Title of Invention	METHOD AND ARRANGEMENT FOR LOCATING A MOBILE TERMINAL IN A MULTICELL RADIO ARRANGEMENT
Abstract	The invention relates to a method for locating a mobile terminal (MEG) in a multicell radio arrangement having a plurality of radio base stations (FB1, FB2, FB3), comprising recording the received field strength of a response message (AN) of the mobile terminal (MEG) at a plurality of measurements points, and with the location of determining the mobile terminal (MEG) by evaluation of the measured values, whereby the radio base stations (FBI, FB2, FB3) are used for measurement, the locations of the radio base stations (FBI, FB2, FB3) forming the measurement points, a plurality or all of the radio base stations (FBI, FB2, FB3) in a fourth step measure the received field strength of the received response message (AN), and transmit said received field strength to a central device (LS), and the central device (LS) determines the location of the mobile terminal (MEG) in a fifth step by using the measured values, in a first step, the mobile terminal (MEG) is switched to an active state, in a second step, a plurality or all of the radio base stations (FB1,FB2,FB3) are set to the radio channel which is used by the mobile terminal (MEG) to be located, and in a third step, the mobile terminal (MEG) is excited to transmit the response message (AN) by transmitting a test data transmission (TD),whereby those of the radio base stations (FB1,FB2,FB3) which carry out time-critical and/or high-priority data transmissions (TD) are excluded from the switching of their radio channel.

Title of Invention

METHOD AND ARRANGEMENT FOR LOCATING A MOBILE TERMINAL IN A MULTICELL RADIO ARRANGEMENT

Abstract

The invention relates to a method for locating a mobile terminal (MEG) in a multicell radio arrangement having a plurality of radio base stations (FB1, FB2, FB3), comprising recording the received field strength of a response message (AN) of the mobile terminal (MEG) at a plurality of measurements points, and with the location of determining the mobile terminal (MEG) by evaluation of the measured values, whereby the radio base stations (FBI, FB2, FB3) are used for measurement, the locations of the radio base stations (FBI, FB2, FB3) forming the measurement points, a plurality or all of the radio base stations (FBI, FB2, FB3) in a fourth step measure the received field strength of the received response message (AN), and transmit said received field strength to a central device (LS), and the central device (LS) determines the location of the mobile terminal (MEG) in a fifth step by using the measured values, in a first step, the mobile terminal (MEG) is switched to an active state, in a second step, a plurality or all of the radio base stations (FB1,FB2,FB3) are set to the radio channel which is used by the mobile terminal (MEG) to be located, and in a third step, the mobile terminal (MEG) is excited to transmit the response message (AN) by transmitting a test data transmission (TD),whereby those of the radio base stations (FB1,FB2,FB3) which carry out time-critical and/or high-priority data transmissions (TD) are excluded from the switching of their radio channel.

