Abstract:
The present disclosure relates to a pre-5th-generation (5G) or 5G communication system to be provided for supporting higher data rates beyond 4th-generation (4G) communication system such as a long term evolution (LTE). An operating method of a user equipment (UE) in a mobile communication system is provided. The operating method includes receiving a service through a first enhanced node B (eNB) for a first time interval period from a first timing point; and receiving the service through a second eNB for a second time interval period from a second timing point, wherein the first timing point is different from the second timing point.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a U.S. National Stage application under 35 U.S.C. §371 of an International application filed on Aug. 8, 2014 and assigned application number PCT/KR2014/007366, which claimed the benefit of a Korean patent application filed on Aug. 8, 2013 in the Korean Intellectual Property Office and assigned Serial number 10-2013-0094343, the entire disclosure of which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to an apparatus and method for performing a switching operation between a macro cell and a small cell in a mobile communication system. More particularly, the present disclosure relates to an apparatus and method for performing a switching operation between a macro cell and a small cell in a mobile communication system where a macro cell and a small cell are co-located. 
       BACKGROUND 
       [0003]    To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’. 
         [0004]    It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems. 
         [0005]    In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like. 
         [0006]    In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed. 
         [0007]    Mobile communication systems have rapidly evolved, and recently have evolved to reflect user&#39;s various demands to support high-speed large-capacity services. Service providers are deploying small cells as well as macro cells in order to support high-speed large-capacity services for a user. The small cell is deployed to use a frequency which is higher than a frequency of the macro cell thereby supporting a data transmit rate which is higher than a data transmit rate of the macro cell. If it is difficult for the macro cell to support a new service which is provided in the mobile communication system, the mobile communication system may support the new service using the small cell which supports the relatively high data transmit rate. 
         [0008]    Generally, even though a macro cell is deployed with a small cell in the mobile communication system, a user equipment (UE) may receive a service through only one of the macro cell and the small cell. However, in an evolved mobile communication system, the UE may receive a service through the both the macro cell and the small cell using a dual connectivity scheme. 
         [0009]    A structure of a mobile communication system where a macro cell and a small cell are co-located is described below with reference to  FIG. 1 . 
         [0010]      FIG. 1  schematically illustrates a structure of a mobile communication system where a macro cell and a small cell are co-located according to the related art. 
         [0011]    Referring to  FIG. 1 , the mobile communication system includes a mobility management entity (MME)  111 , a serving-gateway (S-GW)  113 , a packet-gateway (P-GW)  115 , a macro enhanced node B (eNB)  117 , a plurality of small cell eNBs (e.g., eight small cell eNBs)  119 - 1 ,  119 - 2 ,  119 - 3 ,  119 - 4 ,  121 - 1 ,  121 - 2 ,  121 - 3 , and  121 - 4 , and a UE  123 . The small cell eNBs  119 - 1 ,  119 - 2 ,  119 - 3 , and  119 - 4  are included in a small cell cluster  119 . 
         [0012]    The UE  123  is connected to each of the macro eNB  117  and the small cell eNB  121 - 2 , the macro eNB  117  is connected to each of the MME  111  and the S-GW  113 , and the small cell eNB  121 - 2  is connected to the S-GW  113 . Alternatively, the small cell eNB  121 - 2  may not be connected to the S-GW  113 ; in this case, the small cell eNB  121 - 2  is connected to the macro eNB  117 . The UE  123  may be connected to the macro eNB  117 , the small cell eNB  121 - 2 , or the macro eNB  117  and the small cell eNB  121 - 2 . The UE  123  may have a dual connection with the macro eNB  117  and the small cell eNB  121 - 2 . 
         [0013]    As described above, the UE  123  establishes a connection with each of the macro eNB  117  and the small cell eNB  121 - 2  at the same time (i.e., the UE  123  establishes a dual connection) thereby transmitting/receiving data with the macro eNB  117  and the small cell eNB  121 - 2 . However, if the UE  123  is a hardware device which has a difficulty in establishing a connection with each of the macro eNB  117  and the small cell eNB  121 - 2  at the same time, or there is a difference between a transmit power which is used in the macro eNB  117  and a transmit power which is used in the small cell eNB  121 - 2 , the UE  123  may be restricted on receiving a service through a dual connection from the macro eNB  117  and the small cell eNB  121 - 2 . 
         [0014]    In the mobile communication system, in a case that the macro eNB  117  is deployed to use a relatively low frequency band, and the small cell eNB  121 - 1  is deployed to use a relatively high frequency band which is not adjacent to a frequency band of the macro eNB  117 , an implementation form of the UE  123  that the UE  123  establishes a connection with the macro eNB  117  and the small cell eNB  121 - 1  at the same time to transmit/receive data to/from the macro eNB  117  and the small cell eNB  121 - 1  is easier than an implementation form of the UE  123  that only the small cell eNB  121 - 1  supports relatively high data transmit rate for the UE  123  in terms of implementation. 
         [0015]    Accordingly, in a mobile communication system, a UE may be connected to both a macro eNB and a small cell eNB to receive a service from both the macro eNB and the small cell eNB by separating a timing point at which the UE is connected to a macro eNB and a timing point at which the UE is connected to a small cell eNB (i.e., by using a time division multiplexing (TDM) dual connectivity scheme). There is a need for a scheme that a UE effectively performs a switching operation between a macro eNB and a small cell eNB. There is a need for a scheme of performing a switching operation in order to effectively provide a service to a UE in a case that the UE is connected to different types of cells using a dual connectivity scheme. 
         [0016]    The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure. 
       SUMMARY 
       [0017]    Aspects of the present disclosure are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present disclosure is to provide an apparatus and method for performing a switching operation between a macro cell and a small cell in a mobile communication system. 
         [0018]    Another aspect of the present disclosure is to provide an apparatus and method for performing a switching operation between a macro cell and a small cell in a mobile communication system where the macro cell and the small cell are co-located. 
         [0019]    Another aspect of the present disclosure is to provide an apparatus and method for performing a switching operation between a macro cell and a small cell thereby effectively providing a service in a mobile communication system where the macro cell and the small cell are co-located. 
         [0020]    Another aspect of the present disclosure is to provide an apparatus and method for performing a switching operation between a macro cell and a small cell thereby distributing load of the macro cell to the small cell in a mobile communication system where the macro cell and the small cell are co-located. 
         [0021]    Another aspect of the present disclosure is to provide an apparatus and method for performing a switching operation between a macro cell and a small cell thereby providing a large-capacity service in a mobile communication system where the macro cell and the small cell are co-located. 
         [0022]    Another aspect of the present disclosure is to provide an apparatus and method for performing a switching operation between a macro cell and a small cell thereby increasing system capacity of the entire mobile communication system in a mobile communication system where the macro cell and the small cell are co-located. 
         [0023]    In accordance with an aspect of the present disclosure, a user equipment (UE) in a mobile communication system is provided. The UE includes a processor configured to perform an operation of receiving a service through a macro enhanced node B (eNB) for a first time interval period from a first timing point, and an operation of receiving the service through a small cell eNB for a second time interval period from a second timing point, wherein the first timing point is different from the second timing point. 
         [0024]    In accordance with another aspect of the present disclosure, a first eNB in a mobile communication system is provided. The first eNB includes a processor configured to perform an operation of providing a service to a UE for a first time interval period from a first timing point, wherein the first timing point is different from a second timing point from which a second eNB provides the service to the UE for a second time interval. 
         [0025]    In accordance with another aspect of the present disclosure, a second eNB in a mobile communication system is provided. The second eNB includes a processor configured to perform an operation of providing a service to a UE for a second time interval period from a second timing point, wherein the second timing point is different from a first timing point from which a first eNB provides the service to the UE for a first time interval. 
         [0026]    In accordance with another aspect of the present disclosure, an operating method of a UE in a mobile communication system is provided. The operating method includes receiving a service through a first eNB for a first time interval period from a first timing point, and receiving the service through a second eNB for a second time interval period from a second timing point, wherein the first timing point is different from the second timing point. 
         [0027]    In accordance with another aspect of the present disclosure, an operating method of a first eNB in a mobile communication system is provided. The operating method includes providing a service to a UE for a first time interval period from a first timing point, wherein the first timing point is different from a second timing point from which a second eNB provides the service to the UE for a second time interval. 
         [0028]    In accordance with another aspect of the present disclosure, an operating method of a second eNB in mobile a communication system is provided. The operating method includes providing a service to a UE for a second time interval period from a second timing point, wherein the second timing point is different from a first timing point from which a first eNB provides the service to the UE for a first time interval. 
         [0029]    As is apparent from the foregoing description, embodiments of the present disclosure enables effectively performing a switching operation between a macro cell and a small cell thereby effectively providing a service in a mobile communication system where the macro cell and the small cell are co-located. 
         [0030]    Another embodiment of the present disclosure enables effectively performing a switching operation between a macro cell and a small cell thereby distributing load of the macro cell to the small cell in a mobile communication system where the macro cell and the small cell are co-located. 
         [0031]    Another embodiment of the present disclosure enables effectively performing a switching operation between a macro cell and a small cell thereby providing a large-capacity service in a mobile communication system where the macro cell and the small cell are co-located. 
         [0032]    Another embodiment of the present disclosure enables effectively performing a switching operation between a macro cell and a small cell thereby increasing system capacity of the entire mobile communication system in a mobile communication system where the macro cell and the small cell are co-located. 
         [0033]    Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0035]      FIG. 1  schematically illustrates a structure of a mobile communication system where a macro cell and a small cell are co-located according to the related art; 
           [0036]      FIG. 2A  schematically illustrates a process of supporting a switching operation between a macro cell and a small cell in a case that a user equipment (UE) is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure; 
           [0037]      FIG. 2B  schematically illustrates an example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure; 
           [0038]      FIG. 2C  schematically illustrates an example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure; 
           [0039]      FIG. 3A  schematically illustrates an example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure; 
           [0040]      FIG. 3B  schematically illustrates an example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure; 
           [0041]      FIG. 4A  schematically illustrates an example of operating a UE frame according to event occurrence in a mobile communication system according to an embodiment of the present disclosure; 
           [0042]      FIG. 4B  schematically illustrates an example of operating a UE frame according to event occurrence in a mobile communication system according to an embodiment of the present disclosure; 
           [0043]      FIG. 5  schematically illustrates a process of performing a switching operation between a macro enhanced node B (eNB) and a small cell eNB in a UE in a mobile communication system according to an embodiment of the present disclosure; 
           [0044]      FIG. 6A  schematically illustrates an example of a process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0045]      FIG. 6B  schematically illustrates an example of a process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0046]      FIG. 7  schematically illustrates a process of switching to a macro eNB in order for a UE which receives a service from a small cell eNB to periodically report a measurement process performance result in a mobile communication system according to an embodiment of the present disclosure; 
           [0047]      FIG. 8  schematically illustrates a process of switching to a macro eNB in order for a UE which receives a service from a small cell eNB to report a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure; 
           [0048]      FIG. 9  schematically illustrates an example of a process of switching to a macro eNB in order for a UE to perform a radio resource control (RRC) process in a mobile communication system according to an embodiment of the present disclosure; 
           [0049]      FIG. 10  schematically illustrates an example of a process of switching to a macro eNB in order for a UE to perform a RRC process in a mobile communication system according to an embodiment of the present disclosure; 
           [0050]      FIG. 11  schematically illustrates a process of switching to a macro eNB in order for a UE to resolve a connection failure with a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0051]      FIG. 12  schematically illustrates a process of performing an initial attach process in a UE in a mobile communication system according to an embodiment of the present disclosure; 
           [0052]      FIG. 13  schematically illustrates a process of periodically reporting a measurement process performance result in a UE in a mobile communication system according to an embodiment of the present disclosure; 
           [0053]      FIG. 14  schematically illustrates a process of reporting a measurement process performance result according to event occurrence in a UE in a mobile communication system according to an embodiment of the present disclosure; 
           [0054]      FIG. 15  schematically illustrates a UE operating process in a case that a radio link failure (RLF) occurs in a connection between a UE and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0055]      FIG. 16  schematically illustrates a process of performing an initial attach process with a UE in a macro eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0056]      FIG. 17  schematically illustrates a process of performing an initial attach process with a UE in a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0057]      FIG. 18A  schematically illustrates an example of a process of managing a data path among a macro eNB, a small cell eNB, and GWs for supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0058]      FIG. 18B  schematically illustrates an example of a process of managing a data path among a macro eNB, a small cell eNB, and GWs for supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0059]      FIG. 19  schematically illustrates an example of a process of supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0060]      FIG. 20A  schematically illustrates an example of an operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure; 
           [0061]      FIG. 20B  schematically illustrates an example of an operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure; 
           [0062]      FIG. 21  schematically illustrates an inner structure of a macro eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0063]      FIG. 22  schematically illustrates an inner structure of a small cell eNB in a mobile communication system according to an embodiment of the present disclosure; 
           [0064]      FIG. 23  schematically illustrates an inner structure of a UE in a mobile communication system according to an embodiment of the present disclosure; and 
           [0065]      FIG. 24  schematically illustrates an inner structure of an S-GW in a mobile communication system according to an embodiment of the present disclosure. 
