Patent Publication Number: US-9843978-B2

Title: Wireless communication system and method therein for transferring at least part of services originally provided by a second station to a third station and a first base station in the system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/764,027, filed Jul. 28, 2015, which is a 371 of International Application No. PCT/CN2014/091867, filed Nov. 21, 2014, which claims priority to Chinese Patent Application No. 201310597066.9, filed Nov. 22, 2013. The entire contents of U.S. patent application Ser. No. 14/764,027 are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to the field of wireless communication, and particularly, to a wireless communication system and a method used in the wireless communication system. 
     BACKGROUND OF THE INVENTION 
     Currently, in a wireless communication system, technology of carrying out wireless data connections with a plurality of base stations over different carriers simultaneously by user equipment has been widely discussed. However, a solution under specific scenes has not been launched. 
     SUMMARY OF THE INVENTION 
     A brief summary of the disclosure will be given below to provide basic understanding of some aspects of the disclosure. However, it shall be appreciated that this summary is neither exhaustively descriptive of the disclosure nor intended to define essential or important components or the scope of the disclosure but is merely for the purpose of presenting some concepts of the disclosure in a simplified form and hereby acts as a preamble of more detailed descriptions which will be presented later. 
     Therefore, in view of the above circumstances, an object of the present disclosure is to provide a wireless communication system and a method used in the wireless communication system, which are capable of realizing that in a wireless communication system in which a plurality of base stations perform wireless data connections with user equipment over different carriers simultaneously, if certain conditions are satisfied, the user equipment is triggered to transfer part or all of radio bearers between the user equipment and some base stations to other base stations. Thus, it is possible to ensure the user equipment obtains ideal service quality from the base stations, and effectively improve uplink and downlink data transmission efficiency. 
     According to an aspect of the invention, there is provided a wireless communication system including a first base station, a second base station, a third base station and user equipment, in which the first base station and the second base station perform wireless data connection with the user equipment over different carriers, and a triggering node triggers a transfer procedure if it judges a predetermined transfer condition for transferring services provided to the user equipment by the second base station to the third base station is satisfied, so that the user equipment releases wireless data connection with the second base station and establishes wireless data connection with the third base station, and thus the first base station and the third base station perform wireless data connection with the user equipment over different carriers, wherein at least part of the services originally provided by the second base station is transferred to the third base station. 
     According to a preferred embodiment of the invention, the transfer procedure may further cause part of the services originally provided by the second base station to be transferred to the first base station. 
     According to another preferred embodiment of the invention, the triggering node may be the first base station or the second base station. 
     According to another preferred embodiment of the invention, the triggering node sends a transfer request to the third base station if it judges the predetermined transfer condition is satisfied according to a received mobility measurement result regarding a serving carrier of the second base station, the third base station performs a first admission control according to the transfer request and sends a transfer response to the first base station and/or the second base station to notify a result of the first admission control, in which the transfer response comprises at least one of the following: for which part of radio bearer of the user equipment that the third base station can perform communication, a dedicated preamble code as required when making synchronized access to the third base station, system information of a carrier for communication between the user equipment and the third base station, and configuration information of a control plane protocol for establishing communication between the user equipment and the third base station. 
     According to another preferred embodiment of the invention, if the result of the first admission control indicates that the third base station can not accept all radio bearers between the user equipment and the second base station, then according to the transfer response sent by the third base station or the transfer response sent by the third base station and forwarded to the first base station via the second base station, the first base station performs a second admission control according to the result of the first admission control and notifies the second base station of a result of the second admission control. 
     According to another preferred embodiment of the invention, the first base station or the second base station sends, after acquiring a final result of the first admission control or the second admission control, a notification message to the user equipment to notify the user equipment to perform the transfer procedure according to the final result and the transfer response of the third base station, the notification message comprising at least one of the following: for which part of radio bearer of the user equipment that the first base station can perform communication, for which part of the radio bearer of the user equipment that the third base station can perform communication, a dedicated preamble code as required when making synchronized access to the third base station, system information of a carrier for communication between the user equipment and the third base station, and configuration information of a control plane protocol for establishing communication between the user equipment and the third base station, and the user equipment releases, after receiving the notification message, radio bearers unacceptable by the first base station and the third base station, and releases the wireless data connection with the second base station and performs synchronized access to the third base station at the same time. 
     According to another embodiment of the invention, if data of the first, second and third base stations is directly routed from a core network before triggering the transfer procedure and after completing triggering of the transfer procedure, the second base station performs data forwarding operation to forward data of a first radio bearer acceptable by the third base station to the third base station according to the result of the first admission control, and further performs data forwarding operation to forward data of a second radio bearer acceptable by the first base station to the first base station according to the result of the second admission control, and the first base station or the second base station notifies the core network to switch a path corresponding to the second radio bearer to the first base station. 
     Preferably, if synchronized access to the third base station by the user equipment succeeds, the third base station notifies the core network to switch a path corresponding to the first radio bearer to the third base station; otherwise, if the synchronized access to the third base station by the user equipment fails, the user equipment notifies the first base station, and the first base station notifies the second base station and the third base station after performing a third admission control, so that data of a third radio bearer acceptable by the first base station in the first radio bearer is forwarded to the first base station, and the first base station notifies the core network to switch a path corresponding to the third radio bearer to the first base station and to release a core network bearer corresponding to a radio bearer unacceptable by the first base station in the first radio bearer, and notifies the user equipment to release the radio bearer unacceptable by the first base station in the first radio bearer at the same time. 
     According to another preferred embodiment of the invention, if data of the second base station is forwarded from the first base station, the first base station stops forwarding data to the second base station after completing confirmation of the first admission control or after completing the second admission control, and the second base station performs data forwarding operation to forward data of the first radio bearer acceptable by the third base station to the third base station according to the result of the first admission control, and further performs data forwarding operation to forward data of the second radio bearer acceptable by the first base station to the first base station according to the result of the second admission control. 
     Preferably, the first base station performs data forwarding operation to forward the data of the first radio bearer to the third base station after completing confirmation of the first admission control, or the first base station performs data forwarding operation to forward the data of the first radio bearer to the third base station after receiving a message that synchronized access to the third base station by the user equipment succeeds. 
     Further, preferably, if the synchronized access to the third base station by the user equipment fails, the user equipment notifies the first base station, the first base station stops forwarding data to the third base station, and the first base station notifies the second base station and the third base station after completing a third admission control so that data of a third radio bearer acceptable by the first base station in the first radio bearer is forwarded to the first base station and a radio bearer unacceptable by the first base station in the first radio bearer is released, and notifies the user equipment to release the radio bearer unacceptable by the first base station in the first radio bearer at the same time. 
     Further, preferably, if data of the third base station is directly routed from a core network after completing triggering of the transfer procedure and the synchronized access to the third base station by the user equipment succeeds, the third base station further notifies the core network to modify a core network bearer corresponding to the first radio bearer acceptable by the third base station so that data of the first radio bearer is directly routed to the third base station. 
     According to another preferred embodiment of the invention, if data of the first base station is forwarded via the second base station, the second base station performs data forwarding operation to forward data of the first radio bearer acceptable by the third base station to the third base station according to the result of the first admission control, and performs data forwarding operation to forward data of the second radio bearer acceptable by the first base station to the first base station according to the result of the second admission control. 
     Preferably, if synchronized access to the third base station by the user equipment succeeds, the third base station triggers a core network to perform path switch so that data sent to the second base station from the core network is directly routed to the third base station, the third base station starts forwarding data of a downlink bearer transmitted via the first base station to the first base station after completing the path switch, and the second base station releases information relating to the user equipment and its services after completing data forwarding operation. 
     Further, preferably, if synchronized access to the third base station by the user equipment fails, the user equipment notifies the first base station, the first base station notifies the second base station and the third base station after a third admission control so that data of a third radio bearer acceptable by the first base station in the first radio bearer and data of original services of the first base station is forward to the first base station via the second base station, and notifies the user equipment at the same time, and the second base station stops forwarding data to the third base station after acquiring that the synchronized access fails. 
