Abstract:
The method for identifying objects and triggering interactions functions by means of an acoustically modulated data signal, which is associated with an object, and based on the identification of the line by means of which said signal is sent from a receiving unit to a processing point. The content that is associated with said object is sent by means of said line from the processing point to the receiving unit, and thus an interaction between one of many subscribers by means of the receiving unit thereof and one of many objects is enabled. For this purpose, a station produces an acoustically modulated data signal, which is captured by the sound transducer of a receiving unit located within close range of the sound source of said station and forwarded by the receiving unit to the processing point. The processing point determines that the acoustic pattern has arrived and detects the number of the line on which this occurred. The processing point, based on the knowledge thereof of the station and of the line, provides information to the receiving unit on said line. The device for identifying objects and triggering desired interactions as described above according to said method comprises stations having a tone generator and a sound source, receiving units having a sound transducer, and a processing point. The stations are equipped with an input device, for example keys, a touchscreen, a trackball, a mouse, sensors, or a microphone for voice input.

Description:
[0001]    This invention relates to:
   a. means for identifying objects and triggering desired interactions comprising:
       Stations which produce an acoustically modulated data signal (acoustic pattern) by means of a tone generator and a sound source with acoustic characteristics which allow coupling only at close range   Receiving units having a sound transducer to capture the acoustically modulated data signals produced by the said stations   A processing point for the modulated data signals   
       b. A method for identifying and triggering desired interactions, in which a particular station is associated with a particular receiving unit.   
 
         [0007]    Machine readable bar codes representing digital data and printed or marked directly on labels, packaging, or products are known and are currently being used to provide a product or document identification based on a fixed set of code-marks in connection with coding and scanning technologies. Bar codes can be designed in very different ways, also in two-dimensional patterns. However, all these variations have one thing in common: they are visual representations of codes that have to be read optically, i.e. the code has to be printed or made visible on a screen, and in order to read the code an optical scanner or camera is necessary. 
         [0008]    Many devices, especially portable devices, have an audio output component designed for generating voice signals which can be perceived by human users. A wide range of input components is in use: keys, microphone, touch screen, camera, sensors or special scanners in various forms. 
         [0009]    A solution based exclusively on acoustic signals requires that the input signals also be in acoustic form. In this context a bar code would have to be replaced by an acoustically modulated data signal. A receiving unit which is designed for acoustical input and output requires no additional optical scanning component. If a communication channel for audible signals is provided it can be used to transmit acoustically modulated data signals. 
       Task of the Invention 
       [0010]    The task addressed by the present invention is to establish a method which enables a purely acoustic interaction between one of many participants through their individual receiving unit and a station which is assigned to one of many objects. Further the present invention comprises means by which said method can be implemented. 
       Solution of the Task 
       [0011]    Said task is solved by a method which identifies objects and triggers interactions. Said method features an acoustically modulated data signal sent from a station whereby both the said data signal and the said station are associated with an object. Said method further features the identification of the line connecting the receiving unit with the processing point through which said data signal is transmitted. Content which is associated with said object is then transmitted through said line from said processing point to said receiving unit. Thus an interaction regarding one of many said objects is enabled between one of many participants and said processing point via the participant&#39;s said receiving unit. 
         [0012]    Furthermore said task is solved by identifying objects and triggering desired interactions using acoustically modulated data signals comprising:
       Stations having a tone generator and a sound source   Receiving units having a sound transducer   A processing point       
 
     
    
     
         [0016]    This invention, its method and means and their function will be explained in detail with the help of the attached diagrams and drawings. This will illustrate the range of possible applications, achievable results, advantages and characteristics of the invention: 
           [0017]      FIG. 1 : Shows a synoptic diagram with all components necessary to put the method into operation, 
           [0018]      FIG. 2 : Is an illustration of possible uses of discrete frequencies representing data based on hexadecimal and decimal codes respectively, 
           [0019]      FIG. 3 : Is an illustration of possible compositions of signals used to securely transfer content similar to that of a barcode by means of acoustically modulated data signals. 
       
