WO2012076829A1

WO2012076829A1 - Method and server for locating a mobile terminal

Info

Publication number: WO2012076829A1
Application number: PCT/FR2011/052933
Authority: WO
Inventors: André Schiltz
Original assignee: France Telecom
Priority date: 2010-12-10
Filing date: 2011-12-09
Publication date: 2012-06-14
Also published as: FR2968883A1

Abstract

Method of locating a mobile terminal (2) accessing a telecommunication network (1) implemented by a location server (3), comprising: - a step of obtaining a first item of location information for the mobile terminal (2), characterized in that it comprises: - a step of selecting a group of referent terminals (4) from a list of referent terminals (4) of known location, as a function of said first item of location information, - a step of determining a second item of location information for the mobile terminal, as a function of signals transmitted by wireless links between on the one hand the referent terminals (4) and the mobile terminal (2) and on the other hand fixed stations (6) of said telecommunication network.

Description

METHOD AND SERVER FOR LOCATING A MOBILE TERMINAL

Background of the invention

The invention relates to the field of the location of a mobile terminal.

GPS ("Global Positioning System") offers a satellite tracking technique that can locate a mobile terminal with a precision of about 20 meters. However, this technique has the disadvantage of not allowing a location of a mobile terminal located inside a building, because the wavelength used by the signals emitted by the satellites does not enter the buildings.

When the mobile terminal to be located is a mobile phone, other localization techniques can be used in addition to or instead of the satellite location. These include cell identification ("Cell-ID"), triangulation or time differential. As the wavelengths used can penetrate inside buildings, it is possible to locate a mobile phone located inside a building. However, the accuracy of the location is usually less than the accuracy of a satellite location.

Other localization techniques are based on the detection of WiFi access points or a femtocell access point. In this case also, it is possible to locate a mobile phone located inside a building but the accuracy of the location is limited. In addition, for a telecommunication operator who wishes to offer a location solution to its subscribers, this solution involves deploying a large number of femtocells, which represents a significant cost.

There is therefore a need for a localization technique that makes it possible to locate a mobile terminal in a precise manner, even inside a building.

Object and summary of the invention

The invention aims to meet this need by proposing a method of locating a mobile terminal accessing a telecommunication network implemented by a location server, comprising a step of obtaining a first location information of the terminal mobile. This locating method comprises:

a step of selecting a group of referent terminals in a list of reference terminals of known location, as a function of said first location information,

a step of determining a second location information of the mobile terminal, as a function of signals transmitted by wireless links between the reference terminals and the mobile terminal and secondly fixed stations of said telecommunications network.

Correlatively, the invention proposes a location server of a mobile terminal accessing a telecommunications network, comprising means for obtaining a first location information of the mobile terminal. This location server includes: means for selecting a group of referent terminals in a list of reference terminals of known location, as a function of said first location information,

means for determining a second location information of the mobile terminal, as a function of signals transmitted by wireless links between the reference terminals and the mobile terminal and secondly fixed stations of said telecommunications network.

The first location information can be obtained using one of the techniques mentioned in the introduction, which offers limited accuracy. However, the invention proposes to locate a mobile terminal by reference to at least one referent terminal located nearby.

The referent terminals are, just like the mobile terminal to be located, terminals able to access said telecommunications network and which dialogue by message with at least one of the fixed stations: for their location, their connection to the telecommunications network, during a communication established via the telecommunication network etc.

Thus, in a known manner, the reference terminals, just like the mobile terminal, exchange signals with these fixed stations when they request access to the telecommunications network and / or communicate via this telecommunication network.

These reference terminals are referred to as referents, in particular in that they play a particular role with respect to other terminals accessing said telecommunications network: they serve as a reference because their location is known.

This allows a very precise location.

In one embodiment, the step of determining a second location information comprises:

a step of determining, in the group of reference terminals, the terminal referencing the closest of the mobile terminal, as a function of said signals, and

a step of determining a second location information item of the mobile terminal, as a function of a location information item of the terminal refer to the nearest determined one.

In this case, the invention allows a very precise location of the mobile terminal, with reference to the location of the nearest terminal referent. For example, in the case of a building in which each room contains a terminal referent, the terminal refer to the closest determined is normally the terminal referent located in the same room as the mobile terminal. It is therefore possible to determine in which room of the building is the mobile terminal. In the case of a building in which only certain rooms contain a terminal refer, the accuracy is less. However, it remains possible to determine, for example, the group of adjacent rooms or the floor where the mobile terminal is located. Thus, the accuracy is high compared to the localization techniques discussed in the introduction. In practice, the accuracy of the location depends on the mesh of reference terminals.

