基于角度信息的1比特RIS波束赋形

Angle Information-Based Beamforming for 1-Bit RIS

智能超表面(Reconfigurable Intelligent Surface,RIS)技术是第六代移动通信网络(6th generation mobile networks,6G)的关键支撑技术之一,可显著增强信号强度和质量,减轻通信干扰,提升通信性能;相较于传统有源天线阵列,RIS硬件成本低,被动工作方式带来低功耗的特性。波束赋形技术是RIS辅助通信系统的关键技术之一,过去的研究主要集中在连续相位波束赋形上,解决典型的通信波束赋形目标,包括能量效率最大化、信噪比最大化以及传输速率最大化等。这些研究取得了显著的成果,为通信系统的性能提升做出了贡献。然而,在实际应用中,由于成本和硬件方面的限制,离散波束赋形设计更受青睐。现有的离散波束赋形方案难以保证最优性,且依赖于高开销的RIS级联信道估计。在这一背景下,本文提出了两种1比特RIS波束赋形方法,包括基于分割的最优波束赋形方法和基于贪婪策略的低复杂度波束赋形方法。这两种方法分别通过巧妙的分割和迭代优化,实现了只需角度信息即可生成指定方向高增益波束的目标。具体而言,基于分割的波束赋形方法通过复平面分割的方式,巧妙地设计各RIS单元的相位,可获得最优解;基于贪婪策略的波束赋形方法,通过对各RIS单元相位迭代优化的方式,寻找1比特相位配置,能够取得接近最优的性能且具有更低的复杂度。此外,随着RIS相位误差的增加,分割法相对于贪婪法略显优势。

Reconfigurable intelligent surface(RIS)technology is one of the key supporting technologies for sixthgeneration mobile communication networks(6G).This technology can significantly enhance signal strength and quality,reduce communication interference,and improve communication performance.Compared with the traditional active antenna array,RIS has lower hardware costs,and its passive working mode results in lower power consumption characteristics.Beamforming technology is one of the key technologies in RIS-assisted communication systems.Previous studies have mainly focused on continuous phase beamforming,addressing typical communication beamforming targets,including maximizing energy efficiency,signal-to-noise ratio,and transmission rate.These studies have achieved significant results and contributed to the performance improvement of communication systems.However,in practical applications,because of cost and hardware limitations,discrete-phase beamforming designs are favored.Existing discrete beamforming schemes cannot easily ensure optimality and rely on high-overhead RIS cascaded channel estimation.To address this issue,this study proposes two 1-bit RIS beamforming methods,including an optimal beamforming method based on segmentation and a low-complexity beamforming method based on a greedy strategy.Both beamforming methods require only angle information and achieve high beamforming gains in a specified direction via clever segmentation and iterative optimization,respectively.Specifically,the beamforming method based on segmentation cleverly designs the phase of each RIS unit through complex plane segmentation to obtain an optimal solution.The beamforming method based on a greedy strategy can achieve near-optimal performance and low complexity by iteratively optimizing the phase of each RIS unit to determine a 1-bit phase configuration.In addition,as the phase error of RIS increases,the segmentation method has slight advantages over the greedy method.