Position determination device and method

Abstract

Positioning device (10) comprising the following: - a data input circuit (11) configured to receive magnetic field sensor data acquired by a magnetic field sensor (21), - a separation circuit (12) configured to separate the received magnetic field sensor data into low-frequency sensor data including frequencies below a frequency threshold and high-frequency sensor data including frequencies above the frequency threshold, - a fingerprint combination circuit (13) configured to determine a low-frequency magnetic fingerprint from the low-frequency sensor data and a high-frequency magnetic fingerprint from the high-frequency sensor data, and to combine the low-frequency magnetic fingerprint and the high-frequency magnetic fingerprint to obtain a multidimensional magnetic fingerprint, and - a position determination circuit (14) configured to determine the sensor position of the magnetic field sensor by comparing the multidimensional magnetic fingerprint with a magnetic field map (200).

Description

BACKGROUND OF REVELATION

[0001] The present disclosure relates to a positioning device and a corresponding positioning method for determining the position of the device, particularly indoors. The present disclosure further relates to a mobile device, a positioning system, and a non-transitory computer-readable recording medium. DESCRIPTION OF THE STATE OF THE ART

[0002] Many technologies are being researched for indoor positioning (especially location determination and / or navigation). Geomagnetic fingerprinting technology exploits the fact that the magnetic field inside buildings is uniquely distorted by the building's construction (material). The idea is to collect magnetic field maps of the building (offline phase), which can later be used for positioning / location determination (online phase) in such a way that current magnetic field measurements are matched against the mapped magnetic field profile (magnetic fingerprints). The more components a fingerprint contains, the more unique its evaluation; conversely, the fewer components a fingerprint has, the more matches will be found in the fingerprint map. Of course, a magnetic field map of a building can contain many duplicates or at least similar entries.

[0003] The Earth's magnetic field can be represented by a 3-dimensional vector (i.e., it has x, y, and z components), which in principle allows for the generation of 3-dimensional fingerprints. However, since the measurements depend on the orientation of the magnetic field sensor, which often cannot be detected or can only be partially detected (e.g., using an accelerometer), only one magnetic field component (e.g., magnitude) or only two components (e.g., vertical and horizontal components) can be used as a fingerprint in practice.

[0004] The "Background" description provided herein is intended to provide a general presentation of the context of this disclosure. Work by the presently named inventor(s) to the extent described in this Background section, as well as aspects of the description that could not otherwise be considered prior art at the time of filing, are not expressly or impliedly incorporated as prior art to the present disclosure.

[0005] US 2016 / 0245638 A1 discloses a computer-implemented method for determining the position of a mobile device using magnetic beacons, comprising detecting, by a sensor in the mobile device, a magnetic signal having a unique signature associated with a given magnetic beacon; storing the location and an associated signature for each of a plurality of magnetic beacons in a data store of the mobile device, wherein a different signature is associated with each of the magnetic beacons; extracting the unique signature from the magnetic signal; comparing the extracted signature with each of the signatures stored in the data store; identifying a given magnetic beacon from the plurality of magnetic beacons, wherein the signature for the given beacon matches the extracted signature;and retrieving the location for the given magnetic beacon for the data store and correlating the location of the mobile device with the location of the given magnetic beacon;

[0006] US 4654579 A discloses a frequency divider comprising a thyristor connected in series to a main current circuit, means for counting the wave number of alternating current, a trigger or drive circuit for the thyristor associated with the counting means, and means for resetting the counting means. SUMMARY

[0007] One object is to provide a positioning device that further increases the accuracy of positioning. A further object is to provide a corresponding method, a mobile device, and a positioning system, as well as a corresponding computer program for implementing the method and a non-transitory computer-readable recording medium for implementing the method.

[0008] According to one aspect, a position determining device is provided comprising: - a data input circuit configured to receive magnetic field sensor data detected by a magnetic field sensor, - a separation circuit configured to separate the obtained magnetic field sensor data into low-frequency sensor data including frequencies below a frequency threshold and high-frequency sensor data including frequencies above the frequency threshold, - a fingerprint combination circuit configured to determine a low-frequency magnetic fingerprint from the low-frequency sensor data and a high-frequency magnetic fingerprint from the high-frequency sensor data and to combine the low-frequency magnetic fingerprint and the high-frequency magnetic fingerprint to obtain a multi-dimensional magnetic fingerprint, and - a position determination circuit configured to determine the sensor position of the magnetic field sensor by comparing the multi-dimensional magnetic fingerprint with a magnetic field map.

[0009] According to a further aspect, a mobile device is provided comprising: - a magnetic field sensor for collecting magnetic field sensor data at the position of the mobile device, and - a position determining device as disclosed herein for determining the position of the mobile device based on the acquired magnetic field sensor data.

[0010] According to a further aspect, a positioning system is provided comprising: - a plurality of beacons configured to generate time-varying magnetic fields in a frequency range above a frequency threshold and arranged at different locations, and - a position determining device as disclosed herein or a mobile device as disclosed herein for determining the position of the magnetic field sensor.

[0011] According to still further aspects, a computer program comprising program means for causing a computer to perform the steps of the presently disclosed method when the computer program is executed on a computer, and a non-transitory computer-readable recording medium storing therein a computer program product that, when executed by a processor, causes the presently disclosed method to be performed are provided.

