T1: Near-Field Communications for 6G: Fundamentals, Challenges, Potentials, and Future Directions

Co-chair: Linglong Dai, Tsinghua University, China

Abstract: The promising technologies for 6G including ultra-massive multiple-input-multiple-output (UM-MIMO), reconfigurable intelligent surface (RIS) and terahertz (THz) communications share a common feature: A very large number of antennas is required to achieve their expected performance, i.e., extremely large antenna arrays (ELAA) are essential for these different promising candidate technologies for 6G. ELAA for 6G not only means a sharp increase in the number of antennas, but also results in a fundamental change in the electromagnetic (EM) characteristics. The EM radiation field can generally be divided into far-field and near-field regions. The boundary is determined by the Rayleigh distance, which is proportional to the product of the square of the array aperture and the carrier frequency. With the significant increase of the antenna number and carrier frequency in future 6G systems, the near-field region of ELAA will expand by orders of magnitude. Therefore, near-field communications will become essential for future 6G networks.

In this tutorial, the near-field communication techniques for 6G will be discussed. Specifically, the fundamental difference between far-field and near-field communications will be clarified at first, where we explain the principle to determine the boundary of near-field and far-field regions for MIMO communications and RIS-aided communications. Then we investigate the near-field communication techniques that are designed to compensate for the performance loss of far-field techniques in the near-field region. Moreover, we also introduce the techniques that exploit the nature of near-field spherical wavefront for capacity enhancement and accessibility improvement. Finally, several open problems and future research directions are pointed out.

Co-chair’s Bio:

Linglong Dai

Bio: Linglong Dai (Fellow, IEEE) received the B.S. degree from Zhejiang University, Hangzhou, China, in 2003, the M.S. degree from the China Academy of Telecommunications Technology, Beijing, China, in 2006, and the Ph.D. degree from Tsinghua University, Beijing, in 2011. From 2011 to 2013, he was a Post-Doctoral Researcher with the Department of Electronic Engineering, Tsinghua University, where he was an Assistant Professor from 2013 to 2016, an Associate Professor from 2016 to 2022, and has been a Professor since 2022. His current research interests include massive MIMO, reconfigurable intelligent surface (RIS), near-field communications, millimeter-wave and Terahertz communications, wireless AI, and electromagnetic information theory. He has received 6 conference Best Paper Awards at IEEE ICC/GLOBECOM/VTC, etc. He has received the National Natural Science Foundation of China for Outstanding Young Scholars in 2017, the IEEE ComSoc Leonard G. Abraham Prize in 2020, the IEEE ComSoc Stephen O. Rice Prize in 2022, the IEEE ICC Outstanding Demo Award in 2022, and the National Science Foundation for Distinguished Young Scholars in 2023. He was listed as a Highly Cited Researcher by Clarivate from 2020 to 2023. He was elevated as an IEEE Fellow in 2021.