Abstract:
A method of providing Location Services (LCS) over an Internet Protocol Multimedia Subsystem (IMS) network in a wireless communication system is provided. An LCS client transmits a service connection request message including a message requesting the location information of a User Equipment (UE). The UE transmits the location information to the LCS client.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Method For Providing Location Service On IMS Based Network” filed in the Korean Intellectual Property Office on Apr. 21, 2005 and assigned Serial No. 2005-32964, the contents of which are herein incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a method of providing Location Services (LCS) in an IP (Internet Protocol) Multimedia Subsystem (IMS)-based network environment, and in particular, to a method of providing LCS over an IMS network in a broadband wireless network.  
         [0004]     2. Description of the Related Art  
         [0005]     One of the reasons that an IMS network attracts great interest is that an IMS-based IP core network system provides a vision of the full convergence of wired and wireless services including future-generation mobile communications, Wireless Local Area Network (WLAN), and cable, as well as wired broadband Internet.  
         [0006]     LCS is an application system and a service provisioning technology that accurately locates a person or an object over a mobile communication network and utilizes the accurate location. A 3 rd  Generation Partnership Project (3GPP) Technical Specification (TS) 22.071 notes “Location Services may be considered as a network provided enabling technology consisting of standardized service capabilities which enable the provisioning of location based applications”.  
         [0007]     The implementation of LCS requires advanced positioning, positioning accuracy development, position processing in wireless Internet, spatial data processing, LCS platform-related technology, LCS application software development, an open geographic information system, LCS-related standardization, and LCS application service development. These technologies enable service providers to provide a variety of associated services such as information about surroundings, location tracking, safety, traffic information, delivery and navigation, and location advertisement.  
         [0008]      FIG. 1  is a diagram illustrating a signal flow of an operation for providing LCS over a typical 3GPP network. Communications are conducted by Open Mobile Alliance (OMA) Mobile Location Protocol (MLP) between an LCS client and a Gateway Mobile Location Center (GMLC) (steps  131  and  153 ) and between GMLCs (steps  144  and  148 ). Communications between the GMLC and a Subscription Locator Function (SLF) and between the GMLC and a Home Location Register (HLR)/Home Subscriber System (HSS) (steps  134  to  139 ) are made via an IMS interface, Dh (interface between Requesting Location IMS-Interworking Function (LIMS-IWF) and SLF) or Sh (interface between LIMS-IWF and HSS/HLR), or by Media Access Protocol (MAP). The GMLC is interfaced with a 3G network element such as a Serving General Packet Radio Service (GPRS) Support Node (SGSN) by MAP (steps  145  and  147 ).  
         [0009]     Referring to  FIG. 1 , when an LCS client  100  wants to locate a target User Equipment (UE)  120 , he transmits an LCS Service Request message to a home LIMS-IWF  106  via a requesting GMLC  102  and a requesting LIMS-IWF  104  in steps  131 ,  132  and  133 .  
         [0010]     The requesting GMLC  102  manages an external interface to provide LCS. For example, it is responsible for authentication of an external LCS client, mobility management, determination of the position accuracy of final position estimation for retry and reject, and coordinates transformation for identification of the LCS client. The LIMS-IWF, located within the GMLC, is an interworking function for supporting LCS based on IMS. To obtain the location information of a UE using an IMS Public User Identity (i.e. Session Initiation Protocol-Uniform Resource Identifier (SIP-URI)) in an existing packet-switched network, the LIMS-IWF acquires the Mobile Subscriber ISDN (MSISDN) of the UE.  
         [0011]     The LCS Service Request message is defined with MLP. It carries the ID of the target UE be located (SIP-URI in the IMS network), an LCS type (Immediate or Conditional), LCS requirements, the ID of the UE requesting the location information, and authentication information.  
         [0012]     The home LIMS-IWF  106  gets the address of an HLR/HSS  110  to which the UE  120  has been registered by querying an SLF  108  via a Dh interface (Dh-SLF) in steps  134  and  135 . When two or more HSSs/HLRs reside within the network and they are identified by different addresses, the SLF  108  provides the address of the HSS/HLR  110  to which the UE  120  has been registered.  
         [0013]     The home LIMS-IWF  106  then retrieves the MSISDN of the target UE  120  having an SIP-URI from the HSS/HLR  110  via an Sh interface (Sh-PULL) in steps  136  and  137 .  
