Secure and Robust Beamforming for D2D-Aided ISAC Networks

Abstract

This paper proposes a secure and robust transceiver beamforming scheme to enhance the performance of device-to-device (D2D)-aided full-duplex integrated sensing and communication (ISAC) networks under imperfect channel state information (CSI). A joint optimization framework is developed to simultaneously optimize transceiver beamforming at the ISAC base station (BS) and transmit beamforming at D2D transmitters, with the aim of maximizing the worst-case sensing signal-to-interference-plus-noise ratio (SINR) while guaranteeing secure communication and quality-of-service (QoS) for cellular users (CUs) and D2D pairs. To address the intractable issue of the formulated joint optimization problem, we propose a robust transformation method based on the generalized S-lemma to convert CSI uncertainty constraints into tractable linear matrix inequalities (LMIs), enabling efficient handling of bounded channel errors. Subsequently, we propose an alternating optimization (AO) algorithm integrated with a double-checking strategy via semidefinite relaxation (SDR), where inner-layer feasibility verification and outer-layer rank-one validation ensure solution feasibility, and a rank penalty term accelerates convergence. Numerical results show that, compared to state-of-the-art schemes, the proposed scheme achieves significant performance improvements. These results confirm the robustness of the proposed method against complex interference and active eavesdropping threats, and highlight its superiority in balancing sensing-communication trade-offs for D2D-aided ISAC networks.