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Rethinking Mutual Coupling in Movable Antenna MIMO Systems

Tianyi Liao, Wei Guo, Jun Qian, Shenghui Song, Jun Zhang, Khaled B. Letaief

Abstract

Movable antenna (MA) systems have emerged as a promising technology for future wireless communication systems. The movement of antennas gives rise to mutual coupling (MC) effects, which have been previously ignored and can be exploited to enhance the capacity of multiple-input multiple-output (MIMO) systems. To this end, we first model an MA-enabled point-to-point MIMO communication system with MC effects using a circuit-theoretic framework. The capacity maximization problem is then formulated as a non-concave optimization problem and solved via a block coordinate ascent (BCA)-based algorithm. The subproblem of optimizing MA positions is challenging due to the presence of the analytically intractable MC matrices. To overcome this difficulty, we develop a trust region method (TRM)-based algorithm to optimize MA positions, wherein Sylvester equations are employed to compute the derivatives of the inverse square roots of the MC matrices. Simulation results show significant capacity gains from leveraging MC effects, primarily due to customizable MC matrices and superdirectivity.

Rethinking Mutual Coupling in Movable Antenna MIMO Systems

Abstract

Movable antenna (MA) systems have emerged as a promising technology for future wireless communication systems. The movement of antennas gives rise to mutual coupling (MC) effects, which have been previously ignored and can be exploited to enhance the capacity of multiple-input multiple-output (MIMO) systems. To this end, we first model an MA-enabled point-to-point MIMO communication system with MC effects using a circuit-theoretic framework. The capacity maximization problem is then formulated as a non-concave optimization problem and solved via a block coordinate ascent (BCA)-based algorithm. The subproblem of optimizing MA positions is challenging due to the presence of the analytically intractable MC matrices. To overcome this difficulty, we develop a trust region method (TRM)-based algorithm to optimize MA positions, wherein Sylvester equations are employed to compute the derivatives of the inverse square roots of the MC matrices. Simulation results show significant capacity gains from leveraging MC effects, primarily due to customizable MC matrices and superdirectivity.
Paper Structure (11 sections, 32 equations, 6 figures, 1 algorithm)

This paper contains 11 sections, 32 equations, 6 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model and Problem Formulation
  3. MA-Enabled MIMO System
  4. Circuit-Based Communication Model
  5. Problem Formulation
  6. BCA-Based Algorithm
  7. Update of $\mathbf{Q}$
  8. Update of $t_m$
  9. Update of $r_n$
  10. Simulation Results
  11. Conclusion and Future Work

Figures (6)

  • Figure 1: System model of a point-to-point MIMO communication system equipped with $M$ transmit MAs and $N$ receive MAs.
  • Figure 2: Multiport circuit representation of the MA system with MC.
  • Figure 3: TRM for updating $t_m$.
  • Figure 4: Convergence behaviors of Algorithm \ref{['alg:bca']}.
  • Figure 5: Impact of number of MAs ($M=N$).
  • ...and 1 more figures

Theorems & Definitions (4)

  • Remark 1
  • Remark 2
  • Remark 3
  • Remark 4