WO2003093867A1

WO2003093867A1 - System for locating a person, animal or object using an ultrasonic signal comprising an identification code

Info

Publication number: WO2003093867A1
Application number: PCT/NL2003/000324
Authority: WO
Inventors: Hermanus Josephus Aartsen
Original assignee: Nederlandse Organisatie Voor Toegepast- Natuurwetenschappelijk Onderzoek Tno
Priority date: 2002-05-02
Filing date: 2003-05-02
Publication date: 2003-11-13
Also published as: NL1020514C2; AU2003228138A1

Abstract

A system comprising at least one transmitter (31) and at least one receiver (4x) for locating an animal, person or object equipped with the transmitter (3) or the receiver (4x) using an ultrasonic signal comprising an identification code, in which each transmitter is arranged to transmit the ultrasonic signal with an identification code corresponding to the respective transmitter (3) and each receiver (4x) is arranged to identify, on the basis of the identification code of each received ultrasonic signal, the transmitter (3) from which the ultrasonic signal was transmitted.

Description

System for locating a person, animal or object using an ultrasonic signal comprising an identification code

The invention relates to a system comprising at least one transmitter and at least one receiver for locating an animal, person or object equipped with the transmitter or the receiver using an ultrasonic signal comprising an identification code. The US patent 3,696,384 shows such a system. In the use of this known system, the person is, for instance, equipped with a receiver provided with an identification code. In, for instance, each room where the person can be expected to be present, a transmitter is provided. The transmitter is arranged to transmit an ultrasonic signal and to provide an ultrasonic signal with any identification code which may be desired at a certain moment. In use, the ultrasonic signal comprises an identification code selected from a plurality of identification codes. Upon the receiver receiving ultrasonic signal, the receiver compares the identification code of the signal to the identification code of the receiver. When the identification code of the signal does not correspond to the identification code of the receiver, a responder connected to the receiver is not activated. When the identification code of the ultrasonic signal corresponds to the identification code of the receiver, the responder with which the person is equipped is activated. In that case, the responder emits a signal. This signal can, for instance, also be an ultrasonic signal which can be received by a fixed receiver arranged in the room where the person is present. This fixed receiver can, for instance, pass on the location of the person to a centrally located location unit. In this manner, using the system, for instance, a telephone call coming in elsewhere can be automatically redirected to the room in which the receiver arranged in the room received the ultrasonic signal transmitted by the responder. However, the signal of the responder can also be an audible sound signal, so that the person becomes aware of the system trying to locate him or her. In that case, the person can, for instance, walk to a telephone and call a number to ask why he or she is being paged.

A drawback of such a system is that the system is not suitable for supplying location-related information to the receiver in a simple manner. ^" The invention contemplates providing a system as set forth in the preamble with which also enables location-related information to be supplied to the receiver.

This object is achieved using the system according to the invention which is characterized in that each transmitter is arranged to transmit the ultrasonic signal with an identification code corresponding to the receiver and each^* receiver is arranged to identify the transmitter from which the ultrasonic signal was transmitted on the basis of the identification code of each ultrasonic signal. It is possible, when using the system according to the invention, to equip the person with a receiver and to arrange a transmitter in each room where the person can be expected to be present. In this case, the receiver is preferably movable and the transmitters are fixed. In use, a plurality of ultrasonic signals are transmitted. Each ultrasonic signal is provided with an identification code corresponding to the transmitter from which the ultrasonic signal was transmitted. Upon receiving an ultrasonic signal, the receiver identifies from which transmitter the ultrasonic signal was transmitted on the basis of the identification code. As is known, an ultrasonic signal is hardly, if at all, capable of penetrating walls. A system according to the invention will preferably be arranged to generate ultrasonic signals which cannot penetrate through walls at all. Thus, the ultrasonic signal received by the receiver will come from the transmitter arranged in the room where the person with the receiver is present. In this case, it is possible to provide the receiver with information related to the room using the received signal comprising an identification code of the transmitter present in the room. This manner of using the system will hereinafter be referred to as a use of the system in which the person is equipped with a receiver.

It will be clear that here, the notion of locating can also comprise supplying location-related information to a person equipped with the receiver.

