Near-Field Full-Duplex ISAC Transceiver Hybrid Beamforming Design

Near-field integrated sensing and communication (ISAC) leverages distance and angle information to achieve the fusion of communication and high-precision sensing. When combined with full-duplex (FD) technology, it holds the potential to further enhance system capacity and spectral efficiency. However, the pronounced near-field effects introduce new design challenges for the integration of FD and ISAC. To address this issue, this paper proposes a near-field FD ISAC system based on a partially-connected hybrid analog-digital (HAD) architecture, which enables unified design for uplink/downlink communication and target sensing while reducing hardware overhead by minimizing the number of radio frequency chains. Subsequently, the Cramér–Rao Bound (CRB) for near-field distance and angle sensing is derived, and a hybrid beamforming optimization problem aimed at jointly minimizing the CRB is formulated. To tackle the non-convex coupling among the optimization variables, a dual-penalty decomposition-based alternating iterative algorithm is proposed, which decomposes the original problem and solves it through alternating iterations. Simulation results demonstrate that the proposed near-field FD ISAC scheme achieves a performance improvement of 4.09%–16.93% in angle estimation compared to far-field schemes, while exhibiting significant enhancements of 15.44%–31.77% in distance estimation and 11.31%–39.94% in angle estimation when compared to half-duplex schemes.