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

1. A method for transmitting downlink data in a wireless access system, the method performed by an evolved Node B (eNB) and comprising:

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

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

transmitting, via the PDSCH, downlink data based on the DCI;

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

wherein the downlink data is encoded based on the first MCS index table even though the second MCS index table has been enabled, when a format of the DCI is a DCI format 1A and the DCI format 1A has been scrambled with a semi persistent scheduling radio network temporary identifier (SPS-RNTI).

2. The method according to claim 1 , wherein the DCI format 1A includes an index field representing a modulation and coding scheme (MCS) for the PDSCH.

3. The method according to claim 2 ,

wherein the downlink data is encoded by the eNB using the MCS represented by the index field, and

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

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

5. An evolved Node B (eNB), comprising:

a transmitter; and

a processor;

wherein the processor is configured to encode downlink data using one of two modulation and coding scheme (MCS) tables, and

the processor is configured to control the transmitter to:

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

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

transmit, via the PDSCH, the downlink data based on the DCI;

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

6. The eNB according to claim 5 , wherein the DCI format 1A includes an index field representing a modulation and coding scheme for the PDSCH.

7. The eNB according to claim 6 ,

wherein the downlink data is encoded by the eNB using the MCS represented by the index field, and

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

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

9. A method for receiving downlink 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); and

receiving, via the PDSCH, downlink data based on the DCI;

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 256QAM, and

wherein the downlink data is decoded based on the first MCS index table even though the second MCS index table has been enabled, when a format of the DCI is a DCI format 1A and the DCI format 1A has been scrambled with a semi persistent scheduling radio network temporary identifier (SPS-RNTI).

10. The method according to claim 9 , wherein the DCI format 1A includes an index field representing a modulation and coding scheme for the PDSCH.

11. The method according to claim 10 , wherein the downlink data is encoded by the eNB using the MCS represented by the index field, and

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

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

13. A user equipment (UE), comprising:

a receiver; and

a processor;

wherein the processor is configured to decode downlink data using one of two modulation and coding scheme (MCS) tables, and

the processor is configured to control the transmitter 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, the downlink data based on the DCI;

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

14. The UE according to claim 13 , wherein the DCI format 1A includes an index field representing a modulation and coding scheme for the PDSCH.

15. The UE according to claim 14 , wherein the downlink data is encoded by the eNB using the MCS represented by the index field, and a modulation order and a transport block size (TBS) index is determined depending upon an MCS index in the first MCS index table.

16. The UE according to claim 13 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.