CN115015851A - Method, radar system and software product for avoiding interference between radar sensors of a motor vehicle - Google Patents

Abstract

A method, a radar system and a software product for avoiding interference between radar sensors (14, 16) of a motor vehicle, the radar sensors are each connected to a node (24) of a wireless communication network (26), in the method, each node (24) transmits information about the state of the connected radar sensors (14, 16) into the network and receives information about the state of the other radar sensors from the network, characterized in that in each node (24) at least one digital map (28, 30) is created on the basis of the information received, said at least one digital map describing the expected intensity of said interference as a function of time (t) and of the frequency (f) used by the connected radar sensor, and for the radar sensor, determining a trajectory (32) in time/frequency space from the map.

Description

Method, radar system and software product for avoiding interference between radar sensors of a motor vehicle

Technical Field

The invention relates to a method for avoiding interference between radar sensors of a motor vehicle, which are each connected to a node of a wireless communication network, wherein each node transmits information about the state of the connected radar sensor into the network and receives information about the state of the other radar sensors from the network.

Background

In motor vehicles, radar sensors are used in conjunction with driver assistance systems to detect traffic situations, in particular to locate other traffic participants. In particular, FMCW radar sensors are used for this purpose, in which the frequency of the transmitted radar signal is modulated in a ramp-like manner. If other vehicles which are likewise equipped with radar sensors are located in the surroundings of the vehicle, this can lead to interfering interferences if the frequency bands used by the radar sensors overlap one another.

In order to reduce interference with one another, a method of the above-mentioned type is proposed in DE 102017216435 a1, which is based on radio communication between radar sensors. However, this method is essentially limited to radar sensors that can be operated in separate frequency regions and essentially discusses a method for negotiating an interference-optimized frequency allocation between the participating radar sensors. This negotiation begins after the presence of the coordination criteria.

Radarmamac in j.khousy, r.ramamatsuan, d.mcclose, r.smith and t.campbell: a solution is proposed to mitigate radar interference in autonomous vehicles (13 th annual IEEE international conference on sensing, communication and networking (SECON 2016, london, 2016, pages 1-9) in 2016), which sets a central governing body for mediating between radar sensors of the same kind.

RADCHAT: spectrum sharing for automotive radar interference mitigation (IEEE exchange for intelligent transportation systems, 1 month 2019), communication with radar is integrated in the same frequency band.

A method for so-called spectrum sensing (also called pre-measurement analysis, ABM) is also known from practice, by means of which information is collected about interference situations outside the frequency range used for transmission.

In the radio communication standards IEEE 802.11P,2010 and 3GPP TS 22.186, V16, TECHNICAL SPECIFICATION GROUP SERVICES AND SYSTEM ASPECTS, ENHANCEMENT OF 3GPP SUPPORT FOR V2X sensors, 2019, the following radio standards are specified: the radio standard may be used exemplarily for transmitting data necessary for interference reduction.

Disclosure of Invention

The object of the present invention is to provide a method which allows an efficient suppression of interference even when the involved radar sensors differ substantially from one another with regard to their design and their properties.

According to the invention, this object is achieved by: in each node, at least one digital map is created based on the received information, said at least one digital map describing the expected strength of the interference as a function of time and frequency used by the connected radar sensor, and for which the trajectory in time/frequency space is determined from the map.

In this method, the information avoidance strategy is neither coordinated between the participating radar sensors nor predefined by a central authority. Instead, each radar sensor also provides the relevant information available at the location of the radar sensor via a communication interface (so-called node) to the remaining radar sensors in the other vehicles. Thus, in each node and thus also in each radar sensor connected to the node, the totality of all information of all radar sensors present in the environment is available and constitutes the basis for predicting the expected interference in the form of a function in a two-dimensional time/frequency space, the function being a measure of the strength of the interference. This function of the variables time and frequency is represented by a digital map in which each time/frequency cell is provided with a calculated function value. The map extends in the time dimension from now over a certain period of time into the future. In the control device of each radar sensor, it is known at which frequency (center frequency of the frequency band) the sensor is currently operating, so that the current position of the radar sensor can be located in time/frequency space. If, starting from this position, the movement is carried out on a map in the direction of the time axis, it is possible to predict whether the interference situation will improve or deteriorate in the future. Likewise, it can be seen how the interference situation will develop for other frequencies deviating from the current own frequency, so that in case of an imminent deterioration, an alternative strategy can be developed, the core of which lies in the alternative of a frequency at which the expected degree of interference is smaller. The point which describes the center frequency of the radar system itself at a given point in time is then not moved linearly in the time direction, but also in the direction of the frequency axis and thus describes a trajectory in the time/frequency space which is optimized with regard to the degree of interference.

