Beam Misalignment Fading in THz D2D ISAC: From Communication to Sensing

Terahertz (THz) integrated sensing and communication (ISAC) systems promise ultra-high data rates and precise sensing capabilities, enabled by narrow and directional beams. However, such beams are susceptible to beam misalignment (BM) fading caused by platform instability. While statistical models for BM fading exist for communication links, their extension to sensing applications, especially in drone-to-drone (D2D) scenarios, remains unexplored. In D2D ISAC networks, misalignment effects from the aerial platforms impact both the forward and return paths. This paper presents closed-form statistical models for BM fading in THz ISAC, addressing both monostatic (co-located transceivers) and bistatic (separated transceivers) sensing configurations, and considering both the spot-filling regime (target larger than beam) and the spot-limited regime (target smaller than beam). The proposed models facilitate the extension of BM fading analysis to sensing in drone-to-drone THz ISAC systems and have been validated through Monte Carlo simulations.