However, when using the system according to the invention, it is also possible that the person is equipped with the transmitter and that a receiver is arranged in each room where the person may be expected to be present. In this case, the transmitter is movable and the receivers are fixed. Now, the transmitter only needs to transmit ultrasonic signals with an identification code corresponding to the transmitter. The receiver, which is present in the room in which the person with the transmitter is present, receives the ultrasonic signal and can then identify the transmitter from which the ultrasonic signal was transmitted. The receiver will only receive the ultrasonic signal transmitted by a transmitter present in the room in which the receiver is present. As stated above, ultrasonic signals are not well capable of penetrating walls. The reason is that the ultrasonic signal transmitted by a transmitter in an adjacent room will hardly be received by the receiver, if at all. In other words, a receiver only receives an ultrasonic signal of a transmitter when the receiver is in the acoustic range of the transmitter. When using the system according to this manner, the system is capable of locating the person. The information about the location of the person initially goes to the system which can then send or show the information to a user. This user will mostly not be the person equipped with the transmitter. Such a use of the system will hereinafter be described as a use of the system in which the person is equipped with the transmitter.

The system preferably comprises a plurality of receivers. In the use of the system in which a person is equipped with a transmitter, this will involve the person being locatable in many mutually different places. In the use of the system in which a person is equipped with a receiver, this involves a plurality of mutually different persons being locatable.

Further, the system preferably comprises a plurality of transmitters. In the use of the system in which persons are each equipped with a transmitter, it is, in that case, possible to locate many mutually different persons. In the use of the system in which the person is equipped with a - receiver, this involves the person being locatable in many mutually different places.

A preferred embodiment of the system according to the invention comprises a plurality of transmitters and a plurality of receivers.

In an alternative embodiment, each transmitter and each receiver is arranged to be moved. This offers the advantage that each person equipped with a receiver can determine which transmitter is present nearby and/or in the same room on the basis of the identification code of a received signal. A particular embodiment of the system according to the invention is characterized in that each receiver is arranged to select, upon receiving a plurality of mutually different ultrasonic signals, an ultrasonic signal for identifying on the basis of intensity differences between the received ultrasonic signals. For instance, the receiver can select the ultrasonic signal having the highest intensity for identifying the transmitter from which the ultrasonic signal was transmitted on the basis of the identification code of the ultrasonic signal. In the use of the system in which the person is equipped with a receiver, the person is located in this manner using the transmitter arranged in a room in which the person is present. It is also possible that a rough locating takes place using, for instance, the intensities of ultrasonic signals with mutually different identification codes. Here, use is made of the insight that the intensity of an ultrasonic signal decreases as the distance of the transmitter which transmitted the ultrasonic signal increases. In the case where the person is equipped with the transmitter, this particular embodiment involves a receiver being able to select one ultrasonic signal for identification using intensity differences between the ultrasonic signals. This will preferably be the ultrasonic signal with the highest intensity. This means that a receiver identifies only the ultrasonic - signal of a transmitter which is closest to this receiver and thereby locates only one person who is closest to the receiver. This can offer advantages when, for instance, in one large space, a plurality of transmitters are movably present and a plurality of receivers are set up spatially separate from each other. In addition, a receiver will not select an ultrasonic signal of a transmitter belonging to a person in an adjacent room separated by a wall for identification of the ultrasonic signal if this ultrasonic signal is still received by the receiver, in spite of the walls.

Further, it is possible for the system to be arranged to determine, on the basis of an intensity of a particular ultrasonic signal measured by each receiver, a location of the receiver of that particular ultrasonic signal.

In a further embodiment, the system is characterized in that the system is provided with a location unit for collecting information signals which each comprise information related to a reception of an identified ultrasonic signal and for locating the animal, the person or the object on the basis of the information signals.

In the use of the system in which the person is equipped with a receiver, the person can also be equipped with the location unit. In a large open space in which a plurality of transmitters are arranged at mutually different and spatially separate positions, this offers the advantage that the person is locatable at a relative position within the large open space. In other words, the person can obtain information on his or her position in relation to the fixed positions of the transmitters.