Full Text	The invention relates to a method for locating a mobile terminal in a multicell radio arrangement. The invention further relates to an arrangement for locating a mobile terminal. • In modern communication environments, there is a frequent requirement to locate a user and his associated communication terminal, that is to say to determine his position. In line switching communication networks, for example in "traditional" telephone systems, one specific connection (telephone number) is generally permanently associated with one specific location (for example a connecting box, "connection position" or a room Number), and the associated terminal can therefore easily be located. In contrast, other terminals, particularly those operated without the use of wires, are mobile and therefore cannot be associated with a specific location all the time. Particularly in multicell radio arrangements, for example GSM networks, WLAN arrangements, DECT multicell arrangements etc., the location of a mobile terminal is not simply restricted to the radio area of one transmitter (radio base station), but it may be operated by so-called roaming at any given point throughout the entire multicell radio network (radio arrangement). In order to find the position of a mobile terminal such as this, it is known to use the network to which the radio base stations are connected (DS= distribution system) to find that radio base station which is associated with the mobile terminal at the time in question. The position of the mobile terminal can therefore be limited at least to the area. which is covered by the relevant radio base station. For more accurate location of a mobile terminal, various manufacturers (for example Aruba - www.arubanetworks.com, Newbury - www.newburynetworks.com) offer a multiplicity of measurement stations which are distributed in the form of a grid over, the possible area of operation of the mobile terminal : and each measure the received field strength with which the .; .mobile;: terminal being searched for can be received at the ;■ various' positions of the measurement stations. Since the received field strength, generally decreases the further the mobile terminal is away from the respective measurement point (whose position is known), a form of triangulation can be used to calculate, or at least to estimate, the position of the mobile' terminal from a plurality of measured values from different measurement stations. In addition to the described process of locating mobile terminals, corresponding methods can also be used to record . radio devices.. For example, it is known in WLAN radio networks for ; radio base stations to be provided with knowledge about their adjacent radio base stations or about a "foreign" radio network by the recording radio base station switching the receiving mode for a time period for each available radio channel, and thus recording the' so-called beacons, that is to say radio beacons, of the adjacent radio base stations. The beacons .are-in this case radio signals which are transmitted periodically and on the basis of which the respective radio base station can be identified. Nearby radio base stations can be recorded on the basis of the received field strength of the respective "beacons" recorded in this way, thus making it possible to avoid.'use of the radio channels that they are using, thus resulting in interference-free operation. The described methods for .recording and locating mobile terminals are associated with disadvantages because mobile terminals, in' contrast to the - stationary - radio base stations, generally do not transmit any periodic identification signals or. other transmissions when they are not actively transmitting data. Admittedly, mobile terminals can in many cases be configured such that they transmit such radio signals continuously or quasi-continuously, although this disadvantageously increases the energy consumption of the mobile.terminals. Furthermore, the separate measurement devices (measurement stations) which are used to locate mobile terminals represent an investment that must additionally be provided for this purpose. '/Printed document US 6,839,560 Bl Bahl et al. "Using a derived table of signal strength data • to locate and track a user in a J wireless network" shows a method and an arrangement according j to the precharacterizing clause of patent claim_ 1 and / or 7 respectively, in which the respective received field strength of'a transmission of a mobile terminal is recorded by means of the radio base stations and whereby the measured values are compared with a reference table so that the location of the ' mobile terminal is determined by means of the nearest table entries. Printed document US 2002/0098852 Al Goren at al. "Methods and apparatus for identifying asset location in communication networks" also shows a method- and an arrangement for locating mobile, terminals.. Here essentially field strengths of a transmitter (e.g. PDA and. mobile phone) received by access points.; are recorded to estimate the position of the transmitter by means of triangu.lation. For measuring the field strength said access points interrupt their operation and switch to the frequency of the transmitter -the position of which is to be determined. '-:;! One object of the present invention is therefore to improve the process of locating mobile terminals in multicell radio arrangements with a multiplicity of radio channel to the effect that regular operation of the radio base stations is affected as little as possible. The object is achieved by a method as claimed in patent claim' 1, and by, an. arrangement as claimed in patent claim 7. The method "which is used to achieve the object in this case provides that, in order to locate a mobile terminal in a multicell radio arrangement having a plurality of radio base stations,' the received field strength .of at least one data transmission from the mobile, terminal is recorded at a plurality of : measurement points, and this received field-strength; is" transmitted to a central device, for the evaluation of the measured values, where it is processed to determine the position. In this case, a multichannel radio data network is used .as the multicell radio arrangement, for example a WLAN network, with the radio base stations being used for the measurement points. . In this case, the mobile terminal is switched to' an active state, and a plurality of the radio base stations are set to the radio channel being used by the mobile terminal to be located. A data transmission to the mobile terminal excites it to transmit a response message, on the' basis of . which the received field strength which can be measured by this response message is recorded at the radio base stations that have been set to the corresponding radio channel, transmitted to the central device, and is used there to find the position of the mobile terminal. This method makes it .possible to locate even those appliances, that is to say mobile terminals, which are being operated passively ("power-saving mode") -, in which case the radio base stations which exist in any case can be used to record the. received field strengths. Switching to the respective radio channel of the mobile terminal .to be located means that the mobile terminal can be located even in those situations in which a plurality or all of the radio base stations in whose reception area the mobile terminal is arranged are using different radio channels. This avoids the.same radio channel-having to be selected all the time in all the radio, base stations in the multicell radio arrangement: for location purposes, which, although technically feasible, would, however, lead to a reduced data throughput in the radio arrangement. Therefore the normal operation of the radio base stations may .be interrupted for location purposes and for the radio channel switching associated with this. In this case, the central device which initiates the location process, or else each radio base station, is configured so as to suppress switching of the radio channel and/or interruption .of. normal operation for location purposes in those cases in which data transmission, and possibly even only a high-priority data transmission, is currently being carried out by the respective radio base station. The solution to the problem also envisages an arrangement for locating a mobile terminal, using a multicell radio arrangement having a plurality of radio base stations and a plurality of radio channels, with the radio base stations and the mobile terminal each being associated with one of the radio channels. In this case, the radio base stations are each designed to record a received field strength of a data transmission which is transmitted from the mobile terminal, and the radio base stations are designed to transmit a data transmission to the mobile terminals, with the mobile terminal being designed to transmit a response data transmission. The radio base stations are designed to be temporarily switched to the radio channel associated with the mobile terminal, and the radio base stations are designed to transmit the respectively recorded received field strength of the response message to a central device. In this case, the -central device is designed to determine the location of.the mobile terminal on the basis of the transmitted received field strengths. An arrangement such as this means that it is possible to locate a mobile terminal even in those multicell radio arrangements in-which: the various radio base stations are used in different radio, channels. In this case, there is no need to install a measurement infrastructure, since