Method for transmitting a buffer status reporting for LTE-WLAN aggregation system and a device therefor

A User Equipment (UE) operating in a wireless communication system, the UE comprising:

• a transceiver;
• and
• a processor configured to:
• control the transceiver,
• trigger a Power Headroom Reporting (PHR) if a PHR triggering condition is met,
• obtain information for power status for data transmission over a Long Term Evolution (LTE) network,
• generate a PHR Medium Access Control (MAC) Control Element (CE) including the information for power status for the LTE network,
• wherein the PHR MAC CE includes a plurality of octets,
• wherein a starting octet of the plurality of octets includes a 7-bit Ci field and a specific 1-bit field,
• wherein the Ci field corresponding to a cell index i is for the LTE network,
• wherein the specific 1-bit field is a least significant bit of the starting octet, which is an indication field indicating information for power status for data transmission over a Wireless Local Area Network (WLAN) network is included or not,
• wherein in a case that a value of the indication field is set to a first value, the PHR MAC CE includes the information for the power status for the WLAN network at a last octet of the PHR MAC CE, and
• wherein in a case that the value of the indication field is set to a second value, the PHR MAC CE does not includes the information for the power status for the WLAN network.