Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/88—Radar or analogous systems specially adapted for specific applications
  • G01S13/93—Radar or analogous systems specially adapted for specific applications for anti-collision purposes
  • G01S13/931—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of land vehicles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/40—Means for monitoring or calibrating
  • G01S7/4004—Means for monitoring or calibrating of parts of a radar system
  • G01S7/4026—Antenna boresight
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/40—Means for monitoring or calibrating
  • G01S7/4004—Means for monitoring or calibrating of parts of a radar system
  • G01S7/4026—Antenna boresight
  • G01S7/4034—Antenna boresight in elevation, i.e. in the vertical plane
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/88—Radar or analogous systems specially adapted for specific applications
  • G01S13/93—Radar or analogous systems specially adapted for specific applications for anti-collision purposes
  • G01S13/931—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of land vehicles
  • G01S2013/9327—Sensor installation details
  • G01S2013/93271—Sensor installation details in the front of the vehicles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/40—Means for monitoring or calibrating
  • G01S7/4052—Means for monitoring or calibrating by simulation of echoes
  • G01S7/4082—Means for monitoring or calibrating by simulation of echoes using externally generated reference signals, e.g. via remote reflector or transponder
  • G01S7/4091—Means for monitoring or calibrating by simulation of echoes using externally generated reference signals, e.g. via remote reflector or transponder during normal radar operation

