Method and device for determining the position of mobile identification transmitters

Abstract

Device for determining the position of a mobile identification transmitter (30) in relation to a vehicle (10), wherein the device has a first antenna (31) arranged in the mobile identification transmitter (30) and at least two antennas (2n) arranged in the vehicle (10), and wherein the device is configured the received field strengths (P 31->2n ) of signals (S2n, S31) transmitted between the first antenna (31) and the at least two antennas (2n) arranged in the vehicle (10); at least a ratio of two different measured received field strengths (P 31->2n ) to form; Each of the at least one formed ratio is to be compared with at least one first threshold and one second threshold; and to determine the attenuation of the signal between the two antennas (2n) arranged in the vehicle (10) by means of a signal transmitted between them, wherein the position of the mobile identification transmitter (30) is determined by means of of the comparison of at least one ratio with at least one first and second threshold is determined.

Description

[0001] The invention relates to a method and a device for determining the position of mobile identification transmitters, in particular in a vehicle.

[0002] Keyless vehicle access and start systems such as the Passive Start Entry (PASE) system are automatic systems that unlock a vehicle without actively using a car key and start it simply by pressing the start button. A transmitter unit is installed in the vehicle and sends out signals. These are, for example, electromagnetic signals in the LF (low frequency) or HF (high frequency) range. These signals are received by a transponder unit when it is near the vehicle and then evaluated and / or further processed. Following evaluation and / or further processing in the transponder unit, corresponding response signals can be sent back to the transmitter unit in the vehicle. The response signals are sent, for example, in the UHF frequency band and can be evaluated by an evaluation unit in the vehicle.If a response signal is recognized as correct and the transponder unit is thus identified as belonging to the vehicle, the vehicle can be unlocked or started. Other functions in the vehicle can also be controlled in this way.

[0003] In some cases, the position of the transponder unit is also determined. Allowing and / or enabling a function may then also depend on the position of the transponder unit. For example, starting the vehicle can only be enabled if the transponder unit is detected as being inside the vehicle.

[0004] There are various known ways of determining the position of a transponder unit. In newer systems, the functions of the transponder unit (vehicle key) are increasingly being taken over by portable electronic devices, such as smartphones. Signals according to a Bluetooth standard, such as the Bluetooth Low Energy (BLE) standard, are often used for communication between the portable electronic devices and the vehicle. The known methods for determining positions cannot simply be applied to communication via Bluetooth because, in contrast to LF signals, signals according to a Bluetooth standard can be significantly attenuated, for example due to shadowing effects (e.g. by the user's body). Due to shadowing, position determination using conventional methods when using Bluetooth devices can be very inaccurate.

[0005] The document DE 10 2011 079 052 A1 discloses a method for validating a vehicle-to-X message, in which the vehicle-to-X message is received by an antenna arrangement of a vehicle-to-X communication device having at least two antenna elements. Due to different reception characteristics of the at least two antenna elements, an electromagnetic field strength of the vehicle-to-X message is picked up by the at least two antenna elements with different power densities. The vehicle-to-X message includes an absolute position of a transmitter, and an absolute position of a receiver is determined based on a global satellite navigation method and / or based on a map comparison. A first relative position of the transmitter to the receiver is calculated from the absolute position of the receiver and the absolute position of the transmitter.On the receiver side, a second relative position of the transmitter to the receiver is calculated from the ratio of the power densities received by the at least two antenna elements of the antenna arrangement or read out from a reference map, wherein a comparison of the first relative position with the second relative position is carried out and if it is detected that the first relative position corresponds as closely as possible to the second relative position, the vehicle-to-X message is validated and / or if it is detected that the first relative position deviates as far as possible from the second relative position, the vehicle-to-X message is discarded.

