FI102500B - Cellular radio access network and location update in a wireless telecommunication network - Google Patents

Description

102500

Cellular radio access network and location update in a wireless communication system

The invention relates generally to mobility management in wireless communication systems, and more particularly to location updating in a cellular radio access network connected to more than one other communication network.

Third Sulo dome mobile communication systems such as the Universal Mobile Communication System (UMTS) and the Future Public Land Mobile Telecommunication System (FPLMTS), later renamed IMT-2000 (International Mobile Telecommunication 2000), are currently being developed. UMTS is under standardization work in 15 ETSI (European Telecommunication Standards Institute), while the International Telecommunication Union (ITU) standardizes the IMT-2000 system. These systems of the future are very similar in their basic features. In the following, 20 UMTS systems will be discussed in more detail.

Like all mobile communication systems, UMTS provides wireless data transmission service to mobile users. The system supports hiking, i.e.

· UMTS users can be reached and • can make calls • · 25 anywhere they are within UMTS coverage. UMTS is expected to meet a wide range of future service needs, such as high-speed data services (multimedia) and video services, such as video calling. Many of the 30 services needed in the future are difficult to predict today. It is also difficult to predict the use of different services, which makes it impossible to optimize UMTS for only one service group. One conclusion from this is that UMTS needs to be built in a way that is flexible and can be further developed. Therefore, a modular approach has been adopted in the network design, which makes it possible to implement OMTS efficiently in different environments.

According to the current view, UMTS consists of two or 5 parts, as illustrated in Figure 1: UMTS access network 1 (or UMTS base station system, UMTS-BSS) and core network 2,3,4 and 5. Below UMTS access network is commonly referred to as also as a radio access network. The UMTS access network 1 is mainly responsible for matters related to the 10 radio paths, i.e. it provides the core network with the radio access needed for wireless operation. Core network 2, 3, 4 or 5 is a traditional or future telecommunication network modified to make efficient use of a UMTS access network for wireless communication. Telecommunications networks that have been thought of as suitable core networks are second generation mobile communication systems such as GSM (Global System for Mobile Communication), ISDN (Integrated Services Digital Network), B-ISDN (Broadband Integrated Services Digital 20 Network), Packet Data Network (PDN). , ATM (Asynchronous Transfer Mode), etc.

The UMTS access network must therefore enable support for various core networks, including those developed in the future. making available. Similarly, UMTS access networks should make it possible to connect different radio interfaces to the core network (narrowband, wideband, CDMA, TDMA, etc.). Typically, the UMTS access network is still connected to several core networks at the same time, in which case it must be able to support different core networks, 30 and their subscribers at the same time.

One of the most important requirements for wireless communications is subscriber mobility management. Since in wireless communication the subscriber does not have a fixed ac-access point in the network, the network registers must pass the information about the current location of the subscriber with a suitable accuracy. For example, the location information may tell the subscriber's current cell, but more preferably it tells the subscriber's current location range, which consists of several cells. Each time the cell or location-5 area is changed, the mobile station sends a location update request to the network, which causes the location information to be updated in the network registers. By using larger location areas, the load on the radio path caused by location updates can be reduced. The disadvantage is that the ha-10 messages must be sent to the mobile station in all cells of the location area. In general, the size of the location area is a compromise between location update signaling and paging signaling.

As stated above, the UMTS access network may be connected to more than one core network CN.

Each core network has its own mobility management protocol (MM) and its own location areas (LA). Therefore, the UMTS access network must send the CA area codes of all the core networks to the signaling channel-20. This allows each subscriber terminal active in one or more core networks to monitor the broadcast location area identifiers of the desired core network (s) and send a location update message to the access network when it crosses a location area limit. If the boundary of the location area of several different core networks is exceeded at the same time, the subscriber terminal has to send several location update messages over the air interface, one for each core network. This causes a significant signaling load on the radio interface. 30 over. This is contrary to normal design objectives, which aim to minimize the number of MM messages and generally signaling over the radio interface.

