Near-field wideband channel estimation for extremely large-scale MIMO
image: Figure 1. Bilinear pattern of near-field beam split view more
Credit: ©Science China Press
Extremely large-scale multiple-input-multiple-output (XL-MIMO) at millimeter-wave (mmWave) and terahertz (THz) bands plays an important role in 6G networks for its merits of extreme high beamforming gain, abundant spectrum resources, etc. To unleash the superiority of XL-MIMO, accurate channel estimation is of great importance to perform efficient precoding. Unfortunately, as opposed to classical 5G massive MIMO, channel estimation for high-frequency XL-MIMO in 6G faces a serious challenge of “near-field beam split”.
To elaborate, high-frequency XL-MIMO brings the qualitative paradigm shift from conventional far-field planar-wave communications to its near-field spherical-wave counterpart. In addition, the ultra-large bandwidth at mmWave and THz make the electromagnetic wavefront of different frequency components differ from each other, leading to the undesired beam split effect. The coupling of near-field and beam split effects gives rise to a complex structure of wireless channels, whose estimation is intractable for existing methods.
A research, titled "Near-Field Wideband Channel Estimation for Extremely Large-Scale MIMO", was published in SCIENCE CHINA Information Sciences. It is co-authored by Mr. Mingyao Cui (first author) and Prof. Linglong Dai (corresponding author) from Tsinghua University, China.
In this article, a bilinear pattern detection (BPD) based approach was proposed to accurately recover the high-frequency XL-MIMO channel. First, the bilinear pattern of the near-field beam split effect is revealed as shown in Figure 1, which implies that the sparse support set of near-field channels in both the angle and distance domains can be regarded as a linear function against frequency. Then, this bilinear pattern is used to estimate the angle-of-arrival (AoA) and distance parameters of each near-field path component via a modified simultaneously orthogonal matching pursuit algorithm. Finally, Simulation results demonstrated their scheme is capable of achieving high channel estimation accuracy in all far-field/near-field/narrowband/wideband conditions.
This paper provides a solution to channel estimation in the presence of near-field beam split. It is expected that the bilinear pattern could be extended to various near-field wideband communication scenarios for addressing near-field beam split issues, such as reconfigurable intelligent surface communications and cell-free massive MIMO communications.
See the article:
Cui M Y, Dai L L. Near-field wideband channel estimation for extremely large-scale MIMO. Sci China Inf Sci, 2023, 66(7): 172303, doi: 10.1007/s11432-022-3654-y