[0006] Document CN 1 02 045 122A discloses a method for solving the problem of adjacent channel interference by co-locating multiple antennas and is applicable to parallel ETC (Electronic Toll Collection) antenna systems. It comprises the following steps: In a first step, scaling points are distributed. In a second step, distances between the scaling points and a first and second antenna are calculated. In a third step, fundamental link transmission losses of the first antenna and the second antenna relative to the scaling points are determined. In a fourth step, an uplink signal strength value of each scaling point is theoretically calculated, which is received by a first antenna receiver. In a fifth step, an uplink signal strength value of each scaling point is theoretically calculated, which is received by a second antenna receiver.In a sixth step, the uplink signal strength value of each scaling point received by the first antenna receiver is adjusted by actual measurement to obtain a reference value. In a seventh step, the uplink signal strength value of each scaling point received by the second antenna receiver is adjusted to obtain a reference value. Furthermore, in an eighth step, the position of a vehicle is determined by adjusting it to the reference values.

[0007] The object of the invention is to provide an improved device and an improved method for determining the position of mobile identification transmitters (portable electronic devices).

[0008] This object is achieved by a device according to claim 1 and a method according to claim 12. Embodiments and developments of the inventive concept are the subject of dependent claims.

[0009] A device for determining the position of a mobile identification transmitter with respect to a vehicle has a first antenna arranged in the mobile identification transmitter and at least two antennas arranged in the vehicle. The device is designed to determine the received field strengths of signals transmitted between the first antenna and the at least two antennas arranged in the vehicle, to form at least one ratio from two different measured received field strengths, and to compare each of the at least one formed ratio with at least one first threshold and a second threshold. Based on a signal transmitted between two antennas arranged in the vehicle, an attenuation of the signal between the two antennas is determined. The position of the mobile identification transmitter is determined based on the comparison of the at least one ratio with the at least one first and second threshold.

[0010] By creating ratios of different reception field strengths, signal interference or specific characteristics of the mobile identification transmitter in use can be compensated. Specific characteristics can, for example, affect the type or orientation of the antennas used. This makes position determination more accurate and less susceptible to interference.

[0011] Of the antennas arranged in the vehicle, at least one antenna can be arranged in the interior of the vehicle and at least one antenna can be arranged in the exterior of the vehicle.

[0012] Alternatively or in addition to the antennas arranged in the interior and exterior of the vehicle, at least one antenna can be arranged in the area of ​​the hood of the vehicle and at least one antenna in the area of ​​the trunk of the vehicle and / or one antenna can be arranged in the area of ​​the right side of the vehicle and at least one antenna in the area of ​​the left side of the vehicle and / or two antennas can be arranged at two diagonally opposite corners of the vehicle.

[0013] This results in positions with particularly high contrast, which can improve the accuracy of positioning.

[0014] The ratio can be calculated from two reception field strengths, which refer to antennas in the vehicle that are more than 10 cm, more than 50 cm, more than 1 m, or more than 2 m apart. This also results in antenna positions with the highest possible contrast, which in turn can improve the accuracy of positioning.

[0015] The signals can be sent from the antennas arranged in the vehicle to the mobile identification transmitter, and the mobile identification transmitter can be configured to determine the reception field strengths of the received signals. Alternatively, however, it is also possible to send the signals from the first antenna arranged in the mobile identification transmitter to the antennas arranged in the vehicle. In this second case, the device can further comprise a control unit that is connected to the antennas arranged in the vehicle and that is configured to determine the reception field strengths of the received signals. Position determination can thus take place both in the vehicle and in the mobile identification transmitter.

[0016] The same thresholds can be used for each of the formed ratios. Alternatively, however, it is also possible to use different thresholds for at least two of the formed ratios. Different zones can be defined in and / or around the vehicle in which a mobile identification transmitter can be detected. The thresholds can depend on the size and shape of the desired zones.

[0017] The reception field strength with respect to an antenna arranged in the vehicle depends on the distance of the mobile identification transmitter to the corresponding antenna.

[0018] By comparing each ratio with a first threshold and a second threshold, the size and shape of the zones can be changed.

[0019] The at least one threshold can then depend, for example, on the specific damping.

[0020] A mobile identification transmitter has a first antenna, and a vehicle has at least two antennas. A method for determining the position of the mobile identification transmitter with respect to the vehicle comprises determining the received field strengths of signals transmitted between the first antenna and the at least two antennas arranged in the vehicle, forming at least one ratio from two different measured received field strengths, comparing each of the formed ratios with at least a first threshold and a second threshold, transmitting a signal between two antennas arranged in the vehicle, and determining an attenuation of the signal transmitted between the antennas. The position of the mobile identification transmitter is determined based on the comparison of the ratios with the at least one first and second threshold.

