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A Primer on Near-Field Beamforming for Arrays and Reconfigurable Intelligent Surfaces
KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS. Linköping University, Linköping, Sweden.ORCID iD: 0000-0002-5954-434x
2021 (English)In: 2021 55th Asilomar Conference on Signals, Systems, and Computers, 2021, p. 105-112Conference paper, Published paper (Refereed)
Abstract [en]

Wireless communication systems have almost exclusively operated in the far-field of antennas and antenna arrays, which is conventionally characterized by having propagation distances beyond the Fraunhofer distance. This is natural since the Fraunhofer distance is normally only a few wavelengths. With the advent of active arrays and passive reconfigurable intelligent surfaces (RIS) that are physically large, it is plausible that the transmitter or receiver is located in between the Fraunhofer distance of the individual array/surface elements and the Fraunhofer distance of the entire array. An RIS then can be configured to reflect the incident waveform towards a point in the radiative near-field of the surface, resulting in a beam with finite depth, or as a conventional angular beam with infinity focus, which only results in amplification in the far-field. To understand when these different options are viable, an accurate characterization of the near-field behaviors is necessary. In this paper, we revisit the motivation and approximations behind the Fraunhofer distance and show that it is not the right metric for determining when near-field focusing is possible. We obtain the distance range where finite-depth beamforming is possible and the distance where the beamforming gain tapers off.

Place, publisher, year, edition, pages
2021. p. 105-112
National Category
Telecommunications
Identifiers
URN: urn:nbn:se:kth:diva-313400DOI: 10.1109/IEEECONF53345.2021.9723331Scopus ID: 2-s2.0-85127037906OAI: oai:DiVA.org:kth-313400DiVA, id: diva2:1663804
Conference
Asilomar Conference on Signals, Systems, and Computers
Note

QC 20220615

Available from: 2022-06-02 Created: 2022-06-02 Last updated: 2022-06-25Bibliographically approved

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Björnson, Emil

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CiteExportLink to record
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Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
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Output format
  • html
  • text
  • asciidoc
  • rtf