6G (6th generation wireless technology) is the successor to 5G cellular technology. 6G networks will be able to use higher frequencies than 5G networks and offer higher capacity and lower latency. One of the goals of 6G networks is to support delayed communication of 1 microsecond or even sub-microsecond.
It is expected that 6G communications will support five application scenarios: Enhanced Mobile Broadband Plus (eMBB-Plus), Big Communications (BigCom), Secure Ultra-Reliable Low-Latency Communications (SURLLC), Three-Dimensional Integrated Communications (3D-InteCom), and Unconventional Data Communications (UCDC).
5G began to be deployed in 2019, and it is expected to become the dominant mobile communications technology until at least 2030. Initial 6G deployments are likely to start to appear in the 2030-2035 timeframe.
The 6G network will be committed to creating a fully connected communication world integrating terrestrial communication, satellite communication, and marine communication, and the “blind spots” of today’s mobile communications, such as deserts, uninhabited areas, and oceans, are expected to achieve signal coverage.
6G will be used in spatial communication, intelligent interaction, tactile Internet, emotional and tactile communication, multi-sensory mixed reality, machine-to-machine collaboration, fully automated transportation, etc.
Since the launch of the world’s first cellular mobile communication service by the Japan Telegraph and Telephone Public Corporation (NTT) in December 1979, mobile communication technology has evolved to a new generation of systems every decade.
From the first generation (1G) to the second generation (2G), voice calls were the main means of communication, and simple e-mail became possible. Starting with the third generation (3G), data communication (e.g., i-mode) and multimedia information (e.g., photos, music, and videos) can be communicated via mobile devices. Since the fourth generation (4G), high-speed communication technology of more than 100 Mbps has led to the explosive spread of smartphones due to the adoption of Long Term Evolution (LTE) technology, and the communication speed of nearly 1 Gbps has been reached.
Fifth generation (5G) networks have much higher data transfer rates than previous cellular networks, reaching up to 10 Gbit/s with a network latency of less than 1 millisecond. The sixth generation (6G) is expected to support speeds of 1TB/s. This level of capacity and latency will be unprecedented, and it will expand the performance of 5G applications and expand the range of capabilities to support a growing number of innovative applications in wireless cognition, sensing, and imaging.
Mobile communication systems are technically developed every 10 years, while the change cycle of mobile communication services is about 20 years. Therefore, the “third wave” triggered by 5G is expected to become an even bigger wave through 5G evolution and sixth generation (6G) technology and will support industry and society in the 30s of the 21st century.
Past generations of mobile communication technology have evolved to 6G. In previous generations, each generation has a representative technology. However, since 4G, radio access technology (RAT) based on orthogonal frequency division multiplexing (OFDM) has encompassed a combination of several new technologies, while in 6G, the technology field is considered to become more diverse. This is since OFDM-based technologies have achieved communication quality close to the Shannon limit, and at the same time, the requirements and use cases will be further expanded in the previous generation.
Communication system research in the post-5G era must consider circuit and device manufacturing capabilities, and in 6G, special attention needs to be paid to the battery life of the device, rather than data rate and latency. In addition, it is foreseeable that wireless communications in the future will provide the same level of reliability as wired communications. Blockchain technology-based network decentralization is considered the key to simplifying network management and delivering satisfactory performance in 6G.
Of all the technical work related to 6G, terahertz communications, artificial intelligence (AI) and reconfigurable smart surfaces are the most striking ideas, which are considered revolutionary technologies in wireless communications. AI-enhanced 6G is believed to be able to offer a range of new features, such as self-aggregation, context-aware, self-configuration, and more.
In addition, 6G with AI capabilities will unlock the full potential of radio signals and enable the transition from cognitive to intelligent radio. Machine learning is especially important for enabling AI-based 6G.
Intelligent 6G network architecture based on artificial intelligence
High security, confidentiality, and privacy
Limited by Shannon restrictions, it is difficult to improve the spectral efficiency of 6G on a large scale. Instead, new technologies should greatly enhance the security, confidentiality, and privacy of 6G communications. While other use cases will become ubiquitous and increasingly important, traditional mobile communications will remain the most important application of 6G in the 2030s. Therefore, 6G networks should be human-centric, not machine-centric, application-centric, or data-centric. According to this principle, high security, confidentiality and privacy should be the key features of 6G. In addition, user experience will be used as a key metric in 6G communication networks.
