Summary:

The development of communication services requires lower latency, higher system capacity, higher data rate, higher security and higher quality of service. 6G technology came into being. The key characteristics and applications of the potential technologies of 6G, such as artificial intelligence, terahertz communication, quantum communication, unmanned aerial vehicle, and cellular communication, are analyzed to provide reference for the future research of 6G communication.

01summary

The rapid development of AI, VR, IoT and other automatic system applications has brought huge traffic. Automatic systems are popular in various fields of society. Millions of sensors are integrated into various environments such as cities, industries, cars and homes to provide intelligent and automated work and life. High data rates with more reliable connections are required to support these applications.

Compared with 4G communication, although 5G network provides large bandwidth, new QoS, new technologies such as millimeter wave, the rapid growth of data centric automation system has exceeded the capacity of 5G wireless network. 5G communication largely ignores the integration of communication, intelligence, sensing, control, computing and other functions. Future Internet of Things applications will need to integrate specific equipment, requiring at least 10Gbit/s data rate, As the 5G capacity reaches its limit, the new design goal requires the introduction of 6G technology.

02Service capability of 6G communication technology

Compared with 4G/5G communication, 6G network technology and support capability are required to be higher, as shown in Table 1.

Table 1 Comparison of 6G, 4G and 5G communication technology capabilities

The development of 6G emerging technologies includes terahertz band, artificial intelligence, optical wireless communication (OWC), 3D network, unmanned aerial vehicle (UAV), intelligent reflective surface IRS and wireless power transmission. Through the integration of these new technologies, 6G communication will realize various system functional characteristics: ubiquitous mobile ultra wideband (uMUB), ultra-high speed low delay communication (uHSLLC), large-scale machine communication (mMTC), ultra-high data density (uHDD). The application scenario is shown in Figure 1.

Figure 1 Application architecture scenario of 6G communication

03Key technologies of 6G communication

From the development history of mobile networks, most of the 6G network technologies are based on the 5G architecture, inheriting the advantages of 5G and adding and improving some new technologies.

3.1 Artificial intelligence

5G communication system supports partial or very limited AI, while 6G will fully support AI automation. AI will play a full role in the 6G phase to realize the transformation from cognitive wireless to intelligent wireless. The progress of machine learning has created more intelligent networks for real-time communication in 6G. The introduction of AI in communication will simplify and improve the transmission of real-time data.

Machine learning may be applied to RF signal processing, spectrum mining and spectrum mapping. It combines photon technology with machine learning to promote the evolution of artificial intelligence in 6G, so as to build a photon based cognitive radio system. The physical layer adopts the codec based on artificial intelligence, deep learning channel state estimation, automatic modulation classification. In the data link layer and transmission layer, deep learning based resource allocation, intelligent traffic prediction and control are widely studied to meet the 6G requirements. AI technology will help to achieve the goal of uMUB, uHSLLC, mMTC and uHDD services in 6G communication.

3.2 Terahertz communication

Terahertz (THz) wave, also known as submillimeter radiation, usually refers to the 0.1-10 THz band, and the corresponding wavelength is 0.03-3 mm. According to ITU-R recommendations, 275 GHz - 3THz is the main part of the terahertz communication frequency band. The capacity of 6G communication will be increased by increasing the terahertz band (275 GHz - 3THz) to the mmWave band (30-300 GHz). The bands in the range of 275 GHz to 3 THz have not been allocated for any purpose globally, so they have the potential to achieve ideal high data rates. When this terahertz band is added to the existing mmWave band, the total band capacity will increase at least 11.11 times.

5G introduces mmWave frequency to achieve higher data rate and support new applications. However, the goal of 6G is to push the band boundary to terahertz to meet higher requirements. The terahertz band will become the leading field of high data rate communication in 6G communication.

