{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,22]],"date-time":"2026-08-22T05:23:32Z","timestamp":1787376212679,"version":"build-2736575974"},"reference-count":30,"publisher":"MDPI AG","issue":"16","license":[{"start":{"date-parts":[[2026,8,20]],"date-time":"2026-08-20T00:00:00Z","timestamp":1787184000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004735","name":"Hunan Provincial Natural Science Foundation of China","doi-asserted-by":"crossref","award":["2025JJ70301 and 2025JJ70361"],"award-info":[{"award-number":["2025JJ70301 and 2025JJ70361"]}],"id":[{"id":"10.13039\/501100004735","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Scientific Research Project of Hunan Provincial Education Department","award":["25A0620"],"award-info":[{"award-number":["25A0620"]}]},{"award":["25A0620"],"award-info":[{"award-number":["25A0620"]}],"id":[{"id":"https:\/\/ror.org\/026meb765","id-type":"ROR","asserted-by":"publisher"}]},{"name":"Aid program for Science and Technology Innovative Research Team in Higher Educational Institute of Hunan Province,","award":["no grant number"],"award-info":[{"award-number":["no grant number"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Driven by the vision of sixth-generation (6G) communication networks, Space\u2013Air\u2013Ground Integrated Vehicular Networks (SAGVNs) address the connectivity blind spots inherent in traditional networks by integrating unmanned aerial vehicles (UAVs) as highly mobile relay nodes. However, the high bit error rates (BERs) and prolonged propagation delays characteristic of satellite links, coupled with the highly dynamic topologies and multi-hop transmission nature of UAVs and terrestrial vehicles, present significant challenges to reliable end-to-end data streaming. To mitigate the performance degradation caused by link asymmetries in heterogeneous networks, this paper proposes a reliable transmission optimization scheme for UAV-relayed SAGVNs. By comprehensively modeling the transmission dynamics of long-delay, high-BER satellite links and mobile multi-hop UAV networks, the proposed scheme introduces an enhanced slow-start mechanism to accelerate throughput growth, thereby mitigating the startup lag induced by extensive propagation delays. Furthermore, an accurate packet loss differentiation model is established during the congestion avoidance phase. This model effectively decouples non-congestion packet losses\u2014triggered by random channel errors or topology handovers due to high-speed node mobility\u2014from genuine congestion-induced losses caused by buffer overflows at bottleneck nodes. Simulation results demonstrate that the proposed adaptive scheme demonstrates notable improvements over classical loss-based and delay-based baselines in reducing queuing delays at UAV relay nodes, enhances the transmission efficiency of multi-hop terminals, and effectively maintains end-to-end goodput stability in high-latency environments.<\/jats:p>","DOI":"10.3390\/s26165279","type":"journal-article","created":{"date-parts":[[2026,8,20]],"date-time":"2026-08-20T12:57:53Z","timestamp":1787230673000},"page":"5279","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Reliable Transmission Optimization for UAV-Relayed Space\u2013Air\u2013Ground Integrated Vehicular Networks"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0009-0009-4107-7091","authenticated-orcid":false,"given":"Liang","family":"Zong","sequence":"first","affiliation":[{"name":"College of Information, Hunan University of Humanities, Science and Technology, Loudi 417000, China"},{"name":"College of Information Science and Engineering, Shaoyang University, Shaoyang 422000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yun","family":"Cheng","sequence":"additional","affiliation":[{"name":"College of Information, Hunan University of Humanities, Science and Technology, Loudi 417000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yi","family":"Yao","sequence":"additional","affiliation":[{"name":"College of Information, Hunan University of Humanities, Science and Technology, Loudi 417000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"18461","DOI":"10.1109\/JIOT.2024.3477573","article-title":"MBPD: A Robust Algorithm for Polar-Domain Channel Estimation in Near-Field Wideband XL-MIMO Systems","volume":"12","author":"Wang","year":"2025","journal-title":"IEEE Internet Things J."