Abstract:
The invention proposes a method to support a handover of a service of a user equipment between a source eNB and a destination eNB in a wireless communication network with carrier aggregation, which includes the steps of: the destination eNB determining a primary component carrier jointly with the source eNB; transmitting a handover command to be transmitted to the user equipment to the source eNB, the handover command including indication information of the primary component carrier and dedicated preamble assignment information; the source eNB receiving the handover command to be transmitted to the user equipment from the destination eNB and forwarding the handover command to the user equipment; and then the user equipment accessing the destination eNB in response to the handover command. Also apparatuses performing the foregoing method in the source eNB, the destination eNB and the user equipment are proposed correspondingly. The technical solution of the invention improves the smoothness and efficiency of handing over a service of a user equipment between two eNBs in a carrier aggregation scenario and simplifies data transmission between the source eNB and the destination eNB in the handover procedure of the user equipment.

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to the field of communication in a wireless communication network and particularly to a method and apparatus for handing over a user equipment between two eNBs in a wireless communication network with carrier aggregation. 
     BACKGROUND OF THE INVENTION 
     At present a User Equipment (UE) is configured with only one carrier resource of no more than 20M in a Long Term Evolution (LTE) system, and since there is only one carrier in the system, a handover procedure is performed directly over the carrier when the user equipment in the system is handed over from an eNB originally serving the user equipment (i.e., a source eNB) to another eNB (i.e., a destination eNB). 
     Carrier aggregation supported in LTE-Advanced includes aggregation of consecutive carriers as well as in-band and inter-band aggregation of inconsecutive carriers and has a maximum bandwidth that can be aggregated of up to 100 MHz. Thus 1 to 5 component carriers can be supported in a macro cell, and each component carrier shall be able to be configured as a carrier backward compatible with LTE in order to make LTE-A compatible with LTE, so each component carrier has a bandwidth of no more than 20M. In the foregoing application scenario of carrier aggregation, a component carrier has to be selected in the handover procedure while the user equipment is being handed over from the source eNB to the destination eNB. Unfortunately a technical solution of supporting the handover of the user equipment from the source eNB to the destination eNB in the carrier aggregation scenario has been absent in the existing LTE-A system. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problem of lacking a technical solution to a handover of a service of a user equipment between two eNBs in a carrier aggregation scenario, the invention proposes a method and apparatus for handing over a user equipment from a source eNB to a destination eNB in a wireless communication network in an application scenario of carrier aggregation. 
     According to an embodiment of the invention, there is provided a method, in a source eNB in a wireless communication network with carrier aggregation, of handing over a service of a user equipment to a destination eNB. The method comprises the steps of: determining a primary component carrier jointly with the destination eNB; receiving a handover command transmitted from the destination eNB to the user equipment, the handover command including indication information of the primary component carrier; and forwarding the handover command to the user equipment. 
     According to another embodiment of the invention, there is provided a method, in a destination eNB in a wireless communication network with carrier aggregation, of handing over a service of a user equipment from a source eNB to the destination eNB. The method comprises the steps of: determining a primary component carrier jointly with the source eNB; and transmitting a handover command to be transmitted to the user equipment to the source eNB, the handover command including indication information of the primary component carrier. 
     According to a further embodiment of the invention, there is provided a method, in a user equipment in a wireless communication network with carrier aggregation, of handing over a service of the user equipment from a source eNB to a destination eNB. The method comprises the steps of: receiving a handover command from the source eNB, the handover command including indication information of a determined primary component carrier; and accessing the destination eNB. 
     According to a further embodiment of the invention, there is provided an apparatus, in a source eNB in a wireless communication network with carrier aggregation, for handing over a service of a user equipment to a destination eNB. The apparatus comprises: a first determining device configured to determine a primary component carrier jointly with the destination eNB; a first receiving device configured to receive a handover command transmitted from the destination eNB to the user equipment, the handover command including indication information of the primary component carrier; and a command forwarding device configured to forward the handover command to the user equipment. 