[0012] Embodiments are defined in the dependent claims. It is understood that the disclosed method, the disclosed mobile device, the disclosed positioning system, the disclosed computer program, and the disclosed computer-readable recording medium have similar and / or identical further embodiments as the claimed positioning device and as defined in the dependent claims and / or disclosed herein.

[0013] One aspect of the disclosure is to generate an artificial time-varying magnetic field (e.g., near points of interest) that can be acquired together with the geomagnetic field using the same magnetic field sensor, but that can be separated from the geomagnetic field in the frequency domain, i.e., that has one or more frequencies that are generally comparatively low but higher than the frequency of the geomagnetic field, which is generally constant but may slowly change due to the movement of the magnetic field sensor, e.g., when passed by a moving user. The artificial magnetic field significantly increases the size of the feature vector for magnetic field fingerprinting, which in turn drastically reduces the ambiguity in the derived position estimate and thus increases the accuracy of the position determination.

[0014] The foregoing paragraphs have been provided as a general introduction and are not intended to limit the scope of the following claims. The described embodiments, along with additional advantages, are best understood by reference to the following detailed description, taken in conjunction with the accompanying drawings. SHORT DESCRIPTION OF THE DRAWING

[0015] A more complete understanding of the disclosure and many of the attendant advantages thereof will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: Fig. Figure 1 shows examples of recorded magnitude, inclination and azimuth maps of the geomagnetic field in a building, Fig. Figure 2 shows a magnitude map and a spectrum diagram of the magnetic field magnitude obtained in an office building at normal walking speed, Fig. Figure 3 is a diagram illustrating coordinate definitions of a magnetic field vector, Fig. 4 illustrates a schematic diagram of a first embodiment of a position determining device according to the present disclosure, Fig. 5 illustrates a schematic diagram of a first embodiment of a mobile device according to the present disclosure, Fig. 6 illustrates a schematic diagram of a first embodiment of a positioning system according to the present disclosure, Fig. Figure 7 shows diagrams illustrating several solutions for separating signals from different sources in time, Fig. 8 illustrates a schematic diagram of a second embodiment of a mobile device including a second embodiment of a position determining device according to the present disclosure, and Fig. 9 illustrates a flowchart of an embodiment of a method according to the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows, by way of example, the recorded magnitude, the recorded inclination and the recorded azimuth of the static geomagnetic field in a building.

[0017] The magnitude of the geomagnetic field (sometimes referred to as the magnetic field vector) is easily derived from a magnetic field measurement, e.g., from a magnetic field sensor, and the process generally does not involve any additional estimation. Therefore, it is the most reliable information for geomagnetic fingerprinting. Unfortunately, similar magnitude values ​​can often be found at different locations within the building, meaning that a geomagnetic field measurement can be assigned to multiple locations within the building with similar probability if only the magnitude is considered and a corresponding one-dimensional feature vector is used.

[0018] The inclination of the geomagnetic field can be calculated based on the magnetic field measurement and the direction of the Earth's gravitational field, which can be measured by an accelerometer. In addition to gravity, the accelerometer can also measure all other accelerations of the mobile / portable device. Separating the different acceleration sources is difficult and introduces errors in the estimation of the gravitational direction. This, in turn, degrades the estimation accuracy of the inclination of the geomagnetic field. Nevertheless, this information, together with the magnitude of the geomagnetic field, can be used to obtain a two-dimensional feature vector for geomagnetic fingerprinting. Using the two-dimensional feature vector (fingerprint) reduces the number of position ambiguities because the magnitude and inclination of the magnetic field are largely uncorrelated.

[0019] Azimuth information is the most difficult to obtain as an input for geomagnetic fingerprinting. In addition to the gravitational direction, an estimate of the orientation of the mobile / portable device is required, which is prone to estimation errors, particularly due to the inherent drift of gyroscope sensor signal information. As a result, the use of azimuth information for geomagnetic fingerprinting is typically limited to specific applications, such as robot location determination. The sensors are typically attached to the robot body, simplifying the estimation process and thus reducing the number of estimation errors. Often, the z-coordinate is already aligned with the gravitational direction, and the sensor orientation and movement orientation have a fixed relationship, eliminating the need for stride and stride length estimation.

[0020] A comparison made regarding the location accuracy when the feature vector used for geomagnetic fingerprinting contains two or three components of the geomagnetic field shows that the location accuracy drops significantly with a smaller size of the feature vector.

[0021] For geomagnetic fingerprinting, it is generally assumed that the geomagnetic field is constant. Thus, measuring the magnetic field at a fixed position results in a strong DC component, whereas higher frequency components contain only sensor noise. If the position of the magnetic field sensor changes (e.g., due to a user moving while holding a smartphone containing the magnetic field sensor), the measured magnetic field changes over time, and the spectrum of the measured magnetic field becomes broader. Field tests have shown that the relevant spectral components remain within a (unilateral) bandwidth of less than, for example, 3 Hz, even for fast-moving pedestrians. This is because magnetic field fingerprinting is primarily used for indoor location determination, where movement speeds within the range of a walking pedestrian are relevant.In addition, most indoor transportation devices, such as trolleys, conveyor belts, escalators, etc., generally have low movement speeds. On the other hand, the magnetic field sensors available in today's smartphones achieve sampling rates of several tens of Hz, e.g., 50 Hz. Fig. Figure 2 shows an example of the spectrum of a magnetic field signal obtained by a magnetic field sensor of a mobile device while the user is walking in an office building. In this example, the spectral components are well below 1 Hz, indicating a relatively slow walking speed.

