Near-Field Rainbow: Wideband Beam Training for XL-MIMO

05/07/2022
by   Mingyao Cui, et al.
0

Wideband extremely large-scale multiple-input-multiple-output (XL-MIMO) is a promising technique to achieve Tbps data rates in future 6G systems through beamforming and spatial multiplexing. Due to the extensive bandwidth and the huge number of antennas for wideband XL-MIMO, a significant near-field beam split effect will be induced, where beams at different frequencies are focused on different locations. The near-field beam split effect results in a severe array gain loss, so existing works mainly focus on compensating for this loss by utilizing the time delay (TD) beamformer. By contrast, this paper demonstrates that although the near-field beam split effect degrades the array gain, it also provides a new possibility to realize fast near-field beam training. Specifically, we first reveal the mechanism of the near-field controllable beam split effect. This effect indicates that, by dedicatedly designing the delay parameters, a TD beamformer is able to control the degree of the near-field beam split effect, i.e., beams at different frequencies can flexibly occupy the desired location range. Due to the similarity with the dispersion of natural light caused by a prism, this effect is also termed as the near-field rainbow in this paper. Then, taking advantage of the near-field rainbow effect, a fast wideband beam training scheme is proposed. In our scheme, the close form of the beamforming vector is elaborately derived to enable beams at different frequencies to be focused on different desired locations. By this means, the optimal beamforming vector with the largest array gain can be rapidly searched out by generating multiple beams focused on multiple locations simultaneously through only one radio-frequency (RF) chain. Finally, simulation results demonstrate the proposed scheme is able to realize near-optimal nearfield beam training with a very low training overhead.

READ FULL TEXT
research
02/10/2021

Delay-Phase Precoding for Wideband THz Massive MIMO

Benefiting from tens of GHz bandwidth, terahertz (THz) communication is ...
research
09/21/2021

Near-Field Wideband Beamforming for Extremely Large Antenna Array

Extremely large antenna array for wideband communications is a promising...
research
12/16/2022

Near-Field Wideband Channel Estimation for Extremely Large-Scale MIMO

Extremely large-scale multiple-input-multiple-output (XL-MIMO) at millim...
research
06/08/2020

InFocus: A spatial coding technique to mitigate misfocus in near field LoS beamforming

Phased arrays, commonly used in IEEE 802.11ad and 5G radios, are capable...
research
12/30/2022

Hierarchical Beam Training for Extremely Large-Scale MIMO: From Far-Field to Near-Field

Extremely large-scale MIMO (XL-MIMO) is a promising technique for future...
research
01/27/2023

Chirp-based Hierarchical Beam Training for Extremely Large-Scale Massive MIMO

XL-MIMO promises to provide ultrahigh data rates in Terahertz (THz) spec...
research
02/07/2022

Energy-efficient Dynamic-subarray with Fixed True-time-delay Design for Terahertz Wideband Hybrid Beamforming

Hybrid beamforming for Terahertz (THz) ultra-massive multiple-input mult...

Please sign up or login with your details

Forgot password? Click here to reset