Method for operating a plurality of radar sensors with low interference

Abstract

The invention relates to a method for operating a plurality of radar sensors (11, 12, 21, 22, 31, 32) with low interference, which are installed in different vehicles (1, 2, 3) and each emit a transmission signal in an operating range (FA, FB), which is characterized by at least one of the following parameters: frequency, coding, active time window, characterized in that for each radar sensor (11, 12, 21, 22, 31, 32) an operating range (A, B) is assigned in accordance with at least one degree of freedom of movement of the vehicle (1, 2, 3) in which the radar sensor is installed.

Description

Technical Field

[0001] The invention relates to 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 characterized by at least one of the following parameters: frequency, coding, active time window. Background Art

[0002] In motor vehicles, radar sensors are used as positioning devices to detect the traffic environment. Positioning data about the traffic environment forms the basis for various assistance functions, such as distance control, automatic emergency braking systems, automated parking, and the like. With the development of autonomous vehicles, assistance systems are increasingly being expanded to include driving systems that can autonomously control the vehicle without the involvement of a human driver.

[0003] As motor vehicles become increasingly automated, the number of motor vehicles equipped with radar sensors will increase as will the number of radar sensors installed in the same vehicle.

[0004] This increases the likelihood that a radar sensor will receive not only radar echoes caused by its own transmitted signals, but also radar signals from radar sensors of other vehicles, either directly or after reflection from objects. Interference between radar signals from different sources generates interference signals that prevent the correct interpretation of the received signals and can therefore lead to malfunctions or reduced performance of the radar sensor.

[0005] Generally speaking, radar sensors emit radar signals only within certain frequency bands, and disruptive interference to a noticeable extent can only be expected if two radar sensors operate in the same frequency band.

[0006] In most radar sensors, the transmit-receive components are not permanently active either, but only within certain time windows, separated by "transmit pauses" during which the received signals are evaluated. Interference can also be avoided if the active time windows of the transmit-receive components are coordinated so that one radar sensor transmits while another has a transmit pause.

[0007] Radar sensors that operate with coded transmission signals are also under development. This coding allows different transmission signals within the same frequency band to be separated from one another. Therefore, interference can, in principle, also be avoided by operating the radar sensor with differently coded signals.

[0008] The range of frequencies and / or active time windows and / or codes used by a single radar sensor is collectively referred to as the operating range. A common strategy for avoiding interference is to enable different radar sensors to operate in different operating ranges. However, the number of available operating ranges (frequencies, time windows, and codes) is far from sufficient to ensure that each radar sensor on each vehicle has its own operating range. Summary of the Invention

[0009] The object of the present invention is to specify a method which, even with a limited number of usable operating ranges, allows the frequency of interference between different radar sensors to be reduced.

[0010] According to the invention, this object is achieved in that a working range is assigned to each radar sensor according to at least one degree of freedom of movement of the vehicle on which the radar sensor is installed.

[0011] The degrees of freedom of movement of a vehicle represent the location and / or orientation of the vehicle in a global coordinate system. Since the allocation of operating ranges depends on these degrees of freedom of movement, it is possible, for example, to assign different operating ranges to the radar sensors of two vehicles located at approximately the same location to avoid interference. Conversely, if the vehicles are spatially far apart, the radar sensors can operate within the same operating range without risk of interference. Similarly, the operating ranges can also be assigned based on the orientation of the vehicles, for example by assigning different operating ranges to the radar sensors of two vehicles when they are pointing forward relative to their respective vehicles and their orientations are opposite. This makes it possible to prevent interference when each radar sensor directly receives signals transmitted by the other radar sensor. The same applies analogously to pairs of radar sensors that have different orientations relative to their respective vehicles.

[0012] Advantageous embodiments and developments of the invention are specified in the dependent claims.

[0013] The operating range of a given radar sensor can be characterized by the frequency band in which the signal is transmitted, or in the case of a coded signal, by the set of code symbols transmitted by the radar sensor. Likewise, the operating range can also be characterized by different combinations of frequency bands and coding.

[0014] Furthermore, the operating range can be characterized by a defined active time window within which the transmit / receive part of the radar sensor is active. However, in this case, the radar sensors of different vehicles must be synchronized to ensure that the active time windows remain consistently separated from one another. Any wirelessly receivable time signal can be used for synchronization, such as a signal from a Global Navigation Satellite System (GNSS), such as GPS, a time signal from a mobile radio network, or a radio clock signal. The time signal does not have to be continuously receivable; it is sufficient if the local time of the vehicle or radar sensor is synchronized with the time signal at regular intervals.

[0015] The operating range of a radar sensor can also be characterized by a combination of a specific selection of an active time window and a frequency band and / or a coding.