3.3 Optical wireless technology

In addition to radio frequency based communication, optical wireless (OWC) technology can also be used for 6G communication, for all possible devices to access the network, which can also be connected to the front-end/return network connection. Optical fidelity, visible light communication (VLC), optical camera communication, FSO communication based on optical band and other OWC technologies have become well-known technologies. These communication technologies will be widely used in V2X communication, indoor mobile robot positioning, VR, underwater OWC and other applications. Communication based on wireless optical technology can provide very high data rate, low delay and security.

Optical band based lidar is a high-resolution 3D mapping technology in 6G communication. OWC will enhance the support of uMUB, uHSLLC, mMTC and uHDD services in 6G communication systems. The development of light emitting diode (LED) technology and multiplexing technology are two key drivers of the OWC in 6G. White light based on different wavelengths will help to accelerate throughput performance through wavelength division multiplexing, resulting in ultra-high data rate VLC access points reaching 100 Gbps. The large-scale parallelization of micro LED arrays will further improve the data rate of 6G communication target Tbps.

3.4 Wireless optical communication front-end/return network

Due to remote geographical location and complex connection, it is impossible to always have optical fiber connection as a backhaul network. Deploying optical fiber links for small cellular networks may not be an economical and effective solution. FSO front-end/return network is emerging in the super 5G communication system. The transmission and reception characteristics of FSO system are similar to those of optical fiber network. FSO is an excellent technology to provide front-end/return connection in 6G.

With the use of wireless optical communication, communication can even be carried out over a long distance of more than 10000 kilometers. FSO supports high-capacity backhaul connections in remote and non remote areas such as oceans, outer space, underwater and isolated islands. Front end/return of wireless optical communication is a common problem in 5G and 6G networks, but it is more critical in 6G. First, it requires higher front end/return connection capacity. Second, it will require more remote connections than 5G. FSO communication can support these two functions at the same time, becoming a key factor for 6G communication system to improve uMUB and uHSLLC services.

3.5 Large scale MIMO and intelligent reflective surface IRS

Large scale MIMO technology is the key for 6G system to support uHSLLC, mMTC and uHDD services. Compared with 5G, 6G wireless system will change from traditional large-scale MIMO to intelligent reflective surface IRS, providing large surfaces for wireless communication and heterogeneous devices. IRS is a new hardware technology, which has great potential in energy-saving and green communication. It is also called hypersurface. It is composed of many reflective diode units, and can reflect any incoming electromagnetic signal and adjustable phase shift. These reconstituted smart surface materials can integrate exponential modulation to improve the spectral efficiency of the 6G network. Using adjustable reflective phase shift signals and transmission signals, it can also improve the energy efficiency of the system. In the upcoming 6G network, this technology will be considered as a solution to maximize data rate and minimize transmission power.

3.6 Blockchain

Blockchain is a key technology for managing massive data in the future communication system, and it is a form of distributed ledger technology. A distributed ledger is a database distributed on multiple nodes or computing devices. Each node replicates and stores an identical copy of the ledger. The point-to-point network management blockchain can exist without the control of a central authority or server. The data on the blockchain is gathered together and constructed into blocks. These blocks are connected and protected using cryptography. In essence, the blockchain is a perfect complement to the large-scale Internet of Things, with better security, privacy, interoperability, reliability and scalability. Therefore, blockchain technology will provide multiple facilities such as cross device interoperability, traceability of massive data, independent interaction and reliability of different IoT systems for the massive connection of 6G communication system, so as to achieve the goal of uHSLLC services.

3.7 3D Network

The 6G system will integrate ground and airborne networks to provide communication support for vertically expanded users. 3D base stations are provided through low orbit satellites and unmanned aerial vehicles. New dimensions are added in height and related degrees of freedom, making 3D connectivity very different from traditional 2D networks. 6G heterogeneous networks will provide 3D coverage. A decentralized 6G network combining ground networks, unmanned aerial vehicle networks and satellite systems will truly achieve global coverage and strict seamless access, even covering oceans and mountains.