[0022] As a result, there is a frequency range of at least 10-20 Hz that can be used to simultaneously obtain artificial magnetic fields along with the geomagnetic field using the same magnetic field sensor (especially a magnetic field sensor such as those typically used in today's smartphones). Such artificial magnetic fields can be generated, for example, by magnetic field beacons, where each beacon generates an artificial magnetic field with a suitable bandwidth (e.g., in the range between 10 and 20 Hz, so that there is no overlap with the frequency band of the geomagnetic field). In one embodiment, the frequency bands of individual artificial magnetic fields (especially artificial magnetic fields present at one or more identical locations) differ from each other, so that, for example, there is no overlap.This makes the artificial magnetic fields more distinctive and allows them to be separated from each other. Preferably, the beacons are placed at selected locations so that at least one artificial magnetic field is available in areas or positions of particular interest, but not necessarily at all positions within an area / building, etc.

[0023] Before describing details of the present disclosure, some definitions should be provided. The term "magnetic field map" refers either to the magnetic field map (comprising magnetic fingerprints) of an entire area, preferably indoors, such as a building, or to a subsection of the magnetic field map of the entire area, e.g., a subsection of the building, such as a floor or wing of the building. A magnetic field map for use in the presently disclosed embodiments, or a suitable subsection of the magnetic field map, comprises magnetic fingerprints of an area surrounding the magnetic field sensor. It can be generated based on a current position of the magnetic field sensor, e.g., a given location estimate, and optionally its assumed confidence (e.g., estimated position accuracy), or by a user downloading a suitable magnetic field map from a server, etc.be selected.

[0024] Magnetic field measurement data can, for example, be magnetic flux densities in the x-, y-, and z-directions of the sensor's local coordinate system for a 3D sensor. An illustration of different representations of the magnetic field vector is shown in Fig. 3 illustrates the coordinate definitions of a magnetic field vector. Example features of the magnetic field vector are magnetic field magnitude m, magnetic field inclination i, magnetic field azimuth a, vertical magnetic field component v, horizontal magnetic field component h, Cartesian magnetic field components (x, y, z), and their combinations. The magnetic field vector can, for example, be represented by the feature horizontal magnetic field component h and vertical magnetic field component v. Alternatively, a representation by the feature magnetic field magnitude m and magnetic field inclination i can be used. For some situations, a further alternative representation by the magnetic field magnitude m, the magnetic field inclination i, and the magnetic field azimuth a, or a representation by the Cartesian components x, y, and z, can be chosen.

[0025] Fig. 4 illustrates a schematic diagram of a first embodiment of a position-determining device 10 according to the present disclosure. The position-determining device 10 includes a data input circuit 11 configured to receive magnetic field sensor data 101 acquired by a magnetic field sensor 21 (not part of the device 10 in this embodiment). The data input circuit 11 may be represented by a data interface, e.g., a data reception or retrieval interface (such as HDMI, USB, network interface, etc.) for receiving or retrieving the magnetic field sensor data 101 directly from the magnetic field sensor 21 or from a storage medium (e.g., a data carrier, an electronic memory, a buffer, etc.; not shown) in which the magnetic field sensor data 101 is stored or buffered.

[0026] The position-determining device 10 further comprises a separation circuit 12 configured to separate the obtained magnetic field sensor data 101 into low-frequency sensor data 102, which includes frequencies below a frequency threshold (which is the sensor data representing the geomagnetic field), and high-frequency sensor data 103, which includes frequencies above the frequency threshold (which is the sensor data representing the one or more artificial magnetic fields). The separation circuit can be implemented in different ways, e.g., using analog or digital filter elements. The frequency threshold is preferably predetermined and fixed, but in other embodiments, can be set and / or changed by a user. In one embodiment, the threshold can be dynamically adjusted, e.g., based on current information about the movement of the magnetic field sensor.Embodiments of the separation circuit and the frequency threshold are explained below. The frequency threshold can also be understood as a cutoff frequency. In other embodiments, the low-frequency sensor data 102 and the high-frequency sensor data 103 can be defined by a frequency band and / or a bandwidth that preferably do not overlap.

[0027] The positioning device 10 further includes a fingerprint combination circuit 13 configured to determine a combined magnetic fingerprint based on the low-frequency sensor data and the high-frequency sensor data. For example, in one embodiment, a low-frequency magnetic fingerprint (which may also be referred to as a "static magnetic fingerprint" or "quasi-static magnetic fingerprint" to describe the approximately time-invariant geomagnetic field) may be determined from the low-frequency sensor data 102, and a high-frequency magnetic fingerprint may be determined from the high-frequency sensor data 103. The low-frequency magnetic fingerprint and the high-frequency magnetic fingerprint may be combined to obtain the combined magnetic fingerprint 104.

