Description

In many modern technical applications, Bluetooth Low Energy (BLE) devices are integrated. With Bluetooth technology, secure and reliable data exchange between adjacent BLE devices can be provided. A transmission range for BLE 5.0 devices in the free field is usually around 100 m with a data rate of 2 Mbit/s.

Besides data exchange, BLE technology can be used for a variety of different applications, such as authentication processes, remote control services, or the like. Furthermore, BLE devices can be used to roughly determine the distance between two BLE devices.

According to first approaches to BLE ranging, a round trip time of a BLE signal between a first BLE device and a second BLE device is measured, divided by 2, and multiplied with the speed of the signal, which is about 3 x 10 ⁸ m/s. Thus, the distance between the two BLE devices can be determined roughly.

A further approach to BLE ranging is to rely on the phase measurements at multiple frequencies in the BLE band to infer the distance. This method is sometimes referred to in the literature as phase-based ranging.

It has been found that for BLE antenna arrays, the measured distance is dependent on the orientation of the antennas of the BLE device. In the US patent 10,499,363 B1 , the angle of arrival calculation is exploited for the purpose of constructively adding the signals from different antenna elements. Firstly, an angle of arrival (AoA) of the signal is determined by sending a plurality of BLE signals and evaluating phase delays between the antennas of the antenna array. According to that document, the error of the distance measurement can be reduced by the means of being able to coherently combine the signals after determining the AoA. It is therefore an object of the present invention to further reduce the error in the distance measurement by BLE devices. In particular, it is the object of the present invention to create a method for determining a distance between a first Bluetooth device and a second Bluetooth device and a Bluetooth system with a first Bluetooth device and a second Bluetooth device, that provides an improved and more accurate distance measurement in a simple and inexpensive manner.

The above object is achieved by the claims. Accordingly, the problem is solved by a method for determining a distance between a first Bluetooth device and a second Bluetooth device with the features of the independent claim 1 and by a Bluetooth system with a first Bluetooth device and a second Bluetooth device with the features of the subordinate claim 10. Further features and details of the invention emerge from the sub claims, the description, and the drawings. Features and details that are described in connection with the method according to the invention naturally also apply in connection with the Bluetooth system according to the invention and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made to each other.

According to a first aspect of the invention, the object is achieved by a method for determining a distance between a first Bluetooth device and a second Bluetooth device. The method comprises:

- Providing a first Bluetooth device with a first antenna device and a second Bluetooth device with a second antenna device, wherein the first antenna device comprises an antenna array of at least two first antennas and the second antenna device comprises at least one second antenna,

- Providing predetermined first antenna characterizing data of the first antenna device, wherein the predetermined first antenna characterizing data defines a dependence of a phase delay of the first antenna device on a first angle of incidence,

- Determining a first angle of incidence between an axis of reference of the first antenna device and the direction of the incoming signal emanating from the second antenna device, - Determining a first correction factor by applying the first angle of incidence on the predetermined first antenna characterizing data,

- Determining a preliminary distance between the first antenna device and the second antenna device by performing a ranging measurement between the first Bluetooth device and the second Bluetooth device by usage of the first antenna device and the second antenna device, and

- Determining a refined distance between the first Bluetooth device and the second Bluetooth device by adjusting the determined preliminary distance according to the determined first correction factor.

Firstly, the first Bluetooth device and the second Bluetooth device are provided. The first Bluetooth device comprises the first antenna device with an antenna array of at least two first antennas. According to the invention, the first antenna device may comprise three or more first antennas. In this case, it is preferred that the three first antennas are located on one straight axis, wherein a middle first antenna is located in the middle between two outer first antennas. Alternatively, the three first antennas may be arranged to form an isosceles triangle or a part of a circular array.

The second Bluetooth device comprises the second antenna device with at least one second antenna. According to the invention, the second antenna device may comprise two or three second antennas. In the case of three second antennas, it is preferred that the three second antennas be located on one straight axis, wherein a middle second antenna is located in the middle between two outer second antennas.

Alternatively, the three second antennas may be arranged to form an isosceles triangle or a part of a circular array.

