WO2000010356A1 - Method of locating the users of a personal radio communications system and related system and devices - Google Patents

Abstract

In a personal communications system the users' terminals (1) receive from the base station (RFP) to which they are connected at that moment, an identifier (RFPI) corresponding to the base station itself. A location centre (CS) is built up which includes a location data base (DBR) containing information on the correspondence between the base station identifiers (RFPI) and the positions of the respective base stations (RFP). The terminals (1) are so configured as to allow at least a partial retransmission of the identifier (RFPI) to the location centre (CC, CS). The latter has then the capability of correlating the identifiers which have been at least partially retransmitted with the correspondence information retrieved from said location data base (DBR), so as to locate each terminal (1) which has retransmitted its identifier within the cell served by the base station (RFP) corresponding to said retransmitted identifier. Preferred application to services based on location, such as value added services, real-time monitoring of fleets of vehicles, and similar services.

Description

METHOD FOR LOCATING THE USERS OF A RADIO COMMUNICATIONS SYSTEM AND RELATED SYSTEM AND DEVICES

This invention relates to personal communications systems, such as, for instance, communications systems operating according to DECT or GSM/DCS 1800 standards.

The DECT (Digital Enhanced Cordless Telecommunications) standard has been devised and developed to facilitate the use in the telecommunications networks of cordless terminals, capable of communicating within a picoceliular system with their respective base stations.

For an overview of this subject matter, reference can be made to the article "The New DECT Standard for Cordless Communications" by Hans Van der Hoek, published in "Telecommunications", February 1993, pages 77 to 80, or to the article "DECT - Cordless Functionality in New Generation Alcatel PABXs" by V. Werbus, A. Veloso and A. Villanueva, "Electrical Communication", 1993, No. 2, pages 172 to 180.

The GSM/DCS 1800 standard (DCS stands for Digital Cellular System) is an evolution of the well known GSM standard, developed for the use within the 1800

MHz frequency band. The GSM/DCS 1800 mobile network envisages a coverage by cells (similar to the DECT technology) where the cell dimensions vary from 600 m to 3 km in diameter. These dimensions are a function of both the electromagnetic signal propagation and the traffic density.

For a general overview of the GSM/DCS 1800 system, reference can be made to the articles "Implementation of PCNs Using DCS 1800" by A. Robin Potter, IEEE

Communications Magazine, December 1992, pages 32 and ff, or "What are GSM and DCS", by C. Dechaux and R. Scheller, Electrical Communications, 1993, No.

2, pages 119 and ff.

The aim of this invention is to increase the functionalities of a personal communications system, such as a DECT or a GSM/DCS 1800 system, by giving such a system the capability of carrying out services based on location, said term indicating in general all those services connected in some way to the information relating to the user's position within the system.

According to the invention, this aim is attained by a method having the characteristics specifically outlined in the following claims. According to an additional aspect, the invention concerns a system to be used for carrying out the above method, and its component devices.

The solution according to the invention exploits the fact that any terminal of a personal communications system, such as a DECT system or a GSM/DCS 1800 system, is able to univocally determine the area, i.e. typically the cell where it is located at that moment, i.e. the base station (usually called Radio Fixed Part, in short RFP, in a DECT system or Base Station System, in short BSS, in a

GSM/DCS1800 system), to which at that moment it is connected. This is possible thanks to the information sent to the terminal by the base station and contained in the identifier which is called, in the DECT technology, RFPI, i.e. Radio Fixed Part Identity, and in particular to the information fields called Primary Access Rights Identity (PARI) and Radio (Fixed) Part Number (RPN). Such information usually are unique for a given coverage. The same applies to the information called LI, i.e. Location Information, in the GSM/DCS 1800 system. This information can be retransmitted by the individual terminal, for instance by means of DTMF (Dual Tone Multifrequency) tones or through an SMS (Short Message Service) signalling to a service centre connected to a data base capable of associating the cell position to each RFPI or LI. On the basis of the received information, the service centre can prepare a response to be sent to the user via phone or can pass on the data to a cartographic system, such as the geographic information system, currently called GIS.

The solution according to the invention can be used for various applications.

