China is in the forefront of 5G research and development and has begun to study the development of 6G

In the movie "Ready Player One", the protagonist can travel around the world by staying at home. Wearing virtual reality equipment, he can fight together with his friends and get an immersive experience in the game... Such a scene takes place in 2045, but in reality, this may be realized after 2030, that is, in the era of the sixth generation of mobile communications (6G).

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On June 6, the Ministry of Industry and Information Technology issued 5G commercial licenses to China Mobile and four other companies, marking the beginning of the first year of 5G commercialization in China. Commercial mobile communication networks are updated every 10 years, and the commercialization of 5G also means the beginning of the research and development of the next generation of technology.

In July 2018, the International Telecommunication Union established a research group on 2030 network technology. Currently, the United States, China, Japan, South Korea, Finland and other countries have embarked on the 6G research and development track. In February this year, US President Donald Trump tweeted: I want 5G and even 6G to enter the United States as soon as possible. Less than a month later, the United States began to deploy 6G research.

For all countries, mobile communication technology has long been not only a bridge to facilitate communication, but also a reflection of a country's technological competitiveness and even national strength. What is 6G and how far is it from us?

6G, where is the “6”?

For ordinary users, network speed is a KPI to measure the performance of each generation of network. In the 4G era, the amount of data transmitted per second was tens of megabits. In 5G, the data transmission rate will increase by more than 10 times, reaching 1Gbit/s (gigabits per second). When 6G is launched, the network speed will usher in a new leap. Li Shaoqian, professor at the University of Electronic Science and Technology of China and director of the National Key Laboratory of Communication Anti-interference, said in an interview with China News Weekly that in terms of technical indicator setting, the speed of each generation of network must be increased by an order of magnitude compared with the previous generation. "(If) it is higher, it will surpass the technology and cannot be achieved." Therefore, in general scenarios, the speed of 6G will be roughly 10 times that of 5G.

What can large bandwidth and high speed do? In addition to meeting common needs such as ultra-high-definition network TV and virtual reality games, holographic technology has become a promising direction for the industry. The International Telecommunication Union has also included it in the white paper "Prospects for New Network Technologies in 2030 and Beyond".

The so-called holographic technology refers to the technology that can not only see images and hear sounds, but also realize the all-round perception of the five senses such as touch and taste. For example, through holographic images, you can be in a tropical rainforest thousands of miles away without leaving your home. Not only can you see the waterfall and hear the sound of water, but you can also feel the local temperature and humidity and smell the fragrance of the soil. For another example, in a holographic remote meeting, you can touch the other party, and in a holographic surgery, the remote doctor is like being on the scene.

This technology has high requirements for the number of sensors and data transmission rate. Richard Li, chairman of the International Telecommunication Union's 2030 Network Technology Research Group and chief scientist of future networks at Huawei's US headquarters, mentioned in a report that if high-definition holographic projection of a person is to be achieved, the transmission rate must reach 4.62Tbit/s (terabit per second), which is hundreds or thousands of times the speed of 5G network, which is also a challenge for 6G network speed.

The greater power of 6G will be to establish connections between things. In fact, regarding 5G, the industry has proposed three major application scenarios: high-speed and large-bandwidth, ultra-reliable and low-latency communication, and massive machine connections. The theoretical latency of 5G will be reduced from 50 milliseconds in 4G to 1 millisecond. Massive machine connections refer to the number of sensors connected per square kilometer reaching 1 million.

Zhang Ping, professor of the School of Information and Communication Engineering at Beijing University of Posts and Telecommunications and director of the State Key Laboratory of Network and Switching Technology, analyzed that in the past, the upgrade from 1G to 4G only emphasized the high speed dimension. 5G proposed three goals for the first time, but for now, only the first type of scenario has reached an internationally unified technical standard, and 5G commercial use still only meets this scenario. "Ultra-reliable and low-latency communications have not been standardized internationally so far, and will not be determined until March next year." After actual deployment, it is still unknown how the operation effect will be. The priority of standardization of massive machine connections is even lower. At present, the country uses narrowband Internet of Things, which is still at a lower speed in the 4G era, as a technical implementation means. This means that 6G has further room for improvement in these three dimensions.

"The saying '4G changes life, 5G changes society' is actually not scientific," Li Shaoqian believes, and 5G is somewhat deified. In his opinion, the 5G era has only opened the door to the Internet of Everything. With the growth of future demand and the iteration of technology, there is still a long way to go to truly realize the Internet of Everything, which is exactly what the 6G era will do. For example, to build a complete Internet of Vehicles, the problem of wide coverage must be solved first. "If there is no signal in a certain place, cars will crash into each other."

