Abstract:
A communication device for handling system information 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 receiving a radio resource control (RRC) connection release message from a network; and acquiring changed system information, after receiving the RRC connection release message and before initiating a RRC connection establishment procedure.

Description:
Cross Reference To Related Applications 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/291,534 filed on Feb. 5, 2016, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    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 system information. 
         [0004]    2. Description of the Prior Art 
         [0005]    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. 
         [0006]    The eNB may move a UE to a RRC_IDLE state, if the eNB determines that the UE needs to acquire changed system information. However, there is no mechanism for the UE to check if it already has (or obtains) up-to-date system information, before the UE initiates a connection establishment procedure. According to the prior art, the UE obtains system information just enough for entering a RRC_CONNECTED mode. In this situation, the UE may initiate the connection establishment procedure before acquiring all changed system information, and the connection establishment procedure may be failed. Accordingly, the eNB may release the UE to ask the UE to acquire the changed system information. Again, the UE may not obtain all the changed system information, i.e., a deadlock is caused to the interaction between the eNB and the UE. Thus, how the UE handles the system information is an important to be solved. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention therefore provides a communication device and method for handling system information to solve the abovementioned problem. 
         [0008]    A communication device for handling system information 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 receiving a radio resource control (RRC) connection release message from a network; and acquiring changed system information, after receiving the RRC connection release message and before initiating a RRC connection establishment procedure. 
         [0009]    A communication device for handling system information 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 receiving a radio resource control (RRC) connection release message from a network; and acquiring all system information, after receiving the RRC connection release message and before initiating a RRC connection establishment procedure. 
         [0010]    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 
         [0011]      FIG. 1  is a schematic diagram of a wireless communication system according to an example of the present invention. 
           [0012]      FIG. 2  is a schematic diagram of a communication device according to an example of the present invention. 
           [0013]      FIG. 3  is a flowchart of a process according to an example of the present invention. 
           [0014]      FIG. 4  is a flowchart of a process according to an example of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      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 network and a plurality of communication devices. The network and a communication device may communicate with each other via one or more carriers of licensed band(s) and/or unlicensed band(s). The network and the communication device may simultaneously communicate with each other via multiple cells (e.g., multiple carriers) including a primary cell (PCell) and one or more secondary cells (SCells). The abovementioned cells may be operated in the same or different frame structure types, or in the same or different duplexing modes, i.e. frequency-division duplexing (FDD) and time-division duplexing (TDD). For example, the PCell may be operated on a licensed carrier, while the SCell may be operated on an unlicensed carrier. 
         [0016]    In  FIG. 1 , the network and the communication devices are simply utilized for illustrating the structure of the wireless communication system  10 . Practically, the network may be a narrowband (NB) internet of things (IoT) network or an evolved universal terrestrial radio access network (E-UTRAN) including at least one evolved Node-B (eNB). The network may be a fifth generation (5G) network including at least one 5G base station (BS) which employs orthogonal frequency-division multiplexing (OFDM) and/or non-OFDM and a transmission time interval (TTI) shorter than 1 ms (e.g. 100 or 200 microseconds), to communicate with the communication devices. In general, a BS may also be used to refer any of the eNB and the 5G BS. 
         [0017]    Furthermore, the network may also include the GERAN/UTRAN/E-UTRAN and a core network, wherein the core network may include network entities such as Mobility Management Entity (MME), Serving Gateway (S-GW), Packet Data Network (PDN) Gateway (P-GW), Self-Organizing Networks (SON) server and/or Radio Network Controller (RNC), etc. The GERAN is an abbreviation of Global System for Mobile Communications (GSM) Enhanced Data rates for GSM Evolution (EDGE) Radio Access Network. In other words, after the network receives information transmitted by a communication device, the information may be processed only by the UTRAN/E-UTRAN and decisions corresponding to the information are made at the UTRAN/E-UTRAN. Alternatively, the UTRAN/E-UTRAN may forward the information to the core network, and the decisions corresponding to the information are made at the core network after the core network processes the information. In addition, the information may be processed by both the UTRAN/E-UTRAN and the core network, and the decisions are made after coordination and/or cooperation are performed by the UTRAN/E-UTRAN and the core network. 
         [0018]    A communication device may be a user equipment (UE), a machine type communication (MTC) device, a mobile phone, a laptop, a tablet computer, an electronic book, a portable computer system, a vehicle, or an aircraft. In addition, the network and the communication device can be seen as a transmitter or a receiver according to direction (i.e., transmission direction), e.g., for an uplink (UL), the communication device is the transmitter and the network is the receiver, and for a downlink (DL), the network is the transmitter and the communication device is the receiver. 
         [0019]      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 a communication device or the network shown in  FIG. 1 , but is not limited herein. The communication device  20  may include a processing circuit  200  such as a microprocessor or Application Specific Integrated Circuit (ASIC), a storage unit  210  and a communication interfacing unit  220 . The storage unit  210  may be any data storage device that may store a program code  214 , accessed and executed by the processing circuit  200 . Examples of the storage unit  210  include but are not limited to a subscriber identity module (SIM), read-only memory (ROM), flash memory, random-access memory (RAM), 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 and is used to transmit and receive signals (e.g., data, messages and/or packets) according to processing results of the processing circuit  200 . 
         [0020]    In the following embodiments, a UE is used to represent a communication device in  FIG. 1 , to simplify the illustration of the embodiments. 
         [0021]      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 UE, for handling system information. The process  30  maybe compiled into the program code  214  and includes the following steps:
   Step  300 : Start.   Step  302 : Receive a radio resource control (RRC) connection release message from a network.   Step  304 : Acquire changed system information, after receiving the RRC connection release message and before initiating a RRC connection establishment procedure.   Step  306 : End.   
 
