DE102017214283A1 - A method of reproducing pilot tones via an electroacoustic system for locating a mobile terminal in a building and method for locating a mobile terminal in a building using pilot tones - Google Patents

Abstract

The invention relates to a method for reproducing pilot tones (112, 114, 116) via an electroacoustic system (104) for locating a mobile terminal (102) in a building, wherein the electroacoustic system (104) comprises at least one first loudspeaker (LS1) Reproducing a first pilot tone (112), a second loudspeaker (LS2) for reproducing a second pilot tone (114) and a third loudspeaker (LS3) for reproducing a third pilot tone (116). By the method, the first loudspeaker (LS1), the second loudspeaker (LS2) and the third loudspeaker (LS3) are controlled so that the first pilot tone (112), the second pilot tone (114) and the third pilot tone (116) each in be reproduced a frequency range not perceptible by the human ear.

Description

State of the art

The invention is based on a method or a device according to the category of the independent claims. The subject of the present invention is also a computer program.

Outdoor navigation via GPS is an integral part of the state of the art of mobile devices. Within buildings, navigation via GPS is virtually impossible, since the signal strength is often too low and multiple reflections can cause large deviations. The realization of an equivalent indoor navigation represents a very important technological topic. The applications are diverse and the market volume unmanageably large.

A well-known concept for the realization is the use of WLAN routers. In many public buildings, a mobile terminal may receive the signals from a plurality of routers. By correlations with the signal strength and the known positioning of the router can be concluded that the position of the terminal. However, the accuracy is often insufficient. The installation of special additional transmitters in optimized positions is an obvious extension, but requires equipment of the buildings with additional technology.

There are other technical solutions known, but in most cases make it necessary to build a local infrastructure. The high effort and the heterogeneity of the concepts mostly prevent a widespread use.

The pamphlets US 20130188456 A1 and US 9146301 B2 describe methods for location determination by means of the acoustic transit time of pseudo-random sequences and modulated music.

In the publication US 20150156637 A1 is a method for indoor localization with a conventional smartphone with microphone described. In an area in a building several speakers are arranged. Each loudspeaker can transmit an acoustic signal with an acoustic information for the identification of the respective loudspeaker. If an acoustic signal is picked up by the microphone, an ID of the loudspeaker from which the signal comes can be determined on the basis of the acoustic information.

Disclosure of the invention

Against this background, with the approach presented here, a method for reproducing pilot tones via an electroacoustic system for locating a mobile terminal in a building, furthermore a control unit using this method, a method for locating a mobile terminal in a building using Pilot tones, a mobile terminal and finally presented a corresponding computer program according to the main claims. The measures listed in the dependent claims advantageous refinements and improvements of the independent claim device are possible.

The invention relates to a method for reproducing pilot tones via an electroacoustic system for locating a mobile terminal in a building, the electroacoustic system comprising at least a first loudspeaker for reproducing a first pilot tone, a second loudspeaker for reproducing a second pilot tone and a third loudspeaker for reproduction a third pilot tone, the method comprising at least the following step:

Driving the first speaker, the second speaker, and the third speaker to respectively reproduce the first pilot tone, the second pilot tone, and the third pilot tone in a frequency range imperceptible to the human ear.

An electroacoustic system, ELA for short, can be understood to mean a public address system which essentially serves to transmit information in the form of announcements. The electroacoustic system can therefore be optimized for clarity and range. The speakers of the electroacoustic system can be arranged within a room or even separately in different rooms or different floors of the building. The loudspeakers may be, for example, (tightly) distributed, permanently installed loudspeakers. A pilot tone can be understood to mean an acoustic signal which can be transmitted outside and independently of a useful signal via a communication channel of the electroacoustic system and can serve, for example, for monitoring, control, reference or monitoring purposes. For example, for self-test purposes of the electroacoustic system, an electrical signal can be sent via leads to the speakers and there are parasitically converted into a pilot tone in the form of an inaudible acoustic signal. By a mobile terminal, for example, a smartphone, tablet or laptop can be understood. For example, a frequency range imperceptible to the human ear can be understood to be an area above 16 kHz or below 16 Hz.