A first example of application relates to the provision of information to the users in the form of value added services. By using an appropriately configured terminal, the user can receive information exploiting knowledge of the position in which he/she is located. For instance, by pressing a key or a sequence of keys on his terminal, the user can cause the transmission of his RFPI or LI identifier through his terminal to the service centre. After decoding the cell identifier, the service centre can perform a voice synthesis providing the user with one or more information requested: for instance, chemist's shops on duty; the closest open restaurants or petrol stations, etc. In this general framework, particular attention is devoted to services to be provided for instance to blind people. By using a terminal of the type herein described, a blind person can receive information about his/her own position: after decoding the cell identifier, the service centre can perform a voice synthesis of the signals relating to the street and street number at which he/she is positioned, and send these data to the user through the terminal.

An application of particular relevance from the commercial standpoint concerns the possible location of vehicles, mainly fleets of vehicles. A number of companies (taxis, carriers, ambulance services) carry out their activities through vehicles on the move. For this kind of activities it is important to constantly monitor the vehicle positions so as to provide optimum operating instructions as a function of their position. For this application, the RFPI or LI transmission towards the service centre can be performed by the portable terminal or it can take place upon request of the same service centre. Also the response modalities can be different so as to meet the various needs in the best way: as a matter of fact, the response of the service centre may be a voice message, a data service, etc.

The accuracy of the position identification achieved through the solution according to this invention may be compared to the distance between two adjacent antennas of the system and therefore corresponds to an accuracy of the order of a few hundreds of meters.

The invention will be now described by way of a non-limiting example, with reference to the attached drawings, wherein:

Figure 1 shows the structure of the RFPI identifier of a DECT system, Figure 2 shows as a block diagram the possible application of the invention within a terminal for a DECT system, Figures 3 and 4 depict two possible organisation architectures of a system for the provision of location services within a personal communication system.

By way of an example, the structure of the RFPI (Radio Fixed Part Identity) identifier of a DECT system of class C (public system) is represented in Figure 1.

Obviously, the invention is applicable both to picoceliular systems, for instance to

GSM/DCS 1800, and to other DECT systems, for example, to private systems of class B.

The meaning of the different fields of the RFPI identifier is the following: bit E: a Boolean value specifying the presence of the so called SARI list (relating to other DECT systems, which could be hosted by the system for the execution of the interconnection function known as "roaming"). It does not contain position information, therefore it is not necessary to send it to the service centre during the execution of a location function according to the invention;

C (Access Right Code): identifies the system class; in the given example, it specifies that the system involved is a public one, and not a so-called base for domestic use, nor a private exchange (PBX). Also in this case, the information involved is not necessary for the execution of the location function described hereafter;

POC (Public Operator Code): it univocally identifies the operator. Also in this case the information involved does not concern the location, at least in all systems in which the terminals are only registered in a particular network;

FPN (Fixed Part Number): it is a number assigned by the operator and can be used to define different subscription areas, for instance a given urban area; - FPS (Fixed Part Subnumber): it is also assigned by the operator or the installing Company, for instance, to identify a local exchange, and RPN (Radio Fixed Part Number): this too is assigned by the operator. The set of fields from C to FPS forms the PARI information cited above. Fields C and POC usually have a length of 3 bits and 16 bits, respectively. The field limit between FPN and FPS may vary: however the total length must be 12 bits. The RPN length instead is usually 8 bits. As a consequence, the transmission of the complete RFPI requires sending an information contained in 40 bits (13 digits in practice). Although in the sequel of this description reference will be made mainly to the

DECT systems and their terminology, it will be appreciated that what will be said substantially applies also to other personal communication systems, such as the GSM/DCS 1800 systems.

For example, in the case of GSM/DCS 1800 systems, the location information is formed by the following elements:

Mobile Country Code (MCC) and Mobile Network Code (MNC): 3 bytes identifying the country and the GSM/DCS 1800 operator; Location Area Code (LAC): 2 bytes identifying the coverage area within the radio coverage of the GSM/DCS 1800 operator, and - Cell Identity Value (Cell ID): 2 bytes identifying the GSM/DCS 1800 cell.