Moreover, thanks to the step of obtaining a first location information of the mobile terminal and at the step of selecting a group of referent terminals, it is sufficient to search the terminal refers the closest to the mobile terminal in a group of limited size, and not in the entire list of reference terminals.

The second location information may be representative of a hardware environment in which the nearest reference terminal is located. For example, the second location information identifies or describes an equipment in which the terminal refers closest.

According to one embodiment, the location method comprises a step of determining whether a terminal belongs to the group of referring terminals from a subscriber identification.

This embodiment makes it possible in particular to take advantage of a numbering standard making it possible to distinguish between types of objects.

The first location information may be an identification of a cell of said telecommunication network.

The step of obtaining a first location information of the mobile terminal may include obtaining a location area code stored in association with an identification of said mobile terminal in a local subscriber register or a visitor subscriber register said telecommunications network.

In the two aforementioned cases, the step of obtaining a first location information of the mobile terminal can be easily implemented. In particular, it can be implemented in an existing cellular network without requiring substantial modification of the network.

The step of selecting a group of referent terminals can comprise consulting a database which contains, for each terminal referent of the list of referent terminals, a first location information of the terminal referent.

Correlatively, the invention proposes a telecommunications network comprising a location server according to the invention and a plurality of referring terminals, in which the location server has access to a database which contains, for each of said reference terminals, a first location information of the terminal refer and a database which contains, for each of said referent terminals a second terminal location information refer.

These databases make it easy to implement the step of selecting a group of referent terminals with the first location information of the referring terminals, and to assign as second information of the mobile terminal the second location information of the terminal. refer the closest. The aforementioned databases may for example comprise a local subscriber register and a visitor subscriber register for the first location information and a complementary database for the second location information. The mobile terminal and the reference terminals may each be equipped with a subscriber identification card used to identify the terminal considered in the telecommunication network, the first location information being stored in said telecommunication network in association with a telecommunication network. identification of said mobile terminal.

Thus, the location method can be easily implemented in a cellular network.

The invention also relates to a computer program comprising instructions for executing the steps of a localization method according to the invention when said program is executed by a computer.

This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other form desirable shape.

The invention also relates to a recording medium or information carrier readable by a computer, and comprising instructions of a computer program as mentioned above.

The recording media mentioned above can be any entity or device capable of storing the program. For example, the medium may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording medium, for example a floppy disk or a disk. hard.

On the other hand, the recording media may correspond to a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can be downloaded in particular on an Internet type network.

Alternatively, the recording media may correspond to an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

Brief description of the drawings

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures: FIG. 1 represents a telecommunication network in which a localization method according to one embodiment of the invention can be implemented,

FIG. 2 represents a location server of the network of FIG. 1, and FIG. 3 represents the main steps of a localization method according to one embodiment of the invention.

Detailed description of an embodiment

FIG. 1 represents a telecommunication network 1 presenting the architecture of a mobile cellular network in which mobile terminals 2 operate. The telecommunications network 1 is for example a GSM network or a UMTS network.

The telecommunication network 1 comprises:

a location server 3,

- a mobile switching center 8 (MSC for "Mobile Switching

Center "),

a plurality of reference terminals 4 located inside buildings 5, fixed stations, including base stations 6 (BTS for "Base Tranceiver Station") connected to base station controllers 7 (BSC for "Base Station Controller" ").

In Figure 1, only three base stations 6 and a base station controller 7 are shown, but of course the telecommunication network 1 may be more extensive. The base station controllers 7 are connected to the switching center of the mobile service 8. In a known manner, the base stations BTS are stations forming part of the telecommunication network access infrastructure and managing access to the network. of telecommunication 1 of the different terminals. These stations exchange signals with the terminal or terminals wishing to connect to the communication network and communicate via telecommunication network.

In a known manner, the switching center of the mobile service 8 has access in particular to a register 8A of local subscribers (HLR for "Home Location Register") and to a register 8B of the visitor subscribers (VLR for "Visitor Location Register") containing, in particular, a location area code for each of the mobile terminals 2 present in the telecommunications network 1. The telecommunications network 1 further comprises a database 3A forming a register 3A of the referring terminals. This database 3A is either integrated in the register 8A of the local subscribers or in the register 8B of the subscribers visitors or is independent and physically dissociated from these two registers.