The approach presented here is based on the finding that a system for determining the location of mobile terminals in buildings can be implemented on the basis of pilot tones of an electroacoustic system installed in the building. The pilot tones act as acoustic signal lights. By using these acoustic signals for indoor localization common localization techniques can be supplemented in places where, for example, a GPS reception is basically poorly possible, such as in buildings. The acoustic signals are emitted as inaudible pilot tones of several speakers and are distinguishable depending on the embodiment by their timing or spectral design of speaker to speaker. The mobile terminal is typically a receiving device in the form of a mobile phone or tablet with integrated microphone hardware, through which the acoustic signals of all speakers can be recorded. Based on the different durations of the acoustic signals then the respective distances of the receiving device to the speakers can be determined.

The position of the receiving device in the building can be determined, for example, by multilateration on the basis of a map material to be provided, in which the respective positions of the loudspeakers and their characteristic signal properties are entered. Such a localization method, which makes it possible to determine the position within a building by means of an electroacoustic system, can be used, for example, in a navigation application.

Advantageously, such a concept hardly requires additional infrastructure measures, since electroacoustic systems are already installed in many buildings and are designed by default to output pilot tones. The individual speakers may additionally be modified so as to be able to output individual pilot tones. The concept also requires no change in the receiving hardware and can be implemented with standard mobile phones, tablets, laptops or the like. Above all, the concept also enables localization in large building complexes in which no localization options are currently available. In particular, the concept enables position information with an accuracy of less than 1 meter.

Since the electroacoustic system speakers are used both for information transmission and for localization, it should be ensured that the two functions do not interfere with each other. This is achieved with the approach presented here.

According to an embodiment, in the step of driving, the first loudspeaker, the second loudspeaker or the third loudspeaker or at least two of the three loudspeakers may be driven to provide the first pilot tone, the second pilot tone or the third pilot tone or at least two of the three pilot tones in a frequency range between 18 and 30 kHz play. This can ensure that the pilot tones are not perceived by people in the building as annoying sounds or noises.

According to a further embodiment, in the step of driving the first loudspeaker, the second loudspeaker and the third loudspeaker can be controlled to the first pilot tone, the second pilot tone and the third pilot tone as temporally and / or spectrally and / or by different codings deviating acoustic Play signals. As a result, an unambiguous assignment of the pilot tones to each one of the speakers can be ensured.

It is also advantageous if, in the step of the driving, the first loudspeaker, the second loudspeaker and the third loudspeaker are activated in order to time-synchronously reproduce the first pilot tone, the second pilot tone and the third pilot tone. This is to be understood as representing the three pilot tones with respect to a common time base. The three pilot tones can be played either at the same time or at different times. This allows synchronized playback of the pilot tones through the speakers.

Furthermore, in the step of driving, the first speaker, the second speaker or the third speaker may be driven to reproduce the first pilot tone, the second pilot tone and the third pilot tone in pulses, wherein the pulses of the first pilot tone, the pulses of the second pilot tone and spectrally do not overlap the pulses of the third pilot tone. This can be a channel crosstalk while playing the three pilot tones are prevented.

In accordance with a further embodiment, in the step of the activation, at least one further loudspeaker of the electroacoustic system can be activated in order to obtain the first pilot tone if a sound propagating space of the further loudspeaker has no intersection with a sound propagating space of the first loudspeaker, or, additionally or alternatively, reproducing the second pilot sound, if a sound propagating space of the further loudspeaker has no intersection with a sound propagating space of the second loudspeaker, or additionally or alternatively to reproduce the third pilot tone, if a sound propagation space of the further speaker does not intersect with a sound propagation space of the third speaker. A sound propagation space can be understood to mean a spherical or hemispherical space around a loudspeaker, the extent of which in the radial direction depends on an acoustic range of the acoustic signals emitted by the loudspeaker. By means of this embodiment, the channels of further loudspeakers of the electroacoustic system, which are located, for example, at a greater distance from the first, second or third loudspeaker, can be reused to reproduce the first, second or third pilot tone. The first, second or third pilot tone can thus be reproduced several times within the building.

