Phase center compensation for high-precision GNSS antennas

Abstract

The present disclosure provides a method for determining the position of the phase center of an antenna arranged in a mobile device, particularly a vehicle, wherein the antenna is operable to receive satellite signals in a global navigation satellite system, the method comprising: receiving satellite signals from satellites of the global navigation satellite system using the antenna; determining the direction in which the satellite signals are received based on the received satellite signals; and determining the position of the phase center of the antenna based on the direction in which the satellite signals are received and stored correlation information indicating the correlation between the position of the phase center and the direction in which the satellite signals are received.

Description

Background Art

[0001] Today, many mobile devices, including vehicles, use satellite signals from the Global Navigation Satellite System GNSS to determine their position. To this end, signals from multiple satellites are received by the antenna of the mobile device, and these signals are subsequently decoded by the receiver. The receiver determines the position of the antenna based on the received satellite signals. High-precision GNSS systems are able to determine the position of the vehicle antenna with an accuracy in the centimeter or millimeter range. To this end, known high-precision GNSS systems require antennas with stable phase centers. The phase center of an antenna is the point where the conversion from the received wave to the electrical signal appears to occur. However, the phase center depends on the direction from which the incident wave hits the antenna structure. Ideally, this point should be independent of the direction of the incident wave, so that it can be regarded as the position of the antenna within the GNSS. Otherwise, the phase center associated with the signal received from only one satellite, or the average phase center taking into account multiple received satellite signals, can be regarded as the position of the antenna. However, this leads to an inaccurate and unstable determination of the antenna position.

[0002] Typically, antennas that meet the specification of a relatively stable phase center are often too large and expensive to use in conventional manufacturing processes. This results in the use of antenna designs that do not meet the required performance. However, it is still desirable to achieve high positioning accuracy despite the imperfect behavior, i.e., the antenna's phase center is unstable. Summary of the invention

[0003] According to one embodiment among many embodiments, a method is provided for compensating for an offset of a position of a phase center of an antenna relative to a geometric position of an antenna arranged in a mobile device, particularly a vehicle, wherein the antenna is operable to receive satellite signals in a global navigation satellite system, the method comprising: receiving satellite signals from satellites of the global navigation satellite system using an antenna; determining a direction of the received satellite signal based on the received satellite signal; and determining an offset based on the direction of the received satellite signal and stored correlation information indicating a correlation between the position of the phase center and the direction of the received satellite signal.

[0004] The above method is based on the recognition that the phase center of an antenna depends on the direction from which the satellite signal is received. This is particularly applicable to antennas with relatively unstable phase centers, such as antennas used in relatively simple and inexpensive position determination devices. By taking into account the direction from which a mobile antenna (i.e. an antenna without a fixed orientation in a global navigation satellite system) receives the satellite signal, the accuracy of the determined phase center can be improved. In particular, a relatively simple position determination device is enabled to determine the position of the antenna in a highly accurate manner.

[0005] According to one embodiment, determining the offset is further based on the frequency of the received satellite signal, and the stored correlation information further indicates a correlation between the phase center and the frequency of the received satellite signal.

[0006] The phase center of the antenna may also vary depending on the frequency of the received satellite signal. Therefore, taking into account the frequency of the satellite signal further improves the accuracy of the determined antenna position.

[0007] According to one embodiment, the method further comprises determining an orientation of the antenna relative to the satellite; wherein determining the direction of receiving the satellite signal is performed based on the determined orientation of the antenna.

[0008] Therefore, it is taken into account that the mobile antenna can not only perform translational movements, but also rotate around different axes. The rotational movement of the antenna can lead to a change in the direction of the received satellite signal. Since the mobile antenna may not be rotationally symmetric, taking into account the rotational movement further improves the accuracy of the determined phase center.

[0009] According to one embodiment, the orientation of the antenna is determined by an orientation determination device, in particular an orientation determination device arranged in a vehicle.

[0010] An orientation determination device such as an inertial measurement unit, an IMU and / or a GPS device can accurately indicate the orientation of the mobile device or vehicle, in particular independently of the received satellite signals, and can therefore be used to derive the orientation of an antenna arranged in or mounted on the mobile device or vehicle. Thereby, the reliability and accuracy of the determined direction of the received satellite signals is improved.

