Title: Simultaneously Transmitting and Reflecting Surface (STARS) for Terahertz Communications Show Chinese title

Title: 太赫兹通信的同时发射和反射表面

Abstract: A simultaneously transmitting and reflecting surface (STARS) aided terahertz (THz) communication system is proposed. A novel power consumption model is proposed that depends on the type and resolution of the STARS elements. The spectral efficiency (SE) and energy efficiency (EE) are maximized in both narrowband and wideband THz systems by jointly optimizing the hybrid beamforming at the base station (BS) and the passive beamforming at the STARS. 1) For narrowband systems, independent phase-shift STARSs are investigated first. The resulting complex joint optimization problem is decoupled into a series of subproblems using penalty dual decomposition. Low-complexity element-wise algorithms are proposed to optimize the analog beamforming at the BS and the passive beamforming at the STARS. The proposed algorithm is then extended to the case of coupled phase-shift STARS. 2) For wideband systems, the spatial wideband effect at the BS and STARS leads to significant performance degradation due to the beam split issue. To address this, true time delayers (TTDs) are introduced into the conventional hybrid beamforming structure for facilitating wideband beamforming. An iterative algorithm based on the quasi-Newton method is proposed to design the coefficients of the TTDs. Finally, our numerical results confirm the superiority of the STARS over the conventional reconfigurable intelligent surface (RIS). It is also revealed that i) there is only a slight performance loss in terms of SE and EE caused by coupled phase shifts of the STARS in both narrowband and wideband systems, and ii) the conventional hybrid beamforming achieves comparable SE performance and much higher EE performance compared with the full-digital beamforming in narrowband systems but not in wideband systems, where the TTD-based hybrid beamforming is required for mitigating wideband beam split. Show Chinese abstract

Abstract: 一种同时发送和反射表面（STARS）辅助的太赫兹（THz）通信系统被提出。 提出了一种新的功耗模型，该模型取决于STARS元件的类型和分辨率。 通过联合优化基站（BS）的混合波束成形和STARS的被动波束成形，在窄带和宽带THz系统中最大化频谱效率（SE）和能量效率（EE）。 1）对于窄带系统，首先研究了独立相移STARS。 利用惩罚对偶分解将 resulting 复杂的联合优化问题分解为一系列子问题。 提出了低复杂度的逐元素算法来优化BS的模拟波束成形和STARS的被动波束成形。 然后将所提出的算法扩展到耦合相移STARS的情况。 2）对于宽带系统，由于波束分裂问题，BS和STARS的空间宽带效应会导致性能显著下降。 为了解决这个问题，将真时延器（TTDs）引入传统的混合波束成形结构以促进宽带波束成形。 提出了一种基于拟牛顿法的迭代算法来设计TTDs的系数。 最后，我们的数值结果证实了STARS相对于传统可重构智能表面（RIS）的优势。 还发现i）在窄带和宽带系统中，STARS的耦合相移仅导致SE和EE的轻微性能损失，ii）与全数字波束成形相比，传统混合波束成形在窄带系统中实现了相当的SE性能和更高的EE性能，但在宽带系统中则不是这样，其中需要基于TTD的混合波束成形来缓解宽带波束分裂。