Zhang Ping said that due to technical limitations, the current 5G technology is only relatively independent for one of the three major application scenarios, and the future 6G will cover the needs of two or even three scenarios at the same time. For example, the intelligent transportation system of the entire city must process a large amount of real-time data such as vehicles and vehicles, vehicles and people, and vehicles and transportation facilities, which requires large bandwidth and low latency to avoid accidents.

In the eyes of many industry insiders, AI and 6G will complement each other and integrate in the future development. Niu Zhisheng, a professor at the Department of Electronic Engineering of Tsinghua University, said that "the 6G era will be full of AI." He analyzed that AI will play an important role in helping users identify scenarios and optimizing network resource allocation. Shen Jia, a senior 5G researcher at the Standard Research Center of OPPO Research Institute, said that with the popularization of AI technology and application scenarios, new business scenarios represented by intelligent body interaction will appear in the 6G era. For example, it may take decades for a Go master to pass on knowledge and skills to his apprentice, but relying on 6G, robots can quickly learn from each other and impart wisdom in a few seconds.

Li Shaoqian said that in fact, there is still no clear definition of 6G so far. Before 2023, the world will be in the stage of proposing visions, analyzing needs, and researching potential available technologies. After that, academia and industry will discuss, reach consensus, and formulate standards.

6G, how far away is it?

In order to achieve the beautiful vision of 6G, countries around the world have been competing to make plans.

Since the development of 5G, China has been in the first camp of the world's mobile communications industry. In March last year, Miao Wei, Minister of Industry and Information Technology, said in an interview with the media that China has begun to study the development of 6G. In April last year, the Finnish Academy of Sciences listed the "6G-supported Wireless Intelligent Society and Ecosystem" led by the University of Oulu in Finland as a flagship project of the National Research Funding Program, which will receive more than 250 million euros in funding over the next eight years. In January and June of this year, South Korea's two major electronics giants LG and Samsung were reported to have established 6G R&D centers. In March this year, according to the Nihon Keizai Shimbun, Waseda University, electronics manufacturer NEC and Germany's University of Stuttgart will work together to develop mobile communication technologies in the post-5G era.

At the Mobile World Congress Americas in September last year, Jessica Rosenworther, the first commissioner of the Federal Communications Commission (FCC) to talk about 6G technology, mentioned technologies such as terahertz waves and blockchain. In March this year, shortly after Trump sent out a series of tweets, the FCC announced the opening of an experimental frequency band with a frequency range of 95GHz (gigahertz) to 3THz (terahertz), mainly based on "terahertz waves", to provide developers with a 10-year use period.

Terahertz waves have a frequency of 100GHz to 10THz, and a wavelength between millimeter waves and infrared rays. They are high-frequency electromagnetic waves and are considered one of the key technologies that are potentially available for 6G. In the words of Li Shaoqian, this is a new continent that has never been opened up in the field of mobile communications. In the development journey from 1G to 5G, limited low-frequency band resources have been developed first, and the frequency bands used in mobile communications have continued to rise. According to the characteristics of electromagnetic waves, the higher the frequency, the larger the available bandwidth, which is why terahertz waves are favored by the industry.

But like the two sides of a coin, terahertz waves also have fatal flaws. The higher the frequency of electromagnetic waves, the shorter the wavelength. As a result, terahertz waves have a poor ability to bypass obstacles. Terahertz waves cannot penetrate concrete walls and are easily absorbed by water molecules. They are also affected by rainy and foggy weather, leaves, buildings, pedestrians, etc. This means that terahertz wave signals have a large attenuation intensity, cannot be transmitted over long distances, and have a limited coverage range.

In fact, similar problems have already appeared in the 5G era. my country's 5G network currently uses frequency bands below 6GHz, and will use millimeter wave bands in the future. The frequencies are higher than the electromagnetic waves used in the 4G era, and millimeter waves and terahertz waves have similar shortcomings. This will result in a large and dense number of base stations due to the short propagation distance of electromagnetic waves.

In some existing experimental studies, the propagation distance of terahertz waves is mostly tens of meters to hundreds of meters. In 2012, Li Shaoqian's team undertook the first terahertz communication system project of the Ministry of Science and Technology. Initially, he estimated that the propagation distance of terahertz waves was only 5 meters, but experimental measurements showed that in the absence of any obstruction, its transmission distance can reach more than 1 kilometer. He Jiguang, a postdoctoral fellow at the Wireless Communication Center of the University of Oulu, said that if terahertz waves cannot penetrate walls, the problem of transmission from outdoor to indoor spaces must be considered.