[0021] The invention is explained in more detail below with reference to the figures of the drawing, in which identical or similar elements are provided with the same reference numerals. It shows: Fig. 1 shows a sketch of the principle of a keyless vehicle access and start system, Fig. 2 shows a sketch of different zones in a vehicle and the principle of a system for determining the position of a mobile identification transmitter, Fig. 3 shows a block diagram of a system for determining the position of a mobile identification transmitter according to an embodiment of the invention, Fig. 4 shows a schematic representation of a system for determining the position of a mobile identification transmitter according to an embodiment of the invention, and Fig. 5 shows a flowchart of a method for determining the position of a mobile identification transmitter according to an embodiment of the invention.

[0022] Fig. Figure 1 shows a schematic representation of the principle of a keyless vehicle access and start system. A transmitting unit 20 is arranged in the vehicle 10 and is designed to transmit signals. These signals are received by a transponder unit or a mobile identification transmitter 30 when the latter is located near the vehicle 10, and are then evaluated and / or further processed. Conventional transponder units are arranged, for example, in a vehicle key. In newer systems, however, more and more portable electronic devices (mobile identification transmitters) are taking over the functions of conventional vehicle keys. Portable electronic devices can be, for example, smartphones, tablets, laptops, smartwatches, or the like. Following evaluation and / or further processing in the mobile identification transmitter 30, corresponding response signals can be sent back to the transmitting unit 20.The response signals can be generated in the vehicle 10 by one, in . Fig. 1 evaluation unit not shown.

[0023] To receive the signals transmitted by the transmitting unit 20, the mobile identification transmitter 30 must be within a certain radius of the vehicle 10, as the transmitted signals only have a limited range. This radius can be 10 meters, for example. However, this is merely an example. The range can also be greater or lesser.

[0024] The transmitting unit 20 can transmit signals continuously or only in response to a specific event. Such an event could be, for example, touching or pressing a door handle or a vehicle start button. Any other suitable type of event is also possible. If the mobile identification transmitter 30 sends a correct response signal to a signal received from the transmitting unit 20, the vehicle 10 is unlocked.

[0025] For some functions in the vehicle 10, the current position of the mobile identification transmitter 30 also often plays a role. For example, it may be necessary for the mobile identification transmitter 30 to be located inside the vehicle 10 in order for the vehicle 10 to be started. For this purpose, different zones A, B, C, D can be defined in or around the vehicle 10. This is illustrated by way of example in Fig. 2. A first zone A is located, for example, in the interior of the vehicle 10. Further zones B, C, D can be defined, for example, in the area in front of the driver's door, the passenger door or the trunk. Fig. The zones A, B, C, and D shown in Figure 2 are merely examples. In the simplest case, for example, a first zone is defined in the interior of the vehicle 10 and a second zone within a specific radius around the vehicle 10. However, both the interior and the exterior of the vehicle 10 can also be divided into more than one zone. For example, one zone can be defined in the area of ​​the driver's seat, and further zones can be defined in the area of ​​the front passenger seat, the rear seat, and the parcel shelf. The various zones can differ from one another in shape and size.

[0026] In which of the zones A, B, C, D a mobile identification transmitter 30 is located can be detected using one or more antennas 21, 22, 23 in the vehicle 10. In Fig. 2, three antennas 21, 22, 23 are shown. However, in principle, more or fewer antennas can be arranged at any suitable positions in the vehicle 10. The antennas 21, 22, 23 can be connected to a control unit 40. The control unit 40 can be configured to transmit signals via one or more of the antennas 21, 22, 23. Signals received by the antennas 21, 22, 23 can in turn be sent to the control unit 40 for further evaluation. For example, the antennas 21, 22, 23 arranged in the vehicle 10 can transmit signals that are received by the mobile identification transmitter 30. The mobile identification transmitter 30 can measure the reception field strength of each of the received signals. The reception field strength of a signal decreases with increasing distance from the transmitting antenna.Since the position of the antennas in the vehicle 10 is known, the distance to the respective antennas 21, 22, 23 and thus the position of the transponder unit 30 with respect to the vehicle 10 can be determined based on the received signal strengths of one or more signals received at a time.