The approach presented here also creates a control unit which is designed to execute, to control or to implement the steps of a variant of a method presented here in corresponding devices. Also by this embodiment of the invention in the form of a control device, the object underlying the invention can be achieved quickly and efficiently.

For this purpose, the control unit may comprise at least one arithmetic unit for processing signals or data, at least one memory unit for storing signals or data, at least one interface to a sensor or an actuator for reading sensor signals from the sensor or for outputting control signals to the actuator and / or or at least a communication interface for reading or outputting data embedded in a communication protocol. The arithmetic unit may be, for example, a signal processor, a microcontroller or the like, wherein the memory unit may be a flash memory, an EPROM or a magnetic memory unit. The communication interface can be designed to read or output data wirelessly and / or by line, wherein a communication interface that can read or output line-bound data, for example, electrically or optically read this data from a corresponding data transmission line or output in a corresponding data transmission line.

In the present case, a control device can be understood as meaning an electrical device which processes sensor signals and outputs control and / or data signals in dependence thereon. The control unit may have an interface, which may be formed in hardware and / or software. In the case of a hardware-based design, the interfaces can be part of a so-called system ASIC, for example, which contains various functions of the control unit. However, it is also possible that the interfaces are their own integrated circuits or at least partially consist of discrete components. In a software training, the interfaces may be software modules that are present, for example, on a microcontroller in addition to other software modules.

• Ermitteln einer Laufzeit des ersten Pilottons vom ersten Lautsprecher zum mobilen Endgerät, einer Laufzeit des zweiten Pilottons vom zweiten Lautsprecher zum mobilen Endgerät und einer Laufzeit des dritten Pilottons vom dritten Lautsprecher zum mobilen Endgerät unter Verwendung je eines von einem Mikrofon des mobilen Endgeräts erzeugten elektrischen Signals; und
• Bestimmen einer Entfernung des mobilen Endgeräts zum ersten Lautsprecher unter Verwendung der Laufzeit des ersten Pilottons, einer Entfernung des mobilen Endgeräts zum zweiten Lautsprecher unter Verwendung der Laufzeit des zweiten Pilottons und einer Entfernung des mobilen Endgeräts zum dritten Lautsprecher unter Verwendung der Laufzeit des dritten Pilottons, um eine einen Ort des mobilen Endgeräts im Gebäude repräsentierende Ortskoordinate zu erhalten.

The approach presented herein further provides a method for locating a mobile terminal in a building using pilot tones represented by a method according to any one of the preceding embodiments, the method comprising the steps of:

• Determining a duration of the first pilot tone from the first loudspeaker to the mobile terminal, a transit time of the second pilot tone from the second loudspeaker to the mobile terminal, and a transit time of the third pilot tone from the third loudspeaker to the mobile terminal using an electrical signal generated by a microphone of the mobile terminal; and
• Determining a distance of the mobile terminal to the first speaker using the term of the first pilot tone, a distance of the mobile terminal to the second loudspeaker using the transit time of the second pilot tone and a distance of the mobile terminal to the third loudspeaker using the transit time of the third pilot tone to obtain a location coordinate representing a location of the mobile terminal in the building.

The object of the approach presented here is also a mobile terminal with units that are designed to execute and / or control the localization method according to the above embodiments. For this purpose, the mobile terminal, such as a smartphone, tablet or laptop, be equipped with a microphone for the detection of pilot tones.

The methods mentioned in connection with the approach presented here can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a control unit.

Also of advantage is a computer program product or computer program with program code which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and for carrying out, implementing and / or controlling the steps of the method according to one of the embodiments described above is used, especially if the program product or program is on running a computer or a device.

