5. A transmitting User Equipment (TX UE) operating in a wireless communication system, the TX UE comprising:a Radio Frequency (RF) module; and
a processor configured to control the RF module,
wherein the processor is configured to:
receive, from an eNB, a sidelink grant for the TX UE to communicate with a receiving UE (RX UE) directly,
check a size of the received sidelink grant, and
when the size of the received sidelink grant is larger than a minimum size of MAC PDU that includes 6 bytes of a sidelink-shared channel (SL-SCH) MAC subheader, 2 bytes of a MAC subheader, and 1 byte of a RLC subheader:
generate a Medium Access Control Protocol Data Unit (MAC PDU) other than a MAC PDU that includes only padding bits, and
transmit the generated MAC PDU to the RX UE.