AU2002339465B2

AU2002339465B2 - Method for determining the position of a mobile device, in particular an emergency-call device, emergency-call system and an emergency-call device

Info

Publication number: AU2002339465B2
Application number: AU2002339465A
Authority: AU
Inventors: Fridolin Speiser
Original assignee: GPP AG
Current assignee: GPP AG
Priority date: 2001-09-11
Filing date: 2002-09-02
Publication date: 2007-07-12
Anticipated expiration: 2022-09-02
Also published as: NO330971B1; DE50207523D1; PT1427992E; NO20041416L; ES2268102T3; ZA200402745B; HK1074872A1; EP1427992B1; EP1427992A1; CN1585889A; CN100593728C; ATE333087T1; EP1293757A1; DK1427992T3; WO2003023326A1

Abstract

The method involves transmitting base data required for position determination from the central station (10) to the mobile device (11) after establishing a data transmission connection between them. The current position of the mobile device is computed from received satellite data and the base data from the central station. Independent claims are also included for an emergency call device and an emergency call system.

Description

-1- "Method For Determining The Position Of A Mobile Device, In Particlar An Emergency-Call Device, Emergency Call System And An Emergency-Call Device" Field of the Invention The invention relates to a process for determining the position of a mobile device, specifically a distress call device, and a distress call system with a central station and at least one such mobile distress call device and to a distress call device itself.

Background Art It is today possible by means of the satellite-based positioning and locating system GPS (Global Positioning System) to determine a location or geographic position practically anywhere in the world when a suitable GPS module is in use.

This is possible because the GPS module receives constant positioning information from different satellites and can thus constantly determine its position during normal permanent operation.

If, however, such a module is in a switched-off state when at an unknown location, it will then not be able to establish its current position immediately after it is switched on again, since certain basic data have to be calculated from the data received from the satellites before information on the time, the identity of the different satellites from which signals are received and satellite orbits can be obtained. Only after a starting phase lasting several minutes is it possible therefore to establish the precise position of the GPS module after it has been switched on at an unknown location. Such a long delay until the position can be determined is, however, unacceptable for a system intended for use in emergencies where every minute can be vital.

A person and vehicle security system is already state of the art for motor vehicles, which comprises a distress call device equipped with a GPS module that can create a connection to a central station by means of a GSM module (Group -2- Special Mobile or Global System for Mobile Communication) via a mobile telecommunications network. In cases of emergency, the user can press a certain button to transmit to this central station the current position of the vehicle in which the distress call device is installed and at the same time create a voice connection so that the user of the distress call device can notify the central station regarding the nature of the accident.

A device for securing a stretch of way or a location for persons requiring protection, in particular children, is already known from DE 196 47 532 A1, according to which the person to be protected carries on his person a distress call device and can in case of emergency press a distress signal button to activate a distress call signal, which then transmits via a suitable radio network a distress signal to a distress call receiver that in turn receives, displays and/or transfers this distress signal to a reception station. To enable positioning of the person requiring assistance in case of emergency, a transmission crystal installed in the distress call device is activated at the same time as radio contact is made, so that the device can be positioned with the aid of the signal emitted from the transmission crystal.

One significant disadvantage of this system is that the location from which the distress call is sent can be established only with the aid of a suitably complex radio positioning device, which leads to considerable delays, which in turn represents a very serious disadvantage in an emergency situation when each minute saved can be vital for the success of rescue measures.

One state-of-the-art system specifically for locating missing children (DE-Z, Bella, Vol. 33, 2001) entails equipping a child's teddy bear with a special positioning device that can signal the location of the toy with a precision of up to 10 metres via a GSM telephone network to a specific telephone number of the anxious parents.

In addition, a distress signal transmitter for children has been proposed that can be activated at the press of a button or automatically as soon as the child strays too far from a predefined area. The location is then established by means of -3satellites. This proposed distress signal transmitter therefore operates with a satellite-based positioning module, which is permanently switched on and which accordingly constantly consumes energy. The device must therefore be regularly recharged or the battery regularly replaced.