• 1 eine schematische Darstellung eines Steuergeräts und eines mobilen Endgeräts gemäß einem Ausführungsbeispiel;
• 2 ein Blockdiagramm zur Beschreibung eines Signalflusses in einem mobilen Endgerät gemäß einem Ausführungsbeispiel;
• 3 eine schematische Darstellung dreier Lautsprecher einer elektroakustischen Anlage zur Verwendung in einem Verfahren gemäß einem Ausführungsbeispiel;
• 4 ein Ablaufdiagramm eines Wiedergabeverfahrens gemäß einem Ausführungsbeispiel; und
• 5 ein Ablaufdiagramm eines Lokalisierungsverfahrens gemäß einem Ausführungsbeispiel.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. It shows:

• 1 a schematic representation of a control device and a mobile terminal according to an embodiment;
• 2 a block diagram for describing a signal flow in a mobile terminal according to an embodiment;
• 3 a schematic representation of three speakers of an electroacoustic system for use in a method according to an embodiment;
• 4 a flowchart of a reproduction method according to an embodiment; and
• 5 a flowchart of a localization method according to an embodiment.

In the following description of favorable embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and similar acting, with a repeated description of these elements is omitted.

1 shows a schematic representation of a control device 100 and a mobile terminal 102 according to an embodiment. Shown is an arrangement of three speakers LS1 . LS2 . LS3 an electroacoustic system 104 that ever with the control unit 100 are connected. The three speakers LS1 . LS2 . LS3 For example, they are permanently installed in a building. The mobile device 102 is also located in the building. The control unit 100 has a drive unit 105 on, which is trained to the speakers LS1 . LS2 . LS3 by outputting each of a corresponding electrical drive signal 106 . 108 . 110 to control that over the first speaker LS1 a first pilot tone 112 , over the second speaker LS2 a second pilot tone 114 and over the third speaker LS3 a third pilot tone 116 is reproduced in a frequency range imperceptible to the human ear.

According to this embodiment, the drive unit is 105 trained to the speakers LS1 . LS2 . LS3 to head so that the first speaker LS1 the first pilot tone 112 in the form of sound pulses in a first frequency f ₁ , the second loudspeaker LS2 the second pilot tone 114 in the form of sound pulses in a second frequency f ₂ and the third speaker LS3 the third pilot tone 116 in the form of sound pulses in a third frequency f ₃ sends. The mobile device 102 is from the sound pulses of the first frequency f ₁ at a first time t ₁ , from the sound pulses of the second frequency f ₂ at a second time t ₂ and of the sound pulses of the third frequency f ₃ at a third time t ₃ each on a direct path and after corresponding distance-dependent propagation times τ ₁ = t ₁ - t ₀ , τ ₂ = t ₂ - t ₀ and τ ₃ = t ₃ - t ₀ reached.

The sending time t ₀ is initially unknown. Another propagation path outlined here by way of example results from reflection of the sound pulses of the first frequency f ₁ , This reflected portion of the sound pulses reaches the mobile terminal 102 after a time τ _1a ,

Below the schematic representation of the electroacoustic system three graphs are further shown, the amplitude curves of three of a microphone 117 of the mobile terminal 102 when detecting the three pilot tones 112 . 114 . 116 generated received signals 118 . 120 . 122 separated according to the three carrier frequencies f ₁ . f ₂ . f ₃ represent. The mobile device 102 has a determination unit 124 to determine the three terms τ ₁ . τ ₂ . τ ₃ using the three received signals 118 . 120 . 122 on. A determination unit 126 of the mobile terminal 102 is designed to be based on the three of the investigative unit 124 determined transit times τ ₁ . τ ₂ . τ ₃ a respective distance of the mobile terminal 102 to the speakers LS1 . LS2 . LS3 to determine and on the basis of these distances a place of the mobile terminal 102 in the building representing location coordinate 128 to calculate and spend.

For example, the speakers LS1 . LS2 . LS3 mounted at known positions in space and emit short acoustic pulses. To distinguish the speakers, the carrier frequency used varies from speaker to speaker. In particular, the respective carrier frequencies of the loudspeakers are in a band of 18 to 30 kHz. The carrier distances are selected, for example, such that the spectra of the pulses of adjacent loudspeakers do not overlap. Furthermore, a pulse duration dτ is chosen such that, taking into account the speed of sound v, a sufficient spatial resolution of dx = v × dτ is achieved. For an exemplary resolution of dx = 30 cm and v = 330 m / s, for example, results in a maximum pulse duration of dτ = 0.9 ms. In the idealized case of Gaussian pulses, a spectral pulse width of df = 1 / dτ = 1.1 kHz results. Thus, various loudspeakers with 1.1 kHz carrier spacing can transmit if appropriate measures are taken to prevent channel crosstalk. In the frequency band from 18 to 30 kHz can send up to eleven speakers simultaneously.

