles 2 and 3 also have the same set-up of radar sensors 21, 22 and 31, 32, respectively. The radar lobes of the radar sensors are each indicated by stylized waves.

[0031] Each of the three vehicles 1, 2, 3 has its own onboard navigation system, which communicates with GPS satellites 40. Information about the road 4 currently traveled on by the vehicle, as well as about the direction of travel of the reference vehicle, is present in the navigation system.

[0032] In the situation shown in FIG. 1, radar sensor 12 of vehicle 1 and radar sensor 21 of vehicle 2 face each other in such a manner, that radar sensor 12 directly receives the radar waves, which are transmitted by radar sensor 21, and vice versa. Therefore, if the two sensors were to operate in the same frequency band, malfunctions would occur in both sensors due to interference.

[0033] Such interference would have to be expected in the pair of radar sensors 21 and 31.

[0034] If vehicle 3 passes vehicle 2 at a somewhat later time, then radar sensors 22 and 32 also face each other, which means that interference may occur here, as well. In FIG. 1, radar sensors 11 and 22 of vehicles 1 and 2 are actually pointed away from each other, which means that no disturbances are to be expected. However, it may not be ruled out that vehicle 2 overtakes vehicle 1 later, and then, interference could also occur between radar sensors 11 and 22.

[0035] The radar lobes of radar sensors 11, 21, and 32 all point in the same direction, which means that in this case, there is at least no direct signal transmission by one sensor to the other. Interference could occur, at most, to a low degree due to reflections of the radar signals. The same is also true for the three radar sensors 12, 22 and 31.

[0036] In order for the risk of malfunctions due to interference to be reduced, radar sensors 11, 21 and 32 operate in one frequency band FA, and radar sensors 12, 22 and 31 operate in another frequency band FB. Frequency bands FA and FB are staggered so far, that there is no overlap. Since each radar sensor only reacts to received signals, whose frequency lies in its frequency band, disruptive interference is prevented.

[0037] In order to ensure that each radar sensor operates in the correct frequency band, lane 5 is assigned a directional parameter r=1, while lane 6 is assigned a directional parameter r=−1. The radar sensors 11, 21, and 31 pointed forwards in the direction of travel are now assigned an operating range A having frequency band FA, if the directional parameter r for the lane, in which the corresponding vehicle is located, has a value of 1; and assigned an operating range B having frequency band FB, if the directional parameter has a value of −1. In the case of the radar sensors 12, 22 and 32 pointing backwards in the direction of travel, the assignment of operating ranges A and B is exactly the opposite.

[0038] The pairings of radar sensors 11-32, which are “hostile” to each other in the sense that a high risk of interference is present, are shown in a matrix in FIG. 2. These pairings are shown in the matrix, using hatching. For each radar sensor, the corresponding operating range A or B is also indicated at the edge of the matrix. Due to the assignment of the operating ranges as a function of directional parameter r, it is apparent that for each pair of radar sensors, they have operating ranges A and B different from each other, when they are hostile to each other.

[0039] In FIG. 3, radar sensors 11-32 are situated on the horizontal axis, and the frequency f, at which these radar sensors operate, is plotted on the vertical axis. The radar sensors 11, 21, and 32, to which operating range A is assigned, operate in frequency band FA, and the three remaining radar sensors operate in frequency band FB. The frequency bands are staggered in such a manner, that they do not overlap each other, which means that practically no interference occurs.

[0040] The functions of the radar sensors of each of vehicles 1, 2, 3 are controlled by control units not shown, which receive data from the independent onboard navigation system of the respective vehicle. These data also include the directional parameter r, which is valid for the current road 4 and the current direction of travel of the vehicle itself and determines the assignment of operating ranges A and B.

[0041] FIG. 4 shows an example of a digital map 42 including a section of a road network in the region, which is currently being traveled through by one of the vehicles, such as vehicle 1. The radar sensors obtain, from the navigation system, the information that the reference vehicle is currently located on road 4. Directional parameters r for each direction of travel are also stored in the digital map. As usual, the position and the direction of travel of the reference vehicle are indicated by a cursor 44. In light of this information, the operating ranges may be assigned in each vehicle in the manner described above in connection with FIGS. 1 through 3.

[0042] The section of digital map 42 shown in FIG. 4 includes further roads 46 and 48. For these roads 46 and 48, as well, a directional parameter, which indicates which direction of travel has the value 1 and which has the value −1, is stored for each direction of travel. Specific rules may be established for the selection of the directional parameters, for example, r=1 for the northern or eastern direction of travel and r=−1 for the southern or western direction of travel. However, since the course of the roads may be curved, the directional parameter may change during the trip on the same road.