Although this state-of-the-art distress signal transmitter offers the advantage that its position can be directly registered in case of emergency, there is nevertheless the danger that the permanent consumption of energy will lead to the internal power source being insufficient at the time of the emergency with the result that no distress signal can be sent.

The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia or elsewhere as at the priority date of the application.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention In the light of the above, the invention is based on the task of providing a process for determining the position of a mobile device, specifically a distress call device, which allows the position of the device to be determined practically immediately after the device has been switched on, with the result that there is no longer any need for constant operation of a satellite-based positioning module.

One further task of the present invention is to provide a distress call system and a distress call device usable in this system by means of which the position of the distress call device can be determined quickly in case of emergency without this device having to permanently register its position.

-4- These tasks are solved by a process, a distress call system, and a mobile distress call device as described below. Further advantageous refinements and embodiments of the invention are described in the respective sub-claims.

In accordance with one aspect of the invention there is provided a process for calculating the position of a mobile device normally switched-off, specifically a distress call device having a satellite-based positioning module and a transmitter-receiver unit, which is able at least to establish a data transmission connection to a central station, in which upon switching on a data transmission connection is created between the mobile device and the central station, after the data transmission connection has been created between the mobile device and the central station, the basic data required for satellite-based positioning are transmitted from the central station to the mobile device, and the current position data of the mobile device are calculated from received satellite data by means of the basic data transmitted from the central station.

Preferably the process is characterised in that an approximate position of the mobile device is first established after the data transmission connection has been created between the mobile device and the central station, the basic data required for satellite-based positioning corresponding to the approximate position are calculated in the central station.

Preferably the process is characterised in that the calculated position data of the mobile device are transmitted to the central station.

Preferably the process is characterised in that a participant identification number is transmitted from the mobile device to the central station when the data transmission connection is created.

Preferably the process is characterised in that a call type identification is transmitted from the mobile device to the central station when the data transmission connection is created.

Preferably the process is characterised in that a distinction between emergency and test signals can be made in the central station on the basis of the call type identification and that each data transmission connection is stored in the central station together with the relevant call type for documentation purposes.

Preferably the process is characterised in that the basic data required for satellite-based positioning are constantly updated in the central station on the basis of the data received from satellites.

Also in accordance with a second aspect of the invention there is provided a distress call system with a central station and at least one mobile distress call device normally switched-off that is connected to the central station for transmitting a signal via at least one data transmission connection in order to transfer a location of the mobile distress call device ascertained by means of a satellite-based positioning system to the central station, wherein the central station has an input module for receiving satellite data and for determining the basic data required for satellite-based positioning, has an input-output unit for receiving a call from and for dataexchange with a distress call device, has a output unit for issuing the data related to a distress call and a central control unit that controls data exchange between the central station and a mobile distress call device through the data transmission connection as well as output of the data relating to a distress call, and wherein the distress call device has at least a satellite-based positioning module, and a transmitter-receiver unit for transferring current position data -6determined from basic data from the central station and received satellite data to the central station.

Preferably the distress call system is characterised in that the central station has a participant database for participant-specific data as well as a database for telephone numbers and/or connection addresses for rescue and/or assistance centres.

Preferably the distress call system is characterised in that the output unit of the central station comprises a further transmitter-receiver unit for forwarding incoming distress calls to the relevant rescue and/or assistance points.

Preferably the distress call system is characterised in that the output unit of the central station comprises a display unit for displaying information relating to an incoming distress call.

Preferably the distress call system is characterised in that the central station and the distress call device are each fitted with a speech-aural device, so that a speech transmission connection can be constructed through the input-output unit and the transmitter-receiver unit.

In accordance with a third aspect of the present invention there is provided a mobile distress call device specifically for use in a distress call system as described above, with a satellite-based positioning module, a transmitter-receiver unit for establishing a data transmission connection to a central station, a central control unit controlling the creation of a data transmission connection to and data exchange with the central station, and an emergency switch by means of which an internal power supply for switching on the control unit and for activating a distress call transmission program can be connected, wherein upon switching on basic data required -7for satellite-based positioning can be conducted from the central control unit to the satellite-based positioning module).

Preferably the distress call device is characterised in that an alarm siren is provided that can be switched on by means of the emergency switch at the same time as the distress call transmission program is activated.

