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Digital and Hybrid Precoding and RF Chain Selection Designs for Energy Efficient Multi-User MIMO-OFDM ISAC Systems

Po-Chun Kang, Ming-Chun Lee, Tzu-Chien Chiu, Ting-Yao Kuo, Ta-Sung Lee

TL;DR

This work tackles energy efficiency in wideband MIMO-OFDM ISAC systems by jointly optimizing transmit precoding and RF-chain activation under sensing constraints. It develops an FD optimization framework using hyperbolic tangent relaxation, quadratic transform, and WMMSE with SCA, and extends the approach to FC and PC hybrid architectures via matching and BCD strategies, supported by convergence and complexity analyses. The results show substantial EE gains over baseline schemes and demonstrate effective RF-chain ON/OFF control, with extensions to SE–power tradeoffs. The proposed methods offer practical guidance for designing energy-efficient ISAC transceivers in future wideband networks.

Abstract

Using multiple-input multiple-output (MIMO) with orthogonal frequency division multiplexing (OFDM) for integrated sensing and communication (ISAC) has attracted considerable attention in recent years. While most existing works focus on improving MIMO-OFDM ISAC performance, the impact of transmit power and radio-frequency (RF) circuit power consumption on energy efficiency (EE) remains relatively underexplored. To address this gap, this paper investigates joint precoding and RF chain selection for multi-user MIMO-OFDM ISAC systems, and develops energy-efficient designs for both fully digital and hybrid precoding architectures through the joint optimization of precoding and RF-chain activation. Specifically, we first formulate a novel EE maximization problem subject to sensing performance constraints. Then, efficient optimization algorithms are proposed for both architectures, together with analyses of their computational complexity and convergence behavior. Building on the proposed approaches, spectral efficiency-power consumption tradeoff designs are also provided. Simulation results demonstrate that, compared with existing schemes, the proposed approaches achieve significant improvements in the EE-sensing tradeoff for ISAC systems.

Digital and Hybrid Precoding and RF Chain Selection Designs for Energy Efficient Multi-User MIMO-OFDM ISAC Systems

TL;DR

This work tackles energy efficiency in wideband MIMO-OFDM ISAC systems by jointly optimizing transmit precoding and RF-chain activation under sensing constraints. It develops an FD optimization framework using hyperbolic tangent relaxation, quadratic transform, and WMMSE with SCA, and extends the approach to FC and PC hybrid architectures via matching and BCD strategies, supported by convergence and complexity analyses. The results show substantial EE gains over baseline schemes and demonstrate effective RF-chain ON/OFF control, with extensions to SE–power tradeoffs. The proposed methods offer practical guidance for designing energy-efficient ISAC transceivers in future wideband networks.

Abstract

Using multiple-input multiple-output (MIMO) with orthogonal frequency division multiplexing (OFDM) for integrated sensing and communication (ISAC) has attracted considerable attention in recent years. While most existing works focus on improving MIMO-OFDM ISAC performance, the impact of transmit power and radio-frequency (RF) circuit power consumption on energy efficiency (EE) remains relatively underexplored. To address this gap, this paper investigates joint precoding and RF chain selection for multi-user MIMO-OFDM ISAC systems, and develops energy-efficient designs for both fully digital and hybrid precoding architectures through the joint optimization of precoding and RF-chain activation. Specifically, we first formulate a novel EE maximization problem subject to sensing performance constraints. Then, efficient optimization algorithms are proposed for both architectures, together with analyses of their computational complexity and convergence behavior. Building on the proposed approaches, spectral efficiency-power consumption tradeoff designs are also provided. Simulation results demonstrate that, compared with existing schemes, the proposed approaches achieve significant improvements in the EE-sensing tradeoff for ISAC systems.
Paper Structure (28 sections, 2 theorems, 53 equations, 9 figures, 2 tables, 1 algorithm)

This paper contains 28 sections, 2 theorems, 53 equations, 9 figures, 2 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Literature Review
  3. Contributions
  4. System Model
  5. Communication Signal Model
  6. Sensing Signal Model
  7. Power Consumption and Energy Efficiency Models
  8. Transmit Antenna Array Architectures
  9. Energy Efficient Digital Precoding and RF Chain Selection Approaches
  10. Problem Formulation
  11. Proposed Iterative Design Approach
  12. Proposed Alternative Design Approaches
  13. Extension to Spectral Efficiency and Power Consumption Tradeoff Design
  14. Energy Efficient Design under Fully-Connected Architecture
  15. System Model and Problem Formulation
  16. ...and 13 more sections

Key Result

Lemma 1

Suppose that a target exists at angle $\theta$. Let $P_\text{th}$ be some lower bound satisfying $B_k\left(\mathbf{F}_k, \theta\right)\geq P_\text{th}, \forall k$. When the transmitted data symbols satisfy the i.i.d. standard Gaussian distribution assumption, the detection probability can be improve

Figures (9)

  • Figure 1: Illustrations of different antenna architectures.
  • Figure 2: EE-detection probability tradeoff for approaches with FD architecture in setup 1.
  • Figure 3: Number of activated RF chains as a function of $P_\text{th}$ for approaches with FD architecture in setup 1.
  • Figure 4: EE-detection probability tradeoff for approaches with FD architecture in setup 2.
  • Figure 5: EE-detection probability tradeoff for approaches with FC architecture in setup 1.
  • ...and 4 more figures

Theorems & Definitions (4)

  • Lemma 1
  • proof
  • Lemma 2
  • proof