Abstract:
A first base station (BS) for handling a handover with a second BS comprises a storage unit for storing instructions and a processing circuit coupled to the storage unit. The processing circuit is configured to execute the instructions stored in the storage unit. The instructions comprise determining to hand over a first communication device to the second BS; generating a first handover request message, wherein the first handover request message comprises one of first system information and second system information according to whether the first communication device is in coverage enhancement (CE) or according to a type of the first communication device; transmitting the first handover request message to the second BS; receiving a first handover request acknowledgement message from the second BS; and transmitting a first handover command to the first communication device in response to the reception of the first handover request acknowledgement message.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/316,585 filed on Apr. 1, 2016, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0002]    The present invention relates to a device and a method used in a wireless communication system, and more particularly, to a device and a method of handling a handover. 
       2. Description of the Prior Art 
       [0003]    A long-term evolution (LTE) system provides high data rate, low latency, packet optimization, and improved system capacity and improved coverage. The LTE system is evolved continuously to increase peak data rate and throughput by using advanced techniques, such as carrier aggregation (CA), dual connectivity, licensed-assisted access, etc. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes at least one evolved Node-B (eNB) for communicating with at least one user equipment (UE), and for communicating with a core network. The core network may include a mobility management and a Quality of Service (QoS) control of the at least one UE. 
         [0004]    A UE is connected to a first eNB in coverage enhancement (CE) via a cell of the first eNB. It is not clear how the first eNB can initiate a handover to hand over the UE in from the first eNB to a second eNB. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention therefore provides a communication device and method for handling a handover to solve the abovementioned problem. 
         [0006]    A first base station (BS) for handling a handover with a second BS comprises a storage unit for storing instructions and a processing circuit coupled to the storage unit. The processing circuit is configured to execute the instructions stored in the storage unit. The instructions comprise connecting to a first communication device; determining to hand over the first communication device to the second BS; generating a first handover request message in response to the determination, wherein the first handover request message comprises one of first system information and second system information according to whether the first communication device is in coverage enhancement (CE) or according to a type of the first communication device; transmitting the first handover request message to the second BS; receiving a first handover request acknowledgement message in response to the first handover request message from the second BS; and transmitting a first handover command to the first communication device in response to the reception of the first handover request acknowledgement message. 
         [0007]    A second base station (BS) for handling a handover with a first BS comprises a storage unit for storing instructions and a processing circuit coupled to the storage unit. The processing circuit is configured to execute the instructions stored in the storage unit. The instructions comprise connecting to the first BS; receiving a handover request message for a first communication device from the first BS; generating a handover request acknowledgement message in response to the handover request message; generating a first configuration according to first system information and transmitting the handover request acknowledgement message comprising the first configuration to the first BS, if the handover request message comprises the first system information and the first communication device is in coverage enhancement (CE) or a type of the first communication device is a first type; and generating a second configuration according to second system information and transmitting the handover request acknowledgement message comprising the second configuration to the first BS, if the handover request message comprises the second system information and the first communication device is in not CE or the type of the first communication device is a second type. 
         [0008]    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 
         [0009]      FIG. 1  is a schematic diagram of a wireless communication system according to an example of the present invention. 
           [0010]      FIG. 2  is a schematic diagram of a communication device according to an example of the present invention. 
           [0011]      FIG. 3  is a flowchart of a process according to an example of the present invention. 
           [0012]      FIG. 4  is a flowchart of a process according to an example of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  is a schematic diagram of a wireless communication system  10  according to an example of the present invention. The wireless communication system  10  is briefly composed of a communication device  100 , base stations (BSs)  102  and  104 . In  FIG. 1 , the communication device  100 , the BS  102  and the BS  104  and are simply utilized for illustrating the structure of the wireless communication system  10 . Practically, the BS  102  and/or the BS  104  may be BSs in a narrowband (NB) internet of things (IoT) network or in an evolved Universal Terrestrial Radio Access Network (E-UTRAN). The BS  102  and/or the BS  104  may be fifth generation (5G) BSs (e.g., gNBs) in a 5G network. In  FIG. 1 , coverage areas of the BS  102  and the BS  104  may be overlapped or non-overlapped. In general, a BS may also be used to refer any of the eNB and the 5G BS. 