This method achieves effective suppression of interference even when the operating parameters of the participating radar sensors vary over a wide area. Therefore, this method does not presuppose the same modulation scheme, transmission time, measurement cycle time, high frequency bandwidth, and the like.

No special coordination between the participating radar sensors is necessary either, but each radar sensor finds its own path to some extent on the basis of a digital map. Standardization is necessary only insofar as a data format which is understandable for all participant nodes has to be agreed upon for communication between the different nodes.

Advantageous embodiments and configurations of the invention are explained below.

The communication networks used for the method proposed here can have very different configurations. For example, it can relate to a communication device for Vehicle-to-Vehicle communication (V2V) or also to a communication device for communication between Vehicle and Infrastructure (V2X). In the first case, the limitation of the number of nodes communicating with each other has been caused by the limited effective distance of the communication means. In the case of V2X, this restriction may be ensured by the infrastructure. For example, communication may be through the internet, where vehicles communicate with web sites to which they report their current location, orientation, speed, etc., and when status messages arrive from one node, the web site determines from these data for which other nodes the information is of significant relevance.

In one embodiment, each radar sensor is connected via a suitable interface (CAN, Flexray, ethernet, etc.) to a node of the communication network which is responsible for only this one radar sensor. However, if multiple radar sensors are located on a vehicle's balustrade, multiple or all of the vehicle's radar sensors may also use a common node. This has the following advantages: data relating to the vehicle as a whole (e.g. position, speed, acceleration, side-slip velocity, etc.) need only be transmitted once.

The status information relating in particular to individual radar sensors may comprise, for example, one or more of the following data objects:

-a center frequency of the transmitted radar signal,

-the width of the occupied frequency band,

-a transmission power of the radio frequency signal,

-the orientation of the radar sensor relative to the heading direction of the vehicle,

a code (identification code) of a typical transmission antenna pattern (e.g. according to a typical opening angle in azimuth of + -75 deg. +, -60 deg. +, -45 deg. +, -30 deg. +, -10 deg.),

a code (identification code) of a typical polarization characteristic (e.g. horizontal, vertical, +45 °, -45 °, left circular, right circular),

-a code (identification code) for more accurately identifying the steepness of the signed ramp and the modulation scheme,

-a measurement period duration, a transmission duration and a scheduled start time of the measurement period relative to the world time clock signal,

notification of an intentional frequency or scheduled time (Timing) change with a new frequency, a measurement cycle start time and, if necessary, a new modulation characteristic,

information about actively used interference avoidance mechanisms, such as direction-dependent frequency selection.

These data can also be transmitted in part as a key for the corresponding property list, for example an ID for a known operating state of a known sensor.

In a particularly advantageous embodiment, the transmitted information also includes:

intensity of interference measured or estimated in the bandwidth occupied by the sensor, and/or

The intensity of the interference measured or estimated outside the bandwidth occupied by the sensor (result of spectral sensing).

The inclusion of these data makes it possible for the participating nodes to also be exposed to information about expected interferences which are not caused by the participating radar sensors themselves, but by other sources, for example by radar sensors of the vehicle which are not involved in the method described here.

An important factor for strategies to avoid interference is then to plan frequency changes, that is to say to plan the change in the central frequency of the signal transmitted by the own sensor on the basis of a digital map of time/frequency space. The time point and frequency of the planned frequency change then determine the trajectory of the own sensor in the time/frequency space.

One additional strategy for avoiding interference takes full advantage of the following: the radar sensor does not transmit continuously, but intermittently. Since the evaluation of the number of data measured in the measuring cycle cannot be carried out in real time, the measuring cycle (in which the radar signal is transmitted and measured) is periodically interrupted by a gap (in which no transmission takes place, but only the evaluation of the data takes place). Since these gaps are usually of greater duration than a single measuring cycle, the real-time clocks of the measuring cycles of two potentially interfering radar sensors can be matched such that the measuring cycles of one radar sensor are each located in a gap between the measuring cycles of the other radar sensors, so that no interference occurs even when the same frequency band is used. The necessary offset for this of the start times of the individual measuring cycles corresponds to the offset of the trajectory along the time axis.

