Abstract:
The invention relates to a method for selecting a satellite which is designed to send a global navigation satellite system-signal, also known as a GNSS-Signal, to a vehicle, consisting of: measuring measurement position data of the vehicle in relation to the satellite based on the GNSS-Signal; determining redundant reference position data of the vehicle in relation to the measurement position data determined according to the GNSS-Signal; and selecting the satellite when a comparison of the measurement position data and the reference position data meets a predetermined condition.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to German Application Nos. 10 2011 082 534.7, filed Sep. 12, 2011, 10 2011 082 539.8, filed Sep. 12, 2011, 10 2011 086 710.4, filed Nov. 21, 2011, 10 2012 207 297.7, filed May 2, 2012, and International Application No. PCT/EP2012/067866, filed Sep. 12, 2012. 
     
    
     FIELD OF THE INVENTION  
       [0002]    The invention relates to a method for selecting a satellite that is designed to send a GNSS signal to a vehicle, a control apparatus for performing the method and a vehicle having the control apparatus. 
       BACKGROUND OF THE INVENTION  
       [0003]    WO 2011/098333 A1 discloses the practice of using different sensor variables in a vehicle in order to improve already existent sensor variables or to generate new sensor variables and hence to enhance the recordable information. 
         [0004]    It is an object to improve the use of a plurality of sensor variables for enhancing information. 
       SUMMARY AND INTRODUCTORY DESCRIPTION OF THE INVENTION  
       [0005]    The object is achieved by the technical features disclosed herein and by way of the method disclosed herein. 
         [0006]    According to one aspect of the invention, a method for selecting a satellite that is designed to send a global navigation satellite system signal, called a GNSS signal below, to a vehicle comprises the steps of: 
         [0007]    measurement of measurement location data for the vehicle with respect to the satellite on the basis of the GNSS signal, 
         [0008]    determination of reference location data for the vehicle that are redundant relative to the measurement location data determined on the basis of the GNSS signal; and 
         [0009]    selection of the satellite when juxtaposition of the measurement location data and the reference location data satisfies a predetermined condition. 
         [0010]    The specified method is based on the consideration that position information for the vehicle could be derived from the GNSS signal. On the basis of this consideration, however, the specified method involves recognizing that the GNSS signal could, prior to being received at the vehicle, pass through different sources of interference that could add noise to the GNSS signal, as a result of which it no longer indicates the true position of the vehicle. Such sources of interference could be multipath reception, shadowing or reflections. 
         [0011]    On the basis of these considerations, it is a concept of the specified method to stipulate for the GNSS signal an expected value from which a reference for the quality of the GNSS signal can be derived with sufficient precision. If the deviation between the GNSS signal and the expected value used as a reference is sufficiently small, the satellite is selected as a source for the GNSS signal. 
         [0012]    In one development, the juxtaposition of the measurement location data and the reference location data involves a difference being formed between the measurement location data and the reference location data. This development is based on the consideration that although the juxtaposition could be performed on the basis of any desired filter, the difference between the two location data immediately reveals the deviation therein relative to one another, which provides a statistical description of the GNSS signal and hence immediately permits the quality thereof to be assessed. 
         [0013]    In this regard, it may be preferred for a predetermined condition that is permitted to be a maximum admissible error between the measurement location data and the reference location data that is in turn a quality control for the selection of the satellite. 
         [0014]    With particular preference, the maximum admissible error may be dependent on a standard deviation that is calculated on the basis of a sum comprising a reference variance for the reference location data and a measurement variance for the measurement location data. This development is based on the consideration that in this case two statistical values are simultaneously used for the selection of the satellite. The reference value could be determined iteratively, with the quality thereof becoming ever higher with ascending iteration steps. However, this means that the reference value may itself have a high level of noise and contain errors at first, which is why it would not be expedient at this time to select a GNSS signal with a very high quality. Since the maximum admissible error and hence the admissible deviation are chosen on the basis of the variances and hence the noise in the two location data, the maximum admissible error between the location data and the noise in the location data themselves are correlated for the selection. This ensures that the noise from the satellite to be selected matches the deviation between the expected value and the measured value represented by the GNSS signal. 
