Abstract:
The present invention relates to a method for allocating service area identifiers (SAI) for a femto cell ( 200 A) upon the femto cell ( 200 A) being created. According to the method, information is received about detected cells obtained by scanning performed by a femto radio base station ( 210 A) that is serving the femto cell ( 200 A) in addition to information identifying the femto base station ( 210 A) or the femto cell ( 200 A); a request for SAIs, is transmitted to a SAI selection entity ( 250, 400 ) based on the received information, and SAIs selected by a selection entity ( 250 ) are received together with an associated user type. The identifiers are further allocated for the created femto cell ( 200 A). The present invention also relates to an apparatus ( 100, 300 ) and to the selection entity ( 250, 400 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to the field of wireless or mobile communications network systems, and, more specifically, to a method and an apparatus for selecting a service area identifier for a user equipment in the wireless system. 
       BACKGROUND 
       [0002]    Wireless access networks have become a key element of a variety of telecommunications network environments. As to enterprise network environments, they provide convenient wireless access to network resources for employees or customers carrying laptops and/or mobile handheld devices. In addition, wireless access points operable with diverse communication devices, such as laptops, mobile phones, etc., are broadly used in public environment such as e.g., hotels, train stations, airports, restaurants, schools, universities and homes, and are mostly used to offer high-speed interne access. 
         [0003]    The telecommunication industries and operators are currently investigating the possibility to further increase the coverage area offered by cellular communications network systems to home or small areas. Examples of cellular communication network system are: the Universal Mobile Telecommunication Systems (UMTS) network, also known as third generation (3G) cellular network system or wideband code division multiplexing access (WCDMA) network; the Global System for Mobile telecommunications (GSM) network; the General Packet Radio Service (GPRS) network that utilizes the infrastructure of a GSM system; Two further examples of cellular access networks are EDGE and EGPRS which are further enhancements to GSM and GPRS. EDGE refers to enhanced Data rates for GSM Evolution, and EGPRS refers to Enhanced GPRS. 
         [0004]    According to such investigation, a limited number of users (e.g. a user equipment (UE)) may be provided with e.g. WCDMA or 3G coverage using a small radio base stations (RBS) also called a “femto RBS” that would be connected to a radio network controller (RNC) of the 3G network using some kind of internet protocol (IP) based transmission. The coverage area so provided is called a “femto cell” to indicate that the coverage area is relatively small compared with an area of a macro cell of a public land mobile network (PLMN). Other terminology for a femto RBS includes a “Home RBS” and/or a “home 3G access point (H3GAP)” and/or a “home access point (HAP)” and/or a “home Node B (HNB)”. It should be mentioned that small cells known as picocells may serve small areas such as part of a building, a street corner or a airplane cabin and are usually smaller than microcells, which in turn is smaller than a macrocell. The picocells are traditionally provided as coverage or capacity extensions and do not include an access control mechanism. This means that all users that are allowed to access macrocells of a PLMN are also allowed to access microcells and picocells of the same PLMN. 
         [0005]    One alternative for the IP based transmission is to use fixed broadband access (like xDSL, Cable, etc.) to connect the femto RBS to the RNC. Another alternative would be to use mobile broadband access e.g. some WiMAX technologies or HSDPA and enhanced uplink also known as HSPA. 
         [0006]      FIG. 1  illustrates an example of a WCDMA network  1  built with a traditional architecture including one or several RNCs  20  and femto RBSs  40  working as H3GAP. However the RBS&#39;s and RNC&#39;s may as well be collapsed and form a single node in a so called flat architecture. As shown in  FIG. 1 , the network  1  comprises a core network (CN)  80  connected to a RNC  20  that controls all radio base stations connected to it, i.e. macro RBS  30  and femto RBSs  40 . The macro RBS  30  serves a macro cell  31  whereas a femto RBS  40  serves a femto cell  41 . As illustrated, each femto RBS  40  serves its dedicated femto cell  41 . As well known in the art, a RBS is typically situated at an interior (e.g. centre) of the respective cell which the RBS serves, but for the sake of clarity, the macro RBS  30  and the femto RBSs  40  of  FIG. 1  are shown instead as being associated by double headed arrows to their respective cells. At least some of the femto cells  41  are geographically overlayed or overlapped by the macro cell  31 . 