    
    
     BASICS 
       [0020]    In a first step, the basic differences between an optical and an acoustical barcode will be addressed: 
         [0000]    
       
         
               
               
             
           
               
                   
               
               
                 Optical Bar Code 
                 Acoustical Bar Code 
               
               
                   
               
             
             
               
                 Optical Bar Codes must be present in 
                 Acoustical Bar Codes must be  
               
               
                 an optically readable form, i.e. visible 
                 present in an acoustically  
               
               
                   
                 readable form, i.e. audible 
               
               
                 The Optical Bar Codes are read by an 
                 The Acoustical Bar Codes are read  
               
               
                 optical reading device or a camera; ; 
                 by an acoustical reading  
               
               
                 this generally requires a transducer 
                 device or a sound recorder; this 
               
               
                 converting the optical signal into an 
                 generally requires a transducer 
               
               
                 electrical one 
                 converting the acoustical signal  
               
               
                   
                 into an electrical one 
               
               
                 The Optical Bar Code is commonly 
                 In order to be detected, the  
               
               
                 present as an optically passive,  
                 Acoustical Bar Code requires an  
               
               
                 printed pattern which can only be  
                 electrically powered circuit. The  
               
               
                 read if sufficient lighting  
                 level of illumination is 
               
               
                 is provided, the surroundings or by 
                 irrelevant. 
               
               
                 the reading device 
                   
               
               
                 Printed Optical Bar Codes are  
                 An Acoustical Bar Code can be  
               
               
                 passive and static. A dynamic  
                 static or dynamic. It can easily be  
               
               
                 response to varying parameters  
                 modified in response to varying  
               
               
                 (say, ambient illumination) is not  
                 parameters; for example, signal  
               
               
                 possible unless an active display 
                 patterns, signal amplitude, and/or  
               
               
                 is used. 
                 signal length can be modified  
               
               
                   
                 depending on ambient noise level. 
               
               
                 Under sufficient ambient lighting, 
                 Acoustical Bar Codes are only 
               
               
                 Optical Bar Codes are always visible 
                 perceptible as long as they are 
               
               
                 even in the absence of reading 
                 generated. This always occurs in the 
               
               
                 devices. A reading device can operate  
                 same temporal sequence and  
               
               
                 reliably within a broad range of  
                 playback speed. 
               
               
                 orientations and scanning speeds. 
               
               
                   
               
             
          
         
       
     
         [0021]    The principals of transmitting data through a line using audible signals is prior art and well known from the technology of acoustic couplers. Most Applications deal with machine-to-machine communication, such as the communication between fax machines or between terminal and computer, using phone lines and ordinary telephones. 
         [0022]    The fundamental differences between acoustic coupling as used in prior art and as used with Acoustical Bar Codes in the present invention will now be described in some detail. 
         [0000]    
       
         
               
               
             
           
               
                   
               
               
                 Conventional acoustic coupling  
                 Acoustic coupling for Acoustical Bar 
               
               
                 for data transmission 
                 Codes 
               
               
                   
               
             
             
               
                 Acoustic couplers support  
                 With Acoustical Bar Codes, both one- 
               
               
                 simultaneous two-way coupling  
                 way coupling and data transmission  
               
               
                 and data transmission 
                 and two-way coupling and data  
               
               
                   
                 transmission can be selected 
               
               
                 Suitable for the exchange of data 
                 Supports the transmission of data from 
               
               
                 between devices (″machine-to- 
                 one device to another device, and the 
               
               
                 machine″), but not for the exchange  
                 independent transmission of audible 
               
               
                 of information between devices and 
                 information from a device to a human 
               
               
                 humans (″man-to-machine″) 
                 user 
               
               
                 Acoustic couplers are physically 
                 With Acoustical Bar Codes, the 
               
               
                 designed for operation with 
                 geometry of the sound source is aimed 
               