Due to the short range of the acoustic signals of typically less than 100 m, also referred to as pilot tones, it is possible, the channels of other speakers of the electro-acoustic system 104 to reuse at a greater distance. The acoustic signals can thus occur multiple times within the building.

According to a further embodiment, a coarse localization of the mobile terminal is already established via Wi-Fi 102 performed. This ambiguity in the transmitter frequencies can be compensated.

In particular, the pulses of all loudspeakers are sent synchronously, but not necessarily at the same time, with the individual loudspeakers being synchronized either by a conventionally present signal line or by radio communication with the control unit 100 get a common timebase.

The mobile device 102 converts all pulses with the microphone 117 into electrical signals 118 . 120 . 122 and processed in a software, as exemplified in 2 is shown.

2 shows a block diagram for describing a signal flow in a mobile terminal 102 according to an embodiment, such as the above with reference to 1 described terminal. Shown are the microphone 117 , an analog-to-digital converter A / D, a bandpass filter BPF, a rectifier RECT, a low-pass filter TP, a peak detection unit PKD, calculation units τ / r for the distance calculation from the transit times and a multilateration unit ML for calculating location coordinates (x, y, z) in a multilateration process.

First, band pass filtering is performed to separate the signals of the individual speakers. The individual channels are then rectified and low-pass filtered to separate the pulses from their carriers. The arrival times of the pulses are determined, for example, from their maximum values or their edges. In the case of arrival time determination over maximum values, for example, Gaussian curves are fitted to the received signal data, the time of a maximum of the Gaussian curves being taken as the arrival time point. If the arrival time is to be determined from the signal edge of a pulse, the signal is first smoothed to suppress noise influences, and then differentiated in time. Flanks in the original signal then appear as pulses and can be determined by pulse fitting and reading of the maximum time points. In order to use the path on the line of sight for multipath propagation, for example, the respective first pulse is selected, which precedes in pulses of different lengths propagation paths those pulses which were received indirectly. In 1 For example, t ₁ <t _1a , so that accordingly, the directly received pulses of the first pilot tone are selected for localization.

From the measured signal propagation times τ ₁ ... Τ ₃ , using the speed of sound v, the distances r ₁ ... ₃ = τ ₁ ... ₃ × v to the loudspeakers result. Multilateration determines the position of the receiving device in the room from the individual distances to several loudspeakers, as in 3 shown. If only one loudspeaker is within range, the position is limited, for example, to a spherical surface. If a second loudspeaker is in range, a circle results from the intersection of the two spherical surfaces. With a third speaker two circle intersections remain. Often one of the points of intersection can be excluded, for example when it is above a ceiling. Additional speakers can increase the robustness of the system.

3 shows a schematic representation of three speakers LS1 . LS2 . LS3 an electroacoustic system for use in a method according to an embodiment. With the three speakers LS1 . LS2 . LS3 For example, these are the preceding ones based on the 1 and 2 described speakers. Shown is an arrangement of the first speaker LS1 associated first sound propagation space 300 , one to the second speaker LS2 associated second sound propagation space 302 and one the third speaker LS3 associated third sound propagation space 304 , Exemplary are the three sound propagation rooms 300 . 302 . 304 shown as distance hemispheres. The mobile device 102 is in the intervals r ₁ . r ₂ . r ₃ to the respective speakers. From the three distances r ₁ . r ₂ . r ₃ results in a common point of intersection of the sound propagation spaces 300 . 302 . 304 of the position of the mobile terminal 102 in the building corresponds.

