Abstract:
A network searching method for a multi-mode user equipment having a first radio access technology module and a second radio access technology module includes camping on a current cell by the user equipment via the first radio access technology module; obtaining information broadcast by a system of the second radio access technology module via the first radio access technology module when network environment corresponding to the first radio access technology module changes; and instructing the second radio access technology module to perform a network searching.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority of China Patent Application No. 201110258390.9, filed on Sep. 2, 2011, and China Patent Application No. 201210242227.8, filed on Jul. 12, 2012, the entirety of which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a multi-mode dual-standby single-USIM card terminal, and more particularly to a network searching method and apparatus for a multi-mode user equipment. 
         [0004]    2. Description of the Related Art 
         [0005]    The Long Term Evolution (LTE) multi-mode dual-standby single Universal Subscriber Identity Module (USIM) card terminal is a novel mobile terminal When compared with the conventional multi-mode single-standby single-USIM card terminal, the former can access both LTE and 2G (or 3G) radio networks at the same time by using only one USIM card while the later can only access an LTE or 2G (or 3G) radio network at the same time by using one USIM card. 
         [0006]    The LTE multi-mode dual-standby single-USIM card terminal (hereinafter called the terminal for brevity) has four main advantages, including: 1) high speech service quality because the speech traffic is carried on 2G or 3G carrier(s), 2) high flexibility because the packet switch (PS) traffic can be switched between 2G (or 3G) and LTE radio networks according to the current network condition, 3) less effort on configuration and network optimization for operators and 4) stronger roaming ability because the LTE and 2G (or 3G) network can register at different Public Land Mobile Networks (PLMN). 
         [0007]    Because the multi-mode multi-connected User Equipment (UE) has multiple Radio access Technology (RAT) modules (RAT Modem), the multi-mode multi-connected UE can support the standby or connection state of multiple RAT Modems (such as GSM, WCDMA, TD-SCDMA, CDMA2000, LTE, WiMax, WiFi, or others). Therefore, information sharing between multiple RAT modules (such as Modem) has become important and meaningful. 
         [0008]    The mechanism for searching a service network under a 3G CELL_DCH (or 2G DEDICATED) mode for a terminal is: when the terminal moves from an area without LTE coverage to an area with LTE coverage, the PS traffic could be carried on the LTE carrier(s); and when the terminal moves from an area with LTE coverage to an area without LTE coverage, the PS traffic could be carried on the 2G (or 3G) carrier(s). 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    An exemplary embodiment of the invention provides a network searching method for a multi-mode user equipment (UE) comprising a first radio access technology (RAT) module and a second RAT module. The network searching method comprises: camping on a current cell via the first RAT module of the UE; obtaining information broadcast about a system of the second RAT module via the first RAT module when network environment corresponding to the first RAT module changes; and determining whether to instruct the second RAT module to perform a network searching. 
         [0010]    Another exemplary embodiment of the invention provides a network searching method for a multi-mode single-card user equipment (UE) comprising a first radio access technology (RAT) module and a second RAT module. The network searching method comprises: setting an expiry time of a timer to a first length when the first RAT module camps on a current cell and the second RAT module is in a no-service state; enabling the timer; performing a network searching by the second RAT module after the timer expires. 
         [0011]    Another exemplary embodiment of the invention provides a multi-mode user equipment (UE). The multi-mode user equipment comprises a first radio access technology (RAT) module and a second RAT module coupled to the first RAT module. The UE camps on a current cell via the first RAT module and when network environment corresponding to the first RAT module changes, information broadcasted about a system of the second RAT module is obtained via the first RAT module and the second RAT module is determined whether to perform a network searching. 
         [0012]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0014]      FIG. 1A  shows a flow chart of a first method when the terminal is switched to a 3G cell according to an embodiment of the invention; 
           [0015]      FIG. 1B  shows a flow chart of a first method when the terminal is switched to a 2G cell according to an embodiment of the invention; 
           [0016]      FIG. 2A  and  FIG. 2B  show a flow chart of a second method according to an embodiment of the invention; and 
           [0017]      FIG. 3A  and  FIG. 3B  show a flow chart of a third method according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0019]    Some specific terms are used in the specification and claims to refer to specific elements. Those skilled in the art would readily appreciate that the electronic device manufactures can use different terms to name the same element. In the specification and claims, instead of their names, the corresponding functions are utilized to distinguish between different elements. The term “comprise” as referred in the specification and claims is an open term and should be interpreted as “comprise but not limited to”. In addition, the term “couple” refers to any direct or indirect electronic connection. Therefore, when saying a first device is coupled to a second device, the first device can be directly and electronically connected to the second device, or can be indirectly and electronically connected to the second device via other device(s) or connecting method(s). 