Definitions

• the present invention relates to a method for performing radar measurements with a vehicle mounted radar system.
• the invention also relates to the use of such a method in a vehicle mounted radar system.
• Radar systems mounted on vehicles such as cars, buses, lorries and the like are currently being developed.
• the purpose of such systems are to provide functions assisting the driver of the vehicle with features such as cruise control, collision warning and collision avoidance, the functions being based on the detection of vehicles, stationary objects, and other objects in front of the vehicle.
• the system Before such a radar system can be used, the system has to be mounted on the vehicle and be subject to some kind of calibration procedure, either at the vehicle factory or at a service station.
• the requirements on a precise mounting and/or a calibration of the radar system are very high in order to ensure a correct operation of the system. Moreover, it will probably be required to perform re-calibrations of the system at regular intervals at an appropriate service station or the like.
• calibration of the vertical direction of a radar sensor axis is needed in order for the radar beams of a radar signal to be directed towards objects in front of the vehicle rather than up in the air or down into the ground.
• ground level objects are objects on the same level as the vehicle for which one should stay clear of in order to avoid collision
• overhead objects are defined as objects lying well above said ground level, such as road signs and bridges over the road.
• the prior art solves this by using narrow width radar beams being aligned with the axis of the vehicle on which the radar system is mounted. Since elevation resolution is not provided, overhead objects will fall outside of the beam envelope and thus not give rise to any beam reflections. However, the axis of a radar sensor, and thus a radar beam, is also affected by a pitch of the vehicle carrying the radar system. This pitch results in that the radar beams are directed either higher or lower than a normal vertical direction.
• the pitch can be either a static pitch or a dynamic pitch. The static pitch occurs as a result of a heavy loaded vehicle.
• an inexact mounting of the radar sensor with respect to the vertical direction of its axis in relation to the directional axis of the vehicle, will affect radar system measure- ments and classification of objects in the same way as a static vehicle pitch.
• a dynamic pitch occurs when driving the vehicle on a undulated road, i.e. a road having a vertical curvature, and is thus subject to more or less continuous change during the driving.
• the static vehicle pitch also tends to change, although not continuously during driving of the vehicle. Instead, the change may occur from one time to another with changing number of passengers and changing vehicle load.
• the dis- advantage will be that the beams may be pointing in a too high or a too low direction when driving a heavy loaded vehicle or on a road with a vertical curvature. Therefore, in order for the radar system to be functional when driving under such conditions, it is desirable to have either a vertically wider radar beam or several narrow radar beams in order to provide a certain amount of elevation resolution. The problem that then arises is the need for some kind of calibration of the system.
• This calibration is needed in order for a ground level object, being a potential hazard, to be correctly interpreted as a potential hazard, even if its location is vertically above or under the radar sensor axis due to the vertical road curvature, the vehicle load and/or an imprecise mounting of the radar sensor.
• An object with the present invention is to provide a method for performing radar measurements with a vehicle mounted radar system that eliminates the need for calibrating the vertical direction of a radar sensor axis of the radar system at a vehicle manufacturer or at a vehicle service station.
• Another object is to provide a method for performing radar measurements with a vehicle mounted radar system, which measurements are adequate and reliable even though the vehicle is subject to a vehicle pitch.
• the present invention is based on the idea that a radar system or the like that classifies objects in front of a vehicle by means of measuring a vertical angle to an object in order to determine whether the object is a ground level object of potential hazard or an harmless overhead object, has to consider the present vehicle pitch.
• the vehicle pitch has to be estimated and compensated for in order for the system to be able to properly classify objects in front of the vehicle.
• a method for performing radar measurements with a vehicle mounted radar system including the steps of : transmitting a radar microwave signal in the form of radar beams having different elevations; receiving reflected signals from objects positioned in front of said vehicle; measuring amplitude values of the received signals resulting from reflections of said radar beams having different elevations; estimating a pitch of said vehicle based on relationships between said amplitude values; and compensating for the estimated vehicle pitch when performing radar measurements with the radar system.
• the invention provides use of a method in a vehicle mounted radar system for estimating, and compensating for, a vehicle pitch when performing radar measurements with the radar system.
• One advantage with the present invention is that by estimating, and compensating for, a vehicle pitch during normal operational radar measurements, radar measurements can be used at any time for determining, with a great confident, at what vertical location an object in front of the vehicle is located at. Thus, it is possible to correctly classify the object as a ground level object or an overhead object.
• the radar system includes a radar sensor for transmitting and receiving radar beams, and processing means, such as a Signal Processing Unit, for processing measurement data derived from received radar signal reflections.
• processing means such as a Signal Processing Unit
• the provision of a vehicle pitch estimation based on normal operational radar measurements, and the following compensation for the vehicle pitch when operating the radar system is a radar system process that is performed continuously by the radar system when the system is in use on a moving vehicle.
• the invention provides a method which continuously com- pensates for a vehicle pitch while performing normal operational radar measurements.
• said estimating step includes: accumulating several consecutive relationships when the radar beams are reflected by a number of objects in front of the vehicle during a period of time; and estimating a static vehicle pitch based on a said accumulated relationships.
• said estimating step includes: providing a number of simultaneously occurring relationships when said radar beams are reflec- ted by at least one of said objects in front of the vehicle; and estimating a momentary dynamic vehicle pitch based on the provided relationships.
• a relationship provided by performing radar measurements with respect to a specific moving object is continuously evaluated in order to be able to monitor a continuously changing dynamic pitch.
• the estimated dynamic pitch will be a direct measure of the vertical curvature of the road on which the vehicle carrying the radar system is moving.
