Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Coupler Position Optimization and Channel Estimation for Flexible Coupler Aided Multiuser Communication

Xiaodan Shao, Chuangye Shan, Weihua Zhuang, Xuemin Shen

TL;DR

This work introduces a distributed flexible coupler (FC) array where each FC antenna contains one fixed active element and multiple movable passive couplers, enabling mechanical beamforming without moving active ports. By embedding LPUs at each FC site and connecting to a central CPU, the design achieves decentralized processing with reduced data exchange and hardware costs. The authors formulate a joint optimization of coupler positions and digital beamforming to maximize the downlink sum rate under movement and power constraints, and develop a distributed successive convex approximation (SCA) algorithm to solve it. They also propose pilot-assisted centralized and distributed channel-estimation schemes that leverage structured pilots and sparse recovery to accurately reconstruct channel state information with reduced overhead. Simulations show the distributed FC array can closely match the performance of a fully active array while significantly reducing hardware requirements and energy consumption, and that the proposed channel-estimation methods outperform benchmarks in pilot overhead and accuracy.

Abstract

In this paper, we propose a distributed flexible coupler (FC) array to enhance communication performance with low hardware cost. At each FC antenna, there is one fixed-position active antenna and multiple passive couplers that can move within a designated region around the active antenna. Moreover, each FC antenna is equipped with a local processing unit (LPU). All LPUs exchange signals with a central processing unit (CPU) for joint signal processing. We study an FC-aided multiuser multiple-input multiple-output (MIMO) system, where an FC array base station (BS) is deployed to enhance the downlink communication between the BS and multiple single-antenna users. We formulate optimization problems to maximize the achievable sum rate of users by jointly optimizing the coupler positions and digital beamforming, subject to movement constraints on the coupler positions and the transmit power constraint. To address the resulting nonconvex optimization problem, the digital beamforming is expressed as a function of the FC position vectors, which are then optimized using the proposed distributed coupler position optimization algorithm. Considering a structured time domain pattern of pilots and coupler positions, pilot-assisted centralized and distributed channel estimation algorithms are designed under the FC array architecture. Simulation results demonstrate that the distributed FC array achieves substantial rate gains over conventional benchmarks in multiuser systems without moving active antennas, and approaches the performance of fully active arrays while significantly reducing hardware cost and power consumption. Moreover, the proposed channel estimation algorithms outperform the benchmark schemes in terms of both pilot overhead and channel reconstruction accuracy.

Coupler Position Optimization and Channel Estimation for Flexible Coupler Aided Multiuser Communication

TL;DR

This work introduces a distributed flexible coupler (FC) array where each FC antenna contains one fixed active element and multiple movable passive couplers, enabling mechanical beamforming without moving active ports. By embedding LPUs at each FC site and connecting to a central CPU, the design achieves decentralized processing with reduced data exchange and hardware costs. The authors formulate a joint optimization of coupler positions and digital beamforming to maximize the downlink sum rate under movement and power constraints, and develop a distributed successive convex approximation (SCA) algorithm to solve it. They also propose pilot-assisted centralized and distributed channel-estimation schemes that leverage structured pilots and sparse recovery to accurately reconstruct channel state information with reduced overhead. Simulations show the distributed FC array can closely match the performance of a fully active array while significantly reducing hardware requirements and energy consumption, and that the proposed channel-estimation methods outperform benchmarks in pilot overhead and accuracy.

Abstract

In this paper, we propose a distributed flexible coupler (FC) array to enhance communication performance with low hardware cost. At each FC antenna, there is one fixed-position active antenna and multiple passive couplers that can move within a designated region around the active antenna. Moreover, each FC antenna is equipped with a local processing unit (LPU). All LPUs exchange signals with a central processing unit (CPU) for joint signal processing. We study an FC-aided multiuser multiple-input multiple-output (MIMO) system, where an FC array base station (BS) is deployed to enhance the downlink communication between the BS and multiple single-antenna users. We formulate optimization problems to maximize the achievable sum rate of users by jointly optimizing the coupler positions and digital beamforming, subject to movement constraints on the coupler positions and the transmit power constraint. To address the resulting nonconvex optimization problem, the digital beamforming is expressed as a function of the FC position vectors, which are then optimized using the proposed distributed coupler position optimization algorithm. Considering a structured time domain pattern of pilots and coupler positions, pilot-assisted centralized and distributed channel estimation algorithms are designed under the FC array architecture. Simulation results demonstrate that the distributed FC array achieves substantial rate gains over conventional benchmarks in multiuser systems without moving active antennas, and approaches the performance of fully active arrays while significantly reducing hardware cost and power consumption. Moreover, the proposed channel estimation algorithms outperform the benchmark schemes in terms of both pilot overhead and channel reconstruction accuracy.
Paper Structure (21 sections, 99 equations, 10 figures, 3 algorithms)

This paper contains 21 sections, 99 equations, 10 figures, 3 algorithms.

Table of Contents

  1. Introduction
  2. System Model
  3. Distributed Flexible Coupler Array
  4. Channel Model
  5. Mechanical Beamforming
  6. Signal Model
  7. Optimization of Coupler Positions
  8. Problem Formulation
  9. MMSE-Based Digital Beamforming
  10. Coupler Position Optimization Algorithm
  11. Channel Estimation for Flexible Coupler Systems
  12. Centralized Channel Estimation
  13. Distributed Channel Estimation
  14. Processing at local nodes
  15. Processing at central node
  16. ...and 6 more sections

Figures (10)

  • Figure 1: Proposed distributed FC array for multiuser systems.
  • Figure 2: Structured pilot pattern in the time domain.
  • Figure 3: Channel power gain (dB) between the FC array and the user with $N=1$, $K=1$, $M=5$, $P=30$ dBm, and $L_k=15$.
  • Figure 4: Achievable rate versus maximum transmit power for different schemes with $N=2$, $K=3$, $M=15$, $P=30$ dBm, and $L_k=15$.
  • Figure 5: Achievable rate versus number of users with $N=2$, $M=10$, $P=30$ dBm, and $L_k=15$.
  • ...and 5 more figures