A Vision of 6G URLLC: Physical-Layer Technologies and Enablers

The anticipated advent of 6G communication holds the promise of enabling mission-critical applications such as traffic detection, forest fire recognition, emergency search and rescue, and widespread communication broadcasting. To fulfill these services, 6G demands a robust communication framework with minimal latency. While the current fifth-generation (5G) ultra-reliable low-latency communication (URLLC) as defined by the 3rd Generation Partnership Project (3GPP), provides the requisite reliability (99.99 percent) and latency (< 1ms) to support existing applications, many foundational aspects of URLLC remain uncertain. Therefore, upcoming networks necessitate the integration of the next-generation URLLC, known as xURLLC, to attain the pinnacle of reliability and latency. In this article, we present an overview of both current 5G URLLC technologies and those anticipated for 6G. We succinctly delineate the essential URLLC requirements, and scrutinize the prevailing limitations in URLLC design. Subsequently, we spotlight xURLLC and the groundbreaking physical-layer techniques poised to define 6G URLLC. Additionally, we assess the opportunities and challenges presented by each key xURLLC driver, engaging in a comprehensive discussion of the efficacy of each proposed solution. Finally, we put forth future research directions for the next generation of URLLC.