Atmospheric turbulence-resilient hybrid MIMO RF/FSO communication systems: adaptive N-SM and OAM-OMI assisted M-ary SPPM modulation with advanced diversity multiplexing for next-generation wireless networks
-
Ebrahim E. Elsayed
,
Mohamed A. Yakout
Abstract
This study presents a novel evaluation framework for optimizing free-space optical (FSO) communication systems by integrating multilevel modulation with orbital angular momentum (OAM)-based data stream multiplexing to maximize spectral efficiency (SE). The proposed architecture synergizes pulse-position modulation (PPM) and dense wavelength-division multiplexing (DWDM), while mitigating impairments from optical nonlinearities and atmospheric turbulence. Key innovations include the fusion of N-encoded adaptive spatial modulation (SM) with L-ary spatial PPM (SPPM) and a diversity strategy employing mixed multiple-input multiple-output (MIMO), multiple-input single-output in an M:1 ratio, and single-input single-output (SISO) configurations. Incorporating SM into FSO systems substantially reduces bit error rate by counteracting turbulence-induced signal degradation. The performance of SPPM, MIMO, and hybrid MIMO-SPPM/MPPM schemes is rigorously analyzed across RF, FSO, and hybrid RF/FSO channels under weak turbulence and dynamic atmospheric conditions. Simulations demonstrate that the hybrid MIMO/OAM-SPPM/MPPM model achieves an average symbol error probability of 10−10 at 20 dB signal-to-noise ratio (SNR) – outperforming conventional approaches by orders of magnitude. Optimal SE is attained via hybrid modulation over hybrid RF/FSO links, with 4 × 4 MIMO-RF/DWDM-FSO configurations achieving 49 bits/s/Hz at 25 dB SNR and 55 bits/s/Hz at 17 dB SNR – surpassing SISO RF (16 bits/s/Hz) and FSO (21 bits/s/Hz) benchmarks.
-
Research ethics: Not applicable.
-
Informed consent: Not applicable.
-
Author contributions: All co-authors participated uniformly in the study’s design, manuscript composition, and critical editing. Every contributor approved the final version prior to submission.
-
Use of Large Language Models, AI and Machine Learning Tools: None declared.
-
Conflict of interest: The authors confirm the absence of any competing financial or personal interests.
-
Research funding: This research received no external funding.
-
Data availability: The authors confirm that the data supporting the findings of this study are available within the article.
-
Patient consent statement: Not applicable.
-
Permission to reproduce material from other sources: Not applicable.
-
Clinical trial registration: Not applicable.
References
1. Willebrand, HA, Ghuman, BS. Fiber optics without fiber. IEEE Spectr 2001;38:40–5. https://doi.org/10.1109/6.938713.Suche in Google Scholar
2. Liu, Q, Qiao, C, Mitchell, G, Stanton, S. Optical wireless communication networks for first- and last-mile broadband access [Invited]. SA J Opt Netw 2005;4:807–28. https://doi.org/10.1364/JON.4.000807.Suche in Google Scholar
3. Aladeloba, AO, Woolfson, MS, Phillips, AJ. WDM FSO network with turbulence-accentuated interchannel crosstalk. J Opt Commun Netw 2013;5:641–51. https://doi.org/10.1364/jocn.5.000641.Suche in Google Scholar
4. Zhu, X, Khan, JM. Free-space optical communication through atmospheric turbulence channels. IEEE Trans Commun 2002;50:1293–300. https://doi.org/10.1109/TCOMM.2002.800829.Suche in Google Scholar
