Patent Publication Number: US-11022701-B2

Title: Method for determining a position, control module and storage medium

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase Application No. PCT International Application No. PCT/DE2017/200058, filed Jun. 27, 2017, which claims priority to German Patent Application No. 10 2016 212 919.8, filed Jul. 14, 2016, the contents of such applications being incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to a method for determining a position of a unit, in particular a vehicle. Further, the invention relates to an associated control module and an associated data storage medium. 
     BACKGROUND OF THE INVENTION 
     Determining an accurate position on the Earth&#39;s surface is becoming ever more important for vehicles. Vehicle-to-X communication and autonomous driving are mentioned as examples, with such cases typically not only still requiring an approximate location of the vehicle like for navigation purposes but also an accurate localization of the vehicle on the road, i.e., for example, an assignment to a specific lane. 
     According to the prior art, the position of a vehicle is typically determined by means of satellite navigation, with the procedure known as single-point positioning (SPP) being applied in the process. Based on a time-of-flight measurement, following formula (1) is used in this case:
 
ρ m =√{square root over (( x−x   m ) 2 +( y−y   m ) 2 +( z−z   m ) 2 )}+ cδt   r   (1)
 
     In this case:
         m is an index of a respective satellite,   ρ m  is a time-of-flight value or a value calculated from a time-of-flight value,   x, y, z are components of the vector position of the unit or of the vehicle,   x m , y m , z m  are components of the vector position of the satellite with index m,   c is the speed of light, and   δt r  is a clock error of the unit.       

     Typically, four measurements on the basis of four satellites are required for determining the position in this way. 
     If a velocity should be determined, too, it is possible to resort to a method which is known as single-point velocity (SPV) and which is based on Doppler measurements. In particular, following formula (2) is used in this case: 
     
       
         
           
             
               
                 
                   
                     
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     In this case:
         m is an index of a respective satellite,   {dot over (ρ)} m  is a Doppler value or a value calculated from a Doppler value,   x, y, z are components of the vector position of the unit,   x m , y m , z m  are components of the vector position of the satellite with index m,   v x , v y , v z  are components of the velocity of the unit,   v x   m , v y   m , v z   m  are components of the velocity of the satellite with index m,   c is the speed of light, and   δ{dot over (t)} r  is a derivative of a clock error of the unit.       

     Thus, in order to determine the velocity, use is made in this case of Doppler measurements which are based on the signals received from the satellites. However, this also includes the position of the unit that was established by means of SPP. In subsequent data fusion blocks, for example with data that are obtained from inertial sensors, the position established by means of SPP and the velocity established by means of SPV consequently cannot be considered to be uncorrelated. In particular, this is due to the fact that the SPV velocity depends on the SPP position, for example in relation to ionospheric errors or multipath effects. This limits the level of safety and the performance (in particular the accuracy and the availability of the output of the fusion filter). 
     SUMMARY OF THE INVENTION 
     An aspect of the invention is a method for determining a position of a unit which provides an improvement in comparison with methods known from the prior art. Furthermore, an aspect of the invention is a control module, in particular a satellite navigation module, which is configured to carry out such a method. Moreover, an aspect of the invention is a non-volatile, computer-readable data storage medium which contains program code, during the execution of which a processor carries out such a method. 
     According to an aspect of the invention, this is achieved by a method, a control module, and a data storage medium. Advantageous configurations can be taken from the respective dependent claims, for example. The content of the claims is incorporated in the content of the description by express reference. 
     An aspect of the invention relates to a method for determining a position of a unit by means of satellite navigation. In particular, the unit can be a vehicle or a motor vehicle. The method includes the following steps:
         receiving a plurality of satellite signals, namely at least
           a first satellite signal,   a second satellite signal,   a third satellite signal, and   a fourth satellite signal,   
           performing a plurality of Doppler measurements on the satellite signals, in the process producing   a first Doppler value on the basis of the first satellite signal,   a second Doppler value on the basis of the second satellite signal,   a third Doppler value on the basis of the third satellite signal, and   a fourth Doppler value on the basis of the fourth satellite signal,   calculating the position on the basis of the first Doppler value, the second Doppler value, the third Doppler value and the fourth Doppler value, wherein the position is a variable of the calculation.       