       
    
    
       [0066]    Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
       DETAILED DESCRIPTION 
       [0067]    The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
         [0068]    The terms and words used in the following description and claims are not limited to the bibliographical meanings, but are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purposes only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents. 
         [0069]    It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
         [0070]    Although ordinal numbers such as “first,” “second,” and so forth will be used to describe various components, those components are not limited herein. The terms are used only for distinguishing one component from another component. For example, a first component may be referred to as a second component and likewise, a second component may also be referred to as a first component, without departing from the teaching of the present disclosure. The term “and/or” used herein includes any and all combinations of one or more of the associated listed items. 
         [0071]    The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “has,” when used in this specification, specify the presence of a stated feature, number, operation, component, element, or combination thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, components, elements, or combinations thereof. 
         [0072]    The terms used herein, including technical and scientific terms, have the same meanings as terms that are generally understood by those skilled in the art, as long as the terms are not differently defined. It should be understood that terms defined in a generally-used dictionary have meanings coinciding with those of terms in the related technology. 
         [0073]    An embodiment of the present disclosure proposes an apparatus and method for performing a switching operation between a macro cell and a small cell in a mobile communication system. 
         [0074]    An embodiment of the present disclosure proposes an apparatus and method for performing a switching operation between a macro cell and a small cell in a mobile communication system where the macro cell and the small cell are co-located. 
         [0075]    An embodiment of the present disclosure proposes an apparatus and method for performing a switching operation between a macro cell and a small cell thereby effectively providing a service in a mobile communication system where the macro cell and the small cell are co-located. 
         [0076]    An embodiment of the present disclosure proposes an apparatus and method for performing a switching operation between a macro cell and a small cell thereby distributing load of the macro cell to the small cell in a mobile communication system where the macro cell and the small cell are co-located. 
         [0077]    An embodiment of the present disclosure proposes an apparatus and method for performing a switching operation between a macro cell and a small cell thereby providing a large-capacity service in a mobile communication system where the macro cell and the small cell are co-located. 
         [0078]    An embodiment of the present disclosure proposes an apparatus and method for performing a switching operation between a macro cell and a small cell thereby increasing system capacity of the entire mobile communication system in a mobile communication system where the macro cell and the small cell are co-located. 
         [0079]    A method and apparatus proposed in various embodiments of the present disclosure may be applied to various communication systems such as a long term evolution (LTE) system, an LTE-advanced (LTE-A) system, a high speed downlink packet access (HSDPA) mobile communication system, a high speed uplink packet access (HSUPA) mobile communication system, a high rate packet data (HRPD) mobile communication system proposed in a 3rd generation partnership project 2 (3GPP2), a wideband code division multiple access (WCDMA) mobile communication system proposed in the 3GPP2, a code division multiple access (CDMA) mobile communication system proposed in the 3GPP2, an institute of electrical and electronics engineers (IEEE) mobile communication system, an evolved packet system (EPS), a mobile internet protocol (Mobile IP) system, and/or the like. 
         [0080]    It will be assumed that a mobile communication system which is described in an embodiment of the present disclosure is a mobile communication system in which a macro cell and a small cell are co-located. 
         [0081]    A process of supporting a switching operation between a macro cell and a small cell in a case that a user equipment (UE) is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIGS. 2A to 2C . 
         [0082]    A process of supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 2A . 
         [0083]      FIG. 2A  schematically illustrates a process of supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure. 
         [0084]    Referring to  FIG. 2A , the mobile communication system includes a macro enhanced node B (eNB)  211 , a small cell eNB  213 , a UE # 1   215 , and a UE # 2   217 . The UE # 1   215  is located at a region where a service coverage  219  of the macro eNB  211  overlaps with a service coverage  221  of the small eNB  213 , and the UE # 2   217  is located within the service coverage  219  of the macro eNB  211 . 
         [0085]    The UE # 1   215  receives a service through the macro eNB  211  at an arbitrary time interval t ( 223 ). If the time interval t expires, the UE # 1   215  performs a switching operation from the macro eNB  211  to the small cell eNB  213  ( 225 ) to receive the service through the small cell eNB  213  at a time interval t+1 as a time interval after the time interval t  227 . If the time interval t+1 expires, the UE # 1   215  performs a switching operation from the small cell eNB  213  to the macro eNB  211  ( 229 ) to receive the service through the macro eNB  211  at a time interval t+2 as a time interval after the time interval t+1 ( 231 ). 
         [0086]    An example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 2B . 
         [0087]      FIG. 2B  schematically illustrates an example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure. 
         [0088]    Referring to  FIG. 2B , a macro eNB  211  transmits/receives a control signal to/from a UE  215 , and a small cell eNB  213  transmits/receives a data packet to/from the UE  215 . A control frame and a data frame for the UE  215  are previously determined at a timing point that the UE  215  establishes a dual connection with the macro eNB  211  and the small cell eNB  213 . 
         [0089]    For example, the control frame is used for the UE  215  to transmit/receive a control signal which is necessary for performing a channel measurement report operation or a radio resource control (RRC) operation to/from the macro eNB  211 . The data frame is used for the UE  215  to transmit/receive a data packet to/from the small eNB  213 . In this case, the macro eNB  211  does not need to maintain a resource which is used for processing the data packet, e.g., bearer connection information. 
         [0090]    Another example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 2C . 
         [0091]      FIG. 2C  schematically illustrates another example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure. 
         [0092]    Referring to  FIG. 2C , a macro eNB  211  transmits/receives a control signal to/from the UE  215 , and transmits a downlink data packet to the UE  215 . The small cell eNB  213  receives an uplink data packet from the UE  215 , and transmits a downlink data packet to the UE  215 . 
         [0093]    The UE  215  may simultaneously receive downlink data packets from both the macro eNB  211  and the small cell eNB  213 , or may receive a downlink data packet from one of the macro eNB  211  and the small cell eNB  213 . The UE  215  may transmit an uplink data packet to only the small cell eNB  213 . 
         [0094]    The UE  215  should be connected to the small cell eNB  213  at a timing point that the UE  215  wants to transmit an uplink data packet in order to transmit the uplink data packet. If the UE  215  is connected to the macro eNB  211  when the UE  215  wants to transmit the uplink data packet, the UE  215  should perform a switching operation from the macro eNB  211  to the small cell eNB  213 . In this case, the macro eNB  211  does not need to maintain a resource for the uplink data packet, e.g., bearer connection information. 
         [0095]    In another example, a UE is set to receive different types of services from a macro eNB and a small cell eNB. In this example, the macro eNB provides the first type of service to the UE, and the small cell eNB provides the second type of service to the UE. The UE performs a switching operation between the macro eNB and the small cell eNB according to a timing point that the macro eNB provides the first type of service and a timing point that the small cell eNB provides the second type of service. 
         [0096]    Another example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 3A . 
         [0097]      FIG. 3A  schematically illustrates another example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure. 
         [0098]    Referring to  FIG. 3A , a time interval that a control frame which a macro eNB provides occupies, i.e., a control frame time interval is identical to a control frame time interval that a small cell eNB provides, and a time interval that a data frame which a macro eNB provides occupies, i.e., a data frame time interval is identical to a data frame time interval that a small cell eNB provides. That is, the frame deployment in  FIG. 3A  indicates a frame deployment in a case that it is assumed that the macro eNB and the small cell eNB operate the control frame time interval and the data frame time interval with the same form. 
         [0099]    Another example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 3B . 
         [0100]      FIG. 3B  schematically illustrates another example of a frame deployment for supporting a switching operation between a macro cell and a small cell in a case that a UE is located at a region in which a macro cell coverage overlaps with a small cell coverage in a mobile communication system according to an embodiment of the present disclosure. 
         [0101]    Referring to  FIG. 3B , a control frame time interval which a macro eNB provides is different from a control frame time interval which a small cell eNB provides, and a data frame time interval which the macro eNB provides is different from a data frame time interval which the small cell eNB provides. The frame deployment in  FIG. 3B  indicates a frame deployment in a case that it is assumed that the macro eNB and the small cell eNB operate the control frame time interval and the data frame time interval with the different forms. 
         [0102]    A frame configuration which is used in the macro eNB and a frame configuration which is used in the small cell eNB may be related to information related to time during a UE receives a service from the macro eNB and time during the UE receives a service from the small cell eNB, i.e., UE frame configuration information. The UE frame configuration information denotes time during the UE receives the service from the macro eNB and time during the UE receives the service from the small cell eNB. 
         [0103]    For example, the UE frame configuration information may be transmitted to the UE if the UE attaches to a network. In this case, the UE frame configuration information may be transmitted to the UE using a RRC message. Alternatively, the UE frame configuration information may be transmitted to the UE using a message which sets a service bearer for the UE. 
         [0104]    If the UE frame configuration information needs to be changed after the UE frame configuration information is transmitted to the UE, the changed UE frame configuration information is transmitted to the UE through a message which re-configures a service bearer for the UE, or the changed UE frame configuration information is transmitted to the UE through a RRC message as a new form. Accordingly, the UE frame configuration information which is received in the UE is valid until the UE receives the next UE frame configuration information. 
         [0105]    For example, the UE frame configuration information may be determined based on a time during which the UE receives a service from a macro eNB, or a service type of a service which the UE will receive. 
         [0106]    The UE frame configuration information may be transmitted to the UE if the UE attaches to a network. In this case, the UE frame configuration information may be transmitted to the UE using a RRC message. Alternatively, the UE frame configuration information may be transmitted to the UE using a message which sets a service bearer for the UE. 