[0016] If each vehicle has a navigation system, the operating ranges can be allocated based on the degree of freedom of location. For example, two or more operating ranges can be defined for each road in the digital map used by the navigation system, so that the operating ranges for the two directions of travel on that road are different. This prevents the radar signals of two vehicles that meet on that road from interfering with each other.

[0017] Another possibility for avoiding interference when vehicles encounter each other is to assign the operating ranges according to the orientation of the vehicle or radar sensor relative to the north direction. More precisely, the assignment is such that radar sensors installed in two different vehicles and having opposite orientations (determined by the orientation of the radar sensors relative to the forward direction of the vehicles and the orientation of the vehicles relative to the north direction) have different operating ranges. In this case, the vehicles do not even need to have a navigation system; in principle, a sufficiently accurate compass function is sufficient.

[0018] Frequency bands selected according to the angle may also overlap, but preferably only at the edges. Since received radar signals typically undergo windowing in frequency space during signal analysis, a certain amount of suppression of the received signal occurs at the edges of the frequency bands, thereby also suppressing interference with signals from other radar sensors.

[0019] The allocation of the frequency bands to the different orientation directions of the sensor is preferably selected such that the overlap of the frequency bands decreases the closer the angular difference between the two orientation directions is to 180°.

[0020] Due to similar effects, the active time windows of different radar sensors can also overlap at least at the edges. Windowing, for example over multiple fast chirp ramps in the case of FMCW radar (in one dimension of a two-dimensional Fourier transform), leads to a significant suppression of interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Hereinafter, embodiments will be described in more detail with reference to the drawings.

[0022] The accompanying drawings show:

[0023] Figure 1 A simplified diagram of a traffic situation is shown for explaining the method according to the invention;

[0024] Figure 2 Shown for display in Figure 1 Matrix showing the expected interference between radar sensors in the traffic situation.

[0025] Figure 3 Shown for Figure 1 An example of allocated frequency bands for radar sensors is shown.

[0026] Figure 4 A digital map of a navigation system is shown, the digital map having a specification for the allocation of frequency bands for radar sensors;

[0027] Figure 5 shows a frequency / time diagram for explaining the synchronization of active time windows in the case of two radar sensors;

[0028] Figure 6 A wind rose diagram is shown for illustrating another specific embodiment of the method according to the invention;

[0029] Figure 7 An example is shown for allocating frequency bands to radar sensors based on orientation;

[0030] Figure 8 Shown in accordance with Figure 6 and Figure 7 Graph of the case where the bands overlap. DETAILED DESCRIPTION

[0031] exist Figure 1 : shows the following traffic situation: in this traffic situation, three vehicles 1, 2, 3 are traveling on a road 4, which has a lane 5, 6 for each direction of travel. Vehicles 1 and 2 are traveling in lane 5 in the same direction, while vehicle 3 is approaching them in lane 6.

[0032] Vehicle 1 has a radar sensor 11 at the front pointing forward in the direction of travel and a radar sensor 12 at the rear pointing backward in the direction of travel. Vehicles 2 and 3 also have the same arrangement of radar sensors 21, 22 and 31, 32. The radar beams of the radar sensors are each represented by stylized waves.

[0033] Each of the three vehicles 1, 2, 3 has an onboard navigation system that communicates with GPS satellites 40. The navigation system contains information about the road 4 on which the vehicle is currently traveling and about the direction of travel of the vehicle.

[0034] exist Figure 1 In the situation shown, radar sensor 12 of vehicle 1 and radar sensor 21 of vehicle 2 are positioned opposite each other so that radar sensor 12 directly receives the radar waves transmitted by radar sensor 21, and vice versa. If both sensors operate in the same frequency band, interference would thus occur due to interference between the two sensors.

[0035] Such interference should also be expected in the case of the pair of radar sensors 21 and 31 .

[0036] If vehicle 3 passes vehicle 2 at a slightly later time, radar sensors 22 and 32 are also positioned opposite each other, so that interference can also occur here. Figure 1 1 and 22 are directed away from each other, so that no interference can be expected; however, it cannot be excluded that vehicle 2 will later overtake vehicle 1 , which could then result in interference between radar sensors 11 and 22 .

[0037] The radar beams of radar sensors 11, 21, and 32 all point in the same direction, so there is at least no direct signal transmission from one sensor to another. Interference may occur to a minimal extent at best due to reflections of the radar signals. This also applies to the three radar sensors 12, 22, and 31.

[0038] To reduce the risk of interference due to interference, radar sensors 11, 21, and 32 operate in one frequency band FA, while radar sensors 12, 22, and 31 operate in another frequency band FB. Frequency bands FA and FB are offset far enough from each other that there is no overlap. Since each radar sensor reacts only to received signals with frequencies within its frequency band, disruptive interference is avoided.