Each of the mobile terminals 2 is equipped with a subscriber identification card, for example SIM (for "Subscriber Identity Module") type and can establish wireless links with the base stations 6. The mobile terminals 2 are for example mobile phones. In known manner, such a subscriber identification card serves to identify the terminal and / or the subscriber considered in the telecommunications network 1 and provides by interrogation a subscriber identification, for example in the form of alphanumeric code and / or or number.

Each of the reference terminals 4 is also equipped with a subscriber identification card and can establish wireless links with the base stations 6. The reference terminals 4 are for example fixed telephones, fax machines, desktops, home gateways of the ADSL box type, computer peripherals (printer, etc.). The presence of a SIM card in a terminal refer to 4 allows for example to implement an anti-theft system or a remote management service.

In the context of the present description, the term "terminal refer" refers to a terminal identified as belonging to a set of referent terminals.

The distinction between a mobile terminal 2 and a terminal refer, according to a first variant, by analysis of the subscriber identification provided by the subscriber identification card inserted in the terminal in question.

Subscriber identity card numbering standards are in fact evolving to allow the integration of a large number of objects in M2M (machine-to-machine) applications. The new numbering standards will make it possible, on the basis of the identification number of the SIM card, to distinguish between, on the one hand, the subscriber identification cards dedicated to mobile terminals carried by persons and, on the other hand, the subscriber identification cards dedicated to objects.

Advantageously, the reference terminal database 3A will be able to manage these new numbering standards and the referent terminals will use these future Object M2M 'standards or standards close to these Object M2M' standards to distinguish between simple objects (which require a location search for example) and the objects that will serve as referents.

According to a second variant, usable in the absence of such a standard, the database 3A references only the list of terminals of the telecommunication network 1 which are part of the set of reference terminals. From a subscriber identification, it is thus possible to determine if a terminal is a referent terminal, by interrogating the database 3A to search for a record concerning a terminal associated with such a subscriber identification. If such a record is found, it is concluded that this terminal is a terminal referent. In the opposite case, it is concluded that this terminal is not a terminal referent.

Such a terminal referent is supposed to remain permanently in a room of a building 5, but can be moved in the room. FIG. 1 shows a building 5 in which each room contains a reference terminal 4, and another building 5 in which only certain rooms contain a terminal referenced 4. For such a terminal refer, two separate information on the location of this terminal referenced are stored in association with a subscriber identification.

The location server 3 is a computer server for locating the mobile terminals 2. It may be a computer server specific to the location. In a variant, the location server 3 is integrated with another piece of equipment of the telecommunications network 1, for example at the switching center of the mobile service 8. The location server 3 has access to the database 3A of the referring terminals 4 as well as to the local subscriber register 8A (HLR) and the register 8B of the visitor subscribers (VLR).

The local subscriber register 8A (HLR) and / or the visitor subscriber register 8B (VLR) includes a list of terminals accessing the telecommunication network. For each terminal there is stored in association with a subscriber identification, a first location information. The local subscriber register 8A (HLR) and / or the register 8B of the visitor subscribers (VLR) thus contains a first location information for the reference terminals 4 referenced in the database 3A.

This first location information is a location information used for the terminal location within the telecommunications network and the routing of communications to the terminal in question or from this terminal. This first location information is for example the location area code of the terminal referenced 4 or the geographical position of the terminal referenced 4. This location area is for example a cell of the telecommunications network 1.

The database 3A contains the list of reference terminals 4 of the telecommunications network 1 and, for each terminal referenced 4, in association with a subscriber identification of this terminal refer, a second location information. Optionally this database 3A, also contains in association with a subscriber identification of this terminal refer, the first location information.

The second location information is a location information complementary to the first location information and which, unlike the first location information, is not necessary or used for the purposes of routing communications to the terminal considered.

The second location information is for example a location in a building, a city, or more generally a specific space. It can be based on any location system: GPS position (Glocal Positioning System), postal address, coordinates in a three-dimensional space, etc.

This second location information may also be representative of a hardware environment in which the terminal in question is located:

- it identifies or describes a material object located near the terminal refer to: printer, fax, photocopier, beverage dispenser, room of a building, etc., when the terminal refers is in a building; or else street, monument, park, public furniture, fountain, metro station, bus station, etc., when the terminal refers to is outside a building, in a city or natural area; and / or - it identifies or describes (network alias, network address, type of equipment, manufacturer, model, etc.) the equipment (printer, fax, photocopier, beverage dispenser, etc.) integrating and / or constituting the terminal referent. This second location information is thus more accurate than the first location information and / or gives additional information with respect to those provided by the first location information. In the embodiment described here, the second location information is composed of the postal address of the building 5 in which is the terminal referenced 4, a floor number and a room number (for example office or room number).

