Method and apparatus for removing a serving cell in a wireless communication system

Abstract

A method and apparatus are disclosed for removing a serving cell in a wireless communication system. The method includes a UE is served by a first cell controlled by a first eNB. The method also includes the UE is configured with a second cell controlled by a second eNB. The method further includes the UE is configured with a radio bearer, wherein there is a PDCP entity corresponding to the RB and there are two RLC entities corresponding to the RB, one RLC entity for data transfer via the first cell and the other RLC entity for data transfer via the second cell. In addition, the method includes the UE delivers out-of-sequence RLC SDUs reassembled by the RLC entity corresponding to the first cell to the PDCP entity in response to reception of an instruction to remove the second cell. In one embodiment, the method also includes the UE transmits a PDCP status report to the first eNB to indicate which PDCP packets of the RB need to be retransmitted if the PDCP status report is configured as required to the RB.

What is claimed is: 
     
         1 . A method for removing a serving cell in a wireless communication system, comprising:
 a UE (User Equipment) is served by a first cell controlled by a first eNB (evolved Node B);   the UE is configured with a second cell controlled by a second eNB;   the UE is configured with a radio bearer (RB), wherein there is a PDCP (Packet Data Convergence Protocol) entity corresponding to the RB and there are two RLC (Radio Link Control) entities corresponding to the RB, one RLC entity for data transfer via the first cell and the other RLC entity for data transfer via the second cell; and   the UE delivers out-of-sequence RLC SDUs (Service Data Units) reassembled by the RLC entity corresponding to the first cell to the PDCP entity in response to reception of an instruction to remove the second cell.   
     
     
         2 . The method of  claim 1 , further comprising:
 the UE transmits a PDCP status report to the first eNB to indicate which PDCP packets of the RB need to be retransmitted if the PDCP status report is configured as required to the RB.   
     
     
         3 . The method of  claim 1 , further comprising:
 the UE re-establishes the RLC entity corresponding to the RB for the first cell.   
     
     
         4 . The method of  claim 1 , wherein there are two separate MAC (Medium Access Control) entities in the UE to support the first eNB and the second eNB. 
     
     
         5 . The method of  claim 1 , wherein the RB is used for U-plane data transmission. 
     
     
         6 . The method of  claim 1 , wherein the RLC entity is configured with an Acknowledged Mode (AM). 
     
     
         7 . The method of  claim 2 , wherein the PDCP packets are PDCP SDUs or PDCP PDUs. 
     
     
         8 . A method for removing a serving cell in a wireless communication system, comprising:
 a UE (User Equipment) is served by a first cell controlled by a first eNB (evolved Node B);   the UE is configured with a second cell controlled by a second eNB;   the UE is configured with a radio bearer (RB), wherein there is a PDCP (Packet Data Convergence Protocol) entity corresponding to the RB and there are two RLC (Radio Link Control) entities corresponding to the RB, one RLC entity for data transfer via the first cell and the other RLC entity for data transfer via the second cell; and   the UE transmits a PDCP status report to the first eNB, in response to reception of an instruction to remove the second cell, to indicate which PDCP packets of the RB need to be retransmitted if the PDCP status report is configured as required to the RB.   
     
     
         9 . The method of  claim 8 , further comprising:
 the UE delivers out-of-sequence RLC SDUs (Service Data Units) reassembled by the RLC entity corresponding to the first cell to the PDCP entity.   
     
     
         10 . The method of  claim 8 , further comprising:
 the UE re-establishes the RLC entity corresponding to the RB for the first cell.   
     
     
         11 . The method of  claim 8 , wherein there are two separate MAC (Medium Access Control) entities in the UE to support the first eNB and the second eNB. 
     
     
         12 . The method of  claim 8 , wherein the RB is used for U-plane data transmission. 
     
     
         13 . The method of  claim 8 , wherein the RLC entity is configured with an Acknowledged Mode (AM). 
     
     
         14 . The method of  claim 8 , wherein the PDCP packets are PDCP SDUs or PDCP PDUs. 
     
     
         15 . A method for removing a serving cell in a wireless communication system, wherein a UE (User Equipment) is served by a first cell controlled by a first eNB (evolved Node B), comprising:
 the first eNB configures a second cell controlled by a second eNB to the UE;   the first eNB configures a radio bearer (RB) to the UE, wherein there is a PDCP (Packet Data Convergence Protocol) entity corresponding to the RB in the first eNB and there are two RLC entities corresponding to the RB, one in the first eNB and the other in the second cell eNB;   the first eNB transmits a RRC (Radio Resource Control) message to the UE to remove the second cell; and   the first eNB receives a PDCP status report from the UE, wherein the PDCP status report is transmitted by the UE in response to a removal of the second cell to indicate which PDCP packets of the RB need to be retransmitted.   
     
     
         16 . The method of  claim 15 , further comprising:
 the first eNB retransmits the PDCP packets indicated in the PDCP status report.   
     
     
         17 . The method of  claim 15 , wherein the RB is used for U-plane data transmission. 
     
     
         18 . The method of  claim 15 , wherein the RLC entity is configured with an Acknowledged Mode (AM). 
     
     
         19 . The method of  claim 15 , wherein the PDCP packets are PDCP SDUs or PDCP PDUs. 
     
     
         20 . The method of  claim 15 , wherein the RRC message is a RRC Connection Reconfiguration message.