An ns-3-Based Study of Mobile Network Characteristics in Low-Altitude UTM Service Environments: Receiver Freshness and Background Delay

Periodic aircraft state reporting for unmanned aircraft system traffic management (UTM) motivates evaluating receiver freshness alongside packet delivery. We compare first-in, first-out (FIFO) service with a STATUS-priority service-order rule in a long-term evolution (LTE)/evolved packet core (EPC) simulation with competing uplink traffic. Packet lineage connects radio link control (RLC) enqueue and service events to application reception and continuous-time age of information (AoI). The primary design uses 88 matched run pairs per load condition and equal weighting across aircraft. Under heavy load, the mean of aircraft-specific continuous-time AoI 95th percentiles decreases from AoIpF to AoIpP ms, while background mean delay increases by BGMeanD ms. Deterministic validation, unconditional packet accounting, and paired statistical diagnostics support interpretation of the measurement pipeline. Limited supporting horizon and bearer-separation comparisons assess the scope of the result. The freshness direction persists to 240 s, but its magnitude depends on the observation horizon. The findings describe a simulation-specific freshness–background-delay trade-off; they establish neither operational suitability nor safety benefits.