In December 2013, China’s fourth-generation mobile communication (4G) license was issued, and 4G technology officially went commercial. At the same time, the development of the fifth-generation mobile communications (5G) for the next generation of mobile communications has long been in full swing around the world. What is the process of 5G R&D, and what problems will it encounter during the R&D process? This edition will be published in the "5G Development Series Report" from now on, so stay tuned.
In the evolution of mobile communication, China has experienced various stages of “2G tracking, 3G breakthrough, 4G synchronizationâ€. In the 5G era, China is determined to occupy the technical commanding heights and make full efforts in 5G related work. The organization established the IMT-2020 (5G) promotion group to promote the transformation of the major special "new generation broadband wireless mobile communication network" to 5G, and launched "pre-research and development of 5G systems", from 5G services, frequency, wireless transmission and networking technologies, Evaluate all aspects of test verification technology, standardization and intellectual property to explore the development vision of 5G.
In the case of 5G R&D, how to establish a comprehensive 5G key technology evaluation index system and evaluation method to achieve objective and effective third-party evaluation, service technology and resource management development needs, is also facing the current 5G technology development Important question.
As a national radio management technology organization, the National Radio Monitoring Center (hereinafter referred to as the Monitoring Center) is actively participating in 5G related organizations and research projects. At present, the monitoring center spectrum engineering laboratory is vigorously building an open electromagnetic compatibility analysis test platform based on service-oriented architecture (SOA) to realize the integration and application of large-scale software, hardware and high-performance test instrumentation, which will be the radio management agency. Research institutes and industry-related units provide good radio system research, development and verification experimental environments. For the 5G key technology assessment work, the monitoring center plans to use the platform to build a 5G system test and verification environment, so as to achieve an objective and efficient evaluation of 5G key technologies.
In order to fully grasp the lifeline of 5G technology and ensure that it keeps pace with the times, the monitoring center is actively involved in the tracking and research of 5G key technologies, and reserves technical reserves for 5G frequency planning, monitoring and key technology evaluation and testing. The following is a brief analysis and interpretation of some of the key technologies.
Key technology 1: high frequency transmission
The traditional working frequency band of mobile communication is mainly concentrated below 3 GHz, which makes the spectrum resources very crowded. In the high frequency bands (such as millimeter wave and centimeter wave band), the available spectrum resources are abundant, which can effectively alleviate the current situation of spectrum resources and can achieve extremely high speed and short Distance communication, support for 5G capacity and transmission rate requirements.
The application of high frequency bands in mobile communications is a future development trend, and the industry is highly concerned about this. A sufficient amount of available bandwidth, miniaturized antennas and equipment, and high antenna gain are the main advantages of high-band millimeter-wave mobile communication, but also have short transmission distance, poor penetration and diffraction capability, and are susceptible to climate impacts. Disadvantages. Problems in RF devices and system design are yet to be further studied and resolved.
The Monitoring Centre is currently actively pursuing high-band demand studies and the selection of potential candidate bands. Although the high-band resources are currently abundant, they still need to be scientifically planned and balanced, so that valuable spectrum resources can be optimally configured.
Key Technology 2: New Multi-Antenna Transmission
Multi-antenna technology has gone from passive to active, from two-dimensional (2D) to three-dimensional (3D), from high-order MIMO to large-scale array development, it is expected to achieve spectrum efficiency improvement of dozens of times or even higher. One of the important research directions of 5G technology.
With the introduction of an active antenna array, the number of cooperative antennas that can be supported by the base station side will reach 128. In addition, the original 2D antenna array is expanded into a 3D antenna array, which forms a novel 3D-MIMO technology, supports multi-user beam intelligent shaping, reduces inter-user interference, and combines high-band millimeter-wave technology to further improve wireless signal coverage performance.
Researchers are currently working on large-scale antenna channel measurement and modeling, array design and calibration, pilot channels, codebooks, and feedback mechanisms, and will support more user space division multiple access (SDMA) in the future, significantly reducing Transmit power to achieve green energy saving and improve coverage.