5. Wilson, SG, Brandt-Pearce, M, Cao, Q, Leveque, JH. Freespace optical MIMO transmission with Q-ary PPM. IEEE Trans Commun 2005;53:1402–12. https://doi.org/10.1109/TCOMM.2005.Suche in Google Scholar
6. Cvijetic, N, Wilson, SG, Brandt-Pearce, M. Receiver optimization in turbulent free-space optical MIMO channels with APDs and Q-ary PPM. IEEE Photonics Technol Lett 2007;19:103–5. https://doi.org/10.1109/LPT.2006.889105852836.Suche in Google Scholar
7. Fath, T, Renzo, MD, Haas, H On the performance of space shift keying for optical wireless communications. In: Proceedings of IEEE Globecom 2010, Miami. 2010:pp. 990–994.10.1109/GLOCOMW.2010.5700474Suche in Google Scholar
8. Hwang, SH, Cheng, Y. SIM/SM-aided free-space optical communication with receiver diversity. IEEE J Lightwave Technol 2014;32:2443–50. https://doi.org/10.1109/JLT.2014.2327078.Suche in Google Scholar
9. Elsayed, EE. Atmospheric turbulence mitigation of MIMO-RF/FSO DWDM communication systems using advanced diversity multiplexing with hybrid N-SM/OMI M-ary spatial pulse-position modulation schemes. Opt Commun 2024;562. https://doi.org/10.1016/j.optcom.2024.130558.Suche in Google Scholar
10. Popoola, WO, Poves, E, Haas, H. Spatial pulse position modulation for optical communications. IEEE J. Lightwave Technol 2012;30:2948–54. https://doi.org/10.1109/JLT.2012.2208940.Suche in Google Scholar
11. Shi, Q. Performance limits on M-QAM transmission in hybrid multi-channel AM/QAM fiber optic systems. IEEE Photon Technol Lett 1993;5:1452–5. https://doi.org/10.1109/68.262571.Suche in Google Scholar
12. Shi, Q. Error performance of OFDM-QAM in sub-carrier multiplexed fiber-optic transmission. IEEE Photon Technol Lett 1997;9:845–7. https://doi.org/10.1109/68.585010.Suche in Google Scholar
13. Bekkali, A, Ben Naila, C, Kazaura, K, Wakamori, K, Matsumoto, M. Transmission analysis of OFDM-based wireless services over turbulent radio-on-FSO links modeled by gamma–gamma distribution. IEEE Photon J 2010;2:510–20. https://doi.org/10.1109/jphot.2010.2050306.Suche in Google Scholar
14. Andrews, LC, Phillips, RL. Laser beam propagation through random media, 2nd ed. Bellingham,Washington: SPIE Press; 2005.10.1117/3.626196Suche in Google Scholar
15. Majumdar, AK. Free-space laser communication performance in the ztmospheric channel. J Opt Fiber Commun Rep 2005;2:345–96. https://doi.org/10.1007/s10297-005-0054-0.Suche in Google Scholar
16. Al-Habash, MA, Andrews, LC, Phillips, RL. Mathematical model for the irradiance probability density function of a laser beam propagating through turbulent media. Opt Eng 2001;40:1554–62. https://doi.org/10.1117/1.1386641.Suche in Google Scholar
17. Ghassemlooy, Z, Popoola, W, Rajbhandari, S. Optical wireless communications: system and channel modelling with MATLAB. Boca Raton, FL: Taylor & Francis Group; 2012.Suche in Google Scholar
18. Khalighi, MA, Aitamer, N, Schwartz, N, Bourennane, S. Turbulence mitigation by aperture averaging in wireless optical systems. In: 10th International Conference on Telecommunications; 2009. pp. 59–66.Suche in Google Scholar
19. El-Meadawy, SA, Shalaby, HMH, Ismail, NA, El-Samie, FEA, Soliman, NF, Algarni, AD, et al.. Proposal of hybrid NOAM-MPPM technique for gamma-gamma turbulence channel with pointing error and different deep learning techniques. IEEE Access 2022;10:10295–309. https://doi.org/10.1109/ACCESS.2021.3127139.Suche in Google Scholar
20. Gradshteyn, IS, Ryzhik, IM. Table of integrals, series, and products, 7th ed. New York: Academic; 2007.Suche in Google Scholar
