Patent Publication Number: US-2015065131-A1

Title: Method of performing location registration procedures and communication system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application No. 61/872,771 filed on Sep. 2, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a method of performing location registration procedures and related communication system, and more particularly, to a method of improving the success rate of performing location registration procedures and related communication system. 
     2. Description of the Prior Art 
     In a typical mobile communications environment, a user equipment (UE) may communicate voice and/or data signals with one or more service networks. The wireless communications between the UE and the service networks maybe in compliance with various wireless technologies, such as the Global System for Mobile communications (GSM) technology, Universal Mobile Telecommunications System (UMTS) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, Code Division Multiple Access 2000 (CDMA 2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, and others. 
     In general, a UE is configured to camp on a cellular station with best reception, and perform a location registration procedure via the cellular station to register itself to the service network to which the cellular station belongs.  FIG. 1  is a flowchart illustrating a prior art method of performing location registration procedures in an LTE system and includes the following steps: 
     Step  110 : start. 
     Step  120 : the UE resets a first timer and a second timer; execute step  130 . 
     Step  130 : the UE starts the first timer and sends a radio resource control (RRC) connection request to a target cellular station within the network; execute step  140 . 
     Step  140 : determine if the UE receives a response message from the target cellular station; if yes, execute step  180 ; if no, execute step  150 . 
     Step  150 : determine if the first timer has expired; if yes, execute step  160 ; if no, execute step  140 . 
     Step  160 : the UE starts the second timer; execute step  170 . 
     Step  170 : determine if the second timer has expired; if yes, execute step  120 ; if no, execute step  170 . 
     Step  180 : the UE performs other existing steps for registering itself on the network. 
     In the prior art method depicted in  FIG. 1 , after sending the RRC connection request but no response from the network during a predetermined period of time (controlled by the first timer) in steps  130 - 170 , the UE is configured to wait for a predetermined period of time (controlled by the second timer) and then restart the location registration procedure by sending the RRC connection request again to the target cellular station of the network. In other words, the UE is configured to re-establish RRC connection with the same cellular station of the network over and over again until a network response can be received. 
       FIG. 2  is a flowchart illustrating another prior art method of performing location registration procedures in a UMTS system and includes the following steps: 
     Step  510 : start. 
     Step  520 : the UE resets a first timer, a second timer and a counter; execute step  530 . 
     Step  530 : the UE starts the first timer; execute step  540 . 
     Step  540 : the UE sends an RRC connection request to a target cellular station within the network and increases the counter by 1; execute step  550 . 
     Step  550 : determine if the UE receives a response message from the target cellular station; if yes, execute step  600 ; if no, execute step  560 . 
     Step  560 : determine if the counter exceeds a predetermined value; if yes, execute step  580 ; if no, execute step  570 . 
     Step  570 : determine if the first timer has expired; if yes, execute step  530 ; if no, execute step  570 . 
     Step  580 : the UE starts the second timer; execute step  590 . 
     Step  590 : determine if the second timer has expired; if yes, execute step  520 ; if no, execute step  590 . 
     Step  600 : the UE performs other existing steps for registering itself on the network. 
     In the prior art method depicted in  FIG. 2 , after periodically (controlled by the first timer) sending the RRC connection request N times (determined by the counter) but no response from the network in steps  530 - 570 , the UE is configured to wait for a predetermined period of time (controlled by the second timer) and then restart the location registration procedure by periodically sending the RRC connection request for another N times to the target cellular station of the network. In other words, the UE is configured to re-establish RRC connection with the same cellular station of the network over and over again until a network response can be received. 
