Stacked Intelligent Metasurfaces for Efficient Holographic MIMO Communications in 6G
Stacked Intelligent Metasurfaces for Efficient Holographic MIMO Communications in 6G
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DOI：
10.1109/jsac.2023.3288261
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发表时间：
2023-05
影响因子：
16.4
通讯作者：
Jiancheng An;Chao Xu;D. W. K. Ng;G. C. Alexandropoulos;Chongwen Huang;Chau Yuen;L. Hanzo
中科院分区：
文献类型：
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作者：
Jiancheng An;Chao Xu;D. W. K. Ng;G. C. Alexandropoulos;Chongwen Huang;Chau Yuen;L. Hanzo
一项基于堆叠式智能超表面(SIM)的革命性技术能够直接在原生电磁波(EM)区域进行高级信号处理。SIM是由多个堆叠的亚表面层组成的复杂汞合金制成的，其性能可能优于单层亚表面对应物，如可重新配置的智能表面(RIS)和亚表面透镜。我们利用这种新的SIM来实现全息多输入多输出(HMIMO)通信，而不需要过多的射频(RF)链，这与现有的实现相比是一个巨大的优势。首先，我们提出了一种基于发射端(TX)和接收端(RX)的HMIMO通信系统。与传统的MIMO设计形成鲜明对比的是，SIM能够在电磁波传播时自动完成发射预编码和接收合并。这样，每个空间流可以被直接辐射并从相应的发送和接收端口恢复。其次，我们描述了最小化实际端到端信道矩阵与目标对角线信道矩阵之间的误差的问题，表示了一个无干扰的平行子信道系统。这是通过联合优化与TX-SIM和RX-SIM的所有亚表面层相关联的相移来实现的。然后，我们设计了一个梯度下降算法来解决由此产生的非凸问题。此外，我们从理论上分析了HMIMO的信道容量界限，并提供了一些基本的见解。最后，提供了大量的仿真结果来描述我们的SIM辅助的HMIMO系统，它量化了它的巨大的性能优势，例如，比传统的MIMO和它的RIS辅助的同类系统的容量提高了150%。
A revolutionary technology relying on Stacked Intelligent Metasurfaces (SIM) is capable of carrying out advanced signal processing directly in the native electromagnetic (EM) wave regime. An SIM is fabricated by a sophisticated amalgam of multiple stacked metasurface layers, which may outperform its single-layer metasurface counterparts, such as reconfigurable intelligent surfaces (RIS) and metasurface lenses. We harness this new SIM for implementing holographic multiple-input multiple-output (HMIMO) communications without requiring excessive radio-frequency (RF) chains, which is a substantial benefit compared to existing implementations. First of all, we propose an HMIMO communication system based on a pair of SIM at the transmitter (TX) and receiver (RX), respectively. In sharp contrast to the conventional MIMO designs, SIM is capable of automatically accomplishing transmit precoding and receiver combining, as the EM waves propagate through them. As such, each spatial stream can be directly radiated and recovered from the corresponding transmit and receive port. Secondly, we formulate the problem of minimizing the error between the actual end-to-end channel matrix and the target diagonal one, representing a flawless interference-free system of parallel subchannels. This is achieved by jointly optimizing the phase shifts associated with all the metasurface layers of both the TX-SIM and RX-SIM. We then design a gradient descent algorithm to solve the resultant non-convex problem. Furthermore, we theoretically analyze the HMIMO channel capacity bound and provide some fundamental insights. Finally, extensive simulation results are provided for characterizing our SIM-aided HMIMO system, which quantifies its substantial performance benefits, e.g., 150% capacity improvement over both conventional MIMO and its RIS-aided counterparts.