Figure 2 shows the location server 3 in schematic form. The location server 3 presents the hardware architecture of a computer and comprises in particular a processor 9, a read only memory 10, a random access memory 11 and a communication interface 12. The processor 9 allows the execution of stored computer programs in the read-only memory 10, using the RAM 11. The communication interface 12 makes it possible to communicate with other equipment.

FIG. 3 represents the main steps of a localization method implemented by the location server 3. This localization method is for example implemented by the execution of a computer program stored in the read-only memory. .

The location server 3 executes a prior configuration phase E0 during which it records in the register 8A and / or 8B a first location information for each of the referent terminals. This information is recorded as the terminals of this group connect to the telecommunications network 1. The first location information is, in known manner in the cellular networks, obtained by the location server 3 by application of a technique mobile terminal location in the telecommunication network. This first location information is typically a location area code.

The location server 3 further determines, from a subscriber identification obtained by interrogation of the subscriber identification card of this terminal, whether a terminal connecting to the network belongs to the group of referent terminals. One of the two variants described above is usable: use of a numbering specific to the referent terminals or query of the database 3A.

The location server 3 also records, in the database 3A, for each reference terminal belonging to this group of referent terminals a second location information. This second information provides information on the environment of the terminal refer (postal address, building, room, object nearby, etc.).

This second location information can come from different sources:

reference terminals themselves, the location information being, for example, written in the SIM card (or equivalent) during its allocation and which can be requested by the database server 3A of the referring terminals or via a platform of service dedicated to this task; such a platform remounts the information directly from the mobile to the entity making the request for location information by SMS, email, internet connection, etc. one or more dedicated hosting servers, installed and secured by one or more network operators and searchable from the telecommunications network 1 by the location server 3; such a hosting server containing the second geographical location information (address, building, floor, room, etc.) of the referring terminals, this information having been provided

- by the operators of the networks containing these hosting servers, independently or in cooperation, and / or

- by merchants and / or device manufacturers (computers, fax machines, electronic equipment) likely to serve as reference terminals; and or

- By users of the location service according to the invention, through a server via registration on the internet or by email or SMS.

The location method starts in step El during which the location server 3 receives a location request from a mobile terminal 2. This request specifies an identifier of the mobile terminal 2.

Then, in step E2, the location server 3 obtains a first location information from the mobile terminal 2. The first location information is for example the location area code of the mobile terminal 2, obtained by consulting the register 8A of the mobile terminal 2. local subscribers or register 8B of subscribers. As a variant, the first location information may be for example an estimate of the geographical position of the mobile terminal 2, obtained for example by a cell identification technique (Cell-ID), a triangulation technique or a differential technique of time.

As a reminder, these different localization techniques have the following characteristics.

Cell ID is the least expensive technology because there is no material to put in place. As long as the mobile terminal is in an area covered by the network, it connects to a GSM relay antenna. It is from the identification of this antenna that we can locate the mobile terminal. This location is very fast but it is not precise because it depends on the number of relay antennas and their relative distance. In urban areas, the accuracy varies between 100 and 700 meters.

The triangulation technique crosses the data obtained from signals transmitted by the terminal and received by different relay antennas. Location is more accurate than cell identification, of the order of 150 meters in urban areas.

For the time differential technique, the propagation time of signals exchanged between a mobile terminal and one or more antennas is calculated.

There are also methods of geolocation by satellite (GPS) but they do not work for the location of a terminal inside a building. These techniques are known to those skilled in the art and it is not necessary to give a detailed description. According to the first location information of the mobile terminal 2 obtained in the step E2, the location server 3 selects, in the step E3, a group of referent terminals 4 located near the mobile terminal 2. For example, in in the case where the first location information of the mobile terminal 2 is the location area code of the mobile terminal 2, the location server 3 selects the referring terminals 4 which have the same location area code as the mobile terminal 2. alternatively, in the case where the first location information of the mobile terminal 2 is an estimate of the geographical position of the mobile terminal 2, the location server 3 selects the referring terminals 4 which are located in a vicinity of the mobile terminal 2, for example at most at a maximum distance determined. Then, in step E4, the location server 3 determines, in the reference terminal group 4 selected in step E3, the reference terminal 4 closest to the mobile terminal 2. For this purpose, the signals transmitted by links wireless radio between on the one hand the reference terminals 4 and the mobile terminal 2 and on the other hand base stations 6 are used. For example, it is possible to determine the reference terminal 4 closest to the mobile terminal 2 by using a triangulation technique and / or a time differential technique. For example, a trilateration technique that calculates the distance differentials from the signal delay differentials is appropriate for this determination.