         [0007]    A user equipment (UE)  50  communicates with one or more cells or one or more RBSs over a radio interface. The UE  50  can be a mobile phone (or “cellular phone”), a laptop with mobile termination and thus can be e.g. portable, pocket, handheld, computer-included, or car-mounted mobile device which can communicate voice and/or data with a radio access network. The UE  50  may further communicate with the radio access network via a femto RBS  40  through an internet protocol (IP) based transmission network  60  which, as described earlier, can be either broadband fixed IP based transmission (e.g. xDSL) or broadband mobile IP based transmission (e.g. WiMAX or HSPA) or any other suitable IP based transmission. 
         [0008]    In the wireless communications network system depicted in  FIG. 1 , the interface between the each femto RBS  40  and the RNC  20  can be called the extended tub interface “Iub+” which is usually formed by an IP connection over the IP based transmission network  60 . In some implementations, the Iub+ resembles the Iub interface between the macro RBS  30  and the RNC  20 , but the Iub+ interface is modified for conveying additional information such as the identity of the femto RBS  40  e.g. during the initial power-on procedure of the femto RBS  40 . 
         [0009]    Also illustrated in  FIG. 1 , is the Iu interface used between the RNC  20  and the CN  80 . Note that in a flat architecture there would not necessarily exist any Iub(+) interface because, as described above, in such flat architecture the RBS and the RNC can form a single node. In order to limit the users of UEs  50  of the femto cell  41  to the ones that are allowed, an access control feature can be implemented in the system. This way, at any UE attempt to camp on the femto cell, it is checked if the user is an allowed user. The international subscriber mobile identity (IMSI) of allowed users (or UEs) per femto RBS are stored in a database  70 , known as an access control database (ACDB), to which the stand-alone or integrated RNC has access. This approach is described in the international patent application with publication number WO 2007/136339. 
         [0010]    In prior art WCDMA networks that are based on macro/micro/pico cells of a PLMN i.e. WCDMA networks that do not include femto cells, a service area identifier (SAI) is used to identify an area consisting of one or more cells belonging to the same location area (LA). Such an area is called a service area and can be used for indicating the location of a UE to the core network (CN). A SAI of a current cell is indicated by the RNC to the CN when a signalling connection is established for a UE. The CN can use the SAI for the purposes of routing and charging as well as different location based services i.e. services that are based on the current location of the UE. Examples of such services:
       Emergency call routing (e.g. to route a call to the correct emergency center)   Location calling services (e.g. to route a call to e.g. the closest taxi)   Legal intercept (to find out UE location on service area basis).   Charging indication (e.g. as charging areas).       
 
         [0015]    The CN can also be informed about SAI changes for a UE using standard mechanisms in the Iu-interface and in a so called RANAP (Radio Access Network Application Part) protocol signalling over the Iu-interface. In the 3GPP standard (Third Generation Partnership Project), the SAI is defined as consisting of a service area code (SAC) together with the PLMN-id (consisting of a mobile country code (MCC), a mobile network code (MNC)) and the location area code (LAC)). The SAI can be defined according to the following: 
       SAI=PLMN-id∥LAC∥SAC 
       [0016]    The LAI is also defined as consisting of PLMN-id and LAC and therefore SAI can be also defined as follows: 
       SAI=LAI∥SAC 
       [0017]    The SAC is usually defined by the operator of the network and is normally configured in the RNC via O&amp;M (operation and maintenance). The SAI is further set for a macro/micro/pico cell depending on the location of the macro/micro/pico cell. The SAI values are further coordinated between the radio access network and the CN so that e.g. the relevant location based services in the CN can be configured with this information. The RNC includes separately both the LAI and SAI for the current macro/micro/pico cell towards the CN. The LAI is used by the CN for e.g. mobility management (MM purposes) and the SAI can be used for e.g. location based services as previously described. 
