Enhancing AAV-Enabled Secure Communications via Synthetic Aperture Beamforming

In this paper, we consider a synthetic aperture secure beamforming approach for a virtual multiple-input multiple output (MIMO) broadcast channel in the presence of hybrid wiretapping environments. Our goal is to design the flight node deployment constructed by a single-antenna mobile autonomous aerial vehicle (AAV), corresponding transmission symbol strategy, transmit precoding, and received beamforming to maximize the system channel capacity. Leveraging the synthetic aperture beamforming, we aim to provide spatial gain along a predefined angle in free space while reducing it in others and thus enhance physical layer (PHY) security. To this end, we analyze the expression of the asymptotic channel eigenvalues to optimize the AAV flight node deployment. For the optimal precoding design, an energy-efficient method that minimizes the transmit power consumption is studied based on the given virtual MIMO channel, while meeting the quality of service (QoS) for the base station (BS), leakage tolerance of eavesdroppers (Eves), and per-node power constraints. The power minimization problem is a non convex program, which is then reformulated as a tractable form after some mathematical manipulations. Moreover, we design the received beamforming by applying the linearly constrained minimum variance (LCMV) method such that the jamming can be effectively suppressed. Numerical results demonstrate the superiority of the proposed method in promoting capacity.

💡 Research Summary

This paper proposes a novel physical‑layer security framework for autonomous aerial vehicle (AAV) communications that exploits synthetic aperture beamforming (SAB) realized by a single‑antenna AAV moving along a predefined trajectory. By treating the flight positions of the AAV as elements of a virtual non‑uniform linear array (NULA), the authors create a synthetic aperture that provides directional gain toward a multi‑antenna ground base station (BS) while suppressing radiation in other directions, thereby enhancing secrecy against hybrid wiretappers that can both eavesdrop and jam.

The system model assumes a far‑field line‑of‑sight (LoS) A2G link with the virtual transmit array of length D and L nodes, and a uniform linear array (ULA) of N elements at the BS. Closed‑form expressions for the coordinates of each transmit and receive element are derived, leading to a compact channel matrix H = ρ(R) B_G Ĥ B_A, where B_A and B_G capture the phase shifts due to node positions and Ĥ contains the array response terms. Under the condition R ≫ D N/d, the authors approximate the asymptotic eigenvalue distribution of H and prove that the eigenvalues are minimized when the normalized node spacings δ_l follow the Fejér‑point distribution on