{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,14]],"date-time":"2026-01-14T16:56:08Z","timestamp":1768409768068,"version":"3.49.0"},"reference-count":20,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2025,6,21]],"date-time":"2025-06-21T00:00:00Z","timestamp":1750464000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Natural Science Foundation of China","award":["U21A20450"],"award-info":[{"award-number":["U21A20450"]}]},{"name":"National Natural Science Foundation of China","award":["62171234"],"award-info":[{"award-number":["62171234"]}]},{"name":"National Natural Science Foundation of China","award":["61971440"],"award-info":[{"award-number":["61971440"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>With the growth of Internet of Things (IoT) business demands, NB-IoT integrating low earth orbit (LEO) satellite communication systems is considered a crucial component for achieving global coverage of IoT networks in the future. However, the long propagation delay and significant Doppler frequency shift of the satellite-to-ground link pose substantial challenges to the uplink and downlink synchronization in LEO satellite-based NB-IoT networks. To address this challenge, we first propose a Multiple Segment Auto-correlation (MSA) algorithm to detect the downlink Narrow-band Primary Synchronization Signal (NPSS), specifically tailored for the large Doppler frequency shift of LEO satellites. After detection, downlink synchronization can be realized by determining the arrival time and frequency of the NPSS. Then, to complete the uplink synchronization, we propose a position-based scheme to obtain the Timing Advance (TA) values and pre-compensated Doppler shift value. In this scheme, we formulate a time difference of arrival (TDOA) equation using the arrival times of NPSSs from different satellites or at different times as observations. After solving the TDOA equation using the Chan method, the uplink synchronization is completed by obtaining the TA values and pre-compensated Doppler shift value from the terminal position combined with satellite ephemeris. Finally, the feasibility of the proposed scheme is verified in an Iridium satellite constellation. Compared to conventional GNSS-assisted methods, the approach proposed in this paper reduces terminal power consumption by 15\u201340%. Moreover, it achieves an uplink synchronization success rate of over 98% under negative SNR conditions.<\/jats:p>","DOI":"10.3390\/sym17070984","type":"journal-article","created":{"date-parts":[[2025,6,24]],"date-time":"2025-06-24T10:44:41Z","timestamp":1750761881000},"page":"984","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Positioning-Based Uplink Synchronization Method for NB-IoT in LEO Satellite Networks"],"prefix":"10.3390","volume":"17","author":[{"given":"Qiang","family":"Qi","sequence":"first","affiliation":[{"name":"School of Communication and Information Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210049, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9270-3074","authenticated-orcid":false,"given":"Tao","family":"Hong","sequence":"additional","affiliation":[{"name":"School of Communication and Information Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210049, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6939-1922","authenticated-orcid":false,"given":"Gengxin","family":"Zhang","sequence":"additional","affiliation":[{"name":"School of Communication and Information Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210049, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Yang, M., Dong, X., and Hu, M. (2016, January 12\u201314). Design and simulation for hybrid LEO communication and navigation constellation. Proceedings of the 2016 IEEE Chinese Guidance, Navigation and Control Conference (CGNCC), Nanjing, China.","DOI":"10.1109\/CGNCC.2016.7829041"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1117","DOI":"10.1109\/COMST.2022.3151028","article-title":"Cellular, wide-area, and non-terrestrial IoT: A survey on 5G advances and the road toward 6G","volume":"24","author":"Vaezi","year":"2022","journal-title":"IEEE Commun. Surv. Tutor."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Lin, J., Hou, Z., Zhou, Y., Tian, L., and Shi, J. (2016, January 15\u201318). Map estimation based on Doppler characterization in broadband and mobile LEO satellite communications. 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