Non-terrestrial network (NTN) is a terminal-satellite direct communication technology based on the new air interface technology developed by 3GPP in R17. To solve the problems caused by long distance, fast movement, and wide coverage of satellite communication scenarios with large Doppler frequency deviation, large signal attenuation, and large propagation delay, NTN has designed the air interface enhancement protocol, introduced advanced technologies such as scheduling time sequence management, HARQ function orchestration, uplink transmission delay compensation, and fast satellite-to-ground handover, already provided basic satellite communication capabilities.
The integration of the satellite communication network and the ground 5G cellular network can provide ubiquitous coverage without being restricted by terrain and landform, and form an integrated ubiquitous access network that enables full-scenario on-demand access on earth.
NTN is an important function of the 3GPP R17 standard. It continues to evolve in 5G-Advanced and has become an important part of the 3GPP R18 work plan. NTN includes two workgroups: NTN-IoT (non-terrestrial network-based IoT terminal access) and NTN-NR (non-terrestrial network-based intelligent terminal access). The NTN-IoT focuses on low-complexity NB-IoT/eMTC terminal satellite IoT services, such as global asset tracking (such as sea containers or other terminals beyond the coverage of cellular networks). The NTN-NR uses the 5G NR framework to enable direct-connection between satellites and smartphones to provide data services and voice services.
From the perspective of global cellular network coverage, more than 80% of land areas and 95% of sea areas are not covered by ground networks. With 5G NTN technology, mobile phones can be directly connected to cellular broadband networks through satellites, so that a converged network with ubiquitous connections, abundant scenarios, highly integrated industry chains, and low O&M costs can be built.
On August 26, 2022, China Mobile Research Institute, together with ZTE, CTTIG（China Transport Telecommunication & Information Group）, China Mobile Beijing, and other industry partners, released the technical field test results of the world’s first 5G NTN by operator. Based on the 3GPP R17 NTN protocol, this verification breaks through the two major challenges of ultra-long (36000km) single-way distance and direct connection of mobile phones, forming two innovative solutions: Dynamic compensation of ultra-long delay and conversion of RF signal between satellite and earth networks. It achieves end-to-end full-link 5G NTN technology interconnection, and verifies the feasibility of direct-connection satellite of mobile phones under the prerequisite of meeting the 3GPP protocol.
This pilot result release was hosted by Mr. Deng Wei, deputy director of the Wireless and Terminal Technology R&D Institute of the China Mobile R&D Institute, and jointly announced by Ms. Huang Yuhong, Dean of the China Mobile R&D Institute, Mr. Zhang Wanchun, General Manager of Wireless Product Operation Division, Mr. Guo Chunqi, Senior Vice President (SVP) of CTTIG, and Mr. Yang Yang, deputy general manager of the Beijing Branch of China Mobile.
1) Field Verification Scheme for 5G NTN Technology
Based on the market requirements of satellite IoT and the value of NB-IoT NTN scenarios, China Mobile and its joint partners including ZTE conduct pilot tests based on high-altitude GEO satellites. The test environment is composed of user terminals, satellites, satellite gateway stations, base stations, core networks, and service servers. The network topology is as following figure. The L-band satellites and ground gateway stations are located between NTN terminals and base stations to transmit air-interface messages. The ground gateway stations are interconnected with 5G NTN base stations. Terminals are connected to the ground core network and service platforms through satellites, gateway stations, and NTN base stations to implement end-to-end service interconnection with star-ground integration.
This pilot project included four test fields: Core network equipment room, NTN base station room, satellite gateway station antenna, and NTN terminal service demonstration on the site, see the following figure.
ZTE Shanghai R&D Center
2) Field Verification Result of 5G NTN Technology
This 5G NTN field test of the world’s first operator shows that the actual performance meets expectations. The 5G NTN field test supports SMS and voice intercom services, and fully verifies the implementation capability of the handset direct-connection satellite technology in terms of architecture, protocols, and devices. In terms of test results, the RF ACLR of the base station was better than that of the satellite gateway station，link quality met the expectation. Ping 64-bytes delay was about 4s. The SMS service function was normal. The voice intercom was clear and smooth. The performance met the expectation. This pilot project verified the NTN networking feasibility of high-orbit GEO satellite transparent forwarding in terms of architecture, verified the feasibility of NTN solving problems such as long delay and wide coverage in terms of protocols, and verified the capability of adding the direct connection between satellite and handsets in terms of equipment. This is a breakthrough of the NTN technology from zero to one.
3) Follow-Up Planning for 5G NTN Field Verification
In this field test of the 5G NTN technology, the high-orbit GEO synchronous satellite is directly connected to the ground terminal for the first time, and end-to-end service interconnection is completed. In the future, special pilots for personal emergency communication and IoT information collection will be carried out in Beijing, Yunnan, and other provinces. And in the future, the 5G NTN technology will be further verified and evaluated based on mid-orbit and low-orbit satellites, laying a solid theoretical and technical foundation for handset direct-link with satellites.
In the future, direct satellite connection with mobile phones will be widely used in personal fields and various vertical industry application fields, and will greatly expand the application scope of satellites. Innovation in convergence technologies is actively carried out around the world, the chain of integration is accelerated, and in-depth integration between the satellite industry and cellular industry is promoted. This will bring huge commercial value in the integration of satellite networks and ground networks.
5G NTN will be widely used in the future. In terms of supporting national strategies such as empowering China through dark blue ocean，empowering China through transportation, construction of One Belt&One Road, rural revitalization, and national unified large market, 5G NTN will work together with terrestrial cellular mobile networks to bring huge social values into full play.
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