Method and apparatus for indicating time gap for device-to-device communication in a wireless communication system

A first UE (User Equipment), wherein the first UE is configured or pre-configured with a sidelink resource pool for sidelink transmission, and is triggered to select resources for a TB (Transport Block), comprising:

• a control circuit;
• a processor installed in the control circuit;
• and
• a memory installed in the control circuit and operatively coupled to the processor;
• wherein the processor is configured to execute a program code stored in the memory to:
• select a first resource for transmission of the TB;
• select a second resource such that the second resource is later than the first resource, and a time gap between the first resource and the second resource is larger than or equal to a first time duration when the first UE selects the second resource for HARQ-ACK (Hybrid Automatic Repeat Request-Acknowledgement) based retransmission of the TB;
• transmit a SCI (Sidelink Control Information) and the TB on the first resource in a slot to a second UE, wherein the first UE derives or sets a time gap field in the SCI for indicating the time gap between the first resource and the second resource, and the SCI indicates the first resource and the second resource;
• select a third resource such that a time gap between the first resource and the third resource is allowed to be smaller than the first time duration when the first UE selects the third resource for blind retransmission for the TB;
• and
• transmit a SCI (Sidelink Control Information) and the TB on the first resource in a slot to a second UE, wherein the first UE derives or sets a time gap field in the SCI for indicating the time gap between the first resource and the third resource, and the SCI indicates the first resource and the third resource.