Random access scheme for preventing unnecessary retransmission and user equipment for the same

1. A method for performing random access to a base station by a terminal, the method comprising:

transmitting a random access preamble to the base station;

receiving, from the base station in response to the random access preamble, a random access response message including uplink grant information; and

storing a Medium Access Control Packet Data Unit (MAC PDU) including uplink data and an identifier of the terminal in a message 3 (Msg3) buffer in response to the uplink grant information;

copying the MAC PDU stored in the Msg3 buffer to a first Hybrid Automatic Repeat Request (HARQ) buffer associated with a first HARQ process, wherein the terminal comprises multiple HARQ buffers including the first HARQ buffer;

transmitting the MAC PDU stored in the first HARQ buffer to the base station using the first HARQ process;

starting or restarting a Contention Resolution (CR) timer;

receiving, from the base station, a Physical Downlink Control Channel (PDCCH) signal;

stopping a Timing Alignment Timer (TAT), if the received PDCCH signal or a Physical Downlink Shared Channel (PDSCH) signal associated with the received PDCCH signal does not match the identifier of the terminal or if the CR timer expires; and

flushing the multiple HARQ buffers including the first HARQ buffer, when the TAT expires.

2. The method of claim 1 , wherein the terminal considers a contention resolution as not successful, if the received PDCCH signal or a physical downlink shared channel (PDSCH) signal associated with the received PDCCH signal does not match the identifier of the terminal or if the CR timer expires.

3. The method of claim 2 , wherein the identifier of the terminal is one of a Cell-Radio Network Temporary Identifier (C-RNTI) of the terminal or a UE contention resolution identity of the terminal.

4. The method of claim 3 , wherein the terminal considers the contention resolution as not successful, when the terminal has transmitted the MAC PDU including the C-RNTI of the terminal and the received PDCCH signal is not addressed to the C-RNTI of the terminal.

5. The method of claim 3 , wherein the terminal considers the contention resolution as not successful, when the terminal has transmitted the MAC PDU including the UE contention resolution identity of the terminal and the PDSCH signal associated with the received PDCCH signal does not match the UE contention resolution identity of the terminal.

6. The method of claim 2 , further comprising:

retransmitting the selected random access preamble to the base station according to the failure of the contention resolution;

receiving a random access response message including a Timing Alignment Command (TAC) from the base station;

starting or restarting a Timing Alignment Timer (TAT) according to the reception of the TAC;

copying the MAC PDU stored in the Msg3 buffer to a second HARQ buffer associated with a second HARQ process; and

transmitting the MAC PDU stored in the second HARQ buffer to the base station using the second HARQ process,

wherein the terminal does not transmit the MAC PDU stored in the first HARQ buffer even when the TAT is started or restarted.

7. The method of claim 1 , wherein the first HARQ buffer is flushed, if the received PDCCH signal or the PDSCH signal associated with the received PDCCH signal does not match the identifier of the terminal or if the CR timer expires.

8. A terminal comprising:

a physical layer module including:

a transmission module configured to transmit a random access preamble to a base station, and

a reception module configured to receive a random access response message including uplink grant information from the base station; and

a Medium Access control (MAC) layer module including:

a multiplexing and assembly entity configured to configure a Medium Access Control Packet Data Unit (MAC PDU) including uplink data and an identifier of the terminal according to the uplink grant information received by the reception module,

a message 3 (Msg3) buffer configured to store the MAC PDU configured by the multiplexing and assembly entity according to the reception of the random access response message,

a plurality of Hybrid Automatic Repeat Request (HARQ) process modules and a plurality of HARQ buffers associated with the plurality of HARQ process modules, and

a HARQ entity configured to control operations of the plurality of HARQ process modules,

wherein the MAC layer module copies the MAC PDU stored in the Msg3 buffer to a first HARQ buffer associated with a first HARQ process according to the reception of the random access response message by the reception module, controls the MAC PDU stored in the first HARQ buffer to be transmitted to the base station using the first HARQ process, and starts or restarts a Contention Resolution (CR) timer when transmitting the MAC PDU stored in the first HARQ buffer, and

wherein, if reception of a Physical Downlink Control Channel (PDCCH) signal from the base station is reported from the physical layer module, is the MAC layer module determines whether the PDCCH or a Physical Downlink Shared Channel (PDSCH) signal associated with the PDCCH signal matches the identifier of the terminal or whether the CR timer expires, and stops a Timing Alignment Timer (TAT), if the PDCCH signal or the PDSCH signal associated with the PDCCH signal does not match the identifier of the terminal or if the CR timer expires, wherein the MAC layer module flushes the plurality of HARQ buffers when the TAT expires.

9. The terminal of claim 8 , wherein the MAC layer module considers a contention resolution as not successful, if the received PDCCH signal or the PDSCH signal associated with the received PDCCH signal does not match the identifier of the terminal or if the CR timer expires.

10. The terminal of claim 8 , wherein the identifier of the terminal is one of a Cell-Radio Network Temporary Identifier (C-RNTI) of the terminal or a UE contention resolution identity of the terminal.

11. The terminal of claim 10 , wherein the MAC layer module considers the contention resolution as not successful, when the terminal has transmitted the MAC PDU including the C-RNTI of the terminal and the received PDCCH signal is not addressed to the C-RNTI of the terminal.

12. The terminal of claim 10 , wherein the MAC layer module considers the contention resolution as not successful, when the terminal has transmitted the MAC PDU including the UE contention resolution identity of the terminal and the PDSCH associated with the received PDCCH signal does not match the UE contention resolution identity of the terminal.

13. The terminal of claim 8 , wherein the MAC layer module flushes the first HARQ buffer, if the received PDCCH signal or the PDSCH signal associated with the received PDCCH signal does not match the identifier of the terminal or if the CR timer expires.