UAV-enabled triple-hop mixed RF/FSO networks: reliability and altitude optimization
-
Deepika Latka
and
Swaran Ahuja
Abstract
This paper presents a detailed performance analysis of a UAV-assisted three-hop mixed radio frequency (RF)/free-space optical (FSO) wireless communication system employing decode-and-forward (DF) relaying. The system comprises a source node communicating with a mobile UAV relay over an RF link subject to generalized Rician fading, followed by an FSO link from the UAV to a ground-based relay experiencing Gamma–Gamma atmospheric turbulence with pointing errors. The final hop from the relay to the destination user is modeled as an RF link undergoing Rayleigh fading, with opportunistic user scheduling to enhance link reliability. Closed-form expressions for the end-to-end outage probability are derived, along with an asymptotic analysis that provides insights into the diversity and coding gains. Furthermore, a location optimization framework is proposed, wherein the UAV’s altitude and corresponding elevation angle are jointly optimized to minimize the asymptotic outage probability. Simulation results corroborate the analytical findings, verified through extensive Monte Carlo trials and reveal the significant impact of fading severity, pointing error, UAV altitude, and scheduling strategy on overall system performance. The proposed model offers valuable design guidelines for next-generation UAV-enabled hybrid RF/FSO communication systems.
-
Research ethics: Not applicable.
-
Informed consent: Not applicable.
-
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
-
Use of Large Language Models, AI and Machine Learning Tools: None declared.
-
Conflict of interest: All other authors state no conflict of interest.
-
Research funding: None declared.
-
Data availability: Not applicable.
References
1. Zeng, Y, Zhang, R, Lim, TJ. Wireless communications with unmanned aerial vehicles: opportunities and challenges. IEEE Commun Mag 2016;54:36–42. https://doi.org/10.1109/mcom.2016.7470933.Search in Google Scholar
2. Mondal, A, Hossain, A. Channel characterization and performance analysis of unmanned aerial vehicle-operated communication system with multihop radio frequency – free-space optical link in dynamic environment. Int J Commun Syst 2020;33:1–14. https://doi.org/10.1002/dac.4568.Search in Google Scholar
3. Yang, B, Yang, E. A survey on radio frequency based precise localisation technology for UAV in GPS-denied environment. J Intell Rob Syst 2021;103:38. https://doi.org/10.1007/s10846-021-01500-4.Search in Google Scholar
4. Al-Gailani, SA, Salleh, MFM, Salem, AA, Shaddad, RQ, Sheikh, UU, Algeelani, NA, et al.. A survey of free space optics (FSO) communication systems, links, and networks. IEEE Xplore 2020;9:7353–73.10.1109/ACCESS.2020.3048049Search in Google Scholar
5. Najafi, M, Ajam, H, Jamali, V, Diamantoulakis, PD, Karagiannidis, GK, Schober, R. Statistical modeling of the FSO fronthaul channel for UAV-based communications. arXiv:1905.12424v2 [eess.SP] 2020. https://doi.org/10.1109/tcomm.2020.2981560.Search in Google Scholar
6. Shen, B, Chen, J, Xu, G, Chen, Q, Wang, J. Performance analysis of a drone-assisted FSO communication system over Málaga turbulence under AoA fluctuations. Drones 2023;7:374. https://doi.org/10.3390/drones7060374.Search in Google Scholar
7. Odeyemi, KO, Owolawi, PA. Outage performance of UAV-based relay in FSO downlink satellite communication networks under hovering fluctuations. Int J Microw Opt Technol 2022;17.Search in Google Scholar
8. Clerigues, D, Wubben, J, Calafate, CT, Cano, JC, Manzoni, P. Enabling resilient UAV swarms through multi-hop wireless communications. J Wirel Commun Netw 2024;39. https://doi.org/10.1186/s13638-024-02373-5.Search in Google Scholar
9. Li, P, Xu, J. Placement optimization for UAV-enabled wireless networks with multi-hop backhauls. J Commun Inf Netw 2018;3:64–73. https://doi.org/10.1007/s41650-018-0040-3.Search in Google Scholar
10. Baghnoi, FM, Jamali, J, Taghizadeh, M, Fatehi, MH. Multi-agent based optimal UAV deployment for throughput maximization in 5 G communications. Wirel Netw 2024;30:2285–96. https://doi.org/10.1007/s11276-023-03641-w.Search in Google Scholar
