Strategies to meet the configured repetitions in URLLC Uplink Grant-Free transmission
Trung-Kien Le, Umer Salim, Florian Kaltenberger · 2019
In Ultra-Reliable Low-Latency Communication (URLLC), the user (UE) can be configured to transmit in grant-free/configured-grant (GF/CG) resources for uplink (UL) transmission that does not require the UE to transmit scheduling request (SR) and receive UL grant to reduce latency. In addition, the UE is also configured to transmit automatically a specific number of repetitions without waiting feedback. However, these repetitions are only allowed to carry out in an interval with period P to avoid identity (ID) confusion in a Hybrid automatic repeat request (HARQ) process. Thereby, there is a chance that the UE cannot transmit all repetitions as configured if data arrives late and it leads to a drop of reliability. Two approaches are proposed in this paper to cope with this problem. This first approach requires an usage of the explicit HARQ feedback structure and the second one is related to an additional SR transmitted by the UE in parallel with data. The numerical results show the benefit of these two methods in increasing system performance in case of less configured repetitions made when they help the system to avoid or reduce packet loss due to Demodulation Reference Signal (DMRS) miss-detection.