In the use of the further system in which the person is equipped with a transmitter, this embodiment offers the advantage that, in a large open space in which a plurality of receivers are arranged at mutually different and spatially separate positions, using the location unit, the person is locatable at a relative position within the large open space.

It is further possible that the system is arranged such that the at least one transmitter and the at least one receiver are synchronized with _, ^~ each other in use, preferably using a periodic signal coming from outside the system. This could be the 50 or 60 Hz signal which comes from the mains and is present in practically any building and usually also outside.

An embodiment of a system of which each transmitter and each receiver are synchronized with each other is further preferably characterized in that each transmitter is arranged to generate the ultrasonic signal in such a manner that the ultrasonic signal is provided with information accessible to each receiver concerning a point in time at which the transmission of the ultrasonic signal takes place and in which further, each receiver is arranged to register a point in time at which the reception of the ultrasonic signal takes place. In that case, the receiver and/or the location unit can determine a distance between the receiver and the transmitter from the difference between the point in time at which the ultrasonic signal was transmitted and the point in time at which the ultrasonic signal was received, yielding an even more accurate locating in cases in which the system with a plurality of transmitters and/or a plurality of receivers are arranged in one large open space. The location unit can very accurately determine the position of one or more transmitters using a plurality of such information signals coming from mutually different receivers.

Incidentally, it is also possible for the identification code to comprise the point in time, in absolute or relative terms, at which the transmission of the ultrasonic signal starts. In that case, there will be a situation in which, at a certain moment, one transmitter of the plurality of transmitters transmits an ultrasonic signal according to a predetermined program. The invention will now be elucidated with reference to a drawing, in which:

Fig. 1 diagrammatically shows a first exemplary embodiment of the system according to the invention; Fig. 2 diagrammatically shows a second exemplary embodiment of the system according to the invention;

Fig. 3 diagrammatically shows a third exemplary embodiment of the system according to the invention;

Fig. 4 diagrammatically shows a fourth exemplary embodiment of the system according to the invention;

Fig. 5 diagrammatically shows a fifth exemplary embodiment of the system according to the invention.

Equal parts have equal reference characters.

Fig. 1 diagrammatically shows a space 1 divided into four rooms A, B, C en D by walls 2. Each passage from one room to one of the other rooms is usually closed off by, for instance, doors (not shown). In room A, a person is present who is equipped with a movable transmitter 3 of portable design. The transmitter 3 is arranged to transmit an ultrasonic signal with an identification code corresponding to transmitter 3. In each room, a receiver is present which is arranged to be fixed. In each room X (X = A, B, C, D) a receiver 4.X is present, preferably at a fixed position. So, each receiver will usually be fixed in use, for instance by attachment to the wall 7. Each receiver 4.X is arranged to identify, on the basis of the identification code of each ultrasonic signal, the transmitter from which the ultrasonic signal was transmitted. In other words, when the transmitter 3 is present in room A, the receiver 4A receives the ultrasonic signal with the identification code corresponding to the transmitter 3. On the basis of the identification code, receiver 4A identifies transmitter 3 as the transmitter from which the ultrasonic signal was transmitted. Since an ultrasonic signal hardly penetrates walls, if at all, the receivers 4B in room B, 4C in room C and 4D in room D will hardly receive the ultrasonic signal from transmitter 3, if at all. As a response to the reception of the ultrasonic signal from transmitter 3, the receiver 4A can, for instance, activate a display (not shown) in room A on which information is shown which is specifically intended for the carrier of transmitter 3. It may also be, for instance, that receiver 4A passes on a signal to a central location unit (not shown) which makes it possible for a - telephone call coming in elsewhere, intended for the carrier of transmitter 3, to be redirected to a telephone present in room A. Another possibility is that, for instance, a voice from a loudspeaker in room A addresses the carrier of transmitter 3. In short, on the basis of the locating of the carrier of transmitter 3 by means of this system, it is possible to supply information to the carrier of transmitter 3. Preferably, each transmitter has an entirely unique identification code. However, it can also be the case that a group of transmitters has one and the same identification code. In this particular case, the transmitter with an identification code comprises a group of transmitters, each with the same identification code. An example of a use of such a system would be a group of French-speaking people in a museum. Each individual in this group could be in a different room. When each French-speaking person is equipped with a transmitter with an identification code belonging to the group of French-speaking persons, the information in each room where a French-speaking person is present will be rendered in French. In a room where the receiver does not receive an ultrasonic signal with the identification code belonging to the French- speaking group, no information needs to be rendered in French. The identification code could also belong to a room in a large hotel.