               
                 conventional telephone handsets 
                 at the possible positions of receiving 
               
               
                   
                 devices, especially hand-held mobile 
               
               
                   
                 phones 
               
               
                   
               
             
          
         
       
     
       DESCRIPTION OF THE INVENTION 
       [0023]    An object  2  is identified by identifying the acoustically modulated data signal  4   e  associated according to  105 . This occurs with means as shown in  FIG. 1 , which synoptically represents a diagram of the system and its components. The data signal  4   e  has to be transmitted to the processing point  9  using a receiving unit  3  with a sound transducer  3   a.  The processing point  9  can be part of the portable receiving unit  3  or it can be connected via a transmission path ( 117 ,  5 ,  116 ,  14  and  13 ) or with a wireless connection. If the receiving units  3 —which are represented as cell phones in the diagram—have a common processing point  9  the acoustically modulated data signals  4   e  will be transmitted (transmission path:  117 ,  5 ,  116 ,  14 , and  113 ) detected (detection unit  11 ) and interpreted (interaction manager  8 ). Using these signals  4   e  and a reference  8   a  stored in a memory the assigned station  4  will be identified while the receiving unit  3  can be determined from the identification of the transmission path ( 117 ,  5 ,  116 ,  14  and  113 ) on which the signal is transmitted. On the other hand the processing point  9  can associate a receiving unit  3  which has transmitted an acoustically modulated data signal  4   e  to the vicinity of the station  4  which is associated with this signal  4   e.    
         [0024]    From the sequence of the different acoustically modulated data signals  4   e  received via the transmission path ( 117 ,  5 ,  116 ,  14  and  113 ), the movement of a portable receiving unit  3  relative to the stations  4  implicated in its interactions can be determined. 
         [0025]    In addition to the transmission path ( 117 ,  5 ,  116 ,  14  and  113 ) via the receiving units  3 , the stations  4  can be connected directly to the processing point  9  using an additional path ( 106 ,  6  and  107 ). This additional direct communication path has the following advantages:
       1. The detection of the acoustically modulated data signals  4   e  becomes more reliable because the signal  4   e  to be detected is known a priori.   2. Additional information produced by a station  4  and/or by interaction between a station  4  and a person  1  (e.g. with an input device  4   d ) complementing the limited information conveyed by the acoustically modulated data signal  4   e  can be transmitted to the processing point  9  separately. In the absence of such a direct connection, complementary information would have to be transmitted in the form of dedicated acoustically modulated data signals.   3. If required the processing point  9  can transmit information to a station  4  which is acknowledged by this station with an acoustically modulated data signal  4   e.  This is specially useful in making dynamic and/or user-specific and/or secured transactions possible.       
 
         [0029]    From the description above, three sets of issues of great importance for this invention result:
       1. Design of the acoustically modulated data signals  4   e  (acoustic pattern design): In order for the data signals  4   e  arriving at the processing point  9  to be recognised with a high reliability they have to be designed in a way that they can be distinguished as reliably as possible from other acoustic signals and acoustic signal patterns.   2. Acoustic design of the system: In order to guarantee that a station  4  is identified and that the presence of a receiving unit  3  is determined with high reliability, it is required that the sound transducer  3   a  of the portable receiving unit  3  be in close proximity to the sound source  4   b  of the tone generator  4   a.  It is good practice to design for a good signal-to-noise-ratio of the acoustically modulated data signals  4   e  together with a minimal audibility after a short distance from the sound source  4   b.  Therefore the sound sources  4   b  have to produce a high sound pressure in a close range which diminishes quickly within a moderate distance. For this purpose it is best to use small sound sources  4   b  that move only a very small air column. Also an array of small sound sources  4   b  that are close together can be used which simultaneously transmit the same data signal  4   e  in phase or with a clearly defined phase relationship. An array of sound sources  4   b  will provide a more consistent close-range acoustic irradiation and the choice of a suited phase relationship will favour the cancelling of sound waves after a certain distance.   3. Interaction design: By means of the method described above, interactive systems such as customised information systems can be designed and operated, as illustrated in the following examples.       
 