For the determination of the pulse transit times τ from the reception times t, a common time base of the receiving system with the transmitter system is necessary. This is either, as well as between the speakers, made by radio or transmitted acoustically by one or more other speakers. For example, the terms of the three speakers LS1 . LS2 . LS3 needed for a localization, a reception time t ₄ be used by pulses of the other speaker to determine the time base. This is a system of equations of Multilateration by the unknown quantity t ₀ = t _i - τ _i , with i = 1 ... n extended. Where n indicates the number of associated speaker signals. These additional unknowns require four speakers to determine.

In a transmission of the time base from the transmitter system to the receiver by radio, the control unit for controlling the speaker via an antenna sends out a corresponding synchronization signal, which then at the mobile terminal 102 with an antenna, such as a Wi-Fi antenna. Compared to the speed of sound, the electromagnetic radio signal can be transmitted virtually without delay and the receiver system can be synchronized on the basis of this signal.

4 shows a flowchart of a reproduction process 400 according to an embodiment. The procedure 400 for reproducing pilot tones for locating a mobile terminal in a building, for example, by a control unit, as described above with reference to 1 to 3 is described, executed. It will be in one step 410 at least three speakers of the electro-acoustic system driven to reflect at least three each lying in a frequency range not audible by the human ear pilot tones within the building.

5 shows a flowchart of a localization method 500 according to an embodiment. The procedure 500 for locating a mobile terminal in a building, for example, by using a previously with reference to the 1 to 3 described mobile terminal to be executed. The procedure 500 includes a step 510 in which the respective transit times of the pilot tones reproduced by the loudspeakers of the electroacoustic system are determined on the basis of electrical signals of a microphone of the mobile terminal. The pilot tones are, for example, by the above with reference to 4 generated described method. In a further step 520 the run times are evaluated to determine a respective distance between the mobile terminal and the speakers. The distances thereby yield the three-dimensional location coordinate of the mobile terminal in the building.

The essence of the approach presented here is the use of fixed loudspeakers of an electroacoustic system for the emission of an acoustic signal that can be used by a mobile terminal with a microphone for localization within buildings. For this purpose, the already permanently installed loudspeakers radiate the acoustic signal in the non-audible frequency range, in particular where the acoustic signal differs from loudspeaker to loudspeaker and has an additional temporal or spectral variation. The acoustic signal is detected at the terminal and the individual transit times to the speakers are determined. The respective distances to the loudspeakers are calculated from the corresponding signal propagation times. Using the fixed spatial coordinates of the loudspeakers, the position of the transmitter can be determined by multilateration if there are at least three loudspeakers and a common time base or four loudspeakers without time base.

The signal of different loudspeakers differs, for example, in the carrier frequency, but can also be distinguished by coding, for example using digital orthogonal spreading codes. Depending on the exemplary embodiment, the signals are temporally amplitude, phase or frequency modulated, pulsed or provided with a chirp to determine the transit time. This temporal variation is used on the receiving side to close the signal propagation time and thus the distance between the receiving device and the respective speaker with knowledge of a dispatch time.

The localization concept described here can be used, for example, for navigation within buildings in which the GPS reception is usually too dampened, for example in railway stations, airports, public institutions, large authorities, universities, shopping centers, warehouses or factory buildings. This makes it easier for users to find venues, meeting places, gates, shops or merchandise. In addition, an application-controlled individualized escape route navigation can be realized in case of fire.

If an exemplary embodiment comprises a "and / or" link between a first feature and a second feature, then this is to be read so that the embodiment according to one embodiment, both the first feature and the second feature and according to another embodiment either only first feature or only the second feature.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 20130188456 A1 [0005]
• US 9146301 B2 [0005]
• US 20150156637 A1 [0006]

Claims (11)

