Movable signals have emerged as a third approach to enable smart radio environments (SREs), complementing reconfigurable intelligent surfaces (RISs) and flexible antennas. This paper investigates their potential to enhance multi-user wireless systems. Focusing on two-user systems, we characterize the capacity regions of the multiple access channel (MAC) and broadcast channel (BC). Interestingly, movable signals can dynamically adjust the operating frequency to orthogonalize the user channels, thereby significantly expanding the capacity regions. We also study frequency optimization, constraining it in a limited frequency range, and show that movable signals provide up to 45% sum rate gain over fixed signals.

翻译：可移动信号已作为实现智能无线电环境（SRE）的第三种方法出现，补充了可重构智能表面（RIS）和柔性天线。本文研究了其在增强多用户无线系统方面的潜力。聚焦于双用户系统，我们刻画了多址接入信道（MAC）和广播信道（BC）的容量区域。有趣的是，可移动信号能够动态调整工作频率以正交化用户信道，从而显著扩展容量区域。我们还研究了频率优化，将其约束在有限频率范围内，并表明可移动信号相比固定信号可提供高达45%的和速率增益。