21. Ricklin, JC, Davidson, FM. Atmospheric turbulence effects on a partially coherent Gaussian beam: implications for free space laser communication. J Opt Soc Am A Opt Image Sci 2002;19:1794–802. https://doi.org/10.1364/JOSAA.19.001794.Suche in Google Scholar PubMed
22. Farid, AA, Hranilovic, S. Outage capacity optimization for free-space optical links with pointing errors. J Lightwave Technol 2007;25:1702–10. https://doi.org/10.1109/jlt.2007.899174.Suche in Google Scholar
23. Hien, TTP, Dang, NT. Performance improvement of spatial modulation-assisted FSO systems over gamma–gamma fading channels with geometric spreading. Photonic Netw Commun 2017;34:213–20. https://doi.org/10.1007/s11107-017-0685-0.Suche in Google Scholar
24. Xu, Z, Xu, G, Zheng, Z. BER and channel capacity performance of an FSO communication system over atmospheric turbulence with different types of noise. Sensors 2021;21:3454. https://doi.org/10.3390/s21103454.Suche in Google Scholar PubMed PubMed Central
25. Chandra, S, Jee, R, Singh, M. Transmission performance of hybrid WDM-FSO system for using diversity multiplexing in the presence of optical nonlinearities and fading. In: Region 10 Conference TENCON 2017. IEEE; 2017. p. 2733–8. ISBN 2159-3450.10.1109/TENCON.2017.8228326Suche in Google Scholar
26. Mbah, AM, Walker, JG, Phillips, AJ. Performance evaluation of turbulence accentuated interchannel crosstalk for hybrid fibre and free space optical wavelength division multiplexing systems using digital pulse position modulation. IET Optoelectron 2016;10:11–20. https://doi.org/10.1049/iet-opt.2015.0007.,Suche in Google Scholar
27. Mbah, AM, Walker, JG, Phillips, AJ. Performance evaluation of digital pulse position modulation for wavelength division multiplexing FSO systems impaired by interchannel crosstalk. IET Optoelectron 2014;8:245–55. https://doi.org/10.1049/iet-opt.2013.0145.Suche in Google Scholar
28. Dang, NT, Pham, AT. Performance improvement of FSO/CDMA systems over dispersive turbulence channel using multi-wavelength PPM signaling. OSA Opt Express 2012;20:26786–97. https://doi.org/10.1364/OE.20.026786.Suche in Google Scholar PubMed
29. Cui, B, Cai, S, Zhang, Z. Relaying system based on few-mode EDFA for space division multiplexing wireless optical communication. IEEE Photon J 2022;14:1–7. https://doi.org/10.1109/jphot.2022.3192449.Suche in Google Scholar
30. Xie, G, Li, L, Ren, Y, Huang, H, Yan, Y, Ahmed, N, et al.. Performance metrics and design considerations for a free-space optical orbital-angular-momentum–multiplexed communication link. Optica 2015;2:357–65. https://doi.org/10.1364/optica.2.000357.Suche in Google Scholar
31. International Telecommunication Union. Forward error correction for high bit-rate DWDM submarine systems. ITU-T Recommendation G.975.1, Appendix I.9; 2004.Suche in Google Scholar
32. Molisch, AF. Wireless communications, 2nd ed. Hoboken, NJ, USA: Wiley-IEEE Press; 2011.Suche in Google Scholar
33. Wang, L, Ge, X, Zi, R, Wang, CX. Capacity analysis of orbital angular momentum wireless channels. IEEE Access 2017;5:23069–77. https://doi.org/10.1109/access.2017.2763679.Suche in Google Scholar
34. Opare, KA, Kuang, Y. Performance of an ideal wireless orbital angular momentum communication system using multiple-input multiple-output techniques. In: Proceedings of International Conference on TEMU, Heraklion, Greece; 2014. pp. 144–9.10.1109/TEMU.2014.6917751Suche in Google Scholar
