FIELD OF THE INVENTION 
   This invention relates generally to the field of communication systems, and more particularly to a method of finding and communicating with a mobile station in a wireless communication system. 
   BACKGROUND OF THE INVENTION 
   Mobile users are typically registered with a home wireless communication system. The home wireless communication system includes a database that contains all the subscribers within the home service area of the home wireless communication system. This database is commonly referred to as a Home Location Register (HLR). 
   HLRs are capable of conversing in a particular protocol. In typical wireless communication systems, an HLR is only capable of conversing in a single protocol. 
   Cellular service providers allow mobile users to cross between systems using different protocols. However, HLRs will typically converse in one protocol and ignore messages in any other protocol. This can lead to problems when a mobile user roams from their home coverage area to a coverage area that utilizes a different protocol than their home wireless communication system. This can make determining the location of a mobile station or the delivery of calls to a mobile station difficult or impossible. 
   Wireless service providers have occasion to move subscriber records from a first HLR to a second HLR that converses in a different protocol than the first protocol. When a call request is received for the mobile station, the wireless communication system requests location information relating to the called mobile station from the first HLR. If the subscriber record is not found in the first HLR because it has been moved, the HLR sends a return error message. The return error message will typically include an unassigned directory number for the called mobile station. 
   The wireless communication system then sends a location request for the called mobile station to the second HLR. If the second HLR includes a subscriber record for the called mobile station, the wireless communication system utilizes the information from the second HLR. 
   One problem with this scenario is that the information obtained is not remembered by the wireless communication system. Every time a call for a mobile station is received the same, processor-intensive processing occurs. 
   Therefore, a need exists for a method that allows a service provider to move subscriber records from one HLR to another that utilizes a different protocol without wasting system resources each time a call is received for the moved mobile station. Further, a need exists for a method that allows a wireless communication system to return location information relating to a mobile station whose subscriber record has been moved in a shorter amount of time. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides a method for optimizing home location register (HLR) queries in a wireless communication system. When a subscriber record has been moved from a first HLR to a second HLR that utilizes a different protocol than the first HLR, the wireless communication system sends two queries for location information for the mobile station, one to the first HLR and one to the second HLR, simultaneously. Two responses will be received, one from each of the HLRs. The valid response is recorded in a separate table for future use. The invalid response is discarded. 
   The next time a call comes in for mobile station, the update table is traversed to determine if the HLR of the mobile station has been updated. If so, the location request is sent only to the system in the table. If the table does not include information for the called mobile station, simultaneous queries are sent to the first and second HLRs, as described above, and the same process is followed. 
   The present invention thereby provides a method that allows a service provider to move subscriber records from one HLR to another that utilizes a different protocol without wasting system resources each time a call is received for the moved mobile station. Once the moved subscriber record has been found, this information is stored in the wireless communication system so that the sending of multiple simultaneous queries is no longer necessary. This saves on system resources and minimizes traffic in the wireless communication system. Further, the present invention provides a method that allows a wireless communication system to return location information relating to a mobile station whose subscriber record has been moved with a better response time. 


   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  depicts a wireless communication system in accordance with an exemplary embodiment of the present invention. 
       FIG. 2  depicts a flowchart of a method for sending a location request to multiple HLRs in accordance with an exemplary embodiment of the present invention. 
       FIG. 3  depicts a flowchart of a method for sending a location request to a backup HLR in accordance with an exemplary embodiment of the present invention. 
       FIG. 4  depicts a flowchart of a method for sending a location request to an HLR and updating a update table in accordance with an exemplary embodiment of the present invention. 
       FIG. 5  depicts a table of directory numbers and associated primary HLR and secondary HLR in accordance with an exemplary embodiment of the present invention. 
       FIG. 6  depicts an update table of directory numbers and associated updated HLR in accordance with an exemplary embodiment of the present invention. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  depicts a wireless communication system  100  in accordance with an exemplary embodiment of the present invention. Wireless communication system  100  includes wireless communication network  101 , home location register (HLR) HLR 1   103 , home location register HLR 2   105 , cellular gateway  107 , signal transfer point (STP)  109 , database  111 , and backup database  113 . Wireless communication network  101  comprises functions necessary to operate and maintain wireless communications with mobile stations (not shown). Wireless communication network  101  can be based on any well-known technology, such as analog or digital. 
   HLR 1   103  and HLR 2   105  are both home location registers. A home location register is a database in a cellular system that includes all the subscribers within the home service area of the cellular service provider. In the embodiment depicted in  FIG. 1 , HLR 1   103  utilizes the American National Standards Institute (ANSI) ANSI-41 protocol titled “Cellular Radiotelecommunications Intersystem Operations.” In the embodiment depicted in  FIG. 1 , HLR 2   105  utilizes the Global System for Mobile Communications (GSM) protocol. HLR 1   103  and HLR 2   105  are preferably not able to communicate in a protocol that is different than their own. 
