Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Hybrid Beamfocusing Design for RSMA-Enabled Near-Field Wideband Communications

Jiasi Zhou, Chintha Tellambura

TL;DR

This work tackles the challenge of near-field wideband communications with extremely large antenna arrays by integrating rate-splitting multiple access (RSMA) with true-time-delay (TTD) based hybrid beamfocusing. A penalty-based minorization-maximization framework coupled with block-coordinate descent is developed to jointly optimize frequency-dependent and frequency-independent analog beamfocusing, digital beamfocusing, and common-rate allocation, with extensions to sub-connected architectures. The proposed scheme effectively compensates spatial wideband effects, achieves performance close to full digital beamforming, and outperforms SDMA and far-field approaches, while reducing RF chain requirements. These findings reveal RSMA's robustness and the practicality of TTD-based HAD for scalable, wideband near-field networks, opening avenues for ISAC and imperfect-CSI scenarios.

Abstract

Future wireless networks will utilize extremely large-scale antenna arrays (ELAAs) over high-frequency bands, which, however, produce near-field spherical wavefronts and spatial wideband effects. To exploit and mitigate these, this paper proposes a rate-splitting multiple access (RSMA)-enabled transmit scheme for wideband near-field communications (NFC). Our solution leverages true-time-delay (TTD)-based hybrid beamfocusing architectures to mitigate spatial wideband effect and reduce radio frequency chain requirements. The objective is to maximize the minimum rate by jointly optimizing frequency-dependent analog beamfocusing, frequency-independent analog beamfocusing, digital beamfocusing, and common rate allocation. To solve this complicated non-convex problem, we develop a penalty-based iterative algorithm that partitions the variables into three blocks and then employs block coordinate descent (BCD) to optimize each block alternately. This algorithm is further extended to support the sub-connected TTD-based analog beamfocusing architectures. Comprehensive simulation results indicate that our transmit scheme: 1) effectively compensates for spatial wideband effect, addressing a critical challenge in wideband operation; 2) achieves performance comparable to full digital beamfocusing while maintaining lower hardware complexity; 3) achieves substantial performance gains over the other two benchmarks.

Hybrid Beamfocusing Design for RSMA-Enabled Near-Field Wideband Communications

TL;DR

This work tackles the challenge of near-field wideband communications with extremely large antenna arrays by integrating rate-splitting multiple access (RSMA) with true-time-delay (TTD) based hybrid beamfocusing. A penalty-based minorization-maximization framework coupled with block-coordinate descent is developed to jointly optimize frequency-dependent and frequency-independent analog beamfocusing, digital beamfocusing, and common-rate allocation, with extensions to sub-connected architectures. The proposed scheme effectively compensates spatial wideband effects, achieves performance close to full digital beamforming, and outperforms SDMA and far-field approaches, while reducing RF chain requirements. These findings reveal RSMA's robustness and the practicality of TTD-based HAD for scalable, wideband near-field networks, opening avenues for ISAC and imperfect-CSI scenarios.

Abstract

Future wireless networks will utilize extremely large-scale antenna arrays (ELAAs) over high-frequency bands, which, however, produce near-field spherical wavefronts and spatial wideband effects. To exploit and mitigate these, this paper proposes a rate-splitting multiple access (RSMA)-enabled transmit scheme for wideband near-field communications (NFC). Our solution leverages true-time-delay (TTD)-based hybrid beamfocusing architectures to mitigate spatial wideband effect and reduce radio frequency chain requirements. The objective is to maximize the minimum rate by jointly optimizing frequency-dependent analog beamfocusing, frequency-independent analog beamfocusing, digital beamfocusing, and common rate allocation. To solve this complicated non-convex problem, we develop a penalty-based iterative algorithm that partitions the variables into three blocks and then employs block coordinate descent (BCD) to optimize each block alternately. This algorithm is further extended to support the sub-connected TTD-based analog beamfocusing architectures. Comprehensive simulation results indicate that our transmit scheme: 1) effectively compensates for spatial wideband effect, addressing a critical challenge in wideband operation; 2) achieves performance comparable to full digital beamfocusing while maintaining lower hardware complexity; 3) achieves substantial performance gains over the other two benchmarks.

Paper Structure

This paper contains 25 sections, 47 equations, 8 figures, 1 table, 4 algorithms.

Table of Contents

  1. Introduction
  2. Related Works
  3. Narrowband NFC
  4. Wideband NFC
  5. RSMA-enabled narrowband NFC
  6. Contributions
  7. System model and problem formulation
  8. Near-field wideband channel models
  9. TTD-based hybrid beamfocusing for RSMA systems
  10. RSMA-enabled digital beamfocusing
  11. TTD-based analog beamfocusing
  12. RSMA-enabled message decoding and transmit rate
  13. Problem formulation
  14. Algorithm design and properties analysis
  15. Subproblem w.r.t. $\{\mathbf{P}_m\}$, $\{C^c_{k,m}\}$, and $R_\text{r}$
  16. ...and 10 more sections

Figures (8)

  • Figure 1: Illustration of the multi-path near-field channel model.
  • Figure 2: RSMA-enabled Wideband NFC systems with TTD-based hybrid beamfocusing architecture.
  • Figure 3: Sub-connected TTD architecture for RSMA-enabled wideband NFC.
  • Figure 4: Max-min rate versus the number of users.
  • Figure 5: Max-min rate versus transmit power per subcarrier.
  • ...and 3 more figures