         [0018]    As described above, a SAI of a macro/micro/pico cell in the network is indicated by the RNC to the CN when a signalling connection is established for a UE. If femto cells are introduced in the network, a SAI for each such femto cell needs to be indicated by the RNC and mapped to, for example, a location information in the CN. With manual (or semi-manual) configuration, a femto cell could be given one or more SAIs and a mapping of these SAI(s) to, for example, a location information in the CN could be performed in a similar way as for the pico, micro and macro cells. However manual (or semi-manual) configuration both in the RNC and in the CN, of a huge number of femto cells e.g. hundred of thousands or even millions of femto cells is not considered a feasible solution especially since SAIs are not broadcasted in the network. In addition, it is normally the end users that install the femto cells on their own, without any intervention from the operator personnel. This means that the femto cell installation, including the selection of one or more SAIs, needs to happen automatically. In such a scenario with the huge number of femto cells, the RNC further needs to indicate all the SAIs to the CN which leads to excessive configuration load in the CN because the CN would be involved in all location based services. In addition to location based services, other services such as differentiated charging may also be offered to different UEs that are allowed to access a femto cell, which require additional identifiers to be defined in the CN. This would increase further the configuration load in the CN as well as in the RNC. In the light of the above problems related to the number of the femto cells, different types of UEs accessing a femto cell and the automatic nature of the installation procedure, a solution is needed that automatically selects the correct SAI for a UE accessing a specific femto cell. 
       SUMMARY 
       [0019]    An object of the present invention is thus to obviate at least some of the above disadvantages by providing a method and an apparatus for automatic selection of a SAI that can support both location based services and differentiated charging, for a UE that is allowed to access a femto cell (the femto RBS of a femto cell) without increasing the configuration load in the core network or in the RNC. 
         [0020]    According to a first aspect of the present invention, the above stated problem is solved by means of a method of selecting a SAI for a UE in a femto cell that is being served by a femto RBS. The femto RBS is connected to a wireless communications network. The method comprises: acquiring information identifying the UE that is allowed to access the femto RBS; requesting a database for information on a user type of the UE. The request being based on the acquired information identifying the UE and on an information identifying the femto RBS to which the UE is allowed to access. The method further comprises: selecting a SAI based on the information on the user type of the UE received/retrieved from the database. 
         [0021]    According to a second aspect of the present invention, the above stated problem is solved by means of an apparatus for selecting a SAI for a UE in a femto cell that is being served by a femto RBS that is connected to a wireless communications network. The apparatus comprises: receiver means configured to acquire information identifying the UE that is allowed to access the femto RBS; transmitting means configured to transmit, to a database, a request for information on a user type of the UE. The request including the information identifying the UE and information identifying the femto RBS to which the UE is allowed to access. The apparatus further comprises selecting means configured to select a SAI for the UE based on the information on user type that is received from the database. 
         [0022]    An advantage with the present invention is that the selected SAI can support both location based services and differentiated charging, depending on the user type of the UE and on the femto cell wherein the UE is located. The user type of the UE can for example indicate that the UE is a home user or a visiting user or a roaming user. A home user refers in this context to a subscriber/owner of the femto RBS while a visiting user is here considered to be a user that is allowed by the femto RBS subscriber/owner to use the femto RBS and is a subscriber in the operator&#39;s network. A roaming user is considered to be a user that is allowed by the femto RBS subscriber/owner to use the femto RBS but is not a subscriber in the operator&#39;s network. 
         [0023]    The present invention will now be described in more details by means of several embodiments and with reference to the accompanying drawings, attention to be called to the fact, however, that the following drawings are illustrative only, and that various modifications and changes may be made in the specific embodiments illustrated as described within the scope of the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a block diagram illustrating an exemplary WCDMA wireless communications network including femto radio base stations in which the present invention may be used. 
           [0025]      FIG. 2  illustrates a simplified block diagram illustrating another exemplary wireless communications network in which the present invention may be used. 
           [0026]      FIG. 3  is a table illustrating an example of a table that may be included in a database in accordance with an exemplary embodiment of the present invention. 
           [0027]      FIG. 4  illustrates a signalling diagram illustrating the flow of messages in an exemplary embodiment of the present invention. 
           [0028]      FIG. 5  illustrates an apparatus according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, scenarios, techniques, etc. in order to provide thorough understanding of the present invention. However, it will be apparent from the person skilled in the art that the present invention and its embodiments may be practiced in other embodiments that depart from these specific details. 
         [0030]    The present invention is described herein by way of reference to particular example scenarios. In particular the invention is described in a non-limiting general context in relation to a WCDMA wireless communications network including femto radio base stations that are connected to a radio network control node i.e. a radio network controller (RNC) of the WCDMA wireless network via a fixed IP based broadband access network in a traditional architecture as shown in  FIG. 1 . It should be noted that the present invention and it embodiments may also be applied to other types of radio technologies and architectures such as flat architecture for WCDMA, GSM, LTE (long term evolution), WiMAX etc. 
