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Physics-Compliant Modeling and Optimization of MIMO Systems Aided by Microwave Linear Analog Computers

Matteo Nerini, Bruno Clerckx

Abstract

Microwave linear analog computer (MiLAC) has emerged as a promising architecture for implementing linear multiple-input multiple-output (MIMO) processing in the analog domain, with radio frequency (RF) signals. Existing studies on MiLAC-aided communications rely on idealized channel models and neglect antenna mutual coupling. However, since MiLAC performs processing at RF, mutual coupling becomes critical and alters the implemented operation, not only the channel characteristics. In this paper, we develop a physics-compliant model for MiLAC-aided MIMO systems accounting for mutual coupling with multiport network theory. We derive end-to-end system models for scenarios with MiLACs at the transmitter, the receiver, or both, showing how mutual coupling impacts the linear transformation implemented by the MiLACs. Furthermore, we formulate and solve a mutual coupling aware MiLAC optimization problem, deriving a closed-form globally optimal solution that maximizes the received signal power. We establish the fundamental performance limits of MiLAC with mutual coupling, and derive three analytical results. First, mutual coupling is beneficial in MiLAC-aided systems, on average. Second, with mutual coupling, MiLAC performs as digital architectures equipped with a matching network, while having fewer RF chains. Third, with mutual coupling, MiLAC always outperforms digital architectures with no matching network. Numerical simulations confirm our theoretical findings.

Physics-Compliant Modeling and Optimization of MIMO Systems Aided by Microwave Linear Analog Computers

Abstract

Microwave linear analog computer (MiLAC) has emerged as a promising architecture for implementing linear multiple-input multiple-output (MIMO) processing in the analog domain, with radio frequency (RF) signals. Existing studies on MiLAC-aided communications rely on idealized channel models and neglect antenna mutual coupling. However, since MiLAC performs processing at RF, mutual coupling becomes critical and alters the implemented operation, not only the channel characteristics. In this paper, we develop a physics-compliant model for MiLAC-aided MIMO systems accounting for mutual coupling with multiport network theory. We derive end-to-end system models for scenarios with MiLACs at the transmitter, the receiver, or both, showing how mutual coupling impacts the linear transformation implemented by the MiLACs. Furthermore, we formulate and solve a mutual coupling aware MiLAC optimization problem, deriving a closed-form globally optimal solution that maximizes the received signal power. We establish the fundamental performance limits of MiLAC with mutual coupling, and derive three analytical results. First, mutual coupling is beneficial in MiLAC-aided systems, on average. Second, with mutual coupling, MiLAC performs as digital architectures equipped with a matching network, while having fewer RF chains. Third, with mutual coupling, MiLAC always outperforms digital architectures with no matching network. Numerical simulations confirm our theoretical findings.
Paper Structure (21 sections, 3 theorems, 93 equations, 8 figures, 1 table)

This paper contains 21 sections, 3 theorems, 93 equations, 8 figures, 1 table.

Table of Contents

  1. Introduction
  2. Modeling a MIMO System
  3. Model With Mutual Coupling
  4. Model With No Mutual Coupling
  5. Modeling a MIMO System with MiLAC at the Transmitter
  6. Model With Mutual Coupling
  7. Model With No Mutual Coupling
  8. Modeling a MIMO System with MiLAC at the Receiver
  9. Model With Mutual Coupling
  10. Model With No Mutual Coupling
  11. Modeling a MIMO System with MiLAC at both the Transmitter and Receiver
  12. Model With Mutual Coupling
  13. Model With No Mutual Coupling
  14. Physics-Compliant Optimization of MiLAC
  15. Optimization of MiLAC With Mutual Coupling
  16. ...and 6 more sections

Key Result

Proposition 1

With uncorrelated fading, i.e., when $\mathbb{E}[\mathbf{z}_{RT}^H\mathbf{z}_{RT}]=\rho\mathbf{I}$, mutual coupling between the MiLAC antennas improves the average received signal power, i.e.,

Figures (8)

  • Figure 1: Model of a MIMO system.
  • Figure 2: Model of a MIMO system with MiLAC at the transmitter.
  • Figure 3: Model of a MIMO system with MiLAC at the receiver.
  • Figure 4: Model of a MIMO system with MiLAC at both the transmitter and receiver.
  • Figure 5: Multi-antenna transmitter in a MISO system operating (a) MiLAC-aided beamforming, (b) digital beamforming with matching network, and (c) digital beamforming without matching network.
  • ...and 3 more figures

Theorems & Definitions (5)

  • Proposition 1
  • proof
  • Proposition 2
  • Proposition 3
  • proof