Additionally, the interference can also be further minimized by: other operating parameters of the radar sensor are changed, for example, the slope of the ramp during frequency modulation (influence of the measurable interference power density), the polarization and/or directional properties of the transmitting and receiving antennas, and parameters of the signal processing.

The invention also relates to a corresponding radar system and a corresponding software product.

Drawings

The embodiments are explained in more detail below with reference to the drawings.

The figures show:

FIG. 1 shows a schematic diagram for illustrating the method according to the invention;

figure 2 shows a frequency/time diagram of a signal transmitted by an FFCW radar;

fig. 3 shows a flow chart of the main steps of the method to be implemented for each participating radar sensor; and

fig. 4 shows a block diagram of an exemplary radar sensor, which is configured to carry out the method according to the invention.

Detailed Description

Fig. 1 shows a traffic situation in which three vehicles 10 travel on a road 12 having one lane for each direction of travel. In the example shown, each vehicle has a radar sensor 14 oriented forward in the direction of travel at the front and a radar sensor 16 oriented rearward in the direction of travel at the rear. The radar lobes of the radar sensor are each indicated by a stylized wave.

Each of the three vehicles has an on-board navigation system (not shown) and a communication device 18 for vehicle-to-vehicle communication (V2V). The radar sensors 14, 16 and the communication unit 18 of each vehicle are part of a radar system 20, which is shown separately as a block diagram for one of the vehicles in fig. 1. Furthermore, a processor unit 22 belongs to the radar system 20, which processor unit is connected on the one hand to the radar sensors 14, 16 and on the other hand to the communication device 18 and controls the data exchange between the radar sensor of the own vehicle and the radar sensors of other vehicles which are located in the receiving area of the communication device 18. Thus, the processor unit 22 and the communication device 18 together form a node 24 in a communication network 26 through which data may be transferred from vehicle to vehicle.

If two or more of the radar sensors 14, 16 of the vehicle 10 use the same frequency band, interference may occur which may interfere with the analytical processing of the received signals and may skew the measurement results. Such interference can be generated not only by: the signals transmitted by the radar sensors are received directly by the radar sensors of the other vehicles and can be generated to a lesser extent by: the radar sensors receive signals which are transmitted by the other radar sensors and are then reflected on the object.

The communication network 26 is used to adapt the operating parameters of the radar sensors to one another in such a way that interference is suppressed as much as possible. To this end, each node 24 transmits a set of status messages in a standardized data format, which enable each of the other nodes 24 to calculate in advance, taking into account its own instantaneous status, the expected interference strength in that or those immediately following measurement periods.

The transmitted information includes, on the one hand, position data, in particular the position and orientation, of the host vehicle 10, as well as information about the orientation of the transmission and reception lobes of the radar sensors of the vehicle, information about the frequency band used, the measurement period clock signal, the modulation mode, the polarization, etc. From these data, the processor unit 22 of each radar system is able to calculate for the radar sensor 14 of the own radar system 20 the degree of expected interference caused by each of the radar sensors of the other vehicles, and to note the result in a digital map 28 which maps out the expected interference power or any other suitable measure for the intensity of the interference as a function of the time t and frequency f (center frequency) of the own radar sensor. The results obtained for the different radar sensors of the other vehicles are additively superimposed in the digital map 28, so that the map ultimately identifies the temporal development of the complete intervention activity in the immediate future. A corresponding digital map 30 is also created for the radar sensor 16 of the own vehicle.

A simplified example of a digital map 28 in which the intensity of the interference is a binary function of time t and frequency f is shown in fig. 1. All the following pixels in the digital map are shown hatched: for the pixel, the expected interference intensity is above a determined threshold; whereas in the white areas of the map the interference is below the allowed threshold. A point P on the lower edge of the map marks the center frequency of the frequency band currently used by the radar sensor 14. This point P constitutes the starting point of the trajectory 32, which depicts how the frequency f of the radar sensor 14 should change over time. The trajectory extends parallel to the time axis as long as the frequency does not change. Each change to another frequency is indicated by an abrupt transition of the trajectory in the direction of the frequency axis. In the processor unit 22, the course of the trajectory 32 is calculated by means of a suitable algorithm in such a way that it avoids the following zones (shadows) on the map: in these zones, interference above a threshold may be considered.

