Simultaneously Transmitting and Reflecting Surface (STARS) for Terahertz Communications
Simultaneously Transmitting and Reflecting Surface (STARS) for Terahertz Communications
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DOI：
10.1109/jstsp.2023.3279621
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发表时间：
2022-12
影响因子：
7.5
通讯作者：
Zhao-Jie Wang;Xidong Mu;Jiaqi Xu;Yuanwei Liu
中科院分区：
文献类型：
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作者：
Zhao-Jie Wang;Xidong Mu;Jiaqi Xu;Yuanwei Liu
提出了一种同时发射和反射的星面辅助太赫兹通信系统。提出了一种基于STARS元素类型和分辨率的新型功耗模型。通过共同优化基站混合波束形成和星空被动波束形成，实现窄带和宽带太赫兹系统频谱效率和能量效率的最大化。1)对于窄带系统，首先研究独立相移星。利用惩罚对偶分解将得到的复杂联合优化问题解耦为一系列子问题。提出了一种低复杂度的单元算法来优化BS处的模拟波束形成和STARS处的无源波束形成。然后将该算法推广到相移星耦合的情况。2)对于宽带系统，由于波束分裂问题，在BS和STARS处的空间宽带效应导致性能显著下降。为了解决这个问题，在传统的混合波束形成结构中引入了真时间延迟器（TTDs），以促进宽带波束形成。提出了一种基于拟牛顿法的迭代算法来设计ttd的系数。最后，我们的数值结果证实了STARS相对于传统的可重构智能曲面（RIS）的优越性。研究还发现，在窄带和宽带系统中，由于STARS的耦合相移，在SE和EE方面的性能损失很小；在窄带系统中，传统的混合波束形成与全数字波束形成相比具有相当的SE性能和更高的EE性能，而在宽带系统中则没有，而在宽带系统中，需要基于ttd的混合波束形成来缓解宽带波束分裂。
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.