User equipment and method for small data transmission

1. A method of a User Equipment (UE) for performing Small Data Transmission (SDT), the method comprising:

initiating a Random Access (RA) procedure with a Base Station (BS) while the UE is in a Radio Resource Control (RRC)_INACTIVE state;

transmitting, to the BS, a preamble;

receiving, from the BS, a Random Access Response (RAR) scheduled by first downlink control information (DCI) on a first search space, the first DCI being attached with Cyclic Redundancy Check (CRC) bits scrambled by a Random Access-Radio Network Temporary Identifier (RA-RNTI);

transmitting, to the BS, first Uplink (UL) data on a first UL resource scheduled by the RAR, the first UL data not being from a Common Control Channel (CCCH);

monitoring the first search space for receiving first Downlink (DL) data scheduled by second DCI, the second DCI being attached with CRC bits scrambled by a Temporary Cell-Radio Network Temporary Identifier (TC-RNTI) that is indicated by the RAR;

applying the TC-RNTI as a Cell-Radio Network Temporary Identifier (C-RNTI) while receiving, from the BS, the first DL data;

determining whether the first DL data carries a search space configuration that indicates a second search space;

monitoring the second search space for a second UL resource scheduled by third DCI if the first DL data carries the search space configuration, the third DCI being attached with first CRC bits scrambled by the C-RNTI; and

monitoring the first search space for the second UL resource scheduled by the third DCI if the first DL data does not carry the search space configuration.

2. The method of claim 1 , wherein the first search space is a Common Search Space (CSS) shared with other UEs within a serving cell, and the second search space is a UE specific Search Space (USS).

3. The method of claim 1 , further comprising:

monitoring the second search space for second DL data scheduled by fourth DCI if the first DL data carries the search space configuration, the fourth DCI being attached with second CRC bits scrambled by the C-RNTI; and

monitoring the first search space for the second DL data scheduled by the fourth DCI if the first DL data does not carry the search space configuration.

4. The method of claim 3 , wherein the UE is configured with a timer, the method further comprising:

monitoring the second search space for the second UL resource or the second DL data if the first DL data carries the search space configuration and the timer is running; and

monitoring the first search space for the second UL resource or the second DL data if the first DL data does not carry the search space configuration and the timer is running.

5. A User Equipment (UE) in a wireless communication system for performing Small Data Transmission (SDT), the UE comprising:

at least one processor; and

at least one non-transitory computer-readable medium coupled to the at least one processor, and storing one or more computer-executable instructions that, when executed by the at least one processor, cause the UE to:

initiate a Random Access (RA) procedure with a Base Station (BS) while the UE is in a Radio Resource Control (RRC)_INACTIVE state;

transmit, to the BS, a preamble;

receive, from the BS, a Random Access Response (RAR) scheduled by first downlink control information (DCI) on a first search space, the first DCI being attached with Cyclic Redundancy Check (CRC) bits scrambled by a Random Access-Radio Network Temporary Identifier (RA-RNTI);

transmit, to the BS, first Uplink (UL) data on a first UL resource scheduled by the RAR, the first UL data not being from a Common Control Channel (CCCH);

monitor the first search space for receiving first Downlink (DL) data scheduled by second DCI, the second DCI being attached with CRC bits scrambled by a Temporary Cell-Radio Network Temporary Identifier (TC-RNTI) that is indicated by the RAR;

apply the TC-RNTI as a Cell-Radio Network Temporary Identifier (C-RNTI) while receiving, from the BS, the first DL data;

determine whether the first DL data carries a search space configuration that indicates a second search space;

monitor the second search space for a second UL resource scheduled by third DCI if the first DL data carries the search space configuration, the third DCI being attached with first CRC bits scrambled by the C-RNTI; and

monitor the first search space for the second UL resource scheduled by the third DCI if the first DL data does not carry the search space configuration.

6. The UE of claim 5 , wherein the first search space is a Common Search Space (CSS) shared with other UEs within a serving cell, and the second search space is a UE specific Search Space (USS).

7. The UE of claim 5 , wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to:

monitor the second search space for second DL data scheduled by fourth DCI if the first DL data carries the search space configuration, the fourth DCI being attached with second CRC bits scrambled by the C-RNTI; and

monitor the first search space for the second DL data scheduled by the fourth DCI if the first DL data does not carry the search space configuration.

8. The UE of claim 7 , wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to:

monitor the second search space for the second UL resource or the second DL data if the first DL data carries the search space configuration and the timer is running; and

monitor the first search space for the second UL resource or the second DL data if the first DL data does not carry the search space configuration and the timer is running.