Absfracf -Information of raindrop size distribution (DSD) is important for prediction of the microwave signal attenuation due rain, especially for high microwave frequency applications. The modeling of the raindrop size distribution in temperate and tropical region is different because tropical region has experiences heavy rain rate compared to temperate region. This paper reports the comparison of the rain attenuation measurements from 38 GHz microwave links conducted at Wireless Communication Center, Universiti Teknologi Malaysia (UTM) with the DSD model from Malaysia (KL-Lognormal), Singapore, Brazil and Nigeria using lognormal distribution model. The lognormal parameters are determined by the predicted result from those countries. Thus, direct comparison of the rain attenuation measurement with the various DSD models could be made. The use of DSD establishes for another climate and countries may result in prediction error.
introductionThe rapid growth of telecommunication services, both in satellite and terrestrial links using higher frequency bands is above 10 GHz has highlighted need for estimating the effect of hydrometeors such as rain, clouds, fog and gaseous. The presence of hydrometeors in radio wave propagation, particularly rain, can produce major impairments to microwave propagation. Raindrops can be absorbed and scattered radio wave energy in signal attenuation, which can degrade the reliability and performance of the communication links [I].Rain attenuation can be obtained through measurement or predicted from knowledge of rain rate and drop size distribution. The modeling of the raindrop size distribution in temperate and tropical region is different. It is because tropical region has experiences heavy rain rate compared to temperate region. In temperate region, Law and Parsons Model [2] or negative exponential function as proposed by 0-7803-867 1 -X/04/$20.00 02004 IEEE.Marshall and Palmer [3] and gamma distribution model usually characterizes modeling of raindrop size distribution. While mean, in tropical region, researchers from Brazil [4], Malaysia [5,6], Singapore [7] and Nigeria [8] have conducted raindrop size measurements and proposed raindrop size distribution models. However, the negative exponential is not appropriate for use in tropical regions and gamma model distribution must be too modified [7]. Thus, lognormal raindrop size distribution models are suitable, used to estimate rain attenuation and compared to rain attenuation measurements from microwave links installed at Wireless Communication Centre (WCC), Universiti Teknologi Malaysia, UTM Skudai, Johor. Microwave links is operating at frequency 38 GHz and distance between transmitter and receiver about 301.3 meters.
2.0Rain AttenuationThe rain attenuation can be express as below:where A is the rain attenuation in dB, As is the specific attenuation in dBkm, L is the path length between transmitter and receiver and r is the reduction factor (91. Specific attenuation, A, (dB/km) for an electromagnetic wave that propagates through ra...