Delay Trade-Off and Adaptive Resource Element Framework for URLLC
Yixin Zhang, Wenchi Cheng, Jingqing Wang, Wei Zhang · IEEE Communications Magazine · 2025
With various time-sensitive tasks to be served, ultra-reliable and low-latency communications (URLLC) has become one of the most important scenarios for fifth-generation (5G) wireless communications. The end-to-end delay from the sub-millisecond level to the second level is first put forward for a wide range of delay-sensitive tasks in the future sixth generation (6G) communication networks, which imposes a strict requirement on satisfying various real-time services and applications with different stringent quality of service (QoS) demands. Thus, we need to find a new delay reduction framework to satisfy the more stringent delay requirements. In this article, a state-of-the-art overview of over-the-air delay composition and delay analysis combined with access protocols are elaborated. We reveal the trade-off relationship among transmission delay, queuing delay, and retransmission times with the change of blocklength in the finite blocklength (FBL) regime. Based on the trade-off and by integrating the grant-free (GF) random access (RA) protocol, we propose the adaptive resource element (RE) framework for efficiently reducing the over-the-air delay. Numerical results show that our proposed scheme can significantly reduce over-the-air delay for URLLC.