     According to a further embodiment of the invention, there is provided an apparatus, in a destination eNB in a wireless communication network with carrier aggregation, for handing over a service of a user equipment from a source eNB to the destination eNB. The apparatus comprises: a second determining device configured to determine a primary component carrier jointly with the source eNB; and a command transmitting device configured to transmit a handover command to be transmitted to the user equipment to the source eNB, the handover command including indication information of the primary component carrier. 
     According to a further embodiment of the invention, there is provided an apparatus, in a user equipment in a wireless communication network with carrier aggregation, for handing over a service of the user equipment from a source eNB to a destination eNB. The apparatus comprises: a second receiving device configured to receive a handover command, the handover command including indication information of a determined primary component carrier; and an accessing device configured to access the destination eNB according to dedicated preamble assignment information. 
     With the method and apparatus of the invention, a handover of a user equipment from a source eNB to a destination eNB in a carrier aggregation scenario can be supported. 
     In an embodiment of the invention, the destination eNB and the source eNB jointly determine a primary component carrier: it is not necessary for the source eNB to forward measurement information from the user equipment to the destination eNB when the source eNB determines the primary component carrier with the coordination of the destination eNB. It is not necessary for the destination eNB to notify the source eNB of a traffic load condition of the destination eNB when the destination eNB determines the primary component carrier with the coordination of the source eNB. A traffic load between the source eNB and the destination eNB is alleviated in both of the foregoing scenarios. 
     In another embodiment of the invention, measurement information of channel qualities from the user equipment and information of traffic loads is synthetically considered to thereby determine a primary component carrier; and according to dedicated preamble assignment information in a received handover command, while the user equipment accessing the destination eNB over a primary component carrier or a secondary component carrier corresponding to the information, a higher access/handover success ratio and a smoothed handover procedure of the user equipment and smoothed communication procedures of the user equipment before and after the handover can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Other features, objects and advantages of the invention will become more apparent by reading the following detailed description of non-restrictive embodiments taken with reference to the drawings in which: 
         FIG. 1  is a topology diagram of a system of a wireless communication network including a source eNB, a destination eNB and a user equipment according to an embodiment of the invention; 
         FIG. 2  is a flow chart of a method of handing over a service of a user equipment between a source eNB and a destination eNB in a wireless communication network according to an embodiment of the invention; 
         FIG. 3  is a flow chart of a method for a source eNB to determine a primary component carrier with the coordination of a destination eNB in a wireless communication network according to an embodiment of the invention; 
         FIG. 4  is a flow chart of a method for a destination eNB to determine a primary component carrier with the coordination of a source eNB in a wireless communication network according to an embodiment of the invention; 
         FIG. 5  illustrates a structural diagram of a first handover apparatus, in a source eNB, for handing over a service of a user equipment to a destination eNB according to an embodiment of the invention; 
         FIG. 6  illustrates a structural diagram of a second handover apparatus, in a destination eNB, for handing over a service of a user equipment from a source eNB to the destination eNB according to an embodiment of the invention; and 
         FIG. 7  illustrates a structural diagram of a third handover apparatus, in a user equipment in a wireless communication network with carrier aggregation, for handing over a service of the user equipment from a source eNB to a destination eNB according to an embodiment of the invention. 
     
    
    
     Identical or like reference numerals denote identical or like step features or devices (modules) throughout the drawings. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Non-restrictive embodiments of the invention will be described below in details with reference to the drawings. 
     Without loss of generality, all the following embodiments of the invention can be applicable to an LTE-A network in a carrier aggregation scenario, but those skilled in the art shall appreciate that the invention can also be applicable to other types of network. 
       FIG. 1  is a topology diagram of a system of a wireless communication network according to an embodiment of the invention. As illustrated, the system includes a source eNB  10 , a destination eNB  20  and a user equipment  30 , where a service of the user equipment  30  is handed over from the source eNB  10  to the destination eNB  20 . 