         [0014]    The communication device  100  may be a user equipment (UE), a mobile phone, a laptop, a tablet computer, an electronic book, a portable computer system, a vehicle, or an airplane. For uplink (UL), the communication device  100  is the transmitter and the BS  102  and/or the BS  104  is the receiver, and for downlink (DL), the BS  102  and/or the BS  104  is the transmitter and the communication device  100  is the receiver. 
         [0015]    The communication device  100  may be a bandwidth reduced low complexity (BL) communication device by which the maximum bandwidth for transmission and reception is operated is lower than a system bandwidth operated by the BS. For example, the BL communication device operates in any LTE system bandwidth (e.g., 3, 5, 10, 15 or 20 MHz) but with a limited channel bandwidth of 6 physical resource blocks (PRBs) (corresponding to the maximum channel bandwidth available in a 1.4 MHz LTE system) in DL and UL. The BL communication device may access a cell of the BS  102  or the BS  104 , if system information (e.g., a Master Information Block (MIB)) of the cell indicates that the access of the BL communication device is supported. Otherwise, the BL communication device considers the cell as barred. 
         [0016]    The communication device  100  in coverage enhancement (CE) uses enhanced coverage functionality (e.g., transmit multiple repetitions of data and/or signal, and/or receive multiple repetitions of data and/or signal) to access a cell of the BS  102  or the BS  104 . The communication device  100  may access a cell using enhanced coverage techniques only if system information (e.g., MIB) of the cell indicates that access of UEs in CE is supported. 
         [0017]      FIG. 2  is a schematic diagram of a communication device  20  according to an example of the present invention. The communication device  20  may be the communication device  100 , the BS  102  and/or the BS  104  shown in  FIG. 1 , but is not limited herein. The communication device  20  includes a processing circuit  200  such as a microprocessor or Application Specific Integrated Circuit, a storage unit  210  and a communication interfacing unit  220 . The storage unit  210  may be any data storage device that stores a program code  214 , accessed and executed by the processing circuit  200 . Examples of the storage unit  210  include but are not limited to read-only memory, flash memory, random-access memory, hard disk, optical data storage device, non-volatile storage unit, non-transitory computer-readable medium (e.g., tangible media), etc. The communication interfacing unit  220  is preferably a transceiver used to transmit and receive signals (e.g., data, signals, messages and/or packets) according to processing results of the processing circuit  200 . 
         [0018]    In the following embodiments, a UE is used to represent the communication device  100  in  FIG. 1 , to simplify the illustration of the embodiments. 
         [0019]      FIG. 3  is a flowchart of a process  30  according to an example of the present invention. The process  30  may be utilized in a first BS (e.g., the BS  102 ), to handle a handover with a second BS (e.g., the BS  104 ). The process  30  includes the following steps: 
         [0020]    Step  300 : Start. 
         [0021]    Step  302 : Connect to a first UE. 
         [0022]    Step  304 : Determine to hand over the first UE to the second BS. 
         [0023]    Step  306 : Generate a first handover request message in response to the determination, wherein the first handover request message comprises one of first system information and second system information according to whether the first UE is in CE or according to a type of the first UE. 
         [0024]    Step  308 : Transmit the first handover request message to the second BS. 
         [0025]    Step  310 : Receive a first handover request acknowledgement message in response to the first handover request message from the second BS. 
         [0026]    Step  312 : Transmit a first handover command to the first UE in response to the reception of the first handover request acknowledgement message. 
         [0027]    Step  314 : End. 
         [0028]    According to the process  30 , the first BS connects to a first UE (e.g., the communication device  100 ), and determines to hand over the first UE to the second BS. The first BS generates a first handover request message in response to the determination, wherein the first handover request message comprises one of first system information and second system information according to whether the first UE is in CE or according to a type of the first UE. Then, the first BS transmits the first handover request message to the second BS. The first BS receives a first handover request acknowledgement message in response to the first handover request message from the second BS. Accordingly, the first BS transmits a first handover command to the first UE in response to the reception of the first handover request acknowledgement message. That is, whether a UE is in CE or a type of the UE is used for determining content of a handover request message for handing over the UE. Thus, the handover can be performed adaptively according to a state or mode of the UE or a type of the UE. Performance of the UE can be improved correspondingly. 
         [0029]    Realization of the process  30  is not limited to the above description. The following examples may be applied to the process  30 . 