     However, if the user of the UE is attending a football game, a live concert, firework celebrations, or other events which involve many participants, a cellular station may receive many RRC connection requests from different UEs during the same period, thereby too busy to respond each UE immediately. Since such events normally last for a period of time, the cellular station to which the UE repeatedly sends RRC connection requests may remain busy and cause the location registration procedure to fail for a while. As a result, there is a need for a method of improving the success rate when performing location registration procedures in order to guarantee real-time user experience. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of performing a location registration procedure. The method includes a user equipment acquiring a candidate list by scanning multiple cellular stations within a network; the user equipment selecting a first cellular station from the candidate list as a target cellular station; the user equipment sending a first RRC connection request to the target cellular station; if the user equipment does not receive a response message from the target cellular station when a first predetermined period has elapsed after sending the RRC connection request, the user equipment moving the first cellular station from the candidate list to a standby list; the user equipment selecting a second cellular station from the candidate list as the target cellular station; and the user equipment sending a second RRC connection request to the target cellular station. 
     The present invention also provides a method of performing a location registration procedure. The method includes a user equipment selecting a first cellular station within a network and not included in a standby list as a target cellular station; the user equipment sending a first RRC connection request to the target cellular station; if the user equipment does not receive a response message from the target cellular station when a first predetermined period has elapsed after sending the RRC connection request, the user equipment adding the first cellular station to the standby list; the user equipment selecting a second cellular station within the network and not included in the standby list as the target cellular station; and the user equipment sending a second RRC connection request to the target cellular station. 
     The present invention also provides a communication system for performing a location registration procedure. The communication system includes a network having multiple cellular stations; and a user equipment including a network connectivity unit configured to send RRC connection requests to the network or receive response messages from the network; a scanning unit configured to scan the network for acquiring the multiple cellular stations; a memory unit for storing a standby list; and a processing component configured to select a first cellular station among the multiple cellular stations as a target cellular station; instruct the network connectivity unit to send a first RRC connection request to the target cellular station; add the first cellular station to the standby list if the network connectivity unit does not receive a response message from the target cellular station when a predetermined period has elapsed after sending the RRC connection request, select a second cellular station among the multiple cellular stations as the target cellular station; and instruct the network connectivity unit to send a second RRC connection request to the target cellular station. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart illustrating a prior art method of performing location registration procedures in an LTE system. 
         FIG. 2  is a flowchart illustrating a prior art method of performing location registration procedures in a UMTS system. 
         FIGS. 3 and 4  are flowcharts illustrating methods of performing location registration procedures according to embodiments of the present invention. 
         FIG. 5  is a functional diagram illustrating an embodiment of a user equipment configured to carry out the present method illustrated in  FIG. 3  or  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 3  is a flowchart illustrating a method of performing location registration procedures according to a first embodiment of the present invention. The flowchart in  FIG. 3  includes the following steps: 
     Step  210 : start. 
     Step  220 : the UE selects a cellular station from a candidate list as a target cellular station; execute step  230 . 
     Step  230 : the UE sends an RRC connection request to the target cellular station and starts a first timer; execute step  240 . 
     Step  240 : determine if the UE receives a response message from the target cellular station; if yes, execute step  270 ; if no, execute step  250 . 
     Step  250 : determine if the first timer has expired; if yes, execute step  260 ; if no, execute step  240 . 
     Step  260 : the UE moves the current cellular station selected as the target cellular station from the candidate list to a standby list; execute step  270 . 
     Step  270 : determine if a specific cellular station in the standby list has satisfied a predetermined condition; if yes, execute step  280 ; if no, execute step  220 . 
     Step  280 : the UE moves the specific cellular station from the standby list to the candidate list; execute step  220 . 
     Step  290 : the UE performs other existing steps for registering itself on the network. 
     Before transferring any application data or completing any signaling procedures, the UE needs to make the transition from an RRC idle mode to an RRC connected mode. This RRC connection establishment procedure, as illustrated by steps  220 - 280  in  FIG. 3 , is always initiated by the UE, but can be triggered by either the UE or the network in step  210 . For example, the UE may trigger the RRC connection establishment procedure if the end-user starts an application to browse the Internet, or to send an email. Similarly, the UE may trigger the RRC connection establishment procedure if the UE moves into anew tracking/routing/location area and has to complete the tracking/routing/location area update signaling procedure. The network may trigger the RRC connection establishment procedure by sending a paging message which allows the delivery of an incoming short message service (SMS) or notification of an incoming voice call. 
