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-Terahertz Communications (TeraCom): Challenges and Impact on 6G Wireless Systems

Chong Han, Yongzhi Wu, Zhi Chen, Xudong Wang

https://arxiv.org/abs/1912.06040

Terahertz communications are envisioned as a key technology for 6G, which requires 100+ Gbps data rates, 1-millisecond latency, among other performance metrics. As a fundamental wireless infrastructure, the THz communication can boost abundant promising applications, including next-generation WLAN systems like Tera-WiFi, THz wireless backhaul, as well as other long-awaited novel communication paradigms. Serving as a basis of efficient wireless communication and networking design, this paper highlights the key THz channel features and recent advancements in device technologies. In light of these, impact and guidelines on 6G wireless communication and networking are elaborated. We believe the progress of THz technologies is helping finally close the so called THz Gap, and will realize THz communications as a pillar of 6G wireless systems.

Abstract-Combating the Distance Problem in the Millimeter Wave and Terahertz Frequency Bands

Ian F. Akyildiz,  Chong Han,  Shuai Nie,

https://ieeexplore.ieee.org/document/8387211/

In the millimeter-wave (30-300 GHz) and terahertz (0.1-10 THz) frequency bands, the high spreading loss and molecular absorption often limit the signal transmission distance and coverage range. In this article, four directions to tackle the crucial problem of distance limitation are investigated, namely, a distance-aware physical layer design, ultra-massive MIMO communication, reflectarrays, and intelligent surfaces. Additionally, the potential joint design of these solutions is proposed to combine the benefits and further extend the communication distance. Qualitative and quantitative evaluations are provided to illustrate the benefits of the proposed solutions. The feasibility of mmWave and THz band communications up to 100 m in both line-of-sight and nonline- of-sight areas are demonstrated.

Abstract-Stochastic geometry analysis of interference and coverage in Terahertz networks

Xin-Wei Yao, Chao-Chao Wang, Wan-Liang Wang,  Chong Han,

http://www.sciencedirect.com/science/article/pii/S1878778917300261


Terahertz (THz) band communication has been envisioned as a key wireless technology for providing unprecedented high data rates. However, due to the severe path loss, the transmission distance in THz band is very limited. Therefore, the beamforming techniques are explored to enlarge the communication range in THz networks, particularly employed at Access Points (APs). Interference is a critical factor affecting the performance of THz networks. In this paper, the interference and the coverage probability are investigated for the THz band communications with beamforming APs. First, based on the Line-of-Sight (LoS) and Non-Line-of-Sight (NLoS) ray propagation models of THz signals, the interferences from neighboring users and beamforming APs are modeled in closed forms based on stochastic geometry methods. Then, the Signal-to-Interference-plus-Noise-Ratio (SINR) and the coverage probabilities are further derived based on the THz channel and interference model. Extensive simulations are carried out to evaluate the interference and coverage for the THz band communications with beamforming APs, for the different system parameters, which include SINR threshold, density of APs, transmission frequency, gain of beamforming AP, density of users and radius of interference area. Learning from the simulation results, high density of APs with a small beam-width and the transmission at THz frequencies with low absorption efficient, such as 0.67 THz, are recommended to mitigate the interference and achieve a better coverage performance.

Abstract-A memory-assisted MAC protocol with angular-division-multiplexing in terahertz networks

Chong Han, Wenqian Tong,  Xinyi Wu,

http://ieeexplore.ieee.org/document/7997014/


Terahertz band communication is envisioned as a key technology to satisfy the increasing demand for ultra-highspeed wireless links. In this paper, a memory-assisted medium access control (MAC) protocol with angular-division-multiplexing (ADM) is proposed for the service discovery and communications in the THz network. In particular, the efficiency balance is achieved by equipping the nodes with (i) the omni-directional antennas at the service discovery phase, and (ii) directional antennas for message transmissions. Moreover, the memory is leveraged in the ADM scheme to assist the access point (AP) to skip the unregistered angular slots to improve the network performance. Based on the proposed MAC protocol, the analytical models of the interference, SINR, outage probability, throughput and the delay in the THz network are derived respectively. According to the simulation and numerical analysis, the results show that our proposed MAC protocol can effectively improve the throughput by over 15% and substantially reduce the delay, in comparison with the ADM scheme without the memory guidance.