the radio base stations are themselves used for the measurement process. In this case, the central device that initiates the location process is configured so as . to suppress switching of the radio ^channel and/or interruption of normal operation for location purposes in those cases in. which data transmission, and possibly even only a high-priority data transmission, is. currently being carried out by the respective radio base station. In order to locate mobile terminals which are in a rest state (power-saving mode), the mobile terminal may, for example, be activated by a data transmission that is waiting for the mobile terminal being indicated in the "beacon" of the radio base station associated with that mobile terminal. Advantageous . refinements of the method according to the fc 'invention are specified by the.dependent patent claims 2 to 6. I The features and advantages described in this case also apply 1 in the same sense to the arrangement according to the invention. The regular operation of the radio base stations and thus of the multicell radio arrangement is reproduced as quickly as possible when the radio base stations which have been switched to a different radio channel for the measurement are switched back to their original radio channel once the measurement has been carried, out (switched back), and any data transmissions ; which may have been interrupted for the measurement process are continued. In those situations in which the.mobile terminal is in a rest state (inactive) (for example a power-saving mode) before the measurement (determination) of its position, it can easily be activated by notifying a data transmission for this mobile terminal. This expediently happens by setting an appropriate flag for., this mobile terminal in the "beacon" of one or more radio base stations. If the mobile terminal carries out a -reception activity periodically, the beacon is received and evaluated, so that the mobile terminal then starts a dialog with the radio base station and is thus activated. Dependent on .the configuration of the.mobile terminal, it. may be necessary to use further data transmissions, for example test data transmissions, or the like to prevent the mobile terminal from switching back again . to a rest state, and therefore not being ready to transmit a data transmission which.may be used to locate it. ... The method can be used not just for locating mobile terminals, but also for recording mobile, terminals., that is to say it is first of all possible to use the method to find out whether and which mobile terminals are located in the radio area of one or .more/all of. the radio base■'• stations.. .Appropriate test messages, . that is to say .for example multicast/broadcast messages, are. .sent for this, purpose via one or more radio base stations, with . this being done on all relevant radio channels for recording without any gaps. In this case, the recording and location can either be carried out in two different "runs", or else this may be done in a combined form by means of: a single recording . process. Exemplary embodiments of the method according to the invention will be explained in the following text with reference to the drawing. They should be used at the same time to explain an arrangement according to the invention. In this; case, the single figure shows a multiceli radio arrangement having a plurality of radio base stations, .-a central device and a mobile terminal. The figure shows a WLAN network to the IEEE Standard 802.11 as a.multicell radio arrangement. In this network, the radio base stations FBI, FB2, FB3 (so-called access points) and a central device LS (location server) are connected to one another via a data network DS (distribution system), a local area network based on the Internet Protocol. The figure also shows a mobile terminal MEG, for example a so-called PDA (personal digital •: assistant), with WLAN transmitting/receiving device. The radio base stations FBI, FB2, FB3 are designed such that • they can be instructed by the central server LS to signal to the central server LS the received field strength with which ,a mobile terminal MEG is received. In addition, the radio base stations FBI, FB2, .FB3 may be instructed by the central server LS to 'temporarily change to an undefined radio channel of the WLAN standard" being used. It is, of course, also possible to use a different multicell radio arrangement with associated mobile terminals rather than , the IEEE Standard 802.11 WLAN considered here, for example a GSM •■network, a multicell DECT network (DECT multicell), a UMTS network, or the like. The radio base stations FB1, FB2, FB3 transmit a regular signal (beacon) by means of which they can be identified. A radio base ■'station FBI, FB2, FB3 can embed a message in the beacon, indicating -to a mobile terminal MEG which is registered with the respective radio base station FBI, FB2, FB3 as to whether there is a need to transmit data to this mobile terminal MEG. The mobile "terminal MEG can assume various operating modes, inter alia an "active'-' and an "inactive" operating mode. In the inactive: operating mode, frequently also referred to as the power-save mode, the mobile terminal MEG does not transmit and in addition switches its receiver on only sporadically, for example for a few milliseconds every two seconds. During this short reception phase, the mobile terminal MEG checks whether the beacon of the radio base station, in this case the radio base station FBI, can be received on the radio channel assigned, to it. If this is not the case, the mobile terminal MEG assumes that the' link to "its" radio base station FBI has been interrupted, and initiates appropriate measures, for example a search for a suitable different radio base station FB2, FB3.. However, if the beacon can be received, the mobile terminal MEG also checks.whether, there is any data that.is to be received from this radio base station FBI. If this is the case, this data is. requested from the radio base station FBI, and the mobile terminal MEG remains in the active mode, that is to say ready to receive, for a predefined time (minimum time interval). If no waiting data is indicated, the mobile terminal MEG immediately changes back to the inactive state. If a user (not : shown here) wishes to find the position of the mobile;terminal MEG, it sends an appropriate request message to the central device LS, for example via the data network DS. This request message comprises a designation or an address, for example an IP address (IP = .Internet Protocol) for the mobile terminal MEG being searched for. The central device DS now checks, likewise using request messages via the data network DS, with the radio base stations FBI, FB2, FB3 to. determine' whether the defined mobile terminal MEG is currently associated with one of these radio base stations FBI, FB2, FB3; in this case, it is also said that it is "registered" to one of the radio base stations FBI, FB2, FB3. In this case, the result is that the mobile terminal MEG being searched for is currently associated with the radio base station FBI, and that the mobile terminal MEG, and therefore the radio base station FBI as well, are set to a first radio channel. In contrast to this, the second radio base station FB2 is set to a second radio channel, and the radio base station FB3 is set to a third radio channel. However, in the radio network under consideration here, it is also possible for a plurality of adjacent radio base stations FBI, FB2, FB3 whose radio areas overlap one another to be operated using the same radio channel. The radio base station FBI now, receives the command from the central device • LS to switch the mobile terminal MEG to the active: state, in other words: to "wake it up". For this purpose, an: appropriate "flag" is set for the mobile terminal MEG. in the beacon of the radio base station FBI. Furthermore, a : countdown is started in the central device LS - as an alternative, this can also be done in the radio base station FBI - : and periodically initiates the transmission of test messages ("ping" messages or the like) to the mobile terminal MEG. This, prevents the mobile terminal MEG from switching back to the inactive: state, until the measurements that are required, to locate it have been completed. The central device LS now checks with the radio base stations FBI, FB.2, FB3 to determine whether these radio base stations FBI, FB2,: FB3 are currently transmitting high-priority data, for example real-time communication links. Since this is . currently not the case (otherwise, the corresponding request would be repeated- at periodic, intervals) , the radio base stations. FB2, FB3 are instructed to temporarily change to the first radio channel which is being used by the radio base station FBI. All the radio base stations FBI, FB2, FB3 are then instructed to switch to a so-called "measurement mode", that is to . say to measure the received field strengths of the transmissions from the mobile terminals MEG being received by them, and to buffer store these measurement results. The central device LS now uses the data network DS and the radio base station FBI to transmit a message TD (test data) to the mobile terminal MEG, causing this mobile terminal MEG to transmit a response message" AN. The message TD may, for example, comprise the known "ping command", which is also known from the Internet and requests a return response (response . message AN). The already, described process of "waking up" the mobile terminal MEG can also be avoided; in this case, the data packet in the', message. TD with the "ping command" in any case