         [0015]    In an additional development of the specified method, the maximum admissible error corresponds to a multiple of the standard deviation such that a probability that the measurement location data are below a predetermined threshold value in a scatter range that is dependent on the standard deviation. This ensures that the inevitable scatter in the deviations between the reference location data, that is to say the expected value, and the measured location data, that is to say the measured value, does not select a satellite that is actually suitable on a nonrandom basis. 
         [0016]    According to a further aspect of the specified invention, a method for selecting a satellite that is designed to send a global navigation satellite system signal, called a GNSS signal below, to a vehicle comprises the steps of: 
         [0017]    measurement of measurement location data for the vehicle with respect to the satellite on the basis of the GNSS signal, 
         [0018]    selection of the satellite when the measurement location data satisfy a predetermined condition. 
         [0019]    The specified method is based on the consideration that the satellite could be selected just using hard decision bases, because the vehicle that uses the GNSS signal is subject to particular physical constraints. By way of example, the vehicle must not accelerate arbitrarily and is also unable to travel at an arbitrary speed. These physical constraints can be used as a basis for selecting the satellite without the need for further comparison measurements in order to check the quality of the GNSS signal. 
         [0020]    Therefore, the predetermined condition may preferably be a physical constraint to which the vehicle is subject. 
         [0021]    With particular preference, the physical constraint may be a limit acceleration and/or a limit speed for the vehicle. 
         [0022]    In one particular development of the specified method, the measurement location data may comprise a speed and/or an acceleration, for example, that is derived from the GNSS signal. In this way, it is possible to check directly whether or not the aforementioned physical constraints are satisfied. 
         [0023]    According to a further aspect of the specified invention, a method for selecting a satellite that is designed to send a global navigation satellite system signal, called a GNSS signal below, to a vehicle comprises the steps of: 
         [0024]    recording of a location for at least three satellites among one another, said satellites comprising the satellites to be selected; 
         [0025]    measurement of measurement location data for the vehicle with respect to the satellite on the basis of the GNSS signal from the satellite to be selected, 
         [0026]    selection of the satellite to be selected on the basis of juxtaposition of the location of the three satellites relative to one another and the measurement location data. 
         [0027]    The specified method is based on the consideration that the three satellites with the satellite to be selected may have an inherently known location relative to one another. On the basis of this known location, the vehicle must also move in a manner that is to be expected with respect to these three satellites. This movement that is to be expected can be used as a decision basis for selecting the GNSS signal and hence the satellite to be selected. 
         [0028]    In this case, the specified method involves recognizing that the location of the three satellites relative to one another comprises relative position statements. In order for a GNSS signal to be incorrectly interpreted as error-free, the GNSS signals from all three GNSS satellites would need to be corrupted in an exactly identical manner by shadowing, multiple reflections, and so on, which is as good as ruled out on account of the totally different signal propagation paths, however. Therefore, the specified method delivers a very reliable decision basis for the selection of a satellite. 
         [0029]    In one development of the specified method, the juxtaposition of the location of the three satellites relative to one another and the measurement location data comprises juxtaposition of the distances of the vehicle relative to the three satellites. This development is based on the consideration that the GNSS signals from the three satellites could be examined for any inconsistencies on the basis of the location of the satellites relative to one another. If all three satellites are in front of the vehicle from the point of view of the direction of travel of the vehicle, for example, then all three distances must be shorter. In addition, from trigonometric perspectives, it is possible to determine how quickly individual distances from the vehicle to the relevant satellite can become shorter. The distances of the satellites relative to one another can be derived from information transmitted by the satellites. 
         [0030]    According to a further aspect of the specified invention, a method for selecting a satellite that is designed to send a global navigation satellite system signal, called a GNSS signal below, to a vehicle comprises the steps of: 
         [0031]    recording of a distance for the vehicle relative to the satellite and of a relative speed for the vehicle relative to the satellite in the visual direction of the satellite from the GNSS signal; 
         [0032]    selection of the satellite on the basis of juxtaposition of the recorded distance and the recorded relative speed. 