         [0107]    If the UE frame configuration information needs to be changed after the UE frame configuration information is transmitted to the UE, the changed UE frame configuration information is transmitted to the UE through a message which re-configures a service bearer for the UE, or the changed UE frame configuration information is transmitted to the UE through a RRC message as a new form. Accordingly, the UE frame configuration information which is received in the UE is valid until the UE receives the next UE frame configuration information. 
         [0108]    For example, the UE frame configuration information may be determined based on a time during which the UE receives a service from a macro eNB, or a service type of a service which the UE will receive, and a detailed description will be followed. 
         [0109]    If the UE frame configuration is determined based on the time during which the UE receives the service from the macro eNB, the service which the UE receives from the macro eNB includes, for example, a UE operating control signal transmitting/receiving process, a channel measurement report signal transmitting/receiving process, and a service which is limited to a macro eNB, e.g., a voice over internet protocol (VoIP) service. For example, the time during which the UE receives the service from the macro eNB may correspond to time which is necessary for the UE to report a report measurement to the macro eNB. If the macro eNB provides a default service, e.g., a VoIP service or a best effort service, the time during which the UE receives the service from the macro eNB may correspond to time during which the UE receives the default service from the macro eNB and time which is necessary for the UE to report a measurement result to the macro eNB. The time during which the UE receives the service from the macro eNB may correspond to time during which the UE reports the measurement result to the macro eNB and time during the UE transmits/receives a RRC signal to/from the macro eNB. 
         [0110]    If the UE frame configuration is determined based on the type of the service which the UE will receive, time which is necessary for receiving a default service from the macro eNB may correspond to a time frame of the macro eNB and time which is necessary for receiving a multimedia service from the small cell eNB may correspond to a time frame of the small cell eNB when the UE receives the default service from the macro eNB and the multimedia service from the small cell eNB. 
         [0111]    The UE frame configuration information may be changed while the UE receives the service from at least one of the macro eNB and the small cell eNB. In this case, the UE frame configuration information may be determined based on the time required for a service which is activated for the UE. If a service which the UE receives at an initial setting process through the small cell eNB is the VoIP service, the time required for the UE to receive the VoIP service may correspond to time during which the UE receives a service from the small cell eNB, and remaining time may correspond to time during which the UE receives a service from the macro eNB. 
         [0112]    If the UE additionally receives a video streaming service from the small cell eNB while receiving the VoIP service from the small cell eNB, the time required for receiving the VoIP service and the video streaming service may correspond to time during which the UE receives the service from the small cell eNB, and remaining time to time during which the UE receives the service from the macro eNB. 
         [0113]    On the other hand, the time during which the UE receives the service from the macro eNB and the time during which the UE receives the service from the small cell eNB may be determined using the number of automatic retransmission request (ARQ) blocks which the UE will receive/transmit in each of the macro eNB and the small cell eNB. Each of the macro eNB and the small cell eNB determines the number of ARQ blocks which each of the macro eNB and the small cell eNB will transmit/receive with the UE in advance, the UE processes ARQ blocks of which the number is determined in the macro eNB and switches to the small cell eNB to process ARQ blocks of which the number is determined in the small cell eNB thereby maintaining a dual connection with the macro eNB and the small cell eNB. 
         [0114]    Even though the time during which the UE receives the service from the macro eNB and the time during which the UE receives the service from the small cell eNB are determined based on UE frame configuration information, the UE may not operate using the UE frame configuration information if a specific event occurs. This is described below with reference to  FIGS. 4A and 4B . 
         [0115]      FIG. 4A  schematically illustrates an example of operating a UE frame according to event occurrence in a mobile communication system according to an embodiment of the present disclosure. 
         [0116]    Referring to  FIG. 4A , a region ‘C’ denotes a control frame, and a region ‘D’ denotes a data frame. A UE  430  should receive a user data signal from a small cell eNB  420  in a time interval  411  which is indicated with a dotted line. In the time interval  411 , an event that the UE  430  should transmit an event based channel measurement report message or a RRC message to the macro eNB  410  may occur. In this case, even though the time during which the UE  430  receives a service from the small cell eNB  420  does not end, the UE  430  may switch from the small cell eNB  420  to the macro eNB  410  to perform an event related operation, i.e., a transmitting/receiving operation for an event related message. 
         [0117]    After completing the event related operation with the macro eNB  410 , the UE  430  receives the service from the macro eNB  410  if a related timing point is in a time interval during which the UE  430  receives the service from the macro eNB  410  corresponding to the UE frame configuration information. If the related timing point is a timing point at which the UE  430  receives the service from the small cell eNB  420  corresponding to the UE frame configuration information, the UE  430  switches from the macro eNB  410  to the small cell eNB  420  to receive the service from the small cell eNB  420 . 
         [0118]    Another example of operating a UE frame according to event occurrence in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 4B . 
         [0119]      FIG. 4B  schematically illustrates another example of operating a UE frame according to event occurrence in a mobile communication system according to an embodiment of the present disclosure. 
         [0120]    Referring to  FIG. 4B , a radio link failure (RLF) event where a UE  480  no longer receives service from a small cell eNB A  460  in a time interval during which the UE  480  receives the service from the small cell eNB A  460  according to UE frame configuration information may occur at time  451 . In this case, the UE  480  switches from the small cell eNB A  460  to a macro eNB  450  to report that the RLF occurs in the small cell eNB A  460  to the macro eNB  450 . 
         [0121]    Since the small cell eNB A  460  is no longer providing service UE  480 , the macro eNB  450  may determine a handover for the UE  480  in order for other small cell eNB or macro eNB to provide the service for the UE  480 . If the macro eNB  450  selects other small cell eNB as an eNB which will provide the service for the UE  480 , the macro eNB  450  may directly the service to the UE  480  in order to minimize service time delay for the UE  480  before resuming the service for the UE  480  with the other small cell eNB. If the macro eNB  450  completes preparation of providing the service to the UE  480  with the other small cell eNB while temporarily providing the service to the UE  480  before the other small cell eNB provides the service to the UE  480 , the macro eNB  450  commands the UE  480  to switch to the other small cell eNB. 
         [0122]    Accordingly, the UE  480  switches from the macro eNB  450  to the other small cell eNB (i.e., a small cell eNB B  470 ) to continuously receive the service which the UE  480  has received from the small cell eNB A  460  from the small cell eNB B  470 . That is, the UE  480  maintains a dual connection with the macro eNB  450  and the small cell eNB B  470  corresponding to the UE frame configuration information. 
         [0123]    A process of performing a switching operation between a macro eNB and a small cell eNB in a UE in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 5 . 
         [0124]      FIG. 5  schematically illustrates a process of performing a switching operation between a macro eNB and a small cell eNB in a UE in a mobile communication system according to an embodiment of the present disclosure. 
         [0125]    Referring to  FIG. 5 , the mobile communication system includes a UE  510 , a macro eNB  520 , a small cell eNB A  530 , a small cell eNB B  540 , and a GW  550 . 
         [0126]    After being powered on at operation  511 , the UE  510  performs a cell search process at operation  513 . The UE  510  receives a synchronization channel (SCH) signal and a broadcast channel (BCH) signal from the macro eNB  520  which is selected according to performing the sell search process at operation  515 . The UE  510  transmits a random access channel (RACH) signal to the macro eNB  520  to perform an uplink access process with the macro eNB  520  at operation  517 . 
         [0127]    The UE  510  performs a RRC connection setup process with the macro eNB  520  at operation  519 . In the RRC connection setup process, a RRC connection setup message is exchanged between the UE  510  and the macro eNB  520 . The RRC connection setup message includes switching capability information on the UE  510 , and the switching capability information includes information indicating whether a related UE supports a switching operation between a macro eNB and a small cell eNB. In the example shown in  FIG. 5 , the switching capability information indicates that the related UE (i.e., the UE  510 ) supports the switching operation between the macro eNB and the small cell eNB. The UE  510  performs an authentication process, an encryption process, and a network application support (NAS) connection setup process with the macro eNB  520  and the GW  550  at operation  521 . The detailed description of the authentication process, the encryption process, and the NAS connection setup process will be omitted herein. 
         [0128]    The UE  510  supports the switching operation between the macro eNB and the small cell eNB, so the macro eNB  520  determines whether the UE  510  needs to receive a service from a small cell eNB not the macro eNB  520  at operation  523 . If the UE  510  needs to receive the service from the small cell eNB not the macro eNB  520 , the macro eNB  520  provides small cell eNB information indicating information on small cell eNBs which are connected to the macro eNB  520  to the UE  510 . The UE  510  performs a measurement process for the small cell eNBs at operation  525 . The small cell eNB information includes information necessary for performing a measurement process for each of the small cell eNBs which are connected to the macro eNB  520 , e.g., system information, a measurement metric, a measurement report metric, and the like. After receiving the small cell eNB information, the UE  510  performs a measurement process for small cell eNBs based on the small cell eNB information at operations  527  and  529 . After performing the measurement process for the small cell eNBs, the UE  510  transmits a measurement report message including the measurement process performance result to the macro eNB  520  at operation  531 . 
         [0129]    After receiving the measurement report message from the UE  510 , the macro eNB  520  determines a small cell eNB which will provide the service to the UE  510  based on the measurement process performance result included in the measurement report message. In  FIG. 5 , it will be assumed that the macro eNB  520  determines the small cell eNB which will provide the service to the UE  510  as the small cell eNB A  530 , so the macro eNB  520  performs a bearer setup process with the small cell eNB A  530  and the GW  550  at operation  533 . 
         [0130]    The macro eNB  520  transmits a bearer parameter for a bearer through which the small cell eNB A  530  will provide the service to the UE  510  and path information on a path between the macro eNB  520  and the GW  550  for the bearer to the small cell eNB A  530 . After receiving the bearer parameter and the path information from the macro eNB  520 , the small cell eNB A  530  establishes a path with the GW  550  based on the path information. The GW  550  may or may not recognize existence of the small cell eNB A  530 . If the GW  550  does not recognize the existence of the small cell eNB A  530 , the small cell eNB A  530  intercepts a data packet which is transferred from the GW  550  to transfer the data packet to the UE  520  instead of the macro eNB  520 , and transfers a data packet which is received from the UE  520  to the GW  550  instead of the macro eNB  520 . 
         [0131]    After setting up the bearer, the macro eNB  520  transmits a RRC connection reconfiguration message to the UE  510  at operation  535 . The RRC connection reconfiguration message includes bearer parameters related to the set up bearer, small cell eNB identifier (ID), information on a dedicated RACH resource in a related small cell eNB, UE-frame configuration information, measurement configuration information, and the like. The information on the dedicated RACH resource indicates information on a dedicated RACH resource which is allocated for transmitting a switch indicator indicating that the UE  510  has switched to the small cell eNB A  530 . The RRC connection reconfiguration message includes switch indication information indicating that the UE  510  should switch to the small cell eNB A  530 . 
         [0132]    After receiving the RRC connection reconfiguration message from the macro eNB  520 , the UE  510  switches from the macro eNB  520  to the small cell eNB A  530 , and transmits a switch indicator indicating that the UE  510  switches from the macro eNB  520  to the small cell eNB A  530  using a dedicated RACH resource corresponding to the information on the dedicated RACH resource which is transferred through the RRC connection reconfiguration message. After receiving the RRC connection reconfiguration message, the UE  510  transmits a RACH signal including a switch indicator to the small cell eNB A  530  at operation  537 . After receiving the RACH signal including the switch indicator from the UE  510 , the small cell eNB A  530  transmits a RACH response message to the UE  510  at operation  539 . A communication process for a service indicated by the RRC connection reconfiguration message is performed between the UE  510  and the small cell eNB A  530  at operation  541 . 