Key Technology 3: Simultaneous co-frequency full duplex
In recent years, simultaneous co-frequency full-duplex technology has attracted the attention of the industry. With this technology, in the same spectrum, the transmitting and receiving sides of the communication simultaneously transmit and receive signals, which theoretically can improve the efficiency of the air interface spectrum by one time compared with the conventional TDD and FDD duplex modes.
Full-duplex technology can break through the spectrum resource usage restrictions of FDD and TDD, making the use of spectrum resources more flexible. However, full-duplex technology needs to have extremely high interference cancellation capability, which poses a great challenge to the interference cancellation technology, and there are also problems of co-channel interference in adjacent cells. In multi-antenna and networking scenarios, the application of full-duplex technology is more difficult.
Key Technology 4: D2D
The traditional cellular communication system is based on the base station to achieve cell coverage, while the base station and the relay station cannot move. The network structure has certain limitations on flexibility. With the increasing number of wireless multimedia services, the traditional base station-centric service delivery method can no longer meet the business needs of a large number of users in different environments.
D2D technology can realize direct communication between communication terminals without the help of base stations, and expand network connection and access methods. Due to short-distance direct communication and high channel quality, D2D can achieve higher data rates, lower latency and lower power consumption. Through widely distributed terminals, it can improve coverage and achieve efficient use of spectrum resources. Flexible network architecture and connectivity to increase link flexibility and network reliability. At present, D2D adopts broadcast, multicast and unicast technology solutions, and will develop its enhanced technologies in the future, including D2D-based relay technology, multi-antenna technology and joint coding technology.
Key Technology 5: Dense Network
In the future 5G communication, the wireless communication network is evolving toward the diversification, broadband, integration and intelligence of the network. With the popularity of various smart terminals, data traffic will increase spurt. Future data services will be mainly distributed indoors and hotspots, making ultra-dense networks one of the main means of achieving 1000 times the traffic demand of the future 5G. Ultra-dense networks can improve network coverage, dramatically increase system capacity, and offload traffic, with more flexible network deployment and more efficient frequency reuse. In the future, for high-band and large-bandwidth, a more dense network solution will be adopted, and more than 100 small cells/sectors will be deployed.
At the same time, the increasingly dense network deployment also makes the network topology more complex. Inter-cell interference has become the main factor that restricts the system capacity growth, which greatly reduces the network energy efficiency. Interference cancellation, fast cell discovery, dense inter-cell cooperation, and mobility enhancement schemes based on terminal capability enhancement are all hot research topics in dense networks.
Key Technology 6: New Network Architecture
At present, the LTE access network adopts a network flat architecture, which reduces system delay and reduces network construction cost and maintenance cost. The future 5G may adopt the C-RAN access network architecture. C-RAN is a green radio access network architecture based on centralized processing, collaborative radio and real-time cloud computing architecture. The basic idea of ​​C-RAN is to transmit wireless signals directly between the remote antenna and the centralized central node by making full use of the low-cost high-speed optical transmission network to construct a wireless coverage area of ​​hundreds of base stations, even hundreds of square kilometers of wireless. Access to the system. The C-RAN architecture is suitable for adopting cooperative technology, which can reduce interference, reduce power consumption, improve spectrum efficiency, and facilitate intelligent networking for dynamic use. The centralized processing is beneficial to reduce costs, facilitate maintenance, and reduce operating expenses. The current research content includes the architecture and functions of C-RAN, such as centralized control, baseband pool RRU interface definition, and closer cooperation based on C-RAN, such as base station clusters and virtual cells.
Comprehensively building a 5G-based technology test and evaluation platform can provide an efficient and objective evaluation mechanism for 5G technology, which is conducive to accelerating 5G research and industrialization. The 5G test evaluation platform will smoothly evolve on the basis of the requirements of the existing certification system, thus accelerating the standardization and industrialization of the test platform, which is conducive to China's participation in the future international 5G certification system and build a bridge for the development of 5G technology.
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