35. Yuan, Y, Zhang, Z, Cang, J, Wu, H, Zhong, C. Capacity analysis of UCA-based OAM multiplexing communication system. In: Proceedings of International Conference on WCSP, London, U.K., Oct 2015; 2015. pp. 1–5.10.1109/WCSP.2015.7341308Suche in Google Scholar
36. Yousif, BB, Elsayed, EE, Alzalabani, MM. Atmospheric turbulence mitigation using spatial mode multiplexing and modified pulse position modulation in hybrid RF/FSO orbital-angular-momentum multiplexed based on MIMO wireless communications system. Opt Commun 2019;436:197–208. https://doi.org/10.1016/j.optcom.2018.12.034.Suche in Google Scholar
37. Elsayed, EE, Yousif, BB. Performance enhancement of M-ary pulse-position modulation for a wavelength division multiplexing free-space optical systems impaired by interchannel crosstalk, pointing error, and ASE noise. Opt Commun 2020;475. https://doi.org/10.1016/j.optcom.2020.126219.Suche in Google Scholar
38. Singh, M, Elsayed, EE, Alayedi, M, Aly, MH, Abd El-Mottaleb, SA. Performance analysis in spectral-amplitude-coding-optical-code-division-multiple-access using identity column shift matrix code in free space optical transmission systems. Opt Quant Electron 2024;56:795. https://doi.org/10.1007/s11082-023-05721-9.Suche in Google Scholar
39. Elsayed, EE. Investigations on modified OOK and adaptive threshold for wavelength division multiplexing free-space optical systems impaired by interchannel crosstalk, atmospheric turbulence, and ASE noise. J Opt; 2024:1–14. https://doi.org/10.1007/s12596-024-01929-4.Suche in Google Scholar
40. Yousif, BB, Elsayed, EE. Performance enhancement of an orbital-angular-momentum-multiplexed free-space optical link under atmospheric turbulence effects using spatial-mode multiplexing and hybrid diversity based on adaptive MIMO equalization. IEEE Access 2019;7:84401–12. https://doi.org/10.1109/ACCESS.2019.2924531.Suche in Google Scholar
41. Zhu, L, Deng, M, Lu, B, Guo, X, Wang, A. Turbulence-resistant high-capacity free-space optical communications using OAM mode group multiplexing. Opt Express 2023;31:14454–63. https://doi.org/10.1364/oe.488053.Suche in Google Scholar PubMed
42. Elsayed, EE, Hayal, MR, Nurhidayat, I, Shah, MA, Elfikky, A, Boghdady, AI, et al.. Coding techniques for diversity enhancement of dense wavelength division multiplexing MIMO‐FSO fault protection protocols systems over atmospheric turbulence channels. IET Optoelectron 2024;18:11–31. https://doi.org/10.1049/ote2.12111.Suche in Google Scholar
43. Al-Khaffaf, DAJ. Designing optimized 4 × 20 Gbps FEC-NRZ scheme/HG-MDM based MMF-FSO system for last-mile 5 G users with atmospheric turbulence analysis. Results Eng 2025;25. https://doi.org/10.1016/j.rineng.2025.104531.Suche in Google Scholar
44. Al-Khaffaf, DAJ. Integrated photonic secured reliable DWDM for 5G Xhaul at Ka band frequency. Results Opt. 2023;13. https://doi.org/10.1016/j.rio.2023.100558.Suche in Google Scholar
45. Al-Khaffaf, DAJ. Enabling 6G high spectral efficiency of PDM-OAM over FSOC channel model with weather condition effects in Iraq. J Opt 2024. https://doi.org/10.1007/s12596-024-01795-0.Suche in Google Scholar
46. Elsayed, EE. Performance enhancement in FSO relay systems with MISO via multi-hop M-ary PPM integrating and spatial modulation over gamma–gamma channels. J Opt 2024:1–16. https://doi.org/10.1007/s12596-024-01936-5.Suche in Google Scholar
© 2025 Walter de Gruyter GmbH, Berlin/Boston