       EXAMPLES OF APPLICATIONS 
       [0033]    The interactive solutions described here can provide information, guidance or navigation and can find applications in museums, collections, exhibitions, tutorial paths, sight-seeing tours, historic locations, monuments, viewpoints, tutorials, in retail business (shops, shopping malls, vending machines), in important buildings, airports and train stations as means of information, orientation, etc. This list of application areas is by no means exhaustive, and numerous other application areas can be envisaged. The core feature and the specific characteristics of this technology will always be the identification of objects and the triggering of desired interactions by means of close-range coupling of acoustically modulated data signals. Applications are also possible where input signals are fed electrically e.g. using the electrical interface of a hands-free set in a portable receiving unit. 
         [0034]    In the following the invention, and in particular the aspect of interactive systems, will be illustrated using the special case of audio guides for museums and retail stores, and of cell phones as receiving units, as an example.  FIG. 1  will be used to support the explanations. 
         [0035]    Most museum visitors appreciate being guided through an exhibition. Conventional methods are guided tours with an expert or guide books and brochures. Experts are expensive and not always available, while walking through an exhibition reading a guide book or written comments has the disadvantage that the visitor has to constantly switch his attention between the written explanations and the exhibits—a notoriously tiring and distracting behaviour. 
         [0036]    Guided tours with small audio devices have therefore become widespread. Their advantage is that visitors can enjoy spoken commentaries in their preferred language at any time. This way they can concentrate on the exhibits without having to read constantly. A disadvantage is these portable audio devices are expensive, and have to be serviced on a daily basis. The number of portable audio devices which have to be provided has to be equal to the maximum number of visitors who may attend the exhibition simultaneously, plus the number of devices being cleaned and recharged after use. 
         [0037]    Visitors in a retail store or a shopping mall would like to be informed about products on offer—an important measure in increasing sales. Most shops inform their visitors acoustically through the shop&#39;s public address system. This informs all visitors at the same time rather than individually. The advantage is that of a simple and relatively inexpensive solution, but the disadvantages are often poor speech intelligibility and the lack of any possibility of informing customers individually. Visitors cannot access information in accordance with their specific needs; they cannot be addressed according to their individual customer profile; and there is no way to gather information for the purpose of customer profiling. 
         [0038]    Cell phone based systems which are key, speech or touch-screen controlled or which work in connection with GPS data, smart phone cameras and/or pattern recognition etc. are prior art (e.g. cell phone tours). Their operation confronts the users with:
       complex interactions   a lot of attention directed to the cell phone   limits regarding the cell phones that can be used, e.g. smart phones only   problems due to inaccurate determination of position using GPS       
 
         [0043]    This invention introduces a new kind of interaction which overcomes the above disadvantages. It offers a cell phone based interaction suited for any cell phone, no matter of which type, independently of any special technical feature, while providing a very simple, basic and robust interaction. 
         [0044]    If e.g. a cell phone tour (guided tour based on cell phones) is offered for an exhibition, the visitors dial the exhibition&#39;s service number, and then enters an additional code every time he wishes to hear the information sound track associated to a given exhibit. This imposed behavior is both inconvenient and distracting. The visitor must enter a code for each exhibit for which a sound track is desired; he must divide his attention between exhibits and cell phone; and he must do so under the often poor lighting conditions of exhibitions in which lighting is concentrated only on the exhibits themselves. 
         [0045]    The solution based on this invention sets itself apart from conventional cell phone tours in particular because here data is transmitted acoustically (acoustically modulated data signals) from a cell phone to the processing point using the normal speech channel. This makes the service significantly more convenient to use, as no data has to be entered using keys or the smart phone camera etc. Mistakes made when entering the wrong code, as are common when using keypads or voice control, are eliminated. This simplified interaction makes the system very attractive for visitors. 
       Means for Implementation 
       [0046]    In the following an interactive system is described according to  FIG. 1  which is made to distribute content to cell phones and which consists of following components:
       Stations  4  which have a sensor  4   c,  which detects the presence of a cell phone  3 , a tone generator  4   a  and a sound source  4   b.  The stations  4  in this example are connected to the processing point  9  via  106 ,  6  and  107  and generate on demand an acoustically modulated data signal  4   e  which is associated according to  105  to an exhibit  2  which is in close vicinity.   A mobile phone network  5     Cell phones  3  which receive an acoustically modulated data signal  4   e  and transmit it through the transmission path  117 ,  5 ,  116 ,  14 , and  113  to the processing point  9 .   A processing point  9  including an interaction management  8  having access  111   a  to a data bank  12  which manages the contents  12   a  and, in response to requests, sends the desired content  12   a  associated with exhibit  2  to the cell phone using the transmission path  112 ,  13  (the speech output  13  is controlled  111   b  by the interaction manager),  115 ,  14 ,  116 ,  5 , and  117 .       
 