         [0030]    In one example, the first handover request message includes the first system information when the first UE is in CE, and the first handover request message includes the second system information when the first UE is not in CE. 
         [0031]    In one example, the first handover request message includes the first system information if the type of the first UE is a first type (i.e., a UE with the first type or a first-type UE), and the first handover request message includes the second system information if the type of the first UE is a second type (i.e., a UE with the second type or a second-type UE). In one example, the first type is a first category (e.g., category M1), and the second type is a second category (e.g. non-category M1 category, such as category x, wherein x is a number which may be 1, 2, . . . , 20). In one example, the first type is a (massive) machine type communication ((m)MTC), and the second type is an (evolved) mobile broad band ((e)MBB). In one example, the first type is an Ultra-Reliable and Low Latency Communications (uRLLC), and the second type is an (e)MBB. In one example, a first radio frequency (RF) capability of the first type and a second RF capability of the second type may have different maximum transmitting and/or receiving bandwidths. For example, a UE with the first type is capable of receiving maximum 1.4 MHz (e.g., BL UE), and a UE with the second type is capable of receiving maximum 20 MHz (e.g., not a BL UE). For example, the UE with the first type is capable of receiving maximum 20 MHz (e.g., supports bandwidth class 3), and the UE with the second type is capable of receiving maximum 100 MHz (e.g., supports bandwidth class 5). 
         [0032]    In one example, the first handover request message comprises the first system information when the first UE is in CE or a type of the first UE is the first type. The first BS further connects to a second UE, and determines to hand over the second UE to the second BS. The first BS generates a second handover request message in response to the determination, wherein the second handover request message comprises the second system information when the second UE is not in CE or a type of the second UE is the second type. Then, the first BS transmits the second handover request message to the second BS. The first BS receives a second handover request acknowledgement message in response to the second handover request message from the second BS. Accordingly, the first BS transmits a second handover command to the second UE in response to the reception of the second handover request acknowledgement message. In other words, the process  30  can be applied to the handovers of multiple UEs. 
         [0033]    In one example, the first handover request message includes a UE configuration of the first UE. The UE configuration includes at least one of a security configuration (e.g., security algorithm), a measurement configuration and a data radio bearer (DRB) configuration. In one example, the first handover request acknowledgement message includes the first handover command. Similarly, the second handover request message includes a UE configuration of the second UE. Further, the UE configuration includes at least one of a security configuration (e.g., security algorithm), a measurement configuration and a DRB configuration. In one example, the second handover request acknowledgement message includes the second handover command. 
         [0034]    In one example, the first system information includes at least one first system information block (SIB) for the UE in CE or the first type UE, and the second system information may include at least one second SIB for the UE not in CE or the second type UE. In one example, the at least one first SIB includes a SystemInformationBlockType1-BR, and the at least one second SIB includes a SystemInformationBlockType1. In one example, the at least one first SIB includes a first SystemInformationBlockType2, and the at least one second SIB includes a second SystemInformationBlockType2. For example, the first SystemInformationBlockType2 may be included in SystemInformation-BR in a BCCH-DL-SCH-Message-BR transmitted by the first BS, and the second SystemInformationBlockType2 may be included in SystemInformation in BCCH-DL-SCH-Message transmitted by the first BS. 
         [0035]    In one example, the first system information includes at least one IE which is not comprised in the second system information. In one example, the first and second system information includes an IE. The IE in the first system information and the IE in the second system information may have the same value or different values. 
         [0036]    In one example, the first system information may be broadcasted by the first BS for the first UE with the first type and/or for the first UE in CE. The second system information may be broadcasted by the first BS for the first UE with the second type and/or for the first UE not in CE. In one example, the first system information and the second system information may be broadcasted by the first BS in different frequency resources and/or different time in a same carrier. For example, the first system information may be transmitted within 1.4 MHz bandwidth in the same carrier (e.g., 20 MHz) for a UE with the first type UE, and the second system information may be transmitted within more than 1.4 MHz bandwidth in the same carrier. For example, the first system information may be transmitted in more repetitions in the same carrier than the second system information in the same carrier. 
         [0037]      FIG. 4  is a flowchart of a process  40  according to an example of the present invention. The process  40  may be utilized in a second BS (e.g., the BS  104 ), to handle a handover with a first BS (e.g., the BS  102 ). The process  40  includes the following steps: 
         [0038]    Step  400 : Start. 
