Let 5G play a role earlier and make 5G technology 4G

The popularity and application of 4G has opened the door to the development of mobile Internet. With the progress and development of consumer electronics, mobile communication technology is constantly changing people's lives and stimulating the further development of mobile communication needs. As a mobile communication system for 2020 and beyond, 5G will be applied in all areas of society. As an infrastructure, it will provide a full range of services for the future society and promote the transformation and upgrading of all industries.

5G will provide fiber-like wireless access speed and "zero latency" experience, allowing information to break through time and space limitations and be presented instantly; 5G will provide the ability to connect hundreds of billions of devices and provide a seamless interactive experience, enabling intelligent interconnection between people and everything; 5G will provide ultra-high traffic density and ultra-high mobility connection support, allowing users to get consistent performance experience anytime, anywhere; at the same time, more than 100 times the energy efficiency improvement and extremely low bit cost will also ensure the sustainable development of the industry. With ultra-high speed, ultra-low latency, ultra-high mobility, ultra-strong connection capability, ultra-high traffic density, and more than 100 times improvement in energy efficiency and cost, 5G will eventually realize the vision of "information at your fingertips and everything at your fingertips".

In order to realize the vision of 5G development and meet the needs of future business development, the key technical capabilities that 5G should possess include supporting user experience rates of 0.1~1Gbit/s and peak rates of more than 10Gbit/s, supporting a connection density of millions per square kilometer, supporting millisecond-level end-to-end latency, supporting a traffic density of tens of Tbit/s per square kilometer, and supporting a mobile rate of more than 500km/h.

In addition, in order to maintain the sustainable development of the mobile communications industry, 5G also needs to further improve the efficiency and convenience of network construction, deployment, and operation. For example, compared with 4G, spectrum efficiency is increased by 5 to 15 times, energy efficiency is increased by 100 times, and cost efficiency is increased by more than 100 times.

5G technology is springing up like mushrooms

In order to achieve the development goals of 5G, organizations such as ITU, 3GPP, and NGMN have launched research and standardization work for 5G. 3GPP launched discussions on 5G in 2015, and started research and standardization of 5G from the perspectives of network architecture and wireless access network. The new 5G technology has the following characteristics.

Service-oriented cloud networking enables end-to-end network slicing

The most prominent feature of 5G network architecture is that it is based on SDN/NFV technology and realizes end-to-end network slicing through service-oriented cloud networks, thereby achieving flexible and rapid deployment of services. The network slice based on SDN/NFV is shown in Figure 1. In order to meet many requirements such as low latency, high speed, and high efficiency, wireless networks need to introduce many new technologies and designs in addition to the CU/DU separation in the base station architecture.

Figure 1 Network slicing based on SDN/NFV

3D-MIMO

As shown in Figure 2, 3D-MIMO generally uses a large-scale two-dimensional antenna array, which not only has a large number of antenna ports, but also can flexibly adjust the beam direction in the horizontal and vertical dimensions to form a narrower and more precise directional beam, thereby greatly improving the signal energy received by the terminal and enhancing the cell coverage. Traditional 2D-MIMO has a small number of antenna ports, resulting in a wider beam, and can only adjust the beam direction in the horizontal dimension, unable to concentrate the energy in the vertical dimension on the terminal. It can only distinguish users in the horizontal dimension, which limits the number of users that can be served at the same time and frequency. 3D-MIMO can make full use of the antenna freedom in the vertical and horizontal dimensions, serve more users at the same time and frequency, greatly improve system capacity, and can also reduce interference between cells by coordinating the vertical beam directions of multiple cells.

Figure 2 Technical principles of 3D-MIMO

Compared with traditional antennas, 3D-MIMO has better performance in improving the efficiency of reception and transmission, the number of paired users of multi-user MIMO, and reducing interference between cells. It is the core technology of 5G to improve spectrum efficiency.

NOM

In the face of the overall demand for higher spectrum efficiency, larger capacity, more connections and lower latency proposed by 5G, the resource utilization efficiency of 5G multi-access must be higher. Therefore, in the past two years of domestic and foreign 5G research, the user multi-access method with non-exclusive resources has attracted widespread attention. In this multi-access method, no user is exclusive in any resource dimension, so joint detection of multiple user signals must be performed at the receiving end. Thanks to the improvement of chip technology and data processing capabilities, multi-user joint detection at the receiving end has become an implementable solution.

