Terahertz Series: Part 2 Communication Standards and Potential of Terahertz Technology

1. Communication Standards for Terahertz Communication

In the future, communication standards will be essential for the practical application of communication technology. For mobile communication, standards such as LTE and 5G-NR have been standardized and put into practical use by the 3GPP (3rd Generation Partnership Project), a global telecommunications standards organization.
Generally, the overall standardization of cellular networks is promoted at 3GPP, and detailed specifications covering the core network, access network, and terminal architecture are formulated.
The 802.15.3D standard was approved in 2017 by the IEEE (Institute of Electrical and Electronics Engineers), a U.S.-based technical standardization body for terahertz communication standards. Within the IEEE working groups, the standardization of technical specifications—such as the physical layer, data link layer, and access control—is being advanced at an early stage in collaboration with device manufacturers and universities. 3GPP and IEEE collaborate and mutually influence each other in their activities.

One well-known communication standard standardized by IEEE is the Wi-Fi® standard for wireless LANs. High-speed wireless communication standards such as 802.11ac and 802.11ad have been established by the IEEE 802 working group.

802.15.3D targets the 300GHz frequency band and provides specific standards for achieving high-speed, high-capacity communication. Key features of IEEE 802.15.3D include the securing of wideband channels and efficient data transmission technology. This standard, established in 2017, focuses on high-speed data transfer in short-range communication, aiming for speeds close to 100Gbps.

Moreover, many technical challenges are being discussed in the standardization process of this protocol. For example, issues such as radio propagation loss and atmospheric attenuation due to the high-frequency characteristics of the 300GHz band, and the necessity for directional antennas and beamforming technology. Since 802.15.3D is still in its standardization phase, researchers are exploring new material technologies, circuit designs, and energy efficiency improvements to address these challenges and bring terahertz communication into practical use.

Figure1. Channel Assignment of 802.15.3D

2. Global Trends Toward the Realization of Terahertz Communication

The 2019 World Radiocommunication Conference (WRC-19) was recognized as a significant event for making important decisions regarding the use of the terahertz band. The WRC, organized by the International Telecommunication Union (ITU), brings together regulatory agencies and representatives from the telecommunications industry worldwide to discuss and set standards and policies for radio communications. At WRC-19, usage regulations for frequency bands above 275GHz were established. The initiatives by organizations such as 3GPP and IEEE mentioned earlier can only be implemented after gaining consensus from national authorities at the WRC.
The conference discussed specific frequency range allocations within the terahertz band and rules to prevent interference between different services. For example, technical guidelines were set to enable coexistence between astronomical observation and terahertz communication. Additionally, each country's frequency allocation policies and regulations for commercial use were clarified.
As a result, a total of 234.5GHz of frequency bandwidth between 100GHz and 450GHz was designated for communication use. Considering that, as of November 2024, the combined frequency bandwidth allocated for service to Japan's mobile communication operators is about 3GHz, the possibility of utilizing 80 times more frequency bandwidth than currently available was realized.

Figure2. Frequency map of WRC-19 results

In many countries worldwide, research and development focused on utilizing the terahertz band for communication, driven by the anticipation of 6G commercial applications, has gained significant momentum.. In Japan, numerous research and development initiatives have been advanced with support from the Ministry of Internal Affairs and Communications and NICT (National Institute of Information and Communications Technology).
SoftBank, in particular, has been conducting research and development to utilize the terahertz band for mobile communication in the future.
At the WRC-23 held in 2024, due to urgent demands for the practical use of other frequency bands, it was decided that discussions regarding the mobile use of frequencies above 100GHz would be deferred until WRC-27, four years later. As a result, the timeline for the practical application of terahertz communication as mobile usage has been somewhat delayed. However, it is considered essential to explore the terahertz band to achieve ultra-high-speed communication in the future. Consequently, research on terahertz communication continues in a wide range of fields, not limited to mobile applications.

3. Use Cases of Terahertz Communication

The theoretical communication speed can be calculated using Shannon's theorem, which is determined by signal power, noise power, and frequency bandwidth. For instance, substituting a bandwidth of 10 [GHz] available in the terahertz band for B, and assuming a sufficient signal-to-noise ratio (S/N ratio) of 10 (10dB) for digital communication, a communication speed of approximately 34.6Gbps can be achieved. In an optimal communication environment (S/N ratio of 1000 (30dB)), speeds of around 49.5Gbps are possible. Additionally, applying technologies such as MIMO (Multiple Input Multiple Output), beamforming, and coding can enable even faster data communication.
As introduced in Chapter 2, the wide frequency range of the terahertz band allows for unprecedented ultra-high-speed data communication. It is expected that in the future, terahertz communication could achieve speeds exceeding 1Tbps (terabits per second), far surpassing the capabilities of current 5G technology.

Formula. Shannon's theorem

Furthermore,the practical implementation of terahertz communication could enable wireless solutions for items that have traditionally relied on cables.For example, in everyday life, it is anticipated that all types of cables—such as HDMI cables for TVs and monitors, LAN cables, and USB cables—could be replaced wirelessly in an eco-friendly manner.
In the industrial sector, terahertz communication could help reduce bundled communication cables in data centers and replace optical fibers required for base station construction with wireless alternatives, offering a significant reduction in cabling needs.
Currently, experiments have shown that terahertz communication can achieve speeds exceeding 100Gbps,with even higher speeds expected in the future. However, challenges remain, such as signal attenuation and spatial propagation issues associated with high-frequency bands, as well as the high costs of equipment. Despite these challenges, the potential of terahertz communication is immense, and it is increasingly regarded as a promising next-generation communication technology.
Additionally, as mentioned in the previous article, high frequencies are not only used for communication but also serve as wireless sensors. One notable example is the use of terahertz waves in body scanning at airport security checks overseas. Looking ahead, innovative uses of radio waves are anticipated, such as simultaneous communication and environmental monitoring utilizing the terahertz band.

4. Preview of the Next Article

Terahertz communication is a pioneering area that conventional communication technologies have not been able to reach. The use of high-frequency bands enables ultra-high-speed and large-capacity data communication, which has the potential to bring significant transformation to our lives and industries.
However, numerous technical challenges must be addressed for its realization. For instance, increasing the frequency bandwidth also increases the amount of noise within that band. As a result, higher signal power is required. However, high frequencies suffer from significant attenuation during air propagation, and amplifier efficiency is low, making it more difficult to boost signal power compared to existing frequencies. To address this low power, extensive research is being conducted into antenna technologies such as Massive MIMO and beamforming. Yet, the short wavelength of terahertz waves leads to extremely small elements, which require a high degree of manufacturing precision, even for a single antenna.
From these perspectives, it has been said that terahertz communication is difficult to implement effectively over very short distances (e.g., within the vicinity of the human body). SoftBank is actively working on addressing these challenges to utilize terahertz for mobile applications. In the next blog, we will introduce SoftBank's initiatives.