         [0020]    When a terminal is operated under a 3G cell Dedicated Channel (CELL_DCH) or a 2G dedicated channel (2G DEDICATED) mode and then is moved from an area without LTE coverage to an area with LTE coverage, the terminal is not aware of the appearance of the LTE coverage for the following two main reasons: 1) based on the current standard, the terminal does not listen to the broadcast System information block  19  (SIB  19 ) or the System Information Type  2  Quarter (SI 2  Quarter), in which information regarding LTE neighbor cell(s) is carried, when the terminal is operated under the 3G CELL_DCH or 2G DEDICATED mode, and 2) for the terminal developed according to a standard with a version lower than release 7 (REL7) (including the REL7), it is specified in the standards that the network will not notify the terminal of the appearance of the LTE neighbor cell in the Measurement Control or Measurement Information message when the terminal operates under the 3G CELL_DCH or 2G DEDICATED mode, because the terminal will inform the network that the LTE related procedure is not supported when the terminal reports the network support capability to the network. 
         [0021]    In view of the above problems, some solutions are provided in the specification. A location of the terminal operating under a connected mode, such as the 3G CELL_DCH or 2G DEDICATED mode, may change due to the movement of the UE, and the network environment may also changes with time. The above-mentioned two conditions reveals that a major change of the network environment of the terminal may occur, which means that the terminal may move from an area without LTE coverage to an area with LTE coverage. When the terminal has detected the above changes, the LTE module (for example, the LTE Modem) may be triggered or instructed to search for a service network as soon as possible so as to hand off the PS traffic to the LTE network. If the terminal has not detected the above changes, the LTE module may operates in a power saving mode. In this manner, both the power saving and fast LTE service recovery can be achieved. Based on the concept, three methods are provided. In method 1, no matter whether the terminal is switched to a 3G cell or a 2G cell, the LTE neighbor cell information carried in the obtained cell system information are provided to the LTE Modem for determining network environment change. In method 2, the terminal determines network environment change by determining a handover or neighbor cell change under 3G CELL_DCH or 2G DEDICATED mode. In method 3, the terminal uses the supplemental device, such as a Global Positioning System (GPS) module or an Assisted Global Positioning System (AGPS) module, to determine network environment change under a 3G CELL_DCH mode or a 2G DEDICATED mode. 
         [0022]      FIG. 1A  shows a flow chart of a first method when the terminal is switched to a 3G cell according to an embodiment of the invention. When the UE camps on a cell (Step  101 ) and cell handover occurs, for example, the UE is switched to a 3G cell (such as a TD-SCDMA cell) (Step  102 ), the UE receives the SIB  19  from the current cell (which the UE camps on) or a neighbor cell and determines whether the SIB  19  comprises the LTE neighbor cell information (Step  103 ). When the received SIB  19  comprises the LTE neighbor cell information, the LTE neighbor cell information in the SIB  19  is provided to the LTE module (such as the LTE Modem) (Step  104 ) to trigger and speed up the LTE network searching. Those skilled in the art would readily appreciate that network searching may also be referred to as finding a service network. 
         [0023]      FIG. 1B  shows a flow chart of method  1  when the terminal is switched to a 2G cell according to an embodiment of the invention. When the UE camps on a cell (Step  110 ) and cell handover occurs, for example, the UE is switched from a 3G cell to a 2G cell (Step  111 ), the UE may receive the SI 2  Quarter from the current cell which the UE camps on or a neighbor cell and determine whether the SI 2  Quarter comprises the LTE neighbor cell information (Step  112 ). When the received SI 2  Quarter comprises the LTE neighbor cell information, the LTE neighbor cell information in the SI 2  Quarter is provided to the LTE module, such as the LTE Modem (Step  113 ), to trigger and speed up the LTE network searching. 
         [0024]    According to an embodiment of the invention, a network searching apparatus performing the methods as shown in  FIG. 1A  and  FIG. 1B  may be implemented by an UE camping on a current cell, such as a 3G cell or a 2G cell, via a first RAT module. The UE may further detect network environment change via the first RAT module. The network environment change may be, for example, handover. When the network environment change has been detected, the first RAT module may obtain broadcast system information, such as the SIB  19  or SI 2  Quarter, from the current cell or a neighbor cell, and provide the obtained LTE neighbor cell information to the second RAT module (LTE module) so as to instruct the second RAT module (LTE module) to perform a network searching. 