       FIG. 2  is a flow chart of a method according to an embodiment of the invention, which is applied to a handover of a service of the user equipment  30  between the source eNB  10  and the destination eNB  20  in the wireless communication network. As illustrated, the method comprises three steps S 11 , S 12  and S 13  performed by the source eNB  10 , two steps S 21  and S 22  performed by the destination eNB  20  and steps S 31  and S 32  performed by the user equipment  30 . 
     In the step S 11 , the source eNB  10  determines a primary component carrier jointly with the destination eNB  20 . 
     In the step S 21 , the destination eNB  20  determines a primary component carrier jointly with the source eNB  10 . 
     With the foregoing steps S 11  and S 21 , the source eNB  10  and the destination eNB  20  coordinate with each other to determine the primary component carrier. Next in the step S 22 , the destination eNB  20  transmits a handover command to be transmitted to the user equipment  30  to the source eNB  10 , and the handover command includes indication information of the primary component carrier. 
     Next in the step S 12 , the source eNB  10  receives the handover command to be transmitted to the user equipment from the destination eNB, and the handover command includes the indication information of the primary component carrier. Then in the step S 13 , the source eNB  10  forwards the handover command to the user equipment  30 . 
     Next in the step S 31 , the user equipment  30  receives the handover command from the source eNB  10 , wherein the handover command includes the indication information of the determined primary component carrier. Next in the step S 32 , the user equipment  30  accesses the destination eNB  20 . 
       FIG. 3  is a flow chart of the step S 11  in which the source eNB  10  acts as a dominator device for determining the primary component carrier with the coordination of the destination eNB in the wireless communication network according to an embodiment of the invention. As illustrated, the step S 11  comprises three sub-steps S 111 , S 112  and S 113  in this embodiment. 
     In the step S 111 , the source eNB  10  receives measurement information from the user equipment. Next in the step S 112 , the source eNB  10  determines a predetermined primary component carrier according to the measurement information. Then in the step S 113 , the source eNB  10  sequentially notifies the destination eNB of indication information of the predetermined primary component carrier. 
       FIG. 4  is a flow chart of a method for the source eNB  10  to act as a dominator device for determining the primary component carrier with the coordination of the source eNB in the wireless communication network according to an embodiment of the invention. As illustrated, the step S 21  includes two sub-steps S 211  and S 212  in this embodiment. 
     In the step S 211 , the destination eNB  20  receives indication information of the predetermined primary component carrier from the source eNB  10 . In the step S 212 , the destination eNB  20  determines whether to determine the predetermined primary component carrier as the primary component carrier according to the measurement information and the traffic load. Optionally the destination eNB  20  can further determine whether to determine the predetermined primary component carrier as the primary component carrier according to the measurement information and other information. 
     A method of handing over a service of the user equipment  30  from the source eNB  10  to the destination eNB  20  will be described in details below with reference to  FIG. 1  to  FIG. 4 . 
     In an embodiment of the invention, the destination eNB  20  is configured with three component carriers CC 1 , CC 2  and CC 3  (not illustrated). 
     In an embodiment of the invention, the source eNB  10  is a dominator and the destination eNB  20  assists the source eNB  10  in determining a primary component carrier in a step of determining the primary component carrier in a handover procedure. Firstly in the step S 11 , the source eNB  10  determines a primary component carrier from the foregoing three component carriers jointly with the destination eNB  20 . 
     In this embodiment, the step S 11  includes three sub-steps S 111 , S 112  and S 113 . 
     Firstly in the step S 111 , the source eNB  10  receives measurement information from the user equipment  30 , and the measurement information identifies the channel quality, etc. 
     Secondly in the step S 112 , the source eNB  10  determines a predetermined primary component carrier according to the measurement information from the user equipment  30 . For example, the measurement information indicates that CC 1  is of better channel quality, then the source eNB  10  can determine the component carrier CC 1  as the predetermined primary component carrier. Optionally in the step S 112 , the source eNB  10  can further determine two or more predetermined primary component carriers from the component carriers with better channel qualities for the destination eNB  20  to determine a primary component carrier in the step S 212  eventually. 
