Abstract:
In a method for operating a radar system and a radar system for performing the method, in particular a microwave radar system for applications in or on motor vehicles, in which at least one target object and at least one possible concealing object are detected using radar technology, it is provided in particular that a detection is made of whether a concealment situation of the at least one target object by the at least one concealing object exists, and in the case of a detected concealment situation a loss of the target object is not automatically assumed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for operating a radar system, in particular a microwave radar system, for applications in or on motor vehicles, as well as a radar system for performing the method. 
     BACKGROUND INFORMATION 
     Radar systems using electromagnetic waves, in particular using microwaves having frequencies over 100 MHz, are widely known and are used for detecting objects and for determining velocities, distances, and directions of these objects. 
     The use of such radar systems in a motor vehicle for detecting the positions of preceding vehicles and possibly for lane assignment of these preceding vehicles is known. 
     A directional antenna provided in the particular radar system and having a radar sensor measures, in a manner essentially known, reflexes from waves incident on an object to be sensed (target object). The directional antenna may detect the object only if the direct path between the radar sensor and the target object is not concealed by another object or a plurality of other objects. 
     A target object may be concealed by another object in vehicle traffic, for example, in a sharp right curve of the highway, where the host vehicle moves in the left-hand lane behind a target vehicle at a relatively great time interval or approaches the latter, specifically in the case where another vehicle, for example, a truck, is moving in the right-hand lane and at least partially blocks the direct view between the radar sensor and the target vehicle, which therefore cannot be detected. 
     In the known radar systems, a radar sensor is now situated approximately in the vehicle center, preferably in the center of the vehicle&#39;s bumper, and the driver thus sits to the left of the sensor. This may cause the driver to be still able to see the target vehicle, although it is already concealed by the other vehicle for the radar sensor. In such a scenario, the target object is often lost, which is puzzling to the driver because of the target vehicle still being detected by the driver. 
     A concealment situation as just described occurs, for example, in traffic jams involving a plurality of vehicles and it often happens that potentially relevant target vehicles are briefly concealed by other vehicles even before they become relevant. 
     It is therefore desirable to improve the above-described radar system in such a way that measurement results that are puzzling or contradictory to the driver are avoided. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the idea of improving the tracking of a target object with the aid of a radar system of the present invention by recognizing whether a concealment situation with respect to the target object exists and, in the event of a recognized concealment situation, not automatically assuming a loss of the target object. 
     Such a concealment situation is preferably handled by checking the plausibility of the existence of such a concealing object, a plausibility value (i.e., “plausibility of the object”) being increased or incremented if the radar system detects or, after the occurrence of a concealment, redetects, preferably in one measurement cycle, a tracked object, referred to hereinafter as “target object,” the plausibility value being decreased or decremented if the radar system, preferably in one measurement cycle, detects no radar reflexes of the object. If the current plausibility value is less than a lower empirically predefinable threshold value, it is assumed that the target object has totally disappeared, since no reflexes have been detected for a longer time period. Only in this case is the target object deleted from the detection and thus no longer tracked. Using this procedure, the target object is thus not automatically deleted if it has not been detected within one measurement cycle. 
     According to the present invention, the plausibility of a target object is decreased more slowly since, in the event of a possible concealment situation, the target object cannot be detected, although it is actually still there. 
     It may furthermore be provided that the increments for the above-mentioned increase or decrease of the plausibility values of a target object be made a function of the sensitivity or measurement resolution of the particular radar sensor used, which substantially increases the reliability of the radar system. 
     Due to the present invention, a target object is assumed as existing for a longer time, and in most cases is detected again by the radar sensor after a short time interval. In the meantime, the target object is communicated to the driver as still existing and thus does not result in the intermediate result described above, which is puzzling to the driver. The above-described unjustified target object losses are thus avoidable and a result that is better understandable to the driver is obtained. 
     The above-mentioned recognition of a concealment situation occurs according to the present invention preferably by evaluating the relative position of the detected objects with respect to each other and by marking objects that are possibly concealed by other objects. The resulting information is preferably further processed in the above-named or an alternative plausibility algorithm to slow down or totally suppress the decrease in the plausibility value for the target object in the event of a recognized concealment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows the geometric relationships when calculating a concealment situation according to a preferred specific embodiment of the present invention. 
         FIG. 2  shows a preferred specific embodiment of the method according to the present invention using a flow chart. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically shows the preferred procedure according to the present invention in the case of a purely geometric calculation of a concealment situation of a target object  100 . The assumed position of a radar sensor is labeled with the reference numeral  105 . Furthermore, an object  110 , situated in the measuring field of radar sensor  105  and concealing target object  100 , is assumed. 
     It is assumed that concealing object  110  has a rectangular object footprint having width 2*B and length L. The purpose of the concealment detection is to determine angles φ 1  through φ 4  of all four corners of object  110  and to determine the minimum and maximum of these angles (in the figure only angle φ 1  is shown for the sake of clarity). Objects further removed, which are situated between these two angles, in the present case the two angles φ 1  and φ 3 , are affected by this concealment. 
     Relative angle α of object  110  may be estimated by different methods, for example via eigenradius R, also shown in  FIG. 1 . 
     Variables dx 0  and dy 0  are the coordinates of concealing object  110 , as provided by known algorithms for determining the position of objects (so-called “tracking algorithms”). 
     The computations to be derived from  FIG. 1  are based on the two above-mentioned variables R and α. Eigenradius R may be computed according to  FIG. 1  from the host vehicle&#39;s velocity v_ego and its yaw rate psidt_ego, according to the relationship R=v_ego/psidt_ego. Relative angle α of object  110  results, according to  FIG. 1 , from the relationship α=arcsin(dx 0 /R). 
     Using coordinate transformation, the following relationships are obtained for angles φ 1  through φ 4 :
 