     Further, preferably, if the synchronized access to the third base station by the user equipment fails, after completing the third admission control by the first base station, the first base station or the second base station notifies the core network to switch a path for data forwarded to the first base station via the second base station to the first base station and release a core network bearer corresponding to a radio bearer unacceptable by the first base station in the first radio bearer, and notifies the user equipment to release the radio bearer unacceptable by the first base station in the first radio bearer at the same time. 
     According to another aspect of the invention, there is provided a method used in a wireless communication system, the wireless communication system including a first base station, a second base station, a third base station and user equipment, wherein the first base station and the second base station perform wireless data connection with the user equipment over different carriers, the method including: a judging step of judging, by a triggering node, whether a predetermined transfer condition for transferring services provided to the user equipment by the second base station to the third base station is satisfied; and a triggering step of triggering the transfer procedure if it is judged that the predetermined transfer condition is satisfied, so that the user equipment releases wireless data connection with the second base station and establishes wireless data connection with the third base station, and thus the first base station and the third base station perform wireless data connection with the user equipment over different carriers, wherein at least part of the services originally provided by the second base station is transferred to the third base station. 
     According to another aspect of the invention, there is also provided a storage medium including machine readable program codes which when executed on an information processing apparatus, cause the information processing apparatus to perform the following steps: a judging step of judging, by a triggering node, whether a predetermined transfer condition for transferring services provided to user equipment by a second base station to a third base station is satisfied, and a triggering step of triggering the transfer procedure if it is judged that the predetermined transfer condition is satisfied, so that the user equipment releases wireless data connection with the second base station and establishes wireless data connection with the third base station, and thus a first base station and the third base station perform wireless data connection with the user equipment over different carriers, wherein at least part of the services originally provided by the second base station is transferred to the third base station. Particularly, the first base station, the second base station, the third base station and the user equipment are included in a wireless communication system, and the first base station and the second base station perform wireless data connection with the user equipment over different carriers. 
     According to another aspect of the invention, there is also provided a program product including machine executable instructions which when executed on an information processing apparatus cause the information processing apparatus to perform the following steps: a judging step of judging, by a triggering node, whether a predetermined transfer condition for transferring services provided to user equipment by a second base station to a third base station is satisfied; and a triggering step of triggering the transfer procedure if it is judged that the predetermined transfer condition is satisfied, so that the user equipment releases wireless data connection with the second base station and establishes wireless data connection with the third base station, and thus a first base station and the third base station perform wireless data connection with the user equipment over different carriers, wherein at least part of the services originally provided by the second base station is transferred to the third base station. Particularly, the first base station, the second base station, the third base station and the user equipment are included in a wireless communication system, and the first base station and the second base station perform wireless data connection with the user equipment over different carriers. 
     Other aspects of the embodiments of the disclosure will be presented in the following detailed description serving to fully disclose preferred embodiments of the disclosure but not to limit the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be better understood with reference to the detailed description given below in conjunction with the accompanying drawings, throughout which identical or like reference signs denote identical or like components. The accompanying drawings together with the following detailed description are incorporated into and form a part of the specification and serve to further illustrate the preferred embodiments of the disclosure and to explain the principle and advantages of the disclosure by way of example. In the drawings: 
         FIG. 1  is a schematic block diagram illustrating a wireless communication system according to an embodiment of the disclosure; 
         FIG. 2  is a schematic diagram illustrating an exemplary scene in which a first base station serves as a triggering node to trigger a transfer procedure according to an embodiment of the disclosure; 
         FIG. 3  is a schematic diagram illustrating an exemplary scene in which a second base station serves as a triggering node to trigger a transfer procedure according to an embodiment of the disclosure; 
         FIG. 4  is a schematic diagram illustrating an exemplary scene in a case that data of first, second and third base stations is directly routed from a core network before triggering a transfer procedure and after completing triggering of the transfer procedure and synchronized access to the third base station by user equipment succeeds according to an embodiment of the disclosure; 
         FIG. 5  is a schematic diagram illustrating an exemplary scene in a case that data of a second base station comes directly from a core network and synchronized access to a third base station by user equipment fails according to an embodiment of the disclosure; 
         FIG. 6A  is a schematic diagram illustrating an exemplary scene in a case that data of a second base station and a third base station is forwarded via a first base station and synchronized access to the third base station by user equipment succeeds according to an embodiment of the disclosure; 
         FIG. 6B  is a schematic diagram illustrating another exemplary scene in a case that data of a second base station and a third base station is forwarded via the first base station and synchronized access to the third base station by user equipment succeeds according to an embodiment of the disclosure; 
         FIG. 6C  is a schematic diagram illustrating an exemplary scene in a case that data of a second base station is forwarded via the first station while data of a third base station is directly routed from the core network after completing triggering of a transfer procedure and synchronized access to the third base station by user equipment succeeds according to an embodiment of the disclosure; 
         FIG. 7  is a schematic diagram illustrating an exemplary scene in a case that data of a second base station is forwarded via a first base station and synchronized access to a third base station by user equipment fails according to an embodiment of the disclosure; 
         FIG. 8  is a schematic diagram illustrating an exemplary scene in a case that data of a first base station is forwarded via a second base station and synchronized access to a third base station by user equipment succeeds according to an embodiment of the disclosure; 
         FIG. 9  is a schematic diagram illustrating an exemplary scene in a case that data of a first base station is forwarded via a second base station and synchronized access to a third base station by user equipment fails according to an embodiment of the disclosure; 
         FIG. 10  is a block diagram illustrating an example of functional configuration of a first base station serving as a connection maintaining node according to an embodiment of the disclosure; 
         FIG. 11  is a block diagram illustrating an example of functional configuration of a first base station serving as a connection maintaining node according to another embodiment of the disclosure; 
         FIG. 12  is a block diagram illustrating an example of functional configuration of a second base station serving as a connection transfer source node according to an embodiment of the disclosure; 
         FIG. 13  is a block diagram illustrating an example of functional configuration of a second base station serving as a connection transfer source node according to another embodiment of the disclosure; 
         FIG. 14  is a block diagram illustrating an example of functional configuration of a third base station serving as a connection transfer target node according to an embodiment of the disclosure; 
         FIG. 15  is a block diagram illustrating an example of functional configuration of user equipment according to an embodiment of the disclosure; 
         FIG. 16  is a flow chart illustrating an example of a procedure of a method used in the wireless communication system according to an embodiment of the disclosure; and 
         FIG. 17  is a block diagram illustrating an exemplary structure of a personal computer as an information processing apparatus that may be used in an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary embodiments of the present disclosure will be described below in conjunction with the accompanying drawings. For the sake of clarity and conciseness, not all the features of practical implementations are described in the specification. However, it is to be appreciated that numerous implementation-specific decisions shall be made during developing any of such practical implementations so as to achieve the developer&#39;s specific goals, for example, to comply with system- and service-related constraining conditions which will vary from one implementation to another. Moreover, it shall also be appreciated that such a development effort might be very complex and time-consuming but may simply be a routine task for those skilled in the art benefiting from this disclosure. 
     It shall further be noted that only those device structures and/or process steps closely relevant to the solutions of the disclosure are illustrated in the drawings while other details less relevant to the disclosure are omitted so as not to obscure the disclosure due to those unnecessary details. 
     Embodiments of the disclosure will be described with reference to  FIGS. 1-17  below. First, an example of a wireless communication system according to an embodiment of the disclosure will be described with reference to  FIG. 1 .  FIG. 1  is a schematic block diagram illustrating a wireless communication system according to an embodiment of the disclosure. 
     As shown in  FIG. 1 , the wireless communication system  100  according to the embodiment of the disclosure may include a first base station  102 , a second base station  104 , a third base station  106  and user equipment  108 . Particularly, the first base station  102  and the second base station  104  perform wireless data connection with the user equipment  108  over different carriers, and a triggering node triggers a transfer procedure if it judges a predetermined transfer condition for transferring services provided to the user equipment  108  by the second base station  104  to the third base station  106  is satisfied, so that the user equipment  108  releases wireless data connection with the second base station  104  and establishes wireless data connection with the third base station  106 , and thus the first base station  102  and the third base station  106  perform wireless data connection with the user equipment  108  over different carriers, and at least part of the services originally provided by the second base station  104  is transferred to the third base station  106 . 