[0027] In principle, it is also possible for the mobile identification transmitter 30 to transmit signals and for each of the antennas 21, 22, 23 to determine the received field strength of these signals. In this case, the mobile identification transmitter 30 thus serves as a transmitter, and the antennas 21, 22, 23 in the vehicle 10 as receivers. The further the respective antenna 21, 22, 23 is from the mobile identification transmitter 30, the lower the measured received field strength of the signals. From the measured received field strengths, the distance of the mobile identification transmitter 30 to each of the antennas 21, 22, 23 can then be deduced. If the distance to each of the antennas 21, 22, 23 is known, the position of the mobile identification transmitter 30 relative to the vehicle 10 can be deduced.

[0028] However, it is often not absolutely necessary for the exact position of the mobile identification transmitter 30 to be known. It is generally sufficient to detect which of the zones A, B, C, or D the mobile identification transmitter 30 is located in. For example, it can be detected that the mobile identification transmitter 30 is located in zone A in the interior of the vehicle 10 if the reception field strength measured with respect to an antenna located in the vehicle 10 exceeds a certain threshold.

[0029] The signals transmitted by the antennas 21, 22, 23 or the mobile identification transmitter 30 can be interfered with by other devices in the vehicle. These can be either uniform interferers, e.g. mobile radio devices or radio broadcasting devices, which permanently overlay the signals from the antennas 21, 22, 23, or so-called peak interferers, e.g. ignition pulses which briefly overlay the signals from the antennas 21, 22, 23. In addition, the measured received field strength depends on a wide variety of other factors. These can be, for example, shadowing effects, which can be caused by the vehicle body or the user's body. Nowadays, as already described above, classic vehicle keys are increasingly being replaced by smartphones or other portable electronic devices or mobile identification transmitters, which can take over the key function.Communication between the mobile identification transmitter and the vehicle often takes place via Bluetooth or WiFi.

[0030] However, different electronic devices (e.g., different smartphone types) can have different characteristics (e.g., different antenna types, different antenna orientations, etc.), which can cause the absolute measured reception field strength of the transmitted signals to vary depending on the type of electronic device used. Particularly with measured reception field strengths in the GHz range, very large fluctuations can occur. This can result in the positioning described above being incorrect, and the mobile identification transmitter 30 may be detected in the wrong zone A, B, C, or D. The fluctuations in the measured absolute values ​​can, for example, be in the range of 20 dB (factor 100) or more.

[0031] The present invention is intended to prevent or minimize these disadvantages.

[0032] Fig. Figure 3 schematically shows a system for determining the position of a mobile identification transmitter according to one embodiment of the invention. An electromagnetic signal S21, S22, S23 is transmitted via a plurality of antennas 21, 22, 23 in the vehicle. The signals transmitted between the antennas 21, 22, 23 and the mobile identification transmitter 30 can, for example, be signals according to a Bluetooth standard, for example, the Bluetooth Low Energy (BLE) standard.

[0033] Bluetooth is an internationally standardized data interface. For example, data or files can be exchanged between two devices, or music and voice can be transmitted via Bluetooth. Bluetooth devices transmit at a frequency of 2.4 GHz and enable data transmission over a short range, typically less than 50 meters. Various Bluetooth standards are currently known, for example, Bluetooth 1.0 and 1.0B (1999), Bluetooth 2.0 + EDR (2004), or Bluetooth 4.0 (2009). For the purposes of the present invention, it is not important which standard the vehicle 10 and the mobile identification transmitter 30 use to communicate with each other. However, to enable communication, it is generally necessary for two Bluetooth-enabled devices between which a connection is to be established to communicate using the same standard. However, some of the standards are compatible with each other.

[0034] Bluetooth devices typically consume a relatively high amount of power. However, power consumption is often critical, especially in vehicles and the associated mobile identification devices (e.g., smartphones). Therefore, so-called Bluetooth Low Energy (BLE) devices are increasingly found in vehicles and external devices. Bluetooth Low Energy is often also referred to as Bluetooth Smart. BLE is based on classic Bluetooth technology, but has significantly lower power consumption and is generally more cost-effective. When BLE devices are used in a mobile identification device (30), the battery of the mobile identification device (30) (or the electronic device) is less stressed than with conventional Bluetooth devices.