In known manner, these techniques use signals exchanged between a mobile terminal and one or more fixed stations of the terrestrial radio network.

In triangulation or AOA (Angle Of Arrival) techniques, measurements are made on the reception angles of the signals coming from the mobile terminal by particular antennas at the reference points. It is also possible to measure the two-dimensional position of a mobile terminal: it is necessary to have two angle measurements and a measurement of the distance between two reference points, the position of the mobile terminal 2 is then represented by the intersection of the two directions defined by the measured angles of arrival. The position can also be measured in three dimensions: it is then necessary to have, in addition to the previous measurements, a measurement of the azimuth.

In trilateration techniques, the position of the mobile terminal is calculated by measuring the distance between the latter and several reference points (3 non-collinear points in 2D and 4 non-coplanar points in 3D). The intersection of the circles or parabolas deduced from the calculation makes it possible to estimate the position of the mobile. In fact, the distance is calculated by measuring the propagation time of the signal. This approach is used by several positioning systems (TOA, OTDOA, U-TDOA, EOTD ...). In the context of the invention, the radio signal or signals exchanged with the fixed stations (antennas) by each of the reference terminals on the one hand, and by the mobile terminal 2, on the other hand, are compared: their characteristics are analyzed. and compared to identify the terminal refer the closest.

For example, in the triangulation technique, where the reception angles of the signals between the mobile terminal 2 and the antennas are measured, the location server 3 also measures the reception angles of the signals between the reference terminals and the antennas. and compares them with the measurement made for the mobile terminal 2 to determine which is the closest fixed reference terminal.

In the same manner, in the trilateration technique, where the distance is calculated by measuring the propagation time of the signals between the mobile terminal 2 and the antennas, the location server 3 also performs the measurement of the propagation time of the signals between the reference terminals and the antennas and compares them with the measurement made for the mobile terminal 2 in order to determine which terminal is the closest fixed terminal.

The signals used here are for example those used in a standard way by the operators (GSM, etc.) during the establishment of a communication with the terminal and / or during a phase of locating the terminal and / or when a phase of connection of the terminal to the network.

For example, the signals are the radio signals used in current and future known mobile technologies, which are being standardized:

- technologies from 2G to 3G networks such as GSM 900 or GSM 1800 for voice, GPRS (2.5G technology) and EDGE (2.75G technology) for data transmissions, UMTS (3G technology) for voice and data transmissions, including CDMA, W-CDMA, FOMA, TD-SCDMA, etc .;

- the 4G family of technologies (LTE Long Term Evolution and LTE-Advanced for Long Term Evolution Advanced).

It should be noted that all these families of present and future signals will be compatible with the technique described in the invention. Then, in step E5, the location server 3 determines a second location information of the mobile terminal 2, deduced from the second location information of the closest referenced terminal 4 determined in step E4.

The second location information of the mobile terminal 2 is, for example, chosen equal to the second location information of the terminal referenced 4 closest determined. This second location information may further be completed by an indication of the distance to which the mobile terminal 2 is located with respect to the terminal referenced 4: "2 meters from the photocopier X" or "2 meters from the room Y". In a variant, it is determined which are the three referent terminals closest to the terminal 2, the relative distance of the mobile terminal 2 is determined relative to the three closest reference terminals by using a technique of differential time and triangulation above and the exact position of the terminal 2 is deduced. When a plane of the building or of the space in which the three closest reference terminals are located is available, the position of the mobile terminal 2 can also be indicated on this plane.

Finally, in step E6, the location server 3 sends a response to the request of the step E1, containing the second location information of the mobile terminal 2.

The locating method of FIG. 3 therefore makes it possible to locate a mobile terminal 2 located inside a building 5, with reference to a location information of a reference terminal 4 located nearby. This allows a very precise location.