• said step of estimating a vehicle pitch includes estimating a mean value of a set of critical vertical angles, with respect to a directional axis of the vehicle, for a ground level object, each of said critical vertical angles being a function of a respective relationship.
• a single critical vertical angle is provided using the function with respect to a mean value of several relationships.
• a correct classification of the object is provided regardless of the present vehicle pitch.
• the radar system is adapted to be mounted on a land based vehicle, such as a car, bus or lorry.
• the radar sensor included by the radar system is preferably an FMC -radar sensor (Frequency Modulated Continuous Wave) .
• FIG. 1 schematically shows a side view of a vehicle on which a radar system according to the present invention has been mounted;
• Fig. 2 schematically illustrates a situation where a radar sensor axis has a normal and optimal vertical direction in relation to an object in front of the vehicle ;
• Figs. 3a and 3b schematically illustrate two situations where a vehicle carrying a radar system is subject to a static pitch
• Figs. 4a and 4b schematically illustrate two situations where a vehicle carrying a radar system is subject to a dynamic pitch
• Figs. 5a and 5b schematically illustrate the deter- mination of a critical vertical angle for a ground level object and the utilisation of this angle when compensating for a static pitch;
• Fig. 6 schematically illustrates the determination of a critical vertical angle for a ground level object and the utilisation of this angle when compensating for a dynamic pitch
• Fig. 7 illustrates a critical vertical angle for a ground level object as a function of time.
• a radar system according to the present invention is schematically shown.
• the radar system is mounted on a vehicle 110 and includes a radar sensor 100, having a radar sensor axis 105, and signal processing means 130.
• the radar which transmits a radar microwave signal, is a horizontally scanning radar which at a first scan transmits the radar signal as a number of radar beams with a certain horizontal level and which at the return scan transmits the radar signal as a number of radar beams having an elevated level.
• the radar signal can be regarded as comprised of two sets of radar beams having different elevations.
• two radar beams 107, 108 having different elevations are depicted.
• Each of these two radar beams 107, 108 is included in a respective set of said two sets of radar beams.
• the radar sensor 100 is located in the front of the vehicle 110 and the transmitted radar microwave signal, i.e. the radar beams 107, 108, are reflected by objects (not shown) positioned in front of the vehicle 110.
• the radar sensor 100 receives the thus reflected signals and transfers radar measurement data derived from the reflected signals to the signal processing means 130, which is electrically connected to the radar sensor 100.
• a number of other means are also mounted on the vehicle 110, such as means for engine and brake control, a man-machine inter- face, and so on (not shown) .
• the radar sensor 100 and its axis 105, the radar beams 107 and 108, the signal processing means 130, and also the other means described, are all present in Figs. 2 - 5, even though not always explicitly indicated.
• a situation is schematically illustrated in which, due to proper mounting and calibration of the radar sensor (not shown) , the radar sensor axis 105 has a proper vertical direction in relation to an object 200 in front of the vehicle 110 carrying the radar system.
• the proper vertical direction of the radar sensor axis is when it is pointing towards a ground level object in front of the vehicle 110, which proper vertical direction in this case coincides with the actual direction of the radar sensor axis 105 of the vehicle 110. Since the radar sensor axis 105, and thus the two radar beams 107 and 108, is directed towards object 200, this object will be classified as a ground level object.
• a situation in which a vehicle 110 carrying a radar system is subject to a static pitch is schematically illustrated.
• the static pitch may, as previously described, occur as a result of an imprecise mounting of the radar sensor (not shown) or a heavy load being carried by the vehicle. Due to the static pitch, the sensor axis 105, and thus the two radar beams 107, 108, is pointing slightly up into the air. The proper direction of the sensor axis, and the radar beams, would be to point along a horizontal level where one would find a ground level object, this proper direction is indicated as arrow 315 .
• the overhead object 300 in this case a bridge 300 over the road 310 on which the vehicle 110 is moving, will be classified as a ground level object, rather than an overhead object, as the vehicle 110 approaches the bridge 300.
• Fig. 3b shows another example of a static vehicle pitch, resulting from, for example, an imprecise mounting of the radar sensor (not shown) or a lighter load being carried by the vehicle 110 than during the last calibration. Since the sensor axis 105 and the radar beams in this situation are pointing vertically too low, the object 350 in front of the vehicle, being for example an obstacle on the road, will be wrongly classified as an overhead object, rather than a ground level object.
• FIG. 4a an exemplified situation schematically illustrates the occurrence of a dynamic pitch situation.
• a dynamic pitch occurs, as previously described, as a result of a vertical curvature of a road 410.
• the radar sensor axis 105 is aligned with a directional axis of the vehicle 110, in the same way as described with reference to Fig. 2.
• the vertical position of an object 400 located in front of the vehicle 110 is at a level above the ground level on which the vehicle 110 is moving.
• the sensor axis 105 and the radar beams will point too low with respect to the ground level object 400, which object then will be classified as an overhead object rather than a ground level object being a potential hazard.
• a sensor axis 105 being slightly elevated vertically with respect to a directional axis of the vehicle would be more optimal, in order for the object 400 to be classi- fied as the ground level object it is.
• Fig. 4b shows another exemplified situation in which a vehicle 110 is subject to a dynamic pitch.
• the dynamic pitch situation occurs as a result of a vertical curvature of the road 415 on which the vehicle 110 is moving.
• the sensor axis 105 again being aligned with a directional axis of the vehicle 110, will have a vertical direction that is too high compared with a direction towards a ground level located on the road 415 which would be a more optimal direction. Therefore, an overhead object 450 in front of the vehicle 110, which overhead object for example could be a bridge over the road 415, will be classified as a ground level object of potential hazard rather than as a harmless overhead object.
• Fig. 5a shows a vehicle 110 being subject to a static pitch and having its radar sensor axis 105 pointing in a too low direction.
• a moving object 500 in front of the vehicle 110 will reflect the two radar beams 107 and 108, having different elevations, and each reflected radar beam will result in a radar signal being received by the radar sensor, previously shown in Fig. 1, mounted in the front of the vehicle 110.
• the radar signals received by the radar sensor will give rise to radar picture data which will be transferred to the signal processing means, previously shown in Fig. 1, for further processing.