     The method is based on the discovery of the inventors of the present application that time-of-flight measurements need not necessarily be used for the purposes of determining the position of a vehicle; instead, Doppler measurements are sufficient. Below, further explanations and examples are provided in relation to precisely how this can work. This is connected to a fundamental departure from methods known from the prior art when performing satellite navigation since, as a matter of principle, the position is initially determined on the basis of time-of-flight measurements in methods according to the prior art. 
     In the method according to an aspect of the invention, the position can be determined precisely independently of time-of-flight measurements, and so the above-described problems with the correlation between position and velocity and the error propagation do not occur. 
     Preferably, all satellite signals are received by different satellites in each case. In particular, this means that each satellite signal is assigned to a respective satellite and that no other satellite signal is assigned to this satellite. This can increase the accuracy. 
     In particular, the position is calculated independently of time-of-flight measurements. In particular, this can mean that no position determined from time-of-flight measurements is included in the calculation. 
     According to a development, further, a derivative of a clock error of the unit is calculated during the calculation step on the basis of the Doppler values used for calculating the position, wherein the derivative of a clock error is a variable of the calculation. Hence, it is also still possible to calculate a derivative of the clock error in addition to the position, said derivative of the clock error possibly being required for other calculation steps or other applications, for example. 
     According to one embodiment, the method is carried out when the unit is stationary on the Earth&#39;s surface. Here, whether the unit is stationary can be identified by means of odometry, for example, in particular by means of a camera or else by other sensor systems, for example by wheel rotational speed sensors, radar sensors or inertial sensors (IMUs). Combinations thereof are also possible. 
     In the case of a unit that is stationary on the Earth&#39;s surface, no velocities, in particular, are required as variables in the calculation as these can be assumed to be zero. This simplifies the calculation and may reduce the number of satellites required to perform the method. 
     It is understood that the embodiments for a unit that is stationary on the Earth&#39;s surface and for a moving unit, as described herein, can also be combined with one another, in particular, and so both embodiments are implemented in a control module or software, for example. Here, different embodiments can be carried out depending on whether or not the unit is currently in motion. 
     Further, according to one embodiment, during the reception step
         a fifth satellite signal,   a sixth satellite signal, and   a seventh satellite signal
 
are received.
       

     Here, further, during the step of performing a plurality of Doppler measurements,
         a fifth Doppler value is produced on the basis of the fifth satellite signal,   a sixth Doppler value is produced on the basis of the sixth satellite signal, and   a seventh Doppler value is produced on the basis of the seventh satellite signal.       

     Here, during the calculation step, the position is also calculated on the basis of the fifth Doppler value, the sixth Doppler value and the seventh Doppler value, wherein the position and components of the velocity vector of the unit are variables of the calculation. 
     Thus, seven satellites or seven satellite signals are used precisely in this case such that the position according to the method according to an aspect of the invention can be calculated in the general case of a unit moving on the Earth&#39;s surface, in which the three vector components of the velocity vector of the unit on the Earth&#39;s surface are variables of the calculation. 
     Typically, the Doppler values are values which indicate a velocity that was established on the basis of Doppler measurements. 
     It is understood that, typically, four satellites or four satellite signals are sufficient in the case of a vehicle that is stationary on the Earth&#39;s surface. 
     According to one embodiment, the method is carried out in the case of a unit moving on the Earth&#39;s surface. By way of example, this can be implemented as just described above. 
     By way of example, the position can be calculated on the basis of the following formula: 
                       ρ   .     m     =           [       (     x   -     x   m       )     ⁢     (     y   -     y   m       )     ⁢     (     z   -     z   m       )       ]             (     x   -     x   m       )     2     +       (     y   -     y   m       )     2     +       (     z   -     z   m       )     2           ⁡     [           (       v   x     -     v   x   m       )               (       v   y     -     v   y   m       )               (       v   z     -     v   z   m       )           ]       +     c   ⁢           ⁢   δ   ⁢           ⁢       t   .     r                 (   2   )               
or a linearization thereof, where
         m is an index of a respective satellite,   {dot over (ρ)} m  is a Doppler value or a value calculated from a Doppler value,   x, y, z are components of the vector position of the unit,   x m , y m , z m  are components of the vector position of the satellite with index m,   v x , v y , v z  are components of the velocity of the unit,   v x   m , v y   m , v z   m  are components of the velocity of the satellite with index m,   c is the speed of light, and   δ{dot over (t)} r  is a derivative of a clock error of the unit.       

