Method for establishing a signaling connection with a mobile station

[0002] This is a U.S. national stage application under 35 U.S.C. §371 of international stage, application No. PCT/FI99/00276, filed on Jan. 4, 1999. Priority is claimed under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) from Finnish Patent Application No. 980783, which was filed on Apr. 3, 1998, and from which priority was properly claimed in the aforementioned international stage application.

[0003] FIG. 1 illustrates the basic digital mobile communications system architecture. Typically, a mobile communications network comprises at least one core network CN and one or more radio access networks RAN. A core network CN comprises mobile switching centers MSC and possibly other service nodes. A “node” is here a generic name for network components that take part in the switching; thus it also covers mobile switching centers and other exchange equipment. The radio access networks are located between the core network and the terminal equipment. A radio access network comprises base transceiver stations BTS and a radio network controller RNC. Each base transceiver station BTS is connected in a fixed manner with the radio network controller RNC of the radio access network in question. Each radio network controller is in turn connected in a fixed manner with at least one core network node.

[0004] The general principle of paging in digital mobile communications networks is according to FIG. 2 as follows. When a call has arrived in a mobile switching center MSC in the traffic area in which the called subscriber is located at that moment, the switching center sends a paging request via radio network controllers to those base transceiver stations in whose area the register data indicate the called subscriber is. The base transceiver stations send the paging message to the radio path on their paging channels PCH. A mobile station that detects its own subscriber identity on a paging channel which it monitors, sends a response to the base transceiver station. This way the network will know the location of the called subscriber with an accuracy of one cell, and the data connection can be established. In this description and in the claims attached hereto, “data connection” refers to a connection established for the transmitted signal proper. Usually, the most common type of data connection is a voice connection.

[0005] In third-generation mobile communications networks, a mobile station may have several international mobile subscriber identities IMSI, and may also have multiple simultaneous data connections under different subscriber identities. If a mobile station has no data connection, an incoming call according tothe prior art always initiates the paging process described above. If the mobile station has a data connection via a given core network node under a subscriber identity, and another node receives a call associated with another subscriber identity of the mobile station, the normal paging process is initiated in this case, too. A disadvantage of this procedure is that, in principle, the network's signaling capacity is used unnecessarily since the location information of the mobile station in question is already in the network, and that the mobile station possibly has to listen to several paging channels. Arrangements according to the prior art do not support calls directed to one and the same mobile station from different core networks. Establishment of data connections from different core networks to a single mobile station is in principle possible, but it requires that the paging message coming from one of the core networks be distributed to all base transceiver stations and all paging channels, and that the called mobile station listen to all paging channels used in the cell in question. If the paging message is sent only on a given paging channel, it may happen that due to an existing connection the mobile station is unable to listen to the paging channel in question.

[0006] An object of the present invention is to minimize the aforementioned disadvantages associated with the prior art. The method according to the invention is characterized by what is expressed in the independent claim. Preferred embodiments of the invention are described in the dependent claims.

[0007] The basic idea of the invention is as follows. In a suitable network node, such as the radio network controller RNC of each radio access network, a paging database is created in order to reduce signaling needed for the establishment of data connections. Data useful in connecting the called mobile station are collected in the paging database. For example, when a data connection has been established to a mobile station under a given subscriber identity, the mobile station informs the network in an agreed manner about all the subscriber identities in its use e.g. during call set-up or later during the connection or using e.g. a separate message independent of the possible connections. The network stores these identities in the paging database together with the mobile station location information and signaling connection data possibly associated with said data connection. If, during said connection, the mobile station moves into another cell, the data relating to the mobile station are updated in the paging database. If, during said or a subsequent connection, another subscriber identity of the same mobile station is paged at any node, the network checks the paging database and uses the data found therein to establish a signaling connection.

[0008] Advantageously, when the mobile station's data connection(s) is/are terminated, the data associated with the mobile station are kept in the paging database for at least a certain predetermined period of time after the termination of the connection(s).