Preferably the distress call device is characterised in that the emergency switch is designed so that when the power supply has been switched on it can no longer be switched off.

Preferably the distress call device is characterised in that a test switch through which the internal power supply for switching on the control unit and for activating a test signal transmission program can be connected and an output device is provided issuing a signal indicating whether the device is functioning or not.

The invention therefore specifies for the process that, after a data transmission connection has been made between the mobile station and the central station, the basic data required for a satellite-based positioning system in an emergency are transmitted from the central station to the mobile device, so that the current position can be determined immediately in the mobile device from the data received from the satellite by means of the basic data transmitted from the central station.

The process in accordance with the invention therefore enables the position of the mobile device to be determined to a precision of 10 metres within the briefest time (less than 30 seconds) after the device has been switched on and a data transmission connection created, and with no need for the device to be constantly switched on. The process in accordance with the invention accordingly enables a mobile device, specifically a distress call device, to remain operable practically without maintenance over several years. If, for example, the mobile device is run on batteries that can retain their energy over a period of at least seven years, such a device can remain reliably on stand-by over a five-year period after -8deduction of a safety margin of two years), as no energy is used when in stand-by mode.

In order to reduce further the necessary computing work in satellite-based positioning systems, and thus also the time required for the calculation, a further advantage is provided in that the approximate position of the mobile device will be established initially after the data transmission connection has been established between the mobile device and the central station, and that the basic data required for satellite-based positioning will be calculated in the central station according to this approximate position. The approximate position of the device can be easily determined especially when the mobile device uses a cellular mobile telecommunications network to create a data transmission connection to the central station.

Although it is generally conceivable that the basic data required for satellite-based positioning can be accessed by a central station, while the distress call itself is transmitted directly to a special rescue service or some similar point, one practical refinement of the invention provides that the calculated position data of the mobile device are transmitted to the central station, wherein, when the data transmission connection is being established, the mobile device transmits a participant identification number to the central station.

In this way, the central station can establish, in addition to the location of the emergency, also the identity of the person in the emergency situation, particularly when an internationally unique number is used as participant identification, which is preferably encoded in the hardware of the mobile device and which is matched uniquely with the personal data of the participant in the central station.

In order to distinguish between whether the process in accordance with the invention is being carried out to raise the alarm or for some other reason, for example, to test the mobile device, it is provided as a further advantage that the mobile device transmits a call type identification code to the central station when the data transmission connection is being established.

Use of such call type identification furthermore means that the process in accordance with the invention can also be used together with devices that, for example, provide the user with the possibility of not only sending a distress call but also of establishing his geographical position quickly and reliably without having to keep the device in permanent operation or having to wait unnecessarily long for the positioning result.

One practical refinement of the invention is characterised in that this call type identification is used in the central station to make a distinction between emergency and test signals, and that each data transmission connection is stored for documentation in the central station together with the relevant call type. This in turn means that the remaining battery capacity can be estimated in the central station on the basis of the number and duration of the test calls carried out, so that the user can be informed when the battery of his distress call device could have become too low as a result of such test calls.

In a further practical refinement of the invention, it is provided that the basic data required for satellite-based positioning are constantly updated in the central station on the basis of the data received from the satellite.

The process in accordance with the invention can be used in a particularly advantageous way in a distress call system with a central station and at least one, but preferably a plurality of mobile distress call devices, that can be connected to the central station for transmitting a call through at least one data transmission connection in order to transmit to the central station the location of the mobile distress call device calculated by means of a satellite-based positioning system.

The central station comprises therein an input module for receiving satellite data and for determining the basic data required for satellite-based positioning, an input-output unit for receiving a call from and for exchanging data with a distress call device, an output unit for issuing the data relating to a distress call and a central control unit that controls data exchange between the central station and a mobile distress call device via the data transmission connection as well as issue of the data relating to a distress call, while the distress call device is provided with at least one satellite-based positioning module and one transmitter-receiver unit in Sorder to determine the current position data and to transmit these to the central station.

