Enhancing URLLC Uplink Configured-grant Transmissions

Abstract

The 3rd Generation Partnership Project (3GPP) has defined Ultra-Reliable Low-Latency Communication (URLLC) as one of the main objectives of 5G development to satisfy the applications with stringent requirements of latency and reliability. Uplink (UL) configured-grant (CG) transmission where the user equipment (UE) transmits a packet without scheduling request (SR) and UL grant is standardized by 3GPP Release 15 to reduce latency. The UE also transmits automatically a configured number of repetitions without feedback from the base station (gNB) to increase reliability.Nevertheless, the repetitions are not allowed to transmit outside the hybrid automatic repeat request (HARQ) process containing the first repetition. It might cause a smaller number of transmitted repetitions than configuration that is harmful to the performance of URLLC.This paper uses the reserved resources where the UEs can transmit the repetitions outside the original HARQ process until the configured number is reached. The scheme is developed further when the gNB is equipped with a successive interference cancellation (SIC) receiver so it can decode multiple repetitions of the different UEs in the same reserved resource. The use of reserved resources ensures the performance of UL CG transmission while SIC receiver minimizes the reserved resource's consumption. The numerical results show a higher transmission reliability and lower reserved resource consumption of the proposed scheme compared to the related works.