Abstract:
The invention relates to a method for providing a global navigation satellite system signal, referred to as a GNSS signal in the following, for determining a position of a vehicle, the method including: receiving an unfiltered GNSS signal, filtering the unfiltered GNSS signal on the basis of an ambient condition around the vehicle, and emitting the filtered GNSS signal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase Application of PCT/EP2013/076359, filed Dec. 12, 2013, which claims priority to German Patent Application No. 10 2012 224 104.3, filed Dec. 20, 2012, the contents of such applications being incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for providing a GNSS signal, a control device to carry out the method and a vehicle with the control device. 
       BACKGROUND OF THE INVENTION 
       [0003]    From DE 10 2007 038 697 A1, which is incorporated by reference, it is known to exploit statistical properties of an error of a global satellite navigation signal, referred to as a GNSS signal, formed as a Global Positioning System signal, referred to as a GPS signal, in a navigation device in order to improve the position estimation with the GNSS signal. 
       SUMMARY OF THE INVENTION 
       [0004]    An aspect of the invention is to improve the use of a plurality of sensor sizes in order to increase information. 
         [0005]    According to one aspect of the invention, a method for providing a GNSS signal for position determination of a vehicle comprises the steps of receiving the GNSS signal, filtering the GNSS signal on the basis of an ambient condition around the vehicle and outputting the filtered GNSS signal. 
         [0006]    The aforementioned GPS signal, a                                         signal, referred to as a GLONASS signal for short, and/or a Galileo signal can be used as the GNSS signal. 
         [0007]    The indicated method is based on the consideration that the statistical properties of the error must first be measured in the aforementioned navigation device in order to be able to use said properties in order to improve the position estimation based on the GNSS signal. The indicated method is furthermore based on the consideration that the error could originate from the ambient condition around the vehicle, such as, for example, from shadowing effects which, in the context of the aforementioned navigation device, could be taken into account to improve the signal only if the GNSS signal is poorer due to the shadowing effects and the error manifests itself as measurable due to the statistical recording. It is subsequently possible to respond to the error, in whatever form it takes, only a posteriori following a deteriorating signal quality of the GNSS signal. 
         [0008]    In order to be able to respond more quickly to the signal quality of the GNSS signal deteriorating due to the error, the indicated method is based on the consideration of estimating the signal quality on the basis of the ambient conditions influencing the signal quality. In this way, an expectation value is provided for the signal quality of the GNSS signal which, in the case of a deteriorating signal quality, can be interpreted as a static property of an error of the GNSS signal. It is possible to respond to this expected value, in whatever form it takes, a priori, before the expected deterioration in the signal quality of the GNSS signal actually occurs. 
         [0009]    In one development of the indicated method, the ambient condition can be detected by means of environment sensors on the vehicle. In the context of the development, environment sensors are understood above all to mean sensors from which possible shadowing of the GNSS signal can be estimated. Camera sensors, radar sensors, lidar sensors or V2X sensors, for example, can be used for this purpose, said sensors being in any case present on modern vehicles and thus requiring no structural conversion measures on the vehicle for the implementation of the indicated method. 
         [0010]    In an additional development of the indicated method, the GNSS signal is weighted for filtering on the basis of an output signal of the environment sensor. In this way, it is possible to classify the environment around the vehicle and, for example, to output the degree of shadowing and therefore the signal quality for the further use of the GNSS signal, for example for error correction, to other modules which use the GNSS signal. 
         [0011]    In one further development of the indicated method, the output signal could describe an object on a road on which the vehicle is travelling. In this way, the aforementioned weighting can be carried out according to the structure of the recognized objects, which then essentially indicates how strongly the GNSS signal is shadowed. A tunnel, for example, results, as expected, in a complete shadowing of all available GNSS signals, whereas trees close to the road weakly shadow at least some GNSS signals. Walls of buildings close to the road, on the other hand, can result in a complete shadowing of some GNSS signals and/or in reflections of some GNSS signals. In addition, the reception angle of the GNSS signal can also be taken into account in the weighting of the GNSS signal on the basis of the output signal describing the object, in order to thus further improve the expectation value for the estimated shadowing from the position of the object and the reception angle. 
