Which frequency will be used in 6G?

#FSOC/Terahertz

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1.The Nationwide Deployment Status of 5G Millimeter Wave

Mobile communication, after 5G, is not only limited to communication with people (such as smartphones), but also there is a growing demand for communication with objects, leading to further predicted increase in communication traffic.

To accommodate the future increase in communication traffic, frequency bands with wide bandwidth, such as the millimeter wave band (28 GHz band, etc.), have been allocated for 5G usage.

Looking at the commercialization status of 5G millimeter wave technology worldwide, it is extensively deployed in the United States and Japan, followed by Europe, South Korea, Taiwan, Southeast Asia, and Australia, with commercial services initiated by 28 operators globally. It is anticipated that the number of operators will continue to increase in tandem with the allocation of frequencies.

According to the Ministry of Internal Affairs and Communications in Japan, as of the end of March 2023, the total number of 5G base stations across four mobile network operators in Japan amounted to approximately 170,000, covering over 96.6% of the population. However, only about 14% (approximately 23,000 stations) of these are millimeter wave (mmWave) base stations.
Each operator has been allocated a 400MHz bandwidth in the mmWave spectrum, which accounts for about 50% of the existing assigned frequencies. However, the current situation is that, when looking at the traffic volume by bandwidth, less than 0.1% of the total is being used.

Millimeter wave (mmWave) frequencies have been allocated in many countries, and commercial services have begun. However, the reality is that their usage has not significantly advanced. This is due to the nature of mmWave signals, which have difficulty reaching long distances and are easily weakened by obstacles, making it challenging to establish widespread coverage areas. Additionally, the number of devices (such as smartphones) that support mmWave is limited, contributing to its limited use.

2. Expectations for Centimeter Wave Technology

The frequencies defined in 5G include the frequency bands that were used in previous generations (up to 4G), as well as two additional frequency bands: Sub6 (3.3GHz - 7.1GHz) and millimeter wave (24.25GHz - 43.5GHz). These are referred to as FR 1 and FR 2, respectively.

Currently, there are discussions about defining frequencies above 43.5GHz as FR2-2, and the range of 7.1GHz to 24.25GHz as FR3. FR3, also known as centimeter wave, has been garnering attention because its wavelength ranges from approximately 1cm to 4cm, making it distinct from millimeter waves.

One of the reasons centimeter waves are garnering interest is because they exhibit less attenuation compared to millimeter waves and have a greater ability to bend around obstacles, such as the backside of buildings.

As the frequency increases, the propagation loss of the radio waves also increases in proportion to the distance. For example, comparing the distance at which a signal losses by 100dB between millimeter waves (28GHz) and centimeter waves (10GHz), at 28GHz the distance is approximately 86m, while at 10GHz it becomes 240m. This means that centimeter waves can reach nearly three times farther compared to millimeter waves. (In free space conditions)

Furthermore, the 10GHz band is currently used in radar systems to measure velocity, which raises expectations that this frequency can bring new functionalities to communication signals in the future.

Figure: Frequency definition range of 4G, 5G and 6G

3. Centimeter Wave status in ITU-R

As some of you may know, the use of radio waves is regulated globally. The usage of radio frequencies is discussed by an organization known as the ITU (International Telecommunication Union), and every four years, a conference called the World Radiocommunication Conference (WRC) is held to deliberate on these matters. Most recently, WRC-23 took place in November 2023 in Dubai, where discussions were held regarding the frequencies for 6G communications.

As a result of WRC-23, the frequency bands 7.125 GHz - 8.4 GHz and 14.8 GHz - 15.35 GHz within the centimeter wave range have been identified for discussion as potential communication frequencies for 6G. The upcoming MRC in 2027 (WRC-27) is scheduled to discuss whether the frequencies will be used for telecommunications.

4. Usage and Challenges of Centimeter Waves in Japan

In Japan, efforts are being made towards the early realization of 6G, led by organizations such as the Beyond5G Promotion Consortium, which was established by the Ministry of Internal Affairs and Communications in 2020. These organizations are responsible for compiling information on the usage status of the aforementioned frequency bands, among other aspects.

SoftBank is also participating in the Beyond5G Promotion Consortium and actively engaging in discussions to facilitate the early realization of 6G.

Furthermore, Softbank’s Research Institution of Advanced Technology is conducting research ahead of 6G implementation, combining the study of millimeter and terahertz waves with the integration of communication and sensing technologies. This endeavor aims to advance research towards the effective utilization of centimeter waves.

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