An open question in the development of the UMTS access network is how it can implement a unified MM-35 protocol supporting different core networks with CN and minimize the number of 4 102500 MM communicators, especially over the radio interface. One idea put forward has been that the UMTS access network itself must have some sort of subscriber register in which location information is managed. It has even been suggested 5 that an access network cannot function without its own registers. However, the registers require their own interfaces to the core networks CN or the intelligent network IN. In addition, a special mobility management protocol should be standardized for the access network. If separate registers could be omitted, standardization and design work would be saved, and radio access network products would become simpler and cheaper. It is an object of the invention to minimize the location update signaling transmitted over a radio interface in a radio access network connected to a plurality of core networks.

Yet another object of the invention is to avoid separate subscriber registers in a radio access network connected to several core networks.

One aspect of the invention is a location update method according to claim 1 20.

Another feature of the invention is a cellular radio access network according to claim 9.

The radio access network is connected to more than one core network, each with its own location areas and location management protocols. Each cell in the radio access network transmits the identifiers of the location areas of all the core networks to which that cell belongs. The subscriber terminal monitors the broadcast location area identifiers, and when moving from the old cell to the new one. The 30 cell sends a location update message to the radio access network if one of the location area identifiers broadcast by the new cell differs from the location area identifiers broadcast by the old cell stored in the subscriber terminal. However, in the invention, the subscriber terminal 35 sends only one location update message to the radio access network, regardless of how many core network location areas change simultaneously as the subscriber terminal moves from one cell to another. Based on the information contained in the location update message, the radioac cess network determines the core networks and location areas to which the location update applies. The radio access network then sends information on the new location area of the subscriber or subscriber unit separately to each of the relevant core networks. This information may preferably be sent as a (core network specific) location update message according to the core network mobility management protocol. By means of the invention, the number of location update messages in the radio interface can be limited to one regardless of the actual number of location updates to be performed on the core networks. In practice, this is a significant saving of radio interface capacity. This saving is achieved regardless of whether the radio access network uses its own subscriber registers or not. However, the location update according to the invention enables support even without subscriber registers. The only feature required in a radio access network is the ability to derive information from a single location update message about the core networks and location areas affected by the location update, and • forward the information to the relevant core networks.

25 However, this does not require subscriber-specific operations or registers, but only the conversion of a kind of radio access network location update message into location update messages for core networks. That transformation requires no more than simple tables or records with 30 fixed contents. Dynamic subscriber-specific information and thus subscriber registers are unnecessary for the invention.

The location update message sent by the subscriber terminal contains the identifier of at least one location area that changed. In this case, the radio access network checks from 6 102500 look-up tables or the corresponding stored data structure whether this change in the location area of one core network also means a change in the location area of another core network. In other words, a lookup table or the like tells the connections between the location areas of different core networks. If the subscriber terminal crossed (in addition to the specified core network location area boundary) the boundary of another core network location area, the radio access network receives the new location-10 areas of these other core networks from the look-up table, and sends location update information to the relevant core networks.

In one embodiment of the invention, the location update message sent by the subscriber terminal device contains, in addition to the new location area of one core network, information about the other core networks to which the location update applies. In this case, the radio access network retrieves from the look-up table or the like by means of said one location area the new location areas of the other core networks indicated by the subscriber terminal. The notification of the subscriber terminal 20, in turn, is based on its own observation of a change in the location areas of the core networks in question. This embodiment also makes it possible to avoid unnecessary location updates on a subscriber-by-subscriber basis for core networks with a subscriber terminal. or the subscriber is not currently active. This is possible because the subscriber terminal typically has information on which core networks it is registered or active in such a way that a location update would have to be performed on the core network. When this information is transmitted in a location update message to the radio access network, the location update process can be optimized on a per-subscriber basis without the need for dynamic subscriber information in the radio access network.

In one embodiment of the invention, the location update message sends the identifiers of all the location areas that have changed. In this case, a look-up table of the type described above is not necessarily required in the radio network, but only the ability to send the new location area information in the correct format to the core networks concerned. However, the disadvantage of this approach is the considerably long position update messages over the radio interface, which contributes to the signaling load. It is even possible that the capacity specified for the location update message in the radio access network is not sufficient to transmit all location area information at one time.