         [0012]    Any given ambient conditions, such as, for example, interference signal fields which influence the signal quality of the GNSS signal could, in principle, be detected in order to estimate the signal quality of the GNSS signal. In one particular development of the indicated method, the GNSS signal is filtered on the basis of an expected degree of shadowing of the GNSS signal by the object as an ambient condition. 
         [0013]    According to one further aspect of the invention, a method for determining a position of a vehicle on the basis of a GNSS signal comprises the steps of providing the GNSS signal with an indicated method and determining the position of the vehicle based on the provided GNSS signal. 
         [0014]    Through the use of the indicated method for providing a GNSS signal in the position determination, it is possible to respond to anticipated errors in the reception of the GNSS signal and therefore in the position determination before the errors are introduced into the position determination system. For example, before an expected complete shadowing of a GNSS signal, it would be possible, by means of an a priori adaptation of the aforementioned weightings, to switch over successively to a different GNSS signal which replaces the then shadowed GNSS signal. 
         [0015]    In one development, the indicated method comprises the step of checking the plausibility of the determined position of the vehicle on the basis of an output signal of an environment sensor of the vehicle. 
         [0016]    The development is based on the consideration that, for example, the aforementioned object, the structure of which can be used for the aforementioned weighting of the GNSS signal describing the signal quality, can also be used to check the calculated position of the vehicle on the basis of the GNSS signal. Thus, for example, a change of lane of the vehicle on the road could be tracked with the GNSS signal and the position of the vehicle on the road determined in this way and the plausibility of the GNSS signal could this be checked. 
         [0017]    In a different development, the indicated method comprises the steps of detecting reference position data of the vehicle and defining more precisely the position of the vehicle by means of a filtering of the detected position of the vehicle based on the reference position data. 
         [0018]    The reference position data could be dependent, for example, on vehicle dynamics data and/or odometry data of the vehicle. This development is based on the consideration that the reference position data could be more precisely defined on the basis of the GNSS signal, for example in a fusion filter. This could be done, for example, by comparing the reference position data with the GNSS signal itself in a filter or by comparing said reference position data with position data derived from the GNSS signal, such as the measuring position data in an observer. An observer of this type may comprise any filter which allows an analog or digital state observation of the vehicle. Thus, for example, a Luenberger observer may be used. If noise is also to be taken into account, a Kalman filter could be considered. If the form of the noise is also to be taken into account, a particle filter could, where appropriate, also be used which has a basic set of available noise scenarios and selects the noise scenario to be taken into account in the elimination, for example by means of a Monte Carlo simulation. The observer is preferably a Kalman filter which delivers an optimum result in terms of its required processing resources. 
         [0019]    In one particular development of the indicated method, the more precisely defined position is approximated depending on an information content of the determined position. 
         [0020]    The indicated development is based on the consideration that the reference data could represent redundant position data for correcting the position data derived from the GNSS signal. However, a difference between the reference position data and the position data derived from the GNSS signal is required for this correction, in the context of which it would not initially be clear in which of the two available data the error is located. However, this can be determined by means of the aforementioned plausibility check on the position data derived from the GNSS signal and an integrity measure depending, for example, on the communication information content can be allocated to the position data derived from the GNSS signal. The greater/smaller the integrity measure and therefore the communication information content of the position data derived from the GNSS signal, the greater/smaller the error in the reference data must be. The position data derived from the GNSS signal can then be corrected accordingly. 
         [0021]    According to one further aspect of the invention, a method for outputting a measuring signal in a vehicle comprises the steps of: 
         [0022]    detecting a sensor signal, 
         [0023]    detecting a comparison sensor signal, 
         [0024]    weighting at least one of the sensor signals on the basis of an estimated error, and 
         [0025]    filtering the sensor signal on the basis of the comparison sensor signal to output the measurement after the weighting. 