[0039] To ensure that each radar sensor operates in the correct frequency band, lane 5 is assigned a direction parameter r = 1, while lane 6 is assigned a direction parameter r = -1. If the direction parameter r for the lane in which the vehicle is located has the value 1, radar sensors 11, 21, and 31 pointing forward in the direction of travel are assigned an operating range A with frequency band FA, while if the direction parameter r has the value -1, they are assigned an operating range B with frequency band FB. For radar sensors 12, 22, and 32 pointing backward in the direction of travel, the assignment of operating ranges A and B is reversed.

[0040] exist Figure 2 shows a matrix of pairs of radar sensors 11-32 that are "hostile" to one another in the sense of presenting a high risk of interference. These pairs are shown shaded in the matrix. Furthermore, the edges of the matrix indicate the associated operating range A or B for each radar sensor. As can be seen, since the operating ranges are assigned based on the directional parameter r, for each pair of radar sensors, the following applies: when the radar sensors are hostile to one another, they have different operating ranges A and B.

[0041] exist Figure 3 In the figure, radar sensors 11-32 are arranged on the horizontal axis, and the frequency f at which they operate is plotted on the vertical axis. Radar sensors 11, 21, and 32, which are assigned operating range A, operate in frequency band FA, while the other three radar sensors operate in frequency band FB. These frequency bands are offset so that they do not overlap, effectively preventing interference.

[0042] The functions of the radar sensors in each of vehicles 1, 2, and 3 are controlled by a control unit (not shown), which receives data from the onboard navigation system of the respective vehicle. This data also includes a direction parameter r for the current road 4 and the current direction of travel of the host vehicle, which determines the allocation of operating ranges A and B.

[0043] Figure 4 An example of a digital map 42 is shown, which has a section of the road network in the area in which one of the vehicles (for example, vehicle 1) is currently traveling. The radar sensor receives the following information from the navigation system: the vehicle is currently located on road 4. The digital map also stores a direction parameter r for each direction of travel. The position and direction of travel of the vehicle are indicated by a cursor 44, as is customary. Based on this information, it is possible to Figures 1 to 3 The operating range is allocated in each vehicle as described in the context of FIG.

[0044] Digital Map 42 Figure 4The section shown in FIG also includes additional roads 46 and 48. For these roads 46 and 48, a direction parameter is also stored for each driving direction, which indicates which driving direction has the value 1 and which driving direction has the value -1. Specific rules can be set for selecting the direction parameter, for example, r = 1 for a driving direction north or east, and r = -1 for a driving direction south or west. However, due to the potentially curved course of the road, it is possible that the direction parameter changes while driving on the same road.

[0045] A particularly reliable method for determining a direction parameter is to assign a unique and unambiguous direction parameter to each road and each direction of travel in a convention that is binding on all navigation systems.

[0046] The operating range of a radar sensor can vary not only in frequency bands but also, for example, in the time windows during which the transmit-receive portion of the radar sensor is active. Typically, radar sensors for motor vehicles (e.g., FMCW radar sensors) transmit a periodic sequence of frequency-modulated signals, alternating between active time windows (transmission and reception) and inactive windows (neither transmission nor reception occurs). During the active time windows, the received data is digitized, stored, and passed to a processor, which then takes over further evaluation. However, the evaluation of the digital data typically requires more time than the data collection during the measurement phase. For this reason, the active time windows are separated by inactive windows, during which the evaluation of the data recorded in the previous measurement cycle is terminated.

[0047] Figure 5 An example of frequency modulation patterns MA and MB for two radar sensors is shown. Each modulation pattern contains a periodic sequence of active time windows 50, during which measurements are taken—that is, radar signals are transmitted and received—and quiet windows 52, during which the transmission and reception components are inactive and only data is evaluated. The modulation patterns MA and MB of the hostile radar sensors are synchronized so that the active time window 50 of one radar sensor lies within the quiet window 52 of the other. This prevents interference between the signals of the two radar sensors. However, this presupposes that the local clock generators of the radar sensors are synchronized with each other via a global time signal, which determines the sequence of active and quiet time windows. The global time signal can, for example, be a signal received by a GPS satellite 40.

[0048] Thus, the operating ranges of the radar sensors can differ from one another not only in terms of the frequency bands used, but also in terms of the positions of the corresponding active time windows 50. If the operating ranges can differ from one another not only in terms of the frequency bands used, but also in terms of the corresponding active time windows, the number of usable operating ranges can be increased. It is also possible for the radar sensors to transmit coded signals. In this case, the operating ranges can also differ in terms of the code symbols used.