         [0033]    The specified method is based on the consideration that the distance from the vehicle to the satellite and the relative speed of the vehicle with respect to the satellite are dependent on one another, that is to say correlated. In addition, the specified method is based on the consideration that the relative speed could be recorded from the GNSS signal, for example on the basis of Doppler effects, while the distance from the vehicle to the satellite could be recorded on the basis of a propagation time of the GNSS signal, for example, and hence independently of the measurement for recording the relative speed. The concept of the specified method is thus that it is nevertheless necessary for both measurements to match, that the measured variables to be recorded, that is to say the relative speed and the distance, are dependent on one another. 
         [0034]    The juxtaposition can be effected arbitrarily on the basis of difference formation or other filtering. Difference formation immediately reveals the decision basis for selection of the satellite with minimum computation time. 
         [0035]    For all methods specified above, the following developments can also be implemented: 
         [0036]    The measurement location data for the vehicle and the reference location data for the vehicle may each comprise a distance from the satellite and/or a relative speed in the visual direction of the satellite. That is to say that the method specified according to the last aspect of the invention selects the satellite on the basis of an analysis of the measurement location data in themselves, this making use of the advantage that the GNSS signal transmits the measurement location data using principles that can be recorded by measurement in two different ways. 
         [0037]    In a preferred development of one of the specified methods, the distance from the satellite and/or the relative speed in the visual direction of the satellite can be ascertained as appropriate from a code measurement and a phase measurement for the GNSS signal. 
         [0038]    The GNSS signal used may be a global positioning system signal, GPS signal for short, a                                         signal, GLONASS signal for short, or a Galileo signal, for example. Hence, an alternative or additional comparison variable for the vehicle longitudinal speed would be available, on the basis of which the information content of the tire radius to be recorded could be improved. By way of example, the GNSS signal allows network subscribers in an onboard network on the vehicle, such as sensors, to have their timing synchronized with a correspondingly high level of precision on account of the high-precision timestamp of said signal. Such synchronization is currently the focus of current development pertaining to Car2X communication, that is to say data interchange from a vehicle to other vehicles or systems in the surroundings, such as traffic lights or other infrastructure components. The interchange of information about accidents and other hazard locations, about the condition of the road, road signs and much more makes it possible to attain an increase in safety and convenience. In many cases, this needs to involve the information being provided in real time. in order to ensure this real time, the information can be provided with a high-precision timestamp, for example, which is linked to the information by the respective network subscriber. This timestamp needs to have a correspondingly high level of precision, however, which is ensured by the selection of an uncorrupted GNSS signal. 
         [0039]    In another development of one of the specified methods, the reference location data are dependent on driving dynamics data and/or odometry data for the vehicle. This development is based on the consideration that the reference location data can be defined more precisely on the basis of the GNSS signal, for example in a fusion filter. This could be accomplished by juxtaposing the reference location data with the GNSS signal itself or location data derived from the GNSS signal, like the measurement location data, in an observer, for example. Such an observer may include any filter that permits analog or digital state observation of the vehicle. It is thus possible to use a Luenberger observer, for example. If the noise also needs to be taken into account, a Kalman filter would be suitable. If the shape of the noise also needs to be taken into account, it would be possible, if need be, to use a particle filter, which has a basic set of available noise scenarios and selects the noise scenario that is to be taken into account for the elimination using a Monte Carlo simulation, for example. The observer is preferably a Kalman filter, which provides an optimum result in respect of the computation resources that it requires. The observation makes the reference location data ever more precise over time and said data therefore also allow ever more precise GNSS signals to be selected. 
         [0040]    According to a further aspect of the invention, a control apparatus is set up to perform one of the specified methods. 
         [0041]    In one development of the specified control apparatus, the specified apparatus has a memory and a processor. In this case, a specified method is stored in the memory in the form of a computer program, and the processor is provided for the purpose of executing the method when the computer program is loaded from the memory into the processor. 
         [0042]    According to a further aspect of the invention, a computer program comprises program code means in order to perform all the steps of one of the specified methods when the computer program is executed on a computer or one of the specified apparatuses. 
         [0043]    According to a further aspect of the invention, a computer program product contains a program code that is stored on a computer-readable data storage medium and that, when executed on a data processing device, performs one of the specified methods. 