     Thirdly in the step S 113 , the source eNB  10  notifies the destination eNB  20  of indication information of the predetermined primary component carrier, i.e., that the CC 1  is determined as the predetermined primary component carrier. Optionally the source eNB  10  further notifies the destination eNB  20  of a security key related to the predetermined primary component carrier CC 1 ; and if a secondary component carrier has been predetermined or determined, for example, as the CC 3 , then the source eNB  10  further notifies the destination eNB  20  of indication information of the secondary component carrier CC 3 , etc. 
     In correspondence to the step S 11  performed by the source eNB  10 , the destination eNB  20  determines a primary component carrier jointly with the source eNB  10  in the step S 21  at the side of the destination eNB  20 . 
     In this embodiment, the step S 21  includes two sub-steps S 211  and S 212 . 
     In the step S 211 , the destination eNB  20  receives indication information of the predetermined primary component carrier from the source eNB  10 , that is, the component carrier CC 1  being determined as the predetermined primary component carrier. 
     In the step S 212 , the destination eNB  20  determines whether to determine the predetermined primary component carrier CC 1  as the primary component carrier according to the traffic load. Optionally the destination eNB  20  can further determine whether to determine the predetermined primary component carrier CC 1  as the primary component carrier according to the measurement information and other information. 
     For example, if the traffic load over the component carrier CC 1  is in a reasonable range enabling it to be used as a primary component carrier, then the destination eNB  20  confirms the predetermined primary component carrier CC 1  as the primary component carrier. 
     Optionally the destination eNB  20  can further perform connection admission control over the predetermined primary component carrier notified by the source eNB  10  between the step S 211  and the step S 212 . 
     In this embodiment, if the destination eNB  20  determines that the predetermined primary component carrier CC 1  is not suitable to be the primary component carrier in the step S 212 , for example, in the case of the component carrier CC 1  having a traffic load above those of the component carriers CC 2  and CC 3  and approximating a full load in this embodiment, then the destination eNB  20  notifies the source eNB  10  of indication information of a component carrier with a lower traffic load than the predetermined primary component carrier. That is, the component carrier CC 2  with the lowest traffic load in the system is selected, and the source eNB  10  is notified of the component carrier CC 2  with the lowest traffic load in the system and its traffic load related information, or the source eNB  10  is notified of both of the component carriers CC 2  and CC 3  and their traffic load related information, wherein both the component carriers CC 2  and CC 3  have traffic loads lower than that of the component carrier CC 1  in this embodiment. Next after the source eNB  10  receives the information of the component carriers CC 2  and CC 3  with lower traffic loads from the destination eNB  20 , the source eNB  10  then determines a primary component carrier synthetically considering the measurement information, from the user equipment  30 , reflecting a channel quality, etc. For example, the CC 2  with the lowest traffic load and a better channel quality is selected as the primary component carrier and the destination eNB  20  is notified of that the component carrier CC 2  is determined the primary component carrier. 
     Those skilled in the art shall appreciate here that while the process of determining the primary component carrier is completed after only one interactive coordination between the source eNB  10  and the destination eNB  20  in the foregoing embodiments of the invention, when the destination eNB  20  is notified of the primary component carrier (e.g., the CC 2 ) determined by the source eNB  10  after synthetically considering the measurement information of the component carriers from the user equipment and the traffic loads, the destination eNB  20  can further notify the source eNB  10  of indication information of a component carrier with a lower traffic load than the primary component carrier CC 2  determined by the source eNB  10  (e.g., the CC 3 ) for the source eNB  10  to re-determine the primary component carrier, if the destination eNB  20  finds out from a current traffic load condition of the component carrier that the current traffic load condition of the component carrier CC 2  still does not satisfy the condition of being a primary component carrier. This process can be performed repeatedly until the primary component carrier re-determined by the source eNB  10  is confirmed by the destination eNB  20 . The invention will not be limited to the above mentioned specific number of times of the interactions between the source eNB  10  and the destination eNB  20  to confirm the primary component carrier in the method according to this embodiment of the invention. 