[0035] However, the signals transmitted between antennas 21, 22, 23 and the mobile identification transmitter 30 can also be signals according to the Wi-Fi standard, for example. Any other type of signal is also possible.

[0036] In Fig. Figure 3 shows three antennas 21, 22, and 23 arranged in the vehicle. However, this is merely an example. In principle, a number of n antennas can be used, with n ≥ 2. However, the larger the number of antennas 2n, the greater the accuracy of the position determination, as described below.

[0037] The mobile identification transmitter 30 has a further antenna 31. The electromagnetic signals S2n can be received via this further antenna 31. The reception field strengths P 31->21 , P 31->22 , P 31->23of the individual signals S2n. These are, for example, a first reception field strength P 31->21 a first signal S21 which is sent from a first antenna 21 in the vehicle to the mobile identification transmitter 30, a second reception field strength P 31->22 a second signal S22 which is sent from a second antenna 22 in the vehicle to the mobile identification transmitter 30 and has a third reception field strength P 31->23 a third signal S23 which is sent from a third antenna 23 arranged in the vehicle to the mobile identification transmitter 30. In principle, the mobile identification transmitter 30 has a greater reception field strength P 31->2n of a signal S2n is detected, the closer it is to the corresponding antenna 2n. The determined value of the received field strength P 31->2nis thus dependent on the distance between the corresponding antenna 2n and the mobile identification transmitter 30. Inaccuracies in the measurement, which are caused, for example, by the type of electronic device used as the mobile identification transmitter 30, occur when measuring each of the reception field strengths P 31->2n on.

[0038] Instead of an absolute measurement of the reception field strengths P 31->2n and a comparison of each of the reception field strengths P 31->2n with one or more threshold values ​​(absolute value), the measured values ​​of at least two of the reception field strengths P 31->2n According to the invention, they are related to each other. Uncertainties that occur equally in all measurements appear in both the numerator and the denominator and are thus compensated.

[0039] This is done with reference to Fig. 4 using the example of an arrangement with two antennas 21, 22 in the vehicle. In the example in Fig. 4, two antennas 21, 22 are arranged in the vehicle. For example, one antenna 21 can be arranged in the interior of the vehicle, and a second antenna 22 can be arranged outside the vehicle, for example on the vehicle roof. If a mobile identification transmitter 30 (or a portable electronic device) with an antenna 31 is located near the vehicle, the mobile identification transmitter can receive signals from both antennas 21, 22 on the vehicle and determine the corresponding reception field strengths P 31->21 , P 31->22 of these signals. These reception field strengths P 31->21 , P 31->22 are then put into a relationship with each other and this relationship is compared with a threshold, e.g.: P31→21 / P31→22>Threshold

[0040] If the mobile identification transmitter 30 is located as in Fig. 4 shown as an example within the vehicle (zone A, cf. Fig. 2), the reception field strength P measured with respect to the first antenna 21 in the vehicle is 31->21 significantly greater than the reception field strength P measured with respect to the second antenna 22 outside the vehicle 31->22, assuming that the signals are each transmitted with the same strength. The signals transmitted by the second antenna 22 are attenuated, for example, by the vehicle roof, while the signals from the first antenna 21 arrive at the mobile identification transmitter 30 almost unattenuated. This means that in this case, the ratio of the two values ​​shown above results in a relatively large value (e.g., >1). The threshold can, for example, be selected as 1 (threshold = 1). However, any other value greater or less than 1 is also possible (e.g., threshold = 0.5, threshold = 2, or threshold = 3). The selected threshold depends, for example, on the shape and size of the various zones and on the arrangement of the antennas 21, 22 in the vehicle.

[0041] If the mobile identification transmitter 30 is located outside the vehicle, for example, Fig. 4, the reception field strength P measured with respect to the second antenna 22 outside the vehicle 31->22 significantly greater than the reception field strength P measured with respect to the first antenna 21 in the vehicle 31->21 In this case, the signals from the first antenna 21 would be attenuated by the vehicle body, while the signals from the second antenna 22 would arrive at the mobile identification transmitter 30 essentially unattenuated. Thus, in the example described above, the ratio of the two values ​​would be relatively small (e.g., <1).