In the embodiment of the invention currently being preferred, for the execution of the location function in a DECT environment the retransmission of the RFPI identifier by the terminal is not complete but only partial, as it is limited to the only FPN, FPS and RPN fields, for 20 bits in total, and this requires the availability of 7 decimal digits. Also in the case of GSDM/DCS 1800 systems, the retransmission of the LI information may be only partial, involving for instance the only Cell ID field. In Figure 2 (derived from the article by Werbus et alii, cited in the introduction of the present specification) reference numeral 1 shows a mobile terminal connected within a telecommunications system operating according to the DECT standard (or similar ones). As a matter of fact, terminal 1 may be seen as a conventional cordless telephone set, capable of communicating with a base station (RFP), which is designed for the connection to one or more mobile terminals. The basic components of terminal 1 are: group 2 for coding/decoding the voice signal (ADPCM coding/decoding), connected to a microphone 3 and to a loudspeaker 4 respectively; control group 5, charged with dialling and signalling functions, as well as with a possible displaying function of the called/calling party number, and usually associated with a keyboard 5b and a display unit (not shown), a group 6, operating as management logic of the MAC (Medium Access Control) layer and as generator/decoder of the DECT frames, modulator 7, radio-frequency synthesiser 8, - radio-frequency transmission stage 9a, radio-frequency receiving stage 9b, and antenna group 10. The interconnection criteria of the different modules mentioned above and their operation modalities should be considered as commonly known in the technique and as such they do not require to be described herein, also because they are not essential for the comprehension of the invention.

To this end it is instead important for terminal 1 to be able to know the RFPI identifier so as to selectively perform the (re)transmission towards the base station in view of the possible use of such identifier for the location function. The above retransmission is selective, being determined by a positive command given by the mobile terminal user, for instance by acting on the keyboard 5b, or by a command received from the base station. Furthermore, in the implementation of the invention presently being preferred, retransmission is only partial, since it is limited to the FPN, FPS and RPN fields which actually contain the position information, i.e. the fields which in fact identify the respective cell. To simplify, in the sequel the term "RFPI identifier" will in any way be used.

In essence, so as it has been configured in view of the implementation of the invention, terminal 1 is a standard DECT terminal, preferably with a GAP/CAP profile, exhibiting additionally the capability of transmitting towards a service centre the RFPI identifier. Further, terminal 1 preferably includes: the presence for instance within keyboard 5b of keys for generating specific signals (for example alarms) selected by the operator; the possibility of being connected to a set of detectors to automatically generate signals, such as alarms, and/or - the capability of opening voice connections with operators of the service centre. The block diagrams of Figures 3 and 4 describe the connection of a base station RFP, to which a certain number of mobile terminals situated in the respective picocell become connected from time to time. The station RFP is connected via a respective local exchange LEX to a service centre CS that manages a geographic information system GIS, which has associated thereto a data base relating to the services, called DBS. In the architecture depicted in Figure 3, the service centre CS also directly manages an additional data base DBR, hereinafter called "location data base", containing the information relating to the geographic distribution of base stations RFP.

In more detail, sub-block CC in Figure 3 represents a so called call centre, including: an interface II, for instance an ISDN interface, which controls all communications from and towards the mobile terminal; an application program interface API, and a part of a so called core C, formed for instance by the operating system of a personal computer and designed to dialogue with the management system DBM of the two data bases DBR (locations of base stations) and DBS (services). The data bases in turn dialogue with location system GIS, connected to user interfaces VI, of known type. The alternative architecture shown in Figure 4 is in principle identical to that shown in Figure 3, with the difference that data base DBR is not directly managed by service centre CS, and it is instead controlled by call centre CC, which is connected in an independent manner to the system network (exchange LEX). The choice of adopting the architecture shown in Figure 3 or the alternative one shown in Figure 4 is mainly due to a possible different sharing of the tasks in the management of location services.

The architecture shown in Figure 3 can be adopted for instance in those cases in which the service centre CS reports to the organisation managing the communications system. The alternative architecture of Figure 4 may instead be preferred in those situations where service centre CS is managed by an organisation different from the organisation managing the communications system. In this case the system management organisation does not need to make the content of data base DBR (relating to the geographical positions of the base stations) accessible to service centre CS. Call centre CC performs then autonomously (in respect to service centre CS) the user location and thereafter transfers the relating position information to the same service centre CS. Service centre CS, like in Figure 3, is connected to the system network so as to set up the requested connection with mobile terminals 1.