• the signal processing means will extract a radar signal amplitude value from the radar picture data of each received reflected radar beam.
• the amplitude values of the received signals resulting from reflections of radar beams 107 and 108 are measured. These amplitude values are denoted A and B, respectively .
• the signal processing means (not shown) then estimates the pitch of the vehicle 110 by estimating a verti- cal angle a to the vertical location of the moving object 500 with respect to the direction of the sensor axis 105.
• the estimation of the vertical angle a is based on a relationship between the amplitude values A and B of the respective reflected radar beams 107 and 108. As shown in equation (1) below, the vertical angle a is equal to a function of the quotient between amplitude A and amplitude B.
• the signal processing means will determine that the mean relationship between the values of amplitude A and amplitude B, which are observed during a period of time, corresponds to a relationship which is to be associated with a ground level object. Using equation (1), this mean relationship is then used when determining a critical vertical angle a c to be associated with a ground level object.
• the critical vertical angle a Q is calculated as the mean value of all vertical angles , each a being associated with a registered relationship between two amplitude values in accordance with equation (1) during a period of time.
• the optimal and proper direction of the radar sensor axis 105 would be to point towards any ground level objects in front of the vehicle 110.
• the critical vertical angle c will be used as a measure of a deviation of the radar sensor axis from this optimal and proper direction.
• Fig. 5b illustrates the same situation as previously illustrated in Fig. 3b.
• the signal processing means (not shown) will derive a current vertical angle c curr to the radar measured object based on the current amplitude relationship of the two radar beams using equation (1) as described above.
• the derived angle will be compensated for the deviation of the radar sensor axis 105 from an optimal and proper direction.
• the compensation is per- formed by subtracting the previously derived critical vertical angle a c from the current measured vertical angle fir curr in accordance with equation (2) below.
• the resulting compensated angle ⁇ comp is then used when classifying the object in front of the vehicle 110.
• a ground level object 550 and an overhead object 560 Since the radar sensor axis 105 points in a too low direction, both of the current measured vertical angles ⁇ cu m an d Curr2 ' being related to object 550 and 560, respectively, will get such high values that both of objects will be classified as overhead objects. However, by compensating the measured values o currl and a curr2 for the previously derived critical vertical angle a c , the classification of the objects 550 and 560 will be based on compensated vertical angles a compl and ex comp2 , respectively. In Fig.
• the compensated vertical angle a compl to object 550 will get a value which is zero or negative ( a c subtracted from measured angle value or currl ) , thus, object 550 will be classified as a ground level object.
• object 560 will get a compensated vertical angle value ex c 2 which is positive ( a c subtracted from measured angle value curr2 ) , and will therefore be classified as the overhead object it is.
• the system could be arranged so that the compensated vertical angle must have a value equal to at least a predetermined threshold value in order for an object to be classified as an overhead object.
• the value of the critical vertical angle will in this embodiment be negative.
• the value of a measured vertical angle to any object having a vertical location below the sensor axis will also be negative and the measured angle value to any object above the axis will be positive.
• an object with a compensated value which is negative will be classified as a ground level object and an object with a compensated value which is positive as an overhead object.
• the result is a correct classification of the object using equation (2) .
• FIG. 6 shows a vehicle 110 being subject to a dynamic pitch and having its radar sensor axis 105 pointing in a too low direction, with respect to a ground level object 600 in front of the vehicle 110.
• a time axis with respect to the movement of the vehicle 110 on the road 610 is also indicated.
• vehicle 110 has a corresponding position on the road 610.
• vehicle 110 is located at a part of the road 610 which has a vertical curvature, and at t 2 vehicle 110 has moved to a part of the road 610 which no longer has a vertical curvature.
• the basic operation of the radar system and the calculation of a critical vertical angle a c in the embodiment referring to Fig. 6 is the same as what has previously been described above with reference to Fig. 5a. Also, the classification of an object based on this critical angle is the same as previously described with reference to Fig. 5b. The difference is that when calcu- lating a critical vertical angle a c in a dynamic pitch situation, the accumulation of relationships between amplitude values on which the calculation is based are performed in a different way. Instead of accumulating a number of relationships during a period of time, the critical angle is based on a number of simultaneously occurring relationships at a specific point of time, such as t, indicated on the time axis in Fig. 6.
• the relationships are the result of radar measurements performed with respect to either a number of moving ground level objects (not shown) , or, a number of stationary objects (not shown) having the same vertical location, in front of the vehicle 110 at the specific point of time t, .
• the road 110 has moved to a location on the road 610 corresponding to time t 1 , the road no longer has a vertical curvature and the dynamic vehicle pitch is zero.
• a vehicle may of course be subject to both a static and a dynamic pitch at the same time.
• vehicle 110 may also be subject to a static pitch.
• the critical vertical angle a c calculated will then have a static part and a dynamic part.
• Fig. 7 is a diagram in which the critical vertical angle a c , and thus the vehicle pitch, of vehicle 110 in Fig. 6 is plotted against a time axis. It can be seen that vehicle 110 has a static pitch being continuously present and contributing to the critical vertical angel a c with a vertical angle component e c _ s . Between time t, and t 2 , corresponding to t ] and t, in Fig. 6, vehicle 110 also has a dynamic pitch due to the vertical curvature of road 610 which contributes to the critical vertical angel a c with a vertical angle component

Landscapes

• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Physics & Mathematics (AREA)
• Computer Networks & Wireless Communication (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Radar Systems Or Details Thereof (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20415974

Family Applications (1)

Country Status (3)

Cited By (5)

Citations (3)

• 1999
  • 1999-06-08 SE SE9902141A patent/SE9902141L/sv not_active Application Discontinuation
• 2000
  • 2000-05-25 WO PCT/SE2000/001066 patent/WO2000075686A1/en active Application Filing
  • 2000-05-25 AU AU54343/00A patent/AU5434300A/en not_active Abandoned

Patent Citations (3)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events