In 5G networks, traditional encryption algorithms based on the RSA public key cryptography system are still being used to provide transmission security and confidentiality. Under the pressure of big data and AI technology, the RSA cryptosystem has become insecure. The most effective way to improve network throughput, reliability, latency, and the number of service users in communications is to densify the network and use higher frequencies to transmit signals. Physical layer security technologies and quantum key distribution via visual optical communication (VLC) will be the solution to the 6G data security challenge. More advanced quantum computing and quantum communication technologies may also be deployed to provide tight protection against various cyberattacks.
High endurance and full customization
From a human-centric perspective, technological success should not directly or indirectly increase the financial burden or deprive users of choice. Therefore, high affordability and full customization should be two important technical indicators for 6G communication. Full customization allows users to choose the mode of service and adjust their personal preferences. For example, some users may want to get a low speed but reliable data service, others may tolerate unreliable data service in exchange for lower communication fees, others may still only care about the energy consumption of their devices, and some may even want to get rid of smart features due to concerns about data security and privacy. All users will be granted the right to choose what they like in 6G, and these rights should not be diminished by smart technology or unnecessary system configurations. Therefore, the performance analysis of 6G communication systems should also integrate multiple performance indicators into a whole, rather than treating them independently. User experience will be clearly defined and used as a key indicator for performance evaluation in the 6G era.
Low energy consumption and long battery life
The daily charging demand for smartphones and tablets in 4G/LTE networks will continue. In order to overcome the daily charging limitations of most communication devices and facilitate communication services, low energy consumption and long battery life are two research priorities for 6G communication. In order to reduce energy consumption, the computing tasks of the user’s equipment can be offloaded to a smart base station with a reliable power supply or a ubiquitous smart radio space. Cooperative relays, communications, and the densification of networks will also help reduce the transmit power of mobile devices by reducing the distance traveled per hop. To achieve a long battery life, various energy harvesting methods will be applied in 6G, which will collect energy not only from the surrounding RF signals, but also from micro-vibrations and sunlight. Remote wireless charging will also be a promising way to extend battery life.
High intelligence
The high intelligence of 6G will be beneficial to network operation, wireless transmission environment, and communication services, which refer to operational intelligence, environmental intelligence, and service intelligence, respectively. Conventional network operations involve many multi-objective performance optimization problems that are subject to a complex set of constraints. Resources including communication equipment, frequency bands, transmission power, etc., need to be deployed in an appropriate manner to achieve a satisfactory level of network operation. In addition, these multi-objective performance optimization problems are often difficult to solve and difficult to obtain optimal solutions in real time. With the development of machine learning techniques, especially deep learning, the control center of a base station or core network equipped with a graphics processing unit can execute relevant learning algorithms to efficiently allocate resources to achieve near-optimal performance.
The terahertz band, defined between 0.1 THz and 10 THz, is known as the gap band between the microwave and optical spectra, but terahertz electron, photon, and hybrid electron-photon approaches have now been developed. Therefore, hybrid terahertz/free-space optical systems are expected to be implemented in 6G using hybrid electron-photonic transceivers, where optical lasers can be used to generate terahertz signals or transmit optical signals. The wireless data networks of the future will have to achieve higher transmission rates and lower latency, while also providing more and more end devices. For this, a network structure consisting of many small radio cells will be required. To connect these batteries, high-frequency, high-performance transmission lines up to the terahertz range will be required. In addition, if possible, seamless connectivity to optical networks must be ensured.
Future wireless communication networks will have to handle data rates of tens or even hundreds of Gbit/s per link, which will require the use of carrier frequencies on unallocated terahertz (THz) spectrum. In this context, it is important to seamlessly integrate the THz link into the existing fiber optic infrastructure to complement the inherent portability and flexibility advantages of wireless networks with reliable and virtually unlimited optical transmission systems. On a technical level, this requires new equipment and signal processing concepts to directly convert the data stream.
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