         [0133]    Although  FIG. 5  illustrates a process of performing a switching operation between a macro eNB and a small cell eNB in a UE in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 5 . For example, although shown as a series of operations, various operations in  FIG. 5  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0134]    A process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIGS. 6A and 6B . 
         [0135]    An example of a process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 6A . 
         [0136]      FIG. 6A  schematically illustrates an example of a process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0137]    Referring to  FIG. 6A , the mobile communication system includes a UE  610 , a macro eNB  620 , a small cell eNB  630 , a mobility management entity (MME)  640 , and a serving-gateway (S-GW) or packet-gateway (P-GW)  650 . 
         [0138]    The MME  640  transmits an initial context setup request message for the UE  610  to the macro eNB  620  which is connected to the UE  610  which performs a network entry process at operation  611 . The MME  640  transmits an attach accept message to the UE  610  at operation  613 . After receiving the initial context setup request message from the MME  640 , the macro eNB  620  determines a small cell eNB from which the UE  610  will receive a service at operation  615 . 
         [0139]    After receiving the attach accept message from the MME  640 , the UE  610  performs an access stratum (AS) security setup process with the macro eNB  620  at operation  617 . After performing the AS security setup process with the UE  610 , the macro eNB  620  transmits a bearer setup command message to the small cell eNB  630  at operation  619 . The bearer setup command message is a message which commands to set up a data path, and includes a UE ID of a UE to which the small cell eNB  630  will provide a service, i.e., the UE  610 , an S1 S-GW tunnel endpoint ID (TEID) as a UE data path ID of a UE data path between the S-GW  650  and the macro eNB  620 , an S1 eNB TEID as a UE data path ID of a UE data path between the macro eNB  620  and the small cell eNB  630 , an AS security key, and the like. 
         [0140]    After receiving the bearer setup command message from the macro eNB  620 , the small cell eNB  630  transmits a bearer setup notify message as a response message to the bearer setup command message to the macro eNB  620  at operation  621 . After receiving the bearer setup notify message from the small cell eNB  630 , the macro eNB  620  transmits a RRC connection reconfiguration message to the UE  610  at operation  623 . The RRC connection reconfiguration message includes a small cell eNB ID of a small cell eNB from which the UE  610  will receive a service, i.e., the small cell eNB  630 , a switching indication information which commands the UE  610  to switch to a small cell eNB corresponding to the small cell eNB ID, information on a service which the UE  610  will receive from the small cell eNB  630 , bearer parameters, and information on a RACH resource which is used for the UE  610  to transmit a switch indicator indicating that the UE  610  switches to the small cell eNB  630  to the small cell eNB  630 . 
         [0141]    After receiving the RRC connection reconfiguration message from the macro eNB  620 , the UE  610  switches to the small cell eNB  630  corresponding to the RRC connection reconfiguration message, and performs a data radio bearer (DRB) establish process with the small cell eNB  630  at operation  625 . After the DRB establish process between the UE  610  and the small cell eNB  630  is completed, the small cell eNB  630  transmits a bearer setup complete message indicating that a bearer setup has been completed to the macro eNB  620  at operation  627 . The bearer setup complete message includes a UE ID of the UE  610 , an S1 eNB TEID, and the like. 
         [0142]    After receiving the bearer setup complete message from the small cell eNB  630 , the macro eNB  620  transmits an initial context setup response message as a response message to the initial context setup message to the MME  640  at operation  629 . The initial context setup response message includes an eNB TEID, EPS bearer ID, and the like. The EPS bearer ID denotes a UE data path ID of a UE data path between the macro eNB  620  and the S-GW  650 , i.e., an ID of an EPS bearer between the macro eNB  620  and the S-GW  650 . 
         [0143]    After completing the DRB establish process with the small cell eNB  630 , the UE  610  transmits an attach complete message indicating that a network attach has been completed to the MME  640  at operation  631 . The attach complete message includes an EPS bearer ID. After receiving the attach complete message from the UE  610 , the MME  640  transmits a modify bearer message to the S-GW  650  at operation  633 . The modify bearer message includes an S1 eNB TEID, and an EPS bearer ID. 
         [0144]    Although  FIG. 6A  illustrates an example of a process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 6A . For example, although shown as a series of operations, various operations in  FIG. 6A  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0145]    Another example of a process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 6B . 
         [0146]      FIG. 6B  schematically illustrates another example of a process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0147]    Referring to  FIG. 6B , the mobile communication system includes a UE  610 , a macro eNB  620 , a small cell eNB  630 , an MME  640 , and a S-GW (or P-GW)  650 . 
         [0148]    The MME  640  transmits an initial context setup request message for the UE  610  to the macro eNB  620  which is connected to the UE  610  which performs a network entry process at operation  651 . The MME  640  transmits an attach accept message to the UE  610  at operation  653 . After receiving the initial context setup request message from the MME  640 , the macro eNB  620  determines a small cell eNB from which the UE  610  will receive a service at operation  655 . 
         [0149]    After receiving the attach accept message from the MME  640 , the UE  610  performs an AS security setup process with the macro eNB  620  at operation  657 . After performing the AS security setup process with the UE  610 , the macro eNB  620  transmits a bearer setup command message to the small cell eNB  630  at operation  659 . The bearer setup command message is a message which commands to set up a data path, and includes a UE ID of a UE to which the small cell eNB  630  will provide a service, i.e., the UE  610 , an X2 m-eNBTEID as a UE data path ID of a UE data path between the macro eNB  620  and the small cell eNB  630 , an AS security key, and the like. 
         [0150]    After receiving the bearer setup command message from the macro eNB  620 , the small cell eNB  630  transmits a bearer setup notify message as a response message to the bearer setup command message to the macro eNB  620  at operation  661 . After receiving the bearer setup notify message from the small cell eNB  630 , the macro eNB  620  transmits a RRC connection reconfiguration message to the UE  610  at operation  663 . The RRC connection reconfiguration message includes a small cell eNB ID of a small cell eNB from which the UE  610  will receive a service, i.e., the small cell eNB  630 , switching indication information which commands the UE  610  to switch to a small cell eNB corresponding to the small cell eNB ID, information on a service which the UE  610  will receive from the small cell eNB  630 , bearer parameters, information on a RACH resource which is used for the UE  610  to transmit a switch indicator indicating that the UE  610  switches to the small cell eNB  630  to the small cell eNB  630 . 
         [0151]    After receiving the RRC connection reconfiguration message from the macro eNB  620 , the UE  610  switches to the small cell eNB  630  corresponding to information included in the RRC connection reconfiguration message, and performs a DRB establish process with the small cell eNB  630  at operation  665 . After the DRB establish process between the UE  610  and the small cell eNB  630  is completed, the small cell eNB  630  transmits a bearer setup complete message indicating that a bearer setup has been completed to the macro eNB  620  at operation  667 . The bearer setup complete message includes a UE ID of the UE  610 , an X2 s-eNB TEID, and the like. 
         [0152]    After receiving the bearer setup complete message from the small cell eNB  630 , the macro eNB  620  transmits an initial context setup response message as a response message to the initial context setup message to the MME  640  at operation  669 . The initial context setup response message includes an S1 eNB TEID, an EPS bearer ID, and the like. The EPS bearer ID denotes a UE data path ID of a UE data path between the macro eNB  620  and the S-GW  650 , i.e., an ID of an EPS bearer between the macro eNB  620  and the S-GW  650 . 
         [0153]    After completing the DRB establish process with the small cell eNB  630 , the UE  610  transmits an attach complete message indicating that a network attach has been completed to the MME  640  at operation  671 . The attach complete message includes an EPS bearer ID. After receiving the attach complete message from the UE  610 , the MME  640  transmits a modify bearer message to the S-GW  650  at operation  673 . The modify bearer message includes an S1 eNB TEID, and an EPS bearer ID. 
         [0154]    Although  FIG. 6B  illustrates another example of a process of setting up a data path which supports that a UE performs a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 6B . For example, although shown as a series of operations, various operations in  FIG. 6B  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0155]    A process of switching to a macro eNB in order for a UE which receives a service from a small cell eNB to periodically report a measurement process performance result in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 7 . 
         [0156]      FIG. 7  schematically illustrates a process of switching to a macro eNB in order for a UE which receives a service from a small cell eNB to periodically report a measurement process performance result in a mobile communication system according to an embodiment of the present disclosure. 
         [0157]    Referring to  FIG. 7 , the mobile communication system includes a UE  710 , a macro eNB  720 , and a small cell eNB  730 . 
         [0158]    The macro eNB  720  selects a small cell eNB which will provide a service to the UE  710 , e.g., the small cell eNB  730 , and transmits a bearer setup command message to the small cell eNB  730  at operation  711 . The bearer setup command message includes a UE ID of the UE  710 , UE frame configuration information for the UE  710 , measurement process perform information for the UE  710 , and the like. The measurement process perform information for the UE  710  included in the bearer setup command message includes measurement report period information as information on a period by which the UE  710  performs a measurement report process. 
         [0159]    The macro eNB  720  transmits a RRC connection reconfiguration message to the UE  710  at operation  713 . The RRC connection reconfiguration message includes small cell eNB information of a small cell eNB to which the UE  710  will switch, measurement configuration information, and UE frame configuration information. The measurement configuration information includes period information denoting a period by which the UE  710  performs a measurement report process, event condition information denoting an event condition at which the UE  710  performs the measurement report process, and the like. The UE  710  performs the measurement report process upon satisfying the event condition. 
         [0160]    After receiving the RRC connection reconfiguration message from the macro eNB  720 , the UE  710  switches to the small cell eNB  730  corresponding to the information included in the RRC connection reconfiguration message, and receives a service from the small cell eNB  730  at operation  715 . If a current timing point is a timing point at which the UE  710  transmits a measurement process performance result to the macro eNB  720  corresponding to the measurement configuration information, i.e., a timing point at which the UE  710  transmits a measurement report message, the UE  710  switches from the small cell eNB  730  to the macro eNB  720  at operation  717 . After switching to the macro eNB  720 , the UE  710  transmits the measurement report message to the macro eNB  720  at operation  719 . The time after the timing point at which the UE  710  switches to the macro eNB  720  for transmitting the measurement report message becomes the time during which a service for the UE  710  is invalid in the small cell eNB  730  at operation  721 . 
         [0161]    After transmitting the measurement report message to the macro eNB  720 , the UE  710  detects that a current timing point is a timing point at which the UE  710  will switch to the small cell eNB  730  corresponding to UE frame configuration information at operation  723 . Accordingly, the UE  710  switches to the small cell eNB  730 , and receives a service from the small cell eNB  730  at operation  725 . 
         [0162]    The switching process in  FIG. 7  is a switching process which occurs according to periodically reporting the measurement process performance result. However, it will be understood by those of ordinary skill in the art that the switching process may be periodically performed. 
         [0163]    Although  FIG. 7  illustrates a process of switching to a macro eNB in order for a UE which receives a service from a small cell eNB to periodically report a measurement process performance result in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 7 . For example, although shown as a series of operations, various operations in  FIG. 7  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0164]    A process of switching to a macro eNB in order for a UE which receives a service from a small cell eNB to report a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 8 . 
         [0165]      FIG. 8  schematically illustrates a process of switching to a macro eNB in order for a UE which receives a service from a small cell eNB to report a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure. 
