Abstract:
A method and an apparatus for selecting a location platform for a user equipment to roam and a method for determining the location of the user equipment using the same. The method for selecting a location platform includes: checking a visiting network of the UE in response to a location request message transmitted from the UE which is roaming; and selecting a location platform to calculate a location of the UE by comparing positioning capability information of the checked visiting network and positioning capability information of a home network of the UE. According to such a method, it is possible to efficiently perform the positioning of the UE, regardless of the location of the UE, thereby improving the quality of the positioning service.

Description:
PRIORITY 
     This application claims to the benefit under 35 U.S.C. 119(a) of an application entitled “Method and Apparatus for Selecting Location Platform for User Equipment to Roam and Method for Determining Location of User Equipment using The Same” filed in the Korean Intellectual Property Office on May 17, 2004 and assigned Serial No. 2004-34608, the entire contents of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a mobile communication system, and more particularly to an apparatus and a method for determining a location of a user equipment (UE). 
     2. Description of the Related Art 
     Recently, the wide spread use of UEs has expanded throughout the world. Further, in a global mobile communication system, many users want to receive application services (e.g., traffic, daily information, etc.) using location information of UEs equipments. Accordingly, user location information acquisition systems using UEs have been commercialized in some countries and mobile communication network areas (e.g., SK telecom and KTF in Korean mobile communication network area, and NTT, DoCoMo, Sprint PCS, KDDI, Vodafone in Japan and Western mobile communication network areas). 
     In order to provide application services using location information, it is necessary to determine a location of a UE in advance. That is, the application services using location information are created on the basis of geographical position information of a UE, which is determined from the location of the UE. 
     In order to acquire the geographical position information of a UE, the UE must receive a positioning service, regardless of the location of the UE. That is, the UE must receive the positioning service, regardless of whether the UE is located in a home area or a roaming area. 
     The positioning service is provided by a location platform (LP) contained in a network. For example, a home location platform (HLP) contained in a home network or a visiting location platform (VLP) contained in a roaming network provides auxiliary location information (e.g., auxiliary GPS information) to the UE or performs a location calculation using information received from the UE, in order to provide the positioning service. 
     The location of a UE in the mobile communication network can be determined by various ways, including three representative examples, which will be described below. 
     First, the location of a UE can be determined for each cell by using information of the cell nearest to the location of the UE or by using information of the cell managing the UE. 
     Second, the location of a UE can be determined based on the network. In this network-based positioning, intensity of transmission and reception signals between a node B (or base station), a UE a time-of-arrival (TOA) of a radio wave signal transmitted from the node B to the UE, or a time-difference-of-arrival (TDOA) of a radio wave signal between the UE each of multiple node Bs is calculated. Thereafter, triangulation is performed using the TOA or TDOA, in order to determine the location of the UE. 
     Third, the location of a UE can be determined by using a global positioning system (GPS) developed by the U.S. Department of Defense. 
     From among the above-described positioning schemes, the positioning scheme using the GPS is employed in the mobile communication network together with supplementation of the GPS technique. Such a positioning scheme using a supplemented GPS is called a network assisted GPS (NA-GPS). The NA-GPS transmits auxiliary GPS information, which is necessary to determine the location of a UE using a network (particularly, using the mobile communication network), to the UE, thereby shortening the time-to-first-fix (TTFF) of the UE. 
     The auxiliary GPS information transmitted to the UE in a network includes satellite IDs of the respective satellites, almanac data, satellite orbit information, a clock error correction value, an ionosphere correction value, a differential GPS (DGPS) correction value, and a list of invisible satellites. The almanac data is location information (e.g., a model) of a satellite according to time sections for a predetermined time period, which is used to detect an approximate location of the satellite, particularly to distinguish a visible satellite. The satellite orbit information and the clock error correction value are information for providing an accurate model of a satellite location to a UE. The ionosphere correction value is used to correct an ionosphere delay error, which occurs when a radio signal passes through an ionosphere contained in a pseudo distance between a satellite and a UE, by about 50%. The ionosphere correction value changes slower than other information. 
     The DGPS correction value improves the accuracy of a UE location, by enabling a basic node B to calculate and remove a deviation error contained in the pseudo distance. The almanac data, the satellite orbit information, the clock error correction value, and the DGPS correction value must be determined according to satellites. 