[0028] The positioning device 10 further includes a positioning circuit 14 configured to determine the sensor position 105 of the magnetic field sensor 21 by comparing the combined magnetic fingerprint 104 with a magnetic field map 106. The magnetic field map 106 is generally obtained in advance and provided, for example, by a service provider, the owner or operator of a building in which the positioning is to be used, etc., and may be stored in a storage means (not shown; not part of the device 10 in this embodiment) or provided by a server 200 (generally not part of the device 10), for example, via the Internet or another network.For example, a user may download a magnetic field map of a location they wish to visit, or an appropriate magnetic field map may be automatically downloaded or provided based on current position information of the magnetic field sensor 21 (a device including or connected to it) (such as GPS information obtained before entering a building or upon detection of a Bluetooth beacon placed at an entrance to a building, etc.).

[0029] The separation circuit 12 and / or the fingerprint combination circuit 13 and / or the position determination circuit 14 may be implemented in (common or separate) hardware and / or software, e.g., a suitably programmed processor or computer.

[0030] In one embodiment, the separation circuit 12 is configured to separate the obtained magnetic field sensor data 101 into DC sensor data as low-frequency sensor data 102 containing the DC component of the magnetic field sensor data, and AC sensor data as high-frequency sensor data 103 containing AC components of the magnetic field sensor data. In another embodiment, the separation circuit 12 is configured to use a frequency in the range of 0.1 to 10 Hz, in particular in the range of 1 to 5 Hz, as a frequency threshold.

[0031] It should be noted that the bandwidth of each frequency component (which, at the receiver end, actually depends on the speed of movement of the device) can be adjusted accordingly to ensure that the frequency components are sufficiently separated in frequency. The geomagnetic field is quasi-constant. Measuring the geomagnetic field at a fixed location results in a measured signal with a bandwidth of ~0 Hz. However, as soon as the sensor changes its position during the measurement, the observed signal is no longer constant. In fact, the bandwidth of the observed signal increases with the speed of the sensor movement. The same indeed occurs with the transmitted beacon signal (e.g., a sine wave at 10 Hz) when it is received by a moving sensor.The beacon signal observed by the moving sensor exhibits an increased bandwidth (or at least a shifted center frequency). Consequently, the beacon frequencies and receive filters are preferably designed depending on the application (e.g., indoor human location, assuming a certain maximum walking speed).

[0032] In another embodiment, the separation circuit 12 is configured to separate the high-frequency sensor data into two or more high-frequency sensor data pieces, and the fingerprint combination circuit 13 is configured to determine two or more high-frequency magnetic fingerprint pieces from the two or more high-frequency sensor data pieces and combine the low-frequency magnetic fingerprint and the two or more high-frequency magnetic fingerprint pieces to obtain the combined magnetic fingerprint. Hereby, the separation circuit may be configured to separate the high-frequency sensor data into two or more high-frequency sensor data pieces by using a frequency shift of the respective sensor data pieces, e.g., into the baseband, to apply a common low-pass filter and separate the low-frequency frequency component from the other frequency components in the baseband.In one embodiment, a phase-correct carrier modulation can be applied from the center frequency to the frequency of 0 Hz. The combined magnetic fingerprint is then generated at baseband.

[0033] In the context of the present disclosure, the magnetic field map may comprise multiple dimensions, i.e., more components (in particular, separate components for low-frequency sensor data and high-frequency sensor data) than a conventional magnetic field map (which generally includes magnitude, inclination, and azimuth of the magnetic field). In this case, these (additional) components may be used alone or in addition to the generally available components for magnetic field fingerprinting (and for position determination). The present approach is thus backward compatible, even if the magnetic field map comprises more dimensions than the measured fingerprint vector. For this purpose, the magnetic field map preferably comprises all components (i.e., the generally known components and the additional components), e.g., in the form of a multiplexed vector of the magnetic fingerprint.From this multiplexed magnetic fingerprint vector, any desired format of a magnetic fingerprint vector can be derived and used for comparison with a fingerprint vector derived from the measured data.

[0034] Fig. 5 illustrates a schematic diagram of a first embodiment of a mobile device 20 according to the present disclosure. The mobile device 20 may be, for example, a handheld device, a portable device, a mobile phone, a smartphone, a portable phone, a camera, a smartwatch, a vital signs monitor, a laptop, a tablet, smart glasses, or any other portable device that can be carried around by a user. The mobile device 20 includes a magnetic field sensor 21 (e.g., as shown in Fig. 4) for acquiring magnetic field sensor data 101 at the position of the mobile device and a position determining device 10 as disclosed herein (e.g. as shown in Fig. 4) for determining the position of the magnetic field sensor 21 or the mobile device 20 based on the acquired magnetic field sensor data.

[0035] Fig. 6 illustrates a schematic diagram of a positioning system 30 according to the present disclosure. The positioning system 30 comprises a plurality of beacons 31, 32, 33 configured to generate time-varying magnetic fields in a frequency range above a frequency threshold and arranged at different locations. The beacons 31, 32, 33 may be any elements, e.g., coils or inductive loops, that generate a time-varying (dynamic) magnetic field with a frequency above the aforementioned frequency threshold, e.g., above 3 Hz. The plurality of beacons and their arrangement thus enable the determination of the position of the magnetic field sensor 21. The positioning system 30 may thus further comprise a positioning device 10 (e.g., as shown in Fig. 4) and / or a mobile device 20 as disclosed herein (e.g. as shown in Fig. 5) for determining the position of the magnetic field sensor 21.