ensures that the mobile terminal MEG will change to the active mode. Since, • however, the mobile . terminal MEG switches on its receiver only at relatively long time intervals in the inactive state ("opens it"), the time period during which the radio base stations FB2, FB3 must change to a "foreign" radio channel is in some cire'umstances likewise very long in a situation such as this. There may therefore be considerable interference with the operation of the multicell radio arrangement if it is necessary to contact or to record (to find) a large number of mobile terminals. MEG, if the method step of "waking up" is dispensed with. .; :The actual measurement process is completed by the transmission of .. the response message AN., and the registration of the resultant received field strengths at the positions of the radio base stations FBI, FB2-, FB3, so that the radio base .stations FB2, FB3 can now resume their "normal" operation, and can switch back to their original radio channels (second radio : channel, third radio channel). The measured received field . strengths for the mobile terminal MEG are now checked (called up) by the central device LS from the radio base stations FB1> FB2, FB3, and are processed further,, using a triangulation method that is known per se, to form location information for the. mobile ..terminal MEG being searched for. Furthermore, the "measurement mode" is switched off for the radio base stations FBI,, FB2, FB3. . The described.control of the measurement process by the central device. LS allows both the mobile terminal MEG and the radio . base stations FBI, FB2, FB3 to be operated largely in accordance with the standard. However, individual processes or else all the processes which are required for position finding (location) may, of course, be controlled by one of the radio base stations FB1, FB2, FB3. This functionality can be added to these radio base stations or to one of the radio base stations for example by means of a so-called firmware update. So-called, multicast messages (broadcast messages) can be used in the data network and therefore also in the multicell radio arrangement under consideration to address a plurality or all of the mobile terminals MEG on one radio channel. If a search process such as this is also carried out simultaneously or ,■ successively on all the radio channels, all of the mobile terminals ..MEG, that is to say including those which are not .' registered with any of the radio base stations FBI, FB2, FB3, will therefore be found. When a "scan" such as this is carried out, a plurality of radio base stations FBI, FB2, FB3 can likewise be . set to the same radio channel and can be switched to a measurement mode, so that the positions of' the mobile terminals MEG are also determined at the same time that they are being recorded, and can be stored for subsequent use, for example in a database in the central device LS. Alternatively or in addition to the described "RSS" method (RSS = received signal strength), it is feasible to evaluate the signal; propagation times between the radio base stations FBI, FB2., FB3 : and the mobile terminal MEG. In fact, signal propagation times can be recorded only with major effort with the required precision (resolution), especially in geographically small WLAN radio networks. In contrast to this, modern receivers and receiving modules in any case have circuits . which record the received field strength of the respectively selected radio channel and provide this information via an appropriate digital interface, so that there is no need for a separate/additional measurement device. As the number of radio base stations FBI, FB2, . FB3 being used for measurement' increases, the location precision- that can be achieved is also increasing. We Claim: 1. A method for locating a mobile terminal (MEG) in a multicell radio arrangement having a plurality of radio base stations (FBI, FB2, FB3), comprising: - recording the received field strength of a response message (AN) of the mobile terminal (MEG) at a plurality of measurements points, and with the location of determining the mobile terminal (MEG) by evaluation of the measured values, whereby - the radio base stations (FBI, FB2, FB3) are used for measurement, the locations of the radio base stations (FBI, FB2, FB3) forming the measurement points, - a plurality or all of the radio base stations (FBI, FB2, FB3) in a fourth step measure the received field strength of the received response message (AN), and transmit said received field strength to a central device (LS), and - the central device (LS) determines the location of the mobile terminal (MEG) in a fifth step by using the measured values, characterized in that -in a first step, the mobile terminal (MEG) is switched to an active state, -in a second step, a plurality or all of the radio base stations (FB1,FB2,FB3) are set to the radio channel which is used by the mobile terminal (MEG) to be located, and -in a third step, the mobile terminal (MEG) is excited to transmit the response message (AN) by transmitting a test data transmission (TD), whereby those of the radio base stations (FB1,FB2,FB3) which carry out time-critical and/or high-priority data transmissions (TD) are excluded from the switching of their radio channel. 2. The method as claimed in claim 1, wherein, after the fifth step, the radio base stations (FBI, FB2, FB3) are switched back to their respective original radio channel. 3. The method as claimed in one of the preceding claims, wherein in the first step, the mobile terminal (MEG) is switched to the active state by the radio base station (FBI) which is associated with this mobile terminal (MEG) notifying a data transmission (TD) for the mobile terminal (MEG). 4. The method as claimed in one of the preceding claims, wherein, after the first step, the mobile terminal (MEG) is kept in the active state by further data transmissions until the third method step has been carried out. 5. The method as claimed in one of the preceding claims, wherein, in the second step, the radio base stations (FB2, FB3) to be switched to the radio channel have their normal operation interrupted. 6. The method as claimed in one of the preceding claims, wherein the method is used for recording and/or locating a plurality or all of the mobile terminals (MEG) in the multicell radio arrangement in that the mobile terminals (MEG) which are associated with the respective radio channel are activated on one radio channel or successively on a plurality of radio channels, are excited in order to transmit a data transmission (TD), and the received field strengths of this data transmission (TD) are recorded by measurement. 7. An arrangement for locating a mobile terminal (MEG), using a multicell radio arrangement having a plurality of radio base stations (FBI, FB2, FB3) and a plurality of radio channels, with the radio base stations (FBI, FB2, FB3) and the mobile terminal (MEG) each being associated with one of the radio channels, whereby the radio base stations (FBI, FB2, FB3) are each designed to record a received field strength of a data transmission which is transmitted from the mobile terminal (MEG), at least one of the radio base stations (FBI) is designed to transmit a data transmission (TD) to the mobile terminal (MEG), the radio base stations (FBI, FB2,FB3) are designed to transmit the respectively recorded received field strength of a response message (AN) to a central device (LS), and in that the central device (LS) is designed to determine the location of the mobile terminal (MEG) on the basis of the transmitted received field strengths, characterized in that the mobile terminal (MEG) is designed to transmit the response messae (AN), the radio base stations (FB2,FB3) are designed to temporarily switch to the radio channel associated with the mobile terminal (MEG), and the central device (LS) is designed to exclude those of the radio base stations (FB1,FB2,FB3) which carry out time-critical and/or high-priority data transmissions (TD) from the switching of their radio channel. ABSTRACT TITLE: METHOD AND ARRANGEMENT FOR LOCATING A MOBILE TERMINAL IN A MULTICELL RADIO ARRANGEMENT The invention relates to a method for locating a mobile terminal (MEG) in a multicell radio arrangement having a plurality of radio base stations (FB1, FB2, FB3), comprising recording the received field strength of a response message (AN) of the mobile terminal (MEG) at a plurality of measurements points, and with the location of determining the mobile terminal (MEG) by evaluation of the measured values, whereby the radio base stations (FBI, FB2, FB3) are used for measurement, the locations of the radio base stations (FBI, FB2, FB3) forming the measurement points, a plurality or all of the radio base stations (FBI, FB2, FB3) in a fourth step measure the received field strength of the received response message (AN), and transmit said received field strength to a central device (LS), and the central device (LS) determines the location of the mobile terminal (MEG) in a fifth step by using the measured values, in a first step, the mobile terminal (MEG) is switched to an active state, in a second step, a plurality or all of the radio base stations (FB1,FB2,FB3) are set to the radio channel which is used by the mobile terminal (MEG) to be located, and in a third step, the mobile terminal (MEG) is excited to transmit the response message (AN) by transmitting a test data transmission (TD),whereby those of the radio base stations (FB1,FB2,FB3) which carry out time-critical and/or high-priority data transmissions (TD) are excluded from the switching of their radio channel.