         [0166]    Referring to  FIG. 8 , the mobile communication system includes a UE  810 , a macro eNB  820 , and a small cell eNB  830 . 
         [0167]    The UE  810  switches to the small cell eNB  830  to receive a service from the small cell eNB  830  at operation  811 . While receiving the service from the small cell eNB  830 , the UE  810  detects that an event in which the UE  810  should report that a measurement process performance result occurs at operation  813 . The UE  810  determines whether a current timing point is a timing point at which the UE  810  switches to the macro eNB  820  using UE frame configuration information at operation  815 . 
         [0168]    If the current timing point is not the timing point which the UE  810  switches to the macro eNB  820 , the UE  810  transmits a medium access control protocol data unit (MAC PDU) including a switch indicator indicating that the UE  810  will switch to the macro eNB  820  to the small cell eNB  830  at operation  817 . After receiving the MAC PDU from the UE  810 , the macro eNB  820  transmits a switch confirm indicator indicating that the small cell eNB  830  has detected that the UE  810  will switch to the macro eNB  820  to the UE  810  at operation  819 . The MPC PDUs at operations  817  and  819  may be one of layer 2 (L2) messages, codes which are transmitted through a physical layer (PHY) channel, codes which are transmitted through a channel quality indicator (CQI) channel, and codes which are transmitted through a RACH. Each of the codes may include the UE ID, or may be allocated to the UE  810  in advance. 
         [0169]    If the current timing point is the timing point at which the UE  810  switches to the macro eNB  820 , the UE  810  switches to the macro eNB  820  at operation  821 . According to switching to the macro eNB  820 , the UE  810  may not receive the service from the small cell eNB  830  at operation  823 . 
         [0170]    The UE  810  transmits a measurement report message including a measurement process performance result to the macro eNB  820  at operation  825 . After receiving the measurement report message from the UE  810 , the macro eNB  820  calculates a time during which the UE  810  should be connected to the macro eNB  820  and a timing point at which the UE  810  may switch to the small cell eNB  830  again. The macro eNB  820  transmits a UE switch indicator message to the small cell eNB  830  at operation  827 . The UE switch indicator message includes reason information indicating why the UE  810  should be connected to the macro eNB  820  and time information indicating the time during which the UE  810  should be connected to the macro eNB  820 . The macro eNB  820  transmits a measurement report acknowledgement (ACK) message as a response message to the measurement report message to the UE  810  at operation  829 . The measurement report ACK message includes the time information indicating the time during which the UE  810  should be connected to the macro eNB  820 . 
         [0171]    After the time corresponding to the time information included in the measurement report ACK message has elapsed, the UE  810  switches to the small cell eNB  830  again if related time is included in a time interval during which the UE  810  receives the service from the small cell eNB  830  according to UE frame configuration information at operation  831 . The UE  810  receives the service from the small cell eNB  830  at operation  833 . 
         [0172]    Although  FIG. 8  illustrates a process of switching to a macro eNB in order for a UE which receives a service from a small cell eNB to report a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 8 . For example, although shown as a series of operations, various operations in  FIG. 8  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0173]    An example of a process of switching to a macro eNB in order for a UE to perform a RRC process in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 9 . 
         [0174]      FIG. 9  schematically illustrates an example of a process of switching to a macro eNB in order for a UE to perform a RRC process in a mobile communication system according to an embodiment of the present disclosure. 
         [0175]    Referring to  FIG. 9 , the mobile communication system includes a UE  910 , a macro eNB  920 , and a small cell eNB  930 . 
         [0176]    The UE  910  switches to the small cell eNB  930  to receive a service from the small cell eNB  930  at operation  911 . While the UE  910  receives the service from the small cell eNB  930 , the macro eNB  920  determines whether the UE  910  needs to perform a RRC process at operation  913 . If the UE  910  needs to periodically transmit a measurement report message, or the UE  910  needs to transmit the measurement report message according to event occurrence, or a specific event occurs, the macro eNB  920  may determine that the UE  910  needs to perform the RRC process. If the UE  910  needs to perform the RRC process, the macro eNB  920  determines whether a current timing point is a timing point at which the UE  910  switches to the macro eNB  920  based on frame configuration information of the UE  910  at operation  915 . 
         [0177]    The macro eNB  920  calculates the time during which the UE  910  should be connected to the macro eNB  920  and a timing point at which the UE  910  may switch to the small cell eNB  930  again. The macro eNB  920  transmits a UE switch indicator message to the small cell eNB  930  at operation  917 . The UE switch indicator message includes reason information indicating why the UE  910  should be connected to the macro eNB  920  and time information indicating the time during which the UE  910  should be connected to the macro eNB  920 . 
         [0178]    If the current timing point is not the timing point which the UE  910  should switch to the macro eNB  920 , the small cell eNB  930  transmits a MAC PDU including switching indication information indicating that the UE  910  should switch to the macro eNB  920 , the reason information why the UE  910  should switch to the macro eNB  920 , and the time information indicating the time during which the UE  910  should be connected to the macro eNB  920  to the macro eNB  920  at operation  919 . After receiving the MAC PDU from the small cell eNB  930 , the UE  910  transmits a MAC PDU including a switch confirm indicator indicating that the UE  910  confirms a schedule for switching to the macro eNB  920  to the small cell eNB  930  at operation  921 . The MPC PDUs at operations  919  and  921  may be one of an L2 message, a code which is transmitted through a PHY channel, a code which is transmitted through a CQI channel, and a code which is transmitted through a RACH. Each of the codes may include the UE ID, or may be allocated to the UE  910  in advance. 
         [0179]    If the current timing point is the timing point at which the UE  910  should switch to the macro eNB  920 , the UE  910  switches from the small cell eNB  930  to the macro eNB  920  at operation  923 . According to switching from the small cell eNB  930  to the macro eNB  920 , the UE  910  may not receive the service from the small cell eNB  930  at operation  925 . 
         [0180]    After switching from the small cell eNB  930  to the macro eNB  920 , the UE  910  performs a RRC transaction, i.e., a RRC message transmitting/receiving process with the macro eNB  920  at operation  927 . A RRC message transmitted from the macro eNB  920  to the UE  910  includes information on the time during which the UE  910  should be connected to the macro eNB  920 . 
         [0181]    Although  FIG. 9  illustrates an example of a process of switching to a macro eNB in order for a UE to perform a RRC process in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 9 . For example, although shown as a series of operations, various operations in  FIG. 9  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0182]    Another example of a process of switching to a macro eNB in order for a UE to perform a RRC process in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 10 . 
         [0183]      FIG. 10  schematically illustrates another example of a process of switching to a macro eNB in order for a UE to perform a RRC process in a mobile communication system according to an embodiment of the present disclosure. 
         [0184]    Referring to  FIG. 10 , the mobile communication system includes a UE  1010 , a macro eNB  1020 , and a small cell eNB  1030 . 
         [0185]    The UE  1010  switches to the small cell eNB  1030  to receive a service from the small cell eNB  1030  at operation  1011 . In  FIG. 10 , the UE  1010  switches to the small cell eNB  1030  in order to receive only an uplink data packet from the small cell eNB  1030 . The UE  1010  may receive a downlink data packet and a control signal without performing a switching operation between the macro eNB  1020  and the small cell eNB  1030 . 
         [0186]    While the UE  1010  receives the service from the small cell eNB  1030 , the macro eNB  1020  determines whether the UE  1010  needs to perform a RRC process at operation  1013 . If the UE  1010  needs to periodically transmit a measurement report message, or the UE  1010  needs to transmit the measurement report message according to event occurrence, or a specific event occurs, the macro eNB  1020  may determine that the UE  1010  needs to perform the RRC process. 
         [0187]    If the UE  1010  needs to perform the RRC process, the macro eNB  1020  transmits a RRC transaction request message to the UE  1010  at operation  1015 . The RRC transaction request message includes switching indication information indicating that the UE  1010  should switch to the macro eNB  1020  and information indicating time during which the UE  1010  should be connected to the macro eNB  1020 . The RRC transaction request message indicates that a RRC control process is performed. 
         [0188]    The macro eNB  1020  transmits a RRC message indicating that the UE  1010  should temporarily switch from the small cell eNB  1030  to the macro eNB  1020  to the small cell eNB  1030  at operation  1017 . The RRC message includes a UE temporal switch indicator and a UE ID of the UE  1010 , and the UE temporal switch indicator indicates that a related UE should temporarily switch from an eNB to which the related UE is currently connected to other eNB. 
         [0189]    According to the reception of the RRC transaction request message from the macro eNB  1020 , the UE  1010  detects that the UE  1010  should switch from the small cell eNB  1030  to the macro eNB  1020  at operation  1019  and switches from the small cell eNB  1030  to the macro eNB  1020  at operation  1021 . The UE  1010  transmits a RRC transaction response message as a response message to the RRC transaction request message to the macro eNB  1020  at operation  1023 . 
         [0190]    After receiving the RRC transaction response message from the UE  1010 , the macro eNB  1020  transmits a RRC message including a switch indicator indicating that the UE  1010  has switched from the small cell eNB  1030  to the macro eNB  1020  to the small cell eNB  1030  at operation  1025 . The RRC message includes a reason why the UE  1010  should switch to the macro eNB  1020  and information on time during which the UE  1010  should be connected to the macro eNB  1020 . After switching from the small cell eNB  1030  to the macro eNB  1020 , the UE  1010  may not receive the service from the small cell eNB  1030  at operation  1027 . 
         [0191]    The UE  1010  and the macro eNB  1020  process remaining RRC transaction, and an uplink data packet of the UE  1010  may be served through the macro eNB  1020  while the UE  1010  is connected to the macro eNB  1020  at operation  1029 . 
         [0192]    Although  FIG. 10  illustrates another example of a process of switching to a macro eNB in order for a UE to perform a RRC process in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 10 . For example, although shown as a series of operations, various operations in  FIG. 10  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0193]    A process of switching to a macro eNB in order for a UE to resolve a connection failure with a small cell eNB in a mobile communication system according to an embodiment of the present disclosure will be described with reference to  FIG. 11 . 
         [0194]      FIG. 11  schematically illustrates a process of switching to a macro eNB in order for a UE to resolve a connection failure with a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0195]    Referring to  FIG. 11 , the mobile communication system includes a UE  1110 , a macro eNB  1120 , and a small cell eNB  1130 . 
         [0196]    The UE  1110  switches to the small cell eNB  1130  to receive a service from the small cell eNB  1130  at operation  1111 . While receiving the service from the small cell eNB  1130 , the UE  1110  detects that an RLF between the UE  1110  and the small cell eNB  1130  occurs at operation  1113 . The UE  1110  switches from the small cell eNB  1130  to the macro eNB  1120  to transmit an RLF indicator message to the macro eNB  1120  at operation  1115 . The RLF indicator message is a message indicating that a RLF occurs, and may be implemented with an L2 message, a RRC message, a code which is transmitted through a PHY channel, a code which is transmitted through a CQI channel, or a code which is transmitted through a RACH channel. Each of the codes includes a UE ID of the UE  1110 , or may be a code which is allocated to the UE  1110  in advance. 
         [0197]    After receiving the RLF indicator message from the UE  1110 , the macro eNB  1120  processes the RLF of the UE  1110  at operation  1117 . Simultaneously, the macro eNB  1120  performs a process which searches a new small cell eNB which will provide a service to the UE  1110 . The macro eNB  1120  transmits a RLF indicator message and a UE DRB release request message to the small cell eNB  1130  at operation  1119 . The UE DRB release request message is a message which commands to release information and a resource which the small cell eNB  1130  maintains for providing the service to the UE  1110 . 