         [0031]    In  FIG. 2  and for sake of simplicity only a single femto RBS  210  is illustrated connected to a communications network  2  comprising an IP based network  260 , an RNC  271 , a database (DB)  272  and a CN  273 . The CN  273  may comprise many elements such as MSC, SGSN, GGSN etc. A femto cell (e.g. home/office)  200  is served by the femto RBS  210 . The femto RBS  210  is aimed to be used by allowed users of the home or enterprise/office where it is located. The femto RBS  210  is further integrated into the wireless network  2  and may thus share the radio frequency spectrum (or part of it) allocated to the wireless WCDMA network. A user equipment (UE)  230  can thus roam from the femto cell  200  to another macro radio cell (not shown) when leaving the coverage of the femto RBS  210 , or can roam to the femto cell  200  from another macro cell (not shown) when located in the vicinity of the femto RBS  210 . The femto RBS  210  may further be equipped with a connection for an Ethernet local area network within the home/enterprise and can therefore connect to one or several personal computers  220  over the Ethernet. A personal computer  220  that is equipped with a WCDMA (3G) UE functionality can connect to the femto RBS  210  and is thus, in this context, also referred to as a UE  220 . The femto RBS  210  may further be equipped with or is connected, to an xDSL (e.g. ADSL, VDSL, ADSL2+, etc.) customer premises equipment (CPE) (not shown) which may have the function of a multi-mode modem, thus enabling it to provide IP connection over an IP network  260 , to the wireless network using e.g. a digital subscriber line (DSL). As known, a femto cell  200  differs from a macro cell in that the location of a macro cell is known and planned by the operator of the network, whereas a femto cell can be dynamically installed/created in any place by the owner of the femto RBS without any operator intervention. 
         [0032]    Referring to  FIG. 2 , as UE  230  is camping or accessing the femto cell  200  that is being served by the femto RBS  210 , it is checked whether the UE is allowed to access the femto cell i.e. if the user of the UE is an allowed user. The information identifying allowed users (UEs) per femto RBS are stored in the database  272  to which an apparatus according to the present invention has access. In accordance with an embodiment of the present invention, such apparatus can be configured as radio network control node such as the RNC  271  depicted in  FIG. 2 . According to another embodiment of the present invention, such apparatus can be configured as a radio network control node incorporating the femto RBS  210 . According to yet another embodiment of the present invention, such apparatus can be configured as a femto RBS such as the femto RBS  210 . In such case, the femto RBS  210  communicates directly with the database  272  via the IP network  260 . Such a scenario can be applicable in e.g. LTE. 
         [0033]    As mentioned above, the database  272  stores information regarding the femto RBS  210  and which UEs that are allowed/authorized to access the femto RBS  210 . Each UE,  230  can be identified using an information such as the international mobile subscriber identity (IMSI) or by some other permanent mobile identity, and the femto RBS  210  is identified using, for example, a preconfigured femto RBS identity (femto RBS-ID) such as a hardware identity. The database  272  is shown in  FIG. 2  as a standalone unit. However, it is a functional entity that alternatively may be incorporated in the RNC  271 , in the femto RBS  210  or any other node that is accessible by e.g. the femto RBS  210  (in for example a flat architecture). Furthermore, the database  272  can store information regarding a plurality of femto RBSs and which UEs that are allowed to access each femto RBS. In other words, the database  272  is not necessarily restricted to a single femto RBS  210 . The database  272  is thus organised such that it can be queried using the femto RBS-ID as a search criteria to retrieve the allowed IMSIs or the allowed permanent mobile identities. The information concerning allowed IMSIs (or permanent mobile identities) is administered by the owner/subscriber of the femto RBS  210 . A network operator may also administer the information concerning allowed IMSIs. 
         [0034]    According to exemplary embodiments of the present invention, the information in the database is extended with the user type of the UE (UEs) accessing the femto cell  200 . The user type can for example indicate if a UE is a home user, a visiting, a roaming user etc. as will be described in greater details below. As mentioned earlier, a home user refers in this context to a subscriber/owner of the femto RBS while a visiting user is here considered to be a user that is allowed by the femto RBS subscriber/owner to use the femto RBS and a subscriber in the operator&#39;s network. A roaming user is considered to be a user that is allowed by the femto RBS subscriber/owner to use the femto RBS but is not a subscriber in the operator&#39;s network. 