The design of 5G new multiple access will start from the most basic modulation, mapping and other modules of the physical layer, introduce hybrid non-orthogonal coding superposition of power domain and code rate, and introduce multi-user joint detection at the receiving end to realize decoding of non-orthogonal data layer.

After single-user channel coding, the transmitter enters the core codebook mapping module, including modulation mapping, code domain expansion and power optimization. These three parts can also be designed jointly to obtain additional coding gain. At the receiving end, the soft information after multi-user joint detection can be input into the decoding module of the single-user error correction coding for decoding, or the channel decoding result can be returned and substituted into the multi-user joint detector for large-scale iterative decoding to further improve performance. In this general structure diagram, the difference between uplink and downlink multi-access lies in the different positions of multi-user signal superposition. The downlink multi-user signal is superimposed at the transmitting end before passing through the channel, while the uplink multi-user signal is superimposed at the receiving end after passing through the wireless channel.

Compared with the physical layer process of 4G OFDMA orthogonal multiple access, the motivations for introducing new module changes in the new 5G non-orthogonal multiple access physical layer process are mainly as follows: through the new (multi-dimensional) modulation mapping design, coding gain and shaping gain are obtained to improve the access spectrum efficiency; through (sparse) code domain expansion, diversity gain is obtained to enhance transmission robustness and whiten the interference between data streams within or between cells; through power optimization between non-orthogonal layers, the capacity area of ​​multi-user superposition is optimized.

Self-contained frame structure

In order to further reduce the transmission delay, the 5G system has made a new design for the time slot structure and the feedback of transmission and reception. For the TDD system, by introducing more uplink and downlink conversion points, the response time between transmission and feedback is shortened. This frame structure design is also called a self-contained frame structure; for the FDD system, the transmission delay can be shortened through a shorter scheduling and transmission cycle. The subframe format defined by 5G is shown in Figure 3.

Figure 3 Subframe format defined by 5G

Faster state transitions

In order to achieve a lower control plane latency, such as 10ms, 5G introduces a new intermediate state between the existing connected state and idle state in 4G, called the deactivated state, as shown in Figure 4. This state retains the connection state of the core network and deletes the connection state of the wireless side. When needed, the connection on the wireless side can be quickly established, thereby greatly reducing the transition latency from the original idle state to the connected state.

User-Centric Network

The 5G network needs to provide the best user experience based on user behavior, preferences, terminals, network status and capabilities, and implement user-centric network deployment. The main design concepts of the 5G network architecture are shown in Figure 5.

Figure 5 5G wireless network architecture

Intelligent perception of users and business content

With the goal of intelligent wireless pipeline, by introducing a more refined service and user differentiation mechanism, according to the service scenario, user capability, user preference and network capability, the air interface technology and system parameters are adaptively configured to achieve end-to-end refined and diversified network connection, service and content differentiation and processing. The 5G network architecture will be able to support adaptive air interface access and management, end-to-end refined and diversified service and content differentiation and processing based on the prediction, analysis, response and processing capabilities of services and users, provide more accurate and complete user personalization, customized resource configuration and network services to meet the diverse user and service needs, and ensure a consistent and high-quality user experience.

Business sinking and business data localization processing

In terms of logical functions, the functional reconstruction based on the core network and the wireless network has prompted the core network to focus on user contracting, policy management, and centralized control. Its user plane and service bearing functions continue to sink, and the management of service bearing and the routing and distribution of service data can be deployed in the access network closer to the user, thereby building a more optimized service channel, making the service routing channel more simplified, avoiding service bottlenecks, and reducing centralized transmission load. At the same time, based on the refined perception of data and service content, the access network can not only generate, map, cache, and distribute data locally, but also realize local and nearby intelligent distribution and push of services.

Support multi-network integration and multi-connection transmission

In the foreseeable future, multiple networks such as 4G/5G/Wi-Fi will coexist for a long time. Therefore, the 5G network architecture must support the deep integration of multiple networks, realize the unified and coordinated management of multiple wireless technologies/resources, and realize unified control regardless of the access method based on the separation of bearer and signaling, and the decoupling of signaling and standard, so as to maximize the utilization of wireless resources. At the same time, future terminals will generally have the ability to connect and transmit multiple standards and multiple wireless networks at the same time. Based on multi-dimensional service acceptance and control, the 5G network will support accurate network selection and wireless transmission paths and methods based on delay tolerance, packet loss sensitivity, and different apps and service providers to achieve optimal resource matching.

