Effective Spectral Efficiency Maximization for Directional Pinching-Antenna-Assisted Multi-User MIMO Systems

Pinching-antenna systems (PASSs) have emerged as a promising waveguide-based architecture for high-frequency wireless communications. Recent directional PASS studies have shown that practical pinching antennas (PAs) exhibit directional, pencil-like radiation rather than idealized omnidirectional radiation. However, most existing designs focus on PA placement or instantaneous sum-rate maximization and neglect the reconfiguration time required for PA movement and rotation. This paper investigates reconfiguration-aware joint optimization for a multi-user downlink directional PASS with a finite frame duration. To evaluate transmission performance, an effective spectral efficiency metric is defined to account for both reconfiguration-induced rate gain and effective transmission-time reduction. Based on this metric, a joint optimization problem is formulated for user scheduling, PA positions, PA orientations, and digital beamforming. To tackle this mixed discrete–continuous non-convex problem, a reconfiguration-aware alternating optimization algorithm is developed by combining weighted minimum mean-square error (WMMSE)-based beamforming, local orientation search, projected position update, and restricted user scheduling. Simulation results show that the proposed scheme achieves higher effective spectral efficiency than representative fixed-configuration, sum-rate-oriented, and joint-search schemes. These results indicate that reconfiguration overhead should be considered, since instantaneous-rate-oriented designs may cause excessive PA movement or rotation and degrade effective spectral efficiency.