Guest Editorial: Intelligent Ultra-Reliable and Low-Latency Communications in 6G

As one of the new communication scenarios in the Fifth Generation (5G) mobile communications, Ultra-Reliable and Low-Latency Communications (URLLC) are crucial for enabling a wide range of emerging applications, including industrial automation, intelligent transportation, telemedicine, Tac-tile Internet, and Virtual/Augmented Reality (VR/AR). According to the requirements in 5G standards, to support emerging mission-critical applications, the End-to-End (E2E) delay cannot exceed 1 ms and the packet loss probability should be 10 ⁻⁵ ~ 10 ⁻⁷ . Compared with the existing cellular networks, the delay and reliability require significant improvements by at least two orders of magnitude for 5G networks. This capability gap cannot be fully resolved by the 5G New Radio (NR), i.e., the physical-layer technology for 5G, even though the transmission delay in Radio Access Networks (RANs) achieves the 1 ms target. Transmission delay contributes only a small fraction of the E2E delay, as the stochastic delays in upper networking layers, such as queuing delay, processing delay, and access delay, are key bottlenecks for achieving URLLC. Beyond 5G systems or so-called Sixth Generation (6G) systems should guarantee the E2E delay bound with high reliability.