(In order to transmit information from the central station to a rescue service, the rescue or assistance point closest to the emergency location, for example the nearest police station, regarding not only the location and the fact of an emergency, an advantageous refinement of the invention specifies that the central a station is provided with a participant database for storing participant-specific data N and a database for telephone numbers and/or connection addresses of rescue

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Oand/or assistance points.

One specific advantage is when the output unit of the central station comprises a further transmitter-receiver unit so that an in-coming distress call can be transmitted to the relevant rescue and/or assistance point, wherein the output unit in the central station is provided with a display unit for displaying the information regarding a received distress call.

In order to allow the user who happens to find himself in an emergency situation inform the emergency station of the location of the emergency, one other embodiment of the invention provides for the central station and the distress call device being each equipped with a speech-aural device, so that a voice transmission connection can be established via the input-output unit and the transmitter-receiver unit.

A mobile distress call device that can be used advantageously in the distress call system in accordance with the invention comprises a satellite-based positioning module, a transmitter-receiver unit for establishing a data transmission connection to a central station, a central control unit that controls the data transmission connection to and data exchange with the central station as well as an emergency switch which can connect this to an internal power supply for switching the control unit and activating a distress call transmission program.

Use of a single emergency switch that switches on and off not only the internal power supply, and thus activates the distress call device, but which at the same -11 time also activates a distress call transmission program, means that a distress call Ndevice can be provided which, when integrated suitably in a distress call system, allows its users, in an emergency situation, the possibility of making a distress call Nwithin seconds and without thinking. Because there is only one single switch to activate, the device can be quickly and reliably operated by a user even in hectic k or traumatic situations.

It is also provided as a practical solution that the satellite-based positioning N module can be fed basic data from the central control unit that are required for

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O satellite-based positioning.

To enable the distress call device in accordance with the invention to be used not only for triggering a distress call to a remote rescue service point or police station, but also to summon help in the vicinity of the emergency, as well as to discourage would-be attackers, it is provided in one particularly preferred embodiment that an alarm siren is fitted that can be activated by the emergency switch at the same time as the activation of the distress call transmission program, wherein the emergency switch is designed so that when the power supply has been switched on it cannot be switched off again.

With the aid of the integrated alarm siren in accordance with the invention, the distress call device of the invention will become, on the one hand, a kind of selfdefence device, that can be activated in case of danger, and which then in very many cases will frighten away the would-be attacker, who normally wants to keep his crime concealed to avoid discovery and detection. On the other hand, the acoustic signal emitted by means of the alarm siren also functions as a call for assistance, which will facilitate discovery of the person in the emergency situation.

Specifically in cases where the distress call device is used as an acoustic weapon of self-defence against an attacker, the fact that the distress call device cannot be switched off by the culprit prevents transmission of the alarm signal being interrupted.

Because the distress call device in accordance with the patent is carried by the user and must be potentially usable over several years, it is practical when a test -12switch through which the internal power supply for switching the control unit and for activating a test call transmission program can be connected and an output device are provided that emit a signal indicating whether the device is operable or not. This allows the user to test the distress call device from time to time, so that he can have constant reassurance that the device is operating correctly.

Brief Description of the Drawings The invention is described in the following, by way of example, on the basis of drawings: Fig. 1 shows a schematic simplified representation to demonstrate the structure of the distress call system in accordance with the invention.

Fig. 2 shows a schematic simplified block circuit diagram of a distress call device in accordance with the invention.

Fig. 3 shows a schematic simplified block circuit diagram of a central station of the distress call system in accordance with the invention.

Best Mode(s) for Carrying Out the Invention The different figures of the drawing show corresponding components with the same reference.

As shown in Fig. 1, the distress call system is provided with a central station and preferably a plurality of mobile distress call devices 11, of which only one is illustrated. The central station 10 comprises an input module 12 with a corresponding antenna 13 for receiving satellite data transmitted from a plurality of satellites 14, as is illustrated in Fig. 1 by arrow 15 indicating the relevant transmission path. Satellites 14 belong to a satellite-based positioning system, for example to the GPS system that is today preferably used.

