Benefits of emerging near-field communications:
The progression of 5G mobile communication commercialization has spurred anticipation for 6G communication. To support emerging applications like digital twins, holographic video, and augmented reality (AR), extremely large-scale antenna array (ELAA) is regarded as key candidates for future 6G mobile communication due to its potential to enhance spectrum efficiency.
"Compared with 5G massive multiple-input multiple-output (MIMO) systems, 6G ELAA not only entails an increase in the number of antennas, but also signifies a fundamental shift in electromagnetic field from far-field planar waves to near-field spherical waves." Said by Prof. Linglong Dai, a Full Professor in the Department of Electronic Engineering of Tsinghua University, "The spherical-wave-based near-field communications brought new possibilities for performance enhancement of wireless communications."
In contrast to far-field massive MIMO systems primarily relying on the orthogonality of far-field beams in the angular domain, the spherical wave propagation characteristics enable near-field beams to possess the additional radial focusing ability. In such a way, multiple users could be simultaneously served by different near-field beams, which is promising to further enhance the spectrum efficiency in multi-user communications.
Degradation of radial focusing ability with UCA:
To enable more users to benefit from near-field communications, it is desired to expand the near-field range through array topology design. However, existing research on classical circular arrays claimed that, while significantly expanding the near-field range in the azimuthal dimension, circular array faces reduced near-field range in the broadside direction, rendering users unable to fully exploit near-field communication gains.
Methods:
To overcome this challenge, a novel method was proposed in a recent article [1] of Prof. Dai's research team, where the classical UCA topology was generalized into UCCA to enhance the radial focusing ability of arrays. "As the elevation angle increases, the phase differences of electromagnetic waves between different antennas are decreasing in spherical-wave model, resulting the declining radial focusing ability", noted by Zidong Wu, one team member of Prof. Dai's lab. To address this, the article proposes to generalize UCA into UCCA, transforming single-ring array configurations into multi-ring array configurations to further increase the phase difference of electromagnetic waves, thereby enhancing the resolution near-field beams of ELAA.
Through numerical simulations, it is demonstrated that UCCA-based ELAA could not only improve the spatial utilization efficiency while also significantly enhancing radial beam focusing capability. With the improvement of radial focusing capability, UCCA can significantly expand the near-field range in the broadside direction, providing new possibilities for enhancing the performance of multi-user near-field communication systems.
