Mr. Feng Fan Profile

Feng Fan

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Proceedings Article | 18 March 2024 Paper

Network Time Protocol (NTP) implementation for laser inter-satellite networks

Rui Zhang, Zhiwei Hu, Jianjun Li, Feng Fan, Feng Wen

Proceedings Volume 13104, 131046T (2024) https://doi.org/10.1117/12.3023868

KEYWORDS: Satellites, Clocks, Internet, Satellite communications, Reliability, Local area networks

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The network time protocol (NTP) has been used since the 80s to synchronize the time of various terminal devices in the network, and is one of the oldest network protocols still in use today. Thanks to its excellent design and implementation, it can show good synchronization performance and stability even in complex network environments (such as terrestrial Internet). In recent years, with the expansion of the scale of the satellite Internet, the satellite network structure has gradually changed from a simple point-to-point connection mode to a complex networking mode, and the frequently changing inter-orbital inter-satellite links have brought great complexity to the network. Therefore, it is important to perform the time synchronization in complex satellite networks, especially when the laser-based transmission technology applied. In this paper, we introduce the NTP system into the laser inter-satellite networks. To the best of our knowledge, this is the first time the two systems working together, enabling performing the data transmission in the simple, but effective way. We investigate two kinds of transmission scenarios: the time synchronization happened in the co-orbit and the crossorbit cases. To perform the investigation, we set up a 30-satellites simulation platform, where their virtual connections were followed by the rule of laser inter-satellite networks. The NTP details were discussed by the two transmission scenarios, including the implementation structure, the delay results and the factors that could impact the synchronization performance. By successful implementation in laser inter-satellite networks, the NTP suggests an alternative approach to perform the time synchronization in the simple and low-cost way, by dealing with the complex and free-access networks across the whole earth.

Proceedings Article | 4 April 2023 Paper

Delay performance comparison across seven Low-Earth-Orbit (LEO) satellite constellations

Zhiwei Hu, Feng Wen, Juan Yong, Feng Fan, Baojian Wu, Kun Qiu

Proceedings Volume 12617, 126171T (2023) https://doi.org/10.1117/12.2664563

KEYWORDS: Satellites, Satellite communications, Iridium, Telecommunications, Internet, Computer simulations, Switching, Mobile communications, Error analysis, Algorithms

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We carry out the thoughtful investigations on the end-to-end delay comparison based on seven proposed low-earth-orbit (LEO) satellite constellations, i.e., GlobalStar, Iridium, TeleSat, Kuiper, StarLink, OneWeb with 720 and 1764 satellite nodes, which include two major constellation types-polar and inclined orbits. The discussion focuses on the future satellite operation in space by gradually increasing the number of satellites nodes and analyzes the impact of the constellation scale on the performance of the inter-communication delay. The shortest path algorithm is used to simulate both international (Beijing to New York) and domestic (Beijing to Chengdu) scenarios for each constellation to calculate the shortest transmission delay and its corresponding hop count. Our results show that with the expansion of the number of satellites, the end-to-end delay could touch the floor. The optimized delay is achieved when the number of satellites is close to 1000 for both international and domestic scenarios, which values are 44ms and 6ms, respectively. There is no impressive improvement on the delay performance when further expanding the constellation scale. Moreover, as the number of satellites continue to accumulate, both the long-distance and short-distance communication scenarios, the large-scale star chain clusters aggravate the frequency of inter-star switching, easily leading to unstable transmission delay, which is not conducive to obtaining the best delay benefits. Therefore, for the delay performance-driven service, it is necessary to reasonably optimize the constellation structure to meet the user's communication needs through the appropriate number of satellites in the constellation.

Proceedings Article | 15 November 2022 Paper

Channel modeling and noise analysis for laser intersatellite links (LISLs)

Juan Yong, Feng Wen, Feng Fan, Kun Qiu

Proceedings Volume 12448, 1244816 (2022) https://doi.org/10.1117/12.2638382

KEYWORDS: Doppler effect, Sun, Satellites, Signal attenuation, Satellite communications, Telecommunications, Signal detection, Receivers, Laser communications, Interference (communication)

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Laser intersatellite link (LISL) offers a large bandwidth, low power loss and high reliability transmission scheme to the satellite communication. With the rise of commercial applications of giant constellations, the LISL technology could be used to build the free-space backbone network to deliver the information all over the world. However, the operational scheme on the new frequency-carrier also brings new issues. The transmission performance is highly dependent on the channel quality, i.e., the laser channel for our case. In this paper, we build up the theoretical model of the transmission channel for the LISL system, considering the sun outage, the doppler frequency shift and the platform vibration as the major noise sources for the free-space laser communication system. The numerical simulation is carried out to quantify the detail impacts from these sources and to define the operational region of the QPSK transmission system. According to our calculations, the large elevation angle, the low frequency shift and the less vibration could improve the transmission performance.

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