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Performance Analysis and Optimization for Movable Antenna Aided Wideband Communications

Lipeng Zhu, Wenyan Ma, Zhenyu Xiao, Rui Zhang

TL;DR

This work analyzes movable antennas (MAs) for wideband OFDM in frequency-selective channels, introducing a general multi-tap channel model where MA positions at the transmitter and receiver modulate both amplitudes and phases of path components. It derives a high-SNR upper bound on the OFDM rate under the arbitrarily large-region (ALR) assumption and the linearly independent over Q (LIA) condition, showing that MA positioning can realize maximum tap gains with flexible phase control. A parallel greedy ascent (PGA) algorithm and a simplified PGA are proposed to optimize MA positions under finite regions, with water-filling used for power allocation; simulations demonstrate that these methods closely approach the rate bound and outperform fixed-position antenna systems, especially in channels with many paths per tap or numerous taps. The results highlight the potential of MA-aided wideband communications to exploit spatial DoFs for substantial spectral efficiency gains, and point to future work in multiuser/multibeam configurations and MA-aware channel estimation.

Abstract

Movable antenna (MA) has emerged as a promising technology to enhance wireless communication performance by enabling the local movement of antennas at the transmitter (Tx) and/or receiver (Rx) for achieving more favorable channel conditions. As the existing studies on MA-aided wireless communications have mainly considered narrow-band transmission in flat fading channels, we investigate in this paper the MA-aided wideband communications employing orthogonal frequency division multiplexing (OFDM) in frequency-selective fading channels. Under the general multi-tap field-response channel model, the wireless channel variations in both space and frequency are characterized with different positions of the MAs. Unlike the narrow-band transmission where the optimal MA position at the Tx/Rx simply maximizes the single-tap channel amplitude, the MA position in the wideband case needs to balance the amplitudes and phases over multiple channel taps in order to maximize the OFDM transmission rate over multiple frequency subcarriers. First, we derive an upper bound on the OFDM achievable rate in closed form when the size of the Tx/Rx region for antenna movement is arbitrarily large. Next, we develop a parallel greedy ascent (PGA) algorithm to obtain locally optimal solutions to the MAs' positions for OFDM rate maximization subject to finite-size Tx/Rx regions. To reduce computational complexity, a simplified PGA algorithm is also provided to optimize the MAs' positions more efficiently. Simulation results demonstrate that the proposed PGA algorithms can approach the OFDM rate upper bound closely with the increase of Tx/Rx region sizes and outperform conventional systems with fixed-position antennas (FPAs) under the wideband channel setup.

Performance Analysis and Optimization for Movable Antenna Aided Wideband Communications

TL;DR

This work analyzes movable antennas (MAs) for wideband OFDM in frequency-selective channels, introducing a general multi-tap channel model where MA positions at the transmitter and receiver modulate both amplitudes and phases of path components. It derives a high-SNR upper bound on the OFDM rate under the arbitrarily large-region (ALR) assumption and the linearly independent over Q (LIA) condition, showing that MA positioning can realize maximum tap gains with flexible phase control. A parallel greedy ascent (PGA) algorithm and a simplified PGA are proposed to optimize MA positions under finite regions, with water-filling used for power allocation; simulations demonstrate that these methods closely approach the rate bound and outperform fixed-position antenna systems, especially in channels with many paths per tap or numerous taps. The results highlight the potential of MA-aided wideband communications to exploit spatial DoFs for substantial spectral efficiency gains, and point to future work in multiuser/multibeam configurations and MA-aware channel estimation.

Abstract

Movable antenna (MA) has emerged as a promising technology to enhance wireless communication performance by enabling the local movement of antennas at the transmitter (Tx) and/or receiver (Rx) for achieving more favorable channel conditions. As the existing studies on MA-aided wireless communications have mainly considered narrow-band transmission in flat fading channels, we investigate in this paper the MA-aided wideband communications employing orthogonal frequency division multiplexing (OFDM) in frequency-selective fading channels. Under the general multi-tap field-response channel model, the wireless channel variations in both space and frequency are characterized with different positions of the MAs. Unlike the narrow-band transmission where the optimal MA position at the Tx/Rx simply maximizes the single-tap channel amplitude, the MA position in the wideband case needs to balance the amplitudes and phases over multiple channel taps in order to maximize the OFDM transmission rate over multiple frequency subcarriers. First, we derive an upper bound on the OFDM achievable rate in closed form when the size of the Tx/Rx region for antenna movement is arbitrarily large. Next, we develop a parallel greedy ascent (PGA) algorithm to obtain locally optimal solutions to the MAs' positions for OFDM rate maximization subject to finite-size Tx/Rx regions. To reduce computational complexity, a simplified PGA algorithm is also provided to optimize the MAs' positions more efficiently. Simulation results demonstrate that the proposed PGA algorithms can approach the OFDM rate upper bound closely with the increase of Tx/Rx region sizes and outperform conventional systems with fixed-position antennas (FPAs) under the wideband channel setup.
Paper Structure (19 sections, 3 theorems, 31 equations, 11 figures, 1 algorithm)

This paper contains 19 sections, 3 theorems, 31 equations, 11 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. Overview of Movable Antenna (MA)
  3. Related Works
  4. Motivation and Contribution
  5. Organization and Notation
  6. System Model
  7. Channel Model
  8. Problem Formulation
  9. Performance Analysis
  10. Optimization Algorithms
  11. PGA Algorithm
  12. Simplified PGA Algorithm
  13. Simulation Results
  14. Simulation Setup and Benchmark Schemes
  15. Numerical Results
  16. ...and 4 more sections

Key Result

Lemma 1

If PDFs $\{f_{\Theta_{\tau}^{\ell}}(\hat{\vartheta}_{\tau}^{\ell})\}$ are continuous and bounded, then we always have where $\mathcal{J}$ denotes the set of all vectors in $N$-dimensional interval $[-1,1]^{N}$ which satisfy the LIA condition.

Figures (11)

  • Figure 1: Illustration of the considered MA-OFDM wideband communication system.
  • Figure 2: Illustration of the local 3D coordinate systems at the Tx/Rx and the corresponding AoDs/AoAs.
  • Figure 3: Evaluation of the convergence of the proposed PGA algorithm under different $K_{\max}$.
  • Figure 4: Evaluation of the convergence of the proposed simplified PGA algorithm under different $K_{\max}$.
  • Figure 5: Demonstration of the variation of the achievable rate and the normalized CIR power within the Rx region.
  • ...and 6 more figures

Theorems & Definitions (6)

  • Lemma 1
  • proof
  • Theorem 1
  • proof
  • Theorem 2
  • proof