 dx 1 =dx 0+cos(α)*0−sin(α)*(− B )
 
 dy 1 =dy 0+sin(α)*0+cos(α)*(− B )
 
φ1=arctan( dy 1 /dx 1)
 
 dx 2 =dx 0+cos(α)*0−sin(α)*(+ B )
 
 dy 2 =dy 0+sin(α)*0+cos(α)*(+ B )
 
φ2=arctan( dy 2 /dx 2)
 
 dx 3 =dx 0+cos(α)* L −sin(α)*(+ B )
 
 dy 3 =dy 0+sin(α)* L +cos(α)*(+ B )
 
φ3=arctan( dy 3 /dx 3)
 
 dx 4 =dx 0+cos(α)* L −sin(α)*(− B )
 
 dy 4 =dy 0+sin(α)* L +cos(α)*(− B )
 
φ4=arctan( dy 4 /dx 4)
 
     As mentioned previously, finally the concealment angle “φ_concealment  115 ” results, according to the relationship φ_concealment=[min(φ 1  . . . φ 4 ); max(φ 1  . . . φ 4 )]. All objects having an angle situated in the area of φ_concealment are possibly affected by the concealment. 
       FIG. 2  describes a preferred procedure according to the present invention when operating a radar system referenced herein in the event of an assumed concealment situation. 
     The procedure shown there, which may be implemented, for example, as a control code of a radar control unit or in the form of a special circuit, for example, in a motor vehicle, is composed of two subroutines  200  and  205  running, in the present example, independently of and/or parallel to each other. However, it is understood that, basically, first subroutine  200  may also be implemented as part of second subroutine  205 , for example, between steps  225  and  230  of the latter. 
     First subroutine  200  carries out, preferably as a loop as described in  FIG. 1 , an evaluation  210  of the relative position of the objects (i, j, k, . . . ) actually located in the measuring field of the radar system. In the following step  215 , those objects j, which are possibly concealed by other objects k, are marked as “possibly concealed” based on the result of this evaluation  210 , and objects k thus marked are buffered  220 . This buffered concealment-relevant information is used in subroutine  205  here running independently and/or parallel as described below. 
     Second subroutine  205  includes preferably executed process steps for performing the above-named plausibility check procedure. Process steps  225  through  255  shown within dashed line  205  represent the steps of an nth measurement cycle of the basic radar system and are iterated with the aid of the loop shown until step  260  is executed, which ends the entire subroutine  205 . 
     It should be pointed out that the use of the plausibility check procedure described below is only preferred, and the general inventive idea of the present invention is basically also applicable in other methods such as, for example, in computing the probability of existence of an object P exist . 
     In the nth measurement cycle shown here, in a first step  225 , a certain target object is measured, i.e., tracked with the aid of a radar sensor of the radar system having a directional antenna. It is understood that the depicted measurement cycle may also be used in parallel for a plurality of target objects to thus track a plurality of target objects simultaneously. 
     In a following processing step  230 , a check is performed as to whether the target object has been detected. If this is the case, the current plausibility value P for the target object is incremented in step  235  by an empirically predefinable value k and a jump is performed back to beginning  225  of subroutine  205  to perform the (n+1)th measurement cycle on the present target object. Step  235  is, however, executed only if the condition P&lt;P max =const. is met. 