         [0198]    The macro eNB  1120  and the UE  1110  perform a RRC connection reconfiguration transaction process at operation  1121 . According to performing the RRC connection reconfiguration transaction, the macro eNB  1120  informs the new small cell eNB which may provide the service to the UE  1110 , or transmits a macro cell indicator indicating that the macro eNB  1120  directly provides the service to the UE  1110  to the UE  1110 . 
         [0199]    If a new small cell eNB not the macro eNB  1120  is determined to serve the UE  1110 , the UE  1110  performs a process for resuming the service with the new small cell eNB. The process for resuming the service with new the small cell eNB includes a process in which the macro eNB  1120  transmits switching indication information indicating that the UE  1110  will switch to the new small cell eNB. 
         [0200]    While performing the process for resuming the service with the new small cell eNB with the UE  1110 , the macro eNB  1120  may directly provide a data packet to the UE  1110  at operation  1123 . 
         [0201]    After receiving the UE DRB release request message from the macro eNB  1120 , the small cell eNB  1130  releases the information and the resource which the small cell eNB  1130  maintains for providing the service to the UE  1110 , and transmits a UE DRB release confirm message as a response message to the UE DRB release request message to the macro eNB  1120  at operation  1125 . 
         [0202]    Although  FIG. 11  illustrates a process of switching to a macro eNB in order for a UE to resolve a connection failure with a small cell eNB in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 11 . For example, although shown as a series of operations, various operations in  FIG. 11  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0203]    A process of performing an initial attach process in a UE in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 12 . 
         [0204]      FIG. 12  schematically illustrates a process of performing an initial attach process in a UE in a mobile communication system according to an embodiment of the present disclosure. 
         [0205]    Referring to  FIG. 12 , after being powered on, the UE performs a cell search process at operation  1211 . The cell search process corresponds to a process in which the UE selects a macro eNB. The UE selects the macro eNB corresponding to the result of the cell search process, and performs a random access process for attaching to the selected macro eNB at operation  1213 . The UE transmits a RRC connection setup request message to the macro eNB at operation  1215 . The RRC connection setup request message includes dual connection support information indicating whether the UE supports a dual connection with the macro eNB and a small cell eNB. 
         [0206]    The UE performs an authentication and on-access stratum (NAS) connection establishment process through the macro eNB at operation  1217 . The UE determines whether a small cell eNB search/measurement request message is received from the macro eNB at operation  1219 . If the small cell eNB search/measurement request message is received from the macro eNB, the UE performs a small cell eNB search process and a measurement process corresponding to information included in the small cell eNB search/measurement request message at operation  1221 . The UE transmits a measurement report message including the result of performing the small cell eNB search process and the measurement process to the macro eNB at operation  1223 . 
         [0207]    If the small cell eNB search/measurement request message is not received from the macro eNB, the UE determines whether a RRC connection reconfiguration request message is received from the macro eNB at operation  1225 . If the RRC connection reconfiguration request message is not received from the macro eNB, the UE performs a general process which is performed in a case that the RRC connection reconfiguration request message is not received from the macro eNB in a general mobile communication system at operation  1227 . The general process which is performed in the case that the RRC connection reconfiguration request message is not received from the macro eNB in the general mobile communication system will be omitted herein. 
         [0208]    If the small cell eNB search/measurement request message is received from the macro eNB, the UE determines whether switching indication information is included in the RRC connection reconfiguration request message at operation  1229 . If the switching indication information is not included in the RRC connection reconfiguration request message, the UE performs a connection establishment process with the macro eNB at operation  1231 . 
         [0209]    If the switching indication information is included in the RRC connection reconfiguration request message, the UE switches to the small cell eNB and performs a connection establishment process with the small cell eNB at operation  1233 . The UE uses a dual connection with the macro eNB and the small cell eNB based on UE frame configuration information to receive a communication service at operation  1235 . 
         [0210]    In  FIG. 12 , the UE performs the authentication and NAS connection establishment process, determines whether the small cell eNB search/measurement request message is received from the macro eNB, and performs the search and measurement process for the small cell eNB based on the determined result. However, it will be understood by those of ordinary skill in the art that the UE may directly perform an operation of determining whether a RRC reconfiguration request message is received from the macro eNB without performing the search and measurement process for the small cell eNB, i.e., an operation as described in operation  1225 . 
         [0211]    Although  FIG. 12  illustrates a process of performing an initial attach process in a UE in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 12 . For example, although shown as a series of operations, various operations in  FIG. 12  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0212]    A process of periodically reporting a measurement process performance result in a UE in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 13 . 
         [0213]      FIG. 13  schematically illustrates a process of periodically reporting a measurement process performance result in a UE in a mobile communication system according to an embodiment of the present disclosure. 
         [0214]    Referring to  FIG. 13 , while switching to a small cell eNB to receive a service from the small cell eNB at operation  1311 , the UE determines whether a current timing point is a timing point at which the UE periodically reports a measurement process performing result corresponding to measurement operation information received from a macro eNB at operation  1313 . If the current timing point is the timing point at which the UE periodically reports the measurement process performing result, the UE switches from the small cell eNB to the macro eNB since the UE currently receives the service from the small cell eNB at operation  1315 . The UE transmits a measurement report message including the measurement process performing result to the macro eNB at operation  1317 . 
         [0215]    The UE operates in a waiting mode until a timing point at which the UE switches from the macro eNB to the small cell eNB again corresponding to UE frame configuration information at operation  1319 , and determines a current timing point is the timing point at which the UE switches from the macro eNB to the small cell eNB again at operation  1321 . If the current timing point is the timing point at which the UE switches from the macro eNB to the small cell eNB again, the UE switches from the macro eNB to the small cell eNB and receives a service from the small cell eNB at operation  1323 . 
         [0216]    If the current timing point is not the timing point at which the UE switches from the macro eNB to the small cell eNB again, the UE returns to operation  1319  to wait until the timing point at which the UE switches from the macro eNB to the small cell eNB again. 
         [0217]    Although  FIG. 13  illustrates a process of periodically reporting a measurement process performance result in a UE in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 13 . For example, although shown as a series of operations, various operations in  FIG. 13  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0218]    A process of reporting a measurement process performance result according to event occurrence in a UE in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 14 . 
         [0219]      FIG. 14  schematically illustrates a process of reporting a measurement process performance result according to event occurrence in a UE in a mobile communication system according to an embodiment of the present disclosure. 
         [0220]    Referring to  FIG. 14 , while switching to a small cell eNB to receive a service from the small cell eNB at operation  1411 , the UE determines whether an event that the UE reports measurement process performing result according to measurement operation information received from the macro eNB occurs at operation  1413 . If the event occurs, the UE determines whether a timing point is a timing point at which the UE switches to the macro eNB based on UE frame configuration information at operation  1415 . 
         [0221]    If the timing point is not the timing point at which the UE switches to the macro eNB, the UE transmits a message indicating that the UE will temporarily switch from the small cell eNB to the macro eNB to the small cell eNB at operation  1417 . The message includes a UE temporal switch indicator and a UE ID of the UE, and the UE temporal switch indicator indicates that a related UE should temporarily switch from an eNB to which the related UE is currently connected to other eNB. The message may be implemented with one of an L2 message, a code which is transmitted through an arbitrary PHY channel, a code which is transmitted through a CQI channel, a code which is transmitted through a RACH, and the like. Each of the codes includes the UE ID of the UE, or is a code which is allocated to the UE. 
         [0222]    If the timing point is the timing point at which the UE switches to the macro eNB, the UE switches from the small cell eNB to the macro eNB since the UE currently receives a communication service form the small cell eNB at operation  1421 . The UE transmits a measurement report message including a measurement process performing result to the macro eNB at operation  1421 . The UE operates in a waiting mode until a timing point at which the UE switches from the macro eNB to the small cell eNB again corresponding to UE frame configuration information at operation  1423 , and determines a current timing point is the timing point at which the UE switches from the macro eNB to the small cell eNB again at operation  1425 . If the current timing point is the timing point at which the UE switches from the macro eNB to the small cell eNB again, the UE switches from the macro eNB to the small cell eNB and receives the communication service from the small cell eNB at operation  1427 . 
         [0223]    If the current timing point is not the timing point at which the UE switches from the macro eNB to the small cell eNB again, the UE returns to operation  1423  to wait until the timing point at which the UE switches from the macro eNB to the small cell eNB again. 
         [0224]    Although  FIG. 14  illustrates a process of reporting a measurement process performance result according to event occurrence in a UE in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 14 . For example, although shown as a series of operations, various operations in  FIG. 14  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0225]    A UE operating process in a case that a RLF occurs in a connection between a UE and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 15 . 
         [0226]      FIG. 15  schematically illustrates a UE operating process in a case that a RLF occurs in a connection between a UE and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0227]    Referring to  FIG. 15 , while switching to a small cell eNB to receive a service from the small cell eNB at operation  1511 , the UE determines whether a RLF occurs in a connection between the UE and the small cell eNB at operation  1513 . 
         [0228]    If the RLF occurs in the connection between the UE and the small cell eNB, the UE switches from the small cell eNB to the macro eNB at operation  1515 . The UE transmits a message indicating that the RLF occurs in the connection between the UE and the small cell eNB to the macro eNB at operation  1517 . 
         [0229]    The UE receives a RRC connection reconfiguration message from the macro eNB at operation  1519 . The RRC connection reconfiguration message includes information on a new small cell eNB from which the UE will receive the service, or information indicating that the UE should receive the service from the macro eNB. In  FIG. 15 , it will be assumed that the information included in the RRC connection reconfiguration message which is received from the macro eNB is the information indicating that the UE should receive the service from the new small cell eNB. 
         [0230]    The UE performs a connection establishment process with the new small cell eNB in operation  1521  according to the information included in the RRC connection reconfiguration message which is received from the macro eNB to receive a service from the new small cell eNB. 
         [0231]    If the information included in the RRC connection reconfiguration message which is received from the macro eNB is the information indicating that the UE should receive the service from the macro eNB, it will be understood by those of ordinary skill in the art that the UE no longer performs the connection establishment process with the small cell eNB, and may directly receive the service from the macro eNB. 
         [0232]    Although  FIG. 15  illustrates a UE operating process in a case that a RLF occurs in a connection between a UE and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 15 . For example, although shown as a series of operations, various operations in  FIG. 15  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0233]    A process of performing an initial attach process with a UE in a macro eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 16 . 
         [0234]      FIG. 16  schematically illustrates a process of performing an initial attach process with a UE in a macro eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0235]    Referring to  FIG. 16 , the macro eNB receives a RRC connection setup request message from a UE at operation  1611 . The RRC connection setup request message includes dual connection support information indicating whether the UE supports a dual connection. The macro eNB determines whether the dual connection support information included in the RRC setup request message indicates that the UE supports the dual connection at operation  1613 . If the dual connection support information does not indicate that the UE supports the dual connection, the macro eNB receives a data path setup message from a core network, i.e., an S-GW, to setup a data path with the S-GW at operation  1615 . The macro eNB transmits a RRC connection reconfiguration message to the UE at operation  1617 . The macro eNB sets up a data path with the UE at operation  1619 . 