In the diagram of Figure 4 it will be appreciated that modules II (ISDN interface), API (application interface), C (core) and DBM (data base management system) are as a matter of fact split into a respective modules 111 and II2, AP1 and AP2, C1 and C2, as well as DBM1 and DBM2, designed to perform their functions, separately, for call centre CC and for service centre CS. It will be also appreciated that module

DBM1 co-operates with data base DBR (base station positions), whereas module DBM2 co-operates with data base DBS (services) and therefore with the system GIS.

It will also be noted that call centre CC includes a data interface ID1 which dialogues with a corresponding interface ID2 at service centre CS so as to allow call centre CC to supply service centre CS with the position information necessary for the service provision. All this obviously takes place on an individual basis, i.e. the information about the position of the mobile terminal to be served is processed at call centre CC, thus without informing the service centre CS about the content and organisation of data base DBR.

In both cases the service centre CS can be configured simply as a machine that is formed by a telephone board provided for instance with ISDN access and application programming interface and that is able to: access the calling party number, - access the called party number, transfer a call identify the cause of the release (of a call, for instance), to inform that the call is released after the successful transmission of the position information. The geographic information system (GIS) can be structured in different ways and adequately equipped with one or more display screens capable of showing on a map the position of the different localised terminals.

Service data base DBS contains in general the information relating to the signals which may be received (alarms) and transmitted, the data of each terminal (usually the terminal identifier CLI), the access information, etc.

Regardless of the architectural choice, the solution according to the invention may be so configured as to operate according at least two different way, namely. by starting the location action upon request of the concerned terminal 1 or upon request of service centre CS.

In the case of location upon request of the terminal, it is the terminal itself which upon a specific action of the user (over keyboard 5b) or automatically and/or periodically, i.e. at time intervals or at any cell change, or yet in the event of an alarm, etc, informs the base station RFP to which it is connected (and therefore call centre CC) about its position (in practice the current RFPI identifier).

The position notification to call centre CC (possibly integrated into the service centre CS) takes place by following a call protocol which in practice corresponds to a common attempt of calling a telephone number formed by the following chain: - prefix of service centre CS service signal code (for instance corresponding to an alarm signal or simply to the position information), a possible request for setting up a voice channel: this request can be compacted within the service signal codes previously seen: for example, if three digits are foreseen for the signal code, by reserving values from

0 to 499 for the case in which the setting up of the voice channel is not required and values from 500 to 599 for requesting a voice channel, RFPI identifier. Referring for sake of simplicity to the architecture depicted in Figure 3, service centre CS, linked to exchange LEX through an ISDN access, can analyse, prior to serving the call: the calling party number, to know, by accessing data base DBS, the data relating to the terminal that has generated the location information and/or the alarm signal, if any (for instance in case of monitoring public transport means, line number and driver's name), the called party number (i.e. the base station to which the calling terminal is connected at that moment) to know, by accessing data base DBR, the position of the calling terminal and, by accessing data base DBS, the signal code (for instance, alarm); the possible request of setting up of a voice channel so as to transfer, in the affirmative, the call to an operator's position. In the negative, service centre CS releases the call and assigns an appropriate value to the release reasons.

To receive updated information about the positions of the terminals (for example, to localise the vehicles of a fleet), or for cost reasons, so as to avoid frequent calls to the service centre, the location can be carried out upon request of the service centre, according to usual criteria of execution of a polling action. In such a case, upon receiving an incoming call, called terminal 1 automatically answers, so making the control group 5 send the RPFI identifier to the service centre, according to modalities which are substantially the same as those previously examined.

Also in case of a location upon request of the service centre, there is the possibility of setting up voice connections. For this reason, after sending the last digit of the identifier, terminal 1 keeps waiting for some seconds. If during this time interval the service centre CS has effected the call release, this means that the call was only aimed at the location, without involving the terminal's user. If however, at the end of the waiting interval, the call is still active, a signal (typically an acoustic warning signal) is issued towards the user, who can in this way cause the connection of the set microphone 3-earphone 4 to the so called U plane, thus starting the communication with the operator's position of service centre CS.

