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Array Geometry-Centric Axial Sidelobe Interference Analysis for Near-Field Multi-User MIMO

Ahmed Hussain, Asmaa Abdallah, Abdulkadir Celik, Ahmed M. Eltawil

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.

Array Geometry-Centric Axial Sidelobe Interference Analysis for Near-Field Multi-User MIMO

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.
Paper Structure (13 sections, 23 equations, 9 figures, 1 table)

This paper contains 13 sections, 23 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. System Model
  3. Achievable Rate
  4. Axial Sidelobes
  5. Axial Beam Pattern
  6. Uniform Linear Array
  7. Uniform Rectangular Array
  8. Uniform Circular Array
  9. Uniform Concentric Circular Array
  10. Simulation Results
  11. Sidelobe level vs. Array Geometry
  12. Achievable Sumrate
  13. Conclusion

Figures (9)

  • Figure 1: Interference due to axial sidelobes in MU-MIMO.
  • Figure 2: A ULA aligned along the $y$-axis and a NF UE at $(\varphi, r)$.
  • Figure 3: Normalized array gain for ULA and USA with respect to $\gamma$.
  • Figure 4: Peak sidelobe levels with respect to $\hat{\eta}=\tfrac{\gamma_2}{\gamma_1}$.
  • Figure 5: A UCA in the $xy$-plane and a NF UE is located $(r,\varphi, \theta)$.
  • ...and 4 more figures