[0036] According to embodiments of the present disclosure, the magnetic field beacons 31, 32, 33 can be deployed in a building (e.g., at specific points of interest) and generate magnetic fields in a frequency range above the frequency threshold, e.g., above 3 Hz, and below half the (average) sampling rate (e.g., 50 Hz) of the magnetic field sensors typically used in mobile devices. Up to three additional feature vector components (e.g., magnitude, inclination, and azimuth) can be obtained from each additional and separable beacon signal. In this way, the size of the feature vector used for magnetic field fingerprinting can be significantly increased, ambiguities can be minimized, and positioning accuracy can be maximized.

[0037] In the case that two or more magnetic field beacons are visible at a specific position by a mobile device, one embodiment ensures on the beacon side (e.g., scheduling side) that the beacon information can be separated on the mobile device side to maximize the size of the feature vector, e.g., by allocating certain time slots and / or frequencies. In this embodiment, up to three additional feature vector components can be obtained per visible beacon. Possible solutions for separating signals from different sources (e.g., beacons) in time are schematically shown in Fig. Figure 7 illustrates signals S1-S4 (indicating beacon (or source) signals), including frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). Another option (not shown) is spatial multiplexing.

[0038] Fig. 8 illustrates a schematic diagram of a second embodiment of a mobile device 20' including a second embodiment of a positioning device 10' according to the present disclosure. It also illustrates a storage unit 200, e.g., a server, on which the magnetic field map 201 is stored, which may be subjected to a coordinate transformation in a transformation unit 202 before being used by the positioning circuit 14.

[0039] Compared to the first embodiment of the position determining device 10, the position determining device 10' comprises a preprocessing circuit 15 for preprocessing the obtained magnetic field sensor data 101. The preprocessing circuit 15 comprises a resampling circuit 150 for resampling the obtained magnetic field sensor data 101 and / or a calibration circuit 151 for calibrating the resampled magnetic field sensor data 101 and / or an orientation compensation circuit 152 for correcting the orientation in order to align the orientation for comparison with the orientation of the fingerprints stored in the magnetic field map.

[0040] The separation circuit in this embodiment is implemented as a filtering and / or demodulation and / or demultiplexing circuit 12' to separate the multiplexed magnetic fingerprints according to one of the modes described above, i.e., to obtain low-frequency sensor data 102 and high-frequency sensor data 103. In the case of FDMA, it may, for example, comprise a mixer for shifting each frequency component (generated, for example, by a magnetic field beacon) to baseband, followed by a filter that separates the baseband signal from the other frequency components. To separate the geomagnetic field from other frequency components, the mixer frequency would be zero.

[0041] It should be noted that the sequence of one or more blocks of the position determining device may be changed depending on the implementation, e.g., the sensor preprocessing circuit for each individual path may be located after the filtering and / or demodulation and / or demultiplexing circuit 12'.

[0042] The fingerprint combination circuit 13' in this embodiment may include a coordinate transformation circuit 130, 131 in each path, e.g., for converting Cartesian coordinates (xyz) to magnitude and inclination. Furthermore, a combination circuit 132 is provided for combining (e.g., multiplexing) the different fingerprints (FPs) to form the multidimensional fingerprint 104, which is then compared in the position determination circuit 14 with the (multidimensional) magnetic fingerprints stored in the magnetic field map 106 to determine the sensor position of the magnetic field sensor 21 and thus of the mobile device 20'.

[0043] The multidimensional fingerprint 104 depends on the implementation of the combination (e.g., multiplexing) mode and the coordinate transformations. An example can be the following: [m e i e a e m f1 i f1 af1 ]. In this example, the magnitude m / the inclination i and the azimuth a of the Earth's magnetic field (specified by the subscript "e") and a magnetic field beacon operating at a frequency f1 are used to form the combined (e.g., multiplexed) fingerprint vector. In another example, only the magnitude m and the inclination i of the magnetic field are used, and two magnetic field beacons are employed. The combined fingerprint vector in this case can be formed as follows: [m e i e m f1 i f1 m f2 i f2 ]. It is also possible to use other fingerprint dimensions of the combined paths, e.g., [m e i e m f1 m f2 i f2 a f2 ], or to use difference signals as a fingerprint vector, e.g., [m e - m f1 i e - i f2 a e - a f2 ].

[0044] In the previous embodiment, the combining circuit 132 simply combines (e.g., multiplexes) the magnetic fingerprints from the various paths. In another embodiment, the combining circuit 132 may additionally include a weighting factor for the individual fingerprint dimensions (i.e., the number of components of the fingerprint vector). If the reliability of a particular fingerprint component is low, this may be indicated by a low weighting for that fingerprint component. For example, if the distance to a certain magnetic field beacon is high, the artificial magnetic field of that beacon is weakened (compared to the Earth's magnetic field or the artificial magnetic field of other magnetic field beacons) and therefore less reliable.In this case, all components of the combined fingerprint obtained based on the beacon's artificial magnetic field (i.e., based on the high-frequency sensor data or the high-frequency sensor data portion corresponding to the beacon) can be assigned a low weight. In another embodiment, some fingerprint dimensions could be rejected entirely (i.e., by setting the weight to 0). The rejection criterion can be implemented using predefined thresholds.