If the location areas of different core networks are defined to be completely independent of each other overlapping, the look-up table or the like may also include some information about the overlap of location areas, e.g.

15 with a single cell or base station accuracy. Information about the cell or base station through which the location update message is received is normally available on the radio access network, so it does not need to be transmitted over the radio interface.

20 However, the cellular structure of a radio access network is completely under the control of the radio access network operator, so that he is usually free to determine which cells belong to which location area. Restrictions, if any. is at all, may be, for example, the recommendations of the networks and the needs for the size of the location areas, or for example the nature of the traffic of the core networks (e.g. the location area must be optimized for packet data or voice). Therefore, in the preferred embodiment of the invention, the boundaries of the location areas of the different core networks are defined in such a way that based on the change in the location area of one core network, the possibly changed location areas of the other core networks can be unambiguously determined. In the most preferred approach, the different sized location areas of the core networks are defined as nested so that the smaller location areas of one core-35 network are always within the larger location areas of the other core network. In this case, for example, on the basis of a smaller (smallest) location area, it is always possible to unambiguously define larger location areas at the same location. Such a structure 5 also contributes to reducing the need for location updates at different times, which in turn further reduces the signaling load over the radio interface.

In yet another embodiment of the invention, the radio access network uses different identifiers for the location area of the core network than the identifiers used in the core network. In other words, the radio access network may have a location area format format completely independent of the core network. The need for such a solution may arise, for example, from the fact that the identification format used in the radio access network does not fit into the field update message field of the core network, or vice versa. The radio access network performs the conversion between different identification formats and may for this purpose include a table describing the location area identifier of the radio access network to the identifier used in the core network 20, and vice versa. The opposite action is necessary when sending paging messages to the subscriber terminal.

Similarly, it is possible that the location area structure (cellular structure) of the radio access network differs slightly from the location area structure of the core network. In this case, the radio access network may have a table or the like, on the basis of which the cell / location area structure of the radio access network is described as the location area structure of the core network, and vice versa. Such a solution may in some situations give the operator of the radio-30 access network more freedom to optimize the signaling of the radio access network, for example, regardless of the search characteristics of the core network.

The invention will now be described in more detail by means of preferred embodiments with reference to the accompanying drawings, in which Fig. 1 generally illustrates a UMTS access network and the core networks connected thereto, Fig. 2 is a diagram illustrating in more detail a possible structure of a UMTS access network; Fig. 4 shows a look-up table according to the invention, Fig. 5 shows a location area structure in which the location areas of the different core networks are arbitrarily overlapped, Fig. 6 shows a look-up table suitable for use. in connection with the location area structure of Fig. 5, Fig. 7 shows a conversion table containing descriptions between the location area identifiers of the radio access network and the core network.

Preferred embodiments of the invention will now be described as implemented in a radio access network according to the principles of the UMTS system, but it is not intended to limit the invention to the UMTS system. The invention is suitable for use in any ra-; in a dioaccess network connected to more than one core network (communication system) with different location areas.

Figure 2 shows in more detail a network architecture of a UMTS access network. However, it should be noted that this network architecture is just one of many options.

‘30 The network architecture shown in Figure 2 is based on the scenario that the functions of the UMTS access network are strictly limited to the radio access functions. Thus, it mainly includes functions for controlling radio resources (handover, retrieval) and controlling the network service (bearer service) (controlling the radio network service). More specific modes of operation, such as registers, registration functions and mobility and location management, are located in each core network. For example, in the preferred embodiment of the invention, all signaling due to location updates is considered to be transmitted to the core networks, after processing according to the present invention.