     Consequently, it is possible to resort to the known formula in this case, said formula, however, being used in the form where position and velocity are based not on time-of-flight measurements but rather on Doppler measurements. 
     It is understood that, in the case of a unit that is stationary on the Earth&#39;s surface, the components of the velocity, i.e. v x , v y , v z , in particular, can each be set to zero in this formula. 
     According to a development, further, a further satellite navigation signal is received during the reception step, and the method further includes the following steps:
         performing a time-of-flight measurement on the basis of the further satellite navigation signal, producing a time-of-flight value in the process, and   calculating a clock error of the unit on the basis of the position and the time-of-flight value.       

     Hence, the method can also be used to calculate the clock error, which may be required for other applications, for example. 
     In particular, the clock error can be calculated on the basis of the following formula:
 
ρ m =√{square root over (( x−x   m ) 2 +( y−y   m ) 2 +( z−z   m ) 2 )}+ cδt   r   (1)
 
or a linearization thereof, where
         m is an index of a respective satellite,   ρ m  is a time-of-flight value or a value calculated from a time-of-flight value,   x, y, z are components of the vector position of the unit,   x m , y m , z m  are components of the vector position of the satellite with index m,   c is the speed of light, and   δt r  is a clock error of the unit.       

     Thus, in this case, too, it is possible to resort to the known formula. 
     Preferably, the method is carried out using a terrestrially centered and terrestrially fixed coordinate system. This means that a unit that is stationary on the Earth&#39;s surface has a velocity of zero. The positions and velocities of the satellites are preferably also specified in this coordinate system, with these positions and velocities typically being known or being transmitted via various almanac data and ephemeris data to satellite navigation modules or other units that utilize satellite signals. 
     In particular, the unit can be a motor vehicle. However, in principle, the method is also applicable in other units such as, for example, a cellular telephone, a portable satellite navigation appliance, a watercraft or an aircraft. 
     An aspect of the invention further relates to a control module, in particular a satellite navigation module, which is configured to carry out a method according to an aspect of the invention. Moreover, an aspect of the invention relates to a non-volatile, computer-readable data storage medium which contains program code, during the execution of which a processor carries out a method according to an aspect of the invention. In respect of the method according to an aspect of the invention, reference can be made, in principle, to all of the described embodiments and variants. 
     Below, certain aspects or concepts of the invention are described separately, wherein, in principle, the aspects and concepts mentioned below can be combined amongst themselves and also with all other disclosures of this application in any desired way. However, they can also be independent aspects of the invention. 
     According to a first concept, a position of the unit or an antenna position can be implemented purely on the basis of Doppler measurements. 
     At rest, i.e., if v x =0, v y =0, v z =0 applies, which may be identified, in particular, by odometry or other sensor systems, the position solution x, y, z, δ{dot over (t)} r  can be obtained by the aforementioned equation (2) or a linearization thereof, wherein, typically, use can be made of at least four Doppler measurements. 
     In general situations, i.e., if v x ≠0, v y ≠0, v z ≠0 applies or is at least to be expected, the position solution (and velocity solution) x, y, z, v x , v y , v z , δ{dot over (t)} r  can be obtained by the aforementioned equation (2) or a linearization thereof. Here, typically, use can be made of at least seven Doppler measurements. 
     According to a further concept, the position can be obtained on the basis of a mixture of time-of-flight measurement and Doppler measurements. 
     At rest, i.e., if v x =0, v y =0, v z =0 applies, which may be identified, in particular, by odometry and/or other sensor systems, the position solution x, y, z, δ{dot over (t)} r , δt r  can be obtained by the aforementioned equations (1) and (2) or a respective linearization thereof, typically using at least five measurements. Here, the measurements are both time-of-flight measurements and Doppler measurements. 
     In the general case, i.e., if v x ≠0, v y ≠0, v z ≠0 applies, the position solution (and velocity solution) x, y, z, v x , v y , v z , δ{dot over (t)} r , δt r  can be obtained by means of equations (1) and (2) or a linearization thereof, typically using at least eight measurements. Once again, the measurements are both time-of-flight measurements and Doppler measurements. 
     In particular, the following points can be specified as advantages of the method according to an aspect of the invention:
         Doppler measurements are influenced less by ionospheric effects and multipath effects.   Independent solutions are provided both for the position and for the velocity, and so there is no cross-correlation between time-of-flight-based solutions and Doppler-based solutions, no error propagation and a higher accuracy in the case of data fusion.   It is possible to perform a check between SPP and SPV, which further increases the level of safety, in particular in the case of data fusion.   Fewer satellites are required to determine the position if the unit or the vehicle is stationary.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages will be gathered by a person skilled in the art from the exemplary embodiment described below with reference to the appended drawing in which: 
       The FIGURE shows an arrangement for performing the method according to an aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The FIGURE shows a vehicle  10 , which is only illustrated schematically here. In principle, the vehicle  10  is embodied to move on the Earth&#39;s surface. However, this is not discussed in any more detail here. 
     The vehicle  10  comprises a satellite navigation module  20 . This is an electronic control module which contains processor means and data storage means, wherein the data storage means store program code, during the execution of which the processor means carry out a method according to an aspect of the invention. 
     The vehicle  10  further comprises a camera  22 , which is embodied to identify, by way of odometry, whether the vehicle  10  is currently at rest or in motion. Here, the Earth&#39;s surface, which can be seen by the camera  22 , is the reference system. 
     Moreover, the FIGURE illustrates four satellites, namely a first satellite  31 , a second satellite  32 , a third satellite  33  and a fourth satellite  34 . The satellites  31 ,  32 ,  33 ,  34  emit satellite signals, which are received by the vehicle  10  or the satellite navigation module  20  thereof. 
     Here, velocities and positions of the satellites  31 ,  32 ,  33 ,  34  are known to the satellite navigation module  20 , in particular by way of transmitted ephemeris data and almanac data. 
     The FIGURE illustrates, by way of example, the situation in which the vehicle  10  is stationary and consequently four satellites suffice to determine the position according to the intended method. It is understood that typically seven satellites are used for determining the position according to the method according to an aspect of the invention in the general case. 
     Consequently, if the camera  22  identifies that the vehicle  10  is not moving on the Earth&#39;s surface, the satellite navigation module  20  thus establishes respective Doppler values from received satellite signals of the four satellites  31 ,  32 ,  33 ,  34  by way of Doppler measurements. Then, the Doppler values are used to determine the position of the vehicle  10  without the involvement of time-of-flight measurements. In particular, this can be implemented as described further above. Repetition is dispensed with here; rather, reference is made to the explanations made above. 
     Mentioned steps of the method according to an aspect of the invention can be executed in the indicated order. However, they can also be executed in a different order. In one of its embodiments, for example with a specific combination of steps, the method according to an aspect of the invention can be executed in such a way that no further steps are executed. However, in principle, further steps can also be executed, even steps of a kind which have not been mentioned. 
     The claims that are part of the application do not represent any dispensing with the attainment of further protection. 
     If it turns out in the course of the proceedings that a feature or a group of features is not absolutely necessary, then the applicant aspires right now to a wording for at least one independent claim that no longer has the feature or the group of features. This may be, by way of example, a subcombination of a claim present on the filing date or may be a subcombination of a claim present on the filing date that is limited by further features. Claims or combinations of features of this kind requiring rewording can be understood to be covered by the disclosure of this application as well. 
     It should further be pointed out that configurations, features and variants of aspects of the invention that are described in the various embodiments or exemplary embodiments and/or shown in the FIGURES can be combined with one another in any way. Single or multiple features can be interchanged with one another in any way. Combinations of features arising therefrom can be understood to be covered by the disclosure of this application as well. 
     Back-references in dependent claims are not intended to be understood as dispensing with the attainment of independent substantive protection for the features of the back-referenced dependent claims. These features can also be combined with other features in any way. 
     Features that are disclosed only in the description or features that are disclosed in the description or in a claim only in conjunction with other features may fundamentally be of independent significance essential to the invention. They can therefore also be individually included in claims for the purpose of distinction from the prior art.