[0042] In the same way, various zones in and around the vehicle can be defined. For example, the first antenna 21 could be mounted on the driver's door (e.g., left side), while the second antenna 22 could be mounted on the opposite side of the vehicle on the passenger door (e.g., right side). If a user with the mobile identification transmitter 30 were to stand exactly in the center behind the vehicle, the resulting ratio of the reception field strengths P 31->21 / P 31->22 of almost 1, assuming that the signals are transmitted with the same strength. The further the mobile identification transmitter 30 moves towards the driver's door, the greater the reception field strength P measured with respect to the first antenna 21 would be. 31->21 and the smaller the reception field strength P measured with respect to the second antenna 22 31->22. The calculated ratio would thus yield increasingly larger values. For example, it could be specified that the mobile identification transmitter 30 is located in a zone B (see Fig. 2) is detected in front of the driver's door when P31→21 / P31→22>2.

[0043] Another possibility, for example, is to mount one antenna on the hood and another antenna in the trunk area, and then to relate the measured reception field strengths to each other and compare them with a suitable threshold. It is also possible, for example, to mount two antennas at diagonally opposite corners of the vehicle 10. For example, one antenna at the right front corner and the other antenna at the diagonally opposite left rear corner.

[0044] In the simplest case, two antennas 21, 22 are arranged in or on the vehicle. However, any other number n of antennas (with n≥2) is also possible. The received field strength measured with respect to one antenna can be compared to only one other received field strength, or even to several different received field strengths.

[0045] For example, three different antennas 21, 22, 23 could be arranged in the vehicle. A first antenna 21 can be located in the interior of the vehicle, a second antenna 22 on the driver's door, and a third antenna 23 on the passenger door. The mobile identification transmitter 30 could, for example, be detected in one of the zones if the following applies: P31→21 / P31→22>Threshold_1, AND P31→21 / P31→23>Threshold_2, AND P31→22 / P31→23>Threshold_3.

[0046] For example, as described above, different antennas can be arranged at particularly contrasting positions in the vehicle. For example, different antennas are not arranged in close proximity to one another. The distance between two antennas can be, for example, more than 10 cm, more than 50 cm, more than 1 m, or more than 2 m. Two antennas can also be arranged in close proximity to one another, for example, if one antenna is located inside the vehicle while the other antenna is located on the outside of the vehicle. Examples of high-contrast positions include interior / exterior, right / left, front / rear, diagonally opposite corners, etc.

[0047] In the example above, a mobile ID transmitter is recognized as being in a zone if the resulting ratios are each greater than a specified threshold. However, this is merely an example. Lower thresholds can also be specified, which must be exceeded by one or more of the ratios: P31→21 / P31→22>Threshold_1, AND P31→21 / P31→23 <Schwelle_2, AND P31→22 / P31→23>Threshold_3.

[0048] For one or more of the formed ratios, for example, two different thresholds can be defined. These can be a lower threshold Xnmin and an upper threshold Xnmax. It can then be determined whether the respectively determined ratio of the received field strengths is greater or smaller than the respective thresholds. By appropriately combining the thresholds, different zones can be defined, for example, by forming intersections. For example, a mobile identification transmitter 30 can be detected as being located in a first zone A if the following applies: X1min_A <P31→21 / P31→22<X1max_A AND X2min_A <P31→21 / P31→23<X2max_A AND X3min_A <P31→22 / P31→23<X3max_A.

[0049] A mobile identification transmitter 30 can, for example, be detected as being located in a second zone B if: X1min_B <P31→21 / P31→22<X1max_B AND X2min_B <P31→21 / P31→23<X2max_B AND X3min_B <P31→22 / P31→23<X3max_B.

[0050] However, these are merely examples. Different zones can be defined using any combination of thresholds. The threshold values ​​can be chosen according to the desired size and shape of the zones.