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"3862","DOI":"10.1109\/TNSE.2025.3618771","article-title":"MAMoE: A Multi-Agent Mixture-of-Experts Framework for LLM-Assisted 3D Object Reconstruction and Transmission","volume":"13","author":"Liang","year":"2026","journal-title":"IEEE Trans. Netw. Sci. Eng."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"73","DOI":"10.1109\/MWC.2026.3687488","article-title":"SIM-Empowered LAINs: A Unified Channel Model-Driven Optimization Framework","volume":"33","author":"Ma","year":"2026","journal-title":"IEEE Wirel. Commun."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"754","DOI":"10.1109\/TITS.2022.3145363","article-title":"Channel Parameter Estimation of mmWave MIMO System in Urban Traffic Scene: A Training Channel-Based Method","volume":"25","author":"Wang","year":"2024","journal-title":"IEEE Trans. Intell. Transp. Syst."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"3875","DOI":"10.1109\/TCCN.2025.3622130","article-title":"Hybrid-RIS-Assisted Cellular ISAC Networks for UAV-Enabled Low-Altitude Economy via Deep Reinforcement Learning with Mixture-of-Experts","volume":"12","author":"Ma","year":"2025","journal-title":"IEEE Trans. Cogn. Commun. Netw."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Ma, Z., Lu, S., Peng, Y., Zhou, J., Xu, J., Luo, G., and Luo, M. (2026). Geometrical-Based Modeling for Aerial Intelligent Reflecting Surface-Based MIMO Channels. Electronics, 15.","DOI":"10.3390\/electronics15040875"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"18273","DOI":"10.1109\/TVT.2025.3580859","article-title":"Deep Reinforcement Learning for Energy Efficiency Maximization in RSMA-IRS-Assisted ISAC System","volume":"74","author":"Ma","year":"2025","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"4215","DOI":"10.1109\/TII.2021.3133885","article-title":"End-to-end transmission control for cross-regional industrial internet of things in industry 5.0","volume":"18","author":"Zong","year":"2021","journal-title":"IEEE Trans. Ind. Inform."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"3422","DOI":"10.1109\/TII.2020.2995598","article-title":"Low Complexity MIMO-FBMC Sparse Channel Parameter Estimation for Industrial Big Data Communications","volume":"17","author":"Wang","year":"2021","journal-title":"IEEE Trans. Ind. Inform."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"13521","DOI":"10.1109\/TVT.2026.3658351","article-title":"Energy-Efficient Transmission in STAR-RIS Assisted Secure ISAC Networks With RSMA: An MoE-RBPPO Approach","volume":"75","author":"Ma","year":"2026","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"70","DOI":"10.1109\/IOTM.001.2300067","article-title":"Digital twins for intelligent space-air-ground integrated vehicular network: Challenges and solutions","volume":"6","author":"Hui","year":"2023","journal-title":"IEEE Internet Things Mag."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Cao, X., and Zhang, X. (2023). SaTCP: Link-layer informed TCP adaptation for highly dynamic LEO satellite networks. Proceedings of the IEEE INFOCOM 2023-IEEE Conference on Computer Communications, New York, NY, USA, 17\u201320 May 2023, IEEE.","DOI":"10.1109\/INFOCOM53939.2023.10228914"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Zhang, P., Chen, S., and Zheng, X. (2025). UAV communication in space\u2013air\u2013ground integrated networks (SAGINs): Technologies, applications, and challenges. Drones, 9.","DOI":"10.3390\/drones9020108"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"48291","DOI":"10.1109\/JIOT.2025.3607090","article-title":"Energy-Efficient Resource Allocation for Space-Air-Ground Integrated Vehicular Network","volume":"12","author":"Xu","year":"2025","journal-title":"IEEE Internet Things J."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"12396","DOI":"10.1109\/TCOMM.2025.3573456","article-title":"STAR-RIS assisted train-to-ground communications in space-air-ground integrated networks","volume":"73","author":"Liu","year":"2025","journal-title":"IEEE Trans. Commun."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"8700","DOI":"10.1109\/TMC.2025.3649432","article-title":"Space-Air-Ground Integrated Dynamic Partial Task Offloading Optimization for Vehicular Networks Using Deep Reinforcement Learning","volume":"25","author":"Abbas","year":"2025","journal-title":"IEEE Trans. Mob. Comput."