Method and apparatus for performing mode 1 SL communication in NR V2X

A first device adapted to perform wireless communication, the first device comprising:

• at least one transceiver;
• at least one processor;
• and
• at least one memory connected to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising:
• controlling the at least one transceiver to receive, from a base station, information related to a maximum number of times that a medium access control (MAC) protocol data unit (PDU) can be transmitted using a first sidelink (SL) grant;
• controlling the at least one transceiver to transmit, to a second device, the MAC PDU based on the first SL grant and a SL process;
• flushing a hybrid automatic repeat request (HARM) buffer related to the SL process, based on that a number of transmissions of the MAC PDU has been reached to the maximum number of times;
• controlling the at least one transceiver to receive, from the base station through a physical downlink control channel (PDCCH), a second SL grant for retransmission of the MAC PDU, wherein the second SL grant is related to the SL process of which the HARQ buffer is empty;
• and
• ignoring the second sidelink grant, based on the second SL grant related to the SL process of which the HARQ buffer is empty.

A processing device adapted to control a first device, the processing device comprising:

• at least one processor;
• and
• at least one memory connected to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising:
• receiving, from a base station, information related to a maximum number of times that a medium access control (MAC) protocol data unit (PDU) can be transmitted using a first sidelink (SL) grant;
• transmitting, to a second device, the MAC PDU based on the first SL grant and a SL process;
• flushing a hybrid automatic repeat request (HARQ) buffer related to the SL process, based on that a number of transmissions of the MAC PDU has been reached to the maximum number of times;
• receive, from the base station through a physical downlink control channel (PDCCH), a second SL grant for retransmission of the MAC PDU, wherein the second SL grant is related to the SL process of which the HARQ buffer is empty;
• and
• ignore the second sidelink grant, based on the second SL grant related to the SL process of which the HARQ buffer is empty.