From what set forth before, one derives that the architecture depicted in Figure 3 leaves substantially unaltered the pre-existent network structure of the communications system, and allows therefore quick development times. The adoption of this solution takes for granted the availability at service centre CS of location data base DBR. On the other hand it can also be useful to foresee appropriate modalities to avoid that, in case of a call, terminal 1 answers and sends its position, even if the calling party is not a service centre. These implementation aspects are taken up by making resort to the architecture depicted in Figure 4, where in essence it is envisaged that the information relating to the position sent by the terminal towards the base station RFP involved, is transferred from the network (herein represented by exchange LEX) not directly towards service centre CS, but towards call centre CC, that is preferably located at the system operating company. Call centre CC has the main task of effecting the conversion of the position identifier (RFPI) into position co-ordinates starting from the content of data base DBR, with no need for the availability of the latter data base at service centre CS.

In the solution schematised in Figure 4, call centre CC is interfaced with the terminal through the same interface as the one which, with reference to architecture in Figure 3, has been assumed as directly implemented by service centre CS. With the architecture of Figure 4, therefore, call centre CC must be able to access the calling party number and called party number (for the location effected from terminal) and to recognise the DTMF tones or the SMS signalling in case of a call upon request of the service centre.

When the architecture of Figure 4 is adopted, the interface connecting call centre CC service centre CS may be, for example, of two different types. In a first possible embodiment it is simply an ISDN access, so that service centre CS, is substantially similar to service centre CS used in the architecture of Figure 3. In particular, it can be assumed that the call centre CC send the position (and no longer RFPI identifier), the signal code (alarm) and the voice request still within the called party number in the ISDN configuration. To allow service centre CS to know the terminal that has generated such items of information within the called party number, call centre CC must also add a code derived from the calling party identifier CLI.

An alternative is the setting up of a data link between call centre CC and service centre CS: this solution obviates the need for a large number of call attempts towards service centre CS.

As to the execution of the location function, the only substantial difference between the architectures shown in Figures 3 and 4 concerns the way in which service centre CS identifies the terminal. In case of the architecture of Figure 4, since service centre CS cannot recognise the calling party from identifier CLI only, it is necessary that call centre CC specifically conveys the terminal's code to service centre CS.

In case the location is performed upon request of service centre CS, to know a terminal position, service centre CS must request call centre CC to: open a connection with the terminal, receive the cell identifier (RFPI), effect, on the basis of the content of data base DBR, the conversion of the above cited identifier into a position information, and - send the answer to call centre CC.

In the case in which the connection between service centre CS and call centre

CC takes place through a data link, requests and answers are sent in accordance to a given data protocol. Otherwise, if an ISDN link is used, service centre will then use DTMF tones or SMS signalling to send the code of the terminal to be localised, and to receive the position.

To avoid that call centre CC, which is charged with the conversion of RFPI identifier into co-ordinates, is also to manage the voice calls, it can be appropriate to handle voice calls in a different way from calls which are aimed at location. In other terms, if the service centre CS must set up a voice connection with the terminal, it is more advantageous that it directly dials the number of the terminal without engaging call centre CC.

Since the terminal is unable to distinguish the voice call from a call aimed at location, it will any way send its RFPI identifier towards base station RFP: however, this information is transferred toward call centre CC and does not reach service centre CS.

Like DECT, the GSM/DCS 1800 technology allows knowing the identifiers of the antennas covering the area in which the mobile terminal is located. This characteristic allows the application of the same considerations set forth about DECT to the location in a GSM/DCS 1800 network. In high population density urban areas, the location over a GSM/DCS 1800 network attains an accuracy of the order of the cell size, i.e. a maximum accuracy of about 600 m.

It is evident that, leaving unchanged the principle of the invention, implementation details and practical embodiments may be considerably varied with respect to what already described and depicted, however without departing from the scope of the invention itself, as disclosed in the following claims.

