An, J., Xu, C., Ng, D. W. K., Alexandropoulos, G. C., Huang, C., Yuen, C., & Hanzo, L. (2023). Stacked Intelligent Metasurfaces for Efficient Holographic MIMO Communications in 6G. IEEE Journal on Selected Areas in Communications, 41(8), 2380–2396. https://doi.org/10.1109/jsac.2023.3288261
Abstract:
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.
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Funding Info:
This research / project is supported by the Ministry of Education, Singapore - Tier 2
Grant Reference no. : MOE-T2EP50220-0019
This research / project is supported by the Agency for Science, Technology and Research - Science and Engineering Research Council - MTC Programmatic Grant
Grant Reference no. : M22L1b0110
This research / project is supported by the Australian Research Council’s Discovery Project - N/A
Grant Reference no. : DP210102169, DP230100603
This research / project is supported by the EU’s Horizon Europe research and innovation programme - SNS JU TERRAMETA project
Grant Reference no. : 101097101
This research / project is supported by the China National Key R&D Program - N/A
Grant Reference no. : 2021YFA1000500
This research / project is supported by the National Natural Science Foundation of China - N/A
Grant Reference no. : 62101492
This research / project is supported by the Zhejiang Provincial Natural Science Foundation of China - N/A
Grant Reference no. : LR22F010002
This research / project is supported by the Zhejiang University Global Partnership Fund, Zhejiang University Education Foundation Qizhen Scholar Foundation, and Fundamental Research Funds for the Central Universities - N/A
Grant Reference no. : 2021FZZX001-21
This research / project is supported by the Engineering and Physical Sciences Research Council - N/A
Grant Reference no. : EP/W016605/1, EP/X01228X/1
This research / project is supported by the European Research Council’s Advanced Fellow Grant QuantCom - N/A
Grant Reference no. : 789028