Research PaperV/Ka-band LEO high-throughput satellite and integrated satellite–terrestrial network experiment system: First two years flight results
Introduction
High-throughput satellite (HTS) technology utilizes high-frequency bands, such as Ku, Ka, Q/V, and multipoint beams, each of which can adopt a different combination of frequency and polarization mode [1], [2], [3]. The significant increase in communication capacity is achieved by reusing limited frequency resources. Compared with fixed-satellite service, HTS can provide tens of Gbps to hundreds of Gbps of capacity [4], [5]. The utilization of high-gain antenna technology gives rise to an increase in satellite G/T value, which supports miniaturized ground terminals. Although HTS utilizes the same frequency resources as traditional communication satellites, technologies such as multipoint beam, frequency reuse, and high-gain beam effectively increase the communication capacity and transmission rate, and significantly reduce the unit cost of bandwidth. These technologies have been widely used on high Earth orbit communication satellites. Since the launch of the first HTS Thaicom-4 in 2005, nearly 100 high-throughput communication satellites have been launched by numerous satellite communication companies such as ViaSat, SES, Hughes, Eutelsat, Intelsat, etc [6], [7], [8].
The application of high-throughput communication satellite technology to Low Earth orbit (LEO) satellites reduces the coverage area of a single satellite. It requires hundreds or even thousands of small LEO communication satellites to form a satellite constellation in order to achieve global coverage [9], [10], [11], [12], [13], [14]. In recent years, with the progress of satellite manufacturing technology, the batch production capacity of satellites has improved a lot, and the manufacturing cost and launch cost have decreased significantly. The rapid deployment of the LEO mega-constellations has gradually become eligible. With the advantages of global coverage, high communication rate, low cost, and low latency, the constellation of LEO high-throughput communication satellites can be integrated into terrestrial networks to achieve global communication coverage, which contributes to high economic added value and potential military value. Therefore, a worldwide trend in constructing LEO mega-constellations has been started. The United States and some European countries have successively launched constellation deployment plans represented by Starlink and OneWeb. An American aerospace manufacturer as well as a communications corporation, SpaceX, has deployed 2441 Starlink satellites (1717 operational) through 45 launches (as of 29 April 2022) [15], completing continuous coverage of the area between the and latitudes [16]. In addition, SpaceX has built a considerable number of gateway stations in the United States, Canada, Europe, South America, Australia, and started to provide broadband network services. Another communications company, OneWeb, has deployed 428 LEO satellites through 13 launches to achieve continuous coverage of areas north of latitude including the United Kingdom, Northern Europe, Canada, Alaska, and the Arctic Region [17], [18], [19]. OneWeb, headquartered in London, has signed an agreement with the US military to provide polar-zone broadband communications services.
To alleviate handover delays, signaling overheads, and decision making loads in Integrated terrestrial–satellite networks (ITSNs), Ji et al. [20] proposed a flexibly configurable distributed mobility management architecture and a clustering and game-based lightweight handover framework. To take full advantage of multi-access edge computing (MEC), Xie et al. [21] stored computing resources in multi-layer heterogeneous edge computing clusters, thus enabling task processing directly on the satellite. The above mentioned studies are mainly about the architecture of ITSNs, and the next studies [22], [23] to be presented focus on the application of ITSNs. Combining the advantages of ITSNs and the demands of sixth-generation (6G) networks, Zhu et al. [22] provided a detailed investigation of ITSNs toward 6G from multiple perspectives, and then gave valuable guidance for the development of ITSNs. Also focusing on ITSNs toward 6G, Peng et al. [23] carried out a study for integrated terrestrial and satellite multibeam systems (ITSMS), specifically investigating interference mitigation techniques in ITSMS toward 6G communication. However, the above studies on ITSNs and their applications are conducted from theoretical and simulation perspectives, this work tests the system from an experimental perspective and obtains impressive results.
Established in April 2018, GalaxySpace has become a fast-developing corporation in China’s private satellite industry, with its own smart satellite factory being built in Jiangsu province. To perform key satellite Internet technology demonstrations, the YINHE-1 program was proposed in May 2018. After 18 months of development, the satellite design and manufacture were completed. YINHE-1 weighs 225 kg and is equipped with 16 sets of transponders, 2 sets of Q/V mechanical movable point beam antennas, and 16 sets of Ka-band fixed reflective surface antennas. LEO high-throughput satellites with high-frequency bands and the constructed communication system need to solve a series of technical challenges, including the conflict between RF performance of high-frequency payload and lightweight design demands, high-precision attitude control and tracking, low-cost manufacturing, satellite–terrestrial time synchronization, etc. GalaxySpace has addressed these difficulties by the lightweight design of RF rotary joints, combined mechanism of program tracking and automatic tracking, manufacturing process innovation, and introduction of industrial devices. The satellite was launched at Jiuquan Satellite Launch Center, with an altitude of 640 km and an inclination of . At present, nearly a thousand in-orbit tests have been carried out, and an integrated satellite–terrestrial network experiment system has been established. Sun et al. [24] conducted a practical experiment based on our established system to validate the feasibility of 5G+LEO satellite communication. This paper focuses on the overall scheme of satellite design and a detailed analysis of two-year in-orbit testing results.
Section snippets
Overall scheme of the GalaxySpace’s first satellite
YINHE-1 is an LEO high-throughput satellite, that is equipped with a transparent broadband communication payload for in-orbit tests on Satellite Internet and communications. Due to the fact that multi satellites are packed onto one rocket when launching into orbit, the shape of YINHE-1 is designed to be trapezoidal in cross-section, and a miniaturized electric propulsion system is utilized to reduce the weight of the satellite. The main tasks of the satellite include:
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Realize normal operations
Integrated satellite–terrestrial network experiment system
The integrated satellite–terrestrial communication experiment system consists of several satellites, gateway stations, and user terminals, so as to verify the key technologies and concepts in the early stage of LEO satellite constellation system construction. Fig. 20 illustrates the experiment system framework.
GalaxySpace launched its first LEO broadband satellite, i.e., YINHE-1, in January 2020. The satellite has a Ka-band user beam and uses the Q/V band in the feeder link. Based on YINHE-1,
Experiment results of the satellite in orbit
In the past two years, we carried out verification and validation (V&V) of key technologies such as Q/V-band feeder chain construction of gateway station, Ka-band user beam chain construction, user access, and switching, as well as performance such as throughput, latency, etc.
Integration test of terrestrial mobile communication network and satellite network
(1) LTE and satellite network integration test
LTE’s femtocell base stations (i.e., LTE home eNB) can be connected to the core network via the Internet and standard IP protocols, as shown in Fig. 33. The LEO satellite communication system can be used to connect the femtocell base station to the Internet and make voice calls through the integrated network. The LEO satellite communication link replaces the fiber-optical of the carrier network between the femtocell base station and the core network
Conclusion
After two years of in-orbit testing and verification, the test results showed that the design of YINHE-1 was reasonable, and the antenna, RF, and satellite platform subsystems can adapt to the requirements of feeder tracking and attitude/orbit control under low-orbit conditions. With the cooperation with the terrestrial system, the satellite–terrestrial communication mission was completed successfully. The performance test of the satellite–terrestrial communication link showed that the indexes
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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