According to UMTS terminology, the whole UMTS access network is called a Generic 10 Radio Access Network (GRAN). The GRAN is further divided into a Radio Access Network (RAN) and an Interworking Unit (IWU). As a rule, there is a separate IWU between each core network 2-5 and the RAN, as in Figure IWUs 1-4. The purpose of the IWU is to switch between the core network and the 15 RANs. Therefore, the IWU includes the necessary adaptations and other possible interoperability functions. The interface between IWU-CN is core network specific. This allows the core networks and the RAN to be developed independently. For example, the IWU may connect to the base station system BSS of the GSM network 20. Correspondingly, the IWU2 can be connected to, for example, a local exchange in an ISDN network.

In Fig. 1, the radio access network RAN comprises a transport network TN (Transport Network), a radio network controller. RNC, as well as base station BS. In the network architecture shown, the base stations are connected to a transmission network TN, which carries user data to the IWUs and control signaling to the radio network controller RNC. All the intelligence that controls the GRAN is located in the base stations (BS) and the radio network controller (RNC). As stated earlier, this oh- ·. The division is typically limited to radio access control functions as well as the connection of connections through the transmission network TN. The transmission network TN may be, for example, an ATM network.

It should be noted that the private structure of the UMTS access network is not relevant to the invention. For example, the network structure of Figure 2 may further include subscriber registers. In general, the term radio access network in this application means any radio access network and network structure connected to more than one core network.

Figure 2 further illustrates how the coverage areas of base stations BS1, BS2, BS3 and BS4 form cells C1, C2, C3 and C4, respectively. By combining these physical radio cells with an exact geographical location 10 and size, different logical location areas LA can be formed. In fact, the location area LA is just a set of physical cells defined in the database, whose identifier or name is called the location area identifier. Because the location areas are logical, they can be arbitrarily defined in the cellular structure of the radio access network. In addition, there may be several, in principle arbitrary, numbers of different location area levels (e.g. location areas of different sizes). When each core network has its own location ranges, they can be easily described as their own location range levels in the cellular structure of the radio access network. Figures 3 and 5 show two examples of how the location areas of the core networks 2 and 3 can be superimposed.

Each base station BS broadcasts in the cell the location area identifiers of the location areas of all «25 core networks to which that cell belongs. The subscriber device MS monitors at least the broadcast location area identifiers of the core networks in which it is currently active. Each time a cell or location area is changed, the subscriber terminal, i.e. the mobile station MS, sends a location update request to the radio access network, which causes the location information to be updated in the registers of the core network (or radio access network). As previously stated, if the limit 35 of the location area of several different core networks is exceeded simultaneously, in such a solution, the MS may have to send several location update messages over the air interface, one for each core network.

In the present invention, this is avoided by sending only one location update message, on the basis of which the radio access network is able to determine the core networks and location areas to which the location update applies.

An arrangement according to a preferred embodiment of the invention which implements the above principle will be described below. For the sake of clarity 10, only the location areas of the core networks 2 and 3 are used in the example, but in practice there may be an arbitrary number of location area levels. Referring to Figure 3, the location areas of the core networks 2 and 3 are of different sizes and nested. More specifically, the location areas LA3.1-15 LA3.16 of the core network 3 are located inside the location areas LA2.1-LA2.4 of the core network 2. The principle is that none of the location areas LA3.1-LA3.16 extends to the area of the two core network location areas LA2.1-LA2.4. In this way, the location area of the core network 2, which is at the same point in the cellular structure of the radio access network, can also be unambiguously determined on the basis of the location area pe-20 of the core network. Such a nested location area structure greatly simplifies the practice of the present invention, as will be described below.

According to the invention, the radio access network has a look-up table or other similar data structure which indicates which location areas of the core network 3 are within the location area of each core network 2. An example of such a look-up table lock is shown in Figure 4. Correspondingly, the number of nested * · 30 location area levels can be increased, whereby the tau lock further expands. For example, it can be seen from the table that the location area LA3.10 is within the location area LA2.3 of the core network 2.

