Abstract-Prospective Beamforming Technologies for Ultra-Massive MIMO in Terahertz Communications: A Tutorial

 

Boyu Ning, Zhongbao Tian, Zhi Chen, Chong Han, Jinhong Yuan, Shaoqian Li

https://arxiv.org/abs/2107.03032

Terahertz (THz) communications with a frequency band 0.1-10 THz are envisioned as a promising solution to the future high-speed wireless communication. Although with tens of gigahertz available bandwidth, THz signals suffer from severe free-spreading loss and molecular-absorption loss, which limit the wireless transmission distance. To compensate the propagation loss, the ultra-massive multiple-input-multiple-output (UM-MIMO) can be applied to generate a high-gain directional beam by beamforming technologies. In this paper, a tutorial on the beamforming technologies for THz UM-MIMO systems is provided. Specifically, we first present the system model of THz UM-MIMO and identify its channel parameters and architecture types. Then, we illustrate the basic principles of beamforming via UM-MIMO and introduce the schemes of beam training and beamspace MIMO for THz communications. Moreover, the spatial-wideband effect and frequency-wideband effect in the THz beamforming are discussed. The joint beamforming technologies in the intelligent-reflecting-surface (IRS)-assisted THz UM-MIMO systems are introduced. Further, we present the corresponding fabrication techniques and illuminate the emerging applications benefiting from THz beamforming. Open challenges and future research directions on THz UM-MIMO systems are finally highlighted.

Abstract-Massive MIMO Performance Comparison of Beamforming and Multiplexing in the Terahertz Band

Sayed Amir Hoseini, Ding Ming, Mahbub Hassan

https://arxiv.org/abs/1710.09031

(Submitted on 25 Oct 2017)

In this paper, we compare the performance of two main MIMO techniques, beamforming and multiplexing, in the Terahertz (THz) band. The main problem with the THz band is its huge propagation loss, which is caused by the tremendous signal attenuation due to molecule absorption of the electro-magnetic wave. To overcome the path loss issue, massive MIMO has been suggested to be employed in the network and is expected to provide Tbps for a distance within a few meters. In this context, beamforming is studied recently as the main technique to take advantage of MIMO in THz and overcome the very high path loss with the assumption that the THz communication channel is Line-of-Sight (LoS) and there are not significant multipath rays. On the other hand, recent studies also showed that the well-known absorbed energy by molecules can be re-radiated immediately in the same frequency. Such re-radiated signal is correlated with the main signal and can provide rich scattering paths for the communication channel. This means that a significant MIMO multiplexing gain can be achieved even in a LoS scenario for the THz band. Our simulation results reveal a surprising observation that the MIMO multiplexing could be a better choice than the MIMO beamforming under certain conditions in THz communications.

Abstract-Consideration of antenna directions for high frequency wireless body area networks during human walking movement

Takahiro Aoyagi,

http://ieeexplore.ieee.org/document/7928279/

As increased requirements for much high speed and capacity in wireless communications, frequency bands become higher, such as millimeter wave or terahertz wave. In these high frequency bands, beamforming is employed to gain stable connectivity. On-body body area network is one of fascinate application of these high capacity frequency bands. However, directions of on-body antennas largely varies and shadowing frequently occurs due to human movements. In this paper, variation of antenna directions and shadowing of on-body propagation during human walk movement is investigated. As a result, range of antenna rotation and shadowing rate, which can be used future system design of high frequency body area networks, is clarified.