[0009] An advantage of the invention is that the paging channel load in the cells is reduced since no paging process is needed for the incoming calls, at least not if a data connection already exists at the mobile station. From the mobile station's point of view this means that during a data connection it does not have to listen to the paging channels. Another advantage of the invention is that when a mobile station is called that has no data connections but has information about it in the database according to the invention, it possibly suffices to send the paging message to one paging channel only. From the point of view of the mobile station this means that it only needs to listen to one paging channel. Yet another advantage of the invention is that connections from different core networks to one and the same radio access network will become practical. This is due to the fact that if a subscriber identity associated with a call coming from an “outside” core network is found in the database according to the invention, the information associated with the identity can be used to direct the paging. For such calls, a mobile station only needs to listen to one paging channel, and not even that in the best case. A further advantage of the invention is that when the general packet radio service GPRS is used, there is no need to transfer subscriber identity information between the mobile switching center MSC and the serving GPRS support node SGSN. A yet further advantage of the invention is that the setting up of simultaneous connections of a mobile station becomes quicker.

[0010] The invention is below described in detail. Reference is made to the accompanying drawing in which

[0011] FIG. 1 shows an example of a network architecture in which the invention is applicable,

[0012] FIG. 2 illustrates signaling in the paging according to the prior art,

[0013] FIG. 3 shows an example of signaling according to a preferred embodiment of the invention,

[0014] FIG. 4 shows by way of example a block diagram illustrating the operation according to a preferred embodiment of the invention,

[0015] FIG. 5 shows in the form of block diagram a second example of the operation according to a preferred embodiment of the invention,

[0016] FIG. 6 shows an example of the transfer of subscriber identity information according to a preferred embodiment of the invention, and

[0017] FIG. 7 shows a second example of the transfer of subscriber identity information according to a preferred embodiment of the invention.

[0018] Like elements in the drawing are denoted by like reference designators.

[0019] FIG. 1 was already discussed regarding the basic network architecture. FIG. 1 shows two core networks CN1 and CN2 which may belong to mobile communications networks of different operators. In this example, core network CN1 comprises at least one mobile switching center MSC1 and one serving GPRS support node SGSN. Radio access networks RAN1 and RAN2, for example, are found in the traffic area of the switching center MSC1 in core network CN1. Controller RNC1 of radio access network RAN1 and controller RNC2 of radio access network RAN2 are connected in a fixed manner to both switching center MSC1 and node SGSN. Terminals in the network are connected via the radio path to base transceiver stations. In FIG. 1, a mobile station MS is in the traffic area, or cell, of base transceiver station BTS1 of radio access network RAN1, and is connected to the base transceiver station BTS1.

[0020] In FIG. 1 there is, unlike in the usual arrangement, a connection from controller RNC1 of radio access network RAN1 to a switching center MSC2 of another core network CN2. Such a connection may be provided e.g. if the operator of core network CN2 wants to lease traffic capacity from radio access network RAN1. Furthermore, radio network controller RNC1 of FIG. 1 has a paging database 101 according to the invention to enhance traffic control. For simplicity, FIG. 1 shows no additional hardware or software components of radio access networks RAN1 and RAN2 of core networks CN1 and CN2.

