Decomposing URLLC Deadline Failures in Beam-Managed 6G Networks: Implications for Mission-Critical Wireless Systems

Abstract

Mission-critical wireless systems require ultra-reliable low-latency communications (URLLC), which sixth-generation (6G) millimeter-wave (mmWave) beam-managed networks are designed to provide. However, the reported URLLC deadline miss rate often masks the specific causes of packet failures. This paper introduces a framework that categorizes missed URLLC packets into three causes: queueing-limited (Q), transmission-limited (T), and beam-tracking-limited (B). Our analysis across ten scenarios with antenna counts from $64$ to $4096$ reveals three key findings. First, the dominant cause of missed packets shifts from Q to B when the antenna count exceeds roughly $1825$. Therefore, operators of hyper-massive arrays should focus on improving beam-tracking accuracy to reduce the miss rate. Second, the beam-sweep period ($T_{\mathrm{sw}}$) significantly affects B-misses, while Q and T remain relatively unchanged. Reducing $T_{\mathrm{sw}}$ from $20$ms to $10$ms can cut the B-misses by more than half, without requiring a redesign of the scheduler. Third, Q-misses reach a cumulative distribution function (CDF) of approximately $0.98$ by $0.8$ms, so modest latency-budget relaxation can accommodate most overruns. In contrast, B-misses remain unsaturated at $12$ms, making them difficult to accommodate within practical application-layer latency limits. Overall, this framework transforms an ambiguous aggregate miss-rate metric into a clear three-way diagnostic tool that directly informs remedial actions for network operators.