         [0236]    If the dual connection support information indicates that the UE supports the dual connection, the macro eNB transmits information on a small cell eNB to the UE and commands the UE to report measurement process performing result for the small cell eNB at the same time in order to determine the small cell eNB from which the UE will receive a service at operation  1621 . The macro eNB receives a measurement report message including measurement process performing result for the small cell eNB from the UE at operation  1623 . The macro eNB selects the small cell eNB from which the UE will receive a service based on the measurement process performing result included in the measurement report message which is received from the UE at operation  1625 . 
         [0237]    The macro eNB determines whether a data path setup message which commands the UE to set up a data path from the S-GW at operation  1627 . If the data path setup message is received from the S-GW, the macro eNB sets up a data path with the S-GW at operation  1629 . The macro eNB transmits a data path setup message which commands to set up a data path with the S-GW to the selected small cell eNB which provides the service to the UE at operation  1631 . The macro eNB transmits a RRC connection reconfiguration message to the UE at operation  1633 . The RRC connection reconfiguration message includes information on the small cell eNB from which the UE will receive the service. 
         [0238]    In  FIG. 16 , as described in operation  1631 , the macro eNB commands the UE to set up the data path with the S-GW. However, it will be understood by those of ordinary skill in the art that the macro eNB may command the UE to set up a data path with the macro eNB not the S-GW. 
         [0239]    Although  FIG. 16  illustrates a process of performing an initial attach process with a UE in a macro eNB in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 16 . For example, although shown as a series of operations, various operations in  FIG. 16  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0240]    A process of performing an initial attach process with a UE in a small cell eNB in a mobile communication system according to an embodiment of the present disclosure will be described with reference to  FIG. 17 . 
         [0241]      FIG. 17  schematically illustrates a process of performing an initial attach process with a UE in a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0242]    Referring to  FIG. 17 , the small cell eNB determines whether a data path setup message which commands a UE to set up a data path with an S-GW is received from a macro eNB at operation  1711 . If the data path setup message is received, the small cell eNB acquires parameter information necessary for setting up a data path for the UE from the data path setup message at operation  1713 . The small cell eNB sets up the data path for the UE based on the acquired parameter information with the S-GW at operation  1715 . The small cell eNB determines whether a message including a switch indicator indicating that the UE has switched to the small cell eNB is received from the UE at operation  1717 . If the message including the switch indicator is received from the UE, the small cell eNB sets up a data path with the UE at operation  1719 . 
         [0243]    Alternatively, if the macro eNB and the small cell eNB directly set up the data path for the UE without passing the S-GW, the small cell eNB receives the parameter information from the macro eNB and awaits reception of a message including the switch indicator from the UE. 
         [0244]    Although  FIG. 17  illustrates a process of performing an initial attach process with a UE in a small cell eNB in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 17 . For example, although shown as a series of operations, various operations in  FIG. 17  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0245]    A process of managing a data path among a macro eNB, a small cell eNB, and GWs for supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIGS. 18A and 18B . 
         [0246]    First, an example of a process of managing a data path among a macro eNB, a small cell eNB, and GWs for supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 18A . 
         [0247]      FIG. 18A  schematically illustrates an example of a process of managing a data path among a macro eNB, a small cell eNB, and GWs for supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0248]    Referring to  FIG. 18A , the process of managing the data path in  FIG. 18A  indicates a process of managing a data path in a case that a data path for transferring a data packet for a UE is established between the small cell eNB and an S-GW. 
         [0249]    The mobile communication system includes a UE  1810 , a macro eNB  1820 , a small cell eNB  1830 , an S-GW  1840 , and a P-GW  1850 . 
         [0250]    A data path setup process according to providing a service to the UE  1810  which attaches to the macro eNB  1820  includes a data path (S1, and S5 to S8) setup process  1811  among the S-GW  1840 , the P-GW  1850 , and the macro eNB  1820  and a data path setup process  1813  between the UE  1810  and the macro eNB  1820 . 
         [0251]    If the UE  1810  receives a data service from the small cell eNB  1830 , a data path setup process includes a data path (S1, and S5 to S8) setup process  1815  between the small cell eNB  1830  and the S-GW  1840  and a data path setup process  1817  between the small cell eNB  1830  and the UE  1810 . If the S-GW  1840  does not recognize the data path setup with the small cell eNB  1830 , the S-GW  1840  recognizes the small cell eNB  1830  as the macro eNB  1820 , and the small cell eNB  1830  acquires a parameter necessary for the data path setup with the S-GW  1840  from the macro eNB  1820 . Here, the service which is provided to the UE  1810  through the data path setup process and quality of service (QoS) parameter information corresponding to the service which is provided to the UE  1810  are exchanged. 
         [0252]    Another example of a process of managing a data path among a macro eNB, a small cell eNB, and GWs for supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 18B . 
         [0253]      FIG. 18B  schematically illustrates another example of a process of managing a data path among a macro eNB, a small cell eNB, and GWs for supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0254]    Referring to  FIG. 18B , the process of managing the data path in  FIG. 18B  indicates a process of managing a data path in a case that a data path for transferring a data packet for a UE is established between the small cell eNB and the macro eNB. 
         [0255]    The mobile communication system includes a UE  1810 , a macro eNB  1820 , a small cell eNB  1830 , an S-GW  1840 , and a P-GW  1850 . 
         [0256]    A data path setup process according to providing a service to the UE  1810  which attaches to the macro eNB  1820  includes a data path (S1, and S5 to S8) setup process  1851  among the S-GW  1840 , the P-GW  1850 , and the macro eNB  1820  and a data path setup process  1853  between the UE  1810  and the macro eNB  1820 . 
         [0257]    If the UE  1810  receives a data service from the small cell eNB  1830 , a data path setup process includes a data path setup process  1855  between the small cell eNB  1830  and the macro eNB  1820  and a data path setup process  1857  between the small cell eNB  1830  and the UE  1810 . 
         [0258]    The service which is provided to the UE  1810  through the data path setup process and QoS parameter information corresponding to the service which is provided to the UE  1810  are exchanged. 
         [0259]    Another example of a process of supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference  FIG. 19 . 
         [0260]      FIG. 19  schematically illustrates another example of a process of supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0261]    Referring to  FIG. 19 , the mobile communication system includes a UE  1910 , a macro eNB  1920 , an old small cell eNB  1930 , and a new S-GW  1940 . 
         [0262]    The UE  1910  transmits a measurement report message to the macro eNB  1920  at operation  1911 . After receiving the measurement report message from the UE  1910 , the macro eNB  1920  determines whether there is a need for changing a small cell eNB which provides a service to the UE  1910  based on information included in the measurement report message at operation  1913 . The macro eNB  1920  transmits a switching indication message including switching indication information indicating that the UE  1910  should switch from an old small cell eNB from which the UE  1910  currently receives a service as an old small cell eNB  1930  to a new small cell eNB, i.e., a new small cell eNB  1940 , to the UE  1910  at operation  1915 . The switching indication message may include information indicating time during which the UE  1910  will be connected to the old small cell eNB  1930 . 
         [0263]    The macro eNB  1920  transmits a bearer setup command message as a data path setup command message which commands to set up a data path with the UE  1910  to the new small cell eNB  1940  at operation  1917 . The bearer setup command message may include a UE ID of the UE  1910 , an X2 m-eNB TEID as path setup information for the UE  1910  between the macro eNB  1920  and the new small cell eNB  1940  (or S1 m-eNB TEID as path setup information for the UE  1910  between the new small cell eNB  1940  and a S-GW (not shown in  FIG. 19 )), AS security information of the UE  1910 , and the like. After receiving the bearer setup command message from the macro eNB  1920 , the new small cell eNB  1940  transmits a bearer setup notify message as a response message to the bearer setup command message to the macro eNB  1920  at operation  1919 . 
         [0264]    After receiving the bearer setup notify message from the new small cell eNB  1940 , the macro eNB  1920  transmits a bearer release command message to the small cell eNB  1930  at operation  1921 . The bearer release command message may include the UE ID, and the X2 m-eNB TEID (or S1 m-eNB TEID). After receiving the bearer release command message from the macro eNB  1920 , the old small cell eNB  1930  transmits a bearer release confirm message as a response message to the bearer release command message to the macro eNB  1920  at operation  1923 . The bearer release confirm message includes data information for the UE  1910  to which the old small cell eNB  1930  provides the service until a related timing point. 
         [0265]    The macro eNB  1920  transmits a bearer status update message to the new small cell eNB  1940  at operation  1925 . The bearer status update message may include the last data status which is received from the old small cell eNB  1930 , i.e., data service information. The macro eNB  1920  transmits a RRC connection reconfiguration message to the UE  1910  at operation  1927 . The RRC connection reconfiguration message may include switching indication information indicating that the UE  1910  should switch to the new small cell eNB  1940 , an eNB ID of the new small cell eNB  1940 , information on a RACH resource which is allocated for transmitting a switch indicator indicating that the UE  1910  has switched to the new small cell eNB  1940 , and the like. 
         [0266]    After receiving the RRC connection reconfiguration message from the old small cell eNB  1930 , the UE  1910  transmits a RACH signal to the new small cell eNB  1940  at operation  1929 . After receiving the RACH signal from the UE  1910 , the new small cell eNB  1940  transmits a RACH response signal as a response message to the RACH signal to the UE  1910  at operation  1931 . After receiving the RACH response signal, the UE  1910  switches from the old small cell eNB  1930  to the new small cell eNB  1940  and sets up a data path with the new small cell eNB  1940 . 
         [0267]    After transmitting the RACH response signal to the UE  1910 , the new small cell eNB  1940  sets up the data path with the UE  1910  and transmits a bearer setup complete message to the macro eNB  1920  at operation  1933 . The bearer setup complete message may include a UE ID of the UE  1910  and an X2 m-eNB TEID (or S1 m-eNB TEID). 
         [0268]    Although  FIG. 19  illustrates another example of a process of supporting a switching operation between a macro eNB and a small cell eNB in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 19 . For example, although shown as a series of operations, various operations in  FIG. 19  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0269]    An operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIGS. 20A and 20B . 
         [0270]    First, an example of an operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure will be described with reference to  FIG. 20A . 
         [0271]      FIG. 20A  schematically illustrates an example of an operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure. 
         [0272]    Referring to  FIG. 20A , the mobile communication system includes a UE  2010 , a macro eNB  2020 , and a small cell eNB  2030 . 
         [0273]    The UE  2010  switches to the small cell eNB  2030  to receive a service at operation  2011 . The UE  2010  detects that a measurement report event according to an event occurrence which is not periodically performed occurs at operation  2013 , and transmits an event report code for requesting a resource which is used for transmitting a measurement process performance result according to the measurement report event occurrence to the macro eNB  2020  if a current timing point is not a timing point at which the UE  2010  switches to the macro eNB  2020  at operation  2015 . After receiving the event report code from the UE  2010  at operation  2017 , the macro eNB  2020  allocates a resource which the UE  2010  uses for transmitting the measurement process performance result according to the measurement report event occurrence, i.e., an event measurement report resource, to the UE  2010  at operation  2019 . After being allocated the event measurement report resource from the macro eNB  2020 , the UE  2010  reports the measurement process performance result to the macro eNB  2020  using the event measurement report resource at operation  2021 . 
         [0274]    Although not shown in  FIG. 20A , it will be understood by those of ordinary skill in the art that the UE  2010  may additionally request an uplink resource to the macro eNB  2020  to report an additional measurement process performance result. 