For example, in the case of a building 5 in which each room contains a terminal referenced 4, the terminal referencing 4 the closest determined in step E4 is normally the terminal referenced 4 located in the same room as the mobile terminal 2 It is therefore possible to determine in which room of the building 5 is the mobile terminal 2.

In the case of a building 5 in which only certain rooms contain a terminal refer to 4, the accuracy is less. However, it remains possible to determine for example the group of adjacent parts or the floor where the mobile terminal 2 is located. Thus, the accuracy is high compared to the localization techniques discussed in the introduction. In practice, the accuracy of the location depends on the mesh of reference terminals 4.

With the aforementioned steps E2 and E3, it is sufficient to look for the terminal referenced 4 closest to the mobile terminal 2 in a group of limited size, and not in the entire database 3A referent terminals. Step E4 is therefore relatively easy to implement.

The locating method makes it possible, for example, to precisely locate, within a building, a lost person equipped with a mobile terminal 2.

Furthermore, in an alternative embodiment, the telecommunication network 1 also includes referring terminals 4 located outside the buildings 5, which ensures continuity of the location service.

The invention allows a geolocation whose accuracy will depend on the accuracy of the mesh by the referring terminals.

The location accuracy is superior to that of the geolocation used in the standard GSM network. It makes it possible to locate a terminal at a room of a building if there is a sufficient number of reference terminals in the geographical area covering this building.

Claims

A method of locating a mobile terminal (2) accessing a telecommunication network (1) implemented by a location server (3), comprising:

a step (E2) of obtaining a first location information of the mobile terminal (2), characterized in that it comprises:

a step (E3) of selecting a group of referent terminals (4) in a list of referent terminals (4) of known location, as a function of said first location information,

a step of determining a second location information of the mobile terminal, as a function of signals transmitted by wireless links between the reference terminals (4) and the mobile terminal (2) and stations fixed (6) of said telecommunication network.

2. The locating method according to claim 1, wherein the step of determining a second location information comprises:

a step (E4) of determining, in the group of referent terminals (4), the terminal referencing (4) closest to the mobile terminal (2), as a function of said signals, and

- A step (E5) for determining a second location information of the mobile terminal (2), according to a location information of the terminal refer (4) closest determined.

The locating method according to claim 2, wherein the second location information is representative of a hardware environment in which the closest referenced terminal is located.

4. The locating method according to claim 3, wherein the second location information identifies or describes an equipment in which the terminal refers closest.

The locating method according to claim 1, comprising a step (E0) of determining whether a terminal belongs to the group of referring terminals (4) from a subscriber identification.

The locating method according to claim 1, wherein the first location information is an identification of a cell of said telecommunication network (1).

7. A method of locating according to claim 1, wherein the step (E2) for obtaining a first location information of the mobile terminal (2) comprises obtaining a location area code stored in association with an identification of said mobile terminal (2) in a register (8A) of local subscribers or a register (8B) of the visitor subscribers of said telecommunication network (1).

8. A method of locating according to claim 1, wherein the step (E3) for selecting a group of referent terminals (4) comprises consulting a database (8A, 8B) which contains, for each terminal refer (4) of the list of referent terminals (4), a first terminal location information refer (4).

9. A location method according to claim 1, wherein said mobile terminal (2) and said referent terminals (4) are each equipped with a subscriber identification card used to identify the terminal considered in said telecommunications network ( 1), said first location information being stored within said telecommunication network (1) in association with an identification of said mobile terminal (2).

A computer program comprising instructions for executing the steps of the locating method according to claim 1 when said program is executed by a computer.

Computer-readable information carrier having instructions of a computer program according to claim 10. Locating server (3) of a mobile terminal (2) accessing a telecommunication network (1) ), comprising:

means (9, 10, 11, 12) for obtaining a first location information of the mobile terminal (2),

characterized in that it comprises:

means (9, 10, 11, 12) for selecting a group of referent terminals (4) in a list of reference terminals (4) of known location, as a function of said first location information,

means (9, 10, 11,

12) for determining a second location information of the mobile terminal, as a function of signals transmitted by wireless links between on the one hand the reference terminals (4) and the mobile terminal (2) and on the other hand fixed stations (6) of said telecommunication network.

Telecommunication network (1) comprising a location server (3) according to claim 12 and a plurality of referent terminals (4), in which the location server (3) has access to a database (8A, 8B). ) which contains, for each of said referent terminals (4), a first location information of the referent terminal (4) and a database (3A) which contains, for each of said referent terminals a second location information of the terminal refer ( 4).