When URLLC is Worse than Rayleigh: Error Rates of Lomax Fading

Ultra-Reliable Low-Latency Communication (URLLC) is a key component of 5G New Radio (NR), providing support for applications requiring highly reliable communication with latencies as low as 1 millisecond. URLCC is relevant for military communications, which demand real-time situational awareness, autonomous system support, and robust coordination. The Lomax distribution has emerged as a prime candidate for modeling URLLC channels due to its ability to capture rare but extreme fading events that are "worse" than Rayleigh fading and its good fit to empirical data. This paper presents a novel approach for deriving closed-form expressions for the symbol and bit error rates of coherently detected linear modulation, both with and without channel coding, under a class of fading distributions that include Lomax. We extend this approach to selection combining (SC), relevant for URLLC’s preemptive repeat transmissions and diversity techniques such as frequency and space diversity. Additionally, we analyze performance under double scattering, which is relevant to amplify-and-forward relaying. Our findings provide critical insights into URLLC system performance under Lomax fading, supporting the development of robust communication strategies for mission-critical military applications in harsh environments.