Outage-Constrained Max-Min Rate Optimization Design for STARS in Near-Field Communications

This letter investigates a near-field communication network assisted by simultaneously transmitting and reflecting surfaces (STARS), focusing on achieving rate fairness among users under both perfect and imperfect transmission designs. To maximize the worst user rate, we jointly optimize the programmable independent phase shifts of STARS and the transmit beamforming at the base station. The problem is ad dressed via an iterative algorithm combined with a penalty-based convex optimization procedure. We further extend the analysis from the perfect channel state information case to an outage constrained scenario, where user rates are defined based on outage probability. Numerical examples validate the effectiveness and feasibility of the proposed approach. The outage-constrained design successfully suppresses the average outage rate to the required level while also maximizing the worst-case transmission rate.