         [0026]    The indicated method is based on the consideration that errors can only be detected in a fusion sensor as known, for example, from document WO 2011/098 333 A1, which is incorporated by reference, if they have already occurred, since the fusion sensor compares the sensor signal and the comparison signal, interprets differences between the two sensor signals as errors and eliminates the error in the form of a feedback. This results in a corresponding dead time which the estimation of the error in advance and therefore its taking into account before it actually occurs can be avoided. 
         [0027]    One of the two sensor signals may, for example, represent the aforementioned reference position data derived from vehicle dynamics data from an inertial sensor, whereas the other sensor signal may, for example, represent the position data derived from a GNSS signal, wherein both sensor signals and the measuring signal indicate a position of the vehicle comprising an absolute position, a speed, an acceleration and a heading of the vehicle. The two sensor signals can be filtered using a filter as described above. 
         [0028]    According to one further aspect of the invention, a control device is configured to carry out one of the indicated methods. 
         [0029]    In one development of the indicated control device, the indicated device has a memory and a processor. Here, of one indicated method is stored in the memory in the form of computer program and the processor is provided to carry out the method when the computer program is loaded from the memory into the processor. 
         [0030]    According to one further aspect of the invention, a computer program comprises program code means in order to carry out all steps of one of the indicated methods when the computer program is executed on the computer or on one of the indicated devices. 
         [0031]    According to one further aspect of the invention, a computer program product contains a program code which is stored on a computer-readable data medium and which, when it is executed on a data processing device, carries out one of the indicated methods. 
         [0032]    According to one further aspect of the invention, a vehicle comprises an indicated control device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The characteristics, features and advantages of this invention described above and the manner in which they are achieved will become clearer and more readily understandable in connection with the following description of the example embodiments which are explained in detail with reference to the drawings, wherein: 
           [0034]      FIG. 1  shows a schematic diagram of a vehicle on a road, 
           [0035]      FIG. 2  shows a schematic diagram of a fusion sensor in the vehicle shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    In the figures, identical technical elements are denoted with identical reference numbers and are described once only. 
         [0037]    Reference is made to  FIG. 1 , which shows a schematic diagram of a vehicle  2  on a road  4 . 
         [0038]    The vehicle  2  moves on the road  4  in a direction of movement  6 . An object in the form of a building  10  toward which the vehicle is travelling is located in this direction of movement  6  at the edge of the road  4  in front of the vehicle  2 . 
         [0039]    In the present embodiment, the vehicle  2  is intended to receive a GNSS signal via an antenna  11  from a global satellite navigation system, referred to below as GNSS, via a plurality of GNSS satellites, of which one GNSS satellite  14  is shown in  FIG. 1 , and a position  16  of the vehicle  2  on the road  4  indicated in  FIG. 2  is to be determined on the basis of a trilateration known per se. 
         [0040]    However, it may occur during the trilateration that the signal quality of at least one of the GNSS signals deteriorates, which may influence the precision of the determined position  16  of the vehicle  2 . In the present embodiment, the indicated GNSS satellite  12  is hidden by the building  10  as the vehicle  2  travels in the direction of movement  6 , as a result of which the GNSS signal  12  is shadowed in relation to the vehicle and can no longer be used with a sufficiently high signal quality for a precise determination of the position of the vehicle  2 . 
         [0041]    In the context of the present embodiment, precautions must be taken here sufficiently quickly in order to reduce the effects of the shadowing of the GNSS signal  12  as far as possible. 
         [0042]    For this purpose, a camera  18  shown in  FIG. 2  is disposed in the vehicle  2 , said camera recording an image  20  which, viewed in the direction of movement  6  of the vehicle  2 , is positioned in front of the vehicle  2 . The building  10  can be recognized in this image  20 , as a result of which the imminent shadowing of the GNSS signal  12  by the building is also recognizable. 
         [0043]    This idea is intended to be used in the present embodiment to minimize the effects of the shadowing of the GNSS signal  12  by the building. 