[0011] According to one embodiment, the orientation of the antenna is determined and stored repeatedly, in particular periodically or continuously.

[0012] Thus, when receiving satellite signals, the method can immediately use data specifying the current orientation of the antenna. Thus, the time required to determine the vehicle's position is reduced.

[0013] According to one embodiment, the method further comprises, before receiving the satellite signal, determining and storing correlation information based on reference signals received from one or more reference directions at a reference geometric position of the antenna.

[0014] The determination of the correlation information may be performed in a laboratory environment, in which the geometrical position and orientation of the antenna are well known, i.e. known with a desired accuracy. The reference satellite signal may be a signal received from an entity simulating a reference satellite in the laboratory environment. The position of the entity may also be known with a desired accuracy. Thus, determining the phase center of the antenna using different known directions of receiving the reference satellite signal relative to the orientation of the antenna and comparing the determined phase center with the known geometrical position of the antenna may result in an accurate determination of an offset between the determined phase center of the antenna and the actual geometrical position of the antenna respectively associated with each of the different known directions.

[0015] According to one embodiment, determining the correlation information is further performed based on one or more frequencies of the received reference signal.

[0016] As indicated above, the frequency of the received reference satellite signal may have a significant impact on the offset of the antenna's phase center relative to the geometric position. Taking into account the frequency of the received reference satellite signal improves the quality of the stored information and thus improves the accuracy of the determined phase center.

[0017] According to one embodiment, determining correlation information includes: using an antenna to receive a satellite signal as a reference signal; determining the position of a reference phase center of the antenna based on the received reference satellite signal; obtaining a reference geometric position of the antenna; and comparing the determined reference phase center with the obtained reference geometric position.

[0018] Thus, the determination of the correlation information may be performed in a reference area rather than in a laboratory environment while receiving satellite signals of available satellites. In the reference area, the geometrical position of the antenna may be well known or may be determined using positioning methods other than methods based on satellite signals. That is, the correlation information may be determined while using an antenna or, for example, a vehicle. Thus, the database containing the correlation information may be regularly updated, thereby increasing the amount of stored correlation information or improving the quality or accuracy of the correlation information and, therefore, improving the accuracy of the determined phase center.

[0019] According to another embodiment, there is provided a positioning system comprising a mobile antenna operable to receive satellite signals in a global navigation satellite system, the positioning system being configured to perform a method according to any one of the preceding claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention may be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0021] Figure 1A flow chart showing a method for compensating for a shift in the position of a phase center of an antenna relative to a geometric position of an antenna arranged in a mobile device;

[0022] Figure 2 A flow chart showing a method for determining the direction from which a satellite signal is received;

[0023] Figure 3 A flow chart showing a method for determining correlation information indicative of a correlation between an offset and a direction in which a satellite signal is received;

[0024] Figure 4 A calibration environment for determining correlation information is shown;

[0025] and Figure 5 A global navigation satellite system including a plurality of satellites and an antenna mounted on a vehicle is shown. DETAILED DESCRIPTION

[0026] Figure 1 A flow chart of a method 100 for compensating for an offset of a position of a phase center of an antenna relative to a geometric position of an antenna arranged in a mobile device is shown. In this example, the mobile device is a vehicle. Alternatively, the mobile device may be a mobile phone or any other mobile electronic device.

[0027] In step 110, a satellite signal is received using an antenna disposed in the vehicle. The satellite signal may be received from a plurality of satellites of a global navigation satellite system GNSS.

[0028] In step 120, the direction of the received satellite signal is determined at least in part based on the received satellite signal. Specifically, a corresponding direction may be determined for one, more than one or each of the received satellite signals. The direction is determined relative to the antenna, i.e., relative to the vehicle comprising the antenna. The determined direction may be a vector indicating an azimuth and / or elevation angle relative to the orientation of the antenna. Therefore, in a constellation diagram in which the position of the satellite from which the satellite signal is received remains constant and the position or orientation of the vehicle relative to the satellite changes, the direction of the received satellite signal, i.e., the azimuth and elevation angle, also changes. The determination of the direction may be performed by a receiver included in the vehicle. Reference is made below to Figure 2 Exemplary methods for determining direction are described in more detail.