   Although only two HLRs are depicted in  FIG. 1 , it should be understood that the present invention works with any number of HLRs utilizing the methods and concepts described in accordance with the exemplary embodiment of  FIG. 1 . Further, although only ANSI-41 and GSM protocols are depicted, it should be understood that the present invention works with HLRs utilizing a variety of protocols. In addition, the present invention also applies to HLRs that are using the same protocol that may not be compatible due to changes in versions of the protocol. For example, an updated GSM protocol may not be compatible with an earlier GSM protocol, and the present invention would work in this scenario as well. 
   Cellular gateway  107  is an entrance into wireless communication network  101 . Cellular gateway  107  is responsible for determining the location of mobile stations within communication system  100 . Cellular gateway  107  accomplishes location determination by interfacing with HLRs, such as HLR 1   103  and HLR 2   105 . 
   Signal transfer point (STP)  109  is a node within wireless communication network  101  that routes messages between cellular gateway  107  and HLR 1   103  and HLR 2   105 . 
   Database  111  and backup database  113  are data storage mechanisms that are capable of storing data and receiving and sending data to and from cellular gateway  107 . As depicted in  FIG. 1 , database  111  and backup database  113  are depicted as two separate physical databases, but they can also be separate logical databases within one physical database. In an exemplary embodiment, database  111  stores table  500 , which is depicted in  FIG. 5 , and backup database  113  stores update table  600 , which is depicted in  FIG. 6 . 
     FIG. 2  depicts a flowchart  200  of a method for sending a location request to multiple HLRs in accordance with an exemplary embodiment of the present invention. 
   Wireless communication network  101  receives ( 201 ) a location request for a mobile station. The location request, such as a call request, is a request to locate a mobile station. The location request can originate from a wireline or wireless communication network. 
   Wireless communication network  101  sends ( 203 ) a location request message to a plurality of HLRs. The location request message goes from cellular gateway  107  through wireless communication network  101  via STP  109  to HLR 1   103  and HLR 2   105 . 
   Wireless communication network  101  receives ( 205 ) a location request response from each of the plurality of HLRs. The location request responses should arrive at approximately the same time, and the timing of arrival will depend upon communication lag, processor speed, and other factors. The location request response includes a directory number (DN). 
   Wireless communication system determines ( 207 ) if the mobile station is in the responding HLR. If the DN in the location request response is unassigned, the wireless communication system knows that the mobile station is not currently located at the HLR that sent the location request response. If the mobile station is not at the HLR, wireless communication network  101  returns to step  205  to receive location request responses from the plurality of HLRs. If all HLRs respond with an unassigned DN, or if a timeout timer expires, an announcement will be played to the caller and the call attempt will be ended. If the mobile station is in the responding HLR, wireless communication system updates ( 209 ) an update table with information received from the responding HLR. 
   Wireless communication network  101  completes ( 211 ) the call to the mobile station in the responding HLR. 
     FIG. 3  depicts a flowchart  300  of a method for sending a location request to an updated HLR in accordance with an exemplary embodiment of the present invention. 
   Wireless communication network  101  receives ( 301 ) a location request for a mobile station. The location request, such as a call request, is a request to locate a mobile station. The location request can originate from a wireline or wireless communication network. 
   Wireless communication network  101  checks an update table, which is depicted in  FIG. 6 , and determines ( 303 ) if a record for the called mobile station includes an updated HLR. If so, wireless communication network  101  completes ( 313 ) the call by connecting the caller with the mobile station at the stored HLR. 
   If the backup HLR does not include an updated HLR for the called mobile station, wireless communication network  101  sends ( 305 ) a location request message to a plurality of HLRs. Wireless communication network  101  sends ( 203 ) the location request message goes from cellular gateway  107  through wireless communication network  101  via STP  109  to HLR 1   103  and HLR 2   105 . The process at this point is similar to that depicted in  FIG. 2 . 
   Wireless communication network  101  receives ( 307 ) a location request response from each of the plurality of HLRs. The location request responses should arrive at approximately the same time, and the timing of arrival will depend upon communication lag, processor speed, and other factors. The location request response includes a directory number (DN). 
   Wireless communication system determines ( 309 ) if the mobile station is in the responding HLR. If the DN in the location request response is unassigned, the wireless communication system knows that the mobile station is not currently located at the HLR that sent the location request response. If the mobile station is not at the HLR, wireless communication network  101  returns to step  307  to receive location request responses from the plurality of HLRs. If all HLRs respond with an unassigned DN, or if a timeout timer expires, an announcement will be played to the caller and the call attempt will be ended. If the mobile station is in the responding HLR, wireless communication system updates ( 311 ) an update table with information received from the responding HLR. 