         [0014]     The HSS/HLR  110  manages LCS subscription information and location information for terminated routing, to thereby track access. It also provides user profile information directly or via a server and performs authentication.  
         [0015]     In steps  138  and  139 , the home LIMS-IWF  106  retrieves the network ID of a home GMLC  112  using a MAP message with the MSISDN of the UE  120 . The home LIMS-IWF  106  forwards the LCS Service Request message to the home GMLC  112  according to the network ID in step  140 .  
         [0016]     In step  141 , the home GMLC  112  performs a privacy check to determine whether the LCS client  100  is allowed to locate the UE  120 . If the privacy check passes, i.e. permission is granted to locate the UE  120 , the home GMLC  112  queries the HSS/HLR  110  using a Send Routing Info for LCS message being a MAP message with the MSISDN of the UE  120  to get the address of a visited GMLC  114  in step  142 . The HSS/HLR  110  transmits the network ID of the visited GMLC  114  to the home GMLC  112  by a Send Routing Info for LCS Ack message being a MAP message in step  143 .  
         [0017]     The home GMLC  112  forwards the LCS Service Request message to the visited GMLC  114  according to its network ID in step  144 . In step  145 , the visited GMLC  114  translates the LCS Service Request message to a Location Request message in the form of a Radio Resource LCS Protocol (RRLP) message and transmits the Location Request message to an SGSN  116 . The SGSN  116  contains functionality responsible for management of LCS routing information and authentication of LCS subscribers. The SGSN  116  forwards the Location Request message to the UE  120  via a Base Station System (BSS)  118  and measures the location of the UE  120  in step  146 .  
         [0018]     After the location measurement, the SGSN  116  notifies the LCS client  100  of the location of the UE  120  by an LCS Service Response message in steps  147  to  153 . During the transmission of the location information of the UE  120 , the home GMLC  112  performs a privacy check to determine whether the LCS client  100  is allowed to locate the UE  120  in step  149 . Only when the privacy check passes, the subsequent steps are carried out.  
         [0019]      FIG. 2  is a diagram illustrating a signal flow of an operation for providing a conditional LCS over the typical 3GPP network. The conditional LCS is a location service contingent on some current or future event specified by an LCS client. Only when the event occurs, the location information of a target LE is provided to the LCS client.  
         [0020]     Referring to  FIG. 2 , when an LCS client  200  wants to locate a target LE  214 , he transmits an LCS Service Request message to a requesting GMLC  202  in step  221 . The LCS Service Request message is defined with MLP. It carries the ID of the target UE (SIP-URI), an LCS type (Immediate or Conditional), LCS requirements, the ID of the UE requesting the location information, and authentication information. The SIP-URI is an IMS public user ID.  
         [0021]     In step  222 , the requesting GMLC  202  forwards the LCS Service Request message to a visited GMLC  208  via a home GMLC  204  and an HLR/HSS  206  in the same manner as in steps  134  to  144  of  FIG. 1 .  
         [0022]     The visited GMLC  208  requests the location information of the UE  214  to a Mobile Switching Center (MSC)/SGSN  210  by a Provide Subscriber Location message being a MAP message in step  223 . The MSC/SGSN  210  contains functionality responsible for management of LCS routing information, and control of authentication of LCS subscribers and LCS provisioning.  
         [0023]     The MSC/SGSN  210  locates the LE  214  via a Random Access Network  212  and performs operations needed to communicate with the UE  214 , including authentication, in step  224 . If a connection is established to the LE  214 , the MSC/SGSN  210  transmits an LCS Area Event Invoke message to the UE  214  to indicate that an LCS area event has been set in step  225 . In steps  226  to  230 , the UE  214  transmits an LCS Service Response message to the LCS client  200 , notifying of an acknowledgement for the invoked LCS area event. For example, the LCS area event to be reported is the LE  214  being in an area set by the LCS client  200  (e.g. Cupertino in Santa Clara County).  
