INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS Int. J. Commun. Syst. (2011) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/dac.1315 SHORT COMMUNICATION Rain attenuation measurements over terrestrial microwave links operating at 15 GHz in Malaysia A. Y. Abdulrahman 1, * ,† , T. Abdul Rahman 1 , S. K. Abdulrahim 1 and Md. Rafiqul Islam 2 1 Wireless Communications Center, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia 2 Electrical and Computer Engineering Department, Islamic International University Malaysia, Kuala Lumpur, Malaysia SUMMARY This paper presents the experimental results of rain rate and rain attenuation measurements on six terrestrial microwave links in tropical Malaysia. The rain attenuation data were collected from six DIGI MINI-LINKs (DiGi Telecommunications Sdn. Bhd., Malaysia, Shah Alam, Selangor Darul Ehsan, Malaysia) operat- ing at 15 GHz with 99.95 % availability. The experimental results were compared with the International Telecommunication Union Radiocommunication Sector (ITU-R) method and other existing rain attenuation prediction models. The main focus is on the ITU-R prediction method, which underestimates the measured rain attenuation, more especially at extremely higher rain rates. The relationship between ITU-R predic- tion errors and rainfall rates was studied, and it is shown that the two quantities are related by a quadratic function. The study will provide useful information on the design and planning of terrestrial radio links in Malaysia and similar tropical environments. Copyright © 2011 John Wiley & Sons, Ltd. Received 21 March 2011; Revised 26 May 2011; Accepted 8 June 2011 KEY WORDS: rain-induced attenuation; ITU-R prediction model; regression techniques; tropical environments 1. INTRODUCTION Rain attenuation adversely affects the performance of microwave communication systems operating at frequencies above 10 GHz. The effect is more severe in tropical regions, which are characterized by heavy rainfall intensity and the presence of large raindrops [1]. Raindrop size distribution changes with geographical location and it can strongly influence rain-specific attenuation and, consequently, total rain attenuation [2]. Usually, propagation impairments have a significant effect only for less than 1 % of the time dur- ing a year; therefore, the system gain must be enhanced through an additional fade margin to meet the desired availability and QoS specifications [3]. One of the main objectives of the telecommu- nications community is to seek a model that can predict rain attenuation in any climate across the world with a better accuracy [4]. The International Telecommunication Union Radiocommunication Sector (ITU-R) has provided a methodological approach for predicting rain attenuation on any terrestrial radio link. However, the model does not perform well in tropical climates because it is based on data collected from tem- perate regions of the world [5]. Emphasis on the inappropriateness of the ITU-R method in tropical *Correspondence to: A. Y. Abdulrahman, Wireless Communications Center, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia. † E-mail: abdulrahman.yusuf@yahoo.com Copyright © 2011 John Wiley & Sons, Ltd.