Base station apparatus and method thereof

Abstract

A secondary base station (2) receives an SeNB addition request message (302) from a second master base station (3) while providing a radio terminal (4) with a secondary cell group (SCG) for DC in cooperation with a first master base station (1). If the SeNB addition request message (302) explicitly or implicitly indicates that a master base station in DC for the radio terminal (4) is to be changed from the first master base station (1) to the second master base station (3), the secondary base station (2) considers that the SeNB addition request message (302) requests modification of the SCG that has already been configured. It is thus, for example, possible to contribute to performing a procedure for changing a master base station in Dual Connectivity (DC) by using existing inter-base station interface procedures and inter-base station signaling messages.

1 - 17 . (canceled) 
     
     
         18 . A Secondary Radio Access Network (RAN) node comprising:
 at least one memory storing instructions; and   at least one processor configured to process the instructions to:
 operate a Secondary Cell Group (SCG); 
 communicate with a radio terminal configured to perform dual connectivity using the SCG and a Master Cell Group (MCG) operated by a first Master RAN node; 
 receive from a second Master RAN node, during a handover procedure from the first Master RAN node to the second Master RAN node, a Secondary RAN Node Addition Request message including a Secondary RAN node UE X2AP ID; and 
 reject a Secondary RAN Node Addition Request procedure corresponding to the Secondary RAN Node Addition Request message by using a Secondary RAN Node Addition Reject message, in a case where the Secondary RAN node UE X2AP ID included in the Secondary RAN Node Addition Request message does not match any identity that is used to identify the radio terminal in the Secondary RAN node. 
   
     
     
         19 . The Secondary RAN node according to  claim 18 , wherein
 the Secondary RAN node UE X2AP ID is an identifier that is used to uniquely identify the radio terminal on the interface between the first Master RAN node and the Secondary RAN Node.   
     
     
         20 . The Secondary RAN node according to  claim 19 , wherein the Secondary RAN node UE X2AP ID implicitly indicates a change of a master RAN node in the dual connectivity for the radio terminal. 
     
     
         21 . The Secondary RAN node according to  claim 18 , wherein the at least one processor is configured to, in response to receiving a Secondary RAN Node Release Request message from the first Master RAN node in a case where the Secondary RAN node UE X2AP ID included in the Secondary RAN node Addition Request message matches the identity that is used to identify the radio terminal in the Secondary RAN node, replace an SCG configuration for the dual connectivity in cooperation with the first Master RAN node with a modified SCG configuration for dual connectivity in cooperation with the second Master RAN node. 
     
     
         22 . A method in a Secondary Radio Access Network (RAN) node, the method comprising:
 receiving a Secondary RAN node Addition Request message from a second Master RAN node, during a handover procedure from the first Master RAN node to the second Master RAN node, the Secondary RAN node Addition Request message including a Secondary RAN node UE X2AP ID; and   transmitting a Secondary RAN Node Addition Reject message to reject a Secondary RAN Node Addition Request procedure corresponding to the Secondary RAN Node Addition Request message, in a case where the Secondary RAN node UE X2AP ID included in the Secondary RAN node Addition Request message does not match any identity that is used to identify the radio terminal in the Secondary RAN node.   
     
     
         23 . The method according to  claim 22 , wherein the Secondary RAN node UE X2AP ID is an identifier that is used to uniquely identify the radio terminal on the interface between the first Master RAN node and the Secondary RAN Node. 
     
     
         24 . The method according to  claim 23 , wherein the Secondary RAN node UE X2AP ID implicitly indicates a change of a master RAN node in the dual connectivity for the radio terminal. 
     
     
         25 . The method according to  claim 22 , further comprising replacing an SCG configuration for the dual connectivity in cooperation with the first Master RAN node with a modified SCG configuration for dual connectivity in cooperation with the second Master RAN node, in response to receiving a Secondary RAN node Release Request message from the first Master RAN node in a case where the Secondary RAN node UE X2AP ID included in the Secondary RAN node Addition Request message matches the identity that is used to identify the radio terminal in the Secondary RAN node. 
     
     
         26 . A radio terminal comprising:
 at least one radio transceiver to communicate with a first Master Radio Access Network (RAN) node, a second Master RAN node, and a Secondary RAN Node; and   at least one processor configured to communicate with the first Master RAN node and the second Master RAN node and to change a master RAN node in the dual connectivity from the first Master RAN node to the second Master RAN node while keeping a connection to a Secondary Cell Group (SCG) in the secondary RAN node, wherein   the Secondary RAN Node is configured to:
 receive from the second Master RAN node, during a handover procedure from the first Master RAN node to the second Master RAN node, a Secondary RAN node Addition Request message including a Secondary RAN node UE X2AP ID; and 
 reject the Secondary RAN node Addition Request message by using a Secondary RAN Node Addition Reject message, in a case where the Secondary RAN node UE X2AP ID included in the Secondary RAN node Addition Request message does not match any identity that is used to identify the radio terminal in the Secondary RAN node. 
   
     
     
         27 . The radio terminal according to  claim 26 , wherein the Secondary RAN node UE X2AP ID is an identifier that is used to uniquely identify the radio terminal on the interface between the first Master RAN node and the Secondary RAN Node. 
     
     
         28 . The radio terminal according to  claim 27 , wherein the Secondary RAN node UE X2AP ID implicitly indicates a change of a master RAN node in the dual connectivity for the radio terminal. 
     
     
         29 . The radio terminal according to  claim 26 , wherein the Secondary RAN Node is configured to, in response to receiving a Secondary RAN node Release Request message from the first Master RAN node in a case where the Secondary RAN node UE X2AP ID included in the Secondary RAN node Addition Request message matches the identity that is used to identify the radio terminal in the Secondary RAN node, replace an SCG configuration for the dual connectivity in cooperation with the first Master RAN node with a modified SCG configuration for dual connectivity in cooperation with the second Master RAN node.