Method and apparatus for random access in a wireless communication system that supports multiple carriers
The present invention relates to a wireless communication system. According to one embodiment of the present invention, a method in which a terminal performs a random access procedure comprises the following steps: transmitting a random access preamble to a base station; and receiving, from said base station and as a response to said random access preamble, a random access response message indicated by a physical downlink control channel (PDCCH) for a cell identifier of said terminal.
1. A method for a user equipment (UE) to perform a random access procedure, the method comprising:
transmitting a random access preamble for a secondary serving cell (SCell) to a base station (BS);
receiving, from the BS, a physical downlink control channel (PDCCH) including an indicator indicating that the PDCCH is for a random access response (RAR) in response to the random access preamble;
determining that the PDCCH indicates that a physical downlink shared channel (PDSCH) includes a RAR; and
receiving, the PDSCH from the BS, and decoding the PDSCH,
wherein the UE determines that the PDSCH includes the RAR before receiving and decoding the PDSCH, and
wherein the PDSCH contains downlink data.
2. The method of claim 1 , wherein the RAR includes a timing advance command (TAC) and a timing advance group (TAG) identifier, but does not include a temporary cell-radio network temporary identifier (TC-RNTI),
wherein the TAG identifier indicates a TAG to which the TAC is applied.
3. The method of claim 1 , wherein the UE determines that the PDSCH includes the RAR, even if the PDSCH is not correctly decoded.
4. The method of claim 1 , further comprising:
transmitting a negative acknowledgement (NACK) for the RAR to the BS if the PDSCH is not correctly decoded.
5. The method of claim 1 , wherein a window for a reception of the RAR is configured by the base station.
6. The method of claim 5 , wherein a size of the window is configured user equipment-specific.
7. The method of claim 1 , wherein the RAR is transmitted by the BS by using hybrid automatic repeat and request (HARQ) scheme and wherein a maximum HARQ retransmission count of the RAR is set up by the BS.
8. The method of claim 1 , wherein a plurality of serving cells are configured for the user equipment and wherein the RAR is received on the SCell.
9. The method of claim 8 , wherein the PDCCH is monitored in a user equipment-specific search space (USS) on the SCell.
10. The method of claim 8 , wherein the random access preamble is transmitted on the SCell.
11. The method of claim 8 , wherein the SCell belongs to a TAG configured with SCells only.
12. A user equipment (UE) for performing a random access procedure, the UE comprising:
a receiving module that receives a downlink signal from a base station (BS);
a transmitting module that transmits an uplink signal to the BS; and
a processor that:
controls the transmitting module to transmit a random access preamble for a secondary serving cell (SCell) to the BS;
controls the receiving module to receive, from the BS, a physical downlink control channel (PDCCH) including an indicator indicating that the PDCCH is for a random access response (RAR) in response to the random access preamble;
determines that the PDCCH indicates that a physical downlink shared channel (PDSCH) includes a RAR;
receive, from the BS, and decode the PSDSCH,
wherein the processor determines that the PDSCH includes the RAR before receiving and decoding the PDSCH; and
wherein the PDSCH carries downlink data.