         [0035]    According to an embodiment of the present invention, the user type of each UE can be stored in the database together with the IMSI or the permanent mobile identity of the UE and the femto RBS-ID to which the UE is allowed to access. 
         [0036]    Referring to  FIG. 3  there is illustrated an example of a table that can be included in the database  272 , in accordance with an exemplary embodiment of the present invention. Each row in the table represents the relation between a femto RBS-ID, a permanent mobile identity (or IMSI) and a user type. 
         [0037]    In the example shown in  FIG. 3 , information for two different femto cells (or femto RBSs) identified as RBS- 1  and RBS- 2  are included in the table. The information on these cells is further shown for three different users (or UEs) identified as IMSI- 1 , IMSI- 2  and IMSI- 3 . The information in the table of  FIG. 3  can be read as follows:
       —When UE- 1  with IMSI- 1  is accessing RBS- 1 , then the user type of UE- 1  is “home user”.   When UE- 2  with IMSI- 2  is accessing RBS- 1 , then the user type of UE- 2  is “visiting user”.   When UE- 3  with IMSI- 3  is accessing RBS- 1 , then the user type of UE- 3  is “roaming user”.   When UE- 1  with IMSI- 1  is accessing RBS- 2 , then the user type of UE- 1  is “visiting user”.   When UE- 2  with IMSI- 2  is accessing RBS- 2 , then the user type of UE- 2  is “home user”.       
 
         [0043]    As will be described later, the user type of a UE is further used to indicate a charging tariff for the user of the UE when selecting a SAI for the UE. 
         [0044]    Referring to  FIG. 4  there is illustrated a signalling diagram illustrating the flow of messages in an exemplary embodiment of the method of selecting a SAI for a UE  10  according to an exemplary embodiment of the present invention. The UE  10  is here considered to be allowed to access the femto RBS  11  of the femto cell. The UE  10  is initially camped ( 1 ) on a femto cell that is served by a femto RBS  11  which in this exemplary embodiment is connected to an apparatus represented here by a radio network control node (RNC)  12 . The UE  10  performs in ( 2 ) a connection establishment e.g. a radio resource control (RRC) connection establishment indicating the reason of the establishment. This could be because of Location Update, Mobile Originated Call, SMS, a response to a Paging or for any other reason. The RRC layer in the UE  10  triggers RRC connection establishment by sending a RRC CONNECTION REQUEST message ( 2 ) to the RNC  12 . The RRC connection establishment may be established using existing principles as defined in 3GPP TS 25.331. In ( 3 ) the first Layer 3 message is sent from the UE on the established RRC connection. The message could be for example a CM (connection management) SERVICE REQUEST message or a LOCATION UPDATING REQUEST message or a PAGING RESPONSE message. The message from the UE  10  comprises a mobile identity identifying the UE  10 . The mobile identity may be a temporary mobile identity such as a temporary mobile subscriber identity (TMSI) or a packet TMSI (P-TMSI). The mobile identity may also be a permanent mobile identity such as the international mobile subscriber identity (IMSI). 
         [0045]    When the RNC  12  receives in ( 3 ) the Layer 3 message from the UE  10 , it stores the message. The RNC  12  already knows from which femto cell or from which femto RBS  11  the RRC connection was established i.e. it already knows the information identifying the femto RBS  11  (femto RBS-ID). The femto RBS-ID was e.g. provided to the RNC  12  as part of the Iub+ interface during the initial femto RBS start-up procedure. 
         [0046]    If the TMSI or the P-TMSI was used as the mobile identity in the Layer 3 message (e.g. the LOCATION UPDATING REQUEST message) from the UE  10 , the RNC  12  triggers an identification procedure towards the UE  10  by sending an identity request message ( 4 ) to the UE  10 . The identity type requested by the RNC  12  indicates “IMSI” or some other permanent mobile identity of the UE  10 . The messages and information elements are as defined in 3GPP TS 24.008 with the main exception that the procedure is performed from the RNC  12  towards the UE  10  rather than from the CN  14 . 