Full Text

The invention relates to a method for locating a mobile terminal in a multicell radio arrangement. The invention further relates to an arrangement for locating a mobile terminal.
• In modern communication environments, there is a frequent requirement to locate a user and his associated communication terminal, that is to say to determine his position. In line switching communication networks, for example in "traditional" telephone systems, one specific connection (telephone number) is generally permanently associated with one specific location (for example a connecting box, "connection position" or a room Number), and the associated terminal can therefore easily be located. In contrast, other terminals, particularly those operated without the use of wires, are mobile and therefore cannot be associated with a specific location all the time. Particularly in multicell radio arrangements, for example GSM networks, WLAN arrangements, DECT multicell arrangements etc., the location of a mobile terminal is not simply restricted to the radio area of one transmitter (radio base station), but it may be operated by so-called roaming at any given point throughout the entire multicell radio network (radio arrangement).
In order to find the position of a mobile terminal such as this, it is known to use the network to which the radio base stations are connected (DS= distribution system) to find that radio base station which is associated with the mobile terminal at the time in question. The position of the mobile terminal can therefore be limited at least to the area.

which is covered by the relevant radio base station.
For more accurate location of a mobile terminal, various
manufacturers (for example Aruba - www.arubanetworks.com,
Newbury - www.newburynetworks.com) offer a multiplicity of
measurement stations which are distributed in the form of a
grid over, the possible area of operation of the mobile terminal
: and each measure the received field strength with which the
.; .mobile;: terminal being searched for can be received at the
;■ various' positions of the measurement stations. Since the
received field strength, generally decreases the further the
mobile terminal is away from the respective measurement point
(whose position is known), a form of triangulation can be used
to calculate, or at least to estimate, the position of the
mobile' terminal from a plurality of measured values from
different measurement stations.
In addition to the described process of locating mobile terminals, corresponding methods can also be used to record . radio devices.. For example, it is known in WLAN radio networks for ; radio base stations to be provided with knowledge about their adjacent radio base stations or about a "foreign" radio network by the recording radio base station switching the receiving mode for a time period for each available radio channel, and thus recording the' so-called beacons, that is to say radio beacons, of the adjacent radio base stations. The beacons .are-in this case radio signals which are transmitted periodically and on the basis of which the respective radio base station can be identified. Nearby radio base stations can be recorded on the basis of the received field strength of the respective "beacons" recorded in this way, thus making it possible to avoid.'use of the radio channels that they are using, thus resulting in interference-free operation.
The described methods for .recording and locating mobile terminals are associated with disadvantages because mobile

terminals, in' contrast to the - stationary - radio base stations, generally do not transmit any periodic

identification signals or. other transmissions when they are not actively transmitting data. Admittedly, mobile terminals can in many cases be configured such that they transmit such radio signals continuously or quasi-continuously, although this disadvantageously increases the energy consumption of the mobile.terminals. Furthermore, the separate measurement devices (measurement stations) which are used to locate mobile terminals represent an investment that must additionally be provided for this purpose.
'/Printed document US 6,839,560 Bl Bahl et al. "Using a derived table of signal strength data • to locate and track a user in a J wireless network" shows a method and an arrangement according j to the precharacterizing clause of patent claim_ 1 and / or 7 respectively, in which the respective received field strength of'a transmission of a mobile terminal is recorded by means of the radio base stations and whereby the measured values are compared with a reference table so that the location of the ' mobile terminal is determined by means of the nearest table entries.
Printed document US 2002/0098852 Al Goren at al. "Methods and
apparatus for identifying asset location in communication
networks" also shows a method- and an arrangement for locating
mobile, terminals.. Here essentially field strengths of a
transmitter (e.g. PDA and. mobile phone) received by access
points.; are recorded to estimate the position of the transmitter
by means of triangu.lation. For measuring the field strength
said access points interrupt their operation and switch to the
frequency of the transmitter -the position of which is to be
determined. '-:;!
One object of the present invention is therefore to improve the process of locating mobile terminals in multicell radio arrangements with a multiplicity of radio channel to the effect

that regular operation of the radio base stations is affected as little as possible.
The object is achieved by a method as claimed in patent claim'
1, and by, an. arrangement as claimed in patent claim 7.
The method "which is used to achieve the object in this case provides that, in order to locate a mobile terminal in a multicell radio arrangement having a plurality of radio base stations,' the received field strength .of at least one data transmission from the mobile, terminal is recorded at a plurality of : measurement points, and this received field-strength; is" transmitted to a central device, for the evaluation of the measured values, where it is processed to determine the position. In this case, a multichannel radio data network is used .as the multicell radio arrangement, for example a WLAN network, with the radio base stations being used for the measurement points. . In this case, the mobile terminal is switched to' an active state, and a plurality of the radio base stations are set to the radio channel being used by the mobile terminal to be located. A data transmission to the mobile terminal excites it to transmit a response message, on the' basis of . which the received field strength which can be