     The predetermined transfer condition under which the services provided to the user equipment  108  by the second base station  104  is transferred to the third base station  106  includes one or more of the following factors: service quality of the third base station  106  is higher than service quality of the second base station  104  by a predetermined threshold; the service quality of the third base station  106  is higher than a predetermined threshold; the service quality of the second base station  104  is lower than a first predetermined threshold and the service quality of the third base station  106  is higher than a second predetermined threshold; and so on. It is to be understood that the above predetermined transfer condition has been described assuming that an object to be transferred has been determined among the first base station  102  and the second base station  104 . 
     On the other hand, when both base stations which perform wireless data connection with the user equipment over different carriers satisfy the predetermined transfer condition at the same time, in a case that it has not been determined which base station is to be transferred first (that is, during a two-step transfer procedure, which base station is the first base station  102 , which base station is the second base station  104  and which base station is the third base station  106 ), as an alternative example, the above described predetermined transfer condition may further include for example the service quality of one base station is higher than that of another base station. 
     Preferably, when determining the object to be transferred among the above two base stations, measurement results regarding serving carriers of these two base stations should be reported to the triggering node, then the triggering node will determine the transfer procedure with respect to which base station is to be started first based on a type of the base station (for example, master node/slave node, macro base station/low power node, and the like), channel quality or load condition or the like. As an alternative example, if the channel quality of one base station is lower than a predetermined threshold and approximates failure while another base station is looking for a better neighbor, then a base station with poorest channel quality is determined as the object to be transferred, and the transfer procedure with respect to this base station is started first. As another alternative example, if two base stations have substantially the same channel quality, then a base station with heavier load will be determined as the object to be transferred, and the transfer procedure with respect to this base station is started first. 
     Further, preferably, in a case that all of the services originally provided by the second base station  104  can not be transferred to the third base station  106 , the transfer procedure further causes part of the services originally provided by the second base station  104  to be transferred to the first base station  102 . It is to be noted that although  FIG. 1  shows only one first base station  102 , the number of the first base station  102  is not limited thereto, and the first base station  102  may be a set of base stations including a plurality of first base stations, for example, a plurality of coordinated base stations in Joint Processing technology, and thus during the above transfer procedure, part of the services originally provided by the second base station  104  may be transferred to one or more first base stations in the set of base stations. Further, in this case, the service quality of the plurality of first base stations is measured in a cell unit, for example, in case of Coordinated Multiple Point (CoMP) transmission, the service quality of multiple coordinated base stations may be measured by regarding a carrier coordinated by the multiple base stations as one cell. 
     Further, it is to be understood that during the above transfer procedure, the first base station  102  always maintains the wireless data connection with the user equipment, the services provided by the second base station  104  is transferred, and at least part of the services originally provided by the second base station  104  is transferred to the third base station  106 , and thus in some embodiments of the invention, the first base station  102  may be also referred to as a connection maintaining node, the second base station  104  may be also referred to as a connection transfer source node, and the third base station  106  may be also referred to as a connection transfer target node. The above described triggering node may be one serving node to which the user equipment  108  is connected currently, for example, may be the first base station  102  as the connection maintaining node, and may be also the second base station  104  as the connection transfer source node. 
     Further, it is to be understood that the terms “first”, “second” and “third” used herein are only used for distinguishing to facilitate description but not limitation, for example, when the first base station  102  conforms to characteristics of the connection transfer source node or the connection transfer target node, the first base station  102  can of course be the connection transfer source node or the connection transfer target node, and this also applies to the second base station  104  and the third base station  106 . 
     Specifically, in a case that the triggering node judges the predetermined transfer condition is satisfied according to mobility measurement result regarding serving carriers of at least the second base station  104  and optionally the first base station  102  and the third base station  106 , the triggering node sends a transfer request containing relevant information of the first base station and the second base station to the third base station  106 , and the third base station  106  performs a first admission control according to the transfer request and sends a transfer response to notify a result of the first admission control. Particularly, the third base station  106  may return the transfer response directly to the triggering node, or may send the transfer response to another serving node connected with the user equipment  108 . 
     Preferably, the transfer response may include for which part of radio bearer of the user equipment  108  that the third base station  108  can perform communication, a dedicated preamble code as required when making synchronized access to the third base station  106 , system information about a carrier for communication between the user equipment  108  and the third base station  106  and configuration information about a control plane protocol for establishing communication between the user equipment  108  and the third base station  106 . 
     Preferably, if the result of the first admission control indicates that the third base station  106  can not accept all the radio bearers between the user equipment  108  and the second base station  104 , then according to the transfer response of the third base station  106  (the transfer response directly received from the third base station  106  or the transfer response of the third base station  106  forwarded to the first base station  102  via the second base station  104 ), the first base station  102  performs a second admission control according to the result of the first admission control and notifies a result of the second admission control to the second base station  104 . 
     Further, preferably, the first base station  102  or the second base station  104  sends, after acquiring the final result of the first admission control or the second admission control, a notification message to the user equipment  108  to notify the user equipment  108  to perform the transfer procedure according to the final result and the transfer response of the third base station  106 . The notification message includes at least one of: for which part of radio bearer of the user equipment that the first base station  102  can perform communication, for which part of radio bearer of the user equipment  108  that the third base station  106  can perform communication, a dedicated preamble code as required when making synchronized access to the third base station  106 , system information about a carrier for communication between the user equipment  108  and the third base station  106  and configuration information about a control plane protocol for establishing communication between the user equipment  108  and the third base station  106 . Also, the user equipment  108  releases radio bearers which can not be accepted by the first base station  102  and the third base station  106  after receiving the notification message, releases the wireless data connection with the second base station  104  and performs synchronized access operation to the third base station  106 . 
     Further, preferably, the above described triggering node may be the first base station  102  or the second base station  104 . 
     Examples of scenes of the transfer procedure in cases that the first base station  102  and the second base station  104  serve as the triggering node respectively will be described with reference to  FIGS. 2 and 3  below.  FIG. 2  is a schematic diagram illustrating an exemplary scene in which the first base station serves as the triggering node to trigger the transfer procedure according to an embodiment of the disclosure, and  FIG. 3  is a schematic diagram illustrating an exemplary scene in which the second base station serves as the triggering node to trigger the transfer procedure according to an embodiment of the disclosure. 
     As shown in  FIG. 2 , in a case that the first base station  102  serves as the triggering node, the user equipment  108  may send the mobility measurement result to the second base station  104 , and the second base station  104  forwards the mobility measurement result to the first base station  102  as shown by solid-line arrows in  FIG. 2  as reference for the first base station  102  to trigger the transfer procedure. An advantage of this example lies in reducing modifications to the existing standard (the user equipment directly reports to a serving base station the mobility carrier measurement result of the serving base station). Further, the user equipment  108  may also send the mobility measurement result regarding a serving carrier (containing at least a primary carrier) of the second base station  104  to the first base station  102  in “measurement report” for example, as shown by a broken-line arrow in  FIG. 2 . An advantage of this example lies in that the user equipment  108  may directly send the measurement report regarding the serving carrier of the second base station  104  to the first base station  102 , thereby saving information interaction between the second base station  104  and the first base station  102 . 
     Next, the first base station  102  may send a transfer request to the third base station  106  in “transfer request” for example after judging the above predetermined transfer condition is satisfied according to the received information of the mobility measurement result, then the third base station  104  performs the first admission control according to the transfer request, and sends a response to the transfer request to the first base station  102  in “transfer response” for example so as to notify the result of the first admission control to the first base station  102 . The result of the first admission control indicates whether the third base station  106  can accept all the radio bearers between the user equipment  108  and the second base station  104  or which part of the radio bearers can be accepted by the third base station  106 . 
     Thereafter, the first base station  102  or the third base station  106  notifies the result of the first admission control to the second base station  104  in “transfer notification” for example, and the first base station  102  or the second base station  104  notifies the user equipment  108  to perform the transfer procedure in “transfer confirmation” for example according to the result and the transfer response of the third base station  106 . The specific contents contained in the notification message “transfer confirmation” have been described above, and no repeated description will be made herein. 
