Raindrop Size Distribution and Wind-Driven Rain Specific Attenuation: CCDF-Based Analysis at 18 and 38 GHz in Tropical Country

Nurul Najwa Md Yusof; Omar Abdul Aziz; Lam Hong Yin; Jafri Din

doi:10.31436/iiumej.v27i2.4008

Authors

Nurul Najwa Md Yusof University of Technology Malaysia https://orcid.org/0009-0001-5610-9385
Omar Abdul Aziz University of Technology Malaysia
Lam Hong Yin Tun Hussein Onn University of Malaysia https://orcid.org/0000-0002-5528-4130
Jafri Din University of Technology Malaysia

DOI:

https://doi.org/10.31436/iiumej.v27i2.4008

Keywords:

5G, 6G, Rain Attenuation, DSD, specific attenuation, mm-wave

Abstract

Seasonal monsoons, frequency dependence, and wind effects were investigated for rain-specific attenuation at millimeter-wave (mm-wave) frequencies in a tropical environment. Using one-minute RD-69 DSD data and matched wind observations, CCDFs of specific attenuation were evaluated at 18 and 38 GHz for three monsoon phases (SW, NE, IM) and four wind-direction sectors under unconstrained and constrained winds (9–11 m/s). The CCDF results show clear seasonal variability, with the SW monsoon producing the strongest attenuation and the largest mismatch from ITU-R P.838-3, particularly at 38 GHz. Error statistics show that the maximum deviation occurs in the SW 270°–360° sector, with an RMSE of 1.550 dB/km and a positive bias, confirming ITU-R underestimation. Meanwhile, the NE monsoon exhibits smaller overall deviations (worst-case RMSE below about 0.6 dB/km at 38 GHz). The IM period exhibits mixed behavior, where wind direction can shift the deviation between under- and overestimation under constrained winds. Exceedance levels of 0.01% and 0.001% were emphasized as design-relevant extremes, corresponding to approximately 52.6 min/year and 5.26 min/year, respectively, under one-minute sampling. Overall, the results indicate that ITU-R P.838-3 accuracy in tropical conditions depends on monsoon phase and wind direction, supporting monsoon-aware, direction-sensitive fade-margin planning and link-orientation considerations for robust 5G/6G terrestrial mm-wave systems.

ABSTRAK: Monsun bermusim, kebergantungan frekuensi, dan kesan angin telah dikaji terhadap pelemahan spesifik hujan pada frekuensi gelombang milimeter (mm-wave) dalam persekitaran tropika. Menggunakan data DSD RD-69 beresolusi satu minit dan melalui pemerhatian padanan angin, pelemahan CCDF spesifik dinilai pada 18 dan 38 GHz untuk tiga fasa monsun (SW, NE, IM) dan empat sektor arah angin di bawah angin tidak terkekang serta angin terkekang (9–11 m/s). Penyimpangan terbesar daripada ITU-R P.838-3 berlaku pada 38 GHz, khususnya semasa monsun barat daya (SW), apabila sektor 270°–360° di bawah angin tidak terkekang menunjukkan RMSE = 1.550 dB/km dan bias = +1.193 dB/km, menandakan ITU-R bernilai lebih rendah; di bawah angin terkekang, penyimpangan kekal tinggi (RMSE = 1.383 dB/km). Tempoh peralihan (IM) juga menunjukkan kebergantungan pada sektor angin terkekang, dengan RMSE = 1.212 dB/km dan bias = +0.936 dB/km pada 38 GHz, manakala monsun timur laut (NE) menunjukkan penyimpangan lebih kecil (RMSE terburuk adalah kurang daripada kira-kira 0.6 dB/km pada 38 GHz di bawah angin tidak terkekang). Tahap kebarangkalian lebihan 0.01% dan 0.001% ditekankan sebagai ekstrem yang relevan bagi reka bentuk, bersamaan kira-kira 52.6 min/tahun dan 5.26 min/tahun, masing-masing, pada pensampelan satu minit. Secara keseluruhan, dapatan kajian menunjukkan ketepatan ITU-R P.838-3 dalam keadaan tropika bergantung pada fasa monsun dan arah angin, sekaligus menyokong perancangan margin-pudaran yang peka monsun dan peka arah angin serta menimbang orientasi pautan untuk sistem gelombang-mm 5G/6G terestrial yang lebih berdaya tahan.

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Author Biographies

Omar Abdul Aziz, University of Technology Malaysia

Dr. Omar bin Abdul Aziz is a distinguished Senior Lecturer in the Faculty of Electrical Engineering at Universiti Teknologi Malaysia (UTM). With a robust academic and professional background, he is recognized for his contributions to the field of communications engineering. His expertise is centered on advanced topics, including wireless communications, sophisticated antenna design, and the application of machine learning to enhance wireless systems. Beyond the classroom, Dr. Omar is an active and respected researcher whose work has been published in numerous journals and conference proceedings, demonstrating his influence in the academic community. Holding a Ph.D. in Electrical, Electronics, and Communications Engineering from UTM, along with a Master of Engineering from the same institution and a Bachelor of Engineering from Universiti Teknologi PETRONAS (UTP), Dr. Omar's extensive qualifications provide a strong foundation for his authoritative work thus shaping the next generation of engineers and contributing to cutting-edge research in wireless technology.

Lam Hong Yin, Tun Hussein Onn University of Malaysia

Lam Hong Yin received the M. Eng. and Ph.D. degrees in electrical engineering from the Universiti Teknologi Malaysia (UTM), Johor, Malaysia, in 2009 and 2013, respectively. He then served as a postdoctoral fellow in 2014. Since 2015, he is a senior lecturer at the Faculty of Engineering Technology, Universiti Tun Hussein Onn, Malaysia, and currently the department head of electrical engineering technology at Pagoh Campus. Lam is a graduate member of BEM, registered Professional Technologist MBOT, Member of IEEE, and American Association for the Advancement of Science. He serves as a reviewer for various international journals such as IEEE Transaction on Antennas & Propagation, IEEE Antennas and Propagation Magazine, International Journal of Antennas & Propagation. Besides research activities, he is also actively involved as an Engineering Technology Accreditation Council and MBOT academic program evaluation panel, as well as a quality assurance audit ISO 9001:2015 lead auditor.

Jafri Din, University of Technology Malaysia

Professor Dr. Jafri bin Din is a distinguished Professor and Dean of the Faculty of Electrical Engineering at UTM, known for his eminent expertise in radio wave propagation, satellite technology, and microwave communications. As a celebrated academic, his work is widely cited, reflecting his profound impact on the field through extensive publications and research projects. His leadership and vision have also been instrumental in advancing his faculty's standing, with its Electrical & Electronic Engineering programmes consistently ranking among the top 100 globally. Prof. Jafri is a seasoned researcher and leader, having served as a Director for UTM's Wireless Communication Centre (WCC) and been involved in numerous strategic industry partnerships, showcasing his significant contributions to both academia and industry.

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