THz band UAV communications under beam misalignment fading: tractable performance analysis

Official URL: https://dx.doi.org/10.1109/OJCOMS.2026.3706997

The Terahertz (THz) band enables ultra-high data rate Unmanned Aerial Vehicle (UAV) communications, but its highly directional beams are prone to mobility and platform instability-induced beam misalignment (BM) fading, which, although mitigated by stabilization and motion control, cannot be fully eliminated. This makes BM fading essential to analyze for its impact on THz band UAV communications. In this paper, we study and analyze the effect of BM fading for THz band UAV communications, in terms of ergodic capacity and outage capacity, by deriving tractable and simple closed-form expressions for both metrics. Via both capacity metrics for performance analysis under BM fading, we investigate the behavior of the THz band UAV channel across various parameters, distance, altitude, and frequency. Our expression for outage capacity under BM fading is presented for the first time in the literature, and our derived closed-form expression for ergodic capacity is simple and tractable, providing insight and intuition, unlike the existing expression in the literature. In addition to accuracy with low complexity, our expressions for both capacity metrics enable limit analysis for diversity order under BM fading, where both approach the additive white Gaussian noise (AWGN) capacity for large diversity order, i.e., the BM fading-free case. Besides capacity analysis, we also revisit the average BER under BM fading, considering bounded signal-to-noise-ratio (SNR) conditions. The proposed expressions can be directly employed for link-level performance evaluation and system design of THz band UAV communications, and can be extended to incorporate additional channel impairments or more advanced system configurations such as multi-antenna and non-terrestrial network (NTN) scenarios.