Failure-Aware Cognitive Spectrum Handoff for UAV Command-and-Control Links: Calibrated Sensing, Transactional Recovery, and Multi-Band Evaluation

Reliable UAV command-and-control (C2) links require spectrum adaptation that responds to detected incumbent activity while keeping the ground station and aircraft synchronized. This study evaluates an incumbent-aware handoff workflow integrating FFT energy sensing, three-state temporal stabilization, pair-specific spectral admissibility filtering, bidirectional link-margin ranking, and a PROPOSE–ACK–EXECUTE transaction with retries and ordered backups. With a clean 32-window history, the corrected K=768 detector produced empirical Pfa=0.0997 [0.0980, 0.1014] and Pd=0.9012 [0.8995, 0.9029] at −10 dB. The point detection target was attained, while the 95% lower confidence bound was 0.8995. A representative logical detector-to-protocol composition at −10 dB and 10% independently imposed symmetric IID signaling loss gave a binary detection and recovery probability of 0.844 for the clean-history corrected K=768 profile, compared with 0.258 for corrected K=51; 95% occupied history reduced the K=768 value to 0.121. This composition does not exercise the mobility-coupled packet pathway or a common RF realization across sensing and signaling. In matched protocol trials, the full policy achieved PH=0.9321 [0.9270, 0.9369] while removing EXECUTE; retries, backups, or margin-based ranking reduced reliability and changed the signaling–latency trade-off. Three idempotent EXECUTE transmissions reduced unresolved desynchronization to 0.008, and adding rendezvous recovery increased the eventual-recovery probability to 0.9582 at the cost of a 341-ms 95th-percentile recovery time. At 10% IID loss, the deadline-constrained success probability under the 250-ms internal interruption benchmark was 0.894. Bursty loss produced the largest degradation among the evaluated stress conditions. The results quantify how detector history quality, commit recovery, and protocol redundancy jointly affect reliability and latency. All reported quantitative validation is simulation-based or analytical/software verification; the fifteen-band by five-environment sweep is a static configuration-dependent operating envelope rather than field, hardware, or mobility-coupled validation. The reported detector–protocol integration is logical rather than fully RF-coupled, and no incumbent receiver or secondary-to-incumbent interference path is modeled.