[0029] In step 130, the position of the phase center of the antenna associated with the received satellite signals is determined. Specifically, the position of the phase center associated with one or some of the received satellite signals is determined. More specifically, the offset of the position of the phase center of the antenna relative to the geometric position of the antenna is determined. The determination of the position or offset of the phase center is performed based on the determined direction of the received satellite signal.

[0030] The determination of the position of the phase center is further performed based on correlation information stored in a storage device of the vehicle or stored in a storage device accessible to the vehicle. The storage device accessible to the vehicle may represent a server wirelessly coupled to the vehicle. The correlation information includes an indication of a correlation between the position of the phase center of the antenna and the direction in which the associated one or more satellite signals are received. The correlation information may, for example, indicate a displacement or offset of the phase center relative to the geometric center of the antenna or any other geometric position of the antenna based on the direction in which the one or more satellite signals are received. The correlation information may include a compensation value for compensating for the displacement or offset of the phase center relative to the geometric center. The compensation value may be a vector including multiple components to compensate for the three-dimensional displacement or offset.

[0031] Thereby, the dependency of the position or offset of the phase center of the antenna on the direction in which the antenna receives the satellite signal is taken into account and compensated. Thus, the position of the antenna, ie the position of the vehicle in the GNSS, can be accurately determined.

[0032] In addition to the direction of receiving the satellite signal, the position or offset of the antenna phase center may also depend on the frequency of the received satellite signal. Therefore, the correlation information may further indicate the dependence of the position or offset of the phase center on the frequency of the received satellite signal. Therefore, the determination of the position or offset of the phase center associated with the received satellite signal may be further performed based on the determined frequency of the received satellite signal.

[0033] Figure 2 A flow chart of an exemplary method 200 for determining the direction from which a satellite signal is received is shown. Figure 2 In the example, steps 210 and 220 correspond to Figure 1 Steps 110 and 120 of method 100 are shown.

[0034] In step 210, satellite signals are received using an antenna. In step 220, the direction from which the satellite signals are received is determined based on the received satellite signals. Step 220 then includes several sub-steps.

[0035] In sub-step 222, the preliminary position of the antenna is determined. The preliminary position may be determined based on the received satellite signals. For example, in step 210, satellite signals are received from a plurality of satellites, in particular from at least three satellites of the GNSS. The received satellite signals may indicate the position of each of the plurality of satellites and the distance between each of the plurality of satellites and the position of the antenna. The distance between the satellite and the position of the antenna may be derived from the time between the satellite transmitting the signal and the antenna receiving the signal, i.e., from the flight time of the received signal. The preliminary position of the antenna may be determined based on the corresponding positions of the plurality of satellites and the corresponding distances to the plurality of satellites. Specifically, the preliminary geometric position of the antenna or the preliminary position of the vehicle within the GNSS may be determined.

[0036] In sub-step 224, the orientation of the antenna relative to the satellite from which the satellite signal is received is determined. The orientation of the antenna may represent a fixed direction relative to the antenna or the vehicle. The orientation of the antenna may be defined by a vector orthogonal to the longitudinal extension of the antenna. The vector may always point in the direction of travel of the vehicle. That is, if the antenna rotates around one or more independent rotation axes, the orientation of the antenna relative to the satellite changes. In one example, the orientation of the antenna changes when the vehicle is placed on a plane and rotates around a rotation axis perpendicular to the plane. In another example, if the vehicle rotates around a rotation axis parallel to the plane, that is, when the antenna is tilted relative to the plane, the orientation of the antenna changes. Another example may include a situation where the vehicle is traveling up and down or parallel to a slope.

[0037] The orientation of the antenna may be determined by an orientation determination device, such as a device including an inertial measurement unit IMU and / or a global positioning system GPS device. The orientation determination device may be arranged in the vehicle. Additionally or alternatively, the orientation of the antenna may be derived from the movement of the vehicle based on the most recently determined vehicle position. That is, the orientation of the antenna or the vehicle may be determined based on received satellite signals or by other entities arranged in the vehicle.