         [0039]    Step  402 : Connect to the first BS. 
         [0040]    Step  404 : Receive a handover request message for a first UE from the first BS. 
         [0041]    Step  406 : Generate a handover request acknowledgement message in response to the handover request message. 
         [0042]    Step  408 : Generate a first configuration according to first system information and transmit the handover request acknowledgement message comprising the first configuration to the first BS, if the handover request message comprises the first system information and the first UE is in CE or a type of the first UE is a first type. 
         [0043]    Step  410 : Generate a second configuration according to second system information and transmit the handover request acknowledgement message comprising the second configuration to the first BS, if the handover request message comprises the second system information and the first UE is in not CE or the type of the first UE is a second type. 
         [0044]    Step  412 : End. 
         [0045]    According to the process  40 , the second BS connects to the first BS, and receives a handover request message for a first UE from the first BS. The second BS generates a handover request acknowledgement message in response to the handover request message. Accordingly, the second BS generates a first configuration according to first system information and transmits the handover request acknowledgement message comprising the first configuration to the first BS, if the handover request message comprises the first system information and the first UE is in CE or a type of the first UE is a first type. The second BS generates a second configuration according to second system information and transmits the handover request acknowledgement message comprising the second configuration to the first BS, if the handover request message comprises the second system information and the first UE is in not CE or the type of the first UE is a second type. The first configuration and the second configuration may be different. That is, whether a UE is in CE or a type of the UE is taken into consideration, when a configuration is generated according to system information in a handover request message for handing over the UE. Thus, the handover can be performed adaptively according to a state of the UE or a type of the UE. Performance of the UE can be improved correspondingly. 
         [0046]    Realization of the process  40  is not limited to the above description. Examples described regarding the process  30  for the first system information and the second system information may be applied herein and not repeated. The following examples may be applied to the process  40 . 
         [0047]    In one example, the first configuration may be for updating a first value comprised in the first system information, and the second configuration may be for updating a second value comprised in the second system information. In one example, the first configuration may be for configuring a third configuration which is not comprised in the first system information, and the second configuration may be for configuring a fourth configuration which is not comprised in the second system information. 
         [0048]    In one example, the first configuration includes a first RadioResourceConfigCommon, and the second configuration includes a second RadioResourceConfigCommon. In one example, the first RadioResourceConfigCommon includes a first IE which is not comprised in the second RadioResourceConfigCommon. In one example, the first RadioResourceConfigCommon and the second RadioResourceConfigCommon have at least one of a second IE and a third IE. A first value of the second IE of the first RadioResourceConfigCommon and a second value of the second IE of the second RadioResourceConfigCommon may be different. In one example, a first value of the third IE of the first RadioResourceConfigCommon and a second value of the third IE of the second RadioResourceConfigCommon may be the same. 
         [0049]    In one example, the first configuration includes a first RLF-TimersAndConstants, and the second configuration includes a second RLF-TimersAndConstants. In one example, the first RLF-TimersAndConstants includes a first IE which is not comprised in the second RLF-TimersAndConstants. In one example, the first RLF-TimersAndConstants and the second RLF-TimersAndConstants have at least one of a second UE and a third IE. A first value of the second IE of the first RLF-TimersAndConstants and a second value of the second IE of the second RLF-TimersAndConstants may be different. In one example, a first value of the third IE of the first RLF-TimersAndConstants and a second value of the third IE of the second RLF-TimersAndConstants may be the same. 
         [0050]    Those skilled in the art should readily make combinations, modifications and/or alterations on the abovementioned description and examples. The abovementioned description, steps and/or processes including suggested steps can be realized by means that could be hardware, software, firmware (known as a combination of a hardware device and computer instructions and data that reside as read-only software on the hardware device), an electronic system, or combination thereof. An example of the means may be the communication device  20 . Any of the processes above may be compiled into the program code  214 . 
         [0051]    To sum up, the present invention provides a device and a method for handling a handover. Whether a UE is in CE or a type of the UE is used for determining content of a handover request message for handing over the UE. Thus, the handover can be performed adaptively according to a state of the UE or a type of the UE. Performance of the UE can be improved correspondingly. 
         [0052]    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.