Method for transmitting data in dual connectivity and a device therefor

1. A method for a user equipment (UE) communicating with a first base station (BS) and a second BS simultaneously in a wireless communication system, the method comprising:

configuring, based on a radio resource control (RRC) signal from the first BS or the second BS, that uplink (UL) data is to be transmitted to the first BS for when an amount of data available for transmission in a packet data convergence protocol (PDCP) entity is less than a threshold;

receiving a first PDCP data from an upper layer;

transmitting a buffer status report (BSR) for the first PDCP data to request an UL grant to the second BS;

receiving a second PDCP data from the upper layer;

receiving the UL grant from the second BS in response to the BSR; and

transmitting both of the first PDCP data and the second PDCP data on the UL grant to the second BS even when an amount of the data available for transmission in the PDCP entity at the time of a transmission of the first PDCP data and the second PDCP data is less than the threshold.

2. The method according to claim 1 ,

wherein remaining resources of the UL grant received from the second BS are filled with padding.

3. The method according to claim 1 , further comprising:

configuring the threshold for the PDCP entity.

4. The method according to claim 1 ,

wherein the first BS is a secondary BS and the second BS is a master BS, or the first BS is the master BS and the second BS is the secondary BS.

5. The method according to claim 1 ,

wherein a radio bearer for the first PDCP data comprises one PDCP entity, and two radio link control (RLC) entities, and two medium access control (MAC) entities.

6. A method for a user equipment (UE) communicating with a first Base Station (BS) and a second BS simultaneously in a wireless communication system, the method comprising:

receiving, by a packet data convergence protocol (PDCP) entity, a radio resource control (RRC) signaling indicating that uplink (UL) data is only to be submitted to a first radio link control (RLC) entity if an amount of data available for transmission in the PDCP entity is less than a threshold, wherein the PDCP entity is associated with the first RLC entity and a first medium access control (MAC) entity for the first BS and associated with a second RLC entity and a second MAC entity for the second BS for a radio bearer;

receiving, by the PDCP entity, a first PDCP data from an upper layer and a second PDCP data from the upper layer; and

submitting, by the PDCP entity, the first PDCP data and the second PDCP data to the second RLC entity when an amount of the first PDCP data has been indicated to the second MAC entity without an amount of the second PDCP data, wherein an amount of the data available for transmission in the PDCP entity at a time of the submission of the first PDCP data and the second PDCP data is less than the threshold.

7. The method according to claim 6 , further comprising:

configuring the threshold for the PDCP entity.

8. The method according to claim 6 ,

wherein the first BS is a secondary BS and the second BS is a master BS, or the first BS is the master BS and the second BS is the secondary BS.

9. A User Equipment (UE) for communicating with a first base station (BS) and a second BS simultaneously in a wireless communication system, the UE comprising:

a Radio Frequency (RF) module; and

a processor operably coupled with the RF module and configured to:

configure, based on a radio resource control (RRC) signal from the first BS or the second BS, that uplink (UL) data is to be transmitted to the first, if BS for when an amount of data available for transmission in a packet data convergence protocol (PDCP) entity is less than a threshold;

receive a first PDCP data from an upper layer;

transmit a buffer status report (BSR) for the first PDCP data to request an UL grant to the second BS;

receive a second PDCP data from the upper layer;

receive the UL grant from the second BS in response to the BSR; and

transmit both of the first PDCP data and the second PDCP data on the UL grant to the second BS even when an amount of the data available for transmission in the PDCP entity at a time of the transmission of the first PDCP data and the second PDCP data is less than the threshold.

10. The UE according to claim 9 ,

wherein remaining resources of the UL grant received from the second BS are filled with padding.

11. The UE according to claim 9 , wherein the processor is further configured to:

configure the threshold for the PDCP entity.

12. The UE according to claim 9 ,

wherein the first BS is a secondary BS and the second BS is a master BS, or the first BS is the master BS and the second BS is the secondary BS.

13. The UE according to claim 9 ,

wherein a radio bearer for the PDCP data comprises one PDCP entity, and two radio link control (RLC) entities, and two medium access control (MAC) entities.

14. A User Equipment (UE) for communicating with a first base station (BS) and a second BS simultaneously in a wireless communication system, the UE comprising:

a Radio Frequency (RF) module; and

a processor operably coupled with the RF module and configured to:

receive, by a packet data convergence protocol (PDCP) entity, a radio resource control (RRC) signaling indicating that uplink (UL) data is only to be transmitted to the first BS, if an amount of data available for transmission in the PDCP entity is less than a threshold, wherein the PDCP entity is associated with a first radio link control (RLC) entity and a first medium access control (MAC) entity for the first BS and associated with a second RLC entity and a second MAC entity for the second BS for a radio bearer;

receive, by the PDCP entity, a first PDCP data from an upper layer and a second PDCP data from the upper layer; and

submit, by the PDCP entity, the first PDCP data and the second PDCP data to the second RLC entity when an amount of the first PDCP data has been indicated to the second MAC entity without an amount of the second PDCP data, wherein the amount of the data available for transmission in the PDCP entity at a time of the submission of the PDCP data is less than the threshold.

15. The UE according to claim 14 , wherein the processor is further configured to:

configure the threshold for the PDCP entity.

16. The UE according to claim 14 ,

wherein the first BS is a secondary BS and the second BS is a master BS, or the first BS is the master BS and the second BS is the secondary BS.