     Preferably, if the result of the first admission control performed by the third base station  106  indicates that the third base station  106  can not accept all the radio bearers between the user equipment  108  and the second base station  104 , the first base station  102  may perform the second admission control according to the result of the first admission control contained in the received “transfer response”, as shown by broken-line block in  FIG. 2 . It is to be understood that by performing the second admission control by the first base station  102  to transfer at least part of the radio bearers that can not be accepted by the third base station  106  to the first base station  102 , it is possible to further ensure the user equipment  108  obtains excellent service quality. This is merely a preferred example of course but not limitation, and it is also possible to directly notify the user equipment  108  to release the services unacceptable by the third base station  108  after performing the first admission control, without performing the second admission control by the first base station  102 . After judging through the first admission control and/or the second admission control, the second base station  104  releases the radio bearers which are originally transmitted by the second base station  104  and which can not be accepted by the third base station  106  and the first base station  102 , and notifies the core network to release core network bearers corresponding to the radio bearers. 
     It is to be noted that in this case, the first base station  102  may notify the final result about the first admission control and the second admission control to the second base station  104  in “transfer notification” for example after performing the second admission control, then the first base station  102  or the second base station  104  notifies the final result to the user equipment  108  in “transfer confirmation” for example, and thus the radio bearer acceptable by the third base station can be transferred to the third base station  106  and the radio bearer acceptable by the first base station  102  can be transferred to the first base station  102 . 
     After receiving the above notification message “transfer confirmation”, the user equipment  108  releases the services that can not be accepted by the first base station  102  and the third base station  106 , releases the wireless data connection with the second base station  104  and performs the synchronized access operation to the third base station  106 . 
     A basic signaling flow of the transfer procedure in a case that the first base station  102  serves as the triggering node has been described in detail with reference to  FIG. 2  above, and next, an example of a scene of the transfer procedure in a case that the second base station  104  serves as the triggering node will be described in detail with reference to  FIG. 3 . 
     As shown in  FIG. 3 , since the triggering node is the second base station  104  at this time, the user equipment  108  only needs to notify the carrier mobility measurement result to the second base station  104 , and the second base station  104  sends the transfer request to the third base station  106  after judging the predetermined transfer condition is satisfied according to the measurement result so as to trigger the transfer procedure. Then, the third base station  106  sends to the second base station  104  a response message “transfer response” for the transfer request after performing the first admission control, so as to notify the result of the first admission control to the second base station  104 . Next, the second base station  104  or the third base station  106  may notify the result to the first base station  102 , and the second base station  104  sends the notification message to the user equipment  108  in “transfer confirmation” according to the received “transfer response”. 
     Preferably, similar to the case described in  FIG. 2 , the first base station  102  may also perform the second admission control according to the received result of the first admission control. Specifically, when the “transfer response” of the third base station  106  received by the second base station  104  indicates that the third base station  106  can not accept all the radio bearers between the user equipment  108  and the second base station  104 , the second base station  104  sends “transfer request” to the first base station  102  with respect to the radio bearers that can not be by the third base station  106 , the first base station  102  performs the second admission control according to the “transfer request” and notifies the final result of the admission control to the second base station  104  in “transfer response” for example. Then, the second base station  104  sends a notification to the user equipment  108  according to the final result. In this example, the “transfer response” sent by the first base station includes for which part of the radio bearers of the user equipment that the first base station  102  can perform communication. 
     As can be seen from comparison of  FIGS. 2 and 3 , the transfer procedures in these two cases are similar to each other, and the difference only lies in that the base stations serving as the triggering node are different, thereby leading to differences in transmitting and receiving nodes and timings for some signaling. Therefore, parts which are not described in detail in  FIG. 3  can be referred to  FIG. 2 , and no repeated description will be made herein. 
     Examples of scenes for basic signaling interactions of the transfer procedure in different cases have been described in detail with reference to  FIGS. 2 and 3 , and examples of scenes for data forwarding and path switch among network nodes in different cases after the basic signaling interaction of the transfer procedure will be described in detail with reference to  FIGS. 4-9  below. 
       FIG. 4  is a schematic diagram illustrating an exemplary scene in a case that the data of the first, second and third base stations is directly routed from the core network before triggering the transfer procedure and after completing triggering of the transfer procedure and synchronized access to the third base station by the user equipment succeeds according to an embodiment of the disclosure. 
     Specifically, if the data of the first base station  102 , the second base station  104  and the third base stations  106  is directly routed from the core network before triggering the transfer procedure and after completing triggering of the transfer procedure, the second base station  104  performs data forwarding operation to forward data of a first radio bearer acceptable by the third base station  106  to the third base station  106  according to the result of the first admission control, and further performs data forwarding operation to forward data of a second radio bearer acceptable by the first base station  102  to the first base station  102  according to the result of the second admission control, and the first base station  102  or the second base station  104  notifies the core network to switch a path corresponding to the second radio bearer to the first base station  102 . 
     It is to be noted that if the result of the first admission control indicates that the third base station  106  can accept all the radio bearers, then only data of the first radio bearer accepted by the third base station  106  is needed to be forwarded to the third base station  106 , otherwise, data of the second radio bearer accepted by the first base station  102  also needs to be forwarded to the first base station  102  at the same time. 
     After the data forwarding operation, as shown in  FIG. 4 , if the synchronized access to the third base station  106  by the user equipment  108  succeeds, the third base station  106  notifies the core network to switch a path corresponding to the first radio bearer to the third base station  106 . Specifically, the third base station  106  may send “path switch request” for example to a mobility management entity (MME). After receiving the request, the mobility management entity sends “bearer modifying request” for example to a gateway, and after receiving the request, the gateway performs switching downlink path operation and thus the data of the first radio bearer acceptable by the third base station  106  is directly routed to the third base station  106 , and the gateway sends to the second base station  104  an end flag to inform a number of a last data packet forwarded to the third base station  106  via the second base station  104 . Thereafter, the gateway sends “bearer modifying response” for example to the mobility management entity, and meanwhile, after receiving the response, the mobility management entity sends “path switch confirmation” for example as confirmation for the path switch request. Then, the third base station  106  may notify the second base station  104  to release relevant user equipment information, and the second base station  104  may release the resources related to the user equipment  108  and services thereof after receiving the notification. 
     Otherwise, as shown in  FIG. 5 , if the synchronized access to the third base station  106  by the user equipment  108  fails, the user equipment  108  will notify the first base station  102 , and the first base station  102  performs a third admission control to perform admission control on the first radio bearer and notifies the second base station  104  and the third base station  106  after the third admission control, to notify the failure of the synchronized access and cause data of a third radio bearer acceptable by the first base station  102  in the first radio bearer to be forwarded to the first base station  102 . The first base station  102  also notifies the core network to switch a path corresponding to the third radio bearer to the first base station  102 . Meanwhile, the first base station  102  notifies the user equipment  108  of which data can be transmitted over carriers of the first base station  102  and which data needs to be released, notifies the second base station  104  and the third base station  106  of which radio bearers should be released and notifies the core network to release core network bearers corresponding to the radio bearers. 
     It is to be noted that in a case that the synchronized access fails, as shown in  FIG. 5 , except that the mobility management entity is notified by the first base station  102  at this time, specific path switch operations related to the core network end are similar to the procedure as described above with reference to  FIG. 4 , and thus, no repeated description will be made herein. 
     As can be seen from the above description with reference to  FIGS. 4 and 5 , for the second radio bearer determined according to the result of the second admission control performed by the first base station  102 , irrespective of success or failure of the synchronized access to the third base station  106  by the user equipment  108 , the core network is notified to switch corresponding path to the first base station  102 . As for the first radio bearer determined according to the result of the first admission control performed by the third base station  106 , only if the synchronized access to the third base station  106  by the user equipment  108  succeeds, the core network is notified to switch path corresponding to the first radio bearer to the third base station  106 , and if the synchronized access fails, the first base station  102  performs the third admission control for the first radio bearer and notifies the core network to switch path corresponding to the third radio bearer determined according to the result of the third admission control to the first base station  102 . That is to say, for the services corresponding to the second radio bearer and the third radio bearer which are originally provided by the second base station  104 , the first base station  102  provides these services at this time. Further, in a case that the synchronized access fails, it also needs to notify the user equipment  108  that the third radio bearer should be transferred to the first base station  102  for transmission and to notify the user equipment  108  to release the radio bearers unacceptable by the first base station  102  after the third admission control. 