         [0044]    According to a further aspect of the invention, a vehicle comprises a specified control apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0045]    The properties, features and advantages of this invention that are described above and also the manner in which these are achieved become more clearly and more distinctly comprehensible in connection with the description below of the exemplary embodiments, which are explained in more detail in connection with the figures, in which: 
           [0046]      FIG. 1  shows a basic illustration of a vehicle with a fusion sensor, 
           [0047]      FIG. 2  shows a basic illustration of the fusion sensor from  FIG. 1 , and 
           [0048]      FIG. 3  shows a schematic illustration of a vehicle receiving a GNSS signal. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0049]    In the figures, technical elements that are the same are provided with the same reference symbols and are described only once. 
         [0050]    Reference is made to  FIG. 1 , which shows a basic illustration of a vehicle  2  with a fusion sensor  4 . 
         [0051]    In the present embodiment, the fusion sensor  4  uses an inherently known GNSS receiver  6  to receive location data  8  for the vehicle  2 , which data comprise an absolute position for the vehicle  2  on a road  10 . Besides the absolute position, the location data  8  from the GNSS receiver  6  also comprise a speed for the vehicle  2 . In the present embodiment, the location data  8  from the GNSS receiver  6  are derived—in a manner that is known to a person skilled in the art—in the GNSS receiver  6  from a GNSS signal  12  that is received via a GNSS antenna  13  and that is therefore called GNSS location data  8  below. For details in this regard, reference is made to the relevant specialist literature in this regard. 
         [0052]    The fusion sensor  4  is designed—in a manner that is yet to be described—to enhance the information content of the GNSS location data  8  derived from the GNSS signal  12 . This is firstly necessary because the GNSS signal  12  may have a very high signal-to-noise band ratio and may thus be very imprecise. Secondly, the GNSS signal  12  is not always available. 
         [0053]    In the present embodiment, the vehicle  2  also has an inertial sensor  14  that captures driving dynamic data  16  for the vehicle  2 . These are known to include a longitudinal acceleration, a lateral acceleration and also a vertical acceleration and a roll rate, a pitch rate and also a yaw rate for the vehicle  2 . In the present embodiment, these driving dynamics data  16  are used in order to enhance the information content of the GNSS location data  8  and, by way of example, to define the position and the speed of the vehicle  2  on the road  10  more precisely. The more precisely defined location data  18  can then be used by a navigation appliance  20  itself even when the GNSS signal  12  is not available at all, for example in a tunnel. 
         [0054]    To further enhance the information content of the GNSS location data  8 , the present embodiment may optionally also make use of wheel speed sensors  22  that record the wheel speeds  24  of the individual wheels  26  of the vehicle  2 . 
         [0055]    Reference is made to  FIG. 2 , which shows a basic illustration of the fusion sensor  4  from  FIG. 1 . 
         [0056]    The fusion sensor  4  receives the measurement data already mentioned in  FIG. 1 . The fusion sensor  4  is intended to output the more precisely defined location data  18 . The basic concept in this regard is that of juxtaposing the information from the GNSS location data  8  with the driving dynamics data  16  from the inertial sensor  14  into a filter  30  and thus increasing a signal-to-noise band ratio in the location data  8  from the GNSS receiver  6  or the driving dynamics data  16  from the inertial sensor  14 . To this end, although the filter may be in any form, a Kalman filter achieves this object most effectively with comparatively low computational resource requirement. Therefore, the filter  30  below will preferably be a Kalman filter  30 . 
         [0057]    The Kalman filter  30  receives the more precisely defined location data  18  for the vehicle  2  and comparison location data  34  for the vehicle  2 . In the present embodiment, the more precisely defined location data  18  are generated from the driving dynamics data  16  using a strapdown algorithm  36 , which is known from DE 10 2006 029 148 A1, for example. Said data contain more precisely defined position information about the vehicle, but also other location data about the vehicle  2 , such as the speed thereof, the acceleration thereof and the heading thereof. By contrast, the comparison location data  34  are obtained from a model  38  of the vehicle  2  that is first of all fed with the GNSS location data  8  from the GNSS receiver  6 . These GNSS location data  8  are then used in the model  38  to determine the comparison location data  34 , which contain the same information as the more precisely defined location data  18 . The more precisely defined location data  18  and the comparison location data  34  differ only in terms of their values. 
