Method for calculating and reporting a buffer status and device therefor

1. A method for a user equipment (UE) operating in a wireless communication system, the method comprising:

calculating a first buffer status for a first base station (BS) and a second buffer status for a second BS respectively, by dividing an amount of data available for transmission in a Packet Data Convergence Protocol (PDCP) entity based on a PDCP data transmission ratio;

starting a timer for the first BS when the calculated first buffer status is reported to the first BS;

updating the PDCP data transmission ratio using an offset value, when the timer for the first BS expires without an uplink grant for the buffer status having been received from the first BS;

re-calculating the first buffer status for the first BS and the second buffer status for the second BS respectively, by dividing the amount of data available for transmission in the PDCP entity based on the updated PDCP data transmission ratio; and

transmitting the re-calculated first buffer status to the first BS and the re-calculated second buffer status to the second BS,

wherein the PDCP data transmission ratio and the offset value used for updating the PDCP data transmission ratio is configured in a radio bearer comprising the PDCP entity connected with the first BS and the second BS simultaneously.

2. The method according to claim 1 , wherein the PDCP data transmission ratio and the offset value are received from either the first BS or the second BS.

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

receiving a value of the timer for the first BS through Radio Resource Control (RRC) signaling from either the first BS or the second BS.

4. The method according to claim 1 , wherein if the offset value is ‘0%’, the first buffer status for the first BS is re-calculated as ‘0’.

5. The method according to claim 4 , wherein if the re-calculated first buffer status is ‘0’, the first buffer status is not reported to the first BS.

6. A user equipment (UE) operating in a wireless communication system, the UE comprising:

a transmitter;

a receiver; and

a processor operably coupled with the transmitter and the receiver and configured to:

calculate a first buffer status for a first base station (BS) and a second buffer status for the second BS respectively, by dividing an amount of data available for transmission in a Packet Data Convergence Protocol (PDCP) entity based on a PDCP data transmission ratio,

start a timer for the first BS when the calculated first buffer status is reported to the first BS,

update the PDCP data transmission ratio using an offset value, when the timer for the first BS expires without an uplink grant for the buffer status having been received from the first BS,

re-calculate the first buffer status for the first BS and the second buffer status for the second BS respectively, by dividing the amount of data available for transmission in the PDCP entity based on the updated PDCP data transmission ratio, and

transmit the re-calculated first buffer status to the first BS and the re-calculated second buffer status to the second BS,

wherein the PDCP data transmission ratio and the offset value used for updating the PDCP data transmission ratio is configured in a radio bearer comprising the PDCP entity connected with the first BS and the second BS simultaneously.

7. The UE according to claim 6 , wherein the PDCP data transmission ratio and the offset value are received from either the first BS or the second BS.

8. The UE according to claim 6 , wherein the processor is further configured to receive a value of the timer for the first BS through Radio Resource Control (RRC) signaling from either the first BS or the second BS.

9. The UE according to claim 6 , wherein if the offset value is ‘0%’, the first buffer status for the first BS is re-calculated as ‘0’.

10. The UE according to claim 9 , wherein if the re-calculated first buffer status is ‘0’, the first buffer status is not reported to the first BS.