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1665","DOI":"10.1007\/s11276-026-04149-9","article-title":"Optimizing quality of service-based resource allocation in air-space-ground vehicular communication systems via Q-learning","volume":"32","author":"Pandey","year":"2026","journal-title":"Wirel. Netw."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"2060","DOI":"10.1016\/j.fmre.2025.12.034","article-title":"Hyper-Converged Space-Air-Ground Integrated Low-Altitude Aerial Vehicular Networks: Architecture, Challenges, and Technologies","volume":"6","author":"Zhou","year":"2026","journal-title":"Fundam. Res."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"0264","DOI":"10.34133\/space.0264","article-title":"Collaborative federated learning of unmanned aerial vehicles in space\u2013air\u2013ground integrated network","volume":"5","author":"Li","year":"2025","journal-title":"Space Sci. Technol."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"456","DOI":"10.1007\/s42154-024-00284-1","article-title":"UFC3: UAV-aided fog computing based congestion control strategy for emergency message dissemination in 5G internet of vehicles","volume":"7","author":"Hemmati","year":"2024","journal-title":"Automot. Innov."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"9341","DOI":"10.1038\/s41598-024-59823-9","article-title":"Joint cooperative caching and power control for UAV-assisted internet of vehicles","volume":"14","author":"Wang","year":"2024","journal-title":"Sci. Rep."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Ye, M., Zhou, Z., Zhu, L., Huang, F., Li, T., Wang, D., Yi, J., and He, Y. (2024). Improving Transmission in Integrated Unmanned Aerial Vehicle\u2013Intelligent Connected Vehicle Networks with Selfish Nodes Using Opportunistic Approaches. Drones, 9.","DOI":"10.3390\/drones9010012"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Ali Shah, S.A., Fernando, X., and Kashef, R. (2024). A survey on artificial-intelligence-based internet of vehicles utilizing unmanned aerial vehicles. Drones, 8.","DOI":"10.3390\/drones8080353"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"17464","DOI":"10.1109\/TASE.2024.3373007","article-title":"Joint communication and safe 3D path optimization for multi-UAV assisted mobile Internet of Vehicles on an uneven terrain","volume":"22","author":"Savkin","year":"2024","journal-title":"IEEE Trans. Autom. Sci. Eng."},{"key":"ref_25","first-page":"100874","article-title":"UAV-assisted Internet of vehicles: A framework empowered by reinforcement learning and Blockchain","volume":"52","author":"Alagha","year":"2025","journal-title":"Veh. Commun."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"14326","DOI":"10.1109\/TVT.2026.3653679","article-title":"UAV-Assisted Geo-Edge Routing Protocol for Internet of Vehicles Based On Reinforcement Learning Strategy","volume":"75","author":"Zhang","year":"2026","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"333","DOI":"10.23919\/JCC.ja.2022-0656","article-title":"Computational offloading and resource allocation for Internet of vehicles based on UAV-assisted mobile edge computing system","volume":"22","author":"Fang","year":"2025","journal-title":"China Commun."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"133","DOI":"10.1109\/90.842137","article-title":"Modeling TCP Reno performance: A simple model and its empirical validation","volume":"8","author":"Padhye","year":"2002","journal-title":"IEEE\/ACM Trans. Netw."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"216","DOI":"10.1109\/JSAC.2002.807336","article-title":"TCP Veno: TCP enhancement for transmission over wireless access networks","volume":"21","author":"Fu","year":"2003","journal-title":"IEEE J. Sel. Areas Commun."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"547","DOI":"10.1002\/sat.799","article-title":"TCP Hybla: A TCP enhancement for heterogeneous networks","volume":"22","author":"Caini","year":"2004","journal-title":"Int. J. Satell. Commun. Netw."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/16\/5279\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,8,22]],"date-time":"2026-08-22T04:28:08Z","timestamp":1787372888000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/16\/5279"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,20]]},"references-count":30,"journal-issue":{"issue":"16","published-online":{"date-parts":[[2026,8]]}},"alternative-id":["s26165279"],"URL":"https:\/\/doi.org\/10.3390\/s26165279","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,20]]}}}