The first 5G NR NSA standard was officially frozen at the 3GPP plenary meeting #78 in Lisbon, Portugal in December 2017. At the 3GPP plenary meeting #80 in Santiago in June 2018, the first 5G NR SA standard was officially frozen. This means that the global mobile communication industry is about to carry out full-scale 5G NR deployment, and the 5G era is coming. Because the NSA standard is six months earlier than the SA standard, and terminals support the same pace, most operators select the NSA standard to deploy 5G networks in the early stage of global 5G deployment. Although NSA deployment can accelerate the commercial use of 5G, NSA technology limitations restrict the full development of 5G service potential. In particular, the adjustment between 4G and 5G in the deployment phase restricts and affects each other, greatly increasing network deployment costs. URLLC, slicing, new QoS mechanisms, and edge computing all require ultimate standard SA. However, the direct change from NSA to SA results in the failure of early-stage NSA terminals to work in SA networks, greatly affecting 5G construction and promotion. Therefore, the smooth transition from NSA to SA becomes the focus of operators.
The NSA&SA hybrid network can solve this difficulty.The NSA&SA hybrid network allows multi-mode terminals (4G, NSA, NSA&SA, and SA) to coexist in the network at the same time, completely solving the bottleneck problem in which multi-mode terminals cannot adapt to the 5G network (Fig. 1). The priority of network resources can also be guaranteed for NSA&SA and SA terminals. For example, if there is no mandatory restriction on the network side, the terminal will prefer the SA mode to access the network. The performance of the 5G NR side is outstanding, especially on the uplink side, which will be 50% higher than that of the NSA uplink.
The Chinese government proposed the strategy of speeding up 5G deployment, and gradually put it into practice based on the NSA model in 2019. China's network conversion experience is worthy of reference. The 5G commercial use and the maturity of the NSA industry chain in China are all ahead of the SA development. The SA network is expected to be a long-term process in the industry. China sold tens of millions of 5G handsets in 2019, but most of them only support NSA. Operators need to consider the compatibility of these users and NSA handsets roaming to China in overseas markets, as well as the increasing demands for 5G applications in the industry.
China's 5G construction is represented by China Mobile. With more than 3 million base stations and more than 900 million mobile users, China Mobile is the largest operator in the world. Its 5G deployment experience is a reference model for global operators. China Mobile responds positively to China's national 5G development strategy. To meet the needs of initial NSA and evolved SA users, China mobile actively promotes the NSA&SA hybrid networking solution for smooth evolution from NSA to SA in the industry. Its 5G network can be deployed in the following three stages:
—Stage 1: In 2019, China Mobile started 5G deployment to integrate necessary resources for network development and verify its commercial performance. Considering the actual 5G development and China's market competition, combined with the maturity of its industry, China Mobile uses different network architectures to meet the needs of different stages of network development. Its 5G network started with NSA for friendly users in key cities. In the early stage, China Mobile made friendly users use NSA single-mode terminals and sent a clear signal to the industry that SA was the target network.
—Stage 2: In 2020, China Mobile entered the stage of large-scale 5G deployment. The scale of its eMBB users began to grow, while SA was fully deployed. Its NSA users attracted in the first stage of 5G deployment in 2019 will face the problem of terminal replacement, which will have a great impact on China Mobile's brand building and operational costs. Therefore, developing the NSA&SA hybrid networking mode is an important transition stage for the evolution from NSA to SA in key cities.
—Stage 3: China Mobile will develop vertical industry users. It will promote the applications of 5G industry users, enrich 5G business models, and transition to SA networking.
Together with China Mobile, ZTE has built the world's first 5G NSA&SA hybrid commercial network in China's Fuzhou University City. Based on 3GPP standards, this network implements end-to-end NSA&SA dual-mode access from the core network, RAN, to 5G terminals, providing users with a high-speed 5G network experience that is not restricted by the 5G terminal system anytime and anywhere. After thorough tests and network optimization, the current network fully meets the performance requirements after NSA and SA terminals are connected at the same time in commercial mode, bringing an average download rate of over 1 Gbps and better 5G experience to users. The test shows that the performance and user experience of NSA&SA dual-mode sites are basically the same as those of single-mode SA or NSA site. The NSA&SA dual-mode capability can effectively protect the investment of operators and ensure both NSA and SA user experience. The construction of 5G NSA&SA dual-mode networking and network optimization also provide China Mobile with valuable dual-mode commercial experience and more comprehensive technical accumulation in the study of smooth evolution of 5G network.
China Mobile plans to deploy over 300 thousand 5G base stations in 2020, and will fully deploy SA on a large scale to accelerate the evolution from NSA to SA target network and ensure the provision of 5G SA commercial services in all prefecture-level cities in China within 2020. As a bridge of evolution, the NSA&SA hybrid network will help China Mobile deploy 5G networks on a large and efficient scale.