Referring to Figure 3, it is initially assumed that the MS of the travel-35 message moves from point A to point B. At point A

13 The location information of the mobile station MS (or subscriber) in the core network CN2 is the identifier of the location area LA2.3 and in the core network CN3 the identifier of the location area LA3.11. As the MS moves from point A to point B, it crosses the boundary between the location areas LA3.11 and LA3.9 of the core network CN3. Upon detecting a change of location area, the MS sends a location update message according to the invention, which contains a new location area identifier LA3.9 and an old location area identifier LA3.11. The location update message is transmitted from the base station BS to the radio network controller RNC, which in the preferred embodiment of the invention includes the look-up table according to FIG. The RNC retrieves from the look-up table the location area identifier of the core network CN2 corresponding to the new location area identifier LA3.9 of the core network CN3, which is 15 LA2.3. Correspondingly, the RNC retrieves from the look-up table a location area identifier of the core network CN2 corresponding to the old location area identifier LA3.11 of the core network CN3, which is the same LA2.3. The RNC compares the new and old location area identifiers of the core network CN2 with each other, and since they are the same, 20 concludes that a location update to the core network CN2 is not required. Correspondingly, the RNC can retrieve location areas for other core networks CN4-CN5 from the look-up table. Assume that the location area has not changed in these either. In this case, the RNC sends a general location update message to the co-operation unit IWU2, which is connected to the core network CN3. Since the location update message sent by the RNC is preferably in the general format used within the radio access network, the IWU2 in the preferred embodiment of the invention converts the general location update-30 message to the format specified for the core network CN3. The core network CN3 updates the location information LA3.9 of the location information of the MS or the subscriber.

Referring again to Figure 3, it is assumed that the MS moves from point B to point C. In this case, the MS crosses both the boundary between the location areas LA3.9 and LA3.7 of the core network CN3 and the boundary between the location areas LA2.3 and LA2.2 of the core network CN2. Upon detecting a border crossing, according to the invention, the MS sends only one location update message containing the identifier of the new location area LA3.7 and the identifier of the old location area LA3.9 of the core network CN3. The location update message is forwarded again to the RNC. From the look-up table of Fig. 4, the RNC retrieves the new location area LA3.7 of the core network CN3 and the location areas LA2.3 10 and LA2.2 of the core network CN2 corresponding to the old location area LA3.9, respectively. The RNC compares the new and old location areas of the core network CN2 with each other, and when they find that they are different, concludes that the location update must also be performed on the core network CN2. The RNC then sends a general location update message to the IWU2 containing at least the identifier of the new location area LA3.7. If necessary, the IWU2 changes the format used by the core network CN3 of the location update message and sends it to the core network CN3, which updates the subscriber's location information. Accordingly, the RNC sends a second general location update message to the IWU1 connected to the core network CN2. This general location update message contains the new location area LA2.2 of the core network CN2. The IWU1 converts the general location update message to the format used by the core network CN2, if necessary, and sends a location update message to the core network CN2, which updates the subscriber's location information. Thus, location update is recommended for two core networks using only one location update message on the radio path and without the need for separate subscriber registers or location management functions in the radio access. In the same way, a location update can be performed on an arbitrary number of core networks.

In the above example, the mobile station always transmitted the location area information of the core network with the smallest location area structure. To enable this, priority information may be stored in the mobile station 35, which indicates the order in which the location areas of the core networks should be selected in the location update message. The MS can select the core network with the highest priority in the location update message in which it is active.

The location update message sent by the mobile station MS may also contain information about the core networks CN to which the location update applies. In this case, the RNC only needs to retrieve from the look-up table the new location areas of those core networks. For example, the MS may indicate those core networks whose location range it has detected to be changing and / or in which it is currently active.

The location update message may also include new location areas for all core networks. In this case, the look-up table of Figure 4 is not required. The RNC can generate the required number of new location update messages from one of the 15 location update messages, which are sent to the relevant co-operation units IWU. The location update message sent by the MS. * Can also be forwarded directly (without switching through the RNC) to all IWUs. In this case, those IWUs -20t whose location area CN of the corresponding core network is included in the message forward the location update to the core network.

It is also possible that the radio access network uses different locations for the locations of the core network.