     In another embodiment of the invention, the destination eNB  20  is a dominator and the source eNB  10  assists the destination eNB  20  in determining a primary component carrier in the step of determining the primary component carrier in a coordinated way in a handover procedure. 
     Firstly in the step S 11 , the source eNB  10  determines a primary component carrier from the foregoing three component carriers jointly with the destination eNB  20 . In this embodiment, the step S 11  comprises the following sub-steps: firstly the source eNB  10  receives measurement information about the component carriers CC 1 , CC 2  and CC 3  of the destination eNB  20  from the user equipment  30 , and the information can reflect quality conditions of corresponding channels; and next the source eNB  10  forwards the foregoing measurement information to the destination eNB  20 , and optionally the information forwarded from the source eNB  10  to the destination eNB  20  further includes security keys related to the respective component carriers, and if a secondary component carrier has been determined by the source eNB  10 , then the information forwarded from the source eNB  10  to the destination eNB  20  can further include indication information of the secondary component carrier, etc. 
     In correspondence with the step S 11  performed by the source eNB  10 , the destination eNB  20  determines a primary component carrier jointly with the source eNB  10  in the step S 21  at the side of the destination eNB  20 . In this embodiment, the step S 21  comprises the following steps: firstly the destination eNB  20  receives measurement information reported by the user equipment  30  from the source eNB  10 ; and next the destination eNB  20  synthetically considers the foregoing measurement information of the component carriers and traffic loads of the component carriers CC 1 , CC 2  and CC 3  with which the destination eNB  20  itself is configured to determine a primary component carrier. For example, if the component carrier CC 2  has a lower traffic load while the measurement information reflects that its channel quality is better, then the destination eNB  20  determines the component carrier CC 2  as the primary component carrier. 
     With the foregoing steps, the component carrier CC 2  is determined as the primary component carrier, and then in the step S 22 , the destination eNB  20  transmits a handover command to be transmitted to the user equipment  30  to the source eNB  10 , and the handover command includes indication information that the component carrier CC 2  is determined as the primary component carrier. Optionally the handover command further includes assignment information of a dedicated preamble over the respective component carriers CC 1 , CC 2  and CC 3 . Then in the step S 12 , the source eNB  10  receives the foregoing handover command to be transmitted to the user equipment  30  from the destination eNB  20 . Next in the step S 13 , the source eNB  10  forwards the handover command to the user equipment  30 . 
     Correspondingly a flow chart of a method of handing over a service of the user equipment from the source eNB  10  to the destination eNB  20  at the side of the user equipment  30  includes the step S 31  and the step S 32 . 
     In the step S 31 , the user equipment  30  receives a handover command forwarded from the source eNB  10 , wherein the handover command includes indication information of a determined primary component carrier CC 2 . Optionally the handover command further includes assignment information of a dedicated preamble. 
     Next in the step S 32 , the user equipment  30  accesses the destination eNB  20 . For example, the user equipment  30  accesses the destination eNB  20  according to the assignment information of the dedicated preamble included in the handover command. Alternatively the user equipment  30  can directly perform a contention-based access to the destination eNB  20  in the case that the handover command does not include any dedicated preamble assignment information. The handover command includes assignment information of a dedicated preamble over the respective component carriers CC 1 , CC 2  and CC 3 . For example, the dedicated preamble is assigned over the determined primary component carrier CC 2 , and then the user equipment  30  performs a contention-free access over the primary component carrier CC 2 . If there is insufficient preamble resource over the primary component carrier CC 2  so that the destination eNB  20  assigns a dedicated preamble over a secondary component carrier, e.g., over the CC 3 , then the user equipment  30  performs a contention-free access over the component carrier CC 3 . Optionally if the contention-free access performed over the secondary component carrier CC 3  fails, then the user equipment  30  further performs a contention-based access over the primary component carrier CC 2 . Also optionally if the contention-free access performed by the user equipment  30  over the primary component carrier CC 2  fails, then a contention-based access can be performed again over the primary component carrier CC 2 . Of course, the contention-free access performed over the primary component carrier CC 2  may fail at this time due to a severe channel condition of the carrier, which can not be alleviated in a short period of time, so it is not necessary for the user equipment  30  to perform a contention-based access over the primary component carrier CC 2  again. At this time the user equipment  30  can directly announce an access/handover failure after the contention-free access performed over the primary component carrier CC 2  fails. 