       FIG. 1  is a block diagram schematically illustrating a conventional mobile communication system. More specifically,  FIG. 1  illustrates a mobile location service (MLS) system for determining the location of a UE in a mobile communication network. The mobile communication system for determining the location of a UE includes a UE  110 , a node B (or base station)  120 , a radio network controller (RNC)  130 , a home location platform (HLP)  140 , a core network (CN)  150  and a mobile location service client (MLS client)  160 . 
     The node B  120  transmits a radio wave signal to the UE  110  located in a specific cell. Also, the node B  120  measures a radio wave signal received from the UE  110 , and transmits predetermined data (e.g., TODA) required to determine the location of the UE  110  to the RNC  130 . In this case, a Uu interface is used for communication between the node B  120  and the UE  110 . 
     The RNC  130  manages the radio resources of the node B  120 , controls a procedure for determining the location of the UE  110 , and performs location calculation. In this case, an Iub interface is used for communication between the RNC  130  and the node B  120 . 
     The HLP  140 , which is also called a location platform (or location server), provides auxiliary location information to the UE  110 , and performs a location information service by performing location calculation and the like. For example, the HLP  140  transmits the auxiliary GPS information to the UE  110 , which is one of the auxiliary location information, thereby enabling a network-assisted GPS service to be provided to UEs  110  located in a relevant network. 
     The CN  150  manages information about the UEs  110  and performs mobility management, session management, and call management. Accordingly, the CN  150  and the RNC  130  communicate with each other using an Iu interface. 
     The MLS client  160  is connected to the network and provides a service in relation to locations of the UEs  110 . That is, the MLS client  160  requests location information of a specific UE  110  from the CN  150  and provides a location service to the relevant UE  110  using the location information. In this case, the MLS client  160  and the CN  150  communicate with each other using an Le interface. 
     In the above-described system of  FIG. 1 , when the UE  110  is located in a home network, the UE  110  receives auxiliary location information (e.g., auxiliary GPS information) from the HLP  140  contained in the home network. The HLP  140  may calculate the location of the UE  110 , i.e., the location of the UE  110  is determined by the HLP  140 . 
     Referring to  FIG. 2 , when the UE  110  roams from a home network  100  to another network  200 , i.e., when the UE  110  visits another network  200 , the UE  110  may determine the location of the UE  110 , by using either a visiting location platform (VLP)  240  contained in the network  200  (in which the UE  110  is roaming) or the HLP  140  contained in the home network  100 . 
     However, in order to determine the location of a roaming UE  110  using the VLP  240 , the VLP  240  must be able to have a positioning capability, such as information about whether or not various positioning schemes according to required location accuracy are supported and information about whether or not an assisted GPS (A-GPS) scheme in a control plane and a user plane is supported, according to a request of the UE  110 , and personal location information of the UE  110  must be kept secret. Therefore, when the roaming UE  110  requests auxiliary location information for determining a location in a user-plane A-GPS scheme, the positioning scheme using the VLP  240  may cause a number of problems. That is, if the VLP  240  supports only a control-plane A-GPS scheme, the VLP  240  cannot provide auxiliary GPS information to the UE  110 . Further, there is another problem in that the personal location information of the UE  110  is disclosed as soon as the positioning service begins between the VLP  240  and the UE  110 . 
     In order to determine the location of a roaming UE  110  using the HLP  140 , a regional range where the HLP  140  can provide auxiliary location information (e.g., auxiliary GPS information) must include a visiting area where the UE  110  is located. 
     In addition, although the positioning scheme using the HLP  140  has a superior capability in security and protection of personal location information, the positioning scheme using the HLP  140  has a disadvantage in that the accuracy of auxiliary location information (or auxiliary GPS information) is poor, as compared with the case of using the VLP  240 . Therefore, in order to improve the quality of the positioning service, it is preferred that the UE  110  selects a location platform in consideration of both the positioning capability of the HLP  140  or the VLP  240 , and capability factors requested by the UE  110 , e.g., location accuracy, protection of personal location information, security, etc. 
     However, until now, there has been no such a method capable of permitting a roaming UE  110  to select a location platform in consideration of the above-described positioning capability and capability factors requested by the UE  110 , in order to determine the location of the UE  110 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been designed to solve the above and other problems occurring in the prior art. An object of the present invention is to provide an apparatus and a method for improving the quality of a positioning service, regardless of the location of a user equipment. 