         [0051]    All active cell phones  3  pick up ambient noise and other acoustic signals and constantly transmit them to the processing point  9  making the task of detection more difficult. There is a probability that these interfering signals can be erroneously recognised as an acoustically modulated data signal, thus triggering an unwanted interaction. 
         [0052]    The acoustically modulated data signals  4   e  need to be designed specifically in such a way that the probability of being simulated by speech, singing, noise, sound, etc is very low. This is done by giving the signals  4   e  characteristics (amplitude range, signal frequency, signal duration, sequence of these characteristics, signal redundancy, time stamp) which can be verified in the process of detection  11 . Suitable measures for designing signals for very reliable detection and a low probability of mis-detection are known from coding theory and can be applied selectively, also taking into account the properties of the interfering signals. 
         [0053]    If cell phones are being used as mobile receiving units  3  the particular specifications of the mobile phone system also have to be taken into consideration. 
         [0054]    In a mobile phone network the speech channel is the only easily accessible and open transmission channel, whereas dedicated and general-purpose data channels are frequently not accessible, are not implemented, and/or require an inconvenient interaction with the user  1 . 
         [0055]    The present solution features an acoustically modulated data signal  4   e  consisting of a sequence of superimposed oscillations. As this data signal has to be transmitted through the speech channel of the phone network the frequencies that are being transmitted have to lie within the transmittable range, i.e. between 300 Hz and 3′400 Hz. 
         [0056]    Because the frequencies of the human voice as well as of ambient noise also lie within this range there is, as mentioned previously, the risk that such signals might be mis-interpreted as a full data signal  4   e  or at least as a part of it. 
         [0057]    With this in mind, for example, the DTMF-system (Dual Tone Multi Frequency) which has been known for many years in telephony (ETSI ES 201 235-1 Specification of Dual Tone Multi Frequency (DTMF)—Transmitters and Receivers; Part 1: General) has the following behaviour:
       either DTMF-signals are being transmitted while the speech path is muted (thus suppressing all possible extraneous noise superimposed over the DTMF-signals)   or only speech signals are transmitted, while the path for possible DTMF-signals is muted       
 