         [0047]    In ( 5 ) the UE  10  responds with the IMSI (or some other permanent mobile identity). The RNC  12  thus now holds both the IMSI of UE  10  and the femto RBS-ID of femto RBS  11 . According to an embodiment of the present invention, the RNC  12  requests in ( 6 ) the database  13  for information on a user type of the UE  10 . In the request, both the IMSI of UE  10  and the femto RBS-ID are included. As previously described in conjunction with  FIG. 3 , the database (DB)  13  holds in its table information on the femto RBS (RBS-ID) and information identifying the UE  10  (i.e. IMSI). In addition and according to an embodiment of the present invention, DB  13  also holds information on the user type of UE  10 . Therefore, as the RNC  12  queries in ( 6 ) the DB with RBS-ID and IMSI, the user type configured for this association in DB  13  is retrieved/returned to the RNC  12 . As described earlier, the user type indicates if UE  10  is a home user, a visiting user or a roaming user. 
         [0048]    When RNC  12  received the information of the user type, the RNC  12 , according to an embodiment of the present invention, selects a service area identifier (SAI) for the UE  10 . The selection of a SAI for UE  10  is thus dependent on the user type retrieved from DB  13 . In addition, the selection of the SAI is also dependent on the femto cell wherein the UE  10  is located. 
         [0049]    As previously mentioned, the user type of a UE also indicates a charging tariff for the user of the UE when selecting a SAI for the UE. If for example UE  10  is a home user, the charging tariff may indicate a low tariff to charged user by UE  10  (e.g. free tariff). If the UE  10  is a visiting user the charging tariff may indicate a medium tariff. If the UE  10  is a roaming user, the charging tariff may indicate a higher tariff. Thus according to the present invention, the selection of the SAI not only depends on femto cell where the UE is located but also depends on the user type of the UE. 
         [0050]    Referring back to  FIG. 4 , after the RNC  12  has selected the correct SAI for the UE  10 , the RNC  12  triggers in ( 8 ) the establishment of a Iu signalling connection by sending a INITIAL UE MESSAGE to the CN  14 . This message contains the Layer 3 message previously stored in ( 3 ). According to an embodiment of the present invention, the selected SAI is also included in the message together with other information. The Iu signalling connection may be established using existing principles defined in 3GPP TS 25.413 and in other relevant 3GPP specifications. 
         [0051]    In the above description, it was assumed that the Layer 3 message sent from the UE  10  to the RNC  12  in ( 3 ) included the TMSI or the P-TMSI as mobile identity identifying UE  10 . However, if the permanent mobile identity or the IMSI of UE  10  is included in the Layer 3 message instead of the TMSI (or the P-TMSI), then signalling messages ( 4 ) and ( 5 ) may be skipped. In this case, the RNC  12  queries in ( 6 ) the DB  13  with femto RBS-ID and IMSI of UE  10 , and the user type configured for this association in DB  13  is retrieved/returned to the RNC  12 . The RNC  12  then selects a SAI based on the user type of UE  10  and based on the femto cell (or femto RBS  11 ) where UE  10  is located. Following the selection of the SAI, the RNC  12  includes the selected SAI in a message to CN  14  upon triggering an establishment of a signalling connection towards CN  14  as previously described. 
         [0052]    According to another embodiment of the present invention, the RNC  12  can create an association between the temporary mobile identity of UE  10  and the permanent mobile identity of UE  10  and stores the association DB  13  during the access control. In such case the table of the database shown in  FIG. 3  is extended with an additional field, namely the temporary mobile identity of UE  10 . It should be noted that the DB  13  may store the association or associations between a temporary mobile identity and a permanent mobile identity for each allowed UE in a new table. 
         [0053]    In this exemplary embodiment of the present invention, the UE  10  transmits to the RNC  12 , the Layer 3 message containing the temporary mobile identity (e.g. TMSI or P-TMSI) of the UE  10 . The RNC  12  then indicates in the request to DB  13 , the TMSI or P-TMSI of UE  10  and the information identifying the femto RBS, i.e. femto RBS-ID. Since DB  13  has in its table the created association between the mobile identities of UE  10  i.e. IMSI and TMSI (or P-TMSI) in addition to the femto RBS-ID, it can inform the RNC  12  of the IMSI of the UE  10  and check the user type of UE  10 . The user type of UE  10  is thereafter sent to the RNC  12  which, as previously described, selects a SAI based on the user type and on the femto cell (or femto RBS) where the UE  10  is located. Again, the charging tariff for the user of UE  10  is dependent on the user type retrieved from DB  13 . Similarly to the previously described exemplary embodiment of the present invention, the RNC  12  includes the selected SAI in a message to CN  14  upon triggering an establishment of a signalling connection towards the CN  14 . 