     In step  220 , the UE may acquire the candidate list in any form by scanning multiple cellular stations within the network. In an embodiment, the cellular station selected as the target cellular station in step  220  may be the one having the best signal quality among multiple cellular stations in the candidate list. The UE may update the candidate list and the corresponding standby list in step  260  or  280 , which will be explained in subsequent paragraphs. 
     In step  230 , the UE is configured to send the RRC connection request to the target cellular station and starts the first timer. The expiry period of the first timer may be determined by the parameter T300 defined in related 3rd Generation Partnership Project (3GPP) technical specifications, such as TS 25.331, TS 24.008, TS 36.331 or TS 24.301. The setting of the parameter T300 determines how long the UE waits for the network response after sending the RRC connection request and can be set to one of the following values: 400, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000, 3000, 4000, 6000, 8000 ms. 
     If it is determined in steps  220 - 250  that the RRC establishment procedure fails when the first timer expires before receiving a corresponding response message from the target cellular station, the UE is configured to move the current cellular station selected as the target cellular station from the candidate list to the standby list in step  260 . A cellular station included in the standby list indicates that a prior attempt to establish RRC connection between this cellular station and the UE has failed recently. Under such circumstance, an immediate attempt to establish another RRC connection between this cellular station and the UE may very likely be unsuccessful. 
     If it is determined in step  270  that the specific cellular station in the standby list has satisfied the predetermined condition, the UE is then configured to move the specific cellular station from the standby list to the candidate list in step  280 . 
     In one embodiment, the predetermined condition may be determined by a second timer. More specifically, the UE may further start the second timer when adding the specific cellular station to the standby list, and the predetermined condition is satisfied when the second timer has expired. 
     In another embodiment, the predetermined condition may be determined by a counter. More specifically, the UE may further activate the counter for recording how many times any cellular station in the candidate list has been selected after adding the specific cellular station to the standby list, and the predetermined condition is satisfied when the value of the counter exceeds a predetermined limit. 
     After step  270  or  280 , the present method loops back to step  220  for attempting to establish an RRC connection between another cellular station in the candidate list and the network. If the UE can receive a response message from the current target cellular station in step  240 , step  290  is then executed so that the UE may perform other existing steps defined in related 3GPP specifications (such as TS 25.331, TS 24.008, TS 36.331 or TS 24.301) for registering itself on the network. If the UE still fails to receive any response message from the current target cellular station in step  240 , all available cellular stations in the candidate list maybe sequentially selected until the RRC connection establishment procedure is successful. Therefore, the method according to the first embodiment of the present invention can improve the success rate of location registration procedures when certain cells within the network are busy. 
       FIG. 4  is a flowchart illustrating a method of performing location registration procedures according to a second embodiment of the present invention. The flowchart in  FIG. 4  includes the following steps: 
     Step  310 : start. 
     Step  320 : the UE selects a cellular station within the network and not included in a standby list as a target cellular station; execute step  330 . 
     Step  330 : the UE sends an RRC connection request to the target cellular station and starts a first timer; execute step  340 . 
     Step  340 : determine if the UE receives a response message from the target cellular station; if yes, execute step  390 ; if no, execute step  350 . 
     Step  350 : determine if the first timer has expired; if yes, execute step  360 ; if no, execute step  340 . 
     Step  360 : the UE moves the current cellular station selected as the target cellular station to the standby list; execute step  370 . 
     Step  370 : determine if a specific cellular station in the standby list has satisfied a predetermined condition; if yes, execute step  380 ; if no, execute step  320 . 
     Step  380 : the UE deletes the specific cellular station from the standby list; execute step  320 . 
     Step  390 : the UE performs other existing steps for registering itself on the network. 
     In the flowchart illustrated in  FIG. 4 , steps  310 ,  330 - 350 ,  370  and  390  may be execute in the same manner as the corresponding steps  210 ,  230 - 250 ,  270  and  290  in the flowchart illustrated in  FIG. 3 . However, the second embodiment of the present invention differs from the first embodiment of the present invention in the method of selecting the target cellular station (steps  320 ,  360  and  380 ). 
