This paper proposes an energy-efficient scheme for multicell multiple-input, multiple-output (MIMO) simultaneous transmit and reflect (STAR) reconfigurable intelligent surfaces (RIS)-assisted broadcast channels by employing rate splitting (RS) and improper Gaussian signaling (IGS). Regular RISs can only reflect signals. Thus, a regular RIS can assist only when the transmitter and receiver are in the reflection space of the RIS. However, a STAR-RIS can simultaneously transmit and reflect, thus providing a 360-degrees coverage. In this paper, we assume that transceivers may suffer from I/Q imbalance (IQI). To compensate for IQI, we employ IGS. Moreover, we employ RS to manage intracell interference. We show that RIS can significantly improve the energy efficiency (EE) of the system when RIS components are carefully optimized. Additionally, we show that STAR-RIS can significantly outperform a regular RIS when the regular RIS cannot cover all the users. We also show that RS can highly increase the EE comparing to treating interference as noise.

翻译：本文针对多小区多输入多输出（MIMO）同时透射反射（STAR）可重构智能表面（RIS）辅助的广播信道，提出一种结合速率分割（RS）与非高斯信令（IGS）的能效方案。传统RIS仅能反射信号，因此仅当发射机与接收机位于RIS的反射空间时才能提供辅助。然而，STAR-RIS可同时实现透射与反射，从而提供360度全覆盖。本文假设收发机可能遭受I/Q不平衡（IQI）影响，为此采用IGS进行补偿，并利用RS管理小区内干扰。研究表明，当RIS元件经过精心优化时，RIS可显著提升系统能效（EE）。此外，当传统RIS无法覆盖所有用户时，STAR-RIS的性能远超传统RIS。结果还表明，相较于将干扰视作噪声的处理方式，RS能大幅提升系统能效。