We investigate cross-layer performance diagnostics for an O-RAN instance by jointly analyzing application-level latency and radio-layer behavior from a real measurement campaign. Measurements were conducted at multiple link distances (2, 6 and 11 meters) using two representative UE configurations (a commercial smartphone and a modem-based device), under both static conditions and a controlled dynamic obstruction scenario. Rather than relying on averages, the study adopts tail-focused latency characterization (e.g., 95th percentile and exceedance probabilities) and connects it to scheduler- and link-adaptation indicators (e.g., block error behavior, modulation/coding selection and signal quality). The results reveal (i) UE-dependent differences that primarily manifest in the latency tail, (ii) systematic scaling of tail latency with distance and payload and (iii) cases where radio-layer dynamics are detectable even when end-to-end latency appears stable, motivating the need for cross-layer evidence. Distinct from much of the existing literature (often centered on throughput, simulated setups, or single-layer KPIs) this work contributes a measurement-driven methodology for interpretable O-RAN diagnostics and proposes lightweight, window-based "degradation flags" that combine tail latency and radio indicators to support practical monitoring and troubleshooting.

翻译：本研究通过联合分析实际测量活动中获取的应用层延迟与无线层行为，对某O-RAN实例开展跨层性能诊断。测量在静态条件及受控动态遮挡场景下，采用两种典型用户设备配置（商用智能手机与基于调制解调器的设备），在多种链路距离（2米、6米及11米）下进行。本研究摒弃传统均值分析，采用尾部聚焦的延迟表征方法（如第95百分位数及超限概率），并将其与调度器及链路自适应指标（如块错误行为、调制编码方案选择及信号质量）建立关联。研究结果表明：（i）用户设备相关的差异主要体现在延迟尾部；（ii）尾部延迟随距离与负载呈现系统性变化规律；（iii）存在端到端延迟表现稳定而无线层动态仍可被检测的案例，这印证了跨层证据的必要性。与现有多数文献（常聚焦于吞吐量、仿真设置或单层关键性能指标）不同，本工作提出了一种可解释的测量驱动型O-RAN诊断方法，并设计了轻量级的基于时间窗的“劣化标志”——该标志融合尾部延迟与无线层指标，可为实际监控与故障排查提供支持。