     In another embodiment of the invention, the source eNB  10  can be a dominator device for determining a secondary component carrier of the destination eNB  20 . In this embodiment, the following steps are performed at the side of the source eNB  10 : the source eNB  10  determines a secondary component carrier for the user equipment  30 ; and transmits indication information of the secondary component carrier to the destination eNB  20 . Then in the step S 12 , the handover command received by the source eNB  10  can further include the indication information of the determined secondary component carrier. 
     For example, the source eNB  10  determines one or more predetermined secondary component carriers, e.g., the CC 3 , for the user equipment  30  according to the measurement information obtained by the source eNB  10  from the user equipment  30 , and notifies the destination eNB  20  of indication information that the CC 3  is determined as a secondary component carrier. The destination eNB  20  can directly accept the predetermined secondary component carrier determined by the source eNB  10  as the secondary component carrier of the user equipment  30  or determines one or more of the plurality of predetermined secondary component carriers determined by the source eNB  10  as the secondary component carrier or carriers of the user equipment  30  according to a traffic load condition of the destination eNB  20  and optionally further according to the measurement information reported by the user equipment  30 . Next the destination eNB  20  transmits a handover command including indication information of the secondary component carrier or carriers to the source eNB  10 , and the source eNB  10  forwards the handover command to the user equipment  30 . The user equipment  30  accesses the destination eNB  20  according to the indication information of the primary component carrier and the secondary component carrier or carriers included in the handover command and assignment information of a dedicated preamble over the component carriers. 
     In a further embodiment of the invention, the destination eNB  20  can be a dominator device for determining a secondary component carrier. In this embodiment, the step of determining one or more secondary component carriers for the user equipment  30  is performed at the side of the destination eNB  20 . Then in the step S 21 , the handover command transmitted by the destination eNB  20  can further include indication information of the determined secondary component carrier or carriers. 
     For example, the source eNB  10  forwards all of measurement information from the user equipment  30  to the destination eNB  20 , and the destination eNB  20  receives the measurement information from the user equipment  30  and then determines a secondary component carrier or carriers, e.g., the CC 1  and the CC 3 , for the user equipment  30  according to the information and traffic load information of the destination eNB  20 . And in the step S 22 , the destination eNB  20  notifies the user equipment  30  of indication information of the determined secondary component carrier or carriers in a handover command. 
     Those skilled in the art shall appreciate that after a reasonable variation, the method in the foregoing embodiments of the invention can also be applicable for a scenario where a secondary component carrier shall be determined during a handover of a service of a user equipment between two eNBs. By synthetically considering measurement information from the user equipment  30  and traffic load information of the destination eNB  20 , the secondary component carrier or carriers are determined and forwarded to the user equipment for which a serving eNB is to be switched. The foregoing variation to the invention also falls into the scope of the invention. Different application objects are not limiting the scope of the invention. 
       FIG. 5  illustrates a structural diagram of a first handover apparatus  100 , in a source eNB, for handing over a service of a user equipment to a destination eNB according to an embodiment of the invention. As illustrated, the first handover apparatus  100  comprises a first determining device  101 , a first receiving device  102  and a command forwarding device  103 . 