[0043] One particularly reliable method for determining the directional parameters is to unequivocally assign each road and each direction of travel a directional parameter in a convention, which is binding for all navigation systems.

[0044] The operating ranges of the radar sensors may differ not only with regard to the frequency band, but also, for example, with regard to the time windows, within which the transmitting and receiving part of the radar sensor is active. Normally, the radar sensors for motor vehicles, for example, FMCW radar sensors, transmit a periodic sequence of frequency-modulated signals, in which activity time windows, in which transmission and reception occur, and inoperative windows, in which neither transmission, nor reception occur, alternate with each other. During the activity time window, the received data are digitized and stored and transferred to a processor, which then takes over the further processing. However, the evaluation of the digital data generally takes up more time than the collection of the data during a measuring phase. For this reason, the activity time windows are separated by the inoperative windows, in which the evaluation of the data recorded in the previous measuring period is completed.

[0045] FIG. 5 shows an example of frequency modulation patterns MA and MB of two radar sensors. Each modulation pattern includes a periodic sequence of activity time windows 50, in which measuring is carried out, that is, radar signals are transmitted and received, and inoperative windows 52, in which the transmitting and receiving part is inactive and only an evaluation of the data takes place. In this case, modulation patterns MA and MB of the hostile radar sensors are synchronized in such a manner, that in each instance, activity time window 50 of the one radar sensor lies in inoperative window 52 of the other sensor. In this manner, interference between the signals of the two radar sensors is prevented. However, it is required that the local clock generators of the radar sensors, which determine the sequence of activity time windows and inoperative time windows, be synchronized with each other by a global time signal. The global time signal may be, for example, a signal, which is received by GPS satellites 40.

[0046] Therefore, in general, the operating ranges of the radar sensors may differ from each other not only with regard to the frequency bands used, but also with regard to the position of respective activity time windows 50. The number of available operating ranges may be increased, if the operating ranges are able to differ both with regard to the frequency bands and with regard to the activity time windows. It is equally possible for the radar sensors to transmit coded signals. In this case, the operating ranges may also differ with regard to the code symbols used.

[0047] A modified exemplary embodiment, in which a larger number of different operating ranges are worked with and the assignment of the operating ranges takes place as a function of the orientation of the respective sensor in a global coordinate system, for example, relative to a particular cardinal direction, shall be explained in light of FIGS. 6 through 8.

[0048] A wind rose, in which an arrow 52 indicates the orientation (that is, the chief transmitting and receiving direction) of a radar sensor relative to the southern direction s, is shown in FIG. 6. The angle between arrow 52 and southern direction S is designated by α and varies in the interval (−π, π] (upper limit π belongs to the interval, but lower limit −π does not). Angle α may vary quasi-continuously or in certain increments, such as 1°, 15°, etc.

[0049] The operating ranges may also be characterized by a continuous parameter, such as center f.sub.c of the frequency band, the start of an activity time window, and the like. The assignment of the operating ranges is then determined with the aid of a function, which characterizes the parameter, the operating range, as a function of angle α.

[0050] FIG. 7 illustrates an example, in which the operating ranges are frequency bands F(α) having a fixed width BW and a center frequency f.sub.c varying as a function of angle α. All of the frequency bands lie with an overall band 54 having width BW.sub.Band and center frequency f.sub.c,Band.

[0051] In the example shown, width BW of the individual frequency bands is one quarter of width BW.sub.Band of the overall band, and center frequencies f.sub.c are selected in such a manner, that the overall band is completely exhausted, when α is varied in the range of −π to +π, and that if two radar sensors are hostile to each other, that is, angles α of these two sensors differ by π (180°, the corresponding frequency bands do not overlap each other. The assignment of the frequency bands shown in FIG. 7 is based on the formula:

f.sub.c=f.sub.c,Band+(α/π)(BW.sub.Band−BW)/2.

[0052] If the difference between angles α of the two radar sensors becomes smaller, the corresponding frequency bands approach each other, and they start to overlap each other, if the angular difference becomes less than π/2 (90°). However, in this configuration, it is already highly improbable that radiation transmitted by one sensor is received directly by the other sensor.

[0053] The overlap between the frequency bands inevitably becomes larger, when width BW makes up a larger portion of overall width BW.sub.Band.

[0054] For an overall band having a width BW.sub.Band=5 GHz, the extent of the overlap of the frequency bands (in MHz) for different widths BW of the frequency bands (in MHz) and for different angular differences Δα between the orientations of the radar sensors, are represented graphically in FIG. 8.