         [0060]    The DTMF-system comprises on the side of the transmitter a DTMF tone generator and on the side of the receiver a DTMF decoder. The generator is controlled by the phone key. The receiver consists of an electronic circuit devised to detect DTMF frequencies and a program which reconstructs the transmitted codes from the properties of the detected signals. The signals consist of two short simultaneous and superimposed signal sequences each one of which is selected from two separate groups, a low group (697 Hz, 770 Hz, 852 Hz and 941 Hz) and a high group (1209 Hz, 1336 Hz, 1477 Hz and 1633 Hz), each group providing four signaling frequencies in the middle range of speech frequencies. 
         [0061]    In contrast with the DTMF system, which can only transmit either speech signals or DTMF signals at any given time, externally generated acoustically modulated data signals and/or noise can be transmitted simultaneously when using cell phone. There is no clear specification for the reliable detection of DTMF signals by a common DTMF receiver in the presence of speech or noise at significant levels. This means that conventional DTMF receivers can not be used under these circumstances. 
         [0062]    There are further arguments against using conventional DTMF signals. The specified frequencies were chosen as a set of numbers that are as mutually incommensurate to each other as possible, in order to avoid interference caused by harmonic components. This means that signal sections including frequency tolerances can not have a common period. Assembling signals from pre-recorded digital signal components of finite and constant length is therefore frequently associated with discontinuities in amplitude. Furthermore a detection of DTMF signals based on a short-term discrete Fourier Transformation delivers frequency values which do not correspond to the DTMF frequencies themselves, which in turn leads to systematic measuring errors. When detecting signal frequencies over finite measuring intervals (not only but especially when using correlation detection) interfering products result. Finally transmission errors can lead to the repetition by the transmission channel of the mobile telephone network of single frames (these are sequences of samples e.g. 160 samples or 20 milliseconds with GSM). This causes signal discontinuities, generally connected to phase jumps, which can interfere massively with a correlation detection or detection with Goertzel Filters as commonly used in DTMF technology. 
         [0063]    As, for the above reasons, existing DTMF technology is not suited for acoustic coupling, a proprietary system of frequencies and patters has been developed for the acoustically modulated data signals, which is part of this invention and is explained in  FIG. 2 . 
         [0064]    It makes sense to use a new set of frequencies which are multiples of a basic frequency. This allows simple generation and switching in a fine time grid avoiding amplitude jumps. If in addition the basic frequency is equal to or a multiple of the frame frequency, repeating a frame will not cause a phase jump. Furthermore when detecting the frequency components of the data signal, detection components from other system frequencies will be exactly zero at the end of the frames, which in turn significantly increases the reliability of the detection. 
         [0065]    With a frame frequency of 50 Hz which corresponds to a frame length of 20 milliseconds, the above considerations lead to alternatives to the DTMF frequencies using a grid based on frequencies of 50 Hz, 100 Hz, 150 Hz, etc. Instead of using the hitherto existing DTMF frequencies e.g. the following new DDTMF frequencies could be used: 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 DTMF 
               
             
          
           
               
                 Group 1 
                 697 
                 770 
                 852 
                 941 
                   
               
               
                 Group 2 
                 1209 
                 1336 
                 1477 
                 1633 
               
               
                   
               
             
          
           
               
                 DDTMF 
               
             
          
           
               
                 Group 1 
                 700 
                 800 
                 900 
                 1000 
                 1100 
               
               
                 Group 2 
                 1200 
                 1300 
                 1400 
                 1500 
                 1600 
               
               
                   
               
             
          
         
       
     