     According to the first embodiment of the present invention, the UE may acquire the candidate list in any form by scanning multiple cellular stations within the network in step  220 , and then update the candidate list and the corresponding standby list in step  260  or  280 . According to the second embodiment of the present invention, the UE may perform real-time scan on the network and verify if a scanned cellular station is included in the standby list in step  320 , and then update the standby list in step  360  or  380 . Therefore, the method according to the second embodiment of the present invention can also improve the success rate of location registration procedures when certain cells within the network are busy. 
     In the present invention, the UE may include transportable electronic devices, such as mobile telephones, personal digital assistants, handheld, tablet, nettop, or laptop computers, or other devices with similar telecommunication capabilities.  FIG. 5  is a functional diagram illustrating an embodiment of a UE  400  configured to carry out the present method illustrated in  FIG. 3  or  FIG. 4 . The UE  400  includes a network connectivity unit  410 , a scanning unit  420 , random access memory (RAM)  430 , read only memory (ROM)  440 , a storage device  450 , a processing component  460 , and a digital signal processor (DSP)  470 . These components might communicate with one another via a bus  480 . In some cases, some of these components may not be present or may be combined in various combinations with one another or with other components not shown. These components might be located in a single physical entity or in more than one physical entity. Any actions described herein as being taken by the processing component  460  may be taken by the processing component  460  alone or by the processing component  460  in conjunction with one or more components shown or not shown in the drawing, such as with the DSP  470 . Although the DSP  470  is shown as a separate component, the DSP  470  might be incorporated into the processing component  460 . 
     The network connectivity unit  410  may include one or multiple modems, modem banks, Ethernet devices, universal serial bus (USB) interface devices, serial interfaces, token ring devices, fiber distributed data interface (FDDI) devices, wireless local area network (WLAN) devices, radio transceiver devices such as code division multiple access (CDMA) devices, GSM/UMTS/LTE radio transceiver devices, worldwide interoperability for microwave access (WiMAX) devices, and/or other well-known devices for connecting to other network entities. The network connectivity unit  410  allows the processing component  460  to communicate with the Internet or one or more telecommunications networks (not shown) for sending the RRC connection request or receiving network response messages. 
     The scanning unit  420  is configured to scan all available cellular stations within the network and select one of the scanned cellular stations as the target cellular station according to the candidate list or the standby list in step  220  or  320 . 
     The RAM  430  may be used to store volatile data and instructions that are executed by the processing component  460 . The ROM  440  may be used to store instructions and data that are read during execution of the instructions. The storage device  450  may include various disk-based systems such as hard disk, floppy disk, or optical disk and may be used to store programs that are loaded into the RAM  430  when such programs are selected for execution. Access to both the RAM  430  and the ROM  440  is typically faster than access to the storage device  450 , but the storage device  250  can provide larger memory capacity. In the present invention, the candidate list, the standby list and the settings of N and the first timer may be stored in the available memory space of the RAM  430 , ROM  440  and/or the storage device  450 . 
     The processing component  460  is configured to execute instructions, codes, computer programs, or scripts which may be accessed from the network connectivity units  420 , RAM  430 , ROM  440 , or the storage device  450 , such as performing steps  230 - 280  or  330 - 380 . The processing component  460  may include one or multiple processors CPU 1 ˜CPUn for executing the present method simultaneously, serially, or otherwise by one processor. 
     In present application, when an attempt to establish an RRC connection between a first cellular station within the network and the UE fails, the UE is configured to perform another RRC connection establishment procedure on a second cellular station within the network. When a first RRC connection establishment procedure fails due to no response from a specific cellular station within the network, the specific cellular station is excluded in subsequent RRC connection attempts for a predetermined period or after a predetermined number of another RRC connection attempts have been made. Therefore, when certain cells within the network are busy, the present invention can improve the success rate of location registration procedures by requesting RRC connection with other available and less busy cells within the network. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.