3.8 Quantum Communication

Advanced quantum computing and quantum communication technologies will be deployed in 6G to provide strict security against various network attacks. The emerging quantum computing paradigm, quantum machine learning and its synergy with the communication network are considered to be the core contributing factors of 6G. The upgrading of quantum computing and engineering needs to solve complex tasks. Quantum communication uses quantum keys based on quantum non cloning theorem and uncertainty principle, providing strong security. These information are encoded in quantum states by photons or quantum particles. According to the full quantum principle, they cannot be accessed or cloned without tampering. In addition, due to the superposition of quantum bits, quantum communication improves the throughput.

3.9 UAV

UAV is a basic element of 6G wireless communication. In many cases, UAV technology is used to provide high data rate wireless connectivity. The base station is physically mounted on the UAV to provide cellular connectivity. UAV has some features that are not available in the fixed base station infrastructure, such as easy deployment, strong line of sight connection and controllable mobility. In emergencies such as natural disasters, the implementation of ground communication infrastructure is not economically feasible, and sometimes it is impossible to provide any services in a turbulent environment. UAVs can easily handle these situations. UAV will become a new way of wireless communication. This technology can meet the basic needs of wireless networks such as uMUB, uHSLLC, mMTC and uHDD. UAVs can also be used for a variety of purposes, such as strengthening network connectivity, fire detection, emergency services in the event of disasters, safety and monitoring, pollution monitoring, parking monitoring, accident monitoring, etc.

3.10 No cellular communication

The tight integration of multi frequency and different communication technologies will be the key to the 6G system. Therefore, users will seamlessly move from one network to another without any manual configuration in the device. In 6G, the traditional concepts of cellular communication and quadrature communication will be transformed into non cellular communication and non positive traffic communication respectively. The best network is automatically selected from existing communication technologies, which will break the limitation of cellular concept in wireless communication.

6G cellless communication will overcome all the problems of handover failure, handover delay, data loss and ping-pong effect, and provide better quality of service. Cellular free communication will be achieved through multi connectivity and multi-layer hybrid technologies, as well as the use of different and heterogeneous wireless technologies in devices.

3.11 Integration of wireless information and energy transmission

The integration of wireless information and energy transmission (WIET) will be one of the most innovative technologies in the field of communication. WIET uses the same field and band as wireless communication systems. Sensors and smart phones are charged through wireless power transmission during communication. WIET is a technology that extends the life of wireless battery charging systems. Therefore, devices without batteries can also support 6G connections.

3.12 Perceptual communication integration

A key driver of autonomous wireless networks is the ability to continuously perceive the dynamic state of the environment and exchange information between different nodes. In 6G, the sensing system will be closely integrated with the communication system to support the autonomous system. Massive perceptual objects, complex communication resources, multi-level computing resources and multi-level cache resources are the real challenges to achieve this integration.

3.13 Access back network integration

The density of the 6G access network will be huge. Each access network involves backhaul connections, such as optical fiber and FSO networks. The tight integration of access and return networks is sufficient to handle most access network accesses.

3.14 Dynamic network slice

Dynamic network slicing allows network operators to allow private virtual networks to support the optimal delivery of any service to a wide range of users, vehicles, machines and industries. In the 6G communication system, many users connect to a large number of heterogeneous networks, which is one of the basic elements of management. The virtualization of software defined networks and network functions is the basic technology to achieve dynamic network slicing, which also affects the standardization of cloud computing in network management. For example, the network has a centralized controller to dynamically guide and manage traffic, and orchestrates network resource allocation to achieve performance optimization.

3.15 Holographic beam

Beam forming is a signal processing process, through which the antenna array can be guided to transmit radio signals in a specific direction. It is a subset of smart antennas or advanced antenna systems. The beamforming technology has the advantages of high signal-to-noise ratio, strong anti-interference ability and high network efficiency. Holographic beam forming (HBF) is a new beam forming method. It uses software defined antennas, which is very different from MIMO systems. HBF is an effective and flexible method to transmit and receive signals from multi antenna communication equipment in 6G. HBF can play an important role in the fields of physical layer security, wireless power transmission, increasing network coverage and positioning.