         [0044]    For this purpose, reference is made to  FIG. 2 , which shows a fusion sensor  22  in the vehicle  2  shown in  FIG. 1 . 
         [0045]    In the present embodiment, the fusion sensor  22  receives the aforementioned position  16  of the vehicle  2 , via a GNSS receiver  24  still to be described, in the form of data which may comprise an absolute position of the vehicle  2  on a road  4 . Along with the absolute position, the position data  16  from the GNSS receiver  6  may also comprise a speed of the vehicle  2  and its heading in relation to the GNSS satellite  14 . Since the position data  16  are derived from the GNSS signals  12 , they are referred to below as GNSS position data  16 . 
         [0046]    The fusion sensor  22  is designed in a manner still to be described in such a way as to increase the information content of the GNSS position data  16  derived from the GNSS signal  12 . On the one hand, this is necessary since the GNSS signal  12  may have a very high signal-to-noise ratio and may thus be very inaccurate. On the other hand, as already explained, the GNSS signal  12  is not constantly available due to shadowing. 
         [0047]    In the present embodiment, the vehicle  2  has an inertial sensor  26  for this purpose which detects vehicle dynamics data  28  of the vehicle  2 . As is known, said data include a longitudinal acceleration, a transverse acceleration and a vertical acceleration, and a roll rate, pitch rate and yaw rate of the vehicle  2 . These vehicle dynamics data  26  are used in the present embodiment in order to increase the information content of the GNSS position data  16  and, for example, to precisely define the speed of the vehicle  2  on the road  4 . The precisely defined position data  30  can then, for example, be used by a navigation device  32  in the vehicle  2  even if the GNSS signal  12  is no longer available at all, for example due to the shadowing building  10 . 
         [0048]    Wheel rotational speed sensors  34  which detect the wheel rotational speeds  36  of the individual wheels, which are not referenced in detail, of the vehicle  2  can optionally also be used in the present embodiment in order to further increase the information content of the GNSS position data  16 . 
         [0049]    In order to increase the aforementioned basic idea of the fusion sensor  22 , the signal-to-noise ratio in the position data  16  and/or the vehicle dynamics data  28 , the information from the GNSS position data  16  are compared with the vehicle dynamics data  28  from the inertial sensor  14  in a filter  38 . To do this, the filter  38  may be designed in any way, but a Kalman filter achieves this object most effectively with a comparatively low processing resource requirement. The filter  38  below is therefore preferably intended to be a Kalman filter  38 . 
         [0050]    The precisely defined position data  30  of the vehicle  2  and the comparison position data  40  of the vehicle  2  are fed into the Kalman filter  38 . In the present embodiment, the precisely defined position data  30  are generated from the vehicle dynamics data  28  in a strapdown algorithm  42  known, for example, from DE 10 2006 029 148 A1, which is incorporated by reference. They contain precisely defined position information relating to the vehicle, but also other position data relating to the vehicle  2 , such as, for example its speed, its acceleration and its heading. On the other hand, the comparison position data  40  are obtained from a model  44  of the vehicle  2  which is initially fed from the GNSS receiver  24  with the GNSS position data  16 . The comparison data  40 , which contain the same information as the precisely defined position data  30 , are then determined in the model  44  from these GNSS position data  16 . The precisely defined position data  30  and the comparison data  40  differ only in their values. 
         [0051]    The Kalman filter  38  calculates an error budget  46  for the precisely defined position data  30  and an error budget  48  for the comparison data  40  on the basis of the precisely defined position data  30  and the comparison position data  40 . An error budget is intended to be understood below to mean a total error in a signal which consists of different individual errors in the acquisition and transmission of the signal. In the GNSS signal  12  and therefore in the GNSS position data  16 , a corresponding error budget may comprise errors of the satellite orbit, the satellite clock, the residual refraction effects and errors in the GNSS receiver  24 . 