Furthermore, the predetermined first antenna characterizing data of the first antenna device is provided. Preferably, the predetermined first antenna characterizing data is provided by an electronic data storage medium. The predetermined first antenna characterizing data defines a dependence of a first angle of incidence with a phase delay of the first antenna device. A phase difference is applicable to antenna systems with two or more antennas. When the distance between the two first antennas and the second antenna is different, the signals emitted from the first antennas will be received by the second antenna at different times. Moreover, the signal sent from the second antenna will be received by the two first antennas at different times as well, from which an angle of arrival may be derived. On the other hand, a phase delay is applicable to antenna systems with at least one antenna element. This is emanating from the group delay of the antenna, which can me quantified by measurements using conventional high frequency equipment or simulated using a corresponding electromagnetic simulation tool. The group delay may be angle dependent but also frequency dependent. An angle or frequency dependent group delay introduces a nonlinear phase delay or equivalently an inconstant time delay which is in turn angle dependent. If the total phase delay is used for deriving a ranging result (distance estimation) as is the case typically with phase-based ranging for instance, then this dependency will introduce a ranging error which is dependent on the angle and/or frequency. The predetermined first antenna characterizing data defines the phase delay in dependence on the first angle of incidence. With the predetermined first antenna characterizing data, for each first angle of incidence, the phase delay can be easily determined. In case this phase delay is determined, it can be de-embedded from the total phase for obtaining a corrected phase reading for each Angle of Arrival and/frequency of operating. This leads in turn to a refined ranging calculation with improved accuracy.

Furthermore, the first angle of incidence between the first antenna device and the second antenna device is determined. Preferably, this is performed under the control of a control device of the first Bluetooth device. The first angle of incidence is defined as an angle between the direction of a radio signal - in this case, the radio signal of the second antenna device towards the first antenna device - and an axis of reference of the first antenna device. There are many techniques available for determining the first angle of incidence.

The first correction factor is determined by applying the first angle of incidence on the predetermined first antenna characterizing data. Preferably, this is performed by the control device of the first Bluetooth device. The first correction factor is proportional to the phase delay.

Moreover, the preliminary distance between the first antenna device and the second antenna device is determined. Preferably, this is performed under the control of the control device of the first Bluetooth device. The determination of the preliminary distance is done by performing a ranging measurement between the first Bluetooth device and the second Bluetooth device. For the ranging measurement, the first antenna device and the second antenna device are used.

Finally, the determined preliminary distance is adjusted by taking into account the first correction factor. Preferably, this is performed by the control device of the first Bluetooth device. Thus, the refined distance between the first Bluetooth device and the second Bluetooth device is determined. Furthermore, distances between the antennas and outer skins of the devices, such as housings or the like, can be considered for determining a refined distance between the first Bluetooth device and the second Bluetooth device. Alternatively, the phase maybe first adjusted, then the refined distance may be directly derived. For round-trip time-based ranging, the same calibration and correction technique is applicable. This can be done while translating the angle dependent phase delay to a time delay. For narrowband wireless technologies, a single time delay value per a single carrier frequency may be sufficient since the phase delay is not expected to vary considerably for the modulated signal so to make a significant impact on the calculation.

A method for determining a distance between a first Bluetooth device and a second Bluetooth device according to the invention has the advantage over conventional methods that, in a simple and inexpensive way, the distance between two Bluetooth devices can be determined with improved high accuracy. Moreover, since the first antenna device is already characterized by the predetermined first antenna characterizing data, complex phase delay measurements of the first antenna device do not have to be performed again for each distance determination. Therefore, the computing effort, energy consumption, and time expenditure of the method are comparatively low.

According to a preferred further development of the invention, the method can provide that the predetermined first antenna characterizing data is generated in a workshop by delay measurement for at least two predetermined first angles of incidence and/or simulation for multiple other first angles of incidence. Preferably, the predetermined first antenna characterizing data is generated along the production line of the first Bluetooth device. Alternatively, the predetermined first antenna characterizing data can be generated during an inspection of the first Bluetooth device in a lab environment and/or simulation environment. During this process, the predetermined angle of incidence is fixed for the first Bluetooth device relative to a second Bluetooth device and the respective phase delay for this angle of incidence is measured. Furthermore, a hybrid process using simulation and measurement may be employed to obtain the dependence of the phase delays on the first angles of incidence (and frequencies) and therefore construct a first antenna characterization data set. The basis for the hybrid process for the multiple other first angles of incidence are the measured phase delays and previous first antenna characterizing data, e.g. from laboratory experiment during the development of the first Bluetooth device or during production quality inspections, combined with electromagnetic simulation tool generated data. Moreover, it is preferred that actual data from previous measurements is considered in this process to improve the quality of the hybrid fitted result. This has the advantage that in a simple and inexpensive way, each first antenna device is characterized individually. By these means, production tolerances are considered. At the same time, simulation reduces time and costs.