         [0275]    Although  FIG. 20A  illustrates an example of an operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 20A . For example, although shown as a series of operations, various operations in  FIG. 20A  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0276]    Another example of an operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure will be described with reference to  FIG. 20B . 
         [0277]      FIG. 20B  schematically illustrates another example of an operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure. 
         [0278]    Referring to  FIG. 20B , the mobile communication system includes a UE  2010 , a macro eNB  2020 , and a small cell eNB  2030 . 
         [0279]    The UE  2010  switches to the small cell eNB  2030  to receive a service at operation  2051 . The UE  2010  detects that a measurement report event according to an event occurrence which is not periodically performed occurs at operation  2053 , and transmits a measurement report event occurrence notify message indicating that a measurement report event occurs to the small cell eNB  2030  if a current timing point is not a timing point at which the UE  2010  switches to the macro eNB  2020  at operation  2055 . After receiving the measurement report event occurrence notify message from the UE  2010 , the small cell eNB  2030  transmits the measurement report event occurrence notify message indicating that the measurement report event occurs to the macro eNB  2020  at operation  2057 . 
         [0280]    After receiving the measurement report event occurrence notify message from the small cell eNB  2030 , the macro eNB  2020  allocates a resource which the UE  2010  uses for transmitting a measurement process performance result according to the measurement report event occurrence, i.e., an event measurement report resource, to the UE  2010  at operation  2059 . After being allocated the event measurement report resource from the macro eNB  2020 , the UE  2010  reports the measurement process performance result to the macro eNB  2020  using the event measurement report resource at operation  2061 . 
         [0281]    Although not shown in  FIG. 20B , it will be understood by those of ordinary skill in the art that the UE  2010  may additionally request an uplink resource to the macro eNB  2020  to report an additional measurement process performance result. 
         [0282]    Although  FIG. 20B  illustrates another example of an operating process among a UE, a macro eNB, and a small cell eNB for reporting a measurement process performance result according to event occurrence in a mobile communication system according to an embodiment of the present disclosure, various changes could be made to  FIG. 20B . For example, although shown as a series of operations, various operations in  FIG. 20B  could overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0283]    An inner structure of a macro eNB in a mobile communication system according to an embodiment of the present disclosure is described below with reference to  FIG. 21 . 
         [0284]      FIG. 21  schematically illustrates an inner structure of a macro eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0285]    Referring to  FIG. 21 , a macro eNB  2100  includes a receiver  2111 , a controller  2113 , a storage unit  2115 , and a transmitter  2117 . 
         [0286]    The controller  2113  controls the overall operation of the macro eNB  2100 . The controller  2113  controls the macro eNB  2100  to perform an operation related to an operation of supporting a switching operation between the macro eNB  2100  and a small cell eNB in a UE. The operation related to the operation of supporting the switching operation between the macro eNB  2100  and the small cell eNB in the UE is performed in the manner described with reference to  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0287]    The receiver  2111  receives various messages and the like from small cell eNBs, UEs, an S-GW, and the like under a control of the controller  2113 . The various messages received in the receiver  2111  have been described in  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0288]    The storage unit  2115  stores the messages received in the receiver  2111 , various programs necessary for the operation of the macro eNB  2100 , various data which occurs on the operation of the macro eNB  2100 , and the like. 
         [0289]    The transmitter  2117  transmits various messages and the like to the small cell eNBs, the UEs, the S-GW, and the like under a control of the controller  2113 . The various messages transmitted in the transmitter  2117  have been described in  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0290]    While the receiver  2111 , the controller  2113 , the storage unit  2115 , and the transmitter  2117  are described as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the receiver  2111 , the controller  2113 , the storage unit  2115 , and the transmitter  2117  may be incorporated into a single unit. 
         [0291]    An inner structure of a small cell eNB in a mobile communication system according to an embodiment of the present disclosure will be described with reference to  FIG. 22 . 
         [0292]      FIG. 22  schematically illustrates an inner structure of a small cell eNB in a mobile communication system according to an embodiment of the present disclosure. 
         [0293]    Referring to  FIG. 22 , a small cell eNB  2200  includes a receiver  2211 , a controller  2213 , a storage unit  2215 , and a transmitter  2217 . 
         [0294]    The controller  2213  controls the overall operation of the small cell eNB  2200 . The controller  2213  controls the small cell eNB  2200  to perform an operation related to an operation of supporting a switching operation between a macro eNB and the small cell eNB  2200  in a UE. The operation related to the operation of supporting the switching operation between the macro eNB and the small cell eNB  2200  in the UE is performed in the manner described with reference to  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0295]    The receiver  2211  receives various messages and the like from a macro eNB, other small cell eNBs, UEs, an S-GW, and the like under a control of the controller  2213 . The various messages received in the receiver  2211  have been described in  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0296]    The storage unit  2215  stores the messages received in the receiver  2211 , various programs necessary for the operation of the small cell eNB  2200 , various data which occurs on the operation of the small cell eNB  2200 , and the like. 
         [0297]    The transmitter  2217  transmits various messages and the like to the macro eNB, the other small cell eNBs, the UEs, the S-GW, and the like under a control of the controller  2213 . The various messages transmitted in the transmitter  2217  have been described in  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0298]    While the receiver  2211 , the controller  2213 , the storage unit  2215 , and the transmitter  2217  are described as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the receiver  2211 , the controller  2213 , the storage unit  2215 , and the transmitter  2217  may be incorporated into a single unit. 
         [0299]    An inner structure of a UE in a mobile communication system according to an embodiment of the present disclosure will be described with reference to  FIG. 23 . 
         [0300]      FIG. 23  schematically illustrates an inner structure of a UE in a mobile communication system according to an embodiment of the present disclosure. 
         [0301]    Referring to  FIG. 23 , a UE  2300  includes a receiver  2311 , a controller  2313 , a storage unit  2315 , and a transmitter  2317 . 
         [0302]    The controller  2313  controls the overall operation of the UE  2300 . The controller  2313  controls the UE  2300  to perform an operation related to an operation of supporting a switching operation between a macro eNB and a small cell eNB. The operation related to the operation of supporting the switching operation between the macro eNB and the small cell eNB is performed in the manner described with reference to  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0303]    The receiver  2311  receives various messages and the like from a macro eNB, small cell eNBs, an S-GW, and the like under a control of the controller  2313 . The various messages received in the receiver  2311  have been described in  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0304]    The storage unit  2315  stores the messages received in the receiver  2311 , various programs necessary for the operation of the UE  2300 , various data which occurs on the operation of the UE  2300 , and the like. 
         [0305]    The transmitter  2317  transmits various messages and the like to the macro eNB, the small cell eNBs, the S-GW, and the like under a control of the controller  2313 . The various messages transmitted in the transmitter  2317  have been described in  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0306]    While the receiver  2311 , the controller  2313 , the storage unit  2315 , and the transmitter  2317  are described as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the receiver  2311 , the controller  2313 , the storage unit  2315 , and the transmitter  2317  may be incorporated into a single unit. 
         [0307]    An inner structure of an S-GW in a mobile communication system according to an embodiment of the present disclosure will be described with reference to  FIG. 24 . 
         [0308]      FIG. 24  schematically illustrates an inner structure of an S-GW in a mobile communication system according to an embodiment of the present disclosure. 
         [0309]    Referring to  FIG. 24 , an S-GW  2400  includes a receiver  2411 , a controller  2413 , a storage unit  2415 , and a transmitter  2417 . 
         [0310]    The controller  2413  controls the overall operation of the S-GW  2400 . The controller  2413  controls the S-GW  2400  to perform an operation related to an operation of supporting a switching operation between a macro eNB and a small cell eNB in a UE. The operation related to the operation of supporting the switching operation between the macro eNB and the small cell eNB in the UE is performed in the manner described with reference to  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0311]    The receiver  2411  receives various messages and the like from a macro eNB, small cell eNBs, UEs, and the like under a control of the controller  2413 . The various messages received in the receiver  2411  have been described in  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0312]    The storage unit  2415  stores the messages received in the receiver  2411 , various programs necessary for the operation of the S-GW  2400 , various data which occurs on the operation of the S-GW  2400 , and the like. 
         [0313]    The transmitter  2417  transmits various messages and the like to the macro eNB, the small cell eNBs, the UEs, and the like under a control of the controller  2413 . The various messages transmitted in the transmitter  2417  have been described in  FIGS. 2A to 20B  and a description thereof will be omitted herein. 
         [0314]    While the receiver  2411 , the controller  2413 , the storage unit  2415 , and the transmitter  2417  are described as separate units, it is to be understood that this is merely for convenience of description. In other words, two or more of the receiver  2411 , the controller  2413 , the storage unit  2415 , and the transmitter  2417  may be incorporated into a single unit. 
         [0315]    As described above, after being powered on, a UE receives information on a small cell eNB from a macro eNB while performing an initial attach procedure, and determines a small cell eNB to which the UE will switch. However, it will be understood by those of ordinary skill in the art that after completing the initial attach procedure, the UE may receive the information on the small cell eNB from the macro eNB while receiving a service from the macro eNB, and determine the small cell eNB to which the UE will switch. While communicating with the UE, the macro eNB provides information on small cell eNBs which the UE will search/measure, and determines a small cell eNB to which the UE will switch, and the UE receives switching indicator indicating a switch to the small cell eNB from the macro eNB, and performs a procedure of switching to the small cell eNB. In this case, a procedure in which the small cell eNB receives switching information for the UE and establishes a data path may be performed with the manner described above. 
         [0316]    Certain aspects of the present disclosure may also be embodied as computer readable code on a non-transitory computer readable recording medium. A computer readable recording medium is any data storage device that can store data, which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), compact disc (CD)-ROMs, magnetic tapes, floppy disks, and optical data storage devices. Also, functional programs, code, and code segments for accomplishing the present disclosure can be easily construed by programmers skilled in the art to which the present disclosure pertains. 
         [0317]    It can be appreciated that a method and apparatus according to an embodiment of the present disclosure may be implemented by hardware, software and/or a combination thereof. The software may be stored in a non-volatile storage, for example, an erasable or re-writable ROM, a memory, for example, a RAM, a memory chip, a memory device, or a memory integrated circuit (IC), or an optically or magnetically recordable non-transitory machine-readable, e.g., computer-readable, storage medium, e.g., a CD, a digital versatile disc (DVD), a magnetic disk, or a magnetic tape. A method and apparatus according to an embodiment of the present disclosure may be implemented by a computer or a mobile terminal that includes a controller and a memory, and the memory may be an example of a non-transitory machine-readable, e.g., computer-readable, storage medium suitable to store a program or programs including instructions for implementing various embodiments of the present disclosure. 
         [0318]    The present disclosure may include a program including code for implementing the apparatus and method as defined by the appended claims, and a non-transitory machine-readable, e.g., computer-readable, storage medium storing the program. The program may be electronically transferred via any media, such as communication signals, which are transmitted through wired and/or wireless connections, and the present disclosure may include their equivalents. 
         [0319]    An apparatus according to an embodiment of the present disclosure may receive the program from a program providing device which is connected to the apparatus via a wire or a wireless and store the program. The program providing device may include a memory for storing instructions which instruct to perform a contents protect method which has been already installed, information necessary for the contents protect method, and the like, a communication unit for performing a wired or a wireless communication with a graphic processing device, and a controller for transmitting a related program to a transmitting/receiving device based on a request of the graphic processing device or automatically transmitting the related program to the transmitting/receiving device. 
         [0320]    While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.