         [0052]    The error budget  46  of the precisely defined position data  18  and the error budget  48  of the comparison position data  34  are then fed accordingly to the strapdown algorithm  36  and the model  44  for correcting the precisely defined position data  30  and the comparison data  40 . This means that the precisely defined position data  30  and the comparison position data  40  are iteratively purged of their errors. By the same token, the error budget  48  of the comparison position data  40  can also be fed to the GNSS receiver  24  so that the latter can iteratively eliminate the aforementioned errors of the satellite orbit, the satellite clock and the residual refraction effects. A GNSS system of this type is also referred to as a deeply coupled GNSS. 
         [0053]    In the present embodiment, the GNSS receiver  24  has a selection and correction device  50  and a trilateration device  52  for this purpose. 
         [0054]    The selection and correction device  50  selects four GNSS signals  12  from all received GNSS signals  12 . The GNSS position data  16  of the vehicle  2  are then determined in the trilateration device  52  in a manner known to the person skilled in the art from the GNSS signals  54  selected in this way, not all of which are denoted with a reference number in  FIG. 2  for the sake of clarity. 
         [0055]    The aforementioned selection of the GNSS signals  12  is carried out in the present embodiment on the basis of a weighting of the GNSS signals  12 , wherein the individual weighting factors can be determined on the basis of the error budget  48 . In principle, however, an error that could be fed back must first exist for this weighting. Until the existing error is fed back into the selection and correction device  50  of the GNSS receiver  24 , a time, known to the person skilled in the art as the dead time, elapses in which an errored GNSS signal continually increases an error in the GNSS position data  16  and therefore in the precisely defined position data  30 . 
         [0056]    It would therefore be desirable to bridge this dead time. 
         [0057]    As already mentioned above in the context of  FIG. 1 , the shadowing of the GNSS satellite  14  similarly represents an aforementioned error which would manifest itself in the error budget  48  and therefore in the fed back error. However, the dead time can be bridged here since the error is already detected in advance from the image  20  which the aforementioned camera  18  records in the direction of movement  6  in front of the vehicle  2 . 
         [0058]    On the basis of the information from this image  20 , the GNSS signals  12  could similarly be weighted and thus selected, whereby a defective GNSS satellite  14  could be predictively detected. In this way, for example, the weighting of the GNSS satellite  14  shown in  FIG. 1  could be successively modified until the GNSS satellite  14  is extracted in a timely manner by the selection and correction device  50  of the GNSS receiver  24  before it introduces errors into the GNSS position data  16  due to its shadowing. 
         [0059]    To implement this idea, the selection and correction device  50  of the GNSS receiver  24  receives the image  20  and carries out an object recognition, not represented in further detail but known to the person skilled in the art, on the image  20 . The object recognition can be carried out in terms of specific classes of objects. For example, these object classes can be divided up as follows: 
         [0060]    tunnels completely shadowing all GNSS signals  12 , 
         [0061]    buildings  10  shadowing some of the GNSS signals  12 , or 
         [0062]    trees only partially shadowing some of the GNSS signals  12 . 
         [0063]    If a potential shadowing object, such as, for example, the building  10  shown in  FIG. 1 , is recognized, the GNSS satellites  14  which would be affected by a shadowing due to the shadowing object can be determined on the basis of the comparison data  40  (or other available position data of the vehicle  2 ). The distance from the vehicle to this shadowing object and therefore information indicating when the shadowing object shadows the affected GNSS satellite  14  could then be determined. Correspondingly, the selection and correction device  50  of the GNSS receiver  24  can then successively increase the weighting of the affected GNSS signal  12  in the manner described above. 
         [0064]    The idea described above could also be implemented alternatively or additionally in the Kalman filter  38  (or any other of the aforementioned filters) in order to detect an error in the comparison position data  40  compared with the precisely defined position data  30  in a timely manner before its occurrence. The Kalman filter  38  could receive the image  20 , detect the shadowing object in the image  20  and weight the comparison position data  40  in the case of an error in such a way that the comparison position data  40  are taken into account less heavily in the filtering of the comparison position data  40  and the precisely defined position data  30 .