         [0024]     If the area event occurs, for example, the UE  214  enters Cupertino in Santa Clara County in step  231 , the UE  214  transmits its location information to the LCS client  200  by an LCS Service Response message in steps  232  to  238 . If the UE  214  moves and thus a network element managing the location information of the UE  214  is changed, the home GMLC  204  retransmits the LCS Service Request message to the changed network element to which the UE  214  is now registered in step  235 . During the transmission of the location information of the UE  214 , the home GMLC  204  performs a privacy check to determine whether the LCS client  200  is allowed to locate the UE  214  in step  236 . Only when the privacy check passes, the subsequent steps are carried out.  
         [0025]     As described above, the MLC and the 3G network communicate with each other via the MAP interface to provide LCS. However, implementation of the MAP interface for LCS is inefficient to a network that provides an IP multimedia service independently of a bearer network.  
         [0026]     Moreover, when the UE roams and the network element managing its location information is changed in the conditional LCS, the GMLC inconveniently has to retransmit the LCS Service Request message to the new network element.  
       SUMMARY OF THE INVENTION  
       [0027]     An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide a method of providing LCS over an IMS network in a wireless communication system. Another object of the present invention is to provide a method of providing a conditional LCS over an IMS network in a wireless communication system. A further object of the present invention is to provide a method of transmitting a location service request message in the form of an IMS-based SIP message in a wireless communication system. The above objects are achieved by providing a method of providing LCS over an IMS network in a wireless communication system.  
         [0028]     According to one aspect of the present invention, in a method of providing a location service over an IMS network in a wireless communication system, a location service client transmits a service connection request message including a message requesting the location information of a UE. The UE transmits the location information to the location service client.  
         [0029]     According to another aspect of the present invention, in a method of providing a conditional location service over an IMS network in a broadband wireless communication system, a location service client transmits a service connection request message including a message requesting the location information of a UE. The UE checks a condition that triggers transmission of the location information in the service connection request message and transmits a response message indicating reception of the service connection request message to the location service client. If the condition is fulfilled, the UE transmits the location information to the location service client by the UE. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0031]      FIG. 1  is a diagram illustrating a signal flow for an operation for providing LCS over a typical 3GPP network;  
         [0032]      FIG. 2  is a diagram illustrating a signal flow for an operation for providing conditional LCS over the typical 3GPP network;  
         [0033]      FIG. 3  is a diagram illustrating a signal flow of an operation for providing LCS over an IMS network according to an embodiment of the present invention; and  
         [0034]      FIG. 4  is a diagram illustrating a signal flow of an operation for providing conditional LCS over the IMS network according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
         [0036]     The present invention is intended to provide a method of providing LCS over an IMS network.  
         [0037]     In the present invention as described below, an Extensible Markup Language (XML)-based MLP message carrying LCS information between an LCS client and a server is included in an Session Description Protocol (SDP) area of an SIP message, for transmission to a UE, by way of example. Since the use of SIP messages obviates the need for an additional server to interpret MLP messages between the LCS client and a UE, only Proxy (P)/Serving (S)/Interrogating (I)-Call Session Control Functions (CSCFs) are involved in the message transmission/reception.  
         [0038]      FIG. 3  is a diagram illustrating a signal flow of an operation for providing LCS over an IMS network according to the present invention.  
         [0039]     Referring to  FIG. 3 , when an LCS client  300  wants to locate a target UE  318 , it transmits an INVITE (SDP offer) message to a P-CSCF  302 , requesting the location information of the UE  318  in step  331 . The P-CSCF  302  has stored the address of an S-CSCF  304  in advance. In the presence of a SIP message destined for the S-CSCF  304 , the P-CSCF  302  transmits it to the S-CSCF  304 . The INVITE message is an SIP message including an MLP message in an SDP area.  
         [0040]     The P-CSCF  302  forwards the INVITE message to the S-CSCF  304  in step  332 . The S-CSCF  304  performs service profile validation and necessary service control in step  333  and forwards the INVITE message to an I-CSCF  306  in step  334 .  
         [0041]     The I-CSCF  306  serves as a contact point for every incoming call for subscribers within the network and a contact point into the network for other network subscribers. Thus, the I-CSCF  306  functions as a firewall and hides the configuration, topology and capacity of the provider network from the outside. In accordance with the present invention, the I-CSCF  306  queries an HSS  308  to detect an S-CSCF to receive the INVITE message, i.e. an S-CSCF  310  to which the UE  318  has been registered in step  335 . The HSS  308  tracks access by managing the location information of UEs. It also provides user profiles directly or via a server.  