     Next, exemplary scenes in a case that the data of the second base station  104  is forwarded via the first base station  102  will be described with reference to  FIGS. 6A, 6B, 6C and 7 .  FIG. 6A  is a schematic diagram illustrating an exemplary scene in a case that the data of the second base station and the third base station is forwarded via the first base station and the synchronized access to the third base station by the user equipment succeeds according to an embodiment of the disclosure;  FIG. 6B  is a schematic diagram illustrating another exemplary scene in a case that the data of the second base station and the third base station is forwarded via the first base station and the synchronized access to the third base station by the user equipment succeeds according to an embodiment of the disclosure;  FIG. 6C  is a schematic diagram illustrating an exemplary scene in a case that the data of the second base station is forwarded via the first station while the data of the third base station is directly routed from the core network after completing triggering of the transfer procedure and the synchronized access to the third base station by the user equipment succeeds according to an embodiment of the disclosure; and  FIG. 7  is a schematic diagram illustrating an exemplary scene in a case that the data of the second base station is forwarded via the first base station and the synchronized access to the third base station by the user equipment fails according to an embodiment of the disclosure. 
     Specifically, if the data of the second base station  104  and the third base station  106  is forwarded from the first base station  102 , the first base station  102  stops forwarding data to the second base station  104  after completing confirmation for the first admission control or completing the second admission control, and the second base station  104  performs data forwarding operation according to the result of the first admission control to forward the data of the first radio bearer acceptable by the third base station  106  to the third base station  106  and also performs data forwarding operation according to the result of the second admission control to forward the data of the second radio bearer acceptable by the first base station  102  to the first base station  102 . 
     At this time, the data of the second base station  104  is forwarded from the first base station  102 , and thus the first base station  102  also needs to perform data forwarding operation for the third base station  106 , and the first base station  102  may perform, after completing confirmation for the first admission control, the data forwarding operation simultaneously with the second base station  104  so as to forward the data of the first radio bearer to the third base station  106  regardless of success or failure of the synchronized access between the user equipment  108  and the third base station  106 , as shown in  FIG. 6A . Alternatively, the first base station  102  may also perform data forwarding operation only after acquiring the success of the synchronized access between the user equipment  108  and the third base station  106 , as shown in  FIG. 6B , which is more suitable for a situation in which the first base station  102  and the second base station  104  transmit services for one same radio bearer at the same time. 
     Further, the second base station  104  automatically releases resources related to the services of the user equipment  108  after completing the data forwarding operation. 
     Particularly, if the result of the first admission control indicates that the third base station  106  can not accept all the radio bearers, while the data forwarding operation for the first radio bearer accepted by the third base station  106  is performed, in addition to stopping forwarding data to the second base station  104  by the first base station  102 , the second base station  104  also needs to transfer the data of the second radio bearer accepted by the first base station  102  back to the first base station  102  for transmission. 
     Alternatively, as shown in  FIG. 6C , if the data of the second base station  104  is forwarded from the first base station  102  while the data of the third base station  106  is directly routed from the core network after completing triggering of the transfer procedure, in a case that the synchronized access to the third base station  106  by the user equipment  108  succeeds, in addition to the processing procedures described above with reference to  FIGS. 6A and 6B , operations at the core network end are also involved, that is, the third base station  106  needs to notify the core network to modify the core network bearer corresponding to the first radio bearer acceptable by the third base station  106 . Specifically, after the synchronized access to the third base station  106  by the user equipment  108  succeeds, the third base station  106  further sends “path switch request” for example to the mobility management entity, the mobility management entity sends, after receiving the request, “bearer modifying request” for example to the gateway, and the gateway performs switching downlink path operation after receiving the request and thus the data of the first radio bearer acceptable by the third base station  106  is directly routed to the third base station  106 , and the gateway sends an end flag to the first base station  102  to inform the number of the last data packet forwarded to the third base station  106  via the first base station. Thereafter, the gateway sends “bearer modifying response” for example to the mobility management entity, and the mobility management entity sends, after receiving the response, “path switch confirmation” for example as confirmation for the “path switch request” to the third base station  106 , thereby notifying the third base station  106  of completion of the path switch operation at the core network end. 
     However, if the synchronized access to the third base station  106  by the user equipment  108  fails, as shown in  FIG. 7 , similar to the scene described with reference to  FIG. 5 , the user equipment  108  first notifies the first base station  102 , the first base station  102  stops forwarding data to the third base station  106  after receiving the notification, and the first base station  102  notifies the second base station  104  and the third base station  106  after performing the third admission control to notify the failure of the synchronized access and cause the second base station  104  and the third base station  106  to perform data forwarding operation for the third radio bearer acceptable by the first base station  102  in the first radio bearer, so that the data of the third radio bearer acceptable by the first base station  102  in the first radio bearer is forwarded to the first base station  102  and the radio bearer unacceptable by the first base station  102  in the first radio bearer is released. Meanwhile, the first base station  102  notifies the user equipment  108  of which data can be transmitted over carriers of the first base station  102  and which data needs to be released. 
     As can be seen from above description with reference to  FIGS. 6A, 6B and 7 , under these scenes, the first base station  102  is responsible for forwarding data to other base stations in the wireless communication system, and thus, no path switch operation at the core network end will be involved in both cases of success and failure of the synchronized access operation. 
     Further, it is to be noted that although  FIG. 7  shows that the first base station  102  and the second base station  104  performs data forwarding operation for the third base station  106  at the same time, but this is merely an example, and similar to  FIG. 6B , the first base station  102  may also not perform data forwarding operation for the third base station  106  at first, which is not limited herein. 
     Exemplary scenes in a case that the data of the first base station is forwarded via the second base station will be described with reference to  FIGS. 8 and 9  below.  FIG. 8  is a schematic diagram illustrating an exemplary scene in a case that the data of the first base station is forwarded via the second base station and the synchronized access to the third base station by the user equipment succeeds according to an embodiment of the disclosure; and  FIG. 9  is a schematic diagram illustrating an exemplary scene in a case that the data of the first base station is forwarded via the second base station and the synchronized access to the third base station by the user equipment fails according to an embodiment of the disclosure. 
     Specifically, if the data of the first base station  102  is forwarded via the second base station  104 , the second base station  104  performs data forwarding operation according to the result of the first admission control to forward the data of the first radio bearer acceptable by the third base station  106  to the third base station  106 , and performs data forwarding operation according to the result of the second admission control to forward the data of the second radio bearer acceptable by the first base station  102  to the first base station  102 . 
     If the synchronized access to the third base station  106  by the user equipment  108  succeeds, as shown in  FIG. 8 , the third base station  106  triggers the core network to perform path switch to route the data sent from the core network to the second base station  104  directly to the third base station  106 , and after completing the path switch, the third base station  106  starts forwarding the data of downlink bearer transmitted via the first base station  102  to the first base station  102 , and the second base station  104  releases information related to the user equipment and services thereof after completing the data forwarding operation. Specifically, after succeeding in the synchronized access, the third base station  106  sends “path switch request” for example to the mobility management entity, the mobility management entity sends, after receiving the request, “bearer modifying request” for example to the gateway, and the gateway performs switching downlink path operation after receiving the request and thus the data of the first radio bearer acceptable by the third base station  106  is directly routed to the third base station  106 , and the gateway sends an end flag to the second base station  104 . Then, the second base station  104  forwards this end flag to the first base station  102  to inform the first base station of the number of last data packet forwarded via the second base station  104 . Thereafter, the gateway sends “bearer modifying response” for example to the mobility management entity, and the mobility management entity sends “path switch confirmation” for example as confirmation for the “path switch request” to the third base station  106  after receiving the response, and thus notifies the third base station  106  that the path switch operation at the core network end has been completed. 
     As can be seen from  FIG. 8 , in a case that the synchronized access succeeds, after receiving the end flag for the services transmitted by the first base station  102 , the second base station  104  forwards the flag to the first base station  102 , and then releases all resources related to the user equipment  108  after receiving a message “user equipment information release” sent by the third base station  106  and/or the first base station  102 . 