11. Liu, C, Guo, Y, Li, N, Zhou, B. Multi-UAV cooperative trajectory optimisation for a multi-hop UAV relaying network. Electron Lett 2021;57. https://doi.org/10.1049/ell2.12262.Search in Google Scholar
12. Feng, Z, Na, Z, Xiong, M, Ji, C. Multi-UAV collaborative wireless communication networks for single cell edge users. Mobile Network Appl 2022);27:1578–92. https://doi.org/10.1007/s11036-021-01876-5.Search in Google Scholar
13. Luo, Y, Fu, G. UAV based device to device communication for 5G/6G networks using optimized deep learning models. Wirel Netw 2023;30:7137–51. https://doi.org/10.1007/s11276-023-03578-0.Search in Google Scholar
14. Yang, L, Yuan, J, Liu, X, Hasna, MO. On the performance of LAP-based multiple-hop RF/FSO systems. IEEE Trans Aerosp Electron Syst 2018;55:499–505. https://doi.org/10.1109/taes.2018.2852399.Search in Google Scholar
15. Ge, X, Jin, H, Li, X, Leung, VCM. Opportunistic fair resource sharing with secrecy considerations in uplink wiretap channels. In: IEEE wireless communications and networking conference. New Orleans, LA, USA; 2015:1422–7 pp.10.1109/WCNC.2015.7127677Search in Google Scholar
16. Wang, L, Cheng, Y. A statistical mobile-to-mobile Rician fading channel model. In: Proceedings IEEE 61st vehicular technology conference. Stockholm, Sweden; 2005, vol 1:6367 p.Search in Google Scholar
17. Yang, L, Chen, J, Hasna, MO, Yang, H-C. Outage performance of UAV-assisted relaying systems with RF energy harvesting. IEEE Commun Lett 2018:1. https://doi.org/10.1109/lcomm.2018.2876869.Search in Google Scholar
18. Al-Hourani, A, Kandeepan, S, Lardner, S. Optimal LAP altitude for maximum coverage. IEEE Wirel Commun Lett 2014;3:569–72. https://doi.org/10.1109/lwc.2014.2342736.Search in Google Scholar
19. Aggarwal, M, Garg, P, Puri, P. Analysis of subcarrier intensity modulation-based optical wireless DF relaying over turbulence channels with path loss and pointing error impairments. IET Commun 2014;8:3170–8. https://doi.org/10.1049/iet-com.2014.0292.Search in Google Scholar
20. Safi, H, Dargahi, A, Cheng, J, Safari, M. Analytical channel model and link design optimization for ground-to-HAP free-space optical communications. J Lightwave Technol 2020;38:5036–47. https://doi.org/10.1109/jlt.2020.2997806.Search in Google Scholar
21. Alnagar, SI, Salhab, AM, Zummo, SA. Unmanned aerial vehicle relay system:performance evaluation and 3D location optimization. IEEE Access 2020;8:67635–45. https://doi.org/10.1109/ACCESS.2020.2986182.Search in Google Scholar
22. Latka, D, Aggarwal, M, Ahuja, S. Performance analysis of UAV-enabled dual-hop mixed RF-FSO communication systems with user scheduling. J Opt Commun 2024. https://doi.org/10.1515/joc-2024-0254.Search in Google Scholar
23. Yadav, S, Vats, A, Aggarwal, M, Ahuja, S. Performance analysis and altitude optimization of UAV-enabled dual-hop mixed RF-UWOC system. IEEE Trans Veh Technol 2021;70:12651–61. https://doi.org/10.1109/tvt.2021.3118569.Search in Google Scholar
24. Dale, M. The algebra of random variables. New York, NY: Wiley; 1979, vol 1.Search in Google Scholar
25. Gradshteyn, IS, Ryzhik, IM. Table of integrals, series, and products, 7th ed. San Diego, CA: Academic; 2007.Search in Google Scholar
26. Latka, D, Aggarwal, M, Ahuja, S. UAV-assisted dual-hop RF communication: performance analysis of outage probability and altitude optimization for multi-user systems. Phys Commun 2025;68:102546. https://doi.org/10.1016/j.phycom.2024.102546.Search in Google Scholar
27. Latka, D, Aggarwal, M, Ahuja, S. Outage probability analysis and altitude optimization of a UAV-enabled triple-hop mixed RF-FSO-Based wireless communication system. Photonics 2024;11:1145. https://doi.org/10.3390/photonics11121145.Search in Google Scholar
28. Vats, A, Aggarwal, M, Ahuja, S. Outage and error analysis of three hop hybrid VLC/FSO/VLC – based relayed optical wireless communication system. Trans Emerg Telecommun Technol 2019;30:e3544. https://doi.org/10.1002/ett.3544.Search in Google Scholar
© 2025 Walter de Gruyter GmbH, Berlin/Boston
