Method and device for performing groupcast transmission in wireless communication system

An apparatus that performs a groupcast transmission, the apparatus comprising:

• a transceiver;
• at least one memory;
• and
• at least one processor operably coupled with the at least one memory and the transceiver,
• wherein the processor is adapted to:
• transmit a synchronization signal block (SSB) via an SSB beam;
• receive a discovery message in response to the SSB from each of a plurality of UEs;
• determine, based on the discovery message, a groupcast transmission timing for specific UEs among the plurality of UEs;
• transmit a group transmission-reception (Tx-Rx) timing message informing of the groupcast transmission timing to the specific UEs;
• and
• perform a groupcast transmission using the SSB beam to the specific UEs at the groupcast transmission timing.

A method of operating a receiving user equipment (UE) in a wireless communication system, the method comprising:

• receiving a synchronization signal block (SSB) from a transmitting UE through an SSB beam;
• transmitting a discovery message to the transmitting UE in response to the SSB;
• receiving a group transmission-reception (Tx-Rx) timing message indicating a groupcast transmission timing based on the discovery message from the transmitting UE;
• and
• receiving groupcast data from the transmission UE using the SSB beam at the groupcast transmission timing.