It will be appreciated that the function that plots the intensity of the interference as a function of time and frequency may also be a multi-valued or quasi-continuous function in practice. In this case, the algorithm for determining the trajectory 32 searches the following path in time/frequency space: the expected interference is minimal on said path.

Fig. 2 illustrates a simple frequency modulation pattern of the FMCW radar sensor. Modulated transmission frequency f of a radar sensor _m Shown as a function of time t. This function is in the form of a sequence of frequency ramps 34 having the same slope and the same frequency offset and having a center frequency f. However, the sequence of frequency ramps is not transmitted without interruption, but rather is transmitted only for the duration of the temporally limited measurement period 36. Each measurement period 36 is followed by a rest period 38 in which no signal is sent. Because the processor responsible for the evaluation of the received radar signals has only a limited computing capacity, a quiescent period 38 is required in order to process and evaluate the signals received in the preceding measuring periods 36. This intermittent operation of the radar sensor is the reason why the hatched surfaces in the digital map 28 in fig. 1 have a rectangular shape, which are separated from one another in the time direction by gaps. The width of each of these rectangles in direction f corresponds to the width of the frequency band of the radar sensor (of one of the other vehicles) transmitting at the center frequency, and the height of the rectangle corresponds to the duration of the measurement period 36 for this radar sensor. The length and repetition rate of the measurement period may vary from sensor to sensor. For this reason, the hatched rectangles in fig. 1 form vertical columns

In the vertical columns, the rectangles each have the same height and the same distance, wherein the height and distance, however, differ from column to column.

Furthermore, it is also considered in the map 28 that the vehicle 10 moves in a predictable manner and it is therefore foreseeable from when the own radar sensor receives a signal from one of the other vehicles and when it will leave the area of influence of this vehicle again. Thus, some of the columns in the map 28 are interrupted at some point in time, while other columns are newly added.

In addition, the digital map 28 also takes into account its own clock signal of the measuring period. If the measurement period 36 of the own radar sensor is in the rest period 38 of the other radar sensors using the same frequency band, no interference occurs and the sensor does not contribute to the digital map 28.

One possibility of avoiding the impending interference is therefore to shift the clock signal of the measuring cycle without changing the frequency band in such a way that the measuring cycle itself falls into the rest cycles of the other sensors. Such a shift of the clock signal inevitably results in that the measurement result from the next measurement cycle becomes available with a certain delay. Such a shift of the clock signal is therefore only possible within the following ranges: within said range, delayed arrival of the measurement results can be tolerated.

In fig. 3, the main steps of the method for interference avoidance, which is to be implemented in each of the nodes 24, are shown as a block diagram.

In step S1, all important relevant data is received from the other nodes 24 via the communication network 26.

In step S2, the received data is filtered according to the importance correlation. In particular, the following data relating to the radar sensor are hidden here: no interference is expected from the data due to the position of the vehicle involved and the orientation of the radar sensor.

The effective range over which V2V communicates is typically hundreds of meters. However, currently important relevant sensors are, for example, only those sensors which are located in the vicinity of the sensor itself (approximately <10-50m) in the next measuring cycle. Here, the evaluation of the vicinity may be defined, for example, in terms of a geometrical surface, for example a rectangle, which contains the sensor. The number of nodes of significant relevance may also be limited taking into account the expected interference power. In this case, only the N potential interferers with the highest expected interference power are considered.

For example, the primary filtering of important relevant vehicles may be performed according to the following context table: in the environment table, all vehicles located in the receiving area are listed. The environment table is generated and transmitted by the communication device 18.

In step S3, the interference power density expected in the next measurement cycle is extrapolated or estimated from the transmitted data. The expected interference power density is estimated from the distance, the pattern of the antenna diagram and the transmitted transmission power as a measure for the interference expected in the baseband on the basis of the information transmitted by the other sensors about the modulation characteristics, in particular the slope steepness and the slope repetition rate. The estimation can also be improved by the information from the last radar measurement, by also simultaneously taking into account the reflection of the interference of a sensor with a similar orientation to itself on the target measured by the radar itself.

