通过堆叠智能超表面实现无基带宽带多用户多输入多输出正交频分复用
Baseband-Free Wideband MU-MIMO OFDM via Stacked Intelligent Metasurfaces
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中文总结 AI 辅助
研究提出由两个级联堆叠智能超表面实现的无基带宽带MU-MIMO OFDM发射机架构，将相关调制等从数字基带移至波域，通过特定设计和框架解决问题，验证了该架构在MU-MIMO OFDM性能等方面的有效性。
中文摘要 AI 辅助
本文提出了一种由两个级联堆叠智能超表面（SIM）实现的新型无基带宽带多用户多输入多输出正交频分复用（MU-MIMO OFDM）发射机架构。与传统无线发射机不同，该设计将符号加载、MU-MIMO预编码和OFDM调制从数字基带转移到波域。具体而言，在第一个SIM（SIM₁）中，可编程符号加载接口将一个堆叠虚拟子载波系数向量加载到公共单色载波上，其余层执行从数据流到端口子载波域的信道自适应MU-MIMO预编码。然后，第二个SIM（SIM₂）通过直接在波域实现离散傅里叶逆变换（IDFT）和循环前缀（CP）插入算子来实现离线配置的波域OFDM调制。基于此架构，开发了一个波域系统模型，明确表征从块级系数到辐射OFDM子载波的虚拟到物理转换。SIM₁和SIM₂的设计分别被公式化为两个算子拟合问题，分别针对块对角宽带预编码器和理想OFDM调制算子。在实际离散相位约束下，为两个SIM阶段开发了基于量化感知训练的梯度下降（QAT-GD）框架。数值结果验证了所提出优化的有效性、合成波域功能的正确性以及所得架构的强大端到端MU-MIMO OFDM性能。
英文摘要
This paper proposes a novel baseband-free wideband MU-MIMO OFDM transmitter architecture enabled by two cascaded stacked intelligent metasurfaces (SIMs). Unlike conventional wireless transmitters, the proposed design shifts symbol loading, MU-MIMO precoding, and OFDM modulation from digital baseband to the wave domain. Specifically, in the first SIM (SIM$_1$), a programmable symbol-loading interface first loads one stacked virtual-subcarrier coefficient vector onto a common monochromatic carrier, while the remaining layers perform channel-adaptive MU-MIMO precoding from the data streams to the port-subcarrier domain. Then, the second SIM (SIM$_2$) realizes offline-configured wave-domain OFDM modulation by implementing the inverse discrete Fourier transform (IDFT) and cyclic-prefix (CP) insertion operator directly in the wave domain. Based on this architecture, we develop a wave-domain system model that explicitly characterizes the virtual-to-physical transition from block-level coefficients to radiated OFDM subcarriers. The designs of SIM$_1$ and SIM$_2$ are formulated as two operator-fitting problems, respectively targeting a block-diagonal wideband precoder and the ideal OFDM modulation operator. Under practical discrete phase constraints, we develop a quantization-aware training-based gradient descent (QAT-GD) framework for both SIM stages. Numerical results verify the effectiveness of the proposed optimization, the correctness of the synthesized wave-domain functionalities, and the strong end-to-end MU-MIMO OFDM performance of the resulting architecture.