[0051] By forming ratios, shadowing effects, for example, can be canceled out. This will be explained using an example below. For example, a user is standing in front of their vehicle facing the vehicle. Their smartphone, which acts as their vehicle key, is in the user's back trouser pocket. This means that signals sent between the antennas in the vehicle and the smartphone are shadowed by the user's body. This applies to an antenna located inside as well as outside the vehicle. Both signals are therefore essentially equally attenuated by the user's body. The ratio of the two received field strengths to each other is therefore essentially the same value as for the unattenuated signals.Comparing the ratio of the signals to each other with one or more thresholds thus provides essentially the same result (e.g. user is in zone A) as in the case where the signals are not attenuated.

[0052] After the reception field strengths P 31->2n have been determined, it can transmit a response signal S31 via the further antenna 31 (cf. Fig. 3). The response signal S31 is also an electromagnetic signal. The signal S31 contains information about the measured received field strengths P 31->2n . A single signal can be transmitted, which provides information about all measured reception field strengths P 31->2nHowever, a separate response signal S31 can also be transmitted for each of the received signals S2n, which are each received by the corresponding antennas 2n. Each of these response signals S31 can then contain information about the received field strength P 31->2n of the signal from the corresponding antenna 2n. The antennas 2n are connected to a control unit 40. Response signals S31 received via the antennas 2n can be sent to the control unit 40 for further processing. The control unit 40 thus receives the information about the measured reception field strengths P 31->2n, can form the corresponding relationships and can determine the position of the mobile identification transmitter 30, or determine in which zone the mobile identification transmitter 30 is located. However, it is also possible that a position determination already takes place in the mobile identification transmitter 30 and the mobile identification transmitter 30 transmits information about the specific position or the specific zone in the response signal S31.

[0053] In the above example, the antennas 2n in the vehicle 10 serve as transmitting antennas, and the antenna 31 in the mobile identification transmitter 30 serves as the receiving antenna. The determination of the receiving field strengths P 31->2n takes place in the mobile identification transmitter 30. However, it is alternatively also possible that the determination of the reception field strengths P 31->2nis not carried out in the mobile identification transmitter 30. Instead of transmitting signals S2n from each of the antennas 2n in the vehicle, the mobile identification transmitter 30 can transmit one or more signals S31, which are received by the antennas 2n. In such a case, the antenna 31 in the mobile identification transmitter 30 serves as the transmitting antenna, and the antennas 2n in the vehicle 10 serve as receiving antennas. The receiving field strength P can then be determined in the control unit 40. 31->2n each of the received signals S31 are determined and the reception field strengths P 31->2n are set in relation to one another accordingly and compared with corresponding threshold values. This in turn allows the position of the mobile identification transmitter 30 relative to the vehicle 10 to be determined.

[0054] The position and shape of the zones A, B, C, D are known in the mobile identification transmitter 30 and / or in the control unit 40. Based on the determined reception field strengths P 31->2n , or the conditions formed, it can thus be determined in which zone A, B, C, D the mobile identification transmitter 30 is located. Depending on the zone in which the mobile identification transmitter 30 is located, a corresponding function in the vehicle can then be permitted or prohibited.

[0055] The system can, for example, be recalibrated during operation. As described in Fig. 4, the attenuation of the signals can be determined, for example, with the help of signals between the first antenna 21 and the second antenna 22. This means that it is possible to determine how strongly a signal is attenuated on the path x3 between the first antenna 21 and the second antenna 22. In this way, it is possible, for example, to detect when changes in attenuation occur over time. For example, a signal between the first antenna 21 and the second antenna 22 may not be significantly attenuated initially. However, due to changes to the vehicle, for example, it may happen that at a later point in time there are objects in the radio path between the first antenna 21 and the second antenna 22, which cause a significant attenuation of signals transmitted between the first and second antennas 21, 22.The determined damping can be used, for example, for diagnostic purposes, particularly for self-calibration of the system, for example, to estimate and adjust the value of the (relative) threshold(s) against which the determined conditions are compared. For example, if the (relative) threshold(s) have preset values ​​upon delivery of a vehicle, these can be recalibrated at a later date, if necessary, to adapt the system to possible changes.

