Patent Publication Number: US-2016234747-A1

Title: Mobile device and method for handling neighbor cell measurement

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mobile device attached to a mobile network. More particularly, the present invention relates to a mobile device and a method for handling neighbor cell measurement. 
     2. Description of the Related Art 
     According to the standard specifications defined by The 3rd Generation Partnership Project (3GPP), a mobile device should perform a cell change decision to determine whether to change the serving cell to make sure the mobile device always camps on the cell with the best signal quality to maintain good quality for the services subscribed by the user, such as mobile telephone service and mobile network service. The cell change decision includes neighbor cell measurement, cell evaluation, cell ranking, and cell reselection. 
     The cell change decision must be performed periodically or in response to a trigger event when the mobile device is in service. However, the performing of the cell change decision, especially the neighbor cell measurement, significantly consumes power, which is a limited resource in mobile devices. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a mobile device and a method for handling neighbor cell measurement. The mobile device and the method can selectively perform neighbor cell measurement based on the signal quality of the serving cell and the movement of the mobile device to provide the benefit of power saving. 
     According to an embodiment of the present invention, a mobile device is provided. The mobile device includes a transceiver and a processor. The transceiver receives wireless signals of a plurality of cells of a mobile network. The cells include a serving cell and at least a neighbor cell. The processor is coupled to the transceiver. The processor performs neighbor cell measurement periodically or in response to a trigger event based on the wireless signal of the neighbor cell. The processor suspends the neighbor cell measurement when the serving cell is not changed for a period of time and a first signal quality of the serving cell is equal to or higher than a first threshold. 
     According to another embodiment of the present invention, a method for handling neighbor cell measurement is provided. The method is executed by a mobile device having a serving cell in a mobile network, and includes the following steps: performing neighbor cell measurement periodically or in response to a trigger event; and suspending the neighbor cell measurement when the serving cell is not changed for a period of time and a first signal quality of the serving cell is equal to or higher than a first threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram showing a mobile device and a mobile network according to an embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing a mobile device according to an embodiment of the present invention. 
         FIG. 3  is a flow chart showing a method for handling neighbor cell measurement according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 1  is a schematic diagram showing a mobile device  110  and a mobile network  120  according to an embodiment of the present invention. The mobile network  120  may be any cellular network based on the standard specifications defined by 3GPP, such as a Global System for Mobile Communications (GSM) network, a General Packet Radio Service (GPRS) network, a Universal Mobile Telecommunications system (UMTS) network or a Long Term Evolution (LTE)/LTE-Advanced network, etc. The mobile device  110  may be any portable electronic device capable of attaching to a mobile network, such as a cell phone or a smartphone. The mobile network  120  includes a plurality of cells, such as the cells  130 ,  140  and  150 . From the point of view of the mobile device  110 , the cell  130  is the serving cell which the mobile device  110  camps on, while the cells  140  and  150  are neighbor cells. Although  FIG. 1  shows two neighbor cells, the number of neighbor cells is not limited in the present invention. 
       FIG. 2  is a schematic diagram showing the mobile device  110  according to an embodiment of the present invention. The mobile device  110  includes a transceiver  210  and a processor  220 . The processor  220  is coupled to the transceiver  210 . The transceiver  210  can transmit wireless signals to the mobile network  120  and receive wireless signals from the mobile network  120 , so that the processor  220  can communicate with the mobile network  120  through the transceiver  210 . The processor  220  may execute the method for handling neighbor cell measurement shown in  FIG. 3 , which suspends and resumes the neighbor cell measurement adaptively according to the signal quality of the serving cell and the movement of the mobile device  110  to reduce power consumption of the mobile device  110 . In the following discussions, the signal quality of a cell may include the signal strength of the same cell. The processor  220  performs serving/neighbor cell measurement based on the wireless signal of the serving/neighbor cell of the mobile network  120  received by the transceiver  210 . 
       FIG. 3  is a flow chart showing a method for handling neighbor cell measurement according to an embodiment of the present invention. The method shown in  FIG. 3  may be executed by the processor  220  of the mobile device  110 . In step  305 , the processor  220  starts a timer. The processor  220  monitors the signal quality of the serving cell (such as the serving cell  130  in  FIG. 1 ) in a period of time. The length of the period of time can be predetermined or dynamically adjusted. The processor  220  measures the period of time with the timer. The timer may be a hardware counter or a software counter. 
     In step  310 , the processor  220  checks whether the timer reaches a timer value S or not. The timer reaching the value S means the end of the period of time mentioned above. When the timer does not reach the value S yet, the flow proceeds to step  345 . In step  345 , the processor  220  checks whether the serving cell is changed or not. When the serving cell is changed, the processor  220  resets the timer in step  350 , and then the flow proceeds to step  360 . When the serving cell is not changed, the flow proceeds directly to step  360 . The resetting of the timer in step  350  means resetting the timer to the initial value used by the processor  220  to start the timer in step  305 . 