measured by this response message is recorded at the radio base stations that have been set to the corresponding radio channel,

transmitted to the central device, and is used there to find the position of the mobile terminal. This method makes it .possible to locate even those appliances, that is to say mobile terminals, which are being operated passively ("power-saving mode") -, in which case the radio base stations which exist in any case can be used to record the. received field strengths. Switching to the respective radio channel of the mobile terminal .to be located means that the mobile terminal can be located even in those situations in which a plurality or all of the radio base stations in whose reception area the mobile terminal is arranged are using different radio channels. This avoids the.same radio channel-having to be selected all the time in all the radio, base stations in the multicell radio arrangement: for location purposes, which, although technically feasible, would, however, lead to a reduced data throughput in the radio arrangement.
Therefore the normal operation of the radio base stations may .be interrupted for location purposes and for the radio channel switching associated with this. In this case, the central device which initiates the location process, or else each radio base station, is configured so as to suppress switching of the radio channel and/or interruption .of. normal operation for location purposes in those cases in which data transmission, and possibly even only a high-priority data transmission, is currently being carried out by the respective radio base station.
The solution to the problem also envisages an arrangement for locating a mobile terminal, using a multicell radio arrangement having a plurality of radio base stations and a plurality of radio channels, with the radio base stations and the mobile terminal each being associated with one of the radio channels. In this case, the radio base stations are each designed to record a received field strength of a data transmission which is transmitted from the mobile terminal, and the radio base

stations are designed to transmit a data transmission to the mobile terminals, with the mobile terminal being designed to transmit a response data transmission. The radio base stations are designed to be temporarily switched to the radio channel associated with the mobile terminal, and the radio base stations are designed to transmit the respectively recorded received field strength of the response message to a central device. In this case, the -central device is designed to determine the location of.the mobile terminal on the basis of the transmitted received field strengths. An arrangement such

as this means that it is possible to locate a mobile terminal even in those multicell radio arrangements

in-which: the various radio base stations are used in different radio, channels. In this case, there is no need to install a measurement infrastructure, since the radio base stations are themselves used for the measurement process.
In this case, the central device that initiates the location process is configured so as . to suppress switching of the radio ^channel and/or interruption of normal operation for location
purposes in those cases in. which data transmission, and
possibly even only a high-priority data transmission, is.
currently being carried out by the respective radio base
station.
In order to locate mobile terminals which are in a rest state (power-saving mode), the mobile terminal may, for example, be activated by a data transmission that is waiting for the mobile terminal being indicated in the "beacon" of the radio base station associated with that mobile terminal.
Advantageous . refinements of the method according to the fc
'invention are specified by the.dependent patent claims 2 to 6. I
The features and advantages described in this case also apply 1
in the same sense to the arrangement according to the invention.
The regular operation of the radio base stations and thus of the multicell radio arrangement is reproduced as quickly as possible when the radio base stations which have been switched to a different radio channel for the measurement are switched back to their original radio channel once the measurement has been carried, out (switched back), and any data transmissions ; which may have been interrupted for the measurement process are continued.
In those situations in which the.mobile terminal is in a rest state (inactive) (for example a power-saving mode) before the

measurement (determination) of its position, it can easily be activated by notifying a data transmission for this mobile terminal. This expediently happens by setting an appropriate flag for., this mobile terminal in the "beacon" of one or more radio base stations. If the mobile terminal carries out a
-reception activity periodically, the beacon is received and evaluated, so that the mobile terminal then starts a dialog with the radio base station and is thus activated. Dependent on
.the configuration of the.mobile terminal, it. may be necessary

to use further data transmissions, for example test data transmissions,

or the like to prevent the mobile terminal from switching back again . to a rest state, and therefore not being ready to transmit a data transmission which.may be used to locate it.

... The method can be used not just for locating mobile terminals, but also for recording mobile, terminals., that is to say it is first of all possible to use the method to find out whether and which mobile terminals are located in the radio area of one or .more/all of. the radio base■'• stations.. .Appropriate test messages,
. that is to say .for example multicast/broadcast messages, are. .sent for this, purpose via one or more radio base stations, with
. this being done on all relevant radio channels for recording without any gaps. In this case, the recording and location can either be carried out in two different "runs", or else this may be done in a combined form by means of: a single recording
. process.
Exemplary embodiments of the method according to the invention will be explained in the following text with reference to the drawing. They should be used at the same time to explain an arrangement according to the invention.
In this; case, the single figure shows a multiceli radio arrangement having a plurality of radio base stations, .-a central device and a mobile terminal.

The figure shows a WLAN network to the IEEE Standard 802.11 as a.multicell radio arrangement. In this network, the radio base stations FBI, FB2, FB3 (so-called access points) and a central device LS (location server) are connected to one another via a data network DS (distribution system), a local area network based on the Internet Protocol. The figure also shows a mobile terminal MEG, for example a so-called PDA (personal digital •: assistant), with WLAN transmitting/receiving device.
The radio base stations FBI, FB2, FB3 are designed such that • they can be instructed by the central server LS to signal to the central server LS the received field strength with which ,a mobile terminal MEG is received. In addition, the radio base stations FBI, FB2, .FB3 may be instructed by the central server LS to 'temporarily change to an undefined radio channel of the WLAN standard" being used.
It is, of course, also possible to use a different multicell radio arrangement with associated mobile terminals rather than , the IEEE Standard 802.11 WLAN considered here, for example a GSM •■network, a multicell DECT network (DECT multicell), a UMTS network, or the like.
The radio base stations FB1, FB2, FB3 transmit a regular signal (beacon) by means of which they can be identified. A radio base ■'station FBI, FB2, FB3 can embed a message in the beacon, indicating -to a mobile terminal MEG which is registered with the respective radio base station FBI, FB2, FB3 as to whether there is a need to transmit data to this mobile terminal MEG.
The mobile "terminal MEG can assume various operating modes, inter alia an "active'-' and an "inactive" operating mode. In the inactive: operating mode, frequently also referred to as the power-save mode, the mobile terminal MEG does not transmit and in addition switches its receiver on only sporadically,