[0056] Fig.5 shows a flowchart of a method for determining the position of a transponder unit relative to a vehicle. The transponder unit has a first antenna, and the vehicle has at least two antennas. One method includes determining the received field strengths of signals transmitted between the first antenna and the at least two antennas arranged in the vehicle (step 501). At least two of the determined received field strengths are set in a ratio to one another (step 502). Each of the at least one formed ratio is compared with at least one threshold (step 503). The position of the transponder unit is determined based on the comparison of the ratios with the at least one threshold (step 504). List of reference symbols 10 vehicles 20 transmitter unit 2n antennas S2n electromagnetic signals 30 mobile identification transmitters 31 Antenna S31 electromagnetic signal 40 Control unit A, B, C, D zones

Claims

[1] Device for determining the position of a mobile identification transmitter (30) in relation to a vehicle (10), wherein the device has a first antenna (31) arranged in the mobile identification transmitter (30) and at least two antennas (2n) arranged in the vehicle (10), and wherein the device is designed to the reception field strengths (P 31->2n ) of signals (S2n, S31) transmitted between the first antenna (31) and the at least two antennas (2n) arranged in the vehicle (10); at least one ratio of two different measured reception field strengths (P 31->2n ) to form; comparing each of the at least one formed ratio with at least a first threshold and a second threshold; and to determine an attenuation of the signal between the two antennas (2n) based on a signal sent between two antennas (2n) arranged in the vehicle (10), wherein the position of the mobile identification transmitter (30) is determined based on comparing the at least one ratio with the at least one first and second threshold. [2] Device according to claim 1, wherein of the antennas (2n) arranged in the vehicle (10), at least one antenna is arranged in the interior of the vehicle (10) and at least one antenna is arranged in the exterior of the vehicle (10). [3] Apparatus according to claim 1 or 2, wherein at least one of: of the antennas (2n) arranged in the vehicle (10), at least one antenna is arranged in the region of the bonnet of the vehicle (10) and at least one antenna is arranged in the region of the trunk of the vehicle (10); of the antennas (2n) arranged in the vehicle (10), at least one antenna is arranged in the region of the right side of the vehicle (10) and at least one antenna is arranged in the region of the left side of the vehicle (10); and of the antennas (2n) arranged in the vehicle (10), two antennas are arranged at diagonally opposite corners of the vehicle (10). [4] Device according to claim 1, 2 or 3, wherein the ratio of two reception field strengths (P 31->2n ) which relate to antennas in the vehicle (10) which are spaced apart by more than 10 cm, more than 50 cm, more than 1 m or more than 2 m. [5] Device according to one of claims 1 to 4, wherein the signals (S2n) are sent from the antennas (2n) arranged in the vehicle (10) to the mobile identification transmitter (30) and the mobile identification transmitter (30) is designed to determine the reception field strengths (P 31->2n) of the received signals (S2n), or the signals (S31) are sent from the first antenna (31) arranged in the mobile identification transmitter (30) to the antennas (2n) arranged in the vehicle (10), and the device further comprises a control unit (40) which is connected to the antennas (2n) arranged in the vehicle and which is designed to determine the reception field strengths (P 31->2n ) of the received signals (S31). [6] Device according to one of claims 1 to 5, wherein the same thresholds are used for each of the formed ratios. [7] Device according to one of claims 1 to 5, wherein different thresholds are used for at least two of the formed ratios. [8] Device according to one of the preceding claims, wherein the reception field strength (P 31->2n) with respect to an antenna (2n) arranged in the vehicle depends on the distance of the mobile identification transmitter (30) to the corresponding antenna (2n). [9] Device according to one of the preceding claims, wherein the at least one threshold depends on the determined attenuation. [10] Method for determining the position of a mobile identification transmitter (30) in relation to a vehicle (10), wherein the mobile identification transmitter (30) has a first antenna (31) and the vehicle (10) has at least two antennas (2n), and wherein the method comprises Determining the reception field strengths (P 31->2n ) of signals transmitted between the first antenna (31) and the at least two antennas (2n) arranged in the vehicle (10); Forming at least one ratio of two different measured reception field strengths (P 31->2n ); Comparing each of the formed ratios with at least one first threshold and one second threshold; and Sending a signal between two antennas (2n) arranged in the vehicle (10) and determining an attenuation of the signal sent between the antennas (2n), wherein the position of the mobile identification transmitter (30) is determined based on the comparison of the conditions with the at least one first and second threshold.

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