         [0042]     In step  336 , the I-CSCF  306  forwards the INVITE message to the S-CSCF  310 . In step  337 , the S-CSCF  310  determines whether to proceed by checking the privacy class of the UE  318  (e.g. LCS availability, privacy strictness, and classes of LCS clients for which location is allowed) in a subscriber profile received from the HSS  308 .  
         [0043]     If the LCS client  300  is allowed to locate the UE  318  according to the privacy class of the UE  318 , the S-CSCF  310  forwards the INVITE message to an Access Control Router (ACR)  314  via a P-CSCF  312  in steps  338  and  339 . The ACR  314  leaves the INVITE message pending while establishing a connection with the UE  318  in step  340 .  
         [0044]     The ACR  314  performs operations regarding communications with the UE  318  via a Radio Access Station (RAS)  316 , inclueing location and authentication in step  341 . If the ACR  314  is connected to the UE  318 , it forwards the INVITE message to the UE  318  in step  342 . If the UE  318  is in an idle mode, the ACR  314  activates the UE  318 , prior to the forwarding.  
         [0045]     In steps  343  to  349 , the UE  318  transmits its location information to the LCS client  300  by a 200 OK message. In the process of transmission of the 200 OK message, the S-CSCF  310  checks the privacy class of the UE  318  (e.g. LCS availability, privacy strictness, and classes of LCS clients for which location is allowed) in step  345 . Only when the privacy class of the UE  318  allows the LCS client  300  to locate the UE  318 , does the S-CSCF  310  performs the next step.  
         [0046]      FIG. 4  is a diagram illustrating a signal flow of an operation for providing a conditional LCS over the IMS network according to another embodiment of the present invention.  
         [0047]     Referring to  FIG. 4 , when an LCS client  400  wants to locate a target UE  418 , it transmits an INVITE (SDP offer) message to a P-CSCF  412  via a P-CSCF  402 , an S-CSCF  404 , an I-CSCF  406 , an HSS  408 , and an S-CSCF  410  in steps  431  to  438  in the same manner as in steps  331  to  338  of  FIG. 3 . The INVITE message is an SIP message including an MLP message in an SDP area. It also indicates an event that triggers locating the UE  418 , as set by the LCS client  400 . For instance, the event may be the UE  418  being in an area set by the LCS client  400  (e.g. Cupertino in Santa Clara County).  
         [0048]     As in step  341  of  FIG. 3 , the P-CSCF  412  forwards the INVITE message to the UE  418  via an ACR  414  and an RAS  416  by establishing a connection to the UE  418  in step  439 . The UE  418  replies to the LCS client  400  with a Ringing message in steps  440  to  446 . During the transmission of the Ringing message, the S-CSCF  410 , which has received the location information of the UE  418 , checks the privacy class of the UE  418  (e.g. LCS availability, privacy strictness, and classes of LCS clients for which location is allowed) in step  441 . Only when the privacy class of the UE  418  allows the LCS client  400  to locate the UE  418 , the S-CSCF  410  performs the next step.  
         [0049]     When the event occurs, for example, the UE  418  enters Cupertino in Santa Clara County in step  447 , the UE  418  transmits its current location information to the LCS client  400  by a 200 OK message in steps  448  to  454 . During the transmission of the 200 OK message, the S-CSCF  410 , which has received the location information of the UE  418 , checks the privacy class of the UE  418  (e.g. LCS availability, privacy strictness, and classes of LCS clients for which location is allowed) in step  450 . Only when the privacy class of the UE  418  allows the LCS client  400  to locate the UE  418 , the S-CSCF  410  performs the next step.  
         [0050]     As described above, LCS provisioning using SIP over an IMS network in a wireless communication system obviates the need for MAP interfaces and associated messages for interworking with 3G network elements in the conventional LCS. Therefore, LCS can be provided between wireless networks ensuring mobility.  
         [0051]     Regarding conditional LCS in a case where an access network is changed, while location information cannot be transmitted until the network information of a new attach point (e.g. SGSN/MSC) is acquired in the conventional technology, the location information is transmitted using a known IP address of a P-CSCF in the present invention, thereby simplifying an LCS providing process.  
         [0052]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.