[0045] In another embodiment, the magnitude of the magnetic field can be obtained directly from its x, y, and z components. Therefore, it is quite reliable information. The inclination of the magnetic field is more difficult to obtain and requires an additional (noisy) sensor input (accelerometer, gyroscope). The estimation errors reduce the reliability of the inclination estimate compared to the magnitude estimate. In yet another embodiment, beacon signals received at high magnetic field intensity are typically more reliable than beacon signals received at low magnetic field intensity.

[0046] In the case of densely deployed beacons and / or limitations in the available frequency bandwidth, the non-separable beacon signals can be additionally phase-aligned with a constant phase offset in another embodiment. Due to its availability in the building, this embodiment proposes, for example, using the AC signal of the low-voltage system (e.g., 230 V, 50 Hz in Germany) as reference frequency and phase information to derive the carrier frequencies (e.g., integer divisors) for the magnetic field beacons. Nevertheless, dedicated reference signals could also be used for synchronization, such as

[0047] The magnetic field beacons 31, 32, 33 used as herein may consist of coils that possess geometric symmetries. The resulting artificial magnetic field then also possesses such symmetries (neglecting distortions caused by the building structure). Such symmetries could reduce the diversity of the artificial magnetic field caused by multiple beacons. Therefore, in one embodiment, the orientation of the magnetic field beacons may be considered in beacon network planning in addition to typical frequency reuse strategies known from communication systems. Furthermore, in one embodiment, assumptions about the speed statistics of the mobile devices may be considered in the beacon network planning strategy, in particular at which locations beacons are arranged and / or what number of beacons is required and / or which frequencies are used.In this way, the available spectrum can be used in an optimal way.

[0048] Furthermore, in one embodiment, the magnetic field of the beacons can be modulated to transmit information (e.g., beacon position, beacon signal strength, beacon ID, etc.). Such information can be used, for example, to further improve the position estimation of the mobile device. For this, the mobile device requires appropriate demodulation circuitry and an enhanced or additional positioning device.

[0049] In addition to using a coil or inductive loop dedicated to generating the artificial magnetic field and / or transmitting information, it is also possible to apply this approach to a coil or inductive loop used for other purposes. For example, the information can be transmitted using a vehicle detection loop. Another example is transmitting the information signal using an audio induction loop (such as hearing loops). If the coil or inductive loop is used for multiple purposes, this system can support both modes (i.e., the first mode, where the coil or inductive loop is used for its original purpose, and the second mode, where the coil or inductive loop is used to generate the artificial magnetic field and / or transmit information) either alternately or simultaneously.Systems that support multiple modes simultaneously can avoid conflicts using one (or a combination of) the separation techniques mentioned above. In the case of hearing loops, this can be achieved with frequency division multiplexing, transmitting the additional information signal at a frequency outside the human audible frequency range. That is, by transmitting the additional information at a frequency below 20 Hz or above 20 kHz, the system can avoid interference with the analog audio signal.

[0050] The arrangement of the magnetic field beacons can change from time to time. For example, magnetic field beacons can be added or removed. For a trade fair, for example, each booth might have its own beacon, which would mean that the artificial magnetic field would be different for each trade fair. Of course, the magnetic field map would have to be redrawn if there were any changes in the arrangement of the magnetic field beacons.

[0051] Fig.9 illustrates a flowchart of an embodiment of a method 70 according to the present disclosure. In a first step S10, magnetic field sensor data detected by a magnetic field sensor is obtained (retrieved or received). In a second step S11, the obtained magnetic field sensor data is separated into low-frequency sensor data including frequencies below a frequency threshold and high-frequency sensor data including frequencies above the frequency threshold. In a third step S12, a combined magnetic fingerprint is obtained from the low-frequency sensor data and the high-frequency sensor data. In a fourth step S13, the sensor position of the magnetic field sensor is determined by comparing the combined magnetic fingerprint with a magnetic field map.

[0052] In summary, the size of the feature vector that can be applied in magnetic field fingerprinting for indoor location determination can be increased according to the present disclosure. This minimizes the problem of ambiguities in position estimation and thus enables the use of magnetic field fingerprinting as a standalone positioning technology (no PDR required), e.g., for indoor locations. The present disclosure generally does not require any additional hardware on the mobile device side.

[0053] Thus, the foregoing discussion merely discloses and describes embodiments of the present disclosure. As will be understood by those skilled in the art, the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not to limit the scope of the disclosure, as well as other claims. The disclosure, including any readily observable variations of the present teachings, in part defines the scope of the foregoing claim terminology such that no inventive subject matter is directed to the public.

[0054] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may perform the functions of several of the subject-matter recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of those measures cannot be used to advantage.

[0055] To the extent that embodiments of the disclosure have been described, at least in part, as being implemented in a software-controlled data processing device, it is understood that a non-transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, a semiconductor memory, or the like, is also considered to represent an embodiment of the present disclosure. Furthermore, such software may be distributed in other forms, such as over the Internet or other wired or wireless telecommunications systems.

[0056] The elements of the disclosed devices, apparatus, and systems can be implemented by appropriate hardware and / or software elements, such as dedicated circuits. A circuit is a structural arrangement of electronic components, including conventional circuit elements, integrated circuits, including application-specific integrated circuits, standard integrated circuits, application-specific off-the-shelf products, and field-programmable gate arrays. Furthermore, a circuit includes central processing units, graphics processing units, and microprocessors programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the hardware described above that executes software.