When a person present in another room far from the room is equipped with a transmitter arranged to transmit ultrasonic signals with an identification code belong to a specific room, this system enables the activation of signposting to the room in the hotel rented by the person. Near each fixed receiver receiving an ultrasonic signal with the identification code belonging to the specific room, for instance, an arrow in the direction of the room can be illuminated.

In a particular embodiment of the system according to the invention, each receiver is arranged to select, upon receiving a plurality of ultrasonic signals, an ultrasonic signal for identifying on the basis of intensity differences between the ultrasonic signals. For instance, it is possible for the receiver to be arranged to identify the transmitter from which the ultrasonic signal was transmitted only on the basis of the identification code of the ultrasonic signal having the highest intensity. A person equipped with a transmitter can, for instance, deliberately proceed in the direction of the receiver to be supplied with information. After all, when transmitters each transmit an ultrasonic signal of equal strength, the ultrasonic signal of the nearest transmitter will have the highest intensity. The receiver will thus only identify the transmitter of this signal and activate a predetermined response on the basis thereof.

It is also possible for each receiver to be arranged to ignore ultrasonic signals received with a specific intensity when this specific intensity is lower than a predetermined intensity. Such receivers make it possible to ignore ultrasonic signals which are still received from an adjacent room in spite of the presence of walls. It is of course possible to provide each room with a receiver so that at each moment when the transmitter transmits an ultrasonic signal, one of the receivers can locate a person equipped with the transmitter. It is of course also possible to provide only one or a few rooms with such a receiver. In this manner, for instance, when a track has to be covered by a person, it can be determined whether a person has passed a specific position.

Fig. 2 shows an embodiment of the system in which a person is equipped with a movable receiver 4 of portable design. Each room A, B, C, D is provided with a transmitter 3A, 3B, 3C, 3D. These transmitters are arranged to be fixed. Preferably, each transmitter is fixed, for instance by attachment to the wall. Due to the fact that an ultrasonic signal hardly penetrates a wall, if at all, each transmitter 3A, 3B, 3C, 3D has an acoustic range which is limited to the room A, B, C, D, respectively. After all, the rooms are generally separated by doors (not shown). So, in use, the receiver 4 only receives an ultrasonic signal coming from the transmitter present in the room in which the receiver is present. In this case, each transmitter 3A, 3B, 3C, 3D has its own unique identification code corresponding to the room X in which the transmitter 3.X is present. On the basis of the identification code of the ultrasonic signal, the receiver 4 identifies the room in which the receiver 4 is present.

In this case, locating a person comprises supplying information to the person, who is equipped with the receiver 4, concerning the location of this person. In this example, the person can be provided with a map with information shown per room. By means of the locating, the person knows which information belongs to the room in which he is present. The person can also be equipped with a CD-ROM walkman on which, upon receiving information about the room in which the person is present, the person can hear information related to the room. Such a use can, for instance, take place in a museum or a hotel. Also in this case, each receiver can be arranged to select, upon receiving a plurality of mutually different ultrasonic signals, an ultrasonic signal for identifying using intensity differences between the ultrasonic signals.

When, for instance, the ultrasonic signal from an adjacent room is still received and an ultrasonic signal from the room in which the person with the receiver 4 is present is received, the receiver can ignore the ultrasonic signal transmitted by a transmitter in an adjacent room on the basis of the intensity differences between the ultrasonic signals.