         [0058]    The Kalman filter  30  takes the more precisely defined location data  18  in the comparison location data  34  as a basis for calculating an error budget  40  for the more precisely defined location data  18  and an error budget  42  for the comparison location data  34 . An error budget is intended to be understood below to mean a total error in a signal, which is made up of various individual errors during the recording and transmission of the signal. In the case of the GNSS signal  12  and hence in the case of the GNSS location data  8 , a corresponding error budget may be made up of errors in the satellite orbit, in the satellite clock, in the residual refraction effects and of errors in the GNSS receiver  6 . 
         [0059]    The error budget  40  for the more precisely defined location data  18  and the error budget  42  for the comparison location data  34  are then supplied as appropriate to the strapdown algorithm  36  and to the model  38  for the purpose of correcting the more precisely defined location data  18  or the comparison location data  34 . This means that the more precisely defined location data  18  and the comparison location data  34  are iteratively purged of their errors. 
         [0060]    In the present development, the GNSS receiver  6  receives the GNSS signal  12  from a GNSS satellite  44  that is shown in  FIG. 3 . The GNSS signal  12  sent by this GNSS satellite  44  may be subject to a greater or lesser level of noise, for which reason the model  38  in the present embodiment is extended by a function that evaluates the GNSS signal  12  itself or the GNSS location data  8  derived on the basis of the GNSS signal  12  and then selects the GNSS satellite  44  as source for the GNSS signal  12  on the basis of the evaluation. 
         [0061]    The methods below, illustrated with reference to  FIG. 3 , can be combined with one another as desired, even if they are described individually by themselves. It is thus not necessary to perform just one of the methods for selecting a satellite. The order is also not important initially. 
         [0062]    Reference is made to  FIG. 3 , which shows a first schematic illustration of a vehicle  2  receiving the GNSS signal  12 . 
         [0063]    The vehicle  2  is moving over the road  10  at a speed  46  and an acceleration  48 . In this case, it is intended to be assumed that the vehicle  2  is slowing down, as a result of which the speed  46  and the acceleration  48  are opposite. The speed  46  and the acceleration  48  can be determined from the GNSS signal  12 . 
         [0064]    This can be accomplished by differentiated carrier phase measurement for the GNSS signal  12 , for example. This involves taking into account an alteration in the carrier phase of the GNSS signal  12  over time, said alteration being obtained on the basis of the Doppler effect caused by the moving vehicle  2 . The result obtained for the differentiated phase measurement is a visual direction speed  50 , which can be converted into the speed  46  and the acceleration  48  in a manner that is known to a person skilled in the art. 
         [0065]    Alternatively or in addition, it is also possible to take into account the position of the vehicle on the basis of a code measurement, from which a distance  52  between vehicle  2  and the satellite  44  is detected by means of propagation time detection for the GNSS signal  12 , from which distance the speed  46  and the acceleration  48  can be calculated likewise in a manner that is known to a person skilled in the art. 
         [0066]    The first of the four methods is described below: 
         [0067]    The core concept of the first method is that the speed  46  and the acceleration  48  must satisfy certain physical constraints that cannot be infringed. An ordinary automobile that is not designed for sporty driving will not travel faster than 300 km/h. In addition, it cannot be slowed down at more than 1.2 times acceleration due to gravity. If the GNSS signal  12  yields values that infringe this constraint, the satellite  44  can be eliminated or can be ignored as a source of information for the GNSS location data  8 , as appropriate. 
         [0068]    The second method is described below: 
         [0069]    The second method is based on the consideration that a visual speed  50 , that is to say the movement of the vehicle in the direction of the satellite, and a distance  52  to the satellite  44  can be recorded directly from the GNSS signal  12 . The visual speed  50  and the distance  52  can be reconstructed on the basis of the more precisely defined location data  18  using alternative measurement principles, which means that the visual speed and distance to the satellite  44  that are derived from the GNSS signal  12  can be regarded as expected values for the visual speed  50  and the distance  52  that are transmitted with the GNSS signal  12 . 
         [0070]    The core concept of the second method is thus that deviations between the expected values and the corresponding information from the GNSS signal  12  must correspond to the total noise, that is to say that a deviation that can be calculated using the total noise corresponds to the aforementioned actual deviation. 