     The first determining device  101  is configured to perform the step S 11  in the foregoing method to determine a primary component carrier jointly with the destination eNB  20 . 
     The first receiving device  102  is configured to perform the step S 12  in the foregoing method to receive a handover command transmitted from the destination eNB  20  to the user equipment  30 , the handover command including indication information of the primary component carrier. Optionally the handover command further includes dedicated preamble assignment information. Optionally the handover command further includes security key information corresponding to the primary component carrier and/or relevant information of a secondary component carrier. 
     The command forwarding device  103  is configured to perform the step S 13  in the foregoing method to forward the handover command to the user equipment  30 . 
       FIG. 6  illustrates a structural diagram of a second handover apparatus  200 , in a destination eNB, for handing over a service of a user equipment from a source eNB to the destination eNB  20  according to an embodiment of the invention. As illustrated, the second handover apparatus  200  comprises a second determining device  201  and a command transmitting device  202 . 
     The second determining device  201  is configured to perform the step S 21  in the foregoing method to determine a primary component carrier jointly with the source eNB  10 . 
     The command transmitting device  202  is configured to perform the step S 22  in the foregoing method to transmit a handover command to be transmitted to the user equipment  30  to the source eNB  10 , the handover command including indication information of the primary component carrier. Optionally the handover command further includes dedicated preamble assignment information. Optionally the handover command further includes security key information corresponding to the primary component carrier and/or relevant information of a secondary component carrier. 
     Optionally the second determining device  201  comprises the following modules (not illustrated in the figure): 
     A receiving module configured to receive measurement information from the user equipment. 
     A first determining module configured to determine a predetermined primary component carrier according to the measurement information. 
     A notifying module configured to notify the destination eNB of indication information of the predetermined primary component carrier. 
     According to another embodiment of the invention, the second determining device  201  comprises the following modules (not illustrated in the figure): 
     A first receiving module configured to receive measurement information about a component carrier of the destination eNB  20  from the user equipment  30 . 
     A forwarding module configured to forward the measurement information to the destination eNB  20 . 
       FIG. 7  illustrates a structural diagram of a third handover apparatus  300 , in a user equipment in a wireless communication network with carrier aggregation, for handing over a service of the user equipment from a source eNB to a destination eNB according to an embodiment of the invention. As illustrated, the third handover apparatus  300  comprises a second receiving device  301  and an accessing device  302 . 
     The second receiving device  301  is configured to perform the step S 31  in the foregoing method to receive a handover command from the side of the source eNB, the handover command including indication information of a determined primary component carrier. Optionally the handover command further includes dedicated preamble assignment information. 
     The accessing device  302  is configured to perform the step S 32  in the foregoing method to access the destination eNB  20 . 
     Optionally the second receiving device  301  further includes the following modules (not illustrated in the figure): 
     A second receiving module configured to receive indication information of a predetermined primary component carrier from the source eNB. 
     A second determining module configured to determine whether to determine the predetermined primary component carrier as the primary component carrier according to a traffic load. 
     According to another embodiment of the invention, the second receiving device  301  further includes the following modules (not illustrated in the figure): 
     A third receiving module configured to receive measurement information of the user equipment from the source eNB. 
     A third determining module configured to determine the primary component carrier according to the measurement information and a traffic load of the destination eNB. 
     It shall be noted that the foregoing embodiments are merely illustrative but not to limit the invention. Any technical solutions without departing from the spirit of the invention shall fall into the scope of invention, including the use of different technical solutions appearing in different embodiments as arranged in any arrangement combination to advantage. Moreover any reference numerals in the claims shall not be construed as limiting the claims in question; the term “comprising” will not preclude another device(s) or step(s) which is (are) listed in the other claim(s) or the description; “a” or “an” preceding a device will not preclude the presence of a plurality of such a device; a function or functions of one or more of a plurality of devices included in an apparatus can be performed by the same device in hardware or software; and the terms “first”, “second”, “third”, etc., are merely intended to designate a name but not to suggest any specific order.