It is preferred, according to the invention, that the measurement is performed for a first angle of incidence taken from a discrete set of values such as 0° and/or +/- 30° and/or +/- 60° and/or +/- 90°. At a first angle of incidence of 0°, an expected phase difference has a minimum value. At a first angle of incidence of +/-90 ⁰ , an expected phase delay has a maximum value. This has the advantage that in a simple and inexpensive way, with these angles, the specific first antenna device can be characterized sufficiently to obtain a reliable characterization data by combining the measurement with simulation for the other angles and applying some data fitting.

Preferably, predetermined first antenna characterizing data is provided, which defines a dependence of the phase delay of the first antenna device on the first angle of incidence and a frequency, wherein the first correction factor is determined by applying the first angle of incidence and a frequency that will be used for determining the preliminary distance on the predetermined first antenna characterizing data. In other words, the predetermined first antenna characterizing data defines a dependence of a group delay of the first antenna device on the first angle of incidence. A group delay defines a total phase distortion of an antenna system. It is defined as the negative of the derivative phase with respect to the frequency:

Group delay shows how consistent or inconsistent the phase delay is, or in other words, how consistently or not the antenna will introduce a phase delay for the incoming or outgoing signal when comparing the phase delays for the same angles of incidence at different frequencies. This has the advantage that in a simple and inexpensive way, the influence of the signal frequency on the ranging process can be eliminated or at least partly compensated. Thus, the accuracy and reliability of the method according to the invention are further improved.

In a particularly preferred embodiment, the second antenna device comprises an antenna array of at least two second antennas, wherein predetermined second antenna characterizing data is provided, wherein the predetermined second antenna characterizing data defines a dependence of a phase delay of the second antenna device on a second angle of incidence, wherein the second angle of incidence is determined, wherein a second correction factor is determined by applying the second angle of incidence on the predetermined second antenna characterizing data, and wherein a corrected distance between the first Bluetooth device and the second Bluetooth device is determined by adjusting the determined refined distance according to the determined second correction factor. In this setup, the second antenna device can be designed the same as or at least similar to the first antenna device. By performing these steps, ranging errors due to a phase delay of the second antenna device can be eliminated or at least reduced significantly. This has the advantage that, in a simple and inexpensive way, the accuracy and reliability of the method according to the invention are further improved.

Preferably, the first angle of incidence is determined by comparing a phase difference of received signals from the at least two first antennas. Preferably, this phase difference is identified while performing the determination of the preliminary distance. From the phase difference, the first angle of incidence can be calculated directly. If applicable, it is preferred that the second angle of incidence is determined likewise. Alternatively, state of the art direction finding algorithm estimation may be applied based on the collected signals from the two antenna elements. This has the advantage that, in a simple and inexpensive way, the determined first angle of incidence is very accurate.

According to a preferred embodiment of the invention, the ranging measurement for determining the preliminary distance between the first antenna device and the second antenna device is performed by measuring a round trip time of a signal between the first antenna device and the second antenna device. For the time measurement, the sending of a modulated signal is preferred. Alternatively, the round trip phase may be measured. For phase-based measurement the usage of a continuous tone signal or plurality of tone is preferred. This has the advantage that, in a simple and inexpensive way, a reliable and accurate range measurement can be performed.

It is preferred that the ranging measurement for determining the preliminary distance between the first antenna device and the second antenna device is performed by measuring a round trip phase between the first antenna device and the second antenna device. A round trip phase can be measured by sending a continuous tone signal. This has the advantage that, in a simple and inexpensive way, a reliable and accurate range measurement can be performed.

Particularly preferred, the predetermined first antenna characterizing data of the first antenna device is provided as an algorithm and/or a diagram and/or a chart and/or a matrix. The predetermined first antenna characterizing data can be provided in any form, which is suitable for generating the correction factor by applying the determined first angle of incidence and - if applicable and useful - the frequency of the signal of the ranging process for determining the preliminary distance. This has the advantage that in a simple and inexpensive way, the method according to the invention can be further improved.

According to a second aspect of the invention, the object is achieved by a Bluetooth system. The Bluetooth system comprises a first Bluetooth device and a second Bluetooth device. According to the invention, the Bluetooth system is configured for executing a method for determining a distance between the first Bluetooth device and the second Bluetooth device according to the first aspect of the invention.