Fig. 3 shows a third embodiment of the system according to the invention. In this case, a person is again equipped with a portable transmitter 3 which transmits ultrasonic signals with an identification code corresponding to the transmitter. In this case, the person is present in a large open space 5. In the large space 5, four spatially separate receivers 4A, 4B, 4C, 4D are fixedly included. The system is also provided with a location unit 6. When the transmitter 3 transmits an ultrasonic signal with an identification code corresponding to the transmitter 3, each receiver 4A, 4B, 4C, 4D will receive this signal and identify transmitter 3 using the identification code. Each receiver 4A, 4B, 4C, 4D is further arranged to determine the intensity of a received ultrasonic signal. The intensity of the ultrasonic signal transmitted by transmitter 3 will be higher upon reception by receiver 4C than upon reception by receiver 4B. The intensity of the ultrasonic signal received by receiver 4B will be higher than the intensity of the signal received by the receiver 4A. The intensity of the signal received by receiver 4A will then be the lowest. These intensity differences are the result of the different distances of the receivers 4A, 4B, 4C, 4D in relation to the transmitter 3. In general, the larger the distance between the transmitter 3 and the receivers 4A, 4B, 4C, 4D, the larger the loss of intensity upon receiving an ultrasonic signal will be in relation to the intensity of the ultrasonic signal transmitted by transmitter 3. In the exemplary embodiment shown in Fig. 3, the location unit 6 collects information signals which each comprise information related to a reception of an identified ultrasonic signal. On the basis of the information signals, the location unit is capable of indicating a location in relation to the receivers 4A, 4B, 4C, 4D of the person carrying the transmitter 3. So, in this case, the system is arranged to determine, on the basis of an intensity of a particular ultrasonic signal measured by each receiver, a location of the transmitter of that particular signal. The information signals can be passed on to the location unit 6 via a network. Such a network can optionally be wireless. The information signals can, for instance, be passed on to the location unit 6 using electromagnetic signals. A user of the location unit 6 then receives the information on the location of the person equipped with the transmitter

Fig. 4 shows a fourth embodiment of the system according to the invention. In this case, a person present in a large space 1 is equipped with a portable receiver 4. In the large open space 5, four spatially separate transmitters 3A, 3B, 3C, 3D are fixedly included Each transmitter 3 X (X = A, B, C, D) transmits an ultrasonic signal with an identification code corresponding to the transmitter 3.X. Receiver 4 receives the ultrasonic signal from each transmitter 3 X. When each transmitter 3 X transmits the ultrasonic signal with a predetermined intensity, upon reception by the receiver 4, the intensity of the signal coming from transmitter 3B will be the highest. The intensity of the ultrasonic signal received by receiver 4 coming from transmitter 3C will be higher than the intensity of the ultrasonic signal received by receiver 4 coming from transmitter 3A. In this case, the system can also be provided with a location unit 6 so that, on the basis of the intensity differences between the ultrasonic signals, it can be determined where a person equipped with the receiver is in the large open space 5 Preferably, the location unit 6 is also present near the person equipped with the receiver 4 In that case, the information signals which each comprise information related to a reception of an identified ultrasonic signal can be passed on directly to the location unit 6. Then, the locating of the person on the basis of these information signals can be made knowable to the person So, also in this case, the system is arranged to determine, on the basis of intensity differences in one ultrasonic signal, a location of the transmitter of the signal concerned

Of course, it is also possible for a person equipped with the receiver to be equipped with a wireless transmission apparatus as well, which transmits the information signals to location unit 6 located elsewhere In this case, the information concerning the locating of the person with the receiver is made knowable to others than this person Fig. 5 shows a fifth embodiment of a system according to the invention. In this case, each receiver 4 and each transmitter 3 are arranged to be movable. When, in use, a transmitter 3 present in room A transmits an ultrasonic signal, a receiver also present in room A will be able to determine, upon receiving a signal from transmitter 3, that transmitter 3 is present in room A. Such an embodiment can be advantageous in a situation in which room A is, for instance, very large and it is not directly visible to a person equipped with the receiver that a person equipped with the transmitter is present in room A. Of course, it is also possible that each object or person moving about the rooms is equipped with both a transmitter and a receiver. In room C, such a situation is shown diagrammatically. It is clear that, in the situation drawn, the person present in room C and equipped with both the receiver and the transmitter will neither be noticed himself by other receivers nor will it notice other transmitters, since the ultrasonic signals from the receiver in C do not reach into A, B or D and the signals of transmitters in A, B or D do not reach into C.