     Otherwise, if the synchronized access to the third base station  106  by the user equipment  108  fails, then as shown in  FIG. 9 , the user equipment  108  notifies the first base station  102 , and the first base station  102  notifies the second base station  104  and the third base station  106  after performing the third admission control to notify the failure of the synchronized access and cause the second base station  104  and the third base station  106  perform data forwarding operation for the third radio bearer acceptable by the first base station  102  in the first radio bearer, and meanwhile notifies the user equipment  108  of which data can be transmitted over carriers of the first base station  102  and which data needs to be released. 
     Preferably, in the case that the synchronized access fails, the data of the services transmitted by the first base station  102  (that is, data of the original services of the first base station  102 , data of the second radio bearer and data of the third radio bearer) may also be forwarded to the first base station  102  via the second base station  104 . In this case, when switching needs to be performed among small base stations, there always exists one anchor base station (for example, the second base station  104  herein) being responsible for data forwarding, and thus it only needs to notify the anchor base station of the transfer the data forwarding. 
     However, alternatively, it is also possible that after completing the third admission control by the first base station  102 , the first base station  102  or the second base station  104  notifies the core network to perform path switch for the data of all the radio bearers accepted by the first base station  102 , so that the path corresponding to the data forwarded to the first base station  102  via the second base station  104  is switched to the first base station  102  and the core network bearer corresponding to the radio bearer unacceptable by the first base station  102  in the first radio bearer is released, and meanwhile notifies the user equipment  108  to release the radio bearer unacceptable by the first base station  102  in the first radio bearer. 
     It is to be noted that in the case that the synchronized access fails, as shown in  FIG. 9 , except that the mobility management entity is notified by the first base station  102  or the second base station  104  at this time, specific path switch operations involving the core network are similar to those described above with reference to  FIG. 8 , and thus no repeated description will be made herein. 
     Although data forwarding and path switch operations after the transfer procedure in various situations have been described above with reference to  FIGS. 4-9 , it should be understood that the drawings and related description thereof are only examples but not limitation, and those skilled in the art may modify the above procedures according to the principle of the invention. For example, although in the above the first base station  102  and the third base station  106  together undertake at least part of the services originally provided by the second base station  104 , it is also possible that the third base station  106  undertakes this individually, while for the services unacceptable by the third base station  106 , the user equipment  108  is notified to release this part of the services. Further, although it only shows the second base station  104  performs data forwarding operation to the third base station  106  in  FIGS. 4-9 , this is merely for the purpose of clarity of illustration but not limitation, it should be understood that in a case that the first base station  102  performs admission control, the second base station  104  also performs data forwarding operation to the first base station  102  with respect to the radio bearer accepted by the first base station  102 . 
     Further, it should be noted that for the purpose of clarity, only signaling interactions closely related to the disclosure are shown in the drawings, and for other well-known signaling interactions in the art, no detailed description will be made herein. 
     As can be understood from the above detailed description of the embodiments of the disclosure, by performing the above transfer procedure in the case that the predetermined transfer condition is satisfied, it is possible to ensure the user equipment obtains optimized service quality while improving data transmission efficiency. 
     An example of functional configuration of a first base station serving as the connection maintaining node according to an embodiment of the disclosure will be described with reference to  FIG. 10  below.  FIG. 10  is a block diagram illustrating an example of functional configuration of a first base station serving as the connection maintaining node according to an embodiment of the disclosure. 
     As shown in  FIG. 10 , the first base station  1000  according to the present embodiment may include a measurement result receiving unit  1002 , a judging unit  1004 , a transfer request sending unit  1006  and a transfer response receiving unit  1008 . Examples of functional configurations of respective units will be described in detail below. 
     The measurement result receiving unit  1002  may be configured to receive, in a case that the first base station  1000  is the triggering node to trigger the above transfer procedure, a mobility measurement result regarding the serving carrier between the user equipment and the second base station from the user equipment or the second base station as the connection transfer source node. 
     The judging unit  1004  may be configured to judge whether the predetermined transfer condition of transferring the services provided to the user equipment by the second base station to the third base station is satisfied based on the mobility measurement result received by the measurement result receiving unit  1002 . 
     The transfer request sending unit  1006  may be configured to send a transfer request to the third base station as the connection transfer target node in a case that the judging unit  1004  judges the predetermined transfer condition is satisfied, so as to trigger the user equipment to release the wireless data connection with the second base station and establish the wireless data connection with the third base station, and thus the first base station and the third base station perform wireless data connection with the user equipment over different carriers. Particularly, at least part of the services originally provided by the second base station is transferred to the third base station. 
     The transfer response receiving unit  1008  may be configured to receive from the third base station the transfer response which may include the result of the admission control performed by the third base station. 
     Preferably, the first base station  1000  may further include a first admission control performing unit  1010 . The first admission control performing unit  1010  may be configured to perform, in a case that the admission control result contained in the transfer response received by the transfer response receiving unit  1008  indicates that the third base station can not accept all radio bearers of the second base station, admission control for radio bearer unacceptable by the third base station, so that the radio bearer acceptable by the first bases station can be transferred to the first base station  1000 . 
     Also, optionally, the first base station  1000  may further include a notifying unit  1012 . The notifying unit  1012  may be configured to notify the result of the admission control performed by the third base station and optionally the result of the admission control performed by the first base station to the user equipment and/or the second base station. 
     Further, optionally, the first base station  1000  may further include a data forwarding unit  1014 . The data forwarding unit  1014  may be configured to perform data forwarding to the third base station in a case that the data of the second base station is forwarded via the first base station. Preferably, the data forwarding unit  1014  may perform data forwarding simultaneously with the second base station after completing the basic signaling interaction of the transfer procedure, or may perform the data forwarding only after receiving a message that the synchronized access between the user equipment and the third base station succeeds. 
     Preferably, the first base station  1000  may further include a second admission control performing unit  1016 . The second admission control performing unit  1016  may be configured to perform, in a case that the synchronized access between the user equipment and the third base station fails, admission control for the radio bearer that should be accepted by the third base station originally, so that the radio bearer acceptable by the first base station is transferred to the first base station  1000 . 
     Further, preferably, the first base station  1000  may further include a core network notifying unit  1018 . The core network notifying unit  1018  may be configured to notify the core network to switch the path corresponding to the radio bearer accepted by the first base station to the first base station in a case that the data of the second base station comes directly from the core network. 
     It is to be understood that all of the first admission control performing unit  1010 , the notifying unit  1012 , the data forwarding unit  1014 , the second admission control performing unit  1016  and the core network notifying unit  1018  are optional, which are shown in broken-line blocks in  FIG. 10 , and those skilled in the art may combine one or more of the above described units as required for example, and any such combinations are considered to fall within the scope of the disclosure. 
     Next, an example of functional configuration of the first base station serving as the connection maintaining node according to another embodiment of the disclosure will be described with reference to  FIG. 11 .  FIG. 11  is a block diagram illustrating an example of functional configuration of the first base station serving as the connection maintaining node according to another embodiment of the disclosure. Except for providing a receiving unit  1102  instead of the measurement result receiving unit  1002 , the transfer request sending unit  1004 , the judging unit  1006  and the transfer response receiving unit  1008 , the functional configuration of the first base station  1100  as shown in  FIG. 11  is the same as that of the first base station  1000  described above with reference to  FIG. 10 , and thus some description will be omitted as appropriate. 
     The receiving unit  1102  may be configured to receive a notification regarding the transfer procedure from the second base station or the third base station serving as the connection transfer target node in a case that the above transfer procedure is triggered by the second base station serving as the connection transfer source node, and the notification may include the result of the admission control performed by the third base station. 
     Further, for the optional first admission control performing unit  1104 , the notifying unit  1106 , the data forwarding unit  1108 , the second admission control performing unit  1110  and the core network notifying unit  1112  as shown in broken-line blocks in  FIG. 11 , functional configurations thereof are the same as those of corresponding units described above with reference to  FIG. 10 , and no repeated description will be made herein. 
     Next, an example of functional configuration of the second base station serving as the connection transfer source node according to an embodiment of the disclosure will be described with reference to  FIG. 12 .  FIG. 12  is a block diagram illustrating an example of functional configuration of the second base station serving as the connection transfer source node according to an embodiment of the disclosure. 
