Fully Discrete and Phase-Coupled STAR-RIS-Aided MIMO Multiuser Communications Using SZFDPC

This paper proposes a practical, high-performance transceiver for STAR-RIS-aided MU-MIMO downlink systems with discrete, phase-coupled, quantized energy-splitting elements. The base station employs successive zero-forcing dirty paper coding to mitigate interference and approach capacity limits. To optimize the phases and energy splits of STAR-RIS, we first decompose its coefficient matrices and develop a powerful method to optimize discrete phases on one side. We then introduce an ingenious transformation that jointly optimizes phase coupling and energy splitting using the same phase optimization framework. Simulations show significant sum-rate gains over existing MU-MISO works and MU-MIMO scenarios, justifying the robustness and practicality of the proposed design.