Data transmission method and user equipment for the same

A user equipment, comprising:

• a reception module adapted to receive an uplink grant (UL Grant) signal from a base station through a Physical Downlink Control Channel (PDCCH) identified by a Cell-Radio Network Temporary Identifier (C-RNTI);
• a transmission module adapted to transmit data to the base station,
• a message 3 (Msg3) buffer adapted to store UL data to be transmitted in a random access procedure;
• and
• a MAC (Medium Access Control) layer module adapted to start a contention resolution (CR) timer when the transmission module transmits the Msg3 of the random access procedure to the base station,
• wherein the Msg3 comprises a Medium Access Control Protocol Data Unit (MAC PDU) in a Hybrid Automatic Repeat Request (HARQ) buffer, and
• wherein the MAC PDU in the HARQ buffer is a copy of a MAC PDU in the Msg3 buffer,
• wherein the MAC layer module further adapted to flush the HARQ buffer used for transmission of the MAC PDU in the Msg3 buffer if the CR timer is expired, and
• wherein the MAC layer module further adapted to
• determine whether the UL Grant signal is received through the PDCCH identified by the C-RNTI and whether the HARQ buffer is empty, and
• control the transmission module to transmit new data to the base station if the UL Grant signal is received through the PDCCH identified by the C-RNTI and the HARQ buffer is empty.