In each abovementioned exemplary embodiment, it is possible for the system to be arranged such that the at least one transmitter and the at least one receiver are synchronized with each other in use. The system can be arranged to perform such a synchronization itself by, for instance, having the central location unit transmitting an RF signal to both the transmitters and the receivers. Preferably, however, the transmitters and the receivers are each arranged for receiving a periodic signal from outside the system for the purpose of synchronization. Here, to be considered is the 50 or 60 Hz signal from the mains. The transmitters and/or receivers can, for instance, be equipped with an optical receiver for light for this purpose. This is because the intensity of artificial light varies with the frequency of the mains. An alternative possibility is that the transmitters and/or the receivers are arranged for picking up electromagnetic waves transmitted by the mains. A once-only synchronization of the system, upon installation or operation, will be required when using such a reference signal. Instead of a signal from the mains, a universal time signal, such as the one transmitted by the DCF-77 time transmitter arranged in Frankfurt (Germany), can also be used.

Also, optionally, a synchronization signal from another local wireless communication system can be used, such as for instance the synchronization signal which synchronizes the handsets in the DECT telephone system. In principle, any carrier wave of any transmitter which can be received continuously can be suitable as synchronization signal.

In each abovementioned exemplary embodiment with a synchronization facility, it is possible for each transmitter to be arranged to generate the ultrasonic signal in such a manner that the ultrasonic signal is provided with information, which is accessible to each receiver, concerning a point in time at which the transmission of the ultrasonic signal starts. Each receiver can further be arranged such that a point in time at which the receiver receives the ultrasonic signal is registered. In this case, on the basis of the transmission time and the reception time of a plurality of ultrasonic signals coming from spatially separate transmitters, a much more accurate position in relation to these transmitters can be determined. Of course, the sound velocity of the medium through which the ultrasonic signals are transmitted should be known. It will be clear to a skilled person that, in this embodiment, use can be made of the transmission of pulses, with information on the time of the transmission of, for instance, a first pulse in a series of successive pulses being stored. The time of receiving the first pulse is registered and stored by the receiver. The so-called Time-Of-Flight (TOF) can then be calculated in a simple manner. The narrower the pulse, the more accurate the TOF and the locating.

However, it is also possible to use a continuous signal such as a carrier wave with a modulation related to a point-in-time transmission code. Preferably, in each variant embodiment, each transmitter is arranged to transmit ultrasonic signals according to a predetermined program. Such a program can be written to prevent interference with other ultrasonic signals. However, it is also possible that such a program can be written with a view to a frequent locating of a person. In addition, such a variant embodiment can involve a very low-energy system, which is especially advantageous for the movable transmitter and/or receiver. In that case, an accumulator or battery can have a small and transportable design. For instance, also due to these advantages, it is also conceivable that each receiver is arranged to actively operate according to a program which corresponds to the predetermined program.

In»a variant embodiment arranged to make use of the TOF of the ultrasonic signals and of which each transmitter is arranged to transmit ultrasonic signals according to a predetermined program, it is possible to consider the time of transmission as the identification code.

A system according to the invention can be manufactured in a simple manner by a skilled person using known technology. The skilled person will preferably arrange the system such that, in any case, the ultrasonic signals cannot penetrate the walls. Preferably, the ultrasonic signal is even such that it cannot penetrate doors. However, in a variant in which, on the basis of intensity differences between received signals, one signal is selected for identifying the transmitter, it is possible for such requirements on the ultrasonic signal to be less stringent. Incidentally, using the technology known per se, the skilled person can arrange the system such that the receivers, upon receiving a plurality of mutually different ultrasonic signals, select an ultrasonic signal for identifying by means of intensity differences between the ultrasonic signals. After all, determining the intensity of a received ultrasonic signal is technology known per se. In this manner, it is also simple to the skilled person to arrange the transmitters and/or the receivers such that these are fixable or movable. A system according to the invention has numerous uses. For instance, both persons and animals can be equipped with a transmitter or a receiver. When used with persons, the system can be set up in department stores, hotels, museums, holiday parks, hospitals and prisons. When used with animals, examples would include large farms, slaughterhouses, cattle markets, and optionally zoos. However, the use is not limited to animals and persons. It is also possible to provide goods with a transmitter or a receiver. This offers possibilities for uses in large warehouses and transportation systems. Although use of the system on land is the most obvious, use of the system in the air or in water is not precluded. When using the system in water, for locating by means of time registration of transmission and receiving the ultrasonic signals, the velocity of the ultrasonic signal in water has to be used. It is also possible to arrange the system such that a sudden change of the intensity of the ultrasonic signal and/or the TOF of the ultrasonic signal can be converted into an indication, to be shown to the user of the system, of a possible change of the medium through which the signal is transmitted. In this manner, it can, for instance, be determined whether a transmitter is present under or above water, which can be useful for, for instance, rescue operations at sea. To prevent disturbing interferences which can, for instance by reflection, locally amplify but also locally quench the signal, a frequency variation can be used. Other techniques known per se can also be used to optimize the ultrasonic signal. It will be clear that, when using points in time for determining the TOF, use can be. made of absolute times. However, preferably, relative times are used.