In step S4, the interference power density thus determined is superimposed, i.e. added, incoherently in the map 28 with the estimated interference power densities of the other sensors. For example, the pixel size of the stored digital map 28 is 50 μ s 10 MHz.

In step S5, radar measurements over a measurement cycle are performed with the current sensor parameters. If necessary, a spectrum sensing (ABM) is connected downstream, in which the sensor also receives outside the frequency band occupied by it, but does not itself transmit.

In step S6, the results of the interference (interference power) measurement in the bandwidth actively occupied by the sensor and, if appropriate, the results of the passively received interference are superimposed incoherently on the map 28, i.e. the power densities are added to those already recorded. The time/frequency map of interference (map 28) then represents an estimate of the interference scale from the information available in the complete radar band (e.g., 76-81 GHz). The interference power density shown should be close to the interference power expected in the baseband.

In order to optimally use the results of the interferometric measurements and spectral sensing, the filtering criteria for these particular data types may be relaxed in step S2. For example, if strong interference radiation from an oncoming vehicle is measured in a preceding vehicle, but the spacing between the own vehicle and the preceding vehicle is so large that the vehicle may be ignored under normal circumstances in step S2, it is expedient to still take into account the results of the interferometric and spectral sensing reported by the vehicle, since these may be very relevant for the own vehicle.

In step S7, the sensor parameters for the next measurement cycle 36 are planned. Sensor parameters have a significant impact on sensor performance. Thus, a plurality of internal sensor parameters (for example the measurement duration, the number of frequency ramps and their inclination) are already defined by the respective sensor function and can be changed only to a small extent if necessary. The parameter center frequency f and the starting point in time of the measuring cycle depend at least on the required sensor function. Therefore, the matching of these parameters constitutes the most important alternative strategy. The map 28 is scanned in terms of the location of minimum interference with a 2D window function, which corresponds to the window function of radar signal processing from the sensors. The step width in time and frequency of such a search results from the spreading of the window function in the time and frequency directions. For the algorithm for determining the trajectory in time/frequency space, different variants are conceivable, of which two variants are presented here as examples.

Variation 1: if a minimum of a single value of the expected interference is identified, the next transmission is planned for these parameters. Here, the change in frequency is limited by the adjustment of the available radar frequency or by the capabilities of the sensor. The selection of a new scheduled time (start time point of transmission) has to take into account the maximum allowed latency of the downstream radar signal processing for the new measurement.

If there are several locations with the same low interference in the time/frequency map of the interference, the selection can be made randomly or a minimum value can be selected at which the scheduled time of the own transmission can be made as constant as possible.

Variation 2: alternatively, it is also possible to select substantially randomly from a list of places in the time-frequency map that are below a threshold value, which is adaptively calculated from the median of the interference power scanned in a 2D window function. Thereby reducing the probability that two sensors may suddenly transition into the same void.

The replacement of the central frequency and/or the replacement of the planning time also significantly takes up the latency of the duration of the at least one communication clock signal, so that information about the replacement is also known in all other nodes. For this purpose, the waiting times can also be selected randomly in order to avoid interference-modulated oscillations distributed over the different sensors.

Likewise, to avoid the following unfavorable conditions: in the unfavorable situation, in which the sensors of different vehicles cyclically operate over and over the same time/frequency location and there interfere strongly, the number of radio resource changes (changes in frequency or planned time) per unit time should be limited. The respective sensor selects the limits according to the overall interference observed in the frequency band and, if necessary, according to the specification of a standardization that is of decisive importance to the manufacturer. Alternatively, a hysteresis mechanism may be used: that is, the radio resource is only changed when the interference expected on the other radio resource is x or more dB lower. Here, x may be located in a region of 3 to 10 dB.

Finally, in step S8, the data of the own sensor is transmitted to another vehicle. The transmitted data has the same data format as the data received in step S1.

Following step S8, a jump back to step S1 is carried out and a new program run is started after the expiration of the determined waiting time, so that the data are respectively transmitted at the determined repetition rate in step S8.

