Reliable Groupcast for NR V2X

With the development of autonomous vehicles, the high reliability and low latency vehicular communication technologies have become more critical. The Third Generation Partnership Project (3GPP) specifies the sidelink (SL) transmission based on New Radio (NR), aiming to meet stringent vehicle-to-everything (V2X) requirements. Compared with Long Term Evolution (LTE) V2X, which only supports broadcast use cases, NR V2X also supports unicast and groupcast. The groupcast operation allows the transmitter to communicate with multiple receivers in the same group at once. In general, the group size for vehicles is limited due to the high-reliability requirement. In this paper, we present reliable blind retransmission for NR V2X groupcast. We improve the groupcast transmission reliability by assigning the proper retransmission user equipment(UE). This paper proposes a retransmission UE assignment. We formulate a retransmission UE selection problem to maximize the group packet reception ratio (GPRR) for NR V2X distributed groupcast. The simulation results show that the proposed retransmission method improves the V2X groupcast in terms of GPRR, packet inter-reception time (PIR), and the available group size.