The input module, which when the GPS system is used is a GPS module 12, and which calculates basic data from the received satellite data, which basic data are required for satellite-based positioning, is provided according to Fig. 3 with a central control unit 16 that controls data exchange between the central station -13and one of the distress call devices 11 through an input-output unit 17. The inputoutput unit 17 can be a mobile telecommunications module with an antenna 18 that can communicate through a GSM mobile telecommunications network with the individual distress call devices 11. Instead of a GSM module, the input-output unit 17 can also be a suitable terrestrial network module, which is connected through an input-output connection 18' to the relevant terrestrial network. The input-output unit 17 can, according to a specific embodiment of the invention, be matched with a speech-aural device 17', so that a voice connection through mobile or terrestrial networks is also possible.

For issuing data relating to a distress call, an output unit 20 is furthermore provided in the central station 10 which output unit is provided with a further transmitter-receiver unit 21 and a display unit 22. The transmitter-receiver unit 21 can be either a terrestrial network module, so that a connection can be made through the terrestrial network to various rescue and/or assistance points or to local rescue or police stations. The transmitter-receiver unit can, however, also be a mobile telecommunications module that operates according to the GSM standard or some other standard that is common now or in the future, for example the UMTS standard. The distress call data can also be fed through a suitable transmitter-receiver unit 21 into a data network, e.g. the Internet, where they can be accessed by rescue and assistance services.

The display unit 22 is designed preferably so that it can give a cartographic illustration of the emergency location, and can also display at the same time information relating to the person raising the alarm that is stored in a relevant database 23 in the central station 10, and that can, in the case of emergency, be transmitted from the central control unit to the display unit 22.

As can be seen best in Figure 2, the distress call device in accordance with the invention comprises a satellite-based positioning module 24, which is, for example, a GPS module with a relevant antenna 25, a transmitter-receiver unit 26 which is, for example, a mobile telecommunications module, specifically a GSM module with the relevant antenna 27, a central control unit 28 that controls the creation of a data transmission connection to and data exchange with the central -14station 10 of the distress call system, as well as an emergency switch 29 by means of which an internal power supply 30 can be connected to the control unit 28 in order to supply this with power and to activate an emergency transmission program. The emergency switch 29 is furthermore connected on the output side to a driver 31 of an alarm siren 32 that acts on a corresponding electroacoustic converter or loudspeaker 33. The transmitter-receiver unit 26 can be, according to a specific embodiment of the invention, be linked to a speech-aural device 26', so that speech connection is also possible. The transmitter-receiver unit 26 is thereby preferably designed in such a way that the distress call device 11 can operate not only in a GSM network but also in any other but preferably a cellular mobile telecommunications network.

To allow test operation of the distress call device 11 as in the invention, a test switch 24 can also be provided that connects the central control unit 28 to the internal power supply 30 through a different input than the emergency switch 29 in order to activate a test transmission program. A display lamp or diode can be provided as output device 35 for a signal indicating whether the distress call device is functioning correctly.

In order to reliably prevent the distress call device being switched off after it has been activated by means of the emergency switch, the emergency switch 29 comprises, in addition to an emergency start switch 29.1, also a locking switch 29.2 which can be designed, for example, as a field-effect transistor.

If the device in accordance with the invention is also to be used for quick and reliable calculation of the current geographical position of the user, a further power supply (not illustrated) would then be necessary, which would be activated through a further switch, which is also no illustrated. A display or announcement device (not illustrated) would also be necessary in order to output the calculated position after it has been established. These devices would also have to be fed from the further power supply so that the main or distress-signal power supply can be used only for distress or test calls.

The functioning of the distress call system in accordance with the invention is described in more detail below.

In an emergency situation, the distress call device in accordance with the invention is simultaneously switched on and activated by a person in the emergency situation by pressing the emergency switch. The emergency switch 29 is designed in such a way that the emergency start switch 29.1 can be felt and activated without need for the user to look. After the power supply to the distress call device has been switched on by means of the emergency switch 29, an alarm signal will be emitted from the alarm siren, which is preferably extremely loud, so that this alarm noise emitted in the case of attack will frighten away approximately of all attackers. A distress transmission program will be activated at the same time as the alarm signal.

