From IP voice in the 1G era, to voice calls and text messages in the 2G era, from audio and video calls in the 3G era, to the mobile Internet in the 4G era, and then to the Internet of Everything in the 5G era, the evolution and iteration of each generation of communication technology have brought revolutionary changes to people's production and lifestyle.
With the continuous development of ultra-high-definition video rendering capabilities and terminal display technology, as well as the increasing maturity of 5G-A technology, communication services are also evolving in the direction of high immersion, strong interaction, and multi-dimensional and multi-modal, further realizing three-dimensional dynamic perception and interaction between people and people, and between people and things, which has stimulated people's pursuit of future lifestyles such as the metaverse, as well as a series of ultra-high-definition immersive business applications, such as XR (extended reality). As the primary core carrier of the metaverse, XR has become an important carrier for consumption upgrading with the continuous improvement of infrastructure construction such as 5G networks, AI, edge computing, and cloud computing, and the content ecology is becoming more and more abundant, injecting new vitality into people's production and lifestyle.
Immersive business end-to-end challenges
XR immersive services are characterized by high immersion, strong interaction, and multi-dimensional and multi-modality, which pose many challenges to the end-to-end industry, involving headsets, service content, network transmission, and experience evaluation.
In terms of headsets, due to factors such as optical solutions and batteries, headsets are still relatively bulky, affecting the comfort of users. VR (Virtual Reality)/MR (Mixed Reality) headsets generally use Fresnel lens optics, with long imaging distance and thick optical components, while new products gradually adopt Pancake (folded optical path) scheme, which helps to shorten the imaging distance and move the battery out of the host through the rear of the battery, the external battery and other ways to avoid increasing the weight of the host. Although the Pancake solution and external battery have "slimmed" the headset device, the weight of the current mainstream headset still reaches 400g~600g, and the battery life is only 2 to 3 hours.
In terms of business content, the current XR content ecosystem focuses on video, games, and social scenarios, and less content in other fields. Due to the high production cost, long cycle, and the small scale of the XR market itself, large manufacturers are still in a wait-and-see mode, resulting in a low proportion of XR content, which is difficult to stimulate consumers' desire to buy.
In terms of network connection, taking the 4K VR service as an example, the network needs to provide a transmission rate of 100 Gigabit/s, a stable network transmission delay of 20 ms, and a motion response delay (MTP) of 70 ms in a single-user scenario. In addition, large-space XR services have mobility requirements, and 5G-A technology needs to be used to ensure a smooth service experience in multi-user concurrent scenarios.
In terms of experience evaluation, the industry has not yet formed an objective and quantitative method for evaluating the user experience of XR services, and there are differences in the statistical methods of indicators of different headsets, cloud platforms, and network vendors, making it difficult to compare them horizontally. Therefore, there is an urgent need to establish a sound evaluation standard and indicator system, clarify the mapping model and evaluation standard between communication network indicators and service experience indicators, and unify the definition of frame-level delay, rate, delay jitter and other indicators of XR services, as well as data collection, measurement reporting, and statistical methods for problem location and demarcation.
5G-A immersive communication technology system
In response to the above challenges, based on the characteristics of XR services and with the core concepts of "cross-layer information sharing, multi-dimensional connection enhancement, and quantitative evaluation of perception", China Mobile proposes millisecond-level service perception assurance technology, frame-level multi-dimensional connection enhancement technology, and 5G indicator system for XR immersive experience, and builds a 5G-A immersive communication technology system for XR services.
Cross-layer perception and collaboration technology for the network industry
For network perception of service information, the current standard scheme is that the service server carries service frame-level information through the RTP (Real-time Transmission Protocol) header and transmits it to the user plane function (UPF) of the core network, and then transmits it to the RAN (Radio Access Network) side through the GTP-U (User Data Transmission Protocol) interface. On this basis, when the service server does not support service information sharing, the base station can start the service frame-level feature fine perception scheme, combined with the intelligent ability of the base station, according to the packet characteristics of the service data to identify the relationship, obtain the frame period, frame size, frame importance and other information of the service, and perform refined scheduling for the frame-level data. At the same time, in view of the perception of the network state by the service, the solution can be based on the service adaptive adjustment technology of the air interface state, and by exposing the network state information such as congestion to the application layer, the application layer can be triggered to dynamically adjust the encoding rate, so that the application rate can continuously adapt to the network state.