         [0066]    Further improvements are possible using DTMF-like signals. It is advantageous for example if the various possible frequency components of a signal are chosen as far apart from each other as possible. Instead of working with two superimposed frequencies, one chosen from a low group of 4 and one from a high group of 4, according to the DTMF principle, i.e. with code values according to 21 and frequency assignments according to 22 and 23, it is more advantageous to avoid combinations of high frequencies of the low group with low frequencies of the high group as is the case e.g. with frequency assignments according to 25 and 26 and a reduced assignment of value pairs to codes according to 24. It becomes apparent that deliberately imposing this restriction on the set of transferable signals which is 16 with DTMF will reduce our new set to exactly 10. This simplifies the use of the described technology for applications which are based on decimally defined data which can be found e.g. with many conventional bar codes as well as PIN codes, whereas conventional DTMF technology is basically hexadecimal. In our case, a well-justified reduction of the set of signals is achieved not through randomly or arbitrarily omitting certain frequency combinations as in the case of DTMF where e.g. the signals A, B, C, D as well as * and # are excluded but through a selection of signal combinations with good properties enhancing the robust detection of the signals. This choice of discrete frequencies which can be combined from two groups which have an ideally large distance between each other and specially suited for transmitting decimally coded data is illustrated in  FIG. 2 . 
         [0067]    Based on such a definition of discrete frequencies which is suited for the transmission of acoustically modulated data signals for hexadecimally or decimally coded data, it is now possible to define data formats which improve the security of data transmission. The example in  FIG. 3  illustrates this principle. The entire signal sequence consists solely of the signal components  30  which are one data frame long, i.e. 20 milliseconds when using GSM frames to which the above described pairs of frequencies are allocated with the exception of the synchronising pattern  31 . The synchronising pattern  31  consists of a suited sequence of frames containing a single frequency which is not part of the two groups (low and high) i.e. 1100 Hz, 1200 Hz and empty frames respectively e.g. 1 empty frame followed by 2 frames with 1200 Hz followed by 2 empty frames followed by 2 frames with 1200 Hz plus one empty frame. These signals can be detected with the same method used to detect data signals, and in addition it is possible to determine the frame border&#39;s time alignment from the detected signals. The synchronising patterns are followed by data packets  36  which contain only frames with frequency pairs. Each data packet contains user data on the one hand and data which is calculated as check sum of the user data ( 33 ,  34 ) on the other hand. As a special case a data packet can be transmitted with a data load representing the check sum of the user data of another data packet. This allows a better fault correction in the case of continuous transmission interferences. Determining suitable synchronising patterns and choosing suited codes for fault protection is known to professionals and therefore a detailed description is not necessary. 
         [0068]    In order to make sure that a cell phone  3  is in close range of a station  4  thus reducing the probability that noise would trigger off an interaction by mistake, the presence of the phone  3  can be detected by the station  4 . The information that a station  4  has detected a cell phone  3  is transmitted to the processing point  9  and used as a condition in connection with the arrival of the respective data signal to trigger off the transmission of the respective content. This can be done without a functional interaction specific to mobile telephony e.g. by activating a sensor  4   c  (mechanical switch, proximity switch, ultrasonic sound sensor, infrared sensor, optical sensor, capacitive or inductive detection, detection of the radiation of the receiving unit, detection with the help of radar, etc.). The combined use of different sensors  4   c  is also possible. If no information is provided regarding the presence of a cell phone all lines have to be monitored constantly with regards to the arrival of an acoustically modulated data signal  4   e  whereas if information regarding presence is gathered centrally the monitoring data signals  4   e  can be reduced to a short span of time slightly longer than the data signal  4   e.  Noise which might simulate data signals  4   e  appearing outside the measuring window will be suppressed effectively. It is also very advantageous that a data signal  4   e  has to be detected only when coming from a station  4  which has detected and signaled the presence of a cell phone. The signal which has to be detected is known a priori. 
         [0069]    Further test procedures are possible in order to avoid a misdetection. A visitor who was detected with a high probability e.g. at exhibit No.  3  will not be able to suddenly appear 10 seconds later at exhibit No.  96  in a remote wing of the museum. The coordinates of the stations  4  and the sequence of their use can also contribute to reducing the probability of a misdetection. 
         [0070]    The following outlines an interaction using an exhibition as an example. A visitor  1  would like to obtain spoken information  12   a  associated with exhibit  2  on his cell phone  3 .
       The cell phone has to be switched on   Visitor  1  has to have dialed a service phone number of the processing point  9  and therefore to have his cell phone connected to this processing point  9  through a phone line which has been allocated by the line management  10 .       
 