     Another object of the present invention is to provide an apparatus and a method for enabling the position of a roaming user equipment to be efficiently determined. 
     Still another object of the present invention is to provide an apparatus and a method for selecting a location platform in consideration of both the positioning capability of a location platform and positioning capability factors requested by a user equipment. 
     Still another object of the present invention is to provide an apparatus and a method for determining the location of a user equipment using a location platform, which is selected by the above-mentioned apparatus and method. 
     To accomplish the above and objects, in accordance with one aspect of the present invention, there is provided a method for selecting a location platform for a user equipment (UE), which is roaming. The method includes the steps of: checking a visiting network of the UE in response to a location request message transmitted from the UE which is roaming; and selecting a location platform to calculate a location of the UE by comparing positioning capability information of the checked visiting network and positioning capability information of a home network of the UE. 
     In accordance with another aspect of the present invention, there is provided a location platform selection apparatus for a user equipment (UE), wherein the location platform selection apparatus compares positioning capabilities information of a home location platform of the UE and a visiting location platform in response to a location information request of the UE which is in roaming, and selects a location platform to calculate a location of the UE. The visiting location platform is contained in a visiting network in which the UE is visiting. 
     In accordance with still another aspect of the present invention, there is provided a method for determining a location of a user equipment (UE). The method includes the steps of: checking a visiting network of the UE in response to a location request message transmitted from the UE which is roaming; selecting a location platform to calculate a location of the UE by comparing positioning capability information of the checked visiting network and positioning capability information of a home network of the UE; acquiring auxiliary information for calculating the location of the UE in the selected location platform by exchanging auxiliary location information between the selected location platform and the UE; and calculating the location of the UE using the acquired auxiliary information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram schematically illustrating a conventional mobile communication system; 
         FIG. 2  is a block diagram illustrating a roaming state of a user equipment (UE); 
         FIG. 3  is a block diagram illustrating a system for determining a position of a roaming UE according to an embodiment of the present invention; 
         FIG. 4  is a flow diagram illustrating a procedure for determining a position of a UE according to an embodiment of the present invention; 
         FIG. 5  is a flow diagram illustrating a procedure for determining a position of a UE according to an embodiment of the present invention; and 
         FIG. 6  illustrates an example of positioning capability information that is used as a criterion for selecting a location platform for the a UE according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred embodiments of the present invention will be described in detail herein below with reference to the accompanying drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention. 
       FIG. 3  is a block diagram illustrating a system for determining a position of a roaming UE according to an embodiment of the present invention. Referring to  FIG. 3 , the system includes two location platforms, i.e., a home location platform (HLP)  140 , which is included in a home network  100  of a UE  110 , and a visiting location platform (VLP)  240 , which is included in a visiting network  200  of the UE  110 . The system manages positioning information of the UEs located in each network and provides a positioning service. Herein, it is preferred that the HLP  140  and the VLP  240  communicate with each other using a roaming location protocol (RLP). 
     The HLP  140  of the home network  100  includes a home-roaming function unit  141 , and the VLP  240  of the visiting network  200  in which the UE  110  is roaming includes a visiting-roaming function unit  241 . The home-roaming function unit  141  and the visiting-roaming function unit  241  perform preparatory work for calculating the position of the roaming UE  110  and determine a location platform for performing position calculation. That is, the home-roaming function unit  141  compares the positioning capability of the HLP  140  and the positioning capability of the VLP  240 , in order to select a location platform to be used for the positioning service. The visiting-roaming function unit  241  provides positioning capability information of the VLP  240  in response to a request of the home-roaming function unit  141 . 
     A mobile location service client (MLS client)  160  located out of the network requests position information of the UE  110  to the HLP  140  in the home network  100 . Herein, it is preferred that the MLS client  160  and the HLP  140  communicate with each other using a mobile location protocol (MLP). 
       FIG. 4  is a flow diagram illustrating a procedure for determining a position of the UE  110  according to an embodiment of the present invention. More specifically,  FIG. 4  illustrates the HLP  140  being selected as a location platform to provide the positioning service when the UE  110  requests information about its own location. 
