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arXiv · 2302.12511

Two-Stage Hierarchical Beam Training for Near-Field Communications

Chenyu Wu·Changsheng You·Yuanwei Liu·Li Chen·Shuo Shi
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Abstract

Extremely large-scale array (XL-array) has emerged as a promising technology to improve the spectrum efficiency and spatial resolution of future wireless systems. However, the huge number of antennas renders the users more likely to locate in the near-field (instead of the far-field) region of the XL-array with spherical wavefront propagation. This inevitably incurs prohibitively high beam training overhead since it requires a two-dimensional (2D) beam search over both the angular and distance domains. To address this issue, we propose in this paper an efficient two-stage hierarchical beam training method for near-field communications. Specifically, in the first stage, we employ the central sub-array of the XL-array to search for a coarse user direction in the angular domain with conventional far-field hierarchical codebook. Then, in the second stage, given the coarse user direction, we progressively search for the fine-grained user direction-and-distance in the polar domain with a dedicatedly designed codebook. Numerical results show that our proposed two-stage hierarchical beam training method can achieve over 99% training overhead reduction as compared to the 2D exhaustive search, yet achieving comparable rate performance.

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Chenyu Wu, Changsheng You, Yuanwei Liu, Li Chen, Shuo Shi. 2023-02-24. Two-Stage Hierarchical Beam Training for Near-Field Communications. https://arxiv.org/abs/2302.12511

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