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Near-field Hybrid Beamforming for Terahertz-band Integrated Sensing and Communications

Ahmet M. Elbir, Abdulkadir Celik, Ahmed M. Eltawil

TL;DR

This work tackles THz ISAC in the near-field where beam-squint and spherical-wavefront effects degrade performance. It introduces a hybrid beamforming framework built on alternating optimization: (i) select analog near-field beams from a dictionary of steering vectors via OMP, (ii) compute baseband and JRC beams, and (iii) employ a beam-squint-aware baseband to transfer squint compensation from the analog domain to digital processing. The key contribution is the BSA approach that achieves SD-like performance without hardware upgrades, enabling efficient THz-ISAC with reduced cost and power. Results show spectral efficiency approaching fully digital designs and outperforming far-field designs, particularly for bandwidths up to about $B=30$ GHz, demonstrating practical viability for near-field THz ISAC systems.

Abstract

Terahertz (THz) band communications and integrated sensing and communications (ISAC) are two main facets of the sixth generation wireless networks. In order to compensate the severe attenuation, the THz wireless systems employ large arrays, wherein the near-field beam-squint severely degrades the beamforming accuracy. Contrary to prior works that examine only either narrowband ISAC beamforming or far-field models, we introduce an alternating optimization technique for hybrid beamforming design in near-field THz-ISAC scenario. We also propose an efficient approach to compensate near-field beam-squint via baseband beamformers. Via numerical simulations, we show that the proposed approach achieves satisfactory spectral efficiency performance while accurately estimating the near-field beamformers and mitigating the beam-squint without additional hardware components.

Near-field Hybrid Beamforming for Terahertz-band Integrated Sensing and Communications

TL;DR

This work tackles THz ISAC in the near-field where beam-squint and spherical-wavefront effects degrade performance. It introduces a hybrid beamforming framework built on alternating optimization: (i) select analog near-field beams from a dictionary of steering vectors via OMP, (ii) compute baseband and JRC beams, and (iii) employ a beam-squint-aware baseband to transfer squint compensation from the analog domain to digital processing. The key contribution is the BSA approach that achieves SD-like performance without hardware upgrades, enabling efficient THz-ISAC with reduced cost and power. Results show spectral efficiency approaching fully digital designs and outperforming far-field designs, particularly for bandwidths up to about GHz, demonstrating practical viability for near-field THz ISAC systems.

Abstract

Terahertz (THz) band communications and integrated sensing and communications (ISAC) are two main facets of the sixth generation wireless networks. In order to compensate the severe attenuation, the THz wireless systems employ large arrays, wherein the near-field beam-squint severely degrades the beamforming accuracy. Contrary to prior works that examine only either narrowband ISAC beamforming or far-field models, we introduce an alternating optimization technique for hybrid beamforming design in near-field THz-ISAC scenario. We also propose an efficient approach to compensate near-field beam-squint via baseband beamformers. Via numerical simulations, we show that the proposed approach achieves satisfactory spectral efficiency performance while accurately estimating the near-field beamformers and mitigating the beam-squint without additional hardware components.
Paper Structure (10 sections, 1 theorem, 28 equations, 3 figures, 1 algorithm)

This paper contains 10 sections, 1 theorem, 28 equations, 3 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model & Problem Formulation
  3. Communications Model
  4. THz Channel Model
  5. Beam-Squint Effect
  6. Radar Model
  7. Problem Formulation
  8. Hybrid Beamformer Design
  9. Numerical Experiments
  10. Summary

Key Result

Theorem 1

Denote $\mathbf{u}\in \mathbb{C}^{N_\mathrm{T}}$ and $\mathbf{v}_m \in \mathbb{C}^{N_\mathrm{T}}$ as the arbitrary near-field steering vectors corresponding to the physical (i.e., $\{\phi_{l},r_{l}\}$) and spatial (i.e., $\{\bar{\phi}_{m,l}, \bar{r}_{m,l}\}$) locations given in (steeringVectorPhy2) where $\eta_m = \frac{f_c}{f_m}$ represents the proportional deviation of DoA/ranges.

Figures (3)

  • Figure 1: Near-field ISAC scenario, wherein received signal wavefront for the communication user/targets in far-field (near-field) is plane-wave (spherical-wave).
  • Figure 2: SE performance versus SNR.
  • Figure 3: SE performance versus bandwidth.

Theorems & Definitions (2)

  • Theorem 1
  • proof