5G NTN Helps to Build Satellite-Ground Converged Network

NTN Leads the Trend of Satellite-Ground Converged Network

Non-terrestrial network (NTN) is a terminal-satellite direct communication technology based on the new radio (NR) interface technology developed by 3GPP in R17, and also an important supplement to the terrestrial cellular communication technology. With the integration of the satellite communication network and the ground 5G network, NTN can provide ubiquitous coverage without being restricted by terrain and landform, and connect the sky, earth, sea and other spaces to form an integrated ubiquitous access network that enables on-demand access in all scenarios.

NTN is an important function of 3GPP R17. It continues to evolve in 5G-Advanced stage and has become an important part of the 3GPP R18 work plan. NTN includes two workgroups: IoT NTN and NR NTN. IoT NTN focuses on satellite IoT services that support low-complexity eMTC and NB-IoT terminals, such as global asset tracking (sea containers or other terminals beyond the coverage of cellular networks). NR NTN uses the 5G NR framework to enable direct-connection between satellites and smartphones to provide voice and data services.

NTN consists of the user equipment (UE), satellite, satellite gateway, base station (gNB), core network (CN) and server. Its architecture will evolve from more feasible transparent payload (Fig. 1) to renewable payload (Fig. 2). At present, the 3GPP Rel-17 specification focuses on transparent payload structure.

To solve the problems caused by long distance, fast movement, and wide coverage of satellite communication scenarios, such as 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, delay compensation, frequency compensation, and fast air-to-ground handover mobility management enhancement, and provided basic capabilities for direct communication between the satellite and UEs.

Highlights of the NTN Solution

Recently, the topics on satellite-ground convergent communications and direct terminal connection to satellite oriented to 5G-Advanced and 6G evolution are very hot in the industry. Industry-leading companies have made many explorations on satellite communications. For example, SpaceX Starlink and T-Mobile announced that they would use Starlink V2.0 satellites to provide connection services for existing terminals on 1.9 GHz frequency band. Globalstar also announced that they would cooperate with Apple to launch the "satellite communications" function on the new iPhone 14 series with Qualcomm chips inside. However, they all have certain restrictions in the areas they use and the contents and objects they send.

Compared with the similar solutions of StarLink, and Apple iphone 14, the 5G NTN solution in full compliance with the 3GPP standard has distinct advantages in terminal penetration, industrial integration and service variety, and will lead the trend of satellite-ground converged network.

IoT-NTN short messages and IoT services take the lead in current 5G NTN. In the future, mobile phones that support NR-NTN voice and data broadband services will be directly connected to satellites. Therefore, 5G NTN is very suitable for constructing all-area ToB and ToC emergency communication networks, and the business model has obvious competitive advantages.

The renewable network architecture supports base station embedded in low earth orbit (LEO) satellites, and allows existing terminals to directly connect to satellites without modification. The existing terminals bring significant economies of scale of satellite links, rapidly reducing satellite connection cost.

Rich Application Scenarios and Huge Value Spaces for 5G NTN

From the perspective of global network coverage, more than 80% of land areas and 95% of sea areas are not covered by ground cellular networks. With 5G NTN, smart phones and IoT terminals can be directly connected to satellites, and can be integrated with terrestrial cellular networks. In this way, a converged network with ubiquitous connections, abundant scenarios, highly integrated industry chains, and lower O&M costs can be built and maintained. 5G NTN can be widely used in emergency communications, minerals, oil and gas, power grids, maritime affairs, logistics, animal protection and agriculture.

For operators, 5G NTN integrates the satellite and ground cellular networks to greatly reduce invalid construction of base stations in remote areas, lower network construction and O&M costs, and expand new markets for emergency communications and wide-area IoT applications. For end users, 5G NTN provides low-cost ubiquitous connections and ToB+ToC services in various scenarios. For the industry, 5G NTN will promote in-depth integration of the satellite and cellular industries, forming a commercial scale effect.

5G NTN will be widely used in the future. In terms of supporting China's national strategies such as strong ocean country, strong transportation country, 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.

ZTE Continues to Forge Ahead in 5G NTN

After the R17 NTN standard was frozen in June 2022, ZTE, together with China Mobile and other industrial partners, released the results of the world's first operator 5G NTN field test in August 2022. Based on 3GPP R17 NTN protocol, this verification broke through two major challenges: ultra-long-distance of 36000 km high-orbit synchronous satellite and direct connection of common UEs, forming two innovative solutions: dynamic ultra-long-distance delay compensation and RF data conversion between satellites and base stations on the ground. It achieves end-to-end full-link 5G NTN interconnection, and verifies the feasibility of direct connection of UEs to satellites under the prerequisite that the 3GPP protocol is met.

Based on the market requirements of satellite IoT and the value of NB-IoT NTN scenarios, ZTE has worked with China Mobile to conduct the pilot test based on the geosynchronous earth orbit (GEO) satellite. The test consists of user terminals, satellites, satellite gateway stations, base stations, core network and server. The L-band satellite and ground gateway station 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 satellite-ground integration.

The world's first operator 5G NTN field test shows that the actual performance meets expectations. This field test supports SMS and short voice intercom services, and fully verifies the implementation capability of UE direct-connection with satellite in terms of architecture, protocols, and devices. According to test results, the adjacent channel leakage ratio (ACLR) of the base station RF was better than that of the gateway base station required, link quality met the expectation, delay of ping 64-byte was about 4s, SMS functions were normal, and short voice intercom was clear and smooth. The test performance met the expectation. This pilot project verified the feasibility of NTN networking with high-orbit satellite transparent forwarding architecture, verified the feasibility of NTN in solving problems such as long delay and wide coverage in terms of protocols, and verified the capability of direct connection between satellite and mobile phones in terms of communication equipment. This is a breakthrough of the NTN technology from zero to one, and has laid a solid theoretical and technical foundation for direct connection of mobile phones with satellites.

ZTE is working with another operator in China to complete the end-to-end interconnection verification of 5G NTN, and will continue to promote and accelerate the commercialization of NTN in the future.