5G technology for 4G

4G has been widely used in the global market. While profoundly changing people's lives, it is also constantly creating new demands and promoting the evolution and development of 4G technology. The large-scale commercial use of 5G will be after 2020, and the market demand before that can only be met by 4G and its evolutionary technologies. At present, 3GPP is considering introducing technologies for 5G applications into 4G systems in advance, and improving and enhancing the technical capabilities and service efficiency of 4G systems without affecting backward compatibility, so that it can meet the requirements of 5G networks as much as possible, and be applied on existing 4G networks as soon as possible.

3D-MIMO

LTE defines various linear array-based MIMO and smart antenna modes in detail, which have been widely used in 4G networks, especially in TD-LTE networks, where 8 antennas have been well popularized and verified. With the research on 5G technology, 3D-MIMO technology has become a hot topic in the industry, and 3GPP has also conducted relevant research and standardization (FD-MIMO) work. Especially for TD-LTE systems, by utilizing the reciprocity of channels, 3D-MIMO technology can be introduced into TD-LTE networks based on implementation without any changes to the standards, which can be compatible with existing terminals and greatly improve the capacity of existing networks. Companies that have made leading progress in TD-LTE product research and development, such as ZTE and Huawei, have released 2.6GHz 3D-MIMO commercial products that support 128 antennas and 64 independent RF channels, and have begun to deploy them in China Mobile's 4G network. Current network tests have shown that 3D-MIMO technology can greatly improve network capacity. The higher the network load, the greater the capacity gain.

Shortened latency

3GPP has considered a technical solution to further reduce transmission delay in LTE R14, allowing the LTE transmission interval (TTI) to be further shortened from the original 1ms. For example, FDD can support TTIs of 2 OFDM symbols, and TDD can support TTI transmissions of 0.5ms. The optimized transmission delay can be reduced to within 1ms and 4ms (TDD configuration 2) respectively. However, for 4G systems, if the network structure is not adjusted accordingly, such a delay reduction will have a negligible reduction in the delay of the entire end-to-end network, and it is difficult to truly meet the requirements of low-latency services. The delay reduction in LTE evolution is shown in Figure 6.

Figure 6 Latency reduction in LTE evolution

Context-aware service distribution and MEC

In the actual service expansion process of 4G network, in order to meet the application needs of enterprise users and the application needs of vertical industries, 4G network needs to optimize the service deployment for some locations and specific environments to improve network efficiency and user experience, that is, it is necessary to introduce MEC technology. However, for the existing 4G network, the wireless side is unaware of the service, that is, the wireless network perceives the service passively through the core network, and the service transmission cannot be truly intelligent on the wireless side. The DPI function can be added near the wireless side of the network to analyze the content of the service, so that MEC can better adapt to the transmission of the service. However, the processing efficiency of this method is low. 3GPP began to consider the optimization of service transmission based on user context, that is, the terminal can actively report the relevant information of the user service, and the base station can optimize the transmission based on this, greatly improving the reliability of transmission. At present, detailed standards have been formulated for the optimization of video services, which is expected to be applied in the evolution of 4G.

Light connection

In terms of latency reduction, 3GPP is also standardizing light connections. By introducing inactive states other than connected and idle states, the energy saving effect of the terminal can be further improved while reducing the latency of terminal access.

As for 4G applications of other 5G technologies, such as non-orthogonal multiple access, 3GPP has discussed non-orthogonal multiple access (NOMA) in the power domain, and non-orthogonal technology in the code domain may also be applied.

In order to meet the needs of 5G, 3GPP has made a new design for the 5G system from the aspects of network architecture, radio frame design, 3D-MIMO, non-orthogonal multiple access, protocol state transition, etc., which has greatly improved the performance in terms of transmission efficiency and latency. Considering that the commercial use of 5G will not be until 2020, it will take some time to truly form actual network capabilities. The biggest attraction of 5G technology is to apply these 5G technologies to the existing 4G network in advance and play a role in advance. At present, experts in the mobile communications industry are working on this. 3D-MIMO, MEC technology, etc. have begun to be applied in 4G networks, and the SDN/NFV transformation of the existing core network has also begun to be piloted. Context-aware service distribution and light connection are being standardized in 3GPP. It is believed that these technologies will eventually be verified and applied in the evolution of 4G networks, making application contributions to the development of 4G.