[0021] FIG. 2 was already briefly discussed above. It shows in the form of timing diagram an example of paging signaling according to the prior art. Participating in the signaling are a mobile switching center MSC, at least one radio network controller RNC, a plurality of base transceiver stations BTS and a mobile station MS. At first, a CALL arrives in the mobile switching center MSC. On the basis of information in the call and in a register in connection with the switching center the switching center associates the call with the subscriber identity IMSI2 used by the mobile station MS. The mobile station MS may simultaneously have a data connection established earlier under a subscriber identity. The switching center sends a PAGING REQUEST, including the subscriber identity IMSI2, to the controllers RNC of the radio access network or networks in the area of which the register data indicate the mobile station MS is located. On the basis of the paging request each controller RNC sends a PAGING message to the base transceiver stations BTS of its area, and each base transceiver station sends a paging message to the radio path on at least one paging channel PCH. Each active mobile station listens to at least one paging channel. Said mobile station MS detects in the paging message its own subscriber identity IMSI2 and sends a RESPONSE message to a base transceiver station in the cell in which it is located. This, in turn, sends a response message to the respective radio network controller RNC which then sends a response message to the switching center MSC. The response message includes information indicative of the cell in which the mobile station MS is located, on the basis of which the MSC sends to the appropriate radio network controller RNC a CONNECT REQUEST for a new data connection. Said controller sends to the appropriate base transceiver station BTS the necessary instructions in a CONNECT message. FIG. 2 does not show the steps associated with the setting up of the data connection proper.

[0022] FIG. 3 shows in the form of timing diagram an example, corresponding to the one shown in FIG. 2, of the operation according to a preferred embodiment of the invention. The initial stages of the operation from the call up to the moment when the paging request is sent to at least one radio network controller RNC are identical with the example of FIG. 2. In this example, the database 101 according to the invention is established in at least one radio network controller RNC. Moreover, in this example, the mobile station MS to which the CALL is targeted at has at the moment of the call a data connection under subscriber identity IMSI1. Because of this earlier connection the database 101 contains information about the location of the mobile station with the accuracy of one cell. As the controller RNC receives a paging request for IMSI2, it checks 301 the paging database 101. As a result of that check, if finds information about the location of the mobile station identified as IMSI2. Therefore, the controller RNC immediately sends a RESPONSE message to the switching center MSC. The paging process proper may thus be skipped. When the switching center has received the response message, the operation continues as in the example of FIG. 2.

[0023] FIG. 4 shows in the form of block diagram an example according to a preferred embodiment of the invention of the use of the paging database 101 in the network of FIG. 1. In block 401, power is switched on at a mobile station MS, which has been assigned at least a first subscriber identity IMSI1 and a second subscriber identity IMSI2, whereby the mobile station enters the active mode. In block 402 a call is made from or to the mobile station MS, whereby a first data connection is established under identity IMSI1 via base transceiver station BTS1, controller RNC1 and switching center MSC1 to another terminal. In block 403 the mobile station MS sends in a fixed-form message all its subscriber identities to a certain signaling channel. In block 404 the radio network controller RNC1 receives said message and the software stores the subscriber identities listed in the message in the paging database 101. At the same time, contactability information for the mobile station MS, which information is known on the basis of the first data connection, is stored in the database 101. In block 405 it is determined the base transceiver station which has the strongest field at the mobile station MS. In case of a handover, the mobile station's contactability information is updated in the database 101, as indicated in block 406. Contactability information refers here and in the claims to data which are useful for the establishment of a signaling connection for the mobile station. Said data may comprise e.g. information about the cell in which the mobile station is located, information about the signaling connections of the mobile station's existing data connections, and information about the primary paging channel monitored by the mobile station.

[0024] In block 407 it is checked whether a call for the mobile station MS has arrived in any of the core network nodes. In block 408 possible calls are divided into two groups: If a call associated with the second subscriber identity IMSI2 has arrived in an “old” node, in this case the switching center MSC1, said switching center can see from the register information that the mobile station corresponding to identity IMSI2 has an existing data connection under identity IMSI1. In block 409 the switching center software finds in the register the information on identity IMSI1. The switching center MSC1 then instructs controller RNC1 to set up a data connection to the same mobile station as with identity IMSI1, but now under identity IMSI2. As shown in block 412, signaling uses the same signaling connection that was used for the first data connection. So, in the branch represented by block 409, a new data connection can be established (block 413) without a new paging but also without the operation according to the invention.

