A method performed by a first user equipment, UE, in a wireless communication system, for groupcast transmission, the method comprising: receiving sidelink control information, SCI, from a second UE; identifying a physical sidelink feedback channel, PSFCH, resource ; and transmitting a PSFCH associated with hybrid automatic repeat request, HARQ, information to the second UE based on the identified PSFCH resource, wherein the SCI includes information indicating whether the HARQ information includes only NACK, first feedback mode, or the HARQ information includes ACK/NACK, second feedback mode, wherein the PSFCH resource is identified based on (UEindexlnGroup + Aspect) mod N PSFCH , in case that the information indicates that the HARQ information includes ACK/NACK, second feedback mode, wherein the UEindexlnGroup is a number indicating an identity of the first UE configured by a higher layer, the Aspect is an identifier of the second UE carried in the SCI, and the N PSFCH is a number of PSFCH resources available for the HARQ information transmitted in the PSFCH, and wherein the PSFCH resource is identified based on Aspect mod N PSFCH , in case that the information indicates that the HARQ information includes only NACK, first feedback mode. receiving sidelink control information, SCI, from a second UE; identifying a physical sidelink feedback channel, PSFCH, resource ; and transmitting a PSFCH associated with hybrid automatic repeat request, HARQ, information to the second UE based on the identified PSFCH resource, wherein the SCI includes information indicating whether the HARQ information includes only NACK, first feedback mode, or the HARQ information includes ACK/NACK, second feedback mode, wherein the PSFCH resource is identified based on (UEindexlnGroup + Aspect) mod N PSFCH , in case that the information indicates that the HARQ information includes ACK/NACK, second feedback mode, wherein the UEindexlnGroup is a number indicating an identity of the first UE configured by a higher layer, the Aspect is an identifier of the second UE carried in the SCI, and the N PSFCH is a number of PSFCH resources available for the HARQ information transmitted in the PSFCH, and wherein the PSFCH resource is identified based on Aspect mod N PSFCH , in case that the information indicates that the HARQ information includes only NACK, first feedback mode. wherein the SCI includes information indicating whether the HARQ information includes only NACK, first feedback mode, or the HARQ information includes ACK/NACK, second feedback mode, wherein the PSFCH resource is identified based on (UEindexlnGroup + Aspect) mod N PSFCH , in case that the information indicates that the HARQ information includes ACK/NACK, second feedback mode, wherein the UEindexlnGroup is a number indicating an identity of the first UE configured by a higher layer, the Aspect is an identifier of the second UE carried in the SCI, and the N PSFCH is a number of PSFCH resources available for the HARQ information transmitted in the PSFCH, and wherein the PSFCH resource is identified based on Aspect mod N PSFCH , in case that the information indicates that the HARQ information includes only NACK, first feedback mode. <EOS>