Adaptive Switching Method for 5G Grant-Free URLLC Scheduling

Ultra-reliable and low latency communication (URLLC) is a major use case scenario of 5G New Radio (NR), requiring high reliability and stringent latency. The grant based scheduling mechanism in long-term evolution (LTE) is not suited to this requirement, so grant-free (GF) access has been developed to reduce latency and signaling overhead. GF mechanism can be deployed over shared or dedicated resources, however, it has issues with reliability and resource utilization which affect system capacity. These challenges still require improvement in order to satisfy the requirements of URLLC. This paper focuses on improving grant-free transmission over shared resources to meet the requirements of URLLC while increasing system capacity. Baseline GF transmission methods defined by 3GPP are taken into account and the proposed method is compared to them. The proposed method uses their respective strengths and weaknesses in a flexible way, thus meeting the necessary requirements for latency and reliability, as well as providing increased capacity through adaptive switching between methods and adaptive parameter selection. The results show that the proposed method improves capacity as compared to other GF retransmission schemes. The percentage of users who cannot transfer their data is decreased by between 4 and 16. While keeping latency and reliability levels constant, it provides efficient utilization of resources.