for example for a few milliseconds every two seconds. During this short reception phase, the mobile terminal MEG checks whether the beacon of the radio base station, in this case the radio base station FBI, can be received on the radio channel assigned, to it. If this is not the case, the mobile terminal MEG assumes that the' link to "its" radio base station FBI has been interrupted, and initiates appropriate measures, for example a search for a suitable different radio base station FB2, FB3.. However, if the beacon can be received, the mobile terminal MEG also checks.whether, there is any data that.is to be received from this radio base station FBI. If this is the case, this data is. requested from the radio base station FBI, and the mobile terminal MEG remains in the active mode, that is to say ready to receive, for a predefined time (minimum time interval). If no waiting data is indicated, the mobile terminal MEG immediately changes back to the inactive state.
If a user (not : shown here) wishes to find the position of the mobile;terminal MEG, it sends an appropriate request message to the central device LS, for example via the data network DS. This request message comprises a designation or an address, for example an IP address (IP = .Internet Protocol) for the mobile terminal MEG being searched for. The central device DS now checks, likewise using request messages via the data network DS, with the radio base stations FBI, FB2, FB3 to. determine' whether the defined mobile terminal MEG is currently associated with one of these radio base stations FBI, FB2, FB3; in this case, it is also said that it is "registered" to one of the radio base stations FBI, FB2, FB3. In this case, the result is that the mobile terminal MEG being searched for is currently associated with the radio base station FBI, and that the mobile terminal MEG, and therefore the radio base station FBI as well, are set to a first radio channel. In contrast to this, the second radio base station FB2 is set to a second radio channel, and the radio base station FB3 is set to a third radio channel. However, in the radio network under consideration here, it is

also possible for a plurality

of adjacent radio base stations FBI, FB2, FB3 whose radio areas overlap one another to be operated using the same radio channel.
The radio base station FBI now, receives the command from the central device • LS to switch the mobile terminal MEG to the active: state, in other words: to "wake it up". For this purpose, an: appropriate "flag" is set for the mobile terminal MEG. in the beacon of the radio base station FBI. Furthermore, a : countdown is started in the central device LS - as an alternative, this can also be done in the radio base station FBI - : and periodically initiates the transmission of test messages ("ping" messages or the like) to the mobile terminal MEG. This, prevents the mobile terminal MEG from switching back to the inactive: state, until the measurements that are required, to locate it have been completed.
The central device LS now checks with the radio base stations FBI, FB.2, FB3 to determine whether these radio base stations FBI, FB2,: FB3 are currently transmitting high-priority data, for example real-time communication links. Since this is . currently not the case (otherwise, the corresponding request would be repeated- at periodic, intervals) , the radio base stations. FB2, FB3 are instructed to temporarily change to the first radio channel which is being used by the radio base station FBI. All the radio base stations FBI, FB2, FB3 are then instructed to switch to a so-called "measurement mode", that is to . say to measure the received field strengths of the transmissions from the mobile terminals MEG being received by them, and to buffer store these measurement results. The central device LS now uses the data network DS and the radio base station FBI to transmit a message TD (test data) to the mobile terminal MEG, causing this mobile terminal MEG to transmit a response message" AN. The message TD may, for example, comprise the known "ping command", which is also known

from the Internet and requests a return response (response . message AN).

The already, described process of "waking up" the mobile terminal MEG can also be avoided; in this case, the data packet in the', message. TD with the "ping command" in any case ensures that the mobile terminal MEG will change to the active mode. Since, • however, the mobile . terminal MEG switches on its receiver only at relatively long time intervals in the inactive state ("opens it"), the time period during which the radio base stations FB2, FB3 must change to a "foreign" radio channel is in some cire'umstances likewise very long in a situation such as this. There may therefore be considerable interference with the operation of the multicell radio arrangement if it is necessary to contact or to record (to find) a large number of mobile terminals. MEG, if the method step of "waking up" is dispensed with. .;
:The actual measurement process is completed by the transmission of .. the response message AN., and the registration of the resultant received field strengths at the positions of the radio base stations FBI, FB2-, FB3, so that the radio base
.stations FB2, FB3 can now resume their "normal" operation, and
can switch back to their original radio channels (second radio
: channel, third radio channel). The measured received field
. strengths for the mobile terminal MEG are now checked (called
up) by the central device LS from the radio base stations FB1>
FB2, FB3, and are processed further,, using a triangulation
method that is known per se, to form location information for
the. mobile ..terminal MEG being searched for. Furthermore, the
"measurement mode" is switched off for the radio base stations
FBI,, FB2, FB3. .
The described.control of the measurement process by the central device. LS allows both the mobile terminal MEG and the radio . base stations FBI, FB2, FB3 to be operated largely in accordance with the standard. However, individual processes or else all the processes which are required for position finding (location) may, of course, be controlled by one of the radio

base stations FB1, FB2, FB3. This functionality can be added to these radio base stations or to one of the radio

base stations for example by means of a so-called firmware update.
So-called, multicast messages (broadcast messages) can be used in the data network and therefore also in the multicell radio arrangement under consideration to address a plurality or all of the mobile terminals MEG on one radio channel. If a search process such as this is also carried out simultaneously or ,■ successively on all the radio channels, all of the mobile terminals ..MEG, that is to say including those which are not .' registered with any of the radio base stations FBI, FB2, FB3, will therefore be found. When a "scan" such as this is carried out, a plurality of radio base stations FBI, FB2, FB3 can likewise be . set to the same radio channel and can be switched to a measurement mode, so that the positions of' the mobile terminals MEG are also determined at the same time that they are being recorded, and can be stored for subsequent use, for example in a database in the central device LS.
Alternatively or in addition to the described "RSS" method (RSS = received signal strength), it is feasible to evaluate the signal; propagation times between the radio base stations FBI, FB2., FB3 : and the mobile terminal MEG. In fact, signal propagation times can be recorded only with major effort with the required precision (resolution), especially in geographically small WLAN radio networks. In contrast to this, modern receivers and receiving modules in any case have circuits . which record the received field strength of the respectively selected radio channel and provide this information via an appropriate digital interface, so that there is no need for a separate/additional measurement device. As the number of radio base stations FBI, FB2, . FB3 being used for measurement' increases, the location precision- that can be achieved is also increasing.