     In step S 401 , the UE  110  in roaming transmits a location request message to the HLP  140  in order to determine its own location. In this case, the location request message is provided to begin a location session and a location procedure between the HLP  140  and the UE  110 . The location request message includes an identifier (MS-ID) of the UE  110 , positioning capability information of the UE  110 , a specific identifier (location ID) of a cell or an area in which the UE  110  is located, an identifier (MLS-client-ID) of a service client to perform a service requested by the UE  110 , etc. 
     The positioning capability of the UE  110  includes positioning schemes supported by the UE  110 . That is, the positioning capability of the UE  110  includes characteristics of bearer such as GSM, CDMA, and WLAN, information about a subject to perform location calculation such as MS-Based, MS-Assisted, etc., whether or not a control-plane A-GPS and a user-plane A-GPS are supported. 
     The HLP  140  having received the location request message checks the identifier of the UE  110  contained in the location request message, and determines if the UE  110  can receive the location service. When it is determined that the UE  110  can receive the location service, the HLP  140  assigns a new session to the UE  110  in step S 403 . In step S 405 , the HLP  140  determines the VLP  240  as a location platform with reference to the location ID contained in the location request message. 
     In step S 407 , the HLP  140  requests information about the positioning capability of the VLP  240  and conversion of the coordinates (xy coordinates) of the location ID of an area reported by the UE  110 , from the VLP  240  determined in step S 405 , using a start roaming location immediate request (SRLIR) message of the RLP. The SRLIR message includes a session identifier (ID) of a session assigned in step S 403 , a location ID, and a positioning capability information request symbol (LPC req.: Location Platform Capability request). In this case, the coordinates converted by the request are used in place of the location of a node B. That is, a location platform (LP), which determines the location of the UE  110 , generates auxiliary location information using an approximate location of the UE  110  (e.g., a location of a node B in which the UE  110  is located) and provides the auxiliary location information to the UE  110 . 
     In step S 409 , the VLP  240 , having received the SRLIR message in step S 407 , responds to the HLP (Home Location Platform)  140  using a start roaming location immediate answer (SRLIA) message of the RLP. The SRLIA message includes the session ID, information about a positioning capability (e.g., LP capability), and approximate coordinate information (e.g., coarse position) of the location ID. 
     An example of information about the positioning capability (LP capability) contained in the SRLIA message is illustrated in  FIG. 6 . However, this information will be described later in more detail with reference to  FIG. 6 . 
     The HLP  140 , having received the SRLIA message (response message) from the VLP  240  in step S 409 , compares the positioning capability (LP capability) information of the VLP  240  contained in the SRLIA message with positioning capability (LP capability) information of the HLP  140  stored in advance in the HLP  140 , and selects a location platform to provide a location information service to the UE  110  in step S 411 . 
     For example, when it is possible for the HLP  140  to support the user-plane A-GPS positioning scheme but it is impossible for the VLP  240  to support the user-plane A-GPS positioning scheme, the HLP  140  selects the HLP  140  as a location platform. However, when it is impossible for the HLP  140  to support the user-plane A-GPS positioning scheme but it is possible for the VLP  240  to support the user-plane A-GPS positioning scheme, the HLP  140  selects the VLP  240  as a location platform. When both of the HLP  140  and the VLP  240  can support the user-plane A-GPS positioning scheme, the HLP  140  selects one of the HLP  140  and the VLP  240  as a location platform, by comparing protection of personal location information, charge, security, positioning capabilities, etc., between the HLP  140  and the VLP  240 . 
     When the HLP  140  already has information about the positioning capability of the VLP  240 , the HLP  140  selects a location platform using the already-known positioning capability information. Here, it is possible to omit the items for the positioning capability information included in the SRLIR and SRLIA messages transmitted in steps S 407  and S 409 . 
       FIG. 4  illustrates the HLP  140  being selected as a location platform in step S 411 . Therefore, the HLP  140 , having been determined as a location platform, calculates the location of the UE  110  using auxiliary location information of the UE  110  in step S 413 . 
     Accordingly, the HLP  140  exchanges auxiliary location information with the UE  110  in step S 414 . Herein, the HLP  140  acquires auxiliary location information using either an MS-assisted scheme or an MS-based scheme, and calculates the position of the UE  110  using the acquired auxiliary location information. The MS-assisted scheme calculates auxiliary location information (e.g., estimated value of location) using a measured value received from the UE  110 , and the MS-based scheme acquires an auxiliary location information (e.g., estimated value of location) calculated from the UE  110 . 
