Method and apparatus for transmitting and receiving MCS index for 256QAM in wireless access system

1. A method for decoding data in a wireless access system, the method performed by a user equipment (UE) and comprising:

receiving a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled;

receiving, via a physical downlink control channel (PDCCH), downlink control information (DCI) for scheduling a physical downlink shared channel (PDSCH);

receiving, via the PDSCH, data; and

decoding the received data using one of two modulation and coding scheme (MCS) index tables,

wherein the UE has a first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to the 256QAM, and

wherein the received data is decoded based on the first MCS index table even though the second MCS index table has been enabled to the UE, when a format of the DCI is a DCI format 1A.

2. The method according to claim 1 , further comprising:

determining a modulation order and a transport block size (TBS) index depending upon an MCS index in the first MCS index table.

3. The method according to claim 1 , wherein the DCI format 1A includes an index field representing a MCS for the PDSCH.

4. The method according to claim 3 , wherein the UE decodes the PDSCH using a modulation scheme indicated by the index field at the first MCS index table.

5. The method according to claim 1 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.

6. A method for decoding data in a wireless access system, the method performed by a user equipment (UE) and comprising:

receiving a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled;

receiving, via a physical downlink control channel (PDCCH), downlink control information (DCI) including an index field representing a modulation and coding scheme (MCS);

receiving data via a physical downlink shared channel (PDSCH) scheduled by the PDCCH; and

decoding the received data using the MCS represented by the index field,

wherein the UE has a first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to the 256QAM, and

wherein the received data is decoded based on only the first MCS index table even though the second MCS index table has been enabled to the UE, when the PDCCH has been scrambled with a paging-radio network temporary identifier (P-RNTI), a system information (SI)-RNTI, or a random access (RA)-RNTI.

7. The method according to claim 6 , further comprising:

determining a modulation order and a transport block size (TBS) index depending upon an MCS index in the first MCS index table.

8. The method according to claim 6 , wherein the UE decodes the received data using a modulation scheme indicated by the index field at the first MCS index table.

9. The method according to claim 6 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.

10. A user equipment (UE), comprising:

a receiver configured to:

receive a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled,

receive, via a physical downlink control channel (PDCCH), downlink control information (DCI) for scheduling a physical downlink shared channel (PDSCH), and

receive, via the PDSCH, data; and

a processor configured to decode the received data using one of two modulation and coding scheme (MCS) tables,

wherein the UE has a first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to the 256QAM, and

wherein the received data is decoded by the processor based on the first MCS index table even though the second MCS index table has been enabled to the UE, when a format of the DCI is a DCI format 1A.

11. The UE according to claim 10 , wherein the processor is further configured to determine a modulation order and a transport block size (TBS) index depending upon an MCS index in the first MCS index table.

12. The UE according to claim 10 , wherein the DCI format 1A includes an index field representing a MCS for the PDSCH.

13. The UE according to claim 12 , wherein the UE decodes the PDSCH using a modulation scheme indicated by the index field at the first MCS index table.

14. The UE according to claim 10 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.

15. A user equipment (UE), comprising:

a receiver configured to:

receive a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled,

receive, via a physical downlink control channel (PDCCH), downlink control information (DCI) including an index field representing a modulation and coding scheme (MCS), and

receive data via a physical downlink shared channel (PDSCH) scheduled by the PDCCH; and

a processor configured to decode the received data using the MCS represented by the index field,

wherein the UE has the first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to the 256QAM, and

wherein the received data is decoded by the processor based on only the first MCS index table even though the second MCS index table has been enabled to the UE, when the PDCCH has been scrambled with a paging-radio network temporary identifier (P-RNTI), a system information (SI)-RNTI, or a random access (RA)-RNTI.

16. The UE according to claim 15 , wherein the processor is further configured to determine a modulation order and a transport block size (TBS) index depending upon an MCS index in the first MCS index table.

17. The UE according to claim 15 , wherein the UE decodes the received data using a modulation scheme indicated by the index field at the first MCS index table.

18. The UE according to claim 15 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.