3.16 Big data analysis

Big data analysis is a complex process of analyzing various big data sets or big data, revealing information, such as hidden patterns, unknown associations and customer preferences, to ensure comprehensive data management. Big data is collected from a variety of sources, such as video, social networks, images and sensors. This technology is widely used in 6G systems to process large amounts of data. The prospect of using massive data, big data analysis and deep learning tools is expected to promote the 6G network through automation and self optimization. An example of big data analysis application is end-to-end delay reduction. The combination of machine learning and big data will determine the best path for user data through prediction analysis to reduce the end-to-end delay of the 6G system.

3.17 Backscatter communication

Environmental backscatter wireless communication enables two battery free devices to interact with each other by using existing RF signals, such as ambient TV and cellular transmission, to achieve a reasonable data rate in a short communication range. Small monitoring signals can be transmitted through sensors that do not consume any energy. The battery free nodes in the backscatter communication system make it a candidate technology for large-scale connection in the future 6G network. In such a system, it is a key requirement to obtain the accurate phase and channel state of network nodes, and incoherent communication can be considered as a promising enabling to meet these requirements. In addition, incoherent backscatter communication can provide optimized resource utilization and service enhancement in network devices.

3.18 Active Cache

Large scale deployment of 6G small cellular network is one of the key means to significantly improve network capacity, coverage and mobility management, which will cause huge downlink traffic overload on the base station. Active caching has become a basic solution to reduce access delay and traffic offloading, and improve the quality of user experience. It is essential for 6G communication to study the joint optimization of active content caching, interference management, intelligent coding scheme and scheduling technology.

3.19 moving edge computing

Due to distributed massive cloud applications, mobile enhanced edge computing (MEEC) has become an important part of 6G technology. The implementation of MEEC based on artificial intelligence will make full use of big data analysis and system control computing. Edge intelligence is a new specification, which meets the exciting requirements of the upcoming heterogeneous computing, communication and high-dimensional intelligent configuration of general service scenarios.

046G communication network characteristics

Among the technical capabilities of 6G, the simultaneous wireless connectivity of the system will be 1000 times higher than that of the 5G system. Compared with the enhanced mobile broadband (eMBB) in 5G, 6G will provide ubiquitous network services uMUB. Ultra reliable low latency is a key feature of 5G communication, and it will also become a key factor in providing 6G communication of uHSLLC. The 6G communication system will provide large-scale connection equipment (up to 10 million/km2), Gbit/s rate in any coverage area, and even new coverage environments such as sky (10000 km) and ocean (20 n miles). The 6G system will provide ultra long battery life and advanced battery technology for energy collection. In the 6G system, mobile devices do not need to be charged separately.

According to different types of 6G services, the applicable 6G technologies under different characteristic services of uMUB, uHSLLC, mMTC and uHDD can be displayed. Each technology can enhance one or more services, as shown in Table 2.

Table 2 Characteristics of emerging technologies under different 6G services

05Discussion on the Application Prospect of 6G Network

All artificial intelligence will be integrated into the 6G communication system. All network instruments, management, physical layer signal processing, resource management, business based communication, etc. will be integrated using AI, which will promote the digital transformation of industrial manufacturing.

5.1 Super intelligent society

M2M communication and energy collection based on artificial intelligence of 6G network will accelerate the construction of intelligent society. At present, the development of data centric automation system has exceeded the level of 5G. In some application fields, such as XR equipment, the transmission rate is even required to exceed 10Gbit/s. The 6G system will help to promote the real deployment of unmanned vehicles and other businesses. The mMUB and uHLSLLC services in the 6G system will provide reliable vehicle to everything and vehicle to server connection support, and support the ground controller and the system communication between the UAV and the ground. Through the use of intelligent mobile devices, 6G wireless connection will make society super intelligent.