[0038] In sub-step 226 , the direction in which the satellite signal is received relative to the orientation of the antenna is determined based on the preliminary position of the antenna determined in step 222 and the orientation of the antenna determined in step 224 .

[0039] Based on the determined preliminary position of the antenna, a preliminary direction for receiving satellite signals may be determined. The preliminary direction may be represented by a vector pointing from the preliminary position to one of the satellites. In other words, the preliminary direction may determine the direction for receiving satellite signals in the satellite coordinate system taking into account the position of the satellite and the preliminary position of the antenna or the vehicle. In other words, the preliminary direction is independent of the rotational movement of the antenna performed at the preliminary position.

[0040] Based on the determined orientation of the antenna, the direction of receiving the satellite signal can be determined in the vehicle coordinate system, in which the orientation vector of the antenna always points to the same direction. That is, using the orientation of the antenna in the satellite coordinate system and the direction of receiving the satellite signal in the satellite coordinate system, the direction of receiving the satellite signal can be determined relative to the orientation of the antenna, that is, relative to the vehicle coordinate system.

[0041] Figure 3 A flow chart is shown of a method 300 for determining correlation information indicative of a correlation between a position or offset of a phase center and a direction in which a satellite signal is received.

[0042] In step 310, one or more reference signals are received from one or more reference directions using an antenna. The reference signals may be received from satellites of a GNSS in a reference area. Alternatively, the reference signals may be received in a calibration environment during a calibration process. Figure 4 An example of a calibration environment is described in more detail. The reference direction for receiving a reference signal in a reference area or calibration environment and the frequency of the reference signal may be known. Specifically, the location of the transmitter of the reference signal and the location of the antenna may be known.

[0043] In step 320, the location of the reference phase center associated with the received reference signal is determined. Specifically, the phase center associated with one or more received reference signals is determined. As described above, the determined reference phase center may not be consistent with the location of the antenna.

[0044] In step 330, a reference position of the antenna is obtained. The reference position may be a geometric reference position such as a geometric center of the antenna and may be derived from a reference position of the vehicle. The reference position of the antenna may be obtained from a reference positioning system configured to accurately determine a reference position of the antenna in a reference area, for example based on accurate laser range sensor data. Alternatively, the position of the antenna is a predetermined position in a calibration environment.

[0045] In step 314, the determined position of the reference phase center is compared with the obtained reference position. Based on the comparison, an offset of the reference phase center relative to the reference position of the antenna can be determined. Specifically, a dependency of the position or offset of the phase center on the known direction of receiving the reference signal and the known frequency of the reference signal can be determined. Subsequently, correlation information indicating the determined dependency is stored. Using the stored correlation information, the position or offset of the phase center can be determined based on the received non-reference satellite signal, such as the reference Figure 1 described.

[0046] Figure 4A calibration environment 400 is shown, which includes: a reference signal transmitter 440; a rotatable platform 450; and a vehicle 460 including an antenna 470 placed on the rotatable platform 450. The rotatable platform 450 is arranged parallel to a horizontal plane defined by an independent first coordinate system axis 410 and a second coordinate system axis 420. The rotatable platform 450 can rotate around a rotation axis orthogonal to the horizontal plane. The rotation axis can include a geometric center of the rotatable platform and / or a geometric center of the antenna 470. The rotating platform can further be tilted relative to the horizontal plane defined by the first axis 420 and the second axis 420. The reference signal transmitter 440 can be translated parallel to a third independent coordinate system axis 430, and the third channel 430 can be orthogonal to the horizontal plane.

[0047] When using for example reference Figure 3 While method 300 is described, calibration environment 400 allows for determining correlation information indicative of correlation between the position or offset of the phase center and different directions from which satellite signals are received.

[0048] During the calibration process, the antenna 470 receives a reference signal from the reference signal transmitter 440. The received reference signal may have a different reference frequency. During the transmission of the reference signal and the reception of the reference signal, both the transmitter 440 and the rotatable platform 450 remain at a known fixed position. Based on the known fixed position, the direction in which the antenna receives the reference signal can be clearly determined. The receiver 478 contained in the vehicle can determine the position of the phase center associated with the received reference signal. Since the geometric position of the antenna in the calibration environment is known, the offset of the position of the phase center relative to the geometric position of the antenna associated with the direction of receiving the reference signal and / or the frequency of the reference signal can be determined and stored in a database, matrix or other storage device.

