Bessel Beam Optimization for Near-Field THz Communications under UE Location Uncertainty

2026-07-08

AI Summary

This work addresses the challenge in terahertz communications where user equipment (UE) often resides within the near-field region of antenna arrays with uncertain positioning, rendering conventional far-field beamforming ineffective. To overcome this, the paper proposes a phase-only controllable Bessel-like near-field beamforming scheme that optimizes the Bessel cone angle to maximize downlink spectral efficiency. For deterministic, Gaussian, and uniform UE location uncertainties, the authors derive, for the first time, low-complexity closed-form approximations enabling analytical optimization of near-field Bessel beams. The proposed method achieves performance within 0.1% of exhaustive search across diverse frequencies, UE locations, and array sizes, while reducing configuration complexity to O(1).

Abstract

To achieve the desired coverage and capacity levels, future terahertz (THz) wireless systems are envisioned to utilize extremely large antenna arrays. At THz frequencies, the combination of short wavelengths and large array apertures often makes many of the conventional far-field assumptions invalid in practice. As a result, many UEs operate in the radiative near-field zone, where novel near-field beam synthesis methods become viable. This paper studies phase-only Bessel-like near-field beam configurations for downlink THz multiple-input multiple-output links under imperfect UE location knowledge. We first formulate a spectral efficiency maximization problem with respect to the "Bessel cone angle''. We then derive low-complexity closed-form approximations for the optimal Bessel beam configuration for: (i)deterministic UE location; (ii)Gaussian and (iii)uniform error in the UE location. Finally, through extensive simulations across multiple signal frequencies, UE locations, and array sizes, we show that our proposed simple closed-form approximations closely match (under 0.1% difference) the best performance achieved via exhaustive search, while simultaneously reducing the configuration complexity down to as low as O(1).

Problem

• Bessel beam
• near-field
• THz communications
• UE location uncertainty
• beamforming

Innovation

• Bessel beam
• near-field THz communications
• phase-only beamforming
• location uncertainty
• closed-form optimization