     After completing the location calculation, the HLP  140  ends the session (e.g., a location session) assigned in step S 403  and notifies the UE  110  of the end of the session in step S 415 . Accordingly, the HLP  140  transmits a positioning end message to the UE  110 , and then the UE  110  releases the occupation of all resources, which the UE  110  has occupied in relation to the location session. 
       FIG. 5  is a flow diagram illustrating a procedure for determining a position of a UE  110  according to an embodiment of the present invention. More specifically,  FIG. 5  illustrates the VLP  240  being selected as a location platform to provide the positioning service when the UE  110  requests information about its own location. However, because steps S 501  to S 511  in  FIG. 5  are the same as steps S 401  to S 411  in  FIG. 4 , the detailed description of steps S 501  to S 511  will be omitted and the following description will be made with regard to the steps following step S 511 . 
     Referring to  FIG. 5 , the HLP  140  determines the VLP  240  as a location platform in step S 511 , and the HLP  140  notifies the relevant VLP  240  that the VLP  240  has been determined as a location platform in step S 513 . After the HLP  140  notifies the relevant VLP  240  of the location platform determination, the HLP  140  receives an acknowledgment signal (ACK) in response to the notification in step S 515 . 
     The VLP  240 , having received the notification of the location platform determination, calculates the location of the UE  110  using auxiliary location information of the UE  110  in step S 517 . 
     Accordingly, the VLP  240  performs an auxiliary location information exchange process with the UE  110  via the HLP  140 . That is, when the VLP  240  requests auxiliary location information the HLP  140  in step S 518 , the HLP  140  obtains the auxiliary location information through auxiliary location information exchange with the UE  110  in step S 519  and transmits the obtained auxiliary location information to the VLP  240  in step S 521 . Then, the VLP  240  calculates the location of the UE  110  using the auxiliary location information. 
     In this case, the VLP  240  acquires auxiliary location information using either an MS-assisted scheme or an MS-based scheme, and calculates the position of the UE  110  using the acquired auxiliary location information. Herein, the MS-assisted scheme calculates auxiliary location information (e.g., estimated value of location) using a measured value received from the UE  110 , and the MS-based scheme acquires an auxiliary location information (e.g., estimated value of location) calculated from the UE  110 . 
     After the location calculation is completed, the HLP  140  ends the session (e.g., a location session) assigned in step S 503  and notifies the UE  110  of the end of the session in step S 523 . The HLP  140  transmits a positioning end message (location END message) to the UE  110 , and the UE  110  releases the occupation of all resources, which the UE  110  has occupied in relation to the location session. 
     Although the embodiments of the present invention described above with reference to  FIGS. 4 and 5  are made with respect to the case in which a UE requests information about its own location, the above-described procedures of the present invention can also be used when a network requests the location information of a UE. In such a case in which a network requests the location information of a UE, there is little difference except that the subject of location request and the object of session end notification change. Therefore, embodiments for the case in which a network request the location information of a UE will be omitted. 
       FIG. 6  illustrates an example of positioning capability information that is used as a criterion for selecting a location platform for the a UE according to an embodiment of the present invention. The positioning capability information includes a network identifier (ID), a specific identifier (LP ID) of a location platform, a type of network, information about whether or not a roaming location service is supported, a supported positioning scheme (e.g., a cell ID positioning scheme, a network-based positioning scheme, such as TDOA and the like, a GPS positioning scheme, etc.), a degree of accuracy of each positioning scheme, and information about an A-GPS positioning scheme, which includes a kind of supported A-GPS (a control-plane A-GPS or a user-plane A-GPS) and an auxiliary location information generation scheme (MS-based, MS-assisted, etc.). 
     As described above, according to an embodiment of the present invention, a location platform is selected based on the positioning capability of the location platform and positioning capability factors requested by a UE, and the location of the UE is determined using the selected location platform. Therefore, the present invention can efficiently perform the positioning of the UE, regardless of the location of a UE (e.g., regardless of whether the UE is located in a home area or a roaming area), thereby improving the quality of the positioning service. 
     While the present 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 present invention as defined by the appended claims. Accordingly, the scope of the present invention is not to be limited by the above embodiments, but by the following claims and the equivalents thereof.