LAUSR

This letter proposes a novel energy-efficient design for RIS-assisted integrated sensing and communication (ISAC) systems by explicitly incorporating Cramér-Rao Bound (CRB) constraints into the joint beamforming optimization. Unlike existing methods that rely on heuristic sensing metrics, we rigorously enforce DOA estimation accuracy through CRB constraints while meeting SINR and power limits. An alternating optimization algorithm is developed, leveraging SCA-based SOCP for transmit beamforming and an exact-penalty projected gradient method for sensing design. Simulation results show that the proposed method achieves notable improvements in both energy efficiency and sensing accuracy under limited power budgets.