The repetition rate may be influenced on the one hand by the load on the channel but also by the rate of change of the message content. For example, if changes are placed on the radar antenna pattern that result in changes in the interference power density, these changes must be quickly transmitted to other nodes. The interference power density which is repeated in contrast to this can be marked as such and must be transmitted less frequently.

In the embodiment shown here, steps S1-S4 and S6-S8 are implemented on the processor unit 22. In other embodiments, steps S7 and S8 and, if appropriate, S3, S4 and S6 may be implemented on the processor of the respective radar sensor, so that the processor unit 22 undertakes only data reception and filtering. In yet other embodiments, all steps may be performed discretely on the radar sensor.

The basic capability of a radar sensor for interference reduction is shown in fig. 4 in terms of a block diagram. The bold-faced boxes represent modules that are added to a conventional radar sensor in order to enable implementation of the methods described herein.

As in conventional FMCW radar sensors, the high-frequency signal to be transmitted is generated in a modulator 40 and transmitted via amplifiers 42, 44 to an antenna array 46 and transmitted. The radar echo received by the antenna array 46 is transmitted via an amplifier 48 to a mixer 50 and mixed there with the output signal of the amplifier 42 down into a baseband signal 52. The baseband signal is then handed over to the detection module 56 via the analog/digital converter 54, and the interference signal is detected in said detection module 56. The detection results are transmitted to the processor unit 22, which processor unit 22 furthermore also receives information of the remaining nodes 24 from the communication device 18 and determines an alternative strategy for avoiding future interference based on this information. In parallel, the nodes 24 in the other vehicles are informed by means of the communication device 18 via an alternative strategy planned in the processor unit 22.

Alternative strategies include, among others, the following signals: which causes modulator 40 to change the frequency band and/or time signal of the measurement period. As indicated by the dashed arrows, the transmit power (amplifier 44) and directional characteristics of the antenna array 46 may additionally also be modified.

In addition, the detection results of the detection module 56 are also forwarded to a correction module 58, which compensates the interference effect on the basis of the existing information about the interference source. The time signal corrected in this way is then windowed and subjected to a Fast Fourier Transform (FFT) in the FFT module 60. The spectrum thus obtained is evaluated in an evaluation module 62 in order to calculate the distance, the relative speed and the localization angle of the located object. Finally, in the tracking module 64, the positioning data thus obtained are compared with the positioning data from the preceding measurement cycle and finally output to the following system in the form of an object hypothesis 66.

Claims (9)

1. A method for avoiding interference between radar sensors (14, 16) of a motor vehicle, the radar sensors are each connected to a node (24) of a wireless communication network (26), in the method, each node (24) transmits information about the status of the connected radar sensors (14, 16) into the network and receives information about the status of the other radar sensors from the network, characterized in that at least one digital map (28, 30) is created in each node (24) on the basis of the received information, said at least one digital map describing the expected intensity of said interference as a function of said time (t) and of the frequency (f) used by the connected radar sensor, and, for the radar sensor, determining a trajectory (32) in time/frequency space from the map.

2. Method according to claim 1, in which method the communication network (26) is a vehicle-to-vehicle network (V2V).

3. The method according to claim 1, in which method the communication network is a vehicle and infrastructure network (V2X).

4. The method according to any of the preceding claims, having the step of filtering (S2) data received by different nodes (24) according to importance relevance.

5. Method according to any of the preceding claims, in which method the interference measured in the own node is fused with information received over the communication network (26) on the digital map (28).

6. Method according to claim 5, in which method, in at least one of the radar sensors (14, 16), signals at the following frequencies are received: the frequency lies outside the frequency band used by the radar sensor for transmission, and in the method information about the signal received at the frequency is transmitted to other nodes over the communication network (26).

7. Method according to any of the preceding claims, in which method a plurality of radar sensors (14, 16) of a vehicle (10) are connected to a common node (24), and at least one method step to be implemented in the node is implemented in a central processor unit (22) of the node outside the radar sensors (14, 16).

8. A radar system (20) for a motor vehicle (10), characterized in that the radar system (20) is configured for participating in a method according to any one of claims 1 to 7.

9. A software product with program code which, when run on a control computing device of a radar system of a motor vehicle, makes the radar system as claimed in claim 8.

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