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Stacked Intelligent Metasurface-Enhanced MIMO OFDM Wideband Communication Systems

Zheao Li, Jiancheng An, Chau Yuen

TL;DR

This work introduces a fully-analog stacked intelligent metasurface (SIM) architecture for wideband MIMO-OFDM that performs beamforming in the electromagnetic wave domain to diagonalize the end-to-end channel and suppress inter-antenna interference. By cascading multiple metasurface layers (L TX-SIM and K RX-SIM), the system creates parallel subchannels and enables fully-analog spatial multiplexing with $N_{RF}=N_{TX}=S$, reducing baseband processing. The authors formulate a multi-carrier phase-shift optimization problem and solve it with a BCD-PCCP algorithm, achieving near-diagonal end-to-end channels across a finite effective bandwidth $B_e$ (around 20 MHz in their setup) and demonstrating substantial capacity gains (e.g., >$300\%$ over center-frequency configurations at 28 GHz with 16 subcarriers). Compared with fully-digital, hybrid, and DMA-based metasurface approaches, the SIM_MC configuration delivers significant capacity improvements with lower hardware complexity and energy consumption, highlighting its potential for high-capacity, energy-efficient wideband wireless links.

Abstract

Multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems rely on digital or hybrid digital and analog designs for beamforming against frequency-selective fading, which suffer from high hardware complexity and energy consumption. To address this, this work introduces a fully-analog stacked intelligent metasurfaces (SIM) architecture that directly performs wave-domain beamforming, enabling diagonalization of the end-to-end channel matrix and inherently eliminating inter-antenna interference (IAI) for MIMO OFDM transmission. By leveraging cascaded programmable metasurface layers, the proposed system establishes multiple parallel subchannels, significantly improving multi-carrier transmission efficiency while reducing hardware complexity. To optimize the SIM phase shift matrices, a block coordinate descent and penalty convex-concave procedure (BCD-PCCP) algorithm is developed to iteratively minimize the channel fitting error across subcarriers. Simulation results validate the proposed approach, determining the maximum effective bandwidth and demonstrating substantial performance improvements. Moreover, for a MIMO OFDM system operating at 28 GHz with 16 subcarriers, the proposed SIM configuration method achieves over 300% enhancement in channel capacity compared to conventional SIM configuration that only accounts for the center frequency.

Stacked Intelligent Metasurface-Enhanced MIMO OFDM Wideband Communication Systems

TL;DR

This work introduces a fully-analog stacked intelligent metasurface (SIM) architecture for wideband MIMO-OFDM that performs beamforming in the electromagnetic wave domain to diagonalize the end-to-end channel and suppress inter-antenna interference. By cascading multiple metasurface layers (L TX-SIM and K RX-SIM), the system creates parallel subchannels and enables fully-analog spatial multiplexing with , reducing baseband processing. The authors formulate a multi-carrier phase-shift optimization problem and solve it with a BCD-PCCP algorithm, achieving near-diagonal end-to-end channels across a finite effective bandwidth (around 20 MHz in their setup) and demonstrating substantial capacity gains (e.g., > over center-frequency configurations at 28 GHz with 16 subcarriers). Compared with fully-digital, hybrid, and DMA-based metasurface approaches, the SIM_MC configuration delivers significant capacity improvements with lower hardware complexity and energy consumption, highlighting its potential for high-capacity, energy-efficient wideband wireless links.

Abstract

Multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems rely on digital or hybrid digital and analog designs for beamforming against frequency-selective fading, which suffer from high hardware complexity and energy consumption. To address this, this work introduces a fully-analog stacked intelligent metasurfaces (SIM) architecture that directly performs wave-domain beamforming, enabling diagonalization of the end-to-end channel matrix and inherently eliminating inter-antenna interference (IAI) for MIMO OFDM transmission. By leveraging cascaded programmable metasurface layers, the proposed system establishes multiple parallel subchannels, significantly improving multi-carrier transmission efficiency while reducing hardware complexity. To optimize the SIM phase shift matrices, a block coordinate descent and penalty convex-concave procedure (BCD-PCCP) algorithm is developed to iteratively minimize the channel fitting error across subcarriers. Simulation results validate the proposed approach, determining the maximum effective bandwidth and demonstrating substantial performance improvements. Moreover, for a MIMO OFDM system operating at 28 GHz with 16 subcarriers, the proposed SIM configuration method achieves over 300% enhancement in channel capacity compared to conventional SIM configuration that only accounts for the center frequency.

Paper Structure

This paper contains 18 sections, 1 theorem, 30 equations, 11 figures, 2 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. The Proposed SIM-enhanced MIMO OFDM Wideband Communication System Model
  3. SIM-enhanced MIMO OFDM Transceiver Architecture
  4. Wideband MIMO Channel Model
  5. SIM-Enhanced MIMO OFDM System Model
  6. Problem Formulation and Solution of the Proposed Wideband SIM for MIMO OFDM
  7. Problem Formulation
  8. Solution for Phase Shift Optimization
  9. Performance Analysis of the Proposed BCD-PCCD Algorithm
  10. Convergence Analysis
  11. Complexity Analysis
  12. Results and Analysis
  13. Simulation Configurations and Evaluation Criteria
  14. Performance Evaluation across OFDM Parameters
  15. Performance under Different System Parameters
  16. ...and 3 more sections

Key Result

Lemma 1

By leveraging the matrix vectorization method, the objective function $\mathrm{\Gamma}$ can be transformed into a standard quadratic form w.r.t. w.r.t. $\bm{\phi}^l$ and $\bm{\psi}^k$, respectively, as shown in st.ppp and st.qqq at the top of the next page, where $\mathbf{P}_i = \mathbf{P}_i^\mathbb

Figures (11)

  • Figure 1: The SIM-enhanced wideband MIMO OFDM communication system.
  • Figure 2: The architecture of the SIM.
  • Figure 3: Normalized fitting error $\Omega$ versus system bandwidth $B$, showing the maximum effective bandwidth $B_e$ where interference-free diagonalization is achieved.
  • Figure 4: The per-subcarrier fitting NMSE $\mathcal{S}$ under different $B_e$ setups, where we consider a fixed subcarrier number of $N_e=16$ and varying subcarrier spacing.
  • Figure 5: The channel capacity $C$ versus the number of subcarriers $N_e$ at the fixed optimization bandwidth $B_e = 20$ MHz.
  • ...and 6 more figures

Theorems & Definitions (10)

  • Remark 1
  • Remark 2
  • Remark 3
  • Remark 4
  • Remark 5
  • Remark 6
  • Remark 7
  • Lemma 1
  • proof
  • Remark 8