• I

25 domain identifiers as the core network. It is also possible that the location configuration of the radio access network differs to some extent from the location configuration of the core network. In this case, the radio access network preferably has a conversion table or a similar data structure, which contains a description V 30 between the location area identifiers used by the radio access network and the location area identifiers of the core network. Figure 7 schematically illustrates one such conversion table. The conversion table may be located in the RNC, in which case the location area identifier is already exchanged in the general location update message sent by the RNC according to the core network 16 102500. Alternatively, a conversion table corresponding to each core network is placed in the IWU connected to it. This is particularly advantageous when the IWU otherwise performs the conversion of the location update message to the core network specific.

The placement of the look-up table in the radio network controller RNC has been described above. Alternatively, a similar Lookup Table can be placed, for example, in each IWU. In this case, the location-10 update message sent by the mobile station MS is amplified, for example at the base station BS, into several messages, which are then forwarded to the IWUs. Many other modifications will be apparent to those skilled in the art upon reading this specification.

It is advantageous for the radio access network operator to plan the location of the location areas of the different core networks in the cellular structure of the radio access network so that the connections between the location areas of the different core networks can be described as unambiguously as possible in the look-up table. One of the best solutions for this is the nested structure shown in Figure 3. However, if such design is not possible, the location areas of the different core networks may arbitrarily overlap, typically overlap. In this case, a situation may arise according to Fig. 5, in which it is not possible to say exactly on the basis of the location area 25 of one core network in which location area MS of the other network it is in each case. For example, in Fig. 5, the location area LA3.1 of the core network CN3 exceeds the boundaries of the location areas LA2.1, LA2.3 and LA2.4 of the core network CN2. If the MS indicates in the location update message the location area LA3.1, it may be located in any of the location areas of the core network CN2 or LA2.1, LA2.3 and LA2.4. In this case, information about the cell or base station from which the location update came can be used in the look-up table. This information may already be available in the radio network controller 35 RNC or may be easily associated with the location update message at the base station BS.

17 102500

Figure 6 illustrates an example of a look-up table in which cell information can be utilized. The look-up table indicates that, for example, cell C3 belongs to the location area LA2.3 of the core network CN2, the location area LA3.1 of the core network CN3, etc. Referring to Fig. 5, when the mobile station MS transmits a location update message to the base station BS3 containing e.g. in the location area LA3.1 of the core network CN3, the BTS3 appends the identifier of the cell C3 to the location update message. The radio network controller RNC 10 (or IWU) searches the lookup table (Fig. 6) using cell C3 and location area LA3.1 for a new location area LA2.3 of the core network CN2, and initiates a location update to the core network CN2 either whenever or when the new location area differs from the old location area. In the latter case, the location update message sent by the mobile station MS also contains the old location area of the core network CN3. If the location update message contains information about the core networks whose location area has changed, there is no need to send old location area-20 information over the radio path, but the RNC or IWU knows that the location update should be performed on all reported core networks. In this case, the RNC or IWU retrieves from the look-up table the new location areas corresponding to these core networks. Basically pictorial. the use of a look-up table according to 6 can be taken up to 25 so far that the location update message does not contain any location area information, but only information about the core systems to which the location update applies. The new location areas are then retrieved from the lookup table based on the cell or base station through which the location:: * 30 nin update was received. It is also possible that the cellular or base station information is already included in the location update message sent by the mobile station MS.

The application has been described above with reference to preferred embodiments to illustrate the principles of the invention. The details of the invention may vary within the spirit and scope of the appended claims.

Claims (15)