[0057] The following is a list of further embodiments of the disclosed subject matter: 1. A positioning device comprising: - a data input circuit configured to receive magnetic field sensor data detected by a magnetic field sensor, - a separation circuit configured to separate the obtained magnetic field sensor data into low-frequency sensor data including frequencies below a frequency threshold and high-frequency sensor data including frequencies above the frequency threshold, - a fingerprint combination circuit configured to determine a combined magnetic fingerprint based on the low-frequency sensor data and the high-frequency sensor data, and - a position determination circuit configured to determine the sensor position of the magnetic field sensor by comparing the combined magnetic fingerprint with a magnetic field map. 2. The position determining device as defined in any preceding embodiment, wherein the separation circuit is configured to separate the obtained magnetic field sensor data into DC sensor data as low frequency sensor data containing the DC component of the magnetic field sensor data and AC sensor data as high frequency sensor data containing AC components of the magnetic field sensor data. 3. The position determining device as defined in any preceding embodiment, wherein the isolation circuit is configured to use a frequency in the range of 0.1 to 10 Hz or in the range of 1 to 5 Hz as a frequency threshold. 4. The position determining device as defined in any preceding embodiment, wherein the magnetic field combining circuit is configured to determine a low-frequency magnetic fingerprint from the low-frequency sensor data and a high-frequency magnetic fingerprint from the high-frequency sensor data, and to combine the low-frequency magnetic fingerprint and the high-frequency magnetic fingerprint to obtain the combined magnetic fingerprint. 5. The position determining device as defined in Embodiment 4, wherein the separation circuit is configured to separate the high-frequency sensor data into two or more high-frequency sensor data parts, and wherein the fingerprint combining circuit is configured to determine two or more high-frequency magnetic fingerprint pieces from the two or more high-frequency sensor data pieces and combine the low-frequency magnetic fingerprint and the two or more high-frequency magnetic fingerprint pieces to obtain the combined magnetic fingerprint. 6. The position determining device as defined in embodiment 5, wherein the fingerprint combining circuit is configured to weight and / or select two or more high-frequency magnetic fingerprint pieces from the two or more high-frequency sensor data pieces based on their signal-to-noise ratio and / or energy, and combine the low-frequency magnetic fingerprint and the weighted or selected two or more high-frequency magnetic fingerprint pieces to obtain the combined magnetic fingerprint. 7. The position determining device as defined in Embodiment 5 or 6, wherein the separation circuit comprises a demultiplexing circuit for demultiplexing the high-frequency sensor data into two or more high-frequency sensor data pieces according to a predetermined multiplexing scheme. 8. The positioning device as defined in embodiment 5 or 6, wherein the separation circuit comprises a filter circuit for filtering the high-frequency sensor data into two or more high-frequency sensor data pieces using one or more filter thresholds. 9. The position determining device as defined in any one of embodiments 5 to 8, wherein the separation circuit is configured to separate the high-frequency sensor data into two or more high-frequency sensor data pieces by using a frequency shift of the respective sensor data pieces. 10. The position determining device as defined in any preceding embodiment, further comprising a demodulation circuit for demodulating information modulated onto the radio frequency sensor data. 11. A mobile facility comprising: - a magnetic field sensor for collecting magnetic field sensor data at the position of the mobile device and - a position determining device as defined in embodiment 1 for determining the position of the mobile device based on the acquired magnetic field sensor data. 12. A positioning system comprising: - a plurality of beacons configured to generate time-varying magnetic fields in a frequency range above a frequency threshold and arranged at different locations, and - a mobile device as defined in embodiment 11 for determining the position of the magnetic field sensor. 13. The positioning system as defined in embodiment 12, wherein the beacons are configured to multiplex the time-varying magnetic fields by applying time division multiplexing, frequency division multiplexing, code division multiplexing, or spatial multiplexing. 14. The positioning system as defined in embodiment 12 or 13, wherein the beacons are configured to synchronize the time-varying magnetic fields in time by using a reference signal and to apply a (same or different) constant phase shift to the different time-varying magnetic fields. 15. The positioning system as defined in embodiment 14, wherein the beacons are configured to use the frequency of the mains voltage as a reference signal. 16. The positioning system as defined in any one of embodiments 12 to 15, where the beacons are configured to modulate information onto the time-varying magnetic fields. 17. The positioning system as defined in any one of embodiments 12 to 16, wherein coils of electrical devices are used as the beacons. 18. The positioning system as defined in any one of embodiments 12 to 17, wherein the beacons are configured as detection coils or audio coils or a loudspeaker. 19. A positioning method comprising: - Obtaining magnetic field sensor data acquired by a magnetic field sensor, - Separating the obtained magnetic field sensor data into low-frequency sensor data including frequencies below a frequency threshold and high-frequency sensor data including frequencies above the frequency threshold, - Determining a combined magnetic fingerprint based on the low-frequency sensor data and the high-frequency sensor data and - Determining the sensor position of the magnetic field sensor by comparing the combined magnetic fingerprint with a magnetic field map. 20. A non-transitory computer-readable recording medium storing therein a computer program product that, when executed by a processor, causes the method of embodiment 19 to be performed. 21. A computer program comprising program code means for causing a computer to perform the steps of the method of embodiment 19 when the computer program is executed on a computer.