The Bluetooth system according to the invention has all the advantages that have already been described for a method for determining a distance between a first Bluetooth device and a second Bluetooth device according to the first aspect of the invention. Accordingly, the Bluetooth system according to the invention has the advantage over conventional Bluetooth systems that in a simple and inexpensive way, the distance between two Bluetooth devices can be determined with improved high accuracy. Moreover, since the first antenna device is already characterized by the predetermined first antenna characterizing data, complex phase delay measurements of the first antenna device do not have to be performed again for each distance determination. Therefore, the computing effort, energy consumption, and time expenditure when determining the distance between the first Bluetooth device and the second Bluetooth device are comparatively low. It is preferred, according to the invention, that the first Bluetooth device is configured for being assembled to an automobile or is assembled to the automobile and the second Bluetooth device is assembled to a handheld device. It is preferred that the first Bluetooth device is linked to an on-board computer of the automobile for controlling functions of the automobile. Preferably, the second Bluetooth device is assembled to a remote control of a keyless system of the automobile, e.g. for locking or unlocking the automobile, enabling operation of the automobile, transferring driver preferences to the automobile, or the like. This has the advantage that in a simple and inexpensive way, a distance of a driver of the automobile, who carries the second Bluetooth device, to the automobile can be determined. Thus, specific functions of the automobile can be activated or deactivated with respect to the determined distance.

Further advantages, features and details of the invention unfold from the following description, in which, by reference to drawings, working examples of the present invention are described in detail. Therefore, the features from the claims as well as the features mentioned in the description can be essential for the invention, as taken alone or in an arbitrary combination. In the drawings:

Fig. 1 shows a schematic view of a preferred first embodiment of a Bluetooth system according to the invention,

Fig. 2 shows a schematic view of a preferred second embodiment of a Bluetooth system according to the invention

Fig. 3 shows a schematic view of a preferred third embodiment of a Bluetooth system according to the invention, and

Fig. 4 shows a preferred embodiment of a method according to the invention in a flowchart.

Elements with the same function and effectiveness are denoted in figures 1 to 4 with the same reference numbers.

Fig. 1 shows a preferred first embodiment of a Bluetooth system 7 according to the invention in a schematic view. The Bluetooth system 7 comprises a first Bluetooth device 1 with a first antenna device 3 and a second Bluetooth device 2 with a second antenna device 4. The first antenna device 3 comprises an antenna array of two first antennas 5. The second antenna device 4 comprises a second antenna 6. A first angle of incidence ai is formed between an axis of reference of the two first antennas 5 and the direction of the incoming signal emanating from the second antenna device and a signal path from the second antenna 6 towards the first antenna device 3.

Fig. 2 shows a preferred second embodiment of a Bluetooth system 7 according to the invention in a schematic view. The Bluetooth system 7 comprises a first Bluetooth device 1 with a first antenna device 3 and a second Bluetooth device 2 with a second antenna device 4. The first antenna device 3 comprises an antenna array of two first antennas 5. The second antenna device 4 comprises an antenna array of two second antennas 6. A first angle of incidence ai is formed between an axis of reference of the first antenna device 3, e.g. a perpendicular line to a connection line between the two first antennas 5, and the direction of the incoming signal emanating from the second antenna device 4. A second angle of incidence 02 is formed between an axis of reference of the two second antennas 6 and the direction of the incoming signal emanating from the first antenna device 3 and a signal path from the first antenna device 3 towards the second antenna device 4.

Fig. 3 shows a preferred third embodiment of a Bluetooth system 7 according to the invention in a schematic view. The first Bluetooth device 1 is installed to an automobile 8, the second Bluetooth device 2 is integrated to a handheld device 9 of a keyless system.

Fig. 4 shows a flowchart of a preferred embodiment of a method according to the invention. In a first action 100, a Bluetooth system 7 according to the invention, is provided. In a second action 200, predetermined first antenna characterizing data of the first antenna device 3 is provided on an electronic storage medium. In a third action 300, a first angle of incidence ai between an axis of reference of the first antenna device 3 and the direction of the incoming signal emanating from the second antenna device 4 is determined by a phase difference measurement.

In a fourth action 400, a first correction factor is determined by applying the first angle of incidence ai on the predetermined first antenna characterizing data. In a fifth action 500, a preliminary distance between the first antenna device 3 and the second antenna device 4 is determined. The preliminary distance is determined by performing a ranging measurement between the first Bluetooth device 1 and the second Bluetooth device 2. For the ranging measurement, the first antenna device 3 and the second antenna device 4 are used. In a sixth action 600, a refined distance between the first Bluetooth device 1 and the second Bluetooth device 2 is determined. This is done by adjusting the determined preliminary distance using the determined first correction factor. Alternatively, the correction factor may be applied to the total round trip phase or round trip time, then a refined distance may be obtained.

List of reference signs

1 first Bluetooth device

2 second Bluetooth device

3 first antenna device

4 second antenna device

5 first antenna

6 second antenna

7 Bluetooth system

8 automobile

9 handheld device

100 first action

200 second action

300 third action

400 fourth action

500 fifth action

600 sixth action on first angle of incidence

0(2 second angle of incidence