A communication link aided by a reconfigurable intelligent surface (RIS) is studied in which the transmitter can control the state of the RIS via a finite-rate control link. Channel state information (CSI) is acquired at the receiver based on pilot-assisted channel estimation, and it may or may not be shared with the transmitter. Considering quasi-static fading channels with imperfect CSI, capacity-achieving signalling is shown to implement joint encoding of the transmitted signal and of the response of the RIS. This demonstrates the information-theoretic optimality of RIS-based modulation, or "single-RF MIMO" systems. In addition, a novel signalling strategy based on separate layered encoding that enables practical successive cancellation-type decoding at the receiver is proposed. Numerical experiments show that the conventional scheme that fixes the reflection pattern of the RIS, irrespective of the transmitted information, as to maximize the achievable rate is strictly suboptimal, and is outperformed by the proposed adaptive coding strategies at all practical signal-to-noise ratio (SNR) levels.
翻译:由可重新配置的智能表面(RIS)辅助的通信连接,在这种连接中,发射机可以通过有限节率控制链控制RIS状态。频道状态信息(CSI)是在试点辅助频道估计的基础上在接收器获得的,它可能与发报机共享。考虑到CSI不完善的准静态退缩通道,能力达到信号显示对传输信号和RIS反应进行联合编码。这显示了基于RIS的调制系统或“Single-RF MIMO”系统的信息理论最佳性。此外,还提出了基于不同层层编码的新信号战略,使接收器能够连续进行实际的取消类型解码。数字实验表明,无论传送的信息如何,固定RIS反射模式的传统办法,即最大限度地实现可达到的速率,严格来说是次于最优化的,而且在所有实际信号到氮比率(SNRR)级别上都被拟议的适应编码战略所超越。