[논문 리뷰] Array Geometry-Centric Axial Sidelobe Interference Analysis for Near-Field Multi-User MIMO

Ahmed Hussain, Asmaa Abdallah외 2명|arXiv (Cornell University)|2026. 03. 12.

Antenna Design and Optimization인용 수 0

한 줄 요약

The paper analyzes axial sidelobes in near-field MU-MIMO and shows uniform square arrays (USA) achieve the lowest axial SLLs and highest sum rate under fixed aperture, with closed-form gains and Fresnel/Bessel-based expressions for various geometries.

ABSTRACT

With the deployment of large antenna arrays at high-frequency bands, future wireless communication systems are likely to operate in the radiative near-field (NF). Unlike far-field beam steering, NF beams can be focused on a spatial region with finite depth, enabling user multiplexing in both range and angle. In NF multiuser multiple-input multiple-output (MU-MIMO) systems, achievable rates are limited by interference arising from sidelobes in both the axial (range) and lateral (angle) dimensions. This work investigates how axial sidelobes (ASLs) vary with array geometry. Closed-form array gain expressions are derived to characterize ASLs for uniform planar arrays. Analytical results show that the uniform square array (USA) yields the lowest ASLs, followed by the uniform concentric circular array (UCCA), uniform linear array (ULA), and uniform circular array (UCA). Specifically, the USA achieves a peak sidelobe level (PSLL) of -17.6 dB versus -7.9 dB for the UCA. Numerical simulations confirm that the USA provides superior sidelobe suppression and highest sumrate performance.

연구 동기 및 목표

• Understand how axial sidelobes vary with array geometry in near-field MU-MIMO.
• Derive closed-form array gain expressions for different USA-like geometries.
• Quantify peak and integrated sidelobe levels to identify geometry offering best interference suppression.
• Link sidelobe performance to achievable sum-rate under a fixed aperture constraint.

제안 방법

• Model the NF channel with LoS focus and NF array response vector across azimuth, elevation, and range.
• Define axial pattern gain G_a(phi,theta,r) as the squared inner product of NF array responses.
• Derive PSLL analytically for ULA, URA, UCA, and UCCA using Fresnel integrals and Bessel functions; obtain closed-form PSLL/ISLL expressions (where possible).
• Evaluate PSLL and ISLL numerically from G_a for each geometry under fixed aperture and compare sum-rate via SINR with MR precoding.
• Use Rayleigh distance and NF focusing distance to quantify range-domain sidelobes and their interference impact.

Figure 1 : Interference due to axial sidelobes in MU - MIMO .

실험 결과

연구 질문

• RQ1 How do axial sidelobes (range-domain sidelobes) depend on the array geometry under near-field focusing?
• RQ2 Which homogeneous array geometry minimizes peaks and integrated axial sidelobes, and how does this relate to achievable sum-rate?
• RQ3 What are the closed-form or semi-closed-form expressions for NF axial gains for ULA, URA, UCA, and UCCA?
• RQ4 How does fixing aperture length (instead of element count) affect sidelobe behavior and sum-rate across geometries?
• RQ5 How do PSLL and ISLL translate to interference and rate performance in near-field MU-MIMO?

주요 결과

Geometry	PSLL Range (dB)	PSLL Angle (dB)	ISLL Range (dB)	ISLL Angle (dB)
UCA	-7.9	-7.9	-0.4	1.9
ULA	-8.7	-13.3	-1.3	-9.6
UCCA	-13.4	-17.6	-7.2	-10.4
USA	-17.6	-13.3	-12.1	-9.6

• USA yields the lowest axial sidelobes (PSLL ≈ -17.6 dB in range) and highest sum-rate under fixed aperture.
• UCA has PSLL ≈ -7.9 dB in range and angle domains, the worst among studied geometries.
• UCA’s limited NF focusing leads to higher interference and lower sum-rate.
• UCCA and USA show significant improvements in angle-domain PSLL and overall interference suppression.
• PSLL is geometry-invariant with respect to N under fixed aperture, while ISLL can be reduced by increasing N.
• Numerical results confirm that USA provides the best sum-rate performance, consistent with sidelobe analysis.

Figure 2 : A ULA aligned along the $y$ -axis and a NF UE at $(\varphi,r)$ .