         [0071]    This concept will be described below in a nonrestrictive manner with reference to a comparison of the visual speed  50  obtained from the GNSS signal  12 . The second method can alternatively or additionally be performed in the same manner on the basis of the distance  52  to the satellite  44 . 
         [0072]    The measured noise σ GNSS  for the visual speed  50  from the GNSS signal and an uncertainty about the more precisely defined location data  18  and also the uncertainty of all other measurement data used in the reconstructed visual speed  50  and hence the measured noise σ rec  for the expected value add up to form a total measured noise σ meas =σ GNSS +σ rec . In addition, a deviation μ can be determined between the visual speed  50  and the reconstructed visual speed, that is to say the expected value. For the selection of the satellite, a threshold is now stipulated for the extent to which a standard normal deviation obtained from the total measured noise: 
         [0000]      μ stan =√{square root over (σ GNSS +σ rec )}
 
         [0000]    deviates from the deviation μ in the expected value, that is to say the reconstructed visual speed relative to the visual speed  50  measured from the GNSS signal  12 . 
         [0073]    This ensures that the precision of the measured values  50 ,  52  transmitted with the GNSS signal  12  is matched to the precision of the expected value, that is to say the reconstructed visual speed and/or the reconstructed distance to the satellite from the more precisely defined location data  18  from the fusion sensor  4 . 
         [0074]    So that the specified method does not eliminate too many satellites  44 , the threshold used for the deviation μ may be a multiple of the standard deviation μ stand , the multiple being able to be oriented to the desired spread for the selection. 
         [0075]    The third method is described below. 
         [0076]    The basic concept of the fourth method is to be able to determine the location of the satellite  44  and the further satellites  54 ,  56  relative to one another and from the point of view of the vehicle independently of the visual speed  50  and the distance  52 , that is to say using information that is transmitted with the GNSS signal  12 , for example. 
         [0077]    When the location of the satellites  44 ,  54 ,  56  relative to one another is known, the visual speed  50  and the distance  52  to the individual satellites  44 ,  54 ,  56  cannot change arbitrarily. If all satellites are in front of the vehicle  2  in the direction of travel  46 , for example, then all distances  52  to the individual satellites  44 ,  54 ,  56  must become correspondingly shorter. 
         [0078]    In practice, this can be performed using a trigonometric comparison, for example. If the distances  58  of the satellites from one another are known, and the distances from the vehicle  2  to at least two of the satellites  54 ,  56 , then the distance  52  is overdetermined, since it can be reconstructed from the prior information. Nevertheless, the reconstructed distance must correspond to the actual distance  52 , and the quality of the GNSS signal  12  from the satellite  44  can then be assumed to be sufficient for the fusion sensor  4 . 
         [0079]    Ultimately, an overdetermined equation system that needs to be able to be resolved consistently can be set up from the total distances  58  between the satellites  44 ,  54 ,  56  and the measured distances  52  or the visual speeds  50  of the vehicle  2  relative to the satellites  44 ,  54 ,  56  mathematically using known trigonometric dependencies of the satellites  44 ,  54 ,  56  and the vehicle  2  relative to one another. An advantage of this equation system is that the inconsistency can be located and hence can be attributed to a particular satellite  44 ,  54 ,  56 , as a result of which the relevant satellite  44 ,  54 ,  56  and hence the GNSS signal  12  therefrom can be eliminated. 
         [0080]    Within the framework of the fourth method, it is a basic concept that the visual direction speed  50  and the distance  52  between the vehicle  2  and the satellite  44  are recorded using different measurement methods (carrier phase measurement and code measurement). They nevertheless need to correspond to one another. That is to say that if the distance  52  is derived on the basis of time, the visual direction speed  50  must be obtained. Otherwise, there is an error that can be taken as a basis for eliminating the satellite  44 . 
         [0081]    Preferably, the methods for selecting the satellite  44  are performed in the specified order, since firstly the precision checked by the specified methods and secondly the for performing the specified method increase from the first to the fourth method. It is therefore inconvenient from the point of view of computation to include satellites that are totally implausible on the basis of the physical constraints, which satellites can already be eliminated using the first method, in the equation system of the third method. 
         [0082]    While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope and fair meaning of the accompanying claims.