[0049] according to Figures 6 to 8 A modified exemplary embodiment will be described in which operation is performed with a larger number of different operating ranges and the operating ranges are assigned depending on the orientation of the respective sensor in the global coordinate system, for example relative to a specific compass direction.

[0050] exist Figure 6 , in which arrow 52 illustrates the orientation of the radar sensor relative to the south direction S (i.e., the main transmission and reception directions). The angle between arrow 52 and the south direction S is denoted by α and varies within the interval [−π, π] (the upper limit π belongs to this interval, while the lower limit −π does not). Angle α can vary quasi-continuously or in certain increments (e.g., 1°, 15°, etc.).

[0051] The operating range can also be characterized by a continuous parameter, for example by the center of the frequency band f C , the start of the active time window, and the like. The distribution of the working range is then determined according to a function which describes the parameters marking the working range as a function of the angle α.

[0052] Figure 7 An example is shown in which the operating range is of fixed width BW and has a center frequency f that varies as a function of the angle α. C All frequency bands are located in a frequency band with a width of BW Band and has a center frequency f C,Band The total belt is within 54.

[0053] In the example shown, the width BW of the individual frequency bands is the width BW of the total band Band One quarter of the center frequency f C , so that if α varies in the range from -π to +π, the total band is fully utilized and if two radar sensors are oriented towards each other, i.e. the angle α differs by π (180°) for the two sensors, the relevant frequency bands do not overlap. Figure 7 The frequency band allocation shown in is based on the following formula:

[0054] f c =f c，Band +(α / π)(BW Band -BW) / 2.

[0055] If the difference between the angles α for the two radar sensors becomes smaller, the relevant frequency bands move closer together, and if the angle difference becomes less than π / 2 (90°), they begin to overlap. However, in this configuration, it is already very unlikely that a beam transmitted by one sensor could be directly received by another sensor.

[0056] If the width BW accounts for the total width BW Band With a larger ratio, it is inevitable that the overlap between the frequency bands becomes larger.

[0057] exist Figure 8 For a value with width BW Band =5 GHz, the degree of overlap of the frequency bands (in MHz) is shown graphically for different widths BW of the frequency bands (in MHz) and for different angular deviations Δα between the orientations of the radar sensors.

Claims

1. A method for low-interference operation of a plurality of radar sensors (11, 12, 21, 22, 31, 32), which are installed in different vehicles (1, 2, 3) and each emit a transmission signal in an operating range (A, B), which is characterized by at least one of the following parameters: frequency, coding, active time window, characterized in that A working range (A, B) is assigned to each radar sensor (11, 12, 21, 22, 31, 32) according to at least one degree of freedom of movement of a vehicle (1, 2, 3) in which the sensor is installed, wherein the position of each vehicle (1, 2, 3) is measured in a global coordinate system, and at least one degree of freedom decisive for the allocation of the working range is the location coordinates of the vehicle in the global coordinate system and the orientation of the vehicle with respect to a compass direction (S), Each radar sensor obtains information about the road (4) on which the vehicle is currently traveling from the vehicle's onboard navigation system, assigns a direction parameter (r) to each road (4, 46, 48) for each driving direction, and selects the operating range for each radar sensor based on the direction parameter (r), thereby preventing radar signals of multiple radar sensors (11, 12, 21, 22, 31, 32) from interfering with each other. Therein, the direction parameters are stored in a digital map used by a navigation system of the vehicle.

2. The method according to claim 1, wherein The operating ranges (A, B) differ from one another with regard to the position of the frequency bands (FA, FB) in which the associated radar sensors transmit and receive.

3. The radar sensor according to claim 1 or 2, wherein: The radar sensor transmits an encoded signal, and the operating ranges differ from one another in terms of the code symbols used for encoding.

4. The method according to any one of the preceding claims, wherein The radar sensors are synchronized with one another via a common time signal, and the operating ranges differ with respect to the position of active time windows (50) in which the radar sensors transmit and / or receive.

5. The method according to any one of the preceding claims, wherein The operating range is assigned to the individual radar sensors as a function of their orientation relative to the respective vehicle.

6. A method according to any one of the preceding claims, wherein: Each working range (F(α)) is obtained by continuously changing the parameter (f C ) characterizes and assigns the operating range to each radar sensor according to the following function: the function assigns the parameter (f C ), the angle indicating the orientation of the radar sensor relative to the compass direction.

7. The method according to claim 5 or 6, wherein: The distribution of the operating ranges is achieved in that for each pair of radar sensors installed in two different vehicles and having mutually opposite spatial orientations, the operating ranges of the two radar sensors differ from one another.

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