Zhejiang Lab

6G and the Era of Terahertz Waves

In November 2019, China started researching 6G technology. With massive connections, intelligent networks, and ubiquitous intelligence, 6G brings infinite possibilities to technology and people’s lives. Terahertz (THz) communication is envisioned as a key technology to 6G, because it can transmit data with an ultra-high speed rivalling the speed of optical fibers.

At Zhejiang Lab, the research team for THz communication intends to combine optoelectronics with OAM-based (Orbital Angular Momentum) technology to achieve a communication rate of up to 1 Tbit per second, thereby paving the way for the development of 6G in China. From 2015 to 2018, guided by team leader Doctor Yu Xianbin, the team realized a series of ultra-high-rate THz wireless communication in the frequency range of 300-500 GHz, a world-leading achievement. Recently, Doctor Yu answered a number of questions on the UWell Online Forum, giving us a chance to learn more about 6G and the Terahertz Era.

6G: The Powerful Force behind the Internet of Everything

Q: What is 6G? How is it different from 4G and 5G?

6G is the sixth generation of mobile communication systems. From 4G and 5G to 6G, the transmission rate and other performance indices of every new communication system are ten times higher than those of the previous generation. Whereas 4G, as well as the systems before 4G, applied communication technologies for consumption purposes, 5G and 6G will be gradually used to meet industrial needs. As 5G has already been employed to build the Internet of Everything, 6G will take this effort further. In addition, in terms of driving forces, 5G is driven by consumers’ growing demand for data traffic and the production needs of vertical industries, while 6G is motivated by commercial and social needs.

Q: What is the biggest difference between 6G and 5G?

First of all, the transmission rate and other performance indices of 6G are supposed to be over ten times higher than those of 5G. For example, compared with 5G, 6G will have substantially higher network capacity, with latency lowering to 0.1 millisecond in networks and less than 1 microsecond on synchronized devices. In addition to communication functions, 6G will also support non-communication applications such as computing, radar sensing, perception, and positioning. It can reach a centimeter-level precision for positioning.

Secondly, 5G is essentially driven by commercial needs, while 6G is motivated not only by commercial needs, but also by social needs such as providing fair education and healthcare services to impoverished populations, vulnerable groups, and remote rural residents.

In addition, compared with 5G, 6G is more inclusive and extensible. Therefore, apart from traditional carriers, it will create new ecosystems for its application. For example, as the frequency range used by 6G turns increasingly higher, the networks will be more densely distributed. As a result, we will see more local networks targeting vertical markets. These local networks, which will be deployed by different stakeholders, will cause the emergence of local operators and produce new ecosystems.

THz Communication: A Key Technology for 6G

Q: What are the technical obstacles for THz communication?

Compared with millimeter waves, THz waves require a lower power for transmission, but produce a heavy transmission loss, and a strong effect of frequency selective fading. The signals for ultra-high-rate communications are extremely sensitive to the non-linearity and strong frequency selectivity of THz channels. Consequently, signals will be delayed and distorted with reduced signal-noise ratio during transmission, which substantially increases the difficulties in THz communication.

Q: THz waves are transmitted via bands of high frequencies and travel within short distances. Does this mean that if we enter the era of 6G, we need to build base stations that are more densely distributed?

The frequencies of THz waves are close to the rotational spectra of molecules, which causes the waves to be easily absorbed by water molecules in the air. As a result, the waves can only be transmitted within short distances. We therefore need more base stations to join the relay. The frequency bands used by 5G are higher than those of 4G. Without the influences of other factors, the coverage of 5G base stations is naturally smaller than that of 4G stations. Judging from this perspective, in the era of 6G, we will see base stations that are more densely distributed than ever.

Q: In addition to communications, what else can we do with THz technology?

In addition to communications, THz imaging and THz spectroscopy are two important applications of THz technology. For example, when used for security checks, THz waves can travel through walls to form 3D images of objects behind walls, so that we can detect hidden weapons and armed militants. Also, as many organic macromolecules and explosives show strong abilities to absorb and disperse THz waves, we can use the unique spectral features of THz waves to detect creatures and hazardous substances.

The Future of 6G: A Promising Prospect for Ubiquitous Intelligence

Q: When can we realize the commercial use of 6G?

Our previous experience tells us that the upgrading of mobile communication systems takes place approximately every ten years. As 2019 is the first year of the commercial use of 5G, people in the industry expect that the commercial use of 6G will be realized around 2030. 6G networks will be ubiquitous and intelligent, with a larger bandwidth and an ultra-high rate (1 Tbit per second). They will be ultra-safe and ultra-reliable wireless networks that support the integration of multiple networks (space-air-ground networks), and the combination of different information services.

Q: Would you please describe some possible scenarios in the era of 6G?

In addition to faster networks, 6G may also bring many changes to our lives, work, and learning experiences. It may even incubate many new industries. According to the world’s first white paper about 6G, released by the University of Oulu in Finland, the vision of 6G is to create ubiquitous and intelligent networks with a larger bandwidth. A larger bandwidth is fundamental to high-rate transmission. Ubiquitous means that the networks will provide services to all mobile users, anywhere and anytime. Intelligent means that the networks can provide scenario-based intelligent services and applications to everyone and everything in the world.

After entering the era of 6G, VR, AR, and MR technologies will be integrated with human senses through wearable monitors, sensing devices, and networks, replacing today’s smartphones as the main tools for entertainment, life, and work. According to the white paper, in the era of 6G, the technology of remote holographic interaction can transfer the 3D holographic images of people in different places to the same location through real-time capture, transmission, and rendering, enabling everyone to communicate with each other as though sitting face to face. In the era of 6G, millions of connected autonomous vehicles across the world will operate collaboratively in a 6G network, making transportation and logistics more efficient. In the era of 6G, distributed edge-cloud computing will be unprecedentedly popular, which will alleviate the computing burdens of terminal devices, turning these devices into more portable ones with lower power usage. In the era of 6G, the precision of positioning will be determined by centimeters. We will integrate this achievement with other technologies that have been developing continuously, such as perception and imaging technologies, to create massive new applications.