     In step  360 , the processor  220  performs the neighbor cell measurement based on the wireless signals of the neighbor cell(s) received by the transceiver  210 , and then the flow returns to step  310 . The results of the neighbor cell measurement can be used by the processor  220  to determine whether there is another cell with signal quality better than that of the serving cell and whether to change the serving cell to the better cell or not, i.e. the cell change decision. As mentioned above, the whole process of cell change decision includes neighbor cell measurement, cell evaluation, cell ranking, and cell reselection, which are well defined in the specifications of 3GPP and thus the details thereof will not be described here. 
     When the result of the checking in step  310  is that the timer reaches the value S, the flow proceeds to step  315 . In step  315 , the processor  220  checks whether or not a signal quality Q 1  of the serving cell is equal to or higher than a predetermined threshold T S . In one embodiment, the signal quality Q 1  is the average signal quality of the serving cell in the period of time counted by the timer. The processor  220  may obtain the signal quality Q 1  of the serving cell from performing serving cell measurement. The details of the serving cell measurement are already discussed in the standard specifications of 3GPP. Therefore, those details are not repeated here. 
     When the signal quality Q 1  of the serving cell is lower than the predetermined threshold T S , the flow proceeds to step  350 . When the signal quality Q 1  of the serving cell is equal to or higher than the predetermined threshold T S , the processor  220  stops the timer in step  320 . Next, in step  325 , the processor  220  suspends the neighbor cell measurement performed in step  360 . The meaning of step  325  is that there is no need to change the serving cell when the signal quality of the serving cell is stable and good enough to maintain the quality of services subscribed by the user. In other words, the neighbor cell measurement may be suspended to save power when the signal quality of the serving cell is stable and good enough. 
     Next, in step  330 , the processor  220  performs serving cell measurement based on the wireless signals of the serving cell received by the transceiver  210  to obtain the current signal quality Q 2  of the serving cell. 
     In step  335 , the processor  220  checks whether the mobile device  110  is moving or not. In one embodiment, the processor  220  may detect the movement of the mobile device  110  through conventional sensors such as gyro-sensor, accelerometer and magnetometer. When the mobile device  110  is not moving, the flow proceeds to step  340 . Otherwise, the flow proceeds to step  365 . In one embodiment, when the detected moving speed is zero or below a predetermined value, the mobile device  110  is considered as not moving. In step  340 , the processor  220  checks whether the signal quality Q 2  of the serving cell is lower than a threshold T 1 . When Q 2  is lower than T 1 , the processor  220  restarts the timer in step  370  and then the flow returns to step  310 . The restarting of the timer in step  370  means restarting the timer with the initial value used by the processor  220  to start the timer in step  305 . When Q 2  is not lower than T 1 , the flow returns to step  330 . In step  365 , the processor  220  checks whether the signal quality Q 2  of the serving cell is lower than another threshold T 2 . When Q 2  is lower than T 2 , the processor  220  restarts the timer in step  370  and then the flow returns to step  310 . When Q 2  is not lower than T 2 , the flow returns to step  330 . 
     The meaning of steps  335 ,  340 ,  365  and  370  is that the neighbor cell measurement should be resumed when the signal quality of the serving cell is too low, so that the serving cell may be changed to another cell with better signal quality. Since the tolerance of the mobile device  110  to low signal quality of the serving cell is lower when the mobile device  110  is moving, the threshold used when the mobile device  110  is moving should be higher. Therefore, the processor  220  assigns different values to the thresholds T 1  and T 2 , respectively. The value of the threshold T 1  is lower than the value of the threshold T 2 . 
     In one embodiment, the steps  335 ,  340  and  365  in  FIG. 3  can be replaced by resuming the neighbor cell measurement when the signal quality Q 2  is lower than a threshold T 3 , where the threshold T 3  is dynamically adjusted according to a moving speed of the mobile device  110 . More specifically, the processor  220  detects the moving speed of the mobile device  110 , and determines a value as the threshold T 3  based on the detected moving speed. For example, the higher the detected moving speed is, the larger the value of the threshold T 3  is assigned. Then, the processor  220  determines whether the signal quality Q 2  is lower than the threshold T 3 . If yes, the flow proceeds to step  370 ; otherwise, the flow goes back to step  330 . 
     In summary, the present invention provides a mobile device and a method that adaptively suspend and resume the cell change decision according to the signal quality of the serving cell and the movement of the mobile device to reduce power consumption of the mobile device. By the present invention, the mobile device can still get good subscribed service without constantly performing cell change decision, and further save power because of the suspended cell change decision. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.