Beam-focusing Analysis for Modular XL-arrays: Effect of Time Synchronization Errors

2026-05-31

AI Summary

This study investigates the impact of inter-subarray timing synchronization errors on near-field beam focusing performance in modular extra-large (XL) antenna arrays. Focusing on maximum ratio transmission (MRT) beamforming, the work combines beam pattern modeling, theoretical analysis, and numerical simulations to reveal, for the first time, that in a two-subarray configuration, synchronization errors induce a beam focus shift—yet effective focusing persists, with the angular deviation bounded above by 1/M. In contrast, with multiple subarrays, such errors cause beam pattern overlap rather than coherent focusing. The paper quantifies how timing mismatches translate into focus displacement and demonstrates that, in multiuser systems, these errors substantially degrade the desired signal power while exacerbating inter-user interference.

Abstract

For near-field communications, it is a hardware-efficient means to form an extremely large-scale array (XL-array) by concatenating multiple modular arrays (also referred to as subarrays). In this letter, we aim to investigate the effect of time synchronization errors among transmissions of different subarrays on the beam-focusing performance. To this end, we first characterize the beam pattern function when the transmit beamforming is designed based on maximum ratio transmission (MRT) under the premise of perfect time synchronization. As this function is highly difficult for analysis, we then consider a typical case with two subarrays. Interestingly, we show that for this case, the beam-focusing effect still persists even in the presence of time synchronization errors, while the focused location is deviated from the user location with an angle offset upper-bounded by 1/M, where M denotes the number of antennas in each subarray. Subsequently, for the general case with multiple subarrays, despite analytical intractability, we numerically show that time synchronization errors give rise to an imbricated (instead of focused) beam pattern. This may significantly degrade multi-user communication performance in practice due to the reduced desired signal power and increased inter-user interference.

Problem

• beam-focusing
• time synchronization errors
• modular XL-arrays
• near-field communications
• subarrays

Innovation

• XL-array
• time synchronization error
• beam focusing
• modular subarrays
• near-field communication