Robust Energy Efficient Beamforming Design for ISAC Full-Duplex Communication Systems

This paper examines an integrated sensing and communication (ISAC) scheme for multi-user systems under full-duplex (FD) architecture. We examine an FD-ISAC system where the base station is responsible for target detection and shares the same resources for simultaneous downlink (DL) and uplink (UL) communication. For a green FD-ISAC architecture, our primary focus is addressing the robust energy efficiency maximization (EEM) problem. This involves the integrated beamforming design for the DL, UL, and radar users and UL transmission power. The optimization process follows constraints such as worst-case rate constraints, limitations imposed by bounded channel state information (CSI) error, transmit power constraints, and specific quality of service requirements. To address the EEM problem, we use an iterative algorithm that employs successive convex approximation (SCA) and second-order cone programming (SOCP) to achieve near-optimal resource allocation. Average energy efficiency and average spectral efficiency were compared for the proposed EEM algorithm and the benchmark spectral efficiency maximization (SEM) algorithm. Simulation results show that the FD-ISAC scheme significantly outperforms the conventional half-duplex scheme w.r.t. system performance.