The system is also very suitable for uses in combination with other systems. Here, to be considered are a combination with closed video circuits, control systems at, for instance, stations and/or in trains and at airports and/or in airplanes. Such variants are all considered to be within the scope of the invention.

Claims

1. A system comprising at least one transmitter and at least one receiver for locating an animal, person or object equipped with the transmitter or the receiver using an ultrasonic signal comprising an identification code, characterized in that each transmitter is arranged to transmit the ultrasonic signal with an identification code corresponding to the respective transmitter and each receiver is arranged to identify, on the basis of the identification code of each received ultrasonic signal, the transmitter from which the ultrasonic signal was transmitted.

2. A system according to claim 1, characterized in that the system comprises a plurality of receivers.

3. A system according to claim 1 or 2, characterized in that the system comprises a plurality of transmitters.

4. A system according to any one of the preceding claims, characterized in that each receiver is arranged to be fixed.

5. A system according to claim 4, characterized in that each transmitter is movable and each receiver is fixed.

6. A system according to any one of claims 1-3, characterized in that each transmitter is arranged to be fixed.

7. A system according to claim 6, characterized in that each receiver is movable and each transmitter is fixed.

8. A system according to any one of claims 1-3, characterized in that each transmitter and each receiver is arranged to be moved.

9. A system according to any one of the preceding claims, characterized in that the at least one receiver is arranged to determine the intensity of a received ultrasonic signal.

10. A system according to any one of the preceding claims, characterized in that each receiver is arranged to select, upon receiving a plurality of mutually different ultrasonic signals, an ultrasonic signal for identifying by means of intensity differences between the ultrasonic signals received.

11. A system according to any one of the preceding claims, characterized in that the system is provided with a location unit for collecting information signals which each comprise information related to a reception of an identified ultrasonic signal and for locating the animal, the person or the object on the basis of the information signals.

12. A system according to any one of the preceding claims, insofar as dependent on claim 2, characterized in that the system is arranged to determine, on the basis of an intensity of a particular ultrasonic signal measured by each receiver, a location of the transmitter of that particular ultrasonjc signal.

13. A system according to any one of the preceding claims, characterized in that the system is arranged such that the at least one transmitter and the at least one receiver are synchronized with each other in use.

14. A system according to any one of the preceding claims, characterized in that the at least one transmitter and/or the at least one receiver is arranged for receiving a periodic signal coming from outside the system for the purpose of synchronization.

15. A system according to any one of the preceding claims, characterized in that each transmitter is arranged to generate the ultrasonic signal in such a manner that the ultrasonic signal is provided with information accessible to each receiver concerning a point in time at which the transmission of the ultrasonic signal takes place and in which, further, each receiver is arranged to register a point in time at which the reception of the ultrasonic signal takes place.

16. A system according to any one of the preceding claims, characterized in that each transmitter is arranged to transmit ultrasonic signals according to a predetermined program.

17. A system according to claim 16, characterized in that each receiver is arranged to actively function according to a program which corresponds to the predetermined program.

18. A system according to any one of claims 15-17, characterized in that the identification code comprises the point in time at which the transmission of the ultrasonic signal starts.