In the view of Niu Kai, a professor at Beijing University of Posts and Telecommunications, in the future, the wider application scope of terahertz waves may be indoor short-distance, high-speed transmission, with a rate of up to 1 terabit per second, while outdoor long-distance transmission and even wide coverage still need to rely on low-frequency bands. "After 3G is decommissioned, these frequencies can be used, or some planning can be done in the frequency bands below 6GHz." At the same time, in order to achieve high speeds, MIMO technology (multiple-input, multiple-output technology) can also be relied on. "This is actually equivalent to adding information transmission channels in the spatial dimension." He analyzed that future network coverage must be a combination of multiple frequency bands. Tang Hai, director of the Standard Research Center of OPPO Research Institute and chief scientist of 5G, said that whether base stations will be built more and more densely in the future depends mainly on whether high-quality low-frequency bands can be vacated for use.

Li Shaoqian believes that terahertz wave communication can be used in the future for point-to-point transmission of ultra-high-definition signals from cameras to television ground production centers in sports events. Local large-capacity transmission is a technology that may be applied in 6G. However, whether terahertz waves will eventually be used in 6G in the future and whether they will be adopted through the construction of base stations still needs further discussion.

Another possibility is that in the 6G era, the communication between terminals will no longer go through the "intermediary" of the base station. Shen Jia believes that such a mechanism may become a reality, especially in short-distance, high-frequency communications. "When we use high-frequency point-to-point communication to move a lot of communication traffic from the base station to our mobile phones, the traditional medium and low-frequency resources can also be better used, which is equivalent to the original highway is full of cars. If two people are neighbors, there is no need to detour to the highway." Walid Saad, a professor in the Department of Electronics and Computer Science at Virginia Tech, mentioned in his paper that in the future 6G era, whether it is walls, roads, or entire buildings, a smart material can be used, with antennas installed on the surface to act as base stations to achieve close-range data transmission and reception.

As base stations become more dense and the frequency of electromagnetic waves increases, will radiation increase? This is a question that has already arisen in people's minds before the arrival of 5G.

In this regard, Li Shaoqian explained that there is still insufficient evidence to support whether the higher the frequency, the greater the radiation of electromagnetic waves to humans. "But one thing is certain, high power is not good." The main indicator for measuring electromagnetic wave radiation to the human body is power. The power used in mobile communications is actually not large. In addition, since the coverage range of 5G base stations is smaller, their transmission power can also be further reduced.

Another way to ensure wide coverage is satellite communications. On May 23, SpaceX launched the first batch of 60 low-Earth satellites for its satellite internet project, Starlink. From 2019 to 2024, SpaceX will build a Starlink network consisting of about 12,000 satellites to provide high-speed internet access services from space to the ground, which has been interpreted by many self-media as the US 6G strategy. Satellite startups such as OneWeb, which is funded by Amazon and SoftBank, also have ambitions to build space internet.

Li Shaoqian analyzed that, globally, mobile communications currently cover only 30% of the land area. In the future, satellites will be used to achieve full coverage of deserts, Gobi, poor areas, oceans, etc. However, due to the limitations of satellites, the communication rate will be relatively low. Therefore, it can only complement ground mobile communications and cannot play a role as a substitute. Niu Zhisheng said that since low-Earth satellites are not synchronized with the Earth's rotation, it means that different satellites must "relay" to complete a communication process, and the problem of orbital limitations also needs to be considered.

Li Shaoqian said that mobile communications in the 6G era will be an integrated integration of heaven and earth. At the same time, in the process of iteration of several generations of mobile communication technology, technologies with overlapping functions will be replaced. 3G and 4G provide broadband services, 3G will die, and "2G has a low frequency, good coverage, and provides the most basic communication services" will be retained. Therefore, there will be a situation of "multi-generation coexistence" in the network. From the current point of view, the 5G era is still facing the problems of high base station construction costs and high operating power consumption. Data show that the electricity cost of 5G base stations is equivalent to two to three times that of 4G base stations, which will also be a challenge for 6G. Li Shaoqian believes that power consumption can be reduced by simplifying the structure, increasing the integration of components, and removing unnecessary equipment, but "wanting the horse to run and not eat grass" is difficult to find this balance point.

Zhang Ping believes that the most critical thing at present is to spend more time to "think clearly about what 6G is and what it can bring us."