Reliable groupcasting in wireless communication networks

1 . A first wireless terminal, comprising:

at least one processor;

at least one memory including computer program code,

the at least one memory and the computer program code being configured, with the at least one processor, to cause the first wireless terminal at least to:

receive a groupcast message from a second wireless terminal;

acknowledge the receipt of the groupcast message;

receive, a first retransmission of the groupcast message from the second wireless terminal;

skip, a transmission of a first feedback related to reception of the first retransmission at the first wireless terminal, wherein skipping the transmission of the first feedback comprises refraining from acknowledging successful reception of the first retransmission of the groupcast message based on the acknowledgement of the groupcast message;

monitor, a second feedback from a third wireless terminal, wherein the second feedback is related to reception of the first retransmission at the third wireless terminal, and wherein the monitoring starts after a predetermined number of counted retransmissions of the groupcast message;

based on monitoring, determine that the third wireless terminal did not successfully receive the first retransmission of the groupcast message;

based on the determination that the third wireless terminal did not successfully receive the first retransmission of the groupcast message, generate a derived feedback to the second wireless terminal;

transmit the derived feedback to the second terminal, wherein the derived feedback is related to reception of the first retransmission at the third wireless terminal, and wherein the derived feedback comprises:

an identity of the first wireless terminal,

an identity of the first retransmission,

a Reference Signal Receive Power (RSRP) of the first retransmission, and

a RSRP of a feedback channel associated with the third wireless terminal;

receive a groupcast retransmission delegation request from the second wireless terminal to retransmit the groupcast message, wherein the groupcast retransmission delegation request comprises a timer and a redundancy version parameter, wherein the redundancy version parameter defines a transport block parameter for applying a transmission format identical to the first retransmission;

store data of the groupcast message in the at least one memory until the timer expires; and

in response to receiving the groupcast retransmission delegation request, simultaneously retransmit, with the second wireless terminal, the groupcast message to the third wireless terminal as a second retransmission, wherein the second retransmission utilizes a transmission format based on the redundancy version parameter.

2 . The first wireless terminal of claim 1 , wherein monitoring the second feedback from the third wireless terminal comprises detecting at least one of a negative acknowledgement (NACK) or a discontinuous transmission (DTX) associated with the first retransmission.

3 . The first wireless terminal of claim 2 , wherein the second feedback is transmitted on a Physical Sidelink Feedback Channel (PSFCH) associated with the first retransmission.

4 . The first wireless terminal of claim 3 , wherein storing the data of the groupcast message comprises storing the data in a Medium Access Control (MAC) buffer of the first wireless terminal until expiration of the timer included in the groupcast retransmission delegation request.

5 . The first wireless terminal of claim 4 , wherein retransmitting the groupcast message as the second retransmission is performed only after determining that the first wireless terminal has an available copy of the groupcast message and a valid sidelink connection to the third wireless terminal.

6 . The first wireless terminal of claim 5 , wherein the second retransmission by the first wireless terminal and a retransmission by the second wireless terminal are transmitted in shared time-frequency resources using the identical transmission format defined by the redundancy version parameter, such that the retransmissions constructively combine at the third wireless terminal.

7 . The first wireless terminal of claim 6 , wherein retransmitting the groupcast message as the second retransmission comprises transmitting the second retransmission using a source identity of the second wireless terminal instead of a source identity of the first wireless terminal.

8 . A method comprising:

receiving, by a first wireless terminal, a groupcast message from a second wireless terminal;

acknowledging, by the first wireless terminal, the receipt of the groupcast message;

receiving, by the first wireless terminal, a first retransmission of the groupcast message from the second wireless terminal;

skipping, by the first wireless terminal, a transmission of a first feedback related to reception of the first retransmission at the first wireless terminal, wherein the skipping comprises refraining from acknowledging successful reception of the first retransmission of the groupcast message based on the acknowledgement of the groupcast message;

monitoring, by the first wireless terminal, a second feedback from a third wireless terminal, wherein the second feedback is related to reception of the first retransmission at the third wireless terminal and wherein the monitoring starts after a predetermined number of counted retransmissions of the groupcast message;

based on the monitoring, by the first wireless terminal, determine that the third wireless terminal did not successfully receive the first retransmission of the groupcast message;

based on the determination, by the first wireless terminal, generate a derived feedback to the second wireless terminal;

transmitting, by the first wireless terminal, the derived feedback to the second wireless terminal,

wherein the derived feedback is related to reception of the first retransmission at the third wireless terminal and wherein the derived feedback comprises:

an identity of the first wireless terminal,

an identity of the first retransmission,

a Reference Signal Receive Power (RSRP) of the first retransmission, and

a RSRP of a feedback channel associated with the third wireless terminal;

receiving, by the first wireless terminal, a groupcast retransmission delegation request from the second wireless terminal to retransmit the groupcast message,

wherein the groupcast retransmission delegation request comprises a timer and a redundancy version parameter, and

wherein the redundancy version parameter specifies a transport block parameter for a applying a transmission format of the first retransmission;

storing data of the groupcast message in a memory of the first wireless terminal until the timer expires; and

in response to receiving the groupcast retransmission delegation request, simultaneously retransmitting, with the second wireless terminal, the groupcast message to the third wireless terminal as a second retransmission, wherein the second retransmission utilizes the transmission format based on the redundancy version parameter.