Claims

1. Method of locating the users of a personal communications system comprising a plurality of base stations (RFP), in which user terminals (1) receive from the base station (RFP) to which at that moment they are connected, an identifier (RFPI) corresponding to the station itself, characterised in that it comprises the operations of: providing a location centre (CC, CS) with a location data base (DBR) containing the information about the correspondence between the identifiers (RFPI) of the base stations and the positions of the same base stations (RFP), and configuring said terminals (1) for the retransmission, at least partial, of said identifier (RFPI) towards said location centre; the location centre (CC, CS) being capable of receiving said identifiers (RFPI) at least partially retransmitted by the terminals (1), and of correlating them with the correspondence information retrieved from said location data base (DBR) so as to recognise each terminal (1) that has retransmitted the identifier of the base station (RFPI) as located within a cell served by the base station (RFP) corresponding to said identifier.

2. Method as claimed in claim 1 , characterised by the operation of configuring said terminals so that they retransmit only that part of the identifier (RFPI), received from the base station (RFP) to which at that moment they are linked, which identifies the base station (RFP) itself.

3. Method as claimed in claim 1 or claim 2, characterised by the operation of configuring said terminals (1) for the transmission, concurrent with the at least partial retransmission of said identifier, of at least one service signal chosen within a group comprising: an alarm selected by the user; an alarm automatically generated as a function of detection signals; the request for opening a voice connection with the terminal.

4. Method as claimed in claim 3, characterised by the operation of configuring said terminals (1) for the generation of a service signal code capable of taking up different digital values, with at least some of said values corresponding to the request for opening a voice channel.

5. Method as claimed in any of the previous claims, characterised by the operation of configuring said terminals (1) for the retransmission of said identifier in dependence of at least one event chosen in the group formed by: a transmission command positively expressed (5b) by the terminal's user, and the reception of a location instruction transmitted for the terminal through the personal communications system.

6. Method as claimed in any of the previous claims, characterised in that it comprises the operation of providing a service centre (CS) associated with a service data base (DBS) for the provision of services to the users located by said location centre (CC).

7. Method as claimed in claim 6, characterised in that it comprises the operation of configuring said location centre (CC) and said service centre (CS) as an integrated processing system that accesses both the location data base (DBR) and the service data base (DBS).

8. Method as claimed in claim 6, characterised in that it comprises the operation of configuring said location centre (CC) and said service centre (CS) as separate processing systems, so as to avoid the access of said service centre (CS) to said location data base (DBR); said location centre (CC) being designed for transmitting to said service centre (CS) information about the correspondence between each terminal (1) that has retransmitted its identifier and the position of said terminal (1) within a cell served by the base station

(RFP) corresponding to said identifier.

9. Method as claimed in any of claims from 6 to 8, characterised in that it comprises the operation of configuring said terminals (1) for the transmission, concurrent with the at least partial retransmission of said identifier, of at least one code identifying said service centre (CS).

10. Personal communications system comprising a plurality of base station (RFP) and in which the user terminals (1) receive from the base station (RFP) to which at that moment they are linked, an identifier (RFPI) corresponding to the same station, characterised in that it comprises a location centre (CC, CS) with a data base (DBR) containing the information about the correspondence between the identifiers (RFPI) of the base stations and the positions of the same base stations (RFP), and in that said terminals (1) are configured for the at least partial retransmission of said identifier (RFPI) towards said location centre (CC, CS), the location centre (CC, CS) being capable of receiving said identifiers (RFPI) at least partially retransmitted by the terminals (1) and of correlating them with the correspondence information retrieved in said location data base

(DBR) so as to recognise each terminal (1) that has retransmitted the identifier (RFPI) of the base station as located within the base station (RFP) corresponding to said identifier.

11. System as claimed in claim 10, characterised in that said terminals are configured so as to retransmit only that part (FPN, FPS, RPN) of the identifier (RFPI), received from the base station (RFP) to which at that moment they are linked, which identifies the same base station (RFP).

12. System as claimed in claim 10 or claim 11 , characterised in that said terminals

(1) are configured for the transmission, concurrently with the at least partial retransmission of said identifier, of at least a service signal chosen in the group comprising: an alarm selected by the user, - an alarm automatically generated as function of detection signals, the request for setting up a voice connection with the terminal.