   Wireless communication network  101  completes ( 313 ) the call to the mobile station in the responding HLR. 
     FIG. 4  depicts a flowchart  400  of a method for sending a location request to an HLR and updating a backup HLR in accordance with an exemplary embodiment of the present invention. 
   Wireless communication network  101  receives ( 401 ) a location request for a mobile station. The location request, such as a call request, is a request to locate a mobile station. The location request can originate from a wireline or wireless communication network. 
   Wireless communication network  101  sends ( 403 ) a location request to a primary HLR. The location request message goes from cellular gateway  107  through wireless communication network  101  via STP  109  to HLR 1   103 . 
   Wireless communication network  101  receives ( 405 ) a location request response from the primary HLR. 
   Wireless communication network  101  determines ( 407 ) if the mobile station is in the primary HLR. If the DN in the location request response is unassigned, the wireless communication system knows that the mobile station is not currently located at the primary HLR. If the mobile station is not at the primary HLR, wireless communication network  101  sends ( 411 ) a location request to a secondary HLR. Wireless communication network  101  receives ( 413 ) a location request response from the secondary HLR. Wireless communication network  101  determines ( 415 ) if the mobile station is in the secondary HLR, preferably by checking if the DN field is unassigned. If the mobile station is not at the secondary HLR, wireless communication network  101  plays ( 419 ) an announcement and disconnects the caller. 
   If the mobile station is in the primary HLR as determined at step  407  or in the secondary HLR as determined at step  415 , wireless communication network  101  updates ( 409 ) an update table with information received from the responding HLR. 
   Wireless communication network  101  completes ( 417 ) the call with the mobile station. 
     FIG. 5  depicts a table  500  of directory numbers  501  and associated primary HLR  503  and secondary HLR  505  in accordance with an exemplary embodiment of the present invention. 
   Directory number column  501  includes a plurality of entries for directory numbers. In the embodiment depicted in  FIG. 5 , directory number column  501  includes four rows,  507 ,  509 ,  511 , and  513 . Each row include an entry for directory number, the primary HLR, and the secondary HLR. 
   As depicted in  FIG. 5 , row  507  includes a directory number of (630) 555-1111. The primary HLR for the mobile station associated with this directory number is HLR 2 , which is a GSM HLR. The second HLR for this mobile station is HLR 1 , which is an ANSI-41 HLR. 
   When sending a message to multiple HLRs, as shown in the embodiments depicted in  FIGS. 2 and 3 , the multiple HLRs will be those stored in table  500 . 
     FIG. 6  depicts an update table  600  of directory numbers and associated updated HLR in accordance with an exemplary embodiment of the present invention. Table  600  includes directory number column  601  and updated HLR column  603 . 
   Directory number column  601  includes a plurality of entries for directory numbers. In the embodiment depicted in  FIG. 6 , table  600  includes four rows,  607 ,  609 ,  611 , and  613 . Each row include an entry for directory number and an entry for the updated HLR. 
   As depicted in  FIG. 6 , row  607  includes a directory number of (630) 555-1111. The updated HLR for the mobile station associated with this directory number is HLR 1 , which is an ANSI-41 HLR. Rows  609  and  613  include an updated HLR value of NULL, which indicates that the associated directory numbers do not have an updated HLR value currently associated with them. 
   The present invention thereby provides a method optimizing home location register (HLR) queries in a wireless communication system. By performing simultaneous HLR queries, system response time is improved. By storing an updated HLR for a mobile station, further response time improvements are achieved. Further, the present invention allows the storing of an updated HLR, thereby eliminating the need to send multiple query messages, thereby decreasing system traffic and conserving bandwidth. 
   The present invention thereby provides a method that allows a service provider to move subscriber records from one HLR to another that utilizes a different protocol. By storing the updated HLR, the sending of multiple simultaneous queries is no longer necessary. This saves on system resources and minimizes traffic in the wireless communication system. 
   While this invention has been described in terms of certain examples thereof, it is not intended that it be limited to the above description, but rather only to the extent set forth in the claims that follow.
When a subscriber record is moved from a first HLR to a second HLR that utilizes a different protocol, the wireless communication system sends two queries for location information for the mobile station, one to the first HLR and one to the second HLR, simultaneously. Two responses are received, one from each of the HLRs. The valid response is recorded in a separate table for future use. The invalid response is discarded. The next time a call comes in for the mobile station, the table is traversed to determine if the HLR has been updated for the mobile station. If so, the location request is sent only to the system in the table. If the table does not include information for the called mobile station, simultaneous queries are sent to the first and second HLRs.