Claims

[1] Position determining device (10) comprising: - a data input circuit (11) configured to receive magnetic field sensor data detected by a magnetic field sensor (21), - a separation circuit (12) configured to separate the obtained magnetic field sensor data into low-frequency sensor data including frequencies below a frequency threshold and high-frequency sensor data including frequencies above the frequency threshold, - a fingerprint combination circuit (13) configured to determine a low-frequency magnetic fingerprint from the low-frequency sensor data and a high-frequency magnetic fingerprint from the high-frequency sensor data and to combine the low-frequency magnetic fingerprint and the high-frequency magnetic fingerprint to obtain a multi-dimensional magnetic fingerprint, and - a position determination circuit (14) configured to determine the sensor position of the magnetic field sensor by comparing the multi-dimensional magnetic fingerprint with a magnetic field map (200). [2] The position determining device according to claim 1, wherein the separation circuit (12) is configured to separate the obtained magnetic field sensor data into DC sensor data as low frequency sensor data containing the DC component of the magnetic field sensor data and AC sensor data as high frequency sensor data containing AC components of the magnetic field sensor data. [3] Position determining device according to claim 1 or 2, wherein the separation circuit (12) is configured to use a frequency in the range of 0.1 to 10 Hz or in the range of 1 to 5 Hz as a frequency threshold. [4] Position determining device according to one of the preceding claims, wherein the separation circuit (12) is configured to separate the high-frequency sensor data into two or more high-frequency sensor data parts, and wherein the fingerprint combining circuit is configured to determine two or more high-frequency magnetic fingerprint pieces from the two or more high-frequency sensor data pieces and combine the low-frequency magnetic fingerprint and the two or more high-frequency magnetic fingerprint pieces to obtain the multi-dimensional magnetic fingerprint. [5] The positioning device according to claim 4, wherein the fingerprint combining circuit (13) is configured to weight and / or select two or more high-frequency magnetic fingerprint pieces from the two or more high-frequency sensor data pieces based on their signal-to-noise ratio and / or energy, and combine the low-frequency magnetic fingerprint and the weighted or selected two or more high-frequency magnetic fingerprint pieces to obtain the multi-dimensional magnetic fingerprint. [6] A position determining device according to claim 4 or 5, wherein the separation circuit (12) comprises a demultiplexing circuit for demultiplexing the high-frequency sensor data into two or more high-frequency sensor data pieces according to a predetermined multiplexing scheme. [7] Position determining device according to claim 4 or 5, wherein the separation circuit (12) comprises a filter circuit for filtering the high-frequency sensor data into two or more high-frequency sensor data pieces using one or more filter thresholds. [8] Position determining device according to one of claims 4 to 7, wherein the separation circuit (12) is configured to separate the high-frequency sensor data into two or more high-frequency sensor data pieces by using a frequency shift of the respective sensor data pieces. [9] Position determining device according to one of the preceding claims, further comprising a demodulation circuit (12') for demodulating information modulated onto the radio frequency sensor data. [10] Mobile device (20) comprising: - a magnetic field sensor (21) for detecting magnetic field sensor data at the position of the mobile device and - a position determining device (10) according to one of the preceding claims for determining the position of the mobile device based on the detected magnetic field sensor data. [11] Positioning system comprising: - a plurality of beacons (31, 32, 33) configured to generate time-varying magnetic fields in a frequency range above a frequency threshold and arranged at different locations, and - a position determining device (10) according to one of claims 1 to 9 or a mobile device (20) according to claim 10 for determining the position of the magnetic field sensor. [12] Positioning system according to claim 11, wherein the beacons (31, 32, 33) are configured to multiplex the time-varying magnetic fields by applying one of time division multiplexing, frequency division multiplexing, code division multiplexing, and spatial multiplexing. [13] Positioning system according to claim 11 or 12, wherein the beacons (31, 32, 33) are configured to synchronize the time-varying magnetic fields in time by using a reference signal and to apply a constant phase shift to the different time-varying magnetic fields. [14] Positioning system according to claim 13, wherein the beacons (31, 32, 33) are configured to use the frequency of the mains voltage as a reference signal. [15] Positioning system according to one of claims 11 to 14, wherein the beacons (31, 32, 33) are configured to modulate information onto the time-varying magnetic fields. [16] Positioning system according to one of claims 11 to 15, wherein coils of electrical devices are used as the beacons (31, 32, 33). [17] Positioning system according to one of claims 11 to 16, wherein the beacons (31, 32, 33) are configured as detection coils or audio coils or a loudspeaker. [18] Positioning method comprising: - Obtaining magnetic field sensor data detected by a magnetic field sensor (21), - Separating the obtained magnetic field sensor data into low-frequency sensor data including frequencies below a frequency threshold and high-frequency sensor data including frequencies above the frequency threshold, - Determining a low-frequency magnetic fingerprint from the low-frequency sensor data and a high-frequency magnetic fingerprint from the high-frequency sensor data, - Combining the low-frequency magnetic fingerprint and the high-frequency magnetic fingerprint to obtain a multi-dimensional magnetic fingerprint, and - Determining the sensor position of the magnetic field sensor by comparing the multidimensional magnetic fingerprint with a magnetic field map (200). [19] A computer program comprising program code means for causing a computer to perform the steps of the method of claim 18 when the computer program is executed on a computer.

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