         [0026]    The network may change content of system information broadcasted in a cell of the network. For example, the network may change a value tag of the system information to indicate that there is a system information change and/or which system information is changed. The network may decide that a UE needs to acquire (or reacquire) the changed system information, and may send a RRC connection release message to the UE. According to the process  30 , the UE receives the RRC connection release message from the network. Then, the UE acquires changed system information, after receiving the RRC connection release message and before initiating a RRC connection establishment procedure. That is, the UE obtains all the changed system information, such that the RRC connection establishment procedure can be initiated properly according to the changed system information. Thus, the problem that the UE (e.g., in a RRC_IDLE mode) only obtains system information (which is not all the changed system information) sufficient for entering a RRC_CONNECTED mode is solved. 
         [0027]    Realization of the process  30  is not limited to the above description. The following examples may be applied to the process  30 . 
         [0028]    There are various ways for identifying (or recognizing) when or which system information is changed. In one example, the changed system information is first system information broadcasted by the network, and is different from second system information stored in the UE. That is, all or part of all system information which is different from the stored system information is treated as the changed system information, and the UE acquires all the changed system information accordingly. In one example, the UE compares a first value tag stored in the first system information and a second value tag in the second system information, and considers the first system information as the changed system information if the first value tag and the second value tag are different. That is, all or part of all system information with a value tag different from the stored value tag is treated as the changed system information, and the UE acquires all the changed system information accordingly. 
         [0029]    In one example, the UE stores third system information broadcasted by the network, and starts a timer (e.g., valid timer) for the third system information. Then, the UE considers fourth system information broadcasted by the network as the changed system information, if the timer expires. That is, whether the stored system information is valid (or invalid) is determined according to the timer. The UE decides that the stored system information is invalid, i.e., the stored system information is changed, if the timer expires. In one example, the changed system information may include (or simply be) system information for enhanced coverage (EC). 
         [0030]    In one example, the RRC connection release message may include a release cause. That is, the UE acquires the changed system information, if the release cause is received in the RRC connection release message. In this situation, the UE does not acquire the changed system information, if the RRC connection release message does not include the release cause. Further, the release cause may be configured with (i.e., set to) a first value. That is, the UE acquires the changed system information, if the release cause configured with the first value is received in the RRC connection release message. In this situation, the UE does not acquire the changed system information, if the release cause is configured with a second value different from the first value. 
         [0031]    In one example, the RRC connection release message may include an indicator. That is, the UE acquires the changed system information, if the indicator is received in the RRC connection release message. In this situation, the UE does not acquire the changed system information, if the RRC connection release message does not include the release cause. Further, the indicator may be configured with (i.e., set to) a “TRUE” value. That is, the UE acquires the changed system information, if the release cause configured with the “TRUE” value is received in the RRC connection release message. In this situation, the UE does not acquire the changed system information, if the release cause is configured with a “FALSE” value. 
         [0032]      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 UE, for handling system information. The process  40  maybe compiled into the program code  214  and includes the following steps:
   Step  400 : Start.   Step  402 : Receive a radio resource control (RRC) connection release message from a network.   Step  404 : Acquire all system information, after receiving the RRC connection release message and before initiating a RRC connection establishment procedure.   Step  406 : End.   
 
         [0037]    The network may change content of system information broadcasted in a cell of the network. For example, the network may change a value tag of the system information to indicate that there is a system information change and/or which system information is changed. The network may decide that a UE needs to acquire (or reacquire) the changed system information, and may send a RRC connection release message to the UE. According to the process  40 , the UE receives the RRC connection release message from the network. Then, the UE acquires all system information, after receiving the RRC connection release message and before initiating a RRC connection establishment procedure. That is, the UE obtains all the system information (including changed system information and unchanged system information), such that the RRC connection establishment procedure can be initiated properly according to the changed system information. Thus, the problem that the UE (e.g., in a RRC_IDLE mode) only obtains system information (which is not all the changed system information) sufficient for entering a RRC_CONNECTED mode is solved. 
         [0038]    Realization of the process  40  is not limited to the above description. The following examples may be applied to the process  40 . 
         [0039]    In one example, the changed system information may include (or simply be) system information for EC. 
         [0040]    In the above examples related to the process  30  and/or  40 , the UE may be a Bandwidth reduced Low complexity (BL) UE or a UE in EC. 
         [0041]    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 . 
         [0042]    To sum up, the present invention provides a device and a method for handling system information. Accordingly, a UE can obtain the system information correctly. The problem that the UE (e.g., in a RRC_IDLE mode) only obtains system information (which is not all the changed system information) sufficient for entering a RRC_CONNECTED mode is solved. 
         [0043]    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.