         [0054]    However in this exemplary embodiment of the present invention, the RNC  12  is configured to intercept Layer 3 messages and to check these messages in the downlink (initially only the downlink direction from the CN to the UE). If e.g. protocol discriminator of the Layer 3 messages indicate e.g. MM (mobility management), then the RNC  12  is further configured to analyse the message type and to check whether the message is either TMSI (or P-TMSI) REALLOCATION COMMAND or a LOCATION UPDATING ACCEPT message. If also this is the case, then the RNC  12  analyses whether a new TMSI (or P-TMSI) is included in the message. The RNC  12  is further configured to store any new TMSI (or P-TMSI). 
         [0055]    If all the above conditions are fulfilled, the RNC  12  then enables the interception and the checking of Layer 3 messages in the uplink direction also (i.e. from the UE to the CN). In case any of these indicate e.g. MM and the message type is TMSI (or P-TMSI) REALLOCATION COMPLETE, then the RNC  12  updates the association in the DB  13  regarding the UE  10  with the new TMSI (or P-TMSI) previously stored in the RNC  12 . 
         [0056]    It should be noted that if the current femto cell for the UE changes, the RNC  12  may select another SAI for the user of UE  10  depending on the request received at the DB  13  from RNC  12 . As an example if UE  10  moves to another femto cell served by another femto RBS to which UE  10  is allowed to have access, then the association in the DB  13  for the UE  10  may indicate that the UE  10  is a visiting user in this femto cell which means that the correct SAI is selected based on the new femto cell where the UE  10  is located and based on the charging tariff which now is dependent on that the UE  10  is now a visiting user and not a home user. Therefore, the present invention allows the selection of different SAIs for different allowed users in the femto cells. In addition, each selected SAI, according to embodiments of the present invention, can support both the existing location based services and the above mentioned differentiated charging feature which is dependent on the user type of the UE. 
         [0057]    It should be noted that no hardware changes are required in the UE, the femto RBS or the CN. In addition, no functional changes are needed in the UE or in the femto RBS and only minor functional changes are required in the CN. Although described in terms of an embodiment in a WCDMA network, the invention and its different exemplary embodiments may also be applied to other types of radio technologies such as LTE, GSM, WiMAX networks etc. It should also be contemplated that the selection of the SAI described above is not necessarily performed in the RNC i.e. it could be performed in an apparatus that comprises a RNC or in an apparatus that comprises a RNC and a femto RBS (i.e. an apparatus comprising a combination of the RNC and the femto RBS) or in an apparatus that comprises a femto RBS (for example in a LTE network). 
         [0058]      FIG. 5  illustrates an example of an apparatus for selecting a SAI for a UE in a femto cell, in accordance with an exemplary embodiment of the present invention. 
         [0059]    As shown, apparatus  100  comprises receiver means  110  (RX MEANS) configured to acquire information identifying the UE as previously described. Apparatus  100  further comprises transmitting means  120  (TX MEANS) for transmitting to a database, a request for information on a user type of the UE. In the request, the acquired information identifying the UE is included together with information identifying a femto RBS that is serving the femto cell. Apparatus  100  further comprises selection means  130  for selecting a SAI for the UE based on the information received from the database (i.e. the user type). Note that apparatus  100  may comprise other elements not illustrated in  FIG. 5 . Furthermore, the different blocks of apparatus  100  are not necessarily separated but could be included in a single block. 
         [0060]    The present invention and its embodiments can be realised in many ways. For example, one embodiment of the present invention includes a computer-readable medium having instructions stored thereon that are executable by a computer system located in one or several network nodes (apparatus) of the communication system, for selecting a SAI for a UE. The instructions executable by the computing system and stored on the computer-readable medium perform the method steps of the present invention as set forth in the claims. 
         [0061]    While the invention has been described in terms of several preferred embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent to those skilled in the art upon reading of the specifications and study of the drawings. It is therefore intended that the following appended claims include such alternatives, modifications, permutations and equivalents as fall within the scope of the present invention.