         [0025]      FIG. 2A  and  FIG. 2B  show a flow chart of a second method according to an embodiment of the invention. Referring to  FIG. 2A  and  FIG. 2B , in step  201 , when the terminal operating under a 3G CELL_DCH (or 2G DEDICATED) mode moves to an area without LTE coverage, the LTE module is in a no-service state. At this time, an expiry time of a timer may be set as T=T 0 , a maximum of a timing number of the timer may be set to N and an initial value of the timing number of the timer may be set to 0 in step  215 . In step  202 , the timer for LTE network searching is enabled. Before the timer expires (the NO path for step  207 ), the terminal operates under a power saving mode (step  208 ) and the timer keeps counting. When the timer expires (the YES path for step  207 ), the timing number of the timer is increased by  1  and the LTE network searching may begin (step  209 ). If there is no LTE cell found in step  210  (the NO path for step  210 ), it is further determined that whether the timing number of the timer has exceeded the maximum timing number (step  216 ). When the timing number of the timer has not exceeded the maximum timing number (the NO path for step  216 ), the expiry time of the timer is increased in step  217  (for example, T=T 0 +t 0 , t 0 &gt;0) and the timer for LTE network searching is enabled again in step  202 . On the other hand, when the timing number of the timer has exceeded the maximum timing number (the Yes path for step  216 ), the timer for LTE network searching is disabled (step  212 ). In the above process, when there is any LTE cell found in step  210 , the Non-Access Stratum (NAS) of the terminal may be notified of the LTE coverage information (step  211 ) and the NAS may further determine whether to register at the LTE network. If the handover occurs when the terminal operates under the 3G CELL_DCH (or 2G DEDICATED) mode (the Yes path for step  203 ), the maximum of a timing number of the timer is set to M and the expiry time of the timer for LTE network searching is decreased (for example, T=T−t 1 ,t 1 &gt;0) and the timer for LTE network searching is enabled again in step  202 . If the handover does not occur (the No path for step  203 ), the expiry time of the timer for LTE network searching remains unchanged (step  213 ). If the terminal detects that neighbor cell changes under the 3G CELL_DCH (or 2G DEDICATED) mode (the Yes path for step  206 ), the maximum of the timing number of the timer is set to M and the expiry time of the timer for LTE network searching is decreased (for example, T=T−t 2 ,t 2 &gt;0) and the timer for LTE network searching is enabled again in step  202 . If the terminal does not detect that neighbor cell changes under the 3G CELL_DCH (or 2G DEDICATED) mode (the No path for step  206 ), the expiry time of the timer for LTE network searching remains unchanged (step  214 ). 
         [0026]      FIG. 3A  and  FIG. 3B  show a flow chart of a third method according to an embodiment of the invention. Referring to  FIG. 3A  and  FIG. 3B , in step  301 , when the terminal operating under a 3G CELL_DCH (or 2G DEDICATED) mode moves to an area without LTE coverage, the LTE module is in a no-service state. At this time, in step  302 , an expiry time of a timer may be set as T=T 0 , a maximum of a timing number of the timer may be set to N and an initial value of the timing number of the timer may be set to 0. In addition, the GPS/AGPS module is enabled for recording the coordinate of terminal&#39;s current location (x 0 , y 0 ) in step  311 . After setting the maximum timing number and the expiry time, the timer for LTE network searching is enabled in step  303 . Before the timer expires (the NO path for step  304 ), the terminal operates under a power saving mode (step  306 ) and the timer keeps counting. When the timer expires (the YES path for step  304 ), the timing number of the timer is increased by 1 (step  316 ) and the LTE network searching may begin (step  305 ). If there is no LTE cell found in step  307  (the NO path for step  307 ), it is further determined that whether the timing number of the timer has exceeded the maximum timing number (step  309 ). When the timing number of the timer has not exceeded the maximum timing number (the NO path for step  309 ), the expiry time of the timer is increased in step  315  (for example, T=T 0 +t 0 , t 0 &gt;0) and the timer for LTE network searching is enabled again in step  303 . On the other hand, when the timing number of the timer has exceeded the maximum timing number (the Yes path for step  309 ), the timer for LTE network searching is disabled (step  310 ). When there is any LTE cell found in step  307 , the Non-Access Stratum (NAS) of the terminal may be notified of the LTE coverage information (step  308 ) and the NAS may further determine whether to register at the LTE network. In the above process, after enabling the GPS/AGPS module and recording the coordinate of terminal&#39;s current location (x 0 , y 0 ), when the terminal moves to another location (x 1 ,y 1 ) and it is satisfied that (x 0 −x 1 ) 2 +(y 0 −y 1 ) 2 &gt;=L (the Yes path for step  312 ), the maximum of the timing number of the timer is set to M and the expiry time of the timer for LTE network searching is decreased (for example, T=T−t 2 ,t 2 &gt;0) (step  313 ) and the timer for LTE network searching is enabled again (step  303 ). When the terminal moves to the location (x 1 ,y 1 ) and (x 0 −x 1 ) 2 +(y 0 −y 1 ) 2 &lt;L (the No path for step  312 ), the expiry time of the time for LTE network searching remains unchanged (step  314 ). 
         [0027]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited to LTE terminals. The invention can further be implemented in other 3G terminals, such as WCDMA, TD-SCDMA, CDMA2000, LTE, WiMAX, WiFi and so on. Those who are skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this invention. Therefore, the scope of the present invention shall be defined and protected by the following claims and their equivalents.