CRB-Rate Tradeoff in RSMA-Enabled Near-Field Integrated Multi-Target Sensing and Multi-User Communications

Abstract

Near-field integrated sensing and communication (NF-ISAC) combines wireless communication with simultaneous angle and distance sensing. However, this dual functionality creates a complex interference environment. Existing NF-ISAC designs offer limited flexibility in managing such interference, highlighting the need for more advanced strategies. To address this, we propose a rate-splitting multiple access (RSMA) scheme for NF-ISAC, leveraging both fully and partially connected hybrid analog-digital (HAD) beamforming architectures. We derive the Cramér-Rao bound (CRB) for joint distance and angle sensing and characterize the tradeoff between the max-min communication rate and multi-target CRB. To explore the CRB-rate Pareto boundary, we formulate a sensing-centric optimization problem under communication rate constraints. For the fully connected HAD architecture, a penalty dual decomposition (PDD)-based double-loop algorithm is developed, while a two-stage approach is used to reduce complexity. This framework is also extended to the partially connected case. Simulations show that the proposed schemes achieve performance comparable to a fully digital beamformer with fewer RF chains, effectively balancing hardware efficiency and system performance. Furthermore, the schemes significantly outperform space division multiple access and far-field ISAC, delivering lower sensing error and an expanded CRB-rate region.