For this purpose, the mobile telecommunications module 26 serving as a transmitter-receiver unit is first of all switched on and activated in order to create a data transmission connection to the central station 10 through the relevant communication network in use. At the same time the GPS module 24 commences the reception of satellite data that are received from the relevant satellites.

After the data transmission connection to the central station has been established, a participant identification number will be transmitted by the distress call device, which number is preferably stored on the hardware of the distress call device and is assigned uniquely to the user of the distress call device.

If the distress call device is also equipped with a test function, a call type signal can also be transmitted at the same time as the connection is made, which will show whether the call is a real emergency or a test. It is, however, also conceivable that such a call type signal is transmitted only if a test is to be carried out, so that in the central station absence of a call type signal will be taken to indicate an emergency call.

After the data transmission connection has been established, current basic data required for the positioning operation in the GPS module, the time of day and -16preferably also the approximate position of the distress call device will be sent from the central station to this device. The approximate position of the distress call device can be determined in the case of a data transmission connection established by means of a cellular mobile telecommunications network by positioning the mobile telecommunications cell in which the distress call device is located.

Therefore, after the basic data required for satellite-based positioning has been transmitted from the central station to the mobile distress call device, and thus to the GPS module, the GPS module 24 of the distress call device 11 can calculate on the basis of the satellite data received the precise position data of the distress call device.

Therefore, after the distress call device has been successfully positioned, this position will be transmitted to the central station.

When the basic data for calculating the current position are being transmitted, these can be selected according to the approximate position of the distress call device.

After the participant identification number of the distress call device 11 and the current position have been transmitted to the central station 10, the central station can first of all provide a cartographic illustration of the location from where the distress call was sent. At the same time, the participant data assigned to this participant identification number will be read from the participant database 23 and will preferably also be displayed.

If both the central station 10 and the distress call device 11 are each equipped with a speech-aural device 17', 26', a speech connection will also be created at the same time as the data transmission connection is established, so that the user will also be able to transmit further information regarding his emergency to the central station -17- On the basis of the information regarding the participant sending the distress signal that is now available, it is now possible for various points, such as parents, company, relatives, spouse, police and/or other rescue and assistance services, to be informed of the emergency.

It is specifically possible to forward the distress call to the police or assistance service that is closest to the location of the emergency. This means that the time between the distress call being sent and the arrival of assistance is reduced to a minimum.

Because the distress call device 11 will always continue to operate until the internal power supply, which is formed preferably by a suitable battery, has been used up, it can be established in this time whether the distress call device is moving or stationary. This will enable the police or the notified rescue service to obtain constantly updated information regarding the changing location of the person in the emergency.

If a test signal is transmitted to check the function of the distress call device 11, the test signal switch 34 will be activated instead of the emergency switch 29, so that the data transmission connection to the central station 10 can be established and so that, after the basic data have been transmitted, the current position can be ascertained by means of satellite data. Apart from the fact that in this system the alarm siren 32 is not activated when the distress call device 10 is being tested, and also no distress call is forwarded, the procedure will generally be the same as described above with regard to a distress call. After the distress call device 11 has sent its calculated position to the central station 10, the central station transmits a signal indicating the correct operation back to the distress call device 11, which signal is displayed by means of the output device 35, which can be, for example, a green light diode or something similar.

After the test call has been processed, the test call as such will be registered in the central station for the specific distress call device, so that an estimate can be made of the remaining capacity of the battery 30 in the distress call device 11 on the basis of the number and duration of test calls performed. In this way the -18functioning of the individual distress call devices 11 used in the distress call system can be constantly monitored and the user can be informed in time that the battery in his distress call device no longer has the performance necessary for full functioning in case of emergency and that the battery must therefore be replaced.

The process in accordance with the invention for determining the position of a mobile device, i.e. the position of the distress call device, means that a distress call device can be provided for a distress call system that is not only extremely easy to use, but that also remains potentially functioning over a longer period, because the device is normally passive and thus does not require any energy until it is activated in case of emergency. The process for determining position in accordance with the invention nevertheless allows the position of the device to be established in such a short time that the location of the emergency is already known in the central station of the emergency system 10 to 15 seconds after the emergency signal has been sent, and can then be forwarded to a suitable rescue and assistance service.

