Tutorial 1

Terahertz Communications for 6G Systems

Tuesday, 8 June 2021, 14:00-17:30, Zoom Room

Speaker:

• Chong Han (Shanghai Jiao Tong University, China)
• Josep M. Jornet (Northeastern University, USA)

Motivation and Context

Terahertz (THz)-band (0.1-10 THz) communication is envisioned as a key wireless technology of the next decade. The THz band will help overcome the spectrum scarcity problems and capacity limitations of current wireless networks, by providing an unprecedentedly large bandwidth which can enable applications including Terabit-per second backhaul systems, ultra-high-definition content streaming among mobile devices and wireless high-bandwidth secure communications. In addition, the very small wavelength at THz frequencies enables the development of miniature radios, which can be utilized for new networking paradigms such as wireless massive core computing architectures, wireless nano sensor networks for biomedical applications and the Internet of Nano-Things. The objective of this course is to provide the audience with the necessary knowledge and tools to contribute to the development of wireless communication networks in the THz band, focusing on physical-layer solutions. THz technology has been identified by DARPA as “one of the four major research areas that could eventually have an impact on our society larger than that of the Internet itself”. Beyond traditional applications of wireless networks, the development of a new communication and networking technology to support systems with “billions of connected nano systems” has been identified as “one of the four essential components of the next IT revolution” by the Semiconductor Research Consortium (SRC) and the US National Science Foundation. More recently, THz communications has been identified by IEEE COMSOC as one of the nine communication technology trends to follow. As 5G technology becomes commercial, Terahertz communication is where fundamental scientific and engineering breakthroughs will occur. Nonetheless, the THz band, which lies in between mm-waves and the far infrared, remains still one of the least explored regions in the EM spectrum. For many decades, the lack of compact high-power signal sources and high-sensitivity detectors able to work at room temperature has hampered the use of the THz band for any application beyond sensing. However, many recent advancements with different technologies are finally closing the so-called THz gap. THz-band communication brings many new opportunities to the wireless communication community. The THz band supports huge transmission bandwidths, which range from almost 10 THz for distances below one meter, to multiple transmission windows, each owns tens to hundreds of GHz wide, for distances in the order of a few tens of meters. Nevertheless, this very large bandwidth comes at the cost of a very high propagation loss, mainly because of molecular absorption, which also creates a unique distance dependence on the available bandwidth. All these introduce many challenges to practical THz communication systems and require the development of innovative solutions. Moreover, many of these might be helpful for broadband wireless communication systems below and above the THz band, i.e., mm-waves and optical wireless communications, respectively. Through this tutorial, the audience will learn the necessary knowledge to work in the cutting-edge research field of THz band communications. First, as a review, THz-band devices and THz-band channel models will be surveyed, which provide fundamentals and guidelines for THz communications. As the main focus of this tutorial, novel communication mechanisms tailored to the capabilities of THz devices and the peculiarities, challenges and opportunities introduced by the THz channel will be developed, including hybrid beamforming, ultra-broadband modulations, and physical-layer security. In addition, early works at the link layer that capture the reality of ultra-directional links will be presented, including novel Medium Access Control protocols and strategies for beam discovery and tracking.

Structure and Content

1) Introduction and Applications of THz Communications (1/3 hour)

2) Review of THz Device Technologies and Channel Modeling (1/3 hour)

1. THz Device Technologies
2. THz Channel Modeling
3. Lessons and Guidelines for THz Communications

3) Physical-layer for THz Communications (1.5 hour)

1. Hybrid beamforming
2. Ultra-broadband modulations
3. Physical-layer security

4) Link-layer for THz Networks (1 h)

1. Medium access control
2. Beam discovery, tracking and alignment

5) Summary and Open Research Directions (1/3 hour)