Frame-level multi-dimensional connection enhancement technology
For latency, capacity, China Mobile has carried out multi-dimensional connectivity enhancement and proposed a frame delay scheduling scheme (as shown in Figure 1), which introduces a frame delay constraint into the scheduling algorithm to adjust the scheduling optimization level according to the frame delay margin of the packet to ensure that all data packets are scheduled within the constrained time; a frame integrity scheduling scheme is also proposed to introduce the proportion of transmitted data of the current transmitted frame when there are multiple users, the higher the proportion of the remaining packet of the frame, the higher the scheduling priority of the remaining packets of the frame; and a switching control scheme based on the frame boundary (as shown in Figure 2) is proposed to initiate the handover at the interval between two framesto reduce the impact of switching interruptions on the complete transmission of a frame.
Figure 1 Frame delay scheduling scheme
Fig.2 Switching control scheme based on frame boundaries
5G network metrics for XR immersive experience
In view of the lack of network performance evaluation standards for XR services, China Mobile proposes a frame-level network indicator system, test methods and equipment requirements for XR service experience, and forms a frame-level network KPI indicator definition and statistical methods, including frame-level uplink/downlink network transmission delay, frame-level uplink/downlink air interface transmission delay, frame-level uplink/downlink delay distribution, frame-level uplink/downlink delay jitter, frame-level handover interruption delay, frame-level uplink/downlink network transmission throughput and frame-level uplink/ Establish a mapping model between network indicators and influencing service experience indicators to achieve quantitative perception of user experience, and lead the promotion of relevant industry standard projects in the CCSA (China Communications Standards Association) to guide the industry to form a consensus.
A new paradigm for 5G-A immersive communication applications
In order to ensure that the key technical solutions can be applied and implemented, China Mobile has taken the lead in completing the development of prototypes of various station types, leading the laboratory and field tests, and accelerating the pilot implementation of immersive 5G applications for application scenarios such as culture, sports and entertainment, and creating an application demonstration benchmark.
At the Beijing Workers' Stadium, China Mobile carried out an application pilot based on the new technology of 5G-A network industry integration, adopted a new cloud-network-computing integrated deployment architecture, and innovatively applied 5G-A base station service perception functions, flexible resource management capabilities, and device-edge collaborative rendering solutions to achieve real-time 100 Gigabit bit/s experience rate and frame-level network transmission delay of less than 20ms, fully meeting the requirements of 4K resolution, The 90fps immersive and highly interactive XR service requires network transmission capacity, enabling users to smoothly experience football matches in the virtual space, and providing a new experience of digital-real integration of the metaverse based on China Mobile's 5G network for the workers' sports audience.
Based on the large bandwidth and low latency capabilities provided by the 5G-A network, as well as the "backpack-free" and "cable-free" decoupled rendering solution, China Mobile has carried out a pilot XR competitive game application in indoor ultra-dense immersive scenarios, which can simultaneously provide dozens of users with a real-time experience rate of 100 megabit/s and an average air interface downlink transmission delay of less than 10ms, meeting the network transmission requirements and "zero lag" of XR services to move the local rendering data in the backpack to the cloud for rendering In a space of 1,000 square meters, users can "travel light" and experience a more immersive borderless virtual world.
During the Hangzhou Asian Games, China Mobile launched the application of 5G-A new technology for the high-definition immersive service of the Hangzhou Asian Games, creating new services such as VR e-sports, VR live broadcast, and glasses-free 3D Asian Games, and using 5G service feature perception, frame-level scheduling optimization, multi-stream refined guarantee, precise handover control and other technologies to achieve 20ms service frame-level wireless transmission delay and 125Mbit/ in multi-user and multi-service concurrent scenarios. The s-frame-level guarantee rate effectively guarantees the smooth experience of various types of high-definition and high-interaction 3D cloud services, redefines the "live" experience of the event for the audience, and experiences the "immersive, exciting, and interactive" Metaverse Asian Games.
Looking ahead, with the continuous improvement of network transmission capabilities and headset terminal performance, XR services will also enter an era of full immersion and virtual and real integration, and the mutual perception, collaboration, and integration of services and networks will become more and more close. China Mobile will be committed to promoting the comprehensive development of 5G-A technology, exploring the technical path of 5G-A to carry the metaverse, better supporting the construction of digital China, and making every effort to meet people's all-round needs for spiritual and material life in the future.