A method (400) for reproducing pilot tones (112, 114, 116) via an electroacoustic system (104) for locating a mobile terminal (102) in a building, the electroacoustic system (104) including at least a first loudspeaker (LS1) for reproduction a first pilot tone (112), a second loudspeaker (LS2) for reproducing a second pilot tone (114) and a third loudspeaker (LS3) for reproducing a third pilot tone (116), the method (400) comprising the following step: Driving (410) the first loudspeaker (LS1), the second loudspeaker (LS2) and the third loudspeaker (LS3) to detect the first pilot tone (112), the second pilot tone (114) and the third pilot tone (116) each in one of human ear to reproduce imperceptible frequency range. Method (400) according to Claim 1 in which, in the step of driving (410), the first loudspeaker (LS1) is actuated to reproduce the first pilot tone (112) in a frequency range between 18 and 30 kHz, and / or the second loudspeaker (LS2) is activated to control the first second pilot tone (114) in a frequency range between 18 and 30 kHz, and / or the third loudspeaker (LS3) is driven to reproduce the third pilot tone (116) in a frequency range between 18 and 30 kHz. Method (400) according to one of the preceding claims, in which, in the step of driving (410), the first loudspeaker (LS1), the second loudspeaker (LS2) and the third loudspeaker (LS3) are activated to detect the first pilot tone (112), to reproduce the second pilot tone (114) and the third pilot tone (116) as acoustic signals that differ from one another in time and / or spectral and / or by different encodings. Method (400) according to one of the preceding claims, in which, in the step of driving (410), the first loudspeaker (LS1), the second loudspeaker (LS2) and the third loudspeaker (LS3) are activated to detect the first pilot tone (112), to time synchronously reproduce the second pilot tone (114) and the third pilot tone (116). Method (400) according to one of the preceding claims, in which, in the step of driving (410), the first loudspeaker (LS1), the second loudspeaker (LS2) and the third loudspeaker (LS3) are activated to detect the first pilot tone (112), reproduce the second pilot tone (114) and the third pilot tone (116) in pulses, wherein the pulses of the first pilot tone (112), the pulses of the second pilot tone (114) and the pulses of the third pilot tone (116) do not overlap spectrally. Method (400) according to one of the preceding claims, wherein in the step of driving (410) at least one further loudspeaker of the electroacoustic system (104) is actuated in order to reproduce the first pilot tone (112), provided that a sound propagation space of the further loudspeaker does not intersect with a sound propagation space (300) of the first loudspeaker (LS1), and / or the second pilot sound (114) play, if a sound propagation space of the other speaker has no intersection with a sound propagation space (302) of the second loudspeaker (LS2), and / or the third pilot tone (116), provided that a sound propagation space of the other speaker has no intersection with a sound propagation space (304) of the third loudspeaker (LS3). A control unit (100) comprising a unit (105) adapted to perform the method (400) according to any one of Claims 1 to 6 execute and / or control. A method (500) for locating a mobile terminal (102) in a building using pilot tones (112, 114, 116) generated by a method (400) according to any one of Claims 1 to 6 the method (500) comprising the steps of: determining (510) a transit time (τ ₁ ) of the first pilot tone (112) from the first loudspeaker (LS1) to the mobile terminal (102), a transit time (τ ₂ ) of the second one Pilot tone (114) from the second loudspeaker (LS2) to the mobile terminal (102) and a transit time (τ ₃ ) of the third pilot tone (116) from the third loudspeaker (LS3) to the mobile terminal (102) using one each from a microphone (117 ) the mobile terminal (102) generates electrical signal (118, 120, 122); and determining (520) a distance (r ₁ ) of the mobile terminal (102) to the first loudspeaker (LS1) using the transit time (τ ₁ ) of the first pilot tone (112), a distance (r ₂ ) of the mobile terminal (102) to the second loudspeaker (LS2) using the transit time (τ ₂ ) of the second pilot tone (114) and a distance (r ₃ ) of the mobile terminal (102) to the third loudspeaker (LS3) using the transit time (τ ₃ ) of the third pilot tone (116) to obtain a location coordinate (128) representing a location of the mobile terminal (102) in the building. A mobile terminal (102) having units (117, 124, 126) configured to implement the method (500) of Claim 8 execute and / or control. A computer program configured to perform the method (400) according to any one of Claims 1 to 6 and / or the method (500) according to Claim 8 execute and / or control. Machine-readable storage medium on which the computer program is based Claim 10 is stored.

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