We Claim:
1. A method for locating a mobile terminal (MEG) in a multicell radio arrangement having a plurality of radio base stations (FBI, FB2, FB3), comprising:
- recording the received field strength of a response message (AN) of the mobile terminal (MEG) at a plurality of measurements points, and with the location of determining the mobile terminal (MEG) by evaluation of the measured values, whereby
- the radio base stations (FBI, FB2, FB3) are used for measurement, the locations of the radio base stations (FBI, FB2, FB3) forming the measurement points,
- a plurality or all of the radio base stations (FBI, FB2, FB3) in a fourth step measure the received field strength of the received response message (AN), and transmit said received field strength to a central device (LS), and
- the central device (LS) determines the location of the mobile terminal (MEG) in a fifth step by using the measured values,

characterized in that
-in a first step, the mobile terminal (MEG) is switched to an active state,
-in a second step, a plurality or all of the radio base stations (FB1,FB2,FB3) are set to the radio channel which is used by the mobile terminal (MEG) to be located, and
-in a third step, the mobile terminal (MEG) is excited to transmit the response message (AN) by transmitting a test data transmission (TD),
whereby those of the radio base stations (FB1,FB2,FB3) which carry out time-critical and/or high-priority data transmissions (TD) are excluded from the switching of their radio channel.
2. The method as claimed in claim 1, wherein, after the fifth step, the radio base
stations (FBI, FB2, FB3) are switched back to their respective original radio
channel.
3. The method as claimed in one of the preceding
claims, wherein in the first step, the mobile terminal (MEG) is switched to the
active state by the radio base station (FBI) which is associated with this mobile
terminal (MEG) notifying a data transmission (TD) for the mobile terminal (MEG).

4. The method as claimed in one of the preceding claims, wherein, after the first step, the mobile terminal (MEG) is kept in the active state by further data transmissions until the third method step has been carried out.
5. The method as claimed in one of the preceding claims, wherein, in the second step, the radio base stations (FB2, FB3) to be switched to the radio channel have their normal operation interrupted.
6. The method as claimed in one of the preceding claims, wherein the method is used for recording and/or locating a plurality or all of the mobile terminals (MEG) in the multicell radio arrangement in that the mobile terminals (MEG) which are associated with the respective radio channel are activated on one radio channel or successively on a plurality of radio channels, are excited in order to transmit a data transmission (TD), and the received field strengths of this data transmission (TD) are recorded by measurement.
7. An arrangement for locating a mobile terminal (MEG), using a multicell radio arrangement having a plurality of radio base stations (FBI, FB2, FB3) and a plurality of radio channels, with the radio base stations (FBI, FB2, FB3) and the mobile terminal (MEG) each being associated with one of the radio channels, whereby

the radio base stations (FBI, FB2, FB3) are each designed to record a received field strength of a data transmission which is transmitted from the mobile terminal (MEG),
at least one of the radio base stations (FBI) is designed to transmit a data transmission (TD) to the mobile terminal (MEG),
the radio base stations (FBI, FB2,FB3) are designed to transmit the respectively recorded received field strength of a response message (AN) to a central device (LS), and in that the central device (LS) is designed to determine the location of the mobile terminal (MEG) on the basis of the transmitted received field strengths,
characterized in that the mobile terminal (MEG) is designed to transmit the response messae (AN),
the radio base stations (FB2,FB3) are designed to temporarily switch to the radio channel associated with the mobile terminal (MEG), and

the central device (LS) is designed to exclude those of the radio base stations (FB1,FB2,FB3) which carry out time-critical and/or high-priority data transmissions (TD) from the switching of their radio channel.

ABSTRACT

TITLE: METHOD AND ARRANGEMENT FOR LOCATING A MOBILE TERMINAL IN A MULTICELL RADIO ARRANGEMENT
The invention relates to a method for locating a mobile terminal (MEG) in a multicell radio arrangement having a plurality of radio base stations (FB1, FB2, FB3), comprising recording the received field strength of a response message (AN) of the mobile terminal (MEG) at a plurality of measurements points, and with the location of determining the mobile terminal (MEG) by evaluation of the measured values, whereby the radio base stations (FBI, FB2, FB3) are used for measurement, the locations of the radio base stations (FBI, FB2, FB3) forming the measurement points, a plurality or all of the radio base stations (FBI, FB2, FB3) in a fourth step measure the received field strength of the received response message (AN), and transmit said received field strength to a central device (LS), and the central device (LS) determines the location of the mobile terminal (MEG) in a fifth step by using the measured values, in a first step, the mobile terminal (MEG) is switched to an active state, in a second step, a plurality or all of the radio base stations (FB1,FB2,FB3) are set to the radio channel which is used by the mobile terminal (MEG) to be located, and in a third step, the mobile terminal (MEG) is excited to transmit the response message (AN) by transmitting a test data transmission (TD),whereby those of the radio base stations (FB1,FB2,FB3) which carry out time-critical and/or high-priority data transmissions (TD) are excluded from the switching of their radio channel.

METHOD AND ARRANGEMENT FOR LOCATING A MOBILE TERMINAL IN A MULTICELL RADIO ARRANGEMENT

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