1. Location updating method of a tree-less telecommunication system comprising a cellular radio access network which has been connected to more than one core network, each having its own location areas, the method comprising the following stages: as general broadcast is transmitted in each cell of the radio access network, the characteristics of all the location areas To which respective cells belong, from the subscriber terminal, a location update message is transmitted to the radio access network where some of the location area characteristics transmitted as a general broadcast are changed when transitioning, from an old cell area to a new cell area, which is sent from a subscriber terminal only the core network location areas that are switched at the same time, on the basis of the information in the roaming message are determined in the radio access network the core networks and the location areas to which the roaming refers, from the radio access network sent separately to the each defined core network a location update message announcing the new location range of the subscriber or subscriber apparatus. 2. A method according to claim 1, characterized in that in said position update message information about the new location area of a core network is transmitted, in the radio access network, on the basis of location area for said one core network, the possible new location areas for the other core areas are determined. is changed with the location range of said one core network, from the radio access network sent separately to each defined core network a core network-specific location update message, in which the subscriber or subscriber terminal's new location area is notified. Method according to claim 1, characterized in that in said location update message, information is transmitted about the new location area of a core network and information about the other core networks in which location updating should be performed simultaneously, in the radio access network being determined on the basis of said information. possible new location ranges for said other core networks, in the radio access network, sent separately to each established core network a core network-specific location update message in which the new location area of the subscriber or subscriber terminal is notified. 20 Method according to claim 1, characterized in that in said location update message («the new location ranges for all core networks that have been changed simultaneously in connection with cell exchange, from the radio access network is sent separately to each established core network, a subscriber-specific message location state is sent in or the subscriber's new location range. Method according to claim 2 or 3, characterized in that a search table is maintained in the radio access network which interconnects the different locations of the core networks, said determination of possible new locations for the other core networks comprises a search of these from a search table with the aid of said core network's new location area. 5 Method according to any one of claims 1 to 5, characterized in that in the radio access network and in at least one core network, different location area characteristics are used for the location area of the core network. Method according to any of claims 1 to 6, characterized in that the location areas for different core networks are mutually different in size and are within each other. Method according to claim 7, characterized in that from the mobile phone is transmitted in a location update message information concerning a smaller location area, to which core network belonging to this area the subscriber wishes to receive location update. (roaming), the radio access network determines the new location ranges for other core networks within which said minimum location range 25 is located, from the radio access network sent separately to each defined core network a core network-specific location update message in which the subscriber or subscriber device's new location device message. 9. Cellular radio network (1) connected to more than one core network (2, 3, 4, 5), each having different location ranges, in which radio access network is transmitted as a general broadcast in each cell of the radio access network, the characteristics of all the location ranges to which each cell belongs, and subscriber terminals (MS) have been arranged to transmit to the radio access network a location update message when some of the location area characters transmitted as a general broadcast are switched when a transition occurs from a gaitonal cell area to a new cell area, (MS) has been arranged to transmit only one location update message regardless of how many core network (2, 3, 4, 5) location areas that are simultaneously switched, the radio access network (1) has been arranged to determine on the basis of the information in the location update message, the core networks and the location networks - update refers to, and to separate separately to each defined core networks send a location update message announcing the new location range of the subscriber or subscriber device. Radio access network according to claim 9, characterized in that the location update means. the split contains information about the new location area for said one core network (2, 3, 4, 5), and that the radio access network (1) comprises a search table from which on the base of the location area of a core network possible new location areas for other core networks can be searched. has been switched with the location range for said core network. Radio access network according to claim 9, characterized in that the location update message contains information about the new location area of a core network (2, 3, 4, 5) and information about the other core networks in which the location update should be performed simultaneously, and that the radio update 102500 The access network (1) comprises a search table from which, on the basis of the location area of said one core network, new location areas can be searched for the other core networks defined in the location update message. Radio access network according to claim 9, characterized in that the location update message indicates the new location areas for all core networks (2, 3, 4, 5) that have been changed simultaneously in connection with cell change. Radio access network according to any one of claims 10 - 12, characterized in that in the radio access network (1) and in at least one core network (2, 3, 4, 5) different location area identification characters are used for the location areas of the core network, and that the radio access network (1) has means for converting between the location area characteristics and said location area characteristics for said at least one core network. Radio access network according to any of claims 10- 13, characterized in that the location areas for different core networks (2, 3, 4, 5) are in the radio access network (1) between different Large and located within each other. Radio access network according to any of claims 10 - 13, characterized in that the location areas for different core networks (2, 3, 4, 5) are in the radio access network at least partially overlapping, and that said search table further contains information about base stations or cells within whose range the location ranges for different core networks are overlapping.