[0049] By rotating and tilting the rotatable platform 450 and by moving the transmitter 440 parallel to the third axis 430, all directions in which signals are received relative to the horizontal plane within the northern hemisphere can be assigned to the position of the phase center or to an offset of the phase center relative to the geometric position of the antenna 470. In other words, each direction defined by an azimuth angle between 0° and 360° and an elevation angle between 0° and 90° relative to the orientation of the antenna or the vehicle can be assigned to a position or offset of the phase center.

[0050] In operation, the phase center determined by the receiver 480 disposed in the vehicle 460 may be affected by other entities disposed in the vehicle 460 or other signals received by the vehicle 460. As in the calibration environment shown, the antenna 470 is calibrated after being mounted on or disposed in the vehicle 460, and these further effects are taken into account during the calibration process.

[0051] and Figure 4Similar to the setup in the calibration environment shown, GNSS satellites can be used to perform antenna calibration. In one example, the vehicle can be located at an accurately known location. In another example, the vehicle can accurately determine its location based on satellite signals received from directions that have been included in the correlation. Subsequently, the vehicle can receive satellite signals from new directions that have not yet been associated with the location of the phase center in the correlation information. Figure 3 and Figure 4 Similar to what is described, the vehicle can then determine the position or offset of the phase center associated with the new direction and add the dependency of the corresponding determined phase center on the new direction to the collation information. In this way, the correlation information can be updated or supplemented during operation.

[0052] Figure 5 A global navigation satellite system 500 is shown including satellites 510, 520 and 530. System 500 also includes an antenna 470 mounted on vehicle 460. As shown, antenna 470 receives satellite signals from each of satellites 510, 520 and 530 from different directions, respectively. In the two-dimensional example shown, each direction, in particular the elevation angle, from which a satellite signal is received depends on an angle 540, which defines the tilt angle of the antenna relative to the surface of the earth. The direction is further defined by the direction in which the vehicle is traveling.

[0053] After correlation information indicating the correlation between the position of the phase center and different directions of received satellite signals has been determined and stored, a receiver 480 included in the vehicle 460 is enabled to take into account the direction of received satellite signals when determining the position of the vehicle or the geometric center of the antenna 470 within the GNSS 500.

Claims

1. A method for compensating for a deviation of a position of a phase center of an antenna relative to a geometric position of an antenna arranged in a mobile device, wherein the antenna is operable to receive satellite signals in a global navigation satellite system, the method comprising: receiving satellite signals from the global navigation satellite system using the antenna; determining a direction from which the satellite signal is received; determining the offset based on the direction from which the satellite signal is received and stored correlation information indicating a correlation between the position of the phase center and the direction from which the satellite signal is received, determining and storing the correlation information based on reference signals received from one or more reference directions at a reference geometric position of the antenna before receiving the satellite signal, Wherein determining the direction of receiving the satellite signal comprises: Determine the preliminary location of the antenna; determining an orientation of the antenna relative to a satellite from which a satellite signal is received; and determining a direction from which satellite signals are received relative to the orientation of the antenna based on the preliminary position of the antenna and the orientation of the antenna; Wherein determining the correlation information comprises: Using the antenna to receive a reference satellite signal as the reference signal; determining a position of a reference phase center of the antenna based on the received reference satellite signal; The position of the referenced phase center is compared to the reference geometric position of the antenna.

2. The method of claim 1 , wherein determining the offset is further based on a frequency of the received satellite signal, and the stored correlation information further indicates a correlation between the phase center and the frequency of the received satellite signal. The method of claim 1 , wherein the orientation of the antenna is determined by an orientation determination device. The method according to claim 3 , wherein the orientation determination device is arranged in a vehicle.

5. The method according to claim 3 or 4, wherein the orientation of the antenna is determined and stored repeatedly, periodically or continuously. The method of claim 1 , wherein determining the correlation information is further based on one or more frequencies of the received reference signal.

7. A positioning system comprising a mobile antenna operable to receive satellite signals in a Global Navigation Satellite System, the positioning system being configured to perform a method according to any preceding claim.

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