         [0073]    Close to the exhibit  2  there is a station  4  with a tone generator  4   a  and a sound source  4   b  (loudspeaker, sound transducer) which produces an acoustic signal which identifies the exhibit  2  (as well as a special form of interaction, language . . . if such features are offered). If the microphone  3   a  of a cell phone  3  is held close to the sound source  4   b  the acoustically modulated data signal  4   e  is transmitted to the processing point  9 . There it will be recognised even in the presence of a significant level of noise. Based on the detection  11  of the specific data signal  4   e  and on the identity of the specific line  14  on which it has been detected, it becomes clear that visitor  1  with his cell phone  3  is specifically requesting on his line  14  the content  12   a  associated with the exhibit  2  and the corresponding spoken comment  12   a  can be transmitted. As a result, visitor  1  is supplied the desired information  12   a.    
         [0074]    It is necessary for the allocation of the data signal  4   e  to the line  14  to be performed reliably i.e. the correctly allocated comment  12   a  for an exhibit  2  has to be supplied on the correct line to the visitor  1  who has asked for this content. 
         [0075]    Even though in many cases the system will be aware of the phone number of visitor  1  occupying line  14 , explicit knowledge of this phone number is in no way required. 
         [0076]    As it is not known, prior to the detection  11 , on which line  14  the data signal will be recognised, it is necessary to constantly check all lines  14  for the possible appearance of any data signal  4   e.    
         [0077]    A station  4  can also feature a menu offering interactions for visitor  1  to choose from. This menu could be available in tactile (e.g. keys) ore virtual (e.g. touch screen) form. The menu can e.g. refer to:
       A number of objects  2  (one station  4  in the vicinity of a group of objects).   A changing object  2  e.g. information referring to each slide of a running presentation.   An object  2  for which a number of contents is available e.g. a short and a long comment or a more detailed description of the history of the object  2 .
 
If the station  4  is connected to the processing point  9  the choice from the menu can be transferred to the processing point  9  and the desired content  12   a  can be transferred to the respective visitor  1  whereby this station  4  can always produce the same acoustic pattern  4   e.  But the station  4  can also receive from the processing point  9  a totally or partly specific acoustic pattern associated to the selection from the menu.
       
 
         [0081]    In this case the station  4  serves to identify the line, and can optionally also serve to determine the actual content  12   a  associated with the interaction. 
         [0082]    The following examples of applications require the stations  4  to be directly connected to the processing point  9 : 
         [0083]    A further form of interaction is e.g. a solution for customers or visitors in which a guided tour or a set of information is personalized. Here some examples:
       Somebody wants to visit the Louvre in Paris, France, but in the form of a guided tour with the most important objects  2 , within a tight time schedule (30 minutes) and with the corresponding commentary  12   a.  From the menu of the station  4  at the entrance he selects the fast tour (duration 30 minutes) and is led on this personalized guided tour from one exhibit  2  to the next, receiving the corresponding spoken commentary  12   a  as well as directions guiding him to the next exhibit  2 , thanks to his cell phone  3  and the acoustical patterns of the visited stations  4 .   Somebody visiting a large collection only wants to see a selection of exhibits  2  in connection with a certain topic. From the menu of a station  4  at the entrance he selects the desired topic or puts together his tour with the help of search terms and is then led on this personalized guided tour from one exhibit  2  to the next, again receiving the corresponding spoken commentary  12   a  as well as directions guiding him to the next exhibit  2 , thanks to his cell phone  3  and the acoustical patterns of the visited stations  4 .   Somebody is in a large supermarket and wants to do some shopping quickly. As we all know this can become a very annoying task especially if in an unfamiliar supermarket. From the menu of a station  4  at the entrance the customer selects the desired goods  2 , and is then led through the store with the help of directions guiding him directly from one item location to the next through his cell phone  3  and the acoustical patterns of the visited stations  4 . If an item  2  is not in stock this can be indicated right at the beginning and alternatives can be offered. In addition the customer&#39;s attention can be drawn to special offers, or to offers matching his profile, as he can be identified though his mobile phone number. As an extra service, if customer  1  is on line with his cell phone  3  he can e.g. be put through to his partner at home who he then can ask if anything else is required, whether he should take advantage from a special offer or buy the organic instead of the regular product, etc etc etc.       
 
         [0087]    The applications described here serve to enable interactions according to customer&#39;s requests and choices.