     As shown in  FIG. 12 , the second base station  1200  according to the embodiment of the disclosure may include a receiving unit  1202 . The receiving unit  1202  may be configured to receive a notification regarding the transfer procedure from the first base station or the third base station serving as the connection transfer target node in a case that the transfer procedure is triggered by the first base station serving as the connection maintaining node, and the notification may include the result of the admission control performed by the third base station and optionally the result of the admission control performed by the first base station. 
     Optionally, the second base station  1200  may further include a user equipment notifying unit  1204 . The user equipment notifying unit  1204  may be configured to notify the user equipment of the result of the admission control performed by the third base station and optionally the result of the admission control performed by the first base station. 
     Optionally, the second base station  1200  may further include a data forwarding unit  1206 . The data forwarding unit  1206  may be configured to perform data forwarding operation to the third base station and optionally the first base station, so as to forward the data of the radio bearers acceptable by the third base station and the first base station to the third base station and the first base station respectively. 
     Optionally, the second base station  1200  may further include a core network notifying unit  1208 . The core network notifying unit  1208  may be configured to notify the core network to switch the path corresponding to the radio bearer acceptable by the first base station to the first base station in a case that the data of the second base station directly comes from the core network. 
     Next, an example of the functional configuration of the second base station serving as the connection transfer source node according to another embodiment of the disclosure will be described with reference to  FIG. 13 .  FIG. 13  is a block diagram illustrating an example of the functional configuration of the second base station serving as the connection transfer source node according to another embodiment of the disclosure. Except for providing a measurement result receiving unit  1302 , a judging unit  1304 , a transfer request sending unit  1306  and a transfer response receiving unit  1308  instead of the receiving unit  1202  of the second base station  1200  as shown in  FIG. 12 , the functional configuration of the second base station  1300  as shown in  FIG. 13  is the same as that of the second base station  1200  as shown in  FIG. 12 , and thus description thereof will be omitted as appropriate. 
     The measurement result receiving unit  1302  may be configured to receive a mobility measurement result regarding a serving carrier between the user equipment and the second base station from the user equipment. 
     The judging unit  1304  may be configured to judge whether a predetermined transfer condition of transferring the services provided to the user equipment by the second base station to the third base station is satisfied according to the mobility measurement result received by the measurement result receiving unit  1302 . 
     The transfer request sending unit  1306  may be configured to send a transfer request to the third base station serving as the connection transfer target node in a case that the judging unit  1304  judges the predetermined transfer condition is satisfied, so as to trigger the user equipment to release the wireless data connection with the second base station and establish the wireless data connection with the third base station, and thus the first base station serving as the connection maintaining node and the third base station perform wireless data connection with the user equipment over different carriers, so that at least part of the services originally provided by the second base station is transferred to the third base station. 
     The transfer response receiving unit  1308  may be configured to receive from the third base station a transfer response which may include the result of the admission control performed by the third base station. 
     Further, preferably, the third base station  1300  may further include a transfer confirmation receiving unit  1310 . The transfer confirmation receiving unit  1310  may be configured to receive from the first base station a transfer confirmation which may include the result of the admission control performed by the first base station. 
     Further, for a user equipment notifying unit  1312 , a data forwarding unit  1314  and a core network notifying unit  1316  as shown in broken-line blocks in  FIG. 13 , functional configurations thereof are the same as those of the user equipment notifying unit  1204 , the data forwarding unit  1206  and the core network notifying unit  1208  described above with reference to  FIG. 12 , and no repeated description will be made herein. 
     Further, it is to be noted that similar to the cases as shown in  FIGS. 10 and 11 , the constitute units as shown in broken-line blocks in  FIGS. 12 and 13  are optional, and those skilled in the art may combine one or more of these units according to actual requirements, and any such combinations are considered to fall within the scope of the disclosure. 
     Next, an example of functional configuration of the third base station serving as the connection transfer target node according to an embodiment of the disclosure will be described with reference to  FIG. 14 .  FIG. 14  is a block diagram illustrating an example of functional configuration of the third base station serving as the connection transfer target node according to an embodiment of the disclosure. 
     As shown in  FIG. 14 , the third base station  1400  according to the embodiment of the disclosure may include a transfer request receiving unit  1402 , an admission control performing unit  1404  and a transfer response sending unit  1406 . 
     The transfer request receiving unit  1402  may be configured to receive a transfer request regarding the transfer procedure from the first base station serving as the connection maintaining node or the second base station serving as the connection transfer source node which is the triggering node to make the user equipment release the wireless data connection with the second base station, and in a case that the synchronized access between the user equipment and the third base station succeeds, the first base station and the third base station perform wireless data connection with the user equipment over different carriers so that at least part of the services originally provided by the second base station is transferred to the third base station. 
     The admission control performing unit  1404  may be configured to perform the admission control according to the transfer request received by the transfer request receiving unit  1402  so as to determine the radio bearer of the second base station acceptable by the third base station. 
     The transfer response sending unit  1406  may be configured to send a transfer response which may include the result of the admission control performed by the third base station to the first base station or the second base station which is the triggering node for the transfer procedure. 
     Optionally, the third base station  1400  may further include a core network notifying unit  1408 . The core network notifying unit  1408  may be configured to notify the core network to switch the path corresponding to the radio bearer acceptable by the third base station to the third base station in a case that the data of the second base station directly comes from the core network or the data of the first base station is forwarded via the second base station and the synchronized access between the user equipment and the third base station succeeds. 
     Further, optionally, the third base station  1400  may further include a data forwarding unit  1410 . The data forwarding unit  1410  may be configured to perform data forwarding to the first base station in a case that the synchronized access between the user equipment and the third base station fails, so as to forward the data of the radio bearer acceptable by the first base station in the radio bearer originally accepted by the third base station to the first base station. 
     It is to be understood that both of the core network notifying unit  1408  and the data forwarding unit  1410  as shown in broken-line blocks in  FIG. 14  are optional, and those skilled in the art may combine one or more of these units according to actual requirements and any such combinations are considered to fall within the scope of the disclosure. 
     Next, an example of functional configuration of the user equipment according to an embodiment of the disclosure will be described with reference to  FIG. 15 .  FIG. 15  is a block diagram illustrating an example of functional configuration of the user equipment according to an embodiment of the disclosure. 
     As shown in  FIG. 15 , the user equipment  1500  according to the embodiment of the disclosure may include a measurement result reporting unit  1502 , a first notification receiving unit  1504  and a synchronized accessing unit  1506 . 
     The measurement result reporting unit  1502  may be configured to report a mobility measurement result regarding a serving carrier between the user equipment and the second base station serving as the connection transfer source node to the second base station and optionally the first base station serving as the connection maintaining node, so as to serve as reference for the triggering node to judge whether the predetermined transfer condition of transferring the services provided to the user equipment by the second base station to the third base station is satisfied. 
     The first notification receiving unit  1504  may be configured to receive a notification regarding the transfer procedure from the first base station or the second base station, and the notification may include the result of the admission control performed by the third base station serving as the connection transfer target node and optionally the result of the admission control performed by the first base station. 
     The synchronized accessing unit  1506  may be configured to perform the synchronized access to the third base station according to the notification received by the first notification receiving unit  1504 . 
     Preferably, the user equipment  1500  may further include a second notification receiving unit  1508 . The second notification receiving unit  1508  may be configured to receive a notification from the first base station in a case that the synchronized access to the third base station by the user equipment fails, the notification including information about which data of the user equipment may be transmitted over the carrier of the first base station and which data needs to be released. 
     Similarly, the second notification receiving unit  1508  as shown in broken-line block in  FIG. 15  is also optional. 
     It is to be noted that although the examples of the functional configurations of the first base station, the second base station, the third base station and the user equipment in the wireless communication system according to the embodiments of the disclosure have been described above with reference to  FIGS. 10-15 , it should be understood that this constructs no limitation on the disclosure, and those skilled in the art may combine, sub-combine and alter the above configurations according to the principle of the disclosure. 
