Relay discovery within a sidelink groupcast

A system comprising:

• an apparatus;
• one or more processors;
• and
• a memory storing instructions that, when executed by the one or more processors, cause the one or more processors to:
• indicate that a hybrid automatic repeat request process is initiated for transmitting at least a first hybrid automatic repeat request message comprising an inquiry as the first message of the hybrid automatic repeat request process, wherein the inquiry requests an availability indication of a relay terminal for relaying a communication of a transmitting terminal, wherein the communication is one of the unicast communication and the groupcast communication, and wherein the transmitting terminal and the relay terminal are members of the unicast and groupcast, respectively;
• transmit the first hybrid automatic repeat request message using the hybrid automatic repeat request process, wherein the first hybrid automatic repeat request message comprises an exception criterion for being available as the relay terminal for the relaying of the communication, wherein the first hybrid automatic repeat request message is transmitted on a first resource, and wherein the first resource is excluded for any other hybrid automatic repeat request process comprising a hybrid automatic repeat request message not comprising the inquiry as the first message, and wherein the indicating indicates that the first message is transmitted on the first resource;
• determine that a hybrid automatic repeat request feedback is received from at least one relay terminal in response to the first hybrid automatic repeat request message according to the hybrid automatic repeat request process, wherein the determining is performed on a second resource different from the first resource;
• and the second resource is related to the first resource according to the hybrid automatic repeat request process;
• decide that the at least one relay terminal is available based on the hybrid automatic repeat request feedback being received from the at least one relay terminal;
• and
• based on the at least one relay terminal being available, transmit a second hybrid automatic repeat request message using the hybrid automatic repeat request process, wherein the second hybrid automatic repeat request message does not comprise the inquiry.

A method performed by an apparatus, the method comprising:

• indicating, by the apparatus, that a hybrid automatic repeat request process is initiated for transmitting at least a first hybrid automatic repeat request message comprising an inquiry as the first message of the hybrid automatic repeat request process, wherein the inquiry requests an availability indication of a relay terminal for relaying a communication of a transmitting terminal, wherein the communication is one of the unicast communication and the groupcast communication, and wherein the transmitting terminal and the relay terminal are members of the unicast and groupcast, respectively;
• transmitting, by the apparatus, the first hybrid automatic repeat request message using the hybrid automatic repeat request process, wherein the first hybrid automatic repeat request message comprises an exception criterion for being available as the relay terminal for the relaying of the communication, wherein the first hybrid automatic repeat request message is transmitted on a first resource, and wherein the first resource is excluded for any other hybrid automatic repeat request process comprising a hybrid automatic repeat request message not comprising the inquiry as the first message, and wherein the indicating indicates that the first message is transmitted on the first resource;
• determining, by the apparatus, that a hybrid automatic repeat request feedback is received from at least one relay terminal in response to the first hybrid automatic repeat request message according to the hybrid automatic repeat request process, wherein the determining is performed on a second resource different from the first resource;
• and the second resource is related to the first resource according to the hybrid automatic repeat request process;
• deciding, by the apparatus, that the at least one relay terminal is available based on the hybrid automatic repeat request feedback being received from the at least one relay terminal;
• and
• based on the at least one relay terminal being available, transmitting, by the apparatus, a second hybrid automatic repeat request message using the hybrid automatic repeat request process, wherein the second hybrid automatic repeat request message does not comprise the inquiry.