In a wireless communication system, a grant-free uplink transmission is an uplink transmission sent from a user equipment (UE) to a base station that does not need a dynamic and explicit scheduling grant from the base station. Systems and methods are disclosed for performing hybrid automatic repeat request (HARQ) for grant-free uplink transmissions. Signaling relating to the ACK/NACK for the HARQ, as well as signaling relating to configuring the UE for grant-free uplink transmission, is also disclosed.