[0025] If a call for mobile station MS has arrived in a node other than MSC1, e.g. in node SGSN or switching center MSC2, the node in question sends a paging request for mobile station MS to radio network controller RNC1, as shown in block 410. In block 411 the software in controller RNC1 retrieves the location information corresponding to the second subscriber identity IMSI2 from the paging database 101. On the basis of said information controller RNC1 immediately knows the right base transceiver station to signal with, so that the new connection can be established without the paging process. In addition, information about the signaling connection associated with the first data connection is also fetched from the database 101, which information is then used in setting up the new data connection (block 412). After that, the fast paging described above may be repeated even if the first data connection were released, as long as there exists a connection.

[0026] FIG. 5 shows in the form of block diagram a second example of the use of a paging database 101 according to a preferred embodiment of the invention in the network of FIG. 1. The example illustrates the paging of a mobile station MS the data connections of which have terminated but which is still in active mode. In block 501, the last data connection, under subscriber identity IMSI1, is released. After that, the mobile station is in standby mode. Here and in the claims, the standby mode of a mobile station refers to the mode in which the mobile station is in after the termination of a data connection or data connections and in which the mobile station is ready to receive new calls. During the standby mode the network monitors the location of the mobile station (block 502) with an accuracy of a location area LA, which comprises a plurality of cells. If necessary, contactability information of the mobile station MS is updated in the paging database 101, as shown in block 503. In block 504 it is checked whether a call for the mobile station has arrived in a core network node. If no call arrives in a predetermined time and no connection is initiated by the mobile station, the paging database will be discontinued for the mobile station in question. This time-out monitoring is not shown in FIG. 5. If a new call arrives, the core network node in question sends in the normal manner a paging request to radio network controller RNC1, as shown in block 505. The call may be associated with any subscriber identity used by the mobile station MS. In block 506, the software in controller RNC1 retrieves the information relating to identity IMSI1 from the paging database. In block 507 it is checked whether the location information has changed after the release of the last data connection. If it is found that the mobile station MS is located in a location area LA different than the one where it was when the previous data connection was terminated, a paging process is started in the area in question (block 509). If it is found that the mobile station MS is in the same location area as where it was when the previous data connection was terminated, a paging message is sent to the cell indicated by the location information associated with identity IMSI1 (block 508). This is done because the mobile station MS is then probably in the same cell as where it was when the previous data connection was terminated. If, however, it does not respond, a more extensive paging process has to be initiated. This is not depicted in FIG. 5, nor is the establishment of a new data connection with the signaling associated with it.

[0027] FIG. 6 shows an example of sending subscriber identity information in accordance with a preferred embodiment of the invention. The identity information 61 is placed in a random access message 62 generated in the medium access control (MAC) portion of the data link layer (layer 2) and are sent on a random access channel (RACH).

[0028] FIG. 7 shows an example of sending subscriber identity information in accordance with a second preferred embodiment of the invention. The identity information 71 is placed in a special message 72 generated in the radio resources control (RRC) portion of the network layer (layer 3). The data link layer (layer 2) adds to the message 72 its own control parts. The resulting message 73 is sent on a signal radio bearer (SRB) channel intended for RRC-layer messages.

[0029] The names of signals, channels, systems and system components as well as the names of other objects used in the examples above are in accordance with the plans for a so-called third-generation mobile communications system, which is discussed here only by way of example, so as to provide an example of a possible application of the invention. The application of the invention is not limited to any particular mobile communications system.

[0030] Above it was described functions according to the invention. The invention is not limited to the solutions described above. For example, the paging database may be established at a core network node. The size of the paging database may be limited not only by setting a limit for the time that the data about the mobile stations in standby mode are kept, but also e.g. by specifying, by means of special criteria, the mobile stations the data of which are kept. The subscriber identity information may also be sent e.g. in the paging response message or in a message indicating the mobile station's parameter values. The inventional idea may be modified in various ways within the scope defined by the claims attached hereto.