The method includes mapping a first logical channel group (LCG) including one or more logical channels for transmitting first data to the first base station (BS) to the one medium access control entity (MAC) for the first BS and a second LCG including one or more logical channels for transmitting second data to the second BS to the one MAC entity for the second BS; triggering, by the one MAC entity for the first BS, a first buffer status report to the first BS independently of logical channels of the second LCG; and triggering, by the one MAC entity for the second BS, a second buffer status report to the second BS independently of logical channels of the first LCG.