     Next, an example of a procedure of a method used in the wireless communication system according to an embodiment of the disclosure will be described with reference to  FIG. 16 .  FIG. 16  is a flow chart illustrating an example of a procedure of a method used in the wireless communication system according to an embodiment of the disclosure. The wireless communication system may include a first base station, a second base station, a third base station and user equipment, and the first base station and the second base station perform wireless data connection with the user equipment over different carriers. 
     As shown in  FIG. 16 , the method  1600  according to the embodiment of the disclosure may include a judging step S 1602  and a triggering step S 1604 . 
     In the judging step S 1602 , whether the predetermined transfer condition of transferring the services provided to the user equipment by the second base station to the third base station is satisfied may be judged by the triggering node. The triggering node may be the first base station serving as the connection maintaining node or the second base station serving as the connection transfer source node. 
     Next, in the triggering step S 1604 , the transfer procedure may be triggered in a case that it is judged the predetermined transfer condition is satisfied, so as to make the user equipment release the wireless data connection with the second base station and establish the wireless data connection with the third base station, and thus the first base station and the third base station perform wireless data connection with the user equipment over different carriers. Particularly, at least part of the services originally provided by the second base station is transferred to the third base station. 
     Preferably, the above transfer procedure also causes part of the services originally provided by the second base station to be transferred to the first base station. 
     Further, preferably, the triggering node sends a transfer request to the third base station if it judges the predetermined transfer condition is satisfied according to a received mobility measurement result regarding a serving carrier of the second base station, and the third base station performs the first admission control according to the transfer request and sends a transfer response to the triggering node to notify the result of the first admission control. 
     Further, preferably, if the result of the first admission control indicates that the third base station can not accept all radio bearers between the user equipment and the second base station, the first base station performs the second admission control according to the result of the first admission control and notifies the second base station of the result of the second admission control. 
     Further, preferably, the first base station or the second base station sends, after acquiring the final result of the first admission control or the second admission control, a notification message to the user equipment to notify the user equipment to perform the transfer procedure according to the final result and the transfer response of the third base station, the notification message including at least one of the following: for which part of the radio bearer of the user equipment that the first base station can perform communication, for which part of the radio bearer of the user equipment that the third base station can perform communication, a dedicated preamble code as required when making synchronized access to the third base station, system information of a carrier for communication between the user equipment and the third base station, and configuration information of a control plane protocol for establishing communication between the user equipment and the third base station. Further, the user equipment releases, after receiving the notification message, the radio bearers unacceptable by the first base station and the third base station, and releases the wireless data connection with the second base station and performs synchronized access to the third base station at the same time. 
     It is to be understood that the method used in the wireless communication system according to the embodiment of the disclosure corresponds to the embodiments of the wireless communication system described above, and thus parts which are not described in detail herein may be referred to the foregoing description at previous corresponding positions, and no repeated description will be made herein. 
     Further, the embodiment of the disclosure also provides a storage medium including machine readable program codes which when executed on an information processing apparatus, cause the information processing apparatus to perform the method used in the wireless communication system according to the embodiment of the disclosure as described above, the method including the following steps: a judging step of judging, by a triggering node, whether a predetermined transfer condition for transferring services provided to user equipment by a second base station to a third base station is satisfied; and a triggering step of triggering the transfer procedure if it is judged that the predetermined transfer condition is satisfied, so that the user equipment releases wireless data connection with the second base station and establishes wireless data connection with the third base station, and thus a first base station and the third base station perform wireless data connection with the user equipment over different carriers, wherein at least part of the services originally provided by the second base station is transferred to the third base station. Particularly, the first base station, the second base station, the third base station and the user equipment are included in a wireless communication system, and the first base station and the second base station perform wireless data connection with the user equipment over different carriers. 
     Further, the embodiment of the disclosure also provides a program product including machine executable instructions which when executed on an information processing apparatus cause the information processing apparatus to perform the method used in the wireless communication system according to the embodiment of the disclosure as described above, the method including the following steps: a judging step of judging, by a triggering node, whether a predetermined transfer condition for transferring services provided to user equipment by a second base station to a third base station is satisfied; and a triggering step of triggering the transfer procedure if it is judged that the predetermined transfer condition is satisfied, so that the user equipment releases wireless data connection with the second base station and establishes wireless data connection with the third base station, and thus a first base station and the third base station perform wireless data connection with the user equipment over different carriers, wherein at least part of the services originally provided by the second base station is transferred to the third base station. Particularly, the first base station, the second base station, the third base station and the user equipment are included in a wireless communication system, and the first base station and the second base station perform wireless data connection with the user equipment over different carriers. 
     It should be appreciated that the machine executable instructions in the storage medium and the program product according to the embodiments of the disclosure may also be configured to perform the methods corresponding to the embodiments of the wireless communication system described above, and thus parts which are not described in detail herein may be referred to description at previous corresponding positions, and no repeated description will be made herein. 
     Accordingly, a storage medium on which the above program product storing machine readable instruction codes is carried is also included in the disclosure of the invention. The storage medium includes but not limited to a floppy disk, an optical disk, a magneto-optical disk, a storage card, a memory rod and the like. 
     Furthermore, it shall be noted that the foregoing series of processes and apparatuses can also be embodied in software and/or firmware. In the case of being embodied in software and/or firmware, a program constituting the software is installed from a storage medium or a network to a computer with a dedicated hardware structure, e.g., a general purpose personal computer  1700  illustrated in  FIG. 17 , which can perform various functions when various programs are installed thereon. 
     In  FIG. 17 , a Central Processing Unit (CPU)  1701  performs various processes according to a program stored in a Read Only Memory (ROM)  1702  or loaded from a storage portion  1708  into a Random Access Memory (RAM)  1703  in which data required when the CPU  1701  performs the various processes is also stored as needed. 
     The CPU  1701 , the ROM  1702  and the RAM  1703  are connected to each other via a bus  1704  to which an input/output interface  1705  is also connected. 
     The following components are connected to the input/output interface  1705 : an input portion  1706  including a keyboard, a mouse, etc.; an output portion  1707  including a display, e.g., a Cathode Ray Tube (CRT), a Liquid Crystal Display (LCD), etc., a speaker, etc.; a storage portion  1708  including a hard disk, etc.; and a communication portion  1709  including a network interface card, e.g., an LAN card, a modem, etc. The communication portion  1709  performs a communication process over a network, e.g., the Internet. 
     A driver  1710  is also connected to the input/output interface  1705  as needed. A removable medium  1711 , e.g., a magnetic disk, an optical disk, an magneto optical disk, a semiconductor memory, etc., can be installed on the driver  1710  as needed so that a computer program fetched therefrom can be installed into the storage portion  1808  as needed. 
     In the case that the foregoing series of processes are performed in software, a program constituting the software is installed from a network, e.g., the Internet, etc., or a storage medium, e.g., the removable medium  1711 , etc. 
     Those skilled in the art shall appreciate that such a storage medium will not be limited to the removable medium  1711  illustrated in  FIG. 17  in which the program is stored and which is distributed separately from the device to provide a user with the program. Examples of the removable medium  1711  include a magnetic disk (including a Floppy Disk (a registered trademark)), an optical disk (including Compact Disk-Read Only memory (CD-ROM) and a Digital Versatile Disk (DVD)), a magneto optical disk (including a Mini Disk (MD) (a registered trademark)) and a semiconductor memory. Alternatively the storage medium can be the ROM  1702 , a hard disk included in the storage portion  1708 , etc., in which the program is stored and which is distributed together with the apparatus including the same to the user. 
     It shall further be noted that the steps of the foregoing series of processes may naturally but not necessarily be performed in the sequential order as described chronically. Some of the steps may be performed concurrently or separately from each other. 
     Although the disclosure and the advantages thereof have been described in details, it shall be appreciated that various modifications, substitutions and variations can be made without departing from the spirit and scope of the disclosure as defined by the appended claims. Furthermore, the terms “include”, “comprise” or any variants thereof in the embodiments of the disclosure are intended to encompass nonexclusive inclusion so that a process, method, article or apparatus including a series of elements includes both those elements and other elements which are not listed explicitly or an element(s) inherent to the process, method, article or apparatus. Without much more limitation, an element being defined by a sentence “include/comprise a(n) . . . ” will not exclude presence of an additional identical element(s) in the process, method, article or apparatus including the element.