     If the target object could not be detected by the radar sensor according to step  230 , a check is first performed in step  240  of whether the target object is saved as “possibly concealed”  220 . If this is the case, plausibility P is decremented in step  245 , i.e., reduced by a value k/m, the value of m being empirically selected in such a way that this decrementation of P is performed more slowly, i.e., in any case the condition m&gt;1 applies. 
     In the case where the target object is recognized as not “possibly concealed” in step  240 , the plausibility of the target object is reduced in step  250  by the full value k, since the non-detection of the target object is most probably not caused by concealment. In this case, a check is still performed in a following step  255  of whether the new value of P is smaller than an empirically predefinable minimum value P min . If this condition is not met, a jump is made again back to beginning  225  of subroutine  205 . However, if condition  255  is met, the target object is deleted  260 , since it is now to be assumed that the target object has left the measuring range of the radar system and therefore no longer has to be detected. 
     It is to be pointed out that alternatively a check according to step  255  may be performed also after step  245 ; it is a function in particular of the magnitude of value m, since only for larger decrements of plausibility P, i.e., for relatively small values of m, may the relationship P&lt;P min  be met even in path  245 . 
     With the aid of the above-described procedure, the above-described target object losses, which occur in particular in the event of at least three vehicles following each other when traveling in a multilane curve such as, for example, a preceding target vehicle, followed by another vehicle, and the host vehicle following the two above-mentioned vehicles, are effectively prevented. 
     In the specific embodiment shown in  FIG. 2 , the above-described plausibility check of a target object is performed by computing the probability of existence P exist  of the target object. In this case, essentially the two probabilities are processed, namely the probability (P(D|H1) of measuring, i.e., detecting, the target object, and the probability P(D|H0) of an erroneous measurement in the detection. 
     According to a preferred exemplary embodiment, the value of the probability of existence P exist  is computed on the basis of the following equations:
 
 P   exist/k   =LR   k /(1 +LR   k )
 
where LR k  is the likelihood ratio measured in a cycle number k.
 
     The value of LR k  is computed in this exemplary embodiment from the following equations:
 
 LR   k =min[ P ( D|H 1)/ P ( D|H 0)*LR k-1   ;LR   max],  
 
if the target object has been detected and
 
 LR   k =min[(1 −P ( D|H 1))/(1 −P ( D|H 0))* LR   k-1   ;LR   max],  
 
if no target object has been detected,
 
where P(D|H1) denotes the above-mentioned measurement probability, P(D|H0) the above-mentioned erroneous measurement probability, and LR max  the maximum value of LR.
 
     In the above-mentioned algorithm, a concealment situation is taken into account as follows: In the case of a suspected concealment, P(D|H1) is reduced. The exact value of the reduction may be ascertained in an essentially known manner by statistical methods. It is higher or lower depending on the degree of concealment. Since radar sensors are fully capable of measuring even under vehicles, the value of the measurement or detection probability P(D|H1) will not drop to the value “0.” 
     Deletion of target objects is also preferably handled as mentioned previously via the probability of existence P. In this case, however, no further algorithmic measures are necessary.