A mobile radio communication terminal device, comprising: at least one receiver; at least one transmitter; and one or more processors operatively coupled to a memory that stores computer readable software, wherein the computer readable software, when executed by the one or more processors, causes the mobile radio communication terminal device to: transmit, via the at least one transmitter, to at least a second mobile radio communication terminal device: a sidelink control information, SCI, which includes information associated with NACK resource determination; and a physical sidelink shared channel, PSSCH, data; receive, via the at least one receiver, either a negative-acknowledgment, NACK, feedback message from the second mobile radio communication terminal device or no response, wherein: when the NACK feedback message is received, it indicates the PSSCH data was not successfully decoded; when no response is received, an acknowledgement, ACK, for the PSSCH data is indicated; and a starting resource block and cyclic shift of a sequence for the NACK feedback message are determinable based on the information associated with NACK resource determination included in the SCI; determine whether or not to retransmit the PSSCH data in response to receiving the NACK feedback message or no response; and retransmit, via the at least one transmitter, the PSSCH data if the mobile radio communication terminal device determines to retransmit the PSSCH data, and not retransmit the PSSCH data if the mobile radio communication terminal device determines not to retransmit the PSSCH data. at least one receiver; at least one transmitter; and one or more processors operatively coupled to a memory that stores computer readable software, wherein the computer readable software, when executed by the one or more processors, causes the mobile radio communication terminal device to: transmit, via the at least one transmitter, to at least a second mobile radio communication terminal device: a sidelink control information, SCI, which includes information associated with NACK resource determination; and a physical sidelink shared channel, PSSCH, data; receive, via the at least one receiver, either a negative-acknowledgment, NACK, feedback message from the second mobile radio communication terminal device or no response, wherein: when the NACK feedback message is received, it indicates the PSSCH data was not successfully decoded; when no response is received, an acknowledgement, ACK, for the PSSCH data is indicated; and a starting resource block and cyclic shift of a sequence for the NACK feedback message are determinable based on the information associated with NACK resource determination included in the SCI; determine whether or not to retransmit the PSSCH data in response to receiving the NACK feedback message or no response; and retransmit, via the at least one transmitter, the PSSCH data if the mobile radio communication terminal device determines to retransmit the PSSCH data, and not retransmit the PSSCH data if the mobile radio communication terminal device determines not to retransmit the PSSCH data. transmit, via the at least one transmitter, to at least a second mobile radio communication terminal device: a sidelink control information, SCI, which includes information associated with NACK resource determination; and a physical sidelink shared channel, PSSCH, data; a sidelink control information, SCI, which includes information associated with NACK resource determination; and a physical sidelink shared channel, PSSCH, data; receive, via the at least one receiver, either a negative-acknowledgment, NACK, feedback message from the second mobile radio communication terminal device or no response, wherein: when the NACK feedback message is received, it indicates the PSSCH data was not successfully decoded; when no response is received, an acknowledgement, ACK, for the PSSCH data is indicated; and a starting resource block and cyclic shift of a sequence for the NACK feedback message are determinable based on the information associated with NACK resource determination included in the SCI; when the NACK feedback message is received, it indicates the PSSCH data was not successfully decoded; when no response is received, an acknowledgement, ACK, for the PSSCH data is indicated; and a starting resource block and cyclic shift of a sequence for the NACK feedback message are determinable based on the information associated with NACK resource determination included in the SCI; determine whether or not to retransmit the PSSCH data in response to receiving the NACK feedback message or no response; and retransmit, via the at least one transmitter, the PSSCH data if the mobile radio communication terminal device determines to retransmit the PSSCH data, and not retransmit the PSSCH data if the mobile radio communication terminal device determines not to retransmit the PSSCH data.