13. System as claimed in claim 12, characterised in that said terminals (1) are configured for the generation of a service signal code capable of taking up different digital values, with at least a few of said values corresponding to the request for setting up a voice channel.

14. System as claimed in any of claims 10 to 13, characterised in that said terminals (1) are configured for the retransmission of said identifier as a function of at least one event chosen in the group formed by: a transmission command positively expressed (5b) by the user of the terminal, and - the reception of a location command sent towards the terminal through the personal communications system.

15. System as claimed in any of claims 10 to 14, characterised in that it comprises a service centre (CS) associated with a service data base (DBS) for the provision of services to the users located by said location centre (CC).

16. System as claimed in claim 15, characterised in that said location centre (CC) and said service centre (CS) are configured as an integrated processing system that accesses both the location data base (DBR) and the service data base (DBS).

17. System as claimed in claim 15, characterised in that said location centre (CC) and said service centre (CS) are configured as separate processing systems, said service centre (CS) being inhibited to access said location data base (DBR); said location centre (CC) being configured to transmit to said service centre (CS) the information about the correspondence between each terminal (1) that has transmitted its identifier and the position of said terminal (1) within the cell served by the base station (RFP) corresponding to said identifier at least partially retransmitted.

18. System as claimed in any of claims 15 to 17, characterised in that said terminals (1) are configured for the transmission, concurrently with the at least partial retransmission of said identifier, of at least one code identifying said service centre (CS).

19. Terminal of a personal communications system for carrying out the method as claimed in any of claims 1 to 10, characterised in that it comprises: - means (5, 8, 9a, 10) for the selective and at least partial retransmission of said identifier toward the base station (RFP) to which the terminal (1) is linked at that moment, and control means to switch on said retransmission means (5, 8, 9a, 10), said control means being chosen within the group formed by: - actuating means (5b), sensitive to a transmission command positively expressed (5b) by the terminal's user, and receiving means (6) for receiving a location command sent towards the terminal (1) through the personal communications system.

20. Terminal as claimed in claim 19, characterised in that said means of retransmission (5, 8, 9a, 10) are configured so that they retransmit only that part (FPN, FPS, RPN) of the identifier (RFPI), received from the base station (RFP) to which at that moment the terminal is linked, which identifies the base station (RFP) itself.

21. Terminal as claimed in claim 19 or claim 20, characterised in that said retransmission means are configured for the transmission, concurrently with the at least partial retransmission of said identifier, of at least one service signal chosen in a set formed by: - an alarm selected by the user; an alarm automatically generated as a function of detection signals; the request for opening a voice connection with the terminal.

22. Terminal as claimed in claim 21 , characterised in that said retransmission means (5, 8, 9a, 10) are configured for the generation of a signal code capable of taking up different digital values, at least a few of said values corresponding to the request for opening a voice channel.

23. Location centre for carrying out the method as claimed in any of claims from 1 to 10, characterised in that it comprises a location data base (DBR) containing information about the correspondence between said identifiers (RFPI) of the base stations and the position of the same base stations (RFP), and in that said location centre (CC, CS) is capable of receiving said identifiers (RFPI) at least partially retransmitted by the terminals (1 ) and of correlating said identifiers with the correspondence information retrieved in said location data base (DBR) so as to localise each terminal (1) that has retransmitted the respective identifier (RFPI) of the base station as located within the base station (RFP) corresponding to said identifier.

24. Location centre as claimed in claim 23, characterised in that said location centre (CC) has associated a service centre (CS) with associated a service data base (DBS) for the provision of services to the users located by said location centre (CC).

25. Location centre as claimed in claim 24, characterised in that said location centre (CC) and said service centre (CS) are configured as an integrated processing system that accesses both the location data base (DBR) and the service data base (DBS).

26. Location centre as claimed in claim 24, characterised in that said location centre (CC) and said service centre (CS) are configured as separate processing systems, said service centre (CS) being inhibited from accessing said location data base (DBR); said location centre (CC) being configured for the transmission to said service centre (CS) of information about the correspondence between each terminal (1) that has retransmitted the respective identifier and the position of said terminal (1) within the cell served by the base station (RFP) corresponding to said identifier.