5.2 Expand realistic services

Extended Reality XR refers to the combination of all real and virtual environments and human-computer interaction generated by computer technology and wearable devices, which integrates all forms of augmented reality (AR), mixed reality (MR) and virtual reality (VR). It is the basic feature of 6G communication system. All these functions use 3D objects and AI as their key driving elements.

In addition to providing computing, cognition, storage, human senses, physiology and other perceptual needs, 6G will provide a truly immersive AR/MR/VR experience through joint design integration and high-quality wireless connection. The advanced functions of wearable devices (such as XR), high-definition images, holographic images and five sense communication have accelerated the communication opportunities between people and objects, providing games Sports and other innovative entertainment and enterprise services are not limited by time and location. The high data rate, low latency and highly reliable wireless connection provided by the 6G system promote a true XR experience. The 6G service uHLSLLC will enable XR applications to be successfully deployed in the future.

5.3 Wireless brain computer interaction

Brain computer interface (BCI) is a method to control household appliances used daily in intelligent society, especially household appliances and medical devices. It is a direct communication path between the brain and external devices. BCI acquires brain signals, transmits them to digital devices, and analyzes and interprets these signals as further commands or actions. Compared with 5G, wireless BCI requires high data rate, ultra-low delay and ultra-high reliability. For example, XR, multi brain controlled cinema and brain to object communication require very high throughput (>10 Gbit/s) and ultra reliable connection. The functions of uHLSLLC and uMTC in 6G wireless communication will support the implementation of BCI system in intelligent life.

5.4 Tactile Communication

6G wireless communication will support tactile communication, and remote users can enjoy tactile experience through real-time interaction system. This type of communication is widely used in artificial intelligence, robot sensors and other fields, such as touch learning for the disabled, medical tactile mode in surgery, etc. The uHLSLLC, mMTC and uHDD characteristics of 6G communication network can promote the realization of tactile systems and applications.

5.5 Intelligent medical and biomedical communication

The medical and health system will also benefit from 6G wireless networks, because innovations such as AR / VR, holographic telepresence, mobile edge computing and artificial intelligence will help build intelligent medical systems. The 6G network will provide a reliable remote monitoring system for the medical system, and even remote surgery can be realized through 6G communication. The high data rate, low latency, and ultra reliable 6G network will help to transmit large amounts of medical data quickly and reliably, and improve the accessibility and quality of medical services. In addition, as one of the key technologies of 6G, terahertz has potential applications in medical care services, such as terahertz pulse imaging in dermatology, oral health care, pharmaceutical industry and medical imaging.

In addition, biomedical communication is an important prospect of 6G wireless communication system. In vivo sensors that provide battery free communication technology are mainly used for reliable and long-term monitoring, clinical diagnosis, sports and human-computer interface. 6G uMUB and uHLSLLC services can characterize these applications.

5.6 Internet of Everything

5G is considered as the beginning of IoE, which has solved many challenges from standardization to commercialization. The 6G system will provide comprehensive IoE support. IoE is used in intelligent societies such as smart cars, intelligent health and intelligent industries. The use of energy-saving sensor nodes is considered to be one of the key factors in supporting large-scale IoE connectivity in 6G. Low power consumption wide area network (LPWAN) has the potential to support wide area coverage (up to 20 km) networks, with long battery life (>10 years) and low deployment costs. LPWAN participates in most IoE use cases. This application supports uMUB, uHLSLLC, uHDD and other features of 6G communication.

06Concluding remarks

With the continuous development of information communication, 5G will eventually be unable to fully meet the growing demand for wireless communication, while the research on 6G is still in its infancy and research stage. This paper studies the technology and application prospect of realizing the 6G communication target, deeply discusses the key technical characteristics and deployment of 6G communication, looks forward to the possible application prospect and direction of the future 6G communication target, and provides reference for the subsequent research, design and development of 6G technology.