Claims

19- The Claims Defining the Invention are as Follows 1. A process for calculating the position of a mobile device normally switched-off, specifically a distress call device having a satellite-based positioning module and a transmitter-receiver unit, which is able at least to establish a data transmission connection to a central station, in which upon switching on a data transmission connection is created between the mobile device and the central station, after the data transmission connection has been created between the mobile device and the central station, the basic data required for satellite-based positioning are transmitted from the central station to the mobile device, and the current position data of the mobile device are calculated from received satellite data by means of the basic data transmitted from the central station. 2. Process according to claim 1, characterised in that an approximate position of the mobile device is first established after the data transmission connection has been created between the mobile device and the central station, the basic data required for satellite-based positioning corresponding to the approximate position are calculated in the central station. 3. Process according to claim 1 or 2, characterised in that the calculated position data of the mobile device are transmitted to the central station. 4. Process according to any one of the preceding claims, characterised in that a participant identification number is transmitted from the mobile device to the central station when the data transmission connection is created. 20 Process according to any one of the preceding claims, characterised in that a call type identification is transmitted from the mobile device to the central station when the data transmission connection is created. 6. Process according to claim 5, characterised in that a distinction between emergency and test signals can be made in the central station on the basis of the call type identification and that each data transmission connection is stored in the central station together with the relevant call type for documentation purposes. 7. Process according to any one of the preceding claims, characterised in that the basic data required for satellite-based positioning are constantly updated in the central station on the basis of the data received from satellites. 8. A distress call system with a central station and at least one mobile distress call device normally switched-off that is connected to the central station for transmitting a signal via at least one data transmission connection in order to transfer a location of the mobile distress call device ascertained by means of a satellite-based positioning system to the central station, wherein the central station has an input module for receiving satellite data and for determining the basic data required for satellite-based positioning, has an input-output unit for receiving a call from and for data- exchange with a distress call device, has a output unit for issuing the data related to a distress call and a central control unit that controls data exchange between the central station and a mobile distress call device through the data transmission connection as well as output of the data relating to a distress call, and wherein the distress call device has at least a satellite-based positioning module, and a transmitter-receiver unit for transferring current position data -21 determined from basic data from the central station and received satellite data to the central station. 9. Distress call system according to claim 8, characterised in that the central station has a participant database for participant-specific data as well as a database for telephone numbers and/or connection addresses for rescue and/or assistance centres. Distress call system according to claim 8 or 9, characterised in that the output unit of the central station comprises a further transmitter- receiver unit for forwarding incoming distress calls to the relevant rescue and/or assistance points. 11. Distress call system according to claim 8, 9 or 10, characterised in that the output unit of the central station comprises a display unit for displaying information relating to an incoming distress call. 12. Distress call system according to any one of claims 8 to 11, characterised in that the central station and the distress call device are each fitted with a speech-aural device, so that a speech transmission connection can be constructed through the input-output unit and the transmitter-receiver unit. 13. A mobile distress call device specifically for use in a distress call system according to any one of claims 8 to 12, with a satellite-based positioning module, a transmitter-receiver unit for establishing a data transmission connection to a central station, a central control unit controlling the creation of a data transmission connection to and data exchange with the central station, and an emergency switch by means of which an internal power supply for switching on the control unit and for activating a distress call transmission program can be connected, wherein upon switching on 22 basic data required for satellite-based positioning can be conducted from the central control unit to the satellite-based positioning module). 14. Distress call device according to Claim 13, characterised in that an alarm siren is provided that can be switched on by means of the emergency switch at the same time as the distress call transmission program is activated. Distress call device according to claim 13 or 14, characterised in that the emergency switch is designed so that when the power supply has been switched on it can no longer be switched off. 16. Distress call device according to any one of the preceding claims, characterised in that a test switch through which the internal power supply for switching on the control unit and for activating a test signal transmission program can be connected and an output device is provided issuing a signal indicating whether the device is functioning or not. 17. A process for calculating the position of a mobile device substantially as herein described with reference to the drawings. 18. A distress call system substantially as herein described with reference to the drawings. 19. A mobile distress call device specifically for use in a distress call system according to claim 18.